TY - CONF
AB - In this paper we propose a procedure for estimating the geometric configuration of an arbitrary acoustic sensor placement. It determines the position and the orientation of microphone arrays in 2D while locating a source by direction-of-arrival (DoA) estimation. Neither artificial calibration signals nor unnatural user activity are required. The problem of scale indeterminacy inherent to DoA-only observations is solved by adding time difference of arrival (TDOA) measurements. The geometry calibration method is numerically stable and delivers precise results in moderately reverberated rooms. Simulation results are confirmed by laboratory experiments.
AU - Schmalenstroeer, Joerg
AU - Jacob, Florian
AU - Haeb-Umbach, Reinhold
AU - Hennecke, Marius
AU - Fink, Gernot A.
ID - 11896
T2 - Interspeech 2011
TI - Unsupervised Geometry Calibration of Acoustic Sensor Networks Using Source Correspondences
ER -
TY - CONF
AB - In this paper we address the problem of initial seed selection for frequency domain iterative blind speech separation (BSS) algorithms. The derivation of the seeding algorithm is guided by the goal to select samples which are likely to be caused by source activity and not by noise and at the same time originate from different sources. The proposed algorithm has moderate computational complexity and finds better seed values than alternative schemes, as is demonstrated by experiments on the database of the SiSEC2010 challenge.
AU - Tran Vu, Dang Hai
AU - Haeb-Umbach, Reinhold
ID - 11911
T2 - Interspeech 2011
TI - On Initial Seed Selection for Frequency Domain Blind Speech Separation
ER -
TY - BOOK
ED - Kolossa, Dorothea
ED - Haeb-Umbach, Reinhold
ID - 11945
TI - Robust Speech Recognition of Uncertain or Missing Data --- Theory and Applications
ER -
TY - JOUR
AB - We present an implementation of the GW approximation for the electronic self-energy within the full-potential linearized augmented-plane-wave (FLAPW) method. The algorithm uses an all-electron mixed product basis for the representation of response matrices and related quantities. This basis is derived from the FLAPW basis and is exact for wave-function products. The correlation part of the self-energy is calculated on the imaginary-frequency axis with a subsequent analytic continuation to the real axis. As an alternative we can perform the frequency convolution of the Green function G and the dynamically screened Coulomb interaction W explicitly by a contour integration. The singularity of the bare and screened interaction potentials gives rise to a numerically important self-energy contribution, which we treat analytically to achieve good convergence with respect to the k-point sampling. As numerical realizations of the GW approximation typically suffer from the high computational expense required for the evaluation of the nonlocal and frequency-dependent self-energy, we demonstrate how the algorithm can be made very efficient by exploiting spatial and time-reversal symmetry as well as by applying an optimization of the mixed product basis that retains only the numerically important contributions of the electron-electron interaction. This optimization step reduces the basis size without compromising the accuracy and accelerates the code considerably. Furthermore, we demonstrate that one can employ an extrapolar approximation for high-lying states to reduce the number of empty states that must be taken into account explicitly in the construction of the polarization function and the self-energy. We show convergence tests, CPU timings, and results for prototype semiconductors and insulators as well as ferromagnetic nickel.
AU - Friedrich, Christoph
AU - Blügel, Stefan
AU - Schindlmayr, Arno
ID - 18558
IS - 12
JF - Physical Review B
SN - 1098-0121
TI - Efficient implementation of the GW approximation within the all-electron FLAPW method
VL - 81
ER -
TY - JOUR
AB - 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.
AU - Şaşıoğlu, Ersoy
AU - Schindlmayr, Arno
AU - Friedrich, Christoph
AU - Freimuth, Frank
AU - Blügel, Stefan
ID - 18560
IS - 5
JF - Physical Review B
SN - 1098-0121
TI - Wannier-function approach to spin excitations in solids
VL - 81
ER -
TY - JOUR
AB - Given the density matrix rho of a bipartite quantum state, the quantum separability problem asks whether rho is entangled or separable. In 2003, Gurvits showed that this problem is NP-hard if rho is located within an inverse exponential (with respect to dimension) distance from the border of the set of separable quantum states. In this paper, we extend this NP-hardness to an inverse polynomial distance from the separable set. The result follows from a simple combination of works by Gurvits, Ioannou, and Liu. We apply our result to show (1) an immediate lower bound on the maximum distance between a bound entangled state and the separable set (assuming P != NP), and (2) NP-hardness for the problem of determining whether a completely positive trace-preserving linear map is entanglement-breaking.
