Results for "A. Schweitzer"

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Riemannian manifolds not quasi-isometric to leaves in codimension one foliationsNov 24 2009Every open manifold L of dimension greater than one has complete Riemannian metrics g with bounded geometry such that (L,g) is not quasi-isometric to a leaf of a codimension one foliation of a closed manifold. Hence no conditions on the local geometry ... More
Locally convex hypersurfaces immersed in $H^n \times R$May 02 2012We prove a theorem of Hadamard-Stoker type: a connected locally convex complete hypersurface immersed in $H^n \times R$ (n>1), where $H^n$ is n-dimensional hyperbolic space, is embedded and homeomorphic either to the n-sphere or to $R^n$. In the latter ... More
Frequency dependent transport in the integer quantum Hall effectFeb 23 2001The frequency dependent transport is investigated for a two-dimensional disordered system under QHE conditions. The real and imaginary parts of the conductivity are calculated numerically in linear response using a recursive Green function technique. ... More
Frequency dependent conductivity in the integer quantum Hall effectAug 09 1999Frequency dependent electronic transport is investigated for a two-dimensional disordered system in the presence of a strong perpendicular static magnetic field. The ac-conductivity is calculated numerically from Kubo's linear response theory using a ... More
Azimuthal single spin asymmetries in SIDIS in the light of chiral symmetry breakingOct 28 2003An attempt is made to understand the z-dependence of the azimuthal single spin asymmetries observed by the HERMES collaboration in terms of chiral models based on effective quark and Goldstone boson degrees of freedom. The effects of respectively neglecting ... More
Subgroups of 3-factor direct productsJul 12 2016Extending Goursat's Lemma we investigate the structure of subdirect products of 3-factor direct products. We give several example constructions and then provide a structure theorem showing that every such group is essentially obtained by a combination ... More
$C^\infty$ Functions on the Stone-Čech Compactification of the IntegersOct 03 2014We construct an algebra $A=\ell^{\infty \infty}({\Bbb Z})$ of smooth functions which is dense in the pointwise multiplication algebra $\ell^\infty({\Bbb Z})$ of sup-norm bounded functions on the integers $\Bbb Z$. The algebra $A$ properly contains the ... More
${\mathbb Z}_n$-equivariant $K$-theoryMay 08 2015We construct a sequence of $n-1$ cyclic exact sequences that can be used to compute the $K$-theory of the $C^\star$-algebra crossed product $A \ltimes {\mathbb Z}_n$.
Canonizing Graphs of Bounded Tree Width in LogspaceJun 25 2015Graph canonization is the problem of computing a unique representative, a canon, from the isomorphism class of a given graph. This implies that two graphs are isomorphic exactly if their canons are equal. We show that graphs of bounded tree width can ... More
Dependence of critical level statistics on the sample shapeApr 29 1998The level-spacing distribution of consecutive energy eigenvalues is calculated numerically at the metal insulator transition for 3d systems with different cuboid shapes. It is found that the scale independent critical $P_c(s)$ changes as a function of ... More
Relation between the Correlation Dimensions of Multifractal Wavefunctions and Spectral Measures in Integer Quantum Hall SystemsJan 26 1994We study the time evolution of wavepackets of non-interacting electrons in a two-dimensional disordered system in strong magnetic field. For wavepackets built from states near the metal-insulator transition in the center of the lowest Landau band we find ... More
Critical conductance of the chiral 2d random flux modelAug 27 2007Aug 29 2007The two-terminal conductance of a random flux model defined on a square lattice is investigated numerically at the band center using a transfer matrix method. Due to the chiral symmetry, there exists a critical point where the ensemble averaged mean conductance ... More
