bluuebunny/crossref_metadata_2025_split huggingface dataset:
A space‐domain preconditioned spectral method for non‐linear boundary value problems
Authors: Axelrad V. 
Published: August 2005

AbstractA novel spectral procedure for the numerical solution of non‐linear boundary value problems is presented. The discrete spectral equations are solved by an iterative algorithm using space‐domain preconditioning. The preconditioning operator is obtained by spatial weighting (or windowing) of the exact differential operator.Convergence behaviour of the iterative solution is investigated using an eigenvalue analysis. Theoretical estimates for the convergence rate and accuracy are compared with that achieved in a numerical application—a non‐linear boundary value problem from semiconductor device modelling.The method combines the infinite‐order exponential accuracy of spectral discretizations with the sparse structure of finite difference equations. This offers numerical advantages in comparison to previously developed Fourier–Galerkin algorithms, particularly important for physically ill‐conditioned and strongly non‐linear problems. The tradeoff of achievable accuracy versus computer time is easily controlled, thus making essential speed‐ups possible for moderate accuracy requirements.
Discrete modelling of transport processes in two spatial dimensions
Authors: Enders Peter , de Cogan Donard 
Published: August 2005

AbstractA random flight model of linear transport processes in two spatial dimensions is considered and solved exactly in closed algebraic form. Its one‐dimensional version had been proposed by Taitel as a means to overcome the paradox of infinite speed of propagation within classical heat diffusion theory. The connection with hyperbolic diffusion theory is complemented here by deriving the discrete fluxes and their relaxation term. Moreover, such an approach circumvents the discretization of a continuum model for an intrinsically discrete process, when diffusion processes are to be solved numerically. Finite samples are treated by means of the reflection method. Some applications of these general results are mentioned.
An error parameter in TLM diffusion modelling
Authors: Gui Xiang , Webb Paul W. , de Cogan Donard 
Published: August 2005

AbstractThis paper reports the results of a study of an error parameter, m, which has been proposed as a measure for determining the effects on accuracy of the basic assumptions upon which TLM modelling of diffusion and heat flow has been founded. The nature of the m parameter is studied in detail by using a two‐dimensional thermal diffusion problem. The use of m in the implementation of automatic timestepping is discussed in a practical three‐dimensional engineering problem.
Finite difference time‐domain simulation of electromagnetic fields and microwave circuits
Authors: Wolff Ingo 
Published: August 2005

AbstractAn overview is given on the application of finite difference time‐domain analysis techniques to the simulation of electromagnetic wave phenomena and the design of planar microwave integrated circuits. In particular the application to the analysis of three‐dimensional discontinuities in coplanar microwave circuits is described and numerical and experimental results are presented. Finally the design of planar microwave circuits containing non‐linear active components using the finite difference time‐domain method in combination with a harmonic balance technique is demonstrated using an example of a LUFET circuit.
Multidimensional wave digital filters for discrete‐time modelling of Maxwell's equations
Authors: Fettweis Alfred 
Published: August 2005

AbstractAn approach for numerically integrating the partial differential equations describing passive physical systems consists in modelling the continuous‐domain physical system by means of a passive discrete‐domain system. As has recently been shown, this can be achieved, in particular also for Maxwell's equations, by means of the same principles as known from multidimensional wave digital filters, which offers a number of important advantages. The present paper deals specifically with the application of the approach to Maxwell's equations and supplements corresponding results previously published.
Body fitted grid generation with moving boundary and its application for dielectric waveguides
Authors: Kuroda Shigeaki , Kuroda Michiko 
Published: August 2005

