Sample records for harmonic noise sources

  1. Active Noise Control of Acoustic Sources Using Spherical Harmonics Expansion and a Genetic Algorithm: Simulation and Experiment

    NASA Astrophysics Data System (ADS)

    Martin, T.; Roure, A.

    1998-05-01

    A general method is presented to optimize transducer location in an active noise control problem. The method includes two parts. First, the actuator configuration is determined by using a model of the primary field which is a spherical harmonics expansion. In the second part, a genetic algorithm is used to determine the error sensor configuration. This method is then applied to two real acoustic sources: a dipole and an electrical transformer. In numerical simulations, the primary field of both sources measured in an anechoic room was used to determine the active control configurations. Then, the actuator and error sensor arrangement was tested in an active control experiment involving both primary, sources.

  2. ACTIVE NOISE CONTROL OF ACOUSTIC SOURCES USING SPHERICAL HARMONICS EXPANSION AND A GENETIC ALGORITHM: SIMULATION AND EXPERIMENT

    Microsoft Academic Search

    T. Martin; A. Roure

    1998-01-01

    A general method is presented to optimize transducer location in an active noise control problem. The method includes two parts. First, the actuator configuration is determined by using a model of the primary field which is a spherical harmonics expansion. In the second part, a genetic algorithm is used to determine the error sensor configuration. This method is then applied

  3. Noise Sources in Bulk CMOS

    Microsoft Academic Search

    Kent H. Lundberg

    The noise behavior of bulk CMOS devices is dominated primarily by two noise sources: thermal noise and ?icker (1=f) noise. Other sources that are sometimes present in the noise spectrum are shot noise, generation\\/recombination noise, and \\\\popcorn\\

  4. Understanding Slat Noise Sources

    NASA Technical Reports Server (NTRS)

    Khorrami, Medhi R.

    2003-01-01

    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.

  5. Community noise sources and noise control issues

    NASA Astrophysics Data System (ADS)

    Nihart, Gene L.

    1992-04-01

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

  6. Community noise sources and noise control issues

    NASA Technical Reports Server (NTRS)

    Nihart, Gene L.

    1992-01-01

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

  7. A LOW NOISE RF SOURCE FOR RHIC.

    SciTech Connect

    HAYES,T.

    2004-07-05

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

  8. High speed helicopter noise sources

    NASA Technical Reports Server (NTRS)

    Lee, A.

    1977-01-01

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

  9. 1\\/f noise sources

    Microsoft Academic Search

    F. N. Hooge

    1994-01-01

    This survey deals with 1\\/f noise in homogeneous semiconductor samples. A distinction is made between mobility noise and number noise. It is shown that there always is mobility noise with an ? value with a magnitude in the order of 10-4. Damaging the crystal has a strong influence on ?, ? may increase by orders of magnitude. Some theoretical models

  10. Prediction of far-field harmonic noise from propellers

    NASA Astrophysics Data System (ADS)

    1991-11-01

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

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

    E-print Network

    So, Hing-Cheung

    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

  12. Determination of noise descriptors and criteria for pyrotechnic noise sources

    Microsoft Academic Search

    Weixiong Wu

    2005-01-01

    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

  13. Lower bounds on the estimation of harmonics in colored noise

    Microsoft Academic Search

    Mounir Ghogho; Ananthram Swami

    1997-01-01

    A fast algorithm for the computation of the Fisher information matrix for the parameters of a deterministic signal in Gaussian AR noise is derived. The harmonic signal is studied in detail. In the case of a harmonic signal with random phases, closed-form expressions for the finite-sample posterior Cramer-Rao bounds are established. The fast algorithm is also useful for computing the

  14. Noise Amplification in Echo-Enabled Harmonic Generation (EEHG)

    SciTech Connect

    Stupakov, Gennady

    2010-08-25

    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.

  15. ENERGY DIFFUSION IN HARMONIC SYSTEM WITH CONSERVATIVE NOISE

    E-print Network

    Paris-Sud XI, Université de

    ENERGY DIFFUSION IN HARMONIC SYSTEM WITH CONSERVATIVE NOISE GIADA BASILE AND STEFANO OLLA Abstract with a stochastic pertur- bation of the dynamics that conserves energy and momentum. The results concern pinned proposed, where the added random dynamics conserves the energy. In [7] Fourier Law is proven

  16. Comparisons of noise spectroscopy analyze and microplasma noise sources

    Microsoft Academic Search

    J. Vanek; J. Dolensky; Z. Chobola; M. Lunak

    2010-01-01

    As it was the mechanical noise used for diagnostic of machine in the past, the electronic noise can be used as diagnostic tool for detection defects in electronical devices and systems in the future. This paper deals with comparisons of noise spectroscopy and detection of microplasma noise sources in the three new type of solar cells G1, G3 and G5.

  17. Noise source separation based on the blind source separation

    Microsoft Academic Search

    Yang Yang; Zuoli Li; Xiuqin Wang; Di Zhang

    2011-01-01

    The identification of acoustic source accurately is a fundamental problem in noise control. In the practical project, if the contribution of multi-source-noise to the whole was identified, and then the noise level can be reduced accordingly. To get the accurate noise signal, measurements should be possible while the machines are constantly in action. It is easier to get the mixed

  18. Laboratory annoyance and different traffic noise sources

    Microsoft Academic Search

    E. hrstrm; M. Bjrkman; R. Rylander

    1980-01-01

    The acute annoyance reaction to different noise sources (lorries, aircraft, mopeds and trains) was investigated in a laboratory experiment. Students were exposed to different noise climates at noise levels 70 and 80 dB(A) for 25 minutes, and their reactions were subsequently assessed by using a questionnaire. Their general sensitivity to noise was also evaluated. The results demonstrated that Leq gave

  19. Power station noise sources and spectra

    Microsoft Academic Search

    W. W. Avril; R. A. Popeck

    1977-01-01

    Sound sources within power station boundaries contribute to overall plant noise level with different energy levels, spectra, and radiation characteristics. This paper attempts to identify characteristics and describe major plant sound producing equipment and their noise producing mechanisms with octave band and narrower band width examples. Sound level measurements in the near field of noise source can sometimes distinguish its

  20. Observations of discrete harmonics emerging from equatorial noise.

    PubMed

    Balikhin, Michael A; Shprits, Yuri Y; Walker, Simon N; Chen, Lunjin; Cornilleau-Wehrlin, Nicole; Dandouras, Iannis; Santolik, Ondrej; Carr, Christopher; Yearby, Keith H; Weiss, Benjamin

    2015-01-01

    A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as 'equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes 'ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations. PMID:26169360

  1. A solid state broadband microwave noise source

    Microsoft Academic Search

    R. H. Haitz; F. L. Opp

    1968-01-01

    Recent studies of avalanche breakdown have led to a thorough understanding of the noise properties of a stable-burning avalanche discharge in a reverse biased silicon p-n junction. Avalanche diodes specially designed for uniform breakdown are nearly ideal noise sources because of their high noise output, high efficiency, broad bandwidth, low temperature dependence and high reliability. In order to reduce circuit

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

    NASA Technical Reports Server (NTRS)

    Rickley, E. J.

    1990-01-01

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

  3. On the second harmonic control requirements in balanced common-emitter BJT low noise amplifier

    Microsoft Academic Search

    Antti Heiskanen; Timo Rahkonen

    2004-01-01

    A recently proposed second harmonic controlled frequency-independent third-order intermodulation distortion cancellation technique in a balanced common-emitter configuration gives possibility to optimize linearity independently of noise power. By using simplified Volterra analysis new rules for second harmonic controlled cancellation are given. The results are confirmed by harmonic balance stimulations.

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

    ERIC Educational Resources Information Center

    de Krom, Guus

    1993-01-01

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

  5. [The noise filtering and baseline correction for harmonic spectrum based on wavelet transform].

    PubMed

    Guo, Yuan; Zhao, Xue-Hong; Zhang, Rui; Hu, Ya-Jun; Wang, Yan

    2013-08-01

    The problem of noise and baseline drift is a hot topic in infrared spectral harmonic detection system. This paper presents a new algorithm based on wavelet transform Mallet decomposition to solve the problem of eliminating a variety of complex noise and baseline drift in the harmonic detection. In the algorithm, the appropriate wavelet function and decomposition level were selected to decomposed the noise, baseline drift and useful signal in the harmonic curve into different frequency bands. the bands' information was analysed and a detecting band was set, then the information in useful frequency was reserved by zeroing method of treatment and the coefficient of the threshold. We can just use once transform and reconstruction to remove interference noise and baseline from double-harmonic signal by applying the wavelet transform technique to the harmonic detection spectrum pretreatment. Experiments show that the wavelet transform method can be used to different harmonic detection systems and has universal applicability. PMID:24159870

  6. Source and processing effects on noise correlations

    NASA Astrophysics Data System (ADS)

    Fichtner, Andreas

    2014-05-01

    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.

  7. Phase-Locked High-Order Harmonic Sources

    Microsoft Academic Search

    Raoul Zerne; Carlo Altucci; Marco Bellini; Mette B. Gaarde; T. W. Hnsch; Anne L'Huillier; Claire Lyng; C.-G. Wahlstrm

    1997-01-01

    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

  8. Lifetime increase using passive harmonic cavities insynchrotronlight sources

    SciTech Connect

    Byrd, J.M.; Georgsson, M.

    2000-09-22

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

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

    NASA Astrophysics Data System (ADS)

    Maltezopoulos, Theophilos; Mittenzwey, Manuel; Azima, Armin; Bdewadt, Jrn; Dachraoui, Hatem; Rehders, Marie; Lechner, Christoph; Schulz, Michael; Wieland, Marek; Laarmann, Tim; Robach, Jrg; Drescher, Markus

    2014-04-01

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

  10. Secondary sources of seismic noise

    Microsoft Academic Search

    R. L. Geyer

    1977-01-01

    Examples of terrane response derived from the analysis and interpretation of data obtained by Stanolind Research Party 45 (now Amoco Production Company) in New Mexico, North Dakota, and West Texas, are presented. The secondary sources, the types of waves, the mechanisms of secondary-wave generation, and the relations between secondary waves and reflection quality were identified. Analysis was restricted to waves

  11. Noise Source for Calibrating a Microwave Polarimeter

    NASA Technical Reports Server (NTRS)

    Piepmeier, Jeffrey R.; Kim, Edward J.

    2006-01-01

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

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

    Microsoft Academic Search

    D. B. Hanson; M. R. Fink

    1978-01-01

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

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

    Microsoft Academic Search

    D. B. Hanson; M. R. Fink

    1979-01-01

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

  14. Noise source emissions, Richton Dome site, Mississippi

    SciTech Connect

    Not Available

    1987-05-13

    Noise source data and use factors for modeling the environmental noise environment expected from salt-site repository activity were provided by Battelle Columbus Division. This report has been prepared for the purpose of documenting the development of the data provided to the Repository Project Management (RPM) organization. The data provided encompasses all phases of activity, from site preparation through construction of the exploratory shaft facility (ESF). Noise environments expected from construction and operation of transportation corridors associated with the activity were also modeled. Data for the construction of transportation corridors were provided. The equipment inventory, including sound-power levels for each item is included as Appendix A. Emission source terms provided by Parsons Brinckerhoff/PB-KBB for the ESF were used as a basis for the noise source emission inventory development. Where available, research results containing complete spectra were used. In cases where complete data were not available, a sound-pressure spectrum was synthesized from a characteristic spectrum shape from a similar piece of equipment. For example, a front-shovel excavator might be approximated by data from a front-end loader of similar horsepower range. Sound-power-level spectra were then calculated from the sound-pressure-level data. 14 refs.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels.

  16. Energy Diffusion in Harmonic System with Conservative Noise

    E-print Network

    Giada Basile; Stefano Olla

    2013-06-29

    We prove diffusive behaviour of the energy fluctuations in a system of harmonic oscillators with a stochastic perturbation of the dynamics that conserves energy and momentum. The results concern pinned systems or lattice dimension $d\\ge 3$, where the thermal diffusivity is finite.

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

    Microsoft Academic Search

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

    1989-01-01

    An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in Langley's Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of

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

    Microsoft Academic Search

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

    1990-01-01

    An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in Langley's Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of

  19. Low-frequency noise sources in bipolar junction transistors

    Microsoft Academic Search

    R. C. Jaeger; A. J. Brodersen

    1970-01-01

    Low-frequency noise measurements are made on specially fabricated silicon tetrode planar transistors. The measurements show the existence of three distinct sources of excess noise: a 1\\/fnoise source associated with the surface; a l\\/fnoise source associated with the active base region; and an anomalous burst noise source associated with the forward-biased emitter-base junction. Burst noise which is present in many transistors

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

    NASA Technical Reports Server (NTRS)

    Hanson, D. B.

    1975-01-01

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

  1. Sources of noise in magneto-optical readout

    NASA Technical Reports Server (NTRS)

    Mansuripur, M.

    1991-01-01

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

  2. A GaAs FET Oscillator Noise Model with a Periodically Driven Noise Source

    Microsoft Academic Search

    Heinz J. Siweris; Burkhard Schiek

    1986-01-01

    Measurements and numerical simulations of the phase noise of a GaAs FET oscillator are described. It is shown that simulations with a conventional noise model lead to unsatisfactory agreement with the experimental results. A significantly improved accuracy is obtained with an extended oscillator noise model, which includes a periodically driven noise source.

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

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

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

  4. Effects of Source Redistribution on Jet Noise Shielding Salvador Mayoral*

    E-print Network

    Papamoschou, Dimitri

    between the insertion loss and the axial location of peak noise source. The aggressive chevrons causeEffects of Source Redistribution on Jet Noise Shielding Salvador Mayoral* and Dimitri Papamoschou University of California, Irvine, CA 92697, USA The potential of jet noise shielding from the Hybrid Wing

  5. A Robust Waveguide Millimeter-Wave Noise Source

    NASA Technical Reports Server (NTRS)

    Ehsan, Negar; Piepmeier, Jeffrey R.; Solly, Michael; Macmurphy, Shawn; Lucey, Jared; Wollack, Edward

    2015-01-01

    This paper presents the design, fabrication, and characterization of a millimeter-wave noise source for the 160- 210 GHz frequency range. The noise source has been implemented in an E-split-block waveguide package and the internal circuitry was developed on a quartz substrate. The measured excess noise ratio at 200 GHz is 9.6 dB.

  6. Assessing noise sources at synchrotron infrared ports

    PubMed Central

    Lerch, Ph.; Dumas, P.; Schilcher, T.; Nadji, A.; Luedeke, A.; Hubert, N.; Cassinari, L.; Boege, M.; Denard, J.-C.; Stingelin, L.; Nadolski, L.; Garvey, T.; Albert, S.; Gough, Ch.; Quack, M.; Wambach, J.; Dehler, M.; Filhol, J.-M.

    2012-01-01

    Today, the vast majority of electron storage rings delivering synchrotron radiation for general user operation offer a dedicated infrared port. There is growing interest expressed by various scientific communities to exploit the mid-IR emission in microspectroscopy, as well as the far infrared (also called THz) range for spectroscopy. Compared with a thermal (laboratory-based source), IR synchrotron radiation sources offer enhanced brilliance of about two to three orders of magnitude in the mid-IR energy range, and enhanced flux and brilliance in the far-IR energy range. Synchrotron radiation also has a unique combination of a broad wavelength band together with a well defined time structure. Thermal sources (globar, mercury filament) have excellent stability. Because the sampling rate of a typical IR Fourier-transform spectroscopy experiment is in the kHz range (depending on the bandwidth of the detector), instabilities of various origins present in synchrotron radiation sources play a crucial role. Noise recordings at two different IR ports located at the Swiss Light Source and SOLEIL (France), under conditions relevant to real experiments, are discussed. The lowest electron beam fluctuations detectable in IR spectra have been quantified and are shown to be much smaller than what is routinely recorded by beam-position monitors. PMID:22186638

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

    NASA Technical Reports Server (NTRS)

    Miles, Jeffrey Hilton

    2006-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

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

    Microsoft Academic Search

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

    2011-01-01

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

  11. Source-structure trade-offs in ambient noise correlations

    NASA Astrophysics Data System (ADS)

    Fichtner, Andreas

    2015-07-01

    We analyse the physics and geometry of trade-offs between Earth structure and noise sources in interstation noise correlations. Our approach is based on the computation of off-diagonal Hessian elements that describe the extent to which variations in noise sources can compensate for variations in Earth structure without changing the misfit beyond the measurement uncertainty. Despite the fact that all ambient noise inverse problems are special in terms of their receiver configuration and data, some general statements concerning source-structure trade-offs can be made: (i) While source-structure trade-offs may be reduced to some extent by clever measurement design, there are inherent trade-offs that can generally not be avoided. These inherent trade-offs may lead to a mispositioning of structural heterogeneities when the noise source distribution is unknown. (ii) When attenuation is weak, source-structure trade-offs in ambient noise correlations are a global phenomenon, meaning that there is no noise source perturbation that does not trade-off with some Earth structure, and vice versa. (iii) The most significant source-structure trade-offs occur within two elliptically shaped regions connecting a potential noise source perturbation to each one of the receivers. (iv) Far from these elliptical regions, only small-scale structure can trade off against changes in the noise source. (v) While source-structure trade-offs mostly decay with increasing attenuation, they are nearly unaffected by attenuation when the noise source perturbation is located near the receiver-receiver line. This work is intended to contribute to the development of joint source-structure inversions of ambient noise correlations, and in particular to an understanding of the extent to which source-structure trade-offs may be reduced. It furthermore establishes the foundation of future resolution analyses that properly quantify trade-offs between noise sources and Earth structure.

  12. Analysis of Phase Diffusion Process in Oscillators Due to White and Colored-Noise Sources

    Microsoft Academic Search

    Paolo Maffezzoni; Dario D'Amore

    2011-01-01

    This paper presents an original phase-domain analysis of the diffusion process which occurs in oscillators due to small-signal white and colored-noise sources. It is shown that the proposed analysis is able to predict correctly the oscillator's power spectrum also very closely to the fundamental harmonic. The correctness of the analysis is verified through comparisons with commercially available tools. Index TermsOscillators

  13. Frequency-dependent noise sources in the North Atlantic Ocean

    E-print Network

    Stutzmann, Elonore

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

  14. Phase noise in oscillators: DAEs and colored noise sources

    Microsoft Academic Search

    Alper Demir

    1998-01-01

    Oscillators are key components of electronic systems. Undesired perturbations, i.e. noise, in practical electronic systems adversely affect the spectral and tim- ing properties of oscillators resulting in phase noise, which is a key perfor- mance limiting factor, being a major contributor to bit-error-rate (BER) of RF communication systems, and creating synchronization problems in clocked and sampled-data systems. In this paper,

  15. Phase noise in oscillators: DAEs and colored noise sources

    Microsoft Academic Search

    A. Demir

    1998-01-01

    Oscillators are key components of electronic systems. Undesired perturbations, i.e. noise, in practical electronic systems adversely affect the spectral and timing properties of oscillators resulting in phase noise, which is a key performance limiting factor, being a major contributor to bit-error-rate (BER) of RF communication systems, and creating synchronization problems in clocked and sampled data systems. We first present a

  16. Noise source modeling for cyclostationary noise analysis in large-signal device operation

    Microsoft Academic Search

    Fabrizio Bonani; Simona Donati Guerrieri; Giovanni Ghione

    2002-01-01

    Starting from the analysis of fundamental noise sources in large-signal (LS) periodic operation, a system theory approach is proposed for the modeling of colored noise sources in devices and circuits driven in LS conditions. According to this interpretation, colored sources are generated by low-pass filtering and amplitude modulation of a white unit Gaussian process. The order of the modulation and

  17. Noise-Source Identification for Ducted Fan Systems

    Microsoft Academic Search

    Gareth J. Bennettand; John A. Fitzpatrick

    2008-01-01

    Coherence based source analysis techniques can be used to identify the contribution of combustion noise in the exhaust of a jet engine and hence enable the design of noise reduction devices. However, when the combustion noise propagates in a non-linear fashion the identified contribution using ordinary coherence methods will be inaccurate. In this paper, an analysis technique to enable the

  18. First-passage time of an inverted pendulum subject to high frequency harmonic and Gaussian white noise excitations

    Microsoft Academic Search

    Z. L. Huang; Z. Q. Zhu; X. L. Jin

    2009-01-01

    The first-passage time of an inverted pendulum subject to a combination of high frequency harmonic excitation and Gaussian white noise excitation is investigated. The high frequency harmonic excitation term is simplified to an equivalent autonomous nonlinear stiffness term by using the method of direct partition of motions. Then, the equations of motion of the equivalent system are reduced to an

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

    E-print Network

    Hone, James

    Feedback and harmonic locking of slot-type optomechanical oscillators to external low) We demonstrate feedback and harmonic locking of chip-scale slot-type optomechanical oscillators. The feedback and compensation techniques significantly reduce the close-to-carrier phase noise, especially

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  1. An integrated analog\\/digital random noise source

    Microsoft Academic Search

    W. Timothy Holman; J. Alvin Connelly; Ahmad B. Dowlatabadi

    1997-01-01

    An integrated noise source (INS) has been fabricated in a standard 1.2 ?m digital CMOS technology. Wideband white noise is generated from the amplified thermal noise of large resistors, which in turn is coupled into a comparator to generate a random digital bit stream. The INS generates 100 mV rms of analog output noise over a bandwidth of 3.2 MHz

  2. The Effects of Ambient Conditions on Helicopter Rotor Source Noise Modeling

    NASA Technical Reports Server (NTRS)

    Schmitz, Frederic H.; Greenwood, Eric

    2011-01-01

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

  3. Detection technique of acoustical center of noise source

    NASA Astrophysics Data System (ADS)

    Taratorin, A. A.; Tupov, V. B.

    2015-07-01

    The experimental detection technique of acoustical center of noise source is proposed. It is applicable for noise source without distinct limits and emitting acoustic energy unevenly on the surface area. The constraints of this technique are established and factors influencing on the precision of detection of noise center are discussed. The results of the experiment set under the offered technique are shown and comparison to results of mathematical modeling of steam jet is given.

  4. Noise Characterization of Supercontinuum Sources for Low Coherence Interferometry Applications

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Delker, Collin James

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

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

    PubMed Central

    Petrov, Yury

    2012-01-01

    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

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

    Microsoft Academic Search

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

    2010-01-01

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

  8. Additional noise sources in cross-field microwave devices

    Microsoft Academic Search

    A. A. Nikitin; V. S. Stalmakhov; A. S. Shapovalov

    1982-01-01

    Analysis is made of the additional noise sources in cross-field electron-beam devices. The spectral density of the low-frequency fluctuations of the electron-beam drift velocity due to random changes in the space charge density is calculated. It is pointed out that these fluctuations are related to settling current noise and secondary electron emission.

  9. Optical linear algebra processors - Noise and error-source modeling

    NASA Technical Reports Server (NTRS)

    Casasent, D.; Ghosh, A.

    1985-01-01

    The modeling of system and component noise and error sources in optical linear algebra processors (OLAPs) are considered, with attention to the frequency-multiplexed OLAP. General expressions are obtained for the output produced as a function of various component errors and noise. A digital simulator for this model is discussed.

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

    Microsoft Academic Search

    Alessandro Bongiov; Andrea Cattanei

    2011-01-01

    A method is posed for separating the noise emitted by an aerodynamic source from propagation effects using spectral decomposition. This technique is applied to the power spectra of a fan measured at several rotational speeds. Although it has been conceived for rotating sources as turbomachinery rotors, the method may be easily applied to low speed stationary sources such as jets

  11. Source of overbroadband noise oscillations to diagnostics of electronic devices

    Microsoft Academic Search

    S. N. Vladimirov; V. I. Perfiliev

    2004-01-01

    Sources of broadband or overbroadband noise oscillations are required for diagnostics of various electronic devices. We propose that use of deterministic chaos is a perspective way to generate these sources. Signals are generated on a mixer from two autooscillators. One generator has a fixed frequency of generation. The second is frequency-modulated by a signal from a low-frequency chaotic source in

  12. Towards low-noise fiber sources for coherent Raman microscopy

    NASA Astrophysics Data System (ADS)

    Lamb, Erin S.; Pei, Hanzhang; Wise, Frank W.

    2015-03-01

    A compact, robust, and inexpensive ?ber-based source for coherent Raman imaging would bene?t both re-searchers and the clinical application of these imaging techniques. However, the relative intensity noise of ?ber sources has precluded their use for stimulated Raman scattering microscopy without the use of electronic noise cancellation. A recently demonstrated ?ber optical parametric oscillator was used to achieve high-quality images using coherent anti-Stokes Raman scattering microscopy, and demonstrated that the self-consistent nature of the oscillator aided low-noise frequency conversion. Thus, reducing the intensity noise on the ?ber laser used to pump this device will be a critical step in creating a ?ber-based source for stimulated Raman scattering microscopy. We will report the design and construction of high-energy dissipative soliton ?ber lasers as a potential source of quiet picosecond pulses at 1 ?m, along with application to pumping the optical parametric oscillator.

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

    E-print Network

    Tse, Chi K. "Michael"

    Optimal Design of Repetitive Controller for Harmonic Elimination in PWM Voltage Source Inverters The pulse-width modulation (PWM) voltage source inverter (VSI) is extensively employed in AC power proportional-integral-derivative (PID) controllers that are widely used in the VSI can reduce such harmonic

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

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

    PubMed

    Lutfi, Robert A; Liu, Ching-Ju

    2011-02-01

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

  16. An improved source model for aircraft interior noise studies

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  17. Suppress noise output of YIG-tuned sources

    NASA Astrophysics Data System (ADS)

    Bales, R.

    1980-05-01

    The design of drive circuits aimed to reduce the noise output of YIG-tuned oscillators is presented. The noise reduction technique is illustrated by analysis of a low-noise electronically tunable oscillator in a spectrum analyzer. A variety of noise types (thermal, broadband operational amplifier, and popcorn noise) are evaluated, and measures to avoid the harmful constituents at each stage of the driver are indicated. It is mentioned that in a well-designed driver, operational amplifier noise is the limiting factor. Low-frequency drift as a source of signal variations is considered. Special attention is given to the driver's final stage design, noting the need to consider ground-potential drops resulting in the upset of the voltage/frequency relationships of earlier stages.

  18. Electrical and noise characteristics of graphene field-effect transistors: ambient effects, noise sources and physical mechanisms

    E-print Network

    . Special attention was given to determining the dominant noise sources in these devices and the effect.1088/0953-8984/22/39/395302 Electrical and noise characteristics of graphene field-effect transistors: ambient effects, noise sources-frequency electronic noise come from the graphene layer itself rather than from the contacts. Aging of graphene

  19. Investigation of noise sources in SQUID electronics

    Microsoft Academic Search

    T. R. Clem; M. J. Goldstein; J. W. Purpura; L. H. Allen; J. H. Claassen

    1989-01-01

    The performance of SQUID (superconducting quantum interference device)-based electronics may be degraded from that found in laboratory operation. Investigations on superconducting tubes, wires, and sheets have been conducted to identify contributions to such noise. Results have been obtained for bulk and thin-film samples utilizing both the conventional low-temperature materials and the new high-temperature oxide materials. Experiments have been conducted to

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  1. Screech noise source structure of a supersonic rectangular jet

    NASA Technical Reports Server (NTRS)

    Rice, E. J.; Taghavi, R.

