Results for "Tilmann Hickel"

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Anomalous phonon lifetime shortening in paramagnetic CrN caused by magneto-lattice coupling: A combined spin and ab initio molecular dynamics studyFeb 08 2018We study the mutual coupling of spin fluctuations and lattice vibrations in paramagnetic CrN by combining atomistic spin dynamics and ab initio molecular dynamics. The two degrees of freedom are dynamically coupled leading to non-adiabatic effects. Those ... More
A rigorous analysis using optimal transport theory for a two-reflector design problem with a point sourceAug 17 2009We consider the following geometric optics problem: Construct a system of two reflectors which transforms a spherical wavefront generated by a point source into a beam of parallel rays. This beam has a prescribed intensity distribution. We give a rigorous ... More
Une note à propos du Jacobien de $n$ fonctions holomorphes à l'origine de $\mathbb{C}^n$Feb 04 2008Let $f_1,...,f_n$ be $n$ germs of holomorphic functions at the origin of $\mathbb{C}^n$ such that $f_i(0)=0$, $1\leq i\leq n$. We give a proof based on the J. Lipman's theory of residues via Hochschild Homology that the Jacobian of $f_1,...,f_n$ belongs ... More
Fonction asymptotique de Samuel des sections hyperplanes et multiplicitéJan 12 2009Let $(A,\mathfrak{m}_A,k)$ be a local noetherian ring and $I$ an $\mathfrak{m}_A$-primary ideal. The asymptotic Samuel function (with respect to $I$) $\bar{v}_I$ $:$ $A\longrightarrow \mathbb{R}\cup {+\infty}$ is defined by $\bar{v}_I(x)=lim_{k \to \+infty}\frac{ord_I(x^k}{k}$, ... More
Sur quelques aspects de la géométrie de l'espace des arcs tracés sur un espace analytiqueMay 24 2004Let $(X,x)$ be a germ of real or complex analytic space and $\mathcal{A}_{(X,x)}$ the space of germs of arcs on $(X,x)$. Let us consider $F_{x}: (X,x) \to (Y,y)$ a germ of a morphism and denote by $\mathcal{F}_{x}: \mathcal{A}_{(X,x)} \to \mathcal{A}_{(Y,y)}$ ... More
Proper weak-coupling approach to the periodic s-d(f) exchange modelDec 22 2003The periodic s-d(f) exchange model is characterized by a wide variety of interesting applications, a simple mathematical structure and a limited number of reliable approximations which take care of the quantum nature of the participating spins. We suggest ... More
Multi-component vapor-liquid equilibrium model for LES and application to ECN Spray ASep 27 2016We present and evaluate a detailed multi-species two-phase thermodynamic equilibrium model for large-eddy simulations (LES) of liquid-fuel injection and mixing at high pressure. The model can represent the coexistence of supercritical states and multi-component ... More
On the algebraicity of Puiseux seriesMar 17 2015May 13 2015We deal with the algebraicity of a Puiseux series in terms of the properties of its coefficients. We show that the algebraicity of a Puiseux series for given bounded degree is determined by a finite number of explicit polynomial formulae. Conversely, ... More
Quantum-Confined Stark Effect in polar and nonpolar Wurtzite InN/GaN Heterostructures: Influence on Electronic Structure and Compensation by Coulomb AttractionJan 11 2013In this paper we systematically analyze the electronic structures of polar and nonpolar wurtzite-InN/GaN quantum dots and their modification due to the quantum-confined Stark effect caused by intrinsic fields. This is achieved by combining continuum elasticity ... More
Infinite-dimensional manifolds as ringed spacesMar 23 2014Oct 10 2016We analyze the possibility of defining infinite-dimensional manifolds as ringed spaces. More precisely, we consider three definitions of manifolds modeled on locally convex spaces: in terms of charts and atlases, in terms of ringed spaces, and in terms ... More
A comparison of atomistic and continuum theoretical approaches to determine electronic properties of GaN/AlN quantum dotsNov 10 2008In this work we present a comparison of multiband k.p-models, the effective bond-orbital approach, and an empirical tight-binding model to calculate the electronic structure for the example of a truncated pyramidal GaN/AlN self-assembled quantum dot with ... More
Stochastic models which separate fractal dimension and Hurst effectSep 13 2001Fractal behavior and long-range dependence have been observed in an astonishing number of physical systems. Either phenomenon has been modeled by self-similar random functions, thereby implying a linear relationship between fractal dimension, a measure ... More
Existence and unicity of co-moments in multisymplectic geometryNov 09 2014Given a multisymplectic manifold $(M,\omega)$ and a Lie algebra $\frak{g}$ acting on it by infinitesimal symmetries, Fregier-Rogers-Zambon define a homotopy (co-)moment as an $L_{\infty}$-algebra-homomorphism from $\frak{g}$ to the observable algebra ... More
