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1

The Effects of Crosswind Flight on Rotor Harmonic Noise Radiation  

NASA Technical Reports Server (NTRS)

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.

Greenwood, Eric; Sim, Ben W.

2013-01-01

2

Community noise sources and noise control issues  

NASA Technical Reports Server (NTRS)

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.

Nihart, Gene L.

1992-01-01

3

Applying the harmonic plus noise model in concatenative speech synthesis  

Microsoft Academic Search

This paper describes the application of the harmonic plus noise model (HNM) for concatenative text-to-speech (TTS) synthesis. In the context of HNM, speech signals are represented as a time-varying harmonic component plus a modulated noise component. The decomposition of a speech signal into these two components allows for more natural-sounding modifications of the signal (e.g., by using different and better

Yannis Stylianou

2001-01-01

4

Temporal Characterization of Aircraft Noise Sources  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

5

Tonal strength of harmonic complex tones in machinery noise  

NASA Astrophysics Data System (ADS)

The sounds of machines often contain families of harmonically related sine waves that are referred to as harmonic complex tones. The perceived tonal strength of these types of sounds can adversely influence people's impressions of the sound. While a complex tone is comprised of many sine waves, usually only one prominent pitch sensation is produced. It can be argued that harmonic complex tones are perceived as a single entities, not as a sum of individual tones. A series of psychoacoustics tests was conducted to evaluate tonal prominence of harmonic complex tones. Two sounds of equal loudness were played to subjects. One was a harmonic complex tone in noise and the other was a single tone in noise. Subjects were asked to equalize the perceived tonalness of the two sounds by adjusting the tone to noise ratio of the single tone in noise. Tonalness and Terhardt's pitch perception models were applied to the pairs of sounds used in each test. The feasibility of replacing harmonic complex tones with a tonally equivalent simple sound was investigated, and strong correlations between Aures' tonality for the simple and complex tones were found.

Lee, Kyoung Hoon; Davies, Patricia; Surprenant, Aimee M.

2005-09-01

6

High speed helicopter noise sources  

NASA Technical Reports Server (NTRS)

The state-of-the art of helicopter rotor impulsive noise is reviewed. A triangulation technique for locating impulsive noise sources is developed using once-per-rev index signals as time references. A computer program (INSL) was written implementing this technique. Applying triangulation to the full-scale UH-1 noise data of NASA/Ames Research Center 40- by 80-Foot Wind Tunnel, three different noise sources are found on the rotor disk. The primary sources of thickness noise are in the second quadrant and on the advancing side of rotor disk. Two aerodynamic sources due to blade/vortex interaction are found in the first quadrant.

Lee, A.

1977-01-01

7

SPEECH ENHANCEMENT IN CAR NOISE ENVIRONMENT BASED ON AN ANALYSIS-SYNTHESIS APPROACH USING HARMONIC NOISE MODEL  

E-print Network

SPEECH ENHANCEMENT IN CAR NOISE ENVIRONMENT BASED ON AN ANALYSIS- SYNTHESIS APPROACH USING HARMONIC using harmonic noise model (HNM) in car noise environment. The major advantages of this method are effective suppression of car noise even in very low signal-to-noise ratio environments and mitigation

So, Hing-Cheung

8

Noise cancelling of MRS signals combining model-based removal of powerline harmonics and multichannel Wiener filtering  

NASA Astrophysics Data System (ADS)

The fidelity of magnetic resonance sounding signals is often severely degraded by noise, primarily electrical interference from powerline harmonics and short electromagnetic discharges. In many circumstances, the noise originates from multiple sources. We show that noise cancelling can be improved if the multiple origins of noise are taken into account. In particular, a method is developed where powerline harmonics are efficiently removed through a model-based approach. Subsequently, standard multichannel Wiener filtering can be used to provide a further noise reduction. The performance of the method depends on the distribution of noise on the particular site of measurement. Simulations on synthetic signals embedded in real noise recordings show that the combined approach can improve the signal-to-noise ratio with an accompanying improvement in retrieval of model parameters.

Larsen, Jakob Juul; Dalgaard, Esben; Auken, Esben

2014-02-01

9

Determination of noise descriptors and criteria for pyrotechnic noise sources  

NASA Astrophysics Data System (ADS)

A noise study was conducted to determine appropriate noise descriptors and criteria for assessing pyrotechnic noise sources. The study was carried out to support an environmental impact statement (EIS) that defined sensitive land uses adjacent to reservoirs in New York City area, where potential noise impacts from avian dispersion measures would occur. The pyrotechnic techniques defined as impulsive noise sources are among the avian dispersion measures that would be used at the reservoirs. Determining appropriate noise descriptors and criteria was critical to the EIS because of the distinctive sound characteristics of pyrotechnic impulse noise sources, the lack of published literature on assessing them, and the absence of corresponding noise regulations. Noise descriptors and criteria used for EIS in the United States were investigated, and noise measurements for pyrotechnic noise sources and some impulsive noise sources were also performed. The study results demonstrate that C-weighted DNL is an appropriate descriptor for assessing noise impacts from the pyrotechnics based on the U.S. Army Environmental Noise Management Program criteria, and peak hour A-weighted Leq(1) is a suitable noise descriptor for determining noise impacts for avian dispersion measures, including the pyrotechnics, based on the New York City Environmental Quality Review criteria.

Wu, Weixiong

2005-04-01

10

Noise Cancelling of Multichannel MRS Signals with a Time Dependent Harmonic Model  

NASA Astrophysics Data System (ADS)

Magnetic resonance sounding (MRS) is a non-invasive geophysical technique applicable to groundwater investigations and provides a direct quantification of the subsurface water content from surface measurements. The technique is susceptible to electromagnetic noise and signal processing must be employed to retrieve the NMR signal from noisy measurements. The latest generation of MRS equipment is multichannel systems where a primary coil records the noisy NMR signal. Additional coils, physically displaced from the primary coil, synchronously measure the noise which is then subtracted from the primary coil with multichannel Wiener filtering. Unfortunately, this approach fails to take into account that noise can originate from several sources and as a result the noise cancelling is not always optimum. To remedy this problem it can be utilized that one of the major noise components in MRS signals is powerline harmonics, i.e. the noise is a sum of sinusoidal signals all harmonically related to the same fundamental powerline frequency. This implies that it is possible to create a model of the powerline harmonic noise that can be fitted to the MRS recordings and subtracted from these before employing multichannel Wiener filtering as we have recently demonstrated. A fundamental assumption in that work was that the powerline frequency and the amplitude and phase of each harmonic remained constant throughout a signal record of approximately 1 s duration. This assumption is often valid, but not always. In this study we present an extension of this method where the variations in the powerline signal are accounted for by a time dependent model. The signal records from each coil are divided into short overlapping segments, with a typical duration of 100 ms, and a harmonic model with time independent parameters is fitted to each segment. The fitting parameters from each segment are subsequently splined to a full harmonic model where all parameters; fundamental powerline frequency and phase and amplitude of each powerline harmonic are time dependent. If one of the powerline harmonic frequencies is close to the frequency of the NMR signal, the NMR signal in the primary coil is mistakenly fitted as a variation in the harmonic signal and the retrieved MRS signal is severely distorted. In these cases, the variation in the powerline frequency is instead tracked without this particular harmonic and the variations in amplitude and phase of the harmonic is found with a multichannel algorithm where information on phase and amplitude are obtained from the NMR free signals in the reference channels and fused with data from the primary channel for adequate modeling. We present an evaluation of the proposed method with data recorded on the outskirts of Hannover city centre, Germany. A synthetic NMR signal is embedded in the records and recovered with the new scheme and the standard methods. The benefits and drawbacks of each method are compared.

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

2013-12-01

11

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

ERIC Educational Resources Information Center

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)

de Krom, Guus

1993-01-01

12

International harmonization of approaches to define underwater noise exposure criteria.  

PubMed

An international workshop was held in 2013 with a group comprised of scientists, regulators, and other stakeholders. The workshop focused on how new scientific information related to the effects of underwater noise on marine life influences permitting practices for human activities at sea. Also discussed were how individual countries regulate underwater noise and opportunities for harmonizing approaches on an international scale. The workshop was intended to build momentum toward an international exchange of information and to potentially establish a network for the regulation community. Large gaps in knowledge still exist. In particular, hearing sensitivity in baleen whales, long-term effects of TTS and relevant information on other taxa such as bony fishes, sharks, or invertebrate species, need to be studied more intensively. Regulators need reliable and understandable baseline information on cause-effect relationships. This information could be partially provided through targeted training material for regulators. Another critical regulator need is for opportunities to speak with each other and share knowledge across wide geographic regions. Additional keys to future success are commitments from the regulatory senior management and politicians, invite nations who were not represented in the discussions so far and raise awareness of this topic across a broad audience, including the public. PMID:25236016

Lucke, Klaus; Winter, Erwin; Lam, Frans-Peter; Scowcroft, Gail; Hawkins, Anthony; Popper, Arthur N

2014-04-01

13

The Active Minimisation of Harmonic Enclosed Sound Fields with Particular Application to Propeller Induced Cabin Noise.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. This work considers the use of secondary acoustic sources for the reduction of noise levels in harmonically excited enclosed sound fields. This possibility is studied initially through the use of an analytical model of a single frequency "two-dimensional" rectangular, enclosed sound field of low modal density. Quadratic optimisation theory is used to predict the effectiveness of these active techniques for reducing sound levels. It is shown that if one chooses to minimise the total acoustic potential energy of the sound field then substantial global reductions in sound pressure may be achieved. The conditions required to achieve these reductions are discussed, and in particular the effect of secondary source location is demonstrated. The unsuitability of this as a practical control system cost function is discussed, and as an alternative it is suggested that one can minimise the sum of the squared pressures over a number of discrete sensors. Both theoretical and experimental results from using this cost function are presented. These show good agreement. The importance of both secondary source and error sensor locations is discussed. The reduction of low frequency propeller induced cabin noise is a possible application of active noise control. Simplified analytical models of the structural and internal acoustic response of a 48 seat, twin turboprop passenger aircraft are presented. These consist of the structural response of an isotropic, thin cylindrical shell of finite length and the acoustic response of the enclosed cylindrical sound field. It is shown that, provided the external acoustic pressure forcing of the shell is modelled representatively of measured propeller pressure fields, then these simple models provide results which demonstrate good agreement with measured data, at least for frequencies encompassing the first two propeller blade passage harmonics (88 Hz and 176 Hz). These models are used to predict the effectiveness of active noise control when it is applied to reduce the average sound pressure level over a typical seated head height plane in the passenger cabin. Results of the first two blade passage harmonics are presented for systems consisting of up to 24 secondary sources and 48 error sensors. In general the predictions suggest that active noise control shows promise as a potential method of reducing low frequency propeller induced cabin noise.

Bullmore, Andrew John

14

Excess noise in fiber gyroscope sources  

Microsoft Academic Search

Excess noise was measured in three potential interferometric fiber gyroscope sources, superluminescent diodes at 0.83 and 1.3 micron, and a superfluorescent fiber source at 1.06 micron. All three sources showed limiting signal-to-noise ratios in the 128-132 dB range (1 Hz bandwidth at 100 kHz), in agreement with their measured linewidths. The impact of the excess noise on the fiber gyro

W. K. Burns; R. P. Moeller; A. Dandridge

1990-01-01

15

Excess noise in fiber gyroscope sources  

Microsoft Academic Search

Excess noise was measured in three potential interferometric fiber gyroscope sources, superluminescent diodes at 0.83 and 1.3 ?m, and a superfluorescent fiber source at 1.06 ?m. All three sources showed limiting signal-to-noise ratios in the 128-132 dB range (1 Hz bandwidth at 100 kHz), in agreement with their measured linewidths. The impact of the excess noise on the fiber gyro

W. K. Burns; R. P. Moeller; A. Dandridge

1990-01-01

16

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

NASA Technical Reports Server (NTRS)

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

Rickley, E. J.

1990-01-01

17

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

NASA Astrophysics Data System (ADS)

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

Rickley, E. J.

1990-04-01

18

Source and processing effects on noise correlations  

NASA Astrophysics Data System (ADS)

We quantify the effects of spatially heterogeneous noise sources and seismic processing on noise correlation measurements and their sensitivity to Earth structure. Using numerical wavefield simulations and adjoint techniques, we calculate interstation correlations and sensitivity kernels for arbitrarily distributed noise sources where-as in the real Earth-different frequencies are generated in different locations. While both heterogeneous noise sources and processing can have profound effects on noise correlation waveforms, narrow-band traveltime measurements are less affected, in accord with previous analytical studies. Sensitivities to Earth structure depend strongly on the source distribution and the processing scheme, and they reveal exotic frequency dependencies that go beyond the well-known frequency scaling of the Fresnel zone width. Our results indicate that modern full waveform inversion applied to noise correlations is not possible unless one of the following measures is taken: (1) properly account for noise source distribution and processing, or (2) limit measurements to phase or time shifts in narrow frequency bands. Failure to do so can lead to erroneous misfits, tomographic artefacts, and reduced resolution.

Fichtner, Andreas

2014-06-01

19

Imaging of directional distributed noise sources  

NASA Astrophysics Data System (ADS)

This study relates to the acoustic imaging of noise sources that are distributed and strongly directional, such as in turbulent jets. The goal is to generate high-resolution noise source maps with self-consistency, i.e., their integration over the extent of the noise source region gives the far-field pressure auto-spectrum for a particular emission direction. Self-consistency is possible by including a directivity factor in the formulation of the source cross-spectral density. The resulting source distribution is based on the complex coherence, rather than the cross-spectrum, of the measured acoustic field. For jet noise, whose spectral nature changes with emission angle, it is necessary to conduct the measurements with a narrow-aperture array. Three coherence-based imaging methods were applied to a Mach 0.9 turbulent jet: delay-and-sum beamforming; deconvolution of the beamformer output; and direct spectral estimation that relies on minimizing the difference between the measured and modeled coherences of the acoustic field. The delay-and-sum beamforming generates noise source maps with strong spatial distortions and sidelobes. Deconvolution leads to a five-fold improvement in spatial resolution and significantly reduces the intensity of the sidelobes. The direct spectral estimation produces maps very similar to those obtained by deconvolution. The coherence-based noise source maps, obtained by deconvolution or direct spectral estimation, are similar at small and large observation angles relative to the jet axis.

Papamoschou, D.

2011-05-01

20

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

NASA Technical Reports Server (NTRS)

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.

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

2012-01-01

21

Brilliant high harmonic sources with extended cut-off  

SciTech Connect

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.

Seres, Josef; Spielmann, Christian [Institut fuer Optik und Quantenelektronik Friedrich Schiller Universitaet Jena, Max Wien Platz 07743 Jena (Germany); Physikalisches Institut EP1, Universitaet Wuerzburg, Am Hubland, 97074 Wuerzburg (Germany); Seres, Enikoe [Institut fuer Optik und Quantenelektronik Friedrich Schiller Universitaet Jena, Max Wien Platz 07743 Jena (Germany)

2010-02-02

22

The Source of Propeller Noise  

NASA Technical Reports Server (NTRS)

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.

Ernsthausen, W

1937-01-01

23

SUPERDIFFUSION OF ENERGY IN A CHAIN OF HARMONIC OSCILLATORS WITH NOISE  

E-print Network

SUPERDIFFUSION OF ENERGY IN A CHAIN OF HARMONIC OSCILLATORS WITH NOISE MILTON JARA, TOMASZ and momentum, like random exchange of velocity between neareast neighbors particles [1, 2]. In these mod- els in [4] that energy fluctuations evolve diffusively following the heat equation. The main result

Paris-Sud XI, Université de

24

ON THE IMPLEMENTATION OF THE HARMONIC PLUS NOISE MODEL FOR CONCATENATIVE SPEECH SYNTHESIS  

E-print Network

, speech signals may be encoded by speech models. These models are required to compress the speech database­ PSOLA method. In MBROLA, the voiced parts of the speech database are resynthesized with constant phaseON THE IMPLEMENTATION OF THE HARMONIC PLUS NOISE MODEL FOR CONCATENATIVE SPEECH SYNTHESIS Yannis

Greenberg, Albert

25

ON THE IMPLEMENTATION OF THE HARMONIC PLUS NOISE MODEL FOR CONCATENATIVE SPEECH SYNTHESIS  

E-print Network

, speech signals may be encoded by speech models. These models are required to compress the speech database- PSOLA method. In MBROLA, the voiced parts of the speech database are resynthesized with constant phaseON THE IMPLEMENTATION OF THE HARMONIC PLUS NOISE MODEL FOR CONCATENATIVE SPEECH SYNTHESIS Yannis

Greenberg, Albert

26

Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise  

Microsoft Academic Search

An important source mechanism of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-inch Source Diagnostic Test

M. Nallasamy; E. Envia; S. A. Thorp; A. Shabbir

2002-01-01

27

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

PubMed

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

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

2014-11-01

28

Fan Noise Source Diagnostic Test: Vane Unsteady Pressure Results  

NASA Technical Reports Server (NTRS)

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.

Envia, Edmane

2002-01-01

29

The importance of quadrupole sources in prediction of transonic tip speed propeller noise  

Microsoft Academic Search

A theoretical analysis is presented for the harmonic noise of high speed, open rotors. Far field acoustic radiation equations based on the Ffowcs Williams\\/Hawkings theory are derived for a static rotor with thin blades and zero lift. Near the plane of rotation, the dominant sources are the volume displacement and the varrhou2 quadrupole, where u is the disturbance velocity component

D. B. Hanson; M. R. Fink

1979-01-01

30

The importance of quadrupole sources in prediction of transonic tip speed propeller noise  

Microsoft Academic Search

A theoretical analysis is presented for the harmonic noise of high speed, open rotors. Far field acoustic radiation equations based on the Ffowcs-Williams\\/Hawkings theory are derived for a static rotor with thin blades and zero lift. Near the plane of rotation, the dominant sources are the volume displacement and the rho U(2) quadrupole, where u is the disturbance velocity component

D. B. Hanson; M. R. Fink

1978-01-01

31

Inhomogeneity of the phase space of the damped harmonic oscillator under Lvy noise  

NASA Astrophysics Data System (ADS)

The damped harmonic oscillator under symmetric Lvy white noise shows inhomogeneous phase space, which is in contrast to the homogeneous phase space of the same oscillator under the Gaussian white noise, as shown in a recent paper [Sokolov, Ebeling, and Dybiec, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.83.041118 83, 041118 (2011)]. The inhomogeneity of the phase space shows correlation between the coordinate and the velocity of the damped oscillator under symmetric Lvy white noise. In the present work we further explore the physical origin of these distinguished features and find that it is due to the combination of the damped effect and heavy tail of the noise. We directly demonstrate this in the reduced coordinate x versus velocity ? plots and identify the physics of the antiassociation of the coordinate and velocity.

Cao, Zhan; Wang, Yu-Feng; Luo, Hong-Gang

2012-04-01

32

Modeling helicopter near-horizon harmonic noise due to transient maneuvers  

NASA Astrophysics Data System (ADS)

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.

Sickenberger, Richard D.

33

Confusion noise from LISA capture sources  

SciTech Connect

Captures of compact objects (COs) by massive black holes (MBHs) in galactic nuclei will be an important source for LISA, the proposed space-based gravitational wave (GW) detector. However, a large fraction of captures will not be individually resolvable - either because they are too distant, have unfavorable orientation, or have too many years to go before final plunge - and so will constitute a source of 'confusion noise', obscuring other types of sources. In this paper we estimate the shape and overall magnitude of the GW background energy spectrum generated by CO captures. This energy spectrum immediately translates to a spectral density S{sub h}{sup capt}(f) for the amplitude of capture-generated GWs registered by LISA. The overall magnitude of S{sub h}{sup capt}(f) is linear in the CO capture rates, which are rather uncertain; therefore we present results for a plausible range of rates. S{sub h}{sup capt}(f) includes the contributions from both resolvable and unresolvable captures, and thus represents an upper limit on the confusion noise level. We then estimate what fraction of S{sub h}{sup capt}(f) is due to unresolvable sources and hence constitutes confusion noise. We find that almost all of the contribution to S{sub h}{sup capt}(f) coming from white dwarf and neutron star captures, and at least {approx}30% of the contribution from black hole captures, is from sources that cannot be individually resolved. Nevertheless, we show that the impact of capture confusion noise on the total LISA noise curve ranges from insignificant to modest, depending on the rates. Capture rates at the high end of estimated ranges would raise LISA's overall (effective) noise level [fS{sub h}{sup eff}(f)]{sup 1/2} by at most a factor {approx}2 in the frequency range 1-10 mHz, where LISA is most sensitive. While this slightly elevated noise level would somewhat decrease LISA's sensitivity to other classes of sources, we argue that, overall, this would be a pleasant problem for LISA to have: It would also imply that detection rates for CO captures were at nearly their maximum possible levels (given LISA's baseline design and the level of confusion noise from galactic white dwarf binaries). This paper also contains, as intermediate steps, several results that should be useful in further studies of LISA capture sources, including (i) a calculation of the total GW energy output from generic inspirals of COs into Kerr MBHs (ii) an approximate GW energy spectrum for a typical capture, and (iii) an estimate showing that in the population of detected capture sources, roughly half the white dwarfs and a third of the neutron stars will be detected when they still have > or approx. 10 years to go before final plunge.

Barack, Leor [Department of Physics and Astronomy and Center for Gravitational Wave Astronomy, University of Texas at Brownsville, Brownsville, Texas 78520 (United States); Department of Mathematics, University of Southampton, Southampton, SO17 1BJ (United Kingdom); Cutler, Curt [Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Am Muehlenberg 1, D-14476 Golm (Germany)

2004-12-15

34

Wavepacket Modeling of the Jet Noise Source Dimitri Papamoschou*  

E-print Network

Wavepacket Modeling of the Jet Noise Source Dimitri Papamoschou* University of California, Irvine, CA 92697, USA This research is motivated by the need for physical models for the jet noise source of aerospace applications require physical modeling of the jet noise source. These include diffraction of jet

Papamoschou, Dimitri

35

IMAGING OF DIRECTIONAL DISTRIBUTED NOISE SOURCES Dimitri Papamoschou  

E-print Network

that are distributed and strongly directional, such as in turbulent jets. The goal is to generate noise source maps produced similar noise source maps for a Mach 0.9 cold jet. Nomenclature a = ambient speed of sound b of microphones Mj = jet Mach number R = array radius q(x, , t) = noise source strength Sr = Strouhal number = f

Papamoschou, Dimitri

36

Imaging of directional distributed noise sources D. Papamoschou  

E-print Network

that are distributed and strongly directional, such as in turbulent jets. The goal is to generate high-resolution noise-spectrum, of the measured acoustic field. For jet noise, whose spectral nature changes with emission angle, it is necessary jets issuing from engine exhausts is of paramount interest to aircraft noise. The jet noise source

Papamoschou, Dimitri

37

ACCURATE SHORT-TERM ANALYSIS OF THE FUNDAMENTAL FREQUENCY AND THE HARMONICS-TO-NOISE RATIO OF A SAMPLED SOUND  

Microsoft Academic Search

We present a straightforward and robust algorithm for periodicity detection, working in the lag (autocorrelation) domain. When it is tested for periodic signals and for signals with additive noise or jitter, it proves to be several orders of magnitude more accurate than the methods commonly used for speech analysis. This makes our method capable of measuring harmonics-to-noise ratios in the

Paul Boersma

1993-01-01

38

Assessing noise sources at synchrotron infrared ports  

PubMed Central

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

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

39

Feedback and harmonic locking of slot-type optomechanical oscillators to external low-noise reference clocks  

NASA Astrophysics Data System (ADS)

We demonstrate feedback and harmonic locking of chip-scale slot-type optomechanical oscillators to external low-noise reference clocks, with suppressed timing jitter by three orders of magnitude. The feedback and compensation techniques significantly reduce the close-to-carrier phase noise, especially within the locking bandwidth for the integral root-mean-square timing jitter. Harmonic locking via high-order carrier signals is also demonstrated with similar phase noise and integrated root-mean-square timing jitter reduction. The chip-scale optomechanical oscillators are tunable over an 80-kHz range by tracking the reference clock, with potential applications in tunable radio-frequency photonics platforms.

Zheng, Jiangjun; Li, Ying; Goldberg, Noam; McDonald, Mickey; Luan, Xingsheng; Hati, Archita; Lu, Ming; Strauf, Stefan; Zelevinsky, Tanya; Howe, David A.; Wei Wong, Chee

2013-04-01

40

Effects of Source Redistribution on Jet Noise Shielding Salvador Mayoral*  

E-print Network

Effects of Source Redistribution on Jet Noise Shielding Salvador Mayoral* and Dimitri Papamoschou University of California, Irvine, CA 92697, USA The potential of jet noise shielding from the Hybrid Wing a thin flat plate, had the generic shape of the HWB planform. Redistribution of the jet noise source

Papamoschou, Dimitri

41

Enhancing Sound Source Localization with Noise Separation Methods  

E-print Network

Enhancing Sound Source Localization with Noise Separation Methods L. Lamottea , S. Paillasseura , K aerodynamic turbulence of the nozzle. The second example aims to separate and localize combustion noise from to localize noise sources on the object surface. This diagnostic is limited to the identification of the most

Paris-Sud XI, Université de

42

LOCALIZATION OF MULTIPLE TYPES OF JET NOISE SOURCES Dimitri Papamoschou  

E-print Network

LOCALIZATION OF MULTIPLE TYPES OF JET NOISE SOURCES Dimitri Papamoschou and Ali Dadvar University of California, Irvine, Irvine, California 92697-3975 A small-aperture microphone phased array provides noise source maps for turbulent mixing noise emitted from a cold Mach 0.9 jet in two polar directions

Papamoschou, Dimitri

43

Stochastic response of a ?6 oscillator subjected to combined harmonic and Poisson white noise excitations  

NASA Astrophysics Data System (ADS)

The transient and stationary probability density functions (PDFs) of stochastic response of the ?6 Duffing oscillator under combined harmonic and external and parametric Poisson white noises excitations are investigated by the generalized cell mapping method in this paper. Based on the digraph analysis method, the global qualitative properties are obtained such as attractors, basins of attraction, basin boundaries, saddles and invariant manifolds. The evolutionary process of transient and stationary PDFs are shown based on the matrix analysis method. It is observed that there is a close relationship between evolutionary direction of PDF and the unstable manifold. Monte Carlo (MC) simulation is used to verify the accuracy of the matrix analysis method.

Yue, Xiaole; Xu, Wei; Jia, Wantao; Wang, Liang

2013-07-01

44

Energy fluctuations, hydrodynamics and local correlations in harmonic systems with bulk noises  

E-print Network

In this note, I summarise and comment on joint work with C. Bernardin, V. Kannan and J. L. Lebowitz concerning two harmonic systems with bulk noises whose nonequilibrium steady states (NESS) are nearly identical (they share the same thermal conductivity and two-point function), but whose hydrodynamic properties (convergence towards the NESS) are very different. The goal is to discuss the results in the general context of nonequilibrium properties of dynamical systems, in particular, what they tell us about possible effective models, or predictive approximations, for such systems.

Jani Lukkarinen

2012-06-01

45

NASA/Army supported noise source/noise reduction programs at Langley  

NASA Technical Reports Server (NTRS)

The helicopter noise research related to noise source mechanism identification and reduction includes many of the critical noise problems experienced by the helicopter. These include blade vortex interaction (BVI) noise, broadband turbulence ingestion noise, rotor blade self noise including trailing edge effects, model scale effects evaluations, and to some degree main rotor/tail rotor interaction noise. Issues that arise from this evaluation are; (1) Broadband noise can be a significant contribution to the overall noise problem. (2) Scale model investigations are an effective means of conducting helicopter noise research; however, more model/flight correlation studies are required to develop a high degree of confidence of the use of scale model results in the design process of helicopters. (3) More detailed investigations identifying critical factors affecting the main rotor/tail rotor noise mechanism are required.

Hoad, D. R.

1982-01-01

46

Teaching Doppler Effect with a passing noise source  

NASA Astrophysics Data System (ADS)

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.

Costa, Ivan F.; Mocellin, Alexandra

2010-07-01

47

Prewhitening of colored noise fields for detection of threshold sources  

NASA Astrophysics Data System (ADS)

This report presents an algorithm for the estimation of noise correlations for an array of sensors. The algorithm assumes a mixed spectra model composed of discrete sinusoidal sources and continuous noise components. A spatial autoregressive (AR) process models the continuous component. Previous methods use spatial AR models with real coefficients, restricting the utility of the model to noise sources that impinge on an array at broadside. The complex formulation presented here solves the general problem of arbitrarily oriented noise sources. The technique uses a gradient algorithm for maximization of a likelihood functional to solve for the complex AR coefficients. Once the algorithm determines the noise covariance matrix, prewhitening techniques allow detection of threshold sources. The multiple signal classification (MUSIC) direction finder when applied to the prewhitened observed correlation matrix illustrates the usefulness in detecting low signal-to-noise ratio (SNR) sources. Computational examples use the standardized test case (STC), a realistic model with a challenging range of SNR and difficult source locations.

Barthelemy, Alain C.

1993-11-01

48

Frequency-dependent noise sources in the North Atlantic Ocean  

E-print Network

Frequency-dependent noise sources in the North Atlantic Ocean Amandine Sergeant and Eleonore in the North Atlantic Ocean by coupling noise polarization analysis and source mapping using an ocean wave the distribution of secondary microseism sources in the North Atlantic Ocean using 20 broadband stations located

Stutzmann, Eléonore

49

Sounds on least-squares four-parameter sine-fit errors due to harmonic distortion and noise  

Microsoft Academic Search

Least-squares sine-fit algorithms are used extensively in signal processing applications. The parameter estimates produced by such algorithms are subject to both random and systematic errors when the record of input samples consists of a fundamental sine wave corrupted by harmonic distortion or noise. The errors occur because, in general, such sine-fits will incorporate a portion of the harmonic distortion or

J. P. Deyst; T. M. Souders; O. M. Solomon

1994-01-01

50

An improved source model for aircraft interior noise studies  

Microsoft Academic Search

There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise level. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significnatly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model

J. R. Mahan; C. R. Fuller

1985-01-01

51

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

NASA Technical Reports Server (NTRS)

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.

