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Showing papers on "Wave propagation published in 1989"


Book
01 Jan 1989
TL;DR: In this article, the authors introduce the notion of circular cross-section waveguides and cavities, and the moment method is used to compute the wave propagation and polarization.
Abstract: Time--Varying and Time--Harmonic Electromagnetic Fields. Electrical Properties of Matter. Wave Equation and Its Solutions. Wave Propagation and Polarization. Reflection and Transmission. Auxiliary Vector Potentials, Contruction of Solutions, and Radiation and Scattering Equations. Electromagnetic Theorems and Principles. Rectangular Cross--Section Waveguides and Cavities. Circular Cross--Section Waveguides and Cavities. Spherical Transmission Lines and Cavities. Scattering. Integral Equations and the Moment Method. Geometrical Theory of Diffraction. Greena s Functions. Appendices. Index.

5,693 citations


Journal ArticleDOI
TL;DR: In this paper, the authors characterized the neutral atmosphere for the frequency range from 1 to 300 GHz as a nonturbulent propagation medium and predicted attenuation and propagation delay effects from meteorological data sets: pressure, temperature, humidity, suspended particle concentration, and rain rate.
Abstract: The neutral atmosphere is characterized for the frequency range from 1 to 300 GHz as a nonturbulent propagation medium. Attenuation and propagation delay effects are predicted from meteorological data sets: pressure, temperature, humidity, suspended particle concentration, and rain rate. The physical data base of the propagation model consists of four terms: (a) resonance information for 30 water vapor and 48 oxygen absorption lines in the form of intensity coefficients and center frequency for each line; (b) a composite (oxygen, water vapor, and nitrogen) continuum spectrum; (c) a hydrosol attenuation term for haze, fog, ,and cloud conditions; and (d) a rain attenuation model. Oxygen lines extend into the mesosphere, where they behave in a complicated manner due to the Zeeman effect. The geomagnetic field strength H is required as an additional input parameter. Each 02 line splits proportionally with H into numerous, sub-lines, which are juxtaposed to form a Zeeman pattern spread over a megahertz scale. Patterns for three main polarization cases are calculated. Detailed examples for model atmospheres provide basic millimeter wave propagation information over the height range 0 to 100 km of the neutral atmosphere.

705 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a rigorous model for the propagation of pressure waves in bubbly liquids and show that the model works well up to volume fractions of 1% to 2% provided that bubble resonances play a negligible role.
Abstract: Recent work has rendered possible the formulation of a rigorous model for the propagation of pressure waves in bubbly liquids. The derivation of this model is reviewed heuristically, and the predictions for the small‐amplitude case are compared with the data sets of several investigators. The data concern the phase speed, attenuation, and transmission coefficient through a layer of bubbly liquid. It is found that the model works very well up to volume fractions of 1%–2% provided that bubble resonances play a negligible role. Such is the case in a mixture of many bubble sizes or, when only one or a few sizes are present, away from the resonant frequency regions for these sizes. In the presence of resonance effects, the accuracy of the model is severely impaired. Possible reasons for the failure of the model in this case are discussed.

649 citations




Journal ArticleDOI
TL;DR: In this paper, the authors obtained nonstationary soliton-like solutions for an extended version of the classical massive Thirring model which, in nonlinear optics, describes Bragg-resonant wave propagation in a periodic Kerr medium.

417 citations


Journal ArticleDOI
TL;DR: In this article, a numerical model for hindcasting of short-crested waves in shallow-water is described and comparisons are made between observations and model results in a realistic field situation.

334 citations


Journal ArticleDOI
TL;DR: In this article, an analytical and computational study of the normal-mode small-amplitude waves of high-speed jets is presented, and three families of instability waves have been identified: (1) the familiar Kelvin-Helmholtz instability waves, (2) supersonic instability waves; and (3) subsonic waves.
Abstract: An analytical and computational study of the normal-mode small-amplitude waves of high-speed jets is presented. Three families of instability waves have been identified: (1) the familiar Kelvin-Helmholtz instability waves; (2) supersonic instability waves; and (3) subsonic waves. It is demonstrated that the computed wave patterns and propagation characteristics of these three wave types are consistent with the findings of Oetel (1979, 1980, 1982). The subsonic waves are shown to be unstable only for jets with mixing layers of finite thickness.