    1992-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    This paper presents a status of non-CFD aeroacoustic codes at NASA Langley Research Center for the prediction of helicopter harmonic and Blade-Vortex Interaction (BVI) noise. The prediction approach incorporates three primary components: CAMRAD.Mod1 - a substantially modified version of the performance/trim/wake code CAMRAD; HIRES - a high resolution blade loads post-processor; and WOPWOP - an acoustic code. The functional capabilities and physical modeling in CAMRAD.Mod1/HIRES will be summarized and illustrated. A new multi-core roll-up wake modeling approach is introduced and validated. Predictions of rotor wake and radiated noise are compared with to the results of the HART program, a model BO-105 windtunnel test at the DNW in Europe. Additional comparisons are made to results from a DNW test of a contemporary design four-bladed rotor, as well as from a Langley test of a single proprotor (tiltrotor) three-bladed model configuration. Because the method is shown to help eliminate the necessity of guesswork in setting code parameters between different rotor configurations, it should prove useful as a rotor noise design tool.

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

    NASA Astrophysics Data System (ADS)

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

    1995-10-01

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

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

    Microsoft Academic Search

    Eugene A. Klingshirn

    1985-01-01

    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

  5. Sub-Shot Noise Power Source for Microelectronics

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    Low-current, high-impedance microelectronic devices can be affected by electric current shot noise more than they are affected by Nyquist noise, even at room temperature. An approach to implementing a sub-shot noise current source for powering such devices is based on direct conversion of amplitude-squeezed light to photocurrent. The phenomenon of optical squeezing allows for the optical measurements below the fundamental shot noise limit, which would be impossible in the domain of classical optics. This becomes possible by affecting the statistical properties of photons in an optical mode, which can be considered as a case of information encoding. Once encoded, the information describing the photon (or any other elementary excitations) statistics can be also transmitted. In fact, it is such information transduction from optics to an electronics circuit, via photoelectric effect, that has allowed the observation of the optical squeezing. It is very difficult, if not technically impossible, to directly measure the statistical distribution of optical photons except at extremely low light level. The photoelectric current, on the other hand, can be easily analyzed using RF spectrum analyzers. Once it was observed that the photocurrent noise generated by a tested light source in question is below the shot noise limit (e.g. produced by a coherent light beam), it was concluded that the light source in question possess the property of amplitude squeezing. The main novelty of this technology is to turn this well-known information transduction approach around. Instead of studying the statistical property of an optical mode by measuring the photoelectron statistics, an amplitude-squeezed light source and a high-efficiency linear photodiode are used to generate photocurrent with sub-Poissonian electron statistics. By powering microelectronic devices with this current source, their performance can be improved, especially their noise parameters. Therefore, a room-temperature sub-shot noise current source can be built that will be beneficial for a very broad range of low-power, low-noise electronic instruments and applications, both cryogenic and room-temperature. Taking advantage of recent demonstrations of the squeezed light sources based on optical micro-disks, this sub-shot noise current source can be made compatible with the size/power requirements specific of the electronic devices it will support.

  6. Jet Noise Source Localization Using Linear Phased Array

    NASA Technical Reports Server (NTRS)

    Agboola, Ferni A.; Bridges, James

    2004-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-07-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  11. A ring-source model for jet noise

    NASA Technical Reports Server (NTRS)

    Maestrello, L.

    1978-01-01

    A model consisting of two ring sources was developed to study the direct radiation of jet noise in terms of correlation, coherence, and phase and also to aid in solving the inverse radiation problem of determining the noise source in terms of far-field measurements. The rings consist of discrete sources which are either monopoles or quadrupoles with Gaussian profiles. Only adjacent sources, both within the rings and between rings, are correlated. Results show that from the far-field information can be used to determine when the sources are compact or noncompact with respect to the acoustic wavelength and to distinguish between the types of sources. In addition, from the inverse radiation approach, the center of mass, the location and separation distance of the ring, and the diameters can be recovered.

  12. Improving Separation of Harmonic Sources with Iterative Estimation of Spatial Cues

    E-print Network

    Pardo, Bryan

    Improving Separation of Harmonic Sources with Iterative Estimation of Spatial Cues JINYU. HAN1 in source separation of two-channel mixtures. However, as sources increasingly overlap in the time to separating sources in two-channel anechoic acoustic mixtures. Both use spa- tial cues to estimate time

  13. Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    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.

  14. Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise

    NASA Astrophysics Data System (ADS)

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

    2002-08-01

    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.

  15. Second and Third Harmonic Measurements at the Linac Coherent Light Source

    SciTech Connect

    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

    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.

  16. Electrical and noise characteristics of graphene field-effect transistors: ambient effects, noise sources and physical mechanisms

    Microsoft Academic Search

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

    2010-01-01

    We fabricated a large number of single and bilayer graphene transistors and carried out a systematic experimental study of their low-frequency noise characteristics. Special attention was given to determining the dominant noise sources in these devices and the effect of aging on the current-voltage and noise characteristics. The analysis of the noise spectral density dependence on the area of graphene

  17. Theory of harmonic radiation using a single-electron source model

    SciTech Connect

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

    1989-01-01

    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.

  18. Johnson-noise thermometry based on a quantized-voltage noise source at NIST

    NASA Astrophysics Data System (ADS)

    Pollarolo, A.; Jeong, T.; Benz, S. P.; Dresselhaus, P. D.; Rogalla, H.; Tew, W. L.

    2013-09-01

    Johnson Noise Thermometry is an electronic approach to measuring temperature. For several years, NIST has been developing a switching-correlator-type Johnson-noise thermometer that uses a quantized voltage noise source as an accurate voltage reference. When this method is used to measure resistors at the triple-point of water, the system creates a direct electronic method for determining the ratio of the Boltzmann constant k to the Planck constant h. In 2010, NIST optimized the JNT system for use with 100 ? sense resistors and produced a determination for k with a relative standard uncertainty of 1210-6. In order to further validate and improve the measurement method, we modified the system to operate with a 200 ? resistor source instead of the 100 ? source. In this paper, we summarize the technical challenges and achievements to date and project what is achievable in the near future.

  19. Investigation of Volumetric Sources in Airframe Noise Simulations

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  20. Noise tube sources for the far IR and millimeter region

    NASA Technical Reports Server (NTRS)

    Moller, K. D.; Zoeller, R. G.; Ugras, N. G.; Zablocky, P.; Heaney, James B.; Stewart, K. P.; Boucarut, R. A.

    1988-01-01

    The radiant output of a noise tube designed for the 90-140-GHz (3.3-2.1-mm) frequency range has been compared with that from mercury lamps over the wavelength region from 0.4 to about 6 mm. Lamellar grating and Michelson Fourier transform spectrometers were used in conjunction with He cooled bolometers of NEP from 10 to the -12th to 10 to the -14th W/sq rt H2 to measure relative spectral irradiance. With this instrumental arrangement, the radiant power emitted by the noise tube was observed to be less than that from a mercury lamp, at least to a 3-mm wavelength, but it produced less source noise than an ac operated mercury lamp. When the noise tube operating current was reduced, the spectral irradiance peak shifted to longer wavelengths.

  1. A high-flux high-order harmonic source.

    PubMed

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

    2013-07-01

    We develop and implement an experimental strategy for the generation of high-energy high-order harmonics (HHG) in gases for studies of nonlinear processes in the soft x-ray region. We generate high-order harmonics by focusing a high energy Ti:Sapphire laser into a gas cell filled with argon or neon. The energy per pulse is optimized by an automated control of the multiple parameters that influence the generation process. This optimization procedure allows us to obtain energies per pulse and harmonic order as high as 200 nJ in argon and 20 nJ in neon, with good spatial properties, using a loose focusing geometry (f#?400) and a 20 mm long medium. We also theoretically examine the macroscopic conditions for absorption-limited conversion efficiency and optimization of the HHG pulse energy for high-energy laser systems. PMID:23902040

  2. A battery-based, low-noise voltage source

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

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

  3. 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

    Hong, Kyung-Han

    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 ...

  4. Fundamental noise sources that limit the ultimate resolution of fiber optic sensors

    Microsoft Academic Search

    Kjell Blotekjaer

    1998-01-01

    It is a commonly encountered statement that shot-noise is the most fundamental and ultimately limiting noise source in any photonic device, because all other noise sources can in principle be reduced to insignificant values. However, this perspective is often of little value, since in practice it is impossible to eliminate other, more trivial, noise sources. It is useful to classify

  5. Optical Techniques for Low Noise Microwave Frequency Sources

    NASA Technical Reports Server (NTRS)

    Maleki, Lute

    2005-01-01

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

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

    Microsoft Academic Search

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

    2008-01-01

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

  7. Identification and classification of noise sources in a chain conveyor

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

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

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

    Microsoft Academic Search

    Shaojun Xie; Yu Tang; Chaohua Zhang

    2009-01-01

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

  9. Noise sources in silicon on insulator (SIMOX) MOSFET's

    NASA Astrophysics Data System (ADS)

    Elewa, T.; Boukriss, B.; Haddara, H.; Chovet, A.; Cristoloveanu, S.

    We propose a simple model in order to separate the noise sources related to the front and back Si?SiO 2 interfaces and film volume in silicon on insulator (SOI) MOS transistors. From low-frequency noise measurements in depletion-mode and enhancement-mode SIMOX MOSFET's, single-level traps at the back interface and surface and volume defects are detected in high-temperature annealed wafers. These properties are compared with those of SIMOX films annealed at temperatures below 1250C.

  10. A power transformer as a source of noise.

    PubMed

    Zawieska, Wiktor Marek

    2007-01-01

    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

  11. Noise source emissions, Deaf Smith County site, Texas

    SciTech Connect

    Not Available

    1987-05-13

    Noise source data and use factors for modeling the noise environment expected from salt site repository activity were provided by Battelle Columbus Division. This report has been prepared for the purpose of documenting the development of the data provided to the Repository Project Management (RPM) organization. The data provided encompass all phases of activity from site preparation through construction of the exploratory shaft facility (ESF). Noise environments expected from construction and operation of transportation corridors associated with the activity were also modeled. The equipment inventory, including sound-power levels for each item, is included. Emission source terms provided by Parsons Brinckerhoff/PB-KBB for the ESF were used as a basis for the noise-source emission inventory development. Where available, research results containing complete spectra were used. In cases where complete data were not available, a sound-pressure spectrum was synthesized from a characteristic spectrum shape from a similar piece of equipment. For example, a front-shovel excavator might be approximated by data from a front-end loader of similar horsepower range. Sound-power-level spectra were then calculated from the sound-pressure-level data. 2 refs.

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    This document details the methodology and use of the CAMRAD.Mod1/HIRES codes, which were developed at NASA Langley Research Center for the prediction of helicopter harmonic and Blade-Vortex Interaction (BVI) noise. CANMAD.Mod1 is a substantially modified version of the performance/trim/wake code CANMAD. High resolution blade loading is determined in post-processing by HIRES and an associated indicial aerodynamics code. Extensive capabilities of importance to noise prediction accuracy are documented, including a new multi-core tip vortex roll-up wake model, higher harmonic and individual blade control, tunnel and fuselage correction input, diagnostic blade motion input, and interfaces for acoustic and CFD aerodynamics codes. Modifications and new code capabilities are documented with examples. A users' job preparation guide and listings of variables and namelists are given.

  13. Determining the influence of age and diabetes on the second-harmonic generation strength of dermal collagen fibers in vivo by using electronic noises

    NASA Astrophysics Data System (ADS)

    Hung, Wei-Chun; Sun, Chi-Kuang; Chen, Argon

    2013-02-01

    It is commonly believed that intrinsic skin aging is associated with the change of the collagen structures. The influence of the diabetes on the skin collagen is also considered to be similar to aging. Moreover, second-harmonic-generation (SHG) in collagen fibers is known to reflect the detailed collagen structures. It is thus highly valuable to adopt the SHG intensity as a collagen structure indicator. With the help of SHG, recently one can achieve in vivo imaging which provides the information of what really happens beneath the human skin. However, when analyzing the images, the SHG brightness of each pixel highly depends on the illumination condition, the depth of the SHG source, and the voltage of PMT. Therefore, it is important to calibrate these factors before statistical analysis. In this paper, we present our recent development that calibrates the in vivo SHG images by using noises. We first determine the regions of signals and noises by setting a threshold relating to the standard deviation of the image. By using the assumption that the noise was amplified by PMT with an amplification ratio the same as the SHG signal, we can define the brightness of the noise region as a parameter representing the voltage of PMT, and use this parameter to calibrate all SHG images. After calibrating, we can then compare different images from volunteers and analyze the influence of aging and diabetes on the SHG intensity from collagen fibers, even if the voltage of PMT was not fixed.

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

    Microsoft Academic Search

    Jaydeep P Bardhan; Matthew G Knepley

    2012-01-01

    We present two open-source (BSD) implementations of ellipsoidal harmonic expansions for solving problems of potential theory using separation of variables. Ellipsoidal harmonics are used surprisingly infrequently, considering their substantial value for problems ranging in scale from molecules to the entire solar system. In this paper, we suggest two possible reasons for the paucity relative to spherical harmonics. The first is

  15. Exozodiacal Dust: Noise Source and Signpost for Habitable Planets

    NASA Astrophysics Data System (ADS)

    Hinz, P.

    2014-03-01

    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).

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

    PubMed

    Polikarpov, Maxim; Snigireva, Irina; Snigirev, Anatoly

    2014-05-01

    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

  17. Accurate Extraction of Noise Source Impedance of an SMPS Under Operating Conditions

    Microsoft Academic Search

    Vuttipon Tarateeraseth; Bo Hu; Kye Yak See; Flavio G. Canavero

    2010-01-01

    An accurate measurement method to extract the common mode (CM) and the differential mode (DM) noise source impedances of a switched-mode power supply (SMPS) under its operating condition is developed and validated. With a proper premeasurement calibration process, the proposed method allows extraction of both the CM and the DM noise source impedances with very good accuracy. These noise source

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

    NASA Astrophysics Data System (ADS)

    Ida, Masato

    2009-01-01

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

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

    Microsoft Academic Search

    B. Justus Rabi; R. Arumugam

    2005-01-01

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

  20. Noise source identification and control of a contractor grade table saw

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Bongiov, Alessandro; Cattanei, Andrea

    2011-01-01

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

  2. Modeling and measurement of the impedance of common mode noise source of switching converters

    Microsoft Academic Search

    Henglin Chen; Limin Feng; Wei Chen; Zhaoming Qian

    2006-01-01

    The EMI noise source impedance of an SMPS is essential in its power line EMI filter design, and when ignored, either over design, or system requirements not being met would occur. Because DM noise is easy to identify but CM noise is still hard to characterize, more concerns are with CM noise. This paper deals with the modeling of generation

  3. Acoustic noise, vibration, harmonics, thermal of three phase linear switched reluctance machines

    Microsoft Academic Search

    N. C. Lenin; R. Arumugam

    2010-01-01

    Acoustic noise in the linear switched reluctance motor (LSRM) is caused primarily by the deformation of the stator lamination stack. Acoustic noise is most severe when the periodic excitation of the LSRM phases excites a natural vibration mode of the stack. Noise and vibration are usually high in LSRM because of doubly salient structures. The natural vibration modes and frequencies

  4. Detailed study of an efficient blue laser source by second-harmonic generation in a semimonolithic

    E-print Network

    utility for laser cooling and trapping of earth alkalis by stabilizing the laser to the 461-nm transition alkalis can be trapped with diode lasers or Ti:sapphire lasers, there are few powerful, reliableDetailed study of an efficient blue laser source by second-harmonic generation in a semimonolithic

  5. EMI Radiated Noise Measurement System Using the Source Reconstruction Technique

    Microsoft Academic Search

    Marta Mara Hernando; Arturo Fernandez; Manuel Arias; Miguel Rodriguez; Yuri Alvarez; Fernando Las-Heras

    2008-01-01

    One of the requirements that electronics circuits must satisfy comprises conducted and irradiated noise specifications. Whereas conducted noise is well covered in the literature, radiated noise is not. Radiated noise regulations impose limits on the noise measured 3 or 10 m away from electronic equipment. These measurements are usually made in anechoic rooms, which are very expensive. Moreover, the measurement

  6. Identification of 1\\/f diffusion and recombination noise sources in bipolar transistors

    Microsoft Academic Search

    S. Decoutere; L. Deferm; G. Vanhorebeek; C. Claeys; G. Declerck

    1990-01-01

    A method is proposed to identify 1\\/f noise sources in bipolar transistors related to mobility fluctuations in the base and collector current and to recombination at the surface of the emitter\\/base depletion region. It is shown that the physical location of the 1\\/f noise sources plays a key role in interpreting noise data. Excellent agreement between theory and measurements is

  7. Noise source identification with the lattice Boltzmann method.

    PubMed

    Vergnault, Etienne; Malaspinas, Orestis; Sagaut, Pierre

    2013-03-01

    In this paper the sound source identification problem is addressed with the use of the lattice Boltzmann method. To this aim, a time-reversed problem coupled to a complex differentiation method is used. In order to circumvent the inherent instability of the time-reversed lattice Boltzmann scheme, a method based on a split of the lattice Boltzmann equation into a mean and a perturbation component is used. Lattice Boltzmann method formulation around an arbitrary base flow is recalled and specific applications to acoustics are presented. The implementation of the noise source detection method for two-dimensional weakly compressible (low Mach number) flows is discussed, and the applicability of the method is demonstrated. PMID:23464002

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

    NASA Technical Reports Server (NTRS)

    Meyer, Harold D.

    1999-01-01

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

  9. Coherent diffractive imaging microscope with a high-order harmonic source.

    PubMed

    Dinh, Khuong Ba; Le, Hoang Vu; Hannaford, Peter; Dao, Lap Van

    2015-06-10

    We report the generation of highly coherent extreme ultraviolet sources with wavelengths around 30 and 10nm by phase-matched high-order harmonic generation (HHG) in a gas cell filled with argon and helium, respectively. We then perform coherent diffractive imaging (CDI) by using a focused narrow-bandwidth HHG source with wavelength around 30nm as an illumination beam for two kinds of samples. The first is a transmission sample and the second is a absorption sample. In addition, we report the successful reconstruction of a complex absorption sample using a tabletop high-harmonic source. This will open the path to the realization of a compact soft x-ray microscope to investigate biological samples such as membrane proteins. PMID:26192827

  10. Quadrupole source in prediction of the noise of rotating blades - A new source description

    NASA Astrophysics Data System (ADS)

    Farassat, F.

    1987-10-01

    The aim of this paper is to perform a theoretical study of the quadrupole term of the Ffowcs Williams-Hawkings (FW-H) equation to obtain practical results for applications to rotating blades. The quadrupole term of the FW-H equation is algebraically manipulated into volume, surface and line sources using generalized function theory and differential geometry. The volume source is of the type in Lighthill's jet noise theory. The surface sources are on the blade and shock surfaces and the line source is at the trailing edge. It is shown that contribution of volume sources in the boundary layer and wakes can be written in the form of surface integrals. It is argued that the surface and line sources and the part of the volume sources in the boundary layer, wakes and vortices near the blades should be sufficient in calculation of the noise of high speed rotating blades. The integrals correspoding to the various sources appearing in the formula for calculation of the acoustic pressure are briefly derived.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  13. Fan Noise Source Diagnostic Test: LDV Measured Flow Field Results

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Hernandez-Garcia, J. C.; Pottiez, O.; Ibarra-Escamilla, B.; Estudillo-Ayala, J. M.; Rojas-Laguna, R.; Kuzin, E.; Muoz-Lopez, A.; Filoteo-Razo, J. D.

    2015-03-01

    We study a passively mode-locked double-clad Erbium-Ytterbium fiber ring laser producing noise-like pulse through nonlinear polarization evolution and polarization selection. Single noise-like pulsing is only observed at moderate pump power. As pump power is increased, and through polarization controllers adjustments, harmonic mode-locking of growing order were successively appearing. For pump powers close to the damage threshold of the setup, we reach harmonic orders beyond 1200 and repetition frequencies in excess of a quarter of a GHz. Finally, these experimental results could be useful in the quest for higher pulse energies and higher repetition rates in passively mode-locked fiber lasers.

  15. NON-SQUARE BLIND SOURCE SEPARATION UNDER COHERENT NOISE BY BEAMFORMING AND TIME-FREQUENCY MASKING

    Microsoft Academic Search

    Radu Balan; Justinian Rosca; Scott Rickard

    To be applicable in realistic scenarios, blind source sep- aration approaches should deal evenly with non-square cases and the presence of noise. We consider an additive noise mixing model with an arbitrary number of sensors and pos- sibly more sources than sensors (the non-square case) when sources are disjointly orthogonal. We formulate the max- imum likelihood estimation of the coherent

  16. Highly efficient second, third and fourth harmonic generation from a two- branch femtosecond erbium fiber source

    Microsoft Academic Search

    Konstantinos Moutzouris; Florian Sotier; Florian Adler; Alfred Leitenstorfer

    2006-01-01

    We report on highly efficient second, third and fourth harmonic generation from a femtosecond erbium-doped fiber source operating at 98 MHz repetition rate. By use of quasi-phase-matching in fan-out poled MgO:LiNbO3, we generate pulses at 770 nm, 520 nm and 390 nm, with corresponding average powers of 120 mW, 55 mW and 6 mW, respectively. Our device can be employed

  17. High repetition rate source of narrowband extreme-ultraviolet harmonics for time-resolved ARPES

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    We present a highly efficient table-top source of extreme ultraviolet (XUV) femtosecond pulses operating at 50-kHz repetition rate. A bright XUV source flux of 3x1013 photons/s is generated at 22.3 eV by driving high-harmonic generation with the ultraviolet second-harmonic of a laser amplifier focused tightly into Kr gas. The conversion efficiency (5x10-5) is enhanced by two orders-of-magnitude in this cascaded scheme, exceeding dipole wavelength scaling and evidencing enhanced phase matching conditions as confirmed by simulations. Importantly, the spectral structure enables the direct, high-contrast isolation of a single, narrowband harmonic with 72 meV linewidth. The high repetition rate, narrow bandwidth, and high flux (1011-1012 ph/s at the sample) of this source is ideal for time-resolved photoemission or nanoscale imaging. First applications in time- and angle-resolved photoemission (trARPES) will be discussed. The work was supported by the DOE Office of Science, Materials Sciences and Engineering Division.

  18. Simulation of internal distribution of microwave noise sources in a short-channel nMOSFET

    Microsoft Academic Search

    M. S. Obrecht; Tajinder Manku; Mohamed I. Elmasry

    2000-01-01

    High frequency excess noise in short-channel MOSFETs is discussed from the point of view of internal device characteristics, such as noise source density and current densities. It is demonstrated that the current density component perpendicular to the interface produces a major portion of the high frequency (diffusion) noise in short-channel MOSFETs

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    E-print Network

    Bardhan, Jaydeep P

    2012-01-01

    We present two open-source (BSD) implementations of ellipsoidal harmonic expansions for solving problems of potential theory using separation of variables. Ellipsoidal harmonics are used surprisingly infrequently, considering their substantial value for problems ranging in scale from molecules to the entire solar system. In this article, we suggest two possible reasons for the paucity relative to spherical harmonics. The first is essentially historical---ellipsoidal harmonics developed during the late 19th century and early 20th, when it was found that only the lowest-order harmonics are expressible in closed form. Each higher-order term requires the solution of an eigenvalue problem, and tedious manual computation seems to have discouraged applications and theoretical studies. The second explanation is practical: even with modern computers and accurate eigenvalue algorithms, expansions in ellipsoidal harmonics are significantly more challenging to compute than those in Cartesian or spherical coordinates. The...

  1. Noise radiation of propeller loading sources with angular inflow

    Microsoft Academic Search

    D. B. Hanson

    1990-01-01

    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

  2. Determination of wave noise sources using spectral parametric modeling

    Microsoft Academic Search

    Thierry Werling; Emmanuelle Bourdel; Daniel Pasquet; Ali Boudiaf

    1997-01-01

    A new method for the extraction of a noise correlation matrix is presented in this paper. This method is based on a kind of reflectometric technique which needs two noise-power measurements corresponding to two different input coefficients for the extraction of the wave correlation matrix. Then, we measure those two noise-power densities emanating from the device under test (DUT) transistor

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

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

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

  4. Occupational Noise Sources and Exposures in Construction Industries

    Microsoft Academic Search

    Dale Hattis

    1998-01-01

    This is an assessment of occupational noise exposures in the construction industry based on (1) noise measurements observed during Occupational Safety and Health Administration (OSHA) inspections over the period from 1986 through early 1997 and (2) the observed incidence of noise exposures over 85 dB (A) in a national random sample of construction firms done as part of the NIOSH

  5. An investigation of high-frequency bias-induced tape noise

    Microsoft Academic Search

    H. Ragle; P. Smaller

    1965-01-01

    Bias-induced tape noise remains a major limitation of the SNR in audio magnetic tape recording systems. Defined as the increment in system noise incurred when the bias oscillator is turned on, the noise can originate from a number of different causes; namely, bias oscillator harmonic distortion, magnetized heads, the earth's magnetic field, and an intrinsic noise source. The latter noise

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

    SciTech Connect

    Coulson, R.K.

    1996-12-01

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

  7. Highly efficient second, third and fourth harmonic generation from a two- branch femtosecond erbium fiber source.

    PubMed

    Moutzouris, Konstantinos; Sotier, Florian; Adler, Florian; Leitenstorfer, Alfred

    2006-03-01

    We report on highly efficient second, third and fourth harmonic generation from a femtosecond erbium-doped fiber source operating at 98 MHz repetition rate. By use of quasi-phase-matching in fan-out poled MgO:LiNbO(3), we generate pulses at 770 nm, 520 nm and 390 nm, with corresponding average powers of 120 mW, 55 mW and 6 mW, respectively. Our device can be employed as a two-color source providing radiation from ultraviolet to near infrared. PMID:19503520

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

    NASA Technical Reports Server (NTRS)

    Johnson, E. H.

    1975-01-01

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

  9. Extraction of Correlated Base and Collector Current RF Noise Sources in SiGe HBTs

    Microsoft Academic Search

    Kim-Ming Chen; Guo-Wei Huang; Han-Yu Chen; Hsin-Hui Hu; Wen-Shiang Liao; Chun-Yen Chang

    2007-01-01

    A method for extracting current noise sources in SiGe HBTs is proposed in this work. The base current noise, collector current noise and their correlation are extracted after removing the noise contribution from the extrinsic elements of devices. We simplify the extraction procedure by simple calculations of the four-port Y-parameters of the extrinsic circuit. The proposed procedure prevents the complicated

  10. Simultaneous optical comb frequency stabilization and super-mode noise suppression of harmonically mode-locked semiconductor ring laser using an intracavity etalon

    Microsoft Academic Search

    S. Gee; F. Quinlan; S. Ozharar; P. J. Delfyett

    2005-01-01

    Using an intracavity Pound-Drever-Hall technique, simultaneous optical frequency comb stabilization within 3-MHz range and super-mode phase noise suppression were demonstrated for a 10-GHz harmonically mode-locked semiconductor ring laser. Together with an additional phase-lock loop, timing jitter integrated from 10 Hz to 10 MHz (5 GHz) was 63.5 fs (161 fs).

