Results for "Ralf Srama"

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Counter Data of the Cosmic Dust Analyzer aboard the Cassini spacecraft and possible "dust clouds" at SaturnOct 01 2014We present the impact rates of dust particles recorded by the Cosmic Dust Analyzer (CDA) aboard the Cassini spacecraft. The "dust counters" evaluate the quality of an impact and give rise to the apparent density of dust particles in space. The raw data ... More
Modelling DESTINY+ interplanetary and interstellar dust measurements en route to the active asteroid (3200) PhaethonApr 16 2019The JAXA/ISAS spacecraft DESTINY$^+$ will be launched to the active asteroid (3200) Phaethon in 2022. Among the proposed core payload is the DESTINY+ Dust Analyzer (DDA) which is an upgrade of the Cosmic Dust Analyzer flown on the Cassini spacecraft to ... More
Techniques for Galactic Dust Measurements in the HeliosphereAug 03 1999Galactic interstellar dust (ISD) is the major ingredient in planetary formation. However, information on this important material has been extremely limited. Recently the Ulysses dust detector has identified and measured interstellar dust outside 1.8~AU ... More
Heliospheric modulation of the interstellar dust flow on to EarthNov 14 2018Aims. Based on measurements by the Ulysses spacecraft and high-resolution modelling of the motion of interstellar dust (ISD) through the heliosphere we predict the ISD flow in the inner planetary system and on to the Earth. This is the third paper in ... More
Interstellar Dust in the Solar System: Model versus In-Situ Spacecraft DataMar 01 2019In the early 1990s, contemporary interstellar dust penetrating deep into the heliosphere was identified with the in-situ dust detector on board the Ulysses spacecraft. Later on, interstellar dust was also identified in the data sets measured with dust ... More
Jovian Dust Streams: A monitor of Io's volcanic plume activitySep 01 2003Streams of high speed dust particles originate from Jupiter's innermost Galilean moon Io. After release from Io, the particles collect electric charges in the Io plasma torus, gain energy from the co-rotating electric field of Jupiter's magnetosphere, ... 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
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
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.
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
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
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
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
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
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
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.
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
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
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
\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.
Dirac theory within the Standard-Model ExtensionJan 12 2004The modified Dirac equation in the Lorentz-violating Standard-Model Extension (SME) is considered. Within this framework, the construction of a hermitian Hamiltonian to all orders in the Lorentz-breaking parameters is investigated, discrete symmetries ... More
Threshold analyses and Lorentz violationApr 02 2003In the context of threshold investigations of Lorentz violation, we discuss the fundamental principle of coordinate invariance, the role of an effective dynamical framework, and the conditions of positivity and causality. Our analysis excludes a variety ... More
Theoretical topics in spacetime-symmetry violationsOct 02 2007The Lorentz- and CPT-violating Chern-Simons extension of electrodynamics is considered. In the context of N=4 supergravity in four spacetime dimensions, it is argued that cosmological solutions can generate this extension. Within Chern-Simons electrodynamics, ... More
CPT- and Lorentz-symmetry breaking: a reviewNov 13 2006Dec 28 2006The breakdown of spacetime symmetries has recently been identified as a promising candidate signal for underlying physics, possibly arising through quantum-gravitational effects. This talk gives an overview over various aspects of CPT- and Lorentz-violation ... More
Mass Spectra from Turbulent FragmentationJun 19 2001Turbulent fragmentation determines where and when protostellar cores form, and how they contract and grow in mass from the surrounding cloud material. Molecular cloud regions without turbulent driving sources, or where turbulence is driven on large scales, ... More
