Showing papers on "Noise (radio) published in 1993"
TL;DR: In this article, a model for the response of sedimentary layers to ambient seismic noise is presented, where the noise sources are modeled as a random distribution (in time and space) of point forces located on the Earth's free surface.
Abstract: For over thirty years, attempts have been made to gain information about sediment amplification during earthquakes from observations of ambient seismic noise. While the results of several feasibility studies have been encouraging, theoretical support for the technique is scant. We present a model for the response of sedimentary layers to ambient seismic noise. The noise sources are modeled as a random distribution (in time and space) of point forces located on the Earth's free surface. This model is applied to a site where observed noise spectral ratios, relative to a rock site, have previously been shown to reveal the fundamental resonant frequency of a soft clay layer. Approximating the sediment site as a single layer over a half-space, the horizontal noise spectrum predicted by our model reveals the fundamental resonance and first harmonic of the layer. We also examine an estimate of site response proposed by Nakamura (1989), which is formed by dividing the horizontal-component noise spectrum by that of the vertical component. Nakamura's estimate applied to both observed and predicted noise-spectra was also successful in identifying the fundamental resonance, with a slight (<10%) shift toward lower frequencies. Future work is needed to determine the generality of our results, and to elucidate the influence of the simplifying assumptions.
314 citations
20 Jun 1993
TL;DR: In this article, the effect of frequency modulation on power supply EMI noise is investigated, and significant reduction of EMI emission is possible with the proposed scheme, which is shown to reduce the EMI emissions significantly.
Abstract: Electromagnetic interference (EMI) emission is always of grave concern for power electronic circuit designers. Due to rapid switching of high current and high voltage, interference is a serious problem in switching power circuits. Here, the effect of frequency modulation on power supply EMI noise is investigated. Significant reduction of emission is possible with the proposed scheme. >
296 citations
TL;DR: In this paper, the collective dynamics of a network of globally coupled phase oscillators are studied with emphasis on the existence and the stability of clustering states, and three typical types of dynamics can be observed at large time: a fully synchronized state of the network, a totally incoherent state, and a pair of two-cluster states connected by heteroclinic orbits.
Abstract: We consider a network of globally coupled phase oscillators. The interaction between any two of them is derived from a simple model of weakly coupled biological neurons and is a periodic function of the phase difference with two Fourier components. The collective dynamics of this network is studied with emphasis on the existence and the stability of clustering states. Depending on a control parameter, three typical types of dynamics can be observed at large time: a fully synchronized state of the network (one-cluster state), a totally incoherent state, and a pair of two-cluster states connected by heteroclinic orbits. This last regime is particularly sensitive to noise. Indeed, adding a small noise gives rise, in large networks, to a slow periodic oscillation between the two two-cluster states. The frequency of this oscillation is proportional to the logarithm of the noise intensity. These switching states should occur frequently in networks of globally coupled oscillators.
234 citations
TL;DR: A high-temperature superconducting-receiver system for use in nuclear magnetic resonance (NMR) microscopy is described, and it is demonstrated that thermal noise in the receiver coil is the factor that limits resolution.
Abstract: A high-temperature superconducting-receiver system for use in nuclear magnetic resonance (NMR) microscopy is described. The scaling behavior of sources of sample and receiver-coil noise is analyzed, and it is demonstrated that Johnson, or thermal, noise in the receiver coil is the factor that limits resolution. The behavior of superconductors in the environment of an NMR experiment is examined, and a prototypical system for imaging biological specimens is discussed. Preliminary spin-echo images are shown, and the ultimate limits of the signal-to-noise ratio of the probe are investigated.
212 citations
TL;DR: In this article, potential and current noise data have been collected for pure iron foils which were exposed to 0.5N which was aerated, deaerated, or aerated with added as inhibitor.
Abstract: Potential and current noise data have been collected for pure iron foils which were exposed to 0.5N which was aerated, deaerated, or aerated with added as inhibitor. Data were obtained at the beginning of each hour over a 24 h period. The noise data were displayed as power spectral density plots or as the rms values of potential and current . The potential noise data seem to be affected by fluctuations of mass transport and did not agree with the known corrosion behavior of the systems under investigation. However, good agreement was observed for the current noise data. For the noise resistance similar values as for the polarization resistance determined with EIS at the end of the tests were obtained. The pit index defined by others as , where is the mean current in a noise measurement, did not provide meaningful information. The experimental data obtained in this investigation have been compared with those reported previously by Lumsden et al.
