Variation Of Wave Amplitude Research Articles

Jumps of the electromagnetic wave amplitude under the action of the current pulses

The sharp variations of the electromagnetic wave amplitude are analyzed in the section of the meander or strip line made of pure aluminum. These variations appear at low temperatures when high magnetic field and strong pulses of electric current are parallel. The pulses containing two switching waves are observed. The propagation velocity of this pulses is approximately 106 cm/s. At certain conditions the auto-wave electrodynamical structure arises in high magnetic field. It has been suggested the system of equations that can to explain the main experimental features.

Observations of inertia‐gravity wave motions in the stratosphere over Jicamarca, Peru

We present results obtained with the MST radar at Jicamarca, Peru over 10 days in January, 1993. During this campaign, inertia‐gravity waves with observed periods of ∼36 hours were seen in the stratosphere (19–30 km). The radar was operated with a high (400‐m) range resolution allowing accurate determination of wave propagation characteristics. The large variation of wave amplitude (∼2–10 ms−1) with height and time suggests a superposition of several wave motions. As consistent with upward energy propagation, the phase fronts descended with time, and a vertical wavelength of ∼5 km was inferred from the rate of this phase descent. Orbital ellipses imply largely zonal propagation with an intrinsic period of roughly 30 hours, somewhat less than the observed period. The shorter intrinsic period suggests eastward wave propagation, in opposition to the predominantly westward mean motion.

Wave Propagation in a Fibonacci Transmission Line

We directly observe the wave propagation in a Fibonacci lattice as an electric signal by use of a transmission line, which is constructed under the rule of the Fibonacci sequence. The experimental result shows that the spatial structure of lattice oscillation has a self-similar nested structure. The structure factor for spatial variation of wave amplitude is also calculated.

Radiative damping of equatorial waves in the middle atmosphere

AbstractTheoretical estimates are made of the radiative damping of various Kelvin and Rossby‐gravity (RG) wave modes in the 20–70 km region, for a period of 24 months (1979–80), using the observed monthly mean zonal‐wind profiles at 8.5°N latitude and realistic values of scale‐dependent cooling coefficients. The net changes in wave amplitudes at various height regions are calculated by combining the attenuation due to radiative cooling and the growth due to density decrease. The calculated height variations of wave amplitudes explain quite well several features of the observed height structures of Kelvin waves. They also explain the observed rapid decay of RG waves below about 35 km when their period exceeds 3 days.The calculated momentum flux convergences of various waves are used to estimate the mean‐flow accelerations generated by the damped waves. The Kelvin waves are found to be capable of generating the accelerations needed to drive the westerly phase of the quasi‐biennial oscillation (QBO) and the semi‐annual oscillation (SAO) in the zonal wind. However, RG waves seem to be capable of driving the easterly phase of the QBO but not the SAO. The remarkable consistency of our theoretical results and the observed patterns of wave amplitudes and mean‐flow accelerations demonstrate that radiative damping is the dominant dissipative process for the equatorial waves in the 20–70 km region and our theoretical approach is capable of characterizing the equatorial wave behaviour and the associated flow accelerations with a good quantitative accuracy.

Modelling and compensation of field distortion due to defective elements in planar ultrasonic arrays

The spatial ultrasonic wave amplitude variations caused by continuous and pulsed wave transducer arrays containing inoperative elements have been computer-simulated and analysed. Comparisons are made of the fields generated by ‘perfect’ and defective arrays, where the defective elements are clustered and/or randomly located. Amplitude and phase compensation techniques have been employed to eliminate distortion due to chosen defective elements in the array and the comparative effectiveness of the compensation strategies are discussed.

