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  • Articles  (202)
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  • Engineering  (175)
  • superconductivity  (17)
  • thin films  (10)
  • 1990-1994  (202)
  • 1945-1949
  • Electrical Engineering, Measurement and Control Technology  (202)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 7 (1994), S. 127-130 
    ISSN: 1572-9605
    Keywords: Superconductivity ; thin films ; photoconduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The photoinduced enhancement of superconductivity in RBa2Cu3O x (R=rare earth or yttrium) and Pr y R1−y Ba2Cu3O x was explored through temperature-dependent resistivity, Hall coefficient and mobility, and x-ray diffraction measurements. The increases inT c are enhanced near the metal-insulator transition, although photoinduced changes always exist in oxygendeficient samples. Several explanations, including intergrain Josephson coupling, photoassisted oxygen ordering, and the trapping of photogenerated electrons in oxygen vacancies, are discussed.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 7 (1994), S. 427-428 
    ISSN: 1572-9605
    Keywords: Thermal expansion ; dielectric ; metal ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A negative thermal expansion was measured for Ba1−x K x BiO3. This anomaly decreases with increasingx, still exists atx=0.4, and disappears atx=0.5.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 7 (1994), S. 243-249 
    ISSN: 1572-9605
    Keywords: Electronic specific heat ; superconductivity ; pseudogap ; Fermi statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have determined for the first time the electronic specific heatγ(x, T) of YBa2Cu3O6+x for 0.16≤x≤0.97 from 1.8 to 300 K. Weakly superconducting behavior betweenx=0.4 and 0.8 progresses rapidly to strong coupling BCS-like superconducting and metallic normal state behavior forx〉 0.9. However, the continuous development of the entropyS(x, T) withx andT across the entire series suggests a progressive modification of the low-energy spin spectrum with hole doping rather than a simple band model. Fermi statistics andk-space pairing for allx is indicated by the magnitude andT-dependence ofS(x, T). Pseudogap behavior inS(x, T) is observed over a temperature region aboveT c , which increases rapidly with oxygen depletion to around 200 K forx∼0.7. This loss of entropy reflects normal-state correlations apparently unrelated to the superconducting pairing.
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  • 4
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    Electronic Resource
    Springer
    Journal of superconductivity 7 (1994), S. 231-233 
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; thin films ; large-area deposition ; semiconductor substrates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Our technique of reactive thermal co-evaporation has been extended to fabricate large films (up to 4 in.) of YBa2Cu3O7 with high quality. A rotating substrate holder is used to separate the deposition and oxidation processes. This allows free access of the metal vapors. As large substrate wafers we use Al2O3, Si, and GaAs with buffer layers of CeO2, YSZ, and MgO, respectively. On all substrates, the uniformity of thickness and composition was better than 2%. Inductively measuredT c andj c (77 K) were 87.5±0.2 K and 〉1×106 A/cm2, respectively, across the full wafer area. This holds also for GaAs substrates due to a new procedure of capping by Si3N4.
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  • 5
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    Electronic Resource
    Springer
    Journal of superconductivity 7 (1994), S. 547-553 
    ISSN: 1572-9605
    Keywords: van Hove singularities ; superconductivity ; cuprates ; doped fullerenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We review the main results of the van Hove scenario applied to superconducting cuprates. It is based on the assumption that in these materials, the Fermi level lies near a singularity in the density of states (DOS). This hypothesis has recently been confirmed experimentally. We show that this model explains many properties of the high-T c superconductors. We show that an anaogous model with a peak in the DOS may also be applied to the superconducting doped fullerenes. A general feature of the model is a very short coherence length.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 7 (1994), S. 589-591 
    ISSN: 1572-9605
    Keywords: Two-band ; pair transfer ; superconductivity ; dimer ; Hubbard model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In the two-chain Hubbard model the on-site Coulomb repulsion generates a remarkably large pair-transfer coupling constant between bonding and antibonding orbitals of a dimer made of the two sites lying on the opposite chains and linked by a transfer energy. It leads to a pair-transfer interaction between two bands composed of these orbitals, promoting superconductivity (SC). Since it is found to be as large as intraband Coulomb coupling constants, our previous work suggests that SC can occur in this model. In fact we have obtained a clear indication of SC in restricted-size systems carrying out the exact-diagonalization with 6 electrons and a variational diagonalization with up to 14. The SC occurs in suitable band situations for a wide range of on-site Coulomb energies. We also obtained such an SC indication in a two-dimensional Hubbard model. We mention some candidate materials substantiating the present mechanism and suggest it to be quite general.
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  • 7
    ISSN: 1572-9605
    Keywords: Photoconductivity ; high-T c superconductors ; thin films ; spectral dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Temperature and spectral dependences of photoinduced changes of resistance were measured in YBa2Cu3O x thin films with oxygen content ranging as 6.35 〈x 〈 6.75. The absolute value of efficiency of initiation of photoinduced changes decreases with increase in oxygen content, but the position of peaks in the spectral dependence does not change with a change ofx. Temperature dependences of efficiency have an anomaly atT∽220 K, which is present in all the samples studied, and correlates with anomalies observed by other experimental techniques. Qualitatively similar temperature and spectral dependences of efficiency for the samples in both the insulating and metallic phases may be considered as an indication that the persistent photoconductivity effect in YBCO on both sides of the metal-insulator transition has a common origin.
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  • 8
    Electronic Resource
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    Springer
    Journal of superconductivity 7 (1994), S. 921-924 
    ISSN: 1572-9605
    Keywords: Iodine ; superconductivity ; high pressure ; low temperature ; monatomic phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The superconductivity of metallic iodine is observed at temperatures below 1.2 K under pressures above 28 GPa by magnetization and electrical resistance measurements. The pressure dependence of the superconducting transition temperature is studied up to 74 GPa. This is the first observation of the superconductivity of the molecular-dissociated monatomic metal.
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  • 9
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    Springer
    Journal of superconductivity 7 (1994), S. 175-180 
    ISSN: 1572-9605
    Keywords: Proximity effect ; superconductivity ; pair echoes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Recent experiments on N′-N-S junctions with high-temperature cuprate superconductors have shown that superconductivity can be induced in the adjacent, normal metal at distances many times greater than the few hundred Ångstroms range of the conventional proximity effect. We show that this arises in the particular geometry used in these experiments through the constructive interference of the tails of the de Gennes-Saint-James bound and quasi-bound states of the normal metal N that penetrate into the third metal, N′. This constructive interference results in the re-appearance of a pair amplitude in this metal which is analogous to the “spin echo” of NMR and which we name a “pair echo.”
