Showing papers on "Noise (radio) published in 2001"
TL;DR: It is shown how to use DFA appropriately to minimize the effects of trends, how to recognize if a crossover indicates indeed a transition from one type to a different type of underlying correlation, or if the crossover is due to a trend without any transition in the dynamical properties of the noise.
Abstract: scaling behavior. We find that crossovers result from the competition between the scaling of the noise and the ‘‘apparent’’ scaling of the trend. We study how the characteristics of these crossovers depend on ~i! the slope of the linear trend; ~ii! the amplitude and period of the periodic trend; ~iii! the amplitude and power of the power-law trend, and ~iv! the length as well as the correlation properties of the noise. Surprisingly, we find that the crossovers in the scaling of noisy signals with trends also follow scaling laws—i.e., long-range power-law dependence of the position of the crossover on the parameters of the trends. We show that the DFA result of noise with a trend can be exactly determined by the superposition of the separate results of the DFA on the noise and on the trend, assuming that the noise and the trend are not correlated. If this superposition rule is not followed, this is an indication that the noise and the superposed trend are not independent, so that removing the trend could lead to changes in the correlation properties of the noise. In addition, we show how to use DFA appropriately to minimize the effects of trends, how to recognize if a crossover indicates indeed a transition from one type to a different type of underlying correlation, or if the crossover is due to a trend without any transition in the dynamical properties of the noise.
1,227 citations
TL;DR: It is argued that acoustic thermal fluctuations, with displacement amplitudes of 3 fm, contain substantial ultrasonic information and it is shown that the noise autocorrelation function is the waveform that would be obtained in a direct pulse/echo measurement.
Abstract: Noise generated in an ultrasonic receiver circuit consisting of transducer and amplifier is usually ignored, or treated as a nuisance. Here it is argued that acoustic thermal fluctuations, with displacement amplitudes of 3 fm, contain substantial ultrasonic information. It is shown that the noise autocorrelation function is the waveform that would be obtained in a direct pulse/echo measurement. That thesis is demonstrated in experiments in which direct measurements are compared to correlation functions. The thermal nature of the elastodynamic noise that generates these correlations is confirmed by an absolute measurement of their strength, essentially a measurement of the sample temperature.
611 citations
TL;DR: A measure is introduced for the distance between two spike trains that has a time constant as a parameter and can be used to determine the intrinsic noise of a neuron.
Abstract: The discrimination between two spike trains is a fundamental problem for both experimentalists and the nervous system itself. We introduce a measure for the distance between two spike trains. The distance has a time constant as a parameter. Depending on this parameter, the distance interpolates between a coincidence detector and a rate difference counter. The dependence of the distance on noise is studied with an integrate-and-fire model. For an intermediate range of the time constants, the distance depends linearly on the noise. This property can be used to determine the intrinsic noise of a neuron.
569 citations
TL;DR: In this article, the authors reviewed the effect of facility noise on the trend in transition Reynolds numbers in conventional ground-test facilities, of both conventional and quiet design, at hypersonic and high supersonic speeds.
Abstract: It is well known that the high levels of noise present in conventional hypersonic ground-test facilities cause transition to occur earlier than in e ight. Flight measurements of incoming noise are reviewed and compared with measurements in ground-test facilities, of both conventional and quiet design, at hypersonic and high supersonic speeds. The low noise present in e ight is apparently the reason for the very large transition Reynolds numbers sometimes measured in e ight, when roughness, crosse ow, and other factors are controlled. Design will usually involve consideration of the trend in transition when a parameter is varied. The effect of facility noise on these trends is reviewed. In some cases, the trend of conventional-tunnel data is opposite to the trend in quiet-tunnel data. Thus, transition measurements in conventional ground-test facilities are not reliable predictors of e ight performance, except perhaps in special cases.
344 citations
TL;DR: In this article, it was shown that in a second-generation interferometer composed of arm cavities and a signal recycling cavity, quantum shot noise and quantum radiation pressure-fluctuation noise are dynamically correlated, the noise curve exhibits two resonant dips, and the standard quantum limit can be beaten by a factor of 2, over a frequency range Δf/f∼1.