Reduction Techniques for Graph Isomorphism in the Context of Width ParametersMar 27 2014We study the parameterized complexity of the graph isomorphism problem when parameterized by width parameters related to tree decompositions. We apply the following technique to obtain fixed-parameter tractability for such parameters. We first compute ... More
Pressure-dependent optical investigations of $α$-(BEDT-TTF)$_2$I$_3$: tuning charge order and narrow gap towards a Dirac semimetalJan 19 2016Mar 24 2016Infrared optical investigations of $\alpha$-(BEDT-TTF)$_2$I$_3$ have been performed in the spectral range from 80 to 8000~cm$^{-1}$ down to temperatures as low as 10~K by applying hydrostatic pressure. In the metallic state, $T > 135$~K, we observe a ... More
Normal subgroups of diffeomorphism and homeomorphism groups of R^n and other open manifoldsNov 25 2009Apr 10 2012We determine all the normal subgroups of the group of C^r diffeomorphisms of R^n, r = 1,2,...,infinity, except when r=n+1 or n=4, and also of the group of homeomorphisms of R^n (r=0). We also study the group A_0 of diffeomorphisms of an open manifold ... More
The chirally-odd twist-3 distribution e(x)Dec 03 2002Aug 25 2003Properties of the nucleon twist-3 distribution function e(x) are reviewed. It is emphasized that the QCD equations of motion imply the existence of a delta-function at x=0 in e(x), which gives rise to the pion-nucleon sigma-term. According to the resulting ... More
Search for quantum electronic dipoles in the dimerized κ-(BEDT-TTF)2Cu[N(CN)2]Cl saltOct 12 2012The Mott insulator \kappa-(BEDT-TTF)2Cu[N(CN)2]Cl consists of molecular dimers arranged on an anisotropic triangular lattice and develops a canted antiferromagnetic ground state. It has recently been suggested that this system features purely electronic ... More
Determination of $J/ψ$ chromoelectric polarizability from lattice dataJan 26 2018The chromoelectric polarizability of $J/\psi$ is extracted from lattice QCD data on the nucleon-$J/\psi$ potential in the heavy quark limit. The value of $\alpha(1S) = (1.5 \pm 0.6) \,{\rm GeV}^{-3} $ is obtained. We also comment on the possibility of ... More
Switching Reconstruction of DigraphsAug 03 2013Switching about a vertex in a digraph means to reverse the direction of every edge incident with that vertex. Bondy and Mercier introduced the problem of whether a digraph can be reconstructed up to isomorphism from the multiset of isomorphism types of ... More
D-term, strong forces in the nucleon, and their applicationsJan 17 2018The D-term is a fundamental particle property which is defined through the matrix elements of the energy-momentum tensor and as such in principle on equal footing with mass and spin. Yet the experimental information on the D-term of any hadron is very ... More
TMDs in the bag modelAug 14 2011Oct 13 2011Leading and subleading twist transverse momentum dependent parton distribution functions (TMDs) are studied in a quark model framework provided by the bag model. A complete set of relations among different TMDs is derived, and the question is discussed ... More
Collins effect in semi-inclusive deeply inelastic scattering and in electron positron annihilationMar 07 2006Jun 03 2006The Collins fragmentation function is extracted from HERMES data on azimuthal single spin asymmetries in semi-inclusive deeply inelastic scattering, and BELLE data on azimuthal asymmetries in electron positron annihilations. A Gaussian model is assumed ... More
Transversity distribution in spin asymmetries in semi-inclusive DIS and in the Drell-Yan processDec 30 2004A review is given on single spin asymmetries in deep inelastic semi-inclusive scattering (SIDIS) and their possible theoretical understanding in the framework of QCD-induced factorization approach, wherefore predictions for transversity from the chiral ... More
Transversity distribution function in hard scattering of polarized protons and antiprotons in the PAX experimentMar 11 2004Apr 30 2004Estimates are given for the double spin asymmetry in lepton pair production from collisions of transversely polarized protons and antiprotons for the kinematics of the recently proposed PAX experiment at GSI on the basis of predictions for the transversity ... More
