@article{18560, abstract = {{We present a computational scheme to study spin excitations in magnetic materials from first principles. The central quantity is the transverse spin susceptibility, from which the complete excitation spectrum, including single-particle spin-flip Stoner excitations and collective spin-wave modes, can be obtained. The susceptibility is derived from many-body perturbation theory and includes dynamic correlation through a summation over ladder diagrams that describe the coupling of electrons and holes with opposite spins. In contrast to earlier studies, we do not use a model potential with adjustable parameters for the electron-hole interaction but employ the random-phase approximation. To reduce the numerical cost for the calculation of the four-point scattering matrix we perform a projection onto maximally localized Wannier functions, which allows us to truncate the matrix efficiently by exploiting the short spatial range of electronic correlation in the partially filled d or f orbitals. Our implementation is based on the full-potential linearized augmented-plane-wave method. Starting from a ground-state calculation within the local-spin-density approximation (LSDA), we first analyze the matrix elements of the screened Coulomb potential in the Wannier basis for the 3d transition-metal series. In particular, we discuss the differences between a constrained nonmagnetic and a proper spin-polarized treatment for the ferromagnets Fe, Co, and Ni. The spectrum of single-particle and collective spin excitations in fcc Ni is then studied in detail. The calculated spin-wave dispersion is in good overall agreement with experimental data and contains both an acoustic and an optical branch for intermediate wave vectors along the [100] direction. In addition, we find evidence for a similar double-peak structure in the spectral function along the [111] direction. To investigate the influence of static correlation we finally consider LSDA+U as an alternative starting point and show that, together with an improved description of the Fermi surface, it yields a more accurate quantitative value for the spin-wave stiffness constant, which is overestimated in the LSDA.}}, author = {{Şaşıoğlu, Ersoy and Schindlmayr, Arno and Friedrich, Christoph and Freimuth, Frank and Blügel, Stefan}}, issn = {{1550-235X}}, journal = {{Physical Review B}}, number = {{5}}, publisher = {{American Physical Society}}, title = {{{Wannier-function approach to spin excitations in solids}}}, doi = {{10.1103/PhysRevB.81.054434}}, volume = {{81}}, year = {{2010}}, } @inproceedings{4167, abstract = {{The electromagnetic field in the vicinity of sharp edges needs a special treatment in numeric calculation whenever accurate, fast converging results are necessary. One of the fundamental works concerning field singularities has been proposed in 1972 [1] and states that the electromagnetic energy density must be integrable over any finite domain, even if this domain contains singularities. It is shown, that the magnetic field H(, ϕ) and electric field E(, ϕ) are proportional to ∝ (t−1) for  → 0. The variable  is the distance to the edge and t has to fulfill the integrability condition and thus is restricted to 0 < t < 1. This result is often used to reduce the error corresponding to the singularity without increasing the numerical effort [2 - 5]. For this purpose, a correction factor K is estimated by inserting the proportionality into the wave equation. It is shown, that this method improves the accuracy of the result significantly, however the order of convergence is often not studied. In [4] a method to modify the material parameters in order to use analytic results to improve the numeric calculation is presented. In this contribution we will - inspired by the scheme given in [4] - develop a new method to estimate a correction factor for perfect conducting materials (PEC) and demonstrate the improvement of the results compared to the standard edge correction. Therefore analytic results (comparable to [1]) are consequently merged with the scheme in [4]. The main goal of this work is the calculation of the second harmonic generation (SHG) in the wave response of so-called metamaterials [6]. Frequently these structures contain sharp metallic edges with field singularities at the interfaces which have a strong impact on the SHG signals. Thus, an accurate simulation of singularities is highly important. However, the following approach can also be applied to many other setups, and one of them is shown in the example below.