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  • Engineering  (3,908)
  • Mathematics and Statistics  (525)
  • Wiley-Blackwell  (4,433)
  • 1985-1989  (2,871)
  • 1980-1984  (1,562)
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  • 1
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 115-128 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An absorbing boundary condition for simple layered media is presented. The method enables the modelling of open space radiation and scattering problems when the source (or scatterer) and a plane interface between two media are both located within the finite-difference or finite-element region. The projection operator method is used to take into account the presence of reflected waves at the media interface. The derivation of the projection operator is presented for one, two and three dimensions. Examples of electromagnetic radiation and scattering in two dimensions are presented to illustrate the numerical implementation and validity of the new absorbing boundary condition.
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  • 2
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 129-130 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 3
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 131-136 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A design method for filters having duobinary signal pulses as impulse response is presented.
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  • 4
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 137-151 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Additional Material: 5 Ill.
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  • 5
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 153-164 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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  • 6
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 171-171 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 7
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 165-170 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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  • 8
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 9
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 173-174 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 10
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 175-188 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The asymptotic form, for high frequencies, of the equations of propagation on a nonuniform N-conductor transmission line is considered. Under the assumption of perfect conditions in uniform, isotropic media, all N propagation velocities are the same, but the characteristic impedance matrix is allowed to vary with position along the line. Closed-form solutions are obtained for some cases of interest.
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  • 11
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 12
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 1-15 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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  • 13
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 31-52 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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  • 14
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 227-240 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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  • 15
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 280-280 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 16
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 19-30 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The Boltzmann transport equation is used to derive a set of conservation equations which is capable of describing the electron transport phenomena in a single-valley semiconductor. These conservation equations are averaged over the different valleys of the conduction band to develop another set of equations that can be used to describe accurately the electron transport phenomena in a multi-valley semiconductor, such as GaAs, using the equivalent single-electron gas model whose characteristics are the average weighted characteristics of the constituent gases. The nonstationary effects are included by using energy dependent mobility and electron temperature functions. This program is used to simulate a GaAs MESFET with a 0·5 μm gate length and a 0.2 μm thick active layer. The active layer is doped at 1017 cm-3. A travelling Gunn domain is observed between the gate and the drain. The domain oscillation frequency is much higher than the normal operating frequency of the MESFET. The domain formation's dependence on the gate bias and the active layer thickness are also presented.
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  • 17
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 18
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 61-70 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Two- and three-dimensional electromagnetic resonance calculations have been performed on rising-sun magnetron structures. These calculations have been made using the transmission-line matrix method. Cylindrical coordinates have been used in order to facilitate modelling of the essentially cylindrical device. Recent improvements to the TLM technique, such as the development of the symmetric condensed node for electromagnetics, have been fully exploited. The numerical procedure is described, the modelling process is discussed, and the results obtained are evaluated in comparisons with corresponding empirical data.
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  • 19
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 45-59 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The conventional transverse resonance method, which has been widely used for the approximate characterization of a number of guiding structures and leaky wave antennas, is formulated in a generalized form. The transverse resonance viewpoint combined with the generalized matrix representation of discontinuities yields a rigorous transverse equivalent circuit of the guiding structure.This technique is used to compute the characteristics of both symmetrical and asymmetrical double slot unilateral finlines in terms of phase constant and characteristic impedance of the dominant as well as higher-order modes. Numerical aspects of this method are discussed.In a double-slot finline structure, a coupled-mode regime is established with the onset of the first higher-order mode in addition to the dominant quasi-TEM mode. Symmetrical structures are simply modelled in terms of even and odd mode characteristics, but a more general coupled-line model, in terms of the C-mode and the II-mode must be applied to asymmetrical coupled finlines.
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  • 20
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 71-72 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 21
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 85-91 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Transmission-line models (TLMs) for nonlinear reactive components and mutual inductances are derived. The model for nonlinear reactive components is shown to be an improvement on the previous one. TLM results with the mutual inductance model are compared with the exact solution, and good agreement is found.
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  • 22
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 189-206 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A numerical method using impulse analysis of a transmission-line matrix is used to model the scattering of underwater acoustic waves. The method is demonstrated by observation of plane and curved wavefronts travelling through the medium, and by plane wavefronts being scattered by a reflecting boundary.
