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Showing papers on "Noise (radio) published in 2015"


Journal ArticleDOI
TL;DR: In this paper, the authors present various models for the origin of the electric noise, provide a critical review of the experimental findings, and summarizes the important questions that are still open in this active research area.
Abstract: How can the electric noise in the vicinity of a metallic body be measured and understood? Trapped ions, known as unique tools for metrology and quantum information processing, also constitute very sensitive probes of this electric noise for distances from micrometers to millimeters. This paper presents various models for the origin of the electric noise, provides a critical review of the experimental findings, and summarizes the important questions that are still open in this active research area.

349 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a digital self-interference cancellation technique for full-duplex systems, which is shown to significantly mitigate the selfinterference signal as well as the associated transmitter and receiver impairments, more specifically, transceiver nonlinearities and phase noise.
Abstract: Full-duplex systems are expected to double the spectral efficiency compared to conventional half-duplex systems if the self-interference signal can be significantly mitigated. Digital cancellation is one of the lowest complexity self-interference cancellation techniques in full-duplex systems. However, its mitigation capability is very limited, mainly due to transmitter and receiver circuit's impairments (e.g., phase noise, nonlinear distortion, and quantization noise). In this paper, we propose a novel digital self-interference cancellation technique for full-duplex systems. The proposed technique is shown to significantly mitigate the self-interference signal as well as the associated transmitter and receiver impairments, more specifically, transceiver nonlinearities and phase noise. In the proposed technique, an auxiliary receiver chain is used to obtain a digital-domain copy of the transmitted Radio Frequency (RF) self-interference signal. The self-interference copy is then used in the digital-domain to cancel out both the self-interference signal and the associated transmitter impairments. Furthermore, to alleviate the receiver phase noise effect, a common oscillator is shared between the auxiliary and ordinary receiver chains. A thorough analytical and numerical analysis for the effect of the transmitter and receiver impairments on the cancellation capability of the proposed technique is presented. Finally, the overall performance is numerically investigated showing that using the proposed technique, the self-interference signal could be mitigated to $\sim$ 3 dB higher than the receiver noise floor, which results in up to 76% rate improvement compared to conventional half-duplex systems at 20 dBm transmit power values.

343 citations


Journal ArticleDOI
TL;DR: Dynamical decoupling from the surface noise is demonstrated, paving the way to applications ranging from nanoscale NMR to quantum networks.
Abstract: We report on the noise spectrum experienced by few nanometer deep nitrogen-vacancy centers in diamond as a function of depth, surface coating, magnetic field and temperature. Analysis reveals a double-Lorentzian noise spectrum consistent with a surface electronic spin bath in the low frequency regime, along with a faster noise source attributed to surface-modified phononic coupling. These results shed new light on the mechanisms responsible for surface noise affecting shallow spins at semiconductor interfaces, and suggests possible directions for further studies. We demonstrate dynamical decoupling from the surface noise, paving the way to applications ranging from nanoscale NMR to quantum networks.

242 citations


Journal ArticleDOI
TL;DR: In this paper, a 2D dense and large network with about 2500 receivers with 100m spacing was used to estimate 3D P wave velocities from a single depth image.
Abstract: We retrieve P diving waves by applying seismic interferometry to ambient-noise records observed at Long Beach, California, and invert travel times of these waves to estimate 3-D P wave velocity structure. The ambient noise is recorded by a 2-D dense and large network, which has about 2500 receivers with 100 m spacing. Compared to surface wave extraction, body wave extraction is a much greater challenge because ambient noise is typically dominated by surface wave energy. For each individual receiver pair, the cross-correlation function obtained from ambient-noise data does not show clear body waves. Although we can reconstruct body waves when we stack correlation functions over all receiver pairs, we need to extract body waves at each receiver pair separately for imaging spatial heterogeneity of subsurface structure. Therefore, we employ two filters after correlation to seek body waves between individual receiver pairs. The first filter is a selection filter based on the similarity between each correlation function and the stacked function. After selecting traces containing stronger body waves, we retain about two million correlation functions (35% of all correlation functions) and successfully preserve most of body wave energy in the retained traces. The second filter is a noise suppression filter to enhance coherent energy (body waves here) and suppress incoherent noise in each trace. After applying these filters, we can reconstruct clear body waves from each virtual source. As an application of using extracted body waves, we estimate 3-D P wave velocities from these waves with travel time tomography. This study is the first body wave tomography result obtained from only ambient noise recorded at the ground surface. The velocity structure estimated from body waves has higher resolution than estimated from surface waves.