Wave Separation. Part Two: Applications

Identifying waves in seismic sections sometimes requires the waves to be separated. The geophysicist has a variety of complementary filters at his disposal that can be used to perform optimum separations if they are carefully chosen and combined. The first part of this article was devoted to the principle and methods of wave separation. Wave separation methods can be divided up into three categories : acceptance region methods, inversion methods and matrix methods. The tau-p method and f-k filtering belong to the first category while the parametric method belongs to the second one. Matrix filtering by means of the cross-spectral matrix (SMF : Spectral Matrix Filtering), the singular value decomposition (SVD) and the Karhunen-Loeve method (KLT-Karhunen-Loeve Transform) belong to the third group. Matrix methods are used both to separate waves and to break data down into a signal space and a noise space. Here in the second part, we use synthetic data to compare how well the SVD and SMF methods perform in separating waves with only one eigenvector. We show that SMF filtering can be made much more effective by introducing models and present the SMF method with adapted or constrained models. We also introduce a field example of wave separation by conventional SMF filtering, then a synthetic example and two field examples of wave separation by SMF filtering with models. We demonstrate the advantages of using different wave separation methods together (f-k, KLT and SMF) to achieve optimum separation. The data that serve to illustrate this are full waveform acoustic data acquired in a horizontal drain hole. A VSP-type well survey is used to compare the different methods : f-k, SVD, SMF and the parametric method. The last example shows how SMF processing can be used for anisotropy measurement. The f-k filter requires a large number of traces that have been distance sampled at short intervals. The more stable the wave that is being extracted and the more clearly located it is in the f-k domain, the more efficient the filter is. The method is very cost-effective in CPU time. The KLT or SVD filter requires flattening the wave that is to be extracted, which must additionally be of greater amplitude. Filtering is carried out without any edge effect and the wave amplitude variations are preserved. It serves to separate the normal incidence wave from the other waves and the noise. The SMF filter (spectral matrix) is expensive in CPU time It makes the hypothesis that the wave is locally stable and does not require the data to be flattened. It can be used to separate very close neighboring waves without resorting to restrictive a priori hypotheses. It gives a measurement of time delays and also provides a measurement of variations in amplitude and phase spectra during propagation. This measurement is much better than the one supplied by the Wiener method, since it operates on all the traces. Additionally, it is used to separate data into a signal space and a noise space. The parametric method is the most expensive as regards time. It is simple to implement and requires no flattening or preparation of data. It extracts the waves according to chosen parameters, especially time delays. It is particularly recommended in offset vertical seismic profiling where the slowness of upgoing waves is unknown. It is robust with respect to some input parameters if the noise is low in comparison to the signal that is to be extracted. Many applications to field data have illustrated the effectiveness of these wave separation techniques. However, application to a new type of data often requires performance to be monitored to choose the best method.

Effect of rate and coupling interval on endocardial R wave amplitude variability in permanent ventricular sensing lead systems

Objectives. We have observed sensing errors in third generation implantable cardioverter-defibrillators that appear to be caused by variation in the R wave amplitude during sinus rhythm, particularly after premature beats. The purpose of this study was to quantify spontaneous R wave variability during sinus rhythm and to determine whether abrupt changes in cycle length further augment R wave amplitude variability.Background, Pacemaker sensing algorithms presume a relatively constant R wave signal to establish a sensing threshold. The concept of a fixed sensing threshold is not as applicable in third-generation cardioverter-defibrillators, which depend on automatic gain amplifiers to rapidly detect ventricular fibrillation. These devices may be susceptible to undersensing during sinus rhythm if significant variability in R wave signal characteristics occurs.Methods. Twelve patients with combination bradycardia pacing cardioverter-defibrillators were studied. The device used (Cadence, Ventritex) allowed recording of real time, telemetered electrograms from the sensing lead system. Measurements were made of the maximal range of the R wave amplitude during sinus rhythm and in response to abrupt changes in heart rate produced by premature atrial and ventricular stimuli.Results. The maximal range in R wave amplitude during sinus rhythm was 1.7 ± 1.3 mV, or 23.7 ± 19.2% of the mean R wave amplitude. The R wave amplitude variability increased with abrupt changes in cycle length, with a range of 2.8 ± 1.5 mV, or 38.8 ± 18.3% of the mean R wave amplitude (p < 0.05 compared with sinus rhythm). In most patients, R wave amplitude and coupling interval demonstrated an inverse proportional relation. Conclusions. There is substantial variability in the R wave amplitude during sinus rhythm measured by permanent ventricular sensing lead systems, and this variability is further augmented by abrupt changes in cycle length. This phenomenon may explain the occurrence of undersensing of sinus rhythm in implantable cardioverter-defibrillators with automatic gain sense amplifiers.