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  • 23
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 207-220 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Shooting and bouncing rays (SBR) is a numerical method based on geometric optics developed to compute the electromagnetic scattering from jet inlets and partially open cavity structures. This method is used to study the effects of shaping on the radar cross-section (RCS) of cavities. Two cylindrical cavity structures are analysed: one with a uniform circular cross-section, and the other with a non-uniform cross-section varying from a triangular shape to a circular shape. By bending the longitudinal axis of a cylindrical cavity, a significant reduction in RCS at near axial incidence can be achieved.
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  • 24
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 25
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 1-1 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 26
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 7-17 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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  • 27
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 17-29 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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  • 28
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 29
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 81-92 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A de model for short-channel MOSFETs is presented in this paper. Several second-order effects associated with small-geometry MOSFETs such as mobility degradation, carrier velocity saturation and channel length modulation are included in the model. The analysis emphasizes the modeling of the output conductance and the transconductance which are important in analogue circuit simulation. The theoretical predictions of the model are in good agreement with the experimental data available in the literature.
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  • 30
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 75-80 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A simulation of power transformers following switching operations is presented in which each core section is represented by a non-linear inductance, the differential inductance being determined from the flux density in that section of the core. In analysing the resultant circuit model for the transformer it is shown that the circuit equations have dyadic properties which can be used to give a more efficient numerical solution.
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  • 31
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 93-102 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An approach, based on the finite element method (FEM), is used for evaluating the electromagnetic field distribution in a class of E-plane metal insert filters, operating in the Ka-band. Artificial boundary conditions are inserted directly in a functional, enabling a solution of the scalar wave equation by finite element method.The scattering parameters of the filter, the electromagnetic field and, therefore, the current distributions on the thin metal inserts are computed. Then, the power dissipated in the metallic septa, which is one of the major limitations for the maximum CW-power that can be handled by these types of filter, is evaluated using a perturbational approach. Finally, the maximum field intensity is determined, allowing an estimate of the maximum peak power that these structures can handle.
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  • 32
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 103-111 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The multigrid technique, which is mainly used in the finite difference method, is applied to the TLM (transmission-line matrix or modeling) procedure. In the multigrid TLM, the field region is covered with sets of regular transmission-line matrices of different mesh sizes. The finer grid pattern, which overlaps the coarser grid, fills the region with high field gradients. Data obtained in the coarser grid are transferred to the finer grid through an interpolation process and used as boundary conditions for the latter. The finer grid data are then transferred back to the coarser one, thus improving the coarse grid values. The method is applied to several diffusion problems and significant improvements in accuracy and efficiency are shown.
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  • 33
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 115-115 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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  • 34
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 131-142 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Numerical quadratures encountered in solving integral equations and in finite element analysis often involve singular integrands, or integrands with very rapid local variation whose numerical stability resembles that of singularities. It is shown that specialized quadrature formulae of Gauss-Christoffel type can be generated for such integrands, using a recursive procedure based on the properties of the underlying orthogonal polynomials. Quadrature formulae of moderately high degree can be computed rapidly enough to allow them to be constructed as needed. An algorithm for generating quadrature formulae is given in detail. Singular or near -singular functions encountered in finite element analysis typically require three -point or four -point quadratures; such formulae are readily obtained, to seven -figure accuracy, in computing times short enough to regard the formulae as disposable and not worth preserving in tables.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 187-188 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    Topics: Electrical Engineering, Measurement and Control Technology
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  • 36
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 189-190 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 191-201 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents an overview of the 3D transmission-line matrix method of analysis, describing the various nodes which are available to date: expanded node, asymmetrical condensed node, symmetrical condensed node. The most general scattering matrices of these nodes are given. The various techniques used to implement irregularly graded meshes are also described. A comparison of all the processes applied to the same structure is made. Conclusions on their use are then discussed.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 279-279 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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  • 39
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 249-265 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The application of the transmission-line modelling technique to the design of semiconductor lasers and optical systems is reviewed. Generalized scattering matrices are developed to allow the technique to be applied to novel devices and systems.