A Model for Dwarf Spheroidal Satellite Galaxies without Dark MatterJan 09 1998Self-consistent simulations of the dynamical evolution of low-mass satellite galaxies without dark matter on different orbits interacting with an extended Galactic dark halo are described. The calculations proceed for many orbital periods until well after ... More
The Formation of Stellar Clusters: Mass Spectra from Turbulent Molecular Cloud FragmentationApr 07 2001Turbulent fragmentation determines where and when protostellar cores form, and how they contract and grow in mass from the surrounding cloud material. This process is investigated, using numerical models of self-gravitating molecular cloud dynamics. Molecular ... More
On near Chandrasekhar mass central stars of planetary nebulaeMar 23 2006A recent spectroscopic analysis of central stars of planetary nebulae (CSPNe) claims that the sample includes five CSPNe with masses very close to the Chandrasekhar limit of white dwarfs. This claim should be verified or discarded from the available kinematical ... More
Spectroscopic investigation of old planetaries IV. Model atmosphere analysisAug 17 1999The results of a NLTE model atmosphere analysis of 27 hydrogen-rich central stars of old planetary nebulae (PN) are reported. These stars were selected from a previous paper in this series, where we gave classifications for a total of 38 central stars. ... More
Yang-Mills thermodynamics: The preconfining phaseJul 13 2005Nov 27 2006We summarize recent nonperturbative results obtained for the thermodynamics of an SU(2) and an SU(3) Yang-Mills theory being in its preconfining (magnetic) phase. We focus on an explanation of the involved concepts and derivations, and we avoid technical ... More
Analytical approach to SU(2) Yang-Mills thermodynamicsAug 10 2004We propose an analytical approach to SU(2) Yang-Mills thermodynamics. The existence of a macroscopic and rigid adjoint Higgs field, generated by dilute trivial-holonomy calorons at large temperature $T$ (electric phase), implies a twofold degeneracy of ... More
Galaxies in the infraredJul 21 2000The mid infrared spectra of the starbursts show the 9.7$\mu m$ silicate absorption feature and strong mid infrared emission bands centered at 6.2, 7.7, and 11.3 $\mu$m. Illustrative models of the {\it active} galaxies are presented: As the starbursts ... More
SUSY without R-parity: symmetry breaking and LSP phenomenologyFeb 25 1997We have studied the predictions for the LSP decay within the framework of a radiatively broken unified supergravity model without R-parity. Assuming that Higgs/slepton mixing is the only source of R-parity breaking and responsible for the observed neutrino ... More
Coupling Constant Unification in Extended SUSY ModelsFeb 01 1995The unification of gauge coupling constants in the minimal supersymmetric model (MSSM) is unaffected at the one-loop level by the inclusion of additional mass-degenerate SU(5) multiplets. Perturbativity puts an upper limit on the number of additional ... More
Can the Supersymmetric $μ$ parameter be generated dynamically without a light Singlet?Apr 12 1994It is generally assumed that the dynamical generation of the Higgs mass parameter of the superpotential, $\mu$, implies the existence of a light singlet at or below the supersymmetry breaking scale, $\msusy$. We present a counter-example in which the ... More
Prove or Disprove. 100 Conjectures from the OEISSep 27 2004Nov 27 2004Presented here are over one hundred conjectures ranging from easy to difficult, from many mathematical fields. I also summarize briefly methods and tools that have led to this collection.
On Hopf algebra structures over operadsJul 06 2004Nov 30 2005We study P-Hopf algebras with one coassociative cooperation over different operads P. For example, we consider the Loday-Ronco dendriform Hopf algebra and its isomorphisms with the noncommutative planar Connes-Kreimer Hopf algebra and with a Hopf algebra ... More
Smooth and rough modules over self-induced algebrasNov 19 2009A non-unital algebra in a closed monoidal category is called self-induced if the multiplication induces an isomorphism between A\otimes_A A and A. For such an algebra, we define smoothening and roughening functors that retract the category of modules ... More
On a class of reducible trinomialsNov 04 2013In this short note we give an expression for some numbers $n$ such that the polynomial $x^{2p}-nx^p+1$ is reducible.
P not= NP for infinite time Turing machinesJun 11 2001We state a version of the P=?NP problem for infinite time Turing machines. It is observed that P not= NP for this version.
