@inproceedings{40833, abstract = {{In this work, we derive a maximum likelihood formula for beamsteering in a multi-sensor array. The novelty of the work is that the impinging signal and noises are wide sense stationary (WSS) time series with unknown power spectral densities, unlike in previous work that typically considers white signals. Our approach naturally provides a way of fusing frequency-dependent information to obtain a broadband beamformer. In order to obtain the compressed likelihood, it is necessary to find the maximum likelihood estimates of the unknown parameters. However, this problem turns out to be an ML estimation of a block-Toeplitz matrix, which does not have a closed-form solution. To overcome this problem, we derive the asymptotic likelihood, which is given in the frequency domain. Finally, some simulation results are presented to illustrate the performance of the proposed technique. In these simulations, it is shown that our approach presents the best results.}}, author = {{Ramírez, D. and Vía, J. and Santamaría, I. and Scharf, L. L.}}, booktitle = {{Proc.\ IEEE Work.\ Stat.\ Signal Process.}}, title = {{{Multi-Sensor Beamsteering Based on the Asymptotic Likelihood for Colored Signals}}}, doi = {{10.1109/SSP.2011.5967644}}, year = {{2011}}, } @inproceedings{40828, abstract = {{Spectrum sensing is a key component of the Cognitive Radio paradigm. Multiantenna detectors can exploit different spatial features of primary signals in order to boost detection performance and robustness in very low signal-to-noise ratios. However, in several cases these detectors require additional information, such as the rank of the spatial covariance matrix of the received signal. In this work we study the problem of estimating this rank under Gaussianity assumption using an uncalibrated receiver, i.e. with different (unknown) noise levels at each of the antennas.}}, author = {{Vazquez-Vilar, G. and Ramírez, D. and López-Valcarce, R. and Vía, J. and Santamaría, I.}}, booktitle = {{Proc. Int. Conf. on Cognitive Radio and Advanced Spectrum Management}}, title = {{{Spatial rank estimation in Cognitive Radio Networks with uncalibrated multiple antennas (invited paper)}}}, doi = {{10.1145/2093256.2093291}}, year = {{2011}}, } @inproceedings{40830, abstract = {{Interference Alignment (IA) has been revealed as one of the most attractive transmission techniques for the K-user in- terference channel. In this work, we employ a multiuser Multiple-Input Multiple-Output (MIMO) testbed to analyze, in realistic indoor scenarios, the impact of channel state information errors on the sum-rate performance of IA. We restrict our study to a 3-user interference network in which each user transmits a single data stream using two transmit and two receive antennas. For this MIMO interference network, only two different IA solutions exist. We also evaluate the performance gain obtained in practice by using the IA solution that maximizes the sum-rate.}}, author = {{García-Naya, J. A. and Castedo, L. and Ramírez, D. and Santamaría, I.}}, booktitle = {{Proc.\ Eur.\ Signal Process.\ Conf.}}, title = {{{Experimental Evaluation of Interference Alignment Under Imperfect Channel State Information}}}, year = {{2011}}, } @article{40831, abstract = {{Spectrum sensing is a key component of the Cognitive Radio paradigm. Primary signals are typically detected with uncalibrated receivers at signal-to-noise ratios (SNRs) well below decodability levels. Multiantenna detectors exploit spatial independence of receiver thermal noise to boost detection performance and robustness. We study the problem of detecting a Gaussian signal with rank-$P$ unknown spatial covariance matrix in spatially uncorrelated Gaussian noise with unknown covariance using multiple antennas. The generalized likelihood ratio test (GLRT) is derived for two scenarios. In the first one, the noises at all antennas are assumed to have the same (unknown) variance, whereas in the second, a generic diagonal noise covariance matrix is allowed in order to accommodate calibration uncertainties in the different antenna frontends. In the latter case, the GLRT statistic must be obtained numerically, for which an efficient method is presented. Furthermore, for asymptotically low SNR, it is shown that the GLRT does admit a closed form, and the resulting detector performs well in practice. Extensions are presented in order to account for unknown temporal correlation in both signal and noise, as well as frequency-selective channels.