Showing papers on "Amplitude published in 1995"

Quartz crystal microbalance setup for frequency and Q‐factor measurements in gaseous and liquid environments

Abstract: An experimental setup has been constructed for simultaneous measurements of the frequency, the absolute Q factor, and the amplitude of oscillation of a quartz crystal microbalance (QCM). The technical solution allows operation in vacuum, air, or liquid. The crystal is driven at its resonant frequency by an oscillator that can be intermittently disconnected causing the crystal oscillation amplitude to decay exponentially. From the recorded decay curve the absolute Q factor (calculated from the decay time constant), the frequency of the freely oscillating crystal, and the amplitude of oscillation are obtained. All measurements are fully automated. One electrode of the QCM in our setup was connected to true ground which makes possible simultaneous electrochemistry. The performance is illustrated by experiments in fluids of varying viscosity (gas and liquid) and by proteinadsorptionin situ. We found, in addition to the above results, that the amplitude of oscillation is not always directly proportional to the Q factor, as the commonly used theory states. This puts limitations on the customary use of the amplitude of oscillation as a measure of the Q factor.

Testing mode-coupling theory for a supercooled binary Lennard-Jones mixture I: The van Hove correlation function.

Abstract: We report the results of a large scale computer simulation of a binary supercooled Lennard-Jones liquid. We find that at low temperatures the curves for the mean squared displacement of a tagged particle for different temperatures fall onto a master curve when they are plotted versus rescaled time tD(T), where D(T) is the diffusion constant. The time range for which these curves follow the master curve is identified with the \ensuremath{\alpha}-relaxation regime of mode-coupling theory (MCT). This master curve is fitted well by a functional form suggested by MCT. In accordance with idealized MCT, D(T) shows a power-law behavior at low temperatures. The critical temperature of this power law is the same for both types of particles, and also the critical exponents are very similar. However, contrary to a prediction of MCT, these exponents are not equal to the ones determined previously for the divergence of the relaxation times of the intermediate scattering function [Phys. Rev. Lett. 73, 1376 (1994)]. At low temperatures, the van Hove correlation function (self as well as distinct part) shows almost no sign of relaxation in a time interval that extends over about three decades in time. This time interval can be interpreted as the \ensuremath{\beta}-relaxation regime of MCT. From the investigation of these correlation functions, we conclude the hopping processes are not important on the time scale of the \ensuremath{\beta} relaxation for this system and for the temperature range investigated. We test whether the factorization property predicted by MCT holds and find that this is indeed the case for all correlation functions investigated. The distance dependences of the critical amplitudes are in qualitative agreement with the ones predicted by MCT for some other mixtures. The non-Gaussian parameter for the self part of the van Hove correlation function for different temperatures follows a master curve when plotted against time t.

Three-jet cross sections to next-to-leading order

Abstract: One- and two-jet inclusive quantities in hadron collisions have already been calculated to next-to-leading order accuracy, using both the subtraction and the cone method Since the one-loop corrections have recently been obtained for all five-parton amplitudes, three-jet inclusive quantities can also be predicted to next-to-leading order The subtraction method presented in the literature is based on a systematic use of boost-invariant kinematical variables, and therefore its application to three-jet production is quite cumbersome In this paper we re-analyze the subtraction method and point out the advantage of using angle and energy variables This leads to simpler results and it has complete generality, extending its validity to $n$-jet production The formalism is also applicable to $n$-jet production in $e^+e^-$ annihilation and in photon-hadron collisions All the analytical results necessary to construct an efficient numerical program for next-to-leading order three-jet inclusive quantities in hadroproduction are given explicitly As new analytical result, we also report the collinear limits of all the two-to-four processes

Coalescing binary systems of compact objects to (post)5/2-Newtonian order. V. Spin effects.

