These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Harmonic sources and filtering approaches  

Microsoft Academic Search

This article presents 22 configurations of power filters for the harmonic compensation of nonlinear loads. Some of these configurations are novel and result from the newly discovered characteristics of nonlinear loads and circuitry duality, while the others are well known and used in practice. Nonlinear loads can be characterized into two types of harmonic sources: current-source nonlinear loads and voltage-source

F. Z. Peng

2001-01-01

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

Ratchets Driven by Harmonic and White Noise R. Bartussek, P. Hanggi, a  

E-print Network

of a Langevin equation with two additive noise sources, i.e., â?? x = \\Gamma @V (x) @x + ffl(t) + p 2D ¸ 1 (t): (1 properties of this two­dimensional Gauss­Markov process. 2 Harmonic Noise 2.1 Definition and PropertiesRatchets Driven by Harmonic and White Noise R. Bartussek, P. H¨anggi, a B. Lindner, and L

Lindner, Benjamin

4

Harmonic Noise-Induced Resonant Passing in an Inverse Harmonic Potential  

NASA Astrophysics Data System (ADS)

The problem of a Brownian particle driven by harmonic noise passing over the saddle point in an inverse harmonic potential is studied. The passing probability over the saddle point is obtained analytically. The stationary passing probability is found to arrive at its maximal value when the frequency parameter of the harmonic noise is close to the frequency of the inverse harmonic potential, which results in a resonance phenomenon. With an increase in the frequency parameter of noise, the Brownian particle will recross the barrier, thereby increasing the escape rate and resulting in a decrease in the passing probability.

Han, Jie; Bao, Jing-Dong

2014-12-01

5

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

6

High speed helicopter noise sources  

NASA Technical Reports Server (NTRS)

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

Lee, A.

1977-01-01

7

Nonstationary noise propagation with sources  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

8

Excess noise in fiber gyroscope sources  

Microsoft Academic Search

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

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

1990-01-01

9

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

10

Harmonic potential driven by long-range correlated noise  

NASA Astrophysics Data System (ADS)

The probability distribution of a particle in a quadratic potential driven by Gaussian long-range correlated noise has been obtained. The long-time asymptotic relaxation of the stochastic process has been characterized in terms of the long-range correlated noise appearing in the corresponding stochastic differential equation defining the process. The particular case when the particle is driven by a Gaussian color noise has also been revisited, in this way giving its exact probability distribution for all time. By using a characteristic functional technique reported previously, results for a non-Gaussian long-range correlated noise are also shown. Emphasis has been placed on solving the plane rotator in the presence of arbitrary random torques having long-range correlations. In order to show strong and weak non-Markovian effects coming from different sources of noise, the undamped free particle under the influence of arbitrary accelerations has been analyzed. We also analyze in detail the structure of the trajectories of the overdamped and undamped free particle.

Cáceres, Manuel O.

1999-11-01

11

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

12

Programmable, very low noise current source.  

PubMed

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

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

2014-12-01

13

Programmable, very low noise current source  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

14

Noise Reduction Process with Generalized Harmonics Analysis for High-Temperature Superconducting Quantum Interference Device Magnetocardiography  

NASA Astrophysics Data System (ADS)

Generalized harmonic analysis was applied to a high-temperature superconducting quantum interference device (SQUID) magnetocardiograph signal processing system. The noise frequencies in the signal waveform were calculated by the generalized harmonic analysis (GHA) and the noise components with these frequencies were subtracted from the acquired signal data. Two types of the subtraction procedure were demonstrated: one using the adaptive filtering algorithm and the other a simple subtraction. In both cases, the noise components were reduced. The former system performed rapid calculations but generated an artificial noise in the high-frequency region, because of rough GHA estimation, while in the latter case, the calculation was time-consuming but the noise estimation was carried out accurately, because of the precision of GHA procedure. In the present study, a distinctive noise component at 16 Hz was completely suppressed by the GHA prediction noise reduction process. The proposed systems were well suited for application to an unshielded high-temperature SQUID system.

Sakuta, Ken; Ogawa, Kaname; Tamai, Hideaki; Mizukami, Akifumi; Kobayashi, Takeshi

2002-10-01

15

A high-harmonic generation source for seeding a free-electron laser at 38 nm  

NASA Astrophysics Data System (ADS)

Direct seeding with a high-harmonic generation (HHG) source can improve the spectral, temporal, and coherence properties of a free-electron laser (FEL) and shall reduce intensity and arrival-time fluctuations. In the seeding experiment sFLASH at the extreme ultraviolet FEL in Hamburg FLASH, which operates in the self-amplified spontaneous emission mode (SASE), the 21st harmonic of an 800 nm laser is refocused into a dedicated seeding undulator. For seeding, the external light field has to overcome the noise level of SASE; therefore, an efficient coupling between seed pulse and electron bunch is mandatory. Thus, an HHG beam with a proper divergence, width, beam quality, Rayleigh length, pointing stability, single-shot pulse energy, and stability in the 21st harmonic is needed. Here, we present the setup of the HHG source that seeds sFLASH at 38.1 nm, the optimization procedures, and the necessary diagnostics.

Maltezopoulos, Theophilos; Mittenzwey, Manuel; Azima, Armin; Bödewadt, Jörn; Dachraoui, Hatem; Rehders, Marie; Lechner, Christoph; Schulz, Michael; Wieland, Marek; Laarmann, Tim; Roßbach, Jörg; Drescher, Markus

2014-04-01

16

Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise  

Microsoft Academic Search

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

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

2002-01-01

17

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

18

The Grey Support Vector Regression method in noise source identification  

Microsoft Academic Search

Noise source identification is essential for making noise reduction strategies. This paper presents an approach to acoustic noise identification by introducing modern spectrum estimation, Grey Support Vector Regression (GSVR). Modern spectrum was used to recognize the main noise source and GSVR was used to do curve fitting to recognize the similarity among different curves of power spectrum which made the

Yang Yang; Xiuqin Wang; Di Zhang

2011-01-01

19

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

E-print Network

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

Greenberg, Albert

20

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

E-print Network

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

Greenberg, Albert

21

Parametric model for vocal effort interpolation with Harmonics Plus Noise `Angel Calzada Defez1  

E-print Network

Parametric model for vocal effort interpolation with Harmonics Plus Noise Models `Angel Calzada present a methodology for modi- fying vocal effort level, which can be applied by text-to-speech (TTS by the amount of vocal effort levels available in the corpora. The proposed methodology overcomes

Edinburgh, University of

22

Effects of Gaussian colored noise on time evolution of information entropy in a damped harmonic oscillator  

NASA Astrophysics Data System (ADS)

The effects of Gaussian colored noise on time evolution of information entropy in a damped harmonic oscillator are studied in this paper. The one-dimensional non-Markovian process with Gaussian colored noise is stochastically equivalent to two-dimensional Markovian process and the dimension of Fokker-Planck equation is reduced by the linear transformation. The exact expression of the time dependence of information entropy is derived on the basis of Fokker-Planck equation and the definition of Shannon's information entropy. The relationship between the properties of damping constant, the frequency of the oscillator and Gaussian colored noise and their effect on time evolution of information entropy is also discussed.

Guo, Yong-Feng; Tan, Jian-Guo

2015-02-01

23

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

24

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

NASA Technical Reports Server (NTRS)

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

Hanson, D. B.

1975-01-01

25

Frequency-dependent noise sources in the North Atlantic Ocean  

E-print Network

microseisms are the most energetic waves in the noise spectra between 3 and 10 s. They are generated by ocean in the North Atlantic Ocean by coupling noise polarization analysis and source mapping using an ocean wave in the Arctic and around the ocean. To model the noise sources we adjust empirically the ocean wave coastal

Stutzmann, Eléonore

26

Modeling helicopter near-horizon harmonic noise due to transient maneuvers  

NASA Astrophysics Data System (ADS)

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

Sickenberger, Richard D.

27

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

28

Sediment processes can be significant source of ambient noise  

NASA Astrophysics Data System (ADS)

Many studies of ambient ocean noise have focused on anthropogenic, biological, and weather-related sources, but collisions of sediment grains can also generate a significant amount of background noise.

Balcerak, Ernie

2013-06-01

29

Teaching Doppler Effect with a passing noise source  

NASA Astrophysics Data System (ADS)

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

Costa, Ivan F.; Mocellin, Alexandra

2010-07-01

30

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

31

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

SciTech Connect

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

Yang Shiquan; Bao Xiaoyi [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, K1N 6N5 (Canada)

2006-09-15

32

Single source noise reduction of received HF audio: experimental study  

NASA Astrophysics Data System (ADS)

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

Campbell, Eric C.; Alva, Carlos O.

2014-05-01

33

Phase noise and timing jitter in oscillators with colored-noise sources  

Microsoft Academic Search

Phase noise or timing jitter in oscillators is of major concern in wireless and optical communications, being a major contributor to the bit-error rate of communication systems, and creating synchronization problems in other clocked and sampled-data systems. This paper presents the theory and practical characterization of phase noise in oscillators due to colored, as opposed to white, noise sources. Shot

Alper Demir

2002-01-01

34

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

Microsoft Academic Search

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

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

2004-01-01

35

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

36

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

37

Low frequency noise sources and mechanisms in semiconductor nanowire transistors  

NASA Astrophysics Data System (ADS)

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

Delker, Collin James

38

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

39

Predicting voltage distortion in a system with multiple random harmonic sources  

SciTech Connect

A method for statistically describing system harmonic voltages in terms of the parameters of the harmonic current sources is presented. It is shown that for a large enough number of sources, a complete probabilistic characterization of the harmonic voltages can be found in terms of the second order moments of each current phasor's rectangular components. The method is tested on an existing distribution system by using both simulation and field measurements.

Kaprielian, S.R. (Lafayette Coll., Easton, PA (United States)); Emanuel, A.E. (Worcester Polytechnic Inst., MA (United States)); Dwyer, R.V. (Electrotek Concepts, Inc., Knoxville, TN (United States)); Mehta, H. (EPRI, Palo Alto, CA (United States))

1994-07-01

40

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

41

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

42

Reduction of brain noise influence in evoked neuromagnetic source localization using noise spatial correlation.  

PubMed

In magnetoencephalographic measurements, magnetic fields caused by spontaneous brain activities not related to the neural activities under study are often referred to as brain noise. This is because the accuracy in neural source localization is considerably degraded by such spontaneous neuromagnetic fields. This paper reports the experimental results of applying the previously proposed noise covariance method to reducing the degradation caused by brain noise and to improving the accuracy in localizing auditory-evoked neural sources. Firstly we present the results of our experiments using measured brain noise and computer-generated signal fields. These results confirm that the covariance method can, in principle, improve the accuracy of evoked neural source localization. Next, the method was applied to source localization for actual neuromagnetic fields evoked by speech sounds. The results obtained strongly suggest that the method is effective in processing actual evoked neuromagnetic data. PMID:15551571

Sekihara, K; Takeuchi, F; Kuriki, S; Koizumi, H

1994-06-01

43

Application of noise source identification techniques to information technology equipment  

NASA Astrophysics Data System (ADS)

Conventional noise source identification techniques are usually associated with larger mechanical sources such as engines, gearboxes, and the like, having medium to high noise emissions. The IT industry presents a different problem-set, though, in that the noise sources are usually smaller and are relatively low level. However, this does not prevent use of these techniques, in that they can be adapted to measurements on typical IT products. Tools for doing this include the use of non-contacting transducers such as laser vibrometers as references, making array measurements with a small-geometry transducer such as a probe microphone, and using conventional microphone arrays but with reduced grid spacing. This paper examines the application of these tools to noise source identification techniques such as coherent power, intensity mapping, and stationary and non-stationary near-field acoustical holography, such that they can be used on IT equipment. The different methods are illustrated with noise source identification exercises on a laptop PC and a 3 1/2-in. hard-disk-drive. Finally, the paper discusses the application of beam-forming techniques for noise source identification on IT products in general.

Upton, Roger; Dirks, Gijs

2005-09-01

44

Large bandwidth op-amp based white noise current source  

NASA Astrophysics Data System (ADS)

Electrical noise sources are basic building blocks in many measurement and instrumentation applications and in communication systems. In this paper, we propose a quite simple topology for the realization of a programmable, wide bandwidth, white noise current source that requires only two resistors and one operational amplifier. We validate the proposed approach by means of SPICE simulations and demonstrate, by means of proper measurements, the capability of generating a flat current noise spectrum in a frequency range up to four decades from a few Hz up to 100 kHz.

Giusi, Gino; Scandurra, Graziella; Ciofi, Carmine

2014-02-01

45

Noise source emissions, Davis Canyon site, Utah  

SciTech Connect

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

Not Available

1987-07-01

46

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

47

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

48

MEG Source Localization Using Invariance of Noise Space  

PubMed Central

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

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

2013-01-01

49

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

NASA Technical Reports Server (NTRS)

An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.

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

1996-01-01

50

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

NASA Technical Reports Server (NTRS)

An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.

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

1994-01-01

51

Harmonic source wavefront aberration correction for ultrasound imaging  

PubMed Central

A method is proposed which uses a lower-frequency transmit to create a known harmonic acoustical source in tissue suitable for wavefront correction without a priori assumptions of the target or requiring a transponder. The measurement and imaging steps of this method were implemented on the Duke phased array system with a two-dimensional (2-D) array. The method was tested with multiple electronic aberrators [0.39? to 1.16? radians root-mean-square (rms) at 4.17 MHz] and with a physical aberrator 0.17? radians rms at 4.17 MHz) in a variety of imaging situations. Corrections were quantified in terms of peak beam amplitude compared to the unaberrated case, with restoration between 0.6 and 36.6 dB of peak amplitude with a single correction. Standard phantom images before and after correction were obtained and showed both visible improvement and 14 dB contrast improvement after correction. This method, when combined with previous phase correction methods, may be an important step that leads to improved clinical images. PMID:21303031

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

2011-01-01

52

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

53

Heat conduction in disordered harmonic lattices with energy-conserving noise.  

PubMed

We study heat conduction in a harmonic crystal whose bulk dynamics is supplemented by random reversals (flips) of the velocity of each particle at a rate ?. The system is maintained in a nonequilibrium stationary state (NESS) by contacts with white-noise Langevin reservoirs at different temperatures. We show that the one-body and pair correlations in this system are the same (after an appropriate mapping of parameters) as those obtained for a model with self-consistent reservoirs. This is true both for the case of equal and random (quenched) masses. While the heat conductivity in the NESS of the ordered system is known explicitly, much less is known about the random mass case. Here we investigate the random system with velocity flips. We improve the bounds on the Green-Kubo conductivity obtained by Bernardin [J. Stat. Phys. 133, 417 (2008)]. The conductivity of the one-dimensional system is then studied both numerically and analytically. This sheds some light on the effect of noise on the transport properties of systems with localized states caused by quenched disorder. PMID:21405819

Dhar, Abhishek; Venkateshan, K; Lebowitz, J L

2011-02-01

54

Heat conduction in disordered harmonic lattices with energy-conserving noise  

NASA Astrophysics Data System (ADS)

We study heat conduction in a harmonic crystal whose bulk dynamics is supplemented by random reversals (flips) of the velocity of each particle at a rate ?. The system is maintained in a nonequilibrium stationary state (NESS) by contacts with white-noise Langevin reservoirs at different temperatures. We show that the one-body and pair correlations in this system are the same (after an appropriate mapping of parameters) as those obtained for a model with self-consistent reservoirs. This is true both for the case of equal and random (quenched) masses. While the heat conductivity in the NESS of the ordered system is known explicitly, much less is known about the random mass case. Here we investigate the random system with velocity flips. We improve the bounds on the Green-Kubo conductivity obtained by Bernardin [J. Stat. Phys.JSTPBS0022-471510.1007/s10955-008-9620-1 133, 417 (2008)]. The conductivity of the one-dimensional system is then studied both numerically and analytically. This sheds some light on the effect of noise on the transport properties of systems with localized states caused by quenched disorder.

Dhar, Abhishek; Venkateshan, K.; Lebowitz, J. L.

2011-02-01

55

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

56

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

57

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

58

Harmonic sources and filtering approaches-series\\/parallel, active\\/passive, and their combined power filters  

Microsoft Academic Search

This paper presents 22 configurations of power filters for the harmonic compensation of nonlinear loads. Some of these configurations are novel and result from the newly discovered characteristics of nonlinear loads and circuitry duality, while the others are well known and used in practice. Nonlinear loads are characterized into two types of harmonic sources-current-source nonlinear loads and voltage-source nonlinear loads.

Fang Z. Peng; Donald J. Adams

1999-01-01

59

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

60

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

NASA Technical Reports Server (NTRS)

An algorithm was developed to simulate the expected signal to noise ratios as a function of observation time in the charge coupled device detector plane of an optical telescope located outside the Earth's atmosphere for a signal star, and an optional secondary star, embedded in a uniform cosmic background. By choosing the appropriate input values, the expected point source signal to noise ratio can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument.

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

1984-01-01

61

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

62

Electropneumatic Transducers as Secondary Actuators for Active Noise Control Part Iii: Experimental Control in Ducts with the Subsonic Source  

NASA Astrophysics Data System (ADS)

The possibility of performing active control of periodic noise propagating in ducts using a subsonic electropneumatic acoustic generator as secondary source is investigated. The subsonic generator has been studied both theoretically and experimentally in two companion papers, and this sound source was shown to be highly efficient, but non-linear. The non-linear behaviour of the source decreases as the acoustic pressure at its output is reduced, however, as in the case when the source is used as a secondary actuator in an efficient active control system and thus the source is well suited to such applications. Residual non-linearities of the subsonic source are shown to be due to the mechanical design of the actuator. An harmonic controller is discussed which accounts for the residual non-linear behaviour of the subsonic source. Experiments carried out with a manual version of this controller, that controls the first five harmonic components of the signal driving the subsonic source, reveal that it is efficient in controlling periodic primary sound fields. The implementation of a fully coupled harmonic controller is, however, shown to require large processing capacities. A theoretical analysis of a simplified version of the harmonic controller-the decentralized harmonic controller-is carried out, and simple conditions are established under which the decentralized controller offers similar performances to the fully coupled harmonic controller. These conditions are shown to be satisfied when using the subsonic source as a secondary actuator. The non-linear behaviour of the subsonic source can also cause a further problem, since the error surface experienced by the control system may exhibit local minima. It was found that the likelihood of this happening was much reduced is only the fundamental component of the harmonic controller was adapted initially, and then the other harmonics were changed in a second phase of adaptation. The implementation of a decentralized harmonic controller is considered, using a dual channel signal processing board. A purely linear model for the plant under control is shown to be accurate enough for modelling the system under control and to ensure convergence of the controller. Experiments with the automatic controller reveal that attenuations measured at the monitor microphone are around 25 dB, for sinusoidal primary sound fields.

Blondel, L. A.; Elliott, S. J.

1999-01-01

63

Electropneumatic Transducers as Secondary Actuators for Active Noise Control Part Iii: Experimental Control in Ducts with the Subsonic Source  

NASA Astrophysics Data System (ADS)

The possibility of performing active control of periodic noise propagating in ducts using a subsonic electropneumatic acoustic generator as secondary source is investigated. The subsonic generator has been studied both theoretically and experimentally in two companion papers, and this sound source was shown to be highly efficient, but non-linear. The non-linear behaviour of the source decreases as the acoustic pressure at its output is reduced, however, as in the case when the source is used as a secondary actuator in an efficient active control system and thus the source is well suited to such applications. Residual non-linearities of the subsonic source are shown to be due to the mechanical design of the actuator. An harmonic controller is discussed which accounts for the residual non-linear behaviour of the subsonic source. Experiments carried out with a manual version of this controller, that controls the first five harmonic components of the signal driving the subsonic source, reveal that it is efficient in controlling periodic primary sound fields. The implementation of a fully coupled harmonic controller is, however, shown to require large processing capacities. A theoretical analysis of a simplified version of the harmonic controller—the decentralized harmonic controller—is carried out, and simple conditions are established under which the decentralized controller offers similar performances to the fully coupled harmonic controller. These conditions are shown to be satisfied when using the subsonic source as a secondary actuator. The non-linear behaviour of the subsonic source can also cause a further problem, since the error surface experienced by the control system may exhibit local minima. It was found that the likelihood of this happening was much reduced is only the fundamental component of the harmonic controller was adapted initially, and then the other harmonics were changed in a second phase of adaptation. The implementation of a decentralized harmonic controller is considered, using a dual channel signal processing board. A purely linear model for the plant under control is shown to be accurate enough for modelling the system under control and to ensure convergence of the controller. Experiments with the automatic controller reveal that attenuations measured at the monitor microphone are around 25 dB, for sinusoidal primary sound fields.

Blondel, L. A.; Elliott, S. J.

1999-01-01

64

Theory of harmonic radiation using a single-electron source model  

SciTech Connect

Significant progress has recently been made toward the understanding of the various mechanisms that generate harmonic radiation in plane-polarized free electron lasers. Within the context of a single-frequency coherent-spontaneous emission model, a distributed transverse source function for a single electron has been derived. This source is multiply peaked, with the number of peaks being equal to the harmonic number. The peaks and nulls in the radiation source are analogous to the radiation peaks seen in the spontaneous radiation pattern of a single electron. When the distributed source function is averaged over transverse space, the simplified one-dimensional results are recovered. The distributed source function model predicts the generation of even harmonic radiation with odd-symmetry in the electron wiggle plane (for electrons traveling along the wiggler axis) and odd harmonic radiation patterns with even transverse symmetry. A method for modeling the multi-pole nature of the harmonic radiation on a discrete grid is described. When the transverse electron beam distribution is slowly varying, all the harmonics can be adequately modeled with multi-poles having only a few peaks. This model has been incorporated into the 3-D FEL simulation code FELEX. Simulations of the Los Alamos and Stanford FEL oscillators have been performed. How the harmonic transverse spatial electric field profiles change for different operating conditions is examined. 11 refs., 5 figs.

Schmitt, M.J.; Elliott, C.J.

1989-01-01

65

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

66

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

67

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

NASA Astrophysics Data System (ADS)

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.

Scandurra, Graziella; Giusi, Gino; Ciofi, Carmine

2014-04-01

68

Investigation of jet-installation noise sources under static conditions  

NASA Technical Reports Server (NTRS)

The acoustical effects of operating a 6-cm exit-diameter nozzle in the presence of a wing-flap model under static conditions are examined experimentally. The geometric parameters of the wing-flap model are chosen to represent a realistic jet-engine installation on a wide-body midrange transport airplane. The effects of varying the installation parameters and the noise sources associated with the engine-installation effects are discussed. The major noise sources are the flow interaction of the jet and wing undersurface, the flow interaction of the jet with the side edges of the flap cutout and flap trailing edge, and the reflection of the jet noise off the undersurface of the wing and flap.

Shearin, J. G.

1983-01-01

69

A battery-based, low-noise voltage source  

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

70

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

71

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

72

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

73

Ultralow phase noise MMIC-based 89GHz source module  

Microsoft Academic Search

An ultra low phase noise 89-GHz frequency source module based on MMIC technology is developed. This source module consists of a 5.5625-GHz fundamental-mode dielectric resonator oscillator and a diode doubler using GaAs-based HBT MMIC technology, a 11--to-22 GHz doubler, a 22-to-88 GHz quadrupler, and W-based output amplifiers fabricated using GaAs HEMT MMIC technology. The module is packaged in a miniature

Kwo W. Chang; Huei Wang; David P. Smith; A. Oki; Mike Biedenbender; G. Samuel Dow; Barry R. Allen

1996-01-01

74

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

75

Orthogonal bipolar spherical harmonics measures: Scrutinizing sources of isotropy violation  

NASA Astrophysics Data System (ADS)

The two-point correlation function of the cosmic microwave background temperature anisotropies is generally assumed to be statistically isotropic (SI). Deviations from this assumption could be traced to physical or observational artifacts and systematic effects. Measurement of nonvanishing power in the bipolar spherical harmonic spectra is a standard statistical technique to search for isotropy violations. Although this is a neat tool allowing a blind search for SI violations in the cosmic microwave background sky, it is not easy to discern the cause of isotropy violation by using this measure. In this article, we propose a novel technique of constructing orthogonal bipolar spherical harmonic estimators, which can be used to discern between models of isotropy violation.

Kumar, Saurabh; Rotti, Aditya; Aich, Moumita; Pant, Nidhi; Mitra, Sanjit; Souradeep, Tarun

2015-02-01

76

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

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

77

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. PMID:22412363

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

2012-01-01

78

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

79

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

NASA Astrophysics Data System (ADS)

In this paper, we study noise-like pulse generation in a km-long fibre ring laser including a double-clad erbium–ytterbium fibre and passively mode-locked through nonlinear polarization evolution. Although single noise-like pulsing is only observed at moderate pump power, pulse energies as high as 120?nJ are reached in this regime. For higher pump power, the pulse splits into several noise-like pulses, which then rearrange into a stable and periodic pulse train. Harmonic mode locking from the 2nd to the 48th orders is readily obtained. At pump powers close to the damage threshold of the setup, much denser noise-like pulse trains are demonstrated, reaching harmonic orders beyond 1200 and repetition frequencies in excess of a quarter of a GHz. The mechanisms leading to noise-like pulse breaking and stable high-order harmonic mode locking are discussed.

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

2014-11-01

80

Geopotential Reconstruction, Decomposition, Fast Computation, and Noise Cancellation by Harmonic Wavelets  

Microsoft Academic Search

Harmonic wavelets are introduced within the framework of the Sobolev-like Hilbert space H of potentials with “square-integrable restrictions” to the Earth's (mean) sphere OR. Basic tool is the construction of H-product kernels in terms of an (outer harmonics) orthonormal basis in H. Scaling function and wavelet are defined by means of so-called H-product kernels. Harmonic wavelets are shown to be

Willi Freeden; Erwin Groten; Volker Michel; Kourosh Arfa-Kaboodvand

2003-01-01

81

Jet noise source modification due to forward flight  

NASA Technical Reports Server (NTRS)

The effects of forward flight on the turbulence characteristics of a jet in a co-flowing stream have been determined for a 2.22 inch circular jet in a 36 inch free jet wind tunnel. The nozzle exit velocity was 400 ft/sec, and the tunnel velocity was set at 0, 40, 120 and 200 ft/sec. Measurements of flow properties including mean velocity, turbulence intensity and spectra, convection velocity, integral length scale, and convected integral time scale were carried out using two linearized hot wires. Results were used to predict changes due to flight in the jet acoustic sources. The noise reductions for a cold jet with a velocity of 1000 ft/sec, due to the change in acoustic sources in flight, agreed well at all angles with measured noise reductions.

Larson, R. S.; Mccolgan, C. J.; Packman, A. B.

1977-01-01

82

Noise squeezing and commutation relations in quantum-non-demolition quasistroboscopic schemes for coupled harmonic oscillators  

Microsoft Academic Search

Quantum-non-demolition measurement strategies have been studied for two coupled harmonic oscillators. An estimate for the squeezing factor in a quasistroboscopic measurement scheme has been obtained starting from the Heisenberg uncertainty principle and the commutation relation.

Alessandro Rioli; Ubaldo Tambini

1994-01-01

83

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

SciTech Connect

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

Filho, Faete [ORNL; Maia, Helder Z [UFMS, Department of Electrical Engineering; Mateus, Tiago Henrique D [ORNL; Ozpineci, Burak [ORNL; Tolbert, Leon M [ORNL; Pinto, Joao Onofre P [ORNL

2013-01-01

84

Stochastic dynamic clamping as a method for studying the effects of biological noise sources  

Microsoft Academic Search

A crucial issue in the study of the nervous system is the determination of how biophysical noise from probabilistic voltage-dependent and synaptic processes acts to limit neuronal reliability. Experimental and computational work provides indirect evidence that synaptic noise is the major noise source in many cases, but that intrinsic noise from voltage-gated channels makes important contributions in some cells. Rigorous

John A. White; Julie S. Haas; A. D. Dorval

1999-01-01

85

Source levels and harmonic content of whistles in white-beaked dolphins (Lagenorhynchus albirostris)  

E-print Network

Source levels and harmonic content of whistles in white-beaked dolphins (Lagenorhynchus albirostris 2006 Recordings of white-beaked dolphin whistles were made in Faxaflói Bay Iceland using a three than 5000 whistles were recorded. All recordings were made in sea states 0­1 Beaufort scale . Dolphins

86

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

87

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

88

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

89

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

90

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

91

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

PubMed

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

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

2015-01-01

92

Fan Noise Source Diagnostic Test: LDV Measured Flow Field Results  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

93

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

94

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

NASA Technical Reports Server (NTRS)

The optimal design was investigated of simple structures subjected to dynamic loads, with constraints on the structures' responses. Optimal designs were examined for one dimensional structures excited by harmonically oscillating loads, similar structures excited by white noise, and a wing in the presence of continuous atmospheric turbulence. The first has constraints on the maximum allowable stress while the last two place bounds on the probability of failure of the structure. Approximations were made to replace the time parameter with a frequency parameter. For the first problem, this involved the steady state response, and in the remaining cases, power spectral techniques were employed to find the root mean square values of the responses. Optimal solutions were found by using computer algorithms which combined finite elements methods with optimization techniques based on mathematical programming. It was found that the inertial loads for these dynamic problems result in optimal structures that are radically different from those obtained for structures loaded statically by forces of comparable magnitude.

Johnson, E. H.

1975-01-01

95

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

96

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

97

A temporal and spatial analysis of anthropogenic noise sources affecting SNMR  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

98

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

99

Simplified Three-Phase 18-Step Voltage-Source Inverter by Injecting Harmonics  

NASA Astrophysics Data System (ADS)

A new method for reducing harmonics in the output voltage of a three-phase voltage source inverter is proposed. This method is applied to a conventional six-step inverter with a three-phase output transformer. In the proposed inverter, two capacitors are used as dc source; further, four auxiliary switching devices and a single-phase transformer are included in the inverter, and harmonics are injected to the neutral point of the three-phase transformer. As a result, the output voltage of the proposed inverter becomes almost equal to that of a conventional 18-step inverter, which has 18 switching devices and three three-phase output transformers. In this paper, the circuit performances and output voltage waveforms are discussed, and the optimum parameters are determined by taking into account the effect of harmonics reduction. Then, the characteristics of an inverter system connected to a grid are experimentally investigated. Furthermore, the ratings of several components are clarified by the theoretical results.

Masukawa, Shigeo

100

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

SciTech Connect

The /sup 252/Cf-source-driven neutron noise analysis method has been tested in a wide variety of experiments that have indicated the broad range of applicability of the method. The neutron multiplication factor k/sub eff/ has been satisfactorily detemined for a variety of materials including uranium metal, light water reactor fuel pins, fissile solutions, fuel plates in water, and interacting cylinders. For a uranyl nitrate solution tank which is typical of a fuel processing or reprocessing plant, the k/sub eff/ values were satisfactorily determined for values between 0.92 and 0.5 using a simple point kinetics interpretation of the experimental data. The short measurement times, in several cases as low as 1 min, have shown that the development of this method can lead to a practical subcriticality monitor for many in-plant applications. The further development of the method will require experiments oriented toward particular applications including dynamic experiments and the development of theoretical methods to predict the experimental observables.

