Refine
Year of publication
- 1998 (147) (remove)
Document Type
- Preprint (109)
- Article (21)
- Doctoral Thesis (7)
- Lecture (3)
- Report (3)
- Diploma Thesis (1)
- Master's Thesis (1)
- Periodical Part (1)
- Working Paper (1)
Keywords
- AG-RESY (13)
- PARO (12)
- SKALP (9)
- Case Based Reasoning (4)
- industrial robots (4)
- motion planning (3)
- parallel processing (3)
- CIM-OSA (2)
- HANDFLEX (2)
- Kalman filtering (2)
- TOVE (2)
- coset enumeration (2)
- on-line algorithms (2)
- particle methods (2)
- path planning (2)
- search algorithms (2)
- subgroup problem (2)
- Analysis (1)
- Boltzmann Equation (1)
- C5H3(SiMe3)2-Liganden (1)
- CFD (1)
- Chirale Induktion (1)
- Cobalt-Halbsandwichkomplexe (1)
- Complexity (1)
- Correspondence with other notations (1)
- Dependency Factors (1)
- Dirichlet series (1)
- Distributed Software Development (1)
- EXPRESS-G (1)
- Electron states in low-dimensional structures (1)
- Enterprise modeling (1)
- Enterprise modelling (1)
- Funktionalanalysis (1)
- Grid Graphs (1)
- Gröbner base (1)
- Gröbner bases (1)
- Gröbner bases in monoid and group rings (1)
- HOT (1)
- Hilbert transform (1)
- Ill-Posed Problems (1)
- Indexierung (1)
- Inhaltserschließung (1)
- Integral (1)
- Integration (1)
- Internet Based Software Process Management Environment (1)
- Kallianpur-Robbins law (1)
- Koordinationschemie (1)
- Kristallographie (1)
- LCSH (1)
- Learning systems (1)
- Lebesque-Integral (1)
- Linear Integral Equations (1)
- MEGI (1)
- MILOS (1)
- Monoid and group rings (1)
- Monotone dynamical systems (1)
- Navier-Stokes (1)
- Nonlinear dynamics (1)
- Numerical Simulation (1)
- Ontolingua (1)
- Ontology (1)
- PC-based robot control (1)
- PERA (1)
- Phosphor (1)
- Pn (1)
- Quantum mechanics (1)
- RSWK (1)
- Rarefied Gas Flows (1)
- Rayleigh Number (1)
- Recurrent neural networks (1)
- Riemann-Siegel formula (1)
- Riemannsche Summen (1)
- Robust reliability (1)
- SWEEPING (1)
- Simultaneous quantifier elimination (1)
- Singularity theory (1)
- Treppenfunktionen (1)
- Tunneling (1)
- UML (1)
- Vorlesungsskript (1)
- WETICE 98 (1)
- Wannier-Bloch resonance states (1)
- Wannier-Stark systems (1)
- adaptive grid generation (1)
- area loss (1)
- automated proof planner (1)
- bi-directional search (1)
- center and median problems (1)
- chaos (1)
- cholesterische Phasen (1)
- client/server-architecture (1)
- confluence (1)
- convex models (1)
- crack diagnosis (1)
- cusp forms (1)
- da (1)
- damage diagnosis (1)
- discretization (1)
- distributed and parallel processing (1)
- distributed control system (1)
- distributed processing (1)
- domain decomposition (1)
- exact fully discrete vectorial wavelet transform (1)
- fixpoint theorem (1)
- fluid dynamic equations (1)
- graph search (1)
- higher order (1)
- higher order tableau (1)
- initial value representation (1)
- kinetic equations (1)
- kinetic models (1)
- konvexe Analysis (1)
- level set method (1)
- lifetime statistics (1)
- lifetimes (1)
- locational analysis (1)
- log averaging methods (1)
- molekularer Chiralitätswechselwirkungstensor (1)
- monoid- and group-presentations (1)
