bluuebunny/crossref_metadata_2025 huggingface dataset:
Entropy correcting schemes and non‐hierarchical auto‐adaptive dynamic finite element‐type meshes: Applications to unsteady aerodynamics
Authors: Richter Roland , Leyland Pénélope
Published: August 2005

This paper discusses the different sources of non‐physical entropy production which occur in the numerical resolution of the Euler equations for compressible inviscid flow and proposes several ways of correcting these effects. In particular a hybrid corrected centred, augmented by an accurate upwind scheme near singular boundaries is proposed which satisfies the mathematical entropy condition, and which solves the flow accurately within regions near non‐smooth boundaries of the computational domain. A coupled new dynamic auto‐adaptive mesh algorithm which produces highly accurate solutions is also introduced. This algorithm is non‐hierarchical. i.e. it does not depend on a fixed background mesh, which allows structural and geometrical changes and generates extremely precise discretizations for steady and unsteady flow.
Lagrangian incompressible flow computations in three dimensions by use of space‐time finite elements
Authors: Hansbo Peter
Published: August 2005

In this paper we describe a space‐time finite element method, with elements aligned along the computed characteristics in space‐time, for the computation of incompressible free surface flows in three dimensions.
Hopf bifurcation in annular liquid jets with mass transfer
Authors: Ramos J. I.
Published: August 2005

A numerical study of Hopf bifuractions in annular liquid jets with mass transfer is presented. The study is based on the asymptotic equations which govern the dynamics of inviscid, incompressible, thin, annular liquid jets and on equilibrium conditions for mass transfer at the jet's inner and outer interfaces. It is shown that the amplitude of the time‐periodic motion that results from the Hopf bifurcation increases whereas its frequency decreases as the solubility ratio is increased.
An efficient numerical tank for non‐linear water waves, based on the multi‐subdomain approach with BEM
Authors: Wang Pei , Yao Yitao , Tulin Marshall P.
Published: August 2005

An efficient 2D non‐linear numerical wave tank called LONGTANK has been developed based on a multi‐subdomain (MSD) approach combined with the conventional boundary element method (BEM). The multi‐subdomain approach aims at optimized matrix diagonalization, thus minimizing the computing time and reserved storage. The CPU per time step in LONGTANK simulation is found to increase only linearly with the number of surface nodes, which makes LONGTANK highly efficient especially when simulating long‐time wave evolutions in space.

Appropriate treatment of special points on the boundary ensures high resolution in LONGTANK simulation beyond initial deformation and breaking, which allows detailed study of breaking criterion, breaker morphology, breaking dissipation, vorticity generation, etc.

Detailed numerical implementation has been given with demonstration of LONGTANK simulations.
A Bayesian approach to determining connectivity of the human brain
Authors: Patel Rajan S. , Bowman F. DuBois , Rilling James K.
Published: August 2005

Recent work regarding the analysis of brain imaging data has focused on examining functional and effective connectivity of the brain. We develop a novel descriptive and inferential method to analyze the connectivity of the human brain using functional MRI (fMRI). We assess the relationship between pairs of distinct brain regions by comparing expected joint and marginal probabilities of elevated activity of voxel pairs through a Bayesian paradigm, which allows for the incorporation of previously known anatomical and functional information. We define the relationship between two distinct brain regions by measures of functional connectivity and ascendancy. After assessing the relationship between all pairs of brain voxels, we are able to construct hierarchical functional networks from any given brain region and assess significant functional connectivity and ascendancy in these networks. We illustrate the use of our connectivity analysis using data from an fMRI study of social cooperation among women who played an iterated “Prisoner's Dilemma” game. Our analysis reveals a functional network that includes the amygdala, anterior insula cortex, and anterior cingulate cortex, and another network that includes the ventral striatum, orbitofrontal cortex, and anterior insula. Our method can be used to develop causal brain networks for use with structural equation modeling and dynamic causal models. Hum Brain Mapp, 2005. © 2005 Wiley‐Liss, Inc.
Hemispheric asymmetry of sulcus‐function correspondence: Quantization and developmental implications
Authors: Hasnain Mohammed K. , Fox Peter T. , Woldorff Marty G.
Published: August 2005

Spatial covariances between the geometric centers of human occipital sulci and visual functional areas were calculated to reduce the spatial variance of functional‐area locations between subjects. Seven visual areas in each occipital hemisphere were retinotopically mapped, using horizontal‐ and vertical‐meridian stimuli and 15O PET in 11 subjects. Sulcal locations were determined using anatomic brain models derived from high‐resolution MRI images. Location variability for sulci and functional areas was similar in magnitude, with average standard deviations of (2.7x, 5.3y, 5.7z) mm and (4.3x, 5.4y, 5.3z) mm, respectively. Sulcal locations were predictive of functional‐area locations (i.e., significant spatial covariance) in the minority of structure‐function pairings tested (25 of 168). Location variability was reduced by an average of 27% for functional areas showing significant covariation with sulcal features. Early‐developing sulci were stronger predictors of functional‐area location than late‐developing sulci. Sulcus‐function covariance was stronger in the left occipital lobe than in the right occipital lobe. Notably, the left calcarine fissure demonstrated powerful covariances with functional areas in both hemispheres, suggesting that it serves as a developmental “anchor” for functional areas in the occipital cortex. These findings support the hypothesis that hemispheric lateralization of function is reflected in the strength of correspondence between cortical surface anatomy and function. Hum Brain Mapp, 2005. © 2005 Wiley‐Liss, Inc.
Rat bone marrow stromal cell osteogenic differentiation and fibronectin adsorption on chitosan membranes: The effect of the degree of acetylation
Authors: Amaral I. F. , Lamghari M. , Sousa S. R. , Sampaio P. , Barbosa M. A.
Published: August 2005

