Results for "Stephan Falke"

total 3077took 0.12s
Study of the Born-Oppenheimer Approximation for Mass-Scaling of Cold Collision PropertiesJun 15 2007Asymptotic levels of the A $^1\Sigma_u^+$ state of the two isotopomers $^{39}{\rm K}_2$ and $^{39}{\rm K}^{41}{\rm K}$ up to the dissociation limit are investigated with a Doppler-free high resolution laser-spectroscopic experiment in a molecular beam. ... More
Long range transport of ultra cold atoms in a far-detuned 1D optical latticeApr 16 2012We present a novel method to transport ultra cold atoms in a focused optical lattice over macroscopic distances of many Rayleigh ranges. With this method ultra cold atoms were transported over 5 cm in 250 ms without significant atom loss or heating. By ... More
Absolute Frequency Atlas from 915 nm to 985 nm based on Laser Absorption Spectroscopy of IodineJan 04 2018This article reports on laser absorption spectroscopy of iodine gas between 915 nm and 985 nm. This wavelength range is scanned utilizing a narrow linewidth and mode-hop-free tunable diode-laser whose frequency is actively controlled using a calibrated ... More
Delivering pulsed and phase stable light to atoms of an optical clockAug 18 2011Feb 10 2012In optical clocks, transitions of ions or neutral atoms are interrogated using pulsed ultra-narrow laser fields. Systematic phase chirps of the laser or changes of the optical path length during the measurement cause a shift of the frequency seen by the ... More
High accuracy correction of blackbody radiation shift in an optical lattice clockAug 14 2012Oct 29 2012We have determined the frequency shift that blackbody radiation is inducing on the $5s^2$ $^1$S$_0$ -- $5s5p$ $^3$P$_0$ clock transition in strontium. Previously its uncertainty limited the uncertainty of strontium lattice clocks to $1\times10^{-16}$. ... More
Lattice-induced photon scattering in an optical lattice clockFeb 08 2018Jul 19 2018We investigate scattering of lattice laser radiation in a strontium optical lattice clock and its implications for operating clocks at interrogation times up to several tens of seconds. Rayleigh scattering does not cause significant decoherence of the ... More
Lattice-induced photon scattering in an optical lattice clockFeb 08 2018We investigate scattering of lattice laser radiation in a strontium optical lattice clock and its implications for operating clocks at interrogation times up to several ten seconds. Rayleigh scattering does not cause significant decoherence of the atomic ... More
A compact and efficient strontium oven for laser-cooling experimentsSep 25 2012Here we describe a compact and efficient strontium oven well suited for laser-cooling experiments. Novel design solutions allowed us to produce a collimated strontium atomic beam with a flux of 1.0\times10^13 s^-1 cm^-2 at the oven temperature of 450 ... More
Tackling the blackbody shift in a strontium optical lattice clockSep 10 2010A major obstacle for optical clocks is the frequency shift due to black body radiation. We discuss how one can tackle this problem in an optical lattice clock; in our case 87-Sr: firstly, by a measurement of the dc Stark shift of the clock transition ... More
8E-17 fractional laser frequency instability with a long room-temperature cavityFeb 09 2015Mar 31 2015We present a laser system based on a 48 cm long optical glass resonator. The large size requires a sophisticated thermal control and optimized mounting design. A self balancing mounting was essential to reliably reach sensitivities to acceleration of ... More
Potassium ground state scattering parameters and Born-Oppenheimer potentials from molecular spectroscopyApr 18 2008We present precision measurements with MHz uncertainty of the energy gap between asymptotic and well bound levels in the electronic ground state X $^1\Sigma_{\mathrm{g}}^+$ of the $^{39}$K$_2$ molecule. The molecules are prepared in a highly collimated ... More
