Showing papers by "Eindhoven University of Technology published in 1991"

Designs, graphs, codes, and their links

Abstract: From the Publisher: Although design theory, graph theory and coding theory, had their origins in various areas of applied mathematics, today they are found under the umbrella of discrete mathematics. Here the authors have considerably reworked and expanded their earlier successful books on designs, graphs and codes, into an invaluable textbook. They do not seek to consider each of these three topics individually, but rather to stress the many and varied connections between them. The discrete mathematics needed is developed in the text, making this book accessible to any student with a background of undergraduate algebra. Many exercises and useful hints are included throughout, and a large number of references are given.

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 ℝ n in which some real valued functionf assumes its optimal (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 mathematical 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.

Why is software late? An empirical study of reasons for delay in software development

Abstract: A study of the reasons for delay in software development is described. The aim of the study was to gain an insight into the reasons for differences between plans and reality in development activities in order to be able to take actions for improvement. A classification was used to determine the reasons. 160 activities, comprising over 15000 hours of work, have been analyzed. The results and interpretations of the results are presented. Insight into the predominant reasons for delay enabled actions for improvements to be taken in the department concerned. Because the distribution of reasons for delay varied widely from one department to another, it is recommended that every department should gain an insight into its reasons for delay in order to be able to take adequate actions for improvement. >

Interatomic force fields for silicas, aluminophosphates, and zeolites: Derivation based on ab initio calculations

Abstract: A consistent force field for the description of interatomic interactions within silicas, aluminophosphates, and zeolites 1 is presented. The derivation of parameters is based both on a fit to the potential-energy surface of small clusters, as determined by ab initio quantum-chemical methods, and on fitting of experimental data on alpha-quartz. It is shown that both types of data are essential for the development of an accurate and transferable force field. The accuracy and transferability of the force field is assessed by comparing force-field predictions for the structure and elastic properties of a dozen different systems with experiment. Results obtained with the present approach compare favorably with those obtained with force fields used in the literature. Moreover, the introduction of additional chemical elements into the force field does not seriously affect the accuracy, making these force fields a valuable tool for the modeling of chemically complex zeolites

Penetration of carboplatin and cisplatin into rat peritoneal tumor nodules after intraperitoneal chemotherapy

Abstract: Platinum distribution was studied in rat peritoneal tumors after i.p. treatment with equimolar doses of carboplatin and cisplatin. Low platinum concentrations (4 ppm) were detected in the periphery of the tumor after carboplatin treatment, whereas no platinum was detected 0.5 mm in from the periphery. In contrast, after cisplatin treatment, high platinum concentrations (29 ppm) were measured in the periphery of the tumor and moderate concentrations (14 ppm) were measured in the center. Only following increased carboplatin doses were low platinum concentrations detectable in the tumor. The total platinum concentration in the tumors was determined after equimolar administration of both drugs. In all, 7 times more platinum was detected after cisplatin treatment than after carboplatin treatment, and 10 times more carboplatin than cisplatin had to be injected to obtain comparable platinum concentrations in the tumors. When single cells were incubated with equimolar concentrations of carboplatin and cisplatin, 6-7 times more platinum was found in cells treated with cisplatin. However, pharmacokinetic studies favored i.p. administration of carboplatin because the clearance of this compound from the peritoneal cavity, expressed as t1/2 beta, was lower than that of cisplatin (239 vs 78 min), resulting in an AUC in the peritoneal cavity for both total and ultrafiltered drug that was almost 3 times higher for carboplatin than cisplatin. The AUC for ultrafiltered carboplatin in plasma was 2-fold that for cisplatin (2,801 +/- 210 vs 1,334 +/- 431 microM m). The present study demonstrated that in spite of the pharmacological advantages of carboplatin, its capacity to penetrate into peritoneal tumors and tumor cells is far lower than that of cisplatin.

Verification studies of a simplified model for the removal of dichloromethane from waste gases using a biological trickling filter (part II)

Abstract: The removal of dichloromethane from waste gases in a biological trickling filter was studied experimentally as well as theoretically within the concentration range of 0–10,000 ppm. A stable dichloromethane elimination performance was achieved during two years of operation, while the start-up of the system only amounted to several weeks at constant inlet concentrations. The trickling filter system was operated co-currently as well as counter-currently.

Propagation of barotropic vortices over topography in a rotating tank

Abstract: A small-scale cyclonic vortex in a relatively broad valley tends to climb up and out of the valley in a cyclonic spiral about the centre, and when over a relatively broad hill it tends to climb toward the top in an anticyclonic spiral around the peak. This phenomenon is examined here through two-dimensional numerical simulations and rotating-tank experiments. The basic mechanism involved is shown to be the same as that which accounts for the northwest propagation of cyclones on a β-plane. This inviscid nonlinear effect is also shown to be responsible for the observed translationary motion of barotropic vortices in a free-surface rotating tank. The behaviour of isolated vortices is contrasted with that of vortices with non-vanishing circulation.

Phase relations in the Ti-Si-C system

Abstract: For the system TiSiC phase diagrams at 1373 K and at 1523 K were determined. For that purpose, several alloys and diffusion couples were equilibrated and analysed by EPMA (electron probe microanalysis) polarised light microscopy and X-ray diffraction. With EPMA the composition of the alloys could be determined accurately by measuring the titanium, silicon and carbon contents. Some differences were found with the known diagram from the literature.

