Showing papers by "Technical University of Berlin published in 2003"

Reducing the time complexity of the derandomized evolution strategy with covariance matrix adaptation (CMA-ES)

Abstract: This paper presents a novel evolutionary optimization strategy based on the derandomized evolution strategy with covariance matrix adaptation (CMA-ES). This new approach is intended to reduce the number of generations required for convergence to the optimum. Reducing the number of generations, i.e., the time complexity of the algorithm, is important if a large population size is desired: (1) to reduce the effect of noise; (2) to improve global search properties; and (3) to implement the algorithm on (highly) parallel machines. Our method results in a highly parallel algorithm which scales favorably with large numbers of processors. This is accomplished by efficiently incorporating the available information from a large population, thus significantly reducing the number of generations needed to adapt the covariance matrix. The original version of the CMA-ES was designed to reliably adapt the covariance matrix in small populations but it cannot exploit large populations efficiently. Our modifications scale up the efficiency to population sizes of up to 10n, where n is the problem dimension. This method has been applied to a large number of test problems, demonstrating that in many cases the CMA-ES can be advanced from quadratic to linear time complexity.

Recent Developments in Olefin Cross-Metathesis

Abstract: Among the many types of transition-metal-catalyzed C-C bond-forming reactions, olefin metathesis has come to the fore in recent years owing to the wide range of transformations that are possible with commercially available and easily handled catalysts. Consequently, olefin metathesis is now widely considered as one of the most powerful synthetic tools in organic chemistry. Until recently the intermolecular variant of this reaction, cross-metathesis, had been neglected despite its potential. With the evolution of new catalysts, the selectivity, efficiency, and functional-group compatibility of this reaction have improved to a level that was unimaginable just a few years ago. These advances, together with a better understanding of the mechanism and catalyst-substrate interactions, have brought us to a stage where more and more researchers are employing cross-metathesis reactions in multistep procedures and in the synthesis of natural products. The recent inclusion of alkynes and hindered bicyclic olefins as viable substrates for bimolecular metathesis coupling, the discovery of enantioselective cross-metathesis and cross-metathesis in water, and the successful marriage of metathesis and solid-phase organic synthesis has further widened the scope of this versatile reaction.

A hierarchy of low-dimensional models for the transient and post-transient cylinder wake

Abstract: A hierarchy of low-dimensional Galerkin models is proposed for the viscous, incompressible flow around a circular cylinder building on the pioneering works of Stuart (1958), Deane et al. (1991), and Ma & Karniadakis (2002). The empirical Galerkin model is based on an eight-dimensional Karhunen–Loeve decomposition of a numerical simulation and incorporates a new ‘shift-mode’ representing the mean-field correction. The inclusion of the shift-mode significantly improves the resolution of the transient dynamics from the onset of vortex shedding to the periodic von Karman vortex street. In addition, the Reynolds-number dependence of the flow can be described with good accuracy. The inclusion of stability eigenmodes further enhances the accuracy of fluctuation dynamics. Mathematical and physical system reduction approaches lead to invariant-manifold and to mean-field models, respectively. The corresponding two-dimensional dynamical systems are further reduced to the Landau amplitude equation.

EvalVid – A Framework for Video Transmission and Quality Evaluation

Abstract: With EvalVid we present a complete framework and tool-set for evaluation of the quality of video transmitted over a real or simulated communication network. Besides measuring QoS parameters of the underlying network, like loss rates, delays, and jitter, we support also a subjective video quality evaluation of the received video based on the frame-by-frame PSNR calculation. The tool-set has a modular construction, making it possible to exchange both the network and the codec. We present here its application for MPEG-4 as example. EvalVid is targeted for researchers who want to evaluate their network designs or setups in terms of user perceived video quality. The tool-set is publicly available [11].