- moving contact line (1)
- multi-hypothesis diagnosis (1)
- natural language semantics (1)
- non-linear dynamics (1)
- numerics for pdes (1)
- occupation measure (1)
- off-line programming (1)
- planar Brownian motion (1)
- prefix reduction (1)
- prefix string rewriting (1)
- prefix-rewriting (1)
- proof presentation (1)
- pyramid scheme (1)
- quantum chaos (1)
- quantum mechanics (1)
- quasienergy (1)
- rarefied gas flows (1)
- ratio ergodic theorem (1)
- reinitialization (1)
- resonances (1)
- robot calibration (1)
- robot control architectures (1)
- robot motion planning (1)
- rotating machinery (1)
- scale discrete spherical vector wavelets (1)
- search algorithm (1)
- search alogorithms (1)
- semiclassical (1)
- sequent calculus (1)
- skolemization (1)
- stationary solutions (1)
- steady Boltzmann equation (1)
- strong theorems (1)
- subgroup presentation problem (1)
- theorem prover (1)
- trajectory optimization (1)
- variable cardinality case (1)
- vectorial multiresolution analysis (1)
- vehicular traffic (1)
Faculty / Organisational entity
- Kaiserslautern - Fachbereich Informatik (38)
- Kaiserslautern - Fachbereich Mathematik (35)
- Kaiserslautern - Fachbereich Physik (35)
- Fraunhofer (ITWM) (12)
- Kaiserslautern - Fachbereich Wirtschaftswissenschaften (9)
- Kaiserslautern - Fachbereich Elektrotechnik und Informationstechnik (6)
- Kaiserslautern - Fachbereich Maschinenbau und Verfahrenstechnik (6)
- Kaiserslautern - Fachbereich Biologie (3)
- Kaiserslautern - Fachbereich Chemie (2)
- Universitätsbibliothek (1)
Wavelets on closed surfaces in Euclidean space R3 are introduced starting from a scale discrete wavelet transform for potentials harmonic down to a spherical boundary. Essential tools for approximation are integration formulas relating an integral over the sphere to suitable linear combinations of functional values (resp. normal derivatives) on the closed surface under consideration. A scale discrete version of multiresolution is described for potential functions harmonic outside the closed surface and regular at infinity. Furthermore, an exact fully discrete wavelet approximation is developed in case of band-limited wavelets. Finally, the role of wavelets is discussed in three problems, namely (i) the representation of a function on a closed surface from discretely given data, (ii) the (discrete) solution of the exterior Dirichlet problem, and (iii) the (discrete) solution of the exterior Neumann problem.
Verbale Sacherschließung
(1998)
Das Skript gibt eine Einführung in die Geschichte, die Terminologie und die Verfahren der verbalen Sacherschließung. Im deutschsprachigen und englischsprachigen Raum etablierte Verfahren, wie die "Regeln für den Schlagwortkatalog (RSWK)" und die "Library of Congress Subject Headings (LCSH)", werden eingehend beschrieben und Aspekte der Kooperation und Tauglichkeit für Online-Kataloge diskutiert. Charakteristika sowie Vor- und Nachteile der automatischen Indexierung werden anhand des Verfahrens "Maschinelle Indexierung zur verbesserten Literaturerschließung in Online Systemen (MILOS)" dargestellt.