206 citations


Journal ArticleDOI
TL;DR: This work considers two distinct operation modes, namely, when the phase noise processes at the M BS antennas are identical and when they are independent (nonsynchronous operation), and derives a lower bound on the sum-capacity, and compares their performance.
Abstract: Multiuser multiple-input–multiple-output (MIMO) cellular systems with an excess of base station (BS) antennas (Massive MIMO) offer unprecedented multiplexing gains and radiated energy efficiency. Oscillator phase noise is introduced in the transmitter and receiver radio frequency chains and severely degrades the performance of communication systems. We study the effect of oscillator phase noise in frequency-selective Massive MIMO systems with imperfect channel state information. In particular, we consider two distinct operation modes, namely, when the phase noise processes at the $M$ BS antennas are identical (synchronous operation) and when they are independent (nonsynchronous operation) . We analyze a linear and low-complexity time-reversal maximum-ratio combining reception strategy. For both operation modes, we derive a lower bound on the sum-capacity, and we compare their performance. Based on the derived achievable sum-rates, we show that with the proposed receive processing, an $O(\sqrt{M} ) $ array gain is achievable. Due to the phase noise drift, the estimated effective channel becomes progressively outdated. Therefore, phase noise effectively limits the length of the interval used for data transmission and the number of scheduled users. The derived achievable rates provide insights into the optimum choice of the data interval length and the number of scheduled users.

190 citations


Journal ArticleDOI
TL;DR: In this paper, a resonant electromagnetic detector was proposed to search for hidden-photon dark matter over an extensive range of masses, using a tunable, resonant LC circuit designed to couple to this magnetic field.
Abstract: We propose a resonant electromagnetic detector to search for hidden-photon dark matter over an extensive range of masses. Hidden-photon dark matter can be described as a weakly coupled ``hidden electric field,'' oscillating at a frequency fixed by the mass, and able to penetrate any shielding. At low frequencies (compared to the inverse size of the shielding), we find that the observable effect of the hidden photon inside any shielding is a real, oscillating magnetic field. We outline experimental setups designed to search for hidden-photon dark matter, using a tunable, resonant LC circuit designed to couple to this magnetic field. Our ``straw man'' setups take into consideration resonator design, readout architecture and noise estimates. At high frequencies, there is an upper limit to the useful size of a single resonator set by $1/\ensuremath{ u}$. However, many resonators may be multiplexed within a hidden-photon coherence length to increase the sensitivity in this regime. Hidden-photon dark matter has an enormous range of possible frequencies, but current experiments search only over a few narrow pieces of that range. We find the potential sensitivity of our proposal is many orders of magnitude beyond current limits over an extensive range of frequencies, from 100 Hz up to 700 GHz and potentially higher.

169 citations


Journal ArticleDOI
TL;DR: In this article, the effect of LE serrations on noise reduction was investigated on a flat plate in an open jet wind tunnel and the results showed that the amplitude of the LE amplitude was a key parameter for enhancing the noise reduction.
Abstract: This paper provides an experimental investigation into the use of leading edge (LE) serrations as a means of reducing the broadband noise generated due to the interaction between the aerofoil’s LE and impinging turbulence. Experiments are performed on a flat plate in an open jet wind tunnel. Grids are used to generate isotropic homogeneous turbulence. The leading edge serrations are in the form of sinusoidal profiles of wavelengths, λ, and amplitudes, 2h. The frequency and amplitude characteristics are studied in detail in order to understand the effect of LE serrations on noise reduction characteristics and are compared with straight edge baseline flat plates. Noise reductions are found to be insignificant at low frequencies but significant in the mid frequency range (500 Hz–8 kHz) for all the cases studied. The flat plate results are also compared to the noise reductions obtained on a serrated NACA-65 aerofoil with the same serration profile. Noise reductions are found to be significantly higher for the flat plates with a maximum noise reduction of around 9 dB compared with about 7 dB for the aerofoil. In general, it is observed that the sound power reduction level (ΔPWL) is sensitive to the amplitude, 2h of the LE serrations but less sensitive to the serration wavelength, λ. Thus, this paper sufficiently demonstrates that the LE amplitude acts as a key parameter for enhancing the noise reduction levels in flat plates and aerofoils.