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

1985-01-01

101

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

102

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

E-print Network

electromagnetic or sound noise sources in the environment. On the other hand, a robot can be a rather significant electromagnetic or acous- tic medium. The main application envisaged by our work concerns robotic sound or mi source of electromagnetic and/or acoustic noise. Detecting or hiding the robot to reduce the risk

Garnier, Josselin

103

Auroral kilometric radiation: Wave modes, harmonic and source region electron density structures  

NASA Technical Reports Server (NTRS)

A change from extraordinary (X) mode to ordinary (0) mode dominance is observed in the auroral kilometric radiation (AKR) detected on ISIS 1 topside sounder ionograms as the source region plasma to gyrofrequency ratio fN/fH varies from 0.1 to 1.3. The X and 0 mode AKR, Z (the slow branch of the X mode) and whistler (W) mode are also observed. The Z mode is typically slightly less intense than the 0-mode. Thw W-mode is confined to frequencies less than fH/2, suggesting that it is the result of field aligned ducted signals reaching the satellite from a source at lower altitudes. Harmonic AKR bands are commonly observed and the 2nd harmonic appears to be due to propagating signals. The deduced (fN/fH) at the bottom of the AKR source region is always less than 0.4 and is typically less than 0.2 during the generation of X-mode AKR, but approaches 0.9 for 0-mode AKR. No large density enhancements were observed within AKR source region density cavities. It is suggested that the observed INTENSE AKR IS cyclotron X-mode radiation rather than plasma frequency 0-mode radiation.

Benson, R. F.

1984-01-01

104

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

105

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

106

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

107

Optical second harmonic generation near a black hole horizon as possible source of experimental information on quantum gravitational effects  

E-print Network

Optical second harmonic generation near a black hole horizon is suggested as a source of experimental information on quantum gravitational effects. While absent in the framework of general relativity, second harmonic generation appears in the toy models of sonic and electromagnetic black holes, where spatial dispersion at high frequencies for waves boosted towards the horizon is introduced. Localization effects in the light scattering from random fluctuations of matter fields and space-time metric near the black hole horizon produce a pronounced peak in the angular distribution of second harmonics of light in the direction normal to the horizon. Such second harmonic light has the best chances to escape the vicinity of the black hole. This phenomenon is similar to the well-known strong enhancement of diffuse second harmonic emission from a randomly rough metal surface in the direction normal to the surface.

Igor I. Smolyaninov

2001-08-10

108

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

109

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

110

The 8.4-GHz low-noise maser pump source assembly  

NASA Astrophysics Data System (ADS)

Improved pump source assemblies and new 8.4-GHz low noise traveling-wave masers (TWMs) were installed at the same time at Deep Space Stations 14 and 43 as part of the Mark IVA DSCC Antenna Microwave Subsystems upgrade. The pump source assemblies are part of the new 8.4-GHz TWMs, which are identified as Block IIA Low-Noise TWMs. Improved reliability of the pump source assemblies was required to meet stress analysis criteria.

Cardenas, R.

1987-11-01

111

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. PMID:19890478

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

112

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

113

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

114

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

PubMed Central

Pinhole collimators are widely used for SPECT imaging of small organs and animals. There also has been renewed interest in using pinhole arrays for clinical cardiac SPECT imaging to achieve high sensitivity and complete data sampling. Overall sensitivity of a pinhole array is critical in determining a system’s performance. Conventionally, a point source model has been used to evaluate the sensitivity and optimize the system design. This model is simple but far from realistic. This work addresses the use of more realistic source models to assess the sensitivity performance of pinhole collimation. We have derived an analytical formula for pinhole collimation sensitivity with a general source distribution model using spherical harmonics. As special cases of this general model, we provided the pinhole sensitivity formulae for line, disk and sphere sources. These results show that the point source model is just the zeroth-order approximation of the other source models. The point source model overestimates or underestimates the sensitivity relative to the more realistic model. The sphere source model yields the same sensitivity as a point source located at the center of the sphere when attenuation is not taken into account. In the presence of attenuation, the average path length of emitted gamma-rays is 3/4 of the radius of the sphere source. The calculated sensitivities based on these formulae show good agreement with separate Monte Carlo simulations in simple cases. The general and special sensitivity formulae derived here can be useful for the design and optimization of SPECT systems that utilize pinhole collimators. PMID:20400812

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

2013-01-01

115

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

116

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

NASA Astrophysics Data System (ADS)

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

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

117

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

118

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

NASA Astrophysics Data System (ADS)

Recent NASA and NASA sponsored research on the prediction and control of propeller and rotor source noise, on the analysis and design of fuselage sidewall noise control treatments, and on the measurement and quantification of the response of passengers to aircraft noise is described. Source noise predictions are compared with measurements for conventional low speed propellers, for new high speed propellers (propfans), and for a helicopter. Results from a light aircraft demonstration program are considered which indicates that about 5 dB reduction of flyover noise can be obtained without significant performance penalty. Sidewall design studies are examined for interior noise control in light general aviation aircraft and in large transports using propfan propulsion. The weight of the added acoustic treatment is estimated and tradeoffs between weight and noise reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller-like noise is described. Subject discomfort ratings of combined tone broadband noises are compared with ratings of broadband (boundary layer) noise alone and the relative importance of the propeller tones is examined.

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

1981-04-01

119

Identification and proposed control of helicopter transmission noise at the source  

NASA Technical Reports Server (NTRS)

Helicopter cabin interiors require noise treatment which is expensive and adds weight. The gears inside the main power transmission are major sources of cabin noise. Work conducted by the NASA Lewis Research Center in measuring cabin interior noise and in relating the noise spectrum to the gear vibration of the Army OH-58 helicopter is described. Flight test data indicate that the planetary gear train is a major source of cabin noise and that other low frequency sources are present that could dominate the cabin noise. Companion vibration measurements were made in a transmission test stand, revealing that the single largest contributor to the transmission vibration was the spiral bevel gear mesh. The current understanding of the nature and causes of gear and transmission noise is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that noise. The completed NASA/Army sponsored research that applies to transmission noise reduction is summarized. The continuing research program is also reviewed.

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

1988-01-01

120

A Practical Method for Calibrating a Coaxial Noise Source with a Waveguide Standard  

Microsoft Academic Search

A practical method for calibrating a coaxial noise source with a waveguide standard has been developed by extending the adaptor-changing method reported before, and a practical equation to give its noise temperature, the measurement procedure and the error analysis are described.

Y. Kato; I. Yokoshima

1987-01-01

121

Noise and coherence properties of HHG for FEL seeding  

NASA Astrophysics Data System (ADS)

High harmonics (HHs) are an attractive source for seeding coherent free electron lasers (FELs). Critical to many FEL applications are noise characteristics and the potential manipulation of coherence properties of these sources. We investigate these issues using a numerical model of harmonic generation.

Sheehy, B.; Clarke, J. A.; Thompson, N. R.; McNeil, B. W. J.; Gordon, A.

2008-08-01

122

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

Microsoft Academic Search

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

R. A. Kantola; R. E. Warren

1978-01-01

123

Generalized Wiener Process and Kolmogorov's Equation for Diffusion induced by Non-Gaussian Noise Source  

Microsoft Academic Search

We show that the increments of generalized Wiener process, useful to describe non-Gaussian white noise sources, have the properties of infinitely divisible random processes. Using functional approach and the new correlation formula for non-Gaussian white noise we derive directly from Langevin equation, with such a random source, the Kolmogorov's equation for Markovian non-Gaussian process. From this equation we obtain the

Alexander Dubkov; Bernardo Spagnol

2005-01-01

124

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

125

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

E-print Network

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

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

2014-01-01

126

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

127

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

E-print Network

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

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

2005-12-11

128

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

129

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

130

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

131

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

PubMed Central

We consider a class of neural circuit models with internal noise sources arising in sensory systems. The basic neuron model in these circuits consists of a dendritic stimulus processor (DSP) cascaded with a biophysical spike generator (BSG). The dendritic stimulus processor is modeled as a set of nonlinear operators that are assumed to have a Volterra series representation. Biophysical point neuron models, such as the Hodgkin-Huxley neuron, are used to model the spike generator. We address the question of how intrinsic noise sources affect the precision in encoding and decoding of sensory stimuli and the functional identification of its sensory circuits. We investigate two intrinsic noise sources arising (i) in the active dendritic trees underlying the DSPs, and (ii) in the ion channels of the BSGs. Noise in dendritic stimulus processing arises from a combined effect of variability in synaptic transmission and dendritic interactions. Channel noise arises in the BSGs due to the fluctuation of the number of the active ion channels. Using a stochastic differential equations formalism we show that encoding with a neuron model consisting of a nonlinear DSP cascaded with a BSG with intrinsic noise sources can be treated as generalized sampling with noisy measurements. For single-input multi-output neural circuit models with feedforward, feedback and cross-feedback DSPs cascaded with BSGs we theoretically analyze the effect of noise sources on stimulus decoding. Building on a key duality property, the effect of noise parameters on the precision of the functional identification of the complete neural circuit with DSP/BSG neuron models is given. We demonstrate through extensive simulations the effects of noise on encoding stimuli with circuits that include neuron models that are akin to those commonly seen in sensory systems, e.g., complex cells in V1. PMID:25225477

Lazar, Aurel A.; Zhou, Yiyin

2014-01-01

132

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

133

Examining alternatives to wavelet de-noising for astronomical source finding  

E-print Network

The Square Kilometre Array and its pathfinders ASKAP and MeerKAT will produce prodigious amounts of data that necessitate automated source finding. The performance of automated source finders can be improved by pre-processing a dataset. In preparation for the WALLABY and DINGO surveys, we have used a test HI datacube constructed from actual Westerbork Telescope noise and WHISP HI galaxies to test the real world improvement of linear smoothing, the {\\sc Duchamp} source finder's wavelet de-noising, iterative median smoothing and mathematical morphology subtraction, on intensity threshold source finding of spectral line datasets. To compare these pre-processing methods we have generated completeness-reliability performance curves for each method and a range of input parameters. We find that iterative median smoothing produces the best source finding results for ASKAP HI spectral line observations, but wavelet de-noising is a safer pre-processing technique. In this paper we also present our implementations of ite...

Jurek, Russell

2012-01-01

134

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

135

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

136

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

137

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

138

An ensemble source spectra model for merchant ship-radiated noise  

Microsoft Academic Search

This paper presents an evaluation of the classical model for determining an ensemble of the broadband source spectra of the sound generated by individual ships and proposes an alternate model to overcome the deficiencies in the classical model. The classical model, proposed by Ross [Mechanics of Underwater Noise (Pergamon, New York, 1976)] postulates that the source spectrum for an individual

Stephen C. Wales; Richard M. Heitmeyer

2002-01-01

139

A design methodology for a very low noise figure common-source LNA  

NASA Astrophysics Data System (ADS)

The design of common source (CS) Low Noise Amplifiers (LNA) for wireless receivers is presented. The design trade-offs between main criteria are discussed. An extra gate-to-source capacitor is added to the input transistor to reduce the transistor dimension while still satisfying the noise matching. The small MOSFET also improves the LNA linearity with comparatively small drain-source current. The extra gate-to-source capacitor is introduced by the bonding-pad parasitic capacitor; hence a negative effect parasitic capacitance is turned into a useful capacitor. The simulated Noise Figure (NF) of two single-ended LNAs using 0.18 ?m CMOS process achieve 0.62 dB and 0.92 dB at 2.4 GHz and 5.25 GHz respectively while matching a 50 ohm impedance.

Zhu, Yingbo; Al-Sarawi, Said F.; Liebelt, Michael

2005-02-01

140

New correlation model for the cascade of turbulent pulsations as a noise source in jets  

NASA Astrophysics Data System (ADS)

The mechanisms of noise generation by turbulent jets associated with a cascade of turbulent perturbations are considered from generation of primary eddies to their disintegration. A new correlation model proposed for describing these mechanisms is based on simulation of their generation as a random process with deterministic description of individual eddies. The model makes it possible to analyze available correlation models based on experimental modeling of the correlation function: monopoles, dipoles, or quadrupoles. The main difference between these models is both the different multipole structure of assumed sources and implicit "hard" and "soft" variants of source generation, as well as in the main variable for which the correlation function is developed. This approach is used for developing the correlation model of the noise generation mechanism related to oscillations of surface eddies. The jet noise inferred from the proposed model is well consistent with experimental data on circular jet noise.

Kopiev, V. F.; Chernyshev, S. A.

2012-07-01

141

Noise characterization of supercontinuum sources for low-coherence interferometry applications.  

PubMed

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

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

2014-12-01

142

Noise-robust hands-free speech recognition using SIMO-model-based blind source separation  

Microsoft Academic Search

This paper addresses a noise-robust hands-free speech recognition system in which Single-Input Multiple-Output (SIMO)-model-based blind source separation (BSS) is introduced to achieve a fluent human-machine interaction. The method consists of SIMO-ICA technique and SIMO-model-based binary masking, which can achieve a superior noise reduction with low distortion. In this paper, we investigate the distortion controllability of the two-stage BSS method. The

Y. Mori; T. Takatani; H. Saruwatari; K. Shikano; T. Hiekata; T. Morita

2007-01-01

143

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

144

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

PubMed

We consider a Lotka-Volterra system of two competing species subject to multiplicative ?-stable Lévy noise. The interaction parameter between the species is a random process which obeys a stochastic differential equation with a generalized bistable potential in the presence both of a periodic driving term and an additive ?-stable Lévy noise. We study the species dynamics, which is characterized by two different regimes, exclusion of one species and coexistence of both. We find quasiperiodic oscillations and stochastic resonance phenomenon in the dynamics of the competing species, analyzing the role of the Lévy noise sources. PMID:20866579

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

2010-07-01

145

Experimental determination of the main noise sources in a profan model by analysis of the acoustic spinning modes in the exit plane  

NASA Astrophysics Data System (ADS)

An experimental investigation is described to explore the dominant sound generation mechanisms of the tonal noise components of the MTU-CRISP propfan model. For this purpose, the sound field in the exit plane is measured using 1/4 inch microphones with nose cone. Initial tests proved than the presence of the microphone probes in the exit flow does not interfere with the sound pressure distribution. Experimental results of the mode distributions show that the blade passing frequency component is generated mainly by the interaction mechanisms between the rotors and the struts and/or by a transformation of acoustics modes at the struts. For all higher harmonics, the interaction between the two counter rotating rotors is the main noise source. The relative importance of the various interaction mechanisms is discussed for various shroud geometries, blade profiles, blade stagger angles, thrust conditions, angles of incidence, and wind tunnel speeds.

Holste, F.; Neise, W.

146

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

SciTech Connect

As a first step toward assessing the ability of hydrothermal boiling to explain geothermal ground noise and volcanic tremor observations, we are investigating the acoustic power spectrum of boiling (the source'' spectrum in the above model). We simulate boiling in the lab by injecting high pressure steam from a boiler into a pressure vessel filled with water. The water pressure fluctuations that result from the repeated formation and collapse of steam bubbles at the steam inlet vents are recorded by a hydrophone whose output is digitized at 2 {times} 10{sup 4} samples/second by a computer. The range of pressure and temperature conditions attainable within the pressure vessel is limited to <3.5 bars, <139{degree}C, due to the finite strength of observation windows affixed to the pressure vessel. Therefore, dimensional analysis will be used to correlate the experimental results with the pertinent experimental variables. Besides the overall shape of the boiling power spectrum, we are investigating the absolute spectral levels in frequency bands typical of geothermal ground noise and volcanic tremor (0.5 Hz-10 Hz), and the ratio of acoustic power liberated to total available power. The values of these parameters are critical to hydrothermal boiling's ability to generate ground motion amplitudes in accordance with observation. If it can be shown that the range of observed ground noise/tremor amplitudes can be accounted for by hydrothermal boiling at reasonable heat transfer rates, this knowledge would be invaluable to designers of seismic monitoring experiments who are interested in geothermal resource exploration/evaluation and volcanic eruption prediction.

Not Available

1989-01-01

147

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

NASA Technical Reports Server (NTRS)

A new method of separating the contributions of helicopter main and tail rotor noise sources is presented, making use of ground-based acoustic measurements. The method employs time-domain de-Dopplerization to transform the acoustic pressure time-history data collected from an array of ground-based microphones to the equivalent time-history signals observed by an array of virtual inflight microphones traveling with the helicopter. The now-stationary signals observed by the virtual microphones are then periodically averaged with the main and tail rotor once per revolution triggers. The averaging process suppresses noise which is not periodic with the respective rotor, allowing for the separation of main and tail rotor pressure time-histories. The averaged measurements are then interpolated across the range of directivity angles captured by the microphone array in order to generate separate acoustic hemispheres for the main and tail rotor noise sources. The new method is successfully applied to ground-based microphone measurements of a Bell 206B3 helicopter and demonstrates the strong directivity characteristics of harmonic noise radiation from both the main and tail rotors of that helicopter.

Greenwood, Eric II; Schmitz, Fredric H.

2009-01-01

148

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

149

Improving noise source location using the unwrapped phase method  

NASA Astrophysics Data System (ADS)

Time Delay of Arrival (TDOA) is the key to using a microphone array for sound source location. The Unwrapped Phase (UP) Method has been used to estimate the TDOA, which is proportional to the slope of the phase of the cross-power spectrum plotted versus frequency. However, reflecting surfaces cause ''jumps'' in the phase plot. A Zero-Magnitude of Transfer Function (ZMTF) criterion is proposed to automatically pick up the ''jumps'' to better estimate the TDOA. To verify this, tests were performed in three rooms with different acoustical properties. The sound source consisted of a speaker broadcasting a computer-generated broadband random signal. ZMTF works well in an ordinary room with small reverberation and yields accurate TDOA results. An average error of 0.2% is obtained. In a medium-sized live room, ZMTF identifies ''jumps,'' and an average error of 1.6% is obtained. In a large reverberation room, however, ZMTF only marginally improved the UP method. The norm of residues and Delay Error were found helpful to evaluate the best results.

Wang, Yongxin; Darvennes, Corinne

2002-11-01

150

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

NASA Technical Reports Server (NTRS)

A 48-microphone planar phased array system was used to acquire noise source localization data on a full-scale Williams International FJ44 turbofan engine. Data were acquired with the array at three different locations relative to the engine, two on the side and one in front of the engine. At the two side locations the planar microphone array was parallel to the engine centerline; at the front location the array was perpendicular to the engine centerline. At each of the three locations, data were acquired at eleven different engine operating conditions ranging from engine idle to maximum (take off) speed. Data obtained with the array off to the side of the engine were spatially filtered to separate the inlet and nozzle noise. Tones occurring in the inlet and nozzle spectra were traced to the low and high speed spools within the engine. The phased array data indicate that the Inflow Control Device (ICD) used during this test was not acoustically transparent; instead, some of the noise emanating from the inlet reflected off of the inlet lip of the ICD. This reflection is a source of error for far field noise measurements made during the test. The data also indicate that a total temperature rake in the inlet of the engine is a source of fan noise.

Podboy, Gary G.; Horvath, Csaba

2010-01-01

151

On Acoustic Source Specification for Rotor-Stator Interaction Noise Prediction  

NASA Technical Reports Server (NTRS)

This paper describes the use of measured source data to assess the effects of acoustic source specification on rotor-stator interaction noise predictions. Specifically, the acoustic propagation and radiation portions of a recently developed coupled computational approach are used to predict tonal rotor-stator interaction noise from a benchmark configuration. In addition to the use of full measured data, randomization of source mode relative phases is also considered for specification of the acoustic source within the computational approach. Comparisons with sideline noise measurements are performed to investigate the effects of various source descriptions on both inlet and exhaust predictions. The inclusion of additional modal source content is shown to have a much greater influence on the inlet results. Reasonable agreement between predicted and measured levels is achieved for the inlet, as well as the exhaust when shear layer effects are taken into account. For the number of trials considered, phase randomized predictions follow statistical distributions similar to those found in previous statistical source investigations. The shape of the predicted directivity pattern relative to measurements also improved with phase randomization, having predicted levels generally within one standard deviation of the measured levels.

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

2010-01-01

152

A directional array approach for the measurement of rotor noise source distributions with controlled spatial resolution  

NASA Technical Reports Server (NTRS)

A special array system has been designed to examine noise source distributions over a helicopter rotor model. The particular measurement environment is for a rotor operating in the open jet of an anechoic wind tunnel. An out-of-flow directional microphone element array is used with a directivity pattern whose major directional lobe projects on the rotor disk. If significant contributions from extraneous tunnel noise sources in the direction of the side lobes are excluded, the dominant output from the array would be that noise emitted from the projected area on the rotor disk. The design incorporates an array element signal blending features which serves to control the spatial resolution of the size of the directional lobes. (Without blending, the resolution and side lobe size are very strong functions of frequency, which severely limits the array's usefulness).

Brooks, T. F.; Marcolini, M. A.; Pope, D. S.

1987-01-01

153

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

NASA Technical Reports Server (NTRS)

Significant advancement has been made in the last few years to identify noise sources in high speed jets via direct correlation measurements. In this technique turbulent fluctuations in the flow are correlated with far field acoustics signatures. In the 1970 s there was a surge of work using mostly intrusive probes, and a few using Laser Doppler Velocimetry, to measure turbulent fluctuations. The later experiments established "shear noise" as the primary source for the shallow angle noise. Various interpretations and criticisms from this time are described in the review. Recent progress in the molecular Rayleigh scattering based technique has provided a completely non-intrusive means of measuring density and velocity fluctuations. This has brought a renewed interest on correlation measurements. We have performed five different sets of experiments in single stream jets of different Mach number, temperature ratio and nozzle configurations. The present paper tries to summarize the correlation data from these works.

Bridges, James (Technical Monitor); Panda, Jayanta

2005-01-01

154

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

155

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

PubMed Central

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

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

2011-01-01

156

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

PubMed

Statistical model-based reconstruction methods derive much of their advantage over traditional methods through more accurate forward models of the imaging system. Typical forward models fail to integrate two important aspects of real imaging systems: system blur and noise correlations in the measurements. This work develops an approach that models both aspects using a two-stage approach that includes a regularization deblurring operation followed by generalized penalized weighted least-squares reconstruction. Different reconstruction noise models including standard uncorrelated and correlated presumptions were explored. Moreover, different imaging systems were investigated in which blur was dominated by source effects, dominated by detector effects, or by a combination of source and detector blur. The proposed reconstruction approach that models the correlated noise demonstrated the best performance across all scenarios with the greatest benefits for increased source blur and for reconstructions with finer spatial resolution. This suggests potential application of the method for high resolution systems like dedicated flat-panel cone-beam CT (e.g., head, extremity, dental, mammography scanners) where system resolution is limited by both source and detector blur effects and noise correlations in measurement data are traditionally ignored. PMID:25346949

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

2014-01-01

157

A practical method for calibrating a coaxial noise source with a waveguide standard  

Microsoft Academic Search

A practical method is given for calibrating a coaxial noise source with a waveguide standard without directly evaluating the electrical characteristics of the coax-waveguide adaptor. It is shown that the measurement equation can be simplified when one of the standards is of the room-temperature type and the effective temperature of the radiometer when looking inside from the input port is

Yoshihiko Kato; Ichiro Yokoshima

1987-01-01

158

Detection and localization of multiple sources in noise with unknown covariance  

Microsoft Academic Search

The authors present a novel technique for the detection and localization of multiple sources in the presence of noise with unknown and arbitrary covariance. The technique is applicable to coherent and noncoherent signals and to arbitrary array geometry and is based on Rissanen's minimum description length (MDL) principle (1989) for model selection. Its computational load is comparable to that of

M. Wax

1992-01-01

159

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

E-print Network

source distribution of coaxial jets with a diameter ratio of 1.6 and variable velocity ratio and secondary cores of the jet. For zero velocity ratio (single-stream jet), the region near the nozzle emits strong high-frequency noise. Increasing the secondary-to-primary velocity ratio suppresses the near-nozzle

Papamoschou, Dimitri

160

High signal-to-noise Fourier transform spectroscopy with light emitting diode sources  

NASA Astrophysics Data System (ADS)

A temperature tuned light emitting diode (LED) has several advantages over conventional sources for Fourier transform spectroscopy. The large radiation density of LEDs, concentrated in a small spectral region, is ideal for high resolution Fourier transform spectroscopy where a high signal-to-noise (S/N) ratio is desired. A simple, inexpensive LED source leads to a superior performance at high resolutions exceeding that of a tungsten halogen lamp, in the visible region of spectrum.

Bhosale, J. S.

2011-09-01

161

A study of active power filters using quad-series voltage-source PWM converters for harmonic compensation  

Microsoft Academic Search

An active power filter using quad-series voltage-source pulse-width-modulated (PWM) converters to suppress AC harmonics by injecting compensating currents into the AC system is described. The circuit used to calculate the compensating current references, the compensation characteristics, and the capability of the DC capacitor are discussed theoretically and experimentally. A control circuit for the DC capacitor voltage is proposed. The discussions

FANG-ZHANG PENG; HIROFUMI AKAGI; AKIRA NABAE

1990-01-01

162

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

163

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

PubMed

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

Aliabadi, Mohsen; Golmohammadi, Rostam; Mansoorizadeh, Muharram

2014-03-01

164

Low-frequency noise sources in III-V semiconductor heterostructures  

NASA Astrophysics Data System (ADS)

III-V semiconductor heterostructures have widespread interest in both electrical and optical applications. Their figure-of-merit low-frequency noise level directly sets the limits of the performance of devices and indirectly serves as the indicator of material properties and device reliability. In particular, generation-recombination noise signals in the low-frequency noise range directly indicate the dominant traps that impact device operation. In this dissertation, low-frequency noise source investigations of GaAs/buffer and AlxGa1-xN/GaN heterostructures in the applications of microwave power amplifiers will be presented. For GaAs/buffer heterostructures, low-frequency noise characteristics of GaAs-On-Insulator metal-semiconductor field effect transistors, for which the insulating buffer layer was produced by lateral wet-oxidation of AlAs, are studied. Devices with different gate widths were fabricated resulting in different over-oxidation times for the AlAs layer. Three characteristic generation-recombination noise signatures are observed depending on the measurement temperature and the gate bias. A generation-recombination noise signature with energy level at Ec-0.69 eV is found to increase with the amount of over-oxidation time. This near mid-gap trap shows an increase in concentration towards the oxide interface, and it is tentatively assigned to an arsenic-antisite related defect known from previous studies as EB4. A possible mechanism for the formation and the microscopic origin of this defect are discussed. 1/f interface noise model is applied to analyze the GaAs/buffer interfacial quality. The effective interface state density was found to be as high as 1015 cm-2 and increase with additional over-oxidation. A correlation between the amount of over-oxidation and the number of calculated interface states is observed. For AlxGa1-xN/GaN heterostructures, low-frequency noise characteristics of AlxGa1-xN/GaN HEMTs with Al composition of 28--35% in the barrier layer are studied. A generation-recombination noise signature is attributed to a trap in AlxGa1-x N barrier layer which increases in concentration towards the Al xGa1-xN/GaN interface. The origin and the location of low-frequency noise were differentiated by the drain current dependent measurement. When the long-channel device is operated with an open channel (e.g. VG = 0), the main noise source resides in the gated channel instead of in the ungated region. Hooge's parameter of the gated channel (alpha ˜ 10-4) is found to be independent of the Al composition but dependent on the AlxGa1-x N barrier thickness. This is proposed to correspond to the onset of barrier relaxation. Even though the AlxGa1-xN/GaN HEMT exhibits a low level of gate leakage current (<1% of drain current), the low-frequency noise is still heavily influenced by the gate leakage current at certain bias conditions. The effect of gate leakage current on the low-frequency noise properties is discussed. The surface leakage path appeared to dominate the low-frequency noise properties for devices operated at a high IG/ID ratio.

Tzeng, Susie

165

Second-harmonic generation to the green and yellow using picosecond fiber pump sources and periodically poled waveguides  

NASA Astrophysics Data System (ADS)

Compact yellow (560nm) and green (532nm) picosecond pulse sources are demonstrated that utilize second-harmonic generation in periodically poled potassium titanyl phosphate waveguides. Both systems employ ytterbium-doped fiber pump sources. In the yellow case, efficient single-pass Raman scattering in 25m of dispersion-compensating fiber was additionally used to generate the 1.12?m pump. Raman gain could similarly be used in compact configurations to generate other pump wavelengths for use in frequency upconversion schemes.

Chestnut, D. A.; Popov, S. V.; Taylor, J. R.; Roberts, T. D.

2006-02-01

166

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

NASA Astrophysics Data System (ADS)

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

Shamsalsadati, S.; Weiss, C. J.

2011-12-01

167

Initial-state bremsstrahlung versus final-state hydrodynamic sources of azimuthal harmonics in p + A at RHIC and LHC  

NASA Astrophysics Data System (ADS)

Recent pT < 2 GeV azimuthal correlation data from the Beam Energy Scan (BES) and d + Au runs at RHIC/BNL and, especially, the surprising similarity of 2 ? = 2 , 4 , ⋯-particle cummulant azimuthal n = 2 , 3 , 4 , 5 harmonics, vn { 2 ? } (pT), in p + Pb and Pb + Pb at LHC have challenged the uniqueness of local equilibrium 'perfect fluid' interpretations of those data. We report results derived in [1] on azimuthal harmonics arising from non-equilibrium initial-state non-abelian 'wave interference' effects predicted by perturbative QCD gluon bremsstrahlung and sourced by Color Scintillation Arrays (CSA) of color antennas. CSA are naturally identified with multiple projectile and target beam jets produced in inelastic p + A reactions. We find a remarkable similarity between azimuthal harmonics sourced by initial state CSA and those predicted with final state perfect fluid models of high energy p + A reactions. The question of which mechanism dominates in p + A and A + A remains open at this time.

Gyulassy, M.; Levai, P.; Vitev, I.; Biró, T. S.

