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  • Articles  (801)
  • Wiley-Blackwell
  • Electrical Engineering, Measurement and Control Technology  (801)
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  • 1
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 153-166 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Most methods for the numerical calculation of inverse Laplace transformations f(t) = L-1[F(s)] have serious limitations concerning the class of functions F(s) that can be inverted or the achievable accuracy. The procedures described in the paper can be used to invert rational as well as irrational or transcendental functions of the complex variable s. The required accuracy of the results can be enhanced without changing the algorithm, only at the cost of a longer computation time. The described methods were verified with many examples including transients in lumped/distributed systems with sections of lossy multiconductor transmission lines or with distributed RC elements. © 1998 John Wiley & Sons, Ltd.
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  • 2
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 207-219 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The IMPETUS II code simulates the atomic mixing and particle emission that occurs when a solid is bombarded by energetic particles (as in SIMS or SNMS). The underlying model consists of a system of partial differential equations that are solved by a finite difference method (FDM). Special techniques are also employed to model thin layers and sharp interfaces, to deal efficiently with wide homogeneous layers (when the solution is tending to a steady state), to model linear diffusion in order to smooth the sharp interfaces before they enter to domain of the FDM.In this paper the special techniques are described in detail. Results from test problems, demonstrating these techniques, are shown. An algorithm that describes the way the IMPETUS II code is structured is given. © 1998 John Wiley & Sons, Ltd.
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  • 3
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 273-274 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: No Abstract
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  • 4
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 317-318 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 5
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 255-257 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: We re-examine the potential drop method to give a direct estimation of the absolute error in transmission-line matrix (TLM) diffusion modelling. In particular, the open-circuit boundary is taken into account. Promising results are presented with a structure relevant to thermal analysis of semiconductor devices. © 1998 John Wiley & Sons, Ltd.
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  • 6
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 277-287 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The solution of Maxwell's equations is considered using the finite difference time domain (FDTD) method and the client-server software paradigm on a heterogeneous network of distributed computers. The performance of compilers is evaluated and the PVM 3.3 message-passing harness, in both its conventional and TCP mode of operation, is compared with direct calls to the lesser known TCP/IP routines on the operating system. An example is given showing the impact of using different floating-point representations, in each subdomain, when computing field updates. As far as we are aware to date, there has been no discussion of the actual content of the communication between concurrent FDTD processes; accordingly we have defined one such protocol. © 1998 John Wiley & Sons, Ltd.
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  • 7
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 55-68 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Multiresolution time domain (MRTD) analysis is applied directly to Maxwell's equations to model inhomogeneous dielectric material. In our approach, scaling and wavelet functions are used as a complete basis for the method of moments. The MRTD scheme is used to analyze different types of resonant cavity structures with varying dielectric perturbations in one, two and three dimensions. The results presented here agree very well with those obtained by FDTD, FEM and integral equation methods. MRTD allows for considerable savings in memory and computation time in comparison to FDTD, while maintaining the same accuracy of the results. © 1998 John Wiley & Sons, Ltd.
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  • 8
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 87-103 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An efficient novel algorithm is introduced for ground wave propagation problems. First, ground wave propagation characteristics for a vertically polarized short electric dipole over a smooth spherical earth are reviewed, reducing the vector electromagnetic problem for the three-dimensional spherical geometry to an equivalent two-dimensional rectilinear scalar potential problem which is solved by spectral analysis and synthesis. Alternative evaluations of the spectral integral yield ray optical and normal mode solutions, which are conventionally referred to as the Norton and Wait formulations, respectively. Combining these formulations in an efficient manner yields a hybrid algorithm which is constructed so as to account adaptively for the characteristics of ground wave propagation in interference, intermediate and diffraction regions (including mixed paths) for various source and/or receiver heights. Numerical comparisons are made with reference results obtained via the parabolic equation (PE) method, in parametric ranges where PE is reliable; this permits assessment of the effectiveness of the hybrid approach. © 1998 John Wiley & Sons, Ltd.
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  • 9
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 183-184 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: No Abstract
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  • 10
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 187-187 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: No abstract
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  • 11
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 233-242 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The propagation factors of buried microstrip lines are considered. The associated eigenvalue problems are solved by the edge-based vectorial finite element method (VFEM). To improve the higher-order VFEM solutions, the problem infinite domain is truncated by second-order absorbing boundary conditions (ABCs). This reduces the number of unknowns and, consequently, the numerical effort. Owing to the many advantages of both the edge-based VFEM and the second-order ABCs, this full-wave method is implemented by a general computer program for solving unbounded domain problems involving complex geometries and inhomogeneous media. The examples presented show the validity of this technique. © 1998 John Wiley & Sons, Ltd.
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  • 12
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 299-306 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The application of the FDTD algorithm on generalized non-orthogonal meshes, following the basic ideas of Holland (1983), has been investigated by many authors for several years now, and detailed dispersion analysis as well as convergence studies have been published. Already in 1992 also a general stability criterion was given for the time integration using the standard leap-frog scheme (Lee et al.). Many authors, however, still propose some damped time stepping algorithms to work around unexpected instabilities in the discretization method. In this paper the origin of this type of instability is revealed, and a technique to obtain a stable discretization of Maxwell's equations on non-orthogonal grids is proposed. To obtain more insight into the stability properties of the method, it is reformulated according to the matrix-vector notation of the Finite Integration Technique. © 1998 John Wiley & Sons, Ltd.
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  • 13
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 3-19 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents an efficient space domain integral formulation of planar dielectric structures based on the concepts of multiresolution analysis (MRA) theory. Battle-Lemarie multiresolution expansions are utilized in the moment method solution of a volume integral equation for the unknown electric field. The generation of sparse moment matrices is explained in view of the cancellation property of wavelet basis functions. The formulation is then applied to two- and three-dimensional dielectric structures including waveguides and resonators, and the numerical results and consequences of matrix sparsity are discussed in detail. © 1998 John Wiley & Sons, Ltd.
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  • 14
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 41-54 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The local support and vanishing moment property of wavelet bases have been recently used to obtain a sparse matrix representation of integral equations in the spatial domain. In this paper, an application of the cubic spline and the corresponding semi-orthogonal wavelets in the spectral domain is proposed for the evaluation of the reflection coefficient for open/short transmission lines. Because of the nearly optimal time (space)-frequency (wavenumber)-window product of the cubic spline and wavelet, the double spectral integrals appearing in the formulation can be computed more efficiently than with the commonly used piecewise sinusoidal (PWS) or triangular basis functions. It is shown that the time-frequency-window product of the triangular and PWS function are close to each other, whereas those of the cubic spline/wavelet are close to 0·5, the lowest possible value corresponding to functions of Gaussian class. Both the PWS and wavelet bases are applied to microstrip and coplanar waveguides with isotropic and anisotropic substrates, and the results are compared with published theoretical and experimental data. It is observed that even though the number of splines/wavelets required for an accurate representation of the current distribution in the transmission line is almost twice as high as the number of PWS functions, the overall computation time decreases significantly in the former case. © 1998 John Wiley & Sons, Ltd.
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  • 15
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 105-121 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes a computationally efficient diakoptic algorithm for the solution of closed-mesh electrical network equations. The algorithm is designed for use with time-varying and/or discontinuous equations describing limited size power supply systems, allowing them to be torn into smaller subdivisions in a manner that is independent of their structure. The efficiency of the algorithm is demonstrated by comparing its performance with that obtained when using a more conventional sparse matrix technique, on the basis of the number of floating point operations required for the solution of a range of typical network problems. Mention is made of the parallel processes inherent in the resultant equation structure. © 1998 John Wiley & Sons, Ltd.
