Results for "C. Richter"

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On the hitting times of quantum versus random walksAug 01 2008In this paper we define new Monte Carlo type classical and quantum hitting times, and we prove several relationships among these and the already existing Las Vegas type definitions. In particular, we show that for some marked state the two types of hitting ... More
Open-Sourced Reinforcement Learning Environments for Surgical RoboticsMar 05 2019Reinforcement Learning (RL) is a machine learning framework for artificially intelligent systems to solve a variety of complex problems. Recent years has seen a surge of successes solving challenging games and smaller domain problems, including simple ... More
On the homology and homotopy of commutative shuffle algebrasOct 10 2013Jan 24 2014For commutative algebras there are three important homology theories, Harrison homology, Andre-Quillen homology and Gamma-homology. In general these differ, unless one works with respect to a ground field of characteristic zero. We show that the analogues ... More
An averaging scheme for the efficient approximation of time-periodic flow problemsJun 04 2018We study periodic solutions to the Navier-Stokes equations. The transition phase of a dynamic Navier-Stokes solution to the periodic state can be excessively long and it depends on the domain size and on problem parameters like the viscosity. Several ... More
Assessment and OutlookJan 04 2000Jan 10 2000My assignment at this conference is to assess where we are in high-energy physics and speculate on where we might be going. This frees me from any obligation to summarize all that went on here and allows me to talk just about those topics that interest ... More
Quantum speedup of classical mixing processesSep 26 2006Apr 05 2007Most approximation algorithms for #P-complete problems (e.g., evaluating the permanent of a matrix or the volume of a polytope) work by reduction to the problem of approximate sampling from a distribution $\pi$ over a large set $\S$. This problem is solved ... More
Two remarks on the local Hamiltonian problemDec 27 2007In this note we present two natural restrictions of the local Hamiltonian problem which are BQP-complete under Karp reduction. Restrictions complete for QCMA, QMA_1, and MA were demonstrated previously.
Exact Relativistic Gravitational Field of a Stationary Counterrotating Dust DiskAug 13 1999Disks of collisionless particles are important models for certain galaxies and accretion disks in astrophysics. We present here a solution to the stationary axisymmetric Einstein equations which represents an infinitesimally thin dust disk consisting ... More
Physically Realistic Solutions to the Ernst Equation on Hyperelliptic Riemann SurfacesJun 10 1998Oct 07 1998We show that the class of hyperelliptic solutions to the Ernst equation (the stationary axisymmetric Einstein equations in vacuum) previously discovered by Korotkin and Neugebauer and Meinel can be derived via Riemann-Hilbert techniques. The present paper ... More
Phase-coherent transport in InN nanowires of various sizesFeb 27 2008We investigate phase-coherent transport in InN nanowires of various diameters and lengths. The nanowires were grown by means of plasma-assisted molecular beam epitaxy. Information on the phase-coherent transport is gained by analyzing the characteristic ... More
Riemann-Hilbert Problems for the Ernst Equation and Fibre BundlesNov 12 1998Riemann--Hilbert techniques are used in the theory of completely integrable differential equations to generate solutions that contain a free function which can be used at least in principle to solve initial or boundary value problems. The solution of ... More
Doppler Shift in Andreev Reflection from a Moving Superconducting Condensate in Nb/InAs Josephson JunctionsMar 02 2009Oct 22 2009We study narrow ballistic Josephson weak links in a InAs quantum wells contacted by Nb electrodes and find a dramatic magnetic-field suppression of the Andreev reflection amplitude, which occurs even for in-plane field orientation with essentially no ... More
