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1

An Analysis of Shot Noise Propagation and Amplificationin Harmonic Cascade FELs  

SciTech Connect

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

Huang, Z.; /SLAC

2006-12-11

2

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

3

Understanding Slat Noise Sources  

NASA Technical Reports Server (NTRS)

Model-scale aeroacoustic tests of large civil transports point to the leading-edge slat as a dominant high-lift noise source in the low- to mid-frequencies during aircraft approach and landing. Using generic multi-element high-lift models, complementary experimental and numerical tests were carefully planned and executed at NASA in order to isolate slat noise sources and the underlying noise generation mechanisms. In this paper, a brief overview of the supporting computational effort undertaken at NASA Langley Research Center, is provided. Both tonal and broadband aspects of slat noise are discussed. Recent gains in predicting a slat s far-field acoustic noise, current shortcomings of numerical simulations, and other remaining open issues, are presented. Finally, an example of the ever-expanding role of computational simulations in noise reduction studies also is given.

Khorrami, Medhi R.

2003-01-01

4

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

5

Noise-resistant fitting for spherical harmonics.  

PubMed

Spherical harmonic (SH) basis functions have been widely used for representing spherical functions in modeling various illumination properties. They can compactly represent low-frequency spherical functions. However, when the unconstrained least square method is used for estimating the SH coefficients of a hemispherical function, the magnitude of these SH coefficients could be very large. Hence, the rendering result is very sensitive to quantization noise (introduced by modern texture compression like S3TC, IEEE half float data type on GPU, or other lossy compression methods) in these SH coefficients. Our experiments show that, as the precision of SH coefficients is reduced, the rendered images may exhibit annoying visual artifacts. To reduce the noise sensitivity of the SH coefficients, this paper first discusses how the magnitude of SH coefficients affects the rendering result when there is quantization noise. Then, two fast fitting methods for estimating the noise-resistant SH coefficients are proposed. They can effectively control the magnitude of the estimated SH coefficients and, hence, suppress the rendering artifacts. Both statistical and visual results confirm our theory. PMID:16509384

Lam, Ping-Man; Leung, Chi-Sing; Wong, Tien-Tsin

2006-01-01

6

A LOW NOISE RF SOURCE FOR RHIC.  

SciTech Connect

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

HAYES,T.

2004-07-05

7

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

8

Prediction of far-field harmonic noise from propellers  

NASA Astrophysics Data System (ADS)

A FORTRAN program for estimating the discrete frequency free-field noise from an isolated straight blade single propeller which is in uniform motion or stationary in a lossless atmosphere is given. Blade sweep is unlikely, however, to have a significant effect up to tip Mach numbers of 0.9. It is assumed that the noise sources are compact chordwise so that they are line sources; that assumption excludes advanced propellers and prop fans. The input to the program is ambient static pressure and temperature, source/receiver relative geometry, propeller operating conditions, and blade geometry and lift coefficient at a number of radial stations. If the load distribution is not known, a default distribution is provided for which power supplied and propeller thrust generated is required. Predictions are compared with available limited data measured in a wind-tunnel, and a sketch shows a typical correlation. The program is provided on disc as ESDUpac 9133, and information is given on the format for the input and output, illustrated by two worked examples. A graphical method for the maximum harmonic levels from a static propeller is given in ESDU 76020.

1991-11-01

9

Thermal noise in coupled harmonic oscillators  

NASA Astrophysics Data System (ADS)

The current generation of interferometric gravitational-wave detectors typically uses test masses suspended as single-stage, low-loss pendula. More advanced detectors are expected to suspend test masses from compound pendula to improve both seismic and thermal noise. Predicting the thermal noise in a single pendulum is straightforward, but for compound systems the math required can get hairy. Here we present a practical procedure for calculating thermal noise in a system of coupled oscillators, and a set of simple rules for doing ``back of the envelope'' estimates. We also show how the loss angles for each stage can be inferred from the Q's of the normal modes, and vice versa.

Black, Eric; Cameron, Robert

2000-04-01

10

ECM Noise Source.  

National Technical Information Service (NTIS)

An investigation of the feasibility of utilizing a cascaded series of pressurized gas spark gaps to achieve output noise signals in X-band is presented. This research is of significance to the Air Force as a means of generating broad-band noise signals fo...

A. Mondelli V. Fargo W. Clark

1974-01-01

11

Noise Amplification in Echo-Enabled Harmonic Generation (EEHG)  

SciTech Connect

Two essential elements of a seeded FEL based on the echo-enabled harmonic generation (EEHG) are the undulator-modulators, in which a laser beam modulates the beam energy. We study how the interaction of electrons in these undulators changes the noise properties of the beam. This paper is based on the method of noise analysis developed in Ref. [1] and extends it for the case of EEHG.

Stupakov, Gennady

2010-08-25

12

Harmonic and noise radiometer-scatterometers  

NASA Astrophysics Data System (ADS)

The power levels required for the transmitters of path scatterometers and scanning scatterometers are computed by optimizing measuring conditions at several wavelengths. The energy losses due to the beam displacement during the scanning within the time of radio-wave propagation are calculated, and methods for minimizing these losses are recommended. Special attention is given to the problem of achieving high-precision measurements of radar signals through averaging independent signal samples from airborne and ground scatterometers. The characteristics of noise radiometer-scatterometers and the usefulness of data from such an instrument are discussed.

Gordon, Z. I.

13

Harmonic source and type identification in a radial distribution system  

Microsoft Academic Search

To aid in locating the source and type of harmonics in a distribution system, a computer program called HARM TRACER has been developed. HARM TRACER is a reverse harmonic power flow study program which traces the flow of harmonics in a radial distribution system from the point of measurement to the harmonic source or sources. It does so by considering

Asrat Teshome

1991-01-01

14

A nonlinear method of removing harmonic noise in geophysical data  

NASA Astrophysics Data System (ADS)

A nonlinear, adaptive method to remove the harmonic noise that commonly resides in geophysical data is proposed in this study. This filtering method is based on the ensemble empirical mode decomposition algorithm in conjunction with the logarithmic transform. We present a synthetic model study to investigate the capability of signal reconstruction from the decomposed data, and compare the results with those derived from other 2-D adaptive filters. Applications to the real seismic data acquired by using an ocean bottom seismograph and to a shot gather of the ground penetrating radar demonstrate the robustness of this method. Our work proposes a concept that instead of Fourier-based approaches, the harmonic noise removal in geophysical data can be achieved effectively by using an alternative nonlinear adaptive data analysis method, which has been applied extensively in other scientific studies.

Jeng, Y.; Chen, C.-S.

2011-06-01

15

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

16

Low noise constant current source for bias dependent noise measurements  

SciTech Connect

A low noise constant current source used for measuring the 1/f noise in disordered systems in ohmic as well as nonohmic regime is described. The source can supply low noise constant current starting from as low as 1 {mu}A to a few tens of milliampere with a high voltage compliance limit of around 20 V. The constant current source has several stages, which can work in a standalone manner or together to supply the desired value of load current. The noise contributed by the current source is very low in the entire current range. The fabrication of a low noise voltage preamplifier modified for bias dependent noise measurements and based on the existing design available in the MAT04 data sheet is also described.

Talukdar, D.; Bose, Suvendu; Bardhan, K. K. [Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India); Chakraborty, R. K. [Bidhannagar College, EB - 2, Bidhannagar, Kolkata 700064 (India)

2011-01-15

17

Annoyance due to Combined Community Noise Sources  

NASA Astrophysics Data System (ADS)

The relative contributions of various major noise sources to annoyance have not been clearly established. Two experiments were conducted to assess the effect of combined community noise sources on annoyance. The first experiment established baseline relationships between annoyance and noise level for three community noise sources presented individually (jet aircraft flyovers, traffic, and air conditioner) which differed from one another in spectral and temporal characteristics. Forty-eight subjects rated the annoyance at the end of each session for each noise source presented separately at four different noise levels. The results indicated that the slope of the linear relationship between annoyance and noise level for traffic noise was significantly different from that of aircraft and of air conditioner noise, which had the same slopes. In the second experiment, aircraft noise was defined as the major noise source and traffic and air conditioner as background noise sources. The effects of the noise level differences between aircraft and background noise for three total noise levels and type of background noise source on rated annoyance were determined. This experiment required 216 subjects to make either total or source-specific annoyance judgments, or a combination of the two, for each of 14 experimental noise conditions presented as sessions. For both experiments, an additional dependent measure was investigated as a possible objective correlate to rated annoyance. This measure was the amount of the subjects' subconscious body movements as measured by accelerometers mounted underneath their chairs. Both the type of background noise source and the type or combination of annoyance ratings requested were found to have an effect on annoyance. The results of this research have important implications for community noise criteria and for the application of community noise response prediction models. Both should be designed to account for spectral, duration, and temporal differences between noise sources as well as noise levels. Furthermore, the type of annoyance of interest, e.g., total or source-specific, should be considered. As an attempt to find a correlated measure of annoyance, the body movement results were inconclusive for both experiments.

Willshire, Kelli Francisco

18

Speech perception in noise with a harmonic complex excited vocoder.  

PubMed

A cochlear implant (CI) presents band-pass-filtered acoustic envelope information by modulating current pulse train levels. Similarly, a vocoder presents envelope information by modulating an acoustic carrier. By studying how normal hearing (NH) listeners are able to understand degraded speech signals with a vocoder, the parameters that best simulate electric hearing and factors that might contribute to the NH-CI performance difference may be better understood. A vocoder with harmonic complex carriers (fundamental frequency, f0 = 100 Hz) was used to study the effect of carrier phase dispersion on speech envelopes and intelligibility. The starting phases of the harmonic components were randomly dispersed to varying degrees prior to carrier filtering and modulation. NH listeners were tested on recognition of a closed set of vocoded words in background noise. Two sets of synthesis filters simulated different amounts of current spread in CIs. Results showed that the speech vocoded with carriers whose starting phases were maximally dispersed was the most intelligible. Superior speech understanding may have been a result of the flattening of the dispersed-phase carrier's intrinsic temporal envelopes produced by the large number of interacting components in the high-frequency channels. Cross-correlogram analyses of auditory nerve model simulations confirmed that randomly dispersing the carrier's component starting phases resulted in better neural envelope representation. However, neural metrics extracted from these analyses were not found to accurately predict speech recognition scores for all vocoded speech conditions. It is possible that central speech understanding mechanisms are insensitive to the envelope-fine structure dichotomy exploited by vocoders. PMID:24448721

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

2014-04-01

19

Flow noise source-resonator coupling  

SciTech Connect

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

Pollack, M.L. [Lockheed Martin Corp., Schenectady, NY (United States)

1997-11-01

20

Lifetime increase using passive harmonic cavities insynchrotronlight sources  

SciTech Connect

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

Byrd, J.M.; Georgsson, M.

2000-09-22

21

The sources of jet noise: experimental evidence  

Microsoft Academic Search

The primary objective of this investigation is to determine experimentally the sources of jet mixing noise. In the present study, four different approaches are used. It is reasonable to assume that the characteristics of the noise sources are imprinted on their radiation fields. Under this assumption, it becomes possible to analyse the characteristics of the far-field sound and then infer

CHRISTOPHER K. W. T AM; K. V ISWANATHAN

2008-01-01

22

Use of DFT windows in signal-to-noise ratio and harmonic distortion computations.  

National Technical Information Service (NTIS)

The discrete Fourier transform (DFT) is used frequently used in the computation of the signal-to-noise ratio (SNR) and harmonic distortion. To estimate the SNR or harmonic distortion, a sine wave is applied to the digitizing system under test. When the da...

O. M. Solomon

1993-01-01

23

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. Our analysis is based on numerical wavefield simulations in heterogeneous media. This allows us to calculate inter-station correlations for arbitrarily distributed noise sources where - as in the real Earth - different frequencies are generated in different locations. Using adjoint methods, we compute the exact structural sensitivities for a given combination of source distribution, processing scheme, and measurement technique. The key results of our study are as follows: (1) Heterogeneous noise sources and subjective processing, such as the application of spectral whitening, have profound effects on noise correlation wave forms. (2) Nevertheless, narrow-band traveltime measurements are only weakly affected by heterogeneous noise sources and processing. This result is in accord with previous analytical studies, and it explains the similarity of noise and earthquake tomographies that only exploit traveltime information. (3) Spatially heterogeneous noise sources can lead to structural sensitivities that deviate strongly from the classical cigar-shaped sensitivities. Furthermore, the frequency dependence of sensitivity kernels can go far beyond the well-know dependence of the Fresnel zone width on frequency. Our results imply that a meaningful application of modern full waveform inversion methods to noise correlations is not possible unless both the noise source distribution and the processing scheme are properly taken into account. Failure to do so can lead to erroneous misfit quantifications, slow convergence of optimisation schemes, and to the appearance of tomographic artefacts that reflect the incorrect structural sensitivity. These aspects acquire special relevance in the monitoring of subtle changes of subsurface structure that may be polluted when the time dependence of heterogeneous noise sources is ignored.

Fichtner, Andreas

2014-05-01

24

Investigation of hydraulic transmission noise sources  

NASA Astrophysics Data System (ADS)

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

Klop, Richard J.

25

Integrated quantum voltage noise source for Johnson noise thermometry  

NASA Astrophysics Data System (ADS)

We have been developing a new implementation of quantum voltage noise source (QVNS), an integrated QVNS (IQVNS), for Johnson noise thermometry (JNT) in thermal metrology. We designed an IQVNS chip based on rapid single flux quantum (RSFQ) technology. A general formula for the output power spectrum has been derived by using a Fourier analysis method, which shows that the spectrum is calculable with sufficiently small errors for practical JNT measurements.

Maezawa, Masaaki; Yamada, Takahiro; Urano, Chiharu

2014-05-01

26

Speckle Noise Reduction by Superposing Many Higher Harmonic Images  

Microsoft Academic Search

A novel ultrasonic imaging method offering high resolution and high-quality images for clinical diagnosis has been developed. This method produces an image using many higher harmonic components contained in the echoes from the inside of a human body, generated due to ultrasonic nonlinear propagation through biological tissues. A new ultrasonic probe has been designed to detect higher harmonic components efficiently

Iwaki Akiyama; Akihisa Ohya; Shigemi Saito

2005-01-01

27

Distribution of noise sources for seismic interferometry  

NASA Astrophysics Data System (ADS)

We demonstrate that the distribution of seismic noise sources affects the accuracy of Green's function estimates and therefore isotropic and anisotropic tomographic inversions for both velocity and attenuation. We compare three methods for estimating seismic noise source distributions and quantify the potential error in phase velocity, azimuthal anisotropy and attenuation estimates due to inhomogenous source distributions. The methods include: (1) least-squares inversion of beamformer output, (2) a least-squares inversion of year long stacked noise correlation functions assuming both a 2-D plane wave source density model and (3) a 3-D plane wave source density model. We use vertical component data from the 190 stations of the Southern California Seismic Network and some US Array stations for 2008. The good agreement between the three models suggests the 2-D plane wave model, with the fewest number of unknown parameters, is generally sufficient to describe the noise density function for tomographic inversions. At higher frequencies, 3-D and beamforming models are required to resolve peaks in energy associated with body waves. We illustrate and assess isotropic and azimuthally anisotropic phase velocity and attenuation uncertainties for the noise source distribution in southern California by inverting isotropic lossless synthetic Fourier transformed noise correlation function predictions from modelled 2-D source distribution. We find that the variation in phase velocity with azimuth from inhomogeneous source distribution yields up to 1 per cent apparent peak-to-peak anisotropy. We predict apparent attenuation coefficients from our lossless synthetics on the same order of magnitude as those previously reported for the region from ambient noise. Since noise source distributions are likely inhomogeneous varying regionally and with time, we recommend that noise correlation studies reporting attenuation and anisotropy incorporate source density information.

Harmon, Nicholas; Rychert, Catherine; Gerstoft, Peter

2010-12-01

28

Harmonics in multiplicative and additive noise: parameter estimation using cyclic statistics  

Microsoft Academic Search

The problem of concern here is parameter estimation of harmonics in the presence of multiplicative and additive noise. Cyclic statistics are employed to estimate the frequencies and phases, after which the time series is demodulated and cumulants of the noise processes are estimated. The latter are then supplied to linear or nonlinear cumulant-based algorithms to identify ARMA model parameters for

Georgios B. Giannakis; Guotong Zhou

1995-01-01

29

Ionospheric Observation of VLF Electrostatic Noise Related to Harmonics of the Proton Gyrofrequency.  

National Technical Information Service (NTIS)

An observation of electrostatic noise bands observed with the Javelin 8.46 sounding rocket is presented. It is shown that these noise bands are related to harmonics of the proton gyrofrequency. This observation is believed to be the first confirmation of ...

S. R. Mosier D. A. Gurnett

1969-01-01

30

Investigation of hydraulic transmission noise sources  

Microsoft Academic Search

Advanced hydrostatic transmissions and hydraulic hybrids show potential in new market segments such as commercial vehicles and passenger cars. Such new applications regard low noise generation as a high priority, thus, demanding new quiet hydrostatic transmission designs. In this thesis, the aim is to investigate noise sources of hydrostatic transmissions to discover strategies for designing compact and quiet solutions.^ A

Richard J Klop

2010-01-01

31

Energy Diffusion in Harmonic System with Conservative Noise  

NASA Astrophysics Data System (ADS)

We prove diffusive behaviour of the energy fluctuations in a system of harmonic oscillators with a stochastic perturbation of the dynamics that conserves energy and momentum. The results concern pinned systems in any dimension, or unpinned systems in dimension.

Basile, Giada; Olla, Stefano

2014-06-01

32

The role of load harmonics in audible noise of electrical transformers  

NASA Astrophysics Data System (ADS)

Harmonic components in load currents have a larger impact on the load noise level of transformers than might be expected from their amplitude. There are several reasons for this larger impact: (a) the interaction of higher harmonics with the large fundamental load current at power frequency, (b) the increasing sound radiation efficiency with increasing frequency, and (c) the greater sensitivity of the human ear to higher frequencies, which is considered in sound measurements by applying the A-weighting filter. This paper describes the process of generation, transmission, and emission of load noise in the presence of load harmonics. A calculation scheme is presented that is able to estimate the noise increase and the noise spectrum of electrical transformers under non-sinusoidal load conditions. The proposed calculation scheme is applied to three practical examples.

Ertl, Michael; Voss, Stephan

2014-04-01

33

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

34

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

35

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

2014-04-01

36

Active Control of Aerodynamic Noise Sources  

NASA Technical Reports Server (NTRS)

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

Reynolds, Gregory A.

2001-01-01

37

Comparison of adaptive filter performance in estimating the noise statistics for harmonic models  

Microsoft Academic Search

Electric power system harmonics and interharmonics having random variations in magnitude are modeled as state variables of a discrete-time stochastic system. The problem of adaptively estimating the statistical characteristics of the process and measurement noises is addressed. Incorporating the unknown noise covariance in the system leads to a state-multiplicative-noise model resulting in a nonlinear estimation problem. The main contribution of

E. Yaz; Y. Gao; K. Olejniczak

1999-01-01

38

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

39

Non-linear least squares estimation for harmonics in multiplicative and additive noise  

Microsoft Academic Search

We consider the problem of estimating the frequency of a complex harmonic in Doppler radar signals in the presence of additive and multiplicative noise, which may be colored and non-Gaussian. Two nonlinear least-squares (NLLS) estimators, NLLS1 and NLLS2, are proposed, which consist of matching the data and the squared data, respectively, with a constant amplitude harmonic. Expressions for the asymptotic

M. Ghogho; A. Swami; A. Nandi

1998-01-01

40

Noise-free measurement of harmonic oscillators with instantaneous interactions.  

PubMed

We present a method of measuring the quantum state of a harmonic oscillator through instantaneous probe-system selective interactions of the Jaynes-Cummings type. We prove that this scheme is robust to general decoherence mechanisms, allowing the possibility of measuring fast-decaying systems in the weak-coupling regime. This method could be applied to different setups: motional states of trapped ions, microwave fields in cavity or circuit QED, and even intracavity optical fields. PMID:17358585

França Santos, M; Giedke, G; Solano, E

2007-01-12

41

Quantization noise in digital signal processing by harmonic analysis in a synthetic-aperture radar  

Microsoft Academic Search

The paper derives and analyzes expressions for assessing the effect of quantization noise arising in digital signal processing by harmonic analysis in a synthetic-aperture radar on the output signal for an arbitrary weight function in an FFT processor. The output signal-to-noise ratio is shown to depend on the FFT base size, the digit-representation length in the processing system, and the

N. A. Sazonov

1985-01-01

42

Noise Source for Calibrating a Microwave Polarimeter  

NASA Technical Reports Server (NTRS)

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

Piepmeier, Jeffrey R.; Kim, Edward J.

2006-01-01

43

Aeroacoustic Codes for Rotor Harmonic and Bvi Noise--Camrad.MOD1/Hires.  

National Technical Information Service (NTIS)

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 su...

T. F. Brooks D. D. Boyd C. L. Burley J. R. Jolly

1996-01-01

44

Noise Sources Characterization of Automotive HVAC Systems  

Microsoft Academic Search

The noise sources and mechanisms of the front and rear HVAC systems of an automotive are characterized experimentally. The front system has three main outlet ducts equipped with louvers and operates in two modes of bypass and recirculation. The inlet and outlet sides of the rear system are both located in the cabin; hence, it always works only on the

Vahid Madani

2002-01-01

45

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

46

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

47

Critical impedance based automatic identification of harmonic sources in deregulated power industry  

Microsoft Academic Search

In this paper automatic identification of origin of harmonic source in deregulated power sector has been carried out. It is a well known fact that Critical impedance method for detection of harmonic disturbances caused between utility and source side has already been reported in literature. Taking the critical impedance method as the base harmonic sources are identified in deregulated power

Kriti Vaid; P. Srikanth; Y. R. Sood

2011-01-01

48

TD-PSOLA versus harmonic plus noise model in diphone based speech synthesis  

Microsoft Academic Search

In an effort to select a speech representation for our next generation concatenative text-to-speech synthesizer, the use of two candidates is investigated; TD-PSOLA and the harmonic plus noise model, HNM. A formal listening test has been conducted and the two candidates have been rated regarding intelligibility, naturalness and pleasantness. Ability for database compression and computational load is also discussed. The

Ann Syrdal; Yannis Stylianou; Laurie Garrison; Alistair Conkie; Juergen Schroeter

1998-01-01

49

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

PubMed Central

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

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

2010-01-01

50

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

SciTech Connect

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

Ma, H. [Illinois Inst. of Tech., Chicago, IL (United States). Dept. of Electrical and Computer Engineering; Girgis, A.A. [Clemson Univ., SC (United States). Dept. of Electrical and Computer Engineering

1996-07-01

51

Ranking of compressor station noise sources using sound intensity techniques  

Microsoft Academic Search

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

W. D. Johns; R. H. Porter

1987-01-01

52

Sources of noise in magneto-optical readout  

NASA Technical Reports Server (NTRS)

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

Mansuripur, M.

1991-01-01

53

Forward velocity effects on jet noise with dominant internal noise source  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

54

A single chip broadband noise source for noise measurements at cryogenic temperatures  

Microsoft Academic Search

This paper presents the design and performance of a single chip broadband noise source dedicated for on-chip measurements in a cryogenic environment. The noise source is used to generate the two input noise powers Pc and Ph which are required by the commonly used Y-factor method. High accuracy in temperature control and impedance presented to the device under test is

D. Bruch; F. Schafer; M. Seelmann-Eggebert; B. Aja; I. Kallfass; A. Leuther; M. Schlechtweg; O. Ambacher

2011-01-01

55

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

SciTech Connect

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 noise into their estimate of the fundamental. Bounds are developed for these errors for least-squares four-parameter (amplitude, frequency, phase, and offset) sine-fit algorithms. The errors are functions of the number of periods in the record, the number of samples in the record, the harmonic order, and fundamental and harmonic amplitudes and phases. The bounds do not apply to cases in which harmonic components become aliased.

Deyst, J.P.; Souders, T.M. [National Inst. of Standards and Technology, Gaithersburg, MD (United States); Solomon, O.M. [Sandia National Labs., Albuquerque, NM (United States)

1994-03-01

56

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

57

PSPICE circuit simulation of microbolometer infrared detectors with noise sources  

NASA Astrophysics Data System (ADS)

In this paper, we present a method of incorporating various types of noise in circuit simulation of a microbolometer infrared detector to analyze the effect of noise on its performance. This ability of simulating electro-thermal performance of microbolometers in circuit simulation platform along with their noise performance allows designing of its suitable readout integrated circuit (ROIC). Being an electro-thermal device, a microbolometer has both the electrical and thermal components interacting with each other. Therefore, the noise sources existing in standard circuit simulators cannot predict the noise of a microbolometer correctly. Disturbances coming from the background radiation, device temperature fluctuations, flicker noise and the Johnson noise etc. contribute in the total noise of a microbolometer element. All these components of noise can be incorporated using the proposed simulation technique. The technique also allows modifying the frequency response of the noise in simulations as per the user defined noise spectrum, making it suitable for any type of microbolometer.

Saxena, Raghvendra Sahai; Panwar, Arun; Semwal, S. K.; Rana, P. S.; Gupta, Sudha; Bhan, R. K.

2012-11-01

58

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

NASA Technical Reports Server (NTRS)

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

Miles, Jeffrey Hilton

2006-01-01

59

Harmonics  

NSDL National Science Digital Library

This simulation illustrates the behavior of standing waves in situation where one end fixed, both ends are fixed, and both ends are free. The simulation allows the user to examine the standing wave behavior at the fundamental frequency and when the first three harmonics are added. The user can control the amplitude of each of the harmonics and observe the resulting pattern.

Renault, Pascal

2009-01-22

60

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

61

Localization of aerodynamic noise sources of Shinkansen trains  

NASA Astrophysics Data System (ADS)

Shinkansen noise consists of various noise sources, such as the rolling noise, concrete bridge structure noise, aerodynamic noise and so on. Among these, the aerodynamic noise is the most important at speeds over 270 km/h in some cases because of its strong dependence on train speed. Thus it is necessary to clarify the characteristics of the aerodynamic noise generated by high speed trains for noise reduction. In this paper, wind tunnel tests using a 1/5 scale Shinkansen train model were performed. An acoustic mirror, which consists of an omni-directional microphone and a reflector, was chosen as a measuring device. First, the principle and characteristics of the acoustic mirror are discussed and a method of estimating quantitatively the aerodynamic noise generated by each part of the model is proposed on the basis of wind tunnel test data. Next, the distribution of aerodynamic noise sources generated by the 1/5 scale Shinkansen train model is shown, based on which the contribution of individual noise sources of Shinkansen trains to the wayside noise level is estimated. Finally, the noise source distribution of real Shinkansen trains was measured with the acoustic mirror in a field test. The results of the field test show a good agreement with those of the wind tunnel tests.

Nagakura, K.

2006-06-01

62

Effect of High Frequency Noise Current Sources on Noise Figure for Sub-50nm Node MOSFETs  

NASA Astrophysics Data System (ADS)

The downscaling of CMOS technology has resulted in strong improvement in RF performance of bulk and SOI MOSFETs. In order to realize a low-noise RF circuit, a deeper understanding of the noise performance for MOSFETs is required. Thermal noise is the main noise source of the CMOS device for high frequency performance, and is dominated by the drain channel noise, induced gate noise, and their correlation noise. In this work, we measured the RF noise parameter (Fmin, Rn, ?opt) of 45nm node MOSFETs from 5 to 15GHz and extracted noise sources and noise coefficients P, R, and C by using an extended van der Ziel's model. We found, for the first time, that correlation coefficient C decreases from positive to negative values when the gate length is reduced continuously with the gate length of sub-100nm. We confirmed that Pucel's noise figure model, using noise coefficients P, R, and C, can be considered a good approximation even for sub-50nm MOSFETs. We also discussed a scaling effect of the noise coefficients, especially the correlation noise coefficient C on the minimum noise figure.

Shimomura, Hiroshi; Kakushima, Kuniyuki; Iwai, Hiroshi

63

Aircraft noise source and contour estimation  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

64

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

65

Frequency-dependent noise sources in the North Atlantic Ocean  

NASA Astrophysics Data System (ADS)

Secondary microseisms are the most energetic waves in the noise spectra between 3 and 10 s. They are generated by ocean wave interactions and are predominantly Rayleigh waves. We study the associated noise sources in the North Atlantic Ocean by coupling noise polarization analysis and source mapping using an ocean wave model that takes into account coastal reflections. From the Rayleigh wave polarization analysis, we retrieve the back azimuth to the noise sources in the time-frequency domain. Noise source modeling enables us to locate the associated generation areas at different times and frequencies. We analyze the distribution of secondary microseism sources in the North Atlantic Ocean using 20 broadband stations located in the Arctic and around the ocean. To model the noise sources we adjust empirically the ocean wave coastal reflection coefficient as a function of frequency. We find that coastal reflections must be taken into account for accurately modeling 7-10 s noise sources. These reflections can be neglected in the noise modeling for periods shorter than 7 s. We find a strong variability of back azimuths and source locations as a function of frequency. This variability is largely related to the local bathymetry. One direct cause of the time-dependent and frequency-dependent noise sources is the presence of sea-ice that affects the amplitude and polarization of microseisms at stations in the Arctic only at periods shorter than 4 s.

Sergeant, Amandine; Stutzmann, Eléonore; Maggi, Alessia; Schimmel, Martin; Ardhuin, Fabrice; Obrebski, Mathias

2013-12-01

66

Sources and effects of low-frequency noise.  

PubMed

The sources of human exposure to low-frequency noise and its effects are reviewed. Low-frequency noise is common as background noise in urban environments, and as an emission from many artificial sources: road vehicles, aircraft, industrial machinery, artillery and mining explosions, and air movement machinery including wind turbines, compressors, and ventilation or air-conditioning units. The effects of low-frequency noise are of particular concern because of its pervasiveness due to numerous sources, efficient propagation, and reduced efficacy of many structures (dwellings, walls, and hearing protection) in attenuating low-frequency noise compared with other noise. Intense low-frequency noise appears to produce clear symptoms including respiratory impairment and aural pain. Although the effects of lower intensities of low-frequency noise are difficult to establish for methodological reasons, evidence suggests that a number of adverse effects of noise in general arise from exposure to low-frequency noise: Loudness judgments and annoyance reactions are sometimes reported to be greater for low-frequency noise than other noises for equal sound-pressure level; annoyance is exacerbated by rattle or vibration induced by low-frequency noise; speech intelligibility may be reduced more by low-frequency noise than other noises except those in the frequency range of speech itself, because of the upward spread of masking. On the other hand, it is also possible that low-frequency noise provides some protection against the effects of simultaneous higher frequency noise on hearing. Research needs and policy decisions, based on what is currently known, are considered. PMID:8642114

Berglund, B; Hassmén, P; Job, R F

1996-05-01

67

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.

Petrov, Yury

2012-01-01

68

The Effects of Ambient Conditions on Helicopter Rotor Source Noise Modeling  

NASA Technical Reports Server (NTRS)

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

Schmitz, Frederic H.; Greenwood, Eric

2011-01-01

69

Review of Subcritical Source-Driven Noise Analysis Measurements  

SciTech Connect

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

Valentine, T.E.

1999-11-01

70

Continuous-variable quantum key distribution with Gaussian source noise  

SciTech Connect

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

Shen Yujie; Peng Xiang; Yang Jian; Guo Hong [CREAM Group, State Key Laboratory of Advanced Optical Communication Systems and Networks (Peking University) and Institute of Quantum Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing 100871 (China)

2011-05-15

71

A Study on the Estimation of Noise Temperature of a Microwave Standard Noise Source  

NASA Astrophysics Data System (ADS)

We have experimentally evaluated the equivalent noise temperature (ENT) of a microwave standard noise source. The resistivity and its temperature coefficient of a transmission line (TL) of the noise source were determined by the curve fitting technique based on the TL theory. As a result, the ENT was estimated as 133.3-144.4 K in the frequency range of 0.01-18 GHz.

Iida, Hitoshi; Inaba, Takayuki; Shimada, Yozo; Komiyama, Koji

72

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

73

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

74

An Anti-Harmonic Locking, DLL Frequency Multiplier with Low Phase Noise and Reduced Spur  

Microsoft Academic Search

This paper presents a new programmable delay-locked loop based frequency multiplier with a period error compensation loop (PECL) designed to reduce the output spurious power level. The low bandwidth auxiliary PECL compensates the output period error caused by the in-lock errors from various noise sources. By employing a novel switching control scheme, the circuit is capable of locking to frequencies

Q. J. Du; J. C. Zhuang; T. Kwasniewski

2006-01-01

75

Elimination of harmonics in a multilevel converter with nonequal DC sources  

Microsoft Academic Search

The problem of eliminating harmonics in a multilevel converter in which the separate DC sources vary is considered. That is, given a desired fundamental output voltage, the problem is to find the switching times (angles) that produce the fundamental while not generating specifically chosen harmonics. Assuming that the separate DC sources can be measured, a procedure is given to find

Leon M. Tolbert; John N. Chiasson; Keith J. McKenzie; Zhong Du

2003-01-01

76

Elimination of harmonics in a multilevel converter with nonequal DC sources  

Microsoft Academic Search

Eliminating harmonics in a multilevel converter in which the separate dc sources vary is considered. That is, given a desired fundamental output voltage, the problem is to find the switching times (angles) that produce the fundamental while not generating specifically chosen harmonics. Assuming that the separate dc sources can be measured, a procedure is given to find all sets of

Leon M. Tolbert; John N. Chiasson; Zhong Du; K. J. McKenzie

2005-01-01

77

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

78

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

NASA Astrophysics Data System (ADS)

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

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

1995-10-01

79

Environmentally induced noises in an actively mode-locked erbium fibre laser operating in the second-order rational harmonic mode locking regime  

NASA Astrophysics Data System (ADS)

We investigate the influence of environmentally induced cavity length fluctuations on the energy and phase noises of an optical pulse train generated by an actively mode-locked erbium-doped fibre laser that is operated in the second-order rational harmonic mode-locking regime. Using a simple model that was recently proposed to describe this particular regime, we identify the specific nature of these energy and phase noises, and we demonstrate that their values averaged over two consecutive pulses in the train can be measured directly by implementing the time-domain demodulation technique. For a known cavity length variation, we compare the values of the average energy and phase fluctuations that are obtained both theoretically, using the model, and experimentally, through time-domain demodulation. This study brings out a mechanism of coupling between the energy and phase fluctuations that appears when cavity length fluctuations are at play. This coupling is caused by the periodic intracavity amplitude modulation and strongly depends on the average detuning of the cavity length. Through the measurement of the cross-correlation between energy and phase noises, we identify environmental perturbations as a major source of the noises that affect a pulse train generated through second-order rational harmonic mode locking.

Pottiez, O.; Mégret, P.; Blondel, M.

2002-11-01

80

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

81

Noise source level density due to surf. II. Duck, NC  

Microsoft Academic Search

For pt.I see ibid., vol.22, no.3, p.425-33 (1997). Ambient noise measurements collected off the coast of Duck, NC, were used in conjunction with modeled transmission loss (TL) and estimated ambient noise due to wave-breaking to generate estimates of spectral source level densities (per meter of surf zone) of surf-generated ambient noise. Estimates of both continuous (local) and discrete (distant) components

Josette Paquin Fabre; James H. Wilson

1997-01-01

82

Electrical and Noise Characteristics of Graphene Field-Effect Transistors: Ambient Effects and Noise Sources  

Microsoft Academic Search

We fabricated a large number of single and bilayer graphene transistors and\\u000acarried out a systematic experimental study of their low-frequency noise\\u000acharacteristics. A special attention was given to determining the dominant\\u000anoise sources in these devices and the effect of aging on the current-voltage\\u000aand noise characteristics. The analysis of the noise spectral density\\u000adependence on the area of

S. Rumyantsev; G. Liu; W. Stillman; M. Shur; A. A. Balandin

2010-01-01

83

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

84

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

85

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

86

Target enhancement and noise cancellation in the identification of a rudimentary sound source in noise.  

PubMed

Perturbation analysis was used to determine the relative contribution of target enhancement and noise cancellation in the identification of rudimentary sound source in noise. In a two-interval, forced-choice procedure, listeners identified the impact sound produced by the larger of two stretched membranes as target. The noise on each presentation was the impact sound of a variable-sized plate. For four of five listeners, the relative weights on the noise were positive indicating enhancement, and for the remaining listeners, they were negative indicating cancellation. The results underscore the difficulty with evaluating models of masking solely in terms of measures of performance accuracy. PMID:21361412

Lutfi, Robert A; Liu, Ching-Ju

2011-02-01

87

A low-harmonic electric drive system based on current-source inverter  

Microsoft Academic Search

This paper presents a new electric drive system topology, which is based on a pulse width modulation (PWM) current-source inverter (CSI). It is aimed at reducing the current harmonics drawn from paper mill distribution systems and the electric utility. Additionally, the voltage harmonics feeding into the electric motors are significantly reduced. Furthermore, the voltage rise rate of the PWM-CSI drives

Yuexin Yin; Alex Y. Wu

1998-01-01

88

Harmonic source estimator for distribution systems by means of Bayesian and WLS approaches  

Microsoft Academic Search

The knowledge of the distribution system state is required to operate management and control issues, such as energy dispatching and protection coordination. The authors have proposed a novel procedure for harmonic source estimation, based on a Bayesian approach, aimed at giving distribution network operators information about the presence of harmonic producing loads, along with a key indication about the reliability

G. D'Antona; C. Muscas; P. A. Pegoraro; S. Sulis

2011-01-01

89

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

90

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

91

Frequency Sources in W-band Radar Front-end with Low Phase Noise  

NASA Astrophysics Data System (ADS)

A W-band coherent stepped-frequency pulsed radar front-end is developed. It consists of a millimetre wave transmitting source, a mm-wave local source, a DDS with multi frequency points output and two microwave sources serving as local oscillators. All the sources are coherent with the 120 MHz referenced crystal oscillator. The mm-wave sources are realized by frequency multiplier chain, up-conversion and injection locking. The phase noise of fundamental-wave injection-locked W-band harmonic Gunn oscillator output signal achieves -98 dBc/Hz at 10 kHz offset and the spurious output is less than -50 dBc. The received intermediate frequency signal is also presented.

Zhang, Yonghong; Tang, Xiaohong; Fan, Yong; Wu, Zhengde

2008-02-01

92

Active noise control using noise source having adaptive resonant frequency tuning through stress variation  

NASA Technical Reports Server (NTRS)

A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by an expandable ring embedded in the noise radiating element. Excitation of the ring causes expansion or contraction of the ring, thereby varying the stress in the noise radiating element. The ring is actuated by a controller which receives input of a feedback signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the ring, causing the ring to expand or contract. Instead of a single ring embedded in the noise radiating panel, a first expandable ring can be bonded to one side of the noise radiating element, and a second expandable ring can be bonded to the other side.

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

1995-01-01

93

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

94

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

95

A high-flux high-order harmonic source  

NASA Astrophysics Data System (ADS)

We develop and implement an experimental strategy for the generation of high-energy high-order harmonics (HHG) in gases for studies of nonlinear processes in the soft x-ray region. We generate high-order harmonics by focusing a high energy Ti:Sapphire laser into a gas cell filled with argon or neon. The energy per pulse is optimized by an automated control of the multiple parameters that influence the generation process. This optimization procedure allows us to obtain energies per pulse and harmonic order as high as 200 nJ in argon and 20 nJ in neon, with good spatial properties, using a loose focusing geometry (f#~400) and a 20 mm long medium. We also theoretically examine the macroscopic conditions for absorption-limited conversion efficiency and optimization of the HHG pulse energy for high-energy laser systems.

