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Showing papers on "Noise (radio) published in 1980"


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the duration of the noise emission of a jet by measuring the instantaneous cross-correlation between the far field acoustic pressure and the velocity component in the jet towards the microphone.

133 citations


Proceedings ArticleDOI
01 Jun 1980
TL;DR: In this article, an aerodynamic and acoustic measurements of shock-free and shock-containing plumes were acquired for several supersonic free-jet model nozzles for the purpose of investigating important features of the broadband shock noise generation process.
Abstract: Aerodynamic and acoustic measurements of shock-free and shock-containing plumes were acquired for several supersonic free-jet model nozzles. The purpose was to investigate important features of the broadband shock noise generation process. The aerodynamic measurements include the variation of shock cell spacing and strength as a function of nozzle pressure ratio, and longitudinal turbulent-mass-flux axial development as determined by a hot-film probe. In addition, correlations of the hot-film probe with a near-field microphone were obtained. These measurements provide useful information concerning the relation of peak shock noise frequency and level with variations in shock cell spacing and strength. In general, it is shown that a distinction must be made between plumes containing weak and strong imbedded shocks. Strong shocks diminish the level of emitted shock noise and influence the behavior of the jet mixing noise process. The probable location and spectral content for the shock-shear layer interaction mechanism is indicated by the correlations. Numerical inviscid plume comparisons with experimental data are also included.

126 citations


Journal ArticleDOI
P. Duncan1, A. Hwang1, R. N. Edwards1, R. C. Bailey1, G. D. Garland1 
TL;DR: In this article, a very wide band (0.03 Hz to 15 kHz) electromagnetic (EM) system has been developed, which was used over the band 1 Hz to 10 kHz to determine the electrical structure of the earth's crust from depths of a few meters to over 40 km.
Abstract: A very wide band (0.03 Hz to 15 kHz) electromagnetic (EM) system has been developed. It was used over the band 1 Hz to 10 kHz to determine the electrical structure of the earth’s crust from depths of a few meters to over 40 km. A direct current of from 1 to 5 A was reversed through a long wire bipole transmitter in a pseudo‐random binary sequence (PRBS). Depending upon the frequencies selected, a sensitive one‐component flux gate magnetometer or an air‐core coil was used to monitor temporal changes in the vertical component of the magnetic field at a recording site. The measured signal was crosscorrelated digitally in real time with an exact copy of the transmitted waveform in order to obtain a good signal‐to‐noise ratio at distances up to 5 times the length of the bipole. The output crosscorrelogram was deconvolved from the system input, the autocorrelogram of the transmitted waveform, using a Wiener least‐squares filter to give the impulse response of the earth. This was then transformed into frequency ...

94 citations


Journal ArticleDOI
TL;DR: In this article, the amplitude stability of single-mode channeled-substrate planar diode laser has been measured as a function of frequency (100 Hz-1 MHz) and driving current.
Abstract: The amplitude stability of single‐mode channeled‐substrate planar diode lasers has been measured as a function of frequency (100 Hz–1 MHz) and driving current. The relative noise spectrum showed a decrease with increasing frequency and an overall reduction at all frequencies as the output power of the laser was increased. These results are compared with similar measurements of the most stable commercial single‐mode HeNe lasers. The problems of laser amplitude noise in fiber‐optic sensor systems is briefly discussed.

79 citations


Journal ArticleDOI
TL;DR: In this article, a theoretical model of ambient noise in an isovelocity, shallow water channel with independent, randomly distributed surface sources is presented, where bottom losses in the channel are assumed to be sufficiently small for the modal energy from distant sources to predominate over the continuous radiation from nearfield sources.
Abstract: A theoretical model of ambient noise in an isovelocity, shallow water channel with independent, randomly distributed surface sources is presented. Bottom losses in the channel are assumed to be sufficiently small for the modal energy from distant sources to predominate over the continuous radiation from nearfield sources. For frequencies at which the channel can support about ten or more modes the predicted noise field is essentially homogeneous over a large proportion of the water column away from the boundaries. This allows the vertical spatial coherence of the noise to be expressed in terms of a plane‐wave directional density function. The properties of this function are shown to be characteristic of the modal structure of the noise field.

