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Sample records for harmonic noise sources

  1. On the use of geometric and harmonic means with the generalized cross-correlation in the time domain to improve noise source maps.

    PubMed

    Padois, Thomas; Doutres, Olivier; Sgard, Franck; Berry, Alain

    2016-07-01

    Microphone array techniques are an efficient tool to detect acoustic source positions. The delay and sum beamforming is the standard method. In the time domain, the generalized cross-correlation can be used to compute the noise source map. This technique is based on the arithmetic mean of the spatial likelihood functions. In this study, the classical arithmetic mean is replaced by the more standard generalized mean. The noise source maps provide by the arithmetic, geometric and harmonic means are compared in the case of numerical and experimental data obtained in a reverberant room. The geometric and harmonic means provide the best noise source maps with no side lobes and a better source level estimation. PMID:27475212

  2. Harmonic demodulation of nonstationary shot noise.

    PubMed

    Gray, M B; Stevenson, A J; Bachor, H A; McClelland, D E

    1993-05-15

    We report on experimental demodulation of nonstationary shot noise, which is associated with strongly modulated light. For sinusoidal modulation and demodulation, measurements confirm theoretical predictions of 1.8-dB excess noise in the modulation quadrature and 3-dB noise reduction in the opposite quadrature, relative to the standard quantum limit. Demodulation with a third harmonic produces noise correlated with that which is due to the fundamental. Reducing excess noise by 0.8 dB in the modulation quadrature, by combining the fundamental and third harmonics in a 2:1 ratio, is shown to be feasible. PMID:19802263

  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. Community noise sources and noise control issues

    NASA Astrophysics Data System (ADS)

    Nihart, Gene L.

    1992-04-01

    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.

  7. 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.

  8. Speech synthesis with pitch modification using harmonic plus noise model

    NASA Astrophysics Data System (ADS)

    Lehana, Parveen K.; Pandey, Prem C.

    2003-10-01

    In harmonic plus noise model (HNM) based speech synthesis, the input signal is modeled as two parts: the harmonic part using amplitudes and phases of the harmonics of the fundamental and the noise part using an all-pole filter excited by random white Gaussian noise. This method requires relatively less number of parameters and computations, provides good quality output, and permits pitch and time scaling without explicit estimation of vocal tract parameters. Pitch scaling to synthesize the speech with interpolated original amplitudes and phases at the multiples of the scaled pitch frequency results in an unnatural quality. Our investigation for obtaining natural quality output showed that the frequency scale of the amplitudes and phases of the harmonics of the original signal needed to be modified by a speaker dependent warping function. The function was obtained by studying the relationship between pitch frequency and formant frequencies for the three cardinal vowels naturally occurring with different pitches in a passage with intonation. Listening tests showed that good quality speech was obtained by linear frequency scaling of the amplitude and phase spectra, by the same factor as the pitch-scaling.

  9. 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.

  10. Aerodynamic noise sources

    NASA Astrophysics Data System (ADS)

    Munin, A. G.; Kuznetsov, V. M.; Leontev, E. A.

    A general theory is developed for aerodynamic sound generation and its propagation in an inhomogeneous medium. Results of theoretical and experimental studies of the acoustic characteristics of jets are discussed, and a solution is presented to the problem concerning the noise from a section, free rotor, and a rotor located inside a channel. Sound propagation in a channel with flow and selection of soundproofing liners for the channel walls are also discussed.

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

    NASA Astrophysics Data System (ADS)

    Yamada, Takahiro; Urano, Chiharu; Maezawa, Masaaki

    2016-01-01

    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.

  12. 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

    2015-01-01

    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

  13. 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.

  14. 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.

  15. 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.

  16. A Cepstrum-Based Technique for Determining a Harmonics-to-Noise Ratio in Speech Signals.

    ERIC Educational Resources Information Center

    de Krom, Guus

    1993-01-01

    A new method to calculate a spectral harmonics-to-noise (HNR) ratio is presented. The method discriminates between harmonic and noise energy in the magnitude spectrum by means of a comb-filtering operation in the cepstrum domain. HNR is seen to be a useful parameter in the analysis of voice quality. (Author/DB)

  17. 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

  18. Nonstationary noise propagation with sources

    NASA Astrophysics Data System (ADS)

    Ben-Benjamin, J. S.; Cohen, L.

    2014-06-01

    We discuss a number of topics relevant to noise propagation in dispersive media. We formulate the problem of pulse propagation with a source term in phase space and show that a four dimensional Wigner distribution is required. The four dimensional Wigner distribution is that of space and time and also wavenumber and frequency. The four dimensional Wigner spectrum is equivalent to the space-time autocorrelation function. We also apply the quantum path method to improve the phase space approximation previously obtained. In addition we discuss motion in a Snell's law medium.

  19. Noise sources and noise suppression in CMOS imagers

    NASA Astrophysics Data System (ADS)

    Pain, Bedabrata; Cunningham, Thomas J.; Hancock, Bruce R.

    2004-01-01

    Mechanisms for noise coupling in CMOS imagers are complex, since unlike a CCD, a CMOS imager has to be considered as a full digital-system-on-a-chip, with a highly sensitive front-end. In this paper, we analyze the noise sources in a photodiode CMOS imager, and model their propagation through the signal chain to determine the nature and magnitude of noise coupling. We present methods for reduction of noise, and present measured data to show their viability. For temporal read noise reduction, we present pixel signal chain design techniques to achieve near 2 electrons read noise. We model the front-end reset noise both for conventional photodiode and CTIA type of pixels. For the suppression of reset noise, we present a column feedback-reset method to reduce reset noise below 6 electrons. For spatial noise reduction, we present the design of column signal chain that suppresses both spatial noise and power supply coupling noise. We conclude by identifying problems in low-noise design caused by dark current spatial distribution.

  20. Lifetime increase using passive harmonic cavities insynchrotronlight sources

    SciTech Connect

    Byrd, J.M.; Georgsson, M.

    2000-09-22

    Harmonic cavities have been used in storage rings to increase beam lifetime and Landau damping by lengthening the bunch.The need for lifetime increase is particularly great in the present generation of low to medium energy synchrotron light sources where the small transverse beam sizes lead to relatively short lifetimes from large-angle intrabeam (Touschek) scattering. We review the beam dynamics of harmonic radiofrequency (RF) systems and discuss optimization of the beam lifetime using passive harmonic cavities.

  1. Comparison between MIM and Schottky diodes as harmonic mixers for visible lasers and microwave sources

    NASA Astrophysics Data System (ADS)

    Acef, O.; Hilico, L.; Bahoura, M.; Nez, F.; De Natale, P.

    1994-07-01

    We report our results on high order harmonic mixing between two visible lasers and microwave radiations in point-contact diodes. We have observed up to the 17th harmonic mixing order between two lasers ( Δv = 150 GHz) and a X-band klystron in a Schottky diode. We have been able to monitor very large laser frequency differences, up to 540 GHz (≈ 1.3 nm) with a good signal to noise ratio while using a very low power microwave source (20 mW/90 GHz). These results can be improved by using stabilized lasers and phase-locked microwave sources.

  2. Flow noise source-resonator coupling

    SciTech Connect

    Pollack, M.L.

    1997-11-01

    This paper investigates the coupling mechanism between flow noise sources and acoustic resonators. Analytical solutions are developed for the classical cases of monopole and dipole types of flow noise sources. The effectiveness of the coupling between the acoustic resonator and the noise source is shown to be dependent on the type of noise source as well as its location on the acoustic pressure mode shape. For a monopole source, the maximum coupling occurs when the noise source is most intense near an acoustic pressure antinode (i.e., location of maximum acoustic pressure). A numerical study with the impedance method demonstrates this effect. A dipole source couples most effectively when located near an acoustic pressure node.

  3. Turbofan engine core noise source diagnostics

    NASA Technical Reports Server (NTRS)

    Karchmer, Allen M.

    1987-01-01

    The paper describes a turbofan-engine measurement program utilizing a variety of diagnostic techniques to identify a source of core-generated noise which contributes to the overall external engine noise characteristics. Included in the turbofan engine diagnostics are data examination, time domain correlation, and frequency domain analysis. It is found that the turbulent pressure fluctuations within the combustor are a source for core noise which propagates through the nozzle and radiates to the far-field.

  4. A continuous wavelet transform approach for harmonic parameters estimation in the presence of impulsive noise

    NASA Astrophysics Data System (ADS)

    Dai, Yu; Xue, Yuan; Zhang, Jianxun

    2016-01-01

    Impulsive noise caused by some random events has the main character of short rise-time and wide frequency spectrum range, so it has the potential to degrade the performance and reliability of the harmonic estimation. This paper focuses on the harmonic estimation procedure based on continuous wavelet transform (CWT) when the analyzed signal is corrupted by the impulsive noise. The digital CWT of both the time-varying sinusoidal signal and the impulsive noise are analyzed, and there are two cross ridges in the time-frequency plane of CWT, which are generated by the signal and the noise separately. In consideration of the amplitude of the noise and the number of the spike event, two inequalities are derived to provide limitations on the wavelet parameters. Based on the amplitude distribution of the noise, the optimal wavelet parameters determined by solving these inequalities are used to suppress the contamination of the noise, as well as increase the amplitude of the ridge corresponding to the signal, so the parameters of each harmonic component can be estimated accurately. The proposed procedure is applied to a numerical simulation and a bone vibration signal test giving satisfactory results of stationary and time-varying harmonic parameter estimation.

  5. 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.

  6. 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.

  7. 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.

  8. Brilliant high harmonic sources with extended cut-off

    SciTech Connect

    Seres, Josef; Spielmann, Christian; Seres, Enikoe

    2010-02-02

    The most challenging application of time resolved spectroscopy is to directly watch the structural and electronic dynamics. Here we present several ways for realizing laser driven x-ray sources, offering atomic spatial and temporal resolution. Our approaches are based on high harmonic generation and include quasi-phase matching in two successive gas jets, extending the cut-off by high harmonic generation in an ion channel, and amplification of HHG in a plasma based amplifier.

  9. 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.

  10. 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.

  11. Programmable, very low noise current source

    NASA Astrophysics Data System (ADS)

    Scandurra, G.; Cannatà, G.; Giusi, G.; Ciofi, C.

    2014-12-01

    We propose a new approach for the realization of very low noise programmable current sources mainly intended for application in the field of low frequency noise measurements. The design is based on a low noise Junction Field Effect Transistor (JFET) acting as a high impedance current source and programmability is obtained by resorting to a low noise, programmable floating voltage source that allows to set the sourced current at the desired value. The floating voltage source is obtained by exploiting the properties of a standard photovoltaic MOSFET driver. Proper filtering and a control network employing super-capacitors allow to reduce the low frequency output noise to that due to the low noise JFET down to frequencies as low as 100 mHz while allowing, at the same time, to set the desired current by means of a standard DA converter with an accuracy better than 1%. A prototype of the system capable of supplying currents from a few hundreds of μA up to a few mA demonstrates the effectiveness of the approach we propose. When delivering a DC current of about 2 mA, the power spectral density of the current fluctuations at the output is found to be less than 25 pA/√Hz at 100 mHz and less than 6 pA/√Hz for f > 1 Hz, resulting in an RMS noise in the bandwidth from 0.1 to 10 Hz of less than 14 pA.

  12. The Source of Propeller Noise

    NASA Technical Reports Server (NTRS)

    Ernsthausen, W

    1937-01-01

    A two blade propeller of 40 cm diameter and zero pitch was explored for its noise development; it could be whirled up to 17,000 rpm - i.e., a tip speed of 355 meters/second. To obtain the power loss N(sub m) of the propeller for comparison with the produced acoustical power N(sub A) the engine performance characteristics were measured with and without propeller. The result is the sought-for relation c, that is, curve c' after correction with the engine efficiency.

  13. 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. PMID:26936977

  14. 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.

  15. 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).

  16. 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.

  17. 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. PMID:25373972

  18. Phase effects in masking by harmonic complexes: Detection of bands of speech-shaped noise

    PubMed Central

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

    2014-01-01

    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. PMID:25373972

  19. Programmable, very low noise current source.

    PubMed

    Scandurra, G; Cannatà, G; Giusi, G; Ciofi, C

    2014-12-01

    We propose a new approach for the realization of very low noise programmable current sources mainly intended for application in the field of low frequency noise measurements. The design is based on a low noise Junction Field Effect Transistor (JFET) acting as a high impedance current source and programmability is obtained by resorting to a low noise, programmable floating voltage source that allows to set the sourced current at the desired value. The floating voltage source is obtained by exploiting the properties of a standard photovoltaic MOSFET driver. Proper filtering and a control network employing super-capacitors allow to reduce the low frequency output noise to that due to the low noise JFET down to frequencies as low as 100 mHz while allowing, at the same time, to set the desired current by means of a standard DA converter with an accuracy better than 1%. A prototype of the system capable of supplying currents from a few hundreds of μA up to a few mA demonstrates the effectiveness of the approach we propose. When delivering a DC current of about 2 mA, the power spectral density of the current fluctuations at the output is found to be less than 25 pA/√Hz at 100 mHz and less than 6 pA/√Hz for f > 1 Hz, resulting in an RMS noise in the bandwidth from 0.1 to 10 Hz of less than 14 pA. PMID:25554328

  20. Noise Source for Calibrating a Microwave Polarimeter

    NASA Technical Reports Server (NTRS)

    Piepmeier, Jeffrey R.; Kim, Edward J.

    2006-01-01

    A correlated-noise source has been developed for use in calibrating an airborne or spaceborne Earth-observing correlation microwave polarimeter that operates in a in a pass band that includes a nominal frequency of 10.7 GHz. Deviations from ideal behavior of the hardware of correlation polarimeters are such as to decorrelate the signals measured by such an instrument. A correlated-noise source provides known input signals, measurements of which can be processed to estimate and correct for the decorrelation effect.

  1. 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.

  2. 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.

  3. Consideration of some noise sources due to railway operation

    NASA Astrophysics Data System (ADS)

    Stanworth, C. G.

    1983-03-01

    A number of railway operation noise sources other than those leading to the far field (largely wheel/rail), train pass-by noise, are identified and briefly discussed. People primarily affected by these may include railway staff and passengers on the train, railway trackside staff, and wayside residents. Both environmental pollution and hearing protection may be involved. Sources considered include the following: close proximity wheel/rail noise; locomotive noise; freight vehicle noise; warning signal noise; near field bridge noise; marshalling yard noise; flange squeal on tight curves; maintenance machine noise; and track machinery warning horn noise.

  4. Modeling helicopter near-horizon harmonic noise due to transient maneuvers

    NASA Astrophysics Data System (ADS)

    Sickenberger, Richard D.

    A new first principles model has been developed to estimate the external harmonic noise radiation for a helicopter performing transient maneuvers in the longitudinal plane. This model, which simulates the longitudinal fuselage dynamics, main rotor blade flapping, and far field acoustics, was validated using in-flight measurements and recordings from ground microphones during a full-scale flight test featuring a Bell 206B-3 helicopter. The flight test was specifically designed to study transient maneuvers. The validated model demonstrated that the flapping of the main rotor blades does not significantly affect the acoustics radiated by the helicopter during maneuvering flight. Furthermore, the model also demonstrated that Quasi-Static Acoustic Mapping (Q-SAM) methods can be used to reliably predict the noise radiated during transient maneuvers. The model was also used to identify and quantify the contributions of main rotor thickness noise, low frequency loading noise, and blade-vortex interaction (BVI) noise during maneuvering flight for the Bell 206B-3 helicopter. Pull-up and push-over maneuvers from pure longitudinal cyclic and pure collective control inputs were investigated. The contribution of thickness noise and low frequency loading noise during maneuvering flight was found to depend on the orientation of the tip-path plane relative to the observer. The contribution of impulsive BVI noise during maneuvering flight was found to depend on the inflow through the main rotor and the orientation of the tip-path plane relative to the observer.

  5. Evading surface and detector frequency noise in harmonic oscillator measurements of force gradients

    NASA Astrophysics Data System (ADS)

    Moore, Eric W.; Lee, SangGap; Hickman, Steven A.; Harrell, Lee E.; Marohn, John A.

    2010-07-01

    We introduce and demonstrate a method of measuring small force gradients acting on a harmonic oscillator in which the force-gradient signal of interest is used to parametrically up-convert a forced oscillation below resonance into an amplitude signal at the oscillator's resonance frequency. The approach, which we demonstrate in a mechanically detected electron spin resonance experiment, allows the force-gradient signal to evade detector frequency noise by converting a slowly modulated frequency signal into an amplitude signal.

  6. 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. PMID:21895059

  7. 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.

  8. 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.

  9. 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.

  10. Excess noise sources in depolarized raman pumping system

    NASA Astrophysics Data System (ADS)

    Chluda, Cedric; Myara, Mikhael; Troussellier, Laurent; Perez, Jean-Philippe; Signoret, Philippe; Orsal, Bernard

    2007-06-01

    This paper deals with the study of the various excess noises in copropagative distributed Raman Amplifiers. We study the influence of the biasing system on the laser sources through three simple home-made curent sources. A second step consists in studying the polarization multiplexer noise contribution. Finally, the impact of these noise exces on the amplifier background noise is studied.

  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. 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.

  13. Ultrasound harmonic imaging with reducing speckle noise by spatial-frequency compounding approach

    NASA Astrophysics Data System (ADS)

    Guo, Wei; Wang, Yuanyuan; Yu, Jinhua

    2015-12-01

    Speckle noise is a phenomenon inherent in any coherent imaging process and decreases the signal-to-noise ratio (SNR), which brings down the imaging quality. Speckle noise reduction is particularly important in the tissue harmonic imaging (THI) since it has the lower energy and the poorer SNR than the fundamental imaging (FI). Recently plane wave imaging (PWI) has been widely explored. Since the entire imaging region can be covered in one emission, the frame rate increases greatly. In PWI, speckle can be reduced by incoherently averaging images with different speckle patterns. Such images can be acquired by varying the angle from which a target is imaged (spatial compounding, SC) or by changing the spectrum of the pulse (frequency compounding, FC). In this paper we demonstrate here that each approach is only a partial solution and that combining them provides a better result than applying either approach separately. We propose a spatial-frequency compounding (SFC) method for THI. The new method brings a good speckle suppression result. To illustrate the performance of our method, experiments have been conducted on the simulated data. A nonlinear simulation platform based on the full-wave model is used in the harmonic imaging simulation. Results show that our method brings the SNR an improvement of up to 50% in comparison with the single frame HI while maintaining a far better performance in both terms of resolution and contrast than the FI. Similar results can be obtained from our further experiments.

  14. Identifying noise sources of time-delayed feedback systems

    NASA Astrophysics Data System (ADS)

    Frank, T. D.; Beek, P. J.; Friedrich, R.

    2004-07-01

    We propose a novel method to identify noise sources of stochastic systems with time delays. In particular, we demonstrate how to distinguish between additive and multiplicative noise sources and to determine the structure of multiplicative and parametric noise sources of time-delayed human motor control systems.

  15. Identifying Potential Noise Sources within Acoustic Signals

    NASA Astrophysics Data System (ADS)

    Holcomb, Victoria; Lewalle, Jacques

    2013-11-01

    We test a new algorithm for its ability to detect sources of noise within random background. The goal of these tests is to better understand how to identify sources within acoustic signals while simultaneously determining the strengths and weaknesses of the algorithm in question. Unlike previously published algorithms, the antenna method does not pinpoint events by looking for the most energetic portions of a signal. The algorithm searches for the ideal lag combinations between three signals by taking excerpts of possible events. The excerpt with the lowest calculated minimum distance between possible events is how the algorithm identifies sources. At the minimum distance, the events are close in time and frequency. This method can be compared to the cross correlation and denoising methods to better understand its effectiveness. This work is supported in part by Spectral Energies LLC, under an SBIR grant from AFRL, as well as the Syracuse University MAE department.

  16. Statistical evaluation of telephone noise interference caused by AC power line harmonic currents

    SciTech Connect

    Kuussaari, M. )

    1993-04-01

    A statistical approach is applied for the evaluation of the limits for harmonic currents in AC power lines, the goal being to prevent excessive telephone noise interference voltages in subscriber cables in rural areas. The analysis is based on Monte-Carlo simulation which takes into account the effect of the experiental probability distributions of the relevant parameters. In the Finnish conditions, the properties of communication cables permit equivalent disturbing phase currents of 8 to 10 A. The digital exchanges permit approximately the same currents. Some new telephone types that have a low balance may make it necessary to limit the currents to a level that is somewhat lower.

  17. 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.

  18. 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.

  19. Forward velocity effects on jet noise with dominant internal noise source

    NASA Technical Reports Server (NTRS)

    Vonglahn, U. H.; Goodykoontz, J. H.

    1973-01-01

    Acoustic data, with and without forward velocity, were obtained with a circular nozzle using a quiet flow system and one dominated by a low frequency internal noise source (analogous to combustion noise). Forward velocity effects were obtained by installing the test nozzle in a free jet. Farfield noise data were obtained at jet pressure ratios from 1.3 to 1.7 and forward velocities up to 260 ft/sec. With a quiet flow system, jet noise is reduced by forward velocity. With a dominant low frequency core noise source, the portion of the noise spectra dominated by this source was not appreciably affected by forward velocity.

  20. 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

  1. Assessing noise sources at synchrotron infrared ports.

    PubMed

    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.

  2. Rotor blade-vortex interaction noise reduction and vibration using higher harmonic control

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Booth, Earl R., Jr.

    1990-01-01

    The use of higher harmonic control (HHC) of blade pitch to reduce blade-vortex interaction (BVI) noise is examined by means of a rotor acoustic test. A dynamically scaled, four-bladed, articulated rotor model was tested in a heavy gas (Freon-12) medium. Acoustic and vibration measurements were made for a large range of matched flight conditions where prescribed (open loop) HHC pitch schedules were superimposed on the normal (baseline) collective and cyclic trim pitch. A novel sound power measurement technique was developed to take advantage of the reverberance in the hard walled tunnel. Quantitative sound power results are presented for a 4/rev (4P) collective pitch HHC. By comparing the results using 4P HHC to corresponding baseline (no HHC) conditions, significant midfrequency noise reductions of 5-6 dB are found for low-speed descent conditions where BVI is most intense. For other flight conditions, noise is found to increase with the use of HHC. LF loading noise, as well as fixed and rotating frame vibration levels, show increased levels.

  3. 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.

  4. 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.

  5. 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.

  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. Source-noise limitation of fiber-optic methane sensors.

    PubMed

    Jin, W; Stewart, G; Culshaw, B; Murray, S

    1995-05-01

    The effect of source (LED) noise on the sensitivity of fiber-optic methane sensors is discussed. Once the source is dominant, the system sensitivity cannot be improved by increasing the source power further. PMID:21037787

  8. 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.

  9. Simulation of Series Active and Passive Power Filter Combination System to Mitigate Current Source Harmonics

    NASA Astrophysics Data System (ADS)

    Yusof, Yushaizad; Rahim, Nasrudin Abd.

    2009-08-01

    This paper discusses a combination three phase system of series active power filter and passive power filter used to mitigate current source harmonics produced by a three phase diode rectifier with capacitive loads. A control method based on synchronous reference frame (SRF) is implemented to compensate for the current harmonics. Computer simulation and modelling of the combined filter system is carried out using Matlab/Simulink Power System Blockset (PSB) software. The single tuned passive power filters suppress 5th and 7th order current harmonics, while the series active power filter acts as a harmonic isolator between the source and load. Hence, the proposed system performs very well in mitigating source current harmonics to the level that comply the harmonic standard such as IEEE 519-1992.

  10. Single source noise reduction of received HF audio: experimental study

    NASA Astrophysics Data System (ADS)

    Campbell, Eric C.; Alva, Carlos O.

    2014-05-01

    This paper visits the application of single-source noise reduction on received audio over a HF channel. The noise reduction algorithm is typically used in vocoder noise processing at the transmitter before encoding. This study presents the results of the algorithm effects by objectively measuring audio quality through the use of industry standard PESQ analysis.

  11. Lloyd’s mirror interference lithography with EUV radiation from a high-harmonic source

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-su; Baksh, Peter; Odstrcil, Michal; Miszczak, Magdalena; Frey, Jeremy G.; Juschkin, Larissa; Brocklesby, William S.

    2016-07-01

    We demonstrate interference lithography using a high-harmonic source. Extreme ultraviolet (EUV) radiation is produced by high-harmonic generation with 800 nm light from a femtosecond Ti:sapphire laser (40 fs pulses, 1 kHz, 2 W average power) in argon gas. Interference patterns created using Lloyd’s mirror setup and monochromatized radiation at the 27th harmonic (29 nm) are recorded using a ZEP-520A photoresist, producing features with <200 nm pitch. The effect of the use of femtosecond pulsed EUV radiation on the recorded pattern is investigated. The capability of the high-harmonic source for high-resolution patterning is discussed.

  12. Importance of engine as a source of helicopter external noise

    NASA Technical Reports Server (NTRS)

    Janakiram, R. D.; Smith, M. J.; Tadghighi, H.

    1989-01-01

    A turboshaft engine's importance as a source of helicopter external noise is presently evaluated experimentally and analytically on the basis of test data from an MD500E helicopter, with and without engine muffler, during level flyovers and climbing flight. A strong engine noise component is noted for helicopter positions nearly overhead and beyond observed position, especially in the 200-1000 Hz range; its strong rearward directivity suggests the noise source to be the broadband exhaust or combustion noise radiated from the exhaust duct. The engine muffler furnished estimated perceived noise level reductions of 2-3 dB for the centerline.

  13. 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.

  14. Noise-like pulses generated at high harmonics in a partially-mode-locked km-long Raman fiber laser

    NASA Astrophysics Data System (ADS)

    Boucon, A.; Barviau, B.; Fatome, J.; Finot, C.; Sylvestre, T.; Lee, M. W.; Grelu, P.; Millot, G.

    2012-02-01

    We present a 5-km-long Raman fiber laser that delivers pulses at high harmonics of the fundamental cavity repetition rate, up to 1 GHz. The observed nanosecond pulses that propagate in an anomalous dispersion regime possess a complex noise-like structure with a coherence time of around 1 picosecond.

  15. 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.

  16. 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

  17. 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.

  18. Shot noise effect on noise source and noise parameter of 10-nm-scale quasi-ballistic n-/p-type MOS devices

    NASA Astrophysics Data System (ADS)

    Jeon, Jongwook; Kang, Myounggon

    2016-05-01

    In this work, we investigated the noise source and noise parameters of a quasi-ballistic MOSFET at the high-frequency regime. We presented the shot noise properties in the measured drain current noise and its impact on the induced gate noise and the noise parameters of 10-nm-scale n-/p-type MOS (N/PMOS) devices for the first time. The measured noise sources and noise parameters were carefully analyzed with the shot and thermal noise models in all operation regions. On the basis of the results, new noise parameter models are proposed and the noise performance improvement in the quasi-ballistic regime is shown.

  19. 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.

  20. Low frequency noise sources and mechanisms in semiconductor nanowire transistors

    NASA Astrophysics Data System (ADS)

    Delker, Collin James

    Semiconductor nanowires are attractive candidates for use in future high-speed electronics, transparent/flexible devices, and chemical sensors. Among other materials, III-V semiconductors have gained considerable interest for their high bulk mobility and low band gap, making them promising for high-speed nanoscale devices. However, nanowire devices also exhibit high levels of low-frequency noise due to their low band gap and high surface-to-volume ratio. The sources and mechanisms of this noise must be understood and controlled in order to realize practical applications of nanowire electronics. This work seeks to understand the underlying noise mechanisms of nanowire transistors in order discover ways to reduce noise levels. It also demonstrates how noise can provide a spectroscopy for analyzing device quality. Most traditional noise studies tend to apply standard MOSFET models to nanowire noise and transport, which lump together all possible independent noise sources in a nanowire, ignoring effects of the contacts or multiple gates, and could lead to misestimation of the noise figures for a device. This work demonstrates how noise in a nanowire transistor can stem from the channel, ungated access regions, metal- semiconductor contacts, and tunnel barriers, all independently adding to the total noise. Each source of noise can contribute and may dominate the overall noise behavior under certain bias regimes and temperatures, as demonstrated in this work through various device structures and measurements. For example, the contacts can influence noise even below the threshold voltage under certain conditions, emphasizing the need for high-quality metal-semiconductor interface technology.

  1. 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.

  2. Cross-correlation imaging of ambient noise sources

    NASA Astrophysics Data System (ADS)

    Ermert, Laura; Villaseñor, Antonio; Fichtner, Andreas

    2016-01-01

    We develop and apply a novel technique to image ambient seismic noise sources. It is based on measurements of cross-correlation asymmetry defined as the logarithmic energy ratio of the causal and anticausal branches of the cross-correlation function. A possible application of this technique is to account for the distribution of noise sources, a problem which currently poses obstacles to noise-based surface wave dispersion analysis and waveform inversion. The particular asymmetry measurement used is independent of absolute noise correlation amplitudes. It is shown how it can be forward-modelled and related to the noise source power-spectral density using adjoint methods. Simplified sensitivity kernels allow us to rapidly image variations in the power-spectral density of noise sources. This imaging method correctly accounts for viscoelastic attenuation and is to first order insensitive to unmodelled Earth structure. Furthermore, it operates directly on noise correlation data sets. No additional processing is required, which makes the method fast and computationally inexpensive. We apply the method to three vertical-component cross-correlation data sets of different spatial and temporal scales. Processing is deliberately minimal so as to keep observations consistent with the imaging concept. In accord with previous studies, we image seasonally changing sources of the Earth's hum in the Atlantic, Pacific and the Southern Ocean. The sources of noise in the microseismic band recorded at stations in Switzerland are predominantly located in the Atlantic and show a clear dependence on both season and frequency. Our developments are intended as a step towards full 3-D inversions for the sources of ambient noise in various frequency bands, which may ultimately lead to improvements of noise-based structural imaging.

  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. Coexistence of harmonic soliton molecules and rectangular noise-like pulses in a figure-eight fiber laser.

    PubMed

    Huang, Yu-Qi; Hu, Zi-Ang; Cui, Hu; Luo, Zhi-Chao; Luo, Ai-Ping; Xu, Wen-Cheng

    2016-09-01

    We report the coexistence of high-order harmonic soliton molecules and rectangular noise-like pulses (NLP) in a figure-eight fiber laser mode-locked by a nonlinear amplifying loop mirror. The harmonic soliton molecule has a repetition rate of 936.6 MHz, corresponding to the 466th harmonics 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. PMID:27607971

  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. 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.

  7. 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.

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

    PubMed Central

    Jayakumar, Vignesh; Zechmann, Edward

    2015-01-01

    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. PMID:26366038

  9. Aeroacoustic Codes for Rotor Harmonic and BVI Noise. CAMRAD.Mod1/HIRES: Methodology and Users' Manual

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    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 harmonic and Blade-Vortex Interaction (BVI) noise. 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 noise prediction accuracy are documented, including a new multi-core tip vortex roll-up wake model, higher harmonic 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.

  10. Improved perception of speech in noise and Mandarin tones with acoustic simulations of harmonic coding for cochlear implants.

    PubMed

    Li, Xing; Nie, Kaibao; Imennov, Nikita S; Won, Jong Ho; Drennan, Ward R; Rubinstein, Jay T; Atlas, Les E

    2012-11-01

    Harmonic and temporal fine structure (TFS) information are important cues for speech perception in noise and music perception. However, due to the inherently coarse spectral and temporal resolution in electric hearing, the question of how to deliver harmonic and TFS information to cochlear implant (CI) users remains unresolved. A harmonic-single-sideband-encoder [(HSSE); Nie et al. (2008). Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing; Lie et al., (2010). Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing] strategy has been proposed that explicitly tracks the harmonics in speech and transforms them into modulators conveying both amplitude modulation and fundamental frequency information. For unvoiced speech, HSSE transforms the TFS into a slowly varying yet still noise-like signal. To investigate its potential, four- and eight-channel vocoder simulations of HSSE and the continuous-interleaved-sampling (CIS) strategy were implemented, respectively. Using these vocoders, five normal-hearing subjects' speech recognition performance was evaluated under different masking conditions; another five normal-hearing subjects' Mandarin tone identification performance was also evaluated. Additionally, the neural discharge patterns evoked by HSSE- and CIS-encoded Mandarin tone stimuli were simulated using an auditory nerve model. All subjects scored significantly higher with HSSE than with CIS vocoders. The modeling analysis demonstrated that HSSE can convey temporal pitch cues better than CIS. Overall, the results suggest that HSSE is a promising strategy to enhance speech perception with CIs. PMID:23145619

  11. All-fiber fourth and fifth harmonic generation from a single source.

    PubMed

    Khudus, Muhammad I M Abdul; Lee, Timothy; De Lucia, Francesco; Corbari, Costantino; Sazio, Pier; Horak, Peter; Brambilla, Gilberto

    2016-09-19

    All-fiber fourth and fifth harmonic generation from a single source 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 harmonic. The output is then sent through two optical microfibers that generate the third and fourth harmonic, 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 harmonic generation efficiency and the diameters and lengths of the two microfibers, conversion efficiencies to the fourth harmonic in excess of 25% are theoretically achievable. PMID:27661915

  12. Active noise control using noise source having adaptive resonant frequency tuning through stress 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 an expandable ring embedded in the noise radiating element. Excitation of the ring causes expansion or contraction of the ring, thereby varying the stress in the noise radiating element. The ring is actuated by a controller which receives input of a feedback 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 ring, causing the ring to expand or contract. Instead of a single ring embedded in the noise radiating panel, a first expandable ring can be bonded to one side of the noise radiating element, and a second expandable ring can be bonded to the other side.

  13. Passive synthetic aperture imaging with limited noise sources

    NASA Astrophysics Data System (ADS)

    Garnier, Josselin

    2016-09-01

    We consider a passive synthetic aperture imaging problem. A single moving receiver antenna records random signals generated by one or several distant noise sources and backscattered by one or several reflectors. The sources emit noise signals modeled by stationary random processes. The reflectors can be imaged by summing the autocorrelation functions of the received signals computed over successive time windows, corrected for Doppler factors and migrated by appropriate travel times. In particular, the Doppler effect plays an important role and it can be used for resolution enhancement. When the noise source positions are not known, the reflector can be localized with an accuracy proportional to the reciprocal of the noise bandwidth, even when only a very small number of sources are available. When the noise source positions are known, the reflector can be localized with a cross range resolution proportional to the carrier wavelength and inversely proportional to the length of the receiver trajectory (i.e. the synthetic aperture), and with a range resolution proportional to the reciprocal of the bandwidth, even with only one noise source.

  14. Noise from high speed maglev systems: Noise sources, noise criteria, preliminary design guidelines for noise control, and recommendations for acoustical test facility for maglev research

    NASA Astrophysics Data System (ADS)

    Hanson, C. E.; Abbot, P.; Dyer, I.

    1993-01-01

    Noise levels from magnetically-levitated trains (maglev) at very high speed may be high enough to cause environmental noise impact in residential areas. Aeroacoustic sources dominate the sound at high speeds and guideway vibrations generate noticeable sound at low speed. In addition to high noise levels, the startle effect as a result of sudden onset of sound from a rapidly moving nearby maglev vehicle may lead to increased annoyance to neighbors of a maglev system. The report provides a base for determining the noise consequences and potential mitigation for a high speed maglev system in populated areas of the United States. Four areas are included in the study: (1) definition of noise sources; (2) development of noise criteria; (3) development of design guidelines; and (4) recommendations for a noise testing facility.

  15. BVI impulsive noise reduction by higher harmonic pitch control - Results of a scaled model rotor experiment in the DNW

    NASA Technical Reports Server (NTRS)

    Splettstoesser, Wolf R.; Schultz, KLAUS-J.; Kube, Roland; Brooks, Thomas F.; Booth, Earl R., Jr.; Niesl, Georg; Streby, Olivier

    1991-01-01

    Results are presented of a model rotor acoustics test performed to examine the benefit of higher harmonic control (HHC) of blade pitch to reduce blade-vortex interaction (BVI) impulsive noise. A dynamically scaled, four-bladed, rigid rotor model, a 40-percent replica of the B0-105 main rotor, was tested in the German Dutch Wind Tunnel. Noise characteristics and noise directivity patterns as well as vibratory loads were measured and used to demonstrate the changes when different HHC schedules were applied. Dramatic changes of the acoustic signatures and the noise radiation directivity with the HHC phase variations are found. Compared to the baseline conditions (without HHC), significant mid-frequency noise reductions of locally 6 dB are obtained for low-speed descent conditions where GVI is most intense. For other rotor operating conditions with less intense BVI there is less or no benefit from the use of HHC. LF noise and vibratory loads, especially at optimum noise reduction control settings, are found to increase.

  16. Covariance-based approaches to aeroacoustic noise source analysis.

    PubMed

    Du, Lin; Xu, Luzhou; Li, Jian; Guo, Bin; Stoica, Petre; Bahr, Chris; Cattafesta, Louis N

    2010-11-01

    In this paper, several covariance-based approaches are proposed for aeroacoustic noise source analysis under the assumptions of a single dominant source and all observers contaminated solely by uncorrelated noise. The Cramér-Rao Bounds (CRB) of the unbiased source power estimates are also derived. The proposed methods are evaluated using both simulated data as well as data acquired from an airfoil trailing edge noise experiment in an open-jet aeroacoustic facility. The numerical examples show that the covariance-based algorithms significantly outperform an existing least-squares approach and provide accurate power estimates even under low signal-to-noise ratio (SNR) conditions. Furthermore, the mean-squared-errors (MSEs) of the so-obtained estimates are close to the corresponding CRB especially for a large number of data samples. The experimental results show that the power estimates of the proposed approaches are consistent with one another as long as the core analysis assumptions are obeyed.

  17. Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

    NASA Technical Reports Server (NTRS)

    Burdisso, Ricardo (Inventor); Fuller, Chris R. (Inventor); O'Brien, Walter F. (Inventor); Thomas, Russell H. (Inventor); Dungan, Mary E. (Inventor)

    1996-01-01

    An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise 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 harmonic 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 noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source 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.

  18. Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

    NASA Technical Reports Server (NTRS)

    Burdisso, Ricardo (Inventor); Fuller, Chris R. (Inventor); O'Brien, Walter F. (Inventor); Thomas, Russell H. (Inventor); Dungan, Mary E. (Inventor)

    1994-01-01

    An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise 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 harmonic 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 noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source 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.

  19. Active noise control using noise source having adaptive resonant frequency tuning through variable ring loading

    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 noise radiating structure is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating structure is tuned by a plurality of drivers arranged to contact the noise radiating structure. Excitation of the drivers causes expansion or contraction of the drivers, thereby varying the edge loading applied to the noise radiating structure. The drivers are actuated by a controller which receives input of a feedback 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 drivers, causing them to expand or contract. The noise 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.

  20. High-harmonic XUV source for time- and angle-resolved photoemission spectroscopy

    SciTech Connect

    Dakovski, Georgi L; Li, Yinwan; Durakiewicz, Tomasz; Rodriguez, George

    2009-01-01

    We present a laser-based apparatus for visible pump/XUV probe time- and angle-resolved photoemission spectroscopy (TRARPES) utilizing high-harmonic generation from a noble gas. Femtosecond temporal resolution for each selected harmonic is achieved by using a time-delay-compensated monochromator (TCM). The source has been used to obtain photoemission spectra from insulators (UO{sub 2}) and ultrafast pump/probe processes in semiconductors (GaAs).

  1. Investigation of noise sources in SQUID electronics

    SciTech Connect

    Clem, T.R.; Goldstein, M.J.; Purpura, J.W.; Allen, L.H.; Claassen, J.H.; Gubser, D.U.; Wolf, S.A.

    1989-03-01

    The performance of SQUID-based electronics outside a laboratory-controlled environment may be degraded from that found in laboratory operation. Investigations on superconducting tubes, wires, and sheets have been conducted to identify contributions to such noise. Results have been obtained for bulk and thin film samples utilizing both the conventional low temperature materials, as well as the new high temperature oxide materials. Experiments have been conducted to quantify flux redistribution and flux motion in superconducting samples subjected to temperature changes, temperature gradients, and magnetic field gradients. These investigations have been conducted at magnetic fields typical of many SQUID applications, with field intensities much smaller than the critical values H/sub cl/. Penetration depth effects, flux pinning effects, and flux motion effects have been observed. The various types of experiments conducted along with specific results are described.

  2. Active control of environmental noise, VIII: increasing the response to primary source changes including unpredictable noise

    NASA Astrophysics Data System (ADS)

    Wright, S. E.; Atmoko, H.; Vuksanovic, B.

