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1

The Effects of Crosswind Flight on Rotor Harmonic Noise Radiation  

NASA Technical Reports Server (NTRS)

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

Greenwood, Eric; Sim, Ben W.

2013-01-01

2

Understanding Slat Noise Sources  

NASA Technical Reports Server (NTRS)

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

Khorrami, Medhi R.

2003-01-01

3

Community noise sources and noise control issues  

NASA Astrophysics Data System (ADS)

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

Nihart, Gene L.

1992-04-01

4

Community noise sources and noise control issues  

NASA Technical Reports Server (NTRS)

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

Nihart, Gene L.

1992-01-01

5

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

E-print Network

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

So, Hing-Cheung

6

Noise Amplification in Echo-Enabled Harmonic Generation (EEHG)  

SciTech Connect

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

Stupakov, Gennady

2010-08-25

7

NONEQUILIBRIUM STATIONARY STATES OF HARMONIC CHAINS WITH BULK NOISES  

E-print Network

-equilibrium sta- tionary states (NESS) of systems in contact, at their boundaries, with ther- mal reservoirs for which NESS are known are harmonic crystals [1, 2]. These are described by specifying the positions and to produce NESS with normal transport one may add bulk noise to the system [3]­[8]. The new NESS will, we

8

NONEQUILIBRIUM STATIONARY STATES OF HARMONIC CHAINS WITH BULK NOISES  

E-print Network

-equilibrium sta- tionary states (NESS) of systems in contact, at their boundaries, with ther- mal reservoirs for which NESS are known are harmonic crystals [1, 2]. These are described by specifying the positions and to produce NESS with normal transport one may add bulk noise to the system [3]­[8]. The new NESS will, we

Paris-Sud XI, Université de

9

Determination of noise descriptors and criteria for pyrotechnic noise sources  

NASA Astrophysics Data System (ADS)

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

Wu, Weixiong

2005-04-01

10

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

11

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

12

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

13

The method of separating harmonic signals from multiplicative and additive noises  

Microsoft Academic Search

This paper focuses on the extraction of a harmonic signal from multiplicative and additive noises. A method is proposed in\\u000a two stages: (1) to square the original discrete time series, which includes both signals and noises, and form a new time series.\\u000a By this means, the multiplicative noise is converted to additive noise; and (2) to filter out the noise

Yangyu Fan; Zhengwei Zhang; Xiaorong Wei; Li Zeng; Wei Wei

2007-01-01

14

Phase-Locked High-Order Harmonic Sources  

Microsoft Academic Search

We demonstrate that two harmonic sources generated independently in a xenon gas jet using the same picosecond Nd:YAG laser are locked in phase. The experiment is performed by separating a laser beam into two parallel beams focused at different locations under the nozzle of a gas jet, and therefore producing two independent sources of harmonic radiation, and studying the pattern

Raoul Zerne; Carlo Altucci; Marco Bellini; Mette B. Gaarde; T. W. Hänsch; Anne L'Huillier; Claire Lyngå; C.-G. Wahlström

1997-01-01

15

Source and processing effects on noise correlations  

NASA Astrophysics Data System (ADS)

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

Fichtner, Andreas

2014-05-01

16

Investigation of hydraulic transmission noise sources  

NASA Astrophysics Data System (ADS)

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

Klop, Richard J.

17

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

NASA Technical Reports Server (NTRS)

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

Greenwood, Eric, II; Schmitz, Fredric H.

2010-01-01

18

On the validity of harmonic source detection methods and indices  

Microsoft Academic Search

In this paper, the validity of the single-point measurements methods and indices, which were proposed for harmonic source detection and sharing harmonic responsibility between utility and consumer, are investigated in a typical distribution system which consists of several critical load cases. A parametrical analysis by means of the variation of the utility side impedance's X\\/R ratio is also undertaken. The

M. Erhan Balci

2010-01-01

19

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

20

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

21

Active Control of Aerodynamic Noise Sources  

NASA Technical Reports Server (NTRS)

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

Reynolds, Gregory A.

2001-01-01

22

Pitch strength of noise-vocoded harmonic tone complexes in normal-hearing listeners  

PubMed Central

To study the role of harmonic structure in pitch perception, normal-hearing listeners were tested using noise-vocoded harmonic tone complexes. When tested in a magnitude judgment procedure using vocoded versions generated with 2–128 channels, judgments of pitch strength increased systematically as the number of channels increased and reflected acoustic cues based on harmonic peak-to-valley ratio, but not cues based on periodicity strength. When tested in a fundamental frequency discrimination task, listeners correctly recognized the direction of pitch change with as few as eight noise-vocoded channels. The results suggest that spectral processing contributes substantially to pitch perception in normal-hearing listeners. PMID:23145701

Shofner, William P.; Campbell, Jeannine

2012-01-01

23

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

24

Sources of noise in magneto-optical readout  

NASA Technical Reports Server (NTRS)

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

Mansuripur, M.

1991-01-01

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

Development of a low noise MREIT current source  

Microsoft Academic Search

In MREIT conductivity imaging experiments of animal and human subjects, we should minimize the noise level in measured magnetic flux density data induced by injection currents with low amplitude. Since noise and artifact from an MREIT current source directly affect the quality of the data, a low-noise current source is desirable. In order to be compatible with various MREIT pulse

Young Tae Kim; Pil Joong Yoo; Tong In Oh; Eung Je Woo

2010-01-01

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

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

29

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

SciTech Connect

Least-squares sine-fit algorithms are used extensively in signal processing applications. The parameter estimates produced by such algorithms are subject to both random and systematic errors when the record of input samples consists of a fundamental sine wave corrupted by harmonic distortion or noise. The errors occur because, in general, such sine-fits will incorporate a portion of the harmonic distortion or noise into their estimate of the fundamental. Bounds are developed for these errors for least-squares four-parameter (amplitude, frequency, phase, and offset) sine-fit algorithms. The errors are functions of the number of periods in the record, the number of samples in the record, the harmonic order, and fundamental and harmonic amplitudes and phases. The bounds do not apply to cases in which harmonic components become aliased.

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

1994-03-01

30

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

Microsoft Academic Search

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

Paul Boersma

1993-01-01

31

Aircraft noise source and contour estimation  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

32

IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING, VOL. 9, NO. 1, JANUARY 2001 21 Applying the Harmonic Plus Noise Model in  

E-print Network

the Harmonic Plus Noise Model in Concatenative Speech Synthesis Yannis Stylianou, Member, IEEE Abstract--This paper describes the application of the harmonic plus noise model (HNM) for concatenative text component plus a modulated noise component. The decomposition of a speech signal into these two components

Stylianou, Yannis

33

Wind turbines---low level noise sources interfering with restoration?  

Microsoft Academic Search

Wind turbines generate a low level noise and would thus not be expected to cause annoyance and disturb rest. In a society where people are being exposed to an increasing noise load, moderate and low level noise sources may also be perceived as annoying and hence inhibit restoration. This article presents an analysis of two socio-acoustic studies of wind turbine

Eja Pedersen; Kerstin Persson Waye

2008-01-01

34

Convective amplification of gas turbine engine internal noise sources  

Microsoft Academic Search

A theoretical model is used to determine the convective amplification factor for the internal noise sources of a gas turbine engine, which factor is required to predict in-flight noise levels from engine noise measured in static tests. A general formulation is presented for calculating the propagation of sound in an arbitrary mean flow field, and applied to the static model

R. S. Larson

1981-01-01

35

Railway equivalent noise sources definition: ESM implementation and optimization  

E-print Network

Railway equivalent noise sources definition: ESM implementation and optimization E. Bonginia and H integration of railway system in environment, prediction of trains pass-by noise is a growing concern for railway operators. SNCF has therefore developed the software VAMPPASS dedicated to pass-by noise

Paris-Sud XI, Université de

36

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

37

Importance of engine as a source of helicopter external noise  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

38

The Effects of Ambient Conditions on Helicopter Rotor Source Noise Modeling  

NASA Technical Reports Server (NTRS)

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

Schmitz, Frederic H.; Greenwood, Eric

2011-01-01

39

Continuous-variable quantum key distribution with Gaussian source noise  

SciTech Connect

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

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

2011-05-15

40

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

41

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

PubMed Central

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

Petrov, Yury

2012-01-01

42

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

43

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

44

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

Microsoft Academic Search

Noise levels from magnetically-levitated trains (maglev) at very high speed may be high enough to cause environmental noise impact in residential areas. Aeroacoustic sources dominate the sound at high speeds and guideway vibrations generate noticeable sound at low speed. In addition to high noise levels, the startle effect as a result of sudden onset of sound from a rapidly moving

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

1993-01-01

45

Location and quantification of noise sources on a wind turbine  

NASA Astrophysics Data System (ADS)

Acoustic field measurements were carried out on a three-bladed wind turbine with a rotor diameter of 58 m, in order to characterize the noise sources and to verify whether trailing edge noise from the blades was dominant. To assess the effect of blade roughness, one blade was cleaned, one blade was tripped, and one blade remained untreated. A large horizontal microphone array, positioned about one rotor diameter upwind from the turbine, was used to measure the distribution of the noise sources in the rotor plane and on the individual blades. The operation parameters of the turbine were recorded in parallel to the acoustic tests. In total more than 100 measurements were performed at wind speeds between 6 and 10 m/s. The array results reveal that besides a minor source at the rotor hub, practically all noise (emitted to the ground) is produced during the downward movement of the blades. This strongly asymmetric source pattern can be explained by convective amplification and trailing edge noise directivity. The blade noise is produced at the outer part of the blades (but not at the very tip), and the level scales with the fifth power of the local flow speed. Comparison of the noise from the individual blades shows that the tripped blade is significantly noisier than the other two. Narrowband analysis of the de-dopplerized blade noise spectra indicates that trailing edge bluntness noise is not important. All in all, the test results convincingly show that broadband trailing edge noise is the dominant noise source for this wind turbine.

Oerlemans, S.; Sijtsma, P.; Méndez López, B.

2007-02-01

46

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

NASA Astrophysics Data System (ADS)

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.

1983-07-01

47

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

48

Noise source identification techniques: simple to advanced applications  

E-print Network

required. Practical application examples ranging from hearing aids to wind turbines are presented to optimise the noise emission from a wide range of products including vehicles, household goods and windNoise source identification techniques: simple to advanced applications K.B. Ginn and K. Haddad Br

Paris-Sud XI, Université de

49

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

50

Source localization and power estimation in aeroacoustic noise measurements  

Microsoft Academic Search

Using microphone arrays for noise source localization and power estimation has become common practice in aeroacoustic measurements, with the ultimate goal being the development of acoustic treatments to reduce overall airframe noise. This dissertation discusses the challenges involved in aeroacoustic testing with microphone arrays and develops a number of new signal processing techniques to overcome these challenges. The proposed algorithms

Tarik Yardibi

2009-01-01

51

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

52

Identification of complex diesel engine noise sources based on coherent power spectrum analysis  

Microsoft Academic Search

This paper presents an identification of complex diesel engine noise sources based on coherent power spectrum analysis. Noise sources identification is essential for making noise reduction strategies. The author adopts methods of hierarchy diagnosis together with coherent power spectrum analysis to identify complex noise sources of diesel engine. In investigation of the noise sources, the hierarchy tree and judgment matrix

Gequn Shu; Xingyu Liang

2007-01-01

53

Sources and characteristics of interior noise in general aviation aircraft  

NASA Technical Reports Server (NTRS)

A field study has been conducted to examine the interior noise characteristics of a general aviation aircraft. The purposes of the study were to identify the major noise sources and their relative contribution and to establish the noise transmission paths and their relative importance. Tests were performed on an aircraft operating under stationary conditions on the ground. The results show that the interior noise level of light aircraft is dominated by broadband, low frequencies (below 1,000 Hz). Both the propeller and the engine are dominant sources; however, the contribution from the propeller is significantly more than the engine at its fundamental blade passage frequency. The data suggests that the airborne path is more dominant than the structure-borne path in the transmission of broadband, low-frequency noise which apparently results from the exhaust.

Catherines, J. J.; Jha, S. K.

1976-01-01

54

Sources and characteristics of interior noise in general aviation aircraft  

NASA Technical Reports Server (NTRS)

A field study was conducted to examine the interior noise characteristics of a general aviation aircraft. The goals were to identify the major noise sources and their relative contribution and to establish the noise transmission paths and their relative importance. Tests were performed on an aircraft operating under stationary conditions on the ground. Results show that the interior noise level of light aircraft is dominated by broadband, low frequencies (below 1,000 Hz). Both the propeller and the engine are dominant sources, however, the contribution from the propeller is significantly more than the engine at its fundamental blade passage frequency. The data suggest that the airborne path is more dominant than the structure-borne path in the transmission of broadband, low frequency noise which apparently results from the exhaust.

Catherines, J. J.; Jha, S. K.

1976-01-01

55

Large bandwidth op-amp based white noise current source.  

PubMed

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. PMID:24593378

Giusi, Gino; Scandurra, Graziella; Ciofi, Carmine

2014-02-01

56

Harmonic Filters for Six-Phase and Other Multiphase Motors on Voltage Source Inverters  

Microsoft Academic Search

Inverter-driven motors having five, six, or more phases have smaller torque pulsations and lower rotor I2R loss due to harmonics than do their three-phase counterparts. However, they generally have higher stator harmonic currents. For example, six-phase motors, supplied by a six step voltage source inverters have fifth and seventh harmonic currents which are from two to five times as large

Eugene A. Klingshirn

1985-01-01

57

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

58

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

59

Covariance-based approaches to aeroacoustic noise source analysis.  

PubMed

In this paper, several covariance-based approaches are proposed for aeroacoustic noise source analysis under the assumptions of a single dominant source and all observers contaminated solely by uncorrelated noise. The Crame?r-Rao Bounds (CRB) of the unbiased source power estimates are also derived. The proposed methods are evaluated using both simulated data as well as data acquired from an airfoil trailing edge noise experiment in an open-jet aeroacoustic facility. The numerical examples show that the covariance-based algorithms significantly outperform an existing least-squares approach and provide accurate power estimates even under low signal-to-noise ratio (SNR) conditions. Furthermore, the mean-squared-errors (MSEs) of the so-obtained estimates are close to the corresponding CRB especially for a large number of data samples. The experimental results show that the power estimates of the proposed approaches are consistent with one another as long as the core analysis assumptions are obeyed. PMID:21110583

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

2010-11-01

60

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

61

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

62

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

63

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

64

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

65

Development of a low noise MREIT current source  

NASA Astrophysics Data System (ADS)

In MREIT conductivity imaging experiments of animal and human subjects, we should minimize the noise level in measured magnetic flux density data induced by injection currents with low amplitude. Since noise and artifact from an MREIT current source directly affect the quality of the data, a low-noise current source is desirable. In order to be compatible with various MREIT pulse sequences, it should be also programmable. We have developed a new MREIT current source, which is controlled by a PC program for flexibility. We designed it in such a way that it is located inside the shield room of an MRI system. To minimize noise and artifact, we adopted an optical link for the connection to the PC outside the shield room. The enclosure of the new current source provides a magnetic as well as electric shielding to prevent high frequency switching noise of the current source from interfering with the scanner. It is powered by a rechargeable battery so that the entire current source is isolated from the ground. Equipped with automatic lead switching capability, it simplifies and automates MREIT imaging experiments. Our experimental results show that its performance is superior to the previous version, which is located outside the shield room.

Kim, Young Tae; Yoo, Pil Joong; In Oh, Tong; Woo, Eung Je

2010-04-01

66

Second and Third Harmonic Measurements at the Linac Coherent Light Source  

SciTech Connect

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

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

2011-01-03

67

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

68

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

69

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

70

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

71

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

72

Migration imaging and forward modeling of microseismic noise sources near southern Italy  

Microsoft Academic Search

This study combines migration and forward source modeling techniques to examine the existence and location of persistent seismic noise near southern Italy. Our results demonstrate that noise source modeling is both feasible and recommended in validating the ``ambient source'' assumption prior to noise-based velocity analyses. Persistent noise sources near the Gargano promontory and the Tyrrhenian Sea coast are strongly suggested

Keith Brzak; Yu Jeffrey Gu; Ahmet Ökeler; Michael Steckler; Arthur Lerner-Lam

2009-01-01

73

Constructive influence of noise flatness and friction on the resonant behavior of a harmonic oscillator with fluctuating frequency.  

PubMed

The influences of noise flatness and friction coefficient on the long-time behavior of the first two moments and the correlation function for the output signal of a harmonic oscillator with fluctuating frequency subjected to an external periodic force are considered. The colored fluctuations of the oscillator frequency are modeled as a trichotomous noise. The study is a follow up of the previous investigation of a stochastic oscillator [Phys. Rev. E 78, 031120 (2008)], where the connection between the occurrence of energetic instability and stochastic multiresonance is established. Here we report some unexpected results not considered in the previous work. Notably, we have found a nonmonotonic dependence of several stochastic resonance characteristics such as spectral amplification, variance of the output signal, and signal-to-noise ratio on the friction coefficient and on the noise flatness. In particular, in certain parameter regions spectral amplification exhibits a resonancelike enhancement at intermediate values of the friction coefficient. PMID:19518437

Laas, Katrin; Mankin, Romi; Rekker, Astrid

2009-05-01

74

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

E-print Network

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

Hong, Kyung-Han

75

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

76

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

77

Optimal Design of Repetitive Controller for Harmonic Elimination in PWM Voltage Source  

E-print Network

Optimal Design of Repetitive Controller for Harmonic Elimination in PWM Voltage Source Inverters voltage source inverter systems. A method of analyzing the repetitive control system from the frequency The pulse-width modulation (PWM) voltage source inverter (VSI) is extensively employed in AC power

Tse, Chi K. "Michael"

78

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

79

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

PubMed

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

Scandurra, Graziella; Giusi, Gino; Ciofi, Carmine

2014-04-01

80

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

81

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

82

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

83

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

84

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

85

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

86

Identification of complex diesel engine noise sources based on coherent power spectrum analysis  

NASA Astrophysics Data System (ADS)

This paper presents an identification of complex diesel engine noise sources based on coherent power spectrum analysis. Noise sources identification is essential for making noise reduction strategies. The author adopts methods of hierarchy diagnosis together with coherent power spectrum analysis to identify complex noise sources of diesel engine. In investigation of the noise sources, the hierarchy tree and judgment matrix are given. Through noise sources identification, the main part of radiating surface noise is found. The result shows that the noise of low-frequency belt is mainly machinery noise from oil pump, gear and valve mechanism, etc., and it is radiated mostly from thin-walled part like gear cover and valve cover etc., while the noise of high-frequency belt is mainly combustion noise and oil pan is identified as the main part of noise reduction.

Shu, Gequn; Liang, Xingyu

2007-01-01

87

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

88

A Multisampling SVM Scheme for Current Source Converters With Superior Harmonic Performance  

Microsoft Academic Search

The device switching frequency of current source converters (CSCs) in high-power medium-voltage applications is usually several hundred Hz. Selective harmonic elimination (SHE) has been the dominant modulation scheme because of its capability to eliminate unwanted low-order harmonics at low switching frequencies. Conventional space vector modulation (SVM), as another CSC modulation scheme, provides variable modulation index control but its output contains

Jingya Dai; Yongqiang Lang; Bin Wu; Navid R. Zargari

2009-01-01

89

A power transformer as a source of noise.  

PubMed

This article presents selected results of analyses and simulations carried out as part of research performed at the Central Institute of Labor Protection - the National Research Institute (CIOP-PIB) in connection with the development of a system for active reduction of noise emitted by high power electricity transformers. This analysis covers the transformer as a source of noise as well as a mathematical description of the phenomenon of radiation of vibroacoustic energy through a transformer enclosure modeled as a vibrating rectangular plate. Also described is an acoustic model of the transformer in the form of an array of loudspeakers. PMID:18082020

Zawieska, Wiktor Marek

2007-01-01

90

Identification and modification of dominant noise sources in diesel engines  

NASA Astrophysics Data System (ADS)

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

Hayward, Michael D.

91

Volcanic jet noise: infrasonic source processes and atmospheric propagation  

NASA Astrophysics Data System (ADS)

Volcanic eruption columns are complex flows consisting of (possibly supersonic) injections of ash-gas mixtures into the atmosphere. A volcanic eruption column can be modeled as a lower momentum-driven jet (the gas-thrust region), which transitions with altitude into a thermally buoyant plume. Matoza et al. [2009] proposed that broadband infrasonic signals recorded during this type of volcanic activity represent a low-frequency form of jet noise. Jet noise is produced at higher acoustic frequencies by smaller-scale man-made jet flows (e.g., turbulent jet flow from jet engines and rockets). Jet noise generation processes could operate at larger spatial scales and produce infrasonic frequencies in the lower gas-thrust portion of the eruption column. Jet-noise-like infrasonic signals have been observed at ranges of tens to thousands of kilometers from sustained volcanic explosions at Mount St. Helens, WA; Tungurahua, Ecuador; Redoubt, AK; and Sarychev Peak, Kuril Islands. Over such distances, the atmosphere cannot be considered homogeneous. Long-range infrasound propagation takes place primarily in waveguides formed by vertical gradients in temperature and horizontal winds, and exhibits strong spatiotemporal variability. The timing and location of volcanic explosions can be estimated from remote infrasonic data and could be used with ash cloud dispersion forecasts for hazard mitigation. Source studies of infrasonic volcanic jet noise, coupled with infrasound propagation modeling, hold promise for being able to constrain more detailed eruption jet parameters with remote, ground-based geophysical data. Here we present recent work on the generation and propagation of volcanic jet noise. Matoza, R. S., D. Fee, M. A. Garcés, J. M. Seiner, P. A. Ramón, and M. A. H. Hedlin (2009), Infrasonic jet noise from volcanic eruptions, Geophys. Res. Lett., 36, L08303, doi:10.1029/2008GL036486.

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

2011-12-01

92

Noise reduction for the infrared beamline at the Advanced Light Source  

E-print Network

Noise reduction for the infrared beamline at the Advanced Light Source J. M. Byrd, M. Chin, M, California 94720 ABSTRACT Significant reductions in the noise of the infrared light have been made at Beamline 1.4.3 infrared source at the Advanced Light Source (ALS). The primary source of vibrational noise

93

X-ray harmonics rejection on third-generation synchrotron sources using compound refractive lenses.  