Sivers vs. Collins effect in azimuthal single spin asymmetries in pion production in SIDISMar 07 2003Jul 24 2003Recently it has been argued that the transverse momentum dependent twist-2 Sivers distribution function does not vanish in QCD. Therefore both, the Collins and Sivers effects, should be considered in order to explain the azimuthal single spin asymmetries ... More
Azimuthal asymmetries at CLAS: Extraction of e^a(x) and prediction of A_{UL}Aug 13 2002First information on the chirally odd twist-3 proton distribution function e(x) is extracted from the azimuthal asymmetry, A_{LU}, in the electro-production of pions from deeply inelastic scattering of longitudinally polarized electrons off unpolarized ... More
Predictions for azimuthal asymmetries in pion and kaon production in SIDIS off a longitudinally polarized deuterium target at HERMESDec 12 2001May 16 2002Predictions are made for azimuthal asymmetries in pion and kaon production from SIDIS off a longitudinally polarized deuterium target for HERMES kinematics, based on information on the 'Collins fragmentation function' from DELPHI data and on predictions ... More
Quantum-Hall to insulator transitionAug 18 1998The crossover from the quantum Hall regime to the Hall-insulator is investigated by varying the strength of the diagonal disorder in a 2d tight-binding model. The Hall and longitudinal conductivities and the behavior of the critical states are calculated ... More
Status of Sivers and Collins Single Spin AsymmetriesFeb 15 2007The Sivers and Collins asymmetries are the most interesting Single Spin Asymmetries in semi-inclusive deeply inelastic scattering with transverse target polarization. In this talk we present our understanding of these phenomena.
Collins effect and single spin azimuthal asymmetries in the HERMES and COMPASS experimentsSep 17 2003Jan 22 2004Predictions are made for single spin azimuthal asymmetries due to the Collins effect in pion production from semi-inclusive deeply inelastic scattering off transversely and longitudinally polarized targets for the HERMES and COMPASS experiments. The x-dependence ... More
Phase transitions in social impact models of opinion formationApr 03 2000We study phase transitions in models of opinion formation which are based on the social impact theory. Two different models are discussed: (i) a cellular--automata based model of a finite group with a strong leader where persons can change their opinions ... More
Erratum to "Azimuthal asymmetry in electro-production of neutral pions in semi-inclusive DIS" published in Phys. Lett. B522 (2001) 37Apr 04 2002May 16 2002We correct our analysis of the HERMES experiment for the azimuthal sin(phi)-spin asymmetry in semi-inclusive hadroproduction in DIS on longitudinally (with respect to the lepton momentum) polarized target because of discovered misprint in sign in the ... More
Azimuthal asymmetry in electro-production of neutral pions in SIDISAug 25 2001Sep 27 2001Recently HERMES has observed an azimuthal asymmetry in electro-production of neutral pions in semi-inclusive deep-inelastic scattering of unpolarized positrons off longitudinally polarized protons. This asymmetry (like those observed in the production ... More
Sivers and Collins Single Spin AsymmetriesJan 15 2008Jan 21 2008The Sivers and Collins asymmetries are the most prominent Single Spin Asymmetries (SSA)in Semi-Inclusive Deeply Inelastic Scattering (SIDIS)with transverse target polarization. In this talk we present our understanding of these phenomena.
Transversity in Drell-Yan process of polarized protons and antiprotons in PAX experimentDec 31 2004Estimates are given for the double spin asymmetry in lepton-pair production from collisions of transversely polarized protons and antiprotons for the kinematics of the recently proposed PAX experiment at GSI on the basis of predictions for the transversity ... More
Collins Effect in SIDIS and in ${\bf e^+e^-}$ AnnihilationOct 24 2006Nov 17 2006We review the present understanding of the nucleon transversity distribution and Collins fragmentation function, based on Ref.\cite{Efremov:2006qm}, and discuss how Drell-Yan experiments will improve it.