    2004-07-01

    Conventional adaptive cancellation systems using traditional transverse finite impulse response (FIR) filters, together with least mean square (LMS) adaptive algorithms, well known in active noise control, are slow to adapt to primary source changes. This makes them inappropriate for cancelling rapidly changing noise, including unpredictable noise such as speech and music. Secondly, the cancelling structures require considerable computational processing effort to adapt to primary source and plant changes, particularly for multi-channel systems. This paper describes methods to increase the adaptive speed to primary source changes in large enclosed spaces and outdoor environments. A method is described that increases the response to time varying periodic noise using traditional transverse FIR filters. Here a multi-passband filter, with individual variable adaptive step sizes for each passband is automatically adjusted according to the signal level in each band. This creates a similar adaptive response for all frequencies within the total pass-band, irrespective of amplitude, minimizing the signal distortion and increasing the combined adaptive speed. Unfortunately, there is a limit to the adaptive speed using the above method as classical transverse FIR filters have a finite adaptive speed given by the stability band zero bandwidth. For rapidly changing periodic noise and unpredictable non-stationary noise, a rapid to instantaneous response is required. In this case the on-line adaptive FIR filters are dispensed with and replaced by a time domain solution that gives virtually instantaneous cancellation response (infinite adaptive speed) to primary source changes, and is computationally efficient.

  3. High-order harmonic noise-like pulsing of a passively mode-locked double-clad Er/Yb fibre ring laser

    NASA Astrophysics Data System (ADS)

    Pottiez, O.; Hernández-García, J. C.; Ibarra-Escamilla, B.; Kuzin, E. A.; Durán-Sánchez, M.; González-García, A.

    2014-11-01

    In this paper, we study noise-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 noise-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 noise-like pulses, which then rearrange into a stable and periodic pulse train. Harmonic 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 noise-like pulse trains are demonstrated, reaching harmonic orders beyond 1200 and repetition frequencies in excess of a quarter of a GHz. The mechanisms leading to noise-like pulse breaking and stable high-order harmonic mode locking are discussed.

  4. Sub-Shot Noise Power Source for Microelectronics

    NASA Technical Reports Server (NTRS)

    Strekalov, Dmitry V.; Yu, Nan; Mansour, Kamjou

    2011-01-01

    Low-current, high-impedance microelectronic devices can be affected by electric current shot noise more than they are affected by Nyquist noise, even at room temperature. An approach to implementing a sub-shot noise current source 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 noise 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 noise generated by a tested light source in question is below the shot noise limit (e.g. produced by a coherent light beam), it was concluded that the light source 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 source and a high-efficiency linear photodiode are used to generate photocurrent with sub-Poissonian electron statistics. By powering microelectronic devices with this current source, their performance can be improved, especially their noise parameters. Therefore, a room-temperature sub

  5. Jet Noise Source Localization Using Linear Phased Array

    NASA Technical Reports Server (NTRS)

    Agboola, Ferni A.; Bridges, James

    2004-01-01

    A study was conducted to further clarify the interpretation and application of linear phased array microphone results, for localizing aeroacoustics sources 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 noise sources with bypass and other components separation. The results also showed that a focused near field image provides more realistic noise source localization at low to mid frequencies.

  6. Noise in an acoustic-optic modulated laser source

    SciTech Connect

    Kachelmyer, A.L.; Eng, R.S.

    1989-01-01

    This paper considers the measurement of amplitude modulation (AM) and phase modulation (PM) noise in a tunable CO{sub 2} laser source. Theoretical and experimental heterodyned output power spectrums are used to evaluate the quality of the acousto-optically tuned source.

  7. Planets as background noise sources in free space optical communications

    NASA Technical Reports Server (NTRS)

    Katz, J.

    1986-01-01

    Background noise generated by planets is the dominant noise source in most deep space direct detection optical communications systems. Earlier approximate analyses of this problem are based on simplified blackbody calculations and can yield results that may be inaccurate by up to an order of magnitude. Various other factors that need to be taken into consideration, such as the phase angle and the actual spectral dependence of the planet albedo, in order to obtain a more accurate estimate of the noise magnitude are examined.

  8. Algorithm for astronomical, point source, signal to noise ratio calculations

    NASA Technical Reports Server (NTRS)

    Jayroe, R. R.; Schroeder, D. J.

    1984-01-01

    An algorithm was developed to simulate the expected signal to noise 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 source signal to noise ratio can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument.

  9. General Aviation Interior Noise. Part 1; Source/Path Identification

    NASA Technical Reports Server (NTRS)

    Unruh, James F.; Till, Paul D.; Palumbo, Daniel L. (Technical Monitor)

    2002-01-01

    There were two primary objectives of the research effort reported herein. The first objective was to identify and evaluate noise source/path identification technology applicable to single engine propeller driven aircraft that can be used to identify interior noise sources originating from structure-borne engine/propeller vibration, airborne propeller transmission, airborne engine exhaust noise, and engine case radiation. The approach taken to identify the contributions of each of these possible sources was first to conduct a Principal Component Analysis (PCA) of an in-flight noise and vibration database acquired on a Cessna Model 182E aircraft. The second objective was to develop and evaluate advanced technology for noise source 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 source contributions of the various panel groups leading to the array measurements were then synthesized by solving the inverse problem using the boundary element model.

  10. Investigation of Volumetric Sources in Airframe Noise Simulations

    NASA Technical Reports Server (NTRS)

    Casper, Jay H.; Lockard, David P.; Khorrami, Mehdi R.; Streett, Craig L.

    2004-01-01

    Hybrid methods for the prediction of airframe noise 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 noise predictions on the location of the integration surface used in the solution of the Ffowcs Williams and Hawkings equation. These differences in radiated noise levels are most pronounced between solid-body surface integrals and off-body, permeable surface integrals. Such differences suggest that either a non-negligible volumetric source 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 noise predictions. The case study for this research is a computer simulation for a three-element, high-lift wing profile during landing conditions. The noise radiated from this flow is predicted by a two-dimensional, frequency-domain formulation of the Ffowcs Williams and Hawkings equation. Radiated sound from volumetric sources is assessed by comparison of a permeable surface integration with the sum of a solid-body surface integral and a volume integral. The separate noise predictions are found in good agreement.

  11. An investigation of rotor harmonic noise by the use of small scale wind tunnel models

    NASA Technical Reports Server (NTRS)

    Sternfeld, H., Jr.; Schaffer, E. G.

    1982-01-01

    Noise measurements of small scale helicopter rotor models were compared with noise measurements of full scale helicopters to determine what information about the full scale helicopters could be derived from noise measurements of small scale helicopter models. Comparisons were made of the discrete frequency (rotational) noise 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 noise trends with configuration and test condition changes, and good comparison of absolute noise measurements with the corrections used except for the isolated rotor case. Noise measurements of the isolated rotor show a great deal of scatter reflecting the fact that the rotor in hover is basically unstable.

  12. Propeller sheet cavitation noise source modeling and inversion

    NASA Astrophysics Data System (ADS)

    Lee, Keunhwa; Lee, Jaehyuk; Kim, Dongho; Kim, Kyungseop; Seong, Woojae

    2014-02-01

    Propeller sheet cavitation is the main contributor to high level of noise 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 source model for sheet cavitation, a multi-parameter inversion scheme to find the positions of noise sources 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 noise sources. The suggested approach is applied to the hull pressure data measured in a cavitation tunnel of the Samsung Heavy Industry. Two monopole sources are adequate to model the propeller sheet cavitation noise. The inverted source information is reasonable with the cavitation dynamics of the propeller and the modeled hull pressure shows good agreement with cavitation tunnel experimental data.

  13. A very low noise, high accuracy, programmable voltage source for low frequency noise measurements

    NASA Astrophysics Data System (ADS)

    Scandurra, Graziella; Giusi, Gino; Ciofi, Carmine

    2014-04-01

    In this paper an approach for designing a programmable, very low noise, high accuracy voltage source for biasing devices under test in low frequency noise measurements is proposed. The core of the system is a supercapacitor based two pole low pass filter used for filtering out the noise produced by a standard DA converter down to 100 mHz with an attenuation in excess of 40 dB. The high leakage current of the supercapacitors, however, introduces large DC errors that need to be compensated in order to obtain high accuracy as well as very low output noise. To this end, a proper circuit topology has been developed that allows to considerably reduce the effect of the supercapacitor leakage current on the DC response of the system while maintaining a very low level of output noise. With a proper design an output noise as low as the equivalent input voltage noise of the OP27 operational amplifier, used as the output buffer of the system, can be obtained with DC accuracies better that 0.05% up to the maximum output of 8 V. The expected performances of the proposed voltage source have been confirmed both by means of SPICE simulations and by means of measurements on actual prototypes. Turn on and stabilization times for the system are of the order of a few hundred seconds. These times are fully compatible with noise measurements down to 100 mHz, since measurement times of the order of several tens of minutes are required in any case in order to reduce the statistical error in the measured spectra down to an acceptable level.

  14. A very low noise, high accuracy, programmable voltage source for low frequency noise measurements.

    PubMed

    Scandurra, Graziella; Giusi, Gino; Ciofi, Carmine

    2014-04-01

    In this paper an approach for designing a programmable, very low noise, high accuracy voltage source for biasing devices under test in low frequency noise measurements is proposed. The core of the system is a supercapacitor based two pole low pass filter used for filtering out the noise produced by a standard DA converter down to 100 mHz with an attenuation in excess of 40 dB. The high leakage current of the supercapacitors, however, introduces large DC errors that need to be compensated in order to obtain high accuracy as well as very low output noise. To this end, a proper circuit topology has been developed that allows to considerably reduce the effect of the supercapacitor leakage current on the DC response of the system while maintaining a very low level of output noise. With a proper design an output noise as low as the equivalent input voltage noise of the OP27 operational amplifier, used as the output buffer of the system, can be obtained with DC accuracies better that 0.05% up to the maximum output of 8 V. The expected performances of the proposed voltage source have been confirmed both by means of SPICE simulations and by means of measurements on actual prototypes. Turn on and stabilization times for the system are of the order of a few hundred seconds. These times are fully compatible with noise measurements down to 100 mHz, since measurement times of the order of several tens of minutes are required in any case in order to reduce the statistical error in the measured spectra down to an acceptable level. PMID:24784633

  15. Precision of polarization-resolved second harmonic generation microscopy limited by photon noise for samples with cylindrical symmetry.

    PubMed

    Wasik, Valentine; Réfrégier, Philippe; Roche, Muriel; Brasselet, Sophie

    2015-08-01

    The estimation of parameters in polarization-resolved two-photon microscopy response perturbed by photon noise is analyzed in the context of second harmonic generation for the distribution of molecules presenting cylindrical symmetry. The estimation task is investigated using the Cramer-Rao lower bound for Poisson photon noise. It is shown that a noniterative technique can lead to estimation results that have good efficiencies for most of the physical possible values of the sample parameters for sufficiently high photon levels. The trade-off, between the number of incident polarization states and the total number of measured photons, that can be obtained with the Cramer-Rao lower bound is also discussed.

  16. Global Analysis of Response in the Piezomagnetoelastic Energy Harvester System under Harmonic and Poisson White Noise Excitations

    NASA Astrophysics Data System (ADS)

    Yue, Xiao-Le; Xu, Wei; Zhang, Ying; Wang, Liang

    2015-10-01

    The piezomagnetoelastic energy harvester system subjected to harmonic and Poisson white noise excitations is studied by using the generalized cell mapping method. The transient and stationary probability density functions (PDFs) of response based on the global viewpoint are obtained by the matrix analysis method. Monte Carlo simulation results verify the accuracy of this method. It can be observed that evolutionary direction of transient and stationary PDFs is in accordance with the unstable manifold for this system, and a stochastic P-bifurcation occurs as the intensity of Poisson white noise increases. This study presents an efficient numerical tool to solve the stochastic response of a three-dimensional dynamical system and provides a new idea to analyze the energy harvester system. Supported by the National Natural Science Foundation of China under Grant Nos. 11302170, 11202160, 11302171, and the Fundamental Research Funds for the Central Universities under Grant No. 3102014JCQ01079

  17. Investigation of noise sources and propagation in external gear pumps

    NASA Astrophysics Data System (ADS)

    Opperwall, Timothy J.

    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 noise 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 sources of noise in hydraulic systems. Thus, investigation into the sources of noise and discovering strategies to reduce noise 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 noise generation caused by hydrostatic units. This requires challenging and surpassing current accepted methods in the understanding of noise 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 noise from the sources 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

  18. Adaptive Selective Harmonic Minimization Based on ANNs for Cascade Multilevel Inverters With Varying DC Sources

    SciTech Connect

    Filho, Faete; Maia, Helder Z; Mateus, Tiago Henrique D; Ozpineci, Burak; Tolbert, Leon M; Pinto, Joao Onofre P

    2013-01-01

    A new approach for modulation of an 11-level cascade multilevel inverter using selective harmonic elimination is presented in this paper. The dc sources feeding the multilevel inverter are considered to be varying in time, and the switching angles are adapted to the dc source variation. This method uses genetic algorithms to obtain switching angles offline for different dc source values. Then, artificial neural networks are used to determine the switching angles that correspond to the real-time values of the dc sources for each phase. This implies that each one of the dc sources of this topology can have different values at any time, but the output fundamental voltage will stay constant and the harmonic 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.

  19. Aircraft noise reduction technology. [to show impact on individuals and communities, component noise sources, and operational procedures to reduce impact

    NASA Technical Reports Server (NTRS)

    1973-01-01

    Aircraft and airport noise reduction technology programs conducted by NASA are presented. The subjects discussed are: (1) effects of aircraft noise on individuals and communities, (2) status of aircraft source noise technology, (3) operational procedures to reduce the impact of aircraft noise, and (4) NASA relations with military services in aircraft noise problems. References to more detailed technical literature on the subjects discussed are included.

  20. Optical Techniques for Low Noise Microwave Frequency Sources

    NASA Technical Reports Server (NTRS)

    Maleki, Lute

    2005-01-01

    Optical techniques and mathematical models are described for low noise microwave frequency sources. The contents include: 1) Why Optical Techniques; 2) Wavemixing: Advantages and Disadvantages; 3) Wavemixing with Feedback: The OEO; 4) Feedback in both loops: COEO; and 5) State of the Art and Future Prospects.

  1. Ultrahigh supermode noise suppressing ratio of a semiconductor optical amplifier filtered harmonically mode-locked Erbium-doped fiber laser.

    PubMed

    Lin, Gong-Ru; Wu, Ming-Chung; Chang, Yung-Cheng; Pan, Ci-Ling

    2005-09-01

    The supermode noise suppressing ratio (SMSR) and the phase noise of a harmonically mode-locked Erbium-doped fiber laser (HML-EDFL) with an intra-cavity semiconductor optical amplifier (SOA) and an optical band-pass filter (OBPF) are improved and compared with a state-of-the-art Fabry-Perot laser diode (FPLD) injection-mode-locked EDFL. By driving the intra-cavity SOA based high-pass filter at unitary gain condition, the SMSR of the HML-EDFL is enhanced to 82 dB at the cost of degrading phase noise, increasing jitter, and broadened pulse width. The adding of OBPF further improves the SMSR, pulse width, phase noise, and jitter of the SOA-filtered HML-EDFL to 90 dB, 42 ps, -112 dBc/Hz, and 0.7 ps, respectively. The ultrahigh SMSR of the SOA-filtered HML-EDFL can compete with that of the FPLD injection-mode-locked EDFL without sacrificing its pulse width and jitter performances. PMID:19498744

  2. Diffractive imaging using a polychromatic high-harmonic generation soft-x-ray source

    NASA Astrophysics Data System (ADS)

    Dilanian, Ruben A.; Chen, Bo; Williams, Garth J.; Quiney, Harry M.; Nugent, Keith A.; Teichmann, Sven; Hannaford, Peter; Dao, Lap V.; Peele, Andrew G.

    2009-07-01

    A new approach to diffractive imaging using polychromatic diffraction data is described. The method is tested using simulated and experimental data and is shown to yield high-quality reconstructions. Diffraction data produced using a high-harmonic generation source are considered explicitly here. The formalism can be readily adapted, however, to any short-wavelength source producing a discrete spectrum and possessing sufficient spatial coherence.

  3. A higher harmonic control test in the DNW to reduce impulsive BVI noise

    NASA Technical Reports Server (NTRS)

    Splettstoesser, Wolf R.; Schultz, KLAUS-J.; Kube, Roland; Brooks, Thomas F.; Booth, Earl R., Jr.; Niesl, Georg; Streby, Olivier

    1994-01-01

    A model rotor acoustic test was performed to examine the benefit of higher control (HHC) of blade pitch to reduce blade-vortex interaction (BVI) impulse noise. A 40-percent dynamically scaled, four-bladed model of a BO-105 main rotor was tested in the German-Dutch Wind Tunnel (DNW). Acoustic measurements were made in a large plane underneath the rotor employing a traversing in-flow microphone array in the anechoic environment of the open test section. Noise characteristics and noise directivity patterns as well as vibratory loads were measured and used to demonstrate the changes when different HHC schedules (different modes, amplitudes, phases) were applied. Dramatic changes of the acoustic signatures and the noise radiation directivity with HHC phase variations are found. Compared to the baseline conditions (without HHD), significant mid-frequency noise reductions of as much as 6 dB are obtained for low speed descent conditions where BVI is most intensive. For other rotor operating conditions with less intense BVI there is less or no benefit from the use of HHC. Low frequency loading noise and vibratory loads, especially at optimum noise reduction control settings, are found to increase.

  4. Volcanic jet noise: infrasonic source processes and atmospheric propagation

    NASA Astrophysics Data System (ADS)

    Matoza, R. S.; Fee, D.; Ogden, D. E.

    2011-12-01

    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 noise. Jet noise is produced at higher acoustic frequencies by smaller-scale man-made jet flows (e.g., turbulent jet flow from jet engines and rockets). Jet noise generation processes could operate at larger spatial scales and produce infrasonic frequencies in the lower gas-thrust portion of the eruption column. Jet-noise-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. Source studies of infrasonic volcanic jet noise, 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 noise. Matoza, R. S., D. Fee, M. A. Garcés, J. M. Seiner, P. A. Ramón, and M. A. H. Hedlin (2009), Infrasonic jet noise from volcanic eruptions, Geophys. Res. Lett., 36, L08303, doi:10.1029/2008GL036486.

  5. Superdiffusion of Energy in a Chain of Harmonic Oscillators with Noise

    NASA Astrophysics Data System (ADS)

    Jara, Milton; Komorowski, Tomasz; Olla, Stefano

    2015-10-01

    We consider a one dimensional infinite chain of harmonic 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).

  6. Generation of stable high order harmonic noise-like pulses in a passively mode-locked double clad fiber ring laser

    NASA Astrophysics Data System (ADS)

    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.

    2015-03-01

    We study a passively mode-locked double-clad Erbium-Ytterbium fiber ring laser producing noise-like pulse through nonlinear polarization evolution and polarization selection. Single noise-like pulsing is only observed at moderate pump power. As pump power is increased, and through polarization controllers adjustments, harmonic mode-locking of growing order were successively appearing. For pump powers close to the damage threshold of the setup, we reach harmonic 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.

  7. Towards enabling femtosecond helicity-dependent spectroscopy with high-harmonic sources.

    PubMed

    Lambert, G; Vodungbo, B; Gautier, J; Mahieu, B; Malka, V; Sebban, S; Zeitoun, P; Luning, J; Perron, J; Andreev, A; Stremoukhov, S; Ardana-Lamas, F; Dax, A; Hauri, C P; Sardinha, A; Fajardo, M

    2015-01-01

    Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy. One of the remaining shortages of this source is its restriction to linear polarization, since the yield of generation of elliptically polarized high harmonics has been low so far. We here show how this limitation is overcome by using a cross-polarized two-colour laser field. With this simple technique, we reach high degrees of ellipticity (up to 75%) with efficiencies similar to classically generated linearly polarized harmonics. To demonstrate these features and to prove the capacity of our source for applications, we measure the X-ray magnetic circular dichroism (XMCD) effect of nickel at the M2,3 absorption edge around 67 eV. There results open up the way towards femtosecond time-resolved experiments using high harmonics exploiting the powerful element-sensitive XMCD effect and resolving the ultrafast magnetization dynamics of individual components in complex materials. PMID:25649329

  8. Noise-source turbulence statistics and the noise from a Mach 0.9 jet

    NASA Astrophysics Data System (ADS)

    Freund, J. B.

    2003-06-01

    Turbulence statistics that are relevant to jet noise modeling but difficult to measure in experiments are computed using a previously validated simulation database of a Mach 0.9 cold jet. Initial focus is on fourth-order statistics that are at the core of acoustic analogy based models built on both the Lilley and Lighthill equations. Common simplifications of fourth-order correlations based on normal statistics are found to be accurate. We see that although two-point correlations are well fitted by exponential functions, as is typical of turbulence at all but the lowest Reynolds numbers, the spatially integrated fourth-order space/retarded-time covariances, which are used in the models, are instead very well fitted by Gaussian functions of different widths for different components, which is counter to conventional modeling practice. We also examine the components of Lighthill's analogous noise source that are linear and quadratic in velocity fluctuations, as well as components that are deviations from p'=a∞2ρ'. The spectrum from the linear components is more peaked and more direction dependent than the spectral shape of the quadratic component's noise, which is relatively independent of angle. These two components are also correlated, especially at small angles where their mutual correlation coefficient reaches as low as -0.4, which casts doubt on models that treat these so-called shear noise (linear) and self-noise (quadratic) terms as distinct. The p'-a∞2ρ' contribution is relatively small, but not negligible as might be expected for this nearly isothermal jet. The total radiated power of the quadratic terms is nearly the same as that of all components combined. It is shown that the standard Lighthill framework does not lead to a straight forward designation of what noise comes from what region of the jet.

  9. Identifying the principal noise sources of fixed-wing combat aircraft in high-speed flight

    NASA Astrophysics Data System (ADS)

    Bryce, W. D.; Pinker, R. A.; Strange, P. J. R.

    1992-04-01

    Before considering means for alleviating the noise from modern military combat aircraft operating in high-speed low-level flight, it is important to identify the principal noise sources. To this end, a carefully-controlled flight test program has been carried out using a Tornado aircraft (in standard training configuration) operating at flight speeds from 0.5M to 0.8M. The major sources of the aircraft noise, airframe noise, installed jet mixing noise and jet shock noise, have been successfully identified, quantified and correlated. Although the jet mixing noise tends to be the major source at low flight speeds, and the shock noise at high flight speeds, all three sources are comparable in magnitude during the rapid rise-time of the noise signal and at its peak. Indeed, were it possible to reduce greatly both the jet mixing and shock noise, the peak noise levels would only reduce by about 5 dBA.

  10. Optimization of structures undergoing harmonic or stochastic excitation. Ph.D. Thesis; [atmospheric turbulence and white noise

    NASA Technical Reports Server (NTRS)

    Johnson, E. H.

    1975-01-01

    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 harmonically oscillating loads, similar structures excited by white noise, 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.

  11. A Numerical Investigation of Turbine Noise Source Hierarchy and Its Acoustic Transmission Characteristics

    NASA Technical Reports Server (NTRS)

    VanZante, Dale; Envia, Edmane

    2008-01-01

    Understanding the relative importance of the various turbine noise generation mechanisms and the characteristics of the turbine acoustic transmission loss are essential ingredients in developing robust reduced-order models for predicting the turbine noise signature. A computationally based investigation has been undertaken to help guide the development of a turbine noise 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 sources of turbine noise generation, namely, blade-row viscous interaction, potential field interaction, and entropic source 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 harmonic 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

  12. Bubble-bubble interaction: A potential source of cavitation noise

    NASA Astrophysics Data System (ADS)

    Ida, Masato

    2009-01-01

    The interaction between microbubbles through pressure pulses has been studied to show that it can be a source of cavitation noise. A recent report demonstrated that the acoustic noise generated by a shrimp originates from the collapse of a cavitation bubble produced when the shrimp closes its snapper claw. The recorded acoustic signal contains a broadband noise that consists of positive and negative pulses, but a theoretical model for single bubbles fails to reproduce the negative ones. Using a nonlinear multibubble model, we have shown here that the negative pulses can be explained by considering the interaction of microbubbles formed after the cavitation bubble has collapsed and fragmented: Positive pulses produced at the collapse of the microbubbles hit and impulsively compress neighboring microbubbles to generate reflected pulses whose amplitudes are negative. Discussing the details of the noise generation process, we have found that no negative pulses are generated if the internal pressure of the reflecting bubble is very high when hit by a positive pulse.

  13. Low-noise sub-harmonic injection locked multiloop ring oscillator

    NASA Astrophysics Data System (ADS)

    Weilin, Xu; Di, Wu; Xueming, Wei; Baolin, Wei; Jihai, Duan; Fadi, Gui

    2016-09-01

    A three-stage differential voltage-controlled ring oscillator is presented for wide-tuning and low-phase noise requirement of clock and data recovery circuit in ultra wideband (UWB) wireless body area network. To improve the performance of phase noise 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 noise 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 noise 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.

  14. Mapping the source distribution of microseisms using noise covariogram envelopes

    NASA Astrophysics Data System (ADS)

    Sadeghisorkhani, Hamzeh; Gudmundsson, Ólafur; Roberts, Roland; Tryggvason, Ari

    2016-06-01

    We introduce a method for mapping the noise-source distribution of microseisms which uses information from the full length of covariograms (cross-correlations). We derive a forward calculation based on the plane-wave assumption in 2-D, to formulate an iterative, linearized inversion of covariogram envelopes in the time domain. The forward calculation involves bandpass filtering of the covariograms. The inversion exploits the well-known feature of noise cross-correlation, that is, an anomaly in the noise field that is oblique to the interstation direction appears as cross-correlation amplitude at a smaller time lag than the in-line, surface wave arrival. Therefore, the inversion extracts more information from the covariograms than that contained at the expected surface wave arrival, and this allows us to work with few stations to find the propagation directions of incoming energy. The inversion is naturally applied to data that retain physical units that are not amplitude normalized in any way. By dividing a network into groups of stations, we can constrain the source location by triangulation. We demonstrate results of the method with synthetic data and one year (2012) of data from the Swedish National Seismic Network and also look at the seasonal variation of source distribution around Scandinavia. After preprocessing and cross-correlation, the stations are divided into five groups of 9-12 stations. We invert the envelopes of each group in eight period ranges between 2 and 25 s. Results show that the noise sources at short periods (less than 12 s) lie predominantly in the North Atlantic Ocean and the Barents Sea, and at longer periods the energy appears to have a broader distribution. The strongly anisotropic source distribution in this area is estimated to cause significant biases of velocity measurements compared to the level of heterogeneity in the region. The amplitude of the primary microseisms varies little over the year, but secondary microseisms are much

  15. Spectral decomposition of the aerodynamic noise generated by rotating sources

    NASA Astrophysics Data System (ADS)

    Bongiovì, Alessandro; Cattanei, Andrea

    2011-01-01

    A method is posed for separating the noise emitted by an aerodynamic source from propagation effects using spectral decomposition. This technique is applied to the power spectra of a fan measured at several rotational speeds. Although it has been conceived for rotating sources as turbomachinery rotors, the method may be easily applied to low speed stationary sources such as jets and flows in stators and about isolated airfoils. Based on the similarity theory, a clear description of the structure of the power spectrum of the received noise is given and the effect of rotational speed variations is considered as a means to obtain a data set suitable to perform the spectral decomposition. The problem is analyzed in order to clarify possibilities and limitations of the method and then an algorithm is presented which is based on the solution of the derived equations. Particular care is devoted to both the numerical details and the operative aspects. The validation of the algorithm is performed by means of numerically generated input data. Next, in order to verify the ability of the method in separating scattered from emitted sound, an automotive cooling fan has been tested in the DIMSET hemi-anechoic room in a free-field configuration and with a shielded microphone. These two apparently distinct spectra collapse to within less than 2 dB after the spectral decomposition has been performed. The tests prove the ability of the method despite the modest quantity of input data.

  16. Limits on the prediction of helicopter rotor noise using thickness and loading sources: Validation of helicopter noise prediction techniques

    NASA Technical Reports Server (NTRS)

    Succi, G. P.

    1983-01-01

    The techniques of helicopter rotor noise prediction attempt to describe precisely the details of the noise 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 noise prediction techniques was studied, and high speed helicopter noise prediction using more detailed representations of the thickness and loading noise sources 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 noise sources 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.

  17. Relationship between Spatial Distribution of Noise Sources and Target Scatterings Observed in the 2010 Sea Trial of Ambient Noise Imaging

    NASA Astrophysics Data System (ADS)

    Mori, Kazuyoshi; Ogasawara, Hanako; Nakamura, Toshiaki; Tsuchiya, Takenobu; Endoh, Nobuyuki

    2013-07-01

    An aspherical lens with an aperture diameter of 1.0 m has been designed and fabricated to develop a prototype system for ambient noise imaging (ANI). A sea trial of silent target detection using the prototype ANI system was conducted under only natural ocean ambient noise at Uchiura Bay, in November of 2010. It was verified that the targets are successfully detected under natural ocean ambient noise, mainly generated by snapping shrimps. In this study, we surveyed the relationship between the spatial distribution of noise sources and the target scattering captured by the ANI system. The observation using a pair of tetrahedron arrays was conducted at the same time as the sea trial. The estimated source positions were spread when the noises arrived from the sea bottom. Some of the sources were around the barge, and other sources were around fish preserves. On the other hand, the source positions were coincident with the barge when the noises arrived from the sea surface. The calculated scattering fields of the target showed sharp directivities. The locations of noise sources, where the ANI system can capture target scatterings with high intensities, were roughly determined at the barge around the sea surface.

  18. Combining harmonic generation and laser chirping to achieve high spectral density in Compton sources

    NASA Astrophysics Data System (ADS)

    Terzić, Balša; Reeves, Cody; Krafft, Geoffrey A.

    2016-04-01

    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 sources at high laser intensities: (i) enables the use of higher order harmonics, 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 harmonics can lead to substantial savings in the design, construction and operational costs of the new Compton sources. This is of particular importance to the widely popular laser-plasma accelerator based Compton sources, as the improvement in their beam quality enters the regime where chirping is most effective.

  19. Double simple-harmonic-oscillator formulation of the thermal equilibrium of a fluid interacting with a coherent source of phonons

    NASA Technical Reports Server (NTRS)

    Defacio, B.; Vannevel, Alan; Brander, O.

    1993-01-01

    A formulation is given for a collection of phonons (sound) in a fluid at a non-zero temperature which uses the simple harmonic oscillator twice; one to give a stochastic thermal 'noise' 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 harmonic oscillator is a key structure in both the formulation and the calculations.

  20. Fan Noise Source Diagnostic Test: Rotor Alone Aerodynamic Performance Results

    NASA Technical Reports Server (NTRS)

    Hughes, Christopher E.; Jeracki, Robert J.; Woodward, Richard P.; Miller, Christopher J.

    2005-01-01

    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 Source Diagnostic Test conducted at NASA Glenn. The Source Diagnostic Test was conducted to identify the noise sources within a wind tunnel scale model of a turbofan engine and quantify their contribution to the overall system noise 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.

  1. Wide-field broadband extreme ultraviolet transmission ptychography using a high-harmonic source.

    PubMed

    Baksh, Peter D; Odstrčil, Michal; Kim, Hyun-Su; Boden, Stuart A; Frey, Jeremy G; Brocklesby, William S

    2016-04-01

    High-harmonic generation (HHG) provides a laboratory-scale source of coherent radiation ideally suited to lensless coherent diffractive imaging (CDI) in the EUV and x-ray spectral region. Here we demonstrate transmission extreme ultraviolet (EUV) ptychography, a scanning variant of CDI, using radiation at a wavelength around 29 nm from an HHG source. Image resolution is diffraction-limited at 54 nm and fields of view up to ∼100  μm are demonstrated. These results demonstrate the potential for wide-field, high-resolution, laboratory-scale EUV imaging using HHG-based sources with potential application in biological imaging or EUV lithography pellicle inspection. PMID:27192225

  2. Source Methodology for Turbofan Noise Prediction (SOURCE3D Technical Documentation)

    NASA Technical Reports Server (NTRS)

    Meyer, Harold D.

    1999-01-01

    This report provides the analytical documentation for the SOURCE3D Rotor Wake/Stator Interaction Code. It derives the equations for the rotor scattering coefficients and stator source vector and scattering coefficients that are needed for use in the TFANS (Theoretical Fan Noise Design/Prediction System). SOURCE3D treats the rotor and stator as isolated source elements. TFANS uses this information, along with scattering coefficients for inlet and exit elements, and provides complete noise solutions for turbofan engines. SOURCE3D 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. SOURCE3D 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 noise 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.

  3. General Aviation Interior Noise. Part 2; In-Flight Source/Verification

    NASA Technical Reports Server (NTRS)

    Unruh, James F.; Till, Paul D.; Palumbo, Daniel L. (Technical Monitor)

    2002-01-01

    The technical approach made use of the Cessna Model 182E aircraft used in the previous effort as a test bed for noise control application. The present phase of the project reports on flight test results during application of various passive noise treatments in an attempt to verify the noise sources and paths for the aircraft. The data presented establishes the level of interior noise control that can be expected for various passive noise control applications within the aircraft cabin. Subsequent testing will address specific testing to demonstrate the technology available to meet a specified level of noise control by application of passive and/or active noise control technology.

  4. Separating Turbofan Engine Noise Sources Using Auto and Cross Spectra from Four Microphones

    NASA Technical Reports Server (NTRS)

    Miles, Jeffrey Hilton

    2008-01-01

    The study of core noise from turbofan engines has become more important as noise from other sources such as the fan and jet were reduced. A multiple-microphone and acoustic-source modeling method to separate correlated and uncorrelated sources is discussed. The auto- and cross spectra in the frequency range below 1000 Hz are fitted with a noise propagation model based on a source couplet consisting of a single incoherent monopole source with a single coherent monopole source or a source triplet consisting of a single incoherent monopole source with two coherent monopole point sources. Examples are presented using data from a Pratt& Whitney PW4098 turbofan engine. The method separates the low-frequency jet noise from the core noise at the nozzle exit. It is shown that at low power settings, the core noise is a major contributor to the noise. Even at higher power settings, it can be more important than jet noise. However, at low frequencies, uncorrelated broadband noise and jet noise become the important factors as the engine power setting is increased.

  5. Sources and levels of background noise in the NASA Ames 40- by 80-foot wind tunnel

    NASA Technical Reports Server (NTRS)

    Soderman, Paul T.

    1988-01-01

    Background noise 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 noise dominated the empty test-section background noise at airspeeds below 120 knots. Above 120 knots, the test-section broadband background noise was dominated by wind-induced dipole noise (except at lower harmonics 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 noise levels can be reduced by making improvements to the microphone wind screen or support strut. Empirical equations are presented relating variations of fan noise with fan speed or blade-pitch angle. An empirical expression for typical fan noise spectra is also presented. Fan motor electric power consumption is related to the noise generation. Preliminary measurements of sound absorption by the test-section lining indicate that the 152 mm thick lining will adequately absorb test-section model noise at frequencies above 300 Hz.

  6. Aircraft noise source and computer programs - User's guide

    NASA Technical Reports Server (NTRS)

    Crowley, K. C.; Jaeger, M. A.; Meldrum, D. F.

    1973-01-01

    The application of computer programs for predicting the noise-time histories and noise 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 noise prediction program are core effectiveness, limited input, and variable output reporting.

  7. Noise characteristics of CT perfusion imaging: how does noise propagate from source images to final perfusion maps?

    NASA Astrophysics Data System (ADS)

    Li, Ke; Chen, Guang-Hong

    2016-03-01

    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-noise ratio of CTP maps. To reduce noise and improve image quality, a rigorous study on the noise transfer properties of CTP systems is highly desirable to provide the needed scientific guidance. This paper concerns how noise in the CTP source images propagates to the final CTP maps. Both theoretical deviations and subsequent validation experiments demonstrated that, the noise level of background frames plays a dominant role in the noise of the cerebral blood volume (CBV) maps. This is in direct contradiction with the general belief that noise 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 noise 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 noise of CBV can be effectively reduced using the proposed exposure modulation method.

  8. Noise-induced annoyance from transportation noise: short-term responses to a single noise source in a laboratory.

    PubMed

    Kim, Jaehwan; Lim, Changwoo; Hong, Jiyoung; Lee, Soogab

    2010-02-01

    An experimental study was performed to compare the annoyances from civil-aircraft noise, military-aircraft noise, railway noise, and road-traffic noise. 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 noise was the most annoying, followed by military-aircraft noise, railway noise, and road-traffic noise. 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 noises. 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 noise 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.

  9. Noise-induced annoyance from transportation noise: short-term responses to a single noise source in a laboratory.

    PubMed

    Kim, Jaehwan; Lim, Changwoo; Hong, Jiyoung; Lee, Soogab

    2010-02-01

    An experimental study was performed to compare the annoyances from civil-aircraft noise, military-aircraft noise, railway noise, and road-traffic noise. 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 noise was the most annoying, followed by military-aircraft noise, railway noise, and road-traffic noise. 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 noises. 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 noise 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. PMID:20136203

  10. Intensity noise in long-wavelength superluminescent sources

    NASA Astrophysics Data System (ADS)

    Lee, Chung E.; Taylor, Henry F.

    1991-05-01

    Noise in broadband 1.3-micron superluminescent diodes (SLDs) is investigated experimentally, using a balanced detector arrangement to determine the excess noise factor as a function of photodetector current. Measurements were made in both the low-frequency 1/f regime (below 500 kHz) and the high-frequency quantum noise spectral region. The data at higher frequencies are in agreement with predictions of the quantum amplifier model, with values of the spontaneous emission coupling factor ranging from 1.2 to 1.9. It is also found that noise for one polarization of the light is uncorrelated with the noise for the orthogonal polarization over the 0-1 MHz frequency range. This implies that the 1/f noise is not related to carrier density (gain) fluctuations in the active region of the device. An integrated optic chip design to compensate for the excess intensity noise in fiber gyroscopes is proposed.

  11. Coupling CARS with multiphoton fluorescence and high harmonic generation imaging modalities using a femtosecond laser source

    NASA Astrophysics Data System (ADS)

    Chen, Hongtao; Slipchenko, Mikhail N.; Zhu, Jiabin; Buhman, Kimberly K.; Cheng, Ji-Xin

    2009-02-01

    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 source 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 harmonic generation (SHG) imaging. The signal output at 1290 nm from OPO is used for SHG and third-harmonic 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.

  12. EUV mask observations using a coherent EUV scatterometry microscope with a high-harmonic-generation source

    NASA Astrophysics Data System (ADS)

    Fujino, Takahiro; Tanaka, Yusuke; Harada, Tetsuo; Nagata, Yutaka; Watanabe, Takeo; Kinoshita, Hiroo

    2015-07-01

    In extreme ultraviolet (EUV) lithography, the three-dimensional (3D) structure of the EUV mask, which has an absorber layer and a Mo/Si multilayer on a glass substrate, strongly affects the EUV phase. EUV actinic metrology is required to evaluate the feature of defect printability and the critical dimension (CD) value. The 3D structure modulates the EUV phase, causing the pattern position and focus shift. A microscope that observes in phase contrast necessary. We have developed a coherent EUV scatterometry microscope (CSM) for observing EUV patterns with quantitative phase contrast. The exposure light is coherent EUV light. For the industrial use, we have developed a laboratory coherent source of high-harmonic-generation (HHG) EUV light. High harmonics is pumped by a scale of a Ti:Sapphire laser. In the previous study, a very long exposure time of 1000 s was necessary to detect We upgraded the relay optics. The detection performance of an absorber defect using the new relay optics is We observed the line-end oversize defect and the oversize defect in the 112 nm hole pattern and 180 nm hole pattern. The upgraded system has a detection size limit of a line-end 24-nm-oversize defect with 10 s exposure time, which is 2,688 nm2 (52 × 52 nm2) absorber defect. This result shows high performance capability of HHG-CSM for detecting small defect.

  13. Determination of Jet Noise Radiation Source Locations using a Dual Sideline Cross-Correlation/Spectrum Technique

    NASA Technical Reports Server (NTRS)

    Allen, C. S.; Jaeger, S. M.

    1999-01-01

    The goal of our efforts is to extrapolate nearfield jet noise measurements to the geometric far field where the jet noise sources appear to radiate from a single point. To accomplish this, information about the location of noise sources in the jet plume, the radiation patterns of the noise sources and the sound pressure level distribution of the radiated field must be obtained. Since source locations and radiation patterns can not be found with simple single microphone measurements, a more complicated method must be used.

