bluuebunny/crossref_metadata_2025 huggingface dataset:
A multiplex PCR method for the detection of all five individual genes of ica locus in Staphylococcus epidermidis. A survey on 400 clinical isolates from prosthesis‐associated infections
Authors: Arciola Carla Renata , Gamberini Simonetta , Campoccia Davide , Visai Livia , Speziale Pietro , Baldassarri Lucilla , Montanaro Lucio
Published: August 2005

In Staphylococcus epidermidis, ica locus encodes for the synthesis of a polysaccharide intercellular adhesin (slime or biofilm). A multiplex polymerase chain reaction (PCR) for the detection of the five individual genes of ica locus was developed, with the aim to probe the set of genes in a large collection of Staphylococcus epidermidis clinical isolates. Single representative fragments for icaR, icaA, icaD, icaB, and icaC genes were selected. Multiplex PCR was applied to two reference Staphylococcus epidermidis strains [the non–biofilm‐forming ATCC 12228 and the biofilm‐forming ATCC 35984 (RP62A)] and to 400 clinical isolates of Staphylococcus epidermidis from orthopedic prosthesis associated infections. The gene profile was compared with the phenotypic biofilm‐forming ability, evaluated by means of an optimized Congo red agar (CRA) plate test. Among the clinical isolates, 228 (57%) turned out completely ica positive and were biofilm producing. Among the 172 non–biofilm‐forming strains (43%), 164 (41%) were completely ica negative and 8 strains (2%) harbored all five ica genes. The ica locus thus proves to be a cluster of strictly linked genes, without any evidence of single gene deletion. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005
Defect‐induced fatigue microcrack formation in cement mantle
Authors: Qi Gang , Li Jihui , Mouchon W. Paul , Lewis Gladius
Published: August 2005

Acoustic emission (AE) was used to monitor the progress of the fatigue damage process in the cement mantles of two cemented femur stem constructs that contained naturally occurring defects. After the fatigue tests, morphological features of the defects were investigated using an environmental scanning electron microscope. It showed that the regions with no visible defects were mainly microcrack free, whereas the defect regions were the main sources generating microcracks. Two types of microcracks were identified: type I and type II. Signal energies associated with type I microcracks were about an order of magnitude higher than that of type II. The microstructural investigations of the defects and the areas in the vicinity of the defects suggested their categorization into stable and unstable. The accumulative energy–time relationships revealed that stable and unstable microcrack curves had convex
, and concave
shapes, respectively. The progress of fatigue microcrack formation occurred over three distinct phases: initiation, transition, and stableness. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005
Evaluation of calcium titanate as apatite growth promoter
Authors: Coreño J. , Coreño O.
Published: August 2005

Calcium titanate (CaTiO3, perovskite) has been used to determine its apatite nucleation ability and propose a possible nucleation initial step. Measurements of calcium leaching from the calcium titanate surface and phosphate adsorption experiments were carried out separately by using commercial calcium titanate suspensions at room temperature. Adsorption behaviour determined by ζ potential measurements shows that phosphate is strongly adsorbed on the calcium titanate surface. It was found that the higher the pH, the higher the Ca present on the calcium titanate surface, but phosphate adsorption followed this trend only up to pH 7.4. Results suggest that phosphate ions are not adsorbed only on Ca sites but also on TiO2 groups sites of the surface, formed after calcium leaching from the surface. When both ions are simultaneously added in a modified simulated body fluid containing calcium titanate, at 37°C, apatite growth occurs on its surface after 1 week of immersion. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005
Parathyroid hormone (PTH) and hematopoiesis: New support for some old observations
Authors: Whitfield James F.
Published: August 2005

Forty‐seven years ago, the parathyroid hormone (PTH) in one injection of Lilly's old bovine parathyroid extract, PTE, was found to greatly increase the 30‐day survival of heavily X‐irradiated rats when given from 18 h before to as long as 3 h after irradiation but no later. This was the first indication that PTH might stimulate hematopoiesis. Recent studies have confirmed the relation between PTH and hematopoiesis by showing that hPTH‐(1‐34)OH increases the size of the hematopoietic stem cell pool in mice. The peptide operates through a cyclic AMP‐mediated burst of Jagged 1 production in osteoblastic cells lining the stem cells' niches on trabecular bone surfaces. The osteoblastic cells' Jagged 1 increases the hematopoietic stem cell pool by activating Notch receptors on attached stem cells. PTH‐triggered cyclic AMP signals also directly stimulate the proliferation of the hematopoietic stem cells. However, the single PTH injection in the early experiments using PTE probably increased the survival of irradiated rats mainly by preventing the damaged hematopoietic progenitors from irreversibly initiating self‐destructive apoptogenesis during the first 5 h after irradiation. It has also been shown that several daily injections of hPTH‐(1‐34)OH enable lethally irradiated mice to survive by stimulating the growth of transplanted normal bone marrow cells. If the osteogenic PTHs currently entering or on the verge of entering the market for treating osteoporosis can also drive hematopoiesis in humans as well as rodents, they could be potent tools for reducing the damage inflicted on bone marrow by cytotoxic cancer chemotherapeutic drugs and ionizing radiation. © 2005 Wiley‐Liss, Inc.
Nuclear inositol lipid metabolism: More than just second messenger generation?
Authors: Martelli Alberto M. , Follo Matilde Yung , Evangelisti Camilla , Falà Federica , Fiume Roberta , Billi Anna Maria , Cocco Lucio
Published: August 2005

