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Showing papers on "Noise (radio) published in 2005"


Journal ArticleDOI
TL;DR: In this paper, an estimate of the Green's function between two seismic stations can be obtained from the time-derivative of the long-time average cross correlation of ambient noise between these two stations.
Abstract: [1] It has been demonstrated experimentally and theoretically that an estimate of the Green's function between two seismic stations can be obtained from the time-derivative of the long-time average cross correlation of ambient noise between these two stations. This TDGF estimate from just the noise field includes all tensor components of the Green's function and these Green's function estimates can be used to infer Earth structure. We have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in Southern California. The data processing yielded thousands of cross-correlation pairs, for receiver separations from 4–500 km, which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0.1–2 Hz.

527 citations


Journal ArticleDOI
TL;DR: Sabra et al. as mentioned in this paper used a simple but densely sampled tomographic procedure to estimate the surface wave velocity structure within the frequency range of 0.1-0.2 Hz for a region in Southern California.
Abstract: Received 5 April 2005; revised 23 May 2005; accepted 9 June 2005; published 26 July 2005. [1] Since it has already been demonstrated that point-topoint seismic propagation Green Functions can be extracted from seismic noise, it should be possible to image Earth structure using the ambient noise field. Seismic noise data from 148 broadband seismic stations in Southern California were used to extract the surface wave arrival-times between all station pairs in the network. The seismic data were then used in a simple, but densely sampled tomographic procedure to estimate the surface wave velocity structure within the frequency range of 0.1–0.2 Hz for a region in Southern California. The result compares favorably with previous estimates obtained using more conventional and elaborate inversion procedures. This demonstrates that coherent noise field between station pairs can be used for seismic imaging purposes. Citation: Sabra, K. G., P. Gerstoft, P. Roux, W. A. Kuperman, and M. C. Fehler (2005), Surface wave tomography from microseisms in Southern California, Geophys. Res. Lett., 32, L14311, doi:10.1029/2005GL023155.

526 citations


Journal ArticleDOI
TL;DR: The results of a series of large-eddy simulations of heated and unheated jets using approximately 106 grid points are presented in this article, where the authors show that the jets exhibit a faster centerline mean velocity decay rate relative to the existing data, with a corresponding 3-4'% over-prediction of the peak root-mean-square level.
Abstract: The results of a series of large-eddy simulations of heated and unheated jets using approximately 106 grid points are presented. The computations were performed on jets at operating conditions originally investigated by Tanna in the late 1970s [H. K. Tanna, “An experimental study of jet noise Part I: Turbulent mixing noise,” J. Sound Vib., 50, 405 (1977)]. Three acoustic Mach numbers are investigated (Uj∕a∞=0.5, 0.9, and 1.5) at cold (constant stagnation temperature) and heated conditions (Tj∕T∞=1.8, 2.7, and 2.3, respectively). The jets’ initial annular shear layers are thick relative to experimental jets and are quasi-laminar with superimposed disturbances from linear instability theory. It is observed that qualitative changes in the jets’ mean- and turbulent field structure with Uj and Tj are consistent with previous experimental data. However, the jets exhibit a faster centerline mean velocity decay rate relative to the existing data, with a corresponding 3–4 % over-prediction of the peak root-mean-square level. The acoustic pressure fluctuations in the far field are analyzed in detail. The accuracy of the overall sound pressure level predictions is found to be a strong function of the jet Mach number, with the lowest speed jets being the least accurate. At all conditions the peak acoustic frequency occurs at approximately St=fDj∕Uj=0.25. The limited resolution of the computations is shown to impact the radiated sound by yielding effectively low-pass filtered versions of the experimental spectra, with a maximum frequency of St≈1.2.

286 citations


Journal ArticleDOI
TL;DR: The noise-free transitions between the two basins of attraction that appear in the nonlinear regime are measured, and good agreement with theory is found.
Abstract: We report quantitative measurements of the nonlinear response of a radio frequency mechanical resonator with a very high quality factor. We measure the noise-free transitions between the two basins of attraction that appear in the nonlinear regime, and find good agreement with theory. We measure the transition rate response to controlled levels of white noise, and extract the basin activation energy. This allows us to obtain precise values for the relevant frequencies and the cubic nonlinearity in the Duffing oscillator, with applications to parametric sensing.