  14. A temporal and spatial analysis of anthropogenic noise sources affecting SNMR

    NASA Astrophysics Data System (ADS)

    Dalgaard, E.; Christiansen, P.; Larsen, J. J.; Auken, E.

    2014-11-01

    One of the biggest challenges when using the surface nuclear magnetic resonance (SNMR) method in urban areas is a relatively low signal level compared to a high level of background noise. To understand the temporal and spatial behavior of anthropogenic noise sources like powerlines and electric fences, we have developed a multichannel instrument, noiseCollector (nC), which measures the full noise spectrum up to 10 kHz. Combined with advanced signal processing we can interpret the noise as seen by a SNMR instrument and also obtain insight into the more fundamental behavior of the noise. To obtain a specified acceptable noise level for a SNMR sounding the stack size can be determined by quantifying the different noise sources. Two common noise sources, electromagnetic fields stemming from powerlines and fences are analyzed and show a 1/r2 dependency in agreement with theoretical relations. A typical noise map, obtained with the nC instrument prior to a SNMR field campaign, clearly shows the location of noise sources, and thus we can efficiently determine the optimal location for the SNMR sounding from a noise perspective.

  15. 2.32 THz quantum cascade laser frequency-locked to the harmonic of a microwave synthesizer source.

    PubMed

    Danylov, Andriy A; Light, Alexander R; Waldman, Jerry; Erickson, Neal R; Qian, Xifeng; Goodhue, William D

    2012-12-01

    Frequency stabilization of a THz quantum cascade laser (QCL) to the harmonic of a microwave source has been accomplished using a Schottky diode waveguide mixer designed for harmonic mixing. The 2.32 THz, 1.0 milliwatt CW QCL is coupled into the signal port of the mixer and a 110 GHz signal, derived from a harmonic of a microwave synthesizer, is coupled into the IF port. The difference frequency between the 21st harmonic of 110 GHz and the QCL is used in a discriminator to adjust the QCL bias current to stabilize the frequency. The short-term frequency jitter is reduced from 550 kHz to 4.5 kHz (FWHM) and the long-term frequency drift is eliminated. This performance is compared to that of several other THz QCL frequency stabilization techniques.

  16. Vehicle noise source heights and sub-source spectra. Final report

    SciTech Connect

    Coulson, R.K.

    1996-12-01

    This report describes a turn-key system that was developed and implemented to collect the vehicle source height database for incorporation into the new Traffic Noise Model; `TNM.` A total of 2500 individual vehicle pass-byes were measured with this system at 16 different sites around Florida and this data is presented in the form of averaged curves for each vehicle type. The dependence of source height on speed, pavement type, road grade and acceleration state is also shown for 10 different types of vehicles. The effect of these roadway conditions on the vehicle source heights is small compared to the typical variation in the whole data set. A recommendation is therefore made that the overall average of the date for each vehicle type be used in the TNM model and that variations with speed, pavement, grade and acceleration can be neglected. The data collection system and algorithm used to obtain the source heights is described and the accuracty is demonstrated experimentally with know sources. The measured vehicle source heights are further verified using an alternative Matched Field Processing algorithm which produced very similar results. It is also shown that the single equivalent source height model for a distribution of sources is more accurate that the two sub-source model when used in barrier attenuation calculations.

  17. Fan Noise Source Diagnostic Test: Tone Modal Structure Results

    NASA Technical Reports Server (NTRS)

    Heidelberg, Laurence J.

    2002-01-01

    This investigation is part of a test series that was extremely comprehensive and included aerodynamic and acoustic testing of a fan stage using two different fan rotors and three different stator designs. The test series is known as the Source Diagnostic Test (SDT) and was conducted by NASA Glenn as part of the Advanced Subsonic Technology (AST) Noise Reduction Program. Tone mode measurements of one of the rotors with three different stators were made. The stator designs involve changes in vane count and sweep at constant solidity. The results of both inlet and exhaust tone mode measurements are presented in terms of mode power for both circumferential and radial mode orders. The results show benefits of vane sweep to be large, up to 13 dB in total tone power. At many conditions, the increase in power due to cutting on the rotor/stator interaction is more than offset by vane sweep. The rotor locked mode is shown as an important contributor to tone power when the blade tip speed is near and above Mach one. This is most evident in the inlet when the direct rotor field starts to cut on.

  18. /sup 252/Cf-source-driven neutron noise analysis method

    SciTech Connect

    Mihalczo, J.T.; King, W.T.; Blakeman, E.D.

    1985-01-01

    The /sup 252/Cf-source-driven neutron noise 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.

  19. Bright high-repetition-rate source of narrowband extreme-ultraviolet harmonics beyond 22 eV

    SciTech Connect

    Wang, He; Xu, Yiming; Ulonska, Stefan; Robinson, Joseph S.; Ranitovic, Predrag; Kaindl, Robert A.

    2015-06-11

    Novel table-top sources of extreme-ultraviolet light based on high-harmonic generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-harmonic 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 source of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic 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 harmonics 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 harmonic renders this bright, 50-kHz extreme-ultraviolet source a powerful tool for ultrafast photoemission, nanoscale imaging and other applications.

  20. Bright high-repetition-rate source of narrowband extreme-ultraviolet harmonics beyond 22 eV

    PubMed Central

    Wang, He; Xu, Yiming; Ulonska, Stefan; Robinson, Joseph S.; Ranitovic, Predrag; Kaindl, Robert A.

    2015-01-01

    Novel table-top sources of extreme-ultraviolet light based on high-harmonic generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-harmonic 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 source of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic 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 harmonics 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 harmonic renders this bright, 50-kHz extreme-ultraviolet source a powerful tool for ultrafast photoemission, nanoscale imaging and other applications. PMID:26067922

  1. Experimental study of the equivalent sound source center of the propeller rotating noise

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Gu, Jiajin

    1992-06-01

    The theory and experimental technique for identifying the source of various propeller rotating noises using a cross-spectrum analysis method are discussed. The measurement of the equivalent source center of such noise on the light aircraft AD-200 is presented as an example. The efficiency of the method gives it excellent prospects for large-scale application.

  2. Jet-Surface Interaction Test: Phased Array Noise Source Localization Results

    NASA Technical Reports Server (NTRS)

    Podboy, Gary

    2012-01-01

    Subsonic jets are relatively simple. The peak noise source location gradually moves upstream toward the nozzle as frequency increases. 2) Supersonic jets are more complicated. The peak noise source location moves downstream as frequency increases through a BBSN hump. 3) In both subsonic and supersonic jets the peak noise source location corresponding to a given frequency of noise moves downstream as jet Mach number increases. 4) The noise 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 noise source locations measured with the phased array are blocked by a shielding surface. This consistency validates the phased array data and the stationary monopole source model used to process it. 6) Reflecting surface data illustrate that the law of reflection must be satisfied for noise 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 noise sources may satisfy this requirement. 7) The low frequency noise created when a jet flow impinges on a surface comes primarily from the trailing edge regardless of the axial extent impacted by the flow.

  3. Embedded Acoustic Sensor Array for Engine Fan Noise Source Diagnostic Test: Feasibility of Noise Telemetry via Wireless Smart Sensors

    NASA Technical Reports Server (NTRS)

    Zaman, Afroz; Bauch, Matthew; Raible, Daniel

    2011-01-01

    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 noise concerns. One of the sources of engine noise 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 noise which eventually radiate to the far-field from engine. To investigate the nature of vane pressure fluctuations and the resulting engine noise, unsteady pressure signatures from an array of embedded acoustic sensors are recorded as a part of vane noise source 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 noise 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.

  4. Noise from high speed maglev systems: Noise sources, noise criteria, preliminary design guidelines for noise control, recommendations for acoustical test facility for maglev research. Final report, July 1991-October 1992

    SciTech Connect

    Hanson, C.E.; Abbot, P.; Dyer, I.

    1993-01-01

    Noise levels from magnetically-levitated trains (maglev) at very high speed may be high enough to cause environmental noise impact in residential areas. Aeroacoustic sources dominate the sound at high speeds and guideway vibrations generate noticeable sound at low speed. In addition to high noise levels, the startle effect as a result of sudden onset of sound from a rapidly moving nearby maglev vehicle may lead to increased annoyance to neighbors of a maglev system. The report provides a base for determining the noise consequences and potential mitigation for a high speed maglev system in populated areas of the United States. Four areas are included in the study: (1) definition of noise sources; (2) development of noise criteria; (3) development of design guidelines; and (4) recommendations for a noise testing facility.

  5. Perceptual assessment of quality of urban soundscapes with combined noise sources and water sounds.

    PubMed

    Jeon, Jin Yong; Lee, Pyoung Jik; You, Jin; Kang, Jian

    2010-03-01

    In this study, urban soundscapes containing combined noise sources were evaluated through field surveys and laboratory experiments. The effect of water sounds on masking urban noises was then examined in order to enhance the soundscape perception. Field surveys in 16 urban spaces were conducted through soundwalking to evaluate the annoyance of combined noise sources. Synthesis curves were derived for the relationships between noise levels and the percentage of highly annoyed (%HA) and the percentage of annoyed (%A) for the combined noise sources. Qualitative analysis was also made using semantic scales for evaluating the quality of the soundscape, and it was shown that the perception of acoustic comfort and loudness was strongly related to the annoyance. A laboratory auditory experiment was then conducted in order to quantify the total annoyance caused by road traffic noise and four types of construction noise. It was shown that the annoyance ratings were related to the types of construction noise in combination with road traffic noise and the level of the road traffic noise. Finally, water sounds were determined to be the best sounds to use for enhancing the urban soundscape. The level of the water sounds should be similar to or not less than 3 dB below the level of the urban noises.

  6. Angle-resolved photoemission spectroscopy with a femtosecond high harmonic light source using a two-dimensional imaging electron analyzer

    NASA Astrophysics Data System (ADS)

    Mathias, S.; Miaja-Avila, L.; Murnane, M. M.; Kapteyn, H.; Aeschlimann, M.; Bauer, M.

    2007-08-01

    An experimental setup for time- and angle-resolved photoemission spectroscopy using a femtosecond 1kHz high harmonic light source and a two-dimensional electron analyzer for parallel energy and momentum detection is presented. A selection of the 27th harmonic (41.85eV) from the harmonic spectrum of the light source is achieved with a multilayer Mo /Si double mirror monochromator. The extinction efficiency of the monochromator in selecting this harmonic is shown to be better than 7:1, while the transmitted bandwidth of the selected harmonic is capable of supporting temporal pulse widths as short as 3fs. The recorded E(k ) photoelectron spectrum from a Cu(111) surface demonstrates an angular resolution of better than 0.6° (=0.03Å-1 at Ekin ,e=36eV). Used in a pump-probe configuration, the described experimental setup represents a powerful experimental tool for studying the femtosecond dynamics of ultrafast surface processes in real time.

  7. Breaking wind waves as a source of ambient noise.

    PubMed

    Tkalich, Pavlo; Chan, Eng Soon

    2002-08-01

    A theoretical model for the prediction of ambient noise level due to collective oscillations of air bubbles under breaking wind waves is presented. The model uses a budget of the energy flux from the breaking waves to quantify acoustic power radiation by a bubble cloud. A shift of the noise spectra to lower frequency due to collective bubble oscillation is assumed. The model derives good estimates of the magnitude, slope, and frequency range of the noise spectra using the wind speed or height of breaking waves.

  8. Advanced techniques for noise source identification on a large generator unit

    SciTech Connect

    Williams, R.G.D. ); Yang, S.J. )

    1993-03-01

    Power station acoustic noise assessment, which has experienced increased environmental awareness and subsequently more stringent legislation for a number of years, has received and added stimulus due to the recent advent of powerful measurement and analysis techniques including sound intensity and coherence. These experimental techniques are explained and results, for a generator unit, illustrate their value in providing a unique, correlated insight into noise problems. This includes noise quantification, full explanation of site sound pressure level in terms of the various influences and major noise source identification. These techniques are widely applicable and an invaluable aid to any industrial noise problem.

  9. Source Processes Revealed at Two Guatemalan Volcanoes: Insights from Multidisciplinary Observations of Harmonic Tremor and Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Brill, K. A.; Waite, G. P.

    2012-12-01

    Tremor signals at volcanoes are typically attributed to fluid movement within the system. Characteristics of harmonic tremor (i.e. duration, frequency content, polarization) can convey detailed information about source processes from which they emanate, but decoding these signals poses great challenges due to the complexity of volcanic environments. We recorded instances of harmonic tremor at both Santiaguito and Fuego volcanoes Guatemala, Central America. The instances of harmonic tremor occur both independent from and contemporaneous with explosions, and last anywhere from 30 seconds to tens of minutes. The signals have fundamental frequencies between 0.3 and 2.5 Hz, with as many as 20 overtones, and exhibit spectral gliding of up to 0.75 Hz over the course of an event, changing as quickly as 0.1 Hz/second. Field observations; video recordings; and time-lapse, ultraviolet, and thermal imagery; collected simultaneously with acoustic and seismic recordings allow us to constrain source locations and processes beyond what would otherwise be possible just acoustic and seismic recordings. We propose that the harmonic tremor signals are generated by nonlinear excitation of fracture walls as gas vents out of the systems. Additionally, we investigate the complex wavefield generated by harmonic tremor and the heterogeneous volcanic media. Particle motions at both volcanoes are typically elliptical, but vary dramatically over time as the fundamental frequency glides up and down (see figure). In addition, the particle motions of harmonics often have different polarities from each other and the fundamental frequency. Through finite difference modeling, we isolate the effects of near-field terms, topography, and source mechanism to explore each of these factors' contribution to the unexpected behavior.

  10. Electro-optical system for scanning microscopy of extreme ultraviolet masks with a high harmonic generation source.

    PubMed

    Naulleau, Patrick P; Anderson, Christopher N; Anderson, Erik H; Andreson, Nord; Chao, Weilun; Choi, Changhoon; Goldberg, Kenneth A; Gullikson, Eric M; Kim, Seong-Sue; Lee, Donggun; Miyakawa, Ryan; Park, Jongju; Rekawa, Seno; Salmassi, Farhad

    2014-08-25

    A self-contained electro-optical module for scanning extreme ultraviolet (EUV) reflection microscopy at 13.5 nm wavelength has been developed. The system has been designed to work with stand-alone commercially available EUV high harmonic generation (HHG) sources through the implementation of narrowband harmonic selecting multilayers and off-axis elliptical short focal length zoneplates. The module has been successfully integrated into an EUV mask scanning microscope achieving diffraction limited imaging performance (84 nm point spread function). PMID:25321224

  11. Control of tonal noise from subsonic axial fan. Part 1: reconstruction of aeroacoustic sources from far-field sound pressure

    NASA Astrophysics Data System (ADS)

    Gérard, Anthony; Berry, Alain; Masson, Patrice

    2005-12-01

    An inverse method is investigated to evaluate the unsteady rotating forces (dipole strength distribution) acting by the fan on the fluid from far-field acoustic pressure measurements. A development based on the tonal noise generated by a propeller is used to derive a discretized form of the direct problem. The inversion of this direct problem is ill-posed and requires optimization technique to stabilize the solution for small perturbations in the measured acoustic input data. The reconstruction reveals that the conditioning of the inverse model depends on the aeroacoustic source and far-field sensor locations as well as on the frequency under investigation. Simulations show that an adequate choice of a regularization parameter leads to a satisfactory reconstruction of imposed unsteady rotating forces in the presence of measurement noise, and a correct localization of acoustic "hot spots" on the radiation surface. Preliminary experimental results also show the ability to extrapolate the radiated sound field at blade passage frequency (BPF), and harmonics, from the reconstructed forces. These data are exploited in the second part of this paper to evaluate various active control strategies for tonal fan noise.

  12. Jet-Surface Interaction Test: Phased Array Noise Source Localization Results

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.

    2012-01-01

    An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the noise 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 noise was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array noise source 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 noise sources 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 noise reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the noise sources associated with a given frequency of noise tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The noise source localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces noise at a given frequency within a broadband shock noise 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 noise 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 noise sources may satisfy this requirement.

  13. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    The design and test results of a novel waveguide multimode directional coupler for a CW millimeter-wave satellite beacon source are presented. The coupler separates the second harmonic power from the fundamental output power of a traveling-wave tube amplifier. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37 to 42 GHz) and VW-band (71 to 76 GHz) satellite-to-ground signals.

  14. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    This paper presents the design and test results of a CW millimeter-wave satellite beacon source, based on the second harmonic from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37-42 GHz) and V/W-band (71- 76 GHz) satellite-to-ground signals.

  15. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    This paper presents the design and test results of a CW millimeter-wave satellite beacon source, based on the second harmonic from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon source 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.

  16. Multi-MW 22.8 GHz Harmonic Multiplier - RF Power Source for High-Gradient Accelerator R&D

    SciTech Connect

    Jay L. Hirshfield

    2012-07-26

    Electrodynamic and particle simulation studies have been carried out to optimize design of a two-cavity harmonic 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 harmonic into a TEn11 output cavity. Examples are worked out in detail for 7th and 2nd harmonic 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 harmonic converter components (drive cavity, output cavities, electron beam source and modulator, beam collector) for the two harmonic 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.

  17. (Investigation of subcooled hydrothermal boiling in ground water flow channels as a source of harmonic tremors)

    SciTech Connect

    Not Available

    1989-01-01

    As a first step toward assessing the ability of hydrothermal boiling to explain geothermal ground noise and volcanic tremor observations, we are investigating the acoustic power spectrum of boiling (the source'' 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 noise 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 noise/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.

  18. Noise analysis in photonic true time delay systems based on broadband optical source and dispersion components.

    PubMed

    Xue, Xiaoxiao; Wen, He; Zheng, Xiaoping; Zhang, Hanyi; Guo, Yili; Zhou, Bingkun

    2009-02-01

    The noise in photonic true time delay systems based on broadband optical source and dispersion components is investigated. It is found that the beat noise induced by the optical source begins to dominate and grows far larger than other noise terms quickly, as long as the detected optical power is above some certain value P(thr). When the system dispersion is nonzero, the output carrier-to-noise ratio (CNR) will change periodically with the optical bandwidth due to the noise power increment and the dispersion induced radio frequency signal power degradation. The maximum CNR is the peak value of the first period. For a set of specified system conditions, the P(thr) is calculated to be -21 dBm, and the optimal optical bandwidth is 0.8 nm, at which the maximum CNR is 93.3 dB by considering the noise in a 1 Hz bandwidth. The results are verified experimentally.

  19. Aeroacoustics of Turbulent Jets: Flow Structure, Noise Sources, and Control

    NASA Astrophysics Data System (ADS)

    Gutmark, Ephraim Jeff; Callender, Bryan William; Martens, Steve

    The paper reviews research performed to advance the understanding of state-of-the-art technologies capable of reducing coaxial jet noise simulating the exhaust flow of turbofan engines. The review focuses on an emerging jet noise passive control technology known as chevron nozzles. The fundamental physical mechanisms responsible for the acoustic benefits provided by these nozzles are discussed. Additionally, the relationship between these physical mechanisms and some of the primary chevron geometric parameters are highlighted. Far-field acoustic measurements over a wide range of nozzle operating conditions illustrated the ability of the chevron nozzles to provide acoustic benefits. Detailed mappings of the acoustic near-field provided more insight into the chevron noise suppression mechanisms by successfully identifying two primary chevron effects consistent with the results of the far-field measurements: chevrons penetration and shear velocity across them. Mean and turbulence data identified the physical flow mechanisms responsible for the effects documented in the far- and near-field studies.

  20. Photonic crystal surface-emitting lasers as a pumping light source for second harmonic generation

    NASA Astrophysics Data System (ADS)

    Watanabe, Akiyoshi; Hirose, Kazuyoshi; Kurosaka, Yoshitaka; Sugiyama, Takahiro; Liang, Yong; Noda, Susumu

    2014-02-01

    Photonic crystal surface emitting lasers (PCSELs) have recently been achieved with both a single spectrum and narrow spot beam pattern under several hundred mW of output power. Even though the high coherence properties of PCSELs are expected to be used for various applications, we have focused on a pumping light source for a wavelength conversion system in this work. We fabricated a 1.06 μm PCSEL with a square lattice 2D photonic crystal in which the lattice period corresponded to the lasing wavelength to obtain green light. The fabricated device had a narrow spot beam pattern of less than 0.5 degrees and a single spectrum at 1068 nm under CW output power of more than 200 mW despite the broad emitting area of 200 × 200 μm2. The wavelength conversion system used single pass second-harmonic generation (SHG) that consisted of only the PCSEL and 50 mm long bulk MgO doped periodically with poled lithium niobate (MgO:PPLN) as a nonlinear medium, i.e., it was a lens-free system. It was important to maintain the high brightness of the pumping light in this system with a single spectrum through the MgO:PPLN. As a result, SHG light was obtained at 534 nm with a narrow spot beam pattern, which followed the beam quality of the PCSEL under CW operation.

  1. Sources, control, and effects of noise from aircraft propellers and rotors

    NASA Technical Reports Server (NTRS)

    Mixson, J. S.; Greene, G. C.; Dempsey, T. K.

    1981-01-01

    Recent NASA and NASA sponsored research on the prediction and control of propeller and rotor source noise, on the analysis and design of fuselage sidewall noise control treatments, and on the measurement and quantification of the response of passengers to aircraft noise is described. Source noise 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 noise can be obtained without significant performance penalty. Sidewall design studies are examined for interior noise 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 noise reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller-like noise is described. Subject discomfort ratings of combined tone broadband noises are compared with ratings of broadband (boundary layer) noise alone and the relative importance of the propeller tones is examined.

  2. High-speed helicopter rotor noise - Shock waves as a potent source of sound

    NASA Technical Reports Server (NTRS)

    Farassat, F.; Lee, Yung-Jang; Tadghighi, H.; Holz, R.

    1991-01-01

    In this paper we discuss the problem of high speed rotor noise prediction. In particular, we propose that from the point of view of the acoustic analogy, shocks around rotating blades are sources of sound. We show that, although for a wing at uniform steady rectilinear motion with shocks the volume quadrupole and shock sources 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 sources occurs, yet the remaining shock noise contribution is still potent. A formula for shock noise 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 noise prediction for a hovering model rotor for which experimental noise data exist is presented. The comparison of measured and predicted acoustic data shows good agreement.

  3. Identification and proposed control of helicopter transmission noise at the source

    NASA Technical Reports Server (NTRS)

    Coy, John J.; Handschuh, Robert F.; Lewicki, David G.; Huff, Ronald G.; Krejsa, Eugene A.; Karchmer, Allan M.

    1987-01-01

    Helicopter cabin interiors require noise treatment which is expensive and adds weight. The gears inside the main power transmission are major sources of cabin noise. Work conducted by the NASA Lewis Research Center in measuring cabin interior noise and in relating the noise 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 source of cabin noise and that other low frequency sources are present that could dominate the cabin noise. 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 noise is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that noise. The completed NASA/Army sponsored research that applies to transmission noise reduction is summarized. The continuing research program is also reviewed.

  4. Identification and proposed control of helicopter transmission noise at the source

    NASA Technical Reports Server (NTRS)

    Coy, John J.; Handschuh, Robert F.; Lewicki, David G.; Huff, Ronald G.; Krejsa, Eugene A.; Karchmer, Allan M.; Coy, John J.

    1988-01-01

    Helicopter cabin interiors require noise treatment which is expensive and adds weight. The gears inside the main power transmission are major sources of cabin noise. Work conducted by the NASA Lewis Research Center in measuring cabin interior noise and in relating the noise 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 source of cabin noise and that other low frequency sources are present that could dominate the cabin noise. 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 noise is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that noise. The completed NASA/Army sponsored research that applies to transmission noise reduction is summarized. The continuing research program is also reviewed.

  5. Myosin rods are a source of second harmonic generation signals in skeletal muscle

    NASA Astrophysics Data System (ADS)

    Schürmann, Sebastian; Weber, Cornelia; Fink, Rainer H. A.; Vogel, Martin

    2007-02-01

    Intrinsic second harmonic generation (SHG) signals can be used to visualize the three-dimensional structure of cardiac and skeletal muscle with high spatial resolution. Fluorescence labeling of complementary sarcomeric proteins, e.g. actin, indicates that the observed SHG signals arise from the myosin filaments. Recently, the myosin rod domain or LMM - light meromyosin - has been reported to be the dominant source of this SHG signal. However, to date, mostly negative and indirect evidence has been presented to support this assumption. Here, we show, to our knowledge, the first direct evidences that strong SHG signals can be obtained from synthetic paracrystals. These rod shaped filaments are formed from purified LMM. SDS-PAGE protein analysis confirmed that the LMM crystals lack myosin head domains. Some regions of the LMM paracrystals produce a strong SHG signal whereas others did not. The SHG signals were recorded with a laser-scanning microscope (Leica SP2). A ps laser tuned to 880 nm was used to excite the sample through an 63x objective of 1.2 NA. In order to visualize the synthetic filaments - in addition to SHG imaging -, the LMM was labeled with the fluorescent marker 5-IAF. We were able to observe filaments of 1 to 50 μm in length and of up to 5 μm in diameter. In conclusion, we can show that the myosin rod domain (LMM) is a dominant source for intrinsic SHG signals. There seems, however, a signal dependence on the paracrystals' morphology. This dependence is being investigated.

  6. Harmonic allocation of authorship credit: source-level correction of bibliometric bias assures accurate publication and citation analysis.

    PubMed

    Hagen, Nils T

    2008-01-01

    Authorship credit for multi-authored scientific publications is routinely allocated either by issuing full publication credit repeatedly to all coauthors, or by dividing one credit equally among all coauthors. The ensuing inflationary and equalizing biases distort derived bibliometric measures of merit by systematically benefiting secondary authors at the expense of primary authors. Here I show how harmonic counting, which allocates credit according to authorship rank and the number of coauthors, provides simultaneous source-level correction for both biases as well as accommodating further decoding of byline information. I also demonstrate large and erratic effects of counting bias on the original h-index, and show how the harmonic version of the h-index provides unbiased bibliometric ranking of scientific merit while retaining the original's essential simplicity, transparency and intended fairness. Harmonic decoding of byline information resolves the conundrum of authorship credit allocation by providing a simple recipe for source-level correction of inflationary and equalizing bias. Harmonic counting could also offer unrivalled accuracy in automated assessments of scientific productivity, impact and achievement.

  7. Analysis of jet-airfoil interaction noise sources by using a microphone array technique

    NASA Astrophysics Data System (ADS)

    Fleury, Vincent; Davy, Renaud

    2016-03-01

    The paper is concerned with the characterization of jet noise sources and jet-airfoil interaction sources by using microphone array data. The measurements were carried-out in the anechoic open test section wind tunnel of Onera, Cepra19. The microphone array technique relies on the convected, Lighthill's and Ffowcs-Williams and Hawkings' acoustic analogy equation. The cross-spectrum of the source term of the analogy equation is sought. It is defined as the optimal solution to a minimal error equation using the measured microphone cross-spectra as reference. This inverse problem is ill-posed yet. A penalty term based on a localization operator is therefore added to improve the recovery of jet noise sources. The analysis of isolated jet noise data in subsonic regime shows the contribution of the conventional mixing noise source in the low frequency range, as expected, and of uniformly distributed, uncorrelated noise sources in the jet flow at higher frequencies. In underexpanded supersonic regime, a shock-associated noise source is clearly identified, too. An additional source is detected in the vicinity of the nozzle exit both in supersonic and subsonic regimes. In the presence of the airfoil, the distribution of the noise sources is deeply modified. In particular, a strong noise source is localized on the flap. For high Strouhal numbers, higher than about 2 (based on the jet mixing velocity and diameter), a significant contribution from the shear-layer near the flap is observed, too. Indications of acoustic reflections on the airfoil are also discerned.

  8. Detecting vocal fatigue in student singers using acoustic measures of mean fundamental frequency, jitter, shimmer, and harmonics-to-noise ratio

    NASA Astrophysics Data System (ADS)

    Sisakun, Siphan

    2000-12-01

    The purpose of this study is to explore the ability of four acoustic parameters, mean fundamental frequency, jitter, shimmer, and harmonics-to-noise 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 harmonics-to-noise ratio. The proposed profile requires further investigation.

  9. Effects of noise levels and call types on the source levels of killer whale calls.

    PubMed

    Holt, Marla M; Noren, Dawn P; Emmons, Candice K

    2011-11-01

    Accurate parameter estimates relevant to the vocal behavior of marine mammals are needed to assess potential effects of anthropogenic sound exposure including how masking noise reduces the active space of sounds used for communication. Information about how these animals modify their vocal behavior in response to noise exposure is also needed for such assessment. Prior studies have reported variations in the source levels of killer whale sounds, and a more recent study reported that killer whales compensate for vessel masking noise by increasing their call amplitude. The objectives of the current study were to investigate the source levels of a variety of call types in southern resident killer whales while also considering background noise level as a likely factor related to call source level variability. The source levels of 763 discrete calls along with corresponding background noise were measured over three summer field seasons in the waters surrounding the San Juan Islands, WA. Both noise level and call type were significant factors on call source 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 noise reduces vocal communication space in marine mammals.

  10. GIS-Based Noise Simulation Open Source Software: N-GNOIS

    NASA Astrophysics Data System (ADS)

    Vijay, Ritesh; Sharma, A.; Kumar, M.; Shende, V.; Chakrabarti, T.; Gupta, Rajesh

    2015-12-01

    Geographical information system (GIS)-based noise simulation software (N-GNOIS) has been developed to simulate the noise scenario due to point and mobile sources 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 source technology (QGIS) and open source language (Python). N-GNOIS has unique features like cumulative impact of point and mobile sources, 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 noise and acts as a decision making tool for planning and management of noise component in environmental impact assessment (EIA) studies.

  11. Phased Array Radiometer Calibration Using a Radiated Noise Source

    NASA Technical Reports Server (NTRS)

    Srinivasan, Karthik; Limaye, Ashutoch S.; Laymon, Charles A.; Meyer, Paul J.

    2010-01-01

    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 noise 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 noise 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.

  12. A study of noise source location on a model scale augmentor wing using correlation techniques. [noise measurement of far field noise by wind tunnel tests

    NASA Technical Reports Server (NTRS)

    Wilby, J. F.; Scharton, T. D.

    1975-01-01

    An experimental investigation, conducted on a model-scale augmentor wing to identify the sources of far-field noise, is examined. The measurement procedure followed in the investigation involved the cross-correlation of far field sound pressures with fluctuating pressures on the surface of the augmentor flap and shroud. In addition pressures on the surfaces of the augmentor were cross-correlated. The results are interpreted as showing that the surface pressure fluctuations are mainly aerodynamic in character and are convected in the downstream direction with a velocity which is dependent on the jet exhaust velocity. However the far field sound levels in the mid and high frequency ranges are dominated by jet noise. There is an indication that in the low frequency range trailing edge noise, associated with interaction of the jet flow and the flap trailing edge, plays a significant role in the radiated sound field.

  13. How Common are Noise Sources on the Crash Arc of Malaysian Flight 370

    SciTech Connect

    Fenimore, Edward E.; Kunkle, Thomas David; Stead, Richard J.

    2014-10-21

    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 noise 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 noise events are on the arc of possible locations where Malaysian Flight 370 might have crashed. Few other noise sources were found on the arc. The noise event found by Stead is the strongest. No noise events are seen within the Australian Transportation Safety Board (ATSB) new search location until the 10th strongest event, an event which is very close to the noise level.

  14. Diesel engine noise source identification based on EEMD, coherent power spectrum analysis and improved AHP

    NASA Astrophysics Data System (ADS)

    Zhang, Junhong; Wang, Jian; Lin, Jiewei; Bi, Fengrong; Guo, Qian; Chen, Kongwu; Ma, Liang

    2015-09-01

    As the essential foundation of noise reduction, many noise source identification methods have been developed and applied to engineering practice. To identify the noise source in the board-band frequency of different engine parts at various typical speeds, this paper presents an integrated noise source identification method based on the ensemble empirical mode decomposition (EEMD), the coherent power spectrum analysis, and the improved analytic hierarchy process (AHP). The measured noise 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 noise identification model is applied to identifying a diesel engine surface radiated noise. 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 noise reduction.

  15. Analytic treatment of source photon emission times to reduce noise in implicit Monte Carlo calculations

    SciTech Connect

    Trahan, Travis J.; Gentile, Nicholas A.

    2012-09-10

    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 source photon emission times. We have developed a modification to the Implicit Monte Carlo algorithm that eliminates noise due to sampling of the emission time of source 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 noise relative to standard implicit Monte Carlo in some cases, and comparable noise in all other cases. In conclusion, the improvements are limited to short time scales; over long time scales, noise due to random sampling of spatial and angular variables tends to dominate the noise reduction from the new algorithm.

  16. Tracking Signal Subspace Invariance for Blind Separation and Classification of Nonorthogonal Sources in Correlated Noise

    NASA Astrophysics Data System (ADS)

    Oweiss, Karim G.; Anderson, David J.

    2006-12-01

    We investigate a new approach for the problem of source separation in correlated multichannel signal and noise environments. The framework targets the specific case when nonstationary correlated signal sources contaminated by additive correlated noise impinge on an array of sensors. Existing techniques targeting this problem usually assume signal sources to be independent, and the contaminating noise to be spatially and temporally white, thus enabling orthogonal signal and noise subspaces to be separated using conventional eigendecomposition. In our context, we propose a solution to the problem when the sources are nonorthogonal, and the noise is correlated with an unknown temporal and spatial covariance. The approach is based on projecting the observations onto a nested set of multiresolution spaces prior to eigendecomposition. An inherent invariance property of the signal subspace is observed in a subset of the multiresolution spaces that depends on the degree of approximation expressed by the orthogonal basis. This feature, among others revealed by the algorithm, is eventually used to separate the signal sources in the context of "best basis" selection. The technique shows robustness to source nonstationarities as well as anisotropic properties of the unknown signal propagation medium under no constraints on the array design, and with minimal assumptions about the underlying signal and noise processes. We illustrate the high performance of the technique on simulated and experimental multichannel neurophysiological data measurements.

  17. Harmonic-resonator-based triboelectric nanogenerator as a sustainable power source and a self-powered active vibration sensor.

    PubMed

    Chen, Jun; Zhu, Guang; Yang, Weiqing; Jing, Qingshen; Bai, Peng; Yang, Ya; Hou, Te-Chien; Wang, Zhong Lin

    2013-11-13

    A harmonic-resonator-based triboelectric nanogenerator (TENG) is presented as a sustainable power source and an active vibration sensor. It can effectively respond to vibration frequencies ranging from 2 to 200 Hz with a considerably wide working bandwidth of 13.4 Hz. This work not only presents a new principle in the field of vibration energy harvesting but also greatly expands the applicability of TENGs.

  18. AIRUSE-LIFE+: a harmonized PM speciation and source apportionment in five southern European cities

    NASA Astrophysics Data System (ADS)

    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

    2016-03-01

    The AIRUSE-LIFE+ project aims at characterizing similarities and heterogeneities in particulate matter (PM) sources and contributions in urban areas from southern Europe. Once the main PMx sources 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 source 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 harmonized 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 source 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

  19. Limitations of Phased Array Beamforming in Open Rotor Noise Source Imaging

    NASA Technical Reports Server (NTRS)

    Horvath, Csaba; Envia, Edmane; Podboy, Gary G.

    2013-01-01

    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 noise 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 noise sources of the blade passing frequency tones and interaction tones appear at their nominal Mach radii instead of at the actual noise sources, 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 noise sources interact with the phased array, often giving misleading results, as the apparent sources do not always show where the actual noise sources are located. This suggests that a more sophisticated source model would be required to accurately locate the sources of each tone. The results of this study also have implications with regard to the shielding of open rotor sources by airframe empennages.

  20. Apparent changes in seismic wave velocity related to microseism noise source variations

    NASA Astrophysics Data System (ADS)

    Friderike Volk, Meike; Bean, Christopher; Lokmer, Ivan; Craig, David

    2014-05-01

    Currently there is a strong interest of using cross correlation of ambient noise for imaging of the subsurface or monitoring of various geological settings where we expect rapid changes (e.g. reservoirs or volcanoes). Through cross correlation retrieved Green's function is usually used to calculate seismic velocities of the subsurface. The assumption of this method is that the wavefields which are correlated must be diffuse. That means that the ambient noise sources are uniformly distributed around the receivers or the scattering in the medium is high enough to mitigate any source directivity. The location of the sources is usually unknown and it can change in time. These temporal and spatial variations of the microseism noise sources may lead to changes in the retrieved Green's functions. The changed Green's functions will then cause apparent changes in the calculated seismic velocity. We track the spatial and temporal distribution of the noise sources 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 noise sources in the North Atlantic, allowing a quantification of noise source heterogeneity. Temporal variations in seismic wave velocity are calculated using data recorded in Ireland. The results are compared to the variations in microseism source locations. We also explore the minimum noise trace length required in Ireland 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 sources and assess if and at what frequencies the scattering of the medium in Ireland is high enough to homogenise the coda wavefield.

  1. Volterra dendritic stimulus processors and biophysical spike generators with intrinsic noise sources.

    PubMed

    Lazar, Aurel A; Zhou, Yiyin

    2014-01-01

    We consider a class of neural circuit models with internal noise sources 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 noise sources affect the precision in encoding and decoding of sensory stimuli and the functional identification of its sensory circuits. We investigate two intrinsic noise sources arising (i) in the active dendritic trees underlying the DSPs, and (ii) in the ion channels of the BSGs. Noise in dendritic stimulus processing arises from a combined effect of variability in synaptic transmission and dendritic interactions. Channel noise 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 noise sources 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 noise sources on stimulus decoding. Building on a key duality property, the effect of noise 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 noise 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.

  2. Volterra dendritic stimulus processors and biophysical spike generators with intrinsic noise sources

    PubMed Central

    Lazar, Aurel A.; Zhou, Yiyin

    2014-01-01

    We consider a class of neural circuit models with internal noise sources 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 noise sources affect the precision in encoding and decoding of sensory stimuli and the functional identification of its sensory circuits. We investigate two intrinsic noise sources arising (i) in the active dendritic trees underlying the DSPs, and (ii) in the ion channels of the BSGs. Noise in dendritic stimulus processing arises from a combined effect of variability in synaptic transmission and dendritic interactions. Channel noise 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 noise sources 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 noise sources on stimulus decoding. Building on a key duality property, the effect of noise 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 noise 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

  3. Simulation of 100-300 GHz solid-state harmonic sources

    NASA Technical Reports Server (NTRS)

    Zybura, Michael F.; Jones, J. Robert; Jones, Stephen H.; Tait, Gregory B.

    1995-01-01

    Accurate and efficient simulations of the large-signal time-dependent characteristics of second-harmonic Transferred Electron Oscillators (TEO's) and Heterostructure Barrier Varactor (HBV) frequency triplers have been obtained. This is accomplished by using a novel and efficient harmonic-balance circuit analysis technique which facilitates the integration of physics-based hydrodynamic device simulators. The integrated hydrodynamic device/harmonic-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-harmonic 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 harmonic-balance circuit simulator. This comparison illustrates the importance of representing active devices with physics-based numerical device models rather than analytical device models.

  4. Quantitative Measurement of the Proportions of High-Order Harmonics for the 4B7B Soft-X-Ray Source at Beijing Synchrotron Radiation Facility

    NASA Astrophysics Data System (ADS)

    Zhu, Tuo; Shang, Wanli; Zhang, Wenhai; Yang, Jiamin; Xiong, Gang; Zhao, Yang; Kuang, Longyu; Zhao, Yidong; Zheng, Lei; Cui, Mingqi; Tang, Kun; Ma, Chenyan

    2013-12-01

    A transmission grating coupled with an X-ray charge coupled device (CCD) is used to quantitatively measure the proportion of high-order harmonics of the soft-X-ray source of beam line 4B7B. The results show that the monochromatic X-ray has third-order and second-order harmonics. The proportion of second-order harmonic of 4B7B is less than 9.0% and the third-order harmonic is below 0.7% when no suppressing method is applied. When suppression methods are used, the proportion of second-order harmonic is less than 1.7% and the third-order harmonic is ignorable.

  5. Clutter isolation and cardiac monitoring using harmonic doppler radar with heterodyne receiver and passive RF tags.

    PubMed

    Singh, Aditya; Lubecke, Victor

    2010-01-01

    A harmonic radar employing the use of harmonic 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 harmonic tags in presence of a controlled noise 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 noise from heart-rate in presence of a noise source.