Recovering quantum graphs from their Bloch spectrumJan 31 2011Feb 10 2011We define the Bloch spectrum of a quantum graph to be the collection of the spectra of a family of Schrodinger operators parametrized by the cohomology of the quantum graph. We show that the Bloch spectrum determines the Albanese torus, the block structure ... More
Spectroscopic investigation of old planetaries V. Distance scalesDec 01 2000Jan 08 2001We use the results of our recent NLTE model atmosphere analysis of central stars of old planetary nebulae (PN) to calculate distances. We perform a comparison with three other methods (trigonometric parallaxes, interstellar NaD lines, and Shklovsky distances) ... More
SU(2) and SU(3) Yang-Mills thermodynamics and some implicationsMar 30 2006Nov 27 2006We sketch the development of effective theories for SU(2) and SU(3) Yang-Mills thermodynamics. The most important results are quoted and some implications for particle physics and cosmology are discussed.
Yang-Mills thermodynamics: The deconfining phaseJul 04 2005Nov 27 2006We summarize recent nonperturbative results obtained for the thermodynamics of an SU(2) and an SU(3) Yang-Mills theory being in its deconfining (electric) phase. Emphasis is put on an explanation of the concepts involved. The presentation of technical ... More
Non-perturbative non-locality: $V\pm A$ correlators in euclidean position spaceSep 02 2001Using an OPE modification, which takes non-perturbative non-locality into account, the difference and sum of vector and axial-vector correlators are evaluated in euclidean position space. For distances up to 0.8 fm the calculated behavior is close to ... More
Nonperturbative approach to Yang-Mills thermodynamicsApr 07 2005Nov 28 2006An analytical and nonperturbative approach to SU(2) and SU(3) Yang-Mills thermodynamics is developed and applied. Each theory comes in three phases: A deconfining, a preconfining, and a confining one. We show how macroscopic and inert scalar fields form ... More
A thermal theory for charged leptonsDec 03 2003Jan 29 2004We propose that charged leptons are the `baryons' of the gauge dynamics subject to a SU(2)$_{e}$$\timesSU(2)_{\mu}\timesSU(2)_{\tau}$ symmetry. The `mesons' of this theory are neutral and thus candidates for dark matter. There is, in addition, a gauge ... More
Deconfining by WindingApr 19 2001Apr 23 2001A model for the quantum effective description of the vacuum structure of thermalized SU(3) Yang-Mills theory is proposed. The model is based on Abelian projection leading to a Ginzburg-Landau theory for the magnetic sector. The possibility of topologically ... More
BPS Saturated Vacua Interpolation along One Compact DimensionApr 26 2000Jun 08 2000A class of generalized Wess-Zumino models with distinct vacua is investigated. These models allow for BPS saturated vacua interpolation along one compact spatial dimension. The properties of these interpolations are studied.
Dust Emission by AGN and StarburstsJun 24 2005Present AGN and starburst models aiming to account for the observed infrared SEDs consider a physical description of the dust and a solution of the radiative transfer problem. MIR spectra obtained at different spatial scales (SST-IRS, ISO and TIMMI2) ... More
Supersymmetry at Present and Future CollidersJun 23 1995The theoretical expectations for the supersymmetric particle spectrum is reviewed and a brief overview on present constraints on supersymmetric models from collider experiments is presented. Finally, we discuss the discovery potential of future collider ... More
Top-Down Approach to Unified Supergravity ModelsApr 06 1994Apr 08 1994We introduce a new approach for studying unified supergravity models. In this approach all the parameters of the grand unified theory (GUT) are fixed by imposing the corresponding number of low energy observables. This determines the remaining particle ... More
Neutrino properties and SUSY without $R$-paritySep 30 1996In supersymmetric models without $R$-parity neutrinos naturally become massive and mix with each other. We explore the predictions of a very restricted model with only three free parameters and find that this model naturally yields masses and mixing angles ... More
Book review "The Haskell Road to Logic, Maths and Programming"Dec 24 2005Jun 22 2006The textbook by Doets and van Eijck puts the Haskell programming language systematically to work for presenting a major piece of logic and mathematics. The reader is taken through chapters on basic logic, proof recipes, sets and lists, relations and functions, ... More