A distinct polyphosphoinositide cycle is present in the nucleus, and growing evidence suggests its importance in DNA replication, gene transcription, and apoptosis. Even though it was initially thought that nuclear inositol lipids would function as a source for second messengers, recent findings strongly indicate that lipids present in the nucleus also fulfil other roles. The scope of this review is to highlight the most intriguing advances made in the field over the last few years, such as the possibility that nuclear phosphatidylinositol (4,5) bisphosphate is involved in maintaining chromatin in a transcriptionally active conformation, the new emerging roles for intranuclear phosphatidylinositol (3,4,5) trisphosphate and phosphoinositide 3‐kinase, and the evidence which suggests a tight relationship between a decreased level of nuclear phosphoinositide specific phospholipase C‐β1 and the evolution of myelodisplastic syndrome into acute myeloid leukemia. © 2005 Wiley‐Liss, Inc.
Induction of osteogenic differentiation of human mesenchymal stem cells by histone deacetylase inhibitors
Authors: Cho Hyun Hwa , Park Hyung Taek , Kim Yeon Jeong , Bae Yong Chan , Suh Kuen Taek , Jung Jin Sup
Published: August 2005

Valproic acid (VPA) has been used as an anticonvulsant agent for the treatment of epilepsy, as well as a mood stabilizer for the treatment of bipolar disorder, for several decades. The mechanism of action for these effects remains to be elucidated and is most likely multifactorial. Recently, VPA has been reported to inhibit histone deacetylase (HDAC) and HDAC has been reported to play roles in differentiation of mammalian cells. In this study, the effects of HDAC inhibitors on differentiation and proliferation of human adipose tissue‐derived stromal cells (hADSC) and bone marrow stromal cells (hBMSC) were determined. VPA increased osteogenic differentiation in a dose dependent manner. The pretreatment of VPA before induction of differentiation also showed stimulatory effects on osteogenic differentiation of hMSC. Trichostatin A (TSA), another HDAC inhibitor, also increased osteogenic differentiation, whereas valpromide (VPM), a structural analog of VPA which does not possess HDAC inhibitory effects, did not show any effect on osteogenic differentiation on hADSC. RT‐PCR and Real‐time PCR analysis revealed that VPA treatment increased osterix, osteopontin, BMP‐2, and Runx2 expression. The addition of noggin inhibited VPA‐induced potentiation of osteogenic differentiation. VPA inhibited proliferation of hADSC and hBMSC. Our results suggest that VPA enhance osteogenic differentiation, probably due to inhibition of HDAC, and could be useful for in vivo bone engineering using hMSC. © 2005 Wiley‐Liss, Inc.
An augmented effective core potential basis set for the calculation of molecular polarizabilities
Authors: Labello Nicholas P. , Ferreira Antonio M. , Kurtz Henry A.
Published: August 2005

Calculations of molecular polarizabilities require basis sets capable of accurately describing the responses of the electrons to an external perturbation. Unfortunately, basis sets that yield suitable quantitative results have traditionally been all‐electron sets with large numbers of primitives, making their use computationally intractable even for moderately sized systems. We present a systematic augmentation of the effective core potential basis set of Stevens et al. [J Chem Phys 81, 12 (1984), Can J Chem 70, 612 (1992)] for 39 main group elements based on the procedure used to construct diffuse and polarization functions in the well‐known Sadlej basis sets [Collec Czech Chem Comm 53, 1995 (1988)]. Representative calculations have been performed and we have shown that results to within 1% of all‐electron calculations using the Sadlej basis set can be obtained for <1–35% of the computational cost using this new basis set. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1464–1471, 2005
Nordhaus–Gaddum‐type Theorems for decompositions into many parts
Authors: Füredi Zoltan , Kostochka Alexandr V. , Škrekovski Riste , Stiebitz Michael , West Douglas B.
Published: August 2005

A k‐decomposition (G1,…,Gk) of a graph G is a partition of its edge set to form k spanning subgraphs G1,…,Gk. The classical theorem of Nordhaus and Gaddum bounds χ(G1) + χ(G2) and χ(G1)χ(G2) over all 2‐decompositions of Kn. For a graph parameter p, let p(k;G) denote the maximum of $\sum _{i=1}^k p(G_i)$ over all k‐decompositions of the graph G. The clique number ω, chromatic number χ, list chromatic number χℓ, and Szekeres–Wilf number σ satisfy ω(2;Kn) = χ(2;Kn) = χℓ(2;Kn) = σ(2;Kn) =  n + 1. We obtain lower and upper bounds for ω(k;Kn), χ(k;Kn), χℓ(k;Kn), and σ(k;Kn). The last three behave differently for large k. We also obtain lower and upper bounds for the maximum of χ(k;G) over all graphs embedded on a given surface. © 2005 Wiley Periodicals, Inc. J Graph Theory
Cycle and circle tests of balance in gain graphs: Forbidden minors and their groups
Authors: Rybnikov Konstantin , Zaslavsky Thomas
Published: August 2005