Abstract: We examine the effects of spin-orbit and spin-spin couplings on the inspiral of a coalescing binary system of spinning compact objects and on the gravitational radiation emitted therefrom. Using a formalism developed by Blanchet, Damour, and Iyer we calculate the contributions due to the spins of the bodies to the symmetric trace-free radiative multipole moments which are used to calculate the waveform, energy loss, and angular momentum loss from the inspiraling binary. Using equations of motion which include terms due to spin-orbit and spin-spin couplings we evolve the orbit of a coalescing binary and use the orbit to calculate the emitted gravitational waveform. We find the spins of the bodies affect the waveform in several ways: (1) the spin terms contribute to the orbital decay of the binary, and thus to the accumulated phase of the gravitational waveform; (2) the spins cause the orbital plane to precess, which changes the orientation of the orbital plane with respect to an observer, thus causing the shape of the waveform to be modulated; (3) the spins contribute directly to the amplitude of the waveform. We discuss the size and importance of spin effects for the case of two coalescing neutron stars, and for the case of a neutron star orbiting a rapidly rotating 10${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$ black hole.

Envelope variations and spectral splatter in clipped multicarrier signals

Abstract: This paper presents an investigation into the effects of clipping of both baseband and bandpass multicarrier signals. It will be shown that considerable reductions in the amplitude variations (crest factor) of both classes of signal are possible at the expense of limited inband spectral distortion and some out of band clip noise emissions. The amount of inband distortion and out of band emissions can be traded off directly against reductions in the crest factor of the clipped signal. Novel clipping techniques are presented which give one more control over the various trade-offs.

Waste energy control and management in power amplifiers

Abstract: An amplifying apparatus for linearly amplifying a desired signal using a pair of coupled non-linear amplifiers is disclosed. The amplifying apparatus comprises a limiter for separating amplitude variations from the desired signal and producing a constant amplitude signal bearing the phase of the desired signal and an amplitude related signal. In addition, a drive signal generater produces two drive signals each dependent on the constant amplitude signal and the amplitude related signal such that each drive signal depends on the phase of the desired signal and such that the sum of the squares of the amplitudes of the drive signals is constant. Finally, a coupler couples the two drive signals to produce two constant amplitude signals for driving the pair of non-linear power amplifiers and for coupling the outputs of the power amplifiers to produce two amplified output signals, one of which is the linearly amplified desired signal and the other of which is a waste energy signal.

Spectral wave-current bottom boundary layer flows

Abstract: Based on the linearized governing equations, a bottom roughness specified by the equivalent Nikuradse sand grain roughness, fcjv, and a timeinvariant eddy viscosity analogous to that of Grant and Madsen (1979 and 1986) the solution is obtained for combined wave-current turbulent bottom boundary layer flows with the wave motion specified by its near-bottom orbital velocity directional spectrum. The solution depends on an a priori unknown shear velocity, u*r, used to scale the eddy viscosity inside the wave boundary layer. Closure is achieved by requiring the spectral wavecurrent model to reduce to the Grant-Madsen model in the limit of simple periodic plane waves. To facilitate application of the spectral wave-current model it is used to define the characteristics (near-bottom orbital velocity amplitude, U(,r, radian frequency, uir, and direction of propagation, 4>wr) of a representative periodic wave which, in the context of combined wavecurrent bottom boundary layer flows, is equivalent to the wave specified by its directional spectrum. Pertinent formulas needed for application of the model are derived and their use is illustrated by outlining efficient computational procedures for the solution of wave-current interaction for typical specifications of the current

Naturalistic stimuli increase the rate and efficiency of information transmission by primary auditory afferents

Abstract: Natural sounds, especially communication sounds, have highly structured amplitude and phase spectra. We have quantified how structure in the amplitude spectrum of natural sounds affects coding in primary auditory afferents. Auditory afferents encode stimuli with naturalistic amplitude spectra dramatically better than broad-band stimuli (approximating white noise); the rate at which the spike train carries information about the stimulus is 2-6 times higher for naturalistic sounds. Furthermore, the information rates can reach 90% of the fundamental limit to information transmission set by the statistics of the spike response. These results indicate that the coding strategy of the auditory nerve is matched to the structure of natural sounds; this 'tuning' allows afferent spike trains to provide higher processing centres with a more complete description of the sensory world.

Model for the sawtooth period and amplitude

Abstract: A model for sawtooth oscillations in tokamak experiments is outlined. A threshold criterion for the onset of internal kink modes and a prescription for the relaxed profiles immediately after the sawtooth crash have been implemented in a transport code that evolves the relevant plasma parameters. In this paper, applications of this model to the prediction of the sawtooth period and amplitude in projected ITER discharges are discussed. It is found that sawteeth can be stabilized transiently by the fusion alpha particles in ITER for periods that are long on the energy confinement timescale (). The sawtooth period depends on the amount of reconnected flux at the preceding sawtooth crash. When Kadomtsev's full reconnection model is used, the period can exceed 100 s. The sawtooth mixing radius following long duration sawtooth ramps can easily exceed half the plasma minor radius, raising questions about the desirability of transient sawtooth suppression.