Typed Generic Traversal With Term Rewriting StrategiesMay 14 2002Jul 28 2002A typed model of strategic term rewriting is developed. The key innovation is that generic traversal is covered. To this end, we define a typed rewriting calculus S'_{gamma}. The calculus employs a many-sorted type system extended by designated generic ... More
GRAPESPH with Fully Periodic Boundary Conditions: Fragmentation of Molecular CloudsApr 01 1997A method of adapting smoothed particle hydrodynamics (SPH) with periodic boundary conditions for use with the special purpose device GRAPE is presented. GRAPE (GRAvity PipE) solves the Poisson and force equations for an N-body system by direct summation ... More
Thermal Ground State in Yang-Mills ThermodynamicsSep 27 2011We derive an a useful priori estimate for the thermal ground state of deconfining phase of SU(2) Yang-Mills thermodynamics in four-dimensional, flat spacetime and discuss its implications. Upon a selfconsistent spatial coarse-graining over noninteracting, ... More
"Exotic" quantum effects in the laboratory?Apr 15 2010This Article provides a brief (non-exhaustive) review of some recent developments regarding the theoretical and possibly experimental study of "exotic" quantum effects in the laboratory with special emphasis on cosmological particle creation, Hawking ... More
CPT and Lorentz violation as signatures for Planck-scale physicsJul 08 2009In recent years, the breakdown of spacetime symmetries has been identified as a promising research field in the context of Planck-scale phenomenology. For example, various theoretical approaches to the quantum-gravity problem are known to accommodate ... More
Quasi-isospectrality on quantum graphsMar 16 2012Jan 30 2015Consider two quantum graphs with the standard Laplace operator and non-Robin type boundary conditions at all vertices. We show that if their eigenvalue-spectra agree everywhere aside from a sufficiently sparse set, then the eigenvalue-spectra and the ... More
Onset of magnetic monopole-antimonopole condensationAug 27 2009We determine the critical strength of the effective electric coupling for the onset of Bose condensation of stable magnetic monopoles and antimonopoles in SU(2) Yang-Mills thermodynamics. Two scenarios are considered: infinitely fast and infinitely slow ... More
The Formation of Stellar Clusters: Time Varying Protostellar Accretion RatesJan 16 2001Identifying the processes that determine strength, duration and variability of protostellar mass growth is a fundamental ingredient of any theory of star formation. I discuss protostellar mass accretion rates dM/dt from numerical models which follow molecular ... More
Non-local on-shell field redefinition for the SMESep 23 2006This work instigates a study of non-local field mappings within the Lorentz- and CPT-violating Standard-Model Extension (SME). An example of such a mapping is constructed explicitly, and the conditions for the existence of its inverse are investigated. ... More
Spacetime symmetries and varying scalarsAug 29 2005This talk discusses the relation between spacetime-dependent scalars, such as couplings or fields, and the violation of Lorentz symmetry. A specific cosmological supergravity model demonstrates how scalar fields can acquire time-dependent expectation ... More
Lorentz-violating dispersion relations and threshold analysesFeb 12 2004Remnant low-energy effects of Planck-scale Lorentz breaking in candidate fundamental theories typically include modified one-particle dispersion relations. Theoretical constraints on such modifications are discussed leading to the exclusion of a variety ... More
Fundamental physics and Lorentz violationDec 05 2003The violation of Lorentz symmetry can arise in a variety of approaches to fundamental physics. For the description of the associated low-energy effects, a dynamical framework known as the Standard-Model Extension has been developed. This talk gives a ... More
A matrix-algebraic algorithm for the Riemannian logarithm on the Stiefel manifoldApr 18 2016May 09 2016We derive a numerical algorithm for evaluating the Riemannian logarithm on the Stiefel manifold with respect to the canonical metric. In contrast to the optimization-based approach known from the literature, we work from a purely matrix-algebraic perspective. ... More