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

1996-01-01

52

Harmony: EEG/MEG Linear Inverse Source Reconstruction in the Anatomical Basis of Spherical Harmonics  

PubMed Central

EEG/MEG source localization based on a distributed solution is severely underdetermined, because the number of sources is much larger than the number of measurements. In particular, this makes the solution strongly affected by sensor noise. A new way to constrain the problem is presented. By using the anatomical basis of spherical harmonics (or spherical splines) instead of single dipoles the dimensionality of the inverse solution is greatly reduced without sacrificing the quality of the data fit. The smoothness of the resulting solution reduces the surface bias and scatter of the sources (incoherency) compared to the popular minimum-norm algorithms where single-dipole basis is used (MNE, depth-weighted MNE, dSPM, sLORETA, LORETA, IBF) and allows to efficiently reduce the effect of sensor noise. This approach, termed Harmony, performed well when applied to experimental data (two exemplars of early evoked potentials) and showed better localization precision and solution coherence than the other tested algorithms when applied to realistically simulated data. PMID:23071497

Petrov, Yury

2012-01-01

53

Ranking of compressor station noise sources using sound intensity techniques  

SciTech Connect

Local residential development and the introduction of more restrictive noise regulations in Canada and the United States are creating a need to improve the noise abatement systems at many existing industrial sites including pipeline compressor stations. The initial phase of any silencing program should include a study to identify and rank the noise sources. Until recently, this type of noise study is qualitative and inexact, requiring a trial and error approach which addressed only one or two sources at a time and often resulted in a prolonged and costly silencing program. The use of sound intensity techniques to determine sound power levels of all noise sources results in lower costs, improved job scheduling and greater likelihood of success of a silencing program. This paper discusses a case study which uses sound intensity techniques to rank noise sources at a natural gas compressor plant powered by a gas turbine.

Johns, W.D.; Porter, R.H.

1987-01-01

54

Global analysis of crisis in twin-well Duffing system under harmonic excitation in presence of noise  

Microsoft Academic Search

Evolution of a crisis in a twin-well Duffing system under a harmonic excitation in presence of noise is explored in detail by the generalized cell mapping with digraph (GCMD in short) method. System parameters are chosen in the range that there co-exist chaotic attractors and\\/or chaotic saddles, together with their evolution. Due to noise effects, chaotic attractors and chaotic saddles

Wei Xu; Qun He; Tong Fang; Haiwu Rong

2005-01-01

55

Analysis and Synthesis of Tonal Aircraft Noise Sources  

NASA Technical Reports Server (NTRS)

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.

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

2012-01-01

56

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

NASA Astrophysics Data System (ADS)

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

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

57

Sources, control, and effects of noise from aircraft propellers and rotors. [noise prediction (aircraft  

NASA Technical Reports Server (NTRS)

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 described, indicating that about 5-dB reduction of flyover noise can be obtained without significant performance penalty. Sidewall design studies are described 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.

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

1981-01-01

58

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  

Microsoft Academic Search

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

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

1993-01-01

59

The use of multispectrum in determining airport noise sources  

NASA Astrophysics Data System (ADS)

An airport noise measuring system is described which uses a digital filter analyzer to process the input signals continuously rather than blockwise (as is done by an FFT analyzer. Moreover, this system detects the difference between the airport noise events caused by air traffic and those caused by other noise sources. In addition, significantly less data are needed for this system than when for an FFT analyzer or when actual aural recordings are used.

Bronsdon, Robert

60

Optical linear algebra processors - Noise and error-source modeling  

NASA Technical Reports Server (NTRS)

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.

Casasent, D.; Ghosh, A.

1985-01-01

61

Second and third harmonic measurements at the linac coherent light source  

NASA Astrophysics Data System (ADS)

The linac coherent light source (LCLS) is a self-amplified spontaneous emission (SASE) free-electron laser (FEL) operating at fundamental photon energies from 0.5 to 10 keV. Characterization of the higher harmonics present in the FEL beam is important to users, for whom harder x rays can either extend the useful operating wavelength range or increase experimental backgrounds. We present measurements of the power in both the second and third harmonics, and compare the results to expectations from simulations. We also present studies of the transport of harmonics to the users, and the harmonic power as a function of electron beam quality.

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.

2011-06-01

62

Noise source emissions, Davis Canyon site, Utah  

SciTech Connect

This report has been prepared for the purpose of documenting the development of the data provided to the Repository Project Management (RPM) organization. The data provided encompass all phases of activity, from site preparation through the exploratory shaft facility (ESF) and repository construction and operation, and decommissioning. Noise environments expected from construction and operation of transportation corridors associated with the activity were also modeled. The data for the construction of transportation corridors were provided by Bechtel National, Inc. Use of the quietest equipment available within the proven state of the art was assumed, as was the use of acoustical enclosures to the extent practical. The programmatic assumptions are based on the noise-sensitive nature of the Canyonlands National Park. Another feature of the data is the use of 1/3-octave-band rather than 1/1-octave-band resolution of emission spectra. This was done to permit evaluation of audibility of sounds reaching the park.

Not Available

1987-07-01

63

Second and Third Harmonic Measurements at the Linac Coherent Light Source  

SciTech Connect

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.

Ratner, D.; /Stanford U., Phys. Dept.; 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

64

An improved source model for aircraft interior noise studies  

NASA Technical Reports Server (NTRS)

There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise levels. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significantly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies.

Mahan, J. R.; Fuller, C. R.

1985-01-01

65

An improved source model for aircraft interior noise studies  

NASA Astrophysics Data System (ADS)

There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise level. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significnatly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies.

Mahan, J. R.; Fuller, C. R.

66

An improved source model for aircraft interior noise studies  

NASA Technical Reports Server (NTRS)

There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise level. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significnatly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies.

Mahan, J. R.; Fuller, C. R.

1985-01-01

67

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)

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.

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

1993-01-01

68

Covariance-based approaches to aeroacoustic noise source analysis.  

PubMed

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 Crame?r-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. PMID:21110583

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

2010-11-01

69

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

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

70

MEG source localization using invariance of noise space.  

PubMed

We propose INvariance of Noise (INN) space as a novel method for source localization of magnetoencephalography (MEG) data. The method is based on the fact that modulations of source strengths across time change the energy in signal subspace but leave the noise subspace invariant. We compare INN with classical MUSIC, RAP-MUSIC, and beamformer approaches using simulated data while varying signal-to-noise ratios as well as distance and temporal correlation between two sources. We also demonstrate the utility of INN with actual auditory evoked MEG responses in eight subjects. In all cases, INN performed well, especially when the sources were closely spaced, highly correlated, or one source was considerably stronger than the other. PMID:23505502

Zhang, Junpeng; Raij, Tommi; Hmlinen, Matti; Yao, Dezhong

2013-01-01

71

MEG Source Localization Using Invariance of Noise Space  

PubMed Central

We propose INvariance of Noise (INN) space as a novel method for source localization of magnetoencephalography (MEG) data. The method is based on the fact that modulations of source strengths across time change the energy in signal subspace but leave the noise subspace invariant. We compare INN with classical MUSIC, RAP-MUSIC, and beamformer approaches using simulated data while varying signal-to-noise ratios as well as distance and temporal correlation between two sources. We also demonstrate the utility of INN with actual auditory evoked MEG responses in eight subjects. In all cases, INN performed well, especially when the sources were closely spaced, highly correlated, or one source was considerably stronger than the other. PMID:23505502

Zhang, Junpeng; Raij, Tommi; Hamalainen, Matti; Yao, Dezhong

2013-01-01

72

Inverse transport with isotropic time-harmonic sources Guillaume Bal  

E-print Network

phase arguments, which allow us to exhibit decay of solutions (see also [6]) and errors-harmonic. This is a practical setting in the medical imaging modality called Optical Tomography. As the modulation frequency the convergence of an iterative reconstruction scheme and in particular to prove that certain error operators

Bal, Guillaume

73

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

74

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

NASA Technical Reports Server (NTRS)

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.

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

1996-01-01

75

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

PubMed

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

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

2012-11-01

76

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

PubMed Central

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

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

2012-01-01

77

High-order harmonic generation in Xe, Kr, and Ar driven by a 2.1-?m source: High-order harmonic spectroscopy under macroscopic effects  

E-print Network

We experimentally and numerically study the atomic response and pulse propagation effects of high-order harmonics generated in Xe, Kr, and Ar driven by a 2.1-?m infrared femtosecond light source. The light source is an ...

Hong, Kyung-Han

78

Source Noise Modeling Efforts for Fan Noise in NASA Research Programs  

NASA Technical Reports Server (NTRS)

There has been considerable progress made in fan noise prediction over the past 15 years. NASA has conducted and sponsored research that has improved both tone and broadband fan noise prediction methods. This presentation highlights progress in these areas with emphasis on rotor/stator interaction noise sources. Tone noise predictions are presented for an advanced prediction code called "LINFLUX". Comparisons with data are" included for individual fan duct modes. There has also been considerable work developing new fan broadband noise prediction codes and validation data from wind tunnel model tests. Results from several code validation exercises are presented that show improvement of predicted sound power levels. A summary is included with recommendations for future work.

Huff, Dennis L.

2006-01-01

79

Sub-Shot Noise Power Source for Microelectronics  

NASA Technical Reports Server (NTRS)

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-shot noise current source can be built that will be beneficial for a very broad range of low-power, low-noise electronic instruments and applications, both cryogenic and room-temperature. Taking advantage of recent demonstrations of the squeezed light sources based on optical micro-disks, this sub-shot noise current source can be made compatible with the size/power requirements specific of the electronic devices it will support.

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

2011-01-01

80

Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise  

NASA Astrophysics Data System (ADS)

An important source mechanism of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-inch Source Diagnostic Test fan rig for which broadband noise data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust acoustic power spectra are computed and compared with the measured spectra where possible. In general, the acoustic power levels and shape of the predicted spectra are in good agreement with the measured data. The predicted spectra show the experimentally observed trends with fan tip speed, vane count, and vane sweep. The results also demonstrate the validity of using CFD-based turbulence information for fan broadband noise calculations.

Nallasamy, M.; Envia, E.; Thorp, S. A.; Shabbir, A.

2002-08-01

81

Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise  

NASA Technical Reports Server (NTRS)

An important source mechanism of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-inch Source Diagnostic Test fan rig for which broadband noise data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust acoustic power spectra are computed and compared with the measured spectra where possible. In general, the acoustic power levels and shape of the predicted spectra are in good agreement with the measured data. The predicted spectra show the experimentally observed trends with fan tip speed, vane count, and vane sweep. The results also demonstrate the validity of using CFD-based turbulence information for fan broadband noise calculations.

Nallasamy, M.; Envia, E.; Thorp, S. A.; Shabbir, A.

2002-01-01

82

Planets as background noise sources in free space optical communications  

NASA Technical Reports Server (NTRS)

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.

Katz, J.

1986-01-01

83

Coherent noise source identification in multi channel analysis  

E-print Network

The evaluation of coherent noise can provide useful information in the study of detectors. The identification of coherent noise sources is also relevant for uncertainty calculations in analyse where several channels are combined. The study of the covariance matrix give information about coherent noises. Since covariance matrix of high dimension data could be difficult to analyse, the development of analysis tools is needed. Principal Component Analysis (PCA) is a powerful tool for such analysis. It has been shown that we can use PCA to find coherent noises in ATLAS calorimeter or the CALICE Si-W electromagnetic calorimeter physics prototype. However, if several coherent noise sources are combined, the interpretation of the PCA may become complicated. In this paper, we present another method based on the study of the covariance matrix to identify noise sources. This method has been developed for the study of front end ASICs dedicated to CALICE calorimeters. These calorimeters are designed and studied for experiments at the ILC. We also study the reliability of the method with simulations. Although this method has been developped for a specific application, it can be used for any multi channel analysis.

Thibault Frisson; Roman Poeschl

2014-01-28

84

Seismic noise frequency dependent P and S wave sources  

NASA Astrophysics Data System (ADS)

Seismic noise in the period band 3-10 sec is generated in the oceans by the interaction of ocean waves. Noise signal is dominated by Rayleigh waves but body waves can be extracted using a beamforming approach. We select the TAPAS array deployed in South Spain between June 2008 and September 2009 and we use the vertical and horizontal components to extract noise P and S waves, respectively. Data are filtered in narrow frequency bands and we select beam azimuths and slownesses that correspond to the largest continuous sources per day. Our procedure automatically discard earthquakes which are localized during short time durations. Using this approach, we detect many more noise P-waves than S-waves. Source locations are determined by back-projecting the detected slowness/azimuth. P and S waves are generated in nearby areas and both source locations are frequency dependent. Long period sources are dominantly in the South Atlantic and Indian Ocean whereas shorter period sources are rather in the North Atlantic Ocean. We further show that the detected S-waves are dominantly Sv-waves. We model the observed body waves using an ocean wave model that takes into account all possible wave interactions including coastal reflection. We use the wave model to separate direct and multiply reflected phases for P and S waves respectively. We show that in the South Atlantic the complex source pattern can be explained by the existence of both coastal and pelagic sources whereas in the North Atlantic most body wave sources are pelagic. For each detected source, we determine the equivalent source magnitude which is compared to the model.

Stutzmann, E.; Schimmel, M.; Gualtieri, L.; Farra, V.; Ardhuin, F.

2013-12-01

85

Propeller sheet cavitation noise source modeling and inversion  

NASA Astrophysics Data System (ADS)

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.

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

2014-02-01

86

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)

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.

1973-01-01

87

A battery-based, low-noise voltage source.  

PubMed

A highly stable, low-noise voltage source was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess noise and ground loops, the voltage source is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of +/-15 and +/-5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7 x 10(-7) over 6.5 h and a noise level equal or smaller than 30 nV/square root(Hz) is achieved. PMID:20590260

Wagner, Anke; Sturm, Sven; Schabinger, Birgit; Blaum, Klaus; Quint, Wolfgang

2010-06-01

88

A battery-based, low-noise voltage source  

NASA Astrophysics Data System (ADS)

A highly stable, low-noise voltage source was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess noise and ground loops, the voltage source is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of 15 and 5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 710-7 over 6.5 h and a noise level equal or smaller than 30 nV/?Hz is achieved.

Wagner, Anke; Sturm, Sven; Schabinger, Birgit; Blaum, Klaus; Quint, Wolfgang

2010-06-01

89

A new bound on excess frequency noise in second harmonic generation in PPKTP at the 10-19 level  

NASA Astrophysics Data System (ADS)

Several experiments at the forefront of precision metrology and frequency standards use optical harmonic generation in their experiments. These include iodine stabilized Nd:YAG lasers, optical frequency combs, measurement of optical frequency ratios, and precision atomic spectroscopy. We present an experimental bound on the relative frequency fluctuations introduced in the nonlinear second harmonic generation process using PPKTP to double a 1064nm Nd:YAG laser. We report a measured amplitude spectral density of frequency noise with total RMS frequency deviation of 3mHz and a minimum value of 20 ?Hz/Hz^1/2 over 250 seconds with a measurement bandwidth of 128 Hz, corresponding to an Allan deviation of 10-19 at 20 seconds.

Yeaton-Massey, David; Adhikari, Rana

2013-03-01

90

A method to evaluate harmonic model-based estimations under non-white measured noise  

Microsoft Academic Search

Automatic extracting information from power- system event recordings requires applications of signal-processing estimation techniques whose performance has been verified under white noise. This paper proposes a method to test these techniques under real power-system noise, which is very different from white noise, to evaluate their application feasibility. The first part of the paper describes the evaluation method used to evaluate

Cuong D. Le; Math H. J. Bollen; Irene Y. H. Gu

2011-01-01

91

Temporal Coherence Effects on Coherent Diffractive Imaging of a Binary Sample by a High Harmonic Source  

NASA Astrophysics Data System (ADS)

Coherent Diffractive Imaging (CDI) is performed with single and multiple harmonics from an ultrafast HHG source. The effect of HHG source bandwidth on the effectiveness of the reconstruction algorithms is compared. A low quality reconstruction from broadband data is achieved assuming full coherence in the algorithm.

Parsons, A. D.; Chapman, R. T.; Mills, B.; Bajt, S.; Frey, J. G.; Brocklesby, W. S.

2013-03-01

92

Measurements of nonlinear harmonic generation at the Advanced Photon Source's SASE FEL  

SciTech Connect

SASE saturation was recently achieved at the Advanced Photon Source's SASE FEL in the low-energy undulator test line (LEUTL) at 530 nm and 385 nm. The electron beam microbunching becomes more and more prominent until saturation is achieved. This bunching causes nonlinear harmonic emission that extends the usefulness of a SASE system in achieving shorter FEL wavelengths for the same electron beam energy. They have investigated the intensity of the fundamental and second-harmonic undulator radiation as a function of distance along the undulator line and present the experimental results and compare them to numerical simulations. In addition, they have measured the single-shot second harmonic spectra as well as the simultaneous fundamental and second harmonic spectra and present the experimental results.

Biedron, S.G.; Dejus, E.J.; Huang, Z.; Milton, S.V.; Sajaev, V.; Berg, W.; Borland, M.; Den Hartog, P.K.; Erdmann, M.; Fawley, W.M.; Gluskin, E.; Kim, K.-J.; Lewellen, J.W.; Li, Y.; Moog, E.R.; Nassiri, A.; Wiermerslage, G.; Yang, B.X.

2002-03-01

93

Empirical source noise prediction method with application to subsonic coaxial jet mixing noise  

NASA Technical Reports Server (NTRS)

A general empirical method, developed for source noise predictions, uses tensor splines to represent the dependence of the acoustic field on frequency and direction and Taylor's series to represent the dependence on source state parameters. The method is applied to prediction of mixing noise from subsonic circular and coaxial jets. A noise data base of 1/3-octave-band sound pressure levels (SPL's) from 540 tests was gathered from three countries: United States, United Kingdom, and France. The SPL's depend on seven variables: frequency, polar direction angle, and five source state parameters: inner and outer nozzle pressure ratios, inner and outer stream total temperatures, and nozzle area ratio. A least-squares seven-dimensional curve fit defines a table of constants which is used for the prediction method. The resulting prediction has a mean error of 0 dB and a standard deviation of 1.2 dB. The prediction method is used to search for a coaxial jet which has the greatest coaxial noise benefit as compared with an equivalent single jet. It is found that benefits of about 6 dB are possible.

Zorumski, W. E.; Weir, D. S.

1982-01-01

94

Identification and modification of dominant noise sources in diesel engines  

NASA Astrophysics Data System (ADS)

Determination of dominant noise sources in diesel engines is an integral step in the creation of quiet engines, but is a process which can involve an extensive series of expensive, time-consuming fired and motored tests. The goal of this research is to determine dominant noise source characteristics of a diesel engine in the near and far-fields with data from fewer tests than is currently required. Pre-conditioning and use of numerically robust methods to solve a set of cross-spectral density equations results in accurate calculation of the transfer paths between the near- and far-field measurement points. Application of singular value decomposition to an input cross-spectral matrix determines the spectral characteristics of a set of independent virtual sources, that, when scaled and added, result in the input cross spectral matrix. Each virtual source power spectral density is a singular value resulting from the decomposition performed over a range of frequencies. The complex relationship between virtual and physical sources is estimated through determination of virtual source contributions to each input measurement power spectral density. The method is made more user-friendly through use of a percentage contribution color plotting technique, where different normalizations can be used to help determine the presence of sources and the strengths of their contributions. Convolution of input measurements with the estimated path impulse responses results in a set of far-field components, to which the same singular value contribution plotting technique can be applied, thus allowing dominant noise source characteristics in the far-field to also be examined. Application of the methods presented results in determination of the spectral characteristics of dominant noise sources both in the near- and far-fields from one fired test, which significantly reduces the need for extensive fired and motored testing. Finally, it is shown that the far-field noise time history of a physically altered engine can be simulated through modification of singular values and recalculation of transfer paths between input and output measurements of previously recorded data.

Hayward, Michael D.

95

Volcanic jet noise: infrasonic source processes and atmospheric propagation  

NASA Astrophysics Data System (ADS)

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. Garcs, J. M. Seiner, P. A. Ramn, and M. A. H. Hedlin (2009), Infrasonic jet noise from volcanic eruptions, Geophys. Res. Lett., 36, L08303, doi:10.1029/2008GL036486.

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

2011-12-01

96

Matched Filters for Source Detection in the Poissonian Noise Regime  

E-print Network

A procedure is described for estimating an optimum kernel for the detection by convolution of signals among Poissonian noise. The technique is applied to the detection of x-ray point sources in XMM-Newton data, and is shown to yield an improvement in detection sensitivity of up to 60% over the sliding-box method used in the creation of the 1XMM catalog.

Ian Stewart

2006-03-14

97

Speech intelligibility among modulated and spatially distributed noise sources.  

PubMed

At a cocktail party, listeners are faced with multiple, spatially distributed interfering voices. The dominant interfering voice may change from moment to moment and, consequently, change in spatial location. The ability of the binaural system to deal with such a dynamic scene has not been systematically analyzed. Spatial release from masking (SRM) was measured in simple spatial scenes, simulated over headphones with a frontal speech source. For a single noise at 105, SRM was reduced if that noise modulated (10 Hz square wave, 50% duty cycle, 20 dB modulation depth), but, for two noises in symmetrical locations, SRM increased if the noises were modulated in alternation, suggesting that the binaural system can "switch" between exploiting different spatial configurations. Experiment 2 assessed the contributions of interaural time and level differences as a function of modulation rate (1-20 Hz). Scenes were created using the original head-related impulse responses and ones that had been manipulated to isolate each cue. SRM decreased steeply with modulation rate. The combined effects of interaural time and level differences were consistent with additive contributions. The results indicate that binaural sluggishness limits the contribution of binaural switching to speech understanding at a cocktail party. PMID:23556593

Culling, John F; Mansell, Elizabeth R

2013-04-01

98

Ultrahigh 22-nm resolution EUV coherent diffraction imaging using a tabletop 13-nm high harmonic source  

NASA Astrophysics Data System (ADS)

We implement coherent diffractive imaging (CDI) using a phase-matched high-harmonic generation (HHG) source at 13 nm, demonstrating reconstructed images with a record 22 nm resolution for any tabletop, light-based microscope. We also demonstrate the first reflection-mode CDI using a compact extreme ultraviolet (EUV) source, achieving ~100 nm resolution. A clear path towards even higher spatial resolution reflection-mode tabletop imaging using apertured-illumination schemes will be discussed.

Seaberg, Matthew D.; Adams, Daniel E.; Zhang, Bosheng; Gardner, Dennis F.; Murnane, Margaret M.; Kapteyn, Henry C.

2012-03-01

99

Energy harvesting from harmonic and noise excitation of multilayer piezoelectric stacks: modeling and experiment  

NASA Astrophysics Data System (ADS)

This article theoretically and experimentally studies deterministic and stochastic piezoelectric energy harvesting using a multilayer stack configuration for civil infrastructure system applications that involve large compressive loads, such as vehicular and foot loads acting upon pavements. Modeling of vibrational energy harvesters has been mostly focused on deterministic forms of mechanical excitation as in the typical case of harmonic excitation. In this paper, we present analytical and numerical modeling of piezoelectric energy harvesting from harmonic and random vibrations of multilayer piezoelectric stacks under axial compressive loading. The analytical electromechanical solution is based on the power spectral density (PSD) of random excitation and the voltage - to - pressure input frequency response function (FRF) of the harvester. The first one of the two numerical solution methods employs the Fourier series representation of the vibrational excitation history to solve the resulting ordinary differential equation (ODE), while the second method uses an Euler-Maruyama scheme to directly solve the governing electromechanical stochastic differential equation (SDE). The electromechanical model is validated through several experiments for a multilayer PZT-5H stack under harmonic and random excitations. The analytical predictions and numerical simulations exhibit very good agreement with the experimental measurements for a range of resistive loads and input excitation levels.

Zhao, S.; Erturk, A.

2013-04-01

100

Modeling of Jet Noise Sources and their Diffraction with Uniform Flow  

E-print Network

Modeling of Jet Noise Sources and their Diffraction with Uniform Flow Dimitri Papamoschou for treating the propagation of elementary jet noise sources in the presence of a uniform mean flow model for the jet noise source has shown some promise in this regard.1 The wavepacket, in combination

Papamoschou, Dimitri

101

Crystal-MUSIC: Accurate Localization of Multiple Sources in Diffuse Noise Environments  

E-print Network

Crystal-MUSIC: Accurate Localization of Multiple Sources in Diffuse Noise Environments Using: Diffuse noise, DOA estimation, microphone arrays, MU- SIC, source localization 1 Introduction DOA-MUSIC, a method for DOA esti- mation of multiple sources in the presence of diffuse noise. MUSIC is well known

Paris-Sud XI, Université de

102

NOISE SOURCE LOCALIZATION IN AN ATTENUATING MEDIUM HABIB AMMARI, ELIE BRETIN, JOSSELIN GARNIER, AND ABDUL WAHAB  

E-print Network

NOISE SOURCE LOCALIZATION IN AN ATTENUATING MEDIUM HABIB AMMARI, ELIE BRETIN, JOSSELIN GARNIER- crowave noise source localization and tracking; see, for instance, [12, 13, 14, 15, 21]. It is a quite. Moreover, we address the problem of localizing spatially correlated noise sources. In particular, we

Garnier, Josselin

103

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

NASA Technical Reports Server (NTRS)

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.

Johnson, E. H.

1975-01-01

104

Fan Noise Source Diagnostic Test Completed and Documented  

NASA Technical Reports Server (NTRS)

The specially organized session offered an international forum to disseminate the results from a year long test that was conducted in 1999 in NASA Glenn Research Center s 9- by 15-Foot Low-Speed Wind Tunnel on a 22-in. scale-model turbofan bypass stage, which was designed to be representative of current aircraft engine technology. The test was a cooperative effort involving Glenn, the NASA Langley Research Center, GE Aircraft Engines, and the Boeing Company. The principal objective of the project was to study the source mechanisms of noise in a modern high-bypass-ratio turbofan engine through detailed aerodynamic and acoustic measurements.

Envia, Edmane

2003-01-01

105

A study on propeller noise source localization in a cavitation tunnel  

Microsoft Academic Search

Localizing noise sources in cavitation experiments is an important research subject along with predicting noise levels. A cavitation tunnel propeller noise localization method is presented. Propeller noise measurement experiments were performed in the MOERI cavitation tunnel. To create cavitating conditions, a wake-generating dummy body was devised. In addition, 10 hydrophones were put inside a wing-shaped casing to minimize the unexpected

Hanshin Seol; Kwangsoo Kim; Woojae Seong

2009-01-01

106

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

Microsoft Academic Search

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

Bruce E. Walker

2005-01-01

107

Fan Noise Source Diagnostic Test: Rotor Alone Aerodynamic Performance Results  

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

108

Source Methodology for Turbofan Noise Prediction (SOURCE3D Technical Documentation)  

NASA Technical Reports Server (NTRS)

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.

Meyer, Harold D.

1999-01-01

109

Axonal noise as a source of synaptic variability.  

PubMed

Post-synaptic potential (PSP) variability is typically attributed to mechanisms inside synapses, yet recent advances in experimental methods and biophysical understanding have led us to reconsider the role of axons as highly reliable transmission channels. We show that in many thin axons of our brain, the action potential (AP) waveform and thus the Ca++ signal controlling vesicle release at synapses will be significantly affected by the inherent variability of ion channel gating. We investigate how and to what extent fluctuations in the AP waveform explain observed PSP variability. Using both biophysical theory and stochastic simulations of central and peripheral nervous system axons from vertebrates and invertebrates, we show that channel noise in thin axons (<1 m diameter) causes random fluctuations in AP waveforms. AP height and width, both experimentally characterised parameters of post-synaptic response amplitude, vary e.g. by up to 20 mV and 0.5 ms while a single AP propagates in C-fibre axons. We show how AP height and width variabilities increase with a power-law as diameter decreases and translate these fluctuations into post-synaptic response variability using biophysical data and models of synaptic transmission. We find for example that for mammalian unmyelinated axons with 0.2 m diameter (matching cerebellar parallel fibres) axonal noise alone can explain half of the PSP variability in cerebellar synapses. We conclude that axonal variability may have considerable impact on synaptic response variability. Thus, in many experimental frameworks investigating synaptic transmission through paired-cell recordings or extracellular stimulation of presynaptic neurons, causes of variability may have been confounded. We thereby show how bottom-up aggregation of molecular noise sources contributes to our understanding of variability observed at higher levels of biological organisation. PMID:24809823

Neishabouri, Ali; Faisal, A Aldo

2014-05-01

110

Fan Noise Source Diagnostic Test: LDV Measured Flow Field Results  

NASA Technical Reports Server (NTRS)

Results are presented of an experiment conducted to investigate potential sources of noise in the flow developed by two 22-in. diameter turbofan models. The R4 and M5 rotors that were tested were designed to operate at nominal take-off speeds of 12,657 and 14,064 RPMC, respectively. Both fans were tested with a common set of swept stators installed downstream of the rotors. Detailed measurements of the flows generated by the two were made using a laser Doppler velocimeter system. The wake flows generated by the two rotors are illustrated through a series of contour plots. These show that the two wake flows are quite different, especially in the tip region. These data are used to explain some of the differences in the rotor/stator interaction noise generated by the two fan stages. In addition to these wake data, measurements were also made in the R4 rotor blade passages. These results illustrate the tip flow development within the blade passages, its migration downstream, and (at high rotor speeds) its merging with the blade wake of the adjacent (following) blade. Data also depict the variation of this tip flow with tip clearance. Data obtained within the rotor blade passages at high rotational speeds illustrate the variation of the mean shock position across the different blade passages.

Podboy, Gary C.; Krupar, Martin J.; Hughes, Christopher E.; Woodward, Richard P.

2003-01-01

111

Recent developments in noise research at Deutsche Bahn (noise assessment, noise source localization and specially monitored track)  

Microsoft Academic Search

To strengthen the environmental friendliness of railway traffic in Germany, Deutsche Bahn (DB) is in the process of performing a major research programme concerning noise reduction. To realize this, the DB Low Noise Railway programme deals simultaneously with the noise treatment of trains and the wheel\\/rail system as well as other topics.The assessment of a particular sound experience as annoying

B. Schulte-Werning; K. Jger; R. Strube; L. Willenbrink

2003-01-01

112

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

NASA Technical Reports Server (NTRS)

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.

Miles, Jeffrey Hilton

2008-01-01

113

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

NASA Technical Reports Server (NTRS)

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.

Soderman, Paul T.

1988-01-01

114

Sudden noise source localization system for intelligent automobile application with acoustic sensors  

Microsoft Academic Search

This paper suggests an automotive application for finding direction of sudden noise source in driving situation. The system applies sound source localization algorithm using microphone array sensor and finds the direction of the abrupt abnormal noise sources. Representative experimental results demonstrate its feasibility as new safety car electronic component.

Suwon Shon; Eric Kim; Jongsung Yoon; Hanseok Ko

2012-01-01

115

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 1991October 1992  

Microsoft Academic Search

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

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

1993-01-01

116

Instantaneous Io flux tube as the source of Jovian DAM - Possible second harmonic emissions  

NASA Technical Reports Server (NTRS)

To determine if the source of the Jovian Io-dependent DAM (decametric) emission is along the instantaneous Io flux tube (IIFT), the results of ray-tracing calculations are compared with radio emission data obtained by the Planetary Radio Astronomy instruments on Voyager 1 and 2. RX mode gyroemission at frequencies near the local gyrofrequency and sources along field lines within the active sector between 150 and 270 deg longitude are assumed. The results indicate good agreement with the observations if the source is within 20 deg of the IIFT, but the maximum gyrofrequency of the model magnetic field is smaller than the observed maximum frequency of the DAM for the assumed active field line. While errors in the magnetic-field model coupled with emission at large Doppler shift might explain this discrepancy, a more natural explanation is that the higher-frequency component of the DAM is due to second-harmonic gyroemission.

