Results for "Ralf Drautz"

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Discovery of new stable and high-temperature Ti-Ta-X shape memory alloys from first principles calculationsMay 14 2019In conventional Ti-Ta shape memory alloys (SMAs), high (>100{\deg}C) transformation temperatures cannot be achieved without compromising the stability of the shape memory effect. A solution to this problem is the addition of other elements to form Ti-Ta-X ... More
Linear-scaling electronic structure theory: Electronic temperature in the Kernel Polynomial MethodJan 06 2017Linear-scaling electronic structure methods based on the calculation of moments of the underlying electronic Hamiltonian offer a computationally efficient and numerically robust scheme to drive large-scale atomistic simulations, in which the quantum-mechanical ... More
Kinetic Monte Carlo simulations of vacancy diffusion in non-dilute Ni-X (X=Re,W,Ta) alloysDec 12 2018The mobility of vacancies in alloys may limit dislocation climb. Using a combined density functional theory and kinetic Monte Carlo approach we investigate vacancy diffusion in Ni-Re, Ni-W, and Ni-Ta binary alloys up to 10 at.% solute concentration. We ... More
Diffusion of hydrogen within idealised grains of bcc-Fe: A kinetic Monte Carlo studyJun 11 2012Structural defects in materials such as vacancies, grain boundaries, and dislocations may trap hydrogen and a local accumulation of hydrogen at these defects can lead to the degradation of the materials properties. An important aspect in obtaining insight ... More
Comparison of analytic and numerical bond-order potentials for W and MoJun 06 2016Bond-order potentials (BOPs) are derived from the tight-binding (TB) approximation and provide a linearly-scaling computation of the energy and forces for a system of interacting atoms. While the numerical BOPs involve the numerical integration of the ... More
Topologically close-packed phases in binary transition-metal compounds: matching high-throughput ab initio calculations to an empirical structure mapMay 17 2016In steels and single-crystal superalloys the control of the formation of topologically close-packed (TCP) phases is critical for the performance of the material. The structural stability of TCP phases in multi-component transition-metal alloys may be ... More
Optimized Orthogonal Basis Tight Binding. Application to IronApr 18 2011The formal link between the linear combination of atomic orbitals approach to density functional theory and two-center Slater-Koster tight-binding models is used to derive an orthogonal $d$-band tight-binding model for iron with only two fitting parameters. ... More
Accelerating spin-space sampling by auxiliary spin-dynamics and temperature-dependent spin-cluster expansionFeb 06 2019Atomistic simulations of thermodynamic properties of magnetic materials rely on an accurate modelling of magnetic interactions and an efficient sampling of the high-dimensional spin space. Recent years have seen significant progress with a clear trend ... More
First principles characterization of reversible martensitic transformationsOct 12 2018Oct 15 2018Reversible martensitic transformations (MTs) are the origin of many fascinating phenomena, including the famous shape memory effect. In this work, we present a fully ab initio procedure to characterize MTs in alloys and to assess their reversibility. ... More
Electronic structure based descriptor for characterizing local atomic environmentsOct 08 2018A quantitative descriptor of local atomic environments is often required for the analysis of atomistic data. Descriptors of the local atomic environment ideally provide physically and chemically intuitive insight. This requires descriptors that are low-dimensional ... More
Unusual composition dependence of transformation temperatures in Ti-Ta-X shape memory alloysApr 12 2018Ti-Ta-X (X = Al, Sn, Zr) compounds are emerging candidates as high-temperature shape memory alloys (HTSMAs). The stability of the one-way shape memory effect (1WE), the exploitable pseudoelastic (PE) strain intervals as well as the transformation temperature ... More
