Results for "Christian Burkert"

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Tracking Users across the Web via TLS Session ResumptionOct 16 2018User tracking on the Internet can come in various forms, e.g., via cookies or by fingerprinting web browsers. A technique that got less attention so far is user tracking based on TLS and specifically based on the TLS session resumption mechanism. To the ... More
QUICker connection establishment with out-of-band validation tokensApr 12 2019May 03 2019QUIC is a secure transport protocol that improves the performance of HTTPS. An initial QUIC handshake that enforces a strict validation of the client's source address requires two round-trips. In this work, we extend QUIC's address validation mechanism ... More
The Effect of Gas Loss on the Formation of Bound Stellar ClustersJul 27 2000The effect of gas ejection on the structure and binding energy of newly formed stellar clusters is investigated. The star formation efficiency (SFE), necessary for forming a gravitationally bound stellar cluster, is determined. Two sets of numerical N-body ... More
Simulations of Direct Collisions of Gas Clouds with the Central Black HoleAug 07 2009Oct 27 2010We perform numerical simulations of clouds in the Galactic Centre (GC) engulfing the nuclear super-massive black hole and show that this mechanism leads to the formation of gaseous accretion discs with properties that are similar to the expected gaseous ... More
QUICker connection establishment with out-of-band validation tokensApr 12 2019QUIC is a secure transport protocol and aims to improve the performance of HTTPS traffic. It is a design goal of QUIC to reduce the delay overhead of its connection establishment. However, an initial handshake enforcing strict validation of the client's ... More
Enhanced Performance and Privacy for TLS over TCP Fast OpenMay 09 2019Small TCP flows make up the majority of web flows. For them, the TCP three-way handshake represents a significant delay overhead. The TCP Fast Open (TFO) protocol provides zero round-trip time (0-RTT) handshakes for subsequent TCP connections to the same ... More
Physics of the Galactic Center Cloud G2, on its Way towards the Super-Massive Black HoleJan 06 2012The origin, structure and evolution of the small gas cloud, G2, is investigated, that is on an orbit almost straight into the Galactic central supermassive black hole (SMBH). G2 is a sensitive probe of the hot accretion zone of Sgr A*, requiring gas temperatures ... More
Do dwarf spheroidal galaxies contain dark matter?Oct 24 1996The amount of dark matter in the four galactic dwarf spheroidals with large mass-to-light ratios is investigated. Sextans has a cut-off radius which is equal to the expected tidal radius, assuming a high mass-to-light ratio. This satellite very likely ... More
The Challenge of Modelling Galactic DisksDec 10 2008Dec 12 2008Detailed models of galactic disk formation and evolution require knowledge about the initial conditions under which disk galaxies form, the boundary conditions that affect their secular evolution and the micro-physical processes that drive the multi-phase ... More
Star Formation in Turbulent Molecular CloudsMay 17 2001Recent progress in the understanding of star formation is summarized. A consistent picture is emerging where molecular clouds form with turbulent velocity fields and clumpy substructure, imprinted already during their formation. The clouds are initially ... More
The structure of dark matter halos. Observation versus theoryMar 10 1997The rotation curves of dark matter dominated dwarf galaxies are analysed. The observations show that dark matter halos represent a one-parameter family with self similar density profiles. The global halo parameters, like total mass and scale length are ... More
Balance among gravitational instability, star formation, and accretion determines the structure and evolution of disk galaxiesMay 13 2013May 15 2013Over the past 10 Gyr, star-forming galaxies have changed dramatically, from clumpy and gas rich, to rather quiescent stellar-dominated disks with specific star formation rates lower by factors of a few tens. We present a general theoretical model for ... More
Self-Interacting Cold Dark Matter HalosDec 08 2000The evolution of halos consisting of weakly self-interacting dark matter particles is summarized. The halos initially contain a central density cusp as predicted by cosmological models. Weak self-interaction leads to the formation of an isothermal, low-density ... More
The structure and evolution of weakly self-interacting cold dark matter halosFeb 22 2000Apr 18 2000The evolution of halos consisting of weakly self-interacting dark matter particles is investigated using a new numerical Monte-Carlo N-body method. The halos initially contain kinematically cold, dense 1/r-power-law cores. For interaction cross sections ... More
Galactic Disk Formation and the Angular Momentum ProblemAug 10 2009Galactic disk formation requires knowledge about the initial conditions under which disk galaxies form, the boundary conditions that affect their secular evolution and the micro-physical processes that drive the multi-phase interstellar medium and regulate ... More