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  • 10
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    Springer
    Journal of superconductivity 7 (1994), S. 643-645 
    ISSN: 1572-9605
    Keywords: Pure and doped C60 ; inelastic neutron scattering ; superconductivity ; phonon density of states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Via inelastic neutron scattering (INS) generalized phonon densities of states are obtained for C60 and superconducting A3C60 (A=K, Rb). Changes in the intramolecular modes agree with and augment recent Raman (RA), infrared (IR), and INS measurements, i.e., in the vicinity of the high-frequency modes of C60 [H g (8),A g (2),H g (7)] we find a pronounced shift of about 10 meV toward smaller energy transfers upon intercalating with potassium. Separated from these vibrations by a gap are the intermolecular spectra which for the doped samples display well-defined optic modes at 11 and 14 meV due to the vibrations of Rb and K ions. Indications of a weak anomalous temperature dependence of low-energy phonons (ħω 〈3 meV) nearT c are observed for K3C60.
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  • 11
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    Springer
    Journal of superconductivity 7 (1994), S. 639-642 
    ISSN: 1572-9605
    Keywords: Alkali-metal-doped fullerenes ; normal-state transport ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The normal-state transport properties of alkali-metal-doped fullerene crystals are explored. The Hall effect has been measured in KxC60 from room temperature toT c . The electrical resistivityρ for K3C60 and Rb3C60 has been measured over a wide temperature range (20–650 K), and notable differences are observed for the materials at both low and high temperatures. The electrical resistivity of Rb3C60 has been measured in hydrostatic pressures up to 9 kbar. The resistivity is highly pressure sensitive. The transport results give an insight into the normal-state conduction mechanism and thus have consequences for the superconductivity mechanism.
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  • 12
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    Springer
    Journal of superconductivity 7 (1994), S. 849-851 
    ISSN: 1572-9605
    Keywords: High-temperature superconductors ; thin films ; critical current ; flux creep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Flux creep characteristics ofc-axis-oriented Bi2Sr2CaCu2O x thin films grown by the method of electron beam evaporation of stoichiometric target and subsequent annealing have been investigated in the absence of external magnetic field. A decrease of the pinning potential with decreasing temperature is obtained fromI–V curves. This result is explained by the presence of the spatially nonlinear pinning potential.
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  • 13
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    Journal of superconductivity 7 (1994), S. 767-771 
    ISSN: 1572-9605
    Keywords: Tl cuprates ; thin films ; ex-situ thin film processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Anex situ process has been developed to produce thin superconducting Tl2Ba2CaCu2O8 films. The properties of films grown on different substrates using different annealing regimes were studied. Critical temperatures of 103–107 K were measured on films prepared in a broad range of annealing temperatures on SrTiO3, LaAlO3, and Y-ZrO2 substrates. A critical current density,J c, of 2×106 A/cm2 at 77 K was measured on LaAlO3. Film morphology was studied by SEM, AFM, and STM.
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  • 14
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. i 
    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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  • 15
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 75-75 
    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
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 127-139 
    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 this paper the traditional square mesh 2D-TLM algorithm is generalized for rectangular meshes of arbitrary aspect ratio. It is shown that the anisotropic rectangular TLM network can be conceived in such a way that the propagation vector remains independent of the direction of propagation in the infinitesimal approximation. A full dispersion analysis of the rectangular mesh in then performed for the general case, and results are compared to that of the traditional square mesh.
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  • 17
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 155-166 
    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 radiation field patterns of rectangular waveguides and horns of finite dimensions are obtained numerically. The electric field integral equation is formulated to relate their radiation patterns to the surface current distribution. These currents are determined numerically by reducing the integral equation to a matrix equation, using the moment method. The computed currents are then used to calculate the radiation patterns and cross-polar fields of the finite wavegiudes and horns. The method is numerically efficient and can be applied to the computation and optimization of the antenna feed configurations.
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  • 18
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 167-177 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Ray-besed methods have been previously developed for accurately predicting the electromagnetic scattering from cavity interiors that allowed for realistic modelling of complex cavities such as jet engine inlets. An analytic geometric model is developed for bifurcated cavities based on connecting sections of generalized super-ellipse functions. The electromagnetic scattering from such cavities using the ‘shooting and bouncing rays’ (SBR) method is discussed.
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  • 19
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 209-221 
    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 theoretical analysis has been developed to study the crosstalk in crossed bundles of parallel lines. The model is based on the theory of the coupled transmission lines and the resulting system of differential equations has been solved by means of the finite difference, time-domain (FDTD) method. The frequency response of the network has been achieved by the discrete fourier transform (DFT) algorithm; measurements, performed with a vectorial network analyser, show a good agreement with numerical simulation.
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  • 20
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 35-41 
    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 eigenmodes in electromagnetic cavities, loaded with arbitrarily shaped dielectric materials, are computed by the edge element method. The computation shows that the well known ‘spurious modes’ no longer appear. Formulae are given and verified so that the number of zero eigenvalues, which come from ∇ × H = 0, may be accurately predicted. Formulae for the order and density of the global matrices are given for a rectangular cavity regularly divided into bricks and tetrahedra, allowing an associated comparison between the contrasting edge and nodal element formulations. Comparison of the computed results with available theoretical and previously published data show the edge element approach to be a robust, accurate and effective method.
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  • 21
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 253-265 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A numerical frequence-domain modelling of two-terminal, non-linear microwave circuits is presented. It basically relies on a process allowing the solution of the frequency-domain curcuit harmonic balance equations while accounting for the semiconductor device by means of an accurate numerical macroscopic physical model. In its present state of development, the model allows the study of a single two-terminal device circuit operating in harmonic mode. Its capabilites are illustrated by means of the results of a study devoted to the optimization of the load curcuit configuration of a millimetre-wave avalanche diode frequency multiplier. The influence of the output load impedance level on the circuit output RF performance has been investigated for different input power levels in direct frequency multiplication mode and in the presence of additional circuit tunings at low harmonic rank idler frequencies.
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  • 22
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    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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  • 23
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 309-319 
    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 a rigorous and systematic procedure to derive a non-linear distributed FET model that an easily be implemented in CAD routines of simulators based on harmonic balance techniques. The new model is derived from a knowldge of the conventional linear lumped equivalent circuit, from non-linear current sources extracted with pulsed measurements, and from the physical dimensions of the FET.For fundamental and haromonic requencies, the FET is modelled by N identical cells. Each cell is made up of a non-linear two-port section inserted between two linear four-port sections that simulate the coupling and the distributed effects along the electrodes of the FET in the width direction only. This non-linear distributed scaling approach to FET modelling has been applied to the analysis of a submicrometre-gate GaAs FET at Millimetre-wave frequencies, and the results were compared to the non-linear lumped element approach. This approach can be applied to other transistors used in non-linear regions at microwave and millimetre-wave frequencies.
