Science.gov

Sample records for harmonic noise sources

  1. Perceptual interaction of the harmonic source and noise in voice.

    PubMed

    Kreiman, Jody; Gerratt, Bruce R

    2012-01-01

    Although the amount of inharmonic energy (noise) present in a human voice is an important determinant of vocal quality, little is known about the perceptual interaction between harmonic and inharmonic aspects of the voice source. This paper reports three experiments investigating this issue. Results indicate that perception of the harmonic slope and of noise levels are both influenced by complex interactions between the spectral shape and relative levels of harmonic and noise energy in the voice source. Just-noticeable differences (JNDs) for the noise-to-harmonics ratio (NHR) varied significantly with the NHR and harmonic spectral slope, but NHR had no effect on JNDs for NHR when harmonic slopes were steepest, and harmonic slope had no effect when NHRs were highest. Perception of changes in the harmonic source slope depended on NHR and on the harmonic source slope: JNDs increased when spectra rolled off steeply, with this effect in turn depending on NHR. Finally, all effects were modulated by the shape of the noise spectrum. It thus appears that, beyond masking, understanding perception of individual parameters requires knowledge of the acoustic context in which they function, consistent with the view that voices are integral patterns that resist decomposition.

  2. REVIEW ARTICLE: Harmonically mode-locked semiconductor-based lasers as high repetition rate ultralow noise pulse train and optical frequency comb sources

    NASA Astrophysics Data System (ADS)

    Quinlan, F.; Ozharar, S.; Gee, S.; Delfyett, P. J.

    2009-10-01

    Recent experimental work on semiconductor-based harmonically mode-locked lasers geared toward low noise applications is reviewed. Active, harmonic mode-locking of semiconductor-based lasers has proven to be an excellent way to generate 10 GHz repetition rate pulse trains with pulse-to-pulse timing jitter of only a few femtoseconds without requiring active feedback stabilization. This level of timing jitter is achieved in long fiberized ring cavities and relies upon such factors as low noise rf sources as mode-lockers, high optical power, intracavity dispersion management and intracavity phase modulation. When a high finesse etalon is placed within the optical cavity, semiconductor-based harmonically mode-locked lasers can be used as optical frequency comb sources with 10 GHz mode spacing. When active mode-locking is replaced with regenerative mode-locking, a completely self-contained comb source is created, referenced to the intracavity etalon.

  3. An Analysis of Shot Noise Propagation and Amplificationin Harmonic Cascade FELs

    SciTech Connect

    Huang, Z.; /SLAC

    2006-12-11

    The harmonic generation process in a harmonic cascade (HC) FEL is subject to noise degradation which is proportional to the square of the total harmonic order. In this paper, we study the shot noise evolution in the first-stage modulator and radiator of a HC FEL that produces the dominant noise contributions. We derive the effective input noise for a modulator operating in the low-gain regime, and analyze the radiator noise for a density-modulated beam. The significance of these noise sources in different harmonic cascade designs is also discussed.

  4. The Effects of Crosswind Flight on Rotor Harmonic Noise Radiation

    NASA Technical Reports Server (NTRS)

    Greenwood, Eric; Sim, Ben W.

    2013-01-01

    In order to develop recommendations for procedures for helicopter source noise characterization, the effects of crosswinds on main rotor harmonic noise radiation are assessed using a model of the Bell 430 helicopter. Crosswinds are found to have a significant effect on Blade-Vortex Interaction (BVI) noise radiation when the helicopter is trimmed with the fuselage oriented along the inertial flight path. However, the magnitude of BVI noise remains unchanged when the pilot orients the fuselage along the aerodynamic velocity vector, crabbing for zero aerodynamic sideslip. The effects of wind gradients on BVI noise are also investigated and found to be smaller in the crosswind direction than in the headwind direction. The effects of crosswinds on lower harmonic noise sources at higher flight speeds are also assessed. In all cases, the directivity of radiated noise is somewhat changed by the crosswind. The model predictions agree well with flight test data for the Bell 430 helicopter captured under various wind conditions. The results of this investigation would suggest that flight paths for future acoustic flight testing are best aligned across the prevailing wind direction to minimize the effects of winds on noise measurements when wind cannot otherwise be avoided.

  5. Community noise sources and noise control issues

    NASA Technical Reports Server (NTRS)

    Nihart, Gene L.

    1992-01-01

    The topics covered include the following: community noise sources and noise control issues; noise components for turbine bypass turbojet engine (TBE) turbojet; engine cycle selection and noise; nozzle development schedule; NACA nozzle design; NACA nozzle test results; nearly fully mixed (NFM) nozzle design; noise versus aspiration rate; peak noise test results; nozzle test in the Low Speed Aeroacoustic Facility (LSAF); and Schlieren pictures of NACA nozzle.

  6. Controlling of stochastic resonance and noise enhanced stability induced by harmonic noises in a bistable system

    NASA Astrophysics Data System (ADS)

    Wang, Chao-Jie; Long, Fei; Zhang, Pei; Nie, Lin-Ru

    2017-04-01

    Stochastic resonance (SR) and noise enhanced stability (NES) in a bistable system driven by an additive harmonic noise and a multiplicative harmonic noise is investigated. Through numerical simulation, we obtained the power spectrum by the Fourier transformation on time series. The results indicate that (i) for certain values of the parameters of additive harmonic noise Γ, Ω and the noise intensity D, the SR phenomenon occurs. It means we can control the SR phenomenon by modulating the parameters of harmonic noise; (ii) the NES phenomenon occurs at certain values of the parameters of multiplicative harmonic noise Γ, Ω and the multiplicative noise intensity Q. Most important, the NES phenomenon can also be controlled by modulating the parameters of harmonic noise.

  7. A LOW NOISE RF SOURCE FOR RHIC.

    SciTech Connect

    HAYES,T.

    2004-07-05

    The Relativistic Heavy Ion Collider (RHIC) requires a low noise rf source to ensure that beam lifetime during a store is not limited by the rf system. The beam is particularly sensitive to noise from power line harmonics. Additionally, the rf source must be flexible enough to handle the frequency jump required for rebucketing (transferring bunches from the acceleration to the storage rf systems). This paper will describe the design of a Direct Digital Synthesizer (DDS) based system that provides both the noise performance and the flexibility required.

  8. Temporal Characterization of Aircraft Noise Sources

    NASA Technical Reports Server (NTRS)

    Grosveld, Ferdinand W.; Sullivan, Brenda M.; Rizzi, Stephen A.

    2004-01-01

    Current aircraft source noise prediction tools yield time-independent frequency spectra as functions of directivity angle. Realistic evaluation and human assessment of aircraft fly-over noise require the temporal characteristics of the noise signature. The purpose of the current study is to analyze empirical data from broadband jet and tonal fan noise sources and to provide the temporal information required for prediction-based synthesis. Noise sources included a one-tenth-scale engine exhaust nozzle and a one-fifth scale scale turbofan engine. A methodology was developed to characterize the low frequency fluctuations employing the Short Time Fourier Transform in a MATLAB computing environment. It was shown that a trade-off is necessary between frequency and time resolution in the acoustic spectrogram. The procedure requires careful evaluation and selection of the data analysis parameters, including the data sampling frequency, Fourier Transform window size, associated time period and frequency resolution, and time period window overlap. Low frequency fluctuations were applied to the synthesis of broadband noise with the resulting records sounding virtually indistinguishable from the measured data in initial subjective evaluations. Amplitude fluctuations of blade passage frequency (BPF) harmonics were successfully characterized for conditions equivalent to take-off and approach. Data demonstrated that the fifth harmonic of the BPF varied more in frequency than the BPF itself and exhibited larger amplitude fluctuations over the duration of the time record. Frequency fluctuations were found to be not perceptible in the current characterization of tonal components.

  9. Symmetry based frequency domain processing to remove harmonic noise from surface nuclear magnetic resonance measurements

    NASA Astrophysics Data System (ADS)

    Hein, Annette; Larsen, Jakob Juul; Parsekian, Andrew D.

    2017-02-01

    Surface nuclear magnetic resonance (NMR) is a unique geophysical method due to its direct sensitivity to water. A key limitation to overcome is the difficulty of making surface NMR measurements in environments with anthropogenic electromagnetic noise, particularly constant frequency sources such as powerlines. Here we present a method of removing harmonic noise by utilizing frequency domain symmetry of surface NMR signals to reconstruct portions of the spectrum corrupted by frequency-domain noise peaks. This method supplements the existing NMR processing workflow and is applicable after despiking, coherent noise cancellation, and stacking. The symmetry based correction is simple, grounded in mathematical theory describing NMR signals, does not introduce errors into the data set, and requires no prior knowledge about the harmonics. Modelling and field examples show that symmetry based noise removal reduces the effects of harmonics. In one modelling example, symmetry based noise removal improved signal-to-noise ratio in the data by 10 per cent. This improvement had noticeable effects on inversion parameters including water content and the decay constant T2*. Within water content profiles, aquifer boundaries and water content are more accurate after harmonics are removed. Fewer spurious water content spikes appear within aquifers, which is especially useful for resolving multilayered structures. Within T2* profiles, estimates are more accurate after harmonics are removed, especially in the lower half of profiles.

  10. Symmetry based frequency domain processing to remove harmonic noise from surface nuclear magnetic resonance measurements

    NASA Astrophysics Data System (ADS)

    Hein, Annette; Larsen, Jakob Juul; Parsekian, Andrew D.

    2016-11-01

    Surface nuclear magnetic resonance (NMR) is a unique geophysical method due to its direct sensitivity to water. A key limitation to overcome is the difficulty of making surface NMR measurements in environments with anthropogenic electromagnetic noise, particularly constant frequency sources such as powerlines. Here we present a method of removing harmonic noise by utilizing frequency domain symmetry of surface NMR signals to reconstruct portions of the spectrum corrupted by frequency-domain noise peaks. This method supplements the existing NMR processing workflow and is applicable after despiking, coherent noise cancellation, and stacking. The symmetry based correction is simple, grounded in mathematical theory describing NMR signals, does not introduce errors into the dataset, and requires no prior knowledge about the harmonics. Modeling and field examples show that symmetry based noise removal reduces the effects of harmonics. In one modeling example, symmetry based noise removal improved signal to noise ratio in the data by 10%. This improvement had noticeable effects on inversion parameters including water content and the decay constant T2*. Within water content profiles, aquifer boundaries and water content are more accurate after harmonics are removed. Fewer spurious water content spikes appear within aquifers, which is especially useful for resolving multi-layered structures. Within T2* profiles, estimates are more accurate after harmonics are removed, especially in the lower half of profiles.

  11. Source distance determination based on the spherical harmonics

    NASA Astrophysics Data System (ADS)

    Koutny, Adam; Jiricek, Ondrej; Thomas, Jean-Hugh; Brothanek, Marek

    2017-02-01

    This paper deals with the processing of signals measured by a spherical microphone array, focusing on the utilization of near-field information of such an array. The processing, based on the spherical harmonics decomposition, is performed in order to investigate the radial-dependent spherical functions and extract their argument - distance to the source. Using the low-frequency approximation of these functions, the source distance is explicitly expressed. The source distance is also determined from the original equation (using no approximation) by comparing both sides of this equation. The applicability of both methods is first presented in the noise-less data simulation, then validated with data contaminated by the additive white noise of different signal-to-noise ratios. Finally, both methods are tested for real data measured by a rigid spherical microphone array of radius 0.15 m, consisting of 36 microphones for a point source represented by a small speaker. The possibility of determination of the source distance using low-order spherical harmonics is shown.

  12. Equity prices as a simple harmonic oscillator with noise

    NASA Astrophysics Data System (ADS)

    Ataullah, Ali; Tippett, Mark

    2007-08-01

    The centred return on the London Stock Exchange's FTSE All Share Index is modelled as a simple harmonic oscillator with noise over the period from 1 January, 1994 until 30 June 2006. Our empirical results are compatible with the hypothesis that there is a period in the FTSE All Share Index of between two and two and one half years. This means the centred return will on average continue to increase for about a year after reaching the minimum in its oscillatory cycle; alternatively, it will continue on average to decline for about a year after reaching a maximum. Our analysis also shows that there is potential to exploit the harmonic nature of the returns process to earn abnormal profits. Extending our analysis to the low energy states of a quantum harmonic oscillator is also suggested.

  13. Demonstration of Johnson noise thermometry with all-superconducting quantum voltage noise source

    SciTech Connect

    Yamada, Takahiro Urano, Chiharu; Maezawa, Masaaki

    2016-01-25

    We present a Johnson noise thermometry (JNT) system based on an integrated quantum voltage noise source (IQVNS) that has been fully implemented using superconducting circuit technology. To enable precise measurement of Boltzmann's constant, an IQVNS chip was designed to produce intrinsically calculable pseudo-white noise to calibrate the JNT system. On-chip real-time generation of pseudo-random codes via simple circuits produced pseudo-voltage noise with a harmonic tone interval of less than 1 Hz, which was one order of magnitude finer than the harmonic tone interval of conventional quantum voltage noise sources. We estimated a value for Boltzmann's constant experimentally by performing JNT measurements at the temperature of the triple point of water using the IQVNS chip.

  14. Observations of discrete harmonics emerging from equatorial noise.

    PubMed

    Balikhin, Michael A; Shprits, Yuri Y; Walker, Simon N; Chen, Lunjin; Cornilleau-Wehrlin, Nicole; Dandouras, Iannis; Santolik, Ondrej; Carr, Christopher; Yearby, Keith H; Weiss, Benjamin

    2015-07-14

    A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as 'equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes 'ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations.

  15. Observations of discrete harmonics emerging from equatorial noise

    NASA Astrophysics Data System (ADS)

    Balikhin, Michael A.; Shprits, Yuri Y.; Walker, Simon N.; Chen, Lunjin; Cornilleau-Wehrlin, Nicole; Dandouras, Iannis; Santolik, Ondrej; Carr, Christopher; Yearby, Keith H.; Weiss, Benjamin

    2015-07-01

    A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as `equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes `ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations.

  16. Noise Hazard Evaluation Sound Level Data on Noise Sources

    DTIC Science & Technology

    1975-01-01

    AD-A021 465 NOISE HAZARD EfALUATION SOUND LEVEL DATA ON NOISE SOURCES Jeffrey Goldstein Army Environmental Hygiene Agency Prepared for: Army Health ...A. Noise Hazard Evaluation. B. Engineering Noise Control. C. Health Education. D. Audiometry. E. Hearing Protection. This technical guide concerns the...SOUND LEVEL DATA OF NOISE SOURCES Approved for public release, distribution unlimited. jGI4A C4C SENTINEL HEALTH I 5 US ARMY ENVIROIN.MENTAL HYGIENE

  17. Accurate tempo estimation based on harmonic + noise decomposition

    NASA Astrophysics Data System (ADS)

    Alonso, Miguel; Richard, Gael; David, Bertrand

    2006-12-01

    We present an innovative tempo estimation system that processes acoustic audio signals and does not use any high-level musical knowledge. Our proposal relies on a harmonic + noise decomposition of the audio signal by means of a subspace analysis method. Then, a technique to measure the degree of musical accentuation as a function of time is developed and separately applied to the harmonic and noise parts of the input signal. This is followed by a periodicity estimation block that calculates the salience of musical accents for a large number of potential periods. Next, a multipath dynamic programming searches among all the potential periodicities for the most consistent prospects through time, and finally the most energetic candidate is selected as tempo. Our proposal is validated using a manually annotated test-base containing 961 music signals from various musical genres. In addition, the performance of the algorithm under different configurations is compared. The robustness of the algorithm when processing signals of degraded quality is also measured.

  18. Tuning third harmonic generation of impurity doped quantum dots in the presence of Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Saha, Surajit; Ghosh, Manas

    2016-03-01

    We perform a broad exploration of profiles of third harmonic generation (THG) susceptibility of impurity doped quantum dots (QDs) in the presence and absence of noise. We have invoked Gaussian white noise in the present study. A Gaussian impurity has been introduced into the QD. Noise has been applied to the system additively and multiplicatively. A perpendicular magnetic field emerges out as a confinement source and a static external electric field has been applied. The THG profiles have been pursued as a function of incident photon energy when several important parameters such as electric field strength, magnetic field strength, confinement energy, dopant location, Al concentration, dopant potential, relaxation time and noise strength assume different values. Moreover, the role of the pathway through which noise is applied (additive/multiplicative) on the THG profiles has also been deciphered. The THG profiles are found to be decorated with interesting observations such as shift of THG peak position and maximization/minimization of THG peak intensity. Presence of noise alters the characteristics of THG profiles and sometimes enhances the THG peak intensity. Furthermore, the mode of application of noise (additive/multiplicative) also regulates the THG profiles in a few occasions in contrasting manners. The observations highlight the possible scope of tuning the THG coefficient of doped QD systems in the presence of noise and bears tremendous technological importance.

  19. A simulation study of harmonics regeneration in noise reduction for electric and acoustic stimulation

    PubMed Central

    Hu, Yi

    2010-01-01

    Recent research results show that combined electric and acoustic stimulation (EAS) significantly improves speech recognition in noise, and it is generally established that access to the improved F0 representation of target speech, along with the glimpse cues, provide the EAS benefits. Under noisy listening conditions, noise signals degrade these important cues by introducing undesired temporal-frequency components and corrupting harmonics structure. In this study, the potential of combining noise reduction and harmonics regeneration techniques was investigated to further improve speech intelligibility in noise by providing improved beneficial cues for EAS. Three hypotheses were tested: (1) noise reduction methods can improve speech intelligibility in noise for EAS; (2) harmonics regeneration after noise reduction can further improve speech intelligibility in noise for EAS; and (3) harmonics sideband constraints in frequency domain (or equivalently, amplitude modulation in temporal domain), even deterministic ones, can provide additional benefits. Test results demonstrate that combining noise reduction and harmonics regeneration can significantly improve speech recognition in noise for EAS, and it is also beneficial to preserve the harmonics sidebands under adverse listening conditions. This finding warrants further work into the development of algorithms that regenerate harmonics and the related sidebands for EAS processing under noisy conditions. PMID:21117763

  20. A simulation study of harmonics regeneration in noise reduction for electric and acoustic stimulation.

    PubMed

    Hu, Yi

    2010-05-01

    Recent research results show that combined electric and acoustic stimulation (EAS) significantly improves speech recognition in noise, and it is generally established that access to the improved F0 representation of target speech, along with the glimpse cues, provide the EAS benefits. Under noisy listening conditions, noise signals degrade these important cues by introducing undesired temporal-frequency components and corrupting harmonics structure. In this study, the potential of combining noise reduction and harmonics regeneration techniques was investigated to further improve speech intelligibility in noise by providing improved beneficial cues for EAS. Three hypotheses were tested: (1) noise reduction methods can improve speech intelligibility in noise for EAS; (2) harmonics regeneration after noise reduction can further improve speech intelligibility in noise for EAS; and (3) harmonics sideband constraints in frequency domain (or equivalently, amplitude modulation in temporal domain), even deterministic ones, can provide additional benefits. Test results demonstrate that combining noise reduction and harmonics regeneration can significantly improve speech recognition in noise for EAS, and it is also beneficial to preserve the harmonics sidebands under adverse listening conditions. This finding warrants further work into the development of algorithms that regenerate harmonics and the related sidebands for EAS processing under noisy conditions.

  1. [The noise filtering and baseline correction for harmonic spectrum based on wavelet transform].

    PubMed

    Guo, Yuan; Zhao, Xue-Hong; Zhang, Rui; Hu, Ya-Jun; Wang, Yan

    2013-08-01

    The problem of noise and baseline drift is a hot topic in infrared spectral harmonic detection system. This paper presents a new algorithm based on wavelet transform Mallet decomposition to solve the problem of eliminating a variety of complex noise and baseline drift in the harmonic detection. In the algorithm, the appropriate wavelet function and decomposition level were selected to decomposed the noise, baseline drift and useful signal in the harmonic curve into different frequency bands. the bands' information was analysed and a detecting band was set, then the information in useful frequency was reserved by zeroing method of treatment and the coefficient of the threshold. We can just use once transform and reconstruction to remove interference noise and baseline from double-harmonic signal by applying the wavelet transform technique to the harmonic detection spectrum pretreatment. Experiments show that the wavelet transform method can be used to different harmonic detection systems and has universal applicability.

  2. Observations of discrete harmonics emerging from equatorial noise

    PubMed Central

    Balikhin, Michael A.; Shprits, Yuri Y.; Walker, Simon N.; Chen, Lunjin; Cornilleau-Wehrlin, Nicole; Dandouras, Iannis; Santolik, Ondrej; Carr, Christopher; Yearby, Keith H.; Weiss, Benjamin

    2015-01-01

    A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as ‘equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes ‘ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations. PMID:26169360

  3. Speech perception in noise with a harmonic complex excited vocoder.

    PubMed

    Churchill, Tyler H; Kan, Alan; Goupell, Matthew J; Ihlefeld, Antje; Litovsky, Ruth Y

    2014-04-01

    A cochlear implant (CI) presents band-pass-filtered acoustic envelope information by modulating current pulse train levels. Similarly, a vocoder presents envelope information by modulating an acoustic carrier. By studying how normal hearing (NH) listeners are able to understand degraded speech signals with a vocoder, the parameters that best simulate electric hearing and factors that might contribute to the NH-CI performance difference may be better understood. A vocoder with harmonic complex carriers (fundamental frequency, f0 = 100 Hz) was used to study the effect of carrier phase dispersion on speech envelopes and intelligibility. The starting phases of the harmonic components were randomly dispersed to varying degrees prior to carrier filtering and modulation. NH listeners were tested on recognition of a closed set of vocoded words in background noise. Two sets of synthesis filters simulated different amounts of current spread in CIs. Results showed that the speech vocoded with carriers whose starting phases were maximally dispersed was the most intelligible. Superior speech understanding may have been a result of the flattening of the dispersed-phase carrier's intrinsic temporal envelopes produced by the large number of interacting components in the high-frequency channels. Cross-correlogram analyses of auditory nerve model simulations confirmed that randomly dispersing the carrier's component starting phases resulted in better neural envelope representation. However, neural metrics extracted from these analyses were not found to accurately predict speech recognition scores for all vocoded speech conditions. It is possible that central speech understanding mechanisms are insensitive to the envelope-fine structure dichotomy exploited by vocoders.

  4. En route noise: NASA propfan test aircraft (calculated source noise

    NASA Technical Reports Server (NTRS)

    Rickley, E. J.

    1990-01-01

    The second phase of a joint National Aeronautics and Space Administration (NASA) and Federal Aviation Administration (FAA) program to study the high-altitude, low-frequency acoustic noise propagation characteristics of the Advanced Turboprop (propfan) Aircraft was conducted on April 3-13, 1989 at the White Sands Missile Range (WSMR), New Mexico. The first phase was conducted on October 26-31, 1987 in Huntsville, Alabama. NASA (Lewis) measured the source noise of the test aircraft during both phases while NASA (Langley) measured surface noise only during the second phase. FAA/NASA designed a program to obtain noise level data from the propfan test bed aircraft, both in the near field and at ground level, during simulated en route flights (35,000 and 20,000 feet ASL), and to test low frequency atmospheric absorption algorithms and prediction technology to provide insight into the necessity for regulatory measures. The curves of calculated source noise versus emission angle are based on a second order best-fit curve of the peak envelope of the adjusted ground data. Centerline and sideline derived source noise levels are shown to be in good agreement. A comparison of the Alabama chase plane source data and the calculated source noise at centerline for both the Alabama and New Mexico data shows good agreement for the 35,000 and the 20,000 feet (ASL) overflights. With the availability of the New Mexico in-flight data, further in depth comparisons will be made.

  5. Investigation of hydraulic transmission noise sources

    NASA Astrophysics Data System (ADS)

    Klop, Richard J.

    Advanced hydrostatic transmissions and hydraulic hybrids show potential in new market segments such as commercial vehicles and passenger cars. Such new applications regard low noise generation as a high priority, thus, demanding new quiet hydrostatic transmission designs. In this thesis, the aim is to investigate noise sources of hydrostatic transmissions to discover strategies for designing compact and quiet solutions. A model has been developed to capture the interaction of a pump and motor working in a hydrostatic transmission and to predict overall noise sources. This model allows a designer to compare noise sources for various configurations and to design compact and inherently quiet solutions. The model describes dynamics of the system by coupling lumped parameter pump and motor models with a one-dimensional unsteady compressible transmission line model. The model has been verified with dynamic pressure measurements in the line over a wide operating range for several system structures. Simulation studies were performed illustrating sensitivities of several design variables and the potential of the model to design transmissions with minimal noise sources. A semi-anechoic chamber has been designed and constructed suitable for sound intensity measurements that can be used to derive sound power. Measurements proved the potential to reduce audible noise by predicting and reducing both noise sources. Sound power measurements were conducted on a series hybrid transmission test bench to validate the model and compare predicted noise sources with sound power.

  6. A Parameter Identification Method for Helicopter Noise Source Identification and Physics-Based Semi-Empirical Modeling

    NASA Technical Reports Server (NTRS)

    Greenwood, Eric, II; Schmitz, Fredric H.

    2010-01-01

    A new physics-based parameter identification method for rotor harmonic noise sources is developed using an acoustic inverse simulation technique. This new method allows for the identification of individual rotor harmonic noise sources and allows them to be characterized in terms of their individual non-dimensional governing parameters. This new method is applied to both wind tunnel measurements and ground noise measurements of two-bladed rotors. The method is shown to match the parametric trends of main rotor Blade-Vortex Interaction (BVI) noise, allowing accurate estimates of BVI noise to be made for operating conditions based on a small number of measurements taken at different operating conditions.

  7. Frequency synchronization of Fourier domain harmonically mode locked fiber laser by monitoring the supermode noise peaks.

    PubMed

    Li, Feng; Zhang, Aiqin; Feng, Xinhuan; Wai, P K A

    2013-12-16

    In a harmonically mode locked laser, the supermode noise peaks in the RF spectrum can be observed directly because they are separated from the driving frequency and its harmonics of the active mode locker. Using a simple theoretical model, we showed that the intensities of the supermode noise peaks will decrease if the coherence of the laser output decreases. We harmonically mode locked a Fourier domain mode locked (FDML) fiber laser to the third order. We observed that the supermode noise peak intensities decrease significantly when the detune between the sweeping frequency of the tunable filter and the cavity resonant frequency increases. It is therefore possible to use the supermode noise peaks to monitor the frequency detune of the tunable filter for auto-calibration of FDML fiber lasers.

  8. Duct Liner Optimization for Turbomachinery Noise Sources

    DTIC Science & Technology

    1975-11-01

    AD-A279 441lIIIflhIh* NASA TECHNICAL NASA TMA X-72789 MEMORANDUM oo £ 00 r-:. DUCT LINER OPTIMIZATION FOR TURBOMACHINERY w NOISE SOURCES By Harold C...Recipient’s r.atalog No. NASA TM X-72789! 4 Title diid Subtitle 5. Rewrt Date Duct Liner Optimization for Turbomachinery Noise Sources November 1975...profiles is combined wit., a numerical minimization algorithm to predict optimal liner configurations having one, two, and three sections. Source models

  9. The Effects of Ambient Conditions on Helicopter Harmonic Noise Radiation: Theory and Experiment

    NASA Technical Reports Server (NTRS)

    Greenwood, Eric; Sim, Ben W.; Boyd, D. Douglas, Jr.

    2016-01-01

    The effects of ambient atmospheric conditions, air temperature and density, on rotor harmonic noise radiation are characterized using theoretical models and experimental measurements of helicopter noise collected at three different test sites at elevations ranging from sea level to 7000 ft above sea level. Significant changes in the thickness, loading, and blade-vortex interaction noise levels and radiation directions are observed across the different test sites for an AS350 helicopter flying at the same indicated airspeed and gross weight. However, the radiated noise is shown to scale with ambient pressure when the flight condition of the helicopter is defined in nondimensional terms. Although the effective tip Mach number is identified as the primary governing parameter for thickness noise, the nondimensional weight coefficient also impacts lower harmonic loading noise levels, which contribute strongly to low frequency harmonic noise radiation both in and out of the plane of the horizon. Strategies for maintaining the same nondimensional rotor operating condition under different ambient conditions are developed using an analytical model of single main rotor helicopter trim and confirmed using a CAMRAD II model of the AS350 helicopter. The ability of the Fundamental Rotorcraft Acoustics Modeling from Experiments (FRAME) technique to generalize noise measurements made under one set of ambient conditions to make accurate noise predictions under other ambient conditions is also validated.

  10. Flat supercontinuum generation by a F8L in high-energy harmonic noise-like pulsing regime

    NASA Astrophysics Data System (ADS)

    Hernandez-Garcia, J. C.; Estudillo-Ayala, J. M.; Pottiez, O.; Filoteo-Razo, J. D.; Lauterio-Cruz, J. P.; Sierra-Hernandez, J. M.; Rojas-Laguna, R.

    2016-12-01

    We propose the use of a figure eight fiber laser cavity in fundamental and harmonic mode-locking noise-like pulsing regimes, with output pulse energies as high as 302.8 nJ, as an improved supercontinuum source. The absence of a polarizer in the laser setup, so that the state of polarization along the cavity is not restricted, allows enhanced performances compared to other similar schemes. Noise-like pulses with durations of a few tens of ns were generated and a coherence length in the order of ps. For proper adjustments, self-starting passive mode-locking is obtained and a supercontinuum spectrum is observed at the laser output. We observe that the spectrum flatness is significantly improved in the harmonic mode-locking regime of the fiber laser. These results were achieved without the need to insert any high-nonlinearity propagation medium in the setup or at the laser output.

  11. An open-loop RFOG based on harmonic division technique to suppress LD's intensity modulation noise

    NASA Astrophysics Data System (ADS)

    Ying, Diqing; Wang, Zeyu; Mao, Jianmin; Jin, Zhonghe

    2016-11-01

    A harmonic division technique is proposed for an open-loop resonator fiber optic gyro (RFOG) to suppress semiconductor laser diode's (LD's) intensity modulation noise. The theoretical study indicates the RFOG with this technique is immune to the intensity noise. The simulation and experimental results show this technique would lead to a diminished linear region, which still could be acceptable for an RFOG applied to low rotation rate detection. The tests for the gyro output signal are carried out with/without noise suppressing methods, including the harmonic division technique and previously proposed signal compensation technique. With the harmonic division technique at the rotation rate of 10 deg/s, the stability of gyro output signal is improved from 1.07 deg/s to 0.0361 deg/s, whose noise suppressing ratio is more than 3 times as that of the signal compensation technique. And especially, a 3.12 deg/s signal jump is significantly removed with the harmonic division technique; in contrast, a residual 0.36 deg/s signal jump still exists with the signal compensation technique. It is concluded the harmonic division technique does work in intensity noise suppressing under dynamic condition, and it is superior to the signal compensation technique.

  12. Active Control of Aerodynamic Noise Sources

    NASA Technical Reports Server (NTRS)

    Reynolds, Gregory A.

    2001-01-01

    Aerodynamic noise sources become important when propulsion noise is relatively low, as during aircraft landing. Under these conditions, aerodynamic noise from high-lift systems can be significant. The research program and accomplishments described here are directed toward reduction of this aerodynamic noise. Progress toward this objective include correction of flow quality in the Low Turbulence Water Channel flow facility, development of a test model and traversing mechanism, and improvement of the data acquisition and flow visualization capabilities in the Aero. & Fluid Dynamics Laboratory. These developments are described in this report.

  13. Localized, Non-Harmonic Active Flap Motions for Low Frequency In-Plane Rotor Noise Reduction

    NASA Technical Reports Server (NTRS)

    Sim, Ben W.; Potsdam, Mark; Kitaplioglu, Cahit; LeMasurier, Philip; Lorber, Peter; Andrews, Joseph

    2012-01-01

    A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels.

  14. Radiation Sources at Electron Cyclotron Harmonic Frequencies.

    DTIC Science & Technology

    1983-01-28

    KEY WORDS (Continue on reverse side it necesear and Identify by block number) Radiation source, electron cyclotron frequency, gyrotron, travelling ...investigation of gyrotron devices operating in cylindrical geometry. Specific topics include an analysis of oscillations in a gyrotron travelling wave...amplifier, the study of the effects of velocity spread and wall resistivity on gain and bandwidth in a gyrotron travell - ing wave amplifier, an

  15. Harmonic Generation from Solid Targets - Optmization of Source Parameters

    NASA Astrophysics Data System (ADS)

    Zepf, Matthew; Watts, I. F.; Dangor, A. E.; Norreys, P. A.; Chambers, D. M.; Machacek, A.; Wark, J. S.; Tsakiris, G. D.

    1998-11-01

    High harmonics from solid targets have received renewed interest over the last few years. Theoretical predictions using 1 1/2 D codes suggest that very high orders (>100 ) can be generated at conversion efficiencies in excess of 10-6 [1,2] at Iλ^2 > 10^19 W/cm^2. Experiments have since been performed with pulses varying from 100 fs to 2.5 ps in duration [3-6]. The steep density gradient necessary to generate the harmonics can be generated by either ponderomotive steepening or by using ultraclean pulses which preserve the initial solid vacuum boundary. The two regimes are compared in terms of their dependence on the laser parameters and the emitted harmonic radiation. Particular emphasis will be given to measurements of the holeboring velocity, the polarisation of the harmonics and the intensity scaling in the two regimes. This comparison enables us to find the ideal parameter range for the optimization of harmonic source. [1] R. Lichters et al., Physics of Plasmas 3, 3425, (1996). [2] P. Gibbon, IEEE J. of Q. Elec. 33, 1915 (1997). [3] S. Kohlweyer, et al., Optics Comm. 177, 431 (1995). [4] P. Norreys et al., Phys. Rev. Lett., 76, 1832 (1995). [5] D. von der Linde et al., Phys. Rev. A, 52, R25 (1995) [6] M. Zepf, et al., submitted for publication in Phys. Rev. Lett.

  16. Macaque retinal ganglion cell responses to visual patterns: harmonic composition, noise, and psychophysical detectability.

    PubMed

    Cooper, Bonnie; Lee, Barry B; Cao, Dingcai

    2016-06-01

    The goal of these experiments was to test how well cell responses to visual patterns can be predicted from the sinewave tuning curve. Magnocellular (MC) and parvocellular (PC) ganglion cell responses to different spatial waveforms (sinewave, squarewave, and ramp waveforms) were measured across a range of spatial frequencies. Sinewave spatial tuning curves were fit with standard Gaussian models. From these fits, waveforms and spatial tuning of a cell's responses to the other waveforms were predicted for different harmonics by scaling in amplitude for the power in the waveform's Fourier expansion series over spatial frequency. Since higher spatial harmonics move at a higher temporal frequency, an additional scaling for each harmonic by the MC (bandpass) or PC (lowpass) temporal response was included, together with response phase. Finally, the model included a rectifying nonlinearity. This provided a largely satisfactory estimation of MC and PC cell responses to complex waveforms. As a consequence of their transient responses, MC responses to complex waveforms were found to have significantly more energy in higher spatial harmonic components than PC responses. Response variance (noise) was also quantified as a function of harmonic component. Noise increased to some degree for the higher harmonics. The data are relevant for psychophysical detection or discrimination of visual patterns, and we discuss the results in this context.

  17. Garner Valley Vibroseis Data Processing Using Time-Frequency Filtering Techniques to Remove Unwanted Harmonics and External Noise

    NASA Astrophysics Data System (ADS)

    Lord, N. E.; Wang, H. F.; Fratta, D.; Lancelle, C.; Chalari, A.

    2015-12-01

    Time-frequency filtering techniques can greatly improve data quality when combined with frequency swept seismic sources (vibroseis) recorded by seismic arrays by removing unwanted source harmonics or external noise sources (e.g., cultural or ambient noise). A source synchronous filter (SSF) is a time-frequency filter which only passes a specified width frequency band centered on the time varying frequency of the seismic source. A source delay filter (SDF) is a time-frequency filter which only passes those frequencies from the source within a specified delay time range. Both of these time-frequency filters operate on the uncorrelated vibroseis data and allow separate analysis of the source fundamental frequency and each harmonic. In either technique, the time-frequency function of the source can be captured from the source encoder or specified using two or more time-frequency points. SSF and SDF were both used in the processing of the vibroseis data collected in the September 2013 seismic experiment conducted at the NEES@UCSB Garner Valley field site. Three vibroseis sources were used: a 45 kN shear shaker, a 450 N portable mass shaker, and a 26 kN vibroseis truck. Seismic signals from these sources were recorded by two lines of 1 and 3 component accelerometers and geophones, and the Silixa Ltd's intelligent Distributed Acoustic Sensing (iDASTM ) system connected to 762 m of trenched fiber optical cable in a larger rectangular area. SSF and SDF improved vibroseis data quality, simplified data interpretation, and allowed new analysis techniques. This research is part of the larger DOE's PoroTomo project (URL: http://geoscience.wisc.edu/feigl/porotomo).

  18. Physical models for the source of Lascar's harmonic tremor

    NASA Astrophysics Data System (ADS)

    Hellweg, M.

    2000-08-01

    Over an 18 h interval in April 1994, the tremor at Lascar volcano, Chile, was characterized by a spectrum with narrow peaks at a fundamental freqency of about 0.63 Hz and more than 25 overtones at exact integer multiples. This harmonic tremor was recorded at four three-component, high-dynamic range stations during the deployment of the Proyecto de Investigación Sismológica de la Cordillera Occidental 94 (PISCO'94). Usually this tremor's source is modeled as the resonance of a fluid-filled crack or organ pipe-like structure in the volcano. The resonance of a real, physical structure, however, can produce neither as many overtones nor such exact multiples as those observed in the harmonic tremor at Lascar. Harmonics also occur in a spectrum if the source signal is repetitive but nonsinusoidal. Fluid dynamics offers at least three realistic source models for harmonic tremor which produce repetitive, nonsinusoidal waveforms: the release of gas through a very small outlet (the soda bottle model), slug flow in a narrow conduit, and von Kármán vortices produced at obstacles. These models represent different flow regimes, each with its own characteristic range of Reynolds numbers. For each model the fundamental frequency of the tremor is related to the Reynolds number for the flow. Combining the Reynolds numbers for each model with typical kinematic viscosities for the possible fluids present in a volcano—magma, water, steam, air or some combination, at appropriate temperatures and pressures—provides limits on such physical parameters of the volcano as the dimensions of the flow conduit and the flow velocity of the fluid generating the tremor. If any single one of these three models is actually the process in the volcano which generates harmonic tremor, then the tremor is caused by movements of water or gases in the hydrothermal system near the volcano's surface.

  19. Stochastic resonance in a fractional harmonic oscillator subject to random mass and signal-modulated noise

    NASA Astrophysics Data System (ADS)

    Guo, Feng; Zhu, Cheng-Yin; Cheng, Xiao-Feng; Li, Heng

    2016-10-01

    Stochastic resonance in a fractional harmonic oscillator with random mass and signal-modulated noise is investigated. Applying linear system theory and the characteristics of the noises, the analysis expression of the mean output-amplitude-gain (OAG) is obtained. It is shown that the OAG varies non-monotonically with the increase of the intensity of the multiplicative dichotomous noise, with the increase of the frequency of the driving force, as well as with the increase of the system frequency. In addition, the OAG is a non-monotonic function of the system friction coefficient, as a function of the viscous damping coefficient, as a function of the fractional exponent.

  20. Phase effects in masking by harmonic complexes: detection of bands of speech-shaped noise.

    PubMed

    Deroche, Mickael L D; Culling, John F; Chatterjee, Monita

    2014-11-01

    When phase relationships between partials of a complex masker produce highly modulated temporal envelopes on the basilar membrane, listeners may detect speech information from temporal dips in the within-channel masker envelopes. This source of masking release (MR) is however located in regions of unresolved masker partials and it is unclear how much of the speech information in these regions is really needed for intelligibility. Also, other sources of MR such as glimpsing in between resolved masker partials may provide sufficient information from regions that disregard phase relationships. This study simplified the problem of speech recognition to a masked detection task. Target bands of speech-shaped noise were restricted to frequency regions containing either only resolved or only unresolved masker partials, as a function of masker phase relationships (sine or random), masker fundamental frequency (F0) (50, 100, or 200 Hz), and masker spectral profile (flat-spectrum or speech-shaped). Although masker phase effects could be observed in unresolved regions at F0s of 50 and 100 Hz, it was only at 50-Hz F0 that detection thresholds were ever lower in unresolved than in resolved regions, suggesting little role of envelope modulations for harmonic complexes with F0s in the human voice range and at moderate level.

  1. Fan Noise Source Diagnostic Test: Vane Unsteady Pressure Results

    NASA Technical Reports Server (NTRS)

    Envia, Edmane

    2002-01-01

    To investigate the nature of fan outlet guide vane pressure fluctuations and their link to rotor-stator interaction noise, time histories of vane fluctuating pressures were digitally acquired as part of the Fan Noise Source Diagnostic Test. Vane unsteady pressures were measured at seven fan tip speeds for both a radial and a swept vane configuration. Using time-domain averaging and spectral analysis, the blade passing frequency (BPF) harmonic and broadband contents of the vane pressures were individually analyzed. Significant Sound Pressure Level (SPL) reductions were observed for the swept vane relative to the radial vane for the BPF harmonics of vane pressure, but vane broadband reductions due to sweep turned out to be much smaller especially on an average basis. Cross-correlation analysis was used to establish the level of spatial coherence of broadband pressures between different locations on the vane and integral length scales of pressure fluctuations were estimated from these correlations. Two main results of this work are: (1) the average broadband level on the vane (in dB) increases linearly with the fan tip speed for both the radial and swept vanes, and (2) the broadband pressure distribution on the vane is nearly homogeneous and its integral length scale is a monotonically decreasing function of fan tip speed.

  2. New Evidence That Nonlinear Source-Filter Coupling Affects Harmonic Intensity and fo Stability During Instances of Harmonics Crossing Formants.

    PubMed

    Maxfield, Lynn; Palaparthi, Anil; Titze, Ingo

    2017-03-01

    The traditional source-filter theory of voice production describes a linear relationship between the source (glottal flow pulse) and the filter (vocal tract). Such a linear relationship does not allow for nor explain how changes in the filter may impact the stability and regularity of the source. The objective of this experiment was to examine what effect unpredictable changes to vocal tract dimensions could have on fo stability and individual harmonic intensities in situations in which low frequency harmonics cross formants in a fundamental frequency glide. To determine these effects, eight human subjects (five male, three female) were recorded producing fo glides while their vocal tracts were artificially lengthened by a section of vinyl tubing inserted into the mouth. It was hypothesized that if the source and filter operated as a purely linear system, harmonic intensities would increase and decrease at nearly the same rates as they passed through a formant bandwidth, resulting in a relatively symmetric peak on an intensity-time contour. Additionally, fo stability should not be predictably perturbed by formant/harmonic crossings in a linear system. Acoustic analysis of these recordings, however, revealed that harmonic intensity peaks were asymmetric in 76% of cases, and that 85% of fo instabilities aligned with a crossing of one of the first four harmonics with the first three formants. These results provide further evidence that nonlinear dynamics in the source-filter relationship can impact fo stability as well as harmonic intensities as harmonics cross through formant bandwidths.

  3. Reduction of blade-vortex interaction noise using higher harmonic pitch control

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Booth, Earl R., Jr.; Jolly, J. Ralph, Jr.; Yeager, William T., Jr.; Wilbur, Matthew L.

    1989-01-01

    An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in Langley's Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of matched flight conditions, where prescribed (open-loop) higher harmonic pitch was superimposed on the normal (baseline) collective and cyclic trim pitch. For the inflow-microphone noise measurements, advantage was taken of the reverberance in the hard walled tunnel by using a sound power determination approach. Initial findings from on-line data processing for three of the test microphones are reported for a 4/rev (4P) collective pitch control for a range of input amplitudes and phases. By comparing these results to corresponding baseline (no control) conditions, significant noise reductions (4 to 5 dB) were found for low-speed descent conditions, where helicopter BVI noise is most intense. For other rotor flight conditions, the overall noise was found to increase. All cases show increased vibration levels.

  4. Reduction of blade-vortex interaction noise through higher harmonic pitch control

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Booth, Earl R., Jr.; Jolly, J. Ralph, Jr.; Yeager, William T., Jr.; Wilbur, Matthew L.

    1990-01-01

    An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in Langley's Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of matched flight conditions, where prescribed (open-loop) higher harmonic pitch was superimposed on the normal (baseline) collective and cyclic trim pitch. For the inflow-microphone noise measurements, advantage was taken of the reverberance in the hard walled tunnel by using a sound power determination approach. Initial findings from on-line data processing for three of the test microphones are reported for a 4/rev (4P) collective pitch control for a range of input amplitudes and phases. By comparing these results to corresponding baseline (no control) conditions, significant noise reductions (4 to 5 dB) were found for low-speed descent conditions, where helicopter BVI noise is most intense. For other rotor flight conditions, the overall noise was found to increase. All cases show increased vibration levels.

  5. Aeroacoustic sources of motorcycle helmet noise.

    PubMed

    Kennedy, J; Adetifa, O; Carley, M; Holt, N; Walker, I

    2011-09-01

    The prevalence of noise in the riding of motorcycles has been a source of concern to both riders and researchers in recent times. Detailed flow field information will allow insight into the flow mechanisms responsible for the production of sound within motorcycle helmets. Flow field surveys of this nature are not found in the available literature which has tended to focus on sound pressure levels at ear as these are of interest for noise exposure legislation. A detailed flow survey of a commercial motorcycle helmet has been carried out in combination with surface pressure measurements and at ear acoustics. Three potential noise source regions are investigated, namely, the helmet wake, the surface boundary layer and the cavity under the helmet at the chin bar. Extensive information is provided on the structure of the helmet wake including its frequency content. While the wake and boundary layer flows showed negligible contributions to at-ear sound the cavity region around the chin bar was identified as a key noise source. The contribution of the cavity region was investigated as a function of flow speed and helmet angle both of which are shown to be key factors governing the sound produced by this region.

  6. Identification and tracking of harmonic sources in a power system using a Kalman filter

    SciTech Connect

    Ma, H.; Girgis, A.A.

    1996-07-01

    In this paper, two problems have been addressed on harmonic sources identification: the optimal locations of a limited number of harmonic meters and the optimal dynamic estimates of harmonic source locations and their injections in unbalanced three-phase power systems. A Kalman filtering is used to attack these problems. System error covariance analysis by the Kalman filter associated with a harmonic injection estimate determines the optimal arrangement of limited harmonic meters. Based on the optimally-arranged harmonic metering locations, the Kalman filter then yields the optimal dynamic estimates of harmonic injections with a few noisy harmonic measurements. The method is dynamic and has the capability of identifying, analyzing and tracking each harmonic injection at all buses in unbalanced three-phase power systems. Actual recorded harmonic measurements and simulated data in a power distribution system are provided to prove the efficiency of this approach.

  7. Sparse maximum harmonics-to-noise-ratio deconvolution for weak fault signature detection in bearings

    NASA Astrophysics Data System (ADS)

    Miao, Yonghao; Zhao, Ming; Lin, Jing; Xu, Xiaoqiang

    2016-10-01

    De-noising and enhancement of the weak fault signature from the noisy signal are crucial for fault diagnosis, as features are often very weak and masked by the background noise. Deconvolution methods have a significant advantage in counteracting the influence of the transmission path and enhancing the fault impulses. However, the performance of traditional deconvolution methods is greatly affected by some limitations, which restrict the application range. Therefore, this paper proposes a new deconvolution method, named sparse maximum harmonics-noise-ratio deconvolution (SMHD), that employs a novel index, the harmonics-to-noise ratio (HNR), to be the objective function for iteratively choosing the optimum filter coefficients to maximize HNR. SMHD is designed to enhance latent periodic impulse faults from heavy noise signals by calculating the HNR to estimate the period. A sparse factor is utilized to further suppress the noise and improve the signal-to-noise ratio of the filtered signal in every iteration step. In addition, the updating process of the sparse threshold value and the period guarantees the robustness of SMHD. On this basis, the new method not only overcomes the limitations associated with traditional deconvolution methods, minimum entropy deconvolution (MED) and maximum correlated kurtosis deconvolution (MCKD), but visual inspection is also better, even if the fault period is not provided in advance. Moreover, the efficiency of the proposed method is verified by simulations and bearing data from different test rigs. The results show that the proposed method is effective in the detection of various bearing faults compared with the original MED and MCKD.

  8. The Effect of Non-Harmonic Active Twist Actuation on BVI Noise

    NASA Technical Reports Server (NTRS)

    Fogarty, David E.; Wilbur, Matthew L.; Sekula, Martin K.

    2011-01-01

    The results of a computational study examining the effects of non-harmonic active-twist control on blade-vortex interaction (BVI) noise for the Apache Active Twist Rotor are presented. Rotor aeroelastic behavior was modeled using the Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics code and the rotor noise was predicted using the acoustics code PSU-WOPWOP. The application of non-harmonic active-twist inputs to the main rotor blade system comprised three parameters: azimuthal location to start actuation, azimuthal duration of actuation, and magnitude of actuation. The acoustic analysis was conducted for a single low-speed flight condition of advance ratio mu=0.14 and shaft angle-of-attack, a(sub s)=+6deg. BVI noise levels were predicted on a flat plane of observers located 1.1 rotor diameters beneath the rotor. The results indicate significant reductions of up to 10dB in BVI noise using a starting azimuthal location for actuation of 90?, an azimuthal duration of actuation of 90deg, and an actuation magnitude of +1.5 ft-lb.

  9. Jet engine noise source and noise footprint computer programs

    NASA Technical Reports Server (NTRS)

    Dunn, D. G.; Peart, N. A.; Miller, D. L.; Crowley, K. C.

    1972-01-01

    Calculation procedures are presented for predicting maximum passby noise levels and contours (footprints) of conventional jet aircraft with or without noise suppression devices. The procedures have been computerized and a user's guide is presented for the computer programs to be used in predicting the noise characteristics during aircraft takeoffs, fly-over, and/or landing operations.

  10. Experimental observation of excess noise in a detuned phase-modulation harmonic mode-locking laser

    SciTech Connect

    Yang Shiquan; Bao Xiaoyi

    2006-09-15

    The intracavity phase-modulated laser can work in two distinct stages: 1) phase mode-locking when the applied modulation frequency is equal to the cavity's fundamental frequency or one of its harmonics, and 2) the FM laser oscillation at a moderate detuned modulation frequency. In this paper, we experimentally studied the noise buildup process in the transition from FM laser oscillation to phase mode-locking in a phase-modulated laser. We found that the relaxation oscillation frequency varies with the modulation frequency detuning and the relaxation oscillation will occur twice in the transition region. Between these two relaxation oscillations, the supermode noise can be significantly enhanced, which is evidence of excess noise in laser systems. All of these results can be explained by the theory of Floquet modes in a phase-modulated laser cavity.

  11. Phase noise mitigation of QPSK signal utilizing phase-locked multiplexing of signal harmonics and amplitude saturation.

    PubMed

    Mohajerin-Ariaei, Amirhossein; Ziyadi, Morteza; Chitgarha, Mohammad Reza; Almaiman, Ahmed; Cao, Yinwen; Shamee, Bishara; Yang, Jeng-Yuan; Akasaka, Youichi; Sekiya, Motoyoshi; Takasaka, Shigehiro; Sugizaki, Ryuichi; Touch, Joseph D; Tur, Moshe; Langrock, Carsten; Fejer, Martin M; Willner, Alan E

    2015-07-15

    We demonstrate an all-optical phase noise mitigation scheme based on the generation, delay, and coherent summation of higher order signal harmonics. The signal, its third-order harmonic, and their corresponding delayed variant conjugates create a staircase phase-transfer function that quantizes the phase of quadrature-phase-shift-keying (QPSK) signal to mitigate phase noise. The signal and the harmonics are automatically phase-locked multiplexed, avoiding the need for phase-based feedback loop and injection locking to maintain coherency. The residual phase noise converts to amplitude noise in the quantizer stage, which is suppressed by parametric amplification in the saturation regime. Phase noise reduction of ∼40% and OSNR-gain of ∼3  dB at BER 10(-3) are experimentally demonstrated for 20- and 30-Gbaud QPSK input signals.

  12. Resonant behavior of a harmonic oscillator with fluctuating mass driven by a Mittag-Leffler noise

    NASA Astrophysics Data System (ADS)

    Zhong, Suchuan; Yang, Jianqiang; Zhang, Lu; Ma, Hong; Luo, Maokang

    2017-02-01

    The resonant behavior of a generalized Langevin equation (GLE) in the presence of a Mittag-Leffler noise is studied analytically in this paper. Considering that a GLE with a Mittag-Leffler friction kernel is very useful for modeling anomalous diffusion processes with long-memory and long-range dependence, and the surrounding molecules do not only collide with the Brownian particle but also adhere to the Brownian particle for random time. Thus, we consider the Brownian particle with fluctuating mass, and the fluctuations of the mass are modelled as a dichotomous noise. Applying the stochastic averaging method, we obtain the exact expression of the output amplitude gain of the system. By studying the impact of the driving frequency and the noise parameters, we find the non-monotonic behaviors of the output amplitude gain. The results indicate that the bona fide SR, the wide sense SR and the conventional SR phenomena occur in the proposed harmonic oscillator with fluctuating mass driven by Mittag-Leffler noise. It is found that when we consider the output amplitude gain versus the driving frequency, the phenomena of stochastic multi-resonance (SMR) with two, three and four peaks are observed, and the quadruple-peaks SR phenomenon had never been observed in previous literature. Besides, when we investigate the dependence of output amplitude gain on the memory exponent, the inverse stochastic resonance (ISR) phenomenon takes place, in contrast to the well-known phenomenon of stochastic resonance. Furthermore, we compare the corresponding ordinary harmonic oscillator without memory to our generalized model, and found that the properties of long-memory and long-range dependence endows our generalized model with more abundant dynamic behaviors than the ordinary harmonic oscillator without memory.

  13. Study of noise sources in a subsonic fan using measured blade pressures and acoustic theory

    NASA Technical Reports Server (NTRS)

    Hanson, D. B.

    1975-01-01

    Sources of noise in a 1.4 m (4.6 ft) diameter subsonic tip speed propulsive fan running statically outdoors are studied using a combination of techniques. Signals measured with pressure transducers on a rotor blade are plotted in a format showing the space-time history of inlet distortion. Study of these plots visually and with statistical correlation analysis confirms that the inlet flow contains long, thin eddies of turbulence. Turbulence generated in the boundary layer of the shroud upstream of the rotor tips was not found to be an important noise source. Fan noise is diagnosed by computing narrowband spectra of rotor and stator sound power and comparing these with measured sound power spectra. Rotor noise is computed from spectra of the measured blade pressures and stator noise is computed using the author's stator noise theory. It is concluded that the rotor and stator sources contribute about equally at frequencies in the vicinity of the first three harmonics of blade passing frequency. At higher frequencies, the stator contribution diminishes rapidly and the rotor/inlet turbulence mechanism dominates. Two parametric studies are performed by using the rotor noise calculation procedure which was correlated with test. In the first study, the effects on noise spectrum and directivity are calculated for changes in turbulence properties, rotational Mach number, number of blades, and stagger angle. In the second study the influences of design tip speed and blade number on noise are evaluated.

  14. Multiple-source multiple-harmonic active vibration control of variable section cylindrical structures: A numerical study

    NASA Astrophysics Data System (ADS)

    Liu, Jinxin; Chen, Xuefeng; Gao, Jiawei; Zhang, Xingwu

    2016-12-01

    Air vehicles, space vehicles and underwater vehicles, the cabins of which can be viewed as variable section cylindrical structures, have multiple rotational vibration sources (e.g., engines, propellers, compressors and motors), making the spectrum of noise multiple-harmonic. The suppression of such noise has been a focus of interests in the field of active vibration control (AVC). In this paper, a multiple-source multiple-harmonic (MSMH) active vibration suppression algorithm with feed-forward structure is proposed based on reference amplitude rectification and conjugate gradient method (CGM). An AVC simulation scheme called finite element model in-loop simulation (FEMILS) is also proposed for rapid algorithm verification. Numerical studies of AVC are conducted on a variable section cylindrical structure based on the proposed MSMH algorithm and FEMILS scheme. It can be seen from the numerical studies that: (1) the proposed MSMH algorithm can individually suppress each component of the multiple-harmonic noise with an unified and improved convergence rate; (2) the FEMILS scheme is convenient and straightforward for multiple-source simulations with an acceptable loop time. Moreover, the simulations have similar procedure to real-life control and can be easily extended to physical model platform.

  15. Prewhitening of Colored Noise Fields for Detection of Threshold Sources

    DTIC Science & Technology

    1993-11-07

    determines the noise covariance matrix, prewhitening techniques allow detection of threshold sources. The multiple signal classification ( MUSIC ...SUBJECT TERMS 1S. NUMBER OF PAGES AR Model, Colored Noise Field, Mixed Spectra Model, MUSIC , Noise Field, 52 Prewhitening, SNR, Standardized Test...EXAMPLE 2: COMPLEX AR COEFFICIENT .............................................. 5 EXAMPLE 3: MUSIC IN A COLORED BACKGROUND NOISE ...................... 6

  16. Sources of noise in magneto-optical readout

    NASA Technical Reports Server (NTRS)

    Mansuripur, M.

    1991-01-01

    The various sources of noise which are often encountered in magneto-optical readout systems are analyzed. Although the focus is on magneto-optics, most sources of noise are common among the various optical recording systems and one can easily adapt the results to other media and systems. A description of the magneto-optical readout system under consideration is given, and the standard methods and the relevant terminology of signal and noise measurement are described. The characteristics of thermal noise, which originates in the electronic circuitry of the readout system, are described. The most fundamental of all sources of noise, the shot noise, is considered, and a detailed account of its statistical properties is given. Shot noise, which is due to random fluctuations in photon arrival times, is an ever-present noise in optical detection. Since the performance of magneto-optical recording devices in use today is approaching the limit imposed by the shot noise, it is important that the reader have a good grasp of this particular source of noise. A model for the laser noise is described, and measurement results which yield numerical values for the strength of the laser power fluctuations are presented. Spatial variations of the disk reflectivity and random depolarization phenomena also contribute to the overall level of noise in readout; these and related issues are treated. Numerical simulation results describing some of the more frequently encountered sources of noise which accompany the recorded waveform itself, namely, jitter noise and signal-amplitude fluctuation noise are presented.

  17. Assessing noise sources at synchrotron infrared ports

    PubMed Central

    Lerch, Ph.; Dumas, P.; Schilcher, T.; Nadji, A.; Luedeke, A.; Hubert, N.; Cassinari, L.; Boege, M.; Denard, J.-C.; Stingelin, L.; Nadolski, L.; Garvey, T.; Albert, S.; Gough, Ch.; Quack, M.; Wambach, J.; Dehler, M.; Filhol, J.-M.

    2012-01-01

    Today, the vast majority of electron storage rings delivering synchrotron radiation for general user operation offer a dedicated infrared port. There is growing interest expressed by various scientific communities to exploit the mid-IR emission in microspectroscopy, as well as the far infrared (also called THz) range for spectroscopy. Compared with a thermal (laboratory-based source), IR synchrotron radiation sources offer enhanced brilliance of about two to three orders of magnitude in the mid-IR energy range, and enhanced flux and brilliance in the far-IR energy range. Synchrotron radiation also has a unique combination of a broad wavelength band together with a well defined time structure. Thermal sources (globar, mercury filament) have excellent stability. Because the sampling rate of a typical IR Fourier-transform spectroscopy experiment is in the kHz range (depending on the bandwidth of the detector), instabilities of various origins present in synchrotron radiation sources play a crucial role. Noise recordings at two different IR ports located at the Swiss Light Source and SOLEIL (France), under conditions relevant to real experiments, are discussed. The lowest electron beam fluctuations detectable in IR spectra have been quantified and are shown to be much smaller than what is routinely recorded by beam-position monitors. PMID:22186638

  18. Raman fiber laser harmonically mode-locked by exploiting the intermodal beating of CW multimode pump source.

    PubMed

    Luo, Z Q; Ye, C C; Fu, H Y; Cheng, H H; Wang, J Z; Cai, Z P

    2012-08-27

    We report here the first demonstration of a harmonic mode-locked Raman fiber laser using the intermodal beating of a continuous-wave (CW) multiple-longitudinal-mode pump laser. By matching the Raman-cavity round-trip frequency with the intermodal-beating one of a 1064 nm CW pump source, harmonic mode-locking in phosphosilicate Raman fiber laser is stably initiated at the first-order Stokes of 1239.5 nm, and generates rectangular-shape nanosecond pulses with the pulse energy up to 4.25 nJ. Using the new type of mode-locking, the harmonic order can be discretely tuned from 78 th- to 693 rd-order, and the cavity supermode is suppressed up to 51.1 dB with the signal-to-noise ratio of more than 65 dB.

  19. A Robust Waveguide Millimeter-Wave Noise Source

    NASA Technical Reports Server (NTRS)

    Ehsan, Negar; Piepmeier, Jeffrey R.; Solly, Michael; Macmurphy, Shawn; Lucey, Jared; Wollack, Edward

    2015-01-01

    This paper presents the design, fabrication, and characterization of a millimeter-wave noise source for the 160- 210 GHz frequency range. The noise source has been implemented in an E-split-block waveguide package and the internal circuitry was developed on a quartz substrate. The measured excess noise ratio at 200 GHz is 9.6 dB.

  20. Procedure for Separating Noise Sources in Measurements of Turbofan Engine Core Noise

    NASA Technical Reports Server (NTRS)

    Miles, Jeffrey Hilton

    2006-01-01

    The study of core noise from turbofan engines has become more important as noise from other sources like the fan and jet have been reduced. A multiple microphone and acoustic source modeling method to separate correlated and uncorrelated sources has been developed. The auto and cross spectrum in the frequency range below 1000 Hz is fitted with a noise propagation model based on a source couplet consisting of a single incoherent source with a single coherent source or a source triplet consisting of a single incoherent source with two coherent point sources. Examples are presented using data from a Pratt & Whitney PW4098 turbofan engine. The method works well.

  1. Teaching Doppler Effect with a passing noise source

    NASA Astrophysics Data System (ADS)

    Costa, Ivan F.; Mocellin, Alexandra

    2010-07-01

    The noise pitch variation of a passing noise source allows a low cost experimental approach to calculate speed and, for the first time, distance. We adjusted the recorded noise pitch variation to the Doppler shift equation for sound. We did this by taking into account the frequency delay due to the sound source displacement and performing a Fast Fourier Transform (FFT) of the noise signal using free software. This experimental method was successfully applied to aircraft and automobiles.

  2. Duct liner optimization for turbomachinery noise sources. [aircraft noise/engine noise - numerical analysis

    NASA Technical Reports Server (NTRS)

    Lester, H. C.; Posey, J. W.

    1975-01-01

    An acoustical field theory for axisymmetric, multisectioned lined ducts with uniform flow profiles was combined with a numerical minimization algorithm to predict optimal liner configurations having one, two, and three sections. Source models studied include a point source located on the axis of the duct and rotor/outlet-stator viscous wake interaction effects for a typical research compressor operating at an axial flow Mach number of about 0.4. For this latter source, optimal liners for equipartition-of energy, zero-phase, and least-attenuated-mode source variations were also calculated and compared with exact results. It is found that the potential benefits of liner segmentation for the attenuation of turbomachinery noise is greater than would be predicted from point source results. Furthermore, effective liner design requires precise knowledge of the circumferential and radial modal distributions.

  3. Identification of Noise Sources and Design of Noise Reduction Measures for a Pneumatic Nail Gun.

    PubMed

    Jayakumar, Vignesh; Kim, Jay; Zechmann, Edward

    An experimental-analytical procedure was implemented to reduce the operating noise level of a nail gun, a commonly found power tool in a construction site. The procedure is comprised of preliminary measurements, identification and ranking of major noise sources and application of noise controls. Preliminary measurements show that the impact noise transmitted through the structure and the exhaust related noise were found to be the first and second major contributors. Applying a noise absorbing foam on the outside of the nail gun body was found to be an effective noise reduction technique. One and two-volume small mufflers were designed and applied to the exhaust side of the nail gun which reduced not only the exhaust noise but also the impact noise. It was shown that the overall noise level could be reduced by as much as 3.5 dB, suggesting that significant noise reduction is possible in construction power tools without any significant increase of the cost.

  4. Modeling Helicopter Near-Horizon Harmonic Noise Due to Transient Maneuvers

    DTIC Science & Technology

    2013-01-01

    processor to compare BVI noise with wind tunnel data [8]. The results showed good agreement with the wind tunnel , but highlighted the dependence on...first principles models of the dominant noise sources with analytical models from wind tunnel experiments and flight tests to form a semi-empirical...While wind tunnel experiments may seem like an attractive option for obtaining this acoustic data, they do not always yield accurate measurements

  5. Aircraft noise source and contour estimation

    NASA Technical Reports Server (NTRS)

    Dunn, D. G.; Peart, N. A.

    1973-01-01

    Calculation procedures are presented for predicting the noise-time histories and noise contours (footprints) of five basic types of aircraft; turbojet, turofan, turboprop, V/STOL, and helicopter. The procedures have been computerized to facilitate prediction of the noise characteristics during takeoffs, flyovers, and/or landing operations.

  6. Aeroacoustic Codes For Rotor Harmonic and BVI Noise--CAMRAD.Mod1/HIRES

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Boyd, D. Douglas, Jr.; Burley, Casey L.; Jolly, J. Ralph, Jr.

    1996-01-01

    This paper presents a status of non-CFD aeroacoustic codes at NASA Langley Research Center for the prediction of helicopter harmonic and Blade-Vortex Interaction (BVI) noise. The prediction approach incorporates three primary components: CAMRAD.Mod1 - a substantially modified version of the performance/trim/wake code CAMRAD; HIRES - a high resolution blade loads post-processor; and WOPWOP - an acoustic code. The functional capabilities and physical modeling in CAMRAD.Mod1/HIRES will be summarized and illustrated. A new multi-core roll-up wake modeling approach is introduced and validated. Predictions of rotor wake and radiated noise are compared with to the results of the HART program, a model BO-105 windtunnel test at the DNW in Europe. Additional comparisons are made to results from a DNW test of a contemporary design four-bladed rotor, as well as from a Langley test of a single proprotor (tiltrotor) three-bladed model configuration. Because the method is shown to help eliminate the necessity of guesswork in setting code parameters between different rotor configurations, it should prove useful as a rotor noise design tool.

  7. Advances in automated noise data acquisition and noise source modeling for power reactors

    SciTech Connect

    Clapp, N.E. Jr.; Kryter, R.C.; Sweeney, F.J.; Renier, J.A.

    1981-01-01

    A newly expanded program, directed toward achieving a better appreciation of both the strengths and limitations of on-line, noise-based, long-term surveillance programs for nuclear reactors, is described. Initial results in the complementary experimental (acquisition and automated screening of noise signatures) and theoretical (stochastic modeling of likely noise sources) areas of investigation are given.

  8. Noise optimization of the source follower of a CMOS pixel using BSIM3 noise model

    NASA Astrophysics Data System (ADS)

    Mahato, Swaraj; Meynants, Guy; Raskin, Gert; De Ridder, J.; Van Winckel, H.

    2016-07-01

    CMOS imagers are becoming increasingly popular in astronomy. A very low noise level is required to observe extremely faint targets and to get high-precision flux measurements. Although CMOS technology offers many advantages over CCDs, a major bottleneck is still the read noise. To move from an industrial CMOS sensor to one suitable for scientific applications, an improved design that optimizes the noise level is essential. Here, we study the 1/f and thermal noise performance of the source follower (SF) of a CMOS pixel in detail. We identify the relevant design parameters, and analytically study their impact on the noise level using the BSIM3v3 noise model with an enhanced model of gate capacitance. Our detailed analysis shows that the dependence of the 1/f noise on the geometrical size of the source follower is not limited to minimum channel length, compared to the classical approach to achieve the minimum 1/f noise. We derive the optimal gate dimensions (the width and the length) of the source follower that minimize the 1/f noise, and validate our results using numerical simulations. By considering the thermal noise or white noise along with 1/f noise, the total input noise of the source follower depends on the capacitor ratio CG/CFD and the drain current (Id). Here, CG is the total gate capacitance of the source follower and CFD is the total floating diffusion capacitor at the input of the source follower. We demonstrate that the optimum gate capacitance (CG) depends on the chosen bias current but ranges from CFD/3 to CFD to achieve the minimum total noise of the source follower. Numerical calculation and circuit simulation with 180nm CMOS technology are performed to validate our results.

  9. The Effects of Ambient Conditions on Helicopter Rotor Source Noise Modeling

    NASA Technical Reports Server (NTRS)

    Schmitz, Frederic H.; Greenwood, Eric

    2011-01-01

    A new physics-based method called Fundamental Rotorcraft Acoustic Modeling from Experiments (FRAME) is used to demonstrate the change in rotor harmonic noise of a helicopter operating at different ambient conditions. FRAME is based upon a non-dimensional representation of the governing acoustic and performance equations of a single rotor helicopter. Measured external noise is used together with parameter identification techniques to develop a model of helicopter external noise that is a hybrid between theory and experiment. The FRAME method is used to evaluate the main rotor harmonic noise of a Bell 206B3 helicopter operating at different altitudes. The variation with altitude of Blade-Vortex Interaction (BVI) noise, known to be a strong function of the helicopter s advance ratio, is dependent upon which definition of airspeed is flown by the pilot. If normal flight procedures are followed and indicated airspeed (IAS) is held constant, the true airspeed (TAS) of the helicopter increases with altitude. This causes an increase in advance ratio and a decrease in the speed of sound which results in large changes to BVI noise levels. Results also show that thickness noise on this helicopter becomes more intense at high altitudes where advancing tip Mach number increases because the speed of sound is decreasing and advance ratio increasing for the same indicated airspeed. These results suggest that existing measurement-based empirically derived helicopter rotor noise source models may give incorrect noise estimates when they are used at conditions where data were not measured and may need to be corrected for mission land-use planning purposes.

  10. Review of Subcritical Source-Driven Noise Analysis Measurements

    SciTech Connect

    Valentine, T.E.

    1999-11-01

    Subcritical source-driven noise measurements are simultaneous Rossia and randomly pulsed neutron measurements that provide measured quantities that can be related to the subcritical neutron multiplication factor. In fact, subcritical source-driven noise measurements should be performed in lieu of Rossia measurements because of the additional information that is obtained from noise measurements such as the spectral ratio and the coherence functions. The basic understanding of source-driven noise analysis measurements can be developed from a point reactor kinetics model to demonstrate how the measured quantities relate to the subcritical neutron multiplication factor.

  11. Sources of noise in Brillouin optical time-domain analyzers

    NASA Astrophysics Data System (ADS)

    Urricelqui, Javier; Soto, Marcelo A.; Thévenaz, Luc

    2015-09-01

    This paper presents a thorough study of the different sources of noise affecting Brillouin optical time-domain analyzers (BOTDA), providing a deep insight into the understanding of the fundamental limitations of this kind of sensors. Analytical and experimental results indicate that the noise source ultimately fixing the sensor performance depends basically on the fiber length and the input pump-probe powers. Thus, while the phase-to-intensity noise conversion induced by stimulated Brillouin scattering can have a dominating effect at short distances, a combination of sources determines the noise in longrange sensing, basically dominated by probe double Rayleigh scattering.

  12. Noise characterization of mode-locked lasers by comparing the power spectra of the fundamental and second-harmonic pulses

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Chen, L. P.; Liu, J. M.

    1995-10-01

    By comparing the noise power spectra of the fundamental pulses and those of the second-harmonic pulses, the peak intensity fluctuation, the pulse-width fluctuation, the pulse timing jitter, and the cross correlation between the pulse width and the peak intensity fluctuations of a mode-locked pulse train can be separately quantified. The noise characteristics of an actively mode-locked Nd:YLF laser are presented to demonstrate this technique.

  13. Continuous-variable quantum key distribution with Gaussian source noise

    SciTech Connect

    Shen Yujie; Peng Xiang; Yang Jian; Guo Hong

    2011-05-15

    Source noise affects the security of continuous-variable quantum key distribution (CV QKD) and is difficult to analyze. We propose a model to characterize Gaussian source noise through introducing a neutral party (Fred) who induces the noise with a general unitary transformation. Without knowing Fred's exact state, we derive the security bounds for both reverse and direct reconciliations and show that the bound for reverse reconciliation is tight.

  14. Noise Characterization of Supercontinuum Sources for Low Coherence Interferometry Applications

    PubMed Central

    Brown, William J.; Kim, Sanghoon; Wax, Adam

    2015-01-01

    We examine the noise properties of supercontinuum light sources when used in low coherence interferometry applications. The first application is a multiple-scattering low-coherence interferometry (ms2/LCI) system where high power and long image acquisition times are required to image deep into tissue. For this system we compare the noise characteristics of two supercontinuum sources from different suppliers. Both sources have long term drift that limits the amount of time over which signal averaging is advantageous for reducing noise. The second application is a high resolution optical coherence tomography system where broadband light is needed for high axial resolution. For this system we compare the noise performance of the two supercontinuum sources and a light source based on four superluminescent diodes (SLDs) using imaging contrast as a comparative metric. We find that the NKT SuperK has superior noise performance compared to the Fianium SC-450-4 but neither meets the performance of the SLDs. PMID:25606759

  15. Analysis and Synthesis of Tonal Aircraft Noise Sources

    NASA Technical Reports Server (NTRS)

    Allen, Matthew P.; Rizzi, Stephen A.; Burdisso, Ricardo; Okcu, Selen

    2012-01-01

    Fixed and rotary wing aircraft operations can have a significant impact on communities in proximity to airports. Simulation of predicted aircraft flyover noise, paired with listening tests, is useful to noise reduction efforts since it allows direct annoyance evaluation of aircraft or operations currently in the design phase. This paper describes efforts to improve the realism of synthesized source noise by including short term fluctuations, specifically for inlet-radiated tones resulting from the fan stage of turbomachinery. It details analysis performed on an existing set of recorded turbofan data to isolate inlet-radiated tonal fan noise, then extract and model short term tonal fluctuations using the analytic signal. Methodologies for synthesizing time-variant tonal and broadband turbofan noise sources using measured fluctuations are also described. Finally, subjective listening test results are discussed which indicate that time-variant synthesized source noise is perceived to be very similar to recordings.

  16. Noise sources in laser radar systems.

    PubMed

    Letalick, D; Renhorn, I; Steinvall, O; Shapiro, J H

    1989-07-01

    To understand the fundamental limit of performance with a given laser radar system, the phase noise of a testbed laser radar has been investigated. Apart from the phase noise in the transmitter laser and the local oscillator laser, additional phase noise was introduced by vibrations caused by fans in power supplies and cooling systems. The stability of the mechanical structure of the platform was also found to be of great importance. Furthermore, a model for the signal variations from diffuse targets has been developed. This model takes into account the stray light, the speckle decorrelation, and Doppler shift due to moving targets.

  17. Second and Third Harmonic Measurements at the Linac Coherent Light Source

    SciTech Connect

    Ratner, D.; Brachmann, A.; Decker, F.J.; Ding, Y.; Dowell, D.; Emma, P.; Fisher, A.; Frisch, J.; Gilevich, S.; Huang, Z.; Hering, P.; Iverson, R.; Krzywinski, J.; Loos, H.; Messerschmidt, M.; Nuhn, H.D.; Smith, T.; Turner, J.; Welch, J.; White, W.; Wu, J.; /SLAC

    2011-01-03

    The Linac Coherent Light Source (LCLS) started user commissioning in October of 2009, producing Free Electron Laser (FEL) radiation between 800 eV and 8 keV [1]. The fundamental wavelength of the FEL dominates radiation in the beamlines, but the beam also produces nonnegligible levels of radiation at higher harmonics. The harmonics may be desirable as a source of harder X-rays, but may also contribute backgrounds to user experiments. In this paper we present preliminary measurements of the second and third harmonic content in the FEL. We also measure the photon energy cutoff of the soft X-ray mirrors to determine the extent to which higher harmonics reach the experimental stations. We present preliminary second and third harmonic measurements for LCLS. At low energies (below 1 keV fundamental) we measure less than 0.1% second harmonic content. The second harmonic will be present in the soft X-ray beam line for fundamental photon energies below approximately 1.1 keV. At low and high energies, we measure third harmonic content ranging from 0.5% to 3%, which is consistent with expectations. For both second and third harmonics, experimental work is ongoing. More rigorous analysis of the data will be completed soon.