Finite dimensional quotients of commutative operator algebrasOct 17 1997The matrix normed structure of the unitization of a (non-selfadjoint) operator algebra is determined by that of the original operator algebra. This yields a classification up to completely isometric isomorphism of two-dimensional unital operator algebras. ... More
A closed-form update for orthogonal matrix decompositions under arbitrary rank-one modificationsNov 22 2017Jun 08 2018We consider rank-one adaptations $X_{new} = X+ab^T$ of a given matrix $X\in \mathbb{R}^{n\times p}$ with known matrix factorization $X = UW$, where $U\in\mathbb{R}^{n\times p}$ is column-orthogonal, i.e. $U^TU=I$. Arguably the most important methods that ... More
On a representation of the idele class group related to primes and zeros of L-functionsNov 26 2003Mar 16 2005Let K be a global field. Using natural spaces of functions on the adele ring and the idele class group of K, we construct a virtual representation of the idele class group of K whose character is equal to the Weil distribution that occurs in Andre Weil's ... More
Cuspidal representations of reductive p-adic groups are relatively injective and projectiveApr 10 2015Nov 21 2015Cuspidal representations of a reductive p-adic group G over a field of characteristic different from p are relatively injective and projective with respect to extensions that split by a U-equivariant linear map for any subgroup U that is compact modulo ... More
Categorical aspects of bivariant K-theoryFeb 06 2007Feb 26 2007This survey article on bivariant Kasparov theory and E-theory is mainly intended for readers with a background in homotopical algebra and category theory. We approach both bivariant K-theories via their universal properties and equip them with extra structure ... More
Defining amalgams of compact Lie groupsAug 11 2007For $n \geq 2$ let $\Delta$ be a Dynkin diagram of rank $n$ and let $I = {1, >..., n}$ be the set of labels of $\Delta$. A group $G$ admits a weak Phan system of type $\Delta$ over $\mathbb{C}$ if $G$ is generated by subgroups $U_i$, $i \in I$, which ... More
A geometric note on subspace updates and orthogonal matrix decompositions under rank-one modificationsNov 22 2017Mar 05 2019In this work, we consider rank-one adaptations $X_{new} = X+ab^T$ of a given matrix $X\in \mathbb{R}^{n\times p}$ with known matrix factorization $X = UW$, where $U\in\mathbb{R}^{n\times p}$ is column-orthogonal, i.e. $U^TU=I$. Arguably the most important ... More
Floer homology of algebraically finite mapping classesApr 02 2002Apr 25 2002We compute the Floer homology of mapping classes which do not have any pseudo-Anosov components in the sense of Thurston's theory of surface diffeomorphisms. The formula for the Floer homology is obtained from a topological separation of fixed points ... More
Generalized fixed point algebras and square-integrable group actionsNov 13 2000We analzye Rieffel's construction of generalized fixed point algebras in the setting of group actions on Hilbert modules. Let G be a locally compact group acting on a C*-algebra B. We construct a Hilbert module F over the reduced crossed product of G ... More
Heat trace asymptotics for quantum graphsDec 12 2012We consider a quantum graph where the operator contains a potential. We show that this operator admits a heat kernel. Under some assumptions on the potential, this heat kernel admits an asymptotic expansion at t=0 with coefficients that depend on the ... More
On cluster algebras arising from unpunctured surfaces IISep 15 2008Sep 18 2008We study cluster algebras with principal and arbitrary coefficient systems that are associated to unpunctured surfaces. We give a direct formula for the Laurent polynomial expansion of cluster variables in these cluster algebras in terms of certain paths ... More
Cross-lingual keyword assignmentSep 12 2006This paper presents a language-independent approach to controlled vocabulary keyword assignment using the EUROVOC thesaurus. Due to the multilingual nature of EUROVOC, the keywords for a document written in one language can be displayed in all eleven ... More
Treating `Free Word Order' in Machine TranslationSep 08 1994In `free word order' languages, every sentence is embedded in its specific context. Among others, the order of constituents is determined by the categories `theme', `rheme' and `contrastive focus'. This paper shows how to recognise and to translate these ... More