160 citations


Journal ArticleDOI
TL;DR: In this article, the phase dynamics in ballistic graphene-based short Josephson junctions were studied by numerical methods. And the authors investigated the effects of thermal and correlated fluctuations on the escape time from these metastable states, when the system is driven by an oscillating bias current.
Abstract: We study by numerical methods the phase dynamics in ballistic graphene-based short Josephson junctions. A superconductor-graphene-superconductor system exhibits superconductive quantum metastable states similar to those present in normal current-biased Josephson junctions. We investigate the effects of thermal and correlated fluctuations on the escape time from these metastable states, when the system is driven by an oscillating bias current in the presence of Gaussian white and colored noise sources. Varying the intensity and the correlation time of the noise source, it is possible to analyze the behavior of the escape time, or switching time, from a superconductive metastable state in different temperature regimes. Moreover, we are able to clearly distinguish dynamical regimes characterized by the dynamic resonant activation effect, in the absence of noise source, and the stochastic resonant activation phenomenon induced by the noise. For low initial values of the bias current, the dynamic resonant activation shows double-minimum structures, strongly dependent on the value of the damping parameter. Noise-enhanced stability is also observed in the system investigated. We analyze the probability density function (PDF) of the switching times. The PDFs for frequencies within the dynamic resonant activation minima are characterized by single peaks with exponential tails. The PDFs for noise intensities around the maxima of the switching time, peculiarity of the noise-enhanced stability phenomenon, are composed of regular sequences of two peaks for each period of the driving current, with exponentially decaying envelopes.

119 citations


Journal ArticleDOI
TL;DR: In this article, the authors present the characteristics of electromagnetic waves propagating inside human body at terahertz frequencies and an initial study of the system performance of nano-network, based on the calculation of path losses and noise level for THz wave propagation, the channel capacity is studied to give an insight of future nano-communications within the human body.
Abstract: This paper presents the characteristics of electromagnetic waves propagating inside human body at Terahertz frequencies and an initial study of the system performance of nano-network. It has been observed that the path loss is not only the function of distance and frequency but also related to the dielectric loss of human tissues. Numerical results have been compared with analytical studies and a good match has been found which validates the proposed numerical model. Based on the calculation of path losses and noise level for THz wave propagation, the channel capacity is studied to give an insight of future nano-communications within the human body. Results show that at the distance of millimeters, the capacity can reach as high as 100 Terabits per second (Tbps) depending on the environment and exciting pulse types.

105 citations


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

90 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe the phenomenon of scintillation from its physical origins to its effect on photometry, and show that Young's scintillator-noise approximation used by many astronomers tends to underestimate the median noise at several major observatories around the world.
Abstract: Scintillation noise due to the Earth's turbulent atmosphere can be a dominant noise source in high-precision astronomical photometry when observing bright targets from the ground. Here we describe the phenomenon of scintillation from its physical origins to its effect on photometry. We show that Young's scintillation-noise approximation used by many astronomers tends to underestimate the median scintillation noise at several major observatories around the world. We show that using median atmospheric optical turbulence profiles, which are now available for most sites, provides a better estimate of the expected scintillation noise and that real-time turbulence profiles can be used to precisely characterize the scintillation-noise component of contemporaneous photometric measurements. This will enable a better understanding and calibration of photometric noise sources and the effectiveness of scintillation correction techniques. We also provide new equations for calculating scintillation noise, including for extremely large telescopes where the scintillation noise will actually be lower than previously thought. These equations highlight the fact that scintillation noise and shot noise have the same dependence on exposure time and so if an observation is scintillation limited, it will be scintillation limited for all exposure times. The ratio of scintillation noise to shot noise is also only weakly dependent on telescope diameter and so a bigger telescope may not yield a reduction in fractional scintillation noise.