  6. Instability waves as a source of subsonic jet noise

    NASA Astrophysics Data System (ADS)

    Suponitsky, V.; Sandham, N. D.

    The current work aims to get a further insight into the role of large scale structures/instability waves in noise generation in subsonic jets by carrying out direct numerical simulations. It is a continuation of earlier works [1, 2] in which a non-linear mechanism of subsonic jet noise generation was proposed and studied using the parabolized stability equations. The mechanism proposes an explanation of the experimental results (e.g. [3]) which show that a peak in sound radiation occurs at frequencies lower (St ≈ 0.2) than those of the most energetic hydrodynamic modes (St ≈ 0.45). The key point of this mechanism is that the `difference frequency' modes arising from a nonlinear interaction between two primary instability waves make major contributions to far-field sound radiation from a subsonic jet. These modes are characterized by relatively low frequency, high amplitude and by a compact shape of the wave packet, and therefore can be efficient sound radiators in subsonic jets [4].

  7. Instability waves as a source of subsonic jet noise

    NASA Astrophysics Data System (ADS)

    Suponitsky, V.; Sandham, N. D.

    The current work aims to get a further insight into the role of large scale structures/instability waves in noise generation in subsonic jets by carrying out direct numerical simulations. It is a continuation of earlier works [1, 2] in which a non-linear mechanism of subsonic jet noise generation was proposed and studied using the parabolized stability equations. The mechanism proposes an explanation of the experimental results (e.g. [3]) which show that a peak in sound radiation occurs at frequencies lower (St ≈ 0.2) than those of the most energetic hydrodynamic modes (St ≈ 0.45). The key point of this mechanism is that the 'difference frequency' modes arising from a nonlinear interaction between two primary instability waves make major contributions to far-field sound radiation from a subsonic jet. These modes are characterized by relatively low frequency, high amplitude and by a compact shape of the wave packet, and therefore can be efficient sound radiators in subsonic jets [4].

  8. Suppression of fiber modal noise induced radial velocity errors for bright emission-line calibration sources

    SciTech Connect

    Mahadevan, Suvrath; Halverson, Samuel; Ramsey, Lawrence; Venditti, Nick

    2014-05-01

    Modal noise in optical fibers imposes limits on the signal-to-noise 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 sources like laser frequency combs and Fabry-Perot etalons to achieve precision sufficient to detect terrestrial-mass planets. These high-precision calibration sources often use single-mode fibers or highly coherent sources. 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 noise measured by the spectrograph. We present a commercial off-the-shelf solution that significantly mitigates modal noise 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 noise 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 sources by removing a major source of systematic noise.

  9. Basic research in fan source noise: Inlet distortion and turbulence noise

    NASA Technical Reports Server (NTRS)

    Kantola, R. A.; Warren, R. E.

    1978-01-01

    A widely recognized problem in jet engine fan noise 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 noise 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.

  10. Jet-Surface Interaction Test: Phased Array Noise Source Localization Results

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.

    2013-01-01

    An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the noise 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 noise was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array noise source localization measurements were obtained. This paper discusses phased array results, while a companion paper (Brown, C.A., "Jet-Surface Interaction Test: Far-Field Noise Results," ASME paper GT2012-69639, June 2012.) discusses far-field results. The phased array data show that the axial distribution of noise sources 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 noise reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the noise sources associated with a given frequency of noise tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The noise source localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces noise at a given frequency within a broadband shock noise 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 noise 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 noise sources may satisfy this requirement.

  11. Helicopter main-rotor noise: Determination of source contributions using scaled model data

    NASA Astrophysics Data System (ADS)

    Brooks, Thomas F.; Jolly, J. Ralph, Jr.; Marcolini, Michael A.

    1988-08-01

    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 noise contributions from different rotor noise sources. Key results include a component breakdown of the noise contributions, in terms of noise criteria calculations of a weighted sound pressure level (dBA) and perceived noise 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) noise is the dominant contributor to the noise. In level flight and mild climb, broadband blade-turbulent wake interaction (BWI) noise is dominant due to the absence of BVI activity. At high climb angles, BWI is reduced and self-noise from blade boundary-layer turbulence becomes the most prominent.

  12. Helicopter main-rotor noise: Determination of source contributions using scaled model data

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Jolly, J. Ralph, Jr.; Marcolini, Michael A.

    1988-01-01

    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 noise contributions from different rotor noise sources. Key results include a component breakdown of the noise contributions, in terms of noise criteria calculations of a weighted sound pressure level (dBA) and perceived noise 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) noise is the dominant contributor to the noise. In level flight and mild climb, broadband blade-turbulent wake interaction (BWI) noise is dominant due to the absence of BVI activity. At high climb angles, BWI is reduced and self-noise from blade boundary-layer turbulence becomes the most prominent.

  13. Characteristics of Love and Rayleigh waves in ambient noise: wavetype ratio, source location and seasonal behavior

    NASA Astrophysics Data System (ADS)

    Juretzek, C.; Perleth, M.; Hadziioannou, C.

    2015-12-01

    Ambient seismic noise has become an important source of signal for tomography and monitoring purposes. Better understanding of the noise field characteristics is crucial to further improve noise applications. Our knowledge about the common and different origins of Love and Rayleigh waves in the microseism bands is still limited. This applies in particular to constraints on source locations and source mechanisms of Love waves. Here, 3-component beamforming is used to distinguish between the differently polarized wave types present in the noise field recorded at several arrays across Europe. The focus lies on frequencies around the primary and secondary microseismic bands. We compare characteristics of Love and Rayleigh wave noise, such as source directions and frequency content. Further, Love to Rayleigh wave ratios are measured at each array, and a dependence on direction is observed. We constrain the corresponding source regions of both wave types by backprojection. By using a full year of data in 2013, we are able to track the seasonal changes in our observations of Love-to-Rayleigh ratio and source locations.

  14. Exposures to transit and other sources of noise among New York City residents.

    PubMed

    Neitzel, Richard L; Gershon, Robyn R M; McAlexander, Tara P; Magda, Lori A; Pearson, Julie M

    2012-01-01

    To evaluate the contributions of common noise sources to total annual noise exposures among urban residents and workers, we estimated exposures associated with five common sources (use of mass transit, occupational and nonoccupational 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 source to total noise exposure and also compared our estimated exposures to the recommended 70 dBA annual exposure limit. We found that one in ten transit users had noise 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 source 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 noise-induced hearing loss and that, for many individuals, this risk is driven primarily by exposures other than occupational noise.

  15. A low phase noise microwave source for atomic spin squeezing experiments in {sup 87}Rb

    SciTech Connect

    Chen Zilong; Bohnet, Justin G.; Weiner, Joshua M.; Thompson, James K.

    2012-04-15

    We describe and characterize a simple, low cost, low phase noise microwave source that operates near 6.800 GHz for agile, coherent manipulation of ensembles of {sup 87}Rb. Low phase noise is achieved by directly multiplying a low phase noise 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 source to provide the desired phase, amplitude, and frequency control. Before modulation, the source has a single sideband phase noise 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 source is estimated to contribute added spin-noise variance 16 dB below the quantum projection noise level during quantum nondemolition measurements of the clock transition in an ensemble 7 x 10{sup 5} {sup 87}Rb atoms.

  16. Exposures to Transit and Other Sources of Noise among New York City Residents

    PubMed Central

    Neitzel, Richard L.; Gershon, Robyn R. M.; McAlexander, Tara P.; Magda, Lori A.; Pearson, Julie M.

    2015-01-01

    To evaluate the contributions of common noise sources to total annual noise exposures among urban residents and workers, we estimated exposures associated with five common sources (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 source to total noise exposure and also compared our estimated exposures to the recommended 70 dBA annual exposure limit. We found that one in ten transit users had noise 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 source 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 noise-induced hearing loss and that, for many individuals, this risk is driven primarily by exposures other than occupational noise. PMID:22088203

  17. Doubling the spectrum of time-domain induced polarization by harmonic de-noising, drift correction, spike removal, tapered gating and data uncertainty estimation

    NASA Astrophysics Data System (ADS)

    Olsson, Per-Ivar; Fiandaca, Gianluca; Larsen, Jakob Juul; Dahlin, Torleif; Auken, Esben

    2016-11-01

    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 noise 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 harmonics. Furthermore, an efficient processing scheme for identifying and removing spikes in TDIP data was developed. The noise 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 noise 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

  18. Spatial resolution limits for the localization of noise sources using direct sound mapping

    NASA Astrophysics Data System (ADS)

    Fernandez Comesaña, D.; Holland, K. R.; Fernandez-Grande, E.

    2016-08-01

    One of the main challenges arising from noise 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 noise sources. The direct visualization of sound, in particular sound intensity, has extensively been used for many years to locate sound sources. However, it is not yet well defined when two sources 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, noise 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 sources than sound pressure or sound intensity, especially in the acoustic near-field.

  19. Dynamics of two competing species in the presence of Lévy noise sources

    NASA Astrophysics Data System (ADS)

    La Cognata, A.; Valenti, D.; Dubkov, A. A.; Spagnolo, B.

    2010-07-01

    We consider a Lotka-Volterra system of two competing species subject to multiplicative α -stable Lévy noise. The interaction parameter between the species is a random process which obeys a stochastic differential equation with a generalized bistable potential in the presence both of a periodic driving term and an additive α -stable Lévy noise. We study the species dynamics, which is characterized by two different regimes, exclusion of one species and coexistence of both. We find quasiperiodic oscillations and stochastic resonance phenomenon in the dynamics of the competing species, analyzing the role of the Lévy noise sources.

  20. Separation of Main and Tail Rotor Noise Sources from Ground-Based Acoustic Measurements Using Time-Domain De-Dopplerization

    NASA Technical Reports Server (NTRS)

    Greenwood, Eric II; Schmitz, Fredric H.

    2009-01-01

    A new method of separating the contributions of helicopter main and tail rotor noise sources 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 noise 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 noise sources. The new method is successfully applied to ground-based microphone measurements of a Bell 206B3 helicopter and demonstrates the strong directivity characteristics of harmonic noise radiation from both the main and tail rotors of that helicopter.

  1. Source localization for active control of turbofan rotor-stator broadband noise

    NASA Astrophysics Data System (ADS)

    Walker, Bruce E.

    2005-09-01

    In order to identify a reference signal source for an active noise cancellation system, cross-correlation techniques were used to localize broadband noise source regions on exit guide vanes of the NASA Glenn Research Center Advance Noise Control Fan (ANCF). Arrays of surface pressure sensors were imbedded in one guide vane and in the wall of the fan. Synchronous sampling was used with a multichannel data acquisition system to allow removal of periodic components from the signals. The signals were then cross-correlated to assess radiation directivity and the relationship between vane surface pressure and in-duct acoustic noise. The results of these measurements indicated that broadband unsteady pressures near the leading edge tip of the guide vane were well enough correlated with acoustic radiation that 2-3 dB active noise cancellation could be achieved using a simple gain-delay control algorithm and actuator array. After successful simulation in a wind tunnel environment the concept was incorporated on 15 guide vanes and tested in ANCF. Cross-correlation measurements were further used to evaluate system performance and to identify competing noises from rotating and stationary sources within the fan.

  2. Multi-MW K-Band Harmonic Multiplier: RF Source For High-Gradient Accelerator R and D

    SciTech Connect

    Solyak, N. A.; Yakovlev, V. P.; Kazakov, S. Yu.; Hirshfield, J. L.

    2009-01-22

    A preliminary design is presented for a two-cavity harmonic multiplier, intended as a high-power RF source for use in experiments aimed at developing high-gradient structures for a future collider. The harmonic 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} harmonic 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.

  3. Optical system design of a speckle-free ultrafast Red-Green-Blue (RGB) source based on angularly multiplexed second harmonic generation from a TZDW source

    NASA Astrophysics Data System (ADS)

    Yao, Yuhong; Knox, Wayne H.

    2015-03-01

    We report the optical system design of a novel speckle-free ultrafast Red-Green-Blue (RGB) source based on angularly multiplexed simultaneous second harmonic 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 source 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 source (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 harmonic generation. With proper optical design of the free-space harmonic 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 sources, the source 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 source features a very simple system geometry, its potential for power scaling is discussed with currently available technologies.

  4. A boundary element approach to optimization of active noise control sources on three-dimensional structures

    NASA Technical Reports Server (NTRS)

    Cunefare, K. A.; Koopmann, G. H.

    1991-01-01

    This paper presents the theoretical development of an approach to active noise control (ANC) applicable to three-dimensional radiators. The active noise control technique, termed ANC Optimization Analysis, is based on minimizing the total radiated power by adding secondary acoustic sources on the primary noise source. ANC Optimization Analysis determines the optimum magnitude and phase at which to drive the secondary control sources in order to achieve the best possible reduction in the total radiated power from the noise source/control source combination. For example, ANC Optimization Analysis predicts a 20 dB reduction in the total power radiated from a sphere of radius at a dimensionless wavenumber ka of 0.125, for a single control source representing 2.5 percent of the total area of the sphere. ANC Optimization Analysis is based on a boundary element formulation of the Helmholtz Integral Equation, and thus, the optimization analysis applies to a single frequency, while multiple frequencies can be treated through repeated analyses.

  5. Preliminary study of a hydrogen peroxide rocket for use in moving source jet noise tests

    NASA Technical Reports Server (NTRS)

    Plencner, R. M.

    1977-01-01

    A preliminary investigation was made of using a hydrogen peroxide rocket to obtain pure moving source jet noise 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 source jet noise 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.

  6. Transient changes in intercellular protein variability identify sources of noise in gene expression.

    PubMed

    Singh, Abhyudai

    2014-11-01

    Protein levels differ considerably between otherwise identical cells, and these differences significantly affect biological function and phenotype. Previous work implicated various noise mechanisms that drive variability in protein copy numbers across an isogenic cell population. For example, transcriptional bursting of mRNAs has been shown to be a major source of noise in the expression of many genes. Additional expression variability, referred to as extrinsic noise, arises from intercellular variations in mRNA transcription and protein translation rates attributed to cell-to-cell differences in cell size, abundance of ribosomes, etc. We propose a method to determine the magnitude of different noise sources in a given gene of interest. The method relies on blocking transcription and measuring changes in protein copy number variability over time. Our results show that this signal has sufficient information to quantify both the extent of extrinsic noise and transcription bursting in gene expression. Moreover, if the mean mRNA count is known, then the relative contributions of transcription versus translation rate fluctuations to extrinsic noise can also be determined. In summary, our study provides an easy-to-implement method for characterizing noisy protein expression that complements existing techniques for studying stochastic dynamics of genetic circuits.

  7. DC modeling and the source of flicker noise in passivated carbon nanotube transistors.

    PubMed

    Kim, Sunkook; Kim, Seongmin; Janes, David B; Mohammadi, Saeed; Back, Juhee; Shim, Moonsub

    2010-09-24

    DC and intrinsic low-frequency noise properties of p-channel depletion-mode carbon nanotube field effect transistors (CNT-FETs) are investigated. To characterize the intrinsic noise properties, a thin atomic layer deposited (ALD) HfO(2) gate dielectric is used as a passivation layer to isolate CNT-FETs from environmental factors. The ALD HfO(2) gate dielectric in these high-performance top-gated devices is instrumental in attaining hysteresis-free current-voltage characteristics and minimizes low-frequency noise. Under small drain-source voltage, the carriers in the CNT channel are modulated by the gate electrode and the intrinsic 1/f noise is found to be correlated with charge trapping/detrapping from the oxide substrate as expected. When thermionic emission is the dominant carrier transport mechanism in CNT-FETs under large drain-source voltages, the excess 1/f noise is attributed to the noise stemming from metal-CNT Schottky barrier contacts as revealed by the measurements.

  8. Qubit dephasing due to photon shot noise from coherent and thermal sources

    NASA Astrophysics Data System (ADS)

    Gustavsson, S.; Yan, F.; Kamal, A.; Orlando, T. P.; Oliver, W. D.; Birenbaum, J.; Sears, A.; Hover, D.; Gudmundsen, T.; Yoder, J.

    We investigate qubit dephasing due to photon shot noise in a superconducting flux qubit transversally coupled to a coplanar microwave resonator. Due to the AC Stark effect, photon fluctuations in the resonator cause frequency shifts of the qubit, which in turn lead to dephasing. While this is universally understood, we have made the first quantitative spectroscopy of this noise for both thermal (i.e., residual photons from higher temperature stages) and coherent photons (residual photons from the readout and control pulses). We find that the bandwidth of the shot noise from thermal and coherent photons differ by approximately a factor of two, which we attribute to differences in the correlation time for the two noise sources. By comparing the results with noise spectra measured without any externally applied photons, we conclude that the qubit coherence times in our setup were limited by photon shot noise from thermal radiation, with an average resonator photon population of 0.006. Equipped with this knowledge, we improved the filtering for thermal noise and thereby improved the qubit coherence times by more than a factor of two, with T2 echo times approaching 100 us. From the measured T2 decay, we determine an upper bound on the residual photon population of 0.0004. This research was funded by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA) via MIT LL under Air Force Contract No. FA8721-05-C-0002.

  9. Powerline noise elimination in biomedical signals via blind source separation and wavelet analysis.

    PubMed

    Akwei-Sekyere, Samuel

    2015-01-01

    The distortion of biomedical signals by powerline noise from recording biomedical devices has the potential to reduce the quality and convolute the interpretations of the data. Usually, powerline noise 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 noise is additive in nature, it is intuitive to model powerline noise 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 noise via blind source 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 noise frequency range with higher fidelity in comparison with the mentioned techniques, especially at low signal-to-noise ratio. PMID:26157639

  10. Powerline noise elimination in biomedical signals via blind source separation and wavelet analysis

    PubMed Central

    2015-01-01

    The distortion of biomedical signals by powerline noise from recording biomedical devices has the potential to reduce the quality and convolute the interpretations of the data. Usually, powerline noise 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 noise is additive in nature, it is intuitive to model powerline noise 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 noise via blind source 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 noise frequency range with higher fidelity in comparison with the mentioned techniques, especially at low signal-to-noise ratio. PMID:26157639

  11. Interacting noise sources shape patterns of arm movement variability in three-dimensional space.

    PubMed

    Apker, Gregory A; Darling, Timothy K; Buneo, Christopher A

    2010-11-01

    Reaching movements are subject to noise in both the planning and execution phases of movement production. The interaction of these noise sources during natural movements is not well understood, despite its importance for understanding movement variability in neurologically intact and impaired individuals. Here we examined the interaction of planning and execution related noise during the production of unconstrained reaching movements. Subjects performed sequences of two movements to targets arranged in three vertical planes separated in depth. The starting position for each sequence was also varied in depth with the target plane; thus required movement sequences were largely contained within the vertical plane of the targets. Each final target in a sequence was approached from two different directions, and these movements were made with or without visual feedback of the moving hand. These combined aspects of the design allowed us to probe the interaction of execution and planning related noise with respect to reach endpoint variability. In agreement with previous studies, we found that reach endpoint distributions were highly anisotropic. The principal axes of movement variability were largely aligned with the depth axis, i.e., the axis along which visual planning related noise would be expected to dominate, and were not generally well aligned with the direction of the movement vector. Our results suggest that visual planning-related noise plays a dominant role in determining anisotropic patterns of endpoint variability in three-dimensional space, with execution noise adding to this variability in a movement direction-dependent manner.

  12. Source-based subjective responses to sleep disturbance from transportation noise.

    PubMed

    Douglas, O; Murphy, E

    2016-01-01

    There is increasing evidence to suggest that the use of subjective responses to questions concerning night-time environmental noise exposure is a robust method of assessing sleep disturbance from road traffic noise. However, there have only been a few studies exploring this issue in a real world context beyond controlled laboratory settings. This paper presents results from such a study. It utilises 208 household questionnaire surveys to assess subjective responses to levels of night-time sleep disturbance and annoyance from four different residential sites. Each residential site is characterised by a dominant noise source - road, light rail, and aircraft - and these sites are compared to a control site that is relatively free from transportation noise. The results demonstrate the inadequacy of continuous equivalent noise level measures as indicators of night-time disturbance. Furthermore, they suggest that the use of these measures alone is likely to result in inaccurate appraisals of night-time sleep disturbance from transportation noise. Ultimately, the research implies that measurement data should be used in conjunction with subjective response data to accurately gauge the level of night-time disturbance from transportation noise. PMID:27164553

  13. Study of the intensity noise and intensity modulation in a of hybrid soliton pulsed source

    SciTech Connect

    Dogru, Nuran; Oziazisi, M Sadetin

    2005-10-31

    The relative intensity noise (RIN) and small-signal intensity modulation (IM) of a hybrid soliton pulsed source (HSPS) with a linearly chirped Gaussian apodised fibre Bragg grating (FBG) are considered in the electric-field approximation. The HSPS is described by solving the dynamic coupled-mode equations. It is shown that consideration of the carrier density noise in the HSPS in addition to the spontaneous noise is necessary to analyse accurately noise in the mode-locked HSPS. It is also shown that the resonance peak spectral splitting (RPSS) of the IM near the frequency inverse to the round-trip time of light in the external cavity can be eliminated by selecting an appropriate linear chirp rate in the Gaussian apodised FBG. (laser applications and other topics in quantum electronics)

  14. Noise power spectral density of a fibre scattered-light interferometer with a semiconductor laser source

    SciTech Connect

    Alekseev, A E; Potapov, V T

    2013-10-31

    Spectral characteristics of the noise intensity fluctuations at the output of a scattered-light interferometer, caused by phase fluctuations of semiconductor laser radiation are considered. This kind of noise 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 noise power spectral density at the interferometer output versus the degree of a light source 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 noise power spectral density agrees with experimental normalised power spectra with a high accuracy. (interferometry of radiation)

  15. Phased Array Noise Source Localization Measurements Made on a Williams International FJ44 Engine

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.; Horvath, Csaba

    2010-01-01

    A 48-microphone planar phased array system was used to acquire noise source 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 noise. 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 noise emanating from the inlet reflected off of the inlet lip of the ICD. This reflection is a source of error for far field noise measurements made during the test. The data also indicate that a total temperature rake in the inlet of the engine is a source of fan noise.

  16. Identification of Noise Sources in High Speed Jets via Correlation Measurements: A Review

    NASA Technical Reports Server (NTRS)

    Bridges, James (Technical Monitor); Panda, Jayanta

    2005-01-01

    Significant advancement has been made in the last few years to identify noise sources 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 noise" as the primary source for the shallow angle noise. 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.

  17. On Acoustic Source Specification for Rotor-Stator Interaction Noise Prediction

    NASA Technical Reports Server (NTRS)

    Nark, Douglas M.; Envia, Edmane; Burley, Caesy L.

    2010-01-01

    This paper describes the use of measured source data to assess the effects of acoustic source specification on rotor-stator interaction noise predictions. Specifically, the acoustic propagation and radiation portions of a recently developed coupled computational approach are used to predict tonal rotor-stator interaction noise from a benchmark configuration. In addition to the use of full measured data, randomization of source mode relative phases is also considered for specification of the acoustic source within the computational approach. Comparisons with sideline noise measurements are performed to investigate the effects of various source descriptions on both inlet and exhaust predictions. The inclusion of additional modal source 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 source 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.

  18. Tunable coherent soft X-ray source based on the generation of high-order harmonic of femtosecond laser radiation in gas-filled capillaries

    SciTech Connect

    Malkov, Yu A; Yashunin, D A; Kiselev, A M; Stepanov, A N; Andreev, N E

    2014-05-30

    We have carried out experimental and theoretical investigations of a tunable coherent soft X-ray radiation source in the 30 – 52 nm wavelength range based on the generation of high-order harmonics of femtosecond laser radiation propagating in a dielectric xenon-filled capillary. The long path of laser pulse propagation through the capillary permits tuning the generated harmonic wavelengths to almost completely span the range under consideration. (interaction of radiation with matter)

  19. Obtaining Measurements of Stationary Environmental Noise Sources. Module 2. Vocational Education Training in Environmental Health Sciences.

    ERIC Educational Resources Information Center

    Consumer Dynamics Inc., Rockville, MD.

    This module, one of 25 on vocational education training for careers in environmental health occupations, contains self-instructional materials on obtaining measurements of stationary environmental noise sources. Following guidelines for students and instructors and an introduction that explains what the student will learn are three lessons: (1)…

  20. Integrated Study of Time-Frequency Representations and Their Applications in Source Identification of Mechanical Noise

    NASA Astrophysics Data System (ADS)

    Pan, Min-Chun

    Three computation schemes of time-frequency representations have been developed and implemented to identify different components of mechanical noise emitted from the transmission system of electrical vehicles. This study explores the close relationships between three time-frequency representations, i. e. the spectrogram based on windowed Fourier transform, the Wigner-Ville distribution, and the smoothed Wigner-Ville distribution. One main purpose is to pursue the efficiency of computing the smoothed Wigner-Ville distribution of a dynamic signature. The revised scheme can tremendously reduce the computation time to a scale of around 1/90, compared with the original scheme. To assess the validation of these time-frequency representation schemes, firstly, four synthetic signals are designed and processed. Secondly, the developed time-frequency representations are applied to distinguish different spectral components of transmission noise, and identify their sources. This study takes an electrical scooter with a continuous variable transmission system as a test bench. The continuous-variable-transmission-belt noise, helical-gear whine noise, and fan noise can be clearly identified via the processing of the time-frequency representations. These obtained conclusions can be used as references for machine element modification to reduce annoying noise.

  1. Use of a Microphone Phased Array to Determine Noise Sources in a Rocket Plume

    NASA Technical Reports Server (NTRS)

    Panda, J.; Mosher, R.

    2010-01-01

    A 70-element microphone phased array was used to identify noise sources 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 sources 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 noise. The beamform map was superimposed on a photo of the rocket plume to readily identify the source distribution. It was found that the plume made an exceptionally long, >30 diameter, noise source over a large frequency range. The shock pattern created spatial modulation of the noise source. Interestingly, the concrete pad of the horizontal test stand was found to be a good acoustic reflector: the beamform map showed two distinct source 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 noise sources at lower frequencies and produced excessive side-lobes at higher frequencies. The "advanced" beamform

  2. Objective approach for analysis of noise source characteristics and acoustic conditions in noisy computerized embroidery workrooms.

    PubMed

    Aliabadi, Mohsen; Golmohammadi, Rostam; Mansoorizadeh, Muharram

    2014-03-01

    It is highly important to analyze the acoustic properties of workrooms in order to identify best noise control measures from the standpoint of noise exposure limits. Due to the fact that sound pressure is dependent upon environments, it cannot be a suitable parameter for determining the share of workroom acoustic characteristics in producing noise pollution. This paper aims to empirically analyze noise source characteristics and acoustic properties of noisy embroidery workrooms based on special parameters. In this regard, reverberation time as the special room acoustic parameter in 30 workrooms was measured based on ISO 3382-2. Sound power quantity of embroidery machines was also determined based on ISO 9614-3. Multiple linear regression was employed for predicting reverberation time based on acoustic features of the workrooms using MATLAB software. The results showed that the measured reverberation times in most of the workrooms were approximately within the ranges recommended by ISO 11690-1. Similarity between reverberation time values calculated by the Sabine formula and measured values was relatively poor (R (2) = 0.39). This can be due to the inaccurate estimation of the acoustic influence of furniture and formula preconditions. Therefore, this value cannot be considered representative of an actual acoustic room. However, the prediction performance of the regression method with root mean square error (RMSE) = 0.23 s and R (2) = 0.69 is relatively acceptable. Because the sound power of the embroidery machines was relatively high, these sources get the highest priority when it comes to applying noise controls. Finally, an objective approach for the determination of the share of workroom acoustic characteristics in producing noise could facilitate the identification of cost-effective noise controls. PMID:24214295

  3. Noise Sources in a Low-Reynolds-Number Turbulent Jet at Mach 0.9

    NASA Technical Reports Server (NTRS)

    Freund, Jonathan B.

    2001-01-01

    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 source in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic source 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 source is coincident with neither the peak of the full unfiltered source 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 noise sources convect at a single velocity. Space-time correlations demonstrate that the sources are not acoustically compact in the streamwise direction and that the portion of the source that radiates at angles greater than 45 deg. is stationary. Filtering non-radiating wavenumber components of the source at single frequencies reveals that a simple modulated wave forms for the source, as might be predicted by linear stability analysis. At small angles from the jet axis the noise from these modes is highly directional, better described by an exponential than a standard Doppler factor.

  4. Supersonic jet noise prediction and noise source investigation for realistic baseline and chevron nozzles based on hybrid RANS/LES simulations

    NASA Astrophysics Data System (ADS)

    Du, Yongle

    Jet noise 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 noise generation mechanisms of shock-containing supersonic hot jets and the noise reduction mechanisms of chevron nozzles. A hybrid methodology combining advanced CFD technologies and the acoustic analogy is used for supersonic jet noise simulations. Unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved to predict the turbulent noise sources 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. Noise 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 noise 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 noise 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

  5. Required distribution of noise sources for Green's function recovery in diffusive fields

    NASA Astrophysics Data System (ADS)

    Shamsalsadati, S.; Weiss, C. J.

    2011-12-01

    In the most general sense, noise is the part of the signal of little or no interest, due to a multitude of reasons such as operator error, imperfect instrumentation, experiment design, or inescapable background interference. Considering the latter, it has been shown that Green's function can be extracted from cross-correlation of the ambient, diffusive wavefields arising from background random noise sources. Pore pressure and low-frequency electromagnetic induction are two such examples of diffusive fields. In theory, applying Green's function method in geophysical exploration requires infinity of volumetrically distributed sources; however, in the real world the number of noise sources in an area is limited, and furthermore, unevenly distributed in time, space and spectral content. Hence, quantification of the requisite noise sources that enable us to calculate Green's function acceptably well remains an open research question. The purpose of this study is to find the area of noise sources that contribute most to the Green's function estimation in diffusive systems. We call such a region the Volume of Relevance (VoR). Our analysis builds upon recent work in 1D homogeneous system where it was shown that sources located between two receivers positions are the most important ones for the purpose of Green's function recovery. Our results confirm the previous finding but we also examine the effect of heterogeneity, dimensionality and receiver location in both 1D and 2D at a fixed frequency. We demonstrate that for receivers located symmetrically across an interface between regions of contrasting diffusivity, the VoR rapidly shifts from one side of the interface to the other, and back again, as receiver separation increases. We also demonstrate that where the receiver pair is located on the interface itself, the shifting is less rapid, and for moderate to high diffusivity contrasts, the VoR remains entirely on the more diffusive side. In addition, because classical

  6. Ocean-Based Seismic Noise Sources Recorded by a Moderate Aperture Array in Antarctica

    NASA Astrophysics Data System (ADS)

    Pratt, M. J.; Winberry, J. P.; Wiens, D.; Anandakrishnan, S.; Euler, G. G.

    2015-12-01

    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 noise sources. The location of Antarctica, surrounded by the Southern Ocean and the seasonal effect of sea ice on shallow water noise 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 noise 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 sourced 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 sourced 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 noise spectra showing diminishment in the 15 s and 6 s bands [Grob et al. 2011]. Modeling of secondary microseism sources [Ardhuin et al. 2011] provides insight on the sources of surface wave noise at higher frequencies. We backproject daily P and PKPbc body wave microseism signals found at lower ray parameters sourced at distances of ~20-90° and ~145-155° respectively. The ocean sources for these arrivals remain fairly consistent, suggesting a

  7. Further Progress in Noise Source Identification in High Speed Jets via Causality Principle

    NASA Technical Reports Server (NTRS)

    Panda, J.; Seasholtz, R. G.; Elam, K. A.

    2004-01-01

    To locate noise sources 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 noise floor. Among all correlations < puu; p/> showed the highest values. Interestingly, , in all respects, were very similar to . The and correlations with 90deg microphone fell below the noise floor. By moving the laser probe at various locations in the jet it was found that the strongest noise source 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 noise 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 noise floor.

  8. RF dynamic and noise performance of Metallic Source/Drain SOI n-MOSFETs

    NASA Astrophysics Data System (ADS)

    Martin, Maria J.; Pascual, Elena; Rengel, Raúl

    2012-07-01

    This paper presents a detailed study of the RF and noise 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 noise 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 noise 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 noise sources 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 noise performance of the SB-MOSFET has no significant impact on high-frequency noise FoMs as NFmin, Rn and Gass for low SBH and large gate overdrive conditions. The role of the SBH on Γopt, optimum noise reactance and susceptance has been also analyzed.

  9. Methods for designing treatments to reduce interior noise of predominant sources and paths in a single engine light aircraft

    NASA Technical Reports Server (NTRS)

    Hayden, Richard E.; Remington, Paul J.; Theobald, Mark A.; Wilby, John F.

    1985-01-01

    The sources and paths by which noise enters the cabin of a small single engine aircraft were determined through a combination of flight and laboratory tests. The primary sources of noise were found to be airborne noise from the propeller and engine casing, airborne noise from the engine exhaust, structureborne noise from the engine/propeller combination and noise 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 noise was found to enter the cabin primarily through the panels in the vicinity of the exhaust outlet although exhaust noise entering the cabin through the firewall is a distinct possibility. A number of noise control techniques were tried, including firewall stiffening to reduce engine and propeller airborne noise, to stage isolators and engine mounting spider stiffening to reduce structure-borne noise, and wheel well covers to reduce air flow noise.

  10. Phase noise measurement of wideband microwave sources based on a microwave photonic frequency down-converter.

    PubMed

    Zhu, Dengjian; Zhang, Fangzheng; Zhou, Pei; Pan, Shilong

    2015-04-01

    An approach for phase noise measurement of microwave signal sources 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 noise 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 noise measurement sensitivity can be achieved since the signal degradation caused by electrical amplifiers is avoided. An experiment is carried out. The phase noise 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 noise 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.

  11. Phase noise measurement of wideband microwave sources based on a microwave photonic frequency down-converter.

    PubMed

    Zhu, Dengjian; Zhang, Fangzheng; Zhou, Pei; Pan, Shilong

    2015-04-01

    An approach for phase noise measurement of microwave signal sources 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 noise 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 noise measurement sensitivity can be achieved since the signal degradation caused by electrical amplifiers is avoided. An experiment is carried out. The phase noise 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 noise 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. PMID:25831324

  12. Evaluation of online information sources on alien species in Europe: the need of harmonization and integration.

    PubMed

    Gatto, Francesca; Katsanevakis, Stelios; Vandekerkhove, Jochen; Zenetos, Argyro; Cardoso, Ana Cristina

    2013-06-01

    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. Harmonization, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites. PMID:23609303

  13. Evaluation of Online Information Sources on Alien Species in Europe: The Need of Harmonization and Integration

    NASA Astrophysics Data System (ADS)

    Gatto, Francesca; Katsanevakis, Stelios; Vandekerkhove, Jochen; Zenetos, Argyro; Cardoso, Ana Cristina

    2013-06-01

    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. Harmonization, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites.

  14. Evaluation of online information sources on alien species in Europe: the need of harmonization and integration.

    PubMed

    Gatto, Francesca; Katsanevakis, Stelios; Vandekerkhove, Jochen; Zenetos, Argyro; Cardoso, Ana Cristina

    2013-06-01

    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. Harmonization, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites.

  15. Power Output of Noise Sources Operating Near Elastic Scatterers of Finite Dimensions

    NASA Astrophysics Data System (ADS)

    TOMILINA, T. M.; BOBROVNITSKII, YU. I.; YASHKIN, V. B.; KOCHKIN, A. A.

    1999-09-01

    The problem of variation of the sound power output of noise sources due to reflecting boundaries and elastic scatterers is considered experimentally and numerically. In the laboratory experiment with a source of loudspeakers operating near a resonant scatterer, the increase in the radiated power obtained is about one hundred. An important role of the source near field in the power enhancement is shown. In computer simulation, a two-dimensional radiation problem for a circle vibrating near a finite elastic beam is studied. Most attention is paid to revealing physical mechanisms of the power output variations. It is shown that, for the source and elastic scatterer of finite dimensions, the radiated power can reach orders of magnitude of the free-field value. Especially, high-power amplification can be obtained at low frequencies for the sources that are poor radiators in free space, i.e., behave as multipoles of high order: presence of a scatterer or reflector makes such a source to be of monopole or dipole type. The results presented can be useful in better understanding sound generation mechanisms in complicated industrial noise sources.

  16. Single-Shot Diffractive Imaging with a Table-Top Femtosecond Soft X-Ray Laser-Harmonics Source

    SciTech Connect

    Ravasio, A.; Gauthier, D.; Billon, M.; Caumes, J-P.; Garzella, D.; Geleoc, M.; Gobert, O.; Hergott, J-F.; Pena, A-M.; Perez, H.; Carre, B.; Maia, F. R. N. C.; Bourhis, E.; Gierak, J.; Madouri, A.; Mailly, D.; Schiedt, B.; Fajardo, M.; Gautier, J.; Zeitoun, P.

    2009-07-10

    Coherent x-ray diffractive imaging is a powerful method for studies on nonperiodic structures on the nanoscale. Access to femtosecond dynamics in major physical, chemical, and biological processes requires single-shot diffraction data. Up to now, this has been limited to intense coherent pulses from a free electron laser. Here we show that laser-driven ultrashort x-ray sources offer a comparatively inexpensive alternative. We present measurements of single-shot diffraction patterns from isolated nano-objects with a single 20 fs pulse from a table-top high-harmonic x-ray laser. Images were reconstructed with a resolution of 119 nm from the single shot and 62 nm from multiple shots.

  17. Windmill Noise Annoyance, Visual Aesthetics, and Attitudes towards Renewable Energy Sources

    PubMed Central

    Klæboe, Ronny; Sundfør, Hanne Beate

    2016-01-01

    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 noise 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 noise 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 source (hydropower is an important alternative source of renewables in Norway). Attitudes play an important role in addition to visual aesthetics in determining the acceptance of windmills and the resulting noise annoyance. To compare results from different wind turbine noise studies it seems necessary to assess the impact of important modifying factors. PMID:27455301

  18. Windmill Noise Annoyance, Visual Aesthetics, and Attitudes towards Renewable Energy Sources.

    PubMed

    Klæboe, Ronny; Sundfør, Hanne Beate

    2016-07-23

    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 noise 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 noise 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 source (hydropower is an important alternative source of renewables in Norway). Attitudes play an important role in addition to visual aesthetics in determining the acceptance of windmills and the resulting noise annoyance. To compare results from different wind turbine noise studies it seems necessary to assess the impact of important modifying factors.

  19. Windmill Noise Annoyance, Visual Aesthetics, and Attitudes towards Renewable Energy Sources.

    PubMed

    Klæboe, Ronny; Sundfør, Hanne Beate

    2016-01-01

    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 noise 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 noise 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 source (hydropower is an important alternative source of renewables in Norway). Attitudes play an important role in addition to visual aesthetics in determining the acceptance of windmills and the resulting noise annoyance. To compare results from different wind turbine noise studies it seems necessary to assess the impact of important modifying factors. PMID:27455301

  20. Noise-Source Separation Using Internal and Far-Field Sensors for a Full-Scale Turbofan Engine

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.; Miles, Jeffrey H.

    2009-01-01

    Noise-source separation techniques for the extraction of the sub-dominant combustion noise from the total noise 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-noise prediction capability of the Aircraft Noise Prediction Program (ANOPP). A new additional phase-angle-based discriminator for the three-signal method is also introduced.