  18. Development of Harmonic-Noise Reduction Technology in Diagnostic Method using AC Loss Current for Water Treed XLPE Cable

    NASA Astrophysics Data System (ADS)

    Tsujimoto, Tomiyuki; Nakade, Masahiko; Yagi, Yukihiro; Ishii, Noboru

    Water tree is one of the degradation aspects of XLPE cables used for under-ground distribution or transmission lines. We have developed the loss current method using 3rd harmonic in AC loss current for cable diagnosis. Harmonic components in loss current arise as a result of the non-linear voltage-current characteristics of water trees. We confirmed that the 3rd harmonic in AC loss current had good correlation with water tree growth and break down strength. After that, we have applied this method to the actual 66kV XLPE cable lines. Up to now, the number of the application results is more than 120 lines. In this method, it is sometimes said that the degradation signal (3rd harmonic in loss current) is affected by the 3rd harmonic in the test voltage. To indicate and solve this problem, we investigated the extent of influence by 3rd harmonic in the test voltage, and found the rule of the influence. As a result, we developed a new technique of harmonic-noise reduction in loss current method that enabled a more highly accurate diagnosis and confirmed the effectiveness of this new technique by simulations and experiments with actual cables.

  19. Inverting seismic noise cross-correlations for noise source distribution: A step towards reducing source-induced bias in seismic noise interferometry

    NASA Astrophysics Data System (ADS)

    Ermert, Laura; Afanasiev, Michael; Sager, Korbinian; Gokhberg, Alexey; Fichtner, Andreas

    2016-04-01

    We report on the ongoing development of a new inversion method for the space- and time-dependent power spectral density distribution of ambient seismic noise sources. The method, once complete, will mainly serve two purposes: First, it will allow us to construct more realistic forward models for noise cross-correlation waveforms, thereby opening new possibilities for waveform imaging by ambient noise tomography. Second, it may provide new insights about the properties of ambient noise sources, complementing studies based on beamforming or numerical modeling of noise based on oceanographic observations. To invert for noise sources, we consider surface wave signal energy measurements on the 'causal' (station A to B) and on the 'acausal' (station B to A) correlation branch, and the ratio between them. These and similar measurements have proven useful for locating noise sources using cross-correlations in several past studies. The inversion procedure is the following: We construct correlation forward models based on Green's functions from a spectral element wave propagation code. To construct these models efficiently, we use source-receiver reciprocity and assume spatial uncorrelation of noise sources. In such a setting, correlations can be calculated from a pre-computed set of Green's functions between the seismic receivers and sources located at the Earth's surface. We then calculate spatial sensitivity kernels for the noise source distribution with respect to the correlation signal energy measurements. These in turn allow us to construct a misfit gradient and optimize the source distribution model to fit our observed cross-correlation signal energies or energy ratios. We will present the workflow for calculation of the forward model and sensitivity kernels, as well as results for both forward modeling and kernels for an example data set of long-period noise or 'hum' at a global scale. We will also provide an outlook on the noise source inversion considering the

  20. Initial results of a model rotor higher harmonic control (HHC) wind tunnel experiment on BVI impulsive noise reduction

    NASA Astrophysics Data System (ADS)

    Splettstoesser, W. R.; Lehmann, G.; van der Wall, B.

    1989-09-01

    Initial acoustic results are presented from a higher harmonic control (HHC) wind tunnel pilot experiment on helicopter rotor blade-vortex interaction (BVI) impulsive noise reduction, making use of the DFVLR 40-percent-scaled BO-105 research rotor in the DNW 6m by 8m closed test section. Considerable noise reduction (of several decibels) has been measured for particular HHC control settings, however, at the cost of increased vibration levels and vice versa. The apparently adverse results for noise and vibration reduction by HHC are explained. At optimum pitch control settings for BVI noise reduction, rotor simulation results demonstrate that blade loading at the outer tip region is decreased, vortex strength and blade vortex miss-distance are increased, resulting altogether in reduced BVI noise generation. At optimum pitch control settings for vibration reduction adverse effects on blade loading, vortex strength and blade vortex miss-distance are found.

  1. Active source cancellation of the blade tone fundamental and harmonics in centrifugal fans

    NASA Astrophysics Data System (ADS)

    Koopmann, G. H.; Fox, D. J.; Neise, W.

    1988-10-01

    An active source method is shown to effectively cancel the blade tone fundamental and harmonics in centrifugal fans for a variety of fan loading conditions and duct terminations. The special case is considered where the frequency of the blade tone harmonics lies just above the cut-on frequency of the first higher order mode of the fan ducting. The results suggest that the present active control mechanism involves a local alteration of the aerodynamic source pressures.

  2. Selective harmonic elimination strategy in eleven level inverter for PV system with unbalanced DC sources

    NASA Astrophysics Data System (ADS)

    Ghoudelbourk, Sihem.; Dib, D.; Meghni, B.; Zouli, M.

    2017-02-01

    The paper deals with the multilevel converters control strategy for photovoltaic system integrated in distribution grids. The objective of the proposed work is to design multilevel inverters for solar energy applications so as to reduce the Total Harmonic Distortion (THD) and to improve the power quality. The multilevel inverter power structure plays a vital role in every aspect of the power system. It is easier to produce a high-power, high-voltage inverter with the multilevel structure. The topologies of multilevel inverter have several advantages such as high output voltage, lower total harmonic distortion (THD) and reduction of voltage ratings of the power semiconductor switching devices. The proposed control strategy ensures an implementation of selective harmonic elimination (SHE) modulation for eleven levels. SHE is a very important and efficient strategy of eliminating selected harmonics by judicious selection of the firing angles of the inverter. Harmonics elimination technique eliminates the need of the expensive low pass filters in the system. Previous research considered that constant and equal DC sources with invariant behavior; however, this research extends earlier work to include variant DC sources, which are typical of lead-acid batteries when used in system PV. This Study also investigates methods to minimize the total harmonic distortion of the synthesized multilevel waveform and to help balance the battery voltage. The harmonic elimination method was used to eliminate selected lower dominant harmonics resulting from the inverter switching action.

  3. A study of interior noise levels, noise sources and transmission paths in light aircraft

    NASA Technical Reports Server (NTRS)

    Hayden, R. E.; Murray, B. S.; Theobald, M. A.

    1983-01-01

    The interior noise levels and spectral characteristics of 18 single-and twin-engine propeller-driven light aircraft, and source-path diagnosis of a single-engine aircraft which was considered representative of a large part of the fleet were studied. The purpose of the flight surveys was to measure internal noise levels and identify principal noise sources and paths under a carefully controlled and standardized set of flight procedures. The diagnostic tests consisted of flights and ground tests in which various parts of the aircraft, such as engine mounts, the engine compartment, exhaust pipe, individual panels, and the wing strut were instrumented to determine source levels and transmission path strengths using the transfer function technique. Predominant source and path combinations are identified. Experimental techniques are described. Data, transfer function calculations to derive source-path contributions to the cabin acoustic environment, and implications of the findings for noise control design are analyzed.

  4. Optical linear algebra processors - Noise and error-source modeling

    NASA Technical Reports Server (NTRS)

    Casasent, D.; Ghosh, A.

    1985-01-01

    The modeling of system and component noise and error sources in optical linear algebra processors (OLAPs) are considered, with attention to the frequency-multiplexed OLAP. General expressions are obtained for the output produced as a function of various component errors and noise. A digital simulator for this model is discussed.

  5. Optical linear algebra processors: noise and error-source modeling.

    PubMed

    Casasent, D; Ghosh, A

    1985-06-01

    The modeling of system and component noise and error sources in optical linear algebra processors (OLAP's) are considered, with attention to the frequency-multiplexed OLAP. General expressions are obtained for the output produced as a function of various component errors and noise. A digital simulator for this model is discussed.

  6. Modulating optical rectification, second and third harmonic generation of doped quantum dots: Interplay between hydrostatic pressure, temperature and noise

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Saha, Surajit; Bera, Aindrila; Ghosh, Manas

    2016-10-01

    We examine the profiles of optical rectification (OR), second harmonic generation (SHG) and third harmonic generation (THG) of impurity doped QDs under the combined influence of hydrostatic pressure (HP) and temperature (T) in presence and absence of Gaussian white noise. Noise has been incorporated to the system additively and multiplicatively. In order to study the above nonlinear optical (NLO) properties the doped dot has been subjected to a polarized monochromatic electromagnetic field. Effect of application of noise is nicely reflected through alteration of peak shift (blue/red) and variation of peak height (increase/decrease) of above NLO properties as temperature and pressure are varied. All such changes again sensitively depends on mode of application (additive/multiplicative) of noise. The remarkable influence of interplay between noise strength and its mode of application on the said profiles has also been addressed. The findings illuminate fascinating role played by noise in tuning above NLO properties of doped QD system under the active presence of both hydrostatic pressure and temperature.

  7. Low-noise pulsed current source for magnetic-field measurements of magnets for accelerators

    NASA Astrophysics Data System (ADS)

    Omelyanenko, M. M.; Borisov, V. V.; Donyagin, A. M.; Khodzhibagiyan, H. G.; Kostromin, S. A.; Makarov, A. A.; Shemchuk, A. V.

    2017-01-01

    The schematic diagram, design, and technical characteristics of the pulsed current source developed and produced for the magnetic-field measurement system of superconducting magnets for accelerators are described. The current source is based on the current regulator with pass transistor bank in the linear mode. Output current pulses (0-100 A) are produced by utilizing the energy of the preliminarily charged capacitor bank (5-40 V), which is additionally charged between pulses. The output current does not have the mains frequency and harmonics ripple. The relative noise level is less than-100 dB (or 10-5) of RMS value (it is defined as the ratio of output RMS noise current to a maximal output current of 100 A within the operating bandwidth, expressed in dB). The work was performed at the Veksler and Baldin Laboratory of High Energy Physics, Joint Institute for Nuclear Research (JINR).

  8. Active noise control using noise source having adaptive resonant frequency tuning through stiffness variation

    NASA Technical Reports Server (NTRS)

    Pla, Frederic G. (Inventor); Rajiyah, Harindra (Inventor); Renshaw, Anthony A. (Inventor); Hedeen, Robert A. (Inventor)

    1995-01-01

    A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by a plurality of force transmitting mechanisms which contact the noise radiating element. Each one of the force transmitting mechanisms includes an expandable element and a spring in contact with the noise radiating element so that excitation of the element varies the spring force applied to the noise radiating element. The elements are actuated by a controller which receives input of a signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the spring force applied to the noise radiating element to be varied. The force transmitting mechanisms can be arranged to either produce bending or linear stiffness variations in the noise radiating element.

  9. Intrinsic Noise Level of Noise Cross-Correlation Functions and its Implication to Source Population of Ambient noises

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Nien; Gung, Yuancheng; Chiao, Ling-Yun; Rhie, Junkee

