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Sample records for phase noise measurements

  1. A Gaussian measure of quantum phase noise

    NASA Technical Reports Server (NTRS)

    Schleich, Wolfgang P.; Dowling, Jonathan P.

    1992-01-01

    We study the width of the semiclassical phase distribution of a quantum state in its dependence on the average number of photons (m) in this state. As a measure of phase noise, we choose the width, delta phi, of the best Gaussian approximation to the dominant peak of this probability curve. For a coherent state, this width decreases with the square root of (m), whereas for a truncated phase state it decreases linearly with increasing (m). For an optimal phase state, delta phi decreases exponentially but so does the area caught underneath the peak: all the probability is stored in the broad wings of the distribution.

  2. Phase noise measurement of phase modulation microwave photonic links

    NASA Astrophysics Data System (ADS)

    Ye, Quanyi; Chen, Zhengyu; Xu, Zhiguo; Gao, Yingjie

    2015-10-01

    Microwave photonic links (MPLs) can provide many advantages over traditional coaxial and waveguide solutions due to its low loss, small size, lightweight, large bandwidth, superior stability and immunity to external interference. It has been considered in various applications such as: the transmission of radio frequency (RF) signal over optical carriers, video television transmission, radar and communication systems. Stability of phase of the microwave photonic links is a critical issue in several realistic applications. The delay line technique for phase noise measurement of phase modulation microwave photonic links is measured for the first time. Using this approach, the input signal noise and power supply noise can be effectively cancelled, and it does not require phase locking. The phase noise of a microwave photonic links with a 10 GHz sinusoidal signal is experimentally demonstrated.

  3. Phase Noise Measurement in PEP II and the Linac

    SciTech Connect

    Getaneh, Mesfin

    2003-09-05

    The Goal of this project is to provide a measurement of the phase of the radio frequency (RF) relative to electron beam traveling down the Stanford Linear Accelerator Center (SLAC). Because the Main Drive Line (MDL) supplies the RF drive and phase reference for the entire accelerator system, the phase accuracy and amount of phase noise present in the MDL are very critical to the functionality of the accelerator. Therefore, a Phase Noise Measurement System was built to measure the phase noise in the liner accelerator (Linac) and PEP II. The system was used to determine the stability of the PEP II RF reference system. In this project a low noise Phase Locked Loop system (PLL) was built to measure timing jitter about sub picoseconds level. The phase noise measured in Master Oscillator using PLL indicates that phase noise is low enough for PEP II to run.

  4. Phase-Noise and Amplitude-Noise Measurement of Low-Power Signals

    NASA Technical Reports Server (NTRS)

    Rubiola, Enrico; Salik, Ertan; Yu, Nan; Maleki, Lute

    2004-01-01

    Measuring the phase fluctuation between a pair of low-power microwave signals, the signals must be amplified before detection. In such cases the phase noise of the amplifier pair is the main cause of 1/f background noise of the instrument. this article proposes a scheme that makes amplification possible while rejecting the close in 1/f (flicker) noise of the two amplifiers. Noise rejection, which relies upon the understanding of the amplifier noise mechanism does not require averaging. Therefore, our scheme can also be the detector of a closed loop noise reduction system. the first prototype, compared to a traditional saturated mixer system under the same condition, show a 24 dB noise reduction of the 1/f region.

  5. A novel phase noise measurement of phase modulation microwave photonic links

    NASA Astrophysics Data System (ADS)

    Ye, Quanyi; Gao, Yingjie; Yang, Chun

    2016-07-01

    Microwave photonic links can provide many advantages over traditional coaxial due to its low loss, small size, lightweight, large bandwidth and immunity to external interference. In this paper, a novel phase noise measurement system is built, since the input signal and the power supply noise can be effectively cancelled by a two-arm configuration without the phase locking. Using this approach, the phase noise performance of the 10-GHz phase modulation photonic link has been measured for the first time, evaluated the values of -124 dBc/Hz at 1 kHz offset and -132 dBc/Hz at 10 kHz offset is obtained. Theoretical analysis on the phase noise measurement system calibration is also discussed.

  6. Does measurement noise increase as a phase transition is approached?

    NASA Astrophysics Data System (ADS)

    Chen, Zhi; Yu, Clare C.

    2007-06-01

    We study the energy and magnetization noise spectra associated with first and second order phase transitions by using Monte Carlo simulations of the Ising model and 5-state Potts model in 2D. For a finite size system, the total noise power and the low frequency white noise S(f < f knee) increase as T c is approached. In the thermodynamic limit S(f < f knee) diverges but f knee --> 0 and the total noise power vanishes. f -1 knee is approximately the equilibration time. At high frequencies S(f > f knee) ~ f -μ. For the Ising model, we relate μ to the critical exponents.

  7. Experimental clean combustor program noise measurement addendum, phase 1

    NASA Technical Reports Server (NTRS)

    Emmerling, J. J.

    1975-01-01

    The test results of combustor noise measurements taken with waveguide probes are presented. Waveguide probes were shown to be a viable measurement technique for determining high sound pressure level broadband noise. A total of six full-scale annular combustors were tested and included the three advanced combustor designs: swirl-can, radial/axial, and double annular.

  8. Residual phase noise measurements of the input section in a receiver

    SciTech Connect

    Mavric, Uros; Chase, Brian; /Fermilab

    2007-10-01

    If not designed properly, the input section of an analog down-converter can introduce phase noise that can prevail over other noise sources in the system. In the paper we present residual phase noise measurements of a simplified input section of a classical receiver that is composed of various commercially available mixers and driven by an LO amplifier.

  9. Frequency-resolved noise figure measurements of phase (in)sensitive fiber optical parametric amplifiers.

    PubMed

    Malik, R; Kumpera, A; Lorences-Riesgo, A; Andrekson, P A; Karlsson, M

    2014-11-17

    We measure the frequency-resolved noise figure of fiber optical parametric amplifiers both in phase-insensitive and phase-sensitive modes in the frequency range from 0.03 to 3 GHz. We also measure the variation in noise figure due to the degradation in pump optical signal to noise ratio and also as a function of the input signal powers. Noise figure degradation due to stimulated Brillouin scattering is observed.

  10. Experimental clean combustor program; noise measurement addendum, Phase 2

    NASA Technical Reports Server (NTRS)

    Emmerling, J. J.; Bekofske, K. L.

    1976-01-01

    Combustor noise measurements were performed using wave guide probes. Test results from two full scale annular combustor configurations in a combustor test rig are presented. A CF6-50 combustor represented a current design, and a double annular combustor represented the advanced clean combustor configuration. The overall acoustic power levels were found to correlate with the steady state heat release rate and inlet temperature. A theoretical analysis for the attenuation of combustor noise propagating through a turbine was extended from a subsonic relative flow condition to include the case of supersonic flow at the discharge side. The predicted attenuation from this analysis was compared to both engine data and extrapolated component combustor data. The attenuation of combustor noise through the CF6-50 turbine was found to be greater than 14 dB by both the analysis and the data.

  11. Measurement-Noise Maximum as a Signature of a Phase Transition

    NASA Astrophysics Data System (ADS)

    Chen, Zhi; Yu, Clare C.

    2007-02-01

    We propose that a maximum in measurement noise can be used as a signature of a phase transition. As an example, we study the energy and magnetization noise spectra associated with first- and second-order phase transitions by using Monte Carlo simulations of the Ising model and 5-state Potts model in two dimensions. For a finite size system, the total noise power and the low frequency white noise S(fnoise power vanishes. fknee-1 is approximately the equilibration time.

  12. Low noise buffer amplifiers and buffered phase comparators for precise time and frequency measurement and distribution

    NASA Technical Reports Server (NTRS)

    Eichinger, R. A.; Dachel, P.; Miller, W. H.; Ingold, J. S.

    1982-01-01

    Extremely low noise, high performance, wideband buffer amplifiers and buffered phase comparators were developed. These buffer amplifiers are designed to distribute reference frequencies from 30 KHz to 45 MHz from a hydrogen maser without degrading the hydrogen maser's performance. The buffered phase comparators are designed to intercompare the phase of state of the art hydrogen masers without adding any significant measurement system noise. These devices have a 27 femtosecond phase stability floor and are stable to better than one picosecond for long periods of time. Their temperature coefficient is less than one picosecond per degree C, and they have shown virtually no voltage coefficients.

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

    PubMed

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

    2015-04-01

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

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

    PubMed

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

    2015-04-01

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

  15. Quantum phase noise reduction in soliton collisions and application to nondemolition measurements

    SciTech Connect

    Rand, Darren; Prucnal, Paul R.; Steiglitz, Ken

    2005-10-15

    We show that soliton collisions can reduce propagation-induced quantum phase noise. This effect originates from a negative correlation between self- and cross-phase-modulation-induced phase fluctuations. Furthermore, we show how this effect can be applied directly to improve the quality of soliton-based quantum nondemolition measurements, simply by adjusting the parameter regime in which the measurement is performed. Optimal implementation, which we show to be technologically feasible, favors short propagation distances, small wavelength separation between solitons, and approximately equal soliton amplitudes.

  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. Truly random number generation based on measurement of phase noise of a laser.

    PubMed

    Guo, Hong; Tang, Wenzhuo; Liu, Yu; Wei, Wei

    2010-05-01

    We present a simple approach to realize truly random number generator based on measuring the phase noise of a single-mode vertical cavity surface emitting laser. The true randomness of the quantum phase noise originates from the spontaneous emission of photons and the random bit generation rate is ultimately limited only by the laser linewidth. With the final bit generation rate of 20 Mbit/s, the truly random bit sequence guaranteed by the uncertainty principle of quantum mechanics passes the three standard randomness tests (ENT, Diehard, and NIST Statistical Test Suites). Moreover, a continuously generated random bit sequence, with length up to 14 Gbit, is verified by two additional criteria for its true randomness.

  18. Simple digital phase-measuring algorithm for low-noise heterodyne interferometry

    NASA Astrophysics Data System (ADS)

    Kokuyama, Wataru; Nozato, Hideaki; Ohta, Akihiro; Hattori, Koichiro

    2016-08-01

    We present a digital algorithm for measuring the phase of a sinusoidal signal that combines the modified digital fringe-counting method with two-sample zero crossing to enable sequential signal processing. This technique can be applied to a phase meter for measuring dynamic phase differences between two sinusoidal signals with high resolution, particularly for heterodyne interferometry. The floor noise obtained from a demonstration with an electrical apparatus is 5× {{10}-8} \\text{rad}\\text{/}{{\\sqrt{\\text{Hz}}}{}} at frequencies above approximately 0.1 Hz for 80 kHz signal frequency. In addition, by applying this method to a commercial heterodyne interferometer with a modulation frequency of 80 MHz, the floor-noise level is confirmed to be 7× {{10}-14}\\text{m}\\text{/}{{\\sqrt{\\text{Hz}}}{}} from 4 kHz to 1 MHz. We also confirm the validity of the algorithm by comparing its results with those from a standard homodyne interferometer for measuring shock-motion peak acceleration greater than 5000 \\text{m} {{\\text{s}}-2} and a 10 mm stroke.

  19. Passive coherent discriminator using phase diversity for the simultaneous measurement of frequency noise and intensity noise of a continuous-wave laser

    NASA Astrophysics Data System (ADS)

    Michaud-Belleau, V.; Bergeron, H.; Light, P. S.; Hébert, N. B.; Deschênes, J. D.; Luiten, A. N.; Genest, J.

    2016-10-01

    The frequency noise and intensity noise of a laser set the performance limits in many modern photonics applications and, consequently, must often be characterized. As lasers continue to improve, the measurement of these noises however becomes increasingly challenging. Current approaches for the characterization of very high-performance lasers often call for a second laser with equal or higher performance to the one that is to be measured, an incoherent interferometer having an extremely long delay-arm, or an interferometer that relies on an active device. These instrumental features can be impractical or problematic under certain experimental conditions. As an alternative, this paper presents an entirely passive coherent interferometer that employs an optical 90° hybrid coupler to perform in-phase and quadrature detection. We demonstrate the technique by measuring the frequency noise power spectral density of a highly-stable 192 THz (1560 nm) fiber laser over five frequency decades. Simultaneously, we are able to measure its relative intensity noise power spectral density and characterize the correlation between its amplitude noise and phase noise. We correct some common misconceptions through a detailed theoretical analysis and demonstrate the necessity to account for normal imperfections of the optical 90° hybrid coupler. We finally conclude that this passive coherent discriminator is suitable for reliable and simple noise characterization of highly-stable lasers, with bandwidth and dynamic range benefits but susceptibility to additive noise contamination.

  20. Quantum phase slip noise

    NASA Astrophysics Data System (ADS)

    Semenov, Andrew G.; Zaikin, Andrei D.

    2016-07-01

    Quantum phase slips (QPSs) generate voltage fluctuations in superconducting nanowires. Employing the Keldysh technique and making use of the phase-charge duality arguments, we develop a theory of QPS-induced voltage noise in such nanowires. We demonstrate that quantum tunneling of the magnetic flux quanta across the wire yields quantum shot noise which obeys Poisson statistics and is characterized by a power-law dependence of its spectrum SΩ on the external bias. In long wires, SΩ decreases with increasing frequency Ω and vanishes beyond a threshold value of Ω at T →0 . The quantum coherent nature of QPS noise yields nonmonotonous dependence of SΩ on T at small Ω .

  1. Modeling and measurement of the noise figure of a cascaded non-degenerate phase-sensitive parametric amplifier.

    PubMed

    Tong, Zhi; Bogris, Adonis; Lundström, Carl; McKinstrie, C J; Vasilyev, Michael; Karlsson, Magnus; Andrekson, Peter A

    2010-07-01

    Semi-classical noise characteristics are derived for the cascade of a non-degenerate phase-insensitive (PI) and a phase-sensitive (PS) fiber optical parametric amplifier (FOPA). The analysis is proved to be consistent with the quantum theory under the large-photon number assumption. Based on this, we show that the noise figure (NF) of the PS-FOPA at the second stage can be obtained via relative-intensity-noise (RIN) subtraction method after averaging the signal and idler NFs. Negative signal and idler NFs are measured, and <2 dB NF at >16 dB PS gain is estimated when considering the combined signal and idler input, which is believed to be the lowest measured NF of a non-degenerate PS amplifier to this date. The limitation of the RIN subtraction method attributed to pump transferred noise and Raman phonon induced noise is also discussed.

  2. Measurement of Integrated Low Frequency Flux Noise in Superconducting Flux/Phase Qubits

    SciTech Connect

    Mao Bo; Qiu Wei; Han Siyuan

    2008-11-07

    We measured the integrated low frequency flux noise ({approx}1 m{phi}{sub 0}) of an rf SQUID as a flux qubit by fitting the resonant peaks from photon assistant tunneling (PAT). The energy relaxation time Tl between the ground and first excited states in the same potential well, measured directly in time domain, is 3 ns. From these results we identified low frequency flux noise as the dominant source of decoherence. In addition, we found that the measured values of integrated flux noise in three qubits of various sizes differ more than an order of magnitude.

  3. Experimental clean combustor program, phase 3: Noise measurement addendum. [CF6-50 high bypass turbofan engine noise

    NASA Technical Reports Server (NTRS)

    Doyle, V. L.

    1978-01-01

    The acoustic characteristics of the double annular combustor in a CF6-50 high bypass turbofan engine were investigated. Internal fluctuating pressure measurements were made in the combustor region and in the core exhaust. The transmission loss across the turbine and nozzle was determined from the measurements and compared to previous component results and present theory. The primary noise source location in the combustor was investigated. Spectral comparisons of test rig results were made with the engine results. The measured overall power level was compared with component and engine correlating parameters.

  4. Modeling phase noise in multifunction subassemblies.

    PubMed

    Driscoll, Michael

    2012-03-01

    Obtaining requisite phase noise performance in hardware containing multifunction circuitry requires accurate modeling of the phase noise characteristics of each signal path component, including both absolute (oscillator) and residual (non-oscillator) circuit contributors. This includes prediction of both static and vibration-induced phase noise. The model (usually in spreadsheet form) is refined as critical components are received and evaluated. Additive (KTBF) phase noise data can be reasonably estimated, based on device drive level and noise figure. However, accurate determination of component near-carrier (multiplicative) and vibration-induced noise usually must be determined via measurement. The model should also include the effects of noise introduced by IC voltage regulators and properly discriminate between common versus independent signal path residual noise contributors. The modeling can be easily implemented using a spreadsheet.

  5. Two-Receiver Measurements of Phase Velocity: Cross-Validation of Ambient-Noise and Earthquake-Based Observations

    NASA Astrophysics Data System (ADS)

    Kästle, Emanuel D.; Soomro, Riaz; Weemstra, Cornelis; Boschi, Lapo; Meier, Thomas

    2016-09-01

    Phase velocities derived from ambient-noise cross-correlation are compared with phase velocities calculated from cross-correlations of waveform recordings of teleseismic earthquakes whose epicenters are approximately on the station-station great circle. The comparison is conducted both for Rayleigh and Love waves using over 1000 station pairs in central Europe. We describe in detail our signal-processing method which allows for automated processing of large amounts of data. Ambient-noise data are collected in the 5 to 80 s, period range, whereas teleseismic data are available between about 8 and 250 s, resulting in a broad common period range between 8 and 80 s. At intermediate periods around 30 s and for shorter inter-station distances, phase velocities measured from ambient noise are on average between 0.5% and 1.5% lower than those observed via the earthquake-based method. This discrepancy is small compared to typical phase-velocity heterogeneities ( 10% peak-to-peak or more: see, e.g., Ek18 stroöm (2014)), observed in this period range. We nevertheless conduct a suite of synthetic tests to evaluate whether known biases in ambient-noise cross-correlation measurements could account for this discrepancy; we specifically evaluate the effects of heterogeneities in source distribution, of azimuthal anisotropy in surface-wave velocity, and of the presence of near-field, rather than far-field only, sources of seismic noise. We find that these effects can be quite important comparing individual station pairs. The systematic discrepancy is presumably due to a combination of factors, related to differences in sensitivity of earthquake vs. noise data to lateral heterogeneity. The datasets from both methods are used to create some preliminary tomographic maps that are characterized by velocity heterogeneities of similar amplitude and pattern, confirming the overall agreement between the two measurement methods.

  6. Measurements and simulations analysing the noise behaviour of grating-based X-ray phase-contrast imaging

    NASA Astrophysics Data System (ADS)

    Weber, T.; Bartl, P.; Durst, J.; Haas, W.; Michel, T.; Ritter, A.; Anton, G.

    2011-08-01

    In the last decades, phase-contrast imaging using a Talbot-Lau grating interferometer is possible even with a low-brilliance X-ray source. With the potential of increasing the soft-tissue contrast, this method is on its way into medical imaging. For this purpose, the knowledge of the underlying physics of this technique is necessary.With this paper, we would like to contribute to the understanding of grating-based phase-contrast imaging by presenting results on measurements and simulations regarding the noise behaviour of the differential phases.These measurements were done using a microfocus X-ray tube with a hybrid, photon-counting, semiconductor Medipix2 detector. The additional simulations were performed by our in-house developed phase-contrast simulation tool “SPHINX”, combining both wave and particle contributions of the simulated photons.The results obtained by both of these methods show the same behaviour. Increasing the number of photons leads to a linear decrease of the standard deviation of the phase. The number of used phase steps has no influence on the standard deviation, if the total number of photons is held constant.Furthermore, the probability density function (pdf) of the reconstructed differential phases was analysed. It turned out that the so-called von Mises distribution is the physically correct pdf, which was also confirmed by measurements.This information advances the understanding of grating-based phase-contrast imaging and can be used to improve image quality.

  7. The Autonomous Cryocooled Sapphire Oscillator: A Reference for Frequency Stability and Phase Noise Measurements

    NASA Astrophysics Data System (ADS)

    Giordano, V.; Grop, S.; Fluhr, C.; Dubois, B.; Kersalé, Y.; Rubiola, E.

    2016-06-01

    The Cryogenic Sapphire Oscillator (CSO) is the microwave oscillator which feature the highest short-term stability. Our best units exhibit Allan deviation σy (τ) of 4.5x10-16 at 1s, ≈ 1.5x10-16 at 100 s ≤ t ≤ 5,000 s (floor), and ≤ 5x10-15 at one day. The use of a Pulse-Tube cryocooler enables full two year operation with virtually no maintenance. Starting with a short history of the CSO in our lab, we go through the architecture and we provide more details about the resonator, the cryostat, the oscillator loop, and the servo electronics. We implemented three similar oscillators, which enable the evaluation of each with the three- cornered hat method, and provide the potential for Allan deviation measurements at parts of 10-17 level. One of our CSOs (ULISS) is transportable, and goes with a small customized truck. The unique feature of ULISS is that its σy (τ) can be validated at destination by measuring before and after the roundtrip. To this extent, ULISS can be regarded as a traveling standard of frequency stability. The CSOs are a part of the Oscillator IMP project, a platform dedicated to the measurement of noise and short-term stability of oscillators and devices in the whole radio spectrum (from MHz to THz), including microwave photonics. The scope spans from routine measurements to the research on new oscillators, components, and measurement methods.

  8. Passive Phase Noise Cancellation Scheme

    PubMed Central

    Kenig, Eyal; Cross, M. C.; Lifshitz, Ron; Karabalin, R. B.; Villanueva, L. G.; Matheny, M. H.; Roukes, M. L.

    2013-01-01

    We introduce a new method for reducing phase noise in oscillators, thereby improving their frequency precision. The noise reduction is realized by a passive device consisting of a pair of coupled nonlinear resonating elements that are driven parametrically by the output of a conventional oscillator at a frequency close to the sum of the linear mode frequencies. Above the threshold for parametric instability, the coupled resonators exhibit self-oscillations which arise as a response to the parametric driving, rather than by application of active feedback. We find operating points of the device for which this periodic signal is immune to frequency noise in the driving oscillator, providing a way to clean its phase noise. We present results for the effect of thermal noise to advance a broader understanding of the overall noise sensitivity and the fundamental operating limits. PMID:23004985

  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. Shot-noise-limited measurement of sub-parts-per-trillion birefringence phase shift in a high-finesse cavity

    SciTech Connect

    Durand, Mathieu; Morville, Jerome; Romanini, Daniele

    2010-09-15

    We report on a promising approach to high-sensitivity anisotropy measurements using a high-finesse cavity locked by optical feedback to a diode laser. We provide a simple and effective way to decouple the weak anisotropy of interest from the inherent mirror's birefringence whose drift may be identified as the key limiting parameter in cavity-based techniques. We demonstrate a shot-noise-limited phase shift resolution previously inaccessible in an optical cavity, readily achieving the state-of-the-art level of 3x10{sup -13} rad.

  11. Development and Calibration of a Field-Deployable Microphone Phased Array for Propulsion and Airframe Noise Flyover Measurements

    NASA Technical Reports Server (NTRS)

    Humphreys, William M., Jr.; Lockard, David P.; Khorrami, Mehdi R.; Culliton, William G.; McSwain, Robert G.; Ravetta, Patricio A.; Johns, Zachary

    2016-01-01

    A new aeroacoustic measurement capability has been developed consisting of a large channelcount, field-deployable microphone phased array suitable for airframe noise flyover measurements for a range of aircraft types and scales. The array incorporates up to 185 hardened, weather-resistant sensors suitable for outdoor use. A custom 4-mA current loop receiver circuit with temperature compensation was developed to power the sensors over extended cable lengths with minimal degradation of the signal to noise ratio and frequency response. Extensive laboratory calibrations and environmental testing of the sensors were conducted to verify the design's performance specifications. A compact data system combining sensor power, signal conditioning, and digitization was assembled for use with the array. Complementing the data system is a robust analysis system capable of near real-time presentation of beamformed and deconvolved contour plots and integrated spectra obtained from array data acquired during flyover passes. Additional instrumentation systems needed to process the array data were also assembled. These include a commercial weather station and a video monitoring / recording system. A detailed mock-up of the instrumentation suite (phased array, weather station, and data processor) was performed in the NASA Langley Acoustic Development Laboratory to vet the system performance. The first deployment of the system occurred at Finnegan Airfield at Fort A.P. Hill where the array was utilized to measure the vehicle noise from a number of sUAS (small Unmanned Aerial System) aircraft. A unique in-situ calibration method for the array microphones using a hovering aerial sound source was attempted for the first time during the deployment.

  12. Phase discrepancy induced from least squares wavefront reconstruction of wrapped phase measurements with high noise or large localized wavefront gradients

    NASA Astrophysics Data System (ADS)

    Steinbock, Michael J.; Hyde, Milo W.

    2012-10-01

    Adaptive optics is used in applications such as laser communication, remote sensing, and laser weapon systems to estimate and correct for atmospheric distortions of propagated light in real-time. Within an adaptive optics system, a reconstruction process interprets the raw wavefront sensor measurements and calculates an estimate for the unwrapped phase function to be sent through a control law and applied to a wavefront correction device. This research is focused on adaptive optics using a self-referencing interferometer wavefront sensor, which directly measures the wrapped wavefront phase. Therefore, its measurements must be reconstructed for use on a continuous facesheet deformable mirror. In testing and evaluating a novel class of branch-point- tolerant wavefront reconstructors based on the post-processing congruence operation technique, an increase in Strehl ratio compared to a traditional least squares reconstructor was noted even in non-scintillated fields. To investigate this further, this paper uses wave-optics simulations to eliminate many of the variables from a hardware adaptive optics system, so as to focus on the reconstruction techniques alone. The simulation results along with a discussion of the physical reasoning for this phenomenon are provided. For any applications using a self-referencing interferometer wavefront sensor with low signal levels or high localized wavefront gradients, understanding this phenomena is critical when applying a traditional least squares wavefront reconstructor.

  13. Spectral Properties of THz Quantum-Cascade Lasers: Frequency Noise, Phase-Locking and Absolute Frequency Measurement

    NASA Astrophysics Data System (ADS)

    Ravaro, Marco; Jagtap, Vishal; Manquest, Christophe; Gellie, Pierre; Santarelli, Giorgio; Sirtori, Carlo; Khanna, Suraj P.; Linfield, Edmund H.; Barbieri, Stefano

    2013-06-01

    Quantum cascade lasers combine desirable features, namely high optical power and compactness, as no other coherent source in the field of THz generation. While their maximum operating temperature is progressively increasing, getting close to the range accessible by Peltier cooling, their range of application is expanding into new fields, such us molecular spectroscopy and their use as local oscillators. These applications would benefit from the investigation and improvement of the laser coherence properties. In this contribution we report the exploitation of electro-optic coherent detection based on a near-IR frequency comb to measure the frequency noise of a free running 2.5 THz quantum cascade laser. An intrinsic linewidth quantum limit of ~230 Hz has been measured, in good agreement with the Schawlow-Townes theoretical prediction. The same detection scheme is then exploited to phase-lock the quantum cascade laser line to a multiple of the comb tooth spacing, while a second comb allows to precisely measure the THz frequency. Such a dual frequency comb experimental setup thus yields a narrow line THz emission traceable to a microwave frequency standard.

  14. Phase Noise in Photonic Phased-Array Antenna Systems

    NASA Technical Reports Server (NTRS)

    Logan, Ronald T., Jr.; Maleki, Lute

    1998-01-01

    The total noise of a phased-array antenna system employing a photonic feed network is analyzed using a model for the individual component noise including both additive and multiplicative equivalent noise generators.

  15. High Precision Noise Measurements at Microwave Frequencies

    SciTech Connect

    Ivanov, Eugene; Tobar, Michael

    2009-04-23

    We describe microwave noise measurement system capable of detecting the phase fluctuations of rms amplitude of 2{center_dot}10{sup -11} rad/{radical}(Hz). Such resolution allows the study of intrinsic fluctuations in various microwave components and materials, as well as precise tests of fundamental physics. Employing this system we discovered a previously unknown phenomenon of down-conversion of pump oscillator phase noise into the low-frequency voltage fluctuations.

  16. Cosmological flux noise and measured noise power spectra in SQUIDs

    NASA Astrophysics Data System (ADS)

    Beck, Christian

    2016-06-01

    The understanding of the origin of 1/f magnetic flux noise commonly observed in superconducting devices such as SQUIDs and qubits is still a major unsolved puzzle. Here we discuss the possibility that a significant part of the observed low-frequency flux noise measured in these devices is ultimately seeded by cosmological fluctuations. We consider a theory where a primordial flux noise field left over in unchanged form from an early inflationary or quantum gravity epoch of the universe intrinsically influences the phase difference in SQUIDs and qubits. The perturbation seeds generated by this field can explain in a quantitatively correct way the form and amplitude of measured low-frequency flux noise spectra in SQUID devices if one takes as a source of fluctuations the primordial power spectrum of curvature fluctuations as measured by the Planck collaboration. Our theoretical predictions are in excellent agreement with recent low-frequency flux noise measurements of various experimental groups. Magnetic flux noise, so far mainly considered as a nuisance for electronic devices, may thus contain valuable information about fluctuation spectra in the very early universe.

  17. Cosmological flux noise and measured noise power spectra in SQUIDs.

    PubMed

    Beck, Christian

    2016-06-20

    The understanding of the origin of 1/f magnetic flux noise commonly observed in superconducting devices such as SQUIDs and qubits is still a major unsolved puzzle. Here we discuss the possibility that a significant part of the observed low-frequency flux noise measured in these devices is ultimately seeded by cosmological fluctuations. We consider a theory where a primordial flux noise field left over in unchanged form from an early inflationary or quantum gravity epoch of the universe intrinsically influences the phase difference in SQUIDs and qubits. The perturbation seeds generated by this field can explain in a quantitatively correct way the form and amplitude of measured low-frequency flux noise spectra in SQUID devices if one takes as a source of fluctuations the primordial power spectrum of curvature fluctuations as measured by the Planck collaboration. Our theoretical predictions are in excellent agreement with recent low-frequency flux noise measurements of various experimental groups. Magnetic flux noise, so far mainly considered as a nuisance for electronic devices, may thus contain valuable information about fluctuation spectra in the very early universe.

  18. Cosmological flux noise and measured noise power spectra in SQUIDs.

    PubMed

    Beck, Christian

    2016-01-01

    The understanding of the origin of 1/f magnetic flux noise commonly observed in superconducting devices such as SQUIDs and qubits is still a major unsolved puzzle. Here we discuss the possibility that a significant part of the observed low-frequency flux noise measured in these devices is ultimately seeded by cosmological fluctuations. We consider a theory where a primordial flux noise field left over in unchanged form from an early inflationary or quantum gravity epoch of the universe intrinsically influences the phase difference in SQUIDs and qubits. The perturbation seeds generated by this field can explain in a quantitatively correct way the form and amplitude of measured low-frequency flux noise spectra in SQUID devices if one takes as a source of fluctuations the primordial power spectrum of curvature fluctuations as measured by the Planck collaboration. Our theoretical predictions are in excellent agreement with recent low-frequency flux noise measurements of various experimental groups. Magnetic flux noise, so far mainly considered as a nuisance for electronic devices, may thus contain valuable information about fluctuation spectra in the very early universe. PMID:27320418

  19. Cosmological flux noise and measured noise power spectra in SQUIDs

    PubMed Central

    Beck, Christian

    2016-01-01

    The understanding of the origin of 1/f magnetic flux noise commonly observed in superconducting devices such as SQUIDs and qubits is still a major unsolved puzzle. Here we discuss the possibility that a significant part of the observed low-frequency flux noise measured in these devices is ultimately seeded by cosmological fluctuations. We consider a theory where a primordial flux noise field left over in unchanged form from an early inflationary or quantum gravity epoch of the universe intrinsically influences the phase difference in SQUIDs and qubits. The perturbation seeds generated by this field can explain in a quantitatively correct way the form and amplitude of measured low-frequency flux noise spectra in SQUID devices if one takes as a source of fluctuations the primordial power spectrum of curvature fluctuations as measured by the Planck collaboration. Our theoretical predictions are in excellent agreement with recent low-frequency flux noise measurements of various experimental groups. Magnetic flux noise, so far mainly considered as a nuisance for electronic devices, may thus contain valuable information about fluctuation spectra in the very early universe. PMID:27320418

  20. Phase noise in RF and microwave amplifiers.

    PubMed

    Boudot, Rodolphe; Rubiola, Enrico

    2012-12-01

    Understanding amplifier phase noise is a critical issue in many fields of engineering and physics, such as oscillators, frequency synthesis, telecommunication, radar, and spectroscopy; in the emerging domain of microwave photonics; and in exotic fields, such as radio astronomy, particle accelerators, etc. Focusing on the two main types of base noise in amplifiers, white and flicker, the power spectral density of the random phase φ(t) is Sφ(f) = b(0) + b(-1)/f. White phase noise results from adding white noise to the RF spectrum in the carrier region. For a given RF noise level, b(0) is proportional to the reciprocal of the carrier power P(0). By contrast, flicker results from a near-dc 1/f noise-present in all electronic devices-which modulates the carrier through some parametric effect in the semiconductor. Thus, b(-1) is a parameter of the amplifier, constant in a wide range of P(0). The consequences are the following: Connecting m equal amplifiers in parallel, b(-1) is 1/m times that of one device. Cascading m equal amplifiers, b(-1) is m times that of one amplifier. Recirculating the signal in an amplifier so that the gain increases by a power of m (a factor of m in decibels) as a result of positive feedback (regeneration), we find that b(-1) is m(2) times that of the amplifier alone. The feedforward amplifier exhibits extremely low b(-1) because the carrier is ideally nulled at the input of its internal error amplifier. Starting with an extensive review of the literature, this article introduces a system-oriented model which describes the phase flickering. Several amplifier architectures (cascaded, parallel, etc.) are analyzed systematically, deriving the phase noise from the general model. There follow numerous measurements of amplifiers using different technologies, including some old samples, and in a wide frequency range (HF to microwaves), which validate the theory. In turn, theory and results provide design guidelines and give suggestions for CAD and

  1. Phase Noise Reduction of Laser Diode

    NASA Technical Reports Server (NTRS)

    Zhang, T. C.; Poizat, J.-Ph.; Grelu, P.; Roch, J.-F.; Grangier, P.; Marin, F.; Bramati, A.; Jost, V.; Levenson, M. D.; Giacobino, E.

    1996-01-01

    Phase noise of single mode laser diodes, either free-running or using line narrowing technique at room temperature, namely injection-locking, has been investigated. It is shown that free-running diodes exhibit very large excess phase noise, typically more than 80 dB above shot-noise at 10 MHz, which can be significantly reduced by the above-mentioned technique.

  2. Noise in strong laser-atom interactions: Phase telegraph noise

    SciTech Connect

    Eberly, J.H.; Wodkiewicz, K.; Shore, B.W.

    1984-11-01

    We discuss strong laser-atom interactions that are subjected to jump-type (random telegraph) random-phase noise. Physically, the jumps may arise from laser fluctuations, from collisions of various kinds, or from other external forces. Our discussion is carried out in two stages. First, direct and partially heuristic calculations determine the laser spectrum and also give a third-order differential equation for the average inversion of a two-level atom on resonance. At this stage a number of general features of the interaction are able to be studied easily. The optical analog of motional narrowing, for example, is clearly predicted. Second, we show that the theory of generalized Poisson processes allows laser-atom interactions in the presence of random telegraph noise of all kinds (not only phase noise) to be treated systematically, by means of a master equation first used in the context of quantum optics by Burshtein. We use the Burshtein equation to obtain an exact expression for the two-level atom's steady-state resonance fluorescence spectrum, when the exciting laser exhibits phase telegraph noise. Some comparisons are made with results obtained from other noise models. Detailed treatments of the effects ofmly jumps, or as a model of finite laser bandwidth effects, in which the laser frequency exhibits random jumps. We show that these two types of frequency noise can be distinguished in light-scattering spectra. We also discuss examples which demonstrate both temporal and spectral motional narrowing, nonexponential correlations, and non-Lorentzian spectra. Its exact solubility in finite terms makes the frequency-telegraph noise model an attractive alternative to the white-noise Ornstein-Uhlenbeck frequency noise model which has been previously applied to laser-atom interactions.

  3. Intensity and phase noise caused by stimulated Brillouin scattering

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Meng, Zhou

    2011-05-01

    Stimulated Brillouin scattering (SBS) induced noise is harmful to long-haul fiber sensing systems. We use the localized fluctuating model to study SBS in a single-mode fiber (SMF) and obtain the relation between the intensity fluctuations and the input power. Experimental results show that relative intensity noise (RIN) is small when the input power is below the SBS threshold and increases dramatically at first and then becomes flat gradually when the input power is above the threshold, which agrees well with the theory. We also use an unbalanced Michelson interferometer with the optical path difference (OPD) of 1 m as well as the phase-generated carrier (PGC) technique to measure the phase noise and find that the curves of phase noise versus input power at different frequencies are similar to that of RIN. We also infer that the increase of the phase noise is mainly due to the broadening of the linewidth caused by SBS.

  4. Multipurpose exciter with low phase noise

    NASA Technical Reports Server (NTRS)

    Conroy, B.; Le, D.

    1989-01-01

    Results of an effort to develop a lower-cost exciter with high stability, low phase noise, and controllable phase and frequency for use in Deep Space Network and Goldstone Solar System Radar applications are discussed. Included is a discussion of the basic concept, test results, plans, and concerns.

  5. Noise in phase-preserving linear amplifiers

    SciTech Connect

    Pandey, Shashank; Jiang, Zhang; Combes, Joshua; Caves, Carlton M.

    2014-12-04

    The purpose of a phase-preserving linear amplifier is to make a small signal larger, so that it can be perceived by instruments incapable of resolving the original signal, while sacrificing as little as possible in signal-to-noise. Quantum mechanics limits how well this can be done: the noise added by the amplifier, referred to the input, must be at least half a quantum at the operating frequency. This well-known quantum limit only constrains the second moments of the added noise. Here we provide the quantum constraints on the entire distribution of added noise: any phasepreserving linear amplifier is equivalent to a parametric amplifier with a physical state σ for the ancillary mode; σ determines the properties of the added noise.

  6. Cross-spectrum measurement of thermal-noise limited oscillators.

    PubMed

    Hati, A; Nelson, C W; Howe, D A

    2016-03-01

    Cross-spectrum analysis is a commonly used technique for the detection of phase and amplitude noise of a signal in the presence of interfering uncorrelated noise. Recently, we demonstrated that the phase-inversion (anti-correlation) effect due to amplitude noise leakage can cause complete or partial collapse of the cross-spectral function. In this paper, we discuss the newly discovered effect of anti-correlated thermal noise that originates from the common-mode power divider (splitter), an essential component in a cross-spectrum noise measurement system. We studied this effect for different power splitters and discuss its influence on the measurement of thermal-noise limited oscillators. We provide theory, simulation and experimental results. In addition, we expand this study to reveal how the presence of ferrite-isolators and amplifiers at the output ports of the power splitters can affect the oscillator noise measurements. Finally, we discuss a possible solution to overcome this problem. PMID:27036804

  7. Residual phase noise modeling of amplifiers using silicon bipolar transistors.

    PubMed

    Theodoropoulos, Konstantinos; Everard, Jeremy

    2010-03-01

    In this paper, we describe the modeling of residual 1/f phase noise for Si bipolar amplifiers operating in the linear region. We propose that for Si bipolar amplifiers, the 1/f phase noise is largely caused by the base emitter recombination flicker noise. The up-conversion mechanism is described through linear approximation of the phase variation of the amplifier phase response by the variation of the device parameters (C(b)c, C(be), g(m), r(e)) caused by the recombination 1/f noise. The amplifier phase response describes the device over the whole frequency range of operation for which the influence of the poles and zeros is investigated. It is found that for a common emitter amplifier it is sufficient to only incorporate the effect of the device poles to describe the phase noise behavior over most of its operational frequency range. Simulations predict the measurements of others, including the flattening of the PM noise at frequencies beyond f(3dB), not predicted by previous models.

  8. Qubit Metrology of Ultralow Phase Noise Using Randomized Benchmarking

    NASA Astrophysics Data System (ADS)

    O'Malley, P. J. J.; Kelly, J.; Barends, R.; Campbell, B.; Chen, Y.; Chen, Z.; Chiaro, B.; Dunsworth, A.; Fowler, A. G.; Hoi, I.-C.; Jeffrey, E.; Megrant, A.; Mutus, J.; Neill, C.; Quintana, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Korotkov, A. N.; Cleland, A. N.; Martinis, John M.

    2015-04-01

    A precise measurement of dephasing over a range of time scales is critical for improving quantum gates beyond the error correction threshold. We present a metrological tool based on randomized benchmarking capable of greatly increasing the precision of Ramsey and spin-echo sequences by the repeated but incoherent addition of phase noise. We find our superconducting-quantum-interference-device-based qubit is not limited by 1 /f flux noise at short time scales but instead observe a telegraph noise mechanism that is not amenable to study with standard measurement techniques.

  9. 14 CFR 36.801 - Noise measurement.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION Helicopters § 36.801 Noise measurement. For primary, normal, transport, or restricted category helicopters for which certification is sought under appendix H of this part, the noise generated by the helicopter must be measured at the noise measuring points and...

  10. 14 CFR 36.801 - Noise measurement.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION Helicopters § 36.801 Noise measurement. For primary, normal, transport, or restricted category helicopters for which certification is sought under appendix H of this part, the noise generated by the helicopter must be measured at the noise measuring points and...

  11. 14 CFR 36.801 - Noise measurement.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION Helicopters § 36.801 Noise measurement. For primary, normal, transport, or restricted category helicopters for which certification is sought under appendix H of this part, the noise generated by the helicopter must be measured at the noise measuring points and...

  12. 14 CFR 36.801 - Noise measurement.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION Helicopters § 36.801 Noise measurement. For primary, normal, transport, or restricted category helicopters for which certification is sought under appendix H of this part, the noise generated by the helicopter must be measured at the noise measuring points and...

  13. 14 CFR 36.801 - Noise measurement.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION Helicopters § 36.801 Noise measurement. For primary, normal, transport, or restricted category helicopters for which certification is sought under appendix H of this part, the noise generated by the helicopter must be measured at the noise measuring points and...

  14. Microwave-to-millimeter-wave synthesis chain phase noise performance.

    PubMed

    Bara-Maillet, Romain; Parker, Stephen R; Nand, Nitin R; Le Floch, Jean-Michel; Tobar, Michael E

    2015-10-01

    We report on the phase noise measurement of a millimeter-wave synthesis chain developed for a continuous wave (CW) source exhibiting high frequency stability. We quantify the performance of each multiplication stage in terms of phase spectral purity. From the initial cryogenic sapphire oscillator generating 12.97 GHz, a total multiplication factor of eight is applied through two stages to reach a frequency of 103.75 GHz. We find that the chain performance is primarily limited by the phase noise of the initial frequency doubler.

  15. Should helicopter noise be measured differently from other aircraft noise? A review of the psychoacoustic literature

    NASA Technical Reports Server (NTRS)

    Molino, J. A.

    1982-01-01

    A review of 34 studies indicates that several factors or variables might be important in providing a psychoacoustic foundation for measurements of the noise from helicopters. These factors are phase relations, tail rotor noise, repetition rate, crest level, and generic differences between conventional aircraft and helicopters. Particular attention was given to the impulsive noise known as blade slap. Analysis of the evidence for and against each factor reveals that, for the present state of scientific knowledge, none of these factors should be regarded as the basis for a significant noise measurement correction due to impulsive blade slap. The current method of measuring effective perceived noise level for conventional aircraft appears to be adequate for measuring helicopter noise as well.

  16. Measurement of hearing aid internal noise.

    PubMed

    Lewis, James D; Goodman, Shawn S; Bentler, Ruth A

    2010-04-01

    Hearing aid equivalent input noise (EIN) measures assume the primary source of internal noise to be located prior to amplification and to be constant regardless of input level. EIN will underestimate internal noise in the case that noise is generated following amplification. The present study investigated the internal noise levels of six hearing aids (HAs). Concurrent with HA processing of a speech-like stimulus with both adaptive features (acoustic feedback cancellation, digital noise reduction, microphone directionality) enabled and disabled, internal noise was quantified for various stimulus levels as the variance across repeated trials. Changes in noise level as a function of stimulus level demonstrated that (1) generation of internal noise is not isolated to the microphone, (2) noise may be dependent on input level, and (3) certain adaptive features may contribute to internal noise. Quantifying internal noise as the variance of the output measures allows for noise to be measured under real-world processing conditions, accounts for all sources of noise, and is predictive of internal noise audibility. PMID:20370034

  17. Measurement of hearing aid internal noise1

    PubMed Central

    Lewis, James D.; Goodman, Shawn S.; Bentler, Ruth A.

    2010-01-01

    Hearing aid equivalent input noise (EIN) measures assume the primary source of internal noise to be located prior to amplification and to be constant regardless of input level. EIN will underestimate internal noise in the case that noise is generated following amplification. The present study investigated the internal noise levels of six hearing aids (HAs). Concurrent with HA processing of a speech-like stimulus with both adaptive features (acoustic feedback cancellation, digital noise reduction, microphone directionality) enabled and disabled, internal noise was quantified for various stimulus levels as the variance across repeated trials. Changes in noise level as a function of stimulus level demonstrated that (1) generation of internal noise is not isolated to the microphone, (2) noise may be dependent on input level, and (3) certain adaptive features may contribute to internal noise. Quantifying internal noise as the variance of the output measures allows for noise to be measured under real-world processing conditions, accounts for all sources of noise, and is predictive of internal noise audibility. PMID:20370034

  18. Engine Validation of Noise and Emission Reduction Technology Phase I

    NASA Technical Reports Server (NTRS)

    Weir, Don (Editor)

    2008-01-01

    This final report has been prepared by Honeywell Aerospace, Phoenix, Arizona, a unit of Honeywell International, Inc., documenting work performed during the period December 2004 through August 2007 for the NASA Glenn Research Center, Cleveland, Ohio, under the Revolutionary Aero-Space Engine Research (RASER) Program, Contract No. NAS3-01136, Task Order 8, Engine Validation of Noise and Emission Reduction Technology Phase I. The NASA Task Manager was Dr. Joe Grady of the NASA Glenn Research Center. The NASA Contract Officer was Mr. Albert Spence of the NASA Glenn Research Center. This report is for a test program in which NASA funded engine validations of integrated technologies that reduce aircraft engine noise. These technologies address the reduction of engine fan and jet noise, and noise associated with propulsion/airframe integration. The results of these tests will be used by NASA to identify the engineering tradeoffs associated with the technologies that are needed to enable advanced engine systems to meet stringent goals for the reduction of noise. The objectives of this program are to (1) conduct system engineering and integration efforts to define the engine test-bed configuration; (2) develop selected noise reduction technologies to a technical maturity sufficient to enable engine testing and validation of those technologies in the FY06-07 time frame; (3) conduct engine tests designed to gain insight into the sources, mechanisms and characteristics of noise in the engines; and (4) establish baseline engine noise measurements for subsequent use in the evaluation of noise reduction.

  19. Removing Background Noise with Phased Array Signal Processing

    NASA Technical Reports Server (NTRS)

    Podboy, Gary; Stephens, David

    2015-01-01

    Preliminary results are presented from a test conducted to determine how well microphone phased array processing software could pull an acoustic signal out of background noise. The array consisted of 24 microphones in an aerodynamic fairing designed to be mounted in-flow. The processing was conducted using Functional Beam forming software developed by Optinav combined with cross spectral matrix subtraction. The test was conducted in the free-jet of the Nozzle Acoustic Test Rig at NASA GRC. The background noise was produced by the interaction of the free-jet flow with the solid surfaces in the flow. The acoustic signals were produced by acoustic drivers. The results show that the phased array processing was able to pull the acoustic signal out of the background noise provided the signal was no more than 20 dB below the background noise level measured using a conventional single microphone equipped with an aerodynamic forebody.

  20. Physical measures of sound and noise

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The physical measurement of sound is examined through basic definitions and measuring techniques. The terminology of acoustics is presented with noise characterization, graphs, and mathematical formulas included.

  1. Physical measures of sound and noise

    NASA Astrophysics Data System (ADS)

    1984-07-01

    The physical measurement of sound is examined through basic definitions and measuring techniques. The terminology of acoustics is presented with noise characterization, graphs, and mathematical formulas included.

  2. Phase noise analysis of the sapphire loaded superconducting niobium cavity oscillator

    NASA Astrophysics Data System (ADS)

    Tobar, Michael; Blair, David G.

    1994-02-01

    Measured phase noise of two GaAs FET amplifiers and a varactor phase shifter at 9.7 GHz reveal that optimum bias conditions change when cooling from room to liquid helium temperatures. This understanding enables optimization of the electronic noise in an all cryogenic tunable sapphire loaded superconducting cavity (SLOSC) X-Band loop oscillator. The measured phase noise was limited by vibrations of the tuning mechanism. In a fixed frequency SLOSC oscillator the phase noise was limited by the amplifier noise, and has been measured to be -140 dBc/Hz at 1 kHz from the unfiltered port of loop oscillator. Comparison of component and oscillator phase noise allows us to calculate the phase noise at the filtered port to be -175 dBc/ Hz at 1 kHz offset.

  3. Flyover-noise measurement and prediction

    NASA Technical Reports Server (NTRS)

    Peart, Noel A.

    1991-01-01

    Details are presented for the measurement and prediction of aircraft flyover noise to be used for certification, research and development, community noise surveys, airport monitors, and pass fail criteria. Test details presented are applicable to all types of aircraft, both large and small, and the use of Federal Aviation Regulations (FAR) Part 36 (ref. 1) is emphasized. Accuracy of noise measurements is important. Thus, a pass-fail criterion should be used for all noise measurements. Finally, factors which influence the sound propagation and noise prediction procedures, such as atmospheric and ground effects, are also presented.

  4. General Aviation Interior Noise. Part 3; Noise Control Measure Evaluation

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    The work reported herein is an extension to the work accomplished under NASA Grant NAG1-2091 on the development of noise/source/path identification techniques for single engine propeller driven General Aviation aircraft. The previous work developed a Conditioned Response Analysis (CRA) technique to identify potential noise sources that contributed to the dominating tonal responses within the aircraft cabin. The objective of the present effort was to improve and verify the findings of the CRA and develop and demonstrate noise control measures for single engine propeller driven General Aviation aircraft.

  5. Advanced noise reduction techniques for ultra-low phase noise optical-to-microwave division with femtosecond fiber combs.

    PubMed

    Zhang, Wei; Xu, Zhenyu; Lours, Michel; Boudot, Rodolphe; Kersalé, Yann; Luiten, Andre N; Le Coq, Yann; Santarelli, Giorgio

    2011-05-01

    We report what we believe to be the lowest phase noise optical-to-microwave frequency division using fiber-based femtosecond optical frequency combs: a residual phase noise of -120 dBc/Hz at 1 Hz offset from an 11.55 GHz carrier frequency. Furthermore, we report a detailed investigation into the fundamental noise sources which affect the division process itself. Two frequency combs with quasi-identical configurations are referenced to a common ultrastable cavity laser source. To identify each of the limiting effects, we implement an ultra-low noise carrier-suppression measurement system, which avoids the detection and amplification noise of more conventional techniques. This technique suppresses these unwanted sources of noise to very low levels. In the Fourier frequency range of ∼200 Hz to 100 kHz, a feed-forward technique based on a voltage-controlled phase shifter delivers a further noise reduction of 10 dB. For lower Fourier frequencies, optical power stabilization is implemented to reduce the relative intensity noise which causes unwanted phase noise through power-to-phase conversion in the detector. We implement and compare two possible control schemes based on an acousto-optical modulator and comb pump current. We also present wideband measurements of the relative intensity noise of the fiber comb. PMID:21622045

  6. An ultralow noise preamplifier for low frequency noise measurements.

    PubMed

    Cannatà, Gianluca; Scandurra, Graziella; Ciofi, Carmine

    2009-11-01

    Low frequency noise measurements are among the most sensitive tools for the investigation of the quality and of the reliability of semiconductor devices. The sensitivity that can be obtained depends on the background noise of the low noise preamplifier coupled to the device under test (DUT) that, at very low frequencies, is dominated by flicker noise. The low frequency noise produced by the DUT, on the other end, is very often the most interesting signal to be detected and analyzed. In this work we propose a very simple topology for the realization of a general purpose low noise preamplifier whose noise performances, at very low frequencies (below 10 Hz), are significantly better than those that can be obtained by the most popular commercial instrumentation. Indeed, a gain of 80 dB with a pass band extending from a few tens of mHz up to a few kHz with an equivalent input voltage noise as low as 14 nV/square root(Hz) (100 mHz), 1.4 nV/square root(Hz) (1 Hz), 1.0 nV/square root(Hz) (10 Hz), and 0.8 nV/square root(Hz) (1 kHz) are consistently obtained by using quite standard electronic components and with no need for trimming and/or calibration steps. Moreover, the junction field-effect transistor input stage of the amplifier is characterized by an equivalent input current noise below 4 fA/square root(Hz) in the entire bandwidth, resulting in negligible background noise degradation for DUT impedances in excess of 100 kohms. PMID:19947746

  7. Phase retrieval tomography in the presence of noise

    NASA Astrophysics Data System (ADS)

    Arhatari, B. D.; Gates, W. P.; Eshtiaghi, N.; Peele, A. G.

    2010-02-01

    We describe the use of single-plane phase retrieval tomography using a laboratory-based x-ray source, under conditions where the retrieval is not formally valid, to present images of the internal structure of an Aerosil granule and a hydrated bentonite gel. The technique provides phase images for samples that interact weakly with the x-ray beam. As the method is less affected by noise than an alternative two-plane phase retrieval method that is otherwise formally valid, object structure can be observed that would not otherwise be seen. We demonstrate our results for phase imaging in tomographic measurements.

  8. Low Noise Borehole Triaxial Seismometer Phase II

    SciTech Connect

    Kerr, James D; McClung, David W

    2006-11-06

    This report describes the preliminary design and the effort to date of Phase II of a Low Noise Borehole Triaxial Seismometer for use in networks of seismic stations for monitoring underground nuclear explosions. The design uses the latest technology of broadband seismic instrumentation. Each parameter of the seismometer is defined in terms of the known physical limits of the parameter. These limits are defined by the commercially available components, and the physical size constraints. A theoretical design is proposed, and a preliminary prototype model of the proposed instrument has been built. This prototype used the sensor module of the KS2000. The installation equipment (hole locks, etc.) has been designed and one unit has been installed in a borehole. The final design of the sensors and electronics and leveling mechanism is in process. Noise testing is scheduled for the last quarter of 2006.

  9. Landing approach airframe noise measurements and analysis

    NASA Technical Reports Server (NTRS)

    Lasagna, P. L.; Mackall, K. G.; Burcham, F. W., Jr.; Putnam, T. W.

    1980-01-01

    Flyover measurements of the airframe noise produced by the AeroCommander, JetStar, CV-990, and B-747 airplanes are presented for various landing approach configurations. Empirical and semiempirical techniques are presented to correlate the measured airframe noise with airplane design and aerodynamic parameters. Airframe noise for the jet-powered airplanes in the clean configuration (flaps and gear retracted) was found to be adequately represented by a function of airplane weight and the fifth power of airspeed. Results show the airframe noise for all four aircraft in the landing configuration (flaps extended and gear down) also varied with the fifth power of airspeed, but this noise level could not be represented by the addition of a constant to the equation for clean-configuration airframe noise.

  10. Speckle phase noise in coherent laser ranging: fundamental precision limitations.

    PubMed

    Baumann, Esther; Deschênes, Jean-Daniel; Giorgetta, Fabrizio R; Swann, William C; Coddington, Ian; Newbury, Nathan R

    2014-08-15

    Frequency-modulated continuous-wave laser detection and ranging (FMCW LADAR) measures the range to a surface through coherent detection of the backscattered light from a frequency-swept laser source. The ultimate limit to the range precision of FMCW LADAR, or any coherent LADAR, to a diffusely scattering surface will be determined by the unavoidable speckle phase noise. Here, we demonstrate the two main manifestations of this limit. First, frequency-dependent speckle phase noise leads to a non-Gaussian range distribution having outliers that approach the system range resolution, regardless of the signal-to-noise ratio. These outliers are reduced only through improved range resolution (i.e., higher optical bandwidths). Second, if the range is measured during a continuous lateral scan across a surface, the spatial pattern of speckle phase is converted to frequency noise, which leads to additional excess range uncertainty. We explore these two effects and show that laboratory results agree with analytical expressions and numerical simulations. We also show that at 1 THz optical bandwidth, range precisions below 10 μm are achievable regardless of these effects. PMID:25121872

  11. Phase-Locked Loop Noise Reduction via Phase Detector Implementation for Single-Phase Systems

    SciTech Connect

    Thacker, Timothy; Boroyevich, Dushan; Burgos, Rolando; Wang, Fei

    2011-01-01

    A crucial component of grid-connected converters is the phase-locked loop (PLL) control subsystem that tracks the grid voltage's frequency and phase angle. Therefore, accurate fast-responding PLLs for control and protection purposes are required to provide these measurements. This paper proposes a novel feedback mechanism for single-phase PLL phase detectors using the estimated phase angle. Ripple noise appearing in the estimated frequency, most commonly the second harmonic under phase-lock conditions, is reduced or eliminated without the use of low-pass filters, which can cause delays to occur and limits the overall performance of the PLL response to dynamic changes in the system. The proposed method has the capability to eliminate the noise ripple entirely and, under extreme line distortion conditions, can reduce the ripple by at least half. Other modifications implemented through frequency feedback are shown to decrease the settling time of the PLL up to 50%. Mathematical analyses with the simulated and experimental results are provided to confirm the validity of the proposed methods.

  12. An analytical formulation for phase noise in MEMS oscillators.

    PubMed

    Agrawal, Deepak; Seshia, Ashwin

    2014-12-01

    In recent years, there has been much interest in the design of low-noise MEMS oscillators. This paper presents a new analytical formulation for noise in a MEMS oscillator encompassing essential resonator and amplifier nonlinearities. The analytical expression for oscillator noise is derived by solving a second-order nonlinear stochastic differential equation. This approach is applied to noise modeling of an electrostatically addressed MEMS resonator-based square-wave oscillator in which the resonator and oscillator circuit nonlinearities are integrated into a single modeling framework. By considering the resulting amplitude and phase relations, we derive additional noise terms resulting from resonator nonlinearities. The phase diffusion of an oscillator is studied and the phase diffusion coefficient is proposed as a metric for noise optimization. The proposed nonlinear phase noise model provides analytical insight into the underlying physics and a pathway toward the design optimization for low-noise MEMS oscillators.

