Showing papers by "Eindhoven University of Technology published in 1992"

A course in combinatorics

Abstract: This is the second edition of a popular book on combinatorics, a subject dealing with ways of arranging and distributing objects, and which involves ideas from geometry, algebra and analysis. The breadth of the theory is matched by that of its applications, which include topics as diverse as codes, circuit design and algorithm complexity. It has thus become essential for workers in many scientific fields to have some familiarity with the subject. The authors have tried to be as comprehensive as possible, dealing in a unified manner with, for example, graph theory, extremal problems, designs, colorings and codes. The depth and breadth of the coverage make the book a unique guide to the whole of the subject. The book is ideal for courses on combinatorical mathematics at the advanced undergraduate or beginning graduate level. Working mathematicians and scientists will also find it a valuable introduction and reference.

Job Shop Scheduling by Simulated Annealing

Abstract: We describe an approximation algorithm for the problem of finding the minimum makespan in a job shop. The algorithm is based on simulated annealing, a generalization of the well known iterative improvement approach to combinatorial optimization problems. The generalization involves the acceptance of cost-increasing transitions with a nonzero probability to avoid getting stuck in local minima. We prove that our algorithm asymptotically converges in probability to a globally minimal solution, despite the fact that the Markov chains generated by the algorithm are generally not irreducible. Computational experiments show that our algorithm can find shorter makespans than two recent approximation approaches that are more tailored to the job shop scheduling problem. This is, however, at the cost of large running times.

Quantitative temporal reasoning

Abstract: A substantially large class of programs operate in distributed and real-time environments, and an integral part of their correctness specification requires the expression of time-critical properties that relate the occurrence of events of the system. We focus on the formal specification and reasoning about the correctness of such programs. We propose a system of temporal logic, RTCTL (Real-Time Computation Tree Logic), that allows the melding of qualitative temporal assertions together with real-time constraints to permit specification and reasoning at the twin levels of abstraction: qualitative and quantitative. We argue that many practically useful correctness properties of temporal systems, which need to express timing as an essential part of their functionality requirements, can be expressed in RTCTL. We develop a model-checking algorithm for RTCTL whose complexity is linear in the size of the RTCTL specification formula and in the size of the structure. We also present an essentially optimal, exponential time tableau-based decision procedure for the satisfiability of RTCTL formulae. Finally, we consider several variants and extensions of RTCTL for real-time reasoning.

Why are some titanium silicalite-1 samples active and others not?

Abstract: Titanium silicalite-1 samples of different particle size are synthesized. X-ray diffraction (XRD), infrared (IR),29Si magic angle spinning nuclear magnetic resonance (MAS NMR), diffuse reflectance electron absorption spectrometry (DREAS), thermogravimetric analysis (TGA), pore volume and particle size measurements are used to characterize these samples. In the hydroxylation of phenol with hydrogen peroxide large differences in activity are found between different TS-1 samples. Using XRD, IR,29Si MAS NMR, and DREAS measurements it is impossible to differentiate between active and less active samples. Particle size determination (directly by scanning electron microscopy (SEM), Coulter Counter, and Malvern and indirectly by TGA and adsorption measurements) however can explain these differences. Smaller particles are more active than larger particles. From calculations of the Weisz modulus it can be concluded that large zeolite particle are not fully utilized because of pore diffusion limitations. The product distribution is also influenced by particle size.

A finite element analysis of the push‐out test: Influence of test conditions

Abstract: The commonly used method for quantitative evaluation of the strength of a bone-implant interface is the push-out test. In order to give an impulse to standardization and to gain more insight in the biomechanics of the push-out test, a finite element analysis of this test was performed. This study focused on the influence of test conditions on the push-out results. The influence of the following four parameters on the interface stress distribution was tested: (a) clearance of the hole in the support jig, (b) Young's modulus of the implant; (c) cortical thickness; and (d) implant diameter. The distance between the implant and the support jig turned out to be very critical for the occurrence of peak stresses in the interface. Variations of the Young's modulus of the implants resulted in a wide range of interface shear stresses. Variation of the cortical thickness showed a reciprocal relationship between cortical thickness and interface shear stress. However, the interface stress distribution remained uniform under the specific test circumstances. These findings also hold for variations in implant diameter. The present investigation shows that the clearance of the hole in the support jig, and the Young's modulus of the implant are parameters which most strongly influence the interface stress distribution. The clearance of the hole in the support jig is the most critical parameter, but also the parameter that can be controlled most easily. Lack of standardization with regard to these parameters can lead to uninterpretable test results. It is recommended that the clearance of the hole in the support jig is at least 0.7 mm and that push-out results are only compared with each other when materials with similar Young's modulus are concerned.