Stellar Feedback Processes: Their Impact on Star Formation and Galactic EvolutionApr 01 2004The conditions that lead to self-regulated star formation, star bursts and the formation of massive stellar clusters are discussed. Massive stars have a strong impact on their environment, especially on the evolution of dwarf galaxies which are the building ... More
The Formation of the Milky Way in the Cosmological ContextMay 17 2001The formation of the Milky Way is discussed within the context of the cold dark matter scenario. Several problems arise which can be solved if the Galaxy experienced an early phase of gas heating and decoupling from the dark matter substructure. This ... More
The geometry and origin of ultra-diffuse ghost galaxiesAug 31 2016Sep 02 2016The geometry and intrinsic ellipticity distribution of ultra diffuse galaxies (UDGs) is determined from the line-of-sight distribution of axial ratios q of a large sample of UDGs, detected by Koda et al. (2015) in the Coma cluster. With high significance ... More
The Structure of Dark Matter Haloes in Dwarf GalaxiesApr 12 1995Recent observations indicate that dark matter haloes have flat central density profiles. Cosmological simulations with non-baryonic dark matter predict however self similar haloes with central density cusps. This contradiction has lead to the conclusion ... More
On the Formation of Elliptical GalaxiesMar 07 1994It is shown that the violent relaxation of dissipationless stellar systems leads to universal de Vaucouleurs profiles only outside 1.5 effective radii $R_e$. Inside $1.5 R_e$ the surface density profiles depend strongly on the initial conditions and are ... More
The Cosmological Angular Momentum Problem of Low-Mass Disk GalaxiesJul 05 2000The rotational properties of the visible and dark components of low-mass disk galaxies (vrot<=100 km/s) are investigated using the Swaters sample. The rotational parameter lambda'=lambda_DM*(j_d/m_d) is determined, where lambda_DM is the dark halo spin ... More
The Structure and Dark Halo Core Properties of Dwarf Spheroidal GalaxiesJan 26 2015Jun 22 2015The structure and dark matter halo core properties of dwarf spheroidal galaxies (dSphs) are investigated. A double-isothermal model of an isothermal stellar system, embedded in an isothermal dark halo core provides an excellent fit to the various observed ... More
The Turbulent Interstellar MediumMay 03 2006An overview is presented of the main properties of the interstellar medium. Evidence is summarized that the interstellar medium is highly turbulent, driven on different length scales by various energetic processes. Large-scale turbulence determines the ... More
Recent results on the nucleon resonance spectrum and structure from the CLAS detectorAug 17 2015The CLAS detector at Jefferson Lab has provided the dominant part of all available worldwide data on exclusive meson electroproduction off protons in the resonance region. New results on the $\gamma_{v}pN^*$ transition amplitudes (electrocouplings) are ... More
Thermal Quantum Fields without Cut-offs in 1+1 Space-time DimensionsMar 26 2004We construct interacting quantum fields in 1+1 dimensional Minkowski space, representing neutral scalar bosons at positive temperature. Our work is based on prior work by Klein and Landau and Hoegh-Krohn
On the relativistic KMS condition for the P(φ)_2 modelSep 29 2006The relativistic KMS condition introduced by Bros and Buchholz provides a link between quantum statistical mechanics and quantum field theory. We show that for the $P(\phi)_2$ model at positive temperature, the two point function for fields satisfies ... More
Friction force: from mechanics to thermodynamicsNov 17 2009Jul 01 2010We study some mechanical problems in which a friction force is acting on the system. Using the fundamental concepts of state, time evolution and energy conservation we explain how to extend Newtonian mechanics to thermodynamics. We arrive at the two laws ... More
Duck Traps: Two-dimensional Critical Manifolds in Planar SystemsAug 30 2018Nov 05 2018In this work we consider two-dimensional critical manifolds in planar fast-slow systems near fold and so-called canard (=`duck') points. These higher-dimension, and lower-codimension, situation is directly motivated by the case of hysteresis operators ... More
Relaxed Logarithmic Barrier Function Based Model Predictive Control of Linear SystemsMar 11 2015In this paper, we investigate the use of relaxed logarithmic barrier functions in the context of linear model predictive control. We present results that allow to guarantee asymptotic stability of the corresponding closed-loop system, and discuss further ... More
A stabilizing iteration scheme for model predictive control based on relaxed barrier functionsMar 15 2016Apr 06 2016We propose and analyze a stabilizing iteration scheme for the algorithmic implementation of model predictive control for linear discrete-time systems. Polytopic input and state constraints are considered and handled by means of so-called relaxed logarithmic ... More
