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

Inference of hand movements from local field potentials in monkey motor cortex

Abstract: The spiking of neuronal populations in motor cortex provides accurate information about movement parameters. Here we show that hand movement target and velocity can be inferred from multiple local field potentials (LFPs) in single trials approximately as efficiently as from multiple single-unit activity (SUA) recorded from the same electrodes. Our results indicate that LFPs can be used as an additional signal for decoding brain activity, particularly for new neuroprosthetic applications.

scatterplot3d - An R Package for Visualizing Multivariate Data

Abstract: Scatterplot3d is an R package for the visualization of multivariate data in a three dimensional space. R is a "language for data analysis and graphics". In this paper we discuss the features of the package. It is designed by exclusively making use of already existing functions of R and its graphics system and thus shows the extensibility of the R graphics system. Additionally some examples on generated and real world data are provided.

A special-purpose peer-to-peer file sharing system for mobile ad hoc networks

Abstract: Establishing peer-to-peer (P2P) file sharing for mobile ad hoc networks (MANET) requires the construction of a search algorithm for transmitting queries and search results as well as the development of a transfer protocol for downloading files matching a query. In this paper, we present a special-purpose system for searching and file transfer tailored to both the characteristics of MANET and the requirements of peer-to-peer file sharing. Our approach is based on an application layer overlay network. As innovative feature, overlay routes are set up on demand by the search algorithm, closely matching network topology and transparently aggregating redundant transfer paths on a per-file basis. The transfer protocol guarantees low transmission overhead and a high fraction of successful downloads by utilizing overlay routes. In a detailed ns-2 simulation study, we show that both the search algorithm and the transfer protocol outperform off-the-shelf approaches based on a P2P file sharing system for the wireline Internet, TCP and a MANET routing protocol.

How asymmetry helps load balancing

Abstract: This article deals with randomized allocation processes placing sequentially n balls into n bins. We consider multiple-choice algorithms that choose d locations (bins) for each ball at random, inspect the content of these locations, and then place the ball into one of them, for example, in a location with minimum number of balls. The goal is to achieve a good load balancing. This objective is measured in terms of the maximum load, that is, the maximum number of balls in the same bin.Multiple-choice algorithms have been studied extensively in the past. Previous analyses typically assume that the d locations for each ball are drawn uniformly and independently from the set of all bins. We investigate whether a nonuniform or dependent selection of the d locations of a ball may lead to a better load balancing. Three types of selection, resulting in three classes of algorithms, are distinguished: (1) uniform and independent, (2) nonuniform and independent, and (3) nonuniform and dependent.Our first result shows that the well-studied uniform greedy algorithm (class 1) does not obtain the smallest possible maximum load. In particular, we introduce a nonuniform algorithm (class 2) that obtains a better load balancing. Surprisingly, this algorithm uses an unfair tie-breaking mechanism, called Always-Go-Left, resulting in an asymmetric assignment of the balls to the bins. Our second result is a lower bound showing that a dependent allocation (class 3) cannot yield significant further improvement.Our upper and lower bounds on the maximum load are tight up to additive constants, proving that the Always-Go-Left algorithm achieves an almost optimal load balancing among all sequential multiple-choice algorithm. Furthermore, we show that the results for the Always-Go-Left algorithm can be generalized to allocation processes with more balls than bins and even to infinite processes in which balls are inserted and deleted by an oblivious adversary.

Methods for the Analysis of Evolutionary Algorithms on Pseudo-Boolean Functions

Abstract: Many experiments have shown that evolutionary algorithms are useful randomized search heuristics for optimization problems In order to learn more about the reasons for their efficiency and in order to obtain proven results on evolutionary algorithms it is necessary to develop a theory of evolutionary algorithms Such a theory is still in its infancy A major part of a theory is the analysis of different variants of evolutionary algorithms on selected functions Several results of this kind have been obtained during the last years Here important analytical tools are presented, discussed, and applied to well-chosen example functions

Optical detection of the Aharonov-Bohm effect on a charged particle in a nanoscale quantum ring.

Abstract: We study spectroscopically the current produced by a charged particle moving in a nanosize semiconductor quantum ring subject to a perpendicular magnetic field. Several Aharonov-Bohm oscillations are observed in the emission of a charged exciton confined in a single ring structure. The magnetic field period of the oscillations correlates well with the size of the rings.

Trion, biexciton, and exciton dynamics in single self-assembled CdSe quantum dots

Abstract: We present an analysis of time- and polarization-resolved data taken in microphotoluminescence experiments on individual CdSe/ZnSe quantum dots grown by molecular beam epitaxy. The identification of individual dots was performed by a spectral jitter correlation technique and by their polarization properties and density dependences. Decay times are given for exciton, trion, and biexciton states and evidence is shown for a spin-relaxation-limited energy relaxation of the trion. For the bright-exciton state the temperature dependence of the decay time is studied and a repopulation from the dark-exciton state is observed. Trion binding energies of 15–22 meV and biexciton binding energies of 19–26 meV are found.

Random knapsack in expected polynomial time

Abstract: In this paper, we present the first average-case analysis proving an expected polynomial running time for an exact algorithm for the 0/1 knapsack problem. In particular, we prove, for various input distributions, that the number of dominating solutions (i.e., Pareto-optimal knapsack fillings) to this problem is polynomially bounded in the number of available items. An algorithm by Nemhauser and Ullmann can enumerate these solutions very efficiently so that a polynomial upper bound on the number of dominating solutions implies an algorithm with expected polynomial running time.The random input model underlying our analysis is very general and not restricted to a particular input distribution. We assume adversarial weights and randomly drawn profits (or vice versa). Our analysis covers general probability distributions with finite mean, and, in its most general form, can even handle different probability distributions for the profits of different items. This feature enables us to study the effects of correlations between profits and weights. Our analysis confirms and explains practical studies showing that so-called strongly correlated instances are harder to solve than weakly correlated ones.