Adaptive local thresholding by verification-based multithreshold probing with application to vessel detection in retinal images

Abstract: In this paper, we propose a general framework of adaptive local thresholding based on a verification-based multithreshold probing scheme. Object hypotheses are generated by binarization using hypothetic thresholds and accepted/rejected by a verification procedure. The application-dependent verification procedure can be designed to fully utilize all relevant informations about the objects of interest. In this sense, our approach is regarded as knowledge-guided adaptive thresholding, in contrast to most algorithms known from the literature. We apply our general framework to detect vessels in retinal images. An experimental evaluation demonstrates superior performance over global thresholding and a vessel detection method recently reported in the literature. Due to its simplicity and general nature, our novel approach is expected to be applicable to a variety of other applications.

Rosseland and Planck mean opacities for protoplanetary discs

Abstract: In this paper, we present mean gas and dust opacities relevant to the physical conditions typical of protoplanetary discs. As the principal absorber for temperatures below ∼1500 K, we consider spherical and aggregate dust particles of various sizes, chemical structure, and porosity, consisting of ice, organics, troilite, silicates, and iron. For higher temperatures, ions, atoms, molecules, and electrons are included as the main opacity sources. Rosseland and Planck mean opacities are calculated for temperatures between 5 K and 10 000 K and gas densities ranging from 10 −18 gc m −3 to 10 −7 gc m −3 . The dependence on the adopted model of dust grains is investigated. We compare our results with recent opacity tables and show how different opacity models affect the calculated hydrodynamical structure of accretion discs.

Classification of Integrable Equations on Quad-Graphs. The Consistency Approach

Abstract: A classification of discrete integrable systems on quad–graphs, i.e. on surface cell decompositions with quadrilateral faces, is given. The notion of integrability laid in the basis of the classification is the three–dimensional consistency. This property yields, among other features, the existence of the discrete zero curvature representation with a spectral parameter. For all integrable systems of the obtained exhaustive list, the so called three–leg forms are found. This establishes Lagrangian and symplectic structures for these systems, and the connection to discrete systems of the Toda type on arbitrary graphs. Generalizations of these ideas to the three–dimensional integrable systems and to the quantum context are also discussed.

A Nation-Wide Laboratory: Examining Trust and Trustworthiness by Integrating Behavioral Experiments into Representative Surveys

Abstract: Die experimentelle Okonomie fuhrt typischerweise Labor-Untersuchungen durch, die mit homogenen und selektiven Versuchspersonen arbeiten. Reprasentative Surveys leiden hingegen unter Mesfehlern und der Frage, ob hypothetisches Verhalten, das erhoben wird, mit tatsachlichem Verhalten korrespondiert. Deswegen prasentieren wir eine Methode, mit der man die Schwachen beider Ansatze uberwindet, indem man Survey-Daten mit Experimenten kombiniert. Die von uns entwickelte Methode hat den Vorzug, dass sie es auf preiswerte Art und Weise erlaubt, Experimente, die die Interaktion zweier Personen erfordern, mit Standard-Surveys zu kombinieren, die auf der Unabhangigkeit der befragten Personen beruhen. Wir illustrieren die Moglichkeiten unserer Methodik mit einer Untersuchung uber Vertrauen und Vertrauenswurdigkeit in Deutschland, bei der eine reprasentative Umfrage mit einem Experiment uber eine Dilemma-Situation verbunden wurde. Unsere Resultate zeigen zum einen, dass nicht alle Survey-Fragen uber Vertrauen mit den Ergebnissen des Experiments korrelieren. Zum zweiten zeigen unsere Ergebnisse, dass altere Menschen (65 Jahre und alter), Hochqualifizierte und Personen, die in grosseren Haushalten leben, im Experiment unterdurchschnittlich Vertrauen offenbaren. Fur Auslander, Katholiken und die Anhanger der grosen Volksparteien finden wir uberdurchschnittliches Vertrauen. Vertrauenswurdigkeit bzw. Altruismus zeigen im Experiment Altere und Befragte mit gutem Gesundheitszustand. Unterdurchschnittliche Vertrauenswudigkeit bzw. Altruismus zeigen jungere Befragte (bis zu 35 Jahren), arbeitslos Gemeldete und Befragte ohne eine Parteineigung.

