Showing papers by "University of Paderborn published in 1994"

Erbium-doped single- and double-pass Ti:LiNbO/sub 3/ waveguide amplifiers

Abstract: Single-pass and double-pass Er-diffused Z- and X-cut Ti:LiNbO/sub 3/ waveguide amplifiers, optically pumped at /spl lambda//sub p//spl ap/1484 nm, have been investigated. With a 48 mm long Z-cut amplifier device, Er-diffusion doped at 1100/spl deg/C, 6.7 dB (coupled pump power P/sub p,c/=170 mW) and 14.7 dB (P/sub p,c/=90 mW) net small-signal gain have been achieved with a single-pass and a double-pass configuration, respectively, at the signal wavelength /spl lambda//sub s/=1531 nm. A Z-cut sample doped at 1135/spl deg/C showed a considerably improved behavior. 11.3 dB single-pass net small-signal gain has been obtained (P/sub p,c/=170 mW; sample length 5.7 cm). Theoretical calculations predict gain figures up to 20 dB in single-pass and 40 dB in double-pass Er:Ti:LiNbO/sub 3/ amplifiers with increased (realistic) lengths of 10 cm. >

Pulsewidth modulation based on real-time solution of algebraic harmonic elimination equations

Abstract: Determination of pulse patterns for the elimination of some low-order harmonics of a PWM inverter necessitates solution of a system of nonlinear transcendental equations. When Newton's algorithm is applied, it can be estimated that at each iteration, 2/spl times/N/sup 2/ trigonometric functions have to be evaluated, N being the number of unknown switching angles in the first quarter-period interval. This is very time-consuming when the equations are to be solved in real-time, even when a digital signal processor (DSP) is used. A new system of algebraic harmonic elimination equations, in which no trigonometric function appears explicitly, are derived in this paper. The time necessary for solving the equations using a DSP is thus reduced. For single-phase inverters, the local linear model, which is to be formulated at each iteration and then solved to provide a new iterative solution, is a special Vandermonde system. Since algorithms which are more efficient than Gauss elimination can be used to solve a linear Vandermonde system, total solution time can be further reduced. >

Studying overheads in massively parallel MIN/MAX-tree evaluation

Abstract: Studying Overheads in Massively Parallel Min/Max-lllee Evaluation (Extended Abstract) “t Rainer Feldmann and Peter Mysliwietz and Burkhard Monien Email: chess@uni-paderborn.de Department of Mathematics and Computer Science, University of Paderborn, Germany In this paper we study the overheads arising in our algorithm for distributed evaluation of Min/Max trees. The overheads are classified into search overhead, performance loss, and decrease of work load. Several mechanisms are investigated to cope with these overheads in order to achieve a high performance. We study a combination of local, medium range, and global load distribution strategies that does not only show a good behavior in terms of work load, but also has a positive influence on the search overhead. The efficient use of a virtual shared memorv. that is distributed among the processors, shows also a big ‘contribution to the overal~performance of the system. A carefully restricted application of parallelism using an improved version of the Young Brothers Wait Concept (YBWC) leads to a perfect behavior for minimal Min/Max trees and to a quite low search overhead, if well ordered trees are searched. Well ordered trees const itute the most important case in practice, since a couple of move ordering mechanisms are known that achieve a nearly optimal move ordering in many applications. The resulting combination of the methods shows an efficiency better than any previous approach. Experiments carried out using 256 DeBruijn-connected Transputers result in a speedup of 142 even applying restricted timing constraints. With a system consisting of 1024 grid connected Transputers we obtain a speedup of 344. Moreover the algorithm shows a very good scalability, especially using interconnection networks with logarithmic diameter. The experiments have been carried out using a Min/Max search program that incorporates all important state-of-theart search techniques ( ZUGZWANG, current vice world champion in computer chess) and therefore makes sure, that no artificial or simplifying assumptions on the structure of the problem are made. *This work was partly supported by the ESPRIT proJect GPMIMD and the ESPRIT Basic Research Action No. 7141 (ALCOM II) tThe paderborn Center for Parallel Computing PC2 provided Us with the parallel hardware for our experiments Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association of Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. SPAA 94-6194 Cape May, N.J, USA (3 1994 ACM 0-89791-671 -9N410006..$3.5O

Note on the Flux Problem for Stationary Incompressible Navier-Stokes Equations in Domains with a Multiply Connected Boundary

Abstract: In this paper we present a new proof for the existence of Navier-Stokes flows with nonhomogeneous boundary conditions in domains with multiply connected boundaries. For sufficiently small fluxes, we show the existence of at least one stationary solution with an improved smallness assumption.