217 citations


Journal ArticleDOI
TL;DR: In this article, a power/ground planes design for efficiently eliminating the ground bounce noise (GBN) in high-speed digital circuits is proposed by using low-period coplanar electromagnetic bandgap (LPC-EBG) structure.
Abstract: A power/ground planes design for efficiently eliminating the ground bounce noise (GBN) in high-speed digital circuits is proposed by using low-period coplanar electromagnetic bandgap (LPC-EBG) structure. Keeping solid for the ground plane and designing an LPC-EBG pattern on the power plane, the proposed structure omnidirectionally behaves highly efficiently in suppression of GBN (over 50 dB) within the broad-band frequency range (over 4 GHz). In addition, the proposed designs suppress radiated emission (or electromagnetic interference) caused by the GBN within the stopband. These extinctive behaviors of low radiation and broad-band suppression of the GBN is demonstrated numerically and experimentally. Good agreements are seen. The impact of the LPC-EBG power plane on the signal integrity for the signals referring to the power plane is investigated. Two possible solutions, differential signals and an embedded LPC-EBG power plane concept, are suggested and discussed to reduce the impact.

214 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed noise model for Doppler radio science experiments is presented. But the model focuses primarily on the Fourier range ≈10−4-1 Hz, but the authors briefly discuss noise in lower-frequency observations.
Abstract: [1] We discuss noise in Doppler tracking of deep space probes and provide a detailed noise model for Doppler radio science experiments. The most sensitive current experiments achieve fractional frequency fluctuation noise of about 3 × 10−15 at 1000-s integration time, corresponding to better than 1 micron per second velocity noise. Our noise model focuses primarily on the Fourier range ≈10−4–1 Hz, but we briefly discuss noise in lower-frequency observations. We indicate applications of the noise model to experiment planning, identify phenomena limiting current Doppler sensitivity, and discuss the prospects for significant sensitivity improvements.

174 citations


DissertationDOI
01 Nov 2005
TL;DR: The Microwave Kinetic Inductance Detectors (MKIDs) as mentioned in this paper make use of the change in the surface impedance of a superconductor as incoming photons break up Cooper pairs.
Abstract: Low temperature detectors have been a subject of intense interest to the scientific community over the last decade. These detectors work at very low temperatures, often well below 1 Kelvin, to minimize the noise in the measurement of photons. This leads to very powerful detectors applicable to a broad wavelength range. Since these detectors are so sensitive even single pixels and small arrays (up to several hundred pixels) enable deeper explorations of the cosmos than ever before. Instruments based on these technologies have been used at submillimeter, optical, and X-ray wavelengths. The scientific prospects for these detectors increase as they grow in pixel count. For some applications, especially for Cosmic Microwave Background (CMB) polarization work, a large focal plane will not only increase efficiency but will also enable new and vital science. Current superconducting technologies, such as Transition Edge Sensors (TESs), can currently deliver extremely high sensitivity in the submillimeter and read-noise free imaging spectroscopy at Optical/UV and X-ray wavelengths, but the largest arrays contain less that 100 pixels. In order to make real progress these arrays must contain many thousands of pixels. This is a formidable technical challenge. This thesis will explore a promising emerging technology called Microwave Kinetic Inductance Detectors (MKIDs). MKIDs make use of the change in the surface impedance of a superconductor as incoming photons break up Cooper pairs. This is accomplished by making the strip of superconductor part of a microwave resonant circuit, and monitoring the phase of a signal transmitted through (or past) the resonator. The primary advantage of this technology is that by using resonant circuits with high quality factors, passive frequency domain multiplexing will allow up to thousands of resonators to be read out through a single coaxial cable and a single HEMT amplifier. This eliminates the cryogenic electronics (SQUIDS) and wiring problems associated with current superconducting devices. Inexpensive and powerful room-temperature readout electronics can leverage the microwave integrated circuits developed for wireless communications. When this project started four years ago MKIDs were just a concept. In this thesis I will recount the progress we have made in taking this concept and turning it into a detector technology, building on the work we published in Nature in 2003. I will demonstrate that we have overcome the major technical obstacles and shown conclusively that MKIDs work, and should provide much larger arrays than are possible with other technologies. Due to our work at Caltech and JPL, MKIDs are considered one of the leading technologies to reach the ambitious goals set for future ground and space missions. The noise performance is already good enough for sky-limited, ground-based, submillimeter astronomy. Despite MKIDs acceptable noise performance for ground-based astronomy, there are many applications which require lower detector noise. The simple MKIDs we measure in this thesis still exhibit a noise higher than theory would predict which could limit their usefulness for some applications. In Chapters 7-9 we perform several experiments which identify the source of the excess noise as the substrate. In the course of these experiments to characterize and identify the noise, we successfully demonstrate two distinct approaches which dramatically reduce the noise excess.