286 citations


Journal ArticleDOI
TL;DR: In this article, a method of generating multiple support inputs for any given set of n surface locations having space coordinates xi and yi which are compatible with the main wave propagation properties observed in the Strong Motion Array Taiwan (SMART-1).

277 citations


Journal ArticleDOI
TL;DR: The linear mode conversion theory of Jones (1976, 1980), which in the past has been considered by some to be too inefficient to account for the observed wave amplitudes, is considered here as mentioned in this paper.
Abstract: It is generally accepted that electrostatic wave energy is the source of terrestrial myriametric radiation (TMR), but there are several theories to suggest how this energy is converted into TMR. The linear mode conversion “window” theory of Jones (1976, 1980), which in the past has been considered by some to be too inefficient to account for the observed wave amplitudes, is considered here. First, the ray tracing program HOTRAY is described. This program is used to trace electromagnetic and electrostatic waves in a hot magnetized plasma and to calculate the path-integrated growth rates for a realistic unstable particle distribution function. A density model is constructed from wave observations made by DE 1 of an event where TMR was beamed to northern and southern latitudes from a source very close to the magnetic equator. Ray tracing shows that backward propagating electrostatic waves can refract into electromagnetic Z mode waves and transport energy to the so-called radio window at the equator. At this point, mode conversion of energy into O mode radiation is assumed to take place. Ray tracing of O mode radiation from the radio window shows that TMR is beamed to northern and southern latitudes as observed and as predicted by the theory. Path-integrated growth rates show that the electrostatic waves amplify by a factor ≥42 from the background fluctuation level before reaching the window. This is sufficient to account for the observed TMR wave amplitudes which require the waves to amplify by a factor ≥20. Increasing the depth of the loss cone, or increasing the hot plasma density, to within observed limits, increases the wave amplification up to a factor of 104. Strong Landau and cyclotron damping from the hot plasma component restricts the efficient transfer of energy to the radio window to within a few tenths of a degree in latitude about the magnetic equator. Thus the strongest TMR is emitted from the equator. In general, TMR beamed to northern latitudes from radio windows north of the equator is stronger than that beamed to southern latitudes; conversely, TMR beamed to northern latitudes from radio windows south of the equator is generally weaker than that beamed to southern latitudes. It is shown that electrostatic wave energy can still be transported efficiently to the radio window for magnetic field intensity variations of 1 or 2%. Thus the generation of TMR is not sensitive to variations in the magnetic field strength of this magnitude.

232 citations


Journal ArticleDOI
TL;DR: In this paper, a computational model for highly nonlinear 2D water waves in which a high-order Boundary Element Method is coupled with a high order explicit time stepping technique for the temporal evolution of the waves is presented.
Abstract: The paper presents a computational model for highly nonlinear 2-D water waves in which a high order Boundary Element Method is coupled with a high order explicit time stepping technique for the temporal evolution of the waves. The choice of the numerical procedures is justified from a review of the literature. Problems of the wave generation and absorption are investigated. The present method operates in the physical space and applications to four different wave problems are presented and discussed (space periodic wave propagation and breaking, solitary wave propagation, run-up and radiation, transient wave generation). Emphasis in the paper is given to describing the numerical methods used in the computation.

Journal ArticleDOI
TL;DR: In this article, an approximate dispersion relation was developed to 0(e2) for arbitrary current U(z) in water of finite depth in linear wave theory for waves riding on a weak current of 0 e compared to the wave phase speed.
Abstract: Assuming linear wave theory for waves riding on a weak current of 0(e) compared to the wave phase speed, an approximate dispersion relation is developed to 0(e2) for arbitrary current U(z) in water of finite depth. The 0(e2) approximation is shown to be a significant improvement over the 0(e) result, in comparison with numerical and analytic results for the full problem. Various current profiles in the full range of water depths are considered. Comments on approximate action conservation and application to depth-averaged wave models are included.