Journal ArticleDOI
TL;DR: In this paper, an electrical modulation cancellation method (E-MOCAM) was proposed to suppress the background noise in the case of the excitation light source with a poor beam quality.
Abstract: A novel electrical modulation cancellation method (E-MOCAM) is proposed to suppress the background noise in the case of the excitation light source with a poor beam quality. For its practical implementation, an E-MOCAM based on-beam QEPAS NO 2 sensor by use of a commercial high-power wide-stripe LED is developed. The E-MOCAM ultimately suppressed the background noise caused by the stray light by three orders of magnitude. A 1 σ detection limit of 1.3 ppb (part per billion by volume) was achieved at 1 s integration time in this experiment, which corresponds to a normalized noise equivalent absorption coefficient (NNEA) 4.2 × 10 −9 W cm −1 Hz −1/2 . A 9 h continuous on-line monitoring of ambient atmospheric NO 2 was carried out on the campus of Shanxi University.

Journal ArticleDOI
TL;DR: A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux noise, so it is proposed that the heretofore mysterious spins producing flux noise could be O_{2} molecules adsorbed on the surface.
Abstract: A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux noise. We propose that the heretofore mysterious spins producing flux noise could be O_{2} molecules adsorbed on the surface. Using density functional theory calculations, we find that an O_{2} molecule adsorbed on an α-alumina surface has a magnetic moment of ~1.8 μ_{B}. The spin is oriented perpendicular to the axis of the O-O bond, the barrier to spin rotations is about 10 mK. Monte Carlo simulations of ferromagnetically coupled, anisotropic XY spins on a square lattice find 1/f magnetization noise, consistent with flux noise in Al SQUIDs.

Journal ArticleDOI
TL;DR: In this article, the authors investigate a route to reduction of the turbulent boundary layer-trailing edge interaction noise, which is generated by surface pressure fluctuations beneath a turbulent boundary and scattered at the trailing edge of wind turbine blades.
Abstract: In the current study, we investigate a route to reduction of the turbulent boundary layer–trailing edge interaction noise. The trailing edge noise is generated by surface pressure fluctuations beneath a turbulent boundary and scattered at the trailing edge of wind turbine blades. Trailing edge noise is considered to be the dominant noise source of modern wind turbines. Therefore, efforts are constantly made to attenuate the noise. Today, noise emission can be reduced by proper airfoil design or passive devices, such as trailing edge serrations. A further improved candidate technology for trailing edge noise attenuation is active flow control in the form of wall-normal suction. With active flow control, the boundary layer features responsible for trailing edge noise generation can be manipulated, and correspondingly the trailing edge noise can be reduced. Detailed experimental investigations were performed at the Universities of Tel-Aviv and Stuttgart. The tests showed that steady wall-normal suction has a positive effect on the trailing edge noise by reducing the boundary layer thickness, and with it the integral length scales of the eddies within the boundary layer.

Journal ArticleDOI
TL;DR: In this paper, the authors constructed timing solutions for 81 -ray pulsars covering more than five years of Fermi data, including radio-quiet or radio-faint pulsars which cannot be timed with other telescopes.
Abstract: We have constructed timing solutions for 81 -ray pulsars covering more than five years of Fermi data. The sample includes 37 radio-quiet or radio-faint pulsars which cannot be timed with other telescopes. These timing solutions and the corresponding pulse times of arrival are prerequisites for further study, e.g. phase-resolved spectroscopy or searches for mode switches. Many -ray pulsars are strongly affected by timing noise, and we present a new method for characterizing the noise process and mitigating its effects on other facets of the timing model. We present an analysis of timing noise over the population using a new metric for characterizing its strength and spectral shape, namely

Journal ArticleDOI
TL;DR: In this article, an acoustic interferometer that uses sound waves in a toroidal Bose-Einstein condensate to measure rotation was proposed, where spatially patterned light beams were used to excite counterpropagating sound waves within the condensates and use in situ absorption imaging to characterize their evolution.
Abstract: The precision of most compact inertial sensing schemes using trapped- and guided-atom interferometers has been limited by uncontrolled phase errors caused by trapping potentials and interactions. Here we propose an acoustic interferometer that uses sound waves in a toroidal Bose-Einstein condensate to measure rotation, and we demonstrate experimentally several key aspects of this type of interferometer. We use spatially patterned light beams to excite counterpropagating sound waves within the condensate and use in situ absorption imaging to characterize their evolution. We present an analysis technique by which we extract separately the oscillation frequencies of the standing-wave acoustic modes, the frequency splitting caused by static imperfections in the trapping potential, and the characteristic precession of the standing-wave pattern due to rotation. Supported by analytic and numerical calculations, we interpret the noise in our measurements, which is dominated by atom shot noise, in terms of rotation noise. While the noise of our acoustic interferometric sensor, at the level of $\ensuremath{\sim}\text{rad}\phantom{\rule{0.16em}{0ex}}{\text{s}}^{\ensuremath{-}1}/\sqrt{\text{Hz}}$, is high owing to rapid acoustic damping and the small radius of the trap, the proof-of-concept device does operate at the high densities and small volumes of trapped Bose-Einstein condensed gases.