Global phase velocity maps of Love and Rayleigh waves between 40 and 150 seconds

Abstract: SUMMARY Although much is known of the 3-D structure of the Earth, existing models do not make use of much that is known about the large structural perturbations near the surface. It has long been known, for example, that continental and oceanic crustal structures are quite different, and that these differences are evident in the dispersion of Love and Rayleigh waves sampling continental and oceanic paths. Such differences are largest at periods of less than about 100 s. Existing global models do not adequately account for such data, and make allowances for crustal structure in a very approximate way, owing to the incompleteness of information on the global distribution of crustal parameters. As a result, variations in, for example, crustal thickness translate themselves into model artefacts extending to great depth. This can be seen as one aspect of the imperfect resolution of the existing global models. In order to construct higher resolution models of the Earth's outer shell (0-200 km depth), it is necessary to gain more precise knowledge of near-surface structure by incorporating data that have sensitivity to the details of the depth distribution of heterogeneity near the surface. As a first step we analyse a large data set of fundamental-mode Rayleigh and Love waveforms to obtain global phase-velocity maps in the period range 40–150 s. Minor and major arc phase velocities have been determined from about 24 000 digital GDSN and GEOSCOPE seismograms recorded between 1980 and 1990. In order to make such measurements in an automatic way, we have developed a method, using non-linear waveform inversion, in which velocity and amplitude, as a function of frequency, are expanded in B-splines. The waveform data are inverted for the B-spline coefficients, with the application of an explicit smoothness constraint that protects against unwanted effects, such as those due to notches in the amplitude spectra, and avoids some of the problems associated with the phase ambiguity. The cost function (which is minimized in a least-squares sense) presents many local minima, and a good initial model is needed; this is derived by integration of group velocities. The measurements made using this new technique are then used in a global inversion for phase-velocity distributions of Love and Rayleigh waves, expressed in terms of a spherical harmonic expansion. We show resulting phase-velocity maps up to degree and order 40. These maps are corrected for possible artefacts due to the truncation of the spherical harmonic expansion. We present a detailed resolution analysis which shows that global lateral resolution for surface-wave tomography is of the order of 2000 km. Love-wave phase velocities show a high correlation with known upper mantle structure at long periods and with crustal structure at shorter periods. Similarly, Rayleigh-wave phase velocities correlate well with known tectonic features, but show no clear crustal signature owing to their different sampling of the structure with depth.

Multiple wave-vector extensions of the NMR pulsed-field-gradient spin-echo diffusion measurement.

Abstract: Multiple wave-vector extensions of NMR pulsed-field-gradient diffusion measurements are discussed in the context of diffractionlike effects of restricted diffusion. In the case of two independent wave vectors, it is shown that the dependence of the amplitude on the relative angle between the wave vectors carries information that is absent in the usual single-wave-vector amplitude. It is shown that a two-wave-vector measurement is sensitive to restricted diffusion even at small wave vectors, in contrast with the single-wave-vector case. It is proposed that the angular dependence noted above may be used to distinguish effects of restricted diffusion from those arising from a distribution of diffusion constants.

Rotating magnet for distance and direction measurements from a first borehole to a second borehole

Abstract: A method for determining the distance and direction from a first borehole to a second borehole includes generating, by way of a rotating magnetic field source at a first location in a second borehole, and elliptically polarized magnetic field in the region of the first borehole. First and second sensors positioned at an observation point in the first borehole measure the amplitude and relative phase of respective first and second components of the polarized magnetic field and from these measurements, the direction, relative to the sensors, from the observation point to the first location is determined. The distance between these points is determined by measuring at plural observation points amplitude variations with depth of the rotating magnetic field in the first borehole, and computing theoretical variations in the amplitude for different assumed distances between the observation points and the location of the magnetic field source. The measured amplitude variations are compared with theoretical variations to determine the distance between the first and second boreholes.