185 citations
TL;DR: In this paper, a noise reduction circuit for a hearing aid having an adaptive filter for producing a signal which estimates the noise components present in an input signal is presented. But the circuit also includes a signal combiner for combining the input signal with the adjusted noise-estimating signal to produce a noise reduced output signal.
Abstract: A noise reduction circuit for a hearing aid having an adaptive filter for producing a signal which estimates the noise components present in an input signal. The circuit includes a second filter for receiving the noise-estimating signal and modifying it as a function of a user's preference or as a function of an expected noise environment. The circuit also includes a gain control for adjusting the magnitude of the modified noise-estimating signal, thereby allowing for the adjustment of the magnitude of the circuit response. The circuit also includes a signal combiner for combining the input signal with the adjusted noise-estimating signal to produce a noise reduced output signal.
171 citations
TL;DR: In this paper, the authors investigate the effect of electric and magnetic fields at the fundamental frequency of power transmission (typically 60 Hz in North America) and its harmonics on geophysicists.
Abstract: Harmonic noise generated by power lines and electric railways has plagued geophysicists for decades. The noise occurs as electric and magnetic fields at the fundamental frequency of power transmission (typically 60 Hz in North America) and its harmonics. It may be recorded directly during time‐domain measurements of electric and magnetic felds, or indirectly, by geophone cables during the acquisition of seismic data.
105 citations
TL;DR: Two dynamical systems in R 2 given by an ODE are provided: one which explodes in finite time for every initial condition but becomes stable by adding white noise of arbitrary positive intensity and another which becomes explosive when it is perturbed by additive white noise.
Abstract: We provide two dynamical systems in R 2given by an ODE:One which explodes in finite time for every initial condition but becomes stable by adding white noise of arbitrary positive intensity in the sense that the system becomes nonexplosive and even positive recurrent and another system which is globally asymptotically stable and which becomes explosive when it is perturbed by additive white noise
103 citations
11 Jan 1993
101 citations
TL;DR: A linear stability analysis and numerical simulations show that convective structures appear in a regime in which a deterministic analysis predicts a homogeneous solution.
Abstract: The Swift-Hohenberg equation is studied in the presence of a multiplicative noise. This stochastic equation could describe a situation in which a noise has been superimposed on the temperature gradient between the two plates of a Rayleigh-Benard cell. A linear stability analysis and numerical simulations show that, in constrast to the additive-noise case, convective structures appear in a regime in which a deterministic analysis predicts a homogeneous solution
90 citations
TL;DR: In this paper, the authors present evidence that the quasi-periodic oscillations (QPO) and very low frequency noise (VLFN) characteristic of many accretion sources are different aspects of the same physical process.
Abstract: We present evidence that the quasi-periodic oscillations (QPO) and very low frequency noise (VLFN) characteristic of many accretion sources are different aspects of the same physical process. We analyzed a long, high time resolution EXOSAT observation of the low-mass X-ray binary (LMXB) Sco X-1. The X-ray luminosity varies stochastically on time scales from milliseconds to hours. The nature of this variability - as quantified with both power spectrum analysis and a new wavelet technique, the scalegram - agrees well with the dripping handrail accretion model, a simple dynamical system which exhibits transient chaos. In this model both the QPO and VLFN are produced by radiation from blobs with a wide size distribution, resulting from accretion and subsequent diffusion of hot gas, the density of which is limited by an unspecified instability to lie below a threshold.
TL;DR: In this paper, an ultrasound system that enables determination of layer thicknesses and contours of a multi-layer organic body includes a transmitter/receiver for obtaining a radio frequency signal from echoes over a plurality of points on the organic surface.