In dieser Arbeit wurden Cophoto- und Cothermolysen einer Serie von alkylierten und silylierten Cyclopentadienylcobaltcarbonylen mit weißem Phosphor untersucht. Dazu wurden einige neue Komplexe des Typus [CpRCo(CO)2] mit CpR= (C5(Me2-1,3)iPr3), (C5H3(Me3Si)2-1,3), (C5H2(Me3Si)3-1,2,4) sowie des Zweikernkomplexes [{CpRCo(micro-CO)}2] mit CpR= (C5(Me2-1,3)iPr3) hergestellt. Neben den vorgenannten Komplexen wurden die bereits literaturbekannten Verbindungen [CpRCo(CO)2] mit CpR= (C5Me5), (C5H4(Me3Si)) als Edukte eingesetzt. Die präparative Zugänglichkeit von drei- bis vierkernigen Cobaltkomplexen mit unsubstituierten P8-, P10- und P12-Liganden konnte beträchtlich erweitert werden. Die thermische Reaktion von Dicarbonyl(trimethylsilylcyclopentadienyl)cobalt mit weißem Phosphor führt in sehr guten Ausbeuten zur Bildung des Clusters [{CpRCo}4P4] (CpR= C5H4(Me3Si)). Die Röntgenstrukturanalyse eines Trillingskristalls läßt lediglich eine ungefähre Bestimmung des Schweratomgerüstes als quadratisches Antiprisma zu. Die Umsetzung von Dicarbonyl(1,3-bis(trimethylsilyl)cyclopentadienyl)cobalt mit weißem Phosphor ergibt unter geeigneten Bedingungen (140°C, 3d) selektiv und in sehr hoher Ausbeute den Vierkernkomplex [{CpRCo}4P10] (I) (CpR= C5H3(Me3Si)2-1,3). Mit I konnte erstmals ein Cobaltkomplex mit einem P10-Liganden röntgenographisch charakterisiert werden. Der Schweratomkäfig in I läßt sich von der Nortricyclanstruktur ableiten. Interessantes Merkmal ist die Koordination eines Cobaltfragmentes an eine P-P-Kante in einer Weise, die einen Zustand zwischen der side-on-Koordination an diese sigma-Bindung und der Insertion in diese Kante darstellt (d(P-P) = 2.47 Å). Die photochemische Reaktion von Dicarbonyl(1,3-bis(trimethylsilyl)cyclopentadienyl)cobalt mit weißem Phosphor ergibt je nach Stöchiometrie die Komplexe [{CpRCo}3P4(CO)] (II) bzw. [{CpRCo}2P4] (III) (CpR= C5H3(Me3Si)2-1,3), die röntgenographisch charakterisiert wurden. Komplex II ist ein arachno-Cluster, der formal von einem zweifach überkappten trigonalen Prisma abgeleitet werden kann. Die längsten P-P-Abstände in II liegen mit d(P-P, Mw.) = 2.51 Å an der Obergrenze bekannter bindender P-P-Wechselwirkungen. Verbindung III ist ein Vertreter einer Serie von [{CpRCo}2(micro,eta2:2-P2)2]-Komplexen, welche ein rechteckig verzerrtes Co2P4-Oktaeder als Schweratomgerüst aufweisen. Es wurden Röntgenstrukturen der Komplexe mit CpR= (C5((CH3)2-1,3)iPr3), (C5H3(Me3Si)2-1,3), (C5H2(Me3Si)3-1,2,4) bestimmt. Diese Verbindungen weisen kurze P-P-Abstände mit d(P-P) = 2.054 bis 2.064 Å sowie P-P-Kontakte von d(P...P) = 2.679 bis 2.713 Å auf.
We have computed ensembles of complete spectra of the staggered Dirac operator using four-dimensional SU(2) gauge fields, both in the quenched approximation and with dynamical fermions. To identify universal features in the Dirac spectrum, we compare the lattice data with predictions from chiral random matrix theory for the distribution of the low-lying eigenvalues. Good agreement is found up to some limiting energy, the so-called Thouless energy, above which random matrix theory no longer applies. We determine the dependence of the Thouless energy on the simulation parameters using the scalar susceptibility and the number variance.
Although several systematic analyses of existing approaches to adaptation have been published recently, a general formal adaptation framework is still missing. This paper presents a step into the direction of developing such a formal model of transformational adaptation. The model is based on the notion of the quality of a solution to a problem, while quality is meant in a more general sense and can also denote some kind of appropriateness, utility, or degree of correctness. Adaptation knowledge is then defined in terms of functions transforming one case into a successor case. The notion of quality provides us with a semantics for adaptation knowledge and allows us to define terms like soundness, correctness and completeness. In this view, adaptation (and even the whole CBR process) appears to be a special instance of an optimization problem.