Combining Predictive DistributionsJun 08 2011Predictive distributions need to be aggregated when probabilistic forecasts are merged, or when expert opinions expressed in terms of probability distributions are fused. We take a prediction space approach that applies to discrete, mixed discrete-continuous ... More
Optical design of two-reflector systems, the Monge-Kantorovich mass transfer problem and Fermat's principleMar 31 2003May 22 2003It is shown that the problem of designing a two-reflector system transforming a plane wave front with given intensity into an output plane front with prescribed output intensity can be formulated and solved as the Monge-Kantorovich mass transfer problem. ... More
Integration of vector fields on smooth and holomorphic supermanifoldsOct 03 2012Dec 29 2012We give a new and self-contained proof of the existence and unicity of the flow for an arbitrary (not necessarily homogeneous) smooth vector field on a real supermanifold, and extend these results to the case of holomorphic vector fields on complex supermanifolds. ... More
Theory of the time-resolved Kerr rotation on trapped holesOct 22 2009Sep 13 2010We formulate a model of the time-resolved Kerr rotation experiment on a single hole in a semiconductor nanostructure (e.g., a quantum dot) or on an ensemble of trapped holes (e.g., in a quantum well) in a tilted magnetic field. We use a generic Markovian ... More
Iterative scheme for solving optimal transportation problems arising in reflector designOct 13 2011Nov 04 2011We consider the geometric optics problem of finding a system of two reflectors that transform a spherical wavefront into a beam of parallel rays with prescribed intensity distribution. Using techniques from optimal transportation theory, it has been shown ... More
The distribution function of the Galaxy's dark haloSep 23 2015Starting from the hypothesis that the Galaxy's dark halo responded adiabatically to the infall of baryons, we have constructed a self-consistent dynamical model of the Galaxy that satisfies a large number of observations, including measurements of gas ... More
The geodesic flow on a Riemannian supermanifoldJul 09 2011We give a natural definition of geodesics on a Riemannian supermanifold and extend the usual geodesic flow defined on the cotangent bundle of the body of the supermanifold, associated to the induced Riemannian structure on the body, to a geodesic "superflow" ... More
On the geometry and quantization of symplectic Howe pairsOct 05 2009We study the orbit structure and the geometric quantization of a pair of mutually commuting hamiltonian actions on a symplectic manifold. If the pair of actions fulfils a symplectic Howe condition, we show that there is a canonical correspondence between ... More
Exact solution for the two-site Kondo-Lattice Model - a limiting case for an insulatorNov 28 2002The Kondo-lattice model is well established as a method to describe an exchange coupling between single conduction electrons and localized magnetic moments. As a nontrivial exact result the zero-bandwidth limit (atomic limit) can be used to test approximations ... More
Carrier trapping in a quantum dash: optical signaturesJul 25 2012We theoretically study the optical properties and the electronic structure of highly elongated quantum dots (quantum dashes) and show how geometrical fluctuations affect the excitonic spec- trum of the system. The dependence of the absorption intensities ... More
Kinematics in galactic tidal tails - A source for Hypervelocity stars?Oct 04 2011[abridged] In this work we study in detail the kinematics of tidal debris stars to investigate the implications of the new scenario that the observed sample of Hypervelocity stars could partly originate from a dwarf-host galaxy collision. We use a suite ... More
Exact solution for the two-site correlated Kondo-Lattice Model - a limiting case for a metalNov 28 2002The correlated Kondo-lattice model is used to describe the interaction of electrons in a single conduction band with localized magnetic moments as well as their mutual repulsion. It is our intension to provide an analytical exact result for this model ... More
Implicit Large Eddy Simulation of Cavitation in Micro Channel FlowsJan 25 2014We present a numerical method for Large Eddy Simulations (LES) of compressible two-phase flows. The method is validated for the flow in a micro channel with a step-like restriction. This setup is representative for typical cavitating multi-phase flows ... More
Using proper divergence functions to evaluate climate modelsJan 24 2013Jul 16 2013It has been argued persuasively that, in order to evaluate climate models, the probability distributions of model output need to be compared to the corresponding empirical distributions of observed data. Distance measures between probability distributions, ... More
Estimators of Fractal Dimension: Assessing the Roughness of Time Series and Spatial DataJan 07 2011Jul 25 2012The fractal or Hausdorff dimension is a measure of roughness (or smoothness) for time series and spatial data. The graph of a smooth, differentiable surface indexed in $\mathbb{R}^d$ has topological and fractal dimension $d$. If the surface is nondifferentiable ... More