Phase transitions in titanium with an analytic bond-order potentialMay 03 2019Titanium is the base material for a number of technologically important alloys for energy conversion and structural applications. Atomic-scale studies of Ti-based metals employing first-principles methods, such as density functional theory, are limited ... More
{110} planar faults in strained bcc metals: Origins and implications of a commonly observed artifact of classical potentialsOct 03 2018Large-scale atomistic simulations with classical potentials can provide valuable insights into microscopic deformation mechanisms and defect-defect interactions in materials. Unfortunately, these assets often come with the uncertainty of whether the observed ... More
Yang-Mills thermodynamicsOct 04 2007Nov 05 2009We present a quantitative analysis of Yang-Mills thermodynamics in 4D flat spacetime. The focus is on the gauge group SU(2). Results for SU(3) are mentioned in passing. Although all essential arguments and results were reported elsewhere we summarize ... More
Spontaneously broken, local Z$_2$ symmetry and the anatomy of a leptonDec 03 2003Feb 11 2004In the framework of the gauge symmetry ${SU(2)}_{\tiny{CMB}}\times {SU(2)}_{\tiny{e}}\times {SU(2)}_{\tiny{\mu}}\times {SU(2)}_{\tiny{\tau}}$ we provide a microscopic argument why a spontaneously broken, local Z$_2$ symmetry surviving the 1$^{\tiny{st}}$ ... More
Reshuffling the OPE: Delocalized Operator ExpansionJul 29 2002A generalization of the operator product expansion for Euclidean correlators of gauge invariant QCD currents is presented. Each contribution to the modified expansion, which is based on a delocalized multipole expansion of a perturbatively determined ... More
Modifying operator product expansions by non-perturbative non-localitySep 02 2001Nov 12 2001Local quark-hadron duality violations in conventional applications of the operator product expansion are proposed to have their origin in the fact that the QCD vacuum or a hadronic state is not only characterized by nonvanishing expectation values of ... More
Confinement, Chiral Symmetry Breaking, and Axial Anomaly from Domain Formation at Intermediate ResolutionMar 26 2001Jul 02 2001Based on general renormalization group arguments, Polyakov's loop-space formalism, and recent analytical lattice arguments, suggesting, after Abelian gauge fixing, a description of pure gluodynamics by means of a Georgi-Glashow like model, the corresponding ... More
Analytical approach to nonperturbative Yang-Mills thermodynamicsDec 03 2003Dec 05 2003An analytical and inductive approach to hot SU(N) Yang-Mills dynamics is developed. For N=2,3 pressure and energy density are pointwise compared with lattice data.
Towards OPE based local quark-hadron duality: Light-quark channelsSep 02 2001Various light-quark channel current-current correlators are subjected to the concept of a non-perturbative component of coarse graining in operator product expansions introduced in a parallel work. This procedure allows for low-energy structure of the ... More
Neutrino Masses and Mixing Angles in SUSY-GUT Theories with explicit R-Parity BreakingNov 10 1995Sep 10 1996In minimal SUSY GUT models the $R$-parity breaking terms are severely constrained by SU(5) gauge invariance. We consider the particular case where the explicit $R$-parity breaking occurs only via dimension 2 terms of the superpotential. This model possesses ... More
Towards Generic RefactoringMar 01 2002We study program refactoring while considering the language or even the programming paradigm as a parameter. We use typed functional programs, namely Haskell programs, as the specification medium for a corresponding refactoring framework. In order to ... More
Neutral pions and eta mesons as probes of the expanding hadronic fireball in nucleus-nucleus collisions at SISMar 02 1998The production of neutral pions and eta mesons in collisions of light, intermediate-mass, and heavy nuclei at beam energies between 0.8 A GeV and 2.0 A GeV is discussed in the framework of a model assuming equilibrium at hadrochemical and thermal freeze-out, ... More
A mapping between Lorentz-violating and conventional electrodynamicsNov 29 2007Feb 17 2011The Chern-Simons-type term in the photon sector of the Lorentz- and CPT-breaking minimal Standard-Model Extension (mSME) is considered. It is argued that under certain circumstances this term can be removed from the mSME. In particular, it is demonstrated ... More