  1. Source localization of turboshaft engine broadband noise using a three-sensor coherence method

    NASA Astrophysics Data System (ADS)

    Blacodon, Daniel; Lewy, Serge

    2015-03-01

    Turboshaft engines can become the main source of helicopter noise 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 noise levels. A broadband component is the most annoying but its sources are not well known (it is called internal or core noise). Present study was made in the framework of the European project TEENI (Turboshaft Engine Exhaust Noise Identification). Its main objective was to localize the broadband sources in order to better reduce them. Several diagnostic techniques were implemented by the various TEENI partners. As regards ONERA, a first attempt at separating sources was made in the past with Turbomeca using a three-signal coherence method (TSM) to reject background non-acoustic noise. 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 source and can be attributed to indirect combustion noise (accuracy decreases above 700 Hz because coherence is lower, but far-field sound spectra

  2. Activation process in excitable systems with multiple noise sources: One and two interacting units.

    PubMed

    Franović, Igor; Todorović, Kristina; Perc, Matjaž; Vasović, Nebojša; Burić, Nikola

    2015-12-01

    We consider the coaction of two distinct noise sources on the activation process of a single excitable unit and two interacting excitable units, which are mathematically described by the Fitzhugh-Nagumo equations. We determine the most probable activation paths around which the corresponding stochastic trajectories are clustered. The key point lies in introducing appropriate boundary conditions that are relevant for a class II excitable unit, which can be immediately generalized also to scenarios involving two coupled units. We analyze the effects of the two noise sources on the statistical features of the activation process, in particular demonstrating how these are modified due to the linear or nonlinear form of interactions. Universal properties of the activation process are qualitatively discussed in the light of a stochastic bifurcation that underlies the transition from a stochastically stable fixed point to continuous oscillations. PMID:26764778

  3. Activation process in excitable systems with multiple noise sources: One and two interacting units

    NASA Astrophysics Data System (ADS)

    Franović, Igor; Todorović, Kristina; Perc, Matjaž; Vasović, Nebojša; Burić, Nikola

    2015-12-01

    We consider the coaction of two distinct noise sources on the activation process of a single excitable unit and two interacting excitable units, which are mathematically described by the Fitzhugh-Nagumo equations. We determine the most probable activation paths around which the corresponding stochastic trajectories are clustered. The key point lies in introducing appropriate boundary conditions that are relevant for a class II excitable unit, which can be immediately generalized also to scenarios involving two coupled units. We analyze the effects of the two noise sources on the statistical features of the activation process, in particular demonstrating how these are modified due to the linear or nonlinear form of interactions. Universal properties of the activation process are qualitatively discussed in the light of a stochastic bifurcation that underlies the transition from a stochastically stable fixed point to continuous oscillations.

  4. Ambient noise tomography with non-uniform noise sources and low aperture networks: case study of deep geothermal reservoirs in northern Alsace, France

    NASA Astrophysics Data System (ADS)

    Lehujeur, Maximilien; Vergne, Jérôme; Maggi, Alessia; Schmittbuhl, Jean

    2016-10-01

    We developed and applied a method for ambient noise surface wave tomography that can deal with noise cross-correlation functions governed to first order by a non-uniform distribution of the ambient seismic noise sources. The method inverts the azimuthal distribution of noise sources 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 noise 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 noise 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 noise 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.

  5. Polarization of microwave noise source radiation in the 30 GHz to 300 GHz range

    NASA Technical Reports Server (NTRS)

    Poutous, M. K.; Petrone, P.; Ghaemi, A.; Moller, K. D.; Heaney, J. B.

    1988-01-01

    Radiation spectra have been obtained in order to calculate the frequency bandwidth and polarization of three microwave noise sources. Results were obtained in the 1-10-mm wavelength region using a lamellar grating Fourier transform spectrometer and a helium-cooled bolometer detector. A secondary transmission region was found to have an input current as well as a polarization dependence, despite the directional output of the waveguide antenna.

  6. Sound Source Identification Through Flow Density Measurement and Correlation With Far Field Noise

    NASA Technical Reports Server (NTRS)

    Panda, J.; Seasholtz, R. G.

    2001-01-01

    Sound sources 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 noise. 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.

  7. Three-Dimensional Application of DAMAS Methodology for Aeroacoustic Noise Source Definition

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Humphreys, William M., Jr.

    2005-01-01

    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 Sources (DAMAS) was developed which decouples the array design and processing influence from the noise being measured, using a simple and robust algorithm. For several prior airframe noise studies, it was shown to permit an unambiguous and accurate determination of acoustic source 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 source 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 noise 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 noise source distributions in a difficult hard-wall wind tunnel environment.

  8. Sources of noise during accumulation of evidence in unrestrained and voluntarily head-restrained rats

    PubMed Central

    Scott, Benjamin B; Constantinople, Christine M; Erlich, Jeffrey C; Tank, David W; Brody, Carlos D

    2015-01-01

    Decision-making behavior is often characterized by substantial variability, but its source remains unclear. We developed a visual accumulation of evidence task designed to quantify sources of noise 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 source of noise 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 noise could be important in accumulation of evidence tasks generally. DOI: http://dx.doi.org/10.7554/eLife.11308.001 PMID:26673896

  9. Closely Spaced MEG Source Localization and Functional Connectivity Analysis Using a New Prewhitening Invariance of Noise Space Algorithm.

    PubMed

    Zhang, Junpeng; Cui, Yuan; Deng, Lihua; He, Ling; Zhang, Junran; Zhang, Jing; Zhou, Qun; Liu, Qi; Zhang, Zhiguo

    2016-01-01

    This paper proposed a prewhitening invariance of noise space (PW-INN) as a new magnetoencephalography (MEG) source analysis method, which is particularly suitable for localizing closely spaced and highly correlated cortical sources under real MEG noise. Conventional source localization methods, such as sLORETA and beamformer, cannot distinguish closely spaced cortical sources, especially under strong intersource correlation. Our previous work proposed an invariance of noise space (INN) method to resolve closely spaced sources, but its performance is seriously degraded under correlated noise between MEG sensors. The proposed PW-INN method largely mitigates the adverse influence of correlated MEG noise by projecting MEG data to a new space defined by the orthogonal complement of dominant eigenvectors of correlated MEG noise. Simulation results showed that PW-INN is superior to INN, sLORETA, and beamformer in terms of localization accuracy for closely spaced and highly correlated sources. Lastly, source connectivity between closely spaced sources can be satisfactorily constructed from source time courses estimated by PW-INN but not from results of other conventional methods. Therefore, the proposed PW-INN method is a promising MEG source analysis to provide a high spatial-temporal characterization of cortical activity and connectivity, which is crucial for basic and clinical research of neural plasticity.

  10. Closely Spaced MEG Source Localization and Functional Connectivity Analysis Using a New Prewhitening Invariance of Noise Space Algorithm

    PubMed Central

    Zhang, Junpeng; Cui, Yuan; Deng, Lihua; He, Ling; Zhang, Junran; Zhang, Jing; Zhou, Qun; Liu, Qi; Zhang, Zhiguo

    2016-01-01

    This paper proposed a prewhitening invariance of noise space (PW-INN) as a new magnetoencephalography (MEG) source analysis method, which is particularly suitable for localizing closely spaced and highly correlated cortical sources under real MEG noise. Conventional source localization methods, such as sLORETA and beamformer, cannot distinguish closely spaced cortical sources, especially under strong intersource correlation. Our previous work proposed an invariance of noise space (INN) method to resolve closely spaced sources, but its performance is seriously degraded under correlated noise between MEG sensors. The proposed PW-INN method largely mitigates the adverse influence of correlated MEG noise by projecting MEG data to a new space defined by the orthogonal complement of dominant eigenvectors of correlated MEG noise. Simulation results showed that PW-INN is superior to INN, sLORETA, and beamformer in terms of localization accuracy for closely spaced and highly correlated sources. Lastly, source connectivity between closely spaced sources can be satisfactorily constructed from source time courses estimated by PW-INN but not from results of other conventional methods. Therefore, the proposed PW-INN method is a promising MEG source analysis to provide a high spatial-temporal characterization of cortical activity and connectivity, which is crucial for basic and clinical research of neural plasticity. PMID:26819768

  11. Improved PHIP polarization using a precision, low noise, voltage controlled current source.

    PubMed

    Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn

    2013-10-01

    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 source (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 source (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low noise 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 noise, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low noise, 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 noise 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 noise, 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.

  12. Improved PHIP polarization using a precision, low noise, voltage controlled current source

    NASA Astrophysics Data System (ADS)

    Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn

    2013-10-01

    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 source (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 source (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low noise 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 noise, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low noise, 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 noise 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 noise, 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.

  13. Icequakes and ambient noise sources detected by a geophone array at the Kaskawulsh glacier

    NASA Astrophysics Data System (ADS)

    Aso, N.; Tsai, V. C.; Schoof, C.; Whiteford, A.; Flowers, G. E.

    2015-12-01

    Both sliding and meltwater drainage processes of glaciers are expected to generate seismic signals. The confluence of the North and Central arms of the Kaskawulsh glacier in the Yukon Territory is an especially attractive place to study such phenomena not only because of the confluence but also because a nearby ice-dammed lake fills and drains rapidly every summer. We analyzed geophone data from nine stations at the Kaskawulsh glacier during the summer of 2014 to detect and locate icequakes and ambient noise sources. We first detected icequakes automatically by picking arrivals. Then we located events using differential arrival times between stations obtained precisely by cross-correlations, and also applied a double-difference relocation technique. During the 1-month observation period, we found 183 events that clustered near the medial moraine. More icequakes are observed from midnight to noon, potentially due to lower noise levels. These events are distributed on a dipping plane sub-parallel to the glacier flow direction. The depths below the surface range from 200m on the shallower side to 500m on the deeper side. This structure may correspond to the basal slope of the medial moraine and implies that these icequake signals come from either shear basal sliding or an englacial splay fault. We also determined ambient noise source locations for each 1-hour record sequence using the same process as for the icequakes. We located 31 sequences, among which more sequences were observed in the afternoon, possibly related to melting of the glacier. Most of the ambient noise sequences were located in two vertical clusters, with each cluster potentially corresponding to a crevasse or a moulin. We interpret this ambient noise as being produced by meltwater drainage. In both analyses, we find that inter-station differential arrival times obtained by cross-correlations provide effective information to locate sliding or meltwater drainage processes.

  14. Improved PHIP polarization using a precision, low noise, voltage controlled current source.

    PubMed

    Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn

    2013-10-01

    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 source (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 source (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low noise 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 noise, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low noise, 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 noise 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 noise, 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. PMID:23988431

  15. Correction of phase velocity bias caused by strong directional noise sources in high-frequency ambient noise tomography: a case study in Karamay, China

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Luo, Yinhe; Yang, Yingjie

    2016-05-01

    We collect two months of ambient noise 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 noise data between all station pairs. Array beamforming analysis of the ambient noise data shows that ambient noise sources are unevenly distributed and the most energetic ambient noise mainly comes from azimuths of 40°-70°. As a consequence of the strong directional noise sources, 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 noise 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 noise sources, 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 noise 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 noise sources 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

  16. Experimentation Toward the Analysis of Gear Noise Sources Controlled by Sliding Friction and Surface Roughness

    NASA Technical Reports Server (NTRS)

    Asnani, Vivake M.

    2004-01-01

    In helicopters and other rotorcraft, the gearbox is a major source of noise 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, noise levels are still relatively high though transmission errors might be somewhat minimal. This suggests that sliding friction is indeed a dominant noise source for high power density rotorcraft gearboxes. In reality, friction source 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-Noise 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

  17. A comparison between exposure-response relationships for wind turbine annoyance and annoyance due to other noise sources.

    PubMed

    Janssen, Sabine A; Vos, Henk; Eisses, Arno R; Pedersen, Eja

    2011-12-01

    Surveys have shown that noise from wind turbines is perceived as annoying by a proportion of residents living in their vicinity, apparently at much lower noise levels than those inducing annoyance due to other environmental sources. The aim of the present study was to derive the exposure-response relationship between wind turbine noise exposure in L(den) and the expected percentage annoyed residents and to compare it to previously established relationships for industrial noise and transportation noise. 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 sources of environmental noise, annoyance due to wind turbine noise was found at relatively low noise 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 noise sensitivity had similar effects on annoyance to those found in research on annoyance by other sources.

  18. A comparison between exposure-response relationships for wind turbine annoyance and annoyance due to other noise sources.

    PubMed

    Janssen, Sabine A; Vos, Henk; Eisses, Arno R; Pedersen, Eja

    2011-12-01

    Surveys have shown that noise from wind turbines is perceived as annoying by a proportion of residents living in their vicinity, apparently at much lower noise levels than those inducing annoyance due to other environmental sources. The aim of the present study was to derive the exposure-response relationship between wind turbine noise exposure in L(den) and the expected percentage annoyed residents and to compare it to previously established relationships for industrial noise and transportation noise. 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 sources of environmental noise, annoyance due to wind turbine noise was found at relatively low noise 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 noise sensitivity had similar effects on annoyance to those found in research on annoyance by other sources. PMID:22225031

  19. Noise suppression of a dipole source by tensioned membrane with side-branch cavities.

    PubMed

    Liu, Y; Choy, Y S; Huang, L; Cheng, L

    2012-09-01

    Reducing the ducted-fan noise 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 noise 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 noise 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 source. Experimental validation is conducted with a loudspeaker as the dipole source and good agreement between the predicted and measured insertion loss is achieved.

  20. Noise suppression of a dipole source by tensioned membrane with side-branch cavities

    PubMed Central

    Liu, Y.; Choy, Y. S.; Huang, L.; Cheng, L.

    2012-01-01

    Reducing the ducted-fan noise 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 noise 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 noise 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 source. Experimental validation is conducted with a loudspeaker as the dipole source and good agreement between the predicted and measured insertion loss is achieved. PMID:22978868

  1. AIRUSE-LIFE+: a harmonized PM speciation and source apportionment in 5 Southern European cities

    NASA Astrophysics Data System (ADS)

    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.

    2015-09-01

    The AIRUSE-LIFE+ project aims at characterising similarities and heterogeneities in PM sources and contributions in urban areas from the Southern Europe. Once the main PMx sources 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 source 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 source 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

  2. Comparison of Noise Source Localization Data with Flow Field Data Obtained in Cold Supersonic Jets and Implications Regarding Broadband Shock Noise

    NASA Technical Reports Server (NTRS)

    Podboy, Gary; Wernet, Mark; Clem, Michelle; Fagan, Amy

    2013-01-01

    Phased array noise source localization have been compared with 2 types of flow field data (BOS and PIV). The data show that: 1) the higher frequency noise in a BBSN hump is generated further downstream than the lower frequency noise. 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 noise. 5) Some of the shocks responsible for producing the first hump also produce the second hump.

  3. A perspective on 30 years of progress in ambient noise: Source mechanisms and the characteristics of the sound field

    NASA Astrophysics Data System (ADS)

    Cato, Douglas H.

    2012-11-01

    The last 30 years has seen substantial progress in ocean ambient noise research, particularly in understanding the mechanisms of sound generation by the sources of ambient noise, the way in which the noise field is affected by sound propagation, and improvements in quantifying the relationship between noise and environmental parameters. This has led to significant improvements in noise 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 noise to measure properties of the environment and in its significance to marine life. There have been significant changes in the ambient noise itself over the last 30 years. The contribution from human activities appears to have increased, particularly that due to increases in shipping numbers. Biological noise 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 noise on marine animals as well as the way they exploit the noise has led to renewed interest in ambient noise.

  4. A study of rotor broadband noise mechanisms and helicopter tail rotor noise

    NASA Technical Reports Server (NTRS)

    Chou, Shau-Tak Rudy

    1990-01-01

    The rotor broadband noise 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 noise source for typical helicopters' main rotors at low- and mid-frequencies. Due to the size difference, isolated helicopter tail rotor broadband noise is not important compared to the much louder main rotor broadband noise. However, the inflow turbulence noise 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 source of tail rotor broadband noise. The harmonic noise due to ingestion of main rotor tip vortices is studied.

  5. In-situ source path contribution analysis of structure borne road noise

    NASA Astrophysics Data System (ADS)

    Elliott, A. S.; Moorhouse, A. T.; Huntley, T.; Tate, S.

    2013-11-01

    Source-path-contribution (SPC) analysis, also known as transfer path analysis (TPA), is a technique widely used in the automotive industry for rank ordering noise and vibration sources. The SPC approach is known to provide reliable diagnostic information but is time consuming to apply. In this paper, a faster SPC approach that allows all measurements to be performed in-situ is outlined and tested. For validation purposes a classic example consisting of a vehicle's suspension system (considered a vibration source) attached to a vehicle body (receiver) is analysed. It is found that structure borne noise inside the vehicle can be predicted well by either the conventional or the novel in-situ SPC approaches and that both methods give the same diagnostic information in terms of the rank ordering of path contributions. Thus, the new in-situ approach provides results at least as reliable as the conventional inverse SPC approach but has significant practical advantages in terms of reduced test time, transferability of data and flexibility in the location of the source-receiver interface. An additional investigation also demonstrates the feasibility of including rotational motions and moments in the analysis and it is shown that improved accuracy can be achieved as a result.

  6. Identification and Control of Noise Source Mechanisms in a Transonic Axisymmetric Jet

    NASA Astrophysics Data System (ADS)

    Hall, Andre; Pinier, Jeremy; Glauser, Mark

    2006-11-01

    An experimental examination aimed at characterizing the aeroacoustic effect linked to the turbulent mixing of the exhausted jet plume with the ambient air in high-speed jets is comprised of a 50.8mm nozzle at Mach 0.85, operated under both heated (260oC) and room temperature (0oC) conditions. Both the hydrodynamic near- field and acoustic far-field pressure regions are examined. The near- field using an azimuthal array of fifteen (15) dynamic response pressure transducers positioned near the jet’s lip, and the far- field using a boom array of six (6) acoustic microphones (6.35mm in diameter). Instantaneous 3 component velocity measurements are acquired, simultaneously, in the r, theta plane at several streamwise positions between z/D=3:8 (the region where the sound producing events are found to be dominant) using a stereo PIV system. This data set is utilized in conjunction with multi-point low-dimensional techniques to characterize a low-dimensional description of the velocity field, with minimal effect on far-field acoustics. The low- dimensional description of the velocity field is examined to identify the dominant noise source mechanism in both jets. Calculation of a modified Lighthill source term, and azimuthal modal forcing, are used as a measure of source intensity and a gauge for noise reduction schemes, respectively. Where control of noise sources is concerned, a modal analysis of the near-field region has shown that modal forcing may prove a promising method. We greatly acknowledge the support of the AFOSR and the CNY-PR AGEP Alliance.

  7. Low Speed, 2-D Rotor/Stator Active Noise Control at the Source Demonstration

    NASA Technical Reports Server (NTRS)

    Simonich, John C.; Kousen, Ken A.; Zander, Anthony C.; Bak, Michael; Topol, David A.

    1997-01-01

    Wake/blade-row interaction noise 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 noise control at the source for active rotor/stator noise control at the source, 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

  8. Research In Helicopter Noise

    NASA Technical Reports Server (NTRS)

    Yu, Yung H.; Schmitz, Frederic H.; Morse, Andrew H.

    1991-01-01

    Progress in aeroacoustical theory and experiments reviewed. Report summarizes continuing U.S. Army programs of research into causes of noise generated by helicopters. Topics of study include high-speed impulsive noise, blade/vortex-interaction noise, and low-frequency harmonic noise.

  9. Quantifying noise sources in the KSTAR 2014 Thomson Scattering system from the measured variation on electron temperature

    NASA Astrophysics Data System (ADS)

    Oh, T.-S.; Kim, K. H.; Lee, J. H.; Lee, S. H.; Scannell, R.; Field, A. R.; Cho, K.; Bawa'aneh, M. S.; Ghim, Y.-c.

    2016-03-01

    With the Thomson scattering (TS) system in KSTAR, temporal evolution of electron temperature (Te) is estimated using a weighted look-up table method with fast sampling (1.25 or 2.5 GS/s) digitizers during the 2014 KSTAR campaign. Background noise level is used as a weighting parameter without considering the photon noise due to the absence of information on absolute photon counts detected by the TS system. Estimated electron temperature during a relatively quiescent discharge are scattered, i.e., 15% variation on Te with respect to its mean value. We find that this 15% variation on Te cannot be explained solely by the background noise level which leads us to include photon noise effects in our analysis. Using synthetic data, we have estimated the required photon noise level consistent with the observation and determined the dominant noise source in KSTAR TS system.

  10. Effects of shallow trench isolation on low frequency noise characteristics of source-follower transistors in CMOS image sensors

    NASA Astrophysics Data System (ADS)

    Kwon, Sung-Kyu; Kwon, Hyuk-Min; Choi, Woon-Il; Song, Hyeong-Sub; Lee, Hi-Deok

    2016-05-01

    The effects of the shallow trench isolation (STI) edge on low frequency noise characteristics of source-follower (SF) transistors in CMOS image sensors (CIS) were investigated. Random telegraph signal (RTS) noise and 1/f noise were measured in a CIS operating voltage region for a realistic assessment. SF transistor with STI edge in contact with channel shows a lower probability of generating RTS noise but greater RTS amplitude due to the enhanced trap density induced by STI-induced damage. SF MOSFETs without STI exhibit a much lower 1/f noise power spectral density in spite of the greater RTS generation probability, which is due to the decreased trap density. Therefore, SF transistors without STI edge in contact with channel are promising candidates for low noise CIS applications.

  11. Aeroacoustics of Flight Vehicles: Theory and Practice. Volume 1: Noise Sources

    NASA Technical Reports Server (NTRS)

    Hubbard, Harvey H. (Editor)

    1991-01-01

    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 noise, rotor noise, turbomachinery noise, jet noise classical theory and experiments, noise from turbulent shear flows, jet noise generated by large-scale coherent motion, airframe noise, propulsive lift noise, combustion and core noise, and sonic booms.

  12. Noise control of dipole source by using micro-perforated panel housing

    NASA Astrophysics Data System (ADS)

    Xi, Q.; Choy, Y. S.; Cheng, L.; Tang, S. K.

    2016-02-01

    Mitigating low-frequency noise 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 noise 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 source, 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 source. Experimental validation is conducted with a loudspeaker to simulate the dipole source, and good agreement between the predicted and measured insertion loss (IL) is achieved.

  13. Sensitivity of earthquake source inversions to atmospheric noise and corrections of InSAR data

    NASA Astrophysics Data System (ADS)

    Scott, Chelsea Phipps; Lohman, Rowena Benfer

    2016-05-01

    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 noise 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 source 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 source parameter error bounds decrease in size after applying the atmospheric corrections. Our approach for evaluating the impact of atmospheric noise on inferred fault parameters is easily adaptable to other regions and source mechanisms.

  14. Differential near-edge coherent diffractive imaging using a femtosecond high-harmonic XUV light source.

    PubMed

    Weise, Fabian; Neumark, Daniel M; Leone, Stephen R; Gessner, Oliver

    2012-11-19

    Element-specific contrast enhancement in tabletop coherent diffractive imaging (CDI) is demonstrated by employing an ultrafast extreme ultraviolet (XUV) light source with tunable photon energy. By combining two measurements performed at energies below and above the Al L(2,3) absorption edge, the spatial autocorrelation function of a micron-scale double pinhole in a 300 nm thick aluminum foil is retrieved despite a dominant background signal from directly transmitted light across the entire range of detectable diffraction angles. The fringe visibility in the diffraction patterns is 0 below the Al L(2,3) edge, 0.53 ± 0.06 above the edge, and 0.73 ± 0.08 in the differential image that combines the two measurements. The proof-of-principle experiment demonstrates that the variations of XUV optical constants in the vicinity of an inner-shell absorption edge can be utilized to improve the chemical sensitivity and image reconstruction quality of laboratory-based ultrafast imaging experiments.

  15. Advanced turbo-prop airplane interior noise reduction-source definition

    NASA Technical Reports Server (NTRS)

    Magliozzi, B.; Brooks, B. M.

    1979-01-01

    Acoustic pressure amplitudes and phases were measured in model scale on the surface of a rigid semicylinder mounted in an acoustically treated wind tunnel near a prop-fan (an advanced turboprop with many swept blades) model. Operating conditions during the test simulated those of a prop-fan at 0.8 Mach number cruise. Acoustic pressure amplitude and phase contours were defined on the semicylinder surface. Measurements obtained without the semi-cylinder in place were used to establish the magnitude of pressure doubling for an aircraft fuselage located near a prop-fan. Pressure doubling effects were found to be 6dB at 90 deg incidence decreasing to no effect at grazing incidence. Comparisons of measurements with predictions made using a recently developed prop-fan noise prediction theory which includes linear and non-linear source terms showed good agreement in phase and in peak noise amplitude. Predictions of noise amplitude and phase contours, including pressure doubling effects derived from test, are included for a full scale prop-fan installation.

  16. Time Delay Analysis of Turbofan Engine Direct and Indirect Combustion Noise Sources

    NASA Technical Reports Server (NTRS)

    Miles, Jeffrey Hilton

    2008-01-01

    The core noise components of a dual spool turbofan engine were separated by the use of a coherence function. A source 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 noise 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 noise. Results are presented herein for engine power settings of 48, 54, and 60 percent of the maximum power setting

  17. A miniaturized electron source based on dielectric laser accelerator operation at higher spatial harmonics and a nanotip photoemitter

    NASA Astrophysics Data System (ADS)

    McNeur, Joshua; Kozak, Martin; Ehberger, Dominik; Schönenberger, Norbert; Tafel, Alexander; Li, Ang; Hommelhoff, Peter

    2016-02-01

    Here we propose a miniaturized electron source driven by recent experimental results of laser-triggered electron emission from tungsten nanotips and dielectric laser acceleration of sub relativistic electrons with velocities as low as 5.7× {10}7 {{m}} {{{s}}}-1 or energies as low as 9.6 keV, less than 20% of the speed of light. The recently observed laser-triggered emission of coherent low-emittance electron pulses from tungsten nanotips naturally lends itself towards incorporation with subrelativistic dielectric laser accelerators (DLAs). These structures have previously been shown to accelerate 28 keV electrons and here we report on the utilization of the 4th and 5th spatial harmonics of near fields in the single grating DLA to achieve acceleration of electrons with kinetic energies of 15.2 and 9.6 keV. We then propose the combination of needle tip emitters with subrelativistic accelerators to form a mm-scale device capable of producing electrons with arbitrary energies.

  18. Control of Environmental Noise

    ERIC Educational Resources Information Center

    Jensen, Paul

    1973-01-01

    Discusses the physical properties, sources, physiological effects, and legislation pertaining to noise, especially noise characteristics in the community. Indicates that noise reduction steps can be taken more intelligently after determination of the true noise sources and paths. (CC)

  19. Military jet noise source imaging using multisource statistically optimized near-field acoustical holography.

    PubMed

    Wall, Alan T; Gee, Kent L; Neilsen, Tracianne B; McKinley, Richard L; James, Michael M

    2016-04-01

    The identification of acoustic sources is critical to targeted noise reduction efforts for jets on high-performance tactical aircraft. This paper describes the imaging of acoustic sources 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 source 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 source location; sources 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 source regions, which is a phenomenon relatively recently reported for full-scale jets. PMID:27106340

  20. To Be or not to Be a Source of Shot Noise: an Open Problem of Generation Recombination Noise

    NASA Astrophysics Data System (ADS)

    Gomila, G.; Reggiani, L.

    2003-05-01

    We address the fundamental question wether generation recombination noise can transform into shot noise at increasing values of the applied bias (current or voltage). From the seminal work of Van Vliet and Fassett (1965) the analytical answer to this question is affirmative. By contrast, recent numerical results by Bonani and Ghione (1999) provided a negative answer. For a simple semiconductor two level model consisting of a conducting band and an impurity level which provides charge carriers we solve exactly the appropriate second order stochastic differential equation self-consistently coupled with the Poisson solver. The effect of the diffusion current, neglected in the first analytical approach, is found to inhibit the cross-over between generation-recombination and shot noise, thus confirming more recent numerical results. Open problems related to the microscopic interpretation of these new results are pointed out.

  1. Tracking Paths of Ocean Source Ambient Seismic Noise into, and through, the 3D Earth

    NASA Astrophysics Data System (ADS)

    Reading, A. M.; Gal, M.; Morse, P. E.; Koper, K. D.; Hemer, M. A.; Rawlinson, N.; Salmon, M.; De Kool, M.; Kennett, B. L. N.

    2014-12-01

    Array measurements of seismic noise (microseisms) are emerging as independent observables that inform our knowledge of ocean storms. Using an improved implementation of IAS Capon analysis, we can infer the location and amplitude of multiple sources of seismic noise over multiple decades. For the Southern Ocean, we can use seismic records to assist in identifying shifting patterns of ocean storms. Thus we can investigate topics such as the disparity between wave height trends identified using calibrated satellite records, which appear to be in increasing over multiple decades, and wave heights measured directly using a wave-rider buoy, which does not show a significant change over the same time frame. The passage of wave energy from the water column to the solid Earth, and through the 3D Earth to the seismic array must be tracked effectively. In this contribution, we focus on understanding the passage of seismic noise through the 3D Earth. In particular, we investigate path deviations from 1D Earth models for body waves sources from a variety of locations in the Southern Ocean recorded at Australian seismic arrays. We also investigate path deviations of surface waves travelling across the Australian continent, using the AusREM Earth model. We also appraise other factors affecting the interpretation of slowness, backazimuth and amplitude from seismic array records. These include the effect of the bathymetry-related transfer function controlling energy entering the solid Earth from the water column and the impact of local geology at the site of the seismic array. For a season of storms in the southern hemisphere winter, we simulate the path of energy from a representative range of locations to Australia seismic arrays. We employ a wavefront tracking technique, fast marching, that can support heterogeneous structure and the consideration of multiple arrivals. We find that storms in some locations are subject to a much larger deviation from the expected path of energy

  2. Methods for addressing noise and error in controlled source electromagnetic data

    NASA Astrophysics Data System (ADS)

    MacLennan, Kristopher

    Controlled source electromagnetic geophysical surveys are excellent ways to obtain information about the conductivity structure of the earth, with applications including hydrocarbon and mining prospecting, hydrogeophysical detection and monitoring, and civil and archaeological studies. Invariably, however, various types of noise and errors obscure signal for desired targets, making interpretation difficult. In the case of time-lapse surveys, the magnitude of the measured difference is often on the order of the noise. Complex conductivity effects distort the measurements, leading to incorrect inversion results. This work develops a method for extracting signal from noisy electromagnetic data sets from both time- and frequency-domain surveys using a novel application of the equivalent source technique. It improves data contaminated by uncorrelated random noise, such as that due to receiver coil misalignment and location errors in time-domain EM surveys, and can remove static shifts in the observed electric field amplitude data due to near-surface geologic features in frequency-domain EM surveys. The equivalent source method can either be applied individually to data from each measured time-gate or frequency, or simultaneously to data from all times or frequencies measured. The method can be used in addition to traditional processing techniques and requires little user input. The effectiveness of the method is demonstrated through application to single-survey and time-lapsed noisy time- and frequency-domain EM data, both synthetically generated and collected in the field. The presence of low-frequency (≤ 1 kHz) polarization effects in earth porous materials noticeably increases the amplitude and decreases the phase of measured electromagnetic fields in frequency-domain surveys. By analyzing the sensitivity of cross-well EM measurements to the in-phase and quadrature conductivities, the contribution of the quadrature conductivity (directly associated with the low

  3. Identifying seismic noise sources and their amplitude from P wave microseisms.

    NASA Astrophysics Data System (ADS)

    Neale, Jennifer; Harmon, Nicholas; Srokosz, Meric

    2016-04-01

    Understanding sources of seismic noise is important for a range of applications including seismic imagery, time-lapse, and climate studies. For locating sources from seismic data, body waves offer an advantage over surface waves because they can reveal the distance to the source 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 source (Ardhuin & Herbers, 2013). Here, we undertake a quantitative comparison between observed body wave microseisms and modelled sources- in terms of location, amplitude, and spectral shape- with the aim of understanding how well sources 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 sources using Wavewatch III and site effect coefficients calculated following Ardhuin and Herbers (2013). We output the beamformer and the modelled sources 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 source and the logarithm of the beamformer output are well described by a two-term exponential model

  4. Do tidal peaks help to discriminate the oceanic microseismic noise sources?

    NASA Astrophysics Data System (ADS)

    Beucler, E.; Mocquet, A.; Schimmel, M.; Chevrot, S.; Vergne, J.; Sylvander, M.; Quillard, O.

    2013-12-01

    Since the pioneer years of the seismology, the ubiquitous high-level of seismic energy in the period range 1-20 s, namely microseismic noise, has been clearly associated with the ocean wave activity. This noise bandwidth of the seismic spectrum defines the frontier between long-period and high-frequency transient seismology. The ``transient seismology'' terms comprise all research based on signals due to known sources such as earthquakes or volcano eruptions. Recently, many studies used the noisy unexploited part of the signal and revealed strong features for the seismic tomography and monitoring. One of the main hypothesis for noise cross-correlation techniques resides however in the assumption that the source distribution provides a random wave field between two stations. Due to the highly non-linear process of oceanic-to-seismic wave conversion, the characterization of a given source contribution is not unique. The Longuet-Higgins theory (later generalized for random waves by Hasselman) explains the existence of a primary peak around 14 s and a secondary microseismic peak (SMP) around 7 s, both. The latter, often named double-frequency peak, is much more energetic and lay between periods of 1 to 10 s; its origin (coastal or deep-ocean) is still under debate. In this study we use a few seismic broadband stations of the temporary PYROPE deployement, located on the French Atlantic coast, to analyze the seismic energy. For each component, high resolution Power Spectral Densities (PSD) are computed for time windows of 6 min. with a 60 s overlapping window; the median of four PSD is finally retained for each 20 minutes of the signal. PSD are computed between 0.01 and 10 Hz. Using the spectacular strong tidal effects on this coast as proxies, it is obvious that the behaviour of the short period range of the SMP is different from the energy observed at the frequency value corresponding to the double of the primary peak. This suggest that the SMP may be split into (at

  5. In-flight source noise of an advanced full-scale single-rotation propeller

    NASA Technical Reports Server (NTRS)

    Woodward, Richard P.; Loffler, Irvin J.

    1991-01-01

    Flight tests to define the far-field tone source at cruise conditions have been completed on the full-scale SR-7L advanced turboprop, which was installed on the left wing of a Gulfstream II aircraft. These measurements defined source levels for input into long-distance propagation models to predict en route noise. Infight data were taken for seven test cases. The sideline directivities measured showed expected maximum levels near 105 deg from the propeller upstream axis. However, azimuthal directivities based on the maximum observed sideline tone levels showed highest levels below the aircraft. The tone level reduction associated with reductions in propeller tip speed is shown to be more significant in the horizontal plane than below the aircraft.

  6. Broadband Seismic Analyses of the Crust and Noise Sources in Alberta, Canada

    NASA Astrophysics Data System (ADS)

    Shen, Luyi

    Cross-correlation of continuous seismic recordings has been proven effective in extracting the Green's function between two seismic stations. Travel-time and waveform source migration calculations jointly suggest a persistent noise source near Lesser Slave Lake (LSL), a large ice-covered lake in Alberta, Canada, during winter months. Subspace inversions of effective Green's functions from five narrow frequency bands (0.002-0.2 Hz) reveal low velocities in the upper crust beneath Alberta basin, which indicates strong effects from the thick platform sedimentary cover. Consistently low velocities are also observed beneath Wabamun domain but the areal coverage is considerably smaller than the published domain boundaries. The lower-crustal velocities beneath southern Loverna Block is 10% faster than the regional average. As the possible remnant cratonic core of the Hearne province, this northeast-striking anomaly extends to the western part of Medicine Hat Block and contributes to a strong east-west structural gradient in the latter domain.

  7. Identification of Noise Sources During Rocket Engine Test Firings and a Rocket Launch Using a Microphone Phased-Array

    NASA Technical Reports Server (NTRS)

    Panda, Jayanta; Mosher, Robert N.; Porter, Barry J.

    2013-01-01

    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 noise sources. The duct exit was found to be the primary source during the static test firing; the large amount of water injected beneath the nozzle exit and inside the plume duct quenched all other sources. The maps of the noise sources during launch were found to be time-dependent. As the engines came to full power and became louder, the primary source switched from the duct inlet to the duct exit. Further elevation of the vehicle caused spilling of the hot plume, resulting in a distributed noise 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 noise source. These maps of the noise sources provide vital insight for optimization of sound suppression systems for future Antares launches.

  8. Source impedance, transient response, and noise characterization of the TOPAZ 2 reactors

    SciTech Connect

    Kusnierkiewicz, D.Y.

    1995-01-20

    Electrical measurements have been performed on the TOPAZ 2 V-71 and Ya-21 Reactors, in order to characterize the source 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 noise 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 source 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 noise 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}

  9. Empirical sensitivity kernels of noise correlations with respect to virtual sources

    NASA Astrophysics Data System (ADS)

    Boué, P.; Stehly, L.; Nakata, N.; Beroza, G. C.

    2014-12-01

    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 sources. 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 source distribution. In this study, we discuss the possibility to use the correlation of ambient noise correlation (similar to C3 method) to map the contribution of different source 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 source. 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 noise 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.

  10. Multi-gamma-source CT imaging system: a feasibility study with the Poisson noise

    NASA Astrophysics Data System (ADS)

    Wi, Sunhee; Cho, Seungryong

    2016-03-01

    This study was performed to test the feasibility of multi-gamma-source CT imaging system. Gamma-source CT employs radioisotopes that emit monochromatic energy gamma-rays. The advantages of gamma-source 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-source CT would suffer from high noise in data. To address this problem, we proposed a multi-gamma source 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-source 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 sources. 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 sources 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.

  11. High-repetition-rate and high-photon-flux 70 eV high-harmonic source for coincidence ion imaging of gas-phase molecules.

    PubMed

    Rothhardt, Jan; Hädrich, Steffen; Shamir, Yariv; Tschnernajew, Maxim; Klas, Robert; Hoffmann, Armin; Tadesse, Getnet K; Klenke, Arno; Gottschall, Thomas; Eidam, Tino; Limpert, Jens; Tünnermann, Andreas; Boll, Rebecca; Bomme, Cedric; Dachraoui, Hatem; Erk, Benjamin; Di Fraia, Michele; Horke, Daniel A; Kierspel, Thomas; Mullins, Terence; Przystawik, Andreas; Savelyev, Evgeny; Wiese, Joss; Laarmann, Tim; Küpper, Jochen; Rolles, Daniel

    2016-08-01

    Unraveling and controlling chemical dynamics requires techniques to image structural changes of molecules with femtosecond temporal and picometer spatial resolution. Ultrashort-pulse x-ray free-electron lasers have significantly advanced the field by enabling advanced pump-probe schemes. There is an increasing interest in using table-top photon sources enabled by high-harmonic generation of ultrashort-pulse lasers for such studies. We present a novel high-harmonic source driven by a 100 kHz fiber laser system, which delivers 1011 photons/s in a single 1.3 eV bandwidth harmonic at 68.6 eV. The combination of record-high photon flux and high repetition rate paves the way for time-resolved studies of the dissociation dynamics of inner-shell ionized molecules in a coincidence detection scheme. First coincidence measurements on CH3I are shown and it is outlined how the anticipated advancement of fiber laser technology and improved sample delivery will, in the next step, allow pump-probe studies of ultrafast molecular dynamics with table-top XUV-photon sources. These table-top sources can provide significantly higher repetition rates than the currently operating free-electron lasers and they offer very high temporal resolution due to the intrinsically small timing jitter between pump and probe pulses. PMID:27505779

  12. Extraction of the local phase velocity and the group velocity from surface noise source in microseismic monitoring.

    NASA Astrophysics Data System (ADS)

    Chmiel, Malgorzata; Roux, Philippe; Bardainne, Thomas

    2015-04-01

    The aim of this work is to demonstrate the extraction of the local phase velocity and the group velocity from surface noise source in microseismic monitoring. One of the biggest challenges in microseismic monitoring is surface seismic noise. Microseismic surface studies are often contaminated with instrumental and ambient seismic noise, originating from both natural (wind, rain) and anthropogenic sources (injection, pumps, infrastructure, traffic). The two primary ways to attenuate the undesired surface noise sources 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 noise sources 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 noise source 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 noise sources per patch. The combination of all the maps per patch

  13. The differential Howland current source with high signal to noise ratio for bioimpedance measurement system

    SciTech Connect

    Liu, Jinzhen; Li, Gang; Lin, Ling; Qiao, Xiaoyan; Wang, Mengjun; Zhang, Weibo

    2014-05-15

    The stability and signal to noise ratio (SNR) of the current source 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 source 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 source 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 source 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.

  14. The differential Howland current source with high signal to noise ratio for bioimpedance measurement system.

    PubMed

    Liu, Jinzhen; Qiao, Xiaoyan; Wang, Mengjun; Zhang, Weibo; Li, Gang; Lin, Ling

    2014-05-01

    The stability and signal to noise ratio (SNR) of the current source 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 source 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 source 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 source 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.

  15. Combustion noise

    NASA Technical Reports Server (NTRS)

    Strahle, W. C.

    1977-01-01

    A review of the subject of combustion generated noise is presented. Combustion noise is an important noise source 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 noise importance, understanding, prediction and scaling is presented for these systems. The fundamentals and available theories of combustion noise are given. Controversies in the field are discussed and recommendations for future research are made.