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  • 24
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 375-375 
    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 7 (1994), S. ii 
    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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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 399-405 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Symbolic computational systems introduce some unique features in computational engineering. There have been several papers published on the solution of differential equations under given boundary conditions by symbolic systems. The finite element formalism has received prime attention in the course of development of symbolic computation in engineering. The main idea has been to develop a symbolic FEM package to reduce the burden of manual algebra, eliminate errors introduced by numerical quadrature, and improve the efficiency of element generation.This work discusses a symbolic solution to electromagnetic linear antenna problems. The solution is a method of moments that transforms Pocklington's integral equation to a matrix equation. The symbolic system is used to produce (1) analytical integration, (2) the parametric expression for the input impedance and (3) computational code for forward and reverse problem of the input impedance.
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  • 27
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 419-432 
    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 a new finite element formulation in the Laplace domain for both diffusion and wave equations with applications in the field of electrical engineering. With the aid of congruence transformation of matrices, the finite element equations in the Laplace domain are solved and time-domain results can be obtained through the inverse Laplace transform. In a test problem, good agreement between the numerical results derived with the present method and the analytical solutions has been found. For applications in which only Dirichlet and Neumann boundary conditions are involved, this new finite element approach can be applied and provide both frequency-domain and time-domain results in one run without any timestepping scheme. The limitations of using the congruence transformation in solving propagation problems are also addressed in this paper.
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  • 28
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 433-452 
    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 hybrid method obtained as a combination of the coupled-mode method (CMM) and the mode-matching method (MMM) is developed and applied in the analysis of multiple dielectric and magnetic discontinuities in rectangular waveguides. As both are moment methods, some kind of truncation has to be carried out in the computer implementation. It is shown that selection of a different number of modes in the two methods is not necessary, unless low-permittivity meida inside the waveguide are considered. As a consequence, the procedure for slecting the number of basis functions is only done in one of the methods. Numerical examples are presented showing the behaviour of the method and the proofs of convergence. Examples are included illustrating the power of this hybrid technique, especially in relation to non-reciprocal structures containing magnetized ferrites.
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  • 29
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    Topics: Electrical Engineering, Measurement and Control Technology
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  • 30
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 15-24 
    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 the boundary element method to solving two-dimensional steady slow viscous flow problems (creeping flow) in thermal silicon oxidation. The proposed method used the velocity-pressure formulation. The use of the incompressibility condition as a boundary condition and the application of the second Green's identity to transform the domain integral into a boundary integral result in a system of three boundary integral equations for velocity components and pressure. Solution of this system to be an ill-posed problem because of the presence of boundary conditions of the first kind. Two methods of regularization are employed. The numerical results for trench oxidation process are presented.
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  • 31
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    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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  • 32
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 43-67 
    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 particle-in-cell method is coupled with boundary-fitted co-ordinates in order to model the stationary Maxwell-Lorentz problem in technical devices. New numerical algorithms describing the transition between the grid model and the mesh-free model are developed and the existing techniques of finite difference schemes for equidistant grids are extended to non-equidistant, arbitrarily shaped, convex four-point meshes. The modelling process is described, and both the numerical approximation and the algorithms are discussed. Applications in different technical devices show the flexibility of the method.
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  • 33
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 77-84 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Series function expansion algorithms of the time-domain analysis of boundary value problems are discussed. Electromagnetic fields inside a structure under investigation are expanded into series of basis functions and the expansion coefficients are found by means of the Galerkin method. The numerical cost of algorithms is discussed and a cost efficient approach is proposed for formulations using sine and cosine expansion functions. Compared with conventional time-domain methods the algorithms described show the time evolution of the expansion coefficients rather than the samples of a physical continuum at discrete nodes.
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  • 34
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. ii 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 189-199 
    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 rigorous technique for studying a thin wire circular loop antenna excited by a magnetic frill is developed. The exact kernel is derived and used to improve the accuracy. The scheme is applicable to small as well as large loops. Results obtained are nearly indistinguishable from those determined by the Fourier expansion method for non-resonant loops. A disagreement of 2 per cent is generally observed when the loop is close to reasonant for βb 〉 2. Compared with the conventional numerical method where a loop is represented by a polygon of straight wires, the present scheme is much faster and more accurate. Extension of this method to cover an antenna system of arbitrarily oriented loops intermingled with straight wires can be easily achieved.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 239-252 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Simulation results for a n+-n-n+ two-valley semiconductor device obtained by use of a shock capturing numerical agorithm are presented. The one-dimensional problem is modelled by two systems of Euler equations connected by their source terms, and the Poisson equation. The resulting system of seven equations is hyperbolic and non-linear, and it is a great problem to find an adequate numerical approximation of its time-dependent discontinuities. There are additional complications due to the stiffness of the source terms.The numerical method used in this paper is first-order acurate in time but of high spatial order in regions of smoothness. Before the method is applied, the system has to be transformed to a characteristic form. The adopted shock capturing algorithm enables the choice of the order of the accuracy by the appropriate choice of the reconstruction polynomial. Reconstructions of the second and fourth order are tested and some numerical results are presented. Because of the stiffness of the source terms, the sixth-order accurate scheme breaks down. The results presented, and especially the response obtained of the structure to the step and periodic applied voltage, prove the correctness of the used schemes.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 283-304 
    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 algorithm is developed to evaluate the responses of discontinuous coplanar strip-lines excited by external electromagnetic fields. The algorithm uses the cascade chain matrix method which employs the distributed circuit parameters to model the external field coupling to the line and it is applicable to most commonly encountered discontinuities in microwave integrated circuit interconnects on lossy substrates. A general CAD program is developed based on this model and it is applied to realistic coplanar strip-line interconnections with geometric and resistive discontinuities to illustrate the capabilities of the algorithm. These interconnect models are selected from a practical microwave integrated circuit design. Simplicity and fast speed of the algorithm enable computer-aided analysis of externally induced electromagnetic noise in integrated circuits to be carried out. The effects of dielectric losses in the integrated circuit substrates and the discontinuities in the conducting tracks on the wave coupling are investigated in isolation.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 329-342 