Leucocytes, lymphocytes, activation parameters and cell adhesion molecules in middle-distance runners under different training conditions.

Abstract: 20 young male track and field runners (400 m-3000 m) with a 4 mmol/l lactic acid threshold of x = 4.97 +/- 0.35 m/s were tested after three different training periods: 1. at the end of a two month endurance training, practised nearly every day; 2. after a period of speed and strength training, which was specific with respect to their discipline, with anaerobic lactic energy production up to 15 mmol/l lactic acid; 3. during the competition period. The blood samples were taken at rest (4 p.m.) and 22 hrs after the last exercise. On the cell surface the antigens CD3+, CD20+CD23+, CD4+HLADR, CD4+CD25+, CD8+CD28+, CD4+CD45RO+, CD16+CD56+, CD54+ and in the blood serum the concentrations of s-IL-2-R, s-ICAM-1 were analysed. 13 students of physical education served as a control group. The main results were: Only at the end of the endurance training period (1) an increase of s-ICAM-1 was found, which may be interpreted as a protective mechanism against infections. Compared with the control group CD20+CD23+ antigen was constantly elevated and during the transition from the training to the competition period the CD4+CD45RO+ subset increased. These results may provide evidence for a connection to a susceptibility to allergic disease and to overtraining. Furthermore, an activation of the specific immune system was indicated by an elevation of the s-IL-2-R and an activation of the monocytic-phagocytic system was shown by increased levels of ICAM-1. The importance of these results for the training process and with regard to susceptibility to infections is discussed.

A comparison of two lower-bound methods for communication complexity

Abstract: The methods “Rank” and “Fooling Set” for proving lower bounds on the deterministic communication complexity of Boolean functions are compared. The main results are as follows. (i) The Rank method provides the lower bound n on communication complexity for almost all Boolean functions of 2n variables, whereas the Fooling Set method provides only the lower bound d(n) ≤ log2n + log2 10. A specific sequence of Boolean functions {f2n} n=1 ∞ of 2n variables, is constructed, such that the Rank method provides exponentially higher lower bounds for f2n than the Fooling Set method. (ii) A specific sequence of Boolean functions {f2n} n=1 ∞ is constructed such that the Fooling Set method provides a lower bound of n for h2n, whereas the Rank method provides only (log2 3)/2 · n ≈ 0.79 · n as a lower bound. (iii) It is proved that lower bounds obtained by the Fooling Set method are better by at most a factor of two compared with lower bounds obtained by the Rank method.

Conversion of substituted naphthalenesulfonates by Pseudomonas sp. BN6

Abstract: The range of substituted naphthalenesulfonates which are metabolized by Pseudomonas sp. BN6 were investigated. Resting cells from strain BN6 oxidized 1- and 2-naphthalenesulfonate, 1-hydroxynaphthalene-2-sulfonate, 2,6-naphthalenedisulfonate and all monosulfonated naphthalene-2-sulfonates which carry one or two substitutents in the positions 4-, 5-, 6-, 7- or 8- of the naphthalene ring-system. With the exception of (substituted) 4- or 5-amino- and 4-hydroxynaphthalene-2-sulfonates these compounds were converted to the corresponding salicylates. Strain BN6 did not oxidize substituted naphthalene-1-sulfonates, 3-substituted naphthalenesulfonates and substituted naphthalenedisulfonates. Turnover of 4-amino- or 4-hydroxynaphthalene-2-sulfonates resulted in the accumulation of the corresponding naphthoquinones in the culture medium. Thus, degradation of 4-amino- and 4-hydroxynaphthalenesulfonates was restricted by the rapid autoxidation of the substituted 1,2-dihydroxynaphthalenes formed as metabolites. Catabolic activities of strain BN6 for naphthalenesulfonates were induced by salicylate, 3- or 6-hydroxysalicylate, and 3-, 4- or 5-aminosalicylate but not by 4- and 5-hydroxysalicylate. All naphthalenesulfonates that were not converted into the corresponding salicylates, were found to be inefficient as effectors. It was therefore concluded that (substituted) salicylates are the inducers of the relevant enzymes. The degradation of 2-naphthalene-sulfonate by a pure culture of strain BN6 was prevented by the toxicity of the dead-end product salicylate. Substituted salicylates were less toxic and allowed growth of strain BN6 in axenic culture with various substituted naphthalenesulfonates.

Direct measurement of cascaded nonlinearity in lithium niobate channel waveguides

Abstract: We report on interferometric measurements of nonlinear phase shifts of the fundamental mode that are due to cascading in a second-harmonic-generation experiment in lithium niobate channel waveguides. With temperature tuning of the wave-vector mismatch the nonlinear phase shifts were adjustable in sign and magnitude. Varying the wave-vector matching condition along the waveguide leads to large phase shifts with low depletion and dispersion of the fundamental.