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

    NASA Astrophysics Data System (ADS)

    Masukawa, Shigeo

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

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

    PubMed

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

    2010-02-01

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

  13. Scalable non-square blind source separation in the presence of noise

    Microsoft Academic Search

    Radu Balan; Justinian Rosca; Scott Rickard

    2003-01-01

    Few source separation and independent component analysis approaches attempt to deal with noisy data. We consider an additive noise mixing model with an arbitrary number of sensors and possibly more sources than sensors (the \\

  14. Electrical and noise characteristics of graphene field-effect transistors: ambient effects, noise sources and physical mechanisms

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

    We fabricated a large number of single and bilayer graphene transistors and carried out a systematic experimental study of their low-frequency noise characteristics. Special attention was given to determining the dominant noise sources in these devices and the effect of aging on the current-voltage and noise characteristics. The analysis of the noise spectral density dependence on the area of graphene channel showed that the dominant contributions to the low-frequency electronic noise come from the graphene layer itself rather than from the contacts. Aging of graphene transistors due to exposure to ambient conditions for over a month resulted in substantially increased noise, attributed to the decreasing mobility of graphene and increasing contact resistance. The noise spectral density in both single and bilayer graphene transistors either increased with deviation from the charge neutrality point or depended weakly on the gate bias. This observation confirms that the low-frequency noise characteristics of graphene transistors are qualitatively different from those of conventional silicon metal-oxide-semiconductor field-effect transistors.

  15. Noise Sources in GaN\\/AlGaN Quantum Wells and Devices

    Microsoft Academic Search

    S. Rumyantsev

    We will examine possible sources of generation-recombination and 1\\/f noise in GaN\\/AlGaN 2D structures, quantum wells, and\\u000a devices including contacts, bulk and quantum well itself and show that sources of g-r noise, and most probably of 1\\/f noise\\u000a in HFETs are located in GaN or AlGaN layers within some distance from the 2D channel.

  16. FET noise sources and their effects on amplifier performance at low frequencies

    Microsoft Academic Search

    M. B. Das

    1972-01-01

    In this brief review paper analytical results concerning the low-frequency (LF) amplifier noise performance of FET's are presented. The effects of interaction between the device basic noise sources, the small-signal model parameters, and the signal source admittance parameters are clearly indicated. The noise performance is found to be essentially determined by the effective surface-state density and the gate insulator thickness

  17. Extraction of device noise sources from measured data using circuit simulator software

    Microsoft Academic Search

    P. K. Ikalainen

    1993-01-01

    A procedure is presented for extracting the properties of device noise sources from experimental data. The extraction procedure can be implemented using commercially available circuit simulators. An example concerning a low-noise pseudomorphic high-electron-mobility transistor (HEMT) shows that the two noise sources extracted from experimental data are largely uncorrelated provided that parasitic elements are de-embedded from the measurement and that the

  18. XXXVII. Helix Type Gaseous Discharge Noise Sources at Low Plasma Densities

    Microsoft Academic Search

    H. SCHKITGEE

    1957-01-01

    The behaviour of the positive column of a gaseous discharge in helium within a helical line as a noise source is investigated in the range of relatively low plasma densities. The use of a helical line for establishing the h.f. electric field increases considerably the possibilities for the application of the gaseous discharge noise sources and, at the same time.

  19. Decomposition of baseline noise sources in hard disk position error signals using the PES Pareto method

    Microsoft Academic Search

    Daniel Abramovitch; Terril Hurst; Dick Henze

    1997-01-01

    This paper uses the position error signal (PES) Pareto method and measurement techniques for isolating noise sources to decompose the PES of a Lynx II hard disk drive manufactured by Hewlett-Packard. This accomplishes three things: it demonstrates the utility of the PES Pareto method in a practical example, it allows us to discover which noise sources are insignificant to PES,

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

    E-print Network

    Garnier, Josselin

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

  1. Reducing ion beam noise of vacuum arc ion sources

    SciTech Connect

    Anders, Andre; Hollinger, Ralph

    2001-08-29

    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.

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

    NASA Technical Reports Server (NTRS)

    Heidelberg, Laurence J.

    2002-01-01

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

  3. Auroral kilometric radiation - Wave modes, harmonics, and source region electron density structures

    NASA Technical Reports Server (NTRS)

    Benson, R. F.

    1985-01-01

    A change from extraordinary (X) mode to ordinary (O) 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 O 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 O-mode. The 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 O-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 O-mode radiation.

  4. HSCT nozzle source noise programs at Pratt and Whitney

    NASA Astrophysics Data System (ADS)

    Stern, Alfred M.

    1992-04-01

    The topics covered include the following: 20 dB jet noise suppression; ejector nozzle technology program - noise reduction vs. flow augmentation; mixer ejector nozzle technology challenges; 1989 High Speed Civil Transport (HSCT) 2-D ejector model test in NASA's 9 x 15 ft. tunnel; tertiary airflow 1989 2-D ejector test; shock noise dominates 2-D ejector test; lessons learned - 2-D mixer/ejector in 9 x 15 ft. tunnel; 1990 HSCT axisymmetric ejector model test in Boeing's Low Speed Aeroacoustic Facility (LSAF); axisymmetric mixer/ejector mach contours - peak and valley - NASTAR pre-test predictions; tertiary airflow objectives accomplished - 1990 AXI model; and HSCT low noise exhaust technology programs.

  5. Source mapping analysis, a multi-source method for the interpretation and analysis of magnetic Barkhausen noise signals

    NASA Astrophysics Data System (ADS)

    Prez-Benitez, J. A.; Espina-Hernndez, J. H.

    2013-01-01

    This work proposes a method to study multiple sources in the magnetic Barkhausen noise signal. The method is termed source mapping analysis and is based on the generation of a map of signals using a set of elementary sources. The evolution of Barkhausen noise signals as a function of two microstructural features, i.e. carbon content and level of plastic deformation, is studied by placing the input signal on the map. The position of the magnetic Barkhausen noise signal in the map follows a trajectory depending on these microstructural features, which could be used to simultaneously estimate their values.

  6. Source Attribution of Helicopter Noise in Pristine National Park Landscapes

    Microsoft Academic Search

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

    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.

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

    NASA Technical Reports Server (NTRS)

    Zaman, Afroz; Bauch, Matthew; Raible, Daniel

    2011-01-01

    Aircraft engines have evolved into a highly complex system to meet ever-increasing demands. The evolution of engine technologies has primarily been driven by fuel efficiency, reliability, as well as engine noise concerns. One of the sources of engine noise is pressure fluctuations that are induced on the stator vanes. These local pressure fluctuations, once produced, propagate and coalesce with the pressure waves originating elsewhere on the stator to form a spinning pressure pattern. Depending on the duct geometry, air flow, and frequency of fluctuations, these spinning pressure patterns are self-sustaining and result in noise which eventually radiate to the far-field from engine. To investigate the nature of vane pressure fluctuations and the resulting engine noise, unsteady pressure signatures from an array of embedded acoustic sensors are recorded as a part of vane noise source diagnostics. Output time signatures from these sensors are routed to a control and data processing station adding complexity to the system and cable loss to the measured signal. "Smart" wireless sensors have data processing capability at the sensor locations which further increases the potential of wireless sensors. Smart sensors can process measured data locally and transmit only the important information through wireless communication. The aim of this wireless noise telemetry task was to demonstrate a single acoustic sensor wireless link for unsteady pressure measurement, and thus, establish the feasibility of distributed smart sensors scheme for aircraft engine vane surface unsteady pressure data transmission and characterization.

  8. Saturated and subcooled hydrothermal boiling in groundwater flow channels as a source of harmonic tremor

    NASA Astrophysics Data System (ADS)

    Leet, Robert C.

    1988-05-01

    The potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor (a relatively monochromatic ground vibration associated with volcanic activity) is examined. We use simple "organ pipe" theory of normal-mode fluid vibration and fundamental energy considerations to develop a first-order analytical model of a hydrothermal-boiling source of harmonic tremor. We use this model to estimate order-of-magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0.5-5 Hz and surface wave reduced displacements of up to 100 cm2. Depending on groundwater sound speed, flow channel lengths of the order of 1-1000 m are required to produce fluid vibration eigenfrequencies in the range 0.5-5 Hz. The boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor. Saturated boiling produces groundwater vibration via steam bubble growth, whereas subcooled boiling produces groundwater vibration via steam bubble collapse. We find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling "thermal" power to seismic power. For example, the boiling heat transfer rates required to produce 1-Hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts; for saturated boiling, the required boiling heat transfer rates are several orders of magnitude larger than this. The highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 MW. Taking this value as a first-order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems, our results suggest that saturated hydrothermal boiling is capable of generating only low-amplitude harmonic tremor, with surface wave reduced displacements no higher than a few square centimeters. However, subcooled hydrothermal boiling could potentially generate high-amplitude harmonic tremor, with reduced displacements as large as several hundred square centimeters. As a specific application of our model, we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active Mount St. Helens and Nevado Del Ruiz volcanoes. We conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes. Saturated boiling also could explain the Nevado Del Ruiz tremor but probably not the more powerful Mount St. Helens tremor.

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

    SciTech Connect

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

    1993-03-01

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

  10. Broadband flat-noise Raman amplifier using low-noise bidirectionally pumping sources

    Microsoft Academic Search

    S. Kado; Y. Emori; S. Namiki; N. Tsukiji; J. Yoshida; T. Kimura

    2001-01-01

    We propose and experimentally demonstrate an optimised bidirectional pumping scheme that realizes a less than 0.7 dB flatness over C- and L-bands for both Raman gain and optical noise figure, simultaneously. In order to use forward-pumping for the proposed method, a new type of pump laser having low relative intensity noise is also developed.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  12. The 8.4-GHz low-noise maser pump source assembly

    NASA Technical Reports Server (NTRS)

    Cardenas, R.

    1987-01-01

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

  13. The 8.4-GHz low-noise maser pump source assembly

    NASA Astrophysics Data System (ADS)

    Cardenas, R.

    1987-11-01

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

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

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.

    2012-01-01

    An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the noise radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet noise was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array noise source localization measurements were obtained. This paper discusses phased array results, while a companion paper discusses far-field results. The phased array data show that the axial distribution of noise sources in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of noise reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the noise sources associated with a given frequency of noise tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The noise source localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces noise at a given frequency within a broadband shock noise hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet noise to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet noise sources may satisfy this requirement.

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

    PubMed

    Tkalich, Pavlo; Chan, Eng Soon

    2002-08-01

    A theoretical model for the prediction of ambient noise level due to collective oscillations of air bubbles under breaking wind waves is presented. The model uses a budget of the energy flux from the breaking waves to quantify acoustic power radiation by a bubble cloud. A shift of the noise spectra to lower frequency due to collective bubble oscillation is assumed. The model derives good estimates of the magnitude, slope, and frequency range of the noise spectra using the wind speed or height of breaking waves. PMID:12186026

  16. Noise radiation of propeller loading sources with angular inflow

    NASA Astrophysics Data System (ADS)

    Hanson, D. B.

    1990-10-01

    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 effect is well known; the second effect has only recently been recognized and is the subject of this paper. The noise formulas exhibit the same spinning mode behavior seen in previous analyses but with higher levels radiated into the crossflow. Since the modes are no longer purely spinning, the term 'wobbling mode' has been coined to describe their behavior. This paper explores the radiation formulas in detail, compares them with related theoretical treatments, and presents some calculations that explore the magnitude of the effect.

  17. Electronically-tunable narrow-band noise source

    Microsoft Academic Search

    M. Wright

    1969-01-01

    A new narrow-bandwidth noise generator that can be electronically tuned over a wide frequency range has been developed. The device is based on the frequency-selective power-limiting characteristic of YIG materials.

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

    NASA Astrophysics Data System (ADS)

    Grard, Anthony; Berry, Alain; Masson, Patrice

    2005-12-01

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

  19. Investigation of noise sources in platinum silicide Schottky barrier diodes

    Microsoft Academic Search

    S. Papatzika; N. A. Hastas; C. T. Angelis; C. A. Dimitriadis; G. Kamarinos; J. I. Lee

    2002-01-01

    Low-frequency noise measurements have been carried out in platinum silicide Schottky diodes on n-type silicon in the forward conduction regime and with the forward current IF as a parameter. The power spectral density of the current fluctuations shows a 1\\/f behavior and is proportional to IFbeta (with 1noise data have been successfully explained by an existing model

  20. Regression Models for Identifying Noise Sources in Magnetic Resonance Images.

    PubMed

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

    2009-06-01

    Stochastic noise, susceptibility artifacts, magnetic field and radiofrequency inhomogeneities, and other noise components in magnetic resonance images (MRIs) can introduce serious bias into any measurements made with those images. We formally introduce three regression models including a Rician regression model and two associated normal models to characterize stochastic noise in various magnetic resonance imaging modalities, including diffusion-weighted imaging (DWI) and functional MRI (fMRI). Estimation algorithms are introduced to maximize the likelihood function of the three regression models. We also develop a diagnostic procedure for systematically exploring MR images to identify noise components other than simple stochastic noise, and to detect discrepancies between the fitted regression models and MRI data. The diagnostic procedure includes goodness-of-fit statistics, measures of influence, and tools for graphical display. The goodness-of-fit statistics can assess the key assumptions of the three regression models, whereas measures of influence can isolate outliers caused by certain noise components, including motion artifacts. The tools for graphical display permit graphical visualization of the values for the goodness-of-fit statistic and influence measures. Finally, we conduct simulation studies to evaluate performance of these methods, and we analyze a real dataset to illustrate how our diagnostic procedure localizes subtle image artifacts by detecting intravoxel variability that is not captured by the regression models. PMID:19890478

  1. Experimental validation of generalized equations for FET cold noise source design

    Microsoft Academic Search

    Mark H. Weatherspoon; Lawrence P. Dunleavy

    2006-01-01

    This work advances the capabilities of accurately quantifying the microwave noise temperature that exits port one of a two-port active device when port two is terminated with a complex load of known temperature. This noise temperature is of interest when characterizing and designing field-effect transistor (FET)-based cold noise sources or active cold loads that can be used as radiometer calibration

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

    PubMed Central

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

    2013-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  7. New method of DOA estimation for coherent sources under unknown noise field

    Microsoft Academic Search

    Shujing Su; Zenggang Wang; Jinglong Yan

    2009-01-01

    The major shortcomings of the MUSIC algorithm for direction-of arrival (DOA) are that it performs poorly when the sources are highly and when the noise is unknown. A method was proposed to estimate DOA for coherent, noncoherent, and mixed narrowband signals under an unknown spatially noise environment, in this method, the forward-backward spatial smoothing algorithm was employed to decorrelate highly

  8. A 1.4 GHz MMIC Active Cold Noise Source Robert Scheeler and Zoya Popovic

    E-print Network

    Popovic, Zoya

    A 1.4 GHz MMIC Active Cold Noise Source Robert Scheeler and Zoya Popovic Department of Electrical.scheeler@colorado.edu, zoya.popovic@colorado.edu Abstract--A GaAs MMIC active cold load for a wearable microwave radiometer maintaining an input return loss greater than 28 dB is demonstrated. Index Terms--Noise measurement, MMICs. I

  9. Natural noise above 50 MHZ from terrestrial and extraterrestrial sources

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Bardhan, Jaydeep P.; Knepley, Matthew G.

    2012-01-01

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

  11. Algorithm for astronomical, extended source, signal-to-noise radio calculations

    NASA Technical Reports Server (NTRS)

    Jayroe, R. R.

    1984-01-01

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

  12. Measurement of noise source impedance of SMPS using a two probes approach

    Microsoft Academic Search

    Kye Yak See; Junhong Deng

    2004-01-01

    A novel approach to determine common-mode (CM) and differential-mode (DM) noise source impedances of a low-power switched mode power supply (SMPS) has been developed using a two current probes approach. The proposed approach allows measurement of noise source impedance of a SMPS without interrupting its normal operation. With proper setup calibration, the proposed approach can derive an equivalent circuit model,

  13. Noise Source Lumped Circuit Modeling and Identification for Power Converters

    Microsoft Academic Search

    Jin Meng; Weiming Ma; Qijun Pan; Zhihua Zhao; Lei Zhang

    2006-01-01

    In this paper, a general lumped circuit modeling method is proposed to describe the conducted electromagnetic interference (EMI) coupling mechanism for the switching power converters. The EMI characteristics of the converters can be analytically deduced from a circuit theoretical viewpoint. The shunt and series impedance insertion method is introduced to identify the differential-mode (DM) and common-mode (CM) noise impedances and

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

    Phased array beamforming results of the F31/A31 historical baseline counter-rotating open rotor blade set were investigated for measurement data taken on the NASA Counter-Rotating Open Rotor Propulsion Rig in the 9- by 15-Foot Low-Speed Wind Tunnel of NASA Glenn Research Center as well as data produced using the LINPROP open rotor tone noise code. The planar microphone array was positioned broadside and parallel to the axis of the open rotor, roughly 2.3 rotor diameters away. The results provide insight as to why the apparent noise sources of the blade passing frequency tones and interaction tones appear at their nominal Mach radii instead of at the actual noise sources, even if those locations are not on the blades. Contour maps corresponding to the sound fields produced by the radiating sound waves, taken from the simulations, are used to illustrate how the interaction patterns of circumferential spinning modes of rotating coherent noise sources interact with the phased array, often giving misleading results, as the apparent sources do not always show where the actual noise sources are located. This suggests that a more sophisticated source model would be required to accurately locate the sources of each tone. The results of this study also have implications with regard to the shielding of open rotor sources by airframe empennages.

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

    E-print Network

    Alexander Dubkov; Bernardo Spagnol

    2005-05-11

    We show that the increments of generalized Wiener process, useful to describe non-Gaussian white noise sources, have the properties of infinitely divisible random processes. Using functional approach and the new correlation formula for non-Gaussian white noise we derive directly from Langevin equation, with such a random source, the Kolmogorov's equation for Markovian non-Gaussian process. From this equation we obtain the Fokker-Planck equation for nonlinear system driven by white Gaussian noise, the Kolmogorov-Feller equation for discontinuous Markovian processes, and the fractional Fokker-Planck equation for anomalous diffusion. The stationary probability distributions for some simple cases of anomalous diffusion are derived.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  17. Application of fourier and wavelet transforms to the identification of EMI noise sources in SMPSs

    Microsoft Academic Search

    Luisa Coppola; Simone Buso; Qian Liu; Dushan Boroyevich; Amy Bell

    2005-01-01

    The Fourier and wavelet transform are applied to analyze the signals in a power electronics converter. The wavelet transform makes it possible to have important information about the time evolution of the frequency spectrum. Thank to this post-processing, the source of the harmonic peaks found in the Fourier spectrum can be identified in the time evolution of the signals of

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

    PubMed

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

    2015-01-01

    Novel table-top sources of extreme-ultraviolet light based on high-harmonic generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-harmonic generation to high repetition rates portends great experimental benefits, yet efficient extreme-ultraviolet conversion of correspondingly weak driving pulses is challenging. Here, we demonstrate a highly-efficient source of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ?3 10(13)?s(-1) is generated at 22.3?eV, with 5 10(-5) conversion efficiency that surpasses similar harmonics directly driven by the fundamental by two orders-of-magnitude. The enhancement arises from both wavelength scaling of the atomic dipole and improved spatio-temporal phase matching, confirmed by simulations. Spectral isolation of a single 72-meV-wide harmonic renders this bright, 50-kHz extreme-ultraviolet source a powerful tool for ultrafast photoemission, nanoscale imaging and other applications. PMID:26067922

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

    PubMed Central

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

    2015-01-01

    Novel table-top sources of extreme-ultraviolet light based on high-harmonic generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-harmonic generation to high repetition rates portends great experimental benefits, yet efficient extreme-ultraviolet conversion of correspondingly weak driving pulses is challenging. Here, we demonstrate a highly-efficient source of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ?3 1013?s?1 is generated at 22.3?eV, with 5 10?5 conversion efficiency that surpasses similar harmonics directly driven by the fundamental by two orders-of-magnitude. The enhancement arises from both wavelength scaling of the atomic dipole and improved spatio-temporal phase matching, confirmed by simulations. Spectral isolation of a single 72-meV-wide harmonic renders this bright, 50-kHz extreme-ultraviolet source a powerful tool for ultrafast photoemission, nanoscale imaging and other applications. PMID:26067922

  20. Phased Array Radiometer Calibration Using a Radiated Noise Source

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

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

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.

    2013-01-01

    An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the noise radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet noise was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array noise source localization measurements were obtained. This paper discusses phased array results, while a companion paper (Brown, C.A., "Jet-Surface Interaction Test: Far-Field Noise Results," ASME paper GT2012-69639, June 2012.) discusses far-field results. The phased array data show that the axial distribution of noise sources in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of noise reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the noise sources associated with a given frequency of noise tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The noise source localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces noise at a given frequency within a broadband shock noise hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet noise to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet noise sources may satisfy this requirement.

  3. High flux table-top ultrafast soft X-ray source generated by high harmonic generation

    NASA Astrophysics Data System (ADS)

    Thir, Nicolas; Schmidt, Bruno E.; Fourmeaux, Sylvain; Beaulieu, Samuel; Cardin, Vincent; Negro, Matteo; Kieffer, Jean-Claude; Vozzi, Caterina; Legare, Franois

    2014-05-01

    Generation of ultrafast soft X-ray pulses is a major challenge for conventional laboratories. Using the process of HHG enables generation of such short wavelength photons. Intense laser sources in the infrared are necessary to reach the soft X-ray spectral range as the HHG cut-off scales with I?2. However, in the limit of the single atom response, increasing the laser wavelength leads to a significant decrease of the HHG flux. To compensate, one has to increase the number of emitters with high ionization potential. At the Advanced Laser Light Source, we have addressed this challenge by using a new gas cell design and developing a 10 mJ - 30 fs source at 1.8 ?m. Using this setup, we have been able to generate harmonics in the water window spectral range for neon and helium with short time duration (<30 fs) in a conventional laboratory. A flux measurement has been performed showing ~ 2 105 photons/shot between 280 and 540 eV, making it possible to see the carbon k-edge at 280eV in a single shot manner. This soft X-ray beam is also extremely well collimated (0.1 mrad) making it this table-top beamline ideal for a number of applications.

  4. Initial-State Bremsstrahlung versus Final-State Hydrodynamic Sources of Azimuthal Harmonics at RHIC and LHC

    NASA Astrophysics Data System (ADS)

    Gyulassy, Miklos; Levai, Peter; Vitev, Ivan; Biro, Tamas

    2014-09-01

    Recent azimuthal correlation data from the Beam Energy Scan (BES) and d+Au runs at RHIC/BNL and, the surprising similarity of multiparticle cummulant azimuthal harmonics in p+Pb and Pb+Pb at LHC have challenged the uniqueness of local equilibrium ``perfect fluid'' interpretations of those data. We report results derived in arXiv:1405.7825 [hep-ph] on azimuthal harmonics arising from initial-state non-abelian ``wave interference'' effects predicted by perturbative QCD sourced by Color Scintillation Arrays (CSA) of color antennas associated with multiple projectile and target soft beam jets. 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. Recent azimuthal correlation data from the Beam Energy Scan (BES) and d+Au runs at RHIC/BNL and, the surprising similarity of multiparticle cummulant azimuthal harmonics in p+Pb and Pb+Pb at LHC have challenged the uniqueness of local equilibrium ``perfect fluid'' interpretations of those data. We report results derived in arXiv:1405.7825 [hep-ph] on azimuthal harmonics arising from initial-state non-abelian ``wave interference'' effects predicted by perturbative QCD sourced by Color Scintillation Arrays (CSA) of color antennas associated with multiple projectile and target soft beam jets. 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. Supported in part by the US Department of Energy, Office of Science, Office of Nuclear Physics.

  5. Numerical and experimental investigation of noise from small scale axial fans focusing on inflow condition and acoustic source type

    NASA Astrophysics Data System (ADS)

    Shin, Yoon Shik

    The objective of this work was to conduct an experimental and numerical investigation of the noise radiated by a small-scale axial fan from two different points-of-view: the development of an inflow treatment to compensate for unfavorable inflow conditions that result in excessive noise, and a consideration of installation effects for the acoustic source type of small axial fans. The effect of disturbed inflow on axial fans was experimentally investigated by intentionally placing a blockage plate at four different locations upstream of a fan. The blocked inflow made the axial fan perform very poorly; the severely decreased pressure performance introduced an overly strong dependence of flow performance on pressure load condition. An inflow diffuser made from aluminum foam was suggested to improve the aerodynamic and acoustic performance of the axial fan under such unfavorable inflow conditions. The inflow diffuser improved the stability of flow performance and reduced the blade passing tone by a small amount, but the levels of the high frequency harmonics of the blade passing tone were increased. A corresponding numerical model was built to model the flow change due to the inflow foam treatment. The inflow foam diffuser was approximated as a homogeneous porous zone to make the computational cost affordable, and it was shown that the model can predict the foam's influence on the pressure and flow performance of the fan. The aeroacoustic analogy model was applied to the solid surfaces of the fan and its housing to simulate the tonal noise at the blade passing frequency. The validity of the homogeneous foam model in terms of aeroacoustic predictions was also confirmed. As for the second aspect of the axial fan noise source, the dipole-like source behavior of an axial fan at the blade passing frequency was verified by directivity measurements. Thus, dipole modeling of an axial fan was justified. This result is associated with the problem of overestimated fan source strength due to the installation effect when measurements are made using an ISO 10302 plenum. A suggestion was made to compensate for this discrepancy. Further, by using the point dipole assumption as suggested, a method for mapping the sound radiation resistance when a fan is placed within a system enclosure was developed to help guide the positioning of axial fans within an enclosure so that they radiate the minimum sound power.