Ultra-stable laser with average fractional frequency drift rate below $5\times10^{-19}/\mathrm{s}$May 07 2014Cryogenic single-crystal optical cavities have the potential to provide highest dimensional stability. We have investigated the long-term performance of an ultra-stable laser system which is stabilized to a single-crystal silicon cavity operated at 124 ... More
A strontium lattice clock with $3 \times 10^{-17}$ inaccuracy and its frequencyDec 12 2013Aug 15 2014We have measured the absolute frequency of the optical lattice clock based on $^{87}$Sr at PTB with an uncertainty of $3.9\times 10^{-16}$ using two caesium fountain clocks. This is close to the accuracy of today's best realizations of the SI second. ... More
Memory equations as reduced Markov processesApr 06 2018A large class of linear memory differential equations in one dimension, where the evolution depends on the whole history, can be equivalently described as a projection of a Markov process living in a higher dimensional space. Starting with such a memory ... More
Bringing Structure into Summaries: Crowdsourcing a Benchmark Corpus of Concept MapsApr 14 2017Jul 21 2017Concept maps can be used to concisely represent important information and bring structure into large document collections. Therefore, we study a variant of multi-document summarization that produces summaries in the form of concept maps. However, suitable ... More
Satisfiability thresholds beyond k-XORSATDec 09 2011We consider random systems of equations x_1 + ... + x_k = a; 0 <= a <= 2 which are interpreted as equations modulo 3: We show for k >= 15 that the satisfiability threshold of such systems occurs where the 2-core has density 1: We show a similar result ... More
Spin 3/2 dimer modelJan 30 2009Apr 16 2009We present a parent Hamiltonian for weakly dimerized valence bond solid states for arbitrary half-integral S. While the model reduces for S=1/2 to the Majumdar-Ghosh Hamiltonian we discuss this model and its properties for S=3/2. Its degenerate ground ... More
Convergence issues in ChPT: a lattice perspectiveMay 24 2013This review addresses the practical convergence of the ChPT series in the p-regime. In the SU(2) framework there is a number of new results, and improved estimates of \bar\ell_3 and \bar\ell_4 are available. In the SU(3) framework few new lattice computations ... More
Logarithmic link smearing for full QCDSep 26 2007Mar 16 2009A Lie-algebra based recipe for smoothing gauge links in lattice field theory is presented, building on the matrix logarithm. With or without hypercubic nesting, this LOG/HYL smearing yields fat links which are differentiable w.r.t. the original ones. ... More
The phase transition in the multiflavour Schwinger modelSep 12 2000A summary is given of a quantization of the multiflavour Schwinger model on a finite-temperature cylinder with chirality-breaking boundary conditions at its spatial ends, and it is shown that the analytic expression for the chiral condensate implies that ... More
QCD in a finite box: Numerical test studies in the three Leutwyler-Smilga regimesAug 30 2000Nov 07 2000The Leutwyler-Smilga prediction regarding the (ir)relevance of the global topological charge for QCD in a finite box is subject to a test. To this end the lattice version of a suitably chosen analogue (massive 2-flavour Schwinger model) is analyzed in ... More
Inference on 3D Procrustes means: tree bole growth, rank-deficient diffusion tensors and perturbation modelsFeb 03 2010Feb 02 2011The Central Limit Theorem (CLT) for extrinsic and intrinsic means on manifolds is extended to a generalization of Fr\'echet means. Examples are the Procrustes mean for 3D Kendall shapes as well as a mean introduced by Ziezold. This allows for one-sample ... More
Generalization of Conway's "Game of Life" to a continuous domain - SmoothLifeNov 07 2011Dec 07 2011We present what we argue is the generic generalization of Conway's "Game of Life" to a continuous domain. We describe the theoretical model and the explicit implementation on a computer.
