Results for "Sascha Kempf"

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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
Short-Distance Cutoffs in Curved SpaceMar 30 2004It is shown that space-time may possess the differentiability properties of manifolds as well as the ultraviolet finiteness properties of lattices. Namely, if a field's amplitudes are given on any sufficiently dense set of discrete points this could already ... More
On Symmetric Operators in Noncommutative GeometryNov 28 1998In Noncommutative Geometry, as in quantum theory, classically real variables are assumed to correspond to self-adjoint operators. We consider the relaxation of the requirement of self-adjointness to mere symmetry for operators $X_i$ which encode space-time ... More
On the only three Short Distance Structures which can be described by Linear OperatorsJun 01 1998We point out that if spatial information is encoded through linear operators $X_i$, or `infinite-dimensional matrices' with an involution $X_i^*=X_i$ then these $X_i$ can only describe either continuous, discrete or certain "fuzzy" space-time structures. ... More
Recent results on UV-regularisation through UV-modified uncertainty relationsNov 28 1997Assume that in a fundamental theory of quantum gravity spatial information is encoded through elements x_i of an associative, complex and possibly noncommutative algebra in which the involution acts as x^*_i = x_i. Without further assumptions it can be ... More
On Noncommutative Geometric RegularisationFeb 21 1996Studies in string theory and in quantum gravity suggest the existence of a finite lower bound to the possible resolution of lengths which, quantum theoretically, takes the form of a minimal uncertainty in positions $\Delta x_0$. A finite minimal uncertainty ... More
Simple considerations on the behaviour of bosonic modes with quantum group symmetryAug 06 1993While it is possible to introduce quantum group symmetry into the framework of quantum mechanics, the general problem of how to implement quantum group symmetry into $(3+1)$ dimensional quantum field theory has not yet been solved. Here we try to estimate ... More
Unsharp Degrees of Freedom and the Generating of SymmetriesJul 19 1999In quantum theory, real degrees of freedom are usually described by operators which are self-adjoint. There are, however, exceptions to the rule. This is because, in infinite dimensional Hilbert spaces, an operator is not necessarily self-adjoint even ... More
Instability in invariant theoryJul 08 2018Transcriber's note: In the fall of 1976, my advisor, David Mumford, handed me a short preprint by George Kempf to read. It was the first state of what eventually became his influential Annals paper "Instability in Invariant Theory" (Annals of Mathematics, ... More
New methods for creating superoscillationsAug 10 2016Superoscillating functions, i.e., functions that locally oscillate at a rate faster than their highest Fourier component, are of interest for applications from fundamental physics to engineering. Here, we develop a new method which allows one to construct ... More
Towards Spectral Geometric Methods for Euclidean Quantum GravityJan 27 2016Mar 15 2016The unification of general relativity with quantum theory will also require a coming together of the two quite different mathematical languages of general relativity and quantum theory, i.e., of differential geometry and functional analysis respectively. ... More
The Transplanckian Question and the Casimir EffectApr 18 2005It is known that, through inflation, Planck scale phenomena should have left an imprint in the cosmic microwave background. The magnitude of this imprint is expected to be suppressed by a factor $\sigma^n$ where $\sigma\approx 10^{-5}$ is the ratio of ... More
On Information Theory, Spectral Geometry and Quantum GravityAug 01 2007We show that there exists a deep link between the two disciplines of information theory and spectral geometry. This allows us to obtain new results on a well known quantum gravity motivated natural ultraviolet cutoff which describes an upper bound on ... More
Algebraic {$q$}-Integration and Fourier Theory on Quantum and Braided SpacesFeb 07 1994Jun 03 1994We introduce an algebraic theory of integration on quantum planes and other braided spaces. In the one dimensional case we obtain a novel picture of the Jackson $q$-integral as indefinite integration on the braided group of functions in one variable $x$. ... More
Vacuum entanglement enhancement by a weak gravitational fieldAug 29 2010Separate regions in space are generally entangled, even in the vacuum state. It is known that this entanglement can be swapped to separated Unruh-DeWitt detectors, i.e., that the vacuum can serve as a source of entanglement. Here, we demonstrate that, ... More
Driving Quantum Systems with SuperoscillationsOct 14 2015Superoscillations, i.e., the phenomenon that a bandlimited function can temporary oscillate faster than its highest Fourier component, are being much discussed for their potential for `superresolution' beyond the diffraction limit. Here, we consider systems ... More