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  • 16
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 189-205 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The atomic mixing model that forms the basis of the IMPETUS software is described in detail. The model simulates the mixing and particle emission that occurs when a solid is bombarded with energetic particles, such as in SIMS or SNMS. The methods employed for computing the deposition of the bombarding particles and their energies along with the modelling of the particle yield and the surface recession speed are described.The material volume concentrations are governed by a set of partial differential equations. A description of the finite element method that is employed for their solution is given. Results from the application of IMPETUS II to a number of typical structures are given. © 1998 John Wiley & Sons, Ltd.
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  • 17
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 259-271 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: There is a class of material processing simulators which require solution of the diffusion equation over a surface which is evolving due to some physical or chemical process related to the concentration of the diffusing species. Because of its explicit and unconditionally stable nature, the transmission line matrix (TLM) method is well suited to efficiently solve the diffusion equation in these instances. However, the methodology for using TLM on a dynamic problem space is not well established.This paper describes the development of algorithms to handle the insertion, deletion and motion of TLM nodes along the one-dimensional surface of a two-dimensional thin film process simulator called GROFILMS. These routines are completely compatible with concurrent time scaling to increase computational efficiency. Central to this development is the use of an asymmetric TLM cell which provides more flexibility for representation and minimizes the disturbance effects of these nodal operations. The scaling routines apply conservation of charge and continuity of current into the affected region to recompute the scattered or the incident pulses as a result of the evolving network. Verification of these results through comparison with known analytic solutions is achieved where possible. © 1998 John Wiley & Sons, Ltd.
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  • 18
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 69-84 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The use of wavelet expansions in numerical solutions of electromagnetic frequency-domain integral equation formulations is steadily growing. In this paper we review the recently suggested impedance matrix compression (IMC) method for a more effective integration of wavelet-based transforms into existing numerical solvers. The difference between the IMC method and the previous approaches to applying wavelets in computational electromagnetics is twofold. Firstly, the transformation is effected by means of a digital filtering approach. This approach renders the transform algorithm adaptive and facilitates the derivation of a basis which best suits the problem at hand. Secondly, the conventional thresholding procedure applied to the impedance matrix is substituted for by a compression process in which only the significant terms in the expansion of the (yet-unknown) current are retained and hence a substantially smaller number of coefficients has to be determined. A few numerical results are included to demonstrate the advantages of the presented method over the currently used ones. The feasibility of ensuring a slow growth in the number of unknowns even when there is a rapid increase in the problem complexity is shown by an illustrative example. © 1998 John Wiley & Sons, Ltd.
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  • 19
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 123-130 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents the electrode separation method for the boundary condition of a-Si TFT mixed-level simulation. The Poisson equation and the continuity equation are formulated into equivalent circuits. So, a circuit simulator can be used to handle the two-dimensional numerical simulation of a-Si TFT. The boundary condition problem between a semiconductor and an external circuit is solved by the electrode separation method. An electrode is separated into two nodes to fit Kirchhoff's current law and the semiconductor equations, respectively. A simple a-Si TFT/LCD circuit is taken as an example for the electrode separation method. For mixed-level simulation this technique is very useful. © 1998 John Wiley & Sons, Ltd.
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  • 20
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: No abstract
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  • 21
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 167-181 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this study, a software package is described which has been developed for the simulation of detection and tracking in surface wave high frequency (SW-HF) radars. The aim is to investigate the problems related to detection and tracking of surface targets at beyond the horizon ranges. In SW-HF radars target detection and tracking involves stochastic features such as target RCS fluctuations, atmospheric, galactic and/or man-made ambient interference components, and the sea clutter with the dominant resonant Bragg returns which affect target detection are all incorporated in the package. In the model, first, terrain data are fed into the simulator by means of a specially designed graphical user interface. Then, a scenario is prepared where the radar's location, coverage and operational parameters can be defined, together with different targets and their sailing routes. The radial propagation paths for angular resolution cells are extracted from the terrain data with the lengths of (possible) sea-island transitions. The surface wave path losses are calculated over the smooth spherical earth's surface with finite conductivity. Surface roughness and mixed-path propagation effects are also included in these calculations. The target detection is performed in the frequency domain after calculation of the noise floor, signal to noise (SNR) and clutter to noise (CNR) ratios. Since SW-HF radars yield coarse range and azimuth but accurate velocity measurements, different Kalman filter techniques are applied for the target tracking, and algorithms are added to improve the track-measurement data correlation. Various simulation tests are performed and the results are presented. © 1998 John Wiley & Sons, Ltd.
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  • 22
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 221-229 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents a physical-mathematical model for abrupt heterojunction transistors and its solution using numerical methods with application to InP/InGaAs HBTs. The physical model is based on the combination of the drift-diffusion transport model in the bulk with thermionic emission and tunnelling transmission through the emitter-base interface. Fermi-Dirac statistics and bandgap narrowing distribution between the valence and conduction bands are considered in the model. A compact formulation is used that makes it easy to take into account other effects such as the non-parabolic nature of the bands or the presence of various subbands in the conduction process. The simulator has been implemented for distributed memory multicomputers, making use of the MPI message-passing standard library. In order to accelerate the solution process of the linear system, iterative methods with parallel incomplete factorization-based preconditioners have been used. © 1998 John Wiley & Sons, Ltd.
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  • 23
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 273-273 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 24
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 243-254 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Various local absorbing boundary conditions are implemented in the TLM method and their corresponding reflections are compared as a waveguide termination. The instability in different ABCs is discussed and reflections from the terminating walls are computed. An improvement for the matched termination wall is proposed and reflection of this absorbing condition is compared with ordinary matched termination. © 1998 John Wiley & Sons, Ltd.
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  • 25
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 289-298 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Oscillatory flow present in the melt during InSb single crystal growth using an RF-heating Czochralski method has been numerically investigated by means of the finite difference method using the HSMAC algorithm. The thermal boundary conditions required for the numerical simulation model were obtained experimentally by measuring the temperature profile along the crucible of a Czochralski system by means of thermocouples mounted in the crucible. Results of numerical simulations showed that the use of a third-order upwind discretization scheme was necessary to catch the oscillatory behaviour of the fluid flow in the melt. It was shown that this oscillatory behaviour strongly depends on the crystal rotation rate. Indeed, the oscillation period increases when the crystal rotation rate is above a critical rotation rate. In order to avoid such oscillations, crystal rotation rates lower than this critical value of crystal rotation rate must be selected for the growth of high quality crystals free of striations. © 1998 John Wiley & Sons, Ltd.
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  • 26
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 1-1 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 27
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 131-131 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 28
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 133-151 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Most traditional theories of speech production are currently based on plane waves. However, it is well known that, for acoustic waveguides, higher acoustical modes start to propagate and can become predominant above cut-on frequencies. This paper thus presents the transmission line matrix method, a numerical method initially designed for electromagnetic waves, and its adaptation to acoustic waveguides. The method, and in particular the representation of boundary conditions, is validated by comparison with known analytical theories. It is then used to show the dramatic effect of higher order modes upon the radiation characteristics of uniform ducts, as well as the importance of source location. Finally, first applications to bent and bifurcating rectangular ducts are presented, and the transfer function of a vowel [a] is shown to display frequency patterns typical of those measured on human subjects and that cannot be explained by one-dimensional propagation only. © 1998 John Wiley & Sons, Ltd.
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  • 29
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 21-40 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An efficient wavelet-packet-based time-frequency technique is proposed in this paper. This technique has found applications in inverse synthetic aperture radar (ISAR). It combines the Wigner-Ville distribution (WVD) of each sub-band signal partitioned from an input signal by the wavelet-packet transform (WPT). These distributions are used to estimate the parameters in Doppler processing. Similar parametric compensation is carried out in range processing so that a specific scatterer is focused in both range and cross-range. The end result uses the Fourier imaging method to obtain a high-resolution radar image. This technique is primarily based on estimation and compensation of the Doppler scattering parameters of the dominant scatterers for improved focus. It can be of great value to the scattering-oriented ISAR imaging. © 1998 John Wiley & Sons, Ltd.