Aspects of spacetime-symmetry violationsFeb 19 2006The violation of spacetime symmetries provides a promising candidate signal for underlying physics, possibly arising at the Planck scale. This talk gives an overview over various aspects in the field, including some mechanisms for Lorentz breakdown, the ... More
Cosmology and spacetime symmetriesAug 31 2005Cosmological models often contain scalar fields, which can acquire global nonzero expectation values that change with the comoving time. Among the possible consequences of these scalar-field backgrounds, an accelerated cosmological expansion, varying ... More
Quantum-gravity phenomenology, Lorentz symmetry, and the SMEMar 16 2007Violations of spacetime symmetries have recently been identified as promising signatures for physics underlying the Standard Model. The present talk gives an overview over various topics in this field: The motivations for spacetime-symmetry research, ... More
Quantum gravity and spacetime symmetriesDec 30 2006Small violations of spacetime symmetries have recently been identified as promising Planck-scale signals. This talk reviews how such violations can arise in various approaches to quantum gravity, how the emergent low-energy effects can be described within ... More
Lorentz violation as a quantum-gravity signatureAug 29 2005Many theoretical approaches to quantum gravity predict the breakdown of Lorentz symmetry at Planck energies. Kinematical cosmic-ray studies are a sensitive tool in the search for such effects. This talk discusses the construction of test dispersion relations ... More
On the geometry of global function fields, the Riemann-Roch theorem, and finiteness properties of S-arithmetic groupsAug 21 2010Jan 30 2011Harder's reduction theory provides filtrations of euclidean buildings that allow one to deduce cohomological and homological properties of S-arithmetic groups over global function fields. In this survey I will sketch the main points of Harder's reduction ... More
Emergent Horizons in the LaboratoryApr 15 2010The concept of a horizon known from general relativity describes the loss of causal connection and can be applied to non-gravitational scenarios such as out-of-equilibrium condensed-matter systems in the laboratory. This analogy facilitates the identification ... More
Recreating Fundamental Effects in the Laboratory?Apr 14 2010This article provides a brief (non-exhaustive) overview of some possibilities for recreating fundamental effects which are relevant for black holes (and other gravitational scenarios) in the laboratory. Via suitable condensed matter analogues and other ... More
The galactic population of white dwarfsMar 12 2009The contribution of white dwarfs of the different Galactic populations to the stellar content of our Galaxy is only poorly known. Some authors claim a vast population of halo white dwarfs, which would be in accordance with some investigations of the early ... More
Modeling Star Formation from Turbulent FragmentationOct 03 2001Star formation is intimately linked to the dynamical evolution of molecular clouds. Turbulent fragmentation determines where and when protostellar cores form, and how they contract and grow in mass via accretion from the surrounding cloud material. Using ... More
Star Formation from Turbulent FragmentationNov 10 2000Star formation is intimately linked to the dynamical evolution of molecular clouds. Turbulent fragmentation determines where and when protostellar cores form, and how they contract and grow in mass via accretion from the surrounding cloud material. Efficiency, ... More
Lineare Rekurrenzen, Potenzreihen und ihre erzeugenden FunktionenApr 19 2007Apr 20 2007Diese kurze Einfuehrung in Theorie und Berechnung linearer Rekurrenzen versucht, eine Luecke in der Literatur zu fuellen. Zu diesem Zweck sind viele ausfuehrliche Beispiele angegeben. This short introduction to theory and usage of linear recurrences tries ... More
L(R) absoluteness under proper forcingsSep 08 1999We isolate a new large cardinal concept, "remarkability." Consistencywise, remarkable cardinals are between ineffable and omega-Erdos cardinals. They are characterized by the existence of "0^sharp-like" embeddings; however, they relativize down to L. ... More
