Showing papers by "Technical University of Dortmund published in 2002"

Finite-time Analysis of the Multiarmed Bandit Problem

Abstract: Reinforcement learning policies face the exploration versus exploitation dilemma, i.e. the search for a balance between exploring the environment to find profitable actions while taking the empirically best action as often as possible. A popular measure of a policy's success in addressing this dilemma is the regret, that is the loss due to the fact that the globally optimal policy is not followed all the times. One of the simplest examples of the exploration/exploitation dilemma is the multi-armed bandit problem. Lai and Robbins were the first ones to show that the regret for this problem has to grow at least logarithmically in the number of plays. Since then, policies which asymptotically achieve this regret have been devised by Lai and Robbins and many others. In this work we show that the optimal logarithmic regret is also achievable uniformly over time, with simple and efficient policies, and for all reward distributions with bounded support.

Observation of coupled magnetic and electric domains

Abstract: Ferroelectromagnets are an interesting group of compounds that complement purely (anti-)ferroelectric or (anti-)ferromagnetic materials--they display simultaneous electric and magnetic order. With this coexistence they supplement materials in which magnetization can be induced by an electric field and electrical polarization by a magnetic field, a property which is termed the magnetoelectric effect. Aside from its fundamental importance, the mutual control of electric and magnetic properties is of significant interest for applications in magnetic storage media and 'spintronics'. The coupled electric and magnetic ordering in ferroelectromagnets is accompanied by the formation of domains and domain walls. However, such a cross-correlation between magnetic and electric domains has so far not been observed. Here we report spatial maps of coupled antiferromagnetic and ferroelectric domains in YMnO3, obtained by imaging with optical second harmonic generation. The coupling originates from an interaction between magnetic and electric domain walls, which leads to a configuration that is dominated by the ferroelectromagnetic product of the order parameters.

Testing and dating of structural changes in practice

Abstract: The paper presents an approach to the analysis of data that contains (multiple) structural changes in a linear regression setup. We implement various strategies which have been suggested in the literature for testing against structural changes as well as a dynamic programming algorithm for the dating of the breakpoints in the R statistical software package. Using historical data on Nile river discharges, road casualties in Great Britain and oil prices in Germany it is shown that changes in the mean of a time series as well as in the coefficients of a linear regression are easily matched with identifiable historical, political or economic events.

On the existence of soliton solutions to quasilinear Schrödinger equations

Abstract: Variational techniques are applied to prove the existence of standing wave solutions for quasilinear Schrodinger equations containing strongly singular nonlinearities which include derivatives of the second order. Such equations have been derived as models of several physical phenomena. The nonlinearity here corresponds to the superfluid film equation in plasma physics. Direct methods of the calculus of variations and minimax methods like the Mountain Pass Theorem are used. The difficulties introduced by the nonconvex functional \(\Phi(u)=\int | abla u|^2 u^2\) are substantially different from the semilinear case.

The building stock as a research object

Abstract: Activities related to refurbishment of the building stock as a percentage of all building work have been constantly growing in most central European countries over the last 20 years. The main argument in this paper is the need to improve knowledge about composition of the existing building stock, the dynamics of its transformation and to relate this to the different actors in property professions. A review is presented of traditional and new sectoral research approaches to partial or national building stocks to provide a context for assessing an integrated approach to the German building stock with methodological propositions for improving the synergy between different sectoral approaches. Detailed consideration is given to life cycle analysis, building product modelling, historical building research and new simulation techniques. Sustainability indicators and the integration of building stock, infrastructure and land use are discussed. Depuis une vingtaine d'annees, les activites liees a la rehabilitatio...

Inhibition-related ERP components: Variation with modality, age, and time-on-task.