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  • 30
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 11 (1998), S. 307-316 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents an FE modelling approach for the calculation of transient eddy currents in thin conductive layers, where the complexity of the geometry prohibits both a detailed FE modelling and the use of analytical tools. The method allows an estimation of the maximum values of eddy currents at a highly reduced modelling effort and the use of a commercial FE software package. A prerequisite is a slowly varying magnetic field that can be assumed to be unaffected by the eddy currents. It is shown that neither the source of the magnetic field nor the insulating environment has to be modelled. The model is built up exclusively from 2D elements and is excited via the magnetic vector potential. The spatial distribution of the latter is calculated separately in a magnetostatic calculation based on Biot-Savart's law. It is then applied in time-varying form as a dynamic boundary condition at every node of the model. The method was applied to a simple problem for which the results of a detailed FE calculation were available, to document its validity. Further numerical results are presented for the plasma vessel and the heat radiation shield of the Wendelstein 7-X fusion experiment in the case of an emergency discharge. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 277-284 
    ISSN: 1057-9257
    Keywords: calix[4]resorcinarenes ; charge transfer (CT) complexes ; tetracyanoquinodimethane (TCNQ) ; tetracyanoethylene (TCNE) ; non-linear optical (NLO) materials ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Lipophilic calix[4]resorcinarenes - condensation products of resorcinol and lauryl aldehyde comprising four resorcinol units - form electron donor-acceptor complexes with electron acceptors tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE) in organic solvents. Their formation was confirmed by EPR and UV-vis spectroscopy, except for compounds c1 and c3 which did not form charge transfer (CT) complexes with TCNE. Titration experiments involving calixarenes and electron acceptors indicated the presence of species of different stoichiometries. Complexes with ligands c1-c4 were characterised spectroscopically. CT bands appeared in most cases. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 317-324 
    ISSN: 1057-9257
    Keywords: gas sensing ; nitrogen dioxide ; stilbene ; biphenyl ; UV-visible spectroscopy ; thin films ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Thin films of a selection of stilbene and biphenyl side-chain substituted liquid crystal polymers based on polysiloxanes were deposited using an automated dip-coating technique and exposed to either 100 ppm NO2 gas and/or concentrated nitric acid vapour, the consequent effect being monitored by changes in the UV-visible spectra of the material. No effective response to NO2 was observed from the biphenylene analogue, but the stilbene derivatives showed spectral changes to suggest that an interaction occurs between the vapour and the bridge position of the stilbene side-chain. The stilbenes also show a marked pre-conditioning phenomenon upon exposure to nitric acid vapour prior to exposure to nitrogen dioxide. This procedure gives a material that has a more reversible response on exposure to NO2 gas than an anagolous film that has not been pre-treated. Copyright © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 77-80 
    ISSN: 1057-9257
    Keywords: conducting polymers ; polypyrrole ; electrical conductivity ; pressure ; conformation ; glass transition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We describe the observation of a pressure-induced variation in the electrical conductivity of BF-4-doped polypyrrole at pressures below atmospheric pressure. We also show that there are anomalies in the temperature dependence of the electrical conductivity in cyclic measurements at temperatures of 240 and 310 K. The pressure effect is interpreted as a pressure-induced order-disorder conformational transition. The anomalies in the temperature dependence are attributed to the glass transition and melting of the polymer. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 61-76 
    ISSN: 1057-9257
    Keywords: magnetic molecular materials ; conducting molecular materials ; polyoxometalates ; TTF ; ET ; conducting polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The different approaches used by the authors for the synthesis of new molecular materials exhibiting simultaneously magnetic and conducting properties are presented here. The aim is to prepare materials where a magnetic and a conducting sublattice coexist and/or interact in order to obtain either coexistence of properties or coupling between them. The strategy described is a hybrid one that combines various types of inorganic metal complexes with planar organic π-electron donors of the TTF family or with organic matrices made of conducting polymers. There are four main combinations: (i) magnetic polyoxometalates with organic donors - this strategy has already produced more than 10 radical salts where a magnetic character coexists with a conducting or semiconducting one; (ii) small magnetic anions with organic donors - in this case one of the most promising results has been the synthesis of one of the very few known examples of magnetic molecular metals; (iii) ferro- and ferrimagnetic oxalate-bridged bimetallic layers with organic donors; (iv) magnetic polyoxometalates incorporated into electrodeposited films of conducting polymers. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 309-316 
    ISSN: 1057-9257
    Keywords: optical gas sensing ; polysiloxane ; azobenzene ; NO2 ; molecular modelling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Siloxane copolymers having as side-chains azobenzene derivatives bearing different electron-withdrawing and donating substituents were deposited as thin films by dip coating, and their behaviour upon exposure to 100 pm NO2 was studied by UV/visible spectroscopy. Electron-donating substituents at the ortho positions on the aromatic rings in the azo unit have significant influence on the absorbance changes produced by exposure to NO2, and this is explained by modelling, which suggests that interaction between the electrophilic nitrogen atom in NO2 and the electron clouds of the azobenzene skeleton is responsible for the sensing process, rather than the formation of a Wheland intermediate or other product of chemical reaction. Especially effective substituents are methoxy groups in either aromatic ring ortho or the azo linkage, which also produce a significant increase in intensity of the long-wavelength n-π* transition. This moves the optical interrogation signal to a wavelength range of particular benefit for potential applications. Copyright © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 13-22 
    ISSN: 1057-9257
    Keywords: remote PECVD ; silane ; nitrogen ; silicon nitride ; argon dilution ; emission spectroscopy ; metastable states ; atomic nitrogen ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In a series of two papers we describe the effect of argon dilution of the nitrogen passed through the RF discharge region on the plasma composition, growth rate and some characteristics of silicon nitride films deposited by remove PECVD. In this part we report the results of an emission spectroscopic study of the plasma obtained in an SiH4-N2-Ar mixture. It is shown that argon in metastable electronic excited states plays an important role during the RPECVD of silicon nitride films by providing a high concentration of atomic nitrogen which is necessary for the promotion of film growth. In Part II the influence of argon dilution on the growth rate, composition and some properties of silicon nitride films deposited by capacitively and inductively coupled remote PECVD is discussed. © 1998 John Wiley & Sons, Ltd.