  13. Analysis of phase noise in a spin torque oscillator stabilized by phase locked loop

    NASA Astrophysics Data System (ADS)

    Tamaru, Shingo; Kubota, Hitoshi; Yakushiji, Kay; Fukushima, Akio; Yuasa, Shinji

    2016-05-01

    This study analyses phase noise in a spin torque oscillator (STO) stabilized by phase locked loop (PLL). Time domain measurement showed that phase error of the 6.996 GHz signal generated by a STO, which exhibited a random-walk type fluctuation under free running, was suppressed within a standard deviation of 0.408 rad by the PLL. Power spectrum under phase locked oscillation indicated that the PLL had a loop bandwidth of approximately 16 MHz, thus effectively suppressing phase error below 10 MHz. However, it was also found that power spectrum of the residual phase error was distributed much higher than the loop bandwidth.

  14. Understanding the amplitudes of noise correlation measurements

    USGS Publications Warehouse

    Tsai, Victor C.

    2011-01-01

    Cross correlation of ambient seismic noise is known to result in time series from which station-station travel-time measurements can be made. Part of the reason that these cross-correlation travel-time measurements are reliable is that there exists a theoretical framework that quantifies how these travel times depend on the features of the ambient noise. However, corresponding theoretical results do not currently exist to describe how the amplitudes of the cross correlation depend on such features. For example, currently it is not possible to take a given distribution of noise sources and calculate the cross correlation amplitudes one would expect from such a distribution. Here, we provide a ray-theoretical framework for calculating cross correlations. This framework differs from previous work in that it explicitly accounts for attenuation as well as the spatial distribution of sources and therefore can address the issue of quantifying amplitudes in noise correlation measurements. After introducing the general framework, we apply it to two specific problems. First, we show that we can quantify the amplitudes of coherency measurements, and find that the decay of coherency with station-station spacing depends crucially on the distribution of noise sources. We suggest that researchers interested in performing attenuation measurements from noise coherency should first determine how the dominant sources of noise are distributed. Second, we show that we can quantify the signal-to-noise ratio of noise correlations more precisely than previous work, and that these signal-to-noise ratios can be estimated for given situations prior to the deployment of seismometers. It is expected that there are applications of the theoretical framework beyond the two specific cases considered, but these applications await future work.

  15. Effect of measurement noise on Granger causality.

    PubMed

    Nalatore, Hariharan; Sasikumar, N; Rangarajan, Govindan

    2014-12-01

    Most of the signals recorded in experiments are inevitably contaminated by measurement noise. Hence, it is important to understand the effect of such noise on estimating causal relations between such signals. A primary tool for estimating causality is Granger causality. Granger causality can be computed by modeling the signal using a bivariate autoregressive (AR) process. In this paper, we greatly extend the previous analysis of the effect of noise by considering a bivariate AR process of general order p. From this analysis, we analytically obtain the dependence of Granger causality on various noise-dependent system parameters. In particular, we show that measurement noise can lead to spurious Granger causality and can suppress true Granger causality. These results are verified numerically. Finally, we show how true causality can be recovered numerically using the Kalman expectation maximization algorithm.

  16. N-step linear phase-shifting algorithms with optimum signal to noise phase demodulation

    NASA Astrophysics Data System (ADS)

    González, A.; Servin, M.; Estrada, J. C.; Rosu, H. C.

    2011-08-01

    A common way to test an optical wavefront is to use a phase-shifting interferometer along with (for example) a three-step linear phase-shifting algorithm (PSA). The following fundamental question arises: what phase step should be used? Typically, ? , ? or ? are used and, in fact, any phase step within the open interval ? can be employed. In the absence of any measuring noise, all these phase shifts yield the same estimate for the modulating phase. However, which of these phase steps ω 0 is the best to obtain the least noisy phase estimation from a temporal set of three noisy interferograms? Working in frequency space, a general procedure to obtain the optimum phase step ω 0 of a given linear N-step PSA is presented. This general procedure is exemplified for some particular linear PSAs, notably 3-, 5-, 7-, and 27-step PSAs.

  17. [Issues concerning the measurement and assessment of noise in workplaces].

    PubMed

    Peretti, Alessandro

    2011-01-01

    The measurement and assessment of noise in workplaces are affected by several critical aspects. Only the equivalent sound pressure levels are measured and all the other acoustical parameters are almost always neglected; the non-acoustic information that characterize each measurement are not usually reported. The survey about noise in workplaces is not suited to be described by technical standards, but rather by flexible guidelines. The reference standard UNI EN ISO 9612/2011 does not highlight the contribution given by each work phase to the overall exposure level; the uncertainty evaluation may lead to unreliable data. PMID:22073687

  18. Interferometer phase noise due to beam misalignment on diffraction gratings.

    PubMed

    Lodhia, Deepali; Brown, Daniel; Brückner, Frank; Carbone, Ludovico; Fulda, Paul; Kokeyama, Keiko; Freise, Andreas

    2013-12-01

    All-reflective interferometer configurations have been proposed for the next generation of gravitational wave detectors, with diffractive elements replacing transmissive optics. However, an additional phase noise creates more stringent conditions for alignment stability. A framework for alignment stability with the use of diffractive elements was required using a Gaussian model. We successfully create such a framework involving modal decomposition to replicate small displacements of the beam (or grating) and show that the modal model does not contain the phase changes seen in an otherwise geometric planewave approach. The modal decomposition description is justified by verifying experimentally that the phase of a diffracted Gaussian beam is independent of the beam shape, achieved by comparing the phase change between a zero-order and first-order mode beam. To interpret our findings we employ a rigorous time-domain simulation to demonstrate that the phase changes resulting from a modal decomposition are correct, provided that the coordinate system which measures the phase is moved simultaneously with the effective beam displacement. This indeed corresponds to the phase change observed in the geometric planewave model. The change in the coordinate system does not instinctively occur within the analytical framework, and therefore requires either a manual change in the coordinate system or an addition of the geometric planewave phase factor.

  19. Measured Noise from Small Unmanned Aerial Vehicles

    NASA Technical Reports Server (NTRS)

    Cabell, Randolph; McSwain, Robert; Grosveld, Ferdinand

    2016-01-01

    Proposed uses of small unmanned aerial vehicles (UAVs), including home package delivery, have the potential to expose large portions of communities to a new noise source. This paper discusses results of flyover noise measurements of four small UAVs, including an internal combustion-powered model airplane and three battery-powered multicopters. Basic noise characteristics of these vehicles are discussed, including spectral properties and sound level metrics such as sound pressure level, effective perceived noise level, and sound exposure level. The size and aerodynamic characteristics of the multicopters in particular make their flight path susceptible to atmospheric disturbances such as wind gusts. These gusts, coupled with a flight control system that varies rotor speed to maintain vehicle stability, create an unsteady acoustic signature. The spectral variations resulting from this unsteadiness are explored, in both hover and flyover conditions for the multicopters. The time varying noise, which differs from the relatively steady noise generated by large transport aircraft, may complicate the prediction of human annoyance using conventional sound level metrics.

  20. The Advanced Noise Control Fan Baseline Measurements

    NASA Technical Reports Server (NTRS)

    McAllister, Joseph; Loew, Raymond A.; Lauer, Joel T.; Stuliff, Daniel L.

    2009-01-01

    The NASA Glenn Research Center s (NASA Glenn) 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. As part of a complete upgrade, current baseline and acoustic measurements were documented. Extensive in-duct, farfield acoustic, and flow field measurements are reported. This is a follow-on paper to documenting the operating description of the ANCF.

  1. EDFA-based coupled opto-electronic oscillator and its phase noise

    NASA Technical Reports Server (NTRS)

    Salik, Ertan; Yu, Nan; Tu, Meirong; Maleki, Lute

    2004-01-01

    EDFA-based coupled opto-electronic oscillator (COEO), an integrated optical and microwave oscillator that can generate picosecond optical pulses, is presented. the phase noise measurements of COEO show better performance than synthesizer-driven mode-locked laser.

  2. Supersonic Coaxial Jets: Noise Predictions and Measurements

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Papamoschou, Dimitri; Hixon, Ray

    1998-01-01

    The noise from perfectly expanded coaxial jets was measured in an anechoic chamber for different operating conditions with the same total thrust, mass flow, and exit area. The shape of the measured noise spectrum at different angles to the jet axis was found to agree with spectral shapes for single, axisymmetric jets. Based on these spectra, the sound was characterized as being generated by large turbulent structures or fine-scale turbulence. Modeling the large scale structures as instability waves, a stability analysis was conducted for the coaxial jets to identify the growing and decaying instability waves in each shear layer and predict their noise radiation pattern outside the jet. When compared to measured directivity, the analysis identified the region downstream of the outer potential core, where the two shear layers were merging, as the source of the peak radiated noise where instability waves, with their origin in the inner shear layer, reach their maximum amplitude. Numerical computations were also performed using a linearized Euler equation solver. Those results were compared to both the results from the instability wave analysis and to measured data.

  3. Measured Sun Noise Temperatures at 32 Gigahertz

    NASA Astrophysics Data System (ADS)

    Otoshi, T. Y.

    2001-01-01

    Sun experiments were performed to develop methods for accurately mapping the Sun noise temperatures over the entire solar disk at 32 GHz (Ka-band). High-resolution mapping of the Sun's noise temperatures was obtained through the use of the 34-m beam-waveguide (BWG) antenna and the Ka-band monopulse receiving system at DSS 13. Detailed mapping of the solar disk was possible because at 32 GHz the BWG antenna has a full 3-dB beamwidth that is only 17 mdeg compared to the angular Sun diameter of about 0.5 deg. Due to the expected high noise temperature of the Sun (> 10,000 K), methods had to be developed so that the incoming Sun noise-temperature power would not saturate the antenna receiving system. Of several methods investigated, only the absorber and waveguide attenuator methods were considered (1) to be easy and inexpensive to implement into any existing BWG receiving system and (2) to have the potential of giving accurate results. Both of these methods were used to measure the Sun noise temperatures presented in this article. Due to the high solar activity during the experiments, it was not possible to obtain repeatable results on different days and even on the same day. However, useful information has been obtained about the Sun's noise-temperature characteristics during the period of maximum solar activity that occurred in the year 2000. To this author's knowledge, this is the first time that a large (34-m) antenna was used to map the Sun's noise-temperature profile over its entire surface at 32 GHz.

  4. Measurement and analysis of aircraft far-field aerodynamic noise

    NASA Technical Reports Server (NTRS)

    Healy, G. J.

    1974-01-01

    A systematic investigation of aircraft far-field radiated, aerodynamically generated noise was conducted. The test phase of the original program involved the measurement of the noise produced by five gliding aircraft in an aerodynamically clean configuration during low altitude flyovers. These aircraft had gross weights that ranged from 5785 to 173 925N (1300 to 39,000 pounds), fly-by velocities from 30 to 98.5m/sec (58 to 191.5 knots or 98 to 323 ft/sec) and wing aspect ratios from 6.59 to 18.25. The results of these measurements were used to develop an equation relating aerodynamic noise to readily evaluated physical and operational parameters of the aircraft. A non-dimensional frequency spectrum, based on the mean wing thickness, was also developed.

  5. Method for suppressing noise in measurements

    NASA Technical Reports Server (NTRS)

    Carson, Paul J. (Inventor); Madsen, Louis A. (Inventor); Leskowitz, Garett M. (Inventor); Weitekamp, Daniel P. (Inventor)

    2000-01-01

    Techniques of combining separate but correlated measurements to form a second-order or higher order correlation function to suppress the effects of noise in the initial condition of a system capable of retaining memory of an initial state of the system with a characteristic relaxation time. At least two separate measurements are obtained from the system. The temporal separation between the two separate measurements is preferably comparable to or less than the characteristic relaxation time and is adjusted to allow for a correlation between two measurements.

  6. Quantitative appraisal for noise reduction in digital holographic phase imaging.

    PubMed

    Montresor, Silvio; Picart, Pascal

    2016-06-27

    This paper discusses on a quantitative comparison of the performances of different advanced algorithms for phase data de-noising. In order to quantify the performances, several criteria are proposed: the gain in the signal-to-noise ratio, the Q index, the standard deviation of the phase error, and the signal to distortion ratio. The proposed methodology to investigate de-noising algorithms is based on the use of a realistic simulation of noise-corrupted phase data. A database including 25 fringe patterns divided into 5 patterns and 5 different signal-to-noise ratios was generated to evaluate the selected de-noising algorithms. A total of 34 algorithms divided into different families were evaluated. Quantitative appraisal leads to ranking within the considered criteria. A fairly good correlation between the signal-to-noise ratio gain and the quality index has been observed. There exists an anti-correlation between the phase error and the quality index which indicates that the phase errors are mainly structural distortions in the fringe pattern. Experimental results are thoroughly discussed in the paper. PMID:27410587

  7. Quantitative phase-amplitude microscopy. III. The effects of noise.

    PubMed

    Paganin, D; Barty, A; McMahon, P J; Nugent, K A

    2004-04-01

    We explore the effect of noise on images obtained using quantitative phase-amplitude microscopy - a new microscopy technique based on the determination of phase from the intensity evolution of propagating radiation. We compare the predictions with experimental results and also propose an approach that allows good-quality quantitative phase retrieval to be obtained even for very noisy data.

  8. Noise in Bose Josephson junctions: Decoherence and phase relaxation

    SciTech Connect

    Ferrini, G.; Minguzzi, A.; Hekking, F. W. J.; Spehner, D.

    2010-09-15

    Squeezed states and macroscopic superpositions of coherent states have been predicted to be generated dynamically in Bose Josephson junctions. We solve exactly the quantum dynamics of such a junction in the presence of a classical noise coupled to the population-imbalance number operator (phase noise), accounting for, for example, the experimentally relevant fluctuations of the magnetic field. We calculate the correction to the decay of the visibility induced by the noise in the non-Markovian regime. Furthermore, we predict that such a noise induces an anomalous rate of decoherence among the components of the macroscopic superpositions, which is independent of the total number of atoms, leading to potential interferometric applications.

  9. Development of rotorcraft interior noise control concepts. Phase 3: Development of noise control concepts

    NASA Technical Reports Server (NTRS)

    Yoerkie, Charles A.; Gintoli, P. J.; Ingraham, S. T.; Moore, J. A.

    1986-01-01

    The goal of this research is the understanding of helicopter internal noise mechanisms and the development, design, and testing of noise control concepts which will produce significant reductions in the acoustic environment to which passengers are exposed. The Phase 3 effort involved the identification and evaluation of current and advanced treatment concepts, including isolation of structure-borne paths. In addition, a plan was devised for the full-scale evaluation of an isolation concept. Specific objectives were as follows: (1) identification and characterization of various noise control concepts; (2) implementation of noise control concepts within the S-76 SEA (statistical energy analysis) model; (3) definition and evaluation of a preliminary acoustic isolation design to reduce structure-borne transmission of acoustic frequency main gearbox gear clash vibrations into the airframe; (4) formulation of a plan for the full-scale validation of the isolation concept; and (5) prediction of the cabin noise environment with various noise control concepts installed.

  10. Noise Measurements of the VAIIPR Fan

    NASA Technical Reports Server (NTRS)

    Mendoza, Jeff; Weir, Don

    2012-01-01

    This final report has been prepared by Honeywell Aerospace, Phoenix, Arizona, a unit of Honeywell International, Inc., documenting work performed during the period September 2004 through November 2005 for the National Aeronautics and Space Administration (NASA) Glenn Research Center, Cleveland, Ohio, under the Revolutionary Aero-Space Engine Research (RASER) Program, Contract No. NAS3- 01136, Task Order 6, Noise Measurements of the VAIIPR Fan. The NASA Task Manager was Dr. Joe Grady, NASA Glenn Research Center, Mail Code 60-6, Cleveland, Ohio 44135. The NASA Contract Officer was Mr. Albert Spence, NASA Glenn Research Center, Mail Code 60-6, Cleveland, Ohio 44135. This report focuses on the evaluation of internal fan noise as generated from various inflow disturbances based on measurements made from a circumferential array of sensors located near the fan and sensors upstream of a serpentine inlet.

  11. On the origin of flicker noise in carrier-envelope phase stabilization.

    PubMed

    Song, Youjian; Lücking, Fabian; Borchers, Bastian; Steinmeyer, Günter

    2014-12-15

    The origin of a 1/f noise contribution in the long-term carrier-envelope phase (CEP) measurements of mode-locked lasers is discussed. Using two different collinear interferometers for the out-of-loop characterization of feed-forward stabilized Ti:sapphire oscillators, we suppress a possible technical origin of 1/f noise to the extent possible. Both measurements indicate a lower limit of CEP frequency noise of 1  mHz/√Hz. Investigating several possible origins of this noise floor, we find a good agreement with a quantum noise mechanism that is directly induced by intracavity-amplified spontaneous emission (ASE). These findings enable direct access to ASE noise in short-pulse oscillators, which is very hard to characterize via repetition rate fluctuations. Finally, we discuss the possible consequences for frequency-comb-based timekeeping and frequency metrology, as well as for attosecond science. PMID:25503048

  12. Spectral density measurements of gyro noise

    NASA Technical Reports Server (NTRS)

    Truncale, A.; Koenigsberg, W.; Harris, R.

    1972-01-01

    Power spectral density (PSD) was used to analyze the outputs of several gyros in the frequency range from 0.01 to 200 Hz. Data were accumulated on eight inertial quality instruments. The results are described in terms of input angle noise (arcsec 2/Hz) and are presented on log-log plots of PSD. These data show that the standard deviation of measurement noise was 0.01 arcsec or less for some gyros in the passband from 1 Hz down 10 0.01 Hz and probably down to 0.001 Hz for at least one gyro. For the passband between 1 and 100 Hz, uncertainties in the 0.01 and 0.05 arcsec region were observed.

  13. Seismometer Self-Noise and Measuring Methods

    USGS Publications Warehouse

    Ringler, Adam; R. Sleeman,; Hutt, Charles R.; Gee, Lind S.

    2014-01-01

    Seismometer self-noise is usually not considered when selecting and using seismic waveform data in scientific research as it is typically assumed that the self-noise is negligibly small compared to seismic signals. However, instrumental noise is part of the noise in any seismic record, and in particular, at frequencies below a few mHz, the instrumental noise has a frequency-dependent character and may dominate the noise. When seismic noise itself is considered as a carrier of information, as in seismic interferometry (e.g., Chaput et al. 2012), it becomes extremely important to estimate the contribution of instrumental noise to the recordings.

  14. Final Report on DE-FG02-04ER46107: Glasses, Noise and Phase Transitions

    SciTech Connect

    Yu, Clare C.

    2011-12-31

    We showed that noise has distinct signatures at phase transitions in spin systems. We also studied charge noise, critical current noise, and flux noise in superconducting qubits and Josephson junctions.

  15. Very low-phase noise, coherent 94GHz radar for micro-Doppler and vibrometry studies

    NASA Astrophysics Data System (ADS)

    Robertson, Duncan A.; Brooker, Graham M.; Beasley, Patrick D. L.

    2014-05-01

    Micro-Doppler and vibrometry measurements require coherent radars with low phase noise. We report the development of a novel, very low phase noise 94 GHz radar, called T-220, which offers superior performance for micro-Doppler and vibrometry studies compared with our previous work. The radar uses a combination of direct digital synthesis (DDS) chirp generation, frequency upconversion and frequency multiplication to yield very low phase noise and rapid, contiguous chirps, necessary for Doppler studies and other coherent processing applications. Dual fan beam antennas are used to achieve negligible transmit-receive leakage, with fine azimuth resolution and modest elevation coverage. The resulting PPI imagery is very high fidelity with little or no evidence of phase noise effects.

  16. Bosonic Amplification of Noise-Induced Suppression of Phase Diffusion

    SciTech Connect

    Khodorkovsky, Y.; Vardi, A.; Kurizki, G.

    2008-06-06

    We study the effect of noise-induced dephasing on collisional phase diffusion in the two-site Bose-Hubbard model. Dephasing of the quasimomentum modes may slow down phase diffusion in the quantum Zeno limit. Remarkably, the degree of suppression is enhanced by a bosonic factor of order N/logN as the particle number N increases.

  17. Noise Diode Stability Measurements Using a 4.3 GHz Laboratory Radiometer

    NASA Technical Reports Server (NTRS)

    Scherner, M. J.; Lawrence, R. W.

    1997-01-01

    The need for passive microwave radiometry using aperture synthesis and phased arrays for large apertures requiring more stability has generated several studies. The in-flight calibration and, therefore, the stability of such systems is an important design consideration. A 4.3 GHz laboratory radiometry operating in a balanced Dicke mode has been developed for making precise brightness (noise) temperature measurements. The stability of the noise diode source used in the noise-injection loop is of interest. A statistical Allan variance method to characterize the stability of the radiometer and the noise diode is presented in this paper. Noise measurements which demonstrate this approach are also included.

  18. Measured and calculated characteristics of wind turbine noise

    NASA Technical Reports Server (NTRS)

    Greene, G. C.

    1981-01-01

    The results of an analytical and experimental investigation of wind turbine noise are presented. Noise calculations indicate that for configurations with the rotor downwind of the support tower, the primary source of noise is the rapid change in rotor loadings which occurs as the rotor passes through the tower wake. Noise measurements are presented for solid and truss type tower models with both upwind and downwind rotors. Upwind rotor configurations are shown to be significantly quieter than downwind configurations. The model data suggest that averaged noise measurements and noise calculations based on averaged tower wake characteristics may not accurately represent the impulsive noise characteristics of downwind rotor configurations.

  19. Effects of the Noises' Statistics and Spectrum on Noise-Induced Phase Transitions

    NASA Astrophysics Data System (ADS)

    Deza, Roberto R.; Fuentes, Miguel A.; Wio, Horacio S.

    2007-07-01

    The study of the effect of the noises' statistics and spectrum on second-order, purely noise-induced phase transition (NIPT) is of wide interest: It is simplified if the noises are dynamically generated by means of stochastic differential equations driven by white noises, a well known case being that of Ornstein-Uhlenbeck noises with a self-correlation time τ whose effect on the NIPT phase diagram has been studied some time ago. Another case is when the stationary pdf is a (colored) q-Gaussian which, being a fat-tail distribution for q > 1 and a compact-support one for q < 1, allows for a controlled study of the effects of the departure from Gaussian statistics. As done with stochastic resonance and other phenomena, we exploit this tool to study—within a simple mean-field approximation—the combined effect on NIPT of the noises' statistics and spectrum. Even for relatively small τ, it is shown that whereas for fat-tail noise distributions counteract the effect of self-correlation, compact-support ones enhance it.

  20. 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.

  1. Phase noise reveals early category-specific modulation of the event-related potentials

    PubMed Central

    Németh, Kornél; Kovács, Petra; Vakli, Pál; Kovács, Gyula; Zimmer, Márta

    2014-01-01

    Previous studies have found that the amplitude of the early event-related potential (ERP) components evoked by faces, such as N170 and P2, changes systematically as a function of noise added to the stimuli. This change has been linked to an increased perceptual processing demand and to enhanced difficulty in perceptual decision making about faces. However, to date it has not yet been tested whether noise manipulation affects the neural correlates of decisions about face and non-face stimuli similarly. To this end, we measured the ERPs for faces and cars at three different phase noise levels. Subjects performed the same two-alternative age-discrimination task on stimuli chosen from young–old morphing continua that were created from faces as well as cars and were calibrated to lead to similar performances at each noise-level. Adding phase noise to the stimuli reduced performance and enhanced response latency for the two categories to the same extent. Parallel to that, phase noise reduced the amplitude and prolonged the latency of the face-specific N170 component. The amplitude of the P1 showed category-specific noise dependence: it was enhanced over the right hemisphere for cars and over the left hemisphere for faces as a result of adding phase noise to the stimuli, but remained stable across noise levels for cars over the left and for faces over the right hemisphere. Moreover, noise modulation altered the category-selectivity of the N170, while the P2 ERP component, typically associated with task decision difficulty, was larger for the more noisy stimuli regardless of stimulus category. Our results suggest that the category-specificity of noise-induced modulations of ERP responses starts at around 100 ms post-stimulus. PMID:24795689

  2. Measurement with verification of stationary signals and noise in extremely quiet environments: Measuring below the noise floor

    PubMed Central

    Ellingson, Roger M.; Gallun, Frederick J.; Bock, Guillaume

    2015-01-01

    It can be problematic to measure stationary acoustic sound pressure level in any environment when the target level approaches or lies below the minimum measureable sound pressure level of the measurement system itself. This minimum measureable level, referred to as the inherent measurement system noise floor, is generally established by noise emission characteristics of measurement system components such as microphones, preamplifiers, and other system circuitry. In this paper, methods are presented and shown accurate measuring stationary levels within 20 dB above and below this system noise floor. Methodology includes (1) measuring inherent measurement system noise, (2) subtractive energy based, inherent noise adjustment of levels affected by system noise floor, and (3) verifying accuracy of inherent noise adjustment technique. While generalizable to other purposes, the techniques presented here were specifically developed to quantify ambient noise levels in very quiet rooms used to evaluate free-field human hearing thresholds. Results obtained applying the methods to objectively measure and verify the ambient noise level in an extremely quiet room, using various measurement system noise floors and analysis bandwidths, are presented and discussed. The verified results demonstrate the adjustment method can accurately extend measurement range to 20 dB below the measurement system noise floor, and how measurement system frequency bandwidth can affect accuracy of reported noise levels. PMID:25786932

  3. Method for suppressing noise in measurements

    NASA Technical Reports Server (NTRS)

    Carson, Paul L. (Inventor); Madsen, Louis A. (Inventor); Leskowitz, Garett M. (Inventor); Weitekamp, Daniel P. (Inventor)

    2000-01-01

    Methods for suppressing noise in measurements by correlating functions based on at least two different measurements of a system at two different times. In one embodiment, a measurement operation is performed on at least a portion of a system that has a memory. A property of the system is measured during a first measurement period to produce a first response indicative of a first state of the system. Then the property of the system is measured during a second measurement period to produce a second response indicative of a second state of the system. The second measurement is performed after an evolution duration subsequent to the first measurement period when the system still retains a degree of memory of an aspect of the first state. Next, a first function of the first response is combined with a second function of the second response to form a second-order correlation function. Information of the system is then extracted from the second-order correlation function.

  4. Recommendations for field measurements of aircraft noise

    NASA Technical Reports Server (NTRS)

    Marsh, A. H.

    1982-01-01

    Specific recommendations for environmental test criteria, data acquisition procedures, and instrument performance requirements for measurement of noise levels produced by aircraft in flight are provided. Recommendations are also given for measurement of associated airplane and engine parameters and atmospheric conditions. Recommendations are based on capabilities which were available commercially in 1981; they are applicable to field tests of aircraft flying subsonically past microphones located near the surface of the ground either directly under or to the side of a flight path. Aircraft types covered by the recommendations include fixed-wing airplanes powered by turbojet or turbofan engines or by propellers. The recommended field-measurement procedures are consistent with assumed requirements for data processing and analysis.

  5. Recommendations for field measurements of aircraft noise

    NASA Astrophysics Data System (ADS)

    Marsh, A. H.

    1982-04-01

    Specific recommendations for environmental test criteria, data acquisition procedures, and instrument performance requirements for measurement of noise levels produced by aircraft in flight are provided. Recommendations are also given for measurement of associated airplane and engine parameters and atmospheric conditions. Recommendations are based on capabilities which were available commercially in 1981; they are applicable to field tests of aircraft flying subsonically past microphones located near the surface of the ground either directly under or to the side of a flight path. Aircraft types covered by the recommendations include fixed-wing airplanes powered by turbojet or turbofan engines or by propellers. The recommended field-measurement procedures are consistent with assumed requirements for data processing and analysis.

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

    NASA Technical Reports Server (NTRS)

    Podboy, Gary

    2012-01-01

    Subsonic jets are relatively simple. The peak noise source location gradually moves upstream toward the nozzle as frequency increases. 2) Supersonic jets are more complicated. The peak noise source location moves downstream as frequency increases through a BBSN hump. 3) In both subsonic and supersonic jets the peak noise source location corresponding to a given frequency of noise moves downstream as jet Mach number increases. 4) The noise generated at a given frequency in a BBSN hump is generated by a small number of shocks, not from all the shocks at the same time. 5) Single microphone spectrum levels decrease when the noise source locations measured with the phased array are blocked by a shielding surface. This consistency validates the phased array data and the stationary monopole source model used to process it. 6) Reflecting surface data illustrate that the law of reflection must be satisfied for noise to reflect off a surface toward an observer. Depending on the relative locations of the jet, the surface and the observer only some of the jet noise sources may satisfy this requirement. 7) The low frequency noise created when a jet flow impinges on a surface comes primarily from the trailing edge regardless of the axial extent impacted by the flow.

  7. Phase-unwrapping algorithm for images with high noise content based on a local histogram

    NASA Astrophysics Data System (ADS)

    Meneses, Jaime; Gharbi, Tijani; Humbert, Philippe

    2005-03-01

    We present a robust algorithm of phase unwrapping that was designed for use on phase images with high noise content. We proceed with the algorithm by first identifying regions with continuous phase values placed between fringe boundaries in an image and then phase shifting the regions with respect to one another by multiples of 2pi to unwrap the phase. Image pixels are segmented between interfringe and fringe boundary areas by use of a local histogram of a wrapped phase. The algorithm has been used successfully to unwrap phase images generated in a three-dimensional shape measurement for noninvasive quantification of human skin structure in dermatology, cosmetology, and plastic surgery.

  8. Phase-unwrapping algorithm for images with high noise content based on a local histogram.

    PubMed

    Meneses, Jaime; Gharbi, Tijani; Humbert, Philippe

    2005-03-01

    We present a robust algorithm of phase unwrapping that was designed for use on phase images with high noise content. We proceed with the algorithm by first identifying regions with continuous phase values placed between fringe boundaries in an image and then phase shifting the regions with respect to one another by multiples of 2pi to unwrap the phase. Image pixels are segmented between interfringe and fringe boundary areas by use of a local histogram of a wrapped phase. The algorithm has been used successfully to unwrap phase images generated in a three-dimensional shape measurement for noninvasive quantification of human skin structure in dermatology, cosmetology, and plastic surgery.

  9. Ranking of Reactions Based on Sensitivity of Protein Noise Depends on the Choice of Noise Measure

    PubMed Central

    Gokhale, Sucheta; Gadgil, Chetan

    2015-01-01

    Gene expression is a stochastic process. Identification of the step maximally affecting noise in the protein level is an important aspect of investigation of gene product distribution. There are numerous experimental and theoretical studies that seek to identify this important step. However, these studies have used two different measures of noise, viz. coefficient of variation and Fano factor, and have compared different processes leading to contradictory observations regarding the important step. In this study, we performed systematic global and local sensitivity analysis on two models of gene expression to investigate relative contribution of reaction rate parameters to steady state noise in the protein level using both the measures of noise. We analytically and computationally showed that the ranking of parameters based on the sensitivity of the noise to variation in a given parameter is a strong function of the choice of the noise measure. If the Fano factor is used as the noise measure, translation is the important step whereas for coefficient of variation, transcription is the important step. We derived an analytical expression for local sensitivity and used it to explain the distinct contributions of each reaction parameter to the two measures of noise. We extended the analysis to a generic linear catalysis reaction system and observed that the reaction network topology was an important factor influencing the local sensitivity of the two measures of noise. Our study suggested that, for the analysis of contributions of reactions to the noise, consideration of both the measures of noise is important. PMID:26625133

  10. A low-noise delta-sigma phase modulator for polar transmitters.

    PubMed

    Zhou, Bo

    2014-01-01

    A low-noise phase modulator, using finite-impulse-response (FIR) filtering embedded delta-sigma (ΔΣ) fractional-N phase-locked loop (PLL), is fabricated in 0.18 μ m CMOS for GSM/EDGE polar transmitters. A simplified digital compensation filter with inverse-FIR and -PLL features is proposed to trade off the transmitter noise and linearity. Experimental results show that the presented architecture performs RF phase modulation well with 20 mW power dissipation from 1.6 V supply and achieves the root-mean-square (rms) and peak phase errors of 4° and 8.5°, respectively. The measured and simulated phase noises of -104 dBc/Hz and -120 dBc/Hz at 400-kHz offset from 1.8-GHz carrier frequency are observed, respectively.

  11. A Low-Noise Delta-Sigma Phase Modulator for Polar Transmitters

    PubMed Central

    Zhou, Bo

    2014-01-01

    A low-noise phase modulator, using finite-impulse-response (FIR) filtering embedded delta-sigma (ΔΣ) fractional-N phase-locked loop (PLL), is fabricated in 0.18 μm CMOS for GSM/EDGE polar transmitters. A simplified digital compensation filter with inverse-FIR and -PLL features is proposed to trade off the transmitter noise and linearity. Experimental results show that the presented architecture performs RF phase modulation well with 20 mW power dissipation from 1.6 V supply and achieves the root-mean-square (rms) and peak phase errors of 4° and 8.5°, respectively. The measured and simulated phase noises of −104 dBc/Hz and −120 dBc/Hz at 400-kHz offset from 1.8-GHz carrier frequency are observed, respectively. PMID:24719578

  12. Measurement by phase severance

    SciTech Connect

    Noyes, H.P.

    1987-03-01

    It is claimed that the measurement process is more accurately described by ''quasi-local phase severance'' than by ''wave function collapse''. The approach starts from the observation that the usual route to quantum mechanics starting from the Hamilton-Jacobi equations throws away half the degrees of freedom, namely, the classical initial state parameters. To overcome this difficulty, the full set of Hamilton-Jacobi equations is interpreted as operator equations acting on a state vector. The measurement theory presented is based on the conventional S-matrix boundary condition of N/sub A/ free particles in the distant past and N/sub B/ free particles in the distant future and taking the usual free particle wave functions, multiplied by phase factors.

  13. Determination of parameters of a nuclear reactor through noise measurements

    DOEpatents

    Cohn, C.E.

    1975-07-15

    A method of measuring parameters of a nuclear reactor by noise measurements is described. Noise signals are developed by the detectors placed in the reactor core. The polarity coincidence between the noise signals is used to develop quantities from which various parameters of the reactor can be calculated. (auth)

  14. Extraction of triplicated PKP phases from noise correlations

    NASA Astrophysics Data System (ADS)

    Xia, Han H.; Song, Xiaodong; Wang, Tao

    2016-04-01

    Ambient noise correlation method has been widely used to extract surface waves and tomography. The extraction of body waves has been very limited, but recent reports have suggested promises for deep incident waves. Here we report our first observations of triplicated PKP phases (important phases for studying the Earth's core) and confirm observations of other body-wave core phases from noise correlations. We use dense seismic arrays in South America and China Regional Seismic Networks at distances from 145° to the antipode. We can clearly observe different PKP branches (df, bc and ab) in stacks of the station-station correlations. Both ambient noise and earthquake coda contribute to PKP phases. However, the contributions vary with frequency and with body-wave phases. At shorter periods (5-20 s), three branches of PKP (df, bc and ab) can be extracted from ambient noise and the ab phase from earthquake coda. At longer periods (15-50 s), earthquake coda are effective in generating the df branch, but not the ab branch. The generation of the PKIKP phase (df branch) from earthquake coda does not depend on earthquake focal mechanisms or focal depths. However, earthquakes far from the stations contribute more than events closer by. The best coda window is around 10 000-40 000 s and the best magnitude threshold is Mw greater than 6.8 or 6.9. The observation of triplicated PKP branches from noise correlations provides a new type of data for studying the Earth's deep interior, in particularly the inner core anisotropy, which overcomes some of the limitations of traditional earthquake-based studies (such as limited source distributions and source location errors).

  15. 14 CFR 36.101 - Noise measurement and evaluation.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... Section 36.101 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT NOISE STANDARDS: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION Transport Category Large Airplanes and Jet Airplanes § 36.101 Noise measurement and evaluation. For transport category large...

  16. Noise-Induced Phase Transitions: Effects of the Noises' Statistics and Spectrum

    NASA Astrophysics Data System (ADS)

    Deza, Roberto R.; Wio, Horacio S.; Fuentes, Miguel A.

    2007-05-01

    The local, uncorrelated multiplicative noises driving a second-order, purely noise-induced, ordering phase transition (NIPT) were assumed to be Gaussian and white in the model of [Phys. Rev. Lett. 73, 3395 (1994)]. The potential scientific and technological interest of this phenomenon calls for a study of the effects of the noises' statistics and spectrum. This task is facilitated if these noises are dynamically generated by means of stochastic differential equations (SDE) driven by white noises. One such case is that of Ornstein-Uhlenbeck noises which are stationary, with Gaussian pdf and a variance reduced by the self-correlation time τ, and whose effect on the NIPT phase diagram has been studied some time ago. Another such case is when the stationary pdf is a (colored) Tsallis' q-Gaussian which, being a fat-tail distribution for q > 1 and a compact-support one for q < 1, allows for a controlled exploration of the effects of the departure from Gaussian statistics. As done before with stochastic resonance and other phenomena, we now exploit this tool to study—within a simple mean-field approximation and with an emphasis on the order parameter and the "susceptibility"—the combined effect on NIPT of the noises' statistics and spectrum. Even for relatively small τ, it is shown that whereas fat-tail noise distributions (q > 1) counteract the effect of self-correlation, compact-support ones (q < 1) enhance it. Also, an interesting effect on the susceptibility is seen in the last case.

  17. Noise properties of grating-based x-ray phase contrast computed tomography

    SciTech Connect

    Koehler, Thomas; Juergen Engel, Klaus; Roessl, Ewald

    2011-05-15

    Purpose: To investigate the properties of tomographic grating-based phase contrast imaging with respect to its noise power spectrum and the energy dependence of the achievable contrast to noise ratio. Methods: Tomographic simulations of an object with 11 cm diameter constituted of materials of biological interest were conducted at different energies ranging from 25 to 85 keV by using a wave propagation approach. Using a Monte Carlo simulation of the x-ray attenuation within the object, it is verified that the simulated measurement deposits the same dose within the object at each energy. Results: The noise in reconstructed phase contrast computed tomography images shows a maximum at low spatial frequencies. The contrast to noise ratio reaches a maximum around 45 keV for the simulated object. The general dependence of the contrast to noise on the energy appears to be independent of the material. Compared with reconstructed absorption contrast images, the reconstructed phase contrast images show sometimes better, sometimes worse, and sometimes similar contrast to noise, depending on the material and the energy. Conclusions: Phase contrast images provide additional information to the conventional absorption contrast images and might thus be useful for medical applications. However, the observed noise power spectrum in reconstructed phase contrast images implies that the usual trade-off between noise and resolution is less efficient for phase contrast imaging compared with absorption contrast imaging. Therefore, high-resolution imaging is a strength of phase contrast imaging, but low-resolution imaging is not. This might hamper the clinical application of the method, in cases where a low spatial resolution is sufficient for diagnosis.

  18. Ultra-low noise optical phase-locked loop

    NASA Astrophysics Data System (ADS)

    Ayotte, Simon; Babin, André; Costin, François

    2014-03-01

    The relative phase between two fiber lasers is controlled via a high performance optical phase-locked loop (OPLL). Two parameters are of particular importance for the design: the intrinsic phase noise of the laser (i.e. its linewidth) and a high-gain, low-noise electronic locking loop. In this work, one of the lowest phase noise fiber lasers commercially available was selected (i.e. NP Photonics Rock fiber laser module), with sub-kHz linewidth at 1550.12 nm. However, the fast tuning mechanism of such lasers is through stretching its cavity length with a piezoelectric transducer which has a few 10s kHz bandwidth. To further increase the locking loop bandwidth to several MHz, a second tuning mechanism is used by adding a Lithium Niobate phase modulator in the laser signal path. The OPLL is thus divided into two locking loops, a slow loop acting on the laser piezoelectric transducer and a fast loop acting on the phase modulator. The beat signal between the two phase-locked lasers yields a highly pure sine wave with an integrated phase error of 0.0012 rad. This is orders of magnitude lower than similar existing systems such as the Laser Synthesizer used for distribution of photonic local oscillator (LO) for the Atacama Large Millimeter Array radio telescope in Chile. Other applications for ultra-low noise OPLL include coherent power combining, Brillouin sensing, light detection and ranging (LIDAR), fiber optic gyroscopes, phased array antenna and beam steering, generation of LOs for next generation coherent communication systems, coherent analog optical links, terahertz generation and coherent spectroscopy.

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

    SciTech Connect

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

    2012-04-15

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

  20. Noise-enhanced phase synchronization in time-delayed systems.

    PubMed

    Senthilkumar, D V; Shrii, M Manju; Kurths, J

    2012-02-01

    We investigate the phenomenon of noise-enhanced phase synchronization (PS) in coupled time-delay systems, which usually exhibit non-phase-coherent attractors with complex topological properties. As a delay system is essentially an infinite dimensional in nature with multiple characteristic time scales, it is interesting and crucial to understand the interplay of noise and the time scales in achieving PS. In unidirectionally coupled systems, the response system adjust all its time scales to that of the drive, whereas both subsystems adjust their rhythms to a single (main time scale of the uncoupled system) time scale in bidirectionally coupled systems. We find similar effects for both a common and an independent additive Gaussian noise.

  1. 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.

  2. Phase noise reduction in semiconductor lasers by optical negative feedback

    NASA Astrophysics Data System (ADS)

    Yasaka, Hiroshi; Aoyama, Konosuke; Yokota, Nobuhide

    2016-04-01

    Phase noise of a single mode semiconductor laser is reduced drastically by introducing a newly proposed optical negative feedback scheme. Proof-of-concept experiment confirms that the spectral linewidth of a semiconductor laser can be reduced to 1/1,000 successfully by applying the scheme.

  3. Frequency noise measurement of diode-pumped Nd:YAG ring lasers

    NASA Technical Reports Server (NTRS)

    Chen, Chien-Chung; Win, Moe Zaw

    1990-01-01

    The combined frequency noise spectrum of two model 120-01A nonplanar ring oscillator lasers was measured by first heterodyne detecting the IF signal and then measuring the IF frequency noise using an RF frequency discriminator. The results indicated the presence of a 1/f-squared noise component in the power-spectral density of the frequency fluctuations between 1 Hz and 1 kHz. After incorporating this 1/f-squared into the analysis of the optical phase tracking loop, the measured phase error variance closely matches the theoretical predictions.

  4. Development of Field Measurement Systems for Flight Vehicle Noise

    NASA Technical Reports Server (NTRS)

    Yu, James C.; Wright, Kenneth D.; Preisser, John S.; Marcolini, Michael A.

    1999-01-01

    Field measurement of noise radiated from flight vehicles is an important element of aircraft noise research programs. At NASA Langley, a dedicated effort that spans over two decades was devoted to the development of acoustic measurement systems to support the NASA noise research programs. The new challenge for vehicle operational noise reduction through varying glide slope and flight path require noise measurement to be made over a very large area under the vehicle flight path. Such a challenge can be met through the digital remote system currently under final development at NASA Langley.

  5. Evaluation of noise pollution in urban traffic hubs—Noise maps and measurements

    SciTech Connect

    Fiedler, Paulo Eduardo Kirrian; Zannin, Paulo Henrique Trombetta

    2015-02-15

    A study was made of some of the main traffic hubs in a Latin American metropolis, in order to determine the presence or absence of noise by means of noise measurements and acoustic mapping. To characterize noise in the evaluated road stretches, 232 measurements were taken at different points. The Predictor software package was used for the noise mapping calculations. Noise sensitive areas, e.g., hospitals, were identified in the evaluated road stretches. Noise maps were calculated for two hospitals, showing the current levels of noise that reach their facades. Hypothetical scenarios were simulated by making changes in the composition of traffic and total number of vehicles, and an assessment was made of the potential influence of these modifications in reducing the noise levels reaching the facades of the buildings in question. The simulations indicated that a 50% reduction in total traffic flow, or a 50% reduction in heavy vehicle traffic flow, would reduce the noise levels by about 3 dB(A). - Highlights: • Evaluation of noise pollution in urban traffic hubs • Street systems • Environmental noise impacts • Noise mapping.

  6. Noise measurements in a composite niobium/YBCO SQUID and determination of the magnetic noise by direct measurement

    SciTech Connect

    Harrop, S.P.; Keene, M.N.; Muirhead, C.M.; Gough, C.E. )

    1991-03-01

    We have measured the noise performance of a composite niobium/YBCO point contact 2-hole SQUID, at 4.2 K in both rf and dc bias modes. The noise was measured by a technique which allowed the component which was flux noise to be measured. The flux noise was found to be the same in both bias modes. A direct measurement of the noise in a single hole in the same sample was made as a function of temperature and was found to display two peaks. Possible causes are discussed in this paper.

  7. An analysis of FM jamming and noise quality measures

    NASA Astrophysics Data System (ADS)

    Taylor, Timothy N.

    1993-12-01

    This thesis provides a description of FM-by-noise jamming, both at RF and at the output of the radar receiver, in terms of spectra, time-domain waveforms, and univariate probability density of amplitude. Particular emphasis is given to the case where the peak frequency deviation of the FM modulator is sufficiently small that Woodward's Theorem does not provide a good approximation of the RF spectrum. Additionally, noise quality measures which have been used to measure noise quality of radar jammers are considered theoretically and experimentally, and it is concluded that a noise measure which incorporates both a spectral measure and a probability density measure should be adopted. One such measure is proposed here. Lastly, a technique for measuring the noise quality of an operational jammer is demonstrated and the programs necessary to measure noise quality of an operational jammer are included here.

  8. NMR phase noise in bitter magnets.

    PubMed

    Sigmund, E E; Calder, E S; Thomas, G W; Mitrović, V F; Bachman, H N; Halperin, W P; Kuhns, P L; Reyes, A P

    2001-02-01

    We have studied the temporal instability of a high field resistive Bitter magnet through nuclear magnetic resonance (NMR). This instability leads to transverse spin decoherence in repeated and accumulated NMR experiments as is normally performed during signal averaging. We demonstrate this effect via Hahn echo and Carr--Purcell--Meiboom--Gill (CPMG) transverse relaxation experiments in a 23-T resistive magnet. Quantitative analysis was found to be consistent with separate measurements of the magnetic field frequency fluctuation spectrum, as well as with independent NMR experiments performed in a magnetic field with a controlled instability. Finally, the CPMG sequence with short pulse delays is shown to be successful in recovering the intrinsic spin--spin relaxation even in the presence of magnetic field temporal instability.

  9. A measurement model for general noise reaction in response to aircraft noise.

    PubMed

    Kroesen, Maarten; Schreckenberg, Dirk

    2011-01-01

    In this paper a measurement model for general noise reaction (GNR) in response to aircraft noise is developed to assess the performance of aircraft noise annoyance and a direct measure of general reaction as indicators of this concept. For this purpose GNR is conceptualized as a superordinate latent construct underlying particular manifestations. This conceptualization is empirically tested through estimation of a second-order factor model. Data from a community survey at Frankfurt Airport are used for this purpose (N=2206). The data fit the hypothesized factor structure well and support the conceptualization of GNR as a superordinate construct. It is concluded that noise annoyance and a direct measure of general reaction to noise capture a large part of the negative feelings and emotions in response to aircraft noise but are unable to capture all relevant variance. The paper concludes with recommendations for the valid measurement of community reaction and several directions for further research.

  10. 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.

  11. Ultrasonic Cross-Correlation Flow Measurement: Theory, Noise Contamination Mechanisms, and a Noise Mitigation Technique

    SciTech Connect

    Jenkins, D.M.; Lysak, P.D.; Capone, D.E.; Brown, W.L.; Askari, V.

    2006-07-01

    Based on past experience with ultrasonic cross-correlation flow meters in power plant environments, the presence of spatially correlated noise due to pressure waves, vibration, or sources other than transport of turbulent eddies will cause a bias in the time delays measured by the meter. Several techniques were developed to detect the existence of such correlated noise and correct for its effect at plant conditions. An analytical and experimental investigation was performed to further understand the basic physics of the noise mechanisms. The dominant error mechanisms investigated in this work were speed of sound perturbations due to pressure fluctuations and beam path length changes due to wall vibration. An analytical model was formulated which estimates the signal level of the flow meter based on the turbulent velocity field. From this model, an estimate of the system noise which would cause contamination could be determined. A test at a water tunnel facility was performed in order to evaluate the noise mechanisms. During this test, measurements were taken with and without controlled noise sources. Pressure and acceleration measurements were used to evaluate a coherent noise removal technique developed to mitigate the impact of noise in the ultrasonic cross-correlation flow measurement. The coherent noise removal technique was shown to be effective in removing noise during the water tunnel test. (authors)

  12. Core noise measurements on a YF-102 turbofan engine

    NASA Technical Reports Server (NTRS)

    Reshotko, M.; Karchmer, A. M.; Penko, P. F.; Mcardle, J. G.

    1977-01-01

    Core noise from a YF-102 high bypass ratio turbofan engine was investigated through the use of simultaneous measurements of internal fluctuating pressures and far field noise. Acoustic waveguide probes, located in the engine at the compressor exit, in the combustor, at the turbine exit, and in the core nozzle, were employed to measure internal fluctuating pressures. Spectra showed that the internal signals were free of tones, except at high frequency where machinery noise was present. Data obtained over a wide range of engine conditions suggest that below 60% of maximum fan speed the low frequency core noise contributes significantly to the far field noise.

  13. Identification of Noise Sources and Design of Noise Reduction Measures for a Pneumatic Nail Gun

    PubMed Central

    Jayakumar, Vignesh; Zechmann, Edward

    2015-01-01

    An experimental-analytical procedure was implemented to reduce the operating noise level of a nail gun, a commonly found power tool in a construction site. The procedure is comprised of preliminary measurements, identification and ranking of major noise sources and application of noise controls. Preliminary measurements show that the impact noise transmitted through the structure and the exhaust related noise were found to be the first and second major contributors. Applying a noise absorbing foam on the outside of the nail gun body was found to be an effective noise reduction technique. One and two-volume small mufflers were designed and applied to the exhaust side of the nail gun which reduced not only the exhaust noise but also the impact noise. It was shown that the overall noise level could be reduced by as much as 3.5 dB, suggesting that significant noise reduction is possible in construction power tools without any significant increase of the cost. PMID:26366038

  14. Charting environmental pollution. [by noise measurements

    NASA Technical Reports Server (NTRS)

    Halpert, E.; Bizo, F.; Karacsonyi, Z.

    1974-01-01

    It is found that areas affected by different noxious agents are within the limits traced for high noise level areas; consequently, it is suggested that high noise pressure levels should be used as the primary indication of environmental pollution. A complex methodology is reported for charting environmental pollution due to physical, chemical and biological noxious agents on the scale of an industrial district.

  15. Phase-field model of dendritic sidebranching with thermal noise.

    PubMed

    Karma, A; Rappel, W J

    1999-10-01

    We investigate dendritic sidebranching during crystal growth in an undercooled melt by simulation of a phase-field model which incorporates thermal noise of microscopic origin. As a nontrivial quantitative test of this model, we first show that the simulated fluctuation spectrum of a one-dimensional interface in thermal equilibrium agrees with the exact sharp-interface spectrum up to an irrelevant short-wavelength cutoff comparable to the interface thickness. Simulations of dendritic growth are then carried out in two dimensions to compute sidebranching characteristics (root-mean-square amplitude and sidebranch spacing) as a function of distance behind the tip. These quantities are compared quantitatively to the predictions of the existing linear WKB theory of noise amplification. The extension of this study to three dimensions remains needed to determine the origin of noise in experiments.

  16. 14 CFR 36.1101 - Noise measurement and evaluation.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Noise measurement and evaluation. 36.1101 Section 36.1101 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... measurement and evaluation. For tiltrotors, the noise generated must be measured and evaluated under...

  17. The role of amplitude-to-phase conversion in the generation of oscillator flicker phase noise

    NASA Technical Reports Server (NTRS)

    Hearn, C. P.

    1985-01-01

    The role of amplitude-to-phase conversion as a factor in feedback oscillator flicker phase noise is examined. A limiting stage consisting of parallel-connected opposite polarity diodes operating in a circuit environment contining reactance is shown to exhibit amplitude-to-phase conversion. This mechanism coupled with resistive upconversion provides an indirect route for very low frequency flicker noise to be transferred into the phase of an oscillator signal. It is concluded that this effect is more significant in the lower frequency regimes where the onlinear reactances associated with active devices are overwhelmed by linear reactive elements.

  18. Laser phase noise effects on the dynamics of optomechanical resonators

    NASA Astrophysics Data System (ADS)

    Phelps, Gregory; Meystre, Pierre

    2011-05-01

    We present a theoretical analysis of the effects of laser phase noise on the sideband cooling of opto-mechanical oscillators, demonstrating how it limits the minimum occupation number of the phonon mode being cooled and how it modifies optical cooling rate and mechanical frequency shift of the mechanical element. We also comment on the effects of laser phase noise on coherent oscillations of the mechanical element in the blue detuned regime and on the back-action evasion detection method where an additional drive is used to prevent heating of one quadrature of motion of the oscillator. This work was supported by the US Office of Naval Research, the US National Science Foundation, the US Army Research Office and the DARPA ORCHID program through a grant from AFOSR.

  19. Distributions of Conductance and Shot Noise and Associated Phase Transitions

    SciTech Connect

    Vivo, Pierpaolo; Majumdar, Satya N.; Bohigas, Oriol

    2008-11-21

    For a chaotic cavity with two identical leads each supporting N channels, we compute analytically, for large N, the full distribution of the conductance and the shot noise power and show that in both cases there is a central Gaussian region flanked on both sides by non-Gaussian tails. The distribution is weakly singular at the junction of Gaussian and non-Gaussian regimes, a direct consequence of two phase transitions in an associated Coulomb gas problem.

  20. Fast measurement of temporal noise of digital camera's photosensors

    NASA Astrophysics Data System (ADS)

    Cheremkhin, Pavel A.; Evtikhiev, Nikolay N.; Krasnov, Vitaly V.; Rodin, Vladislav G.; Starikov, Rostislav S.; Starikov, Sergey N.

    2015-10-01

    Currently photo- and videocameras are widespread parts of both scientific experimental setups and consumer applications. They are used in optics, radiophysics, astrophotography, chemistry, and other various fields of science and technology such as control systems and video-surveillance monitoring. One of the main information limitations of photoand videocameras are noises of photosensor pixels. Camera's photosensor noise can be divided into random and pattern components. Temporal noise includes random noise component while spatial noise includes pattern noise component. Spatial part usually several times lower in magnitude than temporal. At first approximation spatial noises might be neglected. Earlier we proposed modification of the automatic segmentation of non-uniform targets (ASNT) method for measurement of temporal noise of photo- and videocameras. Only two frames are sufficient for noise measurement with the modified method. In result, proposed ASNT modification should allow fast and accurate measurement of temporal noise. In this paper, we estimated light and dark temporal noises of four cameras of different types using the modified ASNT method with only several frames. These cameras are: consumer photocamera Canon EOS 400D (CMOS, 10.1 MP, 12 bit ADC), scientific camera MegaPlus II ES11000 (CCD, 10.7 MP, 12 bit ADC), industrial camera PixeLink PLB781F (CMOS, 6.6 MP, 10 bit ADC) and video-surveillance camera Watec LCL-902C (CCD, 0.47 MP, external 8 bit ADC). Experimental dependencies of temporal noise on signal value are in good agreement with fitted curves based on a Poisson distribution excluding areas near saturation. We measured elapsed time for processing of shots used for temporal noise estimation. The results demonstrate the possibility of fast obtaining of dependency of camera full temporal noise on signal value with the proposed ASNT modification.

  1. DAMAS Processing for a Phased Array Study in the NASA Langley Jet Noise Laboratory

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Humphreys, William M.; Plassman, Gerald e.

    2010-01-01

    A jet noise measurement study was conducted using a phased microphone array system for a range of jet nozzle configurations and flow conditions. The test effort included convergent and convergent/divergent single flow nozzles, as well as conventional and chevron dual-flow core and fan configurations. Cold jets were tested with and without wind tunnel co-flow, whereas, hot jets were tested only with co-flow. The intent of the measurement effort was to allow evaluation of new phased array technologies for their ability to separate and quantify distributions of jet noise sources. In the present paper, the array post-processing method focused upon is DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources) for the quantitative determination of spatial distributions of noise sources. Jet noise is highly complex with stationary and convecting noise sources, convecting flows that are the sources themselves, and shock-related and screech noise for supersonic flow. The analysis presented in this paper addresses some processing details with DAMAS, for the array positioned at 90 (normal) to the jet. The paper demonstrates the applicability of DAMAS and how it indicates when strong coherence is present. Also, a new approach to calibrating the array focus and position is introduced and demonstrated.

  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. Rescuing a Quantum Phase Transition with Quantum Noise

    NASA Astrophysics Data System (ADS)

    Zhang, Gu; Novais, Eduardo; Baranger, Harold

    We show that placing a quantum system in contact with an environment can enhance non-Fermi-liquid correlations, rather than destroying quantum effects as is typical. The system consists of two quantum dots in series with two leads; the highly resistive leads couple charge flow through the dots to the electromagnetic environment (noise). The similarity to the two impurity Kondo model suggests that there will be a quantum phase transition between a Kondo phase and a local singlet phase. However, this transition is destabilized by charge tunneling between the two leads. Our main result is that sufficiently strong quantum noise suppresses this charge transfer and leads to stabilization of the quantum phase transition. We present the phase diagram, the ground state degeneracy at the four fixed points, and the leading temperature dependence of the conductance near these points. Partially supported by (1) the U.S. DOE, Division of Materials Sciences and Engineering, under Grant No. DE-SC0005237 and (2) FAPESP (BRAZIL) under Grant 2014/26356-9.

