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See detailStatistical Precoding with Decision Feedback Equalization over a Correlated MIMO Channel
Järmyr, Simon; Ottersten, Björn UL; Eduard, Jorswieck

in IEEE Transactions on Signal Processing (2010), 58(12), 6298-6311

The decision feedback (DF) transceiver, combining linear precoding and DF equalization, can establish point-to-point communication over a wireless multiple-input multiple-output channel. Matching the DF ... [more ▼]

The decision feedback (DF) transceiver, combining linear precoding and DF equalization, can establish point-to-point communication over a wireless multiple-input multiple-output channel. Matching the DF-transceiver design parameters to the channel characteristics can improve system performance, but requires channel knowledge. We consider the fast-fading channel scenario, with a receiver capable of tracking the channel-state variations accurately, while the transmitter only has long-term, channel-distribution information. The receiver design problem given channel-state information is well studied in the literature. We focus on transmitter optimization, which amounts to designing a statistical precoder to assist the channel-tailored DF equalizer. We develop a design framework that encompasses a wide range of performance metrics. Common cost functions for precoder optimization are analyzed, thereby identifying a structure of typical cost functions. Transmitter design is approached for typical cost functions in general, and we derive a precoder design formulation as a convex optimization problem. Two important subclasses of cost functions are considered in more detail. First, we explore a symmetry of DF transceivers with a uniform subchannel rate allocation, and derive a simplified convex optimization problem, which can be efficiently solved even as system dimensions grow. Second, we explore the tractability of a certain class of mean square error based cost functions, and solve the transmitter design problem with a simple algorithm that identifies the convex hull of a set of points in R2. The behavior of DF transceivers with optimal precoders is investigated by numerical means. [less ▲]

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See detailStatistical properties and information content of calcium oscillations.
Skupin, Alexander UL; Falcke, Martin

in Genome informatics. International Conference on Genome Informatics (2007), 18

Calcium is the most important second messenger in living cells serving as a critical link between a large variety of extracellular stimuli and the intracellular target. Often, the Ca(2+) signal is carried ... [more ▼]

Calcium is the most important second messenger in living cells serving as a critical link between a large variety of extracellular stimuli and the intracellular target. Often, the Ca(2+) signal is carried by [Ca(2+)] oscillations. Our recent studies have demonstrated that in contrast to traditional ideas Ca(2+) oscillations do not occur by simple synchronization of channel clusters opening and closing in an oscillatory fashion but originate from microscopic fluctuation caused by the stochastic binding of the ligands Ca(2+) and IP(3) to the receptor's binding sites. They are orchestrated spatially on the cell level by wave nucleation. In this paper we analyze the stochastic data and show how internal properties can be determined from global observations. Further, we analyze the information content of spontaneous and stimulated oscillations. [less ▲]

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See detailStatistical shape analysis for the classification of renal tumors affecting children
Schiltz, Jang UL; Giebel, Stefan; Schenk, Jens-Peter

in Pakistan Journal of Statistics (2013), 29(1), 129-138

In this research project, we describe an application of statistical shape analysis. In order to differentiate the various kidney tumours appearing in childhood we use shape analysis on two-dimensional ... [more ▼]

In this research project, we describe an application of statistical shape analysis. In order to differentiate the various kidney tumours appearing in childhood we use shape analysis on two-dimensional magnetic resonance images (MRI). We show that this mathematical procedure can be an interesting tool to assist the radiologist who is required to make a decision based on their intuition and their experience in lack of specific tumour characteristics. This study is the first one using MR images in oncology for statistical shape analysis. Our method is innovative in the way to find suitable landmarks and to test the differences, even if the sample size is small. In order to test the mean shape, the statistical test of Ziezold is used. [less ▲]

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See detailStatistical significance of trends in Zenith Wet Delay from re-processed GPS solutions
Klos, Anna; Hunegnaw, Addisu UL; Teferle, Felix Norman UL et al

in GPS Solutions (2018)

Long series of Zenith Wet Delay (ZWD) obtained as part of a homogeneous re-processing of Global Positioning System solutions constitute a reliable set of data to be assimilated into climate models. The ... [more ▼]