    2017-01-01

    SUMMARYWe present a quantitative procedure to evaluate the intrinsic <span class="hlt">noise</span> level (INL) of the <span class="hlt">noise</span> cross-correlation function (NCF). The method is applied to realistic NCFs derived from the continuous data recorded by the seismic arrays in Taiwan and Korea. The obtained temporal evolution of NCF <span class="hlt">noise</span> level follows fairly the prediction of the theoretical formulation, confirming the feasibility of the method. We then apply the obtained INL to the assessment of data quality and the <span class="hlt">source</span> characteristics of ambient <span class="hlt">noise</span>. We show that the INL-based signal-to-<span class="hlt">noise</span> ratio provides an exact measure for the true <span class="hlt">noise</span> level within the NCF and better resolving power for the NCF quality, and such measurement can be implemented to any time windows of the NCFs to evaluate the quality of overtones or coda waves. Moreover, since NCF amplitudes are influenced by both the population and excitation strengths of <span class="hlt">noises</span>, while INL is primarily sensitive to the overall <span class="hlt">source</span> population, with information from both measurements, we may better constrain the <span class="hlt">source</span> characteristics of seismic ambient <span class="hlt">noises</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27661915','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27661915"><span>All-fiber fourth and fifth <span class="hlt">harmonic</span> generation from a single <span class="hlt">source</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Khudus, Muhammad I M Abdul; Lee, Timothy; De Lucia, Francesco; Corbari, Costantino; Sazio, Pier; Horak, Peter; Brambilla, Gilberto</p> <p>2016-09-19</p> <p>All-fiber fourth and fifth <span class="hlt">harmonic</span> generation from a single <span class="hlt">source</span> is demonstrated experimentally and analyzed theoretically. Light from a fully fiberized high power master oscillator power amplifier is launched into a periodically poled silica fiber generating the second <span class="hlt">harmonic</span>. The output is then sent through two optical microfibers that generate the third and fourth <span class="hlt">harmonic</span>, respectively, via four wave mixing (FWM). For a large range of pump wavelengths in the silica optical transmission window, phase matched FWM can be achieved in the microfibers at two different diameters with relatively wide fabrication tolerances of up to +/-5 nm. Our simulations indicate that by optimizing the second <span class="hlt">harmonic</span> generation efficiency and the diameters and lengths of the two microfibers, conversion efficiencies to the fourth <span class="hlt">harmonic</span> in excess of 25% are theoretically achievable.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850048238&hterms=analytical+results+phase+noise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Danalytical%2Bresults%2Bphase%2Bnoise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850048238&hterms=analytical+results+phase+noise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Danalytical%2Bresults%2Bphase%2Bnoise"><span>An improved <span class="hlt">source</span> model for aircraft interior <span class="hlt">noise</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mahan, J. R.; Fuller, C. R.</p> <p>1985-01-01</p> <p>There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin <span class="hlt">noise</span> level. This concern has stimulated renewed interest in developing aircraft interior <span class="hlt">noise</span> reduction methods that do not significnatly increase take off weight. An existing analytical model for <span class="hlt">noise</span> transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller <span class="hlt">source</span> model for use in aircraft interior <span class="hlt">noise</span> studies. The new <span class="hlt">source</span> model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior <span class="hlt">noise</span> studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850009359','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850009359"><span>An improved <span class="hlt">source</span> model for aircraft interior <span class="hlt">noise</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mahan, J. R.; Fuller, C. R.</p> <p>1985-01-01</p> <p>There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin <span class="hlt">noise</span> levels. This concern has stimulated renewed interest in developing aircraft interior <span class="hlt">noise</span> reduction methods that do not significantly increase take off weight. An existing analytical model for <span class="hlt">noise</span> transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller <span class="hlt">source</span> model for use in aircraft interior <span class="hlt">noise</span> studies. The new <span class="hlt">source</span> model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior <span class="hlt">noise</span> studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014RScI...85b4702G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014RScI...85b4702G"><span>Large bandwidth op-amp based white <span class="hlt">noise</span> current <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Giusi, Gino; Scandurra, Graziella; Ciofi, Carmine</p> <p>2014-02-01</p> <p>Electrical <span class="hlt">noise</span> <span class="hlt">sources</span> are basic building blocks in many measurement and instrumentation applications and in communication systems. In this paper, we propose a quite simple topology for the realization of a programmable, wide bandwidth, white <span class="hlt">noise</span> current <span class="hlt">source</span> that requires only two resistors and one operational amplifier. We validate the proposed approach by means of SPICE simulations and demonstrate, by means of proper measurements, the capability of generating a flat current <span class="hlt">noise</span> spectrum in a frequency range up to four decades from a few Hz up to 100 kHz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27607971','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27607971"><span>Coexistence of <span class="hlt">harmonic</span> soliton molecules and rectangular <span class="hlt">noise</span>-like pulses in a figure-eight fiber laser.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Huang, Yu-Qi; Hu, Zi-Ang; Cui, Hu; Luo, Zhi-Chao; Luo, Ai-Ping; Xu, Wen-Cheng</p> <p>2016-09-01</p> <p>We report the coexistence of high-order <span class="hlt">harmonic</span> soliton molecules and rectangular <span class="hlt">noise</span>-like pulses (NLP) in a figure-eight fiber laser mode-locked by a nonlinear amplifying loop mirror. The <span class="hlt">harmonic</span> soliton molecule has a repetition rate of 936.6 MHz, corresponding to the 466th <span class="hlt">harmonics</span> of the fundamental cavity repetition rate, with soliton separation of 16.5 ps. Meanwhile, the rectangular NLP operates at the fundamental repetition rate. In addition, these two types of pulses could be generated independently by manipulating the polarization controllers. The experimental results demonstrate an interesting operation regime of the fiber laser and contribute to enriching the dynamics of mode-locked pulses in fiber lasers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080007426','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080007426"><span>Active <span class="hlt">noise</span> control using <span class="hlt">noise</span> <span class="hlt">source</span> having adaptive resonant frequency tuning through stress variation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pla, Frederic G. (Inventor); Rajiyah, Harindra (Inventor); Renshaw, Anthony A. (Inventor); Hedeen, Robert A. (Inventor)</p> <p>1995-01-01</p> <p>A <span class="hlt">noise</span> <span class="hlt">source</span> for an aircraft engine active <span class="hlt">noise</span> cancellation system in which the resonant frequency of a <span class="hlt">noise</span> radiating element is tuned to permit <span class="hlt">noise</span> cancellation over a wide range of frequencies. The resonant frequency of the <span class="hlt">noise</span> radiating element is tuned by an expandable ring embedded in the <span class="hlt">noise</span> radiating element. Excitation of the ring causes expansion or contraction of the ring, thereby varying the stress in the <span class="hlt">noise</span> radiating element. The ring is actuated by a controller which receives input of a feedback signal proportional to displacement of the <span class="hlt">noise</span> radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the ring, causing the ring to expand or contract. Instead of a single ring embedded in the <span class="hlt">noise</span> radiating panel, a first expandable ring can be bonded to one side of the <span class="hlt">noise</span> radiating element, and a second expandable ring can be bonded to the other side.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980148012','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980148012"><span>Aeroacoustic Codes for Rotor <span class="hlt">Harmonic</span> and BVI <span class="hlt">Noise</span>. CAMRAD.Mod1/HIRES: Methodology and Users' Manual</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Boyd, D. Douglas, Jr.; Brooks, Thomas F.; Burley, Casey L.; Jolly, J. Ralph, Jr.</p> <p>1998-01-01</p> <p>This document details the methodology and use of the CAMRAD.Mod1/HIRES codes, which were developed at NASA Langley Research Center for the prediction of helicopter <span class="hlt">harmonic</span> and Blade-Vortex Interaction (BVI) <span class="hlt">noise</span>. CANMAD.Mod1 is a substantially modified version of the performance/trim/wake code CANMAD. High resolution blade loading is determined in post-processing by HIRES and an associated indicial aerodynamics code. Extensive capabilities of importance to <span class="hlt">noise</span> prediction accuracy are documented, including a new multi-core tip vortex roll-up wake model, higher <span class="hlt">harmonic</span> and individual blade control, tunnel and fuselage correction input, diagnostic blade motion input, and interfaces for acoustic and CFD aerodynamics codes. Modifications and new code capabilities are documented with examples. A users' job preparation guide and listings of variables and namelists are given.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008PPCF...50l4002H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008PPCF...50l4002H"><span>High <span class="hlt">harmonics</span> from solid surfaces as a <span class="hlt">source</span> of ultra-bright XUV radiation for experiments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hörlein, R.; Nomura, Y.; Osterhoff, J.; Major, Zs; Karsch, S.; Krausz, F.; Tsakiris, G. D.</p> <p>2008-12-01</p> <p>The coherent high-order <span class="hlt">harmonic</span> generation from the interaction of ultra-intense femtosecond laser pulses with solid density plasmas holds promise for tabletop <span class="hlt">sources</span> of extreme ultraviolet (XUV) and soft x-ray radiation with attosecond duration and unprecedented intensities. Together with the generation of mono-energetic electron beams from gas jets and capillaries and the generation of mono-energetic ions from thin foils, this offers a unique tool box of tabletop-laser-generated radiation <span class="hlt">sources</span> for a wide range of applications previously only accessible with large-scale accelerator and synchrotron-radiation facilities. Especially, the generation of high <span class="hlt">harmonics</span> from laser plasmas has the potential of being applied to a wide range of experiments from plasma physics to molecular dynamics. So far the studies addressing the generation of high <span class="hlt">harmonics</span> from laser-generated overcritical plasma surfaces have concentrated mainly on the characterization of the <span class="hlt">harmonic</span> beams themselves not considering how, in a next step, these beams could be applied to experiments. In this paper we discuss the generation of surface <span class="hlt">harmonics</span> with the ATLAS (800 mJ, 40 fs) laser system with the emphasis on the transport, spectral shaping refocusing of the <span class="hlt">harmonic</span> beams, all of these being absolute prerequisites for multi-shot experiments. We also present considerations for future improvements and possible future experiments exploiting the full potential of high <span class="hlt">harmonic</span> radiation from solid targets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080004428','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080004428"><span>Active control of aircraft engine inlet <span class="hlt">noise</span> using compact sound <span class="hlt">sources</span> and distributed error sensors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burdisso, Ricardo (Inventor); Fuller, Chris R. (Inventor); O'Brien, Walter F. (Inventor); Thomas, Russell H. (Inventor); Dungan, Mary E. (Inventor)</p> <p>1994-01-01</p> <p>An active <span class="hlt">noise</span> control system using a compact sound <span class="hlt">source</span> is effective to reduce aircraft engine duct <span class="hlt">noise</span>. The fan <span class="hlt">noise</span> from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first <span class="hlt">harmonic</span> of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet <span class="hlt">noise</span> a viable technology, a compact sound <span class="hlt">source</span> is employed to generate the control field. This control field sound <span class="hlt">source</span> consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080004134','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080004134"><span>Active control of aircraft engine inlet <span class="hlt">noise</span> using compact sound <span class="hlt">sources</span> and distributed error sensors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burdisso, Ricardo (Inventor); Fuller, Chris R. (Inventor); O'Brien, Walter F. (Inventor); Thomas, Russell H. (Inventor); Dungan, Mary E. (Inventor)</p> <p>1996-01-01</p> <p>An active <span class="hlt">noise</span> control system using a compact sound <span class="hlt">source</span> is effective to reduce aircraft engine duct <span class="hlt">noise</span>. The fan <span class="hlt">noise</span> from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first <span class="hlt">harmonic</span> of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet <span class="hlt">noise</span> a viable technology, a compact sound <span class="hlt">source</span> is employed to generate the control field. This control field sound <span class="hlt">source</span> consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23505502','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23505502"><span>MEG <span class="hlt">source</span> localization using invariance of <span class="hlt">noise</span> space.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Junpeng; Raij, Tommi; Hämäläinen, Matti; Yao, Dezhong</p> <p>2013-01-01</p> <p>We propose INvariance of <span class="hlt">Noise</span> (INN) space as a novel method for <span class="hlt">source</span> localization of magnetoencephalography (MEG) data. The method is based on the fact that modulations of <span class="hlt">source</span> strengths across time change the energy in signal subspace but leave the <span class="hlt">noise</span> subspace invariant. We compare INN with classical MUSIC, RAP-MUSIC, and beamformer approaches using simulated data while varying signal-to-<span class="hlt">noise</span> ratios as well as distance and temporal correlation between two <span class="hlt">sources</span>. We also demonstrate the utility of INN with actual auditory evoked MEG responses in eight subjects. In all cases, INN performed well, especially when the <span class="hlt">sources</span> were closely spaced, highly correlated, or one <span class="hlt">source</span> was considerably stronger than the other.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_5 --> <div id="page_6" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="101"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/989768','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/989768"><span>High-<span class="hlt">harmonic</span> XUV <span class="hlt">source</span> for time- and angle-resolved photoemission spectroscopy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dakovski, Georgi L; Li, Yinwan; Durakiewicz, Tomasz; Rodriguez, George</p> <p>2009-01-01</p> <p>We present a laser-based apparatus for visible pump/XUV probe time- and angle-resolved photoemission spectroscopy (TRARPES) utilizing high-<span class="hlt">harmonic</span> generation from a noble gas. Femtosecond temporal resolution for each selected <span class="hlt">harmonic</span> is achieved by using a time-delay-compensated monochromator (TCM). The <span class="hlt">source</span> has been used to obtain photoemission spectra from insulators (UO{sub 2}) and ultrafast pump/probe processes in semiconductors (GaAs).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080007425','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080007425"><span>Active <span class="hlt">noise</span> control using <span class="hlt">noise</span> <span class="hlt">source</span> having adaptive resonant frequency tuning through variable ring loading</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pla, Frederic G. (Inventor); Rajiyah, Harindra (Inventor); Renshaw, Anthony A. (Inventor); Hedeen, Robert A. (Inventor)</p> <p>1995-01-01</p> <p>A <span class="hlt">noise</span> <span class="hlt">source</span> for an aircraft engine active <span class="hlt">noise</span> cancellation system in which the resonant frequency of <span class="hlt">noise</span> radiating structure is tuned to permit <span class="hlt">noise</span> cancellation over a wide range of frequencies. The resonant frequency of the <span class="hlt">noise</span> radiating structure is tuned by a plurality of drivers arranged to contact the <span class="hlt">noise</span> radiating structure. Excitation of the drivers causes expansion or contraction of the drivers, thereby varying the edge loading applied to the <span class="hlt">noise</span> radiating structure. The drivers are actuated by a controller which receives input of a feedback signal proportional to displacement of the <span class="hlt">noise</span> radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the drivers, causing them to expand or contract. The <span class="hlt">noise</span> radiating structure may be either the outer shroud of the engine or a ring mounted flush with an inner wall of the shroud or disposed in the interior of the shroud.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120006513','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120006513"><span>Sub-Shot <span class="hlt">Noise</span> Power <span class="hlt">Source</span> for Microelectronics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Strekalov, Dmitry V.; Yu, Nan; Mansour, Kamjou</p> <p>2011-01-01</p> <p>Low-current, high-impedance microelectronic devices can be affected by electric current shot <span class="hlt">noise</span> more than they are affected by Nyquist <span class="hlt">noise</span>, even at room temperature. An approach to implementing a sub-shot <span class="hlt">noise</span> current <span class="hlt">source</span> for powering such devices is based on direct conversion of amplitude-squeezed light to photocurrent. The phenomenon of optical squeezing allows for the optical measurements below the fundamental shot <span class="hlt">noise</span> limit, which would be impossible in the domain of classical optics. This becomes possible by affecting the statistical properties of photons in an optical mode, which can be considered as a case of information encoding. Once encoded, the information describing the photon (or any other elementary excitations) statistics can be also transmitted. In fact, it is such information transduction from optics to an electronics circuit, via photoelectric effect, that has allowed the observation of the optical squeezing. It is very difficult, if not technically impossible, to directly measure the statistical distribution of optical photons except at extremely low light level. The photoelectric current, on the other hand, can be easily analyzed using RF spectrum analyzers. Once it was observed that the photocurrent <span class="hlt">noise</span> generated by a tested light <span class="hlt">source</span> in question is below the shot <span class="hlt">noise</span> limit (e.g. produced by a coherent light beam), it was concluded that the light <span class="hlt">source</span> in question possess the property of amplitude squeezing. The main novelty of this technology is to turn this well-known information transduction approach around. Instead of studying the statistical property of an optical mode by measuring the photoelectron statistics, an amplitude-squeezed light <span class="hlt">source</span> and a high-efficiency linear photodiode are used to generate photocurrent with sub-Poissonian electron statistics. By powering microelectronic devices with this current <span class="hlt">source</span>, their performance can be improved, especially their <span class="hlt">noise</span> parameters. Therefore, a room-temperature sub</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040070765','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040070765"><span>Jet <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Using Linear Phased Array</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Agboola, Ferni A.; Bridges, James</p> <p>2004-01-01</p> <p>A study was conducted to further clarify the interpretation and application of linear phased array microphone results, for localizing aeroacoustics <span class="hlt">sources</span> in aircraft exhaust jet. Two model engine nozzles were tested at varying power cycles with the array setup parallel to the jet axis. The array position was varied as well to determine best location for the array. The results showed that it is possible to resolve jet <span class="hlt">noise</span> <span class="hlt">sources</span> with bypass and other components separation. The results also showed that a focused near field image provides more realistic <span class="hlt">noise</span> <span class="hlt">source</span> localization at low to mid frequencies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20070007329','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20070007329"><span><span class="hlt">Source</span> <span class="hlt">Noise</span> Modeling Efforts for Fan <span class="hlt">Noise</span> in NASA Research Programs</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Huff, Dennis L.</p> <p>2006-01-01</p> <p>There has been considerable progress made in fan <span class="hlt">noise</span> prediction over the past 15 years. NASA has conducted and sponsored research that has improved both tone and broadband fan <span class="hlt">noise</span> prediction methods. This presentation highlights progress in these areas with emphasis on rotor/stator interaction <span class="hlt">noise</span> <span class="hlt">sources</span>. Tone <span class="hlt">noise</span> predictions are presented for an advanced prediction code called "LINFLUX". Comparisons with data are" included for individual fan duct modes. There has also been considerable work developing new fan broadband <span class="hlt">noise</span> prediction codes and validation data from wind tunnel model tests. Results from several code validation exercises are presented that show improvement of predicted sound power levels. A summary is included with recommendations for future work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020059663','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020059663"><span>General Aviation Interior <span class="hlt">Noise</span>. Part 1; <span class="hlt">Source</span>/Path Identification</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Unruh, James F.; Till, Paul D.; Palumbo, Daniel L. (Technical Monitor)</p> <p>2002-01-01</p> <p>There were two primary objectives of the research effort reported herein. The first objective was to identify and evaluate <span class="hlt">noise</span> <span class="hlt">source</span>/path identification technology applicable to single engine propeller driven aircraft that can be used to identify interior <span class="hlt">noise</span> <span class="hlt">sources</span> originating from structure-borne engine/propeller vibration, airborne propeller transmission, airborne engine exhaust <span class="hlt">noise</span>, and engine case radiation. The approach taken to identify the contributions of each of these possible <span class="hlt">sources</span> was first to conduct a Principal Component Analysis (PCA) of an in-flight <span class="hlt">noise</span> and vibration database acquired on a Cessna Model 182E aircraft. The second objective was to develop and evaluate advanced technology for <span class="hlt">noise</span> <span class="hlt">source</span> ranking of interior panel groups such as the aircraft windshield, instrument panel, firewall, and door/window panels within the cabin of a single engine propeller driven aircraft. The technology employed was that of Acoustic Holography (AH). AH was applied to the test aircraft by acquiring a series of in-flight microphone array measurements within the aircraft cabin and correlating the measurements via PCA. The <span class="hlt">source</span> contributions of the various panel groups leading to the array measurements were then synthesized by solving the inverse problem using the boundary element model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850004526','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850004526"><span>Algorithm for astronomical, point <span class="hlt">source</span>, signal to <span class="hlt">noise</span> ratio calculations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jayroe, R. R.; Schroeder, D. J.</p> <p>1984-01-01</p> <p>An algorithm was developed to simulate the expected signal to <span class="hlt">noise</span> ratios as a function of observation time in the charge coupled device detector plane of an optical telescope located outside the Earth's atmosphere for a signal star, and an optional secondary star, embedded in a uniform cosmic background. By choosing the appropriate input values, the expected point <span class="hlt">source</span> signal to <span class="hlt">noise</span> ratio can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004RScI...75.1323R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004RScI...75.1323R"><span>Low flicker-<span class="hlt">noise</span> amplifier for 50 Ω <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rubiola, Enrico; Lardet-Vieudrin, Franck</p> <p>2004-05-01</p> <p>This article analyzes the design of a low-<span class="hlt">noise</span> amplifier intended as the input front-end for the measurement of the low-frequency components (below 10 Hz) of a 50 Ω <span class="hlt">source</span>. Low residual flicker is the main desired performance. This feature can only be appreciated if white <span class="hlt">noise</span> is sufficiently low, and if an appropriate design ensures dc stability. An optimal solution is proposed, in which the low-<span class="hlt">noise</span> and dc-stability features are achieved at a reasonable complexity. Gain is accurate to more than 100 kHz, which makes the amplifier an appealing external front-end for fast Fourier transform (FFT) analyzers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21180040','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21180040"><span>The effect of shot <span class="hlt">noise</span> on the start up of the fundamental and <span class="hlt">harmonics</span> in free-electron lasers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Freund, H. P.; Miner, W. H. Jr.; Giannessi, L.</p> <p>2008-12-15</p> <p>The problem of radiation start up in free-electron lasers (FELs) is important in the simulation of virtually all FEL configurations including oscillators and amplifiers in both seeded master oscillator power amplifier (MOPA) and self-amplified spontaneous emission (SASE) modes. Both oscillators and SASE FELs start up from spontaneous emission due to shot <span class="hlt">noise</span> on the electron beam, which arises from the random fluctuations in the phase distribution of the electrons. The injected power in a MOPA is usually large enough to overwhelm the shot <span class="hlt">noise</span>. However, this <span class="hlt">noise</span> must be treated correctly in order to model the initial start up of the <span class="hlt">harmonics</span>. In this paper, we discuss and compare two different shot <span class="hlt">noise</span> models that are implemented in both one-dimensional wiggler-averaged (PERSEO) and non-wiggler-averaged (MEDUSA1D) simulation codes, and a three-dimensional non-wiggler-averaged (MEDUSA) formulation. These models are compared for examples describing both SASE and MOPA configurations in one dimension, in steady-state, and time-dependent simulations. Remarkable agreement is found between PERSEO and MEDUSA1D for the evolution of the fundamental and <span class="hlt">harmonics</span>. In addition, three-dimensional correction factors have been included in the MEDUSA1D and PERSEO, which show reasonable agreement with MEDUSA for a sample MOPA in steady-state and time-dependent simulations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24763636','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24763636"><span>X-ray <span class="hlt">harmonics</span> rejection on third-generation synchrotron <span class="hlt">sources</span> using compound refractive lenses.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Polikarpov, Maxim; Snigireva, Irina; Snigirev, Anatoly</p> <p>2014-05-01</p> <p>A new method of <span class="hlt">harmonics</span> rejection based on X-ray refractive optics has been proposed. Taking into account the fact that the focal distance of the refractive lens is energy-dependent, the use of an off-axis illumination of the lens immediately leads to spatial separation of the energy spectrum by focusing the fundamental <span class="hlt">harmonic</span> at the focal point and suppressing the unfocused high-energy radiation with a screen absorber or slit. The experiment was performed at the ESRF ID06 beamline in the in-line geometry using an X-ray transfocator with compound refractive lenses. Using this technique the presence of the third <span class="hlt">harmonic</span> has been reduced to 10(-3). In total, our method enabled suppression of all higher-order <span class="hlt">harmonics</span> to five orders of magnitude using monochromator detuning. The method is well suited to third-generation synchrotron radiation <span class="hlt">sources</span> and is very promising for the future ultimate storage rings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhBio...9b6002N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhBio...9b6002N"><span>Isolating intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> in a stochastic genetic switch</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Newby, Jay M.</p> <p>2012-04-01</p> <p>The stochastic mutual repressor model is analysed using perturbation methods. This simple model of a gene circuit consists of two genes and three promotor states. Either of the two protein products can dimerize, forming a repressor molecule that binds to the promotor of the other gene. When the repressor is bound to a promotor, the corresponding gene is not transcribed and no protein is produced. Either one of the promotors can be repressed at any given time or both can be unrepressed, leaving three possible promotor states. This model is analysed in its bistable regime in which the deterministic limit exhibits two stable fixed points and an unstable saddle, and the case of small <span class="hlt">noise</span> is considered. On small timescales, the stochastic process fluctuates near one of the stable fixed points, and on large timescales, a metastable transition can occur, where fluctuations drive the system past the unstable saddle to the other stable fixed point. To explore how different intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> affect these transitions, fluctuations in protein production and degradation are eliminated, leaving fluctuations in the promotor state as the only <span class="hlt">source</span> of <span class="hlt">noise</span> in the system. The process without protein <span class="hlt">noise</span> is then compared to the process with weak protein <span class="hlt">noise</span> using perturbation methods and Monte Carlo simulations. It is found that some significant differences in the random process emerge when the intrinsic <span class="hlt">noise</span> <span class="hlt">source</span> is removed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030003692','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030003692"><span>Fan <span class="hlt">Noise</span> <span class="hlt">Source</span> Diagnostic Test Computation of Rotor Wake Turbulence <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nallasamy, M.; Envia, E.; Thorp, S. A.; Shabbir, A.</p> <p>2002-01-01</p> <p>An important <span class="hlt">source</span> mechanism of fan broadband <span class="hlt">noise</span> is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband <span class="hlt">noise</span> model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband <span class="hlt">noise</span> spectra. The <span class="hlt">noise</span> model is employed to examine the broadband <span class="hlt">noise</span> characteristics of the 22-inch <span class="hlt">Source</span> Diagnostic Test fan rig for which broadband <span class="hlt">noise</span> data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust acoustic power spectra are computed and compared with the measured spectra where possible. In general, the acoustic power levels and shape of the predicted spectra are in good agreement with the measured data. The predicted spectra show the experimentally observed trends with fan tip speed, vane count, and vane sweep. The results also demonstrate the validity of using CFD-based turbulence information for fan broadband <span class="hlt">noise</span> calculations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014LaPhy..24k5103P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014LaPhy..24k5103P"><span>High-order <span class="hlt">harmonic</span> <span class="hlt">noise</span>-like pulsing of a passively mode-locked double-clad Er/Yb fibre ring laser</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pottiez, O.; Hernández-García, J. C.; Ibarra-Escamilla, B.; Kuzin, E. A.; Durán-Sánchez, M.; González-García, A.</p> <p>2014-11-01</p> <p>In this paper, we study <span class="hlt">noise</span>-like pulse generation in a km-long fibre ring laser including a double-clad erbium-ytterbium fibre and passively mode-locked through nonlinear polarization evolution. Although single <span class="hlt">noise</span>-like pulsing is only observed at moderate pump power, pulse energies as high as 120 nJ are reached in this regime. For higher pump power, the pulse splits into several <span class="hlt">noise</span>-like pulses, which then rearrange into a stable and periodic pulse train. <span class="hlt">Harmonic</span> mode locking from the 2nd to the 48th orders is readily obtained. At pump powers close to the damage threshold of the setup, much denser <span class="hlt">noise</span>-like pulse trains are demonstrated, reaching <span class="hlt">harmonic</span> orders beyond 1200 and repetition frequencies in excess of a quarter of a GHz. The mechanisms leading to <span class="hlt">noise</span>-like pulse breaking and stable high-order <span class="hlt">harmonic</span> mode locking are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AIPA....7b5014M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AIPA....7b5014M"><span>Developing general acoustic model for <span class="hlt">noise</span> <span class="hlt">sources</span> and parameters estimation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Madoliat, Reza; Nouri, Nowrouz Mohammad; Rahrovi, Ali</p> <p>2017-02-01</p> <p><span class="hlt">Noise</span> measured at various points around the environment can be evaluated by a series of acoustic <span class="hlt">sources</span>. Acoustic <span class="hlt">sources</span> with wide surface can be broken down in fluid environment using some smaller acoustic <span class="hlt">sources</span>. The aim of this study is to make a model to indicate the type, number, direction, position and strength of these <span class="hlt">sources</span> in a way that the main sound and the sound of equivalent <span class="hlt">sources</span> match together in an acceptable way. When position and direction of the <span class="hlt">source</span> is given, the strength of the <span class="hlt">source</span> can be found using inverse method. On the other hand, considering the non-uniqueness of solution in inverse method, a different acoustic strength is obtained for the <span class="hlt">sources</span> if different positions are selected. Selecting an arrangement of general <span class="hlt">source</span> and using the optimization algorithm, the least possible mismatch between the main sound and the sound of equivalent <span class="hlt">sources</span> can be achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040073459','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040073459"><span>Investigation of Volumetric <span class="hlt">Sources</span> in Airframe <span class="hlt">Noise</span> Simulations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Casper, Jay H.; Lockard, David P.; Khorrami, Mehdi R.; Streett, Craig L.</p> <p>2004-01-01</p> <p>Hybrid methods for the prediction of airframe <span class="hlt">noise</span> involve a simulation of the near field flow that is used as input to an acoustic propagation formula. The acoustic formulations discussed herein are those based on the Ffowcs Williams and Hawkings equation. Some questions have arisen in the published literature in regard to an apparently significant dependence of radiated <span class="hlt">noise</span> predictions on the location of the integration surface used in the solution of the Ffowcs Williams and Hawkings equation. These differences in radiated <span class="hlt">noise</span> levels are most pronounced between solid-body surface integrals and off-body, permeable surface integrals. Such differences suggest that either a non-negligible volumetric <span class="hlt">source</span> is contributing to the total radiation or the input flow simulation is suspect. The focus of the current work is the issue of internal consistency of the flow calculations that are currently used as input to airframe <span class="hlt">noise</span> predictions. The case study for this research is a computer simulation for a three-element, high-lift wing profile during landing conditions. The <span class="hlt">noise</span> radiated from this flow is predicted by a two-dimensional, frequency-domain formulation of the Ffowcs Williams and Hawkings equation. Radiated sound from volumetric <span class="hlt">sources</span> is assessed by comparison of a permeable surface integration with the sum of a solid-body surface integral and a volume integral. The separate <span class="hlt">noise</span> predictions are found in good agreement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.S51E..02S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.S51E..02S"><span>Seismic <span class="hlt">noise</span> frequency dependent P and S wave <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stutzmann, E.; Schimmel, M.; Gualtieri, L.; Farra, V.; Ardhuin, F.</p> <p>2013-12-01</p> <p>Seismic <span class="hlt">noise</span> in the period band 3-10 sec is generated in the oceans by the interaction of ocean waves. <span class="hlt">Noise</span> signal is dominated by Rayleigh waves but body waves can be extracted using a beamforming approach. We select the TAPAS array deployed in South Spain between June 2008 and September 2009 and we use the vertical and horizontal components to extract <span class="hlt">noise</span> P and S waves, respectively. Data are filtered in narrow frequency bands and we select beam azimuths and slownesses that correspond to the largest continuous <span class="hlt">sources</span> per day. Our procedure automatically discard earthquakes which are localized during short time durations. Using this approach, we detect many more <span class="hlt">noise</span> P-waves than S-waves. <span class="hlt">Source</span> locations are determined by back-projecting the detected slowness/azimuth. P and S waves are generated in nearby areas and both <span class="hlt">source</span> locations are frequency dependent. Long period <span class="hlt">sources</span> are dominantly in the South Atlantic and Indian Ocean whereas shorter period <span class="hlt">sources</span> are rather in the North Atlantic Ocean. We further show that the detected S-waves are dominantly Sv-waves. We model the observed body waves using an ocean wave model that takes into account all possible wave interactions including coastal reflection. We use the wave model to separate direct and multiply reflected phases for P and S waves respectively. We show that in the South Atlantic the complex <span class="hlt">source</span> pattern can be explained by the existence of both coastal and pelagic <span class="hlt">sources</span> whereas in the North Atlantic most body wave <span class="hlt">sources</span> are pelagic. For each detected <span class="hlt">source</span>, we determine the equivalent <span class="hlt">source</span> magnitude which is compared to the model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880053218&hterms=james+stewart&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Djames%2Bstewart','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880053218&hterms=james+stewart&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Djames%2Bstewart"><span><span class="hlt">Noise</span> tube <span class="hlt">sources</span> for the far IR and millimeter region</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Moller, K. D.; Zoeller, R. G.; Ugras, N. G.; Zablocky, P.; Heaney, James B.; Stewart, K. P.; Boucarut, R. A.</p> <p>1988-01-01</p> <p>The radiant output of a <span class="hlt">noise</span> tube designed for the 90-140-GHz (3.3-2.1-mm) frequency range has been compared with that from mercury lamps over the wavelength region from 0.4 to about 6 mm. Lamellar grating and Michelson Fourier transform spectrometers were used in conjunction with He cooled bolometers of NEP from 10 to the -12th to 10 to the -14th W/sq rt H2 to measure relative spectral irradiance. With this instrumental arrangement, the radiant power emitted by the <span class="hlt">noise</span> tube was observed to be less than that from a mercury lamp, at least to a 3-mm wavelength, but it produced less <span class="hlt">source</span> <span class="hlt">noise</span> than an ac operated mercury lamp. When the <span class="hlt">noise</span> tube operating current was reduced, the spectral irradiance peak shifted to longer wavelengths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/814835','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/814835"><span>Review of Subcritical <span class="hlt">Source</span>-Driven <span class="hlt">Noise</span> Analysis Measurements</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Valentine, T.E.</p> <p>1999-11-24</p> <p>Subcritical <span class="hlt">source</span>-driven <span class="hlt">noise</span> measurements are simultaneous Rossi-{alpha} and randomly pulsed neutron measurements that provide measured quantities that can be related to the subcritical neutron multiplication factor. In fact, subcritical <span class="hlt">source</span>-driven <span class="hlt">noise</span> measurements should be performed in lieu of Rossi-{alpha} measurements because of the additional information that is obtained from <span class="hlt">noise</span> measurements such as the spectral ratio and the coherence functions. The basic understanding of <span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis measurements can be developed from a point reactor kinetics model to demonstrate how the measured quantities relate to the subcritical neutron multiplication factor. More elaborate models can also be developed using a generalized stochastic model. These measurements can be simulated using Monte Carlo codes to determine the subcritical neutron multiplication factor or to determine the sensitivity of calculations to nuclear cross section data. The interpretation of the measurement using a Monte Carlo method is based on a perturbation model for the relationship between the spectral ratio and the subcritical neutron multiplication factor. The subcritical <span class="hlt">source</span>-driven <span class="hlt">noise</span> measurement has advantages over other subcritical measurement methods in that reference measurements at delayed critical are not required for interpreting the measurements. Therefore, benchmark or in-situ subcritical measurements can be performed outside a critical experiment facility. Furthermore, a certain ratio of frequency spectra has been shown to be independent of detection efficiency thereby making the measurement more robust and unaffected by drifts or changes in instrumentation during the measurement. Criteria have been defined for application of this measurement method for benchmarks and in-situ subcritical measurements. An extension of the <span class="hlt">source</span>-driven subcritical <span class="hlt">noise</span> measurement has also been discussed that eliminates the few technical challenges for in-situ applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JSV...333.1356L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSV...333.1356L"><span>Propeller sheet cavitation <span class="hlt">noise</span> <span class="hlt">source</span> modeling and inversion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Keunhwa; Lee, Jaehyuk; Kim, Dongho; Kim, Kyungseop; Seong, Woojae</p> <p>2014-02-01</p> <p>Propeller sheet cavitation is the main contributor to high level of <span class="hlt">noise</span> and vibration in the after body of a ship. Full measurement of the cavitation-induced hull pressure over the entire surface of the affected area is desired but not practical. Therefore, using a few measurements on the outer hull above the propeller in a cavitation tunnel, empirical or semi-empirical techniques based on physical model have been used to predict the hull-induced pressure (or hull-induced force). In this paper, with the analytic <span class="hlt">source</span> model for sheet cavitation, a multi-parameter inversion scheme to find the positions of <span class="hlt">noise</span> <span class="hlt">sources</span> and their strengths is suggested. The inversion is posed as a nonlinear optimization problem, which is solved by the optimization algorithm based on the adaptive simplex simulated annealing algorithm. Then, the resulting hull pressure can be modeled with boundary element method from the inverted cavitation <span class="hlt">noise</span> <span class="hlt">sources</span>. The suggested approach is applied to the hull pressure data measured in a cavitation tunnel of the Samsung Heavy Industry. Two monopole <span class="hlt">sources</span> are adequate to model the propeller sheet cavitation <span class="hlt">noise</span>. The inverted <span class="hlt">source</span> information is reasonable with the cavitation dynamics of the propeller and the modeled hull pressure shows good agreement with cavitation tunnel experimental data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1093757','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1093757"><span>Adaptive Selective <span class="hlt">Harmonic</span> Minimization Based on ANNs for Cascade Multilevel Inverters With Varying DC <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Filho, Faete; Maia, Helder Z; Mateus, Tiago Henrique D; Ozpineci, Burak; Tolbert, Leon M; Pinto, Joao Onofre P</p> <p>2013-01-01</p> <p>A new approach for modulation of an 11-level cascade multilevel inverter using selective <span class="hlt">harmonic</span> elimination is presented in this paper. The dc <span class="hlt">sources</span> feeding the multilevel inverter are considered to be varying in time, and the switching angles are adapted to the dc <span class="hlt">source</span> variation. This method uses genetic algorithms to obtain switching angles offline for different dc <span class="hlt">source</span> values. Then, artificial neural networks are used to determine the switching angles that correspond to the real-time values of the dc <span class="hlt">sources</span> for each phase. This implies that each one of the dc <span class="hlt">sources</span> of this topology can have different values at any time, but the output fundamental voltage will stay constant and the <span class="hlt">harmonic</span> content will still meet the specifications. The modulating switching angles are updated at each cycle of the output fundamental voltage. This paper gives details on the method in addition to simulation and experimental results.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010RScI...81f4706W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010RScI...81f4706W"><span>A battery-based, low-<span class="hlt">noise</span> voltage <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wagner, Anke; Sturm, Sven; Schabinger, Birgit; Blaum, Klaus; Quint, Wolfgang</p> <p>2010-06-01</p> <p>A highly stable, low-<span class="hlt">noise</span> voltage <span class="hlt">source</span> was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess <span class="hlt">noise</span> and ground loops, the voltage <span class="hlt">source</span> is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of ±15 and ±5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7×10-7 over 6.5 h and a <span class="hlt">noise</span> level equal or smaller than 30 nV/√Hz is achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20590260','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20590260"><span>A battery-based, low-<span class="hlt">noise</span> voltage <span class="hlt">source</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wagner, Anke; Sturm, Sven; Schabinger, Birgit; Blaum, Klaus; Quint, Wolfgang</p> <p>2010-06-01</p> <p>A highly stable, low-<span class="hlt">noise</span> voltage <span class="hlt">source</span> was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess <span class="hlt">noise</span> and ground loops, the voltage <span class="hlt">source</span> is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of +/-15 and +/-5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7 x 10(-7) over 6.5 h and a <span class="hlt">noise</span> level equal or smaller than 30 nV/square root(Hz) is achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT........58O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT........58O"><span>Investigation of <span class="hlt">noise</span> <span class="hlt">sources</span> and propagation in external gear pumps</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Opperwall, Timothy J.</p> <p></p> <p>Oil hydraulics is widely accepted as the best technology for transmitting power in many engineering applications due to its advantages in power density, control, layout flexibility, and efficiency. Due to these advantages, hydraulic systems are present in many different applications including construction, agriculture, aerospace, automotive, forestry, medical, and manufacturing, just to identify a few. Many of these applications involve the systems in close proximity to human operators and passengers where <span class="hlt">noise</span> is one of the main constraints to the acceptance and spread of this technology. As a key component in power transfer, displacement machines can be major <span class="hlt">sources</span> of <span class="hlt">noise</span> in hydraulic systems. Thus, investigation into the <span class="hlt">sources</span> of <span class="hlt">noise</span> and discovering strategies to reduce <span class="hlt">noise</span> is a key part of applying fluid power systems to a wider range of applications, as well as improving the performance of current hydraulic systems. The present research aims to leverage previous efforts and develop new models and experimental techniques in the topic of <span class="hlt">noise</span> generation caused by hydrostatic units. This requires challenging and surpassing current accepted methods in the understanding of <span class="hlt">noise</span> in fluid power systems. This research seeks to expand on the previous experimental and modeling efforts by directly considering the effect that system and component design changes apply on the total sound power and the sound frequency components emitted from displacement machines and the attached lines. The case of external gear pumps is taken as reference for a new model to understand the generation and transmission of <span class="hlt">noise</span> from the <span class="hlt">sources</span> out to the environment. The lumped parameter model HYGESim (HYdraulic GEar machine Simulator) was expanded to investigate the dynamic forces on the solid bodies caused by the pump operation and to predict interactions with the attached system. Vibration and sound radiation were then predicted using a combined finite element and boundary</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1988hias.rept.....G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1988hias.rept.....G"><span>A high intensity acoustic <span class="hlt">source</span> for active attenuation of exhaust <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glendinning, A. G.; Elliott, S. J.; Nelson, P. A.</p> <p>1988-04-01</p> <p>An electropneumatic sound <span class="hlt">source</span> was developed for active <span class="hlt">noise</span> control systems applied in hostile environments such as the exhaust systems of gas turbines and internal combustion engines. It employs a gas bearing to support the friction free motion of a sliding plate which is used to modulate the supply of compressed air. The sliding plate is driven by an electrodynamic vibrator. Experimental results demonstrate that this arrangement reduces <span class="hlt">harmonic</span> distortion to at least 20 dB below the fundamental driving frequency for most operating conditions. A theoretical analysis of the transducer enables predictions to be made of the acoustic volume velocity (<span class="hlt">source</span> strength) produced by the transducer as a function of the upstream pressure and displacement of the sliding valve. Applicability of the transducer to gas turbine and internal combustion engine exhaust systems was tested, and net power consumption resulting from the operation of the device was estimated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740002804','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740002804"><span>Aircraft <span class="hlt">noise</span> reduction technology. [to show impact on individuals and communities, component <span class="hlt">noise</span> <span class="hlt">sources</span>, and operational procedures to reduce impact</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1973-01-01</p> <p>Aircraft and airport <span class="hlt">noise</span> reduction technology programs conducted by NASA are presented. The subjects discussed are: (1) effects of aircraft <span class="hlt">noise</span> on individuals and communities, (2) status of aircraft <span class="hlt">source</span> <span class="hlt">noise</span> technology, (3) operational procedures to reduce the impact of aircraft <span class="hlt">noise</span>, and (4) NASA relations with military services in aircraft <span class="hlt">noise</span> problems. References to more detailed technical literature on the subjects discussed are included.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002ASAJ..111.2336H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002ASAJ..111.2336H"><span>Identification and classification of <span class="hlt">noise</span> <span class="hlt">sources</span> in a chain conveyor</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Homer, John P.; Vipperman, Jeffrey S.; Reeves, Efrem R.</p> <p>2002-05-01</p> <p><span class="hlt">Noise</span> induced hearing loss (NIHL) is one of the most significant disabilities of workers in the mining industry. In response, the National Institute of Occupational Safety and Health (NIOSH) is conducting a study associated with mining equipment. This study outlines the analysis of a chain conveyor. Band-limited accelerometer, sound-intensity, far-field and near-field microphone measurements were taken along the conveyor section. The sound intensity measurements were used to identify areas with high <span class="hlt">noise</span> as well as to calculate and 1/3-octave sound power levels. The total sound power results were used to classify the dominant <span class="hlt">noise</span> <span class="hlt">sources</span> where the 1/3-octave sound power results were used to identify the most contributive frequency bands to the overall <span class="hlt">noise</span> of the system. Coherence analysis was performed between accelerometer and microphone measurements to identify structure-borne and air-borne <span class="hlt">noise</span> paths of the system. Summary results from the analysis include recommendations for transmission control and damping devices and their ability to reduce <span class="hlt">noise</span> to regulatory acceptable levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820016174','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820016174"><span>An investigation of rotor <span class="hlt">harmonic</span> <span class="hlt">noise</span> by the use of small scale wind tunnel models</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sternfeld, H., Jr.; Schaffer, E. G.</p> <p>1982-01-01</p> <p><span class="hlt">Noise</span> measurements of small scale helicopter rotor models were compared with <span class="hlt">noise</span> measurements of full scale helicopters to determine what information about the full scale helicopters could be derived from <span class="hlt">noise</span> measurements of small scale helicopter models. Comparisons were made of the discrete frequency (rotational) <span class="hlt">noise</span> for 4 pairs of tests. Areas covered were tip speed effects, isolated rotor, tandem rotor, and main rotor/tail rotor interaction. Results show good comparison of <span class="hlt">noise</span> trends with configuration and test condition changes, and good comparison of absolute <span class="hlt">noise</span> measurements with the corrections used except for the isolated rotor case. <span class="hlt">Noise</span> measurements of the isolated rotor show a great deal of scatter reflecting the fact that the rotor in hover is basically unstable.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010APS..4CF.H5005M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010APS..4CF.H5005M"><span>A simple-<span class="hlt">source</span> model of military jet aircraft <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morgan, Jessica; Gee, Kent L.; Neilsen, Tracianne; Wall, Alan T.</p> <p>2010-10-01</p> <p>The jet plumes produced by military jet aircraft radiate significant amounts of <span class="hlt">noise</span>. A need to better understand the characteristics of the turbulence-induced aeroacoustic <span class="hlt">sources</span> has motivated the present study. The purpose of the study is to develop a simple-<span class="hlt">source</span> model of jet <span class="hlt">noise</span> that can be compared to the measured data. The study is based off of acoustic data collected near a tied-down F-22 Raptor. The simplest model consisted of adjusting the origin of a monopole above a rigid planar reflector until the locations of the predicted and measured interference nulls matched. The model has developed into an extended Rayleigh distribution of partially correlated monopoles which fits the measured data from the F-22 significantly better. The results and basis for the model match the current prevailing theory that jet <span class="hlt">noise</span> consists of both correlated and uncorrelated <span class="hlt">sources</span>. In addition, this simple-<span class="hlt">source</span> model conforms to the theory that the peak <span class="hlt">source</span> location moves upstream with increasing frequency and lower engine conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V33A2608M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V33A2608M"><span>Volcanic jet <span class="hlt">noise</span>: infrasonic <span class="hlt">source</span> processes and atmospheric propagation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matoza, R. S.; Fee, D.; Ogden, D. E.</p> <p>2011-12-01</p> <p>Volcanic eruption columns are complex flows consisting of (possibly supersonic) injections of ash-gas mixtures into the atmosphere. A volcanic eruption column can be modeled as a lower momentum-driven jet (the gas-thrust region), which transitions with altitude into a thermally buoyant plume. Matoza et al. [2009] proposed that broadband infrasonic signals recorded during this type of volcanic activity represent a low-frequency form of jet <span class="hlt">noise</span>. Jet <span class="hlt">noise</span> is produced at higher acoustic frequencies by smaller-scale man-made jet flows (e.g., turbulent jet flow from jet engines and rockets). Jet <span class="hlt">noise</span> generation processes could operate at larger spatial scales and produce infrasonic frequencies in the lower gas-thrust portion of the eruption column. Jet-<span class="hlt">noise</span>-like infrasonic signals have been observed at ranges of tens to thousands of kilometers from sustained volcanic explosions at Mount St. Helens, WA; Tungurahua, Ecuador; Redoubt, AK; and Sarychev Peak, Kuril Islands. Over such distances, the atmosphere cannot be considered homogeneous. Long-range infrasound propagation takes place primarily in waveguides formed by vertical gradients in temperature and horizontal winds, and exhibits strong spatiotemporal variability. The timing and location of volcanic explosions can be estimated from remote infrasonic data and could be used with ash cloud dispersion forecasts for hazard mitigation. <span class="hlt">Source</span> studies of infrasonic volcanic jet <span class="hlt">noise</span>, coupled with infrasound propagation modeling, hold promise for being able to constrain more detailed eruption jet parameters with remote, ground-based geophysical data. Here we present recent work on the generation and propagation of volcanic jet <span class="hlt">noise</span>. Matoza, R. S., D. Fee, M. A. Garcés, J. M. Seiner, P. A. Ramón, and M. A. H. Hedlin (2009), Infrasonic jet <span class="hlt">noise</span> from volcanic eruptions, Geophys. Res. Lett., 36, L08303, doi:10.1029/2008GL036486.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9344E..2SH','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9344E..2SH"><span>Generation of stable high order <span class="hlt">harmonic</span> <span class="hlt">noise</span>-like pulses in a passively mode-locked double clad fiber ring laser</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hernandez-Garcia, J. C.; Pottiez, O.; Ibarra-Escamilla, B.; Estudillo-Ayala, J. M.; Rojas-Laguna, R.; Kuzin, E.; Muñoz-Lopez, A.; Filoteo-Razo, J. D.</p> <p>2015-03-01</p> <p>We study a passively mode-locked double-clad Erbium-Ytterbium fiber ring laser producing <span class="hlt">noise</span>-like pulse through nonlinear polarization evolution and polarization selection. Single <span class="hlt">noise</span>-like pulsing is only observed at moderate pump power. As pump power is increased, and through polarization controllers adjustments, <span class="hlt">harmonic</span> mode-locking of growing order were successively appearing. For pump powers close to the damage threshold of the setup, we reach <span class="hlt">harmonic</span> orders beyond 1200 and repetition frequencies in excess of a quarter of a GHz. Finally, these experimental results could be useful in the quest for higher pulse energies and higher repetition rates in passively mode-locked fiber lasers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015CMaPh.339..407J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015CMaPh.339..407J"><span>Superdiffusion of Energy in a Chain of <span class="hlt">Harmonic</span> Oscillators with <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jara, Milton; Komorowski, Tomasz; Olla, Stefano</p> <p>2015-10-01</p> <p>We consider a one dimensional infinite chain of <span class="hlt">harmonic</span> oscillators whose dynamics is perturbed by a stochastic term conserving energy and momentum. We prove that in the unpinned case the macroscopic evolution of the energy converges to the solution of the fractional diffusion equation . For a pinned system we prove that its energy evolves diffusively, generalizing some results of Basile and Olla (J. Stat. Phys. 155(6):1126-1142, 2014).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080047683','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080047683"><span>A Numerical Investigation of Turbine <span class="hlt">Noise</span> <span class="hlt">Source</span> Hierarchy and Its Acoustic Transmission Characteristics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>VanZante, Dale; Envia, Edmane</p> <p>2008-01-01</p> <p>Understanding the relative importance of the various turbine <span class="hlt">noise</span> generation mechanisms and the characteristics of the turbine acoustic transmission loss are essential ingredients in developing robust reduced-order models for predicting the turbine <span class="hlt">noise</span> signature. A computationally based investigation has been undertaken to help guide the development of a turbine <span class="hlt">noise</span> prediction capability that does not rely on empiricism. The investigation relies on highly detailed numerical simulations of the unsteady flowfield inside a modern high-pressure turbine (HPT). The simulations are developed using TURBO, which is an unsteady Reynolds-averaged Navier-Stokes (URANS) code capable of multi-stage simulations. The purpose of this study is twofold. First, to determine an estimate of the relative importance of the contributions to the coherent part of the acoustic signature of a turbine from the three potential <span class="hlt">sources</span> of turbine <span class="hlt">noise</span> generation, namely, blade-row viscous interaction, potential field interaction, and entropic <span class="hlt">source</span> associated with the interaction of the blade rows with the temperature nonuniformities caused by the incomplete mixing of the hot fluid and the cooling flow. Second, to develop an understanding of the turbine acoustic transmission characteristics and to assess the applicability of existing empirical and analytical transmission loss models to realistic geometries and flow conditions for modern turbine designs. The investigation so far has concentrated on two simulations: (1) a single-stage HPT and (2) a two-stage HPT and the associated inter-turbine duct/strut segment. The simulations are designed to resolve up to the second <span class="hlt">harmonic</span> of the blade passing frequency tone in accordance with accepted rules for second order solvers like TURBO. The calculations include blade and vane cooling flows and a radial profile of pressure and temperature at the turbine inlet. The calculation can be modified later to include the combustor pattern factor at the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26428806','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26428806"><span>Fundamental-frequency discrimination using <span class="hlt">noise</span>-band-vocoded <span class="hlt">harmonic</span> complexes in older listeners with normal hearing.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schvartz-Leyzac, Kara C; Chatterjee, Monita</p> <p>2015-09-01</p> <p>Voice-pitch cues provide detailed information about a talker that help a listener to understand speech in complex environments. Temporal-envelope based voice-pitch coding is important for listeners with hearing impairment, especially listeners with cochlear implants, as spectral resolution is not sufficient to provide a spectrally based voice-pitch cue. The effect of aging on the ability to glean voice-pitch information using temporal envelope cues is not completely understood. The current study measured fundamental frequency (f0) discrimination limens in normal-hearing younger and older adults while listening to <span class="hlt">noise</span>-band vocoded <span class="hlt">harmonic</span> complexes with varying numbers of spectral channels. Age-related disparities in performance were apparent across all conditions, independent of spectral degradation and/or fundamental frequency. The findings have important implications for older listeners with normal hearing and hearing loss, who may be inherently limited in their ability to perceive f0 cues due to senescent decline in auditory function.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750017148','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750017148"><span>Optimization of structures undergoing <span class="hlt">harmonic</span> or stochastic excitation. Ph.D. Thesis; [atmospheric turbulence and white <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Johnson, E. H.</p> <p>1975-01-01</p> <p>The optimal design was investigated of simple structures subjected to dynamic loads, with constraints on the structures' responses. Optimal designs were examined for one dimensional structures excited by <span class="hlt">harmonically</span> oscillating loads, similar structures excited by white <span class="hlt">noise</span>, and a wing in the presence of continuous atmospheric turbulence. The first has constraints on the maximum allowable stress while the last two place bounds on the probability of failure of the structure. Approximations were made to replace the time parameter with a frequency parameter. For the first problem, this involved the steady state response, and in the remaining cases, power spectral techniques were employed to find the root mean square values of the responses. Optimal solutions were found by using computer algorithms which combined finite elements methods with optimization techniques based on mathematical programming. It was found that the inertial loads for these dynamic problems result in optimal structures that are radically different from those obtained for structures loaded statically by forces of comparable magnitude.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRA..12110289P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRA..12110289P"><span>Equatorial <span class="hlt">noise</span> emissions with a quasiperiodic modulation observed by DEMETER at <span class="hlt">harmonics</span> of the O+ ion gyrofrequency</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Parrot, Michel; Němec, František; Santolík, Ondřej; Cornilleau-Wehrlin, Nicole</p> <p>2016-10-01</p> <p>The analysis of ionospheric equatorial <span class="hlt">noise</span> (EN) with a quasiperiodic (QP) modulation observed by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) spacecraft is presented. These EN emissions, also called whistler mode or fast magnetosonic waves, play an important role in acceleration of radiation belt electrons. A statistical analysis with 103 events shows that they occur just after intense magnetic storms. Usually, they are generated by unstable proton ring distribution close to the magnetic equator at <span class="hlt">harmonics</span> of the proton gyrofrequency in the inner magnetosphere (2 < L < 8). But at lower L values down in the ionosphere three events have been analyzed and it appears that the EN waves are at <span class="hlt">harmonics</span> of—or very close to—a O+ ion gyrofrequency which can be found close to or slightly above the satellite. The wave propagation analysis indicates that these emissions are coming from an area above the satellite. Concerning one event, the EN emissions are observed on several consecutive orbits and there is a temporal coincidence with observations performed by the Cluster satellites at higher altitudes in the magnetosphere. EN emissions at lower frequencies have been also observed by the Cluster satellites in the same longitudinal sector as DEMETER but at 5 RE. The analysis of the Spatio Temporal Analysis of Field Fluctuations data on board C1 reveals that the magnetic field spectrogram has peaks close to <span class="hlt">harmonics</span> of the local proton gyrofrequency as usually reported. It is shown that the DEMETER and Cluster EN waves have a similar QP modulation but with slightly different period and frequency.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA468464','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA468464"><span>The Mitigation of Radio <span class="hlt">Noise</span> from External <span class="hlt">Sources</span> at Receiving Sites</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2007-05-01</p> <p>receiving site. Step 2—Understand <span class="hlt">sources</span> and <span class="hlt">source</span> mechanisms . Step 3—Locate <span class="hlt">sources</span>. Step 4—Identify the hardware which is generating <span class="hlt">noise</span>...Typical <span class="hlt">noise</span> problems at a receiving site are described in Section 1. Typical <span class="hlt">sources</span>, <span class="hlt">source</span> mechanisms and the temporal and spectral properties...Two common types of <span class="hlt">noise</span> will be encountered along with several less common types. These types are closely related to the <span class="hlt">source</span> mechanisms</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSemi..37i5004W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSemi..37i5004W"><span>Low-<span class="hlt">noise</span> sub-<span class="hlt">harmonic</span> injection locked multiloop ring oscillator</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weilin, Xu; Di, Wu; Xueming, Wei; Baolin, Wei; Jihai, Duan; Fadi, Gui</p> <p>2016-09-01</p> <p>A three-stage differential voltage-controlled ring oscillator is presented for wide-tuning and low-phase <span class="hlt">noise</span> requirement of clock and data recovery circuit in ultra wideband (UWB) wireless body area network. To improve the performance of phase <span class="hlt">noise</span> of delay cell with coarse and fine frequency tuning, injection locked technology together with pseudo differential architecture are adopted. In addition, a multiloop is employed for frequency boosting. Two RVCOs, the standard RVCO without the IL block and the proposed IL RVCO, were fabricated in SMIC 0.18 μm 1P6M Salicide CMOS process. The proposed IL RVCO exhibits a measured phase <span class="hlt">noise</span> of -112.37 dBc/Hz at 1 MHz offset from the center frequency of 1 GHz, while dissipating a current of 8 mA excluding the buffer from a 1.8-V supply voltage. It shows a 16.07 dB phase <span class="hlt">noise</span> improvement at 1 MHz offset compared to the standard topology. Project supported by the National Natural Science Foundation of China (No. 61264001), the Guangxi Natural Science Foundation (Nos. 2013GXNSFAA019333, 2015GXNSFAA139301, 2014GXNSFAA118386), the Graduate Education Innovation Program of GUET (No. GDYCSZ201457), the Project of Guangxi Education Department (No. LD14066B) and the High-Level-Innovation Team and Outstanding Scholar Project of Guangxi Higher Education Institutes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvE..95c3307M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvE..95c3307M"><span>Spheroidal <span class="hlt">harmonic</span> expansions for the solution of Laplace's equation for a point <span class="hlt">source</span> near a sphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Majić, Matt R. A.; Auguié, Baptiste; Le Ru, Eric C.</p> <p>2017-03-01</p> <p>We propose a powerful approach to solve Laplace's equation for point <span class="hlt">sources</span> near a spherical object. The central new idea is to use prolate spheroidal solid <span class="hlt">harmonics</span>, which are separable solutions of Laplace's equation in spheroidal coordinates, instead of the more natural spherical solid <span class="hlt">harmonics</span>. Using electrostatics as an example, we motivate this choice and show that the resulting series expansions converge much faster. This improvement is discussed in terms of the singularity of the solution and its analytic continuation. The benefits of this approach are further illustrated for a specific example: the calculation of modified decay rates of light emitters close to nanostructures in the quasistatic approximation. We expect the general approach to be applicable with similar benefits to the solution of Laplace's equation for other geometries and to other equations of mathematical physics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850044808&hterms=ionograms&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dionograms','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850044808&hterms=ionograms&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dionograms"><span>Auroral kilometric radiation - Wave modes, <span class="hlt">harmonics</span>, and <span class="hlt">source</span> region electron density structures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Benson, R. F.</p> <p>1985-01-01</p> <p>A change from extraordinary (X) mode to ordinary (O) mode dominance is observed in the auroral kilometric radiation (AKR) detected on ISIS 1 topside sounder ionograms as the <span class="hlt">source</span> region plasma to gyrofrequency ratio fN/fH varies from 0.1 to 1.3. The X and O mode AKR, Z (the slow branch of the X mode) and whistler (W) mode are also observed. The Z mode is typically slightly less intense than the O-mode. The W-mode is confined to frequencies less than fH/2, suggesting that it is the result of field aligned ducted signals reaching the satellite from a <span class="hlt">source</span> at lower altitudes. <span class="hlt">Harmonic</span> AKR bands are commonly observed and the 2nd <span class="hlt">harmonic</span> appears to be due to propagating signals. The deduced (fN/fH) at the bottom of the AKR <span class="hlt">source</span> region is always less than 0.4 and is typically less than 0.2 during the generation of X-mode AKR, but approaches 0.9 for O-mode AKR. No large density enhancements were observed within AKR <span class="hlt">source</span> region density cavities. It is suggested that the observed intense AKR is cyclotron X-mode radiation rather than plasma frequency O-mode radiation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6218490','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6218490"><span>Auroral kilometric radiation: wave modes, <span class="hlt">harmonic</span> and <span class="hlt">source</span> region electron density structures</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Benson, R.F.</p> <p>1984-05-01</p> <p>A change from extraordinary (X) mode to ordinary (0) mode dominance is observed in the auroral kilometric radiation (AKR) detected on ISIS 1 topside sounder ionograms as the <span class="hlt">source</span> region plasma to gyrofrequency ratio fN/fH varies from 0.1 to 1.3. The X and 0 mode AKR, Z (the slow branch of the X mode) and whistler (W) mode are also observed. The Z mode is typically slightly less intense than the 0-mode. Thw W-mode is confined to frequencies less than fH/2, suggesting that it is the result of field aligned ducted signals reaching the satellite from a <span class="hlt">source</span> at lower altitudes. <span class="hlt">Harmonic</span> AKR bands are commonly observed and the 2nd <span class="hlt">harmonic</span> appears to be due to propagating signals. The deduced (fN/fH) at the bottom of the AKR <span class="hlt">source</span> region is always less than 0.4 and is typically less than 0.2 during the generation of X-mode AKR, but approaches 0.9 for 0-mode AKR. No large density enhancements were observed within AKR <span class="hlt">source</span> region density cavities. It is suggested that the observed INTENSE AKR IS cyclotron X-mode radiation rather than plasma frequency 0-mode radiation.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840017135','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840017135"><span>Auroral kilometric radiation: Wave modes, <span class="hlt">harmonic</span> and <span class="hlt">source</span> region electron density structures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Benson, R. F.</p> <p>1984-01-01</p> <p>A change from extraordinary (X) mode to ordinary (0) mode dominance is observed in the auroral kilometric radiation (AKR) detected on ISIS 1 topside sounder ionograms as the <span class="hlt">source</span> region plasma to gyrofrequency ratio fN/fH varies from 0.1 to 1.3. The X and 0 mode AKR, Z (the slow branch of the X mode) and whistler (W) mode are also observed. The Z mode is typically slightly less intense than the 0-mode. Thw W-mode is confined to frequencies less than fH/2, suggesting that it is the result of field aligned ducted signals reaching the satellite from a <span class="hlt">source</span> at lower altitudes. <span class="hlt">Harmonic</span> AKR bands are commonly observed and the 2nd <span class="hlt">harmonic</span> appears to be due to propagating signals. The deduced (fN/fH) at the bottom of the AKR <span class="hlt">source</span> region is always less than 0.4 and is typically less than 0.2 during the generation of X-mode AKR, but approaches 0.9 for 0-mode AKR. No large density enhancements were observed within AKR <span class="hlt">source</span> region density cavities. It is suggested that the observed INTENSE AKR IS cyclotron X-mode radiation rather than plasma frequency 0-mode radiation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMNS31A1958F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMNS31A1958F"><span>Doubling the Spectrum of Time-Domain Induced Polarization: Removal of <span class="hlt">Harmonic</span> <span class="hlt">Noise</span> and Self-Potential Drift</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fiandaca, G.; Olsson, P. I.; Auken, E.; Larsen, J. J.; Maurya, P. K.; Dahlin, T.</p> <p>2015-12-01</p> <p>The extraction of spectral information in the inversion process of time-domain (TD) induced polarization (IP) data is changing the use of the IP method. Data interpretation is evolving from a qualitative description of the soil, able only to discriminate the presence of contrasts in chargeability parameters, towards a quantitative analysis of the investigated media, which allows soil-type characterization. Two major limitations restrict the extraction of the spectral information of TDIP data in the field: i) the difficulty of acquiring reliable early-time measurements, in the millisecond range and ii) the self-potential drift in the measured potentials distorting the shape of the late time IP decays, in the second range. For measuring at early-times, we developed a new method for removing the powerline <span class="hlt">noise</span> contained in the data through a model-based approach, localizing the fundamental frequency of the powerline signal in the full-waveform IP recordings. By this, we cancel both the fundamental signal and its <span class="hlt">harmonics</span>. This <span class="hlt">noise</span> cancellation allows the use of earlier and narrower gates, down to a few milliseconds after the current turn-off. Even earlier gates can be measured but they will be inductively "contaminated" which we at present want to avoid. A proper removal of the self-potential drift present between the potential electrodes is essential for preserving the shape of the TD decays, especially for late times. Usually constant or linear drift-removal algorithms are used, but these algorithms fail in removing the background potentials due to the polarization of the electrodes previously used for current injection. We developed a drift-removal scheme that model the polarization effect and efficiently allows for preserving the shape of the IP decays. The removal of both the <span class="hlt">harmonic</span> <span class="hlt">noise</span> and self-potential drift allows for doubling the usable range of TDIP data to more than three decades in time (corresponding to three decays in frequency), and will</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19830017227','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19830017227"><span>Limits on the prediction of helicopter rotor <span class="hlt">noise</span> using thickness and loading <span class="hlt">sources</span>: Validation of helicopter <span class="hlt">noise</span> prediction techniques</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Succi, G. P.</p> <p>1983-01-01</p> <p>The techniques of helicopter rotor <span class="hlt">noise</span> prediction attempt to describe precisely the details of the <span class="hlt">noise</span> field and remove the empiricisms and restrictions inherent in previous methods. These techniques require detailed inputs of the rotor geometry, operating conditions, and blade surface pressure distribution. The Farassat <span class="hlt">noise</span> prediction techniques was studied, and high speed helicopter <span class="hlt">noise</span> prediction using more detailed representations of the thickness and loading <span class="hlt">noise</span> <span class="hlt">sources</span> was investigated. These predictions were based on the measured blade surface pressures on an AH-1G rotor and compared to the measured sound field. Although refinements in the representation of the thickness and loading <span class="hlt">noise</span> <span class="hlt">sources</span> improve the calculation, there are still discrepancies between the measured and predicted sound field. Analysis of the blade surface pressure data indicates shocks on the blades, which are probably responsible for these discrepancies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26176463','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26176463"><span>Integrated quasi-phase-matched second-<span class="hlt">harmonic</span> generator and electro-optic phase modulator for low-<span class="hlt">noise</span> phase-sensitive amplification.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Enbutsu, Koji; Umeki, Takeshi; Tadanaga, Osamu; Asobe, Masaki; Takenouchi, Hirokazu</p> <p>2015-07-15</p> <p>We propose a quasi-phase-matched second-<span class="hlt">harmonic</span> generator integrated with an electro-optic phase modulator in a directly bonded LiNbO3 (DB-LN) waveguide to obtain high signal-to-<span class="hlt">noise</span> ratio (SNR) pump light for a phase-sensitive amplifier (PSA). This integrated device exhibits 1-MHz modulation and 1-W second-<span class="hlt">harmonic</span>-generation properties sufficient for phase-locking between the signal and pump and for PSA gain, respectively. A novel PSA configuration based on the high-input-power tolerance of the device helps to suppress the <span class="hlt">noise</span> from the erbium-doped fiber amplifier used for pump-light generation and leads to an improvement of the SNR of the pump light. The SNR improvement was confirmed by comparing the <span class="hlt">noise</span> figure of a PSA employing the DB-LN waveguide with that of a PSA using a Ti-diffused LN waveguide modulator.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009APS..DMP.M1015V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009APS..DMP.M1015V"><span>Femtosecond Dynamics and Multiphoton Ionization driven with an Intense High Order <span class="hlt">Harmonic</span> <span class="hlt">Source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Tilborg, Jeroen; Allison, Tom; Wright, Travis; Hertlein, Marc; Falcone, Roger; Liu, Yanwei; Merdji, Hamed; Belkacem, Ali</p> <p>2009-05-01</p> <p>We have constructed a high intensity high order <span class="hlt">harmonic</span> <span class="hlt">source</span> at the Lawrence Berkeley National Lab delivering ˜10^9 extreme ultraviolet photons/shot on a gas target and used it to observe multiphoton ionization and conduct femtosecond EUV-pump IR-probe experiments. Following excitation by 20-25 eV photons, we observed that the excited ethylene cation (H2C-CH2)^+ experienced isomerization to the ethylidene configuration (HC-CH3)^+ in 50±25 fs, followed by an H2 stretch motion. Experimental data and analysis from several experiments as well as a future outlook of our efforts will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JPhCS.194c2015V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JPhCS.194c2015V"><span>Femtosecond dynamics and multiphoton ionization driven with an intense high order <span class="hlt">harmonic</span> <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Tilborg, J.; Allison, T. K.; Wright, T. W.; Hertlein, M. P.; Liu, Y.; Merdji, H.; Falcone, R. W.; Belkacem, A.</p> <p>2009-11-01</p> <p>We have constructed a high intensity high order <span class="hlt">harmonic</span> <span class="hlt">source</span> delivering ~ 109 extreme ultraviolet photons/shot on a gas target and used it to observe multiphoton ionization and conduct femtosecond EUV-pump IR-probe experiments. Following excitation by 20-25 eV photons, we observed that the excited ethylene cation (H2C-CH2)+ experienced isomerization to the ethylidene configuration (HC-CHs)+ in 50±25 fs, followed by an H2 stretch motion. Experimental data and analysis from several other performed and planned experiments will be presented as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhRvS..19d4403T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhRvS..19d4403T"><span>Combining <span class="hlt">harmonic</span> generation and laser chirping to achieve high spectral density in Compton <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Terzić, Balša; Reeves, Cody; Krafft, Geoffrey A.</p> <p>2016-04-01</p> <p>Recently various laser-chirping schemes have been investigated with the goal of reducing or eliminating ponderomotive line broadening in Compton or Thomson scattering occurring at high laser intensities. As a next level of detail in the spectrum calculations, we have calculated the line smoothing and broadening expected due to incident beam energy spread within a one-dimensional plane wave model for the incident laser pulse, both for compensated (chirped) and unchirped cases. The scattered compensated distributions are treatable analytically within three models for the envelope of the incident laser pulses: Gaussian, Lorentzian, or hyperbolic secant. We use the new results to demonstrate that the laser chirping in Compton <span class="hlt">sources</span> at high laser intensities: (i) enables the use of higher order <span class="hlt">harmonics</span>, thereby reducing the required electron beam energies; and (ii) increases the photon yield in a small frequency band beyond that possible with the fundamental without chirping. This combination of chirping and higher <span class="hlt">harmonics</span> can lead to substantial savings in the design, construction and operational costs of the new Compton <span class="hlt">sources</span>. This is of particular importance to the widely popular laser-plasma accelerator based Compton <span class="hlt">sources</span>, as the improvement in their beam quality enters the regime where chirping is most effective.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19990028361','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19990028361"><span><span class="hlt">Source</span> Methodology for Turbofan <span class="hlt">Noise</span> Prediction (<span class="hlt">SOURCE</span>3D Technical Documentation)</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Meyer, Harold D.</p> <p>1999-01-01</p> <p>This report provides the analytical documentation for the <span class="hlt">SOURCE</span>3D Rotor Wake/Stator Interaction Code. It derives the equations for the rotor scattering coefficients and stator <span class="hlt">source</span> vector and scattering coefficients that are needed for use in the TFANS (Theoretical Fan <span class="hlt">Noise</span> Design/Prediction System). <span class="hlt">SOURCE</span>3D treats the rotor and stator as isolated <span class="hlt">source</span> elements. TFANS uses this information, along with scattering coefficients for inlet and exit elements, and provides complete <span class="hlt">noise</span> solutions for turbofan engines. <span class="hlt">SOURCE</span>3D is composed of a collection of FORTRAN programs that have been obtained by extending the approach of the earlier V072 Rotor Wake/Stator Interaction Code. Similar to V072, it treats the rotor and stator as a collection of blades and vanes having zero thickness and camber contained in an infinite, hardwall annular duct. <span class="hlt">SOURCE</span>3D adds important features to the V072 capability-a rotor element, swirl flow and vorticity waves, actuator disks for flow turning, and combined rotor/actuator disk and stator/actuator disk elements. These items allow reflections from the rotor, frequency scattering, and mode trapping, thus providing more complete <span class="hlt">noise</span> predictions than previously. The code has been thoroughly verified through comparison with D.B. Hanson's CUP2D two- dimensional code using a narrow annulus test case.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050175875','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050175875"><span>Fan <span class="hlt">Noise</span> <span class="hlt">Source</span> Diagnostic Test: Rotor Alone Aerodynamic Performance Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hughes, Christopher E.; Jeracki, Robert J.; Woodward, Richard P.; Miller, Christopher J.</p> <p>2005-01-01</p> <p>The aerodynamic performance of an isolated fan or rotor alone model was measured in the NASA Glenn Research Center 9- by 15- Foot Low Speed Wind Tunnel as part of the Fan Broadband <span class="hlt">Source</span> Diagnostic Test conducted at NASA Glenn. The <span class="hlt">Source</span> Diagnostic Test was conducted to identify the <span class="hlt">noise</span> <span class="hlt">sources</span> within a wind tunnel scale model of a turbofan engine and quantify their contribution to the overall system <span class="hlt">noise</span> level. The fan was part of a 1/5th scale model representation of the bypass stage of a current technology turbofan engine. For the rotor alone testing, the fan and nacelle, including the inlet, external cowl, and fixed area fan exit nozzle, were modeled in the test hardware; the internal outlet guide vanes located behind the fan were removed. Without the outlet guide vanes, the velocity at the nozzle exit changes significantly, thereby affecting the fan performance. As part of the investigation, variations in the fan nozzle area were tested in order to match as closely as possible the rotor alone performance with the fan performance obtained with the outlet guide vanes installed. The fan operating performance was determined using fixed pressure/temperature combination rakes and the corrected weight flow. The performance results indicate that a suitable nozzle exit was achieved to be able to closely match the rotor alone and fan/outlet guide vane configuration performance on the sea level operating line. A small shift in the slope of the sea level operating line was measured, which resulted in a slightly higher rotor alone fan pressure ratio at take-off conditions, matched fan performance at cutback conditions, and a slightly lower rotor alone fan pressure ratio at approach conditions. However, the small differences in fan performance at all fan conditions were considered too small to affect the fan acoustic performance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930018153','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930018153"><span>Double simple-<span class="hlt">harmonic</span>-oscillator formulation of the thermal equilibrium of a fluid interacting with a coherent <span class="hlt">source</span> of phonons</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Defacio, B.; Vannevel, Alan; Brander, O.</p> <p>1993-01-01</p> <p>A formulation is given for a collection of phonons (sound) in a fluid at a non-zero temperature which uses the simple <span class="hlt">harmonic</span> oscillator twice; one to give a stochastic thermal '<span class="hlt">noise</span>' process and the other which generates a coherent Glauber state of phonons. Simple thermodynamic observables are calculated and the acoustic two point function, 'contrast' is presented. The role of 'coherence' in an equilibrium system is clarified by these results and the simple <span class="hlt">harmonic</span> oscillator is a key structure in both the formulation and the calculations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4014398','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4014398"><span>Axonal <span class="hlt">Noise</span> as a <span class="hlt">Source</span> of Synaptic Variability</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Neishabouri, Ali; Faisal, A. Aldo</p> <p>2014-01-01</p> <p>Post-synaptic potential (PSP) variability is typically attributed to mechanisms inside synapses, yet recent advances in experimental methods and biophysical understanding have led us to reconsider the role of axons as highly reliable transmission channels. We show that in many thin axons of our brain, the action potential (AP) waveform and thus the Ca++ signal controlling vesicle release at synapses will be significantly affected by the inherent variability of ion channel gating. We investigate how and to what extent fluctuations in the AP waveform explain observed PSP variability. Using both biophysical theory and stochastic simulations of central and peripheral nervous system axons from vertebrates and invertebrates, we show that channel <span class="hlt">noise</span> in thin axons (<1 µm diameter) causes random fluctuations in AP waveforms. AP height and width, both experimentally characterised parameters of post-synaptic response amplitude, vary e.g. by up to 20 mV and 0.5 ms while a single AP propagates in C-fibre axons. We show how AP height and width variabilities increase with a ¾ power-law as diameter decreases and translate these fluctuations into post-synaptic response variability using biophysical data and models of synaptic transmission. We find for example that for mammalian unmyelinated axons with 0.2 µm diameter (matching cerebellar parallel fibres) axonal <span class="hlt">noise</span> alone can explain half of the PSP variability in cerebellar synapses. We conclude that axonal variability may have considerable impact on synaptic response variability. Thus, in many experimental frameworks investigating synaptic transmission through paired-cell recordings or extracellular stimulation of presynaptic neurons, causes of variability may have been confounded. We thereby show how bottom-up aggregation of molecular <span class="hlt">noise</span> <span class="hlt">sources</span> contributes to our understanding of variability observed at higher levels of biological organisation. PMID:24809823</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880031424&hterms=hawking&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhawking','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880031424&hterms=hawking&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhawking"><span>Quadrupole <span class="hlt">source</span> in prediction of the <span class="hlt">noise</span> of rotating blades - A new <span class="hlt">source</span> description</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Farassat, F.</p> <p>1987-01-01</p> <p>The aim of this paper is to perform a theoretical study of the quadrupole term of the Ffowcs Williams-Hawkings (FW-H) equation to obtain practical results for applications to rotating blades. The quadrupole term of the FW-H equation is algebraically manipulated into volume, surface and line <span class="hlt">sources</span> using generalized function theory and differential geometry. The volume <span class="hlt">source</span> is of the type in Lighthill's jet <span class="hlt">noise</span> theory. The surface <span class="hlt">sources</span> are on the blade and shock surfaces and the line <span class="hlt">source</span> is at the trailing edge. It is shown that contribution of volume <span class="hlt">sources</span> in the boundary layer and wakes can be written in the form of surface integrals. It is argued that the surface and line <span class="hlt">sources</span> and the part of the volume <span class="hlt">sources</span> in the boundary layer, wakes and vortices near the blades should be sufficient in calculation of the <span class="hlt">noise</span> of high speed rotating blades. The integrals correspoding to the various <span class="hlt">sources</span> appearing in the formula for calculation of the acoustic pressure are briefly derived.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020053652','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020053652"><span>General Aviation Interior <span class="hlt">Noise</span>. Part 2; In-Flight <span class="hlt">Source</span>/Verification</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Unruh, James F.; Till, Paul D.; Palumbo, Daniel L. (Technical Monitor)</p> <p>2002-01-01</p> <p>The technical approach made use of the Cessna Model 182E aircraft used in the previous effort as a test bed for <span class="hlt">noise</span> control application. The present phase of the project reports on flight test results during application of various passive <span class="hlt">noise</span> treatments in an attempt to verify the <span class="hlt">noise</span> <span class="hlt">sources</span> and paths for the aircraft. The data presented establishes the level of interior <span class="hlt">noise</span> control that can be expected for various passive <span class="hlt">noise</span> control applications within the aircraft cabin. Subsequent testing will address specific testing to demonstrate the technology available to meet a specified level of <span class="hlt">noise</span> control by application of passive and/or active <span class="hlt">noise</span> control technology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080047421','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080047421"><span>Separating Turbofan Engine <span class="hlt">Noise</span> <span class="hlt">Sources</span> Using Auto and Cross Spectra from Four Microphones</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miles, Jeffrey Hilton</p> <p>2008-01-01</p> <p>The study of core <span class="hlt">noise</span> from turbofan engines has become more important as <span class="hlt">noise</span> from other <span class="hlt">sources</span> such as the fan and jet were reduced. A multiple-microphone and acoustic-<span class="hlt">source</span> modeling method to separate correlated and uncorrelated <span class="hlt">sources</span> is discussed. The auto- and cross spectra in the frequency range below 1000 Hz are fitted with a <span class="hlt">noise</span> propagation model based on a <span class="hlt">source</span> couplet consisting of a single incoherent monopole <span class="hlt">source</span> with a single coherent monopole <span class="hlt">source</span> or a <span class="hlt">source</span> triplet consisting of a single incoherent monopole <span class="hlt">source</span> with two coherent monopole point <span class="hlt">sources</span>. Examples are presented using data from a Pratt& Whitney PW4098 turbofan engine. The method separates the low-frequency jet <span class="hlt">noise</span> from the core <span class="hlt">noise</span> at the nozzle exit. It is shown that at low power settings, the core <span class="hlt">noise</span> is a major contributor to the <span class="hlt">noise</span>. Even at higher power settings, it can be more important than jet <span class="hlt">noise</span>. However, at low frequencies, uncorrelated broadband <span class="hlt">noise</span> and jet <span class="hlt">noise</span> become the important factors as the engine power setting is increased.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Sci...355..264P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Sci...355..264P"><span>Time-resolved x-ray absorption spectroscopy with a water window high-<span class="hlt">harmonic</span> <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pertot, Yoann; Schmidt, Cédric; Matthews, Mary; Chauvet, Adrien; Huppert, Martin; Svoboda, Vit; von Conta, Aaron; Tehlar, Andres; Baykusheva, Denitsa; Wolf, Jean-Pierre; Wörner, Hans Jakob</p> <p>2017-01-01</p> <p>Time-resolved x-ray absorption spectroscopy (TR-XAS) has so far practically been limited to large-scale facilities, to subpicosecond temporal resolution, and to the condensed phase. We report the realization of TR-XAS with a temporal resolution in the low femtosecond range by developing a tabletop high-<span class="hlt">harmonic</span> <span class="hlt">source</span> reaching up to 350 electron volts, thus partially covering the spectral region of 280 to 530 electron volts, where water is transmissive. We used this <span class="hlt">source</span> to follow previously unexamined light-induced chemical reactions in the lowest electronic states of isolated CF4+ and SF6+ molecules in the gas phase. By probing element-specific core-to-valence transitions at the carbon K-edge or the sulfur L-edges, we characterized their reaction paths and observed the effect of symmetry breaking through the splitting of absorption bands and Rydberg-valence mixing induced by the geometry changes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20400812','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20400812"><span>Analytic derivation of pinhole collimation sensitivity for a general <span class="hlt">source</span> model using spherical <span class="hlt">harmonics</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, Yu-Sheng; Oldendick, James E; Chang, Wei</p> <p>2010-05-07</p> <p>Pinhole collimators are widely used for single photon emission computed tomography (SPECT) imaging of small organs and animals. There has also been renewed interest in using pinhole arrays for clinical cardiac SPECT imaging to achieve high sensitivity and complete data sampling. Overall sensitivity of a pinhole array is critical in determining a system's performance. Conventionally, a point <span class="hlt">source</span> model has been used to evaluate the sensitivity and optimize the system design. This model is simple but far from realistic. This work addresses the use of more realistic <span class="hlt">source</span> models to assess the sensitivity performance of pinhole collimation. We have derived an analytical formula for pinhole collimation sensitivity with a general <span class="hlt">source</span> distribution model using spherical <span class="hlt">harmonics</span>. As special cases of this general model, we provided the pinhole sensitivity formulae for line, disk and sphere <span class="hlt">sources</span>. These results show that the point <span class="hlt">source</span> model is just the zeroth-order approximation of the other <span class="hlt">source</span> models. The point <span class="hlt">source</span> model overestimates or underestimates the sensitivity relative to the more realistic model. The sphere <span class="hlt">source</span> model yields the same sensitivity as a point <span class="hlt">source</span> located at the center of the sphere when attenuation is not taken into account. In the presence of attenuation, the average path length of emitted gamma rays is 3/4 of the radius of the sphere <span class="hlt">source</span>. The calculated sensitivities based on these formulae show good agreement with separate Monte Carlo simulations in simple cases. The general and special sensitivity formulae derived here can be useful for the design and optimization of SPECT systems that utilize pinhole collimators.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4592424','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4592424"><span>Fundamental-frequency discrimination using <span class="hlt">noise</span>-band-vocoded <span class="hlt">harmonic</span> complexes in older listeners with normal hearing</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Schvartz-Leyzac, Kara C.; Chatterjee, Monita</p> <p>2015-01-01</p> <p>Voice-pitch cues provide detailed information about a talker that help a listener to understand speech in complex environments. Temporal-envelope based voice-pitch coding is important for listeners with hearing impairment, especially listeners with cochlear implants, as spectral resolution is not sufficient to provide a spectrally based voice-pitch cue. The effect of aging on the ability to glean voice-pitch information using temporal envelope cues is not completely understood. The current study measured fundamental frequency (f0) discrimination limens in normal-hearing younger and older adults while listening to <span class="hlt">noise</span>-band vocoded <span class="hlt">harmonic</span> complexes with varying numbers of spectral channels. Age-related disparities in performance were apparent across all conditions, independent of spectral degradation and/or fundamental frequency. The findings have important implications for older listeners with normal hearing and hearing loss, who may be inherently limited in their ability to perceive f0 cues due to senescent decline in auditory function. PMID:26428806</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880014855','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880014855"><span><span class="hlt">Sources</span> and levels of background <span class="hlt">noise</span> in the NASA Ames 40- by 80-foot wind tunnel</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Soderman, Paul T.</p> <p>1988-01-01</p> <p>Background <span class="hlt">noise</span> levels are measured in the NASA Ames Research Center 40- by 80-Foot Wind Tunnel following installation of a sound-absorbent lining on the test-section walls. Results show that the fan-drive <span class="hlt">noise</span> dominated the empty test-section background <span class="hlt">noise</span> at airspeeds below 120 knots. Above 120 knots, the test-section broadband background <span class="hlt">noise</span> was dominated by wind-induced dipole <span class="hlt">noise</span> (except at lower <span class="hlt">harmonics</span> of fan blade-passage tones) most likely generated at the microphone or microphone support strut. Third-octave band and narrow-band spectra are presented for several fan operating conditions and test-section airspeeds. The background <span class="hlt">noise</span> levels can be reduced by making improvements to the microphone wind screen or support strut. Empirical equations are presented relating variations of fan <span class="hlt">noise</span> with fan speed or blade-pitch angle. An empirical expression for typical fan <span class="hlt">noise</span> spectra is also presented. Fan motor electric power consumption is related to the <span class="hlt">noise</span> generation. Preliminary measurements of sound absorption by the test-section lining indicate that the 152 mm thick lining will adequately absorb test-section model <span class="hlt">noise</span> at frequencies above 300 Hz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730023214','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730023214"><span>Aircraft <span class="hlt">noise</span> <span class="hlt">source</span> and computer programs - User's guide</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Crowley, K. C.; Jaeger, M. A.; Meldrum, D. F.</p> <p>1973-01-01</p> <p>The application of computer programs for predicting the <span class="hlt">noise</span>-time histories and <span class="hlt">noise</span> contours for five types of aircraft is reported. The aircraft considered are: (1) turbojet, (2) turbofan, (3) turboprop, (4) V/STOL, and (5) helicopter. Three principle considerations incorporated in the design of the <span class="hlt">noise</span> prediction program are core effectiveness, limited input, and variable output reporting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012CS%26D....5a4006B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012CS%26D....5a4006B"><span>Computational science and re-discovery: open-<span class="hlt">source</span> implementation of ellipsoidal <span class="hlt">harmonics</span> for problems in potential theory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bardhan, Jaydeep P.; Knepley, Matthew G.