Rudawski, P.; Heyl, C. M.; Brizuela, F.; Schwenke, J.; Persson, A.; Mansten, E.; Rakowski, R.; Rading, L.; Campi, F.; Kim, B.; Johnsson, P.; L'Huillier, A.

2013-07-01

96

Screech noise source structure of a supersonic rectangular jet  

NASA Technical Reports Server (NTRS)

The near-field of the screech noise source structure of an under-expanded supersonic rectangular jet was studied in detail. A miniature probe microphone was used along with a reference microphone to determine the amplitude and phase of the sound pressure near and in the high speed flow field. The transverse structure of the unsteady pressure field was investigated by moving the probe microphone sufficiently far into the jet so that pressure fall-off was observed. Five islands of high sound pressure level have been distinguished which may be associated with the actual local sources of sound production. These sources of screech noise are closely associated with the jet shock structure as would be expected, with the peak region of noise level being found slightly downstream of each of the five observed shocks. The third and fourth noise sources have the highest levels and are about equal in strength. All of the apparent noise sources have their peak levels in the subsonic flow region. Strong cancellations in the acoustic field are observed in the downstream and sideline directions which may account for the predominant upstream propagation of the fundamental tone noise.

Rice, E. J.; Taghavi, R.

1992-01-01

97

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.

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

2013-01-01

98

A Ratiometric Method for Johnson Noise Thermometry Using a Quantized Voltage Noise Source  

NASA Astrophysics Data System (ADS)

Johnson Noise Thermometry (JNT) involves the measurement of the statistical variance of a fluctuating voltage across a resistor in thermal equilibrium. Modern digital techniques make it now possible to perform many functions required for JNT in highly efficient and predictable ways. We describe the operational characteristics of a prototype JNT system which uses digital signal processing for filtering, real-time spectral cross-correlation for noise power measurement, and a digitally synthesized Quantized Voltage Noise Source (QVNS) as an AC voltage reference. The QVNS emulates noise with a constant spectral density that is stable, programmable, and calculable in terms of known parameters using digital synthesis techniques. Changes in analog gain are accounted for by alternating the inputs between the Johnson noise sensor and the QVNS. The Johnson noise power at a known temperature is first balanced with a synthesized noise power from the QVNS. The process is then repeated by balancing the noise power from the same resistor at an unknown temperature. When the two noise power ratios are combined, a thermodynamic temperature is derived using the ratio of the two QVNS spectral densities. We present preliminary results where the ratio between the gallium triple point and the water triple point is used to demonstrate the accuracy of the measurement system with a standard uncertainty of 0.04 %.

Nam, S. W.; Benz, S. P.; Martinis, J. M.; Dresselhaus, P.; Tew, W. L.; White, D. R.

2003-09-01

99

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

NASA Technical Reports Server (NTRS)

A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of noise radiating structure is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating structure is tuned by a plurality of drivers arranged to contact the noise radiating structure. Excitation of the drivers causes expansion or contraction of the drivers, thereby varying the edge loading applied to the noise radiating structure. The drivers are actuated by a controller which receives input of a feedback signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the drivers, causing them to expand or contract. The noise radiating structure may be either the outer shroud of the engine or a ring mounted flush with an inner wall of the shroud or disposed in the interior of the shroud.

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

1995-01-01

100

Investigation of noise sources in SQUID electronics  

SciTech Connect

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

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

1989-03-01

101

Wind turbines—low level noise sources interfering with restoration?  

NASA Astrophysics Data System (ADS)

Wind turbines generate a low level noise and would thus not be expected to cause annoyance and disturb rest. In a society where people are being exposed to an increasing noise load, moderate and low level noise sources may also be perceived as annoying and hence inhibit restoration. This article presents an analysis of two socio-acoustic studies of wind turbine noise with the emphasis on perception, annoyance and consequences for restoration. It is hypothesized that low and moderate stressors such as wind turbine noise could have an impact on health. The risk seems to be higher if restoration is, or is perceived to be, impaired and also for certain groups of individuals. The observations warrant further studies.

Pedersen, Eja; Persson Waye, Kerstin

2008-01-01

102

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

103

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

NASA Astrophysics Data System (ADS)

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

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

2004-07-01

104

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

105

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

106

Jet Noise Source Localization Using Linear Phased Array  

NASA Technical Reports Server (NTRS)

A study was conducted to further clarify the interpretation and application of linear phased array microphone results, for localizing aeroacoustics sources in aircraft exhaust jet. Two model engine nozzles were tested at varying power cycles with the array setup parallel to the jet axis. The array position was varied as well to determine best location for the array. The results showed that it is possible to resolve jet noise sources with bypass and other components separation. The results also showed that a focused near field image provides more realistic noise source localization at low to mid frequencies.

Agboola, Ferni A.; Bridges, James

2004-01-01

107

Size and shape of seismic noise sources and implications for ambient noise tomography  

NASA Astrophysics Data System (ADS)

Seismic noise has been intensively used for tomographic purpose over the past 5 years and shows promising potential for 4D imaging of the earth interior. Cross-correlation of noise samples allows reconstructing surface- and compressional-waves that carry information of the earth velocity structure comparable to that obtained from earthquakes. Nevertheless, ambient noise tomography is limited by the lack of knowledge on the distribution and lateral extent of sources. Recent numerical modeling (Kedar et al., 2008; Ardhuin et al. J. Geophys. Res. 2011; Stutzmann et al., submitted) has shown that the dominant seismic noise, with periods 3 to 10s, is generated by non linear wave-wave interactions as described by the theory proposed by Longuet-Higgins (1950) and Hasselmann (1963) for double frequency microseisms (DFM). The magnitude of the noise source is conditioned by the angular spectra of the swells and wind seas and the bathymetry. Here we use seismic records and numerical modeling to characterize the distribution of the DFM sources in time and space. Our numerical approach combines a numerical wave model based on the WAVEWATCH III° framework, in which the second-order pressure spectrum is computed, and a ray-tracing algorithm for integrating the seismic source and damping along propagation rays for the different Rayleigh modes that are contained in the microseismic wave field. Noise recorded at broadband stations generally consists of a series of high seismic noise intensity peaks (a few micrometers for the standard deviation of the vertical ground displacement) with durations of about one day. Focusing on the peaks for which the model results fit particularly well to the data, we estimate the width of the source area and use our model to map the area responsible for the DFM signal recorded at a given time and set of stations. These source centroid position and width of sources are validated using an independent estimate from a polarization analysis of the three-axes ground displacement recorded at a set of three or more seismic stations that record the same source (Schimmel et al., Geochem. Geophys. Geosyst. 2011). Our preliminary results show that the strongest sources are not localized only close to the coasts where they are promoted by incoming- and reflected-swell interactions, but rather in deep water where reflection is absent. Our analysis also suggests that most sources span large areas, with a gaussian width at half maximum around 1000 km. Only a few sources, in particular at the lowest frequencies, are more localized (500 km wide). The finiteness of noise sources is thus significant and must be taken into account in tomographic studies.

Obrebski, M. J.; Ardhuin, F.; Schimmel, M.; Stutzmann, E.

2011-12-01

108

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

109

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

110

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

111

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

112

Total annoyance from an industrial noise source with a main spectral component combined with a background noise.  

PubMed

When living close to an industrial plant, people are exposed to a combination of industrial noise sources and a background noise composed of all the other noise sources in the environment. As a first step, noise annoyance indicators in laboratory conditions are proposed for a single exposure to an industrial noise source. The second step detailed in this paper involves determining total annoyance indicators in laboratory conditions for ambient noises composed of an industrial noise source and a background noise. Two types of steady and permanent industrial noise sources are studied: low frequency noises with a main spectral component at 100 Hz, and noises with a main spectral component in middle frequencies. Five background noises are assessed so as to take into account different sound environments which can usually be heard by people living around an industrial plant. One main conclusion of this study is that two different analyses are necessary to determine total annoyance indicators for this type of ambient noise, depending on the industrial noise source composing it. Therefore, two total annoyance indicators adapted to the ambient noises studied are proposed. PMID:21786889

Alayrac, M; Marquis-Favre, C; Viollon, S

2011-07-01

113

Performance analysis of Z - source Inverter based ASD system with reduced harmonics  

Microsoft Academic Search

This paper presents the Z - source inverter for adjustable speed drive system. The Z - source inverter employs a unique impedance network couple with inverter main circuit. By controlling the shoot through duty cycle, the Z - source inverter system using MOSFETS provide ride - through capability during voltage sags, reduces line harmonics, improves power factor and high reliability,

Amitava Das; S. P. Chowdhury; A. Domijan

2008-01-01

114

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

115

Research on third harmonic injection control strategy of improved Z-source inverter  

Microsoft Academic Search

Compared to previous Z-source inverter topology, improved Z-source inverter has advantages such as low Z-source capacitor voltage stress and inherent inrush current limitation. This paper investigates the third harmonic injection control strategy of improved Z-source inverter. Compared to simple boost control, it can reduce the voltage stress and Z-source inductor current ripple. Theoretical analysis, simulation and experimental results were presented

Shaojun Xie; Yu Tang; Chaohua Zhang

2009-01-01

116

Investigation of Volumetric Sources in Airframe Noise Simulations  

NASA Technical Reports Server (NTRS)

Hybrid methods for the prediction of airframe noise involve a simulation of the near field flow that is used as input to an acoustic propagation formula. The acoustic formulations discussed herein are those based on the Ffowcs Williams and Hawkings equation. Some questions have arisen in the published literature in regard to an apparently significant dependence of radiated noise predictions on the location of the integration surface used in the solution of the Ffowcs Williams and Hawkings equation. These differences in radiated noise levels are most pronounced between solid-body surface integrals and off-body, permeable surface integrals. Such differences suggest that either a non-negligible volumetric source is contributing to the total radiation or the input flow simulation is suspect. The focus of the current work is the issue of internal consistency of the flow calculations that are currently used as input to airframe noise predictions. The case study for this research is a computer simulation for a three-element, high-lift wing profile during landing conditions. The noise radiated from this flow is predicted by a two-dimensional, frequency-domain formulation of the Ffowcs Williams and Hawkings equation. Radiated sound from volumetric sources is assessed by comparison of a permeable surface integration with the sum of a solid-body surface integral and a volume integral. The separate noise predictions are found in good agreement.

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

2004-01-01

117

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

118

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

119

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

SciTech Connect

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

Dakovski, Georgi L [Los Alamos National Laboratory; Li, Yinwan [Los Alamos National Laboratory; Durakiewicz, Tomasz [Los Alamos National Laboratory; Rodriguez, George [Los Alamos National Laboratory

2009-01-01

120

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

PubMed

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

Scandurra, Graziella; Giusi, Gino; Ciofi, Carmine

2014-04-01

121

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

122

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

123

Low-noise phase-locked frequency source  

NASA Astrophysics Data System (ADS)

The paper deals with a low-noise phase-locked frequency source, known as the S-8600 system, which was developed on an ELINT receiver system. The system is a frequency synthesizer in the sense that it provides a large number of accurately calibrated frequencies from a single source. Unlike some synthesizers, its output frequencies are present rather than selectable by an operator. The block diagram of S-8600 and the elements of the phase-locked loop are discussed.

Kawakami, K. N.

1980-05-01

124

Identification and classification of noise sources in a chain conveyor  

NASA Astrophysics Data System (ADS)

Noise induced hearing loss (NIHL) is one of the most significant disabilities of workers in the mining industry. In response, the National Institute of Occupational Safety and Health (NIOSH) is conducting a study associated with mining equipment. This study outlines the analysis of a chain conveyor. Band-limited accelerometer, sound-intensity, far-field and near-field microphone measurements were taken along the conveyor section. The sound intensity measurements were used to identify areas with high noise as well as to calculate and 1/3-octave sound power levels. The total sound power results were used to classify the dominant noise sources where the 1/3-octave sound power results were used to identify the most contributive frequency bands to the overall noise of the system. Coherence analysis was performed between accelerometer and microphone measurements to identify structure-borne and air-borne noise paths of the system. Summary results from the analysis include recommendations for transmission control and damping devices and their ability to reduce noise to regulatory acceptable levels.

Homer, John P.; Vipperman, Jeffrey S.; Reeves, Efrem R.

2002-05-01

125

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

126

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

NASA Technical Reports Server (NTRS)

Noise measurements of small scale helicopter rotor models were compared with noise measurements of full scale helicopters to determine what information about the full scale helicopters could be derived from noise measurements of small scale helicopter models. Comparisons were made of the discrete frequency (rotational) noise for 4 pairs of tests. Areas covered were tip speed effects, isolated rotor, tandem rotor, and main rotor/tail rotor interaction. Results show good comparison of noise trends with configuration and test condition changes, and good comparison of absolute noise measurements with the corrections used except for the isolated rotor case. Noise measurements of the isolated rotor show a great deal of scatter reflecting the fact that the rotor in hover is basically unstable.

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

1982-01-01

127

Identification and Proposed Control of Helicopter Transmission Noise at the Source.  

National Technical Information Service (NTIS)

Helicopter cabin interiors require noise treatment which is expensive and adds weight. The gears inside the main power transmission are major sources of cabin noise. Work conducted by the NASA Lewis Research Center in measuring cabin interior noise and in...

J. J. Coy R. F. Handschuh D. G. Lewicki R. G. Huff E. A. Krejsa

1988-01-01

128

Annoyance from industrial noise: indicators for a wide variety of industrial sources.  

PubMed

In the study of noises generated by industrial sources, one issue is the variety of industrial noise sources and consequently the complexity of noises generated. Therefore, characterizing the environmental impact of an industrial plant requires better understanding of the noise annoyance caused by industrial noise sources. To deal with the variety of industrial sources, the proposed approach is set up by type of spectral features and based on a perceptive typology of steady and permanent industrial noises comprising six categories. For each perceptive category, listening tests based on acoustical factors are performed on noise annoyance. Various indicators are necessary to predict noise annoyance due to various industrial noise sources. Depending on the spectral features of the industrial noise sources, noise annoyance indicators are thus assessed. In case of industrial noise sources without main spectral features such as broadband noise, noise annoyance is predicted by the A-weighted sound pressure level L(Aeq) or the loudness level L(N). For industrial noises with spectral components such as low-frequency noises with a main component at 100 Hz or noises with spectral components in middle frequencies, indicators are proposed here that allow good prediction of noise annoyance by taking into account spectral features. PMID:20815449

Alayrac, M; Marquis-Favre, C; Viollon, S; Morel, J; Le Nost, G

2010-09-01

129

Mitochondrial Variability as a Source of Extrinsic Cellular Noise  

PubMed Central

We present a study investigating the role of mitochondrial variability in generating noise in eukaryotic cells. Noise in cellular physiology plays an important role in many fundamental cellular processes, including transcription, translation, stem cell differentiation and response to medication, but the specific random influences that affect these processes have yet to be clearly elucidated. Here we present a mechanism by which variability in mitochondrial volume and functionality, along with cell cycle dynamics, is linked to variability in transcription rate and hence has a profound effect on downstream cellular processes. Our model mechanism is supported by an appreciable volume of recent experimental evidence, and we present the results of several new experiments with which our model is also consistent. We find that noise due to mitochondrial variability can sometimes dominate over other extrinsic noise sources (such as cell cycle asynchronicity) and can significantly affect large-scale observable properties such as cell cycle length and gene expression levels. We also explore two recent regulatory network-based models for stem cell differentiation, and find that extrinsic noise in transcription rate causes appreciable variability in the behaviour of these model systems. These results suggest that mitochondrial and transcriptional variability may be an important mechanism influencing a large variety of cellular processes and properties.

Johnston, Iain G.; Gaal, Bernadett; Neves, Ricardo Pires das; Enver, Tariq; Iborra, Francisco J.; Jones, Nick S.

2012-01-01

130

Quantifying multiscale noise sources in single-molecule time series  

PubMed Central

When analyzing single-molecule data, a low-dimensional set of system observables typically serve as the observational data. We calibrate stochastic dynamical models from time series that record such observables (our focus throughout is on a molecule’s end-to-end distance). Numerical techniques for quantifying noise from multiple time scales in a single trajectory, including experimental instrument and inherent thermal noise, are demonstrated. The techniques are applied to study time series coming from both simulations and experiments associated with the nonequilibrium mechanical unfolding of titin’s I27 domain. The estimated models can be used for several purposes: (1) detect dynamical signatures of “rare events” by analyzing the effective diffusion and force as a function of the monitored observable; (2) quantify the influence that experimentally unobservable conformational degrees of freedom have on the dynamics of the monitored observable; (3) quantitatively compare the inherent thermal noise to other noise sources, e.g. instrument noise, variation induced by conformational heterogeneity, etc.; (4) simulate random quantities associated with repeated experiments; (5) apply pathwise (i.e. trajectory-wise) hypothesis tests to assess the goodness-of-fit of models and even detect conformational transitions in noisy signals. These items are all illustrated with several examples.

Calderon, Christopher P.; Harris, Nolan C.; Kiang, Ching-Hwa; Cox, Dennis D.

2009-01-01

131

Harmonics Study and Comparison of Z-source Inverter with Traditional Inverters  

Microsoft Academic Search

This paper presents an Impedance Source Inverter for A.C electrical drives. The impedance source inverter employs a unique impedance network couple with inverter main circuit and rectifier. By controlling the shoot-through duty cycle, the z-source inverter system using MOSFETS provide ride-through capability during voltage sags, reduces line harmonics, improves power factor and high reliability, and extends output voltage range. Analysis,

B. Justus Rabi; R. Arumugam

2005-01-01

132

A self-synchronizing instrument for harmonic source detection in power systems  

Microsoft Academic Search

The deregulation of energy markets holds out new prospects for contracts between customers and utilities, in which the price of energy can depend on voltage quality and load characteristics, as well as on the responsibility for disturbances caused to supply voltage in power systems. In this context, harmonic source detection is one of the main problems because of equipment sensibility

Massimo Aiello; Antonio Cataliotti; Valentina Cosentino; Salvatore Nuccio

2005-01-01

133

dq-control of high-power current source rectifiers utilizing Selective Harmonic Elimination  

Microsoft Academic Search

Selective harmonic elimination (SHE) is usually the preferred modulation technique for high power converters. When such modulation is used with current source rectifiers (CSR), control of the DC-link current and of the input displacement power factor is typically achieved by adjusting the amplitude and phase of the CSR modulation index. In this paper control of an SHE modulated CSR is

Matteo Tomasini; Ralph Feldman; Patrick Wheeler; Jon Clare; Christian Klumpner; Ushe Mupambireyi

2009-01-01

134

Voltage harmonic control of Z-source inverter for UPS applications  

Microsoft Academic Search

This paper presents a control method for obtaining sinusoidal output voltage regardless of the nonlinear and unbalanced loads. Control of the DC boost stage and capacitor voltage is presented. The resonant regulators are used for selective harmonic cancellation of the output AC voltage. The Z-source inverter is able to provide higher AC voltage related to the DC link voltage than

Arkadiusz Kulka; Tore Undeland

2008-01-01

135

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

NASA Astrophysics Data System (ADS)

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

Freund, J. B.

2003-06-01

136

Assessment of harmonic source correction for ultrasound medical imaging  

NASA Astrophysics Data System (ADS)

Tissue velocity and attenuation inhomogeneities reduce ultrasound image quality in many patients. Over the years a number of methods have been developed to estimate the corrective delays necessary for phase aberration correction. Past methods were based on assumptions of the target or required a separate transducer acting as a transponder point source. A method is proposed which creates a known acoustical source in the tissue suitable for wavefront correction without a priori assumptions of the target or requiring a point source transponder. This method was tested with multiple electronically produced aberrations with RMS focusing errors of 0.25? radians, 0.44? radians, and 0.87? radians at 4.17 MHz. These aberrators were corrected using excised pork kidneys and on the left kidney of human volunteers as targets. Waveform correction on pork kidney led to an improvement in imaging beam amplitude and side-lobe level. Waveform correction on human subjects for a 0.87? radians RMS error aberrator led to a 15.4 dB improvement in imaging beam amplitude and an 11.8 dB improvement in side-lobe level. This method shows promise of overcoming the limitations of previous phase correction methods.

Dianis, Scott W.; von Ramm, Olaf T.

2010-03-01

137

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

138

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

NASA Technical Reports Server (NTRS)

Understanding the relative importance of the various turbine noise generation mechanisms and the characteristics of the turbine acoustic transmission loss are essential ingredients in developing robust reduced-order models for predicting the turbine noise signature. A computationally based investigation has been undertaken to help guide the development of a turbine noise prediction capability that does not rely on empiricism. The investigation relies on highly detailed numerical simulations of the unsteady flowfield inside a modern high-pressure turbine (HPT). The simulations are developed using TURBO, which is an unsteady Reynolds-averaged Navier-Stokes (URANS) code capable of multi-stage simulations. The purpose of this study is twofold. First, to determine an estimate of the relative importance of the contributions to the coherent part of the acoustic signature of a turbine from the three potential sources of turbine noise generation, namely, blade-row viscous interaction, potential field interaction, and entropic source associated with the interaction of the blade rows with the temperature nonuniformities caused by the incomplete mixing of the hot fluid and the cooling flow. Second, to develop an understanding of the turbine acoustic transmission characteristics and to assess the applicability of existing empirical and analytical transmission loss models to realistic geometries and flow conditions for modern turbine designs. The investigation so far has concentrated on two simulations: (1) a single-stage HPT and (2) a two-stage HPT and the associated inter-turbine duct/strut segment. The simulations are designed to resolve up to the second harmonic of the blade passing frequency tone in accordance with accepted rules for second order solvers like TURBO. The calculations include blade and vane cooling flows and a radial profile of pressure and temperature at the turbine inlet. The calculation can be modified later to include the combustor pattern factor at the turbine inlet to include that contribution to turbine noise. We shall present preliminary analysis of the results obtained so far in order to assess the validity of such an approach and to seek feedback on improving the approach. This work addresses both Area 1 (Turbine Tone Noise) and Area 5 (Influence of the Turbine on Combustor Noise) topics.

VanZante, Dale; Envia, Edmane

2008-01-01

139

Selective Harmonic Elimination PWM Control for Cascaded Multilevel Voltage Source Converters: A Generalized Formula  

Microsoft Academic Search

This paper proposes a generalized formulation for selective harmonic elimination pulse-width modulation (SHE-PWM) control suitable for high-voltage high-power cascaded multilevel voltage source converters (VSC) with both equal and nonequal dc sources used in constant frequency utility applications. This formulation offers more degrees of freedom for specifying the cost function without any physical changes to the converter circuit, as compared to

Mohamed S. A. Dahidah; Vassilios G. Agelidis

2008-01-01

140

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

SciTech Connect

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

Dilanian, Ruben A.; Chen Bo; Williams, Garth J.; Quiney, Harry M.; Nugent, Keith A. [ARC Centre of Excellence for Coherent X-ray Science, School of Physics, University of Melbourne, Victoria 3010 (Australia); Teichmann, Sven; Hannaford, Peter; Dao, Lap V. [ARC Centre of Excellence for Coherent X-ray Science and Centre for Atom Optics and Ultrafast Spectroscopy, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Victoria 3122 (Australia); Peele, Andrew G. [Department of Physics, ARC Centre of Excellence for Coherent X-ray Science, La Trobe University, Bundoora, Victoria 3086 (Australia)

2009-07-15

141

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

142

A Method for Improving Signal-to-Noise Ratio of Tissue Harmonic Imaging Based on Bayesian Inference Using Information of Fundamental Echoes  

NASA Astrophysics Data System (ADS)

A medical ultrasound imaging technique with a high spatial resolution and a high signal-to-noise ratio (SNR) is strongly required for precise diagnosis. To obtain high-resolution images, tissue harmonic imaging (THI) can be effectively adopted because of its wide bandwidth characteristics compared with fundamental imaging. However, the amplitude of harmonic components is much smaller than that of a fundamental component. Additionally, frequency dependent attenuation is severe, especially for harmonic components. These phenomena mean that THI is susceptible to noise. From these considerations, in this study, we propose a method for improving the SNR of THI by reducing noise using a signal processing technique. The proposed method is constructed based on the Bayesian inference using fundamental components of echoes, and it can hold the high-resolution nature of THI. We show the effectiveness of the proposed method through simulations.

Yamamura, Takuya; Tanabe, Masayuki; Okubo, Kan; Tagawa, Norio

2012-07-01

143

Determination of noise source heights, part II: Measurement of the equivalent source height of highway vehicles  

NASA Astrophysics Data System (ADS)

This is the second of two companion papers which describe the measurement of the equivalent point source height on highway vehicles. The first paper describes the measurement method, and the second its application to highway vehicles. This paper discusses the measurements on moving highway vehicles. First it is shown how the measurement method is suitable for measuring the equivalent point source height for application to noise barrier design. The measurement of noise source height on 36 heavy trucks, 37 medium vehicles and 25 small vehicles are then described. The results give the equivalent point source height as a function of frequency for each type of vehicle and identify the contributions of engine noise and tire noise. The measured source height was found to be ˜ 1·2 m for heavy vehicles, ˜0·7 m for medium vehicles and ˜0·6 m for small vehicles. These heights are significantly different from those currently used to design noise barriers, and suggest that further work should be undertaken to assess the implications of these results.

Glegg, S. A. L.; Yoon, J. R.

1990-11-01

144

Source of correlated noise in experiments using a /sup 252/Cf source  

SciTech Connect

The /sup 2/%/sup 2/Cf source method to measure reactivities is under intensive study, both theoretically and experimentally, at the Oak Ridge National Lab. Potential applications to the measurement of very large subcriticalities require a careful analysis of the source of correlated noise. Still, /sup 252/Cf experiments are analyzed by applying the Schottky prescription of the source of noise according to Cohn, i.e., without corrections due to the neutrons removed by the detector; this is equivalent to assuming that detector fluctuations are exactly proportional to the fluctuation of the neutron field. If this is true, a nonzero correlation should be measured in a moderator driven by a one-neutron-per-event source, which certainly is not the case. Sheff and Albrecht emphasized later that the Schottky source of noise has to be divided into two components related to multiple neutrons per event (fission) and to a single neutron per event (absorption plus leakage), and that only the first component is the source of correlated noise for the detector. The differences between the two formalisms have very practical implications when the /sup 252/Cf method is applied to measure large subcriticalities. In this paper the authors analyze systems without multiplication in order to emphasize the differences; also additional sources of correlations due to finite resolution time are individualized and quantified. Whenever possible, a master equation approach is used to avoid a posteriori cosmetic to the Langevin/Schottky approach.

Difilippo, F.C.

1987-01-01

145

Noise source identification and control of a contractor grade table saw  

NASA Astrophysics Data System (ADS)

Sponsored by the National Institute for Occupational Safety and Health (NIOSH) as part of their initiative to explore noise reduction strategies for construction equipment, a team of engineering students at Iowa State University studied a contractor grade table saw. Based on standards, published work, and preliminary tests, a repeatable noise measurement procedure was developed for the table saw operation. The wood-feed rate and force were measured. With the saw operating in a standard and consistent manner, noise sources on the saw were identified using sound intensity measurement techniques and through the application of noise control strategies to individual sources. At this stage, noise control strategies, such as enclosing the motor, are effective for noise source identification but not practical. The effectiveness of both approaches to identifying the noise sources will be discussed. Based on rank ordering the contribution of each noise source to the overall sound levels, permanent noise control strategies are suggested.

Bleedorn, Kristin; McKee, Matthew; Yarbough, Dale; Yu, Chen; Zechmann, Edward L.; Mann, J. Adin

2002-05-01

146

Spectral decomposition of the aerodynamic noise generated by rotating sources  

NASA Astrophysics Data System (ADS)

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

Bongiovì, Alessandro; Cattanei, Andrea

2011-01-01

147

Source of correlated noise in experiments using a /sup 252/Cf source  

SciTech Connect

The /sup 252/Cf source method to measure reactivities is under intensive study, both theoretical and experimentally, at the Oak Ridge National Laboratory. The method was already applied to a large variety of multiplicative systems ranging from thermal to fast, homogeneous to heterogeneous and continuous to discrete. Potential applications to the measurement of very large subcriticalities require a careful analysis of the source of correlated noise. Still, /sup 252/Cf experiments are analyzed by applying the Schottky prescription of the source of noise without corrections due to the neutrons removed by the detector; this is equivalent to assuming that detectors' fluctuations are exactly proportional to the fluctuation of the neutron field. Sheff and Albrecht emphasized later that the Schottky source of noise has to be divided into two components related respectively to multiple neutrons per event (fission) and to a single neutron per event (absorption plus leakage), and that only the first component is the source of correlated noise for the detector. The differences between the two formalisms have very practical implications when the /sup 252/Cf method is applied to measure large subcriticalities. This paper analyzes systems without multiplication in order to emphasize the differences; also additional sources of correlations due to finite resolution time are individualized and quantified. Whenever possible, a master equation approach is used to avoid a posteriori cosmetic to the Langevin/Schottky approach. 5 refs., 1 fig.

Difilippo, F.C.

1987-01-01

148

Identification, modelling and reduction potential of railway noise sources: a critical survey  

NASA Astrophysics Data System (ADS)

Environmental requirements for railway operations will become tighter in the future. In particular, annoyance due to railway noise has to be taken carefully into account in the expansion of freight traffic as well as in new high speed line projects. Reduction of noise at source can be more attractive than the use of noise barriers but this requires a thorough understanding of the source mechanisms. This paper presents a critical survey of the identification and modelling of railway noise sources and summarizes the current knowledge of the physical source phenomena (mainly rolling and aerodynamic sources) as well as the potential for noise reduction. Future research perspectives are also given. These concern, in particular, improvements to source modelling, especially for aerodynamic noise, investigation of other sources and development of more advanced models for predicting railway noise in the environment. These should include a better description of the sources, obtained from modelling.

Talotte, C.; Gautier, P.-E.; Thompson, D. J.; Hanson, C.

2003-10-01

149

Active Control of a Moving Noise SOURCE—EFFECT of Off-Axis Source Position  

NASA Astrophysics Data System (ADS)

An optimally arranged multiple-channel active-control system is known to be able to create a large quiet zone in free space for a stationary primary noise source. When the primary noise source moves, the active control of the noise becomes much more difficult, as the primary noise field changes with time in space. In this case, the controller of the control system must respond fast enough to compensate for the change; much research has been focused on this issue. In this paper, it is shown that a moving source also causes difficulties from an acoustical perspective. A moving source not only changes continuously the strengths and phases of the sound field in the space, but also changes the wavefront of the primary sound field continuously. It is known that the efficiency of active noise control is determined mainly by the wavefront matching between the primary and control fields. To keep the control system effective in the case of a moving source, the wavefront of the control field needs to change, in order to continuously match the primary-wavefront change. This paper shows that there are limitations to the control-wavefront change. An optimally pre-arranged, multiple-channel control system is not able to construct a matching wavefront when the primary source moves outside a certain range. In other words, the control system is still able to create a large quiet zone only when the primary source moves within a range around the central axis of the control system. Both the location and the size of the quiet zone change with the location of the primary source.

GUO, J.; PAN, J.; HODGSON, M.

2002-03-01

150

Prediction of aircraft noise source and estimation of noise-level contours  

NASA Technical Reports Server (NTRS)

Two computer programs aid aircraft designers who need to identify noise characteristics of various aircraft and engine configurations; calculated noise levels can then be compared with community goals for noise limitation.

Peart, N. A.

1975-01-01

151

Advanced Control Strategy for Single-Phase Voltage-Source Active Rectifier with Low Harmonic Emission  

NASA Astrophysics Data System (ADS)

This paper introduces the advanced control of single-phase voltage-source active rectifier. This control provide direct control of trolley-wire current and active damping of low-frequency disturbances at the converter ac side. Our proposed control strategy combines PR controller with feed-forward model and low-frequency harmonic compensator based on resonant controllers. Achieved experimental results show excellent converter behavior, where converter is fed by strongly distorted supply voltage.

Blahník, Vojt?ch; Peroutka, Zden?k; Talla, Jakub

2014-03-01

152

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

153

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

154

Sources, Control, and Effects of Noise from Aircraft Propellers and Rotors.  

National Technical Information Service (NTIS)

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...

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

1981-01-01

155

Mitigation of Radio Noise and Interference from On-Site Sources at Radio Receiving Sites.  

National Technical Information Service (NTIS)

Radio noise and interference from sources within the confines of radio-receiving sites is described and effective mitigation techniques are presented along with ineffective techniques. Of special concern is that many signals and most cases of noise and in...

A. A. Parker G. F. Munsch R. W. Adler W. R. Vincent

2009-01-01

156

Axonal Noise as a Source of Synaptic Variability  

PubMed Central

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 µm diameter) causes random fluctuations in AP waveforms. AP height and width, both experimentally characterised parameters of post-synaptic response amplitude, vary e.g. by up to 20 mV and 0.5 ms while a single AP propagates in C-fibre axons. We show how AP height and width variabilities increase with a ¾ power-law as diameter decreases and translate these fluctuations into post-synaptic response variability using biophysical data and models of synaptic transmission. We find for example that for mammalian unmyelinated axons with 0.2 µm diameter (matching cerebellar parallel fibres) axonal 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.

Neishabouri, Ali; Faisal, A. Aldo

2014-01-01

157

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 µm diameter) causes random fluctuations in AP waveforms. AP height and width, both experimentally characterised parameters of post-synaptic response amplitude, vary e.g. by up to 20 mV and 0.5 ms while a single AP propagates in C-fibre axons. We show how AP height and width variabilities increase with a ¾ power-law as diameter decreases and translate these fluctuations into post-synaptic response variability using biophysical data and models of synaptic transmission. We find for example that for mammalian unmyelinated axons with 0.2 µm diameter (matching cerebellar parallel fibres) axonal 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

158

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

159

Development of standalone coherent EUV scatterometry microscope with high-harmonic-generation EUV source  

NASA Astrophysics Data System (ADS)

For extreme ultraviolet (EUV) mask evaluation, we have developed the coherent EUV scatterometry microscope (CSM), which is equipped with a laboratory coherent EUV source for high-harmonic generation (HHG) and acts as a standalone EUV tool. The CSM records the diffraction from mask patterns directly with a charge-coupled-device (CCD) camera, which was illuminated with the coherent EUV light. The pattern image and the critical dimension values are evaluated by using the diffraction image with iterative calculations based on coherent diffraction imaging. The 59th high-order harmonic generation at a wavelength of 13.5 nm was pumped by a tabletop 6 mJ, 32 fs, Ti:sapphire laser system. EUV output energy of 1 ?W was successfully achieved. We observed the EUV mask using the HHG-CSM system. A very small 2 nm-wide line defect was successfully detected while located in an 88 nm line-and-space pattern.

Harada, Tetsuo; Nakasuji, Masato; Watanabe, Takeo; Nagata, Yutaka; Kinoshita, Hiroo

2012-06-01

160

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

161

HSCT Nozzle Source Noise Programs at Pratt and Whitney.  

National Technical Information Service (NTIS)

The topics covered include the following: 20 dB jet noise suppression; ejector nozzle technology program - noise reduction vs. flow augmentation; mixer ejector nozzle technology challenges; 1989 High Speed Civil Transport (HSCT) 2-D ejector model test in ...

A. M. Stern

1992-01-01

162

Aircraft noise source and computer programs - User's guide  

NASA Technical Reports Server (NTRS)

The application of computer programs for predicting the noise-time histories and noise contours for five types of aircraft is reported. The aircraft considered are: (1) turbojet, (2) turbofan, (3) turboprop, (4) V/STOL, and (5) helicopter. Three principle considerations incorporated in the design of the noise prediction program are core effectiveness, limited input, and variable output reporting.

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

1973-01-01

163

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

164

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

PubMed

An experimental study was performed to compare the annoyances from civil-aircraft noise, military-aircraft noise, railway noise, and road-traffic noise. Two-way within-subjects designs were applied in this research. Fifty-two subjects, who were naive listeners, were given various stimuli with varying levels through a headphone in an anechoic chamber. Regardless of the frequency weighting network, even under the same average energy level, civil-aircraft noise was the most annoying, followed by military-aircraft noise, railway noise, and road-traffic noise. In particular, penalties in the time-averaged, A-weighted sound level (TAL) of about 8, 5, and 5 dB, respectively, were found in the civil-aircraft, military-aircraft, and railway noises. The reason could be clarified through the high-frequency component and the variability in the level. When people were exposed to sounds with the same maximum A-weighted level, a railway bonus of about 3 dB was found. However, transportation noise has been evaluated by the time-averaged A-weighted level in most countries. Therefore, in the present situation, the railway bonus is not acceptable for railway vehicles with diesel-electric engines. PMID:20136203

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

2010-02-01

165

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

NASA Technical Reports Server (NTRS)

A formulation is given for a collection of phonons (sound) in a fluid at a non-zero temperature which uses the simple harmonic oscillator twice; one to give a stochastic thermal 'noise' process and the other which generates a coherent Glauber state of phonons. Simple thermodynamic observables are calculated and the acoustic two point function, 'contrast' is presented. The role of 'coherence' in an equilibrium system is clarified by these results and the simple harmonic oscillator is a key structure in both the formulation and the calculations.

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

1993-01-01

166

Second-harmonic-generation microsystem light source at 488 nm for Raman spectroscopy.  

PubMed

A microsystem excitation light source emitting at 488 nm is presented. A direct single-pass nonlinear frequency conversion using a diode laser emission at 976 nm and a periodically poled lithium niobate waveguide crystal for efficient second-harmonic generation is demonstrated. This was realized on a micro-optical bench with a combined thermal management and a footprint of (25 mm x 5 mm). At 217 mW fundamental power a generated power of 56 mW at 488 nm with a conversion efficiency of 26% was achieved. With a power stability below 1%, this wavelength stabilized compact device is well suited for Raman spectroscopy. PMID:19148260

Maiwald, Martin; Jedrzejczyk, Daniel; Sahm, Alexander; Paschke, Katrin; Güther, Reiner; Sumpf, Bernd; Erbert, Götz; Tränkle, Günther

2009-01-15

167

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.

Kœnig, Maxime; Cavalieri, André V. G.; Jordan, Peter; Delville, Joël; Gervais, Yves; Papamoschou, Dimitri

2013-09-01

168

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

169

The Effects of Correlated Noise in Array Observations of Radio Sources  

Microsoft Academic Search

Arrays of radio telescopes are now routinely used not only to map extended radio sources, and make high accuracy astrometric measurement of point sources, but to provide increased signal-to-noise when observing faint sources. In this latter case, calculation of the achievable signal-to-noise becomes complicated if there are radio sources in the field of view other than the target source. These

Rachel J. Dewey

1992-01-01

170

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

171

Reducing ion beam noise of vacuum arc ion sources  

SciTech Connect

Vacuum arc ion sources are known for delivering high currents of metal ion beams. By Langmuir probe and Faraday cup measurements it is shown that fluctuations of the ion beam current are due to the fluctuations of plasma density which in turn are due to the explosive nature of plasma production at cathode spots. Humphries and co-workers and later Oks and co-workers have shown that beam fluctuations can be reduced by inserting biased meshes in the plasma. Here, the idea of ion extraction at kV-level with post-acceleration is investigated. The high voltage allows us to use coarse, ridged meshes or grids. The combination of an extractor operating in the overdense plasma regime with post-acceleration lead to very reproducible, practically ''noiseless'' ion beams however at the expense of low ion current density. The noise reduction is due to ion optics effects. Although the current setup is not suitable for a heavy ion fusion injector due to the low beam current and the risk of extractor voltage breakdown, further development of the concept may lead to reproducible beam pulses of sufficiently high current and brightness.