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    ISSN: 1057-9257
    Keywords: remote PECVD ; silane ; nitrogen ; silicon nitride ; argon dilution ; hydrogen content ; stoichiometry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In Part I we reported the results of an emission spectroscopic study of the plasma obtained in an SiH4-N2-Ar mixture. It was shown that argon in metastable electronic excited states provides a high concentration of atomic nitrogen. In this part we report the results of a study of the influence of argon dilution on the growth rate, composition and properties of silicon nitride films. The exact influence of nitrogen dilution with argon depends on the process parameters and on the method of coupling of the RF power, but it is found in general that a high concentration of atomic nitrogen leads to changes in the relative amounts of Si-Hj and N-Hi bonds and in the Si/N ratio of deposited films. In particular, it is shown that hydrogen incorporation can be reduced and improved stoichiometry can be obtained. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 53-60 
    ISSN: 1057-9257
    Keywords: organic conductors ; electron correlations ; dielectric-metal transition ; superconductivity ; Fermi surface ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The electronic structure and superconductivity of layered organic materials based on the bis(ethylenedithio)tetrathiafulvalene molecule (BEDT-TTF, hereafter ET) with essential intra-ET correlations of electrons are analysed. Taking into account the Fermi surface topology, the superconducting electronic density of states (DOS) is calculated for a realistic model of κ-ET2X salts. A d-symmetry of the superconducting order parameter is obtained and a relation is found between its nodes on the Fermi surface and the superconducting phase characteristics. The results are in agreement with the measured non-activated temperature dependences of the superconducting specific heat and NMR relaxation rate of central 13C atoms in ET. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 81-85 
    ISSN: 1057-9257
    Keywords: conducting polymers ; polypyrrole ; optical absorption ; pressure ; piezochromism ; conformation ; infrared spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: A pressure dependence of the optical absorption spectra of BF-4-doped polypyrrole has been observed at pressures below atmospheric pressure. The two absorption bands at photon energies of 1·2 and 3·0 eV depend on the pressure: a decrease in the high-energy absorption is accompanied by an increase in the low-energy absorption and its shift towards lower energies. The Fourier transformation infrared reflection spectra also depend on the pressure in this region of pressures. The results are interpreted as a pressure-induced conformational transition of the polypyrrole chain. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 87-91 
    ISSN: 1057-9257
    Keywords: friction coefficient ; wear coefficient ; tribology ; conducting polymers ; 2,6-naphthalenedisulphonate (2,6-NDS) ; 1,5-naphthalenedisulphonate (1,5-NDS) and 2-naphthalenesulphonate (NS) polypyrroles ; sliding test ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: It is known that, with careful control of conditions, polypyrrole films with counter-ions of toluene sulphonic acid sodium salt and methane phosphonic acid sodium salt can be produced with friction coefficients comparable with or even better than PTFE. Here we now report a systematic study of polypyrrole with various planar anions for tribological bearing applications. Thus naphthalene disulphonate-doped polypyrrole has a kind of laminar structure with very good adhesion to the surface. Polymer films were electrodeposited on glass lenses and tested in a friction apparatus for friction and wear measurements. The film orientation was measured by low-angle X-ray diffraction and the surface structure was evaluated by both AFM and SEM for different film thicknesses. The friction coefficient and wear rate of such bearings were measured under loads up to 5 N and at speeds up to 30 mm s-1 and were found to be 0·06 and 0·04 nm mm-1 respectively. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 111-119 
    ISSN: 1057-9257
    Keywords: PPV ; conjugated polymers ; quasi-particles ; ab initio calculation ; infrared spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We investigate the quasi-particle conformational defects (excitons, polarons and bipolarons) in phenylene vinylene oligomers (PVOs) consisting of up to 12 repeat units. The conformations are determined by minimisation of the total Hartree-Fock energy calculated at 3-21G level. The Hartree-Fock calculations of the excited states are followed by the CI-Singles calculation. The bond length alternation along the oligomer chain is discussed. On the basis of these results the vibrational transitions are calculated. To correct the basis set truncation error, the vibrational frequencies are multiplied by a uniform scaling factor. The types of vibrations are assigned. The theoretical spectra are in good agreement with the experimental infrared vibrational spectrum of poly(p-phenylene vinylene) (PPV). © 1998 John Wiley & Sons, Ltd.
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  • 42
    ISSN: 1057-9257
    Keywords: As-S wafers ; X-ray exposure ; microstructuring ; bulk optic element ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The possibilities of ‘resistless’ microstructuring of As36·1S63·9 wafers by soft X-ray irradiation and wet alkaline etching have been investigated. Scanning electron microscopy is used to study the influence of the exposure and processing parameters on the depth and acuity of the patterned structures. Structures 1 μm wide are obtained by irradiation with an energy flux of 2000 mJ cm-2, followed by etching in a solution of pH 10·8 at a temperature of 23°C for a processing time of 18 min. It is established that by X-ray irradiation and suitable processing of As36·1S63·9 wafers, microstructures of a depth up to 0·65 μm could be patterned. The structured wafers could be used as diffraction elements for IR optics. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 147-155 
    ISSN: 1057-9257
    Keywords: synthesization ; chalcopyrite ; CuGaSE2 single phase ; X-ray diffraction ; stoichiometric deviations ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The dependence of the structural parameters on compositional deviations of CuGaSe2 has been studied. These deviations have been induced along an ingot by a single fusion of the components at 1150 °C and subsequent slow cooling in a stationary ampoule in a vertical furnace. All along the sample a single chalcopyrite phase is present and a compositional gradient along the ingot was found by energy-dispersive analysis of X-rays (EDAX) measurements, the upper part being rich in Ga (series B) and the lower part in Cu (series A), with Cu/Ga ratios of 0·95 and 1·1 respectively. A hypothesis of the existence of two phases in the melt is proposed to explain these facts. The unit cell parameters, anion displacement and Cu and Ga occupation numbers in their sublattices were analysed by X-ray powder diffraction and Rietveld refinement methods. In series A the occupation numbers are near stoichiometry, while in series B a Cu defect appears. In both series, changes in unit cell parameter are related to changes in Cu content, suggesting the presence of a fraction of Cu ions either as interstitials or at Ga sites when Cu is in excess, or of Cu vacancies in its sublattice when there is a Cu deficiency. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 1-8 
    ISSN: 1057-9257
    Keywords: electrodeposition ; copper-indium-selenide ; thin films ; layer-by-layer deposition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The electrochemical bath used for growing device-quality CIS (CuInSe2) thin films by co-deposition as well as layer-by-layer (LBL) deposition was characterised and optimised with respect to the film properties. The bath composition was varied by changing the Cu, In and Se ion concentrations in specific ratios in both co-deposition and LBL deposition. The film properties were analysed using techniques such as SEM (scanning electron microscopy), EPMA (electron probe microanalysis), AES (Auger electron spectroscopy) and XRD (X-ray diffraction). The structural, morphological and compositional properties of the films were characterised and their variation is attributed to the bath composition and growth conditions. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 9-12 
    ISSN: 1057-9257
    Keywords: LPE growth ; Ga-Bi solution ; ‘purification effect’ ; photoluminescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Thick, intentionally undoped GaAs epitaxial layers grown by LPE from Ga-Bi solution with different contents of Bi in liquid solvent (from 0 to 82 at.%Bi) were studied by photoluminescence (PL) at temperature &helvbi;T&helvbd;=2 K. The dependence of the photoluminescence spectrum on the content of Bi in solution was analysed. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 31-37 
    ISSN: 1057-9257
    Keywords: self-assembled monomolecular layers ; chemical modification ; ATR/FTIR' electrical conductivity ; fluorescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Self-assembled monomolecular layers have been formed on a glass substrate with 3-aminopropyltriethoxysilane. The amino groups were chemically modified with either salicylaldehyde or 4-formylpyridine, then a TCNQ-pyridine CT complex was formed on a limited area of the surface, making a molecular conductive channel. This area is electrically conducting and we have observed it with the aid of SEM and direct measurements. ATR/FTIR and fluorescence spectroscopy were also used to monitor the monomolecular layer formation and modification processes. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 47-52 
    ISSN: 1057-9257
    Keywords: ligand gated ; channel protein ; biomembrane ; biosensor ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We demonstrate a novel protective configuration for a gated channel biosensor. The bilayer membrane containing the channel proteins is formed by a simple self-assembly technique ensuring continuous coverage of the interface between two slabs of agarose gel by a biomimetic lamella in a fluid state. The gel protects both membrane surfaces from mechanical shock and contact with low-energy media while allowing diffusion of biomolecules up to 10 MDa in weight. The technique has been demonstrated using both dioleoyl-phosphatidylcholine (DOPC) and a phosphatidylcholine lipid cross-linked with a short polysiloxane chain (PSPC). The conductance per unit area of the channel-free membrane produced by this method was less than 25 S m-2 for DOPC and 2 S m-2 for PSPC, and the bilayer nature of the barrier in both cases has been demonstrated by measurement of the capacitance. The applicability to sensors has been confirmed using gramicidin-D, a 1·1 kDa unilamellar lipid bilayer pore former, and partially confirmed using valinomycin, a selective ion transporter. On incorporation of gramicidin the membrane conductance increased by over an order of magnitude. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 303-308 