</p> <p>2012-01-01</p> <p>We present two open-<span class="hlt">source</span> (BSD) implementations of ellipsoidal <span class="hlt">harmonic</span> expansions for solving problems of potential theory using separation of variables. Ellipsoidal <span class="hlt">harmonics</span> are used surprisingly infrequently, considering their substantial value for problems ranging in scale from molecules to the entire solar system. In this paper, we suggest two possible reasons for the paucity relative to spherical <span class="hlt">harmonics</span>. The first is essentially historical—ellipsoidal <span class="hlt">harmonics</span> developed during the late 19th century and early 20th, when it was found that only the lowest-order <span class="hlt">harmonics</span> are expressible in closed form. Each higher-order term requires the solution of an eigenvalue problem, and tedious manual computation seems to have discouraged applications and theoretical studies. The second explanation is practical: even with modern computers and accurate eigenvalue algorithms, expansions in ellipsoidal <span class="hlt">harmonics</span> are significantly more challenging to compute than those in Cartesian or spherical coordinates. The present implementations reduce the 'barrier to entry' by providing an easy and free way for the community to begin using ellipsoidal <span class="hlt">harmonics</span> in actual research. We demonstrate our implementation using the specific and physiologically crucial problem of how charged proteins interact with their environment, and ask: what other analytical tools await re-discovery in an era of inexpensive computation?</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28287041','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28287041"><span><span class="hlt">Noise</span> disturbance in open-plan study environments: a field study on <span class="hlt">noise</span> <span class="hlt">sources</span>, student tasks and room acoustic parameters.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Braat-Eggen, P Ella; van Heijst, Anne; Hornikx, Maarten; Kohlrausch, Armin</p> <p>2017-04-03</p> <p>The aim of this study is to gain more insight in the assessment of <span class="hlt">noise</span> in open-plan study environments and to reveal correlations between <span class="hlt">noise</span> disturbance experienced by students and the <span class="hlt">noise</span> <span class="hlt">sources</span> they perceive, the tasks they perform and the acoustic parameters of the open-plan study environment they work in. Data were collected in five open-plan study environments at universities in the Netherlands. A questionnaire was used to investigate student tasks, perceived sound <span class="hlt">sources</span> and their perceived disturbance, and sound measurements were performed to determine the room acoustic parameters. This study shows that 38% of the surveyed students are disturbed by background <span class="hlt">noise</span> in an open-plan study environment. Students are mostly disturbed by speech when performing complex cognitive tasks like studying for an exam, reading and writing. Significant but weak correlations were found between the room acoustic parameters and <span class="hlt">noise</span> disturbance of students. Practitioner Summary: A field study was conducted to gain more insight in the assessment of <span class="hlt">noise</span> in open-plan study environments at universities in the Netherlands. More than one third of the students was disturbed by <span class="hlt">noise</span>. An interaction effect was found for task type, <span class="hlt">source</span> type and room acoustic parameters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9783E..10L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9783E..10L"><span><span class="hlt">Noise</span> characteristics of CT perfusion imaging: how does <span class="hlt">noise</span> propagate from <span class="hlt">source</span> images to final perfusion maps?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Ke; Chen, Guang-Hong</p> <p>2016-03-01</p> <p>Cerebral CT perfusion (CTP) imaging is playing an important role in the diagnosis and treatment of acute ischemic strokes. Meanwhile, the reliability of CTP-based ischemic lesion detection has been challenged due to the noisy appearance and low signal-to-<span class="hlt">noise</span> ratio of CTP maps. To reduce <span class="hlt">noise</span> and improve image quality, a rigorous study on the <span class="hlt">noise</span> transfer properties of CTP systems is highly desirable to provide the needed scientific guidance. This paper concerns how <span class="hlt">noise</span> in the CTP <span class="hlt">source</span> images propagates to the final CTP maps. Both theoretical deviations and subsequent validation experiments demonstrated that, the <span class="hlt">noise</span> level of background frames plays a dominant role in the <span class="hlt">noise</span> of the cerebral blood volume (CBV) maps. This is in direct contradiction with the general belief that <span class="hlt">noise</span> of non-background image frames is of greater importance in CTP imaging. The study found that when radiation doses delivered to the background frames and to all non-background frames are equal, lowest <span class="hlt">noise</span> variance is achieved in the final CBV maps. This novel equality condition provides a practical means to optimize radiation dose delivery in CTP data acquisition: radiation exposures should be modulated between background frames and non-background frames so that the above equality condition is satisïnAed. For several typical CTP acquisition protocols, numerical simulations and in vivo canine experiment demonstrated that <span class="hlt">noise</span> of CBV can be effectively reduced using the proposed exposure modulation method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009SPIE.7183E..15C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009SPIE.7183E..15C"><span>Coupling CARS with multiphoton fluorescence and high <span class="hlt">harmonic</span> generation imaging modalities using a femtosecond laser <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Hongtao; Slipchenko, Mikhail N.; Zhu, Jiabin; Buhman, Kimberly K.; Cheng, Ji-Xin</p> <p>2009-02-01</p> <p>Multimodal nonlinear optical imaging has opened new opportunities and becomes a powerful tool for imaging complex tissue samples with inherent 3D spatial resolution.. We present a robust and easy-to-operate approach to add the coherent anti-stokes Raman scattering (CARS) imaging modality to a widely used multiphoton microscope. The laser <span class="hlt">source</span> composed of a Mai Tai femtosecond laser and an optical parametric oscillator (OPO) offers one-beam, two-beam and three-beam modalities. The Mai Tai output at 790 nm is split into two beams, with 80% of the power being used to pump the OPO. The idler output at 2036 nm from OPO is doubled using a periodically poled lithium niobate (PPLN) crystal. This frequency-doubled idler beam at 1018 nm is sent through a delay line and collinearly combined with the other Mai Tai beam for CARS imaging on a laser-scanning microscope. This Mai Tai beam is also used for multiphoton fluorescence and second <span class="hlt">harmonic</span> generation (SHG) imaging. The signal output at 1290 nm from OPO is used for SHG and third-<span class="hlt">harmonic</span> generation (THG) imaging. External detectors are installed for both forward and backward detection, whereas two internal lamda-scan detectors are employed for microspectroscopy analysis. This new system allows vibrationally resonant CARS imaging of lipid bodies, SHG imaging of collagen fibers, and multiphoton fluorescence analysis in fresh tissues. As a preliminary application, the effect of diacylglycerol acyltransferase 1 (DGAT1) deficiency on liver lipid metabolism in mice was investigated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20136203','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20136203"><span><span class="hlt">Noise</span>-induced annoyance from transportation <span class="hlt">noise</span>: short-term responses to a single <span class="hlt">noise</span> <span class="hlt">source</span> in a laboratory.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kim, Jaehwan; Lim, Changwoo; Hong, Jiyoung; Lee, Soogab</p> <p>2010-02-01</p> <p>An experimental study was performed to compare the annoyances from civil-aircraft <span class="hlt">noise</span>, military-aircraft <span class="hlt">noise</span>, railway <span class="hlt">noise</span>, and road-traffic <span class="hlt">noise</span>. Two-way within-subjects designs were applied in this research. Fifty-two subjects, who were naive listeners, were given various stimuli with varying levels through a headphone in an anechoic chamber. Regardless of the frequency weighting network, even under the same average energy level, civil-aircraft <span class="hlt">noise</span> was the most annoying, followed by military-aircraft <span class="hlt">noise</span>, railway <span class="hlt">noise</span>, and road-traffic <span class="hlt">noise</span>. In particular, penalties in the time-averaged, A-weighted sound level (TAL) of about 8, 5, and 5 dB, respectively, were found in the civil-aircraft, military-aircraft, and railway <span class="hlt">noises</span>. The reason could be clarified through the high-frequency component and the variability in the level. When people were exposed to sounds with the same maximum A-weighted level, a railway bonus of about 3 dB was found. However, transportation <span class="hlt">noise</span> has been evaluated by the time-averaged A-weighted level in most countries. Therefore, in the present situation, the railway bonus is not acceptable for railway vehicles with diesel-electric engines.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/3243682','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/3243682"><span>Current <span class="hlt">source</span> density estimation and interpolation based on the spherical <span class="hlt">harmonic</span> Fourier expansion.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pascual-Marqui, R D; Gonzalez-Andino, S L; Valdes-Sosa, P A; Biscay-Lirio, R</p> <p>1988-12-01</p> <p>A method for the spatial analysis of EEG and EP data, based on the spherical <span class="hlt">harmonic</span> Fourier expansion (SHE) of scalp potential measurements, is described. This model provides efficient and accurate formulas for: (1) the computation of the surface Laplacian and (2) the interpolation of electrical potentials, current <span class="hlt">source</span> densities, test statistics and other derived variables. Physiologically based simulation experiments show that the SHE method gives better estimates of the surface Laplacian than the commonly used finite difference method. Cross-validation studies for the objective comparison of different interpolation methods demonstrate the superiority of the SHE over the commonly used methods based on the weighted (inverse distance) average of the nearest three and four neighbor values.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740003484','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740003484"><span>Radially leaned outlet guide vanes for fan <span class="hlt">source</span> <span class="hlt">noise</span> reduction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kazin, S. B.</p> <p>1973-01-01</p> <p>Two quiet engine program half scale fans one with a subsonic and the other with a supersonic fan tip speed at takeoff were run with 30 degree leaned and radial outlet guide vanes. Acoustic data at takeoff fan speed on the subsonic tip speed fan showed decreases in 200-foot sideline <span class="hlt">noise</span> of from 1 to 2 PNdb. The supersonic tip speed fan a takeoff fan speed, however, showed <span class="hlt">noise</span> increases of up 3 PNdb and a decrease in fan efficiency. At approach fan speed, the subsonic tip speed fan showed a <span class="hlt">noise</span> decrease of 2.3 PNdb at the 200-foot sideline maximum angle and an increase in efficiency. The supersonic tip speed fan showed <span class="hlt">noise</span> increase of 3.5 PNdb and no change in efficiency. The decrease in fan efficiency and the nature of the <span class="hlt">noise</span> increase largely high frequency broadband <span class="hlt">noise</span> lead to the speculation that an aerodynamic problem occurred.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4490359','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4490359"><span>Bright high-repetition-rate <span class="hlt">source</span> of narrowband extreme-ultraviolet <span class="hlt">harmonics</span> beyond 22 eV</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wang, He; Xu, Yiming; Ulonska, Stefan; Robinson, Joseph S.; Ranitovic, Predrag; Kaindl, Robert A.</p> <p>2015-01-01</p> <p>Novel table-top <span class="hlt">sources</span> of extreme-ultraviolet light based on high-<span class="hlt">harmonic</span> generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-<span class="hlt">harmonic</span> generation to high repetition rates portends great experimental benefits, yet efficient extreme-ultraviolet conversion of correspondingly weak driving pulses is challenging. Here, we demonstrate a highly-efficient <span class="hlt">source</span> of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-<span class="hlt">harmonic</span> focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ≈3 × 1013 s−1 is generated at 22.3 eV, with 5 × 10−5 conversion efficiency that surpasses similar <span class="hlt">harmonics</span> directly driven by the fundamental by two orders-of-magnitude. The enhancement arises from both wavelength scaling of the atomic dipole and improved spatio-temporal phase matching, confirmed by simulations. Spectral isolation of a single 72-meV-wide <span class="hlt">harmonic</span> renders this bright, 50-kHz extreme-ultraviolet <span class="hlt">source</span> a powerful tool for ultrafast photoemission, nanoscale imaging and other applications. PMID:26067922</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1241159','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1241159"><span>Bright high-repetition-rate <span class="hlt">source</span> of narrowband extreme-ultraviolet <span class="hlt">harmonics</span> beyond 22 eV</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wang, He; Xu, Yiming; Ulonska, Stefan; Robinson, Joseph S.; Ranitovic, Predrag; Kaindl, Robert A.</p> <p>2015-06-11</p> <p>Novel table-top <span class="hlt">sources</span> of extreme-ultraviolet light based on high-<span class="hlt">harmonic</span> generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-<span class="hlt">harmonic</span> generation to high repetition rates portends great experimental benefits, yet efficient extreme-ultraviolet conversion of correspondingly weak driving pulses is challenging. In this article, we demonstrate a highly-efficient <span class="hlt">source</span> of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-<span class="hlt">harmonic</span> focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ≈3 × 10<sup>13</sup> s<sup>-1</sup> is generated at 22.3 eV, with 5 × 10<sup>-5</sup> conversion efficiency that surpasses similar <span class="hlt">harmonics</span> directly driven by the fundamental by two orders-of-magnitude. The enhancement arises from both wavelength scaling of the atomic dipole and improved spatio-temporal phase matching, confirmed by simulations. Finally, spectral isolation of a single 72-meV-wide <span class="hlt">harmonic</span> renders this bright, 50-kHz extreme-ultraviolet <span class="hlt">source</span> a powerful tool for ultrafast photoemission, nanoscale imaging and other applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26067922','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26067922"><span>Bright high-repetition-rate <span class="hlt">source</span> of narrowband extreme-ultraviolet <span class="hlt">harmonics</span> beyond 22 eV.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, He; Xu, Yiming; Ulonska, Stefan; Robinson, Joseph S; Ranitovic, Predrag; Kaindl, Robert A</p> <p>2015-06-11</p> <p>Novel table-top <span class="hlt">sources</span> of extreme-ultraviolet light based on high-<span class="hlt">harmonic</span> generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-<span class="hlt">harmonic</span> generation to high repetition rates portends great experimental benefits, yet efficient extreme-ultraviolet conversion of correspondingly weak driving pulses is challenging. Here, we demonstrate a highly-efficient <span class="hlt">source</span> of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-<span class="hlt">harmonic</span> focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ≈3 × 10(13) s(-1) is generated at 22.3 eV, with 5 × 10(-5) conversion efficiency that surpasses similar <span class="hlt">harmonics</span> directly driven by the fundamental by two orders-of-magnitude. The enhancement arises from both wavelength scaling of the atomic dipole and improved spatio-temporal phase matching, confirmed by simulations. Spectral isolation of a single 72-meV-wide <span class="hlt">harmonic</span> renders this bright, 50-kHz extreme-ultraviolet <span class="hlt">source</span> a powerful tool for ultrafast photoemission, nanoscale imaging and other applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S34B..01F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S34B..01F"><span><span class="hlt">Source</span>-structure trade-offs in ambient <span class="hlt">noise</span> correlations: Theory and numerical examples</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fichtner, A.; Sager, K.; Ermert, L. A.</p> <p>2015-12-01</p> <p>We analyse the physics and geometry of trade-offs between Earth structure and <span class="hlt">noise</span> <span class="hlt">sources</span> in inter-station <span class="hlt">noise</span> correlations. Our approach is based on the computation of off-diagonal Hessian elements that describe the extent to which variations in <span class="hlt">noise</span> <span class="hlt">sources</span> can compensate for variations in Earth structure without changing the misfit beyond the measurement uncertainty. Despite the fact that all ambient <span class="hlt">noise</span> inverse problems are special in terms of their receiver configuration and data, some general statements concerning <span class="hlt">source</span>-structure trade-offs can be made: (i) While <span class="hlt">source</span>-structure trade-offs may be reduced to some extent by clever measurement design, there are inherent trade-offs that can generally not be avoided. These inherent trade-offs may lead to a mispositioning of structural heterogeneities when the <span class="hlt">noise</span> <span class="hlt">source</span> distribution is unknown. (ii) When attenuation is weak, <span class="hlt">source</span>-structure trade-offs in ambient <span class="hlt">noise</span> correlations are a global phenomenon, meaning that there is no <span class="hlt">noise</span> <span class="hlt">source</span> perturbation that does not trade-off with some Earth structure, and vice versa. (iii) The most significant <span class="hlt">source</span>-structure trade-offs occur within two elliptically shaped regions connecting a potential <span class="hlt">noise</span> <span class="hlt">source</span> perturbation to each one of the receivers. (iv) Far from these elliptical regions, only small-scale structure can trade off against changes in the <span class="hlt">noise</span> <span class="hlt">source</span>. (v) While <span class="hlt">source</span>-structure trade-offs mostly decay with increasing attenuation, they are nearly unaffected by attenuation when the <span class="hlt">noise</span> <span class="hlt">source</span> perturbation is located near the receiver-receiver line. We complement these theoretical considerations by numerical experiments where we model ambient <span class="hlt">noise</span> correlations for arbitrary <span class="hlt">source</span> geometries. The experiments illustrate how and to which extent unknown <span class="hlt">noise</span> <span class="hlt">sources</span> may map into spurious Earth structure. This work is intended to contribute to the development of joint <span class="hlt">source</span>-structure inversions of ambient <span class="hlt">noise</span> correlations, and in particular</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016IJEEP..17..671K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016IJEEP..17..671K"><span><span class="hlt">Harmonic</span> Optimization in Voltage <span class="hlt">Source</span> Inverter for PV Application using Heuristic Algorithms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kandil, Shaimaa A.; Ali, A. A.; El Samahy, Adel; Wasfi, Sherif M.; Malik, O. P.</p> <p>2016-12-01</p> <p>Selective <span class="hlt">Harmonic</span> Elimination (SHE) technique is the fundamental switching frequency scheme that is used to eliminate specific order <span class="hlt">harmonics</span>. Its application to minimize low order <span class="hlt">harmonics</span> in a three level inverter is proposed in this paper. The modulation strategy used here is SHEPWM and the nonlinear equations, that characterize the low order <span class="hlt">harmonics</span>, are solved using Harmony Search Algorithm (HSA) to obtain the optimal switching angles that minimize the required <span class="hlt">harmonics</span> and maintain the fundamental at the desired value. Total <span class="hlt">Harmonic</span> Distortion (THD) of the output voltage is minimized maintaining selected <span class="hlt">harmonics</span> within allowable limits. A comparison has been drawn between HSA, Genetic Algorithm (GA) and Newton Raphson (NR) technique using MATLAB software to determine the effectiveness of getting optimized switching angles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5031880','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5031880"><span>/sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; King, W.T.; Blakeman, E.D.</p> <p>1985-01-01</p> <p>The /sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method has been tested in a wide variety of experiments that have indicated the broad range of applicability of the method. The neutron multiplication factor k/sub eff/ has been satisfactorily detemined for a variety of materials including uranium metal, light water reactor fuel pins, fissile solutions, fuel plates in water, and interacting cylinders. For a uranyl nitrate solution tank which is typical of a fuel processing or reprocessing plant, the k/sub eff/ values were satisfactorily determined for values between 0.92 and 0.5 using a simple point kinetics interpretation of the experimental data. The short measurement times, in several cases as low as 1 min, have shown that the development of this method can lead to a practical subcriticality monitor for many in-plant applications. The further development of the method will require experiments oriented toward particular applications including dynamic experiments and the development of theoretical methods to predict the experimental observables.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013SPIE.8681E..0HZ','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013SPIE.8681E..0HZ"><span>Coherent diffractive imaging microscope with a tabletop high <span class="hlt">harmonic</span> EUV <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Bosheng; Seaberg, Matthew D.; Adams, Daniel E.; Gardner, Dennis F.; Murnane, Margaret M.; Kapteyn, Henry C.</p> <p>2013-04-01</p> <p>Coherent diffractive imaging (CDI) using EUV/X-rays has proven to be a powerful microscopy method for imaging nanoscale objects. In traditional CDI, the oversampling condition limits its applicability to small, isolated objects. A new technique called keyhole CDI was demonstrated on a synchrotron X-ray <span class="hlt">source</span> to circumvent this limitation. Here we demonstrate the first keyhole CDI result with a tabletop extreme ultraviolet (EUV) <span class="hlt">source</span>. The EUV <span class="hlt">source</span> is based on high <span class="hlt">harmonic</span> generation (HHG), and our modified form of keyhole CDI uses a highly reflective curved EUV mirror instead of a lossy Fresnel zone plate, offering a ~10x increase in photon throughput of the imaging system, and a more uniform illumination on the sample. In addition, we have demonstrated a record 22 nm resolution using our tabletop CDI setup, and also the successful extension to reflection mode for a periodic sample. Combining these results with keyhole CDI will open the path to the realization of a compact EUV microscope for imaging general non-isolated and non-periodic samples, in both transmission and reflection mode.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MarGR..37..257H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MarGR..37..257H"><span>The suppression of coherent <span class="hlt">noise</span> from another airgun <span class="hlt">source</span> in marine multi-channel seismic data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsu, Ho-Han; Liu, Char-Shine; Chang, Jih-Hsin; Tsai, You-Tsung; Chiu, Shye-Donq</p> <p>2016-12-01</p> <p>During seismic investigations, multiple and unexpected <span class="hlt">sources</span> may cause serious interference on seismic records, and coherent <span class="hlt">noise</span> generated by another unwanted active <span class="hlt">source</span> could result in extremely poor data quality. Because airgun arrays have been widely used as the sound <span class="hlt">source</span> in marine seismic surveys, the <span class="hlt">noise</span> generated by another airgun array usually has similar characteristics to the primary signals in both frequency bands and wave forms, so the suppression of this type of coherent <span class="hlt">noise</span> is very difficult. In practice, seismic crews try to avoid conducting multiple surveys simultaneously in a same area, so the <span class="hlt">source</span> interference problem normally does not occur, and suppression of coherent <span class="hlt">noise</span> from another active <span class="hlt">source</span> has rarely been discussed and proposed before. This paper presents a dataset in which part of the records are contaminated by shot <span class="hlt">noise</span> from another seismic vessel, and proposes a hybrid approach to suppress the coherent <span class="hlt">noise</span> from that unwanted seismic <span class="hlt">source</span>. <span class="hlt">Noise</span> subtraction and primary signal preservation within different data properties are considered to begin the <span class="hlt">noise</span> suppression. Based on different <span class="hlt">noise</span> characteristics from various <span class="hlt">source</span> directions and wave propagation paths, coherence <span class="hlt">noise</span> can be separated from primary signals in frequency-wave number (F-K), frequency-time (F-T) and intercept time-slowness (tau-p) domains, respectively. This hybrid coherent <span class="hlt">noise</span> suppression approach involves applying three different filters, F-K, F-T and tau-p, to the contaminated dataset. Our results show that most of the coherent <span class="hlt">noise</span> generated by another seismic <span class="hlt">source</span> could be suppressed, and seismic images could be substantially improved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150010120','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150010120"><span>Jet-Surface Interaction Test: Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary</p> <p>2012-01-01</p> <p>Subsonic jets are relatively simple. The peak <span class="hlt">noise</span> <span class="hlt">source</span> location gradually moves upstream toward the nozzle as frequency increases. 2) Supersonic jets are more complicated. The peak <span class="hlt">noise</span> <span class="hlt">source</span> location moves downstream as frequency increases through a BBSN hump. 3) In both subsonic and supersonic jets the peak <span class="hlt">noise</span> <span class="hlt">source</span> location corresponding to a given frequency of <span class="hlt">noise</span> moves downstream as jet Mach number increases. 4) The <span class="hlt">noise</span> generated at a given frequency in a BBSN hump is generated by a small number of shocks, not from all the shocks at the same time. 5) Single microphone spectrum levels decrease when the <span class="hlt">noise</span> <span class="hlt">source</span> locations measured with the phased array are blocked by a shielding surface. This consistency validates the phased array data and the stationary monopole <span class="hlt">source</span> model used to process it. 6) Reflecting surface data illustrate that the law of reflection must be satisfied for <span class="hlt">noise</span> to reflect off a surface toward an observer. Depending on the relative locations of the jet, the surface and the observer only some of the jet <span class="hlt">noise</span> <span class="hlt">sources</span> may satisfy this requirement. 7) The low frequency <span class="hlt">noise</span> created when a jet flow impinges on a surface comes primarily from the trailing edge regardless of the axial extent impacted by the flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110015387','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110015387"><span>Embedded Acoustic Sensor Array for Engine Fan <span class="hlt">Noise</span> <span class="hlt">Source</span> Diagnostic Test: Feasibility of <span class="hlt">Noise</span> Telemetry via Wireless Smart Sensors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zaman, Afroz; Bauch, Matthew; Raible, Daniel</p> <p>2011-01-01</p> <p>Aircraft engines have evolved into a highly complex system to meet ever-increasing demands. The evolution of engine technologies has primarily been driven by fuel efficiency, reliability, as well as engine <span class="hlt">noise</span> concerns. One of the <span class="hlt">sources</span> of engine <span class="hlt">noise</span> is pressure fluctuations that are induced on the stator vanes. These local pressure fluctuations, once produced, propagate and coalesce with the pressure waves originating elsewhere on the stator to form a spinning pressure pattern. Depending on the duct geometry, air flow, and frequency of fluctuations, these spinning pressure patterns are self-sustaining and result in <span class="hlt">noise</span> which eventually radiate to the far-field from engine. To investigate the nature of vane pressure fluctuations and the resulting engine <span class="hlt">noise</span>, unsteady pressure signatures from an array of embedded acoustic sensors are recorded as a part of vane <span class="hlt">noise</span> <span class="hlt">source</span> diagnostics. Output time signatures from these sensors are routed to a control and data processing station adding complexity to the system and cable loss to the measured signal. "Smart" wireless sensors have data processing capability at the sensor locations which further increases the potential of wireless sensors. Smart sensors can process measured data locally and transmit only the important information through wireless communication. The aim of this wireless <span class="hlt">noise</span> telemetry task was to demonstrate a single acoustic sensor wireless link for unsteady pressure measurement, and thus, establish the feasibility of distributed smart sensors scheme for aircraft engine vane surface unsteady pressure data transmission and characterization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740006271','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740006271"><span>Sonic inlet <span class="hlt">noise</span> attenuation and performance with a J-85 turbojet engine as a <span class="hlt">noise</span> <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Groth, H. W.</p> <p>1974-01-01</p> <p>A static test program was conducted to investigate aerodynamic and acoustic performance of a sonic inlet used as a <span class="hlt">noise</span> suppressor. A translating centerbody type inlet with radial vanes was tested ahead of a J85-GE-13 turbojet engine. The inlet when fully choked, maintained high recovery with low distortions while dramatically reducing <span class="hlt">noise</span> emanating from the compressor. Recoveries of 98.1% at simulated takeoff and 95% at approach were attained with associated sound attenuation of 40 db and 38 db respectively. Inlet lip shape was found to have significant effects on <span class="hlt">noise</span> attenuation at these static conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhRvL.115g7002W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhRvL.115g7002W"><span>Candidate <span class="hlt">Source</span> of Flux <span class="hlt">Noise</span> in SQUIDs: Adsorbed Oxygen Molecules</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Hui; Shi, Chuntai; Hu, Jun; Han, Sungho; Yu, Clare C.; Wu, R. Q.</p> <p>2015-08-01</p> <p>A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux <span class="hlt">noise</span>. We propose that the heretofore mysterious spins producing flux <span class="hlt">noise</span> could be O2 molecules adsorbed on the surface. Using density functional theory calculations, we find that an O2 molecule adsorbed on an α-alumina surface has a magnetic moment of ˜1.8 μB . The spin is oriented perpendicular to the axis of the O-O bond, the barrier to spin rotations is about 10 mK. Monte Carlo simulations of ferromagnetically coupled, anisotropic X Y spins on a square lattice find 1 /f magnetization <span class="hlt">noise</span>, consistent with flux <span class="hlt">noise</span> in Al SQUIDs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150006715','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150006715"><span>Traveling-Wave Tube Amplifier Second <span class="hlt">Harmonic</span> as Millimeter-Wave Beacon <span class="hlt">Source</span> for Atmospheric Propagation Studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Simons, Rainee N.; Wintucky, Edwin G.</p> <p>2014-01-01</p> <p>This paper presents the design and test results of a CW millimeter-wave satellite beacon <span class="hlt">source</span>, based on the second <span class="hlt">harmonic</span> from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon <span class="hlt">source</span> is for investigating the atmospheric effects on Q-band (37-42 GHz) and V/W-band (71- 76 GHz) satellite-to-ground signals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140010741','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010741"><span>Traveling-Wave Tube Amplifier Second <span class="hlt">Harmonic</span> as Millimeter-Wave Beacon <span class="hlt">Source</span> for Atmospheric Propagation Studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Simons, Rainee N.; Wintucky, Edwin G.</p> <p>2014-01-01</p> <p>This paper presents the design and test results of a CW millimeter-wave satellite beacon <span class="hlt">source</span>, based on the second <span class="hlt">harmonic</span> from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon <span class="hlt">source</span> is for investigating the atmospheric effects on Q-band (37 to 42 GHz) and V/W-band (71 to 76 GHz) satellite-to-ground signals.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150000875','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150000875"><span>Traveling-Wave Tube Amplifier Second <span class="hlt">Harmonic</span> as Millimeter-Wave Beacon <span class="hlt">Source</span> for Atmospheric Propagation Studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Simons, Rainee N.; Wintucky, Edwin G.</p> <p>2014-01-01</p> <p>The design and test results of a novel waveguide multimode directional coupler for a CW millimeter-wave satellite beacon <span class="hlt">source</span> are presented. The coupler separates the second <span class="hlt">harmonic</span> power from the fundamental output power of a traveling-wave tube amplifier. A potential application of the beacon <span class="hlt">source</span> is for investigating the atmospheric effects on Q-band (37 to 42 GHz) and VW-band (71 to 76 GHz) satellite-to-ground signals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150010121','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150010121"><span>Jet-Surface Interaction Test: Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary G.</p> <p>2012-01-01</p> <p>An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the <span class="hlt">noise</span> radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet <span class="hlt">noise</span> was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array <span class="hlt">noise</span> <span class="hlt">source</span> localization measurements were obtained. This paper discusses phased array results, while a companion paper discusses far-field results. The phased array data show that the axial distribution of <span class="hlt">noise</span> <span class="hlt">sources</span> in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of <span class="hlt">noise</span> reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the <span class="hlt">noise</span> <span class="hlt">sources</span> associated with a given frequency of <span class="hlt">noise</span> tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The <span class="hlt">noise</span> <span class="hlt">source</span> localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces <span class="hlt">noise</span> at a given frequency within a broadband shock <span class="hlt">noise</span> hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet <span class="hlt">noise</span> to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet <span class="hlt">noise</span> <span class="hlt">sources</span> may satisfy this requirement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.S43B2527V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.S43B2527V"><span>Investigation of Apparent Seismic Velocity Changes Caused by Microseism <span class="hlt">Noise</span> <span class="hlt">Source</span> Variability</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Volk, M. F.; Bean, C. J.; Lokmer, I.; Craig, D.</p> <p>2013-12-01</p> <p>Currently there is strong interest in monitoring temporal changes in seismic wave velocity in various geological settings. These settings can range from volcano monitoring to reservoir monitoring amongst others. Green's functions are often used to observe temporal variations in seismic wave velocity as their arrival times contain information about velocity changes. Green's functions are typically retrieved by cross correlating ambient <span class="hlt">noise</span> recorded at given pair of stations. Theoretically the recorded wavefields used for the cross correlation should be diffuse. For applications in seismic imagery, the background <span class="hlt">noise</span> <span class="hlt">sources</span> should be uniformly distributed in space or the wavefield must be highly scattered but neither condition typically occur in nature. However temporal and spatial variations of non-uniformly distributed <span class="hlt">noise</span> <span class="hlt">sources</span> may lead to apparent changes in Green's functions which are related to the <span class="hlt">source</span> not the path. This could lead to a misinterpretation of temporal changes in wave velocity. We track the spatial and temporal distribution of the <span class="hlt">noise</span> <span class="hlt">sources</span> using seismic arrays, located in Ireland. It is a good location in which to study these effects, as it is tectonically very quiet and is relatively close to large microseism <span class="hlt">noise</span> <span class="hlt">sources</span> in the North Atlantic, allowing a quantification of <span class="hlt">noise</span> <span class="hlt">source</span> heterogeneity. The temporal variations in seismic wave velocity are calculated and compared to the temporal and spatial distribution of the microseism <span class="hlt">noise</span> <span class="hlt">sources</span>. The initial results show how the direct arrival waveform and the arrival time of the Green's functions correlate with spatial and temporal variability of the microseism <span class="hlt">noise</span> <span class="hlt">sources</span>. Under these conditions we also explore the minimum <span class="hlt">noise</span> trace length required for the Green's functions to converge. We quantify the degree to which apparent velocity variations using direct arrivals are caused by changes in the <span class="hlt">sources</span> and assess the use of coda wave arrivals in mitigating <span class="hlt">source</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19890053678&hterms=acoustic+reduction+noise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dacoustic%2Breduction%2Bnoise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19890053678&hterms=acoustic+reduction+noise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dacoustic%2Breduction%2Bnoise"><span>NASA/AHS rotorcraft <span class="hlt">noise</span> reduction program - NASA Langley Acoustics Division contributions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Martin, Ruth M.</p> <p>1989-01-01</p> <p>An account is given of the contributions made by NASA-Langley's rotorcraft <span class="hlt">noise</span> research programs over the last five years. Attention has been given to the broadband and blade-vortex interaction <span class="hlt">noise</span> <span class="hlt">sources</span>; both analytical and empirical <span class="hlt">noise</span>-prediction codes have been developed and validated for several rotor <span class="hlt">noise</span> <span class="hlt">sources</span>, and the 'Rotonet' comprehensive system-<span class="hlt">noise</span> prediction capability has been instituted. Among the technologies explored for helicopter <span class="hlt">noise</span> reduction have been higher <span class="hlt">harmonic</span> control and active vibration-suppression.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Nanos...8..835S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Nanos...8..835S"><span>Nanoscale direct mapping of localized and induced <span class="hlt">noise</span> <span class="hlt">sources</span> on conducting polymer films</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shekhar, Shashank; Cho, Duckhyung; Lee, Hyungwoo; Cho, Dong-Guk; Hong, Seunghun</p> <p>2015-12-01</p> <p>The localized <span class="hlt">noise-sources</span> and those induced by external-stimuli were directly mapped by using a conducting-AFM integrated with a custom-designed <span class="hlt">noise</span> measurement set-up. In this method, current and <span class="hlt">noise</span> images of a poly(9,9-dioctylfluorene)-polymer-film on a conducting-substrate were recorded simultaneously, enabling the mapping of the resistivity and <span class="hlt">noise</span> <span class="hlt">source</span> density (NT). The polymer-films exhibited separate regions with high or low resistivities, which were attributed to the ordered or disordered phases, respectively. A larger number of <span class="hlt">noise-sources</span> were observed in the disordered-phase-regions than in the ordered-phase regions, due to structural disordering. Increased bias-voltages on the disordered-phase-regions resulted in increased NT, which is explained by the structural deformation at high bias-voltages. On photo-illumination, the ordered-phase-regions exhibited a rather large increase in the conductivity and NT. Presumably, the illumination released carriers from deep-traps which should work as additional <span class="hlt">noise-sources</span>. These results show that our methods provide valuable insights into <span class="hlt">noise-sources</span> and, thus, can be powerful tools for basic research and practical applications of conducting polymer films.The localized <span class="hlt">noise-sources</span> and those induced by external-stimuli were directly mapped by using a conducting-AFM integrated with a custom-designed <span class="hlt">noise</span> measurement set-up. In this method, current and <span class="hlt">noise</span> images of a poly(9,9-dioctylfluorene)-polymer-film on a conducting-substrate were recorded simultaneously, enabling the mapping of the resistivity and <span class="hlt">noise</span> <span class="hlt">source</span> density (NT). The polymer-films exhibited separate regions with high or low resistivities, which were attributed to the ordered or disordered phases, respectively. A larger number of <span class="hlt">noise-sources</span> were observed in the disordered-phase-regions than in the ordered-phase regions, due to structural disordering. Increased bias-voltages on the disordered-phase-regions resulted in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1046973','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1046973"><span>Multi-MW 22.8 GHz <span class="hlt">Harmonic</span> Multiplier - RF Power <span class="hlt">Source</span> for High-Gradient Accelerator R&D</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jay L. Hirshfield</p> <p>2012-07-26</p> <p>Electrodynamic and particle simulation studies have been carried out to optimize design of a two-cavity <span class="hlt">harmonic</span> frequency multiplier, in which a linear electron beam is energized by rotating fields near cyclotron resonance in a TE111 cavity in a uniform magnetic field, and in which the beam then radiates coherently at the nth <span class="hlt">harmonic</span> into a TEn11 output cavity. Examples are worked out in detail for 7th and 2nd <span class="hlt">harmonic</span> converters, showing RF-to-RF conversion efficiencies of 45% and 88%, respectively at 19.992 GHz (K-band) and 5.712 GHz (C-band), for a drive frequency of 2.856 GHz. Details are shown of RF infrastructure (S-band klystron, modulator) and <span class="hlt">harmonic</span> converter components (drive cavity, output cavities, electron beam <span class="hlt">source</span> and modulator, beam collector) for the two <span class="hlt">harmonic</span> converters to be tested. Details are also given for the two-frequency (S- and C-band) coherent multi-MW test stand for RF breakdown and RF gun studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880003323','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880003323"><span>The 8.4-GHz low-<span class="hlt">noise</span> maser pump <span class="hlt">source</span> assembly</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cardenas, R.</p> <p>1987-01-01</p> <p>Improved pump <span class="hlt">source</span> assemblies and new 8.4-GHz low <span class="hlt">noise</span> traveling-wave masers (TWMs) were installed at the same time at Deep Space Stations 14 and 43 as part of the Mark IVA DSCC Antenna Microwave Subsystems upgrade. The pump <span class="hlt">source</span> assemblies are part of the new 8.4-GHz TWMs, which are identified as Block IIA Low-<span class="hlt">Noise</span> TWMs. Improved reliability of the pump <span class="hlt">source</span> assemblies was required to meet stress analysis criteria.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5644444','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5644444"><span>(Investigation of subcooled hydrothermal boiling in ground water flow channels as a <span class="hlt">source</span> of <span class="hlt">harmonic</span> tremors)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Not Available</p> <p>1989-01-01</p> <p>As a first step toward assessing the ability of hydrothermal boiling to explain geothermal ground <span class="hlt">noise</span> and volcanic tremor observations, we are investigating the acoustic power spectrum of boiling (the <span class="hlt">source</span>'' spectrum in the above model). We simulate boiling in the lab by injecting high pressure steam from a boiler into a pressure vessel filled with water. The water pressure fluctuations that result from the repeated formation and collapse of steam bubbles at the steam inlet vents are recorded by a hydrophone whose output is digitized at 2 {times} 10{sup 4} samples/second by a computer. The range of pressure and temperature conditions attainable within the pressure vessel is limited to <3.5 bars, <139{degree}C, due to the finite strength of observation windows affixed to the pressure vessel. Therefore, dimensional analysis will be used to correlate the experimental results with the pertinent experimental variables. Besides the overall shape of the boiling power spectrum, we are investigating the absolute spectral levels in frequency bands typical of geothermal ground <span class="hlt">noise</span> and volcanic tremor (0.5 Hz-10 Hz), and the ratio of acoustic power liberated to total available power. The values of these parameters are critical to hydrothermal boiling's ability to generate ground motion amplitudes in accordance with observation. If it can be shown that the range of observed ground <span class="hlt">noise</span>/tremor amplitudes can be accounted for by hydrothermal boiling at reasonable heat transfer rates, this knowledge would be invaluable to designers of seismic monitoring experiments who are interested in geothermal resource exploration/evaluation and volcanic eruption prediction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992cacn.agarV....B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992cacn.agarV....B"><span>Reduction of propeller <span class="hlt">noise</span> by active <span class="hlt">noise</span> control</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bschorr, O.; Kubanke, D.</p> <p>1992-04-01</p> <p>Active <span class="hlt">noise</span> control, a method of cancelling <span class="hlt">noise</span> by means of interference with a secondary anti-<span class="hlt">noise</span> <span class="hlt">source</span>, is now in full development. The first commercial application of this technique is in the case of active electronically controlled head sets. The next step will be the active <span class="hlt">noise</span> cancellation in air ducts and in passenger cabins. The aim of this paper is to assess the possibilities of the anti-<span class="hlt">noise</span> technique for reducing propeller <span class="hlt">noise</span>. First, by a mathematical simulation the theoretical <span class="hlt">noise</span> reduction on the ground was calculated and found to be promising for further investigations. In the case of the periodic engine and propeller <span class="hlt">noise</span>, for example, with only a single anti-<span class="hlt">noise</span> <span class="hlt">source</span>, the <span class="hlt">noise</span> foot prints of the lower propeller <span class="hlt">harmonics</span> can be reduced by up to 10 dB. In laboratory tests the theoretical values will be confirmed experimentally. For cancellation of the periodic <span class="hlt">noise</span> one can use synchronous anti-<span class="hlt">noise</span> generators. Compared with the engine and propeller <span class="hlt">noise</span> the reduction of jet <span class="hlt">noise</span> by the anti-<span class="hlt">noise</span> technique is much more difficult. Therefore a sensor and controlling unit are necessary because of the stochastic nature of jet <span class="hlt">noise</span>. Since aircraft <span class="hlt">noise</span> is a severe problem, all methods are to be considered.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992cacn.agar.....P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992cacn.agar.....P"><span>A brief review of the <span class="hlt">source</span> <span class="hlt">noise</span> technology applicable to fixed-wing military aircraft</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pinker, R. A.</p> <p>1992-04-01</p> <p>Although the last two decades have seen major reductions in the <span class="hlt">noise</span> from civil aircraft, <span class="hlt">noise</span> from military operations, both around airfields and from low-flying aircraft, continues to be a <span class="hlt">source</span> of irritation and a potential health hazard. Because of the continuing concern about the <span class="hlt">noise</span> levels produced by combat aircraft, the following paper is intended to provide some of the background to the main conclusions and recommendations reached in the final report of the NATO/Committee on the Challenges of a Modern Society (CCMS) Pilot Study on aircraft <span class="hlt">noise</span>. Although biased towards fixed wing combat aircraft <span class="hlt">noise</span>, the paper also considers other fixed wing military aircraft, but specifically excludes sonic booms and rotary wing aircraft as they both have their own particular <span class="hlt">noise</span> <span class="hlt">sources</span> and problems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930066851&hterms=Natural+gases&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DNatural%2Bgases','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930066851&hterms=Natural+gases&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DNatural%2Bgases"><span>Natural <span class="hlt">noise</span> above 50 MHZ from terrestrial and extraterrestrial <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, E. K.; Flock, W. L.</p> <p>1991-01-01</p> <p>This paper offers a brief overview of natural radio <span class="hlt">noise</span> for frequencies above 50 MHz in terms of brightness temperature as observed from two vantage points. The first is from an Earth station located at 40 degrees north latitude and observing at elevation angles from 0 to 90 degrees with an ideal antenna. The second is a satellite in geostationary orbit communicating with the Earth. Earth station <span class="hlt">noise</span> at VHF and UHF is dominated by galactic and solar <span class="hlt">noise</span>. Emission from the atmosphere, gases and hydrometeors, are dominant at EHF and SHF. Radiative transfer theory is invoked in the calculation of brightness temperature from the atmosphere. The situation is not vastly different from geostationary orbit if communications is with the Earth. Emission from the land and sea, even under idealized conditions, enters significantly. Land is a much more effective emitter than sea water, but at frequencies above 30 GHz the differential becomes much less due to the increasing significance of atmospheric emission.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930045406&hterms=Sound+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DSound%2Bwaves','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930045406&hterms=Sound+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DSound%2Bwaves"><span>High-speed helicopter rotor <span class="hlt">noise</span> - Shock waves as a potent <span class="hlt">source</span> of sound</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Farassat, F.; Lee, Yung-Jang; Tadghighi, H.; Holz, R.</p> <p>1991-01-01</p> <p>In this paper we discuss the problem of high speed rotor <span class="hlt">noise</span> prediction. In particular, we propose that from the point of view of the acoustic analogy, shocks around rotating blades are <span class="hlt">sources</span> of sound. We show that, although for a wing at uniform steady rectilinear motion with shocks the volume quadrupole and shock <span class="hlt">sources</span> cancel in the far field to the order of 1/r, this cannot happen for rotating blades. In this case, some cancellation between volume quadrupoles and shock <span class="hlt">sources</span> occurs, yet the remaining shock <span class="hlt">noise</span> contribution is still potent. A formula for shock <span class="hlt">noise</span> prediction is presented based on mapping the deformable shock surface to a time independent region. The resulting equation is similar to Formulation 1A of Langley. Shock <span class="hlt">noise</span> prediction for a hovering model rotor for which experimental <span class="hlt">noise</span> data exist is presented. The comparison of measured and predicted acoustic data shows good agreement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810013374','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810013374"><span><span class="hlt">Sources</span>, control, and effects of <span class="hlt">noise</span> from aircraft propellers and rotors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mixson, J. S.; Greene, G. C.; Dempsey, T. K.</p> <p>1981-01-01</p> <p>Recent NASA and NASA sponsored research on the prediction and control of propeller and rotor <span class="hlt">source</span> <span class="hlt">noise</span>, on the analysis and design of fuselage sidewall <span class="hlt">noise</span> control treatments, and on the measurement and quantification of the response of passengers to aircraft <span class="hlt">noise</span> is described. <span class="hlt">Source</span> <span class="hlt">noise</span> predictions are compared with measurements for conventional low speed propellers, for new high speed propellers (propfans), and for a helicopter. Results from a light aircraft demonstration program are considered which indicates that about 5 dB reduction of flyover <span class="hlt">noise</span> can be obtained without significant performance penalty. Sidewall design studies are examined for interior <span class="hlt">noise</span> control in light general aviation aircraft and in large transports using propfan propulsion. The weight of the added acoustic treatment is estimated and tradeoffs between weight and <span class="hlt">noise</span> reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller-like <span class="hlt">noise</span> is described. Subject discomfort ratings of combined tone broadband <span class="hlt">noises</span> are compared with ratings of broadband (boundary layer) <span class="hlt">noise</span> alone and the relative importance of the propeller tones is examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870007383','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870007383"><span>Identification and proposed control of helicopter transmission <span class="hlt">noise</span> at the <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Coy, John J.; Handschuh, Robert F.; Lewicki, David G.; Huff, Ronald G.; Krejsa, Eugene A.; Karchmer, Allan M.</p> <p>1987-01-01</p> <p>Helicopter cabin interiors require <span class="hlt">noise</span> treatment which is expensive and adds weight. The gears inside the main power transmission are major <span class="hlt">sources</span> of cabin <span class="hlt">noise</span>. Work conducted by the NASA Lewis Research Center in measuring cabin interior <span class="hlt">noise</span> and in relating the <span class="hlt">noise</span> spectrum to the gear vibration of the Army OH-58 helicopter is described. Flight test data indicate that the planetary gear train is a major <span class="hlt">source</span> of cabin <span class="hlt">noise</span> and that other low frequency <span class="hlt">sources</span> are present that could dominate the cabin <span class="hlt">noise</span>. Companion vibration measurements were made in a transmission test stand, revealing that the single largest contributor to the transmission vibration was the spiral bevel gear mesh. The current understanding of the nature and causes of gear and transmission <span class="hlt">noise</span> is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that <span class="hlt">noise</span>. The completed NASA/Army sponsored research that applies to transmission <span class="hlt">noise</span> reduction is summarized. The continuing research program is also reviewed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880007264','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880007264"><span>Identification and proposed control of helicopter transmission <span class="hlt">noise</span> at the <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Coy, John J.; Handschuh, Robert F.; Lewicki, David G.; Huff, Ronald G.; Krejsa, Eugene A.; Karchmer, Allan M.; Coy, John J.</p> <p>1988-01-01</p> <p>Helicopter cabin interiors require <span class="hlt">noise</span> treatment which is expensive and adds weight. The gears inside the main power transmission are major <span class="hlt">sources</span> of cabin <span class="hlt">noise</span>. Work conducted by the NASA Lewis Research Center in measuring cabin interior <span class="hlt">noise</span> and in relating the <span class="hlt">noise</span> spectrum to the gear vibration of the Army OH-58 helicopter is described. Flight test data indicate that the planetary gear train is a major <span class="hlt">source</span> of cabin <span class="hlt">noise</span> and that other low frequency <span class="hlt">sources</span> are present that could dominate the cabin <span class="hlt">noise</span>. Companion vibration measurements were made in a transmission test stand, revealing that the single largest contributor to the transmission vibration was the spiral bevel gear mesh. The current understanding of the nature and causes of gear and transmission <span class="hlt">noise</span> is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that <span class="hlt">noise</span>. The completed NASA/Army sponsored research that applies to transmission <span class="hlt">noise</span> reduction is summarized. The continuing research program is also reviewed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160013856','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160013856"><span>Full-Scale Turbofan Engine <span class="hlt">Noise-Source</span> Separation Using a Four-Signal Method</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hultgren, Lennart S.; Arechiga, Rene O.</p> <p>2016-01-01</p> <p>Contributions from the combustor to the overall propulsion <span class="hlt">noise</span> of civilian transport aircraft are starting to become important due to turbofan design trends and expected advances in mitigation of other <span class="hlt">noise</span> <span class="hlt">sources</span>. During on-ground, static-engine acoustic tests, combustor <span class="hlt">noise</span> is generally sub-dominant to other engine <span class="hlt">noise</span> <span class="hlt">sources</span> because of the absence of in-flight effects. Consequently, <span class="hlt">noise-source</span> separation techniques are needed to extract combustor-<span class="hlt">noise</span> information from the total <span class="hlt">noise</span> signature in order to further progress. A novel four-signal <span class="hlt">source</span>-separation method is applied to data from a static, full-scale engine test and compared to previous methods. The new method is, in a sense, a combination of two- and three-signal techniques and represents an attempt to alleviate some of the weaknesses of each of those approaches. This work is supported by the NASA Advanced Air Vehicles Program, Advanced Air Transport Technology Project, Aircraft <span class="hlt">Noise</span> Reduction Subproject and the NASA Glenn Faculty Fellowship Program.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993PhDT.......194L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993PhDT.......194L"><span>Vibro-Acoustic Analysis of Computer Disk Drive Components with Emphasis on Electro-Mechanical <span class="hlt">Noise</span> <span class="hlt">Sources</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Ming-Ran</p> <p></p> <p>Vibro-acoustic characteristics of compact electro -mechanical devices are not well understood. This study examines fundamental research issues in this area through the example case of a 3.5" personal computer hard disk drive. In particular, a narrow band mathematical model of the drive has been developed to predict prominent pure tones over the high frequency range (1-6.5 KHz). Through detailed analytical studies, it has been found that the motor torque pulsation of the brushless d.c. motor is the <span class="hlt">source</span> for this <span class="hlt">noise</span> problem. Accordingly, a simplified disk drive model consisting of motor driving a single disk is used to investigate key components, with emphasis on the development of new mathematical models to describe the <span class="hlt">source</span>, path and radiator characteristics. Two different mathematical models have been developed for brushless d.c. motor to predict the torque spectrum associated with invertor switching logic, pulse width modulation control scheme, eccentricity, and magnetic saturation. Frequency contents of predicted variables are identified and matched with measured sound data. Additionally, the Galerkin's method (or modified <span class="hlt">harmonic</span> balance) is also employed successfully to develop an efficient computational scheme which predicts the Fourier coefficients of torque pulsations directly including various effects associated with inductance <span class="hlt">harmonics</span> and the fluctuation of rotor angular velocity. For the radiator (annular disk), modal base formulations of sound radiation have been developed by approximating disk eigen-functions. Specifically, the effects of modal coupling and <span class="hlt">source</span> rotation on radiated sound are investigated. Analytical predictions match well with numerical results obtained by using a boundary element program. New mobility transfer functions (path) are derived to couple the <span class="hlt">source</span> and radiator formulations in order to construct an overall vibro-acoustic model. Potential areas of further research including experimental validation are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22087938','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22087938"><span>Effects of <span class="hlt">noise</span> levels and call types on the <span class="hlt">source</span> levels of killer whale calls.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Holt, Marla M; Noren, Dawn P; Emmons, Candice K</p> <p>2011-11-01</p> <p>Accurate parameter estimates relevant to the vocal behavior of marine mammals are needed to assess potential effects of anthropogenic sound exposure including how masking <span class="hlt">noise</span> reduces the active space of sounds used for communication. Information about how these animals modify their vocal behavior in response to <span class="hlt">noise</span> exposure is also needed for such assessment. Prior studies have reported variations in the <span class="hlt">source</span> levels of killer whale sounds, and a more recent study reported that killer whales compensate for vessel masking <span class="hlt">noise</span> by increasing their call amplitude. The objectives of the current study were to investigate the <span class="hlt">source</span> levels of a variety of call types in southern resident killer whales while also considering background <span class="hlt">noise</span> level as a likely factor related to call <span class="hlt">source</span> level variability. The <span class="hlt">source</span> levels of 763 discrete calls along with corresponding background <span class="hlt">noise</span> were measured over three summer field seasons in the waters surrounding the San Juan Islands, WA. Both <span class="hlt">noise</span> level and call type were significant factors on call <span class="hlt">source</span> levels (1-40 kHz band, range of 135.0-175.7 dB(rms) re 1 [micro sign]Pa at 1 m). These factors should be considered in models that predict how anthropogenic masking <span class="hlt">noise</span> reduces vocal communication space in marine mammals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015FNL....1450005V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015FNL....1450005V"><span>GIS-Based <span class="hlt">Noise</span> Simulation Open <span class="hlt">Source</span> Software: N-GNOIS</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vijay, Ritesh; Sharma, A.; Kumar, M.; Shende, V.; Chakrabarti, T.; Gupta, Rajesh</p> <p>2015-12-01</p> <p>Geographical information system (GIS)-based <span class="hlt">noise</span> simulation software (N-GNOIS) has been developed to simulate the <span class="hlt">noise</span> scenario due to point and mobile <span class="hlt">sources</span> considering the impact of geographical features and meteorological parameters. These have been addressed in the software through attenuation modules of atmosphere, vegetation and barrier. N-GNOIS is a user friendly, platform-independent and open geospatial consortia (OGC) compliant software. It has been developed using open <span class="hlt">source</span> technology (QGIS) and open <span class="hlt">source</span> language (Python). N-GNOIS has unique features like cumulative impact of point and mobile <span class="hlt">sources</span>, building structure and honking due to traffic. Honking is the most common phenomenon in developing countries and is frequently observed on any type of roads. N-GNOIS also helps in designing physical barrier and vegetation cover to check the propagation of <span class="hlt">noise</span> and acts as a decision making tool for planning and management of <span class="hlt">noise</span> component in environmental impact assessment (EIA) studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100032967','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100032967"><span>Phased Array Radiometer Calibration Using a Radiated <span class="hlt">Noise</span> <span class="hlt">Source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Srinivasan, Karthik; Limaye, Ashutoch S.; Laymon, Charles A.; Meyer, Paul J.</p> <p>2010-01-01</p> <p>Electronic beam steering capability of phased array antenna systems offer significant advantages when used in real aperture imaging radiometers. The sensitivity of such systems is limited by the ability to accurately calibrate variations in the antenna circuit characteristics. Passive antenna systems, which require mechanical rotation to scan the beam, have stable characteristics and the <span class="hlt">noise</span> figure of the antenna can be characterized with knowledge of its physical temperature [1],[2]. Phased array antenna systems provide the ability to electronically steer the beam in any desired direction. Such antennas make use of active components (amplifiers, phase shifters) to provide electronic scanning capability while maintaining a low antenna <span class="hlt">noise</span> figure. The gain fluctuations in the active components can be significant, resulting in substantial calibration difficulties [3]. In this paper, we introduce two novel calibration techniques that provide an end-to-end calibration of a real-aperture, phased array radiometer system. Empirical data will be shown to illustrate the performance of both methods.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850004525','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850004525"><span>Algorithm for astronomical, extended <span class="hlt">source</span>, signal-to-<span class="hlt">noise</span> radio calculations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jayroe, R. R.</p> <p>1984-01-01</p> <p>An algorithm was developed to simulate the expected signal-to-<span class="hlt">noise</span> ratio as a function of observation time in the charge coupled device detector plane of an optical telescope located outside the Earth's atmosphere for an extended, uniform astronomical <span class="hlt">source</span> embedded in a uniform cosmic background. By choosing the appropriate input values, the expected extended <span class="hlt">source</span> signal-to-<span class="hlt">noise</span> ratios can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatSR...743411C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatSR...743411C"><span>Direct mapping of electrical <span class="hlt">noise</span> <span class="hlt">sources</span> in molecular wire-based devices</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cho, Duckhyung; Lee, Hyungwoo; Shekhar, Shashank; Yang, Myungjae; Park, Jae Yeol; Hong, Seunghun</p> <p>2017-02-01</p> <p>We report a <span class="hlt">noise</span> mapping strategy for the reliable identification and analysis of <span class="hlt">noise</span> <span class="hlt">sources</span> in molecular wire junctions. Here, different molecular wires were patterned on a gold substrate, and the current-<span class="hlt">noise</span> map on the pattern was measured and analyzed, enabling the quantitative study of <span class="hlt">noise</span> <span class="hlt">sources</span> in the patterned molecular wires. The frequency spectra of the <span class="hlt">noise</span> from the molecular wire junctions exhibited characteristic 1/f2 behavior, which was used to identify the electrical signals from molecular wires. This method was applied to analyze the molecular junctions comprising various thiol molecules on a gold substrate, revealing that the <span class="hlt">noise</span> in the junctions mainly came from the fluctuation of the thiol bonds. Furthermore, we quantitatively compared the frequencies of such bond fluctuations in different molecular wire junctions and identified molecular wires with lower electrical <span class="hlt">noise</span>, which can provide critical information for designing low-<span class="hlt">noise</span> molecular electronic devices. Our method provides valuable insights regarding <span class="hlt">noise</span> phenomena in molecular wires and can be a powerful tool for the development of molecular electronic devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5324066','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5324066"><span>Direct mapping of electrical <span class="hlt">noise</span> <span class="hlt">sources</span> in molecular wire-based devices</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Cho, Duckhyung; Lee, Hyungwoo; Shekhar, Shashank; Yang, Myungjae; Park, Jae Yeol; Hong, Seunghun</p> <p>2017-01-01</p> <p>We report a <span class="hlt">noise</span> mapping strategy for the reliable identification and analysis of <span class="hlt">noise</span> <span class="hlt">sources</span> in molecular wire junctions. Here, different molecular wires were patterned on a gold substrate, and the current-<span class="hlt">noise</span> map on the pattern was measured and analyzed, enabling the quantitative study of <span class="hlt">noise</span> <span class="hlt">sources</span> in the patterned molecular wires. The frequency spectra of the <span class="hlt">noise</span> from the molecular wire junctions exhibited characteristic 1/f2 behavior, which was used to identify the electrical signals from molecular wires. This method was applied to analyze the molecular junctions comprising various thiol molecules on a gold substrate, revealing that the <span class="hlt">noise</span> in the junctions mainly came from the fluctuation of the thiol bonds. Furthermore, we quantitatively compared the frequencies of such bond fluctuations in different molecular wire junctions and identified molecular wires with lower electrical <span class="hlt">noise</span>, which can provide critical information for designing low-<span class="hlt">noise</span> molecular electronic devices. Our method provides valuable insights regarding <span class="hlt">noise</span> phenomena in molecular wires and can be a powerful tool for the development of molecular electronic devices. PMID:28233821</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MeScT..26i5010Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MeScT..26i5010Z"><span>Diesel engine <span class="hlt">noise</span> <span class="hlt">source</span> identification based on EEMD, coherent power spectrum analysis and improved AHP</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Junhong; Wang, Jian; Lin, Jiewei; Bi, Fengrong; Guo, Qian; Chen, Kongwu; Ma, Liang</p> <p>2015-09-01</p> <p>As the essential foundation of <span class="hlt">noise</span> reduction, many <span class="hlt">noise</span> <span class="hlt">source</span> identification methods have been developed and applied to engineering practice. To identify the <span class="hlt">noise</span> <span class="hlt">source</span> in the board-band frequency of different engine parts at various typical speeds, this paper presents an integrated <span class="hlt">noise</span> <span class="hlt">source</span> identification method based on the ensemble empirical mode decomposition (EEMD), the coherent power spectrum analysis, and the improved analytic hierarchy process (AHP). The measured <span class="hlt">noise</span> is decomposed into several IMFs with physical meaning, which ensures the coherence analysis of the IMFs and the vibration signals are meaningful. An improved AHP is developed by introducing an objective weighting function to replace the traditional subjective evaluation, which makes the results no longer dependent on the subject performances and provides a better consistency in the meantime. The proposed <span class="hlt">noise</span> identification model is applied to identifying a diesel engine surface radiated <span class="hlt">noise</span>. As a result, the frequency-dependent contributions of different engine parts to different test points at different speeds are obtained, and an overall weight order is obtained as oil pan  >  left body  >  valve chamber cover  >  gear chamber casing  >  right body  >  flywheel housing, which provides an effectual guidance for the <span class="hlt">noise</span> reduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1160107','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1160107"><span>How Common are <span class="hlt">Noise</span> <span class="hlt">Sources</span> on the Crash Arc of Malaysian Flight 370</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fenimore, Edward E.; Kunkle, Thomas David; Stead, Richard J.</p> <p>2014-10-21</p> <p>Malaysian Flight 370 disappeared nearly without a trace. Besides some communication handshakes to the INMASAT satellite, the Comprehensive Test Ban Treaty monitoring system could have heard the aircraft crash into the southern Indian Ocean. One <span class="hlt">noise</span> event from Cape Leeuwin has been suggested by Stead as the crash and occurs within the crash location suggested by Kunkle at el. We analyze the hydrophone data from Cape Leeuwin to understand how common such <span class="hlt">noise</span> events are on the arc of possible locations where Malaysian Flight 370 might have crashed. Few other <span class="hlt">noise</span> <span class="hlt">sources</span> were found on the arc. The <span class="hlt">noise</span> event found by Stead is the strongest. No <span class="hlt">noise</span> events are seen within the Australian Transportation Safety Board (ATSB) new search location until the 10<sup>th</sup> strongest event, an event which is very close to the <span class="hlt">noise</span> level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20711517','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20711517"><span>Can lightning be a <span class="hlt">noise</span> <span class="hlt">source</span> for a spherical gravitational wave antenna?</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Magalhaes, Nadja Simao; Marinho, Rubens de Melo Jr.; Aguiar, Odylio Denys de; Frajuca, Carlos</p> <p>2005-11-15</p> <p>The detection of gravitational waves is a very active research field at the moment. In Brazil the gravitational wave detector is called Mario SCHENBERG. Because of its high sensitivity it is necessary to model mathematically all known <span class="hlt">noise</span> <span class="hlt">sources</span> so that digital filters can be developed that maximize the signal-to-<span class="hlt">noise</span> ratio. One of the <span class="hlt">noise</span> <span class="hlt">sources</span> that must be considered are the disturbances caused by electromagnetic pulses due to lightnings close to the experiment. Such disturbances may influence the vibrations of the antenna's normal modes and mask possible gravitational wave signals. In this work we model the interaction between lightnings and SCHENBERG antenna and calculate the intensity of the <span class="hlt">noise</span> due to a close lightning stroke in the detected signal. We find that the <span class="hlt">noise</span> generated does not disturb the experiment significantly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1227010','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1227010"><span>Analytic treatment of <span class="hlt">source</span> photon emission times to reduce <span class="hlt">noise</span> in implicit Monte Carlo calculations</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Trahan, Travis J.; Gentile, Nicholas A.</p> <p>2012-09-10</p> <p>Statistical uncertainty is inherent to any Monte Carlo simulation of radiation transport problems. In space-angle-frequency independent radiative transfer calculations, the uncertainty in the solution is entirely due to random sampling of <span class="hlt">source</span> photon emission times. We have developed a modification to the Implicit Monte Carlo algorithm that eliminates <span class="hlt">noise</span> due to sampling of the emission time of <span class="hlt">source</span> photons. In problems that are independent of space, angle, and energy, the new algorithm generates a smooth solution, while a standard implicit Monte Carlo solution is noisy. For space- and angle-dependent problems, the new algorithm exhibits reduced <span class="hlt">noise</span> relative to standard implicit Monte Carlo in some cases, and comparable <span class="hlt">noise</span> in all other cases. In conclusion, the improvements are limited to short time scales; over long time scales, <span class="hlt">noise</span> due to random sampling of spatial and angular variables tends to dominate the <span class="hlt">noise</span> reduction from the new algorithm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000PhDT.......366S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000PhDT.......366S"><span>Detecting vocal fatigue in student singers using acoustic measures of mean fundamental frequency, jitter, shimmer, and <span class="hlt">harmonics-to-noise</span> ratio</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sisakun, Siphan</p> <p>2000-12-01</p> <p>The purpose of this study is to explore the ability of four acoustic parameters, mean fundamental frequency, jitter, shimmer, and <span class="hlt">harmonics-to-noise</span> ratio, to detect vocal fatigue in student singers. The participants are 15 voice students, who perform two distinct tasks, data collection task and vocal fatiguing task. The data collection task includes the sustained vowel /a/, reading a standard passage, and self-rate on a vocal fatigue form. The vocal fatiguing task is the vocal practice of musical scores for a total of 45 minutes. The four acoustic parameters are extracted using the software EZVoicePlus. The data analyses are performed to answer eight research questions. The first four questions relate to correlations of the self-rating scale and each of the four parameters. The next four research questions relate to differences in the parameters over time using one-factor repeated measures analysis of variance (ANOVA). The result yields a proposed acoustic profile of vocal fatigue in student singers. This profile is characterized by increased fundamental frequency; slightly decreased jitter; slightly decreased shimmer; and slightly increased <span class="hlt">harmonics-to-noise</span> ratio. The proposed profile requires further investigation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ACP....16.3289A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ACP....16.3289A"><span>AIRUSE-LIFE+: a <span class="hlt">harmonized</span> PM speciation and <span class="hlt">source</span> apportionment in five southern European cities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Amato, Fulvio; Alastuey, Andrés; Karanasiou, Angeliki; Lucarelli, Franco; Nava, Silvia; Calzolai, Giulia; Severi, Mirko; Becagli, Silvia; Gianelle, Vorne L.; Colombi, Cristina; Alves, Celia; Custódio, Danilo; Nunes, Teresa; Cerqueira, Mario; Pio, Casimiro; Eleftheriadis, Konstantinos; Diapouli, Evangelia; Reche, Cristina; Cruz Minguillón, María; Manousakas, Manousos-Ioannis; Maggos, Thomas; Vratolis, Stergios; Harrison, Roy M.; Querol, Xavier</p> <p>2016-03-01</p> <p>The AIRUSE-LIFE+ project aims at characterizing similarities and heterogeneities in particulate matter (PM) <span class="hlt">sources</span> and contributions in urban areas from southern Europe. Once the main PMx <span class="hlt">sources</span> are identified, AIRUSE aims at developing and testing the efficiency of specific and non-specific measures to improve urban air quality. This article reports the results of the <span class="hlt">source</span> apportionment of PM10 and PM2.5 conducted at three urban background sites (Barcelona, Florence and Milan, BCN-UB, FI-UB and MLN-UB), one suburban background site (Athens, ATH-SUB) and one traffic site (Porto, POR-TR). After collecting 1047 PM10 and 1116 PM2.5 24 h samples during 12 months (from January 2013 on) simultaneously at the five cities, these were analysed for the contents of OC, EC, anions, cations, major and trace elements and levoglucosan. The USEPA PMF5 receptor model was applied to these data sets in a <span class="hlt">harmonized</span> way for each city. The sum of vehicle exhaust (VEX) and non-exhaust (NEX) contributes between 3.9 and 10.8 µg m-3 (16-32 %) to PM10 and 2.3 and 9.4 µg m-3 (15-36 %) to PM2.5, although a fraction of secondary nitrate is also traffic-related but could not be estimated. Important contributions arise from secondary particles (nitrate, sulfate and organics) in PM2.5 (37-82 %) but also in PM10 (40-71 %), mostly at background sites, revealing the importance of abating gaseous precursors in designing air quality plans. Biomass burning (BB) contributions vary widely, from 14-24 % of PM10 in POR-TR, MLN-UB and FI-UB, 7 % in ATH-SUB, to < 2 % in BCN-UB. In PM2.5, BB is the second most important <span class="hlt">source</span> in MLN-UB (21 %) and in POR-TR (18 %), the third one in FI-UB (21 %) and ATH-SUB (11 %), but is again negligible (< 2 %) in BCN-UB. This large variability among cities is mostly due to the degree of penetration of biomass for residential heating. In Barcelona natural gas is very well supplied across the city and is used as fuel in 96 % of homes, while in other cities, PM levels</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140002783','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140002783"><span>Limitations of Phased Array Beamforming in Open Rotor <span class="hlt">Noise</span> <span class="hlt">Source</span> Imaging</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Horvath, Csaba; Envia, Edmane; Podboy, Gary G.</p> <p>2013-01-01</p> <p>Phased array beamforming results of the F31/A31 historical baseline counter-rotating open rotor blade set were investigated for measurement data taken on the NASA Counter-Rotating Open Rotor Propulsion Rig in the 9- by 15-Foot Low-Speed Wind Tunnel of NASA Glenn Research Center as well as data produced using the LINPROP open rotor tone <span class="hlt">noise</span> code. The planar microphone array was positioned broadside and parallel to the axis of the open rotor, roughly 2.3 rotor diameters away. The results provide insight as to why the apparent <span class="hlt">noise</span> <span class="hlt">sources</span> of the blade passing frequency tones and interaction tones appear at their nominal Mach radii instead of at the actual <span class="hlt">noise</span> <span class="hlt">sources</span>, even if those locations are not on the blades. Contour maps corresponding to the sound fields produced by the radiating sound waves, taken from the simulations, are used to illustrate how the interaction patterns of circumferential spinning modes of rotating coherent <span class="hlt">noise</span> <span class="hlt">sources</span> interact with the phased array, often giving misleading results, as the apparent <span class="hlt">sources</span> do not always show where the actual <span class="hlt">noise</span> <span class="hlt">sources</span> are located. This suggests that a more sophisticated <span class="hlt">source</span> model would be required to accurately locate the <span class="hlt">sources</span> of each tone. The results of this study also have implications with regard to the shielding of open rotor <span class="hlt">sources</span> by airframe empennages.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4150400','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4150400"><span>Volterra dendritic stimulus processors and biophysical spike generators with intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lazar, Aurel A.; Zhou, Yiyin</p> <p>2014-01-01</p> <p>We consider a class of neural circuit models with internal <span class="hlt">noise</span> <span class="hlt">sources</span> arising in sensory systems. The basic neuron model in these circuits consists of a dendritic stimulus processor (DSP) cascaded with a biophysical spike generator (BSG). The dendritic stimulus processor is modeled as a set of nonlinear operators that are assumed to have a Volterra series representation. Biophysical point neuron models, such as the Hodgkin-Huxley neuron, are used to model the spike generator. We address the question of how intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> affect the precision in encoding and decoding of sensory stimuli and the functional identification of its sensory circuits. We investigate two intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> arising (i) in the active dendritic trees underlying the DSPs, and (ii) in the ion channels of the BSGs. <span class="hlt">Noise</span> in dendritic stimulus processing arises from a combined effect of variability in synaptic transmission and dendritic interactions. Channel <span class="hlt">noise</span> arises in the BSGs due to the fluctuation of the number of the active ion channels. Using a stochastic differential equations formalism we show that encoding with a neuron model consisting of a nonlinear DSP cascaded with a BSG with intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> can be treated as generalized sampling with noisy measurements. For single-input multi-output neural circuit models with feedforward, feedback and cross-feedback DSPs cascaded with BSGs we theoretically analyze the effect of <span class="hlt">noise</span> <span class="hlt">sources</span> on stimulus decoding. Building on a key duality property, the effect of <span class="hlt">noise</span> parameters on the precision of the functional identification of the complete neural circuit with DSP/BSG neuron models is given. We demonstrate through extensive simulations the effects of <span class="hlt">noise</span> on encoding stimuli with circuits that include neuron models that are akin to those commonly seen in sensory systems, e.g., complex cells in V1. PMID:25225477</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950053968&hterms=harmonic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dharmonic','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950053968&hterms=harmonic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dharmonic"><span>Simulation of 100-300 GHz solid-state <span class="hlt">harmonic</span> <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zybura, Michael F.; Jones, J. Robert; Jones, Stephen H.; Tait, Gregory B.</p> <p>1995-01-01</p> <p>Accurate and efficient simulations of the large-signal time-dependent characteristics of second-<span class="hlt">harmonic</span> Transferred Electron Oscillators (TEO's) and Heterostructure Barrier Varactor (HBV) frequency triplers have been obtained. This is accomplished by using a novel and efficient <span class="hlt">harmonic</span>-balance circuit analysis technique which facilitates the integration of physics-based hydrodynamic device simulators. The integrated hydrodynamic device/<span class="hlt">harmonic</span>-balance circuit simulators allow TEO and HBV circuits to be co-designed from both a device and a circuit point of view. Comparisons have been made with published experimental data for both TEO's and HBV's. For TEO's, excellent correlation has been obtained at 140 GHz and 188 GHz in second-<span class="hlt">harmonic</span> operation. Excellent correlation has also been obtained for HBV frequency triplers operating near 200 GHz. For HBV's, both a lumped quasi-static equivalent circuit model and the hydrodynamic device simulator have been linked to the <span class="hlt">harmonic</span>-balance circuit simulator. This comparison illustrates the importance of representing active devices with physics-based numerical device models rather than analytical device models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22357037','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22357037"><span>Suppression of fiber modal <span class="hlt">noise</span> induced radial velocity errors for bright emission-line calibration <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mahadevan, Suvrath; Halverson, Samuel; Ramsey, Lawrence; Venditti, Nick</p> <p>2014-05-01</p> <p>Modal <span class="hlt">noise</span> in optical fibers imposes limits on the signal-to-<span class="hlt">noise</span> ratio (S/N) and velocity precision achievable with the next generation of astronomical spectrographs. This is an increasingly pressing problem for precision radial velocity spectrographs in the near-infrared (NIR) and optical that require both high stability of the observed line profiles and high S/N. Many of these spectrographs plan to use highly coherent emission-line calibration <span class="hlt">sources</span> like laser frequency combs and Fabry-Perot etalons to achieve precision sufficient to detect terrestrial-mass planets. These high-precision calibration <span class="hlt">sources</span> often use single-mode fibers or highly coherent <span class="hlt">sources</span>. Coupling light from single-mode fibers to multi-mode fibers leads to only a very low number of modes being excited, thereby exacerbating the modal <span class="hlt">noise</span> measured by the spectrograph. We present a commercial off-the-shelf solution that significantly mitigates modal <span class="hlt">noise</span> at all optical and NIR wavelengths, and which can be applied to spectrograph calibration systems. Our solution uses an integrating sphere in conjunction with a diffuser that is moved rapidly using electrostrictive polymers, and is generally superior to most tested forms of mechanical fiber agitation. We demonstrate a high level of modal <span class="hlt">noise</span> reduction with a narrow bandwidth 1550 nm laser. Our relatively inexpensive solution immediately enables spectrographs to take advantage of the innate precision of bright state-of-the art calibration <span class="hlt">sources</span> by removing a major <span class="hlt">source</span> of systematic <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012ApPhL.101v1112B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012ApPhL.101v1112B"><span>An extremely low-<span class="hlt">noise</span> heralded single-photon <span class="hlt">source</span>: A breakthrough for quantum technologies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brida, G.; Degiovanni, I. P.; Genovese, M.; Piacentini, F.; Traina, P.; Della Frera, A.; Tosi, A.; Bahgat Shehata, A.; Scarcella, C.; Gulinatti, A.; Ghioni, M.; Polyakov, S. V.; Migdall, A.; Giudice, A.</p> <p>2012-11-01</p> <p>Low <span class="hlt">noise</span> single-photon <span class="hlt">sources</span> are a critical element for quantum technologies. We present a heralded single-photon <span class="hlt">source</span> with an extremely low level of residual background photons, by implementing low-jitter detectors and electronics and a fast custom-made pulse generator controlling an optical shutter (a LiNbO3 waveguide optical switch) on the output of the <span class="hlt">source</span>. This <span class="hlt">source</span> has a second-order autocorrelation g(2)(0)=0.005(7), and an output <span class="hlt">noise</span> factor (defined as the ratio of the number of <span class="hlt">noise</span> photons to total photons at the <span class="hlt">source</span> output channel) of 0.25(1)%. These are the best performance characteristics reported to date.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140002889','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140002889"><span>Jet-Surface Interaction Test: Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary G.</p> <p>2013-01-01</p> <p>An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the <span class="hlt">noise</span> radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet <span class="hlt">noise</span> was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array <span class="hlt">noise</span> <span class="hlt">source</span> localization measurements were obtained. This paper discusses phased array results, while a companion paper (Brown, C.A., "Jet-Surface Interaction Test: Far-Field <span class="hlt">Noise</span> Results," ASME paper GT2012-69639, June 2012.) discusses far-field results. The phased array data show that the axial distribution of <span class="hlt">noise</span> <span class="hlt">sources</span> in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of <span class="hlt">noise</span> reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the <span class="hlt">noise</span> <span class="hlt">sources</span> associated with a given frequency of <span class="hlt">noise</span> tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The <span class="hlt">noise</span> <span class="hlt">source</span> localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces <span class="hlt">noise</span> at a given frequency within a broadband shock <span class="hlt">noise</span> hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet <span class="hlt">noise</span> to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet <span class="hlt">noise</span> <span class="hlt">sources</span> may satisfy this requirement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21096353','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21096353"><span>Clutter isolation and cardiac monitoring using <span class="hlt">harmonic</span> doppler radar with heterodyne receiver and passive RF tags.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Singh, Aditya; Lubecke, Victor</p> <p>2010-01-01</p> <p>A <span class="hlt">harmonic</span> radar employing the use of <span class="hlt">harmonic</span> passive RF tags can be successfully used to isolate the human respiration from environmental clutter. This paper describes the successful use of heterodyne receiver architecture with Doppler radar to track the heart-rate of a human being using passive body-worn <span class="hlt">harmonic</span> tags in presence of a controlled <span class="hlt">noise</span> generator at distances up to 120 cm. The heterodyne system results have been compared with those of a conventional Doppler radar for cardiopulmonary monitoring that fails to isolate the <span class="hlt">noise</span> from heart-rate in presence of a <span class="hlt">noise</span> <span class="hlt">source</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1988hmrn.rept.....B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1988hmrn.rept.....B"><span>Helicopter main-rotor <span class="hlt">noise</span>: Determination of <span class="hlt">source</span> contributions using scaled model data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brooks, Thomas F.; Jolly, J. Ralph, Jr.; Marcolini, Michael A.</p> <p>1988-08-01</p> <p>Acoustic data from a test of a 40 percent model MBB BO-105 helicopter main rotor are scaled to equivalent full-scale flyover cases. The test was conducted in the anechoic open test section of the German-Dutch Windtunnel (DNW). The measured data are in the form of acoustic pressure time histories and spectra from two out-of-flow microphones underneath and foward of the model. These are scaled to correspond to measurements made at locations 150 m below the flight path of a full-scale rotor. For the scaled data, a detailed analysis is given for the identification in the data of the <span class="hlt">noise</span> contributions from different rotor <span class="hlt">noise</span> <span class="hlt">sources</span>. Key results include a component breakdown of the <span class="hlt">noise</span> contributions, in terms of <span class="hlt">noise</span> criteria calculations of a weighted sound pressure level (dBA) and perceived <span class="hlt">noise</span> level (PNL), as functions of rotor advance ratio and descent angle. It is shown for the scaled rotor that, during descent, impulsive blade-vortex interaction (BVI) <span class="hlt">noise</span> is the dominant contributor to the <span class="hlt">noise</span>. In level flight and mild climb, broadband blade-turbulent wake interaction (BWI) <span class="hlt">noise</span> is dominant due to the absence of BVI activity. At high climb angles, BWI is reduced and self-<span class="hlt">noise</span> from blade boundary-layer turbulence becomes the most prominent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880017523','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880017523"><span>Helicopter main-rotor <span class="hlt">noise</span>: Determination of <span class="hlt">source</span> contributions using scaled model data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brooks, Thomas F.; Jolly, J. Ralph, Jr.; Marcolini, Michael A.</p> <p>1988-01-01</p> <p>Acoustic data from a test of a 40 percent model MBB BO-105 helicopter main rotor are scaled to equivalent full-scale flyover cases. The test was conducted in the anechoic open test section of the German-Dutch Windtunnel (DNW). The measured data are in the form of acoustic pressure time histories and spectra from two out-of-flow microphones underneath and foward of the model. These are scaled to correspond to measurements made at locations 150 m below the flight path of a full-scale rotor. For the scaled data, a detailed analysis is given for the identification in the data of the <span class="hlt">noise</span> contributions from different rotor <span class="hlt">noise</span> <span class="hlt">sources</span>. Key results include a component breakdown of the <span class="hlt">noise</span> contributions, in terms of <span class="hlt">noise</span> criteria calculations of a weighted sound pressure level (dBA) and perceived <span class="hlt">noise</span> level (PNL), as functions of rotor advance ratio and descent angle. It is shown for the scaled rotor that, during descent, impulsive blade-vortex interaction (BVI) <span class="hlt">noise</span> is the dominant contributor to the <span class="hlt">noise</span>. In level flight and mild climb, broadband blade-turbulent wake interaction (BWI) <span class="hlt">noise</span> is dominant due to the absence of BVI activity. At high climb angles, BWI is reduced and self-<span class="hlt">noise</span> from blade boundary-layer turbulence becomes the most prominent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790006704','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790006704"><span>Basic research in fan <span class="hlt">source</span> <span class="hlt">noise</span>: Inlet distortion and turbulence <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kantola, R. A.; Warren, R. E.</p> <p>1978-01-01</p> <p>A widely recognized problem in jet engine fan <span class="hlt">noise</span> is the discrepancy between inflight and static tests. This discrepancy consists of blade passing frequency tones, caused by ingested turbulence that appear in the static tests but not in flight. To reduce the ingested distortions and turbulence in an anechoic chamber, a reverse cone inlet is used to guide the air into the fan. This inlet also has provisions for boundary layer suction and is used in conjunction with a turbulence control structure (TCS) to condition the air impinging on the fan. The program was very successful in reducing the ingested turbulence, to the point where reductions in the acoustic power at blade passing frequency are as high as 18 db for subsonic tip speeds. Even with this large subsonic tone suppression, the supersonic tip speed tonal content remains largely unchanged, indicating that the TCS did not appreciably attenuate the <span class="hlt">noise</span> but effects the generation via turbulence reduction. Turbulence mapping of the inlet confirmed that the tone reductions are due to a reduction in turbulence, as the low frequency power spectra of the streamwise and transverse turbulence were reduced by up to ten times and 100 times, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19960003598&hterms=harmonic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dharmonic','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19960003598&hterms=harmonic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dharmonic"><span>Effect of higher <span class="hlt">harmonic</span> control on helicopter rotor blade-vortex interaction <span class="hlt">noise</span>: Prediction and initial validation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Beaumier, P.; Prieur, J.; Rahier, G.; Spiegel, P.; Demargne, A.; Tung, C.; Gallman, J. M.; Yu, Y. H.; Kube, R.; Vanderwall, B. G.</p> <p>1995-01-01</p> <p>The paper presents a status of theoretical tools of AFDD, DLR, NASA and ONERA for prediction of the effect of HHC on helicopter main rotor BVI <span class="hlt">noise</span>. Aeroacoustic predictions from the four research centers, concerning a wind tunnel simulation of a typical descent flight case without and with HHC are presented and compared. The results include blade deformation, geometry of interacting vortices, sectional loads and <span class="hlt">noise</span>. Acoustic predictions are compared to experimental data. An analysis of the results provides a first insight of the mechanisms by which HHC may affect BVI <span class="hlt">noise</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012RScI...83d4701C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012RScI...83d4701C"><span>A low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> for atomic spin squeezing experiments in 87Rb</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Zilong; Bohnet, Justin G.; Weiner, Joshua M.; Thompson, James K.</p> <p>2012-04-01</p> <p>We describe and characterize a simple, low cost, low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> that operates near 6.800 GHz for agile, coherent manipulation of ensembles of 87Rb. Low phase <span class="hlt">noise</span> is achieved by directly multiplying a low phase <span class="hlt">noise</span> 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency <span class="hlt">source</span> to provide the desired phase, amplitude, and frequency control. Before modulation, the <span class="hlt">source</span> has a single sideband phase <span class="hlt">noise</span> near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting <span class="hlt">source</span> is estimated to contribute added spin-<span class="hlt">noise</span> variance 16 dB below the quantum projection <span class="hlt">noise</span> level during quantum nondemolition measurements of the clock transition in an ensemble 7 × 105 87Rb atoms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22072287','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22072287"><span>A low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> for atomic spin squeezing experiments in {sup 87}Rb</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chen Zilong; Bohnet, Justin G.; Weiner, Joshua M.; Thompson, James K.</p> <p>2012-04-15</p> <p>We describe and characterize a simple, low cost, low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> that operates near 6.800 GHz for agile, coherent manipulation of ensembles of {sup 87}Rb. Low phase <span class="hlt">noise</span> is achieved by directly multiplying a low phase <span class="hlt">noise</span> 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency <span class="hlt">source</span> to provide the desired phase, amplitude, and frequency control. Before modulation, the <span class="hlt">source</span> has a single sideband phase <span class="hlt">noise</span> near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting <span class="hlt">source</span> is estimated to contribute added spin-<span class="hlt">noise</span> variance 16 dB below the quantum projection <span class="hlt">noise</span> level during quantum nondemolition measurements of the clock transition in an ensemble 7 x 10{sup 5} {sup 87}Rb atoms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22559559','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22559559"><span>A low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> for atomic spin squeezing experiments in 87Rb.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Zilong; Bohnet, Justin G; Weiner, Joshua M; Thompson, James K</p> <p>2012-04-01</p> <p>We describe and characterize a simple, low cost, low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> that operates near 6.800 GHz for agile, coherent manipulation of ensembles of (87)Rb. Low phase <span class="hlt">noise</span> is achieved by directly multiplying a low phase <span class="hlt">noise</span> 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency <span class="hlt">source</span> to provide the desired phase, amplitude, and frequency control. Before modulation, the <span class="hlt">source</span> has a single sideband phase <span class="hlt">noise</span> near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting <span class="hlt">source</span> is estimated to contribute added spin-<span class="hlt">noise</span> variance 16 dB below the quantum projection <span class="hlt">noise</span> level during quantum nondemolition measurements of the clock transition in an ensemble 7 × 10(5) (87)Rb atoms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4336190','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4336190"><span>Exposures to Transit and Other <span class="hlt">Sources</span> of <span class="hlt">Noise</span> among New York City Residents</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Neitzel, Richard L.; Gershon, Robyn R. M.; McAlexander, Tara P.; Magda, Lori A.; Pearson, Julie M.