Differential Characters and Geometric ChainsMar 26 2013Apr 09 2013We study Cheeger-Simons differential characters and provide geometric descriptions of the ring structure and of the fiber integration map. The uniqueness of differential cohomology (up to unique natural transformation) is proved by deriving an explicit ... More
Distances and large deviations in the spatial preferential attachment modelSep 26 2018Sep 27 2018We investigate two asymptotic properties of a spatial preferential-attachment model introduced by E. Jacob and P. M\"orters (2013). First, in a regime of strong linear reinforcement, we show that typical distances are at most of doubly-logarithmic order. ... More
On the Vacuum Polarization Density Caused by an External FieldJul 01 2003Feb 11 2004We consider an external potential, $-\lambda \phi$, due to one or more nuclei. Following the Dirac picture such a potential polarizes the vacuum. The polarization density as derived in physics literature, after a well known renormalization procedure, ... More
Quantum field theory meets Hopf algebraNov 14 2006Sep 11 2010This paper provides a primer in quantum field theory (QFT) based on Hopf algebra and describes new Hopf algebraic constructions inspired by QFT concepts. The following QFT concepts are introduced: chronological products, S-matrix, Feynman diagrams, connected ... More
A differential identity for Green functionsFeb 15 2006If P is a differential operator with constant coefficients, an identity is derived to calculate the action of exp(P) on the product of two functions. In many-body theory, P describes the interaction Hamiltonian and the identity yields a hierarchy of Green ... More
Quantum groups and interacting quantum fieldsAug 19 2002If C is a cocommutative coalgebra, a bialgebra structure can be given to the symmetric algebra S(C). The symmetric product is twisted by a Laplace pairing and the twisted product of any number of elements of S(C) is calculated explicitly. This is used ... More
Continuous-Variable Quantum Key Distribution with Entanglement in the MiddleMay 07 2012We analyze the performance of continuous-variable quantum key distribution protocols where the entangled source originates not from one of the trusted parties, Alice or Bob, but from the malicious eavesdropper in the middle. This is in contrast to the ... More
Tight Running Time Lower Bounds for Vertex Deletion ProblemsNov 17 2015May 17 2016For a graph class $\Pi$, the $\Pi$-Vertex Deletion problem has as input an undirected graph $G=(V,E)$ and an integer $k$ and asks whether there is a set of at most $k$ vertices that can be deleted from $G$ such that the resulting graph is a member of ... More
A quantum-information-theoretic complement to a general-relativistic implementation of a beyond-Turing computerMay 21 2014Jun 11 2014There exists a growing literature on the so-called physical Church-Turing thesis in a relativistic spacetime setting. The physical Church-Turing thesis is the conjecture that no computing device that is physically realizable (even in principle) can exceed ... More
Vacuum Polarisation Tensors in Constant Electromagnetic Fields: Part IJan 27 2000Dec 29 2000The string-inspired technique is used for the calculation of vacuum polarisation tensors in constant electromagnetic fields. In the first part of this series, we give a detailed exposition of the method for the case of the QED one-loop N-photon amplitude ... More
Blue Stragglers in Globular Clusters: Observations, Statistics and PhysicsJun 13 2014This chapter explores how we might use the observed {\em statistics} of blue stragglers in globular clusters to shed light on their formation. This means we will touch on topics also discussed elsewhere in this book, such as the discovery and implications ... More
Dualité onde-corpuscule formée par une masselotte oscillante dans un milieu élastique : étude théorique et similitudes quantiquesSep 29 2016We introduce a dual wave-particle macroscopic system, where a bead oscillator oscillates in an elastic media which obeys the Klein-Gordon equation. This theoretical system comes mainly from bouncing drops experiments and also a sliding bead on a vibrating ... More
On the geometry of metric measure spaces with variable curvature boundsJun 10 2015Sep 09 2015Motivated by a classical comparison result of J. C. F. Sturm we introduce a curvature-dimension condition CD(k,N) for general metric measure spaces and variable lower curvature bound k. In the case of non-zero constant lower curvature our approach coincides ... More
On the logarithm of the characteristic polynomial of the Ginibre ensembleJul 30 2015We prove a slightly sharper version of a result of Rider and Vir\'ag who proved that after centering, the logarithm of the absolute value of the characteristic polynomial of the Ginibre ensemble converges in law to the Gaussian Free Field on the unit ... More
Maximum Matching in Turnstile StreamsMay 06 2015We consider the unweighted bipartite maximum matching problem in the one-pass turnstile streaming model where the input stream consists of edge insertions and deletions. In the insertion-only model, a one-pass $2$-approximation streaming algorithm can ... More
