Showing papers by "University of Paderborn published in 1992"

Efficient PRAM simulation on a distributed memory machine

Abstract: We present a randomized simulation of a nlog log (n) log (n)-processor shared memory machine (DMM) with optimal expected delay O(log log (n)) per step of simulation. The time bound for the delay is guaranteed with overwhelming probability. The algorithm is based on hashing and uses a novel simulation scheme. The best previous simulations use a simpler scheme based on hashing and have much larger expected delay: T(log(n)/log log (n)) for the simulation of an n-processor PRAM on an n processor DMM, and T(log(n)) in the case where the simulation preserves the processor-time product.

Averaged modelling of switching power converters: reformulation and theoretical basis

Abstract: Uniform averaged modeling methods for switching power converters (SPCs) are established. Averaging methods for differential equation systems with continuous right-hand sides are discussed and then generalized to discontinuous ones. It is shown that these methods are applicable to most known types of SPC, including PWM, resonant, and quasi-resonant converters. PWM converters under discontinuous conducting mode are taken as examples to further demonstrate the applicability of these methods. It is shown that the currently used state space averaging and its several extensions can be derived from these methods. >

Solving nonlinear equations for selective harmonic eliminated PWM using predicted initial values

Abstract: The authors report novel methods for determining switching angles for selective-harmonics-eliminated pulse-width modulation (SHE PWM) inverters. Such switching angles are defined by a set of nonlinear equations, and to solve these equations a predicting algorithm is used to calculate initial values which are first-order approximations of the exact solutions. With these predicted initial values, the Newton algorithm can be used to find the solutions within usually only one or two iterations. The authors also suggest another approach for solving the SHE PWM problem: an ordinary differential equations approach. The advantages of this approach are discussed, and its applications are demonstrated by some examples. >

Total degradation of EDTA by mixed cultures and a bacterial isolate.

Abstract: A bacterial mixed culture, which was obtained from sewage by a special enrichment procedure, utilized EDTA as the sole source of carbon and nitrogen for growth. High concentrations of mineral salts, particularly CaCl2, or the use of a mineral base without nitrogen protected the cells from inactivation after transfer into fresh medium containing 200-mg/liter (0.67 mM) EDTA. The chemical speciation did not influence the biodegradability of EDTA. However, when resting cells of the mixed culture were incubated with EDTA in the presence of an equivalent molar amount of FeCl3, the reaction came to a halt before the complete consumption of the substrate. A gram-negative isolate from the mixed population, BNC1, also metabolized EDTA in monoculture. Growth of the pure culture was promoted by biotin or folic acid but was always accompanied by the accumulation of unidentified metabolites and was slow (μmax, 0.024 h-1) compared with that of the original community (μmax, 0.036 h-1).

Synthesis and cytotoxic activity of C-glycosidic nicotinamide riboside analogues.

Abstract: The C-glycosidic nicotinamide riboside analogue (2) was prepared by reaction of ribonolactone 24 with the lithiated oxazoline 19 followed by triethylsilane reduction to 26 and deprotection. Selective phosphorylation to the pseudonucleotide 34 was effected via the isopropylidene compound 33. In contrast to the benzoic acid riboside (28) the benzamide riboside (2) showed extremely high cytotoxicity at nanomolar concentrations to S49.1 lymphoma cells but only slightly increased dexamethasone toxicity.

Load balancing for distributed branch & bound algorithms

Abstract: The authors present a new load balancing strategy and its application to distributed branch & bound algorithms and demonstrate its efficiency by solving some NP-complete problems on a network of up to 256 transputers. The parallelization of their branch & bound algorithm is fully distributed. Every processor performs the same algorithm but each on a different part of the solution tree. In this case it is necessary to distribute subproblems among the processors to achieve a well balanced workload. Their load balancing method overcomes the problem of search overhead and idle times by an appropriate load model and avoids trashing effects by a feedback control method. Using this strategy they were able to achieve a speedup of up to 237.32 on a 256 processor network for very short parallel computation times, compared to an efficient sequential algorithm. >

