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Showing papers on "Wave propagation published in 1990"


Journal ArticleDOI
TL;DR: In this paper, a balance of dust particle inertia and plasma pressure is investigated and it is shown that these waves can propagate linearly as a normal mode in a dusty plasma, and non-linearly as supersonic solitons of either positive or negative electrostatic potential.

1,940 citations


Book
01 Dec 1990
TL;DR: In this article, the fundamental field equations of wave propagation in homogeneous and layered media waveguides and cavities have been studied, including the effects of a dipole on the conducting earth, inverse scattering radiometry, and interferometry numerical techniques.
Abstract: Fundamental field equations waves in homogeneous and layered media waveguides and cavities Green's functions radiation from apertures and beam waves periodic structures and coupled mode theory dispersion and anisotropic media antennas, apertures and arrays scattering of waves by conducting and di-electric objects waves in cylindrical structures, spheres and wedges scattering of complex objects geometric theory of diffraction and low fequency techniques planar layers, strip lines, patches and apertures radiation from a dipole on the conducting earth, inverse scattering radiometry, noise temperature and interferometry numerical techniques.

1,050 citations


Journal ArticleDOI
TL;DR: In this paper, a traveling wave is characterized by its time invariant profile and its ability to translate at constant speed in a single spatial dimension, i.e., it is stable relative to perturbations in the initial conditions for solutions of partial differential equations.
Abstract: Travelling waves are special Solutions of partial differential equations in one space variable. They are characterized by their time invariant profile; indeed, s Solutions they evolve by translating at constant speed in the one spatial dimension. These Solutions are often the centerpiece of a physical System s they represent the transport of Information in a single direction. It is of fundamental importance for a given travelling wave to determine its stability relative to perturbations in the initial conditions for Solutions of the f ll partial differential equations. Stable Solutions are the most physically realistic since the external world provides enough perturbations that we can only expect to see waves which will dampen out these perturbations.

514 citations


Journal ArticleDOI
TL;DR: There is a depletion in the photon density of states, seemingly a remnant of the Mie resonance, giving rise to a pseudogap in the spectrum that is quite strong for dielectric-sphere packing fraction.
Abstract: We examine the propagation of electromagnetic waves in periodic dielectric structures by solving the vector Maxwell equations with the plane-wave method. Contrary to experimental reports, as well as results of scalar-wave calculations, we do not find a true gap extending throughout the Brillouin zone in the fcc structure. However, there is a depletion in the photon density of states, seemingly a remnant of the Mie resonance, giving rise to a pseudogap in the spectrum that is quite strong for dielectric-sphere packing fraction \ensuremath{\beta}\ensuremath{\sim}0.3--0.4. An effect analogous to the Borrmann effect in x-ray diffraction is predicted, where certain photon modes will propagate an anomalously long distance before getting absorbed.

440 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an analysis which takes into account a finite shear wave velocity in the backtill, thus allowing for the phase change in a prototype structure.
Abstract: Centrifuge modelling tests show clearly the phase change in lateral acceleration in the backfill behind a retaining wall as shear waves propagate from the base of the model towards the ground surface. However, design calculations for the dynamic lateral earth pressure on a retaining wall which use a pseudo-static approach assume that the backfill experiences a uniform acceleration throughout. Researchers have agreed that the total lateral earth pressure calculated using this approach is approximately correct, but have disagreed over the distribution of the dynamic increment of pressure. The Paper presents an analysis which takes into account a finite shear wave velocity in the backtill, thus allowing for the phase change in a prototype structure. The phase change does not have a significant influence on the magnitude of the total earth pressure, but it has a marked effect on the distribution of the dynamic increment. The resultant pressure is seen to act at a point above one third of the height of the wal...