Lorentz and CPT violation in the Standard-Model ExtensionApr 20 2016Lorentz and CPT invariance are among the symmetries that can be investigated with ultrahigh precision in subatomic physics. Being spacetime symmetries, Lorentz and CPT invariance can be violated by minuscule amounts in many theoretical approaches to underlying ... More
Vibrational band structure of nanoscale phononic crystalsNov 02 2015Nov 24 2017The vibrational properties of two-dimensional phononic crystals are studied with large-scale molecular dynamics simulations and finite element method calculation. The vibrational band structure derived from the molecular dynamics simulations shows the ... More
Electromagnetic waves and photonsJul 21 2015Aug 24 2015We explore how the thermal ground states of two mixing and pure SU(2) Yang-Mills theories, SU(2)$_{\tiny\mbox{CMB}}$ of scale $\Lambda_{\tiny\mbox{CMB}}\sim 10^{-4}\,$eV and SU(2)$_{e}$ of scale $\Lambda_{e}\sim 5\times 10^5\,$eV, associate either wave ... More
Relic photon temperature versus redshift and the cosmic neutrino backgroundJul 02 2014Jan 19 2015Presuming that CMB photons are described by the deconfining phase of an SU(2) Yang-Mills theory with the critical temperature for the deconfining-preconfining phase transition matching the present CMB temperature $T_0\sim 2.725\,$K (SU(2)$_{\tiny{CMB}}$), ... More
Kinematical Lorentz-symmetry tests at particle collidersMar 24 2014Violations of Lorentz symmetry are typically associated with modifications of one-particle dispersion relations. The physical effects of such modifications in particle collisions often grow with energy, so that ultrahigh-energy cosmic rays provide an ... More
Interaction of a Bose-Einstein condensate with a gravitational waveJul 18 2018Nov 20 2018Partly motivated by recent proposals for the detection of gravitational waves, we study their interaction with Bose-Einstein condensates. For homogeneous condensates at rest, the gravitational wave does not directly create phonons (to lowest order), but ... More
Heavy-Flavor Theory at "Hard and Electromagnetic Probes 2018"Jan 18 2019An overview is given of the theoretical developments on heavy quarks and quarkonia in heavy-ion collisions as reported at the "Hard and EM Probes 2018" conference. Specifically, we address progress in the understanding of heavy-flavor diffusion and its ... More
The cyclic homology and K-theory of certain adelic crossed productsDec 16 2003The multiplicative group of a global field acts on its adele ring by multiplication. We consider the crossed product algebra of the resulting action on the space of Schwartz functions on the adele ring and compute its Hochschild, cyclic and periodic cyclic ... More
How reliable are the Powell-Wetherall plot method and the maximum-length approach? Implications for length-based studies of growth and mortalityApr 14 2018Length-based methods are the cornerstone of many population studies and stock assessments. This study tested two widely used methods: the Powell-Wetherall (P-W) plot and the Lmax approach, i.e., estimating Linf directly from Lmax. In most simulations, ... More
Combable groups have group cohomology of polynomial growthOct 28 2004Aug 06 2018Group cohomology of polynomial growth is defined for any finitely generated discrete group, using cochains that have polynomial growth with respect to the word length function. We give a geometric condition that guarantees that it agrees with the usual ... More
On Hopf algebra structures over free operadsApr 26 2005Nov 30 2005The operad Lie can be constructed as the operad of primitives Prim As from the operad As of associative algebras. This is reflected by the theorems of Friedrichs, Poincare'-Birkhoff-Witt and Cartier-Milnor-Moore. We replace As by families of free operads ... More
A matrix-algebraic algorithm for the Riemannian logarithm on the Stiefel manifold under the canonical metricApr 18 2016Mar 17 2017We derive a numerical algorithm for evaluating the Riemannian logarithm on the Stiefel manifold with respect to the canonical metric. In contrast to the existing optimization-based approach, we work from a purely matrix-algebraic perspective. Moreover, ... More