Cosmology and gravitational waves in the Nordstrom-Vlasov system, a laboratory for Dark EnergyJan 24 2013We discuss a cosmological solution of the system which was originally introduced by Calogero and is today popularly known as "Nordstrom-Vlasov system". Although the model is un-physical, its cosmological solution results interesting for the same reasons ... More
Effective temperature for black holesJul 26 2011Jul 28 2011The physical interpretation of black hole's quasinormal modes is fundamental for realizing unitary quantum gravity theory as black holes are considered theoretical laboratories for testing models of such an ultimate theory and their quasinormal modes ... More
A precise response function for the magnetic component of Gravitational Waves in Scalar-Tensor GravityFeb 03 2011Feb 04 2011The important issue of the magnetic component of gravitational waves (GWs) has been considered in various papers in the literature. From such analyses, it resulted that such a magnetic component becomes particularly important in the high frequency portion ... More
A longitudinal component in massive gravitational waves arising from a bimetric theory of gravityNov 06 2008After a brief review of the work of de Paula, Miranda and Marinho on massive gravitational waves arising from a bimetric theory of gravity, in this paper it is shown that the presence of the mass generates a longi- tudinal component in a particular polarization ... More
Analysis of the transverse effect of Einstein's gravitational wavesJul 13 2007The investigation of the transverse effect of gravitational waves (GWs) could constitute a further tool to discriminate among several relativistic theories of gravity on the ground. After a review of the TT gauge, the transverse effect of GWs arising ... More
Interpretation of Mössbauer experiment in a rotating system: a new proof for general relativityFeb 14 2015A historical experiment by K\"undig on the transverse Doppler shift in a rotating system measured with the M\"ossbauer effect has been recently first re-analyzed and then replied [1,2]. The results have shown that a correct re-processing of K\"undig's ... More
Black hole quantum spectrumOct 26 2012Nov 19 2013Introducing a black hole (BH) effective temperature, which takes into account both the non-strictly thermal character of Hawking radiation and the countable behavior of emissions of subsequent Hawking quanta, we recently re-analysed BH quasi-normal modes ... More
Massive relic gravitational waves from f(R) theories of gravity: production and potential detectionJul 23 2010The production of a stochastic background of relic gravitational waves is well known in various works in the literature, where, by using the so called adiabatically-amplified zero-point fluctuations process, it has been shown how the standard inflationary ... More
A review of the stochastic background of gravitational waves in f(R) gravity with WMAP constrainsJan 09 2009Jan 15 2009This paper is a review of previous works on the stochastic background of gravitational waves (SBGWs) which has been discussed in various peer-reviewed journals and international conferences. The SBGWs is analyzed with the aid of the Wilkinson Microwave ... More
A non-geodesic motion in the R^-1 theory of gravity tuned with observationsJan 01 2008Jan 11 2008In the general picture of high order theories of gravity, recently, the R^-1 theory has been analyzed in two different frameworks. In this letter a third context is added, considering an explicit coupling between the R^-1 function of the Ricci scalar ... More
The production of matter from curvature in a particular linearized high order theory of gravity and the longitudinal response function of interferometersMar 26 2007The strict analogy between scalar-tensor theories of gravity and high order gravity is well known in literature. In this paper it is shown that, from a particular high order gravity theory known in literature, it is possible to produce, in the linearized ... More
Scattering theory for Klein-Gordon equations with non-positive energyJan 11 2011Sep 09 2011We study the scattering theory for charged Klein-Gordon equations: \[\{{array}{l} (\p_{t}- \i v(x))^{2}\phi(t,x) \epsilon^{2}(x, D_{x})\phi(t,x)=0,[2mm] \phi(0, x)= f_{0}, [2mm] \i^{-1} \p_{t}\phi(0, x)= f_{1}, {array}. \] where: \[\epsilon^{2}(x, D_{x})= ... More
Spectral and scattering theory of charged $P(\varphi)_2$ modelsJun 30 2009We consider in this paper space-cutoff charged $P(\varphi)_{2}$ models arising from the quantization of the non-linear charged Klein-Gordon equation: \[ (\p_{t}+\i V(x))^{2}\phi(t, x)+ (-\Delta_{x}+ m^{2})\phi(t,x)+ g(x)\p_{\overline{z}}P(\phi(t,x), \overline{\phi}(t,x))=0, ... More
k-Means Clustering Is Matrix FactorizationDec 23 2015We show that the objective function of conventional k-means clustering can be expressed as the Frobenius norm of the difference of a data matrix and a low rank approximation of that data matrix. In short, we show that k-means clustering is a matrix factorization ... More