Anders, Andre; Hollinger, Ralph

2001-08-29

172

Environmentally induced noises in an actively mode-locked erbium fibre laser operating in the second-order rational harmonic mode locking regime  

Microsoft Academic Search

We investigate the influence of environmentally induced cavity length fluctuations on the energy and phase noises of an optical pulse train generated by an actively mode-locked erbium-doped fibre laser that is operated in the second-order rational harmonic mode-locking regime. Using a simple model that was recently proposed to describe this particular regime, we identify the specific nature of these energy

O. Pottiez; P. Mégret; M. Blondel

2002-01-01

173

A hydro-acoustic source model in calculating noise field generated by breaking waves  

Microsoft Academic Search

To develop a complete model for the breaking wave noise, it is necessary to relate the source quantities to the physical parameters of the wave-breaking and noise-generation processes. In this paper, the source structure of an individual breaking wave is simulated using a coupled hydro-acoustic model, which incorporates the physical processes underlying the mechanisms of the generation of the noise.

Xuemei Chen; Steven L. Means; William G. Szymczak; Joel C. W. Rogers

2005-01-01

174

Acoustical Holography Technology for Surface Noise Sources Location on Underwater Cylindrical Shell Structure  

Microsoft Academic Search

Cylindrical Multi-reference Statistically Optimized Near-field Acoustical Holography technology is proposed to apply to surface noise sources locating on underwater cylindrical shell structure. Implementing process of the proposed noise sources locating technology, is compose of arranging reference points for the aimed system, carrying out partial sound field decomposition, reconstructing partial sound field on reconstruction surface and assembling composite vector of sound

Guang-fu Cheng; Bin Xiao; San-de Wang; Wen-shuai Liu

2010-01-01

175

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

176

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

177

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

PubMed

In this study, urban soundscapes containing combined noise sources were evaluated through field surveys and laboratory experiments. The effect of water sounds on masking urban noises was then examined in order to enhance the soundscape perception. Field surveys in 16 urban spaces were conducted through soundwalking to evaluate the annoyance of combined noise sources. Synthesis curves were derived for the relationships between noise levels and the percentage of highly annoyed (%HA) and the percentage of annoyed (%A) for the combined noise sources. Qualitative analysis was also made using semantic scales for evaluating the quality of the soundscape, and it was shown that the perception of acoustic comfort and loudness was strongly related to the annoyance. A laboratory auditory experiment was then conducted in order to quantify the total annoyance caused by road traffic noise and four types of construction noise. It was shown that the annoyance ratings were related to the types of construction noise in combination with road traffic noise and the level of the road traffic noise. Finally, water sounds were determined to be the best sounds to use for enhancing the urban soundscape. The level of the water sounds should be similar to or not less than 3 dB below the level of the urban noises. PMID:20329835

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

2010-03-01

178

Some applications of Hartmann-type sources in aircraft noise research  

NASA Astrophysics Data System (ADS)

Inflight shielding experiments were performed with a slender delta research aircraft fitted with needle stabilized generators having 19mm diameter driving jets operated from the high pressure turbine of the aircraft engine. Acoustic power output is 1 kW and consists of a strong fundamental 2.8 kHz tone and higher harmonics, discernible above engine noise. Comparative wind tunnel experiments employed quarter-scale versions built to match the tunnel model and these operated at 11 kHz, the output level being well above tunnel backgroung noise. Calibration in an anechoic room shows output to be steady and nearly omnidirectional.

Holbeche, T. A.; Jeffrey, R. W.

1980-11-01

179

Computational science and re-discovery: open-source implementation of ellipsoidal harmonics for problems in potential theory  

NASA Astrophysics Data System (ADS)

We present two open-source (BSD) implementations of ellipsoidal harmonic expansions for solving problems of potential theory using separation of variables. Ellipsoidal harmonics are used surprisingly infrequently, considering their substantial value for problems ranging in scale from molecules to the entire solar system. In this paper, we suggest two possible reasons for the paucity relative to spherical harmonics. The first is essentially historical—ellipsoidal harmonics developed during the late 19th century and early 20th, when it was found that only the lowest-order harmonics are expressible in closed form. Each higher-order term requires the solution of an eigenvalue problem, and tedious manual computation seems to have discouraged applications and theoretical studies. The second explanation is practical: even with modern computers and accurate eigenvalue algorithms, expansions in ellipsoidal harmonics are significantly more challenging to compute than those in Cartesian or spherical coordinates. The present implementations reduce the 'barrier to entry' by providing an easy and free way for the community to begin using ellipsoidal harmonics in actual research. We demonstrate our implementation using the specific and physiologically crucial problem of how charged proteins interact with their environment, and ask: what other analytical tools await re-discovery in an era of inexpensive computation?

Bardhan, Jaydeep P.; Knepley, Matthew G.

2012-01-01

180

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

181

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

NASA Astrophysics Data System (ADS)

Multimodal nonlinear optical imaging has opened new opportunities and becomes a powerful tool for imaging complex tissue samples with inherent 3D spatial resolution.. We present a robust and easy-to-operate approach to add the coherent anti-stokes Raman scattering (CARS) imaging modality to a widely used multiphoton microscope. The laser source composed of a Mai Tai femtosecond laser and an optical parametric oscillator (OPO) offers one-beam, two-beam and three-beam modalities. The Mai Tai output at 790 nm is split into two beams, with 80% of the power being used to pump the OPO. The idler output at 2036 nm from OPO is doubled using a periodically poled lithium niobate (PPLN) crystal. This frequency-doubled idler beam at 1018 nm is sent through a delay line and collinearly combined with the other Mai Tai beam for CARS imaging on a laser-scanning microscope. This Mai Tai beam is also used for multiphoton fluorescence and second harmonic generation (SHG) imaging. The signal output at 1290 nm from OPO is used for SHG and third-harmonic generation (THG) imaging. External detectors are installed for both forward and backward detection, whereas two internal lamda-scan detectors are employed for microspectroscopy analysis. This new system allows vibrationally resonant CARS imaging of lipid bodies, SHG imaging of collagen fibers, and multiphoton fluorescence analysis in fresh tissues. As a preliminary application, the effect of diacylglycerol acyltransferase 1 (DGAT1) deficiency on liver lipid metabolism in mice was investigated.

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

2009-02-01

182

Regression Models for Identifying Noise Sources in Magnetic Resonance Images  

PubMed Central

Stochastic noise, susceptibility artifacts, magnetic field and radiofrequency inhomogeneities, and other noise components in magnetic resonance images (MRIs) can introduce serious bias into any measurements made with those images. We formally introduce three regression models including a Rician regression model and two associated normal models to characterize stochastic noise in various magnetic resonance imaging modalities, including diffusion-weighted imaging (DWI) and functional MRI (fMRI). Estimation algorithms are introduced to maximize the likelihood function of the three regression models. We also develop a diagnostic procedure for systematically exploring MR images to identify noise components other than simple stochastic noise, and to detect discrepancies between the fitted regression models and MRI data. The diagnostic procedure includes goodness-of-fit statistics, measures of influence, and tools for graphical display. The goodness-of-fit statistics can assess the key assumptions of the three regression models, whereas measures of influence can isolate outliers caused by certain noise components, including motion artifacts. The tools for graphical display permit graphical visualization of the values for the goodness-of-fit statistic and influence measures. Finally, we conduct simulation studies to evaluate performance of these methods, and we analyze a real dataset to illustrate how our diagnostic procedure localizes subtle image artifacts by detecting intravoxel variability that is not captured by the regression models.

Zhu, Hongtu; Li, Yimei; Ibrahim, Joseph G.; Shi, Xiaoyan; An, Hongyu; Chen, Yashen; Gao, Wei; Lin, Weili; Rowe, Daniel B.; Peterson, Bradley S.

2009-01-01

183

Investigation of Apparent Seismic Velocity Changes Caused by Microseism Noise Source Variability  

NASA Astrophysics Data System (ADS)

Currently there is strong interest in monitoring temporal changes in seismic wave velocity in various geological settings. These settings can range from volcano monitoring to reservoir monitoring amongst others. Green's functions are often used to observe temporal variations in seismic wave velocity as their arrival times contain information about velocity changes. Green's functions are typically retrieved by cross correlating ambient noise recorded at given pair of stations. Theoretically the recorded wavefields used for the cross correlation should be diffuse. For applications in seismic imagery, the background noise sources should be uniformly distributed in space or the wavefield must be highly scattered but neither condition typically occur in nature. However temporal and spatial variations of non-uniformly distributed noise sources may lead to apparent changes in Green's functions which are related to the source not the path. This could lead to a misinterpretation of temporal changes in wave velocity. We track the spatial and temporal distribution of the noise sources using seismic arrays, located in Ireland. It is a good location in which to study these effects, as it is tectonically very quiet and is relatively close to large microseism noise sources in the North Atlantic, allowing a quantification of noise source heterogeneity. The temporal variations in seismic wave velocity are calculated and compared to the temporal and spatial distribution of the microseism noise sources. The initial results show how the direct arrival waveform and the arrival time of the Green's functions correlate with spatial and temporal variability of the microseism noise sources. Under these conditions we also explore the minimum noise trace length required for the Green's functions to converge. We quantify the degree to which apparent velocity variations using direct arrivals are caused by changes in the sources and assess the use of coda wave arrivals in mitigating source related influences.

Volk, M. F.; Bean, C. J.; Lokmer, I.; Craig, D.

2013-12-01

184

A brief review of the source noise technology applicable to fixed-wing military aircraft  

NASA Astrophysics Data System (ADS)

Although the last two decades have seen major reductions in the noise from civil aircraft, noise from military operations, both around airfields and from low-flying aircraft, continues to be a source of irritation and a potential health hazard. Because of the continuing concern about the noise levels produced by combat aircraft, the following paper is intended to provide some of the background to the main conclusions and recommendations reached in the final report of the NATO/Committee on the Challenges of a Modern Society (CCMS) Pilot Study on aircraft noise. Although biased towards fixed wing combat aircraft noise, the paper also considers other fixed wing military aircraft, but specifically excludes sonic booms and rotary wing aircraft as they both have their own particular noise sources and problems.

Pinker, R. A.

1992-04-01

185

On the sources of wayside noise generated by high-speed trains  

Microsoft Academic Search

A linear array of 14 microphones was used to measure radiated noise generated by a four-carriage electric train travelling at speeds between 160 and 250 km\\/h. Most of the results given in this paper pertain to apparent source locations of wheel\\/rail interaction noise, although preliminary data collected in a concurrent study of railway aerodynamic noise are briefly mentioned. An analysis

W. F. King; D. Bechert

1979-01-01

186

Long global gyrokinetic simulations: Source terms and particle noise control  

SciTech Connect

In global gyrokinetic simulations it takes a long time for the turbulence to reach a quasisteady state, and quantitative predictions about the quasisteady state turbulence have been difficult to obtain computationally. In particular, global particle-in-cell gyrokinetic simulations have been inefficient for long simulations due to the accumulation of noise. It is demonstrated that a simple Krook operator can effectively control noise; it also introduces an unphysical dissipation, which damps the zonal flows and can significantly affect simulation results even when the relaxation time is very long. However, it is possible to project out the effects of the Krook operator on the zonal flows. This permits noise accumulation to be controlled while preserving the physics of interest; simulations are then run to determine the level of quasisteady state transport and the variation across the ensemble of turbulent dynamics. Convergence is demonstrated both in the number of computational particles and the unphysical relaxation time.

McMillan, B. F.; Jolliet, S.; Tran, T. M.; Villard, L. [Centre de Recherches en Physique des Plasmas, Association Euratom-Confederation Suisse, Ecole Polytechnique Federale de Lausanne, PPB, 1015 Lausanne (Switzerland); Bottino, A. [Max Planck Institut fur Plasmaphysik, IPP-EURATOM Association, Garching (Germany); Angelino, P. [Association Euraton-CEA, CEA/DSM/DRFC Cadarache (France)

2008-05-15

187

Coherent diffractive imaging microscope with a tabletop high harmonic EUV source  

NASA Astrophysics Data System (ADS)

Coherent diffractive imaging (CDI) using EUV/X-rays has proven to be a powerful microscopy method for imaging nanoscale objects. In traditional CDI, the oversampling condition limits its applicability to small, isolated objects. A new technique called keyhole CDI was demonstrated on a synchrotron X-ray source to circumvent this limitation. Here we demonstrate the first keyhole CDI result with a tabletop extreme ultraviolet (EUV) source. The EUV source is based on high harmonic generation (HHG), and our modified form of keyhole CDI uses a highly reflective curved EUV mirror instead of a lossy Fresnel zone plate, offering a ~10x increase in photon throughput of the imaging system, and a more uniform illumination on the sample. In addition, we have demonstrated a record 22 nm resolution using our tabletop CDI setup, and also the successful extension to reflection mode for a periodic sample. Combining these results with keyhole CDI will open the path to the realization of a compact EUV microscope for imaging general non-isolated and non-periodic samples, in both transmission and reflection mode.

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

2013-03-01

188

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

189

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

190

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

191

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

NASA Technical Reports Server (NTRS)

In this paper we discuss the problem of high speed rotor noise prediction. In particular, we propose that from the point of view of the acoustic analogy, shocks around rotating blades are sources of sound. We show that, although for a wing at uniform steady rectilinear motion with shocks the volume quadrupole and shock sources cancel in the far field to the order of 1/r, this cannot happen for rotating blades. In this case, some cancellation between volume quadrupoles and shock sources occurs, yet the remaining shock noise contribution is still potent. A formula for shock noise prediction is presented based on mapping the deformable shock surface to a time independent region. The resulting equation is similar to Formulation 1A of Langley. Shock noise prediction for a hovering model rotor for which experimental noise data exist is presented. The comparison of measured and predicted acoustic data shows good agreement.

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

1991-01-01

192

Harmonic Generation by Femtosecond Laser-Solid Interaction: A Coherent ``Water-Window'' Light Source?  

Microsoft Academic Search

The generation of harmonics by short, intense laser pulses reflected from a solid-density plasma is investigated using particle-in-cell simulation. High irradiance, obliquely incident p-polarized light generates harmonics via relativistic electrons dragged across the vacuum-solid interface. This mechanism does not exhibit the limitation previously predicted for lower intensities of a maximum harmonic ``cutoff'' nmax = omegap\\/omega0. For Ilambda2>1019 W cm-2 mum2

Paul Gibbon

1996-01-01

193

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

PubMed

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. PMID:21886242

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

2011-09-01

194

Effects of noise radiated from convected ring sources in coaxial dual flow. Part 1: The noise from unheated jets  

NASA Technical Reports Server (NTRS)

The effects of flight on sound radiated from embedded, uncorrelated ring sources convecting along the midst of the primary and the secondary streams of a coaxial dual flow which emerges from a moving nozzle into the ambience are studied. Cold jets are examined. The problem is posed as a double vortex-sheet flow model which involves deliberate suppression of inherent instabilities of the flow and is formulated, as a linear problem, in terms of the combined contributions of two independent uncorrelated quadrupole-type ring sources, the one convecting in the primary flow representing the sources generated due to the interaction at the primary/secondary interface and the other convecting in the secondary flow representing the sources generated due to the interaction at the secondary/ambient interface. The analysis shows that the effects of flight induce (1) amplication of noise in the forward quadrant, (2) reduction of noise in the aft quadrant and (3) absolutely no impact on radiation of noise at Theta = 90 deg to the jet axis.

Dash, R.

1982-01-01

195

Neutron noise transmission characteristics of multiplying media and neutron noise source localization in liquid-metal fast breeder reactors by using the neutron wave propagation technique  

Microsoft Academic Search

The results of a theoretical study of noise transmission characteristics of multiplying media and neutron noise source localization in liquid-metal fast breeder reactors (LMFBRs) by using the neutron wave propagation technique is reported. The study was carried out using one-group as well as multigroup diffusion theory. Both theories show that the noise transmission characteristics are quite sensitive to the multiplication

T. M. John; O. P. Singh

1983-01-01

196

Sources of image degradation in fundamental and harmonic ultrasound imaging using nonlinear, full-wave simulations.  

PubMed

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-andsum beamforming is used to generate point spread functions (PSF) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is reverberation from near-field structures. Reverberation clutter in the harmonic PSF is 26 dB higher than the fundamental PSF. An artificial medium with uniform velocity but unchanged impedance characteristics indicates that for the fundamental PSF, the primary source of degradation is phase aberration. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beamforming algorithm to generate images. These beamformed images are compared with images obtained from convolution of the PSF with a scatterer field to demonstrate that a very large portion of the PSF must be used to accurately represent the clutter observed in conventional imaging. PMID:21507753

Pinton, Gianmarco F; Trahey, Gregg E; Dahl, Jeremy J

2011-04-01

197

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

198

Jet noise source location by cross-correlation of far field microphone signals  

NASA Technical Reports Server (NTRS)

A theoretical analysis is presented for the evaluation of correlation functions of many spatially separated noise sources in a jet. A one-dimensional model is considered in which the noise sources are located on the axis of the jet downstream of the nozzle. The theory for extracting the spatial distribution from far field cross-correlations by signal analysis is derived. The advantage of this method is that difficult numerical inversions are not needed.

Parthasarathy, S. P.

1975-01-01

199

Sound source location and discrimination from background noise in wind-tunnel tests  

Microsoft Academic Search

The applicability of the acoustic mirror technique to sound source location and discrimination from background noise in aero-acoustic wind-tunnel tests was investigated through measurements of the noise of a model source in the open test section of a low-speed wind-tunnel. The spatial resolution and the gain factor of the mirror were found to be diminished by scattering and refraction of

F.-R. Grosche; H. Stiewitt; B. Binder

1975-01-01

200

Phased Array Radiometer Calibration Using a Radiated Noise Source  

NASA Technical Reports Server (NTRS)

Electronic beam steering capability of phased array antenna systems offer significant advantages when used in real aperture imaging radiometers. The sensitivity of such systems is limited by the ability to accurately calibrate variations in the antenna circuit characteristics. Passive antenna systems, which require mechanical rotation to scan the beam, have stable characteristics and the noise figure of the antenna can be characterized with knowledge of its physical temperature [1],[2]. Phased array antenna systems provide the ability to electronically steer the beam in any desired direction. Such antennas make use of active components (amplifiers, phase shifters) to provide electronic scanning capability while maintaining a low antenna noise figure. The gain fluctuations in the active components can be significant, resulting in substantial calibration difficulties [3]. In this paper, we introduce two novel calibration techniques that provide an end-to-end calibration of a real-aperture, phased array radiometer system. Empirical data will be shown to illustrate the performance of both methods.

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

2010-01-01

201

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

SciTech Connect

The detection of gravitational waves is a very active research field at the moment. In Brazil the gravitational wave detector is called Mario SCHENBERG. Because of its high sensitivity it is necessary to model mathematically all known 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 lightnings close to the experiment. Such disturbances may influence the vibrations of the antenna's normal modes and mask possible gravitational wave signals. In this work we model the interaction between lightnings and SCHENBERG antenna and calculate the intensity of the noise due to a close lightning stroke in the detected signal. We find that the noise generated does not disturb the experiment significantly.

Magalhaes, Nadja Simao [Centro Federal de Educacao Tecnologica de Sao Paulo, Rua Pedro Vicente 625, Sao Paulo, SP 01109-010 (Brazil); Departamento de Fisica, Instituto Tecnologico de Aeronautica, Pca. Mal. Eduardo Gomes 50, Sao Jose dos Campos, SP 12228-900 (Brazil); Marinho, Rubens de Melo Jr. [Departamento de Fisica, Instituto Tecnologico de Aeronautica, Pca. Mal. Eduardo Gomes 50, Sao Jose dos Campos, SP 12228-900 (Brazil); Aguiar, Odylio Denys de [Divisao de Astrofisica, Instituto Nacional de Pesquisas Espaciais, Av. dos Astronautas 1758, Sao Jose dos Campos, SP 12227-010 (Brazil); Frajuca, Carlos [Centro Federal de Educacao Tecnologica de Sao Paulo, Rua Pedro Vicente 625, Sao Paulo, SP 01109-010 (Brazil)

2005-11-15

202

Cabin noise source-path identification for AD-200 ultralight aircraft  

NASA Astrophysics Data System (ADS)

A new diagnostic method based on the two microphone cross spectral acoustic intensity technique was applied to identificate the cabin noise source paths. The simulating test using a loudspeaker and an electric-mechanical shaker to simulate the airborne and structureborne noise sources was conducted to prove the confidence of the proposed method. The results show that the discrepancy between measured and separated values of total average acoustic intensity level are respectively 1.7 dB(A) and 0.4 (A) for structureborne and airborne components, which is ac ceptable for engineering application. The static test with engine in operation shows that the airborne noise through the rear board of cabin is the dominant contributor to cabin noise. This is a reasonable result, which gives a guide to cabin noise control treatment.

Hu, Zhangwei; Yin, Jianping; Zhang, Qiang

203

Cortical Dipole Imaging for Multiple Signal Sources Considering Time-Varying Non-Uniform Noise  

NASA Astrophysics Data System (ADS)

Cortical dipole imaging is one of the spatial enhancement techniques from the scalp electroencephalogram. We investigated the dipole imaging for multiple signal sources under time-varying non-uniform noise conditions. The effects of incorporating statistical information of noise into the spatiotemporal inverse filter were examined by computer simulations and experimental studies in three sphere volume conductor model. The parametric projection filter that incorporated with noise covariance was applied to the inverse problem of EEG measurements. The noise covariance matrix was estimated by applying independent component analysis to the scalp potentials. The spatial filter was expanded to apply to the time-varying non-uniform noise conditions such as eye blink artifact. Moreover, multiple dipole distributions were introduced to extract and to visualize individual signal sources. The proposed imaging technique was applied to human experimental data of visual evoked potentials. We obtained reasonable results that coincide to physiological knowledge.

Hori, Junichi; Watanabe, Yoshiki

204

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 Gräfenberg 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, Céline

2014-05-01

205

Numerical noise analysis for nonlinear circuits with a periodic large signal excitation including cyclostationary noise sources  

Microsoft Academic Search

A numerical small signal noise analysis method for nonlinear circuits with a periodic large signal excitation, e.g. mixer circuits and switching circuits, is proposed. For small signal input responses, these nonlinear circuits are modeled as their linear periodic time-varying circuits. First, a numerical calculation method for the time-varying transfer function of a linear periodic time-varying circuit is described. Next, a

Makiko Okumura; Hiroshi Tanimoto; Tetsuro Itakura; Tsutomu Sugawara

1993-01-01

206

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

207

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

208

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

NASA Astrophysics Data System (ADS)

Photonic crystal surface emitting lasers (PCSELs) have recently been achieved with both a single spectrum and narrow spot beam pattern under several hundred mW of output power. Even though the high coherence properties of PCSELs are expected to be used for various applications, we have focused on a pumping light source for a wavelength conversion system in this work. We fabricated a 1.06 ?m PCSEL with a square lattice 2D photonic crystal in which the lattice period corresponded to the lasing wavelength to obtain green light. The fabricated device had a narrow spot beam pattern of less than 0.5 degrees and a single spectrum at 1068 nm under CW output power of more than 200 mW despite the broad emitting area of 200 × 200 ?m2. The wavelength conversion system used single pass second-harmonic generation (SHG) that consisted of only the PCSEL and 50 mm long bulk MgO doped periodically with poled lithium niobate (MgO:PPLN) as a nonlinear medium, i.e., it was a lens-free system. It was important to maintain the high brightness of the pumping light in this system with a single spectrum through the MgO:PPLN. As a result, SHG light was obtained at 534 nm with a narrow spot beam pattern, which followed the beam quality of the PCSEL under CW operation.

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

2014-02-01

209

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

210

Comparison of noise properties of laser sources intended for multidimensional interferometric tools  

NASA Astrophysics Data System (ADS)

This work is oriented towards investigation of displacement measurement uncertainty contribution of different laser sources that are suitable for powering multidimensional interferometric positioning system for local probe microscopy. Main aim of this work was to find a suitable laser source for this measuring system. Most common 633 nm He-Ne lasers were compared with 532 nm frequency-doubled Nd:YAGs of different construction (external cavity doubling, ring configuration laser). We investigated amplitude and frequency noise of several lasers intended for micro- and nano- CMMs (coordinate measurement machines) and compared their noise properties together with the aim to find the best option. Amplitude noise measurements were done directly with the help of low noise photodetector, frequency noise of tested lasers was measured by two approaches - first with the help of Fabry-Perot resonator, which was used as a frequency discriminator converting a frequency (phase) noise into the amplitude one and second directly with the help of interferometer - measuring of interferometric fringe signal and position evaluation - another type of frequency discriminator. Both frequency noise and also amplitude noise measurements were done simultaneously to have a chance to compare both approaches and results.

Hrabina, Jan; Lazar, Josef; ?íp, Ondrej

2012-01-01

211

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

212

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

NASA Technical Reports Server (NTRS)

A widely recognized problem in jet engine fan noise is the discrepancy between inflight and static tests. This discrepancy consists of blade passing frequency tones, caused by ingested turbulence that appear in the static tests but not in flight. To reduce the ingested distortions and turbulence in an anechoic chamber, a reverse cone inlet is used to guide the air into the fan. This inlet also has provisions for boundary layer suction and is used in conjunction with a turbulence control structure (TCS) to condition the air impinging on the fan. The program was very successful in reducing the ingested turbulence, to the point where reductions in the acoustic power at blade passing frequency are as high as 18 db for subsonic tip speeds. Even with this large subsonic tone suppression, the supersonic tip speed tonal content remains largely unchanged, indicating that the TCS did not appreciably attenuate the noise but effects the generation via turbulence reduction. Turbulence mapping of the inlet confirmed that the tone reductions are due to a reduction in turbulence, as the low frequency power spectra of the streamwise and transverse turbulence were reduced by up to ten times and 100 times, respectively.

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

1978-01-01

213

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

National Technical Information Service (NTIS)

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...

C. E. Hughes R. J. Jeracki R. P. Woodward C. J. Miller

2005-01-01

214

Ambient noise energy bursts observation and modeling: Trapping of harmonic structure-soil induced waves in a topmost sedimentary layer  

Microsoft Academic Search

We study the nature of energy bursts that appeared in the frequency range 3-5 Hz in ambient seismic noise recorded in the Grenoble basin (French Alps) during a seismological array experiment. A close agreement is found between the identified azimuths of such noise bursts with the location of an industrial chimney. In-situ measurements of the chimney dynamic characteristics show a

C. Cornou; P. Guéguen; P.-Y. Bard

2004-01-01

215

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

SciTech Connect

We describe and characterize a simple, low cost, low phase noise microwave source that operates near 6.800 GHz for agile, coherent manipulation of ensembles of {sup 87}Rb. Low phase noise is achieved by directly multiplying a low phase noise 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency source to provide the desired phase, amplitude, and frequency control. Before modulation, the source has a single sideband phase noise near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting source is estimated to contribute added spin-noise variance 16 dB below the quantum projection noise level during quantum nondemolition measurements of the clock transition in an ensemble 7 x 10{sup 5} {sup 87}Rb atoms.

Chen Zilong; Bohnet, Justin G.; Weiner, Joshua M.; Thompson, James K. [JILA, National Institute of Standards and Technology, and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

2012-04-15

216

A low phase noise microwave source for atomic spin squeezing experiments in 87Rb.  

PubMed

We describe and characterize a simple, low cost, low phase noise microwave source that operates near 6.800 GHz for agile, coherent manipulation of ensembles of (87)Rb. Low phase noise is achieved by directly multiplying a low phase noise 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency source to provide the desired phase, amplitude, and frequency control. Before modulation, the source has a single sideband phase noise near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting source is estimated to contribute added spin-noise variance 16 dB below the quantum projection noise level during quantum nondemolition measurements of the clock transition in an ensemble 7 × 10(5) (87)Rb atoms. PMID:22559559

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

2012-04-01

217

A low phase noise microwave source for atomic spin squeezing experiments in 87Rb  

NASA Astrophysics Data System (ADS)

We describe and characterize a simple, low cost, low phase noise microwave source that operates near 6.800 GHz for agile, coherent manipulation of ensembles of 87Rb. Low phase noise is achieved by directly multiplying a low phase noise 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency source to provide the desired phase, amplitude, and frequency control. Before modulation, the source has a single sideband phase noise near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting source is estimated to contribute added spin-noise variance 16 dB below the quantum projection noise level during quantum nondemolition measurements of the clock transition in an ensemble 7 × 105 87Rb atoms.

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

2012-04-01

218

A SOUND SOURCE LOCALIZATION TECHNIQUE TO SUPPORT SEARCH AND RESCUE IN LOUD NOISE ENVIRONMENTS  

NASA Astrophysics Data System (ADS)

At some sites of earthquakes and other disasters, rescuers search for people buried under rubble by listening for the sounds which they make. Thus developing a technique to localize sound sources amidst loud noise will support such search and rescue operations. In this paper, we discuss an experiment performed to test an array signal processing technique which searches for unperceivable sound in loud noise environments. Two speakers simultaneously played a noise of a generator and a voice decreased by 20 dB (= 1/100 of power) from the generator noise at an outdoor space where cicadas were making noise. The sound signal was received by a horizontally set linear microphone array 1.05 m in length and consisting of 15 microphones. The direction and the distance of the voice were computed and the sound of the voice was extracted and played back as an audible sound by array signal processing.

Yoshinaga, Hiroshi; Mizutani, Koichi; Wakatsuki, Naoto

219

Highly efficient, low-noise Yb femtosecond fiber source  

Microsoft Academic Search

Summary form only given. With the recent availability of Raman-shifted, widely tunable Er fiber laser pulse sources, the direct injection of Yb fiber amplifiers with femtosecond pulses from a frequency-converted Er-fiber laser has become possible. The exploitation of the unique efficiency and large bandwidth of Yb fiber amplifiers thus allows the construction of highly compact ultrafast laser sources operating at

M. E. Fermann; M. L. Stock; A. Galvanauskas; A. Hariharan; G. Sucha; D. Harter; L. Goldberg

2000-01-01

220

Sound source localization of filtered noises by listeners with normal hearing: A statistical analysis  

PubMed Central

Several measures of sound source localization performance of 45 listeners with normal hearing were obtained when loudspeakers were in the front hemifield. Localization performance was not statistically affected by filtering the 200-ms, 2-octave or wider noise bursts (125 to 500, 1500 to 6000, and 125 to 6000?Hz wide noise bursts). This implies that sound source localization performance for noise stimuli is not differentially affected by which interaural cue (interaural time or level difference) a listener with normal hearing uses for sound source localization, at least for relatively broadband signals. This sound source localization task suggests that listeners with normal hearing perform with high reliability/repeatability, little response bias, and with performance measures that are normally distributed with a mean root-mean-square error of 6.2° and a standard deviation of 1.79°.

Yost, William A.; Loiselle, Louise; Dorman, Michael; Burns, Jason; Brown, Christopher A.

2013-01-01

221

Rotor blade-vortex interaction impulsive noise source identification and correlation with rotor wake predictions  

Microsoft Academic Search

An acoustic source localization scheme applicable to noncompact moving sources is developed and applied to the blade-vortex interaction (BVI) noise data of a 40-percent scale BO-105 model rotor. A generalized rotor wake code is employed to predict possible VBI locations on the rotor disk and is found quite useful in interpreting the acoustic localization results. The highly varying directivity patterns

W. R. Splettstoesser; K. J. Schultz; Ruth M. Martin

1987-01-01

222

Signal-to-noise ratio analysis for a back-action-evading measurement on a double harmonic oscillator  

NASA Astrophysics Data System (ADS)

We compute the sensitivity of a double harmonic oscillator system inserted in a back-action-evasion scheme of electromechanical transduction. This sensitivity is presented by deriving the effective temperature and the optimum observation time of the detector. Finally, the performances of this scheme on a resonant gravitational wave antenna at low temperature are discussed.

Cinquegrana, C.; Majorana, E.; Pergola, N.; Puppo, P.; Rapagnani, P.; Ricci, F.

1994-09-01

223

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

224

Optimum noise source impedance determination for GaAs FETs at room and cryogenic temperatures  

Microsoft Academic Search

An analytical technique is developed to determine the optimum noise source impedance for an extrinsic, or packaged, gallium arsenide field-effect transistor (GaAs FET) using only the small-signal s-parameters and the minimum noise figures available from the manufacturer's data sheet. The procedure is then modified to treat the special case of the intrinsic, or chip, GaAs FET as well. The technique

R. CLARK ROBERTSON; TRI T. HA

1987-01-01

225

Development in Source Modeling and Sound Propagation for Jet Noise Predictions  

NASA Technical Reports Server (NTRS)

The purpose of the research carried out under this cooperative agreement was to develop tools that could be used to improve upon the current state of the art in the prediction of noise emitted by turbulent exhaust jets. Both the source modeling and sound propagation aspects of the prediction of jet noise by acoustic analogy were examined with a view toward the development of methods which yield improved predictions over a wider range of operating conditions.

Leib, Steward

2004-01-01

226

Effect of higher harmonic control on helicopter rotor blade-vortex interaction noise: Prediction and initial validation  

NASA Technical Reports Server (NTRS)

The paper presents a status of theoretical tools of AFDD, DLR, NASA and ONERA for prediction of the effect of HHC on helicopter main rotor BVI noise. Aeroacoustic predictions from the four research centers, concerning a wind tunnel simulation of a typical descent flight case without and with HHC are presented and compared. The results include blade deformation, geometry of interacting vortices, sectional loads and noise. Acoustic predictions are compared to experimental data. An analysis of the results provides a first insight of the mechanisms by which HHC may affect BVI noise.

Beaumier, P.; Prieur, J.; Rahier, G.; Spiegel, P.; Demargne, A.; Tung, C.; Gallman, J. M.; Yu, Y. H.; Kube, R.; Vanderwall, B. G.

1995-01-01

227

Sources of image degradation in fundamental and harmonic ultrasound imaging: a nonlinear, full-wave, simulation study.  