67 citations


Journal ArticleDOI
TL;DR: The spin-modulated noise from the dipole connected to the sounder receiver on the Isis 1 spacecraft has been used along with the computation of ray paths to deduce the direction of propagation of auroral kilometric radiation (AKR) as mentioned in this paper.
Abstract: The spin-modulated noise from the dipole connected to the sounder receiver on the Isis 1 spacecraft has been used along with the computation of ray paths to deduce the direction of propagation of auroral kilometric radiation (AKR). On the basis of three passes with fixed-frequency measurements at 0.48 MHz it is concluded that in the generation region at about 3500-km altitude the wave vectors make an angle between about 60° and 90° with respect to the local magnetic field. That is, they are predominantly downcoming. Also, in using the sounder records the plasma frequency fN is found to be very much less than the gyrofrequency fH in the generation region (fN ≲50 kHz, fH ≃450 kHz). When these Isis observations are combined with previous evidence on AKR, from which it was concluded that it propagates predominantly in the right-hand polarized X mode, serious disagreement with a number of theories, particularly those that predict the left-hand-polarized O mode, results. However, two theories of a quite different nature, direct cyclotron radiation and a three-wave interaction involving an ELF/VLF wave, give some prospect of accommodating all the observations.

61 citations


Journal ArticleDOI
TL;DR: In this article, a model based on a physical picture of boundary layer vorticity being swept around the edge by spanwise flow on the flap was developed and solved and the resulting noise radiation calculated.
Abstract: The recently observed phenomenon of high noise radiation from the side edges of flaps in flow is investigated by way of a simple two-dimensional model problem. The model is based upon a physical picture of boundary layer vorticity being swept around the edge by spanwise flow on the flap. The model problem is developed and solved and the resulting noise radiation calculated. Further, a mathematical condition for the vortex to be captured by the potential flow and swept around the edge is derived. The results show that the sound generation depends strongly upon the strength of the vorticity and distance from the edge and that it can be more intense than the more common trailing edge noise source in agreement with the experimental observations.

58 citations


Journal ArticleDOI
TL;DR: In this paper, a lower bound to the frequency range over which the spectral density of noise increases with decreasing frequency is found, and application of the theory to other strongly inhomogenous systems with percolation-type conduction is proposed.

56 citations


Journal ArticleDOI
TL;DR: In this paper, random fluctuations in the passive current of electrodes under potentiostatic conditions have been measured on aluminum in boric acid: borate solution and on a Fe-Cr-Ni alloy, both in the amorphous and in the crystalline state, in sulfuric acid.

52 citations


Journal ArticleDOI
TL;DR: The nondependence of the magnitude of the optogalvanic signal on the ionization potential of the irradiated atom leads us to postulate a mechanism where the principal effect of laser irradiation is to pump energy into the electron gas.
Abstract: It is demonstrated that the noise in a hollow cathode discharge results mainly from statistical fluctuations of the electrons in the circuit. For the elements Na, U, Eu, and Zr, approximately one extra electron is produced for every one thousand photons absorbed. The nondependence of the magnitude of the optogalvanic signal on the ionization potential of the irradiated atom leads us to postulate a mechanism where the principal effect of laser irradiation is to pump energy into the electron gas.

50 citations


Journal ArticleDOI
TL;DR: In this article, Langevin equations with external non-white noise are considered and a Fokker Planck equation valid in general in first order of the correlation timeτ of the noise is derived.
Abstract: Langevin equations with external non-white noise are considered. A Fokker Planck equation valid in general in first order of the correlation timeτ of the noise is derived. In some cases its validity can be extended to any value ofτ. The effect of a finiteτ in the nonequilibrium phase transitions induced by the noise is analyzed, by means of such Fokker Planck equation, in general, for the Verhulst equation under two different kind of fluctuations, and for a genetic model. It is shown that new transitions can appear and that the threshold value of the parameter can be changed.