PubMed

A new method of harmonics rejection based on X-ray refractive optics has been proposed. Taking into account the fact that the focal distance of the refractive lens is energy-dependent, the use of an off-axis illumination of the lens immediately leads to spatial separation of the energy spectrum by focusing the fundamental harmonic at the focal point and suppressing the unfocused high-energy radiation with a screen absorber or slit. The experiment was performed at the ESRF ID06 beamline in the in-line geometry using an X-ray transfocator with compound refractive lenses. Using this technique the presence of the third harmonic has been reduced to 10(-3). In total, our method enabled suppression of all higher-order harmonics to five orders of magnitude using monochromator detuning. The method is well suited to third-generation synchrotron radiation sources and is very promising for the future ultimate storage rings. PMID:24763636

Polikarpov, Maxim; Snigireva, Irina; Snigirev, Anatoly

2014-05-01

94

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

SciTech Connect

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

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

2002-03-01

95

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

E-print Network

Pitch-Scale Modification using the Modulated Aspiration Noise Source* Daryush Mehta1,2 and Thomas F noise source, we develop an alternate approach to high-quality pitch- scale modification of continuous Terms: pitch modification, aspiration noise, modulated noise, breathiness, voice quality 1. Introduction

96

Matched Filters for Source Detection in the Poissonian Noise Regime  

E-print Network

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

Ian Stewart

2006-03-14

97

Exozodiacal Dust: Noise Source and Signpost for Habitable Planets  

NASA Astrophysics Data System (ADS)

Exozodiacal light, from debris material in other planetary systems, is both a noise source for future exoplanet imaging missions and a signpost of rocky material in, or near, the habitable zone. The LBT Interferometer has been designed to discover and characterize faint exozodiacal dust around nearby stars. This talk will summarize what we currently know about exozodiacal dust and what we aim to learn with the LBTI's survey, the Hunt for Observable Signatures of Terrestrial Planets (HOSTS).

Hinz, P.

2014-03-01

98

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

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

99

Noise of combat aircraft in proximity to air bases: Review of the possibilities of noise reduction at the source  

Microsoft Academic Search

The operations carried out by combat aircraft are a source of nuisance for the populations situated in proximity to air bases. The noise of jet aircraft constitutes the dominant source of noise in the operations in question. The authors propose to approach the question of the reduction of the corresponding sonic nuisances by utilizing experience acquired by SNECMA over the

D. Collin; J. Julliard; G. Riou

1992-01-01

100

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

101

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

102

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

NASA Astrophysics Data System (ADS)

The techniques of helicopter rotor noise prediction attempt to describe precisely the details of the noise field and remove the empiricisms and restrictions inherent in previous methods. These techniques require detailed inputs of the rotor geometry, operating conditions, and blade surface pressure distribution. The Farassat noise prediction techniques was studied, and high speed helicopter noise prediction using more detailed representations of the thickness and loading noise sources was investigated. These predictions were based on the measured blade surface pressures on an AH-1G rotor and compared to the measured sound field. Although refinements in the representation of the thickness and loading noise sources improve the calculation, there are still discrepancies between the measured and predicted sound field. Analysis of the blade surface pressure data indicates shocks on the blades, which are probably responsible for these discrepancies.

Succi, G. P.

1983-04-01

103

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

NASA Technical Reports Server (NTRS)

The techniques of helicopter rotor noise prediction attempt to describe precisely the details of the noise field and remove the empiricisms and restrictions inherent in previous methods. These techniques require detailed inputs of the rotor geometry, operating conditions, and blade surface pressure distribution. The Farassat noise prediction techniques was studied, and high speed helicopter noise prediction using more detailed representations of the thickness and loading noise sources was investigated. These predictions were based on the measured blade surface pressures on an AH-1G rotor and compared to the measured sound field. Although refinements in the representation of the thickness and loading noise sources improve the calculation, there are still discrepancies between the measured and predicted sound field. Analysis of the blade surface pressure data indicates shocks on the blades, which are probably responsible for these discrepancies.

Succi, G. P.

1983-01-01

104

A New Algorithm for Revising Noise Covariance Matrix Disturbance in the Presence of Coherent Sources  

Microsoft Academic Search

A new algorithm is proposed for direction of arrival (DOA) estimation of coherent sources in the presence of colored noise fields, which is called spatial smoothing difference method and is used to solve the question of revising noise covariance matrix disturbance in the presence of coherent sources. This algorithm can eliminate the colored noise effect on the array structure by

Fang ShengLiang; Zhang XiWang

2009-01-01

105

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

NASA Astrophysics Data System (ADS)

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.

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.

2015-02-01

106

Design of MOS transconductors with low noise and low harmonic distortion for minimum current consumption  

Microsoft Academic Search

This paper describes a method for analysis and design of MOS voltage-to-current converters (V–I converters or transconductors) and introduces a novel V–I converter circuit with significantly improved linearity performance. The proposed method uses harmonic compensation for the linearization of the V–I characteristics and introduces a normalized representation of the converter equations. The analysis is applied for several circuit topologies based

Sotir Ouzounov; Engel Roza; Hans Hegt; Gerard V. D. Weide; Arthur H. M. Van Roermund

2007-01-01

107

Order determination and optimum harmonic reconstruction of quasi-periodic signals in noise  

Microsoft Academic Search

This article proposes a new method for determining the order of wide-band quasi-periodic signals from frequency estimates provided either by their short-time Fourier or linear prediction (LP) spectra. The method consists in the search for harmonic patterns in the signal spectrum that minimize an error sum of the estimated frequencies. This error can be thought of as an extension to

Christos Malliopoulos; Stelios Bakamidis; George Carayannis

1999-01-01

108

Source Methodology for Turbofan Noise Prediction (SOURCE3D Technical Documentation)  

NASA Technical Reports Server (NTRS)

This report provides the analytical documentation for the SOURCE3D Rotor Wake/Stator Interaction Code. It derives the equations for the rotor scattering coefficients and stator source vector and scattering coefficients that are needed for use in the TFANS (Theoretical Fan Noise Design/Prediction System). SOURCE3D treats the rotor and stator as isolated source elements. TFANS uses this information, along with scattering coefficients for inlet and exit elements, and provides complete noise solutions for turbofan engines. SOURCE3D is composed of a collection of FORTRAN programs that have been obtained by extending the approach of the earlier V072 Rotor Wake/Stator Interaction Code. Similar to V072, it treats the rotor and stator as a collection of blades and vanes having zero thickness and camber contained in an infinite, hardwall annular duct. SOURCE3D adds important features to the V072 capability-a rotor element, swirl flow and vorticity waves, actuator disks for flow turning, and combined rotor/actuator disk and stator/actuator disk elements. These items allow reflections from the rotor, frequency scattering, and mode trapping, thus providing more complete noise predictions than previously. The code has been thoroughly verified through comparison with D.B. Hanson's CUP2D two- dimensional code using a narrow annulus test case.

Meyer, Harold D.

1999-01-01

109

Does the contribution of infrared and submillimeter sources reveal itself at low harmonics of the CMB?  

NASA Astrophysics Data System (ADS)

We have computed and studied the mosaic correlation maps of the ILC WMAP microwave background data with the positions of infrared and submillimeter sources. Using the histograms of the signal values in pixels and angular power spectra, we studied the statistical properties of these maps. We discovered similar behavior of a number of harmonics in the maps of correlations with the FSC IRAS, 2MASX and Planck catalog objects. The most prominent multipoles among them, which may reflect the actual distribution of radiation sources are the ? = 6 for the FSC and Planck data, and ? = 3 for the Planck source data.

Verkhodanov, O. V.; Naiden, Ya. V.

2012-01-01

110

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

111

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

112

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

113

Axonal Noise as a Source of Synaptic Variability  

PubMed Central

Post-synaptic potential (PSP) variability is typically attributed to mechanisms inside synapses, yet recent advances in experimental methods and biophysical understanding have led us to reconsider the role of axons as highly reliable transmission channels. We show that in many thin axons of our brain, the action potential (AP) waveform and thus the Ca++ signal controlling vesicle release at synapses will be significantly affected by the inherent variability of ion channel gating. We investigate how and to what extent fluctuations in the AP waveform explain observed PSP variability. Using both biophysical theory and stochastic simulations of central and peripheral nervous system axons from vertebrates and invertebrates, we show that channel noise in thin axons (<1 µm diameter) causes random fluctuations in AP waveforms. AP height and width, both experimentally characterised parameters of post-synaptic response amplitude, vary e.g. by up to 20 mV and 0.5 ms while a single AP propagates in C-fibre axons. We show how AP height and width variabilities increase with a ¾ power-law as diameter decreases and translate these fluctuations into post-synaptic response variability using biophysical data and models of synaptic transmission. We find for example that for mammalian unmyelinated axons with 0.2 µm diameter (matching cerebellar parallel fibres) axonal noise alone can explain half of the PSP variability in cerebellar synapses. We conclude that axonal variability may have considerable impact on synaptic response variability. Thus, in many experimental frameworks investigating synaptic transmission through paired-cell recordings or extracellular stimulation of presynaptic neurons, causes of variability may have been confounded. We thereby show how bottom-up aggregation of molecular noise sources contributes to our understanding of variability observed at higher levels of biological organisation. PMID:24809823

Neishabouri, Ali; Faisal, A. Aldo

2014-01-01

114

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

115

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

116

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

117

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

118

Noise radiation of propeller loading sources with angular inflow  

Microsoft Academic Search

Far field propeller loading noise equations are developed using the free-space Green function for the convected wave equation to represent both axial and transverse Mach number components. Inflow angularity influences noise in two distinct ways. First, loading is modulated causing generation of more efficient radiation modes. Second, the radiation modes themselves are modified, causing a further noise increase. The first

D. B. Hanson

1990-01-01

119

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

Microsoft Academic Search

The harmonics in electromagnetic force are a source of mechanical vibration and audible noise in an asynchronous traction motor. This paper describes an approach to reduce the force harmonics by changing the rotor slot number. Both the radial and tangential forces acting on the stator teeth are calculated by Maxwell stress tensor and their time harmonics are examined by the

Byung-Taek Kim; Byun-Il Kwon; Seung-Chan Park

1999-01-01

120

Methodology to Determine Dominant Noise Source in a System-On-Chip Based Implantable Device  

E-print Network

Methodology to Determine Dominant Noise Source in a System-On-Chip Based Implantable Device Zhihua- referred switching noise in a system-on-chip based implantable device, where input sensitivity noise in the frequency domain. An implantable potentiostat that monitors neurochemical activity

Stanacevic, Milutin

121

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

Microsoft Academic Search

Noise levels from magnetically-levitated trains (maglev) at very high speed may be high enough to cause environmental noise impact in residential areas. Aeroacoustic sources dominate the sound at high speeds and guideway vibrations generate noticeable sound at low speed. In addition to high noise levels, the startle effect as a result of sudden onset of sound from a rapidly moving

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

1993-01-01

122

Source localization analysis using seismic noise data acquired in exploration geophysics  

NASA Astrophysics Data System (ADS)

Passive monitoring using seismic noise data shows a growing interest at exploration scale. Recent studies demonstrated source localization capability using seismic noise cross-correlation at observation scales ranging from hundreds of kilometers to meters. In the context of exploration geophysics, classical localization methods using travel-time picking fail when no evident first arrivals can be detected. Likewise, methods based on the intensity decrease as a function of distance to the source also fail when the noise intensity decay gets more complicated than the power-law expected from geometrical spreading. We propose here an automatic procedure developed in ocean acoustics that permits to iteratively locate the dominant and secondary noise sources. The Matched-Field Processing (MFP) technique is based on the spatial coherence of raw noise signals acquired on a dense array of receivers in order to produce high-resolution source localizations. Standard MFP algorithms permits to locate the dominant noise source by matching the seismic noise Cross-Spectral Density Matrix (CSDM) with the equivalent CSDM calculated from a model and a surrogate source position that scans each position of a 3D grid below the array of seismic sensors. However, at exploration scale, the background noise is mostly dominated by surface noise sources related to human activities (roads, industrial platforms,..), which localization is of no interest for the monitoring of the hydrocarbon reservoir. In other words, the dominant noise sources mask lower-amplitude noise sources associated to the extraction process (in the volume). Their location is therefore difficult through standard MFP technique. The Multi-Rate Adaptative Beamforming (MRABF) is a further improvement of the MFP technique that permits to locate low-amplitude secondary noise sources using a projector matrix calculated from the eigen-value decomposition of the CSDM matrix. The MRABF approach aims at cancelling the contributions of the dominant noise source by applying an orthogonal projection to the data matrix. It involves an iterative algorithm that will first detect and isolate the main noise source, and then localize a lower-amplitude source through the MFP procedure applied to the new projected dataset. Such processing was automatically applied to a seismic noise dataset acquired in a zone of shallow hydrocarbon extraction. The dataset consists of five-days continuous recordings by 397 geophones in a kilometer scale area. As expected, locations of dominant surface noise sources were in good agreement with human structures while secondary, weaker sources were located at depth and seem related to the extraction process in the hydrocarbon reservoir.

Roux, P.; Corciulo, M.; Campillo, M.; Dubuq, D.

2011-12-01

123

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

PubMed

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

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

2010-02-01

124

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

125

Radially leaned outlet guide vanes for fan source noise reduction  

NASA Technical Reports Server (NTRS)

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

Kazin, S. B.

1973-01-01

126

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

127

(252)Cf-source-driven neutron noise analysis method  

NASA Astrophysics Data System (ADS)

The Cf-252-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 determined 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.

128

Reducing ion beam noise of vacuum arc ion sources  

SciTech Connect

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

Anders, Andre; Hollinger, Ralph

2001-08-29

129

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

130

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

131

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

132

Source Attribution of Helicopter Noise in Pristine National Park Landscapes  

Microsoft Academic Search

Aircraft overflight noise from helicopter tours is frequently encountered in such national parks as Grand Canyon, Hawaii Volcanoes, Haleakala, and Bryce Canyon. Noise is an environmental stressor and is associated with a variety of physiological and psychological effects, some of which are long-lasting. Psychologically, attributing a stressor to a nonhostile origin (e.g., a helicopter rescue mission) could mitigate stress effects.

Britton L. Mace; Paul A. Bell; Ross J. Loomis; Glenn E. Haas

133

Nonlinear generalized source method for modeling second-harmonic generation in diffraction gratings  

E-print Network

We introduce a versatile numerical method for modeling light diffraction in periodically patterned photonic structures containing quadratically nonlinear non-centrosymmetric optical materials. Our approach extends the generalized source method to nonlinear optical interactions by incorporating the contribution of nonlinear polarization sources to the diffracted field in the algorithm. We derive the mathematical formalism underlying the numerical method and introduce the Fourier-factorization suitable for nonlinear calculations. The numerical efficiency and runtime characteristics of the method are investigated in a set of benchmark calculations: the results corresponding to the fundamental frequency are compared to those obtained from a reference method and the beneficial effects of the modified Fourier-factorization rule on the accuracy of the nonlinear computations is demonstrated. In order to illustrate the capabilities of our method, we employ it to demonstrate strong enhancement of second-harmonic genera...

Weismann, Martin; Panoiu, Nicolae C

2015-01-01

134

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

135

Investigation on Insertion Loss of Noise Barrier for High-speed Moving Sound Source  

Microsoft Academic Search

When a sound source is moving at high speed, the sound source characteristics change, for example the frequency is modulated by the Doppler effect, and these changes increase as the velocity of movement of the sound source increases. That is why the loss for inserting a noise barrier when the sound source is moving at high speed was studied. This

Seigo OGATA; Hideo TSURU; Hirofumi NAKAJIMA; Kyoji FUJIWARA

136

Low-noise computer-controlled current source for quantum coherence experiments  

E-print Network

Low-noise computer-controlled current source for quantum coherence experiments S. Linzen, T. L July 2004) We describe a dual current source designed to provide static flux biases. The source combines digitally programmable potentiometers with a stabilized voltage source. Each channel has

Plourde, Britton L. T.

137

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

138

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

PubMed

Frequency stabilization of a THz quantum cascade laser (QCL) to the harmonic of a microwave source has been accomplished using a Schottky diode waveguide mixer designed for harmonic mixing. The 2.32 THz, 1.0 milliwatt CW QCL is coupled into the signal port of the mixer and a 110 GHz signal, derived from a harmonic of a microwave synthesizer, is coupled into the IF port. The difference frequency between the 21st harmonic of 110 GHz and the QCL is used in a discriminator to adjust the QCL bias current to stabilize the frequency. The short-term frequency jitter is reduced from 550 kHz to 4.5 kHz (FWHM) and the long-term frequency drift is eliminated. This performance is compared to that of several other THz QCL frequency stabilization techniques. PMID:23262736

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

2012-12-01

139

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

140

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

141

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

142

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.

1987-01-01

143

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

144

Natural noise above 50 MHZ from terrestrial and extraterrestrial sources  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

145

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

146

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

PubMed

Accurate parameter estimates relevant to the vocal behavior of marine mammals are needed to assess potential effects of anthropogenic sound exposure including how masking noise reduces the active space of sounds used for communication. Information about how these animals modify their vocal behavior in response to noise exposure is also needed for such assessment. Prior studies have reported variations in the source levels of killer whale sounds, and a more recent study reported that killer whales compensate for vessel masking noise by increasing their call amplitude. The objectives of the current study were to investigate the source levels of a variety of call types in southern resident killer whales while also considering background noise level as a likely factor related to call source level variability. The source levels of 763 discrete calls along with corresponding background noise were measured over three summer field seasons in the waters surrounding the San Juan Islands, WA. Both noise level and call type were significant factors on call source levels (1-40 kHz band, range of 135.0-175.7 dB(rms) re 1 [micro sign]Pa at 1 m). These factors should be considered in models that predict how anthropogenic masking noise reduces vocal communication space in marine mammals. PMID:22087938

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

2011-11-01

147

Determination of Jet Noise Radiation Patterns and Source Locations using 2-Dimensional Intensity Measurements  

NASA Technical Reports Server (NTRS)

Contents include the following: (1) Outline Jet Noise extrapolation to far field. (2) Two dimensional sound intensity. (3) Anechoic chamber cold jet test. (4) Results: Intensity levels. Vector maps. Source location centroids. Directivity. and (5) Conclusions.

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

1999-01-01

148

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

149

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

150

Nonlinear generalized source method for modeling second-harmonic generation in diffraction gratings  

NASA Astrophysics Data System (ADS)

We introduce a versatile numerical method for modeling light diffraction in periodically patterned photonic structures containing quadratically nonlinear non-centrosymmetric optical materials. Our approach extends the generalized source method to nonlinear optical interactions by incorporating the contribution of nonlinear polarization sources to the diffracted field in the algorithm. We derive the mathematical formalism underlying the numerical method and introduce the Fourier-factorization suitable for nonlinear calculations. The numerical efficiency and runtime characteristics of the method are investigated in a set of benchmark calculations: the results corresponding to the fundamental frequency are compared to those obtained from a reference method and the beneficial effects of the modified Fourier-factorization rule on the accuracy of the nonlinear computations is demonstrated. In order to illustrate the capabilities of our method, we employ it to demonstrate strong enhancement of second-harmonic generated in one- and two-dimensional optical gratings resonantly coupled to a slab waveguide. Our method can be easily extended to other types of nonlinear optical interactions by simply incorporating the corresponding nonlinear polarization sources in the algorithm.

Weismann, Martin; Gallagher, Dominic F. G.; Panoiu, Nicolae C.

2015-04-01

151

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

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

152

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

153

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

154

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

155

Fundamental and Harmonic Emission in Type III Solar Radio Bursts – III. Heliocentric Variation of Interplanetary Beam and Source Parameters  

Microsoft Academic Search

The parameters of type III solar radio sources have been observed to vary approximately as powers of the heliocentric distance. Recent theoretical studies of fundamental and harmonic emission are used to express the power-law exponents in terms of five basic ones. The results are then used to obtain a best fit to these five exponents, consistent with observed values of

P. A. Robinson; I. H. Cairns

1998-01-01

156

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

157

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

158

RGB source based on simultaneous quasi-phasematched second and third harmonic generation in periodically poled lithium niobate  

NASA Astrophysics Data System (ADS)

We present a pulsed RGB source based on cascaded nonlinear processes that occur inside a single crystal of PPLN with two poling periodicities placed in tandem. The first periodicity produces a ~1.43 ?m signal through optical parametric generation and the last section simultaneously produces the second (near - IR) and third harmonic (blue). The green is produced by second harmonic generation of the pump and the red is produced by non-phase-matched sum-frequency generation between the signal and pump beam.

Cudney, R. S.; Robles-Agudo, M.; Ríos, L. A.

2006-10-01

159

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

160

A new flexible distributed generation unit for active power generation and harmonic compensation under non-ideal source voltages condition  

Microsoft Academic Search

In this paper a flexible distributed generation (FDG) with a new control scheme is proposed for the purpose of contributing to power generation and harmonic compensation under non-ideal source voltages. The proposed FDG consists of a Solid Oxide Fuel Cell unit (SOFC) as power source and a three-arm full bridge DC-AC PWM inverter as utility interface. The new control scheme

Tohid Nouri; Saeid Ghasemzadeh

2011-01-01

161

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

PubMed

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

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

2012-04-01

162

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

163

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

164

(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

165

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

SciTech Connect

Electrodynamic and particle simulation studies have been carried out to optimize design of a two-cavity harmonic frequency multiplier, in which a linear electron beam is energized by rotating fields near cyclotron resonance in a TE111 cavity in a uniform magnetic field, and in which the beam then radiates coherently at the nth harmonic into a TEn11 output cavity. Examples are worked out in detail for 7th and 2nd harmonic converters, showing RF-to-RF conversion efficiencies of 45% and 88%, respectively at 19.992 GHz (K-band) and 5.712 GHz (C-band), for a drive frequency of 2.856 GHz. Details are shown of RF infrastructure (S-band klystron, modulator) and harmonic converter components (drive cavity, output cavities, electron beam source and modulator, beam collector) for the two harmonic converters to be tested. Details are also given for the two-frequency (S- and C-band) coherent multi-MW test stand for RF breakdown and RF gun studies.