Journal ArticleDOI
TL;DR: In this article, a new wave with periods and alongshore wavelengths of the order of 102 seconds and meters, respectively, was observed in the surf zone and was consistent with a model of vorticity waves generated by the shear instability of the mean longshore current.
Abstract: A new type of alongshore progressive wave with periods and alongshore wavelengths of the order of 102 seconds and meters, respectively, has been observed in the surf zone. These periods fall into the lower end of the much studied infragravity frequency band previously shown to contain surface gravity edge and leaky waves. However, their short wavelengths (more than an order of magnitude smaller than the mode 0 edge wave) distinguish these new waves from surface gravity waves. In addition, they are only observed in the presence of mean longshore current and they change celerity (O(1 m/s)) and direction with the mean current. Alongshore wavenumber-frequency spectra clearly identify these waves, distinct from edge and leaky waves, by their approximately linear dispersion line at wavenumbers greater than the mode 0 edge wave dispersion curve. Their rms horizontal velocities can exceed 30 cm/s. These waves are shown to be consistent with a model [Bowen and Holman, this issue] of vorticity waves generated by the shear instability of the mean longshore current.

Book ChapterDOI
01 Jan 1989
TL;DR: Durr et al. as mentioned in this paper reviewed the results on the motion of a test particle in a nearest neighbors harmonic chain and showed that the test particle's motion in the chain is independent of the distance to the nearest neighbor.
Abstract: We shall review here the results on the motion of a test particle in a nearest neighbors harmonic chain. For details, we refer to [1], [2]. These results were obtained by D.Durr, N.Zanghi and the author.

Journal ArticleDOI
TL;DR: In this article, the inviscid spatial stability of a parallel compressible mixing layer is studied and the parameters of the flow as a function of the Mach number of the moving stream, the ratio of the temperature of the stationary stream to that of a moving stream and the frequency and the direction of propagation of the disturbance wave are given.
Abstract: Presented are the results of a study of the inviscid spatial stability of a parallel compressible mixing layer. The parameters of this study are the Mach number of the moving stream, the ratio of the temperature of the stationary stream to that of the moving stream, the frequency and the direction of propagation of the disturbance wave. Stability characteristics of the flow as a function of these parameters are given. It is shown that if the Mach number exceeds a critical value there are always two groups of unstable waves. One of these groups is fast with phase speeds greater than 1/2, and the other is slow with speeds less than 1/2. Phase speeds for the neutral and unstable modes are given, as well as growth rates for the unstable modes. It is shown that three-dimensional modes have the same general behavior as the two-dimensional modes but with higher growth rates over some range of propagation direction. Finally, a group of very low frequency unstable modes was found for sufficiently large Mach numbers. These modes have very low phase speeds but large growth rates.

Journal ArticleDOI
TL;DR: In this paper, the transformation of monochromatic and directionally-spread irregular waves passing over a submerged elliptical mound was studied in a controlled laboratory experiment, where a directional spectral wave generation was used to generate waves with equal peak frequencies and spectral energy.
Abstract: The transformation of monochromatic and directionally-spread irregular waves passing over a submerged elliptical mound was studied in a controlled laboratory experiment. A directional spectral wave generation was used to generate waves with equal peak frequencies and spectral energy, along with monochromatic waves of equivalent significant height and period. Spectra with both narrow and broad frequency and directional spreads were generated. Results indicate that monochromatic waves provide a poor approximation of irregular wave conditions if there is directional spread or high wave steepness.