Boundary slopes and the logarithmic limit setJun 03 2003The A-polynomial of a manifold whose boundary consists of a single torus is generalised to an eigenvalue variety of a manifold whose boundary consists of a finite number of tori, and the set of strongly detected boundary curves is determined by Bergman's ... More
Quantum interferences in quasicrystalsJul 30 1999Jul 31 1999Contributions of quantum interference effects occuring in quasicrystals are emphasized. First conversely to metallic systems, quasiperiodic ones are shown to enclose original alterations of their conductive properties while downgrading long range order. ... More
Percolation in Finite Matching LatticesMar 23 2016We derive an exact, simple relation between the average number of clusters and the wrapping probabilities for two dimensional percolation. The relation holds for periodic lattices of any size. It can be used to compute a very fast converging estimator ... More
Search for Higgs and New Phenomena at CollidersJan 20 2006The present status of searches for the Higgs boson(s) and new phenomena is reviewed. The focus is on analyses and results from the current runs of the HERA and Tevatron experiments. The LEP experiments have released their final combined MSSM Higgs results ... More
Lattice-Fluid Models derived from Density Functional TheoryMar 08 2015In the current article, we rederive the lattice-fluid excess models UNIQUAC, UNIFAC, and COSMO-RS from a continuum functional. The calculation explains the missing dependence on the particle geometry and how to include the Coulomb interaction, problems ... More
The Kraft sum as a monotone function on the refinement-ordered set of uniquely decipherable codesMay 17 2013Jun 27 2013The set of all uniquely decipherable (UD) codes is partially ordered by refinement, meaning that all strings in the cruder code can be represented as concatenations of strings taken from the finer code. The Kraft sum is a monotone (increasing) function ... More
Damping of Bloch oscillations: Variational solutions of the Boltzmann equation beyond linear responseSep 01 2014Nov 20 2014Variational solutions of the Boltzmann equation usually rely on the concept of linear response. We extend the variational approach for tight-binding models at high entropies to a regime far beyond linear response. We analyze both weakly interacting fermions ... More
Density Functional Theory for Hard Particles in N DimensionsMar 09 2014Recently it has been shown that the heuristic Rosenfeld functional derives from the virial expansion for particles which overlap in one center. Here, we generalize this approach to any number of intersections. Starting from the virial expansion in Ree-Hoover ... More
An obstruction to the smoothability of singular nonpositively curved metrics on 4-manifolds by patterns of incompressible toriDec 08 2013Aug 11 2015We give new examples of closed smooth 4-manifolds which support singular metrics of nonpositive curvature, but no smooth ones, thereby answering affirmatively a question of Gromov. The obstruction comes from patterns of incompressible 2-tori sufficiently ... More
Labeled trees, maps, and an algebraic identityJun 16 2011Jun 23 2011We give a short and direct proof of a remarkable identity that arises in the enumeration of labeled trees with respect to their indegree sequence, where all edges are oriented from the vertex with lower label towards the vertex with higher label. This ... More
A Short Counterexample to the Inverse Generator Problem on non-Hilbertian Reflexive $L^p$-spacesApr 08 2016We show that the bilateral shift group on $L^p(\mathbb{R})$ for $p \in (1, \infty) \setminus \{2\}$ provides a counterexample to the inverse generator problem.
Optimization of the Brillouin operator on the KNL architectureSep 06 2017Jul 09 2018Experiences with optimizing the matrix-times-vector application of the Brillouin operator on the Intel KNL processor are reported. Without adjustments to the memory layout, performance figures of 360 Gflop/s in single and 270 Gflop/s in double precision ... More
Foliations and the cohomology of moduli spaces of bounded global $G$-shtukasOct 19 2016For arbitrary reductive groups $G$ defined over a finite field, we decompose Newton strata in the special fiber of moduli spaces of global $G$-shtukas into a product of Rapoport-Zink spaces and Igusa varieties. This allows us to compare the $\ell$-adic ... More
Three Dirac operators on two architectures with one piece of code and no hassleAug 16 2018Nov 20 2018A simple minded approach to implement three discretizations of the Dirac operator (staggered, Wilson, Brillouin) on two architectures (KNL and core i7) is presented. The idea is to use a high-level compiler along with OpenMP parallelization and SIMD pragmas, ... More
Entropy Analysis of Financial Time SeriesJul 25 2018This thesis applies entropy as a model independent measure to address three research questions concerning financial time series. In the first study we apply transfer entropy to drawdowns and drawups in foreign exchange rates, to study their correlation ... More
Application of Methods for Syntax Analysis of Context-Free Languages to Query Evaluation of Logic ProgramsMay 15 2014My research goal is to employ a parser generation algorithm based on the Earley parsing algorithm to the evaluation and compilation of queries to logic programs, especially to deductive databases. By means of partial deduction, from a query to a logic ... More
Generalized Dicke StatesJan 09 2012Sep 06 2016Quantum master equations are an important tool in quantum optics and quantum information theory. For systems comprising a small to medium number of atoms (or qubits), the non-truncated equations are usually solved numerically. In this paper, we present ... More
A Short Proof of the Reducibility of Hard-Particle Cluster IntegralsMay 18 2011The current article considers Mayer cluster integrals of n-dimensional hard particles in the n>1 dimensional flat Euclidean space. Extending results from Wertheim and Rosenfeld, we proof that the graphs are completely reducible into 1- and 2-point measures, ... More
On a topological fractional Helly theoremJun 20 2005We prove a new fractional Helly theorem for families of sets obeying topological conditions. More precisely, we show that the nerve of a finite family of open sets (and of subcomplexes of cell complexes) in R^d is k-Leray where k depends on the dimension ... More
Note on antichain cutsets in discrete semimodular latticesFeb 26 2011The characterization of level sets of finite Boolean lattices as antichain cutsets, due to Rival and Zaguia, is seen to hold in all discrete semimodular lattices.