Abstract: An ultrasound system that enables determination of layer thicknesses and contours of a multi-layer organic body includes a transmitter/receiver for obtaining a radio frequency signal from echoes over a plurality of points on the organic surface. Each radio frequency signal is then deconvolved to remove apparatus generated noise and filtered to create an analytic signal that exhibits a magnitude related to an instantaneous rate of arrival of total echo energy received by the transmitter/receiver. Analytic signals from adjacent parallel scans are then cross-correlated and magnitude detected to determine energy peaks to enable accurate determination of echo producing surfaces of each layer of the multi-layer organic body across the plurality of interrogation points. In the application of the invention to Corneal Epithelium Mapping, a pupil monitoring system is included that disables the measurement system if the pupil's gaze wanders so as to cause a diversion of the optical axis.
27 Apr 1993
TL;DR: A novel noise suppression algorithm based on a modified maximum likelihood estimate is developed and a speech detector based on the temporal signal-to-noise ratio information of every subband of a bandpass filter bank is proposed.
Abstract: Frequency-domain noise suppression systems with a single microphone are studied for adverse mobile noise environments. A novel noise suppression algorithm based on a modified maximum likelihood estimate is developed. The algorithm takes into account not only minimum voice distortion but also subjective criteria for the noise naturalness. A speech detector based on the temporal signal-to-noise ratio (SNR) information of every subband of a bandpass filter bank is proposed. The speech detector is proven to be very effective and robust in a rapidly changing noisy background. The proposed noise suppression method in mobile telephone systems demonstrates much better subjective and objective test results than the existing methods. A real-time test shows that 10 dB noise reduction and 9 dB SNR improvements have been achieved even in the most adverse mobile situation. >
TL;DR: It is found that the limiting quantum noise is due to the uncertainty associated with the particle sorting between the two branches of the interferometer, and that this noise can be reduced in a sufficiently dense atomic beam by using fermions as opposed to bosons.
Abstract: We derive the quantum limits for an atomic interferometer from a second-quantized theory in which the atoms obey either Bose-Einstein or Fermi-Dirac statistics. It is found that the limiting quantum noise is due to the uncertainty associated with the particle sorting between the two branches of the interferometer, and that this noise can be reduced in a sufficiently dense atomic beam by using fermions as opposed to bosons. As an example, the quantum-limited sensitivity of a generic matter-wave gyroscope is calculated and compared with that of a laser gyroscope.
TL;DR: In this article, the authors show that the physics of the delta-I noise is more complex and that it is related to wave propagation effects, and that the inductive effects are important only for slower transients.
Abstract: Delta-I noise is the voltage induced between the power conductors (e.g. the ground and the V/sub cc/ planes) when a circuit connected between them switches from one state to another. The authors show that the physics of the noise is more complex, and that it is related to wave propagation effects. Delta-I noise should be present not only in integrated circuits (chips), but also in multilayered boards, where it should be pronounced when the transients are of the order of 1 ns or less. Investigation of the delta-I noise is carried out for a simplified model of power planes, using a wire-antenna numerical simulation program. The model includes the wave propagation effects, as well as radiation, but it does not include the effects of the dielectric filling the space between the planes. The results of the analysis clearly show that the inductive effects are important only for slower transients. For fast digital circuits the power planes actually form a resonator,which can have a high quality factor, and the delta-I noise can build up to very high voltage levels. >
TL;DR: In this paper, the authors considered the compressible Rayleigh equation as a model for the Mach wave emission mechanism associated with high temperature supersonic jets and found that the first order instability wave and the Kelvin-Helmholtz first, second, and third order modes have directional radiation characteristics that are in agreement with observed data.
Abstract: The paper considers the compressible Rayleigh equation as a model for the Mach wave emission mechanism associated with high temperature supersonic jets. Solutions to the compressible Rayleigh equation reveal the existence of several families of supersonically convecting instability waves. These waves directly radiate noise to the jet far field. The predicted noise characteristics are compared to previously acquired experimental data for an axisymmetric Mach 2 fully pressure balanced jet operating over a range of jet operating total temperatures from ambient to 1370 K. The results of this comparison show that the first order supersonic instability wave and the Kelvin-Helmholtz first, second, and third order modes have directional radiation characteristics that are in agreement with observed data. The assumption of equal initial amplitudes for all of the waves leads to the conclusion that the flapping mode of instability dominates the noise radiation process of supersonic jets. At a jet temperature of 1370 K, supersonic instability waves are predicted to dominate the noise radiated at high frequency at narrow angles to the jet axis.