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  • 40
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 3-6 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 31-43 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The coupling between incident electromagnetic fields and lossless multiconductor transmission systems is studied using transmission-line modelling-(TLM) and the impedance parameters of the transmission system. This calculation is a two-stage procedure:firstly, the field problem is solved, with no conductors present, to give the incident fields; secondly, the multiconductor transmission-line problem is solved using equivalent voltage and current sources representing coupling from the incident fields. Comparison of these results with previously published work shows excellent agreement. The numerical model presented is particularly suitable for studying electromagnetic compatibility problems.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 73-83 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A discrete model is developed to describe the diffusion of dopant/impurity in a single semiconductor crystal during Czochralski growth. The basic diffusion mechanism is assumed to be substitutional-interstitial interchange for the impurity, together with self-diffusion of the host atoms. In particular, the model incorporates the complicated conditions that result from the simultaneous growth and diffusion taking place at the crystal/melt interface. The high temperature dependence of the process is also taken into account, together with possible vacancy production to counteract vacancy depletion. The numerical model is explicit in time, and conditions for convergence and stability are considered. Results are presented for chromium doping of growing gallium arsenide crystals, and compared with published experimental data.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 93-102 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: One- and two-dimensional algorithms for the transient simulation of semiconductor devices are presented which incorporate a solenoidal total current. The paper includes results from one-dimensional simulation of a p-n junction, including forward-to-reverse bias switching and also switching and also switch-on into high injection in an asymmetric structure. A discretization scheme for the two-dimensional formulation is described with details on handling voltage driven terminals and the associated boundary conditions.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 103-113 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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  • 46
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988), S. 221-238 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The development of numerical models to describe physical problems with irregular boundaries frequently involves the use of very fine or variable Cartesian meshes when a more descriptive mesh might be appropriate. This paper describes the application of the transmission line matrix (TLM) technique to the analysis of orthogonal curvilinear mesh problems. Although very high levels of accuracy are possible, the computational efficiency may be reduced owing to the stub admittance factor, S, and the need for an accurate evaluation of the transmission line parameters.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 61-73 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A new P-N junction device model is presented. It consists of two numerical unidimensional macroscopic models. The first is a drift-diffusion model. The second is an energy model accounting for the carrier energy relaxation effects. Because device optimization requires systematic investigations, the computing time is of paramount importance and, so an accurate comparison between these two models was undertaken under both static steady-state and dynamic 94 GHz conditions in order to point out the relative interest of the energy model. This study is mainly devoted to silicon millimetre-wave IMPATTs. This comparison has highlighted the superiority of the energy model for the description of low field transport phenomena. But as IMPATT RF properties are mainly governed by high field transport, the RF power levels predicted by the two models have been found to be similar. Moreover it has shown that the energy model tends to underestimate both the efficiency and the diode terminal negative resistance level. This parasitic effect is inherent to the description of the carrier generation process by impact ionization which in this model is assumed to be governed by the carrier energy.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 113-113 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 (1988) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 117-129 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The response of capacitive array sensors in the presence of flawed solid materials is simulated using finite elements and infinite elements with exponential decay. Conventional finite elements are used to model the critical regions near the probe and the surface of the solid. Infinite elements are used to represent the farfield conditions of the space surrounding the probe and the solid. The method is first applied to problems with analytic solutions to determine the accuracy of the results obtained using the infinite elements. The response of a capacitive array sensor is then simulated using a line integral which measures the relative change in admittance between flawed and unflawed solids. Examples of capacitive probe responses are given for several parametric variations of the flaw size and dielectric constant of the solid.