Showing papers on "Amplitude published in 1992"

Structure in the COBE differential microwave radiometer first year maps

Abstract: Results of the first year of data from the differential microwave radiometers on the Cosmic Background Explorer are presented. Statistically significant structure that is well described as scale-invariant fluctuations with a Gaussian distribution is shown. The rms sky variation, smoothed to a total 10-deg FWHM Gaussian, is 30 +/-5 micro-K for Galactic latitude greater than 20-deg data with the dipole anisotropy removed. The rms cosmic quadrupole amplitude is 13 +/-4 micro-K. The angular autocorrelation of the signal in each radiometer channel and cross-correlation between channels are consistent and give a primordial fluctuation power-law spectrum with index of 1.1 +/-0.5, and an rms-quadrupole-normalized amplitude of 16 +/-4 micro-K. These features are in accord with the Harrison-Zel'dovich spectrum predicted by models of inflationary cosmology.

A Mechanism for Orbital Period Modulation in Close Binaries

Abstract: Some eclipsing variables are observed to undergo orbital period modulations of amplitude ΔP/P∼10 −5 over time scales of decades or longer. These modulations can be explained by the gravitational coupling of the orbit to variations in the shape of a magnetically active star in the system. The variable deformation of the active star is produced by variations in the distribution of angular momentum as the star goes through its activity cycle. This mechanism typically requires that the active star be variable at the ΔL/L⇒0.1 level, and be differentially rotating at the ΔΩ/Ω⇒0.01 level

High frequency printing mechanism

Abstract: The present invention provides an ink-jet ejection device which is capable of ejection or ink (including hot melt ink) jet frequencies greater than 50,000 Hz. A cantilevered beam of selected shape is mounted at its base to a piezoelectric element which oscillates the base. The beam is shaped so that its moment of inertia is reduced toward its free end. The element is activated by an oscillating electrical signal the frequency of which is equal to or close to a natural frequency of oscillation of the beam. In the preferred embodiment herein a third or higher modal frequency is utilized. Because of the structural configuration of the cantilevered beam and the selected frequency of oscillation thereof, the tip of the beam oscillates over an amplitude which is significantly greater than the oscillation amplitude of the base. The beam is highly damped and made of low density material so that the tip amplitude is extremely responsive to variations in the base amplitude. The tip of the beam is provided with an aperture which is preferably tapered in cross-section. One opening of the tapered aperture is in fluid communication with a reservoir of ink and the other opening of the aperture is positioned at an appropriate distance from a recording medium such as paper towards which individual droplets of ink from the reservoir are to be propelled. When the tip amplitude is above a predetermined threshold the solid-fluid interaction between the tapered aperture and the ink causes a drop of ink to accelerate through the aperture and be ejected upon each excursion of the tip of the beam toward the printing media.

Numerical experiments in broadband receiver function analysis

Abstract: The use of broadband receiver function analysis to estimate the fine-scale S -velocity structure of the lithosphere is becoming increasingly popular. A series of numerical experiments shows several important aspects of this technique, with emphasis on estimation of dipping interfaces. The recent modification introduced to the receiver function analysis technique that preserves absolute amplitudes (Ammon, 1991) is more robust than the previous technique of modeling receiver functions that were normalized to unit amplitude. Using the latter method, shallow (e.g., depths less than ∼2 km) high-velocity contrast interfaces may alter the apparent amplitudes of Ps phases and produce inaccuracies in the Earth model developed. The use of absolute amplitudes minimizes this potential for error. When research targets include deep dipping structure, tight stacking bounds (e.g., ≦ 10° in backazimuth (BAZ ) and epicentral distance (Δ)) should be applied to avoid attenuating Ps phases and to aid in the identification of reverberations or scattered energy. Reverberations sample a relatively large lateral range about the recording site (e.g., a radius of 1 to 1.5 times the depth of the reflecting interface) and in the presence of dipping interfaces exhibit drastic variations in amplitude and arrival time as a function of BAZ and Δ. Thus, they cannot readily be used to provide constraints on the Earth structure. Formal inversion techniques, which attempt to match all arrivals in the waveform, must be used with caution when modeling receiver functions from complex regions. Only those phases whose amplitude and arrival-time variations as a function of BAZ and Δ are consistent with those of Ps conversions should be modeled. Forward modeling may resolve, depending upon the data quality and noise level, S -velocity contrasts greater than ∼ 0.2 to 0.4 km / sec. Layers of thickness 2 to 5 km may be accurately imaged, and transition zones may be examined by considering various frequency bands of the data. In order to better understand the resolving power of the data, the averaging functions associated with the receiver functions may be calculated from the observed data and, if desired, used in the forward modeling process.