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

    PubMed

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

    2012-04-01

    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

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

    PubMed Central

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

    2015-01-01

    To evaluate the contributions of common noise sources to total annual noise exposures among urban residents and workers, we estimated exposures associated with five common sources (use of mass transit, occupational and non-occupational activities, MP3 player and stereo use, and time at home and doing other miscellaneous activities) among a sample of over 4500 individuals in New York City (NYC). We then evaluated the contributions of each source to total noise exposure and also compared our estimated exposures to the recommended 70 dBA annual exposure limit. We found that one in ten transit users had noise exposures in excess of the recommended exposure limit from their transit use alone. When we estimated total annual exposures, 90% of NYC transit users and 87% of nonusers exceeded the recommended limit. MP3 player and stereo use, which represented a small fraction of the total annual hours for each subject on average, was the primary source of exposure among the majority of urban dwellers we evaluated. Our results suggest that the vast majority of urban mass transit riders may be at risk of permanent, irreversible noise-induced hearing loss and that, for many individuals, this risk is driven primarily by exposures other than occupational noise. PMID:22088203

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

    NASA Astrophysics Data System (ADS)

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

    2007-08-01

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

  9. Towards single-channel unsupervised source separation of speech mixtures: The layered harmonics/formants separation-tracking model

    E-print Network

    Ellis, Dan

    /formants separation-tracking model Manuel Reyes-Gomez1 , Nebojsa Jojic2 , Daniel P.W. Ellis1 1 LabROSA, Department@microsoft.com Abstract Speaker models for blind source separation are typically based on HMMs consisting of vast numbers into two additive layers, separately describing the harmonics and for- mant structure. We model smooth

  10. Active control of noise on the source side of a partition to increase its sound isolation

    Microsoft Academic Search

    Marco Tarabini; Alain Roure; Cedric Pinhede

    2009-01-01

    This paper describes a local active noise control system that virtually increases the sound isolation of a dividing wall by means of a secondary source array. With the proposed method, sound pressure on the source side of the partition is reduced using an array of loudspeakers that generates destructive interference on the wall surface, where an array of error microphones

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

    PubMed Central

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

    2013-01-01

    Several measures of sound source localization performance of 45 listeners with normal hearing were obtained when loudspeakers were in the front hemifield. Localization performance was not statistically affected by filtering the 200-ms, 2-octave or wider noise bursts (125 to 500, 1500 to 6000, and 125 to 6000?Hz wide noise bursts). This implies that sound source localization performance for noise stimuli is not differentially affected by which interaural cue (interaural time or level difference) a listener with normal hearing uses for sound source localization, at least for relatively broadband signals. This sound source localization task suggests that listeners with normal hearing perform with high reliability/repeatability, little response bias, and with performance measures that are normally distributed with a mean root-mean-square error of 6.2 and a standard deviation of 1.79. PMID:23654393

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

    NASA Astrophysics Data System (ADS)

    Yoshinaga, Hiroshi; Mizutani, Koichi; Wakatsuki, Naoto

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

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

    NASA Astrophysics Data System (ADS)

    Stepanishen, Peter R.; Brodjonegoro, Irsan

    2002-11-01

    An inverse or backward projection method based on a combined Greens function and singular value decomposition method is developed to locate and to determine the strength of near field harmonic sources from the acoustic field on the surface of a nearby rigid body. A resolution matrix, which is based on the free space Greens function, the geometry of the measurement surface of interest and the field locations of interest, is introduced to determine the resolution and accuracy of the backward projection method. Point source distributions located above a rigid planar surface are addressed both analytically and numerically. In addition, line source distributions located outside of infinite rigid circular and elliptical cylinders are also addressed. It is demonstrated that the method is able to identify the location and to determine the strength of harmonic near-field sources which are separated by less than 0.01 of a wavelength.

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

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Pal, Suvajit; Ghosh, Manas

    2013-11-01

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

  15. Harmonic analysis of cosmic microwave background data I: ring reductions and point-source catalogue

    E-print Network

    Floor van Leeuwen; Anthony D. Challinor; Daniel J. Mortlock; Mark A. J. Ashdown; Michael P. Hobson; Anthony N. Lasenby; George P. Efstathiou; E. Paul. S. Shellard; Dipak Munshi; Vladislav Stolyarov

    2001-12-12

    We present a harmonic model for the data analysis of an all-sky cosmic microwave background survey, such as Planck, where the survey is obtained through ring-scans of the sky. In this model, resampling and pixelisation of the data are avoided. The spherical transforms of the sky at each frequency, in total intensity and polarization, as well as the bright-point-source catalogue, are derived directly from the data reduced onto the rings. Formal errors and the most significant correlation coefficients for the spherical transforms of the frequency maps are preserved. A clean and transparent path from the original samplings in the time domain to the final scientific products is thus obtained. The data analysis is largely based on Fourier analysis of rings; the positional stability of the instrument's spin axis during these scans is a requirement for the data model and is investigated here for the Planck satellite. Brighter point sources are recognised and extracted as part of the ring reductions and, on the basis of accumulated data, used to build a catalogue. The analysis of the rings is performed iteratively, involving a range of geometric and detector response calibrations. The reconstructed spherical transforms of the sky form the input to the subsequent analysis stages. Although the methods in this paper were developed with the data processing for Planck in mind, many aspects should have wider application, such as in the construction of real-space pixelised maps. (Abridged)

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

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

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

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

    Microsoft Academic Search

    R. CLARK ROBERTSON; TRI T. HA

    1987-01-01

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

  18. Low frequency noise sources in InAlAs\\/InGaAs MODFETs

    Microsoft Academic Search

    P. Viktorovitch; P. Rojo-Romeo; J. L. Leclercq; X. Letartre; Jacques Tardy; M. Oustric; M. Gendry

    1996-01-01

    Detailed analysis of the 1\\/f low-frequency noise (LFN) in In0.52Al0.48As\\/InGaAs MODFET structures is performed, for low drain bias (below pinch-off voltage), in order to identify the physical origin and the location of the noise sources responsible for drain current fluctuations in the frequency range 0.1 Hz-105 Hz. Experimental data were analyzed with the support of a general modeling of the

  19. CAA Slat Noise Studies Applying Stochastic Sound Sources Based On Solenoidal Digital Filters

    Microsoft Academic Search

    R. Ewert; R. Emunds

    2005-01-01

    The present paper studies the application of a low-cost CAA approach to a slat noise problem. A new fast and cheap stochastic approach is introduced to model the unsteady turbulent sound sources in the slat-cove. It is based on the spatial filtering of a random white-noise field and incorporates information about the integral length scale and the tur- bulent kinetic

  20. Development in Source Modeling and Sound Propagation for Jet Noise Predictions

    NASA Technical Reports Server (NTRS)

    Leib, Steward

    2004-01-01

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

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

    Microsoft Academic Search

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

    2009-01-01

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

  2. Effect of Vortex Generating Tabs on Noise Sources in an Ideally Expanded Jet

    NASA Astrophysics Data System (ADS)

    Samimy, Mo; Hileman, James

    2002-11-01

    It is known that by attaching small delta shape tabs at the nozzle exit, one can substantially modify the flow as well as the noise emission characteristics of subsonic or supersonic jets. Tabs, which slightly protrude into the flow, generate strong streamwise vortices that greatly alter the development of the jet's mixing layer and noise emission. While the effects of these streamwise vortices on the flow characteristics have been explored in detail, the manner in which they change the noise sources in a jet has not received much attention. Such knowledge would greatly enhance development of effective noise control strategies for high-speed jets. Experiments were conducted with an ideally expanded Mach 1.3 axisymmetric jet with one or two tabs to determine how the tabs modify the noise emission characteristics. Acoustic measurements showed that there is a strong azimuthal directivity at shallow angles with respect to the jet axis. Noise source locations were determined using a 3D microphone array. The results indicate that the noise-generating portion of the jet moved significantly upstream with the addition of tabs and the cross-stream distribution became non-axisymmetric. This corresponds well with the real-time flow visualization images of the jet, taken with a MHz rate imaging system, that show the streamwise vortices are causing the unmixed jet core to be considerably shortened.

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

    PubMed

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

    2014-08-25

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

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

    NASA Technical Reports Server (NTRS)

    Greenwood, Eric II; Schmitz, Fredric H.

    2009-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    This paper presents an improved, efficient approach for assessing noise impacts associated with a complex set of noise sources at multiple receptor locations; noise impacts from typical remedial activities at a contaminated industrial site are used as an example. The noise sources associated with remedial activities at the site and surrounding areas are described, the noise-propagation modeling methods and results are presented, and an impact assessment of the contaminated site is discussed with regard to applicable regulatory standards and individual and community responses. Also discussed is the improved noise assessment approach. The improved features demonstrated are automated approaches for (1) inputting long-term hourly meteorological data (e.g., 8760 hours for a one-year period) into a long-range noise-propagation model for computing noise-level increases at receptor locations and (2) analyzing potential individual and community responses to intrusive noises using the IAP and modified CNR.

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

    SciTech Connect

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

    1994-04-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  8. arXiv:cond-mat/0312490v118Dec2003 LOW-FREQUENCY NOISE AS A SOURCE

    E-print Network

    Johansen, Tom Henning

    arXiv:cond-mat/0312490v118Dec2003 Chapter 1 LOW-FREQUENCY NOISE AS A SOURCE OF DEPHASING OF A QUBIT-state qubits from external decoherence sources, the material-inherent sources of noise start to play crucial role. One representative example is electron traps in the device material or substrate. Electrons can

  9. Spatial localization of 1\\/f noise sources in AlSb\\/InAs high-electron-mobility transistors

    Microsoft Academic Search

    Petru Andrei; Walter Kruppa; J. Brad Boos; Brian R. Bennett

    2009-01-01

    A numerical technique is developed for the spatial localization of 1\\/f noise sources in AlSb\\/InAs high-electron-mobility transistors. The technique is based on the microscopic modeling of 1\\/f noise using the method of Langevin random sources, in which the noise sources are introduced nonuniformly throughout the device. An efficient algorithm is proposed for the determination of the spatial distribution of these

  10. 2009 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics October 18-21, 2009, New Paltz, NY IMPROVING SEPARATION OF HARMONIC SOURCES WITH ITERATIVE

    E-print Network

    Pardo, Bryan

    separation performance of two existing time-frequency masking systems. Index Terms-- Audio Source Separation, Harmonic Mask, Spatial Cues 1. INTRODUCTION Audio source separation is the process of separating individual sources from mixtures of sources in an acoustic mixture. Effective audio source separation will lead

  11. Intense solid state UV laser source using a novel harmonic generation scheme

    Microsoft Academic Search

    A. H. Kung; J. Knittel

    1997-01-01

    This paper reports on a new approach wherein a single external ring cavity is used to enhance the efficiency in fourth harmonic generation of an infrared Nd:YAG solid state laser by incorporating two doubling stages inside one cavity. The principal idea is to trap the second harmonic radiation generated in the first doubling stage inside the cavity. Ideally, then, the

  12. Microseism Noise Sources observed by Earthscope USArray Transportable Array

    NASA Astrophysics Data System (ADS)

    Eakins, J. A.; Vernon, F. L.

    2007-12-01

    The NSF Earthscope USArray Transportable Array deployment of 400+ high quality broadband telemetered seismic stations has created a unique opportunity to study the temporal and spatial microseism distribution as a function of time across the deployment from coastal regions to the continental interior. We examine the effects of geologic provinces and regional differences on power observed in the microseismic bands. We also integrate our results with satellite derived surface wave heights to identify microseismic source regions for different regions of the array.

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

    PubMed Central

    2015-01-01

    The distortion of biomedical signals by powerline noise from recording biomedical devices has the potential to reduce the quality and convolute the interpretations of the data. Usually, powerline noise in biomedical recordings are extinguished via band-stop filters. However, due to the instability of biomedical signals, the distribution of signals filtered out may not be centered at 50/60 Hz. As a result, self-correction methods are needed to optimize the performance of these filters. Since powerline noise is additive in nature, it is intuitive to model powerline noise in a raw recording and subtract it from the raw data in order to obtain a relatively clean signal. This paper proposes a method that utilizes this approach by decomposing the recorded signal and extracting powerline noise via blind source separation and wavelet analysis. The performance of this algorithm was compared with that of a 4th order band-stop Butterworth filter, empirical mode decomposition, independent component analysis and, a combination of empirical mode decomposition with independent component analysis. The proposed method was able to expel sinusoidal signals within powerline noise frequency range with higher fidelity in comparison with the mentioned techniques, especially at low signal-to-noise ratio.

  14. Adsorbed Oxygen Molecules as a Possible Source of Flux Noise in SQUIDs

    NASA Astrophysics Data System (ADS)

    Shi, Chuntai; Wang, Hui; Hu, Jun; Yu, Clare; Wu, Ruqian

    2015-03-01

    One of the dominant source of flux noise in SQUIDs is flux noise which has been attributed to mysterious fluctuating magnetic spins on the surface. We propose that the spins producing flux noise could be adsorbed O2 molecules that have a magnetic moment of about 2 ?B. Using density functional calculations, we studied O2 molecules adsorbed on a sapphire surface. We find that the barrier for spin rotation is small enough to allow almost free spin reorientation due to thermal excitations at low temperatures. Monte Carlo simulations of a 2D XY spin model yields 1 / f noise where f is frequency. This work was supported by 1000 Talent Program of China through Fudan University. Work at UCI was supported by DOE-BES (Grant No. DE-FG02-05ER46237) and the Army Research Office (Grant No. W911NF-10-1-0494).

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

    SciTech Connect

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

    2005-10-31

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

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

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.; Horvath, Csaba

    2010-01-01

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

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

    Microsoft Academic Search

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

    2001-01-01

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

  18. 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

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

    E-print Network

    Paris-Sud XI, Universit de

    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

  20. Mapping the Signal-To-Noise-Ratios of Cortical Sources in Magnetoencephalography and Electroencephalography

    PubMed Central

    Goldenholz, Daniel M.; Ahlfors, Seppo P.; Hmlinen, Matti S.; Sharon, Dahlia; Ishitobi, Mamiko; Vaina, Lucia M.; Stufflebeam, Steven M.

    2010-01-01

    Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-noise-ratios (SNRs) of cortical sources in MEG and EEG. Data from four subjects were used to simulate focal and extended sources located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep sources was larger in EEG than in MEG, whereas the opposite was typically the case for superficial sources. Overall, the SNR maps were more uniform for EEG than for MEG. When using a noise model based on uniformly distributed random sources on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with noise estimated from actual recorded MEG and EEG data. With extended sources, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal sources. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously. PMID:18465745

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Bridges, James (Technical Monitor); Panda, Jayanta

    2005-01-01

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

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

    PubMed

    D?browski, Zbigniew; Stankiewicz, Bartosz

    2013-01-01

    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

  5. Californium252-source-driven noise analysis measurements for characterization of concrete HEU storage vaults

    Microsoft Academic Search

    T. E. Valentine; J. T. Mihalczo

    1993-01-01

    The [sup 252]Cf-source-driven noise analysis method has been used in measurements for subcritical configurations of fissile systems for a variety of applications. Measurements of 25 fissile systems have been performed with a wide variety of materials and configurations. This method has been applied to measurements for the following: (1) initial fuel loading of reactors; (2) quality assurance of reactor fuel

  6. The fast-tuned low phase noise source for C band

    Microsoft Academic Search

    Henryk Ryll; Adam Ryniewicz

    1998-01-01

    This paper presents the design of the fast-tuned low phase noise signal source for C band with many applications in the radar device domain. The operation of this electronic system is described The results of measurements done for the constructed heterodyne are also included

  7. Study of propagating acoustic sources in a fan intake by modal analysis of tone noise

    Microsoft Academic Search

    S. Lewy; S. Canard; P. Kerviel

    1988-01-01

    A new data processing scheme was developed for computing azimuthal wave-number spectra of noise generated in circular or annular ducts; in this method, positive and negative modes are separated. Examples are presented demonstrating that this method makes it possible to characterize the fan or compressor acoustic sources and duct linings. Moreover, the parasitic effects of flow distortions, due to deficiencies

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

    PubMed

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

    2014-01-01

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

  9. Source depth and the spatial coherence of ambient noise in the ocean

    E-print Network

    Buckingham, Michael

    on the acoustic properties of the bubble sources associated with breaking surface waves. 1997 Acoustical Society Ambient noise in shallow water is strongly influenced by the proximity of the seabed, which modifies of the compressional and shear waves in the seabed.3,4 In addition to the bottom, an important factor affecting

  10. Mapping the signal-to-noise-ratios of cortical sources in magnetoencephalography and electroencephalography

    Microsoft Academic Search

    Daniel M. Goldenholz; Seppo P. Ahlfors; Matti S. Hmlinen; Dahlia Sharon; Mamiko Ishitobi; Lucia M. Vaina; Steven M. Stufflebeam

    2009-01-01

    Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-noise-ratios (SNRs) of cortical sources in MEG and EEG. Data from four subjects were used to simulate focal and extended sources located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and

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

    Microsoft Academic Search

    Richard P. Woodward; Irvin J. Loffler

    1991-01-01

    Flight tests to define the far-field tone source at cruise conditions have been completed on the full-scale SR-7L advanced turboprop, which was installed on the left wing of a Gulfstream II aircraft. These measurements defined source levels for input into long-distance propagation models to predict en route noise. Infight data were taken for seven test cases. The sideline directivities measured

  12. Shot-to-shot and average absolute photon flux measurements of a femtosecond laser high-order harmonic photon source

    Microsoft Academic Search

    T. Leitner; A. A. Sorokin; J. Gaudin; H. Kaser; U. Kroth; K. Tiedtke; M. Richter; Ph Wernet

    2011-01-01

    The absolute flux of a femtosecond vacuum-ultraviolet (VUV) photon source based on the high-order harmonic generation of a femtosecond Ti:sapphire laser and monochromatized with a grating monochromator is determined both on a shot-to-shot basis and averaged over seconds by a calibrated gas monitor detector. The average flux is compared with the average flux as determined with a calibrated GaAsP semiconductor

  13. Experimental and Analytical Studies of Shielding Concepts for Point Sources and Jet Noises.

    NASA Astrophysics Data System (ADS)

    Wong, Raymond Lee Man

    This analytical and experimental study explores concepts for jet noise shielding. Model experiments centre on solid planar shields, simulating engine-over-wing installations, and 'sugar scoop' shields. Tradeoff on effective shielding length is set by interference 'edge noise' as the shield trailing edge approaches the spreading jet. Edge noise is minimized by (i) hyperbolic cutouts which trim off the portions of most intense interference between the jet flow and the barrier and (ii) hybrid shields--a thermal refractive extension (a flame); for (ii) the tradeoff is combustion noise. In general, shielding attenuation increases steadily with frequency, following low frequency enhancement by edge noise. Although broadband attenuation is typically only several dB, the reduction of the subjectively weighted perceived noise levels is higher. In addition, calculated ground contours of peak PN dB show a substantial contraction due to shielding: this reaches 66% for one of the 'sugar scoop' shields for the 90 PN dB contour. The experiments are complemented by analytical predictions. They are divided into an engineering scheme for jet noise shielding and more rigorous analysis for point source shielding. The former approach combines point source shielding with a suitable jet source distribution. The results are synthesized into a predictive algorithm for jet noise shielding: the jet is modelled as a line distribution of incoherent sources with narrow band frequency (TURN)(axial distance)('-1). The predictive version agrees well with experiment (1 to 1.5 dB) up to moderate frequencies. The insertion loss deduced from the point source measurements for semi-infinite as well as finite rectangular shields agrees rather well with theoretical calculation based on the exact half plane solution and the superposition of asymptotic closed-form solutions. An approximate theory, the Maggi-Rubinowicz line integral, is found to yield reasonable predictions for thin barriers including cutouts if a certain correction is applied. The more exact integral equation approach (solved numerically) is applied to a more demanding geometry: a half round sugar scoop shield. It is found that the solutions of integral equation derived from Helmholtz formula in normal derivative form show satisfactory agreement with measurements.

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

    NASA Technical Reports Server (NTRS)

    Freund, Jonathan B.

    2001-01-01

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

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

    PubMed

    Aliabadi, Mohsen; Golmohammadi, Rostam; Mansoorizadeh, Muharram

    2014-03-01

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

  16. Temperature dependence and electrical properties of dominant low-frequency noise source in SiGe HBT

    Microsoft Academic Search

    S. Bruce; K. J. Vandamme; Anders Rydberg

    2000-01-01

    The temperature dependence and electrical properties of the dominant low-frequency noise source in a SiGe HBT have been investigated. By employing a temperature variation of the device to get a variation of the base or collector current independently of each other, it is shown that the dominant noise source is strongly dependent on the collector current, but only weakly dependent

  17. Harmonic leakage and image quality degradation in tissue harmonic imaging

    Microsoft Academic Search

    Che-Chou Shen; Pai-Chi Li

    2001-01-01

    Image quality degradation caused by harmonic leakage was studied for finite amplitude distortion-based harmonic imaging. Various sources of harmonic leakage, including transmit waveform, signal bandwidth, and system nonlinearity, were investigated using both simulations and hydrophone measurements. Effects of harmonic leakage in the presence of sound velocity inhomogeneities were also considered. Results indicated that sidelobe levels of the harmonic beam pattern

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

    PubMed

    Van den Bogaert, Tim; Doclo, Simon; Wouters, Jan; Moonen, Marc

    2008-07-01

    This paper evaluates the influence of three multimicrophone noise reduction algorithms on the ability to localize sound sources. Two recently developed noise reduction techniques for binaural hearing aids were evaluated, namely, the binaural multichannel Wiener filter (MWF) and the binaural multichannel Wiener filter with partial noise estimate (MWF-N), together with a dual-monaural adaptive directional microphone (ADM), which is a widely used noise reduction approach in commercial hearing aids. The influence of the different algorithms on perceived sound source localization and their noise reduction performance was evaluated. It is shown that noise reduction algorithms can have a large influence on localization and that (a) the ADM only preserves localization in the forward direction over azimuths where limited or no noise reduction is obtained; (b) the MWF preserves localization of the target speech component but may distort localization of the noise component. The latter is dependent on signal-to-noise ratio and masking effects; (c) the MWF-N enables correct localization of both the speech and the noise components; (d) the statistical Wiener filter approach introduces a better combination of sound source localization and noise reduction performance than the ADM approach. PMID:18646992

  19. A Low Phase-Noise Multi-Phase LO Generator for Wideband Demodulators Based on Reconfigurable SubHarmonic Mixers

    Microsoft Academic Search

    Andrea Mazzanti; Mohammad B. Vahidfar; Marco Sosio; Francesco Svelto

    2010-01-01

    The advent of wideband systems, e.g., software defined radios, cognitive radios and UWB technology, motivates research for new transceiver architectures and circuit topologies to arrive at compact and low power solutions. Reference frequency generation in wideband CMOS receivers is usually power and area hungry. In this paper a wide band quadrature demodulator, based on mixers reconfigurable between fundamental and sub-harmonic

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Du, Yongle

    Jet noise simulations have been performed for a military-style baseline nozzle and a chevron nozzle with design Mach numbers of Md = 1:5 operating at several off-design conditions. The objective of the current numerical study is to provide insight into the noise generation mechanisms of shock-containing supersonic hot jets and the noise reduction mechanisms of chevron nozzles. A hybrid methodology combining advanced CFD technologies and the acoustic analogy is used for supersonic jet noise simulations. Unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved to predict the turbulent noise sources in the jet flows. A modified version of the Detached Eddy Simulation (DES) approach is used to avoid excessive damping of fine scale turbulent fluctuations. A multiblock structured mesh topology is used to represent complex nozzle geometries, including the faceted inner contours and finite nozzle thickness. A block interface condition is optimized for the complex multiblock mesh topology to avoid the centerline singularity. A fourth-order Dispersion-Relation-Preserving (DRP) scheme is used for spatial discretization. To enable efficient calculations, a dual time-stepping method is used in addition to parallel computation using MPI. Both multigrid and implicit residual smoothing are used to accelerate the convergence rate of sub-iterations in the fictitious time domain. Noise predictions are made with the permeable surface Ffowcs Williams and Hawkings (FWH) solution. All the numerical methods have been implemented in the jet flow simulation code "CHOPA" and the noise prediction code "PSJFWH". The computer codes have been validated with several benchmark cases. A preliminary study has been performed for an under-expanded baseline nozzle jet with Mj = 1:56 to validate the accuracy of the jet noise simulations. The results show that grid refinement around the jet potential core and the use of a lower artificial dissipation improve the resolution of the predicted high frequency noise spectra. The results also show that the predicted low frequency noise spectra are sensitive to the axial extent of the acoustic data surface, and the high frequency noise spectra are affected by the radial size of the acoustic data surface. The baseline nozzle has been studied at several off-design conditions with Mj = 1:36, 1.47 and 1.56. Although the noise levels at mid to high frequencies are over-predicted at several shallow polar angles, the predicted noise spectra in the peak noise radiation direction and upstream directions agree very well with the experimental measurements. More encouraging is that the frequencies and amplitudes of the broadband shock-associated noise (BBSAN) are captured accurately at all three operating conditions. Three techniques are used to examine the noise source characteristics. The two-point space-time correlation method is used to analyze the statistical characteristics of the turbulent eddies. The direct flow-acoustic correlation technique and the beamformed acoustic pressures are used to reveal the different noise generation mechanisms of the large-scale and fine-scale turbulent fluctuations. The chevron nozzle simulations have been performed at the same operating conditions to evaluate the noise reduction effects. Special treatments are proposed to address the numerical difficulties caused by the chevrons. The impact of chevrons on the near-field noise sources and far-field noise radiation is simulated using the immersed boundary method (IBM) to overcome the great difficulties in grid generation. A non-matching block interface condition is developed to allow the grids to be greatly refined around chevrons for a higher accuracy of simulations without increasing the mesh size significantly. The predicted noise spectra agree very well with the acoustic measurements of the baseline nozzle, considering the small noise reductions of the chevrons at the given operating conditions. No apparent over-prediction is observed. However, the noise reductions are over-predicted because of the over-pr

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

    NASA Astrophysics Data System (ADS)

    Yao, Yuhong; Knox, Wayne H.

    2015-03-01

    We report the optical system design of a novel speckle-free ultrafast Red-Green-Blue (RGB) source based on angularly multiplexed simultaneous second harmonic generation from the efficiently generated Stokes and anti-Stokes pulses from a commercially available photonic crystal fiber (PCF) with two zero dispersion wavelengths (TZDW). We describe the optimized configuration of the TZDW fiber source which supports excitations of dual narrow-band pulses with peak wavelengths at 850 nm, 1260 nm and spectral bandwidths of 23 nm, 26 nm, respectively within 12 cm of commercially available TZDW PCF. The conversion efficiencies are as high as 44% and 33% from the pump source (a custom-built Yb:fiber master-oscillator-power-amplifier). As a result of the nonlinear dynamics of propagation, the dual pulses preserve their ultrashort pulse width (with measured autocorrelation traces of 200 fs and 227 fs,) which eliminates the need for dispersion compensation before harmonic generation. With proper optical design of the free-space harmonic generation system, we achieve milli-Watt power level red, green and blue pulses at 630 nm, 517 nm and 425 nm. Having much broader spectral bandwidths compared to picosecond RGB laser sources, the source is inherently speckle-free due to the ultra-short coherence length (<37 ?m) while still maintaining an excellent color rendering capability with >99.4% excitation purities of the three primaries, leading to the coverage of 192% NTSC color gamut (CIE 1976). The reported RGB source features a very simple system geometry, its potential for power scaling is discussed with currently available technologies.

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

    E-print Network

    Igor Franovi?; Kristina Todorovi?; Matja Perc; Neboja Vasovi?; Nikola Buri?

    2015-07-12

    We consider the coaction of two distinct noise sources on the activation process of a single or two interacting excitable units represented by the Fitzhugh-Nagumo model. The nonlocal approach involving Hamiltonian formalism is adapted to obtain the most probable activation paths around which the corresponding stochastic trajectories are clustered. The key point lies in introducing the boundary conditions relevant for a class II excitable unit, which further allow an immediate generalization to scenarios involving a couple of units. We also analyze the effects of two noise sources on the statistical features of the activation process, demonstrating how these are modified due to the linear/nonlinear form of interactions. Universal properties of activation process are qualitatively discussed in light of stochastic bifurcation, underlying transition from stochastically stable fixed point to continuous oscillations.