The Virial Relation and Intrinsic Shape of Early-Type GalaxiesSep 22 2016Sep 26 2016Early-type galaxies (ETGs) are supposed to follow the virial relation $M = k_e \sigma_*^2 R_e / G$, with $M$ being the mass, $\sigma_*$ being the stellar velocity dispersion, $R_e$ being the effective radius, $G$ being Newton's constant, and $k_e$ being ... More
Generalized roll-call model for the Shapley-Shubik indexFeb 13 2016In 1996 Dan Felsenthal and Mosh\'e Machover considered the following model. An assembly consisting of $n$ voters exercises roll-call. All $n!$ possible orders in which the voters may be called are assumed to be equiprobable. The votes of each voter are ... More
Additional Information on Heavy Quark Parameters from Charged Lepton Forward-Backward AsymmetryFeb 08 2016The determination of $|V_{cb}|$ using inclusive and exclusive (semi-)leptonic decays exhibits a long-standing tension of varying ${\cal O}(3 \sigma)$ significance. For the inclusive determination the decay rate is expanded in $1/m_b$ using heavy quark ... More
A Survey on Reproducibility in Parallel ComputingNov 13 2015We summarize the results of a survey on reproducibility in parallel computing, which was conducted during the Euro-Par conference in August 2015. The survey form was handed out to all participants of the conference and the workshops. The questionnaire, ... More
On minimum sum representations for weighted voting gamesMar 08 2011A proposal in a weighted voting game is accepted if the sum of the (non-negative) weights of the "yea" voters is at least as large as a given quota. Several authors have considered representations of weighted voting games with minimum sum, where the weights ... More
Semiglobal Numerical Calculations of Asymptotically Minkowski SpacetimesDec 06 2001This talk reports on recent progress toward the semiglobal study of asymptotically flat spacetimes within numerical relativity. The development of a 3D solver for asymptotically Minkowski-like hyperboloidal initial data has rendered possible the application ... More
Kohomologie von Periodenbereichen ueber endlichen KoerpernJul 15 1999Periodenbereiche sind gewisse offene Unterraeume von verallgemeinerten Flaggenvarietaeten, welche durch Semistabilitaetsbedingungen beschrieben werden. In dem Fall eines endlichen Grundkoerpers bilden diese eine Zariski-offene Untervarietaet, im Fall ... More
Spectral synthesis provides 2-D videos on a 1-D screen with 360°-visibility and mirror-immunityFeb 07 2014Spatial-light-modulator (SLM)-based tunable sources have complex setups. A simpler setup, comprising an SLM-projector and a dispersive element, synthesizes light as effectively, based on a Superposition of Newtonian Spectra (SNS). As a generalization ... More
The "Missing Mass Problem" in Astronomy and the Need for a Modified Law of GravityJan 23 2014Since the 1930s, astronomical observations have accumulated evidence that our understanding of the dynamics of galaxies and groups of galaxies is grossly incomplete: assuming the validity of Newton's law of gravity on astronomical scales, the observed ... More
A Simplified Treatment of Gravitational Interaction on Galactic ScalesNov 20 2012Jan 31 2013I present a simple scheme for the treatment of gravitational interactions on galactic scales. In analogy to known mechanisms of quantum field theory, I assume ad hoc that gravitation is mediated by virtual exchange particles - gravitons - with very small ... More
Ground states of dipolar gases in quasi-1D ring trapsNov 25 2011Dec 15 2011We compute the ground state of dipoles in a quasi-one-dimensional ring trap using few-body techniques combined with analytic arguments. The effective interaction between two dipoles depends on their center-of-mass coordinate and can be tuned by varying ... More
Integral point sets over finite fieldsApr 08 2008We consider point sets in the affine plane $\mathbb{F}_q^2$ where each Euclidean distance of two points is an element of $\mathbb{F}_q$. These sets are called integral point sets and were originally defined in $m$-dimensional Euclidean spaces $\mathbb{E}^m$. ... More
Exponential Stability for Linear Evolutionary EquationsFeb 28 2013Jun 14 2013We give an approach to exponential stability within the framework of evolutionary equations due to [R. Picard. A structural observation for linear material laws in classical mathematical physics. Math. Methods Appl. Sci., 32(14):1768-1803,2009]. We derive ... More
Equivariant vector bundles on Drinfeld's upper half spaceJun 15 2006Jun 24 2007Let X be Drinfeld's upper half space of dimension d over a finite extension K of Q_p. We construct for every homogeneous vector bundle F on the projective space P^d a GL_{d+1}(K)-equivariant filtration by closed K-Frechet spaces on F(X). This gives rise ... More
Upper bounds for partial spreadsJun 28 2016Apr 04 2017A partial $t$-spread in $\mathbb{F}_q^n$ is a collection of $t$-dimensional subspaces with trivial intersection such that each non-zero vector is covered at most once. We present some improved upper bounds on the maximum sizes.