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 143-152 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 153-186 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Rigorous full -wave analysis techniques are presently receiving much attention in the design of MICs and, in particular, of MMICs due to increasing circuit packing densities and structural complexity. In this paper, the problems associated with such techniques and previous related work are briefly outlined in the introduction. To obtain self -consistency, the electrodynamic Green's functions and related terms are then formulated for the shielded (M)MIC problem. The final operator equation for the numerical solutions derived and the associated functions space are presented and discussed. The central portion of the paper describes a new numerical solution using a discretized Green's function database technique. The resulting linear system of equations is solved by direct inversion for geometrical complexities involving up to about 1000 unknowns; for a higher number of unknowns, an iterative solution is generated. As an alternative to the database technique developed, a variety of spectral domain iterative solutions has been written and tested as well. This includes application of the conjugate gradient method to the normal operator equation (CGN algorithm), an implicit iterative Galerkin approximation called the modified planar conjugate gradient technique (MPCG) and monotonically convergent iteration procedure being a version of the conjugate residual algorithm (CR). Supplementary to this, the extraction of (M)MIC design data from the numerical 3D solutions obtained and error considerations are presented. The paper concludes with a variety of analysis examples of medium to high geometrical complexity and with verification of some results by comparison with measurements and with numerical data from other sources.CPU times required on typical workstations (Micro VAX, HP 9000, etc.) are moderate, thus rendering the techniques presented as useful in the solution of MIC and MMIC design problems.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 53-60 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 203-214 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: 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 number k or 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 factor s is 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 factor s and the maximum allowed frequency Fmax for the best numerical results, is proposed in this paper.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 241-248 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The TLM technique has been enhanced to allow the accurate modelling of EM diffusion through advanced composite material shells. This is a significant development owing to the rapidly increasing use of conducting composite materials in aerospace vehicle design. The accurate EM modelling of this class of materials is important for correct design of vehicles with regard to electromagnetic compatibility (EMC).Existing 3-D time-domain TLM models a non-perfectly conducting shell using a resistive sheet (or sheets) to simulate the surface. The results from this model are shown to be slightly inaccurate and require lengthy computer solution times. A separate 1-D, frequency-domain transmission-line model has been developed elsewhere to better analyse the diffusion properties of composite materials. The incorporation of the results from this frequency domain code into the 3-D time-domain TLM algorithm is outlined.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 267-278 
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    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The calculation of the radar cross-section (RCS) of complex bodies using the symmetrical condensed TLM method is presented. The technique is based on a near-to-far field transformation of the TLM calculated near fields. Several two-dimensional examples are presented which validate the method. The main advantage of utilizing techniques such as TLM for RCS computation lies in the ability to model arbitrary bodies with complex material compositions.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 215-225 
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    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A new TLM-based concept analogous to the Green's function approach in classical electromagnetic theory is presented. It employs the procedure known as time domain diakoptics. The response of a TLM mesh to a unit impulse excitation at selected input points is interpreted as a discrete Green's function in the time domain, and the term ‘Johns matrix’ is proposed for this characteristic response. As in classical theory, the response of the mesh to an arbitrary excitation is found by convolving the excitation with its Johns matrix. This concept extends the generalized scattering parameter concept into the time dimension, opens unprecedented possibilities for partioning time domain problems at the field level, and permits large-scale preprocessing of substructures for computer-aided design. It also represents and elegant way of modelling broadband absorbing boundary conditions, imperfectly conducting walls and general frequency dispersive boundaries in the time domain.
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    Mathematical Methods in the Applied Sciences 2 (1980) 
    ISSN: 0170-4214
    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 235-250 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: We study the behavior of the solution E of the Maxwell's boundary value problem ∇ × ∇ × E + λE = F, n × E|r = 0 in domains Ω which have conical boundary points. In a neighbourhood K(R) = B(a,R) ∩ Ω of a singular boundary point a the field E is expanded using a theorem of N. Weck. It e.g. turns out that the solution lies in H1(3)(K(R)) if K(R) is convex.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 288-302 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: For Hill's equation the lowest eigenvalue a0 of the boundary value problem y(x + 1) = y(x) is considered. Introducing Lp norms of the function f(x), lower bounds for a0 which depend only on this norm are derived for p = 1,2 and ∞ by solving a variational principle. For these lower bounds analytical expressions are obtained. The quality of the approximations thus obtained is discussed for Mathieu's equation and an application in magnetohydrodynamics is considered.