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

    Microsoft Academic Search

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

    1990-01-01

    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 10 {sub - 4} to 0.01\\/s. These

  5. Physics of the ²⁵²Cf-source-driven noise analysis measurement

    Microsoft Academic Search

    T. E. Valentine; J. T. Mihalczo; R. B. Perez; J. K. Mattingly

    1997-01-01

    The ²⁵²Cf-source-driven noise analysis method is a versatile measurements tool that has been applied to measurements for initial loading of reactors, quality assurance of reactor fuel elements, fuel processing facilities, fuel reprocessing facilities, fuel storage facilities, zero-power testing of reactors, verification of calculational methods, process monitoring, characterization of storage vaults, and nuclear weapons identification. This method`s broad range of application

  6. Detector effects in sup 252 Cf-source-driven noise analysis measurements

    Microsoft Academic Search

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

    1989-01-01

    Detector effects in the ²⁵²Cf-source-driven noise measurements of subcriticality are important not only for planning experiments but for interpretation of the data. The detectors must be of a type and location such that the assumptions of the theory used to interpret the data are valid. Although a general theory will be helpful for fully understanding the method, point kinetics with

  7. Analysis of Landau-Zener tunneling with an Ohmic reservoir and a noise source

    Microsoft Academic Search

    Tatsuya Usuki

    1998-01-01

    To determine the possibility of single-electron operation in electronic devices, we investigated the Landau-Zener (LZ) tunneling process with dissipation. This work presents an analytical formula and detailed numerical results for dynamical tunneling phenomena with an Ohmic reservoir and a noise source. First, we calculated the transient and final density matrices of a single-electron system coupled to a reservoir at zero

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  9. A study of noise source location on a model scale augmentor wing using correlation techniques

    Microsoft Academic Search

    J. F. Wilby; T. D. Scharton

    1975-01-01

    An experimental investigation, conducted on a model-scale augmentor wing to identify the sources of far-field noise, is examined. The measurement procedure followed in the investigation involved the cross-correlation of far field sound pressures with fluctuating pressures on the surface of the augmentor flap and shroud. In addition pressures on the surfaces of the augmentor were cross-correlated. The results are interpreted

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

    Microsoft Academic Search

    Fang Xu; Mohammad-Ali Khalighi; Salah Bourennane

    2011-01-01

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

  11. VIBRATION OF A BEAM INDUCED BY HARMONIC MOTION OF A HEAT SOURCE

    Microsoft Academic Search

    J. Kidawa-Kukla

    1997-01-01

    In this paper, a solution to the problem of thermally induced vibration of a uniform, simply supported beam is presented. The effect of internal damping on the vibration is considered. The temperature of the rectangular beam changes as a result of heating by a laser beam. The centre of the laser spot moves harmonically around a fixed point of the

  12. Conducted EMI Noise Prediction and Characterization for Multi-phase-leg Converters Based on Modular-Terminal-Behavioral (MTB) Equivalent EMI Noise Source Model

    Microsoft Academic Search

    Qian Liu; Fred Wang; Dushan Boroyevich

    2006-01-01

    This paper presents a new frequency-domain method for predicting conducted electromagnetic interference (EMI) noise in phase-leg-based power converters. Based on modular-terminal-behavioral (MTB) equivalent EMI source model for a switch module (half of a phase-leg) developed at a given operating condition, the proposed approach applies the MTB model to predict EMI noise for the converter consisting of multiple phase-legs. Use of

  13. Electrocardiogram signal processing for baseline noise removal using blind source separation techniques: A comparative analysis

    Microsoft Academic Search

    Akram Rashid; Zahooruddin; Ijaz Mansoor Qureshi; Aamer Saleem

    2011-01-01

    Efficient processing of Electrocardiogram (ECG) signal is a major goal of this paper. ECG signal measured from the surface of human body is badly effected by different noises like power line noise, muscle noise, lung noise baseline noise. The main causes of baseline noise are breathing, lose sensor contact and body movements. Baseline noise is a low frequency signal. Baseline

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  15. Low-frequency noise sources in as-prepared and aged GaN-based light-emitting diodes

    Microsoft Academic Search

    S. Bychikhin; D. Pogany; L. K. J. Vandamme; G. Meneghesso; E. Zanoni

    2005-01-01

    The low-frequency noise sources are investigated in as-prepared and aged GaN light-emitting diodes (LEDs). Accelerated aging is performed by thermal (300 h at 240 C) and electrical forward-bias stressing (20 and 50 mA for 2500 h). At low currents Inoise is dominated by random telegraph signal (RTS) noise on top of

  16. Low-frequency noise sources in polysilicon emitter bipolar transistors: Influence of hot-electron-induced degradation

    Microsoft Academic Search

    A. Mounib; F. Balestra; N. Mathieu; J. Brini; G. Ghibaudo; A. Chovet; A. Chantre; A. Nouailhat

    1993-01-01

    The noise properties of polysilicon emitter bipolar transistors are studied. The influences of the various chemical treatments and annealing temperatures, prior and after polysilicon deposition, on the noise magnitude are shown. The impact of hot-electron-induced degradation and post-stress recovery on the base and collector current fluctuations are also investigated in order to determine the main noise sources of these devices.

  17. Shot-to-shot and average absolute photon flux measurements of a femtosecond laser high-order harmonic photon source

    NASA Astrophysics Data System (ADS)

    Leitner, T.; Sorokin, A. A.; Gaudin, J.; Kaser, H.; Kroth, U.; Tiedtke, K.; Richter, M.; Wernet, Ph

    2011-09-01

    The absolute flux of a femtosecond vacuum-ultraviolet (VUV) photon source based on the high-order harmonic generation of a femtosecond Ti:sapphire laser and monochromatized with a grating monochromator is determined both on a shot-to-shot basis and averaged over seconds by a calibrated gas monitor detector. The average flux is compared with the average flux as determined with a calibrated GaAsP semiconductor photodiode. We found that the photodiode is a reliable and easy-to-use tool for estimating the order of magnitude of the average photon flux but that, due to saturation losses, it underestimates the average flux by up to -15%.

  18. September 15, 1995 / Vol. 20, No. 18 / OPTICS LETTERS 1877 Noise reduction by harmonic injection locking of passively

    E-print Network

    Eisenstein, Gadi

    was 0.6 ps, comparable with that of actively stabilized fiber lasers. 1995 Optical Society of America optical data streams and for all-optical signal-processing applications. To assess its capabilities the injected signal was optimized for low noise characteristics, and the PMFL intrinsic classical and quantum

  19. Quadrupole source in prediction of the noise of rotating blades - A new source description

    Microsoft Academic Search

    F. Farassat

    1987-01-01

    The aim of this paper is to perform a theoretical study of the quadrupole term of the Ffowcs Williams-Hawkings (FW-H) equation to obtain practical results for applications to rotating blades. The quadrupole term of the FW-H equation is algebraically manipulated into volume, surface and line sources using generalized function theory and differential geometry. The volume source is of the type

  20. Effects of vortex generating tabs on noise sources in an ideally expanded mach 1.3 jet

    Microsoft Academic Search

    J. Hileman; M. Samimy

    2003-01-01

    The flow and acoustic fields of an ideally expanded Mach 1.3 axisymmetric jet with delta tabs were examined to explore the effects of the tabs on noise sources. This work continues research that was performed on a baseline (no-tab) jet. Noise measurements were made at an angle of 30? to the downstream jet axis to allow a direct comparison to

  1. Semiconductor device and noise sources modeling: design methods and tools oriented to nonlinear H.F. oscillator CAD

    Microsoft Academic Search

    Jean-Christophe Nallatamby; Raphael Sommet; Michel Prigent; Juan Obregon

    2004-01-01

    Designing oscillator circuits at RF and microwaves requires specific knowledge in extremely varied fields of electronics. The following items will be the core of the presentation: - The physical processes leading to low-frequency noise in semi-conductor devices and the nonlinear behavior of the noise sources in large signal operating conditions will be detailed - Transistor modeling: A special emphasis will

  2. Comprehensive Study of Total Ionizing Dose Damage Mechanisms and Their Effects on Noise Sources in a 90 nm CMOS Technology

    Microsoft Academic Search

    Valerio Re; Luigi Gaioni; Massimo Manghisoni; Lodovico Ratti; Gianluca Traversi

    2008-01-01

    Irradiation tests on 90 nm CMOS devices at different total ionizing doses lead to new insights into degradation mechanisms in gate oxides and lateral isolation structures and into their impact on gate and drain current noise sources. The action of lateral parasitic transistors and their physical parameters are studied in different operating conditions. The main focus is on 1\\/f noise,

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  4. SCALABLE NON-SQUARE BLIND SOURCE SEPARATION IN THE PRESENCE OF NOISE Radu Balan, Justinian Rosca, Scott Rickard

    E-print Network

    Balan, Radu V.

    SCALABLE NON-SQUARE BLIND SOURCE SEPARATION IN THE PRESENCE OF NOISE Radu Balan, Justinian Rosca, Scott Rickard Siemens Corporate Research, 755 College Road East, Princeton, NJ 08540 radu.balan,justinian

  5. Analysis of Different Harmonic and Intermodulation Distortions for CATV Systems

    NASA Astrophysics Data System (ADS)

    Singh, Sandeep; Kamaljit, Singh Bhatia; Anurag, Sharma; Kaur, Harsimrat

    2015-06-01

    In this paper, after examining all the basic design issues of CATV systems, prominent distortions like harmonic and intermodulation distortions are taken into account for different order. Besides outer distortions for CATV sources, inner distortion of relative intensity to noise is disabled for current analysis.

  6. Adsorbed Oxygen Molecules as a Source of Flux Noise in SQUIDs

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Wang, Zhe; Hu, Jun; Shi, Chuntai; Yu, Clare C.; Wu, Ruqian; Department of Physics, Fudan University, Shanghai 200433, China Collaboration; Department of Physics; Astronomy, University of California, Irvine, CA 92697-4575, USA Collaboration

    2015-03-01

    A major obstacle for using superconducting quantum interference devices (SQUIDs) as qubits is the flux noise generated by fluctuating magnetic spins on the surface of SQUIDs. Using density functional theory (DFT) calculations, we investigated O2 adsorbates and various vacancies on an ?-alumina surface as spin candidates. Their spectroscopic features are directly compared to experimental data using the x-ray magnetic circular dichroism. The calculated magnetic anisotropy energy for the spin of O2 to rotate within a plane perpendicular to the axis of the O-O bond is only about 12 mK (or ~ 1 ?eV) so we believe that O2 molecules are the main source of flux noise in Al SQUIDs. Work at Fudan was supported by the 1000-Telent funds. Work at UCI was supported by DOE-BES (Grant No. DE- FG02-05ER46237) and by NERSC for computing time.

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Chou, Shau-Tak Rudy

    1990-01-01

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

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

    Microsoft Academic Search

    J. T. Mihalczo; G. E. Ragan; E. D. Blakeman

    1988-01-01

    A portable measurement system consisting of a personal computer used as a Fourier analyzer and three detection channels (with associated electronics that provide the signals to analog-to-digital (A\\/D) convertors) has been assembled to measure subcriticality by the ²⁵²Cf-source-driven neutron noise analysis method. The ²⁵²Cf-source-driven neutron noise analysis method for obtaining the subcritical neutron multiplication factor of a configuration of fissile

  10. Analysis on the frequency-domain numerical method to compute the noise radiated from rotating sources

    NASA Astrophysics Data System (ADS)

    Tang, Hongtao; Qi, Datong; Mao, Yijun

    2013-11-01

    A frequency-domain solution of the Ffowcs Williams-Hawkings equation with a penetrable data surface is presented for the thickness, loading and quadrupole noise to avoid the singularities that exist in the time-domain methods. Since this method is based on the numerical integration over source time, there is no need to solve the retarded-time equation or to perform the interpolation on time-domain data, and the time-domain source information obtained by modern CFD codes can be utilized directly. The acoustic pressure spectra of monopole, dipole and quadrupole point sources in subsonic and supersonic rotation are calculated with the presented method, and the results agree well with those obtained by the retarded-time method and frequency-domain analytical method.

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  12. BLIND HARMONIC ADAPTIVE DECOMPOSITION APPLIED TO SUPERVISED SOURCE Benoit Fuentes, Roland Badeau, Gal Richard

    E-print Network

    Badeau, Roland

    model), a first latent variable is intro- duced in order to decompose as a estimation in order to measure the quality of the decomposition, and in a task of user-guided melody, the statistical framework that is employed to model the noise and the polyphonic part of a CQT is described

  13. Modulation of excitation kinetics of impurity doped quantum dots by the interplay between confinement sources and multiplicative Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Pal, Suvajit; Ghosh, Manas

    2013-11-01

    We investigate the excitation kinetics of a repulsive impurity doped quantum dot initiated by the application of multiplicative Gaussian white noise. The noise strength and the dot confinement sources of electric and magnetic origin have been found to produce the said kinetics in a subtle way. In addition to this the dopant location also plays some crucial role. The present study sheds light on how the individual or combined variation of different confinement sources could design the excitation kinetics in presence of noise. The investigation reveals maximization and saturation in the excitation kinetics as a result of complex interplay between the confinement potentials of the dot, the dopant location, and the noise strength. The present investigation is believed to provide some useful perceptions of the functioning of mesoscopic systems where noise plays some profound role.

  14. Interferometric coherence measurement and radio frequency noise characterization of the 1.3 ?m femtosecond intense Stokes continuum from a TZDW source

    NASA Astrophysics Data System (ADS)

    Yao, Yuhong; Knox, Wayne H.

    2015-02-01

    Photonic crystal fiber (PCF) with two closely spaced zero dispersion wavelengths (TZDW) offers a unique route to efficient energy transfer to two spectrally localized continua beyond either side of the ZDWs, which we have employed in previous work for mid-IR difference frequency generation and speckle-free red-green-blue generation. In this manuscript, we report the interferometric coherence characterization and radio frequency (RF) noise measurements of the Stokes side TZDW component. With a custom-built 1.3 W, 1035 nm, 40 MHz, 240 fs Yb:fiber chirped pulse amplifier as the pump source, we use 12 cm of commercially available TZDW PCF to excite the dual narrow-band continua from which the Stokes pulse is filtered out with a 1180 nm long wave pass filter. We achieve 0.8 to 3 nJ of narrow-band pulses within the spectral range of 1200 - 1315 nm at an average power conversion efficiency of 33%. Employing an un-balanced Michelson interferometer, measured mutual spectral coherence of the Stokes pulse is in excess of 0.76 with pump Soliton order as high as N ~70. Its measured RF noise spectrum at the first harmonic of the laser repetition rate shows less than 8 dBc/Hz increase in relative intensity noise (RIN) compared to that of the power amplifier, which is consistent with reported studies employing sub-100 fs pulses from relatively low noise oscillators. In contrast to the broadband continuum from a single ZDW PCF wherein severe de-coherence is found with pumping at high soliton order and longer pump pulse width, the reported TZDW fiber source shows preservation of intensity stability and phase coherence against variation in pump pulse parameters, which not only attests to the stability of our reported method for mid-IR generation, but also shows promising potential towards an all-fiber, efficient and low noise ultrafast source that can be helpful for applications such as biomedical deep-tissue imaging.

  15. 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

    Vasquez, Juan Carlos

    .; 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

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

    NASA Technical Reports Server (NTRS)

    Magliozzi, B.; Brooks, B. M.

    1979-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Hubbard, Harvey H. (editor)

    1991-01-01

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

  18. Removal of cultural noise from high-resolution aeromagnetic data using a two stage equivalent source approach

    NASA Astrophysics Data System (ADS)

    Salem, Ahmed; Lei, Kaxia; Green, Chris; Fairhead, J. Derek; Stanley, Gerry

    2010-06-01

    High-resolution aeromagnetic surveys are commonly used to locate subtle anomalies that are important in mineral and oil exploration. However, such anomalies, especially in highly populated areas, are often masked by undesirable magnetic signals from near surface man-made objects - known as `cultural noise' - making post processing and interpretation of the aeromagnetic data difficult. Magnetic data need to be cleaned of this cultural noise before applying advanced processing and interpretation methods. Conventional algorithms for cultural noise removal tend to identify and remove noise signals, either manually or using non-linear filters. These methods are often combined with Fast Fourier Transform filters to smooth the result. These algorithms usually introduce artificial anomalies, have difficulty interpolating across edited sections and rarely yield clean data. For these reasons, we have developed a semi-automated two stage equivalent source approach to remove cultural noise and image subtle geological anomalies. A theoretical example that combines a magnetic anomaly due to a dyke with three cultural noise sources is used to test the effectiveness of the proposed method. Comparison of the equivalent source and conventional results shows that the equivalent source method more closely recovers the original magnetic data. We then demonstrate the practical utility of the two stage equivalent source approach using a high-resolution aeromagnetic dataset from Harberton Bridge, Ireland.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. Inflight source noise of an advanced full-scale single-rotation propeller

    NASA Technical Reports Server (NTRS)

    Woodward, Richard P.; Loeffler, Irvin J.

    1991-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Woodward, Richard P.; Loffler, Irvin J.

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Maryanto, Sukir; Iguchi, Masato; Tameguri, Takeshi

    2008-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Chmiel, Malgorzata; Roux, Philippe; Bardainne, Thomas

    2015-04-01

    The aim of this work is to demonstrate the extraction of the local phase velocity and the group velocity from surface noise source in microseismic monitoring. One of the biggest challenges in microseismic monitoring is surface seismic noise. Microseismic surface studies are often contaminated with instrumental and ambient seismic noise, originating from both natural (wind, rain) and anthropogenic sources (injection, pumps, infrastructure, traffic). The two primary ways to attenuate the undesired surface noise sources are via processing and acquisition strategies. At the acquisition stage, one solution is through the use of patch array. One patch is a group of 48 vertical sensors densely distributed on the area of~150m*150m, and one trace is the array of 12 vertical geophones. In the present work, 44 patches were sparsely distributed on a 41 square kilometer area. Benefitting from continuous recording, we used Matched Field Processing (MFP) methods to extract local phase and group velocities over the whole area. The aim of this technique is to detect and locate uncoherent noise sources while using array-processing methods. The method is based on the comparison between a recorded wave field per patch (the data vector) and a theoretical (or modeled) wave-field (the replica vector) in the frequency domain. The replica vector is a Green's function at a given frequency, which depends on the following parameters: position (x,y) in 2D-grid and a phase velocity. The noise source location is obtained by matching the data vector with the replica vector using a linear "low-resolution" algorithm or a nonlinear "high-resolution" adaptive processor. These algorithms are defined for each point in the 2D - grid and for each phase velocity. The phase velocity per patch is optimal if it maximizes the processor output. As a result, an ambiguity surface is produced which shows the probability of presence of primary noise sources per patch. The combination of all the maps per patch reveals the position of the strongest surface noise source. When properly identified and localized, the surface noise source provides information about a group velocity between each patch in the propagation medium. To do so, the data are cross-correlated between patches and a move-out is applied to cross-correlation functions using the phase velocity per patch. The remaining time shift between the envelopes of the cross-correlation functions gives a value of the group velocities between the patches. The technique can be generalized to every pair of patches depending on the number of surface noise source identified at the surface.

  4. Magnetic flux density measurement in magnetic resonance electrical impedance tomography using a low-noise current source

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    Current injected into an electrically conducting object induces distributions of magnetic flux density as well as voltage and current density. In magnetic resonance electrical impedance tomography (MREIT), we measure the induced magnetic flux density using an MRI scanner to reconstruct cross-sectional conductivity images of the object. The current injection must be synchronized with a chosen MRI pulse sequence and the current source needs to be programmable to accommodate various pulse sequences. For an injected current of 1 mA, for example, we may expect an induced magnetic flux density of a few nanoteslas, and noise reduction in measured magnetic flux density data is important for better conductivity image quality. In this paper, we describe how to reduce noise in measured magnetic flux density data based on analyses of noise sources in MREIT. Given an MRI scanner and an imaging object, we found that the current source including lead wires becomes a major noise source. We designed a low-noise programmable current source with optical links, batteries and electromagnetic shields. Equipped with lead switching capability, it automates MREIT imaging experiments using multiple pairs of electrodes. We found that the new current source improves the output current SNR by about 10 dB and the MR magnitude image SNR by about 30%. Placing it near an imaging object inside the shielded room, we could reduce the noise standard deviation in measured magnetic flux density data by 40%. We propose use of this low-noise current source for in vivo animal and human MREIT imaging studies.

  5. Noise upon the sinusoids

    Microsoft Academic Search

    Kristoffer Jensen; Niels Bohrsvej

    2005-01-01

    Sinusoids are used for making harmonic and other sounds. In order to having life in the sounds and adding a wide variety of noises, irregularities are inserted in the frequency and amplitudes. A simple and intuitive noise model is presented, consisting of a low-pass filtered noise, and having control for strength and bandwidth. The noise is added on the frequency

  6. Effect of a single interfering noise or speech source upon the binaural sentence intelligibility of aged persons.

    PubMed

    Duquesnoy, A J

    1983-09-01

    The free-field speech-reception threshold (SRT) for sentences was investigated in quiet and under nine conditions involving noise or competing speech for a group of 20 elderly subjects (ten male, age 75-85; ten female, age 76-88) and a reference group of ten young normal-hearing subjects. The noise source had the same long-term average spectrum as the competing speech. The interfering signals were presented at a constant level of 55 dBA. All elderly subjects had moderate, nearly symmetrical pure-tone hearing losses with an average loss at 500, 1000, and 2000 Hz of between 9 and 40 dB re: ISO-389. The main results are (1) the SRT values in noise and competing speech are about equal, whereas the normal-hearing subjects showed a lower SRT (7 dB lower for the condition that both sound sources are in front) in competing speech than in noise; apparently, the elderly subjects do not benefit from the relatively silent periods in competing speech; (2) the gain obtained by moving the interfering noise source from the front to the lateral position is only 2.5 dB, in contrast to a gain of 9.6 dB for the young subjects; apparently, the elderly are unable to make full use of the spatial divergence between primary speaker and noise source. PMID:6630729

  7. Extreme ultraviolet mask observations using a coherent extreme ultraviolet scatterometry microscope with a high-harmonic-generation source

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    In extreme ultraviolet (EUV) lithography, the three-dimensional structure of an EUV mask, which has an absorber layer and a Mo/Si multilayer on a glass substrate, strongly affects the EUV phase. We have developed a coherent EUV scatterometry microscope (CSM) to observe EUV patterns with a quantitative phase contrast based on the coherent-diffraction-imaging method, which is a simple system without an objective. A coherent stand-alone high-harmonic-generation (HHG) EUV source has been developed for practical use. Although the throughput of the relay optics in the previous study was insufficient to compensate for the fluctuation of the beam position, herein the beam position is stabilized and the relay optics are upgraded, increasing the throughput of the EUV power 130-fold. Consequently, the detection time for the same defect size is markedly reduced from 1000 to 1 s. Furthermore, a 52 52 nm2 absorber defect is detected in 10 s.

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

    SciTech Connect

    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

    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.

  9. Dominant Noise Source of Low-Frequency Fluctuation in AlGaAs\\/InGaAs High Electron Mobility Transistors

    Microsoft Academic Search

    Shinya Nishiyama; Katsuhiko Higuchi

    2003-01-01

    We present an equivalent circuit model for the low-frequency noise (LFN) in high electron mobility transistors (HEMTs). Our model correctly describes the dependence of LFN on gate voltage under low-drain-voltage conditions. Our model also allows us to investigate the location of the noise sources in HEMTs and leads to the fact that LFN arising from the extrinsic region is not

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

    PubMed

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

    2013-06-01

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

  11. Identification and characterization of excess noise sources in ICS by correlation analysis

    Microsoft Academic Search

    M. Conti; G. Corda

    1973-01-01

    Correlation measurement of voltage noise present at input, output and other terminals of a linear IC makes possible the identification of the noisy components in spite of the circuit complexity. Structural defects responsible for noise have been identified both in the case of high 1\\/f noise and of burst noise. The role of stacking faults, dislocation loops and slip line

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

    Microsoft Academic Search

    H. Grieb; K. Heinig

    1986-01-01

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

  13. Acoustic sources joint localization and characterization using compressive sampling

    E-print Network

    Boyer, Edmond

    and identification in terms of spherical harmonics components. We study the case of sources located in a 3D space to be found mixes location and spherical harmonics decomposition. The identification strategy is evaluated. Identification aims at an objective description of the acoustic phenomenon generating a perturbing noise

  14. Location of low-frequency noise sources in submicrometer bipolar transistors

    Microsoft Academic Search

    Theo G. M. Kleinpenning

    1992-01-01

    Expressions are derived for the low-frequency noise (1\\/f noise, shot noise, Nyquist noise) in bipolar transistors. Particular attention has been paid to the influence of the internal base and emitter series resistance. The expressions have been compared with experimental results from submicrometer silicon bipolar transistors. It is found at low forward currents that the 1\\/f noise is dominated by 1\\/f

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

    E-print Network

    Kushner, Mark

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

  16. The MRI: A noise source of concern in the health care industry

    NASA Astrophysics Data System (ADS)

    Standlee, Kerrie G.; Begin, Joseph C.

    2003-10-01

    Two recent trends in the development and use of magnetic resonance imaging (MRI) equipment have created challenges for acoustical engineers: (1) the trend toward more powerful MRI machines with greater magnetic field strengths, and (2) the tendency of health care facilities to locate these machines, which were previously located in basements or on grade, on upper floors adjacent to (and in some cases above) other critical use areas. For newer, 3-T MRI machines, sound levels well over 100 dBA in the examination room are common. Along with these trends, some equipment manufacturers are now providing design recommendations to address the issues of airborne and structure-borne noise within hospitals and clinics. In addition, MRI manufacturers sometimes have strict requirements for acceptable levels of building vibration from other sources, to prevent potential image quality problems. This paper discusses experience gained during the course of addressing MRI-generated noise on several projects. Data for airborne sound levels measured inside MRI rooms and adjacent rooms and vibration levels measured below MRI units will be presented.

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

    NASA Astrophysics Data System (ADS)

    Tenney, Andrew; Lewalle, Jacques

    2013-11-01

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

  18. Flap noise

    NASA Technical Reports Server (NTRS)

    Dorsch, R. G.; Lasagna, P. L.; Maglieri, D. J.; Olsen, W. A.

    1972-01-01

    Externally-blown-flap noise research can be summarized by the following remarks: With lower-surface blowing, the sources of the flap noise are begining to be understood and the noise scaling laws have been established. Further, progress has been made on suppressing the flap interaction noise at the large flap deflections used during landing. Recent small-scale noise tests of configurations using external upper-surface blowing indicate that engine-over-the-wing configurations may be promising.

  19. Inverse Problem for the Wave Equation with a White Noise Source

    NASA Astrophysics Data System (ADS)

    Helin, Tapio; Lassas, Matti; Oksanen, Lauri

    2014-12-01

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

  20. Exploiting continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation methods for noise source identification

    NASA Astrophysics Data System (ADS)

    Chiariotti, Paolo; Martarelli, Milena; Revel, Gian Marco

    2014-07-01

    This paper proposes the use of continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation techniques that aim at characterizing the structure-borne contributions of the noise emission of a mechanical system. The time domain correlation technique presented in this paper is based on the use of FIR (finite impulse response) filters obtained from the vibro-acoustic transfer matrix when vibration data are collected by laser Doppler vibrometry (LDV) exploited in continuous scan mode (CSLDV). The advantages, especially in terms of source decorrelation capabilities, related to the use of CSLDV for such purpose, with respect to standard discrete scan (SLDV), are discussed throughout the paper. To validate this approach, vibro-acoustic measurements were performed on a planetary gear motor for home appliances. The analysis of results is also supported by a simulation.