Abstract: In Go/Nogo tasks, the ERP after Nogo stimuli generally reveals a negativity (Nogo-)N2 and a subsequent positivity (Nogo-)P3 over fronto-central scalp regions. These components are probably related to different subprocesses serving response inhibition, namely, modality-specific and general inhibition, respectively. In the present study we investigate whether aging or prolonged work (“time-on-task”) have an effect on N2 and P3. Twelve young and 12 elderly subjects performed simple Go/Nogo tasks to visual or auditory letter stimuli. Reaction times were longer after visual than after auditory stimuli, and longer in the elderly than in the young. The ERP results reveal a slight impairment of modality-specific inhibition (N2) in the elderly after visual, but not after auditory, stimuli. General inhibition (P3) was delayed in the elderly for both modalities, as was Go-P3 and RT. Hence, it appears that the response slowing of the elderly is the result of a slowing of the decision process whether to respo...

Rabi oscillations in the excitonic ground-state transition of InGaAs quantum dots

Abstract: We present measurements and calculations of optical Rabi oscillations in the excitonic ground-state transition of an InGaAs quantum dot ensemble at low temperature. Rabi oscillations which are damped versus pulse area and change period when changing pulse duration are observed. Comparisons with calculations show that the observed damping is not intrinsic to a single dot. Dephasing processes and the biexciton resonance change the amplitude and the period of the oscillations, respectively, while the damping versus pulse area is due to a distribution of transition dipole moments in the ensemble.

Noisy Optimization With Evolution Strategies

Abstract: Foreword. Acknowledgments. 1. Introduction. 2. Preliminaries. 3. The (1+1)-ES: Overvaluation. 4. The (mu, lambda)-ES: Distributed Populations. 5. The (mu/mu, lambda-ES: Genetic Repair. 6. Comparing Approaches to Noisy Optimization. 7. Conclusions. Appendices. A. Some Statistical Basics. B. Some Useful Identities. C. Computing the Overvaluation. D. Determining the Effects of Sampling and Selection. References. Index.

Nanomechanical Devices Based on DNA

Abstract: Biomolecular compounds, such as proteins and nucleic acids, which are evolutionary optimized, with respect to specificity of binding to their target structure as well as to functionality, for distinct biochemical transformation and translocation, are currently explored as building blocks in the ™bottom-up∫ self-assembly of nanometer-scale functional devices. [1] So far, applications include the organization of metal and semiconductor nanoclusters, [2] numerous bioana-lytical techniques, [1] as well as biomolecular electronics [3] and nanomechanical devices. While the development of the latter was, in past years, mainly focused on motor proteins, such as actin, kinesin, and myosin, [4] nowadays an increasing number of reports are being devoted to the construction of nano-mechanical devices from DNA. This biomolecule plays an outstanding role in the development of artificial biomolecular hybrid elements, since the specificity of simple AT and G-C base pairing as well as its robust physicochemical nature allows for the fabrication of nanostructured molecular scaffolding and surface architecture, [5] and to selectively position proteins, [6] inorganic colloidal components, [2] carbohydrates , [7] organometallics, [8] and reactive chemical compounds [9] on the nanometer length scale. Another interesting property of the DNA double helix is its intrinsic susceptibility to external stimuli mediated by small molecules or ions, which opens up ways to fabricate nano-mechanical devices. For example, the contour length and the flexibility of a DNA molecule can be effectively altered by use of intercalators, such as acridinium or ethidium bromide derivatives, which bind in between the stacked nucleobases of the double helix and thereby significantly increase the DNA contour length. [10] Seeman and co-workers made use of this phenomenon: They reported on the induced change in torque of a circular DNA molecule containing a partially mobile branched DNA junction on intercalation of ethidium bromide as a potential supercoiling motion for nanomechanical elements. More recently, the Seeman group established an elegant means to utilize electrostatic interaction of Co 3‡ ions for switching a DNA device comprised of two rigid DNA double-crossover motifs. The latter were covalently linked to each other by a short d(CG) 10 proto-Z sequence which is capable of changing its conformation from a right-handed B-to a left-handed Z-DNA double helix (Figure 1 A). [12] The conforma-tional change leads to a spatial separation of two fluorescent labels, attached to each of the two double-crossover moieties, which can be measured by fluorescence resonance energy transfer (FRET). In a different approach, the increase in concentration of …

A distributed search service for peer-to-peer file sharing in mobile applications

Abstract: In this paper, we present the concept of passive distributed indexing, a general-purpose distributed search service for mobile file sharing applications, which is based on peer-to-peer technology. The service enables resource-effective searching for files distributed across mobile devices based on simple queries. Building blocks of PDI constitute local broadcast transmission of query- and response messages, together with caching of query results at every device participating in PDI. Based on these building blocks, the need for flooding the entire network with query messages can be eliminated for most application. In extensive simulation studies, we demonstrate the performance of PDI. Because the requirements of a typical mobile file sharing application are not known-or even do not exist at all-we study the performance of PDI for different system environments and application requirements. We show that due to the flexible design PDI can be employed for several kinds of applications.