    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 finite element method (FEM) with local absorbing boundary conditions has been recently applied to compute electromagnetic scattering from large 3-D geometries. In this paper, we present details pertaining to code implementation and optimization. Various types of sparse matrix storage schemes are discussed and their performance is examined in terms of vectorization and net storage requirements. The system of linear equations is solved using a preconditioned biconjugate gradient (BCG) algorithm and a fairly detailed study of existing point and block preconditioners (diagonal and incomplete LU) is carried out. A modified ILU preconditioning scheme is also introducted which works better than the traditional version for our matrix systems. The parallelization of the iterative sparse solver and the matrix generation/assembly as implemented on the KSR1 multiprocessor is described and the interprocessor communication patterns are analysed in detail. Near-linear speed-up is obtained for both the iterative solver and the matrix generation/assembly phases. Results are presented for a problem having 224,476 unknowns and validated by comparison with measured data.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 371-372 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 357-370 
    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 calculation of potentials in homogeneous and isotropic media by the boundary element method has the advantage that a harmonic solution of Laplace's equation is obtained for given approximated boundary conditions. The technique leads to the solution of linear systems with full matrices of dimension 1000-10,000 for medium- and large-sized three-dimensional problems, An efficient solution procedure of the linear systems is required.While the iterative solution of the large and sparse linear systems arising from the finite difference or the finite element method is well documented, the systems resulting from the boundary element method are typically solved by direct methods. However, in many cases an iterative solver needs far fewer operations to achieve a sufficient accuracy. Importantly, there are many alternative methods, each of them well suited for different types of problem.Here, we provide an overview of state-of-the-art iterative solvers. We will discuss the particular methods that have been successfully applied to systems arising from field calculations in the high-voltage engineering by the boundary element method. The selection of appropriate methods is discussed. We demonstrate that iterative solutions can be much faster than direct solvers with regards to the number of operations. Furthermore, these solvers are optimally suited for today's supercomputers because they can be efficiently vectorized and parallelized.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 407-418 
    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 provides details of a widely applicable technique of hybrid modelling of thermal and particle diffusion which can help to reduce computational load in explicit formulation. The undesirable effects of artificial boundaries, which are introduced when a simulation is truncated or when an expanding mesh is used, can be eliminated by the use of discrete Green's functions. The technique can also be applied to problems involving infinite or near-infinite domains or problems where a complex thermal region is embedded within a larger, more simply described domain.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 179-188 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A convex hexahedral TLM mesh of arbitrary shape is presented and the transmission-line matrix method extended to any non-orthogonal configuration. The novel mesh constitutes a natural generalization of Johns' condensed node. The associated TLM process is analysed and reconstructed as a genuine finite difference time-domain algorithm. Nodal S-parameters are derived from discretized Maxwell's equations and canonical stability criteria yield the TLM timestep. Unitarity is discussed and energy conservation confirmed in the non-conductive case.A given block-diagonal representation of the S-matrix restrains processing time per node and iteration within the range of traditional methods. The shortcomings of the rigid classical grid, as the need for inaccurate staircasing approximations, are, however, ruled out.Our analysis takes advantage of the recently developed propagator integral approach.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 201-207 
    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 existing treatment of an instantaneous endothermic change of state is extended to deal both with exothermic effects and with first order Arrhenius changes. These extended treatments are used to model complex changes of phase occurring during the firing of ball clay and china clay, both of which are constitutents of the slip used in the production of vitreous china ware. The adequacy of the treatments is investigated for both clays by comparing a TLM simulation of a DSC (differential scanning calorimetry) experiment with measurements made during the experiment.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 321-328 
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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 paper describes and compares the wave-chain and transmission matrix approaches to the calculation of transfer-function coefficients for ladder circuits (semi-symbolic analysis). It is found that the wave-chain matrix approach can be computationally more efficient.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 343-355 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: To make possible the application of the three-dimensional finite element method to electrically large problems, it is combined with the analytical solutions of arbitrary large cavity with aperture. In this paper, detailed analysis for this hybrid method is presented. The element matrices necessary for coupling the finite element method to analytical solutions are given. The proposed hybrid method significantly reduces the number of unknown since only the inhomogeneity needs to be discretized. Thus computer memory and storage demands are reduced. In addition. This hybrid method employs the edge element which is not expected to produce spurious solutions. Also, the formulation presented in this paper preserves the sparsity of the finite element matrix, and does not require any matrix inversion. This new hybrid method is used to compute the field distributions in various partially filled rectangular enclosure. The results match well with the pure edgebased finite element method and analytical solutions.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 377-398 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Field computations by mathematical and numerical methods are presented in the time and frequency domain. The techniques used are discretization and modal expansion. The effects of modelling and frequency range on the accuracy and calculation requirements are investigated and discussed. By way of application, several results of RF-filter designs are presented, where these methods have been implemented in CAD programs.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 453-453 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 1-14 
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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: Variational boundary element formulations are developed. Two functionals based on the dual and complementary energy approach are considered, which provide the upper and lower bound of the solution. Calculated examples of electrostatic fields are demonstrated for their field distributions and capacitances. Validity and the solution accuracy are discussed in comparison with the conventional boundary element solution.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 25-33 
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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 method of effective penetration depth is used to produce a novel scalar or polarized finite difference approach for the solution of optical rib waveguide field problems. The new method is quicker than previous finite difference approaches and requires less computer memory. Propagation constant values are presented for a range of semiconductor rib waveguides and are found to be indistinguishable from benchmark results produced using earlier methods of analysis. A simple polarization correction formula recently derived is confirmed by utilizing the good accuracy of these results. This enables discussion of the relationship between quasi-TE, quasi-TM and scalar modes, and a further substantial reduction of the cpu time.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 69-74 