For the numerical simulation of 3D radiative heat transfer in glasses and glass melts, practically applicable mathematical methods are needed to handle such problems optimal using workstation class computers. Since the exact solution would require super-computer capabilities we concentrate on approximate solutions with a high degree of accuracy. The following approaches are studied: 3D diffusion approximations and 3D ray-tracing methods.
Thermal Properties of Interacting Bose Fields and Imaginary-Time Stochastic Differential Equations
(1998)
Abstract: Matsubara Green's functions for interacting bosons are expressed as classical statistical averages corresponding to a linear imaginary-time stochastic differential equation. This makes direct numerical simulations applicable to the study of equilibrium quantum properties of bosons in the non-perturbative regime. To verify our results we discuss an oscillator with quartic anharmonicity as a prototype model for an interacting Bose gas. An analytic expression for the characteristic function in a thermal state is derived and a Higgs-type phase transition discussed, which occurs when the oscillator frequency becomes negative.
In the present paper we investigate the Rayleigh-Benard convection in rarefied gases and demonstrate by numerical experiments the transition from purely thermal conduction to a natural convective flow for a large range of Knudsen numbers from 0.02 downto 0.001. We address to the problem how the critical value for the Rayleigh number defined for incompressible vsicous flows may be translated to rarefied gas flows. Moreover, the simulations obtained for a Knudsen number Kn=0.001 and Froude number Fr=1 show a further transition from regular Rayleigh-Benard cells to a pure unsteady behavious with moving vortices.
This paper presents a brief overview of the INRECA-II methodology for building and maintaining CBR applications. It is based on the experience factory and the software process modeling approach from software engineering. CBR development and maintenance experience is documented using software process models and stored in a three-layered experience packet.
The critical points of the continuous series are characterized by two complex numbers l_1,l_2 (Re(l_1,l_2)< 0), and a natural number n (n>=3) which enters the string susceptibility constant through gamma = -2/(n-1). The critical potentials are analytic functions with a convergence radius depending on l_1 or l_2. We use the orthogonal polynomial method and solve the Schwinger-Dyson equations with a technique borrowed from conformal field theory.
In system theory, state is a key concept. Here, the word state refers to condition, as in the example Since he went into the hospital, his state of health worsened daily. This colloquial meaning was the starting point for defining the concept of state in system theory. System theory describes the relationship between input X and output Y, that is, between influence and reaction. In system theory, a system is something that shows an observable behavior that may be influenced. Therefore, apart from the system, there must be something else influencing and observing the reaction of the system. This is called the environment of the system.
We consider N coupled linear oscillators with time-dependent coecients. An exact complex amplitude - real phase decomposition of the oscillatory motion is constructed. This decomposition is further used to derive N exact constants of motion which generalise the so-called Ermakov-Lewis invariant of a single oscillator. In the Floquet problem of periodic oscillator coecients we discuss the existence of periodic complex amplitude functions in terms of existing Floquet solutions.
The notion of formal description techniques for timed systems (T-FDTs) has been introduced in [EDK98a] to provide a unifying framework for description techniques that are formal and that allow to describe the ongoing behavior of systems. In this paper we show that three well known temporal logics, MTL, MTL-R , and CTL*, can be embedded in this framework. Moreover, we provide evidence that a large number of dioeerent kinds of temporal logics can be considered as T-FDTs.
Abstract: Random Matrix Theory (RMT) is a powerful statistical tool to model spectral fluctuations. This approach has also found fruitful application in Quantum Chromodynamics (QCD). Importantly, RMT provides very efficient means to separate different scales in the spectral fluctuations. We try to identify the equivalent of a Thouless energy in complete spectra of the QCD Dirac operator for staggered fermions from SU(2) lattice gauge theory for different lattice size and gauge couplings. We focus on the bulk of the spectrum. In disordered systems, the Thouless energy sets the universal scale for which RMT applies. This relates to recent theoretical studies which suggest a strong analogy between QCD and disordered systems. The wealth of data allows us to analyze several statistical measures in the bulk of the spectrum with high quality. We find deviations which allows us to give an estimate for this universal scale. Other deviations than these are seen whose possible origin is discussed. Moreover, we work out higher order correlators as well, in particular three-point correlation functions.