168 citations


Journal ArticleDOI
TL;DR: The results imply that ion channel noise contributes significantly to membrane voltage fluctuations at the subthreshold voltage range, and that Na+ conductance plays a key role in determining the amplitude of this noise by acting as a voltage‐dependent amplifier of low‐frequency transients.
Abstract: Neurones are noisy elements. Noise arises from both intrinsic and extrinsic sources, and manifests itself as fluctuations in the membrane potential. These fluctuations limit the accuracy of a neurone's output but have also been suggested to play a computational role. We present a detailed study of the amplitude and spectrum of voltage noise recorded at the soma of layer IV–V pyramidal neurones in slices taken from rat neocortex. The dependence of the noise on holding potential, synaptic activity and Na+ conductance is systematically analysed. We demonstrate that voltage noise increases non-linearly as the cell depolarizes (from a standard deviation (s.d.) of 0.19 mV at −75 mV to an s.d. of 0.54 mV at −55 mV). The increase in voltage noise is accompanied by an increase in the cell impedance, due to voltage dependence of Na+ conductance. The impedance increase accounts for the majority (70%) of the voltage noise increase. The increase in voltage noise and impedance is restricted to the low-frequency range (0.2–2 Hz). At the high frequency range (5–100 Hz) the voltage noise is dominated by synaptic activity. In our slice preparation, synaptic noise has little effect on the cell impedance. A minimal model reproduces qualitatively these data. Our results imply that ion channel noise contributes significantly to membrane voltage fluctuations at the subthreshold voltage range, and that Na+ conductance plays a key role in determining the amplitude of this noise by acting as a voltage-dependent amplifier of low-frequency transients.

152 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the correlation between turbulent fluctuations along the lip shear layer of a high-speed jet and its potential core and found that the strongest noise source lies downstream of the end of the potential core.
Abstract: To locate noise sources in high-speed jets, the far-field sound pressure fluctuations microphone showed weaker values. By moving the laser probe to various locations in the jet, it was found that the strongest noise source lay downstream of the end of the potential core and extended many diameters beyond. Correlation measurements from turbulent fluctuations along the lip shear layer showed a Mach-number dependency: significant values were measured in supersonic jets, while correlations fell below the noise floor for subsonic jets. Various additional analyses showed that fluctuations from large coherent structures mostly contributed to the measured correlation, while that from small-scale structures fell below the noise floor.

149 citations


Journal ArticleDOI
TL;DR: A model of active Brownian agents interacting via a harmonic attractive potential in a two-dimensional system in the presence of noise possesses a noise-induced transition characterized by the breakdown of translational motion and the onset of swarm rotation as the noise intensity is increased.
Abstract: We consider a model of active Brownian agents interacting via a harmonic attractive potential in a two-dimensional system in the presence of noise. By numerical simulations, we show that this model possesses a noise-induced transition characterized by the breakdown of translational motion and the onset of swarm rotation as the noise intensity is increased. Statistical properties of swarm dynamics in the weak noise limit are further analytically investigated.