}}, author = {{Classen, C and Förstner, Jens and Meier, Torsten and Schuhmann, R}}, booktitle = {{2010 IEEE Antennas and Propagation Society International Symposium}}, isbn = {{9781424449675}}, keywords = {{tet_topic_numerics}}, location = {{Toronto, ON, Canada}}, publisher = {{IEEE}}, title = {{{Enhanced FDTD edge correction for nonlinear effects calculation}}}, doi = {{10.1109/aps.2010.5562017}}, year = {{2010}}, } @article{4172, abstract = {{Microdisks made from GaAs with embedded InAs quantum dots are immersed in the liquid crystal 4-cyano-4’-pentylbiphenyl (5CB). The quantum dots serve as emitters feeding the optical modes of the photonic cavity. By changing temperature, the liquid crystal undergoes a phase transition from the isotropic to the nematic state, which can be used as an effective tuning mechanism of the photonic modes of the cavity. In the nematic state, the uniaxial electrical anisotropy of the liquid crystal molecules can be exploited for orienting the material in an electric field, thus externally controlling the birefringence of the material. Using this effect, an electric field induced tuning of the modes is achieved. Numerical simulations using the finite-differences time-domain (FDTD) technique employing an anisotropic dielectric medium allow to understand the alignment of the liquid crystal molecules on the surface of the microdisk resonator.}}, author = {{Piegdon, Karoline A. and Declair, Stefan and Förstner, Jens and Meier, Torsten and Matthias, Heiner and Urbanski, Martin and Kitzerow, Heinz-Siegfried and Reuter, Dirk and Wieck, Andreas D. and Lorke, Axel and Meier, Cedrik}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, number = {{8}}, publisher = {{The Optical Society}}, title = {{{Tuning quantum-dot based photonic devices with liquid crystals}}}, doi = {{10.1364/oe.18.007946}}, volume = {{18}}, year = {{2010}}, } @inproceedings{24065, author = {{Pottebaum, Jens and Japs, Anna Maria and Prödel, Stephan and Koch, Rainer}}, booktitle = {{ISCRAM 2010 -- 7th International Conference on Information Systems for Crisis Response and Management}}, editor = {{French, Simon and Tomaszewski, Brian and Zobel, Chris}}, keywords = {{Command and control process, Command and control systems, Design and modeling, Domain ontologies, Emergency response, Fire extinguishers, Fire protection, Heterogeneous domains, Information analysis, Information sharing, Information systems, Interoperability, Ontology language, Semantic technologies, Semantic Web, Semantics}}, title = {{{Design and modeling of a domain ontology for fire protection}}}, year = {{2010}}, } @book{30778, author = {{Kullmann, Harry}}, isbn = {{978383092396}}, keywords = {{Beispiel, Gymnasium, Kooperation, Lehrerkooperation, Unterricht}}, publisher = {{Waxmann}}, title = {{{Lehrerkooperation – Ausprägung und Wirkungen am Beispiel des naturwissenschaftlichen Unterrichts an Gymnasien}}}, volume = {{Band 26}}, year = {{2010}}, } @misc{2896, author = {{Liske, Gennadij}}, title = {{{Analyse und Evaluation eines identitätsbasierten Signcryption-Verfahrens}}}, year = {{2009}}, } @inproceedings{1930, author = {{Jacob, Riko and Ritscher, Stephan and Scheideler, Christian and Schmid, Stefan}}, booktitle = {{Algorithms and Computation, 20th International Symposium, ISAAC 2009, Honolulu, Hawaii, USA, December 16-18, 2009. Proceedings}}, pages = {{771----780}}, publisher = {{Springer}}, title = {{{A Self-stabilizing and Local Delaunay Graph Construction}}}, doi = {{10.1007/978-3-642-10631-6_78}}, volume = {{5878}}, year = {{2009}}, } @article{4182, abstract = {{We demonstrate that an optically driven spin of a carrier in a quantum dot undergoes indirect dephasing via conditional optically induced charge evolution even in the absence of any direct interaction between the spin and its environment. A generic model for the indirect dephasing with a three-component system with spin, charge, and reservoir is proposed. This indirect decoherence channel is studied for the optical spin manipulation in a quantum dot with a microscopic description of the charge-phonon interaction taking into account its non-Markovian nature.}}, author = {{Grodecka, A. and Machnikowski, P. and Förstner, Jens}}, issn = {{1050-2947}}, journal = {{Physical Review A}}, keywords = {{tet_topic_qd}}, number = {{4}}, publisher = {{American Physical Society (APS)}}, title = {{{Indirect spin dephasing via charge-state decoherence in optical control schemes in quantum dots}}}, doi = {{10.1103/physreva.79.042331}}, volume = {{79}}, year = {{2009}}, } @inproceedings{5597, abstract = {{Der Beitrag diskutiert die kontroversen Ans{\"a}tze ? Verifizierung versus Evaluation/Zertifizierung ? zur Sicherung elektronischer Wahlen mit Wahlger{\"a}ten. Dabei spielt das Urteils des Bundesverfassungsgerichts [BVG099] eine zentrale Rolle. Hierin wird entschieden, dass die Zertifizierung des Wahlger{\"a}tes nicht ausreicht und es werden Verifizierungsfunktionen gefordert, die den W{\"a}hlern die M{\"o}glichkeit geben sich von der Integrit{\"a}t des Wahlergebnisses zu {\"u}berzeugen. Der Beitrag zeigt auf, dass auch mit der Implementierung entsprechender Verifizierungsfunktionen nicht auf Zertifizierung verzichtet werden kann, da an ein Wahlger{\"a}t auch andere Anforderungen wie etwa hinsichtlich des Wahlgeheimnisses gestellt werden. Es wird au{\ss}erdem die Frage diskutiert, warum der Zertifizierung hinsichtlich dieser zus{\"a}tzlichen Anforderungen vertraut werden kann, w{\"a}hrend dies nicht der Fall bei der Integrit{\"a}tsanforderung ist.