REGIONAL SYNCHRONIES AND AMPLITUDE CHANGES IN THE JANUARY 500-MB MIDDLE LATITUDE GEOPOTENTIAL HEIGHT RECORD

The relationship between middle tropospheric long wave circulation and surface weather is recognized as an important component in the middle latitude climate system. Regional variations in long wave position and temporal variations in long wave amplitude exert a considerable influence on surface temperature and precipitation. This study seeks to organize the spatial and temporal structure of the long wave system within a climate regionalization that is based upon associated trends in the middle tropospheric geopotential height record for the purpose of assessing wave amplitude variations within these regions. This regionalization is performed using January 500-mb geopotential height data over the northern hemispheric middle latitudes for the period 1946–1987 and is constructed using a cluster analysis, in which the resultant clusters represent regions of synchronous height behavior during the data record. The resultant clusters are related spatially to long wave ridge and trough positions, and are charact...

Theory of magnetohydrodynamic waves: The WKB Approximation revisited

Past treatments of the eikonal or WKB theory of the propagation of magnetohydrodynamic waves have assumed a strictly isentropic background. If in fact there is a gradient in the background entropy, then in second order in the WKB ordering, adiabatic fluctuations (in the Lagrangian sense) are not strictly isentropic in the Eulerian sense. This means that in the second order of the WKB expansion, which determines the variation of wave amplitude along rays, the violation of isentropy must be accounted for. The present paper revisits the derivation of the WKB approximation for small‐amplitude magnetohydrodynamic waves, allowing for possible spatial variation of the background entropy. The equation of variation of wave amplitude is rederived; it is a bilinear equation which, it turns out, can be recast in the action conservation form. It is shown that this action conservation equation is in fact equivalent to the action conservation law obtained from Lagrangian treatments (Dewar, 1970; Jacques, 1977a, b).

Variational principles for surface wave propagation on a laterally heterogeneous Earth--II. Frequency-domain JWKB theory

SUMMARY We present a JWKB theory for the propagation of monochromatic Love and Rayleigh waves on a smooth, laterally heterogeneous Earth model. The analysis is based upon a slowly varying Lagrangian which yields local Love and Rayleigh eigenfunctions, local dispersion relations, and transport equations which determine the variation in surface wave amplitude along a ray. The amplitude of a monochromatic Love or Rayleigh wave varies only as a result of geometrical spreading; the amplitude diverges and the phase is shifted by n/2 each time the wave passes through a caustic singularity, where the width of the ray tube vanishes. We obtain the JWKB surface wave Green’s tensor and derive an explicit expression for the JWKB response to a moment tensor source. The theory allows for slowly varying topography of the Earth’s surface and any internal discontinuities, and incorporates the effect of self-gravitation and slight anelasticity on surface wave propagation.

Variational principles for surface wave propagation on a laterally heterogeneous Earth--I. Time-domain JWKB theory

SUMMARY We present a JWKB theory for the propagation of monochromatic Love and Rayleigh waves on a smooth, laterally heterogeneous Earth model. The analysis is based upon a slowly varying Lagrangian which yields local Love and Rayleigh eigenfunctions, local dispersion relations, and transport equations which determine the variation in surface wave amplitude along a ray. The amplitude of a monochromatic Love or Rayleigh wave varies only as a result of geometrical spreading; the amplitude diverges and the phase is shifted by n/2 each time the wave passes through a caustic singularity, where the width of the ray tube vanishes. We obtain the JWKB surface wave Green’s tensor and derive an explicit expression for the JWKB response to a moment tensor source. The theory allows for slowly varying topography of the Earth’s surface and any internal discontinuities, and incorporates the effect of self-gravitation and slight anelasticity on surface wave propagation.