A Two Stage CVT / Eikonal Convection Mesh Deformation Approach for Large Nodal DeformationsNov 27 2014A two step mesh deformation approach for large nodal deformations, typically arising from non-parametric shape optimization, fluid-structure interaction or computer graphics, is considered. Two major difficulties, collapsed cells and an undesirable parameterization, ... More
On the large sieve with sparse sets of moduliDec 12 2005Extending a method of D. Wolke, we establish a general result on the large sieve with sparse sets S of moduli which are in a sense well-distributed in arithmetic progressions. We then use this result together with Fourier techniques to obtain large sieve ... More
On the large sieve with square moduliAug 22 2005We prove an estimate for the large sieve with square moduli which improves a recent result of L. Zhao. Our method uses an idea of D. Wolke and some results from Fourier analysis.
Standard bases with respect to the Newton filtrationApr 15 1999The aim of this article is to introduce standard bases of ideals in polynomial rings with respect to a class of orderings which are not necessarily semigroup orderings. Our approach generalises the concept of standard bases with respect to semigroup orderings ... More
Spherical varieties over large fieldsMay 04 2018Oct 02 2018Let k_0 be a field of characteristic 0, k its algebraic closure, G a connected reductive group defined over k. Let H\subset G be a spherical subgroup. We assume that k_0 is a large field, for example, k_0 is either the field R of real numbers or a p-adic ... More
Continuity of the Maximum-Entropy InferenceFeb 14 2012Apr 21 2014We study the inverse problem of inferring the state of a finite-level quantum system from expected values of a fixed set of observables, by maximizing a continuous ranking function. We have proved earlier that the maximum-entropy inference can be a discontinuous ... More
Information topologies on non-commutative state spacesMar 29 2010Jan 18 2013We define an information topology (I-topology) and a reverse information topology (rI-topology) on the state space of a C*-subalgebra of Mat(n,C). These topologies arise from sequential convergence with respect to the relative entropy. We prove that open ... More
Regularity of Semigroups via the Asymptotic Behaviour at ZeroMar 25 2012Sep 05 2013An interesting result by T. Kato and A. Pazy says that a contractive semigroup (T(t)) on a uniformly convex space X is holomorphic iff limsup_{t \downarrow 0} ||T(t)-Id|| < 2. We study extensions of this result which are valid on arbitrary Banach spaces ... More
Diophantine approximation on lines in \mathbb{C}^2 with Gaussian prime constraints - enhanced versionJun 20 2017We study the problem of Diophantine approximation on lines in $\mathbb{C}^2$ with numerators and denominators restricted to Gaussian primes. To this end, we develop analogs of well-known results on small fractional parts of $p\gamma$, $p$ running over ... 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.
