Showing papers by "Eindhoven University of Technology published in 1994"

Encapsulation of guest molecules into a dendritic box.

Abstract: Dendrimers are well-defined, highly branched macromolecules that emanate from a central core and are synthesized through a stepwise, repetitive reaction sequence. The synthesis and characterization of dendritic boxes, based on the construction of a chiral shell of protected amino acids onto poly(propyleneimine) dendrimers with 64 amine end groups, is reported here. Nuclear magnetic resonance-relaxation and optical data show that a dense shell with solid-phase character is formed. Guest molecules were captured within the internal cavities of the boxes when these boxes were constructed in the presence of guest molecules. The diffusion of guest molecules out of the boxes into solution was unmeasurably slow because of the close packing of the shell. These monomolecular dendritic containers of 5-nanometer dimensions with physically locked-in guest molecules were characterized spectroscopically.

1/f noise sources

Abstract: This survey deals with 1/f noise in homogeneous semiconductor samples. A distinction is made between mobility noise and number noise. It is shown that there always is mobility noise with an /spl alpha/ value with a magnitude in the order of 10/sup -4/. Damaging the crystal has a strong influence on /spl alpha/, /spl alpha/ may increase by orders of magnitude. Some theoretical models are briefly discussed none of them can explain all experimental results. The /spl alpha/ values of several semiconductors are given. These values can be used in calculations of 1/f noise in devices. >

Noise as a diagnostic tool for quality and reliability of electronic devices

Abstract: Experimental facts about noise are presented which help us to understand the correlation between noise in a device and its reliability. The main advantages of noise measurements are that the tests are less destructive, faster and more sensitive than DC measurements after accelerated life tests. The following topics are addressed: 1) the kind of noise spectra in view of reliability diagnostics such as thermal noise, shot noise, the typical poor-device indicators like burst noise and generation-recombination noise and the 1/f/sup 2/ and 1/f noise; 2) why conduction noise is a quality indicator; 3) the quality of electrical contacts and vias; 4) electromigration damage; 5) the reliability in diode type devices like solar cells, laser diodes, and bipolar transistors; and 6) the series resistance in modern short channel MESFET, MODFET, and MOST devices. >

Assessment of energy expenditure for physical activity using a triaxial accelerometer

Abstract: A triaxial accelerometer was used to evaluate the relationship between energy expenditure due to physical activity (EEact) and body acceleration during different types of activity. In a laboratory experiment, 11 male subjects performed sedentary activities and walked on a motor driven treadmill (3-7 km.h-1). EEact was calculated from total energy expenditure (EEtot), as measured by indirect calorimetry, and sleeping metabolic rate (SMR): EEact = EEtot--SMR. Body accelerations were measured with a triaxial accelerometer at the low back. Special attention was paid to the analysis of unidirectional and three-directional accelerometer output. During sedentary activities a linear relationship between EEact and the sum of the integrals of the absolute value of accelerometer output from all three measurement directions (IAAtot) was found (r = 0.82, P < 0.001, Sy,x = 0.22 W.kg-1). During walking EEact was highly correlated with the integral of absolute accelerometer output in antero-posterior direction (IAAx; r = 0.96, P < 0.001, Sy,x = 0.53 W.kg-1). When all examined activities were included in a regression analysis, a strong linear relationship between EEact and IAAtot was found (r = 0.95, P < 0.001, Sy,x = 0.70 W.kg-1). Using this relationship, EEact during sedentary activities as well as EEact during walking could be estimated with an accuracy of about 15%. Although sedentary activities and walking represent a large part of normal daily physical activity, the validity and usefulness of the triaxial accelerometer--measuring IAAtot--to predict EEact in daily life must be studied under free-living conditions.

Age differences and changes in reaction time: the Baltimore Longitudinal Study of Aging.

Abstract: This study analyzed auditory reaction time (RT) data from 1,265 community-dwelling volunteers (833 males and 432 females) who ranged in age from 17 to 96. Cross-sectional analyses revealed slowing of simple (SRT) and relatively greater slowing of disjunctive (DRT; aka "go-no-go") reaction time across decades for both males and females. Repeated testing within participants (longitudinal analyses) over eight years showed consistent slowing and increased variability with age. Males were faster than females cross age groups, RT tasks, and visits. Beginning at about age 20, RTs increased at a rate of approximately 0.5 msec/yr for SRT and 1.6 msec/yr for DRT. Errors also increased, making unlikely a tradeoff of accuracy for faster responses. The findings are consistent with the hypotheses that slowing of behavior is: (a) a continuous process over the adult life span; (b) characterized by age-associated increases in within-participant variability; (c) a direct function of task complexity and, presumably, the degree of mediation by higher regions in the central nervous system; and (d) greater in women than men.