Journal ArticleDOI
TL;DR: In this article, it was shown that the LFC radiation observed in the solar wind is in the form of longitudinal plasma waves rather than transverse electromagnetic waves, and the observed spectral characteristics were found to be a function of antenna length.
Abstract: The low frequency continuum (LFC) noise between 30 and 200 kHz has been investigated from the ISEE 3 spacecraft in the solar wind by means of a radio astronomy experiment more sensitive than previously available. It is demonstrated that the LFC radiation observed in the solar wind is in the form of longitudinal plasma waves rather than transverse electromagnetic waves. The observed spectral characteristics are found to be a function of antenna length. In addition, both the absence of antenna spin modulation and the fact that these plasma waves do not propagate to large distances imply a local origin for the LFC.

Journal ArticleDOI
TL;DR: In this article, a semi-empirical model for predicting the noise generated by jets exhausting from circular nozzles is presented and compared with small-scale static and simulated flight data.
Abstract: A semi‐empirical model for predicting the noise generated by jets exhausting from circular nozzles is presented and compared with small‐scale static and simulated‐flight data. The present method is an updated version of that part of the original NASA Aircraft Noise Prediction Program (1974) relating to circular jet noise. The earlier method has been shown to agree reasonably well with experimental static and flight data for jet velocities up to ∼ 520 m/s. The poorer agreement at higher jet velocities appeared to be due primarily to the manner in which supersonic convection effects were formulated. The purely empirical supersonic convection formulation is replaced in the present method by one based on theoretical considerations. Other improvements of an empirical nature have been included based on model‐jet/free‐jet simulated‐flight tests. The effects of nozzle size, jet velocity, jet temperature, and flight are included.

Journal ArticleDOI
TL;DR: In this article, the authors reported the results of a systematic study of the current-induced noise at the superconducting transition in thin, high-resistivity films of aluminum and tin.
Abstract: This Letter reports the results of a systematic study of the current-induced noise at the superconducting transition in thin, high-resistivity films of aluminum and tin. Analysis of the noise suggests that the onset of resistance is due to discrete phase slips of magnitude less than 2..pi... The results are discussed in terms of the vortex umbinding models of the superconducting transition in two dimensions.

Journal ArticleDOI
J.L. Doane1
TL;DR: A feedforward tracking technique is described and its application to single frequency millimeter-wave interferometry and Doppler-shift scattering measurements on tokamak plasmas is described.
Abstract: Superheterodyne stimulus‐response measurements can be made with high dynamic range, but are often sensitive to oscillator frequency drift and noise. The usual techniques for reducing this sensitivity often become impractical at millimeter‐wave frequencies and above. This paper describes a feedforward tracking technique and its application to single frequency millimeter‐wave interferometry and Doppler‐shift scattering measurements on tokamak plasmas. Swept frequency transmission measurements can also be made with high dynamic range using this technique.

Journal ArticleDOI
TL;DR: In this article, the authors developed a method for monitoring control rod vibrations by neutron noise measurements, and the noise induced by two-dimensional vibrations of control elements was investigated, and two possible diagnostical applications were considered: (a) the reconstruction of the mechanical trajectory of the vibrating element, and (b) the possibility of locating the vibration element in the core.

Proceedings ArticleDOI
01 Jun 1980
TL;DR: In this paper, the authors investigated the peak shock associated noise from unheated supersonic jets through acoustic measurements in both the near and far fields, and found that the relative importance of shock noise with respect to jet mixing noise is maximum near the pressure ratio at which a Mach disc begins to form in the jet.
Abstract: Shock associated noise from unheated supersonic jets is investigated through acoustic measurements in both the near and far fields. The peak Helmholtz number of broadband shock noise is found to be independent of nozzle pressure ratio when based on the length of the shock cells and the ambient speed of sound. This indicates that the acoustic wavelengths generated in the shock noise process are limited in size by the shock cell spacing. Excellent agreement between power spectral densities measured at various far-field angles is obtained at and above the peak shock noise frequency when source convection effects are included. Results show a directivity of broadband shock noise pointed in the upstream direction, with omnidirectionality being approached only at high pressure ratios. The relative importance of shock noise with respect to jet mixing noise is found to be maximum near the pressure ratio at which a Mach disc begins to form in the jet. Near-field measurements point to the downstream shock cells as the region where the dominant shock noise eminates from the jet.