Book•
30 Aug 1993
TL;DR: In this paper, the authors present a link budget orbits for communications Satellites Radio Frequencies Modulation, Multiplexing, and Multiple Access Antennas Power, EIRP, and Illumination Transmission Losses and Power Flux Density Receivers and Noise Temperatures System Performance Telemetry, Tracking, and Command Electric Power Spacecraft Attitude Propulsion Structure Thermal Control Spacecraft Testing Reliability Index.
Abstract: Introduction to Link Budgets Orbits for Communications Satellites Radio Frequencies Modulation, Multiplexing, and Multiple Access Antennas Power, EIRP, and Illumination Transmission Losses and Power Flux Density Receivers and Noise Temperatures System Performance Telemetry, Tracking, and Command Electric Power Spacecraft Attitude Propulsion Structure Thermal Control Spacecraft Testing Reliability Index.
TL;DR: In this article, a study of the relative intensity noise (RIN) of two all semiconductor vertical cavity surface emitting lasers is presented, and it is shown that the slope of the low frequency RIN agrees with theory for the fundamental mode only and that transverse modes introduce sharp changes in the RIN and put a limit on the minimum attainable RIN.
Abstract: A study of the relative intensity noise (RIN) of two all semiconductor vertical cavity surface emitting lasers is presented. We find that the slope of the low frequency RIN agrees with theory for the fundamental mode only and that transverse modes introduce sharp changes in the RIN and put a limit on the minimum attainable RIN. For the fundamental mode, both devices achieve a RIN of less than −140 dB/Hz for optical powers less than 1 mW. This good performance is attributed to the high reflectivity of the cavity mirrors.
TL;DR: In this paper, the influence of the nonlinear refractive index and the group-velocity dispersion of optical fibers on optical-amplifier noise was studied and a new method was used to calculate the spectrum of the amplified spontaneous emission.
Abstract: The influence of the nonlinear refractive index and the group-velocity dispersion of optical fibers on optical-amplifier noise is studied. A new method is used to calculate the spectrum of the amplified spontaneous emission. The result shows that the positive dispersion is favorable for suppressing the enhancement of the amplifier noise. >
TL;DR: In this article, a stochastic formulation of the large amplitude and high frequency components of residual accelerations found in a typical microgravity environment (or g-jitter) is introduced to study the linear response of a fluid surface to such residual acceleration, and an explicit form of the stability boundary valid for arbitrary frequencies is proposed, which interpolates smoothly between the low frequency and the near resonance limits with no adjustable parameter, and extrapolates to higher frequencies.
Abstract: A stochastic formulation is introduced to study the large amplitude and high‐frequency components of residual accelerations found in a typical microgravity environment (or g‐jitter). The linear response of a fluid surface to such residual accelerations is discussed in detail. The analysis of the stability of a free fluid surface can be reduced in the underdamped limit to studying the equation of the parametric harmonic oscillator for each of the Fourier components of the surface displacement. A narrow‐band noise is introduced to describe a realistic spectrum of accelerations, that interpolates between white noise and monochromatic noise. Analytic results for the stability of the second moments of the stochastic parametric oscillator are presented in the limits of low‐frequency oscillations, and near the region of subharmonic parametric resonance. Based upon simple physical considerations, an explicit form of the stability boundary valid for arbitrary frequencies is proposed, which interpolates smoothly between the low frequency and the near resonance limits with no adjustable parameter, and extrapolates to higher frequencies. A second‐order numerical algorithm has also been implemented to simulate the parametric stochastic oscillator driven with narrow‐band noise. The simulations are in excellent agreement with our theoretical predictions for a very wide range of noise parameters. The validity of previous approximate theories for the particular case of Ornstein–Uhlenbeck noise is also checked numerically. Finally, the results obtained are applied to typical microgravity conditions to determine the characteristic wavelength for instability of a fluid surface as a function of the intensity of residual acceleration and its spectral width.