[S IV] in the NGC 5253 Supernebula: Ionized Gas Kinematics at High ResolutionJun 05 2012The nearby dwarf starburst galaxy NGC 5253 hosts a deeply embedded radio-infrared supernebula excited by thousands of O stars. We have observed this source in the 10.5{\mu}m line of S+3 at 3.8 kms-1 spectral and 1.4" spatial resolution, using the high ... More
The nature of NV absorbers at high redshiftJul 29 2008Jan 23 2009We present a study of NV absorption systems at 1.5 < z < 2.5 in the optical spectra of 19 QSOs. Our analysis includes both absorbers arising from the intergalactic medium as well as systems in the vicinity of the background quasar. We construct detailed ... More
Assessing robustness of radiomic features by image perturbationJun 18 2018Image features need to be robust against differences in positioning, acquisition and segmentation to ensure reproducibility. Radiomic models that only include robust features can be used to analyse new images, whereas models with non-robust features may ... More
Almost uniform sampling via quantum walksJun 24 2006Sep 18 2006Many classical randomized algorithms (e.g., approximation algorithms for #P-complete problems) utilize the following random walk algorithm for {\em almost uniform sampling} from a state space $S$ of cardinality $N$: run a symmetric ergodic Markov chain ... More
Dust depletion of Ca and Ti in QSO absorption line systemsMay 10 2016To explore the role of titanium- and calcium-dust depletion in gas in and around galaxies we systematically study Ti/Ca abundance ratios in intervening absorption-line systems at low and high redshift. We investigate high-resolution optical spectra obtained ... More
Magnetotransport through graphene nanoribbons at high magnetic fieldsNov 18 2011May 23 2012We have investigated the magnetoresistance of lithographically prepared single-layer graphene nanoribbons in pulsed, perpendicular magnetic fields up to 60 T and performed corresponding transport simulations using a tight-binding model and several types ... More
Triggering and probing of phase-coherent spin packets by time-resolved spin transport across an Fe/GaAs Schottky barrierApr 19 2012Time-resolved electrical spin transport is used to generate and probe spin currents in GaAs electrically. We use high bandwidth current pulses to inject phase-coherent spin packets from Fe into n-GaAs. By means of time-resolved Faraday rotation we demonstrate ... More
Towards a semiclassical understanding of chaotic single- and many-particle quantum dynamics at post-Heisenberg time scalesMar 22 2019Despite considerable progress during the last decades in devising a semiclassical theory for classically chaotic quantum systems a quantitative semiclassical understanding of their dynamics at late times (beyond the so-called Heisenberg time $T_H$) is ... More
Quantile Regression Deep Reinforcement LearningJun 27 2019Policy gradient based reinforcement learning algorithms coupled with neural networks have shown success in learning complex policies in the model free continuous action space control setting. However, explicitly parameterized policies are limited by the ... More
Finite Element Error Estimates under Geometric UncertaintyFeb 20 2019We develop error estimates for the finite element approximation of elliptic partial differential equations under geometric uncertainty, i.e. when the computational domain does not match the real geometry. The result shows that the uncertainty related ... More
The J_1-J_2 antiferromagnet with Dzyaloshinskii-Moriya interaction on the square lattice: An exact diagonalization studyApr 11 1996We examine the influence of an anisotropic interaction term of Dzyaloshinskii-Moriya (DM) type on the groundstate ordering of the J_1-J_2 spin-1/2-Heisenberg antiferromagnet on the square lattice. For the DM term we consider several symmetries corresponding ... More
Nonclassical characteristic functions for highly sensitive measurementsJan 29 2007Oct 26 2007Characteristic functions are shown to be useful for highly sensitive measurements. Redistributions of motional Fock states of a trapped atom can be directly monitored via the most fragile nonclassical part of the characteristic function. The method can ... More