Galilean IsometriesMar 09 2009We introduce three nested Lie algebras of infinitesimal `isometries' of a Galilei space-time structure which play the r\^ole of the algebra of Killing vector fields of a relativistic Lorentz space-time. Non trivial extensions of these Lie algebras arise ... More
The Mössbauer rotor experiment and the general theory of relativityFeb 12 2016Feb 16 2016This paper is a rebuttal to Eur. Phys. Jour. Plus 130, 191 (2015), which claims that the results in arXiv:1502.04911 (Ann. Phys. 355, 360 (2015)) are incorrect. For this reason, some of the results in arXiv:1502.04911 have been reviewed and clarified. ... More
A quantitative theory for the continuity equationFeb 09 2016Mar 24 2016In this work, we provide stability estimates for the continuity equation with Sobolev vector fields. The results are inferred from contraction estimates for certain logarithmic Kantorovich--Rubinstein distances. As a by-product, we obtain a new proof ... More
Magnetically driven outflows from Jovian circum-planetaryaccretion disksOct 01 2003We discuss the possibility to launch outflows from the close vicinity of a protoplanetary core considering a scenario where the protoplanet surrounded by a circum-planetary accretion disk is located in a circum-stellar disk. For the circum-planetary disk ... More
Moments and Classification for Conjugation-Invariant Rotations and Fake Uniformity in the Stochastic Radon TransformMar 06 2012We consider a generalisation of the stochastic Radon transform, introduced for an inverse problem in tomography by Panaretos. Specifically, we allow the distribution of the three-dimensional rotation in the statistical model of that work to be different ... More
Varieties of *-regular ringsApr 09 2019Apr 11 2019Given a subdirectly irreducible *-regular ring R, we show that R is a homomorphic image of a regular *-subring of an ultraproduct of the (simple) eRe, e in the minimal ideal of R; moreover, R (with unit) is directly finite if all eRe are unit-regular. ... More
Quantum correlations are weaved by the spinors of the Euclidean primitivesMay 30 2018The exceptional Lie group E8 plays a prominent role in both mathematics and theoretical physics. It is the largest symmetry group associated with the most general possible normed division algebra, namely, that of the non-associative real octonions, which ... More
On a Surprising Oversight by John S. Bell in the Proof of his Famous TheoremApr 03 2017Nov 11 2018Bell inequalities are usually derived by assuming locality and realism, and therefore experimental violations of Bell inequalities are usually taken to imply violations of either locality or realism, or both. But, after reviewing an oversight by Bell, ... More
Refutation of Richard Gill's Argument Against my Disproof of Bell's TheoremMar 12 2012Mar 06 2017I identify a number of errors in Richard Gill's purported refutation (arXiv:1203.1504) of my disproof of Bell's theorem. In particular, I point out that his central argument is based, not only on a rather trivial misreading of my counterexample to Bell's ... More
Restoring Local Causality and Objective Reality to the Entangled PhotonsJun 03 2011May 02 2012Unlike our basic theories of space and time, quantum mechanics is not a locally causal theory. Moreover, it is widely believed that any hopes of restoring local causality within a realistic theory have been undermined by Bell's theorem and its supporting ... More
Disproofs of Bell, GHZ, and Hardy Type Theorems and the Illusion of EntanglementApr 28 2009Oct 24 2010An elementary topological error in Bell's representation of the EPR elements of reality is identified. Once recognized, it leads to a topologically correct local-realistic framework that provides exact, deterministic, and local underpinning of at least ... More
Disproof of Bell's Theorem: Reply to CriticsMar 26 2007Jan 03 2008This is a collection of my responses to the criticisms of my argument against the impossibility proof of John Bell, which aims to undermine any conceivable local realistic completion of quantum mechanics. I plan to periodically update this preprint instead ... More
Testing Gravity-Driven Collapse of the Wavefunction via Cosmogenic NeutrinosMar 01 2005Oct 12 2005It is pointed out that the Diosi-Penrose ansatz for gravity-induced quantum state reduction can be tested by observing oscillations in the flavor ratios of neutrinos originated at cosmological distances. Since such a test would be almost free of environmental ... More
Why the Quantum Must Yield to GravityOct 26 1998Mar 08 1999After providing an extensive overview of the conceptual elements -- such as Einstein's `hole argument' -- that underpin Penrose's proposal for gravitationally induced quantum state reduction, the proposal is constructively criticised. Penrose has suggested ... More
Disproof of Bell's TheoremMar 09 2011Oct 15 2015We illustrate an explicit counterexample to Bell's theorem by constructing a pair of spin variables in S^3 that exactly reproduces the EPR-Bohm correlation in a manifestly local-realistic manner.