2014-11-01

168

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

NASA Technical Reports Server (NTRS)

To locate noise sources in high-speed jets, the sound pressure fluctuations p/, measured at far field locations, were correlated with each of density p, axial velocity u, radial velocity v, puu and pvv fluctuations measured from various points in fully expanded, unheated plumes of Mach number 0.95, 1.4 and 1.8. The velocity and density fluctuations were measured simultaneously using a recently developed, non-intrusive, point measurement technique based on molecular Rayleigh scattering (Seasholtz, Panda, and Elam, AIAA Paper 2002-0827). The technique uses a continuous wave, narrow line-width laser, Fabry-Perot interferometer and photon counting electronics. The far field sound pressure fluctuations at 30 to the jet axis provided the highest correlation coefficients with all flow variables. The correlation coefficients decreased sharply with increased microphone polar angle, and beyond about 60 all correlation mostly fell below the experimental noise floor. Among all correlations < puu; p/> showed the highest values. Interestingly, , in all respects, were very similar to . The and correlations with 90deg microphone fell below the noise floor. By moving the laser probe at various locations in the jet it was found that the strongest noise source lies downstream of the end of the potential core and extends many diameters beyond. Correlation measurement from the lip shear layer showed a Mach number dependency. While significant correlations were measured in Mach 1.8 jet, values were mostly below the noise floor for subsonic Mach 0.95 jet. Various additional analyses showed that fluctuations from large organized structures mostly contributed to the measured correlation, while that from small scale structures fell below the noise floor.

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

2004-01-01

169

Measurements and kernels for source-structure inversions in noise tomography  

NASA Astrophysics Data System (ADS)

Seismic noise cross-correlations are used to image crustal structure and heterogeneity. Typically, seismic networks are anisotropically illuminated by seismic noise, a consequence of the non-uniform distribution of sources. Here, we study the sensitivity of such a seismic network to structural heterogeneity in a 2-D setting. We compute finite-frequency cross-correlation sensitivity kernels for traveltime, waveform-energy and waveform-difference measurements. In line with expectation, wave speed anomalies are best imaged using traveltimes and the source distribution using cross-correlation energies. Perturbations in attenuation and impedance are very difficult to image and reliable inferences require a high degree of certainty in the knowledge of the source distribution and wave speed model (at least in the case of transmission tomography studied here). We perform single-step Gauss-Newton inversions for the source distribution and the wave speed, in that order, and quantify the associated Cramér-Rao lower bound. The inversion and uncertainty estimate are robust to errors in the source model but are sensitive to the theory used to interpret of measurements. We find that when classical source-receiver kernels are used instead of cross-correlation kernels, errors appear in the both the inversion and uncertainty estimate, systematically biasing the results. We outline a computationally tractable algorithm to account for distant sources when performing inversions.

Hanasoge, Shravan M.

2014-02-01

170

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

NASA Technical Reports Server (NTRS)

Noise-source separation techniques for the extraction of the sub-dominant combustion noise from the total noise signatures obtained in static-engine tests are described. Three methods are applied to data from a static, full-scale engine test. Both 1/3-octave and narrow-band results are discussed. The results are used to assess the combustion-noise prediction capability of the Aircraft Noise Prediction Program (ANOPP). A new additional phase-angle-based discriminator for the three-signal method is also introduced.

Hultgren, Lennart S.; Miles, Jeffrey H.

2009-01-01

171

Impact of different noise sources on the performance of PIN and APD-based FSO receivers  

Microsoft Academic Search

P-i-N (PIN) diodes and avalanche photo-diodes (APD) are the most commonly used photo-detectors in terrestrial FSO systems. In this paper, we review the photo- detection process for the cases of PIN- and APD-based receivers and provide a comprehensive study of different noise sources that affect signal detection in an FSO system. We present a complete and precise model for the

Fang Xu; Mohammad-Ali Khalighi; Salah Bourennane

2011-01-01

172

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

NASA Technical Reports Server (NTRS)

At the 2004 AIAA/CEAS Aeroacoustic Conference, a breakthrough in acoustic microphone array technology was reported by the authors. A Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) was developed which decouples the array design and processing influence from the noise being measured, using a simple and robust algorithm. For several prior airframe noise studies, it was shown to permit an unambiguous and accurate determination of acoustic source position and strength. As a follow-on effort, this paper examines the technique for three-dimensional (3D) applications. First, the beamforming ability for arrays, of different size and design, to focus longitudinally and laterally is examined for a range of source positions and frequency. Advantage is found for larger array designs with higher density microphone distributions towards the center. After defining a 3D grid generalized with respect to the array s beamforming characteristics, DAMAS is employed in simulated and experimental noise test cases. It is found that spatial resolution is much less sharp in the longitudinal direction in front of the array compared to side-to-side lateral resolution. 3D DAMAS becomes useful for sufficiently large arrays at sufficiently high frequency. But, such can be a challenge to computational capabilities, with regard to the required expanse and number of grid points. Also, larger arrays can strain basic physical modeling assumptions that DAMAS and all traditional array methodologies use. An important experimental result is that turbulent shear layers can negatively impact attainable beamforming resolution. Still, the usefulness of 3D DAMAS is demonstrated by the measurement of landing gear noise source distributions in a difficult hard-wall wind tunnel environment.

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

2005-01-01

173

BEAMSPACE BASED DOA ESTIMATION METHODS OF COHERENT SOURCES IN THE PRESENCE OF IMPULSIVE NOISE  

Microsoft Academic Search

This paper is concerned with the direction of arrival (DOA) estimation of coherent sources in impulse noise fields modeled as symmetric alpha stable (SalphaS) distribution. Robust covariation based MUSIC (ROC-MUSIC) and fractional lower moment based MUSIC (FLOM-MUSIC) cannot be used to estimate the DOA under these conditions. Firstly, new forward-backward smoothing (FBS)-covariation matrices and FBS-FLOM matrices are defined by applying

Li Hongsheng; He You; Yang Rijie; Guan Jian

2006-01-01

174

Dynamics of protein noise can distinguish between alternate sources of gene-expression variability  

PubMed Central

Within individual cells, two molecular processes have been implicated as sources of noise 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 noise source 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 sources of noise in gene expression. PMID:22929617

Singh, Abhyudai; Razooky, Brandon S; Dar, Roy D; Weinberger, Leor S

2012-01-01

175

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

NASA Astrophysics Data System (ADS)

A preliminary design is presented for a two-cavity harmonic multiplier, intended as a high-power RF source for use in experiments aimed at developing high-gradient structures for a future collider. The harmonic multiplier is to produce power at selected frequencies in K-band (18-26.5 GHz) using as an RF driver an XK-5 S-band klystron (2.856 GHz). The device is to be built with a TE111 rotating mode input cavity and interchangeable output cavities running in the TEn11 rotating mode, with n = 7,8,9 at 19.992, 22.848, and 25.704 GHz. An example for a 7th harmonic multiplier is described, using a 250 kV, 20 A injected laminar electron beam; with 10 MW of S-band drive power, 4.7 MW of 20-GHz output power is predicted. Details are described of the magnetic circuit, cavities, and output coupler.

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

2009-01-01

176

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

PubMed

Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage source (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current source (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low noise VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low noise, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low noise, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low noise and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f noise, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files. PMID:23988431

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

2013-10-01

177

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

NASA Astrophysics Data System (ADS)

Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage source (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current source (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low noise VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low noise, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low noise, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low noise and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f noise, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files.

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

2013-10-01

178

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

PubMed

Surveys have shown that noise from wind turbines is perceived as annoying by a proportion of residents living in their vicinity, apparently at much lower noise levels than those inducing annoyance due to other environmental sources. The aim of the present study was to derive the exposure-response relationship between wind turbine noise exposure in L(den) and the expected percentage annoyed residents and to compare it to previously established relationships for industrial noise and transportation noise. In addition, the influence of several individual and situational factors was assessed. On the basis of available data from two surveys in Sweden (N=341, N=754) and one survey in the Netherlands (N=725), a relationship was derived for annoyance indoors and for annoyance outdoors at the dwelling. In comparison to other sources of environmental noise, annoyance due to wind turbine noise was found at relatively low noise exposure levels. Furthermore, annoyance was lower among residents who received economical benefit from wind turbines and higher among residents for whom the wind turbine was visible from the dwelling. Age and noise sensitivity had similar effects on annoyance to those found in research on annoyance by other sources. PMID:22225031

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

2011-12-01

179

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

NASA Astrophysics Data System (ADS)

The last 30 years has seen substantial progress in ocean ambient noise research, particularly in understanding the mechanisms of sound generation by the sources of ambient noise, the way in which the noise field is affected by sound propagation, and improvements in quantifying the relationship between noise and environmental parameters. This has led to significant improvements in noise prediction. Activity was probably strongest in the 1980s and 1990s, as evident, for example, in the Sea Surface Sound conferences and their published proceedings (four over 10 years). Although much of the application has been to sonar, there has also been interest in using ambient noise to measure properties of the environment and in its significance to marine life. There have been significant changes in the ambient noise itself over the last 30 years. The contribution from human activities appears to have increased, particularly that due to increases in shipping numbers. Biological noise has also increased with the significant increases in populations of some whale species following the cessation of broad scale whaling in the 1960s and early 1970s. Concern about the effects of noise on marine animals as well as the way they exploit the noise has led to renewed interest in ambient noise.

Cato, Douglas H.

2012-11-01

180

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

NASA Technical Reports Server (NTRS)

Phased array noise source localization have been compared with 2 types of flow field data (BOS and PIV). The data show that: 1) the higher frequency noise in a BBSN hump is generated further downstream than the lower frequency noise. This is due to a) the shock spacing decreasing and b) the turbulent structure size increasing with distance downstream. 2) BBSN can be created by very weak shocks. 3) BBSN is not created by the strong shocks just downstream of the nozzle because the turbulent structures have not grown large enough to match the shock spacing. 4) The point in the flow where the shock spacing equals the average size of the turbulent structures is a hot spot for shock noise. 5) Some of the shocks responsible for producing the first hump also produce the second hump.

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

2013-01-01

181

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

182

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

NASA Technical Reports Server (NTRS)

The rotor broadband noise mechanisms considered are the following: (1) lift fluctuation due to turbulence ingestion; (2) boundary layer/trailing edge interaction; (3) tip vortex formation; and (4) turbulent vortex shedding from blunt trailing edge. Predictions show good agreement with available experimental data. The study shows that inflow turbulence is the most important broadband noise source for typical helicopters' main rotors at low- and mid-frequencies. Due to the size difference, isolated helicopter tail rotor broadband noise is not important compared to the much louder main rotor broadband noise. However, the inflow turbulence noise from a tail rotor can be very significant because it is operating in a highly turbulent environment, ingesting wakes from upstream components of the helicopter. The study indicates that the main rotor turbulent wake is the most important source of tail rotor broadband noise. The harmonic noise due to ingestion of main rotor tip vortices is studied.

Chou, Shau-Tak Rudy

1990-01-01

183

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

NASA Technical Reports Server (NTRS)

Wake/blade-row interaction noise produced by the Annular Cascade Facility at Purdue University has been modeled using the LINFLO analysis. Actuator displacements needed for complete cancellation of the propagating acoustic response modes have been determined, along with the associated actuator power requirements. As an alternative, weighted least squares minimization of the total far-field sound power using individual actuators has also been examined. Attempts were made to translate the two-dimensional aerodynamic results into three-dimensional actuator requirements. The results lie near the limit of present actuator technology. In order to investigate the concept of noise control at the source for active rotor/stator noise control at the source, various techniques for embedding miniature actuators into vanes were examined. Numerous miniature speaker arrangements were tested and analyzed to determine their suitability as actuators for a demonstration test in the Annular Cascade Facility at Purdue. The best candidates demonstrated marginal performance. An alternative concept to using vane mounted speakers as control actuators was developed and tested. The concept uses compression drivers which are mounted externally to the stator vanes. Each compression driver is connected via a tube to an air cavity in the stator vane, from which the driver signal radiates into the working section of the experimental rig. The actual locations and dimensions of the actuators were used as input parameters for a LINFLO computational analysis of the actuator displacements required for complete cancellation of tones in the Purdue experimental rig. The actuators were designed and an arrangement determined which is compatible with the Purdue experimental rig and instrumentation. Experimental tests indicate that the actuators are capable of producing equivalent displacements greater than the requirements predicted by the LINFLO analysis. The acoustic output of the actuators was also found to be unaffected by the presence of air flow representative of the Purdue experimental rig. A test of the active noise control at the source concept for rotor/stator active noise control was demonstrated. This 2-D test demonstrated conclusively the simultaneous reduction of two acoustic modes. Reductions of over 10 dB were obtained over a wide operating range.

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

1997-01-01

184

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

NASA Technical Reports Server (NTRS)

Methodology recommended to evaluate aeroacoustic related problems is provided, and approaches to their solutions are suggested without extensive tables, nomographs, and derivations. Orientation is toward flight vehicles and emphasis is on underlying physical concepts. Theoretical, experimental, and applied aspects are covered, including the main formulations and comparisons of theory and experiment. The topics covered include: propeller and propfan noise, rotor noise, turbomachinery noise, jet noise classical theory and experiments, noise from turbulent shear flows, jet noise generated by large-scale coherent motion, airframe noise, propulsive lift noise, combustion and core noise, and sonic booms.

Hubbard, Harvey H. (editor)

1991-01-01

185

Advanced turbo-prop airplane interior noise reduction-source definition  

NASA Technical Reports Server (NTRS)

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

Magliozzi, B.; Brooks, B. M.

1979-01-01

186

An ensemble source spectra model for merchant ship-radiated noise.  

PubMed

This paper presents an evaluation of the classical model for determining an ensemble of the broadband source spectra of the sound generated by individual ships and proposes an alternate model to overcome the deficiencies in the classical model. The classical model, proposed by Ross [Mechanics of Underwater Noise (Pergamon, New York, 1976)] postulates that the source spectrum for an individual ship is proportional to a baseline spectrum with the constant of proportionality determined by a power-law relationship on the ship speed and length. The model evaluation, conducted on an ensemble of 54 source spectra over a 30-1200-Hz to 1200-Hz frequency band, shows that this assumption yields large rms errors in the broadband source level for the individual ships and significantly overestimates the variability in the source level across the ensemble of source spectra. These deficiencies are a consequence of the negligible correlation between the source level and the ship speed and the source level and the ship length. The alternate model proposed here represents the individual ship spectra by a modified rational spectrum where the poles and zeros are restricted to the real axis and the exponents of the terms are not restricted to integer values. An evaluation of this model on the source spectra ensemble indicates that the rms errors are significantly less than those obtained with any model where the frequency dependence is represented by a single baseline spectrum. Furthermore, at high frequencies (400 to 1200 Hz), a single-term rational spectrum model is sufficient to describe the frequency dependence and, at the low frequencies (30 to 400 Hz), there is only a modest reduction in the rms error for a higher order model. Finally, a joint probability density on the two parameters of the single term model based on the measured histograms of these parameters is proposed. This probability density provides a mechanism for generating an ensemble of ship spectra. PMID:11931298

Wales, Stephen C; Heitmeyer, Richard M

2002-03-01

187

An ensemble source spectra model for merchant ship-radiated noise  

NASA Astrophysics Data System (ADS)

This paper presents an evaluation of the classical model for determining an ensemble of the broadband source spectra of the sound generated by individual ships and proposes an alternate model to overcome the deficiencies in the classical model. The classical model, proposed by Ross [Mechanics of Underwater Noise (Pergamon, New York, 1976)] postulates that the source spectrum for an individual ship is proportional to a baseline spectrum with the constant of proportionality determined by a power-law relationship on the ship speed and length. The model evaluation, conducted on an ensemble of 54 source spectra over a 30-1200-Hz to 1200-Hz frequency band, shows that this assumption yields large rms errors in the broadband source level for the individual ships and significantly overestimates the variability in the source level across the ensemble of source spectra. These deficiencies are a consequence of the negligible correlation between the source level and the ship speed and the source level and the ship length. The alternate model proposed here represents the individual ship spectra by a modified rational spectrum where the poles and zeros are restricted to the real axis and the exponents of the terms are not restricted to integer values. An evaluation of this model on the source spectra ensemble indicates that the rms errors are significantly less than those obtained with any model where the frequency dependence is represented by a single baseline spectrum. Furthermore, at high frequencies (400 to 1200 Hz), a single-term rational spectrum model is sufficient to describe the frequency dependence and, at the low frequencies (30 to 400 Hz), there is only a modest reduction in the rms error for a higher order model. Finally, a joint probability density on the two parameters of the single term model based on the measured histograms of these parameters is proposed. This probability density provides a mechanism for generating an ensemble of ship spectra.

Wales, Stephen C.; Heitmeyer, Richard M.

2002-03-01

188

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

NASA Technical Reports Server (NTRS)

A 70 microphone, 10-foot by 10-foot, microphone phased array was built for use in the harsh environment of rocket launches. The array was setup at NASA Wallops launch pad 0A during a static test firing of Orbital Sciences' Antares engines, and again during the first launch of the Antares vehicle. It was placed 400 feet away from the pad, and was hoisted on a scissor lift 40 feet above ground. The data sets provided unprecedented insight into rocket noise sources. The duct exit was found to be the primary source during the static test firing; the large amount of water injected beneath the nozzle exit and inside the plume duct quenched all other sources. The maps of the noise sources during launch were found to be time-dependent. As the engines came to full power and became louder, the primary source switched from the duct inlet to the duct exit. Further elevation of the vehicle caused spilling of the hot plume, resulting in a distributed noise map covering most of the pad. As the entire plume emerged from the duct, and the ondeck water system came to full power, the plume itself became the loudest noise source. These maps of the noise sources provide vital insight for optimization of sound suppression systems for future Antares launches.

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

2013-01-01

189

Methods for addressing noise and error in controlled source electromagnetic data  

NASA Astrophysics Data System (ADS)

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

MacLennan, Kristopher

190

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

NASA Technical Reports Server (NTRS)

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

Woodward, Richard P.; Loffler, Irvin J.

1991-01-01

191

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

SciTech Connect

Electrical measurements have been performed on the TOPAZ 2 V-71 and Ya-21 Reactors, in order to characterize the source impedance as a function of DC operating point and frequency. The response of the reactor to step changes in load current, as well as the frequency content of the electrical noise generated by the reactor have also been measured. These parameters are important to know in order to design power regulation circuitry which maintains a constant load on the reactor during spacecraft operations for any flight application of the TOPAZ 2 reactors. Voltage spikes at the reactor interface induced by load transients must be limited; the power regulation circuitry must have adequate bandwidth to compensate for spacecraft load dynamics. The methods used to make these measurements will be discussed. Results of the measurements on the Ya-21 reactor indicate the source impedance is dominated by a series resistance and inductance. The equivalent DC leakage resistance from the reactor output to structure was also measured. The self generated noise of the reactor is benign; load induced transients will be sufficiently controlled with capacitive filtering and active regulation circuitry external to the reactor/power distribution system. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}

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

1995-01-20

192

Two-microphone spatial filtering improves speech reception for cochlear-implant users in reverberant conditions with multiple noise sources.  

PubMed

This study evaluates a spatial-filtering algorithm as a method to improve speech reception for cochlear-implant (CI) users in reverberant environments with multiple noise sources. The algorithm was designed to filter sounds using phase differences between two microphones situated 1?cm apart in a behind-the-ear hearing-aid capsule. Speech reception thresholds (SRTs) were measured using a Coordinate Response Measure for six CI users in 27 listening conditions including each combination of reverberation level (T60=0, 270, and 540?ms), number of noise sources (1, 4, and 11), and signal-processing algorithm (omnidirectional response, dipole-directional response, and spatial-filtering algorithm). Noise sources were time-reversed speech segments randomly drawn from the Institute of Electrical and Electronics Engineers sentence recordings. Target speech and noise sources were processed using a room simulation method allowing precise control over reverberation times and sound-source locations. The spatial-filtering algorithm was found to provide improvements in SRTs on the order of 6.5 to 11.0?dB across listening conditions compared with the omnidirectional response. This result indicates that such phase-based spatial filtering can improve speech reception for CI users even in highly reverberant conditions with multiple noise sources. PMID:25330772

Goldsworthy, Raymond L

2014-01-01

193

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

PubMed Central

This study evaluates a spatial-filtering algorithm as a method to improve speech reception for cochlear-implant (CI) users in reverberant environments with multiple noise sources. The algorithm was designed to filter sounds using phase differences between two microphones situated 1?cm apart in a behind-the-ear hearing-aid capsule. Speech reception thresholds (SRTs) were measured using a Coordinate Response Measure for six CI users in 27 listening conditions including each combination of reverberation level (T60?=?0, 270, and 540?ms), number of noise sources (1, 4, and 11), and signal-processing algorithm (omnidirectional response, dipole-directional response, and spatial-filtering algorithm). Noise sources were time-reversed speech segments randomly drawn from the Institute of Electrical and Electronics Engineers sentence recordings. Target speech and noise sources were processed using a room simulation method allowing precise control over reverberation times and sound-source locations. The spatial-filtering algorithm was found to provide improvements in SRTs on the order of 6.5 to 11.0?dB across listening conditions compared with the omnidirectional response. This result indicates that such phase-based spatial filtering can improve speech reception for CI users even in highly reverberant conditions with multiple noise sources. PMID:25330772

2014-01-01

194

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

SciTech Connect

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

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)

2009-07-10

195

Signal-to-noise ratio for source determination and for a comodulated masker in goldfish, Carassius auratus  

PubMed Central

The masking effects of white and amplitude comodulated noise were studied with respect to simple signal detection and sound source determination in goldfish. A stimulus generalization method was used to determine the signal-to-noise 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 noise is at least 4 dB greater than previously thought, based on critical masking ratios. However, for amplitude comodulated noise 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 noise. PMID:21568437

Fay, Richard R.

2011-01-01

196

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

PubMed

Europe is severely affected by alien invasions, which impact biodiversity, ecosystem services, economy, and human health. A large number of national, regional, and global online databases provide information on the distribution, pathways of introduction, and impacts of alien species. The sufficiency and efficiency of the current online information systems to assist the European policy on alien species was investigated by a comparative analysis of occurrence data across 43 online databases. Large differences among databases were found which are partially explained by variations in their taxonomical, environmental, and geographical scopes but also by the variable efforts for continuous updates and by inconsistencies on the definition of "alien" or "invasive" species. No single database covered all European environments, countries, and taxonomic groups. In many European countries national databases do not exist, which greatly affects the quality of reported information. To be operational and useful to scientists, managers, and policy makers, online information systems need to be regularly updated through continuous monitoring on a country or regional level. We propose the creation of a network of online interoperable web services through which information in distributed resources can be accessed, aggregated and then used for reporting and further analysis at different geographical and political scales, as an efficient approach to increase the accessibility of information. Harmonization, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites. PMID:23609303

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

2013-06-01

197

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

NASA Astrophysics Data System (ADS)

Europe is severely affected by alien invasions, which impact biodiversity, ecosystem services, economy, and human health. A large number of national, regional, and global online databases provide information on the distribution, pathways of introduction, and impacts of alien species. The sufficiency and efficiency of the current online information systems to assist the European policy on alien species was investigated by a comparative analysis of occurrence data across 43 online databases. Large differences among databases were found which are partially explained by variations in their taxonomical, environmental, and geographical scopes but also by the variable efforts for continuous updates and by inconsistencies on the definition of "alien" or "invasive" species. No single database covered all European environments, countries, and taxonomic groups. In many European countries national databases do not exist, which greatly affects the quality of reported information. To be operational and useful to scientists, managers, and policy makers, online information systems need to be regularly updated through continuous monitoring on a country or regional level. We propose the creation of a network of online interoperable web services through which information in distributed resources can be accessed, aggregated and then used for reporting and further analysis at different geographical and political scales, as an efficient approach to increase the accessibility of information. Harmonization, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites.

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

2013-06-01

198

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

NASA Astrophysics Data System (ADS)

The stability and signal to noise ratio (SNR) of the current source circuit are the important factors contributing to enhance the accuracy and sensitivity in bioimpedance measurement system. In this paper we propose a new differential Howland topology current source and evaluate its output characters by simulation and actual measurement. The results include (1) the output current and impedance in high frequencies are stabilized after compensation methods. And the stability of output current in the differential current source circuit (DCSC) is 0.2%. (2) The output impedance of two current circuits below the frequency of 200 KHz is above 1 M?, and below 1 MHz the output impedance can arrive to 200 K?. Then in total the output impedance of the DCSC is higher than that of the Howland current source circuit (HCSC). (3) The SNR of the DCSC are 85.64 dB and 65 dB in the simulation and actual measurement with 10 KHz, which illustrates that the DCSC effectively eliminates the common mode interference. (4) The maximum load in the DCSC is twice as much as that of the HCSC. Lastly a two-dimensional phantom electrical impedance tomography is well reconstructed with the proposed HCSC. Therefore, the measured performance shows that the DCSC can significantly improve the output impedance, the stability, the maximum load, and the SNR of the measurement system.

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

2014-05-01

199

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

Microsoft Academic Search

It is shown that noise reduction on high bypass ratio turbofans for civil airliners is well established. The noise levels achieved meet the internationally agreed regulations (FAR 36). The same holds true for large military transport aircraft. Helicopter noise is caused essentially by the main and tail rotors. Noise reduction on afterburner and dry engines for combat and strike aircraft,

H. Grieb; K. Heinig

1986-01-01

200

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

E-print Network

Recent pTflow'' harmonics in $p+Pb$ and $Pb+Pb$ at LHC have challenged the uniqueness of local equilibrium ``perfect fluid'' interpretations of those data. We report results at QM14 on azimuthal harmonics associated with initial-state non-abelian ``wave interference'' effects predicted by perturbative QCD gluon bremsstrahlung and sourced by Color Scintillation Arrays (CSA) of color antennas. CSA are naturally identified with multiple projectile and target beam jets produced in inelastic p+A reactions. We find a remarkable similarity between azimuthal harmonics sourced by initial state CSA and those predicted with final state perfect fluid models of high energy p+A reactions. The question of which mechanism dominates in $p+A$ and $A+A$ remains open at this time.

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

2014-07-28

201

Combustion noise  

NASA Technical Reports Server (NTRS)

A review of the subject of combustion generated noise is presented. Combustion noise is an important noise source in industrial furnaces and process heaters, turbopropulsion and gas turbine systems, flaring operations, Diesel engines, and rocket engines. The state-of-the-art in combustion noise importance, understanding, prediction and scaling is presented for these systems. The fundamentals and available theories of combustion noise are given. Controversies in the field are discussed and recommendations for future research are made.

Strahle, W. C.

1977-01-01

202

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

PubMed

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

Collin, Benjamin; Lavandier, Mathieu

2013-08-01

203

Ambient noise as the new source for urban engineering seismology and earthquake engineering: a case study from Beijing metropolitan area  

NASA Astrophysics Data System (ADS)

In highly populated urban centers, traditional seismic survey sources can no longer be properly applied due to restrictions in modern civilian life styles. The ambient vibration noise, including both microseisms and microtremor, though are generally weak but available anywhere and anytime, can be an ideal supplementary source 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 noise. Thus, it can be essentially regarded as a passive seismic method. In this paper we first make a brief survey of the ambient vibration noise, followed by a quick summary of digital signal processing for passive seismic surveys. Then the applications of ambient noise 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 noise. By showing these examples we argue that the ambient noise can be treated as a new source that is economical, practical, and particularly valuable to engineering seismology and earthquake engineering projects for seismic hazard mitigation in urban areas.

Liu, Lanbo; Chen, Qi-fu; Wang, Weijun; Rohrbach, Eric

2014-02-01

204

7.9 Wenchuan Earthquake fault zone revealed by ambient noise and ACROSS active source data  

NASA Astrophysics Data System (ADS)

We continuously monitor the long-term seismic velocity variation of one of the major ruptured faults of the devastating 2008 M w 7.9 Wenchuan earthquake in China from July 2009 to January 2012, jointly using accurately controlled routinely operated signal system active source and seismic noise-based monitoring technique. Our measurements show that the temporal velocity change is not homogeneous and highly localized in the damaged fault zone and the adjacent areas. Velocity variations from the active and passive methods are quite consistent, which both are characterized by ±0.2 % seasonal variation, with peak and trough at winter and summer, respectively. The periodic velocity variation within fault zone exhibits remarkably positive correlation with barometric pressure with stress sensitivity in the order of 10-6 Pa-1, suggesting that the plausible mechanism might be the crack density variation of the shallow subsurface medium of the damaged fault zone in response to the cyclic barometric pressure loading.

Chen, Haichao; Ge, Hongkui; Niu, Fenglin

2014-10-01

205

Inverse Problem for the Wave Equation with a White Noise Source  

NASA Astrophysics Data System (ADS)

We consider a smooth Riemannian metric tensor g on and study the stochastic wave equation for the Laplace-Beltrami operator . Here, F = F( t, x, ?) is a random source that has white noise distribution supported on the boundary of some smooth compact domain . We study the following formally posed inverse problem with only one measurement. Suppose that g is known only outside of a compact subset of M int and that a solution is produced by a single realization of the source . We ask what information regarding g can be recovered by measuring on ? We prove that such measurement together with the realization of the source determine the scattering relation of the Riemannian manifold ( M, g) with probability one. That is, for all geodesics passing through M, the travel times together with the entering and exit points and directions are determined. In particular, if ( M, g) is a simple Riemannian manifold and g is conformally Euclidian in M, the measurement determines the metric g in M.

Helin, Tapio; Lassas, Matti; Oksanen, Lauri

2014-12-01

206

High speed full range imaging with harmonic detection swept source optical coherence tomography  

Microsoft Academic Search

A complication of Fourier domain optical coherence tomography (OCT) methods, such as spectral domain and swept source OCT, is the complex conjugate ambiguity due to inverse Fourier transform of real-valued data. As a result, the image is symmetric to the zero plane, and only half of the theoretical imaging depth range is used to avoid overlapping \\

Chuanyong Huang; Steven M. Massick; Kristen A. Peterson; Andrei B. Vakhtin

2010-01-01

207

Green light source by single-pass second harmonic generation with laser and crystal in a tilted butt joint setup  

NASA Astrophysics Data System (ADS)

In this work a compact green laser light source is presented based on a single-pass second harmonic generation (SHG) in non-linear material. The green light source 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.

Wiedmann, J.; Scholz, F.; Tekin, T.; Marx, S.; Lang, G.; Schröder, H.; Brox, O.; Erbert, G.

2009-02-01

208

Performance of an optical sectored receiver for indoor wireless communication systems in presence of artificial and natural noise sources  

NASA Astrophysics Data System (ADS)

This paper gives special attention to wireless local area networks using infrared technology mainly with respect to the reception techniques and presents the performance evaluation of optical sectored receivers for indoor wireless communication systems in the presence of artificial and natural noise sources. Performance evaluation was extended to four distinct sectored receiver configurations which result in significant gains over a non-sectored optical receiver. A characterization of the ambient light noise distribution due artificial light was performed. Also, the radiation patterns of some directional incandescent lamps were measured and modeled through a generalized Lambertian function. The feasibility of optical sectored receivers in the presence of directional light sources is demonstrated.

Tavares, Antonio M.; Valadas, Rui J. M. T.; de Oliveira Duarte, A. M.