Understanding the differences between how novice and experienced designers approach design tasks

Abstract: Research was undertaken to understand how to provide the most appropriate support for novice designers in engineering design. However, how designers apply their experience and knowledge is not understood and further research in this area is required. This paper describes an observational study to understand how novice and experienced designers approach design tasks.

AGG: A Graph Transformation Environment for Modeling and Validation of Software

Abstract: AGG is a general development environment for algebraic graph transformation systems which follows the interpretative approach. Its special power comes from a very flexible attribution concept. AGG graphs are allowed to be attributed by any kind of Java objects. Graph transformations can be equipped with arbitrary computations on these Java objects described by a Java expression. The AGG environment consists of a graphical user interface comprising several visual editors, an interpreter, and a set of validation tools. The interpreter allows the stepwise transformation of graphs as well as rule applications as long as possible. AGG supports several kinds of validations which comprise graph parsing, consistency checking of graphs and conflict detection in concurrent transformations by critical pair analysis of graph rules. Applications of AGG include graph and rule-based modeling of software, validation of system properties by assigning a graph transformation based semantics to some system model, graph transformation based evolution of software, and the definition of visual languages based on graph grammars.

Super-peer-based routing and clustering strategies for RDF-based peer-to-peer networks

Abstract: RDF-based P2P networks have a number of advantages compared with simpler P2P networks such as Napster, Gnutella or with approaches based on distributed indices such as CAN and CHORD. RDF-based P2P networks allow complex and extendable descriptions of resources instead of fixed and limited ones, and they provide complex query facilities against these metadata instead of simple keyword-based searches.In previous papers, we have described the Edutella infrastructure and different kinds of Edutella peers implementing such an RDF-based P2P network. In this paper we will discuss these RDF-based P2P networks as a specific example of a new type of P2P networks, schema-based P2P networks, and describe the use of super-peer based topologies for these networks. Super-peer based networks can provide better scalability than broadcast based networks, and do provide perfect support for inhomogeneous schema-based networks, which support different metadata schemas and ontologies (crucial for the Semantic Web). Furthermore, as we will show in this paper, they are able to support sophisticated routing and clustering strategies based on the metadata schemas, attributes and ontologies used. Especially helpful in this context is the RDF functionality to uniquely identify schemas, attributes and ontologies. The resulting routing indices can be built using dynamic frequency counting algorithms and support local mediation and transformation rules, and we will sketch some first ideas for implementing these advanced functionalities as well.

Microcystin Biosynthesis in Planktothrix: Genes, Evolution, and Manipulation

Abstract: Microcystins represent an extraordinarily large family of cyclic heptapeptide toxins that are nonribosomally synthesized by various cyanobacteria. Microcystins specifically inhibit the eukaryotic protein phosphatases 1 and 2A. Their outstanding variability makes them particularly useful for studies on the evolution of structure-function relationships in peptide synthetases and their genes. Analyses of microcystin synthetase genes provide valuable clues for the potential and limits of combinatorial biosynthesis. We have sequenced and analyzed 55.6 kb of the potential microcystin synthetase gene (mcy) cluster from the filamentous cyanobacterium Planktothrix agardhii CYA 126. The cluster contains genes for peptide synthetases (mcyABC), polyketide synthases (PKSs; mcyD), chimeric enzymes composed of peptide synthetase and PKS modules (mcyEG), a putative thioesterase (mcyT), a putative ABC transporter (mcyH), and a putative peptide-modifying enzyme (mcyJ). The gene content and arrangement and the sequence of specific domains in the gene products differ from those of the mcy cluster in Microcystis, a unicellular cyanobacterium. The data suggest an evolution of mcy clusters from, rather than to, genes for nodularin (a related pentapeptide) biosynthesis. Our data do not support the idea of horizontal gene transfer of complete mcy gene clusters between the genera. We have established a protocol for stable genetic transformation of Planktothrix, a genus that is characterized by multicellular filaments exhibiting continuous motility. Targeted mutation of mcyJ revealed its function as a gene coding for a O-methyltransferase. The mutant cells produce a novel microcystin variant exhibiting reduced inhibitory activity toward protein phosphatases.