Journal ArticleDOI
TL;DR: In this article, the authors modeled the observed photon counts as the sum of a diffuse and a point-like photon flux, convolved with the instrumental beam and subject to Poissonian shot noise.
Abstract: We analyze the 6.5 year all-sky data from the Fermi Large Area Telescope that are restricted to γ -ray photons with energies between 0.6–307.2 GeV. Raw count maps show a superposition of diffuse and point-like emission structures and are subject to shot noise and instrumental artifacts. Using the D3 PO inference algorithm, we modeled the observed photon counts as the sum of a diffuse and a point-like photon flux, convolved with the instrumental beam and subject to Poissonian shot noise. The D3 PO algorithm performs a Bayesian inference without the use of spatial or spectral templates; that is, it removes the shot noise, deconvolves the instrumental response, and yields separate estimates for the two flux components. The non-parametric reconstruction uncovers the morphology of the diffuse photon flux up to several hundred GeV. We present an all-sky spectral index map for the diffuse component. We show that the diffuse γ -ray flux can be described phenomenologically by only two distinct components: a soft component, presumably dominated by hadronic processes, tracing the dense, cold interstellar medium, and a hard component, presumably dominated by leptonic interactions, following the hot and dilute medium and outflows such as the Fermi bubbles. A comparison of the soft component with the Galactic dust emission indicates that the dust-to-soft-gamma ratio in the interstellar medium decreases with latitude. The spectrally hard component exists in a thick Galactic disk and tends to flow out of the Galaxy at some locations. Furthermore, we find the angular power spectrum of the diffuse flux to roughly follow a power law with an index of 2.47 on large scales, independent of energy. Our first catalog of source candidates includes 3106 candidates of which we associate 1381 (1897) with known sources from the second (third) Fermi source catalog. We observe γ -ray emission in the direction of a few galaxy clusters hosting known radio halos.

Journal ArticleDOI
TL;DR: In this paper, the air-gap flux density is obtained by 2-D finite element analysis (FEA), allowing to compute the electromagnetic pressure, which then serves as input of mechanical and acoustical 3-D FEA models of the stator with carter.
Abstract: In low- to medium-power-rated brushless machines, noise of electromagnetic origin is generally prevailing over mechanical and aerodynamic sources. The appropriate combination of pole and slot of a permanent magnet synchronous motor is one of the keys to its performances among which stands noise reduction. This paper investigates configurations regarding this aspect for distributed overlapping and single-layer concentrated nonoverlapping winding configurations. Chosen combinations are 8 poles 48 slots (8p48s), 8p72s, 46p48s and 50p48s. The air-gap flux density is obtained by 2-D finite element analysis (FEA), allowing to compute the electromagnetic pressure. It then serves as input of mechanical and acoustical 3-D FEA models of the stator with carter.

Journal ArticleDOI
TL;DR: In this paper, the noise generated by a rod-airfoil configuration was investigated using unstructured Large-Eddy simulation coupled with a Ffowcs-Williams and Hawkings technique.
Abstract: The noise generated by a rod–airfoil configuration is investigated using unstructured Large-Eddy simulation coupled with a Ffowcs-Williams and Hawkings technique. The detailed experimental database and several numerical simulations available enable an extensive validation of the proposed methodology. Similar or improved results are obtained both in the near field (surface coefficient distributions and velocity profiles) and in the acoustic far field (power spectral densities obtained with both porous and solid surfaces, and directivities) compared with the best and most recent simulations. Dipolar noise radiation at the rod vortex-shedding frequency and its harmonics are found to be dominant. Some additional quadrupolar source contributions are seen at low and high frequencies. The rod is shown to have a significant contribution to the far-field noise at grazing angles. Constructive interferences occur normal to the rod–airfoil axis, whereas destructive interferences appear at grazing angles.