Squaring the square with integer linear programmingJan 24 2014We consider so-called squaring the square-puzzles where a given square (or rectangle) should be dissected into smaller squares. For a specific instance of such problems we demonstrate that a mathematically rigorous solution can be quite involved. As an ... More
Corrections to the Emergent Canonical Commutation Relations Arising in the Statistical Mechanics of Matrix ModelsSep 15 1997Sep 18 1997We study the leading corrections to the emergent canonical commutation relations arising in the statistical mechanics of matrix models, by deriving several related Ward identities, and give conditions for these corrections to be small. We show that emergent ... More
Examples of Black Holes in Two-Time PhysicsJul 11 1999Sep 13 1999Two time theory is derived via localization of the global Sp(2) [or Osp(1/2), Osp(N/2), Sp(2N),...] symmetry in phase space in order to give a self contained introduction to two time theory. Then it is shown that from the two-times physics point of view ... More
The cohomology of period domains for reductive groups over finite fieldsJul 15 1999The goal of this paper is to give an explicit formula for the l-adic cohomology of period domains over finite fields for arbitrary reductive groups. The result is a generalisation of the computation in math.AG/9907098 which treats the case of the general ... More
Nature: "I have Two Times"Jul 07 1999Jul 11 1999This is a slightly extended version of a seminar given the 8th of June at the TASI 99 at Colorado University in Boulder. The motivations behind two time theory are explained and the theory is introduced via one of the theory's easier gauges of a particle ... More
Seeing lens imaging as a superposition of multiple viewsOct 12 2015In the conventional approach to lens imaging, rays are used to map object points to image points. However, many students have a need to think of the image as a whole. To answer this need, lens imaging is reinterpreted as a superposition of sharp images ... More
AGN Broad Line Regions Scale with Bolometric LuminosityJun 15 2015The masses of supermassive black holes in active galactic nuclei (AGN) can be derived spectroscopically via virial mass estimators based on selected broad optical/ultraviolet emission lines. These estimates commonly use the line width as a proxy for the ... More
Trip-Based Public Transit RoutingApr 27 2015Jul 02 2015We study the problem of computing all Pareto-optimal journeys in a public transit network regarding the two criteria of arrival time and number of transfers taken. We take a novel approach, focusing on trips and transfers between them, allowing fine-grained ... More
On Integro-Differential Inclusions with Operator-valued KernelsAug 22 2013We study integro-differential inclusions in Hilbert spaces with operator-valued kernels and give sufficient conditions for the well-posedness. We show that several types of integro-differential equations and inclusions are covered by the class of evolutionary ... More
Enumeration of integral tetrahedraApr 08 2008We determine the numbers of integral tetrahedra with diameter $d$ up to isomorphism for all $d\le 1000$ via computer enumeration. Therefore we give an algorithm that enumerates the integral tetrahedra with diameter at most $d$ in $O(d^5)$ time and an ... More
The Passage of Ultrarelativistic Neutralinos through the Matter of the MoonSep 29 2008I consider the prospect to use the outer layer of the Moon as a detector volume for ultra-high energy (UHE) neutrino fluxes and the flux of the lightest neutralino which I assume is the lightest supersymmetric particle (LSP). For this purpose, I calculate ... More
On the dimensions of attractors of random self-similar graph directed iterated function systemsNov 11 2015In this paper we propose a new model of random graph directed fractals that extends the current well-known model of random graph directed iterated function systems, $V$-variable attractors, and fractal and Mandelbrot percolation. We study its dimensional ... More
The cohomology of Deligne-Lusztig varieties for the general linear groupFeb 02 2013Nov 13 2014We propose two inductive approaches for determining the cohomology of Deligne-Lusztig varieties in the case of the general linear group
A lower bound for 4-regular planar unit distance graphsJan 17 2014We perform an exhaustive search for the minimum 4-regular unit distance graph resulting in a lower bound of 34 vertices.