  1. Eigen oscillation of a fluid sphere and source mechanism of harmonic volcanic tremor

    Microsoft Academic Search

    Eisuke Fujita; Yoshiaki Ida; Jun Oikawa

    1995-01-01

    The eigen oscillation of a fluid sphere embedded in an infinite elastic medium is analyzed to understand the source mechanism of volcanic tremor that vibrates nearly monotonically and attenuates slowly. The dimensionless eigen frequencies of the sinusoidal oscillation are calculated in a complex form with the attenuation factor in its imaginary part for various combinations of the three parameters: the

  2. Analysis of the effect of heated jet flow on the far field radiation from a noise source

    NASA Technical Reports Server (NTRS)

    Gerhold, C.

    1982-01-01

    The influence on jet noise radiation of the interaction with the heated moving flow of a parallel twin jet is investigated. An analytical model of jet shielding is developed which consists of the sound field emitted from a stationary, discrete frequency point source impinging on a cylinder of locally parallel flow. The zones in which the various shielding mechanisms dominate are analyzed using the model. The effects of parameters such as jet temperature and flow speed are examined. It is found that the results obtained using the model are comparable to the experimental results for a point noise source impinging on a subsonic isothermal air jet.

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

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

    Microsoft Academic Search

    Sukir Maryanto; Masato Iguchi; Takeshi Tameguri

    2008-01-01

    Vulcanian-type eruptive activity has occurred from the summit crater of Sakurajima volcano, Japan, since 1955. Over this period, harmonic tremors have commonly occurred either several hours after swarms of B-type earthquakes (herein termed HTB: Harmonic Tremor following B-type earthquake swarm) or immediately after explosive eruptions (herein termed HTE: Harmonic Tremor after an Eruption). In this study, we analyzed the spectra

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

    Microsoft Academic Search

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

    2009-01-01

    Multimodal nonlinear optical imaging has opened new opportunities and becomes a powerful tool for imaging complex tissue samples with inherent 3D spatial resolution.. We present a robust and easy-to-operate approach to add the coherent anti-stokes Raman scattering (CARS) imaging modality to a widely used multiphoton microscope. The laser source composed of a Mai Tai femtosecond laser and an optical parametric

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  7. Binaural prediction of speech intelligibility in reverberant rooms with multiple noise sources.

    PubMed

    Lavandier, Mathieu; Jelfs, Sam; Culling, John F; Watkins, Anthony J; Raimond, Andrew P; Makin, Simon J

    2012-01-01

    When speech is in competition with interfering sources in rooms, monaural indicators of intelligibility fail to take account of the listener's abilities to separate target speech from interfering sounds using the binaural system. In order to incorporate these segregation abilities and their susceptibility to reverberation, Lavandier and Culling [J. Acoust. Soc. Am. 127, 387-399 (2010)] proposed a model which combines effects of better-ear listening and binaural unmasking. A computationally efficient version of this model is evaluated here under more realistic conditions that include head shadow, multiple stationary noise sources, and real-room acoustics. Three experiments are presented in which speech reception thresholds were measured in the presence of one to three interferers using real-room listening over headphones, simulated by convolving anechoic stimuli with binaural room impulse-responses measured with dummy-head transducers in five rooms. Without fitting any parameter of the model, there was close correspondence between measured and predicted differences in threshold across all tested conditions. The model's components of better-ear listening and binaural unmasking were validated both in isolation and in combination. The computational efficiency of this prediction method allows the generation of complex "intelligibility maps" from room designs. PMID:22280586

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

    SciTech Connect

    Mackenzie, Alistair; Honey, Ian D. [KCARE, King's College Hospital, Denmark Hill, London, SE5 9RS (United Kingdom)

    2007-08-15

    The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and noise characteristics. The main aim was to characterize and quantify the noise sources in the images. The systems tested were (1) Agfa CR 25.0, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX-S, a line-scanning CR reader with needle crystal phosphor image plates (HD 5.0). For both systems, the standard metrics of presampled modulation transfer function (MTF), normalized noise power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various noise sources contributing to the NNPS were separated by using knowledge of their relationship with air kerma, MTF, absorption efficiency and antialiasing filters. The DX-S MTF was superior compared with the CR 25.0. The maximum difference in MTF between the DX-S scan and CR 25.0 subscan directions was 0.13 at 1.3 mm{sup -1}. For a nominal detector air kerma of 4 {mu}Gy, the peak DQE of the DX-S was 43({+-}3)%, which was over double that of the CR 25.0 of 18({+-}2)%. The additive electronic noise was negligible on the CR 25.0 but calculated to be constant 3.4x10{sup -7} ({+-}0.4x10{sup -7}) mm{sup 2} at 3.9 {mu}Gy on the DX-S. The DX-S has improved image quality compared with a traditional flying spot reader. The separation of the noise sources indicates that the improvements in DQE of the DX-S are due not only to the higher quantum, efficiency and MTF, but also the lower structure, secondary quantum, and excess noise.

  9. Active control of propeller induced noise fields inside a flexible cylinder

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    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.

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

    PubMed

    Lim, Geunsik; Manzur, Tariq; Kar, Aravinda

    2014-12-20

    An uncooled photon detector is fabricated for the mid-wave infrared (MWIR) wavelength of 4.21 ?m by doping an n-type 4H-SiC substrate with gallium using a laser doping technique. The dopant creates a p-type energy level of 0.3 eV, which is the energy of a photon corresponding to the MWIR wavelength 4.21 ?m. This energy level was confirmed by optical absorption spectroscopy. The detection mechanism involves photoexcitation of carriers by the photons of this wavelength absorbed in the semiconductor. The resulting changes in the carrier densities at different energy levels modify the refractive index and, therefore, the reflectance of the semiconductor. This change in the reflectance constitutes the optical response of the detector, which can be probed remotely with a laser beam such as a He-Ne laser and the power of the reflected probe beam can be measured with a conventional laser power meter. The noise mechanisms in the probe laser, silicon carbide MWIR detector, and laser power meter affect the performance of the detector in regards to aspects such as the responsivity, noise equivalent temperature difference (NETD), and detectivity. For the MWIR wavelengths of 4.21 and 4.63 ?m, the experimental detectivity of the optical photodetector of this study was found to be 1.0710(10)??cmHz(1/2)/W, while the theoretical value was 1.1110(10)??cmHz(1/2)/W. The values of NETD are 404 and 15.5 mK based on experimental data for an MWIR radiation source with a temperature of 25C and theoretical calculations, respectively. PMID:25608189

  11. Analysis of optical phase noise in fiber-optic systems employing a laser source with arbitrary coherence time

    Microsoft Academic Search

    Behzad Moslehi

    1986-01-01

    Performance of many optical circuits and systems, such as signal processing and sensing devices, is influenced by random fluctuations of the optical source emission field. This paper outlines a formalism for the analysis of laser phase noise effects on a general linear time-invariant optical system. Theoretical expressions are presented for the autocovariance function of the instantaneous output intensity which are

  12. Investigation of hydrothermal boiling and steam quenching as possible sources of volcanic tremor and geothermal ground noise

    Microsoft Academic Search

    Leet

    1991-01-01

    Volcanic tremor and geothermal ground noise are sustained seismic emissions associated with volcanic and geothermal activity. In this study I investigate whether such signals could be caused by boiling or steam quenching in liquid-dominated zones of subterranean hydrothermal systems. The framework for the study is a conceptual model that assumes: (1) the fundamental source of seismic energy is the growth\\/collapse

  13. A synthesis procedure for pass-by noise of automotive vehicles employing numerically evaluated source-receiver transfer functions

    NASA Astrophysics Data System (ADS)

    Huijssen, Jacobus; Hallez, Raphael; Pluymers, Bert; Desmet, Wim

    2013-07-01

    A synthesis procedure is presented for the prediction of the sound pressure level (SPL) of passenger vehicles in a pass-by noise test. The proposed synthesis procedure translates the noise from the sources in the moving vehicle to the receivers in two steps. Firstly, the steady-state receiver contributions of the sources are computed as they would arise from a number of static vehicle positions along the drive path. Secondly, these contributions are then combined into a single transient signal from a moving vehicle for each source-receiver pair by means of a travel time correction. The multiple source-receiver transfer functions are numerically evaluated by employing the Fast Multipole Boundary Element Method (FMBEM), which allows for pass-by noise SPL estimation on the basis of the CAD/CAE computer models that are available early in the design stage. Results are presented that show the accuracy of the synthesis procedure and that show the ability of the combination of the synthesis procedure and numerically evaluated transfer functions to predict pass-by noise SPL for a realistic case in an evaluation time of less than a day.

  14. MCNP-DSP calculations of the ²⁵²Cf-source-driven noise analysis measurements of highly enriched uranium metal cylinders

    Microsoft Academic Search

    T. E. Valentine; J. T. Mihalczo

    1995-01-01

    This paper presents calculations of the ²⁵²Cf-source-driven noise analysis measurements for subcritical highly enriched uranium metal cylinders using the Monte Carlo code MCNP-DSP. This code directly calculates the noise analysis data from the ²⁵²Cf- source-driven noise analysis method for both neutron and gamma ray detectors. Direct calculation of experimental observables by the Monte Carlo method allows for the benchmarking of

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

    NASA Technical Reports Server (NTRS)

    Panda, Jayanta; Seasholtz, Richard G.

    2003-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

  17. 1\\/f Noise Sources in Dual-Gated Indium Arsenide Nanowire Transistors

    Microsoft Academic Search

    Collin J. Delker; Seongmin Kim; Mattias Borg; Lars-Erik Wernersson; David B. Janes

    2012-01-01

    1\\/f noise is studied in dual-gated InAs nanowire transistors consisting of an omega top gate with high- $k$ atomic layer deposited dielectric and silicon dioxide to substrate back gate. Noise spectra at varying gate bias combinations are compared from devices with differing top-gate lengths to separate the noise contributions of the top-gated channel from the ungated access portion, including the

  18. Low frequency noise sources in AlGaN\\/GaN HEMTs

    Microsoft Academic Search

    J. A. Garrido; F. Calle; E. Muoz; I. Izpura; J. L. Snchez-Rojas; R. Li; K. L. Wang

    1999-01-01

    Low-frequency noise has been studied in Al0.15Ga0.85N\\/GaN high electron mobility transistors grown on sapphire substrates by metal organic vapor phase epitaxy. By varying the gate voltage (VGS), three regions of drain 1\\/f noise were clearly established under VDS=50 mV biasing. From VGS=-4 V (pinch-off) to 0 V, noise power generated at the transistor channel, which scales with device area, dominates.

  19. Advances in tilt rotor noise prediction

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    Microsoft Academic Search

    C. L. Jaeck

    1976-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Kieffer, Susan Werner

    1984-09-01

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

  2. An optimized kHz two-colour high harmonic source for seeding free-electron lasers and plasma-based soft x-ray lasers

    NASA Astrophysics Data System (ADS)

    Lambert, G.; Gautier, J.; Hauri, C. P.; Zeitoun, Ph; Valentin, C.; Marchenko, T.; Tissandier, F.; Goddet, J. Ph; Ribiere, M.; Rey, G.; Fajardo, M.; Sebban, S.

    2009-08-01

    Free-electron lasers (FEL) and plasma-based soft x-ray lasers (PSXL) have been recently evolving very fast from the vacuum ultraviolet to the soft x-ray region. Once seeded with high harmonics, these schemes are considered as the next generation soft x-ray light sources delivering ultrashort pulses with high temporal and spatial coherence. Here, we present a detailed experimental study of a kHz two-colour high harmonic generation performed in various gases and investigate its potential as a suitable evolution of the actual seeding sources. It turns out that this double harmonic content source is highly tuneable, controllable and delivers intense radiation (measured here with a calibrated photodiode) with only one order of magnitude difference in the photon yield from 65 to 13 nm. Then, first and foremost, injections could be achieved at wavelengths shorter than what was previously accessible in FEL and PSXL and/or additional energy could be extracted. Also, such a strong and handy seed could allow the saturation range of FEL devices to be greatly extended to shorter wavelengths and would bring higher spectral as well as intensity stabilities in this spectral zone.

  3. Optimal control subsumes harmonic control Amine Boumaza

    E-print Network

    Paris-Sud XI, Universit de

    of trajectory planning with optimal control in a space with isotropic noise1 , when the noise level tends that discuss both harmonic and optimal control, we did not find any that highlights such a specific- to that present harmonic and optimal control as unrelated but complemen- tary paradigms. Trajectories derived from

  4. Noise Models

    Microsoft Academic Search

    Alper Demir; Alberto Sangiovanni-Vincentelli

    \\u000a To reach the final goal of simulating and characterizing the effect of noise on the performance of an electronic circuit or\\u000a system, we first need to investigate the actual noise sources in the system and develop models for these noise sources in\\u000a the framework of the theory of signals and systems we will be operating with. The models we are

  5. Noise pollution resources compendium

    NASA Technical Reports Server (NTRS)

    1973-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Vergne, Jerome; Blachet, Antoine; Lehujeur, Maximilien

    2015-04-01

    Monitoring local or regional seismic activity requires stations having a low level of background seismic noise at frequencies higher than few tenths of Hertz. Network operators are well aware that the seismic quality of a site depends on several aspects, among them its geological setting and the proximity of roads, railways, industries or trees. Often, the impact of each noise source is only qualitatively known which precludes estimating the quality of potential future sites before they are tested or installed. Here, we want to take advantage of a very dense temporary network deployed in Northern Alsace (France) to assess the effect of various kinds of potential sources on the level of seismic noise observed in the frequency range 0.2-50 Hz. In September 2014, more than 250 seismic stations (FairfieldNodal@ Zland nodes with 10Hz vertical geophone) have been installed every 1.5 km over a ~25km diameter disc centred on the deep geothermal sites of Soultz-sous-Forts and Rittershoffen. This region exhibits variable degrees of human imprints from quite remote areas to sectors with high traffic roads and big villages. It also encompasses both the deep sedimentary basin of the Rhine graben and the piedmont of the Vosges massif with exposed bedrock. For each site we processed the continuous data to estimate probability density functions of the power spectral densities. At frequencies higher than 1 Hz most sites show a clear temporal modulation of seismic noise related to human activity with the well-known variations between day and night and between weekdays and weekends. Moreover we observe a clear evolution of the spatial distribution of seismic noise levels with frequency. Basically, between 0.5 and 4 Hz the geological setting modulates the level of seismic noise. At higher frequencies, the amplitude of seismic noise appears mostly related to the distance to nearby roads. Based on road maps and traffic estimation, a forward approach is performed to model the induced seismic noise. Effects of other types of seismic sources, such as industries or wind, are also observed but usually have a more limited spatial extension and a specific signature in the spectrograms.

  7. Effect of Vortex Generating Tabs on Noise Sources in an Ideally Expanded Jet

    Microsoft Academic Search

    Mo Samimy; James Hileman

    2002-01-01

    It is known that by attaching small delta shape tabs at the nozzle exit, one can substantially modify the flow as well as the noise emission characteristics of subsonic or supersonic jets. Tabs, which slightly protrude into the flow, generate strong streamwise vortices that greatly alter the development of the jet's mixing layer and noise emission. While the effects of

  8. Application of a microphone phased array to identify noise sources on a horizontal vibrating screen

    Microsoft Academic Search

    David S. Yantek; Hugo E. Camargo; Rudy J. Matetic

    In coal preparation plants, workers are often exposed to sound levels exceeding 90 dB(A). Vibrating screens are viewed as a significant contributor to preparation plant noise. Reducing the sound levels generated by vibrating screens could reduce the noise exposures of preparation plant employees. The National Institu te for Occupational Safety and Health (NIOSH) measured the sound power level generated by

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

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

    SciTech Connect

    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

    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.

  13. Subcritical measurements using the ²⁵²Cf source-driven neutron noise analysis method

    Microsoft Academic Search

    J. T. Mihalczo; E. D. Blakeman; G. E. Ragan; R. C. Kryter

    1985-01-01

    This paper describes recent measurements of the subcritical neutron multiplication factor using the ²⁵²Cf source-driven neutron noise analysis method. This work was supported by a program of collaboration between the United States Department of Energy and the Power Reactor and Nuclear Fuel Development Corporation of Japan related to the development of fast breeder technology. The experiment reported consists of a

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

    Microsoft Academic Search

    J. T. Mihalczo; G. E. Ragan

    1987-01-01

    A portable system has been assembled that is capable of measuring the subcriticality of fissile materials using the ²⁵²CF-source-driven neutron noise analysis method. The measurement system consists of a parallel-plate ionization chamber containing ²⁵²CF, two ³He 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

  15. Microwave noise sources in AlGaAs\\/GaAs HBTs

    Microsoft Academic Search

    Paulius Sakalas; Michael Schrter; Pete Zampardi; Herbert Zirath; R. Welse

    2002-01-01

    Scattering and noise parameters of AlGaAs\\/GaAs HBTs from Conexant with 30 and 35% of Al mole content were measured and modeled. De-embedding of the pad parasitics was accurately performed by using a \\

  16. ANALYSIS OF THE MICROWAVE NOISE SOURCES IN HEMTs, MOSFETs AND HBTs

    Microsoft Academic Search

    P. SAKALAS; M. SCHRTER

    Noise parameters of AIIIBV HEMTs, PHEMTs, HBTs and MOSFETs were measured and modeled using an equivalent circuit approach in the microwave frequency band. Microwave pad parasitic elements were de-embedded by using \\

  17. Signal-to-noise ratio of modulated sources of ASE transmitted over dispersive fiber

    Microsoft Academic Search

    G. J. Pendock; D. D. Sampson

    1997-01-01

    We investigate, both theoretically and experimentally, the signal-to-noise ratio (SNR) of modulated amplified spontaneous emission (ASE) transmitted over dispersive fiber. We observe two significant effects; firstly, the signal-to-excess-noise ratio (SNRex) varies across the pulse reaching its maximum value near the peak of the detected signal; and secondly, this maximum value decreases with increasing fiber dispersion-induced pulse broadening. Accurate calculation of

  18. Experimental study and modeling of the white noise sources in submicron Pand N-MOSFETs

    Microsoft Academic Search

    V. Re; I. Bietti; R. Castello; M. Manghisoni; V. Speziali; F. Svelto

    2001-01-01

    This paper presents the results of the experimental characterization of the channel thermal noise in MOSFETs belonging to a submicron gate process, with minimum gate length L=0.35 ?m. The data are compared with a noise model taking into account short-channel effects such as velocity saturation and hot carriers. The contribution of gate and substrate parasitic resistors is also evaluated and

  19. Sources of high-speed jet noise: Analysis of LES data and modeling

    Microsoft Academic Search

    Sanjiva K. Lele; Simon Mendez; Jaiyoung Ryu; Joseph Nichols; Mohammad Shoeybi; Parviz Moin

    2010-01-01

    Results from recent LES studies of high-speed jet flows and its near and far-field noise (Mendez et al. AIAA2010-271) are reviewed with an emphasis on validation of the LES results. Far-field noise is predicted using data collected on a conical FW-H surface. Very good agreement with the measurement reported by Bridges & Wernet (AIAA-2008-2834) is observed. Data analysis of the

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

    SciTech Connect

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

    2010-04-15

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

  1. Low-frequency noise sources in polysilicon emitter BJT's: influence of hot-electron-induced degradation and post-stress recovery

    Microsoft Academic Search

    Ahmed Mounib; Francis Balestra; Nathalie Mathieu; Jean Brini; Gerard Ghibaudo; Alain Chovet; A. Chantre; A. Nouailhat

    1995-01-01

    The noise properties of polysilicon emitter bipolar transistors are studied. The influences of the various chemical treatments and annealing temperatures, prior and after polysilicon deposition, on the noise magnitude are shown. The impact of hot-electron-induced degradation and post-stress recovery on the base and collector current fluctuations are also investigated in order to determine the main noise sources of these devices

  2. Low-Frequency Noise Sources in Polysilicon Emiter Bipolar Transistors: Influence of Hot-Electron-Induced Degradation and Post-Stress Recovery

    Microsoft Academic Search

    A. Mounib; F. Balestra; N. Mathieu; J. Brini; G. Ghibaudo; A. Chovet; A. Chantre; A. Nouailhat

    1993-01-01

    The noise properties of polysilicon emitter bipolar transistors are studied. The influences of the various chemical treatments and annealing temperatures, prior and after polysilicon deposition, on the noise magnitude are shown. The impact of hot-electron-induced degradation and post-stress recovery on the base and collector current fluctuations are also investigated in order to determine the main noise sources of these devices.

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

    NASA Technical Reports Server (NTRS)

    Pla, F. G.; Rajiyah, H.

    1995-01-01

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

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

    Microsoft Academic Search

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

    1992-01-01

    Type III radio emission generated in the vicinity of the Ulysses spacecraft has been detected at both the fundamental and harmonic of the local plasma frequency. The observations represent the first clear evidence of locally generated type III radio emission. This local emission shows no evidence of frequency drift, exhibits a relatively short rise time, is less intense than the

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

    SciTech Connect

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

    2000-10-11

    A new and different time variant pulse processing system has been developed based on a simple CR-RC filter and two analog switches. The new pulse processing technique combines both ballistic deficit immunity and resilience to parallel noise without a significant compromise to the low energy resolution, generally considered a mutually exclusive requirement. The filter is realized by combining two different pulse-shaping techniques. One of the techniques creates a low rate of curvature at the pulse peak, which reduces ballistic deficit, while the second technique increases the tolerance to low frequency noise by modifying the noise history. Several experimental measurements are presented, including tests on a co-planar grid CdZnTe detector. Improvements on both the resolution and line shape are shown for the 662 keV line of 137Cs.

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

    E-print Network

    Stylianou, Yannis

    of representation and concate- nation of acoustic units. TD-PSOLA [1] performs a pitch- synchronous "analysis problems in the time domain by resynthesizing voiced parts of the speech data- base with constant phase-to-speech (TTS) synthesis. In the context of HNM, speech signals are represented as a time-varying harmonic

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

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.

    1975-01-01

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

  8. Community Response to Noise

    Microsoft Academic Search

    Sandy Fidell

    2008-01-01

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

  9. Community Response to Noise

    NASA Astrophysics Data System (ADS)

    Fidell, Sandy

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

  10. Correlation measurement of carrier multiplication noise sources in MOS transistors at low frequencies

    Microsoft Academic Search

    Dominique Rigaud; Matteo Valenza

    1994-01-01

    Low frequency techniques of cross spectrum and correlation coefficient measurements are presented and applied to investigate drain and substrate noises of MOS transistors when multiplication occurs in the channel. For low substrate currents it is shown that the experimental data agree with theoretical expectations: the correlation coefficient is maximum at low frequencies and reaches its minimum value which is only

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

    NASA Technical Reports Server (NTRS)

    Kahraman, Ahmet; Singh, Rajendra

    1989-01-01

    An analytical technique for estimating noise generation by spur-gear pairs with backlash is developed using the results obtained by Comparin and Singh (1989). The derivation of the governing equations is outlined, and numerical results for sample problems are presented in graphs. Good agreement with published experimental data (Munro, 1962) is demonstrated.

  12. Journal of Biomechanics 40 (2007) 861870 Snoring source identification and snoring noise prediction

    E-print Network

    Luo, Xiaoyu

    2007-01-01

    prediction Z.S. Liua,, X.Y. Luob , H.P. Leea,c , C. Lua a Institute of High Performance Computing, 1 Science Park Road, #01-01 The Capricorn, Singapore Science Park II, Singapore 117528, Singapore b Department of the upper airway in the nasal cavity is generated. The snoring noise level is predicted for a prescribed

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

    Microsoft Academic Search

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

    2001-01-01

    A new and different time-variant pulse processing system has been developed based on a simple CR-RC filter and two analog switches. The new pulse processing technique combines both ballistic deficit immunity and resilience to parallel noise without a significant compromise to the low energy resolution, generally considered a mutually exclusive requirement. The filter is realized by combining two different pulse

  14. Combined Source Tracking and Noise Reduction for Application in Hearing Aids

    E-print Network

    ) the estimation of the direction of arrival (DOA) and thus for auto- matic beam-steering, (ii) a higher noise transfer functions have been measured, both in an anechoic and an office environment (room reverberation in an office and in a cafe

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

    NASA Technical Reports Server (NTRS)

    Meyer, H. D.

    1993-01-01

    The Acoustic Radiation Code (ARC) is a finite element program used on the IBM mainframe to predict far-field acoustic radiation from a turbofan engine inlet. In this report, requirements for developers of internal aerodynamic codes regarding use of their program output an input for the ARC are discussed. More specifically, the particular input needed from the Bolt, Beranek and Newman/Pratt and Whitney (turbofan source noise generation) Code (BBN/PWC) is described. In a separate analysis, a method of coupling the source and radiation models, that recognizes waves crossing the interface in both directions, has been derived. A preliminary version of the coupled code has been developed and used for initial evaluation of coupling issues. Results thus far have shown that reflection from the inlet is sufficient to indicate that full coupling of the source and radiation fields is needed for accurate noise predictions ' Also, for this contract, the ARC has been modified for use on the Sun and Silicon Graphics Iris UNIX workstations. Changes and additions involved in this effort are described in an appendix.

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

    NASA Technical Reports Server (NTRS)

    Zaman, Khairul B.

    2002-01-01

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

  17. General adjoint approach to the physics-based noise modeling of semiconductor devices through Langevin sources

    NASA Astrophysics Data System (ADS)

    Huang, Mingwei; Mayergoyz, Isaak; Andrei, Petru

    2007-01-01

    A general approach to the numerical analysis of noise in physics-based semiconductor devices is proposed. This approach is based on the Riesz representation theorem and can be applied to most partial-differential-equation-based semiconductor device models. Explicit expressions of Green's functions for both open-circuit and short-circuit configurations are provided. Our approach is conceptually simpler than Branin's method developed through the network analogy and it is flexible in the sense that it can be applied to any network configuration without additional matrix transformations. Numerical results of the noise in short-channel metal-oxide-semiconductor field-effect transistors and 4H-Si metal-semiconductor field-effect transistors are presented and discussed.

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

    PubMed

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

    2011-06-01

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

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

    NASA Technical Reports Server (NTRS)

    Stimpert, D. L.

    1975-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  1. Theory for noise of propellers in angular inflow with parametric studies and experimental verification

    Microsoft Academic Search

    Donald B. Hanson; David J. Parzych

    1993-01-01

    This report presents the derivation of a frequency domain theory and working equations for radiation of propeller harmonic noise in the presence of angular inflow. In applying the acoustic analogy, integration over the tangential coordinate of the source region is performed numerically, permitting the equations to be solved without approximation for any degree of angular inflow. Inflow angle is specified

  2. Blind source separation of ship-radiated noise based on generalized Gaussian model

    Microsoft Academic Search

    Wei Kong; Bin Yang

    2006-01-01

    When the distribution of the sources cannot be estimated accurately, the ICA algorithms failed to separate the mixtures blindly. The generalized Gaussian model (GGM) is presented in ICA algorithm since it can model non-Gaussian statistical structure of different source signals easily. By inferring only one parameter, a wide class of statistical distributions can be characterized. By using maximum likelihood (ML)

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

    E-print Network

    Plumbley, Mark

    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

  4. Activation process in excitable systems with multiple noise sources: Large number of units

    E-print Network

    Igor Franovi?; Matja Perc; Kristina Todorovi?; Srdjan Kosti?; Nikola Buri?