    ISSN: 1057-9257
    Keywords: polyaniline ; emeraldine base ; carbon fluoride ; lithium cells ; aprotic solvent ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Polyaniline (PANI) has been used for modification of the electrochemical behaviour of a carbon fluoride ((CFx)n) cathode in a lithium cell. PANI and (CFx)n powders were carefully mixed and the electrochemical properties and kinetic parameters of the composite (CFx)n-PANI cathode were evaluated by galvanostatic and potentiodynamic techniques. An increase in exchange current has been found for electrodes with addition of polyaniline in the form of emeraldine base (EB). During the reduction process of carbon fluoride using 1 M lithium perchlorate solution in organic solvent, the ternary intercalation compound CLixF is formed and then irreversibly decomposed into carbon and lithium fluoride. The insertion of lithium cations into the (CFx)n layered structure is diffusionally controlled, hence improvement in electronic properties of this fluoride material by the presence of conducting PANI chains and enhancement of discharge performance were found for 25% addition of PANI. Copyright © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 181-186 
    ISSN: 1057-9257
    Keywords: poly(4,7-benzothiophene vinylene) ; polymer interfaces ; conjugated polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this paper we determine the LUMO level position of poly(4,7-benzothiophene vinylene) (PBTV), a heterocyclic poly(phenylene vinylene) (PPV) analogue, using tunnelling current measurements. We compare the energy level positions with those measured for PPV and determine their shifts. The experimental results are compared with theoretical predictions and good agreement is observed. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 213-213 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: No abstract
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    Advanced Materials for Optics and Electronics 8 (1998), S. 215-228 
    ISSN: 1057-9257
    Keywords: fullerene ; fullerides ; charge transfer complexes ; spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Some possible uses of vibrational and electronic spectroscopies in characterising the basic interactions in C60 and C70 complexes are pointed out. We report on the wealth of infrared spectra of (usually) single crystals of C60 and C70 clathrates and complexes with organic donors. The changes in the spectral parameters of the complexes in comparison with those of the neutral fullerene molecules are attributed to redistribution of the charge on the spherical C60 or elongated C70 molecules in their compounds. Some general considerations on the origin of the IR, NIR, VIS and UV spectral variations are also given. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 247-262 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The synthesis of a number of side chain liquid crystalline polymers for quadratic non-linear optical (NLO) applications is reported. The active chromophore is a charge transfer (CT) biphenyl derivative which possesses mesogenic properties itself. The liquid crystalline behaviour of these polymers was established by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. The active chromophores were oriented by the standard corona poling technique and the degree of axial ordering was determined as a function of poling conditions by linear optical absorption. Growth of the second-harmonic generation (SHG) signal was used to probe the induction of polar order. These experiments clearly indicated that liquid crystallinity results in an enhancement of the polar order over that of isotropic materials. The second-order NLO susceptibility tensor components d31 and d33 were measured by the SHG technique. The ratio d33/ d31 was found to be much larger than 3, in agreement with molecular statistical models. Values of d33 up to 30-35 pm V-1 were obtained at 1064 nm fundamental wavelength. These values are essentially not resonance-enhanced, since the chromophore absorption occurs below 350 nm. © 1998 John Wiley & Sons, Ltd.
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  • 53
    ISSN: 1057-9257
    Keywords: gallium nitride ; nanocrystallites ; detonation ; gallium azide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: High quality nanoscale, phase-pure hexagonal gallium nitride (GaN) crystallites have been synthesized by the thermal induced detonation of molecular precursors of the type (R3N)Ga(N3)3 (R=CH3, C2H5, etc.). The method allows the control of the particle size regime from 2 to about 1000 nm. X-ray diffraction and Rietveld simulations revealed an anisotropic platelet-like shape of the particles. The obtained GaN material was as well characterized by transmission electron microscopy and electron diffraction, photoluminescence spectroscopy, SEM, IR, RAMAN, thermal gas effusion/mass spectrometry, thermal analysis, elemental analysis. Gas absorption measurements (BET method) showed a specific surface area of about 90 m2 · g-1. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 163-171 
    ISSN: 1057-9257
    Keywords: chemical-based computing ; reaction-diffusion systems ; polymer materials for chemical computing ; Belousov-Zhabotinsky media ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Promising potentialities are opened up by the use of polymer materials for the elaboration of information-processing devices based on reaction-diffusion media. In this work, features of image processing by Belousov-Zhabotinsky media formed on the basis of hydrogel matrices and using catalyst immobilisation on the surface of solid supports have been investigated. Such active media structures have been found to improve significantly the quality of images in the course of their processing by the media. The spatial resolution of the media increases considerably in going from liquid Belousov-Zhabotinsky media and media functioning in polymer matrices to media based on catalyst immobilisation on the surface of solid supports. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 173-180 
    ISSN: 1057-9257
    Keywords: coated hybrid particles ; nanoparticle composites ; surface plasmon resonance ; optical properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Semiconductor/metal hybrid nanoparticle composites have been prepared in a glass host by a modified melt/quench process and examined with respect to their optical properties. The coated hybrid nanoparticles exhibit surface plasmon resonance absorption spectra which are red-shifted compared with that of a dispersion of homogeneous Ag nanoparticles in the same host. The position of the plasmon resonance was a sensitive function of the heat treatment schedule. A theoretical model based on effective medium theory for the coated hybrid particles was used to describe the shift of the plasmon position in the optical spectra as a function of the coating thickness. The calculated absorption spectra of the coated hybrid particles agree well with the experimental results. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 195-199 
    ISSN: 1057-9257
    Keywords: chiral waveguides ; preparation of modified ATR method ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Chiral properties of planar waveguide structures with a core layer formed by a poly(methyl methacrylate) (PMMA) host matrix doped with chiral santonin were investigated by means of a modified attenuated total reflection (ATR) method. Distinct modification of the observed ATR spectra was revealed for right and left circularly polarised incident beams. From comparison of the experimental spectra with theoretical curves, the following specific rotation was obtained: [α]20633=11,200 deg cm2 g-1 (santonin/ PMMA mass ratio 2:1). The origin of the observed optical activity and its influence on the waveguide dispersion characteristics are briefly discussed. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 201-209 
    ISSN: 1057-9257
    Keywords: amorphous molecular semiconductors ; electron-hole pairs ; excitons ; photoconductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Processes of charge carrier photogeneration and recombination are investigated in films of poly-N-epoxypropylcarbazole doped with polymethine dye. Films with blocking contacts were illuminated with light from either the region of dye absorption or beyond this region. The kinetics of accumulation and relaxation of electron-hole pairs with lifetimes greater than tens or hundreds of seconds was studied. It is presumed that the reason for the growth of recombination luminescence intensity in an external electric field is connected with the increase in efficiency of radiative recombination stimulated by electrons captured from photogenerated excitons. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 229-245 
    ISSN: 1057-9257
    Keywords: unimolecular rectifier ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Asymmetries in the macroscopic and the nanoscopic DC electrical conductivity through Langmuir-Blodgett multilayers and monolayers of γ-(n-hexadecyl)quinolinium tricyanoquinodimethanide (HDQ-3CNQ, 1) are due to a transition from the ground-state zwitterion to a probably neutral excited-state conformer, thus confirming without a shadow of a doubt the rectification of electrical current by a single molecule. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 263-267 
    ISSN: 1057-9257
    Keywords: semiconductors ; low-dimensional systems ; crystal structure ; optical properties ; photoluminescence ; Raman spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The structural, optical and related properties (i.e. photoluminescence and resonance Raman spectra) of some synthetic (i.e. unconventional) low-dimensional semiconductor systems such as K2Cd3S4, [CH3SC(NH2)=NH2]3PbI5 and [H3N(CH2)6NH3]BiI5 are reported. They are compared with the properties of the corresponding higher-dimensionality systems. A blue shift of the excitonic bands and an enhancement of their binding energy and intensity were observed by decreasing the dimensionality or the size of the materials active part. The results are similar to those obtained from conventional semiconductors by decreasing the dimensionality or the size and are attributed to quantum confinement of excitons. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 269-276 
    ISSN: 1057-9257