}}, author = {{Ramírez, D. and Vazquez-Vilar, G. and López-Valcarce, R. and Vía, J. and Santamaría, I.}}, journal = {{{IEEE} {T}rans.\ {S}ignal\ {P}rocess.}}, number = {{8}}, pages = {{3764–3774}}, title = {{{Detection of rank-$P$ signals in Cognitive Radio Networks with uncalibrated multiple antennas}}}, doi = {{10.1109/TSP.2011.2146779}}, volume = {{59}}, year = {{2011}}, } @article{40838, abstract = {{A multiple-input multiple-output (MIMO) frequency-domain channel measurement methodology is pre- sented. This methodology can be implemented in any transmit/receive hardware consisting of radio frequency modules and baseband digital processing units. It involves the transmission and reception of frequency and phase-optimized complex exponentials through antenna arrays, followed by an offline frequency estimation, which makes additional synchronization circuitry unnecesary. To test the feasibility of this method, a series of measurements is presented, employing a $4 \times 4$ dual-band (2.4/5 GHz) MIMO test bed.}}, author = {{Gutiérrez, J. and Pérez, J. and Ramírez, D. and Vielva, L. and Ibáñez, J. and Santamaría, I.}}, journal = {{IEEE Trans. Instrum. Meas.}}, number = {{3}}, pages = {{827–838}}, title = {{{Frequency-Domain Methodology for Measuring MIMO Channels Using a Generic Test Bed}}}, doi = {{10.1109/TIM.2010.2082432}}, volume = {{60}}, year = {{2011}}, } @inproceedings{40839, abstract = {{Hardware platforms and testbeds are an essential tool to evaluate, in realistic scenarios, the performance of wireless communications systems. In this work we present a multiuser Multiple-Input Multiple-Output (MIMO) testbed made up of 6 nodes, each one with 4 antennas, which allows us to evaluate Interference Alignment (IA) techniques in indoor scenarios. We specifically study the performance of IA for the 3-user interference channel in the 5 GHz band. Our analysis identifies the main practical issues that potentially degrade the IA performance such as channel estimation errors or collinearity between the desired signal and interference subspaces.}}, author = {{Ramírez, D. and Santamaría, I. and García-Naya, J. A. and Castedo, L.}}, booktitle = {{Proc. Int. ITG Work. on Smart Antennas}}, title = {{{Experimental Validation of Interference Alignment Techniques using a Multiuser MIMO Testbed}}}, doi = {{10.1109/WSA.2011.5741921}}, year = {{2011}}, } @inproceedings{40829, author = {{Vazquez-Vilar, G. and Romero, D. and López-Valcarce, R. and Ramírez, D. and Vía, J. and Santamaría, I. and Sala, J.}}, booktitle = {{Int. Work. COST Action IC0902}}, title = {{{Recent advances in multiantenna spectrum sensing: complexity, noise uncertainty, and signal rank issues}}}, year = {{2011}}, } @inproceedings{40089, author = {{Hellmich, Frank and Fricke, Katharina}}, title = {{{Qualitative und quantitative Forschungsmethoden in der Grundschulforschung. Eingangsreferat zum Nachwuchsworkshop auf der 20. Jahrestagung der Kommission "Grundschulforschung und Pädagogik der Primarstufe" der Deutschen Gesellschaft für Erziehungswissenschaft (DGfE, Sektion Schulpädagogik)}}}, year = {{2011}}, } @inproceedings{38243, author = {{Förster, Sabrina and Niebuhr-Siebert, Sandra and Hellmich, Frank}}, publisher = {{Universität Paderborn}}, title = {{{Förderung der Lesekompetenz durch ein wortschatzbasiertes Lesestrategietraining bei Kindern mit Deutsch als