Journal ArticleDOI
TL;DR: The problem of self-interference cancellation with phase noise suppression in full-duplex systems in terms of both complexity and achieved gain is considered and experimental results in a typical indoor environment are presented.
Abstract: Oscillator phase noise has been shown to be one of the main performance limiting factors in full-duplex systems. In this paper, we consider the problem of self-interference cancellation with phase noise suppression in full-duplex systems. The feasibility of performing phase noise suppression in full-duplex systems in terms of both complexity and achieved gain is analytically and experimentally investigated. First, the effect of phase noise on full-duplex systems and the possibility of performing phase noise suppression are studied. Two different phase noise suppression techniques with a detailed complexity analysis are then proposed. For each suppression technique, both free-running and phase-locked loop-based oscillators are considered. Due to the fact that full-duplex system performance highly depends on hardware impairments that are difficult to fully model, experimental results in a typical indoor environment are presented. The experimental results performed on two different platforms confirm results obtained from numerical simulations. Finally, the tradeoff between the required complexity and the gain achieved using phase noise suppression is discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors extend the analysis to timescales of several days, instead of several hours, to better sample stellar noise that follows from magnetic activity, and find that stellar noise for solar-type stars to be smaller values in comparison to solar values.
Abstract: An earlier study of the Kepler Mission noise properties on timescales of primary relevance to detection of exoplanet transits found that higher than expected noise followed, to a large extent, from the stars rather than instrument or data analysis performance. The earlier study over the first six quarters of Kepler data is extended to the full four years ultimately comprising the mission. Efforts to improve the pipeline data analysis have been successful in reducing noise levels modestly as evidenced by smaller values derived from the current data products. The new analyses of noise properties on transit timescales show significant changes in the component attributed to instrument and data analysis, with essentially no change in the inferred stellar noise. We also extend the analyses to timescales of several days, instead of several hours to better sample stellar noise that follows from magnetic activity. On the longer timescale there is a shift in stellar noise for solar-type stars to smaller values in comparison to solar values.

Journal ArticleDOI
TL;DR: It is believed that the achieved low noise makes the fiber laser a promising candidate in applications such as ultra-long haul coherent optical communication and LIDAR.
Abstract: An all-optical frequency and intensity noise suppression technique of a single-frequency fiber laser is demonstrated. By exploiting the recursive noise reduction effect of a semiconductor optical amplifier (SOA) in a self-injection locked fiber laser, the frequency and intensity noise of the laser are remarkably suppressed in a significantly wide frequency range. In addition to the linewidth suppression from 3.5 kHz to 700 Hz, the frequency noise has been reduced by ∼25 dB. After suppression, the relative intensity noise (RIN) is within 5 dB of the shot noise limit at frequencies from 1.5 to 3 MHz, and the frequency range of the suppression reaches about 30 MHz. The relaxation oscillation peak is observed to shift to lower frequencies and is reduced by about 35 dB from −90 dB/Hz to −125 dB/Hz. It is believed that the achieved low noise makes the fiber laser a promising candidate in applications such as ultra-long haul coherent optical communication and LIDAR.

Journal ArticleDOI
TL;DR: In this paper, the effect of noise on the hysteresis characteristics of a prototypical thermoacoustic system, a horizontal Rijke tube, was investigated and it was shown that the rate of decrease in the hystresis width is constant for all the mass flow rates considered in the present study.
Abstract: We present the effect of noise on the hysteresis characteristics of a prototypical thermoacoustic system, a horizontal Rijke tube. As we increase the noise intensity, we find that the width of the hysteresis zone decreases. However, we find that the rate of decrease in hysteresis width is constant for all the mass flow rates considered in the present study. We also show that the subcritical transition observed in the absence of noise is no longer discernible once the intensity of noise is above a threshold value and the transition appears to be continuous. We compare our experimental observations with the results obtained from a numerical model perturbed with additive Gaussian white noise and we find a qualitative agreement between the experimental and the numerical results.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a simple and rigorous way of removing the shear bias from the source Poisson noise, which can achieve sub-percent level accuracy even for images of signal-to-noise ratio less than 5 in general.
Abstract: For cosmic shear to become an accurate cosmological probe, systematic errors in the shear measurement method must be unambiguously identified and corrected for. Previous work of this series has demonstrated that cosmic shears can be measured accurately in Fourier space in the presence of background noise and finite pixel size, without assumptions on the morphologies of galaxy and PSF. The remaining major source of error is source Poisson noise, due to the finiteness of source photon number. This problem is particularly important for faint galaxies in space-based weak lensing measurements, and for ground-based images of short exposure times. In this work, we propose a simple and rigorous way of removing the shear bias from the source Poisson noise. Our noise treatment can be generalized for images made of multiple exposures through MultiDrizzle. This is demonstrated with the SDSS and COSMOS/ACS data. With a large ensemble of mock galaxy images of unrestricted morphologies, we show that our shear measurement method can achieve sub-percent level accuracy even for images of signal-to-noise ratio less than 5 in general, making it the most promising technique for cosmic shear measurement in the ongoing and upcoming large scale galaxy surveys.