Menietti, J. D.; Curran, D. B.

1990-01-01

117

A temporal and spatial analysis of anthropogenic noise sources affecting SNMR  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

118

Effect of Velocity Ratio on Noise Source Distribution of Coaxial Jets Dimitri Papamoschou  

E-print Network

Effect of Velocity Ratio on Noise Source Distribution of Coaxial Jets Dimitri Papamoschou and Sara. Introduction NOISE from coaxial jets is of great relevance to aeroacoustics because the majority of civilian jets and suggested a method of predicting the noise attenuation when the jet is surrounded

Papamoschou, Dimitri

119

Farfield filtering and source imaging of subsonic jet noise  

NASA Astrophysics Data System (ADS)

Jet noise is analysed using data-processing tools adapted to two particular structural traits of the far field: the strong polar dependence and the temporal intermittency. Proper Orthogonal Decomposition is used to probe the polar structure of the sound field, wavelet transform being used to interrogate the temporal signature. The far field is decomposed, using each of these approaches independently, into a component attributed to 'coherent structures', denoted CS, and a residuum, R. The criteria for the decomposition being different, spatial on one hand and temporal on the other, comparison of the resulting CS components is of considerable interest; both decompositions lead, for instance, to CS components that compare favourably with a wavepacket source Ansatz. Using the two techniques, an analysis methodology is established and applied to data from a Mach 0.9, isothermal jet; a series of metrics are thereby proposed by which to evaluate the data. The methodology and associated metrics are then used to explore the effect of varying Mach number on isothermal and heated jets. The following main results are obtained. Both the unfiltered low-angle sound spectrum and that of the CS component of the isothermal jets are found to scale best with Helmholtz number, indicating that the associated sound source is noncompact. In the heated jet, on the other hand, a Strouhal number scaling is observed, again for both the unfiltered low-angle spectrum and the CS spectrum, suggesting that the associated sources are in this case more compact. Where the intermittency of the farfield signature is concerned it is found that increasing the Mach number of isothermal jets has no discernible impact, whereas in the case of the heated jet this increase is accompanied by a decrease in the intermittency, indicating some kind of associated stabilisation of wavepacket source dynamics. Finally, the unfiltered data is used to perform source imaging, using a wavepacket Ansatz. This allows a more comprehensive eduction of the wavepacket parameters. The trends observed are consistent with known changes in the mean field and with linear stability theory. Finally, the directivity of the wavepackets obtained using the source imaging is compared with those educed from the data using the POD and wavelet filters. Good agreement between all three constitutes a strong evidence supporting the contention that such wavepackets underpin the said, polar and temporal, features of the farfield.

Knig, Maxime; Cavalieri, Andr V. G.; Jordan, Peter; Delville, Jol; Gervais, Yves; Papamoschou, Dimitri

2013-09-01

120

Radially leaned outlet guide vanes for fan source noise reduction  

NASA Technical Reports Server (NTRS)

Two quiet engine program half scale fans one with a subsonic and the other with a supersonic fan tip speed at takeoff were run with 30 degree leaned and radial outlet guide vanes. Acoustic data at takeoff fan speed on the subsonic tip speed fan showed decreases in 200-foot sideline noise of from 1 to 2 PNdb. The supersonic tip speed fan a takeoff fan speed, however, showed noise increases of up 3 PNdb and a decrease in fan efficiency. At approach fan speed, the subsonic tip speed fan showed a noise decrease of 2.3 PNdb at the 200-foot sideline maximum angle and an increase in efficiency. The supersonic tip speed fan showed noise increase of 3.5 PNdb and no change in efficiency. The decrease in fan efficiency and the nature of the noise increase largely high frequency broadband noise lead to the speculation that an aerodynamic problem occurred.

Kazin, S. B.

1973-01-01

121

Characteristics of ambient seismic noise as a source for surface wave tomography  

NASA Astrophysics Data System (ADS)

Interstation cross correlations of ambient seismic noise from 1 year of continuous data at periods between 6 and 50 s are used to study the origin of the ambient noise using stations located in Europe, southern Africa, Asia, and three regions within North America. The signal-to-noise ratios (SNR) of Rayleigh waves for positive and negative correlation time lags at periods of 8, 14, 25 and 50 s are used to determine the azimuthal distribution of strong ambient noise sources. Ambient noise in both the primary (10-20 s) and secondary microseism bands (5-10 s) comes dominantly from the directions of relatively nearby coastlines with stronger noise occurring in the Northern Hemisphere in northern winter and in the Southern Hemisphere in southern winter, consistent with the hypothesis that oceanic microseisms are generating this noise. The observed differences in the directivity of noise in the primary and secondary microseism bands are the consequence of propagation and attenuation, rather than the location of generation. At intermediate and long periods (>20 s), there is much less seasonal variation in both signal strength and directivity. We argue that our results are explained most simply by near-coastal sources rather than deep ocean sources at all periods. Although the dominant ambient noise sources are distributed inhomogeneously in azimuth, strong ambient noise emerges from most directions when using recordings that are 1 year in duration. Simulations illustrate that this is what ensures the accuracy of the empirical Green's functions and ambient noise tomography.

Yang, Yingjie; Ritzwoller, Michael H.

2008-02-01

122

Fan Noise Source Diagnostic Test: Tone Modal Structure Results  

NASA Technical Reports Server (NTRS)

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.

Heidelberg, Laurence J.

2002-01-01

123

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

SciTech Connect

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.

Coulson, R.K.

1996-12-01

124

Harmonic Generation and Soft-X-Ray Laser with LASERIX: Source Development, Applications and Advanced Diagnosis  

NASA Astrophysics Data System (ADS)

The LASERIX facility has restarted operation in the middle of the year 2010. Since then, important work has been achieved on the XUV sources performance, reliability and stability, which lead to the construction of two beamlines. The first one is based on transient collisional soft X-ray laser. In the second one, the high order harmonic generation process is used to convert infrared laser into coherent XUV radiations. Characteristics and some recent works on both of them will be presented. Besides, a complete setup for pump-probe experiments has been developed and successfully tested. Some examples involving this device and dealing with plasma opacity, radiobiology and nanomagnetism will be presented. We will conclude this paper by a discussion on how application experiments can be turned into valuable diagnostics for XUV sources.

Guilbaud, Olivier; Kazamias, Sophie; Cassou, Kevin; Pittman, Moana; Daboussi, Sameh; Delmas, Olivier; Demailly, Julien; Neveu, Olivier; Pouhe, Chris; Vodungbo, Boris; Zeitoun, Philippe; Wilson, Lucy; Tallents, Greg; Dusseix, Antonin; Richet, Gabriel; Gense, Aurelie; Nghiem, Bich-Lien; Cros, Brigitte; Maynard, Gilles; Ros, David

125

Analytic derivation of pinhole collimation sensitivity for a general source model using spherical harmonics  

NASA Astrophysics Data System (ADS)

Pinhole collimators are widely used for single photon emission computed tomography (SPECT) imaging of small organs and animals. There has also been renewed interest in using pinhole arrays for clinical cardiac SPECT imaging to achieve high sensitivity and complete data sampling. Overall sensitivity of a pinhole array is critical in determining a system's performance. Conventionally, a point source model has been used to evaluate the sensitivity and optimize the system design. This model is simple but far from realistic. This work addresses the use of more realistic source models to assess the sensitivity performance of pinhole collimation. We have derived an analytical formula for pinhole collimation sensitivity with a general source distribution model using spherical harmonics. As special cases of this general model, we provided the pinhole sensitivity formulae for line, disk and sphere sources. These results show that the point source model is just the zeroth-order approximation of the other source models. The point source model overestimates or underestimates the sensitivity relative to the more realistic model. The sphere source model yields the same sensitivity as a point source located at the center of the sphere when attenuation is not taken into account. In the presence of attenuation, the average path length of emitted gamma rays is 3/4 of the radius of the sphere source. The calculated sensitivities based on these formulae show good agreement with separate Monte Carlo simulations in simple cases. The general and special sensitivity formulae derived here can be useful for the design and optimization of SPECT systems that utilize pinhole collimators.

Li, Yu-Sheng; Oldendick, James E.; Chang, Wei

2010-05-01

126

On Short Period Ambient Noise of Taiwan (1) Ambient Noise Tomography (2) Probing Source of Ambient Noise  

NASA Astrophysics Data System (ADS)

Retrieving empirical Green functions (EGF) between stations by cross-correlating continuous seismic records has quickly become a popular technique in seismology for its operational simplicity and various advantages over traditional surface wave tomography; in particular, the derived short period Greens functions of surface waves are usually inaccessible from seismic record caused by nature earthquakes. We apply this technique to three component continuous seismic data recorded at 88 short period stations in Taiwan. The data are collected from three seismic networks, including the island-wide Central Weather Bureau Seismic Network, and two temporary local seismic arrays, Tatun Volcanic Area array and Hsinchu array, for the time period from Jan, 2006 to Dec, 2006. For each station pairs, we derive Love waves from T-T (transverse) component cross-correlation functions (CCF), and Rayleigh waves from Z-Z (vertical) and R-R (radial) component CCF respectively. We measure group and phase velocities for the period range from 1 to 5 seconds. The achieved dense path coverage together with the retrieved short period EGF provide an unprecedented resolving power to the shallow crust structure of Taiwan island. With the qualified dispersion curves, we apply a multi-scale inversion technique to derive two dimensional phase, group velocity maps for both Rayleigh and Love waves, and three dimensional Vs structure of shallow crust. Besides tomographic study, we also attempt to probe the sources of ambient noise by several approaches: (1) analyzing the relative strength between the causal and acausal empirical Greens functions (EGF); (2) measuring the relative strength of CCF amplitudes with respect to their own annual average as a function of time and azimuth to determine the background energy flow; and (3) computing power spectra density of continuous record for representative costal stations. With the results, we are able to characterize the spatial and temporal variations of CCF and their possible relationship to the atmospheric perturbations and coastal bathymetry.

Chen, Y.; Gung, Y.; You, S.; Chiao, L.; Liang, W.; Lin, C.

2009-12-01

127

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

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.

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

1993-01-01

128

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

NASA Technical Reports Server (NTRS)

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.

Zaman, Afroz; Bauch, Matthew; Raible, Daniel

2011-01-01

129

Tabletop coherent extreme ultraviolet and soft X-ray sources based on high harmonic generation  

E-print Network

High harmonic generation (HHG) is a fascinating strong-field physics phenomenon that occurs when a laser pulse with a moderate intensity interacts with atoms and partially ionizes the atoms. A series of harmonics are ...

Lai, Chien-Jen, Ph. D. Massachusetts Institute of Technology

2014-01-01

130

Interim prediction method for fan and compressor source noise  

NASA Technical Reports Server (NTRS)

A method is presented for interim use in assessing the noise generated by fans and compressors in turbojet and turbofan engines. One-third octave band sound pressure levels consisting of broadband, discrete tone, and combination-tone noise components are predicted. Spectral distributions and directivity variations are specified. The method is based on that developed by other investigators with modifications derived from an analysis of full-scale, single-stage fan data. Comparisons of predicted and measured noise performance are presented, and requirements for improving the method are discussed.

Heidmann, M. F.

1975-01-01

131

Advanced techniques for noise source identification on a large generator unit  

SciTech Connect

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.

Williams, R.G.D. (GEC Alsthom Turbine Generator Ltd., Stafford (United Kingdom)); Yang, S.J. (Heriot-Watt Univ., Edinburgh (United Kingdom))

1993-03-01

132

Source localization from seismic noise: a methodology applied to seismic exploration.  

NASA Astrophysics Data System (ADS)

The main objective of the present study is to develop a methodology for source localization in seismic exploration contexts, using seismic noise data, which integrates methodologies optimized from acoustics and seismology. Passive imaging from noise cross-correlation is now applied at continental and regional scale. Its use at local scale for seismic exploration purposes is still uncertain. The development of passive imaging using cross-correlated data classically consists in two different tasks, the first one being the extraction of the Green's function from seismic noise and the second one consisting in modelling the velocity field from these observations. All the correlation methods are based on the concept that seismic noise is randomly distributed in space, in other words noise sources are azimuthally distributed around the recording stations. In practice, however, this never happens, especially at local scale and frequency above 1 Hz. A consequence is that the shape of the causal and anti-causal part of noise correlation function differs, which makes ambiguous the extraction of travel times for imaging purposes. Another consequence is that a third task should be added to the first two presented above that consists in the localization of the noise sources when it appears that the noise source distribution is heterogeneous. In our work we used data acquired in Northern America (Canada) on a 1-km side square seismic network. Five days of seismic noise data were collected on a total of 397 stations. Since exploration purposes need to obtain high resolution images and since noise correlation vanishes as frequency increases, we introduce a multistep procedure permitting to start our analysis from low to high frequency content. The seismic noise correlation function performed on the seismic network at low frequency [2-5 Hz] shows a large spatial coherence but also reveals a difference in amplitude for the causal and anti-causal parts of noise-correlated traces. Capitalizing on the strong coherence between station pairs, a methodology was developed, using both linear and non-linear techniques, to localize the seismic noise source(s). The linear technique is based on the minimization, as L2 norm, of the travel-times information extracted from the correlation functions and synthetic travel-times obtained from a local source at depth. Matched-Field Processing (MFP) non-linear techniques developed in ocean acoustics (and analogous to Capon's algorithm used in seismic) were used to further constraint the localization of the noise source on sub-wavelength dimensions. MFP results show that noise sources are quite stable on the 5 days of recording and source localization is well constrained in the low frequency range of interest.

Corciulo, Margherita; Roux, Philippe; Campillo, Michel; Dubucq, Dominique

2010-05-01

133

Investigation of rotor noise source mechanisms with forward speed simulation  

Microsoft Academic Search

The noise of a model propeller was measured with and without forward speed simulation in the open test section of a low speed wind tunnel at velocities up to 45 m\\/s and blade tip Mach numbers up to 0.6. Compared to the static tests, even low wind velocities reduced the propeller noise by up to 20 dB. Strong sound radiation

F.-R. Grosche; H. Stiewitt

1977-01-01

134

Instantaneous Io flux tube as the source of Jovian DAM: Possible second harmonic emissions  

SciTech Connect

To determine if the source of the Jovian Io-dependent DAM (decametric) emission is along the instantaneous Io flux tube (IIFT), the authors compare the results of ray-tracing calculations to radio emission data obtained by the Planetary Radio Astronomy instrument on board Voyager 1 and 2. They assume RX mode gyroemission at frequencies near the local gyrofrequency and sources along field lines within the active sector (150{degree} < longitude < 270{degree}). The results indicate good agreement with the observations if we assume the source is within 20{degree} of the IIFT, but the maximum gyrofrequency of the model magnetic field is smaller than the observed maximum frequency of the DAM for the assumed active field line. While errors in the magnetic field model coupled with emission at large Doppler shift might explain this discrepancy, a more natural explanation is that the higher-frequency component of the DAM is due to second harmonic gyroemission. Possible examples of such emission are indicated in the data.

Menietti, J.D.; Curran, D.B. (Southwest Research Institute, San Antonio, TX (USA))

1990-12-01

135

Coarse-graining microscopic strains in a harmonic, two-dimensional solid and its implications for elasticity: non-local susceptibilities and non-affine noise  

E-print Network

In soft matter systems the local displacement field can be accessed directly by video microscopy enabling one to compute local strain fields and hence the elastic moduli using a coarse-graining procedure. We study this process for a simple triangular lattice of particles connected by harmonic springs in two-dimensions. Coarse-graining local strains obtained from particle configurations in a Monte Carlo simulation generates non-trivial, non-local strain correlations (susceptibilities), which may be understood within a generalized, Landau type elastic Hamiltonian containing up to quartic terms in strain gradients (K. Franzrahe et al., Phys. Rev. E 78, 026106 (2008)). In order to demonstrate the versatility of the analysis of these correlations and to make our calculations directly relevant for experiments on colloidal solids, we systematically study various parameters such as the choice of statistical ensemble, presence of external pressure and boundary conditions. We show that special care needs to be taken for an accurate application of our results to actual experiments, where the analyzed area is embedded within a larger system, to which it is mechanically coupled. Apart from the smooth, affine strain fields, the coarse-graining procedure also gives rise to a noise field made up of non-affine displacements. Several properties of this noise field may be rationalized for the harmonic solid using a simple "cell model" calculation. Furthermore the scaling behavior of the probability distribution of the noise field is studied and a master curve is obtained.

K. Franzrahe; P. Nielaba; S. Sengupta

2009-11-07

136

Natural noise above 50 MHZ from terrestrial and extraterrestrial sources  

NASA Technical Reports Server (NTRS)

This paper offers a brief overview of natural radio noise for frequencies above 50 MHz in terms of brightness temperature as observed from two vantage points. The first is from an Earth station located at 40 degrees north latitude and observing at elevation angles from 0 to 90 degrees with an ideal antenna. The second is a satellite in geostationary orbit communicating with the Earth. Earth station noise at VHF and UHF is dominated by galactic and solar noise. Emission from the atmosphere, gases and hydrometeors, are dominant at EHF and SHF. Radiative transfer theory is invoked in the calculation of brightness temperature from the atmosphere. The situation is not vastly different from geostationary orbit if communications is with the Earth. Emission from the land and sea, even under idealized conditions, enters significantly. Land is a much more effective emitter than sea water, but at frequencies above 30 GHz the differential becomes much less due to the increasing significance of atmospheric emission.

Smith, E. K.; Flock, W. L.

1991-01-01

137

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

NASA Astrophysics Data System (ADS)

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.

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

1981-04-01

138

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

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

139

A summation and inhibition model of annoyance response to multiple community noise sources  

NASA Technical Reports Server (NTRS)

A model of annoyance due to combined noise sources was developed. The model provides for the summation of the subjective magnitudes of annoyance due to the separate noise sources and for the inhibition of the subjective magnitudes of each source by the presence of the other noise sources. The inhibition process is assumed to mathematically obey a power-group transformation. The results of an experiment in which subjects judged the annoyance of 15 minute sessions of combined aircraft and with several other models of combined source annoyance. These comparisons indicated that the model developed herein provides better qualitative and quantitative agreement with experimental responses than the other models. The application of the model to multiple community noises is discussed.

Powell, C. A.

1979-01-01

140

Suppression of Fiber Modal Noise Induced Radial Velocity Errors for Bright Emission-Line Calibration Sources  

E-print Network

Modal noise in optical fibers imposes limits on the signal to noise and velocity precision achievable with the next generation of astronomical spectrographs. This is an increasingly pressing problem for precision radial velocity (RV) spectrographs in the near-infrared (NIR) and optical that require both high stability of the observed line profiles and high signal to noise. 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 (COTS) solution that significantly mitigates modal noise at all optical and NIR wavelengths, and which can be applied to...

Mahadevan, Suvrath; Ramsey, Lawrence; Venditti, Nick

2014-01-01

141

Investigation of Subcooled Hydrothermal Boiling in Ground Water Flow Channels as a Source of Harmonic Tremors: Annual Report.  

National Technical Information Service (NTIS)

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...

1989-01-01

142

On the application of acoustic 'mirror', 'telescope' and 'polar correlation' techniques to jet noise source location  

Microsoft Academic Search

Three techniques for determining jet noise sources are discussed, the acoustic mirror, telescope, and polar correlation methods. In order to formulate a direct, self-consistent comparison of the methods, relevant jet aerodynamic and acoustic parameters are considered. It is noted that the techniques are limited by the spatial resolution which restricts them to jet noise at higher Strouhal and Mach numbers

H. V. Fuchs

1978-01-01

143

Subsonic and Supersonic Jet Noise Predictions from Statistical Source Models  

Microsoft Academic Search

Subsonicandsupersonicjetnoiseisdeterminednumerically from statisticalsourcemodels.Thegoalistodevelop prediction methods for high-speed jet noise for application to aeronautical and space transportation systems. In this framework, a combination of a k-? turbulence closure with an acoustic analogy provides an interesting way to compute such radiated acoustic elds. Three acoustic analogies are investigated. First, the classical Lighthill theory in combination with Ribner' s results is applied

Christophe Bailly; Sbastien Candel; Philippe Lafon

1997-01-01

144

Acoustic imaging of harmonic near-field sources from surface pressure measurements on a body using singular value decomposition  

Microsoft Academic Search

An inverse or backward projection method based on a combined Greens function and singular value decomposition method is developed to locate and to determine the strength of near field harmonic sources from the acoustic field on the surface of a nearby rigid body. A resolution matrix, which is based on the free space Greens function, the geometry of the measurement

Peter R. Stepanishen; Irsan Brodjonegoro

2002-01-01

145

Walk-away VSP using drill noise as a source  

SciTech Connect

The authors describe a method for extracting and deconvolving a signal generated by a drill bit and collected by an array of surface geophones. The drill-noise signature is reduced to an effective impulse by means of a multichannel Wiener deconvolution technique, producing a walk-away reverse vertical seismic profile (VSP) sampled almost continuously in depth. They show how the multichannel technique accounts for noise and for internal drill-string reflections, automatically limiting the deconvolution technique, producing a walk-away reverse vertical seismic profile (VSP) sampled almost continuously in depth. They show how the multichannel technique accounts for noise and for internal drill-string reflections, automatically limiting the deconvolved data to frequencies containing significant energy. They have acquired and processed a data set from a well in Germany while drilling at a depth of almost 4,000 m. The subsurface image derived from these data compares well with corresponding images from a 3-d surface seismic survey, a zero-offset VSP survey, and a walk-away VSP survey acquired using conventional wireline techniques. The effective bandwidth of the deconvolved drill-noise data is comparable to the bandwidth of surface seismic data but significantly smaller than what can be achieved with wireline VSP techniques. Although the processing algorithm does not require the use of sensors mounted on the drill string, these sensors provide a very economic way to compress the data. The sensors on the drill string were also used for accurate timing of the deconvolved drill-noise data.

Haldorsen, J.B.U. [Geco-Prakla, Hannover (Germany)] [Geco-Prakla, Hannover (Germany); Miller, D.E. [Schlumberger-Doll Research, Ridgefield, CT (United States)] [Schlumberger-Doll Research, Ridgefield, CT (United States); Walsh, J.J. [Schlumberger Well Services, Houston, TX (United States)] [Schlumberger Well Services, Houston, TX (United States)

1995-07-01

146

Noise  

Microsoft Academic Search

The proliferation of DNA sequence data has generated a concern about the effects of noise on phylogeny reconstruction. This concern has led to various recommendations for weighting schemes and for separating data types prior to analysis. A new technique is explored to examine directly how noise influences the stability of parsimony reconstruction. By appending purely random characters onto a matrix

John W Wenzel; Mark E Siddall

1999-01-01

147

A moving source problem relevant to jet noise  

Microsoft Academic Search

The total power and power spectrum due to a point source convecting at a uniform subsonic velocity along the axis of a round jet are calculated. The source is a discrete frequency source in its own frame of reference and the jet is assumed to have a slug flow velocity profile with velocity equal to that of the source. The

R. Mani

1972-01-01

148

The effect of multimicrophone noise reduction systems on sound source localization by users of binaural hearing aids  

E-print Network

The effect of multimicrophone noise reduction systems on sound source localization by users on the ability to localize sound sources. Two recently developed noise reduction techniques for binaural hearing of the different algorithms on perceived sound source localization and their noise reduction performance

149

Unifying intensity noise and second-order coherence properties of amplified spontaneous emission sources  

NASA Astrophysics Data System (ADS)

We present joint investigations of relative intensity noise (RIN) and second-order coherence properties of amplified spontaneous emission (ASE) generated by a superluminescent diode. We introduce a generalized intensity noise description for ASE sources that contains the shot noise contribution but also accounts for first- and second-order coherence properties reflecting the process of light generation. We find excellent agreement between pump-current-dependent RIN values and this new description, with the perspective of particular interesting consequences for the realization of low-noise broadband emitters.

Blazek, Martin; Hartmann, Sbastien; Molitor, Andreas; Elsaesser, Wolfgang

2011-09-01

150

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

PubMed

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. PMID:22087938

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

2011-11-01

151

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

NASA Technical Reports Server (NTRS)

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.

Simons, Rainee N.; Wintucky, Edwin G.

2014-01-01

152

Can lightning be a noise source for a spherical gravitational wave antenna?  

E-print Network

The detection of gravitational waves is a very active research field at the moment. In Brazil the gravitational wave detector is called Mario SCHENBERG. Due to its high sensitivity it is necessary to model mathematically all known noise sources so that digital filters can be developed that maximize the signal-to-noise ratio. One of the noise sources that must be considered are the disturbances caused by electromagnetic pulses due to lightning close to the experiment. Such disturbances may influence the vibrations of the antenna's normal modes and mask possible gravitational wave signals. In this work we model the interaction between lightning and SCHENBERG antenna and calculate the intensity of the noise due to a close lightning stroke in the detected signal. We find that the noise generated does not disturb the experiment significantly.

Nadja S. Magalhaes; Rubem M. Marinho Jr.; Odylio D. Aguiar; C. Frajuca

2005-12-11

153

3-component beamforming analysis of ambient seismic noise field for Love and Rayleigh wave source directions  

NASA Astrophysics Data System (ADS)

Our knowledge about common and different origins of Love and Rayleigh waves observed in the microseism band of the ambient seismic noise field is still limited, including the understanding of source locations and source mechanisms. Multi-component array methods are suitable to address this issue. In this work we use a 3-component beamforming algorithm to obtain source directions and polarization states of the ambient seismic noise field within the primary and secondary microseism bands recorded at the Grfenberg array in southern Germany. The method allows to distinguish between different polarized waves present in the seismic noise field and estimates Love and Rayleigh wave source directions and their seasonal variations using one year of array data. We find mainly coinciding directions for the strongest acting sources of both wave types at the primary microseism and different source directions at the secondary microseism.

Juretzek, Carina; Hadziioannou, Cline

2014-05-01

154

Security of two-way continuous-variable quantum key distribution with source noise  

NASA Astrophysics Data System (ADS)

We investigate the security of reverse reconciliation two-way continuous-variable quantum key distribution with source noise at both legitimate sides. Because the source noise originates from imperfect devices, we ascribe it to the legitimate sides rather than the eavesdropper. The trusted model consists of a thermal noise injected into a beam splitter. The expressions of secret key rate are derived against collective entangling cloner attacks for homodyne and heterodyne detections. Simulation results show that by applying the trusted model, the security bound of the reverse reconciliation two-way protocols can be tightened, while the advantage over one-way protocols still maintains.

Wang, Tianyi; Yu, Song; Zhang, Yi-Chen; Gu, Wanyi; Guo, Hong

2014-11-01

155

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

PubMed

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

Lazar, Aurel A; Zhou, Yiyin

2014-01-01

156

Soft X-ray Microscope Constructed with 130-nm Spatial Resolution Using a High Harmonic X-ray Source  

NASA Astrophysics Data System (ADS)

Using high harmonic radiation as an X-ray light source, a soft X-ray microscope with nanometer-scale spatial resolution was investigated. A transmission soft X-ray microscope was constructed using a Mo/Si multilayer concave mirror as a condenser and a Fresnel zone plate as a microscope objective. The high-order harmonic source at 13 nm, emitted from neon atoms driven by intense femtosecond laser pulses, was optimized by controlling laser chirp. Objects, patterned on 160-nm-thick hydrogen silsesquioxane coated on a 100-nm-thick Si3N4 membrane, were used for imaging. The analysis of object images, captured on an X-ray charge-coupled device, showed that the spatial resolution of the microscope was about 130 nm, verifying the usefulness of the tabletop soft X-ray source.

Kim, Deuk Su; Park, Jong Ju; Lee, Kyoung Hwan; Park, Juyun; Nam, Chang Hee

2009-02-01

157

Suppression of Fiber Modal Noise Induced Radial Velocity Errors for Bright Emission-line Calibration Sources  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

158

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

NASA Technical Reports Server (NTRS)

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.

Podboy, Gary G.

2013-01-01

159

An extremely low-noise heralded single-photon source: A breakthrough for quantum technologies  

NASA Astrophysics Data System (ADS)

Low noise single-photon sources are a critical element for quantum technologies. We present a heralded single-photon source with an extremely low level of residual background photons, by implementing low-jitter detectors and electronics and a fast custom-made pulse generator controlling an optical shutter (a LiNbO3 waveguide optical switch) on the output of the source. This source has a second-order autocorrelation g(2)(0)=0.005(7), and an output noise factor (defined as the ratio of the number of noise photons to total photons at the source output channel) of 0.25(1)%. These are the best performance characteristics reported to date.

Brida, G.; Degiovanni, I. P.; Genovese, M.; Piacentini, F.; Traina, P.; Della Frera, A.; Tosi, A.; Bahgat Shehata, A.; Scarcella, C.; Gulinatti, A.; Ghioni, M.; Polyakov, S. V.; Migdall, A.; Giudice, A.

2012-11-01

160

An extremely low-noise heralded single-photon source without temporal post-selection  

NASA Astrophysics Data System (ADS)

With the recent progresses in quantum technologies, single photon sources have gained a primary relevance. Here we present a heralded single photon source characterized by an extremely low level of noise photons, realized by exploiting low-jitter electronics and detectors and fast custom-made electronics used to control an optical shutter (a LiNbO3 waveguide optical switch) at the output of the source. This single photon source showed a second-order autocorrelation function g(2)(0) = 0:005(7), and an Output Noise Factor (defined as the ratio of noise photons to total photons at the source output) of 0:25(1)%, among the best ever achieved.

Piacentini, F.; Traina, P.; Della Frera, A.; Tosi, A.; Scarcella, C.; Ruggeri, A.; Gulinatti, A.; Ghioni, M.; Polyakov, S. V.; Migdall, A.; Giudice, A.; Brida, G.; Degiovanni, I. P.; Genovese, M.

2013-05-01

161

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

E-print Network

Novel table-top sources of extreme ultraviolet (XUV) light based on high-harmonic generation (HHG) yield unique insight into the fundamental properties of molecules, nanomaterials, or correlated solids, and enable advanced applications in imaging or metrology. Extending HHG to high repetition rates portends great experimental benefits, yet efficient XUV conversion of correspondingly weak driving pulses is challenging. Here, we demonstrate a highly-efficient source of femtosecond XUV pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ~3e13 per second is generated at 22.3 eV, with 5e-5 conversion efficiency that surpasses similar directly-driven harmonics by two orders-of-magnitude. This enhancement exceeds the predicted dipole wavelength scaling, evidencing improved phase-matching for ultraviolet-driven HHG under tight focusing as corroborated by simulations. Spectral isolation of a single sub-80 meV harmonic re...