139 citations


Journal ArticleDOI
TL;DR: In this paper, a total of 96 absolute gravity (AG) measurements at the Membach station and 221 at the Proudman Oceanographic Laboratory (POL) were analyzed for noise content.
Abstract: [1] A total of 96 absolute gravity (AG) measurements at the Membach station and 221 at the Proudman Oceanographic Laboratory (POL) is analyzed for noise content. The lengths of the series were around 10 years (POL) and 8 years (Membach). First the noise at frequencies lower than 1 cpd is studied. This noise consists in setup-dependent offsets and geophysical colored sources. The setup white noise is estimated using continuous relative superconducting gravity (SG) measurements at Membach. The colored environmental noise affecting both AG and SG is estimated using the maximum likelihood estimation technique to fit two types of stochastic models to the SG time series, power law noise, and first-order Gauss Markov (FOGM) noise. We estimate the noise amplitudes of a white noise process plus power law model while simultaneously solving for the spectral index and the noise amplitudes of a white noise process plus FOGM noise model is also estimated. The gravity rate of change and the associated uncertainties as a function of the noise structure are then computed. At frequencies higher than 1 cpd, a time-varying white noise component usually dominates AG time series. Finally, the POL and Membach experiments are applied to estimate the uncertainties for AG campaigns repeated once or twice a year to monitor crustal deformation. Such repeated AG measurements should allow one to constrain gravity rate of change with an uncertainty of 1 nm s−2 yr−1 (or 0.5 mm yr−1) after 14 or 24 years, depending on the noise model. Therefore long-term measurements using absolute gravimeters are appropriate for monitoring slow vertical tectonic deformation.

Journal ArticleDOI
TL;DR: The interplay of slow noise with intrinsically non-Gaussian noise sources may explain the rich physics observed in the spectroscopy and in the dynamics of charge based devices.
Abstract: We study decoherence due to low frequency noise in Josephson qubits. Non-Markovian classical noise due to switching impurities determines inhomogeneous broadening of the signal. The theory is extended to include effects of high-frequency quantum noise, due to impurities or to the electromagnetic environment. The interplay of slow noise with intrinsically non-Gaussian noise sources may explain the rich physics observed in the spectroscopy and in the dynamics of charge based devices.

Journal ArticleDOI
TL;DR: In this article, the effects of noise reduction of six tree belts were examined, where an amplifier was placed in front of each tree belt, while a noise meter was placed at various heights and distances behind the tree belt.

Journal ArticleDOI
TL;DR: In this paper, the ambient infrasound noise environment is characterized for 21 globally distributed Infrasound arrays in the frequency band of 0.03 to 7 Hz, and power spectral density (PSD) is measured for one site of each array for 21 intervals at each of four times of day from January 2003 through January 2004.
Abstract: [1] The ambient infrasound noise environment is characterized for 21 globally distributed infrasound arrays in the frequency band of 0.03 to 7 Hz. Power Spectral Density (PSD) is measured for one site of each array for 21 intervals at each of four times of day from January 2003 through January 2004. The ambient noise at infrasound stations is highly variable by season, time of day and station. Noise spectra for an individual station may vary by four orders of magnitude at any given frequency. Preliminary infrasound noise models are defined, which can be used as baselines for evaluating ambient noise at current and new infrasound stations. Median noise levels in the microbarom band centered on 0.2 Hz vary smoothly in an annual pattern, with most stations observing maximum noise during local winter. Noise amplitudes do not have a normal or log-normal distribution, but rather are skewed to larger amplitudes.