1/f noise in MOS devices, mobility or number fluctuations?

Abstract: Recent experimental studies on 1/f noise in MOS transistors are reviewed. Arguments are given for the two schools of thought on the origin of 1/f noise. The consequences of models based on carrier-number /spl Delta/N or mobility fluctuations /spl Delta//spl mu/ on the device geometry and on the bias dependence of the 1/f noise are discussed. Circuit-simulation-oriented equations for the 1/f noise are discussed. The effects of scaling down on the 1/f noise is studied in the ohmic region as well as in saturation. In the ohmic region the contribution of the series resistance often can be ignored. However, in saturation the noise of the gate-voltage-dependent series resistance on the drain side plays a role in lightly doped drain LDD mini-MOST's. Surface and bulk p-channel devices are compared and the differences between n-and p-MOST's often observed is discussed. The relation between degradation effects by hot carriers or by /spl gamma/-irradiation on the one hand and the 1/f noise on the other is considered in terms of a /spl Delta/N or /spl Delta//spl mu/. Experimental results suggest that 1/f noise in n-MOST's is dominated by /spl Delta/N while in p-MOST's the noise is due to /spl Delta//spl mu/. >

Information retrieval in the World-Wide Web: making client-based searching feasible

Abstract: Finding specific information in the World-Wide Web (WWW, or Web for short) is becoming increasingly difficult, because of the rapid growth of the Web and because of the diversity of the information offered through the Web. Hypertext in general is ill-suited for information retrieval as it is designed for stepwise exploration. To help readers find specific information quickly, specific overview documents are often included into the hypertext. Hypertext systems often provide simple searching tools such as full text search or title search, that mostly ignore the “hyper-structure” formed by the links. In the WWW, finding information is further complicated by its distributed nature. Navigation, often via overview documents, still is the predominant method of finding one's way around the Web. Several searching tools have been developed, basically in two types: • A gateway, offering (limited) search operations on small or large parts of the WWW, using a pre-compiled database. The database is often built by an automated Web scanner (a “robot”). • A client-based search tool that does automated navigation, thereby working more or less like a browsing user, but much faster and following an optimized strategy. This paper highlights the properties and implementation of a client-based search tool called the “ fish-search ” algorithm, and compares it to other approaches. The fish-search, implemented on top of Mosaic for X, offers an open-ended selection of search criteria. Client-based searching has some definite drawbacks: slow speed and high network resource consumption. The paper shows how combining the fish search with a cache greatly reduces these problems. The “ Lagoon ” cache program is presented. Caches can call each other, currently only to further reduce network traffic. By moving the algorithm into the cache program, the calculation of the answer to a search request can be distributed among the caching servers.

Job shop scheduling by local search

Abstract: We present a computational performance analysis of local search algorithms for job shop scheduling. The algorithms under investigation are iterative improvement, simulated annealing, threshold accepting and genetic local search. Our study shows that simulated annealing performs best in the sense that it finds better solutions than the other algorithms within the same amount of running time. Compared to more tailored algorithms, simulated annealing still finds the best results but only under the assumption that running time is of no concern.

Measurement of flame temperature and adiabatic burning velocity of methane/air mixtures

Abstract: A simple and accurate method is presented to determine the flame temperature and the adiabatic burning velocity of laminar premixed flat flames, using a specially constructed flat flame burner. The heat loss of the flat flame is determined from measurement of the temperature profile of the burner plate. The adiabatic burning velocity is found when the burner plate temperature profile is uniform, implying that the net heat loss of the flame is zero. Several methods are presented to determine the thermal conductivity of the burner plate. The results for methane/air mixtures are compared with experimental data found in the literature and one-dimensional flame calculations, and close agreement is found. The method is particularly useful in providing an accurate reference for other temperature measurement techniques (e.g. spectroscopic laser diagnostics), and to determine adiabatic burning velocities over the entire range of flamm ability

The U-line balancing problem

Abstract: The traditional line balancing LB problem considers a production line in which stations are arranged consecutively in a line. A balance is determined by grouping tasks into stations while moving forward or backward through a precedence network. Recently many production lines are being arranged in a "U-line," as a consequence of the use of just-in-time production principles in many factories. In this paper the U-line LB problem is introduced and modelled, and solution procedures are developed. It more complex than the traditional LB problem because tasks can be grouped by moving forward, backward, or simultaneously in both directions, through the precedence network. We also show how solution techniques developed for the traditional LB problem can be adapted for use with the new problem. Some computational results for well-known problems from the literature are given.