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

2014-01-01

162

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

163

A MATRIX-PENCIL APPROACH TO BLIND SEPARATIOIN OF NON-WHITE SOURCES IN WHITE NOISE  

Microsoft Academic Search

The problem of blind source separation in additive white noise is an important problem in speech, array and acoustic signal processing. In general this problem requires the use of higher order statistics of the received signals. Nonethe- less, many signal sources such as speech with distinct, non-white power spectral densities, second order statistics of the received signal mixture can be

Chunqi Chang; Zhi Ding; Sze Fong Yau; Francis H Y Chan

1998-01-01

164

A matrix-pencil approach to blind separation of non-white sources in white noise  

Microsoft Academic Search

The problem of blind source separation in additive white noise is an important problem in speech, array and acoustic signal processing. In general this problem requires the use of higher order statistics of the received signals. However for many signal sources, such as speech with distinct non-white power spectral densities, second order statistics of the received signal mixture can be

Chungi Chang; Zhi Ding; Sze Fong Yau; F. H. Y. Chang

1998-01-01

165

Using the FASST source separation toolbox for noise robust speech recognition Alexey Ozerov and Emmanuel Vincent  

E-print Network

Using the FASST source separation toolbox for noise robust speech recognition Alexey Ozerov.vincent}@inria.fr Abstract We describe our submission to the 2011 CHiME Speech Sep- aration and Recognition Challenge. Our source separa- tion can be very helpful to improve speech recognition in noisy or multi

Paris-Sud XI, Université de

166

Pitch-Scale Modification using the Modulated Aspiration Noise Source* Daryush Mehta1,2  

E-print Network

Pitch-Scale Modification using the Modulated Aspiration Noise Source* Daryush Mehta1,2 and Thomas F closure. Inspired by this observation of natural modulations and of fullband energy in the aspiration of its source waveform. Since we have modeled an inherent coupling between the periodic and aspiration

167

Fast accurate MEG source localization using a multilayer perceptron trained with real brain noise  

E-print Network

Fast accurate MEG source localization using a multilayer perceptron trained with real brain noise gradient methods like Levenberg­Marquardt (LM) are in widespread use for source localization from­time localizer. We used an analytical model of quasistatic electromagnetic propagation through a spherical head

Pearlmutter, Barak

168

Fast accurate MEG source localization using a multilayer perceptron trained with real brain noise  

E-print Network

Fast accurate MEG source localization using a multilayer perceptron trained with real brain noise gradient methods like Levenberg-Marquardt (LM) are in widespread use for source localization from-time localizer. We used an analytical model of quasistatic electromagnetic propagation through a spherical head

Pearlmutter, Barak

169

Additive Gaussian white noise modulated excitation kinetics of impurity doped quantum dots: Role of confinement sources  

NASA Astrophysics Data System (ADS)

We investigate the excitation kinetics of a repulsive impurity doped quantum dot initiated by the application of additive Gaussian white noise. The noise and the dot confinement sources of electric and magnetic origin have been found to fabricate the said kinetics in a delicate way. In addition to this the dopant location also plays some prominent role. The present study sheds light on how the individual or combined variation of different confinement sources could design the excitation kinetics in presence of noise. The investigation reveals emergence of maximization and saturation in the excitation kinetics as a result of complex interplay between various parameters that affect the kinetics. The phase space plots are often invoked and they lend credence to the findings. The present investigation is believed to provide some useful perceptions of the functioning of mesoscopic systems where noise plays some profound role.

Ganguly, Jayanta; Pal, Suvajit; Ghosh, Manas

2013-11-01

170

Signal-to-noise ratio of intensity interferometry experiments with highly asymmetric x-ray sources  

SciTech Connect

The authors discuss the signal-to-noise ratio of an intensity interferometry experiment for a highly asymmetric x-ray source using different aperture shapes in front of the photodetectors. It is argued that, under ideal conditions using noiseless detectors and electronics, the use of slit-shaped apertures, whose widths are smaller but whose lengths are much greater than the transverse coherence widths of the beam in the corresponding directions, provides no signal-to-noise advantage over the use of pinhole apertures equal to or smaller than the coherence area. As with pinholes, the signal-to-noise ratio is determined solely by the count degeneracy parameter and the degree of coherence of the beam. This contrasts with the signal-to-noise ratio enhancement achievable using slit-shaped apertures with an asymmetric source in a Young`s experiment.

Feng, Y.P.; McNulty, I.; Xu, Z.; Gluskin, E. [Argonne National Lab., IL (United States). Experimental Facilities Div.

1995-06-23

171

Signal-to-noise ratio of intensity interferometry experiments with highly asymmetric x-ray sources  

SciTech Connect

We discuss the signal-to-noise ratio of an intensity interferometry experiment for a highly asymmetric x-ray source using different aperture shapes in front of the photodetectors. It is argued that, under ideal conditions using noiseless detectors and electronics, the use of slit-shaped apertures, whose widths are smaller but whose lengths are much greater than the transverse coherence widths of the beam in the corresponding directions, provides no signal-to-noise advantage over the use of pinhole apertures equal to or smaller than the coherence area. As with pinholes, the signal-to-noise ratio is determined solely by the count degeneracy parameter and the degree of coherence of the beam. This contrasts with the signal-to-noise ratio enhancement achievable using slit-shaped apertures with an asymmetric source in a Young`s experiment.

Feng, Y.P.; McNulty, I.; Xu, Z.; Gluskin, E.

1997-02-11

172

Interaction of rotor tip flow irregularities with stator vanes as a noise source  

NASA Technical Reports Server (NTRS)

The role of the interaction of rotor tip flow irregularities (vortices and velocity defects) with downstream stator vanes is discussed as a possible fan noise mechanism. This is accomplished by: (1) indicating some of the mothods of formation of these flow irregularities; (2) observing how they would behave with respect to known noise behavior; and (3) attempting to compare the strength of the rotor tip flow irregularity mechanism with the strength of the more common rotor wake-stator mechanism. The rotor tip flow irregularity-stator interaction is indicated as being a probable inflight noise source.

Dittmar, J. H.

1977-01-01

173

Correlation between co-exposures to noise and air pollution from traffic sources  

Microsoft Academic Search

Background:Both air and noise pollution associated with motor vehicle traffic have been associated with cardiovascular disease. Similarities in pollution source and health outcome mean that there is potential for noise to confound studies of air pollution and cardiovascular disease, and vice versa, or for more complex interactions to occur.Methods:The correlations between 2-week average roadside concentrations of nitrogen dioxide (NO2) and

H. W. Davies; J. J. Vlaanderen; S. E. Henderson; M. Brauer

2009-01-01

174

Application Of A Generalized Mathematical Model Of Noise Sources To Optical Media Evaluation  

NASA Astrophysics Data System (ADS)

Extensive data have been taken on the Drexler Technology Corporation's DrexonR recording media. The data have been analyzed to determine the media's response function. The data indicate that the media conforms to a form of the Generalized Mathematical Model of Noise Sources under some recording conditions. A model of the media under these conditions is developed and used to evaluate the effects of recording laser noise.

Mendez, Antonio J.

1987-01-01

175

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

NASA Astrophysics Data System (ADS)

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.

Walker, Bruce E.

2005-09-01

176

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

NASA Technical Reports Server (NTRS)

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.

Greenwood, Eric II; Schmitz, Fredric H.

2009-01-01

177

Simulation of 100-300 GHz solid-state harmonic sources  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

178

An improved assessment approach for noise impacts from stationary point and traffic sources on humans and wildlife  

SciTech Connect

This paper presents an improved, efficient approach for assessing noise impacts associated with a complex set of noise sources at multiple receptor locations; noise impacts form typical remedial activities at a contaminated industrial site are used as an example. The noise sources associated with remedial activities at the site and surrounding areas are described, the noise-propagation modeling methods and results are presented, and an impact assessment of the contaminated site is discussed with regard to applicable regulatory standards and individual and community responses. Also discussed is the improved noise assessment approach. The improved features demonstrated are automate approaches for (1) inputting long-term hourly meterorological data (e.g., 8,760 hours for a one-year period) into a long-range noise-propagation model for computing noise-level increases at receptor locations and (2) analyzing potential individual and community responses to intrusive noises using the IAP and modified CNR.

Chang, Young-Soo; Chun, K.C.

1994-04-01

179

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

180

Numerical spatial marching techniques in duct acoustics. [noise source calculation from far field pressure measurements  

NASA Technical Reports Server (NTRS)

Direct calculation of the internal structure of a ducted noise source from farfield pressure measurements is regarded as an initial value problem, where the pressure and pressure gradient (farfield impedance) are assumed to be known along a line in the farfield. If pressure and impedance are known at the boundary of the farfield, the pressure can be uniquely determined in the vicinity of the inlet and inside the inlet ducting. A marching procedure is developed which, with this information obtained from measurements, enables a description of a ducted noise source. The technique uses a finite difference representation of the homogeneous Helmholtz equation.

Baumeister, K. J.

1979-01-01

181

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

PubMed

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. PMID:20798468

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

2010-09-24

182

Further development of low noise MEVVA ion source  

SciTech Connect

Based on the idea of a space-charge-limited mode of operation, the influence of a pair of electrostatic meshes on the beam parameters of the LBNL MEVVA-5 ion source was investigated. The meshes were placed in the expansion zone of the vacuum arc plasma. Apart from reducing the level of beam current fluctuations, this mode of operation provides significant control over the ion charge state distribution of the extracted beam. These effects can be understood taking not only space charge but also the high-directed ion drift velocities into account that are the same for different ion charge states of a material. The results of simulations of the processes involved are in good agreement with the experimental results.

Oks, Efim; Yushkov, George; Litovko, Irina; Anders, Andre; Brown, Ian

2001-08-28

183

Positions of type II fundamental and harmonic sources in the 30-100 MHZ range  

Microsoft Academic Search

An excellent example of a type III-V burst followed by a type II burst with fundamental and harmonic bands was observed on June 18, 1979 at the Clark Lake Radio Observatory. The observations are described in detail and their implications are discussed with regard to the problem of directionality with respect to the magnetic field lines of the collisionless MHD

H. S. Sawant; T. E. Gergely; M. R. Kundu

1982-01-01

184

Shipping noise in whale habitat: Characteristics, sources, budget, and impact on belugas in SaguenaySt. Lawrence  

E-print Network

Shipping noise in whale habitat: Characteristics, sources, budget, and impact on belugas Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping noise. The echolocation band for this population of belugas was also affected by the shipping noise. [http://dx.doi.org/10

Paris-Sud XI, Université de

185

Investigation of the hot-carrier degradation in Si\\/SiGe HBT's by intrinsic low frequency noise source modeling  

Microsoft Academic Search

The characterization of the excess low-frequency noise (LFN) properties of electronic devices is a useful tool in the field of reliability physics, because LFN is related to the interactions between charge carriers and material imperfections and defects. The LFN behavior of a bipolar transistor can be described in terms of extrinsic or intrinsic noise sources. The noise representation based on

M. Borgarino; J. Kuchenbecker; J. G. Tartarin; L. Bary; T. Kovacic; R. Plana; R. Menozzi; F. Fantini; J. Graffeuil

2001-01-01

186

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

NASA Technical Reports Server (NTRS)

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.

Bridges, James (Technical Monitor); Panda, Jayanta

2005-01-01

187

Structured noise in computed tomography: effects of periodic error sources.  

PubMed

The artifact in computed tomography (CT) images due to cyclic projection errors, such as errors due to periodic fluctuations in x-ray intensity, is derived and verified by computer simulation. Depending upon the relative phase of the error between projections, the artifact is shown to be described by a Bessel function (or functions) of the radial argument which is sinusoidally modulated as a function of angle. Because of the nature of Bessel functions, the artifact is essentially zero up to some minimum radius. When the effects of sampling are neglected, a single fundamental artifact is shown to occur. In fourth-generation scanners, the fundamental artifact (neglecting sampling) will occur at a detector fan angle of about about 39 degrees (depending on the ratio of the axis-to-detector, source-to-axis distances). The radius of appearance of this fundamental artifact is independent of the frequency of the periodic error signal and will only be visible in fourth-generation CT scanners with detector fan angles greater than about 39 degrees. The effects of sampling are derived and illustrated by simulation for first-, third-, and fourth-generation CT-scanner geometries. It is shown that the effect of sampling is to cause an infinite number of such artifacts to be superimposed in the final image. The radius of appearance of all but the fundamental artifact are shown to be dependent on the frequency of the periodic signal. It is shown that by judicious choice of the sampling parameters relative to the frequency of the periodic error, the artifact can be effectively eliminated. PMID:7155075

Parker, D L; Couch, J L; Peschmann, K R; Smith, V

1982-01-01

188

Analysis of a dense seismic array to determine sources of Newtonian gravitational noise at the LIGO sites  

NASA Astrophysics Data System (ADS)

Newtonian gravitational noise will be an important noise contributor for Advanced LIGO and proposed upgrades to Advanced LIGO, between 5Hz and 30Hz. A major step toward subtracting this Newtonian noise and thus improving the astrophysical detection ability of ground-based gravitational wave observatories is determining the dominant sources of seismic noise, which contribute most strongly to the Newtonian noise. An array of 44 sensors was installed at the LIGO Hanford site for 8 months, including the duration of a commissioning test of a 4km Fabry-Perot cavity. We will show results from this array, including application of LIGO data analysis methods to seismic source localization, relative importance of locally generated versus far-field seismic disturbances, and estimates of residual seismic noise and Newtonian noise present in the cavity length data. We will discuss how this information will help improve noise subtraction algorithms, particularly in terms of optimal sensor placement.

Driggers, Jennifer; Harms, Jan; Raymond, Vivien; Adhikari, Rana

2013-04-01

189

Characterization and Analysis of Relative Intensity Noise in Broadband Optical Sources for Optical Coherence Tomography  

PubMed Central

Relative intensity noise (RIN) is one of the most significant factors limiting the sensitivity of an optical coherence tomography (OCT) system. The existing and prevalent theory being used for estimating RIN for various light sources in OCT is questionable, and cannot be applied uniformly for different types of sources. The origin of noise in various sources differs significantly, owing to the different physical nature of photon generation. In this study, we characterize and compare RIN of several OCT light sources including superluminescent diodes (SLDs), an erbium-doped fiber amplifier, multiplexed SLDs, and a continuous-wave laser. We also report a method for reduction of RIN by amplifying the SLD light output by using a gain-saturated semiconductor optical amplifier. PMID:22090794

Shin, Sunghwan; Sharma, Utkarsh; Tu, Haohua; Jung, Woonggyu; Boppart, Stephen A.

2011-01-01

190

Iterative CT Reconstruction using Models of Source and Detector Blur and Correlated Noise  

PubMed Central

Statistical model-based reconstruction methods derive much of their advantage over traditional methods through more accurate forward models of the imaging system. Typical forward models fail to integrate two important aspects of real imaging systems: system blur and noise correlations in the measurements. This work develops an approach that models both aspects using a two-stage approach that includes a regularization deblurring operation followed by generalized penalized weighted least-squares reconstruction. Different reconstruction noise models including standard uncorrelated and correlated presumptions were explored. Moreover, different imaging systems were investigated in which blur was dominated by source effects, dominated by detector effects, or by a combination of source and detector blur. The proposed reconstruction approach that models the correlated noise demonstrated the best performance across all scenarios with the greatest benefits for increased source blur and for reconstructions with finer spatial resolution. This suggests potential application of the method for high resolution systems like dedicated flat-panel cone-beam CT (e.g., head, extremity, dental, mammography scanners) where system resolution is limited by both source and detector blur effects and noise correlations in measurement data are traditionally ignored.

Tilley, Steven; Siewerdsen, Jeffrey H.; Stayman, J. Webster

2014-01-01

191

NOISE SOURCE IDENTIFICATION IN A PROPFAN MODEL BY MEANS OF ACOUSTICAL NEAR FIELD MEASUREMENTS  

Microsoft Academic Search

For the exploration of the dominant aerodynamic noise sources, the pressure fluctuations in the exit plane (near field) of the propfan model CRISP (Counter Rotating Integrated Shrouded Propfan) were measured with conventional 1\\/4 inch microphones. The pressure field of the tone components was resolved into a distribution of duct modes. Knowledge of the dominant modes allows conclusions about the dominant

F. Holste; W. Neise

1997-01-01

192

Optimal Jamming Over Additive Noise: Vector Source-Channel Case Emrah Akyol and Kenneth Rose  

E-print Network

to scalar sources over scalar additive noise channels, to vector spaces. Particularly, we find the saddle point solution to the jamming problem in "vector spaces", within its most general, non-Gaussian setting to the scalar setting, linearity conditions for encoding and decoding mappings play a pivotal role in jamming

California at Santa Barbara, University of

193

Propeller aircraft cabin vibration and noise-excitation, sources, and paths  

Microsoft Academic Search

The potential sources and paths by which the propeller produces structural responses resulting in vibration and noise in the cabin of a transport aircraft are discussed. New low cost, convenient experimental and analytical techniques are described for evaluating the excitations; propeller airborne pressures on the fuselage shells, slip stream induced forces on the wing and tail, and oscillatory forces on

R. E. Donham; F. J. Balena; E. Z. Bochary; O. K. Liehr

1985-01-01

194

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

ERIC Educational Resources Information Center

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)

Consumer Dynamics Inc., Rockville, MD.

195

Improving noise threshold for optical quantum computing with the EPR photon source  

E-print Network

We show that the noise threshold for optical quantum computing can be significantly improved by using the EPR-type of photon source. In this implementation, the detector efficiency $\\eta_{d}$ is required to be larger than 50%, and the source efficiency $\\eta_{s}$ can be an arbitrarily small positive number. This threshold compares favorably with the implementation using the single-photon source, where one requires the combined efficiency $\\eta_{d}\\eta_{s}>2/3$. We discuss several physical setups for realization of the required EPR photon source, including the photon emitter from a single-atom cavity.

Z. -H. Wei; Y. -J. Han; C. H. OH; L. -M. Duan

2009-12-08

196

Luminescence-induced noise in single photon sources based on BBO crystals  

E-print Network

Single-photon sources based on the process of spontaneous parametric down-conversion play a key role in various applied disciplines of quantum optics. We characterize intrinsic luminescence of BBO crystals as a source of non-removable noise in quantum-optics experiments. By analysing its spectral and temporal properties together with its intensity, we evaluate the impact of luminescence on single-photon state preparation using spontaneous parametric down-conversion.

Radek Machulka; Karel Lemr; Ond?ej Haderka; Marco Lamperti; Alessia Allevi; Maria Bondani

2014-05-28

197

Luminescence-induced noise in single photon sources based on BBO crystals  

NASA Astrophysics Data System (ADS)

Single-photon sources based on the process of spontaneous parametric down-conversion play a key role in various applied disciplines of quantum optics. We characterize the intrinsic luminescence of BBO crystals as a source of non-removable noise in quantum-optics experiments. By analysing its spectral and temporal properties together with its intensity, we evaluate the impact of luminescence on single-photon state preparation using spontaneous parametric down-conversion.

Machulka, Radek; Lemr, Karel; Haderka, Ond?ej; Lamperti, Marco; Allevi, Alessia; Bondani, Maria

2014-11-01

198

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

NASA Technical Reports Server (NTRS)

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 routine CLEAN-SC created a series of lumped sources which may be unphysical. We believe that the present effort is the first-ever attempt to directly measure noise source distribution in a rocket plume.

Panda, J.; Mosher, R.

2010-01-01

199

Mapping underwater sound noise and assessing its sources by using a self-organizing maps method.  

PubMed

This study aims to provide an objective mapping of the underwater noise and its sources over an Adriatic coastal marine habitat by applying the self-organizing maps (SOM) method. Systematic sampling of sea ambient noise (SAN) was carried out at ten predefined acoustic stations between 2007 and 2009. Analyses of noise levels were performed for 1/3 octave band standard centered frequencies in terms of instantaneous sound pressure levels averaged over 300 s to calculate the equivalent continuous sound pressure levels. Data on vessels' presence, type, and distance from the monitoring stations were also collected at each acoustic station during the acoustic sampling. Altogether 69 noise surveys were introduced to the SOM predefined 2 2 array. The overall results of the analysis distinguished two dominant underwater soundscapes, associating them mainly to the seasonal changes in the nautical tourism and fishing activities within the study area and to the wind and wave action. The analysis identified recreational vessels as the dominant anthropogenic source of underwater noise, particularly during the tourist season. The method demonstrated to be an efficient tool in predicting the SAN levels based on the vessel distribution, indicating also the possibility of its wider implication for marine conservation. PMID:23464008

Rako, Nikolina; Vilibi?, Ivica; Mihanovi?, Hrvoje

2013-03-01

200

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

PubMed

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)?=?0.23s 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

Aliabadi, Mohsen; Golmohammadi, Rostam; Mansoorizadeh, Muharram

2014-03-01

201

Ambient noise recorded at broadband stations in Portugal and Morocco: Characterization and Sources  

NASA Astrophysics Data System (ADS)

The first broadband (BB) seismic stations were deployed in Portugal in the 1990s, and ever since their number had steadily increased. Portugal is currently covered by a network of 35 broadband stations in mainland Portugal, which is complemented by stations in the islands of Madeira and Azores, as well as stations in Morocco. In the period 2010 - 2012, project WILAS - "West Iberia Lithosphere and Astenosphere Structure" (PTDC/CTE-GIX/097946/2008), deployed 30 additional temporary seismic BB stations in mainland Portugal. The WILAS stations, in addition to the permanent and TOPOIBERIA stations, provided a full and dense coverage of the Iberian Peninsula. In this presentation we will characterize the ambient seismic noise recorded at BB stations deployed in Portugal (mainland, Azores and Madeira) and Morocco. We analyse all time periods of data available since the instruments were installed. The noise is characterized by means of probability density functions (PDFs) of power spectral density (PSDs) of continuous, overlapping, 1-hour segments of data. Time-series of noise levels at different frequencies and spectrograms are computed to visualize the variations of ambient noise over different time periods and frequency bands. We observe the expected diurnal periodicity at high frequencies and seasonal variation at long periods. There is a clear increase of the noise amplitude in the microseismic band during the Winter, when more storms occur in the adjacent Northern Atlantic. We correlate sea level, storm activity, and other atmospheric parameters with the variations in ambient noise level. The analysis performed gives clues concerning data quality (poor quality data is clearly identified), Earth structure (a correlation is visible between sedimentary basins and amplification of seismic noise), and sources of ambient noise at different frequency bands.

Custdio, Susana; Madureira, Guilherme; Corela, Carlos; Alves, Paulo; Haberland, Christian; Carrilho, Fernando; Fonseca, Joao; Caldeira, Bento; Dias, Nuno

2013-04-01

202

Noise sources in a low-Reynolds-number turbulent jet at Mach 0.9  

NASA Astrophysics Data System (ADS)

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 (Stromberg, McLaughlin & Troutt 1980). 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 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.

Freund, Jonathan B.

2001-07-01

203

Propeller aircraft cabin vibration and noise-excitation, sources, and paths  

NASA Astrophysics Data System (ADS)

The potential sources and paths by which the propeller produces structural responses resulting in vibration and noise in the cabin of a transport aircraft are discussed. New low cost, convenient experimental and analytical techniques are described for evaluating the excitations; propeller airborne pressures on the fuselage shells, slip stream induced forces on the wing and tail, and oscillatory forces on the propeller. The techniques described make use of ground determined structural signatures to relate forces with vibrations or noise, and of propeller signatures from flight which define the vibroacoustic contributions of individual propellers.

Donham, R. E.; Balena, F. J.; Bochary, E. Z.; Liehr, O. K.

1985-02-01

204

IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 18, NO. 12, JUNE 15, 2006 1365 Source-Induced Optical Noise in Polarization  

E-print Network

, polarization-mode dispersion (PMD), statistical optics. I. INTRODUCTION SOURCE-INDUCED optical noise may becomeIEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 18, NO. 12, JUNE 15, 2006 1365 Source-Induced Optical Noise in Polarization Measurements Avi Zadok and Avishay Eyal, Member, IEEE Abstract--Formalism is derived

Zadok, Avinoam

205

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

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

206

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

207

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

NASA Astrophysics Data System (ADS)

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 ?opt, optimum noise reactance and susceptance has been also analyzed.

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

2012-07-01

208

Application of sound intensity and partial coherence to identify interior noise sources on the high speed train  

NASA Astrophysics Data System (ADS)

In order to provide a quieter riding environment for passengers, sound quality refinement of rail vehicle is a hot issue. Identification of interior noise sources is the prerequisite condition to reduce the interior noise on high speed train. By considering contribution of noise sources such as rolling noise, mechanical equipment noise, structure-borne noise radiated by car body vibration to the interior noise, the synthesized measurement of sound intensity, sound pressure levels and vibration have been carried out in four different carriages on high speed train. The sound intensity and partial coherence methods have been used to identify the most significant interior noise sources. The statistical analysis results of sound intensity near window and floor on four carriages indicate that sound intensity near floor is higher than that near window at three traveling speeds. Ordinary and partial coherent analysis of vibro-acoustical signals show that the major internal noise source is structural-borne sound radiated by floor vibration. These findings can be utilized to facilitate the reduction of interior noise in the future.

Fan, Rongping; Su, Zhongqing; Meng, Guang; He, Caichun

2014-06-01

209

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

NASA Technical Reports Server (NTRS)

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.

Hultgren, Lennart S.; Miles, Jeffrey H.

2009-01-01

210

Sources of short-term fluctuations in the seismic noise level at NORESS  

NASA Astrophysics Data System (ADS)

Short-term fluctuations in the seismic noise field at the NORESS array have been investigated by analyzing the two-year output of an automatic short-term to long-term average (STA/LTA) power detector. A remarkable feature is the occasional occurrence of a vast increase in the number of noise detections, sometimes lasting for several days. From slowness analysis, the majority of these noise bursts of a few seconds duration are found to originate in the azimuth range 95-105 from NORESS. Apparent velocities less than 3.0 km s -1 suggest that they are propagating Rayleigh waves. The temporal distribution of the noise detections originating in the azimuth range 95-105 shows a strong correlation with the water flow in the nearby River Glomma, although there is in some cases a time lag of 3-5 days between peak water flow and peak detection rates. A detailed analysis of a typical six-hour period has revealed the presence of a continuous source generating Rayleigh waves with azimuth 99.5 0.8, apparent velocity 2.83 0.03 km s -1 and dominant frequencies between 2.5 and 2.9 Hz. There is a strong possibility that these Rayleigh waves are caused by the operation of a nearby hydroelectric power plant, although the source and generation mechanisms of these disturbances have not been explicitly determined.

Kvrna, Tormod

1990-10-01

211

Investigation of phase noise of ring oscillators with time-varying current and noise sources by time-scaling thermal noise  

Microsoft Academic Search

This paper presents a new methodology of analyzing phase noise in a ring oscillator by time-scaling the thermal noise. Close-form solutions that relate the probability distribution and power-spectral density of the phase noise to circuit parameters have been obtained. These close-form solutions characterize the behavior of phase noise even when the circuit is varying with time in a nonlinear fashion.

Bosco H. Leung; Don Mcleish

2004-01-01

212

Probable sources of a noise in crossed-field devices II. Generating tubes  

Microsoft Academic Search

For pt.I, see ibid., vol.0, no.0, p. 246-7 (2003). The paper deals with one of probable sources of noise that is the rotating convective clouds of space charge. The shapes and structures are similar to ones of the true solutions in a magnetron diode. There are two kinds of convective clouds: (1) periodically breaking away from the electron hub and

A. V. Gritsunov; O. M. Nikitenko

2003-01-01

213

Noise sources and levels in the evgenidion hospital intensive care unit  

Microsoft Academic Search

Noise sources and levels were evaluated in a six-bed intensive care unit (ICU) in Athens, Greece. Ten patients (six males,\\u000a four females) completed specifically designed questionnaires, and at the same time nine 8-h sound measuring sessions took\\u000a place. A Bruel and Kjaer 2231 sound-meter was used on the decibel-A scale combined with observation. Human activity, operating\\u000a equipment and construction engineering

C. Tsiou; D. Eftymiatos; E. Theodossopoulou; P. Notis; K. Kiriakou

1998-01-01

214

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

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

215

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

NASA Technical Reports Server (NTRS)

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.

Panda, J.; Seasholtz, R. G.

2001-01-01

216

Positions of type II fundamental and harmonic sources in the 30-100 MHZ range  

NASA Technical Reports Server (NTRS)

An excellent example of a type III-V burst followed by a type II burst with fundamental and harmonic bands was observed on June 18, 1979 at the Clark Lake Radio Observatory. The observations are described in detail and their implications are discussed with regard to the problem of directionality with respect to the magnetic field lines of the collisionless MHD shock wave generated at the start of the flash phase. It is found that the positions of type III and type II (F) bursts at a number of frequencies are essentially the same, which implies that the shock responsible for the type II radiation follows the path of the type III exciter, that is, the shock propagates along the open field lines.

Sawant, H. S.; Gergely, T. E.; Kundu, M. R.

1982-01-01

217

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

PubMed

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

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

2013-10-01

218

Reduction of electromagnetic force harmonics in asynchronous traction motor by adapting the rotor slot number  

SciTech Connect

The harmonics in electromagnetic force are source of the mechanical vibration and the audible noise in an asynchronous traction motor. This paper describes an approach to reduce the force harmonics by changing the rotor slot number. Both the radial and tangential forces acting on the stator teeth are calculated by Maxwell stress tenser and their time harmonics are examined by the discrete Fourier decomposition. As a result, the optimal slot number of the rotor to reduce or eliminate the specific force harmonics is determined.

Kim, B.T.; Kwon, B.I.; Park, S.C.

1999-09-01

219

Constraints on the source mechanism of harmonic tremors based on seismological, ground deformation, and visual observations at Sakurajima volcano, Japan  

NASA Astrophysics Data System (ADS)

Vulcanian-type eruptive activity has occurred from the summit crater of Sakurajima volcano, Japan, since 1955. Over this period, harmonic tremors have commonly occurred either several hours after swarms of B-type earthquakes (herein termed HTB: Harmonic Tremor following B-type earthquake swarm) or immediately after explosive eruptions (herein termed HTE: Harmonic Tremor after an Eruption). In this study, we analyzed the spectra and particle motions of HTBs and HTEs. Both HTBs and HTEs have spectra with peaks at fundamental frequencies and higher frequencies that are integer multiples of the fundamental frequencies. The peak frequencies of HTBs remained within a certain range, whereas those of HTEs showed a gradual increase. The spectra of an HTB that occurred on 20 July 1990 had stable fundamental frequencies of 1.46-1.66 Hz and at least 9 peaks of higher modes; in contrast, the HTE that occurred 3 minutes after an explosive eruption at 11 h 15 m (JST) on 11 October 2002 showed clear frequency gliding from 0.8 to 3.7 Hz in the fundamental mode. The peak frequencies of higher modes of the HTE also showed an increase corresponding to the shift of the fundamental mode towards a higher frequency. Particle motion analysis mainly identified Rayleigh waves from the prograde elliptical motion at the deepest borehole station (HAR) and retrograde motions at the other shallower stations. Love waves were dominant at the stations north and south of the crater. The distribution patterns of Rayleigh and Love waves of HTBs are similar to those of HTEs. The nature of the dominant surface waves of both HTBs and HTEs suggest that the sources of harmonic tremors are located at a shallow depth, corresponding to a gas pocket in the uppermost part of the volcanic conduit. Differences in the temporal characteristics of the HTB and HTE spectra reflect the internal condition of the gas pocket: HTBs are associated with inflation of the conduit, whereas HTEs occur following an eruption, associated with deflationary ground deformation. HTBs are caused by resonance of the gas pocket embedded beneath the lava dome. Although HTEs occur within the open conduit, the small size of vents enables resonance within the bubbly magma conduit. The positive gliding of dominant peaks toward higher frequencies is interpreted to result from shortening of the bubbly magma conduit due to a rise in the bubble nucleation level; this rise results from the re-pressurization that accompanies the ascent of magma from deep within the reservoir.