Cell adhesion, migration, and proliferation of a few anchorage‐dependent cells cultured on chitosan (Ch) matrices are influenced by the degree of N‐acetylation (DA) of Ch. In the present work, we examined the influence of the DA on the attachment, spreading, proliferation, and osteogenic differentiation of rat bone marrow stromal cells (rBMSCs). Ch membranes were characterized in terms of surface morphology, roughness, and wettability, and in terms of adsorption of an adhesive protein, fibronectin (Fn). Chs with DAs in the range of 4 to 49% were used. Among the Ch samples, the DA of 4% led to the highest Fn surface concentration, both from single protein solution and from diluted serum. Furthermore, the levels of Fn adsorbed from serum found for this DA were threefold higher than for the tissue culture polystyrene control, indicating that in the presence of competitive proteins Ch is more specific toward Fn adsorption than tissue culture polystyrene. rBMSCs cultured on Ch carrying a DA of 4% were able to spread, proliferate, and differentiate, reaching a higher level of osteogenic differentiation than on the control, despite the lower cell attachment observed for all Ch samples. Because the Ch sample with a DA of 4% showed the highest Fn adsorption from serum, we suggest that cell adhesion, spreading, and osteogenic differentiation of rBMSCs on Ch may be mediated by the adsorbed layer of Fn. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005
Steroid hormone receptor signaling in tumorigenesis
Authors: Singh Rajesh R. , Kumar Rakesh
Published: August 2005

Excessive activation of the hormone signaling pathways is implicated in several disorders of the target tissues, with cancer being one of the most serious fallouts. Steroid hormone receptors are key proteins through which steroid hormones convey their signals to the cells. Deregulated activity of the hormone receptors due to their altered activation; stability or sub‐cellular localization is heavily implicated in the onset and progress of cancers. The role played by estrogen and its receptors in breast cancer remains the most thoroughly investigated steroid‐dependent cancer system till date. Choosing it as an example, we have summarized the molecular mechanisms underlying the action of the estrogen receptors (ERs) in manifesting the effects of the estrogens in the cells. A special emphasis is placed on the molecular mechanism of their functionality, role of the coactivator proteins, and the reasons for the deregulated signaling. The therapeutic approaches resulting from the mechanistic study of the ER action and their efficacies are also discussed. J. Cell. Biochem. 95: 490–505, 2005. © 2005 Wiley‐Liss, Inc.
Thermal modelling using ASTEC3 software
Authors: Poole N. J. , Sarvar F. , Witting P. A. , McKenzie W. H.
Published: August 2005

This paper describes the application of ASTEC3, a general purpose analogue electronic circuit simulation package, to the analysis of thermal properties of given structures. The modelling of each system is considered for both conduction and convection mechanisms, radiation being assumed to play a very minor role in heat dissipation from most electrical circuits. A procedure is given for the modelling of one‐, two‐ and three‐dimensional thermal problems which is then used for the simulation of relatively simple examples. The results obtained with ASTEC3 are compared with results determined by using more traditional and independent techniques.
A design method for partial‐response filters
Authors: Huber Klaus
Published: August 2005

A design method for filters having duobinary signal pulses as impulse response is presented.
A new time‐domain model for spontaneous emission in semiconductor lasers and its use in predicting their transient response
Authors: Lowery Arthur James
Published: August 2005

Spontaneous emission noise power, although small in magnitude, affects many aspects of the semiconductor laser's operation. An accurate model has been developed for it for use in the transmission‐line laser model (TLLM), which is a time‐domain, wideband, dynamic, non‐adiabatic semiconductor laser model. The effects of approximations used in other dynamic laser models are then investigated by comparison with the results from the TLLM. The study shows that the representation of this noise power has an important bearing on the damping of modelled transient oscillations.
Radio frequency simulation of a complex printed circuit board layout by the quasi‐static boundary element method
Authors: Milsom R. F. , Scott K. J.
Published: August 2005

A method for analysing the electrical effect of a set of conducting strips is presented. This method is applied to modelling the electrical behaviour of conducting tracks on a printed circuit board (PCB). Unlike most other published work, this analysis is not restricted to the case where the tracks are parallel. The problem is formulated in terms of an admittance matrix. A boundary element method incorporating image theory is used to produce a system of linear equations. These are solved to yield the required admittance matrix, which can then be incorporated into a standard circuit analysis package. Comparisons between measured and predicted circuit performance for a complex layout show close agreement up to at least 1 GHz.
A comparison of the dispersion characteristics associated with the TLM and FD‐TD methods
Authors: Choi Dennis H.
Published: August 2005

This paper presents the dispersion characteristics of the FD‐TD algorithm by showing the numerical phase and group velocities of the TEM, TE or TM modal solutions. For the TEM wave propagation, there exist three fundamental directions to which phase and group velocities can be expressed by only a single variable (wave numberkor frequency ω). Those special directions were chosen to show the dispersive nature of the FD‐TD algorithm of which the group and phase velocities depend explicitly on frequencies.