  4. Accurate MTF measurement in digital radiography using noise response

    PubMed Central

    Kuhls-Gilcrist, Andrew; Jain, Amit; Bednarek, Daniel R.; Hoffmann, Kenneth R.; Rudin, Stephen

    2010-01-01

    Purpose: The authors describe a new technique to determine the system presampled modulation transfer function (MTF) in digital radiography using only the detector noise response. Methods: A cascaded-linear systems analysis was used to develop an exact relationship between the two-dimensional noise power spectrum (NPS) and the presampled MTF for a generalized detector system. This relationship was then utilized to determine the two-dimensional presampled MTF. For simplicity, aliasing of the correlated noise component of the NPS was assumed to be negligible. Accuracy of this method was investigated using simulated images from a simple detector model in which the “true” MTF was known exactly. Measurements were also performed on three detector technologies (an x-ray image intensifier, an indirect flat panel detector, and a solid state x-ray image intensifier), and the results were compared using the standard edge-response method. Flat-field and edge images were acquired and analyzed according to guidelines set forth by the International Electrotechnical Commission, using the RQA 5 spectrum. Results: The presampled MTF determined using the noise-response method for the simulated detector system was in close agreement with the true MTF with an averaged percent difference of 0.3% and a maximum difference of 1.1% observed at the Nyquist frequency (fN). The edge-response method of the simulated detector system also showed very good agreement at lower spatial frequencies (less than 0.5 fN) with an averaged percent difference of 1.6% but showed significant discrepancies at higher spatial frequencies (greater than 0.5 fN) with an averaged percent difference of 17%. Discrepancies were in part a result of noise in the edge image and phasing errors. For all three detector systems, the MTFs obtained using the two methods were found to be in good agreement at spatial frequencies less than 0.5 fN with an averaged percent difference of 3.4%. Above 0.5 fN, differences increased to

  5. Thermodynamics aspects of noise-induced phase synchronization

    NASA Astrophysics Data System (ADS)

    Pinto, Pedro D.; Oliveira, Fernando A.; Penna, André L. A.

    2016-05-01

    In this article, we present an approach for the thermodynamics of phase oscillators induced by an internal multiplicative noise. We analytically derive the free energy, entropy, internal energy, and specific heat. In this framework, the formulation of the first law of thermodynamics requires the definition of a synchronization field acting on the phase oscillators. By introducing the synchronization field, we have consistently obtained the susceptibility and analyzed its behavior. This allows us to characterize distinct phases in the system, which we have denoted as synchronized and parasynchronized phases, in analogy with magnetism. The system also shows a rich complex behavior, exhibiting ideal gas characteristics for low temperatures and susceptibility anomalies that are similar to those present in complex fluids such as water.

  6. Thermodynamics aspects of noise-induced phase synchronization.

    PubMed

    Pinto, Pedro D; Oliveira, Fernando A; Penna, André L A

    2016-05-01

    In this article, we present an approach for the thermodynamics of phase oscillators induced by an internal multiplicative noise. We analytically derive the free energy, entropy, internal energy, and specific heat. In this framework, the formulation of the first law of thermodynamics requires the definition of a synchronization field acting on the phase oscillators. By introducing the synchronization field, we have consistently obtained the susceptibility and analyzed its behavior. This allows us to characterize distinct phases in the system, which we have denoted as synchronized and parasynchronized phases, in analogy with magnetism. The system also shows a rich complex behavior, exhibiting ideal gas characteristics for low temperatures and susceptibility anomalies that are similar to those present in complex fluids such as water. PMID:27300893

  7. Characterization of a DFG comb showing quadratic scaling of the phase noise with frequency.

    PubMed

    Puppe, Thomas; Sell, Alexander; Kliese, Russell; Hoghooghi, Nazanin; Zach, Armin; Kaenders, Wilhelm

    2016-04-15

    We characterize an Er:fiber laser frequency comb that is passively carrier envelope phase-stabilized via difference frequency generation at a wavelength of 1550 nm. A generic method to measure the comb linewidth at different wavelengths is demonstrated. By transferring the properties of a comb line to a cw external cavity diode laser, the phase noise is subsequently measured by tracking the delayed self-heterodyne beat note. This relatively simple characterization method is suitable for a broad range of optical frequencies. Here, it is used to characterize our difference frequency generation (DFG) comb over nearly an optical octave. With repetition-rate stabilization, a radiofrequency reference oscillator limited linewidth is achieved. A lock to an optical reference shows out-of-loop linewidths of the comb at the hertz level. The phase noise measurements are in excellent agreement with the elastic tape model with a fix point at zero frequency. PMID:27082368

  8. 14 CFR 36.101 - Noise measurement and evaluation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Noise measurement and evaluation. 36.101 Section 36.101 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... and Jet Airplanes § 36.101 Noise measurement and evaluation. For transport category large...

  9. Noise levels near streets, effectiveness and cost abatement measures

    NASA Technical Reports Server (NTRS)

    Lang, J.

    1980-01-01

    During the years 1975-1978, research was carried concerning the current noise levels near streets, the annoyance felt by the population, possible noise abatement measures for these streets, and the economic impact of such measures. The results of the research are summarized.

  10. 14 CFR 36.101 - Noise measurement and evaluation.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Noise measurement and evaluation. 36.101 Section 36.101 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... and Jet Airplanes § 36.101 Noise measurement and evaluation. For transport category large...

  11. 14 CFR 36.101 - Noise measurement and evaluation.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Noise measurement and evaluation. 36.101 Section 36.101 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... and Jet Airplanes § 36.101 Noise measurement and evaluation. For transport category large...

  12. Noise sensitivity in frequency-resolved optical-gating measurements of ultrashort pulses

    SciTech Connect

    Fittinghoff, D.N.; DeLong, K.W.; Trebino, R.; Ladera, C.L.

    1995-10-01

    Frequency-resolved optical gating (FROG), a technique for measuring ultrashort laser pulses, involves producing a spectrogram of the pulse and then retrieving the pulse intensity and phase with an iterative algorithm. We study how several types of noise---multiplicative, additive, and quantization---affect pulse retrieval. We define a convergence criterion and find that the algorithm converges to a reasonable pulse field, even in the presence of 10% noise. Specifically, with appropriate filtering, 1% rms retrieval error is achieved for 10% multiplicative noise, 10% additive noise, and as few as 8 bits of resolution. For additive and multiplicative noise the retrieval errors decrease roughly as the square root of the amount of noise. In addition, the background induced in the wings of the pulse by additive noise is equal to the amount of additive noise on the trace. Thus the dynamic range of the measured intensity and phase is limited by a noise floor equal to the amount of additive noise on the trace. We also find that, for best results, a region of zero intensity should surround the nonzero region of the trace. Consequently, in the presence of additive noise, baseline subtraction is important. We also find that Fourier low-pass filtering improves pulse retrieval without introducing significant distortion, especially in high-noise cases. We show that the field errors in the temporal and the spectral domains are equal. Overall, the algorithm performs well because the measured trace contains {ital N}{sup 2} data points for a pulse that has only 2{ital N} degrees of freedom; FROG has built in redundancy. {copyright} {ital 1995} {ital Optical} {ital Society} {ital of} {ital America}.

  13. Impact of measurement precision and noise on superresolution image reconstruction.

    PubMed

    Wood, Sally L; Lee, Shu-Ting; Yang, Gao; Christensen, Marc P; Rajan, Dinesh

    2008-04-01

    The performance of uniform and nonuniform detector arrays for application to the PANOPTES (processing arrays of Nyquist-limited observations to produce a thin electro-optic sensor) flat camera design is analyzed for measurement noise environments including quantization noise and Gaussian and Poisson processes. Image data acquired from a commercial camera with 8 bit and 14 bit output options are analyzed, and estimated noise levels are computed. Noise variances estimated from the measurement values are used in the optimal linear estimators for superresolution image reconstruction.

  14. Noise measurements and the dB

    NASA Astrophysics Data System (ADS)

    Maslen, K. R.

    1980-07-01

    The conventional use of the dB in studies of acoustic noise can be said to obscure and complicate simple relationships and lead to the possibility of error because of misunderstandings of the nature of logarithms and because the order of the numbers involved is concealed by the compressed scale. Examples of errors and inaccuracies are given and some cases where consideration of noise in terms of rms pressure would be simpler, or would lead to better understanding of the processes involved, are discussed. It is suggested that although the dB may be a convenient unit for many purposes, more emphasis on the physical nature of noise would help in the interpretation of phenomena and prevent some of the confusions that arise, especially in dealing with the general public.

  15. Filtering with perfectly correlated measurement noise.

    NASA Technical Reports Server (NTRS)

    Reasenberg, R.

    1972-01-01

    Examination of (radar) Doppler data which are formed by mi1ing the returning microwave signal with a replica of the transmitted signal, counting the cycles of the beat, and sampling the counter at evenly spaced intervals t sub i. It is shown that the amount of information which can be extracted from a set of data may be larger if the associated noise is perfectly correlated than if it is white, and that the use of the white noise assumption in the filter may result in the loss of some of this information.

  16. Phase synchronization of neuronal noise in mouse hippocampal epileptiform dynamics.

    PubMed

    Serletis, Demitre; Carlen, Peter L; Valiante, Taufik A; Bardakjian, Berj L

    2013-02-01

    Organized brain activity is the result of dynamical, segregated neuronal signals that may be used to investigate synchronization effects using sophisticated neuroengineering techniques. Phase synchrony analysis, in particular, has emerged as a promising methodology to study transient and frequency-specific coupling effects across multi-site signals. In this study, we investigated phase synchronization in intracellular recordings of interictal and ictal epileptiform events recorded from pairs of cells in the whole (intact) mouse hippocampus. In particular, we focused our analysis on the background noise-like activity (NLA), previously reported to exhibit complex neurodynamical properties. Our results show evidence for increased linear and nonlinear phase coupling in NLA across three frequency bands [theta (4-10 Hz), beta (12-30 Hz) and gamma (30-80 Hz)] in the ictal compared to interictal state dynamics. We also present qualitative and statistical evidence for increased phase synchronization in the theta, beta and gamma frequency bands from paired recordings of ictal NLA. Overall, our results validate the use of background NLA in the neurodynamical study of epileptiform transitions and suggest that what is considered "neuronal noise" is amenable to synchronization effects in the spatiotemporal domain. PMID:23273129

  17. Infinite-noise criticality: Nonequilibrium phase transitions in fluctuating environments

    NASA Astrophysics Data System (ADS)

    Vojta, Thomas; Hoyos, Jose

    We study the effects of time-varying environmental noise on nonequilibrium phase transitions in spreading and growth processes. Using the examples of the logistic evolution equation as well as the contact process, we show that such temporal disorder gives rise to a distinct type of critical points at which the effective noise amplitude diverges on long time scales. This leads to enormous density fluctuations characterized by an infinitely broad probability distribution at criticality. We develop a real-time renormalization-group theory that provides a general framework for the effects of temporal disorder on nonequilibrium processes. We also discuss how general this exotic critical behavior is, we illustrate the results by computer simulations, and we touch upon experimental applications of our theory. Supported by the NSF under Grant No. DMR-1205803, by Simons Foundation, by FAPESP under Grant No. 2013/09850-7, and by CNPq under Grant Nos. 590093/2011-8 and 305261/2012-6.

  18. A novel crystal-analyzer phase retrieval algorithm and its noise property.

    PubMed

    Bao, Yuan; Wang, Yan; Li, Panyun; Wu, Zhao; Shao, Qigang; Gao, Kun; Wang, Zhili; Ju, Zaiqiang; Zhang, Kai; Yuan, Qingxi; Huang, Wanxia; Zhu, Peiping; Wu, Ziyu

    2015-05-01

    A description of the rocking curve in diffraction enhanced imaging (DEI) is presented in terms of the angular signal response function and a simple multi-information retrieval algorithm based on the cosine function fitting. A comprehensive analysis of noise properties of DEI is also given considering the noise transfer characteristic of the X-ray source. The validation has been performed with synchrotron radiation experimental data and Monte Carlo simulations based on the Geant4 toolkit combined with the refractive process of X-rays, which show good agreement with each other. Moreover, results indicate that the signal-to-noise ratios of the refraction and scattering images are about one order of magnitude better than that of the absorption image at the edges of low-Z samples. The noise penalty is drastically reduced with the increasing photon flux and visibility. Finally, this work demonstrates that the analytical method can build an interesting connection between DEI and GDPCI (grating-based differential phase contrast imaging) and is widely suitable for a variety of measurement noise in the angular signal response imaging prototype. The analysis significantly contributes to the understanding of noise characteristics of DEI images and may allow improvements to the signal-to-noise ratio in biomedical and material science imaging.

  19. Direct frequency comb synthesis with arbitrary offset and shot-noise-limited phase noise

    NASA Astrophysics Data System (ADS)

    Koke, Sebastian; Grebing, Christian; Frei, Harald; Anderson, Alexandria; Assion, Andreas; Steinmeyer, Günter

    2010-07-01

    Carrier-envelope phase stabilization has opened an avenue towards achieving frequency metrology with unprecedented precision and optical pulse generation on the previously inaccessible attosecond timescale. Recently, sub-100-as pulse generation has been demonstrated, approaching the timescale of the fastest transients in atomic physics. However, further progress in attophysics appears to be limited by the performance of the traditional feedback approach used for carrier-envelope phase stabilization. Here, we demonstrate a conceptually different self-referenced feed-forward approach to phase stabilization. This approach requires no complicated locking electronics, does not compromise laser performance, and is demonstrated with 12-as residual timing jitter, which is below the atomic unit of time. This surpasses the precision of previous methods by more than a factor of five and has potential for resolving even the fastest transients in atomic or molecular physics. Such shot-noise-limited comb synthesis may also simplify progress in current research in frequency metrology.

  20. Occupational noise exposure: how should we measure it

    SciTech Connect

    Barry, J.P.

    1982-01-01

    Historically, the American hygiene community has measured occupational noise exposure with a general purpose (ANSI type 2) sound level meter set to indicate A-weighted sound levels at slow response and a watch to indicate the exposure duration. Occupational noise exposures have been calculated by summing the fractions of the actual exposure time at a given A-weighted sound level over the permissible exposure time for that level. If the noise dose obtained by this method exceeded unity or 100%, then excessive exposure was documented for hearing conservation purposes. With the advent of the US Department of Labor's statutorily enforceable occupational noise standards in 1969 and 1971, the need arose for a less time-consuming way to do a workplace noise exposure survey. The answer was the personal noise dosimeter which automatically measures the A-weighted sound levels with slow dynamic characteristics and time weights the dose in concert with the standard of interest. In recent years the physical accuracy of noise dosimeter measurements has been questioned by a few acoustical consultants, particularly when rapidly time-varying or impulsive waveforms are encountered. Since noise dosimeters provide simple and economical documentation of employee daily noise exposure for hearing conservation and regulatory compliance purposes a discussion of their accuracy is necessary to clear up any confusion.

  1. Noise in x-ray grating-based phase-contrast imaging

    SciTech Connect

    Weber, Thomas; Bartl, Peter; Bayer, Florian; Durst, Juergen; Haas, Wilhelm; Michel, Thilo; Ritter, Andre; Anton, Gisela

    2011-07-15

    Purpose: Grating-based x-ray phase-contrast imaging is a fast developing new modality not only for medical imaging, but as well for other fields such as material sciences. While these many possible applications arise, the knowledge of the noise behavior is essential. Methods: In this work, the authors used a least squares fitting algorithm to calculate the noise behavior of the three quantities absorption, differential phase, and dark-field image. Further, the calculated error formula of the differential phase image was verified by measurements. Therefore, a Talbot interferometer was setup, using a microfocus x-ray tube as source and a Timepix detector for photon counting. Additionally, simulations regarding this topic were performed. Results: It turned out that the variance of the reconstructed phase is only dependent of the total number of photons used to generate the phase image and the visibility of the experimental setup. These results could be evaluated in measurements as well as in simulations. Furthermore, the correlation between absorption and dark-field image was calculated. Conclusions: These results provide the understanding of the noise characteristics of grating-based phase-contrast imaging and will help to improve image quality.

  2. Prediction of Landing Gear Noise Reduction and Comparison to Measurements

    NASA Technical Reports Server (NTRS)

    Lopes, Leonard V.

    2010-01-01

    Noise continues to be an ongoing problem for existing aircraft in flight and is projected to be a concern for next generation designs. During landing, when the engines are operating at reduced power, the noise from the airframe, of which landing gear noise is an important part, is equal to the engine noise. There are several methods of predicting landing gear noise, but none have been applied to predict the change in noise due to a change in landing gear design. The current effort uses the Landing Gear Model and Acoustic Prediction (LGMAP) code, developed at The Pennsylvania State University to predict the noise from landing gear. These predictions include the influence of noise reduction concepts on the landing gear noise. LGMAP is compared to wind tunnel experiments of a 6.3%-scale Boeing 777 main gear performed in the Quiet Flow Facility (QFF) at NASA Langley. The geometries tested in the QFF include the landing gear with and without a toboggan fairing and the door. It is shown that LGMAP is able to predict the noise directives and spectra from the model-scale test for the baseline configuration as accurately as current gear prediction methods. However, LGMAP is also able to predict the difference in noise caused by the toboggan fairing and by removing the landing gear door. LGMAP is also compared to far-field ground-based flush-mounted microphone measurements from the 2005 Quiet Technology Demonstrator 2 (QTD 2) flight test. These comparisons include a Boeing 777-300ER with and without a toboggan fairing that demonstrate that LGMAP can be applied to full-scale flyover measurements. LGMAP predictions of the noise generated by the nose gear on the main gear measurements are also shown.

  3. Amplitude and phase noises of a spin-transfer nano-oscillator synchronized by a phase-lock loop

    NASA Astrophysics Data System (ADS)

    Mitrofanov, A. A.; Safin, A. R.; Udalov, N. N.

    2015-08-01

    We have studied the amplitude and phase noises of a spin-transfer nano-oscillator (STNO) with a phase synchronization system (phase-lock loop, PLL). Spectral characteristics of the amplitude and phase noises of the isochronous and nonisochronous STNO are obtained and compared to the analogous characteristics of an autonomous (nonsynchronized) oscillator. The PLL bandwidth is determined.

  4. Baseline noise and measurement uncertainty in liquid chromatography.

    PubMed

    Kitajima, Akihito; Kashirajima, Takeshi; Minamizawa, Takao; Sato, Hiroyasu; Iwaki, Kazuo; Ueda, Taisuke; Kimura, Yoshio; Toyo'oka, Toshimasa; Maitani, Tamio; Matsuda, Rieko; Hayashi, Yuzuru

    2007-09-01

    The stochastic properties of baseline noise in HPLC systems with a UV photo-diode array, photo-multiplier and gamma-ray detector were examined by dividing the noise into auto-correlated random process (Markov process) and an independent process (white noise). The present work focused on the effect of the stochastic noise properties on a theoretical estimation of the standard deviation (SD) of area measurements in instrumental analyses. An estimation theory, called FUMI theory (Function of Mutual Information), was taken as an example. A computer simulation of noise was also used. It was shown that the reliability (confidence intervals) of theoretical SD estimates mainly depends on the following factors: the ratio of the white noise and Markov process occurring in the baselines; the number of data points used for the estimation; the width of a target peak for which the SD is estimated.

  5. Correction of phase velocity bias caused by strong directional noise sources in high-frequency ambient noise tomography: a case study in Karamay, China

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Luo, Yinhe; Yang, Yingjie

    2016-05-01

    We collect two months of ambient noise data recorded by 35 broad-band seismic stations in a 9 × 11 km area (1-3 km station interval) near Karamay, China, and do cross-correlation of noise data between all station pairs. Array beamforming analysis of the ambient noise data shows that ambient noise sources are unevenly distributed and the most energetic ambient noise mainly comes from azimuths of 40°-70°. As a consequence of the strong directional noise sources, surface wave components of the cross-correlations at 1-5 Hz show clearly azimuthal dependence, and direct dispersion measurements from cross-correlations are strongly biased by the dominant noise energy. This bias renders that the dispersion measurements from cross-correlations do not accurately reflect the interstation velocities of surface waves propagating directly from one station to the other, that is, the cross-correlation functions do not retrieve empirical Green's functions accurately. To correct the bias caused by unevenly distributed noise sources, we adopt an iterative inversion procedure. The iterative inversion procedure, based on plane-wave modeling, includes three steps: (1) surface wave tomography, (2) estimation of ambient noise energy and biases and (3) phase velocities correction. First, we use synthesized data to test the efficiency and stability of the iterative procedure for both homogeneous and heterogeneous media. The testing results show that: (1) the amplitudes of phase velocity bias caused by directional noise sources are significant, reaching ˜2 and ˜10 per cent for homogeneous and heterogeneous media, respectively; (2) phase velocity bias can be corrected by the iterative inversion procedure and the convergence of inversion depends on the starting phase velocity map and the complexity of the media. By applying the iterative approach to the real data in Karamay, we further show that phase velocity maps converge after 10 iterations and the phase velocity maps obtained using

  6. The influence of noise on image quality in phase-diverse coherent diffraction imaging

    NASA Astrophysics Data System (ADS)

    Wittler, H. P. A.; van Riessen, G. A.; Jones, M. W. M.

    2016-02-01

    Phase-diverse coherent diffraction imaging provides a route to high sensitivity and resolution with low radiation dose. To take full advantage of this, the characteristics and tolerable limits of measurement noise for high quality images must be understood. In this work we show the artefacts that manifest in images recovered from simulated data with noise of various characteristics in the illumination and diffraction pattern. We explore the limits at which images of acceptable quality can be obtained and suggest qualitative guidelines that would allow for faster data acquisition and minimize radiation dose.

  7. Cancellation of simulated environmental noise as a tool for measuring vocal performance during noise exposure.

    PubMed

    Ternström, Sten; Södersten, Maria; Bohman, Mikael

    2002-06-01

    It can be difficult for the voice clinician to observe or measure how a patient uses his voice in a noisy environment. We consider here a novel method for obtaining this information in the laboratory. Worksite noise and filtered white noise were reproduced over high-fidelity loudspeakers. In this noise, 11 subjects read an instructional text of 1.5 to 2 minutes duration, as if addressing a group of people. Using channel estimation techniques, the site noise was suppressed from the recording, and the voice signal alone was recovered. The attainable noise rejection is limited only by the precision of the experimental setup, which includes the need for the subject to remain still so as not to perturb the estimated acoustic channel. This feasibility study, with 7 female and 4 male subjects, showed that small displacements of the speaker's body, even breathing, impose a practical limit on the attainable noise rejection. The noise rejection was typically 30 dB and maximally 40 dB down over the entire voice spectrum. Recordings thus processed were clean enough to permit voice analysis with the long-time average spectrum and the computerized phonetogram. The effects of site noise on voice sound pressure level, fundamental frequency, long-term average spectrum centroid, phonetogram area, and phonation time were much as expected, but with some interesting differences between females and males.

  8. Real Time Phase Noise Meter Based on a Digital Signal Processor

    NASA Technical Reports Server (NTRS)

    Angrisani, Leopoldo; D'Arco, Mauro; Greenhall, Charles A.; Schiano Lo Morille, Rosario

    2006-01-01

    A digital signal-processing meter for phase noise measurement on sinusoidal signals is dealt with. It enlists a special hardware architecture, made up of a core digital signal processor connected to a data acquisition board, and takes advantage of a quadrature demodulation-based measurement scheme, already proposed by the authors. Thanks to an efficient measurement process and an optimized implementation of its fundamental stages, the proposed meter succeeds in exploiting all hardware resources in such an effective way as to gain high performance and real-time operation. For input frequencies up to some hundreds of kilohertz, the meter is capable both of updating phase noise power spectrum while seamlessly capturing the analyzed signal into its memory, and granting as good frequency resolution as few units of hertz.

  9. Phased-Array Study of Dual-Flow Jet Noise: Effect of Nozzles and Mixers

    NASA Technical Reports Server (NTRS)

    Soo Lee, Sang; Bridges, James

    2006-01-01

    A 16-microphone linear phased-array installed parallel to the jet axis and a 32-microphone azimuthal phased-array installed in the nozzle exit plane have been applied to identify the noise source distributions of nozzle exhaust systems with various internal mixers (lobed and axisymmetric) and nozzles (three different lengths). Measurements of velocity were also obtained using cross-stream stereo particle image velocimetry (PIV). Among the three nozzle lengths tested, the medium length nozzle was the quietest for all mixers at high frequency on the highest speed flow condition. Large differences in source strength distributions between nozzles and mixers occurred at or near the nozzle exit for this flow condition. The beamforming analyses from the azimuthal array for the 12-lobed mixer on the highest flow condition showed that the core flow and the lobe area were strong noise sources for the long and short nozzles. The 12 noisy spots associated with the lobe locations of the 12-lobed mixer with the long nozzle were very well detected for the frequencies 5 KHz and higher. Meanwhile, maps of the source strength of the axisymmetric splitter show that the outer shear layer was the most important noise source at most flow conditions. In general, there was a good correlation between the high turbulence regions from the PIV tests and the high noise source regions from the phased-array measurements.

  10. Impulsive noise of printers: measurement metrics and their subjective correlation

    NASA Astrophysics Data System (ADS)

    Baird, Terrence; Otto, Norman; Bray, Wade; Stephan, Mike

    2005-09-01

    In the office and home computing environments, printer impulsive noise has become a significant contributor to user perceived quality or lack thereof, and can affect the user's comfort level and ability to concentrate. Understanding and quantifying meaningful metrics for printer impulsivity is becoming an increasingly important goal for printer manufacturers. Several methods exist in international standards for measuring the impulsivity of noise. For information technology equipment (ITE), the method for detection of impulsive noise is provided in ECMA-74 and ISO 7779. However, there is a general acknowledgement that the current standard method of determining impulsivity by simply measuring A-weighted sound pressure level (SPL) with the impulsive time weighting, I, applied is inadequate to characterize impulsive noise and ultimately to predict user satisfaction and acceptance. In recent years, there has been a variety of new measurement methods evaluated for impulsive noise for both environmental and machinery noise. This paper reviews several of the available metrics, applies the metrics to several printer impulsive noise sources, and makes an initial assessment of their correlation to the subjective impressions of users. It is a review and continuation of the work presented at InterNoise 2005 (Baird, Bray, and Otto).

  11. Recommended procedures for measuring aircraft noise and associated parameters

    NASA Technical Reports Server (NTRS)

    Marsh, A. H.

    1977-01-01

    Procedures are recommended for obtaining experimental values of aircraft flyover noise levels (and associated parameters). Specific recommendations are made for test criteria, instrumentation performance requirements, data-acquisition procedures, and test operations. The recommendations are based on state-of-the-art measurement capabilities available in 1976 and are consistent with the measurement objectives of the NASA Aircraft Noise Prediction Program. The recommendations are applicable to measurements of the noise produced by an airplane flying subsonically over (or past) microphones located near the surface of the ground. Aircraft types covered by the recommendations are fixed-wing airplanes powered by turbojet or turbofan engines and using conventional aerodynamic means for takeoff and landing. Various assumptions with respect to subsequent data processing and analysis were made (and are described) and the recommended measurement procedures are compatible with the assumptions. Some areas where additional research is needed relative to aircraft flyover noise measurement techniques are also discussed.

  12. Geometric phase of a qubit driven by a phase noise laser under non-Markovian dynamics

    SciTech Connect

    Berrada, K.

    2014-01-15

    Robustness of the geometric phase (GP) with respect to the environmental effects is a basic condition for an effective quantum computation. Here, we study quantitatively the GP of a two-level atom system driven by a phase noise laser under non-Markovian dynamics in terms of different parameters involved in the whole system. We find that with the change of the damping coupling, the GP is very sensitive to its properties exhibiting long collapse and revival phenomena, which play a significant role in enhancing the stabilization and control of the system dynamics. Moreover, we show that the GP can be considered as a tool for testing and characterizing the nature of the qubit–environment coupling. Due to the significance of how a system is quantum correlated with its environment in the construction of a scalable quantum computer, the entanglement dynamics between the qubit with its environment under external classical noise is evaluated and investigated during the time evolution. -- Highlights: •Geometric phase under noise phase laser. •Dynamics of the geometric phase under non-Markovian dynamics in the presence of classical noise. •Solution of master equation of the system in terms atomic inversion. •Nonlocal correlation between the system and its environment under non-Markovianity.

  13. Measurements and Predictions of High Frequency Ambient Noise

    NASA Astrophysics Data System (ADS)

    Holden, Andrew

    2004-11-01

    A great deal has been published on ambient noise. Most of this has covered (a) omni directional levels, and (b) the vertical and horizontal directivity of shipping noise at low frequencies. There is some published material on the vertical directivity of wind generated noise at lower frequencies, but very little at higher frequencies. In order to study wind generated ambient noise at higher frequencies, work has recently started using a small planar array from QinetiQ Bincleaves. As well as measurements, a model called CANARY has been written to predict ambient noise vertical directivity and array responses to this noise. This paper contains some comparisons between CANARY predictions and (a) previous measured vertical directivity data at 4.5 kHz, (b) measured omni-directional data, and (c) initial analysis of the planar array measurements. The paper shows the nature of the ambient noise vertical structure at higher frequencies and that the CANARY predictions are in good agreement with the measurements.

  14. Noise levels from a model turbofan engine with simulated noise control measures applied

    NASA Technical Reports Server (NTRS)

    Hall, David G.; Woodward, Richard P.

    1993-01-01

    A study of estimated full-scale noise levels based on measured levels from the Advanced Ducted Propeller (ADP) sub-scale model is presented. Testing of this model was performed in the NASA Lewis Low Speed Anechoic Wind Tunnel at a simulated takeoff condition of Mach 0.2. Effective Perceived Noise Level (EPNL) estimates for the baseline configuration are documented, and also used as the control case in a study of the potential benefits of two categories of noise control. The effect of active noise control is evaluated by artificially removing various rotor-stator interaction tones. Passive noise control is simulated by applying a notch filter to the wind tunnel data. Cases with both techniques are included to evaluate hybrid active-passive noise control. The results for EPNL values are approximate because the original source data was limited in bandwidth and in sideline angular coverage. The main emphasis is on comparisons between the baseline and configurations with simulated noise control measures.

  15. Improving the accuracy of smart devices to measure noise exposure.

    PubMed

    Roberts, Benjamin; Kardous, Chucri; Neitzel, Richard

    2016-11-01

    Occupational noise exposure is one of the most frequent hazards present in the workplace; up to 22 million workers have potentially hazardous noise exposures in the U.S. As a result, noise-induced hearing loss is one of the most common occupational injuries in the U.S. Workers in manufacturing, construction, and the military are at the highest risk for hearing loss. Despite the large number of people exposed to high levels of noise at work, many occupations have not been adequately evaluated for noise exposure. The objective of this experiment was to investigate whether or not iOS smartphones and other smart devices (Apple iPhones and iPods) could be used as reliable instruments to measure noise exposures. For this experiment three different types of microphones were tested with a single model of iPod and three generations of iPhones: the internal microphones on the device, a low-end lapel microphone, and a high-end lapel microphone marketed as being compliant with the International Electrotechnical Commission's (IEC) standard for a Class 2-microphone. All possible combinations of microphones and noise measurement applications were tested in a controlled environment using several different levels of pink noise ranging from 60-100 dBA. Results were compared to simultaneous measurements made using a Type 1 sound level measurement system. Analysis of variance and Tukey's honest significant difference (HSD) test were used to determine if the results differed by microphone or noise measurement application. Levels measured with external microphones combined with certain noise measurement applications did not differ significantly from levels measured with the Type 1 sound measurement system. Results showed that it may be possible to use iOS smartphones and smart devices, with specific combinations of measurement applications and calibrated external microphones, to collect reliable, occupational noise exposure data under certain conditions and within the limitations of the

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

    NASA Astrophysics Data System (ADS)

    Scandurra, Graziella; Giusi, Gino; Ciofi, Carmine

    2014-04-01

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

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

    PubMed

    Scandurra, Graziella; Giusi, Gino; Ciofi, Carmine

    2014-04-01

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

  18. Measurement of Trailing Edge Noise Using Directional Array and Coherent Output Power Methods

    NASA Technical Reports Server (NTRS)

    Hutcheson, Florence V.; Brooks, Thomas F.

    2002-01-01

    The use of a directional (or phased) array of microphones for the measurement of trailing edge (TE) noise is described and tested. The capabilities of this method arc evaluated via measurements of TE noise from a NACA 63-215 airfoil model and from a cylindrical rod. This TE noise measurement approach is compared to one that is based on thc cross spectral analysis of output signals from a pair of microphones placed on opposite sides of an airframe model (COP method). Advantages and limitations of both methods arc examined. It is shown that the microphone array can accurately measures TE noise and captures its two-dimensional characteristic over a large frequency range for any TE configuration as long as noise contamination from extraneous sources is within bounds. The COP method is shown to also accurately measure TE noise but over a more limited frequency range that narrows for increased TE thickness. Finally, the applicability and generality of an airfoil self-noise prediction method was evaluated via comparison to the experimental data obtained using the COP and array measurement methods. The predicted and experimental results are shown to agree over large frequency ranges.

  19. Phase noise mitigation of QPSK signal utilizing phase-locked multiplexing of signal harmonics and amplitude saturation.

    PubMed

    Mohajerin-Ariaei, Amirhossein; Ziyadi, Morteza; Chitgarha, Mohammad Reza; Almaiman, Ahmed; Cao, Yinwen; Shamee, Bishara; Yang, Jeng-Yuan; Akasaka, Youichi; Sekiya, Motoyoshi; Takasaka, Shigehiro; Sugizaki, Ryuichi; Touch, Joseph D; Tur, Moshe; Langrock, Carsten; Fejer, Martin M; Willner, Alan E

    2015-07-15

    We demonstrate an all-optical phase noise mitigation scheme based on the generation, delay, and coherent summation of higher order signal harmonics. The signal, its third-order harmonic, and their corresponding delayed variant conjugates create a staircase phase-transfer function that quantizes the phase of quadrature-phase-shift-keying (QPSK) signal to mitigate phase noise. The signal and the harmonics are automatically phase-locked multiplexed, avoiding the need for phase-based feedback loop and injection locking to maintain coherency. The residual phase noise converts to amplitude noise in the quantizer stage, which is suppressed by parametric amplification in the saturation regime. Phase noise reduction of ∼40% and OSNR-gain of ∼3  dB at BER 10(-3) are experimentally demonstrated for 20- and 30-Gbaud QPSK input signals.

  20. Event-triggered feedback in noise-driven phase oscillators

    NASA Astrophysics Data System (ADS)

    Kromer, Justus A.; Lindner, Benjamin; Schimansky-Geier, Lutz

    2014-03-01

    Using a stochastic nonlinear phase oscillator model, we study the effect of event-triggered feedback on the statistics of interevent intervals. Events are associated with the entering of a new cycle. The feedback is modeled by an instantaneous increase (positive feedback) or decrease (negative feedback) of the oscillator frequency whenever an event occurs followed by an exponential decay on a slow time scale. In addition to the known excitable and oscillatory regimes, which are separated by a saddle node on invariant circle bifurcation, positive feedback can lead to bistable dynamics and a change of the system's excitability. The feedback has also a strong effect on noise-induced phenomena like coherence resonance or anticoherence resonance. Both positive and negative feedback can lead to more regular output for particular noise strengths. Finally, we investigate serial correlations in the sequence of interevent intervals that occur due to the additional slow dynamics. We derive approximations for the serial correlation coefficient and show that positive feedback results in extended positive interval correlations, whereas negative feedback yields short-ranging negative correlations. Investigating the interplay of feedback and the nonlinear phase dynamics close to the bifurcation, we find that correlations are most pronounced for optimal feedback strengths.

  1. 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.

  2. Impulsive noise reduction in digital phase-sensitive demodulation by nonlinear filtering

    NASA Astrophysics Data System (ADS)

    Cui, Ziqiang; Wang, Huaxiang; Yin, Wuliang; Yang, Wuqiang

    2015-07-01

    Phase-sensitive demodulation is widely used in many systems, e.g. impedance measurement, communication, sonar and radar. In most cases, white noise is assumed in system design and analysis. However, impulsive noise is often encountered in many applications, which imposes challenges for a phase-sensitive demodulator (PSD). This paper presents a nonlinear filter for removing impulsive noise prior to the PSD. Unlike its linear counterparts, it is analysed in the time domain rather than in the frequency domain, making it easier to implement. The performance of the proposed method is compared to a standard PSD with a low-pass filter to suppress the impulsive noise and the theoretical limits of the signal-to-noise ratio (SNR) is analysed. The theoretical prediction has been validated by numerical simulation and experiment. Experimental results show that the proposed method can achieve SNR improvement of 10.8 dB or greater when impulse rate α = 0.01. Statistical analysis shows that 97.2% of the impulses can be rejected by the median filter of length 3 when impulse rate is less than or equal to 0.1.

  3. Noise analysis of grating-based x-ray differential phase contrast imaging

    SciTech Connect

    Revol, Vincent; Kottler, Christian; Kaufmann, Rolf; Urban, Claus; Straumann, Ulrich

    2010-07-15

    The sensitivity of x-ray radiographic images, meaning the minimal detectable change in the thickness or in the index of refraction of a sample, is directly related to the uncertainty of the measurement method. In the following work, we report on the recent development of quantitative descriptions for the stochastic error of grating-based differential phase contrast imaging (DPCi). Our model includes the noise transfer characteristics of the x-ray detector and the jitter of the phase steps. We find that the noise in DPCi depends strongly on the phase stepping visibility and the sample properties. The results are supported by experimental evidence acquired with our new instrument with a field of view of 50x70 mm{sup 2}. Our conclusions provide general guidelines to optimize grating interferometers for specific applications and problems.

  4. Data Quality Assurance for Supersonic Jet Noise Measurements

    NASA Technical Reports Server (NTRS)

    Brown, Clifford A.; Henderson, Brenda S.; Bridges, James E.

    2010-01-01

    The noise created by a supersonic aircraft is a primary concern in the design of future high-speed planes. The jet noise reduction technologies required on these aircraft will be developed using scale-models mounted to experimental jet rigs designed to simulate the exhaust gases from a full-scale jet engine. The jet noise data collected in these experiments must accurately predict the noise levels produced by the full-scale hardware in order to be a useful development tool. A methodology has been adopted at the NASA Glenn Research Center s Aero-Acoustic Propulsion Laboratory to insure the quality of the supersonic jet noise data acquired from the facility s High Flow Jet Exit Rig so that it can be used to develop future nozzle technologies that reduce supersonic jet noise. The methodology relies on mitigating extraneous noise sources, examining the impact of measurement location on the acoustic results, and investigating the facility independence of the measurements. The methodology is documented here as a basis for validating future improvements and its limitations are noted so that they do not affect the data analysis. Maintaining a high quality jet noise laboratory is an ongoing process. By carefully examining the data produced and continually following this methodology, data quality can be maintained and improved over time.

  5. Improved Measurement of Coherence in Presence of Instrument Noise

    NASA Technical Reports Server (NTRS)

    Merceret, Francis J.

    2003-01-01

    A method for correcting measured coherence spectra for the effect of incoherent instrument noise has been developed and demonstrated. Coherence measurements are widely used in engineering and science to determine the extent to which two signals are alike. The signals may come from two different sources or from the same source at different times. The coherence of time-lagged signals from a single source is an excellent indication of the effective lifetime of the signal components as a function of their frequency. Unfortunately, incoherent instrument noise will bias the measurement to lower values and may lead the user of the data to false conclusions about the longevity of significant features. The new method may be used whenever both the signal and noise power spectra are known and the noise is incoherent both with the signal and with itself at the applicable time delays. It provides a corrected coherence spectrum given the measured coherence and power spectra. For powerlaw signal spectra and instrumental white noise, the correction formula takes a particularly simple and explicit form. Since many geophysical signals exhibit powerlaw behavior and most instrument noise spectra approach white noise, the simplified form should be widely applicable in meteorology, oceanography, geology, and planetary geophysics.

  6. Coherence, modulation, and phase-noise effects in Sagnac interferometers

    NASA Astrophysics Data System (ADS)

    Wanser, Keith H.

    1988-03-01

    A formalism is presented that unifies coherence, phase modulation, and dispersive propagation in Sagnac interferometers and is valid for large amplitude phase modulation. Several effects have been found as a result. For the fiber optic gyroscope, parasitic amplitude modulation effects that are maximum at the loop frequency have been found, in contrast to several effects that vanish when operating at the loop frequency. A correction to the gyroscope scale factor that is dependent on modulation amplitude and source bandwidth has also been found. In addition, there exists a maximum rotation rate limited by coherence effects, or maximum sensed phase shift for the Sagnac acoustic sensor. Phase noise effects caused by environmental or other disturbances can cause signal fade out and loss of information for the Sagnac data ring, and the magnitude of these effects are calculated. The Fm/Am conversion effect and its relevance for Sagnac interferometers is also treated. Finally, the use of a frequency shifting approach or various types of modulation to reduce these effects is discussed.

  7. Time domain phase measuring apparatus

    NASA Technical Reports Server (NTRS)

    Reinhardt, V. S. (Inventor)

    1978-01-01

    The phase and/or period stability of a device is determined by connecting the device in one orthogonal arm of a phase detector having a mixer. In the other arm is an adjustable, variable phase shift device. The output of the mixer is fed through an active low pass filter to derive a DC voltage indicative of the phase shift. The variable phase device is adjusted so that the DC voltage will nullify the phase shift of the tested device under normal conditions. The DC voltage level is converted into a time interval indicative of the phase change of the tested device by determining when the level equals the amplitude of a low frequency ramp voltage. The interval between adjacent equality points can be measured or the period between a reference point on the ramp voltage and the quality be measured.

  8. Wide band low phase noise QVCO based on superharmonic injection locking

    NASA Astrophysics Data System (ADS)

    Yalan, Xu; Jinguang, Jiang; Jianghua, Liu

    2016-01-01

    A wide band, injection-coupled LC quadrature voltage control oscillator is presented. In the proposed circuit, two oscillators are injection locked by coupling their second-order harmonics in anti-phase, forcing the outputs of two oscillators into a quadrature phase state. As the common-mode point sampling the second harmonic frequency, flicker noise of the tail current is suppressed, the phase noise is reduced. The proposed design accomplishes a wide tuning frequency range by a combination of using a 5-bit switch capacitor array (SCA) for discrete tuning in addition to linearly varying AMOS varactors for continuous tuning. The proposed design has been fabricated and verified in a 0.18 μm TSMC CMOS technology process. The measurement indicates that the quadrature voltage controlled oscillator has a 41.7% tuning range from 3.53 to 5.39 GHz. The measured phase noise is 127.98 dBc/Hz at 1 MHz offset at a 1.8 V supply voltage with a power consumption of 12 mW at a carrier frequency of 4.85 GHz. Project supporteded by the National Natural Science Foundation of China (No. 41274047) and the Guangdong Province Science and Technology Program (No. 2013B090500049).

  9. Core noise measurements from a small, general aviation turbofan engine

    NASA Astrophysics Data System (ADS)

    Reshotko, M.; Karchmer, A.

    1980-11-01

    As part of a program to investigate combustor and other core noises, simultaneous measurements of internal fluctuating pressure and far field noise were made with a JT15D turbofan engine. Acoustic waveguide probes, located in the engine at the combustor, at the turbine exit and in the core nozzle wall, were used to measure internal fluctuating pressures. Low frequency acoustic power determined at the core nozzle exit corresponds in level to the far field acoustic power at engine speeds below 65% of maximum, the approach condition. At engine speeds above 65% of maximum, the jet noise dominates in the far field, greatly exceeding that of the core. From coherence measurements, it is shown that the combustor is the dominant source of the low frequency core noise. The results obtained from the JT15D engine were compared with those obtained previously from a YF102 engine, both engines having reverse flow annular combustors and being in the same size class.

  10. A bootstrapped, low-noise, and high-gain photodetector for shot noise measurement.

    PubMed

    Zhou, Haijun; Yang, Wenhai; Li, Zhixiu; Li, Xuefeng; Zheng, Yaohui

    2014-01-01

    We presented a low-noise, high-gain photodetector based on the bootstrap structure and the L-C (inductance and capacitance) combination. Electronic characteristics of the photodetector, including electronic noise, gain and frequency response, and dynamic range, were verified through a single-frequency Nd:YVO4 laser at 1064 nm with coherent output. The measured shot noise of 50 μW laser was 13 dB above the electronic noise at the analysis frequency of 2 MHz, and 10 dB at 3 MHz. And a maximum clearance of 28 dB at 2 MHz was achieved when 1.52 mW laser was illuminated. In addition, the photodetector showed excellent linearities for both DC and AC amplifications in the laser power range between 12.5 μW and 1.52 mW.

  11. A bootstrapped, low-noise, and high-gain photodetector for shot noise measurement

    SciTech Connect

    Zhou, Haijun; Yang, Wenhai; Li, Zhixiu; Li, Xuefeng; Zheng, Yaohui

    2014-01-15

    We presented a low-noise, high-gain photodetector based on the bootstrap structure and the L-C (inductance and capacitance) combination. Electronic characteristics of the photodetector, including electronic noise, gain and frequency response, and dynamic range, were verified through a single-frequency Nd:YVO{sub 4} laser at 1064 nm with coherent output. The measured shot noise of 50 μW laser was 13 dB above the electronic noise at the analysis frequency of 2 MHz, and 10 dB at 3 MHz. And a maximum clearance of 28 dB at 2 MHz was achieved when 1.52 mW laser was illuminated. In addition, the photodetector showed excellent linearities for both DC and AC amplifications in the laser power range between 12.5 μW and 1.52 mW.

  12. Noise in two-color electronic distance meter measurements revisited

    USGS Publications Warehouse

    Langbein, J.

    2004-01-01

    Frequent, high-precision geodetic data have temporally correlated errors. Temporal correlations directly affect both the estimate of rate and its standard error; the rate of deformation is a key product from geodetic measurements made in tectonically active areas. Various models of temporally correlated errors are developed and these provide relations between the power spectral density and the data covariance matrix. These relations are applied to two-color electronic distance meter (EDM) measurements made frequently in California over the past 15-20 years. Previous analysis indicated that these data have significant random walk error. Analysis using the noise models developed here indicates that the random walk model is valid for about 30% of the data. A second 30% of the data can be better modeled with power law noise with a spectral index between 1 and 2, while another 30% of the data can be modeled with a combination of band-pass-filtered plus random walk noise. The remaining 10% of the data can be best modeled as a combination of band-pass-filtered plus power law noise. This band-pass-filtered noise is a product of an annual cycle that leaks into adjacent frequency bands. For time spans of more than 1 year these more complex noise models indicate that the precision in rate estimates is better than that inferred by just the simpler, random walk model of noise.

  13. Installation noise measurements of model SR and CR propellers

    NASA Technical Reports Server (NTRS)

    Block, P. J. W.

    1984-01-01

    Noise measurements on a 0.1 scale SR-2 propeller in a single and counter rotation mode, in a pusher and tractor configuration, and operating at non-zero angles of attack are summarized. A measurement scheme which permitted 143 measurements of each of these configurations in the Langley 4- by 7-meter low speed tunnel is also described.

  14. Measurement device for noise factor of microchannel plate.

    PubMed

    Lei, Liu; Zhijian, Huang; Tao, Pan; Yunsheng, Qian

    2012-03-01

    A new method for noise power factor determination of microchannel plates (MCPs) is described in this paper. The new measuring condition and specific measuring instrument are reported. The system consists of a vacuum chamber, an electron gun, a high-voltage supply, an imaging luminance meter, control units, a signal processing circuit, an A/D converter, a D/A converter, a communication unit, an industrial computer, and measurement software. This measuring method fills a void in measuring technology for the noise factor of MCPs, and it can make a scientific assessment of MCP noise characteristics and provide theoretical direction and technology support for the research and development of high-performance low light level (LLL) devices.

  15. Quantum noise in the position measurement of a cavity mirror undergoing Brownian motion

    NASA Astrophysics Data System (ADS)

    Jacobs, K.; Tittonen, I.; Wiseman, H. M.; Schiller, S.

    1999-07-01

    We perform a quantum theoretical calculation of the noise power spectrum for a phase measurement of the light output from a coherently driven optical cavity with a freely moving rear mirror. We examine how the noise resulting from the quantum back action appears among the various contributions from other noise sources. We do not assume an ideal (homodyne) phase measurement, but rather consider phase-modulation detection, which we show has a different shot noise level. We also take into account the effects of thermal damping of the mirror, losses within the cavity, and classical laser noise. We relate our theoretical results to experimental parameters, so as to make direct comparisons with current experiments simple. We also show that in this situation, the standard Brownian motion master equation is inadequate for describing the thermal damping of the mirror, as it produces a spurious term in the steady-state phase-fluctuation spectrum. The corrected Brownian motion master equation [L. Diosi, Europhys. Lett. 22, 1 (1993)] rectifies this inadequacy.

  16. Equalization-enhanced phase noise for coherent-detection systems using electronic digital signal processing.

    PubMed

    Shieh, William; Ho, Keang-Po

    2008-09-29

    In coherent optical systems employing electronic digital signal processing, the fiber chromatic dispersion can be gracefully compensated in electronic domain without resorting to optical techniques. Unlike optical dispersion compensator, the electronic equalizer enhances the impairments from the laser phase noise. This equalization-enhanced phase noise (EEPN) imposes a tighter constraint on the receive laser phase noise for transmission systems with high symbol rate and large electronically-compensated chromatic dispersion.

  17. Optical Coatings and Thermal Noise in Precision Measurement

    NASA Astrophysics Data System (ADS)

    Harry, Gregory; Bodiya, Timothy P.; DeSalvo, Riccardo

    2012-01-01

    1. Theory of thermal noise in optical mirrors Y. Levin; 2. Coating technology S. Chao; 3. Compendium of thermal noises in optical mirrors V. B. Braginsky, M. L. Gorodetsky and S. P. Vyatchanin; 4. Coating thermal noise I. Martin and S. Reid; 5. Direct measurements of coating thermal noise K. Numata; 6. Methods of improving thermal noise S. Ballmer and K. Somiya; 7. Substrate thermal noise S. Rowan and I. Martin; 8. Cryogenics K. Numata and K. Yamamoto; 9. Thermo-optic noise M. Evans and G. Ogin; 10. Absorption and thermal issues P. Willems, D. Ottaway and P. Beyersdorf; 11. Optical scatter J. R. Smith and M. E. Zucker; 12. Reflectivity and thickness optimisation I. M. Pinto, M. Principe and R. DeSalvo; 13. Beam shaping A. Freise; 14. Gravitational wave detection D. Ottaway and S. D. Penn; 15. High-precision laser stabilisation via optical cavities M. J. Martin and J. Ye; 16. Quantum optomechanics G. D. Cole and M. Aspelmeyer; 17. Cavity quantum electrodynamics T. E. Northup.

  18. Switching Correlation and Noise Level in Pr3+:YSO Crystal via Dressing Nonlinear Phase

    PubMed Central

    Ahmed, Irfan; Zhang, Zhaoyang; Wen, Feng; Zhang, Da; Li, Changbiao; Wang, Ruimin; Zhang, Yanpeng

    2016-01-01

    We propose and experimentally demonstrate that the intensity noise correlation and the noise level of intensity-difference and intensity-sum in Stokes and anti-Stokes channel can be well controlled by the relative nonlinear phase in spontaneous parametric four-wave mixing process. By modulating the relative nonlinear phase, including self-phase modulation and cross-phase modulation, switching the correlation into anti-correlation and the relative intensity noise level between the intensity-difference and intensity-sum are realized. We also show that the variation tendencies of the relative intensity noise level and the corresponding intensity fluctuations correlation are in accordance with each other. PMID:27650423

  19. Switching Correlation and Noise Level in Pr3+:YSO Crystal via Dressing Nonlinear Phase

    NASA Astrophysics Data System (ADS)

    Ahmed, Irfan; Zhang, Zhaoyang; Wen, Feng; Zhang, Da; Li, Changbiao; Wang, Ruimin; Zhang, Yanpeng

    2016-09-01

    We propose and experimentally demonstrate that the intensity noise correlation and the noise level of intensity-difference and intensity-sum in Stokes and anti-Stokes channel can be well controlled by the relative nonlinear phase in spontaneous parametric four-wave mixing process. By modulating the relative nonlinear phase, including self-phase modulation and cross-phase modulation, switching the correlation into anti-correlation and the relative intensity noise level between the intensity-difference and intensity-sum are realized. We also show that the variation tendencies of the relative intensity noise level and the corresponding intensity fluctuations correlation are in accordance with each other.

  20. Switching Correlation and Noise Level in Pr(3+):YSO Crystal via Dressing Nonlinear Phase.

    PubMed

    Ahmed, Irfan; Zhang, Zhaoyang; Wen, Feng; Zhang, Da; Li, Changbiao; Wang, Ruimin; Zhang, Yanpeng

    2016-01-01

    We propose and experimentally demonstrate that the intensity noise correlation and the noise level of intensity-difference and intensity-sum in Stokes and anti-Stokes channel can be well controlled by the relative nonlinear phase in spontaneous parametric four-wave mixing process. By modulating the relative nonlinear phase, including self-phase modulation and cross-phase modulation, switching the correlation into anti-correlation and the relative intensity noise level between the intensity-difference and intensity-sum are realized. We also show that the variation tendencies of the relative intensity noise level and the corresponding intensity fluctuations correlation are in accordance with each other. PMID:27650423

  1. Wavelet-based noise-model driven denoising algorithm for differential phase contrast mammography.

    PubMed

    Arboleda, Carolina; Wang, Zhentian; Stampanoni, Marco

    2013-05-01

    Traditional mammography can be positively complemented by phase contrast and scattering x-ray imaging, because they can detect subtle differences in the electron density of a material and measure the local small-angle scattering power generated by the microscopic density fluctuations in the specimen, respectively. The grating-based x-ray interferometry technique can produce absorption, differential phase contrast (DPC) and scattering signals of the sample, in parallel, and works well with conventional X-ray sources; thus, it constitutes a promising method for more reliable breast cancer screening and diagnosis. Recently, our team proved that this novel technology can provide images superior to conventional mammography. This new technology was used to image whole native breast samples directly after mastectomy. The images acquired show high potential, but the noise level associated to the DPC and scattering signals is significant, so it is necessary to remove it in order to improve image quality and visualization. The noise models of the three signals have been investigated and the noise variance can be computed. In this work, a wavelet-based denoising algorithm using these noise models is proposed. It was evaluated with both simulated and experimental mammography data. The outcomes demonstrated that our method offers a good denoising quality, while simultaneously preserving the edges and important structural features. Therefore, it can help improve diagnosis and implement further post-processing techniques such as fusion of the three signals acquired.

  2. Structureborne noise measurements on a small twin-engine aircraft

    NASA Technical Reports Server (NTRS)

    Cole, J. E., III; Martini, K. F.

    1988-01-01

    Structureborne noise measurements performed on a twin-engine aircraft (Beechcraft Baron) are reported. There are two overall objectives of the test program. The first is to obtain data to support the development of analytical models of the wing and fuselage, while the second is to evaluate effects of structural parameters on cabin noise. Measurements performed include structural and acoustic responses to impact excitation, structural and acoustic loss factors, and modal parameters of the wing. Path alterations include added mass to simulate fuel, variations in torque of bolts joining wing and fuselage, and increased acoustic absorption. Conclusions drawn regarding these measurements are presented.

  3. Noise Measurements of High Aspect Ratio Distributed Exhaust Systems

    NASA Technical Reports Server (NTRS)

    Bridges, James E.

    2015-01-01

    This paper covers far-field acoustic measurements of a family of rectangular nozzles with aspect ratio 8, in the high subsonic flow regime. Several variations of nozzle geometry, commonly found in embedded exhaust systems, are explored, including bevels, slants, single broad chevrons and notches, and internal septae. Far-field acoustic results, presented previously for the simple rectangular nozzle, showed that increasing aspect ratio increases the high frequency noise, especially directed in the plane containing the minor axis of the nozzle. Detailed changes to the nozzle geometry generally made little difference in the noise, and the differences were greatest at low speed. Having an extended lip on one broad side (bevel) did produce up to 3 decibels more noise in all directions, while extending the lip on the narrow side (slant) produced up to 2 decibels more noise, primarily on the side with the extension. Adding a single, non-intrusive chevron, made no significant change to the noise, while inverting the chevron (notch) produced up to 2decibels increase in the noise. Having internal walls (septae) within the nozzle, such as would be required for structural support or when multiple fan ducts are aggregated, reduced the noise of the rectangular jet, but could produce a highly directional shedding tone from the septae trailing edges. Finally, a nozzle with both septae and a beveled nozzle, representative of the exhaust system envisioned for a distributed electric propulsion aircraft with a common rectangular duct, produced almost as much noise as the beveled nozzle, with the septae not contributing much reduction in noise.

  4. Noise Measurements of High Aspect Ratio Distributed Exhaust Systems

    NASA Technical Reports Server (NTRS)

    Bridges, James

    2015-01-01

    This paper covers far-field acoustic measurements of a family of rectangular nozzles with aspect ratio 8, in the high subsonic flow regime. Several variations of nozzle geometry, commonly proposed for embedded exhaust systems, are explored, including bevels, slants, single broad chevrons and notches, and internal septae. Far-field acoustic results, presented previously for the simple rectangular nozzle, showed that increasing aspect ratio increases the high frequency noise, especially directed in the plane containing the minor axis of the nozzle. Detailed changes to the nozzle geometry generally made little difference in the noise, and the differences were greatest at low speed. Having an extended lip on one broad side ('bevel') did produce up to 3dB more noise in all directions, while extending the lip on the narrow side ('slant') produced up to 2dB more noise, primarily on the side with the extension. Adding a single, non-intrusive chevron, made no significant change to the noise, while inverting the chevron ('notch') produced up to 2dB increase in the noise. Having internal walls ('septae') within the nozzle, such as would be required for structural support or when multiple fan ducts are aggregated, reduced the noise of the rectangular jet, but could produce a highly directional shedding tone from the septae trailing edges. Finally, a nozzle with both septae and a beveled nozzle, representative of the exhaust system envisioned for a distributed propulsion aircraft with a common rectangular duct, produced almost as much noise as the beveled nozzle, with the septae not contributing much reduction in noise.