Abstract: It has long been thought that the sensitivity of laser interferometric gravitational-wave detectors is limited by the free-mass standard quantum limit, unless radical redesigns of the interferometers or modifications of their input or output optics are introduced. Within a fully quantum-mechanical approach we show that in a second-generation interferometer composed of arm cavities and a signal recycling cavity, e.g., the LIGO-II configuration, (i) quantum shot noise and quantum radiation-pressure-fluctuation noise are dynamically correlated, (ii) the noise curve exhibits two resonant dips, (iii) the standard quantum limit can be beaten by a factor of 2, over a frequency range Δf/f∼1, but at the price of increasing noise at lower frequencies.
244 citations
TL;DR: In this article, an active noise control system has a feed-forward control unit for being supplied with reference signals highly correlated to noise from a noise source and generating a noise cancellation signal which is out of phase to noise in the passenger compartment of the vehicle.
Abstract: An active noise control system is capable of canceling out noise in the passenger compartment of a vehicle based on low-frequency road noise. The active noise control system has a feed-forward control unit for being supplied with reference signals highly correlated to noise from a noise source and generating a noise cancellation signal which is out of phase to noise in the passenger compartment of the vehicle, and a canceling sound generating unit disposed in the passenger compartment for generating a noise canceling sound in response to the noise cancellation signal from said feed-forward control unit. The active noise control system also has microphones for generating reference signals which are positioned respectively near the base of the front seat, near the center of a roof, and within a trunk compartment, i.e., respectively at vibrational antinodes of a primary or secondary acoustic normal mode of the passenger compartment in the longitudinal direction thereof. Output signals from the microphones are supplied as the reference signals.
241 citations
TL;DR: This work estimated the scatter fractions and effects of scatter on image noise, and derived a relationship between the noise in a reconstructed image and in an x-ray intensity measurement, and estimated the image noise under relevant clinical conditions.
Abstract: Cone beam CT has a capability for the 3-dimensional imaging of large volumes with isotropic resolution, and has a potentiality for 4-dimensional imaging (dynamic volume imaging), because cone beam CT acquires data of a large volume with one rotation of an x-ray tube-detector pair. However, one of the potential drawbacks of cone beam CT is a larger amount of scattered x-rays, which may enhance the noise in reconstructed images, and thus affect the low-contrast detectablity. Our aim in this work was to estimate the scatter fractions and effects of scatter on image noise, and to seek methods of improving image quality in cone beam CT. First we derived a relationship between the noise in a reconstructed image and in an x-ray intensity measurement. Then we estimated the scatter to primary ratios in x-ray measurements using a Monte-Carlo simulation. From these we estimated the image noise under relevant clinical conditions. The results showed that the scattered radiation made a substantial contribution to the image noise. However, focused collimators could improve it by decreasing the scattered radiation drastically while keeping the primary radiation at nearly the same level. A conventional grid also improved the image noise, though the improvement was less than that of focused collimators.
220 citations
TL;DR: In this article, the generation of electron-acoustic waves in an unmagnetized, four-component plasma consisting of stationary cold and hot Maxwellian electrons, drifting electron beam and ions was examined.
201 citations
TL;DR: Noise enhanced stability of periodically driven metastable states in a system described by piecewise linear potential is studied and the growing of the average escape time with the intensity of the noise is depending on the initial condition of the system.
Abstract: We study the effect of noise-enhanced stability of periodically driven metastable states in a system described by piecewise linear potential. We find that the growing of the average escape time with the intensity of the noise is depending on the initial condition of the system. We analytically obtain the condition for the noise enhanced stability effect and verify it by numerical simulations.
170 citations
TL;DR: In this paper, a method is proposed to reduce the noise contribution to mean turbulence parameters obtained by 3D acoustic Doppler velocity profiler measurements based on a noise spectrum reconstruction from cross-spectra evaluations.
Abstract: A method is proposed to reduce the noise contribution to mean turbulence parameters obtained by 3D acoustic Doppler velocity profiler measurements. It is based on a noise spectrum reconstruction from cross-spectra evaluations of two independent and simultaneous measurements of the same vertical velocity component over the whole water depth. The noise spectra and the noise variances are calculated and removed for the three fluctuating velocity components measured in turbulent, open-channel flow. The corrected turbulence spectra show a −5/3 slope over the whole inertial subrange delimited by the frequency band of the device, while the uncorrected turbulence spectra have flat high-frequency regions typical for noise effects. This method does not require any hypothesis on the flow characteristics nor does it depend on device-dependent parameters. The corrected profiles of turbulence intensities, turbulent kinetic energy, shear stress, and turbulent energy balance equation terms, such as production, t...