In view of similarities between the TLM and FD‐TD algorithms, a comparison of phase velocity characteristics of both methods was made. Under the special condition where the stability factorsis larger than 1/2, the FD‐TD algorithm is found less dispersive than that of the original TLM. However, newly developed symmetrical TLM method appears less dispersive than the FD‐TD algorithm.

In the numerical simulation of waveguide modal solutions, it was found that there exists an optimum frequency which provide least numerical error in the FD‐TD application. A procedure, which determines the stability factorsand the maximum allowed frequencyFmaxfor the best numerical results, is proposed in this paper.
Coupling between electromagnetic fields and multimode transmission systems using TLM
Authors: Naylor P. , Christopoulos C.
Published: August 2005

The coupling between incident electromagnetic fields and lossless, multimode, multiconductor, transmission systems is studied using transmission‐line modelling (TLM). Model predictions compared well with experimental multimode results. The model presented is suitable for studying electromagnetic compatibility problems in the time‐domain.
Concurrent processing: The key to rapid probabilistic potential methods
Authors: Fusco V. F.
Published: August 2005

This paper shows how probabilistic potential methods based on the Monte Carlo approach can be efficiently mapped onto an array of concurrent processors and how the resulting algorithm can provide rapid solutions of harmonic function problems. The method described here exploits the natural concurrency of the Monte Carlo approach. Computation is achieved by use of a low‐cost array of transputers linked to a PC‐AT. The resulting methodology is powerful and the ideas suggested should have application to many other modelling techniques used for field modelling.

A microstrip geometry is used as the discussion vehicle throughout this paper. This geometry was selected since it exhibits a number of the important topological features required in a general problem, e.g. Dirichlet boundary conditions and mixed dielectric. The design of the parallel algorithm used is discussed in detail, and typical results are given.
A computer program for waveguide analysis using high‐order, vector, finite elements
Authors: Webb J. P. , Forghani B.
Published: August 2005

A computer program has been written for the analysis and design of arbitrarily shaped waveguides, containing dielectric and magnetic materials. The program calculates the propagating modes of the waveguide by the three‐component vector finite element method. High accuracy is achieved by the use of high‐order elements, and by the inclusion of singular trial functions near sharp metal edges. An efficient algorithm based on the conjugate gradient method is used to solve the algebraic eigenvalue problem. Results are given for rib waveguide and fin‐line.
Combined fine–coarse mesh transmission‐line modelling method for diffusion problems
Authors: Ait‐Sadi R. , Lowery A. J. , Tuck B.
Published: August 2005

The paper presents a combined fine–coarse mesh TLM method. This technique reduces the memory storage and the computational time when modelling complex structures. In the combined fine–coarse mesh model, the region of interest is covered with a set of transmission‐line fine meshes. The remaining part is covered with regular (or irregular) coarse meshes. The fine‐mesh nodes are connected through busbars to the adjacent coarse‐mesh nodes. The combined fine–coarse mesh TLM technique is applied to some diffusion problems. Significant savings in computational time and memory storage are obtained without loss of accuracy.
Substructuring of space and time in TLM diffusion applications
Authors: Pulko S. H. , Halleron I. A. , Phizacklea C. P.
Published: August 2005

A simple method is described for spatial substructuring of meshes used in TLM diffusion routines in such a way as to enable discontinuous mesh lines to be used. A method of operating TLM diffusion routines using different timesteps in different spatial regions is also described. For both aspects, results are compared with those derived using standard TLM techniques.
Electromagnetic scattering from conductor‐coated material bodies
Authors: Analoui Morteza , Kagawa Yukio
Published: August 2005

A moment method solution is presented to compute electromagnetic scattering from material bodies. The bodies are supposed to be homogeneous, arbitrarily shaped and lossy; they can be coated with very thin perfect conductors in some parts. A formulation of the scattering problem is made in terms of the equivalent surface current densities for which mixed potentials are used. The equivalent currents are expanded in the space‐domain by a triangular expansion function on the triangulated surfaces of the scatterer. The Galerkin procedure is carried out to test boundary integral equations and reduce the functional form of the equations to a partitioned matrix equation. The solution is applied to the scattering problem of a dielectric slab, a thin conductor coated by absorber material and a rectangular patch on a grounded dielectric slab. The computed backscattering radar cross‐section and surface current densities of the structures are presented and some of the results are compared with experimental data.
Large signal periodic time‐domain simulation
Authors: Whight K. R. , Gough P. A. , Walker P.
Published: August 2005