Reductive dehalogenation of chlorinated dioxins by an anaerobic bacterium

Abstract: Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs and PCDFs) are among the most notorious environmental pollutants. Some congeners, particularly those with lateral chlorine substitutions at positions 2, 3, 7 and 8, are extremely toxic and carcinogenic to humans. One particularly promising mechanism for the detoxification of PCDDs and PCDFs is microbial reductive dechlorination. So far only a limited number of phylogenetically diverse anaerobic bacteria have been found that couple the reductive dehalogenation of chlorinated compounds--the substitution of a chlorine for a hydrogen atom--to energy conservation and growth in a process called dehalorespiration. Microbial dechlorination of PCDDs occurs in sediments and anaerobic mixed cultures from sediments, but the responsible organisms have not yet been identified or isolated. Here we show the presence of a Dehalococcoides species in four dioxin-dechlorinating enrichment cultures from a freshwater sediment highly contaminated with PCDDs and PCDFs. We also show that the previously described chlorobenzene-dehalorespiring bacterium Dehalococcoides sp. strain CBDB1 (ref. 3) is able to reductively dechlorinate selected dioxin congeners. Reductive dechlorination of 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD) demonstrates that environmentally significant dioxins are attacked by this bacterium.

Distributed algorithms for transmission power control in wireless sensor networks

Abstract: In a wireless, multi-hop sensor network, choosing transmission power levels has an important impact on energy efficiency and network lifetime. Two algorithms for dynamically adjusting transmission power level on a per-node basis are proposed here. Network lifetime, convergence speed as well as resulting network connectivity are used as figures of merit for these two algorithms. They have been evaluated in an indoor sensor environment. The network lifetime metrics of these two local algorithms are also benchmarked against power control algorithms using global information. We show that these local algorithms outperform fixed power level assignment and that the lifetime achieved by them is usually within a factor of two of globally computed solution while being scalable.

Radical scavenging activity of black cumin (Nigella sativa L.), coriander (Coriandrum sativum L.), and niger (Guizotia abyssinica Cass.) crude seed oils and oil fractions.

Abstract: Crude vegetable oils are usually oxidatively more stable than the corresponding refined oils. Tocopherols, phospholipids (PL), phytosterols, and phenols are the most important natural antioxidants in crude oils. Processing of vegetable oils, moreover, could induce the formation of antioxidants. Black cumin (Nigella sativa L.), coriander (Coriandrum sativum L.), and niger (Guizotia abyssinica Cass.) crude seed oils were extracted with n-hexane and the oils were further fractionated into neutral lipids (NL), glycolipids (GL), and PL. Crude oils and their fractions were investigated for their radical scavenging activity (RSA) toward the stable galvinoxyl radical by electron spin resonance (ESR) spectrometry and toward 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical by spectrophotometric method. Coriander seed oil and its fractions exhibited the strongest RSA compared to black cumin and niger seed oils. The data correlated well with the total content of polyunsaturated fatty acids, unsaponifiables, and PL, as well as the initial peroxide values of crude oils. In overall ranking, RSA of oil fractions showed similar patterns wherein the PL exhibited greater activity to scavenge both free radicals followed by GL and NL, respectively. The positive relationship observed between the RSA of crude oils and their color intensity suggests the Maillard reaction products may have contributed to the RSA of seed oils and their polar fractions. The results demonstrate the importance of minor components in crude seed oils on their oxidative stability, which will reflect on their food value and shelf life. As part of the effort to assess the potential of these seed oils, the information is also of importance in processing and utilizing the crude oils and their byproducts.

Relativistic effects in gas-phase ion chemistry: An experimentalist's view

Abstract: Gas-phase experiments provide information which, in conjunction with results from electronic structure calculations, help to unravel the critical role relativistic effects play in many areas of transition-metal chemistry. Examples include the thermochemical data of gold halides in different oxidation states, the fascinating structural properties of gold(I) complexes, the dramatic effects of ligands on the ionization energy of gold, or the binding in cationic metal-carbene complexes. Furthermore, in the context of methane functionalization, special emphasis is paid to the chemistry of cationic metal-carbene complexes, and at uncovering the mechanistic details of important carbon-heteroatom coupling reactions. It is the interplay of conducting experiments of "isolated" molecules under well-defined conditions with reliable electronic structure calculations that has considerably improved our understanding of the role relativistic effects play in the context of transition-metal chemistry, catalysis, and beyond.