367 citations


Book ChapterDOI
01 Jan 1990
TL;DR: In this article, a discussion of fundamental concepts including parcel oscillations in a stable atmosphere, wave propagation, and the fluid motions associated with vertically propagating internal gravity waves are discussed. But the authors focus on the case of air flowing over a series of sinusoidal ridges in a basic state with uniform wind speed and stability.
Abstract: In an effort to enhance the reader’s physical understanding, this chapter begins with a discussion of fundamental concepts including parcel oscillations in a stable atmosphere, wave propagation, and the fluid motions associated with vertically propagating internal gravity waves. This is followed by a brief review of the theory of small-amplitude mountain waves, beginning with the case of air flowing over a series of sinusoidal ridges in a basic state with uniform wind speed and stability. The linear theory is then extended to cover isolated mountains and situations with vertical variations in the basic-state wind speed and stability.

312 citations


Journal ArticleDOI
TL;DR: In this paper, an eigenstructure-based method for direction finding in the presence of sensor gain and phase uncertainties is presented, which provides estimates of the Directions of Arrival (DOA) of all the radiating sources as well as calibration of the gain and phases of each sensor in the observing array.
Abstract: An eigenstructure-based method for direction finding in the presence of sensor gain and phase uncertainties is presented. The method provides estimates of the Directions of Arrival (DOA) of all the radiating sources as well as calibration of the gain and phase of each sensor in the observing array. The technique is not limited to a specific array configuration and can be implemented in a'ny eigenstructure-based DOA system to improve its performance.

284 citations


Journal ArticleDOI
30 Mar 1990-Science
TL;DR: The revised model shows curvature and dispersion effects comparable to those of continuous models, it predicts rotating spiral wave solutions in quantitative accord with the theory of continuous excitable media, and it is parameterized so that the spatial step size of the automation can be adjusted for finer resolution of traveling waves.
Abstract: Excitable media are spatially distributed systems characterized by their ability to propagate signals undamped over long distances. Wave propagation in excitable media has been modeled extensively both by continuous partial differential equations and by discrete cellular automata. Cellular automata are desirable because of their intuitive appeal and efficient digital implementation, but until now they have not served as reliable models because they have lacked two essential properties of excitable media. First, traveling waves show dispersion, that is, the speed of wave propagation into a recovering region depends on the time elapsed since the preceding wave passed through that region. Second, wave speed depends on wave front curvature: curved waves travel with normal velocities noticeably different from the plane-wave velocity. These deficiencies of cellular automation models are remedied by revising the classical rules of the excitation and recovery processes. The revised model shows curvature and dispersion effects comparable to those of continuous models, it predicts rotating spiral wave solutions in quantitative accord with the theory of continuous excitable media, and it is parameterized so that the spatial step size of the automation can be adjusted for finer resolution of traveling waves.

262 citations


Journal ArticleDOI
TL;DR: In this article, the effects of nonwelded interfaces on seismic wave propagation are analyzed using effective moduli, in terms of which seismic wave propagates independent of frequency and without loss, unless the moduli include imaginary terms.
Abstract: Many rock structures include multiple, near-parallel, planar discontinuities such as bedding planes or joints. The effects of these nonwelded interfaces on seismic wave propagation are often analyzed using effective moduli, in terms of which seismic wave propagation is independent of frequency and without loss, unless the moduli include imaginary terms. An alternative approach is to treat these interfaces as a boundary condition in the seismic wave equation, across which seismic stress is continuous, but seismic particle displacements are discontinuous. The ratio of the stress to displacement is called the specific stiffness of the interface and characterizes the elastic properties of a fracture. For a completely elastic system this results in frequency-dependent reflection and transmission coefficients for each interface as well as a frequency-dependent group time delay. Using multiple, parallel displacement discontinuities and ignoring converted and reflected waves, expressions derived for transmitted wave amplitudes and group velocities show that these depend on frequency, angle of incidence, and polarization in the case of shear waves. Measurements on a laminated steel block show that shear pulses propagating parallel to the laminations and polarized parallel and perpendicular to the plane of the laminations both travel at the velocity for solid steel, although the spectra of these pulses differ considerably. However, the energy of the pulse polarized perpendicular to the laminations may propagate as an interface wave between each pair of laminations. Predictions of the displacement discontinuity model have features quite distinct from many crustal observations to date. We suggest that we are able to model dense populations of coplanar cracks that cannot be treated by effective moduli methods which require a dilute concentration of cracks.