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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 application of multigrid techniques to the computation of the static solutions of electromagnetic field problems governed by Laplace's equation is described. This technique is compared with the conventional successive over-relaxation (SOR) method for solving finite difference problems. In contrast to SOR, the number of iterations of multigrid needed to achieve convergence is largely independent of the grid size. It is shown that the relative performance of multigrid is excellent on large grids where the number of iterations of SOR needed to achieve convergence becomes prohibitively large. The technique is illustrated by applying a parallel implementation of multigrid to find a quasistatic solution of a boxed microstrip problem.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 85-97 
    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 approach to efficiently compute the low-frequency eigenmodes of a time-domain model approximating a linear physical system is proposed. The method is based on principles known from digital signal processing, in particular from parametic spectrum estimation, so it is not surprising that the achievable accuracy is much higher than the accuracy of the usual non-parametric discrete Fourier transform approach. The algorithm works in the general lossy case even for a very large number of unknowns and can easily be extended to calculate steady-state solutions under sinusoidal excitations for several different frequencies simultaneously.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 99-125 
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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: In this paper we demonstrate the use of differential equations by means of an example from network analysis and show that differential/algebraic equations (DAE), rather than explicit ordinary differential equations (ODE), are more suitable for the description of electrical systems and networks. The main ideas of numerical integration of ODEs are presented. We consider this material from the point of view of replacing the ODE by a difference equation (DE). In particular, the relationship between the ODE and the associated DE is discussed. In the last Section the application of integration methods for OEDs upon DAEs and its difficulties are discussed. The paper is intended as a review; but a few new results are also included.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 141-153 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Applying the method of moments to Maxwell's equations, Yee's two-dimensional FDTD scheme with central difference approximations and the two-dimensional TLM method are dervied from first principles of field theory. By comparing the eigenvalues of the two methods, the differences between two-dimensional FDTD and TLM are illustrated.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 225-238 
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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: Transverse transmission concepts in the Fourier transmission domain for multilayer planar transmission medium are presented. This complete transverse transmission theory (TTT) is found to be a superset of different Fourier-transform-based numerical techniques widely used in guided wave analysis, namely the modematching method and the spectral-domain approach. The features of the theory are: the expansion of field quantities in longitudinal section (LSE/LSM) modes, the concept of rotation of the transverse field vectors, and a comprehnsive algorithm using recursive matrix standard form. It is shown that the mode-matching method and spectral-domain approach are generally equivalent except for the last step of imposing the final boundary conditions, and can therefore be summarized in a unified theory within the framework of TTT. In addition, a new parameter, the polarization coefficient, has been introduced to describe the field polarization of the guided wave in a quantitative manner. It is believed that the present theory will help us to gain more insight into hybrid mode propagation in multilayer planar circuits.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 267-281 
    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 considers the adaptation of drift-diffusion device simulation methodology to study Auger-recombination-induced hot electron transport characteristics in InGaAsP/InP double heterostructure laser diodes. In order to model the transport behaviour of the Auger hot electrons, we decompose the conventional electron current continuity equation into two components, with one for the Auger hot electrons and the other for the low-energy electrons. These equations, which use the energy relaxation time parameter to model the dynamics of the Auger hot electrons, are then coupled with the hole current continuity equation and the Poisson equation to obtain self-consistent solutions. Results from the case studies of one-dimensional N-p-P InGaAsP/InP double heterojunction laser diodes with material composition corresponding to 1·3 μm and 1·55 μm wavelength emissions are presented. We have observed that hot electrons generated through Auger recombination inside the active region can spread into both the N- and the P-InP cladding layers. Within the drift-diffusion framework, it is demonstrated that the hot electron concentration in the N-InP cladding layer can be five orders of magnitude higher than that in the P-InP cladding layer. Because energy transport of the hot electrons in not modelled under the drift-diffusion approximation, the simulated results are discussed to highlight some of the possible limitations in using drift-diffusion physics to study Auger hot electron transport behaviour. The importance of taking energy transport into account is emphasized.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 307-307 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    Journal of superconductivity 6 (1993), S. 1-17 
    ISSN: 1572-9605
    Keywords: Superconductors ; thin films ; thin-film processing ; thin-film deposition ; sputtering ; coevaporation ; activated reactive evaporation ; molecular beam epitaxy ; laser ablation ; CVD ; MO-CVD ; PA-CVD ; multilayers ; heterostructures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This review of high-T c superconducting thin-film processing focuses on the developments in thin-film deposition technologies since 1987. The common deposition processes are described with reference to their effects on superconductor film performance. A comparative evaluation of the potential of the technologies is also given. The development of multilayers and heterostructures is an important requirement for future device applications and is also described. The latest results of the deposition of novel superconducting materials and deposition on uncommon substrates are discussed. The outlook on some imminent topics of future development in process technologies for high-T c superconducting thin films is discussed.
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    Journal of superconductivity 6 (1993), S. 107-109 
    ISSN: 1572-9605
    Keywords: BiSrCaCuO ; superconductivity ; phase structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract With XRD,R-T curves, and a.cϰ measurements, the doping and codoping effects of Sb and V to a Cu-deficient Pb-doped Bi system have been studied. A sample singly doped with V possesses aT c about 2 K lower than that of a sample singly doped with Sb. This is attributed to the different sites of their substitution. It was observed that for promoting 2223 phase formation, Sb and V works cooperatively, and the codoping of Sb may enhance the 2223 phase formed. With a low doping level of Sb, the optimum doping amount of V is 0.3, i.e., with a nominal composition of Bi1.5Pb0.3Sb0.06Sr2Ca2Cu2.4V0.3O y . A sample in which the 2223 phase is the dominant phase and which has a zero resistance transition temperature of 105 K has been obtained.
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    Journal of superconductivity 6 (1993), S. 119-160 
    ISSN: 1572-9605
    Keywords: High-T c superconductivity ; microwave devices ; thin films ; surface resistance ; microwave device fabrication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract High-T c superconductivity has generated a great deal of interest because of the challenges it presents in the fields of material science, condensed matter physics, and electrical engineering, and because of the potential applications which may result from these research efforts. Thin-film passive microwave components may become the first high-temperature superconducting (HTS) devices available for widespread use and commercialization. In this article, we review aspects of material science, physics, and engineering which directly impact high-T c superconducting microwave devices and discuss issues which determine the performance of these devices. Methods of growing HTS thin films on large-area substrates, techniques for fabricating single-level HTS passive microwave components, and the relevant properties of high-T c superconducting films are discussed, with a focus on thin films of the HTS material YBa2Cu3O7−δ. Several known mechanisms for microwave loss in both the superconductor and the dielectric substrate are presented. An overview of the general classes of superconducting passive microwave devices is given, and representative microwave devices which have been recently demonstrated are described in detail. Examples of a select few HTS active microwave components are also presented. Potential microwave applications are illustrated with comparisons to current technology.