Surface layering in liquid gallium: An X-ray reflectivity study.

Abstract: Surface-induced atomic layering in liquid gallium has been observed using x-ray reflectivity, ultrahigh vacuum conditions, and sputtered clean surfaces. Reflectivity data, collected on a supercooled liquid sample to momentum transfers as large as {ital q}{sub {ital z}}=3.0 A{sup {minus}1}, exhibit a strong maximum near 2.4 A{sup {minus}1} indicating a layer spacing that is comparable to its atomic dimensions. The amplitude of the electron density oscillations decays with a characteristic length of 6 A. This is unexpectedly twice that of recent results for Hg, and the difference may be related to covalent bonding or supercooling.

Analysis of programmable ultrashort waveform generation using liquid-crystal spatial light modulators

Abstract: A rigorous analysis of ultrashort pulse shaping by the spectral filtering of dispersed frequency components is presented. Particular attention is directed toward the case of two liquid-crystal spatial light modulators used to provide programmable manipulation of both the phase and the amplitude profiles of the shaped waveform in the time domain. Different optical configurations are evaluated and their theoretical and practical effects determined. An important result is that, even with optimal alignment and components, the diffraction arising from spectral filtering necessarily produces a transverse spatial shift that varies linearly along the temporal profile of the shaped waveform. Despite this effect it is shown that the technique can generate arbitrary phase and amplitude temporal profiles (subject to limitations in temporal extent and temporal resolution) for the Gaussian spatial component of the shaped output waveform.

Linear and nonlinear modes in nonrelativistic electron-positron plasmas

Abstract: A comprehensive two-fluid model is developed for collective modes in a nonrelativistic electron-positron plasma. Longitudinal and transverse electrostatic and electromagnetic modes, both in the presence and absence of a magnetic field, are studied. Wave properties are discussed in terms of dispersion relations, wave normal surfaces, and cylindrical mirror analyzer clemmow-Mullaly-Allis diagrams. The results are extended to include the two-stream instability and ion acoustic solitary waves. For the two-stream instability, a similar result is found as in the electron-ion plasma. For ion acoustic solitary waves, only subsonic solutions are found to exist. Furthermore, their width is proportional to their amplitude, unlike the electron-ion plasma case, where the speed is proportional to the amplitude.

Adaptive phase measurements of optical modes: Going beyond the marginal Q distribution.

Abstract: In standard single-shot measurements of the phase of an optical mode, the phase and amplitude quadratures are jointly measured, and the latter information discarded. These techniques are consequently suboptimal. Here I suggest an adaptive scheme, whereby the phase is estimated from the results so far and fed back to control the phase of the local oscillator so as to measure the (estimated) phase quadrature only. I show that adaptive phase measurements can approach optimal phase measurements for states with both low and high mean photon numbers.

Three-Dimensional Simulation of a Magnitude 7.75 Earthquake on the San Andreas Fault

Abstract: Simulation of 2 minutes of long-period ground motion in the Los Angeles area with the use of a three-dimensional finite-difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7.75 earthquake along the 170-kilometer section of the San Andreas fault between Tejon Pass and San Bernardino. Maximum ground velocities are predicted to occur near the fault (2.5 meters per second) and in the Los Angeles basin (1.4 meters per second) where large amplitude surface waves prolong shaking for more than 60 seconds. Simulated spectral amplitudes for some regions within the Los Angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the San Andreas fault.

A new method for parameterization of phase shift and backscattering amplitude

Abstract: Parameterization of phase and backscattering amplitude with cubic splines is described. Using the cubic spline, the analytical partial derivatives of the plane wave EXAFS function can be calcalated. The use of analytical partial derivatives decreases the CPU time needed for a refinement by over 60% for a three shell system compared to a refinement with partial derivaties calculated with the finite difference method.

A two‐dimensional tidal model for the Mediterranean Sea

Abstract: The tidal propagation in the Mediterranean Sea is described through a high-resolution, two-dimensional hydrodynamic model forced by the equilibrium tide and the incoming tide at the Strait of Gibraltar. The four most significant constituents, M2, S2, K1, and O1, are included in the model. Good agreement with a set of 63 coastal gauges is achieved. The significance of the equilibrium tide and the forcing at the open boundary is investigated. The incoming wave from the Strait of Gibraltar is important in tuning the tides in the whole of the Mediterranean. For the north Aegean Sea the solution without the forcing at Gibraltar results in a doubling of the amplitudes of the semidiurnal tides. The estimated energy dissipation due to bottom friction is 8.8×108 W. The major area of dissipation is the Gulf of Gabes. Energy fluxes through the major straits are calculated.