  5. Relation between measures of speech-in-noise performance and measures of efferent activity

    NASA Astrophysics Data System (ADS)

    Smith, Brad; Harkrider, Ashley; Burchfield, Samuel; Nabelek, Anna

    2003-04-01

    Individual differences in auditory perceptual abilities in noise are well documented but the factors causing such variability are unclear. The purpose of this study was to determine if individual differences in responses measured from the auditory efferent system were correlated to individual variations in speech-in-noise performance. The relation between behavioral performance on three speech-in-noise tasks and two objective measures of the efferent auditory system were examined in thirty normal-hearing, young adults. Two of the speech-in-noise tasks measured an acceptable noise level, the maximum level of speech-babble noise that a subject is willing to accept while listening to a story. For these, the acceptable noise level was evaluated using both an ipsilateral (story and noise in same ear) and a contralateral (story and noise in opposite ears) paradigm. The third speech-in-noise task evaluated speech recognition using monosyllabic words presented in competing speech babble. Auditory efferent activity was assessed by examining the resulting suppression of click-evoked otoacoustic emissions following the introduction of a contralateral, broad-band stimulus and the activity of the ipsilateral and contralateral acoustic reflex arc was evaluated using tones and broad-band noise. Results will be discussed relative to current theories of speech in noise performance and auditory inhibitory processes.

  6. Laser noise measurement techniques and applications of femtosecond encoding in the frequency domain

    NASA Astrophysics Data System (ADS)

    Scott, Ryan Patrick

    This dissertation investigates mode-locked laser noise measurement techniques, the concept and measurement of a laser's noise transfer function, and then two applications of spectral encoding of optical pulses. The one application is optical code division multiple access (O-CDMA) and the other is optical arbitrary waveform generation (OAWG). The relationship between source stability, encoding, and overall system performance in O-CDMA is also discussed. Techniques for making sensitive and high-dynamic-range measurements of laser amplitude and envelope phase noise (timing jitter) in the frequency domain at the shot-noise limit are described. The short term stability of a Kerr-lens modelocked (KLM) Ti:sapphire laser is shown to be close to that of the precision crystal oscillators used in its characterization. The amplitude and envelope phase noise of a KLM Ti:sapphire laser are shown to depend directly on the pump laser amplitude stability. The sensitivity of this process is described by a noise transfer function (NTF) which represents the magnitude of the amplitude-to-amplitude modulation and amplitude-to-phase modulation conversion gain of the pump-induced amplitude and phase noise, respectively. A spectral phase-encoded time-spreading (SPECTS) O-CDMA testbed is described. The testbed employs a fiber-pigtailed, bulk-optics arrangement that utilizes a two-dimensional spatial light phase modulator for encoding multiple channels. The time-gated SPECTS O-CDMA receiver is composed of a nonlinear optical loop mirror (NOLM) and a nonlinear thresholder Experimentally measured performance is compared to numerical simulations. Finally, an optical frequency comb with 20-GHz spacing is shaped by an integrated silica arrayed-waveguide grating (AWG) pair to produce optical waveforms with high fidelity. Characterization of both the intensity and phase of the crafted opitical fields is accomplished with cross-correlation frequency-resolved optical gating (XFROG) which has been

  7. Atomic multiwave interferometer for Aharonov-Casher-phase measurements

    NASA Astrophysics Data System (ADS)

    Zhou, Min-Kang; Zhang, Ke; Duan, Xiao-Chun; Ke, Yi; Shao, Cheng-Gang; Hu, Zhong-Kun

    2016-02-01

    We present an atomic multiwave interferometer with magnetic sublevels to precisely determine the Aharonov-Casher (AC) geometric phase. Simulations show that this interferometer has sharper fringes than a normal two-wave interferometer, which means a higher phase resolution can be achieved. Moreover, atoms evolving in a single hyperfine structure state make the interferometer insensitive to the dc Stark phase shift. This dc Stark shift is one of the main noise sources in AC phase measurements. The constraint of the photon rest mass is also discussed when using this atomic interferometer to measure the Aharonov-Casher phase.

  8. Adaptive anisotropic diffusion for noise reduction of phase images in Fourier domain Doppler optical coherence tomography.

    PubMed

    Xia, Shaoyan; Huang, Yong; Peng, Shizhao; Wu, Yanfeng; Tan, Xiaodi

    2016-08-01

    Phase image in Fourier domain Doppler optical coherence tomography offers additional flow information of investigated samples, which provides valuable evidence towards accurate medical diagnosis. High quality phase images are thus desirable. We propose a noise reduction method for phase images by combining a synthetic noise estimation criteria based on local noise estimator (LNE) and distance median value (DMV) with anisotropic diffusion model. By identifying noise and signal pixels accurately and diffusing them with different coefficients respectively and adaptive iteration steps, we demonstrated the effectiveness of our proposed method in both phantom and mouse artery images. Comparison with other methods such as filtering method (mean, median filtering), wavelet method, probabilistic method and partial differential equation based methods in terms of peak signal-to-noise ratio (PSNR), equivalent number of looks (ENL) and contrast-to-noise ratio (CNR) showed the advantages of our method in reserving image energy and removing noise. PMID:27570687

  9. Adaptive anisotropic diffusion for noise reduction of phase images in Fourier domain Doppler optical coherence tomography

    PubMed Central

    Xia, Shaoyan; Huang, Yong; Peng, Shizhao; Wu, Yanfeng; Tan, Xiaodi

    2016-01-01

    Phase image in Fourier domain Doppler optical coherence tomography offers additional flow information of investigated samples, which provides valuable evidence towards accurate medical diagnosis. High quality phase images are thus desirable. We propose a noise reduction method for phase images by combining a synthetic noise estimation criteria based on local noise estimator (LNE) and distance median value (DMV) with anisotropic diffusion model. By identifying noise and signal pixels accurately and diffusing them with different coefficients respectively and adaptive iteration steps, we demonstrated the effectiveness of our proposed method in both phantom and mouse artery images. Comparison with other methods such as filtering method (mean, median filtering), wavelet method, probabilistic method and partial differential equation based methods in terms of peak signal-to-noise ratio (PSNR), equivalent number of looks (ENL) and contrast-to-noise ratio (CNR) showed the advantages of our method in reserving image energy and removing noise. PMID:27570687

  10. Low Frequency Noise Measurement and Analysis of Capacitive Micro-Accelerometers: Temperature Effect

    NASA Astrophysics Data System (ADS)

    Mohd-Yasin, Faisal; Nagel, David J.; Ong, D. S.; Korman, Can E.; Chuah, H. T.

    2008-06-01

    A noise measurements of micro-accelerometers were performed using a special measurement system. A common spectral behavior of noise is found, with 1/ f noise dominating at low frequencies and white thermal noise being the limiting factor at higher frequencies. A temperature dependent and an acceleration dependant of the noise are found in the accelerometers, in agreement and contract of the theories, respectively.

  11. Analysis and reduction of errors caused by Poisson noise for phase diversity technique.

    PubMed

    Yu, Hongli; Yang, Chengliang; Xu, Zihao; Zhang, Peiguang; Xu, Huanyu; Cao, Zhaoliang; Mu, Quanquan; Xuan, Li

    2016-09-19

    An effective method for reducing the sensitivity of phase diversity (PD) technique to Poisson noise is proposed. The denoising algorithm based on blocking-matching and 3D filtering is first introduced in the wavefront sensing field as a preprocessing stage. Then, the PD technique is applied to the denoised images. Results of the numerical simulations and experiments demonstrate that our approach is better than the traditional PD technique in terms of both the root-mean-square error (RMSE) of phase estimates and the structural similarity index metrics (SSIM). The RMSEs of phase estimates on synthetic data are decreased by approximately 40% across noise levels within the range of 58.7-18.8 dB in terms of peak signal-to-noise ratio (PSNR). Meanwhile, the overall decline range of SSIM is significantly decreased from 49% to 9%. The experiment and simulation results are in good agreement. The approach may be widely used in various domains, such as the measurements of intrinsic aberrations in optical systems and compensations for atmospheric turbulence. PMID:27661938

  12. Measurement and prediction of Energy Efficient Engine noise

    NASA Technical Reports Server (NTRS)

    Lavin, S. P.; Ho, P. Y.; Chamberlin, R.

    1984-01-01

    The NASA/GE Energy Efficient Engine (E3) static noise levels were measured in an acoustic arena on the Integrated Core and Low Spool Test System. These measured levels were scaled to the appropriate size to power four study aircraft and were projected to flight for evaluation of noise levels relative to FAR36, Stage III limits. As a result of these evaluations, it is predicted that the NASA/GE E3 engine with a wide spacing cut-on blade/vane ratio fan and a forced mixer nozzle can meet FAR36 Stage III limits with sufficient design margin.

  13. Amplitude measurements in ambient noise correlations -- application to attenuation and site response measurements

    NASA Astrophysics Data System (ADS)

    Bowden, D. C.; Tsai, V. C.; Lin, F.

    2013-12-01

    Traditional ambient noise cross correlations between seismic stations have proven to be an effective means of extracting travel time information of surface waves. However, while the raw noise data is usually processed in a way which suppresses large amplitude earthquake events, it also distorts all relative amplitude information. Such information is the key to accurately retrieving attenuation and local site response measurements. Previous work using earthquake sources to track wave front propagation across the U.S. Array has been used to distinguish between effects on amplitude variation. Applying a similar approach to ambient noise studies offers potentially increased flexibility in such studies. We attempt a varied application of the methods which should preserve relative amplitudes in the Noise Correlation Function (NCF) across a given day or hour. Considering each station as a virtual source, a large number of travel time and relative amplitude maps can be constructed. By applying spatial differential operators to these maps, we track the effect of phase-front focusing and defocusing. By comparing amplitude variation for waves propagating in opposite directions, we attempt to independently infer the effects of seismic intrinsic attenuation and local site response. We have applied the approach on two datasets of vastly different scale. A dense array of single-component, broadband seismometers in Long Beach, CA (>4000 in an area around 100 sq-km) allows us to explore the higher frequency end of these measurements, up to 4Hz. In contrast, data collected over 4 years from the U.S. Array provide continental scale application, with useful periods of 8-30 seconds and depth sensitivities down to the uppermost mantle. We compare our results with previous studies based on earthquakes.

  14. Model building and measurement of the temporal noise for thermal infrared imager

    NASA Astrophysics Data System (ADS)

    Yu, Xun; Nie, Liang; Hu, Tieli; Jiang, Xu; Wang, Fang

    2008-09-01

    In the measurement of the infrared imager, noise is the primary parameter in evaluating the quality of the infrared imager. In the engineering application of the infrared imager, three-dimensional noise pattern is not applied widely in the hard technology of the infrared imager due to its pattern is complex, physical significance is not definite and visualized. Noise parameters include the temporal noise and the spatial noise. The temporal noise can be divided into high frequency temporal noise and low frequency temporal noise (namely 1/f noise), and the spatial noise can be divided into high frequency spatial noise (namely fixed pattern noise, FPN) and low frequency spatial noise (un-uniform noise). The strict definition about high frequency temporal noise and low frequency temporal noise is given in this paper. The algorithm and measuring methods for low frequency temporal noise equivalent temperature difference are proposed. The algorithms and measuring methods of high frequency noise equivalent temperature difference are given, ignoring low frequency temporal noise in short-time during measuring high frequency noise equivalent temperature difference or not. Moreover, the uncertainty of measurement results for high frequency temporal noise equivalent temperature difference is analyzed in the paper.

  15. Mitigating the effects of measurement noise on Granger causality

    SciTech Connect

    Nalatore, Hariharan; Ding Mingzhou; Rangarajan, Govindan

    2007-03-15

    Computing Granger causal relations among bivariate experimentally observed time series has received increasing attention over the past few years. Such causal relations, if correctly estimated, can yield significant insights into the dynamical organization of the system being investigated. Since experimental measurements are inevitably contaminated by noise, it is thus important to understand the effects of such noise on Granger causality estimation. The first goal of this paper is to provide an analytical and numerical analysis of this problem. Specifically, we show that, due to noise contamination (1) spurious causality between two measured variables can arise and (2) true causality can be suppressed. The second goal of the paper is to provide a denoising strategy to mitigate this problem. Specifically, we propose a denoising algorithm based on the combined use of the Kalman filter theory and the expectation-maximization algorithm. Numerical examples are used to demonstrate the effectiveness of the denoising approach.

  16. Experimental demonstration of a noise-tunable delay line with applications to phase synchronization

    NASA Astrophysics Data System (ADS)

    Pessacg, F.; Taitz, A.; Patterson, G. A.; Fierens, P. I.; Grosz, D. F.

    2015-05-01

    In this paper we propose and demonstrate a discrete circuit capable of generating arbitrary time delays dependent on noise, either added externally or already present in the signal of interest due to a finite signal-to-noise ratio. We then go on to demonstrate an application to phase locking of signals by means of a standard Phase-Locked Loop (PLL) design, where the usual Voltage-Controlled Oscillator (VCO) is replaced by the noise-tunable delay line.

  17. Reduction of phase noise in nanowire spin orbit torque oscillators

    PubMed Central

    Yang, Liu; Verba, Roman; Tiberkevich, Vasil; Schneider, Tobias; Smith, Andrew; Duan, Zheng; Youngblood, Brian; Lenz, Kilian; Lindner, Jürgen; Slavin, Andrei N.; Krivorotov, Ilya N.

    2015-01-01

    Spin torque oscillators (STOs) are compact, tunable sources of microwave radiation that serve as a test bed for studies of nonlinear magnetization dynamics at the nanometer length scale. The spin torque in an STO can be created by spin-orbit interaction, but low spectral purity of the microwave signals generated by spin orbit torque oscillators hinders practical applications of these magnetic nanodevices. Here we demonstrate a method for decreasing the phase noise of spin orbit torque oscillators based on Pt/Ni80Fe20 nanowires. We experimentally demonstrate that tapering of the nanowire, which serves as the STO active region, significantly decreases the spectral linewidth of the generated signal. We explain the observed linewidth narrowing in the framework of the Ginzburg-Landau auto-oscillator model. The model reveals that spatial non-uniformity of the spin current density in the tapered nanowire geometry hinders the excitation of higher order spin-wave modes, thus stabilizing the single-mode generation regime. This non-uniformity also generates a restoring force acting on the excited self-oscillatory mode, which reduces thermal fluctuations of the mode spatial position along the wire. Both these effects improve the STO spectral purity. PMID:26592432

  18. Helicopter rotor rotational noise predictions based on measured high-frequency blade loads

    NASA Technical Reports Server (NTRS)

    Hosier, R. N.; Ramakrishnan, R.

    1974-01-01

    In tests conducted at the Langley helicopter rotor test facility, simultaneous measurements of up to 200 harmonics of the fluctuating aerodynamic blade surface pressures and far-field radiated noise were made on a full-scale nontranslating rotor system. After their characteristics were determined, the measured blade surface pressures were converted to loading coefficients and used in an existing theory to predict the far-field rotational noise. A comparison of the calculated and measured noise shows generally good agreement up to 300 to 600 Hz, depending on the discreteness of the loading spectrum. Specific attention is given to the effects of the blade loading coefficients, chordwise loading distributions, blade loading phases, and observer azimuthal position on the calculations.

  19. Sediment-generated noise (SGN): Laboratory determination of measurement volume

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Passive acoustic technology has the potential to allow continuous measurement of bedload moving through streams by recording Sediment-Generated Noise (SGN) from interactions between coarse bedload particles. The technology is relatively economical and is amenable to automated operation. While the ...

  20. Magnetic noise measurements using cross-correlated Hall sensor arrays

    NASA Astrophysics Data System (ADS)

    Jung, G.; Ocio, M.; Paltiel, Y.; Shtrikman, H.; Zeldov, E.

    2001-01-01

    An experimental technique for measuring magnetic fluctuations by means of a double-layer Hall sensor array is described. The technique relies on cross-correlating Hall signals from two independent sensors positioned one above the other in two separate two-dimensional-electron-gas layers of a GaAs/AlGaAs heterostructure. The effectiveness of the technique is demonstrated by a reduction of the magnitude of the background noise floor of the correlated sensors with respect to the noise level of the best single sensor.

  1. Accurate frequency noise measurement of free-running lasers.

    PubMed

    Schiemangk, Max; Spiessberger, Stefan; Wicht, Andreas; Erbert, Götz; Tränkle, Günther; Peters, Achim

    2014-10-20

    We present a simple method to accurately measure the frequency noise power spectrum of lasers. It relies on creating the beat note between two lasers, capturing the corresponding signal in the time domain, and appropriately postprocessing the data to derive the frequency noise power spectrum. In contrast to methods already established, it does not require stabilization of the laser to an optical reference, i.e., a second laser, to an optical cavity or to an atomic transition. It further omits a frequency discriminator and hence avoids bandwidth limitation and nonlinearity effects common to high-resolution frequency discriminators.

  2. Measurements of nuclear spin dynamics by spin-noise spectroscopy

    SciTech Connect

    Ryzhov, I. I.; Poltavtsev, S. V.; Kozlov, G. G.; Zapasskii, V. S.; Kavokin, K. V.; Glazov, M. M.; Vladimirova, M.; Scalbert, D.; Cronenberger, S.; Lemaître, A.; Bloch, J.

    2015-06-15

    We exploit the potential of the spin noise spectroscopy (SNS) for studies of nuclear spin dynamics in n-GaAs. The SNS experiments were performed on bulk n-type GaAs layers embedded into a high-finesse microcavity at negative detuning. In our experiments, nuclear spin polarisation initially prepared by optical pumping is monitored in real time via a shift of the peak position in the electron spin noise spectrum. We demonstrate that this shift is a direct measure of the Overhauser field acting on the electron spin. The dynamics of nuclear spin is shown to be strongly dependent on the electron concentration.

  3. Estimation of Noise-Free Variance to Measure Heterogeneity

    PubMed Central

    Winkler, Tilo; Melo, Marcos F. Vidal; Degani-Costa, Luiza H.; Harris, R. Scott; Correia, John A.; Musch, Guido; Venegas, Jose G.

    2015-01-01

    Variance is a statistical parameter used to characterize heterogeneity or variability in data sets. However, measurements commonly include noise, as random errors superimposed to the actual value, which may substantially increase the variance compared to a noise-free data set. Our aim was to develop and validate a method to estimate noise-free spatial heterogeneity of pulmonary perfusion using dynamic positron emission tomography (PET) scans. On theoretical grounds, we demonstrate a linear relationship between the total variance of a data set derived from averages of n multiple measurements, and the reciprocal of n. Using multiple measurements with varying n yields estimates of the linear relationship including the noise-free variance as the constant parameter. In PET images, n is proportional to the number of registered decay events, and the variance of the image is typically normalized by the square of its mean value yielding a coefficient of variation squared (CV2). The method was evaluated with a Jaszczak phantom as reference spatial heterogeneity (CVr2) for comparison with our estimate of noise-free or ‘true’ heterogeneity (CVt2). We found that CVt2 was only 5.4% higher than CVr2. Additional evaluations were conducted on 38 PET scans of pulmonary perfusion using 13NN-saline injection. The mean CVt2 was 0.10 (range: 0.03–0.30), while the mean CV2 including noise was 0.24 (range: 0.10–0.59). CVt2 was in average 41.5% of the CV2 measured including noise (range: 17.8–71.2%). The reproducibility of CVt2 was evaluated using three repeated PET scans from five subjects. Individual CVt2 were within 16% of each subject's mean and paired t-tests revealed no difference among the results from the three consecutive PET scans. In conclusion, our method provides reliable noise-free estimates of CVt2 in PET scans, and may be useful for similar statistical problems in experimental data. PMID:25906374

  4. Critical phenomena and noise-induced phase transitions in neuronal networks.

    PubMed

    Lee, K-E; Lopes, M A; Mendes, J F F; Goltsev, A V

    2014-01-01

    We study numerically and analytically first- and second-order phase transitions in neuronal networks stimulated by shot noise (a flow of random spikes bombarding neurons). Using an exactly solvable cortical model of neuronal networks on classical random networks, we find critical phenomena accompanying the transitions and their dependence on the shot noise intensity. We show that a pattern of spontaneous neuronal activity near a critical point of a phase transition is a characteristic property that can be used to identify the bifurcation mechanism of the transition. We demonstrate that bursts and avalanches are precursors of a first-order phase transition, paroxysmal-like spikes of activity precede a second-order phase transition caused by a saddle-node bifurcation, while irregular spindle oscillations represent spontaneous activity near a second-order phase transition caused by a supercritical Hopf bifurcation. Our most interesting result is the observation of the paroxysmal-like spikes. We show that a paroxysmal-like spike is a single nonlinear event that appears instantly from a low background activity with a rapid onset, reaches a large amplitude, and ends up with an abrupt return to lower activity. These spikes are similar to single paroxysmal spikes and sharp waves observed in electroencephalographic (EEG) measurements. Our analysis shows that above the saddle-node bifurcation, sustained network oscillations appear with a large amplitude but a small frequency in contrast to network oscillations near the Hopf bifurcation that have a small amplitude but a large frequency. We discuss an amazing similarity between excitability of the cortical model stimulated by shot noise and excitability of the Morris-Lecar neuron stimulated by an applied current.

  5. Impact of laser phase and amplitude noises on streak camera temporal resolution

    SciTech Connect

    Wlotzko, V.; Uhring, W.; Summ, P.

    2015-09-15

    Streak cameras are now reaching sub-picosecond temporal resolution. In cumulative acquisition mode, this resolution does not entirely rely on the electronic or the vacuum tube performances but also on the light source characteristics. The light source, usually an actively mode-locked laser, is affected by phase and amplitude noises. In this paper, the theoretical effects of such noises on the synchronization of the streak system are studied in synchroscan and triggered modes. More precisely, the contribution of band-pass filters, delays, and time walk is ascertained. Methods to compute the resulting synchronization jitter are depicted. The results are verified by measurement with a streak camera combined with a Ti:Al{sub 2}O{sub 3} solid state laser oscillator and also a fiber oscillator.

  6. A phase-modulated laser system of ultra-low phase noise for compact atom interferometers

    NASA Astrophysics Data System (ADS)

    Lee, Ki-Se; Kim, Jaewan; Lee, Sang-Bum; Park, Sang Eon; Kwon, Taek Yong

    2015-07-01

    A compact and robust laser system is essential for mobile atom interferometers. Phase modulation can provide the two necessary phase-coherent frequencies without sophisticated phase-locking between two different lasers. However, the additional laser frequencies generated can perturb the atom interferometer. In this article, we report on a novel method to produce a single high-power laser beam composed of two phase-coherent sidebands without the perturbing carrier mode. Light from a diode laser is phase-modulated by using a fiber-coupled electro-optic modulator driven at 3.4 GHz and passes through a Fabry-Perot cavity with a 6.8 GHz free spectral range. The cavity filters the carrier mode to leave the two first-order sidebands for the two-photon Raman transition between the two hyperfine ground states of 87Rb. The laser beam is then fed to a single tapered amplifier, and the two sidebands are both amplified without mode competition. The phase noise is lower than that of a state-of-the-art optically phase-locked external-cavity diode laser (-135 dBrad2/Hz at 10 kHz) at frequencies above 10 Hz. This technique can be used in all-fiber-based laser systems for future mobile atom interferometers.

  7. Measurement noise 100 times lower than the quantum-projection limit using entangled atoms.

    PubMed

    Hosten, Onur; Engelsen, Nils J; Krishnakumar, Rajiv; Kasevich, Mark A

    2016-01-28

    Quantum metrology uses quantum entanglement--correlations in the properties of microscopic systems--to improve the statistical precision of physical measurements. When measuring a signal, such as the phase shift of a light beam or an atomic state, a prominent limitation to achievable precision arises from the noise associated with the counting of uncorrelated probe particles. This noise, commonly referred to as shot noise or projection noise, gives rise to the standard quantum limit (SQL) to phase resolution. However, it can be mitigated down to the fundamental Heisenberg limit by entangling the probe particles. Despite considerable experimental progress in a variety of physical systems, a question that persists is whether these methods can achieve performance levels that compare favourably with optimized conventional (non-entangled) systems. Here we demonstrate an approach that achieves unprecedented levels of metrological improvement using half a million (87)Rb atoms in their 'clock' states. The ensemble is 20.1 ± 0.3 decibels (100-fold) spin-squeezed via an optical-cavity-based measurement. We directly resolve small microwave-induced rotations 18.5 ± 0.3 decibels (70-fold) beyond the SQL. The single-shot phase resolution of 147 microradians achieved by the apparatus is better than that achieved by the best engineered cold atom sensors despite lower atom numbers. We infer entanglement of more than 680 ± 35 particles in the atomic ensemble. Applications include atomic clocks, inertial sensors, and fundamental physics experiments such as tests of general relativity or searches for electron electric dipole moment. To this end, we demonstrate an atomic clock measurement with a quantum enhancement of 10.5 ± 0.3 decibels (11-fold), limited by the phase noise of our microwave source.

  8. Measurement noise 100 times lower than the quantum-projection limit using entangled atoms.

    PubMed

    Hosten, Onur; Engelsen, Nils J; Krishnakumar, Rajiv; Kasevich, Mark A

    2016-01-28

    Quantum metrology uses quantum entanglement--correlations in the properties of microscopic systems--to improve the statistical precision of physical measurements. When measuring a signal, such as the phase shift of a light beam or an atomic state, a prominent limitation to achievable precision arises from the noise associated with the counting of uncorrelated probe particles. This noise, commonly referred to as shot noise or projection noise, gives rise to the standard quantum limit (SQL) to phase resolution. However, it can be mitigated down to the fundamental Heisenberg limit by entangling the probe particles. Despite considerable experimental progress in a variety of physical systems, a question that persists is whether these methods can achieve performance levels that compare favourably with optimized conventional (non-entangled) systems. Here we demonstrate an approach that achieves unprecedented levels of metrological improvement using half a million (87)Rb atoms in their 'clock' states. The ensemble is 20.1 ± 0.3 decibels (100-fold) spin-squeezed via an optical-cavity-based measurement. We directly resolve small microwave-induced rotations 18.5 ± 0.3 decibels (70-fold) beyond the SQL. The single-shot phase resolution of 147 microradians achieved by the apparatus is better than that achieved by the best engineered cold atom sensors despite lower atom numbers. We infer entanglement of more than 680 ± 35 particles in the atomic ensemble. Applications include atomic clocks, inertial sensors, and fundamental physics experiments such as tests of general relativity or searches for electron electric dipole moment. To this end, we demonstrate an atomic clock measurement with a quantum enhancement of 10.5 ± 0.3 decibels (11-fold), limited by the phase noise of our microwave source. PMID:26751056

  9. Measurement noise 100 times lower than the quantum-projection limit using entangled atoms

    NASA Astrophysics Data System (ADS)

    Hosten, Onur; Engelsen, Nils J.; Krishnakumar, Rajiv; Kasevich, Mark A.

    2016-01-01

    Quantum metrology uses quantum entanglement—correlations in the properties of microscopic systems—to improve the statistical precision of physical measurements. When measuring a signal, such as the phase shift of a light beam or an atomic state, a prominent limitation to achievable precision arises from the noise associated with the counting of uncorrelated probe particles. This noise, commonly referred to as shot noise or projection noise, gives rise to the standard quantum limit (SQL) to phase resolution. However, it can be mitigated down to the fundamental Heisenberg limit by entangling the probe particles. Despite considerable experimental progress in a variety of physical systems, a question that persists is whether these methods can achieve performance levels that compare favourably with optimized conventional (non-entangled) systems. Here we demonstrate an approach that achieves unprecedented levels of metrological improvement using half a million 87Rb atoms in their ‘clock’ states. The ensemble is 20.1 ± 0.3 decibels (100-fold) spin-squeezed via an optical-cavity-based measurement. We directly resolve small microwave-induced rotations 18.5 ± 0.3 decibels (70-fold) beyond the SQL. The single-shot phase resolution of 147 microradians achieved by the apparatus is better than that achieved by the best engineered cold atom sensors despite lower atom numbers. We infer entanglement of more than 680 ± 35 particles in the atomic ensemble. Applications include atomic clocks, inertial sensors, and fundamental physics experiments such as tests of general relativity or searches for electron electric dipole moment. To this end, we demonstrate an atomic clock measurement with a quantum enhancement of 10.5 ± 0.3 decibels (11-fold), limited by the phase noise of our microwave source.

  10. Reprint of : Measuring the Luttinger liquid parameter with shot noise

    NASA Astrophysics Data System (ADS)

    Kühne, J. K.; Protopopov, I. V.; Oreg, Y.; Mirlin, A. D.

    2016-08-01

    We explore the low-frequency noise of interacting electrons in a one-dimensional structure (quantum wire or interaction-coupled edge states) with counterpropagating modes, assuming a single channel in each direction. The system is driven out of equilibrium by a quantum point contact (QPC) with an applied voltage, which induces a double-step energy distribution of incoming electrons on one side of the device. A second QPC serves to explore the statistics of outgoing electrons. We show that measurement of a low-frequency noise in such a setup allows one to extract the Luttinger liquid constant K which is the key parameter characterizing an interacting 1D system. We evaluate the dependence of the zero-frequency noise on K and on parameters of both QPCs (transparencies and voltages).

  11. Anatomical background noise power spectrum in differential phase contrast breast images

    NASA Astrophysics Data System (ADS)

    Garrett, John; Ge, Yongshuai; Li, Ke; Chen, Guang-Hong

    2015-03-01

    In x-ray breast imaging, the anatomical noise background of the breast has a significant impact on the detection of lesions and other features of interest. This anatomical noise is typically characterized by a parameter, β, which describes a power law dependence of anatomical noise on spatial frequency (the shape of the anatomical noise power spectrum). Large values of β have been shown to reduce human detection performance, and in conventional mammography typical values of β are around 3.2. Recently, x-ray differential phase contrast (DPC) and the associated dark field imaging methods have received considerable attention as possible supplements to absorption imaging for breast cancer diagnosis. However, the impact of these additional contrast mechanisms on lesion detection is not yet well understood. In order to better understand the utility of these new methods, we measured the β indices for absorption, DPC, and dark field images in 15 cadaver breast specimens using a benchtop DPC imaging system. We found that the measured β value for absorption was consistent with the literature for mammographic acquisitions (β = 3.61±0.49), but that both DPC and dark field images had much lower values of β (β = 2.54±0.75 for DPC and β = 1.44±0.49 for dark field). In addition, visual inspection showed greatly reduced anatomical background in both DPC and dark field images. These promising results suggest that DPC and dark field imaging may help provide improved lesion detection in breast imaging, particularly for those patients with dense breasts, in whom anatomical noise is a major limiting factor in identifying malignancies.

  12. SPECTRON, a neutron noise measurement system in frequency domain

    SciTech Connect

    Izarra, G. de; Jammes, C. Destouches, C.; Geslot, B.; Di Salvo, J.

    2015-11-15

    This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the β{sub eff} parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON.

  13. SPECTRON, a neutron noise measurement system in frequency domain.

    PubMed

    de Izarra, G; Jammes, C; Geslot, B; Di Salvo, J; Destouches, C

    2015-11-01

    This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the β(eff) parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON. PMID:26628176

  14. SPECTRON, a neutron noise measurement system in frequency domain

    NASA Astrophysics Data System (ADS)

    de Izarra, G.; Jammes, C.; Geslot, B.; Di Salvo, J.; Destouches, C.

    2015-11-01

    This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the βeff parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON.

  15. SPECTRON, a neutron noise measurement system in frequency domain.

    PubMed

    de Izarra, G; Jammes, C; Geslot, B; Di Salvo, J; Destouches, C

    2015-11-01

    This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the β(eff) parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON.

  16. Phase measurement system using a dithered clock

    DOEpatents

    Fairley, C.R.; Patterson, S.R.

    1991-05-28

    A phase measurement system is disclosed which measures the phase shift between two signals by dithering a clock signal and averaging a plurality of measurements of the phase differences between the two signals. 8 figures.

  17. Effect of phase noise on quantum correlations in Bose-Josephson junctions

    SciTech Connect

    Ferrini, G.; Minguzzi, A.; Hekking, F. W. J.; Spehner, D.

    2011-10-15

    In a two-mode Bose-Josephson junction the dynamics induced by a sudden quench of the tunnel amplitude leads to the periodic formation of entangled states. For instance, squeezed states are formed at short times and macroscopic superpositions of phase states at later times. In atom interferometry, the two modes of the junction play the role of the two arms of a Mach-Zehnder interferometer; use of multiparticle entangled states allows the enhancement of phase sensitivity with respect to that obtained from uncorrelated atoms. Decoherence due to the presence of noise degrades quantum correlations between atoms, thus reducing phase sensitivity. We consider decoherence due to stochastic fluctuations of the energies of the two modes of the junction. We analyze its effect on squeezed states and macroscopic superpositions and calculate the squeezing parameter and the quantum Fisher information during the quenched dynamics. The latter quantity measures the amount of quantum correlations useful in interferometry. For moderate noise intensities, we show that it increases on time scales beyond the squeezing regime. This suggests multicomponent superpositions of phase states as interesting candidates for high-precision atom interferometry.

  18. Microwave oscillator with reduced phase noise by negative feedback incorporating microwave signals with suppressed carrier

    NASA Technical Reports Server (NTRS)

    Dick, G. J.; Saunders, J.

    1989-01-01

    Oscillator configurations which reduce the effect of 1/f noise sources for both direct feedback and stabilized local oscillator (STALO) circuits are developed and analyzed. By appropriate use of carrier suppression, a small signal is generated which suffers no loss of loop phase information or signal-to-noise ratio. This small signal can be amplified without degradation by multiplicative amplifier noise, and can be detected without saturation of the detector. Together with recent advances in microwave resonator Qs, these circuit improvements will make possible lower phase noise than can be presently achieved without the use of cryogenic devices.

  19. Laser phase noise compensation in long-range OFDR by using an optical fiber delay loop

    NASA Astrophysics Data System (ADS)

    Wang, Bin; Fan, Xinyu; Wang, Shuai; Yang, Guangyao; Liu, Qingwen; He, Zuyuan

    2016-04-01

    We propose and experimentally demonstrate a novel technique to compensate the laser phase noise in long-range OFDR by using an optical fiber delay loop, which mainly consists of a delay fiber and a frequency shifter. The delay fiber is used to shorten the optical path difference between two arms of the interferometer, and the frequency shifter works as a counter for taking the number of lightwave circulated in the loop. The preliminary experiment shows a successful compensation effect, and a 10 cm spatial resolution over 30 km measurement range is realized by using this method.

  20. Trailing edge noise prediction from measured surface pressures

    NASA Technical Reports Server (NTRS)

    Brooks, T. F.; Hodgson, T. H.

    1981-01-01

    Trailing edge (TE) noise is investigated for the case of a two-dimensional airfoil embedded in a uniform low Mach number flow, and the usefulness of several TE noise theories is examined by applying them to the measured data. The TE noise spectra and directivity are quantitatively determined for the case of a high Reynolds number and a fully turbulent boundary layer. Parameters include angle of attack, flow velocity and TE bluntness. Evanescent wave theories by Chase (1975) and Chandiramani (1974) are compared to the present results and show good agreement. Agreement of the near field pressure scatter phenomenon analysis with measurements implies that the basic assumptions used in the analysis are correct, i.e., the turbulent boundary layer (TBL) flow passes the trailing edge into the wake region. No hydrodynamic wake shedding activity is confirmed for the two-sided TBL flow, and a method incorporating the principles of the coherent output power method is used to determine the sound field. The near field edge scatter model is found to not only establish optimum sizing of edge treatment for noise control, but also to separate and identify the scattered field from the incident hydrodynamic field.

  1. Reduction of frequency noise and frequency shift by phase shifting elements in frequency modulation atomic force microscopy

    SciTech Connect

    Kobayashi, Kei; Yamada, Hirofumi; Matsushige, Kazumi

    2011-03-15

    We recently reported the analysis of the frequency noise in the frequency modulation atomic force microscopy (FM-AFM) both in high-Q and low-Q environments [Rev. Sci. Instrum. 80, 043708 (2009)]. We showed in the paper that the oscillator noise, the frequency fluctuation of the oscillator, becomes prominent in the modulation frequency lower than f{sub 0}/2Q, where f{sub 0} and Q are the resonance frequency and Q-factor. The magnitude of the oscillator noise is determined by the slope of the phase versus frequency curve of the cantilever at f{sub 0}. However, in actual FM-AFM in liquids, the phase versus frequency curve may not be always ideal because of the existence of various phase shifting elements (PSEs). For example, the spurious resonance peaks caused by the acoustic excitation and a band-pass filter in the self-oscillation loop increase the slope of the phase versus frequency curve. Due to those PSEs, the effective Q-factor is often increased from the intrinsic Q-factor of the cantilever. In this article, the frequency noise in the FM-AFM system with the PSEs in the self-oscillation loop is analyzed to show that the oscillator noise is reduced by the increase of the effective Q-factor. It is also shown that the oscillation frequency deviates from the resonance frequency due to the increase of the effective Q-factor, thereby causing the reduction in the frequency shift signal with the same factor. Therefore the increase of the effective Q-factor does not affect the signal-to-noise ratio in the frequency shift measurement, but it does affect the quantitativeness of the measured force in the FM-AFM. Furthermore, the reduction of the frequency noise and frequency shift by the increase of the effective Q-factor were confirmed by the experiments.

  2. Combustion noise from gas turbine aircraft engines measurement of far-field levels

    NASA Technical Reports Server (NTRS)

    Krejsa, Eugene A.

    1987-01-01

    Combustion noise can be a significant contributor to total aircraft noise. Measurement of combustion noise is made difficult by the fact that both jet noise and combustion noise exhibit broadband spectra and peak in the same frequency range. Since in-flight reduction of jet noise is greater than that of combustion noise, the latter can be a major contributor to the in-flight noise of an aircraft but will be less evident, and more difficult to measure, under static conditions. Several methods for measuring the far-field combustion noise of aircraft engines are discussed in this paper. These methods make it possible to measure combustion noise levels even in situations where other noise sources, such as jet noise, dominate. Measured far-field combustion noise levels for several turbofan engines are presented. These levels were obtained using a method referred to as three-signal coherence, requiring that fluctuating pressures be measured at two locations within the engine core in addition to the far-field noise measurement. Cross-spectra are used to separate the far-field combustion noise from far-field noise due to other sources. Spectra and directivities are presented. Comparisons with existing combustion noise predictions are made.

  3. Blood pressure measurement in noise intensive environments using adaptive interference cancellation.

    PubMed

    Pinto, Lisa; Dhanantwari, Amar; Wong, Winnie; Stergiopoulos, Stergios; Maris, Mike

    2002-05-01

    The traditional auscultatory technique and current methodologies for measuring human blood pressure are limited when used in situations where extreme vibration or acoustic noise is present. In this study, human subjects were used to establish the effectiveness of a novel adaptive blood pressure monitoring (ABPM) system in determining systolic-diastolic pressure in vibration and noise intense environments. To remove the effects of noise and vibration from the audible Korotkoff sounds, the proposed ABPM system employs two acoustic sensors in the pressure cuff. The primary acoustic sensor is placed on the brachial artery to record the Korotkoff sounds while the secondary acoustic sensor is placed away from the artery to record background noise and vibrations. The signals from the two acoustic sensors are provided to the input of an adaptive interference canceller to remove the noise effects in the signal of the primary acoustic sensor. In two phases of clinical testing, the ABPM system was first employed in a noiseless environment and then near and onboard search and rescue helicopters. The results from both phases deliver a successful demonstration of the ABPM system's capabilities to provide blood pressure estimates in noisy environments where the conventional auscultatory and other techniques have limited use.

  4. Noise texture and signal detectability in propagation-based x-ray phase-contrast tomography

    SciTech Connect

    Chou, Cheng-Ying; Anastasio, Mark A.

    2010-01-15

    Purpose: X-ray phase-contrast tomography (PCT) is a rapidly emerging imaging modality for reconstructing estimates of an object's three-dimensional x-ray refractive index distribution. Unlike conventional x-ray computed tomography methods, the statistical properties of the reconstructed images in PCT remain unexplored. The purpose of this work is to quantitatively investigate noise propagation in PCT image reconstruction. Methods: The authors derived explicit expressions for the autocovariance of the reconstructed absorption and refractive index images to characterize noise texture and understand how the noise properties are influenced by the imaging geometry. Concepts from statistical detection theory were employed to understand how the imaging geometry-dependent statistical properties affect the signal detection performance in a signal-known-exactly/background-known-exactly task. Results: The analytical formulas for the phase and absorption autocovariance functions were implemented numerically and compared to the corresponding empirical values, and excellent agreement was found. They observed that the reconstructed refractive images are highly spatially correlated, while the absorption images are not. The numerical results confirm that the strength of the covariance is scaled by the detector spacing. Signal detection studies were conducted, employing a numerical observer. The detection performance was found to monotonically increase as the detector-plane spacing was increased. Conclusions: The authors have conducted the first quantitative investigation of noise propagation in PCT image reconstruction. The reconstructed refractive images were found to be highly spatially correlated, while absorption images were not. This is due to the presence of a Fourier space singularity in the reconstruction formula for the refraction images. The statistical analysis may facilitate the use of task-based image quality measures to further develop and optimize this emerging

  5. A low phase noise microwave frequency synthesis for a high-performance cesium vapor cell atomic clock

    SciTech Connect

    François, B.; Boudot, R.; Calosso, C. E.; Danet, J. M.

    2014-09-15

    We report the development, absolute phase noise, and residual phase noise characterization of a 9.192 GHz microwave frequency synthesis chain devoted to be used as a local oscillator in a high-performance cesium vapor cell atomic clock based on coherent population trapping (CPT). It is based on frequency multiplication of an ultra-low phase noise 100 MHz oven-controlled quartz crystal oscillator using a nonlinear transmission line-based chain. Absolute phase noise performances of the 9.192 GHz output signal are measured to be −42, −100, −117 dB rad{sup 2}/Hz and −129 dB rad{sup 2}/Hz at 1 Hz, 100 Hz, 1 kHz, and 10 kHz offset frequencies, respectively. Compared to current results obtained in a state-of-the-art CPT-based frequency standard developed at LNE-SYRTE, this represents an improvement of 8 dB and 10 dB at f = 166 Hz and f = 10 kHz, respectively. With such performances, the expected Dick effect contribution to the atomic clock short term frequency stability is reported at a level of 6.2 × 10{sup −14} at 1 s integration time, that is a factor 3 higher than the atomic clock shot noise limit. Main limitations are pointed out.

  6. A low phase noise microwave frequency synthesis for a high-performance cesium vapor cell atomic clock

    NASA Astrophysics Data System (ADS)

    François, B.; Calosso, C. E.; Danet, J. M.; Boudot, R.

    2014-09-01

    We report the development, absolute phase noise, and residual phase noise characterization of a 9.192 GHz microwave frequency synthesis chain devoted to be used as a local oscillator in a high-performance cesium vapor cell atomic clock based on coherent population trapping (CPT). It is based on frequency multiplication of an ultra-low phase noise 100 MHz oven-controlled quartz crystal oscillator using a nonlinear transmission line-based chain. Absolute phase noise performances of the 9.192 GHz output signal are measured to be -42, -100, -117 dB rad2/Hz and -129 dB rad2/Hz at 1 Hz, 100 Hz, 1 kHz, and 10 kHz offset frequencies, respectively. Compared to current results obtained in a state-of-the-art CPT-based frequency standard developed at LNE-SYRTE, this represents an improvement of 8 dB and 10 dB at f = 166 Hz and f = 10 kHz, respectively. With such performances, the expected Dick effect contribution to the atomic clock short term frequency stability is reported at a level of 6.2 × 10-14 at 1 s integration time, that is a factor 3 higher than the atomic clock shot noise limit. Main limitations are pointed out.

  7. A low phase noise microwave frequency synthesis for a high-performance cesium vapor cell atomic clock.

    PubMed

    François, B; Calosso, C E; Danet, J M; Boudot, R

    2014-09-01

    We report the development, absolute phase noise, and residual phase noise characterization of a 9.192 GHz microwave frequency synthesis chain devoted to be used as a local oscillator in a high-performance cesium vapor cell atomic clock based on coherent population trapping (CPT). It is based on frequency multiplication of an ultra-low phase noise 100 MHz oven-controlled quartz crystal oscillator using a nonlinear transmission line-based chain. Absolute phase noise performances of the 9.192 GHz output signal are measured to be -42, -100, -117 dB rad(2)/Hz and -129 dB rad(2)/Hz at 1 Hz, 100 Hz, 1 kHz, and 10 kHz offset frequencies, respectively. Compared to current results obtained in a state-of-the-art CPT-based frequency standard developed at LNE-SYRTE, this represents an improvement of 8 dB and 10 dB at f = 166 Hz and f = 10 kHz, respectively. With such performances, the expected Dick effect contribution to the atomic clock short term frequency stability is reported at a level of 6.2 × 10(-14) at 1 s integration time, that is a factor 3 higher than the atomic clock shot noise limit. Main limitations are pointed out. PMID:25273756

  8. Wavelet-based coherence measures of global seismic noise properties

    NASA Astrophysics Data System (ADS)

    Lyubushin, A. A.

    2015-04-01

    The coherent behavior of four parameters characterizing the global field of low-frequency (periods from 2 to 500 min) seismic noise is studied. These parameters include generalized Hurst exponent, multifractal singularity spectrum support width, the normalized entropy of variance, and kurtosis. The analysis is based on the data from 229 broadband stations of GSN, GEOSCOPE, and GEOFON networks for a 17-year period from the beginning of 1997 to the end of 2013. The entire set of stations is subdivided into eight groups, which, taken together, provide full coverage of the Earth. The daily median values of the studied noise parameters are calculated in each group. This procedure yields four 8-dimensional time series with a time step of 1 day with a length of 6209 samples in each scalar component. For each of the four 8-dimensional time series, a multiple correlation measure is estimated, which is based on computing robust canonical correlations for the Haar wavelet coefficients at the first detail level within a moving time window of the length 365 days. These correlation measures for each noise property demonstrate essential increasing starting from 2007 to 2008 which was continued till the end of 2013. Taking into account a well-known phenomenon of noise correlation increasing before catastrophes, this increasing of seismic noise synchronization is interpreted as indicators of the strongest (magnitudes not less than 8.5) earthquakes activation which is observed starting from the Sumatra mega-earthquake of 26 Dec 2004. This synchronization continues growing up to the end of the studied period (2013), which can be interpreted as a probable precursor of the further increase in the intensity of the strongest earthquakes all over the world.

  9. Phase stability in fMRI time series: effect of noise regression, off-resonance correction and spatial filtering techniques.

    PubMed

    Hagberg, Gisela E; Bianciardi, Marta; Brainovich, Valentina; Cassara, Antonino Mario; Maraviglia, Bruno

    2012-02-15

    Although the majority of fMRI studies exploit magnitude changes only, there is an increasing interest regarding the potential additive information conveyed by the phase signal. This integrated part of the complex number furnished by the MR scanners can also be used for exploring direct detection of neuronal activity and for thermography. Few studies have explicitly addressed the issue of the available signal stability in the context of phase time-series, and therefore we explored the spatial pattern of frequency specific phase fluctuations, and evaluated the effect of physiological noise components (heart beat and respiration) on the phase signal. Three categories of retrospective noise reduction techniques were explored and the temporal signal stability was evaluated in terms of a physiologic noise model, for seven fMRI measurement protocols in eight healthy subjects at 3T, for segmented CSF, gray and white matter voxels. We confirmed that for most processing methods, an efficient use of the phase information is hampered by the fact that noise from physiological and instrumental sources contributes significantly more to the phase than to the magnitude instability. Noise regression based on the phase evolution of the central k-space point, RETROICOR, or an orthonormalized combination of these were able to reduce their impact, but without bringing phase stability down to levels expected from the magnitude signal. Similar results were obtained after targeted removal of scan-to-scan variations in the bulk magnetic field by the dynamic off-resonance in k-space (DORK) method and by the temporal off-resonance alignment of single-echo time series technique (TOAST). We found that spatial high-pass filtering was necessary, and in vivo a Gaussian filter width of 20mm was sufficient to suppress physiological noise and bring the phase fluctuations to magnitude levels. Stronger filters brought the fluctuations down to levels dictated by thermal noise contributions, and for 62

  10. Influence of laser phase noise on Brillouin optical time-domain analysis sensors

    NASA Astrophysics Data System (ADS)

    Minardo, A.; Zeni, L.

    2016-05-01

    This paper presents a numerical study of the phase noise from the laser in Brillouin Optical Time-Domain analysis (BOTDA) sensors. Due to laser phase noise, the phase shift cumulated by pump and probe beams during interaction in a generic fiber position is a stochastic variable, with zero mean and variance increasing with pulse duration. For negligibly small pulse leakage, the induced noise is independent of fiber length; otherwise, it increases with fiber length as long as the laser coherence length is longer than fiber.

  11. Development of a highway noise prediction model using an Leq20 s measure of basic vehicular noise

    NASA Astrophysics Data System (ADS)

    Pamanikabud, P.; Tansatcha, M.; Brown, A. L.

    2008-09-01

    The objective of the study reported here was to build a highway traffic noise simulation model for free-flow traffic conditions in Thailand employing a technique utilizing individual vehicular noise modelling based on the equivalent sound level over 20 s ( Leq20 s). This Leq20 s technique provides a more accurate measurement of noise energy from each type of vehicle under real running conditions. The coefficient of propagation and ground effect for this model was then estimated using a trial-and-error method, and applied to the highway traffic noise simulation model. This newly developed highway traffic noise model was tested for its goodness-of-fit to field observations. The test shows that this new model provides good predictions for highway noise conditions in Thailand. The concepts and techniques that are modeled and tested in this study can also be applied for prediction of traffic noise for local conditions in other countries.

  12. 23 CFR 772.9 - Analysis of traffic noise impacts and abatement measures.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 23 Highways 1 2010-04-01 2010-04-01 false Analysis of traffic noise impacts and abatement measures... AND ENVIRONMENT PROCEDURES FOR ABATEMENT OF HIGHWAY TRAFFIC NOISE AND CONSTRUCTION NOISE § 772.9 Analysis of traffic noise impacts and abatement measures. (a) The highway agency shall determine...

  13. 23 CFR 772.9 - Analysis of traffic noise impacts and abatement measures.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 23 Highways 1 2011-04-01 2011-04-01 false Analysis of traffic noise impacts and abatement measures... AND ENVIRONMENT PROCEDURES FOR ABATEMENT OF HIGHWAY TRAFFIC NOISE AND CONSTRUCTION NOISE § 772.9 Analysis of traffic noise impacts and abatement measures. (a) The highway agency shall determine...

  14. Analysis of a Shock-Associated Noise Prediction Model Using Measured Jet Far-Field Noise Data

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Sharpe, Jacob A.

    2014-01-01

    A code for predicting supersonic jet broadband shock-associated noise was assessed using a database containing noise measurements of a jet issuing from a convergent nozzle. The jet was operated at 24 conditions covering six fully expanded Mach numbers with four total temperature ratios. To enable comparisons of the predicted shock-associated noise component spectra with data, the measured total jet noise spectra were separated into mixing noise and shock-associated noise component spectra. Comparisons between predicted and measured shock-associated noise component spectra were used to identify deficiencies in the prediction model. Proposed revisions to the model, based on a study of the overall sound pressure levels for the shock-associated noise component of the measured data, a sensitivity analysis of the model parameters with emphasis on the definition of the convection velocity parameter, and a least-squares fit of the predicted to the measured shock-associated noise component spectra, resulted in a new definition for the source strength spectrum in the model. An error analysis showed that the average error in the predicted spectra was reduced by as much as 3.5 dB for the revised model relative to the average error for the original model.

  15. Phase velocity tomography of surface waves using ambient noise cross correlation and array processing

    NASA Astrophysics Data System (ADS)

    Boué, Pierre; Roux, Philippe; Campillo, Michel; Briand, Xavier

    2014-01-01

    Continuous recordings of ambient seismic noise across large seismic arrays allows a new type of processing using the cross-correlation technique on broadband data. We propose to apply double beamforming (DBF) to cross correlations to extract a particular wave component of the reconstructed signals. We focus here on the extraction of the surface waves to measure phase velocity variations with great accuracy. DBF acts as a spatial filter between two distant subarrays after cross correlation of the wavefield between each single receiver pair. During the DBF process, horizontal slowness and azimuth are used to select the wavefront on both subarray sides. DBF increases the signal-to-noise ratio, which improves the extraction of the dispersive wave packets. This combination of cross correlation and DBF is used on the Transportable Array (USArray), for the central U.S. region. A standard model of surface wave propagation is constructed from a combination of the DBF and cross correlations at different offsets and for different frequency bands. The perturbation (phase shift) between each beam and the standard model is inverted. High-resolution maps of the phase velocity of Rayleigh and Love waves are then constructed. Finally, the addition of azimuthal information provided by DBF is discussed, to construct curved rays that replace the classical great-circle path assumption.

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

    NASA Technical Reports Server (NTRS)

    Panda, J.; Mosher, R.

    2010-01-01

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

  17. Simplified phase noise model for negative-resistance oscillators and a comparison with feedback oscillator models.

    PubMed

    Everard, Jeremy; Xu, Min; Bale, Simon

    2012-03-01

    This paper describes a greatly simplified model for the prediction of phase noise in oscillators which use a negative resistance as the active element. It is based on a simple circuit consisting of the parallel addition of a noise current, a negative admittance/resistance, and a parallel (Qlimited) resonant circuit. The transfer function is calculated as a forward trans-resistance (VOUT/IIN) and then converted to power. The effect of limiting is incorporated by assuming that the phase noise element of the noise floor is kT/2, i.e., -177 dBm/Hz at room temperature. The result is the same as more complex analyses, but enables a simple, clear insight into the operation of oscillators. The phase noise for a given power in the resonator appears to be lower than in feedback oscillators. The reasons for this are explained. Simulation and experimental results are included.

  18. Noise characteristics of the Skylab S-193 altimeter altitude measurements

    NASA Technical Reports Server (NTRS)

    Hatch, W. E.

    1975-01-01

    The statistical characteristics of the SKYLAB S-193 altimeter altitude noise are considered. These results are reported in a concise format for use and analysis by the scientific community. In most instances the results have been grouped according to satellite pointing so that the effects of pointing on the statistical characteristics can be readily seen. The altimeter measurements and the processing techniques are described. The mathematical descriptions of the computer programs used for these results are included.

  19. In-flight jet engine noise measurement system

    NASA Technical Reports Server (NTRS)

    Knight, V. H., Jr.

    1981-01-01

    An instrumentation system in flight tests for noise research is described which utilizes miniature transducers to measure low-amplitude, high-frequency fluctuating pressures in a jet engine mounted under the wing of a turboprop aircraft. The system employs a rotor-mounted FM telemeter to acquire data from eight fan-blade-mounted transducers which are subjected to up to 75,000 g's of loading. Data is transmitted from the rotor to an antenna mounted in the inlet-duct wall using a low-power, close-coupled RF link. The blade pressures and other inlet and stator-vane fluctuating pressures are recorded on airborne, magnetic-tape recorders. The flight instrumentation described also includes PCM techniques to encode and record a variety of quasi-static measurements to provide engine and aircraft performance data. The instrumentation and experimental measurements are of value to an improved understanding of noise sources in jet engines and for the advancement of jet-engine ground noise testing techniques.

  20. How to measure community tolerance levels for noise.

    PubMed

    Taraldsen, Gunnar; Gelderblom, Femke B; Gjestland, Truls T

    2016-07-01

    Relationships between noise exposure and transportation noise induced annoyance have been studied extensively for several decades. The annoyance due to aircraft noise exposure is in the present paper assumed to be influenced by the day-night yearly average sound level (DNL). It has long been recognized that the annoyance also depends on non-DNL factors, but this is complicated-resulting in a variety of different modeling strategies. Motivated by this, the community tolerance level (CTL) was introduced in 2011 for a loudness-based psychometric function. It is a single parameter that accounts for the aggregate influence of other factors. This paper suggests and investigates different methods for the measurement of the CTL. The methods are illustrated on data found in the literature, on recent surveys around two Norwegian airports, and on simulated data. The results from the presented methods differ significantly. An elementary method is shown to give a measurement of the CTL with smaller uncertainty, and is recommended as a replacement for the originally suggested least-squares method. Methods for evaluating the measurement uncertainty are also presented. PMID:27475190

  1. Biomagnetic measurement system for supine subjects with expanded sensor array and real-time noise reduction.

    PubMed

    Adachi, Yoshiaki; Kawabata, Shigenori; Sasano, Tetsuo; Oyama, Yasuhiro Haruta Daisuke; Uehara, Gen; Sekihara, Kensuke

    2015-01-01

    A biomagnetic measurement system was developed, suitable for the detection of magnetospinogram (MSG) and magnetocardiogram (MCG) signals from the dorsal surface of supine subjects. It is effective for noninvasively observing the electric activity of the spinal cord and/or heart. These biomagnetic signals are extremely weak, and magnetic flux sensors based on superconducting quantum interference devices (SQUIDs) are necessary to detect them. However, highly sensitive magnetic field measurement often suffers from ultra low-band circumstance noise mainly caused by transportation in urban areas. We applied reference sensors for monitoring the circumstance noise, and their outputs multiplied by appropriate weight coefficients were directly input to the feedback coil of a SQUID gradiometer. Synthesized in-phase components reduced the ultra low-band noise by approximately 90%. Both the MSG and MCG signals were successfully detected in a moderately magnetically shielded room. Even though the MCG signal band overlapped the ultra low-band noise, the signal-to-noise ratio was improved.