Mechanism of mechanical press joining

Abstract: Mechanical press joining has been studied for many years in the hope of achieving quality joints for dissimilar sheet metals or materials with different surfaces and thicknesses. In most of the manufacturing practices involved, the workpieces are first cut or drawn by proper punching. Then, the workpieces are clamped together by an impact extrusion between a punch and a female die. This process has been a recent resurgence in the field of permanently fastening precoated or dissimilar sheet metals, sandwich panels made of plastic and metal and pre-formed sheet metal assemblies with screws and nuts. This paper is concerned with the basic mechanism of mechanical press joining, which is useful for designing such joining elements. Some basic terms, such as the mechanical contact chains and their symbols and the joint networks, are introduced to establish a basic theory for analyzing the joining mechanism. Using joint networks consisting of the symbols of contact chains an efficient design method is presented. Some widely used mechanical press joining elements are discussed in detail in view of their mechanical behavior.

User modeling for adaptive visualization systems

Abstract: Meaningful scientific visualizations benefit the interpretation of scientific data, concepts and processes. To ensure meaningful visualizations, the visualization system needs to adapt to desires, disabilities and abilities of the user, interpretation aim, resources (hardware, software) available, and the form and content of the data to be visualized. We suggest describing these characteristics with four models: user model, problem domain/task model, resource model and data model. The paper makes suggestions for the generation of a user model as a basis for an adaptive visualization system. We propose to extract information about the user by involving the user in interactive computer tests and games. Relevant abilities tested are color perception, color memory, color ranking, mental rotation, and fine motor coordination. >

A Comparison of the Computational Power of Sigmoid and Boolean Threshold Circuits

Abstract: Research on neural networks has led to the investigation of massively parallel computational models that consist of analog computational elements. Usually these analog computational elements are assumed to be smooth threshold gates, i.e. γ-gates for some nondecreasing differentiate function γ: ℝ → ℝ. A γ-gate with weights w 1,…, w m ∈ ℝ; and threshold t ∈ ℝ is defined to be a gate that computes the function (x1,...,xm) \(\mapsto \gamma \left( {\sum olimits_{i = 1}^m {{w_i}{x_i} - t} } \right)\) from ℝ m into ℝ. A γ-circuit is defined as a directed acyclic circuit that consists of γ-gates. The most frequently considered special case of a smooth threshold circuit is the sigmoid threshold circuit, which is a σ-circuit for σ ℝ → ℝ defined by \( \sigma (x) = \frac{1}{{1 + \exp ( - x)}} \)

Polarization independent, integrated optical, acoustically tunable wavelength filters/switches with tapered acoustical directional coupler

Abstract: Enhanced sidelobe suppression of the filter characteristics of tunable acousto-optical mode converters in LiNbO/sub 3/ has been achieved using for the first time tapered acoustical directional couplers. A sidelobe suppression of more than 15.5 dB could be demonstrated in a single stage device. By combining the mode converter with two integrated optical polarization splitters a polarization independent filter/wavelength selective switch has been fabricated with less than 3 dB intrinsic insertion loss, a polarization dependence of less than 1 dB, and a sidelobe suppression exceeding 14 dB. >

Respiratory rhythm detection with photoplethysmographic methods

Abstract: A transmittance type infrared photoelectric plethysmograph (PPG) is described that performs time and frequency analysis of the peripheral finger volume pulse using an IBM 386 computer. It was revealed that in addition to the heart action the respiratory rhythm and waveform could be obtained from the peripheral volume pulse signal. This result was confirmed with the aid of a true respiration signal from a thermistor in different experiments: (1) varying breathing rates; (2) breathing-stop. The authors conclude that their new method may be useful for clinical noninvasive breath monitoring. >

Decentralized remapping of data parallel computations with the generalized dimension exchange method

Abstract: The Generalized Dimension Exchange (GDE) method is a fully distributed load balancing method that is most suitable for multicomputers with a direct communication network. It is extremely easy to implement and can yield optimal performance given a proper tuning. We propose a decentralized remapping method that uses the GDE algorithm periodically to balance (remap) the system's load. We implemented this remapping method in two data parallel applications and found it to be effective in reducing the computation time. The gains in performance (5-15%) due to remapping are reasonably substantial given the fact that the two applications by their very nature do not necessarily favor remapping. >

Wild Canonical Algebras and Rings of Automorphic Forms

Abstract: This paper aims to show that the modern representation theory of finite dimensional algebras, usually judged to be of fairly recent origin, has strong roots within classical mathematics. We do justify this claim by exploring the links between tame hereditary algebras ∑ and simple surface singularities (corresponding to the invariant theory of binary polyhedral groups) wild canonical algebras Λ and automorphic forms, respectively.

