Showing papers on "Amplitude published in 1984"

A faulting model for the 1979 Imperial Valley earthquake

Abstract: By comparing synthetic particle velocities with the near-source strong motion data we have constructed, by trial and error, a faulting model for the 1979 Imperial Valley earthquake The calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the Imperial Valley and the spatial variation of the slip rate parameters on the fault plane The independent slip rate parameters are (1) the strike-slip rate amplitude, (2) the dip-slip rate amplitude, (3) the duration that slip rate is nonzero (the rise time of the slip function) and (4) the rupture time, which determines when the slip rate is initiated Our faulting model has the following principal features: (1) Faulting occurred on the Imperial fault and on the Brawley fault, rupture on the Brawley fault being triggered by rupture on the Imperial fault (2) The Imperial fault is a plane 35 km long and 13 km wide with a strike of 323°, measured clockwise from north, and a dip of 80° NE The Brawley fault is a 10 km long and 8 km wide plane with a strike of 360° and a dip of 90° (3) Faulting on the Imperial fault is primarily right-lateral strike slip with a small component of normal dip slip in the sediments at its northern end The larger strike-slip rates are generally confined between depths of 5 and 13 km with maximum values of about 10 m/s The duration varies on the fault with a maximum of 19 s, which is considerably shorter than the total time for the rupture to take place (4) The rupture velocity on the Imperial fault is highly variable Locally, it exceeds the shear wave velocity and, in one instance, the compressional wave velocity The average rupture velocity, though, is less than the shear wave velocity (5) Although the slip on the Brawley fault contributes only about 4% of the total moment, it greatly affects the ground motion at nearby stations (6) The total seismic moment is 67×1018 N m where the Imperial fault contributes 64×1018 N m and the Brawley fault contributes 27×1017 N m In the process of trying almost 300 faulting models, we found that given the elastic parameters of the medium, the synthetic seismograms were most sensitive to the specification of the rupture time Although the slip rate amplitudes are linearly related to the data, the rupture time and the duration are not The parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

Magnetotelluric responses of three-dimensional bodies in layered earths

Abstract: The electromagnetic fields scattered by a three‐dimensional (3-D) inhomogeneity in the earth are affected strongly by boundary charges. Boundary charges cause normalized electric field magnitudes, and thus tensor magnetotelluric (MT) apparent resistivities, to remain anomalous as frequency approaches zero. However, these E‐field distortions below certain frequencies are essentially in‐phase with the incident electric field. Moreover, normalized secondary magnetic field amplitudes over a body ultimately decline in proportion to the plane‐wave impedance of the layered host. It follows that tipper element magnitudes and all MT function phases become minimally affected at low frequencies by an inhomogeneity. Resistivity structure in nature is a collection of inhomogeneities of various scales, and the small structures in this collection can have MT responses as strong locally as those of the large structures. Hence, any telluric distortion in overlying small‐scale extraneous structure can be superimposed to ar...

Electronic traps and Pb centers at the Si/SiO2 interface: Band‐gap energy distribution

Abstract: Energy distribution of Pb centers (⋅Si≡Si3) and electronic traps (Dit) at the Si/SiO2 interface in metal‐oxide‐silicon (MOS) structures was examined by electric‐field‐controlled electron paramagnetic resonance (EPR) and capacitance‐voltage (C‐V) analysis on the same samples Chips of (111)‐oriented silicon were dry‐oxidized for maximum Pb and trap density, and metallized with a large MOS capacitor for EPR and adjacent small dots for C‐V measurements Analysis of C‐V data shows two Dit peaks of amplitude 2×1013 eV−1 cm−2 at Ev+026 eV and Ev+084 eV The EPR spin density reflects addition or subtraction of an electron from the singly occupied paramagnetic state and shows transitions of amplitude 15×1013 eV−1 cm−2 at Ev+031 eV and Ev+080 eV This correlation of electrical and EPR responses and their identical chemical and physical behavior are strong evidence that ⋅Si≡Si3 is a major source of interface electronic traps in the 015–095 eV region of the Si band gap in unpassivated material

On the control of magnetospheric convection by the spatial distribution of ionospheric conductivities