  2. Analyses and Measures of GPR Signal with Superimposed Noise

    NASA Astrophysics Data System (ADS)

    Chicarella, Simone; Ferrara, Vincenzo; D'Atanasio, Paolo; Frezza, Fabrizio; Pajewski, Lara; Pavoncello, Settimio; Prontera, Santo; Tedeschi, Nicola; Zambotti, Alessandro

    2014-05-01

    The influence of EM noises and environmental hard conditions on the GPR surveys has been examined analytically [1]. In the case of pulse radar GPR, many unwanted signals as stationary clutter, non-stationary clutter, random noise, and time jitter, influence the measurement signal. When GPR is motionless, stationary clutter is the most dominant signal component due to the reflections of static objects different from the investigated target, and to the direct antenna coupling. Moving objects like e.g. persons and vehicles, and the swaying of tree crown, produce non-stationary clutter. Device internal noise and narrowband jamming are e.g. two potential sources of random noises. Finally, trigger instabilities generate random jitter. In order to estimate the effective influence of these noise signal components, we organized some experimental setup of measurement. At first, we evaluated for the case of a GPR basic detection, simpler image processing of radargram. In the future, we foresee experimental measurements for detection of the Doppler frequency changes induced by movements of targets (like physiological movements of survivors under debris). We obtain image processing of radargram by using of GSSI SIR® 2000 GPR system together with the UWB UHF GPR-antenna (SUB-ECHO HBD 300, a model manufactured by Radarteam company). Our work includes both characterization of GPR signal without (or almost without) a superimposed noise, and the effect of jamming originated from the coexistence of a different radio signal. For characterizing GPR signal, we organized a measurement setup that includes the following instruments: mod. FSP 30 spectrum analyser by Rohde & Schwarz which operates in the frequency range 9 KHz - 30 GHz, mod. Sucoflex 104 cable by Huber Suhner (10 MHz - 18 GHz), and HL050 antenna by Rohde & Schwarz (bandwidth: from 850 MHz to 26.5 GHz). The next analysis of superimposed jamming will examine two different signal sources: by a cellular phone and by a

  3. A fully integrated CMOS VCXO-IC with low phase noise, wide tuning range and high tuning linearity

    NASA Astrophysics Data System (ADS)

    Yanjun, Yang; Yun, Zeng

    2015-06-01

    This paper describes a low phase noise, wide tuning range and high tuning linearity CMOS voltage controlled crystal oscillator IC (VCXO-IC) with LVCMOS and LVPECL output. A differential coupled frequency doubling Colpitts oscillator is adopted to obtain low noise 2× frequency output. Wide tuning range and high linearity are simultaneously achieved by using MOS varactor arrays. The measurement results show that the designed VCXO-IC achieves -134 dBc/Hz phase noise at 1 kHz offset frequency and ± 135 ppm output frequency tuning range within 3% linearity by using 40 MHz fundamental AT-cut crystal. The VCXO-IC is fabricated in the chartered 0.35 μm standard CMOS process and occupies a total silicon area of 2.4 mm2. Project supported by the National Natural Science Foundation of China (No. 61350007).

  4. An efficient two-phase L(1)-TV method for restoring blurred images with impulse noise.

    PubMed

    Chan, Raymond H; Dong, Yiqiu; Hintermüller, Michael

    2010-07-01

    A two-phase image restoration method based upon total variation regularization combined with an L(1)-data-fitting term for impulse noise removal and deblurring is proposed. In the first phase, suitable noise detectors are used for identifying image pixels contaminated by noise. Then, in the second phase, based upon the information on the location of noise-free pixels, images are deblurred and denoised simultaneously. For efficiency reasons, in the second phase a superlinearly convergent algorithm based upon Fenchel-duality and inexact semismooth Newton techniques is utilized for solving the associated variational problem. Numerical results prove the new method to be a significantly advance over several state-of-the-art techniques with respect to restoration capability and computational efficiency.

  5. Application of MEMS Microphone Array Technology to Airframe Noise Measurements

    NASA Technical Reports Server (NTRS)

    Humphreys, William M., Jr.; Shams, Qamar A.; Graves, Sharon S.; Sealey, Bradley S.; Bartram, Scott M.; Comeaux, Toby

    2005-01-01

    Current generation microphone directional array instrumentation is capable of extracting accurate noise source location and directivity data on a variety of aircraft components, resulting in significant gains in test productivity. However, with this gain in productivity has come the desire to install larger and more complex arrays in a variety of ground test facilities, creating new challenges for the designers of array systems. To overcome these challenges, a research study was initiated to identify and develop hardware and fabrication technologies which could be used to construct an array system exhibiting acceptable measurement performance but at much lower cost and with much simpler installation requirements. This paper describes an effort to fabricate a 128-sensor array using commercially available Micro-Electro-Mechanical System (MEMS) microphones. The MEMS array was used to acquire noise data for an isolated 26%-scale high-fidelity Boeing 777 landing gear in the Virginia Polytechnic Institute and State University Stability Tunnel across a range of Mach numbers. The overall performance of the array was excellent, and major noise sources were successfully identified from the measurements.

  6. Aerodynamic Performance Measurements for a Forward Swept Low Noise Fan

    NASA Technical Reports Server (NTRS)

    Fite, E. Brian

    2006-01-01

    One source of noise in high tip speed turbofan engines, caused by shocks, is called multiple pure tone noise (MPT's). A new fan, called the Quiet High Speed Fan (QHSF), showed reduced noise over the part speed operating range, which includes MPT's. The QHSF showed improved performance in most respects relative to a baseline fan; however, a partspeed instability discovered during testing reduced the operating range below acceptable limits. The measured QHSF adiabatic efficiency on the fixed nozzle acoustic operating line was 85.1 percent and the baseline fan 82.9 percent, a 2.2 percent improvement. The operating line pressure rise at design point rotational speed and mass flow was 1.764 and 1.755 for the QHSF and baseline fan, respectively. Weight flow at design point speed was 98.28 lbm/sec for the QHSF and 97.97 lbm/sec for the baseline fan. The operability margin for the QHSF approached 0 percent at the 75 percent speed operating condition. The baseline fan maintained sufficient margin throughout the operating range as expected. Based on the stage aerodynamic measurements, this concept shows promise for improved performance over current technology if the operability limitations can be solved.

  7. Simulations & Measurements of Airframe Noise: A BANC Workshops Perspective

    NASA Technical Reports Server (NTRS)

    Choudhari, Meelan; Lockard, David

    2016-01-01

    Airframe noise corresponds to the acoustic radiation due to turbulent flow in the vicinity of airframe components such as high-lift devices and landing gears. Since 2010, the American Institute of Aeronautics and Astronautics has organized an ongoing series of workshops devoted to Benchmark Problems for Airframe Noise Computations (BANC). The BANC workshops are aimed at enabling a systematic progress in the understanding and high-fidelity predictions of airframe noise via collaborative investigations that integrate computational fluid dynamics, computational aeroacoustics, and in depth measurements targeting a selected set of canonical yet realistic configurations that advance the current state-of-the-art in multiple respects. Unique features of the BANC Workshops include: intrinsically multi-disciplinary focus involving both fluid dynamics and aeroacoustics, holistic rather than predictive emphasis, concurrent, long term evolution of experiments and simulations with a powerful interplay between the two, and strongly integrative nature by virtue of multi-team, multi-facility, multiple-entry measurements. This paper illustrates these features in the context of the BANC problem categories and outlines some of the challenges involved and how they were addressed. A brief summary of the BANC effort, including its technical objectives, strategy, and selective outcomes thus far is also included.

  8. Prediction, Measurement, and Suppression of High Temperature Supersonic Jet Noise

    NASA Technical Reports Server (NTRS)

    Seiner, John M.; Bhat, T. R. S.; Jansen, Bernard J.

    1999-01-01

    The photograph in figure 1 displays a water cooled round convergent-divergent supersonic nozzle operating slightly overexpanded near 2460 F. The nozzle is designed to produce shock free flow near this temperature at Mach 2. The exit diameter of this nozzle is 3.5 inches. This nozzle is used in the present study to establish properties of the sound field associated with high temperature supersonic jets operating fully pressure balanced (i.e. shock free) and to evaluate capability of the compressible Rayleigh model to account for principle physical features of the observed sound emission. The experiment is conducted statically (i.e. M(sub f) = 0.) in the NASA/LaRC Jet Noise Laboratory. Both aerodynamic and acoustic measurements are obtained in this study along with numerical plume simulation and theoretical prediction of jet noise. Detailed results from this study are reported previously by Seiner, Ponton, Jansen, and Lagen.

  9. Noise measurement on thermal systems with narrow band

    NASA Astrophysics Data System (ADS)

    Burks, Stephen D.; Haefner, David P.; Doe, Joshua M.

    2016-05-01

    Thermal systems with a narrow spectral bandpass and mid-wave thermal imagers are useful for a variety of imaging applications. Additionally, the sensitivity for these classes of systems is increasing along with an increase in performance requirements when evaluated in a lab. Unfortunately, the uncertainty in the blackbody temperature along with the temporal instability of the blackbody could lead to uncontrolled laboratory environmental effects which could increase the measured noise. If the temporal uncertainty and accuracy of a particular blackbody is known, then confidence intervals could be adjusted for source accuracy and instability. Additionally, because thermal currents may be a large source of temporal noise in narrow band systems, a means to mitigate them is presented and results are discussed.

  10. Analysis of a Shock-Associated Noise Prediction Model Using Measured Jet Far-Field Noise Data

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Sharpe, Jacob A.

    2014-01-01

    A code for predicting supersonic jet broadband shock-associated noise was assessed us- ing a database containing noise measurements of a jet issuing from a convergent nozzle. The jet was operated at 24 conditions covering six fully expanded Mach numbers with four total temperature ratios. To enable comparisons of the predicted shock-associated noise component spectra with data, the measured total jet noise spectra were separated into mixing noise and shock-associated noise component spectra. Comparisons between predicted and measured shock-associated noise component spectra were used to identify de ciencies in the prediction model. Proposed revisions to the model, based on a study of the overall sound pressure levels for the shock-associated noise component of the mea- sured data, a sensitivity analysis of the model parameters with emphasis on the de nition of the convection velocity parameter, and a least-squares t of the predicted to the mea- sured shock-associated noise component spectra, resulted in a new de nition for the source strength spectrum in the model. An error analysis showed that the average error in the predicted spectra was reduced by as much as 3.5 dB for the revised model relative to the average error for the original model.

  11. Continuous Stern-Gerlach effect: Noise and the measurement process

    PubMed Central

    Dehmelt, Hans

    1986-01-01

    This paper resumes the discussion of the continuous Stern-Gerlach effect, a method to continuously and nondestructively determine the spin state of the same individual electron, quasipermanently confined in a Penning trap in ultrahigh vacuum at liquid helium temperatures. Here the focus is on limitations to spin-state detection due to thermal and zero-point noise and on the quantum-mechanical measurement process. Illustrations of the continuous spin measurement process in the presence of selected perturbations are provided. The alteration of the spin state brought about by the frequency measurement process is exhibited. To resolve Zeno's paradox in a specific example, a slow resonant spin flip is discussed, when interrupted by frequent spin-state measurements. The continuous Stern-Gerlach effect is shown to be a near-ideal example for the quantum mechanical measurement process, for which all steps may be followed in quantitative detail. PMID:16593696

  12. Continuous Stern--Gerlach Effect: Noise and the Measurement Process

    NASA Astrophysics Data System (ADS)

    Dehmelt, Hans

    1986-05-01

    This paper resumes the discussion of the continuous Stern-Gerlach effect, a method to continuously and nondestructively determine the spin state of the same individual electron, quasipermanently confined in a Penning trap in ultrahigh vacuum at liquid helium temperatures. Here the focus is on limitations to spin-state detection due to thermal and zero-point noise and on the quantum-mechanical measurement process. Illustrations of the continuous spin measurement process in the presence of selected perturbations are provided. The alteration of the spin state brought about by the frequency measurement process is exhibited. To resolve Zeno's paradox in a specific example, a slow resonant spin flip is discussed, when interrupted by frequent spin-state measurements. The continuous Stern-Gerlach effect is shown to be a near-ideal example for the quantum mechanical measurement process, for which all steps may be followed in quantitative detail.

  13. Continuous Stern-Gerlach effect: Noise and the measurement process.

    PubMed

    Dehmelt, H

    1986-05-01

    This paper resumes the discussion of the continuous Stern-Gerlach effect, a method to continuously and nondestructively determine the spin state of the same individual electron, quasipermanently confined in a Penning trap in ultrahigh vacuum at liquid helium temperatures. Here the focus is on limitations to spin-state detection due to thermal and zero-point noise and on the quantum-mechanical measurement process. Illustrations of the continuous spin measurement process in the presence of selected perturbations are provided. The alteration of the spin state brought about by the frequency measurement process is exhibited. To resolve Zeno's paradox in a specific example, a slow resonant spin flip is discussed, when interrupted by frequent spin-state measurements. The continuous Stern-Gerlach effect is shown to be a near-ideal example for the quantum mechanical measurement process, for which all steps may be followed in quantitative detail. PMID:16593696

  14. Neutron noise measurements at the Delphi subcritical assembly

    SciTech Connect

    Szieberth, M.; Klujber, G.; Kloosterman, J. L.; De Haas, D.

    2012-07-01

    The paper presents the results and evaluations of a comprehensive set of neutron noise measurements on the Delphi subcritical assembly of the Delft Univ. of Technology. The measurements investigated the effect of different source distributions (inherent spontaneous fission and {sup 252}Cf) and the position of the detectors applied (both radially and vertically). The evaluation of the measured data has been performed by the variance-to-mean ratio (VTMR, Feynman-{alpha}), the autocorrelation (ACF, Rossi-{alpha}) and the cross-correlation (CCF) methods. The values obtained for the prompt decay constant show a strong bias, which depends both on the detector position and on the source distribution. This is due to the presence of higher modes in the system. It has been observed that the {alpha} value fitted is higher when the detector is close to the boundary of the core or to the {sup 252}Cf point-source. The higher alpha-modes have also been observed by fitting functions describing two alpha-modes. The successful set of measurement also provides a good basis for further theoretical investigations including the Monte Carlo simulation of the noise measurements and the calculation of the alpha-modes in the Delphi subcritical assembly. (authors)

  15. Effect of laser phase noise on the fidelity of optomechanical quantum memory

    NASA Astrophysics Data System (ADS)

    Farman, F.; Bahrampour, A. R.

    2015-03-01

    Optomechanical and electromechanical cavities have been widely used in quantum memories and quantum transducers. We theoretically investigate the robustness of optomechanical and electromechanical quantum memories against the noise of the control laser. By solving the Langevin equations and using the covariance matrix formalism in the presence of laser noise, the storing fidelity of Gaussian states is obtained. It is shown that the destructive effect of phase noise is more significant in higher values of coupling laser amplitude and optomechanical coupling strength G . However, by further increasing the coupling coefficient, the interaction time between photons and phonons decreases below the coherence time of laser frequency noise and the destructive effect of laser phase noise on the storing fidelity drops as well.

  16. The non-contact precision measurement and noise reduction method for liquid volume metrology

    NASA Astrophysics Data System (ADS)

    Wang, Jintao; Liu, Ziyong; Tong, Lin; Zhang, Long; Guo, Ligong; Bao, Xuesong

    2011-12-01

    Liquid volume is one important metrology method for commercial transaction in international trade, and vertical tank is used as main metrology tool. One non-contact optical measurement system was raised by using laser scanning method. The coordinates of vertical tank shell were acquired by phase-shift ranging method and angular measurement, and the set of coordinates is named as data cloud. The measurement errors of distance and angle are 2mm and 2" respectively. Wavelet was applied to noise reduction and curve feature extraction for data cloud. Iterative method was used to deduce the radius at each course height. One 1000m3 vertical tank used as test object, comparison experiment was carried out with strap method (international arbitral standard). The experimental results show that the noise due to tank shell surface characteristics and laser scanning devices could be filtered satisfactorily, and the local curve features of tank shell were described correctly.

  17. Measurement of Model Noise in a Hard-Wall Wind Tunnel

    NASA Technical Reports Server (NTRS)

    Soderman, Paul T.

    2006-01-01

    Identification, analysis, and control of fluid-mechanically-generated sound from models of aircraft and automobiles in special low-noise, semi-anechoic wind tunnels are an important research endeavor. Such studies can also be done in aerodynamic wind tunnels that have hard walls if phased microphone arrays are used to focus on the noise-source regions and reject unwanted reflections or background noise. Although it may be difficult to simulate the total flyover or drive-by noise in a closed wind tunnel, individual noise sources can be isolated and analyzed. An acoustic and aerodynamic study was made of a 7-percent-scale aircraft model in a NASA Ames 7-by-10-ft (about 2-by-3-m) wind tunnel for the purpose of identifying and attenuating airframe noise sources. Simulated landing, takeoff, and approach configurations were evaluated at Mach 0.26. Using a phased microphone array mounted in the ceiling over the inverted model, various noise sources in the high-lift system, landing gear, fins, and miscellaneous other components were located and compared for sound level and frequency at one flyover location. Numerous noise-alleviation devices and modifications of the model were evaluated. Simultaneously with acoustic measurements, aerodynamic forces were recorded to document aircraft conditions and any performance changes caused by geometric modifications. Most modern microphone-array systems function in the frequency domain in the sense that spectra of the microphone outputs are computed, then operations are performed on the matrices of microphone-signal cross-spectra. The entire acoustic field at one station in such a system is acquired quickly and interrogated during postprocessing. Beam-forming algorithms are employed to scan a plane near the model surface and locate noise sources while rejecting most background noise and spurious reflections. In the case of the system used in this study, previous studies in the wind tunnel have identified noise sources up to 19 d

  18. Effect of noise on Frequency-Resolved Optical Gating measurements of ultrashort pulses

    SciTech Connect

    Fittinghoff, D.N.; DeLong, K.W.; Ladera, C.L.; Trebino, R.

    1995-02-01

    We study the effects of noise in Frequency-Resolved Optical Gating measurements of ultrashort pulses. We quantify the measurement accuracy in the presence of additive, muliplicative, and quantization noise, and discuss filtering and pre-processing of the data.

  19. A study of GPS measurement errors due to noise and multipath interference for CGADS

    NASA Technical Reports Server (NTRS)

    Axelrad, Penina; MacDoran, Peter F.; Comp, Christopher J.

    1996-01-01

    This report describes a study performed by the Colorado Center for Astrodynamics Research (CCAR) on GPS measurement errors in the Codeless GPS Attitude Determination System (CGADS) due to noise and multipath interference. Preliminary simulation models fo the CGADS receiver and orbital multipath are described. The standard FFT algorithms for processing the codeless data is described and two alternative algorithms - an auto-regressive/least squares (AR-LS) method, and a combined adaptive notch filter/least squares (ANF-ALS) method, are also presented. Effects of system noise, quantization, baseband frequency selection, and Doppler rates on the accuracy of phase estimates with each of the processing methods are shown. Typical electrical phase errors for the AR-LS method are 0.2 degrees, compared to 0.3 and 0.5 degrees for the FFT and ANF-ALS algorithms, respectively. Doppler rate was found to have the largest effect on the performance.

  20. Field-Deployable Acoustic Digital Systems for Noise Measurement

    NASA Technical Reports Server (NTRS)

    Shams, Qamar A.; Wright, Kenneth D.; Lunsford, Charles B.; Smith, Charlie D.

    2000-01-01

    Langley Research Center (LaRC) has for years been a leader in field acoustic array measurement technique. Two field-deployable digital measurement systems have been developed to support acoustic research programs at LaRC. For several years, LaRC has used the Digital Acoustic Measurement System (DAMS) for measuring the acoustic noise levels from rotorcraft and tiltrotor aircraft. Recently, a second system called Remote Acquisition and Storage System (RASS) was developed and deployed for the first time in the field along with DAMS system for the Community Noise Flight Test using the NASA LaRC-757 aircraft during April, 2000. The test was performed at Airborne Airport in Wilmington, OH to validate predicted noise reduction benefits from alternative operational procedures. The test matrix was composed of various combinations of altitude, cutback power, and aircraft weight. The DAMS digitizes the acoustic inputs at the microphone site and can be located up to 2000 feet from the van which houses the acquisition, storage and analysis equipment. Digitized data from up to 10 microphones is recorded on a Jaz disk and is analyzed post-test by microcomputer system. The RASS digitizes and stores acoustic inputs at the microphone site that can be located up to three miles from the base station and can compose a 3 mile by 3 mile array of microphones. 16-bit digitized data from the microphones is stored on removable Jaz disk and is transferred through a high speed array to a very large high speed permanent storage device. Up to 30 microphones can be utilized in the array. System control and monitoring is accomplished via Radio Frequency (RF) link. This paper will present a detailed description of both systems, along with acoustic data analysis from both systems.

  1. GMTI Direction of Arrival Measurements from Multiple Phase Centers.

    SciTech Connect

    Doerry, Armin W.; Bickel, Douglas L.

    2015-03-01

    Ground Moving Target Indicator (GMTI) radar attempts to detect and locate targets with unknown motion. Very slow-moving targets are difficult to locate in the presence of surrounding clutter. This necessitates multiple antenna phase centers (or equivalent) to offer independent Direction of Arrival (DOA) measurements. DOA accuracy and precision generally remains dependent on target Signal-to-Noise Ratio (SNR), Clutter-toNoise Ratio (CNR), scene topography, interfering signals, and a number of antenna parameters. This is true even for adaptive techniques like Space-Time-AdaptiveProcessing (STAP) algorithms.

  2. Noise robustness of the incompatibility of quantum measurements

    NASA Astrophysics Data System (ADS)

    Heinosaari, Teiko; Kiukas, Jukka; Reitzner, Daniel

    2015-08-01

    The existence of incompatible measurements is a fundamental phenomenon having no explanation in classical physics. Intuitively, one considers given measurements to be incompatible within a framework of a physical theory, if their simultaneous implementation on a single physical device is prohibited by the theory itself. In the mathematical language of quantum theory, measurements are described by POVMs (positive operator valued measures), and given POVMs are by definition incompatible if they cannot be obtained via coarse-graining from a single common POVM; this notion generalizes noncommutativity of projective measurements. In quantum theory, incompatibility can be regarded as a resource necessary for manifesting phenomena such as Clauser-Horne-Shimony-Holt (CHSH) Bell inequality violations or Einstein-Podolsky-Rosen (EPR) steering which do not have classical explanation. We define operational ways of quantifying this resource via the amount of added classical noise needed to render the measurements compatible, i.e., useless as a resource. In analogy to entanglement measures, we generalize this idea by introducing the concept of incompatibility measure, which is monotone in local operations. In this paper, we restrict our consideration to binary measurements, which are already sufficient to explicitly demonstrate nontrivial features of the theory. In particular, we construct a family of incompatibility monotones operationally quantifying violations of certain scaled versions of the CHSH Bell inequality, prove that they can be computed via a semidefinite program, and show how the noise-based quantities arise as special cases. We also determine maximal violations of the new inequalities, demonstrating how Tsirelson's bound appears as a special case. The resource aspect is further motivated by simple quantum protocols where our incompatibility monotones appear as relevant figures of merit.

  3. Comparison between occupational noise measurement strategies: why is it important?

    PubMed

    Costa, Susana; Arezes, Pedro

    2012-01-01

    The international standard ISO 9612:2009, regarding the determination of occupational noise exposure through an engineering method, establishes a methodology for evaluating the exposure of workers to occupational noise, through the specification of three different strategies, namely: task-based measurement (TBM); job-based measurement (JBM) and; full day measurement (FDM). In this work, questions are raised, "resulting in a literature review regarding the need to test the functionality of the three strategies, through the systematic comparison between them and analysis of their application impact at several levels. There is a need to test the compare these three strategies, since there are no peer-review studies in this domain. In fact, there are still no studies that systematically do the comparison between them and analyze the impact of their application at various levels, such as the precision and accuracy of the results, the required equipment, time spent and, most important, the estimation of the uncertainty associated to the measurements. PMID:22317172

  4. An Overview of Recent Phased Array Measurements at NASA Glenn

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.

    2008-01-01

    A review of measurements made at the NASA Glenn Research Center using an OptiNAV Array 48 phased array system is provided. Data were acquired on a series of round convergent and convergent-divergent nozzles using the Small Hot Jet Acoustic Rig. Tests were conducted over a range of jet operating conditions, including subsonic and supersonic and cold and hot jets. Phased array measurements were also acquired on a Williams International FJ44 engine. These measurements show how the noise generated by the engine is split between the inlet-radiated and exhaust-radiated components. The data also show inlet noise being reflected off of the inflow control device used during the test.

  5. JT8D-100 turbofan engine, phase 1. [noise reduction

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The JT8D turbofan engine, widely used in short and medium range transport aircraft, contributes substantially to airport community noise. The jet noise is predominant in the JT8D engine and may be reduced in a modified engine, without loss of thrust, by increasing the airflow to reduce jet velocity. A configuration study evaluated the effects of fan airflow, fan pressure ratio, and bypass ratio on noise, thrust, and fuel comsumption. The cycle selected for the modified engine was based upon an increased diameter, single-stage fan and two additional core engine compressor stages, which replace the existing two-stage fan. Modifications were also made to the low pressure turbine to provide the increased torque required by the larger diameter fan. The resultant JT8D-100 engine models have the following characteristics at take-off thrust, compared to the current JT8D engine: Airflow and bypass ratio are increased, and fan pressure ratio and engine speed are reduced. The resultant engine is also longer, larger in diameter, and heavier than the JT8D base model, but these latter changes are compensated by the increased thrust and decreased fuel comsumption of the modified engine, thus providing the capability for maintaining the performance of the current JT8D-powered aircraft.

  6. Jet transport noise - A comparison of predicted and measured noise for ILS and two-segment approaches

    NASA Technical Reports Server (NTRS)

    White, K. C.; Bourquin, K. R.

    1974-01-01

    Centerline noise measured during standard ILS and two-segment approaches in DC-8-61 aircraft were compared with noise predicted for these procedures using an existing noise prediction technique. Measured data is considered to be in good agreement with predicted data. Ninety EPNdB sideline locations were calculated from flight data obtained during two-segment approaches and were compared with predicted 90 EPNdB contours that were computed using three different models for excess ground attenuation and a contour with no correction for ground attenuation. The contour not corrected for ground attenuation was in better agreement with the measured data.

  7. Noise performance of a feed-forward scheme for carrier-envelope phase stabilization

    NASA Astrophysics Data System (ADS)

    Koke, S.; Anderson, A.; Frei, H.; Assion, A.; Steinmeyer, G.

    2011-09-01

    The noise performance of a feed-forward scheme for carrier-envelope phase stabilization is discussed. This scheme uses an acousto-optic frequency shifter to directly correct for fluctuations of the carrier-envelope phase in a pulse train emitted by a mode-locked laser without manipulating the intracavity dispersion. Generation of zero-offset frequency combs is demonstrated. Furthermore, it is shown that pump laser noise has only a minor effect on the achievable performance. Limited only by the travel time of the acoustic wave in the shifter, pump laser noise can be corrected up to near-megahertz frequencies, which yields superior noise performance compared to traditional feedback operation. Residual phase jitters down to 45 mrad are experimentally verified.

  8. Temporal phase mask encrypted optical steganography carried by amplified spontaneous emission noise.

    PubMed

    Wu, Ben; Wang, Zhenxing; Shastri, Bhavin J; Chang, Matthew P; Frost, Nicholas A; Prucnal, Paul R

    2014-01-13

    A temporal phase mask encryption method is proposed and experimentally demonstrated to improve the security of the stealth channel in an optical steganography system. The stealth channel is protected in two levels. In the first level, the data is carried by amplified spontaneous emission (ASE) noise, which cannot be detected in either the time domain or spectral domain. In the second level, even if the eavesdropper suspects the existence of the stealth channel, each data bit is covered by a fast changing phase mask. The phase mask code is always combined with the wide band noise from ASE. Without knowing the right phase mask code to recover the stealth data, the eavesdropper can only receive the noise like signal with randomized phase. PMID:24515055

  9. Temporal phase mask encrypted optical steganography carried by amplified spontaneous emission noise.

    PubMed

    Wu, Ben; Wang, Zhenxing; Shastri, Bhavin J; Chang, Matthew P; Frost, Nicholas A; Prucnal, Paul R

    2014-01-13

    A temporal phase mask encryption method is proposed and experimentally demonstrated to improve the security of the stealth channel in an optical steganography system. The stealth channel is protected in two levels. In the first level, the data is carried by amplified spontaneous emission (ASE) noise, which cannot be detected in either the time domain or spectral domain. In the second level, even if the eavesdropper suspects the existence of the stealth channel, each data bit is covered by a fast changing phase mask. The phase mask code is always combined with the wide band noise from ASE. Without knowing the right phase mask code to recover the stealth data, the eavesdropper can only receive the noise like signal with randomized phase.

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

    SciTech Connect

    Yang Shiquan; Bao Xiaoyi

    2006-09-15

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

  11. Extended Kalman filtering for joint mitigation of phase and amplitude noise in coherent QAM systems.

    PubMed

    Pakala, Lalitha; Schmauss, Bernhard

    2016-03-21

    We numerically investigate our proposed carrier phase and amplitude noise estimation (CPANE) algorithm using extend Kalman filter (EKF) for joint mitigation of linear and non-linear phase noise as well as amplitude noise on 4, 16 and 64 polarization multiplexed (PM) quadrature amplitude modulation (QAM) 224 Gb/s systems. The results are compared to decision directed (DD) carrier phase estimation (CPE), DD phase locked loop (PLL) and universal CPE (U-CPE) algorithms. Besides eliminating the necessity of phase unwrapping function, EKF-CPANE shows improved performance for both back-to-back (BTB) and transmission scenarios compared to the aforementioned algorithms. We further propose a weighted innovation approach (WIA) of the EKF-CPANE which gives an improvement of 0.3 dB in the Q-factor, compared to the original algorithm. PMID:27136830

  12. Temporal averaging of phase measurements in the presence of spurious phase drift - Application to phase-stepped real-time holographic interferometry

    NASA Technical Reports Server (NTRS)

    Ovryn, B.; Haacke, E. M.

    1993-01-01

    A technique that compensates for low spatial frequency spurious phase changes during an interference experiment is developed; it permits temporal averaging of multiple-phase measurements, made before and after object displacement. The method is tested with phase-stepped real-time holographic interferometry applied to cantilever bending of a piezoelectric bimorph ceramic. Results indicate that temporal averaging of the corrected data significantly reduces the white noise in a phase measurement without incurring systematic errors or sacrificing spatial resolution. White noise is reduced from 3 deg to less than 1 deg using these methods.

  13. Extremely low-phase-noise SAW resonators and oscillators: design and performance.

    PubMed

    Montress, G K; Parker, T E; Loboda, M J; Greer, J A

    1988-01-01

    The authors describe prototype low-noise SAW (surface acoustic wave) resonator oscillators which have demonstrated state-of-the-art phase-noise performance not only at their fundamental operating frequencies in the 400- to 600-MHz range but also after 16x frequency multiplication to X-band as well. SAW resonator designs with overmoded cavities, very wide apertures, and dual apertures, as well as modified fabrication techniques, have been used to realize an overall reduction in an oscillator's phase-noise spectrum, i.e. white phiM, flicker FM, and random-walk FM. The S resonators can typically handle incident RF power in excess of +20 dBm, a key requirement to achieving an extremely low oscillator-phase-noise floor. A novel burn-in procedure at relatively high incident-RF-power levels (>27 dBm) was used to reduce both the flicker FM and random-walk FM phase-noise levels. Using these various techniques, a 5- to 15-dB improvement in the overall phase-noise spectrum for several prototype oscillators was demonstrated. PMID:18290201

  14. Phase noise in pulsed Doppler lidar and limitations on achievable single-shot velocity accuracy

    NASA Technical Reports Server (NTRS)

    Mcnicholl, P.; Alejandro, S.

    1992-01-01

    The smaller sampling volumes afforded by Doppler lidars compared to radars allows for spatial resolutions at and below some sheer and turbulence wind structure scale sizes. This has brought new emphasis on achieving the optimum product of wind velocity and range resolutions. Several recent studies have considered the effects of amplitude noise, reduction algorithms, and possible hardware related signal artifacts on obtainable velocity accuracy. We discuss here the limitation on this accuracy resulting from the incoherent nature and finite temporal extent of backscatter from aerosols. For a lidar return from a hard (or slab) target, the phase of the intermediate frequency (IF) signal is random and the total return energy fluctuates from shot to shot due to speckle; however, the offset from the transmitted frequency is determinable with an accuracy subject only to instrumental effects and the signal to noise ratio (SNR), the noise being determined by the LO power in the shot noise limited regime. This is not the case for a return from a media extending over a range on the order of or greater than the spatial extent of the transmitted pulse, such as from atmospheric aerosols. In this case, the phase of the IF signal will exhibit a temporal random walk like behavior. It will be uncorrelated over times greater than the pulse duration as the transmitted pulse samples non-overlapping volumes of scattering centers. Frequency analysis of the IF signal in a window similar to the transmitted pulse envelope will therefore show shot-to-shot frequency deviations on the order of the inverse pulse duration reflecting the random phase rate variations. Like speckle, these deviations arise from the incoherent nature of the scattering process and diminish if the IF signal is averaged over times greater than a single range resolution cell (here the pulse duration). Apart from limiting the high SNR performance of a Doppler lidar, this shot-to-shot variance in velocity estimates has a

  15. Challenges and Techniques in Measurements of Noise, Cryogenic Noise and Power in Millimeter-Wave and Submillimeter-Wave Amplifiers

    NASA Technical Reports Server (NTRS)

    Samoska, Lorene

    2014-01-01

    We will present the topic of noise measurements, including cryogenic noise measurements, of Monolithic Microwave Integrated Circuit (MMIC) and Sub-Millimeter-Wave Monolithic Microwave Integrated Circuit (S-MMIC) amplifiers, both on-wafer, and interfaced to waveguide modules via coupling probes. We will also present an overview of the state-of-the-art in waveguide probe techniques for packaging amplifier chips, and discuss methods to obtain the lowest loss packaging techniques available to date. Linearity in noise measurements will be discussed, and experimental methods for room temperature and cryogenic noise measurements will be presented. We will also present a discussion of power amplifier measurements for millimeter-wave and submillimeter-wave amplifiers, and the tools and hardware needed for this characterization.

  16. Impact of plasma noise on a direct thrust measurement system

    NASA Astrophysics Data System (ADS)

    Pottinger, S. J.; Lamprou, D.; Knoll, A. K.; Lappas, V. J.

    2012-03-01

    In order to evaluate the accuracy and sensitivity of a pendulum-type thrust measurement system, a linear variable differential transformer (LVDT) and a laser optical displacement sensor have been used simultaneously to determine the displacement resulting from an applied thrust. The LVDT sensor uses an analog interface, whereas the laser sensor uses a digital interface to communicate the displacement readings to the data acquisition equipment. The data collected by both sensors show good agreement for static mass calibrations and validation with a cold gas thruster. However, the data obtained using the LVDT deviate significantly from that of the laser sensor when operating two varieties of plasma thrusters: a radio frequency (RF) driven plasma thruster, and a DC powered plasma thruster. Results establish that even with appropriate shielding and signal filtering the LVDT sensor is subject to plasma noise and radio frequency interactions which result in anomalous thrust readings. Experimental data show that the thrust determined using the LVDT system in a direct current plasma environment and a RF discharge is approximately a factor of three higher than the thrust values obtained using a laser sensor system for the operating conditions investigated. These findings are of significance to the electric propulsion community as LVDT sensors are often utilized in thrust measurement systems and accurate thrust measurement and the reproducibility of thrust data is key to analyzing thruster performance. Methods are proposed to evaluate system susceptibility to plasma noise and an effective filtering scheme presented for DC discharges.

  17. Stability and Phase Noise Tests of Two Cryo-Cooled Sapphire Oscillators

    NASA Technical Reports Server (NTRS)

    Dick, G. John; Wang, Rabi T.

    1998-01-01

    A cryocooled Compensated Sapphire Oscillator (CSO), developed for the Cassini Ka-band Radio Science experiment, and operating in the 8K - 10K temperature range was previously demonstrated to show ultra-high stability of sigma(sub y) = 2.5 x 10 (exp -15) for measuring times 200 seconds less than or equal to tau less than or equal to 600 seconds using a hydrogen maser as reference. We present here test results for a second unit which allows CSO short-term stability and phase noise to be measured for the first time. Also included are design details of a new RF receiver and an intercomparison with the first CSO unit. Cryogenic oscillators operating below about 10K offer the highest possible short term stability of any frequency sources. However, their use has so far been restricted to research environments due to the limited operating periods associated with liquid helium consumption. The cryocooled CSO is being built in support of the Cassini Ka-band Radio Science experiment and is designed to operate continuously for periods of a year or more. Performance targets are a stability of 3-4 x 10 (exp -15) (1 second less than or equal to tau less than or equal to 100 seconds) and phase noise of -73dB/Hz @ 1Hz measured at 34 GHz. Installation in 5 stations of NASA's deep space network (DSN) is planned in the years 2000 - 2002. In the previous tests, actual stability of the CSO for measuring times tau less than or equal to 200 seconds could not be directly measured, being masked by short-term fluctuations of the H-maser reference. Excellent short-term performance, however, could be inferred by the success of an application of the CSO as local oscillator (L.O.) to the JPL LITS passive atomic standard, where medium-term stability showed no degradation due to L.O. instabilities at a level of (sigma)y = 3 x 10 (exp -14)/square root of tau. A second CSO has now been constructed, and all cryogenic aspects have been verified, including a resonator turn-over temperature of 7.907 K

  18. Bandwidth of non-contact vital sign detection with a noise suppression phase locked loop

    NASA Astrophysics Data System (ADS)

    Xia, Zongyang; Zhang, Ying

    2016-04-01

    In a dual-carrier vital sign detection system, we have designed a noise suppression scheme that uses phase locked loop (PLL) to automatically suppress the noise induced by range correlation and transmission paths. The system uses two microwave carriers at 5.6 and 5.68 GHz generated by two phase locked signal generators to extract the noise and vital sign respectively. The feedback microwave signals are mixed with local 5.68-GHz signal to transfer to the vial sign signal and low frequency intermediate frequency (IF) signal. When the IF signal corresponding to 5.68 GHz microwave signal is locked to a highly stable low noise reference, the noises of IF signal and vital sign signal are suppressed as their corresponding microwave signals are highly correlated. In this system, the noise suppression performance is related to the bandwidth of the PLL, which needs to be carefully designed. Through the theoretical analysis, initial bandwidth is chosen to be 200 Hz. Then the charge pump current is changed to adjust the bandwidth and the corresponding noise suppression performance is evaluated using experiments. The results show the system with a charge pump current 0.625 mA, which corresponds to about 50 Hz bandwidth, exhibits a better noise performance. In addition, at different bandwidth, the vital sign detection system is compared with a design scheme with unlocked PLL and demonstrates superior performance at all bandwidths.

  19. New technique for the direct measurement of core noise from aircraft engines. [YF 102 turbofan engine

    NASA Technical Reports Server (NTRS)

    Krejsa, E. A.

    1981-01-01

    The core noise levels from gas turbine aircraft engines were measured using a technique which requires that fluctuating pressures be measured in the far field and at two locations within the engine core. The cross spectra of these measurements are used to determine the levels of the far-field noise that propagated from the engine vore. The technique makes it possible to measure core noise levels even when other noise sources dominate. The technique was applied to signals measured from an Avco Lycoming YF102 turbofan engine. Core noise levels as a function of frequency and radiation angle were measured and are presented over a range of power settings.

  20. JOHNSON NOISE THERMOMETRY FOR DRIFT-FREE MEASUREMENTS

    SciTech Connect

    Britton Jr, Charles L; Ezell, N Dianne Bull; Roberts, Michael; Holcomb, David Eugene; Wood, Richard Thomas

    2014-01-01

    In order for Johnson Noise Thermometry (JNT) to be beneficial to SMR designers, it must offer advantages beyond the current state-of-the-art technology. Comparisons to traditional RTDs and thermocouples will involve life-cycle costs, installation footprint, reliability, and accuracy. With JNT, there is additional equipment beyond what is required for the traditional RTD measurement. Therefore, the JNT-RTD system will involve additional complexity and this additional complexity must be justified. Operators will want to know that the measurement is reliable and trustworthy. It is also important that the sensor involve little, if any, additional ongoing maintenance work and that it has a low probability of causing any malfunction of the primary measurement channel. If these features can be successfully demonstrated, the JNT-RTD system could potentially save money and increase plant reliability.

  1. Low phase noise oscillator using two parallel connected amplifiers

    NASA Technical Reports Server (NTRS)

    Kleinberg, Leonard L.

    1987-01-01

    A high frequency oscillator is provided by connecting two amplifier circuits in parallel where each amplifier circuit provides the other amplifier circuit with the conditions necessary for oscillation. The inherent noise present in both amplifier circuits causes the quiescent current, and in turn, the generated frequency, to change. The changes in quiescent current cause the transconductance and the load impedance of each amplifier circuit to vary, and this in turn results in opposing changes in the input susceptance of each amplifier circuit. Because the changes in input susceptance oppose each other, the changes in quiescent current also oppose each other. The net result is that frequency stability is enhanced.

  2. Reduction of phase-induced intensity noise in a fiber-based coherent Doppler lidar using polarization control.

    PubMed

    Rodrigo, Peter John; Pedersen, Christian

    2010-03-01

    Optimization of signal-to-noise ratio is an important aspect in the design of optical heterodyne detection systems such as a coherent Doppler lidar (CDL). In a CDL, optimal performance is achieved when the noise in the detector signal is dominated by local oscillator shot-noise. Most modern CDL systems are built using rugged and cost-efficient fiber optic components. Unfortunately, leakage signals such as residual reflections inherent within fiber components (e.g. circulator) can introduce phase-induced intensity noise (PIIN) to the Doppler spectrum in a CDL. Such excess noise may be a few orders of magnitude above the shot-noise level within the relevant CDL frequency bandwidth--corrupting the measurement of typically weak backscattered signals. In this study, observation of PIIN in a fiber-based CDL with a master-oscillator power-amplifier tapered semiconductor laser source is reported. Furthermore, we experimentally demonstrate what we believe is a newly proposed method using a simple polarization scheme to reduce PIIN by more than an order of magnitude.

  3. Reduction of phase-induced intensity noise in a fiber-based coherent Doppler lidar using polarization control.

    PubMed

    Rodrigo, Peter John; Pedersen, Christian

    2010-03-01

    Optimization of signal-to-noise ratio is an important aspect in the design of optical heterodyne detection systems such as a coherent Doppler lidar (CDL). In a CDL, optimal performance is achieved when the noise in the detector signal is dominated by local oscillator shot-noise. Most modern CDL systems are built using rugged and cost-efficient fiber optic components. Unfortunately, leakage signals such as residual reflections inherent within fiber components (e.g. circulator) can introduce phase-induced intensity noise (PIIN) to the Doppler spectrum in a CDL. Such excess noise may be a few orders of magnitude above the shot-noise level within the relevant CDL frequency bandwidth--corrupting the measurement of typically weak backscattered signals. In this study, observation of PIIN in a fiber-based CDL with a master-oscillator power-amplifier tapered semiconductor laser source is reported. Furthermore, we experimentally demonstrate what we believe is a newly proposed method using a simple polarization scheme to reduce PIIN by more than an order of magnitude. PMID:20389545

  4. Mechanical monolithic sensor for low frequency seismic noise measurement

    NASA Astrophysics Data System (ADS)

    Acernese, Fausto; De Rosa, Rosario; Giordano, Gerardo; Romano, Rocco; Barone, Fabrizio

    2007-10-01

    This paper describes a mechanical monolithic sensor for geophysical applications developed at the University of Salerno. The instrument is basically a monolithic tunable folded pendulum, shaped with precision machining and electric-discharge-machining, that can be used both as seismometer and, in a force-feedback configuration, as accelerometer. The monolithic mechanical design and the introduction of laser interferometric techniques for the readout implementation make it a very compact instrument, very sensitive in the low-frequency seismic noise band, with a very good immunity to environmental noises. Many changes have been produced since last version (2006), mainly aimed to the improvement of the mechanics and of the optical readout of the instrument. In fact, we have developed and tested a prototype with elliptical hinges and mechanical tuning of the resonance frequency together with a new laser optical lever and laser interferometer readout system. The theoretical sensitivity curve for both laser optical lever and laser interferometric readouts, calculated on the basis of suitable theoretical models, shows a very good agreement with the experimental measurements. Very interesting scientific result is that the measured natural resonance frequency of the instrument is ~ 70mHz with a Q ~ 140 in air without thermal stabilization, demonstrating the feasibility of a monolithic FP sensor with a natural resonance frequency of the order of 5 mHz with a more refined mechanical tuning.

  5. Mechanical monolithic horizontal sensor for low frequency seismic noise measurement

    NASA Astrophysics Data System (ADS)

    Acernese, Fausto; Giordano, Gerardo; Romano, Rocco; De Rosa, Rosario; Barone, Fabrizio

    2008-07-01

    This paper describes a mechanical monolithic horizontal sensor for geophysical applications developed at the University of Salerno. The instrument is basically a monolithic tunable folded pendulum, shaped with precision machining and electric discharge machining, that can be used both as seismometer and, in a force-feedback configuration, as accelerometer. The monolithic mechanical design and the introduction of laser interferometric techniques for the readout implementation makes it a very compact instrument, very sensitive in the low frequency seismic noise band, with a very good immunity to environmental noises. Many changes have been produced since last version (2007), mainly aimed to the improvement of the mechanics and of the optical readout of the instrument. In fact, we have developed and tested a prototype with elliptical hinges and mechanical tuning of the resonance frequency together with a laser optical lever and a new laser interferometer readout system. The theoretical sensitivity curve for both laser optical lever and laser interferometric readouts, evaluated on the basis of suitable theoretical models, shows a very good agreement with the experimental measurements. Very interesting scientific result is the measured natural resonance frequency of the instrument of 70mHz with a Q =140 in air without thermal stabilization. This result demonstrates the feasibility of a monolithic folded pendulum sensor with a natural resonance frequency of the order of millihertz with a more refined mechanical tuning.

  6. Laboratory studies of scales for measuring helicopter noise

    NASA Technical Reports Server (NTRS)

    Ollerhead, J. B.

    1982-01-01

    The adequacy of the effective perceived noise level (EPNL) procedure for rating helicopter noise annoyance was investigated. Recordings of 89 helicopters and 30 fixed wing aircraft (CTOL) flyover sounds were rated with respect to annoyance by groups of approximately 40 subjects. The average annoyance scores were transformed to annoyance levels defined as the equally annoying sound levels of a fixed reference sound. The sound levels of the test sounds were measured on various scales, with and without corrections for duration, tones, and impulsiveness. On average, the helicopter sounds were judged equally annoying to CTOL sounds when their duration corrected levels are approximately 2 dB higher. Multiple regression analysis indicated that, provided the helicopter/CTOL difference of about 2 dB is taken into account, the particular linear combination of level, duration, and tone corrections inherent in EPNL is close to optimum. The results reveal no general requirement for special EPNL correction terms to penalize helicopter sounds which are particularly impulsive; impulsiveness causes spectral and temporal changes which themselves adequately amplify conventionally measured sound levels.

  7. Numerical Verification of an Analytical Model for Phase Noise in MEMS Oscillators.

    PubMed

    Agrawal, D K; Bizzarri, F; Brambilla, A; Seshia, A A

    2016-08-01

    A new analytical formulation for phase noise in MEMS oscillators was recently presented encompassing the role of essential nonlinearities in the electrical and mechanical domains. In this paper, we validate the effectiveness of the proposed analytical formulation with respect to the unified theory developed by Demir et al. describing phase noise in oscillators. In particular, it is shown that, over a range of the second-order mechanical nonlinear stiffness of the MEMS resonator, both models exhibit an excellent match in the phase diffusion coefficient calculation for a square-wave MEMS oscillator. PMID:27295660

  8. Numerical Verification of an Analytical Model for Phase Noise in MEMS Oscillators.

    PubMed

    Agrawal, D K; Bizzarri, F; Brambilla, A; Seshia, A A

    2016-08-01

    A new analytical formulation for phase noise in MEMS oscillators was recently presented encompassing the role of essential nonlinearities in the electrical and mechanical domains. In this paper, we validate the effectiveness of the proposed analytical formulation with respect to the unified theory developed by Demir et al. describing phase noise in oscillators. In particular, it is shown that, over a range of the second-order mechanical nonlinear stiffness of the MEMS resonator, both models exhibit an excellent match in the phase diffusion coefficient calculation for a square-wave MEMS oscillator.

  9. On estimating the phase of periodic waveform in additive Gaussian noise, part 2

    NASA Astrophysics Data System (ADS)

    Rauch, L. L.

    1984-11-01

    Motivated by advances in signal processing technology that support more complex algorithms, a new look is taken at the problem of estimating the phase and other parameters of a periodic waveform in additive Gaussian noise. The general problem was introduced and the maximum a posteriori probability criterion with signal space interpretation was used to obtain the structures of optimum and some suboptimum phase estimators for known constant frequency and unknown constant phase with an a priori distribution. Optimal algorithms are obtained for some cases where the frequency is a parameterized function of time with the unknown parameters and phase having a joint a priori distribution. In the last section, the intrinsic and extrinsic geometry of hypersurfaces is introduced to provide insight to the estimation problem for the small noise and large noise cases.

  10. Effect of Directional Array Size on the Measurement of Airframe Noise Components

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    A study was conducted to examine the effects of overall size of directional (or phased) arrays on the measurement of aeroacoustic components. An airframe model was mounted in the potential core of an open-jet windtunnel, with the directional arrays located outside the flow in an anechoic environment. Two array systems were used; one with a solid measurement angle that encompasses 31.6 deg.of source directivity and a smaller one that encompasses 7.2 deg. The arrays, and sub-arrays of various sizes, measured noise from a calibrator source and flap edge model setups. In these cases, noise was emitted from relatively small, but finite size source regions, with intense levels compared to other sources. Although the larger arrays revealed much more source region detail, the measured source levels were substantially reduced due to finer resolution compared to that of the smaller arrays. To better understand the measurements quantitatively, an analytical model was used to define the basic relationships between array to source region sizes and measured output level. Also, the effect of noise scattering by shear layer turbulence was examined using the present data and those of previous studies. Taken together, the two effects were sufficient to explain spectral level differences between arrays of different sizes. An important result of this study is that total (integrated) noise source levels are retrievable and the levels are independent of the array size as long as certain experimental and processing criteria are met. The criteria for both open and closed tunnels are discussed. The success of special purpose diagonal-removal processing in obtaining integrated results is apparently dependent in part on source distribution. Also discussed is the fact that extended sources are subject to substantial measurement error, especially for large arrays.

  11. Current noise measurements of surface defect states in amorphous silicon

    SciTech Connect

    West, P.W.; Kakalios, J.

    1999-07-01

    Measurements of conductance fluctuations in coplanar hydrogenated amorphous silicon (a-Si:H) are reported as a function of surface etching treatments. The noise power spectrum displays a broadened Lorentzian peak, associated with surface damage by CF{sub 4} reactive ion etching (RIE), whereas surface etches using ion milling or wet chemicals remove the Lorentzian spectral feature and only a 1/f spectral form for frequency f is observed. The Lorentzian spectral feature can be explained by trapping-detrapping from surface states induced by the RIE etch, which cause fluctuations in the depletion width of the space charge region near the film surface. The thermally activated Lorentzian corner frequency is a measure of the degree of band bending and the Fermi energy at the thin film surface.

  12. High Resolution Viscosity Measurement by Thermal Noise Detection

    PubMed Central

    Aguilar Sandoval, Felipe; Sepúlveda, Manuel; Bellon, Ludovic; Melo, Francisco

    2015-01-01

    An interferometric method is implemented in order to accurately assess the thermal fluctuations of a micro-cantilever sensor in liquid environments. The power spectrum density (PSD) of thermal fluctuations together with Sader’s model of the cantilever allow for the indirect measurement of the liquid viscosity with good accuracy. The good quality of the deflection signal and the characteristic low noise of the instrument allow for the detection and corrections of drawbacks due to both the cantilever shape irregularities and the uncertainties on the position of the laser spot at the fluctuating end of the cantilever. Variation of viscosity below 0.03 mPa·s was detected with the alternative to achieve measurements with a volume as low as 50 μL. PMID:26540061

  13. High Resolution Viscosity Measurement by Thermal Noise Detection.

    PubMed

    Sandoval, Felipe Aguilar; Sepúlveda, Manuel; Bellon, Ludovic; Melo, Francisco

    2015-01-01

    An interferometric method is implemented in order to accurately assess the thermal fluctuations of a micro-cantilever sensor in liquid environments. The power spectrum density (PSD) of thermal fluctuations together with Sader's model of the cantilever allow for the indirect measurement of the liquid viscosity with good accuracy. The good quality of the deflection signal and the characteristic low noise of the instrument allow for the detection and corrections of drawbacks due to both the cantilever shape irregularities and the uncertainties on the position of the laser spot at the fluctuating end of the cantilever. Variation of viscosity below 0:03mPa·s was detected with the alternative to achieve measurements with a volume as low as 50 µL. PMID:26540061

  14. Noise-and delay-induced phase transitions of the dimer-monomer surface reaction model

    NASA Astrophysics Data System (ADS)

    Zeng, Chunhua; Wang, Hua

    2012-06-01

    The effects of noise and time-delayed feedback in the dimer-monomer (DM) surface reaction model are investigated. Applying small delay approximation, we construct a stochastic delayed differential equation and its Fokker-Planck equation to describe the state evolution of the DM reaction model. We show that the noise can only induce first-order irreversible phase transition (IPT) characteristic of the DM model, however the combination of the noise and time-delayed feedback can simultaneously induce first- and second-order IPT characteristics of the DM model. Therefore, it is shown that the well-known first- and second-order IPT characteristics of the DM model may be viewed as noise-and delay-induced phase transitions.

  15. Measurement of thermal noise in multilayer coatings with optimized layer thickness

    SciTech Connect

    Villar, Akira E.; Black, Eric D.; DeSalvo, Riccardo; Libbrecht, Kenneth G.; Michel, Christophe; Morgado, Nazario; Pinard, Laurent; Pinto, Innocenzo M.; Pierro, Vincenzo; Galdi, Vincenzo; Principe, Maria; Taurasi, Ilaria

    2010-06-15

    A standard quarter-wavelength multilayer optical coating will produce the highest reflectivity for a given number of coating layers, but in general it will not yield the lowest thermal noise for a prescribed reflectivity. Coatings with the layer thicknesses optimized to minimize thermal noise could be useful in future generation interferometric gravitational wave detectors where coating thermal noise is expected to limit the sensitivity of the instrument. We present the results of direct measurements of the thermal noise of a standard quarter-wavelength coating and a low noise optimized coating. The measurements indicate a reduction in thermal noise in line with modeling predictions.

  16. Unscented Kalman filters for polarization state tracking and phase noise mitigation.

    PubMed

    Jignesh, Jokhakar; Corcoran, Bill; Zhu, Chen; Lowery, Arthur

    2016-09-19

    Simultaneous polarization and phase noise tracking and compensation is proposed based on an unscented Kalman filter (UKF). We experimentally demonstrate the tracking under noise-loading and after 800-km single-mode fiber transmission with 20-Gbaud QPSK and 16-QAM signals. These experiments show that the proposed UKF outperforms both conventional blind tracing algorithms and a previously proposed extended Kalman filter, at the cost of higher complexity. Additionally, we propose and test modified Kalman filter algorithms to reduce computational complexity.

  17. Measuring and interpreting the mechanical thermal noise spectrum in a MEMS

    NASA Astrophysics Data System (ADS)

    Rocha, L. A.; Cretu, E.; Wolffenbuttel, R. F.

    2005-07-01

    The meta-stability of the pull-in displacement of an electrostatically operated parallel plate micromechanical structure is used for the capacitive measurement of the mechanical-thermal noise spectrum in a MEMS. Pull-in time depends on force and is not affected by the input-referred noise of the readout circuit. Repeatedly bringing the microstructure to pull-in while measuring the pull-in time followed by FFT enables the measurement of the mechanical noise spectrum with a non-mechanical noise level set primarily by the resolution of the time measurement. The white noise level is found to be in agreement with the theory on damping. The 1/f noise spectrum is found to be independent of ambient gas pressure with a 1/f noise-white noise cross-over frequency at 0.007 Hz for a 1 bar gas pressure and is reproducible for devices fabricated in the same process and the same run.

  18. Noise and measurement errors in a practical two-state quantum bit commitment protocol

    NASA Astrophysics Data System (ADS)

    Loura, Ricardo; Almeida, Álvaro J.; André, Paulo S.; Pinto, Armando N.; Mateus, Paulo; Paunković, Nikola

    2014-05-01

    We present a two-state practical quantum bit commitment protocol, the security of which is based on the current technological limitations, namely the nonexistence of either stable long-term quantum memories or nondemolition measurements. For an optical realization of the protocol, we model the errors, which occur due to the noise and equipment (source, fibers, and detectors) imperfections, accumulated during emission, transmission, and measurement of photons. The optical part is modeled as a combination of a depolarizing channel (white noise), unitary evolution (e.g., systematic rotation of the polarization axis of photons), and two other basis-dependent channels, namely the phase- and bit-flip channels. We analyze quantitatively the effects of noise using two common information-theoretic measures of probability distribution distinguishability: the fidelity and the relative entropy. In particular, we discuss the optimal cheating strategy and show that it is always advantageous for a cheating agent to add some amount of white noise—the particular effect not being present in standard quantum security protocols. We also analyze the protocol's security when the use of (im)perfect nondemolition measurements and noisy or bounded quantum memories is allowed. Finally, we discuss errors occurring due to a finite detector efficiency, dark counts, and imperfect single-photon sources, and we show that the effects are the same as those of standard quantum cryptography.

  19. Note: Precise phase and frequency comparator based on direct phase-time measurements

    NASA Astrophysics Data System (ADS)

    Prochazka, Ivan; Panek, Petr; Kodet, Jan

    2014-12-01

    We are reporting on the design, performance, and application results of a phase and frequency comparator based on the direct phase-time measurement using a high performance event timer. The advantages of this approach are the simple implementation, a broad frequency range, and the clear interpretation of the measured results. Primarily we analyzed the background instability of the instrument in a common-clock test when a 200 MHz clock signal was connected to both inputs and the noise bandwidth was kept at 5 Hz by a preprocessing of the measured data. The results show that the Allan deviation of the background instability follows 4 × 10-14/τ for a wide range of averaging intervals from 0.1 s up to 104 s. These results are better than background instability of commercially available state-of-the-art instruments based on the phase difference multiplication. Finally the instrument was used for comparison of two H-masers. This experiment proofed that one of possible applications is a comparison of low-noise highly stable frequency sources and measurement of their frequency stability in the time-domain. The noise background of the instrument was negligible for averaging intervals longer than 100 ms.

