Showing papers by "Technical University of Dortmund published in 2005"

R2WinBUGS: A Package for Running WinBUGS from R

Abstract: The R2WinBUGS package provides convenient functions to call WinBUGS from R. It automatically writes the data and scripts in a format readable by WinBUGS for processing in batch mode, which is possible since version 1.4. After the WinBUGS process has finished, it is possible either to read the resulting data into R by the package itself—which gives a compact graphical summary of inference and convergence diagnostics—or to use the facilities of the coda package for further analyses of the output. Examples are given to demonstrate the usage of this package.

Wetting and self-cleaning properties of artificial superhydrophobic surfaces

Abstract: The wetting and the self-cleaning properties (the latter is often called the “Lotus-Effect”) of three types of superhydrophobic surfaces have been investigated: silicon wafer specimens with different regular arrays of spikes hydrophobized by chemical treatment, replicates of water-repellent leaves of plants, and commercially available metal foils which were additionally hydrophobized by means of a fluorinated agent. Water droplets rolled off easily from those silicon samples which had a microstructure consisting of rather slender spikes with narrow pitches. Such samples could be cleaned almost completely from artificial particulate contaminations by a fog consisting of water droplets (diameter range, 8−20 μm). Some metal foils and some replicates had two levels of roughening. Because of this, a complete removal of all particles was not possible using artificial fog. However, water drops with some amount of kinetic impact energy were able to clean these surfaces perfectly. A substrate where pronounced str...

Internal Circulation within the Liquid Slugs of a Liquid-Liquid Slug-Flow Capillary Microreactor

Abstract: A so-called “slug-flow” capillary microreactor has been proposed for the investigation of mass-transfer-limited liquid−liquid reactions. Internal circulation within the slug leads to an intensified and tunable mass transfer. Understanding the development of the circulatory flows and the influence of operating parameters upon them is thus crucial. In this study, experiments were carried out to visualize the internal circulations using particle image velocimetry (PIV) technique. State-of-the-art computational fluid dynamics (CFD) simulations were used to predict the internal circulation within the liquid slugs and a CFD particle tracing algorithm employed to visualize them. Each slug was modeled as a distinct single-phase flow domain. The effect of the flow velocity and slug length on the velocity profile and stagnant zones of the internal circulations for a slug with and without a wall film is discussed. The internal circulations could be qualitatively and quantitatively characterized with the help of the ...

Quantum information processing and communication: strategic report on current status, visions and goals for research in Europe

Abstract: We present an excerpt of the document "Quantum Information Processing and Communication: Strategic report on current status, visions and goals for research in Europe", which has been recently published in electronic form at the website of FET (the Future and Emerging Technologies Unit of the Directorate General Information Society of the European Commission, http://www.cordis.lu/ist/fet/qipc-sr.htm). This document has been elaborated, following a former suggestion by FET, by a committee of QIPC scientists to provide input towards the European Commission for the preparation of the Seventh Framework Program. Besides being a document addressed to policy makers and funding agencies (both at the European and national level), the document contains a detailed scientific assessment of the state-of-the-art, main research goals, challenges, strengths, weaknesses, visions and perspectives of all the most relevant QIPC sub-fields, that we report here.

klaR Analyzing German Business Cycles

Abstract: Decision making often asks for classification. We will present a new R package klaR including functions to build, check, tune, visualize, and compare classification rules. The software is illustrated by means of a case study of prediction of the German economy’s business cycle phases.

Cofactor regeneration at the lab scale.

Abstract: Progress made in lab-scale applications of various coenzyme regeneration systems over the last two decades has mainly focused on the applications of NAD+/NADH- and NADP+/NADPH-dependent oxidoreductase reactions. In situ regeneration systems for these reactions, as well as whole cell, enzymatic, electro-enzymatic, chemical, and photochemical reactions are presented, including details about their efficiency and novelty. The progress of enzyme reaction engineering is also reported.

Sequential parameter optimization

Abstract: Sequential parameter optimization is a heuristic that combines classical and modern statistical techniques to improve the performance of search algorithms. To demonstrate its flexibility, three scenarios are discussed: (1) no experience how to choose the parameter setting of an algorithm is available, (2) a comparison with other algorithms is needed, and (3) an optimization algorithm has to be applied effectively and efficiently to a complex real-world optimization problem. Although sequential parameter optimization relies on enhanced statistical techniques such as design and analysis of computer experiments, it can be performed algorithmically and requires basically the specification of the relevant algorithm's parameters

On the Choice of the Offspring Population Size in Evolutionary Algorithms

Abstract: Evolutionary algorithms (EAs) generally come with a large number of parameters that have to be set before the algorithm can be used. Finding appropriate settings is a difficult task. The influence of these parameters on the efficiency of the search performed by an evolutionary algorithm can be very high. But there is still a lack of theoretically justified guidelines to help the practitioner find good values for these parameters. One such parameter is the offspring population size. Using a simplified but still realistic evolutionary algorithm, a thorough analysis of the effects of the offspring population size is presented. The result is a much better understanding of the role of offspring population size in an EA and suggests a simple way to dynamically adapt this parameter when necessary.