AbstractThe stress birefringence and mode coupling effects in polarization‐preserving fibres are most important problems which need to be improved. For a realization of some optical devices, the dielectric waveguide with sinusoidally varying circular cross‐section has been investigated. It becomes very important to analyse the electromagnetic field distribution in a dielectric waveguide with a time‐dependent moving boundary. This paper shows that numerical methods can simulate the effect of the external disturbance on the dielectric waveguide from time to time. The author has discussed body fitted grid generation with moving boundary for the Poisson and Laplace equations.1,2 We have extended this technique for Maxwell's equation. The technique employs a kind of an expanded numerical grid generation. As the author adds the time component to grid generation, the time dependent co‐ordinate system which coincides with a contour of moving boundary can be transformed into a fixed rectangular co‐ordinate system. We could show the electric distribution in the waveguide time by time to verify the possibility of an application for an optical fibre. This technique makes it possible not only to analyse the effect of the external disturbance in a coherent optical communication system but also to fabricate optical devices.
An E‐plane sectoral horn fitted with side‐lobe suppression devices
Authors: Ata O. W. , Benson T. M. , Marincic A. 
Published: August 2005

AbstractA finite difference method is used to design a new type of sectoral horn antenna with corner channel inserts which produces a tapered aperture amplitude distribution in the E‐plane. The channel inserts, which present a simple modification to the horn aperture geometry, act as effective side‐lobe suppression devices. The efficiency of the suppression technique was successfully tested on an experimental horn whose performance is compared to that of a horn with similar geometrical dimensions but with no channel sections.
A comparative study of two TLM networks for the modelling of diffusion processes
Authors: Gui Xiang , Webb Paul W. 
Published: August 2005

AbstractA comparative study of two alternative networks for TLM modelling of diffusion processes has been undertaken. Some of their inherent advantages and disadvantages are analysed according to the ratio between the impedance of the lossless transmission lines and the lumped resistance. Their relative accuracy and utility in controlling the timestep automatically are examined.
An extended frequency‐domain prony's method for transfer function parameter estimation
Authors: Chakrabarti Swapan , Demarest Kenneth R. , Miller Edmund K. 
Published: August 2005

AbstractThe estimation of transfer‐function parameters, such as poles and zeros, is useful for characterizing and identifying electromagnetic scatterers. The conventional frequency‐domain Prony's technique can estimate these parameters from sampled, frequency‐domain data. However, it fails to estimate the true parameters when the sampled data contains contributions from out‐of‐band poles. In this paper, an extended frequency‐domain Prony's technique is developed that circumvents this problem by adding polynomial terms to the standard, Prony pole series. This new technique is shown to be very effective for estimating the poles of transfer functions over very wide bandwidths, without the need for large numbers of simultaneous equations, even when the data are corrupted by noise.
Finite deffernce time‐domain approximation of Maxwell's equations with non‐orthogonal condensed TLM mesh
Authors: Hein Steffen 
Published: August 2005

AbstractA convex hexahedral TLM mesh of arbitrary shape is presented and the transmission‐line matrix method extended to any non‐orthogonal configuration. The novel mesh constitutes a natural generalization of Johns' condensed node. The associated TLM process is analysed and reconstructed as a genuine finite difference time‐domain algorithm. Nodal S‐parameters are derived from discretized Maxwell's equations and canonical stability criteria yield the TLM timestep. Unitarity is discussed and energy conservation confirmed in the non‐conductive case.A given block‐diagonal representation of the S‐matrix restrains processing time per node and iteration within the range of traditional methods. The shortcomings of the rigid classical grid, as the need for inaccurate staircasing approximations, are, however, ruled out.Our analysis takes advantage of the recently developed propagator integral approach.
Transverse tranśmission theory for multilayer planar microwave circuits
Authors: Wu Ke , Tong Cheuk‐Yu Edward , Saguet Pierre 
Published: August 2005

AbstractTransverse transmission concepts in the Fourier transmission domain for multilayer planar transmission medium are presented. This complete transverse transmission theory (TTT) is found to be a superset of different Fourier‐transform‐based numerical techniques widely used in guided wave analysis, namely the modematching method and the spectral‐domain approach. The features of the theory are: the expansion of field quantities in longitudinal section (LSE/LSM) modes, the concept of rotation of the transverse field vectors, and a comprehnsive algorithm using recursive matrix standard form. It is shown that the mode‐matching method and spectral‐domain approach are generally equivalent except for the last step of imposing the final boundary conditions, and can therefore be summarized in a unified theory within the framework of TTT. In addition, a new parameter, the polarization coefficient, has been introduced to describe the field polarization of the guided wave in a quantitative manner. It is believed that the present theory will help us to gain more insight into hybrid mode propagation in multilayer planar circuits.
Symbolic approach to inverse problems in method of moments
Authors: Analoui Morteza , Fujimoto Masayoshi , Kagawa Yukio 
Published: August 2005