Long series of Zenith Wet Delay (ZWD) obtained as part of a homogeneous re-processing of Global Positioning System solutions constitute a reliable set of data to be assimilated into climate models. The correct stochastic properties, i.e. the noise model of these data, have to be identified to assess the real value of ZWD trend uncertainties since assuming an inappropriate noise model may lead to over- or underestimated error bounds leading to statistically insignificant trends. We present the ZWD time series for 1995–2017 for 120 selected globally distributed stations. The deterministic model in the form of a trend and significant seasonal signals were removed prior to the noise analysis. We examined different stochastic models and compared them to widely assumed white noise (WN). A combination of the autoregressive process of first-order plus WN (AR(1) + WN) was proven to be the preferred stochastic representation of the ZWD time series over the generally assumed white-noise-only approach. We found that for 103 out of 120 considered stations, the AR(1) process contributed to the AR(1) + WN model in more than 50% with noise amplitudes between 9 and 68 mm. As soon as the AR(1) + WN model was employed, 43 trend estimates became statistically insignificant, compared to 5 insignificant trend estimates for a white-noise-only model. We also found that the ZWD trend uncertainty may be underestimated by 5–14 times with median value of 8 using the white-noise-only assumption. Therefore, we recommend that AR(1) + WN model is employed before tropospheric trends are to be determined with the greatest reliability. [less ▲]

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See detailA Statistical View on Calcium Oscillations.
Powell, Jake; Falcke, Martin; Skupin, Alexander UL et al

in Advances in experimental medicine and biology (2020), 1131

Transient rises and falls of the intracellular calcium concentration have been observed in numerous cell types and under a plethora of conditions. There is now a growing body of evidence that these whole ... [more ▼]

Transient rises and falls of the intracellular calcium concentration have been observed in numerous cell types and under a plethora of conditions. There is now a growing body of evidence that these whole-cell calcium oscillations are stochastic, which poses a significant challenge for modelling. In this review, we take a closer look at recently developed statistical approaches to calcium oscillations. These models describe the timing of whole-cell calcium spikes, yet their parametrisations reflect subcellular processes. We show how non-stationary calcium spike sequences, which e.g. occur during slow depletion of intracellular calcium stores or in the presence of time-dependent stimulation, can be analysed with the help of so-called intensity functions. By utilising Bayesian concepts, we demonstrate how values of key parameters of the statistical model can be inferred from single cell calcium spike sequences and illustrate what information whole-cell statistical models can provide about the subcellular mechanistic processes that drive calcium oscillations. In particular, we find that the interspike interval distribution of HEK293 cells under constant stimulation is captured by a Gamma distribution. [less ▲]

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See detailA Statistically Efficient Estimator for Co-array Based DoA Estimation
Sedighi, Saeid UL; Shankar, Bhavani UL; Ottersten, Björn UL

Poster (2018, October)

Co-array-based Direction of Arrival (DoA) estimation using Sparse linear arrays (SLAs) has recently gained considerable interest in array processing due to the attractive capability of providing enhanced ... [more ▼]

Co-array-based Direction of Arrival (DoA) estimation using Sparse linear arrays (SLAs) has recently gained considerable interest in array processing due to the attractive capability of providing enhanced degrees of freedom. Although a variety of estimators have been suggested in the literature for co-array-based DoA estimation, none of them are statistically efficient. This work introduces a novel Weighted Least Squares (WLS) estimator for the co-array-based DoA estimation employing the covariance fitting method. Then, an optimal weighting is given so that the asymptotic performance of the proposed WLS estimator coincides with the Cram\'{e}r-Rao Bound (CRB), thereby ensuring statistical efficiency of resulting WLS estimator. This implies that the proposed WLS estimator has significantly better performance compared to existing methods in the literature. Numerical simulations are provided to corroborate the asymptotic statistical efficiency and the improved performance of the proposed estimator. [less ▲]

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See detailStatistically Robust Design of Linear MIMO Transceivers
Zhang, Xi; Palomar, Daniel; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2008), 56(8), 36783689

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See detailStatistics and fluctuation theorem for boson and fermion transport through mesoscopic junctions
Harbola, Upendra; Esposito, Massimiliano UL; Mukamel, Shaul

in Physical Review B (2007), 76(8),

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See detailStatistics of Colloidal Suspensions Stirred by Microswimmers
Ortlieb, Levke; Rafai, Salima; Peyla, Philippe et al

in Physical Review Letters (2019), 122(14),

We present a statistical analysis of the experimental trajectories of colloids in a dilute suspension of the green algae Chlamydomonas reinhardtii. The measured probability density function (pdf) of the ... [more ▼]

We present a statistical analysis of the experimental trajectories of colloids in a dilute suspension of the green algae Chlamydomonas reinhardtii. The measured probability density function (pdf) of the displacements of colloids covers 7 orders of magnitude. The pdfs are characterized by non-Gaussian tails for intermediate time intervals, but nevertheless they collapse when scaled with their standard deviation. This diffusive scaling breaks down for longer time intervals and the pdf becomes Gaussian. However, the mean squared displacements of tracer positions are linear over the complete measurement time interval. Experiments are performed for various tracer diameters, swimmer concentrations, and mean swimmer velocities. This allows a rigorous comparison with several theoretical models. We can exclude a description based on an effective temperature and other mean field approaches that describe the irregular motion as a sum of the fluctuating far field of many microswimmers. The data are best described by the microscopic model by J.-L. Thiffeault, Distribution of particle displacements due to swimming microorganisms, Phys. Rev. E 92, 023023 (2015). [less ▲]