}}, author = {{Volkamer, Melanie and Schryen, Guido and Langer, Lucie and Schmidt, Axel and Buchmann, Johannes}}, booktitle = {{Workshop Elektronische Wahlen, elektronische Teilhabe, Societyware, 39th GI-Jahrestagung}}, title = {{{Elektronische Wahlen: Verifizierung vs. Zertifizierung}}}, year = {{2009}}, } @article{5621, abstract = {{Remote voting through the Internet provides convenience and access to the electorate. At the same time, the security concerns facing any distributed application are magnified when the task is so crucial to democratic society. In addition, some of the electoral process loses transparency when it is encapsulated in information technology. In this paper, we examine the public record of three recent elections that used Internet voting. Our specific goal is to identify any potential flaws that security experts would recognize, but may have not been identified in the rush to implement technology. To do this, we present a multiple exploratory case study, looking at elections conducted between 2006 and 2007 in Estonia, Netherlands, and Switzerland. These elections were selected as particularly interesting and accessible, and each presents its own technical and security challenges. The electoral environment, technical design and process for each election are described, including reconstruction of details which are implied but not specified within the source material. We found that all three elections warrant significant concern about voter security, verifiability, and transparency. Usability, our fourth area of focus, seems to have been well-addressed in these elections. While our analysis is based on public documents and previously published reports, and therefore lacking access to any confidential materials held by electoral officials, this comparative analysis provides interesting insight and consistent questions across all these cases. Effective review of Internet voting requires an aggressive stance towards identifying potential security and operational flaws, and we encourage the use of third party reviews with critical technology skills during design, programming, and voting to reduce the changes of failure or fraud that would undermine public confidence.}}, author = {{Schryen, Guido and Rich, Eliot}}, journal = {{IEEE Transactions on Information Forensics \& Security}}, keywords = {{e-voting, Internet voting, Internet election, security, verifiability, RIES, Estonia, Neuch{\^a}tel}}, number = {{4 Part}}, pages = {{729--744}}, publisher = {{IEEE}}, title = {{{Security in Large-Scale Internet Elections: A Retrospective Analysis of Elections in Estonia, The Netherlands, and Switzerland}}}, volume = {{4}}, year = {{2009}}, } @inproceedings{5625, abstract = {{The increasing availability and deployment of open source software in personal and commercial environments makes open source software highly appealing for hackers, and others who are interested in exploiting software vulnerabilities. This deployment has resulted in a debate ?full of religion? on the security of open source software compared to that of closed source software. However, beyond such arguments, only little quantitative analysis on this research issue has taken place. We discuss the state-of-the-art of the security debate and identify shortcomings. Based on these, we propose new metrics, which allows to answer the question to what extent the review process of open source and closed source development has helped to fix vulnerabilities. We illustrate the application of some of these metrics in a case study on OpenOffice (open source software) vs. Microsoft Office (closed source software).}}, author = {{Schryen, Guido and Kadura, Rouven}}, booktitle = {{24th Annual ACM Symposium on Applied Computing}}, keywords = {{Open source software, Closed source software, Security, Metrics}}, title = {{{Open Source vs. Closed Source Software: Towards Measuring Security}}}, year = {{2009}}, } @inproceedings{5646, abstract = {{While many theoretical arguments against or in favor of open source and closed source software development have been presented, the empirical basis for the assessment of arguments is still weak. Addressing this research gap, this paper presents a comprehensive empirical investigation of the patching behavior of software vendors/communities of widely deployed open source and closed source software packages, including operating systems, database systems, web browsers, email clients, and office systems. As the value of any empirical study relies on the quality of data available, this paper also discusses in detail data issues, explains to what extent the empirical analysis can be based on vulnerability data contained in the NIST National Vulnerability Database, and shows how data on vulnerability patches was collected by the author to support this study. The results of the analysis suggest that it is not the particular software development style that determines patching behavior, but rather the policy of the particular software vendor.