Neutrino interactions in oscillation experiments

Abstract: We calculate the neutrino induced cross sections relevant for oscillation experiments, including the $\ensuremath{\tau}$-lepton threshold for quasielastic, resonance and deep-inelastic scattering. In addition to threshold effects, we include nuclear corrections for heavy targets which are moderate for quasielastic and large for single pion production. The nuclear effects for deep-inelastic reactions are small. We present cross sections together with their nuclear corrections for various channels which are useful for interpreting the experimental results and for determining parameters of the neutrino sector. Finally, we calculate the $\ensuremath{\tau}$-lepton event rates for the OPERA LBL experiment.

Reducing energy consumption by dynamic copying of instructions onto onchip memory

Abstract: The number of mobile embedded systems is increasing and all of them are limited in their uptime by their battery capacity. Several hardware changes have been introduced during the last years, but the steadily growing functionality still requires further energy reductions, e.g. through software optimizations. A significant amount of energy can be saved in the memory hierarchy where most of the energy is consumed. In this paper, a new software technique is presented which supports the use of an onchip scratchpad memory by dynamically copying program parts into it. The set of selected program parts are determined with an optimal algorithm using integer linear programming. Experimental results show a reduction of the energy consumption by nearly 30%, a performance increase by 25% against a common cache system and energy improvements against a static approach of up to 38%.

Effects of Pressure-Induced Membrane Phase Transitions on Inactivation of HorA, an ATP-Dependent Multidrug Resistance Transporter, in Lactobacillus plantarum

Abstract: The effects of pressure on cultures of Lactobacillus plantarum were characterized by determination of the viability and activity of HorA, an ATP-binding cassette multidrug resistance transporter. Changes in the membrane composition of L. plantarum induced by different growth temperatures were determined. Furthermore, the effect of the growth temperature of a culture on pressure inactivation at 200 MPa was determined. Cells were characterized by plate counts on selective and nonselective agar after pressure treatment, and HorA activity was measured by ethidium bromide efflux. Fourier transform-infrared spectroscopy and Laurdan fluorescence spectroscopy provided information about the thermodynamic phase state of the cytoplasmic membrane during pressure treatment. A pressure-temperature diagram for cell membranes was established. Cells grown at 37°C and pressure treated at 15°C lost >99% of HorA activity and viable cell counts within 36 and 120 min, respectively. The membranes of these cells were in the gel phase region at ambient pressure. In contrast, cells grown at 15°C and pressure treated at 37°C lost >99% of HorA activity and viable cell counts within 4 and 8 min, respectively. The membranes of these cells were in the liquid crystalline phase region at ambient pressure. The kinetic analysis of inactivation of L. plantarum provided further evidence that inactivation of HorA is a crucial step during pressure-induced cell death. Comparison of the biological findings and the membrane state during pressure treatment led to the conclusion that the inactivation of cells and membrane enzymes strongly depends on the thermodynamic properties of the membrane. Pressure treatment of cells with a liquid crystalline membrane at 0.1 MPa resulted in HorA inactivation and cell death more rapid than those of cells with a gel phase membrane at 0.1 MPa.

Tuning PSO Parameters Through Sensitivity Analysis

Abstract: In this paper, a first analysis of the Particle Swarm Optimization (PSO) method’s parameters, using Design of Experiments (DOE) techniques, is performed, and important settings as well as interactions among the parameters, are investigated (screening).