Maryanto, Sukir; Iguchi, Masato; Tameguri, Takeshi

2008-03-01

220

Non-Uniform Contrast and Noise Correction for Coded Source Neutron Imaging  

SciTech Connect

Since the first application of neutron radiography in the 1930s, the field of neutron radiography has matured enough to develop several applications. However, advances in the technology are far from concluded. In general, the resolution of scintillator-based detection systems is limited to the $10\\mu m$ range, and the relatively low neutron count rate of neutron sources compared to other illumination sources restricts time resolved measurement. One path toward improved resolution is the use of magnification; however, to date neutron optics are inefficient, expensive, and difficult to develop. There is a clear demand for cost-effective scintillator-based neutron imaging systems that achieve resolutions of $1 \\mu m$ or less. Such imaging system would dramatically extend the application of neutron imaging. For such purposes a coded source imaging system is under development. The current challenge is to reduce artifacts in the reconstructed coded source images. Artifacts are generated by non-uniform illumination of the source, gamma rays, dark current at the imaging sensor, and system noise from the reconstruction kernel. In this paper, we describe how to pre-process the coded signal to reduce noise and non-uniform illumination, and how to reconstruct the coded signal with three reconstruction methods correlation, maximum likelihood estimation, and algebraic reconstruction technique. We illustrates our results with experimental examples.

Santos-Villalobos, Hector J [ORNL; Bingham, Philip R [ORNL

2012-01-01

221

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

NASA Technical Reports Server (NTRS)

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 reliable gear designs, as well as the selection of optimal manufacturing processes.

Asnani, Vivake M.

2004-01-01

222

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)

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.

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

2013-01-01

223

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

NASA Astrophysics Data System (ADS)

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.

Cato, Douglas H.

2012-11-01

224

High average power, depolarized super-continuum generation using a 1.55-mum ASE noise source.  

PubMed

We investigate super-continuum generation by using incoherent noise pulses instead of clean ultra-short pulse trains. In the experiment, we successfully generate flat continuum of 956 nm with a spectral density of over -10 dBm/nm by using an ASE noise source composed of an Erbium-doped fiber amplifier. PMID:19498592

Takushima, Yuichi

2005-07-25

225

Instantaneous Io flux tube as the source of Jovian DAM: Possible second harmonic emissions  

Microsoft Academic Search

To determine if the source of the Jovian Io-dependent DAM (decametric) emission is along the instantaneous Io flux tube (IIFT), the authors compare the results of ray-tracing calculations to radio emission data obtained by the Planetary Radio Astronomy instrument on board Voyager 1 and 2. They assume RX mode gyroemission at frequencies near the local gyrofrequency and sources along field

J. D. Menietti; D. B. Curran

1990-01-01

226

Instantaneous Io flux tube as the source of Jovian DAM - Possible second harmonic emissions  

Microsoft Academic Search

To determine if the source of the Jovian Io-dependent DAM (decametric) emission is along the instantaneous Io flux tube (IIFT), the results of ray-tracing calculations are compared with radio emission data obtained by the Planetary Radio Astronomy instruments on Voyager 1 and 2. RX mode gyroemission at frequencies near the local gyrofrequency and sources along field lines within the active

J. D. Menietti; D. B. Curran

1990-01-01

227

Experimental study of source of background noise in muon radiography using emulsion film detectors  

NASA Astrophysics Data System (ADS)

We study the source of background noise in cosmic-ray muon radiography (muography) using emulsion film detectors. We claim that muography detectors should have a momentum separation function to reduce systematic errors due to non-signal particles with momenta less than 2 GeV c-1. The origin of noise is expected to be electromagnetic components of air-showers or cosmic-ray muons scattered in topographic material. As a demonstration, we construct two types of detectors with different momentum thresholds and perform test measurements of an actual geoscientific target. The analysis of emulsion data is explained in detail, including film inefficiency compensation and momentum selection by applying an upper bound to the chi-square distribution to the data.

Nishiyama, R.; Miyamoto, S.; Naganawa, N.

2013-12-01

228

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

NASA Astrophysics Data System (ADS)

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 jets 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.

Hall, Andre; Pinier, Jeremy; Glauser, Mark

2006-11-01

229

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

NASA Technical Reports Server (NTRS)

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 to be unaffected by the presence of air flow representative of the Purdue experimental rig. A test of the active noise control at the source concept for rotor/stator active noise control was demonstrated. This 2-D test demonstrated conclusively the simultaneous reduction of two acoustic modes. Reductions of over 10 dB were obtained over a wide operating range.

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

1997-01-01

230

Control of Environmental Noise  

ERIC Educational Resources Information Center

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)

Jensen, Paul

1973-01-01

231

Initial-State Bremsstrahlung versus Final-State Hydrodynamic Sources of Azimuthal Harmonics in p+A at RHIC and LHC  

E-print Network

Recent pTdata from the Beam Energy Scan (BES) and D+Au runs at RHIC/BNL and, especially, the surprising similarity of azimuthal $v_n\\{2m\\}(p_T)$ ``transeverse flow'' harmonics in $p+Pb$ and $Pb+Pb$ at LHC have challenged the uniqueness of local equilibrium ``perfect fluid'' interpretations of those data. We report results at QM14 on azimuthal harmonics associated with initial-state non-abelian ``wave interference'' effects predicted by perturbative QCD gluon bremsstrahlung and sourced by Color Scintillation Arrays (CSA) of color antennas. CSA are naturally identified with multiple projectile and target beam jets produced in inelastic p+A reactions. We find a remarkable similarity between azimuthal harmonics sourced by initial state CSA and those predicted with final state perfect fluid models of high energy p+A reactions. The question of which mechanism dominates in $p+A$ and $A+A$ remains open at this time.

Miklos Gyulassy; Peter Levai; Ivan Vitev; Tamas S. Biro

2014-07-28

232

Initial-State Bremsstrahlung versus Final-State Hydrodynamic Sources of Azimuthal Harmonics in p+A at RHIC and LHC  

E-print Network

Recent pTdata from the Beam Energy Scan (BES) and D+Au runs at RHIC/BNL and, especially, the surprising similarity of azimuthal $v_n\\{2m\\}(p_T)$ ``transeverse flow'' harmonics in $p+Pb$ and $Pb+Pb$ at LHC have challenged the uniqueness of local equilibrium ``perfect fluid'' interpretations of those data. We report results at QM14 on azimuthal harmonics associated with initial-state non-abelian ``wave interference'' effects predicted by perturbative QCD gluon bremsstrahlung and sourced by Color Scintillation Arrays (CSA) of color antennas. CSA are naturally identified with multiple projectile and target beam jets produced in inelastic p+A reactions. We find a remarkable similarity between azimuthal harmonics sourced by initial state CSA and those predicted with final state perfect fluid models of high energy p+A reactions. The question of which mechanism dominates in $p+A$ and $A+A$ remains open at this time.

Gyulassy, Miklos; Vitev, Ivan; Biro, Tamas S

2014-01-01

233

Aeroacoustics of flight vehicles: Theory and practice. Volume 1: Noise sources  

NASA Technical Reports Server (NTRS)

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.

Hubbard, Harvey H. (editor)

1991-01-01

234

Improving AFM images with harmonic interference by spectral analysis.  

PubMed

Atomic force microscopy (AFM) is one of the most sensitive tools for nanoscale imaging. As such, it is very sensitive to external noise sources that can affect the quality of collected data. The intensity of the disturbance depends on the noise source and the mode of operation. In some cases, the internal noise from commercial AFM controllers can be significant and difficult to remove. Thus, a new method based on spectrum analysis of the scanned images is proposed to reduce harmonic disturbances. The proposal is a post-processing method and can be applied at any time after measurements. This article includes a few methods of harmonic cancellation (e.g., median filtering, wavelet denoising, Savitzky-Golay smoothing) and compares their effectiveness. The proposed method, based on Fourier transform of the scanned images, was more productive than the other methods mentioned before. The presented data were achieved for images of conductive layers taken in a contact AFM mode. PMID:22214544

Kiwilszo, Marek; Zieli?ski, Artur; Smulko, Janusz; Darowicki, Kazimierz

2012-02-01

235

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

NASA Technical Reports Server (NTRS)

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

Miles, Jeffrey Hilton

2008-01-01

236

Cold-target recoil-ion momentum spectroscopy for diagnostics of high harmonics of the extreme-ultraviolet free-electron laser light source at SPring-8  

NASA Astrophysics Data System (ADS)

We have developed a cold-target recoil-ion momentum spectroscopy apparatus dedicated to the experiments using the extreme-ultraviolet light pulses at the free-electron laser facility, SPring-8 Compact SASE Source test accelerator, in Japan and used it to measure spatial distributions of fundamental, second, and third harmonics at the end station.

Liu, X.-J.; Fukuzawa, H.; Prmper, G.; Okunishi, M.; Shimada, K.; Ueda, K.; Motomura, K.; Saito, N.; Iwayama, H.; Nagaya, K.; Yao, M.; Rudenko, A.; Ullrich, J.; Foucar, L.; Czasch, A.; Schmidt-Bcking, H.; Drner, R.; Nagasono, M.; Higashiya, A.; Yabashi, M.; Ishikawa, T.; Ohashi, H.; Kimura, H.

2009-05-01

237

Cold-target recoil-ion momentum spectroscopy for diagnostics of high harmonics of the extreme-ultraviolet free-electron laser light source at SPring-8.  

PubMed

We have developed a cold-target recoil-ion momentum spectroscopy apparatus dedicated to the experiments using the extreme-ultraviolet light pulses at the free-electron laser facility, SPring-8 Compact SASE Source test accelerator, in Japan and used it to measure spatial distributions of fundamental, second, and third harmonics at the end station. PMID:19485490

Liu, X-J; Fukuzawa, H; Prmper, G; Okunishi, M; Shimada, K; Ueda, K; Motomura, K; Saito, N; Iwayama, H; Nagaya, K; Yao, M; Rudenko, A; Ullrich, J; Foucar, L; Czasch, A; Schmidt-Bcking, H; Drner, R; Nagasono, M; Higashiya, A; Yabashi, M; Ishikawa, T; Ohashi, H; Kimura, H

2009-05-01

238

Harmonic content of electron-impact source functions in inductively coupled plasmas using an ``on-the-fly'' Monte Carlo technique  

E-print Network

Harmonic content of electron-impact source functions in inductively coupled plasmas using an ``on temperatures in low-pressure 10s mTorr inductively coupled plasma ICP reactors operating at 10s MHz do operating at lower pressures 10s mTorr .1 Inductively coupled plasma ICP reactors operating

Kushner, Mark

239

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

SciTech Connect

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}

Kusnierkiewicz, D.Y. [The Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland 20723-6099 (United States)

1995-01-20

240

Combustion noise  

NASA Technical Reports Server (NTRS)

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.

Strahle, W. C.

1977-01-01

241

Near-threshold harmonics from a femtosecond enhancement cavity-based EUV source: effects of multiple quantum pathways on spatial profile and yield.  

PubMed

We investigate the photon flux and far-field spatial profiles for near-threshold harmonics produced with a 66 MHz femtosecond enhancement cavity-based EUV source operating in the tight-focus regime. The effects of multiple quantum pathways in the far-field spatial profile and harmonic yield show a strong dependence on gas jet dynamics, particularly nozzle diameter and position. This simple system, consisting of only a 700 mW Ti:Sapphire oscillator and an enhancement cavity produces harmonics up to 20 eV with an estimated 30-100 ?W of power (intracavity) and > 1?W (measured) of power spectrally-resolved and out-coupled from the cavity. While this power is already suitable for applications, a quantum mechanical model of the system indicates substantial improvements should be possible with technical upgrades. PMID:22273880

Hammond, T J; Mills, Arthur K; Jones, David J

2011-12-01

242

Two-Microphone Spatial Filtering Improves Speech Reception for Cochlear-Implant Users in Reverberant Conditions With Multiple Noise Sources  

PubMed Central

This study evaluates a spatial-filtering algorithm as a method to improve speech reception for cochlear-implant (CI) users in reverberant environments with multiple noise sources. The algorithm was designed to filter sounds using phase differences between two microphones situated 1?cm apart in a behind-the-ear hearing-aid capsule. Speech reception thresholds (SRTs) were measured using a Coordinate Response Measure for six CI users in 27 listening conditions including each combination of reverberation level (T 60?=?0, 270, and 540?ms), number of noise sources (1, 4, and 11), and signal-processing algorithm (omnidirectional response, dipole-directional response, and spatial-filtering algorithm). Noise sources were time-reversed speech segments randomly drawn from the Institute of Electrical and Electronics Engineers sentence recordings. Target speech and noise sources were processed using a room simulation method allowing precise control over reverberation times and sound-source locations. The spatial-filtering algorithm was found to provide improvements in SRTs on the order of 6.5 to 11.0?dB across listening conditions compared with the omnidirectional response. This result indicates that such phase-based spatial filtering can improve speech reception for CI users even in highly reverberant conditions with multiple noise sources. PMID:25330772

2014-01-01

243

Effects of noise from non-traffic-related ambient sources on sleep: review of the literature of 1990-2010.  

PubMed

This article reviews the literature about the effects of specific non-traffic-related ambient noise sources on sleep that appeared in the last two decades. Although everybody is faced with noise of non-traffic and non-industry origin (e.g. sounds made by neighbors, talk, laughter, music, slamming doors, structural equipment, ventilation, heat pumps, noise from animals, barking dogs, outdoor events etc.), little scientific knowledge exists about its effects on sleep. The findings of the present extensive literature search and review are as follows: Only a small number of surveys, laboratory and field studies about mainly neighborhood, leisure and animal noise have been carried out. Most of them indicate that ambient noise has some effect on human sleep. However, a quantitative meta-analysis and comparison is not possible due to the small number of studies available and at times large differences in quality. PMID:21768734

Omlin, Sarah; Bauer, Georg F; Brink, Mark

2011-01-01

244

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

Microsoft Academic Search

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,

H. Grieb; K. Heinig

1986-01-01

245

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

NASA Astrophysics Data System (ADS)

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 M?, and below 1 MHz the output impedance can arrive to 200 K?. 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.

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

2014-05-01

246

Seismic noise sources inferred from dense onshore and offshore deployments in Portugal  

NASA Astrophysics Data System (ADS)

Two dense deployments of broadband seismic stations covered onshore and offshore Portugal in recent years. Project NEAREST deployed a total of 24 ocean bottom seismometers (OBSs) offshore southwest Portugal, in the Gulf of Cadiz, for 11 months (2007-2008). Project WILAS collected data from a total of 52 stations, both permanent and temporary, in mainland Portugal for 2 years (2010-2012). Both deployments have inter-station spacings on the order of 50 km. Although the two deployments did not overlap on time, both contain clear oceanic and atmospheric signatures. We use the two datasets to characterize the seismic noise recorded in Portugal and to infer information on their sources. OBS data shows very clear correlations with local atmospheric and oceanic conditions, as well as with distant oceanic disturbances. Noise in the band 3-4 sec is strongly correlated with atmospheric disturbances, particularly with pressure drops. The primary and secondary microseisms are correlated with both local and distant storms. Some north Atlantic storms end at the Portuguese coast, causing the highest levels of microseismic noise recorded on our OBSs. We will present the signature on seismic records of one of these storms as it evolves from its origin to the Portuguese coast. Land data shows a strong correlation with oceanic conditions, particularly in the microseismic passband. During particularly quiet periods (i.e. northern summer) a strong atmospheric signal can be seen in the long periods, including a clear bi-diurnal periodicity. This work is funded by FCT -- Portuguese Foundation for Science and Technology (PTDC/CTE-GIX/116819/2010; PTDC/GEO-FIQ/3522/2012).

Corela, Carlos; Custdio, Susana; Silveira, Graa; Matias, Luis

2014-05-01

247

Binaural speech intelligibility in rooms with variations in spatial location of sources and modulation depth of noise interferers.  

PubMed

Four experiments investigated the effects on speech intelligibility of reverberation, sound source locations, and amplitude modulation of the interferers. Speech reception thresholds (SRTs) were measured using headphones and stimuli that simulated real-room listening, considering one or two interferers which were stationary or speech-modulated noises. In experiment 1, SRTs for modulated noises showed little variation with increasing interferer reverberation. Reverberation might have increased masking by filling in the modulated noise gaps, but simultaneously changed the noise spectra making them less effective maskers. In experiment 2, SRTs were lower when measured using a unique one-voice modulated interferer rather than a different interferer for each target sentence, suggesting that listeners could take advantage of the predictability of the interferer gaps. In experiment 3, increasing speech reverberation did not significantly affect the difference of SRTs measured with stationary and modulated noises, indicating that the ability to exploit noise modulations was still useful for temporally smeared speech. In experiment 4, spatial unmasking remained constant when applying modulations to the interferers, suggesting an independence of the abilities to exploit these modulations and the spatial separation of sources. Finally, a model predicting binaural intelligibility for modulated noises was developed and provided a good fit to the experimental data. PMID:23927114

Collin, Benjamin; Lavandier, Mathieu

2013-08-01

248

Experimental study of source of background noise in muon radiography using emulsion film detectors  

NASA Astrophysics Data System (ADS)

The aim of this study is to ascertain and confirm the source of background noise in cosmic-ray muon radiography (muography) using emulsion film detectors. For this, we build two types of emulsion detectors with different momentum thresholds and perform test measurements of an actual geoscientific target. This experiment reveals that contamination of nonsignal particles with momenta of less than 2 GeV c-1 cause significant systematic errors for the density estimation of muography. Utilizing the results of precedent studies, we conclude that the origin of these low-momentum particles is either electromagnetic components of air showers or cosmic-ray muons scattered in topographic material. In this paper, we analyze the emulsion data in detail, including the film-inefficiency compensation and momentum selection by applying an upper bound to the chi-square distribution for the data.

Nishiyama, R.; Miyamoto, S.; Naganawa, N.

2014-04-01

249

Rotor noise  

NASA Technical Reports Server (NTRS)

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.

Schmitz, F. H.

1991-01-01

250

Selective Harmonic Elimination PWM Control Scheme on a Three-Phase Four-Leg Voltage Source Inverter  

Microsoft Academic Search

A selective harmonic elimination (SHE) control strategy on a three-phase four-leg inverter is reported in this paper. The control signals of the four legs are calculated as follows: 1) control signals of three legs are mathematically expressed using Fourier-based equations on line-to-line basis as conventional SHE technology, which eliminates lower order nontriplen harmonics, and 2) the fourth leg produces the

Fanghua Zhang; Yangguang Yan

2009-01-01

251

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

NASA Technical Reports Server (NTRS)

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 diameters and types. The inflow microphone support strut is also a source of background noise but this source's impact may be minimized by careful design of the strut. In the present paper, the mechanisms mentioned above are discussed in detail. Their frequency and velocity ranges of dominance are defined and the differences between past and current facility background noise levels are presented. This paper gives valuable information for those wishing to make acoustic measurements in the 40x80. With this report and an estimate of the noise levels produced by the noise source of interest, it should be possible to determine the signal-to-noise ratios and measurement locations to successfully perform aeroacoustic testing in the NASA Ames Research Center's 40- by 80-Foot Wind Tunnel.

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

1999-01-01

252

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

PubMed

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

Gervaise, Cdric; Simard, Yvan; Roy, Nathalie; Kinda, Bazile; Mnard, Nadia

2012-07-01

253

Construction of Electric Exchange System whereby Environmental Noise is Considered to be an Energy Source  

Microsoft Academic Search

Our group has produced the system whereby noise is exchanged for thermal energy, and been able to extract the heat from the noise. Noise is usually absorbed by some substance and finally exchanged for thermal energy. Therefore this system has advantage that it never produces additional heat loads in a global environment. It is also very unique that energy of

Yasuhiro Tokita; Ryu Yoonsun; Yasuhiro Oikawa; Yoshio Yamasaki

254

A practical method of harmonic analysis for power converter  

Microsoft Academic Search

The converter is one important harmonic source in power systems. For the knowledge of harmonic characteristics of a converter, it is very important to evaluate the harmonic situations of AC and DC sides, and also it is very helpful to design the harmonic filters and to suppress harmonic propagation. A practical method of harmonic evaluation for a power converter is

Jianguo Jiang; Weimin Xie; Juan Zhou

2000-01-01

255

Extraction of small boat harmonic signatures from passive sonar.  

PubMed

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. PMID:21682400

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

2011-06-01

256

A reference estimator based on composite sensor pattern noise for source device identification  

NASA Astrophysics Data System (ADS)

It has been proved that Sensor Pattern Noise (SPN) can serve as an imaging device fingerprint for source camera identification. Reference SPN estimation is a very important procedure within the framework of this application. Most previous works built reference SPN by averaging the SPNs extracted from 50 images of blue sky. However, this method can be problematic. Firstly, in practice we may face the problem of source camera identification in the absence of the imaging cameras and reference SPNs, which means only natural images with scene details are available for reference SPN estimation rather than blue sky images. It is challenging because the reference SPN can be severely contaminated by image content. Secondly, the number of available reference images sometimes is too few for existing methods to estimate a reliable reference SPN. In fact, existing methods lack consideration of the number of available reference images as they were designed for the datasets with abundant images to estimate the reference SPN. In order to deal with the aforementioned problem, in this work, a novel reference estimator is proposed. Experimental results show that our proposed method achieves better performance than the methods based on the averaged reference SPN, especially when few reference images used.

Li, Ruizhe; Li, Chang-Tsun; Guan, Yu

2014-02-01

257

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

NASA Technical Reports Server (NTRS)

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.

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

2012-01-01

258

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

NASA Astrophysics Data System (ADS)

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.

Grieb, H.; Heinig, K.

1986-09-01

259

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

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

260

Abstract--During lung sound recordings, an incessant noise source occurs due to heart sounds. The heart sound  

E-print Network

Abstract--During lung sound recordings, an incessant noise source occurs due to heart sounds. The heart sound interference on lung sounds is significant especially at low flow rates. In this paper a new to detect HN segments in the spectrogram of the recorded lung sound signal. Afterwards the algorithm removes

Moussavi, Zahra M. K.

261

The source model of low-energy electrons responsible for type I and type III radio noise storms  

Microsoft Academic Search

The source model of the electrons (110 keV) responsible for the observed impulsive low-energy electron flux events in the solar wind plasma and for type I and III noise storms is considered. The appearance of such a source is associated with the tearing mode instability of a neutral current sheet located above the bipolar region of the solar disk and

V. M. Gubchenko; V. V. Zaitsev

1983-01-01

262

Advances in tilt rotor noise prediction  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

263

Helicopter noise as predicted by three-dimensional monopole and quasi-steady full-potential dipole sources  

NASA Technical Reports Server (NTRS)

A three-dimensional quasi-steady full-potential rotor-flow-analysis program, called ROT22 developed at NASA Ames Research Center is run in conjunction with Farassat's (1981) helicopter-noise-prediction code to assess the thickness and loading noises made by a rotor blade. As a model example, the case of a 1/7th UH-1H NACA-0012-profile straight nonlifting rotor blade in hover is studied. Results for tip Mach numbers ranging from .4 to .962 are presented. Also presented is the effect of blade-tip loading on the overall noise and of profile curvature on the thickness noise. The study confirms that the blade volume displacement is a dominant source of helicopter noise and further concludes that the blade tip makes only a small noise contribution that steadily decreases with increasing tip Mach numbers, and that the inclusion of blade profile curvature tends to improve the negative peak amplitudes overpredicted by Schmitz and Yu (1983).

Aggarwal, H. R.

1984-01-01

264

Effects of flight on noise radiated from convected ring sources in coaxial dual flow. Part 2: The noise from heated jets  

NASA Technical Reports Server (NTRS)

The effects of flight on noise from heated jets are discussed. The effects of the additionally, extraneously-generated dipole and simple source terms which arise as a result of the density gradients across the fluid interfaces were incorporated. The coaxial flows with inverted profiles are shown to be quieter than the conventional profiles; however, the benefit of noise reduction at higher outer-to-inner area ratios is totally offset as the inverted profile incurs a significant massloss and thrust-loss. Amongst all the possible coaxial configurations when on of the coaxial streams is heated-conventional profile (CP), inverted profile (IP) and the variable stream control engine (VSCE) cycle-and at constant massflow and thrust, a VSCE-cycle is the most desirable and the best possible engine cycle inasmuch as it provides over more than 18.0 dB reduction in SPL (as compared against noise from a CP-cycle) at all angles, both statically and in flight, for area ratios Sigma 0.25.

Dash, R.

1982-01-01

265

Suppression of phase and supermode noise in a harmonic mode-locked erbium-doped fiber laser with a semiconductor-optical-amplifier-based high-pass filter  

NASA Astrophysics Data System (ADS)

By operating an intracavity semiconductor-optical-amplifier- (SOA-) based high-pass filter at the nearly transparent current condition, the supermode noise (SMN), the relaxation oscillation, and the single-sideband (SSB) phase noise can be simultaneously suppressed in an actively mode-locked erbium-doped fiber laser (EDFL). The SOA at the nearly transparent condition enhances the SMN suppression ratio of the EDFL from 32to76 dB at the cost of the phase noise degrading from -114to-104.2 dBc/Hz and broadening the pulse width from 36to61 ps. With an optical bandpass filter, the SSB phase noise and the SMN suppression ratio can be further improved to -110 dBc/Hz and 81 dB, respectively. The EDFL pulse can be further shortened to 3.1 ps with a time-bandwidth product of 0.63 after compression.

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

2005-07-01

266

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)

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 arbitrarily-located ANC source plane. The actuator velocities can then be determined to generate the anti-phase mode. The resulting combined fan source/ANC pressure can then be calculated at any desired wall sensor position. The actuator velocities can be determined manually or using a simulation of a control system feedback loop. This will provide a very useful ANC system design and evaluation tool.

Kraft, R. E.

1996-01-01

267

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

NASA Astrophysics Data System (ADS)

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 H 2O rather than viscous magma, there are also remarkable similarities in the problems of heat and mass recharge to the system, in the eruption dynamics, and in the seismicity. Water rises irregularly into the immediate reservoir of Old Faithful as recharge occurs, a fact that suggests that there are two enlarged storage regions: one between 18 and 22 m (the base of the immediate reservoir) and one between about 10 and 12 m depth. Transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water, and by episodes of convective overturn. An eruption occurs when the temperature of the near-surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure-release waves (rarefactions) down the column can bring the liquid water onto the boiling curve. The process of conversion of the liquid water in the conduit at the onset of an eruption into a two-phase liquid-vapor mixture takes on the order of 30 s. The seismicity is directly related to the sequence of filling and heating during the recharge cycle, and to the fluid mechanics of the eruption. Short (0.2-0.3 s), monochromatic, high-frequency events (20-60 Hz) resembling unsustained harmonic tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding bubbles of steam cause transient vibrations of the fluid column. The frequency of the events is determined by the length of the water column and the speed of sound of the fluid in the conduit when these events occur; damping is controlled by the characteristic and hydraulic impedances, which depend on the above parameters, as well as on the recharge rate of the fluid. Two periods of reduced seismicity (of a few tens of seconds to nearly a minute in duration) occur during the recharge cycle, apparently when the water rises rapidly through the narrow regions of the conduit, causing a sudden pressure increase that temporarily suppresses steam bubble formation. A period of decreased seismicity also precedes preplay or an eruption; this appears to be the time when rising steam bubbles move into a zone of boiling that is acoustically decoupled from the wall of the conduit because of the acoustic impedance mismatch between boiling water ( ? c 10 3g cm -2 s -1) and rock ( ? c 3 10 5g cm 2 s -1). Sustained harmonic tremor occurs during the first one to one-and-a-half minutes of an eruption of Old Faithful, but is not detectable in the succeeding minutes of the eruption. The eruption tremor is caused by hydraulic transients propagating within a sublayer of unvesiculated water that underlies the erupting two-phase liquidvapor mixture. The resonant frequencies of the fluid column decrease to about 1 Hz when all of the water in the conduit has been converted to a watersteam mixture. Surges are observed in the flow at this frequency, but the resonance has not been detected seismically, possibly because the two-phase erupting fluid is seismically decoupled from the rock on which seismometers are placed. If Old Faithful is an analogue for volcanic seismicity, this study shows that because the frequency of tremor depends on the acoustic properties of the fluid and on conduit dimensions, both properties must be considered in analysis of tremor in volcanic regions. Because magma sound speed can vary over nearly two orders of magnitude as it changes

Kieffer, Susan Werner

1984-09-01

268

Nonidentifiability of the Source of Intrinsic Noise in Gene Expression from Single-Burst Data  

PubMed Central

Over the last few years, experimental data on the fluctuations in gene activity between individual cells and within the same cell over time have confirmed that gene expression is a noisy process. This variation is in part due to the small number of molecules taking part in some of the key reactions that are involved in gene expression. One of the consequences of this is that protein production often occurs in bursts, each due to a single promoter or transcription factor binding event. Recently, the distribution of the number of proteins produced in such bursts has been experimentally measured, offering a unique opportunity to study the relative importance of different sources of noise in gene expression. Here, we provide a derivation of the theoretical probability distribution of these bursts for a wide variety of different models of gene expression. We show that there is a good fit between our theoretical distribution and that obtained from two different published experimental datasets. We then prove that, irrespective of the details of the model, the burst size distribution is always geometric and hence determined by a single parameter. Many different combinations of the biochemical rates for the constituent reactions of both transcription and translation will therefore lead to the same experimentally observed burst size distribution. It is thus impossible to identify different sources of fluctuations purely from protein burst size data or to use such data to estimate all of the model parameters. We explore methods of inferring these values when additional types of experimental data are available. PMID:18846201

Ingram, Piers J.; Stumpf, Michael P. H.; Stark, Jaroslav

2008-01-01

269

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

NASA Technical Reports Server (NTRS)

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.

Panda, Jayanta; Seasholtz, Richard G.