Book
30 Nov 1989
TL;DR: In this paper, the effect of a periodic external force on an Oscillator's phase plane has been investigated in the context of a continuous medium wave dispersion in a three-dimensional system.
Abstract: One Oscillations and Waves in Linear Systems- 1 Linear Oscillators- 11 General Notes- 12 Two Examples The Phase Plane Diagram of an Oscillator- 13 Resonance The Effect of an Aperiodic External Force on an Oscillator- 14 Normal Oscillations Analogy with Quantum Mechanics Production and Extinction Operators- 2 Oscillations in a System with Two Linked Oscillators- 21 Initial Equations- 22 The Fundamental Oscillations of Two Linked Oscillators- 23 Disturbance of Two Linked Oscillators by an External Force The Reciprocity Principle- 3 Oscillations in an Ensemble of Non-Interacting Oscillators- 31 Classical Theory of Dispersion- 32 Oscillations in an Ensemble of Dissimilar Noninteracting Oscillators with a Given Distribution Function- 4 Oscillations in Ordered Structures Limit for a Continuous medium Waves Dispersion- 41 General Remarks- 42 Oscillations in Ordered Structures (Chains of Linked Particles and Identical Linked Oscillators)- 43 Limiting Transition from an Ordered Structure to a One-dimensional Medium Temporal and Spatial Dispersion Physical Nature of Dispersion- 44 Typical Dispersion Characteristics for Medium Models- 45 Formal Method for Obtaining the Dispersion Equation Waves in a One-Dimensional Resonator Resonance in Wave Systems- 5 Properties of Waves with Small Amplitudes in Continuous media- 51 General Remarks- 52 Equations of Hydrodynamics Dispersion for Sound Waves For Sound Waves- 53 A Stratified Fluid Sound in an Ocean- 54 Gravity Waves in an Incompressible Liquid Internal Waves Rossby Waves- 55 Waves in a Superfluid Liquid- 56 Waves in a Plasma Hydrodynamic Description- 6 Stability and Instability of Linear Systems with Discrete Spectra- 61 General Notes and Definitions- 62 The Raus-Gurvits Criterion and Three-Dimensional Systems- 63 The D-Partition Method- 64 Stability of Non-Autonomous Systems- 65 Instability Mechanisms- 7 Stability of Distributed Systems with Continuous Spectra- 71 General Comments- 72 Examples of Instability- 73 Absolute and Convective Instability The Characteristics Method- 74 Waves in Flows Electron Beams Helmholtz Instability- 75 Amplification and Filtering Separation Criteria- 8 Propagation Velocity of Waves- 81 Various Introductions to the Concept of Group Velocity- 82 Group Velocity of Waves in Some Continuous Media- 9 Energy and Momentum of Waves- 91 Equation for the Transport of the Average Energy Density by Wave Packets in Dispersing Media- 92 Density of the Energy of an Electromagnetic Wave in a Medium with Dispersion- 93 Momentum of a Wave Packet- 10 Waves with Negative Energy Linked Waves- 101 General Notes- 102 Waves with Positive and Negative Energies- 103 Coupled Waves Synchronicity Normal and Anomalous Doppler Effects- 11 Parametric Systems and Parametric Instability- 111 General Comments- 112 Parametric Resonance Floquet's (Blokh's) Theorem Mathieu's Equation- 113 Waves in Periodic Structures The Mathieu Zone and the Brillouin Diagram- 114 Motion in a Rapidly Oscillating Field Kapitsa's Pendulum Free Electron Lasers- 12 Adiabatic Invariants Propagation of Waves in Inhomogeneous Media- 121 The Wentsel-Kramers-Brillouin (VCB) Approximation and Adiabatic Invariants- 122 Equivalence Between a Rotor and an Oscillator- 123 Propagation of Waves in Inhomogeneous Media The Approximation of Geometric Optics- 124 The Propagation of Waves in a Plane-Layer Medium in the Geometric Optics Approximation- 125 Linear Wave Interaction in an Inhomogeneous Medium- Two Oscillations and Waves in Nonlinear Systems- 13 The Nonlinear Oscillator- 131 Initial remarks- 132 Qualitative and Analytical Description Examples of Nonlinear Systems- 133 Nonlinear Resonance- 134 Overlap between Nonlinear Resonances- 14 Periodic Self-Excited Oscillations- 141 Definitions- 142 The Van der Pol Generator Self-Excited Oscillations as a Function of System Parameters- 143 Relaxational Self-Excited Oscillations Fast and Slow Motions- 15 General Properties of Nonlinear Dynamic Systems in Phase Space- 151 Basic Types of Trajectory The Fundamentals of Dynamic Systems (Structural Stability)- 152 Basic Bifurcations on a Plane Poincare Indices- 153 Point Transformations- 154 Bifurcation of Periodic Motions- 155 Homoclinic Structures- 16 Self-Excited Oscillations in Multifrequency Systems- 161 Forced Synchronization- 162 Competition- 163 Mutual Mode Synchronization- 17 Resonance Interactions between Oscillators- 171 Interaction Between Three Coupled Oscillators in a System with Quadratic Nonlinearity- 172 Resonance Interactions Between Waves in Weakly Nonlinear Media with Dispersion- 173 Explosive Instability- 18 Simple Waves and the Formation of Discontinuities- 181 Kinematic Waves- 182 Travelling Waves in a Nonlinear Medium Without Dispersion- 183 Determining the Discontinuity Coordinates- 184 Weak Shock Waves Boundary Conditions at a Discontinuity- 19 Stationary Shock Waves and Solitons- 191 Structure of a Discontinuity- 192 Solitary Waves - Solitons- 193 Solitons as Particles- 194 Higher-Dimensional Solitons- 20 Modulated Waves in Nonlinear Media- 201 General Remarks- 202 Self-Modulation Reversibility- 203 Self-Focusing- 20 4 Interaction Between Wave Beams and Packets- 205 Interactions Between Waves Having Randomly Modulated Phases Wave Kinetics- 21 Self-Excited Oscillations in Distributed Systems- 211 General Remarks- 212 Medium Without Dispersion Discontinuous Waves- 213 Stationary Waves- 214 The Existence and Role of Limiting Cycles- 215 Competition Between Stationary Waves in an Active Medium- 216 Periodic Self-Excited Oscillations in Hydrodynamic Flows- 22 Stochastic Dynamics in Simple Systems- 221 How Randomness Appears in a Dynamic System- 222 The Stochastic Dynamics of One-Dimensional Mappings- 223 Noise Generator Qualitative Description and Experiment- 224 Statistical Description of a Simple Noise Generator- 225 Ways in which Strange Attractors Arise- 226 Dimensionality of Stochastic Sets- 23 The Onset of Turbulence- 231 General Remarks- 232 The Occurrence of Stochastic Self-Excited Oscillations in Experimental Fluid Mechanics- 233 Stochastic Modulation- 234 Ideal Flow and Turbulence- 24 Self-Organization- 241 Main Phenomena, Models, and Mathematical Forms- 242 Travelling Pulsations- 243 Spiral and Cylindrical Waves Travelling Centers- 244 Concerning Self-Organization Mechanisms- References