Journal ArticleDOI
TL;DR: It is suggested that constriction of peripheral blood vessels in response to expected intense low-frequency or wide-band noises is more related to auditory, reflexive protective mechanisms than to autonomic system responses generally considered to be stressful to the organism.
Abstract: Experiments were conducted on the effects of various expected noise conditions upon autonomic system activity in men during rest and work (bicycle ergometer). Skin temperature and heart rate were not appreciably, if at all, affected by any of the noises. Wide-band, predominantly low-frequency noise, at a level of 92 dB, A-weighted, generally caused a decrease in pulse amplitude (indicative of constriction of peripheral blood vessels) during either work or rest, whereas an equally intense one-third octave band of random noise, center frequency of 3150 Hz, had no appreciable effect on pulse amplitude. Repeated exposures to the wide-band noise showed some adaptation or habituation of the pulse amplitude response during conditions of either work or rest. The results were the same for fast rise time (impulsive) bursts of wide-band noise as for bursts with slow, gradual onsets. Rapid interruptions of wide-band noise caused less of a decrease in average pulse amplitude than did uninterrupted noise. It is suggested that constriction of peripheral blood vessels in response to expected intense low-frequency or wide-band noises is more related to auditory, reflexive protective mechanisms than to autonomic system responses generally considered to be stressful to the organism.

Journal ArticleDOI
TL;DR: The Fokker-Planck approximation for n -dimensional nonmarkovian Langevin equations is discussed in this article through an expansion in powers of the correlation time of the noise and an application to brownian motion is presented.

Journal ArticleDOI
TL;DR: Different noise exposure paradigms were studied to determine their teratogenic and embryo-fetotoxic potential in the CF-1 mouse and no significant noise-related changes were noted in the incidence of structural alterations or in the concentration of plasma corticosterone.
Abstract: Different noise exposure paradigms were studied to determine their teratogenic and embryo-fetotoxic potential in the CF-1 mouse. Female mice were exposed from days 1-6 or from days 6-15 of gestation to one of three noise exposure paradigms which differed widely in level, spectral, and temporal characteristics. Paradigms for noise exposure were chosen to represent semi-continuous exposure to extremely high-intensity noise (jet engine noise at 126 dBA, from noon to midnight); to represent startling type noise composed of alarm bells, jet engine noise, or narrow band warning devices at 110 dBA, with pseudorandom onset and duration of each controlled by a microprocessor (exposure time of 18% over each 24 hour period); and finally to represent very high frequency noise (18-20 kHz tones, derived from a device commercially marketed for repelling rodents, with exposure from noon to midnight). On day 18 of gestation the females were sacrificed, their reproduction status determined, and the concepti were examined for toxicity and for external, visceral, and skeletal alterations. Maternal plasma corticosterone levels were measured at different periods of gestation. Significantly decreased pregnancy rate was noted in all groups exposed to noise except in the group exposed to the very high frequency noise from days 6-15 of gestation. Significant embryolethal effects occurred in the group exposed to the extremely high intensity jet noise paradigm, from days 1-6 of gestation, and significant fetolethal effects occurred in the group exposed to the very high frequency noise paradigm from days 6-15 of gestation. No significant noise-related changes were noted in the incidence of structural alterations or in the concentration of plasma corticosterone.