Change of Measure in the Heston Model given a violated Feller ConditionSep 28 2018When dealing with Heston's stochastic volatility model, the change of measure from the subjective measure P to the objective measure Q is usually investigated under the assumption that the Feller condition is satisfied. This paper closes this gap in the ... More
Computing the Power Distribution in the IMFMar 04 2016The International Monetary Fund is one of the largest international organizations using a weighted voting system. The weights of its 188 members are determined by a fixed amount of basic votes plus some extra votes for so-called Special Drawing Rights ... More
Milgrom's Law and Lambda's Shadow: How Massive Gravity Connects Galactic and Cosmic DynamicsJun 02 2015Massive gravity provides a natural solution for the dark energy problem of cosmology and is also a candidate for resolving the dark matter problem. I demonstrate that, assuming reasonable scaling relations, massive gravity can provide for Milgrom's law ... More
On a class of block operator matrices in system theoryFeb 19 2015We consider a class of block operator matrices arising in the study of scattering passive systems, especially in the context of boundary control problems. We prove that these block operator matrices are indeed a subclass of block operator matrices considered ... More
Does the Jet Production Efficiency of Radio Galaxies Control Their Optical AGN Types?Aug 25 2014The jet production efficiency of radio galaxies can be quantified by comparison of their kinetic jet powers P_jet and Bondi accretion powers P_B. These two parameters are known to be related linearly, with the jet power resulting from the Bondi power ... More
On the inverse power index problemNov 27 2012Weighted voting games are frequently used in decision making. Each voter has a weight and a proposal is accepted if the weight sum of the supporting voters exceeds a quota. One line of research is the efficient computation of so-called power indices measuring ... More
Quantum Randi ChallengeJul 23 2012Dec 24 2012Observed violations of Bell type inequalities exclude all relativistic micro causal ("local"), counterfactual definite ("real") hidden variable models of nature. This further relativization of our concept of reality triggers a growing pseudoscientific ... More
Supporting Abstract Relational Space-Time as Fundamental without Doctrinism against EmergenceDec 16 2009Oct 02 2011Modern physics, via the standard model with Higgs mechanism and string theory for example, has supplied ether-like models and emergent general relativity scenarios that substantially weaken the usual defense of orthodox relativity and abstract, relational ... More
How long does it take to consensus in the Hegselmann-Krause model?May 22 2014Hegselmann and Krause introduced a discrete-time model of opinion dynamics with agents having limit confidence. It is well known that the dynamics reaches a stable state in a polynomial number of time steps. However, the gap between the known lower and ... More
Can Massive Gravity Explain the Mass Discrepancy - Acceleration Relation of Disk Galaxies?May 28 2013The empirical mass discrepancy-acceleration (MDA) relation of disk galaxies provides a key test for models of galactic dynamics. In terms of modified laws of gravity and/or inertia, the MDA relation quantifies the transition from Newtonian to modified ... More
A Derivation of Modified Newtonian DynamicsMar 28 2013Modified Newtonian Dynamics (MOND) is a possible solution for the missing mass problem in galactic dynamics; its predictions are in good agreement with observations in the limit of weak accelerations. However, MOND does not derive from a physical mechanism ... More
Historical Parallels between, and Modal Realism underlying Einstein and Everett RelativitiesJan 09 2013A century ago, "past" and "future", previously strictly apart, mixed up and merged. Temporal terminology improved. Today, not actualized quantum states, that is merely "possible" alternatives, objectively "exist" (are real) when they interfere. Again, ... More