Jay L. Hirshfield

2012-07-26

166

Algorithm based comparison between the integral method and harmonic analysis of the timing jitter of diode-based and solid-state pulsed laser sources  

NASA Astrophysics Data System (ADS)

A comparison between two methods of timing jitter calculation is presented. The integral method utilizes spectral area of the single side-band (SSB) phase noise spectrum to calculate root mean square (rms) timing jitter. In contrast the harmonic analysis exploits the uppermost noise power in high harmonics to retrieve timing fluctuation. The results obtained show that a consistent timing jitter of 1.2 ps is found by the integral method and harmonic analysis in gain-switched laser diodes with an external cavity scheme. A comparison of the two approaches in noise measurement of a diode-pumped Yb:KY(WO4)2 passively mode-locked laser is also shown in which both techniques give 2 ps rms timing jitter.

Metzger, N. K.; Su, C.-R.; Edwards, T. J.; Brown, C. T. A.

2015-04-01

167

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.

168

Test on automobile engine noise production source and impact based on sound intensity method  

Microsoft Academic Search

In this paper, we tested the GW 2.4S automobile engine and Mltsublshi2.4S automobile engine by adopting sound intensity method. During the experiment we got the spectrum graph, and by matching the spectrum peak from the spectrum graph and spectrum peak from the total engine noise to conclude the main noise source. By comparing Peak of the low frequency and the

Wang Hai-wei; Lin Xue-dong; Kui Hai-lin; Wang Yun-peng

2010-01-01

169

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

170

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

NASA Astrophysics Data System (ADS)

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

Walker, Bruce E.

2005-09-01

171

Accurate tracking of harmonic signals in VSC-HVDC systems using PSO based unscented transformation  

Microsoft Academic Search

This paper presents the estimation of harmonics in a voltage source converter based HVDC (VSC-HVDC) system for designing AC side filters. The extended Kalman filter (EKF) is well known for estimating amplitude, phase, frequency, and harmonic content of a signal corrupted with noise. However, the EKF algorithm suffers from instability due to linearization and costly calculation of Jacobian matrices, and

P. K. Dash; R. K. Mallick

2011-01-01

172

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

NASA Technical Reports Server (NTRS)

A preliminary investigation was made of using a hydrogen peroxide rocket to obtain pure moving source jet noise data. The thermodynamic cycle of the rocket was analyzed. It was found that the thermodynamic exhaust properties of the rocket could be made to match those of typical advanced commercial supersonic transport engines. The rocket thruster was then considered in combination with a streamlined ground car for moving source jet noise experiments. When a nonthrottlable hydrogen peroxide rocket was used to accelerate the vehicle, propellant masses and/or acceleration distances became too large. However, when a throttlable rocket or an auxiliary system was used to accelerate the vehicle, reasonable propellant masses could be obtained.

Plencner, R. M.

1977-01-01

173

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

SciTech Connect

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

Dogru, Nuran; Oziazisi, M Sadetin [Department of Electrical and Electronics Engineering, University of Gaziantep (Turkey)

2005-10-31

174

Analysis of the Low-Frequency Radio Noise Environment at Satellite Heights from Terrestrial Sources  

NASA Astrophysics Data System (ADS)

We have investigated the propagation of terrestrial radio sources from 1 to 30 MHz (HF spectral region) through the ionosphere for the purpose of characterizing the interference spectrum on potential space-based, low-frequency-radio telescopes. A recent survey of the HF noise environment at satellite heights from 1 to 14 MHz has been conducted using the WIND spacecraft. Radio frequencies for which the interference appears to be sufficiently low for radio telescopes are 1.3, 2.9, 3.1, 8.2, and 11.4 MHz. A model was developed to predict the HF noise environment. Our current model includes a source model, an ionospheric model, and a ray tracing model. The source model was developed using known commercial broadcast stations found in the World Radio TV Handbook. The ICED ionospheric model was used to generate a model ionosphere. By ray tracing a terrestrially based broadcast source through the model ionosphere, an ionospheric transfer function (ITF) was developed. By modifying the source model using the ITF, we were able to simulate the expected noise environment at satellite heights. Comparison of modeled and measured spectra show the majority of the noise environment is due to known commercial broadcasters. Improved modeling is necessary because the slopes of the simulated spectra above the plasma frequency are too shallow, and the plasma cutoff frequencies are too high compared to the measured data.

Taylor, M. F.; Basart, J. P.; McCoy, M.; Rios, E.

1996-05-01

175

Noise sources and dissipation mechanisms of a 120 # SQUID amplifier Paolo Falferi, a) Michele Bonaldi, and Antonella Cavalleri  

E-print Network

Noise sources and dissipation mechanisms of a 120 # SQUID amplifier Paolo Falferi, a) Michele device #SQUID#, based on a commercial sensor, is strongly coupled to an electrical resonator at 11 k of the noise generated by this system, the back action noise of the SQUID amplifier is estimated. The minimum

176

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

E-print Network

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

Paris-Sud XI, Université de

177

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

178

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

179

Methodology of selecting the reference source for an active noise control system in a car.  

PubMed

At the end of the 20th century, a significant development in digital technologies of signal processing made it possible to apply active noise control methods in new domains. A proper selection of the reference signal source is a main problem in implementing such systems. This paper presents an estimation method based on an indicator of the coherent power level. It also presents a simple system of active noise control in a car, operating according to the proposed method of optimising the positioning of reference sources. This system makes it possible to considerably increase the comfort of work of drivers in various kinds of road transport without a great increase in cost. This is especially significant in the case of trucks and vans. Passive barriers are considerably more expensive in them, which results in a higher level of noise than in passenger cars. PMID:23498706

D?browski, Zbigniew; Stankiewicz, Bartosz

2013-01-01

180

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

181

Common-mode noise source and its passive cancellation in full-bridge resonant converter  

Microsoft Academic Search

In this paper the results of systematic investigation into identification of dominant source of CM noise generation in a full bridge resonant converter are presented. It is shown that a small mismatch in an apparently symmetrical circuit can result in large CM injection. Mathematical analysis to predict the CM current injection is presented and is validated using SPICE simulation. For

Mangesh Borage; Sunil Tiwari; S. Kotaiah

2003-01-01

182

Calibration of a Fully Polarimetric Microwave Radiometer Using a Digital Polarimeric Noise Source  

E-print Network

Calibration of a Fully Polarimetric Microwave Radiometer Using a Digital Polarimeric Noise Source of complex correlation. It can supply signals to the input of a microwave radiometer with independently has been evaluated with the NASA Goddard Airborne Earth Science Microwave Imaging Radiometer (AESMIR

Ruf, Christopher

183

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

ERIC Educational Resources Information Center

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

Consumer Dynamics Inc., Rockville, MD.

184

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

E-print Network

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

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

2014-05-28

185

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

NASA Technical Reports Server (NTRS)

A 70-element microphone phased array was used to identify noise sources in the plume of a solid rocket motor. An environment chamber was built and other precautions were taken to protect the sensitive condenser microphones from rain, thunderstorms and other environmental elements during prolonged stay in the outdoor test stand. A camera mounted at the center of the array was used to photograph the plume. In the first phase of the study the array was placed in an anechoic chamber for calibration, and validation of the indigenous Matlab(R) based beamform software. It was found that the "advanced" beamform methods, such as CLEAN-SC was partially successful in identifying speaker sources placed closer than the Rayleigh criteria. To participate in the field test all equipments were shipped to NASA Marshal Space Flight Center, where the elements of the array hardware were rebuilt around the test stand. The sensitive amplifiers and the data acquisition hardware were placed in a safe basement, and 100m long cables were used to connect the microphones, Kulites and the camera. The array chamber and the microphones were found to withstand the environmental elements as well as the shaking from the rocket plume generated noise. The beamform map was superimposed on a photo of the rocket plume to readily identify the source distribution. It was found that the plume made an exceptionally long, >30 diameter, noise source over a large frequency range. The shock pattern created spatial modulation of the noise source. Interestingly, the concrete pad of the horizontal test stand was found to be a good acoustic reflector: the beamform map showed two distinct source distributions- the plume and its reflection on the pad. The array was found to be most effective in the frequency range of 2kHz to 10kHz. As expected, the classical beamform method excessively smeared the noise sources at lower frequencies and produced excessive side-lobes at higher frequencies. The "advanced" beamform routine CLEAN-SC created a series of lumped sources which may be unphysical. We believe that the present effort is the first-ever attempt to directly measure noise source distribution in a rocket plume.

Panda, J.; Mosher, R.

2010-01-01

186

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

PubMed

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

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

2013-03-01

187

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

188

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

NASA Technical Reports Server (NTRS)

The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions. Lighthill's theory is used to define a nominal acoustic source in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic source is Fourier transformed in the axial coordinate and time and then filtered in order to identify and separate components capable of radiating to the far field. This procedure indicates that the peak radiating component of the source is coincident with neither the peak of the full unfiltered source nor that of the turbulent kinetic energy. The phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed which calls into question the commonly made assumption that the noise sources convect at a single velocity. Space-time correlations demonstrate that the sources are not acoustically compact in the streamwise direction and that the portion of the source that radiates at angles greater than 45 deg. is stationary. Filtering non-radiating wavenumber components of the source at single frequencies reveals that a simple modulated wave forms for the source, as might be predicted by linear stability analysis. At small angles from the jet axis the noise from these modes is highly directional, better described by an exponential than a standard Doppler factor.

Freund, Jonathan B.

2001-01-01

189

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

190

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

E-print Network

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

Zadok, Avinoam

191

328 IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING, VOL. 8, NO. 2, MARCH 2000 Noise Source Models for Fricative Consonants  

E-print Network

328 IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING, VOL. 8, NO. 2, MARCH 2000 Noise Source Models for synthesis. Index Terms--Articulatory acoustics, fricatives, magnetic reso- nance images (MRI), noise source and analyzing magnetic resonance images (MRI) and high-quality acoustic recordings from human subjects during

Alwan, Abeer

192

Analysis and prediction of tilt rotor hover noise  

NASA Technical Reports Server (NTRS)

This paper presents new and improved tilt rotor hover noise prediction methods. Calculations include both discrete frequency harmonic noise and broadband noise mechanisms due to the ground plane/fountain recirculating flow. The noise mechanisms studied are thickness, loading, and inflow turbulence noise. In each case aeroacoustic models are developed and compared to noise measurements obtained experimentally for the XV-15 experimental tilt rotor aircraft. Both the effects of the mean and the turbulent fountain flows are found to be important noise sources and have strongly directional radiation patterns toward the rear of the aircraft (the direction of the rotor motion through the fountain flow). Calculations also show that the noise generated by the inflow of ambient atmospheric turbulence can also be an important noise source in hover in some directions. Further development of the methods and models, and precise information about the fountain flow, are needed to improve the predictions and to initiate noise minimization studies.

Coffen, Charles D.; George, Albert R.

1990-01-01

193

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

194

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

195

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

NASA Astrophysics Data System (ADS)

This paper presents a detailed study of the RF and noise performance of n-type Schottky barrier (SB) MOSFETs with a particular focus on the influence of the Schottky barrier height (SBH) on the main dynamic and noise figures of merit. With this aim, a 2D Monte Carlo simulator including tunnelling transport across Schottky interfaces has been developed, with special care to consider quantum transmission coefficients and the influence of image charge effects at the Schottky junctions. Particular attention is paid to the microscopic transport features, including carrier mean free paths or number of scattering events along the channel for investigating the optimization of the device topology and the strategic concepts related to the noise performance of this new architecture. A more effective control of the gate electrode over drain current for low SBH (discussed in terms of internal physical quantities) is translated into an enhanced transconductance gm, cut-off frequency fT, and non-quasistatic dynamic parameters. The drain and gate intrinsic noise sources show a noteworthy degradation with the SBH reduction due to the increased current, influence of hot carriers and reduced number of phonon scatterings. However, the results evidence that this effect is counterbalanced by the extremely improved dynamic performance in terms of gm and fT. Therefore, the deterioration of the intrinsic noise performance of the SB-MOSFET has no significant impact on high-frequency noise FoMs as NFmin, Rn and Gass for low SBH and large gate overdrive conditions. The role of the SBH on ?opt, optimum noise reactance and susceptance has been also analyzed.

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

2012-07-01

196

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

197

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

PubMed

An approach for phase noise measurement of microwave signal sources based on a microwave photonic frequency down-converter is proposed. Using the same optical carrier, the microwave signal under test is applied to generate two +1st-order optical sidebands by two stages of electro-optical modulations. A time delay is introduced between the two sidebands through a span of fiber. By beating the two +1st-order sidebands at a photodetector, frequency down-conversion is implemented, and phase noise of the signal under test can be calculated thereafter. The system has a very large operation bandwidth thanks to the frequency conversion in the optical domain, and good phase noise measurement sensitivity can be achieved since the signal degradation caused by electrical amplifiers is avoided. An experiment is carried out. The phase noise measured by the proposed system agrees well with that measured by a commercial spectrum analyzer or provided by the datasheet. A large operation bandwidth of 5-40 GHz is demonstrated using the proposed system. Moreover, good phase noise floor is achieved (-123??dBc/Hz at 1 kHz and -137??dBc/Hz at 10 kHz at 10 GHz), which is nearly constant over the full measurement range. PMID:25831324

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

2015-04-01

198

Effects of geometric and flow-field variables on inverted-velocity-profile coaxial jet noise and source distributions  

NASA Technical Reports Server (NTRS)

This paper presents relationships between the noise generation characteristics and the flow-field characteristics for inverted-velocity-profile coaxial jets. Noise measurements were made at four different sideline distances in order to determine the apparent noise source locations, and flow-field characteristics were determined from jet plume pressure/temperature surveys. These relationships are based on a published NASA Lewis prediction model, the basic assumptions of which are shown to be consistent with the experimental data reported herein. Improvements to the noise prediction procedure, on the basis of the present study, are included, which increase the accuracy of the high-frequency noise prediction.

Stone, J. R.; Goodykoontz, J. H.; Gutierrez, O. A.

1979-01-01

199

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

200

A collection of formulas for calculation of rotating blade noise - Compact and noncompact source results  

NASA Technical Reports Server (NTRS)

A unified approach is used to derive many of the current formulations for calculation of discrete frequency noise for helicopter rotors and propellers. Both compact and noncompact source formulations are derived. The compact formulations are obtained as the limit of noncompact source results. In particular, the linearized acoustic equations by Hawkings and Lowson, Farassat, Hanson, Woan and Gregorek, Succi, and Jou are derived in this paper. An interesting thickness noise formula by Isom and its recent extension to the near field by Ffowcs Williams are also presented. The paper includes some comparisons of measured and calculated acoustic pressure signatures and spectra for an advanced propeller. The theoretical results are obtained using a computer program developed by the author and P. A. Nystrom.

Farassat, F.

1980-01-01

201

Analysis of the Low-Frequency Radio Noise Environment at Satellite Heights from Terrestrial Sources  

Microsoft Academic Search

We have investigated the propagation of terrestrial radio sources from 1 to 30 MHz (HF spectral region) through the ionosphere for the purpose of characterizing the interference spectrum on potential space-based, low-frequency-radio telescopes. A recent survey of the HF noise environment at satellite heights from 1 to 14 MHz has been conducted using the WIND spacecraft. Radio frequencies for which

M. F. Taylor; J. P. Basart; M. McCoy; E. Rios

1996-01-01

202

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

NASA Technical Reports Server (NTRS)

Sound sources in the plumes of unheated round jets, in the Mach number range 0.6 to 1.8, were investigated experimentally using "casuality" approach, where air density fluctuations in the plumes were correlated with the far field noise. The air density was measured using a newly developed Molecular Rayleigh scattering based technique, which did not require any seeding. The reference at the end provides a detailed description of the measurement technique.

Panda, J.; Seasholtz, R. G.

2001-01-01

203

Dynamic subcriticality measurements using the sup 252 Cf-source-driven noise analysis method  

Microsoft Academic Search

This paper reports on dynamic measurements of the subcritical neutron multiplication factor K{sub eff} using the ²⁵²Cf-source-driven neutron noise analysis method performed for an unreflected 25.1-cm-i.d. cylindrical tank containing aqueous uranyl nitrate as the solution height changed at rates of 1 to 23 cm\\/min, with corresponding changes in k{sub eff} from 4 à 10 {sub - 4} to 0.01\\/s. These

J. T. Mihalczo; E. D. Blakeman; G. E. Ragan; E. B. Johnson; Y. Hachiya

1990-01-01

204

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

205

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

206

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

207

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

NASA Technical Reports Server (NTRS)

In helicopters and other rotorcraft, the gearbox is a major source of noise and vibration (N&V). The two N&V excitation mechanisms are the relative displacements between mating gears (transmission errors) and the friction associated with sliding between gear teeth. Historically, transmission errors have been minimized via improved manufacturing accuracies and tooth modifications. Yet, at high torque loads, noise levels are still relatively high though transmission errors might be somewhat minimal. This suggests that sliding friction is indeed a dominant noise source for high power density rotorcraft gearboxes. In reality, friction source mechanism is associated with surface roughness, lubrication regime properties, time-varying friction forces/torques and gear-mesh interface dynamics. Currently, the nature of these mechanisms is not well understood, while there is a definite need for analytical tools that incorporate sliding resistance and surface roughness, and predict their effects on the vibro- acoustic behavior of gears. Toward this end, an experiment was conducted to collect sound and vibration data on the NASA Glenn Gear-Noise Rig. Three iterations of the experiment were accomplished: Iteration 1 tested a baseline set of gears to establish a benchmark. Iteration 2 used a gear-set with low surface asperities to reduce the sliding friction excitation. Iteration 3 incorporated low viscosity oil with the baseline set of gears to examine the effect of lubrication. The results from this experiment will contribute to a two year project in collaboration with the Ohio State University to develop the necessary mathematical and computer models for analyzing geared systems and explain key physical phenomena seen in experiments. Given the importance of sliding friction in the gear dynamic and vibro-acoustic behavior of rotorcraft gearboxes, there is considerable potential for research & developmental activities. Better models and understanding will lead to quiet and reliable gear designs, as well as the selection of optimal manufacturing processes.

Asnani, Vivake M.

2004-01-01

208

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

209

Sources of Image Degradation in Fundamental and Harmonic Ultrasound Imaging: A Nonlinear, Full-Wave, Simulation Study  

PubMed Central

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-and-sum beamforming is used to generate point spread functions (PSF) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is due to reverberation from near-field structures. Compared to fundamental imaging, reverberation clutter in harmonic imaging is 27.1 dB lower. Simulated tissue with uniform velocity but unchanged impedance characteristics indicates that for fundamental imaging, the primary source of degradation is phase aberration. PMID:21507753

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

2011-01-01

210

HARMONIC VARIABLE-SIZE DICTIONARY LEARNING FOR MUSIC SOURCE Steven K. Tjoa, Matthew C. Stamm, W. Sabrina Lin, and K. J. Ray Liu  

E-print Network

HARMONIC VARIABLE-SIZE DICTIONARY LEARNING FOR MUSIC SOURCE SEPARATION Steven K. Tjoa, Matthew C}@umd.edu ABSTRACT Dictionary learning through matrix factorization has become widely popular for performing music transcription and source separation. These methods learn a concise set of dictionary atoms which repre- sent

Liu, K. J. Ray

211

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

212

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

PubMed Central

Reducing the ducted-fan noise at the low frequency range remains a big technical challenge. This study presents a passive approach to directly suppress the dipole sound radiation from an axial-flow fan housed by a tensioned membrane with cavity backing. The method aims at achieving control of low frequency noise with an appreciable bandwidth. The use of the membrane not only eliminates the aerodynamic loss of flow, but also provides flexibility in controlling the range of the stopband with high insertion loss by varying its tension and mass. A three-dimensional model is presented which allows the performance of the proposed device to be explored analytically. With the proper design, this device can achieve a noise reduction of 5?dB higher than the empty expansion cavity recently proposed by Huang et al. [J. Acoust. Soc. Am. 128, 152–163 (2010)]. Through the detailed modal analysis, even in vacuo modes of the membrane vibration are found to play an important role in the suppression of sound radiation from the dipole source. Experimental validation is conducted with a loudspeaker as the dipole source and good agreement between the predicted and measured insertion loss is achieved. PMID:22978868

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

2012-01-01

213

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

214

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

SciTech Connect

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

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

1999-09-01

215

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

216

Method for experimental determination of the contribution of individual sources to total noise. [using bandpass filter for signal analysis  

NASA Technical Reports Server (NTRS)

Multiple noise sources generating signals in a mechanical device are analyzed by considering the medium transmitting the sound as linear, and by using a band filter with bandpass for synchronous detection and signal transformation.

Rubichev, N. A.

1973-01-01

217

Investigation of noise sources in high-speed jets via correlation measurements  

NASA Astrophysics Data System (ADS)

To locate noise sources in high-speed jets, the far-field sound pressure fluctuations p(') were correlated with each of density rho , axial velocity u, radial velocity v, rho uu and rho vv fluctuations measured from various points in jet plumes. Detailed surveys were conducted in fully expanded, unheated plumes of Mach 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. The technique uses a continuous-wave narrow line-width laser, Fabry Perot interferometer and photon counting electronics. Laser light scattered by air molecules from a 1.06 mm long region on the narrow beam was collected and spectrally resolved by the interferometer. It was observed that the fluctuation spectra for air density inside the plume were in general similar to those of axial velocity spectra, while the radial velocity spectra were somewhat different. For the correlation study, microphone polar angles were varied from 30(°) to 90(°) to the jet axis. The sound pressure fluctuations p(') at the shallowest 30(°) angle provided the highest correlation with turbulent fluctuations. The correlations sharply decreased as the polar angle was increased to 60(°) , beyond which all data mostly fell below the experimental noise floor. Among all turbulent fluctuations ) correlations showed the highest values. Correlation with the first-order terms , ) and third-order terms ) was higher than that from the second-order terms and . Both < v(') ; p(') > and correlations with the 90(°) microphone signal fell below the experimental noise floor, while that from the shallow 30(°) microphone showed weaker values. By moving the laser probe to various locations in the jet, it was found that the strongest noise source lay downstream of the end of the potential core and extended many diameters beyond. Correlation measurements from turbulent fluctuations along the lip shear layer showed a Mach-number dependency: significant values were measured in supersonic jets, while correlations fell below the noise floor for subsonic jets. Various additional analyses showed that fluctuations from large coherent 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.