2003-01-01

270

Aperture Synthesis due to the Motion of a Single Receiver During Direction Finding of the Narrowband Noise Sources  

NASA Astrophysics Data System (ADS)

We consider the possibilities of the aperture synthesis using a single moving receiver during direction finding of the sources emitting a random stationary narrowband signal. It is shown that in this case the coordinates and projections of the source velocities can be determined from the current estimates of the Doppler frequency shift. Using the Cramr-Rao bound, we analyze accuracy of determining the parameters which characterize the rectilinear trajectory of the source during the circumferential receiver motion as functions of the synthetic-aperture size, emittedsignal bandwidth, signal-to-noise ratio, etc. Possible applications of the proposed version of the aperture synthesis in underwater acoustics and radio astronomy are considered.

Ivanenkov, A. S.; Korotin, P. I.; Orlov, D. A.; Rodionov, A. A.; Turchin, V. I.

2014-07-01

271

On the 1/f Noise and Non-Integer Harmonic Decay of the Interaction of a Finger Sliding on Flat and Sinusoidal Surfaces  

E-print Network

INTRODUCTION When sliding on most surfaces, human fingers generate audible noise. If the surface in question into acoustic energy which is dissipated in part in the tissues and in the solid object. Although originating even when sliding a finger on the mirror finish of a glass surface, unless the contact is lubricated

Hartmann, Mitra J. Z.

272

Development of Noise Simulation Model for Stationary and Mobile Sources: A GIS-Based Approach  

Microsoft Academic Search

In the rapidly urbanizing country like India, the transportation sector is growing rapidly, which lead to overcrowded roads\\u000a producing air and noise pollution. Noise of a particular region is influenced by the volume of traffic on the highway, in\\u000a addition to other causative factors like existing infrastructure and industrial setup etc. In the present paper, a geographical\\u000a information system (GIS)-based

Asheesh Sharma; Ritesh Vijay; Veena K. Sardar; R. A. Sohony; Apurba Gupta

2010-01-01

273

Application of Active Noise Cancellation for Source Identification and Monitoring in a Modal Environment  

Microsoft Academic Search

Faulty bearing detection and diagnosis in complex machines often encounter a problem in that the bearing signal may be masked by excessive noise. The ability to process the diagnosed signal to improve its signal-to-noise density ratio (SNR) is critical in detecting and diagnosing the bearing's fault in its early stage. The objective of this research was to develop a real-time

Wen-Shyang Chiu

1990-01-01

274

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

USGS Publications Warehouse

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

Chouet, B.

1988-01-01

275

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

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

276

Sensitivity of the sup 252 Cf-source-driven noise analysis method to fission content of spent LWR fuel  

Microsoft Academic Search

The ²⁵²Cf-source-driven noise analysis method has been suggested as a method of measuring the subcriticality of spent light water reactor (LWR) fuel. A measurement of the subcritical neutron multiplication factor provides the parameter most directly related to criticality safety and can be used to verify the criticality safety margins of spent LWR fuel configurations. Previous measurements by this method have

A. W. Krass; J. T. Mihalczo; T. E. Valentine

1992-01-01

277

Analysis and ranking of the acoustic disturbance potential of petroleum-industry activities and other sources of noise in the environment of marine mammals in Alaska. Final report  

SciTech Connect

The study compares the relative magnitudes and effects on marine mammals of noise from oil and gas industry activities with noise from other sources in Alaska OCS and coastal waters. The study procedure incorporates the receiver, source and path concepts generally used in acoustic analysis. The receiver characterization includes a review of marine mammal distribution in Alaska and a map of the distribution of each major species. Information on species sound production, hearing sensitivity (when known), and observed responses to noise sources is also included. The analysis of noise sources found in the Alaskan marine environment considers natural, industrial, transportation, and cultural sources. Acoustic transmission loss characteristics obtained from measurements and model predictions are used to estimate the effective ranges of the noise sources using available source level information. Information on species distribution was combined with information on source distribution, source level, and transmission loss to determine the most significant sources in terms of their acoustic range and the numbers of mammals potentially affected by developing a Standardized Noise Contribution Model species.

Malme, C.I.; Miles, P.R.; Miller, G.S.; Richardson, W.J.; Roseneau, D.G.

1989-08-01

278

Noise annoyance from stationary sources: Relationships with exposure metric day-evening-night level (DENL) and their confidence intervals  

NASA Astrophysics Data System (ADS)

Relationships between exposure to noise [metric: day-evening-night levels (DENL)] from stationary sources (shunting yards, a seasonal industry, and other industries) and annoyance are presented. Curves are presented for expected annoyance score, the percentage ``highly annoyed'' (%HA, cutoff at 72 on a scale from 0 to 100), the percentage ``annoyed'' (%A, cutoff at 50 on a scale from 0 to 100), and the percentage ``(at least) a little annoyed'' (%LA, cutoff at 28 on a scale from 0 to 100). The estimates of the parameters of the relations are based on the data from a field study (N=1875) at 11 locations (2 shunting yards, 1 seasonal industry, 8 other industries) in the Netherlands. With the same (yearly) DENL, the seasonal industry causes less annoyance than the other industries, while the other industries cause less annoyance than the shunting yards. It appears that annoyance caused by vibrations from shunting yards and annoyance caused by noise from through trains are (partly) responsible for the relatively high annoyance from shunting yards. The relatively low annoyance from the seasonal industry presumably is related to the presence of a relatively quiet period. Results for the two shunting yards and the seasonal industry are based on fewer data than the other industrial sources, and are indicative. The same patterns of influence of age and noise sensitivity that are generally found are also found in this study. For comparison, results regarding transportation sources are also given, including previously unpublished results for expected annoyance.

Miedema, Henk M. E.; Vos, Henk

2004-07-01

279

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)

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.

Pla, F. G.; Rajiyah, H.

1995-01-01

280

Pitch Estimation Based on a Harmonic Sinusoidal Autocorrelation Model and a Time-Domain Matching Scheme  

Microsoft Academic Search

In this paper, a method for the estimation of pitch from noise-corrupted speech observations based on extracting a pitch harmonic and the corresponding harmonic number is pro- posed. Starting from the harmonic representation of clean speech, a simple yet accurate harmonic sinusoidal autocorrelation (HSAC) model is first derived. By employing this HSAC model expressed in terms of the pitch harmonics

Celia Shahnaz; Wei-Ping Zhu; M. Omair Ahmad

2012-01-01

281

Absolute subcriticality measurement without calibration and detection efficiency dependence by the /sup 252/Cf source-driven noise method  

SciTech Connect

The /sup 252/Cf-source-driven noise analysis method determines the subcriticality of a system containing fissionable material from the ratio of cross power spectral densities between the detectors that detect particles from the fission process and between these detectors and an ionization chamber containing a spontaneously fissioning neutron source which provides neutrons to induce fission in the system. This method has two advantages: (1) a calibration is not required and thus subcriticality can be determined from measurements only on the subcritical system of interest, and (2) the subcriticality is independent of the type of detector or its efficiency. These properties of this technique are illustrated by measurements.

Mihalczo, J.T.; King, W.T.

1984-01-01

282

Harmonic Convergence  

NSDL National Science Digital Library

Harmonic convergence refers to a day back in 1987 where there was a particular planetary alignment. New Agers went crazy over the event, and if you want to get a taste of what it was like, enter harmonic convergence into your favorite Internet search engine and sit back and enjoy. This chapter adds to the previous discussion of resonance by expanding the list of vibrating things to metal rods and columns of air.

Robertson, William C.

2003-01-01

283

Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation.  

PubMed

A laser-based tabletop approach to femtosecond time-resolved photoelectron spectroscopy with photons in the vacuum-ultraviolet (VUV) energy range is described. The femtosecond VUV pulses are produced by high-order harmonic generation (HHG) of an amplified femtosecond Ti:sapphire laser system. Two generations of the same setup and results from photoelectron spectroscopy in the gas phase are discussed. In both generations, a toroidal grating monochromator was used to select one harmonic in the photon energy range of 20-30 eV. The first generation of the setup was used to perform photoelectron spectroscopy in the gas phase to determine the bandwidth of the source. We find that our HHG source has a bandwidth of 140 40 meV. The second and current generation is optimized for femtosecond pump-probe photoelectron spectroscopy with high flux and a small spot size at the sample of the femtosecond probe pulses. The VUV radiation is focused into the interaction region with a toroidal mirror to a spot smaller than 100 100 ?m(2) and the flux amounts to 10(10) photons/s at the sample at a repetition rate of 1 kHz. The duration of the monochromatized VUV pulses is determined to be 120 fs resulting in an overall pump-probe time resolution of 135 5 fs. We show how this setup can be used to map the transient valence electronic structure in molecular dissociation. PMID:21721681

Wernet, Philippe; Gaudin, Jrme; Godehusen, Kai; Schwarzkopf, Olaf; Eberhardt, Wolfgang

2011-06-01

284

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

SciTech Connect

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.

Barrett, W.H.; Greenwoll, J.I.; Smith, C.W. [Sandia National Labs., Albuquerque, NM (United States); Johnson, D.E.; De La Cruz, C.F.

1995-08-01

285

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

SciTech Connect

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.

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

2000-10-11

286

Farfield filtering and source imaging of subsonic jet noise Maxime Koenig a,b,n  

E-print Network

(Safran Group), Acoustic Department, Rond Point René Ravaud, 77550 Moissy-Cramayel, France c Instituto a b s t r a c t Jet noise is analysed using data-processing tools adapted to two particular structural Decomposition is used to probe the polar structure of the sound field, wavelet transform being used

Papamoschou, Dimitri

287

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

NASA Technical Reports Server (NTRS)

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.

Kahraman, Ahmet; Singh, Rajendra

1989-01-01

288

Detection of microseismic compressional (P) body waves aided by numerical modeling of oceanic noise sources  

E-print Network

Detection of microseismic compressional (P) body waves aided by numerical modeling of oceanic noise or where ocean waves propagating as swell meet another swell or wind sea. We then emphasize two and surface waves result from distinctive amplification of ocean wave-induced pressure perturbation

Stutzmann, Eléonore

289

Mapping the Signal-To-Noise-Ratios of Cortical Sources in Magnetoencephalography  

E-print Network

School, Boston, Massachusetts Abstract: Although magnetoencephalography (MEG) and electroencephalography. Overall, the SNR maps were more uniform for EEG than for MEG. When using a noise model based on uniformly activity. Our results emphasize the benefits of recording MEG and EEG simultaneously. Hum Brain Mapp 30

Vaina, Lucia M.

290

1. A time harmonic current source, J(Rf, t), of angular frequency q,and located near the origin, 0, isIradiating electromagnetic wave away from the source (into free space), as shown in Fig. I. Eric, an1 engineer, is asked to find the spatial temporal dep  

E-print Network

, isIradiating electromagnetic wave away from the source (into free space), as shown in Fig. I. Eric of the time harmonic electromagnetic waves? Is Eric correct or wrong? Where and why, if wrong? Can you write of the time harmonic electromagnetic waves? (15%) 2. (a) Consider, for example, a pair of closely spaced

Huang, Haimei

291

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

NASA Technical Reports Server (NTRS)

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.

Baumeister, K. J.

1975-01-01

292

Photoionization of ionosphere and near surface atmosphere as a source of electrophonic noises accompanying the Chelyabinsk event  

NASA Astrophysics Data System (ADS)

The bright bolide radiation is able to create a plasma cloud in the ionosphere due to photoioniozation of easy ionizable atmospheric components (NO and others). The spatial distribution of these components in the ionosphere causes formation of plasma cloud with strong concentration gradients across geomagnetic field which are spreaded up to several tens of kilometers. This formation leads to excitation of ion cyclotron gradient drift nonlinear waves. Their evolution creates low frequency electromagnetic radiation flux down to the ground. In the near surface atmosphere easily ionized atmospheric components (NO, NO_2, NH_3, CH_4 etc.) are the basis of area with increased ionization, which reacts on ionospheric radiation. The secondary excitation of oscillations on ion-cyclotron frequencies may be the source of electrophonic noises. This theoretical model is compared with acoustic noises recorded at the Chelyabinsk event in the cyclotronic frequencies range.

Kovaleva, Irina; Popova, Olga; Kovalev, Alexei; Rybnov, Yuri

293

Airframe noise  

NASA Technical Reports Server (NTRS)

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.

Crighton, David G.

1991-01-01

294

Comparative Analyses of Phase Noise in 28 nm CMOS LC Oscillator Circuit Topologies: Hartley, Colpitts, and Common-Source Cross-Coupled Differential Pair  

PubMed Central

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. PMID:24683340

Chlis, Ilias

2014-01-01

295

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)

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.

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

2013-05-01

296

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

NASA Technical Reports Server (NTRS)

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.

Zaman, Khairul B.

2002-01-01

297

Shallow surface-wave simulator for the study of jet-noise sources  

Microsoft Academic Search

A shallow liquid surface-wave analogy to turbulence-induced sound was utilized to investigate the mechanisms of noise generation and propagation in jets. Theoretical analysis was used to determine the wave-power dependence on Mach number and to derive the relationship between wave and turbulence spectra. The experimental investigation utilized a 24-sq ft mercury ripple tank. The waves were produced by the turbulence

W. H. Colwill; G. Reethof

1977-01-01

298

The Alternative Low Noise Fan  

NASA Technical Reports Server (NTRS)

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 source noise generation region may be more effective than similar material outside of the generation region.

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

2000-01-01

299

Transmission characteristics of cyclotron harmonic waves in plasma  

Microsoft Academic Search

In recent years the importance of cyclotron harmonic waves has become apparent in many branches of plasma physics. For example, it has been demonstrated that they are involved in the anomalously high noise radiation near the electron cyclotron harmonic frequencies that has been observed from thermonuclear fusion study devices, and that they can explain the cyclotron harmonic resonances observed in

F. W. Crawford; H. H. Weiss

1966-01-01

300

Noise characterization of broadband fiber Cherenkov radiation as a visible-wavelength source for optical coherence tomography and two-photon fluorescence microscopy.  

PubMed

Optical sources in the visible region immediately adjacent to the near-infrared biological optical window are preferred in imaging techniques such as spectroscopic optical coherence tomography of endogenous absorptive molecules and two-photon fluorescence microscopy of intrinsic fluorophores. However, existing sources based on fiber supercontinuum generation are known to have high relative intensity noise and low spectral coherence, which may degrade imaging performance. Here we compare the optical noise and pulse compressibility of three high-power fiber Cherenkov radiation sources developed recently, and evaluate their potential to replace the existing supercontinuum sources in these imaging techniques. PMID:25321223

Tu, Haohua; Zhao, Youbo; Liu, Yuan; Liu, Yuan-Zhi; Boppart, Stephen

2014-08-25

301

Interior noise in the untreated Gulfstream II Propfan Test Assessment (PTA) aircraft  

NASA Technical Reports Server (NTRS)

Interior noise on the Gulfstream II Propfan Test Assessment (PTA) aircraft was measured using 19 wing, 22 fuselage, and 32 cabin-interior microphones to determine the sources of the cabin noise. Results from ground and flight test acoustic and vibration measurements and analyses show that the major source of cabin noise was the airborne propfan blade passage frequency tones. The radiated sound pressure levels and the richness of the harmonic content of the propfan increased with increasing altitude. The acoustic output of the propfan also depended on the shaft power, helical Mach number, and blade passage frequency.

Kuntz, H. L.; Prydz, R. A.

1989-01-01

302

Exploiting seismic signal and noise in an intracratonic environment to constrain crustal structure and source parameters of infrequent earthquakes  

NASA Astrophysics Data System (ADS)

In many regions of the world characterized by a relatively low rate of seismicity, the determination of local and regional seismic source parameters is often restricted to an analysis of the first onsets of P waves (or first motion analysis) due to incomplete information about Earth structure and the small size of the events. When rare large earthquakes occur in these regions, their waveforms can be used to model Earth structure. This, however, makes the nature of the earthquake source determination problem circular, as source information is mapped as structure. Presented here is one possible remedy to this situation, where through a two-step approach we first constrain Earth structure using data independent of the earthquake of interest. In this study, we focus on a region in Western Australia with low seismicity and minimal instrument coverage and use the CAPRA/LP temporary deployment to demonstrate that reliable structural models of the upper lithosphere can be obtained from an independent collection of teleseismic and ambient noise datasets. Apart from teleseismic receiver functions (RFs), we obtain group velocities from the cross-correlation of ambient noise and phase velocities from the traditional two-station method using carefully selected teleseismic earthquakes and station pairs. Crustal models are then developed through the joint inversion of dispersion data and RFs, and structural Green's functions are computed from a layered composite model. In the second step of this comprehensive approach, we apply full waveform inversion (three-component body and surface waves) to the 2007 ML= 5.3 Shark Bay, Western Australia, earthquake to estimate its source parameters (seismic moment, focal mechanism, and depth). We conclude that the full waveform inversion analysis provides constraints on the orientation of fault planes superior to a first motion interpretation.

Young, Mallory K.; Tkal?i?, Hrvoje; Rawlinson, Nicholas; Reading, Anya M.

2012-03-01

303

Helicopter rotor noise due to ingestion of atmospheric turbulence  

NASA Technical Reports Server (NTRS)

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.

Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.; Greitzer, E. M.

1986-01-01

304

Evaluation of the interim measurement protocol for railway noise source description  

NASA Astrophysics Data System (ADS)

The Dutch national calculation scheme for railway noise has been declared the default interim method for railway noise calculation by the EU, until the introduction of results from the Harmonoise project. It includes a measurement protocol for determining emission input data in the format suitable for the present calculation scheme. The calculation scheme contains a fixed database of emission data for common Dutch rolling stock. The measurement protocol provides for the addition of emission data of new or foreign rolling stock. This is relevant for the Netherlands, as such rolling stock increasingly appears on the network, but also for other European countries that are going to use the interim method, since emission data for their rolling stock have to be established. The protocol features two procedures. Procedure A allows using the existing fixed database of emission data. Selection of a particular dataset (or 'category') can be based on external appearance of rolling stock (without measurements) or pass-by sound pressure level measurements at a site with known rail roughness. If a user finds that none of the existing data sets properly represent its rolling stock, the optional procedure B is available. This procedure assesses pass-by levels, track and wheel roughness levels. The measurement protocol is based on a type-test-like procedure requiring controlled conditions for the vehicle and track. A measurement campaign has been undertaken to test procedures A and B. This campaign coincided with a Swiss campaign to establish the sound emission of freight vehicles equipped with composite block brakes. The test of the protocol was focussed both on the practicability of the required measurements and on the unambiguity and comprehensiveness of the test. Open questions, findings, resulting conclusions and recommendations regarding the protocol are discussed here.

Janssens, M. H. A.; Jansen, H. W.; Dittrich, M. G.

2006-06-01

305

Harmonic engine  

SciTech Connect

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.

Bennett, Charles L. (Livermore, CA)

2009-10-20

306

Construction of Thermal and\\/or Electric Exchange System whereby Environmental Noise is Considered to be an Energy Source  

Microsoft Academic Search

Sound is a rarefactional wave of the air. Therefore, noise can be considered to be a sound energy. By thermoacoustic theory, noise is exchanged for thermal energy and is controlled. In addition, thermal energy is extracted from the noise. There are many applications of thermoacoustic theory such as Stirling engines. This system of heat supply whereby noise is considered to

Y. Tokita; R. Yoonsun; Y. Oikawa; Y. Yamasaki

307

Interface Mobilities for Low-Noise Design of Structure-Borne Sound Sources  

E-print Network

Institute of Fluid Mechanics and Engineering Acoustics, Technische Universität Berlin Secretariat TA7) European Acoustics Association the source's ability to deliver power, while the cou- pling function

Berlin,Technische Universität

308

Numerical evaluation of the jet noise source distribution from far-field cross correlations  

NASA Technical Reports Server (NTRS)

This paper contains the development of techniques to determine the relationship between the unknown source correlation function to the correlation of scattered amplitudes in a jet. This study has application to the determination of forward motion effects. The technique has been developed and tested on a model jet of high subsonic flow. Numerical solution was obtained by solving the Fredholm integral equation of the first kind. Interpretation of the apparent source distribution and its application to flight testing are provided.

Maestrello, L.; Liu, C.-H.

1976-01-01

309

Noise Amplification in HGHG Seeding  

SciTech Connect

An essential element of seeded FEL based on high-gain harmonic generation (HGHG) or echo-enabled harmonic generation (EEHG) is an undulator-modulator, in which interaction with a laser beam modulates the beam energy. We study how the interaction of electrons in this undulator-modulator changes the noise properties of the beam.

Stupakov, Gennady

2010-08-25

310

Stellar Variability And External Noise Sources With The Kepler Mission: Can Stellar Cycle Changes Be Revealed?  

NASA Astrophysics Data System (ADS)

We will provide exploration of stellar and instrument noise properties associated with Kepler Mission data to inform exoplanet detection capabilities, reveal levels of stellar activity in the Kepler sample relative to the Sun, and provide a foundation to determine if Kepler data will support stellar cycle quantifications. Gilliland et al (2011) provided a study separating observed variations in Kepler time series into instrumental and stellar components, taking advantage of the unique way in which the same stars are cycled through different detectors. The latter study concluded the instrument was noisier by a small margin on time scales of transits, while the stars were nearly a factor of two more variable on this few hour time scale than expected prior to launch. That study used data from the first six quarters of Kepler observations; this study will extend the same results by over two additional years (through Quarter 15), and utilize the latest, updated data products. A more powerful study of intrinsic stellar variability can focus on longer (activity) time scales; we will provide such a study in an attempt to resolve a controversy on variability of the Kepler stars relative to the Sun. Last, but far from least, in terms of simple signal-to-noise arguments, data from Kepler should easily reveal stellar cycle variations to well below the 0.1% amplitude seen for the Sun. However, many instrumental drifts and systematics have amplitudes well above the multi-year signal levels expected. We will use Kepler's quietest stars to assess prospects for extensive stellar cycle studies. The goal of this latter effort is to perform all necessary calibrations to demonstrate that Kepler is capable of quantifying stellar cycle variations, or, failing this, to provide a clear explication of remaining problems that need to be overcome. Elucidation of cyclic behavior for thousands of stars would (if feasible) be a future seminal achievement for the Kepler Mission. This will be a one year program. Actual science on stellar cycles would benefit immensely from the longer time series that may be avilable in future proposals. The budget is primarily for research support of Gilliland -- Science PI on this program -- who will lead all phases of the research.

Ramsey, Lawrence

311

A novel approach to minimize line-current harmonics in interfacing renewable energy sources with 3-phase utility systems  

Microsoft Academic Search

An approach to interfacing renewable energy sources such as photovoltaic, wind-electric, and small hydroplants with three-phase utility systems is presented. By modulating the DC-link currents and then reinjecting the modulating currents on the AC side, distortion in the line currents can be reduced to be within the allowable limits. Other advantages include the capability to provide electrical isolation by means

Ned Mohan

1992-01-01

312

Spherical Harmonics YLM Explorer  

NSDL National Science Digital Library

This is a Java applet that creates surface plots of the spherical harmonics. The user can set the L and m indices and the resolution of the plot. There is a restriction that L must be less than or equal to 5. Results are shown as either the amplitude of the function colored by the complex phase or the real part of the function illuminated by an external light source. Plots may be rotated in three dimensions.

Kraus, Martin

2005-04-16

313

Organizational Communication in Emergencies: Using Multiple Channels and Sources to Combat Noise and Capture Attention  

ERIC Educational Resources Information Center

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

Stephens, Keri K.; Barrett, Ashley K.; Mahometa, Michael J.

2013-01-01

314

Effects of background noise on total noise annoyance  

NASA Technical Reports Server (NTRS)

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.

Willshire, K. F.

1987-01-01

315

Acoustic noise associated with the MOD-1 wind turbine: its source, impact, and control  

SciTech Connect

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.

Kelley, N.D.; McKenna, H.E.; Hemphill, R.R.; Etter, C.L.; Garrelts, R.L.; Linn, N.C.

1985-02-01

316

Radiated noise of ducted fans  

Microsoft Academic Search

The differences in the radiated acoustic fields of ducted and unducted propellers of the same thrust operating under similar conditions are investigated. An FEM model is created for the generation, propagation, and radiation of steady, rotor alone noise and exit guide vane interaction noise of a ducted fan. For a specified number of blades, angular mode harmonic, and rotor angular

Walter Eversman

1992-01-01

317

Proceedings of Noise-con 81: Applied noise control technology  

SciTech Connect

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.

Royster, L.H.; Hart, F.D.; Stewart, N.D. (eds.)

1981-01-01

318

Infrared sky noise study  

NASA Technical Reports Server (NTRS)

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.

Westphal, J. A.

1972-01-01

319

A study of methods to predict and measure the transmission of sound through the walls of light aircraft. Numerical method for analyzing the optimal performance of active noise controllers. Thesis  

NASA Technical Reports Server (NTRS)

An optimal active noise controller is formulated and analyzed for three different active noise control problems. The first problem formulated is the active control of enclosed or partially enclosed harmonic sound fields where the noise source strengths and enclosure boundary description are known. The enclosure boundary is described by either pressure, velocity, or impedance boundary conditions. The second problem formulated is the active control of the free field power radiated from a distributed noise source with a known time harmonic surface velocity. The third problem formulated is the active control of enclosed or partially enclosed harmonic sound field where the noise source strengths of enclosure boundary description may not be known. All three formulations are derived using an indirect boundary element technique. Formulation and verification of an indirect boundary element method is presented. The active noise controller formulations for enclosures are capable of analyzing systems with generalized enclosure shapes, point noise sources, and/or locally reacting impedance boundary conditions. For each formulation, representative results of optimal active noise controller case studies are presented, and some general conclusions are drawn.

Mollo, Christopher G.; Bernhard, Robert J.

1987-01-01

320

Conference on STOL Transport Aircraft Noise Certification.  

National Technical Information Service (NTIS)

The proceedings of the conference included papers on STOL development, STOL noise sources, STOL noise abatement operations, and aircraft noise evaluation and are assembled for use in future activities related to STOL noise certification. Examples and figu...

1969-01-01

321

Effect of external pressure environment on the internal noise level due to a source inside a cylindrical tank  

NASA Technical Reports Server (NTRS)

A small cylindrical tank was used to study the effect on the noise environment within a tank of conditions of atmospheric (sea level) pressure or vacuum environments on the exterior. Experimentally determined absorption coefficients were used to calculate transmission loss, transmissibility coefficients and the sound pressure (noise) level differences in the interior. The noise level differences were also measured directly for the two exterior environments and compared to various analytical approximations with limited agreement. Trend study curves indicated that if the tank transmission loss is above 25 dB, the difference in interior noise level between the vacuum and ambient pressure conditions are less than 2 dB.

Clevenson, S. A.; Roussos, L. A.

1984-01-01

322

The spectrum of random ICRF source angular velocities  

NASA Astrophysics Data System (ADS)

The spectrum of the random angular velocities of ICRF sources is analyzed. This spectrum is calculated assuming that the apparent angular velocities of the sources are random and uncorrelated, and that the directions of the motions of each source are uniformly distributed over a circle. The amplitudes of the vector spherical harmonics display a white-noise spectrum. Published observational data are considered, and preliminary conclusions are drawn about the nature of the observed dipole and quadrupole harmonics in the spectrum of angular velocities.

Sazhin, M. V.; Sazhina, O. S.; Marakulin, A. O.

2011-11-01

323

Study of MOSFET Low Frequency Noise Source Fluctuation Using a New Fully Programmable Test Set-up  

Microsoft Academic Search

In this paper we aim to demonstrate the huge spread that can be seen on flicker (1\\/f) noise figures of advanced MOS devices. In order to do so, we set up a new fully programmable test bench including low frequency noise (1Hz-few Mhz) measurement capability. Once all the hurdles we faced during measurement optimization have been overpassed, we show indeed

K. Rochereau; C. Blanc; M. Marin

2007-01-01

324

Enhancing tidal harmonic analysis: Robust (hybrid L1 ) solutions  

E-print Network

Enhancing tidal harmonic analysis: Robust (hybrid L1 =L2 ) solutions Keith E. Leffler ?, David A 24 February 2008 Accepted 28 April 2008 Keywords: Tides Tidal analysis Harmonic analysis Robust is calculated from the power spectrum of the residual, a calculation that filters broad spectrum noise

Jay, David

325

Simple Harmonic Oscillator Model  

NSDL National Science Digital Library

The Ejs Simple Harmonic Oscillator model displays the dynamics of a ball attached to an ideal spring. The spring is initially stretched and the ball has zero initial velocity. The initial position of the ball can be changed by click-dragging the ball when the simulation is paused. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting Open Ejs Model from the pop-up menu item. Ejs Simple Harmonic Oscillator model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_osc_SHO.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for Newtonian mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang

2008-07-05

326

Strange Harmonic Oscillator Model  

NSDL National Science Digital Library

The Ejs Strange Harmonic Oscillator model displays the motion of two masses connected by a massless rigid rod and the masses may move without friction along two perpendicular rails in a horizontal table. The energy of the oscillator system can be changed via a slider. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting Open Ejs Model from the pop-up menu item. Ejs Strange Harmonic Oscillator model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_ehu_oscillations_strange.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for classical mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Aguirregabiria, Juan

2008-11-11

327

Underwater noise of small personal watercraft (jet skis).  

PubMed

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 ?Pa @ 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

Erbe, Christine

2013-04-01

328

Fourth Aircraft Interior Noise Workshop  

NASA Technical Reports Server (NTRS)

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.

Stephens, David G. (compiler)

1992-01-01

329

Unlocking higher harmonics in atomic force microscopy with gentle interactions  

PubMed Central

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

Font, Josep; Verdaguer, Albert

2014-01-01

330

Investigation of interior noise in a twin-engine light aircraft  

NASA Technical Reports Server (NTRS)

This paper describes experimental studies of interior noise in a twin-engine, propeller-driven, light aircraft. An analytical model for this type of aircraft is also discussed. Results indicate that interior noise levels in this aircraft due to propeller noise can be reduced by reducing engine rpm at constant airspeed (about 3 dB), and by synchrophasing the twin engines/propellers (perhaps up to 12 dB). Ground tests show that the exterior noise pressure imposed on the fuselage consists of a complex combination of narrow-band harmonics due to propeller and engine exhaust sources. This noise is reduced by about 20-40 dB (depending on the frequency) by transmission through the sidewall to the cabin interior. The analytical model described uses modal methods and incorporates the flat-side geometrical and skin-stringer structural features of this light aircraft.

Mixson, J. S.; Barton, C. K.; Vaicaitis, R.

1978-01-01

331

Proceedings, inter-noise 84 - international cooperation for noise control. 2 Vols  

SciTech Connect

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.

Maling, G.C. Jr. (ed.)

1984-01-01

332

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)

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.

Stimpert, D. L.; Clemons, A.