TL;DR: In this article, the noise properties of pseudomorphic HEMTs were investigated in the low and intermediate frequency range (10 Hz to 150 MHz) and in the microwave range (4 to 18 GHz).
Abstract: Noise properties of AlGaAs/InGaAs/GaAs pseudomorphic HEMTs (PHEMTs) have been investigated simultaneously in the low and intermediate frequency range (10 Hz to 150 MHz) and in the microwave range (4 to 18 GHz) and compared to the noise of more classical devices such as MESFETs and GaAlAs/GaAs HEMTs. Unlike the other commercially available devices, PHEMTs exhibit the unique capability of providing simultaneously state-of-the-art microwave noise performance and a reasonable low-frequency excess noise. >
Patent•
15 Mar 1993
TL;DR: In this paper, a system and method for the detection and measurement of atmospheric air movement irregularities such as wind velocity vector, clear air turbulence, aircraft induced vorteces and turbulence, by means of electromagnetic waves.
Abstract: A system and method for the detection and measurement of atmospheric air movement irregularities such as wind velocity vector, clear air turbulence, aircraft induced vorteces and turbulence, by means of electromagnetic waves. An air volume (10) un-der investigation is illuminated by a transmitter (1, 1A, 1B) with a beam of coherent electromagnetic energy (1E), and a resulting wave field (2E) is received and subsequently coherently demodulated and processed in process means to derive information on the existence of the said atmospheric irregularities and furthermore to give specific measurements of related parameters. At least one receiver (2, 2A, 2B) for said resulting wave field (2E), which is due to scattering in said air volume (10), is positioned at a bis-tatic location having a selected distance (2R) from said transmitter (1, 1A, 1B). Said electromagnetic energy (1E) is transmitted at microwave frequencies in a concentrated beam. Transmitter and receiver antennas (1A, 1B, 2A, 2B), respectively, are directed so as to cover said air volume (10) with a scattering angle (.THETA.) chosen to have such a (low) value that scattering from atmospheric irregularities in said air volume (10) has a higher power than noise sources in the system.
01 Oct 1993
TL;DR: In this article, a free jet is used to investigate the changes in the noise received from supersonic jets in high speed subsonic flight, and measurements within the free jet show that convection effects on the noise are substantial, and that the point source convective amplification that is proportional to the fourth power of the Doppler factor may apply for broadband shock noise in flight.
Abstract: A free jet is utilized to investigate the changes in the noise received from supersonic jets in high speed subsonic flight. Flight Mach numbers to 0.9 are simulated for supersonic jets with fully expanded Mach numbers between 1 and 2. Plume pressure measurements show only minor changes in the shock structure of off-design jets up to a Mach number of 0.6. Correspondingly, far-field noise measurements indicate little change to the broadband shock noise emitted at right angles to the jet. However, measurements within the free jet show that convection effects on the noise are substantial, and that the point source convective amplification that is proportional to the fourth power of the Doppler factor may apply for broadband shock noise in flight. Measurements of jet mixing noise for an on-design supersonic jet show that the current predictions of mixing noise in flight can be extended to flight Mach numbers of at least 0.5.
TL;DR: Experimental spectra obtained by measuring the laser intensity noise after a broad-bandwidth diode-laser beam passes through a rubidium vapor cell are reported on and numerically calculated spectra based on a phase-diffusion model of the laser field are compared.
Abstract: We report on spectra obtained by measuring the laser intensity noise after a broad-bandwidth diode-laser beam passes through a rubidium vapor cell. The atomic resonance converts laser frequency fluctuations into intensity fluctuations. We compare our experimental spectra with numerically calculated spectra based on a phase-diffusion model of the laser field and find good agreement.
Patent•
02 Jul 1993
TL;DR: In this paper, the U-shaped wires passing through a ferrite core are interconnected to provide impedance to both differential-mode and common-mode noise, and some wires are singly fitted in throughholes, whereas other wires are commonly fitted in a throughhole.
Abstract: An electromagnetic noise filter has a plurality of U-shaped wires passing through a ferrite core. Some of the wires are singly fitted in throughholes, whereas other wires are commonly fitted in throughholes. The wires can be interconnected to provide for impedance to both differential-mode and common-mode noise.
