Showing papers by "University of Paderborn published in 1999"

The PROGRES approach: language and environment

Abstract: Graphs play an important role within many areas of computer science. Rule-based languages, on the other hand, are well-suited for the description of transformation or inference processes on complex data structures. Why not combining two successful principles in one formalism? This is the common vision of the graph transformation community and the main motivation behind the development of PROGRES, a visual language that supports PROgramming with Graph REwriting Systems. The language PROGRES was developed having the following three design goals in mind: (1) Distinguish between data deenition and manipulation activities and use graph schemata to type-check graph transformation rules. (2) Do not rely on the rule-oriented paradigm for all purposes, but support also imperative programming with control structures. (3) Refrain users from the task to guarantee connuence of deened rules by keeping track of rewriting connicts and backtracking out of dead-end derivations. Its accompanying programming environment ooers assistance for creating, analyzing , compiling, and debugging graph transformations as well as for rapid prototyp-ing activities. Being an integrated set of tools with support for intertwining these activities, it combines the exibility of interpreted languages with the safeness of compiled and statically typed languages.

Polarization mode dispersion compensation at 10, 20, and 40 Gb/s with various optical equalizers

Abstract: Polarization mode dispersion (PMD), especially in "old" fibers, is considered harmful for installation and upgrading of trunk lines. An optical PMD equalizer should have several or many differential group delay (DGD) sections with polarization transformers in between which can endlessly transform any input polarization into a principal state of the following DGD section. The sections must practically have fixed DGDs unless there is only one section. The small-signal baseband transfer function for PMD, higher order PMD, and the necessary number of sections as well as their control by the output signals of an electrical filter bank in the receiver are also discussed in this context. Several PMD equalizers have been realized and successfully tested in transmission systems with bit rates of 10, 20, and 40 Gb/s. The systems operated stably with well-opened eye diagrams for DGDs ranging between 0 and 1.7 bit durations. Best performance is obtained from a distributed PMD equalizer with one piece of polarization-maintaining fiber twisted by 64 stepper motors. The principle can also be realized in LiNbO/sub 3/.

Stability and electronic structure of GaN nanotubes from density-functional calculations

Abstract: Density-functional calculations are used to predict the stability and electronic structures of GaN nanotubes. Strain energies of GaN nanotubes are comparable to those of carbon nanotubes, suggesting the possibility for the formation of GaN nanotubes. The zigzag nanotube is a semiconductor with direct band gap, whereas the armchair nanotube has an indirect band gap. The band gaps decrease with decreasing diameter, contrary to the case of carbon nanotubes. We further discuss possible ways of synthesizing GaN nanotubes in conjunction with carbon nanotubes.

Linear time 1/2 -approximation algorithm for maximum weighted matching in general graphs

Abstract: A new approximation algorithm for maximum weighted matching in general edge-weighted graphs is presented. It calculates a matching with an edge weight of at least 1/2 of the edge weight of a maximum weighted matching. Its time complexity is O(|E|), with |E| being the number of edges in the graph. This improves over the previously known 1/2 -approximation algorithms for maximum weighted matching which require O(|E| ċ log(|V|)) steps, where |V| is the number of vertices.

Linear Time 1/2-Approximation Algorithm for Maximum Weighted Matching in General Graphs

Abstract: A new approximation algorithm for maximum weighted matching in general edge-weighted graphs is presented. It calculates a matching with an edge weight of at least of the edge weight of a maximum weighted matching. Its time complexity is O(|E|), with |E| being the number of edges in the graph. This improves over the previously known -approximation algorithms for maximum weighted matching which require O(|E| log(|V|)) steps, where |V| is the number of vertices.

Pentagon adjacency as a determinant of fullerene stability

Abstract: Optimisation of geometries of all 40 fullerene isomers of C40, using methods from molecular mechanics and tight-binding to full abinitio SCF and DFT approaches, confirms minimisation of pentagon adjacency as a major factor in relative stability. The consensus predictions of 11 out of 12 methods are that the isomer of lowest total energy is the D2 cage with the smallest possible adjacency count, and that energies rise linearly with the number of adjacencies. Quantum mechanical methods predict a slope of 80–100 kJ mol-1 per adjacency. Molecular mechanics methods are outliers, with the Tersoff potential giving a different minimum and its Brenner modification a poor correlation and much smaller penalty.

Algebraic Structure of Discrete Zero Curvature Equations and Master Symmetries of Discrete Evolution Equations

Abstract: An algebraic structure related to discrete zero curvature equations is established. It is used to give an approach for generating master symmetries of the first degree for systems of discrete evolution equations and an answer to why there exist such master symmetries. The key of the theory is to generate nonisospectral flows (λt=λl, l⩾0) from the discrete spectral problem associated with a given system of discrete evolution equations. Three examples are given.