Disproof of Bell's Theorem by Clifford Algebra Valued Local VariablesMar 20 2007Apr 22 2010It is shown that Bell's theorem fails for the Clifford algebra valued local realistic variables. This is made evident by exactly reproducing quantum mechanical expectation value for the EPR-Bohm type spin correlations observable by means of a local, deterministic, ... More
Rectangular Statistical Cartograms in R: The recmap PackageJun 01 2016Mar 24 2017Cartogram drawing is a technique for showing geography-related statistical information, such as demographic and epidemiological data. The idea is to distort a map by resizing its regions according to a statistical parameter by keeping the map recognizable. ... More
Towards an Algebraic Theory of Analogical Reasoning in Logic ProgrammingSep 26 2018Analogy-making is an essential part of human intelligence and creativity. This paper proposes an algebraic model of analogical reasoning in logic programming based on the syntactic composition and decomposition of programs. The main idea is to define ... More
Golomb's conjecture on prime gapsApr 23 2016Question 10208b (1992) of the American Mathematical Monthly asked: does there exist an increasing sequence $\{a_k\}$ of positive integers and a constant $B > 0$ having the property that $\{ a_k + n\}$ contains no more than $B$ primes for every integer ... More
Recursive Numerical Evaluation of the Cumulative Bivariate Normal DistributionApr 21 2010We propose an algorithm for evaluation of the cumulative bivariate normal distribution, building upon Marsaglia's ideas for evaluation of the cumulative univariate normal distribution. The algorithm is mathematically transparent, delivers competitive ... More
Constructive homotopy theory of marked semisimplicial setsSep 28 2018We develop the homotopy theory of semisimplicial sets constructively and without reference to point-set topology to obtain a constructive model for $\omega$-groupoids. Most of the development is folklore, but for a few results the author is unaware of ... More
Immersions of surfaces in almost complex 4-manifoldsAug 31 2000In this note, we investigate the relation between double points and complex points of immersed surfaces in almost-complex 4-manifolds and show how estimates for the minimal genus of embedded surfaces lead to inequalities between the number of double points ... More
Modularity experiments on $S_4$-symmetric double octicsOct 08 2018We will invest quite some computer power to find double octic threefolds that are connected to weight four modular forms.
Exponentials form a basis of discrete holomorphic functionsOct 08 2002We show that discrete exponentials form a basis of discrete holomorphic functions. On a convex, the discrete polynomials form a basis as well.