Local performance of the (1 + 1)-ES in a noisy environment

Abstract: While noise is a phenomenon present in many real world optimization problems, the understanding of its potential effects on the performance of evolutionary algorithms is still incomplete. This paper investigates the effects of fitness proportionate Gaussian noise for a (1 + 1)-ES with isotropic normal mutations on the quadratic sphere in the limit of infinite search-space dimensionality. It is demonstrated experimentally that the results provide a good approximation for finite space dimensionality. It is shown that overvaluation as a result of failure to re-evaluate parental fitness leads to both reduced success probabilities and improved performance. Implications for mutation strength adaptation rules are discussed and optimal re-sampling rates are computed.

Die Skalen zum akademischen Selbstkonzept : Konstruktion und Überprüfung eines neuen Instrumentes

Abstract: Wenn Personen Urteile uber ihre eigenen Fahigkeiten abgeben, dann tun sie dies entweder, ohne ausdrucklich Vergleiche vorzunehmen, oder sie verwenden dabei soziale, individuelle und kriterienbezogene Bezugsnormen. In Fragebogen zur Erfassung des akademischen Selbstkonzepts werden jedoch diese Vergleichsarten entweder gar nicht oder nicht in ausgewogener Weise thematisiert. Da die Verwendung unterschiedlicher Bezugsnormen zur Beurteilung eigener Fahigkeiten sowohl entwicklungspsychologisch als auch aus Sicht der Leistungsmotivationsforschung von grosem Interesse ist, wird ein Instrument zum akademischen Selbstkonzept vorgestellt, in dem die drei Bezugsnormen systematisch berucksichtigt werden. In drei Studien wird ein Fragebogen entwickelt und uberpruft, der Fahigkeitsurteile absolut (d.h. ohne Vergleich), sozial, individuell und kriterienbezogen erfasst. Die entwickelten Skalen (in einer Version fur Schuler der Stufen 5 bis 10 und in einer Version fur Studenten) weisen mit .74 bis .92 akzeptable bis gute Re-liabilitaten auf. Die drei Skalen, in denen Bezugsnormen thematisiert werden, konnen faktorenanalytisch identifiziert werden. Korrelationen mit anderen Selbstkonzeptfragebogen, Selbstwirksamkeitserwartung, dem Leistungsmotiv, Prufungsangst und Leistung weisen auf die konvergente und diskriminante Validitat des Verfahrens hin.

Biological availability of traffic-related platinum-group elements (palladium, platinum, and rhodium) and other metals to the zebra mussel (Dreissena polymorpha) in water containing road dust.

Abstract: The uptake and bioaccumulation of 15 road dust metals by the zebra mussel (Dreissena polymorpha) were investigated in laboratory exposure studies with emphasis on the traffic-related platinum-group elements (PGEs) palladium (Pd), platinum (Pt), and rhodium (Rh). The biological availability of the metals may depend on water characteristics, so the mussels were maintained in two types of water: nonchlorinated tap water and humic water of a bog lake, both of which contained dust of a moderately frequented road. After an exposure period of 26 weeks, soft tissues of the mussels were freeze-dried and analyzed for the metals. The metal concentrations in the mussel soft tissue ranged from several hundred micrograms per gram (e.g., for iron [Fe]) to less than 10 ng/g (for PGEs). Metal uptake from the road dust by the mussels was found for the PGEs and silver (Ag), bismuth (Bi), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), Fe, lead (Pb), and antimony (Sb). After maintenance of mussels in road dust-contaminated tap water, bioaccumulation factors (BAF = (c e x p o s e d m u s s e l s - c c o n t r o l m u s s e l s )/c t o t a l m e t a l , w a t e r ; where c is concentration) decreased in the following order: Cu > Cd > Ag > Pd > Sb > Pb > Fe > Pt > Rh. The biological availability of most metals was enhanced by humic water as compared to tap water. Our results show a hitherto unrecognized high availability of Pd for the mussels. Thus, this metal should be monitored more intensively in the environment to assess its distribution in the biosphere.