Modeling of aqueous electrolyte solutions with perturbed-chain statistical associated fluid theory

Abstract: The vapor pressures and liquid densities of single-salt electrolyte solutions containing NaCl, LiCl, KCl, NaBr, LiBr, KBr, NaI, LiI, KI, Li2SO4, Na2SO4, and K2SO4 were modeled with an equation of state based on perturbed-chain statistical associated fluid theory (PC-SAFT). The PC-SAFT model was extended to charged compounds using a Debye−Huckel term for the electrostatic interactions. Two model parameters for each ion were fitted to experimental pVT and vapor-pressure data. The model is able to excellently reproduce the experimental data up to high salt molalities and even to predict vapor pressures in mixed-salt solutions.

Monitoring Structural Change in Dynamic Econometric Models

Abstract: The classical approach to testing for structural change employs retrospective tests using a historical data set of a given length. Here we consider a wide array of fluctuation-type tests in a monitoring situation - given a history period for which a regression relationship is known to be stable, we test whether incoming data are consistent with the previously established relationship. Procedures based on estimates of the regression coefficients are extended in three directions: we introduce (a) procedures based on OLS residuals, (b) rescaled statistics and (c) alternative asymptotic boundaries. Compared to the existing tests our extensions offer better power against certain alternatives, improved size in finite samples for dynamic models and ease of computation respectively. We apply our methods to two data sets, German M1 money demand and U.S. labor productivity.

Dispersive estimates for principally normal pseudodifferential operators

Abstract: The aim of these notes is to describe some recent re- sults concerning dispersive estimates for principally normal pseu- dodifferential operators. The main motivation for this comes from unique continuation problems. Such estimates can be used to prove L q Carleman inequalities, which in turn yield unique continuation results for various partial differential operators with rough poten- tials. Dispersive estimates are L q estimates for nonelliptic partial differ- ential operators which are a consequence of the decay properties of their fundamental solutions. These decay properties follow from spa- tial spreading of the singularities of the solutions. Since solutions prop- agate in directions conormal to the characteristic set of the operator, this spreading can be related to nonzero curvatures of the characteristic set. Dispersive estimates for constant coefficient operators are closely related to the restriction theorem in harmonic analysis. Various types of dispersive estimates are known to be true for op- erators such as the wave operator, the Schrodinger operator and the linear KdV, see Ginibre-Velo (4), Keel-Tao (11). They have proved to be useful in the study of nonlinear problems, as well as of problems with unbounded potentials. More recently, similar estimates have been obtained for wave op- erators with variable coefficients, beginning with the smooth case in Kapitanskii (10), Mockenhaupt, Seeger and Sogge (14), up to operators with C 2 coefficients in Smith (15) and Tataru (21), (23). Similar results were obtained for the Schrodinger equation in Staffilani-Tataru (19) (C 2 coefficients) and in Burq-Gerard-Tzvetkov (1) (smooth coeffic ients). In the variable coefficient elliptic case one should also mention Sogge's L q

How the Liquid-Liquid Transition Affects Hydrophobic Hydration in Deeply Supercooled Water

Abstract: We determine the phase diagram of liquid supercooled water by extensive computer simulations using the TIP5P-E model [J. Chem. Phys. 120, 6085 (2004)]. We find that the transformation of water into a low density liquid in the supercooled range strongly enhances the solubility of hydrophobic particles. The transformation of water into a tetrahedrally structured liquid is accompanied by a minimum in the hydration entropy and enthalpy. The corresponding change in sign of the solvation heat capacity indicates a loss of one characteristic signature of hydrophobic hydration. The observed behavior is found to be qualitatively in accordance with the predictions of the information theory model of Garde et al. [Phys. Rev. Lett. 77, 4966 (1996)].