Azimuthal asymmetries and Collins analyzing powerJun 26 2002Spin azimuthal asymmetries in pion electro-production in deep inelastic scattering off longitudinally polarized protons, measured by HERMES, are well reproduced theoretically with no adjustable parameters. Predictions for azimuthal asymmetries for a longitudinally ... More
Exotic open $4$-manifolds which are non-leavesOct 29 2014Nov 25 2016We study the possibility of realizing exotic smooth structures on punctured simply connected $4$-manifolds as leaves of a codimension one foliation on a compact manifold. In particular, we show the existence of uncountably many smooth open $4$-manifolds ... More
Exotic open $4$-manifolds which are non-leavesOct 29 2014Feb 05 2016We study the possibility of realizing exotic smooth structures on punctured simply connected 4-manifolds as leaves of a codimension 1 foliation on a compact manifold. In particular, we show the existence of a continuum of smooth open 4-manifolds which ... More
Classical invariants of Legendrian knots in the 3-dimensional torusApr 30 2014Feb 26 2015All knots in $R^3$ possess Seifert surfaces, and so the classical Thurston-Bennequin and rotation (or Maslov) invariants for Legendrian knots in a contact structure on $R^3$ can be defined. The definitions extend easily to null-homologous knots in any ... More
Induced Minor Free Graphs: Isomorphism and Clique-widthMay 27 2016Given two graphs $G$ and $H$, we say that $G$ contains $H$ as an induced minor if a graph isomorphic to $H$ can be obtained from $G$ by a sequence of vertex deletions and edge contractions. We study the complexity of Graph Isomorphism on graphs that exclude ... More
Effects of Social Influence on the Wisdom of CrowdsApr 16 2012Wisdom of crowds refers to the phenomenon that the aggregate prediction or forecast of a group of individuals can be surprisingly more accurate than most individuals in the group, and sometimes - than any of the individuals comprising it. This article ... More
Minimal Asymmetric GraphsMay 04 2016Confirming a conjecture of Ne\v{s}et\v{r}il, we show that up to isomorphism there is only a finite number of finite minimal asymmetric undirected graphs. In fact, there are exactly 18 such graphs. We also show that these graphs are exactly the finite ... More
Transverse momentum dependent distribution functions in a covariant parton model approach with quark orbital motionMar 20 2009Transverse parton momentum dependent distribution functions (TMDs) of the nucleon are studied in a covariant model, which describes the intrinsic motion of partons in terms of a covariant momentum distribution. The consistency of the approach is demonstrated, ... More
On LHCb pentaquarks as a baryon-psi(2S) bound state -- prediction of isospin 3/2 pentaquarks with hidden charmJul 24 2016Sep 03 2016The pentaquark $P_c^+(4450)$ recently discovered by LHCb has been interpreted as a bound state of $\Psi(2S)$ and nucleon. The charmonium-nucleon interaction which provides the binding mechanism is given, in the heavy quark limit, in terms of charmonium ... More
Low-frequency charge-carrier dynamics in the vicinity of the Mott transition in quasi-two-dimensional organic superconductors $κ$-(BEDT-TTF)${}_{2}$XMay 17 2011We investigate the dynamics of correlated charge carriers in the vicinity of the Mott metal-to-insulator transition in various of the title quasi-two-dimensional organic charge-transfer salts by means of fluctuation (noise) spectroscopy. The observed ... More
TMDs and Azimuthal Spin Asymmetries in a Light-Cone Quark ModelMar 10 2009The main properties of the leading-twist transverse momentum dependent parton distributions in a light-cone constituent quark model of the nucleon are reviewed, with focus on the role of the spin-spin and spin-orbit correlations of quarks. Results for ... More
The relation between TMDs and PDFs in the covariant parton model approachDec 23 2010We derive relations between transverse momentum dependent distribution functions (TMDs) and the usual parton distribution functions (PDFs) in the 3D covariant parton model, which follow from Lorentz invariance and the assumption of a rotationally symmetric ... More
Pretzelosity distribution function h_1T^perp and the single spin asymmetry A_UT^sin(3phi-phi_S)May 22 2008The leading twist transverse momentum dependent parton distribution function h_1T^perp, which is sometimes called ``pretzelosity,'' is studied. We review the theoretical properties of this function, and present bag model predictions. We observe an interesting ... More
Manifolds that are not leaves of codimension one foliationsNov 11 2011Sep 18 2012We present new open manifolds that are not homeomorphic to leaves of any C^0 codimension one foliation of a compact manifold. Among them are simply connected manifolds of dimension 5 or greater that are non-periodic in homotopy or homology, namely in ... More
Azimuthal spin asymmetries in light-cone constituent quark modelsMar 06 2009We present results for all leading-twist azimuthal spin asymmetries in semi-inclusive lepton-nucleon deep-inelastic scattering due to T-even transverse-momentum dependent parton distribution functions on the basis of a light-cone constituent quark model. ... More
Images of Quark Intrinsic Motion in Covariant Parton ModelAug 23 2010We discuss the relations between TMDs and PDFs in the framework of the covariant parton model. The quark OAM and its connection to TMDs are studied as well.