Generation of asymptotically stable optical solitons and suppression of the Gordon-Haus effect.

Abstract: By a proper design of the frequency-dependent gain characteristic of optical amplifiers, the parameters (amplitude η and velocity κ) of optical solitons in fibers can be made to approach a desired fixed point in κ − η space. The method is effective in controlling the random walk of solitons caused either by initial jitter and/or by amplifier noise (the Gordon–Haus effect) and in overcoming the bit-rate limitation that they provide.

Modulational instabilities in discrete lattices

Abstract: We study analytically and numerically modulational instabilities in discrete nonlinear chains, taking the discrete Klein-Gordon model as an example. We show that discreteness can drastically change the conditions for modulational instability; e.g., at small wave numbers a nonlinear carrier wave is unstable to all possible modulations of its amplitude if the wave amplitude exceeds a certain threshold value. Numerical simulations show the validity of the analytical approach for the initial stage of the time evolution, provided that the harmonics generated by the nonlinear terms are considered. The long-term evolution exhibits chaoticlike states.

Analysis and performance of a large thermoacoustic engine

Abstract: Measurements and analysis of a 13‐cm‐diam thermoacoustic engine are presented. At its most powerful operating point, using 13.8‐bar helium, the engine delivered 630 W to an external acoustic load, converting heat to delivered acoustic power with an efficiency of 9%. At low acoustic amplitudes, where (linear) thermoacoustic theory is expected to apply, measurements of temperature difference and frequency agree with the predictions of theory to within 4%, over conditions spanning factors of 4 in mean pressure, 10 in pressure amplitude, 6 in frequency, and 3 in gas sound speeds. But measurements of the square of pressure amplitude versus heater power differ from the predictions of theory by 20%, twice the estimated uncertainty in the results. At higher pressure amplitudes (up to 16% of the mean pressure), even more significant deviation from existing thermoacoustic theory is observed. Several causes of this amplitude‐dependent deviation are identified, including resonance‐enhanced harmonic content in the acoustic wave, and a new, first‐order temperature defect in thermoacoustic heat exchangers. These causes explain some, but not all, of the amplitude‐dependent deviation of the high‐amplitude measurements from existing (linear) theory.

Convection cells in vibrating granular media

Abstract: We present molecular dynamics simulations of granular material submitted to vibrations in a two-dimensional system. We find various types of convection cells, due either to the existence of walls or to spatial modulations in the amplitude of the vibration. The direction of the motion relative to the walls depends on shear friction. We measure the strength of the convection velocity and find a characteristic resonance frequency as in experiments. We propose an explanation for the mechanisms that are at the origin of the different motions.

Piecewise potential vorticity inversion

Abstract: The treatment of the potential vorticity (PV) distribution as a composite of individual perturbations is central to the diagnostic and conceptual utility of PV. Nonlinearity in the inversion operator for Ertel's potential vorticity renders quantitative piecewise inversion (inversion of individual portions of the potential vorticity field) ambiguous. Several methods of piecewise inversion are compared for idealized and observed potential vorticity anomalies of varying strengths. Even as the Rossby number of the balanced solutions increases well past unity, relative differences among the more plausible methods do not increase significantly near the anomaly. These relative differences are also found to be smaller than those obtained by comparing any of the methods to quasigeostrophic inversion. However, differences above and below anomalies increase with increasing Rossby number, suggesting that one cannot uniquely diagnose the interaction of large amplitude PV anomalies.