Stand des strategischen Controlling-Berichtwesens und Übertragungsmöglichkeiten auf die Universität
(1998)
The dispersions of dipolar (Damon-Eshbach modes) and exchange dominated spin waves are calculated for in-plane magnetized thin and ultrathin cubic films with (111) crystal orientation and the results are compared with those obtained for the other principal planes. The properties of these magnetic excitations are examined from the point of view of Brillouin light scattering experiments. Attention is paid to study the spin-wave frequency variation as a function of the magnetization direction in the film plane for different film thicknesses. Interface anisotropies and the bulk magnetocrystalline anisotropy are considered in the calculation. A quantitative comparison between an analytical expression obtained in the limit of small film thickness and wave vector and the full numerical calculation is given.
Rewriting techniques have been applied successfully to various areas of symbolic computation. Here we consider the notion of prefix-rewriting and give a survey on its applications to the subgroup problem in combinatorial group theory. We will see that for certain classes of finitely presented groups finitely generated subgroups can be described through convergent prefix-rewriting systems, which can be obtained from a presentation of the group considered and a set of generators for the subgroup through a specialized Knuth-Bendix style completion procedure. In many instances a finite presentation for the subgroup considered can be constructed from such a convergent prefix-rewriting system, thus solving the subgroup presentation problem. Finally we will see that the classical procedures for computing Nielsen reduced sets of generators for a finitely generated subgroup of a free group and the Todd-Coxeter coset enumeration can be interpreted as particular instances of prefix-completion. Further, both procedures are closely related to the computation of prefix Gr"obner bases for right ideals in free group rings.
Object-oriented case representations require approaches for similarity assessment that allow to compare two differently structured objects, in particular, objects belonging to different object classes. Currently, such similarity measures are developed more or less in an ad-hoc fashion. It is mostly unclear, how the structure of an object-oriented case model, e.g., the class hierarchy, influences similarity assessment. Intuitively, it is obvious that the class hierarchy contains knowledge about the similarity of the objects. However, how this knowledge relates to the knowledge that could be represented in similarity measures is not obvious at all. This paper analyzes several situations in which class hierarchies are used in different ways for case modeling and proposes a systematic way of specifying similarity measures for comparing arbitrary objects from the hierarchy. The proposed similarity measures have a clear semantics and are computationally inexpensive to compute at run-time.
Programs are linguistic structures which contain identifications of individuals: memory locations, data types, classes, objects, relations, functions etc. must be identified selectively or definingly. The first part of the essay which deals with identification by showing and designating is rather short, whereas the remaining part dealing with paraphrasing is rather long. The reason is that for an identification by showing or designating no linguistic compositions are needed, in contrast to the case of identification by paraphrasing. The different types of functional paraphrasing are covered here in great detail because the concept of functional paraphrasing is the foundation of functional programming. The author had to decide whether to cover this subject here or in his essay Purpose versus Form of Programs where the concept of functional programming is presented. Finally, the author came to the conclusion that this essay on identification is the more appropriate place.
The quasienergy spectrum of a periodically driven quantum system is constructed from classical dynamics by means of the semiclassical initial value representation using coherent states. For the first time, this method is applied to explicitly time dependent systems. For an anharmonic oscillator system with mixed chaotic and regular classical dynamics, the entire quantum spectrum (both regular and chaotic states) is reproduced semiclassically with surprising accuracy. In particular, the method is capable to account for the very small tunneling splittings.
Simultaneous quantifier elimination in sequent calculus is an improvement over the well-known skolemization. It allows a lazy handling of instantiations as well as of the order of certain reductions. We prove the soundness of a sequent calculus which incorporates a rule for simultaneous quantifier elimination. The proof is performed by semantical arguments and provides some insights into the dependencies between various formulas in a sequent.