    Keywords: organic charge transfer salts ; conducting polymers ; electronic properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We are exploring the electronic properties of novel materials such as conducting polymer-coated polyester fibres and charge transfer complexes configured in resistive, gated (FET) and diode configurations. In this paper we will consider several areas where we are attempting to make sensors and/ or primitive devices from molecular materials. Our most successful result so far is the temperature-dependent resistivity of polypyrrole-coated polyester fibres. Here we find that the conductivity is thermally activated and produces a reliable, highly sensitive indicator of temperature in a cryogenic environment. Using parallel configurations of fibres, sensors with different limiting resistances can be fabricated. We have also placed insulated electrical gates on single crystals of various metallic and insulating charge transfer salts and have attempted to alter the charge transfer character by the application of high electric fields. With polymethylmethacrylate (PMMA) insulating layers, gate voltages up to 150 V have been acquired with no leakage or heating. Similar measurements on diode devices fabricated from charge transfer complexes with different electronic structures are also in progress, and our preliminary results will be presented. Prospects and plans for developing these materials into viable sensors and devices are discussed. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 285-294 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Field effect transistors with an organic material as active layer are at present essentially used to determine the mobilities in these materials. Until now, in analysing the measured current characteristics, only the simplest (Shockley) model has been used which accounts neither for this type of thin film transistor (TFT), which operates in depletion and accumulation, nor for the nature of the carriers. Starting from two-dimensional simulations for the analogous silicon TFT, we have developed an analytical model for the TFT that accounts for several peculiarities of the current characteristics of this type of transistor. In addition, a first modification has been developed which describes the situation when the charged states are polarons and bipolarons, as is the case in organic materials. Applications to published experimental current characteristics show that a general reanalysis is needed. Copyright © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 187-193 
    ISSN: 1057-9257
    Keywords: antifouling ; biofouling ; hydrogel ; benzalkonium chloride ; ultraviolet-visible spectroscopy ; underwater optics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: A hydrogel based on poly(2-hydroxyethyl methacrylate) (PHEMA) containing benzalkonium chloride (BAK) can be used as an environmentally acceptable, fouling-resistant material in the marine environment. The loaded hydrogel system is transparent and has the potential to be used in the protection of optical ports in underwater instruments. Ultraviolet-visible (UV-vis) spectroscopy was used to study the optical properties of the material after a marine exposure period. The optical transmittance of PHEMA/ BAK was higher for 10 weeks than that detected for poly(methyl methacrylate) (PMMA), a material currently used in commercial instruments, which confirmed the superior fouling resistance of the PHEMA/ BAK combination. The UV-vis spectroscopic method was quick, relatively cheap and accurate enough to allow the effects of the development of marine fouling on transparent surfaces for use in marine underwater optical applications to be monitored. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 93-96 
    ISSN: 1057-9257
    Keywords: ithiolene ; tetrathiafulvalene ; molecular conductor ; molecular magnetism ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The salt [TTF]2[Fe(tdas)2] has been prepared by electocrystallisation and its conductivity and magnetic properties are reported. The X-ray structure has been determined. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 97-99 
    ISSN: 1057-9257
    Keywords: TCNQ salts ; IR spectra ; melting ; charge transfer, electron-phonon coupling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The infrared spectra (400-7000 cm-1) of three composites based on salts of tetracyano-p-quinodimethane (TCNQ) and methyl-TCNQ with N-alkyl-isoquinolinium cations are measured as a function of temperature (up to about 450 K). The influence of composite melting on the charge transfer and vibrational bands is studied. It is found that melting causes an irreversible transition into a new phase. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 101-105 
    ISSN: 1057-9257
    Keywords: biosensor ; protein immobilisation ; protein modification ; electrochemistry ; nitrotyrosine ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Use of electrosynthetic methodology allows the production of hen egg-white lysozyme (HEWL) either mononitrated at tyrosine 23 or bisnitrated at tyrosines 20 and 23, but never nitrated at tyrosine 53. This is a different sequence from that obtained by the chemical nitrating agent tetranitromethane, and when reduced by dithionite, the selectively modified enzyme can be anchored at pH 5 via the unique aromatic amino group to magnetic beads or other suitable matrices. HEWL so immobilised loses less than 10% of cell-wall lytic activity compared with the approximately 50% loss of activity when immobilised by conventional methodology at pH 9 via essentially random reaction at lysine residues and other functionalities which are nucleophilic at this pH. This result offers promise as a general method for selective protein immobilisation in biosensors and similar applications. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 45-45 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
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    Advanced Materials for Optics and Electronics 8 (1998), S. 121-128 
    ISSN: 1057-9257
    Keywords: self-assembly ; charge transfer ; electron-conducting monolayers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Suitably modified mono- and bimolecular films, including bilayer lipid membranes (BLMs), offer exceptionally good opportunities for probing electric field effects on charge transfer and redox reactions in biosensor and molecular electronics research and development.This work presents the redox reactions of tetracyano-p-quinodimethane (TCNQ) molecules incorporated in a self-assembled octadecanethiol monolayer (SAM) on polycrystalline gold electrodes, depending upon the type of supporting electrolyte cations and their concentration. Our results show that TCNQ-modified Au-SAM electrodes exhibit selectivity versus alkali metal cations in aqueous supporting electrolyte (∽10 kJ mol-1 difference between K+ and Li+ and between Cs+ and K+). The slope of the ‘calibration curves’ for Li+ and K+ is about 59 mV per decade of concentration of the analyte. The explanation of this behaviour is based on the Donnan potential model; however, an ion-pairing effect can also be involved. Our preliminary results show also that the TCNQ molecules within the octadecanethiol monolayer may act as a molecular redox device. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 157-160 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
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    Keywords: conductive polymers ; polyaniline ; palladium dopants ; platinum dopants ; catalytic hydrogenation ; active centres ; catalyst aging ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The chemical and structural surface-aging effects brought about by the presence of water in emeraldine base (EB) polyaniline (PANI) doped with Pd or Pt protonic acids were studied. IR spectroscopy, XRD, XPS and heterogeneous catalytic hydrogenation (alkyne→alkene→alkane) were applied to characterise the PANI-Pd and PANI-Pt. Interpretation of the results gave the surface characteristics, structure, chemical catalytic activity and stability mainly of PANI-Pd specimens. The unique form of catalytically active centres therein was the surface complex [PdCl4]2- with Pd 3d5/2 BE=337·7 eV. The most promising among the PANI-Pd catalysts studied were those dried in a slow, long procedure (3 months, zeolite 5A). Copyright © 1998 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 13-34 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Specifying electromagnetic compatibility (EMC) is a crucial step in the performance evaluation of electrical and electronic systems. This paper describes a circuit formulation for the EMC assessment of large and complex systems.The proposed method is based on breaking the actual structure down into an aggregation of multiport devices: lumped-parameter circuits and distributed-parameter multiports. The multiconductor transmission line (MTL) model is used for the description of signal propagation along system interconnects: uniform, twisted and shielded lines are considered. Accurate prediction models (including line losses and dispersion) are utilized for the quantitative evaluation of both intrasystem compatibility and susceptibility to radiated interference.The description of the network topology makes use of the concept of an incidence matrix which is widely used in lumped-circuit theory. It is extended here to the more general case of distributed networks. The entire analysis is carried out in the frequency domain and a transient response is obtained by using inverse Fourier and Laplace transforms.Noteworthy characteristics of the method can be seen in the simplicity and effectiveness of the prediction models and in the minimal effort required for system description. The proposed method is especially significant for complex systems, where the number of connecting structures can be quite large. © 1997 by John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 1-1 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 177-192 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: When compared with commonly used subdomain moment-method analysis, entire-domain analysis of 3D dielectric scatterers results in a greatly reduced number of unknowns. Unfortunately, the expressions for matrix elements tend to be quite complicated and their calculation extremely time-consuming if evaluated directly. It is shown in the paper that, in a Galerkin-type solution with large trilinear hexahedral basic volume elements and three-dimensional polynomial approximation of volume current inside them, these expressions can be manipulated analytically for optimized rapid non-redundant integration. Consequently, a method for the analysis of 3D dielectric scatterers is obtained that is efficient, rapidly converging with increasing degree of approximation for current, remarkably accurate and very moderate in computer memory requirements. The