The polarized TMDs in the covariant parton model approachJan 20 2011We derive relations between polarized transverse momentum dependent distribution functions (TMDs) and the usual parton distribution functions (PDFs) in the 3D covariant parton model, which follow from Lorentz invariance and the assumption of a rotationally ... More
The pretzelosity distribution function and intrinsic motion of the constituents in nucleonDec 17 2008The pretzelosity distribution function $h_{1T}^\perp$ is studied in a covariant the quark-parton model which describes the structure of the nucleon in terms of 3D quark intrinsic motion. This relativistic model framework supports the relation between ... More
The transverse momentum dependent distribution functions in the bag modelJan 29 2010Leading and subleading twist transverse momentum dependent parton distribution functions (TMDs) are studied in a quark model framework provided by the bag model. A complete set of relations among different TMDs is derived, and the question is discussed ... More
Pretzelosity distribution functionAug 28 2008The 'pretzelosity' distribution is discussed. Theoretical properties, model results, and perspectives to access experimental information on this leading twist, transverse momentum dependent parton distribution function are reviewed. Its relation to helicity ... More
Transverse momentum dependent parton distributions and azimuthal asymmetries in light-cone quark modelsDec 09 2009We review the information on the spin and orbital angular momentum structure of the nucleon encoded in the T-even transverse momentum dependent parton distributions within light-cone quark models. Model results for azimuthal spin asymmetries in semi-inclusive ... More
Quark intrinsic motion and the link between TMDs and PDFs in covariant approachDec 17 2009Jan 28 2010The relations between TMDs and PDFs are obtained from the symmetry requirement: relativistic covariance combined with rotationally symmetric parton motion in the nucleon rest frame. This requirement is applied in the covariant parton model. Using the ... More
Pion mass dependence of the nucleon mass in the chiral quark soliton modelMay 13 2005Jun 03 2006The dependence of the nucleon mass on the mass of the pion is studied in the framework of the chiral quark-soliton model. A remarkable agreement is observed with lattice data from recent full dynamical simulations. The possibility and limitations to use ... More
In-medium modified energy-momentum tensor form factors of the nucleon within the framework of a $π$-$ρ$-$ω$ soliton modelFeb 02 2014May 29 2014We investigate the energy-momentum tensor form factors of the nucleon in nuclear medium, based on an in-medium modified $\pi$-$\rho$-$\omega$ soliton model, with medium modifications of the mesons considered. The results allow us to establish general ... More
The Rise and Fall of R&D NetworksApr 12 2013Mar 17 2016Drawing on a large database of publicly announced R&D alliances, we empirically investigate the evolution of R&D networks and the process of alliance formation in several manufacturing sectors over a 24-year period (1986-2009). Our goal is to empirically ... More
Multifractal properties of critical eigenstates in two-dimensional systems with symplectic symmetryJun 15 1995The multifractal properties of electronic eigenstates at the metal-insulator transition of a two-dimensional disordered tight-binding model with spin-orbit interaction are investigated numerically. The correlation dimensions of the spectral measure $\widetilde{D}_{2}$ ... More
On Zero Divisors with Small Support in Group Rings of Torsion-Free GroupsFeb 29 2012Kaplanski's Zero Divisor Conjecture envisions that for a torsion-free group G and an integral domain R, the group ring R[G] does not contain non-trivial zero divisors. We define the length of an element a in R[G] as the minimal non-negative integer k ... More
Using the Incompressibility Method to obtain Local Lemma results for Ramsey-type ProblemsApr 04 2008We reveal a connection between the incompressibility method and the Lovasz local lemma in the context of Ramsey theory. We obtain bounds by repeatedly encoding objects of interest and thereby compressing strings. The method is demonstrated on the example ... More