Numerical modeling of black holes as sources of gravitational waves in a nutshellDec 23 2008These notes summarize basic concepts underlying numerical relativity and in particular the numerical modeling of black hole dynamics as a source of gravitational waves. Main topics are the 3+1 decomposition of general relativity, the concept of a well-posed ... More
Problems and Successes in the Numerical Approach to the Conformal Field EquationsApr 12 2002This talk reports on the status of an approach to the numerical study of isolated systems with the conformal field equations. We first describe the algorithms used in a code which has been developed at AEI in the last years, and discuss a milestone result ... More
Asymptotically Flat Initial Data for Gravitational Wave Spacetimes, Conformal Compactification and Conformal SymmetryNov 02 1998We study the utilization of conformal compactification within the conformal approach to solving the constraints of general relativity for asymptotically flat initial data. After a general discussion of the framework, particular attention is paid to simplifications ... More
Well-posedness of Linear Integro-Differential Equations with Operator-valued KernelsOct 05 2012Apr 04 2016We study linear integro-differential equations in Hilbert spaces with operator-valued kernels and give sufficient conditions for the well-posedness. We show that several types of integro-differential equations are covered by the class of evolutionary ... More
On the characteristic of integral point sets in $\mathbb{E}^m$Nov 29 2005We generalise the definition of the characteristic of an integral triangle to integral simplices and prove that each simplex in an integral point set has the same characteristic. This theorem is used for an efficient construction algorithm for integral ... More
No finite $5$-regular matchstick graph existsJan 08 2014A graph $G=(V,E)$ is called a unit-distance graph in the plane if there is an injective embedding of $V$ in the plane such that every pair of adjacent vertices are at unit distance apart. If additionally the corresponding edges are non-crossing and all ... More
Fast regocnition of planar non unit distance graphsJan 17 2014We study criteria attesting that a given graph can not be embedded in the plane so that neighboring vertices are at unit distance apart and the straight line edges do not cross.
Ready for the design of voting rules?May 05 2014The design of fair voting rules has been addressed quite often in the literature. Still, the so-called inverse problem is not entirely resolved. We summarize some achievements in this direction and formulate explicit open questions and conjectures.
Concentration for Poisson functionals: component counts in random geometric graphsJun 26 2015Jan 13 2016Upper bounds for the probabilities $\mathbb{P}(F\geq \mathbb{E} F + r)$ and $\mathbb{P}(F\leq \mathbb{E} F - r)$ are proved, where $F$ is a certain component count associated with a random geometric graph built over a Poisson point process on $\mathbb{R}^d$. ... More
Measuring voting power in convex policy spacesDec 20 2013Classical power index analysis considers the individual's ability to influence the aggregated group decision by changing its own vote, where all decisions and votes are assumed to be binary. In many practical applications we have more options than either ... More
The "Graviton Picture": a Bohr Model for Gravitation on Galactic Scales?May 06 2014Modified Newtonian Dynamics (MOND) provides a successful description of stellar and galactic dynamics on almost all astronomical scales. A key feature of MOND is the transition function from Newtonian to modified dynamics which corresponds to the empirical ... More
Against Absolute Actualization: Three "Non-Localities" and Failure of Model-External Randomness made easy with Many-Worlds Models including Stronger Bell-Violation and Correct QM ProbabilityNov 20 2013Jun 05 2014Experimental violation of Bell-inequalities proves actualization of many futures (~ many-worlds); I show that this is not mere interpretation. To show this self-contained pedagogically, I resolve the EPR paradox by starting with a visually intuitive non-quantum ... More