Journal ArticleDOI
TL;DR: This work presents a framework for the analysis of mutually-coupled antennas in a multiple-input multiple-output system and illustrates the performance gains possible from matching the coupled antenna/receive amplifier subsystem for minimum noise figure as compared to matching for maximum signal power transfer.
Abstract: This work presents a framework for the analysis of mutually-coupled antennas in a multiple-input multiple-output system. The approach uses network theory to formulate the transfer matrix relating the signals input to the transmit antennas to the signals at the output of the receiver front end. This transfer function includes the coupled transmit and receive antennas, the multipath propagation channel, the receiver matching network, and a realistic noise model for the receive amplifiers. Application of the formulation to coupled dipole antennas characterized using full-wave electromagnetic analysis illustrates the performance gains possible from matching the coupled antenna/receive amplifier subsystem for minimum noise figure as compared to matching for maximum signal power transfer.

Journal ArticleDOI
TL;DR: In this paper, the design of a three-axis search coil magnetometer in the 1 Hz-20 kHz range developed for the scientific satellite DEMETER was described, which achieved a noise level of 4fTHz−1∕2 at 6 kHz and a mass of 430g for the three search coils and the bracket.
Abstract: The design of a three-axis search coil magnetometer in the 1 Hz–20 kHz range developed for the scientific satellite DEMETER is described. The sensitivity is a critical parameter as the search coil must be able to detect very weak signals in the Earth’s magnetosphere. The sensitivity is mainly constrained by the size and the mass allocated onboard the spacecraft. Significant improvements are made in terms of mass and sensitivity over previous space-borne search coils. We achieve a noise level of 4fTHz−1∕2 at 6 kHz and a mass of 430g for the three search coils and the bracket. A good agreement is observed on the estimation by finite element analysis of the sensor impedance and the measurements. The gain and noise model of the search coil and its preamplifier also agree quite well with measurements.

Journal ArticleDOI
TL;DR: The demodulation of ultra-short light pulses with photodetectors is accompanied by excess phase noise at the pulse repetition rate and harmonics in the spectrum of the photocurrent, which can seriously limit the stability of frequency transfer from optical to microwave domain.
Abstract: The demodulation of ultra-short light pulses with photodetectors is accompanied by excess phase noise at the pulse repetition rate and harmonics in the spectrum of the photocurrent. The major contribution to this noise is power fluctuations of the detected pulse train that, if not compensated for, can seriously limit the stability of frequency transfer from optical to microwave domain. By making use of an infrared femtosecond laser, we measured the spectral density of the excess phase noise, as well as power-to-phase conversion for different types of InGaAs photodetectors. Noise measurements were performed with a novel type of dual-channel readout system using a fiber coupled beam splitter. Strong suppression of the excess phase noise was observed in both channels of the measurement system when the average power of the femtosecond pulse train was stabilized. The results of this study are important for the development of low-noise microwave sources derived from optical "clocks" and optical frequency synthesis.

Journal ArticleDOI
TL;DR: In this paper, the authors present a survey of equatorial noise emissions in the inner magnetosphere close to the geomagnetic equator at frequencies below the local lower hybrid frequency.

Journal ArticleDOI
TL;DR: In this paper, the brightness temperature transformation was applied to microwave data to retrieve Jacobian weighted upper tropospheric relative humidity (UTH) in a broad layer centered roughly between 6 and 8 km altitude.
Abstract: [1] A brightness temperature (BT) transformation method can be applied to microwave data to retrieve Jacobian weighted upper tropospheric relative humidity (UTH) in a broad layer centered roughly between 6 and 8 km altitude. The UTH bias is below 4% RH, and the relative UTH bias below 20%. The UTH standard deviation is between 2 and 6.5% RH in absolute numbers, or between 10 and 27% in relative numbers. The standard deviation is dominated by the regression noise, resulting from vertical structure not accounted for by the simple transformation relation. The UTH standard deviation due to radiometric noise alone has a relative standard deviation of approximately 7% for a radiometric noise level of 1 K. The retrieval performance was shown to be of almost constant quality for all viewing angles and latitudes, except for problems at high latitudes due to surface effects. A validation of AMSU UTH against radiosonde UTH shows reasonable agreement if known systematic differences between AMSU and radiosonde are taken into account. When the method is applied to supersaturation studies, regression noise and radiometric noise could lead to an apparent supersaturation even if there were no supersaturation. For a radiometer noise level of 1 K the drop-off slope of the apparent supersaturation is 0.17% RH−1, for a noise level of 2 K the slope is 0.12% RH−1. The main conclusion from this study is that the BT transformation method is very well suited for microwave data. Its particular strength is in climatological applications where the simplicity and the a priori independence are key advantages.