AU - Gharibian, Sevag
ID - 8179
IS - 3{\&}4
JF - Quantum Information & Computation
TI - Strong NP-hardness of the quantum separability problem
VL - 10
ER -
TY - CONF
AB - In double-sided markets for computing resources an optimal allocation schedule among job offers and requests subject to relevant capacity constraints can be determined. With increasing storage demands and emerging storage services the question how to schedule storage jobs becomes more and more interesting. Since such scheduling problems are often in the class NP-complete an exact computation is not feasible in practice. On the other hand an approximation to the optimal solution can easily be found by means of using heuristics. The problem with this attempt is that the suggested solution may not be exactly optimal and is thus less satisfying. Considering the two above mentioned solution approaches one can clearly find a trade-off between the optimality of the solution and the efficiency to get to a solution at all. This work proposes to apply and combine heuristics in optimization to gain from both of their benefits while reducing the problematic aspects. Following this method it is assumed to get closer to the optimal solution in a shorter time compared to a full optimization.
AU - Finkbeiner, Josef
AU - Bodenstein, Christian
AU - Schryen, Guido
AU - Neumann, Dirk
ID - 5685
KW - Decision Support System
KW - Algorithms
KW - Optimization
KW - Market Engineering
T2 - 18th European Conference on Information Systems (ECIS 2010)
TI - Applying heuristic methods for job scheduling in storage markets
ER -
TY - CONF
AB - In a world, where more and more businesses seem to trade in an online market, the supply of online services to supply the ever-growing demand could quickly reach its capacity limits. Online service providers may find themselves maxed out at peak operation levels during high-traffic timeslots but too little demand during low-traffic timeslots, although the latter is becoming less frequent. At this point not only deciding which user is allocated what level of service becomes essential, but also the magnitude of the service provided, can be controlled by pricing. Pricing is an important factor when efficient and acceptable allocation of resources between individuals must be reached. Without prices, transferring or sharing goods would be impossible. In sharing information, pricing a product however is not as simple as relatively pricing an apple or a pear. Often the costs, and hence the prices are simply unknown. Backed by this scenario, the online services market could be combined with the market design mechanism of diamonds. For this we propose an ultimatum pricing strategy which effectively allows for valuations to be accounted for, but no longer a necessity when pricing in grid, cloud or other online computing environments.
AU - Bodenstein, Christian
AU - Schryen, Guido
AU - Neumann, Dirk
ID - 5690
KW - Posted Price
KW - Ultimatum Game
KW - Energy Efficiency
KW - Mechanism Design
T2 - 18th European Conference on Information Systems (ECIS 2010)
TI - From "Take-it-or-leave-it" offers to "Take-it-or-be-left-out" Ultimatum - A trade mechanism for Online Services
ER -
TY - CONF
AB - 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.
AU - Classen, C
AU - Förstner, Jens
AU - Meier, Torsten
AU - Schuhmann, R
ID - 4167
KW - tet_topic_numerics
SN - 9781424449675
T2 - 2010 IEEE Antennas and Propagation Society International Symposium
TI - Enhanced FDTD edge correction for nonlinear effects calculation
ER -
TY - JOUR
AB - 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.
AU - Piegdon, Karoline A.
AU - Declair, Stefan
AU - Förstner, Jens
AU - Meier, Torsten
AU - Matthias, Heiner
AU - Urbanski, Martin
AU - Kitzerow, Heinz-S.
AU - Reuter, Dirk
AU - Wieck, Andreas D.