2005-08-01

218

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

219

This document is a preprint of the final paper: Savaghebi, M.; Vasquez, J.C.; Jalilian, A.; Guerrero, J.M.; Tzung-Lin Lee; , "Selective harmonic virtual impedance for voltage source inverters with LCL filter in microgrids," Energy Conversion  

E-print Network

.; Guerrero, J.M.; Tzung-Lin Lee; , "Selective harmonic virtual impedance for voltage source inverters://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6342572&isnumber=6342155 Selective Harmonic Virtual Impedance for Voltage Source Inverters with LCL filter source inverters ended with LCL filters for microgrid applications. The control approach consists

Vasquez, Juan Carlos

220

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

Microsoft Academic Search

This paper is devoted to blind separation of combustion noise and piston-slap in diesel engines. The two phenomena are recovered only from signals issued from accelerometers placed on one of the cylinders. A blind source separation (BSS) method is developed, based on a convolutive model of non-stationary mixtures. We introduce a new method based on the joint diagonalisation of the

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

2005-01-01

221

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

Microsoft Academic Search

This paper is devoted to blind separation of combustion noise and piston-slap in diesel engines. The two phenomena are recovered only from signals issued from accelerometers placed on one of the cylinders. A blind source separation (BSS) method is developed, based on a convolutive model of non-stationary mixtures. We introduce a new method based on the joint diagonalisation of the

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

2005-01-01

222

Low noise K?-band hopping reflectometer based on yttrium iron garnet sources at TEXTOR.  

PubMed

The heterodyne hopping reflectometer system based on wide-tuned low noise yttrium iron garnet sources was developed for TEXTOR experiment. Being installed in 1998 it successfully operates more than 10 years providing the measurements of plasma density fluctuations. Owing to the advance multihorn antennae systems installed at three different positions around the tokamak, the correlation properties as well as the propagation measurements of plasma density fluctuations are realized. The reflectometer operates in ordinary polarization mode providing the access mostly to plasma gradient and pedestal region. The capabilities of the diagnostic are illustrated with the examples of measured fluctuation characteristics in the variety of TEXTOR plasmas. PMID:21456743

Soldatov, S; Krämer-Flecken, A; Zorenko, O

2011-03-01

223

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

224

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

225

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

226

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

NASA Technical Reports Server (NTRS)

The core noise components of a dual spool turbofan engine were separated by the use of a coherence function. A source location technique based on adjusting the time delay between the combustor pressure sensor signal and the far-field microphone signal to maximize the coherence and remove as much variation of the phase angle with frequency as possible was used. The discovery was made that for the 130o microphone a 90.027 ms time shift worked best for the frequency band from 0 to 200 Hz while a 86.975 ms time shift worked best for the frequency band from 200 to 400 Hz. Hence, the 0 to 200 Hz band signal took more time than the 200 to 400 Hz band signal to travel the same distance. This suggests the 0 to 200 Hz coherent cross spectral density band is partly due to indirect combustion noise attributed to entropy fluctuations, which travel at the flow velocity, interacting with the turbine. The signal in the 200 to 400 Hz frequency band is attributed mostly to direct combustion noise. Results are presented herein for engine power settings of 48, 54, and 60 percent of the maximum power setting

Miles, Jeffrey Hilton

2008-01-01

227

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

228

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

229

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

NASA Astrophysics Data System (ADS)

Since the pioneer years of the seismology, the ubiquitous high-level of seismic energy in the period range 1-20 s, namely microseismic noise, has been clearly associated with the ocean wave activity. This noise bandwidth of the seismic spectrum defines the frontier between long-period and high-frequency transient seismology. The ``transient seismology'' terms comprise all research based on signals due to known sources such as earthquakes or volcano eruptions. Recently, many studies used the noisy unexploited part of the signal and revealed strong features for the seismic tomography and monitoring. One of the main hypothesis for noise cross-correlation techniques resides however in the assumption that the source distribution provides a random wave field between two stations. Due to the highly non-linear process of oceanic-to-seismic wave conversion, the characterization of a given source contribution is not unique. The Longuet-Higgins theory (later generalized for random waves by Hasselman) explains the existence of a primary peak around 14 s and a secondary microseismic peak (SMP) around 7 s, both. The latter, often named double-frequency peak, is much more energetic and lay between periods of 1 to 10 s; its origin (coastal or deep-ocean) is still under debate. In this study we use a few seismic broadband stations of the temporary PYROPE deployement, located on the French Atlantic coast, to analyze the seismic energy. For each component, high resolution Power Spectral Densities (PSD) are computed for time windows of 6 min. with a 60 s overlapping window; the median of four PSD is finally retained for each 20 minutes of the signal. PSD are computed between 0.01 and 10 Hz. Using the spectacular strong tidal effects on this coast as proxies, it is obvious that the behaviour of the short period range of the SMP is different from the energy observed at the frequency value corresponding to the double of the primary peak. This suggest that the SMP may be split into (at least) two parts: a near field contribution between 6 and 10 s, linked to the oceanic wave interactions on the local coast, and a far field source between 2.5 and 5.5 s. The far field source does not necessarily imply a unique deep ocean signature, since the oceanic wave reflections on distant coasts are also associated of high levels of energy in the SMP range, as previously shown. Probability Density Function of PSD for the E-W component as a function of tide (red: high tide, green: low tide)

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

2013-12-01

230

Inflight 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 were completed on the full scale SR-7L advanced turboprop which was installed on the left wing of a Gulfstream II aircraft. This program, designated Propfan Test Assessment (PTA), involved aeroacoustic testing of the propeller over a range of test conditions. These measurements defined source levels for input into long distance propagation models to predict en route noise. Inflight data were taken for 7 test cases. The sideline directivities measured by the Learjet showed expected maximum levels near 105 degrees from the propeller upstream axis. However, azimuthal directivities based on the maximum observed sideline tone levels showed highest levels below the aircraft. An investigation of the effect of propeller tip speed showed that the tone level of reduction associated with reductions in propeller tip speed is more significant in the horizontal plane than below the aircraft.

Woodward, Richard P.; Loeffler, Irvin J.

1991-01-01

231

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

232

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

NASA Astrophysics Data System (ADS)

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

Shen, Luyi

233

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

234

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

235

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

236

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

PubMed

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

2011-05-01

237

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

238

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

SciTech Connect

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; Li, Gang; Lin, Ling, E-mail: linling@tju.edu.cn [State Key Laboratory of Precision Measurement Technology and Instruments, Tianjin University, Tianjin, People's Republic of China, and Tianjin Key Laboratory of Biomedical Detecting Techniques and Instruments, Tianjin University, Tianjin (China); Qiao, Xiaoyan [College of Physics and Electronic Engineering, Shanxi University, Shanxi (China); Wang, Mengjun [School of Information Engineering, Hebei University of Technology, Tianjin (China); Zhang, Weibo [Institute of Acupuncture and Moxibustion China Academy of Chinese Medical Sciences, Beijing (China)

2014-05-15

239

The Characterised Noise HI Source Finder: Detecting HI Galaxies Using a Novel Implementation of Matched Filtering  

NASA Astrophysics Data System (ADS)

The spectral line datacubes obtained from the Square Kilometre Array (SKA) and its precursors, such as the Australian SKA Pathfinder (ASKAP), will be sufficiently large to necessitate automated detection and parametrisation of sources. Matched filtering is widely acknowledged as the best possible method for the automated detection of sources. This paper presents the Characterised Noise HI (CNHI) source finder, which employs a novel implementation of matched filtering. This implementation is optimised for the 3-D nature of the HI spectral line observations of the planned Wide-field ASKAP Legacy L-band All-sky Blind surveY (WALLABY). The CNHI source finder also employs a novel sparse representation of 3-D objects, with a high compression rate, to implement the Lutz one-pass algorithm on datacubes that are too large to process in a single pass. WALLABY will use ASKAP's phenomenal 30 square degree field of view to image ~70% of the sky. It is expected that WALLABY will find 500000 HI galaxies out to z~0.2.

Jurek, R.

2012-01-01

240

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

NASA Astrophysics Data System (ADS)

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

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

2005-11-01

241

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

242

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

NASA Technical Reports Server (NTRS)

Background noise measurements were made of the acoustic environment in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel (40x80) at NASA Ames Research Center. The measurements were acquired subsequent to the 40x80 Aeroacoustic Modernization Project, which was undertaken to improve the anechoic characteristics of the 40x80's closed test section as well as reduce the levels of background noise in the facility. The resulting 40x80 anechoic environment was described by Soderman et. al., and the current paper describes the resulting 40x80 background noise, discusses the sources of the noise, and draws comparisons to previous 40x80 background noise levels measurements. At low wind speeds or low frequencies, the 40x80 background noise is dominated by the fan drive system. To obtain the lowest fan drive noise for a given tunnel condition, it is possible in the 40x80 to reduce the fans' rotational speed and adjust the fans' blade pitch, as described by Schmidtz et. al. This idea is not new, but has now been operationally implemented with modifications for increased power at low rotational speeds. At low to mid-frequencies and at higher wind speeds, the dominant noise mechanism was thought to be caused by the surface interface of the previous test section floor acoustic lining. In order to reduce this noise mechanism, the new test section floor lining was designed to resist the pumping of flow in and out of the space between the grating slats required to support heavy equipment. In addition, the lining/flow interface over the entire test section was designed to be smoother and quieter than the previous design. At high wind speeds or high frequencies, the dominant source of background noise in the 40x80 is believed to be caused by the response of the in-flow microphone probes (required by the nature of the closed test section) to the fluctuations in the freestream flow. The resulting background noise levels are also different for probes of various diameters and types. The inflow microphone support strut is also a source of background noise but this source's impact may be minimized by careful design of the strut. In the present paper, the mechanisms mentioned above are discussed in detail. Their frequency and velocity ranges of dominance are defined and the differences between past and current facility background noise levels are presented. This paper gives valuable information for those wishing to make acoustic measurements in the 40x80. With this report and an estimate of the noise levels produced by the noise source of interest, it should be possible to determine the signal-to-noise ratios and measurement locations to successfully perform aeroacoustic testing in the NASA Ames Research Center's 40- by 80-Foot Wind Tunnel.

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

1999-01-01

243

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

PubMed

A continuous car ferry line crossing the Saguenay Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping noise in the heart of the Saguenay-St. Lawrence Marine Park. To characterize this noise and examine its potential impact on belugas, a 4-hydrophone array was deployed in the area and continuously recorded for five weeks in May-June 2009. The source levels of the different vessel types showed little dependence on vessel size or speed increase. Their spectral range covered 33 dB. Lowest noise levels occurred at night, when ferry crossing pace was reduced, and daytime noise peaked during whale-watching tour departures and arrivals. Natural ambient noise prevailed 9.4% of the time. Ferry traffic added 30-35 dB to ambient levels above 1 kHz during crossings, which contributed 8 to 14 dB to hourly averages. The whale-watching fleet added up to 5.6 dB during peak hours. Assuming no behavioral or auditory compensation, half of the time, beluga potential communication range was reduced to less than ~30% of its expected value under natural noise conditions, and to less than ~15% for one quarter of the time, with little dependence on call frequency. The echolocation band for this population of belugas was also affected by the shipping noise. PMID:22779457

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

2012-07-01

244

INVITED REVIEW: A review of diagnostic studies on jet-noise sources and generation mechanisms of subsonically convecting jets  

NASA Astrophysics Data System (ADS)

Many efforts have been made to reveal the jet-noise generation mechanisms for more than half a century. Although jet-noise phenomena of some specific types have been well understood, the mechanism of the most fundamental one, i.e. mixing noise, has not been revealed, or at least none of the claims or hypotheses have been widely accepted. To overcome this hurdle, recent acoustic- and flow-diagnostic techniques have been applied to near- and far-field measurements, and the relation between large-scale flow structures and far-field sound as well as properties of jet-noise sources have been investigated in many studies. In this paper, these diagnostic studies are reviewed, particularly focusing on the multi-point measurements including phased-array techniques, and the studies on subsonically convecting round jets, i.e. jets whose phase velocity is less than the speed of sound, are summarized.

Suzuki, Takao

2010-02-01

245

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

246

Active control of propeller induced noise fields inside a flexible cylinder  

NASA Technical Reports Server (NTRS)

An active noise control model has been evaluated for reducing aircraft interior noise. The structural noise transmission properties of an aircraft fuselage were modelled as a flexible cylinder excited by external acoustic dipoles simulating the noise produced by twin propellers. The amplitudes of an internal distribution of monopole control sources were determined such that the area-weighted mean square acoustic pressure was minimized in the propeller plane. The noise control model was evaluated at low frequencies corresponding to the blade passage frequency and first few harmonics of a typical turbo-prop aircraft. Interior noise reductions of 20 25 dB were achieved, over a substantial region of the cylindrical cross-section, with just a few monopole control sources. The most favorable interior noise reductions were achieved when the active noise control model was used in combination with propeller source phasing.

Lester, H. C.; Fuller, C. R.

1986-01-01

247

Glacial Isostatic Adjustment as a Source of Noise for the Interpretation of GRACE Data  

NASA Astrophysics Data System (ADS)

Viscoelastic relaxation in the Earth’s mantle induced by deglaciation following the last glacial maximum, can appear as a secular trend in measurements of the Earth’s time-variable gravity field. Since March 2002, the GRACE mission has been making precise measurements of Earth’s gravity field. GIA signals in northern Canada and Scandinavia are clearly evident in the GRACE data. Although valuable for providing insight on the entire GIA process and for inferring the interior structure of the solid Earth, the GIA signals can be a significant source of noise for other important applications. The GIA signals can not be distinguished from the gravitational effects of water/snow/ice variations on or near the surface of the Earth. Errors in the GIA model, for example due to errors in the assumed mantle viscosity profile, may cause problems for recovering long-term hydrological and, especially, cryospheric signals with GRACE. For instance, GIA model errors are by far the largest source of uncertainty when using GRACE to estimate present-day thinning rates of the Antarctic ice sheet. In this talk, we will discuss the solution of the viscoelastic relaxation problem for a radially stratified Earth, and most importantly, analyze the contributions of GIA signals to GRACE time-variable gravity measurements, with a particular emphasis on what kinds of recovered signals might be particularly susceptible to GIA model errors.

A, G.; Wahr, J. M.; Zhong, S.

2010-12-01

248

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

NASA Technical Reports Server (NTRS)

An Ultrasonic Configurable Fan Artificial Noise Source (UCFANS) was designed, built, and tested in support of the Langley Research Center s 14- by 22-Foot wind tunnel test of the Hybrid Wing Body (HWB) full three-dimensional 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of candidate engines using artificial sources (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft and to provide a database for shielding code validation. A range of frequencies, and a parametric study of modes were generated from exhaust and inlet nacelle configurations. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular to the axis of the nacelle (in its 0 orientation) and three planes parallel were acquired from the array sweep. In each plane the linear array traversed five sweeps, for a total span of 160 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Level, and integrated Power Levels are presented in this paper; as well as the in-duct modal structure.

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

2012-01-01

249

Analysis of light noise sources in a recycled Michelson interferometer with Fabry-Perot arms.  

PubMed

We present a method by which the effect of laser field variations on the signal output of an interferometric gravitational wave detector is rigorously determined. Using the Laser Interferometer Gravitational Wave Observatory (LIGO) optical configuration of a power recycled Michelson interferometer with Fabry-Perot arm cavities as an example, we calculate the excess noise after the input filter cavity (mode cleaner) and the dependence of the detector strain sensitivity on laser frequency and amplitude noise, radio frequency oscillator noise, and scattered-light phase noise. We find that noise on the radio frequency sidebands generally limits the detector's sensitivity. PMID:10641846

Camp, J B; Yamamoto, H; Whitcomb, S E; McClelland, D E

2000-01-01

250

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

E-print Network

Abstract--During lung sound recordings, an incessant noise source occurs due to heart sounds to detect HN segments in the spectrogram of the recorded lung sound signal. Afterwards the algorithm removes. II. METHODOLOGY A. Experimental Procedure The lung sound was recorded by placing a Siemens

Moussavi, Zahra M. K.

251

Two-Dimensional Field Analysis on Electromagnetic Vibration-and-Noise Sources in Permanent-Magnet Direct Current Commutator Motors  

Microsoft Academic Search

This paper concerns the modeling of electromagnetic vibration-and-noise sources in permanent-magnet direct current (PMDC) commutator motors. The electromagnetic sources are considered as an electromagnetic field distributed in the air-gap region of a PMDC motor. The latter is then formulated by the two-dimensional field theory in polar coordinates with the consideration of slotting effects and the armature reaction field. Consequently, based

Guhuan He; Zhenyu Huang; Dayue Chen

2011-01-01

252

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

E-print Network

Recent pTCSA) 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

253

Advances in tilt rotor noise prediction  

NASA Technical Reports Server (NTRS)

The two most serious tilt rotor external noise problems, hover noise and blade-vortex interaction noise, are studied. The results of flow visualization and inflow velocity measurements document a complex, recirculating highly unsteady and turbulent flow due to the rotor-wing-body interactions characteristic of tilt rotors. The wing under the rotor is found to obstruct the inflow, causing a deficit in the inflow velocities over the inboard region of the rotor. Discrete frequency harmonic thickness and loading noise mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various noise prediction methods using the WOPWOP code. The analysis indicates that the partial ground plane created by the wing below the rotor results in a primary sound source for hover.

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

1992-01-01

254

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

255

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

256

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

NASA Astrophysics Data System (ADS)

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

Kieffer, Susan Werner

1984-09-01

257

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

USGS Publications Warehouse

Old Faithful Geyser in Yellowstone National Park, U.S.A., is a relatively isolated source of seismic noise and exhibits seismic behavior similar to that observed at many volcanoes, including "bubblequakes" that resemble B-type "earthquakes", harmonic tremor before and during eruptions, and periods of seismic quiet prior to eruptions. Although Old Faithful differs from volcanoes in that the conduit is continuously open, that rock-fracturing is not a process responsible for seismicity, and that the erupting fluid is inviscid H2O rather than viscous magma, there are also remarkable similarities in the problems of heat and mass recharge to the system, in the eruption dynamics, and in the seismicity. Water rises irregularly into the immediate reservoir of Old Faithful as recharge occurs, a fact that suggests that there are two enlarged storage regions: one between 18 and 22 m (the base of the immediate reservoir) and one between about 10 and 12 m depth. Transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water, and by episodes of convective overturn. An eruption occurs when the temperature of the near-surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure-release waves (rarefactions) down the column can bring the liquid water onto the boiling curve. The process of conversion of the liquid water in the conduit at the onset of an eruption into a two-phase liquid-vapor mixture takes on the order of 30 s. The seismicity is directly related to the sequence of filling and heating during the recharge cycle, and to the fluid mechanics of the eruption. Short (0.2-0.3 s), monochromatic, high-frequency events (20-60 Hz) resembling unsustained harmonic tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding bubbles of steam cause transient vibrations of the fluid column. The frequency of the events is determined by the length of the water column and the speed of sound of the fluid in the conduit when these events occur; damping is controlled by the characteristic and hydraulic impedances, which depend on the above parameters, as well as on the recharge rate of the fluid. Two periods of reduced seismicity (of a few tens of seconds to nearly a minute in duration) occur during the recharge cycle, apparently when the water rises rapidly through the narrow regions of the conduit, causing a sudden pressure increase that temporarily suppresses steam bubble formation. A period of decreased seismicity also precedes preplay or an eruption; this appears to be the time when rising steam bubbles move into a zone of boiling that is acoustically decoupled from the wall of the conduit because of the acoustic impedance mismatch between boiling water (??c ??? 103 g cm-2 s-1) and rock (??c ??? 3 ?? 105 g cm2 s-1). Sustained harmonic tremor occurs during the first one to one-and-a-half minutes of an eruption of Old Faithful, but is not detectable in the succeeding minutes of the eruption. The eruption tremor is caused by hydraulic transients propagating within a sublayer of unvesiculated water that underlies the erupting two-phase liquid-vapor mixture. The resonant frequencies of the fluid column decrease to about 1 Hz when all of the water in the conduit has been converted to a water-steam mixture. Surges are observed in the flow at this frequency, but the resonance has not been detected seismically, possibly because the two-phase erupting fluid is seismically decoupled from the rock on which seismometers are placed. If Old Faithful is an analogue for volcanic seismicity, this study shows that because the frequency of tremor depends on the acoustic properties of the fluid and on conduit dimensions, both properties must be considered in analysis of tremor in volcanic regions. Because magma sound

Kieffer, S.W.

1984-01-01

258

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

NASA Technical Reports Server (NTRS)

Noise sources in high-speed jets were identified by directly correlating flow density fluctuation (cause) to far-field sound pressure fluctuation (effect). The experimental study was performed in a nozzle facility at the NASA Glenn Research Center in support of NASA s initiative to reduce the noise emitted by commercial airplanes. Previous efforts to use this correlation method have failed because the tools for measuring jet turbulence were intrusive. In the present experiment, a molecular Rayleigh-scattering technique was used that depended on laser light scattering by gas molecules in air. The technique allowed accurate measurement of air density fluctuations from different points in the plume. The study was conducted in shock-free, unheated jets of Mach numbers 0.95, 1.4, and 1.8. The turbulent motion, as evident from density fluctuation spectra was remarkably similar in all three jets, whereas the noise sources were significantly different. The correlation study was conducted by keeping a microphone at a fixed location (at the peak noise emission angle of 30 to the jet axis and 50 nozzle diameters away) while moving the laser probe volume from point to point in the flow. The following figure shows maps of the nondimensional coherence value measured at different Strouhal frequencies ([frequency diameter]/jet speed) in the supersonic Mach 1.8 and subsonic Mach 0.95 jets. The higher the coherence, the stronger the source was.