AbstractSymbolic computational systems introduce some unique features in computational engineering. There have been several papers published on the solution of differential equations under given boundary conditions by symbolic systems. The finite element formalism has received prime attention in the course of development of symbolic computation in engineering. The main idea has been to develop a symbolic FEM package to reduce the burden of manual algebra, eliminate errors introduced by numerical quadrature, and improve the efficiency of element generation.This work discusses a symbolic solution to electromagnetic linear antenna problems. The solution is a method of moments that transforms Pocklington's integral equation to a matrix equation. The symbolic system is used to produce (1) analytical integration, (2) the parametric expression for the input impedance and (3) computational code for forward and reverse problem of the input impedance.
Discrete Green's functions and hybrid modelling of thermal and particle diffusion
Authors: De Cogan D. , Enders P. 
Published: August 2005

AbstractThis paper provides details of a widely applicable technique of hybrid modelling of thermal and particle diffusion which can help to reduce computational load in explicit formulation. The undesirable effects of artificial boundaries, which are introduced when a simulation is truncated or when an expanding mesh is used, can be eliminated by the use of discrete Green's functions. The technique can also be applied to problems involving infinite or near‐infinite domains or problems where a complex thermal region is embedded within a larger, more simply described domain.
A Laplace domain finite element method (LDFEM) applied to diffusion and propagation problems in electrical engineering
Authors: Cai X.‐D. , Costache G. I. 
Published: August 2005

AbstractThis paper presents a new finite element formulation in the Laplace domain for both diffusion and wave equations with applications in the field of electrical engineering. With the aid of congruence transformation of matrices, the finite element equations in the Laplace domain are solved and time‐domain results can be obtained through the inverse Laplace transform. In a test problem, good agreement between the numerical results derived with the present method and the analytical solutions has been found. For applications in which only Dirichlet and Neumann boundary conditions are involved, this new finite element approach can be applied and provide both frequency‐domain and time‐domain results in one run without any timestepping scheme. The limitations of using the congruence transformation in solving propagation problems are also addressed in this paper.
Numerical analysis of discontinuities in a rectangular waveguide loaded with isotropic or anisotropic obstacles by means of the coupled‐mode method and the mode‐matching method
Authors: Solano Miguel A. , Vegas Angel , Prieto Andreés 
Published: August 2005

AbstractA hybrid method obtained as a combination of the coupled‐mode method (CMM) and the mode‐matching method (MMM) is developed and applied in the analysis of multiple dielectric and magnetic discontinuities in rectangular waveguides. As both are moment methods, some kind of truncation has to be carried out in the computer implementation. It is shown that selection of a different number of modes in the two methods is not necessary, unless low‐permittivity meida inside the waveguide are considered. As a consequence, the procedure for slecting the number of basis functions is only done in one of the methods. Numerical examples are presented showing the behaviour of the method and the proofs of convergence. Examples are included illustrating the power of this hybrid technique, especially in relation to non‐reciprocal structures containing magnetized ferrites.
Use of the two‐dimensional TLM method in the electromagnetic simulation of thin semiconductor samples
Authors: Dindo Salam F. , Ney Michel M. , Harrison Robert G. 
Published: August 2005

AbstractA two‐dimensional lossy shunt TLM node is incorporated into a TLM system and adapted to model for the first time the Maxwell field equations in thin semiconductor samples. Both the characteristics of the node and the TLM system itself are fully described. By considering a parallel‐plate structure containing a thin GaAs sample, driven by a voltage source, it is shown, with an example, that this TLM technique can simulate the response of non‐stationary electromagnetic fields in a semiconductor to applied excitations.
A survey of various computer architectures for solution of large matrix equations
Authors: Swaminathan Madhavan , Sarkar Tapan K. 
Published: August 2005