Extended Laplace Principle for Empirical Measures of a Markov ChainSep 07 2017We consider discrete time Markov chains with Polish state space. The large deviations principle for empirical measures of a Markov chain can equivalently be stated in Laplace principle form, which builds on the convex dual pair of relative entropy (or ... More
Calculating the correlation coefficients of graph-theoretical indicesAug 30 2006Using a generating function approach, the correlation coefficients of four different graph-theoretical indices, namely the number of independent vertex subsets, the number of matchings, the number of subtrees and the Wiener index, are asymptotically determined ... More
Phase Transition in the Number Partitioning ProblemJul 06 1998Sep 21 1998Number partitioning is an NP-complete problem of combinatorial optimization. A statistical mechanics analysis reveals the existence of a phase transition that separates the easy from the hard to solve instances and that reflects the pseudo-polynomiality ... More
Status of the B^0_{(s)}-\bar B^0_{(s)}} mixing from QCD spectral sum RulesMar 18 2002In this talk, I present new results [1] obtained from QCD spectral sum rules (QSSR), on the bag constant parameters entering in the analysis of the B^0_{(s)}-\bar B^0_{(s)} mass-differences. Taking the average of the results from the Laplace and moment ... More
Light and heavy quark masses, Flavour breaking of chiral condensates, Meson weak leptonic decay constants in QCDFeb 21 2002We review the present status for the determinations of the light and heavy quark masses, the light quark chiral condensate and the decay constants of light and heavy-light (pseudo)scalar mesons from QCD spectral sum rules (QSSR). Bounds on the light quark ... More
A new perspective on the Holstein polaron problemJun 12 1996The single-polaron band structure of the Holstein model in one and two dimensions is studied using a new form of resummed strong-coupling perturbation theory. Well converged results are obtained for phonon frequencies of the order of the hopping integral ... More
Validity of ChPT -- is M_π=135 MeV small enough ?Dec 19 2014I discuss the practical convergence of the SU(2) ChPT series in the meson sector, based on 2+1 flavor lattice data by the Wuppertal-Budapest and Budapest-Marseille-Wuppertal collaborations. These studies employ staggered and clover-improved Wilson fermions, ... More
Theoretical issues with staggered fermion simulationsSep 11 2005The legality of the "rooting trick" in dynamical staggered fermion simulations is discussed, i.e. whether the theory with the Boltzmann weight $\det^{1/4}(D_\mathrm{st})$ yields the right continuum limit. Since the problem is unsolved, pieces of evidence ... More
Prospects of `Topologically Unquenched QCD' from a study of the analogous importance sampling method in the massive Schwinger modelSep 08 1999I give a quick summary of my proposal for simulating an improvement on quenched QCD with dynamical fermions which interact with the gluon configuration only via the topological index of the latter. It amounts to include only the topological part of the ... More
Topology and pion correlators -- a study in the N_f=2 Schwinger modelOct 22 2001I readdress the issue whether the topological charge of the gauge background has an influence on a hadronic observable. To this end pion correlators in the Schwinger model with 2 dynamical flavours are determined on subensembles with a fixed topological ... More
Proposal for Topologically Unquenched QCDJan 06 1998Jan 25 1999A proposal is presented for simulating an improvement on quenched QCD with dynamical fermions which interact with the gluon configuration only via the topological index of the latter. Strengths and shortcomings of the method are discussed and it is argued ... More
On the meaning of mean shapeFeb 03 2010May 12 2011Various concepts of mean shape previously unrelated in the literature are brought into relation. In particular for non-manifolds such as Kendall's 3D shape space, this paper answers the question, for which means one may apply a two-sample test. The answer ... More
How Perfect Offline Wallets Can Still Leak Bitcoin Private KeysJan 02 2015ECDSA has become a popular choice as lightweight alternative to RSA and classic DL based signature algorithms in recent years. As standardized, the signature produced by ECDSA for a pair of a message and a key is not deterministic. This work shows how ... More
Mini-review on QCD spectral sum rulesSep 29 2014Oct 03 2014Taking the example of the most popular and well-established Borel / Laplace / Exponential sum rule (LSR), I shortly review some of its recent applications in hadron physics namely the estimates of non-perturbative condensates, the determination of the ... More
Improved f_{D*_(s)}, f_{B*_(s)} and f_{B_c} from QCD Laplace sum rulesApr 26 2014Jun 01 2015Anticipating future precise measurements of the D- and B-like (semi-)leptonic and hadronic decays for alternative determinations of the CKM mixing angles, we pursue our program on the D- and B-like mesons by improving the estimates of f_{D*_(s)} and f_{B*_(s)} ... More
Stable Roommates Problem with Random PreferencesJan 21 2014Jan 21 2015The stable roommates problem with $n$ agents has worst case complexity $O(n^2)$ in time and space. Random instances can be solved faster and with less memory, however. We introduce an algorithm that has average time and space complexity $O(n^\frac{3}{2})$ ... More
Improved light quark masses from pseudoscalar sum rulesJan 15 2014Aug 27 2014Using ratios of the inverse Laplace transform sum rules within stability criteria for the subtraction point \mu in addition to the ones of the usual tau spectral sum rule variable and continuum threshold t_c, we extract the \pi(1300) and K(1460) decay ... More
Huffman coding as an algorithm to construct chains in partition latticesJun 24 2013The Huffman coding algorithm is interpreted in the lattice of partitions of the source alphabet. Maximal chains in the partition lattice correspond to linear extensions of tree orders, and those among the chains that exhibit a simple greedy property correspond ... More
Decay Constants of Heavy-Light Mesons from QCDNov 18 2015Nov 29 2015We summarize recently improved results for the pseudoscalar [1,2] and vector [3] meson decay constants and their ratios from QCD spectral sum rules where N2LO + estimate of the N3LO PT and power corrections up to d< 6 dimensions have been included in ... More
On the number of colored Birch and Tverberg partitionsAug 02 2012Dec 09 2012In 2009, Blagojevic, Matschke & Ziegler established the first tight colored Tverberg theorem, but no lower bounds for the number of colored Tverberg partitions. We develop a colored version of our previous results (2008), and we extend our results from ... More
A note on inhomogeneous foliations with sectionsOct 03 2013We give an easy example showing that sections of a singular Riemannian foliation on a simply connected space neither have to be isometric nor injectively immersed.