152 citations
TL;DR: In this article, the effect of the noise due to microscopic fluctuations on the position of a one dimensional front propagating from a stable to an unstable region in the "linearly marginal stability case" was studied.
Abstract: We study the effect of the noise due to microscopic fluctuations on the position of a one dimensional front propagating from a stable to an unstable region in the “linearly marginal stability case.” By simulating a very simple system for which the effective number N of particles can be as large as N=10150, we measure the N dependence of the diffusion constant DN of the front and the shift of its velocity vN. Our results indicate that DN∼(log N)−3. They also confirm our recent claim that the shift of velocity scales like vmin−vN≃K(log N)−2 and indicate that the numerical value of K is very close to the analytical expression Kapprox obtained in our previous work using a simple cut-off approximation.
TL;DR: In this paper, the relative intensity (RIN) and optical frequency (νrms) noise of Er-doped fiber Bragg grating lasers are investigated theoretically and experimentally.
Patent•
22 Aug 2001
TL;DR: In this paper, a method and apparatus for reducing or eliminating the transmitter signal leakage, i.e., transmitter noise, in the receiver path of an RF communications system operating in full duplex mode is provided.
Abstract: A method and apparatus is provided for reducing or eliminating the transmitter signal leakage, i.e., transmitter noise, in the receiver path of an RF communications system operating in full duplex mode. In an embodiment of the present invention, a noise cancellation loop produces an estimated transmitter signal leakage and cancels it from the receiver path to produce a received signal with little or no transmitter noise. Some of the advantages are that there is significant improvement in the isolation between the transmitter/receiver circuits, the size of the RF communications circuitry may be reduced, and the RF transmit module along with the RF receive module may be incorporated into a single RF IC chip.
TL;DR: Current popular statements that observation of the magnetic resonance phenomenon relies on the absorption and emission of radio waves are shown to be wrong.
TL;DR: In this article, the authors derived the optimal orbital alignment for cross-correlating a pair of LISA detectors, and provided the first analytic derivation of the Sagnac sensitivity curve.
Abstract: The random superposition of many weak sources will produce a stochastic background of gravitational waves that may dominate the response of the LISA (Laser Interferometer Space Antenna) gravitational wave observatory. Unless something can be done to distinguish between a stochastic background and detector noise, the two will combine to form an effective noise floor for the detector. Two methods have been proposed to solve this problem. The first is to cross-correlate the output of two independent interferometers. The second is an ingenious scheme for monitoring the instrument noise by operating LISA as a Sagnac interferometer. Here we derive the optimal orbital alignment for cross-correlating a pair of LISA detectors, and provide the first analytic derivation of the Sagnac sensitivity curve.
TL;DR: In this paper, the authors used magnetic granular films with thickness of 2/spl mu/m to suppress high frequency conduction noise in the quasimicrowave band.
Abstract: Noise suppression in downsized circuits utilizing magnetic granular films is demonstrated. Films of Fe-Al-O with thickness of 2 /spl mu/m which exhibit very high /spl mu/" dispersion in the quasimicrowave band were found to work as noise suppressors. The films were attached onto a micro-strip line and the transmission characteristics were compared. This work is the first to verify that films with only 2 /spl mu/m thickness can play a role in suppression of high frequency conduction noise in the quasimicrowave band. The results suggest a possibility of thin film noise suppressors which can be integrated into micron scale semiconductor circuits.
TL;DR: In this article, the authors reported the presence of a 106 day cycle in the radio variability of Sagittarius A* based on an analysis of data observed with the Very Large Array over the past 20 years.