    2015-07-12

    We study the activation process in large assemblies of type II excitable units whose dynamics is influenced by two independent noise terms. The mean-field approach is applied to explicitly demonstrate that the assembly of excitable units can itself exhibit macroscopic excitable behavior. In order to facilitate the comparison between the excitable dynamics of a single unit and an assembly, we introduce three distinct formulations of the assembly activation event. Each formulation treats different aspects of the relevant phenomena, including the threshold-like behavior and the role of coherence of individual spikes. Statistical properties of the assembly activation process, such as the mean time-to-first pulse and the associated coefficient of variation, are found to be qualitatively analogous for all three formulations, as well as to resemble the results for a single unit. These analogies are shown to derive from the fact that global variables undergo stochastic bifurcation from the stochastically stable fixed point to continuous oscillations. Local activation processes are analyzed in light of competition between the noise-led and the relaxation-driven dynamics. We also briefly report on a system-size anti-resonant effect displayed by the mean time-to-first pulse.

  5. Effects of seasonal changes in ambient noise sources on monitoring temporal variations in crustal properties

    NASA Astrophysics Data System (ADS)

    Gong, Meng; Shen, Yang; Li, Hongyi; Li, Xinfu; Jia, Jinsheng

    2015-07-01

    Continuous data recorded at 39 broadband stations near the Longmen Shan Fault operated by the China Earthquake Administration from 1 January 2008 to 30 September 2010 are used to study temporal variability in direct surface wave arrivals extracted from ambient noise. We use a cross-correlation technique to compute Empirical green functions (EGFs) for all available station pairs at the frequency range of 0.1 to 0.5Hz. Delay times are measured by cross-correlating reference empirical green functions and moving 60-day stacks of EGFs. By comparing the temporal changes with and without the correction for seasonal variations, our results show that for some station pairs temporal variations were strongly affected by the seasonal variation. After correction for seasonal variations, we measure a 0.5-% maximum velocity drop after the 2008 Ms8.0 earthquake in Sichuan, China. We find that the Sichuan Basin exhibited a larger relative velocity drop than the Tibetan plateau area. Our results suggest that correction for seasonal variation is an important procedure for monitoring temporal variations in crustal properties using the direct arrival surface waves extracted from ambient noise.

  6. Towards single-channel unsupervised source separation of speech mixtures: The layered harmonics\\/formants separation-tracking model

    Microsoft Academic Search

    Manuel Reyes-Gomez; Nebojsa Jojic; Daniel P. W. Ellis

    Speaker models for blind source separation are typically based on HMMs consisting of vast numbers of states to cap- ture source spectral variation, and trained on large amounts of isolated speech. Since observations can be similar be- tween sources, inference relies on sequential constraints from the state transition matrix which are, however, quite weak. To avoid these problems, we propose

  7. Numerical evaluation of the performance of active noise control systems

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    This paper presents a generalized numerical technique for evaluating the optimal performance of active noise controllers. In this technique, the indirect BEM numerical procedures are used to derive the active noise controllers for optimal control of enclosed harmonic sound fields where the strength of the noise sources or the description of the enclosure boundary may not be known. The performance prediction for a single-input single-output system is presented, together with the analysis of the stability and observability of an active noise-control system employing detectors. The numerical procedures presented can be used for the design of both the physical configuration and the electronic components of the optimal active noise controller.

  8. Harmonic Generation

    Microsoft Academic Search

    H. J. Scott; L. J. Black

    1938-01-01

    When plate current in a vacuum-tube amplifier flows for only a portion of the grid-excitation cycle, harmonics appear in the output circuit. The magnitude of any one of these harmonics depends upon the fraction of the fundamental cycle during which plate current flows. In the gradual transition from perfect class A to extreme class C operation, the magnitude of the

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

    E-print Network

    Fernandes, Roland Anthony Savio

    2009-05-15

    Controlled source electromagnetic (CSEM) geophysics has been used with a fair amount of success in near surface hydrogeological studies. Recently, these investigations have been conducted frequently in human impacted field sites containing cultural...

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Type III radio emission generated in the vicinity of the Ulysses spacecraft has been detected at both the fundamental and harmonic of the local plasma frequency. The observations represent the first clear evidence of locally generated type III radio emission. This local emission shows no evidence of frequency drift, exhibits a relatively short rise time, is less intense than the observed remotely generated radio emission, and is temporally correlated with observed in situ Langmuir waves. The observations were made with the unified radio astronomy and wave (URAP) experiment on the Ulysses spacecraft between 1990 November 4 and 1991 April 30, as it traveled from 1 to 3 AU from the sun. During this time period many thousands of bursts were observed. However, only three examples of local emission and associated Langmuir waves were identified. This supports previous suggestions that type III radio emission is generated in localized regions of the interplanetary medium, rather than uniformly along the extent of the electron exciter beam.

  11. Evaluation of the interim measurement protocol for railway noise source description

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

    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.

  12. Rayleigh and Love Wave imaging of Iceland using ambient noise and teleseismic sources

    NASA Astrophysics Data System (ADS)

    Harmon, Nicholas

    2015-04-01

    Iceland is one of the few regions where ridge-plume interaction can be examined with a terrestrial seismic array. Velocity structure from broadband surface wave dispersion measurements can be used to constrain the complicated crustal and upper mantle structure caused by the plume enhanced rifting activity. Here I use data from the ICEMELT and HOTSPOT arrays on Iceland to generate phase velocity dispersion maps of both Rayleigh and Love waves from ambient noise cross correlation and teleseismic events. I invert Rayleigh and Love wave dispersion observed from ambient noise for tomographic velocity structure. For teleseismic Rayleigh waves I use the two-plane wave approximation array-based method of Forsyth and Li [2005]. I also develop and adapt this method for teleseismic Love waves. This requires additional preprocessing of the data to estimate the amplitude and phase for teleseismic Love waves. Specifically, for each station, the vertical component phase observation of the fundamental mode Rayleigh is used to predict and remove the horizontal components of Rayleigh waves. Then I invert for the maximum amplitude and apparent back azimuth at each period of interest of the Love wave from the transverse and radial components. The amplitude and phase measurement is then inverted for phase velocity structure using a modified version of the two plane-wave approximation. Preliminary results indicate a low velocity region at short periods (8-15 s) in both the Rayleigh and Love wave phase velocity maps beneath the active volcanic centers in the middle of the island. At longer periods (20-125 s) a low velocity region is visible beneath central Iceland. The velocity minimum is located to the north of Iceland in the Rayleigh wave maps. These observations are consistent with previous studies in the region.

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

    SciTech Connect

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

    1990-01-01

    Characteristics of the harmonic emission from free-electron lasers (FELs) are examined in the spontaneous, coherent-spontaneous and stimulated emission regimes. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. In the spontaneous emission regime, the transverse radiation patterns including the transverse frequency dependences, are given. How this expression is modified to include energy spread and emittance is described. In the coherent-spontaneous emission and stimulated emission 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.

  14. Helicopter rotor noise due to ingestion of atmospheric turbulence

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  15. 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

    G. C. Maling Jr.

    1980-01-01

    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

  16. A comparison of low-frequency noise characteristics and noise sources in NPN and PNP InP-based heterojunction bipolar transistors

    Microsoft Academic Search

    Shawn S. H. Hsu; Dimitris Pavlidis

    2003-01-01

    Low-frequency noise characteristics of NPN and PNP InP-based heterojunction bipolar transistors (HBTs) were investigated. NPN HBTs showed a lower base noise current level (3.85 10-17 A2\\/Hz) than PNP HBTs (3.10 10-16 A2\\/Hz), but higher collector noise current level (7.16 10-16 A2\\/Hz) than PNP HBTs (1.48 10-16 A2\\/Hz) at 10 Hz under IC=1 mA, VC=1 V. The

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

    E-print Network

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

    2004-01-15

    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.

  18. Very fast blind source separation by signal to noise ratio based stopping threshold for the SHIBBS/SJAD algorithm

    NASA Astrophysics Data System (ADS)

    Liu, Xianhua; Cardoso, Jean-Francois; Randall, Robert B.

    2010-10-01

    This paper works on joint approximate diagonalization of simplified fourth order cumulant matrices for very fast and large scale blind separation of instantaneous mixing model sources. The JADE algorithm is widely accepted but only limited to small scale separation tasks. The SHIBBS algorithm calculates a fraction of the fourth order cumulant set and avoids eigenmatrix decomposition to reduce calculation cost. However, it was seen to be slower than JADE at the time of its first publication and is hence less known. On the other hand, the SJAD algorithm using the same approach is shown to be very fast. This paper studies the iteration convergence criterion and proposes to use a signal to noise ratio based iteration stopping threshold approach. The improved SHIBBS/SJAD algorithm is very fast, and capable of large scale separation. Experimental separation comparisons between the SHIBBS/SJAD and FastICA are presented.

  19. Study into sources of wagon noise: Measurement of sound energy generated by vehicle bodies and running gear

    NASA Astrophysics Data System (ADS)

    Parent de Curzon, E.; Beguet, B.

    1988-01-01

    The paper describes a series of measurements carried out to identify and quantify the sources of sound connected with the bodywork and running gear of railway wagons. Tests were conducted by the S.N.C.F. with the assistance of the METRAVIB Company, in conjunction with the programme of research of ORE Committee C 163 on Noise in the Railway Environment (Office for Research and Experiments of the International Union of Railways). Of the two methods adopted for test purposes, one was a conventional technique using a set of omnidirectional microphones placed vertically at vehicle gauge limit, and the other involved near-field interferometry based on the use of a flat acoustic antenna also placed at the edge of the track. The results of the measurements showed that for the 18 wagons of six different types studied, most of the sound energy radiated came from the running gear.

  20. Fixed-source and fixed-receiver walkaway seismic noise tests: A field comparison

    E-print Network

    Vincent, Paul D.; Tsoflias, Georgios P.; Steeples, Don W.; Sloan, Steven D.

    2006-09-21

    source-moveout as opposed to receiver-moveout F c g F Manuscript received by the Editor May 5, 2005; revised manuscript received Marc 1Chevron, 1500 Louisiana, Room 15054A, Houston, Texas 77002. E-mail: pvince 2The University of Kansas, Department...

  1. Automatic noise limiter-blanker

    NASA Technical Reports Server (NTRS)

    Burhans, R. W.

    1976-01-01

    A blanker system that may be used with audio noise limiters or automatic noise limiters was described. The system employs a pair of silicon diodes and two RC filters connected across the feedback impedance of an operational amplifier so as to counteract impulse noise interference caused by local spherics activity or 60 Hz harmonics radiated from ac motor control systems. The following information is given: circuit diagram and description, operating details, evaluation, discussion of other noise blanking methods.

  2. Virtual instrument based instrumentation for harmonic current emission measurement

    Microsoft Academic Search

    G. Mahesh; Sisir K Das; Bohy George; V. Jayashankar; V. Jagadeesh Kumar

    2003-01-01

    An instrumentation system for the measurement of harmonic emission to IEC 61000-3-2 is a subset of the general problem of harmonic measurements. A condition is derived for the SNR of a signal (with monotonically decaying harmonic amplitudes) to be zero due to quantization errors. This is enlarged to cover Gaussian noise in the analog front end of the measuring system.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  4. Marine seismics with a pulsed combustion source and Pseudo Noise codes

    Microsoft Academic Search

    Bjrn Askeland; Halvor Hobk; Rolf Mjelde

    2007-01-01

    There has been a long-standing debate concerning how dangerous seismic surveys are with respect to marine life. Marine seismic\\u000a work today is dominated by airgun technology, where high energy is generated by a release of compressed air into the water.\\u000a The objective of the Time coded impulse seismic technique project is to examine whether a new low energy acoustic source

  5. NOISE REDUCTION IN PHOTOMETRIC STEREO WITH NON-DISTANT LIGHT SOURCES

    Microsoft Academic Search

    Ryszard Kozera; Lyle Noakes

    In classical photometric stereo, a Lambertian surface is illuminated from multiple distant point light-sources. In the present paper we consider nearby lightsources instead, so that the unknown surface, is illuminated by non-parallel beams of light. In continuous noiseless cases, the recovery of a Lambertian surface from non-distant illuminations, reduces to solving a system of non-linear partial differential equations for a

  6. Effects of background noise on total noise annoyance

    NASA Astrophysics Data System (ADS)

    Willshire, K. F.

    1987-01-01

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

  7. Noise Amplification in HGHG Seeding

    SciTech Connect

    Stupakov, Gennady

    2010-08-25

    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.

  8. Noise estimation in voice signals using short-term cepstral analysis.

    PubMed

    Murphy, Peter J; Akande, Olatunji O

    2007-03-01

    Cepstral-based estimation is used to provide a baseline estimate of the noise level in the logarithmic spectrum for voiced speech. A theoretical description of cepstral processing of voiced speech containing aspiration noise, together with supporting empirical data, is provided in order to illustrate the nature of the noise baseline estimation process. Taking the Fourier transform of the liftered (filtered in the cepstral domain) cepstrum produces a noise baseline estimate. It is shown that Fourier transforming the low-pass liftered cepstrum is comparable to applying a moving average (MA) filter to the logarithmic spectrum and hence the baseline receives contributions from the glottal source excited vocal tract and the noise excited vocal tract. Because the estimation process resembles the action of a MA filter, the resulting noise baseline is determined by the harmonic resolution (as determined by the temporal analysis window length) and the glottal source spectral tilt. On selecting an appropriate temporal analysis window length the estimated baseline is shown to lie halfway between the glottal excited vocal tract and the noise excited vocal tract. This information is employed in a new harmonics-to-noise (HNR) estimation technique, which is shown to provide accurate HNR estimates when tested on synthetically generated voice signals. PMID:17407904

  9. Jet engine exhaust noise due to rough combustion and nonsteady aerodynamic sources

    NASA Technical Reports Server (NTRS)

    Plett, E. G.; Summerfield, M.

    1972-01-01

    Internal sources are accounted for in terms of fluctuations of mass and momentum at the nozzle exit plane. At low Mach numbers, mass flow fluctuations generated at the exit plane by acoustic resonant type fluctuations inside the engine are found to be dominant. In the subsonic Mach number range between 0.3 and 0.5, exit plane mass flow fluctuations at frequencies characteristic of turbulence become most dominant. Above Mach 0.5, the turbulent momentum fluctuations at the exit plane become dominant, and the jet contribution is not found significant at subsonic speeds.

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

    Microsoft Academic Search

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

    2011-01-01

    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

  11. Harmonic Mixing with an Antiparallel Diode Pair

    Microsoft Academic Search

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

    1975-01-01

    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

  12. Harmonic generation at high intensities

    SciTech Connect

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

    1993-06-01

    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.

  13. 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 ...

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

    SciTech Connect

    Kornilov, Oleg; Wilcox, Russell; Gessner, Oliver

    2010-07-09

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

  15. Prediction of the far-field beam pattern of a random noise source from measurements made in the near-field

    Microsoft Academic Search

    J. T. Sanchez

    1976-01-01

    A theory is presented for computing the far field beam patterns from distributed random noise sources. The theoretical model uses the Green's Function for the wave equation and the space-time autocorrelation function for determining the radiation from a randomly vibrating area. The actual far field beam pattern of a horn speaker in an anechoic chamber was obtained, and also near

  16. Noise induced propagation in monostable media.

    PubMed

    Zaikin, A A; Garca-Ojalvo, J; Schimansky-Geier, L; Kurths, J

    2002-01-01

    We show that external fluctuations are able to induce propagation of harmonic signals through monostable media. This property is based on the phenomenon of doubly stochastic resonance, where the joint action of multiplicative noise and spatial coupling induces bistability in an otherwise monostable extended medium, and additive noise resonantly enhances the response of the system to a harmonic forcing. Under these conditions, propagation of the harmonic signal through the unforced medium is observed for optimal intensities of the two noises. This noise-induced propagation is studied and quantified in a simple model of coupled nonlinear electronic circuits. PMID:11800929

  17. Subcriticality measurements for coupled uranium metal cylinders using the ²⁵²Cf-source-driven neutron noise analysis method

    Microsoft Academic Search

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

    1987-01-01

    Experiments performed with two coupled uranium metal cylinders are the first application to coupled systems of the ²⁵²Cf-source-driven neutron noise analysis method for obtaining the subcritical neutron multiplication factor. These coaxial cylinders were separated axially by various thicknesses of either air or borated plaster between the flat surfaces. In all measurements, the ²⁵²Cf neutron source was located at the center

  18. A compact, narrow-band, and low-noise 800-mW laser source at 980 nm

    NASA Astrophysics Data System (ADS)

    Pliska, Tomas; Matuschek, Nicolai; Troger, Joerg; Schmidt, Berthold; Mohrdiek, Stefan; Harder, Christoph

    2005-04-01

    We report on the development of a new cost-effective, small form-factor laser source at a wavelength of 980 nm. The laser module is based on proven technology commonly used for pump laser modules deployed in fiber amplifiers of telecommunication networks. The package uses a state-of-the-art 14-pin butterfly housing with a footprint of 30x15 mm2 with a Fabry-Perot AlGaAs-InGaAs pump laser diode mounted inside having an anti-reflection coating on its front facet. The light is coupled into a single-mode polarization-maintaining fiber with a mode-field diameter of 6.6 micrometer. The spectral properties of the source are defined by a fiber Bragg grating (FBG) that provides feedback in a narrow reflection band. The laser back facet and the FBG form a long resonant cavity of 1.7 m length in which laser light with a low coherence length of a few cm is generated. This configuration with the laser being operated in the coherence-collapse regime has the advantage of being robust against variations in the optical path, thus enabling stable and mode-hop free emission. The laser module has the following properties: a continuous-wave fiber output power exceeding 800 mW, a spectral bandwidth of less than 50 pm, a root-mean square power variation of less than 0.2 % from DC to 2 MHz over the entire power operating range, and a polarization extinction ratio of more than 20 dB. This is a compact, low noise, high power source for frequency conversion with nonlinear optical materials, such as blue light generation.

  19. Proceedings of Noise-con 81: Applied noise control technology

    SciTech Connect

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

    1981-01-01

    The conference was divided into sessions covering noise control regulations and benefits; noise source identification; barriers and enclosures; mufflers; hearing protection devices; textile and fibre industries; metal fabrication industry; transportation and aircraft noise control; punch-press noise control and miscellaneous topics; woodworking industry; tobacco and packaging industries; community noise; and applications of damping materials. One paper has been abstracted separately.

  20. Superconducting Tunnel Junction Noise Generator and SIS Mixers Noise Measurements

    Microsoft Academic Search

    V. Yu Belitsky; V. P. Koshelets; I. L. Serpuchenko; M. A. Tarasov; L. V. Filippenko; S. V. Shitov

    1990-01-01

    In this work the output noise calibration of cryogenically cooled low noise SIS mixers, direct detectors and IF amplifiers by means of SIS noise source was studied experimentally. Applying LO power sufficient to linearize IV curve of SIS one may vary noise temperature from 4,2 to 100 K by changing bias current. Shot noise in series arrays of SIS junctions

  1. Noise Considerations for Closed Loop Digital Accelerometers

    Microsoft Academic Search

    Elena Gaura; Michael Kraft

    This paper investigates the noise shaping properties of a sigma-delta modulator type control system applied to a micromachined accelerometer. Three noise sources are present in such an electromechanical closed loop system: mechanical noise due to Brownian motion, electronic noise introduced by the interface circuit due to thermal noise sources in the electronic devices and quantisation noise due to the analog

  2. Application of active noise control to model propeller noise

    Microsoft Academic Search

    M. Salikuddin; H. K. Tanna; R. H. Burrin; W. E. Carter

    1985-01-01

    The applicability of active noise control to reduce cabin noise of turboprop aircraft is demonstrated by conducting several laboratory experiments. The principle of active noise control is to reduce the noise radiated from a primary source by superimposing a signal from a secondary source, which is made identical in amplitude but opposite in phase to the primary sound signal. A

  3. The assessment of noise, with particular reference to aircraft

    Microsoft Academic Search

    D. W. Robinson

    1977-01-01

    The historical development of aircraft noise assessment procedures reflects a series of responses to landmarks of civil aviation punctuated by key events in noise regulation and standardization. Means for assessing other noises have followed parallel but different paths. Future trends require the harmonization of these discordant practices, for example in setting noise targets based on total environmental noise impact. A

  4. A novel phase noise suppression method for coherent detection by utilizing two adjacent longitudinal modes generated from a supercontinuum multi-wavelength source

    NASA Astrophysics Data System (ADS)

    Pan, D.; Ke, C. J.; Zhu, X. H.; Liu, D. M.

    2011-02-01

    A novel phase noise suppression method for coherent detection is proposed. It uses two adjacent longitudinal modes of a multi-wavelength source, as signal light and coherent light respectively, which are both launched into the optical fiber. And heterodyne synchronous demodulation structure is used in the receiver. The performance of a back-to-back system with 100 Gbit/s NRZ-QPSK utilizing this novel method is investigated by VPI. The simulation results show that phase noise in this coherent detection scheme is suppressed significantly, which is resulted from the correlating phase and fixed frequency spacing of adjacent longitudinal modes.

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

    NASA Astrophysics Data System (ADS)

    Li, Fu-Hai; Shirota, Riichiro

    2013-07-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.; Brown, Cliff; Walker, Bruce E.

    2014-01-01

    An Ultrasonic Configurable Fan Artificial Noise Source (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14x22 wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8% scale model. The UCFANS is a 5.8% rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial sources (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft using the projected signature of the engine currently proposed for the HWB. The modal structures at the rating points were generated from inlet and exhaust nacelle configurations - a flat plate model was used as the shielding surface and vertical control surfaces with correct plan form shapes were also tested to determine their additional impact on shielding. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 inches. Two planes perpendicular, and two planes parallel, to the axis of the nacelle were acquired from the array sweep. In each plane the linear array traversed 4 sweeps, for a total span of 168 inches acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Levels, and integrated Power Levels, from nacelle alone and shielded configurations are presented in this paper; as well as the in-duct mode power levels.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  8. Radiated noise of ducted fans

    Microsoft Academic Search

    Walter Eversman

    1992-01-01

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

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

    Microsoft Academic Search

    Vincent Mosser; Alexandre Kerlain

    2005-01-01

    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

  10. On the high-frequency noise figures of merit and microscopic channel noise sources in fabricated 90 nm PD SOI MOSFETs

    Microsoft Academic Search

    Ral Rengel; Mara J. Martn; Guillaume Pailloncy; Gilles Dambrine; Franois Danneville

    2005-01-01

    A Monte Carlo investigation of the high-frequency noise performance of 90 nm Partially-Depleted Silicon-On-Insulator MOSFETs is presented. The good agreement of the simulation results to the experimental measurements (using only the surface scattering and gate work-function as fitting parameters) confirms the reliability of the simulator as a global tool for predicting the performance of such devices. Velocity fluctuations are investigated

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  12. Inter-noise 76; Proceedings of the International Conference on Noise Control Engineering, Washington, D.C., April 5-7, 1976

    Microsoft Academic Search

    R. L. Kerlin

    1976-01-01

    The papers deal with recent developments in noise control and techniques for measuring and analyzing noise data. General topics include advanced noise-control techniques, machinery noise reduction at the source, aircraft and airport noise, noise measurement and analysis, reduction of in-plant noise exposure, rail transportation noise, noise control engineering in buildings, materials and products for noise control, traffic noise abatement, community

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

    NASA Astrophysics Data System (ADS)

    Vaks, Nir

    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.

  14. In this paper, a system is described for the recognition of mixtures of noise sources in acoustic input signals. The

    E-print Network

    Virtanen, Tuomas

    acoustic surveillance, speech processing in a noisy background, acoustic database queries, noise pollution in acoustic input signals. The problem is approached by utilizing both bottomup signal analysis and top. 1 INTRODUCTION Recognition of acoustic noise mixtures is viewed here as the detection and broad

  15. Active Control of Sound Transmission throughWindows with Carbon Nanotube based Transparent Actuators and Moving Noise Source Identification

    Microsoft Academic Search

    X. Yu; R. Rajamani; K. A. Stelson; T. Cui

    2006-01-01

    This paper explores the development of active sound transmission control systems for windows to achieve significant reduction in noise transmission. Several fundamental challenges need to be addressed in order to make the development of such noise blocking windows feasible. These include the need for a distributed actuation system that is optically transparent and the unavailability of a real-time reference signal

  16. Transcriptional Bursting from the HIV-1 Promoter is a Significant Source of Stochastic Noise in HIV-1 Gene Expression

    SciTech Connect

    Singh, A [University of California, San Diego; Razooky, B [University of California, San Diego; Cox, Chris D. [University of Tennessee, Knoxville (UTK); Simpson, Michael L [ORNL; Weinberger, Leor S. [University of California, San Diego

    2010-01-01

    Analysis of noise in gene expression has proven a powerful approach for analyzing gene regulatory architecture. To probe the regulatory mechanisms controlling expression of HIV-1, we analyze noise in gene-expression from HIV-1 s long terminal repeat (LTR) promoter at different HIV-1 integration sites across the human genome. Flow cytometry analysis of GFP expression from the HIV-1 LTR shows high variability (noise) at each integration site. Notably, the measured noise levels are inconsistent with constitutive gene expression models. Instead, quantification of expression noise indicates that HIV-1 gene expression occurs through randomly timed bursts of activity from the LTR and that each burst generates an average of 2 10 mRNA transcripts before the promoter returns to an inactive state. These data indicate that transcriptional bursting can generate high variability in HIV-1 early gene products, which may critically influence the viral fate-decision between active replication and proviral latency.

  17. Radiated noise characteristics of a modern cargo ship

    PubMed

    Arveson; Vendittis

    2000-01-01

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

  18. Harmonic Analysis

    Microsoft Academic Search

    Vladimir I Clue; William Kelleher; Anatoly Levin

    2005-01-01

    This paper describes a method of calculating the transforms, currently\\u000aobtained via Fourier and reverse Fourier transforms. The method allows\\u000acalculating efficiently the transforms of a signal having an arbitrary\\u000adimension of the digital representation by reducing the transform to a\\u000avector-to-circulant matrix multiplying. There is a connection between harmonic\\u000aequations in rectangular and polar coordinate systems. The connection\\u000aestablished

  19. Evaluation of the ²⁵²Cf-source-driven neutron noise analysis method for measuring the subcriticality of LWR fuel storage casks

    Microsoft Academic Search

    Mihalczo

    1987-01-01

    The ²⁵²Cf-source-driven neutron noise analysis method was evaluated to determine if it could be used to measure the subcriticality of storage casks of burnt LWR fuel submerged in fuel storage pools, fully loaded and as they are being loaded. The motivation for this evaluation was that measurements of k\\/sub eff\\/ would provide the parameter most directly related to the criticality

  20. Evaluation of the ²⁵²Cf-source-driven neutron noise analysis method for measuring the subcriticality of LWR fuel storage casks

    Microsoft Academic Search

    Mihalczo

    1987-01-01

    The ²⁵²Cf-source-driven neutron noise analysis method was evaluated to determine if it could be used to measure the subcriticality of storage casks of burnt light water reactor (LWR) fuel submerged in fuel storage pools, fully loaded and as they are being loaded. Measurements of k\\/sub eff\\/ would provide the parameter most directly related to the criticality safety of storage cask

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

    Microsoft Academic Search

    Edward Patrick Ficaro

    1991-01-01

    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

  2. Anatomy of a controversy: Application of the Langevin technique to the analysis of the Californium252 Source-Driven Noise Analysis method for subcriticality determination

    Microsoft Academic Search

    Stolle

    1991-01-01

    The expressions for the power spectral density of the noise equivalent sources have been calculated explicitly for the (a) stochastic transport equation, (b) the one-speed transport equaton, (c) the one-speed P equations, (d) the one-speed diffusion equation and (e) the point kinetic equation. The stochastic nature of Fick's law in (d) has been emphasized. The Langevin technique has been applied

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

    Microsoft Academic Search

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

    1986-01-01

    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

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

    SciTech Connect

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

    1984-01-01

    A total of 199 papers were presented on noise control engineering, especially in the areas of community noise control, sound intensity, noise emission sources, active sound attenuation and noise reduction by barriers. 4 papers have been abstracted separately.