  16. Extraction of small boat harmonic signatures from passive sonar.

    PubMed

    Ogden, George L; Zurk, Lisa M; Jones, Mark E; Peterson, Mary E

    2011-06-01

    This paper investigates the extraction of acoustic signatures from small boats using a passive sonar system. Noise radiated from a small boats consists of broadband noise and harmonically related tones that correspond to engine and propeller specifications. A signal processing method to automatically extract the harmonic structure of noise radiated from small boats is developed. The Harmonic Extraction and Analysis Tool (HEAT) estimates the instantaneous fundamental frequency of the harmonic tones, refines the fundamental frequency estimate using a Kalman filter, and automatically extracts the amplitudes of the harmonic tonals to generate a harmonic signature for the boat. Results are presented that show the HEAT algorithms ability to extract these signatures.

  17. [Flow of high-voltage current in coal electrodes of arc furnaces as a source of noise of special nature].

    PubMed

    Polanowska, R

    1984-01-01

    The noise level for working arc furnace has been measured. Arc furnaces were found to be the source of infrasounds and acoustic field. The sound pressure levels for infrasounds range from 55 to 77 dB. It has been showed that particular noise level includes the onethird-octave band with middle frequency 100 Hz. The sound pressure levels in this band range from 105 to 110 dB.

  18. Separation of combustion noise and piston-slap in diesel engine—Part II: Separation of combustion noise and piston-slap using blind source separation methods

    NASA Astrophysics Data System (ADS)

    Servière, C.; Lacoume, J.-L.; El Badaoui, M.

    2005-11-01

    This paper is devoted to blind separation of combustion noise and piston-slap in diesel engines. The two phenomena are recovered only from signals issued from accelerometers placed on one of the cylinders. A blind source separation (BSS) method is developed, based on a convolutive model of non-stationary mixtures. We introduce a new method based on the joint diagonalisation of the time varying spectral matrices of the observation records and a new technique to handle the problem of permutation ambiguity in the frequency domain. This method is then applied to real data and the estimated sources are validated by several physical arguments. So, the contribution of the piston-slap and the combustion noise can be recovered for all the sensors. The energy of the two phenomena can then be given with regards to the position of the accelerometers.

  19. Comparison of Methods for Identifying Noise Sources in Far-Field Acoustic Signals

    NASA Astrophysics Data System (ADS)

    Tenney, Andrew; Lewalle, Jacques

    2013-11-01

    Three different methods of extracting intermittent wave packets from unstructured background within complex time series signals were analyzed and compared. The algorithms are denoted ``cross correlation,'' ``denoising,'' and ``TFLE (Time-Frequency-Lag event)'' methods respectively. All three methods utilize Mexican Hat or Morlet wavelets for the transformation of time domain signals into time-frequency domain signals. Within the denoising and cross correlation algorithms, events are identified through comparison of high energy excerpts of each signal captured by individual far-field microphones, while the TFLE algorithm simply defines events by their contributions to positive correlation values. The goal of this analysis is to quantify the advantages and disadvantages of each of these methods. The results lend themselves to determining the validity of these methods as noise source identification algorithms to be used in jet noise characterization. This work is supported in part by Spectral Energies LLC, under an SBIR grant from AFRL; and by the Department of Mechanical and Aerospace Engineering REU Program at SU.

  20. Discriminating non-seismic long-period pulses and noise to improve earthquake source inversion

    NASA Astrophysics Data System (ADS)

    Sakai, Takahide; Kumagai, Hiroyuki; Pulido, Nelson; Bonita, Jun; Nakano, Masaru

    2016-04-01

    Broadband seismometers produce artifacts resembling long-period pulses (non-seismic pulses) that degrade centroid moment tensor (CMT) estimations based on waveform inversion of broadband seismic records in long-period bands (50-200 s). We propose a method to discriminate non-seismic pulses and long-period noise from seismic signals, which can be applied to automatic CMT inversion analysis. In this method, we calculate source amplitudes as peak-to-peak displacement amplitudes in individual long-period seismic records after each event has been corrected for medium attenuation and geometric spreading and then estimate the ratios of individual source amplitudes to the minimum source amplitude. Because source amplitude ratios for non-seismic pulses tend to be greater than those of the seismic signals, we use seismic records in CMT estimations only if their source amplitude ratios are lower than a threshold value ( R). We tested this method using broadband seismic data from the Philippines and found that reprocessed inversion solutions using this method showed a clear improvement when using R = 11, although focal mechanism estimations were not entirely stable. To investigate the general applicability of this method, we analyzed broadband seismic data from F-net in Japan. Our analysis indicated that source amplitude ratios in F-net data ranged up to about 20, indicating that the threshold value may be dependent on station density. Given that F-net is one of the highest density networks in the world, we may assume that a threshold value between 10 and 20 is appropriate for application of our method for most regional broadband networks. Our synthetic tests indicated that source amplitude ratios can be as high as 103, although observed ratios are only within the range 10-20. This suggests that we happened to observe only events having focal mechanisms with source amplitude ratios of 10-20. Alternatively, these high source amplitude ratios can be explained by distortion of

  1. Reduction of beam current noise in the FNAL magnetron ion source

    SciTech Connect

    Bollinger, D. S. Karns, P. R. Tan, C. Y.

    2015-04-08

    The new FNAL Injector Line with a circular dimple magnetron ion source 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 noise [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.

  2. CaF{sub 2} ablation plumes as a source of CaF molecules for harmonic generation

    SciTech Connect

    Oujja, M.; Nalda, R. de; Castillejo, M.; Lopez-Arias, M.; Torres, R.; Marangos, J. P.

    2010-04-15

    Generation of low-order harmonics (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 harmonics 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 harmonic behavior with the temporally and spatially resolved composition and velocity of flight of species in the plume. It is concluded that harmonics 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 harmonic generation in an ablation plume. Implications of these results for the generation of high harmonics in strongly polar molecules which can be aligned in the ablation plasma are discussed.

  3. Surface Wave Tomography of the Central Alps: Merging Traditional Source and Non-traditional Noise Dispersion Measurements

    NASA Astrophysics Data System (ADS)

    Fry, B.; Stehly, L.; Campillo, M.; Boschi, L.; Giardini, D.

    2005-12-01

    The lithospheric structure of the central Alps is complex. Modeling the shear wave velocity structure of this region is hindered by the complexity. Furthermore, traditional passive source tomography is complicated by non-uniform distribution of regional earthquake sources; there is a paucity of regional waves arriving from the north. Recently developed methods of measuring surface wave dispersion from the cross correlation of ambient seismic noise from station couples provide more uniform path coverage. By combining new noise-based dispersion observations with our existing traditional source-station-station (SSS) database, we expect to achieve a dramatic improvement in resolution within the region of interest. We have applied cross correlation and dispersion measurement techniques to month-long continuous data recorded in and proximal to the central Alps (including the TomoCH and SDSNet arrays). Resultant dispersion curves extracted from the ambient seismic noise have been merged with dispersion curves measured with traditional SSS methods to create a broad band dispersion database. We are currently inverting noise and composite SSS-noise data to generate 1D Vs profiles and 2D group velocity maps, testing both linear and non-linear algorithms. Independent control on the resulting models is provided by Vp and moho models based on active and passive source body wave tomography.

  4. Current Background Noise Sources and Levels in the NASA Ames 40- by 80-Foot Wind Tunnel: A Status Report

    NASA Technical Reports Server (NTRS)

    Allen, Christopher S.; Jaeger, Stephen; Soderman, Paul; Koga, Dennis (Technical Monitor)

    1999-01-01

    Background noise 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 noise in the facility. The resulting 40x80 anechoic environment was described by Soderman et. al., and the current paper describes the resulting 40x80 background noise, discusses the sources of the noise, and draws comparisons to previous 40x80 background noise levels measurements. At low wind speeds or low frequencies, the 40x80 background noise is dominated by the fan drive system. To obtain the lowest fan drive noise 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 noise mechanism was thought to be caused by the surface interface of the previous test section floor acoustic lining. In order to reduce this noise 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 source of background noise 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 noise levels are also different for probes of various

  5. Detailed study of an efficient blue laser source by second-harmonic generation in a semimonolithic cavity for the cooling of strontium atoms.

    PubMed

    Klappauf, Bruce G; Bidel, Yannick; Wilkowski, David; Chanelière, Thierry; Kaiser, Robin

    2004-04-20

    We have constructed a blue laser source 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-harmonic 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-harmonic 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. PMID:15119621

  6. Shipping noise in whale habitat: characteristics, sources, budget, and impact on belugas in Saguenay-St. Lawrence Marine Park hub.

    PubMed

    Gervaise, Cédric; Simard, Yvan; Roy, Nathalie; Kinda, Bazile; Ménard, Nadia

    2012-07-01

    A continuous car ferry line crossing the Saguenay Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping noise in the heart of the Saguenay-St. Lawrence Marine Park. To characterize this noise 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 source levels of the different vessel types showed little dependence on vessel size or speed increase. Their spectral range covered 33 dB. Lowest noise levels occurred at night, when ferry crossing pace was reduced, and daytime noise peaked during whale-watching tour departures and arrivals. Natural ambient noise 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 noise 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 noise. PMID:22779457

  7. Shipping noise in whale habitat: characteristics, sources, budget, and impact on belugas in Saguenay-St. Lawrence Marine Park hub.

    PubMed

    Gervaise, Cédric; Simard, Yvan; Roy, Nathalie; Kinda, Bazile; Ménard, Nadia

    2012-07-01

    A continuous car ferry line crossing the Saguenay Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping noise in the heart of the Saguenay-St. Lawrence Marine Park. To characterize this noise 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 source levels of the different vessel types showed little dependence on vessel size or speed increase. Their spectral range covered 33 dB. Lowest noise levels occurred at night, when ferry crossing pace was reduced, and daytime noise peaked during whale-watching tour departures and arrivals. Natural ambient noise 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 noise 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 noise.

  8. Rotor noise

    NASA Astrophysics Data System (ADS)

    Schmitz, F. H.

    1991-08-01

    The physical characteristics and sources of rotorcraft noise as they exist today are presented. Emphasis is on helicopter-like vehicles, that is, on rotorcraft in nonaxial flight. The mechanisms of rotor noise are reviewed in a simple physical manner for the most dominant sources of rotorcraft noise. With simple models, the characteristic time- and frequency-domain features of these noise sources are presented for idealized cases. Full-scale data on several rotorcraft are then reviewed to allow for the easy identification of the type and extent of the radiating noise. Methods and limitations of using scaled models to test for several noise sources are subsequently presented. Theoretical prediction methods are then discussed and compared with experimental data taken under very controlled conditions. Finally, some promising noise reduction technology is reviewed.

  9. Rotor noise

    NASA Technical Reports Server (NTRS)

    Schmitz, F. H.

    1991-01-01

    The physical characteristics and sources of rotorcraft noise as they exist today are presented. Emphasis is on helicopter-like vehicles, that is, on rotorcraft in nonaxial flight. The mechanisms of rotor noise are reviewed in a simple physical manner for the most dominant sources of rotorcraft noise. With simple models, the characteristic time- and frequency-domain features of these noise sources are presented for idealized cases. Full-scale data on several rotorcraft are then reviewed to allow for the easy identification of the type and extent of the radiating noise. Methods and limitations of using scaled models to test for several noise sources are subsequently presented. Theoretical prediction methods are then discussed and compared with experimental data taken under very controlled conditions. Finally, some promising noise reduction technology is reviewed.

  10. Further studies of static to flight effects on fan tone noise using inlet distortion control for source identification

    NASA Technical Reports Server (NTRS)

    Hodder, B. K.

    1976-01-01

    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 noise 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-noise 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-noise generation. Further, use is made of the distortion control inlet to identify other competing tone-noise sources in the test engine such as a rotor-core stator interaction which was confirmed by engine modifications.

  11. Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial Noise Source Generating Simple Modes

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel, L.; Brown, Clifford, A.; Walker, Bruce, E.

    2012-01-01

    An Ultrasonic Configurable Fan Artificial Noise Source (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 sources (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.

  12. Ground motion in the presence of complex topography: Earthquake and ambient noise sources

    USGS Publications Warehouse

    Hartzell, Stephen; Meremonte, Mark; Ramírez-Guzmán, Leonardo; McNamara, Daniel

    2014-01-01

    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 sources 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 noise. 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 sources 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.

  13. Potential Uses of Anthropogenic Noise as a Source of Information in Animal Sensory and Communication Systems.

    PubMed

    Stansbury, Amanda; Deecke, Volker; Götz, Thomas; Janik, Vincent M

    2016-01-01

    Although current research on the impact of anthropogenic noise has focused on the detrimental effects, there is a range of ways by which animals could benefit from increased noise levels. Here we discuss two potential uses of anthropogenic noise. First, local variations in the ambient-noise 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 noise pollution will likely outweigh any positive effects, it is important to acknowledge that such changes may benefit some species. PMID:26611074

  14. Potential Uses of Anthropogenic Noise as a Source of Information in Animal Sensory and Communication Systems.

    PubMed

    Stansbury, Amanda; Deecke, Volker; Götz, Thomas; Janik, Vincent M

    2016-01-01

    Although current research on the impact of anthropogenic noise has focused on the detrimental effects, there is a range of ways by which animals could benefit from increased noise levels. Here we discuss two potential uses of anthropogenic noise. First, local variations in the ambient-noise 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 noise pollution will likely outweigh any positive effects, it is important to acknowledge that such changes may benefit some species.

  15. Estimating attenuation and propagation of noise bands from a distant source using the lookup program and data base

    NASA Astrophysics Data System (ADS)

    White, Michael J.

    1994-10-01

    Unavoidable noise generated by military activities can disturb the surrounding community and become a source of complaint. Military planners must quickly and accurately predict noise levels at distant points from various sound sources to manage noisy operations on a daily basis. This study developed the Lookup computer program and data base to provide rapid estimates of outdoor noise levels from a variety of sound sources. Lookup accesses a data base of archived results (requiring about 5 MB disk space) from typical situations rather than performing fresh calculations for each consultation. Initial timing tests show that Lookup can predict the sound levels from a noise source at distances up to 20 km in 1 second on a DOS-compatible personal computer (PC). This report includes the Lookup program source code, and describes the required input for the program, the contents of the archival data base, and the program output. Lookup was written to compile with MS-Fortran, and will run under DOS on any IBM compatible with 640k random access memory. Lookup also conforms to ANSI 1978 standard Fortran and will run under the Unix operating system.

  16. Noise emission of civil and military aero-engines. Sources of generation and measures for attenuation

    NASA Astrophysics Data System (ADS)

    Grieb, H.; Heinig, K.

    1986-09-01

    It is shown that noise reduction on high bypass ratio turbofans for civil airliners is well established. The noise levels achieved meet the internationally agreed regulations (FAR 36). The same holds true for large military transport aircraft. Helicopter noise is caused essentially by the main and tail rotors. Noise reduction on afterburner and dry engines for combat and strike aircraft, which represent the major noise annoyance to the public, is very difficult because: high specific thrust is mandatory for aircraft performance and effectiveness; jet noise with and without afterburning is predominant; and the design of the reheat section and final (variable) nozzle in practice precludes the application of known concepts for jet noise attenuation in dry and reheated operation.

  17. Characterization of noise sources for two generations of computed radiography systems using powder and crystalline photostimulable phosphors

    SciTech Connect

    Mackenzie, Alistair; Honey, Ian D.

    2007-08-15

    The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and noise characteristics. The main aim was to characterize and quantify the noise sources 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 noise power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various noise sources 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 noise 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 noise sources 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 noise.

  18. Sources, paths, and concepts for reduction of noise in the test section of the NASA Langley 4x7m wind tunnel

    NASA Technical Reports Server (NTRS)

    Hayden, R. E.; Wilby, J. F.

    1984-01-01

    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 noise reduction required to meet NASA's goal for test section background noise was determined, the predominant sources and paths causing the background noise were quantified, and trade-off studies between schemes to reduce fan noise at the source and those to attenuate the sound generated in the circuit between the sources and the test section were carried out. An extensive data base is also presented on circuit sources and paths.

  19. A phantom road experiment reveals traffic noise is an invisible source of habitat degradation.

    PubMed

    Ware, Heidi E; McClure, Christopher J W; Carlisle, Jay D; Barber, Jesse R

    2015-09-29

    Decades of research demonstrate that roads impact wildlife and suggest traffic noise as a primary cause of population declines near roads. We created a "phantom road" using an array of speakers to apply traffic noise to a roadless landscape, directly testing the effect of noise 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 noise, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic noise during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that noise degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact.

  20. A phantom road experiment reveals traffic noise is an invisible source of habitat degradation

    PubMed Central

    Ware, Heidi E.; McClure, Christopher J. W.; Carlisle, Jay D.; Barber, Jesse R.

    2015-01-01

    Decades of research demonstrate that roads impact wildlife and suggest traffic noise as a primary cause of population declines near roads. We created a “phantom road” using an array of speakers to apply traffic noise to a roadless landscape, directly testing the effect of noise 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 noise, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic noise during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that noise degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact. PMID:26324924

  1. A phantom road experiment reveals traffic noise is an invisible source of habitat degradation.

    PubMed

    Ware, Heidi E; McClure, Christopher J W; Carlisle, Jay D; Barber, Jesse R

    2015-09-29

    Decades of research demonstrate that roads impact wildlife and suggest traffic noise as a primary cause of population declines near roads. We created a "phantom road" using an array of speakers to apply traffic noise to a roadless landscape, directly testing the effect of noise 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 noise, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic noise during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that noise degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact. PMID:26324924

  2. Advances in tilt rotor noise prediction

    NASA Technical Reports Server (NTRS)

    George, A. R.; Coffen, C. D.; Ringler, T. D.

    1992-01-01

    The two most serious tilt rotor external noise problems, hover noise and blade-vortex interaction noise, 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 harmonic thickness and loading noise mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various noise 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 source for hover.

  3. Advances in tilt rotor noise prediction

    NASA Astrophysics Data System (ADS)

    George, A. R.; Coffen, C. D.; Ringler, T. D.

    The two most serious tilt rotor external noise problems, hover noise and blade-vortex interaction noise, 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 harmonic thickness and loading noise mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various noise 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 source for hover.

  4. Seismicity at Old Faithful Geyser: an isolated source of geothermal noise and possible analogue of volcanic seismicity

    USGS Publications Warehouse

    Kieffer, S.W.

    1984-01-01

    Old Faithful Geyser in Yellowstone National Park, U.S.A., is a relatively isolated source of seismic noise and exhibits seismic behavior similar to that observed at many volcanoes, including "bubblequakes" that resemble B-type "earthquakes", harmonic 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 harmonic tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding

  5. Active Control of Fan Noise: Feasibility Study. Volume 6; Theoretical Analysis for Coupling of Active Noise Control Actuator Ring Sources to an Annular Duct with Flow

    NASA Technical Reports Server (NTRS)

    Kraft, R. E.

    1996-01-01

    The objective of this effort is to develop an analytical model for the coupling of active noise 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 noise sources. 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 noise 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 source 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 source to be defined in terms of characteristic modes at the fan source plane and predict the propagation to the

  6. Static and wind tunnel near-field/far-field jet noise measurements from model scale single-flow baseline and suppressor nozzles. Volume 1: Noise source locations and extrapolation of static free-field jet noise data

    NASA Technical Reports Server (NTRS)

    Jaeck, C. L.

    1976-01-01

    A test was conducted in the Boeing Large Anechoic Chamber to determine static jet noise source 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.

  7. Resonance of a fluid-driven crack: radiation properties and implications for the source of long-period events and harmonic tremor.

    USGS Publications Warehouse

    Chouet, B.

    1988-01-01

    A dynamic source 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 harmonic tremor share the same source but differ in the boundary conditions for fluid flow and in the triggering mechanism setting up the resonance of the source, 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

  8. Demonstration of short-haul aircraft aft noise reduction techniques on a twenty inch (50.8 cm) diameter fan, volume 1

    NASA Technical Reports Server (NTRS)

    Stimpert, D. L.; Mcfalls, R. A.

    1975-01-01

    Tests of a 20 inch diameter, low tip speed, low pressure ratio fan which investigated aft fan noise reduction techniques are reported. These techniques included source noise reduction features of selection of vane-blade ratio to reduce second harmonic noise, 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 noise. Initial results and selected comparisons are presented.

  9. Sound Sources Identified in High-Speed Jets by Correlating Flow Density Fluctuations With Far-Field Noise

    NASA Technical Reports Server (NTRS)

    Panda, Jayanta; Seasholtz, Richard G.

    2003-01-01

    Noise sources 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 noise 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 noise sources were significantly different. The correlation study was conducted by keeping a microphone at a fixed location (at the peak noise 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 source was.

  10. A de-noising algorithm based on wavelet threshold-exponential adaptive window width-fitting for ground electrical source airborne transient electromagnetic signal

    NASA Astrophysics Data System (ADS)

    Ji, Yanju; Li, Dongsheng; Yu, Mingmei; Wang, Yuan; Wu, Qiong; Lin, Jun

    2016-05-01

    The ground electrical source 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 noise and non-stationary electromagnetic noise (sferics noise, aircraft engine noise and other human electromagnetic noises). These noises will cause degradation of the imaging quality for data interpretation. Based on the characteristics of the GREATEM data and major noises, we propose a de-noising algorithm utilizing wavelet threshold method and exponential adaptive window width-fitting. Firstly, the white noise 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 noise 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 noise are replaced with their fitting results. Thus the non-stationary electromagnetic noise 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 noise and non-stationary electromagnetic noise can be effectively filtered using the wavelet threshold-exponential adaptive window width-fitting algorithm, which enhances the imaging quality.

  11. The 154 MHz radio sky observed by the Murchison Widefield Array: noise, confusion, and first source count analyses

    NASA Astrophysics Data System (ADS)

    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.

    2016-07-01

    We analyse a 154 MHz image made from a 12 h observation with the Murchison Widefield Array (MWA) to determine the noise contribution and behaviour of the source 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 sources above 5σ. The rms noise 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 source count data, we find that the MWA image is affected by sidelobe confusion noise at the ≈3.5 mJy beam-1 level, due to incompletely peeled and out-of-image sources, 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 source 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.

  12. Analytic models of ducted turbomachinery tone noise sources. Volume 1: Analysis

    NASA Technical Reports Server (NTRS)

    Clark, T. L.; Ganz, U. W.; Graf, G. A.; Westall, J. S.

    1974-01-01

    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 harmonic gusts. The models include component interactions and rotor alone.

  13. Three-dimensional simulations of harmonic radiation and harmonic lasing

    NASA Astrophysics Data System (ADS)

    Schmitt, Mark J.; McVey, Brian D.

    Characteristics of the harmonic emission from free electron lasers (FELs) are examined in the spontaneous, coherent-spontaneous and stimulated emission regimes. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. In the spontaneous emission regime, the transverse radiation patterns including the transverse frequency dependences, are given. How this expression is modified to include energy spread and emittance is described. In the coherent-spontaneous emission and stimulated emission regimes, the interaction of the radiation fields with the electrons must be treated self consistently. Here, a single frequency distributed transverse source function for each electron is used in the harmonic version of the 3-D code FELEX to model the harmonic radiation. The code has recently been modified to simultaneously model the fundamental and harmonic interactions for multiple-pass oscillator simulations. These modifications facilitate the examination of FELs under various operating conditions. When the FEL is lasing at the fundamental, the evolution of the harmonic fields can be examined. This evolution is unique in the sense that the electron beam radiates at the harmonic frequencies in the presence of the harmonic radiation circulating in the cavity. As a result, enhancements of the harmonic emission can be observed. Finally, harmonic lasing can occur in cases where there is sufficient gain to overcome cavity losses and lasing at the fundamental can be suppressed. The characteristics and efficiency of these interactions are explored.

  14. Three-dimensional simulations of harmonic radiation and harmonic lasing

    NASA Astrophysics Data System (ADS)

    Schmitt, Mark J.; McVey, Brian D.

    1991-07-01

    Characteristics of the harmonic emission from free electron lasers (FELs) are examined in the spontaneous, coherent-spontaneous and stimulated emission regimes. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. In the spontaneous emission regime, the transverse radiation patterns including the transverse frequency dependences, are given. How this expression is modified to include energy spread and emittance is described. In the coherent-spontaneous emission and stimulated emission (lasing) regimes, the interaction of the radiation fields with the electrons must be treated self-consistently. Here, a single-frequency distributed transverse source function for each electron is used in the harmonic version (HELEX) of the 3D code FELEX to model the harmonic radiation. This code has recently been modified to simultaneously model the fundamental and harmonic interactions for multiple-pass oscillator simulations. These modifications facilitate the examination of FELs under various operating conditions. When the FEL is lasing at the fundamental, the evolution of the harmonic fields can be examined. This evolution is unique in the sense that the electron beam (which is bunched by the fundamental optical field) radiates at the harmonic frequencies in the presence of the harmonic radiation circulating in the cavity. As a result, enhancements of the harmonic emission can be observed. Finally, harmonic lasing can occur in cases where there is sufficient gain to overcome cavity losses and lasing at the fundamental can be suppressed. The characteristics and efficiency of these interactions are explored.

  15. Noise pollution resources compendium

    NASA Technical Reports Server (NTRS)

    1973-01-01

    Abstracts of reports concerning noise pollution are presented. The abstracts are grouped in the following areas of activity: (1) sources of noise, (2) noise detection and measurement, (3) noise abatement and control, (4) physical effects of noise and (5) social effects of noise.

  16. Sources of high frequency seismic noise: insights from a dense network of ~250 stations in northern Alsace (France)

    NASA Astrophysics Data System (ADS)

    Vergne, Jerome; Blachet, Antoine; Lehujeur, Maximilien

    2015-04-01

    Monitoring local or regional seismic activity requires stations having a low level of background seismic noise 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 noise source 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 sources on the level of seismic noise 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 noise 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 noise levels with frequency. Basically, between 0.5 and 4 Hz the geological setting modulates the level of seismic noise. At higher frequencies, the amplitude of seismic noise 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

  17. High- and low-frequency noise in Cs and in liquid metal ion sources.

    PubMed

    Rüdenauer, F; Mitterauer, J; Genovese, A

    2009-04-01

    Fundamental Physics space missions set rigid thrust noise limits for liquid metal ion thrusters used as actuators on drag-free platforms aboard the spacecraft. We have measured current-, voltage- and thrust noise of Cs and In LMIS, foreseen as prime candidates in these missions. In the high-frequency range, quasiperiodic oscillations around approximately 10(5)Hz can be observed for both types of emitters with frequency depending on emission current. In the low-frequency range (1-10(-3)Hz), which is particularly important for drag-free control, different types of noise events are observed, which in some instances show definite signs of deterministic chaos (period doubling, self-similarity). High-frequency current oscillations are generally ascribed to electro-hydrodynamic oscillations of the TAYLOR cone and the jet at its apex, with concomitant emission of charged nanodroplets. Comparison of theory and experiment shows unsatisfactory agreement in predicted vs. measured current oscillation frequencies and large disagreement in droplet emission frequencies. No theory is presently available for describing low-frequency noise events. In terms of a linearized Mair theory it is, however, shown that these noise events can be efficiently described by spontaneous variations in electrical emitter impedance. In spite of this impedance noise, the mission requirements for thrust noise (<0.1microN/Hz(1/2)) can be met by a thrust-stabilized In emitter.

  18. Dislocations as a Noise Source in LWIR HgCdTe Photodiodes

    NASA Astrophysics Data System (ADS)

    Jóźwikowski, Krzysztof; Jóźwikowska, Alina; Martyniuk, Andrzej

    2016-10-01

    The effect of dislocation on the 1/ f noise 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 noise, and thermal noise 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 noise 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 noise and 1/ f G-R noise, the main cause of 1/ f current noise in LN cooled LWIR photodiodes are fluctuations of the carriers mobility determined by 1/ f fluctuations of relaxation times. As the noise current is proportional to the total diode current, growth of G-R dark current caused by dislocations leads to the growth of noise current.

  19. Dislocations as a Noise Source in LWIR HgCdTe Photodiodes

    NASA Astrophysics Data System (ADS)

    Jóźwikowski, Krzysztof; Jóźwikowska, Alina; Martyniuk, Andrzej

    2016-02-01

    The effect of dislocation on the 1/f noise 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 noise, and thermal noise 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 noise 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 noise and 1/f G-R noise, the main cause of 1/f current noise in LN cooled LWIR photodiodes are fluctuations of the carriers mobility determined by 1/f fluctuations of relaxation times. As the noise current is proportional to the total diode current, growth of G-R dark current caused by dislocations leads to the growth of noise current.

  20. Applying the seismic interferometry method to vertical seismic profile data using tunnel excavation noise as source

    NASA Astrophysics Data System (ADS)

    Jurado, Maria Jose; Teixido, Teresa; Martin, Elena; Segarra, Miguel; Segura, Carlos

    2013-04-01

    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 noise 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 source of seismic signal and used in our research as the seismic source 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-noise 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

  1. Phased Array Noise Source Localization Measurements of an F404 Nozzle Plume at Both Full and Model Scale

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.; Bridges, James E.; Henderson, Brenda S.

    2010-01-01

    A 48-microphone planar phased array system was used to acquire jet noise source 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 noise sources 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 source 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 noise source mechanisms, and document some of the differences associated with testing at model-scale versus fullscale.

  2. Noise sources and competition between stimulated Brillouin and Raman scattering: A one-dimensional steady-state approach

    SciTech Connect

    Gong, Tao; Li, Zhichao; Zhao, Bin; Hu, Guang-yue; Zheng, Jian

    2013-09-15

    A 1D steady-state model is developed to deal with stimulated scattering processes. The volume and boundary noise sources for scattered light are discussed in detail. Our results indicate that the boundary noise sources may play a significant role in estimating the reflectivity of stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). With the capability of our model to deal with broadband scattered light, we find that pump depletion could be the main reason to the anti-correlation between SBS and SRS versus electron density observed in experiments. A simple method is proposed to phenomenologically include the effect of nonlinear saturation mechanisms in our model and reasonable results are obtained.

  3. Detection of fundamental and harmonic type III radio emission and the associated Langmuir waves at the source region

    NASA Technical Reports Server (NTRS)

    Reiner, M. J.; Stone, R. G.; Fainberg, J.

    1992-01-01

    Type III radio emission generated in the vicinity of the Ulysses spacecraft has been detected at both the fundamental and harmonic 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.

  4. Feasibility Study for a Seeded Hard X-ray Source Based on a Two-Stage Echo-Enabled Harmonic Generation FEL

    SciTech Connect

    Xiang, Dao; Huang, Z.; Ratner, D.; Stupakov, G.; /SLAC

    2009-12-11

    We propose and analyze a scheme to achieve a seeded hard x-ray source based on a two-stage echo-enabled harmonic generation (EEHG) FEL. In the scheme an 180 nm seed laser covering the whole bunch is first used to modulate the beam when beam energy is 2 GeV. After passing through a strong chicane complicated fine structures are introduced into the phase space. The beam is again modulated by a short 180 nm laser that only interacts with the rear part of the beam and accelerated to 6 GeV. A chicane is then used to convert the energy modulation imparted to the rear part of the beam into density modulation. The density-modulated beam is sent through a radiator to generate intense 6 nm radiation which will be used to interact with the front fresh part of the bunch. Finally we generate in the front part of the beam density modulation at the 1199th harmonic of the seed laser. We will discuss the issues related to the realization of the seeded hard x-ray FEL.

  5. Active Control of Fan Noise-Feasibility Study. Volume 2: Canceling Noise Source-Design of an Acoustic Plate Radiator Using Piezoceramic Actuators

    NASA Technical Reports Server (NTRS)

    Pla, F. G.; Rajiyah, H.

    1995-01-01

    The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling sources for active control of aircraft engine fan noise 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 source for active control of aircraft engine fan noise.

  6. Improved Shear Wave Motion Detection Using Pulse-Inversion Harmonic Imaging With a Phased Array Transducer.

    PubMed

    Pengfei Song; Heng Zhao; Urban, Matthew W; Manduca, Armando; Pislaru, Sorin V; Kinnick, Randall R; Pislaru, Cristina; Greenleaf, James F; Shigao Chen

    2013-12-01

    Ultrasound tissue harmonic 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 noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources 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 harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic 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 harmonic 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 harmonic 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 harmonic imaging can significantly improve shear wave motion tracking and thus potentially

  7. Simultaneous ballistic deficit immunity and resilience to parallel noise sources: A new pulse shaping technique

    SciTech Connect

    Fabris, Lorenzo; Becker, John A.; Goulding, Frederick S.; Madden, Norman W.

    2000-10-11

    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 noise 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 noise by modifying the noise 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.

  8. Interior Noise

    NASA Technical Reports Server (NTRS)

    Mixson, John S.; Wilby, John F.

    1991-01-01

    The generation and control of flight vehicle interior noise is discussed. Emphasis is placed on the mechanisms of transmission through airborne and structure-borne paths and the control of cabin noise by path modification. Techniques for identifying the relative contributions of the various source-path combinations are also discussed along with methods for the prediction of aircraft interior noise such as those based on the general modal theory and statistical energy analysis.

  9. Noise measurements in shunted, shorted, and fully electroded quartz gauges in the Saturn plasma radiation source x-ray simulator

    SciTech Connect

    Barrett, W.H.; Greenwoll, J.I.; Smith, C.W.; Johnson, D.E.; De La Cruz, C.F.

    1995-08-01

    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 noise 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-noise 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 source which show that higher fidelity shunted guard ring gauges can successfully measure stress with acceptable induced noise. We also found that a 50-ohm impedance matching resistor at the gauge reduced the prompt noise amplitude and improved the baseline quality of the measurement prior to shock wave arrival.

  10. Noise measurements in shunted, shorted, and fully electroded quartz gauges in the saturn plasma radiation source x-ray simulator

    NASA Astrophysics Data System (ADS)

    Barrett, W. H.; Greenwoll, J. I.; Smith, C. W.; Johnson, D. E.; de La Cruz, C. F.

    1996-05-01

    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 noise 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-noise 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 high fidelity measurements to about 25 kbars with negligible signal distortion. Experiments were conducted on the Saturn soft x-ray source which show that higher fidelity shunted guard ring gauges can successfully measure stress with acceptable induced noise. We also found that a 50-ohm impedance matching resistor at the gauge reduced the prompt noise amplitude and improved the baseline quality of the measurement prior to shock wave arrival.

  11. Study of noise and inflow distortion sources in the NASA QF-1B fan using measured blade and vane pressures

    NASA Technical Reports Server (NTRS)

    Hanson, D. B.

    1977-01-01

    Pressure transducers were installed on the blades and vanes of QF-1B, a transonic-tip-speed fan from the NASA Quiet Fan Program which was tested on the outdoor quiet fan test facility at NASA-Lewis. Signals from the transducers and from far field microphones were analyzed to determine sources of nonuniform inflow and noise. The nonuniform inflow was mostly unsteady with roughly equal contributions from atmospheric turbulence and rig interference. The rig interference was largest at the bottom and appeared to be generated by the support structure which was located behind the inlet lip under the fan. Interaction of this inflow distortion was the dominant source of noise at 1, 2, and 3 times blade passing frequency (BPF) at 60, 70, and 80 percent of design speed. At 90 percent speed, noise at BPF was dominated by the steady rotor field. A broadband spectrum peak centered at about 2.2 times BPF was identified as rotor/stator interaction stemming from a high frequency rotor exit flow component. The remaining broadband energy from 0.3 to 3.5 times BPF was attributed to the better known type of rotor/stator interaction associated with rotor wake turbulence.

  12. Effect of mean load on the non-linear behavior of spur gear noise source

    NASA Technical Reports Server (NTRS)

    Kahraman, Ahmet; Singh, Rajendra

    1989-01-01

    An analytical technique for estimating noise 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.

  13. Generalized wave envelope analysis of sound propagation in ducts with stepped noise source profiles and variable axial impedance

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.

    1975-01-01

    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 noise source 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 noise 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.

  14. Community Response to Noise

    NASA Astrophysics Data System (ADS)

    Fidell, Sandy

    The primary effects of community noise on residential populations are speech interference, sleep disturbance, and annoyance. This chapter focuses on transportation noise in general and on aircraft noise in particular because aircraft noise is one of the most prominent community noise sources, because airport/community controversies are often the most contentious and widespread, and because industrial and other specialized formsofcommunitynoise generally posemorelocalized problems.

  15. Harmonic engine

    DOEpatents

    Bennett, Charles L.

    2009-10-20

    A high efficiency harmonic 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 harmonic 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.

  16. Comparative analyses of phase noise in 28 nm CMOS LC oscillator circuit topologies: Hartley, Colpitts, and common-source cross-coupled differential pair.

    PubMed

    Chlis, Ilias; Pepe, Domenico; Zito, Domenico

    2014-01-01

    This paper reports comparative analyses of phase noise in Hartley, Colpitts, and common-source cross-coupled differential pair LC oscillator topologies in 28 nm CMOS technology. The impulse sensitivity function is used to carry out both qualitative and quantitative analyses of the phase noise exhibited by each circuit component in each circuit topology with oscillation frequency ranging from 1 to 100 GHz. The comparative analyses show the existence of four distinct frequency regions in which the three oscillator topologies rank unevenly in terms of best phase noise performance, due to the combined effects of device noise and circuit node sensitivity.

  17. Polarisation analysis of magnetotelluric time series using a wavelet-based scheme: A method for detection and characterisation of cultural noise sources

    NASA Astrophysics Data System (ADS)

    Escalas, M.; Queralt, P.; Ledo, J.; Marcuello, A.

    2013-05-01

    The identification and elimination of cultural noise that affects magnetotelluric (MT) time series presents a challenge in the vicinity of industrialised, urban or farming areas. Most noise sources are fixed in space and create a signal with certain polarisation properties. In this paper, we propose a new method for detection and characterisation of cultural noise sources in magnetotelluric time series based on polarisation analysis of the electromagnetic signal in the time-frequency domain using a wavelet scheme. We tested the proposed method with synthetic polarised signals and experimental time series corresponding to a field experiment with a controlled EM source and several MT real cases. The results demonstrated the difference between the polarisation properties of the natural MT signal and the signal contaminated by a controlled source or by cultural noise.

  18. Transonic Resonance Demonstrated To Be a Source of Internal Noise From Mixer-Ejector Nozzles

    NASA Technical Reports Server (NTRS)

    Zaman, Khairul B.

    2002-01-01

    During noise field studies with mixer-ejector nozzles in NASA's High-Speed Research program, tones were often encountered. The tones would persist in the simulated "cutback" condition (shortly after takeoff). Unfortunately, we did not understand their origin and, thus, could not develop a logical approach for suppressing them. We naturally questioned whether or not some of those tones were due to the transonic resonance. This was studied with a 1/13th scale model of the High-Speed Civil Transport nozzle. The first objective was to determine if indeed tones could be detected in the radiated noise. The next objective was to diagnose if those tones were due to the transonic resonance. Agreement of the frequencies with the correlation equation and the effect of boundary layer tripping were to be used in the diagnosis.

  19. Airframe noise

    NASA Astrophysics Data System (ADS)

    Crighton, David G.

    1991-08-01

    Current understanding of airframe noise was reviewed as represented by experiment at model and full scale, by theoretical modeling, and by empirical correlation models. The principal component sources are associated with the trailing edges of wing and tail, deflected trailing edge flaps, flap side edges, leading edge flaps or slats, undercarriage gear elements, gear wheel wells, fuselage and wing boundary layers, and panel vibration, together with many minor protrusions like radio antennas and air conditioning intakes which may contribute significantly to perceived noise. There are also possibilities for interactions between the various mechanisms. With current engine technology, the principal airframe noise mechanisms dominate only at low frequencies, typically less than 1 kHz and often much lower, but further reduction of turbomachinery noise in particular may make airframe noise the principal element of approach noise at frequencies in the sensitive range.

  20. Complete Vector Spherical Harmonic Expansion for Maxwell's Equations

    ERIC Educational Resources Information Center

    Lambert, R. H.

    1978-01-01

    Conventional expansions of solutions to Maxwell's equations in vector spherical harmonics apply only outside the sources. The complete solution, applying both inside and outside the sources, is given here. Harmonic time dependence is assumed. (Author/GA)

  1. Fan Noise Prediction System Development: Source/Radiation Field Coupling and Workstation Conversion for the Acoustic Radiation Code

    NASA Technical Reports Server (NTRS)

    Meyer, H. D.

    1993-01-01

    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 source noise generation) Code (BBN/PWC) is described. In a separate analysis, a method of coupling the source 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 source and radiation fields is needed for accurate noise 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.

  2. The Alternative Low Noise Fan

    NASA Technical Reports Server (NTRS)

    Dittmar, James H.; Elliott, David M.; Jeracki, Robert J.; Moore, Royce D.; Parrott, Tony L.