  20. Relative phase noise induced impairment in M-ary phase-shift-keying coherent optical communication system using distributed fiber Raman amplifier.

    PubMed

    Cheng, Jingchi; Tang, Ming; Fu, Songnian; Shum, Perry Ping; Liu, Deming

    2013-04-01

    We show for the first time, to the best of our knowledge, that, in a coherent communication system that employs a phase-shift-keying signal and Raman amplification, besides the pump relative intensity noise (RIN) transfer to the amplitude, the signal's phase will also be affected by pump RIN through the pump-signal cross-phase modulation. Although the average pump power induced linear phase change can be compensated for by the phase-correction algorithm, a relative phase noise (RPN) parameter has been found to characterize pump RIN induced stochastic phase noise. This extra phase noise brings non-negligible system impairments in terms of the Q-factor penalty. The calculation shows that copumping leads to much more stringent requirements to pump RIN, and relatively larger fiber dispersion helps to suppress the RPN induced impairment. A higher-order phase-shift keying (PSK) signal is less tolerant to noise than a lower-order PSK. PMID:23546241

  1. Adaptive multidirectional frequency domain filter for noise removal in wrapped phase patterns.

    PubMed

    Liu, Guixiong; Chen, Dongxue; Peng, Yanhua; Zeng, Qilin

    2016-08-01

    In order to avoid the detrimental effects of excessive noise in the phase fringe patterns of a laser digital interferometer over the accuracy of phase unwrapping and the successful detection of mechanical fatigue defects, an effective method of adaptive multidirectional frequency domain filtering is introduced based on the characteristics of the energy spectrum of localized wrapped phase patterns. Not only can this method automatically set the cutoff frequency, but it can also effectively filter out noise while preserving the image edge information. Compared with the sine and cosine transform filtering and the multidirectional frequency domain filtering, the experimental results demonstrate that the image filtered by our method has the fewest number of residues and is the closest to the noise-free image, compared to the two aforementioned methods, demonstrating the effectiveness of this adaptive multidirectional frequency domain filter. PMID:27505376

  2. Microwave photonic link with improved phase noise using a balanced detection scheme

    NASA Astrophysics Data System (ADS)

    Hu, Jingjing; Gu, Yiying; Tan, Wengang; Zhu, Wenwu; Wang, Linghua; Zhao, Mingshan

    2016-07-01

    A microwave photonic link (MPL) with improved phase noise performance using a dual output Mach-Zehnder modulator (DP-MZM) and balanced detection is proposed and experimentally demonstrated. The fundamental concept of the approach is based on the two complementary outputs of DP-MZM and the destructive combination of the photocurrent in balanced photodetector (BPD). Theoretical analysis is performed to numerical evaluate the additive phase noise performance and shows a good agreement with the experiment. Experimental results are presented for 4 GHz, 8 GHz and 12 GHz transmission link and an 11 dB improvement of phase noise performance at 10 MHz offset is achieved compared to the conventional intensity-modulation and direct-detection (IMDD) MPL.

  3. Real-time full bandwidth measurement of spectral noise in supercontinuum generation

    PubMed Central

    Wetzel, B.; Stefani, A.; Larger, L.; Lacourt, P. A.; Merolla, J. M.; Sylvestre, T.; Kudlinski, A.; Mussot, A.; Genty, G.; Dias, F.; Dudley, J. M.

    2012-01-01

    The ability to measure real-time fluctuations of ultrashort pulses propagating in optical fiber has provided significant insights into fundamental dynamical effects such as modulation instability and the formation of frequency-shifting rogue wave solitons. We report here a detailed study of real-time fluctuations across the full bandwidth of a fiber supercontinuum which directly reveals the significant variation in measured noise statistics across the spectrum, and which allows us to study correlations between widely separated spectral components. For two different propagation distances corresponding to the onset phase of spectral broadening and the fully-developed supercontinuum, we measure real time noise across the supercontinuum bandwidth, and we quantify the supercontinuum noise using statistical higher-order moments and a frequency-dependent intensity correlation map. We identify correlated spectral regions within the supercontinuum associated with simultaneous sideband generation, as well as signatures of pump depletion and soliton-like pump dynamics. Experimental results are in excellent agreement with simulations. PMID:23193436

  4. Phase noise and squeezing spectra of the output field of an optical cavity containing an interacting Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Dalafi, A.; Naderi, M. H.

    2016-07-01

    We present a theoretical study of the phase noise, intensity and quadrature squeezing power spectra of the transmitted field of a driven optical cavity containing an interacting one-dimensional Bose-Einstein condensate. We show how the pattern of the output power spectrum of the cavity changes due to the nonlinear effect of atomic collisions. Furthermore, it is shown that due to a one-to-one correspondence between the splitting of the peaks in the phase noise power spectrum of the cavity output field and the s-wave scattering frequency of the atom-atom interaction, one can measure the strength of interatomic interaction. In addition, we show how the atomic collisions affect the squeezing behavior of the output field.

  5. Phase noise and squeezing spectra of the output field of an optical cavity containing an interacting Bose–Einstein condensate

    NASA Astrophysics Data System (ADS)

    Dalafi, A.; Naderi, M. H.

    2016-07-01

    We present a theoretical study of the phase noise, intensity and quadrature squeezing power spectra of the transmitted field of a driven optical cavity containing an interacting one-dimensional Bose–Einstein condensate. We show how the pattern of the output power spectrum of the cavity changes due to the nonlinear effect of atomic collisions. Furthermore, it is shown that due to a one-to-one correspondence between the splitting of the peaks in the phase noise power spectrum of the cavity output field and the s-wave scattering frequency of the atom–atom interaction, one can measure the strength of interatomic interaction. In addition, we show how the atomic collisions affect the squeezing behavior of the output field.

  6. Improving Phase Measurement Procedures for Pump-Probe Experiments

    SciTech Connect

    Perkins, Cara P.; /Merrimack Coll. /SLAC

    2011-06-22

    Pump-probe experiments use a visible laser to excite an atom or molecule, while an X-ray pulse measures its shape. The phases and pulse times of each beam are used to calculate the object's positing at a given time - a moving picture of the chemical reaction. Currently, the fastest X-ray pulses can travel a time-length of five femtoseconds. However, present-day phase measurements can only be done as quickly as 50 femtoseconds. The purpose of this research is to explore ways in which phase-timing measurements can be improved. Three experiments are undergone to find the key factors in phase-timing. Different frequency mixers, the radio frequency (RF) components used for phase measurement, are tested for the highest sensitivity. These same mixers are then tested using two different power splitters for the lowest noise-to-sensitivity ratio. Lastly, the temperature dependency of phase is explored by testing each component at a range of temperatures to see how the phase is affected. This research demonstrated that certain mixers were more sensitive than others; on average, one mixer performed the best with a sensitivity of 0.0230 V/ps. The results also showed that same mixer combined with one splitter gave the best noise-to-sensitivity ratio overall with an average of 6.95E-04 fs/{radical}(Hz). All the components tested exhibited a temperature-dependent phase change (ranging from 1.69 to 81.6 fs/{sup o}C); the same mixer that performed at the highest sensitivity with the least noise had a significantly greater phase change than the other two. In conclusion, the experiments showed that a temperature-controlled environment is most appropriate for phase measurement. They also demonstrated that mixers are not significantly noisy and that certain types of mixers may perform better than others, which could be accounted for in their construction. The results of this research encourage further investigation into the study of different mixers and other RF components used in pump

  7. Measurement of mode-locked laser timing jitter by use of phase-encoded optical sampling.

    PubMed

    Juodawlkis, P W; Twichell, J C; Wasserman, J L; Betts, G E; Williamson, R C

    2001-03-01

    The phase-noise characteristics of a harmonically mode-locked fiber laser are investigated with a new measurement technique called phase-encoded optical sampling. A polarization-maintaining ring laser is mode locked by use of the short-pulse electrical output of a resonant-tunneling diode oscillator, enabling it to produce 30-ps pulses at a 208-MHz repetition rate. The interferometric phase-encoded sampling technique provides 60-dB suppression of amplitude-jitter noise and allows supermode phase noise to be observed and quantified. The white-noise pulse-to-pulse timing jitter and the rms supermode timing jitter of the laser are measured to be less than 50 and 70 fs, respectively. PMID:18040304

  8. 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.

  9. Dual apodization with cross-correlation in the presence of phase aberration and noise.

    PubMed

    Yen, Jesse T; Seo, Chi Hyung

    2008-01-01

    We have recently presented a new method to suppress side lobes and clutter in ultrasound imaging called dual apodization with cross-correlation or DAX. This method uses two apodization functions in receive mode which yield point spread functions with very similar main lobes but different side lobes and clutter. These similarities and differences are quantified by using normalized cross-correlation of the radio frequency (RF) data in the axial direction. These cross-correlation coefficients serve as a pixel-by-pixel weighting or filter to pass main lobe dominated signals and suppress clutter dominated signals. In this paper, we evaluate the robustness of DAX in the presence of phase aberration and noise. Aberrating layers of pig skin, fat, and muscle were used experimentally to mimic different level of aberrators. Experimental results are also presented using DAX in the presence of noise. With system signal-to-noise ratio (SNR) of at least 15 dB, we have a contrast-to-noise ratio (CNR) improvement of over 100 % compared to standard beamforming. This work shows that DAX is able to reliably improve contrast-to-noise ratio in the presence of phase aberration and noise. PMID:19163137

  10. Dual apodization with cross-correlation in the presence of phase aberration and noise.

    PubMed

    Yen, Jesse T; Seo, Chi Hyung

    2008-01-01

    We have recently presented a new method to suppress side lobes and clutter in ultrasound imaging called dual apodization with cross-correlation or DAX. This method uses two apodization functions in receive mode which yield point spread functions with very similar main lobes but different side lobes and clutter. These similarities and differences are quantified by using normalized cross-correlation of the radio frequency (RF) data in the axial direction. These cross-correlation coefficients serve as a pixel-by-pixel weighting or filter to pass main lobe dominated signals and suppress clutter dominated signals. In this paper, we evaluate the robustness of DAX in the presence of phase aberration and noise. Aberrating layers of pig skin, fat, and muscle were used experimentally to mimic different level of aberrators. Experimental results are also presented using DAX in the presence of noise. With system signal-to-noise ratio (SNR) of at least 15 dB, we have a contrast-to-noise ratio (CNR) improvement of over 100 % compared to standard beamforming. This work shows that DAX is able to reliably improve contrast-to-noise ratio in the presence of phase aberration and noise. PMID:19163221

  11. Comparative analysis of noise tolerance of quasi-coherent phase shift keying signal demodulators

    NASA Astrophysics Data System (ADS)

    Martirosov, V. Y.; Belousov, N. N.

    1985-01-01

    The noise tolerance of quasi-coherent PSK signal demodulators employing phase-locked loops to filter the reference oscillation is analyzed comparatively for the Siforof scheme, the Costas scheme, the reversible Karshin demodulator, the remodulator-comparator scheme and the adaptive demodulator scheme. The phase of reference oscillation in these quasi-coherent demodulators represents a random process, so that the phase error between the received and references signals is also random. It is found that increasing the initial frequency detuning reduces the noise tolerance of quasi-coherent PSK reception. The reversible and remodulation-comparator schemes have the poorest noise tolerance because of their steady-state phase error, which is twice that of the other schemes. When the frequency instability and amplitude of the received signal are high, it is best to use the adaptive demodulated structure. The formulas derived can be used to select the structure for a quasi-coherent PSK signal demodulator according to the required systemwide indicators of the digital transmission system, and to assess its noise tolerance during the design phase.

  12. Measurement of instrument noise spectra at frequencies below 1 hertz

    NASA Technical Reports Server (NTRS)

    Snare, R. C.; Mcpherron, R. L.

    1973-01-01

    The use of peak-to-peak values in describing output noise of a magnetometer or low frequency amplifier is of questionable value for certain applications. A more precise statement of instrument noise is made with a plot of the noise power spectral density vs frequency. The spectral density plot provides a rich source of information which can be used in the selection and testing of such instrumentation.

  13. Measurement, analysis, and prediction of aircraft interior noise

    NASA Technical Reports Server (NTRS)

    Howlett, J. T.; Williams, L. H.; Catherines, J. J.; Jha, S. K.

    1976-01-01

    Considerations of comfort of passengers and crew in light aircraft and helicopters indicate substantial benefits may be obtained by the reduction of interior noise levels. This paper discusses an ongoing research effort to reduce interior noise in such vehicles. Data from both field and laboratory studies for a light aircraft are presented. The laboratory data indicate that structural vibration is an efficient source of interior noise and should be considered in the reduction of interior noise. Flight data taken on a helicopter before and after installation of acoustic treatment demonstrate that over 30 dB of noise reduction can be obtained in certain portions of the spectra. However, subjective evaluations of the treated vehicle indicate that further reductions in interior noise are desirable. An existing interior noise prediction method which was developed for large jet transports was applied to study low-frequency noise in a light aircraft fuselage. The results indicate that improvements in the analytical model may be necessary for the prediction of interior noise of light aircraft.

  14. Long-term effects of noise reduction measures on noise annoyance and sleep disturbance: the Norwegian facade insulation study.

    PubMed

    Amundsen, Astrid H; Klæboe, Ronny; Aasvang, Gunn Marit

    2013-06-01

    The Norwegian facade insulation study includes one pre-intervention and two post-intervention surveys. The facade-insulating measures reduced indoor noise levels by 7 dB on average. Before the intervention, 43% of the respondents were highly annoyed by noise. Half a year after the intervention, the proportion of respondents who were highly annoyed by road traffic noise had been significantly reduced to 15%. The second post-intervention study (2 yr after the first post-intervention study) showed that the proportion of highly annoyed respondents had not changed since the first post-intervention study. The reduction in the respondents' self-reported sleep disturbances (due to traffic noise) also remained relatively stable from the first to the second post-intervention study. In the control group, there were no statistically significant differences in annoyance between the pre-intervention and the two post-intervention studies. Previous studies of traffic changes have reported that people "overreact" to noise changes. This study indicated that when considering a receiver measure, such as facade insulation, the effect of reducing indoor noise levels could be predicted from exposure-response curves based on previous studies. Thus no evidence of an "overreaction" was found. PMID:23742346

  15. Noise measurements in a 2-hole radio frequency SQUID at liquid nitrogen temperature

    SciTech Connect

    Harrop, S.P.; Colclough, M.S.; Gough, C.E.; Keene, M.N.; Muirhead, C.M.

    1989-03-01

    The authors report measurements of the noise in a 2-hole r.f. SQUID fabricated from bulk YBCO by an erosion technique in the frequency range 30mHz to 1kHz. Above 100Hz the noise is essentially white with an rms value of 5.10/sup -4/..cap alpha..o/..sqrt..Hz and is dominated by noise from the electronics. Below 10Hz the noise power rises as l/f/sup 0.9/.

  16. Potential Misidentification of Love-Wave Phase Velocity Based on Three-Component Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Xu, Zongbo; Xia, Jianghai; Luo, Yinhe; Cheng, Feng; Pan, Yudi

    2016-04-01

    People have calculated Rayleigh-wave phase velocities from vertical component of ambient seismic noise for several years. Recently, researchers started to extract Love waves from transverse component recordings of ambient noise, where "transverse" is defined as the direction perpendicular to a great-circle path or a line in small scale through observation sensors. Most researches assumed Rayleigh waves could be negligible, but Rayleigh waves can exist in the transverse component when Rayleigh waves propagate in other directions besides radial direction. In study of data acquired in western Junggar Basin near Karamay city, China, after processing the transverse component recordings of ambient noise, we obtain two energy trends, which are distinguished with Rayleigh-wave and Love-wave phase velocities, in the frequency-velocity domain using multichannel analysis of surface waves (MASW). Rayleigh waves could be also extracted from the transverse component data. Because Rayleigh-wave and Love-wave phase velocities are close in high frequencies (>0.1 Hz), two kinds of surface waves might be merged in the frequency-velocity domain. Rayleigh-wave phase velocities may be misidentified as Love-wave phase velocities. To get accurate surface-wave phase velocities from the transverse component data using seismic interferometry in investigating the shallow geology, our results suggest using MASW to calculate real Love-wave phase velocities.

  17. Some aspects of sound discomfort caused by streetcar traffic. [noise intensity measurements and health aspects

    NASA Technical Reports Server (NTRS)

    Ursoniu, C.; Puca, N.; Dankner, A.; Moise, G.; Sirbu, A.

    1974-01-01

    Streetcar noise was investigated on different lines and inside different types by sonometer measurements. The results showed variations of the total noise intensity between 88-97 db. In some squares with heavy traffic the total noise intensity reached 106 db. Noise intensity measurements inside different types of streetcars brought to light high values between 101-106 db, while in the case of the new silent type of streetcar the values were 86-87 db. The importance of the sound discomfort produced by streetcar traffic is emphasized, inasmuch as the noise intensity exceeds by far the values recommended by communal hygiene.

  18. Preliminary measurements of aircraft airframe noise with the NASA CV-990 aircraft

    NASA Technical Reports Server (NTRS)

    White, K. C.; Lasagna, P. L.; Putnam, T. W.

    1976-01-01

    Flight tests were conducted in a CV-990 jet transport with engines at idle power to investigate aircraft airframe noise. Test results showed that airframe noise was measured for the aircraft in the landing configuration. The results agreed well with the expected variation with the fifth power of velocity. For the aircraft in the clean configuraton, it was concluded that airframe noise was measured only at higher airspeeds with engine idle noise present at lower speeds. The data show that landing gear and flaps make a significant contribution to airframe noise.

  19. Contrast-to-noise ratio optimization for a prototype phase-contrast computed tomography scanner

    SciTech Connect

    Müller, Mark Yaroshenko, Andre; Velroyen, Astrid; Tapfer, Arne; Bech, Martin; Pauwels, Bart; Bruyndonckx, Peter; Sasov, Alexander; Pfeiffer, Franz

    2015-12-15

    In the field of biomedical X-ray imaging, novel techniques, such as phase-contrast and dark-field imaging, have the potential to enhance the contrast and provide complementary structural information about a specimen. In this paper, a first prototype of a preclinical X-ray phase-contrast CT scanner based on a Talbot-Lau interferometer is characterized. We present a study of the contrast-to-noise ratios for attenuation and phase-contrast images acquired with the prototype scanner. The shown results are based on a series of projection images and tomographic data sets of a plastic phantom in phase and attenuation-contrast recorded with varying acquisition settings. Subsequently, the signal and noise distribution of different regions in the phantom were determined. We present a novel method for estimation of contrast-to-noise ratios for projection images based on the cylindrical geometry of the phantom. Analytical functions, representing the expected signal in phase and attenuation-contrast for a circular object, are fitted to individual line profiles of the projection data. The free parameter of the fit function is used to estimate the contrast and the goodness of the fit is determined to assess the noise in the respective signal. The results depict the dependence of the contrast-to-noise ratios on the applied source voltages, the number of steps of the phase stepping routine, and the exposure times for an individual step. Moreover, the influence of the number of projection angles on the image quality of CT slices is investigated. Finally, the implications for future imaging purposes with the scanner are discussed.

  20. Contrast-to-noise ratio optimization for a prototype phase-contrast computed tomography scanner

    NASA Astrophysics Data System (ADS)

    Müller, Mark; Yaroshenko, Andre; Velroyen, Astrid; Bech, Martin; Tapfer, Arne; Pauwels, Bart; Bruyndonckx, Peter; Sasov, Alexander; Pfeiffer, Franz

    2015-12-01

    In the field of biomedical X-ray imaging, novel techniques, such as phase-contrast and dark-field imaging, have the potential to enhance the contrast and provide complementary structural information about a specimen. In this paper, a first prototype of a preclinical X-ray phase-contrast CT scanner based on a Talbot-Lau interferometer is characterized. We present a study of the contrast-to-noise ratios for attenuation and phase-contrast images acquired with the prototype scanner. The shown results are based on a series of projection images and tomographic data sets of a plastic phantom in phase and attenuation-contrast recorded with varying acquisition settings. Subsequently, the signal and noise distribution of different regions in the phantom were determined. We present a novel method for estimation of contrast-to-noise ratios for projection images based on the cylindrical geometry of the phantom. Analytical functions, representing the expected signal in phase and attenuation-contrast for a circular object, are fitted to individual line profiles of the projection data. The free parameter of the fit function is used to estimate the contrast and the goodness of the fit is determined to assess the noise in the respective signal. The results depict the dependence of the contrast-to-noise ratios on the applied source voltages, the number of steps of the phase stepping routine, and the exposure times for an individual step. Moreover, the influence of the number of projection angles on the image quality of CT slices is investigated. Finally, the implications for future imaging purposes with the scanner are discussed.

  1. Measurement of phase gradients in the EEG.

    PubMed

    Alexander, D M; Trengove, C; Wright, J J; Boord, P R; Gordon, E

    2006-09-30

    Previous research has shown that spatio-temporal waves in the EEG are generally of long spatial wavelength and form smooth patterns of phase gradients at particular time-samples. This paper describes a method to measure smooth phase gradients of long spatial wavelength in the EEG. The method depends on the global pattern of phase at a given frequency and time and is therefore robust to variations, over time, in phase-lag between particular sites. Phases were estimated in the EEG signal using wavelet or short time-series Fourier methods. During an auditory oddball task, phases across the scalp tend to fall within a limited circular range, a range that is not indicative of phase-synchrony nor waves with multiple periods. At times the phases tended to maintain a spatially and temporally ordered relationship. The relative phases were analysed using three phase gradient basis functions, providing a measure of the amount of variance explained, across the electrodes, by smooth changes in relative phase from a single minimum or single maximum. The data from 586 adult subjects were analysed and it was found that the probability of phase gradient events varies with time and frequency in the stimulus-locked average, and with task demands. The temporal extent of spatio-temporal waves was measured by detecting smoothly changing patterns of phase latencies across the scalp. The specific spatial pattern and timing of phase gradients correspond closely to the latency distributions of certain ERPs. PMID:16574240

  2. On The Phase Crossing Statistics and Random FM Noise in Generalized Rice Fading Channels

    NASA Astrophysics Data System (ADS)

    Petković, Marko D.; Stefanović, Mihajlo Č.

    2012-01-01

    In this paper we consider phase process second order statistics of generalized Rice (Beckmann) multipath fading channel. Closed-form expression for JPDF of phase and random FM noise is derived. Furthermore expressions for the PDF and CDF of random FM noise are obtained. The level-crossing rate of the phase process is then obtained for any phase crossing level. Obtained expressions reduces to known ones for Hoyt, Rice and Rayleigh fading channels, since these are the special cases of generalized Rice fading channel. Moreover, derived analytical expressions are compared with results obtained by computer simulation where excellent agreement is achieved. Presented results can be applied for analyzing the statistics of FM spikes in the case of data transmission over generalized Rice fading channels.

  3. Pelvic imaging with phased-array coils: quantitative assessment of signal-to-noise ratio improvement.

    PubMed

    Hayes, C E; Dietz, M J; King, B F; Ehman, R L

    1992-01-01

    The signal-to-noise ratios (S/Ns) of two different pelvic magnetic resonance (MR) imaging phased arrays were compared with that of the body coil. Each array consisted of two coils placed anteriorly and two posteriorly, oriented transversely in one array and longitudinally in the other. S/N measurements were obtained in an adjustable water-filled phantom that stimulated the shape and radio-frequency loading effects of various-size patients. Depending on the simulated anterior-posterior thickness of the patient, the S/N produced by the longitudinal array ranged from 2.3 to 3.1 times higher than that of the body coil. The S/N of the transverse array was 3.1 to 3.4 times higher. The increased coil sensitivity permits imaging with shorter acquisition times, smaller fields of view, finer resolution, and/or thinner sections. Two examples in patients demonstrate the enhanced imaging capability of the phased arrays.

  4. Comparison of the polynomial model against explicit measurements of noise components for different mammography systems

    NASA Astrophysics Data System (ADS)

    Monnin, P.; Bosmans, H.; Verdun, F. R.; Marshall, N. W.

    2014-10-01

    Given the adverse impact of image noise on the perception of important clinical details in digital mammography, routine quality control measurements should include an evaluation of noise. The European Guidelines, for example, employ a second-order polynomial fit of pixel variance as a function of detector air kerma (DAK) to decompose noise into quantum, electronic and fixed pattern (FP) components and assess the DAK range where quantum noise dominates. This work examines the robustness of the polynomial method against an explicit noise decomposition method. The two methods were applied to variance and noise power spectrum (NPS) data from six digital mammography units. Twenty homogeneously exposed images were acquired with PMMA blocks for target DAKs ranging from 6.25 to 1600 µGy. Both methods were explored for the effects of data weighting and squared fit coefficients during the curve fitting, the influence of the additional filter material (2 mm Al versus 40 mm PMMA) and noise de-trending. Finally, spatial stationarity of noise was assessed. Data weighting improved noise model fitting over large DAK ranges, especially at low detector exposures. The polynomial and explicit decompositions generally agreed for quantum and electronic noise but FP noise fraction was consistently underestimated by the polynomial method. Noise decomposition as a function of position in the image showed limited noise stationarity, especially for FP noise; thus the position of the region of interest (ROI) used for noise decomposition may influence fractional noise composition. The ROI area and position used in the Guidelines offer an acceptable estimation of noise components. While there are limitations to the polynomial model, when used with care and with appropriate data weighting, the method offers a simple and robust means of examining the detector noise components as a function of detector exposure.

  5. Comparison of the polynomial model against explicit measurements of noise components for different mammography systems.

    PubMed

    Monnin, P; Bosmans, H; Verdun, F R; Marshall, N W

    2014-10-01

    Given the adverse impact of image noise on the perception of important clinical details in digital mammography, routine quality control measurements should include an evaluation of noise. The European Guidelines, for example, employ a second-order polynomial fit of pixel variance as a function of detector air kerma (DAK) to decompose noise into quantum, electronic and fixed pattern (FP) components and assess the DAK range where quantum noise dominates. This work examines the robustness of the polynomial method against an explicit noise decomposition method. The two methods were applied to variance and noise power spectrum (NPS) data from six digital mammography units. Twenty homogeneously exposed images were acquired with PMMA blocks for target DAKs ranging from 6.25 to 1600 µGy. Both methods were explored for the effects of data weighting and squared fit coefficients during the curve fitting, the influence of the additional filter material (2 mm Al versus 40 mm PMMA) and noise de-trending. Finally, spatial stationarity of noise was assessed.Data weighting improved noise model fitting over large DAK ranges, especially at low detector exposures. The polynomial and explicit decompositions generally agreed for quantum and electronic noise but FP noise fraction was consistently underestimated by the polynomial method. Noise decomposition as a function of position in the image showed limited noise stationarity, especially for FP noise; thus the position of the region of interest (ROI) used for noise decomposition may influence fractional noise composition. The ROI area and position used in the Guidelines offer an acceptable estimation of noise components. While there are limitations to the polynomial model, when used with care and with appropriate data weighting, the method offers a simple and robust means of examining the detector noise components as a function of detector exposure.

  6. Resolving small signal measurements in experimental plasma environments using calibrated subtraction of noise signals

    SciTech Connect

    Fimognari, P. J. Demers, D. R.; Chen, X.; Schoch, P. M.

    2014-11-15

    The performance of many diagnostic and control systems within fusion and other fields of research are often detrimentally affected by spurious noise signals. This is particularly true for those (such as radiation or particle detectors) working with very small signals. Common sources of radiated and conducted noise in experimental fusion environments include the plasma itself and instrumentation. The noise complicates data analysis, as illustrated by noise on signals measured with the heavy ion beam probe (HIBP) installed on the Madison Symmetric Torus. The noise is time-varying and often exceeds the secondary ion beam current (in contrast with previous applications). Analysis of the noise identifies the dominant source as photoelectric emission from the detectors induced by ultraviolet light from the plasma. This has led to the development of a calibrated subtraction technique, which largely removes the undesired temporal noise signals from data. The advantages of the technique for small signal measurement applications are demonstrated through improvements realized on HIBP fluctuation measurements.

  7. Acoustic Environment of Admiralty Inlet: Broadband Noise Measurements

    SciTech Connect

    Xu, Jinshan; Deng, Zhiqun; Martinez, Jayson J.; Carlson, Thomas J.; Myers, Joshua R.; Weiland, Mark A.; Jones, Mark E.

    2011-09-30

    Admiralty Inlet has been selected as a potential tidal energy site. It is located near shipping lanes, is a highly variable acoustic environment, and is frequented by the highly endangered southern resident killer whale (SRKW). Resolving environmental impacts is the first step to receiving approval to deploy tidal turbines at Admiralty Inlet. Of particular concern is the potential for blade strike or other negative interactions between the SRKW and the tidal turbine. A variety of technologies including passive and active monitoring systems are being considered as potential tools to determine the presence of SRKW in the vicinity of the turbines. Broadband noise level measurements are critical for the determination of design and operation specifications of all marine and hydrokinetic energy capture technologies. Acoustic environment data at the proposed site was acquired at different depths using a cabled vertical line array (VLA) with four calibrated hydrophones. The sound pressure level (SPL) power spectrum density was estimated based on the fast Fourier transform. This study describes the first broadband SPL measurements for this site at different depths with frequency ranging from 10 kHz to 480 kHz in combination with other information. To understand the SPL caused by this bedload transport, three different pressure sensors with temperature and conductivity were also assembled on the VLA to measure the conditions at the hydrophone deployment depth. The broadband SPL levels at frequency ranges of 3 kHz to 7 kHz as a function of depth were estimated. Only the hydrophone at an average depth of 40 m showed the strong dependence of SPL with distance from the bottom, which was possibly caused by the cobbles shifting on the seabed. Automatic Identification System data were also studied to understand the SPL measurements.

  8. Measurement-based auralization methodology for the assessment of noise mitigation measures

    NASA Astrophysics Data System (ADS)

    Thomas, Pieter; Wei, Weigang; Van Renterghem, Timothy; Botteldooren, Dick

    2016-09-01

    The effect of noise mitigation measures is generally expressed by noise levels only, neglecting the listener's perception. In this study, an auralization methodology is proposed that enables an auditive preview of noise abatement measures for road traffic noise, based on the direction dependent attenuation of a priori recordings made with a dedicated 32-channel spherical microphone array. This measurement-based auralization has the advantage that all non-road traffic sounds that create the listening context are present. The potential of this auralization methodology is evaluated through the assessment of the effect of an L-shaped mound. The angular insertion loss of the mound is estimated by using the ISO 9613-2 propagation model, the Pierce barrier diffraction model and the Harmonoise point-to-point model. The realism of the auralization technique is evaluated by listening tests, indicating that listeners had great difficulty in differentiating between a posteriori recordings and auralized samples, which shows the validity of the followed approaches.

  9. Analysis of satellite measurements of terrestrial radio noise

    NASA Technical Reports Server (NTRS)

    Bakalyar, G.; Caruso, J. A.; Vargas-Vila, R.; Ziemba, E.

    1974-01-01

    Worldwide distributions of terrestrial radio noise as monitored by Radio Astronomy Explorer 1 (RAE 1) generated and compared with CCIR predictions. These contour maps show the global morphology of radio noise at 6.55 and 9.18 MHz for fall, winter, spring and summer during the local time blocks of 00-08 LT and 16-24 LT. These computer produced maps show general agreement with CCIR predictions over large land masses. The RAE and CCIR maps diverge at high latitudes over Asia and frequently over ocean regions. Higher noise levels observed by RAE at high latitudes are attributed to magnetospheric emission while higher noise levels observed by RAE over Asia are attributable to high power transmitters. Analysis of RAE noise observations in conjunction with various geophysical phenomena showed no obvious correlation.

  10. Phase comparison technique for measuring liquid-liquid phase equilibrium

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Daridon, J. L.; Lagourette, B.; Ye, S.

    1999-04-01

    In this article, a new method is demonstrated to measure the liquid-liquid phase equilibrium for binary systems. A phase comparison technique was employed to real-time display the phase-time curve in a "wave form (time) object" of Hewlett-Packard visual engineering environment. It was found that the phase-time curve showed a distorted wave form when liquid-liquid phase transition took place. The abnormal curve can therefore be used to detect liquid-liquid phase transitions. Measurements were performed in several binary systems such as nitromethane+1-hexanol, nitromethane+butanol, and nitroethane+n-hexane. The experimental results are in good agreement with those in the literature.

  11. Measurement and Assessment of Noise Within Passenger Trains

    NASA Astrophysics Data System (ADS)

    HARDY, A. E. J.

    2000-03-01

    Railways are becoming increasingly market-driven. Consequently, it is important that passengers are provided with a comfortable environment that reflects the operator's desired image for the service. A major factor in determining how passengers perceive the environment within trains is the level and nature of sound to which they are exposed. Unfortunately, the subject of noise within railway vehicles has had less attention in recent years, and is therefore less well developed, than external “environmental” noise. Two specific areas that merit investigation are methods for its quantification and assessment. A variety of criteria are used for assessing the noise environment within buildings, and may be considered appropriate for the quantification of internal train noise. These include “noise criteria” (NC), “preferred noise criteria” (PNC), “noise rating” (NR), and “room criterion” (RC). Recently, the automotive industry has also been using loudness level. Simple descriptors, such as the A-weighted sound level, have not been found to correlate well with perceived acoustic comfort. A complicating factor when considering internal rail vehicle noise is that its level and quality is not constant, with significant variability likely to occur over the duration of a journey. This difficulty is compounded by acoustic spatial variation within a vehicle. The paper considers the problems inherent in the quantification of noise within rail vehicles, and in the determination of the relationship between this noise and passenger response. Methods by which these problems may be overcome are discussed, drawing on real data and on long experience of study in this field.

  12. Noise-induced transition of atoms between dynamic phase-space attractors in a parametrically excited atomic trap

    SciTech Connect

    Kim, Kihwan; Heo, Myoung-Sun; Lee, Ki-Hwan; Ha, Hyoun-Jee; Jang, Kiyoub; Jhe, Wonho; Noh, Heung-Ryoul

    2005-11-15

    We have investigated the noise-induced transition of cold atoms between double or triple phase-space attractors that are produced in the parametrically driven magneto-optical trap. The transition rates between two dynamic attractors, directly measured for various modulation frequencies and amplitudes, are in good agreement with calculations from the dynamic version of Kramers' theory and Monte Carlo simulations. For the triple attractors, the transition rates are measured indirectly through the steady-state population and the results are also in agreement with simulations. Our experiment may be useful for study of nonlinear dynamic problems involving transitions between states far from equilibrium.

  13. Protecting a quantum state from environmental noise by an incompatible finite-time measurement

    SciTech Connect

    Brasil, Carlos Alexandre; Castro, L. A. de; Napolitano, R. d. J.

    2011-08-15

    We show that measurements of finite duration performed on an open two-state system can protect the initial state from a phase-noisy environment, provided the measured observable does not commute with the perturbing interaction. When the measured observable commutes with the environmental interaction, the finite-duration measurement accelerates the rate of decoherence induced by the phase noise. For the description of the measurement of an observable that is incompatible with the interaction between system and environment, we have found an approximate analytical expression, valid at zero temperature and weak coupling with the measuring device. We have tested the validity of the analytical predictions against an exact numerical approach, based on the superoperator-splitting method, that confirms the protection of the initial state of the system. When the coupling between the system and the measuring apparatus increases beyond the range of validity of the analytical approximation, the initial state is still protected by the finite-time measurement, according with the exact numerical calculations.

  14. A low-phase-noise 18 GHz Kerr frequency microcomb phase-locked over 65 THz

    PubMed Central

    Huang, S.-W.; Yang, J.; Lim, J.; Zhou, H.; Yu, M.; Kwong, D.-L.; Wong, C. W.

    2015-01-01

    Laser frequency combs are coherent light sources that simultaneously provide pristine frequency spacings for precision metrology and the fundamental basis for ultrafast and attosecond sciences. Recently, nonlinear parametric conversion in high-Q microresonators has been suggested as an alternative platform for optical frequency combs, though almost all in 100 GHz frequencies or more. Here we report a low-phase-noise on-chip Kerr frequency comb with mode spacing compatible with high-speed silicon optoelectronics. The waveguide cross-section of the silicon nitride spiral resonator is designed to possess small and flattened group velocity dispersion, so that the Kerr frequency comb contains a record-high number of 3,600 phase-locked comb lines. We study the single-sideband phase noise as well as the long-term frequency stability and report the lowest phase noise floor achieved to date with −130 dBc/Hz at 1 MHz offset for the 18 GHz Kerr comb oscillator, along with feedback stabilization to achieve frequency Allan deviations of 7 × 10−11 in 1 s. The reported system is a promising compact platform for achieving self-referenced Kerr frequency combs and also for high-capacity coherent communication architectures. PMID:26311406

  15. The Deep Space Network: Noise temperature concepts, measurements, and performance

    NASA Technical Reports Server (NTRS)

    Stelzried, C. T.

    1982-01-01

    The use of higher operational frequencies is being investigated for improved performance of the Deep Space Network. Noise temperature and noise figure concepts are used to describe the noise performance of these receiving systems. The ultimate sensitivity of a linear receiving system is limited by the thermal noise of the source and the quantum noise of the receiver amplifier. The atmosphere, antenna and receiver amplifier of an Earth station receiving system are analyzed separately and as a system. Performance evaluation and error analysis techniques are investigated. System noise temperature and antenna gain parameters are combined to give an overall system figure of merit G/T. Radiometers are used to perform radio ""star'' antenna and system sensitivity calibrations. These are analyzed and the performance of several types compared to an idealized total power radiometer. The theory of radiative transfer is applicable to the analysis of transmission medium loss. A power series solution in terms of the transmission medium loss is given for the solution of the noise temperature contribution.

  16. Ultra-low phase-noise microwave generation using a diode-pumped solid-state laser based frequency comb and a polarization-maintaining pulse interleaver.

    PubMed

    Portuondo-Campa, Erwin; Buchs, Gilles; Kundermann, Stefan; Balet, Laurent; Lecomte, Steve

    2015-12-14

    We report ultra-low phase-noise microwave generation at a 9.6 GHz carrier frequency from optical frequency combs based on diode-pumped solid-state lasers emitting at telecom wavelength and referenced to a common cavity-stabilized continuous-wave laser. Using a novel fibered polarization-maintaining pulse interleaver, a single-oscillator phase-noise floor of -171 dBc/Hz at 10 MHz offset frequency has been measured with commercial PIN InGaAs photodiodes, constituting a record for this type of detector. Also, a direct optical measurement of the stabilized frequency combs' timing jitter was performed using a balanced optical cross correlator, allowing for an identification of the origin of the phase-noise limitations in the system. PMID:26699033

  17. Investigation of ground reflection and impedance from flyover noise measurements

    NASA Technical Reports Server (NTRS)

    Chapkis, R. L.; Marsh, A. H.

    1978-01-01

    An extensive series of flyover noise tests was conducted for the primary purpose of studying meteorological effects on propagation of aircraft noise. The test airplane, a DC 9-10, flew several level-flight passes at various heights over a taxiway. Two microphone stations were located under the flight path. A total of 37 runs was selected for analysis and processed to obtain a consistant set of 1/3 octave band sound pressure levels at half-second intervals. The goal of the present study was to use the flyover noise data to deduce acoustical reflection coefficients and hence, acoustical impedances.

  18. Nonlinear complex diffusion approaches based on a novel noise estimation for noise reduction in phase-resolved optical coherence tomography (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Xia, Shaoyan; Huang, Yong; Tan, Xiaodi

    2016-03-01

    Partial differential equation (PDE)-based nonlinear diffusion processes have been widely used for image denoising. In the traditional nonlinear anisotropic diffusion denoising techniques, behavior of the diffusion depends highly on the gradient of image. However, it is difficult to get a good effect if we use these methods to reduce noise in optical coherence tomography images. Because background has the gradient that is very similar to regions of interest, so background noise will be mistaken for edge information and cannot be reduced. Therefore, nonlinear complex diffusion approaches using texture feature(NCDTF) for noise reduction in phase-resolved optical coherence tomography is proposed here, which uses texture feature in OCT images and structural OCT images to remove noise in phase-resolved OCT. Taking into account the fact that texture between background and signal region is different, which can be linked with diffusion coefficient of nonlinear complex diffusion model, we use NCDTF method to reduce noises of structure and phase images first. Then, we utilize OCT structure images to filter phase image in OCT. Finally, to validate our method, parameters such as image SNR, contrast-to-noise ratio (CNR), equivalent number of looks (ENL), and edge preservation were compared between our approach and median filter, Gaussian filter, wavelet filter, nonlinear complex diffusion filter (NCDF). Preliminary results demonstrate that NCDTF method is more effective than others in keeping edges and denoising for phase-resolved OCT.

  19. Noise-induced phase space transport in two-dimensional Hamiltonian systems

    SciTech Connect

    Pogorelov, I.V.; Kandrup, H.E.

    1999-08-01

    First passage time experiments were used to explore the effects of low amplitude noise as a source of accelerated phase space diffusion in two-dimensional Hamiltonian systems, and these effects were then compared with the effects of periodic driving. The objective was to quantify and understand the manner in which {open_quotes}sticky{close_quotes} chaotic orbits that, in the absence of perturbations, are confined near regular islands for very long times, can become {open_quotes}unstuck{close_quotes} much more quickly when subjected to even very weak perturbations. For both noise and periodic driving, the typical escape time scales logarithmically with the amplitude of the perturbation. For white noise, the details seem unimportant: Additive and multiplicative noise typically have very similar effects, and the presence or absence of a friction related to the noise by a fluctuation-dissipation theorem is also largely irrelevant. Allowing for colored noise {ital can} significantly decrease the efficacy of the perturbation, but only when the autocorrelation time, which vanishes for white noise, becomes so large that there is little power at frequencies comparable to the natural frequencies of the unperturbed orbit. Similarly, periodic driving is relatively inefficient when the driving frequency is not comparable to these natural frequencies. This suggests that noise-induced extrinsic diffusion, like modulational diffusion associated with periodic driving, is a resonance phenomenon. The logarithmic dependence of the escape time on amplitude reflects the fact that the time required for perturbed and unperturbed orbits to diverge a given distance scales logarithmically in the amplitude of the perturbation. {copyright} {ital 1999} {ital The American Physical Society}

  20. Results of the flight noise measurement program using a standard and modified SH-3A helicopter

    NASA Technical Reports Server (NTRS)

    Pegg, R. J.; Henderson, H. R.; Hilton, D. A.

    1973-01-01

    A field noise measurement program has been conducted using both a standard SH-3A helicopter and an SH-3A helicopter modified to reduce external noise levels. Modifications included reducing rotor speed, increasing the number of rotor blades, modifying the blade-tip shapes, and acoustically treating the engine air intakes and exhaust. The purpose of this study was to document the noise characteristics recorded on the ground of each helicopter during flyby, hover, landing, and take-off operations. Based on an analysis of the measured results, the average of the overhead, overall, ontrack noise levels was approximately 4 db lower for the modified helicopter than for the standard helicopter. The improved in-flight noise characteristics, and associated small footprint areas and time durations, were judged to be mainly due to tail-rotor noise reductions. The noise reductions were obtained at the expense of required power increases at airspeeds greater than 70 knots for the modified helicopter.

  1. Phase shift errors in the theory and practice of surface intensity measurements

    NASA Technical Reports Server (NTRS)

    Mcgary, M. C.; Crocker, M. J.

    1982-01-01

    The surface acoustical intensity method (sometimes known as the microphone-accelerometer cross-spectral method) is a relatively new noise source/path identification tool. Several researchers have had difficulties implementing this method because of instrumentation phase mis-match. A simple technique for measuring and correcting instrumentation phase mis-match has been developed. This new technique has been tested recently on a noise source identification problem of practical interest. The results of the experiments indicate that the surface acoustic intensity method produces reliable data and can be applied to a variety of noise source/path problems.

  2. Unscented Kalman filters for polarization state tracking and phase noise mitigation.

    PubMed

    Jignesh, Jokhakar; Corcoran, Bill; Zhu, Chen; Lowery, Arthur

    2016-09-19

    Simultaneous polarization and phase noise tracking and compensation is proposed based on an unscented Kalman filter (UKF). We experimentally demonstrate the tracking under noise-loading and after 800-km single-mode fiber transmission with 20-Gbaud QPSK and 16-QAM signals. These experiments show that the proposed UKF outperforms both conventional blind tracing algorithms and a previously proposed extended Kalman filter, at the cost of higher complexity. Additionally, we propose and test modified Kalman filter algorithms to reduce computational complexity. PMID:27661962

  3. Optimized tracking of RF carriers with phase noise, including Pioneer 10 results

    NASA Technical Reports Server (NTRS)

    Vilnrotter, V. A.; Hurd, W. J.; Brown, D. H.

    1987-01-01

    The ability to track very weak signals from distant spacecraft is limited by the phase instabilities of the received signal and of the local oscillator employed by the receiver. These instabilities ultimately limit the minimum loop bandwidth that can be used in a phase-coherent receiver, and hence limit the ratio of received carrier power to noise spectral density which can be tracked phase coherently. A method is presented for near real time estimation of the received carrier phase and additive noise spectrum, and optimization of the phase locked loop bandwidth. The method was used with the breadboard Deep Space Network (DSN) Advanced Receiver to optimize tracking of very weak signals from the Pioneer 10 spacecraft, which is now more distant that the edge of the solar system. Tracking with bandwidths of 0.1 Hz to 1.0 Hz reduces tracking signal threshold and increases carrier loop signal to noise ratio (SNR) by 5 dB to 15 dB compared to the 3 Hz bandwidth of the receivers now used operationally in the DSN. This will enable the DSN to track Pioneer 10 until its power sources fails near the end of the century.

  4. High phase noise tolerant pilot-tone-aided DP-QPSK optical communication systems.

    PubMed

    Zhang, Xu; Pang, Xiaodan; Deng, Lei; Zibar, Darko; Monroy, Idelfonso Tafur; Younce, Richard

    2012-08-27

    In this paper we experimentally demonstrate a novel, high phase-noise tolerant, optical dual polarization (DP) quadrature phase-shift keying (QPSK) communication system based on pilot-tone-aided phase noise cancellation (PNC) algorithm. Vertical cavity surface emitting lasers (VCSELs) with approximate 300 MHz linewidth are used as transmitters and local oscillators for coherent detection of optical DP-QPSK signals. The proposed system, with central wavelength at 1540.68 nm, operates at 40 Gb/s over 80 km single mode fiber (SMF) as part of a passive optical network (PON). The deployment of pilot-tone-aided PNC algorithm guarantees a bit error rate (BER) performance below the forward error correction (FEC) threshold. Moreover, we also evaluate a novel digital signal processing (DSP) algorithm for adaptive pilot tone detection.

  5. Robust shot-noise measurement for continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Kunz-Jacques, Sébastien; Jouguet, Paul

    2015-02-01

    We study a practical method to measure the shot noise in real time in continuous-variable quantum key distribution systems. The amount of secret key that can be extracted from the raw statistics depends strongly on this quantity since it affects in particular the computation of the excess noise (i.e., noise in excess of the shot noise) added by an eavesdropper on the quantum channel. Some powerful quantum hacking attacks relying on faking the estimated value of the shot noise to hide an intercept and resend strategy were proposed. Here, we provide experimental evidence that our method can defeat the saturation attack and the wavelength attack.

  6. Objective Measures of Listening Effort: Effects of Background Noise and Noise Reduction

    ERIC Educational Resources Information Center

    Sarampalis, Anastasios; Kalluri, Sridhar; Edwards, Brent; Hafter, Ervin

    2009-01-01

    Purpose: This work is aimed at addressing a seeming contradiction related to the use of noise-reduction (NR) algorithms in hearing aids. The problem is that although some listeners claim a subjective improvement from NR, it has not been shown to improve speech intelligibility, often even making it worse. Method: To address this, the hypothesis…

  7. Bilateral filtering using the full noise covariance matrix applied to x-ray phase-contrast computed tomography

    NASA Astrophysics Data System (ADS)

    Allner, S.; Koehler, T.; Fehringer, A.; Birnbacher, L.; Willner, M.; Pfeiffer, F.; Noël, P. B.

    2016-05-01

    The purpose of this work is to develop an image-based de-noising algorithm that exploits complementary information and noise statistics from multi-modal images, as they emerge in x-ray tomography techniques, for instance grating-based phase-contrast CT and spectral CT. Among the noise reduction methods, image-based de-noising is one popular approach and the so-called bilateral filter is a well known algorithm for edge-preserving filtering. We developed a generalization of the bilateral filter for the case where the imaging system provides two or more perfectly aligned images. The proposed generalization is statistically motivated and takes the full second order noise statistics of these images into account. In particular, it includes a noise correlation between the images and spatial noise correlation within the same image. The novel generalized three-dimensional bilateral filter is applied to the attenuation and phase images created with filtered backprojection reconstructions from grating-based phase-contrast tomography. In comparison to established bilateral filters, we obtain improved noise reduction and at the same time a better preservation of edges in the images on the examples of a simulated soft-tissue phantom, a human cerebellum and a human artery sample. The applied full noise covariance is determined via cross-correlation of the image noise. The filter results yield an improved feature recovery based on enhanced noise suppression and edge preservation as shown here on the example of attenuation and phase images captured with grating-based phase-contrast computed tomography. This is supported by quantitative image analysis. Without being bound to phase-contrast imaging, this generalized filter is applicable to any kind of noise-afflicted image data with or without noise correlation. Therefore, it can be utilized in various imaging applications and fields.

  8. TRISTEN/FRAM IV arctic ambient noise measurements

    NASA Astrophysics Data System (ADS)

    Nielsen, R. J.; Dinapoli, F. R.; Fecher, M. P.; Fisch, N. P.; Potter, D. M.

    1984-03-01

    Multichannel ice camp ambient noise data were recorded by NUSC during the TRISTEN/FRAM IV experiment in the Barents Abyssal Plain, Arctic Ocean during April 1982. Single-hydrophone data were recorded from various elements of both the Massachusetts Institute of Technology/Woods Hole Oceanographic Institute horizontal array and the Naval Research Laboratory vertical array. This paper characteristics the average ambient noise level and its variance as a function of frequency (to 2500 Hz), depth, and time.

  9. Jet Measurements for Development of Jet Noise Prediction Tools

    NASA Technical Reports Server (NTRS)

    Bridges, James E.

    2006-01-01

    The primary focus of my presentation is the development of the jet noise prediction code JeNo with most examples coming from the experimental work that drove the theoretical development and validation. JeNo is a statistical jet noise prediction code, based upon the Lilley acoustic analogy. Our approach uses time-average 2-D or 3-D mean and turbulent statistics of the flow as input. The output is source distributions and spectral directivity.

  10. Identification of structural systems using naturally induced vibration data in the presence of measurement noise

    NASA Technical Reports Server (NTRS)

    Huan, S.-L.; Mcinnis, B. C.; Denman, E. D.

    1983-01-01

    The method of instrument variables for the identification of the parameters of structural systems excited by white noise in the presence of white measurement noise is applied. The requisite equations and the resulting consistent estimator are derived and simulation results for least squares and instrumental variables methods, for light and heavy damping, are compared. The present method gave better results than least squares when measurement noise was presented, and verified the fact that least squares yields an inconsistent estimator unless the measurement noise is zero.

  11. Mechanical modulation method for ultrasensitive phase measurements in photonics biosensing.

    PubMed

    Patskovsky, S; Maisonneuve, M; Meunier, M; Kabashin, A V

    2008-12-22

    A novel polarimetry methodology for phase-sensitive measurements in single reflection geometry is proposed for applications in optical transduction-based biological sensing. The methodology uses altering step-like chopper-based mechanical phase modulation for orthogonal s- and p- polarizations of light reflected from the sensing interface and the extraction of phase information at different harmonics of the modulation. We show that even under a relatively simple experimental arrangement, the methodology provides the resolution of phase measurements as low as 0.007 deg. We also examine the proposed approach using Total Internal Reflection (TIR) and Surface Plasmon Resonance (SPR) geometries. For TIR geometry, the response appears to be strongly dependent on the prism material with the best values for high refractive index Si. The detection limit for Si-based TIR is estimated as 10(-5) in terms Refractive Index Units (RIU) change. SPR geometry offers much stronger phase response due to a much sharper phase characteristics. With the detection limit of 3.2*10(-7) RIU, the proposed methodology provides one of best sensitivities for phase-sensitive SPR devices. Advantages of the proposed method include high sensitivity, simplicity of experimental setup and noise immunity as a result of a high stability modulation.

  12. Circuit models and experimental noise measurements of micropipette amplifiers for extracellular neural recordings from live animals.

    PubMed

    Chen, Chang Hao; Pun, Sio Hang; Mak, Peng Un; Vai, Mang I; Klug, Achim; Lei, Tim C

    2014-01-01

    Glass micropipettes are widely used to record neural activity from single neurons or clusters of neurons extracellularly in live animals. However, to date, there has been no comprehensive study of noise in extracellular recordings with glass micropipettes. The purpose of this work was to assess various noise sources that affect extracellular recordings and to create model systems in which novel micropipette neural amplifier designs can be tested. An equivalent circuit of the glass micropipette and the noise model of this circuit, which accurately describe the various noise sources involved in extracellular recordings, have been developed. Measurement schemes using dead brain tissue as well as extracellular recordings from neurons in the inferior colliculus, an auditory brain nucleus of an anesthetized gerbil, were used to characterize noise performance and amplification efficacy of the proposed micropipette neural amplifier. According to our model, the major noise sources which influence the signal to noise ratio are the intrinsic noise of the neural amplifier and the thermal noise from distributed pipette resistance. These two types of noise were calculated and measured and were shown to be the dominating sources of background noise for in vivo experiments.

  13. Measurements and predictions of flyover and static noise of a TF30 afterburning turbofan engine

    NASA Technical Reports Server (NTRS)

    Burcham, F. W., Jr.; Lasagna, P. L.; Oas, S. C.

    1978-01-01

    The noise of the TF30 afterburning turbofan engine in an F-111 airplane was determined from static (ground) and flyover tests. A survey was made to measure the exhaust temperature and velocity profiles for a range of power settings. Comparisons were made between predicted and measured jet mixing, internal, and shock noise. It was found that the noise produced at static conditions was dominated by jet mixing noise, and was adequately predicted by current methods. The noise produced during flyovers exhibited large contributions from internally generated noise in the forward arc. For flyovers with the engine at nonafterburning power, the internal noise, shock noise, and jet mixing noise were accurately predicted. During flyovers with afterburning power settings, however, additional internal noise believed to be due to the afterburning process was evident; its level was as much as 8 decibels above the nonafterburning internal noise. Power settings that produced exhausts with inverted velocity profiles appeared to be slightly less noisy than power settings of equal thrust that produced uniform exhaust velocity profiles both in flight and in static testing.

  14. Automated measurement of CT noise in patient images with a novel structure coherence feature

    NASA Astrophysics Data System (ADS)

    Chun, Minsoo; Choi, Young Hun; Hyo Kim, Jong

    2015-12-01

    While the assessment of CT noise constitutes an important task for the optimization of scan protocols in clinical routine, the majority of noise measurements in practice still rely on manual operation, hence limiting their efficiency and reliability. This study presents an algorithm for the automated measurement of CT noise in patient images with a novel structure coherence feature. The proposed algorithm consists of a four-step procedure including subcutaneous fat tissue selection, the calculation of structure coherence feature, the determination of homogeneous ROIs, and the estimation of the average noise level. In an evaluation with 94 CT scans (16 517 images) of pediatric and adult patients along with the participation of two radiologists, ROIs were placed on a homogeneous fat region at 99.46% accuracy, and the agreement of the automated noise measurements with the radiologists’ reference noise measurements (PCC  =  0.86) was substantially higher than the within and between-rater agreements of noise measurements (PCCwithin  =  0.75, PCCbetween  =  0.70). In addition, the absolute noise level measurements matched closely the theoretical noise levels generated by a reduced-dose simulation technique. Our proposed algorithm has the potential to be used for examining the appropriateness of radiation dose and the image quality of CT protocols for research purposes as well as clinical routine.

  15. New technique for the direct measurement of core noise from aircraft engines

    NASA Technical Reports Server (NTRS)

    Krejsa, E. A.

    1981-01-01

    A new technique is presented for directly measuring the core noise levels from gas turbine aircraft engines. The technique requires that fluctuating pressures be measured in the far-field and at two locations within the engine core. The cross-spectra of these measurements are used to determine the levels of the far-field noise that propagated from the engine core. The technique makes it possible to measure core noise levels even when other noise sources dominate. The technique was applied to signals measured from an AVCO Lycoming YF102 turbofan engine. Core noise levels as a function of frequency and radiation angle were measured and are presented over a range of power settings.

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

    NASA Technical Reports Server (NTRS)

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

    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 as showing that the surface pressure fluctuations are mainly aerodynamic in character and are convected in the downstream direction with a velocity which is dependent on the jet exhaust velocity. However the far field sound levels in the mid and high frequency ranges are dominated by jet noise. There is an indication that in the low frequency range trailing edge noise, associated with interaction of the jet flow and the flap trailing edge, plays a significant role in the radiated sound field.

  17. Turbulent phase noise on asymmetric two-way ground-satellite coherent optical links

    NASA Astrophysics Data System (ADS)

    Robert, Clélia; Conan, Jean-Marc; Wolf, Peter

    2015-10-01

    Bidirectional ground-satellite laser links suffer from turbulence-induced scintillation and phase distortion. We study how turbulence impacts on coherent detection capacity and on the associated phase noise that restricts clock transfer precision. We evaluate the capacity to obtain a two-way cancellation of atmospheric effects despite the asymmetry between up and down link that limits the link reciprocity. For ground-satellite links, the asymmetry is induced by point-ahead angle and possibly the use, for the ground terminal, of different transceiver diameters, in reception and emission. The quantitative analysis is obtained thanks to refined end-to-end simulations under realistic turbulence and wind conditions as well as satellite cinematic. Simulations make use of the reciprocity principle to estimate both down and up link performance from wave-optics propagation of descending plane waves. These temporally resolved simulations allow characterising the coherent detection in terms of time series of heterodyne efficiency for different system parameters. We show Tip/Tilt correction on ground is mandatory at reception for the down link and as a pre-compensation of the up link. Good correlation between up and down phase noise is obtained even with asymmetric apertures of the ground transceiver and in spite of pointing ahead angle. The reduction to less than 1 rad2 of the two-way differential phase noise is very promising for clock transfer.