Narrow depression in the density of states at the Dirac point in disordered grapheneJul 22 2009Nov 12 2009The electronic properties of non-interacting particles moving on a two-dimensional bricklayer lattice are investigated numerically. In particular, the influence of disorder in form of a spatially varying random magnetic flux is studied. In addition, a ... More
Autour de la cohomologie de Bott-ChernSep 21 2007The goal of the memoir is to develop a new cohomology theory which encompasses De Rham and Dolbeault cohomology as well as Deligne Beilinson cohomology, in the context of general complex analytic manifolds. The special case of the Iwasawa manifold is ... More
Towards an Isomorphism Dichotomy for Hereditary Graph ClassesNov 07 2014In this paper we resolve the complexity of the isomorphism problem on all but finitely many of the graph classes characterized by two forbidden induced subgraphs. To this end we develop new techniques applicable for the structural and algorithmic analysis ... More
Frequency Dependent Electrical Transport in the Integer Quantum Hall EffectMar 11 2003The status of the ac quantum Hall effect is reviewed with emphasis on the theoretical development in recent years. In particular, the numerical approaches for the calculation of the frequency dependent Hall and longitudinal conductivities of non-interacting ... More
Modelling Migration and Economic Agglomeration with Active Brownian ParticlesNov 24 1999We propose a stochastic dynamic model of migration and economic aggregation in a system of employed (immobile) and unemployed (mobile) agents which respond to local wage gradients. Dependent on the local economic situation, described by a production function ... More
Thermal Transient Multisource Simulation Using Cubic Spline Interpolation of Zth FunctionsSep 12 2007This paper presents a very straightforward method to compute the transient thermal response to arbitrary power dissipation profiles in electronic devices with multiple heat sources. Using cubic spline interpolation of simulated or measured unit power ... More
The CARMENES search for exoplanets around M dwarfs - Photospheric parameters of target stars from high-resolution spectroscopyFeb 08 2018The new CARMENES instrument comprises two high-resolution and high-stability spectrographs that are used to search for habitable planets around M dwarfs in the visible and near-infrared regime via the Doppler technique. Characterising our target sample ... More
Are there approximate relations among transverse momentum dependent distribution functions?Sep 20 2007Certain exact relations among transverse momentum dependent parton distribution functions due to QCD equations of motion turn into approximate ones upon the neglect of pure twist-3 terms. On the basis of available data from HERMES we test the practical ... More
Sivers effect in semi-inclusive DIS and in the Drell-Yan processDec 22 2004Apr 01 2005The Sivers parton distribution has been predicted to obey a particular ``universality relation'', namely to have opposite sign in semi-inclusive deeply inelastic scattering (SIDIS) and the Drell-Yan process. We discuss how, on the basis of present HERMES ... More
Sivers effect in semi-inclusive deeply inelastic scatteringSep 08 2005Jan 24 2006The Sivers function is extracted from HERMES data on single spin asymmetries in semi-inclusive deeply inelastic scattering. Our analysis use a simple Gaussian model for the distribution of transverse parton momenta, together with the flavor dependence ... More
Recent developments in nucleon spin structure with focus on h_{1L}^{\perp} and pretzelosity h_{1T}^\perpFeb 04 2009Mar 16 2009The leading twist transverse momentum dependent parton distribution functions h_{1L}^{\perp} and h_{1T}^\perp, which is sometimes called "pretzelosity," are studied. For h_{1L}^{\perp} we consider a "Wandzura-Wilczek-type" approximation, which follows ... More
The Molecular Line Opacity of MgH in Cool Stellar AtmospheresJun 13 2002A new, complete, theoretical rotational and vibrational line list for the A-X electronic transition in MgH is presented. The list includes transition energies and oscillator strengths for all possible allowed transitions and was computed using the best ... More