Conserved quantities on multisymplectic manifoldsOct 18 2016Given a vector field on a manifold M, we define a globally conserved quantity to be a differential form whose Lie derivative is exact. Integrals of conserved quantities over suitable submanifolds are constant under time evolution, the Kelvin circulation ... More
SuperorbitsFeb 15 2015Jun 21 2016We study actions of Lie supergroups, in particular, the hitherto elusive notion of orbits through odd (or more general) points. Following categorical principles, we derive a conceptual framework for their treatment and therein prove general existence ... More
Duality and reciprocity of fluctuation-dissipation relations in conductorsJun 06 2016By analogy with linear-response we formulate the duality and reciprocity properties of current and voltage fluctuations expressed by Nyquist relations including the intrinsic bandwidths of the respective fluctuations. For this purpose we individuate total-number ... More
Uncertainty Quantification in Complex Simulation Models Using Ensemble Copula CouplingFeb 28 2013Dec 23 2013Critical decisions frequently rely on high-dimensional output from complex computer simulation models that show intricate cross-variable, spatial and temporal dependence structures, with weather and climate predictions being key examples. There is a strongly ... More
Expected Shortfall is jointly elicitable with Value at Risk - Implications for backtestingJul 01 2015Jul 12 2015In this note, we comment on the relevance of elicitability for backtesting risk measure estimates. In particular, we propose the use of Diebold-Mariano tests, and show how they can be implemented for Expected Shortfall (ES), based on the recent result ... More
Electron states in a double quantum dot with broken axial symmetryFeb 12 2014We study theoretically the electron states in a system of two vertically stacked quantum dots. We investigate the influence of the geometrical symmetry breaking (caused by the displacement as well as the ellipticity of the dots) on the electron states. ... More
Double quantum dot in a quantum dash: optical propertiesFeb 15 2013We study the optical properties of highly anisotropic quantum dot structures (quantum dashes) characterized by the presence of two trapping centers located along the structure. Such a system can exhibit some of the properties characteristic for double ... More
Singular superspacesApr 28 2013Jun 20 2014We introduce a wide category of superspaces, called locally finitely generated, which properly includes supermanifolds but enjoys much stronger permanence properties, as are prompted by applications. Namely, it is closed under taking finite fibre products ... More
Forecaster's Dilemma: Extreme Events and Forecast EvaluationDec 31 2015In public discussions of the quality of forecasts, attention typically focuses on the predictive performance in cases of extreme events. However, the restriction of conventional forecast evaluation methods to subsets of extreme observations has unexpected ... More
A parametrized non-equilibrium wall-model for large-eddy simulationsNov 30 2015Wall-models are essential for enabling large-eddy simulations (LESs) of realistic problems at high Reynolds numbers. The present study is focused on approaches that directly model the wall shear stress, specifically on filling the gap between models based ... More
The affinely invariant distance correlationOct 09 2012Oct 16 2014Sz\'{e}kely, Rizzo and Bakirov (Ann. Statist. 35 (2007) 2769-2794) and Sz\'{e}kely and Rizzo (Ann. Appl. Statist. 3 (2009) 1236-1265), in two seminal papers, introduced the powerful concept of distance correlation as a measure of dependence between sets ... More
Non-Markovian spin transfer dynamics in magnetic semiconductors despite short memory timesMar 18 2013A quantum kinetic theory of the spin transfer between carriers and Mn atoms in a Mn doped diluted magnetic semiconductor is presented. It turns out that the typical memory time associated with these processes is orders of magnitude shorter than the time ... More
Spatially adaptive, Bayesian estimation for probabilistic temperature forecastsJul 17 2015Jun 15 2016Uncertainty in the prediction of future weather is commonly assessed through the use of forecast ensembles that employ a numerical weather prediction model in distinct variants. Statistical postprocessing can correct for biases in the numerical model ... More
Multiscale dynamics of biological cells with chemotactic interactions: from a discrete stochastic model to a continuous descriptionJan 30 2006The Cellular Potts Model (CPM) has been used for simulating various biological phenomena such as differential adhesion, fruiting body formation of the slime mold Dictyostelium discoideum, angiogenesis, cancer invasion, chondrogenesis in embryonic vertebrate ... More