</p> <p>2015-01-01</p> <p>To evaluate the contributions of common <span class="hlt">noise</span> <span class="hlt">sources</span> to total annual <span class="hlt">noise</span> exposures among urban residents and workers, we estimated exposures associated with five common <span class="hlt">sources</span> (use of mass transit, occupational and non-occupational activities, MP3 player and stereo use, and time at home and doing other miscellaneous activities) among a sample of over 4500 individuals in New York City (NYC). We then evaluated the contributions of each <span class="hlt">source</span> to total <span class="hlt">noise</span> exposure and also compared our estimated exposures to the recommended 70 dBA annual exposure limit. We found that one in ten transit users had <span class="hlt">noise</span> exposures in excess of the recommended exposure limit from their transit use alone. When we estimated total annual exposures, 90% of NYC transit users and 87% of nonusers exceeded the recommended limit. MP3 player and stereo use, which represented a small fraction of the total annual hours for each subject on average, was the primary <span class="hlt">source</span> of exposure among the majority of urban dwellers we evaluated. Our results suggest that the vast majority of urban mass transit riders may be at risk of permanent, irreversible <span class="hlt">noise</span>-induced hearing loss and that, for many individuals, this risk is driven primarily by exposures other than occupational <span class="hlt">noise</span>. PMID:22088203</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001RaSc...36.1659N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001RaSc...36.1659N"><span>Statistical addition method for external <span class="hlt">noise</span> <span class="hlt">sources</span> affecting HF-MF-LF systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Neudegg, David</p> <p>2001-01-01</p> <p>The current statistical method for the addition of external component <span class="hlt">noise</span> <span class="hlt">sources</span> in the LF, MF, and lower HF band (100 kHz to 3 MHz) produces total median <span class="hlt">noise</span> levels that may be less than the largest-component median in some cases. Several case studies illustrate this anomaly. Methods used to sum the components rely on their power (decibels) distributions being represented as normal by the statistical parameters. The atmospheric <span class="hlt">noise</span> component is not correctly represented by its decile values when it is assumed to have a normal distribution, causing anomalies in the <span class="hlt">noise</span> summation when components are similar in magnitude. A revised component summation method is proposed, and the way it provides a more physically realistic total <span class="hlt">noise</span> median for LF, MF, and lower HF frequencies is illustrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhyC..518...85Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhyC..518...85Y"><span>Design and test of component circuits of an integrated quantum voltage <span class="hlt">noise</span> <span class="hlt">source</span> for Johnson <span class="hlt">noise</span> thermometry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yamada, Takahiro; Maezawa, Masaaki; Urano, Chiharu</p> <p>2015-11-01</p> <p>We present design and testing of a pseudo-random number generator (PRNG) and a variable pulse number multiplier (VPNM) which are digital circuit subsystems in an integrated quantum voltage <span class="hlt">noise</span> <span class="hlt">source</span> for Jonson <span class="hlt">noise</span> thermometry. Well-defined, calculable pseudo-random patterns of single flux quantum pulses are synthesized with the PRNG and multiplied digitally with the VPNM. The circuit implementation on rapid single flux quantum technology required practical circuit scales and bias currents, 279 junctions and 33 mA for the PRNG, and 1677 junctions and 218 mA for the VPNM. We confirmed the circuit operation with sufficiently wide margins, 80-120%, with respect to the designed bias currents.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...375...53F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...375...53F"><span>Spatial resolution limits for the localization of <span class="hlt">noise</span> <span class="hlt">sources</span> using direct sound mapping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fernandez Comesaña, D.; Holland, K. R.; Fernandez-Grande, E.</p> <p>2016-08-01</p> <p>One of the main challenges arising from <span class="hlt">noise</span> and vibration problems is how to identify the areas of a device, machine or structure that produce significant acoustic excitation, i.e. the localization of main <span class="hlt">noise</span> <span class="hlt">sources</span>. The direct visualization of sound, in particular sound intensity, has extensively been used for many years to locate sound <span class="hlt">sources</span>. However, it is not yet well defined when two <span class="hlt">sources</span> should be regarded as resolved by means of direct sound mapping. This paper derives the limits of the direct representation of sound pressure, particle velocity and sound intensity by exploring the relationship between spatial resolution, <span class="hlt">noise</span> level and geometry. The proposed expressions are validated via simulations and experiments. It is shown that particle velocity mapping yields better results for identifying closely spaced sound <span class="hlt">sources</span> than sound pressure or sound intensity, especially in the acoustic near-field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JSV...295..781V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JSV...295..781V"><span>Experimental determination of the tonal <span class="hlt">noise</span> <span class="hlt">sources</span> in a centrifugal fan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Velarde-Suárez, Sandra; Ballesteros-Tajadura, Rafael; Pablo Hurtado-Cruz, Juan; Santolaria-Morros, Carlos</p> <p>2006-08-01</p> <p>In this work, an experimental study about the aerodynamic tonal <span class="hlt">noise</span> <span class="hlt">sources</span> in a centrifugal fan with backward-curved blades has been carried out. Acoustic pressure measurements at the fan exit duct and pressure fluctuation measurements on the volute surface have been made for different flow rates. A correlation study of both pressure signals has been made in order to explain some of the features of the aerodynamic tonal <span class="hlt">noise</span> generation. A strong <span class="hlt">source</span> of <span class="hlt">noise</span> caused by the interaction between the fluctuating flow leaving the impeller and the volute tongue is appreciated. The unsteady forces exerted on the fan blades constitute another <span class="hlt">noise</span> generation mechanism, which affects the whole extension of the impeller, thus transmitting pressure fluctuations to the entire volute casing. The relative importance of this mechanism compared to the impeller-tongue interaction depends on the flow rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040191552','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040191552"><span>Development in <span class="hlt">Source</span> Modeling and Sound Propagation for Jet <span class="hlt">Noise</span> Predictions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Leib, Steward</p> <p>2004-01-01</p> <p>The purpose of the research carried out under this cooperative agreement was to develop tools that could be used to improve upon the current state of the art in the prediction of <span class="hlt">noise</span> emitted by turbulent exhaust jets. Both the <span class="hlt">source</span> modeling and sound propagation aspects of the prediction of jet <span class="hlt">noise</span> by acoustic analogy were examined with a view toward the development of methods which yield improved predictions over a wider range of operating conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090035729','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090035729"><span>Separation of Main and Tail Rotor <span class="hlt">Noise</span> <span class="hlt">Sources</span> from Ground-Based Acoustic Measurements Using Time-Domain De-Dopplerization</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greenwood, Eric II; Schmitz, Fredric H.</p> <p>2009-01-01</p> <p>A new method of separating the contributions of helicopter main and tail rotor <span class="hlt">noise</span> <span class="hlt">sources</span> is presented, making use of ground-based acoustic measurements. The method employs time-domain de-Dopplerization to transform the acoustic pressure time-history data collected from an array of ground-based microphones to the equivalent time-history signals observed by an array of virtual inflight microphones traveling with the helicopter. The now-stationary signals observed by the virtual microphones are then periodically averaged with the main and tail rotor once per revolution triggers. The averaging process suppresses <span class="hlt">noise</span> which is not periodic with the respective rotor, allowing for the separation of main and tail rotor pressure time-histories. The averaged measurements are then interpolated across the range of directivity angles captured by the microphone array in order to generate separate acoustic hemispheres for the main and tail rotor <span class="hlt">noise</span> <span class="hlt">sources</span>. The new method is successfully applied to ground-based microphone measurements of a Bell 206B3 helicopter and demonstrates the strong directivity characteristics of <span class="hlt">harmonic</span> <span class="hlt">noise</span> radiation from both the main and tail rotors of that helicopter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9344E..0WY','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9344E..0WY"><span>Optical system design of a speckle-free ultrafast Red-Green-Blue (RGB) <span class="hlt">source</span> based on angularly multiplexed second <span class="hlt">harmonic</span> generation from a TZDW <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yao, Yuhong; Knox, Wayne H.</p> <p>2015-03-01</p> <p>We report the optical system design of a novel speckle-free ultrafast Red-Green-Blue (RGB) <span class="hlt">source</span> based on angularly multiplexed simultaneous second <span class="hlt">harmonic</span> generation from the efficiently generated Stokes and anti-Stokes pulses from a commercially available photonic crystal fiber (PCF) with two zero dispersion wavelengths (TZDW). We describe the optimized configuration of the TZDW fiber <span class="hlt">source</span> which supports excitations of dual narrow-band pulses with peak wavelengths at 850 nm, 1260 nm and spectral bandwidths of 23 nm, 26 nm, respectively within 12 cm of commercially available TZDW PCF. The conversion efficiencies are as high as 44% and 33% from the pump <span class="hlt">source</span> (a custom-built Yb:fiber master-oscillator-power-amplifier). As a result of the nonlinear dynamics of propagation, the dual pulses preserve their ultrashort pulse width (with measured autocorrelation traces of 200 fs and 227 fs,) which eliminates the need for dispersion compensation before <span class="hlt">harmonic</span> generation. With proper optical design of the free-space <span class="hlt">harmonic</span> generation system, we achieve milli-Watt power level red, green and blue pulses at 630 nm, 517 nm and 425 nm. Having much broader spectral bandwidths compared to picosecond RGB laser <span class="hlt">sources</span>, the <span class="hlt">source</span> is inherently speckle-free due to the ultra-short coherence length (<37 μm) while still maintaining an excellent color rendering capability with >99.4% excitation purities of the three primaries, leading to the coverage of 192% NTSC color gamut (CIE 1976). The reported RGB <span class="hlt">source</span> features a very simple system geometry, its potential for power scaling is discussed with currently available technologies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21255263','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21255263"><span>Multi-MW K-Band <span class="hlt">Harmonic</span> Multiplier: RF <span class="hlt">Source</span> For High-Gradient Accelerator R and D</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Solyak, N. A.; Yakovlev, V. P.; Kazakov, S. Yu.; Hirshfield, J. L.</p> <p>2009-01-22</p> <p>A preliminary design is presented for a two-cavity <span class="hlt">harmonic</span> multiplier, intended as a high-power RF <span class="hlt">source</span> for use in experiments aimed at developing high-gradient structures for a future collider. The <span class="hlt">harmonic</span> multiplier is to produce power at selected frequencies in K-band (18-26.5 GHz) using as an RF driver an XK-5 S-band klystron (2.856 GHz). The device is to be built with a TE{sub 111} rotating mode input cavity and interchangeable output cavities running in the TE{sub n11} rotating mode, with n = 7,8,9 at 19.992, 22.848, and 25.704 GHz. An example for a 7{sup th} <span class="hlt">harmonic</span> multiplier is described, using a 250 kV, 20 A injected laminar electron beam; with 10 MW of S-band drive power, 4.7 MW of 20-GHz output power is predicted. Details are described of the magnetic circuit, cavities, and output coupler.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.207..774O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.207..774O"><span>Doubling the spectrum of time-domain induced polarization by <span class="hlt">harmonic</span> de-<span class="hlt">noising</span>, drift correction, spike removal, tapered gating and data uncertainty estimation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Olsson, Per-Ivar; Fiandaca, Gianluca; Larsen, Jakob Juul; Dahlin, Torleif; Auken, Esben</p> <p>2016-11-01</p> <p>The extraction of spectral information in the inversion process of time-domain (TD) induced polarization (IP) data is changing the use of the TDIP method. Data interpretation is evolving from a qualitative description of the subsurface, able only to discriminate the presence of contrasts in chargeability parameters, towards a quantitative analysis of the investigated media, which allows for detailed soil- and rock-type characterization. Two major limitations restrict the extraction of the spectral information of TDIP data in the field: (i) the difficulty of acquiring reliable early-time measurements in the millisecond range and (ii) the self-potential background drift in the measured potentials distorting the shape of the late-time IP responses, in the second range. Recent developments in TDIP acquisition equipment have given access to full-waveform recordings of measured potentials and transmitted current, opening for a breakthrough in data processing. For measuring at early times, we developed a new method for removing the significant <span class="hlt">noise</span> from power lines contained in the data through a model-based approach, localizing the fundamental frequency of the power-line signal in the full-waveform IP recordings. By this, we cancel both the fundamental signal and its <span class="hlt">harmonics</span>. Furthermore, an efficient processing scheme for identifying and removing spikes in TDIP data was developed. The <span class="hlt">noise</span> cancellation and the de-spiking allow the use of earlier and narrower gates, down to a few milliseconds after the current turn-off. In addition, tapered windows are used in the final gating of IP data, allowing the use of wider and overlapping gates for higher <span class="hlt">noise</span> suppression with minimal distortion of the signal. For measuring at late times, we have developed an algorithm for removal of the self-potential drift. Usually constant or linear drift-removal algorithms are used, but these algorithms often fail in removing the background potentials present when the electrodes used for</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhST..166a4030R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhST..166a4030R"><span>Prospects for laser spectroscopy of highly charged ions with high-<span class="hlt">harmonic</span> XUV and soft x-ray <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rothhardt, J.; Hädrich, S.; Demmler, S.; Krebs, M.; Winters, D. F. A.; Kühl, Th; Stöhlker, Th; Limpert, J.; Tünnermann, A.</p> <p>2015-11-01</p> <p>We present novel high photon flux XUV and soft x-ray <span class="hlt">sources</span> based on high <span class="hlt">harmonic</span> generation (HHG). The <span class="hlt">sources</span> employ femtosecond fiber lasers, which can be operated at very high (MHz) repetition rate and average power (>100 W). HHG with such lasers results in ˜1013 photons s-1 within a single <span class="hlt">harmonic</span> line at ˜40 nm (˜30 eV) wavelength, a photon flux comparable to what is typically available at synchrotron beam lines. In addition, resonant enhancement of HHG can result in narrow-band <span class="hlt">harmonics</span> with high spectral purity—well suited for precision spectroscopy. These novel light <span class="hlt">sources</span> will enable seminal studies on electronic transitions in highly-charged ions. For example, at the experimental storage ring 2s1/2-2p1/2 transitions in Li-like ions can be excited up to Z = 47 (˜100 eV transition energy), which provides unique sensitivity to quantum electro-dynamical effects and nuclear corrections. We estimate fluorescence count rates of the order of tens per second, which would enable studies on short-lived isotopes as well. In combination with the Doppler up-shift available in head-on excitation at future heavy-ion storage rings, such as the high energy storage ring, even multi-keV transitions can potentially be excited. Pump-probe experiments with femtosecond resolution could also be feasible and access the lifetime of short-lived excited states, thus providing novel benchmarks for atomic structure theory.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10141287','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10141287"><span>An improved assessment approach for <span class="hlt">noise</span> impacts from stationary point and traffic <span class="hlt">sources</span> on humans and wildlife</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chang, Young-Soo; Chun, K.C.</p> <p>1994-04-01</p> <p>This paper presents an improved, efficient approach for assessing <span class="hlt">noise</span> impacts associated with a complex set of <span class="hlt">noise</span> <span class="hlt">sources</span> at multiple receptor locations; <span class="hlt">noise</span> impacts form typical remedial activities at a contaminated industrial site are used as an example. The <span class="hlt">noise</span> <span class="hlt">sources</span> associated with remedial activities at the site and surrounding areas are described, the <span class="hlt">noise</span>-propagation modeling methods and results are presented, and an impact assessment of the contaminated site is discussed with regard to applicable regulatory standards and individual and community responses. Also discussed is the improved <span class="hlt">noise</span> assessment approach. The improved features demonstrated are automate approaches for (1) inputting long-term hourly meterorological data (e.g., 8,760 hours for a one-year period) into a long-range <span class="hlt">noise</span>-propagation model for computing <span class="hlt">noise</span>-level increases at receptor locations and (2) analyzing potential individual and community responses to intrusive <span class="hlt">noises</span> using the IAP and modified CNR.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002JSV...251..457G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002JSV...251..457G"><span>Active Control of a Moving <span class="hlt">Noise</span> SOURCE—EFFECT of Off-Axis <span class="hlt">Source</span> Position</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>GUO, J.; PAN, J.; HODGSON, M.</p> <p>2002-03-01</p> <p>An optimally arranged multiple-channel active-control system is known to be able to create a large quiet zone in free space for a stationary primary <span class="hlt">noise</span> <span class="hlt">source</span>. When the primary <span class="hlt">noise</span> <span class="hlt">source</span> moves, the active control of the <span class="hlt">noise</span> becomes much more difficult, as the primary <span class="hlt">noise</span> field changes with time in space. In this case, the controller of the control system must respond fast enough to compensate for the change; much research has been focused on this issue. In this paper, it is shown that a moving <span class="hlt">source</span> also causes difficulties from an acoustical perspective. A moving <span class="hlt">source</span> not only changes continuously the strengths and phases of the sound field in the space, but also changes the wavefront of the primary sound field continuously. It is known that the efficiency of active <span class="hlt">noise</span> control is determined mainly by the wavefront matching between the primary and control fields. To keep the control system effective in the case of a moving <span class="hlt">source</span>, the wavefront of the control field needs to change, in order to continuously match the primary-wavefront change. This paper shows that there are limitations to the control-wavefront change. An optimally pre-arranged, multiple-channel control system is not able to construct a matching wavefront when the primary <span class="hlt">source</span> moves outside a certain range. In other words, the control system is still able to create a large quiet zone only when the primary <span class="hlt">source</span> moves within a range around the central axis of the control system. Both the location and the size of the quiet zone change with the location of the primary <span class="hlt">source</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770020173','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770020173"><span>Preliminary study of a hydrogen peroxide rocket for use in moving <span class="hlt">source</span> jet <span class="hlt">noise</span> tests</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Plencner, R. M.</p> <p>1977-01-01</p> <p>A preliminary investigation was made of using a hydrogen peroxide rocket to obtain pure moving <span class="hlt">source</span> jet <span class="hlt">noise</span> data. The thermodynamic cycle of the rocket was analyzed. It was found that the thermodynamic exhaust properties of the rocket could be made to match those of typical advanced commercial supersonic transport engines. The rocket thruster was then considered in combination with a streamlined ground car for moving <span class="hlt">source</span> jet <span class="hlt">noise</span> experiments. When a nonthrottlable hydrogen peroxide rocket was used to accelerate the vehicle, propellant masses and/or acceleration distances became too large. However, when a throttlable rocket or an auxiliary system was used to accelerate the vehicle, reasonable propellant masses could be obtained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSV...386..283C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSV...386..283C"><span>Nonlinear secondary <span class="hlt">noise</span> <span class="hlt">sources</span> for passive defect detection using ultrasound sensors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chehami, Lynda; Moulin, Emmanuel; de Rosny, Julien; Prada, Claire; Chatelet, Eric; Lacerra, Giovanna; Gryllias, Konstantinos; Massi, Francesco</p> <p>2017-01-01</p> <p>This paper introduces the concept of secondary <span class="hlt">noise</span> <span class="hlt">sources</span> for passive defect detection and localization in structures. The proposed solution allows for the exploitation of the principle of Green's function reconstruction from <span class="hlt">noise</span> correlation, even in the absence of an adequate ambient <span class="hlt">noise</span>. The main principle is to convert a part of low-frequency modal vibrations into high-frequency <span class="hlt">noise</span> by exploiting the frictional contact nonlinearities. The device consists of a mass-spring resonator coupled to a flexible beam by a rough frictional interface. The extremity of the beam, attached to the surface of a plate, excites efficiently flexural waves in the plate up to 30 kHz when the primary resonator vibrates around its natural frequency, i.e. a few dozens Hz. A set of such devices is placed at random positions on the plate surface, and low-frequency excitation is provided by a shaker. The generated high-frequency <span class="hlt">noise</span> is recorded by an array of eight piezoelectric transducers attached to the plate. A differential correlation matrix is constructed by subtracting correlation functions computed from <span class="hlt">noise</span> signals at each sensor pairs, before and after the introduction of a local heterogeneity mimicking a defect. A simple array processing then allows for the detection and estimation of the defect location from this differential correlation matrix. Beyond the successful proof of concept, influence of experimental parameters, such as the number of secondary <span class="hlt">sources</span> or the variability of the position of the shaker application point, is also investigated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/788041','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/788041"><span>Further development of low <span class="hlt">noise</span> MEVVA ion <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Oks, Efim; Yushkov, George; Litovko, Irina; Anders, Andre; Brown, Ian</p> <p>2001-08-28</p> <p>Based on the idea of a space-charge-limited mode of operation, the influence of a pair of electrostatic meshes on the beam parameters of the LBNL MEVVA-5 ion <span class="hlt">source</span> was investigated. The meshes were placed in the expansion zone of the vacuum arc plasma. Apart from reducing the level of beam current fluctuations, this mode of operation provides significant control over the ion charge state distribution of the extracted beam. These effects can be understood taking not only space charge but also the high-directed ion drift velocities into account that are the same for different ion charge states of a material. The results of simulations of the processes involved are in good agreement with the experimental results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26157639','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26157639"><span>Powerline <span class="hlt">noise</span> elimination in biomedical signals via blind <span class="hlt">source</span> separation and wavelet analysis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Akwei-Sekyere, Samuel</p> <p>2015-01-01</p> <p>The distortion of biomedical signals by powerline <span class="hlt">noise</span> from recording biomedical devices has the potential to reduce the quality and convolute the interpretations of the data. Usually, powerline <span class="hlt">noise</span> in biomedical recordings are extinguished via band-stop filters. However, due to the instability of biomedical signals, the distribution of signals filtered out may not be centered at 50/60 Hz. As a result, self-correction methods are needed to optimize the performance of these filters. Since powerline <span class="hlt">noise</span> is additive in nature, it is intuitive to model powerline <span class="hlt">noise</span> in a raw recording and subtract it from the raw data in order to obtain a relatively clean signal. This paper proposes a method that utilizes this approach by decomposing the recorded signal and extracting powerline <span class="hlt">noise</span> via blind <span class="hlt">source</span> separation and wavelet analysis. The performance of this algorithm was compared with that of a 4th order band-stop Butterworth filter, empirical mode decomposition, independent component analysis and, a combination of empirical mode decomposition with independent component analysis. The proposed method was able to expel sinusoidal signals within powerline <span class="hlt">noise</span> frequency range with higher fidelity in comparison with the mentioned techniques, especially at low signal-to-<span class="hlt">noise</span> ratio.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22370652','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22370652"><span><span class="hlt">Noise</span> power spectral density of a fibre scattered-light interferometer with a semiconductor laser <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Alekseev, A E; Potapov, V T</p> <p>2013-10-31</p> <p>Spectral characteristics of the <span class="hlt">noise</span> intensity fluctuations at the output of a scattered-light interferometer, caused by phase fluctuations of semiconductor laser radiation are considered. This kind of <span class="hlt">noise</span> is one of the main factors limiting sensitivity of interferometric sensors. For the first time, to our knowledge, the expression is obtained for the average <span class="hlt">noise</span> power spectral density at the interferometer output versus the degree of a light <span class="hlt">source</span> coherence and length of the scattering segment. Also, the approximate expressions are considered which determine the power spectral density in the low-frequency range (up to 200 kHz) and in the limiting case of extended scattering segments. The expression obtained for the <span class="hlt">noise</span> power spectral density agrees with experimental normalised power spectra with a high accuracy. (interferometry of radiation)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996AAS...188.5515T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996AAS...188.5515T"><span>Analysis of the Low-Frequency Radio <span class="hlt">Noise</span> Environment at Satellite Heights from Terrestrial <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Taylor, M. F.; Basart, J. P.; McCoy, M.; Rios, E.</p> <p>1996-05-01</p> <p>We have investigated the propagation of terrestrial radio <span class="hlt">sources</span> from 1 to 30 MHz (HF spectral region) through the ionosphere for the purpose of characterizing the interference spectrum on potential space-based, low-frequency-radio telescopes. A recent survey of the HF <span class="hlt">noise</span> environment at satellite heights from 1 to 14 MHz has been conducted using the WIND spacecraft. Radio frequencies for which the interference appears to be sufficiently low for radio telescopes are 1.3, 2.9, 3.1, 8.2, and 11.4 MHz. A model was developed to predict the HF <span class="hlt">noise</span> environment. Our current model includes a <span class="hlt">source</span> model, an ionospheric model, and a ray tracing model. The <span class="hlt">source</span> model was developed using known commercial broadcast stations found in the World Radio TV Handbook. The ICED ionospheric model was used to generate a model ionosphere. By ray tracing a terrestrially based broadcast <span class="hlt">source</span> through the model ionosphere, an ionospheric transfer function (ITF) was developed. By modifying the <span class="hlt">source</span> model using the ITF, we were able to simulate the expected <span class="hlt">noise</span> environment at satellite heights. Comparison of modeled and measured spectra show the majority of the <span class="hlt">noise</span> environment is due to known commercial broadcasters. Improved modeling is necessary because the slopes of the simulated spectra above the plasma frequency are too shallow, and the plasma cutoff frequencies are too high compared to the measured data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100019469','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100019469"><span>Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Measurements Made on a Williams International FJ44 Engine</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary G.; Horvath, Csaba</p> <p>2010-01-01</p> <p>A 48-microphone planar phased array system was used to acquire <span class="hlt">noise</span> <span class="hlt">source</span> localization data on a full-scale Williams International FJ44 turbofan engine. Data were acquired with the array at three different locations relative to the engine, two on the side and one in front of the engine. At the two side locations the planar microphone array was parallel to the engine centerline; at the front location the array was perpendicular to the engine centerline. At each of the three locations, data were acquired at eleven different engine operating conditions ranging from engine idle to maximum (take off) speed. Data obtained with the array off to the side of the engine were spatially filtered to separate the inlet and nozzle <span class="hlt">noise</span>. Tones occurring in the inlet and nozzle spectra were traced to the low and high speed spools within the engine. The phased array data indicate that the Inflow Control Device (ICD) used during this test was not acoustically transparent; instead, some of the <span class="hlt">noise</span> emanating from the inlet reflected off of the inlet lip of the ICD. This reflection is a <span class="hlt">source</span> of error for far field <span class="hlt">noise</span> measurements made during the test. The data also indicate that a total temperature rake in the inlet of the engine is a <span class="hlt">source</span> of fan <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18465745','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18465745"><span>Mapping the signal-to-<span class="hlt">noise</span>-ratios of cortical <span class="hlt">sources</span> in magnetoencephalography and electroencephalography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Goldenholz, Daniel M; Ahlfors, Seppo P; Hämäläinen, Matti S; Sharon, Dahlia; Ishitobi, Mamiko; Vaina, Lucia M; Stufflebeam, Steven M</p> <p>2009-04-01</p> <p>Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-<span class="hlt">noise</span>-ratios (SNRs) of cortical <span class="hlt">sources</span> in MEG and EEG. Data from four subjects were used to simulate focal and extended <span class="hlt">sources</span> located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep <span class="hlt">sources</span> was larger in EEG than in MEG, whereas the opposite was typically the case for superficial <span class="hlt">sources</span>. Overall, the SNR maps were more uniform for EEG than for MEG. When using a <span class="hlt">noise</span> model based on uniformly distributed random <span class="hlt">sources</span> on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with <span class="hlt">noise</span> estimated from actual recorded MEG and EEG data. With extended <span class="hlt">sources</span>, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal <span class="hlt">sources</span>. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2882168','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2882168"><span>Mapping the Signal-To-<span class="hlt">Noise</span>-Ratios of Cortical <span class="hlt">Sources</span> in Magnetoencephalography and Electroencephalography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Goldenholz, Daniel M.; Ahlfors, Seppo P.; Hämäläinen, Matti S.; Sharon, Dahlia; Ishitobi, Mamiko; Vaina, Lucia M.; Stufflebeam, Steven M.</p> <p>2010-01-01</p> <p>Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-<span class="hlt">noise</span>-ratios (SNRs) of cortical <span class="hlt">sources</span> in MEG and EEG. Data from four subjects were used to simulate focal and extended <span class="hlt">sources</span> located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep <span class="hlt">sources</span> was larger in EEG than in MEG, whereas the opposite was typically the case for superficial <span class="hlt">sources</span>. Overall, the SNR maps were more uniform for EEG than for MEG. When using a <span class="hlt">noise</span> model based on uniformly distributed random <span class="hlt">sources</span> on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with <span class="hlt">noise</span> estimated from actual recorded MEG and EEG data. With extended <span class="hlt">sources</span>, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal <span class="hlt">sources</span>. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously. PMID:18465745</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100024453','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100024453"><span>On Acoustic <span class="hlt">Source</span> Specification for Rotor-Stator Interaction <span class="hlt">Noise</span> Prediction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nark, Douglas M.; Envia, Edmane; Burley, Caesy L.</p> <p>2010-01-01</p> <p>This paper describes the use of measured <span class="hlt">source</span> data to assess the effects of acoustic <span class="hlt">source</span> specification on rotor-stator interaction <span class="hlt">noise</span> predictions. Specifically, the acoustic propagation and radiation portions of a recently developed coupled computational approach are used to predict tonal rotor-stator interaction <span class="hlt">noise</span> from a benchmark configuration. In addition to the use of full measured data, randomization of <span class="hlt">source</span> mode relative phases is also considered for specification of the acoustic <span class="hlt">source</span> within the computational approach. Comparisons with sideline <span class="hlt">noise</span> measurements are performed to investigate the effects of various <span class="hlt">source</span> descriptions on both inlet and exhaust predictions. The inclusion of additional modal <span class="hlt">source</span> content is shown to have a much greater influence on the inlet results. Reasonable agreement between predicted and measured levels is achieved for the inlet, as well as the exhaust when shear layer effects are taken into account. For the number of trials considered, phase randomized predictions follow statistical distributions similar to those found in previous statistical <span class="hlt">source</span> investigations. The shape of the predicted directivity pattern relative to measurements also improved with phase randomization, having predicted levels generally within one standard deviation of the measured levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5362733','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5362733"><span>Computational Acoustic Beamforming for <span class="hlt">Noise</span> <span class="hlt">Source</span> Identification for Small Wind Turbines</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lien, Fue-Sang</p> <p>2017-01-01</p> <p>This paper develops a computational acoustic beamforming (CAB) methodology for identification of <span class="hlt">sources</span> of small wind turbine <span class="hlt">noise</span>. This methodology is validated using the case of the NACA 0012 airfoil trailing edge <span class="hlt">noise</span>. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of <span class="hlt">noise</span> <span class="hlt">sources</span> generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz. PMID:28378012</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050207443','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050207443"><span>Identification of <span class="hlt">Noise</span> <span class="hlt">Sources</span> in High Speed Jets via Correlation Measurements: A Review</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bridges, James (Technical Monitor); Panda, Jayanta</p> <p>2005-01-01</p> <p>Significant advancement has been made in the last few years to identify <span class="hlt">noise</span> <span class="hlt">sources</span> in high speed jets via direct correlation measurements. In this technique turbulent fluctuations in the flow are correlated with far field acoustics signatures. In the 1970 s there was a surge of work using mostly intrusive probes, and a few using Laser Doppler Velocimetry, to measure turbulent fluctuations. The later experiments established "shear <span class="hlt">noise</span>" as the primary <span class="hlt">source</span> for the shallow angle <span class="hlt">noise</span>. Various interpretations and criticisms from this time are described in the review. Recent progress in the molecular Rayleigh scattering based technique has provided a completely non-intrusive means of measuring density and velocity fluctuations. This has brought a renewed interest on correlation measurements. We have performed five different sets of experiments in single stream jets of different Mach number, temperature ratio and nozzle configurations. The present paper tries to summarize the correlation data from these works.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28378012','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28378012"><span>Computational Acoustic Beamforming for <span class="hlt">Noise</span> <span class="hlt">Source</span> Identification for Small Wind Turbines.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ma, Ping; Lien, Fue-Sang; Yee, Eugene</p> <p>2017-01-01</p> <p>This paper develops a computational acoustic beamforming (CAB) methodology for identification of <span class="hlt">sources</span> of small wind turbine <span class="hlt">noise</span>. This methodology is validated using the case of the NACA 0012 airfoil trailing edge <span class="hlt">noise</span>. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of <span class="hlt">noise</span> <span class="hlt">sources</span> generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23498706','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23498706"><span>Methodology of selecting the reference <span class="hlt">source</span> for an active <span class="hlt">noise</span> control system in a car.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dąbrowski, Zbigniew; Stankiewicz, Bartosz</p> <p>2013-01-01</p> <p>At the end of the 20th century, a significant development in digital technologies of signal processing made it possible to apply active <span class="hlt">noise</span> control methods in new domains. A proper selection of the reference signal <span class="hlt">source</span> is a main problem in implementing such systems. This paper presents an estimation method based on an indicator of the coherent power level. It also presents a simple system of active <span class="hlt">noise</span> control in a car, operating according to the proposed method of optimising the positioning of reference <span class="hlt">sources</span>. This system makes it possible to considerably increase the comfort of work of drivers in various kinds of road transport without a great increase in cost. This is especially significant in the case of trucks and vans. Passive barriers are considerably more expensive in them, which results in a higher level of <span class="hlt">noise</span> than in passenger cars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADD020003','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADD020003"><span>Method and Apparatus for Reducing <span class="hlt">Noise</span> from Near Ocean Surface <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2001-10-01</p> <p>reducing the acoustic <span class="hlt">noise</span> from near-surface 4 <span class="hlt">sources</span> using an array processing technique that utilizes 5 Multiple Signal Classification ( MUSIC ...<span class="hlt">sources</span> without 13 degrading the signal level and quality of the TOI. The present 14 invention utilizes a unique application of the MUSIC beamforming...specific algorithm that utilizes a 5 MUSIC technique and estimates the direction of arrival (DOA) of 6 the acoustic signal signals and generates output</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110011070','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110011070"><span>Use of a Microphone Phased Array to Determine <span class="hlt">Noise</span> <span class="hlt">Sources</span> in a Rocket Plume</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, J.; Mosher, R.</p> <p>2010-01-01</p> <p>A 70-element microphone phased array was used to identify <span class="hlt">noise</span> <span class="hlt">sources</span> in the plume of a solid rocket motor. An environment chamber was built and other precautions were taken to protect the sensitive condenser microphones from rain, thunderstorms and other environmental elements during prolonged stay in the outdoor test stand. A camera mounted at the center of the array was used to photograph the plume. In the first phase of the study the array was placed in an anechoic chamber for calibration, and validation of the indigenous Matlab(R) based beamform software. It was found that the "advanced" beamform methods, such as CLEAN-SC was partially successful in identifying speaker <span class="hlt">sources</span> placed closer than the Rayleigh criteria. To participate in the field test all equipments were shipped to NASA Marshal Space Flight Center, where the elements of the array hardware were rebuilt around the test stand. The sensitive amplifiers and the data acquisition hardware were placed in a safe basement, and 100m long cables were used to connect the microphones, Kulites and the camera. The array chamber and the microphones were found to withstand the environmental elements as well as the shaking from the rocket plume generated <span class="hlt">noise</span>. The beamform map was superimposed on a photo of the rocket plume to readily identify the <span class="hlt">source</span> distribution. It was found that the plume made an exceptionally long, >30 diameter, <span class="hlt">noise</span> <span class="hlt">source</span> over a large frequency range. The shock pattern created spatial modulation of the <span class="hlt">noise</span> <span class="hlt">source</span>. Interestingly, the concrete pad of the horizontal test stand was found to be a good acoustic reflector: the beamform map showed two distinct <span class="hlt">source</span> distributions- the plume and its reflection on the pad. The array was found to be most effective in the frequency range of 2kHz to 10kHz. As expected, the classical beamform method excessively smeared the <span class="hlt">noise</span> <span class="hlt">sources</span> at lower frequencies and produced excessive side-lobes at higher frequencies. The "advanced" beamform</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23556597','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23556597"><span>Localizing the <span class="hlt">sources</span> of two independent <span class="hlt">noises</span>: role of time varying amplitude differences.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yost, William A; Brown, Christopher A</p> <p>2013-04-01</p> <p>Listeners localized the free-field <span class="hlt">sources</span> of either one or two simultaneous and independently generated <span class="hlt">noise</span> bursts. Listeners' localization performance was better when localizing one rather than two sound <span class="hlt">sources</span>. With two sound <span class="hlt">sources</span>, localization performance was better when the listener was provided prior information about the location of one of them. Listeners also localized two simultaneous <span class="hlt">noise</span> bursts that had sinusoidal amplitude modulation (AM) applied, in which the modulation envelope was in-phase across the two <span class="hlt">source</span> locations or was 180° out-of-phase. The AM was employed to investigate a hypothesis as to what process listeners might use to localize multiple sound <span class="hlt">sources</span>. The results supported the hypothesis that localization of two sound <span class="hlt">sources</span> might be based on temporal-spectral regions of the combined waveform in which the sound from one <span class="hlt">source</span> was more intense than that from the other <span class="hlt">source</span>. The interaural information extracted from such temporal-spectral regions might provide reliable estimates of the sound <span class="hlt">source</span> location that produced the more intense sound in that temporal-spectral region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020048663&hterms=turbulent+jet&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dturbulent%2Bjet','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020048663&hterms=turbulent+jet&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dturbulent%2Bjet"><span><span class="hlt">Noise</span> <span class="hlt">Sources</span> in a Low-Reynolds-Number Turbulent Jet at Mach 0.9</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Freund, Jonathan B.</p> <p>2001-01-01</p> <p>The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions. Lighthill's theory is used to define a nominal acoustic <span class="hlt">source</span> in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic <span class="hlt">source</span> is Fourier transformed in the axial coordinate and time and then filtered in order to identify and separate components capable of radiating to the far field. This procedure indicates that the peak radiating component of the <span class="hlt">source</span> is coincident with neither the peak of the full unfiltered <span class="hlt">source</span> nor that of the turbulent kinetic energy. The phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed which calls into question the commonly made assumption that the <span class="hlt">noise</span> <span class="hlt">sources</span> convect at a single velocity. Space-time correlations demonstrate that the <span class="hlt">sources</span> are not acoustically compact in the streamwise direction and that the portion of the <span class="hlt">source</span> that radiates at angles greater than 45 deg. is stationary. Filtering non-radiating wavenumber components of the <span class="hlt">source</span> at single frequencies reveals that a simple modulated wave forms for the <span class="hlt">source</span>, as might be predicted by linear stability analysis. At small angles from the jet axis the <span class="hlt">noise</span> from these modes is highly directional, better described by an exponential than a standard Doppler factor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19820048707&hterms=Harmonic+problems&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DHarmonic%2Bproblems','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19820048707&hterms=Harmonic+problems&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DHarmonic%2Bproblems"><span>Positions of type II fundamental and <span class="hlt">harmonic</span> <span class="hlt">sources</span> in the 30-100 MHZ range</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sawant, H. S.; Gergely, T. E.; Kundu, M. R.</p> <p>1982-01-01</p> <p>An excellent example of a type III-V burst followed by a type II burst with fundamental and <span class="hlt">harmonic</span> bands was observed on June 18, 1979 at the Clark Lake Radio Observatory. The observations are described in detail and their implications are discussed with regard to the problem of directionality with respect to the magnetic field lines of the collisionless MHD shock wave generated at the start of the flash phase. It is found that the positions of type III and type II (F) bursts at a number of frequencies are essentially the same, which implies that the shock responsible for the type II radiation follows the path of the type III exciter, that is, the shock propagates along the open field lines.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S31C..02P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S31C..02P"><span>Ocean-Based Seismic <span class="hlt">Noise</span> <span class="hlt">Sources</span> Recorded by a Moderate Aperture Array in Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pratt, M. J.; Winberry, J. P.; Wiens, D.; Anandakrishnan, S.; Euler, G. G.</p> <p>2015-12-01</p> <p>The deployment of a temporary, 60 km aperture, broadband seismic array on the Whillans Ice Stream (WIS), West Antarctica provides an opportunity to analyze ocean-derived seismic <span class="hlt">noise</span> <span class="hlt">sources</span>. The location of Antarctica, surrounded by the Southern Ocean and the seasonal effect of sea ice on shallow water <span class="hlt">noise</span> production, allows for an intriguing experiment as to the production of primary and secondary microseisms. The WIS array was deployed for 2 months between December 2010-January 2011 with its primary objective to study WIS stick-slip events and glacial microseismicity. However, daylong stacks of station-to-station correlograms show directionality of the ambient <span class="hlt">noise</span> field within the frequency bands of the primary and secondary microseisms. Although the WIS array is located close to the grounding line, it lies 700 km from the nearest open water at the end of the austral summer. The array consists of 17 broadband stations arranged in a series of offset concentric circles that minimizes spatial artifacts with regards to the array response. We use beamforming analysis to show that primary microseisms (~15 s) are <span class="hlt">sourced</span> from three azimuthal directions with some ice-free coastline: Antarctic Peninsula, Victoria Land, and Dronning-Maude Land. Long-period secondary microseisms (~10 s) appear to be <span class="hlt">sourced</span> in the deep Southern Ocean and track storm systems. Short-period secondary microseisms (~6 s) show much more dependence on the continental shelf and possibly coastal reflections. This is consistent with year-long <span class="hlt">noise</span> spectra showing diminishment in the 15 s and 6 s bands [Grob et al. 2011]. Modeling of secondary microseism <span class="hlt">sources</span> [Ardhuin et al. 2011] provides insight on the <span class="hlt">sources</span> of surface wave <span class="hlt">noise</span> at higher frequencies. We backproject daily P and PKPbc body wave microseism signals found at lower ray parameters <span class="hlt">sourced</span> at distances of ~20-90° and ~145-155° respectively. The ocean <span class="hlt">sources</span> for these arrivals remain fairly consistent, suggesting a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040082332','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040082332"><span>Further Progress in <span class="hlt">Noise</span> <span class="hlt">Source</span> Identification in High Speed Jets via Causality Principle</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, J.; Seasholtz, R. G.; Elam, K. A.</p> <p>2004-01-01</p> <p>To locate <span class="hlt">noise</span> <span class="hlt">sources</span> in high-speed jets, the sound pressure fluctuations p/, measured at far field locations, were correlated with each of density p, axial velocity u, radial velocity v, puu and pvv fluctuations measured from various points in fully expanded, unheated plumes of Mach number 0.95, 1.4 and 1.8. The velocity and density fluctuations were measured simultaneously using a recently developed, non-intrusive, point measurement technique based on molecular Rayleigh scattering (Seasholtz, Panda, and Elam, AIAA Paper 2002-0827). The technique uses a continuous wave, narrow line-width laser, Fabry-Perot interferometer and photon counting electronics. The far field sound pressure fluctuations at 30 to the jet axis provided the highest correlation coefficients with all flow variables. The correlation coefficients decreased sharply with increased microphone polar angle, and beyond about 60 all correlation mostly fell below the experimental <span class="hlt">noise</span> floor. Among all correlations < puu; p/> showed the highest values. Interestingly, <p; p/>, in all respects, were very similar to <puu; p/>. The <v;p/> and <pvv;p/> correlations with 90deg microphone fell below the <span class="hlt">noise</span> floor. By moving the laser probe at various locations in the jet it was found that the strongest <span class="hlt">noise</span> <span class="hlt">source</span> lies downstream of the end of the potential core and extends many diameters beyond. Correlation measurement from the lip shear layer showed a Mach number dependency. While significant correlations were measured in Mach 1.8 jet, values were mostly below the <span class="hlt">noise</span> floor for subsonic Mach 0.95 jet. Various additional analyses showed that fluctuations from large organized structures mostly contributed to the measured correlation, while that from small scale structures fell below the <span class="hlt">noise</span> floor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012SSEle..73...64M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012SSEle..73...64M"><span>RF dynamic and <span class="hlt">noise</span> performance of Metallic <span class="hlt">Source</span>/Drain SOI n-MOSFETs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, Maria J.; Pascual, Elena; Rengel, Raúl</p> <p>2012-07-01</p> <p>This paper presents a detailed study of the RF and <span class="hlt">noise</span> performance of n-type Schottky barrier (SB) MOSFETs with a particular focus on the influence of the Schottky barrier height (SBH) on the main dynamic and <span class="hlt">noise</span> figures of merit. With this aim, a 2D Monte Carlo simulator including tunnelling transport across Schottky interfaces has been developed, with special care to consider quantum transmission coefficients and the influence of image charge effects at the Schottky junctions. Particular attention is paid to the microscopic transport features, including carrier mean free paths or number of scattering events along the channel for investigating the optimization of the device topology and the strategic concepts related to the <span class="hlt">noise</span> performance of this new architecture. A more effective control of the gate electrode over drain current for low SBH (discussed in terms of internal physical quantities) is translated into an enhanced transconductance gm, cut-off frequency fT, and non-quasistatic dynamic parameters. The drain and gate intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> show a noteworthy degradation with the SBH reduction due to the increased current, influence of hot carriers and reduced number of phonon scatterings. However, the results evidence that this effect is counterbalanced by the extremely improved dynamic performance in terms of gm and fT. Therefore, the deterioration of the intrinsic <span class="hlt">noise</span> performance of the SB-MOSFET has no significant impact on high-frequency <span class="hlt">noise</span> FoMs as NFmin, Rn and Gass for low SBH and large gate overdrive conditions. The role of the SBH on Γopt, optimum <span class="hlt">noise</span> reactance and susceptance has been also analyzed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870008968','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870008968"><span>Methods for designing treatments to reduce interior <span class="hlt">noise</span> of predominant <span class="hlt">sources</span> and paths in a single engine light aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hayden, Richard E.; Remington, Paul J.; Theobald, Mark A.; Wilby, John F.</p> <p>1985-01-01</p> <p>The <span class="hlt">sources</span> and paths by which <span class="hlt">noise</span> enters the cabin of a small single engine aircraft were determined through a combination of flight and laboratory tests. The primary <span class="hlt">sources</span> of <span class="hlt">noise</span> were found to be airborne <span class="hlt">noise</span> from the propeller and engine casing, airborne <span class="hlt">noise</span> from the engine exhaust, structureborne <span class="hlt">noise</span> from the engine/propeller combination and <span class="hlt">noise</span> associated with air flow over the fuselage. For the propeller, the primary airborne paths were through the firewall, windshield and roof. For the engine, the most important airborne path was through the firewall. Exhaust <span class="hlt">noise</span> was found to enter the cabin primarily through the panels in the vicinity of the exhaust outlet although exhaust <span class="hlt">noise</span> entering the cabin through the firewall is a distinct possibility. A number of <span class="hlt">noise</span> control techniques were tried, including firewall stiffening to reduce engine and propeller airborne <span class="hlt">noise</span>, to stage isolators and engine mounting spider stiffening to reduce structure-borne <span class="hlt">noise</span>, and wheel well covers to reduce air flow <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985bbn..rept.....H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985bbn..rept.....H"><span>Methods for designing treatments to reduce interior <span class="hlt">noise</span> of predominant <span class="hlt">sources</span> and paths in a single engine light aircraft</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hayden, Richard E.; Remington, Paul J.; Theobald, Mark A.; Wilby, John F.</p> <p>1985-03-01</p> <p>The <span class="hlt">sources</span> and paths by which <span class="hlt">noise</span> enters the cabin of a small single engine aircraft were determined through a combination of flight and laboratory tests. The primary <span class="hlt">sources</span> of <span class="hlt">noise</span> were found to be airborne <span class="hlt">noise</span> from the propeller and engine casing, airborne <span class="hlt">noise</span> from the engine exhaust, structureborne <span class="hlt">noise</span> from the engine/propeller combination and <span class="hlt">noise</span> associated with air flow over the fuselage. For the propeller, the primary airborne paths were through the firewall, windshield and roof. For the engine, the most important airborne path was through the firewall. Exhaust <span class="hlt">noise</span> was found to enter the cabin primarily through the panels in the vicinity of the exhaust outlet although exhaust <span class="hlt">noise</span> entering the cabin through the firewall is a distinct possibility. A number of <span class="hlt">noise</span> control techniques were tried, including firewall stiffening to reduce engine and propeller airborne <span class="hlt">noise</span>, to stage isolators and engine mounting spider stiffening to reduce structure-borne <span class="hlt">noise</span>, and wheel well covers to reduce air flow <span class="hlt">noise</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002PMB....47.2547J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002PMB....47.2547J"><span>Fast accurate MEG <span class="hlt">source</span> localization using a multilayer perceptron trained with real brain <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jun, Sung Chan; Pearlmutter, Barak A.; Nolte, Guido</p> <p>2002-07-01</p> <p>Iterative gradient methods such as Levenberg-Marquardt (LM) are in widespread use for <span class="hlt">source</span> localization from electroencephalographic (EEG) and magnetoencephalographic (MEG) signals. Unfortunately, LM depends sensitively on the initial guess, necessitating repeated runs. This, combined with LM's high per-step cost, makes its computational burden quite high. To reduce this burden, we trained a multilayer perceptron (MLP) as a real-time localizer. We used an analytical model of quasistatic electromagnetic propagation through a spherical head to map randomly chosen dipoles to sensor activities according to the sensor geometry of a 4D Neuroimaging Neuromag-122 MEG system, and trained a MLP to invert this mapping in the absence of <span class="hlt">noise</span> or in the presence of various sorts of <span class="hlt">noise</span> such as white Gaussian <span class="hlt">noise</span>, correlated <span class="hlt">noise</span>, or real brain <span class="hlt">noise</span>. A MLP structure was chosen to trade off computation and accuracy. This MLP was trained four times, with each type of <span class="hlt">noise</span>. We measured the effects of initial guesses on LM performance, which motivated a hybrid MLP-start-LM method, in which the trained MLP initializes LM. We also compared the localization performance of LM, MLPs, and hybrid MLP-start-LMs for realistic brain signals. Trained MLPs are much faster than other methods, while the hybrid MLP-start-LMs are faster and more accurate than fixed-4-start-LM. In particular, the hybrid MLP-start-LM initialized by a MLP trained with the real brain <span class="hlt">noise</span> dataset is 60 times faster and is comparable in accuracy to random-20-start-LM, and this hybrid system (localization error: 0.28 cm, computation time: 36 ms) shows almost as good performance as optimal-1-start-LM (localization error: 0.23 cm, computation time: 22 ms), which initializes LM with the correct dipole location. MLPs trained with <span class="hlt">noise</span> perform better than the MLP trained without <span class="hlt">noise</span>, and the MLP trained with real brain <span class="hlt">noise</span> is almost as good an initial guesser for LM as the correct dipole location.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007EJASP2008..247C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007EJASP2008..247C"><span>Maximum Likelihood DOA Estimation of Multiple Wideband <span class="hlt">Sources</span> in the Presence of Nonuniform Sensor <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, C. E.; Lorenzelli, F.; Hudson, R. E.; Yao, K.</p> <p>2007-12-01</p> <p>We investigate the maximum likelihood (ML) direction-of-arrival (DOA) estimation of multiple wideband <span class="hlt">sources</span> in the presence of unknown nonuniform sensor <span class="hlt">noise</span>. New closed-form expression for the direction estimation Cramér-Rao-Bound (CRB) has been derived. The performance of the conventional wideband uniform ML estimator under nonuniform <span class="hlt">noise</span> has been studied. In order to mitigate the performance degradation caused by the nonuniformity of the <span class="hlt">noise</span>, a new deterministic wideband nonuniform ML DOA estimator is derived and two associated processing algorithms are proposed. The first algorithm is based on an iterative procedure which stepwise concentrates the log-likelihood function with respect to the DOAs and the <span class="hlt">noise</span> nuisance parameters, while the second is a noniterative algorithm that maximizes the derived approximately concentrated log-likelihood function. The performance of the proposed algorithms is tested through extensive computer simulations. Simulation results show the stepwise-concentrated ML algorithm (SC-ML) requires only a few iterations to converge and both the SC-ML and the approximately-concentrated ML algorithm (AC-ML) attain a solution close to the derived CRB at high signal-to-<span class="hlt">noise</span> ratio.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25831324','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25831324"><span>Phase <span class="hlt">noise</span> measurement of wideband microwave <span class="hlt">sources</span> based on a microwave photonic frequency down-converter.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhu, Dengjian; Zhang, Fangzheng; Zhou, Pei; Pan, Shilong</p> <p>2015-04-01</p> <p>An approach for phase <span class="hlt">noise</span> measurement of microwave signal <span class="hlt">sources</span> based on a microwave photonic frequency down-converter is proposed. Using the same optical carrier, the microwave signal under test is applied to generate two +1st-order optical sidebands by two stages of electro-optical modulations. A time delay is introduced between the two sidebands through a span of fiber. By beating the two +1st-order sidebands at a photodetector, frequency down-conversion is implemented, and phase <span class="hlt">noise</span> of the signal under test can be calculated thereafter. The system has a very large operation bandwidth thanks to the frequency conversion in the optical domain, and good phase <span class="hlt">noise</span> measurement sensitivity can be achieved since the signal degradation caused by electrical amplifiers is avoided. An experiment is carried out. The phase <span class="hlt">noise</span> measured by the proposed system agrees well with that measured by a commercial spectrum analyzer or provided by the datasheet. A large operation bandwidth of 5-40 GHz is demonstrated using the proposed system. Moreover, good phase <span class="hlt">noise</span> floor is achieved (-123  dBc/Hz at 1 kHz and -137  dBc/Hz at 10 kHz at 10 GHz), which is nearly constant over the full measurement range.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EnMan..51.1137G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EnMan..51.1137G"><span>Evaluation of Online Information <span class="hlt">Sources</span> on Alien Species in Europe: The Need of <span class="hlt">Harmonization</span> and Integration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gatto, Francesca; Katsanevakis, Stelios; Vandekerkhove, Jochen; Zenetos, Argyro; Cardoso, Ana Cristina</p> <p>2013-06-01</p> <p>Europe is severely affected by alien invasions, which impact biodiversity, ecosystem services, economy, and human health. A large number of national, regional, and global online databases provide information on the distribution, pathways of introduction, and impacts of alien species. The sufficiency and efficiency of the current online information systems to assist the European policy on alien species was investigated by a comparative analysis of occurrence data across 43 online databases. Large differences among databases were found which are partially explained by variations in their taxonomical, environmental, and geographical scopes but also by the variable efforts for continuous updates and by inconsistencies on the definition of "alien" or "invasive" species. No single database covered all European environments, countries, and taxonomic groups. In many European countries national databases do not exist, which greatly affects the quality of reported information. To be operational and useful to scientists, managers, and policy makers, online information systems need to be regularly updated through continuous monitoring on a country or regional level. We propose the creation of a network of online interoperable web services through which information in distributed resources can be accessed, aggregated and then used for reporting and further analysis at different geographical and political scales, as an efficient approach to increase the accessibility of information. <span class="hlt">Harmonization</span>, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23609303','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23609303"><span>Evaluation of online information <span class="hlt">sources</span> on alien species in Europe: the need of <span class="hlt">harmonization</span> and integration.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gatto, Francesca; Katsanevakis, Stelios; Vandekerkhove, Jochen; Zenetos, Argyro; Cardoso, Ana Cristina</p> <p>2013-06-01</p> <p>Europe is severely affected by alien invasions, which impact biodiversity, ecosystem services, economy, and human health. A large number of national, regional, and global online databases provide information on the distribution, pathways of introduction, and impacts of alien species. The sufficiency and efficiency of the current online information systems to assist the European policy on alien species was investigated by a comparative analysis of occurrence data across 43 online databases. Large differences among databases were found which are partially explained by variations in their taxonomical, environmental, and geographical scopes but also by the variable efforts for continuous updates and by inconsistencies on the definition of "alien" or "invasive" species. No single database covered all European environments, countries, and taxonomic groups. In many European countries national databases do not exist, which greatly affects the quality of reported information. To be operational and useful to scientists, managers, and policy makers, online information systems need to be regularly updated through continuous monitoring on a country or regional level. We propose the creation of a network of online interoperable web services through which information in distributed resources can be accessed, aggregated and then used for reporting and further analysis at different geographical and political scales, as an efficient approach to increase the accessibility of information. <span class="hlt">Harmonization</span>, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27455301','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27455301"><span>Windmill <span class="hlt">Noise</span> Annoyance, Visual Aesthetics, and Attitudes towards Renewable Energy <span class="hlt">Sources</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Klæboe, Ronny; Sundfør, Hanne Beate</p> <p>2016-07-23</p> <p>A small focused socio-acoustic after-study of annoyance from a windmill park was undertaken after local health officials demanded a health impact study to look into neighborhood complaints. The windmill park consists of 31 turbines and is located in the South of Norway where it affects 179 dwellings. Simple exposure-effect relationships indicate stronger reactions to windmills and wind turbine <span class="hlt">noise</span> than shown internationally, with the caveat that the sample size is small (n = 90) and responses are colored by the existing local conflict. Pulsating swishing sounds and turbine engine hum are the main causes of <span class="hlt">noise</span> annoyance. About 60 per cent of those who participated in the survey were of the opinion that windmills degrade the landscape aesthetically, and were far from convinced that land-based windmills are desirable as a renewable energy <span class="hlt">source</span> (hydropower is an important alternative <span class="hlt">source</span> of renewables in Norway). Attitudes play an important role in addition to visual aesthetics in determining the acceptance of windmills and the resulting <span class="hlt">noise</span> annoyance. To compare results from different wind turbine <span class="hlt">noise</span> studies it seems necessary to assess the impact of important modifying factors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4997432','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4997432"><span>Windmill <span class="hlt">Noise</span> Annoyance, Visual Aesthetics, and Attitudes towards Renewable Energy <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Klæboe, Ronny; Sundfør, Hanne Beate</p> <p>2016-01-01</p> <p>A small focused socio-acoustic after-study of annoyance from a windmill park was undertaken after local health officials demanded a health impact study to look into neighborhood complaints. The windmill park consists of 31 turbines and is located in the South of Norway where it affects 179 dwellings. Simple exposure-effect relationships indicate stronger reactions to windmills and wind turbine <span class="hlt">noise</span> than shown internationally, with the caveat that the sample size is small (n = 90) and responses are colored by the existing local conflict. Pulsating swishing sounds and turbine engine hum are the main causes of <span class="hlt">noise</span> annoyance. About 60 per cent of those who participated in the survey were of the opinion that windmills degrade the landscape aesthetically, and were far from convinced that land-based windmills are desirable as a renewable energy <span class="hlt">source</span> (hydropower is an important alternative <span class="hlt">source</span> of renewables in Norway). Attitudes play an important role in addition to visual aesthetics in determining the acceptance of windmills and the resulting <span class="hlt">noise</span> annoyance. To compare results from different wind turbine <span class="hlt">noise</span> studies it seems necessary to assess the impact of important modifying factors. PMID:27455301</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090041558','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090041558"><span><span class="hlt">Noise-Source</span> Separation Using Internal and Far-Field Sensors for a Full-Scale Turbofan Engine</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hultgren, Lennart S.; Miles, Jeffrey H.</p> <p>2009-01-01</p> <p><span class="hlt">Noise-source</span> separation techniques for the extraction of the sub-dominant combustion <span class="hlt">noise</span> from the total <span class="hlt">noise</span> signatures obtained in static-engine tests are described. Three methods are applied to data from a static, full-scale engine test. Both 1/3-octave and narrow-band results are discussed. The results are used to assess the combustion-<span class="hlt">noise</span> prediction capability of the Aircraft <span class="hlt">Noise</span> Prediction Program (ANOPP). A new additional phase-angle-based discriminator for the three-signal method is also introduced.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSV...338..250B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSV...338..250B"><span><span class="hlt">Source</span> localization of turboshaft engine broadband <span class="hlt">noise</span> using a three-sensor coherence method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blacodon, Daniel; Lewy, Serge</p> <p>2015-03-01</p> <p>Turboshaft engines can become the main <span class="hlt">source</span> of helicopter <span class="hlt">noise</span> at takeoff. Inlet radiation mainly comes from the compressor tones, but aft radiation is more intricate: turbine tones usually are above the audible frequency range and do not contribute to the weighted sound levels; jet is secondary and radiates low <span class="hlt">noise</span> levels. A broadband component is the most annoying but its <span class="hlt">sources</span> are not well known (it is called internal or core <span class="hlt">noise</span>). Present study was made in the framework of the European project TEENI (Turboshaft Engine Exhaust <span class="hlt">Noise</span> Identification). Its main objective was to localize the broadband <span class="hlt">sources</span> in order to better reduce them. Several diagnostic techniques were implemented by the various TEENI partners. As regards ONERA, a first attempt at separating <span class="hlt">sources</span> was made in the past with Turbomeca using a three-signal coherence method (TSM) to reject background non-acoustic <span class="hlt">noise</span>. The main difficulty when using TSM is the assessment of the frequency range where the results are valid. This drawback has been circumvented in the TSM implemented in TEENI. Measurements were made on a highly instrumented Ardiden turboshaft engine in the Turbomeca open-air test bench. Two engine powers (approach and takeoff) were selected to apply TSM. Two internal pressure probes were located in various cross-sections, either behind the combustion chamber (CC), the high-pressure turbine (HPT), the free-turbine first stage (TL), or in four nozzle sections. The third transducer was a far-field microphone located around the maximum of radiation, at 120° from the intake centerline. The key result is that coherence increases from CC to HPT and TL, then decreases in the nozzle up to the exit. Pressure fluctuations from HPT and TL are very coherent with the far-field acoustic spectra up to 700 Hz. They are thus the main acoustic <span class="hlt">source</span> and can be attributed to indirect combustion <span class="hlt">noise</span> (accuracy decreases above 700 Hz because coherence is lower, but far-field sound spectra</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050209957','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050209957"><span>Three-Dimensional Application of DAMAS Methodology for Aeroacoustic <span class="hlt">Noise</span> <span class="hlt">Source</span> Definition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brooks, Thomas F.; Humphreys, William M., Jr.</p> <p>2005-01-01</p> <p>At the 2004 AIAA/CEAS Aeroacoustic Conference, a breakthrough in acoustic microphone array technology was reported by the authors. A Deconvolution Approach for the Mapping of Acoustic <span class="hlt">Sources</span> (DAMAS) was developed which decouples the array design and processing influence from the <span class="hlt">noise</span> being measured, using a simple and robust algorithm. For several prior airframe <span class="hlt">noise</span> studies, it was shown to permit an unambiguous and accurate determination of acoustic <span class="hlt">source</span> position and strength. As a follow-on effort, this paper examines the technique for three-dimensional (3D) applications. First, the beamforming ability for arrays, of different size and design, to focus longitudinally and laterally is examined for a range of <span class="hlt">source</span> positions and frequency. Advantage is found for larger array designs with higher density microphone distributions towards the center. After defining a 3D grid generalized with respect to the array s beamforming characteristics, DAMAS is employed in simulated and experimental <span class="hlt">noise</span> test cases. It is found that spatial resolution is much less sharp in the longitudinal direction in front of the array compared to side-to-side lateral resolution. 3D DAMAS becomes useful for sufficiently large arrays at sufficiently high frequency. But, such can be a challenge to computational capabilities, with regard to the required expanse and number of grid points. Also, larger arrays can strain basic physical modeling assumptions that DAMAS and all traditional array methodologies use. An important experimental result is that turbulent shear layers can negatively impact attainable beamforming resolution. Still, the usefulness of 3D DAMAS is demonstrated by the measurement of landing gear <span class="hlt">noise</span> <span class="hlt">source</span> distributions in a difficult hard-wall wind tunnel environment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040201023','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040201023"><span>Sound <span class="hlt">Source</span> Identification Through Flow Density Measurement and Correlation With Far Field <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, J.; Seasholtz, R. G.</p> <p>2001-01-01</p> <p>Sound <span class="hlt">sources</span> in the plumes of unheated round jets, in the Mach number range 0.6 to 1.8, were investigated experimentally using "casuality" approach, where air density fluctuations in the plumes were correlated with the far field <span class="hlt">noise</span>. The air density was measured using a newly developed Molecular Rayleigh scattering based technique, which did not require any seeding. The reference at the end provides a detailed description of the measurement technique.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.tmp..387L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.tmp..387L"><span>Ambient <span class="hlt">noise</span> tomography with non-uniform <span class="hlt">noise</span> <span class="hlt">sources</span> and low aperture networks: case study of deep geothermal reservoirs in northern Alsace, France</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lehujeur, Maximilien; Vergne, Jérôme; Maggi, Alessia; Schmittbuhl, Jean</p> <p>2016-10-01</p> <p>We developed and applied a method for ambient <span class="hlt">noise</span> surface wave tomography that can deal with <span class="hlt">noise</span> cross-correlation functions governed to first order by a non-uniform distribution of the ambient seismic <span class="hlt">noise</span> <span class="hlt">sources</span>. The method inverts the azimuthal distribution of <span class="hlt">noise</span> <span class="hlt">sources</span> that are assumed to be far from the network, together with the spatial variations of the phase and group velocities on an optimized irregular grid. Direct modeling of the two-sided <span class="hlt">noise</span> correlation functions avoids dispersion curve picking on every station pair and minimizes analyst intervention. The method involves station pairs spaced by distances down to a fraction of a wavelength, thereby bringing additional information for tomography. After validating the method on synthetic data, we applied it to a set of long-term continuous waveforms acquired around the geothermal sites at Soultz-sous-Forêts and Rittershoffen (Northern Alsace, France). For networks with limited aperture, we show that taking the azimuthal variations of the <span class="hlt">noise</span> energy into account has significant impact on the surface wave dispersion maps. We obtained regional phase and group velocity models in the 1-7 s period range, which is sensitive to the structures encompassing the geothermal reservoirs. The ambient <span class="hlt">noise</span> in our dataset originates from two main directions, the northern Atlantic Ocean and the Mediterranean Sea, and is dominated by the first Rayleigh wave overtone in the 2 - 5 s period range.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.208..193L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.208..193L"><span>Ambient <span class="hlt">noise</span> tomography with non-uniform <span class="hlt">noise</span> <span class="hlt">sources</span> and low aperture networks: case study of deep geothermal reservoirs in northern Alsace, France</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lehujeur, Maximilien; Vergne, Jérôme; Maggi, Alessia; Schmittbuhl, Jean</p> <p>2017-01-01</p> <p>We developed and applied a method for ambient <span class="hlt">noise</span> surface wave tomography that can deal with <span class="hlt">noise</span> cross-correlation functions governed to first order by a non-uniform distribution of the ambient seismic <span class="hlt">noise</span> <span class="hlt">sources</span>. The method inverts the azimuthal distribution of <span class="hlt">noise</span> <span class="hlt">sources</span> that are assumed to be far from the network, together with the spatial variations of the phase and group velocities on an optimized irregular grid. Direct modelling of the two-sided <span class="hlt">noise</span> correlation functions avoids dispersion curve picking on every station pair and minimizes analyst intervention. The method involves station pairs spaced by distances down to a fraction of a wavelength, thereby bringing additional information for tomography. After validating the method on synthetic data, we applied it to a set of long-term continuous waveforms acquired around the geothermal sites at Soultz-sous-Forêts and Rittershoffen (Northern Alsace, France). For networks with limited aperture, we show that taking the azimuthal variations of the <span class="hlt">noise</span> energy into account has significant impact on the surface wave dispersion maps. We obtained regional phase and group velocity models in the 1-7 s period range, which is sensitive to the structures encompassing the geothermal reservoirs. The ambient <span class="hlt">noise</span> in our dataset originates from two main directions, the northern Atlantic Ocean and the Mediterranean Sea, and is dominated by the first Rayleigh wave overtone in the 2-5 s period range.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4749559','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4749559"><span><span class="hlt">Sources</span> of <span class="hlt">noise</span> during accumulation of evidence in unrestrained and voluntarily head-restrained rats</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Scott, Benjamin B; Constantinople, Christine M; Erlich, Jeffrey C; Tank, David W; Brody, Carlos D</p> <p>2015-01-01</p> <p>Decision-making behavior is often characterized by substantial variability, but its <span class="hlt">source</span> remains unclear. We developed a visual accumulation of evidence task designed to quantify <span class="hlt">sources</span> of <span class="hlt">noise</span> and to be performed during voluntary head restraint, enabling cellular resolution imaging in future studies. Rats accumulated discrete numbers of flashes presented to the left and right visual hemifields and indicated the side that had the greater number of flashes. Using a signal-detection theory-based model, we found that the standard deviation in their internal estimate of flash number scaled linearly with the number of flashes. This indicates a major <span class="hlt">source</span> of <span class="hlt">noise</span> that, surprisingly, is not consistent with the widely used 'drift-diffusion modeling' (DDM) approach but is instead closely related to proposed models of numerical cognition and counting. We speculate that this form of <span class="hlt">noise</span> could be important in accumulation of evidence tasks generally. DOI: http://dx.doi.org/10.7554/eLife.11308.001 PMID:26673896</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23988431','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23988431"><span>Improved PHIP polarization using a precision, low <span class="hlt">noise</span>, voltage controlled current <span class="hlt">source</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn</p> <p>2013-10-01</p> <p>Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage <span class="hlt">source</span> (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current <span class="hlt">source</span> (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low <span class="hlt">noise</span> VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low <span class="hlt">noise</span>, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low <span class="hlt">noise</span>, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low <span class="hlt">noise</span> and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f <span class="hlt">noise</span>, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1035153','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1035153"><span>Non-Uniform Contrast and <span class="hlt">Noise</span> Correction for Coded <span class="hlt">Source</span> Neutron Imaging</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Santos-Villalobos, Hector J; Bingham, Philip R</p> <p>2012-01-01</p> <p>Since the first application of neutron radiography in the 1930s, the field of neutron radiography has matured enough to develop several applications. However, advances in the technology are far from concluded. In general, the resolution of scintillator-based detection systems is limited to the $10\\mu m$ range, and the relatively low neutron count rate of neutron <span class="hlt">sources</span> compared to other illumination <span class="hlt">sources</span> restricts time resolved measurement. One path toward improved resolution is the use of magnification; however, to date neutron optics are inefficient, expensive, and difficult to develop. There is a clear demand for cost-effective scintillator-based neutron imaging systems that achieve resolutions of $1 \\mu m$ or less. Such imaging system would dramatically extend the application of neutron imaging. For such purposes a coded <span class="hlt">source</span> imaging system is under development. The current challenge is to reduce artifacts in the reconstructed coded <span class="hlt">source</span> images. Artifacts are generated by non-uniform illumination of the <span class="hlt">source</span>, gamma rays, dark current at the imaging sensor, and system <span class="hlt">noise</span> from the reconstruction kernel. In this paper, we describe how to pre-process the coded signal to reduce <span class="hlt">noise</span> and non-uniform illumination, and how to reconstruct the coded signal with three reconstruction methods correlation, maximum likelihood estimation, and algebraic reconstruction technique. We illustrates our results with experimental examples.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20050186648&hterms=gear+teeth+torque&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dgear%2Bteeth%2Btorque','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20050186648&hterms=gear+teeth+torque&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dgear%2Bteeth%2Btorque"><span>Experimentation Toward the Analysis of Gear <span class="hlt">Noise</span> <span class="hlt">Sources</span> Controlled by Sliding Friction and Surface Roughness</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Asnani, Vivake M.</p> <p>2004-01-01</p> <p>In helicopters and other rotorcraft, the gearbox is a major <span class="hlt">source</span> of <span class="hlt">noise</span> and vibration (N&V). The two N&V excitation mechanisms are the relative displacements between mating gears (transmission errors) and the friction associated with sliding between gear teeth. Historically, transmission errors have been minimized via improved manufacturing accuracies and tooth modifications. Yet, at high torque loads, <span class="hlt">noise</span> levels are still relatively high though transmission errors might be somewhat minimal. This suggests that sliding friction is indeed a dominant <span class="hlt">noise</span> <span class="hlt">source</span> for high power density rotorcraft gearboxes. In reality, friction <span class="hlt">source</span> mechanism is associated with surface roughness, lubrication regime properties, time-varying friction forces/torques and gear-mesh interface dynamics. Currently, the nature of these mechanisms is not well understood, while there is a definite need for analytical tools that incorporate sliding resistance and surface roughness, and predict their effects on the vibro- acoustic behavior of gears. Toward this end, an experiment was conducted to collect sound and vibration data on the NASA Glenn Gear-<span class="hlt">Noise</span> Rig. Three iterations of the experiment were accomplished: Iteration 1 tested a baseline set of gears to establish a benchmark. Iteration 2 used a gear-set with low surface asperities to reduce the sliding friction excitation. Iteration 3 incorporated low viscosity oil with the baseline set of gears to examine the effect of lubrication. The results from this experiment will contribute to a two year project in collaboration with the Ohio State University to develop the necessary mathematical and computer models for analyzing geared systems and explain key physical phenomena seen in experiments. Given the importance of sliding friction in the gear dynamic and vibro-acoustic behavior of rotorcraft gearboxes, there is considerable potential for research & developmental activities. Better models and understanding will lead to quiet and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.205..715W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.205..715W"><span>Correction of phase velocity bias caused by strong directional <span class="hlt">noise</span> <span class="hlt">sources</span> in high-frequency ambient <span class="hlt">noise</span> tomography: a case study in Karamay, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Kai; Luo, Yinhe; Yang, Yingjie</p> <p>2016-05-01</p> <p>We collect two months of ambient <span class="hlt">noise</span> data recorded by 35 broad-band seismic stations in a 9 × 11 km area (1-3 km station interval) near Karamay, China, and do cross-correlation of <span class="hlt">noise</span> data between all station pairs. Array beamforming analysis of the ambient <span class="hlt">noise</span> data shows that ambient <span class="hlt">noise</span> <span class="hlt">sources</span> are unevenly distributed and the most energetic ambient <span class="hlt">noise</span> mainly comes from azimuths of 40°-70°. As a consequence of the strong directional <span class="hlt">noise</span> <span class="hlt">sources</span>, surface wave components of the cross-correlations at 1-5 Hz show clearly azimuthal dependence, and direct dispersion measurements from cross-correlations are strongly biased by the dominant <span class="hlt">noise</span> energy. This bias renders that the dispersion measurements from cross-correlations do not accurately reflect the interstation velocities of surface waves propagating directly from one station to the other, that is, the cross-correlation functions do not retrieve empirical Green's functions accurately. To correct the bias caused by unevenly distributed <span class="hlt">noise</span> <span class="hlt">sources</span>, we adopt an iterative inversion procedure. The iterative inversion procedure, based on plane-wave modeling, includes three steps: (1) surface wave tomography, (2) estimation of ambient <span class="hlt">noise</span> energy and biases and (3) phase velocities correction. First, we use synthesized data to test the efficiency and stability of the iterative procedure for both homogeneous and heterogeneous media. The testing results show that: (1) the amplitudes of phase velocity bias caused by directional <span class="hlt">noise</span> <span class="hlt">sources</span> are significant, reaching ˜2 and ˜10 per cent for homogeneous and heterogeneous media, respectively; (2) phase velocity bias can be corrected by the iterative inversion procedure and the convergence of inversion depends on the starting phase velocity map and the complexity of the media. By applying the iterative approach to the real data in Karamay, we further show that phase velocity maps converge after 10 iterations and the phase velocity maps obtained using</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JGRA..116.3104S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JGRA..116.3104S"><span>Constraints on coronal turbulence models from <span class="hlt">source</span> sizes of <span class="hlt">noise</span> storms at 327 MHz</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Subramanian, Prasad; Cairns, Iver</p> <p>2011-03-01</p> <p>We seek to reconcile observations of small <span class="hlt">source</span> sizes in the solar corona at 327 MHz with predictions of scattering models that incorporate refractive index effects, inner scale effects, and a spherically diverging wavefront. We use an empirical prescription for the turbulence amplitude CN2(R) based on very long baseline interferometry observations by Spangler et al. of compact radio <span class="hlt">sources</span> against the solar wind for heliocentric distances R ≈ 10-50 R⊙. We use the Coles and <span class="hlt">Harmon</span> model for the inner scale li(R), which is presumed to arise from cyclotron damping. In view of the prevalent uncertainty in the power law index that characterizes solar wind turbulence at various heliocentric distances, we retain this index as a free parameter. We find that the inclusion of spherical divergence effects suppresses the predicted <span class="hlt">source</span> size substantially. We also find that inner scale effects significantly reduce the predicted <span class="hlt">source</span> size. An important general finding for solar <span class="hlt">sources</span> is that the calculations substantially underpredict the observed <span class="hlt">source</span> size. Three possible, nonexclusive, interpretations of this general result are proposed. First and simplest, future observations with better angular resolution will detect much smaller <span class="hlt">sources</span>. Consistent with this, previous observations of small <span class="hlt">sources</span> in the corona at metric wavelengths are limited by the instrument resolution. Second, the spatially varying level of turbulence CN2(R) is much larger in the inner corona than predicted by straightforward extrapolation sunward of the empirical prescription, which was based on observations between 10 and 50 R⊙. Either the functional form or the constant of proportionality could be different. Third, perhaps the inner scale is smaller than the model, leading to increased scattering. These results and interpretations are discussed and compared with earlier work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22225031','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22225031"><span>A comparison between exposure-response relationships for wind turbine annoyance and annoyance due to other <span class="hlt">noise</span> <span class="hlt">sources</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Janssen, Sabine A; Vos, Henk; Eisses, Arno R; Pedersen, Eja</p> <p>2011-12-01</p> <p>Surveys have shown that <span class="hlt">noise</span> from wind turbines is perceived as annoying by a proportion of residents living in their vicinity, apparently at much lower <span class="hlt">noise</span> levels than those inducing annoyance due to other environmental <span class="hlt">sources</span>. The aim of the present study was to derive the exposure-response relationship between wind turbine <span class="hlt">noise</span> exposure in L(den) and the expected percentage annoyed residents and to compare it to previously established relationships for industrial <span class="hlt">noise</span> and transportation <span class="hlt">noise</span>. In addition, the influence of several individual and situational factors was assessed. On the basis of available data from two surveys in Sweden (N=341, N=754) and one survey in the Netherlands (N=725), a relationship was derived for annoyance indoors and for annoyance outdoors at the dwelling. In comparison to other <span class="hlt">sources</span> of environmental <span class="hlt">noise</span>, annoyance due to wind turbine <span class="hlt">noise</span> was found at relatively low <span class="hlt">noise</span> exposure levels. Furthermore, annoyance was lower among residents who received economical benefit from wind turbines and higher among residents for whom the wind turbine was visible from the dwelling. Age and <span class="hlt">noise</span> sensitivity had similar effects on annoyance to those found in research on annoyance by other <span class="hlt">sources</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhDT.......106D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhDT.......106D"><span>Supersonic jet <span class="hlt">noise</span> prediction and <span class="hlt">noise</span> <span class="hlt">source</span> investigation for realistic baseline and chevron nozzles based on hybrid RANS/LES simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Du, Yongle</p> <p></p> <p>Jet <span class="hlt">noise</span> simulations have been performed for a military-style baseline nozzle and a chevron nozzle with design Mach numbers of Md = 1:5 operating at several off-design conditions. The objective of the current numerical study is to provide insight into the <span class="hlt">noise</span> generation mechanisms of shock-containing supersonic hot jets and the <span class="hlt">noise</span> reduction mechanisms of chevron nozzles. A hybrid methodology combining advanced CFD technologies and the acoustic analogy is used for supersonic jet <span class="hlt">noise</span> simulations. Unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved to predict the turbulent <span class="hlt">noise</span> <span class="hlt">sources</span> in the jet flows. A modified version of the Detached Eddy Simulation (DES) approach is used to avoid excessive damping of fine scale turbulent fluctuations. A multiblock structured mesh topology is used to represent complex nozzle geometries, including the faceted inner contours and finite nozzle thickness. A block interface condition is optimized for the complex multiblock mesh topology to avoid the centerline singularity. A fourth-order Dispersion-Relation-Preserving (DRP) scheme is used for spatial discretization. To enable efficient calculations, a dual time-stepping method is used in addition to parallel computation using MPI. Both multigrid and implicit residual smoothing are used to accelerate the convergence rate of sub-iterations in the fictitious time domain. <span class="hlt">Noise</span> predictions are made with the permeable surface Ffowcs Williams and Hawkings (FWH) solution. All the numerical methods have been implemented in the jet flow simulation code "CHOPA" and the <span class="hlt">noise</span> prediction code "PSJFWH". The computer codes have been validated with several benchmark cases. A preliminary study has been performed for an under-expanded baseline nozzle jet with Mj = 1:56 to validate the accuracy of the jet <span class="hlt">noise</span> simulations. The results show that grid refinement around the jet potential core and the use of a lower artificial dissipation improve the resolution of the predicted</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28000727','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28000727"><span>Evidence of Cnidarians sensitivity to sound after exposure to low frequency <span class="hlt">noise</span> underwater <span class="hlt">sources</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Solé, Marta; Lenoir, Marc; Fontuño, José Manuel; Durfort, Mercè; van der Schaar, Mike; André, Michel</p> <p>2016-12-21</p> <p>Jellyfishes represent a group of species that play an important role in oceans, particularly as a food <span class="hlt">source</span> for different taxa and as a predator of fish larvae and planktonic prey. The massive introduction of artificial sound <span class="hlt">sources</span> in the oceans has become a concern to science and society. While we are only beginning to understand that non-hearing specialists like cephalopods can be affected by anthropogenic <span class="hlt">noises</span> and regulation is underway to measure European water <span class="hlt">noise</span> levels, we still don't know yet if the impact of sound may be extended to other lower level taxa of the food web. Here we exposed two species of Mediterranean Scyphozoan medusa, Cotylorhiza tuberculata and Rhizostoma pulmo to a sweep of low frequency sounds. Scanning electron microscopy (SEM) revealed injuries in the statocyst sensory epithelium of both species after exposure to sound, that are consistent with the manifestation of a massive acoustic trauma observed in other species. The presence of acoustic trauma in marine species that are not hearing specialists, like medusa, shows the magnitude of the problem of <span class="hlt">noise</span> pollution and the complexity of the task to determine threshold values that would help building up regulation to prevent permanent damage of the ecosystems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5175278','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5175278"><span>Evidence of Cnidarians sensitivity to sound after exposure to low frequency <span class="hlt">noise</span> underwater <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Solé, Marta; Lenoir, Marc; Fontuño, José Manuel; Durfort, Mercè; van der Schaar, Mike; André, Michel</p> <p>2016-01-01</p> <p>Jellyfishes represent a group of species that play an important role in oceans, particularly as a food <span class="hlt">source</span> for different taxa and as a predator of fish larvae and planktonic prey. The massive introduction of artificial sound <span class="hlt">sources</span> in the oceans has become a concern to science and society. While we are only beginning to understand that non-hearing specialists like cephalopods can be affected by anthropogenic <span class="hlt">noises</span> and regulation is underway to measure European water <span class="hlt">noise</span> levels, we still don’t know yet if the impact of sound may be extended to other lower level taxa of the food web. Here we exposed two species of Mediterranean Scyphozoan medusa, Cotylorhiza tuberculata and Rhizostoma pulmo to a sweep of low frequency sounds. Scanning electron microscopy (SEM) revealed injuries in the statocyst sensory epithelium of both species after exposure to sound, that are consistent with the manifestation of a massive acoustic trauma observed in other species. The presence of acoustic trauma in marine species that are not hearing specialists, like medusa, shows the magnitude of the problem of <span class="hlt">noise</span> pollution and the complexity of the task to determine threshold values that would help building up regulation to prevent permanent damage of the ecosystems. PMID:28000727</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3460980','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3460980"><span><span class="hlt">Noise</span> suppression of a dipole <span class="hlt">source</span> by tensioned membrane with side-branch cavities</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Liu, Y.; Choy, Y. S.; Huang, L.; Cheng, L.</p> <p>2012-01-01</p> <p>Reducing the ducted-fan <span class="hlt">noise</span> at the low frequency range remains a big technical challenge. This study presents a passive approach to directly suppress the dipole sound radiation from an axial-flow fan housed by a tensioned membrane with cavity backing. The method aims at achieving control of low frequency <span class="hlt">noise</span> with an appreciable bandwidth. The use of the membrane not only eliminates the aerodynamic loss of flow, but also provides flexibility in controlling the range of the stopband with high insertion loss by varying its tension and mass. A three-dimensional model is presented which allows the performance of the proposed device to be explored analytically. With the proper design, this device can achieve a <span class="hlt">noise</span> reduction of 5 dB higher than the empty expansion cavity recently proposed by Huang et al. [J. Acoust. Soc. Am. 128, 152–163 (2010)]. Through the detailed modal analysis, even in vacuo modes of the membrane vibration are found to play an important role in the suppression of sound radiation from the dipole <span class="hlt">source</span>. Experimental validation is conducted with a loudspeaker as the dipole <span class="hlt">source</span> and good agreement between the predicted and measured insertion loss is achieved. PMID:22978868</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22978868','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22978868"><span><span class="hlt">Noise</span> suppression of a dipole <span class="hlt">source</span> by tensioned membrane with side-branch cavities.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Y; Choy, Y S; Huang, L; Cheng, L</p> <p>2012-09-01</p> <p>Reducing the ducted-fan <span class="hlt">noise</span> at the low frequency range remains a big technical challenge. This study presents a passive approach to directly suppress the dipole sound radiation from an axial-flow fan housed by a tensioned membrane with cavity backing. The method aims at achieving control of low frequency <span class="hlt">noise</span> with an appreciable bandwidth. The use of the membrane not only eliminates the aerodynamic loss of flow, but also provides flexibility in controlling the range of the stopband with high insertion loss by varying its tension and mass. A three-dimensional model is presented which allows the performance of the proposed device to be explored analytically. With the proper design, this device can achieve a <span class="hlt">noise</span> reduction of 5 dB higher than the empty expansion cavity recently proposed by Huang et al. [J. Acoust. Soc. Am. 128, 152-163 (2010)]. Through the detailed modal analysis, even in vacuo modes of the membrane vibration are found to play an important role in the suppression of sound radiation from the dipole <span class="hlt">source</span>. Experimental validation is conducted with a loudspeaker as the dipole <span class="hlt">source</span> and good agreement between the predicted and measured insertion loss is achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...637979S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...637979S"><span>Evidence of Cnidarians sensitivity to sound after exposure to low frequency <span class="hlt">noise</span> underwater <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Solé, Marta; Lenoir, Marc; Fontuño, José Manuel; Durfort, Mercè; van der Schaar, Mike; André, Michel</p> <p>2016-12-01</p> <p>Jellyfishes represent a group of species that play an important role in oceans, particularly as a food <span class="hlt">source</span> for different taxa and as a predator of fish larvae and planktonic prey. The massive introduction of artificial sound <span class="hlt">sources</span> in the oceans has become a concern to science and society. While we are only beginning to understand that non-hearing specialists like cephalopods can be affected by anthropogenic <span class="hlt">noises</span> and regulation is underway to measure European water <span class="hlt">noise</span> levels, we still don’t know yet if the impact of sound may be extended to other lower level taxa of the food web. Here we exposed two species of Mediterranean Scyphozoan medusa, Cotylorhiza tuberculata and Rhizostoma pulmo to a sweep of low frequency sounds. Scanning electron microscopy (SEM) revealed injuries in the statocyst sensory epithelium of both species after exposure to sound, that are consistent with the manifestation of a massive acoustic trauma observed in other species. The presence of acoustic trauma in marine species that are not hearing specialists, like medusa, shows the magnitude of the problem of <span class="hlt">noise</span> pollution and the complexity of the task to determine threshold values that would help building up regulation to prevent permanent damage of the ecosystems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ACPD...1523989A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ACPD...1523989A"><span>AIRUSE-LIFE+: a <span class="hlt">harmonized</span> PM speciation and <span class="hlt">source</span> apportionment in 5 Southern European cities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Amato, F.; Alastuey, A.; Karanasiou, A.; Lucarelli, F.; Nava, S.; Calzolai, G.; Severi, M.; Becagli, S.; Gianelle, V. L.; Colombi, C.; Alves, C.; Custódio, D.; Nunes, T.; Cerqueira, M.; Pio, C.; Eleftheriadis, K.; Diapouli, E.; Reche, C.; Minguillón, M. C.; Manousakas, M.; Maggos, T.; Vratolis, S.; Harrison, R. M.; Querol, X.