applicability of the method of moments is thereby extended to bodies of electrical sizes greatly exceeding those that can be dealt with by subdomain methods. © 1997 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 265-265 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 313-313 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 35-46 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The circuit and coupling properties of a dipole grid array placed inside a rectangular cross-section waveguide are analysed when also a rectangular aperture is used to couple the resonator energy into a semi-infinite waveguide. A Green function approach is employed to determine the current distribution on the dipole elements by solving an integral equation and taking into account the boundary conditions on the rectangular cavity walls. Both mutual and self-impedance terms are calculated for the dipole grid array, and the effects of the rectangular coupling aperture are also examined. © 1997 by John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 1-2 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 107-119 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A self-consistent numerical transport model based on the hydrodynamic equations obtained from Boltzmann's transport equation (BTE) is presented. The model includes both the temporal and spatial variation in electron velocity. A parallel implementation of the solution method, using FDTD techniques, is illustrated. Numerical results for a GaAs MESFET device are generated using this complete hydrodynamic model (CHM) and compared with results obtained from the more commonly used energy or simplified hydrodynamic model (SHM). The results indicate that for short gate-lengths (less than 0⋅5 μm) the two models lead to different DC steady-state results which in turn lead to different microwave small-signal models for the device. © 1997 by John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 169-176 
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    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes a modelling strategy and a software tool for simulating the dynamical behaviour of an active antenna array. The array consists of active radiating elements placed in a chain, i.e. a collinear array arrangement. To assist modelling of the active antenna array a macro model has been used to represent each of the radiating elements in the array. This simplifies analysis and allows dynamical performance to be efficiently computed, the resulting dynamical behaviour of the array being presented as an animated visualization. A computer program is presented which can simulate the active array in the time domain so that various characteristics, such as mode formation and spacial coupling effects, can be observed. Experimental validation is given in order to justify the mode formation predictions of the simulator. © 1997 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 209-216 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this paper, a generalized approach for the analysis of multistrip multidielectric layer transmission line structures based on the Method of Lines (MoL) is presented. The proposed algorithm is not limited either by the number of dielectric layers or by the number of metallic strips that can be positioned at different interfaces. The program we have written has been successfully tested on various structures and the obtained results are compared with those published by other authors. © 1997 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 245-264 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper deals with absorbing boundary conditions for the finite difference time domain (FDTD) method applied to homogeneous lossless waveguide structures. A theoretical formulation of the so-called ‘modal absorption’ (MA) is developed. On the basis of this theory different implementations available in the literature have been derived and compared. Then, some techniques to enhance the efficiency of the method have been proposed and tested. It is demonstrated that, with the proposed methods, the high level of accuracy of the original formulations is retained, while the computational cost is strongly reduced. © 1997 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 303-312 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    Notes: Monte Carlo methods are generally known for solving field problems one point at a time, unlike other numerical methods such as the finite difference and finite element methods which provide the solution at all the grid nodes simultaneously. This paper provides a Monte Carlo technique for obtaining the solution everywhere at once. The technique uses absorbing Markov chains to obtain the transition probabilities for all of the grid nodes at once. The procedure is illustrated with some examples for homogeneous and inhomogeneous, rectangular and axisymmetric solution regions, and is found to be accurate. © 1997 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 343-353 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: When we solve the wave equation by the finite element method, the order of convergence and the accuracy of the solution are reduced by the presence of sharp edges. The employment of singular elements improves the solution and allows us to reduce the cost of computation.In this paper, three types of scalar singular finite elements with the capacity to handle singularities in the derivative, and which have previously been applied to mechanical problems, are examined, together with standard elements, in the context of homogeneous waveguide analysis.We solve two examples of homogeneous waveguides showing the different behaviour of the singular elements and obtaining information on the order of convergence and the approximation of the gradient of the unknown function. © 1997 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 83-99 
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    Keywords: Engineering ; Numerical Methods and Modeling
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A numerical method is used to solve the integro-differential generalized telegraphists' equations for the total (single and multiple) diffusely scattered radiation wave amplitudes. These equations were derived using a full wave approach. The singularities of the scattering coefficients are removed on integrating by parts. A stationary phase approximation is used to obtain the far fields. The numerical solutions are obtained for one-dimensional deterministic surfaces. The numerical results for the total (single and multiple) diffusely scattered fields are in good agreement with the earlier single scatter analytical results when the maximum surface slope is less than 30 degrees. The earlier single scatter analytical solutions are based on the assumption that the total field impressed upon a rough surface is associated with the incident field only. This assumption is not made for the evaluation of the numerical results presented here. The earlier analytical results are in total agreement with the small perturbation results when the rough surface height and slopes are of the same order of smallness. © 1997 by John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 205-207 
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    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A hybrid representation formulation approach is presented. It avoids some numerical inconveniences and was successfully used as an intermediate step to obtain the differential algebraic equations of PWL modelled VLSI circuits. © 1997 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 217-229 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: We present an analysis of thin microstrip superconducting structures in which the effects of the superconducting material, of finite complex conductivity and finite thickness, are taken into account through the concept of sheet impedance coupled with an extension of the Spectral Domain Immittance Approach. The effect of the magnetic field on the penetration depth in the superconductor is included by solving the Ginzburg-Landau equations within the thin-film approximation (t/λ0 ≪ 1). The state of the material is determined self-consistently in such a way that when the critical field is exceeded, the material systematically shifts from the superconducting to the normal state. Special attention is paid to the behaviour of the system in the neighbourhood of the critical temperature, T/Tc ≃ 1. We report that, in some cases, the propagation constant of a superconducting microstrip line attains a maximum when the real and imaginary parts of the conductivity are approximately equal. Numerical results for a microstrip line and a patch resonator are presented and compared with available data to document the validity of the approach. © 1997 John Wiley & Sons, Ltd.
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  • 86
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 285-301 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A new approach for the time-domain simulation of power electronic circuits is developed. The methodology is based on stepwise identification of circuit topology. The simulation process automatically looks for a valid topology in every step. At each simulation instant, the circuit topology is transformed into a resistive network, giving another superior feature of this method: the avoidance of solving complicated s-domain or differential formulas. No small-signal approximation is assumed. Parasitic resistance of the reactive element is included in the circuit model. Several examples illustrating the generality and computational efficiency of this new method are presented. The simulated results are favourably verified with experimental measurements and available literature. © 1997 John Wiley & Sons, Ltd.
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  • 87
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 315-328 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A strategy is proposed to enhance the performance of some numerical methods used in the solution of electromagnetic problems. The strategy can be extended to any numerical method based on the partitioning of the spatial domain into elementary cells. Two different implementations of the strategy are compared: modified-reversed Cuthill-McKee and tabu search. While the former is well known, the latter is here applied for the first time to such problems. Their application is shown in conjunction with three different numerical methods: mode matching of complex MW circuits, finite difference solution of PDE and FEM analysis of microstrip lines. The efficiency and versatility of the approach is proved for each of the three numerical methods, reaching a reduction in the working times of up to 20 times. © 1997 John Wiley & Sons, Ltd.