260 citations



Journal ArticleDOI
TL;DR: In this paper, a data set of 2600 paths for Rayleigh waves and 2170 paths for Love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70-250 s.
Abstract: A data set of 2600 paths for Rayleigh waves and 2170 paths for Love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70–250 s. The epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of Earth. A synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path. To process such a large data set, a new tomographic technique is designed. A good correlation is found with surface tectonics in the whole period range for Love waves and at shorter periods for Rayleigh waves. The directions of maximum velocities are also well correlated with plate tectonics motions for the 2ψ azimuthal term of Rayleigh waves. When the power spectrum of heterogeneities is computed, it is found that for Love waves the even orders are usually larger than the odd orders. For Rayleigh waves the degrees 2 and 6 dominate only at long periods, suggesting a deep origin for these components.

Journal ArticleDOI
TL;DR: In this article, a frequency-domain approach was proposed to model the wave propagation in complex media for multiple source positions, where solutions for multiple sources are required or when only a limited number of frequency components of the solution are required.
Abstract: The migration, imaging, or inversion of wide-aperture cross-hole data depends on the ability to model wave propagation in complex media for multiple source positions. Computational costs can be considerably reduced in frequency-domain imaging by modeling the frequency-domain steady-state equations, rather than the time-domain equations of motion. I develop a frequency-domain approach in this note that is competitive with time-domain modeling when solutions for multiple sources are required or when only a limited number of frequency components of the solution are required.

Journal ArticleDOI
TL;DR: In this article, the free-space propagation operator in the standard fast Fourier transform beam propagation procedure was modified to handle the high-order Fourier components of the electric field and mirrors the structure of the recently introduced finite-difference beam propagation algorithm.
Abstract: It is shown that suitable modifications of the free-space-propagation operator in the standard fast-Fourier-transform beam propagation procedure yield a far more rapid code in the context of semiconductor rib waveguide calculations. The procedure curtails the diffraction experienced by the high-order Fourier components of the electric field and mirrors the structure of the recently introduced finite-difference beam propagation algorithm. It is used to investigate the propagation losses of a Y-junction composed of single-mode rib waveguides and illuminated by its normalized guided mode. >

Journal ArticleDOI
TL;DR: In this article, the authors analyzed shear wave polarizations from local earthquakes recorded by the Anza network in southern California, using an automated method which provides unbiased and quantitative measurements of the polarization and the duration of linear motion following the linearity interval.
Abstract: We analyze shear wave polarizations from local earthquakes recorded by the Anza network in southern California, using an automated method which provides unbiased and quantitative measurements of the polarization and the duration of linear motion following the shear wave arrival (the linearity interval). Initial shear wave particle motions are strongly aligned at four stations, a feature that is not predicted by focal mechanisms. The particle motion alignment is most likely caused by shear wave splitting due to anisotropy beneath these stations, a result supported by the clear shear wave splitting seen in a borehole recording near one of the Anza stations. These results are consistent with an earlier analysis of these data by Peacock et al. [1988]. However, our analysis does not support claims by Crampin et al. [1990] that shear wave splitting delay times at station KNW exhibit temporal variations which can be correlated with the occurrence of the North Palm Springs earthquake (ML=5.6) of July 8, 1986. Automatically determined linearity intervals scatter widely from 0.02 to 0.15 s and exhibit no clear temporal trends. We find a correlation between earthquake moment and the linearity interval, possibly a result of longer effective source time functions for the larger events. The inability to identify a distinct slow quasi-shear wave pulse for the vast majority of these events indicates that scattering strongly affects the particle motion, even in the very early shear wave coda. Analysis of earthquake clusters with similar waveforms recorded at KNW shows that seismic Green functions are stable throughout the observational period and that most linearity interval variation is due to source and ray path differences between events. If shear wave splitting is causing the observed delay times between horizontal components, the waveform stability for events in these clusters restricts any temporal changes in shear wave splitting delay times to less than 5–10%.