  18. Using phase information to enhance speckle noise reduction in the ultrasonic NDE of coarse grain materials

    SciTech Connect

    Lardner, Timothy; Gachagan, Anthony; Li, Minghui

    2014-02-18

    Materials with a coarse grain structure are becoming increasingly prevalent in industry due to their resilience to stress and corrosion. These materials are difficult to inspect with ultrasound because reflections from the grains lead to high noise levels which hinder the echoes of interest. Spatially Averaged Sub-Aperture Correlation Imaging (SASACI) is an advanced array beamforming technique that uses the cross-correlation between images from array sub-apertures to generate an image weighting matrix, in order to reduce noise levels. This paper presents a method inspired by SASACI to further improve imaging using phase information to refine focusing and reduce noise. A-scans from adjacent array elements are cross-correlated using both signal amplitude and phase to refine delay laws and minimize phase aberration. The phase-based and amplitude-based corrected images are used as inputs to a two-dimensional cross-correlation algorithm that will output a weighting matrix that can be applied to any conventional image. This approach was validated experimentally using a 5MHz array a coarse grained Inconel 625 step wedge, and compared to the Total Focusing Method (TFM). Initial results have seen SNR improvements of over 20dB compared to TFM, and a resolution that is much higher.

  19. Results of the noise measurement program on a standard and modified OH-6A helicopter

    NASA Technical Reports Server (NTRS)

    Henderson, H. R.; Peegg, R. J.; Hilton, D. A.

    1973-01-01

    A field noise measurement program has been conducted on a standard OH-6A helicopter and one that had been modified by reducing the rotor speed, altering rotor tip shape, and treating the engine exhaust and inlet to reduce the external noise levels. The modifications consisted of extensive aircraft design changes resulting in substantial noise reductions following state-of-art noise reduction techniques. The purpose of this study was to document the ground noise characteristics of each helicopter during flyover, hover, landing, and take-off operations. Based on an analysis of the measured results, the average of the overall on-track noise levels of the final modified helicopter was approximately 14 db lower than that for the standard helicopter. Narrow-band-spectra data of the hovering helicopter show a reduction in the overall noise due to the reductions achieved for the lifting main and antitorque tail rotor, engine exhaust, and gear box noise for the modified helicopter. The noise results of the test program are found to correlate generally with noise measurements made previously on this type of aircraft.

  20. Phase transitions in the majority-vote model with two types of noises

    NASA Astrophysics Data System (ADS)

    Vieira, Allan R.; Crokidakis, Nuno

    2016-05-01

    In this work we study the majority-vote model with the presence of two distinct noises. The first one is the usual noise q, that represents the probability that a given agent follows the minority opinion of his/her social contacts. On the other hand, we consider the independent behavior, such that an agent can choose his/her own opinion + 1 or - 1 with equal probability, independent of the group's norm. We study the impact of the presence of such two kinds of stochastic driving in the phase transitions of the model, considering the mean field and the square lattice cases. Our results suggest that the model undergoes a nonequilibrium order-disorder phase transition even in the absence of the noise q, due to the independent behavior, but this transition may be suppressed. In addition, for both topologies analyzed, we verified that the transition is in the same universality class of the equilibrium Ising model, i.e., the critical exponents are not affected by the presence of the second noise, associated with independence.

  1. Signal-Induced Noise Effects in a Photon Counting System for Stratospheric Ozone Measurement

    NASA Technical Reports Server (NTRS)

    Harper, David B.; DeYoung, Russell J.

    1998-01-01

    A significant source of error in making atmospheric differential absorption lidar ozone measurements is the saturation of the photomultiplier tube by the strong, near field light return. Some time after the near field light signal is gone, the photomultiplier tube gate is opened and a noise signal, called signal-induced noise, is observed. Research reported here gives experimental results from measurement of photomultiplier signal-induced noise. Results show that signal-induced noise has several decaying exponential signals, suggesting that electrons are slowly emitted from different surfaces internal to the photomultiplier tube.

  2. Accurate measurement of spatial noise portraits of photosensors of digital cameras

    NASA Astrophysics Data System (ADS)

    Cheremkhin, P. A.; Evtikhiev, N. N.; Krasnov, V. V.; Kulakov, M. N.; Starikov, R. S.

    2016-08-01

    Method of measurement of accurate portraits of light and dark spatial noise of photosensors is described. The method consists of four steps: creation of spatially homogeneous illumination; shooting light and dark frames; digital processing and filtering. Unlike standard technique, this method uses iterative creation of spatially homogeneous illumination by display, compensation of photosensor dark spatial noise portrait and improved procedure of elimination of dark temporal noise. Portraits of light and dark spatial noise of photosensors of a scientific digital camera were found. Characteristics of the measured portraits were compared with values of photo response and dark signal non-uniformities of camera's photosensor.

  3. Calibration and Characterization of Autonomous Recorders Used in the Measurement of Underwater Noise.

    PubMed

    Hayman, Gary; Robinson, Stephen; Lepper, Paul

    2016-01-01

    The use of autonomous recorders is motivated by the need to monitor underwater noise, such as in response to the requirements of the European Union Marine Strategy Framework Directive. The performance of these systems is a crucial factor governing the quality of the measured data, providing traceability for future underwater noise-monitoring programs aimed at the protection of the marine environment from anthropogenic noise. In this paper, a discussion is presented of measurement methodologies for the key acoustic performance characteristics of the recorders, including self-noise, dynamic range, and the absolute sensitivity as a function of frequency of the hydrophone and recorder system. PMID:26610989

  4. Experimental Test of Entropic Noise-Disturbance Uncertainty Relations for Spin-1/2 Measurements.

    PubMed

    Sulyok, Georg; Sponar, Stephan; Demirel, Bülent; Buscemi, Francesco; Hall, Michael J W; Ozawa, Masanao; Hasegawa, Yuji

    2015-07-17

    Information-theoretic definitions for noise and disturbance in quantum measurements were given in [Phys. Rev. Lett. 112, 050401 (2014)] and a state-independent noise-disturbance uncertainty relation was obtained. Here, we derive a tight noise-disturbance uncertainty relation for complementary qubit observables and carry out an experimental test. Successive projective measurements on the neutron's spin-1/2 system, together with a correction procedure which reduces the disturbance, are performed. Our experimental results saturate the tight noise-disturbance uncertainty relation for qubits when an optimal correction procedure is applied.

  5. Experimental Test of Entropic Noise-Disturbance Uncertainty Relations for Spin-1 /2 Measurements

    NASA Astrophysics Data System (ADS)

    Sulyok, Georg; Sponar, Stephan; Demirel, Bülent; Buscemi, Francesco; Hall, Michael J. W.; Ozawa, Masanao; Hasegawa, Yuji

    2015-07-01

    Information-theoretic definitions for noise and disturbance in quantum measurements were given in [Phys. Rev. Lett. 112, 050401 (2014)] and a state-independent noise-disturbance uncertainty relation was obtained. Here, we derive a tight noise-disturbance uncertainty relation for complementary qubit observables and carry out an experimental test. Successive projective measurements on the neutron's spin-1 /2 system, together with a correction procedure which reduces the disturbance, are performed. Our experimental results saturate the tight noise-disturbance uncertainty relation for qubits when an optimal correction procedure is applied.

  6. Calibration and Characterization of Autonomous Recorders Used in the Measurement of Underwater Noise.

    PubMed

    Hayman, Gary; Robinson, Stephen; Lepper, Paul

    2016-01-01

    The use of autonomous recorders is motivated by the need to monitor underwater noise, such as in response to the requirements of the European Union Marine Strategy Framework Directive. The performance of these systems is a crucial factor governing the quality of the measured data, providing traceability for future underwater noise-monitoring programs aimed at the protection of the marine environment from anthropogenic noise. In this paper, a discussion is presented of measurement methodologies for the key acoustic performance characteristics of the recorders, including self-noise, dynamic range, and the absolute sensitivity as a function of frequency of the hydrophone and recorder system.

  7. On the use of mobile phones and wearable microphones for noise exposure measurements: Calibration and measurement accuracy

    NASA Astrophysics Data System (ADS)

    Dumoulin, Romain

    Despite the fact that noise-induced hearing loss remains the number one occupational disease in developed countries, individual noise exposure levels are still rarely known and infrequently tracked. Indeed, efforts to standardize noise exposure levels present disadvantages such as costly instrumentation and difficulties associated with on site implementation. Given their advanced technical capabilities and widespread daily usage, mobile phones could be used to measure noise levels and make noise monitoring more accessible. However, the use of mobile phones for measuring noise exposure is currently limited due to the lack of formal procedures for their calibration and challenges regarding the measurement procedure. Our research investigated the calibration of mobile phone-based solutions for measuring noise exposure using a mobile phone's built-in microphones and wearable external microphones. The proposed calibration approach integrated corrections that took into account microphone placement error. The corrections were of two types: frequency-dependent, using a digital filter and noise level-dependent, based on the difference between the C-weighted noise level minus A-weighted noise level of the noise measured by the phone. The electro-acoustical limitations and measurement calibration procedure of the mobile phone were investigated. The study also sought to quantify the effect of noise exposure characteristics on the accuracy of calibrated mobile phone measurements. Measurements were carried out in reverberant and semi-anechoic chambers with several mobiles phone units of the same model, two types of external devices (an earpiece and a headset with an in-line microphone) and an acoustical test fixture (ATF). The proposed calibration approach significantly improved the accuracy of the noise level measurements in diffuse and free fields, with better results in the diffuse field and with ATF positions causing little or no acoustic shadowing. Several sources of errors

  8. Rayleigh and Love wave phase velocity maps of Iceland from combined ambient noise and teleseismic surface wave analysis.

    NASA Astrophysics Data System (ADS)

    Harmon, N.

    2014-12-01

    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.

  9. Measurement of BSR noise of cockpit module materials for automobiles

    NASA Astrophysics Data System (ADS)

    Woo, C.; Park, H.

    2016-04-01

    Today, the interior noise perceived by occupants is becoming an important factor driving design standards for the design of most of interior assemblies in an automotive vehicles. BSR(Buzz, Squeak and Rattle) is a major contributor towards the perceived noise of annoyance to vehicle occupants. One method of minimizing the possibility of squeak and rattle is by making use of the judicious selection of mating materials pairs. In this paper, the BSR test system was designed and built. Also described is a test instrument that has been developed for such material pair compatibility studies.

  10. White-light interferometry on rough surfaces--measurement uncertainty caused by noise.

    PubMed

    Pavliček, Pavel; Hýbl, Ondřej

    2012-02-01

    White-light interferometry on rough surfaces is an optical method for the measurement of the geometrical form of objects. The longitudinal coordinate of the measured surface is obtained from the measured interferogram by means of an evaluation method. However, the longitudinal coordinate cannot be determined completely accurately because the interferogram is affected by noise. We calculate the lower limit of the longitudinal measurement uncertainty caused by noise by use of the Cramer-Rao inequality. Additionally, we calculate the lower limit of the longitudinal measurement uncertainty caused by shot noise only.

  11. Automated acoustic intensity measurements and the effect of gear tooth profile on noise

    NASA Technical Reports Server (NTRS)

    Atherton, W. J.; Pintz, A.; Lewicki, D. G.

    1987-01-01

    Acoustic intensity measurements were made at NASA Lewis Research Center on a spur gear test apparatus. The measurements were obtained with the Robotic Acoustic Intensity Measurement System developed by Cleveland State University. This system provided dense spatial positioning, and was calibrated against a high quality acoustic intensity system. The measured gear noise compared gearsets having two different tooth profiles. The tests evaluated the sound field of the different gears for two speeds and three loads. The experimental results showed that gear tooth profile had a major effect on measured noise. Load and speed were found to have an effect on noise also.

  12. Low-noise multiple watermarks technology based on complex double random phase encoding method

    NASA Astrophysics Data System (ADS)

    Zheng, Jihong; Lu, Rongwen; Sun, Liujie; Zhuang, Songlin

    2010-11-01

    Based on double random phase encoding method (DRPE), watermarking technology may provide a stable and robust method to protect the copyright of the printing. However, due to its linear character, DRPE exist the serious safety risk when it is attacked. In this paper, a complex coding method, which means adding the chaotic encryption based on logistic mapping before the DRPE coding, is provided and simulated. The results testify the complex method will provide better security protection for the watermarking. Furthermore, a low-noise multiple watermarking is studied, which means embedding multiple watermarks into one host printing and decrypt them with corresponding phase keys individually. The Digital simulation and mathematic analysis show that with the same total embedding weight factor, multiply watermarking will improve signal noise ratio (SNR) of the output printing image significantly. The complex multiply watermark method may provide a robust, stability, reliability copyright protection with higher quality printing image.

  13. A New Technique for Reduction the Phase Induced Intensity Noise in SAC-OCDMA Systems

    NASA Astrophysics Data System (ADS)

    Abd, Thanaa Hussein; Aljunid, Syed Alwee; Fadhil, Hilal Adnan

    2011-12-01

    A new code for reduction the phase induced intensity noise has been presented. The new code is proposed for Spectral Amplitude-Coding Optical Code Division Multiple Accesses (SAC-OCDMA). This new code family we call it Dynamic Cyclic Shift (DCS) code. The DCS code reduced the effect of Multi Access Interference (MAI) due to it is the property of variable cross correlation. We find that the performance of the DCS code is a batter than other SAC-OCDMA codes such as; Random Diagonal (RD) code, Modified Quadratic Congruence (MQC) code and Modified Frequency Hopping (MFH) code. Through the mathematical calculation and simulation analysis, for the bit-error rate of DCS code is significantly better than other SAC-OCDMA codes, the effect of Phase Induced Intensity Noise is reduced. In addition, proofof-principle simulations of 10 Gb/s for 20 km have been successfully demonstrated and achieved low BER compared to the other codes.

  14. Method to Measure Total Noise Temperature of a Wireless Receiver During Operation

    NASA Technical Reports Server (NTRS)

    Young, Lawrence E. (Inventor); Turbiner, Dmitry (Inventor); Esterhuizen, Stephan X. (Inventor)

    2014-01-01

    An electromagnetic signal receiver and methods for determining the noise level and signal power in a signal of interest while the receiver is operating. In some embodiments, the signal of interest is a GPS signal. The receiver includes a noise source that provides a noise signal of known power during intervals while the signal of interest is observed. By measuring a signal-to-noise ratio for the signal of interest and the noise power in the signal of interest, the noise level and signal power of the signal of interest can be computed. Various methods of making the measurements and computing the power of the signal of interest are described. Applications of the system and method are described.

  15. Flight-test measurement of the noise reduction of a jet transport delayed flap approach procedure

    NASA Technical Reports Server (NTRS)

    Foster, J. D.; Lasagna, P. L.

    1976-01-01

    A delayed flap approach procedure was flight tested using the NASA CV-990 airplane to measure and analyze the noise produced beneath the flight path. Three other types of landing approaches were also flight tested to provide a comparison of the noise reduction benefits to the delayed flap approach. The conventional type of approach was used as a baseline to compare the effectiveness of the other approaches. The decelerating approach is a variation of the delayed flap approach. A detailed comparison of the ground perceived noise generated during the approaches is presented. For this comparison, the measured noise data were normalized to compensate for variations in aircraft weight and winds that occurred during the flight tests. The data show that the reduced flap approach offers some noise reduction, while the delayed flap and decelerating approaches offer significant noise reductions over the conventional approach.

  16. Noise measurement flight test: Data-analyses aerospatiale AS-355F TwinStar helicopter

    NASA Astrophysics Data System (ADS)

    Newman, J. S.; Rickley, E. J.; Beattie, K. R.; Bland, T. L.

    1984-08-01

    This report documents the results of a Federal Aviation Administration (FAA) noise measurement flight test program with the TwinStar twin-jet helicopter. The report contains documentary sections describing the acoustical characteristics of the subject helicopter and provides analyses and discussions addressing topics ranging from acoustical propagation to environmental impact of helicopter noise. This test program was designed to address a series of objectives including: (1) acquisition of acoustical data for use in assessing heliport environmental impact, (2) documentation of directivity characteristics for static operation of helicopters, (3) establishment of ground-to-ground and air-to-ground acoustical propagation relationships for helicopters, (4) determination of noise event duration influences on energy dose acoustical metrics, (5) examination of the differences between noise measured by a surface mounted microphone and a microphone mounted at a height of four feet (1.2 meters), and (6) documentation of noise levels acquired using international helicopter noise certification test procedures.

  17. Noise measurement flight test: Data-analyses Aerospatiale AS 350D AStar helicopter

    NASA Astrophysics Data System (ADS)

    Newman, J. S.; Rickley, E. J.; Beattie, K. R.; Bland, T. L.

    1984-09-01

    This report documents the results of a Federal Aviation Administration (FAA) noise measurement flight test program with the AStar helicopter. The report contains documentary sections describing the acoustical characteristics of the subject helicopter and provides analyses and discussions addressing topics ranging from acoustical propagation to environmental impact of helicopter noise. This program was designed to address a series of objectives including: (1) acquisition of acoustical data for use in assessing heliport environmental impact, (2) documentation of directivity characteristics for static operation of helicopters, (3) establishment of ground-to-ground and air-to-ground acoustical propagation relationships for helicopters, (4) determination of noise event duration influences on energy dose acoustical metrics, (5) examination of the differences between noise measured by a surface mounted microphone and a microphone mounted at a height of four feet (1.2 meters), and (6) documentation of noise levels acquired using international helicopter noise certification test procedures.

  18. Subsampling phase retrieval for rapid thermal measurements of heated microstructures.

    PubMed

    Taylor, Lucas N; Talghader, Joseph J

    2016-07-15

    A subsampling technique for real-time phase retrieval of high-speed thermal signals is demonstrated with heated metal lines such as those found in microelectronic interconnects. The thermal signals were produced by applying a current through aluminum resistors deposited on soda-lime-silica glass, and the resulting refractive index changes were measured using a Mach-Zehnder interferometer with a microscope objective and high-speed camera. The temperatures of the resistors were measured both by the phase-retrieval method and by monitoring the resistance of the aluminum lines. The method used to analyze the phase is at least 60× faster than the state of the art but it maintains a small spatial phase noise of 16 nm, remaining comparable to the state of the art. For slowly varying signals, the system is able to perform absolute phase measurements over time, distinguishing temperature changes as small as 2 K. With angular scanning or structured illumination improvements, the system could also perform fast thermal tomography. PMID:27420492

  19. Subsampling phase retrieval for rapid thermal measurements of heated microstructures.

    PubMed

    Taylor, Lucas N; Talghader, Joseph J

    2016-07-15

    A subsampling technique for real-time phase retrieval of high-speed thermal signals is demonstrated with heated metal lines such as those found in microelectronic interconnects. The thermal signals were produced by applying a current through aluminum resistors deposited on soda-lime-silica glass, and the resulting refractive index changes were measured using a Mach-Zehnder interferometer with a microscope objective and high-speed camera. The temperatures of the resistors were measured both by the phase-retrieval method and by monitoring the resistance of the aluminum lines. The method used to analyze the phase is at least 60× faster than the state of the art but it maintains a small spatial phase noise of 16 nm, remaining comparable to the state of the art. For slowly varying signals, the system is able to perform absolute phase measurements over time, distinguishing temperature changes as small as 2 K. With angular scanning or structured illumination improvements, the system could also perform fast thermal tomography.

  20. Direct Measurement of the Fluid Phase Diagram.

    PubMed

    Bao, Bo; Riordon, Jason; Xu, Yi; Li, Huawei; Sinton, David

    2016-07-19

    The thermodynamic phase of a fluid (liquid, vapor or supercritical) is fundamental to all chemical processes, and the critical point is particularly important for supercritical chemical extraction. Conventional phase measurement methods require hours to obtain a single datum on the pressure and temperature diagram. Here, we present the direct measurement of the full pressure-temperature phase diagram, with 10 000 microwells. Orthogonal, linear, pressure and temperature gradients are obtained with 100 parallel microchannels (spanning the pressure range), each with 100 microwells (spanning the temperature range). The phase-mapping approach is demonstrated with both a pure substance (CO2) and a mixture (95% CO2 + 5% N2). Liquid, vapor, and supercritical regions are clearly differentiated, and the critical pressure is measured at 1.2% error with respect to the NIST standard. This approach provides over 100-fold improvement in measurement speed over conventional methods. PMID:27331613

  1. Phase measurements of EUV mask defects

    DOE PAGES

    Claus, Rene A.; Wang, Yow-Gwo; Wojdyla, Antoine; Benk, Markus P.; Goldberg, Kenneth A.; Neureuther, Andrew R.; Naulleau, Patrick P.; Waller, Laura

    2015-02-22

    Extreme Ultraviolet (EUV) Lithography mask defects were examined on the actinic mask imaging system, SHARP, at Lawrence Berkeley National Laboratory. Also, a quantitative phase retrieval algorithm based on the Weak Object Transfer Function was applied to the measured through-focus aerial images to examine the amplitude and phase of the defects. The accuracy of the algorithm was demonstrated by comparing the results of measurements using a phase contrast zone plate and a standard zone plate. Using partially coherent illumination to measure frequencies that would otherwise fall outside the numerical aperture (NA), it was shown that some defects are smaller than themore » conventional resolution of the microscope. We found that the programmed defects of various sizes were measured and shown to have both an amplitude and a phase component that the algorithm is able to recover.« less

  2. Phase measurements of EUV mask defects

    SciTech Connect

    Claus, Rene A.; Wang, Yow-Gwo; Wojdyla, Antoine; Benk, Markus P.; Goldberg, Kenneth A.; Neureuther, Andrew R.; Naulleau, Patrick P.; Waller, Laura

    2015-02-22

    Extreme Ultraviolet (EUV) Lithography mask defects were examined on the actinic mask imaging system, SHARP, at Lawrence Berkeley National Laboratory. Also, a quantitative phase retrieval algorithm based on the Weak Object Transfer Function was applied to the measured through-focus aerial images to examine the amplitude and phase of the defects. The accuracy of the algorithm was demonstrated by comparing the results of measurements using a phase contrast zone plate and a standard zone plate. Using partially coherent illumination to measure frequencies that would otherwise fall outside the numerical aperture (NA), it was shown that some defects are smaller than the conventional resolution of the microscope. We found that the programmed defects of various sizes were measured and shown to have both an amplitude and a phase component that the algorithm is able to recover.

  3. SEMICONDUCTOR INTEGRATED CIRCUITS: An enhanced close-in phase noise LC-VCO using parasitic V-NPN transistors in a CMOS process

    NASA Astrophysics Data System (ADS)

    Peijun, Gao; J, Oh N.; Hao, Min

    2009-08-01

    A differential LC voltage controlled oscillator (VCO) employing parasitic vertical-NPN (V-NPN) transistors as a negative gm-cell is presented to improve the close-in phase noise. The V-NPN transistors have lower flicker noise compared to MOS transistors. DC and AC characteristics of the V-NPN transistors are measured to facilitate the VCO design. The proposed VCO is implemented in a 0.18 μm CMOS RF/mixed signal process, and the measurement results show the close-in phase noise is improved by 3.5-9.1 dB from 100 Hz to 10 kHz offset compared to that of a similar CMOS VCO. The proposed VCO consumes only 0.41 mA from a 1.5 V power supply.

  4. Analysis of VIIRS TEB noise using solar diffuser measurements

    NASA Astrophysics Data System (ADS)

    Choi, Taeyoung; Cao, Changyong; Weng, Fuzhong

    2015-09-01

    The Soumi-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) was launched on October 28th, 2011 and its Sensor Data Record (SDR) product reached maturity status in March of 2014. Although the VIIRS SDR products are declared at the validated maturity level, there remain issues such as residual stripings in some thermal bands along with the scan direction. These horizontal striping issues in the Thermal Emissive Bands (TEB) were reflected in the sea surface temperature (SST) products. The observed striping magnitude can reach to 0.2 K, especially at the band M14 and M15. As an independent source of calibration, the Solar Diffuser (SD) is utilized in this study. The SD is originally designed for the Reflective Solar Band (RSB), however, it is assumed to be thermally stable at the time of SD observation. For each detector, a linear slope is developed by Integrated Calibration and Validation System (ICVS), which is applied on converting digital number (DN) to radiance unit. After the conversion, detector based noise analyses in VIIRS band M15 and M16 are performed on in-scan and scan-by-scan SD responses. Since SD radiance varies within an orbit, the noise calculation must be derived from the neighborhood Allan deviation. The noise derived Allan deviation shows that detector 1 and 2 in band M15 and detector 9 in band M16 have higher noise content compared to other detectors.

  5. Noise analysis in bolometer detector for microwave power measurements.

    PubMed

    Mario, Petrizzelli; Brunetti, Luciano

    2003-01-01

    A study of noise related with a thermal detector used as power standard on the 26.5-40GHz frequency band, is presented. This study starts with electromagnetic and thermal analysis, and is based on a cryogenic resistive thermometer functioning at liquid-He temperatures. In addition, the study fixes the theoretical limit of sensitivity.

  6. The application of wavelet shrinkage denoising to magnetic Barkhausen noise measurements

    SciTech Connect

    Thomas, James

    2014-02-18

    The application of Magnetic Barkhausen Noise (MBN) as a non-destructive method of defect detection has proliferated throughout the manufacturing community. Instrument technology and measurement methodology have matured commensurately as applications have moved from the R and D labs to the fully automated manufacturing environment. These new applications present a new set of challenges including a bevy of error sources. A significant obstacle in many industrial applications is a decrease in signal to noise ratio due to (i) environmental EMI and (II) compromises in sensor design for the purposes of automation. The stochastic nature of MBN presents a challenge to any method of noise reduction. An application of wavelet shrinkage denoising is proposed as a method of decreasing extraneous noise in MBN measurements. The method is tested and yields marked improvement on measurements subject to EMI, grounding noise, and even measurements in ideal conditions.

  7. Ultra-stable, low phase noise dielectric resonator stabilized oscillators for military and commercial systems

    NASA Technical Reports Server (NTRS)

    Mizan, Muhammad; Higgins, Thomas; Sturzebecher, Dana

    1993-01-01

    EPSD has designed, fabricated and tested, ultra-stable, low phase noise microwave dielectric resonator oscillators (DRO's) at S, X, Ku, and K-bands, for potential application to high dynamic range and low radar cross section target detection radar systems. The phase noise and the temperature stability surpass commercially available DROs. Low phase noise signals are critical for CW Doppler radars, at both very close-in and large offset frequencies from the carrier. The oscillators were built without any temperature compensation techniques and exhibited a temperature stability of 25 parts per million (ppm) over an extended temperature range. The oscillators are lightweight, small and low cost compared to BAW & SAW oscillators, and can impact commercial systems such as telecommunications, built-in-test equipment, cellular phone and satellite communications systems. The key to obtaining this performance was a high Q factor resonant structure (RS) and careful circuit design techniques. The high Q RS consists of a dielectric resonator (DR) supported by a low loss spacer inside a metal cavity. The S and the X-band resonant structures demonstrated loaded Q values of 20,300 and 12,700, respectively.

  8. Noise properties of Hilbert transform evaluation

    NASA Astrophysics Data System (ADS)

    Pavliček, Pavel; Svak, Vojtěch

    2015-08-01

    The Hilbert transform is a standard method for the calculation of the envelope and phase of a modulated signal in optical measurement methods. Usually, the intensity of light is converted into an electric signal at a detector. Therefore the actual spatially or temporally sampled signal is always affected by noise. Because the noise values of individual samples are independent, the noise can be considered as white. If the envelope and phase are calculated from the noised signal, they will also be affected by the noise. We calculate the variance and spectral density of both the envelope noise and the phase noise. We determine which parameters influence the variance and spectral density of both the envelope noise and the phase noise. Finally, we determine the influence of the noise on the measurement uncertainty in white-light interferometry and fringe-pattern analysis.

  9. On-road and wind-tunnel measurement of motorcycle helmet noise.

    PubMed

    Kennedy, J; Carley, M; Walker, I; Holt, N

    2013-09-01

    The noise source mechanisms involved in motorcycling include various aerodynamic sources and engine noise. The problem of noise source identification requires extensive data acquisition of a type and level that have not previously been applied. Data acquisition on track and on road are problematic due to rider safety constraints and the portability of appropriate instrumentation. One way to address this problem is the use of data from wind tunnel tests. The validity of these measurements for noise source identification must first be demonstrated. In order to achieve this extensive wind tunnel tests have been conducted and compared with the results from on-track measurements. Sound pressure levels as a function of speed were compared between on track and wind tunnel tests and were found to be comparable. Spectral conditioning techniques were applied to separate engine and wind tunnel noise from aerodynamic noise and showed that the aerodynamic components were equivalent in both cases. The spectral conditioning of on-track data showed that the contribution of engine noise to the overall noise is a function of speed and is more significant than had previously been thought. These procedures form a basis for accurate experimental measurements of motorcycle noise. PMID:23967933

  10. 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.

  11. Phase noise from aircraft motion: Compensation and effect on synthetic aperture radar images

    NASA Technical Reports Server (NTRS)

    Gabriel, Andrew K.; Goldstein, Richard M.

    1986-01-01

    Image degradation of airborne SAR imagery caused by phase errors introduced in the received signal by aircraft motion is discussed. Mechanical motion has a small bandwidth and does not affect the range signal, where the total echo time is typically 60 microsec. However, since the aperture length can be several seconds, the synthesized azimuth signal can have significant errors of which phase noise is the most important. An inertial navigation system can be used to compensate for these errors when processing the images. Calculations to evaluate how much improvement results from compensation are outlined.

  12. Impact of beam deconvolution on noise properties in CMB measurements: Application to Planck LFI

    NASA Astrophysics Data System (ADS)

    Keihänen, E.; Kiiveri, K.; Lindholm, V.; Reinecke, M.; Suur-Uski, A.-S.

    2016-03-01

    We present an analysis of the effects of beam deconvolution on noise properties in CMB measurements. The analysis is built around the artDeco beam deconvolver code. We derive a low-resolution noise covariance matrix that describes the residual noise in deconvolution products, both in harmonic and pixel space. The matrix models the residual correlated noise that remains in time-ordered data after destriping, and the effect of deconvolution on this noise. To validate the results, we generate noise simulations that mimic the data from the Planck LFI instrument. A χ2 test for the full 70 GHz covariance in multipole range ℓ = 0 - 50 yields a mean reduced χ2 of 1.0037. We compare two destriping options, full and independent destriping, when deconvolving subsets of available data. Full destriping leaves substantially less residual noise, but leaves data sets intercorrelated. We also derive a white noise covariance matrix that provides an approximation of the full noise at high multipoles, and study the properties on high-resolution noise in pixel space through simulations.

  13. Ultralow-phase-noise millimetre-wave signal generator assisted with an electro-optics-modulator-based optical frequency comb

    NASA Astrophysics Data System (ADS)

    Ishizawa, A.; Nishikawa, T.; Goto, T.; Hitachi, K.; Sogawa, T.; Gotoh, H.

    2016-05-01

    Low-noise millimetre-wave signals are valuable for digital sampling systems, arbitrary waveform generation for ultra-wideband communications, and coherent radar systems. However, the phase noise of widely used conventional signal generators (SGs) will increase as the millimetre-wave frequency increases. Our goal has been to improve commercially available SGs so that they provide a low-phase-noise millimetre-wave signal with assistance from an electro-optics-modulator-based optical frequency comb (EOM-OFC). Here, we show that the phase noise can be greatly reduced by bridging the vast frequency difference between the gigahertz and terahertz ranges with an EOM-OFC. The EOM-OFC serves as a liaison that magnifies the phase noise of the SG. With the EOM-OFC used as a phase noise “booster” for a millimetre-wave signal, the phase noise of widely used SGs can be reduced at an arbitrary frequency f (6 ≦ f ≦ 72 GHz).

  14. Ultralow-phase-noise millimetre-wave signal generator assisted with an electro-optics-modulator-based optical frequency comb

    PubMed Central

    Ishizawa, A.; Nishikawa, T.; Goto, T.; Hitachi, K.; Sogawa, T.; Gotoh, H.

    2016-01-01

    Low-noise millimetre-wave signals are valuable for digital sampling systems, arbitrary waveform generation for ultra-wideband communications, and coherent radar systems. However, the phase noise of widely used conventional signal generators (SGs) will increase as the millimetre-wave frequency increases. Our goal has been to improve commercially available SGs so that they provide a low-phase-noise millimetre-wave signal with assistance from an electro-optics-modulator-based optical frequency comb (EOM-OFC). Here, we show that the phase noise can be greatly reduced by bridging the vast frequency difference between the gigahertz and terahertz ranges with an EOM-OFC. The EOM-OFC serves as a liaison that magnifies the phase noise of the SG. With the EOM-OFC used as a phase noise “booster” for a millimetre-wave signal, the phase noise of widely used SGs can be reduced at an arbitrary frequency f (6 ≦ f ≦ 72 GHz). PMID:27185040

  15. Ultralow-phase-noise millimetre-wave signal generator assisted with an electro-optics-modulator-based optical frequency comb.

    PubMed

    Ishizawa, A; Nishikawa, T; Goto, T; Hitachi, K; Sogawa, T; Gotoh, H

    2016-01-01

    Low-noise millimetre-wave signals are valuable for digital sampling systems, arbitrary waveform generation for ultra-wideband communications, and coherent radar systems. However, the phase noise of widely used conventional signal generators (SGs) will increase as the millimetre-wave frequency increases. Our goal has been to improve commercially available SGs so that they provide a low-phase-noise millimetre-wave signal with assistance from an electro-optics-modulator-based optical frequency comb (EOM-OFC). Here, we show that the phase noise can be greatly reduced by bridging the vast frequency difference between the gigahertz and terahertz ranges with an EOM-OFC. The EOM-OFC serves as a liaison that magnifies the phase noise of the SG. With the EOM-OFC used as a phase noise "booster" for a millimetre-wave signal, the phase noise of widely used SGs can be reduced at an arbitrary frequency f (6 ≦ f ≦ 72 GHz). PMID:27185040

  16. Interior noise and vibration measurements on operational military helicopters and comparisons with various ride quality criteria

    NASA Technical Reports Server (NTRS)

    Clevenson, S. A.; Leatherwood, J. D.; Hollenbaugh, D. D.

    1983-01-01

    The results of physical measurements of the interior noise and vibration obtained within eight operational military helicopters are presented. The data were extensively analyzed and are presented in the following forms: noise and vibration spectra, overall root-mean-square acceleration levels in three linear axes, peak accelerations at dominant blade passage frequencies, acceleration exceedance data, and overall and ""A'' weighted sound pressure levels. Peak acceleration levels were compared to the ISO 1-hr reduced comfort and fatigue decreased proficiency boundaries and the NASA discomfort criteria. The ""A'' weighted noise levels were compared to the NASA annoyance criteria, and the overall noise spectra were compared to MIL-STD-1294 (""Acoustical Noise Limits in Helicopters''). Specific vibration components at blade passage frequencies for several aircraft exceeded both the ISO reduced comfort boundary and the NASA passenger discomfort criteria. The ""A'' weighted noise levels, corrected for SPH-4 helmet attenuation characteristics, exceeded the NASA annoyance threshold for several aircraft.

  17. Interior noise and vibration measurements on operational military helicopters and comparisons with various ride quality criteria

    NASA Astrophysics Data System (ADS)

    Clevenson, S. A.; Leatherwood, J. D.; Hollenbaugh, D. D.

    1983-08-01

    The results of physical measurements of the interior noise and vibration obtained within eight operational military helicopters are presented. The data were extensively analyzed and are presented in the following forms: noise and vibration spectra, overall root-mean-square acceleration levels in three linear axes, peak accelerations at dominant blade passage frequencies, acceleration exceedance data, and overall and ""A'' weighted sound pressure levels. Peak acceleration levels were compared to the ISO 1-hr reduced comfort and fatigue decreased proficiency boundaries and the NASA discomfort criteria. The ""A'' weighted noise levels were compared to the NASA annoyance criteria, and the overall noise spectra were compared to MIL-STD-1294 (""Acoustical Noise Limits in Helicopters''). Specific vibration components at blade passage frequencies for several aircraft exceeded both the ISO reduced comfort boundary and the NASA passenger discomfort criteria. The ""A'' weighted noise levels, corrected for SPH-4 helmet attenuation characteristics, exceeded the NASA annoyance threshold for several aircraft.

  18. Shape anomaly detection under strong measurement noise: An analytical approach to adaptive thresholding

    NASA Astrophysics Data System (ADS)

    Krasichkov, Alexander S.; Grigoriev, Eugene B.; Bogachev, Mikhail I.; Nifontov, Eugene M.

    2015-10-01

    We suggest an analytical approach to the adaptive thresholding in a shape anomaly detection problem. We find an analytical expression for the distribution of the cosine similarity score between a reference shape and an observational shape hindered by strong measurement noise that depends solely on the noise level and is independent of the particular shape analyzed. The analytical treatment is also confirmed by computer simulations and shows nearly perfect agreement. Using this analytical solution, we suggest an improved shape anomaly detection approach based on adaptive thresholding. We validate the noise robustness of our approach using typical shapes of normal and pathological electrocardiogram cycles hindered by additive white noise. We show explicitly that under high noise levels our approach considerably outperforms the conventional tactic that does not take into account variations in the noise level.

  19. System for automated measurement of full-scale noises and vibrations

    NASA Technical Reports Server (NTRS)

    Lyubashevskiy, G. S.; Tartakovskiy, B. D.; Frishberg, V. E.

    1973-01-01

    On-line devices are described for measuring the electrical spectrum of a signal in the presence of full scale noise and vibrations. The system includes a set of parallel filters with detectors at the filtration channel outlet. A reciprocal spectral density matrix is used to process the information contained in the interacting signals from various noise and vibration sources.

  20. Measuring gene expression noise in early Drosophila embryos: nucleus-to-nucleus variability

    PubMed Central

    Golyandina, Nina E.; Holloway, David M.; Lopes, Francisco J.P.; Spirov, Alexander V.; Spirova, Ekaterina N.; Usevich, Konstantin D.

    2012-01-01

    In recent years the analysis of noise in gene expression has widely attracted the attention of experimentalists and theoreticians. Experimentally, the approaches based on in vivo fluorescent reporters in single cells appear to be straightforward and effective tools for bacteria and yeast. However, transferring these approaches to multicellular organisms presents many methodological problems. Here we describe our approach to measure between-nucleus variability (noise) in the primary morphogenetic gradient of Bicoid (Bcd) in the precellular blastoderm stage of fruit fly (Drosophila) embryos. The approach is based on the comparison of results for fixed immunostained embryos with observations of live embryos carrying fluorescent Bcd (Bcd-GFP). We measure the noise using two-dimensional Singular Spectrum Analysis (2D SSA). We have found that the nucleus-to-nucleus noise in Bcd intensity, both for live (Bcd-GFP) and for fixed immunstained embryos, tends to be signal-independent. In addition, the character of the noise is sensitive to the nuclear masking technique used to extract quantitative intensities. Further, the method of decomposing the raw quantitative expression data into a signal (expression surface) and residual noise affects the character of the residual noise. We find that careful masking of confocal images and use of appropriate computational tools to decompose raw expression data into trend and noise makes it possible to extract and study the biological noise of gene expression. PMID:22723811

  1. Measuring gene expression noise in early Drosophila embryos: nucleus-to-nucleus variability.

    PubMed

    Golyandina, Nina E; Holloway, David M; Lopes, Francisco J P; Spirov, Alexander V; Spirova, Ekaterina N; Usevich, Konstantin D

    2012-01-01

    In recent years the analysis of noise in gene expression has widely attracted the attention of experimentalists and theoreticians. Experimentally, the approaches based on in vivo fluorescent reporters in single cells appear to be straightforward and effective tools for bacteria and yeast. However, transferring these approaches to multicellular organisms presents many methodological problems. Here we describe our approach to measure between-nucleus variability (noise) in the primary morphogenetic gradient of Bicoid (Bcd) in the precellular blastoderm stage of fruit fly (Drosophila) embryos. The approach is based on the comparison of results for fixed immunostained embryos with observations of live embryos carrying fluorescent Bcd (Bcd-GFP). We measure the noise using two-dimensional Singular Spectrum Analysis (2D SSA). We have found that the nucleus-to-nucleus noise in Bcd intensity, both for live (Bcd-GFP) and for fixed immunstained embryos, tends to be signal-independent. In addition, the character of the noise is sensitive to the nuclear masking technique used to extract quantitative intensities. Further, the method of decomposing the raw quantitative expression data into a signal (expression surface) and residual noise affects the character of the residual noise. We find that careful masking of confocal images and use of appropriate computational tools to decompose raw expression data into trend and noise makes it possible to extract and study the biological noise of gene expression.

  2. Measurement and Characterization of Helicopter Noise at Different Altitudes

    NASA Technical Reports Server (NTRS)

    Watts, Michael E.; Greenwood, Eric; Stephenson, James

    2016-01-01

    This paper presents an overview of a flight test campaign performed at different test sites whose altitudes ranged from 0 to 7000 feet above mean sea level (AMSL) between September 2014 and February 2015. The purposes of this campaign were to: investigate the effects of altitude variation on noise generation, investigate the effects of gross weight variation on noise generation, establish the statistical variability in acoustic flight testing of helicopters, and characterize the effects of transient maneuvers on radiated noise for a medium-lift utility helicopter. In addition to describing the test campaign, results of the acoustic effects of altitude variation for the AS350 SD1 and EH-60L aircraft are presented. Large changes in acoustic amplitudes were observed in response to changes in ambient conditions when the helicopter was flown at constant indicated airspeed and gross weight at the three test sites. However, acoustic amplitudes were found to scale with ambient pressure when flight conditions were defined in terms of the non-dimensional parameters, such as the weight coefficient and effective hover tip Mach number.

  3. Laboratory measurements of modal noise on optical fiber

    NASA Astrophysics Data System (ADS)

    Iuzzolino, M.; Sanna, N.; Tozzi, A.; Oliva, E.

    Many scientific instruments are nowadays coupled to the telescope through optical fibers. This is also the case of the current configuration of GIANO, the high resolution near infrared echelle spectrograph installed at the TNG telescope. As experienced and frequent users of the IR optical fiber, the GIANO building team decided to go deep in the characterization of the optical fiber in the IR band, and in particular to understand and analyze the fiber modal noise. This work is also a preparatory study for the future HIRES@E-ELT instrument design. This paper consists in the description of the fiber laboratory tests, and in the explanation of the results. The whole job defines a wider comprehension of the modal noise, and demonstrates the existence of two aspects influencing this noise. The first one, well known in literature, refers to the interferences between the fiber modes at the exit endface of the fiber, and it can be mitigated by mechanical scrambling techniques. The second one, unknown before, is entirely dependent on the way in which light is injected at the entrance of the fiber, and no mitigation have been observed with any classical scrambling technique (e.g. double-scramblers). These considerations apply to both ZBLAN or fused silica optical fiber, and to both circular and octagonal core shape.

  4. Simple-design ultra-low phase noise microwave frequency synthesizers for high-performing Cs and Rb vapor-cell atomic clocks.

    PubMed

    François, B; Calosso, C E; Abdel Hafiz, M; Micalizio, S; Boudot, R

    2015-09-01

    We report on the development and characterization of novel 4.596 GHz and 6.834 GHz microwave frequency synthesizers devoted to be used as local oscillators in high-performance Cs and Rb vapor-cell atomic clocks. The key element of the synthesizers is a custom module that integrates a high spectral purity 100 MHz oven controlled quartz crystal oscillator frequency-multiplied to 1.6 GHz with minor excess noise. Frequency multiplication, division, and mixing stages are then implemented to generate the exact output atomic resonance frequencies. Absolute phase noise performances of the output 4.596 GHz signal are measured to be -109 and -141 dB rad(2)/Hz at 100 Hz and 10 kHz Fourier frequencies, respectively. The phase noise of the 6.834 GHz signal is -105 and -138 dB rad(2)/Hz at 100 Hz and 10 kHz offset frequencies, respectively. The performances of the synthesis chains contribute to the atomic clock short term fractional frequency stability at a level of 3.1 × 10(-14) for the Cs cell clock and 2 × 10(-14) for the Rb clock at 1 s averaging time. This value is comparable with the clock shot noise limit. We describe the residual phase noise measurements of key components and stages to identify the main limitations of the synthesis chains. The residual frequency stability of synthesis chains is measured to be at the 10(-15) level for 1 s integration time. Relevant advantages of the synthesis design, using only commercially available components, are to combine excellent phase noise performances, simple-architecture, low-cost, and to be easily customized for signal output generation at 4.596 GHz or 6.834 GHz for applications to Cs or Rb vapor-cell frequency standards.

  5. Simple-design ultra-low phase noise microwave frequency synthesizers for high-performing Cs and Rb vapor-cell atomic clocks

    SciTech Connect

    François, B.; Calosso, C. E.; Micalizio, S.; Abdel Hafiz, M.; Boudot, R.

    2015-09-15

    We report on the development and characterization of novel 4.596 GHz and 6.834 GHz microwave frequency synthesizers devoted to be used as local oscillators in high-performance Cs and Rb vapor-cell atomic clocks. The key element of the synthesizers is a custom module that integrates a high spectral purity 100 MHz oven controlled quartz crystal oscillator frequency-multiplied to 1.6 GHz with minor excess noise. Frequency multiplication, division, and mixing stages are then implemented to generate the exact output atomic resonance frequencies. Absolute phase noise performances of the output 4.596 GHz signal are measured to be −109 and −141 dB rad{sup 2}/Hz at 100 Hz and 10 kHz Fourier frequencies, respectively. The phase noise of the 6.834 GHz signal is −105 and −138 dB rad{sup 2}/Hz at 100 Hz and 10 kHz offset frequencies, respectively. The performances of the synthesis chains contribute to the atomic clock short term fractional frequency stability at a level of 3.1 × 10{sup −14} for the Cs cell clock and 2 × 10{sup −14} for the Rb clock at 1 s averaging time. This value is comparable with the clock shot noise limit. We describe the residual phase noise measurements of key components and stages to identify the main limitations of the synthesis chains. The residual frequency stability of synthesis chains is measured to be at the 10{sup −15} level for 1 s integration time. Relevant advantages of the synthesis design, using only commercially available components, are to combine excellent phase noise performances, simple-architecture, low-cost, and to be easily customized for signal output generation at 4.596 GHz or 6.834 GHz for applications to Cs or Rb vapor-cell frequency standards.

  6. Simple-design ultra-low phase noise microwave frequency synthesizers for high-performing Cs and Rb vapor-cell atomic clocks.

    PubMed

    François, B; Calosso, C E; Abdel Hafiz, M; Micalizio, S; Boudot, R

    2015-09-01

    We report on the development and characterization of novel 4.596 GHz and 6.834 GHz microwave frequency synthesizers devoted to be used as local oscillators in high-performance Cs and Rb vapor-cell atomic clocks. The key element of the synthesizers is a custom module that integrates a high spectral purity 100 MHz oven controlled quartz crystal oscillator frequency-multiplied to 1.6 GHz with minor excess noise. Frequency multiplication, division, and mixing stages are then implemented to generate the exact output atomic resonance frequencies. Absolute phase noise performances of the output 4.596 GHz signal are measured to be -109 and -141 dB rad(2)/Hz at 100 Hz and 10 kHz Fourier frequencies, respectively. The phase noise of the 6.834 GHz signal is -105 and -138 dB rad(2)/Hz at 100 Hz and 10 kHz offset frequencies, respectively. The performances of the synthesis chains contribute to the atomic clock short term fractional frequency stability at a level of 3.1 × 10(-14) for the Cs cell clock and 2 × 10(-14) for the Rb clock at 1 s averaging time. This value is comparable with the clock shot noise limit. We describe the residual phase noise measurements of key components and stages to identify the main limitations of the synthesis chains. The residual frequency stability of synthesis chains is measured to be at the 10(-15) level for 1 s integration time. Relevant advantages of the synthesis design, using only commercially available components, are to combine excellent phase noise performances, simple-architecture, low-cost, and to be easily customized for signal output generation at 4.596 GHz or 6.834 GHz for applications to Cs or Rb vapor-cell frequency standards. PMID:26429467

  7. Measurement Of Trailing Edge Noise using Directional Array and Coherent Output Power Methods

    NASA Technical Reports Server (NTRS)

    Hutcheson, Florence V.; Brooks, Thomas F.

    2002-01-01

    The use of a directional array of microphones for the measurement of trailing edge (TE) noise is described. The capabilities of this method are evaluated via measurements of TE noise from a NACA 63-215 airfoil model and from a cylindrical rod. This TE noise measurement approach is compared to one that is based on the cross spectral analysis of output signals from a pair of microphones (COP method). Advantages and limitations of both methods are examined. It is shown that the microphone array can accurately measures TE noise and captures its two-dimensional characteristic over a large frequency range for any TE configuration as long as noise contamination from extraneous sources is within bounds. The COP method is shown to also accurately measure TE noise but over a more limited frequency range that narrows for increased TE thickness. Finally, the applicability and generality of an airfoil self-noise prediction method was evaluated via comparison to the experimental data obtained using the COP and array measurement methods. The predicted and experimental results are shown to agree over large frequency ranges.

  8. Auditory brainstem measures predict reading and speech-in-noise perception in school-aged children.

    PubMed

    Hornickel, Jane; Chandrasekaran, Bharath; Zecker, Steve; Kraus, Nina

    2011-01-20

    Reading and speech-in-noise perception, fundamental aspects of human communication, have been linked to neural indices of auditory brainstem function. However, how these factors interact is currently unclear. Multivariate analysis methods (structural equation modeling) were employed to delineate and quantify the relationships among factors that relate to successful reading and speech in noise perception in children. Neural measures of subcortical speech encoding that reflect the utilization of stimulus regularities, differentiation of stop consonants, and robustness of neural synchrony predicted 73% of the variance in reading scores. A different combination of neural measures, specifically, utilization of stimulus regularities, strength of encoding of lower harmonics, and the extent of noise-induced timing delays uniquely predicted 56% of the variance in speech-in-noise perception measures. The neural measures relating to reading and speech-in-noise perception were substantially non-overlapping and resulted in poor fitting models when substituted for each other, thereby suggesting distinct neural signatures for the two skills. When phonological processing and working memory measures were added to the models, brainstem measures still uniquely predicted variance in reading ability and speech-in-noise perception, highlighting the robustness of the relationship between subcortical auditory function and these skills. The current study suggests that objective neural markers may prove valuable in the assessment of reading or speech-in-noise abilities in children.

  9. Spectral Discrete Probability Density Function of Measured Wind Turbine Noise in the Far Field

    PubMed Central

    Ashtiani, Payam; Denison, Adelaide

    2015-01-01

    Of interest is the spectral character of wind turbine noise at typical residential set-back distances. In this paper, a spectral statistical analysis has been applied to immission measurements conducted at three locations. This method provides discrete probability density functions for the Turbine ONLY component of the measured noise. This analysis is completed for one-third octave sound levels, at integer wind speeds, and is compared to existing metrics for measuring acoustic comfort as well as previous discussions on low-frequency noise sources. PMID:25905097

  10. Spectral discrete probability density function of measured wind turbine noise in the far field.

    PubMed

    Ashtiani, Payam; Denison, Adelaide

    2015-01-01

    Of interest is the spectral character of wind turbine noise at typical residential set-back distances. In this paper, a spectral statistical analysis has been applied to immission measurements conducted at three locations. This method provides discrete probability density functions for the Turbine ONLY component of the measured noise. This analysis is completed for one-third octave sound levels, at integer wind speeds, and is compared to existing metrics for measuring acoustic comfort as well as previous discussions on low-frequency noise sources.

  11. Application of an acoustic noise removal method to aircraft-based atmospheric temperature measurements

    NASA Astrophysics Data System (ADS)

    Hugo, Ronald J.; Nowlin, Scott R.; Hahn, Ila L.; Eaton, Frank D.; McCrae, Kim A.

    2003-01-01

    An acoustic noise removal method is used to reject engine acoustical disturbances from aircraft-based atmospheric temperature measurements. Removal of engine noise from atmospheric temperature measurements allows a larger wave number range to be fit while quantifying the magnitude of atmospheric temperature turbulence. The larger wave number range was found to result in a more statistically certain spectral slope estimate, with up to a 50% reduction in the standard deviation of measured spectral slopes. The noise removal technique was found to break down under conditions of weak atmospheric temperature turbulence where the engine acoustical disturbance can be several orders of magnitude larger than atmospheric temperature turbulence.

  12. Spectral discrete probability density function of measured wind turbine noise in the far field.

    PubMed

    Ashtiani, Payam; Denison, Adelaide

    2015-01-01

    Of interest is the spectral character of wind turbine noise at typical residential set-back distances. In this paper, a spectral statistical analysis has been applied to immission measurements conducted at three locations. This method provides discrete probability density functions for the Turbine ONLY component of the measured noise. This analysis is completed for one-third octave sound levels, at integer wind speeds, and is compared to existing metrics for measuring acoustic comfort as well as previous discussions on low-frequency noise sources. PMID:25905097

  13. Pilot study of methods and equipment for in-home noise level measurements

    PubMed Central

    Neitzel, Richard L.; Heikkinen, Maire S.A.; Williams, Christopher C.; Viet, Susan Marie; Dellarco, Michael

    2015-01-01

    Knowledge of the auditory and non-auditory effects of noise has increased dramatically over the past decade, but indoor noise exposure measurement methods have not advanced appreciably, despite the introduction of applicable new technologies. This study evaluated various conventional and smart devices for exposure assessment in the National Children's Study. Three devices were tested: a sound level meter (SLM), a dosimeter, and a smart device with a noise measurement application installed. Instrument performance was evaluated in a series of semi-controlled tests in office environments over 96-hour periods, followed by measurements made continuously in two rooms (a child's bedroom and a most used room) in nine participating homes over a 7-day period with subsequent computation of a range of noise metrics. The SLMs and dosimeters yielded similar A-weighted average noise levels. Levels measured by the smart devices often differed substantially (showing both positive and negative bias, depending on the metric) from those measured via SLM and dosimeter, and demonstrated attenuation in some frequency bands in spectral analysis compared to SLM results. Virtually all measurements exceeded the Environmental Protection Agency's 45 dBA day-night limit for indoor residential exposures. The measurement protocol developed here can be employed in homes, demonstrates the possibility of measuring long-term noise exposures in homes with technologies beyond traditional SLMs, and highlights potential pitfalls associated with measurements made by smart devices. PMID:27053775

  14. Phase transition phenomenon: A compound measure analysis

    NASA Astrophysics Data System (ADS)

    Kang, Bo Soo; Park, Chanhi; Ryu, Doojin; Song, Wonho

    2015-06-01

    This study investigates the well-documented phenomenon of phase transition in financial markets using combined information from both return and volume changes within short time intervals. We suggest a new measure for the phase transition behaviour of markets, calculated as a return distribution conditional on local variance in volume imbalance, and show that this measure successfully captures phase transition behaviour under various conditions. We analyse the intraday trade and quote dataset from the KOSPI 200 index futures, which includes detailed information on the original order size and the type of each initiating investor. We find that among these two competing factors, the submitted order size yields more explanatory power on the phenomenon of market phase transition than the investor type.

  15. Hybrid wide-band, low-phase-noise scheme for Raman lasers in atom interferometry by integrating an acousto-optic modulator and a feedback loop.

    PubMed

    Wang, Kai; Yao, Zhanwei; Li, Runbing; Lu, Sibin; Chen, Xi; Wang, Jin; Zhan, Mingsheng

    2016-02-10

    We report a hybrid scheme for phase-coherent Raman lasers with low phase noise in a wide frequency range. In this scheme, a pair of Raman lasers with a frequency difference of 3.04 GHz is generated by the ±1-order diffracted lights of an acousto-optic modulator (1.52 GHz), where a feedback loop is simultaneously applied for suppressing the phase noise. The beat width of the Raman lasers is narrower than 3 Hz. In the low-frequency range, the phase noise of the Raman lasers is suppressed by 35 dB with the feedback. The phase noise is less than -109  dBc/Hz in the high-frequency range. The sensitivity of an atom gyroscope employing the hybrid Raman lasers can be implicitly improved 10 times. Due to the better high-frequency response, the sensitivity is not limited by the durations of Raman pulses. This work is important for improving the performance of atom-interferometer-based measurements. PMID:26906364

  16. Noise-induced absorbing phase transition in a model of opinion formation

    NASA Astrophysics Data System (ADS)

    Vieira, Allan R.; Crokidakis, Nuno

    2016-08-01

    In this work we study a 3-state (+1, -1, 0) opinion model in the presence of noise and disorder. We consider pairwise competitive interactions, with a fraction p of those interactions being negative (disorder). Moreover, there is a noise q that represents the probability of an individual spontaneously change his opinion to the neutral state. Our aim is to study how the increase/decrease of the fraction of neutral agents affects the critical behavior of the system and the evolution of opinions. We derive analytical expressions for the order parameter of the model, as well as for the stationary fraction of each opinion, and we show that there are distinct phase transitions. One is the usual ferro-paramagnetic transition, that is in the Ising universality class. In addition, there are para-absorbing and ferro-absorbing transitions, presenting the directed percolation universality class. Our results are complemented by numerical simulations.

  17. Analysis of SNR penalty in Brillouin optical time-domain analysis sensors induced by laser source phase noise

    NASA Astrophysics Data System (ADS)

    Minardo, A.; Bernini, R.; Zeni, L.

    2016-02-01

    In this paper, we analyze numerically the effect of phase noise from the laser in Brillouin optical time-domain analysis (BOTDA) sensors. Due to laser phase noise, the phase shift between pump and probe beams is a stochastic variable with zero mean and variance changing with the position along the fiber. The numerical results, carried out for various fiber lengths and pump pulse durations, show that laser phase noise induces a reduction of the average Brillouin gain, as well as an increase of the overall system noise. Preliminary experimental results, carried out by use of a conventional BOTDA system and two DFB diode lasers having different linewidth (63 and 900 kHz), support the numerical analysis.