Supporting hypothesis generation by learners exploring an interactive computer simulation

Abstract: Computer simulations provide environments enabling exploratory learning. Research has shown that these types of learning environments are promising applications of computer assisted learning but also that they introduce complex learning settings, involving a large number of learning processes. This article reports on an instrument for supporting one of these learning processes: stating hypotheses. The resulting instrument, an hypothesis scratchpad, was designed on the basis of a conceptual representation of the simulation model and tested in an experimental study. In this study three versions of the scratchpad, varying in structure, were compared. It was found that support offered for identifying variables, in the form of a selection list, is relatively successful: students who used this list were better in differentiating different types of variables. For identifying relations, a selection list of relations offered to the students proved unhelpful in finding accurate relations: students using this list stated their hypotheses mainly at a very global level. The research reported was conducted in the project SIMULATE. SIMULATE was part of SAFE, a R&D project partially funded by the CEC under contract D1014 within the Exploratory Action of the DELTA programme. The work of SIMULATE is continued in the DELTA main phase project SMISLE.

The continuum emission of an arc plasma

Abstract: We present free-bound Biberman factors (12,000, 13,500 and 14,500 K) for the wavelength range of 250–320 nm and 380–800 nm. These values were determined by measuring the absolute continuum intensity of a thermal argon plasma in a cascade arc (2mm dia) for a pressure range of 2–6×105 Pa and a current range of 20–60 A. The continuum emission is corrected for free-free contributions. Two highly accurate experimental reference values of the free-bound factors were used to check the electron density. Agreement with experiments in the u.v. is good. Comparison with theoretical values also shows good agreement below 430 nm. Above this wavelength, theory predicts an edge structure which is not apparent in the available experimental values. The agreement between our results and recent experimental values (for which the electron density was obtained with two-wavelength interferometry) is good. The influence of non-equilibrium has been found to be negligible. We conclude that absolute continuum measurements are well suited to determine electron densities (visible spectroscopy) and electron temperatures (u.v. spectroscopy) by using the known free-bound Biberman factors. Prediction of the absolute intensity as a function of wavelength is possible within 10%.

A fully abstract model for concurrent constraint programming

Abstract: Recent results [5] have shown that concurrent Logic programming has a very simple model, based on linear sequences, which is fully abstract with respect to the parallel operator and finite observables. This is intrinsically related to the asynchronous and monotonic nature of the communication mechanism, which consists of asking and telling constraints on a common store. We consider here a paradigm for (asynchronous) concurrent programming, based on the above mechanism, and provided with the standard operators of choice, parallelism, prefixing, and hiding of local variables. It comes out that linear sequences still suffice for a compositional description of all the operators. Moreover, we consider the problem of full abstraction. Since our notion of observables implies the removal of silent steps, the presence of the choice operator induces the same problems (for compositionality) as bisimulation in CCS. We show that in our framework this problem has a simple solution which consists of introducing a semantical distinction between the various ways in which deadlock and failure might occur. The resulting semantics is fully abstract and still based on linear sequences.

Critical torque and speed of eddy current brake with widely separated soft iron poles

Abstract: A theoretical model ss derived for eddy current disc brakes with iron pole shoes with a wide spacing. The eddy current in the disc is not a simple periodic function allowing representation by sine functions. In the high speed region, the current distribution around the polo shoe occupies a limited zone width proportional to the air gap. The theory based on this effect leads to reasonably accurate values of the critical torque and speed compared with experimental data. The predicted air gap dependency of the critical values agrees better with experimental results than Rudenberg's theory.< >

Periodic multiprocessor scheduling

Abstract: A number of scheduling and assignment problems are presented involving the execution of periodic operations in a multiprocessor environment. We consider the computational complexity of these problems and propose approximation algorithms for operations with identical periods as well as for operations with arbitrary integer periods.

Analysis of the asymmetric shortest queue problem

Abstract: In this paper we study a system consisting of two parallel servers withdifferent service rates. Jobs arrive according to a Poisson stream and generate an exponentially distributed workload. On arrival a job joins the shortest queue and in case both queues have equal lengths, he joins the first queue with probabilityq and the second one with probability 1 −q, whereq is an arbitrary number between 0 and 1. In a previous paper we showed for the symmetric problem, that is for equal service rates andq = 1/2, that the equilibrium distribution of the lengths of the two queues can be exactly represented by an infinite sum of product form solutions by using an elementary compensation procedure. The main purpose of the present paper is to prove a similar product form result for the asymmetric problem by using a generalization of the compensation procedure. Furthermore, it is shown that the product form representation leads to a numerically efficient algorithm. Essentially, the method exploits the convergence properties of the series of product forms. Because of the fast convergence an efficient method is obtained with upper and lower bounds for the exact solution. For states further away from the origin the convergence is faster. This aspect is also exploited in the paper.

Telescopic mappings in typed lambda calculus

Abstract: The paper develops notation for strings of abstractors in typed lambda calculus, and shows how to treat them more or less as single abstractors.

Which linear codes are algebraic-geometric?

Abstract: An infinite series of curves is constructed in order to show that all linear codes can be obtained from curves using Goppa's construction. If conditions are imposed on the degree of the divisor use, then criteria are derived for linear codes to be algebraic-geometric. In particular. the family of q-ary Hamming codes is investigated, and it is proven that only those with redundancy one or two and the binary (7,4,3) code are algebraic-geometric in this sense. For these codes. the authors explicitly give a curve, rational points, and a divisor. It is proven that this triple is in a certain sense unique in the case of the (7,4,3) code. >