Abstract: We report the presence of a 106 day cycle in the radio variability of Sagittarius A* based on an analysis of data observed with the Very Large Array over the past 20 years. The pulsed signal is most clearly seen at 1.3 cm with a ratio of cycle frequency to frequency width . The periodic signal is also clearly observed at f/Df p 2.2 5 0.3 2 cm. At 3.6 cm the detection of a periodic signal is marginal. No significant periodicity is detected at both 6 and 20 cm. Since the sampling function is irregular, we performed a number of tests to ensure that the observed periodicity is not the result of noise. Similar results were found for a maximum entropy method and a periodogram with a CLEAN method. The probability of false detection for several different noise distributions is less than 5% based on Monte Carlo tests. The radio properties of the pulsed component at 1.3 cm are a spectral index a » (for ), an amplitude , and a characteristic timescale days. a 1.0 5 0.1 S / nD S p 0.42 5 0.04 Jy Dt … 25 5 5 FWHM The lack of a VLBI detection of a secondary component suggests that the variability occurs within Sgr A* on a scale of »5 AU, suggesting an instability of the accretion disk. Subject headings: accretion, accretion disks — black hole physics — galaxies: active — Galaxy: center — radio continuum: galaxies On-line material: color figures
TL;DR: It is found that cavity noise decreases if one of the contacts is further opened and reaches nearly zero for a highly asymmetric cavity.
Abstract: We have experimentally studied shot noise of chaotic cavities defined by two quantum point contacts in series. The cavity noise is determined as $(1/4)2e|I|$ in agreement with theory and can be well distinguished from other contributions to noise generated at the contacts. Subsequently, we have found that cavity noise decreases if one of the contacts is further opened and reaches nearly zero for a highly asymmetric cavity. Heating inside the cavity due to electron-electron interaction can slightly enhance the noise of large cavities and is also discussed quantitatively.
TL;DR: It is confirmed that MRI noise can be substantially reduced by sealing the gradient coil in a vacuum chamber to block airborne vibration propagation, by supporting the gradient Coil independently to block solid vibration propagation and by decreasing the eddy currents induced in RF coils, the RF shield and the static-field-magnet cryostat.
Abstract: Fast scan techniques, which are used to reduce scanning times, have raised scanning noise levels in magnetic resonance imaging (MRI) systems, resulting in greater patient discomfort and stress. It is well known that this noise is caused by vibration of the gradient coil due to the Lorentz forces generated by the current in the gradient coil, which is placed in a static magnetic field. We have confirmed that MRI noise can be substantially reduced by sealing the gradient coil in a vacuum chamber to block airborne vibration propagation, by supporting the gradient coil independently to block solid vibration propagation and by decreasing the eddy currents induced in RF coils, the RF shield and the static-field-magnet cryostat. Based on these findings, we have developed a silent MRI system in which scanning noise is markedly reduced under a wide range of scanning conditions.
TL;DR: The timing properties of the bursting atoll source 4U 1728-34 are studied as a function of its position in the X-ray color-color diagram to find that the frequencies of the kHz QPOs are well correlated with the position of the source in the color- color diagram.
Abstract: We study the timing properties of the bursting atoll source 4U 1728-34 as a function of its position in the X-ray color-color diagram. In the island part of the color-color diagram (corresponding to the hardest energy spectra), the power spectrum of 4U 1728-34 shows several features such as a band-limited noise component present up to a few tens of Hz, a low-frequency quasi-periodic oscillation (LFQPO) at frequencies between 20 and 40 Hz, a peaked noise component around 100 Hz, and one or two QPOs at kHz frequencies. In addition to these, in the lower banana (corresponding to softer energy spectra) we also find a very low frequency noise (VLFN) component below ~1 Hz. In the upper banana (corresponding to the softest energy spectra), the power spectra are dominated by the VLFN, with a peaked noise component around 20 Hz. We find that the frequencies of the kHz QPOs are well correlated with the position in the X-ray color-color diagram. For the frequency of the LFQPO and the break frequency of the broadband noise component, the relation appears more complex. Both of these frequencies increase when the frequency of the upper kHz QPO increases from 400 to 900 Hz, but at this frequency a jump in the values of the parameters occurs. We interpret this jump in terms of the gradual appearance of a QPO at the position of the break at high inferred mass accretion rate, while the previous LFQPO disappears. Simultaneously, another kind of noise appears with a break frequency of ~7 Hz, similar to the NBO of Z sources. The 100 Hz peaked noise does not seem to correlate with the position of the source in the color-color diagram but remains relatively constant in frequency. This component may be similar to several 100 Hz QPOs observed in black hole binaries.