PubMed

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain. This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-and-sum beamforming is used to generate point spread functions (PSFs) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is due to reverberation from near-field structures. Compared with fundamental imaging, reverberation clutter in harmonic imaging is 27.1 dB lower. Simulated tissue with uniform velocity but unchanged impedance characteristics indicates that for harmonic imaging, the primary source of degradation is phase aberration. PMID:21693410

Pinton, Gianmarco F; Trahey, Gregg E; Dahl, Jeremy J

2011-06-01

228

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

229

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

PubMed

A harmonic-resonator-based triboelectric nanogenerator (TENG) is presented as a sustainable power source and an active vibration sensor. It can effectively respond to vibration frequencies ranging from 2 to 200 Hz with a considerably wide working bandwidth of 13.4 Hz. This work not only presents a new principle in the field of vibration energy harvesting but also greatly expands the applicability of TENGs. PMID:23999798

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

2013-11-13

230

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

PubMed

A harmonic radar employing the use of harmonic passive RF tags can be successfully used to isolate the human respiration from environmental clutter. This paper describes the successful use of heterodyne receiver architecture with Doppler radar to track the heart-rate of a human being using passive body-worn harmonic tags in presence of a controlled noise generator at distances up to 120 cm. The heterodyne system results have been compared with those of a conventional Doppler radar for cardiopulmonary monitoring that fails to isolate the noise from heart-rate in presence of a noise source. PMID:21096353

Singh, Aditya; Lubecke, Victor

2010-01-01

231

Source directionality of ambient seismic noise inferred from three-component beamforming  

NASA Astrophysics Data System (ADS)