HERO: Hierarchical EMC-constrained routing

Abstract: The authors point out that, in order to perform the design of printed circuit boards as time- and cost-efficiently as possible, electromagnetic compatability (EMC) phenomena have to be taken into account during layout synthesis. The EMC router HERO offers a robust framework for incorporating EMC constraints and cost criteria into routing. Using HERO, it will not be possible to obtain a completely failsafe layout, in general. However, experimental results for typical boards prove that a great number of EMC problems can be avoided during layout synthesis and that the effects of EMC phenomena can be reduced substantially. Detailed reports of EMC design rule violations provide effective input to the succeeding EMC verification phase. Violations of EMC design rules are mainly caused by an inappropriate placement. Therefore, it seems to be of great promise to combine hierarchical placement methods with this approach for hierarchical routing. >

The cube-connected cycles network is a subgraph of the butterfly network

Abstract: We prove the following results: (a) The Cube-Connected Cycles network of dimension n is a subgraph of the Butterfly network of dimension n. (b) The Shuffle-Exchange network of dimension n is a subgraph of the DeBruijn network of dimension n.

Fluorescence and laser operation in single-mode Ti-diffused Nd:MgO:LiNbO/sub 3/ waveguide structures

Abstract: The spectral properties of the guided-wave Nd fluorescence and results of laser oscillation in Ti-indiffused single-mode Nd:MgO:LiNbO/sub 3/ waveguides and waveguide cavities, respectively, are reported. The splitting and polarization behavior of the fluorescence lines around 0.9, 1.08, and 1.37 mu m were studied. Using a single-mode diode laser as a pump source ( lambda /sub p/=814.6 nm), an oscillation threshold in an 8-mm-long structure of 2.1-mW absorbed pump power has been obtained. An output power up to 310 mu W (limited by the available pump power), a slope efficiency of 16% at power levels >150 mu W, and an emission linewidth of 0.21 nm (at lambda /sub s/=1085 nm) have been measured. >

The influence of oxide impurity on the generation by X-irradiation of F centres in BaFBr

Abstract: Using magneto-optical and optically detected electron paramagnetic resonance methods, it is shown that in BaFBr single crystals grown using standard procedures the ubiquitous oxide impurity is primarily responsible for the X-irradiation-induced formation of F(Br-) centres. The bromide vacancy formed to charge compensate O2- is implicated in the direct trapping of electrons. F(F-) centres are also produced by irradiation, probably by an exciton collapse process requiring thermal activation. Cross relaxation measurements show that many of the F(F-) and F(Br-) centres are spatially correlated, more than expected on statistical grounds. The relevance of these results to the use of rare earth-activated BaFBr materials as storage phosphors is discussed.

Arsenic Antisite-Related Defects in Low-Temperature MBE Grown GaAs

Abstract: GaAs layers grown by the molecular beam epitaxy (MBE) method at low temperatures (200 degrees C) and also MBE samples grown at 300 degrees C highly doped with Be or Si show high concentrations of As antisite-related defects in the optical absorption and in the magnetic circular dichroism of the absorption (MCDA). With optical detection of EPR it is shown that these antisite-related defects have properties similar to those of the EL2 defects except for the EL2 bleaching characteristics and the so called zero phonon line. Their spin-lattice relaxation time is strongly reduced compared with that of EL2+. These differences may be related to their high concentrations, which are of the order of approximately 1019-1020 cm-3. In MBE samples grown at higher temperatures (325 degrees C, 400 degrees C) a new As antisite-related defect was detected with a reduced 75As hyperfine splitting as compared with that of EL2+. This new As antisite-related defect has properties very similar to those of another As antisite-related defect previously detected in horizontal Bridgman n-type GaAs. A comparison of four different As antisite-related defects with similar reduced 75As hyperfine splittings is presented.

Bacterial metabolism of 5-aminosalicylic acid. Initial ring cleavage.