TL;DR: Fay et al. as discussed by the authors conducted a survey in enclosed recirculating raceways, fiberglass and concrete culture tanks, and in outdoor open ponds to understand the effect of environmental waterborne sound on cultured fish.
TL;DR: In this paper, the authors examined the nonlinear propagation of electron-acoustic waves in an unmagnetized, four-component plasma consisting of hot Maxwellian electrons, fluid cold and beam electrons and ions.
TL;DR: In this paper, the Sagnac observable was used to estimate the spectral density of the SAGA signal at low frequencies, where one type of noise strongly dominates and is not substantially correlated between the six main signals generated by the antenna.
Abstract: Armstrong et al. have recently presented new ways of combining signals to precisely cancel laser frequency noise in spaceborne interferometric gravitational wave detectors such as LISA. One of these combinations, which we will call the ``symmetrized Sagnac observable,'' is much less sensitive to external signals at low frequencies than other combinations, and thus can be used to determine the instrumental noise level. We note here that this calibration of the instrumental noise permits smoothed versions of the power spectral density of stochastic gravitational wave backgrounds to be determined with considerably higher accuracy than earlier estimates, at frequencies where one type of noise strongly dominates and is not substantially correlated between the six main signals generated by the antenna. We illustrate this technique by analyzing simple estimators of gravitational wave background power, and show that the instrumental sensitivity to broad-band backgrounds at some frequencies can be improved by a significant factor of as much as $(f\ensuremath{\tau}{/2)}^{1/2}$ in spectral density ${h}_{\mathrm{rms}}^{2}$ over the standard method, where f denotes frequency and $\ensuremath{\tau}$ denotes integration time, comparable to that which would be achieved by cross-correlating two separate antennas. The applications of this approach to studies of astrophysical gravitational wave backgrounds generated after recombination and to searches for a possible primordial background are discussed. With appropriate mission design, this technique allows an estimate of the cosmological background from extragalactic white dwarf binaries and will enable LISA to reach the astrophysical confusion noise of compact binaries from about 0.1 mHz to about 20 mHz. In a smaller-baseline follow-on mission, the technique allows several orders of magnitude improvement in sensitivity to primordial backgrounds up to about 1 Hz.
TL;DR: In this paper, a comprehensive far-field acoustics database was generated for high subsonic, turbulent jets along with mean total pressure and temperature surveys in the flowfield.
Abstract: A comprehensive far-field acoustics database was generated for high subsonic, turbulent jets along with mean total pressure and temperature surveys in the flowfield. The effects of core jet temperature and of external coflow on the far-field noise and mean flowfield characteristics are investigated. The results show peak jet noise generation in aft angles (110 < θ < 150 deg). The mean velocity measurements indicate an average potential core length in the range of 3-8 jet diameters D j , depending on the core jet flow temperatures and speed of external tunnel coflow, after which self-similar velocity decay is evidenced. Mixing devices (tabs) were used to enhance near-field jet mixing and were explored as a means for far-field noise reduction. These devices decreased the peak jet noise but were accompanied by increases in high-frequency noise. The effect of scaling from model-scale to engine-scale conditions shifts spectral peaks to lower frequencies, thereby driving high-frequency mixing noise increases (due to tab-generated flows) into the peak annoyance range.
TL;DR: In this article, the sensitivity and gain bandwidth measurements of phonon-cooled NbN superconducting hot-electron bolometer mixers are presented, and the best receiver noise temperatures are: 700 K at 1.6 THz and 1100 K at 2.5 THz.
Abstract: Sensitivity and gain bandwidth measurements of phonon-cooled NbN superconducting hot-electron bolometer mixers are presented. The best receiver noise temperatures are: 700 K at 1.6 THz and 1100 K at 2.5 THz. Parylene as an antireflection coating on silicon has been investigated and used in the optics of the receiver. The dependence of the mixer gain bandwidth (GBW) on the bias voltage has been measured. Starting from low bias voltages, close to operating conditions yielding the lowest noise temperature, the GBW increases towards higher bias voltages, up to three times the initial value. The highest measured GBW is 9 GHz within the same bias range the noise temperature increases by a factor of two.
TL;DR: In this paper, Larsen et al. used signal-noise separation (SNS) to separate MT and correlated noise signals and derive unbiased MT transfer functions with the SNS-remote-reference technique.