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the phenomenon of forced generation of nonlinear waves by disturbances moving steadily with a transcritical velocity through a layer of shallow water and show that the response of a dynamic system to steady forcing need not asymptotically tend to a steady state, but can be conspicuously periodic, after an impulsive start, when the system is being forced at resonance.
Abstract: In this joint theoretical, numerical and experimental study, we investigate the phenomenon of forced generation of nonlinear waves by disturbances moving steadily with a transcritical velocity through a layer of shallow water. The plane motion considered here is modelled by the generalized Boussinesq equations and the forced Korteweg-de Vries (fKdV) equation, both of which admit two types of forcing agencies in the form of an external surface pressure and a bottom topography. Numerical results are obtained using both theoretical models for the two types of forcings. These results illustrate that within a transcritical speed range, a succession of solitary waves are generated, periodically and indefinitely, to form a procession advancing upstream of the disturbance, while a train of weakly nonlinear and weakly dispersive waves develops downstream of an ever elongating stretch of a uniformly depressed water surface immediately behind the disturbance. This is a beautiful example showing that the response of a dynamic system to steady forcing need not asymptotically tend to a steady state, but can be conspicuously periodic, after an impulsive start, when the system is being forced at resonance. A series of laboratory experiments was conducted with a cambered bottom topography impulsively started from rest to a constant transcritical velocity U, the corresponding depth Froude number F = U/(gh[sub]0)^1/2 (g being the gravitational constant and h[sub]0 the original uniform water depth) being nearly the critical value of unity. For the two types of forcing, the generalized Boussinesq model indicates that the surface pressure can be more effective in generating the precursor solitary waves than the submerged topography of the same normalized spatial distribution. However, according to the fKdV model, these two types of forcing are entirely equivalent. Besides these and some other rather refined differences, a broad agreement is found between theory and experiment, both in respect of the amplitudes and phases of the waves generated, when the speed is nearly critical (0.9 F > 0.2, finally disappear at F ~= 0.2. In the other direction, as the Froude number is increased beyond F ~= 1.2, the precursor soliton phenomenon was found also to evanesce as no finite-amplitude solitary waves can outrun, nor can any two-dimensional waves continue to follow, the rapidly moving disturbance. In this supercritical range and for asymptotically large times, all the effects remain only local to the disturbance. Thus, the criterion of the fascinating phenomenon of the generation of precursor solitons is ascertained.