Spin chains as perfect quantum state mirrors

Abstract: Quantum information transfer is an important part of quantum information processing. Several proposals for quantum information transfer along linear arrays of nearest-neighbor coupled qubits or spins were made recently. Perfect transfer was shown to exist in two models with specifically designed strongly inhomogeneous couplings. We show that perfect transfer occurs in an entire class of chains, including systems whose nearest-neighbor couplings vary only weakly along the chain. The key to these observations is the Jordan-Wigner mapping of spins to noninteracting lattice fermions that display perfectly periodic dynamics if the single-particle energy spectrum is appropriate. After a half-period of that dynamics, any state is transformed into its mirror image with respect to the center of the chain. The absence of fermion interactions preserves these features at an arbitrary temperature and allows for the transfer of nontrivially entangled states of several spins or qubits.

The deterministic part of IPC-4: an overview

Abstract: We provide an overview of the organization and results of the deterministic part of the 4th International Planning Competition, i.e., of the part concerned with evaluating systems doing deterministic planning. IPC-4 attracted even more competing systems than its already large predecessors, and the competition event was revised in several important respects. After giving an introduction to the IPC, we briefly explain the main differences between the deterministic part of IPC-4 and its predecessors. We then introduce formally the language used, called PDDL2.2 that extends PDDL2.1 by derived predicates and timed initial literals. We list the competing systems and overview the results of the competition. The entire set of data is far too large to be presented in full. We provide a detailed summary; the complete data is available in an online appendix. We explain how we awarded the competition prizes.

Superradiance and subradiance in an inhomogeneously broadened ensemble of two-level systems coupled to a low-Q cavity.

Abstract: The collective spontaneous emission of a fully inverted inhomogeneously broadened ensemble of $N$ two-level systems coupled to a single-mode low-$Q$ cavity is investigated numerically using Monte Carlo wave function technique. An intrinsically bi-exponential emission dynamics is found when the time scales of superradiance ${\ensuremath{\tau}}_{\mathrm{sr}}$ and inhomogeneous dephasing ${T}_{2}^{*}\ensuremath{\sim}1/\ensuremath{\Delta}{\ensuremath{\omega}}_{\mathrm{inh}}$ become comparable: a fast superradiant is followed by a slow subradiant decay. Experimental configurations using ensembles of quantum dots coupled to optical microcavities are proposed as possible candidates to observe the combined superradiant and subradiant energy relaxation.

Networked Transport of RTCM via Internet Protocol (NTRIP)

Abstract: Within the framework of EUREF, the Federal Agency for Cartography and Geodesy (BKG) has developed a new technique using the open Internet for the real-time collection and exchange of GNSS data, as well as for broadcasting derived products. A major purpose of these activities is the dissemination of Differential GPS corrections (DGPS) for precise positioning and navigation. This paper describes the http-based technique for streaming GNSS data to mobile users connected to the Internet via Mobile IP-Networks like GSM, GPRS, EDGE, or UMTS. The technique establishes a format called Networked Transport of RTCM via Internet Protocol (Ntrip).

Exciton dephasing via phonon interactions in InAs quantum dots: dependence on quantum confinement

Abstract: We report systematic measurements of the dephasing of the excitonic ground-state transition in a series of InGaAs?GaAs quantum dots having different quantum confinement potentials. Using a highly sensitive four-wave mixing technique, we measure the polarization decay in the temperature range from 5 to 120 K on nine samples having the energy distance from the dot ground-state transition to the wetting layer continuum (confinement energy) tuned from 332 to 69 meV by thermal annealing. The width and the weight of the zero-phonon line in the homogeneous line shape are inferred from the measured polarization decay and are discussed within the framework of recent theoretical models of the exciton-acoustic phonon interaction in quantum dots. The weight of the zero-phonon line is found to decrease with increasing lattice temperature and confinement energy, consistently with theoretical predictions by the independent Boson model. The temperature-dependent width of the zero-phonon line is well reproduced by a thermally activated behavior having two constant activation energies of 6 and 28 meV, independent of confinement energy. Only the coefficient to the 6-meV activation energy shows a systematic increase with increasing confinement energy. These findings rule out that the process of one-phonon absorption from the excitonic ground state into higher energy states is the underlying dephasing mechanism.

High-loading polyglycerol supported reagents for Mitsunobu- and acylation-reactions and other useful polyglycerol derivatives.

Abstract: In this paper we present soluble dendritic polyglycerol (PG) supported reagents PG-DEAD, PG-PPh3, and PG-DCC as well as scavengers PG-carbonate, PG-carbazate, and PG-amine, which all have been synthesized in high overall conversions and yields using simple purification techniques. The supported reagents have been used simultaneously in Mitsunobu and acylation reactions. All polymeric reagents and scavengers can be removed by simple precipitation/filtration protocols to give chromatography-free products of high purity. In the course of the syntheses of the polymeric reagents three intermediates turned out to be precious polyglycerol derivatives: a mixed carbonate as an electrophilic derivative, polyglyceryl carbazate as a scavenger for carbonyl compounds, as well as polyglycerylamines as amino analogues of polyglycerol.