Intermediate 4f bonding structure for samarium under pressure.

Abstract: The crystal structure of the low-symmetry phase Sm(V) was studied by synchrotron x-ray diffraction under isothermal compression at room temperature up to 77 GPa (volume fraction=0.45). Measured lattice spacings and diffraction intensities for Sm(V) in the pressure range beyond the phase mixing show that this phase can be identified as a prototype structure with 3 atoms in the hexagonal unit cell. The occurrence of this low-symmetry structure gives strong evidence for a rapid increase of 4f-electron bonding in Sm in the pressure range above 37 GPa.

Sorting large data sets on a massively parallel system

Abstract: This paper presents a performance study for many of today's popular parallel sorting algorithms. It is the first to present a comparative study on a large scale MIMD system. The machine, a Parsytec GCel, contains 1024 processors connected as a two-dimensional grid. To justify the experimental results, we develop a theoretical model to predict the performance in terms of communication and computation times. We get a very close relation between the experiments and the theoretical model as long as the edge congestion caused by the algorithms is predicted precisely. We compare: Bitonicsort, Shearsort, Gridsort, Samplesort, and Radixsort. Experiments were performed using random instances according to a well known benchmark problem. Results show that for the machine we used, Bitonicsort performs best for smaller numbers of keys per processor ( >

The GroupFlow System: A Scalable Approach to Workflow Management between Cooperation and Automation

Abstract: In this paper, we will discuss business relevance factors, architectural concepts, tool approaches, and user-interface samples of the GroupFlow environment GroupFlow offers business process and technology frameworks to set up versatile and flexible workflow systems for distributed information management within organizations and with their outside communication partners We regard the synergetic approaches being used in the GroupFlow architecture — for the frontend client-workplaces of the several user typologies as well as for the distributed backend server components — as innovative The GroupFlow environment perhaps best can be profiled around integrating concepts that are typically referred to as workgoup computing or Groupware on the one hand, and workflow management or business process design on the other

A Distributed Computing Center Software for the Efficient Use of Parallel Computer Systems

Abstract: Nowadays, Computing systems accessible to researchers with ”Grand Challenge” problems consist of a hardware mixture ranging from clusters of workstations to parallel supercomputers. This hardware is available via geographically distributed networks with various communication capabilities.

Periodic solutions of dry friction problems

Abstract: Dry friction problems lead to discontinuous differential equations, e.g. to $$x'' + xx' + \mu \operatorname{sgn} x' + \beta ^2 x = \varphi (t),$$ where sgn γ=γγ for γ ≠ 0 and sgn (0)=[ − 1. 1]. We study existence of ω-periodic solutions of (1) in case ϕ is ω-periodic. Results forx> 0 are given in the book “Multivalued Differential Equations” (K. Deimling: De Gruyter 1992). and preliminary ones forx=0 are contained in K. Deimling “Multivalued differential equations and dry friction problems” (Proc. Conf. Differential & Delay Equations. World Sci. Publ. 1992). Based on the latter and considerable additional analysis, we give a complete description of the resonant casex=0.β=1. ϕ(t)=sint. In particular, it turned out that for μ e (π 4. 1) there is a unique globally asymptotically stable 2π-periodic solutionxgm, which necessarily has deadzones (i.e.xμ (t) ≡c in certain intervals). In addition, the nonresonant case is solved by means of degree theory for multivalued maps, since in this situation a priori bounds can be found easily.

On the alignment of thermotropic nematic and smectic liquid crystals on lecithin coated surfaces

Abstract: The orientation of thermotropic nematic and smectic liquid crystals at monomolecular films of lecithin on glass as well as germanium substrates has been studied by polarizing microscopy and FTIR spectroscopy. Nematic liquid crystals with only a weak tendency to form smectic phases exhibit a dependence of their orientation on the temperature and the packing density of the monolayer which can be explained by a sterical model. Liquid crystals in the smectic A phase as well as nematics with a strong tendency to build up smectic layers, however, align homeotropically, independent on the packing density of the lecithin film and the temperature. This can be understood as a screening of the lecithin film properties by the smectic-like boundary layers of the nematic liquid crystal.

Depolariser based on acousto-optical TE-TM converters for suppression of polarisation holeburning in long haul EDFA links

Abstract: An acousto-optical Ti:LiNbO/sub 3/ TE-TM converter whose transducer is placed at 1/3 of the interaction length forms a polarisation-independent optical depolariser, suitable to suppress polarisation holeburning in EDFAs. The authors present a double-stage depolariser with