Panda, Jayanta; Seasholtz, Richard G.

2003-01-01

259

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

260

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

261

The MOD2 wind turbine: Aeroacoustical noise sources, emissions, and potential impact  

Microsoft Academic Search

This report summarizes research into characteristics of acoustic noise emissions of the DOE\\/NASA MOD-2 wind turbine. The results of this study showed that the MOD-2 noise levels are well below annoyance thresholds within residential structures a kilometer or more from the turbine rotor. It was also found that the inflow turbulent structure has a major influence on the level and

N. D. Kelley; H. E. McKenna; E. W. Jacobs; R. R. Hemphill; N. J. Birkenheuer

1988-01-01

262

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

263

A source of discrete noise components in the flow path of gas turbines and fans  

Microsoft Academic Search

The central spinner used downstream of the rotor to improve the exhaust channel aerodynamics may lead to a significant amplification of noise in axial-flow blading machinery. Here, the noise amplification process is investigated analytically using a linear model. The boundary conditions are expressed in terms of impedances, and the problem is reduced to an analysis of the change in the

A. V. Baikov; V. N. Iarov

1990-01-01

264

MEG Source Imaging Method using Fast L1 Minimum-norm and its Applications to Signals with Brain Noise and Human Resting-state Source Amplitude Images  

PubMed Central

The present study developed a fast MEG source imaging technique based on Fast Vector-based Spatio-Temporal Analysis using a L1-minimum-norm (Fast-VESTAL) and then used the method to obtain the source amplitude images of resting-state magnetoencephalography (MEG) signals for different frequency bands. The Fast-VESTAL technique consists of two steps. First, L1-minimum-norm MEG source images were obtained for the dominant spatial modes of sensor-waveform covariance matrix. Next, accurate source time-courses with millisecond temporal resolution were obtained using an inverse operator constructed from the spatial source images of Step 1. Using simulations, Fast-VESTAL’s performance of was assessed for its 1) ability to localize multiple correlated sources; 2) ability to faithfully recover source time-courses; 3) robustness to different SNR conditions including SNR with negative dB levels; 4) capability to handle correlated brain noise; and 5) statistical maps of MEG source images. An objective pre-whitening method was also developed and integrated with Fast-VESTAL to remove correlated brain noise. Fast-VESTAL’s performance was then examined in the analysis of human mediannerve MEG responses. The results demonstrated that this method easily distinguished sources in the entire somatosensory network. Next, Fast-VESTAL was applied to obtain the first whole-head MEG source-amplitude images from resting-state signals in 41 healthy control subjects, for all standard frequency bands. Comparisons between resting-state MEG sources images and known neurophysiology were provided. Additionally, in simulations and cases with MEG human responses, the results obtained from using conventional beamformer technique were compared with those from Fast-VESTAL, which highlighted the beamformer’s problems of signal leaking and distorted source time-courses. PMID:24055704

Huang, Ming-Xiong; Huang, Charles W.; Robb, Ashley; Angeles, AnneMarie; Nichols, Sharon L.; Baker, Dewleen G.; Song, Tao; Harrington, Deborah L.; Theilmann, Rebecca J.; Srinivasan, Ramesh; Heister, David; Diwakar, Mithun; Canive, Jose M.; Edgar, J. Christopher; Chen, Yu-Han; Ji, Zhengwei; Shen, Max; El-Gabalawy, Fady; Levy, Michael; McLay, Robert; Webb-Murphy, Jennifer; Liu, Thomas T.; Drake, Angela; Lee, Roland R.

2014-01-01

265

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

NASA Technical Reports Server (NTRS)

A 48-microphone planar phased array system was used to acquire jet noise source localization data on both a full-scale F404-GE-F400 engine and on a 1/4th scale model of a F400 series nozzle. The full-scale engine test data show the location of the dominant noise sources in the jet plume as a function of frequency for the engine in both baseline (no chevron) and chevron configurations. Data are presented for the engine operating both with and without afterburners. Based on lessons learned during this test, a set of recommendations are provided regarding how the phased array measurement system could be modified in order to obtain more useful acoustic source localization data on high-performance military engines in the future. The data obtained on the 1/4th scale F400 series nozzle provide useful insights regarding the full-scale engine jet noise source mechanisms, and document some of the differences associated with testing at model-scale versus fullscale.

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

2010-01-01

266

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

267

Sensitivity of calculations of {sup 252}Cf-source-driven noise analysis measurements to cross sections for aqueous fissile solutions  

SciTech Connect

Previous experiments have shown large changes in measured parameters such as the coherences and ratio of spectral densities for small changes in the measured configuration of fissile material and for small changes in k. This sensitivity was investigated by a variant of the Monte Carlo neutron transport code KENO-V.a, which calculates the time sequences of pulses at two detectors near a fissile assembly from the fission chain multiplication process initiated by a {sup 252}Cf source in or near the fissile assembly. This code directly calculates the noise analysis data from the {sup 252}Cf-source-driven neutron noise measurement method. Direct calculation of the experimental observables by the Monte Carlo method allows the benchmarking of calculational methods and cross sections. These calculations have shown a higher sensitivity of noise-measured quantities to cross sections and calculational methods than the neutron multiplication factor for aqueous fissile solutions. For example, the calculation with ENDF/B-IV cross sections yields a value of the coherence {gamma}{sub 23}{sup 2} 300% larger at low frequency than that from the Hansen-Roach cross sections. The coherence between detectors is a factor of 67 more sensitive to cross sections than the neutron multiplication factor, and this results from the coherence at low k being proportional to the fourth power of (k/{Delta}k). This increased sensitivity to calculational methods means that as far as validating calculational methods, a subcritical experiment at a k {approx} 0.9 by the {sup 252}Cf-source-driven noise analysis method may be more useful than an experiment at k {approx} 1. The noise-measured parameters can easily be obtained from measurements with an accuracy of {plus_minus}1% or less, and the precision of the Monte Carlo calculation of these quantities can also be {plus_minus}1% or less.

Valentine, T.E. [Oak Ridge Associated Universities, Inc., TN (United States); Mihalczo, J.T. [Oak Ridge National Lab., TN (United States)

1993-09-01

268

Numerical investigation of noise chracteristics of telecommunication laser sources for various modulation formats  

NASA Astrophysics Data System (ADS)

We present numerical investigation of noise properties of lasers for telecommunication purposes with emphasis on widely used distributed feedback (DFB) lasers and its influence on multi-level modulation formats. DFB lasers can be used in optical transmitters with internal and external modulation, as well as in optical receivers employing coherent detection, where they act as local oscillator. The main noise factors influencing signal characteristics of semiconductor-based lasers are intensity and phase noise. These random impairments cause degradation of fundamental output laser characteristics such as power and phase fluctuation, which are directly related to the optical signal-to-noise ratio and the laser linewidth. In case of implementation of new modulation formats into the transmission system, these stochastic processes are of main importance and significantly impact the transmission properties of modulated signals and total performance of fiber-optic transmission systems. Throughout this paper, the noise influence on the multi-level modulation formats is evaluated by effective signal-to-noise ratio (SNR) algorithms in combination with bit-error ratio (BER) formulas for appropriate type of modulation format. The obtained results have shown that the noise of DFB laser is serious restriction for multi-level modulation formats and can be improved by higher power levels, yielding to higher SNR, as required for better values of BER.

Litvik, Jan; Benedikovic, Daniel; Dubovan, Jozef; Kuba, Michal

2014-05-01

269

Locating the Source of the Twenty-six-second Microseism by Cross-correlating Records of Ambient Seismic Noise  

NASA Astrophysics Data System (ADS)

The surface-wave part of the Green function can be extracted by cross-correlating records of the ambient seismic noise between pairs of stations. The principal assumption of this method is that noise sources over the Earth's surface are randomly distributed, leading to constructive interference for sources located near the great circle connecting two stations. This condition breaks down if spatially localized, near-permanent noise sources are located off the great-circle line. The most prominent example discovered so far of such noise is the narrow band spectral peak centered on 26 sec period in the seismic background noise observed in seismograms during calm local conditions. Earlier studies identified this signal as Rayleigh waves originating in the equatorial Atlantic near the African coast (e.g., Oliver, 1962, 1963; Holcomb, 1980, 1998). Holcomb (1998) showed that peak amplitudes are strongly seasonal, maximizing during the southern hemisphere winter, suggesting an atmospheric or an oceanic origin of this narrow band microseism. Very strong, narrow band arrivals peaking around 26 sec are observed in cross-correlations of noise records for US, European, and African stations with apparent arrival times that are often smaller than expected for propagation along the great circle between the stations. Inversion of these apparent travel times shows that the narrow band 26 sec arrivals are waves originating off the west African coast in the Gulf of Guinea and propagate with an average speed close to 3.5 km/s; i.e., close to the expected group speed of Rayleigh waves at this period. Inversions using data from different months demonstrate that the source location is temporally stable with amplitudes maximizing during the southern hemisphere winter. A microseism with similar features but with a slightly broader spectral peak is observed at stations in East Asia and in the western Pacific, and originates in the North Fiji Basin. The physical cause or causes of the microseisms originating in the Gulf of Guinea and the North Fiji Basin remain(s) unclear. We believe the most likely cause to be long period oceanic waves that interact with the continental shelf, perhaps reflecting from it, and constructively interfere in a narrow frequency band in the deep ocean. Detailed physical modeling is required before the source mechanism is understood.

Shapiro, N. M.; Ritzwoller, M. H.; Bensen, G. D.

2005-12-01

270

Harmonic retrieval of regenerative machining chatter responses  

NASA Astrophysics Data System (ADS)

Based on cross fourth-order cumulants, a total least square ESPRIT approach to jointly estimating harmonic parameters in hybrid colored noises is presented, which is applied to investigate the harmonic retrieval of regenerative machining chatter responses. Taking into consideration the multiple-regenerative effect, the delayed machining dynamics under the excitation of stochastic noises is modeled, and a recursive algorithm of the solution to the delayed machining dynamics is proposed. The harmonic parameter estimation of regenerative chatter responses is detailed, which include the harmonic frequencies, cross powers, and phase shifts between successive cuts. The results demonstrate that the presented harmonic parameter estimation approach can eliminate the hybrid colored noises, retrieve the harmonic parameters with excellent estimation performance, and extract the evolution features of regenerative machining chatter.

Zhou, Xiaoqin; Wang, Wencai; Lin, Jieqiong

2013-12-01

271

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

272

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

273

The effects of cultural noise on controlled source electromagnetic resonses of subsurface fractures in resistive terrain  

E-print Network

conductors such as metal fences and buried pipes. Cultural noise adds an element of complexity to the geological interpretation of this type of data. This research investigates the influence of mutual induction between two buried targets in a CSEM experiment...

Fernandes, Roland Anthony Savio

2009-05-15

274

Single-Phase Voltage Source Inverter With a Bidirectional Buck–Boost Stage for Harmonic Injection and Distributed Generation  

Microsoft Academic Search

A transformerless single-phase inverter topology is proposed that can operate over a wide dc input voltage range and has the ability to track reference signals with fast dynamics, making it suitable for harmonic elimination and distributed generation applications. The necessary capacitor and inductor are easier to design than those for filtering the output of traditional inverters. Unlike traditional inverters, no

Ahmed Mohamed Salamah; Stephen J. Finney; Barry W. Williams

2009-01-01

275

Noise sources and optoelectronics which affect axial detection performance of time domain, Fourier domain, and swept source optical coherence tomography  

Microsoft Academic Search

Techniques based on spectral interferometry (SD-OCT) have recently been examined, with authors often suggesting superior performance compared to time domain optical coherence tomography (TD-OCT) techniques. While these technologies have similar resolutions and the spectral techniques may currently claim faster acquisition rates, their detection parameters may be inferior. This work examines the theoretical signal to noise ratio and dynamic range of

Bin Liu; Mark E. Brezinski

2006-01-01

276

Harmonic Electromagnetic Forces in Induction Motors  

Microsoft Academic Search

Recently, there has been increasing demand for quiet motors, and the same trend has been observed in the case of induction motors. In induction motors, electromagnetic noise is sometimes the predominant acoustic noise. In small motors, the major cause of vibration and noise is electromagnetic forces resulting from the combination of harmonic fluxes in the air gap. In this study,

Fuminori Ishibashi; Makoto Matsushita; Shinichi Noda

2009-01-01

277

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

278

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

279

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

280

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

281

Application of Phased Array Technology for Identification of Low Frequency Noise Sources  

Microsoft Academic Search

The findings and conclusions in this report have not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy. Reference to specific brand names does not imply endorsement by NIOSH. Summary Noise Induced Hearing Loss (NIHL) is the most common occupational disease in the U.S. with

Hugo E. Camargo; Patricio A. Ravetta; Ricardo A. Burdisso; Adam K. Smith

2009-01-01

282

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

283

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

284

[Perception of approaching and withdrawing sound sources following exposure to broadband noise. The effect of spatial domain].  

PubMed

The spatial specificity of auditory aftereffect was studied after a short-time adaptation (5 s) to the broadband noise (20-20000 Hz). Adapting stimuli were sequences of noise impulses with the constant amplitude, test stimuli--with the constant and changing amplitude: an increase of amplitude of impulses in sequence was perceived by listeners as approach of the sound source, while a decrease of amplitude--as its withdrawal. The experiments were performed in an anechoic chamber. The auditory aftereffect was estimated under the following conditions: the adapting and test stimuli were presented from the loudspeaker located at a distance of 1.1 m from the listeners (the subjectively near spatial domain) or 4.5 m from the listeners (the subjectively near spatial domain) or 4.5 m from the listeners (the subjectively far spatial domain); the adapting and test stimuli were presented from different distances. The obtained data showed that perception of the imitated movement of the sound source in both spatial domains had the common characteristic peculiarities that manifested themselves both under control conditions without adaptation and after adaptation to noise. In the absence of adaptation for both distances, an asymmetry of psychophysical curves was observed: the listeners estimated the test stimuli more often as approaching. The overestimation by listeners of test stimuli as the approaching ones was more pronounced at their presentation from the distance of 1.1 m, i. e., from the subjectively near spatial domain. After adaptation to noise the aftereffects showed spatial specificity in both spatial domains: they were observed only at the spatial coincidence of adapting and test stimuli and were absent at their separation. The aftereffects observed in two spatial domains were similar in direction and value: the listeners estimated the test stimuli more often as withdrawing as compared to control. The result of such aftereffect was restoration of the symmetry of psychometric curves and of the equiprobable estimation of direction of movement of test signals. PMID:25508938

2014-01-01

285

[Perception of approaching and withdrawing sound sources following exposure to broadband noise. The effect of spatial domain].  

PubMed

The spatial specificity of auditory aftereffect was studied after a short-time adaptation (5 s) to the broadband noise (20-20000 Hz). Adapting stimuli were sequences of noise impulses with the constant amplitude, test stimuli--with the constant and changing amplitude: an increase of amplitude of impulses in sequence was perceived by listeners as approach of the sound source, while a decrease of amplitude--as its withdrawal. The experiments were performed in an anechoic chamber. The auditory aftereffect was estimated under the following conditions: the adapting and test stimuli were presented from the loudspeaker located at a distance of 1.1 m from the listeners (the subjectively near spatial domain) or 4.5 m from the listeners (the subjectively near spatial domain) or 4.5 m from the listeners (the subjectively far spatial domain); the adapting and test stimuli were presented from different distances. The obtained data showed that perception of the imitated movement of the sound source in both spatial domains had the common characteristic peculiarities that manifested themselves both under control conditions without adaptation and after adaptation to noise. In the absence of adaptation for both distances, an asymmetry of psychophysical curves was observed: the listeners estimated the test stimuli more often as approaching. The overestimation by listeners of test stimuli as the approaching ones was more pronounced at their presentation from the distance of 1.1 m, i. e., from the subjectively near spatial domain. After adaptation to noise the aftereffects showed spatial specificity in both spatial domains: they were observed only at the spatial coincidence of adapting and test stimuli and were absent at their separation. The aftereffects observed in two spatial domains were similar in direction and value: the listeners estimated the test stimuli more often as withdrawing as compared to control. The result of such aftereffect was restoration of the symmetry of psychometric curves and of the equiprobable estimation of direction of movement of test signals. PMID:25486807

Malinina, E S

2014-01-01

286

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

PubMed Central

This paper reports comparative analyses of phase noise in Hartley, Colpitts, and common-source cross-coupled differential pair LC oscillator topologies in 28?nm CMOS technology. The impulse sensitivity function is used to carry out both qualitative and quantitative analyses of the phase noise exhibited by each circuit component in each circuit topology with oscillation frequency ranging from 1 to 100?GHz. The comparative analyses show the existence of four distinct frequency regions in which the three oscillator topologies rank unevenly in terms of best phase noise performance, due to the combined effects of device noise and circuit node sensitivity. PMID:24683340

Chlis, Ilias

2014-01-01

287

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.

288

Harmonic engine  

Microsoft Academic Search

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

Charles L

2009-01-01

289

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

E-print Network

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

Huang, Haimei

290

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

NASA Technical Reports Server (NTRS)

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

Zaman, Khairul B.

2002-01-01

291

Subcriticality of two uranyl nitrate flat cylindrical tanks spaced in air by [sup 252]Cf-source-driven noise analysis  

Microsoft Academic Search

The subcritical neutron multiplication factors k for two parallel, axially separated, flat cylindrical tanks separated up to 57.91cm in air and containing enriched uranyl (93.1 wt% [sup 235]U) nitrate solution (71.6-cm-i.d. tanks, 8.91-cm solution thickness, 1.555 g\\/cm[sup 3] solution density, and 404g U\\/l uranium density) were measured by the [sup 252]Cf-source-driven noise analysis method with measured k values varying from

J. T. Mihalczo; E. D. Blakeman; V. K. Pare; T. E. Valentine; D. J. Auslander

1993-01-01

292

Low-noise computer-controlled current source for quantum coherence experiments  

Microsoft Academic Search

We describe a dual current source designed to provide static flux biases for a superconducting qubit and for the Superconducting QUantum Interference Device (SQUID) which measures the qubit state. The source combines digitally programmable potentiometers with a stabilized voltage source. Each channel has a maximum output of +\\/-1 mA, and can be adjusted with an accuracy of about +\\/-1 nA.

S. Linzen; T. L. Robertson; T. Hime; B. L. T. Plourde; P. A. Reichardt; John Clarke

2004-01-01

293

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

294

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

295

Output voltage switching noise peaks and utility AC input harmonic current characteristics of delta-sigma modulated AC-DC converter with boost-buck circuit topologies  

Microsoft Academic Search

A high frequency carrier PWM regulator used for various types of switch-mode power converters are based on the digital or analog signal comparison processing. The voltage-mode or current-mode PWM strategies due to comparison signal processing between voltage\\/current reference and periodic carrier signals cause the switching noise peaks dependent on the multiple numbers of carrier signal frequency. In general, the switching

Atsushi Hirota; Sang-Pil Mun; Soon-Kurl Kwon; M. Nakaoka

2009-01-01

296

Discriminating harmonicity  

NASA Astrophysics Data System (ADS)

Simultaneous tones that are harmonically related tend to be grouped perceptually to form a unitary auditory image. A partial that is mistuned stands out from the other tones, and harmonic complexes with different fundamental frequencies can readily be perceived as separate auditory objects. These phenomena are evidence for the strong role of harmonicity in perceptual grouping and segregation of sounds. This study measured the discriminability of harmonicity directly. In a two interval, two alternative forced-choice (2I2AFC) paradigm, the listener chose which of two sounds, signal or foil, was composed of tones that more closely matched an exact harmonic relationship. In one experiment, the signal was varied from perfectly harmonic to highly inharmonic by adding frequency perturbation to each component. The foil always had 100% perturbation. Group mean performance decreased from greater than 90% correct for 0% signal perturbation to near chance for 80% signal perturbation. In the second experiment, adding a masker presented simultaneously with the signals and foils disrupted harmonicity. Both monaural and dichotic conditions were tested. Signal level was varied relative to masker level to obtain psychometric functions from which slopes and midpoints were estimated. Dichotic presentation of these audible stimuli improved performance by 3-10 dB, due primarily to a release from ``informational masking'' by the perceptual segregation of the signal from the masker.

Kidd, Gerald; Mason, Christine R.; Brughera, Andrew; Chiu, Chung-Yiu Peter

2003-08-01

297

Demonstration of short-haul aircraft aft noise reduction techniques on a twenty inch (50.8) diameter fan, volume 2  

NASA Technical Reports Server (NTRS)

Aft fan noise reduction techniques were investigated. The 1/3 octave band sound data were plotted with the following plots included: perceived noise level vs acoustic angle at 2 fan speeds; PWL vs frequency at 2 fan speeds; and sound pressure level vs frequency at 2 aft angles and 2 fan speeds. The source noise plots included: band pass filter sound pressure level vs acoustic angle at 2 fan speeds; and 2nd harmonic SPL acoustic angle at 2 fan speeds.

Stimpert, D. L.