Regular symbolic analysis of dynamic networks of pushdown systems

Abstract: We introduce two abstract models for multithreaded programs based on dynamic networks of pushdown systems. We address the problem of symbolic reachability analysis for these models. More precisely, we consider the problem of computing effective representations of their reachability sets using finite-state automata. We show that, while forward reachability sets are not regular in general, backward reachability sets starting from regular sets of configurations are always regular. We provide algorithms for computing backward reachability sets using word/tree automata, and show how these algorithms can be applied for flow analysis of multithreaded programs.

Exciton fine structure in single CdSe nanorods.

Abstract: We study the optical properties of excitons in one-dimensional (1D) nanostructures at low temperatures. In single $\mathrm{C}\mathrm{d}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}$ core-shell nanorods we observe a fine structure splitting and explain it by exchange interaction. Two peaks are observed with different degrees of linear polarization of $\mathrm{D}\mathrm{L}\mathrm{P}l0.85$ and $\mathrm{D}\mathrm{L}\mathrm{P}g0.95$. For small nanorod radii $R\ensuremath{\le}{a}_{\mathrm{B}}/2$, an increase in the photoluminescence decay time is found when the temperature increases from 10 to 80 K. The observations are explained by a radius-dependent change in the symmetry of the 1D-exciton ground state which transforms from a dark state into bright states below a critical radius of ${R}_{\mathrm{c}\mathrm{r}\mathrm{i}\mathrm{t}}\ensuremath{\approx}3.7\text{ }\text{ }\mathrm{n}\mathrm{m}$.

Crossover is provably essential for the Ising model on trees

Abstract: Due to experimental evidence it is incontestable that crossover is essential for some fitness functions. However, theoretical results without assumptions are difficult. So-called real royal road functions are known where crossover is proved to be essential, i.e., mutation-based algorithms have an exponential expected runtime while the expected runtime of a genetic algorithm is polynomially bounded. However, these functions are artificial and have been designed in such a way that crossover is essential only at the very end (or at other well-specified points) of the optimization process.Here, a more natural fitness function based on a generalized Ising model is presented where crossover is essential throughout the whole optimization process. Mutation-based algorithms such as (μ+λ) EAs with constant population size are proved to have an exponential expected runtime while the expected runtime of a simple genetic algorithm with population size 2 and fitness sharing is polynomially bounded.

Experimental demonstration of efficient and selective population transfer and qubit distillation in a rare-earth-metal-ion-doped crystal

Abstract: In optically controlled quantum computers it may be favorable to address different qubits using light with different frequencies, since the optical diffraction does not then limit the distance between qubits. Using qubits that are close to each other enables qubit-qubit interactions and gate operations that are strong and fast in comparison to qubit-environment interactions and decoherence rates. However, as qubits are addressed in frequency space, great care has to be taken when designing the laser pulses, so that they perform the desired operation on one qubit, without affecting other qubits. Complex hyperbolic secant pulses have theoretically been shown to be excellent for such frequency-addressed quantum computing [I. Roos and K. Molmer, Phys. Rev. A 69, 022321 (2004)]-e.g., for use in quantum computers based on optical interactions in rare-earth-metal-ion- doped crystals. The optical transition lines of the rare-earth-metal-ions are inhomogeneously broadened and therefore the frequency of the excitation pulses can be used to selectively address qubit ions that are spatially separated by a distance much less than a wavelength. Here, frequency-selective transfer of qubit ions between qubit states using complex hyperbolic secant pulses is experimentally demonstrated. Transfer efficiencies better than 90% were obtained. Using the complex hyperbolic secant pulses it was also possible to create two groups of ions, absorbing at specific frequencies, where 85% of the ions at one of the frequencies was shifted out of resonance with the field when ions in the other frequency group were excited. This procedure of selecting interacting ions, called qubit distillation, was carried out in preparation for two-qubit gate operations in the rare-earth-metal-ion-doped crystals. The techniques for frequency-selective state-to-state transfer developed here may be also useful also for other quantum optics and quantum information experiments in these long-coherence-time solid-state systems. (Less)

On the correspondence between conformance testing and regular inference

Abstract: Conformance testing for finite state machines and regular inference both aim at identifying the model structure underlying a black box system on the basis of a limited set of observations. Whereas the former technique checks for equivalence with a given conjecture model, the latter techniques addresses the corresponding synthesis problem by means of techniques adopted from automata learning. In this paper we establish a common framework to investigate the similarities of these techniques by showing how results in one area can be transferred to results in the other and to explain the reasons for their differences.