Formation of hypochlorite, chlorate and oxygen during NaCl electrolysis from alkaline solutions at an RuO2/TiO2 anode

Abstract: On-site electrolysis of a weak alkaline solution of NaCl has been applied to an increasing extent for disinfection. To optimize the electrolytic cell and the electrolysis conditions, the current efficiency for hypochlorite, chlorate and oxygen formation at a commercial RuO2/TiO2 anode were determined under various conditions. It was found that for solution with low NaCl concentrations, (lower than 200 mol m−3), and at 298 K, solution flow velocity of 0.075 ms−1 and high current density, (higher than 2 kA m−2), hypochlorite formation is determined by mass transfer of chloride. The formation of chlorate in weakly alkaline media at a chlorine and oxygen-evolving anode is ascribed to two reactions, namely, the direct oxidation of chloride to chlorate and the conversion of hypochlorite. This is suggested to split the well-known electrochemical Foerster reaction into a chemical reaction for the conversion of hypochlorite in chlorate and the electrochemical oxidation reaction of water. It is proposed that in an acidic reaction layer at the anode the mechanism of chlorate formation may be given by the following:

Conditions for Bose-Einstein condensation in magnetically trapped atomic cesium

Abstract: We study conditions necessary for the observation of Bose-Einstein condensation in a magnetically trapped sample of atomic Cs gas. These conditions are associated with the value of the elastic scattering length, the rate of elastic scattering events, and the lifetime for decay of the density due to both magnetic dipole relaxation in two-body collisions, as well as recombination to Cs2 in three-body collisions. We find that, on the basis of these conditions, the prospects for observing Bose-Einstein condensation are favorable for a gas of ground-state Cs atoms in the highest state of the lowest hyperfine manifold. In all calculated elastic and inelastic two-body rates we find a pronounced resonance structure, which can be understood in terms of the interplay between the singlet-triplet interaction and the hyperfine, Zeeman, and magnetic dipole interactions. The experimental observation of these resonances may help to eliminate present uncertainties about interaction potentials.

Modeling the errors of multi-axis machines : a general methodology

Abstract: A methodology is presented to obtain a generalized error model for multi-axis machines of arbitrary configuration. The model accounts for errors due to inaccuracies in the geometry, finite stiffness, and thermal deformation of the machine's components. Special statistical techniques are applied to the calibration data to obtain an empirical model for each of the errors. In a feedback loop, the identified significant parameters in these models are used for the computer-aided optimization of artefact-based test procedures. Results are shown for a five-axis milling machine and a three-axis coordinate measuring machine.

Orientational dependence of the oscillatory exchange interaction in Co/Cu/Co.

Abstract: A strong oscillatory exchange coupling has been discovered in epitaxial (111) and (110) Co/Cu/Co sandwiches with wedge-shaped Cu layers, deposited by molecular-beam epitaxy (MBE) on single-crystal substrates. This finding proves the intrinsic nature of the strong antiferromagnetic coupling in (111)-textured sputtered Co/Cu multilayers. Combined with recent results on (100) Co/Cu/Co MBE-grown samples, it becomes evident that the nature of the oscillations in Co/Cu/Co depends markedly on growth direction, agreeing with predictions invoking the topology of the Fermi surface of the interlayer Cu.

Redox properties of the iron‐sulfur clusters in activated Fe‐hydrogenase from Desulfovibrio vulgaris (Hildenborough)