AbstractIn electromagnetics, a numerical technique that finds immense application is the method of moments. This method reduces the boundary value problem containing integro‐differential equations into the form AX = Y, where A is a full complex matrix, that is known and X is the unknown to be solved for the given excitation Y. In this paper, the matrix equation has been solved on various computers such as the VAX 3500, VAX 8530, Multimax 320, Alliant FX/80 and IBM 3090‐600E. Two of the established methods, viz. gaussian elimination and the conjugate gradient method have been used to solve the above matrix equations. A detailed timing analysis has been done to bring out the features of various computer architectures.
Parallel and distributed TLM computation with singal processing for electromagnetic field modelling
Authors: So P. P. M. , Eswarappa C. , Hoefer W. J. R. 
Published: August 2005

AbstractThis paper describes the implementation of transmission‐line matirix (TLM) method algorithms on a massively parallel computer (DECmpp 12000), the technique of distributed computing in the UNIX environment, and the combination of TLM analysis with Prony's method as well as with autoregressive moving average (ARMA) digital signal processing for electromagnetic field modelling. By combining these advanced computation techniques, typical electromagnetic field modelling of microwave structures by TLM analysis can be accelerated by a few orders of magnitude.
A connection machine (CM‐2) implementation of a three‐dimensional parallel finite difference time‐domain code for electromagnetic field simulation
Authors: Davidson David B. , Ziolkowski Richard W. 
Published: August 2005

AbstractThis paper describes a parallel three‐dimensional finite difference time‐domain (FDTD) code for electromagnetic field simulation that has been developed for the Connection Machine (CM‐2). The CM‐2 is briefly discussed. Then the FDTD method is reviewed using a one‐dimensional example, and the extensions required for the 3‐D case are outlined. The parallelization of the FDTD method is considered, and a simple analytical timing model is dervied. This model predicts the efficiency of the parallelized algorithm as a function of grain size. Some specific points relating to the implementation of the parallel FDTD algorithm in Fortrans‐90 on the CM‐2 are discussed. Timing data for the parallel 3‐D FDTD code measured on a CM‐2 is presented and compared qualitatively with the theoretical model. These results are then put into perspective for a particular computations electromagnetics problem, viz. the development of software tools for full‐wave modelling of 3‐D optical devices. Finally, we draw some conclusions about this work.
Parallel FDTD simulator for MIMD computers
Authors: Effing U. , Kümpel W. , Wolff I. 
Published: August 2005

AbstractA parallel implementation of the finite difference time‐domain algorithm for the analysis of planar microwave circuits is presented in this paper. For this the FDTD mesh is divided in equal‐sized subspaces. Every processor of the parallel computer calculates the field in one subspace. Furthermore detailed efficiency investigations are made to predict the timing performance of the parallel FDTD simulator.
A distributed implementation of the finite difference time‐domain (FDTD) method
Authors: Rodohan D. P. , Saunders S. R. , Glover R. J. 
Published: August 2005

AbstractThe finite difference time‐domain (FDTD) method is a well known numerical technique that has been used to solve electromagnetic boundary value problems. However, the method requires large computational resources to solve a problem, restricting its use on sequential computers to small problems.This has led to the use of expensive supercomputers in the past to solve larger problems. In this paper we first discuss existing parallel implementations of the FDTD method. We then describe an approach to compute the FDTD equations based on distributed‐ memory computer architectures. Finally we evaluate a low‐cost parallel implementation of the FDTD method that runs on a network of Workstations, utilizing spare network capacity.
Structural Analysis of Lignin by Resonance Raman Spectroscopy
Authors: Barsberg Søren , Matousek Pavel , Towrie Mike 
Published: August 2005