A parallel Newton multigrid framework for monolithic fluid-structure interactionsApr 04 2019Apr 28 2019We present a monolithic parallel Newton-multigrid solver for nonlinear three dimensional fluid-structure interactions in Arbitrary Lagrangian Eulerian formulation. We start with a finite element discretization of the coupled problem, based on a remapping ... More
Trajectory Optimization of Robots with Regenerative Drive Systems: Numerical and Experimental ResultsApr 01 2018We investigate energy-optimal control of robots with ultracapacitor based regenerative drive systems. Based on a previously introduced framework, a fairly generic model is considered for the robot and the drive system. An optimal control problem is formulated ... More
Discrete Time Term Structure Theory and Consistent Recalibration ModelsSep 05 2014We develop theory and applications of forward characteristic processes in discrete time following a seminal paper of Jan Kallsen and Paul Kr\"uhner. Particular emphasis is placed on the dynamics of volatility surfaces which can be easily formulated and ... More
A strictly commutative model for the cochain algebra of a spaceJan 03 2018Sep 24 2018The commutative differential graded algebra $A_{\mathrm{PL}}(X)$ of polynomial forms on a simplicial set $X$ is a crucial tool in rational homotopy theory. In this note, we construct an integral version $A^{\mathcal{I}}(X)$ of $A_{\mathrm{PL}}(X)$. Our ... More
The magnetic susceptibility of disordered non-diffusive mesoscopic systemsMar 17 1999Disorder-induced spectral correlations of mesoscopic quantum systems in the non-diffusive regime and their effect on the magnetic susceptibility are studied. We perform impurity averaging for non-translational invariant systems by combining a diagrammatic ... More
From clean to diffusive mesoscopic systems: A semiclassical approach to the magnetic susceptibilityJun 18 1998We study disorder-induced spectral correlations and their effect on the magnetic susceptibility of mesoscopic quantum systems in the non-diffusive regime. By combining a diagrammatic perturbative approach with semiclassical techniques we perform impurity ... More
Tilings of convex sets by mutually incongruent equilateral triangles contain arbitrarily small tilesNov 24 2017We show that every tiling of a convex set in the Euclidean plane $\mathbb{R}^2$ by equilateral triangles of mutually different sizes contains arbitrarily small tiles. The proof is purely elementary up to the discussion of one family of tilings of the ... More
On the cooperation algebra of the connective Adams summandJun 22 2005Jul 05 2005The aim of this paper is to gain explicit information about the multiplicative structure of l_*l, where l is the connective Adams summand. Our approach differs from Kane's or Lellmann's because our main technical tool is the MU-based Kuenneth spectral ... More
Layout of random circulant graphsJul 14 2017A circulant graph H is defined on the set of vertices V=\left\{ 1,\ldots,n\right\} and edges E=\left\{ \left(i,j\right):\left|i-j\right|\equiv s\left(\textrm{mod}n\right),s\in S\right\} , where S\subseteq\left\{ 1,\ldots,\lceil\frac{n-1}{2}\rceil\right\} ... More
Field-Effect Devices Utilizing LaAlO$_3$-SrTiO$_3$ InterfacesJan 28 2012Using LaAlO$_3$-SrTiO$_3$ bilayers, we have fabricated field-effect devices that utilize the two-dimensional electron liquid generated at the bilayers' {\textit n}-type interfaces as drain-source channels and the LaAlO$_3$ layers as gate dielectrics. ... More
Highly anisotropic magnetic states of Co dimers bound to graphene-vacanciesMay 15 2012The adsorption behavior and the magnetic states of cobalt atoms and dimers on single vacancies in a graphene sheet are investigated by means of relativistic density functional calculations. It is found that local magnetic moments are formed in both cases, ... More
High-resolution observations of two OVI absorbers at z=2 towards PKS 1448-232Oct 20 2011To explore the ionization conditions in highly-ionized absorbers at high redshift we have studied in detail two intervening OVI absorbers at z=2 towards the quasar PKS1448-232, based on high (R=75,000) and intermediate (R=45,000) resolution optical VLT/UVES ... More