A novel algorithm has been implemented within our new semiconductor device simulation program TESSA that allows large signal periodic time‐domain simulation to be performed by integrating over just one period of the excitation. Conventionally the need to integrate out initial transients, over many cycles, had effectively made such simulations impracticable. The algorithm can also be implemented in the field of circuit simulation so a combined large signal circuit/device simulation package is now a practical possibility.
Application of an efficient algorithm for solving the one‐band effective mass equation self‐consistently in the modelling of some low‐dimensional structure devices
Authors: Wilson Stephen P. , Allsopp Duncan W. E. , Morton Christopher G.
Published: August 2005

An efficient algorithm is presented for the self‐consistent numerical solution of the single‐band effective mass equation. This algorithm has a different form depending on whether the effective mass is modelled as continuous or piecewise continuous. Coupled with a Poisson solver, an established algorithm is applied for the attainment of self‐consistency. The rate of convergence to a self‐consistent solution is investigated, and the solvers are applied to three different structures to demonstrate its versatility and robustness. The first of these is a nominally undoped quantum well AlGaAs/GaAs heterostructure, the second a doubly δ‐doped GaAs homostructure and lastly a quasi‐square well modulation‐doped field effect transistor. The algorithm is of sufficient efficiency so as to allow the software to run reasonably quickly on a modern microcomputer.
Time‐domain numerical modelling of microwave non‐linear circuits
Authors: Dalle C. , Rolland P. A. , Friscourt M. R.
Published: August 2005

A numerical time‐domain modelling of non‐linear microwave circuits is presented. It is based on a numerical procedure allowing the solution of the integro‐differential equation driving the instantaneous electrical behaviour of a lumped‐element circuit while accounting for the semiconductor device by means of an accurate numerical macroscopic model. This modelling is firstly validated by studying the DC turn‐on and DC forward–reverse commutation of a PIN diode. The diode voltage and current waveform are qualitatively consistent with experimental ones, Moreover, the predicted recovery time values are found to be in good agreement with those issued from the classical analytical theory. Secondly, in order to illustrate the present capabilities of the model, the whole transient response of a back‐to‐back silicon PIN diode passive power limiter to a high‐input‐RF‐power pulse is described. It is demonstrated that in the present case of a 2 μm‐long PIN diode, the high‐input‐power steady‐state operation only relies on one diode. To our knowledge, it is the first time this kind of simulation is applied to a two‐diode circuit.
Transient response of lossy transmission lines with arbitrary loads
Authors: Wong Chi‐Chung , Chan Yick‐Fung
Published: August 2005

In this paper, the method of transmission‐line modelling is used to determine the transient response of a lossy transmission line. Non‐linearity and frequency‐dependent parameters (R and G) can be included without undue difficulty. Several numerical examples are described and are compared with exact and/or experimental results. In all cases good agreements are obtained.
Parallel implementation of cellular systems for numerical modelling
Authors: Thiele L.
Published: August 2005

There is an increasing interest in the numerical modelling of physical and biological processes using cellular automata or cellular systems. One of the main advantages in using the concept of cellular systems is the inherent high degree of parallelism. The purpose of the contribution is to formally relate two different areas: time‐domain modelling of physical processes using cellular systems and massive parallel implementations. At first, an overview of applications of cellular systems in computation theory and in modelling of physical systems and an overview of implementations of cellular systems is given. The subsequent sections address the following two questions: (1) Which class of algorithms can be interpreted as cellular systems. (2) Can cellular systems be efficiently simulated on a given parallel architecture. Results concerning these issues are presented.
Concurrent boundary element computation
Authors: McDowall D. S. , Lee T. W. , Fusco V. F.
Published: August 2005

A major limitation of the boundary element method (BEM) for the solution of electrical potential problems is the long computational time required. However, a large portion of the calculations involved can be viewed as being parallel in nature and can therefore be computed concurrently. This paper makes an effort to increase the efficiency of the BEM process using transputer‐based multiprocessor computing techniques. The algorithms developed may equally well be applied to any multiprocessor system. The application selected to demonstrate the technique is the solution of an electrostatic problem governed by a two‐dimensional Laplace equation.

A parallel algorithm for problem setup and field extraction using BEM is designed and implemented on a transputer array. Special attention is directed to the utilization of the parallel processors to achieve maximum efficiency. The analysis in this work concentrates on the communication strategies for passing data between processors as well as a consideration of the workload attributed to each processor.