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See detailStatistische Mechanik harter Stäbchen
Schilling, Tanja UL

Presentation (2006, November 10)

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See detailThe Status of GNSS Data Processing Systems to Estimate Integrated Water Vapour for Use in Numerical Weather Prediction Models
Ahmed, Furqan UL; Teferle, Felix Norman UL; Bingley, Richard et al

in Willis, Pascal; Rizos, Chris (Eds.) IAG 150 Years Proceedings of the 2013 IAG Scientific Assembly, Postdam,Germany, 1–6 September, 2013 (2016)

Modern Numerical Weather Prediction (NWP) models make use of the GNSS-derived Zenith Total Delay (ZTD) or Integrated Water Vapour (IWV) estimates to enhance the quality of their forecasts. Usually, the ... [more ▼]

Modern Numerical Weather Prediction (NWP) models make use of the GNSS-derived Zenith Total Delay (ZTD) or Integrated Water Vapour (IWV) estimates to enhance the quality of their forecasts. Usually, the ZTD is assimilated into the NWP models on 3-hourly to 6-hourly intervals but with the advancement of NWP models towards higher update rates e.g. 1-hourly cycling in the Rapid update Cycle (RUC) NWP, it has become of high interest to estimate ZTD on sub-hourly intervals. In turn, this imposes requirements related to the timeliness and accuracy of the ZTD estimates and has lead to a development of various strategies to process GNSS observations to obtain ZTD with different latencies and accuracies. Using present GNSS products and tools, ZTD can be estimated in realtime (RT), near real-time (NRT) and post-processing (PP) modes. The aim of this study is to provide an overview and accuracy assessment of various RT, NRT, and PP IWV estimation systems and comparing their achieved accuracy with the user requirements for GNSS meteorology. The NRT systems are based on Bernese GPS Software 5.0 and use a double-differencing strategy whereas the PP system is based on the Bernese GNSS Software 5.2 using the precise point positioning (PPP) strategy. The RT systems are based on the BKG Ntrip Client 2.7 and the PPP-Wizard both using PPP. The PPP-Wizard allows integer ambiguity resolution at a single station and therefore the effect of fixing integer ambiguities on ZTD estimates will also be presented. [less ▲]

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See detailStatus of text-mining techniques applied to biomedical text
Erhardt, R. A. A.; Schneider, Reinhard UL; Blaschke, C.

in Drug Discovery Today (2006), 11(7-8), 315-325

Scientific progress is increasingly based on knowledge and information. Knowledge is now recognized as the driver of productivity and economic growth, leading to a new focus on the role of information in ... [more ▼]

Scientific progress is increasingly based on knowledge and information. Knowledge is now recognized as the driver of productivity and economic growth, leading to a new focus on the role of information in the decision-making process. Most scientific knowledge is registered in publications and other unstructured representations that make it difficult to use and to integrate the information with other sources (e.g. biological databases). Making a computer understand human language has proven to be a complex achievement, but there are techniques capable of detecting, distinguishing and extracting a limited number of different classes of facts. In the biomedical field, extracting information has specific problems: complex and ever-changing nomenclature (especially genes and proteins) and the limited representation of domain knowledge. [less ▲]

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See detailStatus of the full scale component testing of the KERENA TM emergency condenser and Containment Cooling Condenser
Leyer, Stephan UL; Maisberger, Fabian; Herbst, Vassili et al

in Proceedings of the 2010 International Congress on Advances in Nuclear Power Plants-ICAPP'10 (2010)

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See detailStatus of the full scale component testing of the KERENA ™ emergency condenser and Containment Cooling Condenser
Leyer, Stephan UL; Maisberger, F.; Herbst, V. et al

in International Congress on Advances in Nuclear Power Plants 2010, ICAPP 2010 (2010), 2

KERENA™ (SWR1000) is an innovative boiling water reactor concept with passive safety systems. In order to verify the functionality of the passive components requiredfor the transient and accident ... [more ▼]