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    Journal of superconductivity 6 (1993), S. 185-189 
    ISSN: 1572-9605
    Keywords: Thallium cuprates ; superconductivity ; magnetic hysteresis ; irreversibility ; flux pinning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract dc magnetic hysteresis as well as flux penetration and flux expulsion were investigated in Tl2−y Ba2CaCu2O8−x polycrystals and monocrystals. All measurements were performed at 35 K and in the 0–5 T field range. Hysteresis measurements revealed an irreversibility field of about 2 T. Existing models predict identical field-cooled (fc) and zero-field-cooled (zfc) magnetizations and vanishing time dependence above this field. Although the identical fc and zfc magnetizations are in fact observed, the time dependence vanishes only for flux penetration after zero-field cooling; a remanence is preserved after field cooling and decays with a finite relaxation rate. Activation energies calculated on the basis of the thermal activation model display a pronounced field dependence, and arelower for flux penetration than for flux expulsion in high fields (H≥3 T) for all orientations. This behavior of extreme layered superconductors contradicts classical theoretical models and questions the original definition of the irreversibility line as well. All of our results are consistent with the recent theory of lock-in transition, and can be well interpreted by using those principles.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 167-167 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 183-193 
    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 equivalent circuit for a symmetrical condensed TLM node is presented. The basic circuit has twelve ports and consists of 24 1:1 ideal transformers. Three additional conductances model the conductivity of the medium. The circuit is extended with additional ideal transformers giving six ports for short-circuit and open-circuit stubs which model the permittivity and permeability of the inhomogeneous medium. The scattering matrix of the 18-port network is determined symbolically by solving a set of linear circuit equations. The matrix agrees with previously published results for a symmetrical condensed TLM node, obtained from Maxwell's equations.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 233-236 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: We have extended the one-dimensional transmission-line modelling (TLM) of diffusion, drift and recombination of charge carriers in semiconductors to multiple dimensions. Detailed TLM formulation of the continuity transport equation in a more general form is presented.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 29-45 
    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 Hilbert space representation of the TLM method for time-domain computation of electromagnetic fields and the algebraic computation of the discrete Green's function are investigated. The complete field state is represented by a Hilbert space vector. The space and time evolution of the field state vector is governed by operator equations in Hilbert space. The discrete Green's functions may be represented by a Neumann series in space- and time-shift operators. The Hilbert space representation allows the description of the geometric structures by projection operators, too. The system of difference equations governing the time evolution of the electromagnetic field in configuration space is derived from the operator equation for the field state vector in the Hilbert space.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 67-81 
    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 state and output equations of the overall networks are derived from the state and output equations of individual multiports and knowledge of the interconnections between them. A generalized lumped-distributed L/D multiport is described by its associated state, output and non-linear equations in the time domain. Any network can be considered as composed of a set of multiports and independent sources. These equations have been incorporated into a computer-aided procedure for the analysis of L/D networks. The procedure can be used for the simulation of any non-linear microwave circuit and offers the facility of developing a multiport equivalent circuit for any linear or non-linear device or subcircuit. Several examples are successfully analysed using the developed general program.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 109-126 
    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 difference equations of the scalar linear transmission-line matrix (TLM) routine as introduced by Johns for numerically solving the diffusion equation are shown to be isomorphic to Goldstein's correlated random walk model of diffusion. For the infinite homogeneous bar their exact solution is derived algebraically and given in the form of Jacobi polynomials. This puts the TLM algorithm on a sounder mathematical and physical basis. The accuracy in solving the diffusion equation is investigated in general form and thus its astonishing efficiency explained. Several other basic questions of this numerical technique are also discussed.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 161-164 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A comparative study of two alternative networks for TLM modelling of diffusion processes has been undertaken. Some of their inherent advantages and disadvantages are analysed according to the ratio between the impedance of the lossless transmission lines and the lumped resistance. Their relative accuracy and utility in controlling the timestep automatically are examined.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 237-251 
    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 a rigorous and systematic procedure to derive a non-linear distributed FET model that can easily be implemented in CAD routines of simulators based on harmonic balance techniques. The new model is derived from a knowledge of the conventional linear lumped equivalent circuit, from non-linear current sources extracted from pulsed measurements, and from the physical dimensions of the FET.For fundamental and harmonic frequencies, the FET is modelled by N identical cells. Each cell is made up of a non-linear two-port section inserted between two linear four-port sections that simulate the coupling and the distributed effects along the electrodes of the FET in the width direction only. This non-linear distributed scaling approach to FET modelling has been applied to the analysis of a submicrometre-gate GaAs FET at millimetre-wave frequencies, and the results were compared with the non-linear lumped element approach. This approach can be applied to other transistors used in non-linear regions at microwave and millimetre-wave frequencies.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 283-297 
    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 finite element method formulation is given for solving Schrodinger's wave equation for a single electron in a crystal lattice cell subject to a known periodic potential. The formulation has been implemented for a two-dimensional lattice, with an arbitrary potential profile, modelled by quadratic isoparametric elements, The FEM solver returns a specified number of electronic energy states, En, and nodal values of the complex wavefunctionψn Input data is generated by a standard FEM mesh generator. The postprocessing, given n, for reproducing a full 2-D E-k Brillouin diagram and given k, the electronic distribution, has been implemented. Tests on a 2-D generalized Kronig-Penney energy band model showed excellent agreement; between FEM results and analysis. The solver was further satisfactorily checked against published augmented plane wave calculations for a circular potential well within a square lattice. Specimen results are presented for the same circular well but with graded potential distributions and for a rectangular potential barrier set askew in a square lattice. Two-dimensional energy band solvers have application to superlattice nanostruc- tures, whilst a general, full 3-D FEM quantum solver seems feasible.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 299-304 
    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 major limitation of the transmission-line matrix (TLM) method used to solve Maxwell's equations is the long computation time required. The TLM scattering calculations involved can, however, be viewed as parallel in nature. This paper describes an effort to reduce computational time by using an SIMD, DAP multiprocessor computer employed to solve a two-dimensional TLM electromagnetic field formulation. A parallel algorithm based on the TLM scattering algorithm is designed and implemented using FORTRAN- PLUS Enhanced on an AMT DAP 510 machine. Here the connectivity of the DAP is exploited to simulate the intrinsic scattering behaviour on which the TLM algorithm relies. The results show that parallel processing on an SIMD machine such as the DAP is advantageous, especially for higher-order mesh sizes.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 1-1 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 19-27 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: We show the derivation of parameters in the frequency domain from time-domain data. Far-field characteristics are obtained by a convolution formula with the harmonic field amplitudes, which are obtained via a Fourier transform or by sampling. The electric field of filter ports is expanded into the discrete eigenmodes. By this method, a monochromatic exact open boundary can be formulated and the fields divided into the incident and the reflected part. For wide band operation an a posteriori error correction scheme is presented.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 99-108 
    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 rigorous formulation of the scattering by a magnetized ferrite in a rectangular waveguide is presented. The EM field depends on the dimension, the frequency and the internal static magnetic field of the ferrite post. For some special values of the above quantitites the reflection or the transmission coefficient becomes equal to zero. These values give a family of filters and the results which follow explain their characteristics.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 145-159 
    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 finite difference method is used to design a new type of sectoral horn antenna with corner channel inserts which produces a tapered aperture amplitude distribution in the E-plane. The channel inserts, which present a simple modification to the horn aperture geometry, act as effective side-lobe suppression devices. The efficiency of the suppression technique was successfully tested on an experimental horn whose performance is compared to that of a horn with similar geometrical dimensions but with no channel sections.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 127-134 