We examine two criteria for balance of a gain graph, one based on binary cycles and one on circles. The graphs for which each criterion is valid depend on the set of allowed gain groups. The binary cycle test is invalid, except for forests, if any possible gain group has an element of odd order. Assuming all groups are allowed, or all abelian groups, or merely the cyclic group of order 3, we characterize, both constructively and by forbidden minors, the graphs for which the circle test is valid. It turns out that these three classes of groups have the same set of forbidden minors. The exact reason for the importance of the ternary cyclic group is not clear. © 2005 Wiley Periodicals, Inc. J Graph Theory
The benefit–incidence of public spending: the Caribbean experience
Authors: Gafar John
Published: August 2005

This paper shows that public spending on basic services, to wit, primary and secondary education and basic health care benefit the poor; while the non‐poor are the principal beneficiaries of tertiary and education subsidies and hospital spending. The evidence also shows that expenditures on infrastructure spending in the Caribbean benefit the non‐poor disproportionately more than the poor. Copyright © 2005 John Wiley & Sons, Ltd.
Revisiting privatization in the context of poverty alleviation: the case of Sudan
Authors: Dagdeviren Hulya
Published: August 2005

Privatization programmes in the developing world have often been assessed on the grounds of efficiency. In recent years a more critical literature with a focus on the distributional and poverty impact of privatization has emerged. This article contributes to that literature in two ways. First, it presents a broad framework of empirical analysis of the relationship between privatization and poverty. Second, it applies this framework to the case of Sudan in as much as the existing data and information permit. The results do not lend much support for the arguments that privatization contributes to the efforts of poverty alleviation through various channels such as efficiency, employment creation and revenue generation for government. Copyright © 2005 John Wiley & Sons, Ltd.
Some thoughts on the numerical modelling of electromagnetic processes
Authors: Hammond P.
Published: August 2005

The use of models in giving meaning to sense data is described. It is shown that models are essential to human understanding, but that there are no uniquely ‘best’ models. This leads to the discussion of the design of suitable models for engineering use. The role of physical and mathematical models is mentioned, and attention is drawn to geometrical and physical features. It is stated that numerical methods have overriding advantages, one of which is the possibility of numerical experimentation. The modelling of vector fields is discussed and attention is drawn to the ideas of differential geometry which attach the vector field to the space in which it acts. It is shown that variational methods, together with numerical experiments, can be used to derive invariant parameters which give both global and local information about electromagnetic systems in a particularly economical method of computation.
The modelling of multiaxial discontinuities in quasi‐planar structures with the modified TLM method
Authors: Saguet Pierre , Hoefer Wolfgang J. R.
Published: August 2005

The principal features of the modified TLM method such as the asymmetrical condensed node, graded mesh and dispersion characteristics, are briefly presented. Its general application to multiaxial discontinuities in quasi‐planar structures is described, and the modelling of bilateral finline T‐junctions is demonstrated in particular.
Characterization of wire‐grids for filters in circular waveguides at millimetre wavelengths
Authors: Landrac Gabrielle , Clequin René , Gelin Philippe
Published: August 2005

In order to develop a new kind of filter that makes a compromise between quasi‐optical and more traditional bandpass filtering techniques at millimetre wavelengths, a theoretical modelling of grids in oversize and monomodal waveguides is performed using a variational method.
A comparison between the time‐domain and the frequency‐domain diakoptic methods of solving field problems by transmission‐line modelling
Authors: Naylor Phillip , Christopoulos Christos
Published: August 2005

The nature and significance of time‐domain approximations needed for a diakoptic solution using transmission‐line modelling (TLM) are examined. Truncation, filtering and repeated convolution of time responses result in severe restrictions in the accuracy of time‐domain diakoptics. The frequency‐domain diakoptic method has several advantages, including speed and simplicity, and warrants further study.
Fourier approach to semiconductor device modelling
Authors: Axelrad V.
Published: August 2005

A novel procedure for the numerical modelling of current transport in semiconductor devices is presented. The method is based on high‐order trigonometric expansions (Fourier series) of the solution. The expansion coefficients are calculated in a Galerkin‐type algorithm. The method offers infinite‐order accuracy regardless of the number of spatial dimensions of the model. Well‐conditioning and diagonal dominance of the discrete equations render the numerical procedure stable and effective. Significant advantages are expected, particularly for the solution of strongly non‐linear multidimensional device models. Properties of the algorithm are demonstrated on standard semiconductor devices.
A multicompartment TLM model for solving first‐order rate equations
Authors: Saleh A. H. M.
Published: August 2005

This paper introduces a simple model for solving a system of first‐order rate equations using the TLM numerical method. A general algorithm is developed by setting up a matrix of discrete compartments. The rate constants provide the linkage between each compartment and the neighbouring ones. The method is demonstrated by some examples in which saturation conditions are considered. The TLM solution is compared with analytical solutions and the Rung‐Kutta method of solving differential equations.
Mathematical modelling of a 3 ‐phase to single ‐phase cycloinverter
Authors: Smith I. R. , Vadher V. V. , Kettleborough J. G. , Ahishalilar Y.
Published: August 2005