1995-12-01

209

Wind Turbine Current-Source Converter Providing Reactive Power Control and Reduced Harmonics  

Microsoft Academic Search

This paper presents a current-source inverter topology that is suitable for multi-megawatt wind turbines. The proposed scheme utilizes two series-connected three-phase inverters that employ fully controllable switches and a proper interconnection transformer with the mains. In order to improve the efficiency and to allow the use of high-power devices, the inverters are switched at the mains frequency. The axial-flux permanent-magnet

Pierluigi Tenca; Andrew A. Rockhill; Thomas A. Lipo

2007-01-01

210

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

NASA Technical Reports Server (NTRS)

Current experimental investigations have linked static inflow distortion phenomena such as the ground vortex, atmospheric turbulence, and teststand structure interference to the generation of fan tone noise at the blade passing frequency. Since such distortions do not exist in flight, it is important to remove them from the static test environment and thereby improve the static-to-flight tone-noise correlation. In the course of providing evidence for this position, a recent investigation used a distortion control inlet with a modern day turbofan engine to assess atmospheric turbulence effects. Although the initial results were encouraging, they were incomplete. The present investigation continues this work and shows more completely the effect of atmospheric turbulence on tone-noise generation. Further, use is made of the distortion control inlet to identify other competing tone-noise sources in the test engine such as a rotor-core stator interaction which was confirmed by engine modifications.

Hodder, B. K.

1976-01-01

211

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

NASA Technical Reports Server (NTRS)

NASA is investigating the feasibility of modifying the 4x7m Wind Tunnel at the Langley Research Center to make it suitable for a variety of aeroacoustic testing applications, most notably model helicopter rotors. The amount of noise reduction required to meet NASA's goal for test section background noise was determined, the predominant sources and paths causing the background noise were quantified, and trade-off studies between schemes to reduce fan noise at the source and those to attenuate the sound generated in the circuit between the sources and the test section were carried out. An extensive data base is also presented on circuit sources and paths.

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

1984-01-01

212

Semi-passive piezoelectric noise control in transmission by synchronized switching damping on voltage source  

NASA Astrophysics Data System (ADS)

This paper deals with the so called SSD (stands for Synchronized Switch Damping) technique that is a semi-passive approach developed to address the problem of structural vibration damping and noise reduction. Compared to standard passive piezoelectric damping, this technique offers the advantage of self-adaptation with environmental variations (e.g. temperature). On the contrary to the active damping systems, its implementation does not require any sophisticated signal processing or any bulk power. In the semi passive approach, the piezoelectric element is continuously switched from open circuit to short circuit synchronously to the strain. Due to this switching mechanism, a phase difference appears between the strain induced by an incident acoustic wave and the resulting voltage, thus creating energy dissipation. With the non-linear process, damping performances directly depend on the electromechanical coupling coefficient of the system. For the weakly coefficient coupling systems, the voltage amplitude of the piezoelectric elements can be artificially increased by switching on voltage sources. Using this new method SSDV (stands for Synchronized Switch Damping on Voltage source), 16.1?dB attenuation on the transmitted wave pressure in the tube is obtained whereas only 8?dB were achieved with the classical SSDI (stands for Synchronized Switch Damping on Inductor). Furthermore, as this method is adaptive, attenuation is observed over a 600?Hz-wide frequency band.

Faiz, A.; Guyomar, D.; Petit, L.; Buttay, C.

2005-09-01

213

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

PubMed

The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and noise characteristics. The main aim was to characterize and quantify the noise sources in the images. The systems tested were (1) Agfa CR 25.0, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX-S, a line-scanning CR reader with needle crystal phosphor image plates (HD 5.0). For both systems, the standard metrics of presampled modulation transfer function (MTF), normalized noise power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various noise sources contributing to the NNPS were separated by using knowledge of their relationship with air kerma, MTF, absorption efficiency and antialiasing filters. The DX-S MTF was superior compared with the CR 25.0. The maximum difference in MTF between the DX-S scan and CR 25.0 subscan directions was 0.13 at 1.3 mm(-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 noise 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 noise sources indicates that the improvements in DQE of the DX-S are due not only to the higher quantum, efficiency and MTF, but also the lower structure, secondary quantum, and excess noise. PMID:17879798

Mackenzie, Alistair; Honey, Ian D

2007-08-01

214

Noise sources and improved performance of a mid-wave infrared uncooled silicon carbide optical photodetector.  

PubMed

An uncooled photon detector is fabricated for the mid-wave infrared (MWIR) wavelength of 4.21 ?m by doping an n-type 4H-SiC substrate with gallium using a laser doping technique. The dopant creates a p-type energy level of 0.3 eV, which is the energy of a photon corresponding to the MWIR wavelength 4.21 ?m. This energy level was confirmed by optical absorption spectroscopy. The detection mechanism involves photoexcitation of carriers by the photons of this wavelength absorbed in the semiconductor. The resulting changes in the carrier densities at different energy levels modify the refractive index and, therefore, the reflectance of the semiconductor. This change in the reflectance constitutes the optical response of the detector, which can be probed remotely with a laser beam such as a He-Ne laser and the power of the reflected probe beam can be measured with a conventional laser power meter. The noise mechanisms in the probe laser, silicon carbide MWIR detector, and laser power meter affect the performance of the detector in regards to aspects such as the responsivity, noise equivalent temperature difference (NETD), and detectivity. For the MWIR wavelengths of 4.21 and 4.63 ?m, the experimental detectivity of the optical photodetector of this study was found to be 1.07×1010??cm·Hz1/2/W, while the theoretical value was 1.11×1010??cm·Hz1/2/W. The values of NETD are 404 and 15.5 mK based on experimental data for an MWIR radiation source with a temperature of 25°C and theoretical calculations, respectively. PMID:25608189

Lim, Geunsik; Manzur, Tariq; Kar, Aravinda

2014-12-20

215

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

NASA Astrophysics Data System (ADS)

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

Aggarwal, H. R.

1984-10-01

216

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

NASA Technical Reports Server (NTRS)

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

Aggarwal, H. R.

1984-01-01

217

Contact quality analysis and noise sources determination of CdZnTe-based high-energy photon detectors  

NASA Astrophysics Data System (ADS)

Experimental studies of the transport and noise characteristics of a cadmium-zinc-telluride (CdZnTe) crystal with symmetric gold contacts and a guard ring electrode have been carried out. The current-voltage (IV) characteristics and the noise spectral density were measured at room temperature in the dark. The sample with a disconnected guard ring electrode showed symmetric characteristics for both bias voltage polarities. The shape IV characteristics indicated the presence of carrier injection, leading to IV characteristics nonlinearity. The semiconductor surface has been identified as the main noise and leakage current source. After connecting the guard ring electrode, the leakage currents were suppressed by two orders and the noise spectral density decreased by five orders. In the case of the connected guard ring electrode, the asymmetry of IV characteristics was observed. The contact with worse rectifying properties had a higher contribution of noise to the detector system. Increasing bias voltage causes steeper detector additive noise growth when the guard ring electrode is disconnected.

Sik, O.; Skarvada, P.; Grmela, L.; Elhadidy, H.; Vondra, M.; Sikula, J.; Franc, J.

2013-11-01

218

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

NASA Technical Reports Server (NTRS)

The objective of this effort is to develop an analytical model for the coupling of active noise control (ANC) piston-type actuators that are mounted flush to the inner and outer walls of an annular duct to the modes in the duct generated by the actuator motion. The analysis will be used to couple the ANC actuators to the modal analysis propagation computer program for the annular duct, to predict the effects of active suppression of fan-generated engine noise sources. This combined program will then be available to assist in the design or evaluation of ANC systems in fan engine annular exhaust ducts. An analysis has been developed to predict the modes generated in an annular duct due to the coupling of flush-mounted ring actuators on the inner and outer walls of the duct. The analysis has been combined with a previous analysis for the coupling of modes to a cylindrical duct in a FORTRAN computer program to perform the computations. The method includes the effects of uniform mean flow in the duct. The program can be used for design or evaluation purposes for active noise control hardware for turbofan engines. Predictions for some sample cases modeled after the geometry of the NASA Lewis ANC Fan indicate very efficient coupling in both the inlet and exhaust ducts for the m = 6 spinning mode at frequencies where only a single radial mode is cut-on. Radial mode content in higher order cut-off modes at the source plane and the required actuator displacement amplitude to achieve 110 dB SPL levels in the desired mode were predicted. Equivalent cases with and without flow were examined for the cylindrical and annular geometry, and little difference was found for a duct flow Mach number of 0.1. The actuator ring coupling program will be adapted as a subroutine to the cylindrical duct modal analysis and the exhaust duct modal analysis. This will allow the fan source to be defined in terms of characteristic modes at the fan source plane and predict the propagation to the arbitrarily-located ANC source plane. The actuator velocities can then be determined to generate the anti-phase mode. The resulting combined fan source/ANC pressure can then be calculated at any desired wall sensor position. The actuator velocities can be determined manually or using a simulation of a control system feedback loop. This will provide a very useful ANC system design and evaluation tool.

Kraft, R. E.

1996-01-01

219

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

Microsoft Academic Search

A test was conducted in the Boeing Large Anechoic Chamber to determine static jet noise source locations of six baseline and suppressor nozzle models, and establish a technique for extrapolating near field data into the far field. The test covered nozzle pressure ratios from 1.44 to 2.25 and jet velocities from 412 to 594 m\\/s at a total temperature of

C. L. Jaeck

1976-01-01

220

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

NASA Technical Reports Server (NTRS)

Tests of a 20 inch diameter, low tip speed, low pressure ratio fan which investigated aft fan noise reduction techniques are reported. These techniques included source noise reduction features of selection of vane-blade ratio to reduce second harmonic noise, spacing effects, and lowering the Mach number through a vane row. Aft suppression features investigated included porosity effects, variable depth treatment, and treatment regenerated flow noise. Initial results and selected comparisons are presented.

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

1975-01-01

221

Noise pollution resources compendium  

NASA Technical Reports Server (NTRS)

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

1973-01-01

222

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

223

Combined Source-Channel Coding Schemes for Video Transmission over an Additive White Gaussian Noise Channel  

Microsoft Academic Search

In recent years there has been an increased interest in the transmission ofdigital video over real-world transmission media, such as the direct broadcastsatellite (DBS) channel. Video transmitted over such a channel is subject todegradation due, in part, to additive white Gaussian noise (AWGN). Some formof forward error-control (FEC) coding may be applied in order to reduce theeffect of the noise

M. Bystrom; J. w. Modestino

1997-01-01

224

Investigation on trailing-edge noise sources by means of high-speed PIV  

Microsoft Academic Search

The noise generation of turbulent flows over surfaces and around edges of airplanes and automobiles is a general design problem and its importance increases in times of growing traffic in this globalizing world. Turbulent boundary layers near the trailing-edge of a surface are known to generate intense, broadband scattering noise as well as surface pressure fluctuations. The wake of vortices

A. Schröder; U. Dierksheide; J. Wolf; M. Herr; J. Kompenhans

225

Extraction of small boat harmonic signatures from passive sonar.  

PubMed

This paper investigates the extraction of acoustic signatures from small boats using a passive sonar system. Noise radiated from a small boats consists of broadband noise and harmonically related tones that correspond to engine and propeller specifications. A signal processing method to automatically extract the harmonic structure of noise radiated from small boats is developed. The Harmonic Extraction and Analysis Tool (HEAT) estimates the instantaneous fundamental frequency of the harmonic tones, refines the fundamental frequency estimate using a Kalman filter, and automatically extracts the amplitudes of the harmonic tonals to generate a harmonic signature for the boat. Results are presented that show the HEAT algorithms ability to extract these signatures. PMID:21682400

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

2011-06-01

226

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

NASA Astrophysics Data System (ADS)

In the frame of the research conducted to develop efficient strategies for investigation of rock properties and fluids ahead of tunnel excavations the seismic interferometry method was applied to analyze the data acquired in boreholes instrumented with geophone strings. The results obtained confirmed that seismic interferometry provided an improved resolution of petrophysical properties to identify heterogeneities and geological structures ahead of the excavation. These features are beyond the resolution of other conventional geophysical methods but can be the cause severe problems in the excavation of tunnels. Geophone strings were used to record different types of seismic noise generated at the tunnel head during excavation with a tunnelling machine and also during the placement of the rings covering the tunnel excavation. In this study we show how tunnel construction activities have been characterized as source of seismic signal and used in our research as the seismic source signal for generating a 3D reflection seismic survey. The data was recorded in vertical water filled borehole with a borehole seismic string at a distance of 60 m from the tunnel trace. A reference pilot signal was obtained from seismograms acquired close the tunnel face excavation in order to obtain best signal-to-noise ratio to be used in the interferometry processing (Poletto et al., 2010). The seismic interferometry method (Claerbout 1968) was successfully applied to image the subsurface geological structure using the seismic wave field generated by tunneling (tunnelling machine and construction activities) recorded with geophone strings. This technique was applied simulating virtual shot records related to the number of receivers in the borehole with the seismic transmitted events, and processing the data as a reflection seismic survey. The pseudo reflective wave field was obtained by cross-correlation of the transmitted wave data. We applied the relationship between the transmission response and the reflection response for a 1D multilayer structure, and next 3D approach (Wapenaar 2004). As a result of this seismic interferometry experiment the 3D reflectivity model (frequencies and resolution ranges) was obtained. We proved also that the seismic interferometry approach can be applied in asynchronous seismic auscultation. The reflections detected in the virtual seismic sections are in agreement with the geological features encountered during the excavation of the tunnel and also with the petrophysical properties and parameters measured in previous geophysical borehole logging. References Claerbout J.F., 1968. Synthesis of a layered medium from its acoustic transmision response. Geophysics, 33, 264-269 Flavio Poletto, Piero Corubolo and Paolo Comeli.2010. Drill-bit seismic interferometry whith and whitout pilot signals. Geophysical Prospecting, 2010, 58, 257-265. Wapenaar, K., J. Thorbecke, and D. Draganov, 2004, Relations between reflection and transmission responses of three-dimensional inhomogeneous media: Geophysical Journal International, 156, 179-194.

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

2013-04-01

227

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

NASA Technical Reports Server (NTRS)

The analytic models developed for computing the periodic sound pressure of subsonic fans and compressors in an infinite, hardwall annular duct with uniform flow are described. The basic sound-generating mechanism is the scattering into sound waves of velocity disturbances appearing to the rotor or stator blades as a series of harmonic gusts. The models include component interactions and rotor alone.

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

1974-01-01

228

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

SciTech Connect

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

Gong, Tao [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)

2013-09-15

229

SOURCES AND REMEDIES OF HIGH-FREQUENCY PIPING VIBRATION AND NOISE  

Microsoft Academic Search

In large diameter piping, high-frequency energy can produce excessive noise and vibration, and failures of thermowells, instru- mentation, and attached small-bore piping. In severe cases, the pipe itself can fracture. Perhaps more precisely called \\

Stephen M. Price; Senior Project Engineer

230

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

Microsoft Academic Search

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

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

1992-01-01

231

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

Microsoft Academic Search

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

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

2010-01-01

232

A Study on Trailing Edge Noise Sources Using High~Speed Particle Image Velocimetry  

Microsoft Academic Search

\\u000a The noise generation of turbulent flows near the edges of airplanes and automobiles is a general design problem and its importance\\u000a increases in times of growing traffic. Turbulent boundary layers being convected past the trailing edge into the wake are\\u000a known to generate an intense, broadband scattering noise. In this feasibility study the high-speed PIV technique was applied\\u000a to a

A. Schröfer; M. Herr; T. Lauke; U. Dierksheide

233

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

SciTech Connect

Generation of low-order harmonics (third and fifth) of the fundamental radiation of a Q-switched Nd:YAG laser (1064 nm, pulse 15 ns) was observed in a CaF{sub 2} laser ablation plume. The ablation process is triggered by a second Q-switched Nd:YAG laser operating at 532 or 266 nm. In the scheme employed, the fundamental laser beam propagates parallel to the target surface at controllable distance and temporal delay, allowing to the probing of different regions of the freely expanding plume. The intensity of the harmonics is shown to decrease rapidly as the distance to the target is increased, and for each distance, an optimum time delay between the ablating laser pulse and the fundamental beam is found. In situ diagnosis of the plume by optical emission spectroscopy and laser-induced fluorescence serves to correlate the observed harmonic behavior with the temporally and spatially resolved composition and velocity of flight of species in the plume. It is concluded that harmonics are selectively generated by CaF species through a two-photon resonantly enhanced sum-mixing process exploiting the (B {sup 2{Sigma}+}-X {sup 2{Sigma}+}, {Delta}{nu}=0) transition of the molecule in the region of 530 nm. In this work polar molecules have been shown to be the dominating species for harmonic generation in an ablation plume. Implications of these results for the generation of high harmonics in strongly polar molecules which can be aligned in the ablation plasma are discussed.

Oujja, M.; Nalda, R. de; Castillejo, M. [Instituto de Quimica Fisica Rocasolano, CSIC, Serrano 119, 28006 Madrid (Spain); Lopez-Arias, M. [Instituto de Quimica Fisica Rocasolano, CSIC, Serrano 119, 28006 Madrid (Spain); Unidad Asociada Departamento de Quimica Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid (Spain) and Instituto de Estructura de la Materia, CSIC, Serrano 123, 28006 Madrid (Spain); Torres, R.; Marangos, J. P. [Blackett Laboratory, Imperial College London, SW7 2 BW London (United Kingdom)

2010-04-15

234

Mode-locked laser noise analysis from RF generated by an electrooptic antenna  

NASA Astrophysics Data System (ADS)

Stable sources of radiofrequency radiation are essential for high resolution molecular spectroscopy. One technique for generating radiofrequency radiation is by illuminating an antenna structure fabricated on low temperature grown Gallium Arsenide with femtosecond pulses. The performance of this source is dependent on the stability of the pump mode-locked laser system. This dissertation describes the generation of spectrally narrow, tunable rf pulses by electooptic antennas illuminated by mode-locked laser pulses and explains the limitations on pulse width and tunability presented by fluctuations in the pump Ti:sapphire laser. Unique noise information is obtained by considering high harmonic data from the antenna. As a radiation source, the performance of the laser- driven electroopotic antenna is limited by noise in the source short pulse laser system. The growth of the noise with laser harmonic number number is important to establish in order to predict the behavior of the source at very high harmonics. In this thesis, two components to the noise are established. One is the amplitude noise that is independent of harmonic and the other is the timing jitter noise that grows with harmonic number as n2. The specifications on the electrooptic antenna as a radiofrequency source are also established. Specifically, the resolution at 340 GHz is established to be 7.5 KHz and the timing jitter noise limits the resolution up to n = 6000 or 480 GHz. The J = 27 >= 28 rotational transition in OCS gas is measured to establish the resolution. It is found to be Doppler broadened limited, not laser limited.

Juvan, Kimberly Ann

1997-09-01

235

Local Harmonic Estimation in Musical Sound Rafael A. IRIZARRY  

E-print Network

Local Harmonic Estimation in Musical Sound Signals Rafael A. IRIZARRY Statistical modeling so a local harmonic model that tracks changes in pitch and in the amplitudes of the harmonics is fit estimates of the harmonic signal and of the noise signal. Different musical composition applications may

Irizarry, Rafael A.

236

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

NASA Technical Reports Server (NTRS)

The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling sources for active control of aircraft engine fan noise is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy acoustic plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of acoustic plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable acoustic source for active control of aircraft engine fan noise.

Pla, F. G.; Rajiyah, H.

1995-01-01

237

Controls for Noise Exposure  

MedlinePLUS

... Maintain tools and equipment routinely (such as lubricate gears) Reduce vibration where possible Isolate the noise source ... studies for noise control and Buy-Quiet. Noise Reduction Ideas Bank Washington State Department of Labor & Industries. ...

238

Sources of Signal-Dependent Noise During Isometric Force Production KELVIN E. JONES, ANTONIA F. DE C. HAMILTON AND DANIEL M. WOLPERT  

E-print Network

Sources of Signal-Dependent Noise During Isometric Force Production KELVIN E. JONES, ANTONIA F. DE of signal-dependent noise during isometric force production. J Neurophysiol 88: 1533­1544, 2002; 10.1152/jn of this study was to investi- gate the presence of SDN during isometric force production and deter- mine how

Hamilton, Antonia

239

Compact source of Einstein-Podolsky-Rosen entanglement and squeezing at very low noise frequencies  

SciTech Connect

We report on the experimental demonstration of strong quadrature Einstein-Podolsky-Rosen entanglement and squeezing at very low noise sideband frequencies produced by a single type-II, self-phase-locked, frequency degenerate optical parametric oscillator below threshold. The generated two-mode squeezed vacuum state is preserved for noise frequencies as low as 50 kHz. Designing simple setups able to generate nonclassical states of light in the kHz regime is a key challenge for high sensitivity detection of ultraweak physical effects such as gravitational wave or small beam displacement.

Laurat, J.; Keller, G.; Treps, N.; Fabre, C. [Laboratoire Kastler Brossel, UPMC, Case 74, 4 place Jussieu, 75252 Paris Cedex 05 (France); Coudreau, T. [Laboratoire Kastler Brossel, UPMC, Case 74, 4 place Jussieu, 75252 Paris Cedex 05 (France); Laboratoire Materiaux et Phenomenes Quantiques, Universite Denis Diderot, 2 place Jussieu, 75251 Paris Cedex 05 (France)

2004-10-01

240

Anomalous diffusion for overdamped particles driven by cross-correlated white noise sources  

E-print Network

We study the statistical properties of overdamped particles driven by two cross-correlated multiplicative Gaussian white noises in a time-dependent environment. Using the Langevin and Fokker-Planck approaches, we derive the exact probability distribution function for the particle positions, calculate its moments and find their corresponding long-time, asymptotic behaviors. The generally anomalous diffusive regimes of the particles are classified, and their dependence on the friction coefficient and the characteristics of the noises is analyzed in detail. The asymptotic predictions are confirmed by exact solutions for two examples.

S. I. Denisov; A. N. Vitrenko; W. Horsthemke; P. Hänggi

2006-02-17

241

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

NASA Technical Reports Server (NTRS)

A finite difference formulation is presented for sound propagation in a rectangular two-dimensional duct without steady flow. Before the difference equations are formulated, the governing Helmholtz equation is first transformed to a form whose solution tends not to oscillate along the length of the duct. This transformation reduces the required number of grid points by an order of magnitude. Example solutions indicate that stepped noise source profiles have much higher attenuation than plane waves in a uniform impedance liner. Also, multiple stepped impedance liners are shown to have higher attenuation than uniform ducts if the impedances are chosen properly. For optimum noise reduction with axial variations in impedance, the numerical analysis indicates that for a plane wave input the resistance should be near zero at the entrance of a suppressor duct, while the reactance should be near the optimum value associated with the least-attenuated mode in a uniform duct.

Baumeister, K. J.

1975-01-01

242

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

NASA Astrophysics Data System (ADS)

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

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

243

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

E-print Network

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

Stutzmann, Eléonore

244

Combined Source Tracking and Noise Reduction for Application in Hearing Aids  

E-print Network

) the estimation of the direction of arrival (DOA) and thus for auto- matic beam-steering, (ii) a higher noise a direction of arrival (DOA) estimator in combination with a beam- former that automatically steers than beam- fomers with fixed look-direction for SNR values above -2 dB if the propagation model

245

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

USGS Publications Warehouse

A dynamic source model is presented, in which a 3-D crack containing a viscous compressible fluid is excited into resonance by an impulsive pressure transient applied over a small area DELTA S of the crack surface. The crack excitation depends critically on two dimensionless parameters called the crack stiffness and viscous damping loss. According to the model, the long-period event and harmonic tremor share the same source but differ in the boundary conditions for fluid flow and in the triggering mechanism setting up the resonance of the source, the former being viewed as the impulse response of the tremor generating system and the later representing the excitation due to more complex forcing functions.-from Author

Chouet, B.

1988-01-01

246

Noise group overview Avia0on Noise  

E-print Network

) · Sensi8vity analysis of trailing edge noise · Discrete Empirical Interpola8on Method) · Sensi8vity analysis of trailing edge noise · Discrete Empirical Interpola8on MethodNoise group overview #12;Avia0on Noise · Aircra& amongst the loudest sources

Wang, Wei

247

Spectral characterization of fully phase-matched high harmonics generated in a hollow waveguide for free-electron laser seeding  

NASA Astrophysics Data System (ADS)

We present a bright and coherent soft x-ray source based on high harmonic generation delivering up to 1010 photons per second centered at 120 eV within an 80 eV bandwidth. The source profits from fully phase-matched harmonic generation in an unmodulated hollow waveguide. Under these conditions, the resulting high harmonic spectrum is shown to be flat-top up to the cutoff photon energy and in line with the theoretical single-atom response. The source is characterized in view of seeding a free-electron laser and is shown to overcome the free-electron laser noise floor for wavelengths as short as 8.9 nm. This opens the perspective toward direct high harmonic seeding of a free-electron laser at soft x-ray wavelengths.

Ardana-Lamas, F.; Lambert, G.; Trisorio, A.; Vodungbo, B.; Malka, V.; Zeitoun, P.; Hauri, C. P.

2013-07-01

248

Auditory and Subjective Effects of Airborne Noise from Industrial Ultrasonic Sources  

PubMed Central

This investigation was undertaken primarily to examine the possibility of hearing damage from industrial ultrasonic equipment. In the factory concerned, ultrasonic washers and drills were used at a number of different locations, and girls working 12 ft (3·6 m.) away from one bank of three small washers complained of unpleasant subjective effects which included fatigue, persistent headaches, nausea, and tinnitus. As personnel working in the vicinity of similar washers in other parts of the factory did not complain of these effects, it seemed possible that the noise had been transmitted along a column of air in a bank of dryboxes. Enclosure of these washers by a sliding screen of Perspex had completely abated the trouble. Sound pressure level measurements taken in the positions occupied by the operators indicated that, when the effects occur, they are probably caused by high sound levels at the upper audio-frequencies present with the ultrasonic noise, and this was supported by a limited laboratory investigation. Audiometric investigation showed that hearing damage due to noise from these industrial ultrasonic devices is unlikely. However, extrapolations of currently accepted hearing damage risk criteria may be valid in predicting the occurrence of these subjective effects. Images PMID:6073088

Acton, W. I.; Carson, M. B.

1967-01-01

249

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

PubMed

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

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

2014-08-25

250

Non-harmonic root-pitch individual-blade control for the reduction of blade-vortex interaction noise in rotorcraft  

NASA Astrophysics Data System (ADS)

One of the greatest obstacles to public acceptance of rotorcraft is the high levels of noise they produce, particularly in low-speed descent. In this flight condition, the trailing edge vortex of one blade often passes in close proximity to other blades resulting in impulsive changes in lift. This Blade-Vortex Interaction (BVI) creates high levels of both noise and vibration. The objective of this dissertation is to evaluate the effectiveness of using physically motivated pulse-type Individual Blade Control for reducing the noise associated with the BVI. First, the major parameters that affect the severity of the interaction, such as vortex strength and blade-vortex miss-distance, are analyzed. Second, inputs designed specifically to alter the parameters previously identified as key are explored, resulting in elimination of advancing side noise and overall peak BVI Sound Pressure Level (BVISPL) reductions of up to 4.6 dB. Lastly, different feedback mechanisms for closed-loop control of IBC are examined to allow implementation of the developed inputs.

Malovrh, Brendon D.

251

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

SciTech Connect

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

Wernet, Philippe; Gaudin, Jerome; Godehusen, Kai; Schwarzkopf, Olaf; Eberhardt, Wolfgang [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin (Germany)

2011-06-15

252

The Alternative Low Noise Fan  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

253

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

254

Numerical evaluation of the performance of active noise control systems  

NASA Technical Reports Server (NTRS)

This paper presents a generalized numerical technique for evaluating the optimal performance of active noise controllers. In this technique, the indirect BEM numerical procedures are used to derive the active noise controllers for optimal control of enclosed harmonic sound fields where the strength of the noise sources 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 noise-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 noise controller.

Mollo, C. G.; Bernhard, R. J.

1990-01-01

255

Three-dimensional simulations of harmonic radiation and harmonic lasing  

SciTech Connect

Characteristics of the harmonic emission from free-electron lasers (FELs) are examined in the spontaneous, coherent-spontaneous and stimulated emission regimes. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. In the spontaneous emission regime, the transverse radiation patterns including the transverse frequency dependences, are given. How this expression is modified to include energy spread and emittance is described. In the coherent-spontaneous emission and stimulated emission regimes, the interaction of the radiation fields with the electrons must be treated self-consistently. Here, a single-frequency distributed transverse source function for each electron is used in the harmonic version of the 3-D code FELEX to model the harmonic radiation. The code has recently been modified to simultaneously model the fundamental and harmonic interactions for multiple-pass oscillator simulations. These modifications facilitate the examination of FELs under various operating conditions. When the FEL is lasing at the fundamental, the evolution of the harmonic fields can be examined. This evolution is unique in the sense that the electron beam radiates at the harmonic frequencies in the presence of the harmonic radiation circulating in the cavity. As a result, enhancements of the harmonic emission can be observed. Finally, harmonic lasing can occur in cases where there is sufficient gain to overcome cavity losses and lasing at the fundamental can be suppressed. The characteristics and efficiency of these interactions are explored. 11 refs., 9 figs.

Schmitt, M.J.; McVey, B.D.

1990-01-01

256

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

PubMed

Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the shear wave motion and give consistent shear wave speed measurements of the left ventricular myocardium while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index (BMI) higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve shear wave motion tracking and thus potentially facilitate more robust assessment of tissue elasticity by SWE. PMID:24021638

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

2013-09-01

257

2D DOA estimation with propagator method for correlated sources under unknown symmetric Toeplitz noise  

Microsoft Academic Search

The paper employs the propagator method (PM) to find two-dimensional (2D) direction of arrival angles (DOAs). The proposed algorithm can be applied to the situation when the incident sources are mixed, either with uncorrelated or fully correlated (coherent) sources. Like S. Pasad et al. (see IEEE Trans., vol.ASSP-36, no.5, p.631-41, 1988), we assume a symmetric Toeplitz covariance matrix for the

Nizar Tayem; Hyuck M. Kwon

2005-01-01

258

Evaluation of the interim measurement protocol for railway noise source description  

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

259

Helicopter rotor noise due to ingestion of atmospheric turbulence  

NASA Technical Reports Server (NTRS)

A theoretical study was conducted to develop an analytical prediction method for helicopter main rotor noise due to the ingestion of atmospheric turbulence. This study incorporates an atmospheric turbulence model, a rotor mean flow contraction model and a rapid distortion turbulence model which together determine the statistics of the non-isotropic turbulence at the rotor plane. Inputs to the combined mean inflow and turbulence models are controlled by atmospheric wind characteristics and helicopter operating conditions. A generalized acoustic source model was used to predict the far field noise generated by the non-isotropic flow incident on the rotor. Absolute levels for acoustic spectra and directivity patterns were calculated for full scale helicopters, without the use of empirical or adjustable constants. Comparisons between isotropic and non-isotropic turbulence at the rotor face demonstrated pronounced differences in acoustic spectra. Turning and contraction of the flow for hover and low speed vertical ascent cases result in a 3 dB increase in the acoustic spectrum energy and a 10 dB increase in tone levels. Compared to trailing edge noise, turbulence ingestion noise is the dominant noise mechanism below approximately 30 rotor harmonics, while above 100 harmonics, trailing edge noise levels exceed turbulence ingestion noise by 25 dB.