</p> <p>2015-09-01</p> <p>The AIRUSE-LIFE+ project aims at characterising similarities and heterogeneities in PM <span class="hlt">sources</span> and contributions in urban areas from the Southern Europe. Once the main PMx <span class="hlt">sources</span> are identified, AIRUSE aims at developing and testing the efficiency of specific and non-specific measures to improve urban air quality. This article reports the results of the <span class="hlt">source</span> apportionment of PM10 and PM2.5 conducted at three urban background sites (Barcelona, Florence and Milan, BCN-UB, FI-UB, MLN-UB) one sub-urban background site (Athens, ATH-SUB) and one traffic site (Porto, POR-TR). After collecting 1047 PM10 and 1116 PM2.5 24 h samples from January 2013 to February 2014 simultaneously at the 5 cities, these were analysed for the contents of OC, EC, anions, cations, major and trace elements and levoglucosan. The USEPA PMF5 receptor model was applied to these datasets in a harmonised way for each city. The sum of vehicle exhaust and non-exhaust contributes within 3.9-10.8 μg m-3 (16-32 %) to PM10 and 2.3-9.4 μg m-3 (15-36 %) to PM2.5, although a fraction of secondary nitrate is also traffic-related but could not be estimated. Important contributions arise from secondary particles (nitrate, sulphate and organics) in PM2.5 (37-82 %) but also in PM10 (40-71 %) mostly at background sites, revealing the importance of abating gaseous precursors in designing air quality plans. Biomass burning (BB) contributions vary widely, from 14-24 % of PM10 in POR-TR, MLN-UB and FI-UB, 7 % in ATH-SUB to < 2 % in BCN-UB. In PM2.5, BB is the second most important <span class="hlt">source</span> in MLN-UB (21 %) and in POR-TR (18 %), the third one in FI-UB (21 %) and ATH-SUB (11 %), but again negligible (< 2 %) in BCN-UB. This large variability among cities is mostly due to the degree of penetration of biomass for residential heating. In Barcelona natural gas is very well supplied across the city and used as fuel in 96 % of homes, while, in other cities, PM levels increase on an annual basis by 1-9 μg m-3 due to this</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AIPC.1495..242C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AIPC.1495..242C"><span>A perspective on 30 years of progress in ambient <span class="hlt">noise</span>: <span class="hlt">Source</span> mechanisms and the characteristics of the sound field</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cato, Douglas H.</p> <p>2012-11-01</p> <p>The last 30 years has seen substantial progress in ocean ambient <span class="hlt">noise</span> research, particularly in understanding the mechanisms of sound generation by the <span class="hlt">sources</span> of ambient <span class="hlt">noise</span>, the way in which the <span class="hlt">noise</span> field is affected by sound propagation, and improvements in quantifying the relationship between <span class="hlt">noise</span> and environmental parameters. This has led to significant improvements in <span class="hlt">noise</span> prediction. Activity was probably strongest in the 1980s and 1990s, as evident, for example, in the Sea Surface Sound conferences and their published proceedings (four over 10 years). Although much of the application has been to sonar, there has also been interest in using ambient <span class="hlt">noise</span> to measure properties of the environment and in its significance to marine life. There have been significant changes in the ambient <span class="hlt">noise</span> itself over the last 30 years. The contribution from human activities appears to have increased, particularly that due to increases in shipping numbers. Biological <span class="hlt">noise</span> has also increased with the significant increases in populations of some whale species following the cessation of broad scale whaling in the 1960s and early 1970s. Concern about the effects of <span class="hlt">noise</span> on marine animals as well as the way they exploit the <span class="hlt">noise</span> has led to renewed interest in ambient <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140008691','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140008691"><span>Comparison of <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Data with Flow Field Data Obtained in Cold Supersonic Jets and Implications Regarding Broadband Shock <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary; Wernet, Mark; Clem, Michelle; Fagan, Amy</p> <p>2013-01-01</p> <p>Phased array <span class="hlt">noise</span> <span class="hlt">source</span> localization have been compared with 2 types of flow field data (BOS and PIV). The data show that: 1) the higher frequency <span class="hlt">noise</span> in a BBSN hump is generated further downstream than the lower frequency <span class="hlt">noise</span>. This is due to a) the shock spacing decreasing and b) the turbulent structure size increasing with distance downstream. 2) BBSN can be created by very weak shocks. 3) BBSN is not created by the strong shocks just downstream of the nozzle because the turbulent structures have not grown large enough to match the shock spacing. 4) The point in the flow where the shock spacing equals the average size of the turbulent structures is a hot spot for shock <span class="hlt">noise</span>. 5) Some of the shocks responsible for producing the first hump also produce the second hump.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910012516','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910012516"><span>A study of rotor broadband <span class="hlt">noise</span> mechanisms and helicopter tail rotor <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Chou, Shau-Tak Rudy</p> <p>1990-01-01</p> <p>The rotor broadband <span class="hlt">noise</span> mechanisms considered are the following: (1) lift fluctuation due to turbulence ingestion; (2) boundary layer/trailing edge interaction; (3) tip vortex formation; and (4) turbulent vortex shedding from blunt trailing edge. Predictions show good agreement with available experimental data. The study shows that inflow turbulence is the most important broadband <span class="hlt">noise</span> <span class="hlt">source</span> for typical helicopters' main rotors at low- and mid-frequencies. Due to the size difference, isolated helicopter tail rotor broadband <span class="hlt">noise</span> is not important compared to the much louder main rotor broadband <span class="hlt">noise</span>. However, the inflow turbulence <span class="hlt">noise</span> from a tail rotor can be very significant because it is operating in a highly turbulent environment, ingesting wakes from upstream components of the helicopter. The study indicates that the main rotor turbulent wake is the most important <span class="hlt">source</span> of tail rotor broadband <span class="hlt">noise</span>. The <span class="hlt">harmonic</span> <span class="hlt">noise</span> due to ingestion of main rotor tip vortices is studied.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AIPC..922...95R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AIPC..922...95R"><span>Study of MOSFET Low Frequency <span class="hlt">Noise</span> <span class="hlt">Source</span> Fluctuation Using a New Fully Programmable Test Set-up</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rochereau, K.; Blanc, C.; Marin, M.</p> <p>2007-07-01</p> <p>In this paper we aim to demonstrate the huge spread that can be seen on flicker (1/f) <span class="hlt">noise</span> figures of advanced MOS devices. In order to do so, we set up a new fully programmable test bench including low frequency <span class="hlt">noise</span> (1Hz-few Mhz) measurement capability. Once all the hurdles we faced during measurement optimization have been overpassed, we show indeed 1/f <span class="hlt">noise</span> dispersion over wafer is far larger than simple drive current one. We introduce the first steps of a global study of <span class="hlt">noise</span> <span class="hlt">source</span> fluctuation that has still to be led.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970028895','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970028895"><span>Low Speed, 2-D Rotor/Stator Active <span class="hlt">Noise</span> Control at the <span class="hlt">Source</span> Demonstration</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Simonich, John C.; Kousen, Ken A.; Zander, Anthony C.; Bak, Michael; Topol, David A.</p> <p>1997-01-01</p> <p>Wake/blade-row interaction <span class="hlt">noise</span> produced by the Annular Cascade Facility at Purdue University has been modeled using the LINFLO analysis. Actuator displacements needed for complete cancellation of the propagating acoustic response modes have been determined, along with the associated actuator power requirements. As an alternative, weighted least squares minimization of the total far-field sound power using individual actuators has also been examined. Attempts were made to translate the two-dimensional aerodynamic results into three-dimensional actuator requirements. The results lie near the limit of present actuator technology. In order to investigate the concept of <span class="hlt">noise</span> control at the <span class="hlt">source</span> for active rotor/stator <span class="hlt">noise</span> control at the <span class="hlt">source</span>, various techniques for embedding miniature actuators into vanes were examined. Numerous miniature speaker arrangements were tested and analyzed to determine their suitability as actuators for a demonstration test in the Annular Cascade Facility at Purdue. The best candidates demonstrated marginal performance. An alternative concept to using vane mounted speakers as control actuators was developed and tested. The concept uses compression drivers which are mounted externally to the stator vanes. Each compression driver is connected via a tube to an air cavity in the stator vane, from which the driver signal radiates into the working section of the experimental rig. The actual locations and dimensions of the actuators were used as input parameters for a LINFLO computational analysis of the actuator displacements required for complete cancellation of tones in the Purdue experimental rig. The actuators were designed and an arrangement determined which is compatible with the Purdue experimental rig and instrumentation. Experimental tests indicate that the actuators are capable of producing equivalent displacements greater than the requirements predicted by the LINFLO analysis. The acoustic output of the actuators was also found</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.S52C..03A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.S52C..03A"><span>Numerical wave modelling for seismo-acoustic <span class="hlt">noise</span> <span class="hlt">sources</span>: wave model accuracy issues and evidence for variable seismic attenuation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ardhuin, F.; Lavanant, T.; Obrebski, M. J.; Marié, L.; Royer, J.</p> <p>2012-12-01</p> <p>Nonlinear wave-wave interactions generate <span class="hlt">noise</span> that numerical ocean wave models may simulate. The accuracy of the <span class="hlt">noise</span> <span class="hlt">source</span> predicted by the theory of Longuet-Higgins (1950) and Hasselmann (1963) depends on the realism of the directional wave distribution, which is generally not very well known. Numerical <span class="hlt">noise</span> models developed by Kedar et al. (2008) and Ardhuin et al. (2010) also suffer from poorly known seismic wave propagation and attenuation properties. Here, several seismic and ocean pressure records are used here to assess the effects of wave modelling errors on the magnitude of <span class="hlt">noise</span> <span class="hlt">sources</span>. Measurements within 200~m from the sea surface are dominated by acoustic-gravity modes, for which bottom effects are negligible. These data show that directional wave spectra are well enough reproduced to estimate seismo-acoustic <span class="hlt">noise</span> <span class="hlt">sources</span> at frequencies below 0.3~Hz, whith an underestimation of the <span class="hlt">noise</span> level by about 50%. In larger water depths, the comparison of a numerical <span class="hlt">noise</span> model with hydrophone records from two open-ocean sites near Hawaii and Kerguelen islands reveal that a) deep ocean acoustic <span class="hlt">noise</span> at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, and is well predicted up to 0.4~Hz. b) In particular, evidence of the vertical modes expected theoretically is given by the local maxima in the <span class="hlt">noise</span> spectrum. c) <span class="hlt">noise</span> above 0.6 Hz is not well modeled probably due to a poor estimate of the directional properties of high frequency wind-waves, d) the <span class="hlt">noise</span> level is strongly influenced by bottom properties, in particular the presence of sediments. Further, for continental coastal seismic stations, an accurate model of <span class="hlt">noise</span> level variability near the <span class="hlt">noise</span> spectral peak requires an accurate modelling of coastal reflection (Ardhuin and Roland JGR 2012). In cases where <span class="hlt">noise</span> <span class="hlt">sources</span> are confined to a small area (e.g. Obrebski et al. GRL 2012), the <span class="hlt">source</span> amplitude may be factored out, allowing an estimate of seismic attenuation rates</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...362...39X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...362...39X"><span><span class="hlt">Noise</span> control of dipole <span class="hlt">source</span> by using micro-perforated panel housing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xi, Q.; Choy, Y. S.; Cheng, L.; Tang, S. K.</p> <p>2016-02-01</p> <p>Mitigating low-frequency <span class="hlt">noise</span> in a small ducted fan system such as hairdryer is still a technical challenge. Traditional duct lining with porous materials work ineffectively due to the limitation of its thickness and length of small domestic product with ducted fans. This study presents a passive approach to directly suppress the sound radiation from the fan housed by a short microperforated panel covered with a shallow cavity backing. The <span class="hlt">noise</span> suppression is achieved by the sound cancellation between sound fields from a fan of a dipole nature and sound radiation from a vibrating panel via vibro-acoustic coupling and by sound absorption in micro-perforations to widen the stopband. A two-dimensional theoretical model, capable of dealing with strong coupling among the vibrating micro-perforated panel, sound radiation from the dipole <span class="hlt">source</span>, sound fields inside the cavity and the duct is developed. Through modal analysis, it is found that the even modes of the panel vibration are very important to cancel the sound radiation from the dipole <span class="hlt">source</span>. Experimental validation is conducted with a loudspeaker to simulate the dipole <span class="hlt">source</span>, and good agreement between the predicted and measured insertion loss (IL) is achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRB..121.4031S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRB..121.4031S"><span>Sensitivity of earthquake <span class="hlt">source</span> inversions to atmospheric <span class="hlt">noise</span> and corrections of InSAR data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scott, Chelsea Phipps; Lohman, Rowena Benfer</p> <p>2016-05-01</p> <p>Tropospheric phase delays pose a major challenge to InSAR (interferometric synthetic aperture radar)-based studies of tectonic deformation. One approach to the mitigation of effects from tropospheric <span class="hlt">noise</span> is the application of elevation-dependent corrections based on empirical fits between elevation and interferometric phase. We quantify the effects of corrections with a range of complexity on inferred earthquake <span class="hlt">source</span> parameters using synthetic interferograms with known atmospheric characteristics. We infer statistical properties of the stratified component of the atmosphere using pressure, temperature, and water vapor data from the North America Regional Reanalysis model over our region of interest in the Basin and Range province of the western United States. The statistics of the simulated atmospheric turbulence are estimated from InSAR and Global Positioning System data. We demonstrate potentially significant improvements in the precision of earthquake magnitude, depth, and dip estimates for several synthetic earthquake focal mechanisms following a correction for spatially variable atmospheric characteristics, relative to cases where the correction is based on a uniform delay versus elevation relationship or where no correction is applied. We apply our approach to the 1992 M5.6 Little Skull Mountain, Nevada, earthquake and demonstrate that the earthquake <span class="hlt">source</span> parameter error bounds decrease in size after applying the atmospheric corrections. Our approach for evaluating the impact of atmospheric <span class="hlt">noise</span> on inferred fault parameters is easily adaptable to other regions and <span class="hlt">source</span> mechanisms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5665180','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5665180"><span>Subcritical measurements using the /sup 252/Cf <span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; Blakeman, E.D.; Ragan, G.E.; Kryter, R.C.</p> <p>1985-01-01</p> <p>This paper describes recent measurements of the subcritical neutron multiplication factor using the /sup 252/Cf <span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method. This work was supported by a program of collaboration between the United States Department of Energy and the Power Reactor and Nuclear Fuel Development Corporation of Japan related to the development of fast breeder technology. The experiment reported consists of a configuration of two interacting tanks of uranyl nitrate aqueous solution with different uranium concentrations in each tank. The /sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method obtains the subcriticality from the signals of three detectors: the first, a parallel plate ionization chamber with /sup 252/Cf electroplated on one of its plates that is located in or near the system containing the fissile material, and produces an electrical pulse for every spontaneous fission that occurs and thereby serves as a timed <span class="hlt">source</span> of fission neutrons; and the second and third detectors that are placed in or near the system containing fissile material and serve to detect particles from the fission chain multiplication process. 9 refs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920001380','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920001380"><span>Aeroacoustics of Flight Vehicles: Theory and Practice. Volume 1: <span class="hlt">Noise</span> <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hubbard, Harvey H. (Editor)</p> <p>1991-01-01</p> <p>Methodology recommended to evaluate aeroacoustic related problems is provided, and approaches to their solutions are suggested without extensive tables, nomographs, and derivations. Orientation is toward flight vehicles and emphasis is on underlying physical concepts. Theoretical, experimental, and applied aspects are covered, including the main formulations and comparisons of theory and experiment. The topics covered include: propeller and propfan <span class="hlt">noise</span>, rotor <span class="hlt">noise</span>, turbomachinery <span class="hlt">noise</span>, jet <span class="hlt">noise</span> classical theory and experiments, <span class="hlt">noise</span> from turbulent shear flows, jet <span class="hlt">noise</span> generated by large-scale coherent motion, airframe <span class="hlt">noise</span>, propulsive lift <span class="hlt">noise</span>, combustion and core <span class="hlt">noise</span>, and sonic booms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011RScI...82c3513S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011RScI...82c3513S"><span>Low <span class="hlt">noise</span> Kα-band hopping reflectometer based on yttrium iron garnet <span class="hlt">sources</span> at TEXTOR</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Soldatov, S.; Krämer-Flecken, A.; Zorenko, O.</p> <p>2011-03-01</p> <p>The heterodyne hopping reflectometer system based on wide-tuned low <span class="hlt">noise</span> yttrium iron garnet <span class="hlt">sources</span> was developed for TEXTOR experiment. Being installed in 1998 it successfully operates more than 10 years providing the measurements of plasma density fluctuations. Owing to the advance multihorn antennae systems installed at three different positions around the tokamak, the correlation properties as well as the propagation measurements of plasma density fluctuations are realized. The reflectometer operates in ordinary polarization mode providing the access mostly to plasma gradient and pedestal region. The capabilities of the diagnostic are illustrated with the examples of measured fluctuation characteristics in the variety of TEXTOR plasmas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9347E..15Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9347E..15Y"><span>Interferometric coherence measurement and radio frequency <span class="hlt">noise</span> characterization of the 1.3 μm femtosecond intense Stokes continuum from a TZDW <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yao, Yuhong; Knox, Wayne H.</p> <p>2015-02-01</p> <p>Photonic crystal fiber (PCF) with two closely spaced zero dispersion wavelengths (TZDW) offers a unique route to efficient energy transfer to two spectrally localized continua beyond either side of the ZDWs, which we have employed in previous work for mid-IR difference frequency generation and speckle-free red-green-blue generation. In this manuscript, we report the interferometric coherence characterization and radio frequency (RF) <span class="hlt">noise</span> measurements of the Stokes side TZDW component. With a custom-built 1.3 W, 1035 nm, 40 MHz, 240 fs Yb:fiber chirped pulse amplifier as the pump <span class="hlt">source</span>, we use 12 cm of commercially available TZDW PCF to excite the dual narrow-band continua from which the Stokes pulse is filtered out with a 1180 nm long wave pass filter. We achieve 0.8 to 3 nJ of narrow-band pulses within the spectral range of 1200 - 1315 nm at an average power conversion efficiency of 33%. Employing an un-balanced Michelson interferometer, measured mutual spectral coherence of the Stokes pulse is in excess of 0.76 with pump Soliton order as high as N ~70. Its measured RF <span class="hlt">noise</span> spectrum at the first <span class="hlt">harmonic</span> of the laser repetition rate shows less than 8 dBc/Hz increase in relative intensity <span class="hlt">noise</span> (RIN) compared to that of the power amplifier, which is consistent with reported studies employing sub-100 fs pulses from relatively low <span class="hlt">noise</span> oscillators. In contrast to the broadband continuum from a single ZDW PCF wherein severe de-coherence is found with pumping at high soliton order and longer pump pulse width, the reported TZDW fiber <span class="hlt">source</span> shows preservation of intensity stability and phase coherence against variation in pump pulse parameters, which not only attests to the stability of our reported method for mid-IR generation, but also shows promising potential towards an all-fiber, efficient and low <span class="hlt">noise</span> ultrafast <span class="hlt">source</span> that can be helpful for applications such as biomedical deep-tissue imaging.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080047422','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080047422"><span>Time Delay Analysis of Turbofan Engine Direct and Indirect Combustion <span class="hlt">Noise</span> <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miles, Jeffrey Hilton</p> <p>2008-01-01</p> <p>The core <span class="hlt">noise</span> components of a dual spool turbofan engine were separated by the use of a coherence function. A <span class="hlt">source</span> location technique based on adjusting the time delay between the combustor pressure sensor signal and the far-field microphone signal to maximize the coherence and remove as much variation of the phase angle with frequency as possible was used. The discovery was made that for the 130o microphone a 90.027 ms time shift worked best for the frequency band from 0 to 200 Hz while a 86.975 ms time shift worked best for the frequency band from 200 to 400 Hz. Hence, the 0 to 200 Hz band signal took more time than the 200 to 400 Hz band signal to travel the same distance. This suggests the 0 to 200 Hz coherent cross spectral density band is partly due to indirect combustion <span class="hlt">noise</span> attributed to entropy fluctuations, which travel at the flow velocity, interacting with the turbine. The signal in the 200 to 400 Hz frequency band is attributed mostly to direct combustion <span class="hlt">noise</span>. Results are presented herein for engine power settings of 48, 54, and 60 percent of the maximum power setting</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27106340','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27106340"><span>Military jet <span class="hlt">noise</span> <span class="hlt">source</span> imaging using multisource statistically optimized near-field acoustical holography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wall, Alan T; Gee, Kent L; Neilsen, Tracianne B; McKinley, Richard L; James, Michael M</p> <p>2016-04-01</p> <p>The identification of acoustic <span class="hlt">sources</span> is critical to targeted <span class="hlt">noise</span> reduction efforts for jets on high-performance tactical aircraft. This paper describes the imaging of acoustic <span class="hlt">sources</span> from a tactical jet using near-field acoustical holography techniques. The measurement consists of a series of scans over the hologram with a dense microphone array. Partial field decomposition methods are performed to generate coherent holograms. Numerical extrapolation of data beyond the measurement aperture mitigates artifacts near the aperture edges. A multisource equivalent wave model is used that includes the effects of the ground reflection on the measurement. Multisource statistically optimized near-field acoustical holography (M-SONAH) is used to reconstruct apparent <span class="hlt">source</span> distributions between 20 and 1250 Hz at four engine powers. It is shown that M-SONAH produces accurate field reconstructions for both inward and outward propagation in the region spanned by the physical hologram measurement. Reconstructions across the set of engine powers and frequencies suggests that directivity depends mainly on estimated <span class="hlt">source</span> location; <span class="hlt">sources</span> farther downstream radiate at a higher angle relative to the inlet axis. At some frequencies and engine powers, reconstructed fields exhibit multiple radiation lobes originating from overlapped <span class="hlt">source</span> regions, which is a phenomenon relatively recently reported for full-scale jets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1811553N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1811553N"><span>Identifying seismic <span class="hlt">noise</span> <span class="hlt">sources</span> and their amplitude from P wave microseisms.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Neale, Jennifer; Harmon, Nicholas; Srokosz, Meric</p> <p>2016-04-01</p> <p>Understanding <span class="hlt">sources</span> of seismic <span class="hlt">noise</span> is important for a range of applications including seismic imagery, time-lapse, and climate studies. For locating <span class="hlt">sources</span> from seismic data, body waves offer an advantage over surface waves because they can reveal the distance to the <span class="hlt">source</span> as well as direction. Studies have found that body waves do originate from regions predicted by models (Obrebski et al., 2013), where wave interaction intensity and site effect combine to produce the <span class="hlt">source</span> (Ardhuin & Herbers, 2013). Here, we undertake a quantitative comparison between observed body wave microseisms and modelled <span class="hlt">sources</span>- in terms of location, amplitude, and spectral shape- with the aim of understanding how well <span class="hlt">sources</span> are observed and potentially what they reveal about the underlying ocean wavefield. We used seismic stations from the Southern California Seismic Network, and computed beamformer output as a function of time, frequency, slowness and azimuth. During winter months (October - mid March) the dominant arrivals at frequencies 0.18-0.22 Hz were P waves that originated from the North Pacific, whilst arrivals from the North Atlantic dominated at slightly lower frequencies of 0.16-0.18 Hz. Based on this, we chose to focus on P waves during winter, and back-projected the beamformer energy onto a global grid using P wave travel timetables (following Gerstoft et al., 2008). We modelled the seismic <span class="hlt">sources</span> using Wavewatch III and site effect coefficients calculated following Ardhuin and Herbers (2013). We output the beamformer and the modelled <span class="hlt">sources</span> on a 2° global grid averaged over 6 hour periods from September 2012 to September 2014, at seismic frequencies of 0.06 to 0.3 Hz. We then integrated the spectra over the full frequency range. Here we focus on results from the first winter in the North Pacific. Preliminary results indicate that the logarithm of the modelled <span class="hlt">source</span> and the logarithm of the beamformer output are well described by a two-term exponential model</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=acoustic+AND+reduction+AND+noise&pg=2&id=EJ091713','ERIC'); return false;" href="http://eric.ed.gov/?q=acoustic+AND+reduction+AND+noise&pg=2&id=EJ091713"><span>Control of Environmental <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Jensen, Paul</p> <p>1973-01-01</p> <p>Discusses the physical properties, <span class="hlt">sources</span>, physiological effects, and legislation pertaining to <span class="hlt">noise</span>, especially <span class="hlt">noise</span> characteristics in the community. Indicates that <span class="hlt">noise</span> reduction steps can be taken more intelligently after determination of the true <span class="hlt">noise</span> <span class="hlt">sources</span> and paths. (CC)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140011422','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140011422"><span>Identification of <span class="hlt">Noise</span> <span class="hlt">Sources</span> During Rocket Engine Test Firings and a Rocket Launch Using a Microphone Phased-Array</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, Jayanta; Mosher, Robert N.; Porter, Barry J.</p> <p>2013-01-01</p> <p>A 70 microphone, 10-foot by 10-foot, microphone phased array was built for use in the harsh environment of rocket launches. The array was setup at NASA Wallops launch pad 0A during a static test firing of Orbital Sciences' Antares engines, and again during the first launch of the Antares vehicle. It was placed 400 feet away from the pad, and was hoisted on a scissor lift 40 feet above ground. The data sets provided unprecedented insight into rocket <span class="hlt">noise</span> <span class="hlt">sources</span>. The duct exit was found to be the primary <span class="hlt">source</span> during the static test firing; the large amount of water injected beneath the nozzle exit and inside the plume duct quenched all other <span class="hlt">sources</span>. The maps of the <span class="hlt">noise</span> <span class="hlt">sources</span> during launch were found to be time-dependent. As the engines came to full power and became louder, the primary <span class="hlt">source</span> switched from the duct inlet to the duct exit. Further elevation of the vehicle caused spilling of the hot plume, resulting in a distributed <span class="hlt">noise</span> map covering most of the pad. As the entire plume emerged from the duct, and the ondeck water system came to full power, the plume itself became the loudest <span class="hlt">noise</span> <span class="hlt">source</span>. These maps of the <span class="hlt">noise</span> <span class="hlt">sources</span> provide vital insight for optimization of sound suppression systems for future Antares launches.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910009732','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910009732"><span>Inflight <span class="hlt">source</span> <span class="hlt">noise</span> of an advanced full-scale single-rotation propeller</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Woodward, Richard P.; Loeffler, Irvin J.</p> <p>1991-01-01</p> <p>Flight tests to define the far field tone <span class="hlt">source</span> at cruise conditions were completed on the full scale SR-7L advanced turboprop which was installed on the left wing of a Gulfstream II aircraft. This program, designated Propfan Test Assessment (PTA), involved aeroacoustic testing of the propeller over a range of test conditions. These measurements defined <span class="hlt">source</span> levels for input into long distance propagation models to predict en route <span class="hlt">noise</span>. Inflight data were taken for 7 test cases. The sideline directivities measured by the Learjet showed expected maximum levels near 105 degrees from the propeller upstream axis. However, azimuthal directivities based on the maximum observed sideline tone levels showed highest levels below the aircraft. An investigation of the effect of propeller tip speed showed that the tone level of reduction associated with reductions in propeller tip speed is more significant in the horizontal plane than below the aircraft.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/166026','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/166026"><span><span class="hlt">Source</span> impedance, transient response, and <span class="hlt">noise</span> characterization of the TOPAZ 2 reactors</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kusnierkiewicz, D.Y.</p> <p>1995-01-20</p> <p>Electrical measurements have been performed on the TOPAZ 2 V-71 and Ya-21 Reactors, in order to characterize the <span class="hlt">source</span> impedance as a function of DC operating point and frequency. The response of the reactor to step changes in load current, as well as the frequency content of the electrical <span class="hlt">noise</span> generated by the reactor have also been measured. These parameters are important to know in order to design power regulation circuitry which maintains a constant load on the reactor during spacecraft operations for any flight application of the TOPAZ 2 reactors. Voltage spikes at the reactor interface induced by load transients must be limited; the power regulation circuitry must have adequate bandwidth to compensate for spacecraft load dynamics. The methods used to make these measurements will be discussed. Results of the measurements on the Ya-21 reactor indicate the <span class="hlt">source</span> impedance is dominated by a series resistance and inductance. The equivalent DC leakage resistance from the reactor output to structure was also measured. The self generated <span class="hlt">noise</span> of the reactor is benign; load induced transients will be sufficiently controlled with capacitive filtering and active regulation circuitry external to the reactor/power distribution system. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S43B4558B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S43B4558B"><span>Empirical sensitivity kernels of <span class="hlt">noise</span> correlations with respect to virtual <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boué, P.; Stehly, L.; Nakata, N.; Beroza, G. C.</p> <p>2014-12-01</p> <p>Cross-correlation of time-series, or interferometry, applied to the ambient seismic field is an established method to observe the propagation of waves between pairs of sensors without involving transient <span class="hlt">sources</span>. These reconstructed waves are routinely used to develop high-resolution images of the crust and upper mantle, or in mapping the time-dependent velocity changes associated with tectonic events. Using similar methods, recent work have highlighted more challenging observations, such as higher mode surface wave propagation and body wave reconstruction at various scales of the Earth: from the industrial surveys at the reservoir scale to the global scale. Furthermore, the reconstruction of the correct amplitude information can be used to image the anelastic attenuation of the medium and has led to a new type of ground motion prediction using virtual earthquakes method. The dependability of such amplitude retrieval had been debated and represents a difficult challenge due to uneven <span class="hlt">source</span> distribution. In this study, we discuss the possibility to use the correlation of ambient <span class="hlt">noise</span> correlation (similar to C3 method) to map the contribution of different <span class="hlt">source</span> locations for Rayleigh wave reconstruction between receiver pairs. These maps constructed in terms of traveltime or amplitude perturbations of the Green's function, can be considered as empirical sensitivity kernels with respect to the contribution of each virtual <span class="hlt">source</span>. We propose for the first time to map these kernels using a dataset of continuous records from a dense array of about 2600 sensors deployed at the local-scale in Long Beach (CA, USA). Finally, these maps are used to analyze the impact of the original ambient <span class="hlt">noise</span> directivity on the recovered Green's functions and discuss the effects of the velocity lateral heterogeneity within the array. We aim at understanding, and thereby reducing, the bias in ambient field measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JSV...329..786K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JSV...329..786K"><span>Turbulence and heat excited <span class="hlt">noise</span> <span class="hlt">sources</span> in single and coaxial jets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koh, Seong Ryong; Schröder, Wolfgang; Meinke, Matthias</p> <p>2010-03-01</p> <p>The generation of <span class="hlt">noise</span> in subsonic high Reynolds number single and coaxial turbulent jets is analyzed by a hybrid method. The computational approach is based on large-eddy simulations (LES) and solutions of the acoustic perturbation equations (APE). The method is used to investigate the acoustic fields of one isothermal single stream jet at a Mach number 0.9 and a Reynolds number 400,000 based on the nozzle diameter and two coaxial jets whose Mach number and Reynolds number based on the secondary jet match the values of the single jet. One coaxial jet configuration possesses a cold primary flow, whereas the other configuration has a hot primary jet. Thus, the configurations allow in a first step the analysis of the relationship of the flow and acoustic fields of a single and a cold coaxial jet and in a second step the investigation of the differences of the fluid mechanics and aeroacoustics of cold and hot coaxial jets. For the isothermal single jet the present hybrid acoustic computation shows convincing agreement with the direct acoustic simulation based on large-eddy simulations. The analysis of the acoustic field of the coaxial jets focuses on two <span class="hlt">noise</span> <span class="hlt">sources</span>, the Lamb vector fluctuations and the entropy <span class="hlt">sources</span> of the APE equations. The power spectral density (PSD) distributions evidence the Lamb vector fluctuations to represent the major acoustic <span class="hlt">sources</span> of the isothermal jet. Especially the typical downstream and sideline acoustic generations occur on a cone-like surface being wrapped around the end of the potential core. Furthermore, when the coaxial jet possesses a hot primary jet, the acoustic core being characterized by the entropy <span class="hlt">source</span> terms increases the low frequency acoustics by up to 5 dB, i.e., the sideline acoustics is enhanced by the pronounced temperature gradient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9783E..1UW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9783E..1UW"><span>Multi-gamma-<span class="hlt">source</span> CT imaging system: a feasibility study with the Poisson <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wi, Sunhee; Cho, Seungryong</p> <p>2016-03-01</p> <p>This study was performed to test the feasibility of multi-gamma-<span class="hlt">source</span> CT imaging system. Gamma-<span class="hlt">source</span> CT employs radioisotopes that emit monochromatic energy gamma-rays. The advantages of gamma-<span class="hlt">source</span> CT include its immunity to beam hardening artifacts, its capacity of quantitative CT imaging, and its higher performance in low contrast imaging compared to the conventional x-ray CT. Radioisotope should be shielded by use of a pin-hole collimator so as to make a fine focal spot. Due to its low gamma-ray flux in general, the reconstructed image from a single gamma-<span class="hlt">source</span> CT would suffer from high <span class="hlt">noise</span> in data. To address this problem, we proposed a multi-gamma <span class="hlt">source</span> CT imaging system and developed an iterative image reconstruction algorithm accordingly in this work. Conventional imaging model assumes a single linear imaging system typically represented by Mf = g. In a multi-gamma-<span class="hlt">source</span> CT system however, the inversion problem is not any more based on a single linear system since one cannot separate a detector pixel value into multiple ones that are corresponding to each rays from the <span class="hlt">sources</span>. Instead, the imaging model can be constructed by a set of linear system models each of which assumes an estimated measurement g. Based on this model, the proposed algorithm has a weighting step which distributes each projection data into multiple estimated measurements. We used two gamma <span class="hlt">sources</span> at various positions and with varying intensities in this numerical study to demonstrate its feasibility. Therefore, the measured projection data(g) is separated into each estimated projection data(g1, g2) in this study. The proposed imaging protocol is believed to contribute to both medical and industrial applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.7382C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.7382C"><span>Extraction of the local phase velocity and the group velocity from surface <span class="hlt">noise</span> <span class="hlt">source</span> in microseismic monitoring.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chmiel, Malgorzata; Roux, Philippe; Bardainne, Thomas</p> <p>2015-04-01</p> <p>The aim of this work is to demonstrate the extraction of the local phase velocity and the group velocity from surface <span class="hlt">noise</span> <span class="hlt">source</span> in microseismic monitoring. One of the biggest challenges in microseismic monitoring is surface seismic <span class="hlt">noise</span>. Microseismic surface studies are often contaminated with instrumental and ambient seismic <span class="hlt">noise</span>, originating from both natural (wind, rain) and anthropogenic <span class="hlt">sources</span> (injection, pumps, infrastructure, traffic). The two primary ways to attenuate the undesired surface <span class="hlt">noise</span> <span class="hlt">sources</span> are via processing and acquisition strategies. At the acquisition stage, one solution is through the use of patch array. One patch is a group of 48 vertical sensors densely distributed on the area of~150m*150m, and one trace is the array of 12 vertical geophones. In the present work, 44 patches were sparsely distributed on a 41 square kilometer area. Benefitting from continuous recording, we used Matched Field Processing (MFP) methods to extract local phase and group velocities over the whole area. The aim of this technique is to detect and locate uncoherent <span class="hlt">noise</span> <span class="hlt">sources</span> while using array-processing methods. The method is based on the comparison between a recorded wave field per patch (the data vector) and a theoretical (or modeled) wave-field (the replica vector) in the frequency domain. The replica vector is a Green's function at a given frequency, which depends on the following parameters: position (x,y) in 2D-grid and a phase velocity. The <span class="hlt">noise</span> <span class="hlt">source</span> location is obtained by matching the data vector with the replica vector using a linear "low-resolution" algorithm or a nonlinear "high-resolution" adaptive processor. These algorithms are defined for each point in the 2D - grid and for each phase velocity. The phase velocity per patch is optimal if it maximizes the processor output. As a result, an ambiguity surface is produced which shows the probability of presence of primary <span class="hlt">noise</span> <span class="hlt">sources</span> per patch. The combination of all the maps per patch</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25330772','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25330772"><span>Two-microphone spatial filtering improves speech reception for cochlear-implant users in reverberant conditions with multiple <span class="hlt">noise</span> <span class="hlt">sources</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Goldsworthy, Raymond L</p> <p>2014-10-20</p> <p>This study evaluates a spatial-filtering algorithm as a method to improve speech reception for cochlear-implant (CI) users in reverberant environments with multiple <span class="hlt">noise</span> <span class="hlt">sources</span>. The algorithm was designed to filter sounds using phase differences between two microphones situated 1 cm apart in a behind-the-ear hearing-aid capsule. Speech reception thresholds (SRTs) were measured using a Coordinate Response Measure for six CI users in 27 listening conditions including each combination of reverberation level (T60=0, 270, and 540 ms), number of <span class="hlt">noise</span> <span class="hlt">sources</span> (1, 4, and 11), and signal-processing algorithm (omnidirectional response, dipole-directional response, and spatial-filtering algorithm). <span class="hlt">Noise</span> <span class="hlt">sources</span> were time-reversed speech segments randomly drawn from the Institute of Electrical and Electronics Engineers sentence recordings. Target speech and <span class="hlt">noise</span> <span class="hlt">sources</span> were processed using a room simulation method allowing precise control over reverberation times and sound-<span class="hlt">source</span> locations. The spatial-filtering algorithm was found to provide improvements in SRTs on the order of 6.5 to 11.0 dB across listening conditions compared with the omnidirectional response. This result indicates that such phase-based spatial filtering can improve speech reception for CI users even in highly reverberant conditions with multiple <span class="hlt">noise</span> <span class="hlt">sources</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22308867','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22308867"><span>The differential Howland current <span class="hlt">source</span> with high signal to <span class="hlt">noise</span> ratio for bioimpedance measurement system</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Liu, Jinzhen; Li, Gang; Lin, Ling; Qiao, Xiaoyan; Wang, Mengjun; Zhang, Weibo</p> <p>2014-05-15</p> <p>The stability and signal to <span class="hlt">noise</span> ratio (SNR) of the current <span class="hlt">source</span> circuit are the important factors contributing to enhance the accuracy and sensitivity in bioimpedance measurement system. In this paper we propose a new differential Howland topology current <span class="hlt">source</span> and evaluate its output characters by simulation and actual measurement. The results include (1) the output current and impedance in high frequencies are stabilized after compensation methods. And the stability of output current in the differential current <span class="hlt">source</span> circuit (DCSC) is 0.2%. (2) The output impedance of two current circuits below the frequency of 200 KHz is above 1 MΩ, and below 1 MHz the output impedance can arrive to 200 KΩ. Then in total the output impedance of the DCSC is higher than that of the Howland current <span class="hlt">source</span> circuit (HCSC). (3) The SNR of the DCSC are 85.64 dB and 65 dB in the simulation and actual measurement with 10 KHz, which illustrates that the DCSC effectively eliminates the common mode interference. (4) The maximum load in the DCSC is twice as much as that of the HCSC. Lastly a two-dimensional phantom electrical impedance tomography is well reconstructed with the proposed HCSC. Therefore, the measured performance shows that the DCSC can significantly improve the output impedance, the stability, the maximum load, and the SNR of the measurement system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6989323','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6989323"><span>Living with power system <span class="hlt">harmonics</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Palko, E.</p> <p>1992-06-18</p> <p>This paper reports the effect of <span class="hlt">harmonics</span> on electronic equipment in manufacturing plants which was essentially a nonproblem as recently as nine years ago. In years past, <span class="hlt">harmonics</span> were essentially a problem experienced by electric utility companies, with a relatively few types of industries impressing a serous degree of <span class="hlt">harmonics</span> onto the utility system. Utilities typically solved their <span class="hlt">harmonic</span> problems by imposing limits on the amount of <span class="hlt">harmonics</span> that a customer was permitted to reflect onto the utility system, and assessing heavy financial penalties for noncompliance. Today's electronic equipment creates a problem that feeds on itself: solid-state electronic equipment is a flagrant generator of <span class="hlt">harmonics</span>, and solid-state equipment is, itself, intolerant of <span class="hlt">harmonics</span> and is susceptible to malfunction and failure when served from a <span class="hlt">harmonic</span>-laden power <span class="hlt">source</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21682400','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21682400"><span>Extraction of small boat <span class="hlt">harmonic</span> signatures from passive sonar.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ogden, George L; Zurk, Lisa M; Jones, Mark E; Peterson, Mary E</p> <p>2011-06-01</p> <p>This paper investigates the extraction of acoustic signatures from small boats using a passive sonar system. <span class="hlt">Noise</span> radiated from a small boats consists of broadband <span class="hlt">noise</span> and <span class="hlt">harmonically</span> related tones that correspond to engine and propeller specifications. A signal processing method to automatically extract the <span class="hlt">harmonic</span> structure of <span class="hlt">noise</span> radiated from small boats is developed. The <span class="hlt">Harmonic</span> Extraction and Analysis Tool (HEAT) estimates the instantaneous fundamental frequency of the <span class="hlt">harmonic</span> tones, refines the fundamental frequency estimate using a Kalman filter, and automatically extracts the amplitudes of the <span class="hlt">harmonic</span> tonals to generate a <span class="hlt">harmonic</span> signature for the boat. Results are presented that show the HEAT algorithms ability to extract these signatures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014MeScT..25g5204C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014MeScT..25g5204C"><span>Exploiting continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation methods for <span class="hlt">noise</span> <span class="hlt">source</span> identification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chiariotti, Paolo; Martarelli, Milena; Revel, Gian Marco</p> <p>2014-07-01</p> <p>This paper proposes the use of continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation techniques that aim at characterizing the structure-borne contributions of the <span class="hlt">noise</span> emission of a mechanical system. The time domain correlation technique presented in this paper is based on the use of FIR (finite impulse response) filters obtained from the vibro-acoustic transfer matrix when vibration data are collected by laser Doppler vibrometry (LDV) exploited in continuous scan mode (CSLDV). The advantages, especially in terms of <span class="hlt">source</span> decorrelation capabilities, related to the use of CSLDV for such purpose, with respect to standard discrete scan (SLDV), are discussed throughout the paper. To validate this approach, vibro-acoustic measurements were performed on a planetary gear motor for home appliances. The analysis of results is also supported by a simulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22391461','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22391461"><span>Reduction of beam current <span class="hlt">noise</span> in the FNAL magnetron ion <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bollinger, D. S. Karns, P. R. Tan, C. Y.</p> <p>2015-04-08</p> <p>The new FNAL Injector Line with a circular dimple magnetron ion <span class="hlt">source</span> has been operational since December of 2012. Since the new injector came on line there have been variations in the H- beam current flattop observed near the downstream end of the Linac. Several different cathode geometries including a hollow cathode suggested by Dudnikov [1] were tried. Previous studies also showed that different mixtures of hydrogen and nitrogen had an effect on beam current <span class="hlt">noise</span> [2]. We expanded on those studies by trying mixtures ranging from (0.25% nitrogen, 99.75% hydrogen) to (3% nitrogen, 97% hydrogen). The results of these studies in our test stand will be presented in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800006956','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800006956"><span>Combustion <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Strahle, W. C.</p> <p>1977-01-01</p> <p>A review of the subject of combustion generated <span class="hlt">noise</span> is presented. Combustion <span class="hlt">noise</span> is an important <span class="hlt">noise</span> <span class="hlt">source</span> in industrial furnaces and process heaters, turbopropulsion and gas turbine systems, flaring operations, Diesel engines, and rocket engines. The state-of-the-art in combustion <span class="hlt">noise</span> importance, understanding, prediction and scaling is presented for these systems. The fundamentals and available theories of combustion <span class="hlt">noise</span> are given. Controversies in the field are discussed and recommendations for future research are made.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21408735','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21408735"><span>CaF{sub 2} ablation plumes as a <span class="hlt">source</span> of CaF molecules for <span class="hlt">harmonic</span> generation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Oujja, M.; Nalda, R. de; Castillejo, M.; Lopez-Arias, M.; Torres, R.; Marangos, J. P.</p> <p>2010-04-15</p> <p>Generation of low-order <span class="hlt">harmonics</span> (third and fifth) of the fundamental radiation of a Q-switched Nd:YAG laser (1064 nm, pulse 15 ns) was observed in a CaF{sub 2} laser ablation plume. The ablation process is triggered by a second Q-switched Nd:YAG laser operating at 532 or 266 nm. In the scheme employed, the fundamental laser beam propagates parallel to the target surface at controllable distance and temporal delay, allowing to the probing of different regions of the freely expanding plume. The intensity of the <span class="hlt">harmonics</span> is shown to decrease rapidly as the distance to the target is increased, and for each distance, an optimum time delay between the ablating laser pulse and the fundamental beam is found. In situ diagnosis of the plume by optical emission spectroscopy and laser-induced fluorescence serves to correlate the observed <span class="hlt">harmonic</span> behavior with the temporally and spatially resolved composition and velocity of flight of species in the plume. It is concluded that <span class="hlt">harmonics</span> are selectively generated by CaF species through a two-photon resonantly enhanced sum-mixing process exploiting the (B {sup 2{Sigma}+}-X {sup 2{Sigma}+}, {Delta}{nu}=0) transition of the molecule in the region of 530 nm. In this work polar molecules have been shown to be the dominating species for <span class="hlt">harmonic</span> generation in an ablation plume. Implications of these results for the generation of high <span class="hlt">harmonics</span> in strongly polar molecules which can be aligned in the ablation plasma are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15119621','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15119621"><span>Detailed study of an efficient blue laser <span class="hlt">source</span> by second-<span class="hlt">harmonic</span> generation in a semimonolithic cavity for the cooling of strontium atoms.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Klappauf, Bruce G; Bidel, Yannick; Wilkowski, David; Chanelière, Thierry; Kaiser, Robin</p> <p>2004-04-20</p> <p>We have constructed a blue laser <span class="hlt">source</span> consisting of an amplified, grating tuned diode laser that is frequency doubled by a KNbO3 crystal in a compact standing wave cavity and produces as much as 200 mW of internal second-<span class="hlt">harmonic</span> power. We have analyzed the unusual characteristics of this standing wave cavity to clarify the advantages and disadvantages of this configuration as an alternative to a ring cavity for second-<span class="hlt">harmonic</span> generation. We emphasize its efficiency and stability and the fact that it has an inherent walk-off compensation, similar to twin crystal configurations. We demonstrate its utility for laser cooling and trapping of earth alkalis by stabilizing the laser to the 461-nm transition of strontium, using a heat pipe, and then forming a magneto-optic trap of strontium from a Zeeman-slowed atomic beam.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000101661','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000101661"><span>Current Background <span class="hlt">Noise</span> <span class="hlt">Sources</span> and Levels in the NASA Ames 40- by 80-Foot Wind Tunnel: A Status Report</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Allen, Christopher S.; Jaeger, Stephen; Soderman, Paul; Koga, Dennis (Technical Monitor)</p> <p>1999-01-01</p> <p>Background <span class="hlt">noise</span> measurements were made of the acoustic environment in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel (40x80) at NASA Ames Research Center. The measurements were acquired subsequent to the 40x80 Aeroacoustic Modernization Project, which was undertaken to improve the anechoic characteristics of the 40x80's closed test section as well as reduce the levels of background <span class="hlt">noise</span> in the facility. The resulting 40x80 anechoic environment was described by Soderman et. al., and the current paper describes the resulting 40x80 background <span class="hlt">noise</span>, discusses the <span class="hlt">sources</span> of the <span class="hlt">noise</span>, and draws comparisons to previous 40x80 background <span class="hlt">noise</span> levels measurements. At low wind speeds or low frequencies, the 40x80 background <span class="hlt">noise</span> is dominated by the fan drive system. To obtain the lowest fan drive <span class="hlt">noise</span> for a given tunnel condition, it is possible in the 40x80 to reduce the fans' rotational speed and adjust the fans' blade pitch, as described by Schmidtz et. al. This idea is not new, but has now been operationally implemented with modifications for increased power at low rotational speeds. At low to mid-frequencies and at higher wind speeds, the dominant <span class="hlt">noise</span> mechanism was thought to be caused by the surface interface of the previous test section floor acoustic lining. In order to reduce this <span class="hlt">noise</span> mechanism, the new test section floor lining was designed to resist the pumping of flow in and out of the space between the grating slats required to support heavy equipment. In addition, the lining/flow interface over the entire test section was designed to be smoother and quieter than the previous design. At high wind speeds or high frequencies, the dominant <span class="hlt">source</span> of background <span class="hlt">noise</span> in the 40x80 is believed to be caused by the response of the in-flow microphone probes (required by the nature of the closed test section) to the fluctuations in the freestream flow. The resulting background <span class="hlt">noise</span> levels are also different for probes of various</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22779457','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22779457"><span>Shipping <span class="hlt">noise</span> in whale habitat: characteristics, <span class="hlt">sources</span>, budget, and impact on belugas in Saguenay-St. Lawrence Marine Park hub.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gervaise, Cédric; Simard, Yvan; Roy, Nathalie; Kinda, Bazile; Ménard, Nadia</p> <p>2012-07-01</p> <p>A continuous car ferry line crossing the Saguenay Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping <span class="hlt">noise</span> in the heart of the Saguenay-St. Lawrence Marine Park. To characterize this <span class="hlt">noise</span> and examine its potential impact on belugas, a 4-hydrophone array was deployed in the area and continuously recorded for five weeks in May-June 2009. The <span class="hlt">source</span> levels of the different vessel types showed little dependence on vessel size or speed increase. Their spectral range covered 33 dB. Lowest <span class="hlt">noise</span> levels occurred at night, when ferry crossing pace was reduced, and daytime <span class="hlt">noise</span> peaked during whale-watching tour departures and arrivals. Natural ambient <span class="hlt">noise</span> prevailed 9.4% of the time. Ferry traffic added 30-35 dB to ambient levels above 1 kHz during crossings, which contributed 8 to 14 dB to hourly averages. The whale-watching fleet added up to 5.6 dB during peak hours. Assuming no behavioral or auditory compensation, half of the time, beluga potential communication range was reduced to less than ~30% of its expected value under natural <span class="hlt">noise</span> conditions, and to less than ~15% for one quarter of the time, with little dependence on call frequency. The echolocation band for this population of belugas was also affected by the shipping <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFD.D4009R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFD.D4009R"><span>Towards the characterization of <span class="hlt">noise</span> <span class="hlt">sources</span> in a supersonic three-stream jet using advanced analysis tools</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ruscher, Christopher; Gogineni, Sivaram</p> <p>2016-11-01</p> <p>Strict <span class="hlt">noise</span> regulation set by governing bodies currently make supersonic commercial aviation impractical. One of the many challenges that exist in developing practical supersonic commercial aircraft is the <span class="hlt">noise</span> produced by the engine's exhaust jet. A promising method of jet <span class="hlt">noise</span> reduction for supersonic applications is through the addition of extra exhaust streams. Data for an axisymmetric three-stream nozzle were generated using the Naval Research Laboratory's JENRE code. This data will be compared to experimental results obtained by NASA for validation purposes. Once the simulation results show satisfactory agreement to the experiments, advanced analysis tools will be applied to the simulation data to characterize potential <span class="hlt">noise</span> <span class="hlt">sources</span>. The tools to be applied include methods that are based on proper orthogonal decomposition, wavelet decomposition, and stochastic estimation. Additionally, techniques such as empirical mode decomposition and momentum potential theorem will be applied to the data as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770007084','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770007084"><span>Further studies of static to flight effects on fan tone <span class="hlt">noise</span> using inlet distortion control for <span class="hlt">source</span> identification</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hodder, B. K.</p> <p>1976-01-01</p> <p>Current experimental investigations have linked static inflow distortion phenomena such as the ground vortex, atmospheric turbulence, and teststand structure interference to the generation of fan tone <span class="hlt">noise</span> at the blade passing frequency. Since such distortions do not exist in flight, it is important to remove them from the static test environment and thereby improve the static-to-flight tone-<span class="hlt">noise</span> correlation. In the course of providing evidence for this position, a recent investigation used a distortion control inlet with a modern day turbofan engine to assess atmospheric turbulence effects. Although the initial results were encouraging, they were incomplete. The present investigation continues this work and shows more completely the effect of atmospheric turbulence on tone-<span class="hlt">noise</span> generation. Further, use is made of the distortion control inlet to identify other competing tone-<span class="hlt">noise</span> <span class="hlt">sources</span> in the test engine such as a rotor-core stator interaction which was confirmed by engine modifications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130000448','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130000448"><span>Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> Generating Simple Modes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel, L.; Brown, Clifford, A.; Walker, Bruce, E.</p> <p>2012-01-01</p> <p>An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the Langley Research Center s 14- by 22-Foot wind tunnel test of the Hybrid Wing Body (HWB) full three-dimensional 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of candidate engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft and to provide a database for shielding code validation. A range of frequencies, and a parametric study of modes were generated from exhaust and inlet nacelle configurations. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular to the axis of the nacelle (in its 0 orientation) and three planes parallel were acquired from the array sweep. In each plane the linear array traversed five sweeps, for a total span of 160 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Level, and integrated Power Levels are presented in this paper; as well as the in-duct modal structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70047737','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70047737"><span>Ground motion in the presence of complex topography: Earthquake and ambient <span class="hlt">noise</span> <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hartzell, Stephen; Meremonte, Mark; Ramírez-Guzmán, Leonardo; McNamara, Daniel</p> <p>2014-01-01</p> <p>To study the influence of topography on ground motion, eight seismic recorders were deployed for a period of one year over Poverty Ridge on the east side of the San Francisco Bay Area, California. This location is desirable because of its proximity to local earthquake <span class="hlt">sources</span> and the significant topographic relief of the array (439 m). Topographic amplification is evaluated as a function of frequency using a variety of methods, including reference‐site‐based spectral ratios and single‐station horizontal‐to‐vertical spectral ratios using both shear waves from earthquakes and ambient <span class="hlt">noise</span>. Field observations are compared with the predicted ground motion from an accurate digital model of the topography and a 3D local velocity model. Amplification factors from the theoretical calculations are consistent with observations. The fundamental resonance of the ridge is prominently observed in the spectra of data and synthetics; however, higher‐frequency peaks are also seen primarily for <span class="hlt">sources</span> in line with the major axis of the ridge, perhaps indicating higher resonant modes. Excitations of lateral ribs off of the main ridge are also seen at frequencies consistent with their dimensions. The favored directions of resonance are shown to be transverse to the major axes of the topographic features.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSV...393..425T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSV...393..425T"><span>Algorithmic localisation of <span class="hlt">noise</span> <span class="hlt">sources</span> in the tip region of a low-speed axial flow fan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tóth, Bence; Vad, János</p> <p>2017-04-01</p> <p>An objective and algorithmised methodology is proposed to analyse beamform data obtained for axial fans. Its application is demonstrated in a case study regarding the tip region of a low-speed cooling fan. First, beamforming is carried out in a co-rotating frame of reference. Then, a distribution of <span class="hlt">source</span> strength is extracted along the circumference of the rotor at the blade tip radius in each analysed third-octave band. The circumferential distributions are expanded into Fourier series, which allows for filtering out the effects of perturbations, on the basis of an objective criterion. The remaining Fourier components are then considered as base <span class="hlt">sources</span> to determine the blade-passage-periodic flow mechanisms responsible for the broadband <span class="hlt">noise</span>. Based on their frequency and angular location, the base <span class="hlt">sources</span> are grouped together. This is done using the fuzzy c-means clustering method to allow the overlap of the <span class="hlt">source</span> mechanisms. The number of clusters is determined in a validity analysis. Finally, the obtained clusters are assigned to <span class="hlt">source</span> mechanisms based on the literature. Thus, turbulent boundary layer - trailing edge interaction <span class="hlt">noise</span>, tip leakage flow <span class="hlt">noise</span>, and double leakage flow <span class="hlt">noise</span> are identified.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26611074','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26611074"><span>Potential Uses of Anthropogenic <span class="hlt">Noise</span> as a <span class="hlt">Source</span> of Information in Animal Sensory and Communication Systems.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stansbury, Amanda; Deecke, Volker; Götz, Thomas; Janik, Vincent M</p> <p>2016-01-01</p> <p>Although current research on the impact of anthropogenic <span class="hlt">noise</span> has focused on the detrimental effects, there is a range of ways by which animals could benefit from increased <span class="hlt">noise</span> levels. Here we discuss two potential uses of anthropogenic <span class="hlt">noise</span>. First, local variations in the ambient-<span class="hlt">noise</span> field could be used to perceive objects and navigate within an environment. Second, introduced sound cues could be used as a signal for prey detection or orientation and navigation. Although the disadvantages of <span class="hlt">noise</span> pollution will likely outweigh any positive effects, it is important to acknowledge that such changes may benefit some species.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10641846','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10641846"><span>Analysis of light <span class="hlt">noise</span> <span class="hlt">sources</span> in a recycled Michelson interferometer with Fabry-Perot arms.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Camp, J B; Yamamoto, H; Whitcomb, S E; McClelland, D E</p> <p>2000-01-01</p> <p>We present a method by which the effect of laser field variations on the signal output of an interferometric gravitational wave detector is rigorously determined. Using the Laser Interferometer Gravitational Wave Observatory (LIGO) optical configuration of a power recycled Michelson interferometer with Fabry-Perot arm cavities as an example, we calculate the excess <span class="hlt">noise</span> after the input filter cavity (mode cleaner) and the dependence of the detector strain sensitivity on laser frequency and amplitude <span class="hlt">noise</span>, radio frequency oscillator <span class="hlt">noise</span>, and scattered-light phase <span class="hlt">noise</span>. We find that <span class="hlt">noise</span> on the radio frequency sidebands generally limits the detector's sensitivity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25608189','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25608189"><span><span class="hlt">Noise</span> <span class="hlt">sources</span> and improved performance of a mid-wave infrared uncooled silicon carbide optical photodetector.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lim, Geunsik; Manzur, Tariq; Kar, Aravinda</p> <p>2014-12-20</p> <p>An uncooled photon detector is fabricated for the mid-wave infrared (MWIR) wavelength of 4.21 μm by doping an n-type 4H-SiC substrate with gallium using a laser doping technique. The dopant creates a p-type energy level of 0.3 eV, which is the energy of a photon corresponding to the MWIR wavelength 4.21 μm. This energy level was confirmed by optical absorption spectroscopy. The detection mechanism involves photoexcitation of carriers by the photons of this wavelength absorbed in the semiconductor. The resulting changes in the carrier densities at different energy levels modify the refractive index and, therefore, the reflectance of the semiconductor. This change in the reflectance constitutes the optical response of the detector, which can be probed remotely with a laser beam such as a He-Ne laser and the power of the reflected probe beam can be measured with a conventional laser power meter. The <span class="hlt">noise</span> mechanisms in the probe laser, silicon carbide MWIR detector, and laser power meter affect the performance of the detector in regards to aspects such as the responsivity, <span class="hlt">noise</span> equivalent temperature difference (NETD), and detectivity. For the MWIR wavelengths of 4.21 and 4.63 μm, the experimental detectivity of the optical photodetector of this study was found to be 1.07×10(10)  cm·Hz(1/2)/W, while the theoretical value was 1.11×10(10)  cm·Hz(1/2)/W. The values of NETD are 404 and 15.5 mK based on experimental data for an MWIR radiation <span class="hlt">source</span> with a temperature of 25°C and theoretical calculations, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850006357','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850006357"><span><span class="hlt">Sources</span>, paths, and concepts for reduction of <span class="hlt">noise</span> in the test section of the NASA Langley 4x7m wind tunnel</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hayden, R. E.; Wilby, J. F.</p> <p>1984-01-01</p> <p>NASA is investigating the feasibility of modifying the 4x7m Wind Tunnel at the Langley Research Center to make it suitable for a variety of aeroacoustic testing applications, most notably model helicopter rotors. The amount of <span class="hlt">noise</span> reduction required to meet NASA's goal for test section background <span class="hlt">noise</span> was determined, the predominant <span class="hlt">sources</span> and paths causing the background <span class="hlt">noise</span> were quantified, and trade-off studies between schemes to reduce fan <span class="hlt">noise</span> at the <span class="hlt">source</span> and those to attenuate the sound generated in the circuit between the <span class="hlt">sources</span> and the test section were carried out. An extensive data base is also presented on circuit <span class="hlt">sources</span> and paths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17879798','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17879798"><span>Characterization of <span class="hlt">noise</span> <span class="hlt">sources</span> for two generations of computed radiography systems using powder and crystalline photostimulable phosphors.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mackenzie, Alistair; Honey, Ian D</p> <p>2007-08-01</p> <p>The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and <span class="hlt">noise</span> characteristics. The main aim was to characterize and quantify the <span class="hlt">noise</span> <span class="hlt">sources</span> in the images. The systems tested were (1) Agfa CR 25.0, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX-S, a line-scanning CR reader with needle crystal phosphor image plates (HD 5.0). For both systems, the standard metrics of presampled modulation transfer function (MTF), normalized <span class="hlt">noise</span> power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various <span class="hlt">noise</span> <span class="hlt">sources</span> contributing to the NNPS were separated by using knowledge of their relationship with air kerma, MTF, absorption efficiency and antialiasing filters. The DX-S MTF was superior compared with the CR 25.0. The maximum difference in MTF between the DX-S scan and CR 25.0 subscan directions was 0.13 at 1.3 mm(-1). For a nominal detector air kerma of 4 microGy, the peak DQE of the DX-S was 43 (+/-3)%, which was over double that of the CR 25.0 of 18 (+/-2)%. The additive electronic <span class="hlt">noise</span> was negligible on the CR 25.0 but calculated to be constant 3.4 x 10(-7) (+/-0.4 x 10(-7)) mm2 at 3.9 microGy on the DX-S. The DX-S has improved image quality compared with a traditional flying spot reader. The separation of the <span class="hlt">noise</span> <span class="hlt">sources</span> indicates that the improvements in DQE of the DX-S are due not only to the higher quantum, efficiency and MTF, but also the lower structure, secondary quantum, and excess <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20953510','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20953510"><span>Characterization of <span class="hlt">noise</span> <span class="hlt">sources</span> for two generations of computed radiography systems using powder and crystalline photostimulable phosphors</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mackenzie, Alistair; Honey, Ian D.</p> <p>2007-08-15</p> <p>The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and <span class="hlt">noise</span> characteristics. The main aim was to characterize and quantify the <span class="hlt">noise</span> <span class="hlt">sources</span> in the images. The systems tested were (1) Agfa CR 25.0, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX-S, a line-scanning CR reader with needle crystal phosphor image plates (HD 5.0). For both systems, the standard metrics of presampled modulation transfer function (MTF), normalized <span class="hlt">noise</span> power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various <span class="hlt">noise</span> <span class="hlt">sources</span> contributing to the NNPS were separated by using knowledge of their relationship with air kerma, MTF, absorption efficiency and antialiasing filters. The DX-S MTF was superior compared with the CR 25.0. The maximum difference in MTF between the DX-S scan and CR 25.0 subscan directions was 0.13 at 1.3 mm{sup -1}. For a nominal detector air kerma of 4 {mu}Gy, the peak DQE of the DX-S was 43({+-}3)%, which was over double that of the CR 25.0 of 18({+-}2)%. The additive electronic <span class="hlt">noise</span> was negligible on the CR 25.0 but calculated to be constant 3.4x10{sup -7} ({+-}0.4x10{sup -7}) mm{sup 2} at 3.9 {mu}Gy on the DX-S. The DX-S has improved image quality compared with a traditional flying spot reader. The separation of the <span class="hlt">noise</span> <span class="hlt">sources</span> indicates that the improvements in DQE of the DX-S are due not only to the higher quantum, efficiency and MTF, but also the lower structure, secondary quantum, and excess <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6005410','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6005410"><span>A portable measurement system for subcriticality measurements by the Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; Ragan, G.E.; Blakeman, E.D.</p> <p>1987-01-01</p> <p>A portable measurement system consisting of a personal computer used as a Fourier analyzer and three detection channels (with associated electronics that provide the signals to analog-to-digital (A/D) convertors) has been assembled to measure subcriticality by the /sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method. 8 refs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860060704&hterms=cylinder+noise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D10%26Ntt%3Dcylinder%2Bnoise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860060704&hterms=cylinder+noise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D10%26Ntt%3Dcylinder%2Bnoise"><span>Active control of propeller induced <span class="hlt">noise</span> fields inside a flexible cylinder</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lester, H. C.; Fuller, C. R.</p> <p>1986-01-01</p> <p>An active <span class="hlt">noise</span> control model has been evaluated for reducing aircraft interior <span class="hlt">noise</span>. The structural <span class="hlt">noise</span> transmission properties of an aircraft fuselage were modelled as a flexible cylinder excited by external acoustic dipoles simulating the <span class="hlt">noise</span> produced by twin propellers. The amplitudes of an internal distribution of monopole control <span class="hlt">sources</span> were determined such that the area-weighted mean square acoustic pressure was minimized in the propeller plane. The <span class="hlt">noise</span> control model was evaluated at low frequencies corresponding to the blade passage frequency and first few <span class="hlt">harmonics</span> of a typical turbo-prop aircraft. Interior <span class="hlt">noise</span> reductions of 20 25 dB were achieved, over a substantial region of the cylindrical cross-section, with just a few monopole control <span class="hlt">sources</span>. The most favorable interior <span class="hlt">noise</span> reductions were achieved when the active <span class="hlt">noise</span> control model was used in combination with propeller <span class="hlt">source</span> phasing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984JVGR...22...59K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984JVGR...22...59K"><span>Seismicity at Old Faithful Geyser: an isolated <span class="hlt">source</span> of geothermal <span class="hlt">noise</span> and possible analogue of volcanic seismicity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kieffer, Susan Werner</p> <p>1984-09-01</p> <p>Old Faithful Geyser in Yellowstone National Park, U.S.A., is a relatively isolated <span class="hlt">source</span> of seismic <span class="hlt">noise</span> and exhibits seismic behavior similar to that observed at many volcanoes, including "bubblequakes" that resemble B-type "earthquakes", <span class="hlt">harmonic</span> tremor before and during eruptions, and periods of seismic quiet prior to eruptions. Although Old Faithful differs from volcanoes in that the conduit is continuously open, that rock-fracturing is not a process responsible for seismicity, and that the erupting fluid is inviscid H 2O rather than viscous magma, there are also remarkable similarities in the problems of heat and mass recharge to the system, in the eruption dynamics, and in the seismicity. Water rises irregularly into the immediate reservoir of Old Faithful as recharge occurs, a fact that suggests that there are two enlarged storage regions: one between 18 and 22 m (the base of the immediate reservoir) and one between about 10 and 12 m depth. Transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water, and by episodes of convective overturn. An eruption occurs when the temperature of the near-surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure-release waves (rarefactions) down the column can bring the liquid water onto the boiling curve. The process of conversion of the liquid water in the conduit at the onset of an eruption into a two-phase liquid-vapor mixture takes on the order of 30 s. The seismicity is directly related to the sequence of filling and heating during the recharge cycle, and to the fluid mechanics of the eruption. Short (0.2-0.3 s), monochromatic, high-frequency events (20-60 Hz) resembling unsustained <span class="hlt">harmonic</span> tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70013910','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70013910"><span>Seismicity at Old Faithful Geyser: an isolated <span class="hlt">source</span> of geothermal <span class="hlt">noise</span> and possible analogue of volcanic seismicity</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Kieffer, S.W.</p> <p>1984-01-01</p> <p>Old Faithful Geyser in Yellowstone National Park, U.S.A., is a relatively isolated <span class="hlt">source</span> of seismic <span class="hlt">noise</span> and exhibits seismic behavior similar to that observed at many volcanoes, including "bubblequakes" that resemble B-type "earthquakes", <span class="hlt">harmonic</span> tremor before and during eruptions, and periods of seismic quiet prior to eruptions. Although Old Faithful differs from volcanoes in that the conduit is continuously open, that rock-fracturing is not a process responsible for seismicity, and that the erupting fluid is inviscid H2O rather than viscous magma, there are also remarkable similarities in the problems of heat and mass recharge to the system, in the eruption dynamics, and in the seismicity. Water rises irregularly into the immediate reservoir of Old Faithful as recharge occurs, a fact that suggests that there are two enlarged storage regions: one between 18 and 22 m (the base of the immediate reservoir) and one between about 10 and 12 m depth. Transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water, and by episodes of convective overturn. An eruption occurs when the temperature of the near-surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure-release waves (rarefactions) down the column can bring the liquid water onto the boiling curve. The process of conversion of the liquid water in the conduit at the onset of an eruption into a two-phase liquid-vapor mixture takes on the order of 30 s. The seismicity is directly related to the sequence of filling and heating during the recharge cycle, and to the fluid mechanics of the eruption. Short (0.2-0.3 s), monochromatic, high-frequency events (20-60 Hz) resembling unsustained <span class="hlt">harmonic</span> tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4593122','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4593122"><span>A phantom road experiment reveals traffic <span class="hlt">noise</span> is an invisible <span class="hlt">source</span> of habitat degradation</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ware, Heidi E.; McClure, Christopher J. W.; Carlisle, Jay D.; Barber, Jesse R.</p> <p>2015-01-01</p> <p>Decades of research demonstrate that roads impact wildlife and suggest traffic <span class="hlt">noise</span> as a primary cause of population declines near roads. We created a “phantom road” using an array of speakers to apply traffic <span class="hlt">noise</span> to a roadless landscape, directly testing the effect of <span class="hlt">noise</span> alone on an entire songbird community during autumn migration. Thirty-one percent of the bird community avoided the phantom road. For individuals that stayed despite the <span class="hlt">noise</span>, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic <span class="hlt">noise</span> during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that <span class="hlt">noise</span> degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact. PMID:26324924</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70014779','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70014779"><span>Resonance of a fluid-driven crack: radiation properties and implications for the <span class="hlt">source</span> of long-period events and <span class="hlt">harmonic</span> tremor.</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Chouet, B.</p> <p>1988-01-01</p> <p>A dynamic <span class="hlt">source</span> model is presented, in which a 3-D crack containing a viscous compressible fluid is excited into resonance by an impulsive pressure transient applied over a small area DELTA S of the crack surface. The crack excitation depends critically on two dimensionless parameters called the crack stiffness and viscous damping loss. According to the model, the long-period event and <span class="hlt">harmonic</span> tremor share the same <span class="hlt">source</span> but differ in the boundary conditions for fluid flow and in the triggering mechanism setting up the resonance of the <span class="hlt">source</span>, the former being viewed as the impulse response of the tremor generating system and the later representing the excitation due to more complex forcing functions.-from Author</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16092361','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16092361"><span>Suppression of phase and supermode <span class="hlt">noise</span> in a <span class="hlt">harmonic</span> mode-locked erbium-doped fiber laser with a semiconductor-optical-amplifier-based high-pass filter.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lin, Gong-Ru; Wu, Ming-Chung; Chang, Yung-Cheng</p> <p>2005-07-15</p> <p>By operating an intracavity semiconductor-optical-amplifier- (SOA-) based high-pass filter at the nearly transparent current condition, the supermode <span class="hlt">noise</span> (SMN), the relaxation oscillation, and the single-sideband (SSB) phase <span class="hlt">noise</span> can be simultaneously suppressed in an actively mode-locked erbium-doped fiber laser (EDFL). The SOA at the nearly transparent condition enhances the SMN suppression ratio of the EDFL from 32 to 76 dB at the cost of the phase <span class="hlt">noise</span> degrading from -114 to -104.2 dBc/Hz and broadening the pulse width from 36 to 61 ps. With an optical bandpass filter, the SSB phase <span class="hlt">noise</span> and the SMN suppression ratio can be further improved to -110 dBc/Hz and 81 dB, respectively. The EDFL pulse can be further shortened to 3.1 ps with a time-bandwidth product of 0.63 after compression.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5923513','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5923513"><span>The sup 252 Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> measurements of unreflected uranium hydride cylinder subcriticality</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; Pare, V.K.; Blakeman, E.D. )</p> <p>1991-01-01</p> <p>Subcritical neutron multiplication factors have been measured by the {sup 252}Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis method for unreflected, 15.0-cm-diam uranium hydride cylinders of varying heights. Because of the difficulty and cost of controlling the H/U ratio in damp uranium (93.2 wt% {sup 235}U) oxide power and fabricating sufficient material for experiments, few experiments have been performed with materials of low H/U ratios. These measurements may provide alternate information that can be used for verifying calculational methods since the H/U ratio for this material is 3.00. These measurements, which are the first application of this method to uranium hydride, were performed at the Los Alamos National Laboratory Critical Experiments Facility in 1989. These measurements were used to demonstrate the capability of this measurement method for this type of material and to provide a benchmark experiment for calculational methods with slightly moderated systems. Previous experiments by this method were for a wide variety of well-moderated systems or unmoderated uranium metal cylinders.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970001748','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970001748"><span>Active Control of Fan <span class="hlt">Noise</span>: Feasibility Study. Volume 6; Theoretical Analysis for Coupling of Active <span class="hlt">Noise</span> Control Actuator Ring <span class="hlt">Sources</span> to an Annular Duct with Flow</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kraft, R. E.</p> <p>1996-01-01</p> <p>The objective of this effort is to develop an analytical model for the coupling of active <span class="hlt">noise</span> control (ANC) piston-type actuators that are mounted flush to the inner and outer walls of an annular duct to the modes in the duct generated by the actuator motion. The analysis will be used to couple the ANC actuators to the modal analysis propagation computer program for the annular duct, to predict the effects of active suppression of fan-generated engine <span class="hlt">noise</span> <span class="hlt">sources</span>. This combined program will then be available to assist in the design or evaluation of ANC systems in fan engine annular exhaust ducts. An analysis has been developed to predict the modes generated in an annular duct due to the coupling of flush-mounted ring actuators on the inner and outer walls of the duct. The analysis has been combined with a previous analysis for the coupling of modes to a cylindrical duct in a FORTRAN computer program to perform the computations. The method includes the effects of uniform mean flow in the duct. The program can be used for design or evaluation purposes for active <span class="hlt">noise</span> control hardware for turbofan engines. Predictions for some sample cases modeled after the geometry of the NASA Lewis ANC Fan indicate very efficient coupling in both the inlet and exhaust ducts for the m = 6 spinning mode at frequencies where only a single radial mode is cut-on. Radial mode content in higher order cut-off modes at the <span class="hlt">source</span> plane and the required actuator displacement amplitude to achieve 110 dB SPL levels in the desired mode were predicted. Equivalent cases with and without flow were examined for the cylindrical and annular geometry, and little difference was found for a duct flow Mach number of 0.1. The actuator ring coupling program will be adapted as a subroutine to the cylindrical duct modal analysis and the exhaust duct modal analysis. This will allow the fan <span class="hlt">source</span> to be defined in terms of characteristic modes at the fan <span class="hlt">source</span> plane and predict the propagation to the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930035187&hterms=Aachen&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DAachen','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930035187&hterms=Aachen&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DAachen"><span>Advances in tilt rotor <span class="hlt">noise</span> prediction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>George, A. R.; Coffen, C. D.; Ringler, T. D.</p> <p>1992-01-01</p> <p>The two most serious tilt rotor external <span class="hlt">noise</span> problems, hover <span class="hlt">noise</span> and blade-vortex interaction <span class="hlt">noise</span>, are studied. The results of flow visualization and inflow velocity measurements document a complex, recirculating highly unsteady and turbulent flow due to the rotor-wing-body interactions characteristic of tilt rotors. The wing under the rotor is found to obstruct the inflow, causing a deficit in the inflow velocities over the inboard region of the rotor. Discrete frequency <span class="hlt">harmonic</span> thickness and loading <span class="hlt">noise</span> mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various <span class="hlt">noise</span> prediction methods using the WOPWOP code. The analysis indicates that the partial ground plane created by the wing below the rotor results in a primary sound <span class="hlt">source</span> for hover.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760025884','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760025884"><span>Static and wind tunnel near-field/far-field jet <span class="hlt">noise</span> measurements from model scale single-flow baseline and suppressor nozzles. Volume 1: <span class="hlt">Noise</span> <span class="hlt">source</span> locations and extrapolation of static free-field jet <span class="hlt">noise</span> data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jaeck, C. L.</p> <p>1976-01-01</p> <p>A test was conducted in the Boeing Large Anechoic Chamber to determine static jet <span class="hlt">noise</span> <span class="hlt">source</span> locations of six baseline and suppressor nozzle models, and establish a technique for extrapolating near field data into the far field. The test covered nozzle pressure ratios from 1.44 to 2.25 and jet velocities from 412 to 594 m/s at a total temperature of 844 K.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050214793','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050214793"><span>Sound <span class="hlt">Sources</span> Identified in High-Speed Jets by Correlating Flow Density Fluctuations With Far-Field <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, Jayanta; Seasholtz, Richard G.</p> <p>2003-01-01</p> <p><span class="hlt">Noise</span> <span class="hlt">sources</span> in high-speed jets were identified by directly correlating flow density fluctuation (cause) to far-field sound pressure fluctuation (effect). The experimental study was performed in a nozzle facility at the NASA Glenn Research Center in support of NASA s initiative to reduce the <span class="hlt">noise</span> emitted by commercial airplanes. Previous efforts to use this correlation method have failed because the tools for measuring jet turbulence were intrusive. In the present experiment, a molecular Rayleigh-scattering technique was used that depended on laser light scattering by gas molecules in air. The technique allowed accurate measurement of air density fluctuations from different points in the plume. The study was conducted in shock-free, unheated jets of Mach numbers 0.95, 1.4, and 1.8. The turbulent motion, as evident from density fluctuation spectra was remarkably similar in all three jets, whereas the <span class="hlt">noise</span> <span class="hlt">sources</span> were significantly different. The correlation study was conducted by keeping a microphone at a fixed location (at the peak <span class="hlt">noise</span> emission angle of 30 to the jet axis and 50 nozzle diameters away) while moving the laser probe volume from point to point in the flow. The following figure shows maps of the nondimensional coherence value measured at different Strouhal frequencies ([frequency diameter]/jet speed) in the supersonic Mach 1.8 and subsonic Mach 0.95 jets. The higher the coherence, the stronger the <span class="hlt">source</span> was.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003ASAJ..114..967K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003ASAJ..114..967K"><span>Discriminating <span class="hlt">harmonicity</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kidd, Gerald; Mason, Christine R.; Brughera, Andrew; Chiu, Chung-Yiu Peter</p> <p>2003-08-01</p> <p>Simultaneous tones that are <span class="hlt">harmonically</span> related tend to be grouped perceptually to form a unitary auditory image. A partial that is mistuned stands out from the other tones, and <span class="hlt">harmonic</span> complexes with different fundamental frequencies can readily be perceived as separate auditory objects. These phenomena are evidence for the strong role of <span class="hlt">harmonicity</span> in perceptual grouping and segregation of sounds. This study measured the discriminability of <span class="hlt">harmonicity</span> directly. In a two interval, two alternative forced-choice (2I2AFC) paradigm, the listener chose which of two sounds, signal or foil, was composed of tones that more closely matched an exact <span class="hlt">harmonic</span> relationship. In one experiment, the signal was varied from perfectly <span class="hlt">harmonic</span> to highly inharmonic by adding frequency perturbation to each component. The foil always had 100% perturbation. Group mean performance decreased from greater than 90% correct for 0% signal perturbation to near chance for 80% signal perturbation. In the second experiment, adding a masker presented simultaneously with the signals and foils disrupted <span class="hlt">harmonicity</span>. Both monaural and dichotic conditions were tested. Signal level was varied relative to masker level to obtain psychometric functions from which slopes and midpoints were estimated. Dichotic presentation of these audible stimuli improved performance by 3-10 dB, due primarily to a release from ``informational masking'' by the perceptual segregation of the signal from the masker.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800006824','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800006824"><span>Demonstration of short-haul aircraft aft <span class="hlt">noise</span> reduction techniques on a twenty inch (50.8 cm) diameter fan, volume 1</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stimpert, D. L.; Mcfalls, R. A.</p> <p>1975-01-01</p> <p>Tests of a 20 inch diameter, low tip speed, low pressure ratio fan which investigated aft fan <span class="hlt">noise</span> reduction techniques are reported. These techniques included <span class="hlt">source</span> <span class="hlt">noise</span> reduction features of selection of vane-blade ratio to reduce second <span class="hlt">harmonic</span> <span class="hlt">noise</span>, spacing effects, and lowering the Mach number through a vane row. Aft suppression features investigated included porosity effects, variable depth treatment, and treatment regenerated flow <span class="hlt">noise</span>. Initial results and selected comparisons are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MNRAS.459.3314F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MNRAS.459.3314F"><span>The 154 MHz radio sky observed by the Murchison Widefield Array: <span class="hlt">noise</span>, confusion, and first <span class="hlt">source</span> count analyses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Franzen, T. M. O.; Jackson, C. A.; Offringa, A. R.; Ekers, R. D.; Wayth, R. B.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo, R. J.; Deshpande, A. A.; Gaensler, B. M.; Greenhill, L. J.; Hazelton, B. J.; Johnston-Hollitt, M.; Kaplan, D. L.; Lonsdale, C. J.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Morgan, J.; Oberoi, D.; Ord, S. M.; Prabu, T.; Seymour, N.; Shankar, N. Udaya; Srivani, K. S.; Subrahmanyan, R.; Tingay, S. J.; Trott, C. M.; Webster, R. L.; Williams, A.; Williams, C. L.</p> <p>2016-07-01</p> <p>We analyse a 154 MHz image made from a 12 h observation with the Murchison Widefield Array (MWA) to determine the <span class="hlt">noise</span> contribution and behaviour of the <span class="hlt">source</span> counts down to 30 mJy. The MWA image has a bandwidth of 30.72 MHz, a field-of-view within the half-power contour of the primary beam of 570 deg2, a resolution of 2.3 arcmin and contains 13 458 <span class="hlt">sources</span> above 5σ. The rms <span class="hlt">noise</span> in the centre of the image is 4-5 mJy beam-1. The MWA counts are in excellent agreement with counts from other instruments and are the most precise ever derived in the flux density range 30-200 mJy due to the sky area covered. Using the deepest available <span class="hlt">source</span> count data, we find that the MWA image is affected by sidelobe confusion <span class="hlt">noise</span> at the ≈3.5 mJy beam-1 level, due to incompletely peeled and out-of-image <span class="hlt">sources</span>, and classical confusion becomes apparent at ≈1.7 mJy beam-1. This work highlights that (i) further improvements in ionospheric calibration and deconvolution imaging techniques would be required to probe to the classical confusion limit and (ii) the shape of low-frequency <span class="hlt">source</span> counts, including any flattening towards lower flux densities, must be determined from deeper ≈150 MHz surveys as it cannot be directly inferred from higher frequency data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA098795','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA098795"><span>FET <span class="hlt">Noise</span> Studies.</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1981-03-01</p> <p>The predominant <span class="hlt">sources</span> of nonlinearity in the FET, relevant to oscillator analysis, are the transconductance gm and the <span class="hlt">source</span>-gate capacitance C sg...two general categories of <span class="hlt">noise</span> mechanisms in an FET: intrinsic <span class="hlt">sources</span>, i.e., <span class="hlt">noise</span> associated with the FET operation itself, and extrinsic <span class="hlt">noise</span>...very high drain voltages, also produces white <span class="hlt">noise</span>. <span class="hlt">Noise</span> produced by para- sitic resistance, one of the extrinsic <span class="hlt">noise</span> <span class="hlt">sources</span>, is also flat. These</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740022131','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740022131"><span>Analytic models of ducted turbomachinery tone <span class="hlt">noise</span> <span class="hlt">sources</span>. Volume 1: Analysis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Clark, T. L.; Ganz, U. W.; Graf, G. A.; Westall, J. S.</p> <p>1974-01-01</p> <p>The analytic models developed for computing the periodic sound pressure of subsonic fans and compressors in an infinite, hardwall annular duct with uniform flow are described. The basic sound-generating mechanism is the scattering into sound waves of velocity disturbances appearing to the rotor or stator blades as a series of <span class="hlt">harmonic</span> gusts. The models include component interactions and rotor alone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAG...128....1J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAG...128....1J"><span>A de-<span class="hlt">noising</span> algorithm based on wavelet threshold-exponential adaptive window width-fitting for ground electrical <span class="hlt">source</span> airborne transient electromagnetic signal</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ji, Yanju; Li, Dongsheng; Yu, Mingmei; Wang, Yuan; Wu, Qiong; Lin, Jun</p> <p>2016-05-01</p> <p>The ground electrical <span class="hlt">source</span> airborne transient electromagnetic system (GREATEM) on an unmanned aircraft enjoys considerable prospecting depth, lateral resolution and detection efficiency, etc. In recent years it has become an important technical means of rapid resources exploration. However, GREATEM data are extremely vulnerable to stationary white <span class="hlt">noise</span> and non-stationary electromagnetic <span class="hlt">noise</span> (sferics <span class="hlt">noise</span>, aircraft engine <span class="hlt">noise</span> and other human electromagnetic <span class="hlt">noises</span>). These <span class="hlt">noises</span> will cause degradation of the imaging quality for data interpretation. Based on the characteristics of the GREATEM data and major <span class="hlt">noises</span>, we propose a de-<span class="hlt">noising</span> algorithm utilizing wavelet threshold method and exponential adaptive window width-fitting. Firstly, the white <span class="hlt">noise</span> is filtered in the measured data using the wavelet threshold method. Then, the data are segmented using data window whose step length is even logarithmic intervals. The data polluted by electromagnetic <span class="hlt">noise</span> are identified within each window based on the discriminating principle of energy detection, and the attenuation characteristics of the data slope are extracted. Eventually, an exponential fitting algorithm is adopted to fit the attenuation curve of each window, and the data polluted by non-stationary electromagnetic <span class="hlt">noise</span> are replaced with their fitting results. Thus the non-stationary electromagnetic <span class="hlt">noise</span> can be effectively removed. The proposed algorithm is verified by the synthetic and real GREATEM signals. The results show that in GREATEM signal, stationary white <span class="hlt">noise</span> and non-stationary electromagnetic <span class="hlt">noise</span> can be effectively filtered using the wavelet threshold-exponential adaptive window width-fitting algorithm, which enhances the imaging quality.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19421292','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19421292"><span>Signal-to-<span class="hlt">noise</span> analysis for detection sensitivity of small absorbing heterogeneity in turbid media with single-<span class="hlt">source</span> and dual-interfering-<span class="hlt">source</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Y; Mu, C; Intes, X; Chance, B</p> <p>2001-08-13</p> <p>Previous studies have suggested that the phased-array detection can achieve high sensitivity in detecting and localizing inhomogeneities embedded in turbid media by illuminating with dual interfering <span class="hlt">sources</span>. In this paper, we analyze the sensitivity of single-<span class="hlt">source</span> and dual-interfering-<span class="hlt">source</span> (phased array) systems with signal-to-<span class="hlt">noise</span> ratio criteria. Analytical solutions are presented to investigate the sensitivity of detection using different degrees of absorption perturbation by varying the size and contrast of the object under similar configurations for single- and dual-<span class="hlt">source</span> systems. The results suggest that dual-<span class="hlt">source</span> configuration can provide higher detection sensitivity. The relation between the amplitude and phase signals for both systems is also analyzed using a vector model. The results can be helpful for optimizing the experimental design by combining the advantages of both single- and dual-<span class="hlt">source</span> systems in object detection and localization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.S53C2506W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.S53C2506W"><span>Application of the discontinuous Galerkin method to study the <span class="hlt">source</span> mechanisms for Love waves in ambient <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wenk, S.; Hadziioannou, C.; Igel, H.