Abstract: The periplasmic Fe-hydrogenase from Desulfovibrio vulgaris (Hildenborough) contains three iron-sulfur prosthetic groups: two putative electron transferring [4Fe-4S] ferredoxin-like cubanes (two F-clusters), and one putative Fe/S supercluster redox catalyst (one H-cluster). Combined elemental analysis by proton-induced X-ray emission, inductively coupled plasma mass spectrometry, instrumental neutron activation analysis, atomic absorption spectroscopy and colorimetry establishes that elements with Z > 21 (except for 12–15 Fe) are present in 0.001–0.1 mol/mol quantities, not correlating with activity. Isoelectric focussing reveals the existence of multiple charge conformers with pI in the range 5.7–6.4. Repeated re-chromatography results in small amounts of enzyme of very high H2-production activity determined under standardized conditions (∼ 7000 U/mg). The enzyme exists in two different catalytic forms: as isolated the protein is ‘resting’ and O2-insensitive; upon reduction the protein becomes active and O2-sensitive. EPR-monitored redox titrations have been carried out of both the resting and the activated enzyme. In the course of a reductive titration, the resting protein becomes activated and begins to produce molecular hydrogen at the expense of reduced titrant. Therefore, equilibrium potentials are undefined, and previously reported apparent Em and n values [Patil, D. S., Moura, J. J. G., He, S. H., Teixeira, M, Prickril, B. C., DerVartanian, D. V., Peck, H. D. Jr, LeGall, J. & Huynh, B.-H. (1988) J. Biol. Chem. 263, 18732–18738] are not thermodynamic quantities. In the activated enzyme an S= 1/2 signal (g= 2.11, 2.05, 2.00; 0.4 spin/ protein molecule), attributed to the oxidized H cluster, exhibits a single reduction potential, Em, 7=–307 mV, just above the onset potential of H2 production. The midpoint potential of the two F clusters (2.0 spins/protein molecule) has been determined either by titrating active enzyme with the H2/H+ couple (E'm=–330 mV) or by dithionite-titrating a recombinant protein that lacks the Hcluster active site (Em7.5=–340 mV). There is no significant redox interaction between the two F clusters (n ∼ 1).

TCP WRAPPER : Network monitoring, access control, and booby traps

Abstract: This paper presents a simple tool to monitor and control incoming network traffic. The tool has been successfully used for shielding off systems and for detection of cracker activity. It has no impact on legal computer users, and does not require any change to existing systems software or configuration files. The tool has been installed world-wide on numerous UNIX systems without any source code change.

Learning and Instruction with Computer Simulations: Learning Processes Involved

Abstract: Nowadays prevalent learning theories state that in the study process the learner is actively involved in constructing and reconstructing his/her knowledge base. This conclusion is reflected in modern approaches to teaching that have abandoned viewing the learner as an ‘empty box’ into which knowledge could be poured, and stress the active role of the learner and the importance of his/her foreknowledge. Some forms of Computer Assisted Instruction are well suited for this teaching approach. The use of hypertext-like systems, in which learners are encouraged to explore a domain, is such an example. A second example of CAI that elicits exploratory behaviour is simulation-based learning.

Useful martingales for stochastic storage processes with Lévy-type input

Abstract: We apply the general theory of stochastic integration to identify a martingale associated with a Levy process modified by the addition of a secondary process of bounded variation on every finite interval. This martingale can be applied to queues and related stochastic storage models driven by a Levy process. For example, we have applied this martingale to derive the (non-product-form) steady-state distribution of a two-node tandem storage network with Levy input and deterministic linear fluid flow out of the nodes.

Residential Choice Behaviour of Dual Earner Households: A Decompositional Joint Choice Model:

Abstract: The residential location decision process has been studied for several decades with use of different approaches. One such approach that has received considerable attention in urban planning is the decompositional approach. This approach involves measuring individual preferences. Residential choice behaviour is, however, often the result of a joint decisionmaking process, especially in the case of dual earner households. In the present paper, the original modelling approach is therefore extended to a model of joint decisionmaking. The results of an empirical application in the context of residential choice behaviour in the Netherlands are described.

Parameters affecting the synthesis of titanium silicalite 1

Abstract: The influence of the SiO2 source, crystallization time, stirred and static crystallization conditions, TPAOH source, OH−/Si ratio, Si/Ti ratio and sol concentration were studied. Crystallizations were carried out at 175°C in teflon-lined autoclaves. We were able to synthesize well shaped, homogeneous, highly crystalline batches of TS-1 zeolites with Si/Ti ratio ranging from 24 to infinity (0 to 4 mol-% Ti) and a crystallite size ranging from 0.09 to 12 μm. In order to form small crystallites, seeds are added and the reaction mixture is agitated during crystallization. The best conditions to form small crystallites are; high silicon concentration, low OH− concentration and low water concentration.

Electric Field Driven Separations: Phenomena and Applications

Abstract: The efficiency of separation processes can usually be assured either by an energy input or by external forces. The majority of conventional sep- arations applies mechanical or thermal energy in combination with pressure or gravity forces. The ability of superimposed electric fields to improve separation processes has been well known for many years. The familiar industrial applications range from solid-solid separation in the beneficiation of ores in the mining industry, coalescence of “water-in-oil” emulsion in the petroleum industry, to cleaning of exhaust gases from solid particles in various technologies.

