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Wave Phenomena (wave + phenomenon)
Selected AbstractsBoundary Perturbation Methods for Water WavesGAMM - MITTEILUNGEN, Issue 1 2007David P. Nicholls Abstract The most successful equations for the modeling of ocean wave phenomena are the free,surface Euler equations. Their solutions accurately approximate a wide range of physical problems from open,ocean transport of pollutants, to the forces exerted upon oil platforms by rogue waves, to shoaling and breaking of waves in nearshore regions. These equations provide numerous challenges for theoreticians and practitioners alike as they couple the difficulties of a free boundary problem with the subtle balancing of nonlinearity and dispersion in the absence of dissipation. In this paper we give an overview of, what we term, "Boundary Perturbation" methods for the analysis and numerical simulation of this "water wave problem". Due to our own research interests this review is focused upon the numerical simulation of traveling water waves, however, the extensive literature on the initial value problem and additional theoretical developments are also briefly discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A one-way wave equation for modelling seismic waveform variations due to elastic heterogeneityGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2005D. A. Angus SUMMARY The application of a new one-way narrow-angle elastic wave equation to isotropic heterogeneous media is described. This narrow-angle finite-difference propagator should provide an efficient and accurate method of simulating primary body wave(s) passing through smoothly varying heterogeneous media. Although computationally slower than ray theory, the narrow-angle propagator can model frequency-dependent forward diffraction and scattering as well as the averaging effects due to smooth variations in medium parameters that vary on the sub-Fresnel zone level. Example waveforms are presented for the propagation of body waves in deterministic as well as stochastic heterogeneous 3-D Earth models. Extrapolation within deterministic media will highlight various familiar wave-diffraction and pulse-distortion effects associated with large-scale inhomogeneities, such as geometrical spreading, wavefront folding and creeping-wave diffraction by a compact object. Simulation within stochastic media will examine the effects of varying the correlation lengths of random heterogeneities on wave propagation. In particular, wave phenomena such as frequency-dependent forward scattering, the appearance of random caustics and the generation of seismic coda will be shown. [source] The network behind spatio-temporal patterns: building low-complexity retinal models in CNN based on morphology, pharmacology and physiologyINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 2 2001Csaba Rekeczky Abstract In this paper, a vertebrate retina model is described based on a cellular neural network (CNN) architecture. Though largely built on the experience of previous studies, the CNN computational framework is considerably simplified: first-order RC cells are used with space-invariant nearest-neighbour interactions only. All non-linear synaptic connections are monotonic continuous functions of the pre-synaptic voltage. Time delays in the interactions are continuous represented by additional first-order cells. The modelling approach is neuromorphic in its spirit relying on both morphological and pharmacological information. However, the primary motivation lies in fitting the spatio-temporal output of the model to the data recorded from biological cells (tiger salamander). In order to meet a low-complexity (VLSI) implementation framework some structural simplifications have been made. Large-neighbourhood interaction (neurons with large processes), furthermore inter-layer signal propagation are modelled through diffusion and wave phenomena. This work presents novel CNN models for the outer and some partial models for the inner (light adapted) retina. It describes an approach that focuses on efficient parameter tuning and also makes it possible to discuss adaptation, sensitivity and robustness issues on retinal ,image processing' from an engineering point of view. Copyright © 2001 John Wiley & Sons, Ltd. [source] Transmission through and wave guidance on metal plates perforated by periodic arrays of through-holes of subwavelength coaxial cross-sectionMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2007Vitaliy Lomakin Abstract Perfect electrically conducting (PEC) plates perforated by doubly periodic arrays of through-holes of subwavelength coaxial cross-section permit enhanced transmission of plane waves and support surface wave guidance. The transmission enhancement is attributed to coupling of free-space fields to TEM and TE11 modal fields in holes and occurs via two distinct mechanisms. The first couples incident fields to local resonances (cavity modes) supported by individual holes. The second couples scattered fields (diffraction modes) to global resonances (surface waves). The surface waves arise due to strong interactions between the holes and can have a large propagation wavenumber. The presented PEC model is adequate in the microwave and terahertz regimes and insights into related wave phenomena at optical frequencies.© 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1554,1558, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22484 [source] | ||||||||||