Efficient schemes for nearest neighbor load balancing

Abstract: We design a general mathematical framework to analyze the properties of nearest neighbor balancing algorithms of the diffusion type. Within this framework we develop a new Optimal Polynomial Scheme (OPS) which we show to terminate within a finite number m of steps, where m only depends on the graph and not on the initial load distribution.We show that all existing diffusion load balancing algorithms, including OPS, determine a flow of load on the edges of the graph which is uniquely defined, independent of the method and minimal in the l2-norm. This result can also be extended to edge weighted graphs.The l2-minimality is achieved only if a diffusion algorithm is used as preprocessing and the real movement of load is performed in a second step. Thus, it is advisable to split the balancing process into the two steps of first determining a balancing flow and afterwards moving the load. We introduce the problem of scheduling a flow and present some first results on its complexity and the approximation quality of local greedy heuristics.

Refined phase diagram of boron nitride

Abstract: The equilibrium phase diagram of boron nitride thermodynamically calculated by Solozhenko in 1988 has been now refined on the basis of new experimental data on BN melting and extrapolation of heat capacities of BN polymorphs into high-temperature region using the adapted pseudo-Debye model As compared with the above diagram, the hBN ⇆ cBN equilibrium line is displaced by 60 K toward higher temperatures The hBN−cBN−L triple point has been calculated to be at 3480 ± 10 K and 59 ± 01 GPa, while the hBN−L−V triple point is at T = 3400 ± 20 K and p = 400 ± 20 Pa, which indicates that the region of thermodynamic stability of vapor in the BN phase diagram is extremely small It has been found that the slope of the cBN melting curve is positive whereas the slope of hBN melting curve varies from positive between ambient pressure and 34 GPa to negative at higher pressures

A unified approach towards the development of Swedish as L2: a processability account

Abstract: This paper has two main objectives: (a) to put the vast body of research on Swedish as a second language (SSL) into one coherent framework; and (b) to test the predictions deriving from processability theory (Pienemann, 1998a, 1998b) for Swedish against this empirical database. We will survey the 14 most prominent research projects on SSL covering wide areas of syntax and morphology in longitudinal and cross-sectional studies. This survey is the first to be carried out for Swedish, and it will bring the body of two decades of research into one unified framework. We proceed in the following steps: First, a brief summary of processability theory is given. Then the theory is used to generate a unifying framework for the development of the specific L2 grammatical system (Swedish). Finally, the new framework is tested in the above-mentioned empirical studies. (Less)

A Framework for Constraint Programming Based Column Generation

Abstract: Column generation is a state-of-the-art method for optimally solving difficult large-scale optimization problems such as airline crew assignment. We show how to apply column generation even if those problems have complex constraints that are beyond the scope of pure OR methods. We achieve this by formulating the subproblem as a constraint satisfaction problem (CSP). We also show how to efficiently treat the special case of shortest path problems by introducing an efficient path constraint that exploits dual values from the master problem to exclude nodes that will not lead to paths with negative reduced costs. We demonstrate that this propagation significantly reduces the time needed to solve crew assignment problems.

Risks and Opportunities: Adolescents in Top-Level Sport ñ Growing Up with the Pressures of School and Training

Abstract: Though the involvement of adolescents in top-level sport has been a common theme in the literature for many years, studies with an elaborate theoretical framework and empirically verified data are limited.The aim of the present study was (1) to consider the relationship between involvement in youth elite sport and some elements of adolescent development, and (2) to find out how the young competitors cope with the stress resulting from the demands of school and training. About 700 male and female top athletes from elite sport schools, aged between 12 and 17, were asked to complete Marsh’s self-description questionnaire (SDQ II). This group was compared to a control group from regular schools. Additionally 40 qualitative interviews were conducted focusing on the role of academic achievement. Results revealed significant group main effects. Top-level athletes reported significantly higher general self, peer and parent relations and academic achievement scores. Results of the qualitative interviews showed the...

New Results of Fault Tolerant Geometric Spanners

Abstract: We investigate the problem of constructing spanners for a given set of points that are tolerant for edge/vertex faults. Let S ⊂ IRd be a set of n points and let k be an integer number. A k-edge/vertex fault tolerant spanner for S has the property that after the deletion of k arbitrary edges/vertices each pair of points in the remaining graph is still connected by a short path. Recently it was shown that for each set S of n points there exists a k-edge/vertex fault tolerant spannerwith O(k2n) edges which can be constructed in O(nlogn+ k2n) time. Furthermore, it was shown that for each set S of n points there exists a k-edge/vertex fault tolerant spannerwhose degree is bouned by O(ck+1) for some constant c. Our first contribution is a construction of a k-vertex fault tolerant spanner with O(kn) edges which is a tight bound. The computation takes O(nlogd-1n + knloglogn) time. Then we show that the same k-vertex fault tolerant spanner is also k-edge fault tolerant. Thereafter, we construct a k-vertex fault tolerant spanner with O(k2n) edges whose degree is bounded by O(k2). Finally, we give a more natural but stronger definition of k-edge fault tolerance which not necessarily can be satisfied if one allows only simple edges between the points of S. We investigate the question whether Steiner points help. We answer this question affirmatively and prove ⊖(kn) bounds on the number of Steiner points and on the number of edges in such spanners.