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  • 88
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 47-56 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this paper, a finite element method for solving ionized fields is developed based on a novel solution philosophy. Employing the Galerkin finite element method, the solution problem of an ionized field has been formulated as an optimization problem, i.e. as a problem of minimizing an objective function whose minimum gives the solution. The effect of wind is taken into account by introducing a scalar potential of its velocity. © 1997 by John Wiley & Sons, Ltd.
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  • 89
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 3-11 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents an adapted Gummel method (AGM) used in the two-dimensional device simulation of an amorphous-silicon (a-Si) thin-film transistor (TFT). Firstly, the AGM for amorphous silicon is developed by modifying the Gummel method (GM) for crystalline silicon. Secondly, the AGM is implemented into a two-dimensional device simulator for the simulation of a-Si TFTs. The simulation results show that the AGM converges well while the GM fails to converge for the simulation of a-Si TFTs. Hence, the AGM is a useful technique for the simulation and analysis of a-Si TFTs. © 1997 by John Wiley & Sons, Ltd.
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  • 90
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 57-69 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The modified Gaussian algorithm is introduced for solving the ionized fields of unipolar HVDC lines including the effect of wind. Specific techniques of incorporating in the algorithm the special structure of the optimization problem of the ionized field have been developed to economize the requirements for the computer memory and CPU time. Numerical tests are carried out on a coaxial cylindrical geometry and on a line-plane geometry both in the absence and in the presence of wind. Comparison with available experimental data shows good agreement. © 1997 by John Wiley & Sons, Ltd.
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  • 91
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 101-105 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Recurrence relations are developed to determine the weighting coefficients used in the simulation of random signals and rough surfaces with given statistical characteristics. These results can provide (in real time) straightforward, accurate solutions to the system of non-linear, algebraic equations associated with the method of moving summations. Three possible numerical methods have been reported to obtain approximate solutions to the system of non-linear, algebraic equations. However, none of them is straightforward, and they all require a large amount of computing time. This work can be applied to the numerical solution of the generalized telegraphist's equations used to analyze vertically and horizontally polarized radio wave scattering problems from permeable media with random rough interfaces. © 1997 by John Wiley & Sons, Ltd.
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  • 92
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 139-151 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The response of a p-i-n photodetector made from gallium arsenide to both steady-state and transient illumination has been modelled. Both an ensemble Monte-Carlo model and a drift-diffusion model were used, the latter with the choice of two different mobility models. The effects of high intensity steady-state illumination on the field and carrier distributions in the photodetector were calculated, and a comparative study of the models made. The transient response to pulsed illumination has also been calculated and the different results obtained from the models explained. The effect of high illumination on the response speed of the detector has been demonstrated. In addition, an expression for obtaining the photocurrent from the Monte-Carlo simulation, with much reduced statistical noise over the conventional estimate, has been derived and successfully tested. © 1997 John Wiley & Sons, Ltd.
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  • 93
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 153-167 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A generalized modal scattering matrix formulation is presented for the calculation of discontinuity-distorted waveguide multiport junctions. Unlike common approaches based on three-plane mode-matching techniques, and modifications thereof, which calculate only the fundamental-mode scattering matrix, this algorithm computes the generalized modal scattering matrix of the junction. Therefore, the method allows the computation of components in which other structures are connected as closely as possible to the discontinuity-distorted junction as follows directly from the rigorous incorporation of all higher-order mode interactions. The method is demonstrated at three selected examples: the waveguide corner, the T-junction power divider and the orthomode transducer. Comparison with results obtained by other numerical techniques or measurements available from the literature are found to be in good agreement. © 1997 John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 193-204 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An analysis of arbitrary thin-wire loop antennas and scatterers using periodic orthogonal wavelets is presented. The periodic orthogonal wavelet expansion is applied to solve the thin-wire version of the electric-field integral equation (EFIE). The curved solution domains are mapped into the definition domain [0, 1] of the periodic wavelets. The unknown current over each loop wire is expanded in terms of a basis derived from a periodic orthogonal wavelet through the maps between the curved integration domains and the interval [0,1]. The integral equation under study is converted into a sparse matrix equation by this technique. Numerical examples are provided for a variety of thin-wire loop antennas and scatterers. © 1997 John Wiley & Sons, Ltd.
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  • 95
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 231-243 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The suitability of the transmission line modelling method for studying field-particle interaction devices is assessed through an example of a simple two-cavity klystron amplifier. Two separate numerical studies are presented, covering both beam bunching in the buncher cavity and field generation in the catcher cavity. Also addressed are the possibility of modelling the effect of the finite thickness of the cavity wall and beam coupling. The modelling of these practical aspects has not only resulted in some important insights into the field-particle interaction problem, but also demonstrated that the computer code developed is a powerful and versatile design tool. © 1997 John Wiley & Sons, Ltd.
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  • 96
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 269-284 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A simple, approximate, but very rapid and accurate image method is proposed for the analysis of arbitrary wire antennas above a lossy half-space. The reflected field from vertical and horizontal Hertzian dipoles is approximated by the field of a few ‘optimally’ positioned simple elementary sources. The field of images is incorported into the Hallén-type equations for the current distribution, resulting in equations of essentially the same form as those for an isolated antenna. The equations are solved by the point-matching method and polynomial approximation of current along the antenna segments. The results for the impedance and admittance of antennas assembled of vertical, horizontal and/or oblique segments are in excellent agreement with the exact results (obtained from the Sommerfeld theory). The proposed method is conceptually very simple and on average 25 times faster than the exact method, although in some cases it was found to be faster for even two orders of magnitude. This makes it particularly suitable for numerical optimization and CAD of relatively complicated antennas and other wire structures above a lossy half-space. © 1997 John Wiley & Sons, Ltd.
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  • 97
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 71-82 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this paper we present an efficient method for numerical solution of the transport equation of photogenerated carriers in MSM photodetectors. The method is based on conformal mapping of both the MSM photodetector structure and the system of transport equations into a new space. The mapping enables analytical calculation of the electric field, allowing one to take one of the co-ordinates as a parameter and thus reducing the problem to quasi-one-dimensional. In addition, the method of conformal mapping enables calculation of the normalized current response of a photodetector in the new space. © 1997 by John Wiley & Sons, Ltd.
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  • 98
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 121-136 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents a multigrid method for numerically solving the coupled Poisson-Schrödinger equations in one dimension for a multilayered HEMT device structure. It is shown that this method produces a good speed-up factor over the non-multigrid approach. This should make it suitable for incorporating into the two-dimensional HEMT model involving coupled Poisson, Schrödinger, current continuity and energy transport equations, with the Schrödinger equation being solved in slices perpendicular to the layer structure. The time taken to produce a multigrid solution depends on the size of the coarse grid and on the number of grids used. A method of predicting the time taken for any combination of these values is presented. The method is demonstrated for a 4-layer device. © 1997 by John Wiley & Sons, Ltd.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 371-371 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: No Abstract
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  • 100
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 329-341 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The dynamic analysis of discontinuities in printed circuits has been performed using the mode matching technique. This study concerns the open end of microstrip lines and suspended microstrip lines. The fields on either side of the discontinuity are described by means of the continuous (radiated and evanescent) and guided modes of the structure.The conditions of continuity of the electromagnetic fields are then applied in the plane of the discontinuity. By taking into account the relations of orthogonality of the modes of the same region, a system of coupled Fredholm integral equations is obtained and solved by the iterative method of Neumann's series.The study calls for the use of the continuous spectrum of microstrip lines, which can be obtained analytically only after a great amount of calculation and CPU time. Thus, the first approach consists in neglecting this continuous spectrum. This gives accurate results for the reflection coefficient but it is not sufficient for the derivation of the radiation pattern. So, two simple models for the continuous spectrum, both based on the physical behaviour of such discontinuities, are considered and discussed. © 1997 John Wiley & Sons, Ltd.
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