Abstract: A self-consistent semianalytical model of magnetospheric convection including the effect of the latitude and local time variations of ionospheric conductivities is presented. The motions of the inner edge of the magnetospheric ring current, and the associated field-aligned currents, produced by the externally imposed dawn-to-dusk potential drop across the magnetospheric cavity are computed by using a linear approximation. The coupling between the different diurnal harmonics in the local time variations of fields and currents produced by the local time dependence of ionospheric conductivities is described by an appropriate matrix formalism. The calculations show that the enhancement of auroral conductivities by electron precipitation in the auroral zone significantly enhances both the typical duration and the absolute amplitude of the penetration of convection electric fields to midlatitudes. Furthermore, the local time variations of the convection electric field generated at midlatitudes by a sudden increase of the dawn-to-dusk potential drop are in good agreement, both at the initial time and after the steady state is reached, with the available statistical models of the disturbance midlatitude electric field. The amplitude of the steady state field seems sufficient to explain these observations, thus confirming that the concept of the shielding of midlatitudes from the convection electric fields is basically correct but was overestimated in earlier analytical calculations. The large subauroral electric fields observed by several satellites are also reproduced in the model either by a decrease of the subauroral conductivities below the midlatitude values or by the consideration of a very narrow latitudinal extent of the auroral zone. The overall consistency between the results of the model and the electric field observations thus supports the idea that a large class of phenomena related to magnetospheric convection in the dipole regions of the magnetosphere can be described in a reasonably realistic manner by a linear theory.

On the excitation of long nonlinear water waves by a moving pressure distribution

Abstract: A study is made of the wave disturbance generated by a localized steady pressure distribution travelling at a speed close to the long-water-wave phase speed on water of finite depth The linearized equations of motion are first used to obtain the large-time asymptotic behaviour of the disturbance in the far field; the linear response consists of long waves with temporally growing amplitude, so that the linear approximation eventually breaks down owing to finite-amplitude effects A nonlinear theory is developed which shows that the generated waves are actually of bounded amplitude, and are governed by a forced Korteweg-de Vries equation subject to appropriate asymptotic initial conditions A numerical study of the forced Korteweg-de Vries equation reveals that a series of solitons are generated in front of the pressure distribution

Distortion and harmonic generation in the nearfield of a finite amplitude sound beam

Abstract: Distortion and harmonic generation in the nearfield of a finite amplitude sound beam are considered, assuming time‐periodic but otherwise arbitrary on‐source conditions. The basic equations of motion for a lossy fluid are simplified by utilizing the parabolic approximation, and the solution is derived by seeking a Fourier series expansion for the sound pressure. The harmonics are governed by an infinite set of coupled differential equations in the amplitudes, which are truncated and solved numerically. Amplitude and phase of the fundamental and the first few harmonics are calculated along the beam axis, and across the beam at various ranges from the source. Two cases for the source are considered and compared: one with a uniformly excited circular piston, and one with a Gaussian distribution. Various source levels are used, and the calculations are carried out into the shock region. The on‐axis results for the fundamental amplitude are compared with results derived using the linearized solution modified with various taper functions. Apart from a nonlinear tapering of the amplitude along and near the axis, the results are found to be very close to the linearized solution for the fundamental, and for the second harmonic close to what is obtained from a quasilinear theory. The wave profile is calculated at various ranges. An energy equation for each harmonic is obtained, and shown to be equivalent within our approximation to the three‐dimensional version of Westervelt’s energy equation. Recent works on one‐dimensional propagation are reviewed and compared.

Human auditory steady state potentials.

Abstract: The auditory steady state potentials may be an important technique in objective audiometry. The effects of stimulus rate, intensity, and tonal frequency on these potentials were investigated using both signal averaging and on-line Fourier analysis. Stimulus presentation rates of 40 to 45/sec result in a 40 Hz sinusoidal response which is about twice the amplitude of the 10 and 60/sec responses. No significant effects of subject age or sex were seen. The 40/sec response shows a linear decrease in amplitude and a linear increase in latency when stimulus intensity is decreased from 90 to 20 dB normal hearing level. This response is recordable to within a few decibels of behavioral threshold. Stimuli of different tonal frequency give similar amplitude/rate functions, with absolute amplitude decreasing with increasing tonal frequency. Signal averaging and Fourier analysis provide nearly identical amplitude/rate, amplitude/intensity, and latency/intensity functions. Both methods of analysis may be used, therefore, to record the 40 Hz steady state potential. Fourier analysis, however, may be the faster and less expensive method. Furthermore, techniques ("zoom") are available with Fourier analysis to study the effects of varying stimulus parameters on-line with the Fourier analysis procedure.

