Showing papers by "Eindhoven University of Technology published in 1988"

Global optimization and simulated annealing

Abstract: In this paper we are concerned with global optimization, which can be defined as the problem of finding points on a bounded subset of Rn in which some real valued functionf assumes its optimal (i.e. maximal or minimal) value. We present a stochastic approach which is based on the simulated annealing algorithm. The approach closely follows the formulation of the simulated annealing algorithm as originally given for discrete optimization problems. The mathematic formulation is extended to continuous optimization problems and we prove asymptotic convergence to the set of global optima. Furthermore, we discuss an implementation of the algorithm and compare its performance with other well known algorithms. The performance evaluation is carried out for a standard set of test functions from the literature. Keywords: global optimization, continuous variables, simulated annealing.

Delay-insensitive codes : an overview

Abstract: The problem of delay-insensitive data communication is described. The notion of delay-insensitive code is defined, giving precise conditions under which delay-insensitive data communication is feasible. Examples of these codes are presented and analyzed. It appears that delay-insensitive codes are equivalent with antichains in partially ordered sets and with all unidirectional error-detecting codes.

Intrinsic disc pressure as a measure of integrity of the lumbar spine

Abstract: Intradiscal pressure and volume measurements were made in 84 fresh cadaveric lumbar spine disc spaces. The nucleus was injected with a roentgenographic contrast agent under fluoroscopic examination. The intrinsic pressure, the pressure at which the agent entered the disc, and the maximum pressure that the disc could hold were measured. The discs were graded for degeneration. The intrinsic and maximum pressures were found to be inversely related to disc degeneration grade, and directly related to each other. Relatively greater degeneration was found at lower levels of the lumbar spine as compared to the upper levels. The intrinsic disc pressure may prove to be a useful clinical tool in the evaluation of spinal integrity.

A new method for the preparation of titanium-silicalite (TS-1)

Abstract: Titanium-silicalite can be prepared by subsequent dealumination of ZSM-5 with hydrochloric acid and reaction with titaniumtetrachloride vapour at elevated temperatures. The titanium atoms are probably inserted into lattice vacancies which were formed upon acid leaching.

On the expectation of the product of four matrix-valued Gaussian random variables

Abstract: The formula for the expectation of the product of four scalar real Gaussian random variables is generalized to matrix-valued (real or complex) Gaussian random variables. As an application of the extended formula, a simple derivation is presented of the covariance matrix of instrumental variable estimates of parameters in multivariable regression models. >

Spin-exchange and dipole relaxation rates in atomic hydrogen: Rigorous and simplified calculations.

Abstract: We calculate the magnetic field and temperature dependence of the rates for all two-body spin-exchange and dipolar transitions among hyperfine levels in cryogenic H gas by means of the coupled-channels method. A description of this method and its practical application is presented. A simple interpretation of the rates is given, in some cases with associated simple closed-form formulas, based on the degenerate-internal-states approximation.

Improved sphere bounds on the covering radius of codes

Abstract: The sphere bound is a trivial lower bound on K(n,R), the minimal cardinality of any binary code of length n and with covering radius R. By simple arguments it is considerably improved, to K(n,1)>or=2/sup n//n for n even. A table of lower and upper bounds on K(n,R) for n >

The modeling of continuous mixers. Part I: The corotating twin-screw extruder

Abstract: In many operations in polymer processing, such as polymer blending, devolatilization, or incorporation of fillers in a polymeric matrix, continuous mixers are used; e.g., corotating twin-screw extruders (ZSK), Buss Cokneaders and Farrel Continuous Mixers. Theoretical analysis of these machines tends to emphasize the flow in complex geometries rather than generate results that can be directly used (1–5). In this paper, a simple model is developed for the hot melt closely intermeshing corotating twin-screw extruder, analogous to the analysis of the single-screw extruder carried out in 1922 and 1928 (6, 7). With this model, and more specifically with its extension to the complete nonisothermal, non-Newtonian situation, it is possible to understand the extrusion process and to calculate the energy, specific energy, and temperature rise during the process with respect not only to the viscosity of the melt, but also to the screw geometry (location and number of transport elements, kneading sections and blisters, pitch, positive or negative, screw clearance, and flight width) and screw speed. To support the theoretical analysis, model experiments with a Plexiglas-walled twin-screw extruder were performed, in addition to practical experiments with melts on small- and large-scale extruders, with very reasonable results, In Part 2, the Buss Cokneader will be analyzed analogously.

Compositional semantics for real-time distributed computing

Abstract: We give a compositional denotational semantics for a real-time distributed language, based on the linear history semantics for CSP of Francez et al. Concurrent execution is not modelled by interleaving but by an extension of the maximal parallelism model of Salwicki and Muldner, that allows for the modelling of transmission time for communications. The importance of constructing a semantics (and, in general, a proof theory) for real-time is stressed by such different sources as the problem of formalizing the real-time aspects of Ada and the elimination of errors in the real-time flight control software of the NASA space shuttle (Comm. ACM 27 (1984)).