Proceedings ArticleDOI
23 May 2005
TL;DR: In this article, the use of single dielectric barrier discharge plasma actuator technology for landing gear noise control is explored, and proof-of-concept experiments that use plasma actuators to create an effective "plasma fairing" which minimizes flow separation over the gear are presented.
Abstract: A primary component of airframe noise on both takeoff and landing approach is due to the landing gear. The inherent bluff body characteristics of the landing gear give rise to large-scale flow separation that results in noise production through unsteady wake flow and large-scale vortex instability and deformation. In this paper the use of single dielectric barrier discharge plasma actuator technology for landing gear noise control is explored. Proof-of-concept experiments that use plasma actuators to create an effective "plasma fairing" which minimizes flow separation over the gear are presented. Nomenclature D = cylinder diameter D Re = Reynolds number based on cylinder diameter D St = Strouhal number based on cylinder diameter ∞ U = free stream velocity * b f = body force (per unit volume) vector φ = electric potential D λ = Debye length 0 e = electrical permittivity of free space

Journal ArticleDOI
TL;DR: In this article, a semi-empirical theory for predicting fine-scale turbulence noise from high-temperature jets, up to a temperature ratio above that of present day commercial engines, is presented.
Abstract: Experimental measurements indicate that the noise radiated from a jet depends not just on the jet-exit velocity alone, but is significantly affected by the jet temperature. Now, there is evidence to support the proposition that jet mixing noise consists of two principal components. These are the noise from the large turbulence structures of the jet flow and the fine-scale turbulence. The prediction of fine-scale turbulence noise from hot jets is considered. Earlier Tam and Auriault developed a semi-empirical theory capable of predicting the fine-scale turbulence noise from cold to moderate temperature jets. In this work, their semi-empirical theory is extended to high-temperature jets, up to a temperature ratio above that of present day commercial engines. The density gradient present in hot jets promotes the growth of Kelvin-Helmholtz instability in the jet mixing layer. This causes a higher level of turbulent mixing and stronger turbulence fluctuations. In addition, recent experiments reveal that the two-point space-time correlation function of turbulent mixing for hot jets is substantially different from that for cold jets. The eddy decay time is shorter, and the eddy size is slightly reduced. These changes have an appreciable impact on the noise radiated. In the present extended fine-scale turbulence theory, both effects are taken into account

Journal ArticleDOI
TL;DR: In this article, a method was proposed to control common mode currents produced in electric vehicle (EV) drive systems so as to prevent a series resonance phenomenon from occurring in common current paths formed in EV drive systems.
Abstract: Methods to control electromagnetic interference (EMI) noises, especially common mode currents and radiations that are generated in electric vehicle (EV) drive systems, were studied using an electric vehicle (EV) prototype. Fast fourier transform (FFT) analyses of the voltage and current appearing in the EV drive systems showed that electromagnetic interference (EMI) noise sources are produced by voltage fluctuations occurring at the time of switching operations and the produced noise sources cause common mode currents to flow into the ground when the body frame is connected to the ground. Moreover, the flowing common mode currents induce radiated EMI noises, while the generated EMI noises are transmitted between the inverter, batteries, and motors. Thus, the produced radiated EMI noises have an effect on nearby vehicles. A method was proposed that controls common mode currents produced in EV drive systems so as to prevent a series resonance phenomenon from occurring in common current paths formed in EV drive systems. This method is also effective in controlling radiated EMI noises. Furthermore, to control radiated EMI noises, another method was proposed that cancels the surface currents flowing in P and N power transmission lines between the inverter and batteries. Effectiveness of these proposed EMI noise control methods was verified from simulations and experiments.