Localization in a Driven Two-Level Dynamics

Abstract: A periodically driven two-state dynamics, being analysed within the Floquet formalism, exhibits localization of the amplitude dynamics in an infinite frequency range, extending from the bare tunnel splitting up to infinity. In contrast, the suppression of tunnelling in a driven symmetric double well is restricted to a limited frequency regime, extending from the bare tunnel splitting up to the first resonance frequency with higher-lying states. With the amplitude dynamics of a periodically driven two-level system not being restricted to describe coherent tunnelling transport only, the localization phenomenon within the infinite frequency range does allow for novel applications for systems in strong laser fields.

Coherent measurement of THz optical rectification from electro‐optic crystals

Abstract: We report the results of coherent measurement (phase and amplitude) of optical rectification from a variety of electro‐optic crystals. We also present a comparison of the experimental data with a theoretical calculation.

Nonlinear diffusion of the tidal signal in frictionally dominated embayments

Abstract: The dynamics of many shallow tidal embayments may be usefully represented by a single “zero-inertia” equation for tidal elevation which has the form of a nonlinear diffusion equation. The zero-inertia equation clarifies the lowest order dynamics, namely, a balance between pressure gradient and friction. It also provides insight into the properties of higher-order harmonic components via the identification of compact approximate solutions and governing nondimensional parameters. Approximate analytic solutions which assume a constant diffusion coefficient are governed by the nondimensional parameters x/L and ‖k0‖L, where L is the length of the embayment, and ‖k0‖−1 scales both the length of factional dissipation and the physical length of the diffusive waveform. As ‖k0‖L increases, the speed at which the tidal signal diffuses decreases, and the rate of decay of tidal amplitude with distance increases. The parameter ‖k0‖L increases as depth is reduced, friction is increased, forcing amplitude or frequency is increased, or total embayment width is increased relative to the width of the channel. Approximate analytic solutions which assume a time-varying diffusion coefficient result in additional components at the zeroth, second, and third harmonic frequencies. The zeroth and second harmonics are governed by the parameter γ, as well as x/L and ‖k0‖L. Parameter γ measures the relative importance of time variations of channel depth (γ> 0) versus time variations in embayment width (γ 0, the diffusion coefficient is larger near the crest of the tidal waveform, causing the rising tide to be of shorter duration and mean elevation to be set up. If γ< 0, the diffusion coefficient is larger near the trough, causing the falling tide to be shorter and elevation to be set down. The third harmonic is produced by fluctuations in the diffusion coefficient associated with times of greatest surface gradient. The third harmonic is governed only by the parameters x/L and ‖k0‖L, which indicates the third harmonic is insensitive to time variations in cross-sectional geometry. Comparisons to field observations and to numerical solutions of the full equations including inertia terms indicate that the zero-inertia equation (1) reproduces the results of the more general one-dimensional equations to within the accuracy predicted by scaling arguments and (2) reproduces the main features of the nonlinear tidal signal observed in many shallow tidal embayments.

Generalized seismological data functionals

Abstract: SUMMARY We have formulated a new waveform-analysis procedure to recover phase and amplitude information frorn individual seismograms that makes use of the ability to compute complete seismograms from realistic earth models. The basic tool is the isolation filter, a composite waveform constructed to select data from a desirable portion of the seismogram. When the cross-correlation between this synthetic waveform and an observed seismogram is localized in the time domain by windowing and in the frequency domain by narrow-band filtering, the resulting cross-correlagram can be approximated by a five-parameter Gaussian wavelet. One of these five parameters is the bandwidth of the correlagram, specified by the narrow-band filter; the other four define a set of time-like, frequency-dependent quantities { br, :x = q, p, a, g}, which are functionals of earth structure. bt, is the differential phase delay and at, is the differential group delay of the observed waveform relative to the synthetic, and bt, and 6t, are the corresponding frequency-dependent amplitude parameters. We have developed a procedure for measuring the four generalized seismological data functionals by fitting a Gaussian wavelet to the windowed, filtered cross-correlagram. To relate the GSDFs to earth structure, we apply corrections to the differential times for the effects of windowing and filtering. Solving a linear system of four equations in four unknowns yields a set of differential dispersion parameters { bz, :x = q, p, a, g}. Formulae expressing the perturbations of the GSDFs in terms of the perturbations to the dispersion parameters for the individual component waveforms, including all interference effects, have been derived. Under a set of approximations valid for a large class of isolation filters, these can be simplified to yield easily computed expressions for the FrCchet kernels of the 6~~’s. The calculation of these FrCchet kernels requires no high-frequency approximations, and it can be extended to the investigation three-dimensional earth structure.