Abstract: SUMMARY In the presence of large and continuous correlated noise signals in measured electric and magnetic time-series, even robust remote-reference methods give erroneous estimates of MT transfer functions. If clean remote time-series are available, it is possible to separate MT and correlated noise signals and to derive unbiased MT transfer functions with the signal–noise separation method (SNS) (Larsen et al. 1996). In practice, the remote time series also contain some noise and the results can be improved by using a second remote data set and the SNS-remote-reference technique. We tested this method with data from the Saxonian Granulite Massif (SGM), Germany, where strong correlated noise signals were detected. We used remote data which were recorded 350 km away and, for short periods, data from sites of the profile across the SGM itself (distance 5 km). To show the efficiency of the signal–noise separation we first determined a ‘true’ MT transfer function from time-series with low noise level. In a second step we reproduced the results from processing very noisy data sections. We were able to determine useful MT transfer functions even when the MT variations have less than 10 per cent share of the measured variations. We identified dominant noise in the measured time-series from pipelines and trains.
TL;DR: In this article, the activation energy of local level contributing to noise was found to be Ea≈1 eV, depending on the forward current level, the noise from Schottky barrier or from the series resistance (contacts and/or base) predominates.
Abstract: The low-frequency generation recombination and the 1/f noise in AlGaN Schottky barrier photodetectors with high (40%) Al fraction has been investigated under forward and reverse bias conditions. The activation energy of local level contributing to noise was found to be Ea≈1 eV. Depending on the forward current level, the noise from Schottky barrier or from the series resistance (contacts and/or base) predominates. The upper bound of the Hooge parameter in Al0.4Ga0.6N was estimated as α⩽10.
TL;DR: In this paper, a Mach 2, rectangular nozzle with modified trailing edges was carried out using three microphones, placed 90 deg apart azimuthally in a plane normal to the jet axis.
Abstract: Acoustic measurements of a Mach 2, rectangular nozzle with modified trailing edges were carried out using three microphones, placed 90 deg apart azimuthally in a plane normal to the jet axis. The measurements were obtained at three streamwise locations, with microphone angles of 90, 60, and 30 deg with respect to the jet centerline. The trailing-edge modified nozzles substantially reduced the turbulent mixing and broadband shock associated noise radiation by up to 12 dB for the underexpanded flow regime and up to 7 dB for the overexpanded condition. However, in some symmetric modifications, the very-high-frequency noise was increased for the overexpanded condition. Screech tones in the overexpanded flow condition were either reduced or eliminated for asymmetric modifications, but amplified for symmetric modifications. The trailing-edge modifications were found to not significantly alter the noise field for the ideally expanded flow condition.
TL;DR: In this paper, the authors demonstrate that optical pumping plays a significant role in determining the noise in certain types of laser-pumped vapor-cell microwave frequency standards by changing the way in which the laser's FM noise is converted to AM noise by the optical-absorption profile.
Abstract: We demonstrate that optical pumping plays a significant role in determining the noise in certain types of laser-pumped vapor-cell microwave frequency standards by changing the way in which the laser’s FM noise is converted to AM noise by the optical-absorption profile. When this FM–AM conversion is the dominant noise source, the noise spectrum of the transmitted intensity can be dramatically altered by the optical-pumping process. FM noise at Fourier frequencies larger than the optical-pumping time is converted to AM noise differently from noise at lower Fourier frequencies. This effect can modify the optimum design of vapor-cell frequency references and adds an additional FM–AM-related noise source that cannot be eliminated with laser tuning.
TL;DR: This work treats the noise-activated escape from a one-dimensional potential well of an overdamped particle, to which a periodic force of fixed frequency is applied, and shows how behavior near the well top generalizes the behavior determined by Kramers, in the case without forcing.
Abstract: We treat the noise-activated escape from a one-dimensional potential well of an overdamped particle, to which a periodic force of fixed frequency is applied. Near the well top, the relevant length scales and the boundary layer structure are determined. We show how behavior near the well top generalizes the behavior determined by Kramers, in the case without forcing. Our analysis includes the case when the forcing does not die away in the weak-noise limit. We discuss the relevance of scaling regimes, defined by the relative strengths of the forcing and the noise, to recent optical trap experiments.