Abstract: The metabolism of 5-aminosalicylate (5AS) by a bacterial strain, Pseudomonas sp. BN9, was studied. Intact cells of Pseudomonas sp. BN9 grown with 5AS oxidized 5AS and 2,5-dihydroxybenzoate (gentisate), whereas cells grown with gentisate oxidized only the growth substrate of all substituted salicylates tested. Cell extracts from Pseudomonas sp. BN9 catalysed the stoichiometric reaction of 1 mol of oxygen with 1 mol of 5AS to a metabolite with an intense u.v.-absorption maximum at 352 nm (pH 8.0). This metabolite was accumulated under neutral conditions, but was rapidly destroyed at acid pH. It was identified by m.s. and acid-catalysed deamination to fumarylpyruvate (trans-2,4-dioxohept-5-enedioic acid) as cis-4-amino-6-carboxy-2-oxohexa-3,5-dienoate, thus demonstrating direct cleavage of the monohydroxylated substrate 5AS to a non-aromatic ring-fission product. The enzyme responsible for conversion of 5AS was shown to be Fe(II)-dependent and to be distinct from gentisate 1,2-dioxygenase in strain BN9.

Compact open sets in duals and projections in L1-algebras of certain semi-direct product groups

Abstract: BY KARLHEINZ GROCHENIGDepartment of Mathematics, University of Connecticut, Storrs, CT 06269, U.S.A.EBERHARD KANIUTHFachbereich Mathematik/Informatik, Universitdt Paderborn, D-WA790 Paderborn,GermanyAND KEITH F . TAYLO RDepartment of Mathematics, University of Saskatchewan, Saskatoon, SaskatchewanSIN OWO, Canada(Received 14 March 1991; revised 23 August 1991)1. IntroductionThe main purpos of thi es pape isr t studo y projections is self-adjoin,, that tidempotents, in L

Distributed Game Tree Search on a Massively Parallel System

Abstract: We present our distributed αΒ-algorithm and show how αΒ- enhancements like iterative deepening, transposition tables, history tables etc. that are useful in the sequential game tree search can be applied to a distributed algorithm. The methods we describe are suitable even for large distributed systems. We describe an extension of the Young Brothers Wait Concept that we introduced to reduce the search overhead. For the first time experiments with bigger processor networks (up to 256 Transputers) show good results. We obtained a speedup of 126 running our algorithm with 256 processors.

Nuclear power, energy policy and new politics in Sweden and Germany

Abstract: Over the last two decades new values, new social movements and green parties have become a common feature of most Western industrialised nations. Simultaneously, it has been claimed that these nations have reached the limits of growth. The two aspects are interrelated and can be spelled out in terms of the politicising of production. However, the degree to which production is politicised varies among nations. The literature in the field postulates that Sweden might be a country that departs from this productionist development. This article discusses this hypothesis by comparing (nuclear) energy policy on the one hand, and the attitudes to, and movements against nuclear energy in Sweden and Germany on the other. The analysis arrives at the conclusion that Germany is much more exposed to the politicising of production than is Sweden. These conclusions imply that new politics might have a greater chance of being institutionalised in Germany than in Sweden.

Number Systems and Fractal Geometry

Abstract: Let θ be an algebraic integer over ℚ with minimum polynomial p(x) ∈ Z[x] of order n Let θ = θ1,…, θn be the conjugates of θ Assume that |θi| > 1 holds for i = 1,…, n For an element a = α(θ) ∈ ℚ(θ) the conjugate with respect to θj will be denoted by α(θj) We shall use the notation p j = 1/θj (j = 1,…, n)

The Complexity of Colouring Circle Graphs (Extended Abstract)

Abstract: We study the complexity of the colouring problem for circle graphs We will solve the two open questions of [Un88], where first results were presented 1 Here we will present an algorithm which solves the 3-colouring problem of circle graphs in time O(nlog(n)) In [Un88] we showed that the 4-colouring problem for circle graphs is NP-complete 2 If the largest clique of a circle graph has size k then the 2·k−1-colouring is NP-complete Such circle graphs are 2·k-colourable [Un88]

Immigration into a Population with Fertility below Replacement Level – The Case of Germany

Abstract: In this paper stable population theory is used to study the demographic effects of a steady stream of immigrants into a population with fertility below replacement level. It is assumed that the fertility of foreigners (persons born outside the country) is higher than that of the native-born. We present a discrete-time Leslie-type model and analyse its asymptotic stationary behaviour. We prove that the asymptotic ratio between foreign-born and native-born does not depend on the size of the immigration flow, but solely on the relative fertility of the two groups, the sex ratio, and age distribution of the immigrants. In contrast to the continuous-time approach in which deep results of renewal theory have been used to establish this result, our proof is elementary. The analytical model is supplemented by numerical simulations with German data which show the effects of continuous immigration on the size of the population and on the ratio of foreign-born citizens in the united Germany under different demograph...