A geometric model for cluster categories of type $D_n$Aug 10 2006Aug 30 2006We give a geometric realization of cluster categories of type $D_n$ using a polygon with $n$ vertices and one puncture in its center as a model. In this realization, the indecomposable objects of the cluster category correspond to certain homotopy classes ... More
Homological algebra for Schwartz algebras of reductive p-adic groupsJan 31 2005Jun 02 2005Let G be a reductive group over a non-Archimedean local field. Then the canonical functor from the derived category of smooth tempered representations of G to the derived category of all smooth representations of G is fully faithful. Here we consider ... More
Equivariant Kasparov theory and generalized homomorphismsJan 17 2000Apr 30 2000Let G be a locally compact group. We describe elements of KK^G (A,B) by equivariant homomorphisms, following Cuntz's treatment in the non-equivariant case. This yields another proof for the universal property of KK^G: It is the universal split exact stable ... More
Massively Parallel Computation of Accurate Densities for N-body Dark Matter Simulations using the Phase-Space-Element MethodDec 29 2016Aug 24 2017This paper presents an accurate density computation approach for large dark matter simulations, based on a recently introduced phase-space tessellation technique and designed for massively parallel, heterogeneous cluster architectures. We discuss a memory ... More
The deconfining phase of SU(2) Yang-Mills thermodynamicsJul 17 2006Nov 27 2006We present an overview on nonperturbative thermodynamics in the deconfining phase of an SU(2) Yang-Mills theory. In a unique effective theory the maximal resolution of trivial-topology fluctuations is constrained by coarse-grained, interacting calorons ... More
Nonperturbative and analytical approach to Yang-Mills thermodynamicsApr 29 2004Nov 25 2004An analytical, macroscopic approach to SU(N) Yang-Mills thermodynamics is developed, tested,and applied.
Deconfining by Winding: The Magnetic Monopole Vacua at High TemperaturesJun 15 2000Oct 05 2000Characterizing the vacuum of a thermalized SU(3) Yang-Mills theory in the dual Ginzburg-Landau description, the possibility of topologically nontrivial, classical monopole fields in the deconfining phase is explored. These fields are assumed to be Bogomoln'yi-Prasad-Sommerfield ... More
Gauge boson pair production at LEP and NLCMay 24 1996We compute the dominant one-loop radiative corrections to the cross-section for $e^+ e^- \rightarrow V_1 V_2$ $(V_{1/2} = \gamma, Z, W^\pm$) in the MSSM. We find that the genuine vertex corrections are very small. The oblique corrections are potentially ... More
Lorentz and CPT tests involving antiprotonsFeb 11 2006Lorentz and CPT tests involving matter-antimatter comparisons at low temperatures are discussed. SME predictions for transition frequencies in such systems include both matter-antimatter differences and sidereal variations. In hydrogen-antihydrogen spectroscopy, ... More
Vibrational Bandstructures of Bottom-Up Built Nanoscale Phononic CrystalsNov 02 2015The vibrational properties of a phononic crystal assembled from Si nanoparticles and nanowires is studied with large-scale molecular-dynamics simulations. The phonon dispersion relations derived from the simulations show the existence of acoustic band ... More
Spin dependent fragmentatation functions at BelleMay 17 2006Spin dependent fragmentation functions are an important tool to understand the spin structure of the nucleon. The Collins fragmentation function for example describes the fragmentation of a transversely polarized quark into a hadron via the creation of ... More
Heavy-flavor production at RHICMay 14 2005May 19 2005Experimental results on heavy-quark production in proton-proton, deuteron-gold, and gold-gold collisions at sqrt(s_(NN)) = 200 GeV at the Relativistic Heavy Ion Collider (RHIC) are reviewed.
Refractive index perturbations -- Unruh effect, Hawking radiation or dynamical Casimir effect?Oct 27 2011Motivated by recent experimental progress to manipulate the refractive index of dielectric materials by strong laser beams, we study some aspects of the quantum radiation created by such refractive index perturbations.