The role of Zhang-Rice singlet-like excitations in one-dimensional cupratesJan 27 2000We present the first calculation of the electron-energy loss spectrum of infinite one-dimensional undoped CuO_3 chains within a multi-band Hubbard model. The results show good agreement with experimental spectra of Sr_2CuO_3. The main feature in the spectra ... More
The transition from an ordered antiferromagnet to a quantum disordered spin liquid in a solvable bilayer modelOct 26 1995We present a spin-1/2 bilayer model for the quantum order-disorder transition which (i) can be solved by mean-field theory for bulk quantities, (ii) becomes critical at the transition, and (iii) allows to include intralayer frustration. We present numerical ... More
Cu-O network dependent core-hole screening in low-dimensional cuprates: A theoretical analysisMar 11 2000We analyze the influence of the dimensionality on the Cu 2p_3/2 core level X-ray photoemission spectra of undoped cuprates. Both exchange splitting and delocalization properties are described within one framework using a multi-band Hubbard model. The ... More
Embedding convex geometries and a bound on convex dimensionFeb 06 2015Oct 13 2016The notion of an abstract convex geometry offers an abstraction of the standard notion of convexity in a linear space. Kashiwabara, Nakamura and Okamoto introduce the notion of a generalized convex shelling into $\mathbb{R}$ and prove that a convex geometry ... More
Experimental Test of a Trace Formula for a Chaotic Three Dimensional Microwave CavityJun 18 2002Jul 22 2002We have measured resonance spectra in a superconducting microwave cavity with the shape of a three-dimensional generalized Bunimovich stadium billiard and analyzed their spectral fluctuation properties. The experimental length spectrum exhibits contributions ... More
Coexistence of Magnetic Order and Two-dimensional Superconductivity at LaAlO$_3$/SrTiO$_3$ InterfacesMay 02 2011A two dimensional electronic system with novel electronic properties forms at the interface between the insulators LaAlO$_3$ and SrTiO$_3$. Samples fabricated until now have been found to be either magnetic or superconducting, depending on growth conditions. ... More
Spin filtering and magnetoresistance in ballistic tunnel junctionsMar 21 2001Oct 19 2001We theoretically investigate magnetoresistance (MR) effects in connection with spin filtering in quantum-coherent transport through tunnel junctions based on non-magnetic/semimagnetic heterostructures. We find that spin filtering in conjunction with the ... More
Non-associative Ore extensionsSep 04 2015Sep 19 2016We introduce non-associative Ore extensions, $S = R[X ; \sigma , \delta]$, for any non-associative unital ring $R$ and any additive maps $\sigma,\delta : R \rightarrow R$ satisfying $\sigma(1)=1$ and $\delta(1)=0$. In the special case when $\delta$ is ... More
The sub-DLA toward HE0001-2340: galaxy formation at z=2May 17 2005We present a detailed analysis of chemical abundances in a sub-damped Ly alpha absorber (sub-DLA) at z=2.187 towards the quasar HE0001-2340 (z_em=2.28) using VLT/UVES data. This sub-DLA system consists of at least 25 individual subcomponents spanning ... More
Motion Scaling Solutions for Improved Performance in High Delay Surgical TeleoperationFeb 08 2019Robotic teleoperation brings great potential for advances within the field of surgery. The ability of a surgeon to reach patient remotely opens exciting opportunities. Early experience with telerobotic surgery has been interesting, but the clinical feasibility ... More
Magnetic susceptibility of frustrated spin-s J1-J2 quantum Heisenberg magnets: High-temperature expansion and exact diagonalization dataJan 22 2014Motivated by recent experiments on low-dimensional frustrated quantum magnets with competing nearest-neighbor exchange coupling J1 and next nearest-neighbor exchange coupling J2 we investigate the magnetic susceptibility of two-dimensional J1-J2 Heisenberg ... More