The paper outlines the operating principles of a 3 ‐phase to single ‐phase cycloinverter, as used in heating and melting applications, and presents a digital computer model on which performance predictions may be based. Ideal power switches, an input filter and a compensated heating load are assumed in formulating an initial set of state ‐variable equations which are valid when all the switching devices are conducting. Connection matrix techniques are then used to generate the mesh equations relevant to the continually changing pattern of the switching devices, leading to a very versatile simulation program. Experimental results from a laboratory ‐scale unit are presented for different output power levels, and these are compared with corresponding computed results to illustrate the close similarity that exists.
Characterization of microstrip antennas using the TLM simulation associated with a Prony‐Pisarenko method
Authors: Dubard J. L. , Pompei D. , Le Roux J. , Papiernik A.
Published: August 2005

The transmission‐line matrix (TLM) method enables simulation of interior electromagnetic field propagation problems. With the use of absorbent walls, we can simulate exterior problems such as the radiaition of a microstrip antenna. The input impedance is deduced from the standing wave observed in the feedline. The radiation pattern is determined from the field over a plane located in the immediate vicinity of the antenna, using the theory of radiating apertures. However, the CPU time and memory space involved are excessive. Since the radiating structure has several resonant frequencies, it is convenient to apply classical digital signal processing techniques such as finite impulse response filtering associated with a linear prediction method. The present paper focuses on a Prony–Pisarenko method to improve on the TLM method in terms of both computation time and precision of the frequency‐domain analysis of the results. In this case, overall CPU time is reduced by a factor of 2 to 3. The paper discusses the results obtained for radiation patterns. This represents a new field of application for the TLM method whose drawbacks are reduced by using appropriate signal processing methods.
Adaptive refinement in 2‐D finite element applications
Authors: Golias N. A. , Tsiboukis T. D.
Published: August 2005

An adaptive mesh refinement scheme in the finite element method is presented in this paper. The new criterion Bdiff for adaptive refinement is tested for its validity. A technique for approximating curved boundaries employing the concept of triangle subdivision in conjunction with Delauney triangulation is also considered, so that the mesh produced is optimal. The implementation of the adaptive mesh refinement criterion in conjunction with the proposed technique of including the curved boundaries in the finite element model is described in detail and several examples of its application are given by way of illustration.
The modified semiconductor equations and associated algorithms for physical simulation
Authors: Xue Hongxi , Howes Michael J. , Snowden Christopher M.
Published: August 2005

A set of modified semiconductor equations is described together with novel algorithms for solving them. These ensure a well‐behaved, guaranteed convergent solution for a steady‐state semiconductor model. Examples results on the simulation of a GaAs Dual Gate MESFET are given to demonstrate the efficiency of the new scheme.
Analysis of cross‐talk on high‐speed digital circuits using the finite difference time‐domain method
Authors: Pothecary N. M. , Railton C. J.
Published: August 2005

Cross‐talk and pulse distortion in high‐speed digital circuits have long been major design considerations. With the present trend towards increased speed and packing density the commonly used TEM approximation is no longer capable of producing sufficiently accurate results. In this contribution, the finite‐difference time‐ domain technique incorporating a novel means of launching the pulses is used to provide a rigorous three‐ dimensional simulation of cross‐talk on high‐speed digital circuits. This includes the often‐neglected effects of higher‐order modes and surface waves. Results are presented for pulses propagating along a single track and for coupling between two and three tracks using square, gaussian and raised cosine pulse excitation functions. The results are shown to be in good agreement with other rigorous analyses.
Annotated bibliography of numerical modelling in electromagnetic compatibility
Authors: Sadiku M. N. O. , Obiozor C. N.
Published: August 2005

This paper presents an annotated bibliography of numerical modelling in electromagnetic compatibility with emphasis on coupled transmission lines. Although the papers cited generally appeared in the open literature between 1980 and 1990, very useful works prior to that period are covered.
TLM modelling of diffusion, drift and recombination of charge carriers in semiconductors
Authors: Al‐Zeben M. Y. , Saleh A. H. M. , Al‐Omar M. A.
Published: August 2005

The paper provides an extension to the one‐dimensional TLM diffusion model. The extended diffusion node presented here models the exact transport equation with diffusion drift and recombination of charge carriers in semiconductors. A general algorithm for providing a numerical solution to the transport phenomena is also presented here. The analytical solution for infinitely long semiconductors is compared with the TLM numerical results.
A note on the computational storage in the subsectional basis function approach to the method of moments
Authors: Sattler Sebastian , Russer Peter
Published: August 2005

In order to efficiently store the information of a special class of matrices, a very useful algorithm has been derived and applied to the subsectional basis function approach to the method of moments. The algorithm represents a simple law of mapping and allows a reduction in the required computational storage by several orders of magnitude.
Implementation of timestep changes in transmission‐line matrix diffusion modelling
Authors: Webb Paul W. , Gui Xiang
Published: August 2005

