Search results

The electrical performance of high‐speed integrated circuits and digital networks strongly depends on the behavior of interconnects between various components of these systems. The prediction of such performance can only be achieved by the used of computer‐aided design and simulation tools. The simulation of high‐speed digital circuits has gained a significant role in the past few years since it is critical in the evaluation of noise levels, signal corruption and signal delay in fast switching circuits. This paper explores the various aspects and techniques for transmission line simulation; in particular, two different methods are described: the scattering parameter method and the optimal method.

This paper describes a computer program DOTIG4, for the study in the time domain, of the interaction of transient electromagnetic pulses (EMP) with arbitrary perfect conducting (PEC) surfaces modelled by planar triangular patches. DOTIG4 is based on the solution of the Time Domain Electric Field Integral Equation (TD‐EFIE) by the method of moments (MoM) using a marching‐on‐in‐time procedure. The code is applied to transient scattering of several structures and to calculate the input impedance of several broadband antennas.

The purpose of this paper is to analyze the wave scattering behaviour of an inhomogeneous and eccentric inclusion in a homogeneous matrix material. Another purpose is to evaluate the influence of epistemic uncertainty on the wave scattering behaviour, particularly on the lack of knowledge about this eccentricity. This task calls for a multidisciplinary model.

The inclusion is modelled as a multi‐layered obstacle, with all layers being eccentric with respect to each other. The material behaviour of the embedding matrix is linear elastic and isotropic. In a multidisciplinary approach, the interaction of the inhomogeneous inclusion and the embedding matrix with respect to an incoming shear wave of arbitrary shape is solved analytically. The purely analytical solution process takes place in the frequency‐domain. Due to the lack of knowledge about the eccentric configuration of the matrix inclusion and its influence on the total wave field inside the matrix material, the mechanical model is coupled with fuzzy set theory for modelling this non‐stochastic uncertainty.

An analytical model for describing the wave scattering behaviour of an elastic matrix inclusion with eccentric set‐up is found and intimately connected with the framework of fuzzy set theory. Hence it is shown that the treatment of epistemic uncertainty with the derived analytical model is possible and fruitful. Additionally, it is shown that eccentric configurations lead to highly increased amplitudes with respect to the reference case of a concentric or even homogenous set‐up of the inclusion.

The value of this contribution is in the analytical model, which allows one to predict the wave scattering behaviour of eccentric configurations of multi‐layered fibres including the surrounding interphase, and its coupling with fuzzy set theory to cope with the epistemic uncertainty inherent in the geometric set‐up of the matrix inclusion.

A computer program named DOTIG1 was developed for the study, in the time domain, of the interaction of transient electromagnetic pulses (EMP) with structures modelled by thin wires. The numerical procedure used is described and the results obtained with DOTIG1 are compared with those obtained, in the frequency domain, by other authors, using the Fourier transform. The comparison is specifically applied to the scattering cases from a simple stick model of an aircraft, from a wire cross in front of an infinite perfect conductor and from a junction of two wires with different radii.

Gives a bibliographical review of the error estimates and adaptive finite element methods from the theoretical as well as the application point of view. The bibliography at the end contains 2,177 references to papers, conference proceedings and theses/dissertations dealing with the subjects that were published in 1990‐2000.

The purpose of this paper is to present the method of lines (MOL) solution of the stimulated Brillouin scattering (SBS) equations (a system of three first-order hyperbolic partial differential equations (PDEs)), describing the three-wave interaction resulting from a coupling between light and acoustic waves. The system has complex numbers and boundary values.

System of three first-order hyperbolic PDEs are first transformed and then spatially discretized. Superbee flux limiter is proposed to offset numerical damping and dispersion, brought on by the low order approximation of spatial derivatives in the PDEs. In order to increase computational efficiency, the structured structure of the PDE Jacobian matrix is identified and a sparse integration algorithm option of the ordinary differential equation (ODE) solvers is used. The flux limiter based on higher order approximations eliminates numerical oscillation. Examples are presented, and the performance of the Matlab ODE solvers is evaluated by comparison.

This type of solution provides a rapid means of investigating SBS as a tool in fiber optic sensing.

To the best of the authors' knowledge, MOL solution is proposed for the first time for the modeling of three-wave interaction in a SBS-based fiber optic sensor.

This paper aims to present a SPICE model to represent antennas in receiving mode. The model can be used to evaluate the performance of the antenna when it is coupled to several different nonlinear electric circuits. The proposed methodology is particularly suitable for rectenna applications, as it allows the analysis of different configurations for a rectenna more efficiently than using full-wave analysis simulators coupled directly to each rectifier circuit.