Analytical ground state for the three-band Hubbard modelApr 17 1999For the calculation of charge excitations as those observed in, e.g., photo-emission spectroscopy or in electron-energy loss spectroscopy, a correct description of ground-state charge properties is essential. In strongly correlated systems like the undoped ... More
R-matrix theory of driven electromagnetic cavitiesMar 18 2003Jul 17 2003Resonances of cylindrical symmetric microwave cavities are analyzed in R-matrix theory which transforms the input channel conditions to the output channels. Single and interfering double resonances are studied and compared with experimental results, obtained ... More
The quantum Heisenberg antiferromagnet on the Sierpinski Gasket: An exact diagonalization studyAug 28 2001We present an exact diagonalization study of the quantum Heisenberg antiferromagnet on the fractal Sierpinski gasket for spin quantum numbers s=1/2,s=1 and s=3/2. Since the fractal dimension of the Sierpinski gasket is between one and two we compare the ... More
Low-lying excitations and thermodynamics of an antiferromagnetic Heisenberg fractal system of a dimension between one and twoOct 22 1997We investigate a frustrated Heisenberg spin-1/2 antiferromagnet on a fractal lattice of dimension d=ln3/ln2 (Sierpinski gasket). Calculations were performed using (a) exact diagonalization of all eigenstates and eigenvectors for systems up to N=15 and ... More
Zero-one laws for eventually always hitting points in mixing systemsApr 18 2019Jul 08 2019In this work we study the set of eventually always hitting points in shrinking target systems. These are points whose long orbit segments eventually hit the corresponding shrinking targets for all future times. We focus our attention on systems where ... More
Revisiting the nilpotent polynomial Hales-Jewett theoremJul 18 2016Nov 21 2018Answering a question posed by Bergelson and Leibman in [6], we establish a nilpotent version of the polynomial Hales-Jewett theorem that contains the main theorem in [6] as a special case. Important to the formulation and the proof of our main theorem ... More
Extending Drawings of Graphs to Arrangements of PseudolinesApr 25 2018A pseudoline is a homeomorphic image of the real line in the plane so that its complement is disconnected. An arrangement of pseudolines is a set of pseudolines in which every two cross exactly once. A drawing of a graph is pseudolinear if the edges can ... More
On the crossing number of K_13Jul 12 2013Since the crossing number of K_{12} is now known to be 150, it is well-known that simple counting arguments and Kleitman's parity theorem for the crossing number of K_{2n+1} combine with a specific drawing of K_{13} to show that the crossing number of ... More
Automatic Generation of Bounds for Polynomial Systems with Application to the Lorenz SystemDec 21 2017Jun 06 2018This study covers an analytical approach to calculate positively invariant sets of dynamical systems. Using Lyapunov techniques and quantifier elimination methods, an automatic procedure for determining bounds in the state space as an enclosure of attractors ... More
H_2 absorption in a dense interstellar filament in the Milky Way haloMay 01 2003We investigate interstellar absorption from molecular hydrogen (H_2) and metals in an intermediate-velocity cloud (IVC) in the direction of the LMC star Sk -68 80 (HD 36521), based on data from the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. ... More
The most metal-poor damped Ly alpha system at z<3: constraints on early nucleosynthesisFeb 06 2006To constrain the conditions for very early nucleosynthesis in the Universe we compare the chemical enrichment pattern of an extremely metal-poor damped Lyman alpha (DLA) absorber with predictions from recent explosive nucleosynthesis model calculations. ... More
Graphs with at most one crossingJan 28 2019The crossing number of a graph $G$ is the least number of crossings over all possible drawings of $G$. We present a structural characterization of graphs with crossing number one.
Graphs with at most one crossingJan 28 2019Apr 26 2019The crossing number of a graph $G$ is the least number of crossings over all possible drawings of $G$. We present a structural characterization of graphs with crossing number one.