This paper details general expressions for implementing timestep transformations in transmission‐line matrix (TLM) modelling of diffusion processes. The expressions can be conveniently incorporated into any TLM routine which models multidimensional problems using a variable meshing technique.
The use of transmission‐line modelling (TLM) for the solution of heat diffusion in electric fuses
Authors: Cheim Luiz , Howe Alan F.
Published: August 2005

This paper describes an application of transmission‐line modelling (TLM) for the solution of heat diffusion in a three‐dimensional metallic structure, surrounded by a dielectric material. The example of heat propagation along an electric fuse embedded in granular silica is presented. Heat is generated by the flow of an electric current through the metallic element and results are shown for the variation of temperature with time and temperature distribution along the fuse element.
Calculating frequency‐domain data by time‐domain methods
Authors: Dehler M. , Dohlus M. , Weiland T.
Published: August 2005

We show the derivation of parameters in the frequency domain from time‐domain data. Far‐field characteristics are obtained by a convolution formula with the harmonic field amplitudes, which are obtained via a Fourier transform or by sampling. The electric field of filter ports is expanded into the discrete eigenmodes. By this method, a monochromatic exact open boundary can be formulated and the fields divided into the incident and the reflected part. For wide band operation an a posteriori error correction scheme is presented.
The hilbert space formulation of the TLM method
Authors: Russer Peter , Krumpholz Michael
Published: August 2005

The Hilbert space representation of the TLM method for time‐domain computation of electromagnetic fields and the algebraic computation of the discrete Green's function are investigated. The complete field state is represented by a Hilbert space vector. The space and time evolution of the field state vector is governed by operator equations in Hilbert space. The discrete Green's functions may be represented by a Neumann series in space‐ and time‐shift operators. The Hilbert space representation allows the description of the geometric structures by projection operators, too. The system of difference equations governing the time evolution of the electromagnetic field in configuration space is derived from the operator equation for the field state vector in the Hilbert space.
Consistent finite difference modelling of Maxwell's equations with lossy symmetrical condensed TLM node
Authors: Hein Steffen
Published: August 2005

A propagator integral interpretation for general TLM processes is presented and applied to discretized Maxwell's equations. The approach provides exact algebraic solutions of finite difference equations along a quite universal scheme.

Specifically, Johns's process based on the symmetrical condensed node is reconstructed and generalized as a clear‐cut FD algorithm. The fields computed are exact time‐domain solutions of the FD equations, provided that total voltages and currents are evaluated and stub quantities are not externally excited. Losses are very naturally incorporated into the TLM algorithm.

The structural similarity of the TLM process (properly operated) with the propagator integral appears just as fundamental as general and should have further applications.
New technique for finite difference analysis of optical waveguide problems
Authors: Matin M. A. , Benson T. M. , Kendall P. C. , Stern M. S.
Published: August 2005

The method of effective penetration depth is used to produce a novel scalar or polarized finite difference approach for the solution of optical rib waveguide field problems. The new method is quicker than previous finite difference approaches and requires less computer memory. Propagation constant values are presented for a range of semiconductor rib waveguides and are found to be indistinguishable from benchmark results produced using earlier methods of analysis. A simple polarization correction formula recently derived is confirmed by utilizing the good accuracy of these results. This enables discussion of the relationship between quasi‐TE, quasi‐TM and scalar modes, and a further substantial reduction of the cpu time.
Two‐dimensional FDTD and TLM
Authors: Krumpholz M. , Russer P.
Published: August 2005

Applying the method of moments to Maxwell's equations, Yee's two‐dimensional FDTD scheme with central difference approximations and the two‐dimensional TLM method are dervied from first principles of field theory. By comparing the eigenvalues of the two methods, the differences between two‐dimensional FDTD and TLM are illustrated.
Parallel computation of 3‐D electromagnetic scattering using finite elements
Authors: Chatterjee A. , Volakis J. L. , Windheisser D.
Published: August 2005

The finite element method (FEM) with local absorbing boundary conditions has been recently applied to compute electromagnetic scattering from large 3‐D geometries. In this paper, we present details pertaining to code implementation and optimization. Various types of sparse matrix storage schemes are discussed and their performance is examined in terms of vectorization and net storage requirements. The system of linear equations is solved using a preconditioned biconjugate gradient (BCG) algorithm and a fairly detailed study of existing point and block preconditioners (diagonal and incomplete LU) is carried out. A modified ILU preconditioning scheme is also introducted which works better than the traditional version for our matrix systems. The parallelization of the iterative sparse solver and the matrix generation/assembly as implemented on the KSR1 multiprocessor is described and the interprocessor communication patterns are analysed in detail. Near‐linear speed‐up is obtained for both the iterative solver and the matrix generation/assembly phases. Results are presented for a problem having 224,476 unknowns and validated by comparison with measured data.
Finite element method solutions of field distributions in large cavities
Authors: Tharf Mohammed S. , Costache George I.
Published: August 2005