1975-01-01

298

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

PubMed Central

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 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 W.; Manduca, Armando; Pislaru, Sorin V.; Kinnick, Randall R.; Pislaru, Cristina; Greenleaf, James F.; Chen, Shigao

2013-01-01

299

Blind source separation, wavelet denoising and discriminant analysis for EEG artefacts and noise  

E-print Network

sources: ocular movements, eye blinks, electrocardiogram (ECG), muscular artefacts. Generally the mixture of classical and news features and classes to improve artefact elimination (ocular, high frequency muscle

Paris-Sud XI, Université de

300

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

SciTech Connect

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

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

2009-12-11

301

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

302

Multi-target pitch tracking of vibrato sources in noise using the GM-PHD filter  

E-print Network

as open-source Python code. Probabilistic modelling of audio objects is useful be- cause Bayesian methods often polyphonic, so there is a need to analyse acoustic scenes in which multiple sources may an alternative multiple In 5th International Workshop on Machine Learning and Music, Edinburgh, Scotland, UK

Plumbley, Mark

303

Azimuthal Distribution of the Seismic Noise Source Energy Inverted from Phase Velocity Asymmetries Obtained by Ambient Noise Interferometry: A Case Study in Northeast China  

NASA Astrophysics Data System (ADS)

In this study, we observe systematical deviations between the causal and acausal Rayleigh-wave arrivals retrieved from ambient noise interferometry. We use continuous broadband records from the 127 NECESSArray (the NorthEast China Extended SeiSmic Array) stations and the 138 CEA (Chinese Earthquake Administration) stations in NE China operated between 2009 and 2011 to construct the Green's functions of the ray paths between station pairs. The stations cover the entire area of Northeast China with a station spacing of ~70-80 km. The deviations in measured phase velocity have been clearly shown as a function of the azimuth between two measured stations with a maximum magnitude of ~2 %, strongly implying that they are probably caused by a distribution of inhomogeneous ambient noise energy. We designed a method to estimate the azimuthal variation of ambient noise energy using those measured phase velocity asymmetries given by ambient noise interferometry. The inversion problem is formulated based on a plane wave approximation which relates the estimated Green's Function to the azimuthal distribution of ambient noise energy. To test the inversion method, we first generate synthetic data for given phase velocities and noise distribution across the entire NE China. Our inversion results show that the input modeled noise energy can be recovered. We then apply this inversion method to the real data and obtain azimuthal distribution of the noise energy. Four maxima of noise energy were located approximately in the Northern Pacific, Southern Pacific, Southern Indian Ocean and Northern Atlantic Ocean. Furthermore, we analyze the azimuthal variation of Signal to Noise Ratio (SNR) of the cross correlation functions used in this work, and the results are in good agreement with the results listed above. To confirm the robustness of our inversion method indicated above, more studies are required to be carried out in other parts of the world.

Han, J.; Kang, D.; Ning, J.; Chen, Y. J.; Ni, J.; Niu, F.; Grand, S. P.; Kawakatsu, H.; Tanaka, S.; Obayashi, M.

2013-12-01

304

Ultrasound harmonic imaging using nonlinear chirp for cardiac imaging  

Microsoft Academic Search

Coded excitation techniques have been used to improve a signal-to-noise ratio (SNR) in tissue harmonic imaging. However, a poor separation between fundamental and target harmonic components causes the second harmonic signals to have a high level of range sidelobes after compression. In terms of the separation performance, pulse inversion (PI) is the best method and thus provides the lowest level

Hyun-jae Song; Jaehee Song; Jin Ho Chang; Tai-kyong Song

2010-01-01

305

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

306

The low frequency sound from multipole sources in axisymmetric shear flows, with applications to jet noise  

NASA Technical Reports Server (NTRS)

A closed-form solution for the sound radiation from multipole sources imbedded in an infinite cylindrical jet with an arbitrary velocity profile is obtained. It is valid in the limit where the wavelength is large compared with the jet radius. Simple formulae for the acoustic pressure field due to convected point sources are also obtained. The results show (in a simple way) how the mean flow affects the radiation pattern from the sources. For convected lateral quadrupoles it causes the exponent of the Doppler factor multiplying the far-field pressure signal to be increased from the value of 3 used by Lighthill to 5.

Goldstein, M. E.

1975-01-01

307

Search for non-Gaussianity in pixel, harmonic and wavelet space: compared and combined  

E-print Network

We present a comparison between three approaches to test non-Gaussianity of cosmic microwave background data. The Minkowski functionals, the empirical process method and the skewness of wavelet coefficients are applied to maps generated from non-standard inflationary models and to Gaussian maps with point sources included. We discuss the different power of the pixel, harmonic and wavelet space methods on these simulated almost full-sky data (with Planck like noise). We also suggest a new procedure consisting of a combination of statistics in pixel, harmonic and wavelet space.

Paolo Cabella; Frode Hansen; Domenico Marinucci; Daniele Pagano; Nicola Vittorio

2004-01-15

308

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

309

Subcriticality of two uranyl nitrate flat cylindrical tanks spaced in air by [sup 252]Cf-source-driven noise analysis  

SciTech Connect

The subcritical neutron multiplication factors k for two parallel, axially separated, flat cylindrical tanks separated up to 57.91cm in air and containing enriched uranyl (93.1 wt% [sup 235]U) nitrate solution (71.6-cm-i.d. tanks, 8.91-cm solution thickness, 1.555 g/cm[sup 3] solution density, and 404g U/l uranium density) were measured by the [sup 252]Cf-source-driven noise analysis method with measured k values varying from 0.99 to 0.80. These measurements were performed at the Los Alamos National Laboratory (LANL) Critical Experiments Facility in 1989 and were part of the program of Westinghouse Idaho Nuclear Company (WINCO) to benchmark calculations for the design of the new storage system at Idaho National Engineering Laboratory. Initial subcriticality measurements by the source-jerk method at LANL had indicated that at a calculated neutron multiplication factor k = 0.95, the measured k was 0.975. This discrepancy was of concern to WINCO because the new storage facility was being designed with a k limit of 0.95, and thus, half of the criticality safety margin of the storage design was equal to the discrepancy between early measurements and calculations. The [sup 252]Cf-source-driven noise analysis measurements confirmed the validity of the calculational methods. In addition to providing the neutron multiplication factor from point-kinetics interpretation of the data, these measurements also provided the auto-power and cross-power spectral densities as a function of frequency, which can be calculated directly with recently developed Monte Carlo methods and thus could also be used to validate calculational methods and cross-section sets.

Mihalczo, J.T.; Blakeman, E.D.; Pare, V.K.; Valentine, T.E.; Auslander, D.J. (Oak Ridge National Lab., TN (United States))

1993-09-01

310

A generalized method for optimization of active noise controllers in three-dimensional spaces  

NASA Technical Reports Server (NTRS)

In this investigation, the formulation of an optimal active noise controller for harmonic, enclosed sound fields is derived using an indirect boundary element method. The optimal active noise controller is defined as the volume velocity secondary source strengths which minimize the sound pressure level at a number of discrete interior locations. In addition, the formulation of an optimal active noise controller which minimizes the free field power radiated from a generalized, distributed noise source is presented. Representative results are provided for each formulation. For the enclosure problem, results are given for global control, local control, and passive wall treatments using a rectangular cavity. For the free field radiation problem, the effects of secondary source location and quantity on active noise controller performance are investigated. The relative merits of each formulation are discussed.

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

1987-01-01

311

Subcriticality measurements for two coupled uranyl nitrate solution tanks using /sup 252/Cf-source-driven neutron noise analysis methods  

SciTech Connect

The subcriticality of two interacting solution tanks was determined using /sup 252/Cf-source-driven neutron noise analysis methods. These experiments were the first test of this method for an interacting system with materials (in this case, uranyl nitrate) typical of nuclear materials in processing plants. The experiments were performed to test the conclusions from previous interaction experiments with uranium metal discs for a fissile system with moderation, and to provide data to test theoretical models for coupled systems. The uranium metal experiments showed that the subcritical neutron multiplication factor, k/sub eff/, could be determined using point kinetics without any correction for spatial effects from measurements with the source and detectors located adjacent to the same cylinder, whereas for source-detector configurations with either the source and/or detectors adjacent to different cylinders, a model which incorporates the coupling is required to obtain subcriticality. In the previous experiments with two coupled uranium metal cylinders, the measurements were performed at frequencies (<50 kHz) much lower than the break frequencies (>1 MHz) for the metal discs. Thus, many aspects of the theory relating to the relationships between various spatial models could not be verified in previous experiments. These measurements and their interpretation have shown that (1) point kinetics interpretation of the measured ratios of spectral densities yields the subcritical neutron multiplication factor when the source and detectors are located in or adjacent to one of the cylinders of uranyl nitrate, and (2) the coupling reactivity can be obtained by incorporating a third neutron detector adjacent to the cylinder without the source using the kinetics model of Difilippo, which includes one additional spatial mode in the direction of the coupling.

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

1986-01-01

312

Harmonic generation at high intensities  

SciTech Connect

Atomic electrons subject to intense laser fields can absorb many photons, leading either to multiphoton ionization or the emission of a single, energetic photon which can be a high multiple of the laser frequency. The latter process, high-order harmonic generation, has been observed experimentally using a range of laser wavelengths and intensities over the past several years. Harmonic generation spectra have a generic form: a steep decline for the low order harmonics, followed by a plateau extending to high harmonic order, and finally an abrupt cutoff beyond which no harmonics are discernible. During the plateau the harmonic production is a very weak function of the process order. Harmonic generation is a promising source of coherent, tunable radiation in the XUV to soft X-ray range which could have a variety of scientific and possibly technological applications. Its conversion from an interesting multiphoton phenomenon to a useful laboratory radiation source requires a complete understanding of both its microscopic and macroscopic aspects. We present some recent results on the response of single atoms at intensities relevant to the short pulse experiments. The calculations employ time-dependent methods, which we briefly review in the next section. Following that we discuss the behavior of the harmonics as a function of laser intensity. Two features are notable: the slow scaling of the harmonic intensities with laser intensity, and the rapid variation in the phase of the individual harmonics with respect to harmonic order. We then give a simple empirical formula that predicts the extent of the plateau for a given ionization potential, wavelength and intensity.

Schafer, K.J.; Krause, J.L.; Kulander, K.C.

1993-06-01

313

Noise Amplification in HGHG Seeding  

SciTech Connect

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

Stupakov, Gennady

2010-08-25

314

Complete Vector Spherical Harmonic Expansion for Maxwell's Equations  

ERIC Educational Resources Information Center

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

Lambert, R. H.

1978-01-01

315

Inter-noise 80: Noise control for the 80's; Proceedings of the Ninth International Conference on Noise Control Engineering, Miami, FL, December 8-10, 1980. Volumes 1 & 2  

Microsoft Academic Search

Noise sources are considered along with physical phenomena, noise control elements, vibration generation and reduction, the physical aspects of environmental noise, the effects of noise, analysis, and requirements. Attention is given to noise-generating devices, stationary noise sources, moving noise sources, specialized industrial machinery and equipment, physical mechanisms of noise generation, natural sources of noise, sound propagation in the atmosphere, enclosures

G. C. Maling Jr.

1980-01-01

316

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

317

Acoustic emissions of digital data video projectors- Investigating noise sources and their change during product aging  

NASA Astrophysics Data System (ADS)

Acoustic emission testing continues to be a growing part of IT and telecommunication product design, as product noise is increasingly becoming a differentiator in the marketplace. This is especially true for digital/video display companies, such as InFocus Corporation, considering the market shift of these products to the home entertainment consumer as retail prices drop and performance factors increase. Projectors and displays using Digital Light Processing(tm) [DLP(tm)] technology incorporate a device known as a ColorWheel(tm) to generate the colors displayed at each pixel in the image. These ColorWheel(tm) devices spin at very high speeds and can generate high-frequency tones not typically heard in liquid crystal displays and other display technologies. Also, acoustic emission testing typically occurs at the beginning of product life and is a measure of acoustic energy emitted at this point in the lifecycle. Since the product is designed to be used over a long period of time, there is concern as to whether the acoustic emissions change over the lifecycle of the product, whether these changes will result in a level of nuisance to the average customer, and does this nuisance begin to develop prior to the intended lifetime of the product.

White, Michael Shane

2005-09-01

318

Shielding Characteristics Using an Ultrasonic Configurable Fan Artificial Noise Source to Generate Modes - Experimental Measurements and Analytical Predictions  

NASA Technical Reports Server (NTRS)

An Ultrasonic Configurable Fan Artificial Noise Source (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14x22 wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8% scale model. The UCFANS is a 5.8% rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial sources (no flow). The purpose of the program was to provide an estimate of the acoustic shielding benefits possible from mounting an engine on the upper surface of a wing; a flat plate model was used as the shielding surface. Simple analytical simulations were used to preview the radiation patterns - Fresnel knife-edge diffraction was coupled with a dense phased array of point sources to compute shielded and unshielded sound pressure distributions for potential test geometries and excitation modes. Contour plots of sound pressure levels, and integrated power levels, from nacelle alone and shielded configurations for both the experimental measurements and the analytical predictions are presented in this paper.

Sutliff, Daniel L.; Walker, Bruce E.

2014-01-01

319

Effects of background noise on total noise annoyance  

NASA Technical Reports Server (NTRS)

Two experiments were conducted to assess the effects of combined community noise sources on annoyance. The first experiment baseline relationships between annoyance and noise level for three community noise sources (jet aircraft flyovers, traffic and air conditioners) presented individually. Forty eight subjects evaluated the annoyance of each noise source presented at four different noise levels. Results indicated the slope of the linear relationship between annoyance and noise level for the traffic noise was significantly different from that of aircraft and of air conditioner noise, which had equal slopes. The second experiment investigated annoyance response to combined noise sources, with aircraft noise defined as the major noise source and traffic and air conditioner noise as background noise sources. Effects on annoyance of noise level differences between aircraft and background noise for three total noise levels and for both background noise sources were determined. A total of 216 subjects were required to make either total or source specific annoyance judgements, or a combination of the two, for a wide range of combined noise conditions.

Willshire, K. F.

1987-01-01

320

Dual source CT (DSCT) imaging of obese patients: evaluation of CT number accuracy, uniformity, and noise  

NASA Astrophysics Data System (ADS)

Obese patients present challenges in obtaining sufficient x-ray exposure over reasonable time periods for acceptable CT image quality. To overcome this limitation, the exposure can be divided between two x-ray sources using a dualsource (DS) CT system. However, cross-scatter issues in DS CT may also compromise image quality. We evaluated a DS CT system optimized for imaging obese patients, comparing the CT number accuracy and uniformity to the same images obtained with a single-source (SS) acquisition. The imaging modes were compared using both solid cylindrical PMMA phantoms and a semi-anthropomorphic thorax phantom fitted with extension rings to simulate different size patients. Clinical protocols were used and CTDIvol and kVp were held constant between SS and DS modes. Results demonstrated good agreement in CT number between SS and DS modes in CT number, with the DS mode showing better axial uniformity for the largest phantoms.

Walz-Flannigan, A.; Schmidt, B.,; Apel, A.; Eusemann, C.; Yu, L.; McCollough, C. H.

2009-02-01

321

Computation of Large-Scale Structure Jet Noise Sources With Weak Nonlinear Effects Using Linear Euler  

NASA Technical Reports Server (NTRS)

An approximate technique is presented for the prediction of the large-scale turbulent structure sound source in a supersonic jet. A linearized Euler equations code is used to solve for the flow disturbances within and near a jet with a given mean flow. Assuming a normal mode composition for the wave-like disturbances, the linear radial profiles are used in an integration of the Navier-Stokes equations. This results in a set of ordinary differential equations representing the weakly nonlinear self-interactions of the modes along with their interaction with the mean flow. Solutions are then used to correct the amplitude of the disturbances that represent the source of large-scale turbulent structure sound in the jet.

Dahl, Milo D.; Hixon, Ray; Mankbadi, Reda R.

2003-01-01

322

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

323

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

324

Occupational Noise Exposure  

MedlinePLUS

... reduce worker exposure to noise in a workplace. Engineering controls that reduce sound exposure levels are available and technologically feasible for most noise sources. Engineering controls involve modifying or replacing equipment, or making ...

325

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,

326

Blind source separation and identification of internal combustion engine noise based on independent component and wavelet analysis  

Microsoft Academic Search

The independent component analysis and wavelet transform technology are used to separate and identify the internal combustion engine noise signal. According to the basic principle of independent component analysis, FastICA based on negative entropy great with the good stability and convergence speed algorithm is applied to separate the noise signals of six cylinder diesel engine. And the noise signals are

Xia Wang; Fengrong Bi; Changwen Liu; Xianfeng Du; Kang Shao

2011-01-01

327

Noise sources and acoustic properties of workrooms in the plants of food-processing and pharmaceutical industry  

Microsoft Academic Search

The problems related with noise and its reduction in food-processing and pharmaceutical plants necessitate a specific approach when applying sound absorbing systems and materials in view of high hygienic and sanitary requirements. The choice of suitable materials to design systems satisfying such requirements should be preceded by the measurement of noise characteristics and determination of noise-related hazardous factors in representative

Jan Czuchaj; Antoni ?liwi?ski; Krzysztof ?rodecki

2001-01-01

328

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

329

ARTSTREAM: a neural network model of auditory scene analysis and source segregation  

Microsoft Academic Search

Multiple sound sources often contain harmonics that overlap and may be degraded by environmental noise. The auditory system is capable of teasing apart these sources into distinct mental objects, or streams. Such an ‘auditory scene analysis’ enables the brain to solve the cocktail party problem. A neural network model of auditory scene analysis, called the ARTSTREAM model, is presented to

Stephen Grossberg; Krishna K. Govindarajan; Lonce L. Wyse; Michael A. Cohen

2004-01-01

330

Determination of sound power levels of external noise sources. Part 1: Measurement methods. Part 2: Some Measurements  

NASA Astrophysics Data System (ADS)

A general frame standard for determining sound power levels of external noise sources by in situ measurements is proposed. Suitable ISO standards, a long distance method which permits directivity measurement and a short distance method are incorporated. Measurements can be made in front of walls and in corners. The short distance method uses a parallelepipedical measurement surface, omitting the top microphone position. Recommended measurement distance is or = 5 m. The microphone height h = (height of reference box) + d may be exchanged for height 10 m, giving highest sound pressure level whenever h 10 m. For very large sources, near field corrections are introduced to cancel the effect to sound energy not passing at right angles to the measurement surface. The long distance method uses a 1/2, 1/4 or 1/8 spherical measurement surface. When directivity measurements are made, the number of microphone positions are doubled relative to those of ISO 3746. The directivity index is then calculated as in ISO 3744. Measurements confirm the validity of the methods.

Jonasson, H. G.; Eslon, L.

331

Influence of noise on chaotic laser dynamics  

SciTech Connect

The Nd:YAG laser with an intracavity second harmonic generating crystal is a versatile test bed for concepts of nonlinear time series analysis as well as for techniques that have been developed for control of chaotic systems. Quantitative comparisons of experimentally measured time series of the infrared light intensity are made with numerically computed time series from a model derived here from basic principles. These comparisons utilize measures that help to distinguish between low and high dimensional dynamics and thus enhance our understanding of the influence of noise sources on the emitted laser light. {copyright} {ital 1997} {ital The American Physical Society}

Liu, C.; Abarbanel, H.D.I.; Nunes, K., [Department of Physics and Institute for Nonlinear Science, University of California, San Diego, La Jolla, California 92093 (United States)] [Department of Physics and Institute for Nonlinear Science, University of California, San Diego, La Jolla, California 92093 (United States); Roy, R.; Gills, Z., [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)] [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Abarbanel, H.D.I., [Marine Physical Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093 (United States)] [Marine Physical Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093 (United States); Nunes K., [Department of Physics, University of California, Santa Cruz, California 95064 (United States)

1997-06-01

332

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

SciTech Connect

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

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

1985-02-01

333

Directionality of ambient noise on the Juan de Fuca plate: implications for source locations of the primary and secondary microseisms  

NASA Astrophysics Data System (ADS)

Based on cross-correlations of ambient seismic noise computed using 61 ocean bottom seismometers (OBSs) within the Juan de Fuca (JdF) plate from the Cascadia Initiative experiment and 42 continental stations near the coast of the western United States, we investigate the locations of generation of the primary (11-20 s period) and secondary (5-10 s period) microseisms in the northern Pacific Ocean by analysing the directionality and seasonality of the microseism (Rayleigh wave) signals received in this region. We conclude that (1) the ambient noise observed across the array is much different in the primary and secondary microseism bands, both in its azimuthal content and seasonal variation. (2) The principal secondary microseism signals propagate towards the east, consistent with their generation in deep waters of the North Pacific, perhaps coincident both with the region of observed body wave excitation and the predicted wave-wave interaction region from recent studies. (3) The primary microseism, as indicated by observations of the azimuthal dependence of the fundamental mode Rayleigh wave as well as observations of precursory arrivals, derives significantly from the shallow waters of the eastern Pacific near to the JdF plate but also has a component generated at greater distance of unknown origin. (4) These observations suggest different physical mechanisms for generating the two microseisms: the secondary microseisms are likely to be generated by non-linear wave-wave interaction over the deep Pacific Ocean, while the primary microseism may couple directly into the solid earth locally in shallow waters from ocean gravity waves. (5) Above 5 s period, high quality empirical Green's functions are observed from cross-correlations between deep water OBSs and continental stations, which illustrates that microseisms propagate efficiently from either deep or shallow water source regions onto the continent and are well recorded by continental seismic stations.

Tian, Ye; Ritzwoller, Michael H.

2015-04-01

334

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

335

Feedback-based mitigation of torque harmonics in interior permanent magnet synchronous machines  

NASA Astrophysics Data System (ADS)

Harmonics in the electromagnetic torque are a source of concern in permanent magnet synchronous machine (PMSM) drives. The harmonics are created by non-idealities in the electromagnetic fields produced by the magnets and the stator excitation. They lead to vibration that can cause premature wear of the drivetrain components as well as acoustic noise that may be bothersome to users. In this research, current- and voltage-based control schemes have been developed to mitigate the harmonics in a class of PMSMs in which the magnets are placed interior to the rotor iron. Interior permanent magnet synchronous machines (IPMSMs) have recently gained popularity for applications including hybrid electric vehicles and robot joint control. In the current-based control, a low-cost piezoelectric sensor is used to measure torque harmonics. A conjugate gradient algorithm is then applied to search for harmonics in the stator current that produce a commanded average torque while eliminating the measured torque harmonics. The algorithm is based upon analytical closed-form expressions for the average and harmonic components of torque that have been derived for IPMSMS with arbitrary back-emf waveforms. In the voltage-based control, a time-domain model of the machine is used to map the outputs of the conjugate gradient algorithm to commanded stator voltages. Since both utilize feedback, the controls are insensitive to changes in machine parameters that result from magnetic saturation, temperature, or parameter drift. In addition, the user has flexibility to select the harmonic(s) of torque to be eliminated.