Many Worlds Model resolving the Einstein Podolsky Rosen paradox via a Direct Realism to Modal Realism Transition that preserves Einstein LocalityAug 08 2011The violation of Bell inequalities by quantum physical experiments disproves all relativistic micro causal, classically real models, short Local Realistic Models (LRM). Non-locality, the infamous "spooky interaction at a distance" (A. Einstein), is already ... More
Exploring Inequality Violations by Classical Hidden Variables NumericallyAug 29 2013There are increasingly suggestions for computer simulations of quantum statistics which try to violate Bell type inequalities via classical, common cause correlations. The Clauser-Horne-Shimony-Holt (CHSH) inequality is very robust. However, we argue ... More
The de Rham cohomology of Drinfeld's half spaceApr 10 2013Aug 07 2014Let X be Drinfeld's half space over a p-adic field K. The de Rham cohomology of X was first computed by Schneider and Stuhler. Afterwards there were given different proofs by Alon, de Shalit, Iovita and Spiess. This paper presents yet another approach ... More
Model-independent analysis of Tau -> lll' decaysDec 19 2008Many models for physics beyond the Standard Model predict lepton-flavour violating decays of charged leptons at a level which may become observable very soon. We investigate the decays of a Tau-lepton into three charged leptons (Tau -> lll', l(') = e,\mu ... More
Helium Clusters Capture of Heliophobes, Strong Depletion and Spin dependent Pick-up StatisticsFeb 07 2010This much revised and shortened PhD thesis contains many ideas that I could not follow up on, like self destructing beams in scattering cells, the depletion enhancing Wittig tube, ionic seeding via beta-decay foil or Langmuir-Taylor filaments, analysis ... More
Trip-Based Public Transit Routing Using Condensed Search TreesJul 05 2016Sep 15 2016We study the problem of planning Pareto-optimal journeys in public transit networks. Most existing algorithms and speed-up techniques work by computing subjourneys to intermediary stops until the destination is reached. In contrast, the trip-based model ... More
On Extensions of generalized Steinberg RepresentationsFeb 04 2004Let F be a local non-archimedean field and let G be the group of F-valued points of a reductive algebraic group over F. In this paper we compute the Ext-groups of generalized Steinberg representations in the category of smooth G-representations with coefficients ... More
Autonomous Evolutionary Inclusions with Applications to Problems with Nonlinear Boundary ConditionsDec 10 2012We study an abstract class of autonomous differential inclusions in Hilbert spaces and show the well-posedness and causality, by establishing the operators involved as maximal monotone operators in time and space. Then the proof of the well-posedness ... More
A characterization of boundary conditions yielding maximal monotone operatorsOct 18 2013Aug 13 2014We provide a characterization for maximal monotone realizations for a certain class of (nonlinear) operators in terms of their corresponding boundary data spaces. The operators under consideration naturally arise in the study of evolutionary problems ... More
Prospects for standard SUSY searches at the LHCOct 20 2008We present the recent prospects and strategies of the ATLAS and CMS experiments in the search for signatures of Supersymmetry. The emphasis is placed on standard signatures with missing transverse energy and on the initial data taking periods.
Searches and electroweak measurements at HERANov 10 2004The H1 and ZEUS collaborations have used the HERA I data to search for physics beyond the SM and to test electroweak physics in electron-proton collisions. The new period of data taking (HERA II) has started and first HERA II analyses become available. ... More
Jet production at HERA INov 07 2003This article reviews recent jet physics results from HERA.
Counting polyominoes with minimum perimeterJun 21 2005Nov 02 2015The number of essentially different square polyominoes of order n and minimum perimeter p(n) is enumerated.