To make possible the application of the three‐dimensional finite element method to electrically large problems, it is combined with the analytical solutions of arbitrary large cavity with aperture. In this paper, detailed analysis for this hybrid method is presented. The element matrices necessary for coupling the finite element method to analytical solutions are given. The proposed hybrid method significantly reduces the number of unknown since only the inhomogeneity needs to be discretized. Thus computer memory and storage demands are reduced. In addition. This hybrid method employs the edge element which is not expected to produce spurious solutions. Also, the formulation presented in this paper preserves the sparsity of the finite element matrix, and does not require any matrix inversion. This new hybrid method is used to compute the field distributions in various partially filled rectangular enclosure. The results match well with the pure edgebased finite element method and analytical solutions.
Iterative solution of boundary element approximations for electric and magnetic fields
Authors: Weiss Rüdiger , Meroth Ansgar , Levin Peter
Published: August 2005

The calculation of potentials in homogeneous and isotropic media by the boundary element method has the advantage that a harmonic solution of Laplace's equation is obtained for given approximated boundary conditions. The technique leads to the solution of linear systems with full matrices of dimension 1000–10,000 for medium‐ and large‐sized three‐dimensional problems, An efficient solution procedure of the linear systems is required.

While the iterative solution of the large and sparse linear systems arising from the finite difference or the finite element method is well documented, the systems resulting from the boundary element method are typically solved by direct methods. However, in many cases an iterative solver needs far fewer operations to achieve a sufficient accuracy. Importantly, there are many alternative methods, each of them well suited for different types of problem.

Here, we provide an overview of state‐of‐the‐art iterative solvers. We will discuss the particular methods that have been successfully applied to systems arising from field calculations in the high‐voltage engineering by the boundary element method. The selection of appropriate methods is discussed. We demonstrate that iterative solutions can be much faster than direct solvers with regards to the number of operations. Furthermore, these solvers are optimally suited for today's supercomputers because they can be efficiently vectorized and parallelized.
Numerical algorithms for modelling microwave semiconductor devices
Authors: Cole Eric A. B. , Snowden Christopher M.
Published: August 2005

This paper presents an analysis of the numerical algorithms used to model microwave semiconductor devices. A comparison is made of the relative merits and features of the more popular finite difference schemes. A new generalized Scharfetter–Gummel formulation is presented which is compatible with drift diffusion and energy‐transport formulations, and is suitable for implementing in two‐dimensional simulations on personal computers. The treatment allows for fully degenerate semiconductors, but implementation for the nondegenerate situation is easily obtained as a special case. The convergence and stability properties of the generalized scheme are discussed. The simulation of a planar submicrometre gate length GaAs MESFET is used to illustrate the application of these algorithms.
Efficient material‐gain models for the transmission‐line laser model
Authors: Nguyen Linh V. T. , Lowery Arthur J. , Gurney Phil C. R. , Novak Dalma , Murtonen Casper N.
Published: August 2005

Transmission‐line laser models (TLLMs) are time‐domain models suitable for the simulation of complex phenomena in semiconductor lasers. TLLMs include time‐domain filters based on transmission‐line stubs to model the spectral dependence of the material gain. In this paper, numerical simulations are presented which show that the accuracy of these gain models is dependent on the model's iteration timestep. Analytical formulae are derived that relate the accuracy of the filters to the timestep, filter centre frequency, and filter bandwindth. A new wideband stub filter which allows the material gain to be modelled using a larger timestep is presented. This is equivalent to a digital infinite‐impulse‐response filter, which is more computationally efficient than finite‐impulse‐response filters, and is unconditionally stable. The new gain model can improve the computational speed for simulating for multimode Fabry‐Perot lasers by a factor of 10–100.
An efficient algorithm for computing the transmission through highly conducting thin sheild in TLM
Authors: Fuchs Ch. , Kopp G. , Schwab A. J.
Published: August 2005

This paper presents a new method in TLM for very efficient computation of highly conducting thin shielding walls. Firstly, the impulse response of a finite conducting sheet is computed analytically via inverse Laplace transform. Subsequently, a recursive convolution integral is formulated with the analytical impulse response. This allows a very efficient and accurate calculation of the diffusion process through imperfectly conducting walls.
Transport equations with boundary conditions of reverse reflection type
Authors: Frosali G. , van der Mee C. V. M. , Protopopescu V.
Published: August 2005

A study is performed of transport equations on arbitrary three‐dimensional domains with boundary conditions of reverse reflection type. The existence of the dominant eigenvalue of the criticality problem is proved and its independence of the functional setting and its continuous dependence on a variety of data are established. The corresponding time‐dependent problem is shown to be well‐posed, also for a conservative boundary. The relationship between the criticality and the time‐dependent problem is given explicitly.
Reduction of quasilinear elliptic equations in cylindrical domains with applications
Authors: Mielke Alexander
Published: August 2005

For certain types of semilinear partial differential equations in a cylindrical domain small bounded solutions are known to lie on a so‐called centre manifold of finite dimension. In this paper we prove the result for quasilinear partial differential equations of elliptic and parabolic type.