Ordered capillary-wave states: Quasicrystals, hexagons, and radial waves

Abstract: We report the observation of ordered capillary-wave states generated by three and four standing plane waves. The pattern produced by the four standing plane waves forms the first quasicrystal observed in a fluid dynamical system. The states are observed at aspect ratios above 45, and for amplitudes below the amplitude at which a square-symmetric state is formed. We also report the observation of a capillary-wave state generated by three radial waves.

Scenarios for the nonlinear evolution of alpha-particle-induced Alfvén wave instability

Abstract: Various nonlinear scenarios are given for the evolution of energetic particles that are slowing down in a background plasma and simultaneously causing instability of the background plasma waves. If the background damping is sufficiently weak, a steady-state wave is established as described by Berk and Breizman. For larger background damping rate pulsations develop. Saturation occurs when the wave amplitude rises to where the wave trapping frequency equals the growth rate. The wave then damps due to the small background dissipation present and a relatively long quiet interval exists between bursts while the free energy of the distribution is refilled by classical transport. In this scenario the anomalous energy loss of energetic particles due to diffusion is small compared to the classical collisional energy exchange with the background plasma. However, if at the trapping frequency, the wave amplitude is large enough to cause orbit stochasticity, a phase space ``explosion`` occurs where the wave amplitudes rise to higher levels which leads to rapid loss of energetic particles.

Explaining the amplitude of RTS noise in submicrometer MOSFETs

Abstract: A simple-man's model for the random telegraph signal (RTS) noise amplitude in a submicrometer MOSFET is presented. It is shown that the channel resistance modulation for a specific trap can be expressed as a product of the normalized scattering cross section and of the fractional conductivity change. The model qualitatively describes the experimental temperature and drain current dependence of the RTS amplitude and allows evaluation of the influence of the trap location and nature on the wide scatter in values observed. >

The Angular Dependence of the Three-Point Correlation Function of the Cosmic Microwave Background Radiation as Predicted by Inflationary Cosmologies

Abstract: Inflationary models predict a definite, model independent, angular dependence for the three-point correlation function of $\Delta T/T$ at large angles (greater than $\sim 1^\circ$) which we calculate. The overall amplitude is model dependent and generically unobservably small, but may be large in some specific models. We compare our results with other models of nongaussian fluctuations.

Solitary internal waves with oscillatory tails

Abstract: Solitary internal waves in a density-stratified fluid of shallow depth are considered. According to the classical weakly nonlinear long-wave theory, the propagation of each long-wave mode is governed by the Korteweg-de Vries equation to leading order, and locally confined solitary waves with a 'sech2' profile are possible. Using a singular-perturbation procedure, it is shown that, in general, solitary waves of mode n>1 actually develop oscillatory tails of infinite extent, consisting of lower-mode short waves. The amplitude of these tails is exponentially small with respect to an amplitude parameter, and lies beyond all orders of the usual long-wave expansion. To illustrate the theory, two special cases of stratification are discussed in detail, and the amplitude of the oscillations at the solitary-wave tails is determined explicitly. The theoretical predictions are supported by experimental observations.

Automated first arrival picking: a neural network approach1

Abstract: A back-propagation neural network is successfully applied to pick first arrivals (first breaks) in a background of noise. Network output is a decision whether each half-cycle on the trace is a first or not. 3D plots of the input attributes allow evaluation of the attributes for use in a neural network. Clustering and separation of first break from non-break data on the plots indicate that a neural network solution is possible, and therefore the attributes are suitable as network input. Application of the trained network to actual seismic data (Vibroseis and Poulter sources) demonstrates successful automated first-break selection for the following four attributes used as neural network input: (1) peak amplitude of a half-cycle; (2) amplitude difference between the peak value of the half-cycle and the previous (or following) half-cycle; (3) rms amplitude ratio for a data window (0.3 s) before and after the half-cycle; (4) rms amplitude ratio for a data window (0.06 s) on adjacent traces. The contribution of the attributes based on adjacent traces (4) was considered significant and future work will emphasize this aspect.