The parallel algorithms were implemented using 3L Parallel Fortran; however, the choice of topology for the overall BEM implementation was limited by the fact that certain parts of the algorithm could only utilize a pipeline configuration of processors. Comprehensive results for the parallel BEM algorithm are given and they are encouraging, indicating that parallel processing has much to offer when applied to the boundary element method.
The efficiency of transmission‐line matrix modelling—a rigorous viewpoint
Authors: Enders Peter , De Cogan Donard
Published: August 2005

The difference equations of the scalar linear transmission‐line matrix (TLM) routine as introduced by Johns for numerically solving the diffusion equation are shown to be isomorphic to Goldstein's correlated random walk model of diffusion. For the infinite homogeneous bar their exact solution is derived algebraically and given in the form of Jacobi polynomials. This puts the TLM algorithm on a sounder mathematical and physical basis. The accuracy in solving the diffusion equation is investigated in general form and thus its astonishing efficiency explained. Several other basic questions of this numerical technique are also discussed.
Redundancy and its implications in TLM diffusion models
Authors: Pulko S. H. , Wilkinson A. J. , Gallagher M.
Published: August 2005

Redundancy in the simplest form of a two‐dimensional TLM network is identified and a method of eliminating it is described. Results obtained using the non‐redundant algorithm are compared with those derived from the standard, redundant algorithm. The non‐redundant approach is extended to deal with non‐uniform elemental capacitance; a cylindrical geometry is taken as an example of this. The scope for and benefits of rendering TLM diffusion models non‐redundant are discussed.
A non‐linear and distributed modelling procedure of fets
Authors: Ongareau Éaric , Bosisio Renato G. , Aubourg Michel , Obregon Juan J. , Gayral Michel
Published: August 2005

This paper describes a rigorous and systematic procedure to derive a non‐linear distributed FET model that can easily be implemented in CAD routines of simulators based on harmonic balance techniques. The new model is derived from a knowledge of the conventional linear lumped equivalent circuit, from non‐linear current sources extracted from pulsed measurements, and from the physical dimensions of the FET.

For fundamental and harmonic frequencies, the FET is modelled byNidentical cells. Each cell is made up of a non‐linear two‐port section inserted between two linear four‐port sections that simulate the coupling and the distributed effects along the electrodes of the FET in the width direction only. This non‐linear distributed scaling approach to FET modelling has been applied to the analysis of a submicrometre‐gate GaAs FET at millimetre‐wave frequencies, and the results were compared with the non‐linear lumped element approach. This approach can be applied to other transistors used in non‐linear regions at microwave and millimetre‐wave frequencies.
Electronic band structure for two‐dimensional periodic lattice quantum configurations by the finite element method
Authors: Ferrari R. L.
Published: August 2005

A finite element method formulation is given for solving Schrodinger's wave equation for a single electron in a crystal lattice cell subject to a known periodic potential. The formulation has been implemented for a two‐dimensional lattice, with an arbitrary potential profile, modelled by quadratic isoparametric elements, The FEM solver returns a specified number of electronic energy states, En, and nodal values of the complex wavefunctionψn Input data is generated by a standard FEM mesh generator. The postprocessing, given n, for reproducing a full 2‐D E‐k Brillouin diagram and given k, the electronic distribution, has been implemented. Tests on a 2‐D generalized Kronig‐Penney energy band model showed excellent agreement; between FEM results and analysis. The solver was further satisfactorily checked against published augmented plane wave calculations for a circular potential well within a square lattice. Specimen results are presented for the same circular well but with graded potential distributions and for a rectangular potential barrier set askew in a square lattice. Two‐dimensional energy band solvers have application to superlattice nanostruc‐ tures, whilst a general, full 3‐D FEM quantum solver seems feasible.
Analysis of a thin wire circular loop antenna
Authors: Yung Edward K. N. , Wong Roger S. K.
Published: August 2005

A rigorous technique for studying a thin wire circular loop antenna excited by a magnetic frill is developed. The exact kernel is derived and used to improve the accuracy. The scheme is applicable to small as well as large loops. Results obtained are nearly indistinguishable from those determined by the Fourier expansion method for non‐resonant loops. A disagreement of 2 per cent is generally observed when the loop is close to reasonant for βb> 2. Compared with the conventional numerical method where a loop is represented by a polygon of straight wires, the present scheme is much faster and more accurate. Extension of this method to cover an antenna system of arbitrarily oriented loops intermingled with straight wires can be easily achieved.
TLM treatments of changes of phase
Authors: Hurst A. I. , Pulko S. H.
Published: August 2005

The existing treatment of an instantaneous endothermic change of state is extended to deal both with exothermic effects and with first order Arrhenius changes. These extended treatments are used to model complex changes of phase occurring during the firing of ball clay and china clay, both of which are constitutents of the slip used in the production of vitreous china ware. The adequacy of the treatments is investigated for both clays by comparing a TLM simulation of a DSC (differential scanning calorimetry) experiment with measurements made during the experiment.
FDTD analysis of crosstalk in multilayer printed circuits
Authors: Cerri G. , De Leo R. , Primiani V Mariani , Schiavoni A.
Published: August 2005

A theoretical analysis has been developed to study the crosstalk in crossed bundles of parallel lines. The model is based on the theory of the coupled transmission lines and the resulting system of differential equations has been solved by means of the finite difference, time‐domain (FDTD) method. The frequency response of the network has been achieved by the discrete fourier transform (DFT) algorithm; measurements, performed with a vectorial network analyser, show a good agreement with numerical simulation.
Numerical drift‐diffusion simulation of Auger hot electron transport in Ingaasp/Inp double heterojunction laser diodes
Authors: Chai Kam‐Wing , Li Zhan‐Ming , McAlister Sean P. , Simmons John G.
Published: August 2005