Probabilistic Forecasting and Comparative Model Assessment Based on Markov Chain Monte Carlo OutputAug 24 2016In Bayesian inference, predictive distributions are typically available only through a sample generated via Markov chain Monte Carlo (MCMC) or related algorithms. In this paper, we conduct a systematic analysis of how to make and evaluate probabilistic ... More
Of Quantiles and Expectiles: Consistent Scoring Functions, Choquet Representations, and Forecast RankingsMar 27 2015Apr 17 2015In the practice of point prediction, it is desirable that forecasters receive a directive in the form of a statistical functional, such as the mean or a quantile of the predictive distribution. When evaluating and comparing competing forecasts, it is ... More
The cluster of galaxies Abell 376May 20 2003We present a dynamical analysis of the galaxy cluster Abell 376 based on a set of 73 velocities, most of them measured at Pic du Midi and Haute-Provence observatories and completed with data from the literature. Data on individual galaxies are presented ... More
Quantum dynamics of optical phonons generated by optical excitation of a quantum dotJun 15 2016Jul 15 2016The study of the fundamental properties of phonons is crucial to understand their role in applica- tions in quantum information science, where the active use of phonons is currently highly debated. A genuine quantum phenomenon associated with the fluctuation ... More
Correlating the interstellar magnetic field with protostellar jets and its sourcesSep 09 2011This article combines new CCD polarimetric data with previous information about protostellar objects in a search for correlations involving the interstellar magnetic field. Specifically, we carried out an optical polarimetric study of a sample of 28 fields ... More
Carrier induced ferromagnetism in concentrated and diluted local-moment systemsJun 23 2004For modeling the magnetic properties of concentrated and diluted magnetic semiconductors, we use the Kondo-lattice model. The magnetic phase diagram is derived by inspecting the static susceptibility of itinerant band electrons, which are exchange coupled ... More
Search for an infrared counterpart of IGR J16358-4756Apr 07 2006We report here on near infrared observations of the field around IGR J16358-4756. The source belongs to the new class of highly absorbed X-ray binaries discovered by IBIS/INTEGRAL. Our primary goal was to identify the infrared counterpart of the source, ... More
The OPD Photometric Survey of Open Clusters II. robust determination of the fundamental parameters of 24 open clustersAug 10 2016In the second paper of the series we continue the investigation of open cluster fundamental parameters using a robust global optimization method to fit model isochrones to photometric data. We present optical UBVRI CCD photometry (Johnsons-Cousins system) ... More
The meaning of the concurrence obtained from time-integrated two-photon density matrices in the biexciton cascade in quantum dots coupled to microcavitiesDec 07 2017Dec 12 2017While, theoretically, the degree of entanglement of a two-qubit state can be quantified by the concurrence, the experimental determination of a two-qubit state, such as via quantum state tomography of the two-photon state generated by the biexciton cascade ... More
Optical polarimetry of HH 135/HH 136Jan 31 2007We present optical linear polarimetry in the line of sight to HH135/HH136. The polarimetry of the field stars reveals two populations: one corresponds to a foreground interstellar component; the other originates in the interstellar medium in the vicinity ... More
Optical polarization and near IR photometry of the proto-planetary nebula Hen 3-1475Dec 19 2002We present BVRI CCD aperture polarization and near-infrared photometry of the proto-planetary nebula Hen 3-1475. Its intrinsic polarization is high and shows a strong spectral dependence. The position angles in all bands are perpendicular to the axis ... More
On the Richtmyer-Meshkov instability evolving from a deterministic multimode planar interfaceFeb 06 2014Jun 13 2014We investigate the shock-induced turbulent mixing between a light and heavy gas, where a Richtmyer-Meshkov instability (RMI) is initiated by a $\Ma = 1.5$ shock wave. The prescribed initial conditions define a deterministic multimode interface perturbation ... More
Cyclotron Modeling of the Polar CP TucJan 28 2011CP Tuc (AX J2315-592) is a polar for which two accretion geometries have been put forward. They differ in the location of the accretion column on the white-dwarf surface. In this study, we present new multiband optical photometric and polarimetric data ... More
Solving Big Data Challenges for Enterprise Application Performance ManagementAug 21 2012As the complexity of enterprise systems increases, the need for monitoring and analyzing such systems also grows. A number of companies have built sophisticated monitoring tools that go far beyond simple resource utilization reports. For example, based ... More