14 Jun 1993
TL;DR: The authors describe a fiber-optic link architecture which minimizes noise figure by combining the two complementary outputs of a Y-fed coupler electrooptic modulator in such a way that the optical noise cancels in a balanced receiver module.
Abstract: The authors describe a fiber-optic link architecture which minimizes noise figure by combining the two complementary outputs of a Y-fed coupler electrooptic modulator in such a way that the optical noise cancels in a balanced receiver module. The demonstration link exhibits 9.5-dB insertion loss and 13.5-dB noise figure at 900 MHz. >
TL;DR: In this paper, an extreme scattering event, lasting about 15 days, was detected in timing observations of the millisecond pulsar 1937 + 21, which provides independent evidence for the existence of large-scale structure in the interstellar medium and allows us to constrain the properties of the lensing structure (distance, velocity, linear dimension and electron density) more tightly than has been possible from detections of lensed extragalactic radio sources.
Abstract: LARGE fluctuations in the radio emissions from the quasar 0954 + 658 (ref. 1) attest to the existence of large-scale inhomogeneities in the ionized interstellar medium. These fluctuations, termed extreme scattering events, are caused by the refractive focusing of the radio waves by discrete plasma structures. In principle, the radio emissions of pulsars should also be a sensitive probe of such phenomena2–5, which should be manifest as fluctuations in the flux density and increased delays in the timing measurements. Here we report the detection of an extreme scattering event, lasting about 15 days, in timing observations of the millisecond pulsar 1937 + 21. This event provides independent evidence for the existence of large-scale structure in the interstellar medium, and allows us to constrain the properties of the lensing structure (distance, velocity, linear dimension and electron density) more tightly than has been possible from detections of lensed extragalactic radio sources. Of more practical importance, such events could be the dominant source of timing noise in millisecond pulsars at ∼1 GHz, and will need to be considered when searching for the subtle signature of gravitational waves in pulsar timing measurements.
TL;DR: In this paper, the authors present a qualitative model and data in evidence for the selection and stabilization of neocortical brainwave power spectral modes by slow periodic and fast noise driving by brain stem neurons.
Abstract: We present a qualitative model and data in evidence for the selection and stabilization of neocortical brain-wave power spectral modes by slow periodic and fast noise driving by brain stem neurons. Unlike noise effects in a bistable potential, increasing noise amplitude via more brain stem neurons increases the measure on unstable manifolds trapped in the saddle-sinks of the neural membrane attractor andincreases dwell times. We suggest that the effect of noise in expanding dynamical systems such as the generalized neuronal membrane equations studied here may be analogous to that of many-frequency quasiperiodic driving which leads to the stabilization of the EEG as a strange, nonchaotic attractor.
TL;DR: In this paper, an aircraft engine active noise cancellation system is described, in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies.
Abstract: A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by a plurality of force transmitting mechanisms which contact the noise radiating element. Each one of the force transmitting mechanisms includes an expandable element and a spring in contact with the noise radiating element so that excitation of the element varies the spring force applied to the noise radiating element. The elements are actuated by a controller which receives input of a signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the spring force applied to the noise radiating element to be varied. The force transmitting mechanisms can be arranged to either produce bending or linear stiffness variations in the noise radiating element.
TL;DR: In this article, the effect of stress-induced longitudinal magnetic orientation on the transition noise properties of thin film media was investigated for uniaxial and spatial uniform compressive stress in the recording direction.
Abstract: Transition noise properties in longitudinal thin film media are studied by micromagnetic modeling. The mechanism for enhancement of transition noise at small bit intervals due to intertransition interaction is investigated. The noise dependence on the medium parameters, such as saturation magnetization and film thickness, is calculated. Reducing either the saturation magnetization or the film thickness yields a reduction of transition noise at low recording densities and a reduction of the noise enhancement at high recording densities. The effect of stress-induced longitudinal magnetic orientation is studied for an application of a uniaxial and spatial uniform compressive stress in the recording direction. The calculation shows that films with higher orientation ratio exhibit higher transition noise at small bit intervals. >