AbstractThe increased use of ambient seismic <span class="hlt">noise</span> for seismic imaging requires better understanding of the ambient seismic <span class="hlt">noise</span> wavefield and its <span class="hlt">source</span> locations and mechanisms. Although the <span class="hlt">source</span> regions and mechanisms of Rayleigh waves have been studied extensively, characterization of Love wave <span class="hlt">source</span> processes are sparse or absent. We present here the first systematic comparison of ambient seismic <span class="hlt">noise</span> <span class="hlt">source</span> directions within the primary (~10-20 s period) and secondary (~5-10 s period) microseism bands for both Rayleigh and Love waves in the Southern Hemisphere using vertical- and horizontal-component ambient seismic <span class="hlt">noise</span> recordings from a dense temporary network of 68 broadband seismometers in New Zealand. Our analysis indicates that Rayleigh and Love waves within the primary microseism band appear to be mostly generated in different areas, whereas in the secondary microseism band they arrive from similar backazimuths. Furthermore, the <span class="hlt">source</span> areas of surface waves within the secondary microseism band correlate well with modeled deep-water and near-coastal <span class="hlt">source</span> regions.</p> <div class="credits"> <p class="dwt_author">Behr, Y.; Townend, J.; Bowen, M.; Carter, L.; Gorman, R.; Brooks, L.; Bannister, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">232</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/20798468"> <span id="translatedtitle">DC modeling and the <span class="hlt">source</span> of flicker <span class="hlt">noise</span> in passivated carbon nanotube transistors.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">DC and intrinsic low-frequency <span class="hlt">noise</span> properties of p-channel depletion-mode carbon nanotube field effect transistors (CNT-FETs) are investigated. To characterize the intrinsic <span class="hlt">noise</span> 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 <span class="hlt">noise</span>. Under small drain-<span class="hlt">source</span> voltage, the carriers in the CNT channel are modulated by the gate electrode and the intrinsic 1/f <span class="hlt">noise</span> 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-<span class="hlt">source</span> voltages, the excess 1/f <span class="hlt">noise</span> is attributed to the <span class="hlt">noise</span> stemming from metal-CNT Schottky barrier contacts as revealed by the measurements. PMID:20798468</p> <div class="credits"> <p class="dwt_author">Kim, Sunkook; Kim, Seongmin; Janes, David B; Mohammadi, Saeed; Back, Juhee; Shim, Moonsub</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-09-24</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">233</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010Nanot..21L5203K"> <span id="translatedtitle">DC modeling and the <span class="hlt">source</span> of flicker <span class="hlt">noise</span> in passivated carbon nanotube transistors</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">DC and intrinsic low-frequency <span class="hlt">noise</span> properties of p-channel depletion-mode carbon nanotube field effect transistors (CNT-FETs) are investigated. To characterize the intrinsic <span class="hlt">noise</span> properties, a thin atomic layer deposited (ALD) HfO2 gate dielectric is used as a passivation layer to isolate CNT-FETs from environmental factors. The ALD HfO2 gate dielectric in these high-performance top-gated devices is instrumental in attaining hysteresis-free current-voltage characteristics and minimizes low-frequency <span class="hlt">noise</span>. Under small drain-<span class="hlt">source</span> voltage, the carriers in the CNT channel are modulated by the gate electrode and the intrinsic 1/f <span class="hlt">noise</span> 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-<span class="hlt">source</span> voltages, the excess 1/f <span class="hlt">noise</span> is attributed to the <span class="hlt">noise</span> stemming from metal-CNT Schottky barrier contacts as revealed by the measurements.</p> <div class="credits"> <p class="dwt_author">Kim, Sunkook; Kim, Seongmin; Janes, David B.; Mohammadi, Saeed; Back, Juhee; Shim, Moonsub</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">234</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AIPC.1474..239C"> <span id="translatedtitle">Effective bandwidth extension by combined <span class="hlt">harmonics</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Originating from signal compression techniques in radar, a wide range of ultrasound encoded excitation approaches have been developed for increasing signal strength. These techniques have been extended to nonlinear applications by isolating higher <span class="hlt">harmonic</span> signal components, thus offering higher signal-to-<span class="hlt">noise</span> ratios along with the <span class="hlt">harmonic</span>'s increased radial focusing abilities and a potentially broader bandwidth relative to the fundamental. Unfortunately, such techniques can suffer artifacts caused by overlap between the <span class="hlt">harmonics</span>. We have been investigating an alternative approach to nonlinear compression that combines the fundamental and higher <span class="hlt">harmonics</span>, effectively treating them as a single band. This extended bandwidth permits a significant increase in the ability to compress a signal. Successfully implemented, the method would permit enhanced image resolution while benefiting from the increased SNR offered by encoding. Pulse-inverted sum and difference signals are first used to isolate even and odd <span class="hlt">harmonics</span>. Matched filters specific to the <span class="hlt">source</span> geometry and the transmit signal are then separately applied to each <span class="hlt">harmonic</span> band. Verification experiments are performed using up the third <span class="hlt">harmonic</span> resulting from an underwater chirp excitation. Analysis of signal peaks after scattering indicates increased compression using the extended bandwidth as compared to standard fundamental and 2nd-<span class="hlt">harmonic</span> chirp compression. Further optimization of the compression by altering the transmission signal is also investigated. Overall, results establish the feasibility of extended bandwidth signal compression for simultaneously increasing SNR and signal resolution.</p> <div class="credits"> <p class="dwt_author">Clement, Gregory T.; Nomura, Hideyuki; Adachi, Hideo; Kamakura, Tomoo</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">235</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pdfserv.aip.org/RSINAK/vol_57/iss_7/1444_1.pdf"> <span id="translatedtitle">Low-<span class="hlt">noise</span> ac\\/dc current <span class="hlt">source</span> with continuous zero crossing</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A circuit has been developed for the measurement of the electrical characteristics of devices sensitive to extrinsic <span class="hlt">noise</span> and intrinsic power-supply transients. The circuit comprises two active current <span class="hlt">sources</span> running in opposition. The current can be ramped smoothly through current excursions of a maximum of ±1 A. Provision is also made for the modulation of the dc current output by</p> <div class="credits"> <p class="dwt_author">S. T. Ruggiero; S. Schwarzbek; R. E. Howard; E. Track</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">236</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/4780741"> <span id="translatedtitle">Detection of a Moving <span class="hlt">Source</span> in Speckle <span class="hlt">Noise</span>. Application to Exoplanet Detection</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Astronomical instruments able to detect the direct light of extra solar planets are currently under development. This paper focuses on instruments that will acquire a set of successive images where the planet (the <span class="hlt">source</span> in more general purposes) moves in a known manner on a speckled background. Performant signal processing tools are required to account for the very low signal-to-<span class="hlt">noise</span></p> <div class="credits"> <p class="dwt_author">Isabelle Smith; André Ferrari; Marcel Carbillet</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">237</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51125579"> <span id="translatedtitle">Relative intensity <span class="hlt">noise</span> reduction in superfluorescent fiber <span class="hlt">source</span> based on semi-physical simulation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">m Abstract-Relativ e intensity <span class="hlt">noise</span> (RIN) is one of the most important factors limiting performance in fiber optic gyroscopes (FOG). In order to suppress RIN in the superfluorescent fiber <span class="hlt">source</span> (SFS) of FOG effectively, we propose a semi-physical simulation with SFS signal. The semi­ physical simulation is of much practical value and can depict guideline for RIN reduction in SFS.</p> <div class="credits"> <p class="dwt_author">Haipeng Yu; Wenyuan Xu; Chunxi Zhang</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">238</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/18665176"> <span id="translatedtitle">An equivalent-<span class="hlt">source</span> model for simulating <span class="hlt">noise</span> generation in turbofan engines</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Nowadays, computational aeroacoustics (CAA) is used for simulating wave propagation in ducted turbofans, especially as computational fluid dynamics (CFD) is increasingly employed to model the identified <span class="hlt">noise</span> <span class="hlt">sources</span>. An efficient way to match the CFD and CAA domains is to make some assumptions on flow and duct geometry, so that disturbance fields can be expanded over incoming\\/outgoing acoustic modes. Based</p> <div class="credits"> <p class="dwt_author">C. Polacsek; G. Desquesnes; G. Reboul</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">239</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/50345686"> <span id="translatedtitle">Common-mode <span class="hlt">noise</span> <span class="hlt">source</span> and its passive cancellation in full-bridge resonant converter</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In this paper the results of systematic investigation into identification of dominant <span class="hlt">source</span> of CM <span class="hlt">noise</span> generation in a full bridge resonant converter are presented. It is shown that a small mismatch in an apparently symmetrical circuit can result in large CM injection. Mathematical analysis to predict the CM current injection is presented and is validated using SPICE simulation. For</p> <div class="credits"> <p class="dwt_author">Mangesh Borage; Sunil Tiwari; S. Kotaiah</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">240</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19800007614&hterms=Auto+Analyzer&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DAuto%2BAnalyzer"> <span id="translatedtitle">A study of partial coherence for identifying interior <span class="hlt">noise</span> <span class="hlt">sources</span> and paths on general aviation aircraft</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The partial coherence analysis method for <span class="hlt">noise</span> <span class="hlt">source</span>/path determination is summarized and the application to a two input, single output system with coherence between the inputs is illustrated. The augmentation of the calculations on a digital computer interfaced with a two channel, real time analyzer is also discussed. The results indicate possible <span class="hlt">sources</span> of error in the computations and suggest procedures for avoiding these errors.</p> <div class="credits"> <p class="dwt_author">Howlett, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_11");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_12");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">241</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/10473491"> <span id="translatedtitle">Mapping the signal-to-<span class="hlt">noise</span>-ratios of cortical <span class="hlt">sources</span> in magnetoencephalography and electroencephalography</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-<span class="hlt">noise</span>-ratios (SNRs) of cortical <span class="hlt">sources</span> in MEG and EEG. Data from four subjects were used to simulate focal and extended <span class="hlt">sources</span> located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and</p> <div class="credits"> <p class="dwt_author">Daniel M. Goldenholz; Seppo P. Ahlfors; Matti S. Hämäläinen; Dahlia Sharon; Mamiko Ishitobi; Lucia M. Vaina; Steven M. Stufflebeam</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">242</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1982PhDT........88W"> <span id="translatedtitle">Experimental and Analytical Studies of Shielding Concepts for Point <span class="hlt">Sources</span> and Jet <span class="hlt">Noises</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">This analytical and experimental study explores concepts for jet <span class="hlt">noise</span> shielding. Model experiments centre on solid planar shields, simulating engine-over-wing installations, and 'sugar scoop' shields. Tradeoff on effective shielding length is set by interference 'edge <span class="hlt">noise</span>' as the shield trailing edge approaches the spreading jet. Edge <span class="hlt">noise</span> is minimized by (i) hyperbolic cutouts which trim off the portions of most intense interference between the jet flow and the barrier and (ii) hybrid shields--a thermal refractive extension (a flame); for (ii) the tradeoff is combustion <span class="hlt">noise</span>. In general, shielding attenuation increases steadily with frequency, following low frequency enhancement by edge <span class="hlt">noise</span>. Although broadband attenuation is typically only several dB, the reduction of the subjectively weighted perceived <span class="hlt">noise</span> levels is higher. In addition, calculated ground contours of peak PN dB show a substantial contraction due to shielding: this reaches 66% for one of the 'sugar scoop' shields for the 90 PN dB contour. The experiments are complemented by analytical predictions. They are divided into an engineering scheme for jet <span class="hlt">noise</span> shielding and more rigorous analysis for point <span class="hlt">source</span> shielding. The former approach combines point <span class="hlt">source</span> shielding with a suitable jet <span class="hlt">source</span> distribution. The results are synthesized into a predictive algorithm for jet <span class="hlt">noise</span> shielding: the jet is modelled as a line distribution of incoherent <span class="hlt">sources</span> with narrow band frequency (TURN)(axial distance)('-1). The predictive version agrees well with experiment (1 to 1.5 dB) up to moderate frequencies. The insertion loss deduced from the point <span class="hlt">source</span> measurements for semi-infinite as well as finite rectangular shields agrees rather well with theoretical calculation based on the exact half plane solution and the superposition of asymptotic closed-form solutions. An approximate theory, the Maggi-Rubinowicz line integral, is found to yield reasonable predictions for thin barriers including cutouts if a certain correction is applied. The more exact integral equation approach (solved numerically) is applied to a more demanding geometry: a half round sugar scoop shield. It is found that the solutions of integral equation derived from Helmholtz formula in normal derivative form show satisfactory agreement with measurements.</p> <div class="credits"> <p class="dwt_author">Wong, Raymond Lee Man</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">243</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23464008"> <span id="translatedtitle">Mapping underwater sound <span class="hlt">noise</span> and assessing its <span class="hlt">sources</span> by using a self-organizing maps method.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">This study aims to provide an objective mapping of the underwater <span class="hlt">noise</span> and its <span class="hlt">sources</span> over an Adriatic coastal marine habitat by applying the self-organizing maps (SOM) method. Systematic sampling of sea ambient <span class="hlt">noise</span> (SAN) was carried out at ten predefined acoustic stations between 2007 and 2009. Analyses of <span class="hlt">noise</span> 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 <span class="hlt">noise</span> 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 <span class="hlt">source</span> of underwater <span class="hlt">noise</span>, 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</p> <div class="credits"> <p class="dwt_author">Rako, Nikolina; Vilibi?, Ivica; Mihanovi?, Hrvoje</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">244</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24214295"> <span id="translatedtitle">Objective approach for analysis of <span class="hlt">noise</span> <span class="hlt">source</span> characteristics and acoustic conditions in noisy computerized embroidery workrooms.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">It is highly important to analyze the acoustic properties of workrooms in order to identify best <span class="hlt">noise</span> control measures from the standpoint of <span class="hlt">noise</span> 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 <span class="hlt">noise</span> pollution. This paper aims to empirically analyze <span class="hlt">noise</span> <span class="hlt">source</span> characteristics and acoustic properties of noisy embroidery workrooms based on special parameters. In this regard, reverberation time as the special room acoustic parameter in 30 workrooms was measured based on ISO 3382-2. Sound power quantity of embroidery machines was also determined based on ISO 9614-3. Multiple linear regression was employed for predicting reverberation time based on acoustic features of the workrooms using MATLAB software. The results showed that the measured reverberation times in most of the workrooms were approximately within the ranges recommended by ISO 11690-1. Similarity between reverberation time values calculated by the Sabine formula and measured values was relatively poor (R (2)?=?0.39). This can be due to the inaccurate estimation of the acoustic influence of furniture and formula preconditions. Therefore, this value cannot be considered representative of an actual acoustic room. However, the prediction performance of the regression method with root mean square error (RMSE)?=?0.23 s and R (2)?=?0.69 is relatively acceptable. Because the sound power of the embroidery machines was relatively high, these <span class="hlt">sources</span> get the highest priority when it comes to applying <span class="hlt">noise</span> controls. Finally, an objective approach for the determination of the share of workroom acoustic characteristics in producing <span class="hlt">noise</span> could facilitate the identification of cost-effective <span class="hlt">noise</span> controls. PMID:24214295</p> <div class="credits"> <p class="dwt_author">Aliabadi, Mohsen; Golmohammadi, Rostam; Mansoorizadeh, Muharram</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">245</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2958676"> <span id="translatedtitle">Spontaneous dynamics and response properties of a Hodgkin-Huxley-type neuron model driven by <span class="hlt">harmonic</span> synaptic <span class="hlt">noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">We study statistical properties, response dynamics, and information transmission in a Hodgkin-Huxley–type neuron system, modeling peripheral electroreceptors in paddlefish. In addition to sodium and potassium currents, the neuron model includes fast calcium and slow afterhyperpolarization (AHP) potassium currents. The synaptic transmission from sensory epithelium is modeled by a Poission process with a rate modulated by narrow-band <span class="hlt">noise</span>, mimicking stochastic epithelial oscillations observed experimentally. We study how the interplay of parameters of AHP current and synaptic <span class="hlt">noise</span> affects the statistics of spontaneous dynamics and response properties of the system. In particular, we confirm predictions made earlier with perfect integrate and fire and phase neuron models that epithelial oscillations enhance stimulus–response coherence and thus information transmission in electroreceptor system. In addition, we consider a strong stimulus regime and show that coherent epithelial oscillations may reduce variability of electroreceptor responses to time-varying stimuli.</p> <div class="credits"> <p class="dwt_author">Nguyen, Hoai; Neiman, Alexander B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">246</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.7496C"> <span id="translatedtitle">Ambient <span class="hlt">noise</span> recorded at broadband stations in Portugal and Morocco: Characterization and <span class="hlt">Sources</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> levels at different frequencies and spectrograms are computed to visualize the variations of ambient <span class="hlt">noise</span> 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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span>), and <span class="hlt">sources</span> of ambient <span class="hlt">noise</span> at different frequency bands.</p> <div class="credits"> <p class="dwt_author">Custódio, Susana; Madureira, Guilherme; Corela, Carlos; Alves, Paulo; Haberland, Christian; Carrilho, Fernando; Fonseca, Joao; Caldeira, Bento; Dias, Nuno</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">247</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21255263"> <span id="translatedtitle">Multi-MW K-Band <span class="hlt">Harmonic</span> Multiplier: RF <span class="hlt">Source</span> For High-Gradient Accelerator R and D</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">A preliminary design is presented for a two-cavity <span class="hlt">harmonic</span> multiplier, intended as a high-power RF <span class="hlt">source</span> for use in experiments aimed at developing high-gradient structures for a future collider. The <span class="hlt">harmonic</span> multiplier is to produce power at selected frequencies in K-band (18-26.5 GHz) using as an RF driver an XK-5 S-band klystron (2.856 GHz). The device is to be built with a TE{sub 111} rotating mode input cavity and interchangeable output cavities running in the TE{sub n11} rotating mode, with n = 7,8,9 at 19.992, 22.848, and 25.704 GHz. An example for a 7{sup th} <span class="hlt">harmonic</span> multiplier is described, using a 250 kV, 20 A injected laminar electron beam; with 10 MW of S-band drive power, 4.7 MW of 20-GHz output power is predicted. Details are described of the magnetic circuit, cavities, and output coupler.</p> <div class="credits"> <p class="dwt_author">Solyak, N. A.; Yakovlev, V. P. [Omega-P, Inc., 199 Whitney Ave., New Haven, CT 06511 (United States); Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States); Kazakov, S. Yu. [Omega-P, Inc., 199 Whitney Ave., New Haven, CT 06511 (United States); High Energy Accelerator Research Organization, KEK, Tsukuba, Ibaraki 305-0801 Japan (Japan); Hirshfield, J. L. [Omega-P, Inc., 199 Whitney Ave., New Haven, CT 06511 (United States); Beam Physics Laboratory, Yale University, 272 Whitney Avenue, New Haven, CT 06511 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-22</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">248</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20020048663&hterms=reynold+number&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dreynold%2Bnumber"> <span id="translatedtitle"><span class="hlt">Noise</span> <span class="hlt">Sources</span> in a Low-Reynolds-Number Turbulent Jet at Mach 0.9</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions. Lighthill's theory is used to define a nominal acoustic <span class="hlt">source</span> in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic <span class="hlt">source</span> is Fourier transformed in the axial coordinate and time and then filtered in order to identify and separate components capable of radiating to the far field. This procedure indicates that the peak radiating component of the <span class="hlt">source</span> is coincident with neither the peak of the full unfiltered <span class="hlt">source</span> nor that of the turbulent kinetic energy. The phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed which calls into question the commonly made assumption that the <span class="hlt">noise</span> <span class="hlt">sources</span> convect at a single velocity. Space-time correlations demonstrate that the <span class="hlt">sources</span> are not acoustically compact in the streamwise direction and that the portion of the <span class="hlt">source</span> that radiates at angles greater than 45 deg. is stationary. Filtering non-radiating wavenumber components of the <span class="hlt">source</span> at single frequencies reveals that a simple modulated wave forms for the <span class="hlt">source</span>, as might be predicted by linear stability analysis. At small angles from the jet axis the <span class="hlt">noise</span> from these modes is highly directional, better described by an exponential than a standard Doppler factor.</p> <div class="credits"> <p class="dwt_author">Freund, Jonathan B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">249</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3631260"> <span id="translatedtitle">Localizing the <span class="hlt">sources</span> of two independent <span class="hlt">noises</span>: Role of time varying amplitude differences</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Listeners localized the free-field <span class="hlt">sources</span> of either one or two simultaneous and independently generated <span class="hlt">noise</span> bursts. Listeners' localization performance was better when localizing one rather than two sound <span class="hlt">sources</span>. With two sound <span class="hlt">sources</span>, localization performance was better when the listener was provided prior information about the location of one of them. Listeners also localized two simultaneous <span class="hlt">noise</span> bursts that had sinusoidal amplitude modulation (AM) applied, in which the modulation envelope was in-phase across the two <span class="hlt">source</span> locations or was 180° out-of-phase. The AM was employed to investigate a hypothesis as to what process listeners might use to localize multiple sound <span class="hlt">sources</span>. The results supported the hypothesis that localization of two sound <span class="hlt">sources</span> might be based on temporal-spectral regions of the combined waveform in which the sound from one <span class="hlt">source</span> was more intense than that from the other <span class="hlt">source</span>. The interaural information extracted from such temporal-spectral regions might provide reliable estimates of the sound <span class="hlt">source</span> location that produced the more intense sound in that temporal-spectral region.</p> <div class="credits"> <p class="dwt_author">Yost, William A.; Brown, Christopher A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">250</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=N9325094"> <span id="translatedtitle">Theory for <span class="hlt">Noise</span> of Propellers in Angular Inflow with Parametric Studies and Experimental Verification.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">This report presents the derivation of a frequency domain theory and working equations for radiation of propeller <span class="hlt">harmonic</span> <span class="hlt">noise</span> in the presence of angular inflow. In applying the acoustic analogy, integration over the tangential coordinate of the <span class="hlt">source</span> ...</p> <div class="credits"> <p class="dwt_author">D. B. Hanson D. J. Parzych</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">251</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24718188"> <span id="translatedtitle">Phase <span class="hlt">noise</span> analysis of injected gain switched comb <span class="hlt">source</span> for coherent communications.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">We present experimentally and analytically the phase <span class="hlt">noise</span> characterization of an externally injected gain switched comb <span class="hlt">source</span>. The results reveal the residual high frequency FM <span class="hlt">noise</span> in the comb lines, which stays unnoticed in the optical linewidth value but leads to an increased phase-error variance. The potential impact of the residual phase <span class="hlt">noise</span> is investigated in a 10.7 GBaud optical DQPSK system where a 2 dB power penalty is recorded at BER of 10(-9). In a 10.7 GBaud digital coherent QPSK system no penalty is observed but with 5 GBaud 16-QAM format a 3 dBpenalty exists at the FEC limit of 4.4e-3. PMID:24718188</p> <div class="credits"> <p class="dwt_author">Zhou, Rui; Huynh, Tam N; Vujicic, Vidak; Anandarajah, Prince M; Barry, Liam P</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">252</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/18646992"> <span id="translatedtitle">The effect of multimicrophone <span class="hlt">noise</span> reduction systems on sound <span class="hlt">source</span> localization by users of binaural hearing aids.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">This paper evaluates the influence of three multimicrophone <span class="hlt">noise</span> reduction algorithms on the ability to localize sound <span class="hlt">sources</span>. Two recently developed <span class="hlt">noise</span> reduction techniques for binaural hearing aids were evaluated, namely, the binaural multichannel Wiener filter (MWF) and the binaural multichannel Wiener filter with partial <span class="hlt">noise</span> estimate (MWF-N), together with a dual-monaural adaptive directional microphone (ADM), which is a widely used <span class="hlt">noise</span> reduction approach in commercial hearing aids. The influence of the different algorithms on perceived sound <span class="hlt">source</span> localization and their <span class="hlt">noise</span> reduction performance was evaluated. It is shown that <span class="hlt">noise</span> reduction algorithms can have a large influence on localization and that (a) the ADM only preserves localization in the forward direction over azimuths where limited or no <span class="hlt">noise</span> reduction is obtained; (b) the MWF preserves localization of the target speech component but may distort localization of the <span class="hlt">noise</span> component. The latter is dependent on signal-to-<span class="hlt">noise</span> ratio and masking effects; (c) the MWF-N enables correct localization of both the speech and the <span class="hlt">noise</span> components; (d) the statistical Wiener filter approach introduces a better combination of sound <span class="hlt">source</span> localization and <span class="hlt">noise</span> reduction performance than the ADM approach. PMID:18646992</p> <div class="credits"> <p class="dwt_author">Van den Bogaert, Tim; Doclo, Simon; Wouters, Jan; Moonen, Marc</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">253</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19870008968&hterms=simple+simulation+method+calculate+effective+phase+velocity+attenuation+coefficient+shear+elastic+wave+propagation+composite+materials&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dsimple%2Bsimulation%2Bmethod%2Bcalculate%2Beffective%2Bphase%2Bvelocity%2Battenuation%2Bcoefficient%2Bshear%2Belastic%2Bwave%2Bpropagation%2Bcomposite%2Bmaterials"> <span id="translatedtitle">Methods for designing treatments to reduce interior <span class="hlt">noise</span> of predominant <span class="hlt">sources</span> and paths in a single engine light aircraft</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The <span class="hlt">sources</span> and paths by which <span class="hlt">noise</span> enters the cabin of a small single engine aircraft were determined through a combination of flight and laboratory tests. The primary <span class="hlt">sources</span> of <span class="hlt">noise</span> were found to be airborne <span class="hlt">noise</span> from the propeller and engine casing, airborne <span class="hlt">noise</span> from the engine exhaust, structureborne <span class="hlt">noise</span> from the engine/propeller combination and <span class="hlt">noise</span> associated with air flow over the fuselage. For the propeller, the primary airborne paths were through the firewall, windshield and roof. For the engine, the most important airborne path was through the firewall. Exhaust <span class="hlt">noise</span> was found to enter the cabin primarily through the panels in the vicinity of the exhaust outlet although exhaust <span class="hlt">noise</span> entering the cabin through the firewall is a distinct possibility. A number of <span class="hlt">noise</span> control techniques were tried, including firewall stiffening to reduce engine and propeller airborne <span class="hlt">noise</span>, to stage isolators and engine mounting spider stiffening to reduce structure-borne <span class="hlt">noise</span>, and wheel well covers to reduce air flow <span class="hlt">noise</span>.</p> <div class="credits"> <p class="dwt_author">Hayden, Richard E.; Remington, Paul J.; Theobald, Mark A.; Wilby, John F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">254</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012SSEle..73...64M"> <span id="translatedtitle">RF dynamic and <span class="hlt">noise</span> performance of Metallic <span class="hlt">Source</span>/Drain SOI n-MOSFETs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">This paper presents a detailed study of the RF and <span class="hlt">noise</span> performance of n-type Schottky barrier (SB) MOSFETs with a particular focus on the influence of the Schottky barrier height (SBH) on the main dynamic and <span class="hlt">noise</span> figures of merit. With this aim, a 2D Monte Carlo simulator including tunnelling transport across Schottky interfaces has been developed, with special care to consider quantum transmission coefficients and the influence of image charge effects at the Schottky junctions. Particular attention is paid to the microscopic transport features, including carrier mean free paths or number of scattering events along the channel for investigating the optimization of the device topology and the strategic concepts related to the <span class="hlt">noise</span> performance of this new architecture. A more effective control of the gate electrode over drain current for low SBH (discussed in terms of internal physical quantities) is translated into an enhanced transconductance gm, cut-off frequency fT, and non-quasistatic dynamic parameters. The drain and gate intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> show a noteworthy degradation with the SBH reduction due to the increased current, influence of hot carriers and reduced number of phonon scatterings. However, the results evidence that this effect is counterbalanced by the extremely improved dynamic performance in terms of gm and fT. Therefore, the deterioration of the intrinsic <span class="hlt">noise</span> performance of the SB-MOSFET has no significant impact on high-frequency <span class="hlt">noise</span> FoMs as NFmin, Rn and Gass for low SBH and large gate overdrive conditions. The role of the SBH on ?opt, optimum <span class="hlt">noise</span> reactance and susceptance has been also analyzed.</p> <div class="credits"> <p class="dwt_author">Martin, Maria J.; Pascual, Elena; Rengel, Raúl</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">255</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014MSSP...46..481F"> <span id="translatedtitle">Application of sound intensity and partial coherence to identify interior <span class="hlt">noise</span> <span class="hlt">sources</span> on the high speed train</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In order to provide a quieter riding environment for passengers, sound quality refinement of rail vehicle is a hot issue. Identification of interior <span class="hlt">noise</span> <span class="hlt">sources</span> is the prerequisite condition to reduce the interior <span class="hlt">noise</span> on high speed train. By considering contribution of <span class="hlt">noise</span> <span class="hlt">sources</span> such as rolling <span class="hlt">noise</span>, mechanical equipment <span class="hlt">noise</span>, structure-borne <span class="hlt">noise</span> radiated by car body vibration to the interior <span class="hlt">noise</span>, 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 <span class="hlt">noise</span> <span class="hlt">sources</span>. 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 <span class="hlt">noise</span> <span class="hlt">source</span> is structural-borne sound radiated by floor vibration. These findings can be utilized to facilitate the reduction of interior <span class="hlt">noise</span> in the future.</p> <div class="credits"> <p class="dwt_author">Fan, Rongping; Su, Zhongqing; Meng, Guang; He, Caichun</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">256</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20090041558&hterms=Hultgren&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DHultgren%252C%2BA."> <span id="translatedtitle"><span class="hlt">Noise-Source</span> Separation Using Internal and Far-Field Sensors for a Full-Scale Turbofan Engine</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Noise-source</span> separation techniques for the extraction of the sub-dominant combustion <span class="hlt">noise</span> from the total <span class="hlt">noise</span> signatures obtained in static-engine tests are described. Three methods are applied to data from a static, full-scale engine test. Both 1/3-octave and narrow-band results are discussed. The results are used to assess the combustion-<span class="hlt">noise</span> prediction capability of the Aircraft <span class="hlt">Noise</span> Prediction Program (ANOPP). A new additional phase-angle-based discriminator for the three-signal method is also introduced.</p> <div class="credits"> <p class="dwt_author">Hultgren, Lennart S.; Miles, Jeffrey H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">257</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014QuEle..44..484M"> <span id="translatedtitle">Tunable coherent soft X-ray <span class="hlt">source</span> based on the generation of high-order <span class="hlt">harmonic</span> of femtosecond laser radiation in gas-filled capillaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have carried out experimental and theoretical investigations of a tunable coherent soft X-ray radiation <span class="hlt">source</span> in the 30 – 52 nm wavelength range based on the generation of high-order <span class="hlt">harmonics</span> of femtosecond laser radiation propagating in a dielectric xenon-filled capillary. The long path of laser pulse propagation through the capillary permits tuning the generated <span class="hlt">harmonic</span> wavelengths to almost completely span the range under consideration.</p> <div class="credits"> <p class="dwt_author">Malkov, Yu A.; Yashunin, D. A.; Kiselev, A. M.; Andreev, N. E.; Stepanov, A. N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">258</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=ADD011473"> <span id="translatedtitle"><span class="hlt">Noise</span> Jammer Discrimination by <span class="hlt">Noise</span> Modulation Bandwidth.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">A method is described for distinguishing between multiple <span class="hlt">noise</span> jammer <span class="hlt">sources</span> having different <span class="hlt">noise</span> modulation bandwidths. <span class="hlt">Noise</span> signals are detected by a receiver having a bandwidth substantially the same as the bandwidth of the jammer <span class="hlt">noise</span> <span class="hlt">source</span>. Th...</p> <div class="credits"> <p class="dwt_author">C. D. Wise</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">259</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3140000"> <span id="translatedtitle"><span class="hlt">Sources</span> of Image Degradation in Fundamental and <span class="hlt">Harmonic</span> Ultrasound Imaging: A Nonlinear, Full-Wave, Simulation Study</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-and-sum beamforming is used to generate point spread functions (PSF) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary <span class="hlt">source</span> of degradation in fundamental imaging is due to reverberation from near-field structures. Compared to fundamental imaging, reverberation clutter in <span class="hlt">harmonic</span> imaging is 27.1 dB lower. Simulated tissue with uniform velocity but unchanged impedance characteristics indicates that for fundamental imaging, the primary <span class="hlt">source</span> of degradation is phase aberration.</p> <div class="credits"> <p class="dwt_author">Pinton, Gianmarco F.; Trahey, Gregg E.; Dahl, Jeremy J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">260</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3435505"> <span id="translatedtitle">Dynamics of protein <span class="hlt">noise</span> can distinguish between alternate <span class="hlt">sources</span> of gene-expression variability</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Within individual cells, two molecular processes have been implicated as <span class="hlt">sources</span> of <span class="hlt">noise</span> in gene expression: (i) Poisson fluctuations in mRNA abundance arising from random birth and death of individual mRNA transcripts or (ii) promoter fluctuations arising from stochastic promoter transitions between different transcriptional states. Steady-state measurements of variance in protein levels are insufficient to discriminate between these two mechanisms, and mRNA single-molecule fluorescence in situ hybridization (smFISH) is challenging when cellular mRNA concentrations are high. Here, we present a perturbation method that discriminates mRNA birth/death fluctuations from promoter fluctuations by measuring transient changes in protein variance and that can operate in the regime of high molecular numbers. Conceptually, the method exploits the fact that transcriptional blockage results in more rapid increases in protein variability when mRNA birth/death fluctuations dominate over promoter fluctuations. We experimentally demonstrate the utility of this perturbation approach in the HIV-1 model system. Our results support promoter fluctuations as the primary <span class="hlt">noise</span> <span class="hlt">source</span> in HIV-1 expression. This study illustrates a relatively simple method that complements mRNA smFISH hybridization and can be used with existing GFP-tagged libraries to include or exclude alternate <span class="hlt">sources</span> of <span class="hlt">noise</span> in gene expression.</p> <div class="credits"> <p class="dwt_author">Singh, Abhyudai; Razooky, Brandon S; Dar, Roy D; Weinberger, Leor S</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_12");' href="#" title="Previous Page"> <img 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</div> </div> </div><!-- page_13 div --> <div id="page_14" class="hiddenDiv"> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_13");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return 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href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_15");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">261</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/22929617"> <span id="translatedtitle">Dynamics of protein <span class="hlt">noise</span> can distinguish between alternate <span class="hlt">sources</span> of gene-expression variability.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Within individual cells, two molecular processes have been implicated as <span class="hlt">sources</span> of <span class="hlt">noise</span> in gene expression: (i) Poisson fluctuations in mRNA abundance arising from random birth and death of individual mRNA transcripts or (ii) promoter fluctuations arising from stochastic promoter transitions between different transcriptional states. Steady-state measurements of variance in protein levels are insufficient to discriminate between these two mechanisms, and mRNA single-molecule fluorescence in situ hybridization (smFISH) is challenging when cellular mRNA concentrations are high. Here, we present a perturbation method that discriminates mRNA birth/death fluctuations from promoter fluctuations by measuring transient changes in protein variance and that can operate in the regime of high molecular numbers. Conceptually, the method exploits the fact that transcriptional blockage results in more rapid increases in protein variability when mRNA birth/death fluctuations dominate over promoter fluctuations. We experimentally demonstrate the utility of this perturbation approach in the HIV-1 model system. Our results support promoter fluctuations as the primary <span class="hlt">noise</span> <span class="hlt">source</span> in HIV-1 expression. This study illustrates a relatively simple method that complements mRNA smFISH hybridization and can be used with existing GFP-tagged libraries to include or exclude alternate <span class="hlt">sources</span> of <span class="hlt">noise</span> in gene expression. PMID:22929617</p> <div class="credits"> <p class="dwt_author">Singh, Abhyudai; Razooky, Brandon S; Dar, Roy D; Weinberger, Leor S</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">262</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23988431"> <span id="translatedtitle">Improved PHIP polarization using a precision, low <span class="hlt">noise</span>, voltage controlled current <span class="hlt">source</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage <span class="hlt">source</span> (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current <span class="hlt">source</span> (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low <span class="hlt">noise</span> VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low <span class="hlt">noise</span>, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low <span class="hlt">noise</span>, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low <span class="hlt">noise</span> and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f <span class="hlt">noise</span>, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files. PMID:23988431</p> <div class="credits"> <p class="dwt_author">Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">263</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JMagR.235...77A"> <span id="translatedtitle">Improved PHIP polarization using a precision, low <span class="hlt">noise</span>, voltage controlled current <span class="hlt">source</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage <span class="hlt">source</span> (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current <span class="hlt">source</span> (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low <span class="hlt">noise</span> VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low <span class="hlt">noise</span>, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low <span class="hlt">noise</span>, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low <span class="hlt">noise</span> and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f <span class="hlt">noise</span>, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files.</p> <div class="credits"> <p class="dwt_author">Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">264</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=N19990028361"> <span id="translatedtitle"><span class="hlt">Source</span> Methodology for Turbofan <span class="hlt">Noise</span> Prediction (<span class="hlt">SOURCE</span>3D Technical Documentation).</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">This report provides the analytical documentation for the <span class="hlt">SOURCE</span>3D Rotor Wake/Stator Interaction Code. It derives the equations for the rotor scattering coefficients and stator <span class="hlt">source</span> vector and scattering coefficients that are needed for use in the TFANS...</p> <div class="credits"> <p class="dwt_author">H. D. Meyer</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">265</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24663644"> <span id="translatedtitle">Speckle <span class="hlt">noise</span> reduction on a laser projection display via a broadband green light <span class="hlt">source</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">A broadband green light <span class="hlt">source</span> was demonstrated using a tandem-poled lithium niobate (TPLN) crystal. The measured wavelength and temperature bandwidth were 6.5 nm and 100 °C, respectively, spectral bandwidth was 36 times broader than the periodically poled case. Although the conversion efficiency was smaller than in the periodic case, the TPLN device had a good figure of merit owing to the extremely large bandwidth for wavelength and temperature. The developed broadband green light <span class="hlt">source</span> exhibited speckle <span class="hlt">noise</span> approximately one-seventh of that in the conventional approach for a laser projection display. PMID:24663644</p> <div class="credits"> <p class="dwt_author">Yu, Nan Ei; Choi, Ju Won; Kang, Heejong; Ko, Do-Kyeong; Fu, Shih-Hao; Liou, Jiun-Wei; Kung, Andy H; Choi, Hee Joo; Kim, Byoung Joo; Cha, Myoungsik; Peng, Lung-Han</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-02-10</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">266</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009JSV...323..697P"> <span id="translatedtitle">An equivalent-<span class="hlt">source</span> model for simulating <span class="hlt">noise</span> generation in turbofan engines</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Nowadays, computational aeroacoustics (CAA) is used for simulating wave propagation in ducted turbofans, especially as computational fluid dynamics (CFD) is increasingly employed to model the identified <span class="hlt">noise</span> <span class="hlt">sources</span>. An efficient way to match the CFD and CAA domains is to make some assumptions on flow and duct geometry, so that disturbance fields can be expanded over incoming/outgoing acoustic modes. Based on this approach, this paper presents an original matching model in which the outgoing modes are generated by means of equivalent monopole distributions defined as <span class="hlt">source</span> terms in the equations governing the acoustic propagation, instead of a conventional inflow boundary condition (BC). Advantages and limits of the method are discussed. The process to get back to the <span class="hlt">sources</span> and its numerical implementing are described. Although initially focused on tones, an extension of the method to broadband <span class="hlt">noise</span> generation is tackled too. The method then is validated on a simplified turbofan exhaust configuration. Numerical solutions obtained by implementing the <span class="hlt">source</span> terms in a high-order time-domain Euler code are compared to analytical solutions, either in a uniform or in a radially shear mean flow (provided by RANS). The parallel shear flow solution is obtained by solving the Pridmore-Brown equation. The ability to accurately simulate the standing waves due to acoustic reflections at duct ends is also assessed by comparing the numerical solutions computed using both <span class="hlt">source</span>-based and BC-based options in the Euler solver.</p> <div class="credits"> <p class="dwt_author">Polacsek, C.; Desquesnes, G.; Reboul, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">267</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012SPIE.8296E..14S"> <span id="translatedtitle">Non-uniform contrast and <span class="hlt">noise</span> correction for coded <span class="hlt">source</span> neutron imaging</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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?m range, and the relatively low neutron count rate of neutron <span class="hlt">sources</span> compared to other illumination <span class="hlt">sources</span> restricts time resolved measurement. One path toward improved resolution is the use of magnification; however, to date neutron optics are inefficient, expensive, and difficult to develop. There is a clear demand for cost-effective scintillator-based neutron imaging systems that achieve resolutions of 1?m or less. Such imaging system would dramatically extend the application of neutron imaging. For such purposes a coded <span class="hlt">source</span> imaging system is under development. The current challenge is to reduce artifacts in the reconstructed coded <span class="hlt">source</span> images. Artifacts are generated by non-uniform illumination of the <span class="hlt">source</span>, gamma rays, dark current at the imaging sensor, and system <span class="hlt">noise</span> from the reconstruction kernel. In this paper, we describe how to pre-process the coded signal to reduce <span class="hlt">noise</span> and non-uniform illumination, and how to reconstruct the coded signal with three reconstruction methods correlation, maximum likelihood estimation, and algebraic reconstruction technique. We illustrates our results with experimental examples.</p> <div class="credits"> <p class="dwt_author">Santos-Villalobos, Hector J.; Bingham, Philip R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">268</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050186648&hterms=source+level&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsource%2Blevel"> <span id="translatedtitle">Experimentation Toward the Analysis of Gear <span class="hlt">Noise</span> <span class="hlt">Sources</span> Controlled by Sliding Friction and Surface Roughness</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">In helicopters and other rotorcraft, the gearbox is a major <span class="hlt">source</span> of <span class="hlt">noise</span> and vibration (N&V). The two N&V excitation mechanisms are the relative displacements between mating gears (transmission errors) and the friction associated with sliding between gear teeth. Historically, transmission errors have been minimized via improved manufacturing accuracies and tooth modifications. Yet, at high torque loads, <span class="hlt">noise</span> levels are still relatively high though transmission errors might be somewhat minimal. This suggests that sliding friction is indeed a dominant <span class="hlt">noise</span> <span class="hlt">source</span> for high power density rotorcraft gearboxes. In reality, friction <span class="hlt">source</span> mechanism is associated with surface roughness, lubrication regime properties, time-varying friction forces/torques and gear-mesh interface dynamics. Currently, the nature of these mechanisms is not well understood, while there is a definite need for analytical tools that incorporate sliding resistance and surface roughness, and predict their effects on the vibro- acoustic behavior of gears. Toward this end, an experiment was conducted to collect sound and vibration data on the NASA Glenn Gear-<span class="hlt">Noise</span> Rig. Three iterations of the experiment were accomplished: Iteration 1 tested a baseline set of gears to establish a benchmark. Iteration 2 used a gear-set with low surface asperities to reduce the sliding friction excitation. Iteration 3 incorporated low viscosity oil with the baseline set of gears to examine the effect of lubrication. The results from this experiment will contribute to a two year project in collaboration with the Ohio State University to develop the necessary mathematical and computer models for analyzing geared systems and explain key physical phenomena seen in experiments. Given the importance of sliding friction in the gear dynamic and vibro-acoustic behavior of rotorcraft gearboxes, there is considerable potential for research & developmental activities. Better models and understanding will lead to quiet and reliable gear designs, as well as the selection of optimal manufacturing processes.</p> <div class="credits"> <p class="dwt_author">Asnani, Vivake M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">269</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/22225031"> <span id="translatedtitle">A comparison between exposure-response relationships for wind turbine annoyance and annoyance due to other <span class="hlt">noise</span> <span class="hlt">sources</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Surveys have shown that <span class="hlt">noise</span> from wind turbines is perceived as annoying by a proportion of residents living in their vicinity, apparently at much lower <span class="hlt">noise</span> levels than those inducing annoyance due to other environmental <span class="hlt">sources</span>. The aim of the present study was to derive the exposure-response relationship between wind turbine <span class="hlt">noise</span> exposure in L(den) and the expected percentage annoyed residents and to compare it to previously established relationships for industrial <span class="hlt">noise</span> and transportation <span class="hlt">noise</span>. In addition, the influence of several individual and situational factors was assessed. On the basis of available data from two surveys in Sweden (N=341, N=754) and one survey in the Netherlands (N=725), a relationship was derived for annoyance indoors and for annoyance outdoors at the dwelling. In comparison to other <span class="hlt">sources</span> of environmental <span class="hlt">noise</span>, annoyance due to wind turbine <span class="hlt">noise</span> was found at relatively low <span class="hlt">noise</span> exposure levels. Furthermore, annoyance was lower among residents who received economical benefit from wind turbines and higher among residents for whom the wind turbine was visible from the dwelling. Age and <span class="hlt">noise</span> sensitivity had similar effects on annoyance to those found in research on annoyance by other <span class="hlt">sources</span>. PMID:22225031</p> <div class="credits"> <p class="dwt_author">Janssen, Sabine A; Vos, Henk; Eisses, Arno R; Pedersen, Eja</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">270</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3460980"> <span id="translatedtitle"><span class="hlt">Noise</span> suppression of a dipole <span class="hlt">source</span> by tensioned membrane with side-branch cavities</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Reducing the ducted-fan <span class="hlt">noise</span> at the low frequency range remains a big technical challenge. This study presents a passive approach to directly suppress the dipole sound radiation from an axial-flow fan housed by a tensioned membrane with cavity backing. The method aims at achieving control of low frequency <span class="hlt">noise</span> with an appreciable bandwidth. The use of the membrane not only eliminates the aerodynamic loss of flow, but also provides flexibility in controlling the range of the stopband with high insertion loss by varying its tension and mass. A three-dimensional model is presented which allows the performance of the proposed device to be explored analytically. With the proper design, this device can achieve a <span class="hlt">noise</span> reduction of 5?dB higher than the empty expansion cavity recently proposed by Huang et al. [J. Acoust. Soc. Am. 128, 152–163 (2010)]. Through the detailed modal analysis, even in vacuo modes of the membrane vibration are found to play an important role in the suppression of sound radiation from the dipole <span class="hlt">source</span>. Experimental validation is conducted with a loudspeaker as the dipole <span class="hlt">source</span> and good agreement between the predicted and measured insertion loss is achieved.</p> <div class="credits"> <p class="dwt_author">Liu, Y.; Choy, Y. S.; Huang, L.; Cheng, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">271</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011JGRA..116.3104S"> <span id="translatedtitle">Constraints on coronal turbulence models from <span class="hlt">source</span> sizes of <span class="hlt">noise</span> storms at 327 MHz</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We seek to reconcile observations of small <span class="hlt">source</span> sizes in the solar corona at 327 MHz with predictions of scattering models that incorporate refractive index effects, inner scale effects, and a spherically diverging wavefront. We use an empirical prescription for the turbulence amplitude CN2(R) based on very long baseline interferometry observations by Spangler et al. of compact radio <span class="hlt">sources</span> against the solar wind for heliocentric distances R ? 10-50 R?. We use the Coles and <span class="hlt">Harmon</span> model for the inner scale li(R), which is presumed to arise from cyclotron damping. In view of the prevalent uncertainty in the power law index that characterizes solar wind turbulence at various heliocentric distances, we retain this index as a free parameter. We find that the inclusion of spherical divergence effects suppresses the predicted <span class="hlt">source</span> size substantially. We also find that inner scale effects significantly reduce the predicted <span class="hlt">source</span> size. An important general finding for solar <span class="hlt">sources</span> is that the calculations substantially underpredict the observed <span class="hlt">source</span> size. Three possible, nonexclusive, interpretations of this general result are proposed. First and simplest, future observations with better angular resolution will detect much smaller <span class="hlt">sources</span>. Consistent with this, previous observations of small <span class="hlt">sources</span> in the corona at metric wavelengths are limited by the instrument resolution. Second, the spatially varying level of turbulence CN2(R) is much larger in the inner corona than predicted by straightforward extrapolation sunward of the empirical prescription, which was based on observations between 10 and 50 R?. Either the functional form or the constant of proportionality could be different. Third, perhaps the inner scale is smaller than the model, leading to increased scattering. These results and interpretations are discussed and compared with earlier work.</p> <div class="credits"> <p class="dwt_author">Subramanian, Prasad; Cairns, Iver</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">272</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21347047"> <span id="translatedtitle">Single-Shot Diffractive Imaging with a Table-Top Femtosecond Soft X-Ray Laser-<span class="hlt">Harmonics</span> <span class="hlt">Source</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Coherent x-ray diffractive imaging is a powerful method for studies on nonperiodic structures on the nanoscale. Access to femtosecond dynamics in major physical, chemical, and biological processes requires single-shot diffraction data. Up to now, this has been limited to intense coherent pulses from a free electron laser. Here we show that laser-driven ultrashort x-ray <span class="hlt">sources</span> offer a comparatively inexpensive alternative. We present measurements of single-shot diffraction patterns from isolated nano-objects with a single 20 fs pulse from a table-top high-<span class="hlt">harmonic</span> x-ray laser. Images were reconstructed with a resolution of 119 nm from the single shot and 62 nm from multiple shots.</p> <div class="credits"> <p class="dwt_author">Ravasio, A.; Gauthier, D.; Billon, M.; Caumes, J-P.; Garzella, D.; Geleoc, M.; Gobert, O.; Hergott, J-F.; Pena, A-M.; Perez, H.; Carre, B. [Commissariat a l'Energie Atomique, Service des Photons, Atomes et Molecules, Batiment 522, Centre d'Etude de Saclay, 91191 Gif-sur-Yvette (France); Maia, F. R. N. C. [Laboratory of Molecular Biophysics, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3 (Box 596), SE-751 24 Uppsala (Sweden); Bourhis, E.; Gierak, J.; Madouri, A.; Mailly, D.; Schiedt, B. [Laboratoire de Photonique et Nanostructures, CNRS-UPR20, Route de Nozay, F-91460 Marcoussis (France); Fajardo, M. [Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Avenue Rovisco Pais, 1049-001 Lisboa (Portugal); Gautier, J.; Zeitoun, P. [Laboratoire d'Optique Appliquee, Ecole Nationale Superieure de Technique Avancees, Ecole Polytechnique, CNRS UMR7639, Chemin de la Huniere, 91761 Palaiseau Cedex (France)</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-07-10</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">273</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23609303"> <span id="translatedtitle">Evaluation of online information <span class="hlt">sources</span> on alien species in Europe: the need of <span class="hlt">harmonization</span> and integration.