Journal ArticleDOI
TL;DR: In this article, the first-order perturbation method is used to evaluate approximate phase velocities and polarization vectors in elastic anisotropic media, no matter whether the unperturbed medium is isotropic or anisomorphic.
Abstract: The first-order perturbation method is used to evaluate approximate phase velocities and polarization vectors in elastic anisotropic media. Formulae are given which make possible computations of perturbations of these parameters for quasi-compressional as well as quasi-shear waves, no matter whether the unperturbed medium is isotropic or anisotropic. Approximate results for an extremely anisotropic material and relatively large deviations of parameters of unperturbed and perturbed media closely resemble the results computed exactly. It is, therefore, expected that the application of the perturbation method to realistic media with generally weaker anisotropy and for smaller deviations between unperturbed and perturbed medium parameters should give satisfactory results. The method will find the most important applications in the investigation of high-frequency wave propagation in inhomogeneous anisotropic media and in solving inverse problems for anisotropic structures. Several possible applications are listed and briefly discussed.

Journal ArticleDOI
TL;DR: In this article, a new decomposition of exact solutions to the scalar wave equation into bidirectional, forward and backward, traveling plane wave solutions is described, which is a natural basis for synthesizing pulse solutions that can be tailored to give directed energy transfer in space.
Abstract: A new decomposition of exact solutions to the scalar wave equation into bidirectional, forward and backward, traveling plane wave solutions is described. The resulting representation is a natural basis for synthesizing pulse solutions that can be tailored to give directed energy transfer in space. The development of known free‐space solutions, such as the focus wave modes, the electromagnetic directed energy pulse trains, the spinor splash pulses, and the Bessel beams, in terms of this decomposition will be given. The efficacy of this representation in geometries with boundaries, such as a propagation in a circular waveguide, will also be demonstrated.