Concealed-Canonical Algebras and Separating Tubular Families

Abstract: We characterise those concealed-canonical algebras which arise as endomorphism rings of tilting modules, all of whose indecomposable summands have strictly positive rank, as those artin algebras whose module categories have a separating exact subcategory (that is, a separating tubular family of standard tubes). This paper develops further the technique of shift automorphisms which arises from the tubular structure. It is related to the characterisation of hereditary noetherian categories with a tilting object as the categories of coherent sheaves on a weighted projective line.

A comparative study of MP2, B3LYP, RHF and SCC-DFTB force fields in predicting the vibrational spectra of N-acetyl-L-alanine-N'-methyl amide: VA and VCD spectra

Abstract: Recently we have looked for spectroscopic probes for secondary structural elements in the vibrational spectra of N-acetyl-L-alanine-N'-methyl amide (NALANMA), L-alanine (LA), N-acetyl-L-alanyl-L-alanine-N'-methyl amide (NALALANMA) and L-alanyl-L-alanine (LALA). Our goal has been to identify spectroscopic probes which can be used to identify specific secondary structural elements in peptides, polypeptides and proteins. In this work we present our comparative analysis of the MP2, B3LYP, RHF and SCC-DFTB quantum force fields to predict the vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra of NALANMA. We have utilised MP2/6-31G*, B3LYP/6-31G*, RHF/6-31G* and SCC-DFTB level theory to determine the geometries and Hessians, atomic polar tensors (APT) and atomic axial tensors (AAT) which are required for simulating the VA and VCD spectra. We have also calculated the AAT at the RHF/6-31G** level and utilised the above force fields to document the difference between the RHF and B3LYP methodologies for the calculation of these tensors. The VA and VCD simulations are compared with the experimentally measured spectra for NALANMA.

FunState—an internal design representation for codesign

Abstract: In this paper, an internal design model called FunState (functions driven by state machines) is presented that enables the representation of different types of system components and scheduling mechanisms using a mixture of functional programming and state machines.It is shown here how properties relevant for scheduling and verification of specification models like boolcan dataflow, cyclostatic dataflow, synchronous dataflow, marked graphs, and communicating state machines as well as Petri nets may be represented in the FunState model. Examples of methods suited for FunState are described, such as scheduling and verification. They are based on the representation of the model's state transitions in form of a periodic graph.

Stiffness degradation induced by multilayer intralaminar cracking in composite laminates

Abstract: A theoretical model for the prediction of the elastic properties of a general symmetric laminate containing multilayer matrix cracks is proposed. A five-layer equivalent constraint model (ECM) laminate [S L /ϕ p / θ q /φ r /S R ] s and seven others degenerated from such a model laminate by eliminating some of the sublaminates, [ϕ p ],[φ r ], S L and S R , are designed for the analyses of the degraded stiffnesses of the cracked laminae in the laminate; the crack configuration in the θ-lamina is explicitly represented (designated by underline `_') while the primary and secondary constraining effects are taken into account by the stiffness-equivalent homogeneous layers, [ϕ p ] and [φ r ], as well as S L and S R . A sublaminate-wise first-order shear deformation laminate theory is developed to analyze the stress and displacement fields in the ECM laminates under the combined tension–shear loading. The in-situ damage effective functions (IDEFs), Λ 22 and Λ 66 , for characterizing the in-plane stiffness reductions of a cracked lamina constrained, are then expressed as explicit functions of the transverse ply crack spacing in such a lamina, as well as of the stiffness properties and the geometric parameters of the constraining layers by using the obtained stress field. The theory's predictions are in a good agreement with the experimental E -modulus data for [0/90/±45] s glass fiber reinforced epoxy composite laminates under fatigue.

