Modeling and simulation of the resource allocation process in abandwidth-on-demand satellite communications network

The authors describe the modeling and simulation of a frequency-division multiple-access (FDMA) satellite bandwidth-on-demand (BOD) service. The class of resource allocation processes to which the satellite BOD application belongs is identified and contrasted with more common resource allocation processes. Several unique features of BOD service complicate the performance specification, modeling, and analysis. The authors divide the modeling problem into three fundamental components: modeling the resource algorithm and modeling the processing of individual resource requests. These modeling components are illustrated with the satellite BOD application. In addition, simulation of the resource allocation requires three additional components: an easy-to-use user input interface, performance measures and statistics gathering, and presentation of simulation results (user output interface). The architecture of the simulation software (resource allocation analysis program, or RAAP) is presented in terms of these six components. To illustrate RAAP's capabilities, example simulation results are given     

ON THE LENGTH EFFECT OF THE HEAT DISPERSION PARAMETERS

Considerable attention has been paid to the dispersion of heat in fixed beds passed by a flowing gas. This is best documented by ample experimental evidence and correlations available in the literature. However, the results of individual studies differ often significantly. As a possible cause of the discrepancies have been put forth various experimental techniques and data processing methods (Gunn, 1970; Froment, 1972; Li and Finlayson, 1977), particularly the use of different mathematical models.

As a fact of considerable significance, however, remains the dependence of results on the geometry of the experiment. All parameters of the pseudohomogeneous one- and two-dimensional models have been found to depend on the length of the bed (Li and Finlayson, 1977; De Wasch and Froment, 1972; Bunell el al., 1949; Calderbank and Pogorski, 1957), while their values invariably decrease with the increasing length. In contrast, neither of the existing models predicts such a dependence, nor is there a satisfactory explanation for the phenomenon at hand.

The aim of this work has been to carry out experimental measurements of the effective radial thermal conductivity in a fixed bed passed by flowing air and to analyze in detail the length dependence of the results. The experiments consisted of measurement of the steady state outlet temperature profiles corresponding to a radially distributed inlet profile.     

Three-dimensional computer reconstruction of large tissue volumes based on composing series of high-resolution confocal images by GlueMRC and LinkMRC software

Computer-based visualization of large tissue volumes with high resolution based on composing series of high-resolution confocal images is presented. GlueMRC and LinkMRC programs are introduced, implementing composition of overlapping series of optical sections captured by a confocal microscope, registration and subsequent composition of successive confocal stacks. Both programs are using an interactive approach in combination with automatic algorithms for image registration. Further, the method for obtaining surface renderings of microscopical structure under study is described. For this purpose, structure contours visible in the sections are interactively digitized using a Colon plug-in module running in Ellipse environment. Then the coordinates of the contours are processed by special modules in the graphic programming environment IRIS Explorer and the structure surface is rendered. The method is shown on the 3-D reconstruction of the capillary bed of human placental villi and chick embryonic gut and its vascular bed.     

Noise and transport characterisation of tantalum capacitors

A low frequency noise and charge carrier transport mechanisms were investigated on tantalum capacitors made by various producers. The model of Ta–Ta₂O₅–MnO₂ MIS structure was used to give physical interpretation of I–V characteristics in normal and reverse modes. The noise in time and frequency domain was examined and noise sources were identified. We evaluated correlation between leakage current and noise spectral density and discussed corresponding quality and reliability indicators.     

Recursive approximation by ARX model: A tool for grey box modelling

The presented procedure computes approximate probabilistic models of complex dynamic phenomena recursively with respect to an increasing amount of observed evidence. Measured, fictitious as well as simulated data can be used in combination for obtaining a reasonably conservative approximate model. Thus information from a number of sources can be systematically merged using a refinement of the recently proposed method of Bayesian pooling of imprecise opinions from a variety of experts. It can be applied recursively as the number of treated items grows. The procedure provides (i) a new tool needed for grey as well as black box modelling, (ii) a novel adaptation of probabilistic models and (iii) an approximation of a given model by a simpler one. The general procedure is applied to the autoregressive model with exogenous variables (AM). This example illustrates the adopted approach and conmbutes to the solution of the following tasks: (i) estimation of an appropriate model structure; (ii) incorporation of prior knowledge into the initial conditions of recursive least squares; (iii) construction of a reference for an advanced forgetting technique; (iv) approximation of a complex analytic/simulation model by an ARX model. The behaviour of the procedure is illustrated on typical examples.     

Anisotropic properties and structure of amorphous films of selenium

It is shown experimentally that anisotropic columnar inhomogeneous structures form in evaporated amorphous selenium films. The angle of orientation of the structures corresponds to the angle of incidence of the molecular flow. The diameter and density of inhomogeneities in the amorphous films, evaporated at an acute angle, changed by a factor of 30 with a change in the substrate temperature from 20 to 60°C, as a result of diffusion mass transfer of condensed material on the substrate.     

Optimum load time history for non-linear analysis using dynamic relaxation

A modification of the dynamic relaxation method is proposed which facilitates static analysis of non-linear problems. Continuous loading in time is adopted instead of the ordinary step function of time. Inertia and damping forces arising during the loading process are kept at a minimum using an optimum load time history. This results from the stationary condition of an appropriate functional. The equation of motion is included as a subsidiary condition. Continuous load—deflection curves can be obtained. An incremental solution is avoided. Application of the method is extremely simple. Existing programs based on explicit time integration schemes can be easily adapted for it. Sample solutions are presented.