Possible applications include free surface waves and problems in non‐linear elasticity. Here we investigate, pars pro toto, the stationary inviscid potential flow in a channel with a free surface and an obstacle at the bottom.
Application of the Schwarz function to boundary problems for Laplace's equation
Authors: Millar R. F.
Published: August 2005

A method is described for studying analytic boundary problems for the Laplace equation in a simplyconnected domain D of the plane. The aim is ultimately to obtain solutions in closed form when D is bounded by a simple analytic curve C with Schwarz function G. The basis for the procedure is that a functional F of the incompletely known boundary Cauchy data determines the solution and is analytic in D, and that there exists a further integral relation between these data and the analytic function G. Elimination of the unknown data from the latter relation by using the former leads to an integral on C that relates F to prescribed data and which, in some cases, may be solved for F in D. Some necessary properties of G are derived; in particular, it is shown that C must be a circle if G is analytic in D except for a single, simple pole (Theorem 1), or if a certain integral that appears prominently in this work is analytic throughout D (Theorem 2). The Dirichlet problem is treated in some detail. If C is a circle, a representation for the solution is obtained that is equivalent to one given by P. J Davis, and to the Poisson integral. When G is meromorphic in D and C is not a circle, Theorem 2 implies that the Davis result is not applicable, and the problem is reduced to that of solving Schröder's functional equation. Integral equations for F are obtained when C is an ellipse and G is multivalued in D. Other linear boundary value problems that can be handled are noted. A class of non‐linear Riemann‐Hilbert problems is described and studied briefly. For all these problems, closed solutions have been obtained when C is a circle; it is not clear whether closed solutions for other forms of C can be found without the explicit use of conformal mapping techniques. Finally, some possible generalizations to different equations and more complicated geometries are mentioned.
On the instability of resonances in parallel‐plane waveguides
Authors: Morgenröther K. , Werner P.
Published: August 2005

It has been observed13 that the propagation of acoustic waves in the region Ω0= ℝ2 × (0, 1), which are generated by a time‐harmonic force density with compact support, leads to logarithmic resonances at the frequencies ω = 1, 2,… As we have shown9 in the case of Dirichlet's boundary condition U = 0 on ∂Ω, the resonance at the smallest frequency ω = 1 is unstable and can be removed by a suitable small perturbation of the region. This paper contains similar instability results for all resonance frequencies ω = 1, 2,… under more restrictive assumptions on the perturbations Ω of Ω0. By using integral equation methods, we prove that absence of admissible standing waves in the sense of Reference 7 implies the validity of the principle of limit amplitude for every frequency ω ≥ 0 in the region Ω =Ω0 −B, where B is a smooth bounded domain with B̄⊂Ω0. In particular, it follows from Reference 7 in the case of Dirichlet's boundary condition that the principle of limit amplitude holds for every frequency ω ≥ 0 if n·x′ ⩽ 0 on ∂ B, where x′ = (x1, x2, 0) and n is the normal unit vector pointing into the interior B of ∂ B. In the case of Neumann's boundary condition, the logarithmic resonance at ω = 0 is stable under the perturbations considered in this paper. The asymptotic behaviour of the solution for arbitary local perturbations of Ω0 will be discussed in a subsequent paper.
Continuous dependence on the time and spatial geometry for the equations of thermoelasticity
Authors: Song J. C. , Payne L. E.
Published: August 2005

In this paper we establish the stability of the solution of the standard initial‐boundary value problem of linear anisotropic thermoelasticity under perturbations of the initial time geometry and of the spatial geometry. This is done by deriving appropriate explicit a priori inequalities which permit us to bound in particular the L2 integral of the perturbation in terms of some well defined measure of the perturbation in the geometry.
Three‐dimensional stochastic vortex flows
Authors: Esposito R. , Pulvirenti M. , Neunzert H.
Published: August 2005

We discuss the stochastic structure of the Navier–Stokes flow in ℝ3 and prove that it can be approximated by means of a finite‐dimensional stochastic process. Such a process reduces to an algorithm already discussed in Reference 4 for the Euler case, when the viscosity coefficient vanishes.
Stationary solutions of the non‐linear Boltzmann equation in a bounded spatial domain
Authors: van der Mee C. V. M. , Neunzert H.
Published: August 2005

A contraction mapping (or, alternatively, an implicit function theory) argument is applied in combination with the Fredholm alternative to prove the existence of a unique stationary solution of the non‐linear Boltzmann equation on a bounded spatial domain under a rather general reflection law at the piecewise C1 boundary. The boundary data are to be small in a weighted L∞‐norm.
Finite element solution for the transcritical shallow‐water equations
Authors: Goutal Nicole , Nedelec J. C.
Published: August 2005

A new solution of the two‐dimensional shallow‐water equations, using a finite element method is described. The formulation is based on the velocity and height variables and follows two steps. In the first step, the convective terms are solved by a characteristic method and in the second step the propagative and diffusion terms are taken into account. The close relation between the latter operator and a Stokes penalized problem is shown; an algorithm of Uzawa type is then used for its solution. Acceleration convergence is obtained by preconditioning, and new methods are presented, the quality of the convergence being shown on application to some sample tests. The overall method has revealed quite efficient and application to industrial cases is already planned.
Bifurcation from the essential spectrum for some non‐compact non‐linearities
Authors: Stuart C. A. , Kirchgässner K.
Published: August 2005