Magnetohydrodynamic wave propagation and local energy balance.

The propagation of hydromagnetic waves is considered in the approximation of geometrical optics. The variation of wave amplitudes in space and time is determined from the energy balance---in contrast to the usual WKB procedure. While Alfv\'en waves are unaffected by the equilibrium pressure gradient, we find a gradient-driven instability of outgoing fast and ingoing slow magnetosonic waves due to diffraction or self-interaction. The corresponding wave vectors are in the range 1/ak1/ \ensuremath{\surd}${\mathit{L}}_{\mathit{c}}$a , where a is the inhomogeneity scale perpendicular to the magnetic field and ${\mathit{L}}_{\mathit{c}}$\ensuremath{\approxeq}\ensuremath{\eta}/\ensuremath{\beta}${\mathit{v}}_{\mathit{A}}$ for the fast magnetosonic waves.

Eccentric dipole sources in fluid-filled boreholes: Numerical and experimental results

A frequency-wavenumber (ω−k) representation is given for the response of eccentric multipole sensors in a fluid-filled borehole. Specializing to eccentric dipole sensors, synthetic time-domain waveforms from an array of receivers deployed along the axis of the borehole are displayed for a range of eccentricity magnitude and orientation, formation slowness, and borehole radius. Flexural wave slowness estimates within several frequency bands are extracted from the synthetic waveforms using a semblance technique. For eccentricity small relative to the borehole radius, the character of dipole waveforms and the estimated flexural slowness are little changed. When the eccentricity is a substantial fraction of the borehole radius, flexural wave amplitude is greatly increased, and strong nonmonotonic trends are introduced due to interference with other modes. If eccentricity is not parallel to the transmitting dipole axis, substantial signals are detected on cross-dipole receivers, perpendicular to that of the transmitting dipole. Eccentricity effects decrease with frequency. Even for large eccentricity, flexural slowness estimates are affected only slightly. Scaled laboratory experiments confirm the numerical results. Comparison of the experimental and numerical waveforms is made for both centered and eccentric dipoles in several model formations. The predicted increase and nonmonotonic variation of flexural wave amplitude versus receiver offset for eccentric sensors is observed. Experimental and numerical waveforms overlay with excellent agreement.

BV photometry of UX Arietis

DifferentialBV photometry of UX Ari obtained on 58 nights during 1984-85, 1985-86, 1986-87, and 1987-88 observing season is presented. We find that (B-V) is phase dependent with the system being reddest at the light maximum and we interpret this as due to the variable fractional contribution by the G5 V component to the total light at shorter wavelengths. An analysis of the available data indicates that at larger amplitudes of the photometric wave the brightness at maximum increases and that at minimum decreases and both converge to δV ≃ −1.0 mag at very low amplitudes. It implies that the low wave amplitudes are essentially due to more homogeneity in the surface distribution of spots rather than due to low levels of spot activity. The variation in wave amplitude is found to be near-sinusoidal with a period around 13–14 years

The effect of variable currents on internal solitary waves

The effect of variable currents on internal solitary waves is described within the context of a variable coefficient Korteweg-de Vries (KdV) equation, and the approximate slowly varying, solitary-wave solution of this equation. The general theory which leads to the variable coefficient KdV equation is described; a derivation for the special case when the solitary wave and the current are aligned in the same direction is given in the Appendix. Using further simplifications and approximations, a number of analytical expressions are obtained for the variation in the solitary wave amplitude resulting from variable shear in the basic current or from when the basic current is a depth-independent flow which is a simple representation of a geostrophic current, tidal flow or inertial wave.