Nonlinear effects on shoaling surface gravity waves

Abstract: Two nonlinear models that describe the shoaling of unidirectional surface gravity waves are developed. Based on variants of Boussinesq’s equations, the models are cast as a set of coupled evolution equations for the amplitudes and phases of the temporal Fourier modes of the wave field. Triad interactions across the entire wind wave frequency band (0.05-0.25 Hz) provide the mechanism for cross spectral energy transfers and modal phase modifications as the waves propagate shoreward through the shoaling region (10-3 m depth). A field experiment, designed to test the operational validity of the nonlinear shoaling models, provided data on wave parameters over a wide range of conditions. Three representative data sets illustrating different initial spectral shapes and subsequent evolutions are compared with predictions of the nonlinear shoaling models and linear, finite-depth theory. Power spectral comparisons, as well as spectra of coherence and relative phase between model predictions and data, indicate that the nonlinear models accurately predict Fourier coefficients of the wave field through the shoaling region sets. Differences between the predictions of the various models are related to differences in the models9 dispersion relations. Although generally inferior to the nonlinear models, linear, finite-depth theory accurately predicts Fourier coefficients in regions of physical and frequency space where nonlinear evolution of the power spectrum is not observed, thus verifying the validity of the linear, finite-depth dispersion relation in limited portions of physical and frequency space in the shoaling region.

Statistical properties of single sodium channels.

Abstract: Single channel currents were obtained from voltage-activated sodium channels in outside-out patches of tissue-cultured GH3 cells, a clonal line from rat pituitary gland. In membrane patches where the probability of overlapping openings was low, the open time histograms were well fit by a single exponential. Most analysis was done on a patch with exactly one channel. We found no evidence for multiple open states at -25 and -40 mV, since open times, burst durations, and autocorrelation functions were time independent. Amplitude histograms showed no evidence of multiple conductance levels. We fit the gating with 25 different time-homogeneous Markov chain models having up to five states, using a maximum likelihood procedure to estimate the rate constants. For selected models, this procedure yielded excellent predictions for open time, closed time, and first latency density functions, as well as the probability of the channel being open after a step depolarization, the burst duration distribution, autocorrelation, and the distribution of number of openings per record. The models were compared statistically using likelihood ratio tests and Akaike's information criterion. Acceptable models allowed inactivation from closed states, as well as from the open state. Among the models eliminated as unacceptable by this survey were the Hodgkin-Huxley model and any model requiring a channel to open before inactivating.

Parametrically excited solitary waves

Abstract: A modulated cross-wave of resonant frequencyω1, carrier frequencyω =ω1 {1 + O(e)}, slowly varying complex amplitude O(e½b), longitudinal scale b/e½ and timescale 1/eω is induced in a long channel of breadth b that contains water of depth d and is subjected to a vertical oscillation of amplitude O(eb) and frequency 2ω, where 0 0.045 for d/b [gsim ] 1. The corresponding cnoidal waves (of which the solitary wave is a limiting case) are considered in an appendix.

Packetized ensemble modem

Abstract: A high speed digital data modem (10) particularly suited for use in a dial up telephone line. For the transmit ensemble (30), the telephone pass-band is divided into sixty-four sub-bands each with a carrier located approximately in the center of each sub-band. Each carrier is amplitude and phase modulated in order to encode five (5) bits. One carrier is used as a reference signal for phase and amplitude. The modulated carriers can be changed in data content every epoch. By use of packetization of data, individual amplitude correction, (104), and individual phase correction (118, 120, 124) for each carrier, the high speed modem may achieve up to 12000 bps over a dial up line with a simultaneous 300 bps reverse channel.

Turbulent flow over large-amplitude wavy surfaces

Abstract: The laser-Doppler velocimeter is used to measure the mean and the fluctuating velocity for turbulent flow over a solid sinusoidal wave surface having a wavelength λ of 50.8 mm and a wave amplitude of 5.08 mm. For this flow, a large separated region exists, extending from x/λ = 0.14 to 0.69. From the mean velocity measurements, the time-averaged streamlines and therefore the extent of the separated region are calculated. Three flow elements are identified: the separated region, an attached boundary layer, and a free shear layer formed by the detachment of the boundary layer from the wave surface. The characteristics of these flow elements are discussed in terms of the properties of the mean and fluctuating velocity fields.