Optimal drawings of $K_{p,q}$ in surfaces, $p$ fixed, $q$ largeJun 11 2018For a fixed positive integer $p$ and surface $\Sigma$, there is a finite set $\mathcal{D}(p,\Sigma)$ of `good' drawings of complete bipartite graphs $K_{p,r}$ (with possible varying $r$) such that, for every good drawing $D$ of $K_{p,q}$, there is a good ... More
The Surface Topography of a Magnetic Fluid -- a Quantitative Comparison between Experiment and Numerical SimulationApr 05 2006Jul 20 2006The normal field instability in magnetic liquids is investigated experimentally by means of a radioscopic technique which allows a precise measurement of the surface topography. The dependence of the topography on the magnetic field is compared to results ... More
OpenCL 2.0 for FPGAs using OCLAccAug 28 2015Designing hardware is a time-consuming and complex process. Realization of both, embedded and high-performance applications can benefit from a design process on a higher level of abstraction. This helps to reduce development time and allows to iteratively ... More
Magnetic traveling-stripe-forcing: enhanced transport in the advent of the Rosensweig instabilityApr 23 2010A new kind of contactless pumping mechanism is realized in a layer of ferrofluid via a spatio-temporally modulated magnetic field. The resulting pressure gradient leads to a liquid ramp, which is measured by means of X-rays. The transport mechanism works ... More
First steps in tropical geometryJun 25 2003Dec 09 2003Tropical algebraic geometry is the geometry of the tropical semiring $(\mathbb{R},\min,+)$. Its objects are polyhedral cell complexes which behave like complex algebraic varieties. We give an introduction to this theory, with an emphasis on plane curves ... More
Microdeflectometry - a novel tool to acquire 3D microtopography with nanometer height resolutionOct 24 2007Feb 15 2008We introduce "microdeflectometry", a novel technique for measuring the microtopography of specular surfaces. The primary data is the local slope of the surface under test. Measuring the slope instead of the height implies high information efficiency and ... More
The Variability and Period Analysis for the BL Lac AO 0235+164Feb 19 2017Variability is one of the extreme observational properties of BL Lacertae objects. AO 0235+164 is a well studied BL Lac through the whole electro-magnetic wavebands. In the present work, we show its optical R band photometric observations carried out ... More
Evidence for Superconducting Phase Coherence in the Metallic/Insulating Regime of the LaAlO3-SrTiO3 Interface Electron SystemDec 18 2015A superconducting phase with an extremely low carrier density of the order of 10^13 cm^-2 is present at LaAlO3-SrTiO3 interfaces. If depleted from charge carriers by means of a gate field, this superconducting phase undergoes a transition into a metallic/insulating ... More
Large Negative Electronic Compressibility of LaAlO3-SrTiO3 Interfaces with Ultrathin LaAlO3 LayersJul 27 2012A two-dimensional electron liquid is formed at the n-type interface between SrTiO3 and LaAlO3. Here we report on Kelvin probe microscopy measurements of the electronic compressibility of this electron system. The electronic compressibility is found to ... More
The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity cloudsJan 07 2013We use archival UV absorption-line data from HST/STIS to statistically analyse the absorption characteristics of the high-velocity clouds (HVCs) in the Galactic halo towards more than 40 extragalactic background sources. We determine absorption covering ... More
A Symbiotic Scenario for the Rapid Formation of Supermassive Black HolesNov 17 2006The most massive black holes, lurking at the centers of large galaxies, must have formed less than a billion years after the big bang, as they are visible today in the form of bright quasars at redshift larger than six. Their early appearance is mysterious, ... More
Response of a ferrofluid to traveling-stripe forcingMar 20 2008We observe the dynamics of waves propagating on the surface of a ferrofluid under the influence of a spatially and temporarily modulated field. In particular, we excite plane waves by a travelling lamellar modulation of the magnetization. By this external ... More
Prospects for the Search for a Standard Model Higgs Boson in ATLAS using Vector Boson FusionFeb 24 2004The potential for the discovery of a Standard Model Higgs boson in the mass range m_H < 2 m_Z in the vector boson fusion mode has been studied for the ATLAS experiment at the LHC. The characteristic signatures of additional jets in the forward regions ... More