Journal ArticleDOI
TL;DR: In this article, it was shown that the onset of instability in many GaAs DH lasers that are capable of self-induced modulation is always preceded by the strong emission of noise.
Abstract: We find that the onset of instability in many GaAs DH lasers that are capable of self‐induced modulation is always preceded by the strong emission of noise. The longitudinal optical‐mode width is fairly narrow, typically 0.1–0.3 A, when the optical power contains noise. It is only after the optical power exhibits coherent self‐induced modulation that the apparent longitudinal mode width increases to 1–2 A. This apparent increase in longitudinal mode width is attributed to a wavelength that changes periodically (sinusoidally, for small signals) with time. The wavelength oscillation is due to variations in refractive index brought about by oscillations in the carrier concentration. The implication is that in these lasers, the instantaneous longitudinal optical mode width is relatively narrow regardless of the temporal instability of the light output. In addition, it is shown analytically that there is a critical noise level above which a laser becomes unstable, i.e., exhibits coherent self‐induced modulation.

Journal ArticleDOI
TL;DR: In this article, the average temperature of an isolated thin film on a substrate was investigated and the noise was due to two causes: (i) fluctuations in blackbody radiation absorbed and emitted by the front surface; (ii) thermal diffusion in the sample and the substrate.
Abstract: A computation is given of the fluctuations in average temperature of an isolated thin film on a substrate, the noise being due to two causes: (i) fluctuations in blackbody radiation absorbed and emitted by the front surface; (ii) thermal diffusion in the sample and the substrate. The surface source results in a large 1/f range, the level of which decreases with increasing heat conductivity of the substrate; the noise goes over into a 1/f2 spectrum at high frequencies. The noise due to the volume source results in a 1/f1/2 spectrum, going over into a 1/f3/2 spectrum at higher frequencies; the noise also decreases with increasing heat conductivity of the substrate. The integrated total noise is of the order kT20/C . Under most circumstances the spectrum due to the volume source dominates.

Journal ArticleDOI
TL;DR: In this article, the major noise types observed were white noise, low frequency noise, and high frequency proportional noise, which increased with concentration of analyte and radio frequency input power.

Journal ArticleDOI
TL;DR: In this paper, the response of a subsonic round jet to internal excitation by an acoustic wave has been examined using flow visualization and noise measurements, and large-scale vortex ring structures were observed in the jet mixing layer.
Abstract: The response of a subsonic round jet to internal excitation by an acoustic wave has been examined using flow visualization and noise measurements. The jet was subjected to pulse excitation and to harmonic excitation. In both cases large-scale vortex ring structures were observed in the jet mixing layer. With pulse excitation, interactions between the vortex rings were observed, but no associated noise emission could be detected.

Journal ArticleDOI
TL;DR: In this paper, germanium avalanche photodiodes with n+-n-p and p+n-n structures were devised for improved excess noise and high quantum efficiency performance.
Abstract: New kinds of germanium avalanche photodiodes with n+-n-p and p+-n structures were devised for improved excess noise and high quantum efficiency performance. Multiplication noise, quantum efficiency, and pulse response were studied and compared with those of the conventional n+-p structure diode. Multiplication noise of the new type of diodes were measured in the wavelength range between 0.63 and 1.52 μm. The effective ionization coefficient ratio of the p+-n diode was lower than unity at a wavelength longer than 1.1 μm and 0.6-0.7 at 1.52 μm, and that of the n+-n-p diode was 0.6-0.7 in the whole sensitive wavelength region. Response times were evaluated by using a mode-locked Nd:YAG laser beam and a frequency bandwidth wider than 1 GHz was estimated. Receiving optical power levels were compared with each other using parameters measured in this study.

Journal ArticleDOI
TL;DR: In this article, an extension of the noise measurements of Fleming and Grimes is reported for frequencies up to 100 MHz and at various temperatures, and it is attributed to coupled relaxation oscillators and suggest that the voltage-frequency relation reflects the distribution of CDW segments.