Evidence for superlocalization on a fractal network in conductive carbon-black-polymer composites.

Abstract: The dc conductivity of carbon-black-polymer composites has been measured as a function of carbonblack concentration from just above the percolation threshold p c up to 33p c , and in the temperature range from 4 to 300 K. To explain the temperature dependence we have modified the Mott-Deutscher model for variable-range hopping between superlocalized states on a fractal by assuming Coulomb-dominated hopping. Our data then yield the first experimental evidence of electron superlocalization, with a superlocalization exponent ζ=1.94±0.06, close to theoretical estimates

Dynamics of the customer order decoupling point : impact on information systems for production control

Abstract: The difficulty of information support for production control in hybrid production situations is discussed. This means in production situations in which make-to-stock, assemble-to-order and engineer-to-order are combined and where the combination may also be dynamic. The first part describes the main information requirements in different production situations. Different types of hybrid situations and the specific information support required in such situations are described. In the second part a commercial system is described that offers functions for different production situations and which at least partly supports production hybridity.

Order acceptance strategies in a production-to-order environment with setup times and due-dates

Abstract: SUMMARY A production situation is considered in which different items are produced on one machine. Setup times are incurred between the production of orders of different items. Production is driven by customer orders; each order concerns a batch of one product type and is furthermore completely characterized by its batchsize and (customer determined) due-date. Acceptance of orders may be refused if these orders are likely to cause late deliveries. The problem is to determine good acceptance strategies which naturally raises the question on what information such acceptance decisions have to be based. Three basic approaches are explored in this paper. In the monolithic approach, the acceptance decision is based on detailed information on a current production schedule for all formerly accepted orders. In the hierarchic approach, the acceptance strategy is based on global capacity load profiles only, while detailed scheduling of accepted orders takes place at a lower level (possibly later in time). In the myo...

On the p -Rank of the Adjacency Matrices of Strongly Regular Graphs

Abstract: Let Γ be a strongly regular graph with adjacency matrix A. Let I be the identity matrix, and J the all-1 matrix. Let p be a prime. Our aim is to study the p-rank (that is, the rank over \Bbb {F}_p, the finite field with p elements) of the matrices M e aA + bJ + cI for integral a, b, c. This note is based on van Eijl l8r.

IC defect sensitivity for footprint-type spot defects

Abstract: While it is important to exhaustively verify IC designs for their functional performance, it is equally important to verify their robustness against spot defects, that is, to foresee what will happen to the design when it is exposed to defect conditions in a real manufacturing environment. One such verification is done by extracting the layout sites where defects can induce a functional failure of the design. Initial attempts to perform this verification task were based on a 'critical area extraction' of one layer at a time, neglecting the electrical significance of interrelationships between layers. A novel method to construct deterministically multilayer critical areas is presented. These critical areas are established on the theoretical basis of defect semantics and on the new concept of 'susceptible sites'. A system comprising several algorithms which in principle maintain simultaneously as many scan lines as the number of layers, in such a way that it is possible to keep track of the vertical and horizontal effects of defects, is developed. >

Brownian particles in shear flow and harmonic potentials: A study of long-time tails.

Abstract: In this paper we present the results of a study of the mean-square displacement of a Brownian particle in a harmonic potential and of a Brownian particle in shear flow. We have focused on the long-time behavior of the mean-square displacement. In contrast with earlier results, presented by others who studied the Stokes limit of these problems, we have studied this problem using the time-dependent linearized incompressible Navier-Stokes equations to describe the fluid motion. Then we see that the mean-square displacement is strongly influenced by backflow effects in the fluid, resulting, among other things, in long-time tails of correlation functions. We have compared our results with those calculated in the Stokes limit; important differences exist between them. The main differences are the long-time tails in correlation functions and, related with them, the larger time scales that should be considered to obtain diffusive behavior in the case of a Brownian particle in a harmonic potential or to obtain the cubic regime in the mean-square displacement of a Brownian particle in shear flow. Furthermore, we have studied the velocity autocorrelation function of a Brownian particle in a harmonic potential. In the overdamped case we have shown a ${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}7/2}$ long-time tail instead of the exponential tail that can be obtained in the Stokes limit. Also the sign of both tails differ.

Wideband indoor radio propagation measurements at 58 GHz

Abstract: Wideband measurements of indoor radio channels operating in a 2 GHz frequency band centred around 58 GHz were performed using a frequency step sounding technique. The results are presented of cell coverage and RMS delay spreas under both line-of-sight (LOS) and obstructed (OBS) situations.