}}, author = {{Schryen, Guido}}, booktitle = {{5th International Conference on IT Security Incident Management \& IT Forensics}}, title = {{{A comprehensive and comparative analysis of the patching behavior of open source and closed source software vendors}}}, year = {{2009}}, } @inproceedings{5647, abstract = {{Reviewing literature on open source and closed source security reveals that the discussion is often determined by biased attitudes toward one of these development styles. The discussion specifically lacks appropriate metrics, methodology and hard data. This paper contributes to solving this problem by analyzing and comparing published vulnerabilities of eight open source software and nine closed source software packages, all of which are widely deployed. Thereby, it provides an extensive empirical analysis of vulnerabilities in terms of mean time between vulnerability disclosures, the development of disclosure over time, and the severity of vulnerabilities, and allows for validating models provided in the literature. The investigation reveals that (a) the mean time between vulnerability disclosures was lower for open source software in half of the cases, while the other cases show no differences, (b) in contrast to literature assumption, 14 out of 17 software packages showed a significant linear or piecewise linear correlation between time and the number of published vulnerabilities, and (c) regarding the severity of vulnerabilities, no significant differences were found between open source and closed source.}}, author = {{Schryen, Guido}}, booktitle = {{15th Americas Conference on Information Systems}}, keywords = {{Vulnerabilities, security, open source software, closed source software, empirical comparison}}, title = {{{Security of open source and closed source software: An empirical comparison of published vulnerabilities}}}, year = {{2009}}, } @inproceedings{11723, abstract = {{In this paper we present a novel vehicle tracking algorithm, which is based on multi-level sensor fusion of GPS (global positioning system) with Inertial Measurement Unit sensor data. It is shown that the robustness of the system to temporary dropouts of the GPS signal, which may occur due to limited visibility of satellites in narrow street canyons or tunnels, is greatly improved by sensor fusion. We further demonstrate how the observation and state noise covariances of the employed Kalman filters can be estimated alongside the filtering by an application of the Expectation-Maximization algorithm. The proposed time-variant multi-level Kalman filter is shown to outperform an Interacting Multiple Model approach while at the same time being computationally less demanding.}}, author = {{Bevermeier, Maik and Peschke, Sven and Haeb-Umbach, Reinhold}}, booktitle = {{6th Workshop on Positioning Navigation and Communication (WPNC 2009)}}, keywords = {{covariance matrices, expectation-maximisation algorithm, expectation-maximization algorithm, global positioning system, Global Positioning System, GPS, inertial measurement unit, interacting multiple model approach, Kalman filters, multilevel sensor fusion, narrow street canyons, narrow tunnels, online parameter estimation, parameter estimation, road vehicles, robust vehicle localization, sensor fusion, state noise covariances, time-variant multilevel Kalman filter, vehicle tracking algorithm}}, pages = {{235--242}}, title = {{{Robust vehicle localization based on multi-level sensor fusion and online parameter estimation}}}, doi = {{10.1109/WPNC.2009.4907833}}, year = {{2009}}, } @inproceedings{11724, abstract = {{In this paper we present a novel vehicle tracking method which is based on multi-stage Kalman filtering of GPS and IMU sensor data. After individual Kalman filtering of GPS and IMU measurements the estimates of the orientation of the vehicle are combined in an optimal manner to improve the robustness towards drift errors. The tracking algorithm incorporates the estimation of time-variant covariance parameters by using an iterative block Expectation-Maximization algorithm to account for time-variant driving conditions and measurement quality. The proposed system is compared to an interacting multiple model approach (IMM) and achieves improved localization accuracy at lower computational complexity. Furthermore we show how the joint parameter estimation and localizaiton can be conducted with streaming input data to be able to track vehicles in a real driving environment.