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

1986-01-01

260

Core noise source diagnostics on a turbofan engine using correlation and coherence techniques  

NASA Technical Reports Server (NTRS)

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 source region for acoustic propagation through the core nozzle and out to the far field. The relation between source 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 source term.

Karchmer, A. M.; Reshotko, M.

1976-01-01

261

Low kilovoltage cardiac dual-source CT: attenuation, noise, and radiation dose  

Microsoft Academic Search

The purpose of this study was to investigate the effect of low kilovoltage dual-source computed tomography coronary angiography\\u000a (CTCA) on qualitative and quantitative image quality parameters and radiation dose. Dual-source CTCA with retrospective ECG\\u000a gating was performed in 80 consecutive patients of normal weight. Forty were examined with a standard protocol (120 kV\\/330mAs),\\u000a 20 were examined at 100 kV\\/330mAs, and 20 at

Sebastian Leschka; Paul Stolzmann; Florian T. Schmid; Hans Scheffel; Bjoern Stinn; Borut Marincek; Hatem Alkadhi; Simon Wildermuth

2008-01-01

262

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

ERIC Educational Resources Information Center

This study relies on information theory, social presence, and source credibility to uncover what best helps people grasp the urgency of an emergency. We surveyed a random sample of 1,318 organizational members who received multiple notifications about a large-scale emergency. We found that people who received 3 redundant messages coming through at…

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

2013-01-01

263

Location of Multiple Coincident Noise Sources in the N.E. Atlantic, offshore Ireland.  

NASA Astrophysics Data System (ADS)

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 sources 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 source 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 source 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 source 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 source areas in the region.

Craig, David; Bean, Chris; Moni, Aishwarya; Lokmer, Ivan; Donne, Sarah

2014-05-01

264

Transmission characteristics of cyclotron harmonic waves in plasma  

Microsoft Academic Search

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

F. W. Crawford; H. H. Weiss

1966-01-01

265

A noise source identification technique using an inverse Helmholtz integral equation method  

NASA Technical Reports Server (NTRS)

A technique is developed which utilizes numerical models and field pressure information to characterize acoustic fields and identify acoustic sources. The numerical models are based on boundary element numerical procedures. Either pressure, velocity, or passive boundary conditions, in the form of impedance boundary conditions, may be imposed on the numerical model. Alternatively, if no boundary information is known, a boundary condition can be left unspecified. Field pressure data may be specified to overdetermine the numerical problem. The problem is solved numerically for the complete sound field from which the acoustic sources may be determined. The model can then be used to idenfify acoustic intensity paths in the field. The solution can be modified and the model used to evaluate design alternatives. In this investigation the method is tested analytically and verified. In addition, the sensitivity of the method to random and bias error in the input data is demonstrated.

Gardner, B. K.; Bernhard, R. J.

1988-01-01

266

Abstract -Substrate noise is the major source of performance limitation in mixed-signal integrated circuits. This paper studies  

E-print Network

stochastic model for the substrate noise is proposed. This model is then uti- lized to derive the phase noise profiles. However, since the resistivity of the heavily doped p+ substrate in a low epitaxial layer

Heydari, Payam

267

Harmonic Mixing with an Antiparallel Diode Pair  

Microsoft Academic Search

An analytical and experimental investigation of the properties of an antiparallel diode pair is presented. Such a configuration has the following unique and advantageous characteristics as a harmonic mixer: 1) reduced conversion loss by suppressing fundamental mixing products; 2) lower noise figure through suppression of local oscillator noise sidebands; 3) suppression of direct video detection; 4) inherent self protection against

MARVIN COHN; JAMES E. DEGENFORD; BURTON A. NEWMAN

1975-01-01

268

A note on the Strouhal number dependence of the relative importance of internal and external flow noise sources in IC engine exhaust systems  

NASA Astrophysics Data System (ADS)

This note discusses issues related to the estimation of flow noise emission from rear mufflers in IC engine exhaust systems, through the analysis of measurements performed in a steady cold flow bench. First, the net acoustic power transmitted along the outlet pipe is obtained from in-duct pressure measurements. The in-duct power is then compared with noise measurements carried out in a semianechoic chamber, in order to distinguish between flow noise contributions associated with internal generation (muffler and tailpipe) and flow noise produced in the discharge process (interaction between the outgoing flow and the outside atmosphere). The ratio between the tailpipe in-duct acoustic power and the radiated acoustic power is analysed as a function of the Strouhal number. The results provide some information about the relative importance of internal and external sources.

Torregrosa, A. J.; Broatch, A.; Climent, H.; Andrés, I.

2005-04-01

269

Measuring Noise Pollution  

NSDL National Science Digital Library

Through investigating the nature, sources and level of noise produced in their environment, students are introduced to the concept of noise pollution. They learn about the undesirable and disturbing effects of noise 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 noise level emitted by various sources. They are introduced to engineering concepts such as sensors, decibel (dB) measurements, and sound pressure used to measure the noise level. Students are introduced to impairments resulting from noise exposure such as speech interference, hearing loss, sleep disruption and reduced productivity. They identify potential noise pollution sources, and based on recorded data, they classify these sources into levels of annoyance. Students also explore the technologies designed by engineers to protect against the harmful effects of noise pollution.

AMPS GK-12 Program,

270

Noise-tolerance analysis for detection and reconstruction of absorbing inhomogeneities with diffuse optical tomography using single- and phase-correlated dual-source schemes  

NASA Astrophysics Data System (ADS)

An iterative reconstruction procedure is used to invert intensity data from both single- and phase-correlated dual-source illuminations for absorption inhomogeneities. The Jacobian for the dual source is constructed by an algebraic addition of the Jacobians estimated for the two sources separately. By numerical simulations, it is shown that the dual-source scheme performs superior to the single-source system in regard to (i) noise tolerance in data and (ii) ability to reconstruct smaller and lower contrast objects. The quality of reconstructions from single-source data, as indicated by mean-square error at convergence, is markedly poorer compared to their dual-source counterpart, when noise in data was in excess of 2%. With fixed contrast and decreasing inhomogeneity diameter, our simulations showed that, for diameters below 7 mm, the dual-source scheme has a higher percentage contrast recovery compared to the single-source scheme. Similarly, the dual-source scheme reconstructs to a higher percentage contrast recovery from lower contrast inhomogeneity, in comparison to the single-source scheme.

Kanmani, B.; Vasu, R. M.

2007-03-01

271

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

NASA Astrophysics Data System (ADS)

Extensive research by staff of the Solar Energy Research Institute and its subcontractors conducted to establish the origin and possible amelioration of acoustic disturbances associated with the operation of the DOE/NASA MOD-1 wind turbine installed in 1979 near Boone, North Carolina is summarized. Results have shown that the source of this acoustic annoyance was the transient, unsteady aerodynamic lift imparted to the turbine blades as they passed through the lee wakes of the large, cylindrical tower supports. Nearby residents were annoyed by the low-frequency, acoustic impulses propagated into the structures in which the complainants lived. The situation was aggravated further by a complex sound propagation process controlled by terrain and atmospheric focusing. Several techniques for reducing the abrupt, unsteady blade load transients were researched and are discussed.

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

1985-02-01

272

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

SciTech Connect

A compact, versatile device for VUV beam characterization is presented. It combines the functionalities of a VUV spectrometer and a VUV beam profiler in one unit and is entirely supported by a standard DN200 CF flange. The spectrometer employs a silicon nitride transmission nanograting in combination with a micro-channel plate based imaging detector. This enables the simultaneous recording of wavelengths ranging from 10 nm to 80 nm with a resolution of 0.25 nm to 0.13 nm. Spatial beam profiles with diameters up to 10 mm are imaged with 0.1 mm resolution. The setup is equipped with an in-vacuum translation stage that allows for in situ switching between the spectrometer and beam profiler modes and for moving the setup out of the beam. The simple, robust design of the device is well suited for non-intrusive routine characterization of emerging laboratory- and accelerator-based VUV light sources. Operation of the device is demonstrated by characterizing the output of a femtosecond high-order harmonic generation light source.

Kornilov, Oleg; Wilcox, Russell; Gessner, Oliver

2010-07-09

273

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

Microsoft Academic Search

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

Ned Mohan

1992-01-01

274

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

NASA Technical Reports Server (NTRS)

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

Mollo, Christopher G.; Bernhard, Robert J.

1987-01-01

275

Impact of Source/Drain Junction and Cell Shape on Random Telegraph Noise in NAND Flash Memory  

NASA Astrophysics Data System (ADS)

A comprehensive numerical study of threshold voltage fluctuation (?VT) in scaled NAND flash memory caused by random telegraph noise (RTN) and discrete dopant fluctuation (RDF) in both the channel and the cell-to-cell space [source/drain (S/D)] region was carried out. Following a three-dimensional (3D) Monte Carlo (MC) procedure, the statistical distribution of ?VT is estimated, considering the effects of both the random placement of discrete doping atoms and a discrete single trap at the tunnel oxide/substrate interface. The result demonstrates the significant influence of the doping in the S/D regions. For the cells with and without an S/D junction, the electron concentration in the S/D region is determined by the pass voltage of the unselected cell (Vpass) and the neighboring cell VT (VT(n)), owing to the fringing fields of neighboring floating gates (FGs). As a result, ?VT increases in the S/D region as Vpass - VT(n) decreases. The fluctuation amplitude strongly depends on the [single-trap RTN] position along the cell length (L) and width (W) directions. For the cell shape with rounding of the active area (AA) at the shallow trench isolation (STI) edge, the results indicate that the high ?VT area moves from the AA edge towards the center area along the W-direction.

Li, Fu-Hai; Shirota, Riichiro

2013-07-01

276

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

277

A series LC filter for harmonic compensation of AC drives  

Microsoft Academic Search

This paper characterizes typical nonlinear loads into two types of harmonic sources-harmonic current source and harmonic voltage source-which produce inherent current and voltage distortion, respectively. The conventional approach of harmonic compensation has been the parallel (or shunt) LC filter in which shunt low impedance branches traditionally consisting of 5th and 7th tuned LC series resonant and high-pass circuitry are connected

Fang Z. Peng; Gui-Jia Su; George Farquharson

1999-01-01

278

Harmonic engine  

DOEpatents

A high efficiency harmonic engine based on a resonantly reciprocating piston expander that extracts work from heat and pressurizes working fluid in a reciprocating piston compressor. The engine preferably includes harmonic oscillator valves capable of oscillating at a resonant frequency for controlling the flow of working fluid into and out of the expander, and also preferably includes a shunt line connecting an expansion chamber of the expander to a buffer chamber of the expander for minimizing pressure variations in the fluidic circuit of the engine. The engine is especially designed to operate with very high temperature input to the expander and very low temperature input to the compressor, to produce very high thermal conversion efficiency.

Bennett, Charles L. (Livermore, CA)

2009-10-20

279

Intrinsic and extrinsic 1/f noise sources in proton-irradiated n-GaAs epitaxial layers  

NASA Astrophysics Data System (ADS)

The low-frequency resistance noise of proton-irradiated n-GaAs epitaxial layers was studied at temperatures from 77 to 300 K. Two types of 1/f noise were identified from the temperature dependence of the 1/f noise parameter ?. One type of 1/f noise that is dominating at high temperatures seems to be of intrinsic origin related to lattice phonon scattering. The other dominating one at lower temperatures is, then, of extrinsic origin induced by the irradiation. The extrinsic type of 1/f noise is consistent with the quantum ``local-interference'' effect and can reasonably be described by the Dutta-Dimon-Horn model [P. Dutta and P. M. Horn, Rev. Mod. Phys. 53, 497 (1981)].

Ren, L.

1993-10-01

280

Inductively coupled plasma spectrometry: Noise characteristics of aerosols, application of generalized standard additions method, and Mach disk as an emission source  

SciTech Connect

This dissertation is focused on three problem areas in the performance of inductively coupled plasma (ICP) source. The noise characteristics of aerosols produced by ICP nebulizers are investigated. A laser beam is scattered by aerosol and detected by a photomultiplier tube and the noise amplitude spectrum of the scattered radiation is measured by a spectrum analyzer. Discrete frequency noise in the aerosol generated by a Meinhard nebulizer or a direct injection nebulizer is primarily caused by pulsation in the liquid flow from the pump. A Scott-type spray chamber suppresses white noise, while a conical, straight-pass spray chamber enhances white noise, relative to the noise seen from the primary aerosol. Simultaneous correction for both spectral interferences and matrix effects in ICP atomic emission spectrometry (AES) can be accomplished by using the generalized standard additions method (GSAM). Results obtained with the application of the GSAM to the Perkin-Elmer Optima 3000 ICP atomic emission spectrometer are presented. The echelle-based polychromator with segmented-array charge-coupled device detectors enables the direct, visual examination of the overlapping lines Cd (1) 228.802 nm and As (1) 228.812 nm. The slit translation capability allows a large number of data points to be sampled, therefore, the advantage of noise averaging is gained. An ICP is extracted into a small quartz vacuum chamber through a sampling orifice in a water-cooled copper plate. Optical emission from the Mach disk region is measured with a new type of echelle spectrometer equipped with two segmented-array charge-coupled-device detectors, with an effort to improve the detection limits for simultaneous multielement analysis by ICP-AES.

Shen, Luan

1995-10-06

281

Noise Meter  

MedlinePLUS

... Programs NIOSH NOISE AND HEARING LOSS PREVENTION Noise Meter Play around with the Noise Meter and hear the different sounds and sound intensities ... newer version of Adobe Flash Player. Download Noise Meter (.exe file) Download and play the Noise Meter ...

282

A source of illumination for low-noise ‘Violin-Mode’ shadow sensors, intended for use in interferometric gravitational wave detectors  

NASA Astrophysics Data System (ADS)

A low-noise source of illumination is described for shadow sensors having a displacement sensitivity of (69? ± ?13) picometres (rms)/?Hz, at 500?Hz, over a measuring span of ±0.1?mm. These sensors were designed to detect ‘Violin-Mode’ resonances in the suspension fibres of the test-masses/mirrors for the Advanced LIGO (Laser Interferometer Gravitational wave Observatory) gravitational wave detectors. The source of illumination (emitter) described here used a single column of 8 × miniature near infrared LEDs (? = 890?nm). These emitters cast the shadows of 400??m diameter fused silica suspension fibres onto their complementary shadow-displacement detectors, located at a distance of 74 fibre diameters (29.6?mm) behind the axes of the fibres themselves. Violin-Mode vibrations of each fibre were sensed as differential ac photocurrents in the corresponding ‘split-photodiode’ detector. This paper describes the design, construction, noise analysis, and measures that were taken in the conception of the emitters, in order to produce high-contrast shadows at such distant detectors. In this way it proved possible to obtain, simultaneously, a very high transfer sensitivity to Violin-Mode vibration of the fibres, and a very low level of detection noise—close to the fundamental shot noise limit—whilst remaining within the constraints of this simple design of emitter. The shadow detector is described in an accompanying paper.

Lockerbie, N. A.; Tokmakov, K. V.; Strain, K. A.

2014-12-01

283

Underwater noise of small personal watercraft (jet skis).  

PubMed

Personal watercraft (water scooters, jet skis) were recorded under water in Bramble Bay, Queensland, Australia. Underwater noise emissions consisted of broadband energy between 100 Hz and 10 kHz due to the vibrating bubble cloud generated by the jet stream, overlain with frequency-modulated tonals corresponding to impeller blade rates and harmonics. Broadband monopole source levels were 149, 137, and 122 dB re 1 ?Pa @ 1 m (5th, 50th, and 95th percentiles). Even though these are lower than those of small propeller-driven boats, it is not necessarily the broadband source level that correlates with the bioacoustic impact on marine fauna. PMID:23556699

Erbe, Christine

2013-04-01

284

Fourth Aircraft Interior Noise Workshop  

NASA Technical Reports Server (NTRS)

The fourth in a series of NASA/SAE Interior Noise Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft noise with emphasis on source noise prediction; cabin noise prediction; cabin noise control, including active and passive methods; and cabin interior noise procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues.

Stephens, David G. (compiler)

1992-01-01

285

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

Microsoft Academic Search

A three-dimensional quasi-steady full-potential rotor-flow-analysis program, called ROT22 developed at NASA Ames Research Center is run in conjunction with Farassat's (1981) helicopter-noise-prediction code to assess the thickness and loading noises made by a rotor blade. As a model example, the case of a 1\\/7th UH-1H NACA-0012-profile straight nonlifting rotor blade in hover is studied. Results for tip Mach numbers ranging

H. R. Aggarwal

1984-01-01

286

Reduction of helicopter blade-vortex interaction noise by active rotor control technology  

NASA Astrophysics Data System (ADS)

Helicopter blade-vortex interaction noise is one of the most severe noise sources and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor blade-vortex interaction noise and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor blade-vortex interaction noise reduction, including higher harmonic pitch control, individual blade control, and on-blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of noise reduction mechanism and controlling aerodynamic or structural parameters of a blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations.

Yu, Yung H.; Gmelin, Bernd; Splettstoesser, Wolf; Philippe, Jean J.; Prieur, Jean; Brooks, Thomas F.

287

Reduction of Helicopter Blade-Vortex Interaction Noise by Active Rotor Control Technology  

NASA Technical Reports Server (NTRS)

Helicopter blade-vortex interaction noise is one of the most severe noise sources and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor blade-vortex interaction noise and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor blade vortex interaction noise reduction, including higher harmonic pitch control, individual blade control, and on-blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of noise reduction mechanism and controlling aerodynamic or structural parameters of a blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations, Published by Elsevier Science Ltd.

Yu, Yung H.; Gmelin, Bernd; Splettstoesser, Wolf; Brooks, Thomas F.; Philippe, Jean J.; Prieur, Jean

1997-01-01

288

Harmonics and Fourier Series Model  

NSDL National Science Digital Library

The Ejs Harmonics and Fourier Series model displays the sum of harmonics via a Fourier series to yield a new wave. The amplitude of each harmonic as well as the phase of that harmonic 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 Harmonics 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_harmonics.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for classical mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Aguirregabiria, Juan

2008-11-11

289

Harmonic engine  

DOEpatents

An engine based on a reciprocating piston engine that extracts work from pressurized working fluid. The engine includes a harmonic oscillator inlet valve capable of oscillating at a resonant frequency for controlling the flow of working fluid into of the engine. In particular, the inlet valve includes an inlet valve head and a spring arranged together as a harmonic oscillator so that the inlet valve head is moveable from an unbiased equilibrium position to a biased closed position occluding an inlet. Upon releasing the inlet valve the inlet valve head undergoes a single oscillation past the equilibrium positio to a maximum open position and returns to a biased return position close to the closed position to choke the flow and produce a pressure drop across the inlet valve causing the inlet valve to close. Protrusions carried either by the inlet valve head or piston head are used to bump open the inlet valve from the closed position and initiate the single oscillation of the inlet valve head, and protrusions carried either by the outlet valve head or piston head are used to close the outlet valve ahead of the bump opening of the inlet valve.

Bennett, Charles L.; Sewall, Noel; Boroa, Carl

2014-08-19

290

Computation of rotor wake turbulence noise  

Microsoft Academic Search

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

M. Nallasamy; E. Envia

2005-01-01

291

Aircraft noise prediction program theoretical manual, part 2  

NASA Technical Reports Server (NTRS)

Detailed prediction methods for specific aircraft noise sources are given. These sources are airframe noise, combustion noise, fan noise, single and dual stream jet noise, and turbine noise. Modifications to the NASA methods which comply with the International Civil Aviation Organization standard method for aircraft noise prediction are given.

Zorumski, W. E.

1982-01-01

292

Aircraft interior noise reduction by alternate resonance tuning  

NASA Astrophysics Data System (ADS)

Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at lower frequencies, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is being studied which considers aircraft fuselage lined with panels alternately tuned to frequencies above and below the frequency that must be attenuated. Adjacent panels would oscillate at equal amplitude, to give equal source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to become cutoff, and therefore be non-propagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is currently being investigated both theoretically and experimentally. This new concept has potential application to reducing interior noise due to the propellers in advanced turboprop aircraft as well as for existing aircraft configurations.

Bliss, Donald B.; Gottwald, James A.; Srinivasan, Ramakrishna; Gustaveson, Mark B.

1990-08-01

293

All solid-state 191.7 nm deep-UV light source by seventh harmonic generation of an 888 nm pumped, Q-switched 1342 nm Nd:YVO? laser with excellent beam quality.  

PubMed

In this paper we report on the realization of a deep-UV light source using the 1.3 ?m transition of neodymium as pumping wavelength. The 191.7 nm radiation was obtained by generating the seventh harmonic of a high-power Q-switched 1342 nm Nd:YVO4 laser. A cesium lithium borate crystal was used for sum frequency mixing of the sixth harmonic and the fundamental. With a total of four conversion stages, up to 240 mW were achieved, with excellent beam quality at 155 mW (M2 < 1.7) and 190 mW (M2 < 1.9). PMID:24921559

Koch, Peter; Bartschke, Juergen; L'huillier, Johannes A

2014-06-01

294

Enhancing tidal harmonic analysis: Robust (hybrid L1 ) solutions  

E-print Network

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

Jay, David

295

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

E-print Network

of anthropogenic noise on marine life is a worldwide concern that has been the object of several reviews recently). Such a broad band covers the hearing sensitivity and communication bands of several marine organisms in Saguenay­St. Lawrence Marine Park hub Ce´dric Gervaise GIPSA-Lab, Dept. Image-Signal, 11 rue des Mathe

Paris-Sud XI, Université de

296

Measurement of Terrestrial Radio Noise  

Microsoft Academic Search

The terrestrial noise experiment on the Ariel III satellite is designed to measure the radio noise from lighting discharges, and to deduce the distribution of the sources. The measurements are made at high frequencies; at optimum frequencies the noise penetrates the ionosphere only at near vertical incidence and the sources can therefore be localized. The receivers operate in narrow bandwidths

F. Horner; R. B. Bent

1969-01-01

297

Discrete-frequency radiated noise and unsteady rotor force from a subsonic axial flow fan  

NASA Astrophysics Data System (ADS)

Noise radiated by a subsonic, axial-flow fan at its rotational frequency and harmonics is related to the non-steady force field created at the rotor blade/fluid interface. This unsteady field is highly dependent on the time-invariant flow distortions that enter the fan. In this study, a typical cooling fan used in the electronic industry was instrumented with a shaft unsteady axial force sensor. Its output is proportional to the total unsteady axial force created by the rotor. On-axis sound pressure levels were measured and compared to coherent output power spectra involving the unsteady force sensor and the microphone. Very good coherence at the discrete tones is observed. The fan's inflow field was systematically distorted by placing a small cylinder at various positions in the inlet plane. The non-uniform, 3-D flow field entering the rotor was measured by traversing a set of miniature five-hole pressure probes. The total pressure outputs from this probe can be related to the axial, tangential, and radial velocity vectors. Fourier decomposition of the inflow velocity data is coupled with analysis to give information on the unsteady rotor force harmonic content. A simplified Curle's equation was then used to compute the discrete-frequency radiated noise at the Blade Passage Frequency (BPF) and its harmonics. The predicted and measured noise levels are in close agreement at the BPF and the first harmonic when the fan is a compact source.

Chiu, Wen-Shyang; Lauchle, G. C.; Thompson, D. E.

1988-07-01

298

A statistical evaluation of effective time constants of random telegraph noise with various operation timings of in-pixel source follower transistors  

NASA Astrophysics Data System (ADS)

We evaluated effective time constants of random telegraph noise (RTN) with various operation timings of in-pixel source follower transistors statistically, and discuss the dependency of RTN time constants on the duty ratio (on/off ratio) of MOSFET which is controlled by the gate to source voltage (VGS). Under a general readout operation of CMOS image sensor (CIS), the row selected pixel-source followers (SFs) turn on and not selected pixel-SFs operate at different bias conditions depending on the select switch position; when select switch locate in between the SF driver and column output line, SF drivers nearly turn off. The duty ratio and cyclic period of selected time of SF driver depends on the operation timing determined by the column read out sequence. By changing the duty ratio from 1 to 7.6 x 10-3, time constant ratio of RTN (time to capture noise reduction, detection and analysis of in pixel-SF with RTN.

Yonezawa, A.; Kuroda, R.; Teramoto, A.; Obara, T.; Sugawa, S.

2014-03-01

299

High noise immunity one shot  

NASA Technical Reports Server (NTRS)

Multivibrator circuit, which includes constant current source, isolates line noise from timing circuitry and field effect transistor controls circuit's operational modes. Circuit has high immunity to supply line noise.

Schaffer, G. L.

1972-01-01

300

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

NASA Technical Reports Server (NTRS)

The NASA Glenn Research Center's Advanced Noise Control Fan (ANCF) was developed in the early 1990s to provide a convenient test bed to measure and understand fan-generated acoustics, duct propagation, and radiation to the farfield. A series of tests were performed primarily for the use of code validation and tool validation. Rotating Rake mode measurements were acquired for parametric sets of: (i) mode blockage, (ii) liner insertion loss, (iii) short ducts, and (iv) mode reflection.

Sutliff, Daniel L.

2014-01-01

301

An experimental investigation of the sources of propeller noise due to the ingestion of turbulence at low speeds  

Microsoft Academic Search

Noise radiation from a four bladed, 10 in. diameter propeller operating in air at a rotational speed of 3000 RPM and a freestream velocity of 33 ft\\/s was experimentally analyzed using hot-wire and microphone measurements in an anechoic wind tunnel. Turbulence levels from 0.2 to 5.5% at the propeller location were generated by square-mesh grids upstream of the propeller. Autobicoherence

D. F. Scharpf; T. J. Mueller

1995-01-01

302

Approximations to camera sensor noise  

NASA Astrophysics Data System (ADS)

Noise is present in all image sensor data. Poisson distribution is said to model the stochastic nature of the photon arrival process, while it is common to approximate readout/thermal noise by additive white Gaussian noise (AWGN). Other sources of signal-dependent noise such as Fano and quantization also contribute to the overall noise profile. Question remains, however, about how best to model the combined sensor noise. Though additive Gaussian noise with signal-dependent noise variance (SD-AWGN) and Poisson corruption are two widely used models to approximate the actual sensor noise distribution, the justification given to these types of models are based on limited evidence. The goal of this paper is to provide a more comprehensive characterization of random noise. We concluded by presenting concrete evidence that Poisson model is a better approximation to real camera model than SD-AWGN. We suggest further modification to Poisson that may improve the noise model.

Jin, Xiaodan; Hirakawa, Keigo

2013-02-01

303

Prediction of airframe noise  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

304

Core-Noise  

NASA Technical Reports Server (NTRS)

This presentation is a technical progress report and near-term outlook for NASA-internal and NASA-sponsored external work on core (combustor and turbine) noise funded by the Fundamental Aeronautics Program Subsonic Fixed Wing (SFW) Project. Sections of the presentation cover: the SFW system level noise metrics for the 2015, 2020, and 2025 timeframes; the emerging importance of core noise and its relevance to the SFW Reduced-Noise-Aircraft Technical Challenge; the current research activities in the core-noise area, with some additional details given about the development of a high-fidelity combustion-noise prediction capability; the need for a core-noise diagnostic capability to generate benchmark data for validation of both high-fidelity work and improved models, as well as testing of future noise-reduction technologies; relevant existing core-noise tests using real engines and auxiliary power units; and examples of possible scenarios for a future diagnostic facility. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The SFW Reduced-Noise-Aircraft Technical Challenge aims to enable concepts and technologies to dramatically reduce the perceived aircraft noise outside of airport boundaries. This reduction of aircraft noise is critical for enabling the anticipated large increase in future air traffic. Noise generated in the jet engine core, by sources such as the compressor, combustor, and turbine, can be a significant contribution to the overall noise signature at low-power conditions, typical of approach flight. At high engine power during takeoff, jet and fan noise have traditionally dominated over core noise. However, current design trends and expected technological advances in engine-cycle design as well as noise-reduction methods are likely to reduce non-core noise even at engine-power points higher than approach. In addition, future low-emission combustor designs could increase the combustion-noise component. The trend towards high-power-density cores also means that the noise generated in the low-pressure turbine will likely increase. Consequently, the combined result from these emerging changes will be to elevate the overall importance of turbomachinery core noise, which will need to be addressed in order to meet future noise goals.

Hultgren, Lennart S.

2010-01-01

305

Rotorcraft noise  

NASA Technical Reports Server (NTRS)

The establishment of a realistic plan for NASA and the U.S. helicopter industry to develop a design-for-noise methodology, including plans for the identification and development of promising noise reduction technology was discussed. Topics included: noise reduction techniques, scaling laws, empirical noise prediction, psychoacoustics, and methods of developing and validing noise prediction methods.

Huston, R. J. (compiler)

1982-01-01

306

Nonlinearly driven harmonics of Alfvén modes  

SciTech Connect

In order to study the leading order nonlinear magneto-hydrodynamic (MHD) harmonic response of a plasma in realistic geometry, the AEGIS code has been generalized to account for inhomogeneous source terms. These source terms are expressed in terms of the quadratic corrections that depend on the functional form of a linear MHD eigenmode, such as the Toroidal Alfvén Eigenmode. The solution of the resultant equation gives the second order harmonic response. Preliminary results are presented here.

Zhang, B., E-mail: bozhang@austin.utexas.edu; Breizman, B. N.; Zheng, L. J.; Berk, H. L. [Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States)] [Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States)

2014-01-15

307

Simulated flight effects on noise characteristics of a fan inlet with high throat Mach number  

NASA Technical Reports Server (NTRS)

An anechoic wind tunnel experiment was conducted to determine the effects of simulated flight on the noise characteristics of a high throat Mach number fan inlet. Comparisons were made with the performance of a conventional low throat Mach number inlet with the same 50.8 cm fan noise source. Simulated forward velocity of 41 m/sec reduced perceived noise levels for both inlets, the largest effect being more than 3 db for the high throat Mach number inlet. The high throat Mach number inlet was as much as 7.5 db quieter than the low throat Mach number inlet with tunnel airflow and about 6 db quieter without tunnel airflow. Effects of inlet flow angles up to 30 deg were seemingly irregular and difficult to characterize because of the complex flow fields and generally small noise variations. Some modifications of tones and directivity at blade passage harmonics resulting from inlet flow angle variation were noted.

Wesoky, H. L.; Dietrich, D. A.; Abbott, J. M.