Nonlinear wave loads on a slender vertical cylinder

Abstract: The diffraction of water waves by a vertical circular cylinder is considered in the regime where the wave amplitude A and cylinder radius a are of the same order, and both are small compared to the wavelength. The wave slope is small, and a conventional linear analysis applies in the outer domain far from the cylinder. Significant nonlinear effects exist in the complementary inner domain close to the cylinder, associated with the free-surface boundary condition. Using inner coordinates scaled with respect to a, it is shown that the leading-order nonlinear contribution to the velocity potential includes terms proportional to both A2a and A3. The wave load which acts on the cylinder near the free surface includes second- and third-harmonic components which are proportional respectively to A2a2 and A3a. In a conventional perturbation analysis, where A [Lt ] a, these components would be ordered in magnitude corresponding to the different powers of A, but here they are of the same order. The second- and third-order components of the total force are of comparable magnitude for practical values of the wave slope.

Optical propagation in non-Kolmogorov atmospheric turbulence

Abstract: Several observations of atmospheric turbulence statistics have been reported which do not obey Kolmogorov's power spectral density model. These observations have prompted the study of optical propagation through turbulence described by non-classical power spectra. This paper presents an analysis of optical propagation through turbulence which causes fluctuations in the index of refraction. The index fluctuations are assumed to have spatial power spectra that obey arbitrary power laws. The spherical and plane wave structure functions are derived using Mellin transform techniques. The wave structure function is used to compute the Strehl ratio of a focused plane wave propagating in turbulence as the power law for the spectrum of the index of refraction fluctuations is varied from -3 to -4. The relative contributions of the log amplitude and phase structure functions to the wave structure function are computed. At power laws close to -3, the magnitude of the log amplitude and phase perturbations are determined by the system Fresnel ratio. At power laws approaching -4, phase effects dominate in the form of random tilts.

Auditory steady‐state responses to tones amplitude‐modulated at 80–110 Hz

Abstract: Steady‐state responses can be recorded from the human scalp in response to tones that are sinusoidally modulated in amplitude at rates between 60 and 120 Hz. For 60 dB SPL 1000‐Hz tones the maximum baseline‐to‐peak amplitude of about 0.06 μV occurs for modulation rates between 80 and 95 Hz. The phase of the response does not change with modulation depths greater than 25% and the amplitude saturates at modulation depths greater than 50%. The presence or absence of a response can be accurately determined by frequency‐domain statistics and the response becomes clearly recognizable at intensities that are 16±8 dB above behavioral thresholds. With increasing intensity the response increases in amplitude at 1.9 nV/dB until an intensity of 70 dB SPL. As the intensity increases above 70 dB SPL the response increases in amplitude more rapidly at 7.8 nV/dB (at 1000 Hz) and contains significant energy at harmonics of the modulation frequency. This second stage of the intensity function is more prominent for stimuli with lower carrier frequencies (500 more than 1000 more than 2000 Hz) and is attenuated by high‐pass masking. These steady‐state responses should be helpful in evaluating human auditory physiology and in objective audiometry.

Resonance Oscillation Of Radiative Shock Waves In Accretion Disks Around Compact Objects

Abstract: We extend our previous numerical simulation of accretion disks with shock waves when cooling effects are also included. We consider bremsstrahlung and other power law processes: $\Lambda \propto T^{\alpha} \rho^2$ to mimic cooling in our simulation. We employ {\it Smoothed Particle Hydrodynamics} technique as in the past. We observe that for a given angular momentum of the flow, the shock wave undergoes a steady, radial oscillation with the period is roughly equal to the cooling time. Oscillations seem to take place when the disk and cooling parameters (i.e., accretion rate, cooling process) are such that the infall time from shock is of the same order as the post-shock cooling time. The amplitude of oscillation could be up to ten percent of the distance of the shock wave from the black hole when the black hole is accreting. When the accretion is impossible due to the centrifugal barrier, the amplitude variation could be much larger. Due to the oscillation, the energy output from the disk is also seen to vary quasi-periodically. We believe that these oscillations might be responsible for the quasi periodic oscillation (QPO) behaviors seen in several black hole candidates, in neutron star systems as well as dwarf novae outbursts such as SS Cygni and VW Hyi.