Journal ArticleDOI
Z. Bilicki1, J. Kestin1
TL;DR: In this paper, the authors explore the potential of the homogeneous relaxation model (HRM) as a basis for the description of adiabatic, one-dimensional, two-phase flows.
Abstract: The paper explores the potential of the homogeneous relaxation model (HRM) as a basis for the description of adiabatic, one-dimensional, two-phase flows. To this end, a rigorous mathematical analysis highlights the similarities and differences between this and the homogeneous equilibrium model (HEM) emphasizing the physical and qualitative aspects of the problem. Special attention is placed on a study of dispersion, characteristics, choking and shock waves. The most essential features are discovered with reference to the appropriate and convenient phase space Ω for HRM, which consists of pressure P , enthalpy h , dryness fraction x , velocity w , and length coordinate z . The geometric properties of the phase space Ω enable us to sketch the topological pattern of all solutions of the model. The study of choking is intimately connected with the occurrence of singular points of the set of simultaneous first-order differential equations of the model. The very powerful centre manifold theorem allows us to reduce the study of singular points to a two-dimensional plane Π , which is tangent to the solutions at a singular point, and so to demonstrate that only three singular-point patterns can appear (excepting degenerate cases), namely saddle points, nodal points and spiral points. The analysis reveals the existence of two limiting velocities of wave propagation, the frozen velocity a f and the equilibrium velocity a e . The critical velocity of choking is the frozen speed of sound. The analysis proves unequivocally that transition from ω a f to w > a f can take place only via a singular point. Such a condition can also be attained at the end of a channel. The paper concludes with a short discussion of normal, fully dispersed and partly dispersed shock waves.

Journal ArticleDOI
TL;DR: In this article, an approximate wave equation for sound propagation in an inhomogeneous fluid with ambient properties and flow that vary both with position and time is derived, assuming that the characteristic length scale and characteristic time scale for the ambient medium are larger than the corresponding scales for the acoustic disturbance.
Abstract: An approximate wave equation is derived for sound propagation in an inhomogeneous fluid with ambient properties and flow that vary both with position and time. The derivation assumes that the characteristic length scale and characteristic time scale for the ambient medium are larger than the corresponding scales for the acoustic disturbance. For such a circumstance, it is argued that accumulative effects of inhomogeneities and the ambient unsteadiness are satisfactorily taken into account by a wave equation that is correct to first order in the derivatives of the ambient quantities. A derivation that consistently neglects second‐ and higher‐order terms leads to a concise wave equation similar to the familiar ordinary wave equation of acoustics. The wide applicability of this equation is established by showing that it reduces to previously known wave equations for special cases and by showing, with the eikonal approximation, that it yields the geometrical acoustics equations for ray propagation in moving inhomogeneous media.

Journal ArticleDOI
TL;DR: In this paper, the dispersion of an elastic wave propagating in a 76.2mm-diameter (3 in.) split Hopkinson pressure bar system was investigated with two consecutive pulses recorded in the transmitter bar.
Abstract: Dispersion of an elastic wave propagating in a 76.2-mm-diameter (3 in.) Split Hopkinson Pressure Bar system was investigated with two consecutive pulses recorded in the transmitter bar. Assuming that the dispersive high frequency oscillatory components riding on the top of the main pulse originate from the first mode vibration, the dispersion was corrected by using the Fast Fourier Transform and Fourier series expansion numerical schemes

Journal ArticleDOI
TL;DR: Shear Alfven waves with amplitudes greater than 100 mV/m were observed on two recent sounding rocket flights as mentioned in this paper, showing a downward propagation direction and implying insignificant reflection from the ionosphere at frequencies greater than 1 Hz.
Abstract: Shear Alfven waves with amplitudes greater than 100 mV/m were observed on two recent sounding rocket flights The largest waveforms are best described as a series of step functions, rather than as broadband noise or as single frequency waves Complete two-dimensional E and B measurements at 4-ms time resolution were made, showing a downward propagation direction and implying insignificant reflection from the ionosphere at frequencies greater than 1 Hz Intense, field-aligned, low-energy electron fluxes accompany the waves Acceleration of these electrons by the Alfven waves is shown to be feasible The waves in at least one case have a sufficently large ponderomotive potential to generate the observed density fluctuations of order one