This paper considers the adaptation of drift‐diffusion device simulation methodology to study Auger‐recombination‐induced hot electron transport characteristics in InGaAsP/InP double heterostructure laser diodes. In order to model the transport behaviour of the Auger hot electrons, we decompose the conventional electron current continuity equation into two components, with one for the Auger hot electrons and the other for the low‐energy electrons. These equations, which use the energy relaxation time parameter to model the dynamics of the Auger hot electrons, are then coupled with the hole current continuity equation and the Poisson equation to obtain self‐consistent solutions. Results from the case studies of one‐dimensional N‐p‐P InGaAsP/InP double heterojunction laser diodes with material composition corresponding to 1·3 μm and 1·55 μm wavelength emissions are presented. We have observed that hot electrons generated through Auger recombination inside the active region can spread into both the N‐ and the P‐InP cladding layers. Within the drift‐diffusion framework, it is demonstrated that the hot electron concentration in the N‐InP cladding layer can be five orders of magnitude higher than that in the P‐InP cladding layer. Because energy transport of the hot electrons in not modelled under the drift‐diffusion approximation, the simulated results are discussed to highlight some of the possible limitations in using drift‐diffusion physics to study Auger hot electron transport behaviour. The importance of taking energy transport into account is emphasized.
Calculation of scattering parameters by orthogonal expansion and finite integration method
Authors: Geib B. , Dohlus M. , Weiland T.
Published: August 2005

Field computations by mathematical and numerical methods are presented in the time and frequency domain. The techniques used are discretization and modal expansion. The effects of modelling and frequency range on the accuracy and calculation requirements are investigated and discussed. By way of application, several results of RF‐filter designs are presented, where these methods have been implemented in CAD programs.
Parallel implementation of a Monte Carlo particle simulation coupled to Maxwell's equations
Authors: Goodnick Stephen M. , Pennathur Shankar S. , Ranawake Udaya A. , Lenders Patrick M. , Tripathi Vijai K.
Published: August 2005

PMC‐3D, a parallel three‐dimensional (3‐D) Monte Carlo device simulator for multicomputers is discussed. The parallel algorithm is and extension of the standard Monte Carlo device simulation model in three dimensions, that combines the stockastic Monte Carlo particle simulation method with a solution of Poisson equation for quasi‐static problems, and full Maxwell's equations for microwave or electro‐optic phenomena. While our implementation of the Poisson solver is based on an iterative method that uses and odd/even ordering with Chebyshev acceleration, a simple leapfrog method based upon the computational unit of Yee cell is used in a finite‐difference, time‐domain (FDTD) formulation to solve Maxwell's equations.

The parallel algorithms were implemented on a 1024‐node distributed memory nCUBE multicomputer. In this work, we present the application of PMC‐3D to generate the static current‐Voltage characteristics of GaAs MESFET, and to simulate photogenerated femtosecond electrical transients produced in coplanar stripline on a GaAs substrate.
Modelling of high‐frequency multilayered interconnects using parallel processing techniques
Authors: Jatou F. , Van Deventer T. E.
Published: August 2005

This paper examines the use of parallel processing techniques for the electromagnetic field analysis of multilayered microwave interconnects. These techniques are applied to a full‐wave formulation using an integral equation approach in the frequency domain. In order to demonstrate the feasibility of parallelization and to assess its performance advantages, several variations of the computer code have been developed. Performance tests using domain partitioning and load balancing were conducted on a 32‐processor shared‐memory machine (KSR1).
Re‐working of two standard moment‐method codes for execution on parallel processors
Authors: Excell P. S. , Porter G. J. , Tang Y. K. , Yip K. W.
Published: August 2005

Two separate exercises on a similar theme are reported. In the first, the moment‐method program NEC was extensively modified in order to optimize its performance on a four‐processor Cray X‐MP computer. In the second exercise, the MININEC moment‐method program was completely rewritten into the occam programming language so that it could be executed directly by a transputer system. The NEC exercise exploited judicious use of vectorization and alternative parallelization techniques and achieved a reduction of run times by factors of about five or more. The MININEC exercise has so far achieved only a modest reduction in run‐time but it has the potential for a much greater improvement if an optimum strategy for configuring the transputer network is implemented.
A paraller planar generalized Yee algorithm for the analysis of microwave circuit devices
Authors: Gedney Stephen D. , Lansing Faiza
Published: August 2005