Journal ArticleDOI
TL;DR: In this paper, a numerical simulation of a subsonic turbulent hot jet is performed using large-eddy simulation, where a geometrical tripping is used in order to trigger the turbulence at the nozzle exit.
Abstract: In the framework of jet noise computation, a numerical simulation of a subsonic turbulent hot jet is performed using large-eddy simulation. A geometrical tripping is used in order to trigger the turbulence at the nozzle exit. In a first part, the validity of the simulation is assessed by comparison with experimental measurements. The mean and rms velocity fields show good agreement, so do the azimuthal composition of the near pressure field and the far field spectra. Discrepancies remain close to the nozzle exit which lead to a limited overestimation of the pressure levels in both near and far fields, especially near the 90∘ angular sector. Two point correlation analyses are then applied to the data obtained from the simulation. These enable to link the downstream acoustic radiation, which is the main direction of radiation, to pressure waves developing in the shear layer and propagating toward the potential core end. The intermittency of the downstream acoustic radiation is evidenced and related to the coherent structures developing in the shear layer.

Journal ArticleDOI
29 Dec 2015-Energies
TL;DR: In this article, the authors investigated the noise emission from a vertical axis wind turbine (VAWT) at wind speed 8 m/s, 10 m above ground, to 96.2 dBA.
Abstract: The noise emission from a vertical axis wind turbine (VAWT) has been investigated. A noise measurement campaign on a 200 kW straight-bladed VAWT has been conducted, and the result has been compared to a semi-empirical model for turbulent-boundary-layer trailing edge (TBL-TE) noise. The noise emission from the wind turbine was measured, at wind speed 8 m/s, 10 m above ground, to 96.2 dBA. At this wind speed, the turbine was stalling as it was run at a tip speed lower than optimal due to constructional constraints. The noise emission at a wind speed of 6 m/s, 10 m above ground was measured while operating at optimum tip speed and was found to be 94.1 dBA. A comparison with similar size horizontal axis wind turbines (HAWTs) indicates a noise emission at the absolute bottom of the range. Furthermore, it is clear from the analysis that the turbulent-boundary-layer trailing-edge noise, as modeled here, is much lower than the measured levels, which suggests that other mechanisms are likely to be important, such as inflow turbulence.

Journal ArticleDOI
TL;DR: The behavior of the GMI noise diodes using the hot load and cold sky views for the first 6 months of operations is examined, showing the on-orbit nonlinearity is trended over the first6 months and shown to be stable over that time period.
Abstract: With rising demand for smaller, lower mass microwave instruments, internal calibration using noise diodes is becoming increasingly more attractive for space-borne radiometer applications. Since noise diodes can exhibit on-orbit excess temperature drift, internally calibrated systems typically require vicarious on-orbit recharacterization. The GMI is the first instrument of its kind to include both internal (noise diodes) and external (hot load/cold sky) calibration systems. The dual-calibration system provides the unprecedented capability to directly measure transient behaviors in the hot load, cold sky view, and receiver nonlinearity. Furthermore, the behavior of the noise diodes can be directly evaluated, which may shed light on improvements to internal calibration for future missions. This paper directly examines the behavior of the GMI noise diodes using the hot load and cold sky views for the first 6 months of operations. Two of the seven channels with noise diodes have exhibited on-orbit noise diode excess temperature drift of about 1 K. The other noise diodes have remained exceptionally stable. The noise diodes are used to evaluate transient behaviors in the GMI hot load, cold sky view, and nonlinearity. The hot-load brightness temperature variation due to gradients is re-evaluated and shown to be smaller at the lower frequencies than at preflight calibration. Radio frequency interference (RFI) in the cold view is evaluated using the noise diode backup calibration. The on-orbit nonlinearity is trended over the first 6 months and shown to be stable over that time period.