1977-01-01

333

Computation of rotor wake turbulence noise  

Microsoft Academic Search

A major source of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a Reynolds averaged NavierStokes code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-in source diagnostic

M. Nallasamy; E. Envia

2005-01-01

334

A Study of the Magnitude of Transportation Noise Generation and Potential Abatement. Volume VI. Community Transportation Noise.  

National Technical Information Service (NTIS)

Community noise levels result from transportation and nontransportation noise sources. The extent to which transportation noise dominates other sources and the exposure to it is a measure of the magnitude of the transportation noise problem. A prototype m...

1970-01-01

335

Aircraft noise prediction program theoretical manual, part 2  

NASA Technical Reports Server (NTRS)

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.

Zorumski, W. E.

1982-01-01

336

Cumulant-based approach to the harmonic retrieval problem  

Microsoft Academic Search

A time-series consisting of sinusoids observed in additive i.i.d. noise or in additive colored Gaussian noise of unknown spectral density is considered. The number of harmonics, as well as their amplitudes and frequencies are determined using the one-dimensional diagonal slice of the fourth-order cumulant. Applications to the detection of cubic phase coupling are discussed

Ananthram Swami; Jerry M. Mendel

1988-01-01

337

Cumulant-based approach to harmonic retrieval and related problems  

Microsoft Academic Search

A frequently encountered problem in signal processing is that of estimating the frequencies and amplitudes of harmonics observed in additive colored Gaussian noise. In practice, the observed signals are contaminated with spatially and temporally colored noise of unknown power spectral density. A cumulant-based approach to these problems is proposed. The cumulants of complex processes are defined, and it is shown

Ananthram Swami; Jerry M. Mendel

1991-01-01

338

High order harmonic generation in rare gases  

SciTech Connect

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.

Budil, K.S.

1994-05-01

339

Active Interior Noise Control Studies  

NASA Technical Reports Server (NTRS)

Analytical and experimental investigations into the control of noise in the interior of a three-dimensional enclosure with a flexible boundary are presented. The rigid boundaries are constructed from acrylic material, and in the different cases considered the flexible boundary is constructed from either aluminum or composite material. Noise generated by an external speaker is transmitted into the enclosure through the flexible boundary and active control is realized by using Lead Zirconate Titanate (PZT) piezoelectric actuators bonded to the flexible boundary. Condenser microphones are used for noise measurements inside and outside the enclosure. Minimization schemes for global and local noise control in the presence of a harmonic disturbance are developed and discussed. In the experiments, analog feedforward control is implemented by using the harmonic disturbance as a reference signal.

Park, J.; Veeramani, S.; Sampath, A.; Balachandran, B.; Wereley, N.

1996-01-01

340

Signal-to-noise ratios in IUE SWP-LO spectra of chromospheric emission-line sources  

NASA Technical Reports Server (NTRS)

The short-wavelength-prime (SWP) detector of the International Ultraviolet Explorer should operate near the photon-counting limit, but the noise levels in flat-field images are several times higher. The exaggerated noise can be traced to the incomplete removal of the pixel-to-pixel granularity of the television frames by the prevailing spectral image processing system. An empirical noise model for the current-epoch photometric linearization strategy and one for a hypothetical processing system that achieves complete flat fielding of the raw images are derived. A formula is then proposed to predict the signal-to-noise ratio in the measured flux of an emission line (possibly superimposed on a smooth continuum) in an IUE low-dispersion (5 A resolution) far-ultraviolet (1150 A-1950 A) spectrum as recorded with the SWP camera. For illustration, the formula is specialized to the important C IV 1549 A feature of F-K stars. The S/N relation permits one to determine sensitivity limits, upper limits in faint exposures, and optimum exposure times.

Ayres, Thomas R.

1990-01-01

341

Original superconducting quantum interference device (SQUID) design and measurement technique for flux noise source localization in SQUID systems  

Microsoft Academic Search

We present an original method for studying the low frequency flux noise due to vortices in superconducting quantum interference device (SQUID) systems. We use two SQUIDs connected to the same washer in order to study the correlation of their outputs. A dedicated electronic system has been built so as to operate both SQUIDs at the same time. It was thus

M. Lam Chok Sing; S. Flament; X. Ridereau; C. Gunther; L. Mchin; D. Bloyet

2003-01-01

342

Higher-Order Harmonic Generation from Fullerene by Means of the Plasma Harmonic Method  

SciTech Connect

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.

Ganeev, R. A. [Institut National de la Recherche Scientifique, Energie, Materiaux et Telecommunications, 1650 Lionel-Boulet, Varennes, Quebec J3X 1S2 (Canada); Scientific Association Akadempribor, Academy of Sciences of Uzbekistan, Akademgorodok, Tashkent 100125 (Uzbekistan); Bom, L. B. Elouga; Abdul-Hadi, J.; Ozaki, T. [Institut National de la Recherche Scientifique, Energie, Materiaux et Telecommunications, 1650 Lionel-Boulet, Varennes, Quebec J3X 1S2 (Canada); Wong, M. C. H.; Brichta, J. P.; Bhardwaj, V. R. [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5 (Canada)

2009-01-09

343

Iterative joint source-channel decoding of speech spectrum parameters over an additive white Gaussian noise channel  

Microsoft Academic Search

In this paper, we show how the Gaussian mixture modeling framework used to develop efficient source encoding schemes can be further exploited to model source statistics during channel decoding in an iterative framework to develop an effective joint source-channel decoding scheme. The joint probability density function (PDF) of successive source frames is modeled as a Gaussian mixture model (GMM). Based

Anand D. Subramaniam; William R. Gardner; Bhaskar D. Rao

2006-01-01

344

Caractrisation des sources de bruit arodynamique sur un ventilateur centrifuge flux axial  

Microsoft Academic Search

This paper is an experimental investigation of the aerodynamic noise sources in a centrifuga1 fan with outlet guide vanes and axial outflow. Special piezoplastic sensors are used for the measurement of the pressure Iluctuations on the blades. Classical signal processing procedures provide the blade loadings harmonics. When the fan operates at a relatively high flow rate and low efficiency, it

C. RAFFAITIN; M. ROGER; L. RUFER; M. FABICKI

1994-01-01

345

Noise characteristics in IFOG  

NASA Astrophysics Data System (ADS)

IFOG (Interferometric Fiber Optic Gyroscope) is the most promising angular velocity sensor in the inertial guidance market due to its attractive advantages, which is often regarded as the next generation gyro that can ultimately replace the traditional mechanical gyroscope. In order to improve the performance of IFOG, especially to low down the bias drift and angle random walk (ARW) of IFOG, it is valuable to research the noise characteristics of IFOG. In this paper, the ultra low frequency random noise and the relatively high frequency random noise has been investigated respectively. The experimental data of a practical open loop IFOG is obtained by different sampling frequency, through which the different frequency scope of the noise can be researched separately. The frequency spectral analysis of the noise deduces the follow result: (1) the relative high frequency (higher than about 0.001 Hz) random noise can be approximately modeled as Gaussian white noise (GWN), and its spectral range is determined by the system bandwidth of IFOG. The angle random walk of IFOG is determined by this kind of noise. (2) The ultra low frequency (lower than about 0.001 Hz) random noise can not be Gaussian white noise, which is much more great than other noises, and with the rise of frequency, the power of the relevant frequency component is lower down sharply. The ultra low frequency noise is often regarded as the source of bias drift of IFOG.

Chang, Jianxin; Wang, Peng; Qin, BingKun; Chen, Shufen

2000-10-01

346

Rotorcraft noise  

NASA Technical Reports Server (NTRS)

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.

Huston, R. J. (compiler)

1982-01-01

347

Full characterization of self-phase-modulation based low-noise, cavity-less pulse source for photonic-assisted analog-to-digital conversion.  

PubMed

A high quality cavity-less pulse source, realized as a combination of linear pulse compression and self-phase-modulation (SPM) based regeneration is demonstrated and strictly characterized for the first time. The regenerated pulses, with 3.6 GHz repetition rate, are optimized through rigorous relative intensity-noise (RIN) measurement. Temporal intensity and chirp characterizations demonstrate that the pulses exhibit characteristic of low RIN, and are chirp- and pedestal-free. The cavity-less pulse source is further tested in a photonic-assisted analog-to-digital (ADC) configuration as the sampling source. A record result of more than 8 effective quantization bits at 202 MHz is demonstrated. PMID:23262840

Liu, Lan; Tong, Zhi; Wiberg, Andreas O J; Myslivets, Evgeny; Alic, Nikola; Radic, Stojan

2012-12-10

348

A Mode Propagation Database Suitable for Code Validation Utilizing the NASA Glenn Advanced Noise Control Fan and Artificial Sources  

NASA Technical Reports Server (NTRS)

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.

Sutliff, Daniel L.

2014-01-01

349

Core-Noise  

NASA Technical Reports Server (NTRS)

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 the combustion-noise component. The trend towards high-power-density cores also means that the noise generated in the low-pressure turbine will likely increase. Consequently, the combined result from these emerging changes will be to elevate the overall importance of turbomachinery core noise, which will need to be addressed in order to meet future noise goals.

Hultgren, Lennart S.

2010-01-01

350

[Study of the effect of light source stability on the signal to noise ratio in degenerate four wave mixing experiment].  

PubMed

The effects of the stability of dye laser on the signal to noise ratio in degenerate four-wave mixing (DFWM) were first investigated in iodine vapor using forward geometries. Frequency-doubled outputs from a multi-mode Nd : YAG laser pumped dye laser with laser dye PM580 dissolved in ethanol was used. With the help of forward compensated beam-split technique and imaging detecting system, the saturation intensity of DFWM spectrum in the iodine vapor at 5 554.013 nm was first measured to be 290 microJ under the condition of atmospheric pressure and room temperature. The features of the dye laser such as wavelength ranges, beam quality and energy conversion efficiency decreased gradually with increasing pumping service use, pulse number and intensity. Additionally, with the comparison of the stable and unstable dye laser output, it was found that the instability of dye laser output had greatly influenced the DFWM signal and decreased the signal to background noise ratio. Shot to shot jitter and the broadening in the output frequency leads to an effective broadening of the recorded spectrum and loss of the DFWM signal to noise ratio under the same pumping intensity at different time. The study is of importance to the detection of trace atom, molecule and radical in combustion diagnosis. PMID:20384146

Wang, Wei-Bo; Chen, De-Ying; Fan, Rong-Wei; Xia, Yuan-Qin

2010-02-01

351

Prediction of airframe noise  

NASA Technical Reports Server (NTRS)

Methods of predicting airframe noise generated by aircraft in flight under nonpowered conditions are discussed. Approaches to predictions relying on flyover data and component theoretical analyses are developed. A nondimensional airframe noise spectrum of various aircraft is presented. The spectrum was obtained by smoothing all the measured spectra to remove any peculiarities due to airframe protrusions, normalizing each spectra by its overall sound pressure level and a characteristics frequency, and averaging the spectra together. A chart of airframe noise sources is included.

Hardin, J. C.; Fratello, D. J.; Hayden, R. E.; Kadman, Y.; Africk, S.

1975-01-01

352

Harmonic power flow for unbalanced systems  

SciTech Connect

In this paper a harmonic power flow that analyzes harmonics in unbalanced systems is presented. The developed algorithm has two steps which are executed successively: the first is a fundamental frequency power flow for the ac linear network in which non-linear loads are represented by current sources. The second is a frequency-domain iterative Newton-Raphson method to calculate the harmonics generated by non-linear loads. In this second step, the ac linear network is represented by a generalized Thevenin equivalent with respect to the non-linear loads, obtained from the power flow solution. Both linear and non-linear loads are considered in terms of power.

Valcarcel, M.; Mayordomo, J.G. (Univ. Politecnica de Madrid (Spain). Dept. de Ingenieria Electrica)

1993-10-01

353

Core Noise - Increasing Importance  

NASA Technical Reports Server (NTRS)

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 designs could increase the combustion-noise component. The trend towards high-power-density cores also means that the noise generated in the low-pressure turbine will likely increase. Consequently, the combined result from these emerging changes will be to elevate the overall importance of turbomachinery core noise, which will need to be addressed in order to meet future noise goals.

Hultgren, Lennart S.

2011-01-01

354

GRACE Harmonic and Mascon Solutions at JPL  

NASA Astrophysics Data System (ADS)

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.

Watkins, M. M.; Yuan, D.; Kuang, D.; Bertiger, W.; Kim, M.; Kruizinga, G. L.

2005-12-01

355

Single Phase Harmonic Limits  

Microsoft Academic Search

The International Electrotechnical Commission (IEC) sets limits for harmonics in the current of small single-phase or three-phase loads, less than 16 A per phase, in Electromagnetic compatibility (EMC) - Part 3-2: Limits - Limits for harmonic current emissions (IEC 61000-3-2). The IEEE Single Phase Harmonics Task Force (P1495) is developing a similar standard for single phase loads of less than

Ward Jewell; Daniel J. Ward; Principal Engineer; Dominion Virginia Power

2002-01-01

356

Workshop on Harmonic Oscillators  

NASA Technical Reports Server (NTRS)

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.

Han, D. (editor); Kim, Y. S. (editor); Zachary, W. W. (editor)

1993-01-01

357

Noise in electric machines: a review  

Microsoft Academic Search

Increasing awareness of industrial noise pollution and emerging stricter standards have made noise an important topic of research in electric machines. This work is a state-of-the-art review on the identification of noise sources and techniques to mitigate noise. It points the reader to relevant research in the past on acoustic noise identification and mitigation techniques. The paper also describes the

Praveen Vijayraghavan; R. Krishnan

1999-01-01

358

Noise analysis in laser speckle contrast imaging  

Microsoft Academic Search

Laser speckle contrast imaging (LSCI) is becoming an established method for full-field imaging of blood flow dynamics in animal models. A reliable quantitative model with comprehensive noise analysis is necessary to fully utilize this technique in biomedical applications and clinical trials. In this study, we investigated several major noise sources in LSCI: periodic physiology noise, shot noise and statistical noise.

Shuai Yuan; Yu Chen; Andrew K. Dunn; David A. Boas

2010-01-01

359

5th International Meeting Wind Turbine Noise  

E-print Network

1 5th International Meeting on Wind Turbine Noise Denver 28 ­ 30 August 2013 Wind Turbine Noise Broadband noise generated aerodynamically is the dominant noise source for a modern wind turbine(Brooks et, clean energy. While profiting from wind energy, the noise produced by a modern wind turbine becomes

Paris-Sud XI, Université de

360

Bias in calculated k{sub eff} from subcritical measurements by the {sup 252}Cf-source-driven noise analysis method  

SciTech Connect

The development of MCNP-DSP, which allows direct calculation of the measured time and frequency analysis parameters from subcritical measurements using the {sup 252}Cf-source-driven noise analysis method, permits the validation of calculational methods for criticality safety with in-plant subcritical measurements. In addition, a method of obtaining the bias in the calculations, which is essential to the criticality safety specialist, is illustrated using the results of measurements with 17.771-cm-diam, enriched (93.15), unreflected, and unmoderated uranium metal cylinders. For these uranium metal cylinders the bias obtained using MCNP-DSP and ENDF/B-V cross-section data increased with subcriticality. For a critical experiment [height (h) = 12.629 cm], it was {minus}0.0061 {+-} 0.0003. For a 10.16-cm-high cylinder (k {approx} 0.93), it was 0.0060 {+-} 0.0016, and for a subcritical cylinder (h = 8.13 cm, k {approx} 0.85), the bias was {minus}0.0137 {+-} 0.0037, more than a factor of 2 larger in magnitude. This method allows the nuclear criticality safety specialist to establish the bias in calculational methods for criticality safety from in-plant subcritical measurements by the {sup 252}Cf-source-driven noise analysis method.

Mihalczo, J.T.; Valentine, T.E.

1995-07-01

361

Evaluation of the annoyance due to helicopter rotor noise  

NASA Technical Reports Server (NTRS)

A program was conducted in which 25 test subjects adjusted the levels of various helicopter rotor spectra until the combination of the harmonic noise and a broadband background noise was judged equally annoying as a higher level of the same broadband noise spectrum. The subjective measure of added harmonic noise was equated to the difference in the two levels of broadband noise. The test participants also made subjective evaluations of the rotor noise signatures which they created. The test stimuli consisted of three degrees of rotor impulsiveness, each presented at four blade passage rates. Each of these 12 harmonic sounds was combined with three broadband spectra and was adjusted to match the annoyance of three different sound pressure levels of broadband noise. Analysis of variance indicated that the important variables were level and impulsiveness. Regression analyses indicated that inclusion of crest factor improved correlation between the subjective measures and various objective or physical measures.

Sternfeld, H., Jr.; Doyle, L. B.

1978-01-01

362

THE TECHNICAL AND ECOLOGICAL ANALYSIS OF WIND ENERGETICS AND WIND ENERGY POWER STATIONS, AS SOURCES OF NOISE POLLUTION  

Microsoft Academic Search

The usage of alternative sources of electric energy is one of the ways to solve the problems of global warming, environmental pollution and natural resources conservation. The dynamics of wind energetics development, as one of the representatives of such sources of energy, was described. The comparative data of electric energy production in different countries of the world is provided. Along

Y. Serikov; H. Parhomenko

2008-01-01

363

Characterization of generationrecombination noise using a physics-based device noise simulator  

E-print Network

the Shockley±Read±Hall model, the strength of each local g±r noise source is calculated based on the carrier and hole conti- nuity equations. The eect of each local, distributed noise source at the contact terminals±r noise spectral voltage density contact contribution from each local g±r noise source can be calculated

Florida, University of

364

Covariant harmonic oscillators and coupled harmonic oscillators  

NASA Technical Reports Server (NTRS)

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.

Han, Daesoo; Kim, Young S.; Noz, Marilyn E.

1995-01-01

365

Proceedings of the 1986 international conference on noise control engineering. Volume 1  

SciTech Connect

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.

Lotz, R.

1986-01-01

366

Axisymmetric generalized harmonic evolution code  

SciTech Connect

We describe the first axisymmetric numerical code based on the generalized harmonic formulation of the Einstein equations, which is regular at the axis. We test the code by investigating gravitational collapse of distributions of complex scalar field in a Kaluza-Klein spacetime. One of the key issues of the harmonic formulation is the choice of the gauge source functions, and we conclude that a damped-wave gauge is remarkably robust in this case. Our preliminary study indicates that evolution of regular initial data leads to formation both of black holes with spherical and cylindrical horizon topologies. Intriguingly, we find evidence that near threshold for black hole formation the number of outcomes proliferates. Specifically, the collapsing matter splits into individual pulses, two of which travel in the opposite directions along the compact dimension and one which is ejected radially from the axis. Depending on the initial conditions, a curvature singularity develops inside the pulses.

Sorkin, Evgeny [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Muehlenberg 1, D-14476, Golm (Germany)

2010-04-15

367

Fan Noise Prediction  

NASA Technical Reports Server (NTRS)

Aircraft noise emission level restrictions in and around airports continue to grow more stringent every few years. Thus, it is important to predict noise emissions from aircraft accurately. Predicting noise from the engine(s) is an integral part of the efforts to characterize the noise signature of an aircraft. An important source of engine noise is the rotor-stator interaction noise produced as a result of impingement of fan rotor wakes on the fan exit guide vanes. Interaction noise propagates through the inlet and exhaust ducts of the engine and radiates to the far field. noise levels for a range of model fans stages that represent current aircraft engine designs. Eversman's radiation codes calculate both the inlet and exhaust noise radiation by propagating the internally measured rotor-stator interaction noise to the far field. Predicted far field sound pressure levels are then compared to the measured levels from wind tunnel tests. This effort's objective is to prove that the predicted levels actually describe the measured levels.

France, Joshua I.

2004-01-01

368

Rotorcraft Noise Model  

NASA Technical Reports Server (NTRS)

The Rotorcraft Noise Model (RNM) is an aircraft noise impact modeling computer program being developed for NASA-Langley Research Center which calculates sound levels at receiver positions either on a uniform grid or at specific defined locations. The basic computational model calculates a variety of metria. Acoustic properties of the noise source are defined by two sets of sound pressure hemispheres, each hemisphere being centered on a noise source of the aircraft. One set of sound hemispheres provides the broadband data in the form of one-third octave band sound levels. The other set of sound hemispheres provides narrowband data in the form of pure-tone sound pressure levels and phase. Noise contours on the ground are output graphically or in tabular format, and are suitable for inclusion in Environmental Impact Statements or Environmental Assessments.

Lucas, Michael J.; Marcolini, Michael A.

1997-01-01

369

Mathematical modeling and statistical analysis of SPE-OCDMA systems utilizing second harmonic generation effect in thick crystal receivers  

NASA Astrophysics Data System (ADS)

In this paper we analytically study and evaluate the performance of a Spectral-Phase-Encoded Optical CDMA system for different parameters such as the user's code length and the number of users in the network. In this system an advanced receiver structure in which the Second Harmonic Generation effect imposed in a thick crystal is employed as the nonlinear pre-processor prior to the conventional low speed photodetector. We consider ASE noise of the optical amplifiers, effective in low power conditions, besides the multiple access interference (MAI) noise which is the dominant source of noise in any OCDMA communications system. We use the results of the previous work which we analyzed the statistical behavior of the thick crystals in an optically amplified digital lightwave communication system to evaluate the performance of the SPE-OCDMA system with thick crystals receiver structure. The error probability is evaluated using Saddle-Point approximation and the approximation is verified by Monte-Carlo simulation.

Matinfar, Mehdi D.; Salehi, Jawad A.

2009-11-01

370

Effect of at-the-source noise reduction on performance and weights of a tilt-rotor aircraft  

NASA Technical Reports Server (NTRS)

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.

Gibs, J.; Stepniewski, W. Z.; Spencer, R.

1975-01-01

371

Analysis of Vibration and Acoustic Noise in Permanent Magnet Motors.  

NASA Astrophysics Data System (ADS)

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. The effect of various design parameters on the output torque and torque ripple are discussed. Design parameters include winding patterns, magnetization direction, magnet arc length, number of segments in poles and magnet pole shaping. New designs of trapezoidal BEMF motors are proposed to reduce the electromagnetic torque ripple. Magnet stepping and magnet edge shaping with reduced arc length, significantly reduce torque ripple, with minimal sacrifice of the maximum output torque. Acoustic noise of electromagnetic origin is investigated using a magnetic frame which emulates a DC motor. The driving electromagnetic force is calculated using finite element analysis and the resulting vibration and acoustic noise is measured. Acoustic noise of purely electromagnetic origin was also tested with a DC brushless motor to confirm the results of the magnetic frame. The mechanism of noise generation in a DC motor is a quasi-static response of a stator not only at the fundamental frequency but also at higher harmonic frequencies of alternating switched DC, which is a current characteristic of a DC motor. Noise generation is significantly aggravated when some of those harmonics are close to the resonant frequencies of the stator. Therefore, acoustic noise is highly dependent upon the excitation current shape, as higher harmonics may match with resonant frequencies of the stator.

Hwang, Sangmoon

372

The effects of noise on man  

SciTech Connect

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.

Kryter, K.D.

1985-01-01

373

Noise reduction in DEXA image based on system noise modeling  

Microsoft Academic Search

Denoising X-ray image is an important preprocessing process to measure BMD (Bone Mineral Density) correctly. In this paper, we deal with denoising X-ray image in DEXA (Dual-Energy X-ray Absorptiometry) system. Image noise in DEXA is modeled by separating source and detector noises. Using the noise model in DEXA, a noise reduction method is proposed. The proposed denoising method consists of

J. W. Kwon; S. I. Cho; Y. B. Ahn; Y. M. Ro

2009-01-01

374

Noise in the nervous system.  

PubMed

Noise--random disturbances of signals--poses a fundamental problem for information processing and affects all aspects of nervous-system function. However, the nature, amount and impact of noise in the nervous system have only recently been addressed in a quantitative manner. Experimental and computational methods have shown that multiple noise sources contribute to cellular and behavioural trial-to-trial variability. We review the sources of noise in the nervous system, from the molecular to the behavioural level, and show how noise contributes to trial-to-trial variability. We highlight how noise affects neuronal networks and the principles the nervous system applies to counter detrimental effects of noise, and briefly discuss noise's potential benefits. PMID:18319728

Faisal, A Aldo; Selen, Luc P J; Wolpert, Daniel M

2008-04-01

375

Discrete rotor noise.  

NASA Technical Reports Server (NTRS)

Description of a single unified theory to account generally for the discrete radiation from the whole family of heavily loaded axial flow rotors, including helicopter rotors, propellers, and compressors. The approach used is to analyze, in a Fourier way, the periodic blade loading variation (azimuth profile) into blade loading harmonics (BLH) and then sum the total radiation from each BLH. The basic differences between high and low solidity rotor spectrums are considered, emphasizing the difference between subsonic and supersonic rotor noise. The special effect of helicopter blade slap and compressor rotor-stator interaction is discussed, and measured rotor spectrums have been included to help illustrate the theory.

Wright, S. E.

1972-01-01

376

Low Noise Goods Wagons  

NASA Astrophysics Data System (ADS)

Within the framework of a project called "low noise train", the Deutsche Bahn AG (DB AG) is currently expending a good deal of effort in initiating the development of a goods train that radiates significantly lower levels of wayside noise than do conventional goods trains. The present paper is based upon a collection of results of sound level measurements made by the UIC and the DB AG on wayside noise produced by goods wagons. For A-weighted sound-pressure levels, these results indicate that wheel/rail interactions are the dominant sources at speeds around 80 km/h on most types of wagons. Radiated noise levels are strongly influenced by the kind of braking system as well as by the condition of the rail surfaces. Other parameters appear to play a much smaller role in establishing wayside noise levels. Measurements designed to locate sources of radiated noise on dedicated goods trains have recently been carried out in order to increase our understanding of the mechanisms involved and to study the effects of sound-abatement measures on the level of rolling noise. These measurements were made with one- and two-dimensional configurations of microphone arrays. Several results of these studies are given here. In general, the conclusions drawn from the investigations are very promising, and, at least from an acoustical standpoint, the goal of realizing a "low noise goods train" appears achievable.

Hlzl, G.

1996-05-01

377

Evaluation of Spatial Resolution and Noise Sensitivity of sLORETA Method for EEG Source Localization Using Low-Density Headsets  

E-print Network

Electroencephalography (EEG) has enjoyed considerable attention over the past century and has been applied for diagnosis of epilepsy, stroke, traumatic brain injury and other disorders where 3D localization of electrical activity in the brain is potentially of great diagnostic value. In this study we evaluate the precision and accuracy of spatial localization of electrical activity in the brain delivered by a popular reconstruction technique sLORETA applied to EEG data collected by two commonly used low-density headsets with 14 and 19 measurement channels, respectively. Numerical experiments were performed for a realistic head model obtained by segmentation of MRI images. The EEG source localization study was conducted with a simulated single active dipole, as well as with two spatially separated simultaneously active dipoles, as a function of dipole positions across the neocortex, with several different noise levels in the EEG signals registered on the scalp. The results indicate that while the reconstructio...

Saha, Sajib; Tahtali, Murat; Gureyev, Timur E

2014-01-01

378

Polarization control of high order harmonics in the EUV photon energy  

E-print Network

optimized kHz two-colour high harmonic source for seeding free- electron lasers and plasma-based soft X.-E. Couprie, "Injection of harmonics generated in gas in a free-electron laser providing intense and coherent

379

Sound propagation Measurement of footfall noise  

E-print Network

#12;Institut für Technische Akustik Flow noise · Jet noise » Essentially quadrupole type source © Prof. B.A.T. Petersson #12;Institut für Technische Akustik Flow noise · Jet noise © Prof. B.A.T. Petersson #12;Institut für Technische Akustik Flow noise · Jet noise ­ Co-annular nozzle © Prof. B

Berlin,Technische Universität

380

Effects of age-related hearing loss and background noise on neuromagnetic activity from auditory cortex  

PubMed Central

Aging is often accompanied by hearing loss, which impacts how sounds are processed and represented along the ascending auditory pathways and within the auditory cortices. Here, we assess the impact of mild binaural hearing loss on the older adults ability to both process complex sounds embedded in noise and to segregate a mistuned harmonic in an otherwise periodic stimulus. We measured auditory evoked fields (AEFs) using magnetoencephalography while participants were presented with complex tones that had either all harmonics in tune or had the third harmonic mistuned by 4 or 16% of its original value. The tones (75 dB sound pressure level, SPL) were presented without, with low (45 dBA SPL), or with moderate (65 dBA SPL) Gaussian noise. For each participant, we modeled the AEFs with a pair of dipoles in the superior temporal plane. We then examined the effects of hearing loss and noise on the amplitude and latency of the resulting source waveforms. In the present study, results revealed that similar noise-induced increases in N1m were present in older adults with and without hearing loss. Our results also showed that the P1m amplitude was larger in the hearing impaired than in the normal-hearing adults. In addition, the object-related negativity (ORN) elicited by the mistuned harmonic was larger in hearing impaired listeners. The enhanced P1m and ORN amplitude in the hearing impaired older adults suggests that hearing loss increased neural excitability in auditory cortices, which could be related to deficits in inhibitory control. PMID:24550790

Alain, Claude; Roye, Anja; Salloum, Claire

2014-01-01

381

High-power, low-noise, Yb-doped, cladding-pumped, three-level fiber sources at 980 nm  

Microsoft Academic Search

We present results on a high-power, cladding-pumped, Yb-doped fiber emitting at 977 nm in laser and ampllified-spontaneous-emission source configurations. We obtained up to 1.4 W of fiber-coupled, single-mode output power and slope efficiency as high as 68%. To our knowledge these are the highest powers and efficiencies achieved from a single-mode fiber laser at ~980 nm and the first demonstrated

R. Selvas; J. K. Sahu; L. B. Fu; J. N. Jang; J. Nilsson; A. B. Grudinin; K. H. Yl-Jarkko; S. A. Alam; P. W. Turner; J. Moore

2003-01-01

382

Illustration: The Harmonic Oscillator  

NASA Astrophysics Data System (ADS)

To illustrate the formalism on a simple prototype problem, one may look at the harmonic oscillator. In the spirit of this picture, in fact, one can eschew solving the Schrdinger problem and plugging the wavefunctions into (4)...

Curtright, Thomas L.; Fairlie, David B.; Zachos, Cosmas K.

2014-11-01

383

Simple Harmonic Motion  

NSDL National Science Digital Library

This simulation offers two examples of simple harmonic motion, a mass on a spring and a simple pendulum. The applet allows you to adjust variables and observe the effects these changes have on the movement of the systems.

Pfaff, Raman

2008-07-15

384

Simple Harmonic Motion  

NSDL National Science Digital Library

This site from HyperPhysics presents an introduction to simple harmonic motion. It is explained using a concept map that features equations and diagrams. Links to other concepts involved are also included.

Nave, C. R.; University, Department O.