Impact of temperature on lethality and energy efficiency of apple juice pasteurization by pulsed electric fields treatment

Abstract: The applicability of pulsed electric fields as a non-thermal preservation process for liquid food decontamination has been shown in several studies. However, high costs of operation due to the occurrence of a high amount of dissipated electrical energy inhibited an industrial exploitation so far. In this study the focus was put on improving energy efficiency of this process for pasteurization of apple juice inoculated with Escherichia coli by investigating the relation between achieved reduction in survivor count and electric field strength and treatment temperature. An empirical mathematical model was derived to predict the required input of electrical energy for a given inactivation. Using synergistic effects of elevated treatment temperature of 35–65 °C on microbial inactivation the energy consumption could be reduced from above 100 to less than 40 kJ kg−1 for a reduction of 6 log cycles and the need to preheat the juice before treatment provided a possibility to recover the dissipated electrical energy after treatment, leading to a drastic reduction in operation costs. To evaluate the thermal load of the product the pasteurization unit (PU) and the cook value, key benchmarks for the thermal load, were used to compare PEF and conventional heat treatment.

Development of a polymer stent with shape memory effect as a drug delivery system.

Abstract: The article presents a new concept for vascular endoprothesis (stent). Almost all commercially available stents are made of metallic materials. A common after effect of stent implantation is restenosis. Several studies on metal stents coated with drug show, that the use of a drug delivery system may reduce restenosis. The purpose of this work is to develop a new stent for the drug delivery application. The shape memory properties of thermoplastic polyurethane allow to design a new fully polymeric self-expandable stent. The possibility to use the stent as a drug delivery system is described.

Bilateral teleoperation over the internet: the time varying delay problem

Abstract: This paper addresses the problem of time-varying communication delay in force reflecting bilateral teleoperation. The problem is motivated by the increasing use of the Internet as a communication medium where the time delay is variable depending on factors such as congestion, bandwidth, or distance. The well-known scattering formalism introduced in 111 preserves passivity of the communication channel in general only for constant transmission delay. We demonstrate how to recover both passivity and tracking performance using a modified control architecture that incorporates timevarying gains into the scattering transformatioil and feedforward position control. Experimental results using a single-degree of freedom master/slave system are presented

Phonon-assisted damping of Rabi oscillations in semiconductor quantum dots.

Abstract: Electron-phonon interaction is a major source of optical dephasing in semiconductor quantum dots. Within a density matrix theory the electron-phonon interaction is considered up to the second order of a correlation expansion, allowing the calculation of the quantum kinetic dephasing dynamics of optically induced nonlinearities in GaAs quantum dots for arbitrary pulse strengths and shapes. We find Rabi oscillations renormalized and a damping that depends on the input pulse strength, a behavior not known from exponential dephasing mechanisms.

Sinian-Cambrian stratigraphic framework for shallow- to deep-water environments of the Yangtze Platform: an integrated approach

Abstract: The Sinian (Terminal Proterozoic) and Early Cambrian shallow- to deep-water sequences of the Yangtze Platform were investigated. Based on integrated lithostratigraphic, biostratigraphic, and other approaches, the shallow-water sequence from the base of the Sinian (base of the Doushantuo Formation) to the top of the Qiongzhusian (top of the Yu'anshan Formation) was subdivided into 12 stratigraphic intervals. These 12 intervals were applied in turn to the subdivision and correlation of the sequences present in various facies of the Yangtze Platform. The high-resolution stratigraphic framework here developed can serve as a time frame for ongoing multidisciplinary analyses of the “Cambrian explosion”.