    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 stress birefringence and mode coupling effects in polarization-preserving fibres are most important problems which need to be improved. For a realization of some optical devices, the dielectric waveguide with sinusoidally varying circular cross-section has been investigated. It becomes very important to analyse the electromagnetic field distribution in a dielectric waveguide with a time-dependent moving boundary. This paper shows that numerical methods can simulate the effect of the external disturbance on the dielectric waveguide from time to time. The author has discussed body fitted grid generation with moving boundary for the Poisson and Laplace equations.1,2 We have extended this technique for Maxwell's equation. The technique employs a kind of an expanded numerical grid generation. As the author adds the time component to grid generation, the time dependent co-ordinate system which coincides with a contour of moving boundary can be transformed into a fixed rectangular co-ordinate system. We could show the electric distribution in the waveguide time by time to verify the possibility of an application for an optical fibre. This technique makes it possible not only to analyse the effect of the external disturbance in a coherent optical communication system but also to fabricate optical devices.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), 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: A propagator integral interpretation for general TLM processes is presented and applied to discretized Maxwell's equations. The approach provides exact algebraic solutions of finite difference equations along a quite universal scheme.Specifically, Johns's process based on the symmetrical condensed node is reconstructed and generalized as a clear-cut FD algorithm. The fields computed are exact time-domain solutions of the FD equations, provided that total voltages and currents are evaluated and stub quantities are not externally excited. Losses are very naturally incorporated into the TLM algorithm.The structural similarity of the TLM process (properly operated) with the propagator integral appears just as fundamental as general and should have further applications.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 195-206 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The computer implementation of time-domain finite difference methods for the solution of Maxwell's equations is considered. As the basis of this analysis, Maxwell's equations are expressed as a system of hyperbolic conservation laws. It is shown that, in this form, all the well-known differencing schemes can be easily expressed, thus increasing the applicability of the implementation issues to be discussed. Practical issues, such as computational efficiency and memory requirements, are discussed for the implementation of the finite difference schemes. Advanced programming techniques in the C language are used to implement the finite difference schemes discussed. The example of the penetration of electromagnetic energy through a shield with a thick gap is used to check the performance of the methods. It is shown that, for cases where the disturbance remains localized in the computational mesh, these techniques result in memory and CPU time savings.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 221-231 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Photoconductive circuit elements (PCEs) are suitable for switching applications: they can be turned on and off rapidly, they can conduct a large current in the ‘on’ state when applying a laser or other optical excitation containing high energy photons exceeding the silicon band gap energy, they have a large resistance in the ‘off’ state when the light is off, and they can be fabricated using a simple process. We report the steady- state characteristics of PCEs simulated from a two-dimensional simulator called PISCES-2B. The effects of the conducting channel length, the resistivity of the intrinsic silicon, and the type of contact region on the performance of the PCE will be investigated and discussed. Based on the simulation results, optimal PCE device make-ups will also be suggested.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 269-281 
    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 estimation of transfer-function parameters, such as poles and zeros, is useful for characterizing and identifying electromagnetic scatterers. The conventional frequency-domain Prony's technique can estimate these parameters from sampled, frequency-domain data. However, it fails to estimate the true parameters when the sampled data contains contributions from out-of-band poles. In this paper, an extended frequency-domain Prony's technique is developed that circumvents this problem by adding polynomial terms to the standard, Prony pole series. This new technique is shown to be very effective for estimating the poles of transfer functions over very wide bandwidths, without the need for large numbers of simultaneous equations, even when the data are corrupted by noise.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 3-17 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Ultra-wideband (UWB) pulsed plane wave scattering from a large but finite strip grating in free space is analysed in the frequency domain via decomposition into plane wave spectra, implemented numerically by the method of moments, and then inverted into the time domain (TD). To make this procedure practical under UWB conditions, closed form expressions are derived for interaction integrals involving widely separated expansion and testing functions. These closed forms are based on a judicious choice of the basis functions, and on asymptotic methods for reducing the integrals. Although large separation distances are assumed, the expressions have been found to be accurate for separations as small as 0·1 wavelengths. The TD self terms can also be evaluated efficiently. To test the frequency domain algorithm, comparisons are made with available data in the literature for surface currents and far-field scattering from multiple strips. New short pulse TD results are shown as well.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 47-65 
    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 this paper a new TLM model for the two-dimensional wave equation is introduced. It is synthesized directly from a FD algorithm. The FD algorithm is second-order-accurate in both space and time, and is explicitly time-stepped. The spatial derivatives in the FD algorithm are approximated by the weighted combination of two standard central difference stencils, one oriented as usual, the other rotated by 45° with its arms extended by a factor of (2)1/2. The TLM model is realized as the weighted connection of two original models (with the same geometrical configuration as the FD algorithm). The weighting in the TLM model is accomplished by using a variable intrinsic impedance for specific elemental transmission lines. The FD and TLM methods possess identical dispersion relations if the former is operated at its upper limit of stability. Therefore, under these conditions both represent identical models for the simulation of wave propagation. The propagation characteristics of the new model are investigated and the conditions for approximate numerical isotropy are provided. The numerical implementation (scattering matrix and transfer event) is described. To validate the new model, the calculation of cutoff frequencies of various modes in rectangular waveguide is performed. Comparison with analytical results (for an unfilled waveguide) and other numerical results (for a waveguide partially filled with a dielectric) validate the implementation of the model.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 83-98 
    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 major limitation of the boundary element method (BEM) for the solution of electrical potential problems is the long computational time required. However, a large portion of the calculations involved can be viewed as being parallel in nature and can therefore be computed concurrently. This paper makes an effort to increase the efficiency of the BEM process using transputer-based multiprocessor computing techniques. The algorithms developed may equally well be applied to any multiprocessor system. The application selected to demonstrate the technique is the solution of an electrostatic problem governed by a two-dimensional Laplace equation.A parallel algorithm for problem setup and field extraction using BEM is designed and implemented on a transputer array. Special attention is directed to the utilization of the parallel processors to achieve maximum efficiency. The analysis in this work concentrates on the communication strategies for passing data between processors as well as a consideration of the workload attributed to each processor.The parallel algorithms were implemented using 3L Parallel Fortran; however, the choice of topology for the overall BEM implementation was limited by the fact that certain parts of the algorithm could only utilize a pipeline configuration of processors. Comprehensive results for the parallel BEM algorithm are given and they are encouraging, indicating that parallel processing has much to offer when applied to the boundary element method.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 135-144 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Redundancy in the simplest form of a two-dimensional TLM network is identified and a method of eliminating it is described. Results obtained using the non-redundant algorithm are compared with those derived from the standard, redundant algorithm. The non-redundant approach is extended to deal with non-uniform elemental capacitance; a cylindrical geometry is taken as an example of this. The scope for and benefits of rendering TLM diffusion models non-redundant are discussed.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 165-166 
    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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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 169-181 
    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 approach to the estimation of the current density distribution and the eddy current loss in bundled multi-wire cables using the boundary element method is proposed. Under the assumption of the gradual twist of the bundled wires, the cables are modelled to be two-dimensional with respect to their cross-sections. Three-phase transmission lines of cyclic symmetrical configuration are considered for which a reduction method is utilized to provide efficient computation. Some numerical demonstrations are made for three types of three-phase transmission-line models, consisting of a single wire and three and seven bundled wires. Two cases are considered: one in which the bundled wires are electrically contacted one to another on their surfaces and one in which they are independently insulated. The equivalent resistance is also calculated to examine the skin effect. The skin effect and the effectiveness of the multi-wire configuration to reduce the skin effect are well demonstrated.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 253-268 
    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 commonly used transmission-line modelling (TLM) network of one-dimensional diffusion problems often results in unwanted oscillations. Two different TLM configurations (line boundary (LB) and resistance boundary (RB)), are investigated with some techniques necessary to reduce the oscillations. Comparisons between the various LB and RB models addressed in this paper, indicate that, in general, two-dimensional TLM models produce consistently more accurate results.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 305-307 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    Journal of superconductivity 5 (1992), S. 1-3 
    ISSN: 1572-9605
    Keywords: Bi-Sr-Ca-Cu-O ; superconductivity ; phase structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The effect of oxygen content on superconductivity of the 2212 and 2223 phase has been studied. By comparing the excess oxygen, the modulation vector, the XRD patterns, and the electric resistivity of 2212 and 2223 phase samples obtained with different post-annealing conditions, i.e., annealing at 600°C or quenching from 860°C, it was found that the super-conductivity is markedly influenced by both the defect distribution in non-Bi layers and the interstitial oxygens incorporated in the Bi-O layers. A tentative explanation for this is given.