Journal ArticleDOI
TL;DR: In this paper, the authors discussed the relation between leading shear wave polarization directions and tectonic features of Japan and proposed that at least three phenomena should be taken into account: stress-induced microcracks primarily aligned in vertical or subvertical planes; cracks or fractures in the vicinity of active faults having their orientation parallel to the fault planes; and intrinsic rock anisotropy resulting from preferred orientation of minerals.
Abstract: Shear wave splitting manifested as leading shear wave polarization, that is, parallel alignment of leading shear wave particle motions from a variety of sources, has been observed at a number of seismograph stations in Japan. Detected on shear wave seismograms from crustal earthquakes over a wide range of source zones and source-receiver azimuths, the shear wave splitting can be attributed to crustal anisotropy. This paper discusses the relation between leading shear wave polarization directions and tectonic features of Japan. To explain the observed shear wave splitting, the author proposes that at least three phenomena should be taken into account: stress-induced microcracks primarily aligned in vertical or subvertical planes; cracks or fractures in the vicinity of active faults having their orientation parallel to the fault planes; and intrinsic rock anisotropy resulting from preferred orientation of minerals. Travel time differences between leading and slower split shear waves from crustal and upper mantle earthquakes analyzed for about one third of the stations suggest that the crustal anisotropy which causes the observed shear wave splitting may be limited to the upper 15-25 km. This implies that the density of nonhorizontally aligned cracks or fractures below 15-25 km and into the upper mantle is muchmore » smaller than that in the crust above 15-25 km.« less

Journal ArticleDOI
TL;DR: In this paper, the propagation of infinitesimal surface waves on a half-space of incompressible isotropic elastic material subject to a general pure homogeneous pre-strain is considered.
Abstract: The propagation of infinitesimal surface waves on a half-space of incompressible isotropic elastic material subject to a general pure homogeneous pre-strain is considered. The secular equation for propagation along a principal axis of the pre-strain is obtained for a general strain-energy function, and conditions which ensure stability of the underlying pre-strain are derived

Journal ArticleDOI
TL;DR: In this article, the authors used Boltzmann's superposition principle to express the stress as a time convolution of a fourth rank tensorial relaxation function with the strain tensor.
Abstract: SUMMARY The anisotropic linear viscoelastic rheological relation constitutes a suitable model for describing the variety of phenomena which occur in seismic wavefields. This rheology, known also as Boltzmann’s superposition principle, expresses the stress as a time convolution of a fourth rank tensorial relaxation function with the strain tensor. The first problem is to establish the time dependence of the relaxation tensor in a general and consistent way. Two kernels based on the general standard linear solid are identified with the mean stress and with the deviatoric components of the stress tensor in a. given coordinate system, respectively. Additional conditions are that in the elastic limit the relaxation matrix must give the elasticity matrix, and in the isotropic limit the relaxation matrix must approach the isotropic-viscoelastic matrix. The resulting rheological relation provides the framework for incorporating anelasticity in time-marching methods for computing synthetic seismograms. Through a plane wave analysis of the anisotropic-viscoelastic medium, the phase, group and energy velocities are calculated in function of the complex velocity, showing that those velocities are in general different from each other. For instance, the energy velocity which represents the wave surface, is different from the group velocity unlike in the anisotropic-elastic case. The group velocity loses its physical meaning at the cusps where singularities appear. Each frequency component of the wavefield has a different non-spherical wavefront. Moreover, the quality factors for the different propagating modes are not isotropic. Examples of these physical quantities are shown for transversely isotropic-viscoelastic clayshale and sandstone. As in the isotropic-viscoelastic case, Boltzmann’s superposition principle is implemented in the equation of motion by defining memory variables which circumvent the convolutional relation betweeh stress and strain. The numerical problem is solved by using a new time integration technique specially designed to deal with wave propagation in linear viscoelastic media. As a first application snapshots and synthetic seismograms are computed for 2-D transversely isotropicviscoelastic clayshale and sandstone which show substantial differences in amplitude, waveform and arrival time with the results given by the isotropic and elastic rheologies.