}}, author = {{Bevermeier, Maik and Peschke, Sven and Haeb-Umbach, Reinhold}}, booktitle = {{IEEE 69th Vehicular Technology Conference (VTC 2009 Spring)}}, keywords = {{computational complexity, expectation-maximisation algorithm, Global Positioning System, inertial measurement unit, inertial navigation, interacting multiple model, iterative block expectation-maximization algorithm, Kalman filters, multi-stage Kalman filter, parameter estimation, road vehicles, vehicle positioning, vehicle tracking}}, pages = {{1--5}}, title = {{{Joint Parameter Estimation and Tracking in a Multi-Stage Kalman Filter for Vehicle Positioning}}}, doi = {{10.1109/VETECS.2009.5073634}}, year = {{2009}}, } @inproceedings{11725, author = {{Bevermeier, Maik and Peschke, Sven and Haeb-Umbach, Reinhold}}, booktitle = {{DGON Navigationskonvent 2009}}, title = {{{Eine Plattform fuer Mehrwertdienste im Bereich Logistik - Drahtlose Fahrzeug- und Laderaumueberwachung fuer LKW mit Hilfe einer Maut-On-Board Unit}}}, year = {{2009}}, } @inproceedings{11847, abstract = {{In this paper we present a new feature space dereverberation technique for automatic speech recognition. We derive an expression for the dependence of the reverberant speech features in the log-mel spectral domain on the non-reverberant speech features and the room impulse response. The obtained observation model is used for a model based speech enhancement based on Kalman filtering. The performance of the proposed enhancement technique is studied on the AURORA5 database. In our currently best configuration, which includes uncertainty decoding, the number of recognition errors is approximately halved compared to the recognition of unprocessed speech.}}, author = {{Krueger, Alexander and Haeb-Umbach, Reinhold}}, booktitle = {{Interspeech 2009}}, title = {{{Model based feature enhancement for automatic speech recognition in reverberant environments}}}, year = {{2009}}, } @inproceedings{11859, abstract = {{In this paper we present an Uncertainty Decoding rule which exploits feature reliability information and interframe correlation for noise robust speech recognition. The reliability information can be obtained either from conditional Bayesian estimation, where speech and noise feature vectors are tracked jointly, or by augmenting conventional point estimation methods with heuristics about the estimator's reliability. Experimental results on the AURORA2 database demonstrate on the one hand that Uncertainty Decoding improves recognition performance, while on the other hand it is seen that the severe approximations needed to arrive at computationally tractable solutions have their noticable impact on recognition performance.}}, author = {{Leutnant, Volker and Haeb-Umbach, Reinhold}}, booktitle = {{International Conference on Acoustics (NAG/DAGA 2009)}}, title = {{{On the Estimation and Use of Feature Reliability Information for Noise Robust Speech Recognition}}}, year = {{2009}}, } @inproceedings{11860, abstract = {{In this paper we present an analytic derivation of the moments of the phase factor between clean speech and noise cepstral or log-mel-spectral feature vectors. The development shows, among others, that the probability density of the phase factor is of sub-Gaussian nature and that it is independent of the noise type and the signal-to-noise ratio, however dependent on the mel filter bank index. Further we show how to compute the contribution of the phase factor to both the mean and the vari- ance of the noisy speech observation likelihood, which relates the speech and noise feature vectors to those of noisy speech. The resulting phase-sensitive observation model is then used in model-based speech feature enhancement, leading to significant improvements in word accuracy on the AURORA2 database.}}, author = {{Leutnant, Volker and Haeb-Umbach, Reinhold}}, booktitle = {{Interspeech 2009}}, title = {{{An analytic derivation of a phase-sensitive observation model for noise robust speech recognition}}}, year = {{2009}}, } @inproceedings{11881, abstract = {{A combination of GPS (global positioning system) and INS (inertial navigation system) is known to provide high precision and highly robust vehicle localization. Notably during times when the GPS signal has a poor quality, e.g. due to the lack of a sufficiently large number of visible satellites, the INS, which may consist of a gyroscope and an odometer, will lead to improved positioning accuracy. In this paper we show how velocity information obtained from GSM (global system for mobile communications) signalling, rather than from a tachometer, can be used together with a gyroscope sensor to support localization in the presence of temporarily unavailable GPS data. We propose a sensor fusion system architecture and present simulation results that show the effectiveness of this approach.}}, author = {{Peschke, Sven and Bevermeier, Maik and Haeb-Umbach, Reinhold}}, booktitle = {{6th Workshop on Positioning Navigation and Communication (WPNC 2009)}}, keywords = {{cellular radio, distance measurement, global positioning system, Global Positioning System, global system for mobile communications, GPS positioning approach, GSM velocity, gyroscopes, gyroscope sensor, inertial navigation, inertial navigation system, odometer, sensor fusion system architecture, sensors}}, pages = {{195--202}}, title = {{{A GPS positioning approach exploiting GSM velocity estimates}}}, doi = {{10.1109/WPNC.2009.4907827}}, year = {{2009}}, }