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Europe is severely affected by alien invasions, which impact biodiversity, ecosystem services, economy, and human health. A large number of national, regional, and global online databases provide information on the distribution, pathways of introduction, and impacts of alien species. The sufficiency and efficiency of the current online information systems to assist the European policy on alien species was investigated by a comparative analysis of occurrence data across 43 online databases. Large differences among databases were found which are partially explained by variations in their taxonomical, environmental, and geographical scopes but also by the variable efforts for continuous updates and by inconsistencies on the definition of "alien" or "invasive" species. No single database covered all European environments, countries, and taxonomic groups. In many European countries national databases do not exist, which greatly affects the quality of reported information. To be operational and useful to scientists, managers, and policy makers, online information systems need to be regularly updated through continuous monitoring on a country or regional level. We propose the creation of a network of online interoperable web services through which information in distributed resources can be accessed, aggregated and then used for reporting and further analysis at different geographical and political scales, as an efficient approach to increase the accessibility of information. <span class="hlt">Harmonization</span>, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites. PMID:23609303</p> <div class="credits"> <p class="dwt_author">Gatto, Francesca; Katsanevakis, Stelios; Vandekerkhove, Jochen; Zenetos, Argyro; Cardoso, Ana Cristina</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">274</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/10107515"> <span id="translatedtitle">Skew <span class="hlt">harmonics</span> suppression in electromagnets with application to the Advanced Light <span class="hlt">Source</span> (ALS) storage ring corrector magnet design</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">An analytical expression for prediction of skew <span class="hlt">harmonics</span> in an iron core combined function regular/skew dipole magnet due to arbitrarily positioned electromagnet coils is developed. A structured approach is presented for the suppression of an arbitrary number of <span class="hlt">harmonic</span> components to arbitrarily low values. Application of the analytical <span class="hlt">harmonic</span> strength calculations coupled to the structured <span class="hlt">harmonic</span> suppression approach is presented in the context of the design of the ALS storage ring corrector magnets, where quadrupole, sextupole, and octupole skew <span class="hlt">harmonics</span> were reduced to less than 1.0% of the skew dipole at the beam aperture radius r = 3.0 cm.</p> <div class="credits"> <p class="dwt_author">Schlueter, R.; Halbach, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">275</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1994ITM....30.2126S"> <span id="translatedtitle">Skew <span class="hlt">harmonics</span> suppression in electromagnets with application to the advanced light <span class="hlt">source</span> (ALS) storage ring corrector magnet design</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">An analytical expression for prediction of skew <span class="hlt">harmonics</span> in an iron core combined function regular/skew dipole magnet due to arbitrarily positioned electromagnet coils is developed. A structured approach is presented for the suppression of an arbitrary number of <span class="hlt">harmonic</span> components to arbitrarily low values. Application of the analytical <span class="hlt">harmonic</span> strength calculations coupled to the structured <span class="hlt">harmonic</span> suppression approach is presented in the context of the design of the ALS storage ring corrector magnets, where quadrupole, sextupole, and octupole skew <span class="hlt">harmonics</span> were reduced to less than 1.0% of the skew dipole at the beam aperture radius r = 3.0 cm.</p> <div class="credits"> <p class="dwt_author">Schlueter, R. D.; Halbach, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">276</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55820475"> <span id="translatedtitle">Determination of <span class="hlt">noise</span> <span class="hlt">source</span> heights, part II: Measurement of the equivalent <span class="hlt">source</span> height of highway vehicles</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">This is the second of two companion papers which describe the measurement of the equivalent point <span class="hlt">source</span> height on highway vehicles. The first paper describes the measurement method, and the second its application to highway vehicles. This paper discusses the measurements on moving highway vehicles. First it is shown how the measurement method is suitable for measuring the equivalent point</p> <div class="credits"> <p class="dwt_author">S. A. L. Glegg; J. R. Yoon</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">277</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19970028895&hterms=weighted+least+squares&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2522weighted%2Bleast%2Bsquares%2522"> <span id="translatedtitle">Low Speed, 2-D Rotor/Stator Active <span class="hlt">Noise</span> Control at the <span class="hlt">Source</span> Demonstration</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Wake/blade-row interaction <span class="hlt">noise</span> produced by the Annular Cascade Facility at Purdue University has been modeled using the LINFLO analysis. Actuator displacements needed for complete cancellation of the propagating acoustic response modes have been determined, along with the associated actuator power requirements. As an alternative, weighted least squares minimization of the total far-field sound power using individual actuators has also been examined. Attempts were made to translate the two-dimensional aerodynamic results into three-dimensional actuator requirements. The results lie near the limit of present actuator technology. In order to investigate the concept of <span class="hlt">noise</span> control at the <span class="hlt">source</span> for active rotor/stator <span class="hlt">noise</span> control at the <span class="hlt">source</span>, various techniques for embedding miniature actuators into vanes were examined. Numerous miniature speaker arrangements were tested and analyzed to determine their suitability as actuators for a demonstration test in the Annular Cascade Facility at Purdue. The best candidates demonstrated marginal performance. An alternative concept to using vane mounted speakers as control actuators was developed and tested. The concept uses compression drivers which are mounted externally to the stator vanes. Each compression driver is connected via a tube to an air cavity in the stator vane, from which the driver signal radiates into the working section of the experimental rig. The actual locations and dimensions of the actuators were used as input parameters for a LINFLO computational analysis of the actuator displacements required for complete cancellation of tones in the Purdue experimental rig. The actuators were designed and an arrangement determined which is compatible with the Purdue experimental rig and instrumentation. Experimental tests indicate that the actuators are capable of producing equivalent displacements greater than the requirements predicted by the LINFLO analysis. The acoustic output of the actuators was also found to be unaffected by the presence of air flow representative of the Purdue experimental rig. A test of the active <span class="hlt">noise</span> control at the <span class="hlt">source</span> concept for rotor/stator active <span class="hlt">noise</span> 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.</p> <div class="credits"> <p class="dwt_author">Simonich, John C.; Kousen, Ken A.; Zander, Anthony C.; Bak, Michael; Topol, David A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">278</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19920001380&hterms=mahendra&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2522mahendra%2522"> <span id="translatedtitle">Aeroacoustics of flight vehicles: Theory and practice. Volume 1: <span class="hlt">Noise</span> <span class="hlt">sources</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Methodology recommended to evaluate aeroacoustic related problems is provided, and approaches to their solutions are suggested without extensive tables, nomographs, and derivations. Orientation is toward flight vehicles and emphasis is on underlying physical concepts. Theoretical, experimental, and applied aspects are covered, including the main formulations and comparisons of theory and experiment. The topics covered include: propeller and propfan <span class="hlt">noise</span>, rotor <span class="hlt">noise</span>, turbomachinery <span class="hlt">noise</span>, jet <span class="hlt">noise</span> classical theory and experiments, <span class="hlt">noise</span> from turbulent shear flows, jet <span class="hlt">noise</span> generated by large-scale coherent motion, airframe <span class="hlt">noise</span>, propulsive lift <span class="hlt">noise</span>, combustion and core <span class="hlt">noise</span>, and sonic booms.</p> <div class="credits"> <p class="dwt_author">Hubbard, Harvey H. (editor)</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">279</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005ASAJ..118.1916M"> <span id="translatedtitle">An advanced <span class="hlt">noise</span> <span class="hlt">source</span> identification technique using the inverse boundary-element method</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The application of the inverse BEM method as an advanced, non-contact <span class="hlt">noise</span> <span class="hlt">source</span> identification technique will be discussed. In the first and most conventional experiment, the inverse BEM is used to reconstruct the vibration pattern on the surface of a motorcycle engine oil pan cover. In the second experiment, the inverse BEM is used to determine the distribution of particle velocity on the open end of a rectangular duct. Measurements of the particle velocity using the two-microphone method are compared to those predicted using the inverse BEM. In the third experiment, the inverse BEM is used to identify the mechanism of an aeroacoustics <span class="hlt">noise</span> problem (a vortex tone) created by flow over a circular rod. The spectrum of the tonal sound within the flow field is reconstructed using the inverse BEM, and a near field spatial reconstruction of the sound pressure shows clearly the nature of the vortex <span class="hlt">source</span>. This paper will also show that only a relatively small number sound pressure measurements are required for the inverse BEM and that these measurements need not be in the near field of the <span class="hlt">source</span> nor conformal to it to obtain good results.</p> <div class="credits"> <p class="dwt_author">Martinus, Ferdy</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">280</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002JSV...255..531B"> <span id="translatedtitle">Investigation of Automotive Creep Groan <span class="hlt">Noise</span> with a Distributed-<span class="hlt">Source</span> Excitation Technique</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Creep groan is a high-intensity, low-frequency <span class="hlt">noise</span> and vibration problem that affects road vehicles at very low speeds. It usually persists for short periods of time, but a "skilled" driver can deliberately make it last several seconds by tuning the force exerted on the brake pedal. The original cause is considered to be a self-induced vibration of the brake components, due to the friction material characteristics that make the system prone to a stick-slip behaviour. No clear evidence upon the creep groan and how it is perceived inside the passenger cockpit has yet been analyzed in the literature and no formal methods are yet available for its analysis. The present study focuses on the transmission of the vibration from the brake component regions to the ears of the vehicle occupants. Characterization of the calliper acceleration and <span class="hlt">noise</span> inside the cockpit are described for a test vehicle. Distributed-<span class="hlt">source</span> <span class="hlt">noise</span> excitation via the standard vehicle hi-fi system is proposed as a practical but less rigorous particular application of the exact reciprocity method. Virtual groan (in which sound power is delivered by means of a loudspeaker) dismisses the airbone path and shows that the phenomenon is structure-borne. On the examined vehicle, front brakes contribute more strongly than rear. Groan frequency close to cavity acoustic resonance constitutes the worst case scenario, and has to be avoided.</p> <div class="credits"> <p class="dwt_author">Bettella, M.; Harrison, M. F.; Sharp, R. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-08-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_13");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_14");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">281</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002ASAJ..111.2373P"> <span id="translatedtitle">The ambiguity of the acoustic <span class="hlt">source</span> distributions for divergent <span class="hlt">source</span> fields, with application to aerodynamic <span class="hlt">noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A given uniform applied line force of linear strength F1 falls very rapidly to zero about the ends of its length L1. The wave equation <span class="hlt">source</span> term is monopolelike, ?F1/?y1. The radiation is only from the opposite energy producing monopoles ?(?F1/?y1)dy1=+/-F1 at its extremities, forming a dipole L1F1. The divergence theorem transforms this into the exactly equivalent dipole distribution of strength F1, total strength F1L1, now the ``obvious'' energy <span class="hlt">source</span> for the given excitation. Analogously, a volume L1L2L3 of a quadrupole distribution of uniform strength, say ?u1u2 for an aerodynamic lateral quadrupole, also radiates like opposing line dipoles ?(??u1u2/?y2)dy2L3=+/-?u1u2L3 along the L1 sides L2 apart (for lateral quadrupole L2?u1u2L1L3), replaceable by monopoles ?(?2?u1u2/dy1<th>?y2)dy1<th> dy2L3 at the corners of the face L1L2 (where ?2?u1u2/?y1<th>?y2?0), yielding lateral quadrupole L1L2?u1u2L3. With exactly the same fields, which can be considered physically realistic, like the force? The situation appears quite ambiguous; although note the fictitiousness of the monopoles, the appeal of ??u1u2/?y2 appearing in momentum equation as an applied force, while the energy loss by all elements, directly, of the sound producing flow may perhaps be best associated with the quadrupole distribution.</p> <div class="credits"> <p class="dwt_author">Powell, Alan</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">282</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013PhDT.......197M"> <span id="translatedtitle">Methods for addressing <span class="hlt">noise</span> and error in controlled <span class="hlt">source</span> electromagnetic data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Controlled <span class="hlt">source</span> electromagnetic geophysical surveys are excellent ways to obtain information about the conductivity structure of the earth, with applications including hydrocarbon and mining prospecting, hydrogeophysical detection and monitoring, and civil and archaeological studies. Invariably, however, various types of <span class="hlt">noise</span> and errors obscure signal for desired targets, making interpretation difficult. In the case of time-lapse surveys, the magnitude of the measured difference is often on the order of the <span class="hlt">noise</span>. Complex conductivity effects distort the measurements, leading to incorrect inversion results. This work develops a method for extracting signal from noisy electromagnetic data sets from both time- and frequency-domain surveys using a novel application of the equivalent <span class="hlt">source</span> technique. It improves data contaminated by uncorrelated random <span class="hlt">noise</span>, such as that due to receiver coil misalignment and location errors in time-domain EM surveys, and can remove static shifts in the observed electric field amplitude data due to near-surface geologic features in frequency-domain EM surveys. The equivalent <span class="hlt">source</span> method can either be applied individually to data from each measured time-gate or frequency, or simultaneously to data from all times or frequencies measured. The method can be used in addition to traditional processing techniques and requires little user input. The effectiveness of the method is demonstrated through application to single-survey and time-lapsed noisy time- and frequency-domain EM data, both synthetically generated and collected in the field. The presence of low-frequency (? 1 kHz) polarization effects in earth porous materials noticeably increases the amplitude and decreases the phase of measured electromagnetic fields in frequency-domain surveys. By analyzing the sensitivity of cross-well EM measurements to the in-phase and quadrature conductivities, the contribution of the quadrature conductivity (directly associated with the low-frequency polarization effect) can be quantified. Using an integral equation approach for the forward modeling and a gradient-based approach with Tikhonov regularization for the inverse problem, this work shows that with a reasonable amount of <span class="hlt">noise</span>, the distribution of both the in-phase and quadrature conductivities can be recovered in cross-well tomography. This information may be used in turn to improve the ability to, for instance, monitor saturation changes in oil reservoir production or in geothermal fields.</p> <div class="credits"> <p class="dwt_author">MacLennan, Kristopher</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">283</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009SPIE.7212E...9W"> <span id="translatedtitle">Green light <span class="hlt">source</span> by single-pass second <span class="hlt">harmonic</span> generation with laser and crystal in a tilted butt joint setup</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In this work a compact green laser light <span class="hlt">source</span> is presented based on a single-pass second <span class="hlt">harmonic</span> generation (SHG) in non-linear material. The green light <span class="hlt">source</span> consists of a distributed feedback (DFB) laser with a monolithically integrated power amplifier (PA) and a periodically poled lithium niobate (PPLN) crystal with a ridge waveguide. To achieve the smallest size and to reduce the number of parts to be assembled, a direct coupling approach is implemented without using any lens. The waveguide of the laser is bent and the facet of the crystal is tilted and AR-coated in order to reduce undesired reflections and to increase the stability of operation. By varying the injection current of the amplifier the infrared output power of the laser changes proportionally. The wavelength remains stable during current variation and in that way the green optical output power can also be modulated. No additional external modulator is required for the generation of distinct green light levels. At a wavelength of 530 nm, a green optical output power of more than 35 mW is achieved for injection currents of 93 mA and 400 mA through the DFB section and amplifier section respectively.</p> <div class="credits"> <p class="dwt_author">Wiedmann, J.; Scholz, F.; Tekin, T.; Marx, S.; Lang, G.; Schröder, H.; Brox, O.; Erbert, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">284</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.S23B2487B"> <span id="translatedtitle">Do tidal peaks help to discriminate the oceanic microseismic <span class="hlt">noise</span> <span class="hlt">sources</span>?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Since the pioneer years of the seismology, the ubiquitous high-level of seismic energy in the period range 1-20 s, namely microseismic <span class="hlt">noise</span>, has been clearly associated with the ocean wave activity. This <span class="hlt">noise</span> bandwidth of the seismic spectrum defines the frontier between long-period and high-frequency transient seismology. The ``transient seismology'' terms comprise all research based on signals due to known <span class="hlt">sources</span> such as earthquakes or volcano eruptions. Recently, many studies used the noisy unexploited part of the signal and revealed strong features for the seismic tomography and monitoring. One of the main hypothesis for <span class="hlt">noise</span> cross-correlation techniques resides however in the assumption that the <span class="hlt">source</span> distribution provides a random wave field between two stations. Due to the highly non-linear process of oceanic-to-seismic wave conversion, the characterization of a given <span class="hlt">source</span> contribution is not unique. The Longuet-Higgins theory (later generalized for random waves by Hasselman) explains the existence of a primary peak around 14 s and a secondary microseismic peak (SMP) around 7 s, both. The latter, often named double-frequency peak, is much more energetic and lay between periods of 1 to 10 s; its origin (coastal or deep-ocean) is still under debate. In this study we use a few seismic broadband stations of the temporary PYROPE deployement, located on the French Atlantic coast, to analyze the seismic energy. For each component, high resolution Power Spectral Densities (PSD) are computed for time windows of 6 min. with a 60 s overlapping window; the median of four PSD is finally retained for each 20 minutes of the signal. PSD are computed between 0.01 and 10 Hz. Using the spectacular strong tidal effects on this coast as proxies, it is obvious that the behaviour of the short period range of the SMP is different from the energy observed at the frequency value corresponding to the double of the primary peak. This suggest that the SMP may be split into (at least) two parts: a near field contribution between 6 and 10 s, linked to the oceanic wave interactions on the local coast, and a far field <span class="hlt">source</span> between 2.5 and 5.5 s. The far field <span class="hlt">source</span> does not necessarily imply a unique deep ocean signature, since the oceanic wave reflections on distant coasts are also associated of high levels of energy in the SMP range, as previously shown. Probability Density Function of PSD for the E-W component as a function of tide (red: high tide, green: low tide)</p> <div class="credits"> <p class="dwt_author">Beucler, E.; Mocquet, A.; Schimmel, M.; Chevrot, S.; Vergne, J.; Sylvander, M.; Quillard, O.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">285</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19910009732&hterms=propeller&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dpropeller"> <span id="translatedtitle">Inflight <span class="hlt">source</span> <span class="hlt">noise</span> of an advanced full-scale single-rotation propeller</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Flight tests to define the far field tone <span class="hlt">source</span> at cruise conditions were completed on the full scale SR-7L advanced turboprop which was installed on the left wing of a Gulfstream II aircraft. This program, designated Propfan Test Assessment (PTA), involved aeroacoustic testing of the propeller over a range of test conditions. These measurements defined <span class="hlt">source</span> levels for input into long distance propagation models to predict en route <span class="hlt">noise</span>. Inflight data were taken for 7 test cases. The sideline directivities measured by the Learjet showed expected maximum levels near 105 degrees from the propeller upstream axis. However, azimuthal directivities based on the maximum observed sideline tone levels showed highest levels below the aircraft. An investigation of the effect of propeller tip speed showed that the tone level of reduction associated with reductions in propeller tip speed is more significant in the horizontal plane than below the aircraft.</p> <div class="credits"> <p class="dwt_author">Woodward, Richard P.; Loeffler, Irvin J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">286</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19810025402&hterms=OV-1B&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DOV-1B"> <span id="translatedtitle">Flight test of a pure-tone acoustic <span class="hlt">source</span>. [aircraft <span class="hlt">noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Static and flight testing of a pure-tone acoustic <span class="hlt">source</span> were conducted in order to: (1) determine if a 4-KHz tone radiated by a <span class="hlt">source</span> in flight and mixed with broadband aircraft flyover <span class="hlt">noise</span> could be measured on the ground with a high degree of statistical confidence; (2) determine how well a comparison could be made of flight-to-static tone radiation pattern and a static radiation pattern; and (3) determine if there were any installation effects on the radiation pattern due to the flight vehicle. Narrow-band acoustic data were measured and averaged over eight microphones to obtain a high statistical confidence. The flight data were adjusted to an equivalent static condition by applying corrections for retarded time, spherical spreading, atmospheric absorption, ground impedance, instrumentation constraints, convective amplification, and the Doppler shift. The flight-to-static results are in excellent agreement with the measured static data. No installation effects were observed on the radiation pattern.</p> <div class="credits"> <p class="dwt_author">Mueller, A. W.; Preisser, J. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">287</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013PhDT........28S"> <span id="translatedtitle">Broadband Seismic Analyses of the Crust and <span class="hlt">Noise</span> <span class="hlt">Sources</span> in Alberta, Canada</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Cross-correlation of continuous seismic recordings has been proven effective in extracting the Green's function between two seismic stations. Travel-time and waveform <span class="hlt">source</span> migration calculations jointly suggest a persistent <span class="hlt">noise</span> <span class="hlt">source</span> near Lesser Slave Lake (LSL), a large ice-covered lake in Alberta, Canada, during winter months. Subspace inversions of effective Green's functions from five narrow frequency bands (0.002-0.2 Hz) reveal low velocities in the upper crust beneath Alberta basin, which indicates strong effects from the thick platform sedimentary cover. Consistently low velocities are also observed beneath Wabamun domain but the areal coverage is considerably smaller than the published domain boundaries. The lower-crustal velocities beneath southern Loverna Block is 10% faster than the regional average. As the possible remnant cratonic core of the Hearne province, this northeast-striking anomaly extends to the western part of Medicine Hat Block and contributes to a strong east-west structural gradient in the latter domain.</p> <div class="credits"> <p class="dwt_author">Shen, Luyi</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">288</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010JSV...329..786K"> <span id="translatedtitle">Turbulence and heat excited <span class="hlt">noise</span> <span class="hlt">sources</span> in single and coaxial jets</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The generation of <span class="hlt">noise</span> in subsonic high Reynolds number single and coaxial turbulent jets is analyzed by a hybrid method. The computational approach is based on large-eddy simulations (LES) and solutions of the acoustic perturbation equations (APE). The method is used to investigate the acoustic fields of one isothermal single stream jet at a Mach number 0.9 and a Reynolds number 400,000 based on the nozzle diameter and two coaxial jets whose Mach number and Reynolds number based on the secondary jet match the values of the single jet. One coaxial jet configuration possesses a cold primary flow, whereas the other configuration has a hot primary jet. Thus, the configurations allow in a first step the analysis of the relationship of the flow and acoustic fields of a single and a cold coaxial jet and in a second step the investigation of the differences of the fluid mechanics and aeroacoustics of cold and hot coaxial jets. For the isothermal single jet the present hybrid acoustic computation shows convincing agreement with the direct acoustic simulation based on large-eddy simulations. The analysis of the acoustic field of the coaxial jets focuses on two <span class="hlt">noise</span> <span class="hlt">sources</span>, the Lamb vector fluctuations and the entropy <span class="hlt">sources</span> of the APE equations. The power spectral density (PSD) distributions evidence the Lamb vector fluctuations to represent the major acoustic <span class="hlt">sources</span> of the isothermal jet. Especially the typical downstream and sideline acoustic generations occur on a cone-like surface being wrapped around the end of the potential core. Furthermore, when the coaxial jet possesses a hot primary jet, the acoustic core being characterized by the entropy <span class="hlt">source</span> terms increases the low frequency acoustics by up to 5 dB, i.e., the sideline acoustics is enhanced by the pronounced temperature gradient.</p> <div class="credits"> <p class="dwt_author">Koh, Seong Ryong; Schröder, Wolfgang; Meinke, Matthias</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">289</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3108397"> <span id="translatedtitle">Signal-to-<span class="hlt">noise</span> ratio for <span class="hlt">source</span> determination and for a comodulated masker in goldfish, Carassius auratus</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">The masking effects of white and amplitude comodulated <span class="hlt">noise</span> were studied with respect to simple signal detection and sound <span class="hlt">source</span> determination in goldfish. A stimulus generalization method was used to determine the signal-to-<span class="hlt">noise</span> ratio required to completely determine the signal’s characteristics. It was found that the S/N required for this determination is about 4 dB greater than that required for signal detection, or was about 4 dB greater than the critical masking ratio. This means that the potential harm to fish of a given masking <span class="hlt">noise</span> is at least 4 dB greater than previously thought, based on critical masking ratios. However, for amplitude comodulated <span class="hlt">noise</span> between 10 and 50 Hz modulation rate, the potential harmful effects are up to 5.3 dB less than would be predicted from the critical masking ratio for unmodulated <span class="hlt">noise</span>.</p> <div class="credits"> <p class="dwt_author">Fay, Richard R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">290</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/21768734"> <span id="translatedtitle">Effects of <span class="hlt">noise</span> from non-traffic-related ambient <span class="hlt">sources</span> on sleep: review of the literature of 1990-2010.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">This article reviews the literature about the effects of specific non-traffic-related ambient <span class="hlt">noise</span> <span class="hlt">sources</span> on sleep that appeared in the last two decades. Although everybody is faced with <span class="hlt">noise</span> of non-traffic and non-industry origin (e.g. sounds made by neighbors, talk, laughter, music, slamming doors, structural equipment, ventilation, heat pumps, <span class="hlt">noise</span> 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 <span class="hlt">noise</span> have been carried out. Most of them indicate that ambient <span class="hlt">noise</span> 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</p> <div class="credits"> <p class="dwt_author">Omlin, Sarah; Bauer, Georg F; Brink, Mark</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">291</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53552664"> <span id="translatedtitle">Structure sensitivity and <span class="hlt">sources</span> of contrast in third-<span class="hlt">harmonic</span> generation (THG) microscopy of cells and tissues</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Third-<span class="hlt">harmonic</span> generation (THG) microscopy can provide structural information from unstained biological samples such as developing embryos. However, the contrast mechanisms in THG imaging need to be better characterized in order to develop practical applications. We studied experimentally and theoretically the influence of sample structure and excitation NA (Rayleigh length) on THG signals for various cases (spheres, interfaces). Because the third-<span class="hlt">harmonic</span></p> <div class="credits"> <p class="dwt_author">D. Débarre; W. Supatto; E. Beaurepaire</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">292</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/20588835"> <span id="translatedtitle">Impact of various <span class="hlt">noises</span> on maximum reach in broadband light <span class="hlt">source</span> based high-capacity WDM passive optical networks.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">We investigated the effects of various <span class="hlt">noises</span> on the performance of extended-reach WDM-PONs based on broadband light <span class="hlt">sources</span> (BLSs). The maximum reach in BLS based WDM-PONs was analyzed by taking into account the impact of relative intensity <span class="hlt">noise</span> of optical <span class="hlt">source</span>, chromatic dispersion of transmission fiber and in-band crosstalk. We confirmed that the system's performance of BLS based WDM-PONs would be strongly dependent on the equivalent optical bandwidth of optical <span class="hlt">source</span>. From the results, we found that the maximum reach in BLS based WDM-PONs operating at 1.25 Gb/s could be increased to be approximately 70 km of single-mode fiber as long as the chirp and relative intensity <span class="hlt">noise</span> (RIN) of optical <span class="hlt">source</span> would be suppressed properly. PMID:20588835</p> <div class="credits"> <p class="dwt_author">Kim, Chul Han</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-10</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">293</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19800006956&hterms=AIDS+controversy&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DAIDS%2Bcontroversy"> <span id="translatedtitle">Combustion <span class="hlt">noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A review of the subject of combustion generated <span class="hlt">noise</span> is presented. Combustion <span class="hlt">noise</span> is an important <span class="hlt">noise</span> <span class="hlt">source</span> in industrial furnaces and process heaters, turbopropulsion and gas turbine systems, flaring operations, Diesel engines, and rocket engines. The state-of-the-art in combustion <span class="hlt">noise</span> importance, understanding, prediction and scaling is presented for these systems. The fundamentals and available theories of combustion <span class="hlt">noise</span> are given. Controversies in the field are discussed and recommendations for future research are made.</p> <div class="credits"> <p class="dwt_author">Strahle, W. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">294</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012PASA...29..251J"> <span id="translatedtitle">The Characterised <span class="hlt">Noise</span> HI <span class="hlt">Source</span> Finder: Detecting HI Galaxies Using a Novel Implementation of Matched Filtering</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The spectral line datacubes obtained from the Square Kilometre Array (SKA) and its precursors, such as the Australian SKA Pathfinder (ASKAP), will be sufficiently large to necessitate automated detection and parametrisation of <span class="hlt">sources</span>. Matched filtering is widely acknowledged as the best possible method for the automated detection of <span class="hlt">sources</span>. This paper presents the Characterised <span class="hlt">Noise</span> HI (CNHI) <span class="hlt">source</span> finder, which employs a novel implementation of matched filtering. This implementation is optimised for the 3-D nature of the HI spectral line observations of the planned Wide-field ASKAP Legacy L-band All-sky Blind surveY (WALLABY). The CNHI <span class="hlt">source</span> finder also employs a novel sparse representation of 3-D objects, with a high compression rate, to implement the Lutz one-pass algorithm on datacubes that are too large to process in a single pass. WALLABY will use ASKAP's phenomenal 30 square degree field of view to image ~70% of the sky. It is expected that WALLABY will find 500000 HI galaxies out to z~0.2.</p> <div class="credits"> <p class="dwt_author">Jurek, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">295</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014RScI...85e5111L"> <span id="translatedtitle">The differential Howland current <span class="hlt">source</span> with high signal to <span class="hlt">noise</span> ratio for bioimpedance measurement system</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The stability and signal to <span class="hlt">noise</span> ratio (SNR) of the current <span class="hlt">source</span> circuit are the important factors contributing to enhance the accuracy and sensitivity in bioimpedance measurement system. In this paper we propose a new differential Howland topology current <span class="hlt">source</span> and evaluate its output characters by simulation and actual measurement. The results include (1) the output current and impedance in high frequencies are stabilized after compensation methods. And the stability of output current in the differential current <span class="hlt">source</span> circuit (DCSC) is 0.2%. (2) The output impedance of two current circuits below the frequency of 200 KHz is above 1 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 <span class="hlt">source</span> circuit (HCSC). (3) The SNR of the DCSC are 85.64 dB and 65 dB in the simulation and actual measurement with 10 KHz, which illustrates that the DCSC effectively eliminates the common mode interference. (4) The maximum load in the DCSC is twice as much as that of the HCSC. Lastly a two-dimensional phantom electrical impedance tomography is well reconstructed with the proposed HCSC. Therefore, the measured performance shows that the DCSC can significantly improve the output impedance, the stability, the maximum load, and the SNR of the measurement system.</p> <div class="credits"> <p class="dwt_author">Liu, Jinzhen; Qiao, Xiaoyan; Wang, Mengjun; Zhang, Weibo; Li, Gang; Lin, Ling</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">296</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..1614054C"> <span id="translatedtitle">Seismic <span class="hlt">noise</span> <span class="hlt">sources</span> inferred from dense onshore and offshore deployments in Portugal</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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 <span class="hlt">noise</span> recorded in Portugal and to infer information on their <span class="hlt">sources</span>. OBS data shows very clear correlations with local atmospheric and oceanic conditions, as well as with distant oceanic disturbances. <span class="hlt">Noise</span> 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 <span class="hlt">noise</span> 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).</p> <div class="credits"> <p class="dwt_author">Corela, Carlos; Custódio, Susana; Silveira, Graça; Matias, Luis</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">297</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23927114"> <span id="translatedtitle">Binaural speech intelligibility in rooms with variations in spatial location of <span class="hlt">sources</span> and modulation depth of <span class="hlt">noise</span> interferers.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Four experiments investigated the effects on speech intelligibility of reverberation, sound <span class="hlt">source</span> 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 <span class="hlt">noises</span>. In experiment 1, SRTs for modulated <span class="hlt">noises</span> showed little variation with increasing interferer reverberation. Reverberation might have increased masking by filling in the modulated <span class="hlt">noise</span> gaps, but simultaneously changed the <span class="hlt">noise</span> 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 <span class="hlt">noises</span>, indicating that the ability to exploit <span class="hlt">noise</span> 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 <span class="hlt">sources</span>. Finally, a model predicting binaural intelligibility for modulated <span class="hlt">noises</span> was developed and provided a good fit to the experimental data. PMID:23927114</p> <div class="credits"> <p class="dwt_author">Collin, Benjamin; Lavandier, Mathieu</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">298</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/6472092"> <span id="translatedtitle">[Flow of high-voltage current in coal electrodes of arc furnaces as a <span class="hlt">source</span> of <span class="hlt">noise</span> of special nature].</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The <span class="hlt">noise</span> level for working arc furnace has been measured. Arc furnaces were found to be the <span class="hlt">source</span> of infrasounds and acoustic field. The sound pressure levels for infrasounds range from 55 to 77 dB. It has been showed that particular <span class="hlt">noise</span> level includes the onethird-octave band with middle frequency 100 Hz. The sound pressure levels in this band range from 105 to 110 dB. PMID:6472092</p> <div class="credits"> <p class="dwt_author">Polanowska, R</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">299</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EaSci..27...89L"> <span id="translatedtitle">Ambient <span class="hlt">noise</span> as the new <span class="hlt">source</span> for urban engineering seismology and earthquake engineering: a case study from Beijing metropolitan area</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In highly populated urban centers, traditional seismic survey <span class="hlt">sources</span> can no longer be properly applied due to restrictions in modern civilian life styles. The ambient vibration <span class="hlt">noise</span>, including both microseisms and microtremor, though are generally weak but available anywhere and anytime, can be an ideal supplementary <span class="hlt">source</span> for conducting seismic surveys for engineering seismology and earthquake engineering. This is fundamentally supported by advanced digital signal processing techniques for effectively extracting the useful information out from the <span class="hlt">noise</span>. Thus, it can be essentially regarded as a passive seismic method. In this paper we first make a brief survey of the ambient vibration <span class="hlt">noise</span>, followed by a quick summary of digital signal processing for passive seismic surveys. Then the applications of ambient <span class="hlt">noise</span> in engineering seismology and earthquake engineering for urban settings are illustrated with examples from Beijing metropolitan area. For engineering seismology the example is the assessment of site effect in a large area via microtremor observations. For earthquake engineering the example is for structural characterization of a typical reinforced concrete high-rise building using background vibration <span class="hlt">noise</span>. By showing these examples we argue that the ambient <span class="hlt">noise</span> can be treated as a new <span class="hlt">source</span> that is economical, practical, and particularly valuable to engineering seismology and earthquake engineering projects for seismic hazard mitigation in urban areas.</p> <div class="credits"> <p class="dwt_author">Liu, Lanbo; Chen, Qi-fu; Wang, Weijun; Rohrbach, Eric</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">300</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014GI......3...29N"> <span id="translatedtitle">Experimental study of <span class="hlt">source</span> of background <span class="hlt">noise</span> in muon radiography using emulsion film detectors</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The aim of this study is to ascertain and confirm the <span class="hlt">source</span> of background <span class="hlt">noise</span> 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.</p> <div class="credits"> <p class="dwt_author">Nishiyama, R.; Miyamoto, S.; Naganawa, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_14");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" 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showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_17");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">301</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014MeScT..25g5204C"> <span id="translatedtitle">Exploiting continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation methods for <span class="hlt">noise</span> <span class="hlt">source</span> identification</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">This paper proposes the use of continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation techniques that aim at characterizing the structure-borne contributions of the <span class="hlt">noise</span> emission of a mechanical system. The time domain correlation technique presented in this paper is based on the use of FIR (finite impulse response) filters obtained from the vibro-acoustic transfer matrix when vibration data are collected by laser Doppler vibrometry (LDV) exploited in continuous scan mode (CSLDV). The advantages, especially in terms of <span class="hlt">source</span> decorrelation capabilities, related to the use of CSLDV for such purpose, with respect to standard discrete scan (SLDV), are discussed throughout the paper. To validate this approach, vibro-acoustic measurements were performed on a planetary gear motor for home appliances. The analysis of results is also supported by a simulation.</p> <div class="credits"> <p class="dwt_author">Chiariotti, Paolo; Martarelli, Milena; Revel, Gian Marco</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">302</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20000101661&hterms=source+level&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dsource%2Blevel"> <span id="translatedtitle">Current Background <span class="hlt">Noise</span> <span class="hlt">Sources</span> and Levels in the NASA Ames 40- by 80-Foot Wind Tunnel: A Status Report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Background <span class="hlt">noise</span> measurements were made of the acoustic environment in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel (40x80) at NASA Ames Research Center. The measurements were acquired subsequent to the 40x80 Aeroacoustic Modernization Project, which was undertaken to improve the anechoic characteristics of the 40x80's closed test section as well as reduce the levels of background <span class="hlt">noise</span> in the facility. The resulting 40x80 anechoic environment was described by Soderman et. al., and the current paper describes the resulting 40x80 background <span class="hlt">noise</span>, discusses the <span class="hlt">sources</span> of the <span class="hlt">noise</span>, and draws comparisons to previous 40x80 background <span class="hlt">noise</span> levels measurements. At low wind speeds or low frequencies, the 40x80 background <span class="hlt">noise</span> is dominated by the fan drive system. To obtain the lowest fan drive <span class="hlt">noise</span> for a given tunnel condition, it is possible in the 40x80 to reduce the fans' rotational speed and adjust the fans' blade pitch, as described by Schmidtz et. al. This idea is not new, but has now been operationally implemented with modifications for increased power at low rotational speeds. At low to mid-frequencies and at higher wind speeds, the dominant <span class="hlt">noise</span> mechanism was thought to be caused by the surface interface of the previous test section floor acoustic lining. In order to reduce this <span class="hlt">noise</span> mechanism, the new test section floor lining was designed to resist the pumping of flow in and out of the space between the grating slats required to support heavy equipment. In addition, the lining/flow interface over the entire test section was designed to be smoother and quieter than the previous design. At high wind speeds or high frequencies, the dominant <span class="hlt">source</span> of background <span class="hlt">noise</span> in the 40x80 is believed to be caused by the response of the in-flow microphone probes (required by the nature of the closed test section) to the fluctuations in the freestream flow. The resulting background <span class="hlt">noise</span> levels are also different for probes of various diameters and types. The inflow microphone support strut is also a <span class="hlt">source</span> of background <span class="hlt">noise</span> but this <span class="hlt">source</span>'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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> levels produced by the <span class="hlt">noise</span> <span class="hlt">source</span> of interest, it should be possible to determine the signal-to-<span class="hlt">noise</span> ratios and measurement locations to successfully perform aeroacoustic testing in the NASA Ames Research Center's 40- by 80-Foot Wind Tunnel.</p> <div class="credits"> <p class="dwt_author">Allen, Christopher S.; Jaeger, Stephen; Soderman, Paul; Koga, Dennis (Technical Monitor)</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">303</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE94004009"> <span id="translatedtitle">Skew <span class="hlt">harmonics</span> suppression in electromagnets with application to the Advanced Light <span class="hlt">Source</span> (ALS) storage ring corrector magnet design.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">An analytical expression for prediction of skew <span class="hlt">harmonics</span> in an iron core combined function regular/skew dipole magnet due to arbitrarily positioned electromagnet coils is developed. A structured approach is presented for the suppression of an arbitrary n...</p> <div class="credits"> <p class="dwt_author">R. Schlueter K. Halbach</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">304</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/22779457"> <span id="translatedtitle">Shipping <span class="hlt">noise</span> in whale habitat: characteristics, <span class="hlt">sources</span>, budget, and impact on belugas in Saguenay-St. Lawrence Marine Park hub.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">A continuous car ferry line crossing the Saguenay Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping <span class="hlt">noise</span> in the heart of the Saguenay-St. Lawrence Marine Park. To characterize this <span class="hlt">noise</span> and examine its potential impact on belugas, a 4-hydrophone array was deployed in the area and continuously recorded for five weeks in May-June 2009. The <span class="hlt">source</span> levels of the different vessel types showed little dependence on vessel size or speed increase. Their spectral range covered 33 dB. Lowest <span class="hlt">noise</span> levels occurred at night, when ferry crossing pace was reduced, and daytime <span class="hlt">noise</span> peaked during whale-watching tour departures and arrivals. Natural ambient <span class="hlt">noise</span> prevailed 9.4% of the time. Ferry traffic added 30-35 dB to ambient levels above 1 kHz during crossings, which contributed 8 to 14 dB to hourly averages. The whale-watching fleet added up to 5.6 dB during peak hours. Assuming no behavioral or auditory compensation, half of the time, beluga potential communication range was reduced to less than ~30% of its expected value under natural <span class="hlt">noise</span> conditions, and to less than ~15% for one quarter of the time, with little dependence on call frequency. The echolocation band for this population of belugas was also affected by the shipping <span class="hlt">noise</span>. PMID:22779457</p> <div class="credits"> <p class="dwt_author">Gervaise, Cédric; Simard, Yvan; Roy, Nathalie; Kinda, Bazile; Ménard, Nadia</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">305</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19920001382&hterms=mahendra&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2522mahendra%2522"> <span id="translatedtitle">Rotor <span class="hlt">noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The physical characteristics and <span class="hlt">sources</span> of rotorcraft <span class="hlt">noise</span> as they exist today are presented. Emphasis is on helicopter-like vehicles, that is, on rotorcraft in nonaxial flight. The mechanisms of rotor <span class="hlt">noise</span> are reviewed in a simple physical manner for the most dominant <span class="hlt">sources</span> of rotorcraft <span class="hlt">noise</span>. With simple models, the characteristic time- and frequency-domain features of these <span class="hlt">noise</span> <span class="hlt">sources</span> 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 <span class="hlt">noise</span>. Methods and limitations of using scaled models to test for several <span class="hlt">noise</span> <span class="hlt">sources</span> are subsequently presented. Theoretical prediction methods are then discussed and compared with experimental data taken under very controlled conditions. Finally, some promising <span class="hlt">noise</span> reduction technology is reviewed.</p> <div class="credits"> <p class="dwt_author">Schmitz, F. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">306</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=PATENT3214999"> <span id="translatedtitle"><span class="hlt">Harmonic</span> Drive.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The <span class="hlt">harmonic</span> drive has utility in optical tracking telescopes, radar antenna drives, aircraft control surface actuators, and high precision X-Y plotting equipment. Two <span class="hlt">harmonic</span> drive units, each having its own input motor, are coupled together. One of the...</p> <div class="credits"> <p class="dwt_author">R. H. Lapp</p> <p class="dwt_publisher"></p> <p class="publishDate">1965-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">307</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1994army.reptQ....W"> <span id="translatedtitle">Estimating attenuation and propagation of <span class="hlt">noise</span> bands from a distant <span class="hlt">source</span> using the lookup program and data base</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Unavoidable <span class="hlt">noise</span> generated by military activities can disturb the surrounding community and become a <span class="hlt">source</span> of complaint. Military planners must quickly and accurately predict <span class="hlt">noise</span> levels at distant points from various sound <span class="hlt">sources</span> to manage noisy operations on a daily basis. This study developed the Lookup computer program and data base to provide rapid estimates of outdoor <span class="hlt">noise</span> levels from a variety of sound <span class="hlt">sources</span>. Lookup accesses a data base of archived results (requiring about 5 MB disk space) from typical situations rather than performing fresh calculations for each consultation. Initial timing tests show that Lookup can predict the sound levels from a <span class="hlt">noise</span> <span class="hlt">source</span> at distances up to 20 km in 1 second on a DOS-compatible personal computer (PC). This report includes the Lookup program <span class="hlt">source</span> code, and describes the required input for the program, the contents of the archival data base, and the program output. Lookup was written to compile with MS-Fortran, and will run under DOS on any IBM compatible with 640k random access memory. Lookup also conforms to ANSI 1978 standard Fortran and will run under the Unix operating system.</p> <div class="credits"> <p class="dwt_author">White, Michael J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">308</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20130000448&hterms=ultrasonic&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dultrasonic"> <span id="translatedtitle">Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> Generating Simple Modes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the Langley Research Center s 14- by 22-Foot wind tunnel test of the Hybrid Wing Body (HWB) full three-dimensional 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of candidate engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft and to provide a database for shielding code validation. A range of frequencies, and a parametric study of modes were generated from exhaust and inlet nacelle configurations. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular to the axis of the nacelle (in its 0 orientation) and three planes parallel were acquired from the array sweep. In each plane the linear array traversed five sweeps, for a total span of 160 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Level, and integrated Power Levels are presented in this paper; as well as the in-duct modal structure.</p> <div class="credits"> <p class="dwt_author">Sutliff, Daniel, L.; Brown, Clifford, A.; Walker, Bruce, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">309</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2538572"> <span id="translatedtitle">Nonidentifiability of the <span class="hlt">Source</span> of Intrinsic <span class="hlt">Noise</span> in Gene Expression from Single-Burst Data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">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 <span class="hlt">sources</span> of <span class="hlt">noise</span> 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 <span class="hlt">sources</span> 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.</p> <div class="credits"> <p class="dwt_author">Ingram, Piers J.; Stumpf, Michael P. H.; Stark, Jaroslav</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">310</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.G41B0811A"> <span id="translatedtitle">Glacial Isostatic Adjustment as a <span class="hlt">Source</span> of <span class="hlt">Noise</span> for the Interpretation of GRACE Data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Viscoelastic relaxation in the Earth’s mantle induced by deglaciation following the last glacial maximum, can appear as a secular trend in measurements of the Earth’s time-variable gravity field. Since March 2002, the GRACE mission has been making precise measurements of Earth’s gravity field. GIA signals in northern Canada and Scandinavia are clearly evident in the GRACE data. Although valuable for providing insight on the entire GIA process and for inferring the interior structure of the solid Earth, the GIA signals can be a significant <span class="hlt">source</span> of <span class="hlt">noise</span> for other important applications. The GIA signals can not be distinguished from the gravitational effects of water/snow/ice variations on or near the surface of the Earth. Errors in the GIA model, for example due to errors in the assumed mantle viscosity profile, may cause problems for recovering long-term hydrological and, especially, cryospheric signals with GRACE. For instance, GIA model errors are by far the largest <span class="hlt">source</span> of uncertainty when using GRACE to estimate present-day thinning rates of the Antarctic ice sheet. In this talk, we will discuss the solution of the viscoelastic relaxation problem for a radially stratified Earth, and most importantly, analyze the contributions of GIA signals to GRACE time-variable gravity measurements, with a particular emphasis on what kinds of recovered signals might be particularly susceptible to GIA model errors.</p> <div class="credits"> <p class="dwt_author">A, G.; Wahr, J. M.; Zhong, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">311</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/10641846"> <span id="translatedtitle">Analysis of light <span class="hlt">noise</span> <span class="hlt">sources</span> in a recycled Michelson interferometer with Fabry-Perot arms.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">We present a method by which the effect of laser field variations on the signal output of an interferometric gravitational wave detector is rigorously determined. Using the Laser Interferometer Gravitational Wave Observatory (LIGO) optical configuration of a power recycled Michelson interferometer with Fabry-Perot arm cavities as an example, we calculate the excess <span class="hlt">noise</span> after the input filter cavity (mode cleaner) and the dependence of the detector strain sensitivity on laser frequency and amplitude <span class="hlt">noise</span>, radio frequency oscillator <span class="hlt">noise</span>, and scattered-light phase <span class="hlt">noise</span>. We find that <span class="hlt">noise</span> on the radio frequency sidebands generally limits the detector's sensitivity. PMID:10641846</p> <div class="credits"> <p class="dwt_author">Camp, J B; Yamamoto, H; Whitcomb, S E; McClelland, D E</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">312</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19850006357&hterms=mineral+wool&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2522mineral%2Bwool%2522"> <span id="translatedtitle"><span class="hlt">Sources</span>, paths, and concepts for reduction of <span class="hlt">noise</span> in the test section of the NASA Langley 4x7m wind tunnel</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">NASA is investigating the feasibility of modifying the 4x7m Wind Tunnel at the Langley Research Center to make it suitable for a variety of aeroacoustic testing applications, most notably model helicopter rotors. The amount of <span class="hlt">noise</span> reduction required to meet NASA's goal for test section background <span class="hlt">noise</span> was determined, the predominant <span class="hlt">sources</span> and paths causing the background <span class="hlt">noise</span> were quantified, and trade-off studies between schemes to reduce fan <span class="hlt">noise</span> at the <span class="hlt">source</span> and those to attenuate the sound generated in the circuit between the <span class="hlt">sources</span> and the test section were carried out. An extensive data base is also presented on circuit <span class="hlt">sources</span> and paths.</p> <div class="credits"> <p class="dwt_author">Hayden, R. E.; Wilby, J. F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">313</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17879798"> <span id="translatedtitle">Characterization of <span class="hlt">noise</span> <span class="hlt">sources</span> for two generations of computed radiography systems using powder and crystalline photostimulable phosphors.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and <span class="hlt">noise</span> characteristics. The main aim was to characterize and quantify the <span class="hlt">noise</span> <span class="hlt">sources</span> in the images. The systems tested were (1) Agfa CR 25.0, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX-S, a line-scanning CR reader with needle crystal phosphor image plates (HD 5.0). For both systems, the standard metrics of presampled modulation transfer function (MTF), normalized <span class="hlt">noise</span> power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various <span class="hlt">noise</span> <span class="hlt">sources</span> contributing to the NNPS were separated by using knowledge of their relationship with air kerma, MTF, absorption efficiency and antialiasing filters. The DX-S MTF was superior compared with the CR 25.0. The maximum difference in MTF between the DX-S scan and CR 25.0 subscan directions was 0.13 at 1.3 mm(-1). For a nominal detector air kerma of 4 microGy, the peak DQE of the DX-S was 43 (+/-3)%, which was over double that of the CR 25.0 of 18 (+/-2)%. The additive electronic <span class="hlt">noise</span> was negligible on the CR 25.0 but calculated to be constant 3.4 x 10(-7) (+/-0.4 x 10(-7)) mm2 at 3.9 microGy on the DX-S. The DX-S has improved image quality compared with a traditional flying spot reader. The separation of the <span class="hlt">noise</span> <span class="hlt">sources</span> indicates that the improvements in DQE of the DX-S are due not only to the higher quantum, efficiency and MTF, but also the lower structure, secondary quantum, and excess <span class="hlt">noise</span>. PMID:17879798</p> <div class="credits"> <p class="dwt_author">Mackenzie, Alistair; Honey, Ian D</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">314</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/19257119"> <span id="translatedtitle">Analysis of optical phase <span class="hlt">noise</span> in fiber-optic systems employing a laser <span class="hlt">source</span> with arbitrary coherence time</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Performance of many optical circuits and systems, such as signal processing and sensing devices, is influenced by random fluctuations of the optical <span class="hlt">source</span> emission field. This paper outlines a formalism for the analysis of laser phase <span class="hlt">noise</span> effects on a general linear time-invariant optical system. Theoretical expressions are presented for the autocovariance function of the instantaneous output intensity which are</p> <div class="credits"> <p class="dwt_author">Behzad Moslehi</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">315</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23902900"> <span id="translatedtitle">Adaptive <span class="hlt">noise</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">In biology, <span class="hlt">noise</span> implies error and disorder and is therefore something which organisms may seek to minimize and mitigate against. We argue that such <span class="hlt">noise</span> can be adaptive. Recent studies have shown that gene expression can be noisy, <span class="hlt">noise</span> can be genetically controlled, genes and gene networks vary in how noisy they are and <span class="hlt">noise</span> generates phenotypic differences among genetically identical cells. Such phenotypic differences can have fitness benefits, suggesting that evolution can shape <span class="hlt">noise</span> and that <span class="hlt">noise</span> may be adaptive. For example, gene networks can generate bistable states resulting in phenotypic diversity and switching among individual cells of a genotype, which may be a bet hedging strategy. Here, we review the <span class="hlt">sources</span> of <span class="hlt">noise</span> in gene expression, the extent to which <span class="hlt">noise</span> in biological systems may be adaptive and suggest that applying evolutionary rigour to the study of <span class="hlt">noise</span> is necessary to fully understand organismal phenotypes. PMID:23902900</p> <div class="credits"> <p class="dwt_author">Viney, Mark; Reece, Sarah E</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-22</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">316</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.risknat.org/pages/programme_dep/docs/lgit/1997_Bard_cornou&al_2004.pdf"> <span id="translatedtitle">Ambient <span class="hlt">noise</span> energy bursts observation and modeling: Trapping of <span class="hlt">harmonic</span> structure-soil induced–waves in a topmost sedimentary layer</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We study the nature of energy bursts that appeared in the frequency range 3–5 Hz in ambient seismic <span class="hlt">noise</span> recorded in the Grenoble basin (French Alps) during a seismological array experiment. A close agreement is found between the identified azimuths of such <span class="hlt">noise</span> bursts with the location of an industrial chimney. In-situ measurements of the chimney dynamic characteristics show a</p> <div class="credits"> <p class="dwt_author">C. Cornou; P. Guéguen; P.