Journal ArticleDOI
TL;DR: In this article, the authors consider random phase fluctuations imposed during wave propagation through a turbulent plasma (e.g. ionosphere) as a source of additional noise in interferometric visibilities.
Abstract: In this paper, we consider random phase fluctuations imposed during wave propagation through a turbulent plasma (e.g. ionosphere) as a source of additional noise in interferometric visibilities. We derive expressions for visibility variance for the wide field of view case (FOV ˜10°) by computing the statistics of Fresnel diffraction from a stochastic plasma, and provide an intuitive understanding. For typical ionospheric conditions (diffractive scale ˜5-20 km at 150 MHz), we show that the resulting ionospheric `scintillation noise' can be a dominant source of uncertainty at low frequencies (ν ≲ 200 MHz). Consequently, low-frequency widefield radio interferometers must take this source of uncertainty into account in their sensitivity analysis. We also discuss the spatial, temporal, and spectral coherence properties of scintillation noise that determine its magnitude in deep integrations, and influence prospects for its mitigation via calibration or filtering.

Journal ArticleDOI
TL;DR: In this paper, the authors used a grid of receivers covering an area of 4 km2 over the Lalor Mine, Canada, to test the capability of seismic interferometry to image ore deposits in the crystalline rock environment.
Abstract: Approximately 300 hours of ambient noise data were recorded on a grid of receivers covering an area of 4 km2 over the Lalor Mine, Canada, to test the capability of seismic interferometry to image ore deposits in the crystalline rock environment. Underground mining activities create the main source of ambient noise in the area. Alongside the ambient noise survey, a larger three-dimensional active-source seismic survey was also acquired and used to evaluate the interferometry results. Power spectral density calculations show random ambient noise with a frequency range of 2 Hz–35 Hz. A beamforming analysis identified body waves arriving from the west–northwest (pointing towards the mine) and surface waves propagating from the northeast. The calculated virtual shot gathers retrieved by cross-correlating ambient noise at all receivers were processed following both two-dimensional and three-dimensional approaches using a sequence similar to the one applied to the activesource three-dimensional data. The dip-moveout stacked section reveals a number of events similar to those observed on the processed active seismic sections. In particular, the passive seismic interferometry method is capable to partly image shallowly dipping reflections but did not produce convincing images of steeply dipping reflections. Dip-moveout stacked sections obtained with different cross-correlation time windows indicate that the strength and number of reflections generally increase with longer noise records. However, a few reflections at depth show reduced coherency with longer noise time windows. The passive seismic interferometry results over the Lalor mining area are encouraging, but image quality of the passive survey is lower than the acquired active three-dimensional survey at the area. Future ambient noise surveys with longer offsets, shorter receiver spacing, and wider azimuth distribution are needed in crystalline rock environment to address the potential of the method for mineral exploration.

Journal ArticleDOI
TL;DR: In this article, the collective properties of self-propelled particles (SPPs) moving in two-dimensional heterogeneous space are investigated and it is shown that for strong enough spatial heterogeneity, the well-documented high-density, highordered propagating bands that emerge in homogeneous space disappear.
Abstract: We present a detailed study of the large-scale collective properties of self-propelled particles (SPPs) moving in two-dimensional heterogeneous space. The impact of spatial heterogeneities on the ordered, collectively moving phase is investigated. We show that for strong enough spatial heterogeneity, the well-documented high-density, high-ordered propagating bands that emerge in homogeneous space disappear. Moreover, the ordered phase does not exhibit long-range order, as occurs in homogeneous systems, but rather quasi-long range order: i.e. the SPP system becomes disordered in the thermodynamical limit. For finite size systems, we find that there is an optimal noise value that maximizes order. Interestingly, the system becomes disordered in two limits, for high noise values as well as for vanishing noise. This remarkable finding strongly suggests the existence of two critical points, instead of only one, associated to the collective motion transition. Density fluctuations are consistent with these observations, being higher and anomalously strong at the optimal noise, and decreasing and crossing over to normal for high and low noise values. Collective properties are investigated in static as well as dynamic heterogeneous environments, and by changing the symmetry of the velocity alignment mechanism of the SPPs.