AU - Lorke, Axel
AU - Meier, Cedrik
ID - 4172
IS - 8
JF - Optics Express
KW - tet_topic_qd
KW - tet_topic_microdisk
SN - 1094-4087
TI - Tuning quantum-dot based photonic devices with liquid crystals
VL - 18
ER -
TY - JOUR
AB - A quantum dot molecule doped with a single electron in the presence of diagonal and off-diagonal carrierphonon
couplings is studied by means of a nonperturbative quantum kinetic theory. The interaction with acoustic phonons by deformation potential and piezoelectric coupling is taken into account. We show that the phonon-mediated relaxation is fast on a picosecond time scale and is dominated by the usually neglected off-diagonal coupling to the lattice degrees of freedom leading to phonon-assisted electron tunneling. We show that in the parameter regime of current electrical and optical experiments, the microscopic non-Markovian theory has to be employed.
AU - Grodecka-Grad, A.
AU - Förstner, Jens
ID - 4174
IS - 11
JF - Physical Review B
KW - tet_topic_qd
SN - 1098-0121
TI - Theory of phonon-mediated relaxation in doped quantum dot molecules
VL - 81
ER -
TY - CONF
AB - Emerging digital environments and infrastructures, such as distributed services and computing services, have generated new options of communication, information sharing, and resource utilization in past years. Different distributed trust concepts are applied to increase trust in such systems. However, these concepts yield to rather complex architectures which make it difficult to determine which component or system needs to be trusted. This paper presents a novel trust measurement method for distributed systems which enables the t identification of weak points in the overall system architecture. The measurement method includes the specification of a formal trust language and its representation by means of propositional logic formulas. The applicability of the proposed concepts is demonstrated by conducting a case study on the Internet voting system that was used in the 2007 parliamentary elections in Estonia.
AU - Volkamer, Melanie
AU - Schryen, Guido
ID - 5598
KW - distributed trust concepts
KW - measuring etrust
KW - Internet voting
T2 - Proceedings of the 23rd Bled eConference
TI - Measuring eTrust in distributed systems - General Concept and Application to Internet Voting
ER -
TY - CONF
AB - 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 and the development of models is still weak. Addressing this research gap, this paper presents the first comprehensive empirical investigation of published vulnerabilities and patches of 17 widely deployed open source and closed source software packages, including operating systems, database systems, web browsers, email clients, and office systems. The empirical analysis uses comprehensive vulnerability data contained in the NIST National Vulnerability Database and a newly compiled data set of vulnerability patches. The results suggest that it is not the particular software development style that determines the severity of vulnerabilities and vendors? patching behavior, but rather the specific application type and the policy of the particular development community, respectively.
AU - Schryen, Guido
AU - Eliot, Rich
ID - 5631
T2 - 43rd Annual Hawaii International Conference on System Sciences
TI - Increasing software security through open source or closed source development? Empirics suggest that we have asked the wrong question
ER -
TY - CONF
AB - Enduring doubts about the value of IS investments reveal that IS researchers have not fully managed to identify and to explain the economic benefits of IS. Three research tasks are essential requisites on the path towards addressing this criticism: the synthesis of knowledge, the identification of lack of knowledge, and the proposition of paths for closing knowledge gaps. This paper considers each of these tasks by a) synthesizing key research findings based on a comprehensive literature review, b) identifying and unfolding key limitations of current research, and c) applying a decision-theoretic perspective, which opens new horizons to IS business value research and shows paths for overcoming the limitations. The adoption of this perspective results in a decision-theoretic foundation of IS business value research and includes the proposition of a consistent terminology and a research model that frames further research.
AU - Schryen, Guido
AU - Bodenstein, Christian
ID - 5632
KW - Decision theory
KW - IT value
KW - IS assessment
KW - IS evaluation
T2 - Proceedings of the 18th European Conference on Information Systems (ECIS 2010)
TI - A decision-theoretic foundation of IS business value research
ER -
TY - CONF
AB - This paper presents a fuzzy set based decision support model for taking uncertainty into account when making security investment decisions for distributed systems. The proposed model is complementary to robabilistic approaches and useful in situations where probabilistic information is either unavailable or not appropriate to reliably predict future conditions. We ?rst present the speci?cation of a formal security language that allows to specify under which conditions a distributed system is protected against security violations. We show that each term of the security language can be transformed into an equivalent propositional logic term. Then we use propositional logic terms to de?ne a fuzzy set based decision model. This optimization model incorporates uncertainty with regard to the impact of investments on the achieved security levels of components of the distributed system. The model also accounts for budget and security constraints, in order to be applicable in practice.