Robust Reliability of Diagnostic Multi-Hypothesis Algorithms: Application to Rotating Machinery
(1998)
Damage diagnosis based on a bank of Kalman filters, each one conditioned on a specific hypothesized system condition, is a well recognized and powerful diagnostic tool. This multi-hypothesis approach can be applied to a wide range of damage conditions. In this paper, we will focus on the diagnosis of cracks in rotating machinery. The question we address is: how to optimize the multi-hypothesis algorithm with respect to the uncertainty of the spatial form and location of cracks and their resulting dynamic effects. First, we formulate a measure of the reliability of the diagnostic algorithm, and then we discuss modifications of the diagnostic algorithm for the maximization of the reliability. The reliability of a diagnostic algorithm is measured by the amount of uncertainty consistent with no-failure of the diagnosis. Uncertainty is quantitatively represented with convex models.
Robust facility location
(1998)
Let A be a nonempty finite subset of R^2 representing the geographical coordinates of a set of demand points (towns, ...), to be served by a facility, whose location within a given region S is sought. Assuming that the unit cost for a in A if the facility is located at x in S is proportional to dist(x,a) - the distance from x to a - and that demand of point a is given by w_a, minimizing the total trnsportation cost TC(w,x) amounts to solving the Weber problem. In practice, it may be the case, however, that the demand vector w is not known, and only an estimator {hat w} can be provided. Moreover the errors in sich estimation process may be non-negligible. We propose a new model for this situation: select a threshold valus B 0 representing the highest admissible transportation cost. Define the robustness p of a location x as the minimum increase in demand needed to become inadmissible, i.e. p(x) = min{||w^*-{hat w}|| : TC(w^*,x) B, w^* = 0} and solve then the optimization problem max_{x in S} p(x) to get the most robust location.
In the following an introduction to the level set method will be givenso that one becomes aware of the arising problems, which lead to the needof reinitialization. The problems concerning reinitialization itself will be analysed more detailed and a solution for area loss will be proposed. This solution consists in a combination of the commonly used PDE for reinitialization and extrapolation around the zero level set. Numericalexperiments show rather satisfactory results as far as area loss and computation of curvature are concerned.
Abstract: Generalized single-atom Maxwell-Bloch equations for optically dense media are derived taking into account non-cooperative radiative atom-atom interactions. Applying a Gaussian approximation and formally eliminating the degrees of freedom of the quantized radiation field and of all but a probe atom leads to an effective time-evolution operator for the probe atom. The mean coherent amplitude of the local field seen by the atom is shown to be given by the classical Lorentz-Lorenz relation. The second-order correlations of the field lead to terms that describe relaxation or pump processes and level shifts due to multiple scattering or reabsorption of spontaneously emitted photons. In the Markov limit a non-linear and nonlocal single-atom density matrix equation is derived. To illustrate the effects of the quantum corrections we discuss amplified spontaneous emission and radiation trapping in a dense ensemble of initially inverted two-level atoms and the effects of radiative interactions on intrinsic optical bistability in coherently driven systems.
Transitions from classical to quantum behaviour in a spin system with two degenerate ground states separated by twin energy barriers which are asymmetric due to an applied magnetic field are investigated. It is shown that these transitions can be interpreted as first- or second-order phase transitions depending on the anisotropy and magnetic parameters defining the system in an effective Lagrangian description.
Abstract: We investigate the quantum properties of fields generated by resonantly enhanced wave mixing based on atomic coherence in Raman systems. We show that such a process can be used for generation of pairs of Stokes and anti-Stokes fields with nearly perfect quantum correlations, yielding almost complete (i.e. 100%) squeezing without the use of a cavity. We discuss the extension of the wave mixing interactions into the domain of a few interacting light quanta.
The paper addresses two problems of comprehensible proof presentation, the hierarchically structured presentation at the level of proof methods and different presentation styles of construction proofs. It provides solutions for these problems that can make use of proof plans generated by an automated proof planner.