Multiplicative combinatorial properties of return time sets in minimal dynamical systemsSep 23 2018Sep 16 2019We investigate the relationship between the dynamical properties of minimal topological dynamical systems and the multiplicative combinatorial properties of return time sets arising from those systems. In particular, we prove that for a residual sets ... More
Inhabitants of interesting subsets of the Bousfield latticeFeb 10 2017The set of Bousfield classes has some important subsets such as the distributive lattice $\mathbf{DL}$ of all classes $\langle E\rangle$ which are smash idempotent and the complete Boolean algebra $\mathbf{cBA}$ of closed classes. We provide examples ... More
Uniqueness of circumcenters in generalized Minkowski spacesMar 28 2018Apr 04 2018In an $n$-dimensional normed space every bounded set has a unique circumball if and only if every set of cardinality two has a unique circumball and if and only if the unit ball of the space is strictly convex. When the symmetry of the norm is dropped, ... More
On the implementation of a locally modified finite element method for interface problems in deal.IIJun 04 2018In this work, we describe a simple finite element approach that is able to resolve weak discontinuities in interface problems accurately. The approach is based on a fixed patch mesh consisting of quadrilaterals, that will stay unchanged independent of ... More
Partial Fermionization---Spectral Universality in 1D Repulsive Bose GasesFeb 22 2019Due to the vast growth of the many-body level density with excitation energy, its smoothed form is of central relevance for spectral and thermodynamic properties of interacting quantum systems. We compute the cumulative of this level density for confined ... More
Absorption signatures of warm-hot gas at low redshift: NeVIIIMar 25 2013Oct 07 2013At z<1 a large fraction of the baryons is thought to reside in diffuse gas that has been shock-heated to high temperatures (log T=5-6). Absorption by the 770.41, 780.32 {\AA} doublet of NeVIII in quasar spectra represents a unique tool to study this elusive ... More
How long can it take for a quantum channel to forget everything?May 03 2012We investigate quantum channels, which after a finite number $k$ of repeated applications erase all input information, i.e., channels whose $k$-th power (but no smaller power) is a completely depolarizing channel. We show that on a system with Hilbert ... More
Illuminating and covering convex bodiesAug 04 2013Covering numbers of convex bodies based on homothetical copies and related illumination numbers are well-known in combinatorial geometry and, for example, related to Hadwiger's famous covering problem. Similar numbers can be defined by using proper translates ... More
GPU Accelerated Explicit Time Integration Methods for Electro-Quasistatic FieldsDec 30 2016Electro-quasistatic field problems involving nonlinear materials are commonly discretized in space using finite elements. In this paper, it is proposed to solve the resulting system of ordinary differential equations by an explicit Runge-Kutta-Chebyshev ... More
Ultrafast relaxation of photoexcited superfluid He nanodropletsMay 11 2019The relaxation of photoexcited nanosystems is a fundamental process of light-matter interaction. Depending on the couplings of the internal degrees of freedom, relaxation can be ultrafast, converting electronic energy in a few fs, or slow, if the energy ... More
Ultrafast exciton formation at the ZnO(10${\overline{\textbf{1}}}$0) surfaceSep 30 2014We study the ultrafast quasiparticle dynamics in and below the ZnO conduction band using femtosecond time-resolved two-photon photoelectron spectroscopy. Above band gap excitation causes hot electron relaxation by electron-phonon scattering down to the ... More
High Quality Yttrium Iron Garnet Grown by Room Temperature Pulsed Laser Deposition and Subsequent AnnealingFeb 24 2015Jun 12 2015We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG) by annealing in oxygen atmosphere. Our findings show that well below the melting temperature the material transforms into a fully epitaxial layer with exceptional quality, both ... More
The neutral gas extent of galaxies as derived from weak intervening CaII absorbersAug 12 2010Jan 05 2011(Abridged) We present a systematic study of weak intervening CaII absorbers at low redshift (z<0.5), based on the analysis of archival high resolution (R>45,000) optical spectra of 304 quasars and active galactic nuclei observed with VLT/UVES. Along a ... More
The MeerKAT Fornax SurveySep 05 2017We present the science case and observations plan of the MeerKAT Fornax Survey, an HI and radio continuum survey of the Fornax galaxy cluster to be carried out with the SKA precursor MeerKAT. Fornax is the second most massive cluster within 20 Mpc and ... More