1978-01-01

308

Noise in biological circuits  

Microsoft Academic Search

Noise biology focuses on the sources, processing, and biological consequences of the inherent stochastic fluctuations in molecular transitions or interactions that control cellular behavior. These fluctuations are especially pronounced in small systems where the magnitudes of the fluctuations approach or exceed the mean value of the molecular population. Noise biology is an essential component of nanomedicine where the communication of

Michael L. Simpson; Michael S. Allen; Chris D. Cox; Roy D. Dar; David K Karig; John F. Cooke

2009-01-01

309

High order harmonic generation in rare gases  

SciTech Connect

The process of high order harmonic generation in atomic gases has shown great promise as a method of generating extremely short wavelength radiation, extending far into the extreme ultraviolet (XUV). The process is conceptually simple. A very intense laser pulse (I {approximately}10{sup 13}-10{sup 14} W/cm{sup 2}) is focused into a dense ({approximately}10{sup l7} particles/cm{sup 3}) atomic medium, causing the atoms to become polarized. These atomic dipoles are then coherently driven by the laser field and begin to radiate at odd harmonics of the laser field. This dissertation is a study of both the physical mechanism of harmonic generation as well as its development as a source of coherent XUV radiation. Recently, a semiclassical theory has been proposed which provides a simple, intuitive description of harmonic generation. In this picture the process is treated in two steps. The atom ionizes via tunneling after which its classical motion in the laser field is studied. Electron trajectories which return to the vicinity of the nucleus may recombine and emit a harmonic photon, while those which do not return will ionize. An experiment was performed to test the validity of this model wherein the trajectory of the electron as it orbits the nucleus or ion core is perturbed by driving the process with elliptically, rather than linearly, polarized laser radiation. The semiclassical theory predicts a rapid turn-off of harmonic production as the ellipticity of the driving field is increased. This decrease in harmonic production is observed experimentally and a simple quantum mechanical theory is used to model the data. The second major focus of this work was on development of the harmonic {open_quotes}source{close_quotes}. A series of experiments were performed examining the spatial profiles of the harmonics. The quality of the spatial profile is crucial if the harmonics are to be used as the source for experiments, particularly if they must be refocused.

Budil, K.S.

1994-05-01

310

A near-IR variability study of the Galactic black hole: a red noise source with no detected periodicity  

E-print Network

We present the results of near-infrared (2 and 3 microns) monitoring of Sgr A*-IR with 1 min time sampling using the natural and laser guide star adaptive optics (LGS AO) system at the Keck II telescope. Sgr A*-IR was observed continuously for up to three hours on each of seven nights, between 2005 July and 2007 August. Sgr A*-IR is detected at all times and is continuously variable, with a median observed 2 micron flux density of 0.192 mJy, corresponding to 16.3 magnitude at K'. These observations allow us to investigate Nyquist sampled periods ranging from about 2 minutes to an hour. Using Monte Carlo simulations, we find that the variability of Sgr A* in this data set is consistent with models based on correlated noise with power spectra having frequency dependent power law slopes between 2.0 to 3.0, consistent with those reported for AGN light curves. Of particular interest are periods of ~20 min, corresponding to a quasi-periodic signal claimed based upon previous near-infrared observations and interpreted as the orbit of a 'hot spot' at or near the last stable orbit of a spinning black hole. We find no significant periodicity at any time scale probed in these new observations for periodic signals. This study is sensitive to periodic signals with amplitudes greater than 20% of the maximum amplitude of the underlying red noise component for light curves with duration greater than ~2 hours at a 98% confidence limit.

Tuan Do; Andrea M. Ghez; Mark R. Morris; Sylvana Yelda; Leo Meyer; Jessica R. Lu; Seth D. Hornstein; Keith Matthews

2008-10-02

311

Simple Harmonic Motion in Harmonic Plane Waves.  

ERIC Educational Resources Information Center

Discusses the distribution of kinetic and potential energy in transverse and longitudinal waves and examines the transmission of power and momentum. This discussion is intended to aid in understanding the simple harmonic motion of a particle involved in the propagation of a harmonic mechanical plane wave. (HM)

Benumof, Reuben

1980-01-01

312

Evaluation of the annoyance due to helicopter rotor noise  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

313

Noise equivalent circuit of a semiconductor laser diode  

NASA Technical Reports Server (NTRS)

A small-signal model of a semiconductor laser is extended to include the effects of intrinsic noise by adding current and voltage noise sources. The current noise source represents the shot noise of carrier recombination, while the voltage noise source represents the random process of simulated emission. The usefulness of the noise equivalent circuit is demonstrated by calculating the modulation and noise characteristics of a current-driven diode as a function of bias current and frequency.

Harder, C.; Margalit, S.; Yariv, A.; Katz, J.; Shacham, J.

1982-01-01

314

Urban Noise Protection  

NASA Astrophysics Data System (ADS)

Noise belongs to the severest environmental impairments in towns, with road traffic being the most annoying noise source. The reduction of these impairments and the precaution against new noise impacts is an important task of the communities. However, many of the potential abatement measures are not in the responsibility of the communities. In most European countries, noise emission regulations for road and rail vehicles and outdoor machinery are nowadays enforced by the European Union. Noise reception limits are generally enforced by national laws. Therefore, efficient noise abatement in towns has to be coordinated with the regional, national and supranational, i.e. European noise policy. The most important fields of action for the urban noise abatement are the roads, railways and airports with heavy traffic. For the avoidance of health risks due to noise here short-term reductions are needed, which can generally be achieved only by a combination of measures for which different stakeholders are responsible. This underlines the importance of integrated and coordinated noise abatement concepts.

Jäcker-Cüppers, Michael

315

The effects of noise on man  

SciTech Connect

As a reference source of research concerning effects of noise on people, this book reports and analyzes procedures used in regulation and control of noise. Quantitative relations are formed between physical measures of environmental noise and the reactions of people and communities to noise. The author reviews scientific and engineering research published from 1970 to the present. The Effects of Noise on Man, Second Edition discusses: adverse effects of noise and noise-induced hearing loss on speech communications; damage to hearing from ''everyday'' noise; damage to hearing from industrial noise and gunfire; work performance in noise; effects of noise on non-auditory systems of the body and sleep; aircraft and street traffic noise and its effects on health, annoyance, and house depreciation; physical measurements used for the assessment and control of environmental noise; federal standards and guidelines for community noise and proposed modification based on recent research findings.

Kryter, K.D.

1985-01-01

316

Noise from a vibrating propeller  

NASA Astrophysics Data System (ADS)

This paper is concerned with an analytical study of the noise from a vibrating propeller. The influence of airfoil thickness and of steady loading are also included to provide a basis for comparison. The analysis was based on the concept of distributing sources and doublets on the surface of the blade, which were multiplied by their appropriate strength factors. The noise in the plane of the propeller was dominated by the thickness noise. Moving the observer's position to the propeller axis, the thickness noise and loading noise were zero, and a pure sinusoidal noise was found, caused by the vibrations of the propeller.

Runyan, H. L.

1980-06-01

317

Polynomial Harmonic Morphisms Martin Svensson  

E-print Network

Polynomial Harmonic Morphisms Martin Svensson Examensarbete, 20 poang Lunds Universitet November Chapter 2. Harmonic Maps 13 1. The Second Fundamental Form 13 2. Harmonic Maps 18 3. Harmonic Functions 25 Chapter 3. Harmonic Morphisms 29 1. Horizontal Conformality 29 2. Harmonic Morphisms 33 3. The Existence

Gudmundsson, Sigmundur

318

Third Harmonic Mechanism in Complex Plasmonic Fano Structures  

PubMed Central

We perform third harmonic spectroscopy of dolmen-type nanostructures, which exhibit plasmonic Fano resonances in the near-infrared. Strong third harmonic emission is predominantly radiated close to the low energy peak of the Fano resonance. Furthermore, we find that the third harmonic polarization of the subradiant mode interferes destructively and diminishes the nonlinear signal in the far-field. By comparing the experimental third harmonic spectra with finite element simulations and an anharmonic oscillator model, we find strong indications that the source of the third harmonic is the optical nonlinearity of the bare gold enhanced by the resonant plasmonic polarization.

2014-01-01

319

SEVENTH HARMONIC 20 GHz CO-GENERATOR  

SciTech Connect

To satisfy the need for multi-MW rf sources in frequency ranges where commercial sources do not exist, a study was undertaken on a class of devices based on gyro-harmonic frequency multiplication. This mechanism relies upon adding energy in gyrating motion to a linear electron beam that traverses a rotating-mode TE111-mode drive cavity in a dc magnetic field. The beam then drifts along the magnetic field into a second cavity, operating in the TEn11-mode tuned to the nth harmonic of the drive cavity. Studies of this configuration have been carried out for 2 < n < 7. Results are given for multi-MW, efficient operation of a 7th harmonic device operating at 20 GHz, and a 2nd harmonic device operating at 22.4 GHz.

Hirshfield, Jay L

2014-04-08

320

Harmonic power flow for unbalanced systems  

SciTech Connect

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

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

1993-10-01

321

An online cross-scatter correction algorithm for dual-source CT: effects on CT number accuracy and noise  

Microsoft Academic Search

Dual-source computed tomography (CT) utilizes two x-ray tubes and two detectors simultaneously for the purpose of obtaining 83 msec temporal resolution, 160 kW of x-ray power reserve, or dual-kV (dual-energy) scan capabilities. One inherent constraint of such a design is cross-scatter radiation, which occurs when x-rays from tube A are scattered by the patient and detected by detector B, or

Christian D. Eusemann; Anja Apel; Bernhard Schmidt; Alisa I. Walz-Flannigan; Megan C. Jacobsen; Karl Stierstorfer; Thomas G. Flohr; Cynthia H. McCollough

2009-01-01

322

Synchronization transitions in ensembles of noisy oscillators with bi-harmonic coupling  

E-print Network

We describe synchronization transitions in an ensemble of globally coupled phase oscillators with a bi-harmonic coupling function, and two sources of disorder - diversity of intrinsic oscillatory frequencies and external independent noise. Based on the self-consistent formulation, we derive analytic solutions for different synchronous states. We report on various non-trivial transitions from incoherence to synchrony where possible scenarios include: simple supercritical transition (similar to classical Kuramoto model), subcritical transition with large area of bistability of incoherent and synchronous solutions, and also appearance of symmetric two-cluster solution which can coexist with regular synchronous state. Remarkably, we show that the interplay between relatively small white noise and finite-size fluctuations can lead to metastable asynchronous solution.

Vladimir Vlasov; Maxim Komarov; Arkady Pikovsky

2014-11-12

323

Impact of SiGe source/drain induced-compressive strain on low frequency noise in high-k/metal gate p-channel metal-oxide-semiconductor transistors  

NASA Astrophysics Data System (ADS)

In this paper, the properties of dielectric traps induced by SiGe source/drain (SiGe S/D) induced-compressive stress in high-k/metal gate (HK/MG) p-channel metal-oxide-semiconductor field-effect transistors are demonstrated using random telegraph noise (RTN) and 1/f noise analysis. The correlation between RTN and the 1/f noise parameters is presented. Compared with the control devices, the SiGe S/D HK/MG devices show trap positions that are closer to the SiO2 interfacial layer/Si channel, corresponding to a reduced average tunneling attenuation length (?), and dominate the lower 1/f noise power spectrum.

Lein Wu, San; Tsai, Kai-Shiang; Cheng, Osbert

2013-10-01

324

Intrinsic noise in locust photoreceptors.  

PubMed Central

1. In locust photoreceptors, the amplitude of the response to light pulses lasting less than 20 ms depends solely upon the number of absorbed photons, which can be estimated at low intensities by counting quantum bumps. Consequently, each receptor can be operated as a calibrated photon counter. 2. Three types of noise in receptor responses have been identified--extrinsic or photon noise and two types of intrinsic noise, dark noise (spontaneous activity) and transducer noise (noise in the transduction mechanism). The methods by which the noise sources are measured and identified involves measuring the responses to a train of flashes of constant intensity and converting these voltage values into a series of equivalent quantum catches. Because photon absorptions follow the Poisson distribution, the variance among equivalent catches due to photon noise equals the mean catch, and any excess variance represents intrinsic noise. 3. Dark noise is negligible: spontaneous signals (quantum bumps produced in darkness) occur less than ten times per hour at 25 degrees C, and the combined effects of membrane and electrode noise are unimportant at all but the highest intensities. 4. At low intensities transducer noise is responsible for more than 50% of all receptor noise (variance), and this rises to 90% when bright stimuli are presented to the dark-adapted eye. 5. Two simple models of transduction indicate that variations in the amplitudes and latencies of responses to single photons are a major source of transducer noise. 6. Transducer noise would be difficult to detect from an analysis of response noise alone, without knowledge of absolute photon catch, because in some important respects it mimics photon noise, e.g. it lowers the quantum efficiency without violating the square root relationship relating increment thresholds to mean intensity. PMID:7153928

Laughlin, S B; Lillywhite, P G

1982-01-01

325

When is the product of two planar harmonic mappings harmonic?  

E-print Network

When is the product of two planar harmonic mappings harmonic? Raymond Mortini Lecturas Matem´aticas Volumen 23 (2002), p´aginas 5­10 Abstract. We determine all complex-valued harmonic functions u and v defined on a planar domain for which uv, respectively u2 - v2 is harmonic Key words and phrases. Harmonic

Mortini, Raymond

326

Turbomachinery noise  

NASA Technical Reports Server (NTRS)

Summarized here are key advances in experimental techniques and theoretical applications which point the way to a broad understanding and control of turbomachinery noise. On the experimental side, the development of effective inflow control techniques makes it possible to conduct, in ground based facilities, definitive experiments in internally controlled blade row interactions. Results can now be valid indicators of flight behavior and can provide a firm base for comparison with analytical results. Inflow control coupled with detailed diagnostic tools such as blade pressure measurements can be used to uncover the more subtle mechanisms such as rotor strut interaction, which can set tone levels for some engine configurations. Initial mappings of rotor wake-vortex flow fields have provided a data base for a first generation semiempirical flow disturbance model. Laser velocimetry offers a nonintrusive method for validating and improving the model. Digital data systems and signal processing algorithms are bringing mode measurement closer to a working tool that can be frequently applied to a real machine such as a turbofan engine. On the analytical side, models of most of the links in the chain from turbomachine blade source to far field observation point have been formulated. Three dimensional lifting surface theory for blade rows, including source noncompactness and cascade effects, blade row transmission models incorporating mode and frequency scattering, and modal radiation calculations, including hybrid numerical-analytical approaches, are tools which await further application.

Groeneweg, John F.; Sofrin, Thomas G.; Rice, Edward J.; Gliebe, Phillip R.

1991-01-01

327

Computational Aeroacoustics Cascade Model of Fan Noise  

Microsoft Academic Search

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

Philip Paul LePoudre

2011-01-01

328

Noise. Ag Ed Environmental Education Series.  

ERIC Educational Resources Information Center

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

Tulloch, Rodney W.

329

Active Harmonic Filters  

Microsoft Academic Search

Unlike traditional passive harmonic filters, modern active harmonic filters have the following multiple functions: harmonic filtering, damping,isolation and termination, reactive-power control for power factor correction and voltage regulation, load balancing, voltage-flicker reduction, and\\/or their combinations. Significant cost reductions in both power semiconductor devices and signal processing devices have inspired manufactures to put active filters on the market. This paper deals

HIROFUMI AKAGI

2005-01-01

330

Even harmonic lasing  

SciTech Connect

Operation of a free-electron laser at harmonics of the fundamental frequency is explored with the numerical simulation code HELEX. This code includes coupling to the harmonics caused by misalignment of the electrons with the optical beam and coupling due to transverse gradients. Albeit weak, the transverse gradients produce the dominant coupling of the electrons to the even-harmonic light. Even-harmonic lasing occurs in a TEM{sub 0,2m+1}-like mode where the field on axis is zero. As bunching of the electron beam progresses, radiation at the higher odd harmonics is suppressed owing to the absence of higher-order odd-harmonic Fourier components in the bunch. Growth of the even-harmonic power from small signal requires suppression of competing harmonics (including the fundamental) that have higher gain. Lasing at an even harmonic has yet to be experimentally demonstrated in an open resonator (i.e. optical cavity). Strategies to make such an experiment possible are discussed. 9 refs., 5 figs., 1 tab.

Schmitt, M.J.

1991-01-01

331

A HYBRID APPROACH FOR THE EVALUATION OF THE RADIATED NOISE FROM A TURBULENT NON-PREMIXED JET FLAME BASED ON LARGE EDDY SIMULATION AND EQUIVALENT SOURCE & BOUNDARY ELEMENT METHODS  

Microsoft Academic Search

A hybrid approach based on large eddy simulation (LES) and the equivalent source method (ESM) as well as the boundary element method (BEM) is applied to evaluate the noise radiation of open turbulent non-premixed jet flames. Hybrid approaches are well known and often used for classical non-reacting turbulent flows. The extension to turbulent reacting flows is presented here. For an

F. Flemming; A. Nauert; A. Sadiki; J. Janicka; H. Brick; R. Piscoya; M. Ochmann; P. Költzsch

332

Axisymmetric generalized harmonic evolution code  

SciTech Connect

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

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

2010-04-15

333

HARMONIC AMPLIFIER FREE ELECTRON LASER  

Microsoft Academic Search

The harmonic optical klystron (HOK) in which the second undulator is resonant on the higher harmonic of the first undulator is analysed as a harmonic amplifier. The optical field evolution equation of the HOK is derived analytically for both CHG mode (Coherent Harmonic Generation, the quadratic gain regime) and HGHG mode (High Gain Harmonic Generation, the exponential gain regime), the

Jia Qika

334

Handbook for industrial noise control  

NASA Technical Reports Server (NTRS)

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

1981-01-01

335

Ermakov systems with multiplicative noise  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

336

Active harmonic elimination in multilevel converters using FPGA control  

Microsoft Academic Search

This paper presents an optimal total harmonic distortion (THD) control algorithm referred to as active harmonic elimination method for cascaded H-bridges multilevel converter control with unequal DC sources. First, the multilevel converter is decoupled into unipolar converters, the low order harmonics, such as the 5th, 7th, 11th and 13th are eliminated by using elimination theory, and the minimum THD combination

Zhong Du; Leon M. Tolbert; John N. Chiasson

2004-01-01

337

Rotor blade vortex interaction noise  

NASA Astrophysics Data System (ADS)

Blade-vortex interaction noise-generated by helicopter main rotor blades is one of the most severe noise problems and is very important both in military applications and community acceptance of rotorcraft. Research over the decades has substantially improved physical understanding of noise-generating mechanisms, and various design concepts have been investigated to control noise radiation using advanced blade planform shapes and active blade control techniques. The important parameters to control rotor blade-vortex interaction noise and vibration have been identified: blade tip vortex structures and its trajectory, blade aeroelastic deformation, and airloads. Several blade tip design concepts have been investigated for diffusing tip vortices and also for reducing noise. However, these tip shapes have not been able to substantially reduce blade-vortex interaction noise without degradation of rotor performance. Meanwhile, blade root control techniques, such as higher-harmonic pitch control (HHC) and individual blade control (IBC) concepts, have been extensively investigated for noise and vibration reduction. The HHC technique has proved the substantial blade-vortex interaction noise reduction, up to 6 dB, while vibration and low-frequency noise have been increased. Tests with IBC techniques have shown the simultaneous reduction of rotor noise and vibratory loads with 2/rev pitch control inputs. Recently, active blade control concepts with smart structures have been investigated with the emphasis on active blade twist and trailing edge flap. Smart structures technologies are very promising, but further advancements are needed to meet all the requirements of rotorcraft applications in frequency, force, and displacement.

Yu, Yung H.

2000-02-01

338

Harmonizing Civil Engineering Education  

Microsoft Academic Search

Uniformity never will be the objective of education, yet some level of compatibility can be useful or even indi spensable. Though academic teachers are rather attached to the idea of University autonomy and freedom than to any form of harmonization, some harmonization is necessary to assure readable and comparable professional degrees, as well as comparable criteria of quality assurance, irrespective

Stanisøaw Majewski

339

Electrodynamic spherical harmonic  

E-print Network

Electrodynamic spherical harmonic is a second rank tensor in three-dimensional space. It allows to separate the radial and angle variables in vector solutions of Maxwell's equations. Using the orthonormalization for electrodynamic spherical harmonic, a boundary problem on a sphere can be easily solved.

Andrey Novitsky

2008-03-28

340

Computer program to predict aircraft noise levels  

NASA Technical Reports Server (NTRS)

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

Clark, B. J.

1981-01-01

341

Statistical studies of Pc 3-5 pulsations and their relevance for possible source mechanisms of ULF waves  

NASA Technical Reports Server (NTRS)

A number of statistical studies using spacecraft data have been made of ULF waves in the magnetosphere. These studies provide an overview of ULF pulsation activity for r = 5-15 R(E) and allow an assessment of likely source mechanisms. In this review pulsations are categorized into five general types: compressional Pc 5, poloidal Pc 4, toroidal harmonics, toroidal Pc 5 (fundamental mode), and incoherent noise. The occurrence distributions and/or distributions of wave power of the different types suggest that compressional Pc 5 and poloidal Pc 4 derive their energy locally, most likely from energetic protons. The toroidal pulsations, both harmonic and fundamental mode, appear to be driven by an energy source outside the magnetopause - directly upstream in the sheath and solar wind for harmonics and the flanks for fundamentals. Incoherent pulsations are a prominent pulsation type but from their occurrence distribution alone it is unclear what their dominant energy source may be.

Anderson, Brian J.

1993-01-01

342

Noise propagation in urban and industrial areas  

NASA Technical Reports Server (NTRS)

Noise propagation in streets and the discrepancies between theoretical analyses and field measurements are discussed. A cell-model is used to estimate the general background level of noise due to vehicular sources distributed over the urban area.

Davies, H. G.

1976-01-01

343

Power line harmonic radiation: A systematic study using DEMETER spacecraft  

E-print Network

Power line harmonic radiation: A systematic study using DEMETER spacecraft F. Nemec a,b,*, O of a systematic survey of Power line harmonic radiation (PLHR) observed by the DEMETER spacecraft. DEME- TER frequency spacing corresponds well to the power system frequency at anticipated source locations. Moreover

Santolik, Ondrej

344

Neural Network Based Method for Predicting Nonlinear Load Harmonics  

Microsoft Academic Search

Generation of harmonics and the existence of waveform pollution in power system networks are important problems facing the power utilities. The increased use of nonlinear devices in industry has resulted in direct increase of harmonic distortion in the industrial power system in recent years. Interaction between loads and sources in a power distribution network is a complex process and often

Joy Mazumdar; Ronald G. Harley; Frank C. Lambert; Ganesh K. Venayagamoorthy

2007-01-01

345

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

Microsoft Academic Search

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

FREDRIC J. HARRIS

1978-01-01

346

Aircraft noise prediction program theoretical manual, part 1  

NASA Technical Reports Server (NTRS)

Aircraft noise prediction theoretical methods are given. The prediction of data which affect noise generation and propagation is addressed. These data include the aircraft flight dynamics, the source noise parameters, and the propagation effects.

Zorumski, W. E.

1982-01-01

347

Determination of rotor harmonic blade loads from acoustic measurements  

NASA Technical Reports Server (NTRS)

The magnitude of discrete frequency sound radiated by a rotating blade is strongly influenced by the presence of a nonuniform distribution of aerodynamic forces over the rotor disk. An analytical development and experimental results are provided for a technique by which harmonic blade loads are derived from acoustic measurements. The technique relates, on a one-to-one basis, the discrete frequency sound harmonic amplitudes measured at a point on the axis of rotation to the blade-load harmonic amplitudes. This technique was applied to acoustic data from two helicopter types and from a series of test results using the NASA-Langley Research Center rotor test facility. The inferred blade-load harmonics for the cases considered tended to follow an inverse power law relationship with harmonic blade-load number. Empirical curve fits to the data showed the harmonic fall-off rate to be in the range of 6 to 9 db per octave of harmonic order. These empirical relationships were subsequently used as input data in a compatible far field rotational noise prediction model. A comparison between predicted and measured off-axis sound harmonic levels is provided for the experimental cases considered.

Kasper, P. K.

1975-01-01

348

Effect of Harmonicity on the Detection of a Signal in a Complex Masker and on Spatial Release from Masking  

PubMed Central

The amount of masking of sounds from one source (signals) by sounds from a competing source (maskers) heavily depends on the sound characteristics of the masker and the signal and on their relative spatial location. Numerous studies investigated the ability to detect a signal in a speech or a noise masker or the effect of spatial separation of signal and masker on the amount of masking, but there is a lack of studies investigating the combined effects of many cues on the masking as is typical for natural listening situations. The current study using free-field listening systematically evaluates the combined effects of harmonicity and inharmonicity cues in multi-tone maskers and cues resulting from spatial separation of target signal and masker on the detection of a pure tone in a multi-tone or a noise masker. A linear binaural processing model was implemented to predict the masked thresholds in order to estimate whether the observed thresholds can be accounted for by energetic masking in the auditory periphery or whether other effects are involved. Thresholds were determined for combinations of two target frequencies (1 and 8 kHz), two spatial configurations (masker and target either co-located or spatially separated by 90 degrees azimuth), and five different masker types (four complex multi-tone stimuli, one noise masker). A spatial separation of target and masker resulted in a release from masking for all masker types. The amount of masking significantly depended on the masker type and frequency range. The various harmonic and inharmonic relations between target and masker or between components of the masker resulted in a complex pattern of increased or decreased masked thresholds in comparison to the predicted energetic masking. The results indicate that harmonicity cues affect the detectability of a tonal target in a complex masker. PMID:22028814

Klinge, Astrid; Beutelmann, Rainer; Klump, Georg M.

2011-01-01

349

The Problems with "Noise Numbers" for Wind Farm Noise Assessment  

ERIC Educational Resources Information Center

Human perception responds primarily to sound character rather than sound level. Wind farms are unique sound sources and exhibit special audible and inaudible characteristics that can be described as modulating sound or as a tonal complex. Wind farm compliance measures based on a specified noise number alone will fail to address problems with noise…

Thorne, Bob

2011-01-01

350

Noncommutative quantum mechanics of a harmonic oscillator under linearized gravitational waves  

SciTech Connect

We consider the quantum dynamics of a harmonic oscillator in noncommutative space under the influence of linearized gravitational waves (GWs) in the long-wavelength and low-velocity limit. Following the prescription in Saha and Gangopadhyay [Phys. Lett. B 681, 96 (2009)] we quantize the system. The Hamiltonian of the system is solved by using standard algebraic iterative methods. The solution shows signatures of the coordinate noncommutativity via alterations in the oscillation frequency of the harmonic oscillator system from its commutative counterpart. Moreover, it is found that the response of the harmonic oscillator to periodic GWs, when their frequencies match, will oscillate with a time scale imposed by the noncommutative parameter. We expect this noncommutative signature to show up as some noise source in the GW detection experiments since the recent phenomenological upper bounds set on the spatial noncommutative parameter imply a length scale comparable to the length variations due to the passage of gravitational waves, detectable in the present-day GW detectors.

Saha, Anirban; Gangopadhyay, Sunandan; Saha, Swarup [Department of Physics and Astrophysics, West Bengal State University, Barasat, North 24 Paraganas, West Bengal (India); Debipur, Duttapukur 743248 (India)

2011-01-15

351

Environmental Noise  

NASA Astrophysics Data System (ADS)

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

Rumberg, Martin

352

A simplified approach for the calculation of acoustic emission in the case of friction-induced noise and vibration  

NASA Astrophysics Data System (ADS)

The acoustic response associated with squeal noise radiations is a hard issue due to the need to consider non-linearities of contact and friction, to solve the associated nonlinear dynamic problem and to calculate the noise emissions due to self-excited vibrations. In this work, the focus is on the calculation of the sound pressure in free space generated during squeal events. The calculation of the sound pressure can be performed by the Boundary Element Method (BEM). The inputs of this method are a boundary element model, a field of normal velocity characterized by a unique frequency. However, the field of velocity associated with friction-induced vibrations is composed of several harmonic components. So, the BEM equation has to be solved for each frequency and in most cases, the number of harmonic components is significant. Therefore, the computation time can be prohibitive. The reduction of the number of harmonic component is a key point for the quick estimation of the squeal noise. The proposed approach is based on the detection and the selection of the predominant harmonic components in the mean square velocity. It is applied on two cases of squeal and allows us to consider only few frequencies. In this study, a new method will be proposed in order to quickly well estimate the noise emission in free space. This approach will be based on an approximated acoustic power of brake system which is assumed to be a punctual source, an interpolated directivity and the decrease of the acoustic power levels. This method is applied on two classical cases of squeal with one and two unstable modes. It allows us to well reconstruct the acoustic power levels map. Several error estimators are introduced and show that the reconstructed field is close to the reference calculated with a complete BEM.

Soobbarayen, K.; Besset, S.; Sinou, J.-. J.

2015-01-01

353

REFERENCE SETTINGS IN NOISE MAPPING SOFTWARE - A COMPARISON OF THE SPEED OF CALCULATION FOR DIFFERENT SOFTWARE  

Microsoft Academic Search

Noise mapping is an increasingly important method of assessing environmental noise. Noise maps are being generated for projects ranging from small scale new developments with a single noise source to large agglomerations with many noise sources. The largest noise maps require millions of calculations to be carried out and this can lead to long processing times and significant costs for

Peter Hepworth; James Trow; Vincent Hii

354

USER CONTROLLED SETTINGS IN NOISE MAPPING SOFTWARE - THE EFFECTS ON CALCULATION SPEED AND ACCURACY  

Microsoft Academic Search

Noise mapping is an increasingly important method of assessing environmental noise. Noise maps are being generated for projects ranging from small scale new developments with a single noise source to large agglomerations with many noise sources. The largest noise maps require millions of calculations to be carried out and this can lead to long processing times and significant costs for

Peter Hepworth; James Trow; Vincent Hii

355

Thermal Conductivity for a Noisy Disordered Harmonic Chain  

E-print Network

We consider a $d$-dimensional disordered harmonic chain (DHC) perturbed by an energy conservative noise. We obtain uniform in the volume upper and lower bounds for the thermal conductivity defined through the Green-Kubo formula. These bounds indicate a positive finite conductivity. We prove also that the infinite volume homogenized Green-Kubo formula converges.