Complex seismic trace analysis of thin beds

Abstract: Displays of complex trace attributes can help to define thin beds in seismic sections. If the wavelet in a section is zero phase, low impedance strata whose thicknesses are of the order of half the peak‐to‐peak period of the dominant seismic energy show up as anomalously high‐amplitude zones on instantaneous amplitude sections. These anomalies result from the well‐known amplitude tuning effect which occurs when reflection coefficients of opposite polarity a half period apart are convolved with a seismic wavelet. As the layers thin to a quarter period of the dominant seismic energy, thinning is revealed by an anomalous increase in instantaneous frequency. This behavior results from the less well‐known but equally important phenomenon of frequency tuning by beds which thin laterally. Instantaneous frequency reaches an anomalously high value when bed thickness is about a quarter period and remains high as the bed continues to thin. In this paper, complex trace analysis is applied to a synthetic model of a we...

A unified description of two-layer flow over topography

Abstract: Observations of the flow of a two-layer fluid resulting from the motion of a towed streamlined two-dimensional obstacle are described in some detail. The experiments were designed to further our understanding of the factors governing the nature and magnitude of upstream disturbances in the general flow of stratified fluid over two-dimensional topography, and predictions for arbitrary two-dimensional flows are made from the results of these experiments. In particular, the relationship between uniformly stratified flow and single-layer flow over topography is suggested. Most of the observed features of interest in these experiments are nonlinear in character. Relatively complete descriptions of the observed flows are presented over a wide range of parameter values, and the phenomena observed include upstream undular and turbulent bores, bores with zero energy loss, ‘rarefactions’ (in which the interface height changes monotonically over a transition region of continuously increasing length), and downstream hydraulic drops and jumps. Their properties are shown to be broadly consistent with predictions from a two-layer hydrostatic model based on continuity and momentum considerations, which employs jump criteria and rarefaction equations where appropriate. Bores occur because of nonlinear steepening when the layer containing the obstacle is thinner than the other, and rarefactions occur when this layer thickness is comparable with or greater than that of the other layer. The speed and amplitude of the upstream bores are governed by nonlinear effects, but their character is determined by a balance between nonlinear steepening, wave dispersion and interfacial friction when the bore is non-turbulent. Experimental evidence is presented for two types of hysteresis or ‘multiple equilibria’ - situations where two different flow states may exist for the same external steady conditions. In the first of these hysteresis types, the upstream flow may be supercritical or consist of an upstream bore state. It is analogous to the type anticipated for single-layer flow by Baines & Davies (1980) and described numerically by Pratt (1983), but it is only found experimentally for part of the expected parameter range, apparently because of interfacial stress effects. The second hysteresis type is new, and involves the presence or absence of a downstream hydraulic drop and following jump.

Phase and amplitude uncertainties in heterodyne detection

Abstract: The quantum limits on simultaneous phase and squared-amplitude measurements made via optical heterodyne detection on a single-mode radiation field are established. The analysis proceeds from a fully quantum mechanical treatment of heterodyning with ideal photon detectors. A high mean field uncertainty principle is proven for simultaneous phase and squared-amplitude observations under the condition that the signal and image band states are independent, and the image band has zero mean. Operator representations are developed which show that no such principle applies when arbitrary signal/image band dependence is permitted, although the mean observations are no longer functions of the signal field alone. A multimode two-photon coherent state illustrating this behavior at finite energy is exhibited. Potential applications for the resulting improved accuracy measurements are briefly described.

A consistent picture of protein dynamics.

Abstract: Information about the protein dynamics of myoglobin obtained by x-ray and Mossbauer investigations is analyzed and compared with computer simulations. Computer simulations give correct amplitudes of mean-square displacements but fail in the description of the time dependence of motions. Our model describes protein dynamics at physiological temperatures as an overdamped diffusion-like motion in a restricted space. The fluctuations occur around the average conformation determined by x-ray structure analysis. The gain in entropy drives the molecule into the transition state and, in this way, accounts for its flexibility.

Initial agonist burst duration depends on movement amplitude.

Abstract: The initial burst of EMG activity associated with arm movements made by normal human subjects was studied. Subjects made visually guided, steptracking movements of different amplitudes and speeds. The duration of the initial agonist burst was greater for large than for small amplitude movements. The burst duration was not continuously graded but was either short (70 ms) for small amplitude movements (less than 20 deg) or long (140 ms) for large amplitude ones (greater than 50 deg). Movements of intermediate amplitudes (30–40 deg) were made with both short and long duration bursts. The increase in the duration of the initial agonist burst for large movements was produced by the appearance of a second component in the burst. Both components were of the same duration and occurred before movement peak velocity was reached. Intramuscular recording showed that both components originate from the same muscle. Similar observations were made in both fast and slow movements and in both the biceps and triceps muscles when they were being used as agonists. The data show that the central nervous system has two mechanisms for generation of large amplitude movements: modulation of the magnitude of the initial agonist burst and generation of a second component or pulse of agonist activity at the start of movement.