385

Circumferentially segmented duct lines optimized for axisymmetric and standing wave sources. [reducing noise from turbofan engines galerkin method acoustic attenuation  

NASA Technical Reports Server (NTRS)

Optimum and off-optimum properties of circumferentially segmented duct liners are compared with those of uniform liners to identify any potential benefits of circumferentially segmented liners. High- and low-order spinning-mode sources are considered in the study. The solution for the segmented liner is obtained by a multimodal expansion of the segmented-liner eigenmodes in terms of a series of hardwall duct models. The coefficients in the hard-wall series are obtained by using Galerkin's method. Results show that for some frequencies and duct lengths, circumferentially segmented liners scatter energy equally between a higher and lower order circumferential wave number. Studies for higher order spinning-mode sources show that an optimized segmented liner with a hard-wall/soft-wal admittance variation representing an optimum configuration gives better performance than an optimized uniform liner. Overall, the greatest benefit of the segmented liner over the uniform liner occurs under off-optimum conditions. The optimized segmented liner gives more effective broadband performance than the optimized uniform liner.

Watson, W. R.

1982-01-01

386

Rotor-vortex interaction noise  

NASA Technical Reports Server (NTRS)

A theoretical and experimental study was conducted to develop a validated first principles analysis for predicting noise generated by helicopter main-rotor shed vortices interacting with the tail rotor. The generalized prediction procedure requires a knowledge of the incident vortex velocity field, rotor geometry, and rotor operating conditions. The analysis includes compressibility effects, chordwise and spanwise noncompactness, and treats oblique intersections with the blade planform. Assessment of the theory involved conducting a model rotor experiment which isolated the blade-vortex interaction noise from other rotor noise mechanisms. An isolated tip vortex, generated by an upstream semispan airfoil, was convected into the model tail rotor. Acoustic spectra, pressure signatures, and directivity were measured. Since assessment of the acoustic prediction required a knowledge of the vortex properties, blade-vortes intersection angle, intersection station, vortex stength, and vortex core radius were documented. Ingestion of the vortex by the rotor was experimentally observed to generate harmonic noise and impulsive waveforms.

Schlinker, R. H.; Amiet, R. K.

1983-01-01

387

Prediction of XV-15 tilt rotor discrete frequency aeroacoustic noise with WOPWOP  

NASA Technical Reports Server (NTRS)

The results, methodology, and conclusions of noise prediction calculations carried out to study several possible discrete frequency harmonic noise mechanisms of the XV-15 Tilt Rotor Aircraft in hover and helicopter mode forward flight are presented. The mechanisms studied were thickness and loading noise. In particular, the loading noise caused by flow separation and the fountain/ground plane effect were predicted with calculations made using WOPWOP, a noise prediction program developed by NASA Langley. The methodology was to model the geometry and aerodynamics of the XV-15 rotor blades in hover and steady level flight and then create corresponding FORTRAN subroutines which were used an input for WOPWOP. The models are described and the simplifying assumptions made in creating them are evaluated, and the results of the computations are presented. The computations lead to the following conclusions: The fountain/ground plane effect is an important source of aerodynamic noise for the XV-15 in hover. Unsteady flow separation from the airfoil passing through the fountain at high angles of attack significantly affects the predicted sound spectra and may be an important noise mechanism for the XV-15 in hover mode. The various models developed did not predict the sound spectra in helicopter forward flight. The experimental spectra indicate the presence of blade vortex interactions which were not modeled in these calculations. A need for further study and development of more accurate aerodynamic models, including unsteady stall in hover and blade vortex interactions in forward flight.

Coffen, Charles D.; George, Albert R.

1990-01-01

388

Corneal imaging by second and third harmonic generation microscopy  

Microsoft Academic Search

Advanced imaging methods are essential tools for improved outcome of refractive surgery. Second harmonic generation (SHG) and third harmonic generation (THG) microscopy are noninvasive high-resolution imaging methods, which can discriminate the different layers of the cornea, thus having strong impact on the outcome of laser surgery. In this work, we use an Ytterbium femtosecond laser as the laser source, the

Arnaud Brocas; Louis Jay; Eric Mottay; Isabelle Brunette; Tsuneyuki Ozaki

2008-01-01

389

Suppression of power line harmonic interference in HF surface-wave radar  

Microsoft Academic Search

Experimental data of the Cape Bonavista High-Frequency Surface-Wave Radar (HFSWR) Facility was contaminated by power line harmonics. The harmonics modulate the radar signal (mainly sea clutter) and replicate it into the Doppler spectrum. The spectral replicas distort the noise and sea clutter statistics in the signal. It is necessary to suppress them before the statistics can be obtained. A new

Hank Leong

1992-01-01

390

On the use of windows for harmonic analysis with the discrete Fourier transform  

Microsoft Academic Search

This paper makes available a concise review of data windows and their affect on the detection of harmonic signals in the presence of broad-band noise, and in the presence of nearby strong harmonic interference. We also call attention to a number of common errors in the application of windows when used with the fast Fourier transform. This paper includes a

FREDRIC J. HARRIS

1978-01-01

391

Ermakov Systems with Multiplicative Noise  

E-print Network

Using the Euler-Maruyama numerical method, we present calculations of the Ermakov-Lewis invariant and the dynamic, geometric, and total phases for several cases of stochastic parametric oscillators, including the simplest case of the stochastic harmonic oscillator. The results are compared with the corresponding numerical noiseless cases to evaluate the effect of the noise. Besides, the noiseless cases are analytic and their analytic solutions are briefly presented. The Ermakov-Lewis invariant is not affected by the multiplicative noise in the three particular examples presented in this work, whereas there is a shift effect in the case of the phases

E. Cervantes-Lopez; P. B. Espinoza; A. Gallegos; H. C. Rosu

2014-06-02

392

Perfusion harmonic imaging of the human brain  

NASA Astrophysics Data System (ADS)

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.

Metzler, Volker H.; Seidel, Guenter; Wiesmann, Martin; Meyer, Karsten; Aach, Til

2003-05-01

393

Computational Aeroacoustics Cascade Model of Fan Noise  

Microsoft Academic Search

A Computational Aeroacoustics [CAA] cascade model has been built to study the generation and propagation mechanisms of noise resulting from the interaction of the fan and outlet guide vanes in a high-bypass ratio turbofan engine. Also called rotor-stator interaction noise, this noise source is a dominant contributor to the total tone and broadband noise levels produced by the engine, and

Philip Paul LePoudre

2011-01-01

394

Noise. Ag Ed Environmental Education Series.  

ERIC Educational Resources Information Center

Noise is the subject of the student resource unit to be used with high school vocational agriculture students. The nature of noise as a phenomenon and as a problem is clarified. Sources of noise pollution and the decibel levels they produce are described. Among the effects of noise pollution discussed are hearing loss, annoyance, and accidental

Tulloch, Rodney W.

395

Noise Control in Granite Stone Slicing Factory  

Microsoft Academic Search

Generally, the noise levels in Granite stone slicing factory are relatively higher than the accepted limits for occupational noise exposure. This study aimed to determine suitable and practical methods for controlling noise pollution in the factory. Three controlled areas were studied; (1) control at the noise source by reducing a vibration and friction of stone slicing machine; (2) control at

Banjarata Jolanun; Teerasak Tongparsan

396

Handbook for industrial noise control  

NASA Technical Reports Server (NTRS)

The basic principles of sound, measuring techniques, and instrumentation associated with general purpose noise control are discussed. Means for identifying and characterizing a noise problem so that subsequent work may provide the most efficient and cost effective solution are outlined. A methodology for choosing appropriate noise control materials and the proper implementation of control procedures is detailed. The most significant NASA sponsored contributions to the state of the art development of optimum noise control technologies are described including cases in which aeroacoustics and related research have shed some light on ways of reducing noise generation at its source.

1981-01-01

397

Optical harmonic generator  

DOEpatents

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).

Summers, M.A.; Eimerl, D.; Boyd, R.D.

1982-06-10

398

Noise Protection  

NASA Technical Reports Server (NTRS)

Environmental Health Systems puts forth an increasing effort in the U.S. to develop ways of controlling noise, particularly in industrial environments due to Federal and State laws, labor union insistence and new findings relative to noise pollution impact on human health. NASA's Apollo guidance control system aided in the development of a noise protection product, SMART. The basis of all SMART products is SMART compound a liquid plastic mixture with exceptional energy/sound absorbing qualities. The basic compound was later refined for noise protection use.

1980-01-01

399

A gimbaled low noise momentum wheel  

NASA Technical Reports Server (NTRS)

The bus actuators are the heart and at the same time the Achilles' heel of accurate spacecraft stabilization systems, because both their performance and their perturbations can have a deciding influence on the achievable pointing accuracy of the mission. The main task of the attitude actuators, which are mostly wheels, is the generation of useful torques with sufficiently high bandwidth, resolution and accuracy. This is because the bandwidth of the whole attitude control loop and its disturbance rejection capability is dependent upon these factors. These useful torques shall be provided, without - as far as possible - parasitic noise like unbalance forces and torques and harmonics. This is because such variable frequency perturbations excite structural resonances which in turn disturb the operation of sensors and scientific instruments. High accuracy spacecraft will further require bus actuators for the three linear degrees of freedom (DOF) to damp structural oscillations excited by various sources. These actuators have to cover the dynamic range of these disturbances. Another interesting feature, which is not necessarily related to low noise performance, is a gimballing capability which enables, in a certain angular range, a three axis attitude control with only one wheel. The herein presented Teldix MWX, a five degree of freedom Magnetic Bearing Momentum Wheel, incorporates all the above required features. It is ideally suited to support, as a gyroscopic actuator in the attitude control system, all High Pointing Accuracy and Vibration Sensitive space missions.

Bichler, U.; Eckardt, T.

1993-01-01

400

Univalent ?-Harmonic Mappings  

NASA Astrophysics Data System (ADS)

We study mappings from 2 into 2 whose components are weak solutions to the elliptic equation in divergence form, div (??u)= 0, which we call ?-harmonic mappings. We prove sufficient conditions for the univalence, i.e., injectivity, of such mappings. Moreover we prove local bounds in BMO on the logarithm of the Jacobian determinant of such univalent mappings, thus obtaining the a.e. nonvanishing of their Jacobian. In particular, our results apply to ?-harmonic mapping associated with any periodic structure and therefore they play an important role in homogenization.

Alessandrini, Giovanni; Nesi, Vincenzo

401

Prediction of Jet Noise Shielding Dimitri Papamoschou*  

E-print Network

Prediction of Jet Noise Shielding Dimitri Papamoschou* University of California, Irvine, CA 92697, USA This study is motivated by the development of aircraft that use jet noise shielding for diffraction of sound from omnidirectional point sources. However, the jet noise source is distributed

Papamoschou, Dimitri

402

Aircraft and background noise annoyance effects  

NASA Technical Reports Server (NTRS)

To investigate annoyance of multiple noise sources, two experiments were conducted. The first experiment, which used 48 subjects, was designed to establish annoyance-noise level functions for three community noise sources presented individually: jet aircraft flyovers, air conditioner, and traffic. The second experiment, which used 216 subjects, investigated the effects of background noise on aircraft annoyance as a function of noise level and spectrum shape; and the differences between overall, aircraft, and background noise annoyance. In both experiments, rated annoyance was the dependent measure. Results indicate that the slope of the linear relationship between annoyance and noise level for traffic is significantly different from that of flyover and air conditioner noise and that further research was justified to determine the influence of the two background noises on overall, aircraft, and background noise annoyance (e.g., experiment two). In experiment two, total noise exposure, signal-to-noise ratio, and background source type were found to have effects on all three types of annoyance. Thus, both signal-to-noise ratio, and the background source must be considered when trying to determine community response to combined noise sources.

Willshire, K. F.

1984-01-01

403

Analyzing nocturnal noise stratification.  

PubMed

Pollution associated to traffic can be considered as one of the most relevant pollution sources in our cities; noise is one of the major components of traffic pollution; thus, efforts are necessary to search adequate noise assessment methods and low pollution city designs. Different methods have been proposed for the evaluation of noise in cities, including the categorization method, which is based on the functionality concept. Until now, this method has only been studied (with encouraging results) for short-term, diurnal measurements, but nocturnal noise presents a behavior clearly different on respect to the diurnal one. In this work 45 continuous measurements of approximately one week each in duration are statistically analyzed to identify differences between the proposed categories. The results show that the five proposed categories highlight the noise stratification of the studied city in each period of the day (day, evening, and night). A comparison of the continuous measurements with previous short-term measurements indicates that the latter can be a good approximation of the former in diurnal period, reducing the resource expenditure for noise evaluation. Annoyance estimated from the measured noise levels was compared with the response of population obtained from a questionnaire with good agreement. The categorization method can yield good information about the distribution of a pollutant associated to traffic in our cities in each period of the day and, therefore, is a powerful tool for town planning and the design of pollution prevention policies. PMID:24548881

Rey Gozalo, Guillermo; Barrign Morillas, Juan Miguel; Gmez Escobar, Valentn

2014-05-01

404

Computer program to predict aircraft noise levels  

NASA Technical Reports Server (NTRS)

Methods developed at the NASA Lewis Research Center for predicting the noise contributions from various aircraft noise sources were programmed to predict aircraft noise levels either in flight or in ground tests. The noise sources include fan inlet and exhaust, jet, flap (for powered lift), core (combustor), turbine, and airframe. Noise propagation corrections are available for atmospheric attenuation, ground reflections, extra ground attenuation, and shielding. Outputs can include spectra, overall sound pressure level, perceived noise level, tone-weighted perceived noise level, and effective perceived noise level at locations specified by the user. Footprint contour coordinates and approximate footprint areas can also be calculated. Inputs and outputs can be in either System International or U.S. customary units. The subroutines for each noise source and propagation correction are described. A complete listing is given.

Clark, B. J.

1981-01-01

405

Environmental Noise  

NASA Astrophysics Data System (ADS)

Environmental noise may be defined as unwanted sound that is caused by emissions from traffic (roads, air traffic corridors, and railways), industrial sites and recreational infrastructures, which may cause both annoyance and damage to health. Noise in the environment or community seriously affects people, interfering with daily activities at school, work and home and during leisure time.

Rumberg, Martin

406

Aircraft Noise  

NASA Astrophysics Data System (ADS)

Aircraft industry is exposed to increasing public pressure aiming at a continuing reduction of aircraft noise levels. This is necessary to both compensate for the detrimental effect on noise of the expected increase in air traffic and improve the quality of living in residential areas around airports.

Michel, Ulf; Dobrzynski, Werner; Splettstoesser, Wolf; Delfs, Jan; Isermann, Ullrich; Obermeier, Frank

407

Noise Meter  

MedlinePLUS

... only 2 minutes can become dangerous to the human ear! Content on this page requires a newer version of Adobe Flash Player. Download Noise Meter (.exe file) Download and play the Noise Meter file on any computer, even if Flash is not installed. Print page ...

408

Harmonic Superspaces of Extended Supersymmetry. The Calculus of Harmonic Variables.  

National Technical Information Service (NTIS)

The main technical apparatus of the harmonic superspace approach to extended SUSY, the calculus of harmonic variables on homogeneous spaces of the SUSY automorphism groups, is presented in detail for N=2, 3, 4. The basic harmonics for the coset manifolds ...

E. Ivanov, S. Kalitzin Nguyen Ai Viet, V. Ogievetsky

1984-01-01

409

New aspects of subsonic aerodynamic noise theory  

NASA Technical Reports Server (NTRS)

A theory of aerodynamic noise is presented which differs from Lighthill's theory primarily in the way in which convection of the noise sources is treated. The sound directivity pattern obtained from the present theory agrees better with jet-noise directivity data than does that obtained from Lighthill's theory. The results imply that the shear-noise contribution to jet noise is smaller than previously expected.

Goldstein, M. E.; Howes, W. L.

1973-01-01

410

Fan noise research at NASA  

NASA Technical Reports Server (NTRS)

Results of recent NASA research to reduce aircraft turbofan noise are described. As the bypass ratio of a turbofan engine increases from 5 to as much as 20, the dominant source of engine noise is the fan. A primary mechanism of tone noise generation is the rotor blade wakes interacting with downstream stator vanes. Methods of analyzing rotor-stator tone noise generation are described and sample results are given. The role of an acoustic modal description is emphasized. Wind tunnel tests of model fans and nacelles are described including a novel rotating microphone technique for modal measurement. Sample far field results are given showing the effects of inlet length, and modal measurements are shown which point to a new generation mechanism. Concepts for active fan noise control at the source are addressed. Implications of the research which have general relevance to fan noise generation and control are discussed.

Groeneweg, John F.

1994-01-01

411

Fan noise research at NASA  

NASA Astrophysics Data System (ADS)

Results of recent NASA research to reduce aircraft turbofan noise are described. As the bypass ratio of a turbofan engine increases from 5 to as much as 20, the dominant source of engine noise is the fan. A primary mechanism of tone noise generation is the rotor blade wakes interacting with downstream stator vanes. Methods of analyzing rotor-stator tone noise generation are described and sample results are given. The role of an acoustic modal description is emphasized. Wind tunnel tests of model fans and nacelles are described including a novel rotating microphone technique for modal measurement. Sample far field results are given showing the effects of inlet length, and modal measurements are shown which point to a new generation mechanism. Concepts for active fan noise control at the source are addressed. Implications of the research which have general relevance to fan noise generation and control are discussed.

Groeneweg, John F.

412

Introducing Simple Harmonic Motion.  

ERIC Educational Resources Information Center

Explains the origin and significance of harmonic motion which is an important topic that has wide application in the world. Describes the phenomenon by using an auxiliary circle to help illustrate the key relationships between acceleration, displacement, time, velocity, and phase. (Contains 16 references.) (Author/YDS)

Roche, John

2002-01-01

413

A harmonic motion experiment  

NASA Astrophysics Data System (ADS)

We present a unit comprising theory, simulation and experiment for a body oscillating on a vertical spring, in which the simultaneous use of a force probe and an ultrasonic range finder enables one to explore quantitatively and understand many aspects of simple and damped harmonic motions.

Gluck, P.; Krakower, Zeev

2010-11-01

414

Enhanced Harmonic Up-Conversion Using a Hybrid HGHG-EEHG Scheme  

SciTech Connect

We introduce a novel harmonic generation scheme which can be used, for a given desired harmonic, to achieve higher bunching factors, weaker chicanes, and/or less final energy spread than can be achieved using Echo-Enabled Harmonic Generation. This scheme only requires a single laser with relatively low power, and is a hybrid of High-Gain Harmonic Generation and EEHG. We present a design of this scheme applied to the Next Generation Light Source (NGLS).

Marksteiner, Quinn R. [Los Alamos National Laboratory; Bishofberger, Kip A. [Los Alamos National Laboratory; Carlsten, Bruce E. [Los Alamos National Laboratory; Freund, Henry P. [Los Alamos National Laboratory; Yampolsky, Nikolai A. [Los Alamos National Laboratory

2012-04-30

415

Multichannel active noise control system for local spectral reshaping of multifrequency noise  

NASA Astrophysics Data System (ADS)

This paper discusses the development of a multichannel active system for local spectral reshaping of multitone noise. The aim of this work is to design a real practical system that performs well in local active noise control (ANC) applications, and so improving the comfort sensation produced by enclosed sound fields. The adaptive algorithm implemented in the controller is a multichannel extension of the multifrequency adaptive equalizer developed by Kuo. The philosophy behind these equalizers lies in independently controlling some given frequencies of a primary signal. Moreover, the algorithm should manage to generate usefully sized zones of equalization in order to allow for the head motion of somebody with restricted mobility; for example, a passenger seated in a car. To verify the successful implementation of the multichannel system, experiments were carried out under listening room conditions. The developed prototype consists of an array of up to four microphones used as error sensors and two secondary sources. A 4100-type Bruel and Kjaer mannequin with two calibrated microphones at the ear canals was used to measure sound levels in a hypothetical listener's head. Different synthesized repetitive noises were used, as reference signals, specifically repetitive noise with harmonics of 15, 20, and 28 Hz, as well as an 80 Hz single tone. The equalized points include an area around the error sensor positions, and these are measured using the mannequin and an x- y moving platform. The extent to which the experimental equalization zones obtained favourable results validates the multichannel local ANC equalization system. Different error sensor positions around the listener head were also tested. The residual field inside the equalization zone was measured in all cases.

de Diego, M.; Gonzalez, A.; Ferrer, M.; Piero, G.

2004-07-01

416

Harmonic Fluxes and Electromagnetic Forces of Concentric Winding Brushless Permanent Magnet Motor  

Microsoft Academic Search

Brushless permanent magnet motors have been widely used in home applications and industrial fields. These days, high efficiency and low noise motors are demanded from the view point of environment. Electromagnetic noise and iron loss of the motor are produced by the harmonic fluxes and electromagnetic forces. However, order and space pattern of these have not been discussed in detail.

Fuminori Ishibashi; Ryo Takemasa; Makoto Matsushita; Takashi Nishizawa; Shinichi Noda

2007-01-01

417

Noise and soundscape in Rome  

NASA Astrophysics Data System (ADS)

Noise pollution is an old problem in Rome. In 45 B.C. the Lex Julia Municipalis limited carriage traffic in the city center to specific times. Road traffic constitutes the most important and widespread noise source, and several investigations have been conducted since 1972, some aimed at developing a numerical model for predicting the hourly LAeq level. In order to reduce the large impact of this type of noise some measures have been carried out, including surfacing with porous asphalt, erection of noise barriers, limitation in time and spacing of private traffic, etc. However, most of the public complaints deal with noise from equipment operation and recreational activities rather than transportation systems. Moreover, the most famous tourist areas opened to pedestrians only are not as quiet as expected but their sound environment is usually rated more acceptable than noise from other sources at the same level. In compliance with the Italian legislation on noise, the Municipality of Rome issued a noise zoning code for its own territory, and a noise mapping is in progress, pursuant to the requirements of the 2002/49/EC European directive. A Geographical Information System has been also developed to manage all the aspects of noise pollution.

Brambilla, Giovanni

2001-05-01

418

Proceedings of the 1987 national conference on noise control engineering: High technology for noise control  

SciTech Connect

This book consists of nine sections, each containing several papers. The section titles are: Emission: Noise Sources; Physical Phenomena; Noise Control Elements; Vibration: Generation, Transmission, Isolation and Reduction; Immission: Physical Aspects of Environmental Noise; Immission: Effects of Noise; Analysis; Requirements; and Biomedical Uses of Acoustics.

Tichy, J.; Hayek, S.

1987-01-01

419

Harmonic Spatial Coherence Imaging: An Ultrasonic Imaging Method Based on Backscatter Coherence  

PubMed Central

HSCI and SLSC imaging less sensitive to clutter because it has low spatial coherence. The method is based on the coherence of the second harmonic backscatter. Because the same signals that are used to construct harmonic B-mode images are also used to construct HSCI images, the benefits obtained with harmonic imaging are also applicable to HSCI. Harmonic imaging has been the primary tool for suppressing clutter in diagnostic ultrasound imaging, however second harmonic echoes are not necessarily immune to the effects of clutter. HSCI and SLSC imaging are less sensitive to clutter because it has low spatial coherence. Harmonic Spatial Coherence Imaging shows favorable imaging characteristics such as improved contrast-to-noise ratio (CNR), improved speckle signal-to-noise ratio (SNR), and better delineation of borders and other structures compared to fundamental and harmonic B-mode imaging. CNRs of up to 1.9 were obtained from in vivo imaging of human cardiac tissue with HSCI, compared to 0.6, 0.9, and 1.5 in fundamental B-mode, harmonic B-mode, and SLSC imaging, respectively. In vivo experiments in human liver tissue demonstrated SNRs of up to 3.4 for HSCI compared to 1.9 for harmonic B-mode. Nonlinear simulations of a heart chamber model were consistent with the in vivo experiments. PMID:22547276

Dahl, Jeremy J; Jakovljevic, Marko; Pinton, Gianmarco F.; Trahey, Gregg E.

2012-01-01

420

The Airframe Noise Reduction Challenge  

NASA Technical Reports Server (NTRS)

The NASA goal of reducing external aircraft noise by 10 dB in the near-term presents the acoustics community with an enormous challenge. This report identifies technologies with the greatest potential to reduce airframe noise. Acoustic and aerodynamic effects will be discussed, along with the likelihood of industry accepting and implementing the different technologies. We investigate the lower bound, defined as noise generated by an aircraft modified with a virtual retrofit capable of eliminating all noise associated with the high lift system and landing gear. However, the airframe noise of an aircraft in this 'clean' configuration would only be about 8 dB quieter on approach than current civil transports. To achieve the NASA goal of 10 dB noise reduction will require that additional noise sources be addressed. Research shows that energy in the turbulent boundary layer of a wing is scattered as it crosses trailing edge. Noise generated by scattering is the dominant noise mechanism on an aircraft flying in the clean configuration. Eliminating scattering would require changes to much of the aircraft, and practical reduction devices have yet to receive serious attention. Evidence suggests that to meet NASA goals in civil aviation noise reduction, we need to employ emerging technologies and improve landing procedures; modified landing patterns and zoning restrictions could help alleviate aircraft noise in communities close to airports.

Lockhard, David P.; Lilley, Geoffrey M.

2004-01-01

421

Detecting, Locating, and Characterizing Remote Power Sources  

SciTech Connect

A feasibility study to determine range and back-azimuth detection methods for an isolated generator powering common loads was completed. The study deployed 3-component E and B field sensors with sampling rates of 100 kHz in a low noise test location in Southern California. Scripted power and load cycling was recorded at ranges of 40 meters to 4 km from the generator/load source. Three loads were tested: a 100 meter string of lights, an inverter powering an air blower, and a resistive heater. No E-field or B-field radiated signals were detected at ranges greater than 40 meters with a signal-to-noise ratio greater than one. Large variations in the broadband background electromagnetic noise were observed and may have been responsible for null detections at some measurement locations. At the 40-meter station, a frequency shift upon generator loading was observed for all load types. Harmonics from the detuned generator (operating at 56.7 Hz) could be observed for all load types but were most pronounced for the inverter source. A back-azimuth estimation methodology was applied to detected harmonics with stable and consistent results. For the inverter source, consistent back azimuths to the source were determined for the fundamental and higher detected harmonics up to the 31st. The method was applied to narrow band ''noise'' at 60 Hz and produced bimodal directions that roughly pointed to large population centers. Details of the method are withheld in this report pending a record of invention submittal. Although the generator/load combinations, which utilized wiring that tended to minimize stray signals, cannot yet be detected at large stand-off range without application of noise-filtering methods, the back-azimuth method appears promising and should be applied to other source types and frequency ranges where an E and B field can be detected. A record of invention describing this new back-azimuth method has been submitted to the Intellectual Property Law Group.

Harben, P; Carrigan, C; Kirkendall, B; Simons, D

2005-02-10

422

Noise Pollution  

Microsoft Academic Search

Noise is playing an ever-increasing role in our lives and seems a regrettable but ultimately avoidable corollary of current\\u000a technology. The trend toward the use of more automated equipment, sports and pleasure craft, high-wattage stereo, larger construction\\u000a machinery, and the increasing numbers of ground vehicles and aircraft has created a gradual acceptance of noise as a natural\\u000a byproduct of progress.

James P. Chambers

423

Airframe noise: A design and operating problem  

NASA Technical Reports Server (NTRS)

A critical assessment of the state of the art in airframe noise is presented. Full-scale data on the intensity, spectra, and directivity of this noise source are evaluated in light of the comprehensive theory developed by Ffowcs Williams and Hawkings. Vibration of panels on the aircraft is identified as a possible additional source of airframe noise. The present understanding and methods for prediction of other component sources - airfoils, struts, and cavities - are discussed. Operating problems associated with airframe noise as well as potential design methods for airframe noise reduction are identified.

Hardin, J. C.

1976-01-01

424

NASA progress in aircraft noise prediction  

NASA Technical Reports Server (NTRS)

Langley Research Center efforts to develop a methodology for predicting the effective perceived noise level (EPNL) produced by jet-powered CTOL aircraft to an accuracy of + or - 1.5 dB are summarized with emphasis on the aircraft noise prediction program (ANOPP) which contains a complete set of prediction methods for CTOL aircraft including propulsion system noise sources, aerodynamic or airframe noise sources, forward speed effects, a layered atmospheric model with molecular absorption, ground impedance effects including excess ground attenuation, and a received noise contouring capability. The present state of ANOPP is described and its accuracy and applicability to the preliminary aircraft design process is assessed. Areas are indicated where further theoretical and experimental research on noise prediction are needed. Topics covered include the elements of the noise prediction problem which are incorporated in ANOPP, results of comparisons of ANOPP calculations with measured noise levels, and progress toward treating noise as a design constraint in aircraft system studies.

Raney, J. P.; Padula, S. L.; Zorumski, W. E.

1981-01-01

425

The behavior of quantization spectra as a function of signal-to-noise ratio  

NASA Technical Reports Server (NTRS)

An expression for the spectrum of quantization error in a discrete-time system whose input is a sinusoid plus white Gaussian noise is derived. This quantization spectrum consists of two components: a white-noise floor and spurious harmonics. The dithering effect of the input Gaussian noise in both components of the spectrum is considered. Quantitative results in a discrete Fourier transform (DFT) example show the behavior of spurious harmonics as a function of the signal-to-noise ratio (SNR). These results have strong implications for digital reception and signal analysis systems. At low SNRs, spurious harmonics decay exponentially on a log-log scale, and the resulting spectrum is white. As the SNR increases, the spurious harmonics figure prominently in the output spectrum. A useful expression is given that roughly bounds the magnitude of a spurious harmonic as a function of the SNR.

Flanagan, M. J.

1991-01-01

426

Interactive Evolutionary Computation with Fitness Noise and Its Convergence Robustness  

Microsoft Academic Search

Noise is an important factor that influences the performance of evolutionary computation (EC). Much research on noise was reported in traditional EC, but less in IEC (interactive evolutionary computation). The definition, source, type of noise and methods to deal with noise in EC are reviewed firstly. Secondly, related with the rational user in IEC, the convergence robustness against fitness noise

Guo-Sheng HAO; SHI You-Qun; HUANG Yong-Qing; L Jun-Huai; GUO Guang-Song

2007-01-01

427

State-of-the-art of turbofan engine noise control  

NASA Technical Reports Server (NTRS)

The technology of turbofan engine noise reduction is surveyed. Specific topics discussed include: (1) new fans for low noise; (2) fan and core noise suppression; (3) turbomachinery noise sources; and (4) a new program for improving static noise testing of fans and engines.

Jones, W. L.; Groeneweg, J. F.

1977-01-01

428

Computing prime harmonic sums  

NASA Astrophysics Data System (ADS)

We discuss a method for computing sum_{p le x} 1/p , using time about x^{2/3} and space about x^{1/3} . It is based on the Meissel-Lehmer algorithm for computing the prime-counting function pi(x) , which was adapted and improved by Lagarias, Miller, and Odlyzko. We used this algorithm to determine the first point at which the prime harmonic sum first crosses 4.

Bac