AU - Schryen, Guido
ED - C. Freiling, Felix
ID - 5642
T2 - Sicherheit 2010 : Sicherheit, Schutz und Zuverl{\"a}ssigkeit ; Konferenzband der 5. Jahrestagung des Fachbereichs Sicherheit der Gesellschaft f{\"u}r Informatik e.V. (GI), 5. - 7. Oktober 2010 in Berlin
TI - A Fuzzy Model for IT Security Investments
VL - 170
ER -
TY - CONF
AB - Enduring doubts about the value of IS investments reveal that IS researchers have not fully managed to identify and to explain the economic benefits of IS. This paper assumes that literature reviews, which represent a powerful instrument for the identification and synthesis of knowledge, have not tapped their full potential to address this issue due to deficiencies in methodology. The analysis of 18 literature reviews published in pertinent academic outlets during the past 20 years shows such deficiencies. Two of the most critical weaknesses identified are (1) the lack of theory use in most reviews and (2) a weak linkage of reviews, resulting in little progress in theory and framework development. The systematic identification of these weaknesses and the extraction of promising methodological examples from past literature are the main contributions of this work, which supports the composition of more effective literature reviews in future research.
AU - Schryen, Guido
ID - 5643
KW - Literature review
KW - Business value
KW - Information systems
KW - Methodology
KW - Theory
T2 - Proceedings of the First Scandinavian Conference on Information Systems (SCIS)
TI - An Analysis of Literature Reviews on IS Business Value: How Deficiencies in Methodology and Theory Use Resulted in Limited Effectiveness
ER -
TY - JOUR
AB - The economic relevance of information systems has been studied for many years and has attracted an abundance of research papers. However, the ?productivity paradoxon? of the 90s, Carr?s widely recognized paper ?IT doesn?t matter?, and several studies that do not find a positive correlation between IS investments and economic performance reveal long-lasting difficulties for IS researchers to explain ?IS business value?. Business executives and researchers also continue to question the value of IS investments. This raises the question of whether literature reviews have tapped their potential to address the concerns by covering key research areas of IS business value and preserving their key findings. In order to address this question, this paper identifies and describes 12 key research areas, and synthesizes what literature reviews published in pertinent academic outlets have done to preserve knowledge. The analysis of 22 literature reviews shows that some crucial areas have not been (sufficiently) covered. They provide fertile areas for future literature reviews. As this work is based on the results of more than 200 research papers, it is capable of drawing a comprehensive picture of the current state-of-the-art in IS business value research.
AU - Schryen, Guido
ID - 5644
IS - 4
JF - Business \& Information Systems Engineering (BISE)
KW - Business value
KW - Information systems
KW - Literature review
KW - Meta review
TI - Preserving knowledge on IS business value: what literature reviews have done
VL - 52
ER -
TY - JOUR
AB - The economic relevance of information systems has been studied for many years and has attracted an abundance of research papers. However, the ?productivity paradoxon? of the 1990s, Carr?s widely recognized paper ?IT doesn?t matter?, and several studies that do not find a positive correlation between IS investments and economic performance reveal long-lasting difficulties for IS researchers to explain ?IS business value?. Business executives and researchers also continue to question the value of IS investments. This raises the question of whether literature reviews have tapped their potential to address the concerns by covering key research areas of IS business value and preserving their key findings. In order to address this question, this paper identifies and describes 12 key research areas, and synthesizes what literature reviews published in pertinent academic outlets have done to preserve knowledge. The analysis of 22 literature reviews shows that some crucial areas have not been (sufficiently) covered. They provide fertile areas for future literature reviews. As this work is based on the results of more than 200 research papers, it is capable of drawing a comprehensive picture of the current state-of-the-art in IS business value research.