Vaks, Nir

336

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

337

Time-lapse imaging of fault properties at seismogenic depth using repeating earthquakes, active sources and seismic ambient noise  

NASA Astrophysics Data System (ADS)

The time-varying stress field of fault systems at seismogenic depths plays the mort important role in controlling the sequencing and nucleation of seismic events. Using seismic observations from repeating earthquakes, controlled active sources and seismic ambient noise, five studies at four different fault systems across North America, Central Japan, North and mid-West China are presented to describe our efforts to measure such time dependent structural properties. Repeating and similar earthquakes are hunted and analyzed to study the post-seismic fault relaxation at the aftershock zone of the 1984 M 6.8 western Nagano and the 1976 M 7.8 Tangshan earthquakes. The lack of observed repeating earthquakes at western Nagano is attributed to the absence of a well developed weak fault zone, suggesting that the fault damage zone has been almost completely healed. In contrast, the high percentage of similar and repeating events found at Tangshan suggest the existence of mature fault zones characterized by stable creep under steady tectonic loading. At the Parkfield region of the San Andreas Fault, repeating earthquake clusters and chemical explosions are used to construct a scatterer migration image based on the observation of systematic temporal variations in the seismic waveforms across the occurrence time of the 2004 M 6 Parkfield earthquake. Coseismic fluid charge or discharge in fractures caused by the Parkfield earthquake is used to explain the observed seismic scattering properties change at depth. In the same region, a controlled source cross-well experiment conducted at SAFOD pilot and main holes documents two large excursions in the travel time required for a shear wave to travel through the rock along a fixed pathway shortly before two rupture events, suggesting that they may be related to pre-rupture stress induced changes in crack properties. At central China, a tomographic inversion based on the theory of seismic ambient noise and coda wave interferometry clearly reveals a coseismic velocity decrease region with the strike and length strikingly matching the fault zone of the 2008 M 7.9 Wenchuan earthquake at depth. We speculate the imaged decrease velocity region resulted from decreased crustal stress around the fault zone at upper crust.

Cheng, Xin

2009-12-01

338

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

339

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

NASA Technical Reports Server (NTRS)

An Ultrasonic Configurable Fan Artificial Noise Source (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14- by 22-ft wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial sources (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft using the projected signature of the engine currently proposed for the HWB. The modal structures at the rating points were generated from inlet and exhaust nacelle configurations--a flat plate model was used as the shielding surface and vertical control surfaces with correct plan form shapes were also tested to determine their additional impact on shielding. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular, and two planes parallel, to the axis of the nacelle were acquired from the array sweep. In each plane the linear array traversed four sweeps, for a total span of 168 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Levels, and integrated Power Levels, from nacelle alone and shielded configurations are presented in this paper; as well as the in-duct mode power levels

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

2014-01-01

340

Combustion Noise  

E-print Network

, eved by through on the maining er noise   Figure 2 Com noise a recent combus and stra premixe interact discrete the flam combus LPP sy Furtherm overall typicall 9]. It i method technol [7, 10, 1 2- Moti The indirect process generat 15... no contraction ase rate as tion were i m the open .safran-group turbojet eng ant source h and cut b s lean pr ission [4]. 7]. As disc an instabili tic waves. he combus tability has he rate of c , which can PU) is an y an aircra ent of APU ad-band co le the intr...

Dowling, Ann P.; Mahmoudi, Yasser

2014-01-01

341

Radiated noise characteristics of a modern cargo ship  

PubMed

Extensive measurements were made of the radiated noise of M/V OVERSEAS HARRIETTE, a bulk cargo ship (length 173 m, displacement 25 515 tons) powered by a direct-drive low-speed diesel engine-a design representative of many modern merchant ships. The radiated noise data show high-level tonal frequencies from the ship's service diesel generator, main engine firing rate, and blade rate harmonics due to propeller cavitation. Radiated noise directionality measurements indicate that the radiation is generally dipole in form at lower frequencies, as expected. There are some departures from this pattern that may indicate hull interactions. Blade rate source level (174 dB re 1 microPa/m at 9 Hz, 16 knots) agrees reasonably well with a model of fundamental blade rate radiation previously reported by Gray and Greeley, but agreement for blade rate harmonics is not as good. Noise from merchant ships elevates the natural ambient by 20-30 dB in many areas; the effects of this noise on the biological environment have not been widely investigated. PMID:10641625

Arveson; Vendittis

2000-01-01

342

Interior noise reduction by alternate resonance tuning  

NASA Technical Reports Server (NTRS)

Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at low frequencies, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is studied which considers aircraft fuselages lined with panels alternately tuned to frequencies above and below the frequency that must be attenuated. Adjacent panel would oscillate at equal amplitude, to give equal acoustic source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to be cut off, and therefore be nonpropagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is being investigated theoretically and experimentally. Progress to date is discussed.

Bliss, Donald B.; Gottwald, James A.; Bryce, Jeffrey W.

1987-01-01

343

Strongly Dispersive Transient Bragg Grating for High Harmonics  

SciTech Connect

We create a transient Bragg grating in a high harmonic generation medium using two counterpropagating pulses. The Bragg grating disperses the harmonics in angle and can diffract a large bandwidth with temporal resolution limited only by the source size.

Farrell, J.; Spector, L.S.; /SLAC, PULSE /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.; Gaarde, M.B.; /SLAC, PULSE /Louisiana State U.; McFarland, B.K.; Bucksbaum, P.H.; Guhr, Markus; /SLAC, PULSE /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.

2010-06-04

344

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

345

International Congress and Exposition on Noise Control Engineering  

E-print Network

The 33rd International Congress and Exposition on Noise Control Engineering 1/8 Perception with a systematically varied level of the first pitch harmonics are rank ordered according to their pattern noise

Vormann, Matthias

346

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

347

A portable measurement system for subcriticality measurements by the CF-source-driven neutron noise analysis method  

SciTech Connect

A portable system has been assembled that is capable of measuring the subcriticality of fissile materials using the /sup 252/CF-source-driven neutron noise analysis method. The measurement system consists of a parallel-plate ionization chamber containing /sup 252/CF, two /sup 3/He proportional counters with their associated electronics, and a small computer containing anti-aliasing filters and A/D convertors. The system Fourier analyzes the digitized data and forms the appropriate auto and cross-power spectral densities. These spectra are used to form a ratio of spectral densities, G/sub 12/G/sub 13//G/sub 11/G/sub 23/, where 1 refers to the ionization chamber, and 2 and 3 refer to the /sup 3/He counters, from which subcriticality can be determined. The chamber and detectors are located appropriately near the fissile material. The system is capable of sampling signals at rates of up to 80 kHz and processing these data at rates of 2 kHz to form the appropriate spectra. The presently configured system is a two-channel system, hence the measurement of G/sub 12/, G/sub 13/, and G/sub 23/ must be done sequentially before the ratio of spectral densities is obtained. Future improvements of the system will allow simultaneous measurement of all spectra and will further reduce size, thereby enhancing portability. This measurement system can provide reliable, cost effective, and convenient determination of the subcriticality of a wide variety of fissile materials and moderators.

Mihalczo, J.T.; Ragan, G.E.

1987-01-01

348

Characterization of Low-Frequency Noise Sources in Planar Devices Using Cross-Shaped 4-Terminal Devices  

NASA Astrophysics Data System (ADS)

We promote here the use of cross-shaped 4-terminal devices (Hall crosses) to measure LF noise spectra in planar technologies. The implementation of this method is described. When investigating LF noise for the purpose of material or process characterization, such a procedure is more simple and straightforward compared to conventional differential noise measurements based on a Wheatstone bridge or single-ended measurements based on proprietary electronic circuitry. As an example of application, we then use it to extract information on the energetic as well as spatial location of a trap in Metal-Insulator-Semiconductor PHEMT pseudomorphic heterostructures.

Mosser, Vincent; Kerlain, Alexandre

2005-08-01

349

Normal metal-superconductor decoupling as a source of thermal fluctuation noise in transition-edge sensors  

NASA Astrophysics Data System (ADS)

We have studied the origin of excess noise in superconducting transition-edge sensors (TES) with several different detector designs. We show that most of the observed noise and complex impedance features can be explained by a thermal model consisting of three bodies. We suggest that one of the thermal blocks and the corresponding thermal fluctuation noise arise due to the high-frequency thermal decoupling of the normal and superconducting phase regions inside the TES film. Our results are also consistent with the prediction that in thin bilayer proximitized superconductors, the jump in heat capacity at the critical temperature is smaller than the universal BCS theory result.

Kinnunen, K. M.; Palosaari, M. R. J.; Maasilta, I. J.

2012-08-01

350

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

351

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

352

Occupational Noise Exposure Facts  

MedlinePLUS

... noise to end it. Occupational Noise Facts Noise + Music Facts Recreational Noise Facts Airport Noise Facts Noise ... noise to end it. Occupational Noise Facts Noise + Music Facts Recreational Noise Facts Airport Noise Facts Noise ...

353

Acoustic analysis of aft noise reduction techniques measured on a subsonic tip speed 50.8 cm (twenty inch) diameter fan. [quiet engine program  

NASA Technical Reports Server (NTRS)

Sound data which were obtained during tests of a 50.8 cm diameter, subsonic tip speed, low pressure ratio fan were analyzed. The test matrix was divided into two major investigations: (1) source noise reduction techniques; and (2) aft duct noise reduction with acoustic treatment. Source noise reduction techniques were investigated which include minimizing second harmonic noise by varying vane/blade ratio, variation in spacing, and lowering the Mach number through the vane row to lower fan broadband noise. Treatment in the aft duct which includes flow noise effects, faceplate porosity, rotor OGV treatment, slant cell treatment, and splitter simulation with variable depth on the outer wall and constant thickness treatment on the inner wall was investigated. Variable boundary conditions such as variation in treatment panel thickness and orientation, and mixed porosity combined with variable thickness were examined. Significant results are reported.

Stimpert, D. L.; Clemons, A.

1977-01-01

354

Subcriticality measurements for two coupled uranyl nitrate solution tanks using ²⁵²Cf-source-driven neutron noise analysis methods  

Microsoft Academic Search

The subcriticality of two interacting solution tanks was determined using ²⁵²Cf-source-driven neutron noise analysis methods. These experiments were the first test of this method for an interacting system with materials (in this case, uranyl nitrate) typical of nuclear materials in processing plants. The experiments were performed to test the conclusions from previous interaction experiments with uranium metal discs for a

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

1986-01-01

355

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

Microsoft Academic Search

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

Edward Patrick Ficaro

1991-01-01

356

Active noise control  

Microsoft Academic Search

Active noise control exploits the long wavelengths associated with low frequency sound. It works on the principle of destructive interference between the sound fields generated by the original primary sound source and that due to other secondary sources, acoustic outputs of which can be controlled. The acoustic objectives of different active noise control systems and the electrical control methodologies that

S. J. Elliott; P. A. Nelson

1993-01-01

357

Shanghai alleviates noise pollution  

SciTech Connect

''Environmental noise is now under control in Shanghai, the level of environmental noise is basically holding steady, and in some areas industrial and traffic noise has decreased.'' These were the conclusions of research by Hong Zonghui (3163 1350 6540) and Wang Shixian (3769 6164 6343) of Tongji University's Acoustics Laboratory, as put forward at a recent public academic lecture at Tongji University. In order to eliminate noise from the environment, Tongji University in the early 1970's began conducting investigations and research on noise pollution and its control together with concerned units in this city. After tests in a network of 2,117 points throughout the city, they determined that the most common form of noise pollution is traffic, which accounts for 50 percent of all noise. Since 1979, this city has adopted successive measures in the area of traffic control in order to eliminate the source of noise. Traffic noise has now dropped about 3 decibels in the city. This research report also pointed out that according to the results of regional environmental noise tests, this city does not meet the noise pollution standards set by the state. Tugboats on the Suzhou He blow their whistles late at night, and the noise at riverside homes can reach 82 decibels; the Fangua Lane residential district is close to a railroad where engine noise can reach 89 decibels and affect the residents' health. In addition, rather serious noise pollution is produced by more than 300 handicraft, light industry, textile, and electrical machinery plants.

Ding Runling

1983-07-14

358

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

359

Aircraft interior noise reduction by alternate resonance tuning  

NASA Technical Reports Server (NTRS)

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.

1990-01-01

360

Gravitational waves from BH-NS binaries: Effective Fisher matrices and parameter estimation using higher harmonics  

E-print Network

Inspiralling black hole-neutron star (BH-NS) binaries emit a complicated gravitational wave signature, produced by multiple harmonics sourced by their strong local gravitational field and further modulated by the orbital plane's precession. Some features of this complex signal are easily accessible to ground-based interferometers (e.g., the rate of change of frequency); others less so (e.g., the polarization content); and others unavailable (e.g., features of the signal out of band). For this reason, an ambiguity function (a diagnostic of dissimilarity) between two such signals varies on many parameter scales and ranges. In this paper, we present a method for computing an approximate, effective Fisher matrix from variations in the ambiguity function on physically pertinent scales which depend on the relevant signal to noise ratio. As a concrete example, we explore how higher harmonics improve parameter measurement accuracy. As previous studies suggest, for our fiducial BH-NS binaries and for plausible signal amplitudes, we see that higher harmonics at best marginally improve our ability to measure parameters. For non-precessing binaries, these Fisher matrices separate into intrinsic (mass, spin) and extrinsic (geometrical) parameters; higher harmonics principally improve our knowledge about the line of sight. For the precessing binaries, the extra information provided by higher harmonics is distributed across several parameters. We provide concrete estimates for measurement accuracy, using coordinates adapted to the precession cone in the detector's sensitive band.

Hee-Suk Cho; Evan Ochsner; Richard O'Shaughnessy; Chunglee Kim; Chang-Hwan Lee

2012-09-20

361

Dragline noise survey  

NASA Astrophysics Data System (ADS)

It is estimated that 70%-90% of miners have enough noise induced hearing loss (NIHL) to be classified as a disability (NIOSH, Publication No. 76-172, 1976; Franks, NIOSH Internal Report, 1996). In response, NIOSH is conducting a cross-sectional survey of the mining industry in order to determine the sources of mining noise and offer recommendations on how to mitigate high noise levels, and bring mining operations into compliance with the recent mining noise regulation: 30CFR, Part 62. This paper will outline the results from noise surveys of eight draglines which operate in above-ground coal mining operations. The data recorded include noise dosimetry in conjunction with time-at-task studies and 1/3-octave sound level (Leq, Lmin, and Lmax) measurements. The 1/3-octave band readings were used to create noise contour maps which allowed the spatial and frequency information of the noise to be considered. Comparison of Lmin and Lmax levels offer insight into the variability of the noise levels inside the dragline. The potential for administrative controls is limited due to consistently high noise levels throughout the deck. Implementation of engineering controls is also hindered by the size and number of the noise sources and the frequency content of the noise.

Vipperman, Jeffrey S.; Bauer, Eric R.

2002-05-01

362

In vivo application of short-lag spatial coherence and harmonic spatial coherence imaging in fetal ultrasound.  

PubMed

Fetal scanning is one of the most common applications of ultrasound imaging and serves as a source of vital information about maternal and fetal health. Visualization of clinically relevant structures, however, can be severely compromised in difficult-to-image patients due to poor resolution and the presence of high levels of acoustical noise or clutter. We have developed novel coherence-based beamforming methods called Short-Lag Spatial Coherence (SLSC) imaging and Harmonic Spatial Coherence imaging (HSCI), and applied them to suppress the effects of clutter in fetal imaging. This method is used to create images of the spatial coherence of the backscattered ultrasound as opposed to images of echo magnitude. We present the results of a patient study to assess the benefits of coherence-based beamforming in the context of first trimester fetal exams. Matched fundamental B-mode, SLSC, harmonic B-mode, and HSCI images were generated using raw radio frequency data collected on 11 volunteers in the first trimester of pregnancy. The images were compared for qualitative differences in image texture and target conspicuity as well as using quantitative imaging metrics such as signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and contrast. SLSC and HSCI showed statistically significant improvements across all imaging metrics compared with B-mode and harmonic B-mode, respectively. These improvements were greatest for poor quality B-mode images where contrast of anechoic targets was improved from 15 dB in fundamental B-mode to 27 dB in SLSC and 17 dB in harmonic B-mode to 30 dB in HSCI. CNR improved from 1.4 to 2.5 in the fundamental images and 1.4 to 3.1 in the harmonic case. These results exhibit the potential of coherence-based beamforming to improve image quality and target detectability, especially in high noise environments. PMID:25116292

Kakkad, Vaibhav; Dahl, Jeremy; Ellestad, Sarah; Trahey, Gregg

2015-04-01

363

Unlocking higher harmonics in atomic force microscopy with gentle interactions  

PubMed Central

Summary In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity. PMID:24778948

Font, Josep; Verdaguer, Albert

2014-01-01

364

Noise reduction experience at Hughes Helicopter, Inc.  

NASA Technical Reports Server (NTRS)

Noise reduction is mostly limited to light helicopters whose noise signature is dominated by their tail rotors. It is primarily hardware oriented. Well known noise reduction techniques such as reduction of rotor speeds with an accompanying increase in solidity to maintain performance, engine noise reduction with the use of exhaust mufflers, and acoustic blanketing of transmission and engine compartment are used. The concept of blade phasing as a means of reducing tail rotor noise is also used. Engine noise (exhaust noise), power train noise and airframe noise becomes important at low rotor tip speeds and means must be found to reduce these noise sources if further noise reductions are desired. The use of a special test rig aids in isolating the various noise sources and arriving at the penalties (performance or payload) involved in quieting them. Significant noise reduction are achieved for the light helicopter with minimum performance or weight penalties because of the dominance of a single noise source (the tail rotor).

Janakiram, D. S.

1982-01-01

365

Calculation of Maximum Harmonic Currents and Voltages on Transmission Lines  

Microsoft Academic Search

This paper presents a method for calculating the location and magnitude of the maximum harmonic currents and voltages on a transmission line, given calculated or measured terminal values. This information is normally unavailable. However, as the number of harmonic sources on the system increases, the location and magnitude of these harmonic maximums will be of increasing importance.

R. D. Shultz; R. A. Smith; G. L. Hickey

1983-01-01

366

DGZfP-Proceedings BB 90-CD Lecture 20 EWGAE 2004 Localization of Noise Sources in Large Structures Using AE  

E-print Network

in several steel bridges by applying AE to localize the sound. The AE technique uses high frequency contact to the noise localization problem is that the high frequencies (a few hundred kilohertz) are carried with little attenuation in steel but are quickly attenuated in air. Therefore, an array of high frequency

367

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

368

Noise characteristics in IFOG  

NASA Astrophysics Data System (ADS)

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

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

2000-10-01

369

Supporting Online Material to: Deep harmonic tremor on the  

E-print Network

Supporting Online Material to: Deep harmonic tremor on the San Jacinto fault, southern California G Hz, a typical frequency band for tremor7 detection in other regions.8 A representative daily noise about 9 km apart).37 We found that potential tremor signals frequently exceed the noise levels

Ampuero, Jean Paul

370

SPEECH ENHANCEMENT USING HARMONIC REGENERATION Cyril Plapous 1  

E-print Network

SPEECH ENHANCEMENT USING HARMONIC REGENERATION Cyril Plapous 1 , Claude Marro 1 , Pascal Scalart 2 in enhanced speech because of the non reliability of estimators for small signal- to-noise ratios. We propose The problem of enhancing speech degraded by additive noise, when only the noisy speech is available, has been

Paris-Sud XI, Université de

371

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

372

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

373

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

374

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

375

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

376

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

SciTech Connect

We demonstrate, for the first time, high-order harmonic generation from C{sub 60} by an intense femtosecond Ti:sapphire laser. Laser-produced plasmas from C{sub 60}-rich epoxy and C{sub 60} films were used as the nonlinear media. Harmonics up to the 19th order were observed. The harmonic yield from fullerene-rich plasma is about 25 times larger compared with those produced from a bulk carbon target. Structural studies of plasma debris confirm the presence and integrity of fullerenes within the plasma plume, indicating fullerenes as the source of high-order harmonics.

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

2009-01-09

377

Harmonization of Biodiesel Specifications  

SciTech Connect

Worldwide biodiesel production has grown dramatically over the last several years. Biodiesel standards vary across countries and regions, and there is a call for harmonization. For harmonization to become a reality, standards have to be adapted to cover all feedstocks. Additionally, all feedstocks cannot meet all specifications, so harmonization will require standards to either tighten or relax. For harmonization to succeed, the biodiesel market must be expanded with the alignment of test methods and specification limits, not contracted.

Alleman, T. L.

2008-02-01

378

5th International Meeting Wind Turbine Noise  

E-print Network

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

Paris-Sud XI, Université de

379

Analysis of Noise Characteristics for Diesel Engine  

Microsoft Academic Search

Reducing vehicle noise and vibration is becoming more and more important in the modern market place. The vehicle interior noise is mainly caused by irregularity of road, engine and transmission. So it is important to study on the noise characteristics for diesel engine and identify the main noise source and investigate the effective methods to control noise. In this paper,

Liu Guangpu; Bi Shihua; Pan Hongxia

2006-01-01

380

Core Noise - Increasing Importance  

NASA Technical Reports Server (NTRS)

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

Hultgren, Lennart S.

2011-01-01

381

Wind turbine noise: Prediction tools and design parameter dependence  

Microsoft Academic Search

Wind turbine aerodynamic noise sources are described, and noise predictions and measurements are compared. The influence of design parameters and variable running speed on noise emission is discussed. Results show that prediction tools for blade tower passage noise predict noise emission reasonably well. Prediction tools for high frequency noise are not sufficient. Reliable noise measurements for different machines are needed.

S. Meijer

1984-01-01

382

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

SciTech Connect

These proceedings collect papers on noise pollution. Topics include: noise sources, noise of chain conveyors in mining, control of noise sources in power plants, noise control elements, vibration, a method of noise control in a nuclear power plant, biological effects of noise, statistical audio dosimetry, and power house noise control.

Lotz, R.