The model presented uses reciprocity theory to calculate the ideal voltage source of the Thevenin-equivalent circuit for an antenna. Vector fitting is then used to approximate the model to rational functions that can be converted to Resistor, Inductor and Capacitor circuits. Additional components are added to the circuit to prevent numerical instability.

Two rectennas are used to illustrate the performance of the proposed model, one based on a 2.45-GHz rectangular patch antenna and another based on a planar spiral antenna. The second antenna has impedance with positive and negative real parts along the frequency range, which could lead to numerical instabilities. The proposed method is shown to be stable while working with these negative resistance values, which may appear during circuit parameterization.

The equivalent SPICE circuit model for the antenna makes it easy to simulate nonlinear circuits connected to the antenna and perform transient analyses. The computational cost of antenna analysis is reduced, being more computationally efficient than methods that involve full-wave simulation. This characteristic makes it an interesting approach for working with rectennas, or any application where the time constant of the circuit is much longer than the period of the incident wave.

For most antenna applications, the numerical stability of the circuit can be achieved using passive enforcement. However, depending on the phase response of the antenna, the impedance that represents its far-field characteristic may present a negative real part, in which case, passive enforcement will fail. In this paper, the problem of numerical instability is solved by introducing an offset resistance and a current-controlled voltage source to the model.

The process of industrial relations which has developed in the offshore catering industry is not significantly different from that evident in conventional onshore‐based unionised industries. Data obtained as part of a survey of industrial relations in the Grampian region (1982) covering five of the nine offshore catering companies in the Northern Sector of the North Sea, show that such companies operate in an atypical industrial environment represented by unusual work/lifestyle patterns. A two‐tier system has evolved to meet the communication requirements of a transient and scattered workforce: the management‐workforce relationship in offshore installations being informal, while the onshore relationship between management and trade union officials is far more formal. While the adoption of collective bargaining in this industry is a fairly recent happening, it can be readily explained in terms derived from “traditional” British industry.

The Convolution Quadrature Method (CQM) has been widely applied to solve transient elastodynamic problems because of its stability and generality. However, the CQM suffers from the problems of huge memory requirement in case of direct implementation in time domain or CPU time in case of its reformulation in Laplace domain. The purpose of this paper is to combine the CQM with the pseudo-initial condition method (PICM) to achieve a good balance between memory requirement and CPU time.

The combined methods first subdivide the whole analysis into a few sub-analyses, which is dealt with the PICM, namely, the results obtained by previous sub-analysis are used as the initial conditions for the next sub-analysis. In each sub-analysis, the time interval is further discretized into a number of sub-steps and dealt with the CQM. For non-zero initial conditions, the pseudo-force method is used to transform them into equivalent body forces. The boundary face method is employed in the numerical implementation. Three examples are analyzed. Results are compared with analytical solutions or FEM results and the results of reformulated CQM.

Results demonstrate that the computation time and the storage requirement can be reduced significantly as compared to the CQM, by using the combined approach.

The combined methods can be successfully applied to the problems of long-time dynamic response, which requires a large amount of computer memory when CQM is applied, while preserving the CQM stability. If the number of time steps is high, then the accuracy of the proposed approach can be deteriorated because of the pseudo-force method.

The paper reports on a research project exploring the change in the organizational context of communicators and communication units in higher education and research institutions (HERIs), the importance of informal processes within their daily work and the great diversity of expectations communicators have to tackle.

Based on a literature review, a mixed-methods study combining expert interviews with 54 German HERI heads of communication units, an online-survey and a document analysis of organizational characteristics was conducted. Findings were validated in four focus groups.

The study illuminates the impact of organizational and operational structures of HERIs on communicators and their boundary spanning activities. Due to varying expectations of stakeholders, communicators constantly have to switch roles. Members of HERIs' executive boards affect status and working conditions for communicators in the organization.

Interviews with other HERI actors, especially members of the executive board, are proposed to get more thorough insights into the organizational context of HERIs and the mutual expectations of different internal stakeholders.

Insights from the project may help HERI actors to reflect their organizational context and to identify potentially contentious structures or processes.

Communicating science sometimes clashes with complex organizational and operational structures. Despite the “organizational turn” in HERI research, there is a lack of data on the relation between communicators, their communication units and the larger organizational context. The exploratory study addresses this gap.