Journal ArticleDOI
TL;DR: In this article, the isolation of structures from ground transmitted waves by open and infilled trenches in a 3D context is numerically studied, where the soil medium is assumed to be elastic or viscoelastic, homogeneous and isotropic.
Abstract: The isolation of structures from ground transmitted waves by open and infilled trenches in a three-dimensional context is numerically studied. The soil medium is assumed to be elastic or viscoelastic, homogeneous and isotropic. Waves generated by the harmonic motion of a surface rigid machine foundation are considered in this work. The formulation and solution of the problem is accomplished by the boundary element method in the frequency domain. The infinite space fundamental solution is used requiring discretization of the trench surface, the soil-foundation interface and some portion of the free soil surface. The proposed methodology is first tested for accuracy by solving three characteristic wave propagation problems with known solutions and then applied to several vibration isolation problems involving open and concrete infilled trenches. Three-dimensional graphic displays of the surface displacement pattern around the trenches are also presented.

Journal ArticleDOI
TL;DR: In this article, the authors analyzed a spectabular spread F event that for the first time demonstrates a layering which, the authors argue, is controlled by a gravity wave effect.
Abstract: Studies dating back more than 15 years have presented evidence that atmospheric gravity waves play a role in initiating nighttime equatorial F region instabilities. This paper analyzes a spectabular spread F event that for the first time demonstrates a layering which, the authors argue, is controlled by a gravity wave effect. The 50-km vertical wavelength of a gravity wave which they have found is related theoretically to a plasma layering irregularity that originated at low altitudes and then was convected, intact, to higher altitudes. Gravity waves also seem to have determined bottomside intermediate scale undulations, although this fact is not as clear in the data. The neutral wind dynamo effect yields wave number conditions on the gravity wave's ability to modulate the Rayleigh-Taylor instaiblity process. Finally, after evaluating the gravity wave dispersion relation and spatial resonance conditions, we estimate the properties of the seeding wave.

Journal ArticleDOI
TL;DR: In this paper, a theory to describe the propagation of elastic waves in a porous medium saturated by a mixture of two immiscible, viscous, compressible fluids is presented.
Abstract: A theory to describe the propagation of elastic waves in a porous medium saturated by a mixture of two immiscible, viscous, compressible fluids is presented. First, using the principle of virtual complementary work, the stress–strain relations are obtained for both anisotropic and isotropic media. Then the forms of the kinetic and dissipative energy density functions are derived under the assumption that the relative flow within the porous medium is of laminar type and obeys Darcy’s law for two‐phase flow in porous media. The equations of motion are derived, and a discussion of the different kinds of body waves that propagate in this type of medium is given. A theorem on the existence, uniqueness, and regularity of the solution of the equations of motion under appropriate initial and boundary conditions is stated.

Journal ArticleDOI
TL;DR: In this article, the equivalence principle is used to predict the radiation pattern of a general class of leaky-wave antennas, consisting of a finite-size source which excites a radially propagating leaky wave on some planar surface.
Abstract: Formulas are derived for the far-infrared radiation pattern of cylindrical leaky waves propagating on a planar surface. The formulas can be used to predict the radiation pattern of a general class of leaky-wave antennas, consisting of a finite-size source which excites a radially propagating leaky wave on some planar surface. Leaky-wave antennas consisting of antenna elements embedded in dielectric layers (microstrip elements) fall into this category. Using the equivalence principle, formulas are derived for both transverse electric (TE) and transverse magnetic (TM) leaky waves with arbitrary propagation constants. The formulas allow for radiation from cylindrical apertures of arbitrary size, so that the effect of truncating the supporting planar surface with an absorbing material can be determined. Particular attention is devoted to the case of a leaky wave for which the real and imaginary parts of the complex propagation constant are equal, since this type of wave has been shown to be responsible for broadside radiation in certain leaky-wave antennas comprised of dielectric layers. >

Journal ArticleDOI
TL;DR: In this article, the spectrum of gravity wave at each height is calculated directly from the wave equation and wave dissipation is approximately accounted for by a diffusion term, assuming that many wave dissipations can be approximately described by a scale-dependent diffusion process.
Abstract: For a highly idealized condition, the spectrum of saturated and unsaturated gravity waves at each height is calculated directly from the wave equation. A principal feature of this wave equation is the inclusion of wave dissipation, although in an approximate form. In the absence of wave absorption, reflection, radiation, wind shears, resonant wave–wave interactions and other sources and sinks, this dissipation at each height is determined solely by the “turbulent” or chaotic state caused by off-resonant wave–wave interactions and instability of the (broad) wave spectrum at that height. The dissipation is approximately accounted for by a diffusion term. The appropriate diffusivity is self-consistent with the continuum of spectral waves that cause the chaotic state and is argued to be scale dependent. An inverse calculation is also made of what the observed spectra imply for wave dissipation—again assuming that many wave dissipations can be approximately described by a scale-dependent diffusion pro...