Book
01 Jan 1989

Journal ArticleDOI
TL;DR: In this article, the authors analyzed 12 kinds of spectra related to the Elsasser variables in the solar wind and found that the autocorrelation length for δZ− is much larger than that of Z+ in both the high-speed and low-speed wind.
Abstract: Magnetic field and plasma data, obtained by the Helios 1 and 2 spacecraft in the solar wind near 0.3 AU during the years 1975 to 1976, have been analyzed by calculating 12 kinds of spectra related to the Elsasser variables, δZ+ = δV + δVA, and δZ− = δV − δVA, where δV and δVA are the bulk velocity and Alfven velocity fluctuations, respectively. For small amplitude Alfven waves the fluctuation variable δZ+ simply relates to outward propagation and δZ− to an inward sense of propagation, if the ambient magnetic field B0 is directed inward. The frequency range analysed in this paper is 6×10−6 Hz to 6×10−3 Hz. It is found that (1) the autocorrelation length for δZ− is much larger than for δZ+ in both the high-speed and low-speed wind. (2) The power spectra of δZ−, especially in high-wind speed, are steeper in the low-frequency range and flatten in the high-frequency range. (3) In the low-frequency range, the power spectra for the components of δZ+ tend to be isotropic with respect to the three polarization directions, while the spectra of δZ− are dominated by the radial component. In the high-frequency domain, the spectra of both δZ+ and δZ− are dominated by the transverse component in high-speed wind and are more isotropic in low-speed wind. (4) The spectra related to the residual energy or the cross-correlation in low-speed flows have a power law with the slope near to −5/3. However, in high-speed flows the corresponding data are widely distributed in a cloud of points with an upper envelope near to the spectrum of δZ−. The origin of all these spectra and their importance for the solar wind physics have also been discussed. Several generation mechanisms are suggested as candidates. In the flat part of e− spectrum, the fluctuations may be generated by non-local (in wave number space) interactions with the low-frequency part of the e+ spectrum, or just by parametric decay of the high-frequency part of the e+ spectrum. The steep part of e− (f) may be related to small-scale stream tubes, or be influenced by pressure waves, nonlinear cascading, and the interaction with the outgoing Alfven waves.

Journal ArticleDOI
TL;DR: It was found that during normal aggregation oscillation frequency increases while at the same time wave propagation velocity decreases, which may indicate a more vigorous chemotactic response by individual cells or a better synchronization of the responding cell populations due to shortened Chemotactic deadaptation times.
Abstract: Waves of chemotactic movement during the early phase of aggregation in Dictyostelium discoideum were analyzed by digital image processing in a manner that immediately shows the following parameters: wave propagation velocity, period length, wave amplitude und wave shape. We have characterized the aggregation of AX-2 and the streamer F mutant NP 377 in terms of these parameters and investigated the influence of caffeine and ammonia. It was found that during normal aggregation oscillation frequency increases while at the same time wave propagation velocity decreases. Caffeine, a known inhibitor of cyclic AMP relay, reduces oscillation frequency and wave propagation velocity in a dose-dependent manner but most notably leads to the appearance of bimodal (harmonic) oscillations. These bimodal waves are also found in streamer F mutants without caffeine during early aggregation. The effect of caffeine is interpreted as an increase in the average chemotactic deadaptation time due to elevated cyclic GMP levels after a cyclic AMP stimulus. This increased deadaptation time results in some cells responding to every chemotactic signal, while others respond only to every second signal, leading to mixed population behavior and hence biphasic optical density waves. Ammonia has no significant influence on oscillation frequency and wave propagation velocity but shows a clear increase in the amplitude of the optical density waves. This may indicate a more vigorous chemotactic response by individual cells or a better synchronization of the responding cell populations due to shortened chemotactic deadaptation times.

Journal ArticleDOI
TL;DR: The propagation of Lamb waves in plates has been the subject of numerous investigations since their postulation by Lamb in 1916 [1,2] as discussed by the authors, and theoretical analyses have been reported in plates of cubic [3,4], transversely isotropic [5,6], and orthotropic [7,9] media.
Abstract: The propagation of Lamb waves in plates has been the subject of numerous investigations since their postulation by Lamb in 1916 [1,2]. Most of the work in existence deals with various aspects of these guided waves in plates of isotropic materials. Comparatively speaking a limited number of results has appeared in which Lamb or horizontaly polarized SH wave propagation in anisotropic plates has been considered in any detail. For Lamb waves, theoretical analyses have been reported in plates of cubic [3,4], transversely isotropic [5,6], and orthotropic [7,9] media.