On Chaplygin's investigations of two-dimensional vortex structures in an inviscid fluid

Abstract: This paper describes exact solutions of two-dimensional vortex structures that were published by Chaplygin (1899, 1903) at the turn of the last century, which seem to have escaped the attention of later investigators in this field. Chaplygin's solutions include that of an elliptical patch of uniform vorticity in an exterior field of pure shear and that of a (symmetric or non-symmetric) dipolar vortex with a continuous distribution of vorticity translating steadily along a straight path. In addition, a solution is presented for a non-symmetric vortex dipole moving along a circular trajectory. A concise account of Chaplygin's solutions is given, complemented by a more detailed analysis of some of their relevant properties.

On the information rate of perfect secret sharing schemes

Abstract: We present a method to derive information theoretical upper bounds on the information rate and average information rate of perfect secret sharing schemes. One of the applications is that in perfect secret sharing schemes for some access structures the shares need to be impractically large. >

A Congruence Theorem for Structured Operational Semantics with Predicates and Negative Premises

Abstract: We proposed a syntactic format, the panth format, for structured operational semantics in which besides ordinary transitions also predicates, negated predicates, and negative transitions may occur such that if the rules are stratifiable, strong bisimulation equivalence is a congruence for all the operators that can be defined within the panth format. To show that this format is useful we took some examples from the literature satisfying the panth format but no formats proposed by others. The examples touch upon issues such as priorities, termination, convergence, discrete time, recursion, (infinitary) Hennessy-Milner logic, and universal quantification. Collation: pp. 16, ill. 2, tab. 5, ref. 25.

Oscillatory interlayer exchange coupling in Co/Ru multilayers and bilayers.

Abstract: The interlayer exchange coupling in several Co/Ru multilayers and bilayers prepared by sputtering has been investigated from magnetization and ferromagnetic resonance experiments. The hysteresis loops have been discussed in detail, particularly regarding their dependence on the number of layers and the effect of an easy axis direction perpendicular to the film plane. Ferromagnetic as well as antiferromagnetic coupling strengths have been determined in an extended range of Ru thicknesses up to 44 \AA{}. The analysis yields an oscillatory magnetic coupling as a function of the Ru thickness having a period of approximately 12 \AA{}. The peak-to-peak-distance has been found to be smaller at thinner Ru layers indicating a preasymptotic or multiperiodic behavior in the coupling. The envelope function of the coupling was found to decrease, initially as ${\mathit{t}}_{\mathrm{Ru}}^{\mathrm{\ensuremath{-}}2}$ but considerably faster above a Ru thickness of 20 \AA{}. The latter is discussed in terms of mean-free-path effects and of Fermi surface smearing effects both of which are active as a result of structural defects and of the finite measuring temperatures.

Modeling hierarchical conjoint processes with integrated choice experiments

Abstract: The authors propose and illustrate an extension of the method of Hierarchical Information Integration (HII). HII allows one to handle large numbers of attributes in conjoint tasks by designing sube...

Asynchronous circuits for low power: a DCC error corrector

Abstract: The authors describe a complete low-power digital compact cassette error corrector. Using Tangram, a high-level programming language, they designed two asynchronous circuits that correct errors on DCC specifications. >

A Typology of Production Control Situations in Process Industries

Abstract: Discusses the variety of production control situations within process industries. Following a literature review, a typology is introduced which discriminates between two extreme types of process industries: batch/mix and process/flow businesses. Reviews the research in production and inventory control in each of the extreme types. Identifies a control framework for operations management in process/flow businesses. Notes that although detailed scheduling approaches for batch/mix businesses exist, a control framework for the latter is missing. Concludes that operations management in batch process industries needs considerable research attention.

An algebraic semantics of basic message sequence charts

Abstract: Message Sequence Charts are a widely used technique for the visualization of the communications between system components. We present a formal semantics of Basic Message Sequence Charts, exploiting techniques from process algebra. This semantics is based on the semantics of the full language as being proposed for standardization in the International Telecommunication Union.

Information retrieval in distributed hypertexts

Abstract: Hypertext is a generalization of the conventional linear text into a non-linear text formed by adding cross-reference and structural links between different pieces of text. A hypertext can be regarded as an extension of a textual database by adding a link structure among the different text objects it stores. We present a tool for finding information in a distributed hypertext such as the World-Wide Web (WWW). Such a hypertext is a distributed textual database in which text objects residing at (the same and) different sites have links to each other. In such a database retrieval is limited to the transfer of documents with a known name. Names of documents serve as links between different documents, and finding such references names is only possible by parsing documents that have embedded links to other documents. Full-text search in such hypertexts is not feasible because of the discrepancy between the large size of the hypertext and the relatively low bandwidth of the network. We present an information retrieval algorithm for distributed hypertexts, which does an incomplete search through a part of the hypertext. Heuristics determine the selection of the documents that are to be retrieved and searched. A prototype implementation for the WWW, on top of Mosaic for X, is being used by an increasingly large user base.