-Y. Bard; E. Haghshenas</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">317</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/1489716"> <span id="translatedtitle">Magnetostrictive offset and <span class="hlt">noise</span> in flux gate magnetometers</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Longitudinal magnetostriction of the core material is found to be the principal <span class="hlt">source</span> of offset and <span class="hlt">noise</span> in present state-of-the-art flux gate magnetometers. Magnetostrictive offset is identified with even <span class="hlt">harmonics</span> of the steady-state induced EMF resulting from the periodic elongation (or contraction) of the core material. Magnetostrictive <span class="hlt">noise</span> is identified with random fluctuations of the magnetostrictive offset caused by frictional</p> <div class="credits"> <p class="dwt_author">M. Weiner</p> <p class="dwt_publisher"></p> <p class="publishDate">1969-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">318</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=ADA459963"> <span id="translatedtitle">Dispersion Management in a <span class="hlt">Harmonically</span> Mode-Locked Fiber Soliton Laser.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary"><span class="hlt">Harmonically</span> mode-locked Er-fiber soliton lasers have become a reliable <span class="hlt">source</span> of high-repetition-rate picosecond pulses in high-speed communications and photonic analog-to-digital conversion systems because of their low-<span class="hlt">noise</span>, dropout-free operation. We ...</p> <div class="credits"> <p class="dwt_author">C. R. Menyuk I. I. Duling M. Horowitz T. F. Carruthers</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">319</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19830008966&hterms=48&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3D48%2Bv"> <span id="translatedtitle">Effects of flight on <span class="hlt">noise</span> radiated from convected ring <span class="hlt">sources</span> in coaxial dual flow. Part 2: The <span class="hlt">noise</span> from heated jets</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The effects of flight on <span class="hlt">noise</span> from heated jets are discussed. The effects of the additionally, extraneously-generated dipole and simple <span class="hlt">source</span> 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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> from a CP-cycle) at all angles, both statically and in flight, for area ratios Sigma 0.25.</p> <div class="credits"> <p class="dwt_author">Dash, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">320</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27059566"> <span id="translatedtitle">Minimize Low-Order <span class="hlt">Harmonics</span> in Low-Switching-Frequency Space-Vector-Modulated Current <span class="hlt">Source</span> Converters With Minimum <span class="hlt">Harmonic</span> Tracking Technique</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Gate turnoffs (GTOs) are usually used in high-power current <span class="hlt">source</span> converters (CSCs), i.e., rectifiers and inverters. Space vector modulation (SVM) technique for CSC is established by dividing ac-side line current cycle into six sectors. Each sector is divided into a certain number of SV cycles. SV cycle is divided into three states: two active and one zero state. For low</p> <div class="credits"> <p class="dwt_author">M. F. Naguib; Luiz A. C. Lopes</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a style="font-weight: bold;">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_18");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">321</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930035187&hterms=wopwop&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dwopwop"> <span id="translatedtitle">Advances in tilt rotor <span class="hlt">noise</span> prediction</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The two most serious tilt rotor external <span class="hlt">noise</span> problems, hover <span class="hlt">noise</span> and blade-vortex interaction <span class="hlt">noise</span>, are studied. The results of flow visualization and inflow velocity measurements document a complex, recirculating highly unsteady and turbulent flow due to the rotor-wing-body interactions characteristic of tilt rotors. The wing under the rotor is found to obstruct the inflow, causing a deficit in the inflow velocities over the inboard region of the rotor. Discrete frequency <span class="hlt">harmonic</span> thickness and loading <span class="hlt">noise</span> mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various <span class="hlt">noise</span> prediction methods using the WOPWOP code. The analysis indicates that the partial ground plane created by the wing below the rotor results in a primary sound <span class="hlt">source</span> for hover.</p> <div class="credits"> <p class="dwt_author">George, A. R.; Coffen, C. D.; Ringler, T. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">322</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1992dglr.conf..510G"> <span id="translatedtitle">Advances in tilt rotor <span class="hlt">noise</span> prediction</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The two most serious tilt rotor external <span class="hlt">noise</span> problems, hover <span class="hlt">noise</span> and blade-vortex interaction <span class="hlt">noise</span>, are studied. The results of flow visualization and inflow velocity measurements document a complex, recirculating highly unsteady and turbulent flow due to the rotor-wing-body interactions characteristic of tilt rotors. The wing under the rotor is found to obstruct the inflow, causing a deficit in the inflow velocities over the inboard region of the rotor. Discrete frequency <span class="hlt">harmonic</span> thickness and loading <span class="hlt">noise</span> mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various <span class="hlt">noise</span> prediction methods using the WOPWOP code. The analysis indicates that the partial ground plane created by the wing below the rotor results in a primary sound <span class="hlt">source</span> for hover.</p> <div class="credits"> <p class="dwt_author">George, A. R.; Coffen, C. D.; Ringler, T. D.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">323</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19970001748&hterms=rigid+coupling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Drigid%2Bcoupling"> <span id="translatedtitle">Active Control of Fan <span class="hlt">Noise</span>: Feasibility Study. Volume 6; Theoretical Analysis for Coupling of Active <span class="hlt">Noise</span> Control Actuator Ring <span class="hlt">Sources</span> to an Annular Duct with Flow</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The objective of this effort is to develop an analytical model for the coupling of active <span class="hlt">noise</span> control (ANC) piston-type actuators that are mounted flush to the inner and outer walls of an annular duct to the modes in the duct generated by the actuator motion. The analysis will be used to couple the ANC actuators to the modal analysis propagation computer program for the annular duct, to predict the effects of active suppression of fan-generated engine <span class="hlt">noise</span> <span class="hlt">sources</span>. This combined program will then be available to assist in the design or evaluation of ANC systems in fan engine annular exhaust ducts. An analysis has been developed to predict the modes generated in an annular duct due to the coupling of flush-mounted ring actuators on the inner and outer walls of the duct. The analysis has been combined with a previous analysis for the coupling of modes to a cylindrical duct in a FORTRAN computer program to perform the computations. The method includes the effects of uniform mean flow in the duct. The program can be used for design or evaluation purposes for active <span class="hlt">noise</span> control hardware for turbofan engines. Predictions for some sample cases modeled after the geometry of the NASA Lewis ANC Fan indicate very efficient coupling in both the inlet and exhaust ducts for the m = 6 spinning mode at frequencies where only a single radial mode is cut-on. Radial mode content in higher order cut-off modes at the <span class="hlt">source</span> plane and the required actuator displacement amplitude to achieve 110 dB SPL levels in the desired mode were predicted. Equivalent cases with and without flow were examined for the cylindrical and annular geometry, and little difference was found for a duct flow Mach number of 0.1. The actuator ring coupling program will be adapted as a subroutine to the cylindrical duct modal analysis and the exhaust duct modal analysis. This will allow the fan <span class="hlt">source</span> to be defined in terms of characteristic modes at the fan <span class="hlt">source</span> plane and predict the propagation to the arbitrarily-located ANC <span class="hlt">source</span> plane. The actuator velocities can then be determined to generate the anti-phase mode. The resulting combined fan <span class="hlt">source</span>/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.</p> <div class="credits"> <p class="dwt_author">Kraft, R. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">324</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70013910"> <span id="translatedtitle">Seismicity at Old Faithful Geyser: an isolated <span class="hlt">source</span> of geothermal <span class="hlt">noise</span> and possible analogue of volcanic seismicity</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Old Faithful Geyser in Yellowstone National Park, U.S.A., is a relatively isolated <span class="hlt">source</span> of seismic <span class="hlt">noise</span> and exhibits seismic behavior similar to that observed at many volcanoes, including "bubblequakes" that resemble B-type "earthquakes", <span class="hlt">harmonic</span> tremor before and during eruptions, and periods of seismic quiet prior to eruptions. Although Old Faithful differs from volcanoes in that the conduit is continuously open, that rock-fracturing is not a process responsible for seismicity, and that the erupting fluid is inviscid H2O rather than viscous magma, there are also remarkable similarities in the problems of heat and mass recharge to the system, in the eruption dynamics, and in the seismicity. Water rises irregularly into the immediate reservoir of Old Faithful as recharge occurs, a fact that suggests that there are two enlarged storage regions: one between 18 and 22 m (the base of the immediate reservoir) and one between about 10 and 12 m depth. Transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water, and by episodes of convective overturn. An eruption occurs when the temperature of the near-surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure-release waves (rarefactions) down the column can bring the liquid water onto the boiling curve. The process of conversion of the liquid water in the conduit at the onset of an eruption into a two-phase liquid-vapor mixture takes on the order of 30 s. The seismicity is directly related to the sequence of filling and heating during the recharge cycle, and to the fluid mechanics of the eruption. Short (0.2-0.3 s), monochromatic, high-frequency events (20-60 Hz) resembling unsustained <span class="hlt">harmonic</span> tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding 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 ??? 103 g cm-2 s-1) and rock (??c ??? 3 ?? 105 g cm2 s-1). Sustained <span class="hlt">harmonic</span> 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 liquid-vapor 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 water-steam 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</p> <div class="credits"> <p class="dwt_author">Kieffer, S. W.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">325</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010SPIE.7559E..22K"> <span id="translatedtitle">Suppression of modal <span class="hlt">noise</span> in a multimode fiber optic delivery output from an ultra-broadband supercontinuum light <span class="hlt">source</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have tested various methods to suppress the modal <span class="hlt">noise</span> in multi-mode fiber (MMF) output from an ultrabroadband supercontinuum light which is generated in a nonlinear photonic-crystal fiber (PCF) pumped with a 1.06-?mwavelength, sub-nanosecond-pulse-width, 8-kHz-rep-rate Nd:YAG laser <span class="hlt">source</span>. Significant amount of modal <span class="hlt">noise</span> including spectral fluctuations was observed when the output from the photonic crystal single-mode fiber (SMF) was directly coupled into MMF. Standard mode-exciting and -mixing techniques such as mode scrambling and fiber stretching showed minimal effect on <span class="hlt">noise</span> suppression. We observed significant suppression of modal <span class="hlt">noise</span> by expanding the output beam from the PCF and tightly focus back into MMF using multiple lenses. The resulting spectra of the different MMFs are compared with the output from different SMFs coupled to the supercontinuum <span class="hlt">source</span>, which are necessary to cover the broadband range of the supercontinuum <span class="hlt">source</span> over more than two octaves, from 450 nm up to 2100 nm wavelength.</p> <div class="credits"> <p class="dwt_author">Kim, Do-Hyun; Klein, Karl-Friedrich; Ilev, Ilko K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">326</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27059500"> <span id="translatedtitle">Single-Phase Voltage <span class="hlt">Source</span> Inverter With a Bidirectional Buck–Boost Stage for <span class="hlt">Harmonic</span> Injection and Distributed Generation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A transformerless single-phase inverter topology is proposed that can operate over a wide dc input voltage range and has the ability to track reference signals with fast dynamics, making it suitable for <span class="hlt">harmonic</span> elimination and distributed generation applications. The necessary capacitor and inductor are easier to design than those for filtering the output of traditional inverters. Unlike traditional inverters, no</p> <div class="credits"> <p class="dwt_author">Ahmed Mohamed Salamah; Stephen J. Finney; Barry W. Williams</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">327</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19800006824&hterms=swirl+recovery+vane&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dswirl%2Brecovery%2Bvane"> <span id="translatedtitle">Demonstration of short-haul aircraft aft <span class="hlt">noise</span> reduction techniques on a twenty inch (50.8 cm) diameter fan, volume 1</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Tests of a 20 inch diameter, low tip speed, low pressure ratio fan which investigated aft fan <span class="hlt">noise</span> reduction techniques are reported. These techniques included <span class="hlt">source</span> <span class="hlt">noise</span> reduction features of selection of vane-blade ratio to reduce second <span class="hlt">harmonic</span> <span class="hlt">noise</span>, spacing effects, and lowering the Mach number through a vane row. Aft suppression features investigated included porosity effects, variable depth treatment, and treatment regenerated flow <span class="hlt">noise</span>. Initial results and selected comparisons are presented.</p> <div class="credits"> <p class="dwt_author">Stimpert, D. L.; Mcfalls, R. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1975-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">328</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/18657085"> <span id="translatedtitle">DETERMINATION OF THE DIRECTIVITY OF A PLANAR <span class="hlt">NOISE</span> <span class="hlt">SOURCE</span> BY MEANS OF NEARFIELD ACOUSTICAL HOLOGRAPHY, PART III: MEASUREMENTS ON HOMOGENEOUS, PROFILED AND COMPOSITE PANELS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In two companion papers, a method has been presented for determining the directivity of a planar <span class="hlt">noise</span> <span class="hlt">source</span> by using the technique of Nearfield Acoustical Holography [1, 2]. In this paper, a practical NAH measuring system based upon a single scanning microphone is described. The system is employed to measure the directivity of a number of planar <span class="hlt">noise</span> <span class="hlt">sources</span> consisting</p> <div class="credits"> <p class="dwt_author">M. A. Rowell; D. J. Oldham</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">329</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19730024885&hterms=gas+compressor+station&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522gas%2Bcompressor%2Bstation%2522"> <span id="translatedtitle"><span class="hlt">Noise</span> pollution resources compendium</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Abstracts of reports concerning <span class="hlt">noise</span> pollution are presented. The abstracts are grouped in the following areas of activity: (1) <span class="hlt">sources</span> of <span class="hlt">noise</span>, (2) <span class="hlt">noise</span> detection and measurement, (3) <span class="hlt">noise</span> abatement and control, (4) physical effects of <span class="hlt">noise</span> and (5) social effects of <span class="hlt">noise</span>.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1973-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">330</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=ADA070341"> <span id="translatedtitle">Low <span class="hlt">Noise</span> EBS Jammer.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The objective of this program is to reduce the output power level of spurious <span class="hlt">noise</span> signals, intermodulation (IM) products and <span class="hlt">harmonic</span> distortion generated by deflection modulated electron beam semiconductor (EBS) amplifiers. Work performed during this p...</p> <div class="credits"> <p class="dwt_author">D. B. Clark J. B. Rettig</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">331</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2000APS..GECKR2002S"> <span id="translatedtitle"><span class="hlt">Harmonic</span> Content of Electron Impact <span class="hlt">Source</span> Functions in Inductively Coupled Plasmas Using an ``On-the-Fly" Monte-Carlo Technique</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The electron temperature in low pressure (< 10s mTorr) inductively coupled plasmas (ICPs) excited at 10s MHz typically is not significantly modulated during the rf cycle. The tail of the electron energy distribution (EED) may, however, be modulated thereby producing time dependent electron impact <span class="hlt">source</span> functions for high threshold processes. Computer models based on hybrid techniques typically do not resolve this time dependence since only cycle average electron properties are used due to the computational burden of calculating and storing time and spatially dependent EEDs. In this paper, a new Monte Carlo technique, called ``on-the-fly" (OTF), is described in which moments of the EED are computed, as opposed to the actual EED. In doing so, spatially dependent electron impact <span class="hlt">source</span> functions are directly obtained. By computing Fourier components of the <span class="hlt">source</span> functions ``on-the-fly", the time <span class="hlt">harmonics</span> can also be obtained. The OTF technique was implemented in the Hybrid Plasma Equipment Model, a simulator for low pressure plasmas. The spatially dependent time <span class="hlt">harmonics</span> of electron impact <span class="hlt">source</span> functions will be discussed for ICPs in Ar/molecular gas mixtures.</p> <div class="credits"> <p class="dwt_author">Sankaran, Arvind; Kushner, Mark J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">332</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19740022131&hterms=mn7&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2522mn7%2522"> <span id="translatedtitle">Analytic models of ducted turbomachinery tone <span class="hlt">noise</span> <span class="hlt">sources</span>. Volume 1: Analysis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The analytic models developed for computing the periodic sound pressure of subsonic fans and compressors in an infinite, hardwall annular duct with uniform flow are described. The basic sound-generating mechanism is the scattering into sound waves of velocity disturbances appearing to the rotor or stator blades as a series of <span class="hlt">harmonic</span> gusts. The models include component interactions and rotor alone.</p> <div class="credits"> <p class="dwt_author">Clark, T. L.; Ganz, U. W.; Graf, G. A.; Westall, J. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1974-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">333</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20100033097&hterms=tinnitus&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522tinnitus%2522"> <span id="translatedtitle">Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Measurements of an F404 Nozzle Plume at Both Full and Model Scale</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A 48-microphone planar phased array system was used to acquire jet <span class="hlt">noise</span> <span class="hlt">source</span> localization data on both a full-scale F404-GE-F400 engine and on a 1/4th scale model of a F400 series nozzle. The full-scale engine test data show the location of the dominant <span class="hlt">noise</span> <span class="hlt">sources</span> in the jet plume as a function of frequency for the engine in both baseline (no chevron) and chevron configurations. Data are presented for the engine operating both with and without afterburners. Based on lessons learned during this test, a set of recommendations are provided regarding how the phased array measurement system could be modified in order to obtain more useful acoustic <span class="hlt">source</span> localization data on high-performance military engines in the future. The data obtained on the 1/4th scale F400 series nozzle provide useful insights regarding the full-scale engine jet <span class="hlt">noise</span> <span class="hlt">source</span> mechanisms, and document some of the differences associated with testing at model-scale versus fullscale.</p> <div class="credits"> <p class="dwt_author">Podboy, Gary G.; Bridges, James E.; Henderson, Brenda S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">334</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/10187862"> <span id="translatedtitle">Sensitivity of calculations of {sup 252}Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis measurements to cross sections for aqueous fissile solutions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Previous experiments have shown large changes in measured parameters such as the coherences and ratio of spectral densities for small changes in the measured configuration of fissile material and for small changes in k. This sensitivity was investigated by a variant of the Monte Carlo neutron transport code KENO-V.a, which calculates the time sequences of pulses at two detectors near a fissile assembly from the fission chain multiplication process initiated by a {sup 252}Cf <span class="hlt">source</span> in or near the fissile assembly. This code directly calculates the <span class="hlt">noise</span> analysis data from the {sup 252}Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> measurement method. Direct calculation of the experimental observables by the Monte Carlo method allows the benchmarking of calculational methods and cross sections. These calculations have shown a higher sensitivity of <span class="hlt">noise</span>-measured quantities to cross sections and calculational methods than the neutron multiplication factor for aqueous fissile solutions. For example, the calculation with ENDF/B-IV cross sections yields a value of the coherence {gamma}{sub 23}{sup 2} 300% larger at low frequency than that from the Hansen-Roach cross sections. The coherence between detectors is a factor of 67 more sensitive to cross sections than the neutron multiplication factor, and this results from the coherence at low k being proportional to the fourth power of (k/{Delta}k). This increased sensitivity to calculational methods means that as far as validating calculational methods, a subcritical experiment at a k {approx} 0.9 by the {sup 252}Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis method may be more useful than an experiment at k {approx} 1. The <span class="hlt">noise</span>-measured parameters can easily be obtained from measurements with an accuracy of {plus_minus}1% or less, and the precision of the Monte Carlo calculation of these quantities can also be {plus_minus}1% or less.</p> <div class="credits"> <p class="dwt_author">Valentine, T.E. [Oak Ridge Associated Universities, Inc., TN (United States); Mihalczo, J.T. [Oak Ridge National Lab., TN (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">335</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dsnra.jpl.nasa.gov/development/MM_wave/ALMA_memo311.pdf"> <span id="translatedtitle"><span class="hlt">Noise</span> Measurements of YIG-Tuned Oscillator <span class="hlt">Sources</span> for the ALMA LO</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In this memo, we present measurements of the <span class="hlt">noise</span> of YIG-tuned oscillators (YTOs) at their fundamental frequency and multiplied to millimeter-wave frequencies. Based on these measurements, we verify that the phase <span class="hlt">noise</span> goals for this component can be met with a 300-kHz bandwidth phase lock loop (PLL) as long as the fundamental YTO frequency is not above 27 GHz. We</p> <div class="credits"> <p class="dwt_author">Eric W. Bryerton; Dorsey L. Thacker; Kamaljeet S. Saini; Richard F. Bradley</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">336</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22220615"> <span id="translatedtitle"><span class="hlt">Noise</span> <span class="hlt">sources</span> and competition between stimulated Brillouin and Raman scattering: A one-dimensional steady-state approach</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">A 1D steady-state model is developed to deal with stimulated scattering processes. The volume and boundary <span class="hlt">noise</span> <span class="hlt">sources</span> for scattered light are discussed in detail. Our results indicate that the boundary <span class="hlt">noise</span> <span class="hlt">sources</span> 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.</p> <div class="credits"> <p class="dwt_author">Gong, Tao [Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China) [Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, Sichuan 621900 (China); Li, Zhichao [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, Sichuan 621900 (China)] [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, Sichuan 621900 (China); Zhao, Bin; Hu, Guang-yue; Zheng, Jian [Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)] [Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">337</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70014779"> <span id="translatedtitle">Resonance of a fluid-driven crack: radiation properties and implications for the <span class="hlt">source</span> of long-period events and <span class="hlt">harmonic</span> tremor.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">A dynamic <span class="hlt">source</span> model is presented, in which a 3-D crack containing a viscous compressible fluid is excited into resonance by an impulsive pressure transient applied over a small area DELTA S of the crack surface. The crack excitation depends critically on two dimensionless parameters called the crack stiffness and viscous damping loss. According to the model, the long-period event and <span class="hlt">harmonic</span> tremor share the same <span class="hlt">source</span> but differ in the boundary conditions for fluid flow and in the triggering mechanism setting up the resonance of the <span class="hlt">source</span>, the former being viewed as the impulse response of the tremor generating system and the later representing the excitation due to more complex forcing functions.-from Author</p> <div class="credits"> <p class="dwt_author">Chouet, B.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">338</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/60488028"> <span id="translatedtitle">Sensitivity of the sup 252 Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis method to fission content of spent LWR fuel</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The ²⁵²Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> 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</p> <div class="credits"> <p class="dwt_author">A. W. Krass; J. T. Mihalczo; T. E. Valentine</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">339</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27573083"> <span id="translatedtitle">Measurement of Vertical Distribution of Truck <span class="hlt">Noise</span> <span class="hlt">Sources</span> During Highway Cruise Pass-Bys by Acoustic Beam Forming</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A measurement program was completed to determine the vertical distribution of heavy-truck <span class="hlt">noise</span> <span class="hlt">sources</span> for pass-by events on an in-service highway for vehicles operating under cruise conditions. In addition to data on heavy trucks, some data were obtained for medium trucks and light-duty vehicles. The measurements were performed with acoustic beam forming, which provided visualization of the sound radiation of</p> <div class="credits"> <p class="dwt_author">Paul R. Donavan; Bruce Rymer</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">340</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/7128117"> <span id="translatedtitle">Analysis and ranking of the acoustic disturbance potential of petroleum-industry activities and other <span class="hlt">sources</span> of <span class="hlt">noise</span> in the environment of marine mammals in Alaska. Final report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The study compares the relative magnitudes and effects on marine mammals of <span class="hlt">noise</span> from oil and gas industry activities with <span class="hlt">noise</span> from other <span class="hlt">sources</span> in Alaska OCS and coastal waters. The study procedure incorporates the receiver, <span class="hlt">source</span> 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 <span class="hlt">noise</span> <span class="hlt">sources</span> is also included. The analysis of <span class="hlt">noise</span> <span class="hlt">sources</span> found in the Alaskan marine environment considers natural, industrial, transportation, and cultural <span class="hlt">sources</span>. Acoustic transmission loss characteristics obtained from measurements and model predictions are used to estimate the effective ranges of the <span class="hlt">noise</span> <span class="hlt">sources</span> using available <span class="hlt">source</span> level information. Information on species distribution was combined with information on <span class="hlt">source</span> distribution, <span class="hlt">source</span> level, and transmission loss to determine the most significant <span class="hlt">sources</span> in terms of their acoustic range and the numbers of mammals potentially affected by developing a Standardized <span class="hlt">Noise</span> Contribution Model species.</p> <div class="credits"> <p class="dwt_author">Malme, C.I.; Miles, P.R.; Miller, G.S.; Richardson, W.J.; Roseneau, D.G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-08-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" 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onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_19");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">341</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/50927764"> <span id="translatedtitle">Robust expectation-maximization algorithm for multiple wide-band acoustic <span class="hlt">source</span> localization in the presence of non-uniform <span class="hlt">noise</span> variances</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Wideband <span class="hlt">source</span> localization using acoustic sensor networks has been drawing a lot of research interest recently. The maximum-likelihood is the predominant objective which leads to a variety of <span class="hlt">source</span> localization approaches. In this paper, we would like to combat the <span class="hlt">source</span> localization problem based on the realistic assumption where the <span class="hlt">sources</span> are corrupted by the <span class="hlt">noises</span> with non-uniform spatial variances.</p> <div class="credits"> <p class="dwt_author">Lu Lu; Hsiao-Chun Wu; Kun Yan</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">342</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53112227"> <span id="translatedtitle"><span class="hlt">Noise</span> reduction methods in centrifugal fans</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A <span class="hlt">noise</span> control procedure for centrifugal fans is described which reduces both the <span class="hlt">harmonic</span> and the random <span class="hlt">noise</span> components. This procedure entails the use of an acoustically soft fan-casing volute and anechoically terminated ducts at the fan inlet and outlet. Experimental measurements show that increasing the cutoff clearance reduces the <span class="hlt">noise</span> level of higher <span class="hlt">harmonics</span> of the blade passage frequency,</p> <div class="credits"> <p class="dwt_author">R. Agnon; T. Gikadi; M. Bartenwerfer; W. Neise</p> <p class="dwt_publisher"></p> <p class="publishDate">1976-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">343</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19960003376&hterms=pla&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2522pla%2522"> <span id="translatedtitle">Active Control of Fan <span class="hlt">Noise</span>-Feasibility Study. Volume 2: Canceling <span class="hlt">Noise</span> <span class="hlt">Source</span>-Design of an Acoustic Plate Radiator Using Piezoceramic Actuators</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling <span class="hlt">sources</span> for active control of aircraft engine fan <span class="hlt">noise</span> is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy acoustic plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of acoustic plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable acoustic <span class="hlt">source</span> for active control of aircraft engine fan <span class="hlt">noise</span>.</p> <div class="credits"> <p class="dwt_author">Pla, F. G.; Rajiyah, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">344</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/95297"> <span id="translatedtitle"><span class="hlt">Noise</span> measurements in shunted, shorted, and fully electroded quartz gauges in the Saturn plasma radiation <span class="hlt">source</span> x-ray simulator</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This paper describes recent work to improve the measurement of the stress response of materials to intense, short pulses of radiation. When Saturn fires, large prompt electrical <span class="hlt">noise</span> pulses are induced in stress measurement circuits. The conventional wisdom has been that the shorted guard ring quartz gauge was the only configuration with acceptable prompt signal-to-<span class="hlt">noise</span> characteristics for stress measurements in this pulsed radiation environment. However, because of abnormal signal distortion, the shorted guard ring gauge is restricted to a maximum stress of about 8 kbars. Below this level, the normal, quantified signal distortion is correctable with analytical deconvolution techniques. The shunted guard ring gauge is acceptable for Egli fidelity measurements to about 25 kbars with negligible signal distortion. Experiments were conducted on the Saturn soft x-ray <span class="hlt">source</span> which show that higher fidelity shunted guard ring gauges can successfully measure stress with acceptable induced <span class="hlt">noise</span>. We also found that a 50-ohm impedance matching resistor at the gauge reduced the prompt <span class="hlt">noise</span> amplitude and improved the baseline quality of the measurement prior to shock wave arrival.</p> <div class="credits"> <p class="dwt_author">Barrett, W.H.; Greenwoll, J.I.; Smith, C.W. [Sandia National Labs., Albuquerque, NM (United States); Johnson, D.E.; De La Cruz, C.F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">345</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/565518"> <span id="translatedtitle"><span class="hlt">Noise</span> measurements in shunted, shorted, and fully electroded quartz gauges in the saturn plasma radiation <span class="hlt">source</span> x-ray simulator</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This paper describes recent work to improve the measurement of the stress response of materials to intense, short pulses of radiation. When Saturn fires, large prompt electrical <span class="hlt">noise</span> pulses are induced in stress measurement circuits. The conventional wisdom has been that the shorted guard ring quartz gauge was the only configuration with acceptable prompt signal-to-<span class="hlt">noise</span> characteristics for stress measurements in this pulsed radiation environment. However, because of abnormal signal distortion, the shorted guard ring gauge is restricted to a maximum stress of about 8 kbars. Below this level, the normal, quantified signal distortion is correctable with analytical deconvolution techniques. The shunted guard ring gauge is acceptable for high fidelity measurements to about 25 kbars with negligible signal distortion. Experiments were conducted on the Saturn soft x-ray <span class="hlt">source</span> which show that higher fidelity shunted guard ring gauges can successfully measure stress with acceptable induced <span class="hlt">noise</span>. We also found that a 50-ohm impedance matching resistor at the gauge reduced the prompt <span class="hlt">noise</span> amplitude and improved the baseline quality of the measurement prior to shock wave arrival. {copyright} {ital 1996 American Institute of Physics.}</p> <div class="credits"> <p class="dwt_author">Barrett, W.H.; Greenwoll, J.I.; Smith, C.W. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1159 (United States); Johnson, D.E.; De La Cruz, C.F. [Ktech Corporation, 901 Pennsylvania NE, Albuquerque, New Mexico 87110 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">346</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51038897"> <span id="translatedtitle">Power System <span class="hlt">Harmonics</span> and Unbalance Distribution Calculation Based on Measurement</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The modeling of <span class="hlt">harmonic</span> <span class="hlt">source</span> based on <span class="hlt">harmonic</span> measurement is put forward for the first time. Three-phase fundamental and <span class="hlt">harmonic</span> models of the whole power system are built in the paper. Then, the power system <span class="hlt">harmonics</span> penetration (PSHP) software package is developed on VC++ circumstance. Zhengzhou, Luoyang and Sanmengxia electric power system in Henan grid are studied, and the <span class="hlt">harmonics</span></p> <div class="credits"> <p class="dwt_author">Xilu Zhang; Junyong Wu; Yangyu Hu; Hongjun Fu; Luyu Ji; Honglei Song</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">347</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009SPIE.7448E...5J"> <span id="translatedtitle">Improved efficiency of materials processing by dual action of XUV/Vis-NIR ultrashort laser pulses and comprehensive study of high-order <span class="hlt">harmonic</span> <span class="hlt">source</span> at PALS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We demonstrate a novel experimental method for improvement of efficiency of structural surface modification of various solids (PMMA, amorphous carbon) achieved by simultaneous action of XUV (21.6 nm), obtained from high-order <span class="hlt">harmonic</span> generation (HHG), and VIS-NIR (410/820 nm) laser pulses. Although the fluence of each individual pulse was far below the surface ablation threshold, very efficient and specific material modification was observed after irradiation by a single or a few shots of mixed XUV/VIS-NIR radiation. We also report results on comprehensive characterization of ultrafast coherent X-ray beamline at Prague Asterix Laser System (PALS). The beamline is based on 1 kHz, table-top, high-order <span class="hlt">harmonic</span> generation <span class="hlt">source</span> capable to deliver fully coherent beam in the 30 nm spectral range. Ti:sapphire (810 nm, 1 kHz) laser pulses with a duration of 35 fs and energy 1.2 mJ have been focused into gas cell containing conversion medium (Ar). To achieve highly efficient HHG we will apply the technique of guided laser pulses. <span class="hlt">Source</span> parameters were investigated.</p> <div class="credits"> <p class="dwt_author">Jakubczak, Krzysztof; Mocek, Tomas; Rus, Bedrich; Hrebicek, Jan; Sawicka, Magdalena; Kim, I. Jong; Park, Seung Beom; Kim, Tae Keun; Lee, Gye Hwang; Nam, Chang Hee; Chalupsky, Jaromir; Hajkova, Vera; Juha, Libor; Sobota, Jaroslav; Fort, Tomas</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">348</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=N20010018723"> <span id="translatedtitle">Alternative Low <span class="hlt">Noise</span> Fan.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">A 106 bladed fan with a design takeoff tip speed of 1100 ft/sec was hypothesized as reducing perceived <span class="hlt">noise</span> because of the shift of the blade passing <span class="hlt">harmonics</span> to frequencies beyond the perceived <span class="hlt">noise</span> rating range. A 22 in. model of this Alternative Low...</p> <div class="credits"> <p class="dwt_author">D. M. Elliott J. H. Dittmar R. D. Moore R. J. Jeracki T. L. Parrott</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">349</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012GeoJI.191...88D"> <span id="translatedtitle">Adaptive <span class="hlt">noise</span> cancelling of multichannel magnetic resonance sounding signals</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Adaptive <span class="hlt">noise</span> cancelling of multichannel magnetic resonance sounding (MRS) signals is investigated. An analysis of the <span class="hlt">noise</span> <span class="hlt">sources</span> affecting MRS signals show that the applicability of adaptive <span class="hlt">noise</span> cancelling is primarily limited to cancel powerline <span class="hlt">harmonics</span>. The problems of handling spikes in MRS signals are discussed and an efficient algorithm for spike detection is presented. The optimum parameters for multichannel adaptive <span class="hlt">noise</span> cancelling are identified through simulations with synthetic signals added to <span class="hlt">noise</span>-only recordings from an MRS instrument. We discuss the design and the efficiency of different stacking methods. The results from multichannel adaptive <span class="hlt">noise</span> cancelling are compared to time-domain multichannel Wiener filtering. Our results show that within the experimental uncertainty the two methods give identical results.</p> <div class="credits"> <p class="dwt_author">Dalgaard, E.; Auken, E.; Larsen, J. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">350</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/50819847"> <span id="translatedtitle">Output voltage switching <span class="hlt">noise</span> peaks and utility AC input <span class="hlt">harmonic</span> current characteristics of delta-sigma modulated AC-DC converter with boost-buck circuit topologies</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A high frequency carrier PWM regulator used for various types of switch-mode power converters are based on the digital or analog signal comparison processing. The voltage-mode or current-mode PWM strategies due to comparison signal processing between voltage\\/current reference and periodic carrier signals cause the switching <span class="hlt">noise</span> peaks dependent on the multiple numbers of carrier signal frequency. In general, the switching</p> <div class="credits"> <p class="dwt_author">Atsushi Hirota; Sang-Pil Mun; Soon-Kurl Kwon; M. Nakaoka</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">351</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/18657870"> <span id="translatedtitle">ROTATING BLADE FLOW INSTABILITY AS A <span class="hlt">SOURCE</span> OF <span class="hlt">NOISE</span> IN AXIAL TURBOMACHINES</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">An experimental study is presented to investigate the aeroacoustic generation mechanism of the tip clearance <span class="hlt">noise</span> in axial turbomachines. In addition to the increased broadband levels reported in the literature when the tip clearance is enlarged, significant level increases were observed within narrow frequency bands below the blade passing frequency. Measurements of the pressure fluctuations at the casing wall just</p> <div class="credits"> <p class="dwt_author">F. Kameier; W. Neise</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">352</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19750009957&hterms=sound+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsound%2Bwaves"> <span id="translatedtitle">Generalized wave envelope analysis of sound propagation in ducts with stepped <span class="hlt">noise</span> <span class="hlt">source</span> profiles and variable axial impedance</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A finite difference formulation is presented for sound propagation in a rectangular two-dimensional duct without steady flow. Before the difference equations are formulated, the governing Helmholtz equation is first transformed to a form whose solution tends not to oscillate along the length of the duct. This transformation reduces the required number of grid points by an order of magnitude. Example solutions indicate that stepped <span class="hlt">noise</span> <span class="hlt">source</span> profiles have much higher attenuation than plane waves in a uniform impedance liner. Also, multiple stepped impedance liners are shown to have higher attenuation than uniform ducts if the impedances are chosen properly. For optimum <span class="hlt">noise</span> reduction with axial variations in impedance, the numerical analysis indicates that for a plane wave input the resistance should be near zero at the entrance of a suppressor duct, while the reactance should be near the optimum value associated with the least-attenuated mode in a uniform duct.</p> <div class="credits"> <p class="dwt_author">Baumeister, K. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1975-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">353</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008spa..book.1005F"> <span id="translatedtitle">Community Response to <span class="hlt">Noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The primary effects of community <span class="hlt">noise</span> on residential populations are speech interference, sleep disturbance, and annoyance. This chapter focuses on transportation <span class="hlt">noise</span> in general and on aircraft <span class="hlt">noise</span> in particular because aircraft <span class="hlt">noise</span> is one of the most prominent community <span class="hlt">noise</span> <span class="hlt">sources</span>, because airport/community controversies are often the most contentious and widespread, and because industrial and other specialized formsofcommunitynoise generally posemorelocalized problems.</p> <div class="credits"> <p class="dwt_author">Fidell, Sandy</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">354</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/56456865"> <span id="translatedtitle">Community Response to <span class="hlt">Noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The primary effects of community <span class="hlt">noise</span> on residential populations are speech interference, sleep disturbance, and annoyance. This chapter focuses on transportation <span class="hlt">noise</span> in general and on aircraft <span class="hlt">noise</span> in particular because aircraft <span class="hlt">noise</span> is one of the most prominent community <span class="hlt">noise</span> <span class="hlt">sources</span>, because airport\\/community controversies are often the most contentious and widespread, and because industrial and other specialized formsofcommunitynoise generally</p> <div class="credits"> <p class="dwt_author">Sandy Fidell</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">355</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24683340"> <span id="translatedtitle">Comparative analyses of phase <span class="hlt">noise</span> in 28 nm CMOS LC oscillator circuit topologies: Hartley, Colpitts, and common-<span class="hlt">source</span> cross-coupled differential pair.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">This paper reports comparative analyses of phase <span class="hlt">noise</span> in Hartley, Colpitts, and common-<span class="hlt">source</span> 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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> performance, due to the combined effects of device <span class="hlt">noise</span> and circuit node sensitivity. PMID:24683340</p> <div class="credits"> <p class="dwt_author">Chlis, Ilias; Pepe, Domenico; Zito, Domenico</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">356</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19920041269&hterms=backward+wave+oscillators&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dbackward%2Bwave%2Boscillators"> <span id="translatedtitle">An evaluation of HEMT potential for millimeter-wave signal <span class="hlt">sources</span> using interpolation and <span class="hlt">harmonic</span> balance techniques</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A large-signal analysis method based on an <span class="hlt">harmonic</span> balance technique and a 2-D cubic spline interpolation function has been developed and applied to the prediction of InP-based HEMT oscillator performance for frequencies extending up to the submillimeter-wave range. The large-signal analysis method uses a limited number of DC and small-signal S-parameter data and allows the accurate characterization of HEMT large-signal behavior. The method has been validated experimentally using load-pull measurement. Oscillation frequency, power performance, and load requirements are discussed, with an operation capability of 300 GHz predicted using state-of-the-art devices (fmax is approximately equal to 450 GHz).</p> <div class="credits"> <p class="dwt_author">Kwon, Youngwoo; Pavlidis, Dimitris; Tutt, Marcel N.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">357</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014GeoRL..41.3455R"> <span id="translatedtitle">Dominant seismic <span class="hlt">noise</span> <span class="hlt">sources</span> in the Southern Ocean and West Pacific, 2000-2012, recorded at the Warramunga Seismic Array, Australia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">noise</span> is important in determining Earth structure and also provides an insight into ocean wave patterns and long-term trends in storm activity and global climate. We present a long-duration study of seismic <span class="hlt">noise</span> focused on the Southern Ocean using recordings from the Warramunga Seismic Array, Northern Territory, Australia. Using high-resolution analysis, we determine the seismic slowness and back azimuth of observed seismic <span class="hlt">noise</span>, microseisms, at hourly intervals through over a decade (2000-2012). We identify three dominant <span class="hlt">sources</span> of body wave (P) <span class="hlt">noise</span> in the Southern Ocean which we interpret to originate from a South Atlantic <span class="hlt">source</span> propagating as PP waves, and Kerguelen Island and Philippine Sea <span class="hlt">sources</span> propagating as P waves. We also identify surface waves from around the Australian coast. All <span class="hlt">sources</span> show distinct seasonality and a low, but discernable, interannual variability.</p> <div class="credits"> <p class="dwt_author">Reading, Anya M.; Koper, Keith D.; Gal, Martin; Graham, Leon S.; Tkal?i?, Hrvoje; Hemer, Mark A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">358</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013PEPI..218...31E"> <span id="translatedtitle">Polarisation analysis of magnetotelluric time series using a wavelet-based scheme: A method for detection and characterisation of cultural <span class="hlt">noise</span> <span class="hlt">sources</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The identification and elimination of cultural <span class="hlt">noise</span> that affects magnetotelluric (MT) time series presents a challenge in the vicinity of industrialised, urban or farming areas. Most <span class="hlt">noise</span> <span class="hlt">sources</span> 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 <span class="hlt">noise</span> <span class="hlt">sources</span> 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 <span class="hlt">source</span> 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 <span class="hlt">source</span> or by cultural <span class="hlt">noise</span>.</p> <div class="credits"> <p class="dwt_author">Escalas, M.; Queralt, P.; Ledo, J.; Marcuello, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">359</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050205819&hterms=ejector&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2522ejector%2522"> <span id="translatedtitle">Transonic Resonance Demonstrated To Be a <span class="hlt">Source</span> of Internal <span class="hlt">Noise</span> From Mixer-Ejector Nozzles</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">During <span class="hlt">noise</span> 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 <span class="hlt">noise</span>. 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.</p> <div class="credits"> <p class="dwt_author">Zaman, Khairul B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">360</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19920001387&hterms=Norse&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DNorse"> <span id="translatedtitle">Airframe <span class="hlt">noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Current understanding of airframe <span class="hlt">noise</span> was reviewed as represented by experiment at model and full scale, by theoretical modeling, and by empirical correlation models. The principal component <span class="hlt">sources</span> 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 <span class="hlt">noise</span>. There are also possibilities for interactions between the various mechanisms. With current engine technology, the principal airframe <span class="hlt">noise</span> mechanisms dominate only at low frequencies, typically less than 1 kHz and often much lower, but further reduction of turbomachinery <span class="hlt">noise</span> in particular may make airframe <span class="hlt">noise</span> the principal element of approach <span class="hlt">noise</span> at frequencies in the sensitive range.</p> <div class="credits"> <p class="dwt_author">Crighton, David G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a 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showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a style="font-weight: bold;">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_20");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">361</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19970017414&hterms=generator+avr&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dgenerator%2Bavr"> <span id="translatedtitle">Fan <span class="hlt">Noise</span> Prediction System Development: <span class="hlt">Source</span>/Radiation Field Coupling and Workstation Conversion for the Acoustic Radiation Code</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The Acoustic Radiation Code (ARC) is a finite element program used on the IBM mainframe to predict far-field acoustic radiation from a turbofan engine inlet. In this report, requirements for developers of internal aerodynamic codes regarding use of their program output an input for the ARC are discussed. More specifically, the particular input needed from the Bolt, Beranek and Newman/Pratt and Whitney (turbofan <span class="hlt">source</span> <span class="hlt">noise</span> generation) Code (BBN/PWC) is described. In a separate analysis, a method of coupling the <span class="hlt">source</span> and radiation models, that recognizes waves crossing the interface in both directions, has been derived. A preliminary version of the coupled code has been developed and used for initial evaluation of coupling issues. Results thus far have shown that reflection from the inlet is sufficient to indicate that full coupling of the <span class="hlt">source</span> and radiation fields is needed for accurate <span class="hlt">noise</span> predictions ' Also, for this contract, the ARC has been modified for use on the Sun and Silicon Graphics Iris UNIX workstations. Changes and additions involved in this effort are described in an appendix.</p> <div class="credits"> <p class="dwt_author">Meyer, H. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">362</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/12946195"> <span id="translatedtitle"><span class="hlt">Noise</span>-driven switching and chaotic itinerancy among dynamic states in a three-mode intracavity second-<span class="hlt">harmonic</span> generation laser operating on a Lambda transition.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">We studied the antiphase self-pulsation in a globally coupled three-mode laser operating in different optical spectrum configurations. We observed locking of modal pulsation frequencies, quasiperiodicity, clustering behaviors, and chaos, resulting from the nonlinear interaction among modes. The robustness of [p:q:r] three-frequency locking states and quasiperiodic oscillations against residual <span class="hlt">noise</span> has been examined by using joint time-frequency analysis of long-term experimental time series. Two sharply antithetical types of switching behaviors among different dynamic states were observed during temporal evolutions; <span class="hlt">noise</span>-driven switching and self-induced switching, which manifests itself in chaotic itinerancy. The modal interplay behind observed behaviors was studied by using the statistical dynamic quantity of the information circulation. Well-organized information flows among modes, which correspond to the number of degeneracies of modal pulsation frequencies, were found to be established in accordance with the inherent antiphase dynamics. Observed locking behaviors, quasiperiodic motions, and chaotic itinerancy were reproduced by numerical simulation of the model equations. PMID:12946195</p> <div class="credits"> <p class="dwt_author">Otsuka, Kenju; Ohtomo, Takayuki; Maniwa, Tsuyoshi; Kawasaki, Hazumi; Ko, Jing-Yuan</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">363</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/26787663"> <span id="translatedtitle"><span class="hlt">Noise</span>-Induced Chaos in Duffing Oscillator with Double Wells</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Stochastic Melnikov method is employed to predict <span class="hlt">noise</span>-induced chaotic response in the Duffing oscillator with double wells. The safe basin is simulated to show the <span class="hlt">noise</span>-induced fractal boundary. Three cases are considered: <span class="hlt">harmonic</span> excitation, both <span class="hlt">harmonic</span> and Gaussian white <span class="hlt">noise</span> excitations, and Gaussian white <span class="hlt">noise</span> excitation. The leading Lyapunov exponent estimated by Rosenstein's algorithm is shown to quantify the chaotic</p> <div class="credits"> <p class="dwt_author">Chunbiao Gan</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">364</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/96845"> <span id="translatedtitle">MCNP-DSP calculations of the {sup 252}Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis measurements of highly enriched uranium metal cylinders</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This paper presents calculations of the {sup 252}Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis measurements for subcritical highly enriched uranium metal cylinders using the Monte Carlo code MCNP-DSP. This code directly calculates the <span class="hlt">noise</span> analysis data from the {sup 252}Cf- <span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis method for both neutron and gamma ray detectors. Direct calculation of experimental observables by the Monte Carlo method allows for the benchmarking of the calculational model and the cross sections and for determining the bias in the calculation.</p> <div class="credits"> <p class="dwt_author">Valentine, T.E.; Mihalczo, J.T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">365</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014ApPhL.104h3508H"> <span id="translatedtitle">Observation of bias-dependent <span class="hlt">noise</span> <span class="hlt">sources</span> in a TiOx/TiOy bipolar resistive switching frame</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report the conduction features associated with the evolution of oxygen ions (or vacancies) under bias for a TiOx (oxygen ion-rich)/TiOy (oxygen ion-deficient) bi-layer cell by identifying low-frequency <span class="hlt">noise</span> <span class="hlt">sources</span>. It is believed that a low resistance state enhances the formation of conductive filaments exchanging electrons through a nearest-neighbor hopping process, while a high resistance state (HRS) emphasizes the rupture of conductive filaments inside the insulating TiOx layer and a reduction/oxidation reaction at the oxide interfaces. The high resolution transmission electron microscope images of as-grown and HRS cells are also discussed.</p> <div class="credits"> <p class="dwt_author">Hyung Kim, Joo; Rahm Lee, Ah; Cheol Bae, Yoon; Ho Baek, Kwang; Sik Im, Hyun; Pyo Hong, Jin</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">366</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21428793"> <span id="translatedtitle">Multi-<span class="hlt">Harmonic</span> Cavities for Increasing RF Breakdown Threshold</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">A multi-<span class="hlt">harmonic</span> asymmetric cavity is predicted to sustain higher acceleration gradients than a conventional pillbox cavity, 55% higher in one example, when driven by external RF <span class="hlt">harmonic</span> <span class="hlt">sources</span>. Simulations of multi-<span class="hlt">harmonic</span> excitation in such a cavity are described, either by a charged drive beam or by external RF <span class="hlt">sources</span>. An accelerator structure based on multi-<span class="hlt">harmonic</span> cavity is proposed.