Gaussian Random Particles with Flexible Hausdorff DimensionFeb 05 2015Feb 12 2015Gaussian particles provide a flexible framework for modelling and simulating three-dimensional star-shaped random sets. In our framework, the radial function of the particle arises from a kernel smoothing, and is associated with an isotropic random field ... More
Circular polarimetry of magnetic cataclysmic variablesMay 17 2004Magnetic cataclysmic variables are complex accreting binary systems with short orbital periods. Here we present circular polarimetry of five magnetic cataclysmic variable candidates. 1RXS J161008.0+035222, V1432 Aql, and 1RXS J231603.9-052713 have cyclotron ... More
Optical polarimetry and infrared photometry of two AM Her binaries: 1RXS J161008.0+035222 and 1RXS J231603.9-052713Apr 13 2006We present the first optical circular and linear polarization measurements of two polar candidates from ROSAT: 1RXS J161008.0+035222 and 1RXS J231603.9-052713. We also present H band near-infrared photometry of the last object. The presence of strong ... More
Optical polarimetric monitoring of the type II-plateau SN 2005afApr 25 2006Aims. Core-collapse supernovae may show significant polarization that implies non-spherically symmetric explosions. We observed the type II-plateau SN 2005af using optical polarimetry in order to verify whether any asphericity is present in the supernova ... More
A cut-cell finite volume - finite element coupling approach for fluid-structure interaction in compressible flowNov 20 2015Dec 21 2015We present a loosely coupled approach for the solution of fluid-structure interaction problems between a compressible flow and a deformable structure. The method is based on staggered Dirichlet-Neumann partitioning. The interface motion in the Eulerian ... More
Copula CalibrationJul 29 2013We propose notions of calibration for probabilistic forecasts of general multivariate quantities. Probabilistic copula calibration is a natural analogue of probabilistic calibration in the univariate setting. It can be assessed empirically by checking ... More
DualTable: A Hybrid Storage Model for Update Optimization in HiveApr 28 2014Dec 01 2014Hive is the most mature and prevalent data warehouse tool providing SQL-like interface in the Hadoop ecosystem. It is successfully used in many Internet companies and shows its value for big data processing in traditional industries. However, enterprise ... More
Stokes imaging of AM Her systems using 3D inhomogeneous models-II. Modelling X-ray and optical data of CP TucanaeApr 09 2013The viewing geometry of the polar CP Tuc that better explains its optical and X-ray light curves is controversial. Previous modelling of white-light polarimetric data considered the partial self-eclipse of an extended inhomogeneous emitting region. Alternatively, ... More
DGFIndex for Smart Grid: Enhancing Hive with a Cost-Effective Multidimensional Range IndexApr 23 2014Jul 09 2014In Smart Grid applications, as the number of deployed electric smart meters increases, massive amounts of valuable meter data is generated and collected every day. To enable reliable data collection and make business decisions fast, high throughput storage ... More
Exploring coherence of individual excitons in InAs quantum dots embedded in natural photonic defects: influence of the excitation intensityApr 11 2017The exact optical response of quantum few-level systems depends crucially on the exact choice of the incoming pulse areas. We use four-wave mixing (FWM) spectroscopy to infer the coherent response and dynamics of single InAs quantum dots (QDs) and study ... More
Benchmarking in a rotating annulus: a comparative experimental and numerical study of baroclinic wave dynamicsMar 12 2014The differentially heated rotating annulus is a widely studied tabletop-size laboratory model of the general mid-latitude atmospheric circulation. The two most relevant factors of cyclogenesis, namely rotation and meridional temperature gradient are quite ... More
The selection function of the RAVE surveyNov 02 2016The selection function of a sample of observed objects quantifies the probability that a given target would have been observed and included in the final catalogue. Knowledge of this function is indispensable for any statistical analysis of such a sample. ... More
He II $λ$4686 emission from the massive binary system in $η$ Car: constraints to the orbital elements and the nature of the periodic minimaJan 13 2016{\eta} Carinae is an extremely massive binary system in which rapid spectrum variations occur near periastron. Most notably, near periastron the He II $\lambda 4686$ line increases rapidly in strength, drops to a minimum value, then increases briefly ... More
4MOST - 4-metre Multi-Object Spectroscopic TelescopeJun 28 2012The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop a wide-field (>3 square degree, goal >5 square degree), high-multiplex (>1500 fibres, goal 3000 fibres) spectroscopic survey facility for an ESO ... More