Journal ArticleDOI
TL;DR: The noise properties of pump currents through an open double-quantum-dot setup with nonadiabatic ac driving are investigated and a rotating-wave approximation provides analytical expressions for the current and its noise power and allows to optimize the noise characteristics.
Abstract: The noise properties of pump currents through an open double-quantum-dot setup with nonadiabatic ac driving are investigated. Driving frequencies close to the internal resonances of the double-dot system mark the optimal working points at which the pump current assumes a maximum while its noise power possesses a remarkably low minimum. A rotating-wave approximation provides analytical expressions for the current and its noise power and allows to optimize the noise characteristics. The analytical results are compared to numerical results from a Floquet transport theory.

Journal ArticleDOI
TL;DR: In this article, the authors analyzed nearly 2 years of data, composed of 244 triggered noise records and 44 earthquakes, taking advantage of an improved ver- sion of the Thompson-Haskell propagation matrix method.
Abstract: The aim of this work is to check the stability of the horizontal-to-vertical spectral ratios (HVSRs) calculated at the Venosa station site (Italy). This site lies over a layer of anthropogenic fill (4 m thick), a rigid layer of conglomerates (15 m thick), and a thick layer of clays (about 300 m thick) above the seismic bedrock. The velocity inversion, which takes place at the conglomerates-clays interface, is of main importance for the amplification behavior of this site. We have analyzed nearly 2 years of data, composed of 244 triggered noise records and 44 earthquakes. The results obtained by the two data sets show different site-response characteristics. In particular, the earthquake HVSR is not deamplified in the frequency range 1-8 Hz like the triggered noise HVSR. To find out the origin of this difference, we modeled both the triggered noise and the earthquakes, taking advantage of an improved ver- sion of the Thompson-Haskell propagation matrix method. The differences between triggered-noise- and earthquake-amplification functions might be explained by the difference in composition and propagation of the seismic wave fields. Moreover, we show that the nonlinear behavior of the anthropogenic fill might explain the presence of the misfit of the resonance frequency attributed to this layer between triggered noise and earthquakes.

Journal ArticleDOI
TL;DR: In this paper, a small, high performance fiber optic microphone has been designed, fabricated, and tested using a 1.5μm-thick silicon diaphragm active element.
Abstract: A small, high performance fiber optic microphone has been designed, fabricated, and tested. The device builds on a previous design utilizing a thin, seven-fiber optical probe, but now adds a micromachined 1.5μm thick silicon diaphragm active element. The resulting sensor head is thin (several millimeters) and light, and the overall microphone system is less expensive than conventional microphones with comparable performance. Measurements in the laboratory using a standard free-field technique at high frequencies, an enclosed calibrator at lower frequencies, and pseudostatic pressure changes demonstrate uniform broadband response from near dc (0.01 Hz) up to near 20 kHz. The measured microphone internal noise is nearly flat over this band and does not exhibit noticeable levels of 1∕f noise. Over the audible portion of this band, the minimum detectable pressure is determined to be 680μPa per root Hz with further reductions possible using lower noise∕higher power light sources and∕or improvements in the diap...

Journal ArticleDOI
TL;DR: By scattering theory it is shown that spin current noise in normal electric conductors in contact with nanoscale ferromagnets increases the magnetization noise by means of a fluctuating spin-transfer torque.
Abstract: By scattering theory we show that spin current noise in normal electric conductors in contact with nanoscale ferromagnets increases the magnetization noise by means of a fluctuating spin-transfer torque. Johnson-Nyquist noise in the spin current is related to the increased Gilbert damping due to spin pumping, in accordance with the fluctuation-dissipation theorem. Spin current shot noise in the presence of an applied bias is the dominant contribution to the magnetization noise at low temperatures.