Cedric Bernardin

2008-08-05

356

Analysis of Background Seismic Noise Recorded at the Amundsen-Scott South Pole Station, Antarctica  

NASA Astrophysics Data System (ADS)

A small array of high frequency seismometers was recently placed around the Amundsen-Scott South Pole Station in order to characterize seismic noise generated by the station during operations. This week long experiment, titled, "South Pole Analysis of Machines" or SPAM was conducted in January of 2006 using equipment provided by IRIS PASSCAL to sample the high frequency noise sources generated at the NSF's research base. These data will be correlated to those observed at the ultra quiet GSN seismic station (QSPA) located 5 miles from the base. The purpose of the experiment is to show that although the QSPA sensors are 5 miles away and nearly 1000 feet deep in the ice, there is still a risk of contamination of the signals by cultural noise from the South Pole research base. A Quiet Sector was established around the QSPA station in order to minimize vibrational noise sources, but there is interest in moving some experiments out into the Quiet Sector. Characterizing the noise sources will help us determine the potential reduction in data quality expected at the QSPA station as experiments move closer to the site. Sensors were placed next to the power generators, aircraft taxiway, large antenna towers, as well as at the base of the new station itself. Sensors were also placed between the research base and the QSPA station to get an idea of the propagation of the noise toward the QSPA station. Several high frequency noise sources are clearly seen on all array elements with a number of very clear spectral lines above 1 Hz. These are primarily associated with snow moving tractors and power generators. Smaller signals are seen that may be related to wind loading on the new South Pole elevated station along with harmonics that appear to be correlated with large air handling equipment in the station. Also evident are air operations with landings, takeoffs, taxi and idling C-130's evident. Although greatly attenuated, almost all of these signals are observed at the QSPA station. Therefore, encroachment of any of these noise sources into the Quiet Sector will adversely affect the signal-to-noise ratio in the frequencies above 1 Hz for seismograms recorded at QSPA. At this point, QSPA is by far the quietest seismic station in the world at these high frequencies. We hope that we can preserve these low background noise levels and keep the QSPA one of the quietest places on Earth.

Anderson, K. R.; Aster, R.; Beaudoin, B. C.; Butler, R.

2006-12-01

357

Characterizing computer cooling fan noise  

Microsoft Academic Search

Computer cooling fan noise is studied theoretically, focusing on the radiation from the interaction between rotor blades and motor struts. The source is decomposed into axial thrust, circumferential drag, and radial force. There is no sound-power coupling among the three components. The index of spatial spinning pressure mode plays the key role in noise radiation. The leading modes are the

Lixi Huang

2003-01-01

358

Acoustical properties of a model rotor in nonaxial flight. [wind tunnel model noise measurements  

NASA Technical Reports Server (NTRS)

Wind tunnel measurements on model rotor blade loads and acoustical noise were correlated to a theoretical formulation of the rotational noise of a rotor in non-axial flight. Good correlation between theory and data was achieved using actual measured rotor blade pressure harmonic decay levels and lift, drag and radial force magnitudes. Both pressure and acoustic data exhibited considerable scatter in hover and low speed forward flight which resulted in a fairly wide latitude in the noise level prediction at higher harmonics.

Hinterkeuser, E. G.

1973-01-01

359

Theory of noise in metal oxide semiconductor devices  

Microsoft Academic Search

Noise in MOS diodes arises from different sources: fluctuations in occupation of surface states, shot noise, and leakage noise. Fluctuations in the occupation of surface states produce changes in the surface space-charge distribution which in turn produce currents. Shot noise is produced by fluctuations of the individual drift and diffusion flows toward the surface. Leakage noise is associated with the

A. G. Jordan; N. A. Jordan

1965-01-01

360

On harmonic binomial series  

E-print Network

We evaluate binomial series with harmonic number coefficients, providing recursion relations, integral representations, and several examples. The results are of interest to analytic number theory, the analysis of algorithms, and calculations of theoretical physics, as well as other applications.

Mark W. Coffey

2008-12-09

361

Illustration: The Harmonic Oscillator  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

362

Harmonic Morphisms -Basics Sigmundur Gudmundsson  

E-print Network

Harmonic Morphisms - Basics Sigmundur Gudmundsson Department of Mathematics Faculty of Science Lund University Sigmundur.Gudmundsson@math.lu.se March 11, 2014 #12;Harmonic Maps in Gaussian Geometry Harmonic Maps in Riemannian Geometry Outline 1 Harmonic Maps in Gaussian Geometry Holomorphic Functions in One

Gudmundsson, Sigmundur

363

The Airframe Noise Reduction Challenge  

NASA Technical Reports Server (NTRS)

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

Lockhard, David P.; Lilley, Geoffrey M.

2004-01-01

364

NASA progress in aircraft noise prediction  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

365

New developments in blown flap noise technology  

NASA Technical Reports Server (NTRS)

The noise technology relating to blown-flap systems is reviewed. There are three general sources of noise: turbomachinery, airframe, and the interaction noise of the jet blowing on the flaps. The latter noise-source area is the most critical and the main subject dicussed. Characteristics of lower surface blown and upper surface blown systems are described, including noise spectra, directivity, jet velocity characteristics, aircraft geometric variation effects, and aircraft forward speed effects. Noise reduction concepts are described, including slowing down the jet flow field by devices and engine cycle modifications, structural geometry and shielding modifications, local flow field modifications of the passive and active type, and the absorption of noise. It is concluded that, while there has been considerable progress in the past several years, low noise characteristics in blown flap aircraft must be largely built in by better application of low noise principles during the design.

Gibson, J. S.

1976-01-01

366

Keno-Nr a Monte Carlo Code Simulating the Californium -252-SOURCE-DRIVEN Noise Analysis Experimental Method for Determining Subcriticality  

NASA Astrophysics Data System (ADS)

The ^{252}Cf -source-driven noise analysis (CSDNA) requires the measurement of the cross power spectral density (CPSD) G_ {23}(omega), between a pair of neutron detectors (subscripts 2 and 3) located in or near the fissile assembly, and the CPSDs, G_{12}( omega) and G_{13}( omega), between the neutron detectors and an ionization chamber 1 containing ^{252}Cf also located in or near the fissile assembly. The key advantage of this method is that the subcriticality of the assembly can be obtained from the ratio of spectral densities,{G _sp{12}{*}(omega)G_ {13}(omega)over G_{11 }(omega)G_{23}(omega) },using a point kinetic model formulation which is independent of the detector's properties and a reference measurement. The multigroup, Monte Carlo code, KENO-NR, was developed to eliminate the dependence of the measurement on the point kinetic formulation. This code utilizes time dependent, analog neutron tracking to simulate the experimental method, in addition to the underlying nuclear physics, as closely as possible. From a direct comparison of simulated and measured data, the calculational model and cross sections are validated for the calculation, and KENO-NR can then be rerun to provide a distributed source k_ {eff} calculation. Depending on the fissile assembly, a few hours to a couple of days of computation time are needed for a typical simulation executed on a desktop workstation. In this work, KENO-NR demonstrated the ability to accurately estimate the measured ratio of spectral densities from experiments using capture detectors performed on uranium metal cylinders, a cylindrical tank filled with aqueous uranyl nitrate, and arrays of safe storage bottles filled with uranyl nitrate. Good agreement was also seen between simulated and measured values of the prompt neutron decay constant from the fitted CPSDs. Poor agreement was seen between simulated and measured results using composite ^6Li-glass-plastic scintillators at large subcriticalities for the tank of uranyl nitrate. It is believed that the response of these detectors is not well known and is incorrectly modeled in KENO-NR. In addition to these tests, several benchmark calculations were also performed to provide insight into the properties of the point kinetic formulation.

Ficaro, Edward Patrick

367

Fan and pump noise control  

NASA Technical Reports Server (NTRS)

The development is described of improved, low noise level fan and pump concepts for the space shuttle. In addition, a set of noise design criteria for small fans and pumps was derived. The concepts and criteria were created by obtaining Apollo hardware test data to correlate and modify existing noise estimating procedures. A set of space shuttle selection criteria was used to determine preliminary fan and pump concepts. These concepts were tested and modified to obtain noise sources and characteristics which yield the design criteria and quiet, efficient space shuttle fan and pump concepts.

Misoda, J.; Magliozzi, B.

1973-01-01

368

Advanced subsonic transport approach noise: The relative contribution of airframe noise  

NASA Technical Reports Server (NTRS)

With current engine technology, airframe noise is a contributing source for large commercial aircraft on approach, but not the major contributor. With the promise of much quieter jet engines with the planned new generation of high-by-pass turbofan engines, airframe noise has become a topic of interest in the advanced subsonic transport research program. The objective of this paper is to assess the contribution of airframe noise relative to the other aircraft noise sources on approach. The assessment will be made for a current technology large commercial transport aircraft and for an envisioned advanced technology aircraft. NASA's Aircraft Noise Prediction Program (ANOPP) will be used to make total aircraft noise predictions for these two aircraft types. Predicted noise levels and areas of noise contours will be used to determine the relative importance of the contributing approach noise sources. The actual set-up decks used to make the ANOPP runs for the two aircraft types are included in appendixes.

Willshire, William L., Jr.; Garber, Donald P.

1992-01-01

369

Charge noise and spin noise in a semiconductor quantum device  

E-print Network

Solid-state systems which mimic two-level atoms are being actively developed. Improving the quantum coherence of these systems, for instance spin qubits or single photon emitters using semiconductor quantum dots, involves dealing with noise. The sources of noise are inherent to the semiconductor and are complex. Charge noise results in a fluctuating electric field, spin noise in a fluctuating magnetic field at the location of the qubit, and both can lead to dephasing and decoherence of optical and spin states. We investigate noise in an ultra-pure semiconductor using a minimally-invasive, ultra-sensitive, local probe: resonance fluorescence from a single quantum dot. We distinguish between charge noise and spin noise via a crucial difference in their optical signatures. Noise spectra for both electric and magnetic fields are derived. The noise spectrum of the charge noise can be fully described by the fluctuations in an ensemble of localized charge defects in the semiconductor. We demonstrate the "semiconductor vacuum" for the optical transition at frequencies above 50 kHz: by operating the device at high enough frequencies, we demonstrate transform-limited quantum dot optical linewidths.

Andreas V. Kuhlmann; Julien Houel; Arne Ludwig; Lukas Greuter; Dirk Reuter; Andreas D. Wieck; Martino Poggio; Richard J. Warburton

2013-01-27

370

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

NASA Technical Reports Server (NTRS)

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

Flanagan, M. J.

1991-01-01

371

Non-propulsive aerodynamic noise  

NASA Astrophysics Data System (ADS)

In the first part of the paper, the contribution of airframe noise to total aircraft noise on approach is assessed for a large current technology transport and for the same airframe powered with bypass ratio 10 engines with an additional 5 dB noise suppression applied to the fan and turbine noise sources. The airframe noise of the envisioned advanced subsonic transport is 2 EPNdB less than the largest contributor to the total aircraft noise, the fan inlet. The noise impact of the airframe noise, as measured by noise contour area, is 1/4 that of fan noise. Further fan noise reduction efforts should not view airframe noise as an absolute noise floor. In the second part of the paper, the results from one recent cavity noise wind tunnel experiment is reported. A cavity of dimensions 11.25 in. (28.58 cm) long, 2.5 in. (6.35 cm) wide, and variable depth was tested in the Mach number range of .20 through .90. Reynolds number varied from 5 to 100 million per foot (16 to 328 million per meter). The 1/d ratio was varied from 4.4 to 20.0. The model was tested at yaw angles from 0 to 15 degrees. In general, the deeper the cavity, the greater the amplitude of the acoustic tones. Reynolds number appeared to have little effect on acoustic tone amplitudes. Tone amplitude and bandwidth changed with Mach number. The effect of yaw on acoustic tones varied with Reynolds number, Mach number, 1/h, and mode number. At Mach number 0.90, increased yaw shifted the tone frequencies of the higher modal frequencies to lower frequencies. As cavity depth decreased, the effect of yaw decreased.

Willshire, William L., Jr.; Tracy, Maureen B.

1992-04-01

372

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

SciTech Connect

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

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

2012-04-30

373

Optimal Planning of Harmonic Filters in an Industrial Plant Considering Uncertainty Conditions  

Microsoft Academic Search

This paper presents an integrated approach feasible direction method and genetic algorithm (FDM+GA) to investigate the planning of large-scale passive harmonic filters. The optimal filter scheme can be obtained from a system under abundant harmonic current sources where harmonic amplification problems should be avoided. The constraints of harmonics with orders lower than the filter tuned-points have been set stricter to

SHU-CHEN WANG; CHI-JUI WU; Ying-Pin Chang

2007-01-01

374

Separate measurement of fundamental and high harmonic energy at consumer inlet - a way to enhancement of electricity use efficiency  

Microsoft Academic Search

High harmonics in power systems are caused by both energy sources and consumers. Harmonics essentially decrease the efficiency of electricity use. Therefore the following questions are rather pressing: where the source of high harmonics is and at whose expense the supply network voltage waveform should be improved. Solving these problems is of both technical and administrative character. Electricity consumers can

A. S. Smirnov; N. N. Solonina; K. V. Suslov

2010-01-01

375

Community response to noise.  

PubMed

Activities from 2008 to 2011 by ICBEN community response to noise team were summarized. That is, individual community-based indexes such as community tolerance Level, Zuricher Fluglarm Index (ZFI) and Frankfurter Fluglarm Index (FFI/FNI) were newly proposed, differences in railway bonus between Europe and Asia were discussed by a Swedish survey, socio-acoustic surveys were reported from developing countries, and annoyance equivalents and dominant source models were proposed as the adequate combined noise model. Furthermore, not only negative, but also positive aspects of sound were discussed as soundscape studies. Finally, seven items were listed as future team activities. PMID:23257582

Yano, Takashi; Gjestland, Truls; Lee, Soogab

2012-01-01

376

Aircraft interior noise reduction by alternate resonance tuning  

NASA Astrophysics Data System (ADS)

Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at lower, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is being studied which considers aircraft fuselages lines with panels alternately tuned to frequencies above and below the frequency to be attenuated. Adjacent panels would oscillate at equal amplitude, to give equal source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to become cut off and therefore be non-propagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is currently being investigated both theoretically and experimentally. This new concept has potential application to reducing interior noise due to the propellers in advanced turboprop aircraft as well as for existing aircraft configurations. This program summarizes the work carried out at Duke University during the third semester of a contract supported by the Structural Acoustics Branch at NASA Langley Research Center.

Bliss, Donald B.; Gottwald, James A.; Gustaveson, Mark B.; Burton, James R., III; Castellino, Craig

1989-01-01

377

Noise Minimization in Eukaryotic Gene Expression  

E-print Network

investigated the relationship between transcription and translation rates and stochastic fluctuations source of stochasticity in biological systems is the random noise of transcription and translation, which

Campbell, A. Malcolm

378

Spectral analysis of harmonic tremor signals at Mt. Semeru volcano, Indonesia  

Microsoft Academic Search

A detailed spectral analysis of tremor signals recorded at Mt. Semeru volcano, Indonesia, in October 1992 by the German-Indonesian Volcano Expedition (GIVE'92) reveals clearly harmonic spectra containing up to 11 integer harmonics. The spectral features can be explained by any rhythmically pulsating source producing a temporarily stable source signal. As one realization of this concept we model the source as

Vera Schlindwein; Joachim Wassermann; Frank Scherbaum

1995-01-01

379

Xe/+/ -induced ion-cyclotron harmonic waves  

NASA Astrophysics Data System (ADS)

Xenon ion sources on an ejectable package separated from the main payload during the flights of Porcupine rockets F3 and F4 which were launched from Kiruna, Sweden on March 19 and 31, 1979, respectively. The effects of the xenon ion beam, detected by the LF (f less than 16 kHz) wideband electric field experiment and analyzed by using a sonograph, are discussed. Particular attention is given to the stimulation of the ion-cyclotron harmonic waves which are usually linked to the local proton gyro-frequency, but are sometimes related to half that frequency. It was found that in a plasma dominated by O(+) ions, a small amount (1-10%) of protons could cause an effect such that the O(+) cyclotron harmonic waves are set up by the hydrogen ions, the net result being the observation of harmonic emissions separated by the hydrogen ion gyro frequency.

Jones, D.

380

Second Harmonic Hectometric Radio Emission at Jupiter  

NASA Technical Reports Server (NTRS)

Galileo has been in orbit around Jupiter since December 1995. The plasma wave instrument on board the spacecraft has occasionally detected a rotationally modulated attenuation band in the hectometric (HOM) emission that most likely is due to scattering of the radiation from density fluctuations along the Io L-shell, as reported earlier. The occurrence of the attenuation band is likely to be dependent on Io activity and the presence of density scattering centers along the Io L-shell as well as the location of the source region. Some of the attenuation bands show clear indications of second harmonic emission. Without polarization measurements, it is difficult to place constraints on the local generation conditions based on the cyclotron maser instability, but the results imply that second harmonic emission could be present in the decametric (DAM) radiation as well. A survey of the data has revealed about 30 examples of second harmonic HOM.

Menietti, J. D.; Gurnett, D. A.; Groene, J. B.

1998-01-01

381

Second Harmonic Hectometric Radio Emission at Jupiter  

NASA Technical Reports Server (NTRS)

Galileo has been in orbit around Jupiter since December 1995. The plasma wave instrument on board the spacecraft has occasionally detected a rotationally modulated attenuation band in the hectometric (HOM) emission that most likely is due to scattering of the radiation from density fluctuations along the Io L-shell, as reported earlier. The occurrence of the attenuation band is likely to be dependent on Io activity and the presence of density scattering centers along the Io-L-shell as well as the location of the source region. Some of the attenuation bands show clear indications of second harmonic emission. Without polarization measurements, it is difficult to place constraints on the local generation conditions based on the cyclotron maser instability, but the results imply that second harmonic emission could be present in the decametric (DAM) radiation as well. A survey of the data has revealed about 30 examples of second harmonic HOM.

Menietti, J. D.; Gurnett, D. A.; Groene, J. B.

1998-01-01

382

Optical harmonic generator  

DOEpatents

A pair of uniaxial birefringent crystal elements are fixed together to form a serially arranged, integral assembly which, alternatively, provides either a linearly or elliptically polarized second-harmonic output wave or a linearly polarized third-harmonic output wave. The extraordinary or e directions of the crystal elements are oriented in the integral assembly to be in quadrature (90/sup 0/). For a second-harmonic generation in the Type-II-Type-II angle tuned case, the input fundamental wave has equal amplitude o and e components. For a third-harmonic generation, the input fundamental wave has o and e components whose amplitudes are in a ratio of 2:1 (o:e reference first crystal). In the typical case of a linearly polarized input fundamental wave this can be accomplished by simply rotating the crystal assembly about the input beam direction by 10/sup 0/. For both second and third harmonic generation input precise phase-matching is achieved by tilting the crystal assembly about its two sensitive axeses (o).

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

1982-06-10

383

Optical harmonic generator  

DOEpatents

A pair of uniaxial birefringent crystal elements are fixed together to form a serially arranged, integral assembly which, alternatively, provides either a linearly or elliptically polarized second-harmonic output wave or a linearly polarized third-harmonic output wave. The "extraordinary" or "e" directions of the crystal elements are oriented in the integral assembly to be in quadrature (90.degree.). For a second-harmonic generation in the Type-II-Type-II angle tuned case, the input fundamental wave has equal amplitude "o" and "e" components. For a third-harmonic generation, the input fundamental wave has "o" and "e" components whose amplitudes are in a ratio of 2:1 ("o":"e" reference first crystal). In the typical case of a linearly polarized input fundamental wave this can be accomplished by simply rotating the crystal assembly about the input beam direction by 10.degree.. For both second and third harmonic generation input precise phase-matching is achieved by tilting the crystal assembly about its two sensitive axes ("o").

Summers, Mark A. (Livermore, CA); Eimerl, David (Pleasanton, CA); Boyd, Robert D. (Livermore, CA)

1985-01-01

384

Aircraft turbofan noise  

NASA Technical Reports Server (NTRS)

Turbofan noise generation and suppression in aircraft engines are reviewed. The chain of physical processes which connect unsteady flow interactions with fan blades to far field noise is addressed. Mechanism identification and description, duct propagation, radiation and acoustic suppression are discussed. The experimental technique of fan inflow static tests are discussed. Rotor blade surface pressure and wake velocity measurements aid in the determination of the types and strengths of the generation mechanisms. Approaches to predicting or measuring acoustic mode content, optimizing treatment impedance to maximize attenuation, translating impedance into porous wall structure and interpreting far field directivity patterns are illustrated by comparisons of analytical and experimental results. The interdependence of source and acoustic treatment design to minimize far field noise is emphasized. Area requiring further research are discussed and the relevance of aircraft turbofan results to quieting other turbomachinery installations is addressed.

Groeneweg, J. F.; Rice, E. J.

1983-01-01

385

Road Traffic Noise  

NASA Astrophysics Data System (ADS)

Road traffic is the most interfering noise source in developed countries. According to a publication of the European Union (EU) at the end of the twentieth century [1], about 40% of the population in 15 EU member states is exposed to road traffic noise at mean levels exceeding 55 dB(A). Nearly 80 million people, 20% of the population, are exposed to levels exceeding 65 dB(A) during daytime and more than 30% of the population is exposed to levels exceeding 55 dB(A) during night time. Such high noise levels cause health risks and social disorders (aggressiveness, protest, and helplessness), interference of communication and disturbance of sleep; the long- and short-term consequences cause adverse cardiovascular effects, detrimental hormonal responses (stress hormones), and possible disturbance of the human metabolism (nutrition) and the immune system. Even performance at work and school could be impaired.

Beckenbauer, Thomas

386

Impact of Air Injection on Jet Noise  

NASA Technical Reports Server (NTRS)

The objective of this viewgraph presentation is to review the program to determine impact of core fluidic chevrons on noise produced by dual stream jets (i.e., broadband shock noise - supersonic, and mixing noise - subsonic and supersonic). The presentation reviews the sources of jet noise. It shows designs of Generation II Fluidic Chevrons. The injection impacts shock structure and stream disturbances through enhanced mixing. This may impact constructive interference between acoustic sources. The high fan pressures may inhibit mixing produced by core injectors. A fan stream injection may be required for better noise reduction. In future the modification of Gen II nozzles to allow for some azimuthal control: will allow for higher mass flow rates and will allow for shallower injection angles A Flow field study is scheduled for spring, 2008 The conclusions are that injection can reduce well-defined shock noise and injection reduces mixing noise near peak jet noise angle

Henderson, Brenda; Norum, Tom

2007-01-01

387

Interior noise prediction methodology: ATDAC theory and validation  

NASA Technical Reports Server (NTRS)

The Acoustical Theory for Design of Aircraft Cabins (ATDAC) is a computer program developed to predict interior noise levels inside aircraft and to evaluate the effects of different aircraft configurations on the aircraft acoustical environment. The primary motivation for development of this program is the special interior noise problems associated with advanced turboprop (ATP) aircraft where there is a tonal, low frequency noise problem. Prediction of interior noise levels requires knowledge of the energy sources, the transmission paths, and the relationship between the energy variable and the sound pressure level. The energy sources include engine noise, both airborne and structure-borne; turbulent boundary layer noise; and interior noise sources such as air conditioner noise and auxiliary power unit noise. Since propeller and engine noise prediction programs are widely available, they are not included in ATDAC. Airborne engine noise from any prediction or measurement may be input to this program. This report describes the theory and equations implemented in the ATDAC program.

Mathur, Gopal P.; Gardner, Bryce K.

1992-01-01

388

The development of experimental techniques for the study of helicopter rotor noise  

NASA Technical Reports Server (NTRS)

The features of existing wind tunnels involved in noise studies are discussed. The acoustic characteristics of the MIT low noise open jet wind tunnel are obtained by employing calibration techniques: one technique is to measure the decay of sound pressure with distance in the far field; the other technique is to utilize a speaker, which was calibrated, as a sound source. The sound pressure level versus frequency was obtained in the wind tunnel chamber and compared with the corresponding calibrated values. Fiberglas board-block units were installed on the chamber interior. The free field was increased significantly after this treatment and the chamber cut-off frequency was reduced to 160 Hz from the original designed 250 Hz. The flow field characteristics of the rotor-tunnel configuration were studied by using flow visualization techniques. The influence of open-jet shear layer on the sound transmission was studied by using an Aeolian tone as the sound source. A dynamometer system was designed to measure the steady and low harmonics of the rotor thrust. A theoretical Mach number scaling formula was developed to scale the rotational noise and blade slap noise data of model rotors to full scale helicopter rotors.

Widnall, S. E.; Harris, W. L.; Lee, Y. C. A.; Drees, H. M.

1974-01-01

389

Fan Noise Prediction with Applications to Aircraft System Noise Assessment  

NASA Technical Reports Server (NTRS)

This paper describes an assessment of current fan noise prediction tools by comparing measured and predicted sideline acoustic levels from a benchmark fan noise wind tunnel test. Specifically, an empirical method and newly developed coupled computational approach are utilized to predict aft fan noise for a benchmark test configuration. Comparisons with sideline noise measurements are performed to assess the relative merits of the two approaches. The study identifies issues entailed in coupling the source and propagation codes, as well as provides insight into the capabilities of the tools in predicting the fan noise source and subsequent propagation and radiation. In contrast to the empirical method, the new coupled computational approach provides the ability to investigate acoustic near-field effects. The potential benefits/costs of these new methods are also compared with the existing capabilities in a current aircraft noise system prediction tool. The knowledge gained in this work provides a basis for improved fan source specification in overall aircraft system noise studies.

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

2009-01-01

390

Basic techniques minimize noise in RF amplifiers  

NASA Astrophysics Data System (ADS)

Techniques for minimizing the noise figure for GaAs FETs are suggested. It is pointed out that the associated gain of low-noise microwave transistors is usually 0.5 to 1.5 dB less than the maximum available gain, and that the best approach to low-noise amplifier design depends on whether the transistor is unconditionally stable for all combinations of source and load impedances at the design frequency. If the transistor is unconditionally stable, the source impedance that yields minimum noise figure can be used. When the noise figure is minimized, the amplifier provides more gain. If more gain is needed, it can be obtained at the expense of increased noise figure. If the transistor is potentially unstable, the noise-figure input stability circle should be drawn to ensure that the optimum source impedance can be used with any load impedance without causing oscillations.

Cooke, Harry F.; Omori, Masa

1989-04-01

391

Crackling Noise  

E-print Network

Crackling noise arises when a system responds to changing external conditions through discrete, impulsive events spanning a broad range of sizes. A wide variety of physical systems exhibiting crackling noise have been studied, from earthquakes on faults to paper crumpling. Because these systems exhibit regular behavior over many decades of sizes, their behavior is likely independent of microscopic and macroscopic details, and progress can be made by the use of very simple models. The fact that simple models and real systems can share the same behavior on a wide range of scales is called universality. We illustrate these ideas using results for our model of crackling noise in magnets, explaining the use of the renormalization group and scaling collapses. This field is still developing: we describe a number of continuing challenges.

James P. Sethna; Karin A. Dahmen; Christopher R. Myers

2001-02-06

392

A higher order statistics-based subspace method for the 2-D harmonic retrieval problem  

Microsoft Academic Search

In this paper, we present a new high resolution algorithm for the two-dimensional (2-D) harmonic retrieval problem, which, in particular, is noise insensitive in view of the fact that in many practical applications the contaminated noise may not be white noise. For this purpose, the approach is set in the context of higher-order statistics (HOS), which has demonstrated to be

Yi Chu; Wen-Hsien Fang; Shun-Hsyung Chang

1996-01-01

393

Harmonic reduction in thyristor converters by harmonic current injection  

Microsoft Academic Search

The paper describes analytical and experimental results for a new method of current harmonic reduction in thyristor converters. The principle of the method is to modify the current waveforms on the d.c. windings of the converter transformer by injecting harmonic currents at a particular frequency. In practice, third harmonic currents of the power frequency is most efficient. Experimental results carried

A. Ametani

1976-01-01

394

Effect of tactile vibration on annoyance to synthesized propfan noise  

NASA Technical Reports Server (NTRS)

Design information that maximizes passenger comfort for propfan aircraft is presented. Predicted noise and vibration environments and the resultant passenger acceptability were studied. The effect of high frequency tactile vibration (i.e., greater than 30 Hz) on passenger reactions was analyzed. Passenger reactions to a wide range of noise with and without tactile vibration was studied. The passenger ride quality simulator was employed using subjects who evaluated either synthesized propeller noises only, or these noises combined with seat/arm vibration. The noises ranging from 80-100 dB consisted of a turbulent boundary layer noise with a factorial combination of five blade passage frequencies (50-200 Hz), two harmonic rolloffs, and three tone/noise ratios. It is indicated that passenger reaction (annoyance) to noise is not significantly changed in the presence of tactile vibration.

Clevenson, S. A.

1981-01-01

395

Decameter U-burst Harmonic Pair from a High Loop  

NASA Astrophysics Data System (ADS)

The results of the first observations of solar sporadic radio emission within 10 - 70 MHz by the Giant Ukrainian Radio Telescope (GURT) are presented and discussed. Observations in such a wide range of frequencies considerably facilitate the registration of harmonic pairs. The solar U-burst harmonic pair observed on 8 August 2012 is analyzed. The burst key features were determined. Among them, the time delay between the fundamental and harmonic emissions was of special interest. The fundamental emission was delayed for 7 s with respect to the harmonic emission. A model for explaining the occurrence of such a delay is proposed, in which the emission source is located inside a magnetic loop containing plasma of increased density. In this case, the delay appears due to the difference in group velocities of electromagnetic waves at the fundamental and the harmonic frequencies.

Dorovskyy, V. V.; Melnik, V. N.; Konovalenko, A. A.; Bubnov, I. N.; Gridin, A. A.; Shevchuk, N. V.; Rucker, H. O.; Poedts, S.; Panchenko, M.

2015-01-01

396

Noise absorbing composite materials applied in domestic trucks  

NASA Astrophysics Data System (ADS)

One of the basic indicators of the modern automobile is the low noise level. Noise level decrease is reached due to: 1) sources of noise elimination due to change of a design of elements and automobile systems; 2) application of modern noise insulation and noise absorption materials. The following noise absorption materials in domestic trucks are applied: fiberglass plastic, basaltic fireproof roll material (BFRM), AA SMT, AL-aralamino, isomat.

Gumerov, I. F.; Shafigullin, L. N.; Vakhitova, S. M.; Shaekhova, I. F.

2014-12-01

397

Pulse-modulated second harmonic imaging microscope quantitatively demonstrates marked increase of collagen in tumor after chemotherapy  

E-print Network

Pulse-modulated second harmonic imaging microscopes (PM-SHIMs) exhibit improved signal-to-noise ratio (SNR) over conventional SHIMs on sensitive imaging and quantification of weak collagen signals inside tissues. We quantify ...

Raja, Anju M.

398

Circular current loops, magnetic dipoles and spherical harmonic analysis.  

USGS Publications Warehouse

Spherical harmonic analysis (SHA) is the most used method of describing the Earth's magnetic field, even though spherical harmonic coefficients (SHC) almost completely defy interpretation in terms of real sources. Some moderately successful efforts have been made to represent the field in terms of dipoles placed in the core in an effort to have the model come closer to representing real sources. Dipole sources are only a first approximation to the real sources which are thought to be a very complicated network of electrical currents in the core of the Earth. -Author

Alldredge, L.R.