Measurement of Cosmic Microwave Background Polarization Power Spectra from Two Years of BICEP DataJun 05 2009Feb 23 2010Background Imaging of Cosmic Extragalactic Polarization (BICEP) is a bolometric polarimeter designed to measure the inflationary B-mode polarization of the cosmic microwave background (CMB) at degree angular scales. During three seasons of observing at ... More
Large capacitance enhancement and negative compressibility of two-dimensional electronic systems at LaAlO$_3$/SrTiO$_3$ interfacesJun 14 2010Jul 12 2010Novel electronic systems forming at oxide interfaces comprise a class of new materials with a wide array of potential applications. A high mobility electron system forms at the LaAlO$_3$/SrTiO$_3$ interface and, strikingly, both superconducts and displays ... More
Resonant photoemission with circular polarized light on magnetized LSMOJun 05 2018We have used resonant photoemission with circular polarized light as a new tool to obtain information about the electronic structure of half-metals. After careful sample surface preparation of La0.7Sr0.3MnO3, we have obtained a dichroic signal for the ... More
Experimental vs. Numerical Eigenvalues of a Bunimovich Stadium Billiard -- A ComparisonJun 21 1999We compare the statistical properties of eigenvalue sequences for a gamma=1 Bunimovich stadium billiard. The eigenvalues have been obtained by two ways: one set results from a measurement of the eigenfrequencies of a superconducting microwave resonator ... More
ESA Voyage 2050 white paper: A complete census of the gas phases in and around galaxies, far-UV spectropolarimetry as a prime tool for understanding galaxy evolution and star formationSep 06 2019(abridged) The far-UV wavelength range (912-2000A) provides access to atomic and molecular transitions of many species the interstellar medium (ISM), circumgalactic medium (CGM), and intergalactic medium, within phases spanning a wide range of ionization, ... More
Molecular Gas in the Galactic Halo and BeyondSep 12 2001I review recent observations of molecular gas in the halo of the Milky Way and in the Magellanic Clouds. Far-ultraviolet absorption line studies of molecular hydrogen (H_2) with ORFEUS and FUSE have unveiled the presence of a diffuse molecular hydrogen ... More
ORFEUS II echelle spectra : H_2 measurements in the Magellanic CloudsMay 12 2000More than 20 years after the Copernicus satellite, ORFEUS allows the investigation of molecular hydrogen (H_2) in the diffuse interstellar medium by way of FUV absorption spectroscopy once again. This time, targets in the Magellanic Clouds were also observed, ... More
Dynamic landscape models of coevolutionary gamesNov 28 2016Players of coevolutionary games may update not only their strategies but also their networks of interaction. Based on interpreting the payoff of players as fitness, dynamic landscape models are proposed. The modeling procedure is carried out for Prisoner's ... More
Direct Determination of the HF/H2 Abundance Ratio in Interstellar GasJan 09 2013We report the first detection of the v=1--0, R(0) ro-vibrational transition of HF at 2.499385 microns arising from interstellar gas. The line is seen in absorption toward 3 background sources---HD 154368, Elias 29, and AFGL 2136 IRS 1---all of which have ... More
Floquet oscillations in periodically driven Dirac systemsJun 11 2019Electrons in a lattice exhibit time-periodic motion, known as Bloch oscillation, when subject to an additional static electric field. Here we show that a corresponding dynamics can occur upon replacing the spatially periodic potential by a time-periodic ... More
The DNA Nucleobase Thymine in Motion - Intersystem Crossing Simulated with Surface HoppingOct 14 2016We report ab initio excited-state dynamics simulations on isolated thymine to investigate the mechanism of intersystem crossing, based on CASSCF potential energy surfaces and the \textsc{Sharc} surface hopping method. We show that even though $S_2 \rightarrow ... More
Nonlinear transport of Bose-Einstein condensates through mesoscopic waveguidesJul 12 2007We study the coherent flow of interacting Bose-condensed atoms in mesoscopic waveguide geometries. Analytical and numerical methods, based on the mean-field description of the condensate, are developed to study both stationary as well as time-dependent ... More
Information content of coevolutionary game landscapesMar 20 2018Coevolutionary game dynamics is the result of players that may change their strategies and their network of interaction. For such games, and based on interpreting strategies as configurations, strategy-to-payoff maps can be defined for every interaction ... More