Molecular line opacity of LiCl in the mid-infrared spectra of brown dwarfsJun 07 2004We present a complete line list for the X 1Sigma+ electronic ground state of LiCl computed using fully quantum-mechanical techniques. This list includes transition energies and oscillator strengths in the spectral region 0.3-39,640.7 cm-1 for all allowed ... More
Infrared Spectra and Spectral Energy Distributions of Late-M- and L-DwarfsOct 10 2000We have obtained 1.0-2.5um spectra at R~600 of 14 disk dwarfs with spectral types M6 to L7. For four of the dwarfs we have also obtained infrared spectra at R~3000 in narrow intervals. In addition, we present new L' photometry for four of the dwarfs in ... More
Nucleon form-factors of the energy momentum tensor in the chiral quark-soliton modelFeb 02 2007The nucleon form factors of the energy-momentum tensor are studied in the large-Nc limit in the framework of the chiral quark-soliton model.
Quark orbital angular momentum: can we learn about it from GPDs and TMDs?Aug 11 2010It is known how to access information on quark orbital angular momentum from generalized parton distribution functions, in a certain specified framework. It is intuitively expected, that such information can be accessed also through transverse momentum ... More
Sivers effect at Hermes, Compass and Clas12May 14 2008Single spin asymmetries in semi-inclusive deep-inelastic scattering off transversely polarized targets give information on, among other fascinating effects, a pseudo time-reversal odd parton distribution function, the 'Sivers function'. In this proceeding ... More
Spectral Properties of Brown Dwarfs and Hot JupitersMay 21 2004Brown dwarfs bridge the gap between the stellar and planetary mass regimes. Evolving from conditions very similar to the lowest-mass stars, the atmospheres of older brown dwarfs closely resemble those expected in close-in extrasolar giant planets, and ... More
Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic ConductorOct 20 2006Dec 11 2007Discontinuous changes of the lattice parameters at the Mott metal-insulator transition are detected by high-resolution dilatometry on deuterated crystals of the layered organic conductor $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. The uniaxial expansivities ... More
Ferroelectric properties of charge-ordered alpha-(BEDT-TTF)2I3Jul 01 2014Jun 19 2015A detailed investigation of the out-of-plane electrical properties of charge-ordered alpha-(BEDT-TTF)2I3 provides clear evidence for ferroelectricity. Similar to multiferroic alpha-(BEDT-TTF)2Cu[N(CN)2]Cl, the polar order in this material is ascribed ... More
The pion mass dependence of the nucleon form-factors of the energy momentum tensor in the chiral quark-soliton modelFeb 02 2007The nucleon form factors of the energy-momentum tensor are studied in the large-Nc limit in the framework of the chiral quark-soliton model for model parameters that simulate physical situations in which pions are heavy. This allows for a direct comparison ... More
Determining ethylene group disorder levels in $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]BrOct 24 2006We present a detailed structural investigation of the organic superconductor $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br at temperatures $T$ from 9 to 300 K. Anomalies in the $T$ dependence of the lattice parameters are associated with a glass-like transition ... More
Highlights of Stellar Modeling with PHOENIXSep 03 2002We briefly describe the current version of the PHOENIX code. We then present some illustrative results from the modeling of Type Ia and Type II supernovae, hot stars, and irradiated giant planets. Good fits to observations can be obtained, when account ... More
The Molecular Continuum Opacity of MgH in Cool Stellar AtmospheresJul 01 2002The opacity due to photodissociation of 24MgH is investigated in the atmospheres of cool stars. The lowest two electronic transitions A 2Pi -- X 2Sigma+ and B' 2Sigma+ -- X 2 Sigma+ are considered where the cross sections for the latter were published ... More