1980-01-01

399

Experimental Harmonic Motion  

NASA Astrophysics Data System (ADS)

1. Elementary theory of harmonic motion; 2. Experimental work in harmonic motion; Experiment 1. Determination of g by a simple pendulum; Experiment 2. Harmonic motion of a body suspended by a spring; Experiment 3. Harmonic motion of a rigid body suspended by a torsion wire; Experiment 4. Study of a system with variable moment of inertia; Experiment 5. Dynamical determination of ratio of couple to twist for a torsion wire; Experiment 6. Comparison of the moments of inertia of two bodies; Experiment 7. Experiment with a pair of inertia bars; Experiment 8. Determination of the moment of inertia of a rigid pendulum; Experiment 9. Experiment on a pendulum with variable moment of inertia; Experiment 10. Determination of g by a rigid pendulum; Experiment 11. Pendulum on a yielding support; Experiment 12. Determination of the radius of curvature of a concave mirror by the oscillations of a sphere rolling in it; Experiment 13. Determination of g by the oscillations of a rod rolling on a cylinder; Experiment 14. Study of a vibrating system with two degrees of freedom; Note 1. On the vibration of a body suspended from a light spring; Note 2. Periodic time of a pendulum vibrating through a finite arc; Note 3. Periodic time for finite motion; Note 4. Periodic times of a pendulum with two degrees of freedom.

Searle, G. F. C.

2014-05-01

400

Spherical Harmonic class  

NSDL National Science Digital Library

SphericalHarmonic returns the value of P(theta,phi) where theta and phi are defined in terms of a standard spherical coordinate system (phi measures angle (x,y,z) makes with z axis.) The algorithm is taken from Messiah's Quantum Mechanics, but readers should note that Messiah defines theta and phi in opposite order from this implementation.

Joiner, David; The Shodor Education Foundation, Inc.

401

Stress in Harmonic Serialism  

ERIC Educational Resources Information Center

This dissertation proposes a model of word stress in a derivational version of Optimality Theory (OT) called Harmonic Serialism (HS; Prince and Smolensky 1993/2004, McCarthy 2000, 2006, 2010a). In this model, the metrical structure of a word is derived through a series of optimizations in which the "best" metrical foot is chosen…

Pruitt, Kathryn Ringler

2012-01-01

402

HARMONIC MORPHISMS ON HOMOGENEOUS HADAMARD  

E-print Network

HARMONIC MORPHISMS ON HOMOGENEOUS HADAMARD MANIFOLDS JONAS NORDSTRÃ?M Master's thesis 2010:E14;#12;Abstract In this thesis we investigate the existence of complex-valued harmonic morphisms on Lie groups of their Lie algebra. This decomposi- tion allows us to define harmonic morphisms to Rn , n 2. Any homogeneous

Gudmundsson, Sigmundur

403

Analytic Continuation of Harmonic Sums  

E-print Network

We present a method for calculating any (nested) harmonic sum to arbitrary accuracy for all complex values of the argument. The method utilizes the relation between harmonic sums and (derivatives of) Hurwitz zeta functions, which allows a harmonic sum to be calculated as an expansion valid for large values of its argument. A program for implementing this method is also provided.

S. Albino

2009-03-06

404

Noise Simulation Modeling for Airport Noise Analysis  

Microsoft Academic Search

Noise simulation modeling is now feasible for assessing the noise impacts of airports since computational capabilities have increased. The current aviation noise models use integrated exposure assumptions to calculate the overall noise exposure. However, this assumption greatly restricts the ability to model the effects of terrain, barriers, weather, and aircraft directivity. Noise simulation models, such as NMSim, provide more accurate

J. Micah Downing

405

FET noise studies  

Microsoft Academic Search

The GaAs FET oscillator is an alternative device for voltage-controlled oscillator (VCO) applications because of its inherent wide-band electronic tunability, the variety of operating modes possible such as common source, common gate, etc., and the ease of circuit design. However, it has one major drawback, namely, its high near-carrier 1\\/f noise which makes it unsuitable for many applications, such as

R. A. Pucel

1981-01-01

406

Long-Period Seismic Noise at the Farallon Islands: Island's Tilting due to Infragravity Waves as a Possible Source of Earth's Horizontal Hum  

NASA Astrophysics Data System (ADS)

We present the analysis of long-period noise observed at the broadband seismic station FARB (Streckeisen STS-2) located on the South Farallon Island, 43 km off the coast of San Francisco, CA. Results from our previous work showed that long-period noise (20-500 sec) observed at the ocean-bottom broadband station MOBB located offshore Monterey Bay, CA is mainly due to seafloor deformation under the pressure forcing by long-period ocean surface gravity waves (infragravity waves). Similar type of long-period noise is observed on the vertical and both horizontal components of the Farallon Islands station FARB, but not on the nearby mainland stations. The long-period noise at FARB is best observed on stormy days when it extends all the way to 1000 sec and is even stronger than at MOBB. The long-period noise at FARB is stronger on the E-W than on the N-S component, suggesting that it results from the infragravity waves that propagate from the nearshore region into the deeper ocean. The energy in the infragravity wave band at FARB is, as previously observed at MOBB, modulated in phase with tides. The phase of the modulation observed at FARB agrees with the phase of the local tides, suggesting that infragravity waves observed at FARB are locally generated. Analysis of the infragravity signal following the arrival of a dispersed swell shows that the infragravity waves are generated in the nearshore region from the ocean waves with periods shorter than 23 sec. The comparison of the incoming swell dispersion and the frequency of the resulting infragravity waves further shows that nonlinear interaction between a pair of swell components with frequencies f1 and f2 results in infragravity wave with the difference (f2-f1) frequency. Strong horizontal noise in the infragravity wave band observed at FARB suggests that passing infragravity waves tilt the island. We suggest that the swaying of islands (and underwater mounds) driven by tilting due to infragravity waves can contribute to the recently detected horizontal hum of the Earth.

Rhie, J.; Dolenc, D.; Romanowicz, B.

2008-12-01

407

Backus Effect on a Perpendicular Errors in Harmonic Models of Real vs. Synthetic Data  

NASA Technical Reports Server (NTRS)

Measurements of geomagnetic scalar intensity on a thin spherical shell alone are not enough to separate internal from external source fields; moreover, such scalar data are not enough for accurate modeling of the vector field from internal sources because of unmodeled fields and small data errors. Spherical harmonic models of the geomagnetic potential fitted to scalar data alone therefore suffer from well-understood Backus effect and perpendicular errors. Curiously, errors in some models of simulated 'data' are very much less than those in models of real data. We analyze select Magsat vector and scalar measurements separately to illustrate Backus effect and perpendicular errors in models of real scalar data. By using a model to synthesize 'data' at the observation points, and by adding various types of 'noise', we illustrate such errors in models of synthetic 'data'. Perpendicular errors prove quite sensitive to the maximum degree in the spherical harmonic expansion of the potential field model fitted to the scalar data. Small errors in models of synthetic 'data' are found to be an artifact of matched truncation levels. For example, consider scalar synthetic 'data' computed from a degree 14 model. A degree 14 model fitted to such synthetic 'data' yields negligible error, but amplifies 4 nT (rmss) added noise into a 60 nT error (rmss); however, a degree 12 model fitted to the noisy 'data' suffers a 492 nT error (rmms through degree 12). Geomagnetic measurements remain unaware of model truncation, so the small errors indicated by some simulations cannot be realized in practice. Errors in models fitted to scalar data alone approach 1000 nT (rmss) and several thousand nT (maximum).

Voorhies, C. V.; Santana, J.; Sabaka, T.

1999-01-01

408

Second harmonic inversion for ultrasound contrast harmonic imaging  

NASA Astrophysics Data System (ADS)

Ultrasound contrast agents (UCAs) are small micro-bubbles that behave nonlinearly when exposed to an ultrasound wave. This nonlinear behavior can be observed through the generated higher harmonics in a back-scattered echo. In past years several techniques have been proposed to detect or image harmonics produced by UCAs. In these proposed works, the harmonics generated in the medium during the propagation of the ultrasound wave played an important role, since these harmonics compete with the harmonics generated by the micro-bubbles. We present a method for the reduction of the second harmonic generated during nonlinear-propagation-dubbed second harmonic inversion (SHI). A general expression for the suppression signals is also derived. The SHI technique uses two pulses, p' and p'', of the same frequency f0 and the same amplitude P0 to cancel out the second harmonic generated by nonlinearities of the medium. Simulations show that the second harmonic is reduced by 40 dB on a large axial range. Experimental SHI B-mode images, from a tissue-mimicking phantom and UCAs, show an improvement in the agent-to-tissue ratio (ATR) of 20 dB compared to standard second harmonic imaging and 13 dB of improvement in harmonic power Doppler.

Pasovic, Mirza; Danilouchkine, Mike; Faez, Telli; van Neer, Paul L. M. J.; Cachard, Christian; van der Steen, Antonius F. W.; Basset, Olivier; de Jong, Nico

2011-06-01

409

Effect of individual blade control on noise radiation  

NASA Technical Reports Server (NTRS)

In a joint research program of NASA Ames Research Center, ZF Luftfahrttechnik, the German Aerospace Research Establishment (DLR), and EUROCOPTER Deutschland, a wind tunnel test was performed to evaluate the effects of Individual Blade Control (IBC) on rotor noise. This test was conducted in the 40x80 ft wind tunnel at NASA Ames Research Center, utilizing a full scale MBB-BO 105 four-bladed rotor system. Three microphones were installed for determination of the radiated noise, two of them on a moveable traverse below the advancing blade side and one in a fixed location below the retreating side. Acoustic results are presented for flight conditions with Blade-Vortex-Interaction (BVI) noise radiation. High noise level reductions were measured for single harmonic control inputs. In addition to the single harmonic inputs, multi-harmonic inputs were evaluated by superimposing 2/rev to 6/rev harmonics. For the first time the efficiency of sharp wavelets (60 deg and 90 deg width) on acoustic noise were measured. In order to achieve an adequate wavelet shape at the blade tip, corrections were made to account for the blade torsional behavior. In parallel with the acoustic measurements, vibratory loads were measured during the BVI flight condition to correlate the effects of IBC on noise and vibrations. It is shown how noise levels and vibrations are affected by specific IBC control inputs. In addition, correlations are made between noise levels and acoustic time histories with IBC phase and amplitude variations. For one IBC input mode with high noise reducing efficiency, a sweep of the moveable microphone traverse below the advancing side shows the effect on BVI noise directivity.

Swanson, S. M.; Jacklin, Stephen A.; Niesl, G.; Blaas, Achim; Kube, R.

1995-01-01

410

Noise impact on community: A case study for power generation facility  

Microsoft Academic Search

Power generation plant will make noise impact on the surrounding communities and cause noise complaints from the residences. Noise mitigation treatment for plant is required to achieve the specified noise regulations. In this paper, a case study of the noise control design for a power generation facility is presented. Major noise sources included five engines and generators, five gas conditioning

Yong Ma; Jonathan Chui; Salem Hertil

2005-01-01

411

Modular Engine Noise Component Prediction System (MCP) Technical Description and Assessment Document  

NASA Technical Reports Server (NTRS)

This report describes an empirical prediction procedure for turbofan engine noise. The procedure generates predicted noise levels for several noise components, including inlet- and aft-radiated fan noise, and jet-mixing noise. This report discusses the noise source mechanisms, the development of the prediction procedures, and the assessment of the accuracy of these predictions. Finally, some recommendations for future work are presented.

Herkes, William H.; Reed, David H.

2005-01-01

412

Application of grey relational analysis and hierarchical cluster analysis in regional environmental noise pollution  

Microsoft Academic Search

The main sources of noise, correlations between four representative indicators and urban regional environmental noise pollution were applied by grey relational analysis and hierarchical cluster analysis in Wenzhou from 1997 to 2006. Results indicates that main noise sources of the city of Wenzhou were social life noise and industrial production noise, and hierarchical cluster analysis grouped the 10 years into

Qi Wang

2007-01-01

413

Possible second harmonic gyroemission at Uranus  

NASA Technical Reports Server (NTRS)

During the inbound trajectory toward Uranus, the Planetary Radio Astronomy Instrument on board the Voyager 2 spacecraft observed narrow-band smooth (n-smooth) emission at frequencies centered near 60 kHz. By assuming models of the plasma density for the dayside magnetosphere of Uranus and by using cold plasma theory together with stringent observational constraints, ray-tracing calculations were performed to determine the source location and mode of the n-smooth emission. Ray-tracing calculations suggest that the n-smooth emission with sources near the magnetic equator may be fundamental X mode for certain conditions or second harmonic gyroemission. If the emission is second harmonic gyroemission, the fundamental emission at 30 kHz is expected but apparently not observed. These findings are discussed in the context of the most recent developments in the theory of the cyclotron maser instability.

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

1990-01-01

414

Harmonic multiplication using resonant tunneling  

NASA Technical Reports Server (NTRS)

This paper demonstrates the use of resonant-tunneling diodes as varistors for harmonic multiplication. It is shown that efficient odd-harmonic conversion is possible and that even harmonics do not appear because of the antisymmetry of the current-voltage (I-V) curve. It is also shown that, with the proper choice of resonant-tunneling structure and pump amplitude, most of the harmonic output power can be confined to a single odd-harmonic frequency. Fifth-harmonic multiplication was demonstrated with an output at 21.75 GHz and a power conversion efficiency of 0.5 percent, and a fifth-harmonic efficiency of 2.7 percent was achieved in a circuit simulation using an improved I-V curve.

Sollner, T. C. L. G.; Brown, E. R.; Goodhue, W. D.; Correa, C. A.

1988-01-01

415

Automatic classification of environmental noise events by hidden Markov models  

Microsoft Academic Search

The automatic classification of environmental noise sources from their acoustic signatures recorded at the microphone of a noise monitoring system (NMS) is an active subject of research nowadays. This paper shows how hidden Markov models (HMMs) can be used to build an environmental noise recognition system based on a time-frequency analysis of the noise signal. The performance of the proposed

Paul Gaunard; C. G. Mubikangiey; C. Couvreur; V. Fontaine

1998-01-01

416

Functional roles for noise in genetic circuits Avigdor Eldar1  

E-print Network

in diverse organisms. Recent reviews on noise in gene circuits have focused on the sources of noise in gene that connect noise, the architecture of the gene circuits in which it is present, and the biological functions. Although the potential importance of noise for biological function was appreciated many decades ago

Elowitz, Michael

417

Positive selection for elevated gene expression noise in yeast  

E-print Network

permission. Introduction Gene expression, as other biological processes, is subject to noise (Schrodinger; Maheshri and O'Shea, 2007; Ansel et al, 2008). Expression noise has both intrinsic and extrinsic sources, generate extrinsic noise (Raser and O'Shea, 2005). We focus on intrinsic noise in this study because only

Zhang, Jianzhi

418

Numerical method for predicting ship propeller cavitation noise  

Microsoft Academic Search

During ship travels in high-velocity, propeller cavitation noise predominates in the radiated noise sources. However, experiential data regress method was use to predicate propeller cavitation noise in the past. In this article, propeller cavitation noise has been calculated by numerical computation method. From the engineering point of view, ship propeller has been disposed as a dipole bubble. Bubble volume pulse

Yong-Kun Zhang; Ying Xiong

2011-01-01

419

Ship noise and cortisol secretion in European freshwater fishes  

Microsoft Academic Search

Underwater noise pollution is a growing problem in aquatic environments and as such may be a major source of stress for fish. In the present study, we addressed the effects of ship noise and continuous Gaussian noise on adrenal activity in three European freshwater species. Underwater ship noise recorded in the Danube River and two Austrian lakes was played back

Lidia Eva Wysocki; John P. Dittami; Friedrich Ladich

2006-01-01

420

XUV multiphoton process by high-order harmonics  

Microsoft Academic Search

We report on the generation of intense femtosecond pulses in the soft X-ray region and their application to the the multi-photon processes with a nonlinear interaction between an atom and photons in the soft Xray. 1 Harmonic generation The high-order harmonics generated with femtosecond laser pulses is one of the promising light sources of the intense XUV[1]?soft X-ray. They have

Yasuo Nabekawa; E. J. Takahashi; Hirokazu Hasegawa; Katumi Midorikawa

2005-01-01

421

Action principle for the generalized harmonic formulation of general relativity  

SciTech Connect

An action principle for the generalized harmonic formulation of general relativity is presented. The action is a functional of the spacetime metric and the gauge source vector. An action principle for the Z4 formulation of general relativity has been proposed recently by Bona, Bona-Casas, and Palenzuela. The relationship between the generalized harmonic action and the Bona, Bona-Casas, and Palenzuela action is discussed in detail.

Brown, J. David [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2011-10-15

422

Statistical phase-screen model for second-harmonic beam distortion by body wall tissue in tissue harmonic imaging  

NASA Astrophysics Data System (ADS)

In certain clinical situations, tissue harmonic imaging reduces distortion due to phase aberrations introduced by the body wall layer. A statistical model was developed to describe the effects of random inhomogeneity in the body wall on the second-harmonic beam structure. This inhomogeneity is represented by a thin random phase screen located close to the source. Phase variations across the screen are characterized statistically. An analytical solution was derived for the expected value of the intensity of the second-harmonic field for a source that radiates a focused Gaussian beam. The focal beam pattern for the second-harmonic field is compared with that of the fundamental field as a function of correlation length and variance of the phase screen, for values based on measured human abdominal wall statistics.

Yan, X.; Hamilton, M. F.

2006-05-01

423

Power line harmonic radiation in Newfoundland  

NASA Astrophysics Data System (ADS)

Recent research strongly suggests that harmonic radiation from electrical power distribution networks in industrialized regions (PHLR) has a significant effect on the occurrence of VLF waves and the energetic electron population in the inner magnetosphere, particularly in the American longitude sector. We have measured the PLHR power radiated into the magnetosphere from typical high voltage power transmission lines in Newfoundland due to unbalanced currents flowing in the lines which return through the ground, at harmonics of 60 Hz up to 4.5 kHz. From measurements of the induced a.c. magnetic field at distances from the lines both small and large compared to the skin depth (typically 1 km at 1 kHz), we have been able to estimate both the amplitudes of these unbalanced harmonic currents (~ 1 mA for frequencies 1-4 kHz) and the radiation efficiency of the lines considered as transmitting aerials. We estimate PLHR radiated powers of order 0.05-0.5 ?W per transmission line in a 1 kHz bandwidth around 3.2 kHz. This is probably much too small to stimulate magnetospheric emissions but we expect considerably greater radiated powers in other locations where there are strong single sources of 60 Hz harmonics and also in areas where the power consumption density and hence density of power lines is greater.

Yearby, K. H.; Smith, A. J.; Kaiser, T. R.; Bullough, K.

424

Harmonic cascade FEL designs for LUX  

SciTech Connect

LUX is a design concept for an ultrafast X-ray science facility, based on an electron beam accelerated to GeV energies in are circulating linac. Included in the design are short duration (200 fs or shorter FWHM) light sources using multiple stages of higher harmonic generation, seeded by a 200-250 nm laser of similar duration. This laser modulates the energy of a group of electrons within the electron bunch; this section of the electron bunch then produces radiation at a higher harmonic after entering a second, differently tuned undulator. Repeated stages in a cascade yield increasing photon energies up to 1 keV. Most of the undulators in the cascade operate in the low-gain FEL regime. Harmonic cascades have been designed for each pass of the recirculating linac up to a final electron beam energy of 3.1 GeV. For a given cascade, the photon energy can be selected over a wide range by varying the seed laser frequency and the field strength in the undulators. We present simulation results using the codes GENESIS and GINGER, as well as the results of analytical models which predict FEL performance. We discuss lattice considerations pertinent for harmonic cascade FELs, as well as sensitivity studies and requirements on the electron beam.

Penn, G.; Reinsch, M.; Wurtele, J.; Corlett, J.N.; Fawley, W.M.; Zholents, A.; Wan, W.

2004-07-16

425

Harmonically trapped jellium  

E-print Network

We discuss the model of a $D$-dimensional confined electron gas in which the particles are trapped by a harmonic potential. In particular, we study the non-interacting kinetic and exchange energies of finite-size inhomogeneous systems, and compare the resulting Thomas-Fermi and Dirac coefficients with various uniform electron gas paradigms. We show that, in the thermodynamic limit, the properties of this model are identical to those of the $D$-dimensional Fermi gas.

Loos, Pierre-François

2012-01-01

426

Jet noise modification by the 'whistler nozzle'  

NASA Technical Reports Server (NTRS)

The farfield noise characteristics of a subsonic whistler nozzle jet are measured as a function of Mach number (0.25, 0.37, and, 0.51), emission angle, and excitation mode. It is shown that a whistler nozzle has greater total and broadband acoustic power than an excited contraction nozzle; and that the intensity of far-field noise is a function of emission angle, Mach number, and whistler excitation stage. The whistler nozzle excitation produces broadband noise amplification with constant spectral shape; the broadband noise amplification (without associated whistler tones and harmonics) increases omnidirectionally with emission angle at all Mach numbers; and the broadband amplification factor decreases as Mach number and emission angle increase. Finally the whistler nozzle is described as a very efficient but inexpensive siren with applications in not only jet excitation but also acoustics.

Hasan, M. A. Z.; Islam, O.; Hussain, A. K. M. F.

1984-01-01

427

Noise Properties in the Ideal Kirchhoff-Law-Johnson-Noise Secure Communication System  

PubMed Central

In this paper we determine the noise properties needed for unconditional security for the ideal Kirchhoff-Law-Johnson-Noise (KLJN) secure key distribution system using simple statistical analysis. It has already been shown using physical laws that resistors and Johnson-like noise sources provide unconditional security. However real implementations use artificial noise generators, therefore it is a question if other kind of noise sources and resistor values could be used as well. We answer this question and in the same time we provide a theoretical basis to analyze real systems as well. PMID:24755558

Gingl, Zoltan; Mingesz, Robert

2014-01-01

428

Insights into the nature and control of rotor noise  

NASA Technical Reports Server (NTRS)

The dynamics of four important farfield rotating blade noise sources are summarized and techniques for noise reduction are discussed. These four noise areas include the role of unsteady blade surface loads on rotational noise, the effect of turbulent inflow on the radiated broadband noise of an airfoil, the influence of the trailing vortex on impulsive noise and tail rotor noise, and the effect of blade geometry on high-speed impulsive noise. These noise mechanisms occur to varying degrees on both helicopter rotors and propellers. Considerable theoretical work was done in the area of high-speed impulsive noise resulting from the geometry of the rotating blade system. Both model and full-scale experimental correlation of helicopter and propeller high-speed noise are presented. The effect of blade number and airfoil thickness distribution in reducing the high-speed noise is shown.

Pegg, R. J.

1976-01-01

429

Acceptance and control of aircraft interior noise and vibration  

NASA Technical Reports Server (NTRS)

Ride quality criteria for noise, vibration, and their combination in the helicopter cabin environment are discussed. Results are presented of laboratory and field studies of passenger responses to interior noise and vibration during the performance of a listening task and during reverie, as well as to the interaction of noise with multi-frequency and multi-axis vibration. A study of means for reducing helicopter interior noise based on analytical, experimental and flight studies of the near-field noise source characteristics of the aircraft, the transmission of noise through aircraft structures and the attenuation of noise by various noise control treatments is then presented which has resulted in a reduction of 3 dB in helicopter cabin noise. Finally, a model under development to evaluate passenger acceptance of a helicopter noise and vibration environment is indicated which incorporates the observed noise and vibration effects on comfort and is expected to provide insights for more effective noise and vibration control.

Stephens, D. G.; Leatherwood, J. D.

1980-01-01

430

Generalized Energy Equipartition in Harmonic Oscillators Driven by Active Baths  

NASA Astrophysics Data System (ADS)

We study experimentally and numerically the dynamics of colloidal beads confined by a harmonic potential in a bath of swimming E. coli bacteria. The resulting dynamics is well approximated by a Langevin equation for an overdamped oscillator driven by the combination of a white thermal noise and an exponentially correlated active noise. This scenario leads to a simple generalization of the equipartition theorem resulting in the coexistence of two different effective temperatures that govern dynamics along the flat and the curved directions in the potential landscape.

Maggi, Claudio; Paoluzzi, Matteo; Pellicciotta, Nicola; Lepore, Alessia; Angelani, Luca; Di Leonardo, Roberto

2014-12-01

431

Generalized energy equipartition in harmonic oscillators driven by active baths  

E-print Network

We study experimentally and numerically the dynamics of colloidal beads confined by a harmonic potential in a bath of swimming E. coli bacteria. The resulting dynamics is well approximated by a Langevin equation for an overdamped oscillator driven by the combination of a white thermal noise and an exponentially correlated active noise. This scenario leads to a simple generalization of the equipartition theorem resulting in the coexistence of two different effective temperatures that govern dynamics along the flat and the curved directions in the potential landscape.

Claudio Maggi; Matteo Paoluzzi; Nicola Pellicciotta; Alessia Lepore; Luca Angelani; Roberto Di Leonardo

2014-11-06

432

Generalized energy equipartition in harmonic oscillators driven by active baths.  

PubMed

We study experimentally and numerically the dynamics of colloidal beads confined by a harmonic potential in a bath of swimming E. coli bacteria. The resulting dynamics is well approximated by a Langevin equation for an overdamped oscillator driven by the combination of a white thermal noise and an exponentially correlated active noise. This scenario leads to a simple generalization of the equipartition theorem resulting in the coexistence of two different effective temperatures that govern dynamics along the flat and the curved directions in the potential landscape. PMID:25526168

Maggi, Claudio; Paoluzzi, Matteo; Pellicciotta, Nicola; Lepore, Alessia; Angelani, Luca; Di Leonardo, Roberto

2014-12-01

433

Acoustic noise during functional magnetic resonance imaginga)  

PubMed Central

Functional magnetic resonance imaging (fMRI) enables sites of brain activation to be localized in human subjects. For studies of the auditory system, acoustic noise generated during fMRI can interfere with assessments of this activation by introducing uncontrolled extraneous sounds. As a first step toward reducing the noise during fMRI, this paper describes the temporal and spectral characteristics of the noise present under typical fMRI study conditions for two imagers with different static magnetic field strengths. Peak noise levels were 123 and 138 dB re 20 ?Pa in a 1.5-tesla (T) and a 3-T imager, respectively. The noise spectrum (calculated over a 10-ms window coinciding with the highest-amplitude noise) showed a prominent maximum at 1 kHz for the 1.5-T imager (115 dB SPL) and at 1.4 kHz for the 3-T imager (131 dB SPL). The frequency content and timing of the most intense noise components indicated that the noise was primarily attributable to the readout gradients in the imaging pulse sequence. The noise persisted above background levels for 300-500 ms after gradient activity ceased, indicating that resonating structures in the imager or noise reverberating in the imager room were also factors. The gradient noise waveform was highly repeatable. In addition, the coolant pump for the imager’s permanent magnet and the room air handling system were sources of ongoing noise lower in both level and frequency than gradient coil noise. Knowledge of the sources and characteristics of the noise enabled the examination of general approaches to noise control that could be applied to reduce the unwanted noise during fMRI sessions. PMID:11051496

Ravicz, Michael E.; Melcher, Jennifer R.; Kiang, Nelson Y.-S.

2007-01-01

434

A new approach to harmonic compensation in power systems-a combined system of shunt passive and series active filters  

Microsoft Academic Search

A novel approach to compensating for harmonics in power systems is presented. It is a combined system of a shunt passive filter and a small rated series active filter. The compensation principle is described, and some filtering characteristics are discussed in detail. Excellent practicability and validity to compensate for harmonics in power systems are demonstrated experimentally. Although the source harmonic

F. Z. Peng; H. Akagi; A. Nabae

1990-01-01

435

A new measurement method for separating airborne and structureborne aircraft interior noise  

NASA Astrophysics Data System (ADS)

It is pointed out that interior noise levels of propeller driven aircraft are substantially higher than levels measured for other types of CTOL aircraft. Reduction of interior noise of such aircraft requires a knowledge of the relative importance of the acoustic and structural noise transmission paths. Noise entering the aircraft interior via an acoustic path is the noise radiated by an external noise source (propellers, exhaust noise), which propagates through the acoustic medium (air) and is then transmitted through the aircraft fuselage. This type of incoming noise is referred to as airborne noise. Noise entering the aircraft interior via a structural path is the noise which has its source in the vibrational energy which has been transmitted through the structure from a remote vibrational energy source (engines, wind flutter). This type of incoming noise is referred to as structureborne noise. A new method for separating airborne and structureborne noise is presented. It is based on two-microphone cross spectral acoustic intensity measurements.

McGary, M. C.; Mayes, W. H.

1983-02-01

436

Estimating Noise Levels In An Enclosed Space  

NASA Technical Reports Server (NTRS)

GEGS Acoustic Analysis Program (GAAP) developed to compute composite profile of noise in Spacelab module on basis of data on noise produced by equipment, data on locations of equipment, and equipment-operating schedules. Impetus for development of GAAP provided by noise that generated in Spacelab Module during SLS-1 mission because of concurrent operation of many pieces of experimental and subsystem equipment. Although originally intended specifically to help compute noise in Spacelab, also applicable to any region with multiple sources of noise. Written in FORTRAN 77.

Azzi, Elias

1995-01-01

437

A study of helicopter interior noise reduction  

NASA Technical Reports Server (NTRS)

The interior noise levels of existing helicopters are discussed along with an ongoing experimental program directed towards reducing these levels. Results of several noise and vibration measurements on Langley Research Center's Civil Helicopter Research Aircraft are presented, including measurements taken before and after installation of an acoustically-treated cabin. The predominant noise source in this helicopter is the first stage planetary gear-clash in the main gear box, both before and after installation of the acoustically treated cabin. Noise reductions of up to 20 db in some octave bands may be required in order to obtain interior noise levels comparable to commercial jet transports.

Howlett, J. T.; Clevenson, S. A.

1975-01-01

438

Effect of centerbody scattering on propeller noise  

NASA Technical Reports Server (NTRS)

This paper describes how the effect of acoustic scattering from the hub or centerbody of a propeller will affect the far-field noise levels. A simple correction to Gutin's formula for steady loading noise is given. This is a maximum for the lower harmonics but has a negligible effect on the higher frequency components that are important subjectively. The case of a blade vortex interaction is also considered, and centerbody scattering is shown to have a significant effect on the acoustic far field.

Glegg, Stewart A. L.

1991-01-01

439

Acoustic noise reduction in sinusoidal PWM drives using a randomly modulated carrier  

Microsoft Academic Search

Acoustic noise in an inverter-driven electric machine can be reduced by avoiding the concentration of harmonic energy in distinct tones. One method to spread out the harmonic spectrum without the use of programmed PWM (pulse width modulation) is to make the switching pattern random. It is proposed that the switching pattern can be randomized by modulating the triangle carrier in

Thomas G. Habetler; Deepakraj M. Divan

1991-01-01

440

Transducer profile effect on the second harmonic level  

NASA Astrophysics Data System (ADS)

The measurement of nonlinear parameter of the propagating medium using finite amplitude techniques is based on the detection of the second harmonic generated nonlinearly in the invest