The effect of variable currents on internal solitary waves

The effect of variable currents on internal solitary waves is described within the context of a variable coefficient Korteweg-de Vries (KdV) equation, and the approximate slowly varying, solitary-wave solution of this equation. The general theory which leads to the variable coefficient KdV equation is described; a derivation for the special case when the solitary wave and the current are aligned in the same direction is given in the Appendix. Using further simplifications and approximations, a number of analytical expressions are obtained for the variation in the solitary wave amplitude resulting from variable shear in the basic current or from when the basic current is a depth-independent flow which is a simple representation of a geostrophic current, tidal flow or inertial wave.

Wave Coupling Between Parallel Single-Mode and Multimode Optical Fibers

A directional coupler composed of a single-mode optical fiber and a multimode optical fiber has been considered to be capable of serving as a drop/insert device of a node in optical fiber Iocal area networks. It should couple almost all the local transmitter power into the multimode fiber bus, while removing only a small fraction of the optical power from the bus through the single-mode fiber. In this paper, the underlying fundamental process of the power transfer between two such optical fibers is analyzed utilizing a coupled-mode theory. Numerical calculations show that wave coupling among the guided modes on the fibers is quite complicated and that the wave amplitude variations along the propagation direction are different from the sinusoidal types resulting from two-mode coupling. The theoretical results do support the expected performance of the proposed couplers and provide an important guide for the design of such devices.

Barotropic Continental Shelf Waves on a β-Plane

In this paper we consider the effect of the variation of the Coriolis parameter with latitude on barotropic shelf waves, using a β-plane model. Solutions are constructed using the method of inner and outer asymptotic expansions, where the inner expansions hold over the shelf, and the outer expansions hold in the deep ocean. Three cases are identified, depending on the relationship between the shelf wave frequency and the allowed frequencies for deep-ocean Rossby waves. The connection is provided by the matching of the longshore wave-numbers. In the first case, the shelf wave frequency is too large to permit Rossby wave radiation, and the variation of the shelf wave amplitude is governed by conservation of longshore energy flux. In the second case, the shelf wave frequency is sufficiently small to permit Rossby wave radiation at high latitudes, and in the third case there is Rossby wave radiation at all latitudes. In both these cases the longshore shelf wave energy flux decays at a rate determined by the radiated Rossby wave energy flux.

Nonlinear saturation of the absolute stimulated Raman scattering instability in a finite collisional plasma

Using multiple time scale analysis, the nonlinear saturation of the absolute stimulated Raman scattering instability is examined in a finite homogeneous collisional plasma. The amplitude of the incident wave is assumed to exceed the absolute instability threshold by the fractional amount Δ(≪1). A single backscattered wave and a single plasma wave grow until time-asymptotic saturation occurs. The reflected light intensity is determined analytically and is proportional to Δ. The spatial variation of the saturated wave amplitudes is also obtained. The reflected intensity is compared to the values predicted for the convective instability, for incident intensities which are marginally less than the absolute threshold intensity. In ‘‘short’’ plasmas, i.e., ones which extend over only a few linear convective gain lengths, the reflected light intensity is found to be much higher when the absolute instability is excited.

The Dynamics of the Mesosphere and Lower Thermosphere at Saskatoon (52°N)

Abstract The dynamics of the upper Middle Atmosphere (60–110 km) over Saskatoon (52°N, 107°W) are described, using wind data from a medium frequency radar (2.2 MHz). Seasonal variations of gravity wave intensities (8 h-10 min) and tidal amplitudes and wavelengths (24 h-8 h) are considered. Below ∼80 km, gravity wave amplitudes are larger (≲100%) in winter than in summer months and there are equinoctial minima especially for short periods: tidal amplitudes are also slightly larger (∼40%) in winter, but wavelengths are comparable with season. Between 80 and 95 km seasonal variations of gravity wave amplitudes are small, but above that height winter values are 40–100% greater. The tidal amplitudes vary in similar fashion, mainly due to large semidiurnal tides above ∼90 km. Winter tidal wavelengths also tend to be shorter than in summer above 80 km altitude. These results are compared with recent data from other middle to high-latitude radar observatories: Monpazier (44°N), Christchurch (44°S), Poker Flat (65...