    2000-01-01

    A 106 bladed fan with a design takeoff tip speed of 1100 ft/sec was hypothesized as reducing perceived noise because of the shift of the blade passing harmonics to frequencies beyond the perceived noise rating range. A 22 in. model of this Alternative Low Noise Fan, ALNF, was tested in the NASA Glenn 9x 15 Wind Tunnel. 'Me fan was tested with a 7 vane long chord stator assembly and a 70 vane conventional stator assembly in both hard and acoustically treated configurations. In addition a partially treated 7 vane configuration was tested wherein the acoustic material between the 7 long chord stators was made inactive. The noise data from the 106 bladed fan with 7 long chord stators in a hard configuration was shown to be around 4 EPNdB quieter than a low tip speed Allison fan at takeoff and around 5 EPNdB quieter at approach. Although the tone noise behaved as hypothesized, the majority of this noise reduction was from reduced broadband noise related to the large number of rotor blades. This 106 bladed ALNF is a research fan designed to push the technology limits and as such is probably not a practical device with present materials technology. However, a low tip speed fan with around 50 blades would be a practical device and calculations indicate that it could be 2 to 3 EPNdB quieter at takeoff and 3 to 4 EPNdB quieter at approach than the Allison fan. 7 vane data compared with 70 vane data indicated that the tone noise was controlled by rotor wake-stator interaction but that the broadband noise is probably controlled by the interaction of the rotor with incoming flows. A possible multiple pure tone noise reduction technique for a fan/acoustic treatment system was identified. The data from the fully treated configuration showed significant noise reductions over a large frequency range thereby providing a real tribute to this bulk absorber treatment design. The tone noise data with the partially treated 7 vane configuration indicated that acoustic material in the

  3. Concurrent identification of aero-acoustic scattering and noise sources at a flow duct singularity in low Mach number flow

    NASA Astrophysics Data System (ADS)

    Sovardi, Carlo; Jaensch, Stefan; Polifke, Wolfgang

    2016-09-01

    A numerical method to concurrently characterize both aeroacoustic scattering and noise sources 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 noise 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 noise are validated against experimental measurements over a wide range of frequencies below the cut-off frequency of the duct.

  4. Nanograting-based compact VUV spectrometer and beam profiler for in-situ characterization of high-order harmonic generation light sources

    SciTech Connect

    Kornilov, Oleg; Wilcox, Russell; Gessner, Oliver

    2010-07-09

    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 sources. Operation of the device is demonstrated by characterizing the output of a femtosecond high-order harmonic generation light source.

  5. Activation process in excitable systems with multiple noise sources: Large number of units.

    PubMed

    Franović, Igor; Perc, Matjaž; Todorović, Kristina; Kostić, Srdjan; Burić, Nikola

    2015-12-01

    We study the activation process in large assemblies of type II excitable units whose dynamics is influenced by two independent noise terms. The mean-field approach is applied to explicitly demonstrate that the assembly of excitable units can itself exhibit macroscopic excitable behavior. In order to facilitate the comparison between the excitable dynamics of a single unit and an assembly, we introduce three distinct formulations of the assembly activation event. Each formulation treats different aspects of the relevant phenomena, including the thresholdlike behavior and the role of coherence of individual spikes. Statistical properties of the assembly activation process, such as the mean time-to-first pulse and the associated coefficient of variation, are found to be qualitatively analogous for all three formulations, as well as to resemble the results for a single unit. These analogies are shown to derive from the fact that global variables undergo a stochastic bifurcation from the stochastically stable fixed point to continuous oscillations. Local activation processes are analyzed in the light of the competition between the noise-led and the relaxation-driven dynamics. We also briefly report on a system-size antiresonant effect displayed by the mean time-to-first pulse. PMID:26764779

  6. Harmonic engine

    SciTech Connect

    Bennett, Charles L.; Sewall, Noel; Boroa, Carl

    2014-08-19

    An engine based on a reciprocating piston engine that extracts work from pressurized working fluid. The engine includes a harmonic 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 harmonic 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.

  7. Helicopter rotor noise due to ingestion of atmospheric turbulence

    NASA Technical Reports Server (NTRS)

    Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.; Greitzer, E. M.

    1986-01-01

    A theoretical study was conducted to develop an analytical prediction method for helicopter main rotor noise 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 source model was used to predict the far field noise 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 noise, turbulence ingestion noise is the dominant noise mechanism below approximately 30 rotor harmonics, while above 100 harmonics, trailing edge noise levels exceed turbulence ingestion noise by 25 dB.

  8. Directionality of Ambient Noise on the Juan de Fuca Plate: Implications for Source Locations of the Primary and Secondary Microseism

    NASA Astrophysics Data System (ADS)

    Tian, Y.; Ritzwoller, M. H.

    2014-12-01

    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 noise observed across the array is much different in the primary and secondary microseism bands, both in its azimuthal content and seasonal variation, indicating different source generation locations. (2) The principal secondary microseism signals propagate toward the east, consistent with source 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 sources 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 noise. 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 sources 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 sources and the source of primary microseism having a significant component in the shallow waters of the eastern Pacific

  9. Acoustic Database for Turbofan Engine Core-Noise Sources. I; Volume

    NASA Technical Reports Server (NTRS)

    Gordon, Grant

    2015-01-01

    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 noise. 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

  10. Acoustic emissions of digital data video projectors- Investigating noise sources and their change during product aging

    NASA Astrophysics Data System (ADS)

    White, Michael Shane

    2005-09-01

    Acoustic emission testing continues to be a growing part of IT and telecommunication product design, as product noise 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.

  11. Exploring the source of the mid-level hump for intensity discrimination in quiet and the effects of noise.

    PubMed

    Roverud, Elin; Strickland, Elizabeth A

    2015-03-01

    Intensity discrimination Weber fractions (WFs) measured for short, high-frequency tones in quiet are larger at mid levels than at lower or higher levels. The source of this "mid-level hump" is a matter of debate. One theory is that the mid-level hump reflects basilar-membrane compression, and that WFs decrease at higher levels due to spread-of-excitation cues. To test this theory, Experiment 1 measured the mid-level hump and growth-of-masking functions to estimate the basilar membrane input/output (I/O) function in the same listeners. Results showed the initial rise in WFs could be accounted for by the change in I/O function slope, but there was additional unexplained variability in WFs. Previously, Plack [(1998). J. Acoust. Soc. Am. 103(5), 2530-2538] showed that long-duration notched noise (NN) presented with the tone reduced the mid-level hump even with a temporal gap in the NN. Plack concluded the results were consistent with central profile analysis. However, simultaneous, forward, and backward NN were not examined separately, which may independently test peripheral and central mechanisms of the NN. Experiment 2 measured WFs at the mid-level hump in the presence of NN and narrowband noise of different durations and temporal positions relative to the tone. Results varied across subjects, but were consistent with more peripheral mechanisms.

  12. Exploring the source of the mid-level hump for intensity discrimination in quiet and the effects of noise.

    PubMed

    Roverud, Elin; Strickland, Elizabeth A

    2015-03-01

    Intensity discrimination Weber fractions (WFs) measured for short, high-frequency tones in quiet are larger at mid levels than at lower or higher levels. The source of this "mid-level hump" is a matter of debate. One theory is that the mid-level hump reflects basilar-membrane compression, and that WFs decrease at higher levels due to spread-of-excitation cues. To test this theory, Experiment 1 measured the mid-level hump and growth-of-masking functions to estimate the basilar membrane input/output (I/O) function in the same listeners. Results showed the initial rise in WFs could be accounted for by the change in I/O function slope, but there was additional unexplained variability in WFs. Previously, Plack [(1998). J. Acoust. Soc. Am. 103(5), 2530-2538] showed that long-duration notched noise (NN) presented with the tone reduced the mid-level hump even with a temporal gap in the NN. Plack concluded the results were consistent with central profile analysis. However, simultaneous, forward, and backward NN were not examined separately, which may independently test peripheral and central mechanisms of the NN. Experiment 2 measured WFs at the mid-level hump in the presence of NN and narrowband noise of different durations and temporal positions relative to the tone. Results varied across subjects, but were consistent with more peripheral mechanisms. PMID:25786945

  13. Organizational Communication in Emergencies: Using Multiple Channels and Sources to Combat Noise and Capture Attention

    ERIC Educational Resources Information Center

    Stephens, Keri K.; Barrett, Ashley K.; Mahometa, Michael J.

    2013-01-01

    This study relies on information theory, social presence, and source 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…

  14. Analysis of handling noises on wound strings.

    PubMed

    Pakarinen, J; Penttinen, H; Bank, B

    2007-12-01

    This study analyzes the handling noises that occur when a finger is slid along a wound string. The resulting noise has a harmonic structure due to the periodic texture of the wound string. The frequency of the harmonics and the root-mean-square amplitude of the noise were found to be linearly proportional to the sliding speed. In addition, the sliding excites the longitudinal modes of the string, thus resulting in a set of static harmonics in the noise spectrum. The sliding excites different longitudinal modes depending on the sliding location. PMID:18247641

  15. Computation of Large-Scale Structure Jet Noise Sources With Weak Nonlinear Effects Using Linear Euler

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Hixon, Ray; Mankbadi, Reda R.

    2003-01-01

    An approximate technique is presented for the prediction of the large-scale turbulent structure sound source 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 source of large-scale turbulent structure sound in the jet.

  16. Shielding Characteristics Using an Ultrasonic Configurable Fan Artificial Noise Source to Generate Modes - Experimental Measurements and Analytical Predictions

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.; Walker, Bruce E.

    2014-01-01

    An Ultrasonic Configurable Fan Artificial Noise Source (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 sources (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 sources 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.

  17. Damped harmonics and polynomial phase signals

    NASA Astrophysics Data System (ADS)

    Zhou, Guotong; Giannakis, Georgios B.

    1994-10-01

    The concern here is of retrieving damped harmonics and polynomial phase signals in the presence of additive noise. The damping function is not limited to the exponential model, and in certain cases, the additive noise does not have to be white. Three classes of algorithms are presented, namely DFT based, Kumaresan-Tufts type extensions, and subspace variants including the MUSIC algorithm. Preference should be based on the available data length and frequency separations. In addition, retrieval of self coupled damped harmonics, which may be present when nonlinearities exist in physical systems, is investigated. Simulation examples illustrate main points of the paper.

  18. Photon noise from chaotic and coherent millimeter-wave sources measured with horn-coupled, aluminum lumped-element kinetic inductance detectors

    NASA Astrophysics Data System (ADS)

    Flanigan, D.; McCarrick, H.; Jones, G.; Johnson, B. R.; Abitbol, M. H.; Ade, P.; Araujo, D.; Bradford, K.; Cantor, R.; Che, G.; Day, P.; Doyle, S.; Kjellstrand, C. B.; Leduc, H.; Limon, M.; Luu, V.; Mauskopf, P.; Miller, A.; Mroczkowski, T.; Tucker, C.; Zmuidzinas, J.

    2016-02-01

    We report photon-noise limited performance of horn-coupled, aluminum lumped-element kinetic inductance detectors at millimeter wavelengths. The detectors are illuminated by a millimeter-wave source that uses an active multiplier chain to produce radiation between 140 and 160 GHz. We feed the multiplier with either amplified broadband noise or a continuous-wave tone from a microwave signal generator. We demonstrate that the detector response over a 40 dB range of source power is well-described by a simple model that considers the number of quasiparticles. The detector noise-equivalent power (NEP) is dominated by photon noise when the absorbed power is greater than approximately 1 pW, which corresponds to NEP≈2 ×10-17 W Hz-1 /2 , referenced to absorbed power. At higher source power levels, we observe the relationships between noise and power expected from the photon statistics of the source signal: NEP∝P for broadband (chaotic) illumination and NEP∝P1 /2 for continuous-wave (coherent) illumination.

  19. Reduction of Beam Current Noise in the FNAL Magnetron Ion Source

    SciTech Connect

    Bollinger, D. S.; Karns, P. R.; Tan, C. Y.

    2014-01-01

    The new FNAL Injector Line with a circular dimple magnetron ion source 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.

  20. Strongly Dispersive Transient Bragg Grating for High Harmonics

    SciTech Connect

    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.

    2010-06-04

    We create a transient Bragg grating in a high harmonic generation medium using two counterpropagating pulses. The Bragg grating disperses the harmonics in angle and can diffract a large bandwidth with temporal resolution limited only by the source size.

  1. Effects of background noise on total noise annoyance

    NASA Technical Reports Server (NTRS)

    Willshire, K. F.

    1987-01-01

    Two experiments were conducted to assess the effects of combined community noise sources on annoyance. The first experiment baseline relationships between annoyance and noise level for three community noise sources (jet aircraft flyovers, traffic and air conditioners) presented individually. Forty eight subjects evaluated the annoyance of each noise source presented at four different noise levels. Results indicated the slope of the linear relationship between annoyance and noise level for the traffic noise was significantly different from that of aircraft and of air conditioner noise, which had equal slopes. The second experiment investigated annoyance response to combined noise sources, with aircraft noise defined as the major noise source and traffic and air conditioner noise as background noise sources. Effects on annoyance of noise level differences between aircraft and background noise for three total noise levels and for both background noise sources were determined. A total of 216 subjects were required to make either total or source specific annoyance judgements, or a combination of the two, for a wide range of combined noise conditions.

  2. Acoustic noise associated with the MOD-1 wind turbine: its source, impact, and control

    SciTech Connect

    Kelley, N.D.; McKenna, H.E.; Hemphill, R.R.; Etter, C.L.; Garrelts, R.L.; Linn, N.C.

    1985-02-01

    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 source 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.

  3. High-harmonic gyrotrons

    NASA Astrophysics Data System (ADS)

    McDermott, D. B.; Luhmann, N. C., Jr.

    1984-08-01

    There is currently much interest in the development of moderate to high power (1 kW - 1 MW) millimeter wave sources. Considered applications are mainly related to radar and communication systems. There are, however, also applications in plasma diagnostics, heating, and the nondestructive testing of dielectrics. The dominant source of high-power, high-frequency radiation has become the gyrotron. Jory et al. (1983) have reported operation of a 60 GHz, CW gyrotron, producing output powers in excess of 200 kW. High power, compact submillimeter-wave sources have become possible by making use of the concept of a high-harmonic gyrotron, in which the magnetic field can be reduced by an order of magnitude. Attention is given to synchronism, negative-mass instability, energy requirements, oscillators, efficiency, high power, dielectric loading, the peniotron, and amplifiers.

  4. Influence of noise on chaotic laser dynamics

    SciTech Connect

    Liu, C.; Abarbanel, H.D.I.; Nunes, K.,; Roy, R.; Gills, Z.,; Abarbanel, H.D.I.,; Nunes K.,

    1997-06-01

    The Nd:YAG laser with an intracavity second harmonic generating crystal is a versatile test bed for concepts of nonlinear time series analysis as well as for techniques that have been developed for control of chaotic systems. Quantitative comparisons of experimentally measured time series of the infrared light intensity are made with numerically computed time series from a model derived here from basic principles. These comparisons utilize measures that help to distinguish between low and high dimensional dynamics and thus enhance our understanding of the influence of noise sources on the emitted laser light. {copyright} {ital 1997} {ital The American Physical Society}

  5. Directionality of ambient noise on the Juan de Fuca plate: implications for source locations of the primary and secondary microseisms

    NASA Astrophysics Data System (ADS)

    Tian, Ye; Ritzwoller, Michael H.

    2015-04-01

    Based on cross-correlations of ambient seismic noise 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 noise 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 source regions onto the continent and are well recorded by continental seismic stations.

  6. Impact of noise in holography with extended references in the low signal regime.

    PubMed

    Boutu, W; Gauthier, D; Ge, X; Cassin, R; Ducousso, M; Gonzalez, A I; Iwan, B; Samaan, J; Wang, F; Kovačev, M; Merdji, H

    2016-03-21

    Signal-to-noise ratio is a key factor in lensless imaging, particularly for low diffraction signal experiments in the single shot regime. We present our recent study of the noise impact on holography with extended references. Experimental data have been measured in single shot acquisition using an intense coherent soft X-ray high harmonic source. The impact of hardware and software noise under various detection conditions is discussed. A final comparison between single shot and multi-shot regimes is given. PMID:27136823

  7. Squeezed light from second-harmonic generation: experiment versus theory.

    PubMed

    Ralph, T C; Taubman, M S; White, A G; McClelland, D E; Bachor, H A

    1995-06-01

    We report excellent quantitative agreement between theoretical predictions and experimental observation of squeezing from a singly resonant second-harmonic-generating crystal. Limitations in the noise suppression imposed by the pump laser are explicitly modeled and confirmed by our measurements.

  8. Ultrafast demagnetization dynamics at the M edges of magnetic elements observed using a tabletop high-harmonic soft x-ray source.

    PubMed

    La-O-Vorakiat, Chan; Siemens, Mark; Murnane, Margaret M; Kapteyn, Henry C; Mathias, Stefan; Aeschlimann, Martin; Grychtol, Patrik; Adam, Roman; Schneider, Claus M; Shaw, Justin M; Nembach, Hans; Silva, T J

    2009-12-18

    We use few-femtosecond soft x-ray pulses from high-harmonic generation to extract element-specific demagnetization dynamics and hysteresis loops of a compound material for the first time. Using a geometry where high-harmonic beams are reflected from a magnetized Permalloy grating, large changes in the reflected intensity of up to 6% at the M absorption edges of Fe and Ni are observed when the magnetization is reversed. A short pump pulse is used to destroy the magnetic alignment, which allows us to measure the fastest, elementally specific demagnetization dynamics, with 55 fs time resolution. The use of high harmonics for probing magnetic materials promises to combine nanometer spatial resolution, elemental specificity, and femtosecond-to-attosecond time resolution, making it possible to address important fundamental questions in magnetism. PMID:20366281

  9. Harmonic polynomials, hyperspherical harmonics, and atomic spectra

    NASA Astrophysics Data System (ADS)

    Avery, John Scales

    2010-01-01

    The properties of monomials, homogeneous polynomials and harmonic polynomials in d-dimensional spaces are discussed. The properties are shown to lead to formulas for the canonical decomposition of homogeneous polynomials and formulas for harmonic projection. Many important properties of spherical harmonics, Gegenbauer polynomials and hyperspherical harmonics follow from these formulas. Harmonic projection also provides alternative ways of treating angular momentum and generalised angular momentum. Several powerful theorems for angular integration and hyperangular integration can be derived in this way. These purely mathematical considerations have important physical applications because hyperspherical harmonics are related to Coulomb Sturmians through the Fock projection, and because both Sturmians and generalised Sturmians have shown themselves to be extremely useful in the quantum theory of atoms and molecules.

  10. Proceedings of Noise-con 81: Applied noise control technology

    SciTech Connect

    Royster, L.H.; Hart, F.D.; Stewart, N.D.

    1981-01-01

    The conference was divided into sessions covering noise control regulations and benefits; noise source identification; barriers and enclosures; mufflers; hearing protection devices; textile and fibre industries; metal fabrication industry; transportation and aircraft noise control; punch-press noise control and miscellaneous topics; woodworking industry; tobacco and packaging industries; community noise; and applications of damping materials. One paper has been abstracted separately.

  11. Color harmonization for images

    NASA Astrophysics Data System (ADS)

    Tang, Zhen; Miao, Zhenjiang; Wan, Yanli; Wang, Zhifei

    2011-04-01

    Color harmonization 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 harmonization method that treats the harmonization 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 harmonized with similar harmonic hues. By minimizing the cost function, we get a harmonized image in which the spatial coherence is preserved. A new matching function is proposed to select the best matching harmonic schemes, and a new component-based preharmonization strategy is proposed to preserve the hue distribution of the harmonized images. Our approach overcomes several shortcomings of the existing color harmonization methods. We test our algorithm with a variety of images to demonstrate the effectiveness of our approach.

  12. Infrared sky noise study

    NASA Technical Reports Server (NTRS)

    Westphal, J. A.

    1972-01-01

    The hardware and techniques to measure and compare sky noise at several sites were studied, and a device was developed that would maximize its output and minimize its output for modulation. The instrument and its functions are described. The nature of sky emissions and the fluctuation, gaseous sources of sky noise, and aerosol sources are discussed. It is concluded that sky noise really exists, and the spatial distribution of the sky noise sources are such that observed noise values are linear functions of chopping stroke.

  13. Degradation in finite-harmonic subcarrier demodulation

    NASA Technical Reports Server (NTRS)

    Feria, Y.; Townes, S.; Pham, T.

    1995-01-01

    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 harmonics 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 harmonics in the subcarrier demodulation and found that, for a low loop signal-to-noise ratio, using finite harmonics leads to a lower degradation. The analysis is under the assumption that the phase noise in the subcarrier (SC) loop has a Tikhonov distribution. This assumption is valid for first-order loops.

  14. All solid-state 191.7 nm deep-UV light source by seventh harmonic generation of an 888 nm pumped, Q-switched 1342 nm Nd:YVO₄ laser with excellent beam quality.

    PubMed

    Koch, Peter; Bartschke, Juergen; L'huillier, Johannes A

    2014-06-01

    In this paper we report on the realization of a deep-UV light source using the 1.3 μm transition of neodymium as pumping wavelength. The 191.7 nm radiation was obtained by generating the seventh harmonic 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 harmonic 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).

  15. Unlocking higher harmonics in atomic force microscopy with gentle interactions

    PubMed Central

    Font, Josep; Verdaguer, Albert

    2014-01-01

    Summary In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity. PMID:24778948

  16. Unlocking higher harmonics in atomic force microscopy with gentle interactions.

    PubMed

    Santos, Sergio; Barcons, Victor; Font, Josep; Verdaguer, Albert

    2014-01-01

    In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity.

  17. Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial Noise Source Generating Typical Turbofan Modes

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel l.; Brown, Clifford A.; Walker, Bruce E.

    2014-01-01

    An Ultrasonic Configurable Fan Artificial Noise Source (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 sources (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

  18. Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial Noise Source Generating Typical Turbofan Modes

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.; Brown, Cliff; Walker, Bruce E.

    2014-01-01

    An Ultrasonic Configurable Fan Artificial Noise Source (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 sources (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.

  19. Simple Harmonic Motion in Harmonic Plane Waves.

    ERIC Educational Resources Information Center

    Benumof, Reuben

    1980-01-01

    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 harmonic motion of a particle involved in the propagation of a harmonic mechanical plane wave. (HM)

  20. Radiated noise characteristics of a modern cargo ship

    PubMed

    Arveson; Vendittis

    2000-01-01

    Extensive measurements were made of the radiated noise of M/V OVERSEAS HARRIETTE, a bulk cargo ship (length 173 m, displacement 25 515 tons) powered by a direct-drive low-speed diesel engine-a design representative of many modern merchant ships. The radiated noise data show high-level tonal frequencies from the ship's service diesel generator, main engine firing rate, and blade rate harmonics due to propeller cavitation. Radiated noise directionality measurements indicate that the radiation is generally dipole in form at lower frequencies, as expected. There are some departures from this pattern that may indicate hull interactions. Blade rate source level (174 dB re 1 microPa/m at 9 Hz, 16 knots) agrees reasonably well with a model of fundamental blade rate radiation previously reported by Gray and Greeley, but agreement for blade rate harmonics is not as good. Noise from merchant ships elevates the natural ambient by 20-30 dB in many areas; the effects of this noise on the biological environment have not been widely investigated.

  1. Laboratory study of the effects of sidewall treatment, source directivity and temperature on the interior noise of a light aircraft fuselage

    NASA Technical Reports Server (NTRS)

    Heitman, K. E.; Mixson, J. S.

    1986-01-01

    This paper describes a laboratory study of add-on {coustic treatments for a twin-engine, propeller-driven aircraft fuselage. The sound source was a pneumatic-driver, with attached horn to simulate propeller noise distribution, powered by a white noise 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 source angle and ambient temperature on interior sound pressure level are presented. The sound source 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.

  2. Transcriptional Bursting from the HIV-1 Promoter is a Significant Source of Stochastic Noise in HIV-1 Gene Expression

    SciTech Connect

    Singh, A; Razooky, B; Cox, Chris D.; Simpson, Michael L; Weinberger, Leor S.

    2010-01-01

    Analysis of noise 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 noise 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 (noise) at each integration site. Notably, the measured noise levels are inconsistent with constitutive gene expression models. Instead, quantification of expression noise 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.

  3. Interior noise reduction by alternate resonance tuning

    NASA Technical Reports Server (NTRS)

    Bliss, Donald B.; Gottwald, James A.; Bryce, Jeffrey W.

    1987-01-01

    Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at low frequencies, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is studied which considers aircraft fuselages lined with panels alternately tuned to frequencies above and below the frequency that must be attenuated. Adjacent panel would oscillate at equal amplitude, to give equal acoustic source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to be cut off, and therefore be nonpropagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is being investigated theoretically and experimentally. Progress to date is discussed.

  4. Inductively coupled plasma spectrometry: Noise characteristics of aerosols, application of generalized standard additions method, and Mach disk as an emission source

    SciTech Connect

    Shen, Luan

    1995-10-06

    This dissertation is focused on three problem areas in the performance of inductively coupled plasma (ICP) source. The noise characteristics of aerosols produced by ICP nebulizers are investigated. A laser beam is scattered by aerosol and detected by a photomultiplier tube and the noise amplitude spectrum of the scattered radiation is measured by a spectrum analyzer. Discrete frequency noise 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 noise, while a conical, straight-pass spray chamber enhances white noise, relative to the noise 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 noise 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.

  5. High order harmonic generation in rare gases

    SciTech Connect

    Budil, K.S.

    1994-05-01

    The process of high order harmonic 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 {approximately}10{sup 13}-10{sup 14} W/cm{sup 2}) is focused into a dense ({approximately}10{sup l7} particles/cm{sup 3}) 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 harmonics of the laser field. This dissertation is a study of both the physical mechanism of harmonic generation as well as its development as a source of coherent XUV radiation. Recently, a semiclassical theory has been proposed which provides a simple, intuitive description of harmonic 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 harmonic 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 harmonic production as the ellipticity of the driving field is increased. This decrease in harmonic 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 harmonic {open_quotes}source{close_quotes}. A series of experiments were performed examining the spatial profiles of the harmonics. The quality of the spatial profile is crucial if the harmonics are to be used as the source for experiments, particularly if they must be refocused.

  6. Phobos mass estimations from MEX and Viking 1 data: influence of different noise sources and estimation strategies

    NASA Astrophysics Data System (ADS)

    Kudryashova, M.; Rosenblatt, P.; Marty, J.-C.

    2015-08-01

    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 (noise, coverage, flyby distance). In the present work we are testing the impact of mentioned above error sources 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.

  7. Underwater noise of small personal watercraft (jet skis).

    PubMed

    Erbe, Christine

    2013-04-01

    Personal watercraft (water scooters, jet skis) were recorded under water in Bramble Bay, Queensland, Australia. Underwater noise 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 harmonics. Broadband monopole source 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 source level that correlates with the bioacoustic impact on marine fauna. PMID:23556699

  8. A Low-Noise CMOS THz Imager Based on Source Modulation and an In-Pixel High-Q Passive Switched-Capacitor N-Path Filter.

    PubMed

    Boukhayma, Assim; Dupret, Antoine; Rostaing, Jean-Pierre; Enz, Christian

    2016-01-01

    This paper presents the first low noise complementary metal oxide semiconductor (CMOS) deletedCMOS terahertz (THz) imager based on source 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 source 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 noise 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 noise 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 noise equivalent power of 0 . 6 nW at 270 GHz and 0 . 8 nW at 600 GHz. PMID:26950131

  9. Analysis of SNR penalty in Brillouin optical time-domain analysis sensors induced by laser source phase noise

    NASA Astrophysics Data System (ADS)

    Minardo, A.; Bernini, R.; Zeni, L.

    2016-02-01

    In this paper, we analyze numerically the effect of phase noise from the laser in Brillouin optical time-domain analysis (BOTDA) sensors. Due to laser phase noise, 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 noise induces a reduction of the average Brillouin gain, as well as an increase of the overall system noise. 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.

  10. Higher-Order Harmonic Generation from Fullerene by Means of the Plasma Harmonic Method

    SciTech Connect

    Ganeev, R. A.; Bom, L. B. Elouga; Abdul-Hadi, J.; Ozaki, T.; Wong, M. C. H.; Brichta, J. P.; Bhardwaj, V. R.

    2009-01-09

    We demonstrate, for the first time, high-order harmonic 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. Harmonics up to the 19th order were observed. The harmonic 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 source of high-order harmonics.

  11. Reduction of Helicopter Blade-Vortex Interaction Noise by Active Rotor Control Technology

    NASA Technical Reports Server (NTRS)

    Yu, Yung H.; Gmelin, Bernd; Splettstoesser, Wolf; Brooks, Thomas F.; Philippe, Jean J.; Prieur, Jean

    1997-01-01

    Helicopter blade-vortex interaction noise is one of the most severe noise sources 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 noise 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 noise reduction, including higher harmonic pitch control, individual blade control, and on-blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of noise 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.

  12. Fourth Aircraft Interior Noise Workshop

    NASA Technical Reports Server (NTRS)

    Stephens, David G. (Compiler)

    1992-01-01

    The fourth in a series of NASA/SAE Interior Noise Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft noise with emphasis on source noise prediction; cabin noise prediction; cabin noise control, including active and passive methods; and cabin interior noise procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues.

  13. Acoustic analysis of aft noise reduction techniques measured on a subsonic tip speed 50.8 cm (twenty inch) diameter fan. [quiet engine program

    NASA Technical Reports Server (NTRS)

    Stimpert, D. L.; Clemons, A.

    1977-01-01

    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) source noise reduction techniques; and (2) aft duct noise reduction with acoustic treatment. Source noise reduction techniques were investigated which include minimizing second harmonic noise by varying vane/blade ratio, variation in spacing, and lowering the Mach number through the vane row to lower fan broadband noise. Treatment in the aft duct which includes flow noise 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.

  14. Scan-based near-field acoustical holography and partial field decomposition in the presence of noise and source level variation.

    PubMed

    Lee, Moohyung; Bolton, J Stuart

    2006-01-01

    Practical holography measurements of composite sources are usually performed using a multireference cross-spectral approach, and the measured sound field must be decomposed into spatially coherent partial fields before holographic projection. The formulations by which the latter approach have been implemented have not taken explicit account of the effect of additive noise on the reference signals and so have strictly been limited to the case in which noise superimposed on the reference signals is negligible. Further, when the sound field is measured by scanning a subarray over a number of patches in sequence, the decomposed partial fields can suffer from corruption in the form of a spatially distributed error resulting from source level variation from scan-to-scan. In the present work, the effects of both noise included in the reference signals, and source level variation during a scan-based measurement, on partial field decomposition are described, and an integrated procedure for simultaneously suppressing the two effects is provided. Also, the relative performance of two partial field decomposition formulations is compared, and a strategy for obtaining the best results is described. The proposed procedure has been verified by using numerical simulations and has been applied to holographic measurements of a subsonic jet.

  15. Proceedings, inter-noise 84 - international cooperation for noise control. 2 Vols

    SciTech Connect

    Maling, G.C. Jr.

    1984-01-01

    A total of 199 papers were presented on noise control engineering, especially in the areas of community noise control, sound intensity, noise emission sources, active sound attenuation and noise reduction by barriers. 4 papers have been abstracted separately.

  16. Ultrahigh-resolution optical coherence tomography at 1.3 μm central wavelength by using a supercontinuum source pumped by noise-like pulses

    NASA Astrophysics Data System (ADS)

    You, Yi-Jing; Wang, Chengming; Lin, Yi-Lun; Zaytsev, Alexey; Xue, Ping; Pan, Ci-Ling

    2016-02-01

    We report on the ultrahigh-resolution optical coherence tomography (OCT) with a novel high-power supercontinuum (SC) light source generated by noise-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 source 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.

  17. Ultra-compact Watt-level flat supercontinuum source pumped by noise-like pulse from an all-fiber oscillator.

    PubMed

    Chen, He; Zhou, Xuanfeng; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing

    2015-12-28

    We demonstrate Watt-level flat visible supercontinuum (SC) generation in photonic crystal fibers, which is directly pumped by broadband noise-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 noise-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 noise-like pulse oscillator a competitive candidate to the widely used cascade amplified coherent pulse as the pump source 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 noise-like pulse oscillator. PMID:26831958

  18. Ultra-compact Watt-level flat supercontinuum source pumped by noise-like pulse from an all-fiber oscillator.

    PubMed

    Chen, He; Zhou, Xuanfeng; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing

    2015-12-28

    We demonstrate Watt-level flat visible supercontinuum (SC) generation in photonic crystal fibers, which is directly pumped by broadband noise-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 noise-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 noise-like pulse oscillator a competitive candidate to the widely used cascade amplified coherent pulse as the pump source 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 noise-like pulse oscillator.

  19. Harmonics generated from a DC biased transformer

    SciTech Connect

    Shu Lu; Yilu Liu; Ree, J. De La . The Bradley Dept. of Electrical Engineering)

    1993-04-01

    The paper presents harmonic characteristics of transformer excitation currents under DC bias caused by geomagnetically induced currents (GIC). A newly developed saturation model of a single phase shell form transformer based on 3D finite element analysis is used to calculate the excitation currents. As a consequence, the complete variations of excitation current harmonics with respect to an extended range of GIC bias are revealed. The results of this study are useful in understanding transformers as harmonic sources and the impact on power systems during a solar magnetic disturbance.

  20. Environmental noise and sleep disturbance: research in Central, Eastern and South-Eastern Europe and Newly Independent States.

    PubMed

    Ristovska, Gordana; Lekaviciute, Jurgita

    2013-01-01

    Countries from South-East Europe (SEE), Central and Eastern Europe (CEE) and Newly Independent States (NIS) are in the process of harmonization with European environmental noise legislation. However, research work on noise and health was performed in some countries independently of harmonization process of adoption and implementation of legislation for environmental noise. Aim of this review is to summarize available evidence for noise induced sleep disturbance in population of CEE, SEE and NIS countries and to give directions for further research work in this field. After a systematic search through accessible electronic databases, conference proceedings, PhD thesis, national reports and scientific journals in English and non-English language, we decided to include six papers and one PhD thesis in this review: One paper from former Yugoslavia, one paper from Slovakia, one paper from Lithuania, two papers from Serbia and one paper, as also one PhD thesis from The Former Yugoslav Republic of Macedonia. Noise exposure assessment focused on road traffic noise was mainly performed with objective noise measurements, but also with noise mapping in case of Lithuanian study. Sleep disturbance was assessed with the questionnaire based surveys and was assumed from dose-effect relationship between night-time noise indicator (Lnight ) for road traffic noise and sleep disturbance (for Lithuanian study). Although research evidence on noise and sleep disturbance show to be sufficient for establishing dose response curves for sleep disturbance in countries where studies were performed, further research is needed with particular attention to vulnerable groups, other noise sources, development of laboratory research work and common methodology in assessment of burden of diseases from environmental noise. PMID:23412575

  1. SEVENTH HARMONIC 20 GHz CO-GENERATOR

    SciTech Connect

    Hirshfield, Jay L

    2014-04-08

    To satisfy the need for multi-MW rf sources in frequency ranges where commercial sources do not exist, a study was undertaken on a class of devices based on gyro-harmonic 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 harmonic 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 harmonic device operating at 20 GHz, and a 2nd harmonic device operating at 22.4 GHz.

  2. West Texas array experiment: Noise and source characterization of short-range infrasound and acoustic signals, along with lab and field evaluation of Intermountain Laboratories infrasound microphones

    NASA Astrophysics Data System (ADS)

    Fisher, Aileen

    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-noise ratios and a limited number of studies on regional and short-range noise and source 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 noise 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-noise 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

  3. Aircraft noise prediction program theoretical manual, part 2

    NASA Astrophysics Data System (ADS)

    Zorumski, W. E.

    1982-02-01

    Detailed prediction methods for specific aircraft noise sources are given. These sources are airframe noise, combustion noise, fan noise, single and dual stream jet noise, and turbine noise. Modifications to the NASA methods which comply with the International Civil Aviation Organization standard method for aircraft noise prediction are given.

  4. Workshop on Harmonic Oscillators

    NASA Technical Reports Server (NTRS)

    Han, D. (Editor); Kim, Y. S. (Editor); Zachary, W. W. (Editor)

    1993-01-01

    Proceedings of a workshop on Harmonic Oscillators held at the College Park Campus of the University of Maryland on March 25 - 28, 1992 are presented. The harmonic 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 harmonic oscillator is the bridge between pure and applied physics.

  5. A source of illumination for low-noise ‘Violin-Mode’ shadow sensors, intended for use in interferometric gravitational wave detectors

    NASA Astrophysics Data System (ADS)

    Lockerbie, N. A.; Tokmakov, K. V.; Strain, K. A.

    2014-12-01

    A low-noise source 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 source 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, noise 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 noise limit—whilst remaining within the constraints of this simple design of emitter. The shadow detector is described in an accompanying paper.

  6. Mid-infrared concentration-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy of a continuous supersonic expansion discharge source

    NASA Astrophysics Data System (ADS)

    Talicska, Courtney N.; Porambo, Michael W.; Perry, Adam J.; McCall, Benjamin J.

    2016-06-01

    Concentration-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is implemented for the first time on a continuous gas-flow pinhole supersonic expansion discharge source for the study of cooled molecular ions. The instrument utilizes a continuous-wave optical parametric oscillator easily tunable from 2.5 to 3.9 μm and demonstrates a noise equivalent absorption of ˜1 × 10-9 cm-1. The effectiveness of concentration-modulated NICE-OHMS is tested through the acquisition of transitions in the ν1 fundamental band of HN2+ centered near 3234 cm-1, with a signal-to-noise of ˜40 obtained for the strongest transitions. The technique is used to characterize the cooling abilities of the supersonic expansion discharge source itself, and a Boltzmann analysis determines a rotational temperature of ˜29 K for low rotational states of HN2+. Further improvements are discussed that will enable concentration-modulated NICE-OHMS to reach its full potential for the detection of molecular ions formed in supersonic expansion discharges.

  7. GRACE Harmonic and Mascon Solutions at JPL

    NASA Astrophysics Data System (ADS)

    Watkins, M. M.; Yuan, D.; Kuang, D.; Bertiger, W.; Kim, M.; Kruizinga, G. L.

    2005-12-01

    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 harmonic 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 harmonic 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 harmonic 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 noise and aliasing sensitivity.

  8. West Texas array experiment: Noise and source characterization of short-range infrasound and acoustic signals, along with lab and field evaluation of Intermountain Laboratories infrasound microphones

    NASA Astrophysics Data System (ADS)

    Fisher, Aileen

    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-noise ratios and a limited number of studies on regional and short-range noise and source 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 noise 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-noise 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

  9. Active Noise Control for Dishwasher noise

    NASA Astrophysics Data System (ADS)

    Lee, Nokhaeng; Park, Youngjin

    2016-09-01

    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 noise, 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 noise are about 40 - 50 dBA. It could be achieved by removal of noise sources 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 noise control for dishwasher noise. It is observed that the noise 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-noise are designed for active noise control. Simulation result shows proposed active noise control scheme could have a potential application for dishwasher noise reduction.

  10. New constraints on the magmatic system beneath Newberry Volcano from the analysis of active and passive source seismic data and ambient noise

    NASA Astrophysics Data System (ADS)

    Heath, Benjamin Allen

    Using joint P-wave seismic tomography, receiver functions, and ambient noise we image the magmatic structure beneath Newberry Volcano, located near Bend, Oregon. Use of active source and teleseismic events in a joint tomographic inversion provides the ray crossings necessary to resolve a low velocity body around 4 km depth. Receiver functions show large lateral heterogeneity and are consistent with the location of a low velocity body derived from the tomography but require a larger low velocity anomaly. Ambient noise autocorrelations are used to image a low velocity reflector, located at ~3 km depth, shallower than the imaged low velocity body recovered using tomography and receiver functions. Ultimately, our results reveal a magma chamber at 3-4 km depth beneath Newberry caldera, with an overlying partially molten sill at ~3 km depth. These results show the usefulness of dense seismometer deployments over volcanoes.

  11. The effects of harmonics generated by an over-excited transformer on a multimachine system

    SciTech Connect

    Jalali, J.; Mokhtari, S.

    1995-09-01

    An electric power system consisting of three generators and nine buses is considered. The transformer connected to bus seven is considered as a source of harmonics, and it is modeled accordingly. The harmonic source generates harmonics with 6K {+-} 1 orders for K = 1, 2, 3 ..., n. The harmonics of order 6K {+-} 1 with significant effects on different buses of the power system network are evaluated during the steady state operation of the system by using SKM System Software for HIWAVE. Frequency scan and distortion calculations are studied to determine how the harmonics vary the operation of the power system network. The frequency spectrum of the harmonic source indicates that 5th order harmonic affects the operation of the power system. The effects of harmonics on the system are reduced by modeling a single-tuned shunt filter connected to bus seven parallel to the harmonic source to improve the system operation.