Lineare Rekurrenzen, Potenzreihen und ihre erzeugenden FunktionenApr 19 2007Apr 20 2007Diese kurze Einfuehrung in Theorie und Berechnung linearer Rekurrenzen versucht, eine Luecke in der Literatur zu fuellen. Zu diesem Zweck sind viele ausfuehrliche Beispiele angegeben. This short introduction to theory and usage of linear recurrences tries ... More
Dark matter constraints in the minimal and nonminimal SUSY standard modelSep 05 1997Feb 24 1998We determine the allowed parameter space and the particle spectra of the minimal SUSY standard model (MSSM) and nonminimal SUSY standard model (NMSSM) imposing correct electroweak gauge-symmetry breaking and recent experimental constraints. The parameters ... More
SecDec: a toolbox for the numerical evaluation of multi-scale integralsFeb 22 2018We present a new version of $\texttt{SecDec}$, a program for the numerical computation of parametric integrals in the context of dimensional regularization. By its modular structure, the $\texttt{python}$ rewrite $\texttt{pySecDec}$ is much more customizable ... More
Interacting topological insulators: a reviewApr 27 2018Oct 16 2018The discovery of the quantum spin Hall effect and topological insulators more than a decade ago has revolutionized modern condensed matter physics. Today, the field of topological states of matter is one of the most active and fruitful research areas ... More
Facets of the (s,t)-p-path polytopeJun 13 2006We give a partial description of the (s,t)-p-path polytope of a directed graph D which is the convex hull of the incidence vectors of simple directed (s,t)-paths in D of length p. First, we point out how the (s,t)-p-path polytope is located in the family ... More
A Polya-Vinogradov-type inequality on $\mathbb{Z}[i]$Mar 19 2017Mar 28 2017We establish a Polya-Vinogradov-type bound for finite periodic multipicative characters on the Gaussian integers.
Duality of non-exposed facesJul 12 2011Nov 28 2011Given any polar pair of convex bodies we study its conjugate face maps and we characterize conjugate faces of non-exposed faces in terms of normal cones. The analysis is carried out using the positive hull operator which defines lattice isomorphisms linking ... More
Vector valued theta functions associated with binary quadratic formsMay 11 2015Jun 02 2015We study the space of vector valued theta functions for the Weil representation of a positive definite even lattice of rank two with fundamental discriminant. We work out the relation of this space to the corresponding scalar valued theta functions of ... More
A representation for exchangeable coalescent trees and generalized tree-valued Fleming-Viot processesAug 29 2016Dec 27 2017We give a de Finetti type representation for exchangeable random coalescent trees (formally described as semi-ultrametrics) in terms of sampling iid sequences from marked metric measure spaces. We apply this representation to define versions of tree-valued ... More
Test of Symmetries with Neutrons and NucleiFeb 10 2009Mar 06 2009Precision experiments at low energies probing weak interaction are a very promising and complementary tool for investigating the structure of the electro-weak sector of the standard model, and for searching for new phenomena revealing signs for an underlaying ... More
Maximal Regularity: Positive Counterexamples on UMD-Banach Lattices and Exact Intervals for the Negative Solution of the Extrapolation ProblemNov 16 2014Using methods from Banach space theory, we prove two new structural results on maximal regularity. The first says that there exist positive analytic semigroups on UMD-Banach lattices, namely $\ell_p(\ell_q)$ for $p \neq q \in (1, \infty)$, without maximal ... More
Generalized Gorensteinness and a homological determinant for preprojective algebrasJun 25 2018Studying invariant theory of commutative polynomial rings has motivated many developments in commutative algebra and algebraic geometry. Of particular interest has been to understand under what conditions we can obtain a fixed ring satisfying useful properties. ... More
On a theorem by KippenhahnMay 02 2017Kippenhahn discovered a real algebraic plane curve whose convex hull is the numerical range of a matrix. The correctness of this theorem was called into question when Chien and Nakazato found an example where the spatial analogue fails. They showed that ... More