The planar generalized Yee (PGY) algorithm is an extension of the generalized Yee algorithm and the discrete surface integral (DSI) methods, which are based on explicit time‐marching solutions of Maxwell's equations. Specifically, the PGY algorithm exploits the planar symmetries of printed microwave circuit devices, achieving great savings in both CPU time and memory. Since the PGY algorithm is an explicit method, it has a high degree of parallelism. To this end, a highly scalable parallel algorithm based on a spatial decomposition of the general unstructured mesh is presented. Two spatial decompositions are compared, the recursive inertia partitioning (RIP) algorithm and the Greedy algorithm. The Greedy algorithm provides optimal load balance, whereas the RIP algorithm more effectively minimizes shared boundary interface lengths. Through numerical examples, It is demostrated that the Greedy algorithm provides superior speedups. It is also demonstrated that the parallel PGY algorithm is a highly scalable algorithm.
A comparison of the performance of the finite difference time‐domain, finite element time‐domain, and planar generalized Yee algorithms of high‐performance parallel computers
Authors: Gedney Stephen D. , Navsariwala Umesh
Published: August 2005

Parallel algorithms for the finite difference time‐domain (FDTD), the planar generalized Yee (PGY), and the finite element time‐domain (FETD) methods are presented. The FDTD and the PGY algorithms are both explicit time‐domain solutions of Maxwell's equations, while the PGY algorithm is based on an unstructured grid. The FETD algorithm is a semi‐implicit solution of Maxwell's equations using variational principles, and thus requires a matrix inversion for every time iteration. The three parallel algorithms are based on spatial decompositions of the discrete three‐dimensional problem spaces. A comparative analysis of the parallel algorithms is presented based on their memory and computational efficiency as well as their parallel efficiency.
The complex subspace iteration for the computation of eigenmodes in lossy cavities
Authors: Schmitt D. , Schuhmann R. , Weiland T.
Published: August 2005

A typical application of numerical frequency‐domain computations is the calculation of electromagnetic fields in cavities. Not only the field vectors of the desired modes, but also parameters such as the resonance frequency and, in the lossy case, the damping coefficient and the quality factor of the cavity can be obtained. This problem leads to an analytical eigenvalue equation, which can be transformed in an algebraic, complex, linear eigenvalue problem by the finite integration method.

The consideration of energy losses in materials is straighforward in the analytical theory, using complex material quantities, but it is still a difficult subject area to solve a complex algebraic eigenvalue problem. Generally problems with very large, complex matrices (dimension >100,000) have to be solved, and no commonly applicable algorithm is known so far.

This paper deals with a special variant of subspace iteration with polynomial acceleration, and some problems of the application of the complex Chebyshev polynomials are discussed. Two examples with weakly lossy cavities demonstrate the capability of the new algorithm, which is successfully applied to very large problems of up to 490, 000 real unknowns.
An effective optimization method for the design of broadband microwave absorbers
Authors: Ponnekanti S. , Al‐Khaled F. S. H. , Sali S.
Published: August 2005

A novel procedure for synthesizing multilayered radar absorbing materials (RAMs) is presented. The procedure uses a method for global minimization of multimodal functions of continuous variables based on simulated annealing (SA). The technique is very flexible and reliable, allowing the design of absorbing materials for any grazing or normal angles over the specified frequency bandwidth. The technique is particularly suitable for the efficient design of broadband RAMs and hence for EMC applications.
Effect of Macromolecular Crowding on the Conformation of Confined Chain Polymers
Authors: Martínez‐Haya Bruno , Gordillo M. C.
Published: August 2005

Summary: The conformational behavior of flexible linear chain polymers confined in cylindrical pores and slab pores has been studied, employing a hard‐bead chain model and a modification of a recently proposed recoil‐growth bias Monte Carlo methodology, which improves the sampling efficiency in confined environments. It is found that the scaling law that correlates the unconstrained component of the radius of gyration of the polymer with the pore diameter in cylindrical pores is close but neatly different than the de Gennes mean‐field value. The results also indicate that the addition of spherical particles with sizes within the protein limit may be employed to tune the folding of the confined polymer, since in this case the depletion constraints work against the effective stretching forces induced by confinement. Remarkably, the presence of the depleting particles at sufficiently high concentration leads to appreciable changes in the exponents of the conformational scaling laws with respect to the uncrowded system.

Conformational behavior of flexible hard‐bead chain polymers confined in narrow pores.

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Conformational behavior of flexible hard‐bead chain polymers confined in narrow pores.
On Modelling Surface Directed Spinodal Decomposition
Authors: Henderson Ian C. , Clarke Nigel
Published: August 2005

Summary: Cahn‐Hilliard theory for symmetric binary polymer mixtures is used to study the influence of a surface which is attractive to one component of the polymer blend. We revisit modelling approaches to the dynamics of a polymer blend at or near a surface to show that quantitative agreement with previous models is only possible if a number of issues are resolved. We address the issue of how the numerical length scales chosen during the simulation affect the accuracy of the magnitude of surface segregation when a blend is undergoing spinodal decomposition. Finally we investigate whether equilibration has any effect on the morphology of the blend at the surface or in the bulk after a quench into the two‐phase region has occurred.