Journal ArticleDOI
TL;DR: In this paper, a boundary integral method was used to compute the wave growth on a cylindrical jet and the initial wave growth is in agreement with Rayleigh's linear theory, when followed to completion these waves pinch off large drops separated by smaller satellite drops that decrease in size with decreasing wavelength.
Abstract: Computations of finite‐amplitude, spatially periodic wave growth on a cylindrical jet have been carried out using a boundary integral method. The initial wave growth is in agreement with Rayleigh’s linear theory. When followed to completion these waves pinch off large drops separated by smaller satellite drops (spherules) that decrease in size with decreasing wavelength. The computed sizes of both drops and satellites agree with experiment. It is found that satellites will form for all unstable wave numbers. The small satellites that are computed at wave numbers near the critical wave number were not predicted by near‐linear analysis but are observed in experimental photographs of jet breakup. Computation of the collapse of elongated satellites shows short waves propagating on their surfaces.


Journal ArticleDOI
TL;DR: In this paper, the authors used a 21/2-D MHD time-dependent model to perform a parametric study of interplanetary shock propagation to 1 AU, where the input conditions were represented by the following variables: initial shock velocity, duration of the driving pulse, and width of the pulse at the near-Sun position (18 solar radii).
Abstract: We utilize a 21/2-D MHD time-dependent model to perform a parametric study of interplanetary shock propagation to 1 AU. The input conditions are represented by the following variables:(1) initial shock velocity, (2) duration of the driving pulse, and (3) width of the pulse at the near-Sun position (18 solar radii). The total net energy added to the solar wind was calculated for each pulse. The forward shock's travel time to, and the peak dynamic pressure at, 1 AU as a function of location along the shock front have been studied over a range of total input pulse energies from 1029 to 1032 ergs. For input pulses with modest angular width and temporal duration, we find that the propagation of the resulting interplanetary fast forward shock waves depends primarily upon the net input energy. The dependence of the transit time upon energy is a power law with a -1/3 index which corresponds to the classical, piston driven case. Reverse shocks are also formed behind all but the lowest energy shocks. Their properties, although also a function of input energy, depend upon the specific values of the input pulse shock velocity, width and duration. We also briefly discuss the propagation of the shocks out to 1 AU, and the conditions for which the interplanetary shocks depart from being symmetric about the input pulse central meridian due to magnetic and dynamic effects.

Journal ArticleDOI
TL;DR: The AMPTE CCE spacecraft observed a transverse Pc 5 magnetic pulsation (period of about 200 s) at 2155-2310 UT on November 20, 1985, at a radial distance of 5.7 -7.0 earth radii as discussed by the authors, at a magnetic latitude of 1.2 - 19 deg, and near 1300 magnetic local time.
Abstract: The AMPTE CCE spacecraft observed a transverse Pc 5 magnetic pulsation (period of about 200 s) at 2155-2310 UT on November 20, 1985, at a radial distance of 5.7 - 7.0 earth radii, at a magnetic latitude of 1.2 - 19 deg, and near 1300 magnetic local time. The magnetic pulsation exhibits properties consistent with a standing Alfven wave with a second-harmonic standing structure along the ambient magnetic field. The amplitude and the phase of the flux pulsation are found to be a function of the particle detector look direction and the particle energy. The observed energy dependence of the shift is interpreted as the result of a drift-bounce resonance of the ions with the wave. From this interpretation it follows that the wave propagated westward with an azimuthal wave number of approximately 100. Thus the study demonstrates that particle data can be useful for determining the spatial structure of some types of ULF waves.