Convex hulls of polyominoesFeb 26 2007In this article we prove a conjecture of Bezdek, Brass, and Harborth concerning the maximum volume of the convex hull of any facet-to-facet connected system of n unit hypercubes in the d-dimensional Euclidean space. For d=2 we enumerate the extremal polyominoes ... More
The box dimension of random box-like self-affine setsDec 22 2015In this paper we study two random analogues of the box-like self-affine attractors introduced by Fraser, itself an extension of Sierpi\'nski carpets. We determine the almost sure box-counting dimension for the homogeneous random case ($1$-variable random), ... More
Exponential stability for second order evolutionary problemsAug 01 2014Apr 13 2015We study the exponential stability of evolutionary equations. The focus is laid on second order problems and we provide a way to rewrite them as a suitable first order evolutionary equation, for which the stability can be proved by using frequency domain ... More
Importance in systems with interval decisionsMar 12 2018Aug 06 2018Given a system where the real-valued states of the agents are aggregated by a function to a real-valued state of the entire system, we are interested in the influence or importance of the different agents for that function. This generalizes the notion ... More
The Virial Relation and Intrinsic Shape of Early-Type GalaxiesSep 22 2016Oct 05 2016Early-type galaxies (ETGs) are supposed to follow the virial relation $M = k_e \sigma_*^2 R_e / G$, with $M$ being the mass, $\sigma_*$ being the stellar velocity dispersion, $R_e$ being the effective radius, $G$ being Newton's constant, and $k_e$ being ... More
Caps in $\mathbf{\mathbb{Z}_n^2}$Jan 17 2014We consider point sets in $\mathbb{Z}_n^2$ where no three points are on a line - also called caps or arcs. For the determination of caps with maximum cardinality and complete caps with minimum cardinality we provide integer linear programming formulations ... More
The Missing Memristor: Novel Nanotechnology or rather new Case Study for the Philosophy and Sociology of Science?Mar 01 2012In 2008, it was widely announced that the missing memristor, a basic two-terminal electrical circuit element, had finally been discovered. The memristor is the fourth and last such circuit element and thus completes circuit theory. Predicted already in ... More
Metric Expansion from Microscopic Dynamics in an Inhomogeneous UniverseAug 17 2010Theories with ingredients like the Higgs mechanism, gravitons, and inflaton fields rejuvenate the idea that relativistic kinematics is dynamically emergent. Eternal inflation treats the Hubble constant H as depending on location. Microscopic dynamics ... More
Numerical relativity with the conformal field equationsApr 17 2002I discuss the conformal approach to the numerical simulation of radiating isolated systems in general relativity. The method is based on conformal compactification and a reformulation of the Einstein equations in terms of rescaled variables, the so-called ... More
Black Hole Thermodynamics in Semi-Classical and Superstring TheorySep 24 1997This is a revised and shortened version of a MSc thesis submitted to the University of Sussex, UK. An introduction into the pre-string physics of black holes and related thermodynamics is given. Then, starting with an introduction of how superstring theory ... More
Initial Data for General Relativity Containing a Marginally Outer Trapped TorusJun 15 1996Asymptotically flat, time-symmetric, axially symmetric and conformally flat initial data for vacuum general relativity are studied numerically on $R^3$ with the interior of a standard torus cut out. By the choice of boundary condition the torus is marginally ... More
Upper bounds for partial spreadsJun 28 2016Jul 14 2016A partial $t$-spread in $\mathbb{F}_q^n$ is a collection of $t$-dimensional subspaces with trivial intersection such that each non-zero vector is covered at most once. We present some improved upper bounds on the maximum sizes.
Purely Mechanical Memristors: Perfect Massless Memory Resistors, the Missing Perfect Mass-Involving Memristor, and Massive Memristive SystemsMar 21 2015Aug 15 2015We define a mechanical analog to the electrical basic circuit element M = d{\phi}/dQ, namely the ideal mechanical memristance M = dp/dx; p is momentum. We then introduce a mechanical memory resistor which has M(x) independent of velocity v, so it is a ... More
The continuous cohomology of period domains over local fieldsMay 19 2005In this paper we consider period domains over local fields for quasi-split reductive groups. We compute the continuous l-adic cohomology with compact support of them in the case of a basic isocrystal. This paper is a continuation of [O2] where we considered ... More
Hölder differentiability of self-conformal devil's staircasesJan 07 2013In this paper we consider the probability distribution function of a Gibbs measure supported on a self-conformal set given by an iterated function system (devil's staircase). We use thermodynamic multifractal formalism to calculate the Hausdorff dimension ... More
Complexity of Single-Swap Heuristics for Metric Facility Location and Related ProblemDec 06 2016Metric facility location and $K$-means are well-known problems of combinatorial optimization. Both admit a fairly simple heuristic called single-swap, which adds, drops or swaps open facilities until it reaches a local optimum. For both problems, it is ... More
Optimal control of the convergence time in the Hegselmann--Krause dynamicsNov 18 2014Feb 26 2015We study the optimal control problem of minimizing the convergence time in the discrete Hegselmann--Krause model of opinion dynamics. The underlying model is extended with a set of strategic agents that can freely place their opinion at every time step. ... More
The fundamental group of period domains over finite fieldsNov 23 2007We determine the fundamental group of period domains over finite fields.