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Medicine‐taking behavior: Implications of suboptimal compliance in Parkinson's disease
Authors: Grosset Katherine A. , Reid John L. , Grosset Donald G.
Published: August 2005

Management of Parkinson's disease (PD) depends primarily on oral medication. There are several drug classes and multiple doses and formulations, which make optimizing therapy complex. Variable drug absorption and the short half‐life of most antiparkinson treatments, especially levodopa, are a main focus in understanding complications and have encouraged alternative delivery systems to limit fluctuation and dyskinesia at later stages. Comparatively little attention is paid to the way patients take their oral medication. Variable medicine‐taking behavior can affect the clinician's understanding of the diagnosis and rate of progression, and further prescription of PD medication. Medicine overuse in later stage PD is well documented and causes psychiatric disturbance and increases motor complications, but evidence of undertreatment and erratic intake is emerging, which is likely to affect motor control and quality of life adversely. Methods of quantifying compliance are compared for accuracy and limitations. Understanding medicine‐taking behavior is a first step in optimizing therapy and requires consideration of a patient's personal beliefs about their medicines. Although the benefits of regularizing oral medicine‐taking in a practical, achievable way in PD remain untested, such an approach might prolong and smooth the benefits of oral medication and is worthy of further research. © 2005 Movement Disorder Society
Existence of solutions for a mathematical model of structural phase transitions in shape memory alloys
Authors: Niezgódka Marek , Sprekels Jürgen
Published: August 2005

In this paper a thermomechanical model for the dynamics of structural phase transitions in the so‐called ‘shape memory alloys’ is developed. These materials exhibit rather spectacular hysteresis phenomena. The resulting mathematical model consists of a coupled and highly non‐linear system of partial differential equations reflecting the balance laws of linear momentum and energy. For an appropriate weak formulation the local‐in‐time existence of weak solutions is shown.
On a thermal stress problem for contacting half‐spaces with inclusions of other material involving a new method for computing potentials and singular integrals
Authors: Jentsch Lothar
Published: August 2005

This paper deals with a thermal stress problem for contacting half‐spaces of different materials having an inclusion of other material. With the aid of the contact tensor of two half spaces the problem is reduced to singular integral equations. Some new theorems on potentials with the contact tensor are used. Finally, a potential of the double layer with the contact tensor in the kernel and a singular integral operator, being the direct value of the potential, are calculated. For this a Kupradze method is applied, interpreting this potential as a solution of a contact problem of elastostatics. Some numerical experiments are communicated.
Explicit formula for scalar non‐linear conservation laws with boundary condition
Authors: Le Floch Philippe
Published: August 2005

We prove an uniqueness and existence theorem for the entropy weak solution of non‐linear hyperbolic conservation laws of the form

, with initial data and boundary condition. The scalar function u = u(x, t), x > 0, t > 0, is the unknown; the function f = f(u) is assumed to be strictly convex. We also study the weighted Burgers' equation: α ϵ ℝ

.

We give an explicit formula, which generalizes a result of Lax. In particular, a free boundary problem for the flux f(u(.,.)) at the boundary is solved by introducing a variational inequality. The uniqueness result is obtained by extending a semigroup property due to Keyfitz.
A mathematical study of a continuum‐state cross‐bridge model of muscle contraction
Authors: Comincioli V. , Torelli A.
Published: August 2005

In the framework of the sliding‐filament theory of muscle contraction, we develop a model which describes physioiogical cross‐bridge activity with a continuum of states, from those which are detached and refractory to those which are attached. The latter are kinetically more important.

An analytical study of the non‐linear partial differential equations of the mathematical model shows existence and uniqueness of the solution.
On non‐stationary Navier‐Stokes flows with vanishing viscosity associated with a variational inequality
Authors: An Ton Bui
Published: August 2005

Let
equation image
g is a positive increasing function with 1⩽g(0). The existence of a unique solution of the Navier‐Stokes flow associated with Kε,γ and the convergence of the solution to that of the Euler equations as the viscosity goes to zero are established.
Inversion of the exponential X‐ray transform. I: Analysis
Authors: Hazou Irene A. , Solmon Donald C.
Published: August 2005

The exponential X‐ray transform arises in single photon emission computed tomography and is defined on functions on ℝn by magnified image, where μ is a constant. Approximate inversion, and inversion formulae of filtered back‐projection type are derived for this operator in all dimensions. In particular, explicit formulae are given for convolution kernels (filters) K corresponding to a general point spread function E that can be used to invert the exponential X‐ray transform via a filtered back‐projection algorithm. The results extend and refine work of Tretiak and Metz17.
Injection of ideal fluid from two slots into a stream
Authors: Stojanovic Srdjan
Published: August 2005

A cold gas is injected from two slots into a stream of hot gas. In a simple model this leads to a three‐phase two‐free‐boundary problem. We prove, using the variational theory of Alt, Caffarelli and Friedman, the existence of the classical solution.
Inequalities related to stationary flows of granulated media
Authors: Łukaszewicz Grzegorz , Piskorek A.
Published: August 2005

We investigate some variational inequalities associated with the equations of the stationary motion of granulated media with a constant density. These inequalities replace the usual equations of motion in the case when some additional constraints are imposed on the flow.

We prove the existence of solutions of the inequalities, study their regularity, uniqueness, dependence on data and relations to solutions of the equations of motion.