A partial order approach to branching time logic model checking

Abstract: Partial order techniques enable reducing the size of the state space used for model checking, thus alleviating the “state space explosion” problem. These reductions are based on selecting a subset of the enabled operations from each program state. So far, these methods have been studied, implemented, and demonstrated for assertional languages that model the executions of a program as computation sequences, in particular the linear temporal logic. The present paper shows, for the first time, how this approach can be applied to languages that model the behavior of a program as a tree. We study here partial order reductions for branching temporal logics, e.g., the logics CTL and CTL* (with the next time operator removed) and process algebra logics such as Hennesy–Milner logic (withτactions). Conditions on the selection of subset of successors from each state during the state-space construction, which guarantee reduction that preserves CTL* properties, are given. The experimental results provided show that the reduction is substantial.

Information Systems Engineering: A Formal Approach

Abstract: Engineers and scientists need powerful formalisms to make conceptual models of systems in order to analyze and design them. These models can be used to verify the behavior of the systems, or as an executable specification of them. In this book, Professor van Hee concentrates on discrete dynamic systems, e.g. computer hardware, and information and logistical systems. He develops an integrated formalism that can be used as a prototyping language. It has three components: Petri nets, extended with time, token values and hierarchy; a specification language that is a subset of Z; and a binary data model, extended with complex objects. Much attention is paid to methods for constructing models of systems and analyzing their behavior, i.e., putting the theory into practice. The book is aimed at graduate students and researchers in computer science, electrical engineering, and applied mathematics.

An experimental study of dipolar vortex structures in a stratified fluid

Abstract: This paper describes laboratory experiments on dipolar vortex structures in a linearly stratified fluid. The dipoles are generated by a pulsed horizontal injection of a small volume of fluid, by which a localized three-dimensionally turbulent flow region is created. After the subsequent gravitational collapse the flow becomes approximately two-dimensional, and eventually a single vortex dipole emerges, as the result of the self-organizing properties of such flows. The flow evolution has been visualized both by dye and tracer particles, through which qualitative as well as quantitative information was obtained. By application of digital image analysis, the spatial distribution of the velocity ν, vorticity ω and stream function ψ were determined. It was found that dipoles in the turbulent-injection experiments are characterized by a nonlinear sinh-like relationship between ω and ψ, whereas in the case of laminar injection the (ω, ψ)-scatter plots of the dipoles reveal a linear relationship. Notwithstanding these differences, both types of dipoles show a dynamical structure that agrees very well with the Lamb–Chaplygin dipole, as was found by comparing the size, position of maximum vorticity, cross-sectional distributions of ν and ω, characteristics of the (ω, ψ)-relationship, and the translation speed of the experimental and the model dipole.

Magnetic layer thickness dependence of the interlayer exchange coupling in (001) Co/Cu/Co.

Abstract: A dependence of the strength of the antiferromagnetic coupling across Cu on the Co layer thickness has been observed in an epitaxial fcc (001) triple wedge sample containing two Co wedges and one Cu wedge. Our result is consistent with an oscillation period of 6--7 \AA{} Co---a value that agrees with the period of 3.5 monolayers of Co derived from the extremal wave vector that spans the ellipsoidal hole pocket centered at the X point of the fcc Co spin-down Fermi surface. This shows that the interlayer exchange coupling does not just involve an interaction localized at the interfaces, but is a property of the sandwich as a whole.

A spatiotemporal dipole model of the Stimulus Preceding Negativity (SPN) prior to feedback stimuli

Abstract: Ten subjects performed a time production task, in which they were instructed to press a button four seconds after the presentation of an auditory stimulus. Two seconds after the button press they received either auditory or visual feedback on the temporal accuracy of their response. In such a paradigm negative slow brain potentials can be recorded preceding the response (Movement Preceding Negativity, MPN) as well as preceding the feedback stimulus (Stimulus Preceding Negativity, SPN). Spatiotemporal dipole modelling is used to gain insight in the possible generators of MPN and SPN. From the models it follows that the MPN can be described by one contralateral radial dipole and a bilateral pair of tangential dipoles. All three dipoles are located near central electrode positions, so the generators of the MPN probably reside within the motor cortex. The SPN is modelled by a bilateral frontotemporal pair of dipoles, hypothetically representing activation of the Insulae Reili. The insular cortex is involved in the processing of affective-motivational input, such as carried by the feedback in the present paradigm. However, processing of the information content of the feedback stimulus might by itself also activate the frontal cortex. Both the response and the feedback stimulus are followed by a positive peak, which can be described by the same deep posterior dipole. Both peaks probably represent a P3, which is related to context updating.