A nice acyclic matching on the nerve of the partition latticeApr 12 2012Aug 28 2015The author has already proven that the space \Delta(\Pi_n)/G is homotopy equivalent to a wedge of spheres of dimension n-3 for all natural numbers n>=3 and all subgroups G<S_1 X S_{n-1}. We wish to construct an acyclic matching on \Delta(\Pi_n)/G that ... More
Relativity tests and their motivationFeb 14 2011Some motivations for Lorentz-symmetry tests in the context of quantum-gravity phenomenology are reiterated. The description of the emergent low-energy effects with the Standard-Model Extension (SME) is reviewed. The possibility of constraining such effects ... More
In-Medium Vector Mesons, Dileptons and Chiral RestorationOct 08 2010Medium modifications of the electromagnetic spectral function in hadronic and quark-gluon matter are reviewed. A strong broadening of the $\rho$ meson, which dominates the spectral function in the low-mass regime, is quantitatively consistent with dilepton ... More
Monodromy Groups of Vector Bundles on p-adic CurvesMay 28 2010In [DW05] and [DW07], C. Deninger and A. Werner developed a partial p-adic analogue of the classical Narasimhan-Seshadri correspondence between vector bundles and representations of the fundamental group. We will investigate the various monodromy groups ... More
Tests of Lorentz symmetryAug 10 2010A number of approaches to fundamental physics can lead to the violation of Lorentz and CPT symmetry. This talk discusses the low-energy phenomenology associated with such effects and reviews various sample experiments within this context.
Low-frequency line temperatures of the CMBFeb 16 2009Jul 11 2009Based on SU(2) Yang-Mills thermodynamics we interprete Aracde2's and the results of earlier radio-surveys on low-frequency CMB line temperatures as a phase-boundary effect. We explain the excess at low frequencies by evanescent, nonthermal photon fields ... More
Exoplanet search with astrometryApr 07 2009Searching for extrasolar planets by direct detection is extremely challenging for current instrumentation. Indirect methods, that measure the effect of a planet on its host star, are much more promising and have indeed led to the discovery of nearly all ... More
Comparisons between periodic, analytic and local cyclic cohomologyMay 27 2002Dec 18 2003We compute periodic, analytic and local cyclic cohomology for convolution algebras of compact Lie groups in order to exhibit differences between these theories. A surprising result is that the periodic and analytic cyclic cohomology of the smooth convolution ... More
Monodromy of subvarieties of PEL-Shimura varietiesSep 26 2012The aim of this paper is to generalize results of C.-L. Chai about the monodromy of Hecke invariant subvarieties to Shimura varieties of PEL-type.
Dynamical zero-temperature phase transitions and cosmic inflation/deflationMay 26 2005For a rather general class of scenarios, sweeping through a zero-temperature phase transition by means of a time-dependent external parameter entails universal behavior: In the vicinity of the critical point, excitations behave as quantum fields in an ... More
\nabla_κ, remarkable cardinals, and 0^#May 25 2001For an uncountable regular cardinal \kappa we let \nabla_\kappa(A) be the statement that A \subset \kappa and for all regular \theta > \kappa, the set of all X \in [\theta]^<\kappa such that X \cap \kappa \in \kappa and otp(X \cap OR) is a cardinal in ... More
A universal weasel without large cardinals in VNov 13 2000We prove in the theory "ZFC + there is no inner model with a Woodin cardinal" that there is a universal weasel. This shows in particular that one doesn't have to assume the existence of large cardinals in V to prove the existence of some such weasel.