On approximability of the minimum-cost k-connected spanning subgraph problem

Abstract: We present the first truly pojynomial-time approximation scheme (PTAS) for the mimmum-cost k-vertex(or: kedge-) connected spanning subgraph problem for complete Euclidean graphs in Rd. Previously it was known for every positive constant E how to construct in a polynomial time a graph on a superset of the input points which is k-vertex connected with respect to the input points, and whose cost is within (1 +E) of the minimum-cost of a k-vertex connected graph spanning the input points. We subsume that result by showing for every positive constant E how to construct m a polynomial-time a k-connected subgraph spanning the input points without any Steiner points and having the cost within (1 + E) of the minimum. We also studv hardness of annroximations for the minimum-cost k-v”ertexand k-edge-connected spanning subrrrauh oroblems. The. onlv inannroximabilitv result kno&*so far for the minimumrcost k-vertexand-k-edgeconnected spanning subgraph problems states that the kedge-connectivity problem in unweighted graphs does not have a PTAS unless P = NP, even for k = 2. We present a simpler proof of this result that holds even for aranhs of bounded degree, and provide the first proof that Vfnhing a PTAS for the k-vertex-connectivitv nroblem in unweiehted graphs is NP-hard even for k = 2 aid for graphs of bocnded degree. We further show that our algorithmic results for Euclidean graphs cannot be extended to arbitrarily high dimensions. -We prove that for weighted graphs tfiere-is no PTAS for the k-vertexand the k-edne-connectivitv oroblem unless P = NP, even for Euclidealgraphs in W”g ’ and k = 2.

Ulam's method for random interval maps

Abstract: We consider the approximation of absolutely continuous invariant measures (ACIMs) of systems defined by random compositions of piecewise monotonic transformations. Convergence of Ulam's finite approximation scheme in the case of a single transformation was dealt with by Li (1976 J. Approx. Theory 17 177-86). We extend Ulam's construction to the situation where a family of piecewise monotonic transformations are composed according to either an iid or Markov law, and prove an analogous convergence result. In addition, we obtain a convergence rate for our approximations to the unique ACIM, and provide rigorous bounds for the L1 error of the Ulam approximation.

Quasi-phase-matched difference-frequency generation in periodically poled Ti:LiNbO(3) channel waveguides.

Abstract: Mid-infrared radiation near 2.8 µm was generated by difference-frequency generation in an 80-mm-long periodically poled Ti:LiNbO3 channel waveguide by pump radiation near 1.55 µm (tunable external-cavity laser) and a signal radiation of 3.391 µm (He–Ne laser). We obtained a normalized conversion efficiency of 105% W-1, which is to our knowledge the highest value ever reported.

The Paderborn university BSP (PUB) library-design, implementation and performance

Abstract: The Paderborn University BSP (PUB) library is a parallel C library based on the BSP model. The basic library supports buffered and unbuffered asynchronous communication between any pair of processors, and a mechanism for synchronizing the processors in a barrier style. In addition, it provides routines for collective communication on arbitrary subsets of processors, partition operations, and a zero-cost synchronization mechanism. Furthermore, some techniques used in its implementation deviate significantly from the techniques used in other BSP libraries.

On the Nature of Structure and Its Identification

Abstract: When working on systems of the real world, abstractions in the form of graphs have proven a superior modeling and representation approach. This paper is on the analysis of such graphs. Based on the paradigm that a graph of a system contains information about the system's structure, the paper contributes within the following respects: 1. It introduces a new and lucid structure measure, the so-called weighted partial connectivity, Λ, whose maximization defines a graph's structure (Section 2). 2. It presents a fast algorithm that approximates a graph's optimum Λ-value (Section 3). Moreover, the proposed structure definition is compared to existing clustering approaches (Section 4), resulting in a new splitting theorem concerning the well-known minimum cut splitting measure. A key concept of the proposed structure definition is its implicit determination of an optimum number of clusters. Different applications, which illustrate the usability of the measure and the algorithm, round off the paper (Section 5).

Analysis of Switched Ethernet Networks with Different Topologies Used in Automation Systems

Abstract: Ethernet is the most famous type of communication network used for office applications. Currently, networks used on field level and on office level are different due to their specific requirements. Especially for real-time systems, the deterministic behavior of the network is very important. Now Switched Ethernet seems to be applicable also on field level, because collisions can be avoided and priorities can be used. In this paper Switched Ethernet networks with different topologies are analyzed concerning the transmission delays. Therefore a typical master-slave scenario of an automation system is investigated.

Concentric-shell fullerenes and diamond particles: A molecular-dynamics study

Abstract: Concentric-shell fullerenes are generated from diamond nanoparticles of 1.2 nm to 1.4 nm diameter by means of molecular dynamics simulations based on approximate Kohn-Sham equations. The diamond-to-concentric-shell fullerene transformation observed at temperatures from 1400 K to 2800 K starts at the surface of the diamond particle. Subsequently, the core of the particle gets disordered and the information about the initial atomic structure becomes lost. The final structure consists of two concentric graphitic shells. The intershell spacing of the generated concentric-shell fullerenes is distinctly below the interlayer distance of graphite. It is demonstrated that ${\mathrm{sp}}^{3}$-like cross links appear between the shells. Simulated irradiation accelerates the transformation but reduces the number of cross links.