Zweitsprache. Vortrag auf der 20. Jahrestagung der Kommission "Grundschulforschung und Pädagogik der Primarstufe" der Deutschen Gesellschaft für Erziehungswissenschaft (DGfE, Sektion Schulpädagogik)}}}, year = {{2011}}, } @inproceedings{38231, author = {{Hoya, Fabian Karl and Hellmich, Frank}}, publisher = {{Universität Paderborn}}, title = {{{Erfassung fachdidaktischer Kompetenzen angehender Grundschullehrkräfte – Ergebnisse aus einem empirischen Forschungsprojekt. Vortrag auf der 20. Jahrestagung der Kommission "Grundschulforschung und Pädagogik der Primarstufe" der Deutschen Gesellschaft für Erziehungswissenschaft (DGfE, Sektion Schulpädagogik)}}}, year = {{2011}}, } @inbook{37030, abstract = {{Erziehungswissenschaft ist eine in mehreren Schritten in Deutschland seit Ende des 18. Jahrhunderts entstandene, definitiv seit Anfang des 20. Jahrhunderts etablierte wissenschaftliche Disziplin, die gegenwärtig meist zu den Sozialwissenschaften gerechnet wird. Ihr Gegenstand ist eine Praxis, die mit Grundbegriffen identifiziert wird, zu denen immer Erziehung und Bildung einschließlich Unterricht gehören, oft durch Sozialisation und andere Begriffe aus anderen Disziplinen erweitert. Ihre Methoden entstammen den Geistes- und Sozialwissenschaften.}}, author = {{Landhäußer, Sandra}}, booktitle = {{Lexikon Erziehungswissenschaft}}, editor = {{Horn, Klaus-Peter and Kemnitz , Heidemarie and Marotzki, Winfried and Sandfuchs , Uwe }}, isbn = {{9783838584683}}, pages = {{S. 286--287}}, publisher = {{Julius Klinkhardt}}, title = {{{Soziale Brennpunkte}}}, year = {{2011}}, } @article{37920, author = {{Grotjahn, Rebecca}}, journal = {{Frankfurter Zeitschrift für Musikwissenschaft}}, pages = {{1–25}}, title = {{{Stimmbesitzer und Sängerdarsteller. Die Inszenierung des Singens auf der Musiktheater-Bühne in den ersten Jahrzehnten des 20. Jahrhunderts}}}, doi = {{10.5450/ejm.2011.14.6211 }}, volume = {{14}}, year = {{2011}}, } @article{41261, author = {{Hübner, Michael and Koziej, Dorota and Bauer, Matthias and Barsan, Nicolae and Kvashnina, Kristina and Rossell, Marta D. and Weimar, Udo and Grunwaldt, Jan‐Dierk}}, issn = {{1433-7851}}, journal = {{Angewandte Chemie International Edition}}, keywords = {{General Chemistry, Catalysis}}, number = {{12}}, pages = {{2841--2844}}, publisher = {{Wiley}}, title = {{{The Structure and Behavior of Platinum in SnO 2 ‐Based Sensors under Working Conditions}}}, doi = {{10.1002/anie.201004499}}, volume = {{50}}, year = {{2011}}, } @inproceedings{42031, author = {{Plumhof, J.D and Krápek, V and Ding, F and Jöns, Klaus D. and Hafenbrak, R and Klenovský, P and Herklotz, A and Dörr, K and Michler , P and Rastelli,, A and Schmidt, O.G}}, title = {{{Strain-induced anticrossing of bright exciton levels in single self-assembled GaAs/Al(x)Ga(1−x)As and In(x)Ga(1−x)As/GaAs quantum dots}}}, volume = {{83}}, year = {{2011}}, } @inproceedings{42032, author = {{Jöns, Klaus D. and Hafenbrak, R and Singh, R and Ding, F and Plumhof, J.D and Rastelli, A and Schmidt, O.G and Bester, G and Michler, P}}, pages = {{217402}}, title = {{{Dependence of the Redshifted and Blueshifted Photoluminescence Spectra of Single In(x)Ga(1−x)As/GaAs Quantum Dots on the Applied Uniaxial Stress}}}, volume = {{107}}, year = {{2011}}, } @book{37883, editor = {{Grotjahn, Rebecca and Schmidt, Dörte and Seedorf, Thomas }}, isbn = {{978-3-931264-57-4}}, publisher = {{Edition Argus}}, title = {{{Diva – Die Inszenierung der übermenschlichen Frau. Interdisziplinäre Untersuchungen zu einem kulturellen Phänomen des 19. und 20. Jahrhunderts}}}, volume = {{7}}, year = {{2011}}, } @article{25962, abstract = {{We report the correlation of the aging of Pd-doped SnO2 methane sensors with the change of the oxidation state of Pd. Mesoporous SnO2 doped with palladium species was prepared and exposed to different gas mixtures at high temperature (600 °C) to simulate long term usage. After each exposure step a fraction of the sample