Journal ArticleDOI
TL;DR: In this article, the possibility of detection of an isotropic background gravitational radiation of a stochastic nature by the method of Doppler tracking of spacecraft was considered, and the general formula for the frequency shift of an electromagnetic signal in the gravitational radiation field was shown to be gauge independent.
Abstract: Consideration is given to the possibility of detection of an isotropic background gravitational radiation of a stochastic nature by the method of Doppler tracking of spacecraft. Attention is given in the geometrical optics limit, to the general formula for the frequency shift of an electromagnetic signal in the gravitational radiation field, and it is shown to be gauge independent. The propagation of a free electromagnetic wave in a gravitational radiation field is examined with the conclusion that no resonance phenomena can be expected. Finally, the 'Doppler noise' due to a stochastic background is evaluated, and it is shown to depend on the total energy density of the background and a parameter that is a characteristic of the radiation spectrum and the detection system used.

Journal ArticleDOI
TL;DR: In this paper, a 2D propagation code for Optical ray retracing in stimulated Brillouin backscatter from laser-produced plasmas is studied numerically, using a 2-dimensional propagation code (bounce).
Abstract: Optical ray retracing in stimulated Brillouin backscatter from laser-produced plasmas is studied numerically, using a 2-D propagation code (bounce). This code treats steady-state behavior in the strong damping limit, and includes self-focusing effects. Ray retracing phenomena are grouped into two limiting cases. In the ''whole-beam'' limit, the pump field at the lens has a broad spatial profile that can be focused to a long narrow waist within the plasma. This geometry selectively amplifies only those initial noise components that are propagating back along the axis, where the net gain is highest. The simulations show that such effects exhibit a pronounced threshold due to self-focusing, and disappear when the focal width becomes comparable to the length of the gain medium. In the opposite limit, where the pump radiation at the lens is dominated by small-scale transverse structure, the backscatter can reproduce this structure in detail (i.e., exhibit wavefront reversal) when the far field of the pump produces an interference pattern in the plasma. The plasma then behaves as an active volume hologram as it amplifies the backward-propagating random noise fields.

Journal ArticleDOI
TL;DR: In this article, the theoretical and experimental prospects of detecting a low-frequency, continuous, stochastic background of gravitational waves by Doppler tracking interplanetary spacecraft are examined.
Abstract: We examine the theoretical and experimental prospects of detecting a low-frequency, continuous, stochastic background of gravitational waves by Doppler tracking interplanetary spacecraft. From a theoretical standpoint, such a background may have been generated by various postgalactic processes or by pregalactic black hole formation; there could also exist a primordial background which goes back to the beginning of the universe. We review the characteristic frequency and density ranges which one might anticipate for these backgrounds. From an experimental standpoint, one's ability to detect a background is limited by the finite length of the record available and by an imperfect knowledge of the spectrum of various sources of noise. The fundamental contribution to the noise comes from the clock which regulates the frequency of the tracking waves. If one uses a hydrogen maser clock, this noise becomes progressively less important with decreasing frequency: one might hope to detect a critical density of background radiation at frequencies below 10/sup -2/ Hz and a background with 10/sup -4/ times the critical density at frequencies below 10/sup -5/ Hz. It is encouraging that some of the sorts of background which we anticipate from theoretical considerations fall within the observable regime. We discuss the extent tomore » which other sources of noise may exceed the clock noise and the degree to which they can be eliminated.« less

Journal ArticleDOI
S. Macintyre1
TL;DR: In this paper, the design of a three-axis search coil magnetometer is described which has noise characteristics that are close to or better than comparable superconductor magnetometers over the 20Hz to 2000Hz range.
Abstract: The design of a three-axis search coil magnetometer is described which has noise characteristics that are close to or better than comparable superconductor magnetometers over the 20Hz to 2000Hz range. The sensor coils and electronic conditioning equipment weighs less than 14Kg and can be transported by one person in a 46cm × 46cm × 15cm instrumentation case. The sensing elements consist of three concentric circular coils. The coil signals are processed to provide two outputs: one proportional to frequency, one independent of frequency. Laboratory tests verified that predicted and actual performance agreed quite closely.