In this paper we study the space-time asymptotic behavior of the solutions and derivatives to th incompressible Navier-Stokes equations. Using moment estimates we obtain that strong solutions to the Navier-Stokes equations which decay in \(L^2\) at the rate of \(||u(t)||_2 \leq C(t+1)^{-\mu}\) will have the following pointwise space-time decay \[|D^{\alpha}u(x,t)| \leq C_{k,m} \frac{1}{(t+1)^{ \rho_o}(1+|x|^2)^{k/2}} \]
where \( \rho_o = (1-2k/n)( m/2 + \mu) + 3/4(1-2k/n)\), and \(|a |= m\). The dimension n is \(2 \leq n \leq 5\) and \(0\leq k\leq n\) and \(\mu \geq n/4\)
We prove that there exists a positive \(\alpha\) such thatfor any integer \(\mbox{$d\ge 3$}\) and any topological types \(\mbox{$S_1,\dots,S_n$}\) of plane curve singularities, satisfying \(\mbox{$\mu(S_1)+\dots+\mu(S_n)\le\alpha d^2$}\), there exists a reduced irreducible plane curve of degree \(d\) with exactly \(n\) singular points of types \(\mbox{$S_1,\dots,S_n$}\), respectively. This estimate is optimal with respect to theexponent of \(d\). In particular, we prove that for any topological type \(S\) there exists an irreducible polynomial of degree \(\mbox{$d\le 14\sqrt{\mu(S)}$}\) having a singular point of type \(S\).
The tunneling splitting of the energy levels of a ferromagnetic particle in the presence of an applied magnetic field - previously derived only for the ground state with the path integral method - is obtained in a simple way from Schr"odinger theory. The origin of the factors entering the result is clearly understood, in particular the effect of the asymmetry of the barriers of the potential. The method should appeal particularly to experimentalists searching for evidence of macroscopic spin tunneling.
The Kallianpur-Robbins law describes the long term asymptotic behaviour of the distribution of the occupation measure of a Brownian motion in the plane. In this paper we show that this behaviour can be seen at every typical Brownian path by choosing either a random time or a random scale according to the logarithmic laws of order three. We also prove a ratio ergodic theorem for small scales outside an exceptional set of vanishing logarithmic density of order three.
This paper presents a new approach to parallel motion planning for industrial robot arms with six degrees of freedom in an on-line given 3D environment. The method is based on the A*-search algorithm and needs no essential off-line computations. The algorithm works in an implicitly descrete configuration space. Collisions are detected in the cartesian workspace by hierarchical distance computation based on the given CAD model. By decomposing the 6D configuration space into hypercubes and cyclically mapping them onto multiple processing units, a good load distribution can be achieved. We have implemented the parallel motion planner on a workstation cluster with 9 PCs and tested the planner for several benchmark environments. With optimal discretisation, the new approach usually shows linear, and sometimes even superlinear speedups. In on-line provided environments with static obstacles, the parallel planning times are only a few seconds.
Outsourcing und Übertragungsmöglichkeiten des Outsourcings auf die Universität Kaiserslautern
(1998)
Abstract: Resonant optical pumping in dense atomic media is discussed, where the absorption length is less than the smallest characteristic dimension of the sample. It is shown that reabsorption and multiple scattering of spontaneous photons (radiation trapping) can substantially slow down the rate of optical pumping. A very slow relaxation out of the target state of the pump process is then sufficient to make optical pumping impossible. As model systems an inhomogeneously and a radiatively broadened 3-level system resonantly driven with a strong broad-band pump field are considered.