Normal crossing singularities and Hodge theory over Artin ringsApr 30 2012We develop a Hodge theory for relative simple normal crossing varieties over an Artinian base scheme. We introduce the notion of a mixed Hodge structure over an Artin ring, which axiomatizes the structure that is found on the cohomology of such a variety. ... More
The Saxl Conjecture and the Dominance OrderOct 24 2014May 05 2015In 2012 Jan Saxl conjectured that all irreducible representations of the symmetric group occur in the decomposition of the tensor square of the irreducible representation corresponding to the staircase partition. We make progress on this conjecture by ... More
Geometrically formal 4-manifolds with nonnegative sectional curvatureDec 06 2012Jan 31 2015A Riemannian manifold is called geometrically formal if the wedge product of any two harmonic forms is again harmonic. We classify geometrically formal compact 4-manifolds with nonnegative sectional curvature. If the sectional curvature is strictly positive, ... More
Uniruled Surfaces of General TypeAug 24 2006Nov 06 2006We give a systematic construction of uniruled surfaces in positive characteristic. Using this construction, we find surfaces of general type with non-trivial vector fields, surfaces with arbitrarily non-reduced Picard schemes as well as surfaces with ... More
Non-classical Godeaux SurfacesApr 21 2008Aug 25 2008A non-classical Godeaux surface is a minimal surface of general type with $\chi=K^2=1$ but with $h^{01}\neq0$. We prove that such surfaces fulfill $h^{01}=1$ and they can exist only over fields of positive characteristic at most 5. Like non-classical ... More
Algebraic Surfaces of General Type with Small c_1^2 in Positive CharacteristicFeb 19 2007Oct 26 2007We establish Noether's inequality for surfaces of general type in positive characteristic.Then we extend Enriques' and Horikawa's classification of surfaces on the Noether line, the so-called Horikawa surfaces. We construct examples for all possible numerical ... More
A counterexample for a problem on quasi Baer modulesMay 08 2016Mar 13 2017In this note we answer two questions on quasi-Baer modules raised by Lee and Rizvi in J.Algebra (2016).
The Canonical Map and Horikawa Surfaces in Positive CharacteristicApr 10 2010Dec 20 2011We extend fundamental inequalities related to the canonical map of surfaces of general type to positive characteristic. Next, we classify surfaces on the Noether lines, i.e., even and odd Horikawa surfaces, in positive characteristic. We describe their ... More
On a new collection of words in the Catalan familyApr 07 2014May 23 2014In this note, we provide a bijection between a new collection of words on nonnegative integers of length n and Dyck paths of length 2n-2, thus proving that this collection belongs to the Catalan family. The surprising key step in this bijection is the ... More
Modules Whose Small Submodules Have Krull DimensionJul 21 1998The main aim of this paper is to show that an AB5*-module whose small submodules have Krull dimension has a radical having Krull dimension. The proof uses the notion of dual Goldie dimension.
On the base locus of the linear system of generalized theta functionsJul 23 2007Apr 14 2008Let $\cM_r$ denote the moduli space of semi-stable rank-$r$ vector bundles with trivial determinant over a smooth projective curve $C$ of genus $g$. In this paper we study the base locus $\cB_r \subset \cM_r$ of the linear system of the determinant line ... More
Fake uniformity in a shape inversion formulaMar 06 2012Dec 29 2017We revisit a shape inversion formula derived by Panaretos in the context of a particle density estimation problem with unknown rotation of the particle. A distribution is presented which imitates, or 'fakes', the uniformity or Haar distribution that is ... More
Simple groups of birational transformations in dimension twoFeb 26 2018We classify simple groups that act by birational transformations on compact complex K\"ahler surfaces. Moreover, we show that every finitely generated simple group that acts non-trivially by birational transformations on a projective surface over an arbitrary ... More
emgr - The Empirical Gramian FrameworkNov 02 2016May 28 2018System Gramian matrices are a well-known encoding for properties of input-output systems such as controllability, observability or minimality. These so-called system Gramians were developed in linear system theory for applications such as model order ... More
Reflexivity of Newton-Okounkov bodies of partial flag varietiesFeb 19 2019Assume that the valuation semigroup $\Gamma(\lambda)$ of an arbitrary partial flag variety corresponding to the line bundle $\mathcal L_\lambda$ constructed via a full-rank valuation is finitely generated and saturated. We use Ehrhart theory to prove ... More
There is a $3\times3$ Magic Square of Squares on the Moon - A Lot of Them, ActuallyNov 09 2018Nov 19 2018Magic squares have been well explored here on Earth [1], but there appears to have been little-to-no examination of $\textit{lunar}$ magic squares. Some kinds of magic squares exist on the moon (i.e. under lunar arithmetic) but not on Earth (i.e. under ... More
Theory status of hadronic top-quark pair productionOct 11 2018The status of theoretical predictions for top-quark pair production at hadron colliders is reviewed, focusing on the total cross section, differential distributions, and the description of top-quark production and decay including off-shell effects.