Book ChapterDOI
TL;DR: In this article, the authors describe the nonlinear wave propagation in planar structures and the two categories of integrated all-optical devices can be anticipated on the basis of nonlinear optical phenomena.
Abstract: Publisher Summary This chapter describes the nonlinear wave propagation in planar structures. The two categories of integrated all-optical devices can be anticipated on the basis of the nonlinear optical phenomena. The first class of optical devices is that in which the nonlinear change in the refractive index is small in comparison with the refractive index difference between the guiding media. The second category of nonlinear optical devices is that in which the optically induced change in refractive index is comparable with, or larger than, the index differences among the guiding media. The chapter discusses the study of electromagnetic waves guided by nonlinear interfaces. The basic concepts and method used to analyze nonlinear guided wave phenomena are also discussed. The nonlinear TE polarized waves guided by thin dielectric films are studied. The chapter explains that very thin metal films (nonlinear surface plasmon polaritons) can also guide nonlinear TE polarized waves. The experiments reported on nonlinear guided wave phenomena are reviewed in the chapter.


Book
20 Nov 1989
TL;DR: The Hamiltonian approach to electrodynamics radiation reaction uniformly accelerated charges radiation emitted by relativistic and non-relativistic moving particles synchrotron radiation.
Abstract: The Hamiltonian approach to electrodynamics radiation reaction uniformly accelerated charges radiation emitted by relativistic and non-relativistic moving particles synchrotron radiation electrodynamics of a continuous medium the Cerenkov and Doppler effects transition radiation and transition scattering superluminal sources of radiation reabsorption and transfer of radiation electrodynamics of media with spatial dispersion permittivity and wave propagation in plasmas the energy-momentum tensor and forces in macroscopic electrodynamics, energy and heat liberated in a dispersive absorbing medium fluctuations and van der Waals forces wave scattering in a medium astrophysics of cosmic rays x-ray astronomy gamma-ray astronomy.

Journal ArticleDOI
TL;DR: In this article, a theory based on the concept of trapping of a portion of the sound in the waveguide formed by the ocean surface bubble layer is proposed, which can change significantly over the course of a storm, or from one storm to another.
Abstract: Measurements of the ambient sound generated by breaking waves over the range 40–20 000 Hz reveal well‐defined spectral peaks, the frequency of which may remain generally consistent from one breaking event to the next, but which can change significantly over the course of a storm, or from one storm to another. A theory is proposed, based on the concept of trapping of a portion of the sound in the waveguide formed by the ocean‐surface bubble layer. Simultaneous measurements of the bubble population and size distribution as a function of depth and time were obtained with a multifrequency inverted echo sounder, allowing calculation of the resulting (dispersive) sound‐speed anomaly profile. Theoretical predictions of the spectral peaks, which are associated with modal cutoff frequencies, are in good agreement with the observations. It is suggested that this result might have application to the remote determination of ocean‐surface bubble fields relevant to the study of wave breaking, turbulence, and the air–sea gas flux.


Journal ArticleDOI
TL;DR: In this paper, a phenomenological treatment of the inertial range of isotropic statistically steady magnetohydrodynamic turbulence is presented, extending the theory of Kraichnan [Phys. Fluids 8, 1385 (1965)].
Abstract: A phenomenological treatment of the inertial range of isotropic statistically steady magnetohydrodynamic turbulence is presented, extending the theory of Kraichnan [Phys. Fluids 8, 1385 (1965)]. The role of Alfven wave propagation is treated on equal footing with nonlinear convection, leading to a simple generalization of the relations between the times characteristic of wave propagation, convection, energy transfer, and decay of triple correlations. The theory leads to a closed‐form steady inertial range spectral law that reduces to the Kraichnan and Kolmogorov laws in appropriate limits. The Kraichnan constant is found to be related in a simple way to the Kolmogorov constant; for typical values of the latter constant, the former has values in the range 1.22–1.87. Estimates of the time scale associated with spectral transfer of energy also emerge from the new approach, generalizing previously presented ‘‘golden rules’’ for relating the spectral transfer time scale to the Alfven and eddy‐turnover time scales.