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 12-25 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The paper gives a proof, valid for a large class of bounded domains, of the following compactness statements: Let G be a bounded domain, β be a tensor-valued function on G satisfying certain restrictions, and let {n} be a sequence of vector-valued functions on G where the L2-norms of {n}, {curl n}, and {div(β n)} are bounded, and where all n either satisfy x n = 0 or (β Fn) = 0 at the boundary ∂G of G ( = normal to ∂G): then {n} has a L2-convergent subsequence. The first boundary condition is satisfied by electric fields, the second one by magnetic fields at a perfectly conducting boundary ∂G if β is interpreted as electric dielectricity ∊ or as magnetic permeability μ, respectively.These compactness statements are essential for the application of abstract scattering theory to the boundary value problem for Maxwell's equations.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 68-72 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The problem of plasma confinement in a Tokomak machine has recently attracted considerable mathematical attention. In the present article, gradient bounds for the solution are obtained through the use of differential inequalities and the Hopf maximum principle. These estimates, which take slightly different forms in the plasma and vacuum regions, become exact in the one-dimensional case. An estimate is also given for the distance from the boundary of the interior point where the maximum of the solution is attained.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 73-90 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: It is well known that the free boundary of the one-phase Stefan problem (1.1-5) depends continuously on the boundary data [1]. In this paper we prove that, in addition, the solution operator S which, to each g. assigns the corresponding free boundary, is continuously Frechet differentiable and we give the defining formulas of the Frechet derivative.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 108-129 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: For the Radon transform of functions with circular symmetry an inversion formula is proved in a new and elementary way. The inversion formula combined with Fourier theory is applied to Sommer-feld's integral for Hv1, yielding a representation of products which generalizes Nicholson's integral for |Hv(1)| 2.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 191-208 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: A variational formulation for the integral equation used for the double layer potential solution of the Neumann exterior problem in the Laplace equation was proposed in [4]. This formulation allows the use of a finite element method which we describe and experiment here.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 149-167 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The change of variable for the temperature Θ in the one-phase Stefan problem leads to the evolution inequality, (ut - Δu - f)(v - u) ≥ 0 for all regular v ≥ 0, where u ≥ 0 is required. This inequality is to hold over a space-time domain D = Ω × (0, T) with a Dirichlet boundary condition imposed on ∂ Ω × (0, T) and a zero initial condition. The free boundary phase interface is given in one space dimension by The fully implicit divided difference scheme leads to a sequence of elliptic variational inequalities for {um}. The sequence {um} may be interpolated linearly in t to obtain an approximation UΔt of u. The following results are obtained in this paper: (i) a two-sided weak maximum principle for um - um-1 in N space dimensions, hence the free boundary approximation for N = 1, is a monotone increasing step function; (ii) the uniform convergence of UΔt and ∇UΔt, to u and ∇u, respectively, on D; (iii) the uniform convergence to the Hölder continuous, monotone increasing free boundary x on [0, T] of the piecewise linear sequence xΔt, where xΔt interpolates xΔt, in one space dimension; (iv) a constructive existence proof for u and x in prescribed regularity classes.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 209-220 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: In order to reduce scanning time modern x-ray scanners provide projections only in a restricted range [0, φ] with φ 〈 π. We consider the reconstruction of pictures from p + 1 complete projections in [0, φ]. An extrapolation procedure is given to achieve approximations gp of the data in the whole range. We show that the L2-error of the corresponding picture is of order p-α if the original belongs to the Sobolev space Hoα. The validity of our error estimate is investigated by numerical experiments.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 251-270 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: We study an elastic body comprising an inclusion whose thickness is 2∊ and for which Lamé's constants are λ∊ and μ. We are interested in the limit behaviour of the inclusion, when ∊ → 0 and μ∊ → ∊; that is when the inclusion becomes thiner and more rigid. Different behaviours are possible, according to the rate at which μ∊ converges to infinity; the limit inclusion may “vanish” if it is not very rigid, but also it may be entirely solid.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 327-346 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 347-377 
    ISSN: 0170-4214
    Keywords: Mathematics and Statistics ; Applied Mathematics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Approximation in least squares by Galerkin's method leads to a consideration of strongly minimal systems. Theorems are derived which permit the recognition of systems which are not strongly minimal from the characteristics of the elements themselves. Normalised systems cannot be strongly minimal without their eigenvalues being bounded above.Speared systems, which have desirable properties, are introduced and their main features determined. Convergence earmarks and error bounds are exposed.A new definition of stability, which is self-checking in a computation, is suggested and its attributes delineated.The extension of the theory to equations involving positive-definite operators is mentioned.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 410-418 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: This paper deals with the Neumann problem of the pre-Maxwell partial differential equations for a vector field v defined in a region G ⊂ R3. We approximate its uniquely determined solution (integrability conditions assumed) uniformly on G by explicitly computable particular integrals and linear combinations of vector fields with a “fundamental” sequence of points .