Temporal analysis of capillary jet breakup

Abstract: The temporal instability of a cylindrical capillary jet is analysed numerically for different liquid Reynolds numbers Re, disturbance wavenumbers k, and amplitudes e 0 . The breakup mechanism of viscous liquid jets and the formation of satellite drops are described. The results show that the satellite size decreases with decreasing Re, and increasing k and e 0 . Marginal Reynolds numbers below which no satellite drops are formed are obtained for a large range of wavenumbers. The growth rates of the disturbances are calculated and compared with those from the linear theory. These results match for low-Re jets, however as Re is increased the results from the linear theory slightly overpredict those from the nonlinear analysis. (At the wavenumber of k=0.9, the linear theory underpredicts the nonlinear results.) The breakup time is shown to decrease exponentially with increasing the amplitude of the disturbance. The cut-off wavenumber is shown to be strongly dependent on the amplitude of the initial disturbance for amplitudes larger than approximately 1/3 of the initial jet radius. The stable oscillations of liquid jets are also investigated. The results indicate that liquid jets with Re ∼O(1) do not oscillate, and the disturbances are overdamped. However, liquid jets with higher Re oscillate with a period which depends on Re and e 0 . The period of the oscillation decreases with increasing Re at small e 0 ; however, it increases with increasing Re at large e 0 . Marginal Reynolds numbers below which the disturbances are overdamped are obtained for a wide range of wavenumbers and e 0 =0.05

Visual cortex neurons in monkey and cat: effect of contrast on the spatial and temporal phase transfer functions.

Abstract: The responses of simple cells (recorded from within the striate visual cortex) were measured as a function of the contrast and the frequency of sine-wave grating patterns in order to explore the effect of contrast on the spatial and temporal phase transfer functions and on the spatiotemporal receptive field. In general, as the contrast increased, the phase of the response advanced by approximately 45 ms (approximately one-quarter of a cycle for frequencies near 5 Hz), although the exact value varied from cell to cell. The dynamics of this phase-advance were similar to the dynamics of the amplitude: the amplitude and the phase increased in an accelerating fashion at lower contrasts and then saturated at higher contrasts. Further, the gain for both the amplitude and the phase appeared to be governed by the magnitude of the contrast rather than the magnitude of the response. For the spatial phase transfer function, variations in contrast had little or no systematic effect; all of the phase responses clustered around a single straight line, with a common slope and intercept. This implies that the phase-advance was not due to a change in the spatial properties of the neuron; it also implies that the phase-advance was not systematically related to the magnitude of the response amplitude. On the other hand, for the temporal phase transfer function, the phase responses fell on five straight lines, related to the five steps in contrast. As the contrast increased, the phase responses advanced such that both the slope and the intercept were affected. This implies that the phase-advance was a result of contrast-induced changes in both the response latency and the shape/symmetry of the temporal receptive field.

Estimation of amplitude and phase parameters of multicomponent signals

Abstract: This paper considers the problem of estimating signals consisting of one or more components of the form a(t)e/sup j/spl phi/(t/), where the amplitude and phase functions are represented by a linear parametric model. The Cramer-Rao bound (CRB) on the accuracy of estimating the phase and amplitude parameters is derived. By analyzing the CRB for the single-component case, if is shown that the estimation of the amplitude and the phase are decoupled. Numerical evaluation of the CRB provides further insight into the dependence of estimation accuracy on signal-to-noise ratio (SNR) and the frequency separation of the signal components. A maximum likelihood algorithm for estimating the phase and amplitude parameters is also presented. Its performance is illustrated by Monte-Carlo simulations, and its statistical efficiency is verified. >

Structural Constraints on the Performance of Symmetrical Bimanual Movements with Different Amplitudes

Abstract: In bimanual movements the amplitude of each hand's movement often depends on the concurrent amplitude of the other hand's movement such that both amplitudes become similar (amplitude coupling). We ...