Tapping atomic force microscope

Abstract: An atomic force microscope in which a probe tip is oscillated at a resonant frequency and at amplitude setpoint and scanned across the surface of a sample in contact with the sample, so that the amplitude of oscillation of the probe is changed in relation to the topography of the surface of the sample. The setpoint amplitude of oscillation of the probe is greater than 10 nm to assure that the energy in the lever arm is much higher than that lost in each cycle by striking the sample surface, thereby to avoid sticking of the probe tip to the sample surface. Data is obtained based either on a control signal produced to maintain the established setpoint or directly as a function of changes in the amplitude of oscillation of the probe.

The evoked K-complex: all-or-none phenomenon?

Abstract: The functional significance and topographical variation of the different components of the evoked K-complex were examined. In the first experiment, the intensity of the stimulus (80 and 60 dB SPL) and its rise-and-fall time (2 and 20 milliseconds) were manipulated during nonrapid eye movement sleep. In the second experiment the tonal frequency (500, 1,000 and 2,000 Hz) of the stimulus was manipulated. In the first experiment, nine stimuli were presented every 10 seconds, whereas in the second, 20 consecutive stimuli were presented. The evoked K-complex consisted of two different negative components peaking at approximately 350 and 550 milliseconds, respectively, and followed by a positive component peaking at approximately 900 milliseconds. K-complexes were easier to elicit for high-intensity fast rise-and-fall time stimuli than for low-intensity slow rise-and-fall time stimuli. The probability of occurrence was not affected by the tonal frequency of the stimulus. When a K-complex was evoked, the amplitude and latency of N350, N550 and P900 remained invariant regardless of its intensity, rise-and-fall or its tonal frequency. The N550-P900 portion of the K-complex therefore appears to be an all-or-none phenomenon. On trials in which a K-complex could not be elicited, N350 was still visible although much attenuated. In these trials, its amplitude was further reduced when stimulus intensity was lowered. N350 might need to reach a certain critical threshold before the much larger N550-P900 complex is elicited.

Instabilities of three-dimensional viscous falling films

Abstract: A long-wave evolution equation is used to study a falling film on a vertical plate. For certain wavenumbers there exists a two-dimensional strongly nonlinear permanent wave. A new secondary instability is identified in which the three-dimensional disturbance is spatially synchronous with the two-dimensional wave. The instability grows for sufficiently small cross-stream wavenumbers and does not require a threshold amplitude; the two-dimensional wave is always unstable. In addition, the nonlinear evolution of three-dimensional layers is studied by posing various initial-value problems and numerically integrating the long-wave evolution equation.

Thermal runaway in microwave heated ceramics: A one‐dimensional model

Abstract: The heating of a ceramic slab under TM‐illumination is modeled and analyzed in the small Biot number regime. The temperature distribution is almost spatially uniform in this limit and its evolution in time is governed by a first‐order nonlinear amplitude equation. This equation admits a time independent solution which is a multivalued function of the microwave power. The graph of this steady temperature as a function of the microwave power gives an S‐shaped response curve when the electrical conductivity is modeled either as an exponential function of temperature or an Arranius law. The dynamics of the heating process are deduced from the amplitude equation and the multivalued response, and are dependent upon the microwave power and initial conditions. For certain initial conditions and power levels the system evolves to the upper branch of the response curve which corresponds to thermal runaway. Other initial conditions and power levels force the system to evolve to the lower branch and a safe sintering temperature. This heating process can be controlled in some sense by varying the microwave power in time at a rate commensurate with the thermal changes. Specifically, the power is allowed to change in an exponential fashion from a higher to a lower power level. This relationship is turned into a differential equation, which is appended to the amplitude equation to form an autonomous system of the second order. This system is analyzed using a phase‐plane method. The analysis shows the existence of a stable manifold which divides the phase plane into two parts: Trajectories in the region above this curve correspond to runaway heating while those below yield stable sintering. Various heating scenarios are presented and discussed.