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 445-456 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: Classical theorems about matrices with non-negative elements can be generalized for application in eigenvalue problems of integro-differential form appearing in the description of stationary particle transport. In this way the existence and unicity of positive L1-eigensolutions of the m-quasi-completely-continuous transport operator can be deduced. These solutions can be realized by a method of successive approximation.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 480-488 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: Some monotonicity results are given for the remainder terms in the asymptotic expansion for x → ∞ of the function Jv(x)Jv+n(x) + Yv(x Yv+n(x), v ε R, n ε Z.
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    Mathematical Methods in the Applied Sciences 2 (1980), S. 504-517 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The above equation has some remarkable properties. In general a global solution exists in a weak sense only, and this solution is not reversible in time. Furthermore it is known, that the solutions for different initial values can coincide for all t ≥ t0 〉 0, and the set of the initial values with this property is convex. Conditions assuring that this set contains only one element are given. This means a weak form of time-reversibility.As a global solution exists only in the weak sense, the classical question concerning dependence of the solution on the initial values needs some modification. This problem is dealt with in suitable L1-norms. It is shown, that the L1-norm of the difference of two weak solutions with respect to the space variable does not increase in time.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 38-69 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: This work is devoted to Free Boundary Problems with Laplace equation Δu = f in the domain and the two conditions on the Free Boundary u = 1 and |grad u| = λ = const. In the model problems which we study, three cases arise: 1) f = 0, λ is given, 2) f = 0, λ is unknown and the length of the Free Boundary is given, 3) f ≠ 0, λ = 0 (Obstacle Problem).
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 115-120 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: An Uzawa algorithm of Temam is improved so that the Navier-Stokes boundary value problem is reduced to a sequence of linear Poisson problems. A simple finite element method is shown to give a convergent sequence of approximate solutions. Finally a penalty variant is discussed.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 435-443 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: We investigate the problem of plasma confinement by a magnetic field in an infinite cylinder. We show that if the cylinder has convex cross-section, then there exists an equilibrium plasma configuration with convex cross-section.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 475-487 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The existence of a unique solution to Maxwell's equations defined in an exterior domain with impedance boundary condition is established for all frequencies. This is accomplished by reducing this problem to that of solving a system of singular integral equations and then regularizing this system such that the Riesz theory is applicable. We also consider the inverse problem in which it is desired to determine the impedance from a knowledge of the far field pattern. By restricting the impedance to lie a priori in a compact set results are obtained on the existence, uniqueness, and stability of the solution to this inverse scattering problem.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 523-536 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: Methods using the theory of distributions and Hilbert space operators have been very powerful in the past to achieve uniqueness and existence results for Maxwell's equations. In this paper conditions are given when such abstract “Hilbert space”-solutions represent differentiable “regular” functions which satisfy Maxwell's equations, boundary conditions, and transmission conditions in the classical sense.