KERENA™ (SWR1000) is an innovative boiling water reactor concept with passive safety systems. In order to verify the functionality of the passive components requiredfor the transient and accident management, the test facility INKA (Integral-Versuchstand Karlstein) is build in Karlstein (Germany). The key elements of the KERENA™ passive safety concept -the Emergency Condenser, the Containment Cooling Condenser, the Passive Core Flooding System and the Passive Pressure Pulse Transmitter - will be tested at INKA. The Emergency Condenser system transfer heaty form the reactor pressure vessel to the core flooding pools of the containment. The heat introduced into the containment during accidents will be transferred to the main heat sink for passive accident management (Shielding/Storage Pool) via the Containment Cooling Condensers. Therefore both systems are part of the passive cooling chain connecting the heat source RPV (Reactor Pressure Vessel) with the heat sink. At the INKA test facility both condensers are tested in full scale setup, in order to determine the heat transfer capacity as function of the main input parameters. For the EC these are the RPV pressure, the RPV water level, the containment pressure and the water temperature of the flooding pools. For the Containment Cooling Condenser the heat transfer capacity is a function of the containment pressure, the water temperature of the Shielding/Storage Pooland the fraction of non -condensable gases in the containment. The status of the test program and the available test data will be presented. An outlook of the future test of the passive core flooding system and the integral system test including also the passive pressure pulse transmitter will be given. [less ▲]

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See detailStatus of the Somalia Piracy under International Humanitarian Law
Al Hajjaji, Shams Al Din UL

Presentation (2012, February)

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See detailStatus of TIGA activities at the British Isles continuous GNSS Facility and the University of Luxembourg
Hunegnaw, Addisu UL; Teferle, Felix Norman UL; Bingley, Richard et al

Scientific Conference (2013)

In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to re-analyse all relevant GPS observations from 1995 ... [more ▼]

In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to re-analyse all relevant GPS observations from 1995 to the end of 2012 in order to provide high quality estimates of vertical land motion for monitoring of sea level changes. The TIGA Working Group will also produce a combined solution from the individual TIGA Analysis Centres (TAC) contributions. The consortium of British Isles continuous GNSS Facility (BIGF) and the University of Luxembourg TAC (BLT) will contribute weekly minimally constrained SINEX solutions from its reprocessing using the Bernese GNSS Software (BSW) version 5.2 and the University of Luxembourg will also act as a TIGA Combination Centre (TCC). The BLT will generate two solutions, one based on BSW5.2 using a network double difference (DD) strategy and a second one based on BSW5.2 using a Precise Point Positioning (PPP) strategy. In the DD strategy we have included all IGb08 core stations in order to achieve a consistent reference frame implementation. As an initial test for the TIGA combination, all TACs agreed to provide weekly SINEX solutions for a four-week period in December 2011. Taking these individual TAC solutions the TCC has computed a first combination using two independent combination software packages: CATREF and GLOBK. In this study we will present preliminary results from the BLT reprocessing and from the combination tests. [less ▲]

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See detailStatus of TIGA activities at the British Isles continuous GNSS Facility and the University of Luxembourg
Hunegnaw, Addisu UL; Teferle, Felix Norman UL; Bingley, Richard et al

in International Association of Geodesy Symposia (2016), 143

In 2013 the InternationalGNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to reanalyse all relevant GPS observations from 1995 to ... [more ▼]

In 2013 the InternationalGNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to reanalyse all relevant GPS observations from 1995 to the end of 2012 in order to provide high quality estimates of vertical land motion for monitoring of sea level changes. The TIGA Working Group will also produce a combined solution from the individual TIGA Analysis Centres (TAC) contributions. The consortium of British Isles continuous GNSS Facility (BIGF) and the University of Luxembourg TAC (BLT) will contribute weekly minimally constrained SINEX solutions from its reprocessing using the Bernese GNSS Software (BSW) version 5.2 and the University of Luxembourg will also act as a TIGA Combination Centre (TCC). The BLT will generate two solutions, one based on BSW5.2 using a network double difference (DD) strategy and a second one based on BSW5.2 using a Precise Point Positioning (PPP) strategy. In the DD strategy we have included all IGb08 core stations in order to achieve a consistent reference frame implementation. As an initial test for the TIGA combination, all TACs agreed to provide weekly SINEX solutions for a four-week period in December 2011. Taking these individual TAC solutions the TCC has computed a first combination using two independent combination software packages: CATREF and GLOBK. In this study we will present preliminary results from the BLT reprocessing and from the combination tests [less ▲]

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See detailLe statut du français sur le marché linguistique du Luxembourg
Fehlen, Fernand UL

in Gilles, Peter; Wagner, Mélanie (Eds.) Linguistische und soziolinguistische Bausteine der Luxemburgistik (2011)

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See detailLe statut juridique des entreprises non capitalistes à l’heure des choix
Hiez, David UL

in Revue des sociétés (2012)

Detailed reference viewed: 48 (2 UL)