Identification of the isolated arsenic antisite defect in electron-irradiated gallium arsenide and its relation to the EL2 defect.

Abstract: In semi-insulating GaAs, which was electron irradiated at 4.2 K and kept below 80 K, the isolated arsenic antiste ${\mathrm{As}}_{\mathrm{Ga}}$ defect could be identified with optically detected magnetic resonance (ODMR). It decays at about 300 K while an additional ${\mathrm{As}}_{\mathrm{Ga}}$ related defect is formed. Upon further heating to about 520 K this defect also decays and EL2 is formed. The magnetic circular dichroism of the absorption (MCDA) of the isolated ${\mathrm{As}}_{\mathrm{Ga}}$ defect has a simple derivativelike structure that is explained theoretically. Its MCDA and ODMR spectra are different from the corresponding EL2 spectra indicating the different microscopic structures of the defects. The isolated ${\mathrm{As}}_{\mathrm{Ga}}$ defect cannot be bleached into a metastable state at low temperature under the conditions where EL2 is bleached completely.

Simulation of nonlinear transmission lines by wave digital filter principles

Abstract: It is shown that the lumped-circuit model of a nonlinear transmission line can be simulated using WD (wave digital) filter principles. Solitons which are eigenfunctions of the nonlinear transmission line are observed. The WD circuit simulation confirms that: the velocity of a soliton impulse depends on its amplitudes; the magnetic energy is always greater than the electric energy for a single traveling soliton impulse; the magnetic energy vanishes and is converted to the electric energy at the point of head-on collision; there is no energy exchange for the overtaking collision; and the impulses which pass through one another do not lose their identities. >

Hashing Strategies for Simulating Shared Memory on Distributed Memory Machines

Abstract: We survey shared memory simulations on distributed memory machines (DMMs), that use universal hashing to distribute the shared memory cells over the memory modules of the DMM. We measure their quality in terms of delay, time-processor efficiency, memory contention (how many requests have to be satisfied by one memory module per simulated step) and simplicity. Further we take into consideration different access conflict rules to the modules of the DMM, in particular the c-Collision rule motivated by the idea of communicating between processors and modules using an optical crossbar.

Using VHDL for simulation of SDL specifications

Abstract: The authors present the use of VHSIC hardware description language (VHDL) for the simulation of Specification and Description Language (SDL) specification. SDL is a standardized graphical specification and description language. It is widely used for specifications of software systems that are based on message exchange, e.g., telecommunication systems. The approach presented allows for simulation of the logical correctness of the specification, as well as some kinds of performance simulation. A third application of the approach is the joint simulation of hardware and software. The translation of SDL into VHDL allows for functional, performance, and joint hardware/software simulation of systems specified with SDL. >

On some coercive estimates for the Stokes problem in unbounded domains

Abstract: Here and in what follows we use the standard notation for the Sobolev spaces [1]. The norm in wm,r(!1) and in wm,r(n) is denoted by 11·llm,r = 11·llm,r,n, where bold face letters always indicate spaces of JRn-valued functions. As is well known, the operator Ar is a densely defined closed linear operator in X, and solving the equation Arv = f for given f E X, amounts to solving the exterior stationary Stokes problem + V'p V'. v vir I, (x E !1) 0, (x E n) 0, (S)

Hamiltonian structure and integrability

Abstract: Publisher Summary This chapter discusses the Hamiltonian structure and integrability. The aim is to use harmonic oscillator in a general framework so that they can be carried over to other more complicated system. The chapter introduces some basic notions that describe the connection between symmetries and conserved quantities. The chapter also introduces Lie algebra modules, Lie derivatives, and Lie tensors to have a notation that allows seeing the notions that are geometrically invariant. The notion of bi-Hamiltonian fields on a general level is introduced in the chapter. In the chapter, the concept of compatibility is discussed, especially for Hamiltonian pairs, and the power of this notion by a set of suitable examples is illustrated. Complete integrability in the finite dimensional case is also discussed and the action/angle structure of the multisoliton manifolds is illustrated in the chapter.