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    Mathematical Methods in the Applied Sciences 4 (1982) 
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 33-73 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: One considers an elastic halfspace with depth (x1) dependent density Q and Lamé moduli (λ,m̈). Impulsive stresses τli = δ(x2, x3)δ(t) for x1 = 0 are applied with displacement responses ui = gi(t, x2, x3) at x1 = 0 (i = 1, 2, 3). Let vi(t, x1) = ∫∫uidx2dx3 (i = 1, 2 is enough) and set w(t, x1) = ∫∫x2u1dx2dx3. One obtains a system of 3 differential equations for v1, v2, and w to which the spectral techniques of inverse scattering theory are applied as in [25]. The inverse problems for the uncoupled vi can then be solved to produce 2 functions A1 and A2 involving (Q, λ, μ) as functions of “bound” variables y1 and y2 containing (Q, λ, μ), between which a relation then is determined. Analysis of the coupled equation for w then leads to a Fredholm integral equation whose solution provides an additional relation between (Q, λ, μ) from which (Q, λ, μ) can be determined as functions of x1. The integral equation is reduced to a Volterra type equation by results and techniques of transmutation and then solved by a modification of standard techniques. A number of features and results of independent mathematical interest arise from the transmutation theory.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 123-130 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The Maxwell equations are formulated as an evolution equation in a suitable chosen Hilbert space involving a densely defined closed skew-Hermitian operator which generates a unitary group. A Crank-Nicolsen-Galerkin approximation is then established and convergence is shown by arguments from the theory of approximation of groups of operators.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 143-163 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: By using the method of averaging, we give a complete Hopf bifurcation diagram when the differential equation has more than one parameter. The method is applied to a system of parabolic equations with nonlinear coupling on the boundary. This set of equations is a mathematical model which describes the normalized concentrations of substances in a solution produced by two enzymes.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 243-258 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The buckling of a beam or a plate which is subject to obstacles is typical for the variational inequalities that are considered here. Birfurcation is known to occur from the first eigenvalue of the linearized problem. For a discretization the bifurcation point and the bifurcating branches may be obtained by solving a constrained optimization problem. An algorithm is proposed and its convergence is proved. The buckling of a clamped beam subject to point obstacles is considered in the continuous case and some numerical results for this problem are presented.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 328-335 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: In this paper a finite element approximation scheme for the system curl is considered. The use of pointwise approximation of the boundary condition leads to a nonconforming method. The error estimate is proved and numerically tested.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 424-434 
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    Notes: The trust production by means of a periodic heaving motion of a rigid profile is discussed. It is proved by using Bauer's maximum principle, that when a constraint is put on the magnitude of the amplitude, optimum motions do exist.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 445-455 
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    Topics: Mathematics
    Notes: Motivated by a recent paper of H. Narnhofer and G. Sewell, we investigate the problem of existence and uniqueness of solutions of the Vlasov hierarchy. It is shown that the unique solution of the Vlasow hierarchy is induced by the flow on the space of probability measures on R6 which is obtained from the solution of the Vlasov equation.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 364-392 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: We investigate some integral equations, i. a. the so-called Kupradze functional equations, where the two variables of the kernel belong to two different point sets. An extensive survey of the literature shows the various applications of these equations.By a discretization of the integral equations they are replaced by systems of linear algebraic equations. The condition number of the corresponding matrices is investigated, analytically and numerically. It is thereby quantitatively found in which way the condition of the matrices deteriorates when the two point sets are moved away from each other.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 405-423 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The stiff boundary value problem for the time-independent linear Boltzmann equation is considered in the variational formulation in terms of the coercive symmetric bilinear form. It is shown that it is asymptotically equivalent to the related variational diffusion problem when the stiffness parameter tends to zero. Higher order perturbations are also discussed.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 456-474 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: An integral representation for the solutions of the interior and exterior homogeneous mixed problems on a regular bounded open set in R3 is given in terms of a potential of simple layer on the Dirichlet data and of double layer on the Neumann data. A coercive non-symmetric bilinear form is provided. Singular finite elements containing the first terms of the assymptotic expansion of the singularity are built and error estimates for the surface distributions are given.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 488-505 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The purpose of this paper is to give a systematic analysis for the linear energy dependent diffusion system in reactor dynamics, taking into consideration of delayed neutrons. This analysis includes the existence of a unique positive solution for the time dependent system, the asymptotic behaviour of the solution as t → ∞, the stability and instability of steady-state solutions, and the existence and uniqueness of a steady-state solution for the time-independent system. Using the notion of upper and lower solution, we establish some threshold conditions for insuring the asymptotic behaviour of the solution and the stability and the instability of any given unperturbed solution, including steady-state solution. In fact, these conditions characterize the stability and the instability property of the solution, and yield a bifurcation result in terms of either the size of the diffusion domain or the physical parameters of the diffusion medium. We also discuss the case without the effect of delayed neutrons.