  12. A Low-Noise CMOS THz Imager Based on Source Modulation and an In-Pixel High-Q Passive Switched-Capacitor N-Path Filter

    PubMed Central

    Boukhayma, Assim; Dupret, Antoine; Rostaing, Jean-Pierre; Enz, Christian

    2016-01-01

    This paper presents the first low noise complementary metal oxide semiconductor (CMOS) terahertz (THz) imager based on source 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 source 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 noise 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 noise 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 noise equivalent power of 0.6 nW at 270 GHz and 0.8 nW at 600 GHz. PMID:26950131

  13. On the simulation of harmonically related signals

    NASA Astrophysics Data System (ADS)

    Gerlach, Albert A.; Kunz, Edward L.; Anderson, Wendell L.; Flowers, Kenneth D.

    1988-06-01

    Narrowband harmonically related signals, embedded in broadband noise and other unrelated signals, occur in specific applications. To study these signals and to evaluate techniques for their discernment, it is convenient to model or simulate harmonically related signals in the laboratory. A means of accomplishing this task on a conventional digital computer is developed in discrete algorithm format. The resulting simulator uses parameters that allow one to select the mean frequency and harmonic ratio of the signals and to control both the extent and autocorrelation (or power spectral density) of the random signal-frequency fluctuations. Broadband noise and other nonharmonically related signals may also be accommodated in the simulator concept. Examples, using the algorithm, demonstrate its performance and its conformance with theoretical predictions. Conclusions: A relatively simple algorithm is formulated to simulate harmonically related narrowband signals with random frequency fluctuations in discrete format on a digital computer. Signal parameters are incorporated into the algorithm to select the signal mean frequencies and to control both the spectral bounds and the autocorrelation (or power spectral density) of the signal fluctuations. Examples, using the algorithm, demonstrate the performance of the signal simulator and its conformance with theoretical predictions.

  14. Covariant harmonic oscillators and coupled harmonic oscillators

    NASA Technical Reports Server (NTRS)

    Han, Daesoo; Kim, Young S.; Noz, Marilyn E.

    1995-01-01

    It is shown that the system of two coupled harmonic oscillators shares the basic symmetry properties with the covariant harmonic 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.

  15. Dislocation Detection Through Harmonic Generation

    NASA Astrophysics Data System (ADS)

    Reinhardt, B. T.; Kropf, M.; Boudraeu, K.; Guers, M. J.; Tittmann, B. R.

    2010-02-01

    A fundamental goal of ultrasonic nondestructive evaluation is to characterize material defects before failure. During material fatigue, dislocations tend to nucleate, becoming sources of stress concentration. Eventually, cracks start to form and lead to material failure. Recent research has indicated that nonlinear harmonic generation can be used to distinguish between materials of high and low dislocation densities. This research reports nonlinear harmonic generation measurements to distinguish between those areas of high and low dislocation densities in copper bars. The copper bars were subjected to flexural fatigue. Periodic scans were taken in order to track dislocation development during the fatigue life of the material. We show that this technique provides improved early detection for critical components of failure.

  16. Resolution-Enhanced Harmonic and Interharmonic Measurement for Power Quality Analysis in Cyber-Physical Energy System.

    PubMed

    Liu, Yanchi; Wang, Xue; Liu, Youda; Cui, Sujin

    2016-01-01

    Power quality analysis issues, especially the measurement of harmonic 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. Harmonics 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 harmonic and interharmonic measurement. The proposed method first extracts harmonic 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 noise and fundamental frequency deviation, thus providing a deeper insight into the (inter)harmonic sources or even the whole system. PMID:27355946

  17. Resolution-Enhanced Harmonic and Interharmonic Measurement for Power Quality Analysis in Cyber-Physical Energy System.

    PubMed

    Liu, Yanchi; Wang, Xue; Liu, Youda; Cui, Sujin

    2016-06-27

    Power quality analysis issues, especially the measurement of harmonic 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. Harmonics 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 harmonic and interharmonic measurement. The proposed method first extracts harmonic 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 noise and fundamental frequency deviation, thus providing a deeper insight into the (inter)harmonic sources or even the whole system.

  18. Resolution-Enhanced Harmonic and Interharmonic Measurement for Power Quality Analysis in Cyber-Physical Energy System

    PubMed Central

    Liu, Yanchi; Wang, Xue; Liu, Youda; Cui, Sujin

    2016-01-01

    Power quality analysis issues, especially the measurement of harmonic 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. Harmonics 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 harmonic and interharmonic measurement. The proposed method first extracts harmonic 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 noise and fundamental frequency deviation, thus providing a deeper insight into the (inter)harmonic sources or even the whole system. PMID:27355946

  19. A Mode Propagation Database Suitable for Code Validation Utilizing the NASA Glenn Advanced Noise Control Fan and Artificial Sources

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.

    2014-01-01

    The NASA Glenn Research Center's Advanced Noise 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.

  20. A Mode Propagation Database Suitable for Code Validation Utilizing the NASA Glenn Advanced Noise Control Fan and Artificial Sources

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.

    2014-01-01

    The NASA Glenn Research Center's Advanced Noise 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.

  1. Rotorcraft noise

    NASA Technical Reports Server (NTRS)

    Huston, R. J. (Compiler)

    1982-01-01

    The establishment of a realistic plan for NASA and the U.S. helicopter industry to develop a design-for-noise methodology, including plans for the identification and development of promising noise reduction technology was discussed. Topics included: noise reduction techniques, scaling laws, empirical noise prediction, psychoacoustics, and methods of developing and validing noise prediction methods.

  2. Analyzing correlation functions with tesseral and Cartesian spherical harmonics

    SciTech Connect

    Danielewicz, Pawel; Pratt, Scott

    2007-03-15

    The dependence of interparticle correlations on the orientation of particle relative momentum can yield unique information on the space-time features of emission in reactions with multiparticle final states. In the present paper, the benefits of a representation and analysis of the three-dimensional correlation information in terms of surface spherical harmonics is presented. The harmonics include the standard complex tesseral harmonics and the real Cartesian harmonics. Mathematical properties of the lesser known Cartesian harmonics are illuminated. The physical content of different angular harmonic components in a correlation is described. The resolving power of different final-state effects with regard to determining angular features of emission regions is investigated. The considered final-state effects include identity interference, strong interactions, and Coulomb interactions. The correlation analysis in terms of spherical harmonics is illustrated with the cases of Gaussian and blast-wave sources for proton-charged meson and baryon-baryon pairs.

  3. Beamforming of aeroacoustic sources in the time domain: An investigation of the intermittency of the noise radiated by a forward-facing step

    NASA Astrophysics Data System (ADS)

    Fischer, J.; Valeau, V.; Brizzi, L.-E.

    2016-11-01

    The present study investigates the intermittency of the broadband aeroacoustic noise produced by a forward-facing step in a flow. The noise source is viewed as a random succession of the so-called intermittent events of short duration distributed spatially in a source 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 source 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 noise produced by the step; those random events are likely to be linked to the dynamics of the flow interacting with the step.

  4. Noise in miniature microphones.

    PubMed

    Thompson, Stephen C; LoPresti, Janice L; Ring, Eugene M; Nepomuceno, Henry G; Beard, John J; Ballad, William J; Carlson, Elmer V

    2002-02-01

    The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed. PMID:11863188

  5. Noise in miniature microphones

    NASA Astrophysics Data System (ADS)

    Thompson, Stephen C.; Lopresti, Janice L.; Ring, Eugene M.; Nepomuceno, Henry G.; Beard, John J.; Ballad, William J.; Carlson, Elmer V.

    2002-02-01

    The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed.

  6. Core-Noise Research

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.

    2012-01-01

    This presentation is a technical summary of and outlook for NASA-internal and NASA-sponsored external research on core noise funded by the Fundamental Aeronautics Program Subsonic Fixed Wing (SFW) Project. Sections of the presentation cover: the SFW system-level noise metrics for the 2015 (N+1), 2020 (N+2), and 2025 (N+3) timeframes; SFW strategic thrusts and technical challenges; SFW advanced subsystems that are broadly applicable to N+3 vehicle concepts, with an indication where further noise research is needed; the components of core noise (compressor, combustor and turbine noise) and a rationale for NASA's current emphasis on the combustor-noise component; the increase in the relative importance of core noise due to turbofan design trends; the need to understand and mitigate core-noise sources for high-efficiency small gas generators; and the current research activities in the core-noise area, with additional details given about forthcoming updates to NASA's Aircraft Noise Prediction Program (ANOPP) core-noise prediction capabilities, two NRA efforts (Honeywell International, Phoenix, AZ and University of Illinois at Urbana-Champaign, respectively) to improve the understanding of core-noise sources and noise propagation through the engine core, and an effort to develop oxide/oxide ceramic-matrix-composite (CMC) liners for broadband noise attenuation suitable for turbofan-core application. Core noise must be addressed to ensure that the N+3 noise goals are met. Focused, but long-term, core-noise research is carried out to enable the advanced high-efficiency small gas-generator subsystem, common to several N+3 conceptual designs, needed to meet NASA's technical challenges. Intermediate updates to prediction tools are implemented as the understanding of the source structure and engine-internal propagation effects is improved. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The

  7. High noise immunity one shot

    NASA Technical Reports Server (NTRS)

    Schaffer, G. L.

    1972-01-01

    Multivibrator circuit, which includes constant current source, isolates line noise from timing circuitry and field effect transistor controls circuit's operational modes. Circuit has high immunity to supply line noise.

  8. Core-Noise

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.

    2010-01-01

    This presentation is a technical progress report and near-term outlook for NASA-internal and NASA-sponsored external work on core (combustor and turbine) noise funded by the Fundamental Aeronautics Program Subsonic Fixed Wing (SFW) Project. Sections of the presentation cover: the SFW system level noise metrics for the 2015, 2020, and 2025 timeframes; the emerging importance of core noise and its relevance to the SFW Reduced-Noise-Aircraft Technical Challenge; the current research activities in the core-noise area, with some additional details given about the development of a high-fidelity combustion-noise prediction capability; the need for a core-noise diagnostic capability to generate benchmark data for validation of both high-fidelity work and improved models, as well as testing of future noise-reduction technologies; relevant existing core-noise tests using real engines and auxiliary power units; and examples of possible scenarios for a future diagnostic facility. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The SFW Reduced-Noise-Aircraft Technical Challenge aims to enable concepts and technologies to dramatically reduce the perceived aircraft noise outside of airport boundaries. This reduction of aircraft noise is critical for enabling the anticipated large increase in future air traffic. Noise generated in the jet engine core, by sources such as the compressor, combustor, and turbine, can be a significant contribution to the overall noise signature at low-power conditions, typical of approach flight. At high engine power during takeoff, jet and fan noise have traditionally dominated over core noise. However, current design trends and expected technological advances in engine-cycle design as well as noise-reduction methods are likely to reduce non-core noise even at engine-power points higher than approach. In addition, future low-emission combustor designs could increase

  9. Ultrahigh harmonics generation in a FEL with a seed laser

    SciTech Connect

    Goloviznin, V.V.; Amersfoort, P.W. van

    1995-12-31

    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 noise. 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 source of coherent spontaneous radiation at a very high harmonic 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 (!) harmonic is shown to be as high as 15%. The output radiation is tunable between discrete harmonics of the seed-frequency.

  10. Core Noise - Increasing Importance

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.

    2011-01-01

    This presentation is a technical summary of and outlook for NASA-internal and NASA-sponsored external research on core (combustor and turbine) noise funded by the Fundamental Aeronautics Program Subsonic Fixed Wing (SFW) Project. Sections of the presentation cover: the SFW system-level noise metrics for the 2015, 2020, and 2025 timeframes; turbofan design trends and their aeroacoustic implications; the emerging importance of core noise and its relevance to the SFW Reduced-Perceived-Noise Technical Challenge; and the current research activities in the core-noise area, with additional details given about the development of a high-fidelity combustor-noise prediction capability as well as activities supporting the development of improved reduced-order, physics-based models for combustor-noise 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-noise-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-Noise Technical Challenge aims to develop concepts and technologies to dramatically reduce the perceived aircraft noise outside of airport boundaries. This reduction of aircraft noise is critical to enabling the anticipated large increase in future air traffic. Noise generated in the jet engine core, by sources such as the compressor, combustor, and turbine, can be a significant contribution to the overall noise signature at low-power conditions, typical of approach flight. At high engine power during takeoff, jet and fan noise have traditionally dominated over core noise. However, current design trends and expected technological advances in engine-cycle design as well as noise-reduction methods are likely to reduce non-core noise even at engine-power points higher than approach. In addition, future low-emission combustor

  11. Active control of automotive fan noise

    NASA Astrophysics Data System (ADS)

    Gerard, Anthony; Berry, Alain; Masson, Patrice

    2002-11-01

    Active control for globally reducing the noise radiated by automotive axial engine cooling fans is investigated. First, an aeroacoutic model of the fan is combined with acoustic directivity measurements to derive a distribution of equivalent dipole sources on the fan surface. The results reveal that the fan behaves like a distributed dipole at blade passage tones when the upstream flow through the fan is spatially nonuniform. Numerical simulations of active noise control in the free field have been carried out using the previous aeroacoustic model of the fan and a dipole secondary source in front of the fan. The numerical results show that a single dipole control source is effective in globally controlling the sound radiation of the fan at the blade passage frequency and its first harmonic. Last, an experimental investigation of active control is presented. It consists of a SISO feedforward configuration with either a LMS algorithm (for FIR filters) or a back-retropopagation algorithm (for neural networks) using the Simulink/Dspace environment for real-time implementation.

  12. Detection of volatile and soluble general anesthetics using a fluorescence-based fiber optic sensor: recent progress in chemical sensitivity and noise sources

    NASA Astrophysics Data System (ADS)

    Yager, Paul; Abrams, Susan B.

    1992-04-01

    A fiber optic sensor for general anesthetics based on the phase transition of immobilized phospholipid vesicles is under development. Current work centers on evaluating the sensor response to different anesthetics and instrumentation design. The fluorescence of laurdan- doped liposomes is found to respond linearly to the infusible anesthetics thiopental sodium and Propofol. Preliminary experiments have been performed to determine sources of noise in the optical and electronic components of the sensor as it is now configured. One potential noise source is the liposome sample at the fiber tip; photobleaching and thermal fluctuations due to heating by the illuminating 360 nm radiation can affect measurement of the anesthetic level. Heating of the sample is a factor at high illumination levels, but photobleaching, which reduces the signal intensity, does not alter the intensity ratio upon which the anesthetic concentration measurement is based. Optical microscopy of fiber tips embedded in liposomes allows direct observation of the light intensity near the tip of the fiber despite the extreme turbidity of the suspension. Light intensity drops to less than 10% of its maximum intensity at the fiber tip within 300 micrometers . Further use of this technique should allow monitoring the effects of photobleaching on the spatial distribution of the liposomes responsible for the measured optical signal.

  13. Harmonization Initiatives in Europe

    PubMed Central

    2016-01-01

    Introduction Modern medicine is more and more based on protocols and guidelines; clinical laboratory data play very often a relevant role in these documents and for this reason the need for their harmonization is increasing. To achieve harmonized results the harmonization process must not be limited to only the analytical part, but has to include the pre- and the post-analytical phases. Results To fulfill this need the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) has started several initiatives. A Working Group on harmonization of the total testing process (WG-H) has been created with the aims of: 1) surveying and summarizing national European and pan European harmonization initiatives; 2) promoting and coordinating the dissemination of especially promising harmonization initiatives among the EFLM member societies; and 3) taking initiatives to harmonize nomenclature, units and reference intervals at a European level. The activity of the WG started this year with a questionnaire targeted at surveying the status of various harmonization activities, especially those in the pre- and post-analytical phase categories, among the European laboratory medicine societies. Conclusions Based on the results of the questionnaire, some activities promoting the dissemination of best practice in blood sampling, sample storage and transportation, in collaboration with WG on the pre-analytical phase, will be promoted, and initiatives to spread to all the European countries the use of SI units in reporting, will be undertaken. Moreover, EFLM has created a Task and Finish Group on standardization of the color coding for blood collection tube closures that is actively working to accomplish this difficult task through collaboration with manufacturers. PMID:27683503

  14. Effect of at-the-source noise reduction on performance and weights of a tilt-rotor aircraft

    NASA Technical Reports Server (NTRS)

    Gibs, J.; Stepniewski, W. Z.; Spencer, R.

    1975-01-01

    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 noise 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.

  15. Harmonic 'signatures' of microorganisms.

    PubMed

    Blake-Coleman, B C; Hutchings, M J; Silley, P

    1994-01-01

    The frequency/amplitude effect of various microorganisms exposed to periodic (time varying) electric fields, when proximate to immersed electrodes, has been studied using a novel analytical instrument. The harmonic distribution, in complex signals caused by cells exposed to harmonic free waveforms and occupying part of the electrode/suspension interface volume, was shown to be almost entirely due to the change in the standing interfacial transfer function by the (dielectrically nonlinear) presence of cells. Thus, the characteristic interfacial non-linearity is viewed as variable, being uniquely modulated by the presence of particular cells in the interfacial region. Little can be attributed to bulk (far field) effects. The tendency for subtle (characteristic) signal distortion to occur as a function of particulate (cell or molecular) occupancy of the near electrode interfacial region under controlled current conditions leads to the method of sample characterisation by harmonic (Fourier) analysis. We report here, as a sequel to our original studies (Hutchings et al., 1993; Hutchings and Blake-Coleman, 1993), preliminary results of the harmonic analysis of microbial suspensions under controlled signal conditions using a three-electrode configuration. These data provide three-dimensional graphical representations producing harmonic 'surfaces' for various microorganisms. Thus, cell type differences are characterised by their 'harmonic signature'. The visual distinction provided by these 'surface' forming three-dimensional plots is striking and gives a convincing impression of the ability to identify and enumerate specific microorganisms by acquisition of cell-modulated electrode interfacial Fourier spectra. PMID:8060593

  16. Higher harmonic generation microscopy.

    PubMed

    Sun, Chi-Kuang

    2005-01-01

    Higher harmonic-generation, including second harmonic generation and third harmonic generation, leaves no energy deposition to the interacted matters due to its virtual-level transition characteristic, providing a truly non-invasive modality and is ideal for in vivo imaging of live specimens without any preparation. Second harmonic generation microscopy provides images on stacked membranes and arranged proteins with organized nano-structures due to the bio-photonic crystalline effect. Third harmonic generation microscopy provides general cellular or subcellular interface imaging due to optical inhomogeneity. Due to their virtual-transition nature, no saturation or bleaching in the generated signal is expected. With no energy release, continuous viewing without compromising sample viability can thus be achieved. Combined with its nonlinearity, higher harmonic generation microscopy provides sub-micron three-dimensional sectioning capability and millimeter penetration in live samples without using fluorescence and exogenous markers, offering morphological, structural, functional, and cellular information of biomedical specimens without modifying their natural biological and optical environments.

  17. Analysis of Vibration and Acoustic Noise in Permanent Magnet Motors.

    NASA Astrophysics Data System (ADS)

    Hwang, Sangmoon

    The drive motor is a frequent source of vibration and acoustic noise in many precision spindle motors. One of the electromagnetic sources 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 noise of electromagnetic origin is difficult to predict and its exact mechanism is unclear. The mechanism of noise 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 source 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 harmonics, 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

  18. A new method for both harmonic voltage and harmonic current suppression and power factor correction in industrial power systems

    SciTech Connect

    Cheng, H.; Sasaki, Hiroshi; Yorino, Naoto

    1995-12-31

    This paper proposes a new method for designing a group of single tuned filters for both harmonic current injection suppression and harmonic voltage distortion reduction and power factor correction. The proposed method is based on three purposes: (1) reduction of harmonic voltage distortion in the source terminals to an acceptable level, (2) suppression of harmonic current injection in the source terminals to an acceptable level, (3) improvement of power factor at the source terminals. To determine the size of the capacitor in a group of single tuned filters, three new NLP mathematical formulations will be introduced. The first is to suppress harmonic current injection within an acceptable level. The second is to minimize the fundamental reactive power output while reducing harmonic voltage distortion to an acceptable level. The third is to determine an optimal assignment of reactive power output based on the results of harmonic voltage reduction and power factor correction. This new method has been demonstrated for designing a group of single tuned filters and its validity has been successfully confirmed through numerical simulation in a 35 KV industrial power system. The proposed method can efficiently provide an optimal coordination in a group of single tuned filters relating to suppressing harmonic current injection, reducing harmonic voltage distortion and improving power factor.

  19. Airport noise

    NASA Technical Reports Server (NTRS)

    Pendley, R. E.

    1982-01-01

    The problem of airport noise at several airports and air bases is detailed. Community reactions to the noise, steps taken to reduce jet engine noise, and the effect of airport use restrictions and curfews on air transportation are discussed. The adverse effect of changes in allowable operational noise on airport safety and altenative means for reducing noise pollution are considered. Community-airport relations and public relations are discussed.

  20. A statistical evaluation of effective time constants of random telegraph noise with various operation timings of in-pixel source follower transistors

    NASA Astrophysics Data System (ADS)

    Yonezawa, A.; Kuroda, R.; Teramoto, A.; Obara, T.; Sugawa, S.

    2014-03-01

    We evaluated effective time constants of random telegraph noise (RTN) with various operation timings of in-pixel source follower transistors statistically, and discuss the dependency of RTN time constants on the duty ratio (on/off ratio) of MOSFET which is controlled by the gate to source voltage (VGS). Under a general readout operation of CMOS image sensor (CIS), the row selected pixel-source followers (SFs) turn on and not selected pixel-SFs operate at different bias conditions depending on the select switch position; when select switch locate in between the SF driver and column output line, SF drivers nearly turn off. The duty ratio and cyclic period of selected time of SF driver depends on the operation timing determined by the column read out sequence. By changing the duty ratio from 1 to 7.6 x 10-3, time constant ratio of RTN (time to capture <τc<)/(time to emission <τe<) of a part of MOSFETs increased while RTN amplitudes were almost the same regardless of the duty ratio. In these MOSFETs, <τc< increased and the majority of <τe< decreased and the minority of <τe< increased by decreasing the duty ratio. The same tendencies of behaviors of <τc< and <τe< were obtained when VGS was decreased. This indicates that the effective <τc< and <τe< converge to those under off state as duty ratio decreases. These results are important for the noise reduction, detection and analysis of in pixel-SF with RTN.

  1. Proceedings of the 1986 international conference on noise control engineering. Volume 1

    SciTech Connect

    Lotz, R.

    1986-01-01

    These proceedings collect papers on noise pollution. Topics include: noise sources, noise of chain conveyors in mining, control of noise sources in power plants, noise control elements, vibration, a method of noise control in a nuclear power plant, biological effects of noise, statistical audio dosimetry, and power house noise control.

  2. Nonlinear harmonic generation and proposed experimental verification in SASE FELs.

    SciTech Connect

    Biedron, S. G.; Freund, H. P.; Milton, S. V.

    1999-08-24

    Recently, a 3D, polychromatic, nonlinear simulation code was developed to study the growth of nonlinear harmonics in self-amplified spontaneous emission (SASE) free-electron lasers (FELs). The simulation was applied to the parameters for each stage of the Advanced Photon Source (APS) SASE FEL, intended for operation in the visible, UV, and short UV wavelength regimes, respectively, to study the presence of nonlinear harmonic generation. Significant nonlinear harmonic 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 harmonic generation at the APS SASE FEL will be given.

  3. Comparative Analysis of Instruments Measuring Time Varying Harmonics

    NASA Astrophysics Data System (ADS)

    Belchior, Fernando Nunes; Ribeiro, Paulo Fernando; Carvalho, Frederico Marques

    2016-08-01

    This paper aims to evaluate the performance of commercial class A and class S power quality (PQ) instruments when measuring time-varying harmonics. By using a high precision programmable voltage and current source, two meters from different manufacturers are analyzed and compared. Three-phase voltage signals are applied to PQ instruments, considering 3 situations of time-varying harmonic distortions, whose harmonic distortion values are in accordance with typical values found in power systems. This work is relevant considering that international standardization documents do not pay much attention to this aspect of harmonic distortion.

  4. Investigations on the effect of frequency and noise in a localization technique based on microwave imaging for an in-body RF source

    NASA Astrophysics Data System (ADS)

    Chandra, Rohit; Balasingham, Ilangko

    2015-05-01

    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-noise 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 source. 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-noise 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 noise. 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.

  5. New constraints on the magmatic system beneath Newberry Volcano from the analysis of active and passive source seismic data, and ambient noise

    NASA Astrophysics Data System (ADS)

    Heath, B.; Toomey, D. R.; Hooft, E. E. E.

    2014-12-01

    Magmatic systems beneath arc-volcanoes are often poorly resolved by seismic imaging due to the small spatial scale and large magnitude of crustal heterogeneity in combination with field experiments that sparsely sample the wavefield. Here we report on our continued analysis of seismic data from a line of densely-spaced (~300 m), three-component seismometers installed on Newberry Volcano in central Oregon for ~3 weeks; the array recorded an explosive shot, ~20 teleseismic events, and ambient noise. By jointly inverting both active and passive-source travel time data, the resulting tomographic image reveals a more detailed view of the presumed rhyolitic magma chamber at ~3-5 km depth, previously imaged by Achauer et al. (1988) and Beachly et al. (2012). The magma chamber is elongated perpendicular to the trend of extensional faulting and encircled by hypocenters of small (M < 2) earthquakes located by PNSN. We also model teleseismic waveforms using a 2-D synthetic seismogram code to recreate anomalous amplitudes observed in the P-wave coda for sites within the caldera. Autocorrelation of ambient noise data also reveals large amplitude waveforms for a small but spatially grouped set of stations, also located within the caldera. On the basis of these noise observations and 2-D synthetic models, which both require slow seismic speeds at depth, we conclude that our tomographic model underestimates low-velocity anomalies associated with the inferred crustal magma chamber; this is due in large part to wavefront healing, which reduces observed travel time anomalies, and regularization constraints, which minimize model perturbations. Only by using various methods that interrogate different aspects of the seismic data are we able to more realistically constrain the complicated, heterogeneous volcanic system. In particular, modeling of waveform characteristics provides a better measure of the spatial scale and magnitude of crustal velocities near magmatic systems.

  6. Perfusion harmonic imaging of the human brain

    NASA Astrophysics Data System (ADS)

    Metzler, Volker H.; Seidel, Guenter; Wiesmann, Martin; Meyer, Karsten; Aach, Til

    2003-05-01

    The fast visualisation of cerebral microcirculation supports diagnosis of acute cerebrovascular diseases. However, the commonly used CT/MRI-based methods are time consuming and, moreover, costly. Therefore we propose an alternative approach to brain perfusion imaging by means of ultrasonography. In spite of the low signal/noise-ratio of transcranial ultrasound and the high impedance of the skull, flow images of cerebral blood flow can be derived by capturing the kinetics of appropriate contrast agents by harmonic ultrasound image sequences. In this paper we propose three different methods for human brain perfusion imaging, each of which yielding flow images indicating the status of the patient's cerebral microcirculation by visualising local flow parameters. Bolus harmonic imaging (BHI) displays the flow kinetics of bolus injections, while replenishment (RHI) and diminution harmonic imaging (DHI) compute flow characteristics from contrast agent continuous infusions. RHI measures the contrast agents kinetics in the influx phase and DHI displays the diminution kinetics of the contrast agent acquired from the decay phase. In clinical studies, BHI- and RHI-parameter images were found to represent comprehensive and reproducible distributions of physiological cerebral blood flow. For DHI it is shown, that bubble destruction and hence perfusion phenomena principally can be displayed. Generally, perfusion harmonic imaging enables reliable and fast bedside imaging of human brain perfusion. Due to its cost efficiency it complements cerebrovascular diagnostics by established CT/MRI-based methods.

  7. The effects of noise on man

    SciTech Connect

    Kryter, K.D.

    1985-01-01

    As a reference source of research concerning effects of noise on people, this book reports and analyzes procedures used in regulation and control of noise. Quantitative relations are formed between physical measures of environmental noise and the reactions of people and communities to noise. The author reviews scientific and engineering research published from 1970 to the present. The Effects of Noise on Man, Second Edition discusses: adverse effects of noise and noise-induced hearing loss on speech communications; damage to hearing from ''everyday'' noise; damage to hearing from industrial noise and gunfire; work performance in noise; effects of noise on non-auditory systems of the body and sleep; aircraft and street traffic noise and its effects on health, annoyance, and house depreciation; physical measurements used for the assessment and control of environmental noise; federal standards and guidelines for community noise and proposed modification based on recent research findings.

  8. School Noise and Its Control

    ERIC Educational Resources Information Center

    Ikenberrgy, Larry D.

    1974-01-01

    Sources of noises affecting schools and their hindrance of learning are presented. Noise levels for different activities are tabled and possible methods for controlling such noises are suggested. Internal to the school, shop and music levels are the most severe. More care in site selection and design considerations are recommended. (LS)

  9. Reducing environmental noise impacts: A USAREUR noise management program handbook

    NASA Astrophysics Data System (ADS)

    Feather, Timothy D.; Shekell, Ted K.

    1991-06-01

    Noise pollution is a major environmental problem faced by the U.S. Army in Europe. Noise-related complaints from German citizens can escalate into intense political issues in German communities. This in turn hampers efficient operation of military training and often times threatens the Army's mission. In order to remedy these problems, USAREUR has developed a noise management program. A successful noise management program will limit the impact of unavoidable noise on the populace. This report, a component of the noise management program, is a reference document for noise management planning. It contains guidelines and rules-of-thumb for noise management. This document contains procedures which operation and training level personnel can understand and apply in their day to day noise management planning. Noise mitigation tips are given. Basic technical information that will aid in understanding noise mitigation is provided along with noise management through land use planning. Noise management for specific components of the military community, (airfields, base operations, training areas, and housing and recreation areas) are addressed. The nature of noise generated, means of noise abatement at the source, path, and receiver (both physical and organizational/public relations methods), and a case study example are described.

  10. Optical harmonic generator

    DOEpatents

    Summers, Mark A.; Eimerl, David; Boyd, Robert D.

    1985-01-01

    A pair of uniaxial birefringent crystal elements are fixed together to form a serially arranged, integral assembly which, alternatively, provides either a linearly or elliptically polarized second-harmonic output wave or a linearly polarized third-harmonic output wave. The "extraordinary" or "e" directions of the crystal elements are oriented in the integral assembly to be in quadrature (90.degree.). For a second-harmonic generation in the Type-II-Type-II angle tuned case, the input fundamental wave has equal amplitude "o" and "e" components. For a third-harmonic generation, the input fundamental wave has "o" and "e" components whose amplitudes are in a ratio of 2:1 ("o":"e" reference first crystal). In the typical case of a linearly polarized input fundamental wave this can be accomplished by simply rotating the crystal assembly about the input beam direction by 10.degree.. For both second and third harmonic generation input precise phase-matching is achieved by tilting the crystal assembly about its two sensitive axes ("o").

  11. Optical harmonic generator

    DOEpatents

    Summers, M.A.; Eimerl, D.; Boyd, R.D.

    1982-06-10

    A pair of uniaxial birefringent crystal elements are fixed together to form a serially arranged, integral assembly which, alternatively, provides either a linearly or elliptically polarized second-harmonic output wave or a linearly polarized third-harmonic output wave. The extraordinary or e directions of the crystal elements are oriented in the integral assembly to be in quadrature (90/sup 0/). For a second-harmonic generation in the Type-II-Type-II angle tuned case, the input fundamental wave has equal amplitude o and e components. For a third-harmonic generation, the input fundamental wave has o and e components whose amplitudes are in a ratio of 2:1 (o:e reference first crystal). In the typical case of a linearly polarized input fundamental wave this can be accomplished by simply rotating the crystal assembly about the input beam direction by 10/sup 0/. For both second and third harmonic generation input precise phase-matching is achieved by tilting the crystal assembly about its two sensitive axeses (o).

  12. Playback Experiments for Noise Exposure.

    PubMed

    Holles, Sophie; Simpson, Stephen D; Lecchini, David; Radford, Andrew N

    2016-01-01

    Playbacks are a useful tool for conducting well-controlled and replicated experiments on the effects of anthropogenic noise, particularly for repeated exposures. However, playbacks are unlikely to fully reproduce original sources of anthropogenic noise. Here we examined the sound pressure and particle acceleration of boat noise playbacks in a field experiment and reveal that although there remain recognized limitations, the signal-to-noise ratios of boat playbacks to ambient noise do not exceed those of a real boat. The experimental setup tested is therefore of value for use in experiments on the effects of repeated exposure of aquatic animals to boat noise. PMID:26610992

  13. Stochastic Regulation of her1/7 Gene Expression Is the Source of Noise in the Zebrafish Somite Clock Counteracted by Notch Signalling

    PubMed Central

    Jenkins, Robert P.; Hanisch, Anja; Soza-Ried, Cristian; Sahai, Erik

    2015-01-01

    The somite segmentation clock is a robust oscillator used to generate regularly-sized segments during early vertebrate embryogenesis. It has been proposed that the clocks of neighbouring cells are synchronised via inter-cellular Notch signalling, in order to overcome the effects of noisy gene expression. When Notch-dependent communication between cells fails, the clocks of individual cells operate erratically and lose synchrony over a period of about 5 to 8 segmentation clock cycles (2–3 hours in the zebrafish). Here, we quantitatively investigate the effects of stochasticity on cell synchrony, using mathematical modelling, to investigate the likely source of such noise. We find that variations in the transcription, translation and degradation rate of key Notch signalling regulators do not explain the in vivo kinetics of desynchronisation. Rather, the analysis predicts that clock desynchronisation, in the absence of Notch signalling, is due to the stochastic dissociation of Her1/7 repressor proteins from the oscillating her1/7 autorepressed target genes. Using in situ hybridisation to visualise sites of active her1 transcription, we measure an average delay of approximately three minutes between the times of activation of the two her1 alleles in a cell. Our model shows that such a delay is sufficient to explain the in vivo rate of clock desynchronisation in Notch pathway mutant embryos and also that Notch-mediated synchronisation is sufficient to overcome this stochastic variation. This suggests that the stochastic nature of repressor/DNA dissociation is the major source of noise in the segmentation clock. PMID:26588097

  14. Harmonic uniflow engine

    DOEpatents

    Bennett, Charles L.

    2016-03-22

    A reciprocating-piston uniflow engine includes a harmonic oscillator inlet valve capable of oscillating at a resonant frequency for controlling the flow of working fluid into the engine. In particular, the inlet valve includes an inlet valve head and a spring arranged together as a harmonic oscillator so that the inlet valve head is moveable from an unbiased equilibrium position to a biased closed position occluding an inlet. When released, the inlet valve head undergoes a single oscillation past the equilibrium position 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. In other embodiments, the harmonic oscillator arrangement of the inlet valve enables the uniflow engine to be reversibly operated as a uniflow compressor.

  15. Inlet noise on 0.5-meter-diameter NASA QF-1 fan as measured in an unmodified compressor aerodynamic test facility and in an anechoic chamber

    NASA Technical Reports Server (NTRS)

    Gelder, T. F.; Soltis, R. F.

    1975-01-01

    Narrowband analysis revealed grossly similar sound pressure level spectra in each facility. Blade passing frequency (BPF) noise and multiple pure tone (MPT) noise were superimposed on a broadband (BB) base noise. From one-third octave bandwidth sound power analyses the BPF noise (harmonics combined), and the MPT noise (harmonics combined, excepting BPF's) agreed between facilities within 1.5 db or less over the range of speeds and flows tested. Detailed noise and aerodynamic performance is also presented.

  16. Broadband beam shaping with harmonic diffractive optics.

    PubMed

    Singh, Manisha; Tervo, Jani; Turunen, Jari

    2014-09-22

    We consider spatial shaping of broadband (either stationary or pulsed) spatially coherent light, comparing refractive, standard diffractive, and harmonic diffractive (modulo 2πM) elements. Considering frequency-integrated target profiles we show that, contrary to common belief, standard diffractive (M = 1) elements work reasonably well for, e.g., Gaussian femtosecond pulses and spatially coherent amplified-spontaneous-emission sources such as superluminescent diodes. It is also shown that harmonic elements with M ≥ 5 behave in essentially the same way as refractive elements and clearly outperform standard diffractive elements for highly broadband light.

  17. Noise in biological circuits

    SciTech Connect

    Simpson, Michael L; Allen, Michael S.; Cox, Chris D.; Dar, Roy D.; Karig, David K; McCollum, James M.; Cooke, John F

    2009-01-01

    Noise biology focuses on the sources, processing, and biological consequences of the inherent stochastic fluctuations in molecular transitions or interactions that control cellular behavior. These fluctuations are especially pronounced in small systems where the magnitudes of the fluctuations approach or exceed the mean value of the molecular population. Noise biology is an essential component of nanomedicine where the communication of information is across a boundary that separates small synthetic and biological systems that are bound by their size to reside in environments of large fluctuations. Here we review the fundamentals of the computational, analytical, and experimental approaches to noise biology. We review results that show that the competition between the benefits of low noise and those of low population has resulted in the evolution of genetic system architectures that produce an uneven distribution of stochasticity across the molecular components of cells and, in some cases, use noise to drive biological function. We review the exact and approximate approaches to gene circuit noise analysis and simulation, and reviewmany of the key experimental results obtained using flow cytometry and time-lapse fluorescent microscopy. In addition, we consider the probative value of noise with a discussion of using measured noise properties to elucidate the structure and function of the underlying gene circuit. We conclude with a discussion of the frontiers of and significant future challenges for noise biology.

  18. Harmonic Frequency Lowering

    PubMed Central

    Kirchberger, Martin

    2016-01-01

    A novel algorithm for frequency lowering in music was developed and experimentally tested in hearing-impaired listeners. Harmonic frequency lowering (HFL) combines frequency transposition and frequency compression to preserve the harmonic content of music stimuli. Listeners were asked to make judgments regarding detail and sound quality in music stimuli. Stimuli were presented under different signal processing conditions: original, low-pass filtered, HFL, and nonlinear frequency compressed. Results showed that participants reported perceiving the most detail in the HFL condition. In addition, there was no difference in sound quality across conditions. PMID:26834122

  19. Booster double harmonic setup notes

    SciTech Connect

    Gardner, C. J.

    2015-02-17

    The motivation behind implementing a booster double harmonic include the reduced transverse space charge force from a reduced peak beam current and reduced momentum spread of the beam, both of which can be achieved from flattening the RF bucket. RF capture and acceleration of polarized protons (PP) is first set up in the single harmonic mode with RF harmonic h=1. Once capture and acceleration have been set up in the single harmonic mode, the second harmonic system is brought on and programmed to operate in concert with the single harmonic system.

  20. Ultrafast Harmonic Coherent Compound (UHCC) imaging for high frame rate echocardiography and Shear Wave Elastography

    PubMed Central

    Correia, Mafalda; Provost, Jean; Chatelin, Simon; Villemain, Olivier; Tanter, Mickael; Pernot, Mathieu

    2016-01-01

    Transthoracic shear wave elastography of the myocardium remains very challenging due to the poor quality of transthoracic ultrafast imaging and the presence of clutter noise, jitter, phase aberration, and ultrasound reverberation. Several approaches, such as, e.g., diverging-wave coherent compounding or focused harmonic imaging have been proposed to improve the imaging quality. In this study, we introduce ultrafast harmonic coherent compounding (UHCC), in which pulse-inverted diverging-waves are emitted and coherently compounded, and show that such an approach can be used to enhance both Shear Wave Elastography (SWE) and high frame rate B-mode Imaging. UHCC SWE was first tested in phantoms containing an aberrating layer and was compared against pulse-inversion harmonic imaging and against ultrafast coherent compounding (UCC) imaging at the fundamental frequency. In-vivo feasibility of the technique was then evaluated in six healthy volunteers by measuring myocardial stiffness during diastole in transthoracic imaging. We also demonstrated that improvements in imaging quality could be achieved using UHCC B-mode imaging in healthy volunteers. The quality of transthoracic images of the heart was found to be improved with the number of pulse-inverted diverging waves with reduction of the imaging mean clutter level up to 13.8-dB when compared against UCC at the fundamental frequency. These results demonstrated that UHCC B-mode imaging is promising for imaging deep tissues exposed to aberration sources with a high frame-rate. PMID:26890730