AbstractSummary: Resonance Raman (RR) spectroscopy, combined with Kerr gated fluorescence rejection in the time domain, has recently elucidated lignin structure with unique sensitivity and selectivity. This promises structural studies of fluorescent natural macromolecules, such as lignin, which were previously not possible. Such studies rely on an improved understanding of the RR spectral behavior of lignin, which is today scarcely understood. We explain for the first time this behavior by a semi‐empirical theory, and observe its pertinent features for lignin in vascular plants. We have used well‐defined oxidative treatments as means of probing lignin structural elements, and show that RR sensitivity and selectivity depend crucially on excitation wavelength. Through the theory we relate these results to basic structural aspects of lignin. Spectra obtained by blue light laser excitation (400 nm) are dominated by low redox potential syringyl lignin groups, whereas lower photon energy (500 nm) decreases the selectivity markedly. RR bands depend on molecular structure but also on molecular environment. Thus charge transfer donor‐acceptor interactions within lignin reduce the intensity of bands associated with electron rich moieties. New possibilities for basic and selective structural information on fluorescent natural materials, such as lignin, have thus appeared.Raman scattering in relation to typical electronic state energies of lignin structures.magnified imageRaman scattering in relation to typical electronic state energies of lignin structures.
Terminal and Penultimate Reactivity Ratios in Single‐Site Ethene/Propene Copolymerizations: Comparison of Kakugo and Direct Peak Methods
Authors: Karssenberg Frederik G. , Wang Bing , Friederichs Nic , Mathot Vincent B. F. 
Published: August 2005

AbstractSummary: The original, first‐order Kakugo method is extended to find second‐order reactivity ratios of homogeneous catalysts in ethene/propene copolymerizations based on triad fractions. Subsequently, the first‐ and second‐order reactivity ratios of eight Si‐bridged C2‐symmetric ansa‐zirconocenes or hafnocenes, as obtained by the Direct Peak method, are used to compare with the Kakugo methods. From the results it is clear that the second‐order methods give better descriptions than the first‐order methods. Only the results of the second‐order Direct Peak method are statistically justified, reflecting reliabilities >99.5%. Though the Direct Peak method in all cases gives the most reliable reactivity ratios, the second‐order Kakugo method turns out to be a practical tool to find estimates.Second‐order Kakugo method.imageSecond‐order Kakugo method.
Modeling of Shape Memory Induction and Recovery in Heat‐Shrinkable Polymers
Authors: Morshedian Jalil , Khonakdar Hossein A. , Rasouli Sorour 
Published: August 2005

AbstractSummary: A mechanical model was developed to describe qualitatively and quantitatively the stress‐strain‐time behavior of a prepared shape memory crosslinked polyethylene during hot stretching, stress relaxation under 200% strain at high temperature and strain recovery of the heat shrinkable polymer. The stress‐strain, the stress relaxation and the irrecoverable strain behavior of the model were established by driving the constitutive equation, which could qualitatively represent the behavior of the real material. By choosing significant values for the parameters of the proposed model, an excellent fit was obtained between the experimental behavior of the polymer and that predicted by the model. It was also revealed that the main source responsible for the imperfect recovery of the induced strain observed was the stress relaxation occurring during the stretch holding‐cooling time step.Stress relaxation of crosslinked polyethylene under 200% strain at 160 °C.magnified imageStress relaxation of crosslinked polyethylene under 200% strain at 160 °C.
Very late‐onset Friedreich's ataxia with minimal GAA1 expansion mimicking multiple system atrophy of cerebellar type
Authors: Berciano José , Infante Jon , García Antonio , Polo José Miguel , Volpini Victor , Combarros Onofre 
Published: August 2005

AbstractVery late‐onset Friedreich's ataxia (VLOFA) is characterized by symptomatic onset after 40 years of age and, usually, a benign phenotype. We describe a sporadic case with onset at 53 years of age and a novel VLOFA phenotype mimicking multiple system atrophy (MSA) of cerebellar type associated with minimal GAA1 expansion. We detected several atypical features for a diagnosis of MSA, which should alert to the possibility of an inherited ataxia. © 2005 Movement Disorder Society