Die virtuelle Produktentwicklung in verteilter Umgebung erfordert eine intensive Kommunika-tion zwischen den beteiligten CAx-Systemen. Diese findet bisher in Form des dateibasierten Datenaustausches mit Hilfe von Direktkonvertern oder neutralen Schnittstellen statt. Der Datenaustausch wird hierbei meist in mehreren Iterationsschleifen durchgeführt und ist oft mit Datenverlusten sowie Unterbrechungen der Entwicklungsaktivitäten verbunden. Demgegenüber steht als neuer Ansatz für die Interoperabilität zwischen CAx-Systemen das Konzept eines CAx-Objektbusses auf Basis von CORBA und STEP. Dieser Ansatz ermög-licht eine plattformübergreifende Online-Kopplung heterogener CAx-Systeme. Im Gegensatz zum dateibasierten Datenaustausch ist hierbei ein transparenter Zugriff sowohl auf Daten als auch auf Funktionen der angebundenen Systeme möglich. Dadurch kann die Durchgängigkeit der Produktdaten in der Prozeßkette deutlich erhöht werden. Zur Beurteilung der Praxistauglichkeit wird dieser neue Ansatz dem dateibasierten Daten-austausch am Beispiel virtueller Einbauuntersuchungen gegenübergestellt. Dabei werden für unterschiedliche praxisrelevante Modellgrößen die für die Übertragung von Geometrie und Topologie erforderlichen Zeiten analysiert und verglichen. Weiterhin werden die generellen Vor- und Nachteile der beiden Lösungen dargestellt. Abschließend wird auf die Potentiale des neuen Ansatzes für den Einsatz in anderen Bereichen eingegangen.
This paper is based on a path planning approach we reported earlier for industrial robot arms with 6 degrees of freedom in an on-line given 3D environment. It has on-line capabilities by searching in an implicit and descrete configuration space and detecting collisions in the Cartesian workspace by distance computation based on the given CAD model. Here, we present different methods for specifying the C-space discretization. Besides the usual uniform and heuristic discretization, we investigate two versions of an optimal discretization for an user-predefined Cartesian resolution. The different methods are experimentally evaluated. Additionally, we provide a set of 3- dimensional benchmark problems for a fair comparison of path planner. For each benchmark, the run-times of our planner are between only 3 and 100 seconds on a Pentium PC with 133 MHz.
In this paper, the problem of path planning for robot manipulators with six degrees of freedom in an on-line provided three-dimensional environment is investigated. As a basic approach, the best-first algorithm is used to search in the implicit descrete configuration space. Collisions are detected in the Cartesian workspace by hierarchical distance computation based on the given CAD model. The basic approach is extended by three simple mechanisms and results in a heuristic hierarchical search. This is done by adjusting the stepsize of the search to the distance between the robot and the obstacles. As a first step, we show encouraging experimental results with two degrees of freedom for five typical benchmark problems.
Enhancing the quality of surgical interventions is one of the main goals of surgical robotics. Thus we have devised a surgical robotic system for maxillofacial surgery which can be used as an intelligent intraoperative surgical tool. Up to now a surgeon preoperatively plans an intervention by studying twodimensional X-rays, thus neglecting the third dimension. In course of the special research programme "Computer and Sensor Aided Surgery" a planning system has been developed at our institute, which allows the surgeon to plan an operation on a threedimensional computer model of the patient . Transposing the preoperatively planned bone cuts, bore holes, cavities, and milled surfaces during surgery still proves to be a problem, as no adequate means are at hand: the actual performance of the surgical intervention and the surgical outcome solely depend on the experience and the skill of the operating surgeon. In this paper we present our approach of a surgical robotic system to be used in maxillofacial surgery. Special stress is being laid upon the modelling of the environment in the operating theatre and the motion planning of our surgical robot .
For defining attribute types to be used in the case representation, taxonomies occur quite often. The symbolic values at any node of the taxonomy tree are used as attribute values in a case or a query. A taxonomy type represents a relationship between the symbols through their position within the taxonomy-tree which expresses knowledge about the similarity between the symbols. This paper analyzes several situations in which taxonomies are used in different ways and proposes a systematic way of specifying local similarity measures for taxonomy types. The proposed similarity measures have a clear semantics and are easy to compute at runtime.
We propose a new discretization scheme for solving ill-posed integral equations of the third kind. Combining this scheme with Morozov's discrepancy principle for Landweber iteration we show that for some classes of equations in such method a number of arithmetic operations of smaller order than in collocation method is required to appoximately solve an equation with the same accuracy.