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    Journal of superconductivity 5 (1992), S. 25-27 
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7(Ag) ; superconductivity ; ac losses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract 60-Hz ac lossesP were measured at temperature 77 K for sintered powder (YBa2Cu3O7)1-x Ag x samples as a function of applied magnetic fieldh. Rod-shaped samples were cut from pellets forx= 0 and 0.05. The losses were measured in a uniform ac magnetic fieldh applied parallel to the sample surface. Measurements were made in fields up toh= 1000 A/cm rms at temperature 4.2 K and up toh=600 A/cm rms at temperature 77 K. The results may indicate an increase of the intergranular current density and are discussed in relation to the grain size.
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  • 97
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    Journal of superconductivity 5 (1992), S. 107-114 
    ISSN: 1572-9605
    Keywords: High Tc ; thin films ; flux creep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Critical current density vs. temperature curves and I–V characteristics have been measured onc-axis-oriented BSCCO thin films. The experimental data have been described in terms of flux creep effects. Although the films are not single phase and carry a slightly lower critical current density with respect to those of BSCCO single crystals, the measurements point to the presence of flux thermally activated phenomena with a pinning potentialU 0 of about 25 meV.
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  • 98
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    Journal of superconductivity 5 (1992), S. 301-311 
    ISSN: 1572-9605
    Keywords: Ag substitution ; BPSCCO ; bismuth ; Raman spectroscopy ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The effects of Ag substitution on the formation of the superconducting phases in the BPSCCO system have been investigated by Raman spectroscopy and XRD. The silver was found either to accelerate the formation of the 2212 phase or to reduce the formation temperature of the 2212 phase. Moreover, addition of even a small amount of silver (Bi∶Pb∶Ag=8∶2∶1) poisons or inhibits the formation of the 2223 phase. However, there is no apparent effect on theT c of both the 2212 and 2223 phases. In addition, the presence of silver does not alter the mechanism for the formation of the PBSCCO superconducting phases.
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  • 99
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    Journal of superconductivity 5 (1992), S. 83-94 
    ISSN: 1572-9605
    Keywords: Theory ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Based on a generalized BCS Hamiltonian in which the interaction strengths (V 11,V 22,V 12) among and between “electron” (1) and “hole” (2) Cooper pairs are differentiated, the thermodynamic properties of a type-I superconductor below the critical temperatureT c are investigated. An expression for the ground-state energy,W-W 0, relative to the unperturbed Bloch system is obtained:W-W 0=−1/4[N 1(0)Δ 1 2 +N 2(0)Δ 2 2 ], whereN j(0) represent the electron and hole densities of states at the Fermi energy εF, and Δj are the solutions of the simultaneous equations, $$\Delta _j = \tfrac{1}{2}V_{j1} N_1 (0)\Delta _1 {\text{ sinh}}^{ - {\text{1}}} (\hbar \omega _D /\Delta _1 ) + \tfrac{1}{2}V_{j2} N_2 (0)\Delta 2_2 {\text{ sinh}}^{ - {\text{1}}} (\hbar \omega _D /\Delta _2 )$$ with ωD denoting the Debye frequency. The usual BCS formulas are obtained in the limits: (all)V jl=V0,N 1(0) =N 2(0). Any excitations generated through the BCS interaction Hamiltonian containingV jl must involve Cooper pairs of antiparallel spins and nearly opposite momenta. The nonzero momentum orexcited Cooper pairs belowT c are shown to have an excitation energy band minimum lower than the quasi-electrons, which were regarded as the elementary excitations in the original BCS theory. The energy gapε g(T) defined relative to excited and zero-momentum Cooper pairs (whenV jl〉0) decreases fromε g(0) to 0 as the temperatureT is raised from 0 toT c. If “electrons” only are available as in a monovalent metal like sodium (V 12=0), the energy constant Δ1 is finite but the energy gap vanishes identically for allT. In agreement with the BCS theory, the present theory predicts that a pure nonmagnetic metal in any dimensions should have a Cooper-pair ground state whose energy is lower than that of the Bloch ground state. Additionally it predicts that a monovalent metal should remain normal down to 0K, and that there should be no strictly one-dimensional superconductor.
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  • 100
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    Journal of superconductivity 5 (1992), S. 203-217 
    ISSN: 1572-9605
    Keywords: Cuprates ; superconductivity ; review
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Different ways to optimizeT c 's and the magnetic properties of high-T c superconductive cuprates are described and discussed. Oxygen intercalation-desintercalation phenomena and cationic substitutions (M3+ for M2+ or vice versa) lead to a variation of the hole carrier density and can have a drastic influence onT c 's, as shown for bismuth, thallium, and lead-based cuprates, as well as for La2CuO4 and “123”-type superconductors. In the former, the role of hole reservoirs for the rock salt type layers is outlined. The modification of the hybridization of orbitals can also explain the variations ofT c 's observed in some systems like Y1−x Ca x Ba2Cu3−x :Fe x O7 in which the oxidation state of copper remains constant. A critical current density enhancement can be realized by irradiating high-T c materials by high-energy heavy ions because of the peculiar columnar structure of the heavy ion-induced tracks. The effects of such columnar defects, 70 Å in diameter, on flux pinning, magnetic relaxation, and location of the irreversibility line of bismuth-based 2212 crystals irradiated by 6-GeV Pb ions are reported. We observe a strong shift of the irreversibility line toward high fields and temperatures, indicating that pinning effects must be taken into account in the vortex lattice motion. Such induced changes are accompanied by a strong enhancement of the critical current density and a significant enlargement of the irreversibility region in theH,T plane.
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