Insights on non-perturbative aspects of TMDs from modelsOct 16 2009Transverse momentum dependent parton distribution functions are a key ingredient in the description of spin and azimuthal asymmetries in deep-inelastic scattering processes. Recent results from non-perturbative calculations in effective approaches are ... More
Competition Numbers, Quasi-Line Graphs and HolesOct 13 2011Oct 23 2013The competition graph of a directed acyclic graph D is the undirected graph on the same vertex set as D in which two distinct vertices are adjacent if they have a common out-neighbor in D. The competition number of an undirected graph G is the least number ... More
Dense m-convex Frechet Subalgebras of Operator Algebra Crossed Products by Lie GroupsNov 27 1992Let A be a dense Frechet *-subalgebra of a C*-algebra B. (We do not require Frechet algebras to be m-convex.) Let G be a Lie group, not necessarily con- nected, which acts on both $A$ and B by *-automorphisms, and let \s be a sub- multiplicative function ... More
A Short Proof that $M_{n}(A)$ is local if $A$ is local and FréchetNov 25 1992We give a short and very general proof of the fact that the property of a dense Fr\'echet subalgebra of a Banach algebra being local, or closed under the holomorphic functional calculus in the Banach algebra, is preserved by tensoring with the $n\times ... More
Disordered two-dimensional electron systems with chiral symmetryAug 20 2012Sep 11 2012We review the results of our recent numerical investigations on the electronic properties of disordered two dimensional systems with chiral unitary, chiral orthogonal, and chiral symplectic symmetry. Of particular interest is the behavior of the density ... More
Critical conductance of two-dimensional chiral systems with random magnetic fluxMay 04 2007Aug 23 2007The zero temperature transport properties of two-dimensional lattice systems with static random magnetic flux per plaquette and zero mean are investigated numerically. We study the two-terminal conductance and its dependence on energy, sample size, and ... More
Agent-Based Modeling of Intracellular TransportSep 16 2011We develop an agent-based model of the motion and pattern formation of vesicles. These intracellular particles can be found in four different modes of (undirected and directed) motion and can fuse with other vesicles. While the size of vesicles follows ... More
Graph Isomorphism for Graph Classes Characterized by two Forbidden Induced SubgraphsAug 01 2012Aug 02 2012We study the complexity of the Graph Isomorphism problem on graph classes that are characterized by a finite number of forbidden induced subgraphs, focusing mostly on the case of two forbidden subgraphs. We show hardness results and develop techniques ... More
Modelling Collective Opinion Formation by Means of Active Brownian ParticlesNov 25 1999Feb 08 2000The concept of active Brownian particles is used to model a collective opinion formation process. It is assumed that individuals in community create a two-component communication field that influences the change of opinions of other persons and/or can ... More
Critical level statistics of a quantum Hall system with Dirichlet boundary conditionsOct 19 1998We investigate numerically the influence of Dirichlet boundary conditions on the nearest neighbor level spacing distribution $P(s)$ of a two-dimensional disordered tight-binding model in the presence of a strong perpendicular magnetic field. From the ... More
Spectral Invariance of Dense Subalgebras of Operator AlgebrasNov 27 1992Mar 16 1993We define the notion of strong spectral invariance for a dense Frechet subalgebra A of a Banach algebra B. We show that if A is strongly spectral invariant in a C*-algebra B, and G is a compactly generated polynomial growth Type R Lie group, not necessarily ... More
Floating of critical states and the QH to insulator transitionFeb 27 2001The transition from the quantum Hall state to the insulator is considered for non-interacting electrons in a two-dimensional disordered lattice model with perpendicular magnetic field. Using correlated random disorder potentials the floating up of the ... More