SU(2) Yang-Mills Theory: Waves, Particles, and Quantum ThermodynamicsApr 14 2016We elucidate how Quantum Thermodynamics at temperature $T$ emerges from pure and classical SU(2) Yang-Mills theory on a four-dimensional Euclidean spacetime slice $S_1\times {\bf R}^3$. The concept of a (deconfining) thermal ground state, composed of ... More
On the Critical Exponent of Infinitely Generated Veech GroupsApr 08 2014We prove the existence of Veech groups having a critical exponent strictly greater than any elementary Fuchsian group (i.e. $>\frac{1}{2}$) but strictly smaller than any lattice (i.e. $<1$). More precisely, every affine covering of a primitive L-shaped ... More
Finite- and infinite-volume thermodynamics around the zero of the pressure in deconfining SU(2) Quantum Yang-Mills theorySep 21 2018Jan 02 2019We re-address the self-intersection region in a figure-eight shaped center-vortex loop containing a frequently perturbed {\sl BPS monopole} subject to a core-oscillation frequency $\omega_0$, rectifying a numerical error in estimating the system's radius ... More
SU(2) Quantum Yang-Mills Thermodynamics: Some Theory and Some ApplicationsSep 11 2018Nov 13 2018In the first part of this talk we review some prerequisites for and essential arguments involved in the construction of the thermal-ground-state estimate for the deconfining phase in the thermodynamics of SU(2) Quantum Yang-Mills theory and how this structure ... More
The isolated, uniformly moving electron: Selfintersecting SU(2) Yang-Mills center vortex loop and Louis de Broglie's hidden thermodynamicsJun 27 2017We propose that the one-fold selfintersecting center-vortex loop, being the stable excitation in the confining phase of SU(2) Yang-Mills thermodynamics of scale $\Lambda\sim 0.5\,$MeV, after an electric-magnetically dual interpretation of this theory ... More
Magnetic Resonance Imaging of Granular MaterialsMar 03 2017Magnetic Resonance Imaging (MRI) has become one of the most important tools to screen humans in medicine, virtually every modern hospital is equipped with an NMR tomograph. The potential of NMR in 3D imaging tasks is by far greater, but there is only ... More
Review of recent forward physics results from the CMS experimentApr 29 2019There is a rich program of forward physics measurements within the CMS Collaboration covering a wide range of topics. In many cases there is a connection to quantities and effects relevant for very high energy cosmic ray interaction. Some of the recent ... More
Bornological versus topological analysis in metrizable spacesOct 15 2003Feb 09 2004Given a metrizable topological vector space, we can also use its von Neumann bornology or its bornology of precompact subsets to do analysis. We show that the bornological and topological approaches are equivalent for many problems. For instance, they ... More
Discrete Compactness for p-Version of Tetrahedral Edge ElementsJan 07 2009We consider the first family of $\Hcurl$-conforming Ned\'el\'ec finite elements on tetrahedral meshes. Spectral approximation ($p$-version) is achieved by keeping the mesh fixed and raising the polynomial degree $p$ uniformly in all mesh cells. We prove ... More
Cardinal arithmetic and Woodin cardinalsMar 08 2002Suppose that there is a measurable cardinal. If \aleph_\omega is a strong limit cardinal, but the power of \aleph_\omega is bigger than \aleph_{\omega_1}, then there is an inner model with a Woodin cardinal. Modulo the need of the measurable cardinal ... More
On the work of Rodriguez Hertz on rigidity in dynamicsJun 02 2016This paper is a survey about recent progress in measure rigidity and global rigidity of Anosov actions, and celebrates the profound contributions by Federico Rodriguez Hertz to rigidity in dynamical systems.