Patent
Naoya Uehigashi1
25 Jan 2005
TL;DR: In this paper, a self-propelling cleaner operates a main body in a silent mode and sets the propelling speed of the main body to a low speed lower than a normal speed irrespective whether the selected operation mode is a normal mode or the silent mode.
Abstract: While a receiver 6 receives radio wave of a predetermined frequency transmitted from a transmitter 11, a self-propelling cleaner 1 operates a main body in a silent mode and sets the propelling speed of the main body to a low speed lower than a normal speed irrespective whether the selected operation mode is a normal mode or the silent mode, so that noise generated from the main body can be reduced. Thus, so long as a user merely places the transmitter 11 nearby, noise generated from the main body can be reduced when the self-propelling cleaner 1 approaches the user, so that the user's action taken at this time can not be interfered by noise generated from the self-propelling cleaner 1.

01 Dec 2005
TL;DR: In this paper, the feasibility of using S-to-P converted phases to image the seismic discontinuity structure of the crust and upper mantle was studied, and it was shown that a significant level of P-wave energy arriving before the direct S-wave arrival can interfere with the StoP converted phase of interest and may result in Sp receiver function phases that do not represent true earth structure.
Abstract: SUMMARY We present results from forward modelling to study the feasibility of using S-to-P converted phases to image the seismic discontinuity structure of the crust and upper mantle. We show that a significant level of P-wave energy arriving before the direct S-wave arrival can interfere with the S-to-P converted phases of interest and may result in Sp receiver function phases that do not represent true earth structure. The source of this P-wave energy is attributable to a number of phases, including those that have undergone multiple reflections off the Earth’s surface. For deep focus earthquakes (300‐600 km deep), a significant amount of P-wave energy is observed from pPPP, pPPPP and sPPPP phases, and arrives within the same time window as predicted for S-to-P converted phases from the direct S phase arrival. Furthermore, for earthquakes at all depths, interfering P-wave energy arrives within the same time window as predicted for S-to-P converted phases from the SKS phase arrival, limiting the usefulness of SKSp receiver functions for upper mantle imaging. To isolate true Sp receiver function phases from contamination due to other P-wave phases, we find it necessary to stack receiver functions from a range of epicentral distances and depths in order to aid the suppression of noise and other unwanted phases. We provide constraints on the noise levels to be expected as a function of epicentral distance and earthquake depth. We find that the lowest noise levels are achievable by restricting epicentral distance to less than 75 degrees and the depth of earthquakes used to less than 300 km.

Patent
28 Feb 2005
TL;DR: In this paper, a method of examining a sample comprises exposing the sample to a pump pulse of electromagnetic radiation for a first period of time, exposing the signal to a stimulant pulse for a second period, which overlaps in time with at least a portion of the first exposing, and interfering the signal pulse with a reference pulse of EM radiation, to determine which portions of the signal pulses were produced during the exposing of the sample.
Abstract: A method of examining a sample comprises exposing the sample to a pump pulse of electromagnetic radiation for a first period of time, exposing the sample to a stimulant pulse of electromagnetic radiation for a second period of time which overlaps in time with at least a portion of the first exposing, to produce a signal pulse of electromagnetic radiation for a third period of time, and interfering the signal pulse with a reference pulse of electromagnetic radiation, to determine which portions of the signal pulse were produced during the exposing of the sample to the stimulant pulse. The first and third periods of time are each greater than the second period of time.

Journal ArticleDOI
TL;DR: In this article, the authors used three completely independent datasets to obtain robust estimates in the solar case for � = 1 modes, and they also showed that the height of the solar atmosphere where the modes are observed must be taken into account.
Abstract: Acoustic rates of excitation of solar p modes can be estimated from observations in order to place constraints on the modelling of the excitation process and the layers where it occurs in the star. For several reasons (including a poor signal to noise ratio and mode overlap), this estimation is difficult. In this work, we use three completely independent datasets to obtain robust estimates in the solar case for � = 1 modes. We also show that the height in the solar atmosphere where the modes are observed must be taken into account. Our three sets of results are shown to be consistent, particularly in the lower part of the p-mode spectrum (from 1.8 mHz to 2.8 mHz). At higher frequencies, the agreement is not as good, because of a larger dispersion of the measurements and also because of some systematic differences which might be due to observation height estimation or to a systematic influence of the noise.