A Probabilistic 3-SAT Algorithm Further Improved

Abstract: In [Sch99], Schoning proposed a simple yet efficient randomized algorithm for solving the k-SAT problem. In the case of 3-SAT, the algorithm has an expected running time of poly(n) ? (4/3)n = O(1.3334n) when given a formula F on n variables. This was the up to now best running time known for an algorithm solving 3-SAT. Here, we describe an algorithm which improves upon this time bound by combining an improved version of the above randomized algorithm with other randomized algorithms. Our new expected time bound for 3-SAT is O(1.3302n).

A probabilistic 3-SAT algorithm further improved

Abstract: In [Sch99], Schoning proposed a simple yet efficient randomized algorithm for solving the k-SAT problem. In the case of 3-SAT, the algorithm has an expected running time of poly(n).( (4/3) n = O(1.3334 n ) when given a formula F on n variables. This was the up to now best running time known for an algorithm solving 3-SAT. Here, we describe an algorithm which improves upon this time bound by combining an improved version of the above randomized algorithm with other randomized algorithms. Our new expected time bound for 3-SAT is O(1.3302 n ).

Enhancement of the chemoprotective enzymes glucuronosyl transferase and glutathione transferase in specific organs of the rat by the coffee components kahweol and cafestol

Abstract: The coffee components kahweol and cafestol (K/C) have been reported to protect the colon and other organs of the rat against the formation of DNA adducts by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and aflatoxin B1. PhIP is a cooked-food mutagen to which significant human exposure and a role in colon cancer etiology are attributed, and, interestingly, such cancers appear to develop at a lower rate in consumers of coffees with high amounts of K/C. Earlier studies in rodent liver have shown that a key role in the chemopreventive effect of K/C is likely to be due to the potential of these compounds to induce the detoxification of xenobiotics by glutathione transferase (GST) and to enhance the synthesis of the corresponding co-factor glutathione. However, mutagens like PhIP may also be detoxified by UDP-glucuronosyl transferase (UDPGT) for which data are lacking regarding a potential effect of K/C. Therefore, in the present study, we investigated the effect of K/C on UDPGT and, concomitantly, we studied overall GST and the pattern of individual GST classes, particularly GST-θ, which was not included in earlier experiments. In addition, we analyzed the organ-dependence of these potentially chemopreventive effects. K/C was fed to male F344 rats at 0.122% in the chow for 10 days. Enzyme activities in liver, kidney, lung, colon, salivary gland, pancreas, testis, heart and spleen were quantified using five characteristic substrates and the hepatic protein pattern of GST classes α, µ, and π was studied with affinity chromatography/HPLC. Our study showed that K/C is not only capable of increasing overall GST and GST classes α, µ, and π but also of enhancing UDGPT and GST-θ. All investigated K/C effects were strongest in liver and kidney, and some response was seen in lung and colon but none in the other organs. In summary, our results show that K/C treatment leads to a wide spectrum of increases in phase II detoxification enzymes. Notably, these effects occurred preferentially in the well perfused organs liver and kidney, which may thus not only contribute to local protection but also to anti-carcinogenesis in distant, less stimulated organs such as the colon.

Scalable architecture for spin-based quantum computers with a single type of gate

Abstract: We propose a scalable design for a solid-state spin-based quantum computer. It uses endohedral fullerenes like $\mathrm{N}@{\mathrm{C}}_{60}$ or $\mathrm{P}@{\mathrm{C}}_{60},$ which can be positioned on Si surfaces with a scanning tunneling microscope. Each logical qubit is stored in two physical qubits, corresponding to the nuclear and electronic spins. We discuss the addressing of individual qubits by a magnetic field gradient, and the implementation of one- and two-qubit quantum gates by sequences of radio-frequency and microwave pulses.

Rigidity of Coxeter Groups and Artin Groups

Abstract: A Coxeter group is rigid if it cannot be defined by two nonisomorphic diagrams. There have been a number of recent results showing that various classes of Coxeter groups are rigid, and a particularly interesting example of a nonrigid Coxeter group has been given by Bernhard Muhlherr. We show that this example belongs to a general operation of ‘diagram twisting’. We show that the Coxeter groups defined by twisted diagrams are isomorphic, and, moreover, that the Artin groups they define are also isomorphic, thus answering a question posed by Charney. Finally, we show a number of Coxeter groups are reflection rigid once twisting is taken into account.