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

    NASA Technical Reports Server (NTRS)

    Stimpert, D. L.; Clemons, A.

    1977-01-01

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

  6. Fourth Aircraft Interior Noise Workshop

    NASA Technical Reports Server (NTRS)

    Stephens, David G. (compiler)

    1992-01-01

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

  7. Noise sources across a normal-to-superconducting boundary in bulk YBa2Cu3O7-x

    Microsoft Academic Search

    P. Fang; J. Hall; T. M. Chen; A. J. Dekker; A. Van der Ziel

    1990-01-01

    Experiments in which a normal-to-superconducting (NS) boundary is created in an originally superconducting bar of bulk YBa2Cu 3O7-x is described. The first noise measurements associated with such a boundary are presented. A high-density (5.20 g-cm -3) sample (sample A) and a low density (4.23 g-cm-3 ) sample (sample B) have been investigated. Common to both samples is 1\\/f2 noise observed

  8. Harmonics and Resonance Issues with Wind Plants

    SciTech Connect

    Bradt, M. [IEEE PES Wind Plant Collector System Design Working Group; Badrzadeh, Babak [IEEE PES Wind Plant Collector System Design Working Group; Camm, E H [IEEE PES Wind Plant Collector System Design Working Group; Castillo, Nestor [IEEE PES Wind Plant Collector System Design Working Group; Mueller, David [IEEE PES Wind Plant Collector System Design Working Group; Siebert, T. [IEEE PES Wind Plant Collector System Design Working Group; Schoene, Jens [IEEE PES Wind Plant Collector System Design Working Group; Smith, Travis M [ORNL; Starke, Michael R [ORNL; Walling, R. [IEEE PES Wind Plant Collector System Design Working Group

    2011-01-01

    Wind plants are susceptible to lightly-damped resonances which can attract and amplify ambient grid harmonic distortion and magnify wind turbine harmonic generation. Long-accepted harmonic modeling assumptions and practices are not appropriate for wind plants. VSCs are not ideal current sources and grid impedance is important. Attention to modeling detail and thorough evaluation over range of conditions is critical to meaningful analysis. In general, wind turbines are very slight sources of harmonics. Most harmonic issues are a result of resonance, caused by capacitor banks (for reactive power compensation) or from the extensive underground cabling in a collector system. Converter controls instability can be exacerbated by power system resonances. In some cases this has caused severe voltage distorDon and other problems. The IEEE 519 recommended guidelines are very restrictive. I recommend that they are used to resolve serious harmonic issues, and not to create petty problems.

  9. Aircraft noise prediction program theoretical manual, part 2

    NASA Technical Reports Server (NTRS)

    Zorumski, W. E.

    1982-01-01

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

  10. Aircraft noise prediction program theoretical manual, part 2

    NASA Astrophysics Data System (ADS)

    Zorumski, W. E.

    1982-02-01

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

  11. Aircraft interior noise reduction by alternate resonance tuning

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

  12. Electromagnetic films as lightweight actuators for active noise reduction

    Microsoft Academic Search

    Delf Sachau; Thomas Kletschkowski

    2006-01-01

    The increasing industrialization and markets across the globe do result in noise pollution that affects humans. In order to reduce the sound pressure level (SPL) of disturbing noise active noise control (also known as noise cancellation, active noise reduction (ANR) or anti-noise) is a good option. Herewith unwanted noise from a primary sound source can be reduced significantly by anti-noise

  13. Harmonic engine

    DOEpatents

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

    2014-08-19

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

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

    PubMed

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

    2014-06-01

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

  15. Ultrafast demagnetization dynamics at the M edges of magnetic elements observed using a tabletop high-harmonic soft x-ray source.

    PubMed

    La-O-Vorakiat, Chan; Siemens, Mark; Murnane, Margaret M; Kapteyn, Henry C; Mathias, Stefan; Aeschlimann, Martin; Grychtol, Patrik; Adam, Roman; Schneider, Claus M; Shaw, Justin M; Nembach, Hans; Silva, T J

    2009-12-18

    We use few-femtosecond soft x-ray pulses from high-harmonic generation to extract element-specific demagnetization dynamics and hysteresis loops of a compound material for the first time. Using a geometry where high-harmonic beams are reflected from a magnetized Permalloy grating, large changes in the reflected intensity of up to 6% at the M absorption edges of Fe and Ni are observed when the magnetization is reversed. A short pump pulse is used to destroy the magnetic alignment, which allows us to measure the fastest, elementally specific demagnetization dynamics, with 55 fs time resolution. The use of high harmonics for probing magnetic materials promises to combine nanometer spatial resolution, elemental specificity, and femtosecond-to-attosecond time resolution, making it possible to address important fundamental questions in magnetism. PMID:20366281

  16. Noise reduction experience at Hughes Helicopter, Inc.

    NASA Technical Reports Server (NTRS)

    Janakiram, D. S.

    1982-01-01

    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).

  17. Harmonization of Investment Valuation Standards in Europe

    Microsoft Academic Search

    Clare Eriksson; Alastair Adair; Stanley McGreal; James R. Webb

    The harmonization of valuation standards in Europe is attracting increasing interest from several sources, but little empirical research has been undertaken on the subject. This study reports the findings of an investigation across four European countries. The focus is placed upon arguments relating to the possible implementation of harmonized standards, a comparison of national standards and an evaluation of The

  18. Inlet noise on 0.5-meter-diameter NASA QF1 fan as measured in an unmodified compressor aerodynamic test facility and in an anechoic chamber

    Microsoft Academic Search

    T. F. Gelder; R. F. Soltis

    1975-01-01

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

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

    Microsoft Academic Search

    Anthony Grard; Alain Berry; Patrice Masson

    2005-01-01

    An inverse method is investigated to evaluate the unsteady rotating forces (dipole strength distribution) acting by the fan on the fluid from far-field acoustic pressure measurements. A development based on the tonal noise generated by a propeller is used to derive a discretized form of the direct problem. The inversion of this direct problem is ill-posed and requires optimization technique

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

    Microsoft Academic Search

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

    2003-01-01

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

  1. Combustion and core noise

    NASA Astrophysics Data System (ADS)

    Mahan, J. Robert; Karchmer, Allen

    1991-08-01

    Two types of aircraft power plant are considered: the gas turbine and the reciprocating engine. The engine types considered are: the reciprocating engine, the turbojet engine, the turboprop engine, and the turbofan engine. Combustion noise in gas turbine engines is discussed, and reciprocating-engine combustion noise is also briefly described. The following subject areas are covered: configuration variables, operational variables, characteristics of combustion and core noise, sources of combustion noise, combustion noise theory and comparison with experiment, available prediction methods, diagnostic techniques, measurement techniques, data interpretation, and example applications.

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

    PubMed

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

    2015-04-01

    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

  3. Noise spectrum of pulse excited fluxgate sensor

    Microsoft Academic Search

    Jan Kubik; Pavel Ripka

    2006-01-01

    A low-cost flat miniature fluxgate magnetic field sensor is excited by short current pulses in order to reduce the power consumption. In this mode, the output signal contains very rich spectrum of even harmonics, each of them being sensitive to the measured field. The noise spectrum of individual harmonics, both in the untuned and tuned modes, was measured. The output

  4. Improved noise reduction in single fiber auditory neural responses using template subtraction.

    PubMed

    Woo, Jihwan; Miller, Charles A; Abbas, Paul J; Hong, Sung Hwa; Kim, In Young

    2006-09-15

    When recording single-unit responses from neural systems, a common problem is the accurate detection of spikes (action potentials) in the presence of competing unwanted (noise) signals. While some sources of noise can be readily dealt with through filtering or established "template subtraction" techniques, other sources present a more difficult problem. In particular, noise components introduced by power supplies, which contain harmonics of the power-line frequency, can be particularly troublesome in that they can mimic the shape of the desired spikes. The aforementioned standard techniques typically fail to effectively deal with such "noise". In this study, we propose the use of a novel template-subtraction scheme that involves estimating the power-line noise waveform and using cross-correlation techniques to subtract it from the recordings. This technique requires two key steps: (1) cross-correlation analysis of each recorded waveform to extract a robust representation of the power-line noise waveform and (2) a second level of cross-correlation to successfully subtract that representation from each recorded waveform. This paper describes this algorithm and provides examples of its implementation using actual recorded waveforms that were contaminated with these power-line noise signals. An improvement (reduction) in the noise level is reported, as are suggestions for future implementation of this strategy. PMID:16490259

  5. Spatial filtering of magnetoencephalographic data in spherical harmonics domain

    NASA Astrophysics Data System (ADS)

    Ozkurt, Tolga Esat

    We introduce new spatial filtering methods in the spherical harmonics domain for constraining magnetoencephalographic (MEG) multichannel measurements to user-specified spherical regions of interests (ROI) inside the head. The main idea of the spatial filtering is to emphasize those signals arising from an ROI, while suppressing the signals coming from outside the ROI. We exploit a well-known method called the signal space separation (SSS), which can decompose MEG data into a signal component generated by neurobiological sources and a noise component generated by external sources outside the head. The novel methods presented in this work, expanded SSS (exSSS) and generalized expanded SSS (genexSSS) utilize a beamspace optimization criterion in order to linearly transform the inner signal SSS coefficients to represent the sources belonging to the ROI. The filters mainly depend on the radius and the center of the ROI. The simplicity of the derived formulations of our methods stems from the natural appropriateness to spherical domain and orthogonality properties of the SSS basis functions that are intimately related to the vector spherical harmonics. Thus, unlike the traditional MEG spatial filtering techniques, exSSS and genexSSS do not need any numerical computation procedures on discretized headspace. The validation and performance of the algorithms are demonstrated by experiments utilizing both simulated and real MEG data.

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

    E-print Network

    Bhattad, Kapil

    2008-10-10

    We study the problem of communicating a discrete time analog source over a channel such that the resulting distortion is minimized. For ergodic channels, Shannon showed that separate source and channel coding is optimal. ...

  7. Noise Analysis of a Millimeter-Wave Photoreceiver and Noise Performance Improvement

    E-print Network

    Haddadi, Hamed

    noise sources need to be found. Two noise sources are considered: 1. Shot noise generatedNoise Analysis of a Millimeter-Wave Photoreceiver and Noise Performance Improvement S.R.Magazov and N.J.Gomes Photonics Group, Electronic Engineering Laboratory, University of Kent, Canterbury

  8. Development of an impulsive noise source to study the acoustic reflection characteristics of hard-walled wind tunnels

    Microsoft Academic Search

    M. Salikuddin; R. H. Burrin; K. K. Ahuja; H. W. Bartel

    1986-01-01

    Two impulsive sound sources, one using multiple acoustic drivers and the other using a spark discharge were developed to study the acoustic reflection characteristics of hard-walled wind tunnels, and the results of laboratory tests are presented. The analysis indicates that though the intensity of the pulse generated by the spark source was higher than that obtained from the acoustic source,

  9. Active Interior Noise Control Studies

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

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

  10. Analysis of spectra of acoustical signals at the outlet of a nonlinear system under the action of the sum of the harmonic sources

    NASA Technical Reports Server (NTRS)

    Sverkunov, Y. D.

    1973-01-01

    The establishment of specific relations between components of the spectra at the outlet of a nonlinear system are discussed for simplifying the analysis of noise and vibration for an internal combustion engine.

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

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.

    2014-01-01

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

  12. Degradation in finite-harmonic subcarrier demodulation

    NASA Technical Reports Server (NTRS)

    Feria, Y.; Townes, S.; Pham, T.

    1995-01-01

    Previous estimates on the degradations due to a subcarrier loop assume a square-wave subcarrier. This article provides a closed-form expression for the degradations due to the subcarrier loop when a finite number of harmonics are used to demodulate the subcarrier, as in the case of the buffered telemetry demodulator. We compared the degradations using a square wave and using finite harmonics in the subcarrier demodulation and found that, for a low loop signal-to-noise ratio, using finite harmonics leads to a lower degradation. The analysis is under the assumption that the phase noise in the subcarrier (SC) loop has a Tikhonov distribution. This assumption is valid for first-order loops.

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

    PubMed

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

    2010-02-01

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

  14. Noise in miniature microphones.

    PubMed

    Thompson, Stephen C; LoPresti, Janice L; Ring, Eugene M; Nepomuceno, Henry G; Beard, John J; Ballad, William J; Carlson, Elmer V

    2002-02-01

    The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed. PMID:11863188

  15. Noise in miniature microphones

    NASA Astrophysics Data System (ADS)

    Thompson, Stephen C.; Lopresti, Janice L.; Ring, Eugene M.; Nepomuceno, Henry G.; Beard, John J.; Ballad, William J.; Carlson, Elmer V.

    2002-02-01

    The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed.

  16. Approximations to camera sensor noise

    NASA Astrophysics Data System (ADS)

    Jin, Xiaodan; Hirakawa, Keigo

    2013-02-01

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

  17. New marine harmonic standards

    Microsoft Academic Search

    Tony Hoevenaars; Ian Evans; Andy Lawson

    2010-01-01

    To address concerns associated with electrical power system harmonic distortion on ships and offshore oil rigs and platforms, marine regulating bodies have introduced strict new harmonic standards. These standards define the acceptable level of harmonic voltage distortion allowed on the vessels they certify. High-harmonic distortion levels are appearing as a result of the increased use of power-electronic drive converters for

  18. Core-Noise Research

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.

    2012-01-01

    This presentation is a technical summary of and outlook for NASA-internal and NASA-sponsored external research on core noise funded by the Fundamental Aeronautics Program Subsonic Fixed Wing (SFW) Project. Sections of the presentation cover: the SFW system-level noise metrics for the 2015 (N+1), 2020 (N+2), and 2025 (N+3) timeframes; SFW strategic thrusts and technical challenges; SFW advanced subsystems that are broadly applicable to N+3 vehicle concepts, with an indication where further noise research is needed; the components of core noise (compressor, combustor and turbine noise) and a rationale for NASA's current emphasis on the combustor-noise component; the increase in the relative importance of core noise due to turbofan design trends; the need to understand and mitigate core-noise sources for high-efficiency small gas generators; and the current research activities in the core-noise area, with additional details given about forthcoming updates to NASA's Aircraft Noise Prediction Program (ANOPP) core-noise prediction capabilities, two NRA efforts (Honeywell International, Phoenix, AZ and University of Illinois at Urbana-Champaign, respectively) to improve the understanding of core-noise sources and noise propagation through the engine core, and an effort to develop oxide/oxide ceramic-matrix-composite (CMC) liners for broadband noise attenuation suitable for turbofan-core application. Core noise must be addressed to ensure that the N+3 noise goals are met. Focused, but long-term, core-noise research is carried out to enable the advanced high-efficiency small gas-generator subsystem, common to several N+3 conceptual designs, needed to meet NASA's technical challenges. Intermediate updates to prediction tools are implemented as the understanding of the source structure and engine-internal propagation effects is improved. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The SFW Quiet-Aircraft Subproject aims to develop concepts and technologies to reduce perceived community noise attributable to aircraft with minimal impact on weight and performance. This reduction of aircraft noise is critical to enabling the anticipated large increase in future air traffic.

  19. Nonlinearly driven harmonics of Alfvn modes

    SciTech Connect

    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

    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 Alfvn Eigenmode. The solution of the resultant equation gives the second order harmonic response. Preliminary results are presented here.

  20. Thermal Noise of Epoxies

    NASA Astrophysics Data System (ADS)

    Fair, Hannah; Harry, Gregory; Newport, Jonathan; Penn, Steve

    2015-04-01

    Interferometric precision optical measurement is a powerful tool for investigating the smallest of physical phenomena. Examples of this include gravitational wave detection, precision spectroscopy, and laser ring gyroscopes. The limiting noises sources include thermal fluctuations from optical materials and structures. Epoxies can be used to construct hardware for these experiments, which can significantly contribute to the thermal noise. At American University, we are investigating the elastic properties of various epoxies to better predict thermal noise.

  1. Room-Temperature $\\\\lambda\\\\approx 2.7~\\\\mu{\\\\rm m}$ Quantum Cascade Laser Sources Based on Intracavity Second-Harmonic Generation

    Microsoft Academic Search

    Augustinas Vizbaras; Matthias Anders; Simeon Katz; Christian Grasse; Gerhard Boehm; Ralf Meyer; Mikhail A. Belkin; Markus-Christian Amann

    2011-01-01

    We present experimental results on a short- wavelength quantum cascade laser based on intracavity second- harmonic generation. Our devices consist of an injectorless quan- tum cascade laser, which serves as a pump, and a transversely integrated passive two-well nonlinear section. The presented devices demonstrate above 1 mW output power at 2.65 me mis- sion wavelength with a record high

  2. Detection of volatile and soluble general anesthetics using a fluorescence-based fiber optic sensor: recent progress in chemical sensitivity and noise sources

    NASA Astrophysics Data System (ADS)

    Yager, Paul; Abrams, Susan B.

    1992-04-01

    A fiber optic sensor for general anesthetics based on the phase transition of immobilized phospholipid vesicles is under development. Current work centers on evaluating the sensor response to different anesthetics and instrumentation design. The fluorescence of laurdan- doped liposomes is found to respond linearly to the infusible anesthetics thiopental sodium and Propofol. Preliminary experiments have been performed to determine sources of noise in the optical and electronic components of the sensor as it is now configured. One potential noise source is the liposome sample at the fiber tip; photobleaching and thermal fluctuations due to heating by the illuminating 360 nm radiation can affect measurement of the anesthetic level. Heating of the sample is a factor at high illumination levels, but photobleaching, which reduces the signal intensity, does not alter the intensity ratio upon which the anesthetic concentration measurement is based. Optical microscopy of fiber tips embedded in liposomes allows direct observation of the light intensity near the tip of the fiber despite the extreme turbidity of the suspension. Light intensity drops to less than 10% of its maximum intensity at the fiber tip within 300 micrometers . Further use of this technique should allow monitoring the effects of photobleaching on the spatial distribution of the liposomes responsible for the measured optical signal.

  3. Analysis of individual machine noise in construction (2)

    Microsoft Academic Search

    Hiroshi Yoshinaga; Hiroshi Yamamoto; Akira Hayashi; Kiyoshi Yoshida

    2006-01-01

    Numerous machines used to execute public works projects produce noise, and in the past noise measurements were performed assuming project noise is produced by a single sound source. But to perform practical noise prediction, the quantity of noise from each machine must be obtained. The authors analyzed simulated noise in semi-anechoic room and outdoor construction machinery noise with a straight

  4. 5th International Meeting Wind Turbine Noise

    E-print Network

    Paris-Sud XI, Universit de

    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

  5. FDTD analysis of noise radiation and propagation

    Microsoft Academic Search

    N. H. Younan; C. D. Taylor; M. R. Zunoubi

    2000-01-01

    The analysis of effects from noise illumination of electrical and electronic systems is complicated by stochastic rather than deterministic variables. An analysis technique is presented for noise propagation, where the noise is modeled as a time series of discrete time impulses with amplitudes computed by a white Gaussian noise simulation. Using the noise source to simulate the drive of an

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

    SciTech Connect

    Lotz, R.

    1986-01-01

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

  7. 328 IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING, VOL. 8, NO. 2, MARCH 2000 Noise Source Models for Fricative Consonants

    E-print Network

    Alwan, Abeer

    the acoustics in the vocal tract [4], [8], [23]. In this study, a timedomain simulation method of acoustic a combination of acoustic monopole and distributed dipole sources, and a voice source in the case of the voiced levels are chosen based on an analysis-by-synthesis approach and are motivated by aeroacoustic theory

  8. Effects of frequency separation in periodic active noise control systems

    Microsoft Academic Search

    Sen M. Kuo; Ajay B. Puvvala

    2006-01-01

    In many practical active noise control (ANC) applications, the primary noise contains multiple closely-spaced harmonics. A narrow-band feedforward ANC system consists of an adaptive filter excited by a composite reference signal, which is the sum of multiple sinusoids corresponding to the harmonic frequencies of the primary noise. This paper analyzes and shows that the convergence of this direct-form controller is

  9. Updated Noise Regulations in New York City

    Microsoft Academic Search

    Weixiong Wu

    New York City has three types of noise regulations for evaluating noise impacts, each promulgated by a different authority and dealing with different types of noise sources (mobile traffic, rail, aircraft, construction, and stationary sources). These regulations are the New York City Noise Code 1

  10. Effect of centerbody scattering on propeller noise

    Microsoft Academic Search

    Stewart A. L. Glegg

    1991-01-01

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

  11. High order harmonic generation in rare gases

    SciTech Connect

    Budil, K.S.

    1994-05-01

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

  12. Color harmonization for images

    NASA Astrophysics Data System (ADS)

    Tang, Zhen; Miao, Zhenjiang; Wan, Yanli; Wang, Zhifei

    2011-04-01

    Color harmonization is an artistic technique to adjust a set of colors in order to enhance their visual harmony so that they are aesthetically pleasing in terms of human visual perception. We present a new color harmonization method that treats the harmonization as a function optimization. For a given image, we derive a cost function based on the observation that pixels in a small window that have similar unharmonic hues should be harmonized with similar harmonic hues. By minimizing the cost function, we get a harmonized image in which the spatial coherence is preserved. A new matching function is proposed to select the best matching harmonic schemes, and a new component-based preharmonization strategy is proposed to preserve the hue distribution of the harmonized images. Our approach overcomes several shortcomings of the existing color harmonization methods. We test our algorithm with a variety of images to demonstrate the effectiveness of our approach.

  13. Harness processes and harmonic crystals

    E-print Network

    Pablo A. Ferrari; Beat M. Niederhauser

    2006-01-04

    In the Hammersley harness processes the real-valued height at each site i in Z^d is updated at rate 1 to an average of the neighboring heights plus a centered random variable (the noise). We construct the process "a la Harris" simultaneously for all times and boxes contained in Z^d. With this representation we compute covariances and show L^2 and almost sure time and space convergence of the process. In particular, the process started from the flat configuration and viewed from the height at the origin converges to an invariant measure. In dimension three and higher, the process itself converges to an invariant measure in L^2 at speed t^{1-d/2} (this extends the convergence established by Hsiao). When the noise is Gaussian the limiting measures are Gaussian fields (harmonic crystals) and are also reversible for the process.

  14. Noise equivalent circuit of a semiconductor laser diode

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

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

    E-print Network

    E. A. Huerta; Sean T. McWilliams; Jonathan R. Gair; Stephen R. Taylor

    2015-04-03

    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.

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

    E-print Network

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

    2008-10-02

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

  17. Noise and coherence in optical image processing. II - Noise fluctuations

    Microsoft Academic Search

    Pierre Chavel; Serge Lowenthal

    1978-01-01

    Fluctuations in image illuminance resulting from various sources of optical noise are studied as a function of the spatial coherence of the illumination. It is shown that noise fluctuations caused by the pupil plane can be reduced considerably by using incoherent, or even partially coherent, rather than coherent illumination. Conversely, noise caused by defects in the object plane is not

  18. PSCz-1.2 Jy Comparison: A Spherical Harmonics Approach

    E-print Network

    Luis Teodoro; Enzo Branchini; Carlos Frenk; Will Saunders; Seb Oliver; Oliver Keeble; Michael Rowan-Robinson; Steve Maddox; George Efstathiou; Will Sutherland; Simon White

    1999-08-31

    We perform a detailed comparison of the IRAS PSCz and 1.2-Jy spherical harmonic coefficients of the density and velocity fields in redshift space. The monopole terms predicted from the two surveys show some differences. The mismatch between the velocity monopoles arises from faint sources and disappears when extracting a PSCz subsample of galaxies with fluxes larger than 1.2 Jy. The analysis of PSCz dipole moments confirms the same inconsistencies found by Davis, Nusser and Willick (1996) between the IRAS 1.2-Jy gravity field and MARK III peculiar velocities. We conclude that shot-noise, which is greatly reduced in our PSCz gravity field, cannot be responsible for the observed mismatch.

  19. Foraging bats avoid noise.

    PubMed

    Schaub, Andrea; Ostwald, Joachim; Siemers, Bjrn M

    2008-10-01

    Ambient noise influences the availability and use of acoustic information in animals in many ways. While much research has focused on the effects of noise on acoustic communication, here, we present the first study concerned with anthropogenic noise and foraging behaviour. We chose the greater mouse-eared bat (Myotis myotis) as a model species because it represents the especially vulnerable group of gleaning bats that rely on listening for prey rustling sounds to find food (i.e. 'passive listening'). In a choice experiment with two foraging compartments, we investigated the influence of background noise on foraging effort and foraging success. We tested the hypotheses that: (1) bats will avoid foraging areas with particularly loud background noise; and (2) the frequency-time structure of the noise will determine, in part, the degree to which it deters bats. We found a clear effect of the type of noise on the allocation of foraging effort to the compartments and on the distribution of prey capture events. When playing back silence, the bats made equal use of and were equally successful in both compartments. In the other three treatments (where a non-silent sound was played back), the bats avoided the playback compartment. The degree to which the background noise deterred bats from the compartment increased from traffic noise to vegetation movement noise to broadband computer-generated noise. Vegetation noise, set 12 dB below the traffic noise amplitude, had a larger repellent effect; presumably because of its acoustic similarity with prey sounds. Our experimental data suggest that foraging areas very close to highways and presumably also to other sources of intense, broadband noise are degraded in their suitability as foraging areas for such 'passive listening' bats. PMID:18805817

  20. Mitigation of calorimeter noise.

    SciTech Connect

    Santi, P. A. (Peter A.); Bracken, D. S. (David S.); Smith, M. K. (Morag K.)

    2004-01-01

    One of the main factors that limit the sensitivity of calorimeters is the noise in the calorimeter response. A previous study into the sources of noise in a Wheatstone bridge calorimeter used by Department of Energy (DOE) facilities has shown that the control system for maintaining the water bath at a constant temperature was an important contributor to the noise in the system. In order to minimize the contribution that the control system makes to the noise in the calorimeter response, a new control system for the calorimeter has been developed. An experimental and analytical study has been performed to determine the effectiveness of this new control system in reducing the response noise in a Wheatstone bridge calorimeter. The results of this study are presented along with their implications for future work in minimizing the equilibrium noise of calorimeters.