</p> <p>2012-12-01</p> <p>To produce detailed images of the crust using <span class="hlt">noise</span> correlation studies and to understand the ocean - solid Earth interaction processes we investigate the behavior and distribution of ambient <span class="hlt">noise</span> <span class="hlt">sources</span>, especially focused on the relative contribution of Love waves to the ambient <span class="hlt">noise</span> field. Therefore, we apply the discontinuous Galerkin (DG) method, which makes use of unstructured tetrahedral meshes combined with a time integration scheme solving the arbitrary high-order derivative (ADER) Riemann problem. The ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21721681','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21721681"><span>Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon <span class="hlt">source</span> based on laser high-order <span class="hlt">harmonic</span> generation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wernet, Philippe; Gaudin, Jérôme; Godehusen, Kai; Schwarzkopf, Olaf; Eberhardt, Wolfgang</p> <p>2011-06-01</p> <p>A laser-based tabletop approach to femtosecond time-resolved photoelectron spectroscopy with photons in the vacuum-ultraviolet (VUV) energy range is described. The femtosecond VUV pulses are produced by high-order <span class="hlt">harmonic</span> generation (HHG) of an amplified femtosecond Ti:sapphire laser system. Two generations of the same setup and results from photoelectron spectroscopy in the gas phase are discussed. In both generations, a toroidal grating monochromator was used to select one <span class="hlt">harmonic</span> in the photon energy range of 20-30 eV. The first generation of the setup was used to perform photoelectron spectroscopy in the gas phase to determine the bandwidth of the <span class="hlt">source</span>. We find that our HHG <span class="hlt">source</span> has a bandwidth of 140 ± 40 meV. The second and current generation is optimized for femtosecond pump-probe photoelectron spectroscopy with high flux and a small spot size at the sample of the femtosecond probe pulses. The VUV radiation is focused into the interaction region with a toroidal mirror to a spot smaller than 100 × 100 μm(2) and the flux amounts to 10(10) photons/s at the sample at a repetition rate of 1 kHz. The duration of the monochromatized VUV pulses is determined to be 120 fs resulting in an overall pump-probe time resolution of 135 ± 5 fs. We show how this setup can be used to map the transient valence electronic structure in molecular dissociation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.9164V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.9164V"><span><span class="hlt">Sources</span> of high frequency seismic <span class="hlt">noise</span>: insights from a dense network of ~250 stations in northern Alsace (France)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vergne, Jerome; Blachet, Antoine; Lehujeur, Maximilien</p> <p>2015-04-01</p> <p>Monitoring local or regional seismic activity requires stations having a low level of background seismic <span class="hlt">noise</span> at frequencies higher than few tenths of Hertz. Network operators are well aware that the seismic quality of a site depends on several aspects, among them its geological setting and the proximity of roads, railways, industries or trees. Often, the impact of each <span class="hlt">noise</span> <span class="hlt">source</span> is only qualitatively known which precludes estimating the quality of potential future sites before they are tested or installed. Here, we want to take advantage of a very dense temporary network deployed in Northern Alsace (France) to assess the effect of various kinds of potential <span class="hlt">sources</span> on the level of seismic <span class="hlt">noise</span> observed in the frequency range 0.2-50 Hz. In September 2014, more than 250 seismic stations (FairfieldNodal@ Zland nodes with 10Hz vertical geophone) have been installed every 1.5 km over a ~25km diameter disc centred on the deep geothermal sites of Soultz-sous-Forêts and Rittershoffen. This region exhibits variable degrees of human imprints from quite remote areas to sectors with high traffic roads and big villages. It also encompasses both the deep sedimentary basin of the Rhine graben and the piedmont of the Vosges massif with exposed bedrock. For each site we processed the continuous data to estimate probability density functions of the power spectral densities. At frequencies higher than 1 Hz most sites show a clear temporal modulation of seismic <span class="hlt">noise</span> related to human activity with the well-known variations between day and night and between weekdays and weekends. Moreover we observe a clear evolution of the spatial distribution of seismic <span class="hlt">noise</span> levels with frequency. Basically, between 0.5 and 4 Hz the geological setting modulates the level of seismic <span class="hlt">noise</span>. At higher frequencies, the amplitude of seismic <span class="hlt">noise</span> appears mostly related to the distance to nearby roads. Based on road maps and traffic estimation, a forward approach is performed to model the induced</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1512286J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1512286J"><span>Applying the seismic interferometry method to vertical seismic profile data using tunnel excavation <span class="hlt">noise</span> as <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jurado, Maria Jose; Teixido, Teresa; Martin, Elena; Segarra, Miguel; Segura, Carlos</p> <p>2013-04-01</p> <p>In the frame of the research conducted to develop efficient strategies for investigation of rock properties and fluids ahead of tunnel excavations the seismic interferometry method was applied to analyze the data acquired in boreholes instrumented with geophone strings. The results obtained confirmed that seismic interferometry provided an improved resolution of petrophysical properties to identify heterogeneities and geological structures ahead of the excavation. These features are beyond the resolution of other conventional geophysical methods but can be the cause severe problems in the excavation of tunnels. Geophone strings were used to record different types of seismic <span class="hlt">noise</span> generated at the tunnel head during excavation with a tunnelling machine and also during the placement of the rings covering the tunnel excavation. In this study we show how tunnel construction activities have been characterized as <span class="hlt">source</span> of seismic signal and used in our research as the seismic <span class="hlt">source</span> signal for generating a 3D reflection seismic survey. The data was recorded in vertical water filled borehole with a borehole seismic string at a distance of 60 m from the tunnel trace. A reference pilot signal was obtained from seismograms acquired close the tunnel face excavation in order to obtain best signal-to-<span class="hlt">noise</span> ratio to be used in the interferometry processing (Poletto et al., 2010). The seismic interferometry method (Claerbout 1968) was successfully applied to image the subsurface geological structure using the seismic wave field generated by tunneling (tunnelling machine and construction activities) recorded with geophone strings. This technique was applied simulating virtual shot records related to the number of receivers in the borehole with the seismic transmitted events, and processing the data as a reflection seismic survey. The pseudo reflective wave field was obtained by cross-correlation of the transmitted wave data. We applied the relationship between the transmission</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JEMat..45.4769J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JEMat..45.4769J"><span>Dislocations as a <span class="hlt">Noise</span> <span class="hlt">Source</span> in LWIR HgCdTe Photodiodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jóźwikowski, Krzysztof; Jóźwikowska, Alina; Martyniuk, Andrzej</p> <p>2016-10-01</p> <p>The effect of dislocation on the 1/ f <span class="hlt">noise</span> current in long-wavelength infrared (LWIR) reverse biased HgCdTe photodiodes working at liquid nitrogen (LN) temperature was analyzed theoretically by using a phenomenological model of dislocations as an additional Shockley-Read-Hall (SRH) generation-recombination (G-R) channel in heterostructure. Numerical analysis was involved to solve the set of transport equations in order to find a steady state values of physical parameters of the heterostructure. Next, the set of transport equations for fluctuations (TEFF) was formulated and solved to obtain the spectral densities (SD) of the fluctuations of electrical potential, quasi-Fermi levels, and temperature. The SD of mobility fluctuations, shot G-R <span class="hlt">noise</span>, and thermal <span class="hlt">noise</span> were also taken into account in TEFF. Additional expressions for SD of 1/ f fluctuations of the G-R processes were derived. Numerical values of the SD of <span class="hlt">noise</span> current were compared with the experimental results of Johnson et al. Theoretical analysis has shown that the dislocations increase the G-R processes and this way cause the growth of G-R dark current. Despite the fact that dislocations increase both shot G-R <span class="hlt">noise</span> and 1/ f G-R <span class="hlt">noise</span>, the main cause of 1/ f current <span class="hlt">noise</span> in LN cooled LWIR photodiodes are fluctuations of the carriers mobility determined by 1/ f fluctuations of relaxation times. As the <span class="hlt">noise</span> current is proportional to the total diode current, growth of G-R dark current caused by dislocations leads to the growth of <span class="hlt">noise</span> current.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100033097','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100033097"><span>Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Measurements of an F404 Nozzle Plume at Both Full and Model Scale</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary G.; Bridges, James E.; Henderson, Brenda S.</p> <p>2010-01-01</p> <p>A 48-microphone planar phased array system was used to acquire jet <span class="hlt">noise</span> <span class="hlt">source</span> localization data on both a full-scale F404-GE-F400 engine and on a 1/4th scale model of a F400 series nozzle. The full-scale engine test data show the location of the dominant <span class="hlt">noise</span> <span class="hlt">sources</span> in the jet plume as a function of frequency for the engine in both baseline (no chevron) and chevron configurations. Data are presented for the engine operating both with and without afterburners. Based on lessons learned during this test, a set of recommendations are provided regarding how the phased array measurement system could be modified in order to obtain more useful acoustic <span class="hlt">source</span> localization data on high-performance military engines in the future. The data obtained on the 1/4th scale F400 series nozzle provide useful insights regarding the full-scale engine jet <span class="hlt">noise</span> <span class="hlt">source</span> mechanisms, and document some of the differences associated with testing at model-scale versus fullscale.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730024885','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730024885"><span><span class="hlt">Noise</span> pollution resources compendium</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1973-01-01</p> <p>Abstracts of reports concerning <span class="hlt">noise</span> pollution are presented. The abstracts are grouped in the following areas of activity: (1) <span class="hlt">sources</span> of <span class="hlt">noise</span>, (2) <span class="hlt">noise</span> detection and measurement, (3) <span class="hlt">noise</span> abatement and control, (4) physical effects of <span class="hlt">noise</span> and (5) social effects of <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT.......356M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT.......356M"><span>Non-<span class="hlt">harmonic</span> root-pitch individual-blade control for the reduction of blade-vortex interaction <span class="hlt">noise</span> in rotorcraft</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Malovrh, Brendon D.</p> <p></p> <p>One of the greatest obstacles to public acceptance of rotorcraft is the high levels of <span class="hlt">noise</span> they produce, particularly in low-speed descent. In this flight condition, the trailing edge vortex of one blade often passes in close proximity to other blades resulting in impulsive changes in lift. This Blade-Vortex Interaction (BVI) creates high levels of both <span class="hlt">noise</span> and vibration. The objective of this dissertation is to evaluate the effectiveness of using physically motivated pulse-type Individual Blade Control for reducing the <span class="hlt">noise</span> associated with the BVI. First, the major parameters that affect the severity of the interaction, such as vortex strength and blade-vortex miss-distance, are analyzed. Second, inputs designed specifically to alter the parameters previously identified as key are explored, resulting in elimination of advancing side <span class="hlt">noise</span> and overall peak BVI Sound Pressure Level (BVISPL) reductions of up to 4.6 dB. Lastly, different feedback mechanisms for closed-loop control of IBC are examined to allow implementation of the developed inputs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910032600&hterms=source+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsource%2Bstudy','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910032600&hterms=source+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsource%2Bstudy"><span>Can shock waves on helicopter rotors generate <span class="hlt">noise</span>? - A study of the quadrupole <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Farassat, F.; Tadghighi, H.</p> <p>1990-01-01</p> <p>An analysis has previously established that local shock surfaces attached to helicopter rotor blades moving at high subsonic speeds are potent <span class="hlt">noise</span> generators; in pursuit of this insight, a novel formulation is presented for the prediction of the <span class="hlt">noise</span> of a deformable shock, whose area changes as a function of the azimuthal position of the blade. The derivation of this formulation has its basis in a mapping of the moving shock to a time-independent region. In virtue of this mapping, the implementation of the main result on a computer becomes straightforward enough for incorporation into the available rotor-<span class="hlt">noise</span> prediction code. A problem illustrating the importance of rotor shocks in the generation of high-intensity <span class="hlt">noise</span> is presented.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920041269&hterms=harmonic+function&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dharmonic%2Bfunction','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920041269&hterms=harmonic+function&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dharmonic%2Bfunction"><span>An evaluation of HEMT potential for millimeter-wave signal <span class="hlt">sources</span> using interpolation and <span class="hlt">harmonic</span> balance techniques</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kwon, Youngwoo; Pavlidis, Dimitris; Tutt, Marcel N.</p> <p>1991-01-01</p> <p>A large-signal analysis method based on an <span class="hlt">harmonic</span> balance technique and a 2-D cubic spline interpolation function has been developed and applied to the prediction of InP-based HEMT oscillator performance for frequencies extending up to the submillimeter-wave range. The large-signal analysis method uses a limited number of DC and small-signal S-parameter data and allows the accurate characterization of HEMT large-signal behavior. The method has been validated experimentally using load-pull measurement. Oscillation frequency, power performance, and load requirements are discussed, with an operation capability of 300 GHz predicted using state-of-the-art devices (fmax is approximately equal to 450 GHz).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920065511&hterms=Exciter&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DExciter','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920065511&hterms=Exciter&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DExciter"><span>Detection of fundamental and <span class="hlt">harmonic</span> type III radio emission and the associated Langmuir waves at the <span class="hlt">source</span> region</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Reiner, M. J.; Stone, R. G.; Fainberg, J.</p> <p>1992-01-01</p> <p>Type III radio emission generated in the vicinity of the Ulysses spacecraft has been detected at both the fundamental and <span class="hlt">harmonic</span> of the local plasma frequency. The observations represent the first clear evidence of locally generated type III radio emission. This local emission shows no evidence of frequency drift, exhibits a relatively short rise time, is less intense than the observed remotely generated radio emission, and is temporally correlated with observed in situ Langmuir waves. The observations were made with the unified radio astronomy and wave (URAP) experiment on the Ulysses spacecraft between 1990 November 4 and 1991 April 30, as it traveled from 1 to 3 AU from the sun. During this time period many thousands of bursts were observed. However, only three examples of local emission and associated Langmuir waves were identified. This supports previous suggestions that type III radio emission is generated in localized regions of the interplanetary medium, rather than uniformly along the extent of the electron exciter beam.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JAG....67...66A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JAG....67...66A"><span>A seismic field test with a Low-level Acoustic Combustion <span class="hlt">Source</span> and Pseudo-<span class="hlt">Noise</span> codes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Askeland, Bjørn; Ruud, Bent Ole; Hobæk, Halvor; Mjelde, Rolf</p> <p>2009-01-01</p> <p>The Low-level Acoustic Combustion <span class="hlt">Source</span> (LACS) which can fire its pulses at a high rate, has been tested successfully as a seismic marine <span class="hlt">source</span> on shallow ice-age sediments in Byfjorden at Bergen, Norway. Pseudo-<span class="hlt">Noise</span> pulsed signals with spiky autocorrelation functions were used to detect the sediments. Each transmitted sequence lasted 10 s and contained 43 pulses. While correlation gave a blurry result, deconvolution between the near-field recordings and the streamer recordings gave a clear seismic section. Compared to the section acquired with single air-gun shots along the same profile, the LACS gave a more clear presentation of the sediments and basement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960003376','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960003376"><span>Active Control of Fan <span class="hlt">Noise</span>-Feasibility Study. Volume 2: Canceling <span class="hlt">Noise</span> <span class="hlt">Source</span>-Design of an Acoustic Plate Radiator Using Piezoceramic Actuators</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pla, F. G.; Rajiyah, H.</p> <p>1995-01-01</p> <p>The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling <span class="hlt">sources</span> for active control of aircraft engine fan <span class="hlt">noise</span> is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy acoustic plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of acoustic plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable acoustic <span class="hlt">source</span> for active control of aircraft engine fan <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/776581','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/776581"><span>Simultaneous ballistic deficit immunity and resilience to parallel <span class="hlt">noise</span> <span class="hlt">sources</span>: A new pulse shaping technique</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fabris, Lorenzo; Becker, John A.; Goulding, Frederick S.; Madden, Norman W.</p> <p>2000-10-11</p> <p>A new and different time variant pulse processing system has been developed based on a simple CR-RC filter and two analog switches. The new pulse processing technique combines both ballistic deficit immunity and resilience to parallel <span class="hlt">noise</span> without a significant compromise to the low energy resolution, generally considered a mutually exclusive requirement. The filter is realized by combining two different pulse-shaping techniques. One of the techniques creates a low rate of curvature at the pulse peak, which reduces ballistic deficit, while the second technique increases the tolerance to low frequency <span class="hlt">noise</span> by modifying the <span class="hlt">noise</span> history. Several experimental measurements are presented, including tests on a co-planar grid CdZnTe detector. Improvements on both the resolution and line shape are shown for the 662 keV line of 137Cs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/95297','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/95297"><span><span class="hlt">Noise</span> measurements in shunted, shorted, and fully electroded quartz gauges in the Saturn plasma radiation <span class="hlt">source</span> x-ray simulator</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Barrett, W.H.; Greenwoll, J.I.; Smith, C.W.; Johnson, D.E.; De La Cruz, C.F.</p> <p>1995-08-01</p> <p>This paper describes recent work to improve the measurement of the stress response of materials to intense, short pulses of radiation. When Saturn fires, large prompt electrical <span class="hlt">noise</span> pulses are induced in stress measurement circuits. The conventional wisdom has been that the shorted guard ring quartz gauge was the only configuration with acceptable prompt signal-to-<span class="hlt">noise</span> characteristics for stress measurements in this pulsed radiation environment. However, because of abnormal signal distortion, the shorted guard ring gauge is restricted to a maximum stress of about 8 kbars. Below this level, the normal, quantified signal distortion is correctable with analytical deconvolution techniques. The shunted guard ring gauge is acceptable for Egli fidelity measurements to about 25 kbars with negligible signal distortion. Experiments were conducted on the Saturn soft x-ray <span class="hlt">source</span> which show that higher fidelity shunted guard ring gauges can successfully measure stress with acceptable induced <span class="hlt">noise</span>. We also found that a 50-ohm impedance matching resistor at the gauge reduced the prompt <span class="hlt">noise</span> amplitude and improved the baseline quality of the measurement prior to shock wave arrival.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24021638','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24021638"><span>Improved Shear Wave Motion Detection Using Pulse-Inversion <span class="hlt">Harmonic</span> Imaging With a Phased Array Transducer.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pengfei Song; Heng Zhao; Urban, Matthew W; Manduca, Armando; Pislaru, Sorin V; Kinnick, Randall R; Pislaru, Cristina; Greenleaf, James F; Shigao Chen</p> <p>2013-12-01</p> <p>Ultrasound tissue <span class="hlt">harmonic</span> imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter <span class="hlt">noise</span>. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these <span class="hlt">noise</span> <span class="hlt">sources</span> can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing <span class="hlt">harmonic</span> imaging, specifically pulse-inversion <span class="hlt">harmonic</span> imaging, in shear wave tracking, with the hypothesis that <span class="hlt">harmonic</span> imaging can improve shear wave motion detection based on the same principles that apply to general <span class="hlt">harmonic</span> B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that <span class="hlt">harmonic</span> imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that <span class="hlt">harmonic</span> imaging could robustly track the shear wave motion and give consistent shear wave speed measurements of the left ventricular myocardium while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed <span class="hlt">harmonic</span> imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index higher than 25. These promising results indicate that pulse-inversion <span class="hlt">harmonic</span> imaging can significantly improve shear wave motion tracking and thus potentially</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26906363','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26906363"><span>Performance of a ruthenium beam separator used to separate soft x rays from light generated by a high-order <span class="hlt">harmonic</span> light <span class="hlt">source</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ichimaru, Satoshi; Hatayama, Masatoshi; Ohchi, Tadayuki; Gullikson, Eric M; Oku, Satoshi</p> <p>2016-02-10</p> <p>We describe the design and fabrication of a ruthenium beam separator used to simultaneously attenuate infrared light and reflect soft x rays. Measurements in the infrared and soft x-ray regions showed the beam separator to have a reflectivity of 50%-85% in the wavelength region from 6 to 10 nm at a grazing incidence angle of 7.5 deg and 4.3% at 800 nm and the same angle of grazing incidence, indicating that the amount of attenuation is 0.05-0.09. These results show that this beam separator could provide an effective means for separating IR light from soft x rays in light generated by high-order <span class="hlt">harmonic</span> generation <span class="hlt">sources</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10179438','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10179438"><span><span class="hlt">Harmonic</span> generation at high intensities</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Schafer, K.J.; Krause, J.L.; Kulander, K.C.</p> <p>1993-06-01</p> <p>Atomic electrons subject to intense laser fields can absorb many photons, leading either to multiphoton ionization or the emission of a single, energetic photon which can be a high multiple of the laser frequency. The latter process, high-order <span class="hlt">harmonic</span> generation, has been observed experimentally using a range of laser wavelengths and intensities over the past several years. <span class="hlt">Harmonic</span> generation spectra have a generic form: a steep decline for the low order <span class="hlt">harmonics</span>, followed by a plateau extending to high <span class="hlt">harmonic</span> order, and finally an abrupt cutoff beyond which no <span class="hlt">harmonics</span> are discernible. During the plateau the <span class="hlt">harmonic</span> production is a very weak function of the process order. <span class="hlt">Harmonic</span> generation is a promising <span class="hlt">source</span> of coherent, tunable radiation in the XUV to soft X-ray range which could have a variety of scientific and possibly technological applications. Its conversion from an interesting multiphoton phenomenon to a useful laboratory radiation <span class="hlt">source</span> requires a complete understanding of both its microscopic and macroscopic aspects. We present some recent results on the response of single atoms at intensities relevant to the short pulse experiments. The calculations employ time-dependent methods, which we briefly review in the next section. Following that we discuss the behavior of the <span class="hlt">harmonics</span> as a function of laser intensity. Two features are notable: the slow scaling of the <span class="hlt">harmonic</span> intensities with laser intensity, and the rapid variation in the phase of the individual <span class="hlt">harmonics</span> with respect to <span class="hlt">harmonic</span> order. We then give a simple empirical formula that predicts the extent of the plateau for a given ionization potential, wavelength and intensity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910043630&hterms=noise+linear&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D20%26Ntt%3Dnoise%2Bin%2Blinear','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910043630&hterms=noise+linear&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D20%26Ntt%3Dnoise%2Bin%2Blinear"><span>Effect of mean load on the non-linear behavior of spur gear <span class="hlt">noise</span> <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kahraman, Ahmet; Singh, Rajendra</p> <p>1989-01-01</p> <p>An analytical technique for estimating <span class="hlt">noise</span> generation by spur-gear pairs with backlash is developed using the results obtained by Comparin and Singh (1989). The derivation of the governing equations is outlined, and numerical results for sample problems are presented in graphs. Good agreement with published experimental data (Munro, 1962) is demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA205758','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA205758"><span>A Standard Definition for Wind-Generated, Low-Frequency Ambient <span class="hlt">Noise</span> <span class="hlt">Source</span> Levels</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1989-02-09</p> <p>FUNDING NUMBERS PROGR.AM PROJECT ITASK IWORK UNIT ELEMENT 14O. NO. NO. IACCESSION NO. I I ritLE (include Security Caiafaon) I7Ol A STANDARD DEFINITION...use of a specific propagation code (PE, RAYTRACE, ASTRAL , NORMAL MODE, etc). The specification of <span class="hlt">noise</span> intensity per unit area with respect to/ /P</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750009957','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750009957"><span>Generalized wave envelope analysis of sound propagation in ducts with stepped <span class="hlt">noise</span> <span class="hlt">source</span> profiles and variable axial impedance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Baumeister, K. J.</p> <p>1975-01-01</p> <p>A finite difference formulation is presented for sound propagation in a rectangular two-dimensional duct without steady flow. Before the difference equations are formulated, the governing Helmholtz equation is first transformed to a form whose solution tends not to oscillate along the length of the duct. This transformation reduces the required number of grid points by an order of magnitude. Example solutions indicate that stepped <span class="hlt">noise</span> <span class="hlt">source</span> profiles have much higher attenuation than plane waves in a uniform impedance liner. Also, multiple stepped impedance liners are shown to have higher attenuation than uniform ducts if the impedances are chosen properly. For optimum <span class="hlt">noise</span> reduction with axial variations in impedance, the numerical analysis indicates that for a plane wave input the resistance should be near zero at the entrance of a suppressor duct, while the reactance should be near the optimum value associated with the least-attenuated mode in a uniform duct.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920005567','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920005567"><span>Interior <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mixson, John S.; Wilby, John F.</p> <p>1991-01-01</p> <p>The generation and control of flight vehicle interior <span class="hlt">noise</span> is discussed. Emphasis is placed on the mechanisms of transmission through airborne and structure-borne paths and the control of cabin <span class="hlt">noise</span> by path modification. Techniques for identifying the relative contributions of the various <span class="hlt">source</span>-path combinations are also discussed along with methods for the prediction of aircraft interior <span class="hlt">noise</span> such as those based on the general modal theory and statistical energy analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA219535','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA219535"><span>Identification and Proposed Control of Helicopter Transmission <span class="hlt">Noise</span> at the <span class="hlt">Source</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1987-03-19</p> <p>future work on helicopter <span class="hlt">noise</span> are presented. OH-SB HELICOPTER & TRANSMISION The OH-58C Helicopter is the Army’s Light Scout/Attack helicopter...grinding machine . As currently manufactured, spiral bevel gears do not have conjugate action. Spiral bevel gears with conjugate action were examined...was lost. The process of grinding teeth on a spiral bevel gear is a function of many different settings on the gear grinding machine . Nominally similar</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22984278','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22984278"><span><span class="hlt">Source</span> of statistical <span class="hlt">noises</span> in the Monte Carlo sampling techniques for coherently scattered photons.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Muhammad, Wazir; Lee, Sang Hoon</p> <p>2013-01-01</p> <p>Detailed comparisons of the predictions of the Relativistic Form Factors (RFFs) and Modified Form Factors (MFFs) and their advantages and shortcomings in calculating elastic scattering cross sections can be found in the literature. However, the issues related to their implementation in the Monte Carlo (MC) sampling for coherently scattered photons is still under discussion. Secondly, the linear interpolation technique (LIT) is a popular method to draw the integrated values of squared RFFs/MFFs (i.e. A(Z, v(i)²)) over squared momentum transfer (v(i)² = v(1)²,......, v(59)²). In the current study, the role/issues of RFFs/MFFs and LIT in the MC sampling for the coherent scattering were analyzed. The results showed that the relative probability density curves sampled on the basis of MFFs are unable to reveal any extra scientific information as both the RFFs and MFFs produced the same MC sampled curves. Furthermore, no relationship was established between the multiple small peaks and irregular step shapes (i.e. statistical <span class="hlt">noise</span>) in the PDFs and either RFFs or MFFs. In fact, the <span class="hlt">noise</span> in the PDFs appeared due to the use of LIT. The density of the <span class="hlt">noise</span> depends upon the interval length between two consecutive points in the input data table of A(Z, v(i)²) and has no scientific background. The probability density function curves became smoother as the interval lengths were decreased. In conclusion, these statistical <span class="hlt">noises</span> can be efficiently removed by introducing more data points in the A(Z, v(i)²) data tables.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA133958','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA133958"><span>Experimental and Analytical Studies of Shielding Concepts for Point <span class="hlt">Sources</span> and Jet <span class="hlt">Noise</span>.</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1983-05-01</p> <p>fundarentac property of barriers, permits significant <span class="hlt">noise</span> reduction onit it rilerate an ; Fig. 2-25 %. On the whole, however, a lighter scoop shield...the radiated sound field of a turbulent jet can Localized Extension .57 be derived from the self preservation properties of the turbulence in the...Helmholtz -0 integral states that if some physical property of a sound field such as It can be Shown that when 7.1-e) is satisfied the contribution to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA598418','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA598418"><span>Auditory Masking Patterns in Bottlenose Dolphins from Anthropogenic and Natural <span class="hlt">Noise</span> <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2013-09-30</p> <p>e.g., critical ratios ) are often used to describe and predict auditory masking. For this task, detection thresholds for a 10 kHz tone were measured in...unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 2 determine the relationship between <span class="hlt">noise</span> metrics and masked tonal ...the residual errors (FIG 3) demonstrates that the two-parameter model produces much better fits than critical ratio predictions, while still being</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984aiaa.meetT....W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984aiaa.meetT....W"><span>Prediction of <span class="hlt">sources</span> moving at high speed as applied to helicopter and propeller <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wright, S. E.; Lee, D. J.</p> <p>1984-01-01</p> <p>This paper analyzes the linear acoustic solution concerning the radiation from a rigid body in motion. The body displacement <span class="hlt">source</span> is used as the monopole <span class="hlt">source</span> description, rather than the traditional volume flow rate. The point <span class="hlt">source</span> behavior, particularly in circular motion, and the onset of noncompactness is considered. The effect of finite <span class="hlt">source</span> distributions is established and an efficient method developed to calculate the effect of finite chord and span distributions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1008624','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1008624"><span>Auditory and Subjective Effects of Airborne <span class="hlt">Noise</span> from Industrial Ultrasonic <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Acton, W. I.; Carson, M. B.</p> <p>1967-01-01</p> <p>This investigation was undertaken primarily to examine the possibility of hearing damage from industrial ultrasonic equipment. In the factory concerned, ultrasonic washers and drills were used at a number of different locations, and girls working 12 ft (3·6 m.) away from one bank of three small washers complained of unpleasant subjective effects which included fatigue, persistent headaches, nausea, and tinnitus. As personnel working in the vicinity of similar washers in other parts of the factory did not complain of these effects, it seemed possible that the <span class="hlt">noise</span> had been transmitted along a column of air in a bank of dryboxes. Enclosure of these washers by a sliding screen of Perspex had completely abated the trouble. Sound pressure level measurements taken in the positions occupied by the operators indicated that, when the effects occur, they are probably caused by high sound levels at the upper audio-frequencies present with the ultrasonic <span class="hlt">noise</span>, and this was supported by a limited laboratory investigation. Audiometric investigation showed that hearing damage due to <span class="hlt">noise</span> from these industrial ultrasonic devices is unlikely. However, extrapolations of currently accepted hearing damage risk criteria may be valid in predicting the occurrence of these subjective effects. Images PMID:6073088</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970017414','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970017414"><span>Fan <span class="hlt">Noise</span> Prediction System Development: <span class="hlt">Source</span>/Radiation Field Coupling and Workstation Conversion for the Acoustic Radiation Code</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Meyer, H. D.</p> <p>1993-01-01</p> <p>The Acoustic Radiation Code (ARC) is a finite element program used on the IBM mainframe to predict far-field acoustic radiation from a turbofan engine inlet. In this report, requirements for developers of internal aerodynamic codes regarding use of their program output an input for the ARC are discussed. More specifically, the particular input needed from the Bolt, Beranek and Newman/Pratt and Whitney (turbofan <span class="hlt">source</span> <span class="hlt">noise</span> generation) Code (BBN/PWC) is described. In a separate analysis, a method of coupling the <span class="hlt">source</span> and radiation models, that recognizes waves crossing the interface in both directions, has been derived. A preliminary version of the coupled code has been developed and used for initial evaluation of coupling issues. Results thus far have shown that reflection from the inlet is sufficient to indicate that full coupling of the <span class="hlt">source</span> and radiation fields is needed for accurate <span class="hlt">noise</span> predictions ' Also, for this contract, the ARC has been modified for use on the Sun and Silicon Graphics Iris UNIX workstations. Changes and additions involved in this effort are described in an appendix.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=%22Maxwell%27s+equation+%22&pg=2&id=EJ187556','ERIC'); return false;" href="http://eric.ed.gov/?q=%22Maxwell%27s+equation+%22&pg=2&id=EJ187556"><span>Complete Vector Spherical <span class="hlt">Harmonic</span> Expansion for Maxwell's Equations</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Lambert, R. H.</p> <p>1978-01-01</p> <p>Conventional expansions of solutions to Maxwell's equations in vector spherical <span class="hlt">harmonics</span> apply only outside the <span class="hlt">sources</span>. The complete solution, applying both inside and outside the <span class="hlt">sources</span>, is given here. <span class="hlt">Harmonic</span> time dependence is assumed. (Author/GA)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008spa..book.1005F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008spa..book.1005F"><span>Community Response to <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fidell, Sandy</p> <p></p> <p>The primary effects of community <span class="hlt">noise</span> on residential populations are speech interference, sleep disturbance, and annoyance. This chapter focuses on transportation <span class="hlt">noise</span> in general and on aircraft <span class="hlt">noise</span> in particular because aircraft <span class="hlt">noise</span> is one of the most prominent community <span class="hlt">noise</span> <span class="hlt">sources</span>, because airport/community controversies are often the most contentious and widespread, and because industrial and other specialized formsofcommunitynoise generally posemorelocalized problems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1001787','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1001787"><span><span class="hlt">Harmonic</span> engine</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Bennett, Charles L.</p> <p>2009-10-20</p> <p>A high efficiency <span class="hlt">harmonic</span> engine based on a resonantly reciprocating piston expander that extracts work from heat and pressurizes working fluid in a reciprocating piston compressor. The engine preferably includes <span class="hlt">harmonic</span> oscillator valves capable of oscillating at a resonant frequency for controlling the flow of working fluid into and out of the expander, and also preferably includes a shunt line connecting an expansion chamber of the expander to a buffer chamber of the expander for minimizing pressure variations in the fluidic circuit of the engine. The engine is especially designed to operate with very high temperature input to the expander and very low temperature input to the compressor, to produce very high thermal conversion efficiency.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...377...90S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...377...90S"><span>Concurrent identification of aero-acoustic scattering and <span class="hlt">noise</span> <span class="hlt">sources</span> at a flow duct singularity in low Mach number flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sovardi, Carlo; Jaensch, Stefan; Polifke, Wolfgang</p> <p>2016-09-01</p> <p>A numerical method to concurrently characterize both aeroacoustic scattering and <span class="hlt">noise</span> <span class="hlt">sources</span> at a duct singularity is presented. This approach combines Large Eddy Simulation (LES) with techniques of System Identification (SI): In a first step, a highly resolved LES with external broadband acoustic excitation is carried out. Subsequently, time series data extracted from the LES are post-processed by means of SI to model both acoustic propagation and <span class="hlt">noise</span> generation. The present work studies the aero-acoustic characteristics of an orifice placed in a duct at low flow Mach numbers with the "LES-SI" method. Parametric SI based on the Box-Jenkins mathematical structure is employed, with a prediction error approach that utilizes correlation analysis of the output residuals to avoid overfitting. Uncertainties of model parameters due to the finite length of times series are quantified in terms of confidence intervals. Numerical results for acoustic scattering matrices and power spectral densities of broad-band <span class="hlt">noise</span> are validated against experimental measurements over a wide range of frequencies below the cut-off frequency of the duct.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9499E..0DA','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9499E..0DA"><span>Next generation data <span class="hlt">harmonization</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Armstrong, Chandler; Brown, Ryan M.; Chaves, Jillian; Czerniejewski, Adam; Del Vecchio, Justin; Perkins, Timothy K.; Rudnicki, Ron; Tauer, Greg</p> <p>2015-05-01</p> <p>Analysts are presented with a never ending stream of data <span class="hlt">sources</span>. Often, subsets of data <span class="hlt">sources</span> to solve problems are easily identified but the process to align data sets is time consuming. However, many semantic technologies do allow for fast <span class="hlt">harmonization</span> of data to overcome these problems. These include ontologies that serve as alignment targets, visual tools and natural language processing that generate semantic graphs in terms of the ontologies, and analytics that leverage these graphs. This research reviews a developed prototype that employs all these approaches to perform analysis across disparate data <span class="hlt">sources</span> documenting violent, extremist events.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/262465','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/262465"><span>Field and laboratory studies of moving and temporally variable <span class="hlt">noise</span> <span class="hlt">sources</span> (aircraft); perception of location, movement, and direction.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gunn, W J; Shigehisa, T; Shepherd, W T</p> <p>1979-10-01</p> <p>The conditions were examined under which more valid and reliable estimates could be made of the effects of aircraft <span class="hlt">noise</span> on people. In Exper. 1, 12 Ss in 2 different houses directly under the flight path of a major airport (JFK) indicated 1 of 12 possible flight paths (4 directly overhead and 8 to one side) for each of 3 jet aircraft flyovers: 3% of cases in House A and 56% in House B (which had open windows) were correctly identified. Despite judgment inaccuracy, Ss were more than moderately certain of the correctness of their judgments. In Exper. II. Ss either inside or outside of 2 houses in Wallops Station, Virginia, indicated on diagrams the direction of flyovers. Each of 4 aircraft (Boeing 737, C-54, UE-1 helicopter, Queenaire) made 8 flyovers directly over the houses and 8 to one side. Windows were either open or closed. All flyovers and conditions were counterbalanced. All sound <span class="hlt">sources</span> under all conditions were usually judged to be overhead and moving, but for Ss indoors with windows closed the to-the-side flyovers were judged to be off to the side in 24% of cases. Outdoor Ss reported correct direction in 75% of cases while indoor Ss were correct in only 25% (windows open) or 18% (windows closed). Judgments "to the side" were significantly better (p = less than .02) with windows open vs closed, while with windows closed judgments were significantly better (p = less than .05) for flyovers overhead vs to the side. In Exper. III, Ss localized in azimuth and in the vertical plane recorded <span class="hlt">noises</span> (10 1-oct <span class="hlt">noise</span> bands of CF = 28.12 c/s - 14.4kc/s, spoken voice, and jet aircraft takeoffs and landings), presented through 1, 2, or 4 floor-level loudspeakers at each corner of a simulated living room (4.2 x 5.4m)built inside an IAC soundproof room. Aircraft <span class="hlt">noises</span> presented by 4 loudspeakers were localized as "directly" overhead 80% of the time and "generally overhead" about 90% of the time; other sounds were so localized about 50% and 75% of the time respectively</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21037607','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21037607"><span>Amplitude-modulated circular-<span class="hlt">harmonic</span> filter for pattern recognition.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, X W; Chen, Z P</p> <p>1995-02-10</p> <p>An amplitude-modulated circular-<span class="hlt">harmonic</span> filter is proposed for rotation-invariant pattern recognition. We investigate the filter characteristics by varying two design parameters, A(ρ) and B(ρ), and select optimum values to design an amplitude-modulated circular-<span class="hlt">harmonic</span> filter. When compared with the phase-only circular-<span class="hlt">harmonic</span> filter, the amplitude-modulated circular-<span class="hlt">harmonic</span> filter is found to yield a sharper correlation peak, a better <span class="hlt">noise</span> tolerance, and an improved correlation discrimination.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/985835','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/985835"><span>Nanograting-based compact VUV spectrometer and beam profiler for in-situ characterization of high-order <span class="hlt">harmonic</span> generation light <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kornilov, Oleg; Wilcox, Russell; Gessner, Oliver</p> <p>2010-07-09</p> <p>A compact, versatile device for VUV beam characterization is presented. It combines the functionalities of a VUV spectrometer and a VUV beam profiler in one unit and is entirely supported by a standard DN200 CF flange. The spectrometer employs a silicon nitride transmission nanograting in combination with a micro-channel plate based imaging detector. This enables the simultaneous recording of wavelengths ranging from 10 nm to 80 nm with a resolution of 0.25 nm to 0.13 nm. Spatial beam profiles with diameters up to 10 mm are imaged with 0.1 mm resolution. The setup is equipped with an in-vacuum translation stage that allows for in situ switching between the spectrometer and beam profiler modes and for moving the setup out of the beam. The simple, robust design of the device is well suited for non-intrusive routine characterization of emerging laboratory- and accelerator-based VUV light <span class="hlt">sources</span>. Operation of the device is demonstrated by characterizing the output of a femtosecond high-order <span class="hlt">harmonic</span> generation light <span class="hlt">source</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA241141','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA241141"><span>Aeroacoustics of Flight Vehicles: Theory and Practice. Volume 1. <span class="hlt">Noise</span> <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1991-08-01</p> <p>coso kl (32) -2 [mB(Mr2cosO- M,) ] = t 1 +kMx BD (33) and the phase lag due to sweep is 2Mrt mB MCA _r I _ _’cs - k - (34)Ms- r k1-Mzcos6 k D In equation...indicates sound at blade-passage frequency and its multiples, just as with the steady-loading formulas discussed previously. The factor ( r /C%) - t indicates...Pressures. AIAA-80-0977, June 1980 36 Chou, S - T .; and George, A. R .. Effect of Angle of Attack on Rotor Trading-Edge <span class="hlt">Noise</span>. AIAA J, vol. 22, no 12, Dec</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870026322&hterms=Propellers+aircraft&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DPropellers%2Baircraft','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870026322&hterms=Propellers+aircraft&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DPropellers%2Baircraft"><span>Comparison of two propeller <span class="hlt">source</span> models for aircraft interior <span class="hlt">noise</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mahan, J. R.; Fuller, C. R.</p> <p>1986-01-01</p> <p>The sensitivity of the predicted synchrophasing (SP) effectiveness trends to the propeller <span class="hlt">source</span> model issued is investigated with reference to the development of advanced turboprop engines for transport aircraft. SP effectiveness is shown to be sensitive to the type of <span class="hlt">source</span> model used. For the virtually rotating dipole <span class="hlt">source</span> model, the SP effectiveness is sensitive to the direction of rotation at some frequencies but not at others. The SP effectiveness obtained from the virtually rotating dipole model is not very sensitive to the radial location of the <span class="hlt">source</span> distribution within reasonable limits. Finally, the predicted SP effectiveness is shown to be more sensitive to the details of the <span class="hlt">source</span> model used for the case of corotation than for the case of counterrotation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GeoJI.188.1303Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GeoJI.188.1303Y"><span>Exploiting seismic signal and <span class="hlt">noise</span> in an intracratonic environment to constrain crustal structure and <span class="hlt">source</span> parameters of infrequent earthquakes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Young, Mallory K.; Tkalčić, Hrvoje; Rawlinson, Nicholas; Reading, Anya M.</p> <p>2012-03-01</p> <p>In many regions of the world characterized by a relatively low rate of seismicity, the determination of local and regional seismic <span class="hlt">source</span> parameters is often restricted to an analysis of the first onsets of P waves (or first motion analysis) due to incomplete information about Earth structure and the small size of the events. When rare large earthquakes occur in these regions, their waveforms can be used to model Earth structure. This, however, makes the nature of the earthquake <span class="hlt">source</span> determination problem circular, as <span class="hlt">source</span> information is mapped as structure. Presented here is one possible remedy to this situation, where through a two-step approach we first constrain Earth structure using data independent of the earthquake of interest. In this study, we focus on a region in Western Australia with low seismicity and minimal instrument coverage and use the CAPRA/LP temporary deployment to demonstrate that reliable structural models of the upper lithosphere can be obtained from an independent collection of teleseismic and ambient <span class="hlt">noise</span> datasets. Apart from teleseismic receiver functions (RFs), we obtain group velocities from the cross-correlation of ambient <span class="hlt">noise</span> and phase velocities from the traditional two-station method using carefully selected teleseismic earthquakes and station pairs. Crustal models are then developed through the joint inversion of dispersion data and RFs, and structural Green's functions are computed from a layered composite model. In the second step of this comprehensive approach, we apply full waveform inversion (three-component body and surface waves) to the 2007 ML= 5.3 Shark Bay, Western Australia, earthquake to estimate its <span class="hlt">source</span> parameters (seismic moment, focal mechanism, and depth). We conclude that the full waveform inversion analysis provides constraints on the orientation of fault planes superior to a first motion interpretation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S41A4419T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S41A4419T"><span>Directionality of Ambient <span class="hlt">Noise</span> on the Juan de Fuca Plate: Implications for <span class="hlt">Source</span> Locations of the Primary and Secondary Microseism</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tian, Y.; Ritzwoller, M. H.</p> <p>2014-12-01</p> <p>Based on cross-correlations computed from 61 ocean bottom seismometers (OBSs) within the Juan de Fuca plate from the Cascadia Initiative experiment and 42 continental stations near the western US coast, we investigate the generation locations of the primary (11-20 sec period) and secondary (5-10 sec period) microseisms in the northern Pacific Ocean by analyzing the directionality of the microseism signals received in this region. (1) Ambient <span class="hlt">noise</span> observed across the array is much different in the primary and secondary microseism bands, both in its azimuthal content and seasonal variation, indicating different <span class="hlt">source</span> generation locations. (2) The principal secondary microseism signals propagate toward the east, consistent with <span class="hlt">source</span> generation in deep water of the North Pacific, perhaps coincident with the region of body wave excitation observed by Gerstoft et al. [2008] and Landès et al. [2010]. (3) Local primary microseism <span class="hlt">sources</span> within and near the Juan de Fuca plate are implied by observations of the azimuthal dependence of the fundamental mode Rayleigh wave amplitudes as well as observations of precursory arrivals in cross-correlations of ambient <span class="hlt">noise</span>. The strongest local generation region is observed northwest of the Juan de Fuca plate near the coast of British Columbia perhaps near Graham Island. Weaker local <span class="hlt">sources</span> appear to be oceanward of Vancouver Island and southern Oregon. (4) High quality Green's functions are derived from cross-correlations between deep water OBSs and continental stations proving that deep water generated signals can efficiently propagate onto the continent and are well recorded by continental seismic stations, at least at periods longer than about 5 sec.In conclusion, the primary and secondary microseisms are generated at different locations, with the secondary microseism dominantly coming from deep-water <span class="hlt">sources</span> and the <span class="hlt">source</span> of primary microseism having a significant component in the shallow waters of the eastern Pacific</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JSV...293.1029J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JSV...293.1029J"><span>Evaluation of the interim measurement protocol for railway <span class="hlt">noise</span> <span class="hlt">source</span> description</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Janssens, M. H. A.; Jansen, H. W.; Dittrich, M. G.</p> <p>2006-06-01</p> <p>The Dutch national calculation scheme for railway <span class="hlt">noise</span> has been declared the default interim method for railway <span class="hlt">noise</span> calculation by the EU, until the introduction of results from the Harmonoise project. It includes a measurement protocol for determining emission input data in the format suitable for the present calculation scheme. The calculation scheme contains a fixed database of emission data for common Dutch rolling stock. The measurement protocol provides for the addition of emission data of new or foreign rolling stock. This is relevant for the Netherlands, as such rolling stock increasingly appears on the network, but also for other European countries that are going to use the interim method, since emission data for their rolling stock have to be established. The protocol features two procedures. Procedure A allows using the existing fixed database of emission data. Selection of a particular dataset (or 'category') can be based on external appearance of rolling stock (without measurements) or pass-by sound pressure level measurements at a site with known rail roughness. If a user finds that none of the existing data sets properly represent its rolling stock, the optional procedure B is available. This procedure assesses pass-by levels, track and wheel roughness levels. The measurement protocol is based on a type-test-like procedure requiring controlled conditions for the vehicle and track. A measurement campaign has been undertaken to test procedures A and B. This campaign coincided with a Swiss campaign to establish the sound emission of freight vehicles equipped with composite block brakes. The test of the protocol was focussed both on the practicability of the required measurements and on the unambiguity and comprehensiveness of the test. Open questions, findings, resulting conclusions and recommendations regarding the protocol are discussed here.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1150738','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1150738"><span><span class="hlt">Harmonic</span> engine</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Bennett, Charles L.; Sewall, Noel; Boroa, Carl</p> <p>2014-08-19</p> <p>An engine based on a reciprocating piston engine that extracts work from pressurized working fluid. The engine includes a <span class="hlt">harmonic</span> oscillator inlet valve capable of oscillating at a resonant frequency for controlling the flow of working fluid into of the engine. In particular, the inlet valve includes an inlet valve head and a spring arranged together as a <span class="hlt">harmonic</span> oscillator so that the inlet valve head is moveable from an unbiased equilibrium position to a biased closed position occluding an inlet. Upon releasing the inlet valve the inlet valve head undergoes a single oscillation past the equilibrium positio to a maximum open position and returns to a biased return position close to the closed position to choke the flow and produce a pressure drop across the inlet valve causing the inlet valve to close. Protrusions carried either by the inlet valve head or piston head are used to bump open the inlet valve from the closed position and initiate the single oscillation of the inlet valve head, and protrusions carried either by the outlet valve head or piston head are used to close the outlet valve ahead of the bump opening of the inlet valve.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860015745','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860015745"><span>Helicopter rotor <span class="hlt">noise</span> due to ingestion of atmospheric turbulence</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.; Greitzer, E. M.</p> <p>1986-01-01</p> <p>A theoretical study was conducted to develop an analytical prediction method for helicopter main rotor <span class="hlt">noise</span> due to the ingestion of atmospheric turbulence. This study incorporates an atmospheric turbulence model, a rotor mean flow contraction model and a rapid distortion turbulence model which together determine the statistics of the non-isotropic turbulence at the rotor plane. Inputs to the combined mean inflow and turbulence models are controlled by atmospheric wind characteristics and helicopter operating conditions. A generalized acoustic <span class="hlt">source</span> model was used to predict the far field <span class="hlt">noise</span> generated by the non-isotropic flow incident on the rotor. Absolute levels for acoustic spectra and directivity patterns were calculated for full scale helicopters, without the use of empirical or adjustable constants. Comparisons between isotropic and non-isotropic turbulence at the rotor face demonstrated pronounced differences in acoustic spectra. Turning and contraction of the flow for hover and low speed vertical ascent cases result in a 3 dB increase in the acoustic spectrum energy and a 10 dB increase in tone levels. Compared to trailing edge <span class="hlt">noise</span>, turbulence ingestion <span class="hlt">noise</span> is the dominant <span class="hlt">noise</span> mechanism below approximately 30 rotor <span class="hlt">harmonics</span>, while above 100 <span class="hlt">harmonics</span>, trailing edge <span class="hlt">noise</span> levels exceed turbulence ingestion <span class="hlt">noise</span> by 25 dB.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150021044','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150021044"><span>Acoustic Database for Turbofan Engine Core-<span class="hlt">Noise</span> <span class="hlt">Sources</span>. I; Volume</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gordon, Grant</p> <p>2015-01-01</p> <p>In this program, a database of dynamic temperature and dynamic pressure measurements were acquired inside the core of a TECH977 turbofan engine to support investigations of indirect combustion <span class="hlt">noise</span>. Dynamic temperature and pressure measurements were recorded for engine gas dynamics up to temperatures of 3100 degrees Fahrenheit and transient responses as high as 1000 hertz. These measurements were made at the entrance of the high pressure turbine (HPT) and at the entrance and exit of the low pressure turbine (LPT). Measurements were made at two circumferential clocking positions. In the combustor and inter-turbine duct (ITD), measurements were made at two axial locations to enable the exploration of time delays. The dynamic temperature measurements were made using dual thin-wire thermocouple probes. The dynamic pressure measurements were made using semi-infinite probes. Prior to the engine test, a series of bench, oven, and combustor rig tests were conducted to characterize the performance of the dual wire temperature probes and to define and characterize the data acquisition systems. A measurement solution for acquiring dynamic temperature and pressure data on the engine was defined. A suite of hardware modifications were designed to incorporate the dynamic temperature and pressure instrumentation into the TECH977 engine. In particular, a probe actuation system was developed to protect the delicate temperature probes during engine startup and transients in order to maximize sensor life. A set of temperature probes was procured and the TECH977 engine was assembled with the suite of new and modified hardware. The engine was tested at four steady state operating speeds, with repeats. Dynamic pressure and temperature data were acquired at each condition for at least one minute. At the two highest power settings, temperature data could not be obtained at the forward probe locations since the mean temperatures exceeded the capability of the probes. The temperature data</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985aimm.cong..407M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985aimm.cong..407M"><span>Use of acoustic intensity measurements in the characterization of jet <span class="hlt">noise</span> <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Musafir, R. E.; Slama, J. G.; Zindeluk, M.</p> <p></p> <p>The usefulness of two-microphone acoustic-intensity (AI) measurements for characterizing the acoustic field of a jet flow is investigated by means of numerical simulations. The theoretical principles and data basis for the simulations are explained, and the intensity patterns generated by the simulation are presented graphically. It is found that the vector information in AI data from the near field are useful in understanding complex <span class="hlt">sources</span>, but that far-field intensity charts cannot locate separate <span class="hlt">sources</span> and may be misleading if not analyzed in terms of a sound physical model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017RScI...88c5107B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017RScI...88c5107B"><span>A low <span class="hlt">noise</span> modular current <span class="hlt">source</span> for stable magnetic field control</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Biancalana, Valerio; Bevilacqua, Giuseppe; Chessa, Piero; Dancheva, Yordanka; Cecchi, Roberto; Stiaccini, Leonardo</p> <p>2017-03-01</p> <p>A low cost, stable, programmable, unipolar current <span class="hlt">source</span> is described. The circuit is designed in view of a modular arrangement, suitable for applications where several DC <span class="hlt">sources</span> must be controlled at once. A hybrid switching/linear design helps in improving the stability and in reducing the power dissipation and cross-talking. Multiple units can be supplied by a single DC power supply, while allowing for a variety of maximal current values and compliance voltages at the outputs. The circuit is analogically controlled by a unipolar voltage, enabling current programmability and control through commercial digital-to-analogue conversion cards.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760015333','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760015333"><span>Automatic <span class="hlt">noise</span> limiter-blanker</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burhans, R. W.</p> <p>1976-01-01</p> <p>A blanker system that may be used with audio <span class="hlt">noise</span> limiters or automatic <span class="hlt">noise</span> limiters was described. The system employs a pair of silicon diodes and two RC filters connected across the feedback impedance of an operational amplifier so as to counteract impulse <span class="hlt">noise</span> interference caused by local spherics activity or 60 Hz <span class="hlt">harmonics</span> radiated from ac motor control systems. The following information is given: circuit diagram and description, operating details, evaluation, discussion of other <span class="hlt">noise</span> blanking methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005ASAJ..118.1848W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005ASAJ..118.1848W"><span>Acoustic emissions of digital data video projectors- Investigating <span class="hlt">noise</span> <span class="hlt">sources</span> and their change during product aging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>White, Michael Shane</p> <p>2005-09-01</p> <p>Acoustic emission testing continues to be a growing part of IT and telecommunication product design, as product <span class="hlt">noise</span> is increasingly becoming a differentiator in the marketplace. This is especially true for digital/video display companies, such as InFocus Corporation, considering the market shift of these products to the home entertainment consumer as retail prices drop and performance factors increase. Projectors and displays using Digital Light Processing(tm) [DLP(tm)] technology incorporate a device known as a ColorWheel(tm) to generate the colors displayed at each pixel in the image. These ColorWheel(tm) devices spin at very high speeds and can generate high-frequency tones not typically heard in liquid crystal displays and other display technologies. Also, acoustic emission testing typically occurs at the beginning of product life and is a measure of acoustic energy emitted at this point in the lifecycle. Since the product is designed to be used over a long period of time, there is concern as to whether the acoustic emissions change over the lifecycle of the product, whether these changes will result in a level of nuisance to the average customer, and does this nuisance begin to develop prior to the intended lifetime of the product.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDG20005X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDG20005X"><span>New insights into insect's silent flight. Part II: sound <span class="hlt">source</span> and <span class="hlt">noise</span> control</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xue, Qian; Geng, Biao; Zheng, Xudong; Liu, Geng; Dong, Haibo</p> <p>2016-11-01</p> <p>The flapping flight of aerial animals has excellent aerodynamic performance but meanwhile generates low <span class="hlt">noise</span>. In this study, the unsteady flow and acoustic characteristics of the flapping wing are numerically investigated for three-dimensional (3D) models of Tibicen linnei cicada at free forward flight conditions. Single cicada wing is modelled as a membrane with prescribed motion reconstructed by Wan et al. (2015). The flow field and acoustic field around the flapping wing are solved with immersed-boundary-method based incompressible flow solver and linearized-perturbed-compressible-equations based acoustic solver. The 3D simulation allows examination of both directivity and frequency composition of the produced sound in a full space. The mechanism of sound generation of flapping wing is analyzed through correlations between acoustic signals and flow features. Along with a flexible wing model, a rigid wing model is also simulated. The results from these two cases will be compared to investigate the effects of wing flexibility on sound generation. This study is supported by NSF CBET-1313217 and AFOSR FA9550-12-1-0071.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=social+AND+network+AND+accuracy&pg=3&id=EJ1004715','ERIC'); return false;" href="http://eric.ed.gov/?q=social+AND+network+AND+accuracy&pg=3&id=EJ1004715"><span>Organizational Communication in Emergencies: Using Multiple Channels and <span class="hlt">Sources</span> to Combat <span class="hlt">Noise</span> and Capture Attention</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Stephens, Keri K.; Barrett, Ashley K.; Mahometa, Michael J.</p> <p>2013-01-01</p> <p>This study relies on information theory, social presence, and <span class="hlt">source</span> credibility to uncover what best helps people grasp the urgency of an emergency. We surveyed a random sample of 1,318 organizational members who received multiple notifications about a large-scale emergency. We found that people who received 3 redundant messages coming through at…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012IEITF..95..498L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012IEITF..95..498L"><span>A 24dB Gain 51-68GHz Common <span class="hlt">Source</span> Low <span class="hlt">Noise</span> Amplifier Using Asymmetric-Layout Transistors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Ning; Bunsen, Keigo; Takayama, Naoki; Bu, Qinghong; Suzuki, Toshihide; Sato, Masaru; Kawano, Yoichi; Hirose, Tatsuya; Okada, Kenichi; Matsuzawa, Akira</p> <p></p> <p>At mm-wave frequency, the layout of CMOS transistors has a larger effect on the device performance than ever before in low frequency. In this work, the distance between the gate and drain contact (Dgd) has been enlarged to obtain a better maximum available gain (MAG). By using the asymmetric-layout transistor, a 0.6dB MAG improvement is realized when Dgd changes from 60nm to 200nm. A four-stage common-<span class="hlt">source</span> low <span class="hlt">noise</span> amplifier is implemented in a 65nm CMOS process. A measured peak power gain of 24dB is achieved with a power dissipation of 30mW from a 1.2-V power supply. An 18dB variable gain is also realized by adjusting the bias voltage. The measured 3-dB bandwidth is about 17GHz from 51GHz to 68GHz, and <span class="hlt">noise</span> figure (NF) is from 4.0dB to 7.6dB.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880044398&hterms=metcalf&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dmetcalf','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880044398&hterms=metcalf&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dmetcalf"><span>Structureborne <span class="hlt">noise</span> in aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Clevenson, S. A.; Metcalf, V. L.</p> <p>1987-01-01</p> <p>The amount of <span class="hlt">noise</span> reaching an aircraft's interior by structureborne paths, when high levels of other <span class="hlt">noises</span> are present, involves the measurement of transfer functions between vibrating levels on the wing and interior <span class="hlt">noise</span>. The magnitude of the structureborne <span class="hlt">noise</span> transfer function is established by exciting the aircraft with an electrodynamic shaker; a second transfer function is measured using the same sensor locations with the aircraft engines operating. Attention is given to the case of a twin-turboprop OV-10A aircraft; the resulting transfer function values at the discrete frequencies corresponding to the propeller blade passage frequency and its first four <span class="hlt">harmonics</span> are tabulated and illustrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880060266&hterms=star+shots&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dstar%2Bshots','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880060266&hterms=star+shots&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dstar%2Bshots"><span>Shot <span class="hlt">noise</span> cross-correlation functions and cross spectra - Implications for models of QPO X-ray <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shibazaki, N.; Elsner, R. F.; Bussard, R. W.; Ebisuzaki, T.; Weisskopf, M. C.</p> <p>1988-01-01</p> <p>The cross-correlation functions (CCFs) and cross spectra expected for quasi-periodic oscillation (QPO) shot <span class="hlt">noise</span> models are calculated under various assumptions, and the results are compared to observations. Effects due to possible coherence of the QPO oscillations are included. General formulas for the cross spectrum, the cross-phase spectrum, and the time-delay spectrum for QPO shot models are calculated and discussed. It is shown that the CCFs, cross spectra, and power spectra observed for Cyg X-e2 imply that the spectrum of the shots evolves with time, with important implications for the interpretation of these functions as well as of observed average energy spectra. The possible origins for the observed hard lags are discussed, and some physical difficulties for the Comptonization model are described. Classes of physical models for QPO <span class="hlt">sources</span> are briefly addressed, and it is concluded that models involving shot formation at the surface of neutron stars are favored by observation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150002348','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150002348"><span>Shielding Characteristics Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> to Generate Modes - Experimental Measurements and Analytical Predictions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel L.; Walker, Bruce E.</p> <p>2014-01-01</p> <p>An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14x22 wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8% scale model. The UCFANS is a 5.8% rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the program was to provide an estimate of the acoustic shielding benefits possible from mounting an engine on the upper surface of a wing; a flat plate model was used as the shielding surface. Simple analytical simulations were used to preview the radiation patterns - Fresnel knife-edge diffraction was coupled with a dense phased array of point <span class="hlt">sources</span> to compute shielded and unshielded sound pressure distributions for potential test geometries and excitation modes. Contour plots of sound pressure levels, and integrated power levels, from nacelle alone and shielded configurations for both the experimental measurements and the analytical predictions are presented in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030065909','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030065909"><span>Computation of Large-Scale Structure Jet <span class="hlt">Noise</span> <span class="hlt">Sources</span> With Weak Nonlinear Effects Using Linear Euler</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dahl, Milo D.; Hixon, Ray; Mankbadi, Reda R.</p> <p>2003-01-01</p> <p>An approximate technique is presented for the prediction of the large-scale turbulent structure sound <span class="hlt">source</span> in a supersonic jet. A linearized Euler equations code is used to solve for the flow disturbances within and near a jet with a given mean flow. Assuming a normal mode composition for the wave-like disturbances, the linear radial profiles are used in an integration of the Navier-Stokes equations. This results in a set of ordinary differential equations representing the weakly nonlinear self-interactions of the modes along with their interaction with the mean flow. Solutions are then used to correct the amplitude of the disturbances that represent the <span class="hlt">source</span> of large-scale turbulent structure sound in the jet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880037647&hterms=techniques+method&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dtechniques%252C%2Bmethod','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880037647&hterms=techniques+method&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dtechniques%252C%2Bmethod"><span>A <span class="hlt">noise</span> <span class="hlt">source</span> identification technique using an inverse Helmholtz integral equation method</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gardner, B. K.; Bernhard, R. J.</p> <p>1988-01-01</p> <p>A technique is developed which utilizes numerical models and field pressure information to characterize acoustic fields and identify acoustic <span class="hlt">sources</span>. The numerical models are based on boundary element numerical procedures. Either pressure, velocity, or passive boundary conditions, in the form of impedance boundary conditions, may be imposed on the numerical model. Alternatively, if no boundary information is known, a boundary condition can be left unspecified. Field pressure data may be specified to overdetermine the numerical problem. The problem is solved numerically for the complete sound field from which the acoustic <span class="hlt">sources</span> may be determined. The model can then be used to idenfify acoustic intensity paths in the field. The solution can be modified and the model used to evaluate design alternatives. In this investigation the method is tested analytically and verified. In addition, the sensitivity of the method to random and bias error in the input data is demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009SPIE.7258E..5NW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009SPIE.7258E..5NW"><span>Dual <span class="hlt">source</span> CT (DSCT) imaging of obese patients: evaluation of CT number accuracy, uniformity, and <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walz-Flannigan, A.; Schmidt, B.,; Apel, A.; Eusemann, C.; Yu, L.; McCollough, C. H.</p> <p>2009-02-01</p> <p>Obese patients present challenges in obtaining sufficient x-ray exposure over reasonable time periods for acceptable CT image quality. To overcome this limitation, the exposure can be divided between two x-ray <span class="hlt">sources</span> using a dualsource (DS) CT system. However, cross-scatter issues in DS CT may also compromise image quality. We evaluated a DS CT system optimized for imaging obese patients, comparing the CT number accuracy and uniformity to the same images obtained with a single-<span class="hlt">source</span> (SS) acquisition. The imaging modes were compared using both solid cylindrical PMMA phantoms and a semi-anthropomorphic thorax phantom fitted with extension rings to simulate different size patients. Clinical protocols were used and CTDIvol and kVp were held constant between SS and DS modes. Results demonstrated good agreement in CT number between SS and DS modes in CT number, with the DS mode showing better axial uniformity for the largest phantoms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1326612','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1326612"><span>Reduction of Beam Current <span class="hlt">Noise</span> in the FNAL Magnetron Ion <span class="hlt">Source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bollinger, D. S.; Karns, P. R.; Tan, C. Y.</p> <p>2014-01-01</p> <p>The new FNAL Injector Line with a circular dimple magnetron ion <span class="hlt">source</span> has been operational since December of 2013. Since the new injector came on line there have been variations in the H- beam current flattop observed near the downstream end of the linac. Several different cathode geometries including a hollow cathode suggested by Dudnikov [1] were tried. We expanded on those studies by trying mixtures ranging from 0.25%N, 99.75%H to 3%N, 97%H. The results of these studies in our test stand will be presented in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/981360','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/981360"><span>Strongly Dispersive Transient Bragg Grating for High <span class="hlt">Harmonics</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Farrell, J.; Spector, L.S.; Gaarde, M.B.; McFarland, B.K.; Bucksbaum, P.H.; Guhr, Markus; /SLAC, PULSE /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.</p> <p>2010-06-04</p> <p>We create a transient Bragg grating in a high <span class="hlt">harmonic</span> generation medium using two counterpropagating pulses. The Bragg grating disperses the <span class="hlt">harmonics</span> in angle and can diffract a large bandwidth with temporal resolution limited only by the <span class="hlt">source</span> size.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5875386','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5875386"><span>Acoustic <span class="hlt">noise</span> associated with the MOD-1 wind turbine: its <span class="hlt">source</span>, impact, and control</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kelley, N.D.; McKenna, H.E.; Hemphill, R.R.; Etter, C.L.; Garrelts, R.L.; Linn, N.C.</p> <p>1985-02-01</p> <p>This report summarizes extensive research by staff of the Solar Energy Research Institute and its subcontractors conducted to establish the origin and possible amelioration of acoustic disturbances associated with the operation of the DOE/NASA MOD-1 wind turbine installed in 1979 near Boone, North Carolina. Results have shown that the <span class="hlt">source</span> of this acoustic annoyance was the transient, unsteady aerodynamic lift imparted to the turbine blades as they passed through the lee wakes of the large, cylindrical tower supports. Nearby residents were annoyed by the low-frequency, acoustic impulses propagated into the structures in which the complainants lived. The situation was aggravated further by a complex sound propagation process controlled by terrain and atmospheric focusing. Several techniques for reducing the abrupt, unsteady blade load transients were researched and are discussed in the report.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5949122','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5949122"><span><span class="hlt">Sources</span> of <span class="hlt">noise</span> and vibration in a mechanical system with clearances</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Akay, A.; Bengisu, M.T.</p> <p>1982-01-01</p> <p>Inherent in the design of any mechanism with moving parts is the requirement for clearances. In the case of an engine, this requirement is enhanced by the extremes of both load and temperature under which some parts are expected to function. Collision of the parts in these connections where clearances exist are influenced by transient combustion forces as well as inertial forces. Impacts in the joints of a system are a major <span class="hlt">source</span> of sound, vibration and wear. The mechanism of sound generation follows the dynamic response of the system components. The resulting transient acoustic field is comprised of radiation from the forced and free vibrations of the system. Radiation due to inertial forces are generally of lower frequency whereas sounds produced by the impacts exhibit higher levels with higher spectral content. This study investigates the sound and vibration response of a four-bar mechanism in the absence of external forces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUSM.G13A..01W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUSM.G13A..01W"><span>Glacial Isostatic Adjustment as a <span class="hlt">Source</span> of <span class="hlt">Noise</span> for the Interpretation of GRACE Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wahr, J.; Velicogna, I.; Paulson, A.</p> <p>2009-05-01</p> <p>Viscoelastic relaxation in the Earth's mantle caused by wide-spread deglaciation following the last glacial maximum (LGM), can appear as a secular trend in measurements of the Earth's time-variable gravity field. The presence of this trend can provide an opportunity to use gravity observations to constrain models of the glacial isostatic adjustment (GIA) process. But it can also be a nuisance for people who are using the gravity observations to learn about other things. Gravity observations, whether from satellites or from ground-based gravimeters, can not distinguish between the gravitational effects of water/snow/ice variations on or near the surface, and those caused by density variations deep within the mantle. Unmodeled or mismodeled GIA signals can sometimes make it difficult to use gravity observations to learn about secular changes in water/snow/ice from such places as northern Canada, Scandinavia, Antarctica, and Greenland: places where there was considerable long-term deglaciation following the LGM. These issues have become particularly important since the 2002 launch of the GRACE gravity satellite mission. GIA signals in northern Canada and Scandinavia are clearly evident in the GRACE data. But the presence of GIA signals in these and other regions has sometimes caused problems for long-term hydrological and, especially, cryospheric studies with GRACE. GIA model errors, for example, are by far the largest <span class="hlt">source</span> of uncertainty when using GRACE to estimate present-day thinning rates of the Antarctic ice sheet. This talk will discuss the contributions of the GIA signal to GRACE time-variable gravity measurements; partly as an opportunity to study the GIA process, but mostly as a <span class="hlt">source</span> of uncertainty for other applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870004687','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870004687"><span>Effects of background <span class="hlt">noise</span> on total <span class="hlt">noise</span> annoyance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Willshire, K. F.</p> <p>1987-01-01</p> <p>Two experiments were conducted to assess the effects of combined community <span class="hlt">noise</span> <span class="hlt">sources</span> on annoyance. The first experiment baseline relationships between annoyance and <span class="hlt">noise</span> level for three community <span class="hlt">noise</span> <span class="hlt">sources</span> (jet aircraft flyovers, traffic and air conditioners) presented individually. Forty eight subjects evaluated the annoyance of each <span class="hlt">noise</span> <span class="hlt">source</span> presented at four different <span class="hlt">noise</span> levels. Results indicated the slope of the linear relationship between annoyance and <span class="hlt">noise</span> level for the traffic <span class="hlt">noise</span> was significantly different from that of aircraft and of air conditioner <span class="hlt">noise</span>, which had equal slopes. The second experiment investigated annoyance response to combined <span class="hlt">noise</span> <span class="hlt">sources</span>, with aircraft <span class="hlt">noise</span> defined as the major <span class="hlt">noise</span> <span class="hlt">source</span> and traffic and air conditioner <span class="hlt">noise</span> as background <span class="hlt">noise</span> <span class="hlt">sources</span>. Effects on annoyance of <span class="hlt">noise</span> level differences between aircraft and background <span class="hlt">noise</span> for three total <span class="hlt">noise</span> levels and for both background <span class="hlt">noise</span> <span class="hlt">sources</span> were determined. A total of 216 subjects were required to make either total or <span class="hlt">source</span> specific annoyance judgements, or a combination of the two, for a wide range of combined <span class="hlt">noise</span> conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.201..429T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.201..429T"><span>Directionality of ambient <span class="hlt">noise</span> on the Juan de Fuca plate: implications for <span class="hlt">source</span> locations of the primary and secondary microseisms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tian, Ye; Ritzwoller, Michael H.</p> <p>2015-04-01</p> <p>Based on cross-correlations of ambient seismic <span class="hlt">noise</span> computed using 61 ocean bottom seismometers (OBSs) within the Juan de Fuca (JdF) plate from the Cascadia Initiative experiment and 42 continental stations near the coast of the western United States, we investigate the locations of generation of the primary (11-20 s period) and secondary (5-10 s period) microseisms in the northern Pacific Ocean by analysing the directionality and seasonality of the microseism (Rayleigh wave) signals received in this region. We conclude that (1) the ambient <span class="hlt">noise</span> observed across the array is much different in the primary and secondary microseism bands, both in its azimuthal content and seasonal variation. (2) The principal secondary microseism signals propagate towards the east, consistent with their generation in deep waters of the North Pacific, perhaps coincident both with the region of observed body wave excitation and the predicted wave-wave interaction region from recent studies. (3) The primary microseism, as indicated by observations of the azimuthal dependence of the fundamental mode Rayleigh wave as well as observations of precursory arrivals, derives significantly from the shallow waters of the eastern Pacific near to the JdF plate but also has a component generated at greater distance of unknown origin. (4) These observations suggest different physical mechanisms for generating the two microseisms: the secondary microseisms are likely to be generated by non-linear wave-wave interaction over the deep Pacific Ocean, while the primary microseism may couple directly into the solid earth locally in shallow waters from ocean gravity waves. (5) Above 5 s period, high quality empirical Green's functions are observed from cross-correlations between deep water OBSs and continental stations, which illustrates that microseisms propagate efficiently from either deep or shallow water <span class="hlt">source</span> regions onto the continent and are well recorded by continental seismic stations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA403756','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA403756"><span>Active Control of Fan <span class="hlt">Noise</span> in Ducts Using Magnetic Bearings</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2007-11-02</p> <p>of magnetic bearings. An axial flow fan creates tonal <span class="hlt">noise</span> related to its rotational rate. Additional <span class="hlt">noise</span> exists due to <span class="hlt">harmonics</span> of this frequency...magnetic bearings. An axial flow fan creates tonal <span class="hlt">noise</span> related to its rotational rate. Additional <span class="hlt">noise</span> exists due to <span class="hlt">harmonics</span> of this frequency as well...systems typically have fans that will move air from the heating or cooling system to any desired space. Fan <span class="hlt">noise</span> is characterized first by tonal</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JMOp...60.1475G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JMOp...60.1475G"><span>Sub-100 nanometer lensless probing of Co/Pd magnetic nanodomains using a table-top femtosecond soft X-ray <span class="hlt">harmonic</span> <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ge, X.; Ducousso, M.; Boutu, W.; Tudu, B.; Barbrel, B.; Gauthier, D.; Borta, A.; Gonzalez, A.-I.; Wang, F.; Iwan, B.; Billon, M.; Perdrix, M.; Guillaumet, D.; Lepetit, F.; Vodungbo, B.; Gautier, J.; Hawaldar, R.; Tortarolo, M.; Delaunay, R.; Zeitoun, P.; Lüning, J.; Merdji, H.</p> <p>2013-10-01</p> <p>We present recent developments of our table-top femtosecond high flux <span class="hlt">harmonic</span> beamline towards single-shot probing of magnetic nanostructures. High <span class="hlt">harmonic</span> generation (HHG) optimization in a single and two-color infrared laser pulse mode was investigated at high laser energy. Up to 109 photons per <span class="hlt">harmonic</span> are generated between 40 and 80 eV in a single femtosecond laser shot. These soft X-ray <span class="hlt">harmonic</span> photons are employed to characterize at the nanoscale the magnetic network of Co/Pd multilayer samples using resonant small-angle X-ray scattering. Selecting <span class="hlt">harmonics</span> in the vicinity of magnetically dichroic absorption resonances of cobalt and palladium (Co M2,3 at 60 eV and Pd N2,3 at 51 eV) gives access to the magnetic nanodomain spatial structure. The magnetic scattering efficiency at the Pd edge is found to be comparable to that at the Co edge. This indicates that the Pd layers exhibit a significant induced magnetic moment. Magnetic sample optimization is then performed by characterizing its scattering efficiency as a function of layer composition and number of repetitions. We finally measure the spatial organization of magnetic nanodomains with a sub-100 nm spatial resolution from a single femtosecond X-ray pulse.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PMB....52.1409K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PMB....52.1409K"><span><span class="hlt">Noise</span>-tolerance analysis for detection and reconstruction of absorbing inhomogeneities with diffuse optical tomography using single- and phase-correlated dual-<span class="hlt">source</span> schemes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kanmani, B.; Vasu, R. M.</p> <p>2007-03-01</p> <p>An iterative reconstruction procedure is used to invert intensity data from both single- and phase-correlated dual-<span class="hlt">source</span> illuminations for absorption inhomogeneities. The Jacobian for the dual <span class="hlt">source</span> is constructed by an algebraic addition of the Jacobians estimated for the two <span class="hlt">sources</span> separately. By numerical simulations, it is shown that the dual-<span class="hlt">source</span> scheme performs superior to the single-<span class="hlt">source</span> system in regard to (i) <span class="hlt">noise</span> tolerance in data and (ii) ability to reconstruct smaller and lower contrast objects. The quality of reconstructions from single-<span class="hlt">source</span> data, as indicated by mean-square error at convergence, is markedly poorer compared to their dual-<span class="hlt">source</span> counterpart, when <span class="hlt">noise</span> in data was in excess of 2%. With fixed contrast and decreasing inhomogeneity diameter, our simulations showed that, for diameters below 7 mm, the dual-<span class="hlt">source</span> scheme has a higher percentage contrast recovery compared to the single-<span class="hlt">source</span> scheme. Similarly, the dual-<span class="hlt">source</span> scheme reconstructs to a higher percentage contrast recovery from lower contrast inhomogeneity, in comparison to the single-<span class="hlt">source</span> scheme.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870018052&hterms=numerical+method&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dnumerical%2Bmethod','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870018052&hterms=numerical+method&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dnumerical%2Bmethod"><span>A study of methods to predict and measure the transmission of sound through the walls of light aircraft. Numerical method for analyzing the optimal performance of active <span class="hlt">noise</span> controllers. Thesis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mollo, Christopher G.; Bernhard, Robert J.</p> <p>1987-01-01</p> <p>An optimal active <span class="hlt">noise</span> controller is formulated and analyzed for three different active <span class="hlt">noise</span> control problems. The first problem formulated is the active control of enclosed or partially enclosed <span class="hlt">harmonic</span> sound fields where the <span class="hlt">noise</span> <span class="hlt">source</span> strengths and enclosure boundary description are known. The enclosure boundary is described by either pressure, velocity, or impedance boundary conditions. The second problem formulated is the active control of the free field power radiated from a distributed <span class="hlt">noise</span> <span class="hlt">source</span> with a known time <span class="hlt">harmonic</span> surface velocity. The third problem formulated is the active control of enclosed or partially enclosed <span class="hlt">harmonic</span> sound field where the <span class="hlt">noise</span> <span class="hlt">source</span> strengths of enclosure boundary description may not be known. All three formulations are derived using an indirect boundary element technique. Formulation and verification of an indirect boundary element method is presented. The active <span class="hlt">noise</span> controller formulations for enclosures are capable of analyzing systems with generalized enclosure shapes, point <span class="hlt">noise</span> <span class="hlt">sources</span>, and/or locally reacting impedance boundary conditions. For each formulation, representative results of optimal active <span class="hlt">noise</span> controller case studies are presented, and some general conclusions are drawn.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24921559','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24921559"><span>All solid-state 191.7 nm deep-UV light <span class="hlt">source</span> by seventh <span class="hlt">harmonic</span> generation of an 888 nm pumped, Q-switched 1342 nm Nd:YVO₄ laser with excellent beam quality.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Koch, Peter; Bartschke, Juergen; L'huillier, Johannes A</p> <p>2014-06-02</p> <p>In this paper we report on the realization of a deep-UV light <span class="hlt">source</span> using the 1.3 μm transition of neodymium as pumping wavelength. The 191.7 nm radiation was obtained by generating the seventh <span class="hlt">harmonic</span> of a high-power Q-switched 1342 nm Nd:YVO4 laser. A cesium lithium borate crystal was used for sum frequency mixing of the sixth <span class="hlt">harmonic</span> and the fundamental. With a total of four conversion stages, up to 240 mW were achieved, with excellent beam quality at 155 mW (M2 < 1.7) and 190 mW (M2 < 1.9).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840023156','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840023156"><span>Effect of external pressure environment on the internal <span class="hlt">noise</span> level due to a <span class="hlt">source</span> inside a cylindrical tank</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Clevenson, S. A.; Roussos, L. A.</p> <p>1984-01-01</p> <p>A small cylindrical tank was used to study the effect on the <span class="hlt">noise</span> environment within a tank of conditions of atmospheric (sea level) pressure or vacuum environments on the exterior. Experimentally determined absorption coefficients were used to calculate transmission loss, transmissibility coefficients and the sound pressure (<span class="hlt">noise</span>) level differences in the interior. The <span class="hlt">noise</span> level differences were also measured directly for the two exterior environments and compared to various analytical approximations with limited agreement. Trend study curves indicated that if the tank transmission loss is above 25 dB, the difference in interior <span class="hlt">noise</span> level between the vacuum and ambient pressure conditions are less than 2 dB.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150006713','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150006713"><span>Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> Generating Typical Turbofan Modes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel L.; Brown, Cliff; Walker, Bruce E.</p> <p>2014-01-01</p> <p>An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14x22 wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8% scale model. The UCFANS is a 5.8% rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft using the projected signature of the engine currently proposed for the HWB. The modal structures at the rating points were generated from inlet and exhaust nacelle configurations - a flat plate model was used as the shielding surface and vertical control surfaces with correct plan form shapes were also tested to determine their additional impact on shielding. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 inches. Two planes perpendicular, and two planes parallel, to the axis of the nacelle were acquired from the array sweep. In each plane the linear array traversed 4 sweeps, for a total span of 168 inches acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Levels, and integrated Power Levels, from nacelle alone and shielded configurations are presented in this paper; as well as the in-duct mode power levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140005372','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140005372"><span>Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> Generating Typical Turbofan Modes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel l.; Brown, Clifford A.; Walker, Bruce E.</p> <p>2014-01-01</p> <p>An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14- by 22-ft wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft using the projected signature of the engine currently proposed for the HWB. The modal structures at the rating points were generated from inlet and exhaust nacelle configurations--a flat plate model was used as the shielding surface and vertical control surfaces with correct plan form shapes were also tested to determine their additional impact on shielding. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular, and two planes parallel, to the axis of the nacelle were acquired from the array sweep. In each plane the linear array traversed four sweeps, for a total span of 168 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Levels, and integrated Power Levels, from nacelle alone and shielded configurations are presented in this paper; as well as the in-duct mode power levels</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JEI....20b3001T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JEI....20b3001T"><span>Color <span class="hlt">harmonization</span> for images</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tang, Zhen; Miao, Zhenjiang; Wan, Yanli; Wang, Zhifei</p> <p>2011-04-01</p> <p>Color <span class="hlt">harmonization</span> is an artistic technique to adjust a set of colors in order to enhance their visual harmony so that they are aesthetically pleasing in terms of human visual perception. We present a new color <span class="hlt">harmonization</span> method that treats the <span class="hlt">harmonization</span> as a function optimization. For a given image, we derive a cost function based on the observation that pixels in a small window that have similar unharmonic hues should be <span class="hlt">harmonized</span> with similar <span class="hlt">harmonic</span> hues. By minimizing the cost function, we get a <span class="hlt">harmonized</span> image in which the spatial coherence is preserved. A new matching function is proposed to select the best matching <span class="hlt">harmonic</span> schemes, and a new component-based preharmonization strategy is proposed to preserve the hue distribution of the <span class="hlt">harmonized</span> images. Our approach overcomes several shortcomings of the existing color <span class="hlt">harmonization</span> methods. We test our algorithm with a variety of images to demonstrate the effectiveness of our approach.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19277078','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19277078"><span>Phase <span class="hlt">noise</span> optimization in temporal phase-shifting digital holography with partial coherence light <span class="hlt">sources</span> and its application in quantitative cell imaging.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Remmersmann, Christian; Stürwald, Stephan; Kemper, Björn; Langehanenberg, Patrik; von Bally, Gert</p> <p>2009-03-10</p> <p>In temporal phase-shifting-based digital holographic microscopy, high-resolution phase contrast imaging requires optimized conditions for hologram recording and phase retrieval. To optimize the phase resolution, for the example of a variable three-step algorithm, a theoretical analysis on statistical errors, digitalization errors, uncorrelated errors, and errors due to a misaligned temporal phase shift is carried out. In a second step the theoretically predicted results are compared to the measured phase <span class="hlt">noise</span> obtained from comparative experimental investigations with several coherent and partially coherent light <span class="hlt">sources</span>. Finally, the applicability for <span class="hlt">noise</span> reduction is demonstrated by quantitative phase contrast imaging of pancreas tumor cells.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950025807','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950025807"><span>Degradation in finite-<span class="hlt">harmonic</span> subcarrier demodulation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Feria, Y.; Townes, S.; Pham, T.</p> <p>1995-01-01</p> <p>Previous estimates on the degradations due to a subcarrier loop assume a square-wave subcarrier. This article provides a closed-form expression for the degradations due to the subcarrier loop when a finite number of <span class="hlt">harmonics</span> are used to demodulate the subcarrier, as in the case of the buffered telemetry demodulator. We compared the degradations using a square wave and using finite <span class="hlt">harmonics</span> in the subcarrier demodulation and found that, for a low loop signal-to-<span class="hlt">noise</span> ratio, using finite <span class="hlt">harmonics</span> leads to a lower degradation. The analysis is under the assumption that the phase <span class="hlt">noise</span> in the subcarrier (SC) loop has a Tikhonov distribution. This assumption is valid for first-order loops.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860035113&hterms=sound+temperature&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dsound%2Btemperature','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860035113&hterms=sound+temperature&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dsound%2Btemperature"><span>Laboratory study of the effects of sidewall treatment, <span class="hlt">source</span> directivity and temperature on the interior <span class="hlt">noise</span> of a light aircraft fuselage</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Heitman, K. E.; Mixson, J. S.</p> <p>1986-01-01</p> <p>This paper describes a laboratory study of add-on {coustic treatments for a twin-engine, propeller-driven aircraft fuselage. The sound <span class="hlt">source</span> was a pneumatic-driver, with attached horn to simulate propeller <span class="hlt">noise</span> distribution, powered by a white <span class="hlt">noise</span> signal. Treatments included a double-wall, production-line treatment and various fiberglass and lead-vinyl treatments. Insertion losses, space-averaged across six interior microphone positions, were used to evaluate the treatments. In addition, the effects of sound <span class="hlt">source</span> angle and ambient temperature on interior sound pressure level are presented. The sound <span class="hlt">source</span> angle is shown to have a significant effect on one-third octave band localized sound pressure level. While changes in ambient temperature are shown to have little effect on one-third octave band localized sound pressure level, the change in narrowband localized sound pressure level may be dramatic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/977119','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/977119"><span>Transcriptional Bursting from the HIV-1 Promoter is a Significant <span class="hlt">Source</span> of Stochastic <span class="hlt">Noise</span> in HIV-1 Gene Expression</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Singh, A; Razooky, B; Cox, Chris D.; Simpson, Michael L; Weinberger, Leor S.</p> <p>2010-01-01</p> <p>Analysis of <span class="hlt">noise</span> in gene expression has proven a powerful approach for analyzing gene regulatory architecture. To probe the regulatory mechanisms controlling expression of HIV-1, we analyze <span class="hlt">noise</span> in gene-expression from HIV-1 s long terminal repeat (LTR) promoter at different HIV-1 integration sites across the human genome. Flow cytometry analysis of GFP expression from the HIV-1 LTR shows high variability (<span class="hlt">noise</span>) at each integration site. Notably, the measured <span class="hlt">noise</span> levels are inconsistent with constitutive gene expression models. Instead, quantification of expression <span class="hlt">noise</span> indicates that HIV-1 gene expression occurs through randomly timed bursts of activity from the LTR and that each burst generates an average of 2 10 mRNA transcripts before the promoter returns to an inactive state. These data indicate that transcriptional bursting can generate high variability in HIV-1 early gene products, which may critically influence the viral fate-decision between active replication and proviral latency.