AU - Schryen, Guido
ID - 5645
IS - 4
JF - Wirtschaftsinformatik
TI - Ökonomischer Wert von Informationssystemen - Beitrag von Literatur-Reviews zum Wissenserhalt ( = Preserving Knowledge on IS Business Value. What Literature Reviews Have Done)
VL - 52
ER -
TY - CONF
AB - In this paper we present a robust location estimation algorithm especially focused on the accuracy in vertical position. A loosely-coupled error state space Kalman filter, which fuses sensor data of an Inertial Measurement Unit and the output of a Global Positioning System device, is augmented by height information from an altitude measurement unit. This unit consists of a barometric altimeter whose output is fused with topographic map information by a Kalman filter to provide robust information about the current vertical user position. These data replace the less reliable vertical position information provided the GPS device. It is shown that typical barometric errors like thermal divergences and fluctuations in the pressure due to changing weather conditions can be compensated by the topographic map information and the barometric error Kalman filter. The resulting height information is shown not only to be more reliable than height information provided by GPS. It also turns out that it leads to better attitude and thus better overall localization estimation accuracy due to the coupling of spatial orientations via the Direct Cosine Matrix. Results are presented both for artificially generated and field test data, where the user is moving by car.
AU - Bevermeier, Maik
AU - Walter, Oliver
AU - Peschke, Sven
AU - Haeb-Umbach, Reinhold
ID - 11726
KW - altitude measurement unit
KW - barometers
KW - barometric altimeter
KW - barometric error Kalman filter
KW - barometric height estimation
KW - direct cosine matrix
KW - global positioning system
KW - Global Positioning System
KW - GPS device
KW - height information
KW - height measurement
KW - inertial measurement unit
KW - Kalman filters
KW - loosely-coupled error state space Kalman filter
KW - loosely-coupled Kalman-filter
KW - map matching
KW - robust information
KW - robust location estimation
KW - sensor fusion
KW - topographic map information
KW - vertical user position
T2 - 7th Workshop on Positioning Navigation and Communication (WPNC 2010)
TI - Barometric height estimation combined with map-matching in a loosely-coupled Kalman-filter
ER -
TY - JOUR
AB - In this paper, we present a new technique for automatic speech recognition (ASR) in reverberant environments. Our approach is aimed at the enhancement of the logarithmic Mel power spectrum, which is computed at an intermediate stage to obtain the widely used Mel frequency cepstral coefficients (MFCCs). Given the reverberant logarithmic Mel power spectral coefficients (LMPSCs), a minimum mean square error estimate of the clean LMPSCs is computed by carrying out Bayesian inference. We employ switching linear dynamical models as an a priori model for the dynamics of the clean LMPSCs. Further, we derive a stochastic observation model which relates the clean to the reverberant LMPSCs through a simplified model of the room impulse response (RIR). This model requires only two parameters, namely RIR energy and reverberation time, which can be estimated from the captured microphone signal. The performance of the proposed enhancement technique is studied on the AURORA5 database and compared to that of constrained maximum-likelihood linear regression (CMLLR). It is shown by experimental results that our approach significantly outperforms CMLLR and that up to 80\% of the errors caused by the reverberation are recovered. In addition to the fact that the approach is compatible with the standard MFCC feature vectors, it leaves the ASR back-end unchanged. It is of moderate computational complexity and suitable for real time applications.
AU - Krueger, Alexander
AU - Haeb-Umbach, Reinhold
ID - 11846
IS - 7
JF - IEEE Transactions on Audio, Speech, and Language Processing
KW - ASR
KW - AURORA5 database
KW - automatic speech recognition
KW - Bayesian inference
KW - belief networks
KW - CMLLR
KW - computational complexity
KW - constrained maximum likelihood linear regression
KW - least mean squares methods
KW - LMPSC computation
KW - logarithmic Mel power spectrum
KW - maximum likelihood estimation
KW - Mel frequency cepstral coefficients
KW - MFCC feature vectors
KW - microphone signal
KW - minimum mean square error estimation
KW - model-based feature enhancement
KW - regression analysis
KW - reverberant speech recognition
KW - reverberation
KW - RIR energy
KW - room impulse response
KW - speech recognition
KW - stochastic observation model
KW - stochastic processes
TI - Model-Based Feature Enhancement for Reverberant Speech Recognition
VL - 18
ER -