  18. Measurement and analysis of a microwave oscillator stabilized by a sapphire dielectric ring resonator for ultra-low noise.

    PubMed

    Dick, G J; Saunders, J

    1990-01-01

    Phase-noise measurements are presented for a microwave oscillator whose frequency is stabilized by a whispering gallery mode sapphire ring resonator with Q of 2x10(5). The nature of the mode, which involves little metallic conduction, allows nearly full use of the very low dielectric loss in sapphire. Several mode families have been identified with good agreement with calculated frequency predictions. Waveguide coupling parameters have been characterized for the principal (lowest frequency) mode family, for n=5 to n =10 full waves around the perimeter. For a 5-cm wheel resonator in a 7.6-cm container, Q-values of above 10(5) were found at room temperature for all of the modes in this sequence. Coupling Q-values for the same modes ranged from 10(4) (n =5) to 10(5) (n=10) for a WR112 waveguide port at the center of the cylinder wall of the containing can. Phase noise measurements for a transistor oscillator locked to the n=10 (7.84-GHz) mode showed a 1/f(3) dependence for low offset frequencies, and a value of L(f)=-55 dB/Hz at an offset of 10 Hz from the carrier. The oscillator shows phase noise below the previously reported for any X-band source. PMID:18285050

  19. Low-dose, phase-contrast mammography with high signal-to-noise ratio

    PubMed Central

    Gromann, Lukas B.; Bequé, Dirk; Scherer, Kai; Willer, Konstantin; Birnbacher, Lorenz; Willner, Marian; Herzen, Julia; Grandl, Susanne; Hellerhoff, Karin; Sperl, Jonathan I.; Pfeiffer, Franz; Cozzini, Cristina

    2016-01-01

    Differential phase-contrast X-ray imaging using a Talbot-Lau interferometer has recently shown promising results for applications in medical imaging. However, reducing the applied radiation dose remains a major challenge. In this study, we consider the realization of a Talbot-Lau interferometer in a high Talbot order to increase the signal-to-noise ratio for low-dose applications. The quantitative performance of π and π/2 systems at high Talbot orders is analyzed through simulations, and the design energy and X-ray spectrum are optimized for mammography. It is found that operation even at very high Talbot orders is feasible and beneficial for image quality. As long as the X-ray spectrum is matched to the visibility spectrum, the SNR continuously increases with the Talbot order for π-systems. We find that the optimal X-ray spectra and design energies are almost independent of the Talbot order and that the overall imaging performance is robust against small variations in these parameters. Discontinuous spectra, such as that from molybdenum, are less robust because the characteristic lines may coincide with minima in the visibility spectra; however, they may offer slightly better performance. We verify this hypothesis by realizing a prototype system with a mean fringe visibility of above 40% at the seventh Talbot order. With this prototype, a proof-of-principle measurement of a freshly dissected breast at reasonable compression to 4 cm is conducted with a mean glandular dose of only 3 mGy but with a high SNR. PMID:26977347

  20. Optical Measurement Methods Of Disk Brake Noise Generation

    NASA Astrophysics Data System (ADS)

    Fagan, W. F.; Abendroth, H.

    1986-07-01

    A description is given of how the technique of image derotation is applied to the study of low frequency noise generation of disk brakes. Infra-red imaging is combined with derotation to show the heat emission distribution on the rotor surface during a braking cycle. A series of regularly spaced hot spots are observed on the rotor's surface only when juddering-type, low frequency vibrations are present. This relationship will be discussed and future areas of research will be outlined including the use of laser doppler velocimetry and Electronic Speckle Pattern Interferometry (ESPI)/T.V. Holography techniques to study this phenomena.

  1. Measurements of Operational Wind Turbine Noise in UK Waters.

    PubMed

    Cheesman, Samuel

    2016-01-01

    The effects of wind farm operational noise have not been addressed to the same extent as their construction methods such as piling and drilling of the foundations despite their long operational lifetimes compared with weeks of construction. The results of five postconstruction underwater sound-monitoring surveys on wind farms located throughout the waters of the British Isles are discussed. These wind farms consist of differing turbine power outputs, from 3 to 3.6 MW, and differing numbers of turbines. This work presents an overview of the results obtained and discusses both the levels and frequency components of the sound in several metrics.

  2. Measurements of Operational Wind Turbine Noise in UK Waters.

    PubMed

    Cheesman, Samuel

    2016-01-01

    The effects of wind farm operational noise have not been addressed to the same extent as their construction methods such as piling and drilling of the foundations despite their long operational lifetimes compared with weeks of construction. The results of five postconstruction underwater sound-monitoring surveys on wind farms located throughout the waters of the British Isles are discussed. These wind farms consist of differing turbine power outputs, from 3 to 3.6 MW, and differing numbers of turbines. This work presents an overview of the results obtained and discusses both the levels and frequency components of the sound in several metrics. PMID:26610955

  3. Comparison of Predicted and Measured Attenuation of Turbine Noise from a Static Engine Test

    NASA Technical Reports Server (NTRS)

    Chien, Eugene W.; Ruiz, Marta; Yu, Jia; Morin, Bruce L.; Cicon, Dennis; Schwieger, Paul S.; Nark, Douglas M.

    2007-01-01

    Aircraft noise has become an increasing concern for commercial airlines. Worldwide demand for quieter aircraft is increasing, making the prediction of engine noise suppression one of the most important fields of research. The Low-Pressure Turbine (LPT) can be an important noise source during the approach condition for commercial aircraft. The National Aeronautics and Space Administration (NASA), Pratt & Whitney (P&W), and Goodrich Aerostructures (Goodrich) conducted a joint program to validate a method for predicting turbine noise attenuation. The method includes noise-source estimation, acoustic treatment impedance prediction, and in-duct noise propagation analysis. Two noise propagation prediction codes, Eversman Finite Element Method (FEM) code [1] and the CDUCT-LaRC [2] code, were used in this study to compare the predicted and the measured turbine noise attenuation from a static engine test. In this paper, the test setup, test configurations and test results are detailed in Section II. A description of the input parameters, including estimated noise modal content (in terms of acoustic potential), and acoustic treatment impedance values are provided in Section III. The prediction-to-test correlation study results are illustrated and discussed in Section IV and V for the FEM and the CDUCT-LaRC codes, respectively, and a summary of the results is presented in Section VI.

  4. Signal processing considerations for low signal to noise ratio laser Doppler and phase Doppler signals

    NASA Technical Reports Server (NTRS)

    Ibrahim, K. M.; Wertheimer, G. D.; Bachalo, William D.

    1991-01-01

    The relative performance of current methods used for estimating the phase and the frequency in LDV and phase Doppler applications in low signal to noise ratio conditions is analyzed. These methods include the Fourier analysis and the correlation techniques. Three methods that use the correlation function for frequency and phase estimations are evaluated in terms of accuracy and speed of processing. These methods include: (1) the frequency estimation using zero crossings counting of the auto-correlation function, (2) the Blackman-Tukey method, and (3) the AutoRegressive method (AR). The relative performance of these methods is evaluated and compared with the Fourier analysis method which provides the optimum performance in terms of the Maximum Likelihood (ML) criteria.

  5. Stacked phased array coils for increasing the signal-to-noise ratio in magnetic resonance imaging.

    PubMed

    Dandan Liang; Hon Tat Hui; Tat Soon Yeo; Bing Keong Li

    2013-02-01

    A new concept of using a stacked phased coil array to increase the signal-to-circuit noise ratio (SCNR) in magnetic resonance imaging (MRI) is introduced. Unlike conventional phased coil arrays, the proposed stacked phased coil array is constructed by stacking the coil elements closely together in the vertical direction. Through a proper combination of the coil terminal voltages, the SCNR is shown to increase with the square root of the number of coil elements. A prototype two-element array is constructed and an experimental method is designed to determine the combiner coefficients in a simulated MRI electromagnetic field environment. The experimental results show that the mutual coupling effect among the array coils can be totally removed and the combiner output voltage increases with the number of coil elements. This demonstrates the feasibility of the proposed method.

  6. Microphone Handling Noise: Measurements of Perceptual Threshold and Effects on Audio Quality

    PubMed Central

    Kendrick, Paul; Jackson, Iain R.; Fazenda, Bruno M.; Cox, Trevor J.; Li, Francis F.

    2015-01-01

    A psychoacoustic experiment was carried out to test the effects of microphone handling noise on perceived audio quality. Handling noise is a problem affecting both amateurs using their smartphones and cameras, as well as professionals using separate microphones and digital recorders. The noises used for the tests were measured from a variety of devices, including smartphones, laptops and handheld microphones. The signal features that characterise these noises are analysed and presented. The sounds include various types of transient, impact noises created by tapping or knocking devices, as well as more sustained sounds caused by rubbing. During the perceptual tests, listeners auditioned speech podcasts and were asked to rate the degradation of any unwanted sounds they heard. A representative design test methodology was developed that tried to encourage everyday rather than analytical listening. Signal-to-noise ratio (SNR) of the handling noise events was shown to be the best predictor of quality degradation. Other factors such as noise type or background noise in the listening environment did not significantly affect quality ratings. Podcast, microphone type and reproduction equipment were found to be significant but only to a small extent. A model allowing the prediction of degradation from the SNR is presented. The SNR threshold at which 50% of subjects noticed handling noise was found to be 4.2 ± 0.6 dBA. The results from this work are important for the understanding of our perception of impact sound and resonant noises in recordings, and will inform the future development of an automated predictor of quality for handling noise. PMID:26473498

  7. Microphone Handling Noise: Measurements of Perceptual Threshold and Effects on Audio Quality.

    PubMed

    Kendrick, Paul; Jackson, Iain R; Fazenda, Bruno M; Cox, Trevor J; Li, Francis F

    2015-01-01

    A psychoacoustic experiment was carried out to test the effects of microphone handling noise on perceived audio quality. Handling noise is a problem affecting both amateurs using their smartphones and cameras, as well as professionals using separate microphones and digital recorders. The noises used for the tests were measured from a variety of devices, including smartphones, laptops and handheld microphones. The signal features that characterise these noises are analysed and presented. The sounds include various types of transient, impact noises created by tapping or knocking devices, as well as more sustained sounds caused by rubbing. During the perceptual tests, listeners auditioned speech podcasts and were asked to rate the degradation of any unwanted sounds they heard. A representative design test methodology was developed that tried to encourage everyday rather than analytical listening. Signal-to-noise ratio (SNR) of the handling noise events was shown to be the best predictor of quality degradation. Other factors such as noise type or background noise in the listening environment did not significantly affect quality ratings. Podcast, microphone type and reproduction equipment were found to be significant but only to a small extent. A model allowing the prediction of degradation from the SNR is presented. The SNR threshold at which 50% of subjects noticed handling noise was found to be 4.2 ± 0.6 dBA. The results from this work are important for the understanding of our perception of impact sound and resonant noises in recordings, and will inform the future development of an automated predictor of quality for handling noise. PMID:26473498

  8. Optimization of phase-variation measurements in low-coherence methods: implications for OCE

    NASA Astrophysics Data System (ADS)

    Zaitsev, Vladimir Y.; Matveyev, Alexandr L.; Matveev, Lev A.; Gelikonov, Grigory V.; Sovetsky, Alexander A.; Vitkin, Alex

    2016-04-01

    Phase-resolved measurements found numerous applications in low-coherence methods, in particular in OCT-based compressional elastography, where phase-variation gradients are used for estimating strains produced by the OCT probe pressed onto the tissue. Conventionally, for the reference and deformed pixelated OCT scans, one performs comparison of phases taken from pixels with the same coordinates. This is reasonable in regions of sufficiently small sub-pixel displacements, for which the so-compared pixels contain the same scatterers. Furthermore, to avoid error-prone multiple phase unwrapping for reconstructing displacements, one have to ensure even smaller sub-wavelength displacements. This limits the allowable strains to less than ~10-4-10-3, although such weak phase gradients can be strongly corrupted by measurement noises. Here, we discuss how creation of an order of magnitude greater strains can be used for increasing the signal-to noise ratio in estimating phase gradients by obviating the phase-unwrapping procedures and reducing the influence of decorrelation noise for supra-pixel displacements. This optimized phase-variation measurement makes it possible to perform strain mapping in optical coherence elastography with exceptionally high tolerance to noises due to possibility of using significantly increased strains. We also discuss the effect of "frozen-phase zones" associated with displaced strong scatterers. This effect can result in appearance of artifacts in the form of false stiff inclusions in elastograms in the vicinity of bright scatterers in OCT scans. We present analytical arguments, numerical simulations and experimental examples illustrating the above-mentioned features of the "frozen-phase" effect and advantages of using the proposed optimized phase-variation measurement with pixel-scale displacement compensation in the compared OCT scans.

  9. Numerical phase retrieval from beam intensity measurements in three planes

    NASA Astrophysics Data System (ADS)

    Bruel, Laurent

    2003-05-01

    A system and method have been developed at CEA to retrieve phase information from multiple intensity measurements along a laser beam. The device has been patented. Commonly used devices for beam measurement provide phase and intensity information separately or with a rather poor resolution whereas the MIROMA method provides both at the same time, allowing direct use of the results in numerical models. Usual phase retrieval algorithms use two intensity measurements, typically the image plane and the focal plane (Gerschberg-Saxton algorithm) related by a Fourier transform, or the image plane and a lightly defocus plane (D.L. Misell). The principal drawback of such iterative algorithms is their inability to provide unambiguous convergence in all situations. The algorithms can stagnate on bad solutions and the error between measured and calculated intensities remains unacceptable. If three planes rather than two are used, the data redundancy created confers to the method good convergence capability and noise immunity. It provides an excellent agreement between intensity determined from the retrieved phase data set in the image plane and intensity measurements in any diffraction plane. The method employed for MIROMA is inspired from GS algorithm, replacing Fourier transforms by a beam-propagating kernel with gradient search accelerating techniques and special care for phase branch cuts. A fast one dimensional algorithm provides an initial guess for the iterative algorithm. Applications of the algorithm on synthetic data find out the best reconstruction planes that have to be chosen. Robustness and sensibility are evaluated. Results on collimated and distorted laser beams are presented.

  10. Third phase of HIV decay measured.

    PubMed

    Bartnof, H S

    1997-09-01

    The concept of viral eradication has been seriously discussed since the advent of protease inhibitor therapy. Understanding the reservoirs of HIV in the body and the phases of replication and decay have been the subjects of ongoing research. A hypothetical third phase of HIV decay was recently measured at Johns Hopkins, and the half-life of HIV was estimated at 5.7 months. This measurement, based on CD4 cells, may be used to manage total treatment time until viral eradication. The estimated times will likely only be valid for those who started anti-HIV treatments soon after infection.

  11. Signal to Noise Ratios of Pulsed and Sinewave Modulated Direct Detection Lidar for IPDA Measurements

    NASA Technical Reports Server (NTRS)

    Sun, Xiaoli; Abshire, James B.

    2011-01-01

    The signal-to-noise ratios have been derived for IPDA lidar using a direct detection receiver for both pulsed and sinewave laser modulation techniques, and the results and laboratory measurements are presented

  12. A 220-1100 MHz low phase-noise frequency synthesizer with wide-band VCO and selectable I/Q divider

    NASA Astrophysics Data System (ADS)

    Hua, Chen; Renjie, Gong; Xu, Cheng; Yulin, Zhang; Zhong, Gao; Guiliang, Guo; Yuepeng, Yan

    2014-12-01

    This paper presents a low phase-noise fractional-N frequency synthesizer which provides an in-phase/quadrature-phase (I/Q) signal over a frequency range of 220-1100 MHz for wireless networks of industrial automation (WIA) applications. Two techniques are proposed to achieve the wide range. First, a 1.4-2.2 GHz ultralow gain voltage-controlled oscillator (VCO) is adopted by using 128 tuning curves. Second, a selectable I/Q divider is employed to divide the VCO frequency by 2 or 3 or 4 or 6. Besides, a phase-switching prescaler is proposed to lower PLL phase noise, a self-calibrated charge pump is used to suppress spur, and a detect-boosting phase frequency detector is adopted to shorten settling time. With a 200 kHz loop bandwidth, lowest measured phase noise is -106 dBc/Hz at a 10 kHz offset and -131 dBc/Hz at a 1 MHz offset. Fabricated in the TSMC 0.18 μm CMOS process, the synthesizer occupies a chip area of 1.2 mm2, consumes only 15 mW from the 1.8 V power supply, and settles within 13.2 μs. The synthesizer is optimized for the WIA applications, but can also be used for other short-range wireless communications, such as 433, 868, 916 MHz ISM band applications.

  13. Method to Measure Total Noise Temperature of a Wireless Receiver During Operation

    NASA Technical Reports Server (NTRS)

    Young, Lawrence E.; Esterhuizen, Stephan; Turbiner, Dmitry

    2013-01-01

    A method has been developed to measure the total effective noise power in a GPS receiver, including contributions from the system temperature, the antenna temperature, interference, lossy components, etc. A known level of noise is periodically injected before the preamplifier during normal tracking, with a switch set to a very low duty cycle, so that there is insignificant signal loss for the GPS signals being tracked. Alternately, a signal of known power may be injected. The coupling port is fed with a switch that can be controlled from the receiver s digital processing section. The switch can connect the coupling port to a noise or signal source at a known power level. The combined system noise is measured, and nearly continuous noise calibrations are made. The effect from injected noise/signals on the performance of the GPS receiver can be less than 0.01 dB of SNR loss. Minimal additional components are required. The GPS receiver is used to measure the SNRs required to solve for the noise level. Because this measurement is referenced to the preamplifier input, it is insensitive to variations in the receiver gain.

  14. Phased-Array Measurements of Single Flow Hot Jets

    NASA Technical Reports Server (NTRS)

    Bridges, James; Lee, Sang Soo

    2005-01-01

    A 16 microphone phased-array system has been successfully applied to measure jet noise source distributions. In this study, a round convergent nozzle was tested at various hot and cold flow conditions: acoustic Mach numbers are between 0.35 and 1.6 and static temperature ratios are varied from cold to 2.7. The classical beamforming method was applied on narrowband frequencies. From the measured source distributions locations of peak strength were tracked and found to be very consistent between adjacent narrowband frequencies. In low speed heated and unheated jets, the peak source locations vary smoothly from the nozzle exit to downstream as the frequency is decreased. When the static temperature ratio was kept constant, the peak source position moved downstream with increasing acoustic Mach number for the Strouhal numbers smaller than about 1.5. It was also noted that the peak source locations of low frequencies occur farther downstream than the end of potential core.

  15. Nonlinear interpolation of space-time phase fluctuations of a signal received together with noise

    NASA Astrophysics Data System (ADS)

    Shmelev, A. B.

    An analysis is presented of the optimal space-time interpolation of the field of phase fluctuations of a quasi-harmonic signal observed on a background of white Gaussian noise. The method used involves the generalization to random fields of the equations of the Gaussian approximation describing the combined nonlinear filtering and interpolation of Markov processes. Equations describing the algorithm of space-time processing are obtained, and the rms estimation error is calculated in the case when the spatial fluctuations are caused by wave propagation in the turbulent atmosphere.

  16. Low-phase-noise, single-frequency, single-mode 608 W thulium fiber amplifier.

    PubMed

    Goodno, Gregory D; Book, Lewis D; Rothenberg, Joshua E

    2009-04-15

    A chain of four Tm-doped fibers amplified a single-frequency, 2040 nm diode laser to 608 W with M(2)=1.05+/-0.03, limited by available pump power. Stimulated Brillouin scattering limits were investigated by splicing different lengths of passive fiber to the output of the final amplifier stage. Integrated rms phase noise above 1 kHz was less than lambda/30, suggesting the possibility of further scaling via coherent beam combining. To our knowledge, this is the highest power obtained from any single-frequency, single-mode fiber laser.

  17. Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers

    SciTech Connect

    Hashisaka, Masayuki Ota, Tomoaki; Yamagishi, Masakazu; Fujisawa, Toshimasa; Muraki, Koji

    2014-05-15

    We report a cross-correlation measurement system, based on a new approach, which can be used to measure shot noise in a mesoscopic conductor at milliKelvin temperatures. In contrast to other measurement systems in which high-speed low-noise voltage amplifiers are commonly used, our system employs homemade transimpedance amplifiers (TAs). The low input impedance of the TAs significantly reduces the crosstalk caused by unavoidable parasitic capacitance between wires. The TAs are designed to have a flat gain over a frequency band from 2 kHz to 1 MHz. Low-noise performance is attained by installing the TAs at a 4 K stage of a dilution refrigerator. Our system thus fulfills the technical requirements for cross-correlation measurements: low noise floor, high frequency band, and negligible crosstalk between two signal lines. Using our system, shot noise generated at a quantum point contact embedded in a quantum Hall system is measured. The good agreement between the obtained shot-noise data and theoretical predictions demonstrates the accuracy of the measurements.

  18. Phase-sensitive correlation optical time-domain reflectometer using quantum phase noise of laser light.

    PubMed

    Arias, A; Shlyagin, M G; Miridonov, S V; Manuel, Rodolfo Martinez

    2015-11-16

    We propose and experimentally demonstrate a simple approach to realize a phase-sensitive correlation optical time-domain reflectometer (OTDR) suitable for detection and localization of dynamic perturbations along a single-mode optical fiber. It is based on the quantum phase fluctuations of a coherent light emitted by a telecom DFB diode laser. Truly random probe signals are generated by an interferometer with the optical path difference exceeding the coherence length of the laser light. Speckle-like OTDR traces were obtained by calculating cross-correlation functions between the probe light and the light intensity signals returned back from the sensing fiber. Perturbations are detected and localized by monitoring time variations of correlation amplitude along the fiber length. Results of proof-of-concept experimental testing are presented using an array of ultra-low-reflectivity fiber Bragg gratings as weak reflectors. PMID:26698514

  19. 40 CFR 201.25 - Measurement location and weather conditions for measurement on receiving property of the noise of...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 24 2010-07-01 2010-07-01 false Measurement location and weather conditions for measurement on receiving property of the noise of retarders, car coupling, locomotive load... EQUIPMENT; INTERSTATE RAIL CARRIERS Measurement Criteria § 201.25 Measurement location and...

  20. 40 CFR 201.25 - Measurement location and weather conditions for measurement on receiving property of the noise of...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 25 2014-07-01 2014-07-01 false Measurement location and weather conditions for measurement on receiving property of the noise of retarders, car coupling, locomotive load... EQUIPMENT; INTERSTATE RAIL CARRIERS Measurement Criteria § 201.25 Measurement location and...

  1. 40 CFR 201.25 - Measurement location and weather conditions for measurement on receiving property of the noise of...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 26 2013-07-01 2013-07-01 false Measurement location and weather conditions for measurement on receiving property of the noise of retarders, car coupling, locomotive load... EQUIPMENT; INTERSTATE RAIL CARRIERS Measurement Criteria § 201.25 Measurement location and...

  2. 40 CFR 201.25 - Measurement location and weather conditions for measurement on receiving property of the noise of...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 25 2011-07-01 2011-07-01 false Measurement location and weather conditions for measurement on receiving property of the noise of retarders, car coupling, locomotive load... EQUIPMENT; INTERSTATE RAIL CARRIERS Measurement Criteria § 201.25 Measurement location and...

  3. 40 CFR 201.25 - Measurement location and weather conditions for measurement on receiving property of the noise of...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 26 2012-07-01 2011-07-01 true Measurement location and weather conditions for measurement on receiving property of the noise of retarders, car coupling, locomotive load... EQUIPMENT; INTERSTATE RAIL CARRIERS Measurement Criteria § 201.25 Measurement location and...

  4. Noise measurement flight test: Data-analyses Aerospatiale SA-365N Dauphin 2 helicopter

    NASA Astrophysics Data System (ADS)

    Newman, J. S.; Rickely, E. J.; Daboin, S. A.; Beattie, K. R.

    1984-04-01

    This report documents the results of a Federal Aviation Administration (FAA) noise measurement flight test program with the Dauphin twin-jet helicopter. The report contains documentary sections describing the acoustical characteristics of the subject helicopter and provides analyses and discussions addressing topics ranging from acoustical propagation to environmental impact of helicopter noise. This report is the second in a series of seven documenting the FAA helicopter noise measurement program conducted at Dulles International Airport during the summer of 1983. The Dauphin test program involved the acquisition of detailed acoustical, position and meteorological data. This test program was designed to address a series of objectives including: (1) acquisition of acoustical data for use in assessing heliport environment impact, (2) documentation of directivity characteristics for static operation of helicopters, (3) establishment of ground-to-ground and air-to-ground acoustical propagation relationships for helicopters, (4) determination of noise event duration influences on energy dose acoustical metrics, (5) examination of the differences between noise measured by a surface mounted microphone and a microphone mounted at a height of four feet (1.2 meters), and (6) documentation of noise levels acquired using international helicopter noise certification test procedures.

  5. 1/f noise measurements for faster evaluation of electromigration in advanced microelectronics interconnections

    NASA Astrophysics Data System (ADS)

    Beyne, Sofie; Croes, Kristof; De Wolf, Ingrid; Tőkei, Zsolt

    2016-05-01

    The use of 1/f noise measurements is explored for the purpose of finding faster techniques for electromigration (EM) characterization in advanced microelectronic interconnects, which also enable a better understanding of its underlying physical mechanisms. Three different applications of 1/f noise for EM characterization are explored. First, whether 1/f noise measurements during EM stress can serve as an early indicator of EM damage. Second, whether the current dependence of the noise power spectral density (PSD) can be used for a qualitative comparison of the defect concentration of different interconnects and consequently also their EM lifetime t50. Third, whether the activation energies obtained from the temperature dependence of the 1/f noise PSD correspond to the activation energies found by means of classic EM tests. In this paper, the 1/f noise technique has been used to assess and compare the EM properties of various advanced integration schemes and different materials, as they are being explored by the industry to enable advanced interconnect scaling. More concrete, different types of copper interconnects and one type of tungsten interconnect are compared. The 1/f noise measurements confirm the excellent electromigration properties of tungsten and demonstrate a dependence of the EM failure mechanism on copper grain size and distribution, where grain boundary diffusion is found to be a dominant failure mechanism.

  6. Measurement of SQUID noise levels for SuperCDMS SNOLAB detectors - Final Paper

    SciTech Connect

    Lee, Maxwell

    2015-08-27

    SuperCDMS SNOLAB is a second generation direct dark matter search. In the SuperCDMS SNOLAB experiment, detectors are able to pick up from signals from dark matter nuclear recoil interactions which occur inside the bulk of the detectors. These interactions produce both phonon and charge signals. HEMTs read out charge signals whereas TES are used to detect phonon signals which are then read out by SQUID amplifiers. SQUID amplifiers must add negligible noise to the TES intrinsic noise which has been previously measured and is approximately 50pA/√Hz down to 100Hz for ease of signal distinguishability in dark matter nuclear interactions. The intrinsic noise level of the SQUID was tested in the SLAC 300mK fridge and determined to provide adequately low levels of noise with a floor of approximately 3pA/√Hz. Furthermore, a 10x amplifier was tested for addition of extraneous noise. This noise was investigated with and without this amplifier, and it was found that it did not add a significant amount of noise to the intrinsic SQUID noise.

  7. Evaluation of a Cubature Kalman Filtering-Based Phase Unwrapping Method for Differential Interferograms with High Noise in Coal Mining Areas

    PubMed Central

    Liu, Wanli; Bian, Zhengfu; Liu, Zhenguo; Zhang, Qiuzhao

    2015-01-01

    Differential interferometric synthetic aperture radar has been shown to be effective for monitoring subsidence in coal mining areas. Phase unwrapping can have a dramatic influence on the monitoring result. In this paper, a filtering-based phase unwrapping algorithm in combination with path-following is introduced to unwrap differential interferograms with high noise in mining areas. It can perform simultaneous noise filtering and phase unwrapping so that the pre-filtering steps can be omitted, thus usually retaining more details and improving the detectable deformation. For the method, the nonlinear measurement model of phase unwrapping is processed using a simplified Cubature Kalman filtering, which is an effective and efficient tool used in many nonlinear fields. Three case studies are designed to evaluate the performance of the method. In Case 1, two tests are designed to evaluate the performance of the method under different factors including the number of multi-looks and path-guiding indexes. The result demonstrates that the unwrapped results are sensitive to the number of multi-looks and that the Fisher Distance is the most suitable path-guiding index for our study. Two case studies are then designed to evaluate the feasibility of the proposed phase unwrapping method based on Cubature Kalman filtering. The results indicate that, compared with the popular Minimum Cost Flow method, the Cubature Kalman filtering-based phase unwrapping can achieve promising results without pre-filtering and is an appropriate method for coal mining areas with high noise. PMID:26153776

  8. Evaluation of a Cubature Kalman Filtering-Based Phase Unwrapping Method for Differential Interferograms with High Noise in Coal Mining Areas.

    PubMed

    Liu, Wanli; Bian, Zhengfu; Liu, Zhenguo; Zhang, Qiuzhao

    2015-07-06

    Differential interferometric synthetic aperture radar has been shown to be effective for monitoring subsidence in coal mining areas. Phase unwrapping can have a dramatic influence on the monitoring result. In this paper, a filtering-based phase unwrapping algorithm in combination with path-following is introduced to unwrap differential interferograms with high noise in mining areas. It can perform simultaneous noise filtering and phase unwrapping so that the pre-filtering steps can be omitted, thus usually retaining more details and improving the detectable deformation. For the method, the nonlinear measurement model of phase unwrapping is processed using a simplified Cubature Kalman filtering, which is an effective and efficient tool used in many nonlinear fields. Three case studies are designed to evaluate the performance of the method. In Case 1, two tests are designed to evaluate the performance of the method under different factors including the number of multi-looks and path-guiding indexes. The result demonstrates that the unwrapped results are sensitive to the number of multi-looks and that the Fisher Distance is the most suitable path-guiding index for our study. Two case studies are then designed to evaluate the feasibility of the proposed phase unwrapping method based on Cubature Kalman filtering. The results indicate that, compared with the popular Minimum Cost Flow method, the Cubature Kalman filtering-based phase unwrapping can achieve promising results without pre-filtering and is an appropriate method for coal mining areas with high noise.

  9. Digital signal processing approaches for semiconductor phase noise tolerant coherent transmission systems

    NASA Astrophysics Data System (ADS)

    Iglesias Olmedo, Miguel; Pang, Xiaodan; Schatz, Richard; Zibar, Darko; Tafur Monroy, Idelfonso; Jacobsen, Gunnar; Popov, Sergei

    2015-01-01

    We discuss about digital signal processing approaches that can enable coherent links based on semiconductor lasers. A state-of-the art analysis on different carrier-phase recovery (CPR) techniques is presented. We show that these techniques are based on the assumption of lorentzian linewidth, which does not hold for monolithically integrated semiconductor lasers. We investigate the impact of such lineshape on both 3 and 20 dB linewidth and experimentally conduct a systematic study for 56-GBaud DP-QPSK and 28-GBaud DP-16QAM systems using a decision directed phase look loop algorithm. We show how carrier induced frequency noise has no impact on linewidth but a significant impact on system performance; which rises the question on whether 3-dB linewidth should be used as performance estimator for semiconductor lasers.

  10. Robust sub-shot-noise measurement via Rabi-Josephson oscillations in bimodal Bose-Einstein condensates

    SciTech Connect

    Tikhonenkov, I.; Vardi, A.; Moore, M. G.

    2011-06-15

    Mach-Zehnder atom interferometry requires hold-time phase squeezing to attain readout accuracy below the standard quantum limit. This increases its sensitivity to phase diffusion, restoring shot-noise scaling of the optimal signal-to-noise ratio in the presence of interactions. The contradiction between the preparations required for readout accuracy and robustness to interactions is removed by monitoring Rabi-Josephson oscillations instead of relative-phase oscillations during signal acquisition. Optimizing the signal-to-noise ratio with a Gaussian squeezed input, we find that hold-time number squeezing satisfies both demands and that sub-shot-noise scaling is retained even for strong interactions.

  11. Flow Measurements and Multiple Pure Tone Noise From a Forward Swept Fan

    NASA Technical Reports Server (NTRS)

    Weir, Donald S.; Podboy, Gary G.

    2005-01-01

    A forward-swept fan, designated the Quiet High Speed Fan (QHSF), was tested in the NASA Glenn 9- by 15-foot Low Speed Wind Tunnel to investigate its noise reduction relative to a baseline fan of the same aerodynamic performance. The objective of the Quiet High Speed Fan was a 6-dB reduction in the Effective Perceived Noise Level relative to the baseline fan at the takeoff condition. The intent of the Quiet High Speed Fan design was to provide both a multiple pure tone noise reduction from the forward sweep of the fan rotor and a rotor-stator interaction blade passing tone noise reduction from a leaned stator. The tunnel noise data indicted that the Quiet High Speed Fan was quieter than the baseline fan for a significant portion of the operating line and was 6 dB quieter near the takeoff condition. Although reductions in the multiple pure tones were observed, the vast majority of the EPNdB reduction was a result of the reduction in the blade passing tone and its harmonics. Laser Doppler Velocimetry (LDV) and shroud unsteady pressure measurement data were obtained upstream of the QHSF and baseline rotors to improve the understanding of the shocks which propagate upstream of the two fans when they are operated at high speeds. The flow phenomena that produce multiple pure tone noise is discussed and compared to measurements of the fan acoustic inlet modes and the far field noise signature of the fan.

  12. POF strain sensor using phase measurement techniques

    NASA Astrophysics Data System (ADS)

    Poisel, H.

    2008-03-01

    Polymer optical fiber (POF) elongation sensors have been proposed e.g. by Doering as a low-cost alternative to FBG (single mode Fiber Bragg Gratings) sensors targeting the lower sensitivity range. A recently recovered detection system known from laser distance meters turned out to be very sensitive while staying simple and thus offering low cost potential. The approach is based on measuring the phase shift of a (e.g. sinusoidally) modulated light signal guided in a POF under different tensions resulting in different transit times and thus different phase shifts.

  13. Quantum Fisher information of the GHZ state due to classical phase noise lasers under non-Markovian environment

    NASA Astrophysics Data System (ADS)

    Chen, Yu; Zou, Jian; Yang, Zi-Yi; Li, Longwu; Li, Hai; Shao, Bin

    2016-08-01

    The dynamics of N-qubit GHZ state quantum Fisher information (QFI) under phase noise lasers (PNLs) driving is investigated in terms of non-Markovian master equation. We first investigate the non-Markovian dynamics of the QFI of N-qubit GHZ state and show that when the ratio of the PNL rate and the system-environment coupling strength is very small, the oscillations of the QFIs decay slower which corresponds to the non-Markovian region; yet when it becomes large, the QFIs monotonously decay which corresponds to the Markovian region. When the atom number N increases, QFIs in both regions decay faster. We further find that the QFI flow disappears suddenly followed by a sudden birth depending on the ratio of the PNL rate and the system-environment coupling strength and the atom number N, which unveil a fundamental connection between the non-Markovian behaviors and the parameters of system-environment couplings. We discuss two optimal positive operator-valued measures (POVMs) for two different strategies of our model and find the condition of the optimal measurement. At last, we consider the QFI of two atoms with qubit-qubit interaction under random telegraph noises (RTNs).

  14. The estimation error covariance matrix for the ideal state reconstructor with measurement noise

    NASA Technical Reports Server (NTRS)

    Polites, Michael E.

    1988-01-01

    A general expression is derived for the state estimation error covariance matrix for the Ideal State Reconstructor when the input measurements are corrupted by measurement noise. An example is presented which shows that the more measurements used in estimating the state at a given time, the better the estimator.

  15. System noise analysis of the dumbbell tethered satellite for gravity-gradient measurements

    NASA Technical Reports Server (NTRS)

    Colombo, G.

    1979-01-01

    An analysis of the dumbbell gravity gradiometer concept for measuring short wavelength variations in the earth's gravity gradient is presented. Variations in the gradient are recorded by measuring tension variations in a vertically stabilized satellite consisting of heavy masses connected by a long wire or rod. Tension noise arises from the excitation of various mechanical oscillations of the system. The principal noise sources that were identified are fluctuations in atmospheric drag heating and drag force resulting from density variations and winds. Approximate analytical expressions are presented for the tension noise as a function of the system design parameters for various possible configurations. Computer simulations using numerical integration were performed to study the tension noise for several sample cases. Three designs consistent with Shuttle launch capabilities are discussed.

  16. Measurement of Noise Produced by a Plasma Contactor Operating in Ground Based Facilities

    NASA Technical Reports Server (NTRS)

    Snyder, Steve

    1996-01-01

    Methods to measure electric field fluctuations accurately in a plasma with an active monopole antenna are described. It is shown that the conductive surfaces of the antenna must be adequately isolated from the ambient plasma and that the monopole must be sufficiently short to avoid antenna amplifier saturation. Experimental results illustrate that the noise produced by plasma contactor operation and sensed by the antenna is due to plasma phenomena and is not induced by laboratory power supplies. A good correlation is shown between the current fluctuations in the contactor electrical circuit and the noise detected by the antenna. A large body of experimental data support the conclusion that the majority of noise sensed by the antenna at frequencies less than 1 MHz is due to current fluctuations (electrostatic waves) in the plasma adjacent to the antenna and not to electromagnetic wave radiation. Caution is suggested when comparing antenna noise measurements to conventional specifications for radiated emissions.

  17. Noise and artifact characterization of in vivo Raman spectroscopy skin measurements.

    PubMed

    Ramírez-Elías, Miguel G; Alda, Javier; González, Francisco J

    2012-06-01

    In this work principal component analysis (PCA), a multivariate pattern recognition technique, is used to characterize the noise contribution of the experimental apparatus and two commonly used methods for fluorescence removal used in biomedical Raman spectroscopy measurements. These two methods are a fifth degree polynomial fitting and an iterative variation of it commonly known as the Vancouver method. The results show that the noise in Raman spectroscopy measurements is related to the spectral resolution of the measurement equipment, the intrinsic variability of the biological measurements, and the fluorescence removal algorithm used.

  18. Predictions of Supersonic Jet Mixing and Shock-Associated Noise Compared With Measured Far-Field Data

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.

    2010-01-01

    Codes for predicting supersonic jet mixing and broadband shock-associated noise were assessed using a database containing noise measurements of a jet issuing from a convergent nozzle. Two types of codes were used to make predictions. Fast running codes containing empirical models were used to compute both the mixing noise component and the shock-associated noise component of the jet noise spectrum. One Reynolds-averaged, Navier-Stokes-based code was used to compute only the shock-associated noise. To enable the comparisons of the predicted component spectra with data, the measured total jet noise spectra were separated into mixing noise and shock-associated noise components. Comparisons were made for 1/3-octave spectra and some power spectral densities using data from jets operating at 24 conditions covering essentially 6 fully expanded Mach numbers with 4 total temperature ratios.

  19. Noise and disturbance in quantum measurements: an information-theoretic approach.

    PubMed

    Buscemi, Francesco; Hall, Michael J W; Ozawa, Masanao; Wilde, Mark M

    2014-02-01

    We introduce information-theoretic definitions for noise and disturbance in quantum measurements and prove a state-independent noise-disturbance tradeoff relation that these quantities have to satisfy in any conceivable setup. Contrary to previous approaches, the information-theoretic quantities we define are invariant under the relabelling of outcomes and allow for the possibility of using quantum or classical operations to "correct" for the disturbance. We also show how our bound implies strong tradeoff relations for mean square deviations.

  20. Calibration of the scales of areal surface topography-measuring instruments: part 1. Measurement noise and residual flatness

    NASA Astrophysics Data System (ADS)

    Giusca, Claudiu L.; Leach, Richard K.; Helary, Franck; Gutauskas, Tadas; Nimishakavi, Lakshmi

    2012-03-01

    In this paper, we present methods for determining the measurement noise and residual flatness of areal surface topography-measuring instruments. The methods are compliant with draft international specification standards on areal surface texture. We first introduce the international standards framework and then present current methods based on averaging and subtraction to isolate the measurement noise and residual flatness from the sample surface topography. These methods are relatively difficult to apply and time consuming in practice. An alternative method is presented based on thresholding and filtering techniques. This method is simple to apply in practice. Traceability and measurement uncertainty are discussed.

  1. Measurement of noise and impedance of dry and wet textile electrodes, and textile electrodes with hydrogel.

    PubMed

    Puurtinen, Merja M; Komulainen, Satu M; Kauppinen, Pasi K; Malmivuo, Jaakko A V; Hyttinen, Jari A K

    2006-01-01

    Textile sensors, when embedded into clothing, can provide new ways of monitoring physiological signals, and improve the usability and comfort of such monitoring systems in the areas of medical, occupational health and sports. However, good electrical and mechanical contact between the electrode and the skin is very important, as it often determines the quality of the signal. This paper introduces a study where the properties of dry textile electrodes, textile electrodes moistened with water, and textile electrodes covered with hydrogel were studied with five different electrode sizes. The aim was to study how the electrode size and preparation of the electrode (dry electrode/wet electrode/electrode covered with hydrogel membrane) affect the measurement noise, and the skin-electrode impedance. The measurement noise and skin-electrode impedance were determined from surface biopotential measurements. These preliminary results indicate that noise level increases as the electrode size decreases. The noise level is high in dry textile electrodes, as expected. Yet, the noise level of wet textile electrodes is quite low and similar to that of textile electrodes covered with hydrogel. Hydrogel does not seem to improve noise properties, however it may have effects on movement artifacts. Thus, it is feasible to use textile embedded sensors in physiological monitoring applications when moistening or hydrogel is applied.

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

    PubMed

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

    2014-11-01

    When phase relationships between partials of a complex masker produce highly modulated temporal envelopes on the basilar membrane, listeners may detect speech information from temporal dips in the within-channel masker envelopes. This source of masking release (MR) is however located in regions of unresolved masker partials and it is unclear how much of the speech information in these regions is really needed for intelligibility. Also, other sources of MR such as glimpsing in between resolved masker partials may provide sufficient information from regions that disregard phase relationships. This study simplified the problem of speech recognition to a masked detection task. Target bands of speech-shaped noise were restricted to frequency regions containing either only resolved or only unresolved masker partials, as a function of masker phase relationships (sine or random), masker fundamental frequency (F0) (50, 100, or 200 Hz), and masker spectral profile (flat-spectrum or speech-shaped). Although masker phase effects could be observed in unresolved regions at F0s of 50 and 100 Hz, it was only at 50-Hz F0 that detection thresholds were ever lower in unresolved than in resolved regions, suggesting little role of envelope modulations for harmonic complexes with F0s in the human voice range and at moderate level. PMID:25373972

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

    PubMed Central

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

    2014-01-01

    When phase relationships between partials of a complex masker produce highly modulated temporal envelopes on the basilar membrane, listeners may detect speech information from temporal dips in the within-channel masker envelopes. This source of masking release (MR) is however located in regions of unresolved masker partials and it is unclear how much of the speech information in these regions is really needed for intelligibility. Also, other sources of MR such as glimpsing in between resolved masker partials may provide sufficient information from regions that disregard phase relationships. This study simplified the problem of speech recognition to a masked detection task. Target bands of speech-shaped noise were restricted to frequency regions containing either only resolved or only unresolved masker partials, as a function of masker phase relationships (sine or random), masker fundamental frequency (F0) (50, 100, or 200 Hz), and masker spectral profile (flat-spectrum or speech-shaped). Although masker phase effects could be observed in unresolved regions at F0s of 50 and 100 Hz, it was only at 50-Hz F0 that detection thresholds were ever lower in unresolved than in resolved regions, suggesting little role of envelope modulations for harmonic complexes with F0s in the human voice range and at moderate level. PMID:25373972

  4. 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.

  5. Evaluating the noise in electrically evoked compound action potential measurements in cochlear implants.

    PubMed

    Undurraga, Jaime A; Carlyon, Robert P; Wouters, Jan; van Wieringen, Astrid

    2012-07-01

    Electrically evoked compound action potentials (ECAPs) are widely used to study the excitability of the auditory nerve and stimulation properties in cochlear implant (CI) users. However, ECAP detection can be difficult and very subjective at near-threshold stimulation levels or in spread of excitation measurements. In this study, we evaluated the statistical properties of the background noise (BN) and the postaverage residual noise (RN) in ECAP measurements in order to determine an objective detection criterion. For the estimation of the BN and the RN, a method currently used in auditory brainstem response measurements was applied. The potential benefit of using weighted (Bayesian) averages was also examined. All estimations were performed with a set of approximately 360 ECAP measurements recorded from five human CI users of the CII or HiRes90K device (advanced bionics). Results demonstrated that the BN was normally distributed and the RN decreased according to the square root of the number of averages. No additional benefit was observed by using weighted averaging. The noise was not significantly different either at different stimulation intensities or across recording electrodes along the cochlea. The analysis of the statistical properties of the noise indicated that a signal-to-noise ratio of 1.7 dB as a detection criterion corresponds to a false positive detection rate of 1% with the used measurement setup.

  6. Measurements and observations of noise from a 4.2 megawatt (WTS-4) wind turbine generator

    NASA Technical Reports Server (NTRS)

    Shepherd, K. P.; Hubbard, H. H.

    1983-01-01

    Noise measurements and calculations are being made for large wind turbine generators to develop a data base for use in designing and siting such systems for community acceptance. As part of this program, measurements were made on the WTS-4 wind turbine generator during its acceptance runs. This paper presents the results of these exploratory measurements for power output conditions in the range 1.0 to 4.2 MW. Data include noise levels, spectra, radiation patterns, effects of distance, and the associated perception thresholds for use in the further development of acceptance criteria for this type of machine.

  7. Thermal conductance measurements for the development of ultra low-noise transition-edge sensors with a new method for measuring the noise equivalent power

    NASA Astrophysics Data System (ADS)

    Rostem, Karwan; Glowacka, Dorota M.; Goldie, David J.; Withington, Stafford

    2008-07-01

    Transition-Edge Sensors (TESs) are sensitive devices used in astronomical detectors. Recent projects in ground-based and space astronomy demand the Noise Equivalent Power (NEP) of the TES to be reduced to the limits needed for accurate measurements, for example, of the B-mode polarisation of the CMB. Thus, we have measured thermal conductance of SixNy bridges of various geometries, and present the results that give insight into the phonon transport mechanism inside these low-dimensional structures. We also present a new method for measuring the NEP of TESs using an on-chip black body radiator.

  8. Performance analysis of an all-optical OFDM system in presence of non-linear phase noise.

    PubMed

    Hmood, Jassim K; Harun, Sulaiman W; Emami, Siamak D; Khodaei, Amin; Noordin, Kamarul A; Ahmad, Harith; Shalaby, Hossam M H

    2015-02-23

    The potential for higher spectral efficiency has increased the interest in all-optical orthogonal frequency division multiplexing (OFDM) systems. However, the sensitivity of all-optical OFDM to fiber non-linearity, which causes nonlinear phase noise, is still a major concern. In this paper, an analytical model for estimating the phase noise due to self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) in an all-optical OFDM system is presented. The phase noise versus power, distance, and number of subcarriers is evaluated by implementing the mathematical model using Matlab. In order to verify the results, an all-optical OFDM system, that uses coupler-based inverse fast Fourier transform/fast Fourier transform without any nonlinear compensation, is demonstrated by numerical simulation. The system employs 29 subcarriers; each subcarrier is modulated by a 4-QAM or 16-QAM format with a symbol rate of 25 Gsymbol/s. The results indicate that the phase variance due to FWM is dominant over those induced by either SPM or XPM. It is also shown that the minimum phase noise occurs at -3 dBm and -1 dBm for 4-QAM and 16-QAM, respectively. Finally, the error vector magnitude (EVM) versus subcarrier power and symbol rate is quantified using both simulation and the analytical model. It turns out that both EVM results are in good agreement with each other.

  9. Noise measurements for single and multiple operation of 50 kw wind turbine generators

    NASA Technical Reports Server (NTRS)

    Hubbard, H. H.; Shepherd, K. P.

    1982-01-01

    The noise characteristics of the U.S. Windpower Inc., 50 kw wind turbine generator were measured at various distances from 30 m to 1100 m and for a range of output power. The generated noise is affected by the aerodynamic wakes of the tower legs at frequencies below about 120 Hz and the blade trailing edge thickness at frequencies of about 2 kHz. Rope strakes and airfoil fairings on the legs did not result in substantial noise reductions. Sharpening the blade trailing edges near the tip was effective in reducing broad band noise near 2 kHz. For multiple machines the sound fields are superposed. A three-fold increase in number of machines (from 1 to 3) results in a predicted increase in he sound pressure level of about 5 dB. The detection threshold for 14 machines operating in a 13 - 20 mph wind is observed to be at approximately 1160 m in the downwind direction.

  10. Detailed noise measurements on the SR-7A propeller: Tone behavior with helical tip Mach number

    NASA Technical Reports Server (NTRS)

    Dittmar, James H.; Hall, David G.

    1991-01-01

    Detailed noise measurements were taken on the SR-7A propeller to investigate the behavior of the noise with helical tip Mach number and then to level off as Mach number was increased further. This behavior was further investigated by obtaining detailed pressure-time histories of data. The pressure-time histories indicate that a portion of the primary pressure pulse is progressively cancelled by a secondary pulse which results in the noise leveling off as the helical tip Mach number is increased. This second pulse appears to originate on the same blade as the primary pulse and is in some way connected to the blade itself. This leaves open the possibility of redesigning the blade to improve the cancellation; thereby, the propeller noise is reduced.

  11. Dynamical theory of spin noise and relaxation: Prospects for real-time NMR measurements.

    PubMed

    Field, Timothy R

    2014-11-01

    Recent developments in theoretical aspects of spin noise and relaxation and their interrelationship reveal a modified spin density, distinct from the density matrix, as the necessary object to describe fluctuations in spin systems. These fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments and are observed as "spin noise" in the absence of any radio frequency excitation. With the prospect of ultrafast digitization, the role of spin noise in real-time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this article we outline prospects for harnessing the recent dynamical theory in terms of spin-noise measurement, with attention to real-time properties.

  12. Measurement of speech levels in the presence of time varying background noise

    NASA Technical Reports Server (NTRS)

    Pearsons, K. S.; Horonjeff, R.

    1982-01-01

    Short-term speech level measurements which could be used to note changes in vocal effort in a time varying noise environment were studied. Knowing the changes in speech level would in turn allow prediction of intelligibility in the presence of aircraft flyover noise. Tests indicated that it is possible to use two second samples of speech to estimate long term root mean square speech levels. Other tests were also performed in which people read out loud during aircraft flyover noise. Results of these tests indicate that people do indeed raise their voice during flyovers at a rate of about 3-1/2 dB for each 10 dB increase in background level. This finding is in agreement with other tests of speech levels in the presence of steady state background noise.

  13. Invariant Measures for Monotone SPDEs with Multiplicative Noise Term

    SciTech Connect

    Es-Sarhir, Abdelhadi; Scheutzow, Michael Toelle, Jonas M.; Gaans, Onno van

    2013-10-15

    We study diffusion processes corresponding to infinite dimensional semilinear stochastic differential equations with local Lipschitz drift term and an arbitrary Lipschitz diffusion coefficient. We prove tightness and the Feller property of the solution to show existence of an invariant measure. As an application we discuss stochastic reaction diffusion equations.

  14. Minimizing ultraviolet noise due to mis-matches between detector flow cell and post column mobile phase temperatures in supercritical fluid chromatography: effect of flow cell design.

    PubMed

    Berger, Terry A

    2014-10-17

    A mis-match between the post-column mobile phase temperature and the UV detector flow cell temperature can cause significant UV noise in supercritical fluid chromatography (SFC). Deviations as little as 5 °C can increase noise as much as 5 times, making the detector unsuited for trace analysis. Two approaches were used to minimize this noise. When a flow cell was in direct thermal contact (metal on metal) with the detector optical bench, the mobile phase temperature was actively controlled to the measured flow cell temperature, by using one of the heat exchangers (HX) in the column compartment. However, with some older, but still widely used flow cell designs, this required repeated, hourly monitoring of the flow cell temperature and repeated manual adjustment of the heat exchanger temperature, due to thermal drift. Flow cell design had a strong influence on susceptibility to this thermally induced noise. Thermally insulating the flow cell from the optical bench made some cells much less susceptible to such thermally induced noise. Five different flow cells, some insulated, some un-insulated, were evaluated. Most had a truncated conical flow path, but one had a cylindrical flow path. Using either approach, the ASTM noise, with a 10mm, 13 μL conical flow cell, could be optimized to ≈0.007 mAU at 2.5 Hz, in SFC, which is very near the 0.006 mAU manufacturer's specification for HPLC. The insulated version of this flow cell required far less optimization, compared to the un-insulated version. At 150 bar, an experimental 3mm, 2 μL flow cell, with only one side insulated, yielded noise slightly too high (≈0.16-0.18 mAU) for trace analysis, at 80 Hz. However, at 200 bar, noise at 80 Hz was <0.06 mAU, which should allow quantification of a 1 mAU tall trace component with a signal to noise ratio (S/N) >10. Even partially un-insulated, this flow cell design was much less susceptible to thermally induced noise. Further insulating this flow cell design failed to improve

  15. Minimizing ultraviolet noise due to mis-matches between detector flow cell and post column mobile phase temperatures in supercritical fluid chromatography: effect of flow cell design.

    PubMed

    Berger, Terry A

    2014-10-17

    A mis-match between the post-column mobile phase temperature and the UV detector flow cell temperature can cause significant UV noise in supercritical fluid chromatography (SFC). Deviations as little as 5 °C can increase noise as much as 5 times, making the detector unsuited for trace analysis. Two approaches were used to minimize this noise. When a flow cell was in direct thermal contact (metal on metal) with the detector optical bench, the mobile phase temperature was actively controlled to the measured flow cell temperature, by using one of the heat exchangers (HX) in the column compartment. However, with some older, but still widely used flow cell designs, this required repeated, hourly monitoring of the flow cell temperature and repeated manual adjustment of the heat exchanger temperature, due to thermal drift. Flow cell design had a strong influence on susceptibility to this thermally induced noise. Thermally insulating the flow cell from the optical bench made some cells much less susceptible to such thermally induced noise. Five different flow cells, some insulated, some un-insulated, were evaluated. Most had a truncated conical flow path, but one had a cylindrical flow path. Using either approach, the ASTM noise, with a 10mm, 13 μL conical flow cell, could be optimized to ≈0.007 mAU at 2.5 Hz, in SFC, which is very near the 0.006 mAU manufacturer's specification for HPLC. The insulated version of this flow cell required far less optimization, compared to the un-insulated version. At 150 bar, an experimental 3mm, 2 μL flow cell, with only one side insulated, yielded noise slightly too high (≈0.16-0.18 mAU) for trace analysis, at 80 Hz. However, at 200 bar, noise at 80 Hz was <0.06 mAU, which should allow quantification of a 1 mAU tall trace component with a signal to noise ratio (S/N) >10. Even partially un-insulated, this flow cell design was much less susceptible to thermally induced noise. Further insulating this flow cell design failed to improve

  16. Measurement of Phase Coherence in Space Turbulence

    NASA Astrophysics Data System (ADS)

    Belmont, G.; Panis, J.; Rezeau, L.; Sahraoui, F.

    2008-12-01

    In many space plasmas such as Magnetosheath, intense magnetic fluctuations are permanently observed, with power law spectra. Assuming these fluctuations belong to some kind of turbulence, which can legitimately be suspected, spectra are clearly not sufficient to characterize it. Is this turbulence made of non linear "phase-coherent" structures, like in the classical Kolmogorov image, or is it made of incoherent waves as in weak turbulence? Is it homogeneous in space and scales or is it intermittent? " Many methods allow analyzing the statistical properties of turbulence, and the results obtained by tools such as structure functions or wavelets are of course influenced by all these properties, such providing indirect information about them. But few of them are specifically dedicated to the study of phase coherence so that the consequences that can be inferred from them are generally not univocal for this point of view. We will review those few tools existing in the literature that allow measuring more directly the phase coherence and present a new method, called "phase gradient analysis", which we are presently developing for this analysis. Preliminary results of this new tool will be presented.

  17. Experimental method for reactor-noise measurements of effective beta. [LMFBR

    SciTech Connect

    Bennett, E.F.

    1981-09-01

    A variance-to-mean noise technique, modified to eliminate systematic errors from drifting of reactor power, has been used to infer integral values of effective beta for uranium and plutonium fueled fast reactor modk-ups. The measurement technique, including corrections for a finite detector-electrometer time response, is described together with preliminary beta measurement results.

  18. Electrical Noise and the Measurement of Absolute Temperature, Boltzmann's Constant and Avogadro's Number.

    ERIC Educational Resources Information Center

    Ericson, T. J.

    1988-01-01

    Describes an apparatus capable of measuring absolute temperatures of a tungsten filament bulb up to normal running temperature and measuring Botzmann's constant to an accuracy of a few percent. Shows that electrical noise techniques are convenient to demonstrate how the concept of temperature is related to the micro- and macroscopic world. (CW)

  19. 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

  20. Phase noise reduction by using dual-frequency laser in coherent detection

    NASA Astrophysics Data System (ADS)

    Zheng, Zheng; Changming, Zhao; Haiyang, Zhang; Suhui, Yang; Dehua, Zhang; Hongzhi, Yang; Jiawei, Liu

    2016-06-01

    Dual-frequency laser radar (DFLR) uses laser with two coherent frequency components as transmitting wave. The method is based on the use of an optically-carried radio frequency (RF) signal, which is the frequency difference between the two components. Due to the two optical waves are generally subject to the same first order phase noise, the synthesis wave is predicted to have a stronger resistance to atmospheric turbulence than the single-frequency wave. To the best of our knowledge, the model proposed in this paper is the first model that detailedly illustrates that the dual-frequency laser has an advantage over the single frequency laser in atmospheric turbulence resistance. Experiments are carried out to compare the performances of single and dual frequency lidars under atmospheric turbulence. The experimental results show that, with the increase of atmospheric turbulence intensity, the signal to noise ratio (SNR) of beat signal decreases and its central frequency stability (CFS) becomes worse in conventional single frequency coherent laser radar (SFCLR). While for the DFLR, the SNR and CFS are almost unaffected by atmospheric turbulence, which are in good agreement with the theoretical model.