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MS%26E...78a2010C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MS%26E...78a2010C"><span>Voltage <span class="hlt">harmonic</span> elimination with RLC based interface smoothing filter</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chandrasekaran, K.; Ramachandaramurthy, V. K.</p> <p>2015-04-01</p> <p>A method is proposed for designing a Dynamic Voltage Restorer (DVR) with RLC interface smoothing filter. The RLC filter connected between the IGBT based Voltage <span class="hlt">Source</span> Inverter (VSI) is attempted to eliminate voltage <span class="hlt">harmonics</span> in the busbar voltage and switching <span class="hlt">harmonics</span> from VSI by producing a PWM controlled <span class="hlt">harmonic</span> voltage. In this method, the DVR or series active filter produces PWM voltage that cancels the existing <span class="hlt">harmonic</span> voltage due to any <span class="hlt">harmonic</span> voltage <span class="hlt">source</span>. The proposed method is valid for any distorted busbar voltage. The operating VSI handles no active power but only <span class="hlt">harmonic</span> power. The DVR is able to suppress the lower order switching <span class="hlt">harmonics</span> generated by the IGBT based VSI. Good dynamic and transient results obtained. The Total <span class="hlt">Harmonic</span> Distortion (THD) is minimized to zero at the sensitive load end. Digital simulations are carried out using PSCAD/EMTDC to validate the performance of RLC filter. Simulated results are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=mechanical+AND+power+AND+transmission&id=EJ228681','ERIC'); return false;" href="http://eric.ed.gov/?q=mechanical+AND+power+AND+transmission&id=EJ228681"><span>Simple <span class="hlt">Harmonic</span> Motion in <span class="hlt">Harmonic</span> Plane Waves.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Benumof, Reuben</p> <p>1980-01-01</p> <p>Discusses the distribution of kinetic and potential energy in transverse and longitudinal waves and examines the transmission of power and momentum. This discussion is intended to aid in understanding the simple <span class="hlt">harmonic</span> motion of a particle involved in the propagation of a <span class="hlt">harmonic</span> mechanical plane wave. (HM)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/174678','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/174678"><span>Inductively coupled plasma spectrometry: <span class="hlt">Noise</span> characteristics of aerosols, application of generalized standard additions method, and Mach disk as an emission <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Luan, Shen</p> <p>1995-10-06</p> <p>This dissertation is focused on three problem areas in the performance of inductively coupled plasma (ICP) <span class="hlt">source</span>. The <span class="hlt">noise</span> characteristics of aerosols produced by ICP nebulizers are investigated. A laser beam is scattered by aerosol and detected by a photomultiplier tube and the <span class="hlt">noise</span> amplitude spectrum of the scattered radiation is measured by a spectrum analyzer. Discrete frequency <span class="hlt">noise</span> in the aerosol generated by a Meinhard nebulizer or a direct injection nebulizer is primarily caused by pulsation in the liquid flow from the pump. A Scott-type spray chamber suppresses white <span class="hlt">noise</span>, while a conical, straight-pass spray chamber enhances white <span class="hlt">noise</span>, relative to the <span class="hlt">noise</span> seen from the primary aerosol. Simultaneous correction for both spectral interferences and matrix effects in ICP atomic emission spectrometry (AES) can be accomplished by using the generalized standard additions method (GSAM). Results obtained with the application of the GSAM to the Perkin-Elmer Optima 3000 ICP atomic emission spectrometer are presented. The echelle-based polychromator with segmented-array charge-coupled device detectors enables the direct, visual examination of the overlapping lines Cd (1) 228.802 nm and As (1) 228.812 nm. The slit translation capability allows a large number of data points to be sampled, therefore, the advantage of <span class="hlt">noise</span> averaging is gained. An ICP is extracted into a small quartz vacuum chamber through a sampling orifice in a water-cooled copper plate. Optical emission from the Mach disk region is measured with a new type of echelle spectrometer equipped with two segmented-array charge-coupled-device detectors, with an effort to improve the detection limits for simultaneous multielement analysis by ICP-AES.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015jsrs.conf...100','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015jsrs.conf...100"><span>Phobos mass estimations from MEX and Viking 1 data: influence of different <span class="hlt">noise</span> <span class="hlt">sources</span> and estimation strategies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kudryashova, M.; Rosenblatt, P.; Marty, J.-C.</p> <p>2015-08-01</p> <p>The mass of Phobos is an important parameter which, together with second-order gravity field coefficients and libration amplitude, constrains internal structure and nature of the moon. And thus, it needs to be known with high precision. Nevertheless, Phobos mass (GM, more precisely) estimated by different authors based on diverse data-sets and methods, varies by more than their 1-sigma error. The most complete lists of GM values are presented in the works of R. Jacobson (2010) and M. Paetzold et al. (2014) and include the estimations in the interval from (5.39 ± 0:03).10^5 (Smith et al., 1995) till (8.5 ± 0.7).10^5[m^3/s^2] (Williams et al., 1988). Furthermore, even the comparison of the estimations coming from the same estimation procedure applied to the consecutive flybys of the same spacecraft (s/c) shows big variations in GMs. The indicated behavior is very pronounced in the GM estimations stemming from the Viking1 flybys in February 1977 (as well as from MEX flybys, though in a smaller amplitude) and in this work we made an attempt to figure out its roots. The errors of Phobos GM estimations depend on the precision of the model (e.g. accuracy of Phobos a priori ephemeris and its a priori GM value) as well as on the radio-tracking measurements quality (<span class="hlt">noise</span>, coverage, flyby distance). In the present work we are testing the impact of mentioned above error <span class="hlt">sources</span> by means of simulations. We also consider the effect of the uncertainties in a priori Phobos positions on the GM estimations from real observations. Apparently, the strategy (i.e. splitting real observations in data-arcs, whether they stem from the close approaches of Phobos by spacecraft or from analysis of the s/c orbit evolution around Mars) of the estimations has an impact on the Phobos GM estimation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6219178','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6219178"><span>A portable measurement system for subcriticality measurements by the CF-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; Ragan, G.E.</p> <p>1987-01-01</p> <p>A portable system has been assembled that is capable of measuring the subcriticality of fissile materials using the /sup 252/CF-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method. The measurement system consists of a parallel-plate ionization chamber containing /sup 252/CF, two /sup 3/He proportional counters with their associated electronics, and a small computer containing anti-aliasing filters and A/D convertors. The system Fourier analyzes the digitized data and forms the appropriate auto and cross-power spectral densities. These spectra are used to form a ratio of spectral densities, G/sub 12/G/sub 13//G/sub 11/G/sub 23/, where 1 refers to the ionization chamber, and 2 and 3 refer to the /sup 3/He counters, from which subcriticality can be determined. The chamber and detectors are located appropriately near the fissile material. The system is capable of sampling signals at rates of up to 80 kHz and processing these data at rates of 2 kHz to form the appropriate spectra. The presently configured system is a two-channel system, hence the measurement of G/sub 12/, G/sub 13/, and G/sub 23/ must be done sequentially before the ratio of spectral densities is obtained. Future improvements of the system will allow simultaneous measurement of all spectra and will further reduce size, thereby enhancing portability. This measurement system can provide reliable, cost effective, and convenient determination of the subcriticality of a wide variety of fissile materials and moderators.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25116292','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25116292"><span>In vivo application of short-lag spatial coherence and <span class="hlt">harmonic</span> spatial coherence imaging in fetal ultrasound.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kakkad, Vaibhav; Dahl, Jeremy; Ellestad, Sarah; Trahey, Gregg</p> <p>2015-04-01</p> <p>Fetal scanning is one of the most common applications of ultrasound imaging and serves as a <span class="hlt">source</span> of vital information about maternal and fetal health. Visualization of clinically relevant structures, however, can be severely compromised in difficult-to-image patients due to poor resolution and the presence of high levels of acoustical <span class="hlt">noise</span> or clutter. We have developed novel coherence-based beamforming methods called Short-Lag Spatial Coherence (SLSC) imaging and <span class="hlt">Harmonic</span> Spatial Coherence imaging (HSCI), and applied them to suppress the effects of clutter in fetal imaging. This method is used to create images of the spatial coherence of the backscattered ultrasound as opposed to images of echo magnitude. We present the results of a patient study to assess the benefits of coherence-based beamforming in the context of first trimester fetal exams. Matched fundamental B-mode, SLSC, <span class="hlt">harmonic</span> B-mode, and HSCI images were generated using raw radio frequency data collected on 11 volunteers in the first trimester of pregnancy. The images were compared for qualitative differences in image texture and target conspicuity as well as using quantitative imaging metrics such as signal-to-<span class="hlt">noise</span> ratio (SNR), contrast-to-<span class="hlt">noise</span> ratio (CNR), and contrast. SLSC and HSCI showed statistically significant improvements across all imaging metrics compared with B-mode and <span class="hlt">harmonic</span> B-mode, respectively. These improvements were greatest for poor quality B-mode images where contrast of anechoic targets was improved from 15 dB in fundamental B-mode to 27 dB in SLSC and 17 dB in <span class="hlt">harmonic</span> B-mode to 30 dB in HSCI. CNR improved from 1.4 to 2.5 in the fundamental images and 1.4 to 3.1 in the <span class="hlt">harmonic</span> case. These results exhibit the potential of coherence-based beamforming to improve image quality and target detectability, especially in high <span class="hlt">noise</span> environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26950131','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26950131"><span>A Low-<span class="hlt">Noise</span> CMOS THz Imager Based on <span class="hlt">Source</span> Modulation and an In-Pixel High-Q Passive Switched-Capacitor N-Path Filter.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Boukhayma, Assim; Dupret, Antoine; Rostaing, Jean-Pierre; Enz, Christian</p> <p>2016-03-03</p> <p>This paper presents the first low <span class="hlt">noise</span> complementary metal oxide semiconductor (CMOS) deletedCMOS terahertz (THz) imager based on <span class="hlt">source</span> modulation and in-pixel high-Q filtering. The 31 × 31 focal plane array has been fully integrated in a 0 . 13 μ m standard CMOS process. The sensitivity has been improved significantly by modulating the active THz <span class="hlt">source</span> that lights the scene and performing on-chip high-Q filtering. Each pixel encompass a broadband bow tie antenna coupled to an N-type metal-oxide-semiconductor (NMOS) detector that shifts the THz radiation, a low <span class="hlt">noise</span> adjustable gain amplifier and a high-Q filter centered at the modulation frequency. The filter is based on a passive switched-capacitor (SC) N-path filter combined with a continuous-time broad-band Gm-C filter. A simplified analysis that helps in designing and tuning the passive SC N-path filter is provided. The characterization of the readout chain shows that a Q factor of 100 has been achieved for the filter with a good matching between the analytical calculation and the measurement results. An input-referred <span class="hlt">noise</span> of 0 . 2 μ V RMS has been measured. Characterization of the chip with different THz wavelengths confirms the broadband feature of the antenna and shows that this THz imager reaches a total <span class="hlt">noise</span> equivalent power of 0 . 6 nW at 270 GHz and 0 . 8 nW at 600 GHz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMAE13A0335M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMAE13A0335M"><span><span class="hlt">Noise</span> Filtering For Reception of Very Low Frequency Radio</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mclaughlin, R.; Habash Krause, L.</p> <p>2013-12-01</p> <p>Unwanted emissions and signal <span class="hlt">noise</span> are major problem for VLF radio receivers. These can occur from man made <span class="hlt">sources</span> such as power line hum, which can be prevalent for many <span class="hlt">harmonics</span> after the fundamental 50 or 60 Hz AC <span class="hlt">source</span> or from VLF radio transmissions such as LORAN, used for navigation and communications. Natural emissions can also be detrimental to the quality of recordings as some of the more interesting natural emissions such as whistlers or auroral chorus may be drowned out by the more common sferic emissions. VLF receiver circuitry must selectively filter out unwanted emissions and amplify the filtered signal to a record-able level without degradation of quality.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23556699','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23556699"><span>Underwater <span class="hlt">noise</span> of small personal watercraft (jet skis).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Erbe, Christine</p> <p>2013-04-01</p> <p>Personal watercraft (water scooters, jet skis) were recorded under water in Bramble Bay, Queensland, Australia. Underwater <span class="hlt">noise</span> emissions consisted of broadband energy between 100 Hz and 10 kHz due to the vibrating bubble cloud generated by the jet stream, overlain with frequency-modulated tonals corresponding to impeller blade rates and <span class="hlt">harmonics</span>. Broadband monopole <span class="hlt">source</span> levels were 149, 137, and 122 dB re 1 μPa @ 1 m (5th, 50th, and 95th percentiles). Even though these are lower than those of small propeller-driven boats, it is not necessarily the broadband <span class="hlt">source</span> level that correlates with the bioacoustic impact on marine fauna.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/939542','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/939542"><span><span class="hlt">Harmonization</span> of Biodiesel Specifications</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Alleman, T. L.</p> <p>2008-02-01</p> <p>Worldwide biodiesel production has grown dramatically over the last several years. Biodiesel standards vary across countries and regions, and there is a call for <span class="hlt">harmonization</span>. For <span class="hlt">harmonization</span> to become a reality, standards have to be adapted to cover all feedstocks. Additionally, all feedstocks cannot meet all specifications, so <span class="hlt">harmonization</span> will require standards to either tighten or relax. For <span class="hlt">harmonization</span> to succeed, the biodiesel market must be expanded with the alignment of test methods and specification limits, not contracted.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/79020','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/79020"><span>High order <span class="hlt">harmonic</span> generation in rare gases</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Budil, Kimberly Susan</p> <p>1994-05-01</p> <p>The process of high order <span class="hlt">harmonic</span> generation in atomic gases has shown great promise as a method of generating extremely short wavelength radiation, extending far into the extreme ultraviolet (XUV). The process is conceptually simple. A very intense laser pulse (I ~10<sup>13</sup>-10<sup>14</sup> W/cm<sup>2</sup>) is focused into a dense (~10<sup>17</sup> particles/cm<sup>3</sup>) atomic medium, causing the atoms to become polarized. These atomic dipoles are then coherently driven by the laser field and begin to radiate at odd <span class="hlt">harmonics</span> of the laser field. This dissertation is a study of both the physical mechanism of <span class="hlt">harmonic</span> generation as well as its development as a <span class="hlt">source</span> of coherent XUV radiation. Recently, a semiclassical theory has been proposed which provides a simple, intuitive description of <span class="hlt">harmonic</span> generation. In this picture the process is treated in two steps. The atom ionizes via tunneling after which its classical motion in the laser field is studied. Electron trajectories which return to the vicinity of the nucleus may recombine and emit a <span class="hlt">harmonic</span> photon, while those which do not return will ionize. An experiment was performed to test the validity of this model wherein the trajectory of the electron as it orbits the nucleus or ion core is perturbed by driving the process with elliptically, rather than linearly, polarized laser radiation. The semiclassical theory predicts a rapid turn-off of <span class="hlt">harmonic</span> production as the ellipticity of the driving field is increased. This decrease in <span class="hlt">harmonic</span> production is observed experimentally and a simple quantum mechanical theory is used to model the data. The second major focus of this work was on development of the <span class="hlt">harmonic</span> "<span class="hlt">source</span>". A series of experiments were performed examining the spatial profiles of the <span class="hlt">harmonics</span>. The quality of the spatial profile is crucial if the <span class="hlt">harmonics</span> are to be used as the <span class="hlt">source</span> for experiments, particularly if they must be refocused.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/15017144','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/15017144"><span>MR <span class="hlt">harmonic</span> quad study</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yang, M.-J.; /Fermilab</p> <p>1995-01-01</p> <p>To understand the effect of Main Ring <span class="hlt">harmonic</span> quadruple correctors. Previous data taken with the <span class="hlt">harmonic</span> quads did not agree well with the SYNCH calculation. The ultimate goal of this study was to be able to change the <span class="hlt">harmonic</span> quads and verify the changes in lattice function.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhRvA..88e1802O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhRvA..88e1802O"><span>Asymmetric Gaussian <span class="hlt">harmonic</span> steering in second-<span class="hlt">harmonic</span> generation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Olsen, M. K.</p> <p>2013-11-01</p> <p>Intracavity second-<span class="hlt">harmonic</span> generation is one of the simplest of the quantum optical processes and is well within the expertise of most optical laboratories. It is well understood and characterized, both theoretically and experimentally. We show that it can be a <span class="hlt">source</span> of continuous-variable asymmetric Gaussian <span class="hlt">harmonic</span> steering with fields which have a coherent excitation, hence combining the important effects of <span class="hlt">harmonic</span> entanglement and asymmetric steering in one easily controllable device, adjustable by the simple means of tuning the cavity loss rates at the fundamental and <span class="hlt">harmonic</span> frequencies. We find that whether quantum steering is available via the standard measurements of the Einstein-Podolsky-Rosen correlations can depend on which quadrature measurements are inferred from output spectral measurements of the fundamental and the <span class="hlt">harmonic</span>. Altering the ratios of the cavity loss rates can be used to tune the regions where symmetric steering is available, with the results becoming asymmetric over all frequencies as the cavity damping at the fundamental frequency becomes significantly greater than at the <span class="hlt">harmonic</span>. This asymmetry and its functional dependence on frequency is a potential new tool for experimental quantum information science, with possible utility for quantum key distribution. Although we show the effect here for Gaussian measurements of the quadratures, and cannot rule out a return of the steering symmetry for some class of non-Gaussian measurements, we note here that the system obeys Gaussian statistics in the operating regime investigated and Gaussian inference is at least as accurate as any other method for calculating the necessary correlations. Perhaps most importantly, this system is simpler than any other methods we are aware of which have been used or proposed to create asymmetric steering.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JOpt...18b5601M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JOpt...18b5601M"><span>Analysis of SNR penalty in Brillouin optical time-domain analysis sensors induced by laser <span class="hlt">source</span> phase <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Minardo, A.; Bernini, R.; Zeni, L.</p> <p>2016-02-01</p> <p>In this paper, we analyze numerically the effect of phase <span class="hlt">noise</span> from the laser in Brillouin optical time-domain analysis (BOTDA) sensors. Due to laser phase <span class="hlt">noise</span>, the phase shift between pump and probe beams is a stochastic variable with zero mean and variance changing with the position along the fiber. The numerical results, carried out for various fiber lengths and pump pulse durations, show that laser phase <span class="hlt">noise</span> induces a reduction of the average Brillouin gain, as well as an increase of the overall system <span class="hlt">noise</span>. Preliminary experimental results, carried out by use of a conventional BOTDA system and two DFB diode lasers having different linewidth (63 and 900 kHz), support the numerical analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21180098','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21180098"><span>Higher-Order <span class="hlt">Harmonic</span> Generation from Fullerene by Means of the Plasma <span class="hlt">Harmonic</span> Method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ganeev, R. A.; Bom, L. B. Elouga; Abdul-Hadi, J.; Ozaki, T.; Wong, M. C. H.; Brichta, J. P.; Bhardwaj, V. R.</p> <p>2009-01-09</p> <p>We demonstrate, for the first time, high-order <span class="hlt">harmonic</span> generation from C{sub 60} by an intense femtosecond Ti:sapphire laser. Laser-produced plasmas from C{sub 60}-rich epoxy and C{sub 60} films were used as the nonlinear media. <span class="hlt">Harmonics</span> up to the 19th order were observed. The <span class="hlt">harmonic</span> yield from fullerene-rich plasma is about 25 times larger compared with those produced from a bulk carbon target. Structural studies of plasma debris confirm the presence and integrity of fullerenes within the plasma plume, indicating fullerenes as the <span class="hlt">source</span> of high-order <span class="hlt">harmonics</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980032586','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980032586"><span>Reduction of Helicopter Blade-Vortex Interaction <span class="hlt">Noise</span> by Active Rotor Control Technology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yu, Yung H.; Gmelin, Bernd; Splettstoesser, Wolf; Brooks, Thomas F.; Philippe, Jean J.; Prieur, Jean</p> <p>1997-01-01</p> <p>Helicopter blade-vortex interaction <span class="hlt">noise</span> is one of the most severe <span class="hlt">noise</span> <span class="hlt">sources</span> and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor blade-vortex interaction <span class="hlt">noise</span> and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor blade vortex interaction <span class="hlt">noise</span> reduction, including higher <span class="hlt">harmonic</span> pitch control, individual blade control, and on-blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of <span class="hlt">noise</span> reduction mechanism and controlling aerodynamic or structural parameters of a blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations, Published by Elsevier Science Ltd.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800006843','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800006843"><span>Acoustic analysis of aft <span class="hlt">noise</span> reduction techniques measured on a subsonic tip speed 50.8 cm (twenty inch) diameter fan. [quiet engine program</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stimpert, D. L.; Clemons, A.</p> <p>1977-01-01</p> <p>Sound data which were obtained during tests of a 50.8 cm diameter, subsonic tip speed, low pressure ratio fan were analyzed. The test matrix was divided into two major investigations: (1) <span class="hlt">source</span> <span class="hlt">noise</span> reduction techniques; and (2) aft duct <span class="hlt">noise</span> reduction with acoustic treatment. <span class="hlt">Source</span> <span class="hlt">noise</span> reduction techniques were investigated which include minimizing second <span class="hlt">harmonic</span> <span class="hlt">noise</span> by varying vane/blade ratio, variation in spacing, and lowering the Mach number through the vane row to lower fan broadband <span class="hlt">noise</span>. Treatment in the aft duct which includes flow <span class="hlt">noise</span> effects, faceplate porosity, rotor OGV treatment, slant cell treatment, and splitter simulation with variable depth on the outer wall and constant thickness treatment on the inner wall was investigated. Variable boundary conditions such as variation in treatment panel thickness and orientation, and mixed porosity combined with variable thickness were examined. Significant results are reported.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016LaPhL..13b5101Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016LaPhL..13b5101Y"><span>Ultrahigh-resolution optical coherence tomography at 1.3 μm central wavelength by using a supercontinuum <span class="hlt">source</span> pumped by <span class="hlt">noise</span>-like pulses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>You, Yi-Jing; Wang, Chengming; Lin, Yi-Lun; Zaytsev, Alexey; Xue, Ping; Pan, Ci-Ling</p> <p>2016-02-01</p> <p>We report on the ultrahigh-resolution optical coherence tomography (OCT) with a novel high-power supercontinuum (SC) light <span class="hlt">source</span> generated by <span class="hlt">noise</span>-like pulses from an Yb-doped fiber laser. The SC spectrum is flat with a bandwidth of 420 nm centered around ~1.3 μm. The light <span class="hlt">source</span> is successfully employed in a time-domain OCT (TD-OCT), achieving an axial resolution of 2.3 μm. High resolution fiber-based spectral-domain OCT (SD-OCT) imaging of bio-tissue was also demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920023704','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920023704"><span>Fourth Aircraft Interior <span class="hlt">Noise</span> Workshop</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stephens, David G. (Compiler)</p> <p>1992-01-01</p> <p>The fourth in a series of NASA/SAE Interior <span class="hlt">Noise</span> Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft <span class="hlt">noise</span> with emphasis on <span class="hlt">source</span> <span class="hlt">noise</span> prediction; cabin <span class="hlt">noise</span> prediction; cabin <span class="hlt">noise</span> control, including active and passive methods; and cabin interior <span class="hlt">noise</span> procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910002175','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910002175"><span>Aircraft interior <span class="hlt">noise</span> reduction by alternate resonance tuning</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bliss, Donald B.; Gottwald, James A.; Srinivasan, Ramakrishna; Gustaveson, Mark B.</p> <p>1990-01-01</p> <p>Existing interior <span class="hlt">noise</span> reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at lower frequencies, particularly with respect to the low blade passage <span class="hlt">harmonics</span> with high forcing levels found in propeller aircraft. A method is being studied which considers aircraft fuselage lined with panels alternately tuned to frequencies above and below the frequency that must be attenuated. Adjacent panels would oscillate at equal amplitude, to give equal <span class="hlt">source</span> strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to become cutoff, and therefore be non-propagating and evanescent. This interior <span class="hlt">noise</span> reduction method, called Alternate Resonance Tuning (ART), is currently being investigated both theoretically and experimentally. This new concept has potential application to reducing interior <span class="hlt">noise</span> due to the propellers in advanced turboprop aircraft as well as for existing aircraft configurations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26831958','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26831958"><span>Ultra-compact Watt-level flat supercontinuum <span class="hlt">source</span> pumped by <span class="hlt">noise</span>-like pulse from an all-fiber oscillator.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, He; Zhou, Xuanfeng; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing</p> <p>2015-12-28</p> <p>We demonstrate Watt-level flat visible supercontinuum (SC) generation in photonic crystal fibers, which is directly pumped by broadband <span class="hlt">noise</span>-like pulses from an Yb-doped all-fiber oscillator. The novel SC generator is featured with elegant all-fiber-integrated architecture, high spectral flatness and high efficiency. Wide optical spectrum spanning from 500 nm to 2300 nm with 1.02 W optical power is obtained under the pump of 1.4 W <span class="hlt">noise</span>-like pulse. The flatness of the spectrum in the range of 700 nm~1600 nm is less than 5 dB (including the pump residue). The exceptional simplicity, economical efficiency and the comparable performances make the <span class="hlt">noise</span>-like pulse oscillator a competitive candidate to the widely used cascade amplified coherent pulse as the pump <span class="hlt">source</span> of broadband SC. To the best of our knowledge, this is the first demonstration of SC generation which is directly pumped by an all-fiber <span class="hlt">noise</span>-like pulse oscillator.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT........59F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT........59F"><span>West Texas array experiment: <span class="hlt">Noise</span> and <span class="hlt">source</span> characterization of short-range infrasound and acoustic signals, along with lab and field evaluation of Intermountain Laboratories infrasound microphones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fisher, Aileen</p> <p></p> <p>The term infrasound describes atmospheric sound waves with frequencies below 20 Hz, while acoustics are classified within the audible range of 20 Hz to 20 kHz. Infrasound and acoustic monitoring in the scientific community is hampered by low signal-to-<span class="hlt">noise</span> ratios and a limited number of studies on regional and short-range <span class="hlt">noise</span> and <span class="hlt">source</span> characterization. The JASON Report (2005) suggests the infrasound community focus on more broad-frequency, observational studies within a tactical distance of 10 km. In keeping with that recommendation, this paper presents a study of regional and short-range atmospheric acoustic and infrasonic <span class="hlt">noise</span> characterization, at a desert site in West Texas, covering a broad frequency range of 0.2 to 100 Hz. To spatially sample the band, a large number of infrasound gauges was needed. A laboratory instrument analysis is presented of the set of low-cost infrasound sensors used in this study, manufactured by Inter-Mountain Laboratories (IML). Analysis includes spectra, transfer functions and coherences to assess the stability and range of the gauges, and complements additional instrument testing by Sandia National Laboratories. The IMLs documented here have been found reliably coherent from 0.1 to 7 Hz without instrument correction. Corrections were built using corresponding time series from the commercially available and more expensive Chaparral infrasound gauge, so that the corrected IML outputs were able to closely mimic the Chaparral output. Arrays of gauges are needed for atmospheric sound signal processing. Our West Texas experiment consisted of a 1.5 km aperture, 23-gauge infrasound/acoustic array of IMLs, with a compact, 12 m diameter grid-array of rented IMLs at the center. To optimize signal recording, signal-to-<span class="hlt">noise</span> ratio needs to be quantified with respect to both frequency band and coherence length. The higher-frequency grid array consisted of 25 microphones arranged in a five by five pattern with 3 meter spacing, without</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1127219','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1127219"><span>SEVENTH <span class="hlt">HARMONIC</span> 20 GHz CO-GENERATOR</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hirshfield, Jay L</p> <p>2014-04-08</p> <p>To satisfy the need for multi-MW rf <span class="hlt">sources</span> in frequency ranges where commercial <span class="hlt">sources</span> do not exist, a study was undertaken on a class of devices based on gyro-<span class="hlt">harmonic</span> frequency multiplication. This mechanism relies upon adding energy in gyrating motion to a linear electron beam that traverses a rotating-mode TE111-mode drive cavity in a dc magnetic field. The beam then drifts along the magnetic field into a second cavity, operating in the TEn11-mode tuned to the nth <span class="hlt">harmonic</span> of the drive cavity. Studies of this configuration have been carried out for 2 < n < 7. Results are given for multi-MW, efficient operation of a 7th <span class="hlt">harmonic</span> device operating at 20 GHz, and a 2nd <span class="hlt">harmonic</span> device operating at 22.4 GHz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014MeScT..25l5111L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014MeScT..25l5111L"><span>A <span class="hlt">source</span> of illumination for low-<span class="hlt">noise</span> ‘Violin-Mode’ shadow sensors, intended for use in interferometric gravitational wave detectors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lockerbie, N. A.; Tokmakov, K. V.; Strain, K. A.</p> <p>2014-12-01</p> <p>A low-<span class="hlt">noise</span> <span class="hlt">source</span> of illumination is described for shadow sensors having a displacement sensitivity of (69  ±  13) picometres (rms)/√Hz, at 500 Hz, over a measuring span of ±0.1 mm. These sensors were designed to detect ‘Violin-Mode’ resonances in the suspension fibres of the test-masses/mirrors for the Advanced LIGO (Laser Interferometer Gravitational wave Observatory) gravitational wave detectors. The <span class="hlt">source</span> of illumination (emitter) described here used a single column of 8 × miniature near infrared LEDs (λ = 890 nm). These emitters cast the shadows of 400 μm diameter fused silica suspension fibres onto their complementary shadow-displacement detectors, located at a distance of 74 fibre diameters (29.6 mm) behind the axes of the fibres themselves. Violin-Mode vibrations of each fibre were sensed as differential ac photocurrents in the corresponding ‘split-photodiode’ detector. This paper describes the design, construction, <span class="hlt">noise</span> analysis, and measures that were taken in the conception of the emitters, in order to produce high-contrast shadows at such distant detectors. In this way it proved possible to obtain, simultaneously, a very high transfer sensitivity to Violin-Mode vibration of the fibres, and a very low level of detection noise—close to the fundamental shot <span class="hlt">noise</span> limit—whilst remaining within the constraints of this simple design of emitter. The shadow detector is described in an accompanying paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25540812','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25540812"><span>Third <span class="hlt">Harmonic</span> Mechanism in Complex Plasmonic Fano Structures.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Metzger, Bernd; Schumacher, Thorsten; Hentschel, Mario; Lippitz, Markus; Giessen, Harald</p> <p>2014-06-18</p> <p>We perform third <span class="hlt">harmonic</span> spectroscopy of dolmen-type nanostructures, which exhibit plasmonic Fano resonances in the near-infrared. Strong third <span class="hlt">harmonic</span> emission is predominantly radiated close to the low energy peak of the Fano resonance. Furthermore, we find that the third <span class="hlt">harmonic</span> polarization of the subradiant mode interferes destructively and diminishes the nonlinear signal in the far-field. By comparing the experimental third <span class="hlt">harmonic</span> spectra with finite element simulations and an anharmonic oscillator model, we find strong indications that the <span class="hlt">source</span> of the third <span class="hlt">harmonic</span> is the optical nonlinearity of the bare gold enhanced by the resonant plasmonic polarization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990PASP..102.1420A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990PASP..102.1420A"><span>Signal-to-<span class="hlt">noise</span> ratios in IUE SWP-LO spectra of chromospheric emission-line <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ayres, Thomas R.</p> <p>1990-12-01</p> <p>The short-wavelength-prime (SWP) detector of the International Ultraviolet Explorer should operate near the photon-counting limit, but the <span class="hlt">noise</span> levels in flat-field images are several times higher. The exaggerated <span class="hlt">noise</span> can be traced to the incomplete removal of the pixel-to-pixel granularity of the television frames by the prevailing spectral image processing system. An empirical <span class="hlt">noise</span> model for the current-epoch photometric linearization strategy and one for a hypothetical processing system that achieves complete flat fielding of the raw images are derived. A formula is then proposed to predict the signal-to-<span class="hlt">noise</span> ratio in the measured flux of an emission line (possibly superimposed on a smooth continuum) in an IUE low-dispersion (5 A resolution) far-ultraviolet (1150 A-1950 A) spectrum as recorded with the SWP camera. For illustration, the formula is specialized to the important C IV 1549 A feature of F-K stars. The S/N relation permits one to determine sensitivity limits, upper limits in faint exposures, and optimum exposure times.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SuMi...90..297S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SuMi...90..297S"><span>Modulating nonlinear optical properties of impurity doped quantum dots via the interplay between anisotropy and Gaussian white <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sarkar, Sucharita; Ghosh, Arghya Pratim; Mandal, Arkajit; Ghosh, Manas</p> <p>2016-02-01</p> <p>The influence of anisotropy on various nonlinear optical (NLO) properties such as total optical absorption coefficient (TOAC), nonlinear optical rectification (NOR), second <span class="hlt">harmonic</span> generation (SHG) and third <span class="hlt">harmonic</span> generation (THG) of impurity doped quantum dots (QDs) have been investigated in presence and absence of <span class="hlt">noise</span>. <span class="hlt">Noise</span> has been applied to the system additively and multiplicatively. The impurity potential is modeled by a Gaussian function and the <span class="hlt">noise</span> applied being Gaussian white <span class="hlt">noise</span>. A perpendicular magnetic field emerges out as a confinement <span class="hlt">source</span> and a static external electric field has been applied. Profiles of the optical properties have been monitored as a function of incident photon energy for different values of anisotropy. In this connection the role of mode of application of <span class="hlt">noise</span> (additive/multiplicative) has also been analysed. The interplay between <span class="hlt">noise</span> and anisotropy has been found to profoundly affect the NLO properties. The investigation reveals that there are only one or two anisotropy regimes (depending on the particular NLO property under consideration) where <span class="hlt">noise</span>-induced enhancement of the NLO property can be realized. Thus, anisotropy appears to be the central parameter by which the <span class="hlt">noise</span>-induced enhancement of NLO properties of doped QD systems can be tailored.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20687278','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20687278"><span>Elastography using <span class="hlt">harmonic</span> ultrasonic imaging: a feasibility study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Desai, Raghavendra Reddy; Krouskop, Thomas A; Righetti, Raffaella</p> <p>2010-04-01</p> <p>Tissue <span class="hlt">Harmonic</span> Imaging (THI) is a relatively new modality that has had a significant impact in the ultrasound field. In the recent past, imaging the mechanical properties of tissues using elastography has also gained great interest. In this paper, we investigate the feasibility of combining these two state-of-the-art ultrasound-imaging modalities. The performance of elastograms obtained using <span class="hlt">harmonic</span> ultrasonic signals is studied with simulations and compared to the performance of conventional elastograms using standard statistical methods. Experiments are used as a proof of the technical feasibility of generating tissue-<span class="hlt">harmonic</span> elastograms using experimental <span class="hlt">harmonic</span> signals. The results of our simulation study indicate that all image quality factors considered in this study (elastographic signal-to-<span class="hlt">noise</span> ratio, elastographic contrast-to-<span class="hlt">noise</span> ratio and spatial resolution) may be improved when using <span class="hlt">harmonic</span> ultrasonic signals, provided that the ultrasound system is characterized by high bandwidth, high sampling frequency and large lateral sampling. Preliminary experimental results suggest that it is technically feasible to generate experimental elastograms using <span class="hlt">harmonic</span> signals, provided that the sonographic signal-to-<span class="hlt">noise</span> ratio of the pre- and postcompression <span class="hlt">harmonic</span> frames is sufficiently high to guarantee reliable values of correlation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820012073','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820012073"><span>Aircraft <span class="hlt">noise</span> prediction program theoretical manual, part 2</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zorumski, W. E.</p> <p>1982-01-01</p> <p>Detailed prediction methods for specific aircraft <span class="hlt">noise</span> <span class="hlt">sources</span> are given. These <span class="hlt">sources</span> are airframe <span class="hlt">noise</span>, combustion <span class="hlt">noise</span>, fan <span class="hlt">noise</span>, single and dual stream jet <span class="hlt">noise</span>, and turbine <span class="hlt">noise</span>. Modifications to the NASA methods which comply with the International Civil Aviation Organization standard method for aircraft <span class="hlt">noise</span> prediction are given.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhRvS..19i2801Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhRvS..19i2801Z"><span>Extremum seeking x-ray position feedback using power line <span class="hlt">harmonic</span> leakage as the perturbation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zohar, S.; Kissick, D. J.; Venugopalan, N.; Ogata, C. M.; Makarov, O.; Stepanov, S.; Fischetti, R. F.</p> <p>2016-09-01</p> <p>Small x-ray beam sizes necessary for probing nanoscale phenomena require exquisite stability to prevent data corruption by <span class="hlt">noise</span>. One <span class="hlt">source</span> of instability at synchrotron radiation x-ray beamlines is the slow detuning of x-ray optics to marginal alignment where the onset of clipping increases the beam's susceptibility to higher frequency position oscillations. In this article, we show that a 1 μ m amplitude horizontal x-ray beam oscillation driven by power line <span class="hlt">harmonic</span> leakage into the electron storage ring can be used as perturbation for horizontal position extremum seeking feedback. Feedback performance is characterized by convergence to 1.5% away from maximum intensity at optimal alignment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002ASAJ..111.2336V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002ASAJ..111.2336V"><span>Dragline <span class="hlt">noise</span> survey</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vipperman, Jeffrey S.; Bauer, Eric R.</p> <p>2002-05-01</p> <p>It is estimated that 70%-90% of miners have enough <span class="hlt">noise</span> induced hearing loss (NIHL) to be classified as a disability (NIOSH, Publication No. 76-172, 1976; Franks, NIOSH Internal Report, 1996). In response, NIOSH is conducting a cross-sectional survey of the mining industry in order to determine the <span class="hlt">sources</span> of mining <span class="hlt">noise</span> and offer recommendations on how to mitigate high <span class="hlt">noise</span> levels, and bring mining operations into compliance with the recent mining <span class="hlt">noise</span> regulation: 30CFR, Part 62. This paper will outline the results from <span class="hlt">noise</span> surveys of eight draglines which operate in above-ground coal mining operations. The data recorded include <span class="hlt">noise</span> dosimetry in conjunction with time-at-task studies and 1/3-octave sound level (Leq, Lmin, and Lmax) measurements. The 1/3-octave band readings were used to create <span class="hlt">noise</span> contour maps which allowed the spatial and frequency information of the <span class="hlt">noise</span> to be considered. Comparison of Lmin and Lmax levels offer insight into the variability of the <span class="hlt">noise</span> levels inside the dragline. The potential for administrative controls is limited due to consistently high <span class="hlt">noise</span> levels throughout the deck. Implementation of engineering controls is also hindered by the size and number of the <span class="hlt">noise</span> <span class="hlt">sources</span> and the frequency content of the <span class="hlt">noise</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4813900','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4813900"><span>A Low-<span class="hlt">Noise</span> CMOS THz Imager Based on <span class="hlt">Source</span> Modulation and an In-Pixel High-Q Passive Switched-Capacitor N-Path Filter</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Boukhayma, Assim; Dupret, Antoine; Rostaing, Jean-Pierre; Enz, Christian</p> <p>2016-01-01</p> <p>This paper presents the first low <span class="hlt">noise</span> complementary metal oxide semiconductor (CMOS) terahertz (THz) imager based on <span class="hlt">source</span> modulation and in-pixel high-Q filtering. The 31×31 focal plane array has been fully integrated in a 0.13μm standard CMOS process. The sensitivity has been improved significantly by modulating the active THz <span class="hlt">source</span> that lights the scene and performing on-chip high-Q filtering. Each pixel encompass a broadband bow tie antenna coupled to an N-type metal-oxide-semiconductor (NMOS) detector that shifts the THz radiation, a low <span class="hlt">noise</span> adjustable gain amplifier and a high-Q filter centered at the modulation frequency. The filter is based on a passive switched-capacitor (SC) N-path filter combined with a continuous-time broad-band Gm-C filter. A simplified analysis that helps in designing and tuning the passive SC N-path filter is provided. The characterization of the readout chain shows that a Q factor of 100 has been achieved for the filter with a good matching between the analytical calculation and the measurement results. An input-referred <span class="hlt">noise</span> of 0.2μV RMS has been measured. Characterization of the chip with different THz wavelengths confirms the broadband feature of the antenna and shows that this THz imager reaches a total <span class="hlt">noise</span> equivalent power of 0.6 nW at 270 GHz and 0.8 nW at 600 GHz. PMID:26950131</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930018122','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930018122"><span>Workshop on <span class="hlt">Harmonic</span> Oscillators</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Han, D. (Editor); Kim, Y. S. (Editor); Zachary, W. W. (Editor)</p> <p>1993-01-01</p> <p>Proceedings of a workshop on <span class="hlt">Harmonic</span> Oscillators held at the College Park Campus of the University of Maryland on March 25 - 28, 1992 are presented. The <span class="hlt">harmonic</span> oscillator formalism is playing an important role in many branches of physics. This is the simplest mathematical device which can connect the basic principle of physics with what is observed in the real world. The <span class="hlt">harmonic</span> oscillator is the bridge between pure and applied physics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.G22A..04W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.G22A..04W"><span>GRACE <span class="hlt">Harmonic</span> and Mascon Solutions at JPL</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Watkins, M. M.; Yuan, D.; Kuang, D.; Bertiger, W.; Kim, M.; Kruizinga, G. L.</p> <p>2005-12-01</p> <p>Gravity field solutions at JPL over the past few years have explored use of range, range-rate, and range-acceleration K/Ka-band satellite-satellite data types (with and without GPS), and with both spherical <span class="hlt">harmonic</span> and mascon-type local mass representations. Until recently, resource and computing limitations have limited the scope of our mascon and other local solutions to a few months and/or small spatial regions and the standard GRACE products have remained spherical <span class="hlt">harmonic</span> fields. The use of a new very large (~500 node) beowulf machine at JPL is now enabling a wider range of solutions over longer time spans and deeper understanding of their characteristics. These include much higher spherical <span class="hlt">harmonic</span> degrees, mascons, and hybrids of the two. We will present the current status for several solution types, strengths and weaknesses of each, and our assessments of limiting errors including data <span class="hlt">noise</span> and aliasing sensitivity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840021597&hterms=train+noise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dtrain%2Bnoise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840021597&hterms=train+noise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dtrain%2Bnoise"><span><span class="hlt">Noise</span> reduction experience at Hughes Helicopter, Inc.</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Janakiram, D. S.</p> <p>1982-01-01</p> <p><span class="hlt">Noise</span> reduction is mostly limited to light helicopters whose <span class="hlt">noise</span> signature is dominated by their tail rotors. It is primarily hardware oriented. Well known <span class="hlt">noise</span> reduction techniques such as reduction of rotor speeds with an accompanying increase in solidity to maintain performance, engine <span class="hlt">noise</span> reduction with the use of exhaust mufflers, and acoustic blanketing of transmission and engine compartment are used. The concept of blade phasing as a means of reducing tail rotor <span class="hlt">noise</span> is also used. Engine <span class="hlt">noise</span> (exhaust <span class="hlt">noise</span>), power train <span class="hlt">noise</span> and airframe <span class="hlt">noise</span> becomes important at low rotor tip speeds and means must be found to reduce these <span class="hlt">noise</span> <span class="hlt">sources</span> if further <span class="hlt">noise</span> reductions are desired. The use of a special test rig aids in isolating the various <span class="hlt">noise</span> <span class="hlt">sources</span> and arriving at the penalties (performance or payload) involved in quieting them. Significant <span class="hlt">noise</span> reduction are achieved for the light helicopter with minimum performance or weight penalties because of the dominance of a single <span class="hlt">noise</span> <span class="hlt">source</span> (the tail rotor).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA094293','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA094293"><span>High Velocity Jet <span class="hlt">Noise</span> <span class="hlt">Source</span> Location and Reduction. Task 3 - Experimental Investigation of Suppression Principles. Volume I. Suppressor Concepts Optimization</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1978-12-01</p> <p>multinational corporation in the 1960’s placed extreme emphasis on the need for effective and efficient <span class="hlt">noise</span> suppression devices. Phase I of work...through model and engine testing applicable to an afterburning turbojet engine. Suppressor designs were based primarily on empirical methods. Phase II...using "ray" acoustics. This method is in contrast to the purely empirical method which consists of the curve -fitting of normalized data. In order to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150006712','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150006712"><span>A Mode Propagation Database Suitable for Code Validation Utilizing the NASA Glenn Advanced <span class="hlt">Noise</span> Control Fan and Artificial <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel L.</p> <p>2014-01-01</p> <p>The NASA Glenn Research Center's Advanced <span class="hlt">Noise</span> Control Fan (ANCF) was developed in the early 1990s to provide a convenient test bed to measure and understand fan-generated acoustics, duct propagation, and radiation to the farfield. A series of tests were performed primarily for the use of code validation and tool validation. Rotating Rake mode measurements were acquired for parametric sets of: (1) mode blockage, (2) liner insertion loss, (3) short ducts, and (4) mode reflection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140005371','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140005371"><span>A Mode Propagation Database Suitable for Code Validation Utilizing the NASA Glenn Advanced <span class="hlt">Noise</span> Control Fan and Artificial <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel L.</p> <p>2014-01-01</p> <p>The NASA Glenn Research Center's Advanced <span class="hlt">Noise</span> Control Fan (ANCF) was developed in the early 1990s to provide a convenient test bed to measure and understand fan-generated acoustics, duct propagation, and radiation to the farfield. A series of tests were performed primarily for the use of code validation and tool validation. Rotating Rake mode measurements were acquired for parametric sets of: (i) mode blockage, (ii) liner insertion loss, (iii) short ducts, and (iv) mode reflection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPhCS.744a2189L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.744a2189L"><span>Active <span class="hlt">Noise</span> Control for Dishwasher <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Nokhaeng; Park, Youngjin</p> <p>2016-09-01</p> <p>The dishwasher is a useful home appliance and continually used for automatically washing dishes. It's commonly placed in the kitchen with built-in style for practicality and better use of space. In this environment, people are easily exposed to dishwasher <span class="hlt">noise</span>, so it is an important issue for the consumers, especially for the people living in open and narrow space. Recently, the sound power levels of the <span class="hlt">noise</span> are about 40 - 50 dBA. It could be achieved by removal of <span class="hlt">noise</span> <span class="hlt">sources</span> and passive means of insulating acoustical path. For more reduction, such a quiet mode with the lower speed of cycle has been introduced, but this deteriorates the washing capacity. Under this background, we propose active <span class="hlt">noise</span> control for dishwasher <span class="hlt">noise</span>. It is observed that the <span class="hlt">noise</span> is propagating mainly from the lower part of the front side. Control speakers are placed in the part for the collocation. Observation part of estimating sound field distribution and control part of generating the anti-<span class="hlt">noise</span> are designed for active <span class="hlt">noise</span> control. Simulation result shows proposed active <span class="hlt">noise</span> control scheme could have a potential application for dishwasher <span class="hlt">noise</span> reduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20384146','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20384146"><span>[Study of the effect of light <span class="hlt">source</span> stability on the signal to <span class="hlt">noise</span> ratio in degenerate four wave mixing experiment].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Wei-Bo; Chen, De-Ying; Fan, Rong-Wei; Xia, Yuan-Qin</p> <p>2010-02-01</p> <p>The effects of the stability of dye laser on the signal to <span class="hlt">noise</span> ratio in degenerate four-wave mixing (DFWM) were first investigated in iodine vapor using forward geometries. Frequency-doubled outputs from a multi-mode Nd : YAG laser pumped dye laser with laser dye PM580 dissolved in ethanol was used. With the help of forward compensated beam-split technique and imaging detecting system, the saturation intensity of DFWM spectrum in the iodine vapor at 5 554.013 nm was first measured to be 290 microJ under the condition of atmospheric pressure and room temperature. The features of the dye laser such as wavelength ranges, beam quality and energy conversion efficiency decreased gradually with increasing pumping service use, pulse number and intensity. Additionally, with the comparison of the stable and unstable dye laser output, it was found that the instability of dye laser output had greatly influenced the DFWM signal and decreased the signal to background <span class="hlt">noise</span> ratio. Shot to shot jitter and the broadening in the output frequency leads to an effective broadening of the recorded spectrum and loss of the DFWM signal to <span class="hlt">noise</span> ratio under the same pumping intensity at different time. The study is of importance to the detection of trace atom, molecule and radical in combustion diagnosis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4970000','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4970000"><span>Resolution-Enhanced <span class="hlt">Harmonic</span> and Interharmonic Measurement for Power Quality Analysis in Cyber-Physical Energy System</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Liu, Yanchi; Wang, Xue; Liu, Youda; Cui, Sujin</p> <p>2016-01-01</p> <p>Power quality analysis issues, especially the measurement of <span class="hlt">harmonic</span> and interharmonic in cyber-physical energy systems, are addressed in this paper. As new situations are introduced to the power system, the impact of electric vehicles, distributed generation and renewable energy has introduced extra demands to distributed sensors, waveform-level information and power quality data analytics. <span class="hlt">Harmonics</span> and interharmonics, as the most significant disturbances, require carefully designed detection methods for an accurate measurement of electric loads whose information is crucial to subsequent analyzing and control. This paper gives a detailed description of the power quality analysis framework in networked environment and presents a fast and resolution-enhanced method for <span class="hlt">harmonic</span> and interharmonic measurement. The proposed method first extracts <span class="hlt">harmonic</span> and interharmonic components efficiently using the single-channel version of Robust Independent Component Analysis (RobustICA), then estimates the high-resolution frequency from three discrete Fourier transform (DFT) samples with little additional computation, and finally computes the amplitudes and phases with the adaptive linear neuron network. The experiments show that the proposed method is time-efficient and leads to a better accuracy of the simulated and experimental signals in the presence of <span class="hlt">noise</span> and fundamental frequency deviation, thus providing a deeper insight into the (inter)<span class="hlt">harmonic</span> <span class="hlt">sources</span> or even the whole system. PMID:27355946</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27355946','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27355946"><span>Resolution-Enhanced <span class="hlt">Harmonic</span> and Interharmonic Measurement for Power Quality Analysis in Cyber-Physical Energy System.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Yanchi; Wang, Xue; Liu, Youda; Cui, Sujin</p> <p>2016-06-27</p> <p>Power quality analysis issues, especially the measurement of <span class="hlt">harmonic</span> and interharmonic in cyber-physical energy systems, are addressed in this paper. As new situations are introduced to the power system, the impact of electric vehicles, distributed generation and renewable energy has introduced extra demands to distributed sensors, waveform-level information and power quality data analytics. <span class="hlt">Harmonics</span> and interharmonics, as the most significant disturbances, require carefully designed detection methods for an accurate measurement of electric loads whose information is crucial to subsequent analyzing and control. This paper gives a detailed description of the power quality analysis framework in networked environment and presents a fast and resolution-enhanced method for <span class="hlt">harmonic</span> and interharmonic measurement. The proposed method first extracts <span class="hlt">harmonic</span> and interharmonic components efficiently using the single-channel version of Robust Independent Component Analysis (RobustICA), then estimates the high-resolution frequency from three discrete Fourier transform (DFT) samples with little additional computation, and finally computes the amplitudes and phases with the adaptive linear neuron network. The experiments show that the proposed method is time-efficient and leads to a better accuracy of the simulated and experimental signals in the presence of <span class="hlt">noise</span> and fundamental frequency deviation, thus providing a deeper insight into the (inter)<span class="hlt">harmonic</span> <span class="hlt">sources</span> or even the whole system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...383..464F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...383..464F"><span>Beamforming of aeroacoustic <span class="hlt">sources</span> in the time domain: An investigation of the intermittency of the <span class="hlt">noise</span> radiated by a forward-facing step</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fischer, J.; Valeau, V.; Brizzi, L.-E.</p> <p>2016-11-01</p> <p>The present study investigates the intermittency of the broadband aeroacoustic <span class="hlt">noise</span> produced by a forward-facing step in a flow. The <span class="hlt">noise</span> <span class="hlt">source</span> is viewed as a random succession of the so-called intermittent events of short duration distributed spatially in a <span class="hlt">source</span> region in the flow. An array processing method based on time-domain beamforming has been developed in order to track systematically the intermittent events, both in the time and space domains. Based on a simulated model of the far-field pressure field, the method is validated in terms of event detection and of performance for recovering the pressure spectrum. The method is then applied to experimental array data taken in an anechoic wind-tunnel at low Mach numbers (not exceeding 0.15) for a forward-facing step of height 30 mm. The results show that some very short intermittent events (with a mean duration of the order of 0.15 ms) can be identified from the array data. The spatial distribution of the intermittent events is found to be in agreement with the frequency domain beamform maps. The probability density functions of the events, in terms of widths and apparition times, are shown to be governed by Gamma laws and indicate random phenomena; it is observed that the statistical distributions vary with the streamwise position downstream and upstream of the step, the trends being in agreement with the <span class="hlt">source</span> behavior as evidenced by using the frequency-domain beamforming methods. The proposed method is then shown to identify, in terms of emission time, location and temporal width, a succession of short acoustic events that participate to the broadband aeroacoustic <span class="hlt">noise</span> produced by the step; those random events are likely to be linked to the dynamics of the flow interacting with the step.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003JSV...267..675L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003JSV...267..675L"><span>Train <span class="hlt">noise</span> reduction scenarios for compliance with future <span class="hlt">noise</span> legislation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Leth, S.</p> <p>2003-10-01</p> <p>The Technical Specification for Interoperability (TSI) for high-speed trains on the European market includes limits on <span class="hlt">noise</span> emission. These and other future restrictions on exterior <span class="hlt">noise</span> of high-speed and intercity trains will require that train manufacturers implement <span class="hlt">noise</span> control measures early in the design phase. A fundamental problem faced by manufacturers during the design process is determining how much <span class="hlt">noise</span> reduction is required for each of the various <span class="hlt">noise</span> <span class="hlt">sources</span> on the train in order to achieve an optimal balance. To illustrate this process, estimates are presented of the contributions from different <span class="hlt">sources</span> on existing Bombardier trains, based on measured data, numerical calculations and empirical formulae. In addition, methods of achieving the required <span class="hlt">noise</span> reductions for different <span class="hlt">sources</span> are briefly discussed along with targets for future exterior <span class="hlt">noise</span> emission. Measurement results presented demonstrate the importance of track quality in <span class="hlt">noise</span> emission. <span class="hlt">Noise</span> restrictions, including future legislation, must give proper recognition to this important parameter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950016575','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950016575"><span>Covariant <span class="hlt">harmonic</span> oscillators and coupled <span class="hlt">harmonic</span> oscillators</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Han, Daesoo; Kim, Young S.; Noz, Marilyn E.</p> <p>1995-01-01</p> <p>It is shown that the system of two coupled <span class="hlt">harmonic</span> oscillators shares the basic symmetry properties with the covariant <span class="hlt">harmonic</span> oscillator formalism which provides a concise description of the basic features of relativistic hadronic features observed in high-energy laboratories. It is shown also that the coupled oscillator system has the SL(4,r) symmetry in classical mechanics, while the present formulation of quantum mechanics can accommodate only the Sp(4,r) portion of the SL(4,r) symmetry. The possible role of the SL(4,r) symmetry in quantum mechanics is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21431061','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21431061"><span>Axisymmetric generalized <span class="hlt">harmonic</span> evolution code</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sorkin, Evgeny</p> <p>2010-04-15</p> <p>We describe the first axisymmetric numerical code based on the generalized <span class="hlt">harmonic</span> formulation of the Einstein equations, which is regular at the axis. We test the code by investigating gravitational collapse of distributions of complex scalar field in a Kaluza-Klein spacetime. One of the key issues of the <span class="hlt">harmonic</span> formulation is the choice of the gauge <span class="hlt">source</span> functions, and we conclude that a damped-wave gauge is remarkably robust in this case. Our preliminary study indicates that evolution of regular initial data leads to formation both of black holes with spherical and cylindrical horizon topologies. Intriguingly, we find evidence that near threshold for black hole formation the number of outcomes proliferates. Specifically, the collapsing matter splits into individual pulses, two of which travel in the opposite directions along the compact dimension and one which is ejected radially from the axis. Depending on the initial conditions, a curvature singularity develops inside the pulses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JPhCS.622a2058C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JPhCS.622a2058C"><span>Power System <span class="hlt">Harmonic</span> Elimination to Improve Power Quality</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chandrasekaran, K.; Ramachandaramurthy, V. K.</p> <p>2015-06-01</p> <p>An improvised RLC interface filter for a Dynamic Voltage Restorer (DVR) is proposed. The RLC filter is connected in the front end between the IGBT based Voltage <span class="hlt">Source</span> Inverter (VSI) and the injection transformer and is able to eliminate voltage <span class="hlt">harmonics</span> in the system and also switching <span class="hlt">harmonics</span> generated from VSI. The voltage at the sensitive load end is pure sinusoidal. In this method, the DVR produced Pulse Width Modulation (PWM) voltage with voltage <span class="hlt">harmonic</span> canceling the voltage <span class="hlt">harmonic</span> generated from the supply main. The VSI handles <span class="hlt">harmonic</span> power. The low order switching <span class="hlt">harmonics</span> generated by the IGBT based VSI is suppressed. The DVR has greater voltage injection capability. Good dynamic and transient results recorded and Total <span class="hlt">Harmonic</span> Distortion (THD) at the sensitive load end is minimized. The voltage at the sensitive load is sinusoidal and at 1.0 pu. PSCAD/EMTDC is used to validate the performance of the interface filter and the DVR. Simulated results are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6698744','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6698744"><span>Environmental issues: <span class="hlt">noise</span>, rail <span class="hlt">noise</span>, and high-speed rail</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hall, F.L.; Welland, J.D.; Bragdon, C.R.; Houtman, J.W.; Immers, B.H.</p> <p>1987-01-01</p> <p>The six papers in the report deal with the following areas: the effect of <span class="hlt">noise</span> barriers on the market value of adjacent residential properties; control of airport- and aircraft-related <span class="hlt">noise</span> in the United States; a traffic-assignment model to reduce <span class="hlt">noise</span> annoyance in urban networks; a survey of railroad occupational <span class="hlt">noise</span> <span class="hlt">sources</span>; a prediction procedure for rail transportation ground-borne <span class="hlt">noise</span> and vibration; and high-speed rail in California: the dream, the process, and the reality.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSP...165..809L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSP...165..809L"><span><span class="hlt">Harmonic</span> Chain with Velocity Flips: Thermalization and Kinetic Theory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lukkarinen, Jani; Marcozzi, Matteo; Nota, Alessia</p> <p>2016-12-01</p> <p>We consider the detailed structure of correlations in <span class="hlt">harmonic</span> chains with pinning and a bulk velocity flip <span class="hlt">noise</span> during the heat relaxation phase which occurs on diffusive time scales, for t=O(L^2) where L is the chain length. It has been shown earlier that for non-degenerate <span class="hlt">harmonic</span> interactions these systems thermalize, and the dominant part of the correlations is given by local thermal equilibrium determined by a temperature profile which satisfies a linear heat equation. Here we are concerned with two new aspects about the thermalization process: the first order corrections in 1 / L to the local equilibrium correlations and the applicability of kinetic theory to study the relaxation process. Employing previously derived explicit uniform estimates for the temperature profile, we first derive an explicit form for the first order corrections to the particle position-momentum correlations. By suitably revising the definition of the Wigner transform and the kinetic scaling limit we derive a phonon Boltzmann equation whose predictions agree with the explicit computation. Comparing the two results, the corrections can be understood as arising from two different <span class="hlt">sources</span>: a current-related term and a correction to the position-position correlations related to spatial changes in the phonon eigenbasis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19532204','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19532204"><span>Generation of two-mode bright squeezed light using a <span class="hlt">noise</span>-suppressed amplified diode laser.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Yun; Hayasaka, Kazuhiro; Kasai, Katsuyuki</p> <p>2006-12-25</p> <p>We present the generation of nonclassical state using an amplified diode laser as a light <span class="hlt">source</span>. The intensity <span class="hlt">noise</span> of an amplified diode laser was significantly suppressed and reached the shot <span class="hlt">noise</span> limit at 15 MHz using both a filter cavity and resonant optical feedback. Frequency doubling efficiency of 66% and up to 120 mW output power of green has been achieved in cw second-<span class="hlt">harmonic</span> generation from 1080 nm to 540 nm. Bright two-mode amplitude-squeezed state was generated from a type-II nondegenerate optical parametric amplifier pumped by generated green light. The measured <span class="hlt">noise</span> reduction is 2.1+/-0.2 dB below the shot-<span class="hlt">noise</span> level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930045413&hterms=hawking&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhawking','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930045413&hterms=hawking&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhawking"><span>The influence of quadrupole <span class="hlt">sources</span> in the boundary layer and wake of a blade on helicopter rotor <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Farassat, F.; Brentner, Kenneth S.</p> <p>1991-01-01</p> <p>It is presently noted that, for an observer in or near the plane containing a helicopter rotor disk, and in the far field, part of the volume quadrupole <span class="hlt">sources</span>, and the blade and wake surface quadrupole <span class="hlt">sources</span>, completely cancel out. This suggests a novel quadrupole <span class="hlt">source</span> description for the Ffowcs Williams-Hawkings equation which retain quadrupoles with axes parallel to the rotor disk; in this case, the volume and shock surface sourse terms are dominant.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720000047','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720000047"><span>High <span class="hlt">noise</span> immunity one shot</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schaffer, G. L.</p> <p>1972-01-01</p> <p>Multivibrator circuit, which includes constant current <span class="hlt">source</span>, isolates line <span class="hlt">noise</span> from timing circuitry and field effect transistor controls circuit's operational modes. Circuit has high immunity to supply line <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840021593','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840021593"><span>Rotorcraft <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Huston, R. J. (Compiler)</p> <p>1982-01-01</p> <p>The establishment of a realistic plan for NASA and the U.S. helicopter industry to develop a design-for-<span class="hlt">noise</span> methodology, including plans for the identification and development of promising <span class="hlt">noise</span> reduction technology was discussed. Topics included: <span class="hlt">noise</span> reduction techniques, scaling laws, empirical <span class="hlt">noise</span> prediction, psychoacoustics, and methods of developing and validing <span class="hlt">noise</span> prediction methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/238862','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/238862"><span>Ultrahigh <span class="hlt">harmonics</span> generation in a FEL with a seed laser</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Goloviznin, V.V.; Amersfoort, P.W. van</p> <p>1995-12-31</p> <p>One of the most challenging problems in modern FEL technology is to operate in the X-ray region, especially in the {open_quotes}water window{close_quotes}. Because of the absence of optical resonators in this range of wavelengths, only a single-pass device may be suitable for this task. The Self-Amplified Spontaneous Emission (SASE) mechanism is now under active discussion as a realistic way to provide high-power coherent emission in the X-ray range. Both the undulator parameters and the electron beam parameters required for the lasing are achieveable at today`s technological level. On the other hand, the SASE approach implies a very long and expensive periodic magnetic structure, typically several tens of meters long. This is mainly because of the rather long build-up time necessary to establish a coherent mode from incoherent <span class="hlt">noise</span>. A mechanism of shortening this time would be therefore highly desirable. In the present paper we consider a scheme using two undulators and a seed-laser to produce coherent X-ray emission. The first undulator and the seed-laser provide a pre-modulation of the beam while the second undulator serves as a <span class="hlt">source</span> of coherent spontaneous radiation at a very high <span class="hlt">harmonic</span> of the seed-laser frequency; the whole scheme may then be considered to be an FEL-based frequency upconvertor. The total length of the periodic magnetic structure is shown to be of the order of several meters, nearly an order of magnitude shorter than in the SASE case. For the same beam quality as in the SASE scheme and with realistic seed-laser parameters, the efficiency of the beam pre-modulation at the 50-th (!) <span class="hlt">harmonic</span> is shown to be as high as 15%. The output radiation is tunable between discrete <span class="hlt">harmonics</span> of the seed-frequency.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12678944','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12678944"><span><span class="hlt">Noise</span> Mapping and Annoyance.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Knauss, D.</p> <p>2002-01-01</p> <p>The EC has published a Green Paper on <span class="hlt">noise</span> policy in the EU and has issued a directive on the assessment and reduction of environmental <span class="hlt">noise</span>. This directive will make <span class="hlt">noise</span> mapping mandatory for cities with at least 250.000 inhabitants. Due to the development in computer technology it is possible to calculate <span class="hlt">noise</span> maps for large urban areas using the available data on buildings, ground profile, road and rail traffic. Examples for <span class="hlt">noise</span> mapping are Birmingham (GB), Linz (A) and various German cities. Based on <span class="hlt">noise</span> maps and empirical data on the correlation between annoyance and <span class="hlt">noise</span> levels annoyance maps for different <span class="hlt">sources</span> (rail, road, aircraft) can be calculated. Under the assumption that the annoyance for the different <span class="hlt">sources</span> are only weakly correlated, a combined annoyance map can be calculated. In a second step using the distribution of the population the actual number of annoyed people can be evaluated. This analysis can be used, for example, to identify <span class="hlt">noise</span> hot spots and to assess the impact of major traffic projects - roads, airports- on the <span class="hlt">noise</span> situation as well as the impact on the population. Furthermore, the combined annoyance maps can be used to investigate on health effects and to check whether or not empirical correlations between annoyance and <span class="hlt">noise</span> levels are sufficiently correct.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780016960','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780016960"><span>Evaluation of the annoyance due to helicopter rotor <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sternfeld, H., Jr.; Doyle, L. B.</p> <p>1978-01-01</p> <p>A program was conducted in which 25 test subjects adjusted the levels of various helicopter rotor spectra until the combination of the <span class="hlt">harmonic</span> <span class="hlt">noise</span> and a broadband background <span class="hlt">noise</span> was judged equally annoying as a higher level of the same broadband <span class="hlt">noise</span> spectrum. The subjective measure of added <span class="hlt">harmonic</span> <span class="hlt">noise</span> was equated to the difference in the two levels of broadband <span class="hlt">noise</span>. The test participants also made subjective evaluations of the rotor <span class="hlt">noise</span> signatures which they created. The test stimuli consisted of three degrees of rotor impulsiveness, each presented at four blade passage rates. Each of these 12 <span class="hlt">harmonic</span> sounds was combined with three broadband spectra and was adjusted to match the annoyance of three different sound pressure levels of broadband <span class="hlt">noise</span>. Analysis of variance indicated that the important variables were level and impulsiveness. Regression analyses indicated that inclusion of crest factor improved correlation between the subjective measures and various objective or physical measures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19750034312&hterms=PNL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DPNL','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19750034312&hterms=PNL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DPNL"><span>Effect of at-the-<span class="hlt">source</span> <span class="hlt">noise</span> reduction on performance and weights of a tilt-rotor aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gibs, J.; Stepniewski, W. Z.; Spencer, R.</p> <p>1975-01-01</p> <p>Reduction of far-field acoustic signature through modification of basic design parameters (tip speed, number of blades, disc loading and rotor blade area) was examined, using a tilt-rotor flight research aircraft as a baseline configuration. Of those design parameters, tip speed appeared as the most important. Next, preliminary design of two aircraft was performed, postulating the following reduction of <span class="hlt">noise</span> level from that of the baseline machine, at 500 feet from the spot of OGE hover. In one aircraft, the PNL was lowered by 10 PNdB and in the other, OASPL decreased by 10 dB. The resulting weight and performance penalties were examined. Then, PNL and EPNL aspects of terminal operation were compared for the baseline and quieter aircraft.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860060762&hterms=source+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dsource%2Bstudy','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860060762&hterms=source+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dsource%2Bstudy"><span>Development of an impulsive <span class="hlt">noise</span> <span class="hlt">source</span> to study the acoustic reflection characteristics of hard-walled wind tunnels</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Salikuddin, M.; Burrin, R. H.; Ahuja, K. K.; Bartel, H. W.</p> <p>1986-01-01</p> <p>Two impulsive sound <span class="hlt">sources</span>, one using multiple acoustic drivers and the other using a spark discharge were developed to study the acoustic reflection characteristics of hard-walled wind tunnels, and the results of laboratory tests are presented. The analysis indicates that though the intensity of the pulse generated by the spark <span class="hlt">source</span> was higher than that obtained from the acoustic <span class="hlt">source</span>, the number of averages needed for a particular test may require an unacceptibly long tunnel-run time due to the low spark generation repeat rate because of capacitor charging time. The additional hardware problems associated with the longevity of electrodes and electrode holders in sustaining the impact of repetitive spark discharges, show the multidriver acoustic <span class="hlt">source</span> to be more suitable for this application.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110011338','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110011338"><span>Core <span class="hlt">Noise</span> - Increasing Importance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hultgren, Lennart S.</p> <p>2011-01-01</p> <p>This presentation is a technical summary of and outlook for NASA-internal and NASA-sponsored external research on core (combustor and turbine) <span class="hlt">noise</span> funded by the Fundamental Aeronautics Program Subsonic Fixed Wing (SFW) Project. Sections of the presentation cover: the SFW system-level <span class="hlt">noise</span> metrics for the 2015, 2020, and 2025 timeframes; turbofan design trends and their aeroacoustic implications; the emerging importance of core <span class="hlt">noise</span> and its relevance to the SFW Reduced-Perceived-<span class="hlt">Noise</span> Technical Challenge; and the current research activities in the core-<span class="hlt">noise</span> area, with additional details given about the development of a high-fidelity combustor-<span class="hlt">noise</span> prediction capability as well as activities supporting the development of improved reduced-order, physics-based models for combustor-<span class="hlt">noise</span> prediction. The need for benchmark data for validation of high-fidelity and modeling work and the value of a potential future diagnostic facility for testing of core-<span class="hlt">noise</span>-reduction concepts are indicated. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The SFW Reduced-Perceived-<span class="hlt">Noise</span> Technical Challenge aims to develop concepts and technologies to dramatically reduce the perceived aircraft <span class="hlt">noise</span> outside of airport boundaries. This reduction of aircraft <span class="hlt">noise</span> is critical to enabling the anticipated large increase in future air traffic. <span class="hlt">Noise</span> generated in the jet engine core, by <span class="hlt">sources</span> such as the compressor, combustor, and turbine, can be a significant contribution to the overall <span class="hlt">noise</span> signature at low-power conditions, typical of approach flight. At high engine power during takeoff, jet and fan <span class="hlt">noise</span> have traditionally dominated over core <span class="hlt">noise</span>. However, current design trends and expected technological advances in engine-cycle design as well as <span class="hlt">noise</span>-reduction methods are likely to reduce non-core <span class="hlt">noise</span> even at engine-power points higher than approach. In addition, future low-emission combustor</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/355077','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/355077"><span>Active <span class="hlt">harmonic</span> filter technology and market assessment. Final report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bhattacharya, S.; Divan, D.; Sutherland, P.</p> <p>1998-08-01</p> <p>Non-linear loads such as three-phase rectifiers, adjustable speed drives (ASDs), and arcing loads can cause voltage distortion and other power quality problems due to their interaction with the power grid. This report provides a technical and marketing assessment of active <span class="hlt">harmonic</span> filters, a promising approach to preventing these problems at their <span class="hlt">source</span>. Although predicting the direction and magnitude of <span class="hlt">harmonic</span> currents is difficult due to highly interconnected nature of distribution systems, even small <span class="hlt">harmonic</span> producing loads can result in high levels of <span class="hlt">harmonic</span> current flow between the utility and a customer and can also cause a resonance problem at sites far removed from the <span class="hlt">harmonic</span> producing load. The best way to keep voltage distortion low in a utility system is to constrain the <span class="hlt">harmonic</span> currents at their <span class="hlt">sources</span>. However, since regulation of <span class="hlt">harmonic</span> pollution does not provide any additional value to the customer, it is unlikely that any controls will be implemented on a consistent basis in the absence of mandatory requirements. In the United States, a step toward a standard operating practice is the IEEE 519-1992 recommended <span class="hlt">harmonic</span> standard that provides guidelines for limiting <span class="hlt">harmonic</span> currents by industrial plants. This report identifies the equipment likely to produce <span class="hlt">harmonic</span> loads and explains the kinds of problems that <span class="hlt">harmonic</span> currents can cause in a utility distribution system. It describes possible solutions to these problems, including <span class="hlt">harmonic</span> filtering and other technologies. The report examines the prospects for wider use of active <span class="hlt">harmonic</span> filter technology and discusses the important marketing issues for potential active filter marketers and manufacturers, such as the barriers to and drivers of increased use of active filter technology and the price points for active filters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6737821','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6737821"><span>Stability and <span class="hlt">harmonics</span> in thyristor controlled reactors</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bohmann, L.J.; Lasseter, R.H. )</p> <p>1990-04-01</p> <p><span class="hlt">Harmonics</span> that arise from the interaction of thyristor controlled reactors (TCRs) and power systems can sometimes cause stability problems that are difficult to analyze since the <span class="hlt">harmonics</span> are affected by the power system. The classical method for calculating <span class="hlt">harmonics</span> is to calculate the <span class="hlt">harmonic</span> current assuming an infinite bus at the high side of the TCR transformer. This current is then used as a <span class="hlt">harmonic</span> current <span class="hlt">source</span> on the ac system. The basic problem with this method is that many of the interactions between the ac system and the TCR are neglected. In this paper two methods for studying the neglected interactions are described. The first uses state variables to analyze the circuit containing the TCR. The resulting equations are linear differential equations with periodic coefficients. This formulation allows the study of stability, periodic operation, and resonance which can not be achieved by other methods. The second method uses a fourier matrix description of the TCR. In this model the coupling between the different <span class="hlt">harmonics</span> due to the switching is clearly shown.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9921E..2BV','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9921E..2BV"><span>Absorption of <span class="hlt">harmonic</span> light in plasmonic nanostructures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vincenti, Maria A.; de Ceglia, Domenico; Scalora, Michael</p> <p>2016-09-01</p> <p>Surface plasmons are known for their ability to provide large field enhancement at the interface between a metal and another medium. They can be observed in a variety of structures ranging from plain metallic films to nanoparticles and gratings. Thanks to their large electric field enhancement, surface plasmons have also been exploited for the enhancement of second and third <span class="hlt">harmonic</span> generation. In fact, metals possess a relatively high third order susceptibility and, although dipole-allowed quadratic nonlinearities are not present in the bulk, they also display an effective second order response that arises from symmetry breaking at the surface, magnetic dipoles (Lorentz force), inner-core electrons, convective nonlinear <span class="hlt">sources</span>, and electron gas pressure. While much attention has been devoted to achieve efficient excitation of surface plasmons to improve far-field <span class="hlt">harmonic</span> generation, little or no attention has been paid to the dissipation of the generated <span class="hlt">harmonic</span> light. Therefore, we undertake a discussion of both <span class="hlt">harmonic</span> generation and absorption in simple metallic/dielectric interfaces with or without excitation of surface plasmons. We demonstrate that, despite the best efforts embarked upon to study plasmon excitation, the absorbed <span class="hlt">harmonic</span> energy can far surpass the energy emitted in the far-field. These findings suggest that quantification of the absorbed <span class="hlt">harmonic</span> light should be an important parameter in evaluating designs of plasmonic nanostructures for frequency mixing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994PhDT.......216H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994PhDT.......216H"><span>Analysis of Vibration and Acoustic <span class="hlt">Noise</span> in Permanent Magnet Motors.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hwang, Sangmoon</p> <p></p> <p>The drive motor is a frequent <span class="hlt">source</span> of vibration and acoustic <span class="hlt">noise</span> in many precision spindle motors. One of the electromagnetic <span class="hlt">sources</span> of vibration in permanent magnet motors is the torque ripple, consisting of the reluctance torque and electromagnetic torque fluctuation. This type of vibration is becoming more serious with the advent of new high-grade magnets with increased flux density. Acoustic <span class="hlt">noise</span> of electromagnetic origin is difficult to predict and its exact mechanism is unclear. The mechanism of <span class="hlt">noise</span> generation should be revealed to design a quieter motor which is the modern customer's demand. For motor operation at low speeds and loads, torque ripple due to the reluctance torque is often a <span class="hlt">source</span> of vibration and control difficulty. The reluctance torque in a motor was calculated from the flux density by a finite element method and the Maxwell stress method. Effects of design parameters, such as stator slot width, permanent slot width, airgap length and magnetization direction, were investigated. Magnet pole shaping, by gradually decreasing the magnet thickness toward edges, yields a sinusoidal shape of the reluctance torque with reduced <span class="hlt">harmonics</span>, thus reducing the vibration. This dissertation also presents two motor design techniques: stator tooth notching and rotor pole skewing with magnet pole shaping, and the effect of each method on the output torque. The analysis shows that the reluctance torque can be nearly eliminated by the suggested designs, with minimal sacrifice of the output torque. In permanent magnet DC motors, the most popular design type is the trapezoidal back electro-motive force (BEMF), for switched DC controllers. It is demonstrated that the output torque profile of one phase energized is qualitatively equivalent to the BEMF profile for motors with reduced reluctance torque. It implies that design of BEMF profile is possible by magnetic modeling of a motor, without expensive and time-consuming experiments for different designs</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013NPGeo..20...71P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013NPGeo..20...71P"><span>Wavefield decomposition and phase space dynamics of the seismic <span class="hlt">noise</span> at Volcàn de Colima, Mexico: evidence of a two-state <span class="hlt">source</span> process</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Palo, M.; Cusano, P.</p> <p>2013-01-01</p> <p>We analyse the seismic <span class="hlt">noise</span> recorded at the Colima Volcano (Mexico) in the period December 2005-May 2006 by four broadband three-component seismic stations. Specifically, we characterize the spectral content of the signal and follow its time evolution along all the data set. Moreover, we infer the properties of the attractor in the phase space by false nearest neighbours analysis and Grassberger-Procaccia algorithm, and adopt a time-domain decomposition method (independent component analysis) to find the basic constituents (independent components) of the system. Constraints on the seismic wavefield are inferred by the polarization analysis. We find two states of the background seismicity visible in different time-intervals that are Phase A and Phase B. Phase A has a spectrum with two peaks at 0.15 Hz and 0.3 Hz, with the latter dominating, an attractor of correlation dimension close to 3, three quasi-monochromatic independent components, and a relevant fraction of crater-pointing polarization solutions in the near-field. In Phase B, the spectrum is preserved but with the highest peak at 0.15 Hz, the attractor has a correlation dimension close to 2, two independent components are extracted, and the polarization solutions are dominated by Rayleigh waves incoming from the southwest direction. We depict two <span class="hlt">sources</span> acting on the background seismicity that are the microseismic <span class="hlt">noise</span> loading on the Pacific coastline and a low-energy volcanic tremor. A change in the amplitude of the microseismic <span class="hlt">noise</span> can induce the switching from a state of the system to the other.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9461E..16C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9461E..16C"><span>Investigations on the effect of frequency and <span class="hlt">noise</span> in a localization technique based on microwave imaging for an in-body RF <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chandra, Rohit; Balasingham, Ilangko</p> <p>2015-05-01</p> <p>Localization of a wireless capsule endoscope finds many clinical applications from diagnostics to therapy. There are potentially two approaches of the electromagnetic waves based localization: a) signal propagation model based localization using a priori information about the persons dielectric channels, and b) recently developed microwave imaging based localization without using any a priori information about the persons dielectric channels. In this paper, we study the second approach in terms of a variety of frequencies and signal-to-<span class="hlt">noise</span> ratios for localization accuracy. To this end, we select a 2-D anatomically realistic numerical phantom for microwave imaging at different frequencies. The selected frequencies are 13:56 MHz, 431:5 MHz, 920 MHz, and 2380 MHz that are typically considered for medical applications. Microwave imaging of a phantom will provide us with an electromagnetic model with electrical properties (relative permittivity and conductivity) of the internal parts of the body and can be useful as a foundation for localization of an in-body RF <span class="hlt">source</span>. Low frequency imaging at 13:56 MHz provides a low resolution image with high contrast in the dielectric properties. However, at high frequencies, the imaging algorithm is able to image only the outer boundaries of the tissues due to low penetration depth as higher frequency means higher attenuation. Furthermore, recently developed localization method based on microwave imaging is used for estimating the localization accuracy at different frequencies and signal-to-<span class="hlt">noise</span> ratios. Statistical evaluation of the localization error is performed using the cumulative distribution function (CDF). Based on our results, we conclude that the localization accuracy is minimally affected by the frequency or the <span class="hlt">noise</span>. However, the choice of the frequency will become critical if the purpose of the method is to image the internal parts of the body for tumor and/or cancer detection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AtmEn.148..361H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AtmEn.148..361H"><span>The need for <span class="hlt">harmonization</span> of methods for finding locations and magnitudes of air pollution <span class="hlt">sources</span> using observations of concentrations and wind fields</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hanna, Steven R.; Young, George S.</p> <p>2017-01-01</p> <p>What do the terms "top-down", "inverse", "backwards", "adjoint", "sensor data fusion", "receptor", "<span class="hlt">source</span> term estimation (STE)", to name several appearing in the current literature, have in common? These varied terms are used by different disciplines to describe the same general methodology - the use of observations of air pollutant concentrations and knowledge of wind fields to identify air pollutant <span class="hlt">source</span> locations and/or magnitudes. Academic journals are publishing increasing numbers of papers on this topic. Examples of scenarios related to this growing interest, ordered from small scale to large scale, are: use of real-time samplers to quickly estimate the location of a toxic gas release by a terrorist at a large public gathering (e.g., Haupt et al., 2009);</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750024798','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750024798"><span>Determination of rotor <span class="hlt">harmonic</span> blade loads from acoustic measurements</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kasper, P. K.</p> <p>1975-01-01</p> <p>The magnitude of discrete frequency sound radiated by a rotating blade is strongly influenced by the presence of a nonuniform distribution of aerodynamic forces over the rotor disk. An analytical development and experimental results are provided for a technique by which <span class="hlt">harmonic</span> blade loads are derived from acoustic measurements. The technique relates, on a one-to-one basis, the discrete frequency sound <span class="hlt">harmonic</span> amplitudes measured at a point on the axis of rotation to the blade-load <span class="hlt">harmonic</span> amplitudes. This technique was applied to acoustic data from two helicopter types and from a series of test results using the NASA-Langley Research Center rotor test facility. The inferred blade-load <span class="hlt">harmonics</span> for the cases considered tended to follow an inverse power law relationship with <span class="hlt">harmonic</span> blade-load number. Empirical curve fits to the data showed the <span class="hlt">harmonic</span> fall-off rate to be in the range of 6 to 9 db per octave of <span class="hlt">harmonic</span> order. These empirical relationships were subsequently used as input data in a compatible far field rotational <span class="hlt">noise</span> prediction model. A comparison between predicted and measured off-axis sound <span class="hlt">harmonic</span> levels is provided for the experimental cases considered.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/11802','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/11802"><span>Nonlinear <span class="hlt">harmonic</span> generation and proposed experimental verification in SASE FELs.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Biedron, S. G.; Freund, H. P.; Milton, S. V.</p> <p>1999-08-24</p> <p>Recently, a 3D, polychromatic, nonlinear simulation code was developed to study the growth of nonlinear <span class="hlt">harmonics</span> in self-amplified spontaneous emission (SASE) free-electron lasers (FELs). The simulation was applied to the parameters for each stage of the Advanced Photon <span class="hlt">Source</span> (APS) SASE FEL, intended for operation in the visible, UV, and short UV wavelength regimes, respectively, to study the presence of nonlinear <span class="hlt">harmonic</span> generation. Significant nonlinear <span class="hlt">harmonic</span> growth is seen. Here, a discussion of the code development, the APS SASE FEL, the simulations and results, and, finally, the proposed experimental procedure for verification of such nonlinear <span class="hlt">harmonic</span> generation at the APS SASE FEL will be given.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984icas.conf..841S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984icas.conf..841S"><span>Commercial aircraft <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, M. J.</p> <p></p> <p>The history of aircraft <span class="hlt">noise</span> control development is traced with an eye to forecasting the future. <span class="hlt">Noise</span> control became imperative with the advent of the first generation of commercial jet aircraft, which were extremely loud. The steady increases in the size of turbofans have nearly matched the progress in <span class="hlt">noise</span> reduction capabilities in recent years. Only 5 dB of reduction in fleet <span class="hlt">noise</span> has been achieved since early standards were met. Current engine design is concentrated on increasing fuel efficiency rather than lowering <span class="hlt">noise</span> emissions. Further difficulties exist because of continued flights with older aircraft. Gains in <span class="hlt">noise</span> reduction have been made mainly by decreasing exhaust velocities from 600-700 m/sec to 300-400 m/sec. New techniques being explored comprise mixing the core and bypass flows, interaction tone control, reduction of broadband <span class="hlt">sources</span>, development of acoustic liner technology and alterations in the number of fan blades and stage spacing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSV...357...95P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSV...357...95P"><span>Suppression of tonal <span class="hlt">noise</span> in a centrifugal fan using guide vanes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paramasivam, Kishokanna; Rajoo, Srithar; Romagnoli, Alessandro</p> <p>2015-11-01</p> <p>This paper presents the work aiming for tonal <span class="hlt">noise</span> reduction in a centrifugal fan. In previous studies, it is well documented that tonal <span class="hlt">noise</span> is the dominant <span class="hlt">noise</span> <span class="hlt">source</span> generated in centrifugal fans. Tonal <span class="hlt">noise</span> is generated due to the aerodynamic interaction between the rotating impeller and stationary diffuser vanes. The generation of tonal <span class="hlt">noise</span> is related to the pressure fluctuation at the leading edge of the stationary vane. The tonal <span class="hlt">noise</span> is periodic in time which occurs at the blade passing frequency (BPF) and its <span class="hlt">harmonics</span>. Much of previous studies, have shown that the stationary vane causes the tonal <span class="hlt">noise</span> and generation of non-rotational turbulent <span class="hlt">noise</span>. However, omitting stationary vanes will lead to the increase of non-rotational turbulent <span class="hlt">noise</span> resulted from the high velocity of the flow leaving the impeller. Hence in order to reduce the tonal <span class="hlt">noise</span> and the non-rotational <span class="hlt">noise</span>, guide vanes were designed as part of this study to replace the diffuser vanes, which were originally used in the chosen centrifugal fan. The leading edge of the guide vane is tapered. This modification reduces the strength of pressure fluctuation resulting from the interaction between the impeller outflow and stationary vane. The sound pressure level at blade passing frequency (BPF) is reduced by 6.8 dB, the 2nd BPF is reduced by 4.1 dB and the 3rd BPF reduced by about 17.5 dB. The overall reduction was 0.9 dB. The centrifugal fan with tapered guide vanes radiates lower tonal <span class="hlt">noise</span> compared to the existing diffuser vanes. These reductions are achieved without compromising the performance of the centrifugal fan. The behavior of the fluid flow was studied using computational fluid dynamics (CFD) tools and the acoustics characteristics were determined through experiments in an anechoic chamber.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6831978','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6831978"><span>Evaluation of the /sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method for measuring the subcriticality of LWR fuel storage casks</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.</p> <p>1987-01-01</p> <p>The /sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method was evaluated to determine if it could be used to measure the subcriticality of storage casks of burnt light water reactor (LWR) fuel submerged in fuel storage pools, fully loaded and as they are being loaded. Measurements of k/sub eff/ would provide the parameter most directly related to the criticality safety of storage cask configurations of LWR fuel and could allow proper credit for fuel burnup without reliance on calculations. This, in turn, could lead to more cost-effective cask designs. Evaluation of the method for this application was based on experiments already completed at a critical experiments facility using arrays of pressurized water reactor (PWR) fuel pins typical of the size of storage cask configurations, the existence of neutron detectors that can function in shipping cask environments, and the ability to construct ionization chambers containing /sup 252/Cf of adequate intensity for these measurements.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <center> <div class="footer-extlink text-muted"><small>Some links on this page may take you to non-federal websites. 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