Modeling Statecharts Behaviour in a Fully Abstract Way

Abstract: We present a denotational, strictly syntax-directed, semantics for Statecharts, a graphical, mixed specification/programming language for real-time, developed by Harel [H]. This requires first of all defining a proper syntax for the graphical language. Apart from more conventional syntactical operators and their semantic counterparts, we encounter unconventional ones, dealing with the typical graphical structure of the language. The synchronous nature of Statecharts makes special demands on the semantics, especially with respect to the causal relation between simultaneous events, and requires a refinement of our techniques for obtaining a denotational semantics for OCCAM [HGR]. We prove that the model is fully abstract with respect to some natural notion of observable behaviour. The model presented will serve as a basis for a further study of specification and proof systems within the ESPRIT-project DESCARTES.

Shock wave induced evaporation of water droplets in a gas-droplet mixture

Abstract: A model is presented for the droplet evaporation process induced by a shock wave propagating in a fog. The model is based on the existence of a quasi-steady wet bulb state of the droplets during evaporation. It is shown that for moderate shock strength, Ma = < 2, and droplet radii in the range of 1–5 the, the major part of the evaporation process is governed by a balance between heat conduction and vapour diffusion. The formation of a fog by means of an unsteady adiabatic expansion of humid nitrogen is described. Experimental results of shock induced evaporation are shown for shock Mach numbers from 1.2 to 2.1, droplet mass fraction of 5 · 10-3, and initial droplet radii of 1–1.4 μm. The expected linear relation between droplet radius squared and time during evaporation is observed. Characteristic evaporation times appear to be strongly dependent on shock strength. A variation of about two decades, predicted by theory, was experimentally observed for the Mach number range studied.

Sample enrichment in high speed narrow bore capillary gas chromatography

Abstract: Summary Reduction of the column diameter has proved to be a highly efficient tool to increase the speed of analysis. Unfortunately, the requirementsfor instrumental design with respect tosample input band width, low dead volume interfacing, and time constants of detection and registration systems are the more critical the smaller the inside diameter. Recently we reported input band widths as low as 1 ms [l] for gaseous samples at ppm concentration levels, without any preconcentration, in a study with narrow bore columns and thermal conductivity detection. In this study a simple versatile micro on-column cold trap/ thermodesorption enrichment system for narrow bore columns is introduced and evaluated. The combination of considerable sample enrichment and presenration of the compatibility of the required input band width with column dimensions is critically examined. The process of thermodesorption (reinjection) which is the most critical step, is particulally emphasized. The system consists of a short aluminum coated fused silica or metal capillary with a low mass and a low cost electrical heating. Input band widths down to 1 ms are obtained without extreme demands on electrical power (300 watt). The potential of the system is illustrated with some extremely fast separations.

Experimental Design and Structural Optimization

Abstract: Structural optimization problems are mostly solved iteratively by combining finite element and mathematical progamming methods.

Experimental determination of thermal and adhesion stress in particle filled thermoplasts

Abstract: The phenomena of dewetting in filled thermoplastics were studied by light microscopy and were correlated with variations in the slope of stress-strain diagrams in constant strain rate tests. In such diagrams, kinks in the plots were found to correspond to the dewetting stress. The corresponding local stress at a filler particle is then equal to the sum of the thermal compressive stress and the adhesion stress. It was shown that the adhesion stress was proportional to the reciprocal root of the particle radius. Also, values of dewetting stress predicted for inorganic particles with radii smaller than 2–4 micrometers are higher than the stresses at which crazes and shear-bands are formed near such particles, indicating that dewetting will not occur in those cases, and adhesion aids may be superfluous.

Conditional PASTA

Abstract: Let Y be a stochastic process representing the state of a system and N a doubly stochastic Poisson process whose intensity varies with the state of a random environment represented by a stochastic process X. In this context a generalization of ''Pasta'' (Poisson Arrivals See Time Averages) is shown to be valid. Various applications of the result are given.

Technology mapping for standard-cell generators

Abstract: A novel approach to technology mapping that produces a standard-cell IC implementation from a previously optimized and decomposed set of Boolean functions is presented. Instead of trying to solve the problem for random libraries of standard cells, which proved to be very difficult, it has been solved for cell generators, which are only limited by technology constraints. The completeness of the sets of cells that can be generated by a cell generator, given a certain technology, makes it possible to use an elegant mapping algorithm. The algorithm was coded in CommonLISP, and used to map a large number of benchmark examples. The results compare favorably with published results. >