Conditions ensuring bifurcation from the infimum of the essential spectrum are given. The main result concerns non‐linear eigenvalue problems with variational structure in a Hilbert space. It extends previous results of a similar nature by admitting situations where the non‐linearity is not compact with respect to the graph norm of the linearization. The general result is applied to non‐linear elliptic equations on RN.
Abstract Riccati equations in an L1 space of finite measure and applications to transport theory
Authors: Juang Jonq , Nelson Paul
Published: August 2005

We consider operator‐valued Riccati initial‐value problems of the form R′(t) + TR(t) + R(t)T = TA(t) + TB(t)R(t) + R(t)TC(t) + R(t)TD(t)R(t), R(0) = R0. Here A to D and R0 have values as non‐negative bounded linear operators in L1 (μ), where μ is a finite measure, and T is a closed non‐negative operator in L1 (μ) satisfying additional technical conditions. For such problems the notion of strongly mild solutions is defined, and local existence and uniqueness theorems for such solutions are established. The results of the analysis are applied to the reflection kernels with both isotropically scattering homogeneous and anisotropically scattering inhomogeneous medium.
A hyperbolic singular perturbation of Burgers' equation
Authors: Esham Benjamin F.
Published: August 2005

This paper is concerned with the effect of perturbing Burgers' equation by a small term ϵ2 Utt. It is shown by means of an energy estimate that the solution of Burgers' equation provides a uniform O (ϵ) approximation of the solution of the full hyperbolic problem. Existence and uniqueness of classical solutions for both problems is proved. A related linear problem is first addressed using the Faedo–Galerkin method to obtain key estimates. Important for the hyperbolic problem is the introduction of an ϵ‐dependent energy in order to track the order‐ϵ behaviour of various higher‐order derivatives. Subsequent use of Schauder technique and Banach contraction mapping principle yields solutions of the semilinear problems.
The Sommerfeld half‐plane problem revisited, V: The bifurcated guide with mixed boundary conditions on the septum
Authors: Heins Albert E.
Published: August 2005

We discuss the solution of the boundary value problem in a duct with a centered septum [9]. On the lower wall of the duct a Neumann condition is applied while on the upper wall a Dirichlet condition is applied. On the septum we apply a Dirichlet condition on the lower side and a Neumann condition on the upper one. This problem is formulated as a pair of integral equations of the Wiener–Hopf type for which we supply solutions for two modes of excitation as well as real and complex wave number. A critical examination is made of the construction, which reduces the problem to one in complex analysis. For real wave number, the physical parameters are provided in very simple forms.
On a boundary value problem in the theory of linear water waves
Authors: Weck N.
Published: August 2005

A body Ω floating in a fluid is subjected to small periodic displacement. Under idealized conditions the resulting wave pattern can be described by a linear boundary value problem for the Laplacian in an unbounded domain with a non‐coercive boundary condition on part of the boundary. Nevertheless uniqueness can be shown if Ω is confined to certain subsets of the fluid which can be described explicitly. This extends a result of V. G. Maz'ja saying that uniqueness holds provided that the exterior normal for ∂Ω avoids certain directions.
On critical exponents for some quasilinear parabolic equations
Authors: Levine Howard A. , Lieberman Gary M. , Meier Peter
Published: August 2005

We study the Cauchy problem for the quasilinear parabolic equation
magnified image
where p > 1 is a parameter and ψ is a smooth, bounded function on (1, ∞) with − ⩽ sψ′(s)/ψ(s) ⩽ θ for some θ > 0. If 1 < p < 1 + 2/N, there are no global positive solutions, whereas if p > 1 + 2/N, there are global, positive solutions for small initial data.
On the vanishing viscosity limit for two‐dimensional Navier–Stokes equations with singlular initial data
Authors: Marchioro Carlo
Published: August 2005

We study the solutions of the Navier–Stokes equations when the initial vorticity is concentrated in small disjoint regions of diameter ϵ. We prove that they converge, uniformily in ϵ. for vanishing viscosity to the corresponding solutions of the Euler equations and they are connected to the vortex model.
The scattering of electromagnetic waves by a perfectly conducting infinite cylinder
Authors: Colton David , Monk Peter
Published: August 2005

We consider the scattering of a plane time‐harmonic electromagnetic wave by a perfectly conducting infinite cylinder with axis in the direction k, where k is the unit vector along the z axis. Suppose the incident wave propagates in a direction perpendicular to the cylinder. For a given observation angle θ, let FD(θ, α)k be the far‐field pattern of the electric field corresponding to an incident wave with direction angle α polarized perpendicular to the axis and let FN(θ; α)k be the far‐field pattern of the magnetic field corresponding to an incident wave with direction angle α polarized parallel to the z axis. Let {αn}n=1∞ be a distinct set of angles in [ − π, π] and μ a complex number. Then, necessary and sufficient conditions are given for the set {(1 − μ)FD(θ;αn) + μFN(θ;αn)}n = 1∞ to be complete in L2[ − π, π]. Applications, together with numerical examples, are given to the inverse scattering problem of determining the shape of the cylinder from a knowledge of the far‐field data.