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    Mathematical Methods in the Applied Sciences 3 (1981), S. 537-550 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The relaxation drag of a slender profile or profile arrangement in plane, steady, relaxing subsonic gas flow is studied. Especially, the question is discussed which shapes the profiles must have in order to minimize the relaxation drag. These optimization problems lead to a number of singular integral equations of first kind, one of which is solved as an example with the help of a suitable chosen ansatz.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 15-18 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: In the paper we prove the existence and uniqueness of solutions of the overdetermined elliptic system \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\left( {\rm A} \right)} & {{\rm rot }\upsilon {\rm = }\omega } & {{\rm div }\upsilon {\rm = 0}} & {\upsilon \cdot {\rm }\bar n|_{\partial \Omega } = b} \\ \end{array} $$\end{document} where b, ω are given functions, in a domain Ω C R3 with corners π/n, n = 2, 3, … The proof is divided on two steps, we construct a solution for the Laplace equation in a dihedral angle π/n, using the method of reflection and we get an estimate in the norms of the Sobolev spaces in some neighbourhood of the edge. In the dihedral angle system (A) reduces to the Dirichlet and Neumann problems for the Laplace equation. In the next step we prove the existence of solutions in the Sobolev spaces Wpl(Ω) using the existence of generalized solutions of (A).
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 230-242 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The solvability of a boundary value problem for a nonlinar elliptic partial differential equation in a plane, bounded, multiply connected domain is investigated. The solution of the problem is equal to unknown constants on inner components of the boundary. We want to determine these constants so that the solution satisfies the so-called trailing conditions. The results have immediate applications in hydrodynamics.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 259-271 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The nonlinear potential problem Δ φ = -r2m 0, n = m is studied with r ≥ 0, n ε (½, ∞), m ε (-1, ∞) and n m 〉 0.With various additional conditions we have regular and singular solutions which can be studied explicitly by homology transformation. It is proved that if m - n + 1 = 0 the solution with φ(0) = 1, ≠ (0) = 0 is radiusstable. Numerical analysis of a number of cases with m - n + 1 = 0 yields the same conclusion.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 286-290 
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    Topics: Mathematics
    Notes: Introducing the concept of a supercontinuous operator, we obtain a general convergence theorem for Galerkin approximations. Under the stronger assumption that N is a monotone operator with N(0) = 0, we show norm convergence of the unique Galerkin approximations to the unique solution.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 317-353 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The generalized Feller equation is a linear, autonomous, parabolic equation of a positive space variable and a time variable. Its coefficients are power functions of the space variable, and they depend on four parameters. In general, the equation is singular at the origin and at infinity. It contains as special cases the special Feller equation, the Kepinski equation, and the standard heat equation. The main objective of the present paper is to establish series expansions of solutions of the generalized Feller equation in terms of the elements of two sequences of particular solutions. The elements of one of these sequences are particular initial condition solutions. The two sequences are biorthogonal. The main result is that a solution does have the desired expansion property if and only if it has the Huygens property in some neighborhood of the origin of the time variable.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 354-381 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
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    Topics: Mathematics
    Notes: The problem of stress determination in the area of cut-outs in circular cylindrical shells at given loads is of great interest in industrial practice. This work deals with a mixed boundary value problem of a differential equation derived according to the theory of shallow shells. On part Ct1 of the boundary, the displacements are given, whereas the stresses are specified on the remaining part Ct2. Starting from the Betti-Maxwell principle and with the aid of the fundamental solutions for unit loads and unit displacements, integral representations can be derived for the displacement functions as well as the stress functions.The problem is then transformed into an equivalent system of Fredholm integral equations of the first kind with logarithmic kernels as the main part. As the integral equations together with the auxiliary conditions form a strongly elliptical system of pseudo-differential operators, the Galerkin method converges. Assuming that curves Ct1 and Ct1 do not have points of intersection and that the data are sufficiently regular, the required functions are approximated by cubic splines and, for simplicity's sake, the integral equation system is solved by approximation with a collocation method. In view of the complicated terms of the kernel functions, the kernels are split into a regular and a singular part, the regular part being in turn replaced by cubic splines. The remaining integrations are done numerically by means of Gaussian quadrature formulae. The applicability of the method is demonstrated with the example of a cylinder under internal pressure.
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    Mathematical Methods in the Applied Sciences 4 (1982), S. 451-453 
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    Keywords: Mathematics and Statistics ; Applied Mathematics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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