Divide-and-conquer generating functions. Part I. Elementary sequencesJul 02 2003Divide-and-conquer functions satisfy equations in F(z),F(z^2),F(z^4)... Their generated sequences are mainly used in computer science, and they were analyzed pragmatically, that is, now and then a sequence was picked out for scrutiny. By giving several ... More
Analytic cyclic cohomologyJun 29 1999We prove excision in entire and periodic cyclic cohomology and construct a Chern-Connes character for Fredholm modules over a C*-algebra without summability restrictions, taking values in a variant of Connes's entire cyclic cohomology. Before these results ... More
Fundamental Quantum Effects from a Quantum-Optics PerspectiveApr 14 2010This article provides a brief overview of some fundamental effects of quantum fields under extreme conditions. For the Schwinger mechanism, Hawking radiation, and the Unruh effect, analogies to quantum optics are discussed, which might help to approach ... More
CPT and Lorentz-invariance violationNov 15 2009The largest gap in our understanding of nature at the fundamental level is perhaps a unified description of gravity and quantum theory. Although there are currently a variety of theoretical approaches to this question, experimental research in this field ... More
Representations of *-algebras by unbounded operators: C*-hulls, local-global principle, and inductionJul 15 2016Sep 29 2016We define a C*-hull for a *-algebra, given a notion of integrability for its representations on Hilbert modules. We establish a local-global principle which, in many cases, characterises integrable representations on Hilbert modules through the integrable ... More
Quotients of the topology of the partition lattice which are not homotopy equivalent to wedges of spheresFeb 20 2012Jun 21 2012The reader of doi:10.1016/j.topol.2010.08.006 might conjecture that \Delta(\bar{\Pi}_n)/G is homotopy equivalent to a wedge of spheres for any n>=3 and any subgroup G<S_n. We disprove this by showing that \Delta(\bar{\Pi}_p)/C_p is not homotopy equivalent ... More
Topological versus rheological entanglement length in primitive path analysis protocolsNov 21 2011Primitive path analysis algorithms are now routinely employed to analyze entanglements in computer simulations of polymeric systems, but different analysis protocols result in different estimates of the entanglement length, N_e. Here we argue that standard ... More
General Analysis Tool Box for Controlled PerturbationMar 29 2012The implementation of reliable and efficient geometric algorithms is a challenging task. The reason is the following conflict: On the one hand, computing with rounded arithmetic may question the reliability of programs while, on the other hand, computing ... More
Isospectral Metrics on Projective SpacesApr 12 2011We construct isospectral non isometric metrics on real and complex projective space. We recall the construction using isometric torus actions by Carolyn Gordon in chapter 2. In chapter 3 we will recall some facts about complex projective space. In chapter ... More
Dynamical quantum phase transitionsApr 14 2010A sweep through a quantum phase transition by means of a time-dependent external parameter (e.g., pressure) entails non-equilibrium phenomena associated with a break-down of adiabaticity: At the critical point, the energy gap vanishes and the response ... More
The Lorentz-violating Standard-Model ExtensionJan 16 2004Quantum-gravity effects are expected to be suppressed by the Planck mass. For experimental progress it is therefore important to identify potential signatures from Planck-scale physics that are amenable to ultrahigh-precision tests. It is argued that ... More
Couplings varying on cosmological scales and Lorentz breakingNov 06 2003In the context of N=4 supergravity in four dimensions, we present an exact classical solution that leads to spacetime-dependent electromagnetic couplings and discuss the ensuing Lorentz-violating effects. We comment briefly on experimental bounds.
Apparent Lorentz violation through spacetime-varying couplingsAug 20 2003In this talk, we explore the relation between smoothly varying couplings and Lorentz violation. Within the context of a supergravity model, we present an explicit mechanism that causes the effective fine-structure parameter and the effective electromagnetic ... More
Some Considerations Regarding Lorentz-Violating TheoriesJan 29 2002We investigate the compatibility of Lorentz-violating quantum field theories with the requirements of causality and stability. A general renormalizable model for free massive fermions indicates that these requirements are satisfied at low energies provided ... More
Structure, Formation and Ages of Elliptical GalaxiesJan 27 1997The structural properties of elliptical galaxies are consistent with their formation in a merging hierarchy. In this picture, the role of gaseous processes and dissipation decreased with increasing mass creating preferentially rotationally flattend disky ... More