Multiple-image radiography

Abstract: Conventional radiography produces a single image of an object by measuring the attenuation of an x-ray beam passing through it When imaging weakly absorbing tissues, x-ray attenuation may be a suboptimal signature of diseaserelated information In this paper we describe a new phase-sensitive imaging method, called multiple-image radiography (MIR), which is an improvement on a prior technique called diffraction-enhanced imaging (DEI) This paper elaborates on our initial presentation of the idea in Wernick et al (2002 Proc Int SympBiomedImaging pp 129–32) MIR simultaneously produces several images from a set of measurements made with a single x-ray beam Specifically, MIR yields three images depicting separately the effects of refraction, ultrasmall-angle scatter and attenuation by the object All three images have good contrast, in part because they are virtually immune from degradation due to scatter at higher angles MIR also yields a very comprehensive object description, consisting of the angular intensity spectrum of a transmitted x-ray beam at every image pixel, within a narrow angular range Our experiments are based on data acquired using a synchrotron light source; however, in preparation for more practical implementations using conventional x-ray sources, we develop and evaluate algorithms designed for Poisson noise, which is characteristic of photon-limited imaging The results suggest that MIR is capable of operating at low photon count levels, therefore the method

Fate of Pharmaceuticals During Ground Water Recharge

Abstract: Pharmaceuticals and personal care products (PPCPs) have recently been detected in the aquatic environment. Many studies have identified domestic waste water discharge as the source for detectable concentrations of PPCPs in surface water. PPCPs are a concern for the aquatic environment when production and use are sufficiently large and physicochemical properties are appropriate. Hydrophilic PPCPs present in surface water or waste water may also affect ground water quality where water is used to recharge ground water. However, less is known about how efficiently PPCPs are removed during percolation through the subsurface. The scope of this study was to examine the fate of selected PPCPs during ground water recharge at two water reuse sites where secondary and tertiary treated waste water is used for subsequent ground water recharge. The ground water recharge sites selected differ in aboveground treatment and geohydrological settings. The selected pharmaceutials represent blood lipid regulators, analgesics/anti-inflammatories, blood viscosity agents, and antiepileptics. Organic iodine was used as a surrogate parameter for X-ray contrast agents. Composite samples of treated waste water and from ground water monitoring wells were collected and analyzed for Pharmaceuticals using gas chromatography with mass spectroscopic detection. The study revealed that the stimulant caffeine, analgesic/anti-inflammatory drugs such as diclofenac, ibuprofen, ketoprofen, naproxen, and fenoprofen, and blood lipid regulators such as gemfibrozil were efficiently removed to concentrations near or below the detection limit of the analytical method after retention times of less than six months during ground water recharge. The antiepileptics carbamazepine and primidone were not removed during ground water recharge under either anoxic saturated or aerobic unsaturated flow conditions during travel times of up to eight years. Organic iodine showed a partial removal only under anoxic, saturated conditions as compared to aerobic conditions and persisted in the recharged ground water.

Structure−Antioxidant Efficiency Relationships of Phenolic Compounds and Their Contribution to the Antioxidant Activity of Sea Buckthorn Juice

Abstract: The phenolic composition of juice derived from fruits of sea buckthorn (Hippophae rhamnoides) was investigated by high-performance liquid chromatography (HPLC) with diode array and electrochemical detection Flavonols were found to be the predominating polyphenols while phenolic acids and catechins represent minor components Of the seven flavonols identified, isorhamnetin 3-O-glycosides were the most important representatives quantitatively However, because of their structural properties, they were poor radical scavengers as shown by electron spin resonance spectroscopy Phenolic compounds such as quercetin 3-O-glycosides, catechins, and hydroxybenzoic acids with a catechol structure exhibited good antioxidant capacities, but their concentration in sea buckthorn juice was small These phenolic compounds, determined by HPLC, accounted for less than 5% of the total antioxidant activity of the filtered juice Ascorbic acid was shown to be the major antioxidant in sea buckthorn juice Because of its high concentration of 122 g/L, it contributes approximately 75% to total antioxidant activity The remaining difference can be attributed to higher molecular weight flavan-3-ols (proanthocyanidins), which were determined photometrically after acid depolymerization to colored anthocyanidins