1986-01-01

383

Equivalent Magnetic Noise Limit of Low-Cost GMI Magnetometer  

Microsoft Academic Search

We present a noise analysis of a giant magnetoimpedance (GMI) sensor using a peak detector at the optimal magnetic field working bias point of a sensor wire, by considering internal noise sources (intrinsic GMI device associated noise sources and conditioning electronic noise sources). An expression is obtained for the theoretical expected noise for known electronic design parameters and physical characteristics

Lehui Ding; SÉbastien Saez; Christophe Dolabdjian; Luiz G. C. Melo; Arthur Yelon; David Menard

2009-01-01

384

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. PMID:25540812

2014-01-01

385

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

386

On the detection of eccentric supermassive black hole binaries with pulsar timing arrays: Signal-to-noise ratio calculations  

E-print Network

We present a detailed analysis of the expected signal-to-noise ratios of supermassive black hole binaries on eccentric orbits observed by pulsar timing arrays. We derive several analytical relations that extend the results of Peters and Mathews [Phys. Rev. D 131, 435 (1963)] to facilitate this analysis. We show that eccentricity enhances the signal-to-noise ratio of single resolvable sources whose dominant harmonic is located in the low-frequency sensitivity regime of pulsar timing arrays for continuous wave sources, whereas the expected signal-to-noise ratio of single resolvable sources emitting in the high frequency sensitivity regime of pulsar timing arrays will be attenuated. We also show that the strain of a stochastic, isotropic gravitational wave background generated by a cosmological population of eccentric binaries will be suppressed in the frequency band of pulsar timing arrays relative to a population of circular binaries, which may pose a potential problem for their detection.

Huerta, E A; Gair, Jonathan R; Taylor, Stephen R

2015-01-01

387

Temporal Coherence of Ultrashort High-Order Harmonic Pulses  

Microsoft Academic Search

We have studied the temporal coherence of high-order harmonics (up to the 15th order) produced by focusing 100 fs laser pulses into an argon gas jet. We measure the visibility of the interference fringes, produced when two spatially separated harmonic sources interfere in the far field, as a function of the time delay between the two sources. In general, we

M. Bellini; C. Lyngå; A. Tozzi; M. B. Gaarde; T. W. Hänsch; A. L'Huillier; C.-G. Wahlström

1998-01-01

388

Fan Noise Prediction  

NASA Technical Reports Server (NTRS)

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

France, Joshua I.

2004-01-01

389

Generation mechanism of power line harmonic radiation  

Microsoft Academic Search

The questions concerning the generation of power line harmonic radiation (PLHR) and magne-tospheric line radiation (MLR) are discussed, including the effective source of high harmonics of 50\\/60 Hz, and fine dynamic structure of the frequency spectrum of PLHR and MLR. It is shown, that thyristor-based power regulators used by large electrical power consumers produce the periodic sequences of current pulses

Alexander Kostrov; Mikhail Gushchin; Sergei Korobkov

2010-01-01

390

Context sensitive noise impact mapping  

Microsoft Academic Search

It is impacts and changes in impacts, not exposures, which ultimately provide “meaning” and the policy relevance of altered traffic flows, noise abatement policies or noise reduction at the source. In this paper, easy-to-implement enhancements to traditional noise mapping procedures are introduced that transform available exposure information into impact maps. Their purpose is to provide experts, politicians and the public

R. Klæboe; E. Engelien; M. Steinnes

391

Special topics on noise and vibration control  

NASA Astrophysics Data System (ADS)

As a field, noise and vibration control is well established. The equations that govern the behavior of most structural acoustic systems are well known. However, special topics related to methods of actuation and control strategies are still being investigated. This dissertation developed two such special topics in noise and vibration control. Chapter 1 developed a family of optimal control algorithms in noise control, and chapter 2 develops a control strategy for variable stiffness. The first chapter reviews basic concepts in optimal broadband noise control in one-dimensional enclosures using pressure and pressure rate feedback. A single broadband primary source is located at one end of the enclosure and pressure and pressure rate are fedback at a secondary source located on the opposite end of the enclosure. I first let the primary source be a single tone and feedback pressure at the secondary source, as the acoustic energy in the enclosure is minimized. Next, I feedback pressure and pressure rate and minimize the acoustic energy. Finally, the broadband problem is formulated, and the associated acoustic energy is minimized for the case in which the secondary source employs pressure and pressure rate feedback. This dissertation reveals that pressure rate feedback is optimal in that it minimizes the acoustic energy in the enclosure at all wave numbers. The next part of this chapter describes an experiment in which PZT actuators were successfully employed in a one-dimensional enclosure for the purpose of controlling noise in the enclosure using pressure rate feedback. The implementation was complicated by the PZT dynamics which needed to be compensated for in the control algorithm. This chapter also studies the complications that need to be accounted for a two-dimensional acoustic enclosure. The second chapter applies a control strategy known as Sliding Mode Control (SMC). The objective is to control stiffness. Two types of sliding surfaces are examined. The traditional one passes through the origin in the state space, and the new one doesn't. The two types of sliding surfaces result in significantly different responses and performances. The dissertation shows that the latter is favored in the presence of harmonic excitations. The results also suggest that SMC can be implemented using MR fluids.

Mao, Chi-Min

392

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

NASA Astrophysics Data System (ADS)

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

Matinfar, Mehdi D.; Salehi, Jawad A.

2009-11-01

393

Noise reduction in DEXA image based on system noise modeling  

Microsoft Academic Search

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

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

2009-01-01

394

GRACE Harmonic and Mascon Solutions at JPL  

NASA Astrophysics Data System (ADS)

Gravity field solutions at JPL over the past few years have explored use of range, range-rate, and range-acceleration K/Ka-band satellite-satellite data types (with and without GPS), and with both spherical harmonic and mascon-type local mass representations. Until recently, resource and computing limitations have limited the scope of our mascon and other local solutions to a few months and/or small spatial regions and the standard GRACE products have remained spherical harmonic fields. The use of a new very large (~500 node) beowulf machine at JPL is now enabling a wider range of solutions over longer time spans and deeper understanding of their characteristics. These include much higher spherical harmonic degrees, mascons, and hybrids of the two. We will present the current status for several solution types, strengths and weaknesses of each, and our assessments of limiting errors including data noise and aliasing sensitivity.

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

2005-12-01

395

Gravitational Wave Confusion Noise  

E-print Network

One of the greatest challenges facing gravitational wave astronomy in the low frequency band is the confusion noise generated by the vast numbers of unresolved galactic and extra galactic binary systems. Estimates of the binary confusion noise suffer from several sources of astrophysical uncertainty, such as the form of the initial mass function and the star formation rate. There is also considerable uncertainty about what defines the confusion limit. Various ad-hoc rules have been proposed, such as the one source per bin rule, and the one source per three bin rule. Here information theoretic methods are used to derive a more realistic estimate for the confusion limit. It is found that the gravitational wave background becomes unresolvable when there is, on average, more than one source per eight frequency bins. This raises the best estimate for the frequency at which galactic binaries become a source of noise from 1.45 mHz to 2.54 mHz.

Neil J. Cornish

2003-04-04

396

Using the equivalent source technique to estimate noise in 4D TEM data Kristopher MacLennan* and Yaoguo Li  

E-print Network

electromagnetic (TEM) data set through the use of the equivalent source technique. Particular benefits. Introduction Emerging applications of transient electromagnetic (TEM) surveys, such as monitoring induction with respect to time, tB / , is measured at discrete time gates. Each of these measurements

397

Observation of bias-dependent noise sources in a TiO{sub x}/TiO{sub y} bipolar resistive switching frame  

SciTech Connect

We report the conduction features associated with the evolution of oxygen ions (or vacancies) under bias for a TiO{sub x} (oxygen ion-rich)/TiO{sub y} (oxygen ion-deficient) bi-layer cell by identifying low-frequency noise sources. It is believed that a low resistance state enhances the formation of conductive filaments exchanging electrons through a nearest-neighbor hopping process, while a high resistance state (HRS) emphasizes the rupture of conductive filaments inside the insulating TiO{sub x} layer and a reduction/oxidation reaction at the oxide interfaces. The high resolution transmission electron microscope images of as-grown and HRS cells are also discussed.

Hyung Kim, Joo [Novel Functional Materials and Devices Laboratory, Department of Physics, The Research Institute for Natural Science, Hanyang University, Seoul 133-791 (Korea, Republic of); Rahm Lee, Ah; Cheol Bae, Yoon; Ho Baek, Kwang [Division of Nano-Scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Sik Im, Hyun [Department of Semiconductor Science, Dongguk University, Seoul 100-715 (Korea, Republic of); Pyo Hong, Jin, E-mail: jphong@hanyang.ac.kr [Novel Functional Materials and Devices Laboratory, Department of Physics, The Research Institute for Natural Science, Hanyang University, Seoul 133-791 (Korea, Republic of); Division of Nano-Scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

2014-02-24

398

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

NASA Astrophysics Data System (ADS)

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 the intrinsic oscillators’ frequencies, and external independent noise forces. 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, with the following possible scenarios: simple supercritical transition (similar to classical Kuramoto model); subcritical transition with large area of bistability of incoherent and synchronous solutions; appearance of a symmetric two-cluster solution which can coexist with the regular synchronous state. We show that the interplay between relatively small white noise and finite-size fluctuations can lead to metastability of the asynchronous solution.

Vlasov, Vladimir; Komarov, Maxim; Pikovsky, Arkady

2015-03-01

399

Noise prediction technology for CTOL aircraft  

NASA Technical Reports Server (NTRS)

The application of a new aircraft noise prediction program to CTOL noise prediction is outlined. Noise prediction is based on semiempirical methods for each of the propulsive system noise sources, such as the fan, the combustor, the turbine, and jet mixing, with noise-critical parameter values derived from the thermodynamic cycle of the engine. Comparisons of measured and predicted noise levels for existing CTOL aircraft indicate an acceptable level of accuracy.

Raney, J. P.

1978-01-01

400

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

PubMed Central

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

Alain, Claude; Roye, Anja; Salloum, Claire

2014-01-01

401

Workshop on Harmonic Oscillators  

NASA Technical Reports Server (NTRS)

Proceedings of a workshop on Harmonic Oscillators held at the College Park Campus of the University of Maryland on March 25 - 28, 1992 are presented. The harmonic oscillator formalism is playing an important role in many branches of physics. This is the simplest mathematical device which can connect the basic principle of physics with what is observed in the real world. The harmonic oscillator is the bridge between pure and applied physics.

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

1993-01-01

402

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

403

Inlet noise on 0.5-meter-diameter NASA QF-1 fan as measured in an unmodified compressor aerodynamic test facility and in an anechoic chamber  

NASA Technical Reports Server (NTRS)

Narrowband analysis revealed grossly similar sound pressure level spectra in each facility. Blade passing frequency (BPF) noise and multiple pure tone (MPT) noise were superimposed on a broadband (BB) base noise. From one-third octave bandwidth sound power analyses the BPF noise (harmonics combined), and the MPT noise (harmonics combined, excepting BPF's) agreed between facilities within 1.5 db or less over the range of speeds and flows tested. Detailed noise and aerodynamic performance is also presented.

Gelder, T. F.; Soltis, R. F.

1975-01-01

404

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

405

1/f noise in systems showing stochastic resonance  

SciTech Connect

Stochastic resonator systems with input and/or output 1/f noise have been studied. Disordered magnets/dielectrics serve as examples for the case of output 1/f noise with white noise (thermal excitation) at the input of the resonators. Due to the fluctuation-dissipation theorem, the output noise is related to the out-of-phase component of the periodic peak of the output spectrum. Spin glasses and ferromagnets serve as interesting examples of coupled stochastic resonators. A proper coupling can lead to an extremely large signal-to-noise ratio. As a model system, a 1/f-noise-driven Schmitt trigger has been investigated experimentally to study stochastic resonance with input 1/f noise. Under proper conditions, the authors have found several new nonlinearity effects, such as peaks at even harmonics, holes at even harmonics, and 1/f noise also in the output spectrum. 33 refs., 8 figs.

Kiss, L.B.; Gingl, Z. (JATE Univ., Szeged (Hungary)); Marton, Z. (Hungarian Academy of Sciences, Szeged (Hungary)); Kertsez, J. (Inst. for Technical Physics, Budapest (Hungary) Koeln Univ. (Germany)); Moss, F. (Univ. of St. Louis, MO (United States)); Schmera, G.; Bulsara, A. (NCCOSC-RDT E Division, San Diego, CA (United States))

1993-01-01

406

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

NASA Technical Reports Server (NTRS)

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

Coffen, Charles D.; George, Albert R.

1990-01-01

407

Joint source channel coding for non-ergodic channels: the distortion signal-to-noise ratio (SNR) exponent perspective  

E-print Network

Control. 2 sample) such that d(S; ^S) is minimized where ^S is the reconstruction of S from B. This minimum distortion is given by the distortion rate function DDRF(Rs) = inf P(^S;S):I(^S;S)=Rs d(S; ^S) (1.3) where I(U;V) = E h log P(u;v)P(u)P(v) i denotes... transmitting an analog source over a multiple-input multiple-output (MIMO) channel. The problems difier in the way the channel and the associated side information at the transmitter is modelled. A. Channel Models P1 In the flrst problem, we consider a single...

Bhattad, Kapil

2008-10-10

408

Noise Meter  

MedlinePLUS

... Occupational Hearing Loss Surveillance Other Resources Related Topics Agriculture Construction Firing Ranges Hearing Loss in Mining NIOSH Homepage NIOSH A-Z Workplace Safety & Health Topics Publications and Products Programs NIOSH NOISE AND HEARING LOSS PREVENTION Noise ...

409

Analysis of Dual Rotating Rake Data from the NASA Glenn Advanced Noise Control Fan Duct with Artificial Sources  

NASA Technical Reports Server (NTRS)

The Rotating Rake mode measurement system was designed to measure acoustic duct modes generated by a fan stage. Initially, the mode amplitudes and phases were quantified from a single rake measurement at one axial location. To directly measure the modes propagating in both directions within a duct, a second rake was mounted to the rotating system with an offset in both the axial and the azimuthal directions. The rotating rake data analysis technique was then extended to include the data measured by the second rake. The analysis resulted in a set of circumferential mode levels at each of the two rake microphone locations. Radial basis functions were then least-squares fit to this data to obtain the radial mode amplitudes for the modes propagating in both directions within the duct. Validation experiments have been conducted using artificial acoustic sources. Results are shown for the measurement of the standing waves in the duct from sound generated by one and two acoustic sources that are separated into the component modes propagating in both directions within the duct. Measured reflection coefficients from the open end of the duct are compared to analytical predictions.

Dahl, Milo D.; Sutliff, Daniel L.

2014-01-01

410

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

NASA Technical Reports Server (NTRS)

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

Watson, W. R.

1982-01-01

411

Noise Pollution  

MedlinePLUS

... to noise, and evaluate the effectiveness of existing regulations for protecting the public health and welfare, pursuant to the Noise Control Act of 1972 and the Quiet Communities Act of 1978. Learn more about the Clean Air Act, Noise Control Act of 1972, and the ...

412

Covariant harmonic oscillators and coupled harmonic oscillators  

NASA Technical Reports Server (NTRS)

It is shown that the system of two coupled harmonic oscillators shares the basic symmetry properties with the covariant harmonic oscillator formalism which provides a concise description of the basic features of relativistic hadronic features observed in high-energy laboratories. It is shown also that the coupled oscillator system has the SL(4,r) symmetry in classical mechanics, while the present formulation of quantum mechanics can accommodate only the Sp(4,r) portion of the SL(4,r) symmetry. The possible role of the SL(4,r) symmetry in quantum mechanics is discussed.

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

1995-01-01

413

Glacial Isostatic Adjustment as a Source of Noise for the Interpretation of GRACE and Altimetry Sea Level Data: Modeling With 3D Mantle Rheology  

NASA Astrophysics Data System (ADS)

Viscoelastic relaxation in the Earth's mantle induced by deglaciation following the last glacial maximum, can appear as a secular trend in measurements of the Earth's time-variable gravity field. During the last decade, the GRACE and altimetry missions have been making precise measurements of Earth's gravity field and sea level height. Although valuable for providing insight on the entire GIA process and for inferring the interior structure of the solid Earth, the GIA signals can be a significant source of noise for other important applications. Errors in the GIA model, for example due to errors in the assumed mantle viscosity profile, may cause difficulty in interpreting sea level measurements with altimeters; they may also cause problems for recovering long-term eustatic sea level and, especially, cryospheric signals with GRACE. For instance, GIA model errors are by far the largest source of uncertainty when using GRACE to estimate present-day thinning rates of the Antarctic ice sheet. In this presentation, we will take into account a 3D mantle viscosity structure derived from seismic tomography models and discuss the solution of the 3D viscoelastic relaxation problem. We will study the uncertainty in Antarctic GIA modeling due to the difference in viscosity profiles underlying West and East Antarctica, and most importantly, analyze the contributions of GIA signals to GRACE and altimetry measurements, with a particular emphasis on how GIA errors may affect global sea level change estimates.

A, G.; Wahr, J. M.; Zhong, S.

2011-12-01

414

Rotor-vortex interaction noise  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

415

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

416

On noise modeling for power line communications  

Microsoft Academic Search

This paper reviews existing noise models including both background and impulsive noise for the in-home PLC scenario, highlighting similarities and differences. With reference to the impulsive noise, it is shown that a simple model, in the frequency band up to 100 MHz, can be derived by considering the noise generated at the source and taking into account the effect of

Luca Di Bert; Peter Caldera; David Schwingshackl; Andrea M. Tonello

2011-01-01

417

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

418

A new method for both harmonic voltage and harmonic current suppression and power factor correction in industrial power systems  

SciTech Connect

This paper proposes a new method for designing a group of single tuned filters for both harmonic current injection suppression and harmonic voltage distortion reduction and power factor correction. The proposed method is based on three purposes: (1) reduction of harmonic voltage distortion in the source terminals to an acceptable level, (2) suppression of harmonic current injection in the source terminals to an acceptable level, (3) improvement of power factor at the source terminals. To determine the size of the capacitor in a group of single tuned filters, three new NLP mathematical formulations will be introduced. The first is to suppress harmonic current injection within an acceptable level. The second is to minimize the fundamental reactive power output while reducing harmonic voltage distortion to an acceptable level. The third is to determine an optimal assignment of reactive power output based on the results of harmonic voltage reduction and power factor correction. This new method has been demonstrated for designing a group of single tuned filters and its validity has been successfully confirmed through numerical simulation in a 35 KV industrial power system. The proposed method can efficiently provide an optimal coordination in a group of single tuned filters relating to suppressing harmonic current injection, reducing harmonic voltage distortion and improving power factor.

Cheng, H. [Shanghai Jiao Tong Univ. (China). Dept. of Electrical Power Engineering; Sasaki, Hiroshi; Yorino, Naoto [Hiroshima Univ., Higashi-Hiroshima (Japan). Dept. of Electrical Engineering

1995-12-31

419

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

420

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

421

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

422

A gimbaled low noise momentum wheel  

NASA Technical Reports Server (NTRS)

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

Bichler, U.; Eckardt, T.

1993-01-01

423

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

424

3rd-Harmonic operation of SIT inverter RF source for ICRF heating in the divertor plasma simulator NAGDIS-II  

Microsoft Academic Search

Summary form only given, as follows. In a linear divertor plasma simulator NAGDIS-II the ICRF slow wave heating is employed to heat both the ion and electron. The rf power source used here is a Static Induction Transistor(SIT) inverter, which can generate about 15 kW in CW mode at a gate driving frequency range of 0.25-1.7 MHz. An output current

Y. Uesugi; K. Kawada; T. Imai; S. Takamura

2001-01-01

425

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

Microsoft Academic Search

A dynamic source model is presented, in which a three-dimensional crack containing a viscous compressible fluid is excited into resonance by an impulsive pressure transient applied over a small area DeltaS of the crack surface. The crack excitation depends critically on two dimensionless parameters called the crack stiffness, C=(b\\/mu)(L\\/d), and viscous damping loss, F=(12?L)\\/(rhofd2alpha), where b is the bulk modulus,

Bernard Chouet

1988-01-01

426

Phase locking of a 3.4 THz third-order distributed feedback quantum cascade laser using a room-temperature superlattice harmonic mixer  

NASA Astrophysics Data System (ADS)

We report on the phase locking of a 3.4 THz third-order distributed feedback quantum cascade laser (QCL) using a room temperature GaAs/AlAs superlattice diode as both a frequency multiplier and an internal harmonic mixer. A signal-to-noise level of 60 dB is observed in the intermediate frequency signal between the 18th harmonic of a 190.7 GHz reference source and the 3433 GHz QCL. A phase-lock loop with 7 MHz bandwidth results in QCL emission that is 96% locked to the reference source. We characterize the QCL temperature and electrical tuning mechanisms and show that frequency dependence of these mechanisms can prevent phase-locking under certain QCL bias conditions.

Hayton, D. J.; Khudchenko, A.; Pavelyev, D. G.; Hovenier, J. N.; Baryshev, A.; Gao, J. R.; Kao, T. Y.; Hu, Q.; Reno, J. L.; Vaks, V.

2013-07-01

427

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

428

High level white noise generator  

DOEpatents

A wide band, stable, random noise source with a high and well-defined output power spectral density is provided which may be used for accurate calibration of Johnson Noise Power Thermometers (JNPT) and other applications requiring a stable, wide band, well-defined noise power spectral density. The noise source is based on the fact that the open-circuit thermal noise voltage of a feedback resistor, connecting the output to the input of a special inverting amplifier, is available at the amplifier output from an equivalent low output impedance caused by the feedback mechanism. The noise power spectral density level at the noise source output is equivalent to the density of the open-circuit thermal noise or a 100 ohm resistor at a temperature of approximately 64,000 Kelvins. The noise source has an output power spectral density that is flat to within 0.1% (0.0043 db) in the frequency range of from 1 KHz to 100 KHz which brackets typical passbands of the signal-processing channels of JNPT's. Two embodiments, one of higher accuracy that is suitable for use as a standards instrument and another that is particularly adapted for ambient temperature operation, are illustrated in this application.

Borkowski, Casimer J. (Oak Ridge, TN); Blalock, Theron V. (Knoxville, TN)

1979-01-01

429

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

430

New aspects of subsonic aerodynamic noise theory  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

431

Fan Noise Research at NASA  

NASA Technical Reports Server (NTRS)

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

Groeneweg, John F.