Measurements of mantle wave velocities and inversion for lateral heterogeneity and anisotropy. II - Analysis by the single-station method

Abstract: Phase and group velocities of G_2, G_3, R_2 and R_3 (100-330_s) are measured by the single-station method and are inverted to give a spherical harmonic representation of the velocity lateral variation. Approximately 200 paths have been studied. The results are presented for degrees and orders up to 6. The even harmonics of the phase velocity representation are consistent with those obtained from great circle phase velocities (Paper I). The odd harmonics are less constrained and generally have larger standard deviations than the even harmonics. To suppress the poorly determined harmonics in the velocity contour maps we construct a filter which is derived from an inverse problem formulation. The filter reduces the amplitudes of regional variations, but does not change the overall pattern. The patterns of the regional variations are generally consistent with those obtained by regionalized inversion of great circle data (Paper I). The velocity maps show significant differences within oceans and continents. An analysis is made of correlations of surface wave velocities with heat flow and the non-hydrostatic geoid. The slownesses correlate well with heat flow for l = 1-6. The correlation peaks at l = 2 and 5. The geoid has an anticorrelation with the slownesses at l = 2 and 3, and a positive correlation from l = 4 to 6.

Bénard convection with time‐periodic heating

Abstract: A thin liquid layer, which is heated from below, has its lower boundary modulated sinusoidally in time with amplitude δ. Weakly‐nonlinear stability theory shows that the modulation produces a range of stable hexagons near the critical Rayleigh number. For small δ the range is O(δ4) in size and decreases with modulation frequency. These hexagons bifurcate subcritically and correspond to downflow at cell centers.

Observations of hard-rock site effects

Abstract: Differences were measured in seismograms recorded at eight proximate hardrock sites: five in tunnels and three on outcrops on hills. Tunnel sites affected the amplitude of incident signals by as much as a factor of three, at frequencies inversely proportional to the depth of the site into the tunnel. For example, the maximum effect of a site 12 m deep was at 25 Hz while that of a site 85 m deep was at 11 Hz. Most of the observed tunnel effects could be explained in terms of interference between the incident and surface-reflected waves. Rock outcrop sites on hills affected the amplitude of incident signals by as much as a factor of eight, at frequencies inversely proportional to the dimension of the hill, and more for horizontally than for vertically polarized signals. Hard-rock site effects typically varied by no more than a factor of three for input signals from different earthquakes, having widely different azimuth and incident angles.

A mechanism for the generation of cavitation maxima by pulsed ultrasound

Abstract: A train of 1‐MHz pulses can generate maxima of cavitation activity [V Ciaravino, H G Flynn, and M W Miller, Ultrasound Med Biol 7, 159–166 (1981)] at pulse lengths of 6 and 60 ms and at pressure amplitudes, PA, between 54 and 94 bars (or intensities between 10 and 30 W/cm2) Generation of maxima at PA between these limits on pressure amplitude implies that the increase in cavitation activity originates from gas nuclei with radii lying in a critical size range centered at about 008 μm The mechanism proposed for this phenomenon suggests that nuclei in this critical range are unstabilized nuclei generated in one pulse and surviving to the next with an appreciable fraction of the survivors lying in the critical range Transient cavities that grow from such small nuclei are shown to behave as isolated mechanical systems that on reaching maximum size collapse as imploding spheres The maximum pressures reached in such imploding cavities would then approximate those calculated for the spherical collap

Scaling Methods for Earthquake Response Spectra

Abstract: In current practice, design response spectra are normalized by the three peak ground motions. Alternative scaling factors are evaluated to reduce the dispersion encountered in normalized spectral ordinates. The scaling factors comprise two major groups, one based on ground motion data, and the other on response quanitities. Within the group based on ground motion values are the integrals of the squared acceleration, velocity, and displacement, and the associated root-square, mean-square, and root-mean-square motions. Included within the group based on response quantities are the spectrum intensity and the mean Fourier amplitude. The scaling parameters are evaluated statistically using response spectra for elastic, elastoplastic, and bilinear hysteretic systems, computed from a set of twelve representative earthquake recordings. The results show that a three parameter system of spectrum intensities, computed within low, medium, and high frequency regions, may provide a better means of scaling earthquake response spectra. Significant reductions in dispersion may be realized if elastic spectra are normalized by the spectrum intensities rather than the peak ground motions. The spectrum intensities also reduce the scatter for normalized inelastic spectra, for low to moderate displacement ductilities.