Maximum-entropy inference and inverse continuity of the numerical rangeFeb 13 2015Aug 13 2015We study the continuity of the maximum-entropy inference map for two observables in finite dimensions. We prove that the continuity is equivalent to the strong continuity of the set-valued inverse numerical range map. This gives a continuity condition ... More
A primer on A-infinity-algebras and their Hochschild homologyJan 15 2016We present an elementary and self-contained construction of $A_\infty$-algebras, $A_\infty$-bimodules and their Hochschild homology and cohomology groups. In addition, we discuss the cup product in Hochschild cohomology and the spectral sequence of the ... More
Intrinsic Inference on the Mean Geodesic of Planar Shapes and Tree Discrimination by Leaf GrowthSep 16 2010For planar landmark based shapes, taking into account the non-Euclidean geometry of the shape space, a statistical test for a common mean first geodesic principal component (GPC) is devised. It rests on one of two asymptotic scenarios, both of which are ... More
A note on Diophantine approximation with Gaussian primesSep 28 2016We investigate the distribution of $p\theta$ modulo 1, where $\theta$ is a complex number which is not contained in $\mathbb{Q}(i)$, and $p$ runs over the Gaussian primes.
Introduction to Physical Implementations of Quantum Information ProcessingMar 01 2013This was a contribution to the lecture notes on the 44th IFF Spring School held at Forschungszentrum J\"ulich in 2013 on "Quantum Information Processing". The school as a whole had a strong focus on solid state systems. It was the purpose of this contribution ... More
Recent Progress in Lattice QCDJan 09 2013Recent progress in Lattice QCD is highlighted. After a brief introduction to the methodology of lattice computations the presentation focuses on three main topics: Hadron Spectroscopy, Hadron Structure and Lattice Flavor Physics. In each case a summary ... More
Gauge action improvement and smearingSep 23 2004Dec 28 2005The effect of repeatedly smearing SU(3) gauge configurations is investigated. Six gauge actions (Wilson, Symanzik, Iwasaki, DBW2, Beinlich-Karsch-Laermann, Langfeld; combined with a direct SU(3)-overrelaxation step) and three smearings (APE, HYP, EXP) ... More
Aspects of Quasi-Phasestructure of the Schwinger Model on a Cylinder with Broken Chiral SymmetryMay 19 1998Oct 05 1998We consider the N_f-flavour Schwinger Model on a thermal cylinder of circumference $\beta=1/T$ and of finite spatial length $L$. On the boundaries $x^1=0$ and $x^1=L$ the fields are subject to an element of a one-dimensional class of bag-inspired boundary ... More
Quantum phase transitions of topological insulators without gap closingOct 11 2013Aug 12 2016We consider two-dimensional Chern insulators and time-reversal invariant topological insulators and discuss the effect of perturbations breaking either particle-number conservation or time-reversal symmetry. The appearance of trivial mass terms is expected ... More
Interfacing Constraint-Based Grammars and Generation AlgorithmsAug 07 2000Constraint-based grammars can, in principle, serve as the major linguistic knowledge source for both parsing and generation. Surface generation starts from input semantics representations that may vary across grammars. For many declarative grammars, the ... More
Algorithmic Meta-TheoremsFeb 20 2009Algorithmic meta-theorems are general algorithmic results applying to a whole range of problems, rather than just to a single problem alone. They often have a "logical" and a "structural" component, that is they are results of the form: every computational ... More
Minimal even sets of nodesOct 20 1997We extend some results on even sets of nodes which have been proved for surfaces up to degree 6 to surfaces up to degree 10. In particular, we give a formula for the minimal cardinality of a nonempty even set of nodes.
A Projective Surface of Degree Eight with 168 NodesJul 19 1995The estimate for the maximal number of ordinary double points of a projective surface of degree eight is improved to $168\leq\mu(8)\leq 174$ by constructing a projective surface of degree eight with 168 nodes.