was cooled down to “freeze” the current oxidation state of Pd which was then analyzed by X-ray Absorption Near-Edge Spectroscopy (XANES) using the 'white line' (i.e. the absorption peak corresponding to the transition from the 2p3/2 core level to unoccupied 4 d states) intensity of the L(III) edge as a probe for the oxidation state. The Pd oxidation state correlates with the response of the resistive SnO2 sensor to methane gas, as determined by measuring the gas response to different concentrations of methane. Samples treated with 5000 ppm methane in air show a significant reduction of Pd(II) to Pd(0), depending clearly on the carrier gas (synthetic air, pure nitrogen) and on the temperature (600 °C vs. 300 °C).}}, author = {{Wagner, T. and Bauer, M. and Sauerwald, T. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0040-6090}}, journal = {{Thin Solid Films}}, pages = {{909--912}}, title = {{{X-ray absorption near-edge spectroscopy investigation of the oxidation state of Pd species in nanoporous SnO2 gas sensors for methane detection}}}, doi = {{10.1016/j.tsf.2011.04.187}}, year = {{2011}}, } @article{25963, abstract = {{We report the synthesis of mesoporous tin dioxide (SnO2) materials with well-defined particle morphology. The products consist of uniform spheres with a diameter of 5 μm. The spheres are hierarchically porous with two distinct pore modes of 5.0 nm and 52 nm, respectively. This special porosity is the result of a synthesis procedure which involves a ‘hard templating’ (nanocasting) process. The product forms an approximately homogeneous monolayer of spheres on a sensor substrate and shows promising response to methane gas with low cross-sensitivity to water. The structural properties and gas-sensing performance are compared with a mesoporous SnO2 material without defined morphology, prepared by a ‘soft templating’ procedure.}}, author = {{Smått, J.-H. and Lindén, M. and Wagner, T. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{483--488}}, title = {{{Micrometer-sized nanoporous tin dioxide spheres for gas sensing}}}, doi = {{10.1016/j.snb.2010.12.051}}, year = {{2011}}, } @article{25961, abstract = {{Mesoporous In2O3, synthesized by a nanocasting procedure, is used as a resistive gas sensor for ozone in very low concentrations (from 20 ppb to 2.4 ppm) at room temperature. Its sensing performance is substantially increased by illumination with blue light (460 nm, 2.7 eV). For low ozone concentrations the sensor response increases with increasing humidity. However, higher humidity also results in the occurrence of a saturation of the response at lower ozone concentrations; this is rationalized by assuming a poisoning of surface active sites by hydroxyl groups.}}, author = {{Wagner, T. and Hennemann, J. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0040-6090}}, journal = {{Thin Solid Films}}, pages = {{918--921}}, title = {{{Photocatalytic ozone sensor based on mesoporous indium oxide: Influence of the relative humidity on the sensing performance}}}, doi = {{10.1016/j.tsf.2011.04.181}}, year = {{2011}}, } @article{43259, abstract = {{The extreme nonlinear terahertz response of initially unexcited intrinsic semiconductor nanostructures is studied theoretically by solving extended semiconductor Bloch equations numerically. The coupled dynamics of intraband acceleration and multiphoton interband transitions leads to high-harmonic generation up to several tens of the exciting terahertz frequency. It is shown that the actual cut-off frequency is determined by the band structure and not by the excitation strength.}}, author = {{Golde, D. and Kira, M. and Meier, Torsten and Koch, S.W.}}, journal = {{physica status solidi (b)}}, number = {{4}}, pages = {{863--866}}, publisher = {{WILEY‐VCH Verlag}}, title = {{{Microscopic theory of the extremely nonlinear terahertz response of semiconductors}}}, doi = {{10.1002/pssb.201000840}}, volume = {{248}}, year = {{2011}}, }