</p> <div class="credits"> <p class="dwt_author">Jiang, Y. [Beam Physics Laboratory, Yale University, 272 Whitney Ave., New Haven, CT 06511 (United States); Kazakov, S. Yu. [Omega-P, Inc., 258 Bradley St., New Haven, CT 06510 (United States); Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States); Kuzikov, S. V. [Omega-P, Inc., 258 Bradley St., New Haven, CT 06510 (United States); Institute of Applied Physics, Nizhny Novgorod (Russian Federation); Hirshfield, J. L. [Beam Physics Laboratory, Yale University, 272 Whitney Ave., New Haven, CT 06511 (United States); Omega-P, Inc., 258 Bradley St., New Haven, CT 06510 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-11-04</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">367</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20010018723&hterms=parrott&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dparrott"> <span id="translatedtitle">The Alternative Low <span class="hlt">Noise</span> Fan</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A 106 bladed fan with a design takeoff tip speed of 1100 ft/sec was hypothesized as reducing perceived <span class="hlt">noise</span> because of the shift of the blade passing <span class="hlt">harmonics</span> to frequencies beyond the perceived <span class="hlt">noise</span> rating range. A 22 in. model of this Alternative Low <span class="hlt">Noise</span> 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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> behaved as hypothesized, the majority of this <span class="hlt">noise</span> reduction was from reduced broadband <span class="hlt">noise</span> 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 <span class="hlt">noise</span> was controlled by rotor wake-stator interaction but that the broadband <span class="hlt">noise</span> is probably controlled by the interaction of the rotor with incoming flows. A possible multiple pure tone <span class="hlt">noise</span> reduction technique for a fan/acoustic treatment system was identified. The data from the fully treated configuration showed significant <span class="hlt">noise</span> reductions over a large frequency range thereby providing a real tribute to this bulk absorber treatment design. The tone <span class="hlt">noise</span> data with the partially treated 7 vane configuration indicated that acoustic material in the <span class="hlt">source</span> <span class="hlt">noise</span> generation region may be more effective than similar material outside of the generation region.</p> <div class="credits"> <p class="dwt_author">Dittmar, James H.; Elliott, David M.; Jeracki, Robert J.; Moore, Royce D.; Parrott, Tony L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">368</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/26114604"> <span id="translatedtitle">Frequency <span class="hlt">Sources</span> in W-band Radar Front-end with Low Phase <span class="hlt">Noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A W-band coherent stepped-frequency pulsed radar front-end is developed. It consists of a millimetre wave transmitting <span class="hlt">source</span>,\\u000a a mm-wave local <span class="hlt">source</span>, a DDS with multi frequency points output and two microwave <span class="hlt">sources</span> serving as local oscillators. All\\u000a the <span class="hlt">sources</span> are coherent with the 120 MHz referenced crystal oscillator. The mm-wave <span class="hlt">sources</span> are realized by frequency multiplier\\u000a chain, up-conversion and injection locking.</p> <div class="credits"> <p class="dwt_author">Yonghong Zhang; Xiaohong Tang; Yong Fan; Zhengde Wu</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">369</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/19840834"> <span id="translatedtitle">Transmission characteristics of cyclotron <span class="hlt">harmonic</span> waves in plasma</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In recent years the importance of cyclotron <span class="hlt">harmonic</span> waves has become apparent in many branches of plasma physics. For example, it has been demonstrated that they are involved in the anomalously high <span class="hlt">noise</span> radiation near the electron cyclotron <span class="hlt">harmonic</span> frequencies that has been observed from thermonuclear fusion study devices, and that they can explain the cyclotron <span class="hlt">harmonic</span> resonances observed in</p> <div class="credits"> <p class="dwt_author">F. W. Crawford; H. H. Weiss</p> <p class="dwt_publisher"></p> <p class="publishDate">1966-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">370</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/50125466"> <span id="translatedtitle">An overlap-add free musical <span class="hlt">noise</span> analysis-synthesis system</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">An analysis-synthesis system for audio signals using sinusoidal model-based algorithms for <span class="hlt">harmonic</span> component reconstruction and <span class="hlt">noise</span> modeling for stochastic component synthesis has recently demonstrated the generation of high-quality synthetic signals. However current approaches, which mainly use phase randomization <span class="hlt">noise</span>-driven <span class="hlt">source</span> filter models with overlap-add techniques, have degraded the performance for signals consisting of highly time-localized events such as transients. First,</p> <div class="credits"> <p class="dwt_author">Y. H. Lam; R. W. Stewart</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">371</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012GeoJI.188.1303Y"> <span id="translatedtitle">Exploiting seismic signal and <span class="hlt">noise</span> in an intracratonic environment to constrain crustal structure and <span class="hlt">source</span> parameters of infrequent earthquakes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In many regions of the world characterized by a relatively low rate of seismicity, the determination of local and regional seismic <span class="hlt">source</span> parameters is often restricted to an analysis of the first onsets of P waves (or first motion analysis) due to incomplete information about Earth structure and the small size of the events. When rare large earthquakes occur in these regions, their waveforms can be used to model Earth structure. This, however, makes the nature of the earthquake <span class="hlt">source</span> determination problem circular, as <span class="hlt">source</span> information is mapped as structure. Presented here is one possible remedy to this situation, where through a two-step approach we first constrain Earth structure using data independent of the earthquake of interest. In this study, we focus on a region in Western Australia with low seismicity and minimal instrument coverage and use the CAPRA/LP temporary deployment to demonstrate that reliable structural models of the upper lithosphere can be obtained from an independent collection of teleseismic and ambient <span class="hlt">noise</span> datasets. Apart from teleseismic receiver functions (RFs), we obtain group velocities from the cross-correlation of ambient <span class="hlt">noise</span> and phase velocities from the traditional two-station method using carefully selected teleseismic earthquakes and station pairs. Crustal models are then developed through the joint inversion of dispersion data and RFs, and structural Green's functions are computed from a layered composite model. In the second step of this comprehensive approach, we apply full waveform inversion (three-component body and surface waves) to the 2007 ML= 5.3 Shark Bay, Western Australia, earthquake to estimate its <span class="hlt">source</span> parameters (seismic moment, focal mechanism, and depth). We conclude that the full waveform inversion analysis provides constraints on the orientation of fault planes superior to a first motion interpretation.</p> <div class="credits"> <p class="dwt_author">Young, Mallory K.; Tkal?i?, Hrvoje; Rawlinson, Nicholas; Reading, Anya M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">372</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.S53A2404H"> <span id="translatedtitle">Azimuthal Distribution of the Seismic <span class="hlt">Noise</span> <span class="hlt">Source</span> Energy Inverted from Phase Velocity Asymmetries Obtained by Ambient <span class="hlt">Noise</span> Interferometry: A Case Study in Northeast China</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In this study, we observe systematical deviations between the causal and acausal Rayleigh-wave arrivals retrieved from ambient <span class="hlt">noise</span> interferometry. We use continuous broadband records from the 127 NECESSArray (the NorthEast China Extended SeiSmic Array) stations and the 138 CEA (Chinese Earthquake Administration) stations in NE China operated between 2009 and 2011 to construct the Green's functions of the ray paths between station pairs. The stations cover the entire area of Northeast China with a station spacing of ~70-80 km. The deviations in measured phase velocity have been clearly shown as a function of the azimuth between two measured stations with a maximum magnitude of ~2 %, strongly implying that they are probably caused by a distribution of inhomogeneous ambient <span class="hlt">noise</span> energy. We designed a method to estimate the azimuthal variation of ambient <span class="hlt">noise</span> energy using those measured phase velocity asymmetries given by ambient <span class="hlt">noise</span> interferometry. The inversion problem is formulated based on a plane wave approximation which relates the estimated Green's Function to the azimuthal distribution of ambient <span class="hlt">noise</span> energy. To test the inversion method, we first generate synthetic data for given phase velocities and <span class="hlt">noise</span> distribution across the entire NE China. Our inversion results show that the input modeled <span class="hlt">noise</span> energy can be recovered. We then apply this inversion method to the real data and obtain azimuthal distribution of the <span class="hlt">noise</span> energy. Four maxima of <span class="hlt">noise</span> energy were located approximately in the Northern Pacific, Southern Pacific, Southern Indian Ocean and Northern Atlantic Ocean. Furthermore, we analyze the azimuthal variation of Signal to <span class="hlt">Noise</span> Ratio (SNR) of the cross correlation functions used in this work, and the results are in good agreement with the results listed above. To confirm the robustness of our inversion method indicated above, more studies are required to be carried out in other parts of the world.</p> <div class="credits"> <p class="dwt_author">Han, J.; Kang, D.; Ning, J.; Chen, Y. J.; Ni, J.; Niu, F.; Grand, S. P.; Kawakatsu, H.; Tanaka, S.; Obayashi, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">373</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19870026322&hterms=mahan&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2522mahan%2522"> <span id="translatedtitle">Comparison of two propeller <span class="hlt">source</span> models for aircraft interior <span class="hlt">noise</span> studies</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The sensitivity of the predicted synchrophasing (SP) effectiveness trends to the propeller <span class="hlt">source</span> model issued is investigated with reference to the development of advanced turboprop engines for transport aircraft. SP effectiveness is shown to be sensitive to the type of <span class="hlt">source</span> model used. For the virtually rotating dipole <span class="hlt">source</span> model, the SP effectiveness is sensitive to the direction of rotation at some frequencies but not at others. The SP effectiveness obtained from the virtually rotating dipole model is not very sensitive to the radial location of the <span class="hlt">source</span> distribution within reasonable limits. Finally, the predicted SP effectiveness is shown to be more sensitive to the details of the <span class="hlt">source</span> model used for the case of corotation than for the case of counterrotation.</p> <div class="credits"> <p class="dwt_author">Mahan, J. R.; Fuller, C. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">374</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1993PhDT........13S"> <span id="translatedtitle">An experimental investigation of the <span class="hlt">sources</span> of propeller <span class="hlt">noise</span> due to turbulence ingestion</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Experimental measurements were performed on a four-bladed, 10-inch diameter marine propeller operating in a new open-jet, anechoic wind tunnel. A significant portion of the work consisted of the design, construction, and calibration of the wind tunnel facility. The wind tunnel could be operated from 5-100 ft/s with open-jet lengths from 2-7 feet. When the wind tunnel was installed the majority of the chamber had a low-frequency cut-off of 150 Hz. The freestream velocity and propeller rotational speed were 33 ft/s and 3000 RPM, respectively. Turbulence was generated at the exit plane of the wind tunnel inlet by square-mesh grids composed of cylindrical rods which resulted in turbulence levels at the propeller location from 0.2-5.5 percent. Measurements included steady thrust and torque, detailed hot wire surveys of the incoming flow and propeller wake, and sound pressure levels detailing the acoustic spectra and directivity. Bicoherence measurements in the propeller wake showed high coherence between the blade passage <span class="hlt">harmonics</span> and the broadband frequencies near the hub and tip regions of the blades which indicated that the wake interactions were primarily non-linear. Inflow turbulence reduced this coherence. The integrated broad-band sound pressure level increased by approximately 2 dB for every 1 percent increase in the turbulence. These increases were decomposed into smaller frequency bandwidths and related to the inflow turbulence spectrum.</p> <div class="credits"> <p class="dwt_author">Scharpf, Daniel Francis</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">375</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19900045215&hterms=Bem&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DBem"> <span id="translatedtitle">Numerical evaluation of the performance of active <span class="hlt">noise</span> control systems</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">This paper presents a generalized numerical technique for evaluating the optimal performance of active <span class="hlt">noise</span> controllers. In this technique, the indirect BEM numerical procedures are used to derive the active <span class="hlt">noise</span> controllers for optimal control of enclosed <span class="hlt">harmonic</span> sound fields where the strength of the <span class="hlt">noise</span> <span class="hlt">sources</span> or the description of the enclosure boundary may not be known. The performance prediction for a single-input single-output system is presented, together with the analysis of the stability and observability of an active <span class="hlt">noise</span>-control system employing detectors. The numerical procedures presented can be used for the design of both the physical configuration and the electronic components of the optimal active <span class="hlt">noise</span> controller.</p> <div class="credits"> <p class="dwt_author">Mollo, C. G.; Bernhard, R. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">376</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.S23A2214B"> <span id="translatedtitle">Combining Three Component Beamforming and Wave Hindcast Model Data to Investigate <span class="hlt">Source</span> Regions of Ambient Seismic <span class="hlt">Noise</span>: a New Zealand Case Study</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent studies employing ambient seismic <span class="hlt">noise</span> as an energy <span class="hlt">source</span> have extended our knowledge of crustal and upper mantle structures and of time-variable geological processes. It has further been demonstrated that the combination of earthquake and ambient seismic <span class="hlt">noise</span> signals can potentially overcome restrictions inherent to traditional event-based seismology alone. However, uncertainties in the <span class="hlt">source</span> location and <span class="hlt">source</span> mechanism of ambient seismic <span class="hlt">noise</span> constitute a major obstacle in fully utilizing the results of seismic <span class="hlt">noise</span> investigations. Several authors have addressed this problem but focused on the <span class="hlt">source</span> regions of vertical-component <span class="hlt">noise</span> recordings only. In this study, we conduct plane-wave beamforming using vertical- and horizontal-component seismic <span class="hlt">noise</span> recordings from a dense deployment of 61 broadband instruments on New Zealand's western North Island to investigate the <span class="hlt">source</span> regions and <span class="hlt">source</span> mechanisms of both Rayleigh and Love waves contained in the ambient seismic <span class="hlt">noise</span> wavefield. We compare beamformer observations with locations of potential <span class="hlt">sources</span> inferred from bathymetry and an ocean wave hindcast model of the New Zealand region employing the theoretical framework for microseism excitation of Longuet-Higgins (Phil. Trans. R. Soc. Lon., 1950] and Bromirski and Duennebier (J. Geophys. Res., 2002). Our results indicate that the <span class="hlt">source</span> regions of both the primary and secondary microseisms are mostly located close to New Zealand's coastline and few significant deep water <span class="hlt">sources</span> can be identified. The strongest <span class="hlt">source</span> region appears to be the south-western tip of New Zealand's South Island where large ocean swells coincide with a narrow continental shelf. This observation is underlined by the good correlation between near-coastal ocean significant wave height and seismic significant wave height. However, quantification of this relationship in terms of Longuet-Higgins' [1950] theory requires a more detailed treatment of coastal effects on ocean waves than is currently common in wave hindcast models. We also observe that Rayleigh and Love waves are generated in similar areas but with differing intensities. When averaged over several months, our beamformer results for vertical- and horizontal-component <span class="hlt">noise</span> recordings show broadly similar and homogeneous azimuthal distributions. This is an important result for ongoing studies focused on estimating Green's functions from ambient <span class="hlt">noise</span> cross correlations in New Zealand.</p> <div class="credits"> <p class="dwt_author">Behr, Y.; Townend, J.; Bowen, M. M.; Carter, L.; Gorman, R. M.; Bannister, S. C.; Brooks, L. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">377</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=PB81249260"> <span id="translatedtitle">Vocational Education Training in Environmental Health Sciences: Obtaining Measurements of Stationary Environmental <span class="hlt">Noise</span> <span class="hlt">Sources</span>, Module 2.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">In this instructional module, students learn to determine the level of sound produced by stationary <span class="hlt">sources</span> located in residential, industrial, and commercial land use zones. Training Prerequisites: Before beginning this module, students should have a cou...</p> <div class="credits"> <p class="dwt_author">F. C. May</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">378</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApPhL.102g1102K"> <span id="translatedtitle">Numerical simulations of time-domain interferometric soft X-ray microscope with broadband high-order <span class="hlt">harmonic</span> light <span class="hlt">sources</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A scheme for achieving high spatial resolution in soft X-ray microscopy with coherent broadband light <span class="hlt">sources</span> is proposed, in which the chromatic aberration at a Fresnel zone plate lens can be canceled out by introducing time-delayed double pulses as an input light and by the Fourier transformation of recorded images with respect to the time delay. Numerical simulations of microscope images show that the spatial resolution of the proposed method is determined only by specifications of zone plates even when a broadband soft X-ray is used as a light <span class="hlt">source</span>.</p> <div class="credits"> <p class="dwt_author">Kanya, Reika; Iwasaki, Atsushi; Teramoto, Takahiro; Yamanouchi, Kaoru</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">379</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19770004110&hterms=two+position+coherence+function&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dtwo%2Bposition%2Bcoherence%2Bfunction"> <span id="translatedtitle">Core <span class="hlt">noise</span> <span class="hlt">source</span> diagnostics on a turbofan engine using correlation and coherence techniques</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Fluctuating pressure measurements at several locations within the core of a turbofan engine were made simultaneously with far field acoustic measurements. Correlation and coherence techniques were used to determine the relative amplitude and phase relationships between core pressures at these various locations and between the core pressures and far field acoustic pressure. The combustor is a low frequency <span class="hlt">source</span> region for acoustic propagation through the core nozzle and out to the far field. The relation between <span class="hlt">source</span> pressure and the resulting sound pressure involves a 180 degree phase shift and an amplitude transfer function which varies approximately as frequency squared. This is consistent with a simplified model using fluctuating entropy as a <span class="hlt">source</span> term.</p> <div class="credits"> <p class="dwt_author">Karchmer, A. M.; Reshotko, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1976-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">380</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/992906"> <span id="translatedtitle"><span class="hlt">Noise</span> Amplification in HGHG Seeding</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">An essential element of seeded FEL based on high-gain <span class="hlt">harmonic</span> generation (HGHG) or echo-enabled <span class="hlt">harmonic</span> 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 <span class="hlt">noise</span> properties of the beam.</p> <div class="credits"> <p class="dwt_author">Stupakov, Gennady</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-08-25</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_18");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a 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showDiv("page_21");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">381</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFM.S53C2512R"> <span id="translatedtitle">Seismic <span class="hlt">Noise</span> <span class="hlt">Sources</span> and Storm Severity in the Southern Ocean, Insights from the Warramunga Array (WRA), Northern Territory, Australia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Seismic array recordings of ambient energy (background seismic <span class="hlt">noise</span>) represent an archive of the activity of distant and near-shore ocean waves. Storm events are evident from body wave and surface wave arrivals. High profile meteorological studies, using calibrated satellite observations, have highlighted a disparity between increasing wind speeds and measured wave heights during storm events in the southern ocean. This has profound implications for the global climate system, including the incorporation of atmospheric carbon dioxide into the ocean. Seismic data, in particular, seismic arrays, allow an independent measurement of ocean wave activity back through several decades. We analyse two decades (1990-2009) of data from the Warramunga Seismic Array, located in inland mainland Australia using array techniques, in particular the 'Capon' method which highlights backazimuth and slowness of incoming seismic energy. The inland location allows the nature and location body wave energy to be identified for 3 hourly intervals, throughout this time interval. We find distinct patterns of far field seismic energy <span class="hlt">sources</span>, mostly associated with deep ocean plateau, with implications for the coupling of seismic energy between the ocean and the solid earth. The relationship between storm severity and seismic <span class="hlt">noise</span> amplitude is not linear, however, seismic array recordings represent an important independent observable in the understanding of the complex Southern Ocean system.</p> <div class="credits"> <p class="dwt_author">Reading, A. M.; Graham, L.; Koper, K. D.; Hemer, M. A.; Tkalcic, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">382</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/doepatents/biblio/1001787"> <span id="translatedtitle"><span class="hlt">Harmonic</span> engine</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p class="result-summary">A high efficiency <span class="hlt">harmonic</span> engine based on a resonantly reciprocating piston expander that extracts work from heat and pressurizes working fluid in a reciprocating piston compressor. The engine preferably includes <span class="hlt">harmonic</span> oscillator valves capable of oscillating at a resonant frequency for controlling the flow of working fluid into and out of the expander, and also preferably includes a shunt line connecting an expansion chamber of the expander to a buffer chamber of the expander for minimizing pressure variations in the fluidic circuit of the engine. The engine is especially designed to operate with very high temperature input to the expander and very low temperature input to the compressor, to produce very high thermal conversion efficiency.</p> <div class="credits"> <p class="dwt_author">Bennett, Charles L. (Livermore, CA)</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-10-20</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">383</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012sf2a.conf..613T"> <span id="translatedtitle">Latest results of the CODALEMA experiment: Anthropic <span class="hlt">noise</span> <span class="hlt">sources</span> and polarization analysis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Dedicated to the measurement of the radio transients coming from the extensive air showers (EAS), the CODALEMA experiment was started in 2001 at the Nançay Observatory, in France. Benefiting of an easy deployment and a low cost compared with Cherenkov detectors or fluorescence telescopes, this alternative method appears to be an interesting tool for the understanding of the physics of high energy cosmic rays observed through EAS. A new configuration of the CODALEMA experiment was implemented in 2011 based on a standalone detection, which will be essential for the next generation of giant detector array. One of the major challenges of this promising detection mode is the control (identification and rejection) of the fluctuating and transient <span class="hlt">noise</span> events in an inhabited area and the knowledge of the shower radio-detection capabilities such as the effective efficiency and the data purity. Some results concerning the electric field polarization are also presented and seems to be crucial to the understanding of the secondary emission mechanisms by EAS such as the charge excess.</p> <div class="credits"> <p class="dwt_author">Torres Machado, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">384</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52748258"> <span id="translatedtitle">Introduction to <span class="hlt">noise</span> in solid state devices</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The principal <span class="hlt">noises</span> found in solid state devices, namely shot <span class="hlt">noise</span>, thermal <span class="hlt">noise</span>, 1\\/f <span class="hlt">noise</span>, and generation-recombination <span class="hlt">noise</span> are discussed. A systematic treatment of <span class="hlt">noise</span> in selected solid state devices is presented. Analyses progress from a single <span class="hlt">noise</span> <span class="hlt">source</span> in a circuit element to four <span class="hlt">noises</span> in a device; concomittantly equivalent circuits are developed to facilitate the solution of various</p> <div class="credits"> <p class="dwt_author">J. Cohen</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">385</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE97625543"> <span id="translatedtitle"><span class="hlt">Noise</span> caused by cavitating Butterfly and Monovar Valves. Effects of cavitation on acoustic <span class="hlt">sources</span>; numerical simulation.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">An experimental study of the effects of cavitation was carried out through an analysis of cavitating Butterfly and Monovar valves. For each variation case, the nature of the dominant <span class="hlt">source</span> is determined in relation to frequency. Once the parameters of th...</p> <div class="credits"> <p class="dwt_author">H. Hassis J. F. Lauro A. Boyer E. Dueymes</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">386</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..1613146C"> <span id="translatedtitle">Location of Multiple Coincident <span class="hlt">Noise</span> <span class="hlt">Sources</span> in the N.E. Atlantic, offshore Ireland.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The World's oceans generate persistent low frequency background signals or 'microseisms' through a mechanical coupling with the crust. This can occur through a direct interaction between ocean gravity waves and the crust in shallow water (primary microseisms) or beneath standing waves generated by the interaction of opposing ocean wave fields (secondary microseisms). Secondary microseism <span class="hlt">sources</span> are not limited to shallow water regions. The relationship between the two leads to the possibility of obtaining information on the ocean wave-field from near coastal seismic records by developing a transfer function between an ocean buoy and a near coastal seismic receiver. However, this assumes that the seismic record is dominated by a <span class="hlt">source</span> relatively close to the buoy. Microseisms are also used in passive seismic interferometry where it is assumed that when averaged over a sufficiently long time period the wave field is random. This places importance on understanding the degree of non-uniformity within the seismic <span class="hlt">source</span> region. Both these applications highlight the importance of understanding how the microseism distributions vary both spatially and temporally. Previous studies have identified several regions around the globe that produce strong microseism signals. Here a detailed analysis is carried out on a particular <span class="hlt">source</span> area in the Atlantic region off the coast of Ireland. Through the use of multiple small-scale arrays and conventional frequency-wavenumber analysis we show that in this region the ocean generated microseism spectrum consists of multiple coincidentally arriving signals with a non-uniform distribution. This data is then used to create detailed spatial density maps showing the most significant <span class="hlt">source</span> areas in the region.</p> <div class="credits"> <p class="dwt_author">Craig, David; Bean, Chris; Moni, Aishwarya; Lokmer, Ivan; Donne, Sarah</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">387</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/50770654"> <span id="translatedtitle">High-efficiency power oscillator using <span class="hlt">harmonic</span>-tuned matching network</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">This paper presents a high-efficiency power oscillator, which uses LDMOS (Laterally Diffused Metal Oxide Semiconductor) transistor for high output power and a <span class="hlt">harmonic</span>-tuned matching network to obtain high efficiency characteristic for RF power <span class="hlt">source</span> application. A hair-pin resonator was designed and employed into the high efficiency power oscillator in order to improve phase <span class="hlt">noise</span> characteristic and frequency selectivity. Measurement results</p> <div class="credits"> <p class="dwt_author">Woong Jae Hwang; Suk Woo Shin; Gil Wong Choi; Hyoung Jong Kim; Jin Joo Choi</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">388</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010MSSP...24.2096L"> <span id="translatedtitle">Very fast blind <span class="hlt">source</span> separation by signal to <span class="hlt">noise</span> ratio based stopping threshold for the SHIBBS/SJAD algorithm</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">This paper works on joint approximate diagonalization of simplified fourth order cumulant matrices for very fast and large scale blind separation of instantaneous mixing model <span class="hlt">sources</span>. The JADE algorithm is widely accepted but only limited to small scale separation tasks. The SHIBBS algorithm calculates a fraction of the fourth order cumulant set and avoids eigenmatrix decomposition to reduce calculation cost. However, it was seen to be slower than JADE at the time of its first publication and is hence less known. On the other hand, the SJAD algorithm using the same approach is shown to be very fast. This paper studies the iteration convergence criterion and proposes to use a signal to <span class="hlt">noise</span> ratio based iteration stopping threshold approach. The improved SHIBBS/SJAD algorithm is very fast, and capable of large scale separation. Experimental separation comparisons between the SHIBBS/SJAD and FastICA are presented.</p> <div class="credits"> <p class="dwt_author">Liu, Xianhua; Cardoso, Jean-Francois; Randall, Robert B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">389</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.figes.com.tr/urunler/matlab/teknik.makaleler/BORA_ACARKAN_PAPER_MATLAB-CAE_tam_metin.pdf"> <span id="translatedtitle">ELECTRICAL <span class="hlt">HARMONICS</span> MODELING OF OFFICE EQUIPMENTS USING MATLAB AND SIMULINK</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Harmonic</span> current pollution is a one of the major power quality problem in electrical power systems. In office buildings one of the main <span class="hlt">harmonic</span> <span class="hlt">sources</span> is a large numbers of computer loads. Especially, personal computers apply <span class="hlt">harmonic</span> distortions to their power supply systems. In this study, <span class="hlt">harmonics</span> models of equipments, a MATLAB ® code and single-phase Simulink simulation models are</p> <div class="credits"> <p class="dwt_author">Bora ACARKAN; Osman KILIÇ</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">390</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/786174"> <span id="translatedtitle">Measurement and Analysis of Conducted <span class="hlt">Noise</span> at Main Control Room in Uljin NPP</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Electromagnetic measurements were performed at the power ports of the Plant Control System (PCS) and the Core Protection Calculator (CPC) in Uljin to obtain the conducted <span class="hlt">noise</span> level, which can be utilized to determine the electromagnetic environment test limit for the equipment qualification test, for equipment to be installed in the NPP. The measurements indicated that the maximum <span class="hlt">noise</span> of the continuous conducted <span class="hlt">noise</span> at the low-frequency range of from 30 Hz to 50kHz at the PCS was higher than that at the CPC. It was found that the low-frequency conducted <span class="hlt">noise</span> consists of a 60-Hz power <span class="hlt">source</span> frequency and its even and odd <span class="hlt">harmonic</span> frequencies. The odd <span class="hlt">harmonic</span> was more predominant than the even.</p> <div class="credits"> <p class="dwt_author">Goo, Cheol-Soo; Kim, Bok-Ryul; Cho, Won-Seo</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-06-17</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">391</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/2370939"> <span id="translatedtitle">Fast accurate MEG <span class="hlt">source</span> localization using a multilayer perceptron trained with real brain <span class="hlt">noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Iterative gradient methods such as Levenberg–Marquardt (LM) are in widespread use for <span class="hlt">source</span> localization from electroencephalographic (EEG) and magnetoencephalographic (MEG) signals. Unfortunately, LM depends sensitively on the initial guess, necessitating repeated runs. This, combined with LM's high per-step cost, makes its computational burden quite high. To reduce this burden, we trained a multilayer perceptron (MLP) as a real-time localizer. We</p> <div class="credits"> <p class="dwt_author">Sung Chan Jun; Barak A. Pearlmutter; Guido Nolte</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">392</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.vis.uni-stuttgart.de/~kraus/LiveGraphics3D/java_script/SphericalHarmonics.html"> <span id="translatedtitle">Spherical <span class="hlt">Harmonics</span> YLM Explorer</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">This is a Java applet that creates surface plots of the spherical <span class="hlt">harmonics</span>. 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 <span class="hlt">source</span>. Plots may be rotated in three dimensions.</p> <div class="credits"> <p class="dwt_author">Kraus, Martin</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-04-16</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">393</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1981simt.rept.....J"> <span id="translatedtitle">Determination of sound power levels of external <span class="hlt">noise</span> <span class="hlt">sources</span>. Part 1: Measurement methods. Part 2: Some Measurements</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A general frame standard for determining sound power levels of external <span class="hlt">noise</span> <span class="hlt">sources</span> by in situ measurements is proposed. Suitable ISO standards, a long distance method which permits directivity measurement and a short distance method are incorporated. Measurements can be made in front of walls and in corners. The short distance method uses a parallelepipedical measurement surface, omitting the top microphone position. Recommended measurement distance is or = 5 m. The microphone height h = (height of reference box) + d may be exchanged for height 10 m, giving highest sound pressure level whenever h 10 m. For very large <span class="hlt">sources</span>, near field corrections are introduced to cancel the effect to sound energy not passing at right angles to the measurement surface. The long distance method uses a 1/2, 1/4 or 1/8 spherical measurement surface. When directivity measurements are made, the number of microphone positions are doubled relative to those of ISO 3746. The directivity index is then calculated as in ISO 3744. Measurements confirm the validity of the methods.</p> <div class="credits"> <p class="dwt_author">Jonasson, H. G.; Eslon, L.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">394</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013PhDT........45V"> <span id="translatedtitle">Feedback-based mitigation of torque <span class="hlt">harmonics</span> in interior permanent magnet synchronous machines</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Harmonics</span> in the electromagnetic torque are a <span class="hlt">source</span> of concern in permanent magnet synchronous machine (PMSM) drives. The <span class="hlt">harmonics</span> are created by non-idealities in the electromagnetic fields produced by the magnets and the stator excitation. They lead to vibration that can cause premature wear of the drivetrain components as well as acoustic <span class="hlt">noise</span> that may be bothersome to users. In this research, current- and voltage-based control schemes have been developed to mitigate the <span class="hlt">harmonics</span> in a class of PMSMs in which the magnets are placed interior to the rotor iron. Interior permanent magnet synchronous machines (IPMSMs) have recently gained popularity for applications including hybrid electric vehicles and robot joint control. In the current-based control, a low-cost piezoelectric sensor is used to measure torque <span class="hlt">harmonics</span>. A conjugate gradient algorithm is then applied to search for <span class="hlt">harmonics</span> in the stator current that produce a commanded average torque while eliminating the measured torque <span class="hlt">harmonics</span>. The algorithm is based upon analytical closed-form expressions for the average and <span class="hlt">harmonic</span> components of torque that have been derived for IPMSMS with arbitrary back-emf waveforms. In the voltage-based control, a time-domain model of the machine is used to map the outputs of the conjugate gradient algorithm to commanded stator voltages. Since both utilize feedback, the controls are insensitive to changes in machine parameters that result from magnetic saturation, temperature, or parameter drift. In addition, the user has flexibility to select the <span class="hlt">harmonic(s</span>) of torque to be eliminated.</p> <div class="credits"> <p class="dwt_author">Vaks, Nir</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">395</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.teachengineering.org/view_activity.php?url=collection/nyu_/activities/nyu_noise/nyu_noise_activity1.xml"> <span id="translatedtitle">Measuring <span class="hlt">Noise</span> Pollution</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">Through investigating the nature, <span class="hlt">sources</span> and level of <span class="hlt">noise</span> produced in their environment, students are introduced to the concept of <span class="hlt">noise</span> pollution. They learn about the undesirable and disturbing effects of <span class="hlt">noise</span> and the resulting consequences on people's health, as well as on the health of the environment. They use a sound level meter that consists of a sound sensor attached to the LEGO® NXT Intelligent Brick to record the <span class="hlt">noise</span> level emitted by various <span class="hlt">sources</span>. They are introduced to engineering concepts such as sensors, decibel (dB) measurements, and sound pressure used to measure the <span class="hlt">noise</span> level. Students are introduced to impairments resulting from <span class="hlt">noise</span> exposure such as speech interference, hearing loss, sleep disruption and reduced productivity. They identify potential <span class="hlt">noise</span> pollution <span class="hlt">sources</span>, and based on recorded data, they classify these <span class="hlt">sources</span> into levels of annoyance. Students also explore the technologies designed by engineers to protect against the harmful effects of <span class="hlt">noise</span> pollution.</p> <div class="credits"> <p class="dwt_author">Applying Mechatronics to Promote Science (AMPS) GK-12 Program,</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">396</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1985RpEEE.......59P"> <span id="translatedtitle">Magnetic <span class="hlt">noise</span> in single-machine rotating frequency converters</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The magnetic <span class="hlt">noise</span> in rotating frequency converters with two magnetic fields in a common structure of an induction machine, each field having a different number of pole pairs corresponding to the frequency conversion ratio, is evaluated on the basis of <span class="hlt">harmonic</span> analysis of the resultant magnetic induction in the air gap and the radial forces it generates. The rotor in small and medium-size machines is regarded as a solid cylinder so that the hollow stator cylinder remains the principal <span class="hlt">source</span> of <span class="hlt">noise</span>. Constraints on the numbers of stator slots and rotors slots are established so as to ensure minimum higher-frequency tooth <span class="hlt">noise</span> and vibration, while structural requirements are stipulated for minimizing lower-frequency <span class="hlt">noise</span> and vibration and avoiding resonances at any frequency. Typical design calculations for a three-phase motor-generator machine operating at 1:3 frequency converter are shown, including the amplitudes of design-controlled vibrations of magnetic origin.</p> <div class="credits"> <p class="dwt_author">Popov, V. I.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">397</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/1739935"> <span id="translatedtitle">ARTSTREAM: a neural network model of auditory scene analysis and <span class="hlt">source</span> segregation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Multiple sound <span class="hlt">sources</span> often contain <span class="hlt">harmonics</span> that overlap and may be degraded by environmental <span class="hlt">noise</span>. The auditory system is capable of teasing apart these <span class="hlt">sources</span> into distinct mental objects, or streams. Such an ‘auditory scene analysis’ enables the brain to solve the cocktail party problem. A neural network model of auditory scene analysis, called the ARTSTREAM model, is presented to</p> <div class="credits"> <p class="dwt_author">Stephen Grossberg; Krishna K. Govindarajan; Lonce L. Wyse; Michael A. Cohen</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">398</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.compadre.org/Repository/document/ServeFile.cfm?ID=8289&DocID=897"> <span id="translatedtitle"><span class="hlt">Harmonics</span> and Fourier Series Model</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">The Ejs <span class="hlt">Harmonics</span> and Fourier Series model displays the sum of <span class="hlt">harmonics</span> via a Fourier series to yield a new wave. The amplitude of each <span class="hlt">harmonic</span> as well as the phase of that <span class="hlt">harmonic</span> can be changed via sliders. In addition, several pre-set functions can be chosen to display. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. Ejs <span class="hlt">Harmonics</span> and Fourier Series 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_<span class="hlt">harmonics</span>.jar file will run the program if Java is installed. Ejs is a part of the Open <span class="hlt">Source</span> 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 <span class="hlt">Source</span> Physics, OSP, or Ejs.</p> <div class="credits"> <p class="dwt_author">Aguirregabiria, Juan</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-11-11</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">399</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008SSEle..52.1889G"> <span id="translatedtitle">Impact of strain and <span class="hlt">source</span>/drain engineering on the low frequency <span class="hlt">noise</span> behaviour in n-channel tri-gate FinFETs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The impact of strain-engineering on the low frequency of n-channel tri-gate FinFETs fabricated on silicon on insulator (SOI) substrates <span class="hlt">noise</span> is reported. The work is first focused on the study of nFinFETs with a standard structure and with strain-engineered channel structures, using either global or local straining techniques, or a combination of both. A carrier number fluctuation dominant flicker <span class="hlt">noise</span> has been observed for all devices. Whereas no clear correlation between the applied strain techniques and the 1/ f <span class="hlt">noise</span> level has been found, an unusual <span class="hlt">noise</span> spectral density was observed for the devices with selective epitaxial grown (SEG) <span class="hlt">source</span> and drain regions. This unusual <span class="hlt">noise</span> behaviour has been investigated for different fin widths (0.15 ?m up to 3 ?m) and different temperature conditions (150 K up to 300 K). An empirical model is proposed in order to explain this unusual <span class="hlt">noise</span> behaviour. Moreover, two Lorentzians attributed to defects in the depletion region of the silicon fin were observed, and energy level and cross-section of these defects were estimated.</p> <div class="credits"> <p class="dwt_author">Guo, W.; Cretu, B.; Routoure, J.-M.; Carin, R.; Simoen, E.; Mercha, A.; Collaert, N.; Put, S.; Claeys, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">400</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54041836"> <span id="translatedtitle"><span class="hlt">Harmonic</span> and <span class="hlt">noise</span> radiometer-scatterometers</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The power levels required for the transmitters of path scatterometers and scanning scatterometers are computed by optimizing measuring conditions at several wavelengths. The energy losses due to the beam displacement during the scanning within the time of radio-wave propagation are calculated, and methods for minimizing these losses are recommended. Special attention is given to the problem of achieving high-precision measurements</p> <div class="credits"> <p class="dwt_author">Z. I. Gordon</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_19");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">401</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19840023156&hterms=source+level&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dsource%2Blevel"> <span id="translatedtitle">Effect of external pressure environment on the internal <span class="hlt">noise</span> level due to a <span class="hlt">source</span> inside a cylindrical tank</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A small cylindrical tank was used to study the effect on the <span class="hlt">noise</span> environment within a tank of conditions of atmospheric (sea level) pressure or vacuum environments on the exterior. Experimentally determined absorption coefficients were used to calculate transmission loss, transmissibility coefficients and the sound pressure (<span class="hlt">noise</span>) level differences in the interior. The <span class="hlt">noise</span> level differences were also measured directly for the two exterior environments and compared to various analytical approximations with limited agreement. Trend study curves indicated that if the tank transmission loss is above 25 dB, the difference in interior <span class="hlt">noise</span> level between the vacuum and ambient pressure conditions are less than 2 dB.</p> <div class="credits"> <p class="dwt_author">Clevenson, S. A.; Roussos, L. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">402</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2000IAUJD...7E..21M"> <span id="translatedtitle">The Effect of Solar X-Ray Flares on Earth's Ionosphere as Natural <span class="hlt">Source</span> for Electromagnetic <span class="hlt">Noise</span> and Interference</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Solar X-ray flares causing an sudden ionospheric disturbance (SID) affecting on telecommunications and tel-services as natural <span class="hlt">source</span> for electromagentic <span class="hlt">noise</span> and interference. Daily X-ray back ground and Flare measured by artificial satellite GOES. X-ray background from 25 April 1983 to 31 December 1996 and X-ray Flare from 1 January 1981 to 31 December 1996 daily average, and Flare index from 1 January 1986 to 31 October 1996, and Sudden Ionospheric Disturbance data from 1 January 1981 to 31 December 1995, were analyzed by the periodogram technique to estimate the short and long term variabilities . The data are obtained from NOAA, Boulder, Colorado,USA. It is found that there are short periodicities such as 26 day period of rotation of sun, and 13, 8.33, 4.17, 2.5 day and long and term periodicities such as 182, 121, 90.99, 72.3, 61, 52 day . Also, 11 eleven year cycle are clear in the total period. The variability of the solar radiation entering the upper atmosphere of the Earth directly affect the state of the upper atmosphere and ionosphere through the excitation and ionization of atoms and molecules, Ionospheric variability significantly impacts ground and space-based communications. And can attenuate, totally absorb, reflect, change direction of propagation, and change phase and amplitude of radio waves.</p> <div class="credits"> <p class="dwt_author">Mosalam Shaltout, M. A.; Ei-Genedi, S.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">403</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22167147"> <span id="translatedtitle">STELLAR SURFACE MAGNETO-CONVECTION AS A <span class="hlt">SOURCE</span> OF ASTROPHYSICAL <span class="hlt">NOISE</span>. I. MULTI-COMPONENT PARAMETERIZATION OF ABSORPTION LINE PROFILES</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We outline our techniques to characterize photospheric granulation as an astrophysical <span class="hlt">noise</span> <span class="hlt">source</span>. A four-component parameterization of granulation is developed that can be used to reconstruct stellar line asymmetries and radial velocity shifts due to photospheric convective motions. The four components are made up of absorption line profiles calculated for granules, magnetic intergranular lanes, non-magnetic intergranular lanes, and magnetic bright points at disk center. These components are constructed by averaging Fe I 6302 A magnetically sensitive absorption line profiles output from detailed radiative transport calculations of the solar photosphere. Each of the four categories adopted is based on magnetic field and continuum intensity limits determined from examining three-dimensional magnetohydrodynamic simulations with an average magnetic flux of 200 G. Using these four-component line profiles we accurately reconstruct granulation profiles, produced from modeling 12 Multiplication-Sign 12 Mm{sup 2} areas on the solar surface, to within {approx} {+-}20 cm s{sup -1} on a {approx}100 m s{sup -1} granulation signal. We have also successfully reconstructed granulation profiles from a 50 G simulation using the parameterized line profiles from the 200 G average magnetic field simulation. This test demonstrates applicability of the characterization to a range of magnetic stellar activity levels.</p> <div class="credits"> <p class="dwt_author">Cegla, H. M.; Shelyag, S.; Watson, C. A.; Mathioudakis, M., E-mail: hcegla01@qub.ac.uk [Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, University Road, Belfast BT7 1NN (United Kingdom)</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">404</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20140005372&hterms=paper&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dpaper"> <span id="translatedtitle">Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> Generating Typical Turbofan Modes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14- by 22-ft wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft using the projected signature of the engine currently proposed for the HWB. The modal structures at the rating points were generated from inlet and exhaust nacelle configurations--a flat plate model was used as the shielding surface and vertical control surfaces with correct plan form shapes were also tested to determine their additional impact on shielding. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular, and two planes parallel, to the axis of the nacelle were acquired from the array sweep. In each plane the linear array traversed four sweeps, for a total span of 168 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Levels, and integrated Power Levels, from nacelle alone and shielded configurations are presented in this paper; as well as the in-duct mode power levels</p> <div class="credits"> <p class="dwt_author">Sutliff, Daniel l.; Brown, Clifford A.; Walker, Bruce E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">405</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=ADA012090"> <span id="translatedtitle">Aircraft <span class="hlt">Noise</span> Generation, Emission and Reduction.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The physical properties of aircraft <span class="hlt">noise</span> are summarized, with special emphasis on jet <span class="hlt">noise</span> and fan-compressor-propeller-rotor <span class="hlt">noise</span>. Topics include acoustic fundamentals, <span class="hlt">noise</span> <span class="hlt">source</span> characteristics and interactions, atmospheric propagation, airframe n...</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1975-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">406</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27058047"> <span id="translatedtitle">Passive <span class="hlt">Harmonic</span> Filter Planning in a Power System With Considering Probabilistic Constraints</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">This paper presents a new method for planning single-tuned passive <span class="hlt">harmonic</span> filters to control <span class="hlt">harmonic</span> voltage distortion throughout a power system. In the problem, the probabilistic characteristics of the <span class="hlt">harmonic</span> <span class="hlt">source</span> currents and network <span class="hlt">harmonic</span> impedances in the filter planning are taken into account. The objective is to minimize the total filter installation cost, while the <span class="hlt">harmonic</span> voltage limits and</p> <div class="credits"> <p class="dwt_author">Gary W. Chang; Hung-Lu Wang; Gen-Sheng Chuang; Shou-Yung Chu</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">407</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/50113012"> <span id="translatedtitle">An improved on-wafer <span class="hlt">noise</span> measurement technique</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A novel on-wafer resistive <span class="hlt">noise</span> <span class="hlt">source</span> useful for <span class="hlt">noise</span> characterization of microwave devices with the cold <span class="hlt">noise</span> power measurement technique is described. The <span class="hlt">noise</span> <span class="hlt">source</span> enhances measurement accuracy by providing a calibrated <span class="hlt">noise</span> temperature directly at the device reference plane. A procedure for determining the excess <span class="hlt">noise</span> ratio of the <span class="hlt">noise</span> <span class="hlt">source</span> is presented, and the overall technique is validated</p> <div class="credits"> <p class="dwt_author">P. Beland; L. Roy; S. Labonte; M. Stubbs</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">408</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54355006"> <span id="translatedtitle">Commercial road vehicle <span class="hlt">noise</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A survey of the characteristics of the <span class="hlt">noise</span> emitted by commercial vehicles has been made. The most important single parameter determining the <span class="hlt">noise</span> of a modern diesel-engined vehicle is the engine speed. All of the other parameters such as load, road speed, etc., have only a secondary effect. The <span class="hlt">sources</span> of <span class="hlt">noise</span> on the vehicle are reviewed and it is</p> <div class="credits"> <p class="dwt_author">P. E. Waters</p> <p class="dwt_publisher"></p> <p class="publishDate">1974-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">409</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/10641625"> <span id="translatedtitle">Radiated <span class="hlt">noise</span> characteristics of a modern cargo ship</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Extensive measurements were made of the radiated <span class="hlt">noise</span> of M/V OVERSEAS HARRIETTE, a bulk cargo ship (length 173 m, displacement 25 515 tons) powered by a direct-drive low-speed diesel engine-a design representative of many modern merchant ships. The radiated <span class="hlt">noise</span> data show high-level tonal frequencies from the ship's service diesel generator, main engine firing rate, and blade rate <span class="hlt">harmonics</span> due to propeller cavitation. Radiated <span class="hlt">noise</span> directionality measurements indicate that the radiation is generally dipole in form at lower frequencies, as expected. There are some departures from this pattern that may indicate hull interactions. Blade rate <span class="hlt">source</span> level (174 dB re 1 microPa/m at 9 Hz, 16 knots) agrees reasonably well with a model of fundamental blade rate radiation previously reported by Gray and Greeley, but agreement for blade rate <span class="hlt">harmonics</span> is not as good. <span class="hlt">Noise</span> from merchant ships elevates the natural ambient by 20-30 dB in many areas; the effects of this <span class="hlt">noise</span> on the biological environment have not been widely investigated. PMID:10641625</p> <div class="credits"> <p class="dwt_author">Arveson; Vendittis</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">410</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/174678"> <span id="translatedtitle">Inductively coupled plasma spectrometry: <span class="hlt">Noise</span> characteristics of aerosols, application of generalized standard additions method, and Mach disk as an emission <span class="hlt">source</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This dissertation is focused on three problem areas in the performance of inductively coupled plasma (ICP) <span class="hlt">source</span>. The <span class="hlt">noise</span> characteristics of aerosols produced by ICP nebulizers are investigated. A laser beam is scattered by aerosol and detected by a photomultiplier tube and the <span class="hlt">noise</span> amplitude spectrum of the scattered radiation is measured by a spectrum analyzer. Discrete frequency <span class="hlt">noise</span> in the aerosol generated by a Meinhard nebulizer or a direct injection nebulizer is primarily caused by pulsation in the liquid flow from the pump. A Scott-type spray chamber suppresses white <span class="hlt">noise</span>, while a conical, straight-pass spray chamber enhances white <span class="hlt">noise</span>, relative to the <span class="hlt">noise</span> seen from the primary aerosol. Simultaneous correction for both spectral interferences and matrix effects in ICP atomic emission spectrometry (AES) can be accomplished by using the generalized standard additions method (GSAM). Results obtained with the application of the GSAM to the Perkin-Elmer Optima 3000 ICP atomic emission spectrometer are presented. The echelle-based polychromator with segmented-array charge-coupled device detectors enables the direct, visual examination of the overlapping lines Cd (1) 228.802 nm and As (1) 228.812 nm. The slit translation capability allows a large number of data points to be sampled, therefore, the advantage of <span class="hlt">noise</span> averaging is gained. An ICP is extracted into a small quartz vacuum chamber through a sampling orifice in a water-cooled copper plate. Optical emission from the Mach disk region is measured with a new type of echelle spectrometer equipped with two segmented-array charge-coupled-device detectors, with an effort to improve the detection limits for simultaneous multielement analysis by ICP-AES.</p> <div class="credits"> <p class="dwt_author">Shen, Luan</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-10-06</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">411</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/20366281"> <span id="translatedtitle">Ultrafast demagnetization dynamics at the M edges of magnetic elements observed using a tabletop high-<span class="hlt">harmonic</span> soft x-ray <span class="hlt">source</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">We use few-femtosecond soft x-ray pulses from high-<span class="hlt">harmonic</span> generation to extract element-specific demagnetization dynamics and hysteresis loops of a compound material for the first time. Using a geometry where high-<span class="hlt">harmonic</span> beams are reflected from a magnetized Permalloy grating, large changes in the reflected intensity of up to 6% at the M absorption edges of Fe and Ni are observed when the magnetization is reversed. A short pump pulse is used to destroy the magnetic alignment, which allows us to measure the fastest, elementally specific demagnetization dynamics, with 55 fs time resolution. The use of high <span class="hlt">harmonics</span> for probing magnetic materials promises to combine nanometer spatial resolution, elemental specificity, and femtosecond-to-attosecond time resolution, making it possible to address important fundamental questions in magnetism. PMID:20366281</p> <div class="credits"> <p class="dwt_author">La-O-Vorakiat, Chan; Siemens, Mark; Murnane, Margaret M; Kapteyn, Henry C; Mathias, Stefan; Aeschlimann, Martin; Grychtol, Patrik; Adam, Roman; Schneider, Claus M; Shaw, Justin M; Nembach, Hans; Silva, T J</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-18</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">412</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27092180"> <span id="translatedtitle">New marine <span class="hlt">harmonic</span> standards</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">To address concerns associated with electrical power system <span class="hlt">harmonic</span> distortion on ships and offshore oil rigs and platforms, marine regulating bodies have introduced strict new <span class="hlt">harmonic</span> standards. These standards define the acceptable level of <span class="hlt">harmonic</span> voltage distortion allowed on the vessels they certify. High-<span class="hlt">harmonic</span> distortion levels are appearing as a result of the increased use of power-electronic drive converters for</p> <div class="credits"> <p class="dwt_author">Tony Hoevenaars; Ian Evans; Andy Lawson</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div>