Combination of DNA-directed immobilization and immuno-PCR: very sensitive antigen detection by means of self-assembled DNA-protein conjugates.

Abstract: An assay for very sensitive antigen detection is described which takes advantage of the self- assembly capabilities of semi-synthetic conjugates of DNA and proteins. The general scheme of this assay is similar to a two-sided (sandwich) enzyme-linked immunoassay (ELISA); however, covalent single-stranded DNA-streptavidin (STV) conjugates, capable of hybridizing to complementary surface-bound DNA oligomers, are utilized for the effective immobilization of either capture antibodies or antigens, rather than the chemi- or physisorption usually applied in ELISA. Immuno-PCR (IPCR) is employed as a method for signal generation, utilizing oligomeric reagents obtained by self-assembly of STV, biotinylated DNA and antibodies. In three different model systems, detecting human IgG, rabbit IgG or carcinoembryonic antigen, this combination allowed one to increase the sensitivity of the analogous ELISA approximately 1000-fold. For example, <0.1 amol/ micro l (15 pg/ml) of rabbit IgG was detectable. The immunoassay can be carried out in a single step by tagging the analyte with both reagents for capture and read-out simultaneously, thereby significantly reducing handling time and costs of analysis. Moreover, as the spatial selectivity of target immobilization is determined by the specificity of DNA base pairing, the assay is particularly suited for miniaturized microfluidics and lab-on-a-chip devices.

Interaction of metal salts with cytoskeletal motor protein systems

Abstract: Interactions of chemicals with the microtubular network of cells may lead to genotoxicity. Micronuclei (MN) might be caused by interaction of metals with tubulin and/or kinesin. The genotoxic effects of inorganic lead and mercury salts were studied using the MN assay and the CREST analysis in V79 Chinese hamster fibroblasts. Effects on the functional activity of motor protein systems were examined by measurement of tubulin assembly and kinesin-driven motility. Lead and mercury salts induced MN dose-dependently. The no-effect-concentration for MN induction was 1.1 μM PbCl2, 0.05 μM Pb(OAc)2 and 0.01 μM HgCl2. The in vitro results obtained for PbCl2 correspond to reported MN induction in workers occupationally exposed to lead, starting at 1.2 μM Hg(II) (Vaglenov et al., 2001, Environ. Health Perspect. 109, 295-298). The CREST Analysis indicate aneugenic effects of Pb(II) and aneugenic and additionally clastogenic effects of Hg(II). Lead (chloride, acetate, and nitrate) and mercury (chloride and nitrate) interfered dose-dependently with tubulin assembly in vitro. The no-effect-concentration for lead salts in this assay was 10 μM. Inhibition of tubulin assembly by mercury started at 2 μM. The gliding velocity of microtubules along immobilised kinesin molecules was affected by 25 μM Pb(NO3)2 and 0.1 μM HgCl2 in a dose-dependent manner. Our data support the hypothesis that lead and mercury genotoxicity may result, at least in part, via disturbance of chromosome segregation via interaction with cytoskeletal proteins.

Almost random graphs with simple hash functions

Abstract: We describe a simple randomized construction for generating pairs of hash functions h1,h2 from a universe U to ranges V = [m] = (0,1,...,m-1) and W = [m] so that for every key set S ⊆ U with n = |S| ≤ m/(1 + e) the (random) bipartite (multi)graph with node set V ∪ W and edge set (h1(x),h2(x))| x ∈ S exhibits a structure that is essentially random. The construction combines d-wise independent classes for d a relatively small constant with the well-known technique of random offsets. While keeping the space needed to store the description of h1 and h2 at O(nζ), for ζ

Magnetic neutron scattering study of YVO3: evidence for an orbital Peierls state.

Abstract: Neutron spectroscopy has revealed a highly unusual magnetic structure and dynamics in ${\mathrm{Y}\mathrm{V}\mathrm{O}}_{3}$, an insulating pseudocubic perovskite that undergoes a series of temperature-induced phase transitions between states with different spin and orbital ordering patterns. A good description of the neutron data is obtained by a theoretical analysis of the spin and orbital correlations of a quasi-one-dimensional model. This leads to the tentative identification of one of the phases of ${\mathrm{Y}\mathrm{V}\mathrm{O}}_{3}$ with the ``orbital Peierls state,'' a theoretically proposed many-body state comprised of orbital singlet bonds.

Renal cell cancer risk and occupational exposure to trichloroethylene: Results of a consecutive case‐control study in Arnsberg, Germany

Abstract: Background German studies of high exposure prevalence have been debated on the renal carcinogenicity of trichloroethylene (TRI). Methods A consecutive hospital-based case-control study with 134 renal cell cancer (RCC) cases and 401 controls was conducted to reevaluate the risk of TRI in this region which were estimated in a previous study. Exposure was self-assessed to compare these studies. Additionally, the job history was analyzed, using expert-based exposure information. Results The logistic regression results, adjusted for age, gender, and smoking, confirmed a TRI-related RCC risk in this region. Using the database CAREX for a comparison of industries with and without TRI exposure, a significant excess risk was estimated for the longest held job in TRI-exposing industries (odds ratio (OR) 1.80, 95% confidence interval (CI) 1.01–3.20). Any exposure in “metal degreasing” was a RCC risk factor (OR 5.57, 95% CI 2.33–13.32). Self-reported narcotic symptoms, indicative of peak exposures, were associated with an excess risk (OR 3.71, 95% CI 1.80–7.54). Conclusions The study supports the human nephrocarcinogenicity of trichloroethylene. Am. J. Ind. Med. 43:274–285, 2003. © 2003 Wiley-Liss, Inc.