作者：
SCHMITT, DSCHUHMANN, RWEILAND, TTechnische Hochschule Darmstadt
FB 18 Fachgebiet Theorie Elektromagnetischer Felder D-64289 Darmstadt Germany Dietmar Schmitt was born in Erfurt
Germany in 1965. He received the Dipl.-Ing. degree in electrical engineering from the Technische Hochschule Ilmenau in 1990 and the Ph.D. degree from the Technische Hochschule Darmstadt department of ‘Theory of Electromagnnetic Fields’ in 1994. His main research interest is electromagnetic field theory with emphasis on numerical modelling and simlation. Rolf Schuhmann was born in Osterburken
Germany in 1968. He received the Dipl.-Ing. degree in electrical engineering from the Technische Hochschule Darmstadt in 1994. Theomas Weiland
born in 1951 studied electrical engineering and mathematics at the Technische Hochschule armstadt. In 1977 he received his Ph.D. In his thesis he worked out a finite difference method in the frequency domain and applied it to lossfree and lossy waveguide mode computation which resulted in unique solutionsa priorifree of spurious modes. As fellow at the European Institute for Nuclear Research (CERN Switzerland) he continued his work on electromagnetic computing extending yee's algorithm to include fields of moving charges. At the Deutsches Elektronen Synchrotron DESY in Hamburg he founded in 1983 an international collaboration for three-dimensional electromagnetic simulation. The software paaackage
called MAFIA which resulted from this collaboration has been in use since 1984 in 22 countries and was the first widely distributed 3-D code for radiofrequency field simulation. In 1984 he published a basic paper on the matrix formulation of Maxwells' equations and the uniqueness of numeical solutions. For his contributions to the field of scientific computing he received in 1986 the ‘Physics Prize’ of the German Physical Society
and the ‘Prize for Achievements in Accelerator Physics and Technology’ of the US Particle Accelerator School and the ‘Leibniz Prize’ from the German Research Association in 1987. His work on electrom
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 fre...
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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 straightforward 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.
X-ray microtomography can be used to generate three-dimensional 5123 images of random materials at a resolution of a few micrometers per voxel. This technique has been used to obtain an image of an ASTM C109 mortar sa...
X-ray microtomography can be used to generate three-dimensional 5123 images of random materials at a resolution of a few micrometers per voxel. This technique has been used to obtain an image of an ASTM C109 mortar sample that had been exposed to a sodium sulfate solution. The three-dimensional image clearly shows sand grains, cement paste, air voids, cracks, and needle-like crystals growing in the air voids. Volume fractions of sand and cement paste determined from the image agree well with the known quantities. Implications for the study of microstructure and proposed uses of X-ray microtomography on cement-based composites are discussed.
Antenna arrays can be used to increase system capacity in PCS networks by supporting multiple co-channel users per cell in receive and in transmit. We propose a novel approach for separating multiple digital signals r...
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Antenna arrays can be used to increase system capacity in PCS networks by supporting multiple co-channel users per cell in receive and in transmit. We propose a novel approach for separating multiple digital signals received at an antenna array. Our approach exploits the temporal structure of digital signals to simultaneously determine the array response and the symbol sequence for each signal. Uniqueness of the estimates is established for signals with BPSK modulation format. This approach for separating digital signals is applicable to an unknown array geometry and propagation environment, which is particularly useful in PCS applications. Simulation results are presented to demonstrate the performance of this new technique.< >
Among the most promising elements for digital parallel optical information processing are differential pairs of PnpN optical thyristors. We have shown very recently that these optical detector-generator type of device...
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Among the most promising elements for digital parallel optical information processing are differential pairs of PnpN optical thyristors. We have shown very recently that these optical detector-generator type of devices can be switched-on in very short times (typical 10 ns) with very low switching energies (typical 40 fj of absorbed optical energy), while the problem of slow switch-off times, causing unpractical cycle times, was tackled using a double-heterojunction structure that can be completely depleted by means of a simple negative anode-to-cathode low voltage pulse. In this way PnpN thyristors with switch-off times of 10 ns became available.1
The purpose of this paper is to examine the problem of controlling a linear time-invariant system subject to input saturation in order to have its output track (or reject) a family of reference (or disturbance) signal...
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The purpose of this paper is to examine the problem of controlling a linear time-invariant system subject to input saturation in order to have its output track (or reject) a family of reference (or disturbance) signals produced by some external generator. It is shown that a semi-global framework for this problem is a natural one. Within this framework, a set of solvability conditions are given and feedback laws which solve the problem are constructed. The theory developed in this paper incorporates earlier results established for linear systems without input saturation.< >
In this paper we report on the progress which has been made in the fabrication and use of 2-D optical logic planes consisting of silicon hybrid electrically assisted thermo-optic resonators (HEATORS).1
In this paper we report on the progress which has been made in the fabrication and use of 2-D optical logic planes consisting of silicon hybrid electrically assisted thermo-optic resonators (HEATORS).1
Recently developed ''slowly divergent'' space marching difference schemes, coupled with Tikhonov regularization, can solve the one-dimensional inverse heat conduction problem at values of the nondimens...
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Recently developed ''slowly divergent'' space marching difference schemes, coupled with Tikhonov regularization, can solve the one-dimensional inverse heat conduction problem at values of the nondimensional time step DELTAt+ as low as DELTAt+ = 0.0003. A Lax-Richtmyer analysis is used to demonstrate dramatic differences in error amplification behavior among various space marching algorithms, for the same problem, on the same mesh;maximum error amplification factors may differ by more than 10 orders of magnitude at parameter values that are of interest in rocket nozzle applications. Slowly divergent schemes are characterized by their damping behavior at high frequencies. A widely used benchmark problem, where the surface temperature gradient is a step function, provides a basis for evaluating Tikhonov-regularized marching computations. With standard marching procedures, relatively high values of the regularization parameter r are found to be necessary;the resulting loss of resolution leads to erroneous solutions. When slowly divergent schemes are used, much lower values of r are possible, leading to reasonably accurate reconstruction of thermal histories at the active surface.
A new supplementary a-priori constraint, the slow evolution from the boundary constraint, (SEB), sharply reduces noise contamination in a large class of space-invariant image deblurring problems that occur in medical,...
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In this paper,a Boussinesq hierarchy in the bilinear form is proposed. A Backlund transformation for this hierarchy is presented and the nonlinear superposition formula is proved rigorously.
In this paper,a Boussinesq hierarchy in the bilinear form is proposed. A Backlund transformation for this hierarchy is presented and the nonlinear superposition formula is proved rigorously.
The effect of noise on the possible occurrence of chaos in systems with a homoclinic orbit (e.g., the Duffing equation) was recently considered by Bulsara, Schieve, and Jacobs [Phys. Rev. A 41, 668 (1990)], and Schiev...
The effect of noise on the possible occurrence of chaos in systems with a homoclinic orbit (e.g., the Duffing equation) was recently considered by Bulsara, Schieve, and Jacobs [Phys. Rev. A 41, 668 (1990)], and Schieve and Bulsara [Phys. Rev. A 41, 1172 (1990)], who adopted an approach based on a redefinition of the Melnikov function. We show that this redefinition is unsatisfactory and leads to incorrect results.
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