Results for "Sebastian J. Mielke"

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Spell Once, Summon Anywhere: A Two-Level Open-Vocabulary Language ModelApr 23 2018Nov 23 2018We show how the spellings of known words can help us deal with unknown words in open-vocabulary NLP tasks. The method we propose can be used to extend any closed-vocabulary generative model, but in this paper we specifically consider the case of neural ... More
Are All Languages Equally Hard to Language-Model?Jun 10 2018For general modeling methods applied to diverse languages, a natural question is: how well should we expect our models to work on languages with differing typological profiles? In this work, we develop an evaluation framework for fair cross-linguistic ... More
Counterfactual Data Augmentation for Mitigating Gender Stereotypes in Languages with Rich MorphologyJun 11 2019Gender stereotypes are manifest in most of the world's languages and are consequently propagated or amplified by NLP systems. Although research has focused on mitigating gender stereotypes in English, the approaches that are commonly employed produce ... More
Unsupervised Disambiguation of Syncretism in Inflected LexiconsJun 10 2018Lexical ambiguity makes it difficult to compute various useful statistics of a corpus. A given word form might represent any of several morphological feature bundles. One can, however, use unsupervised learning (as in EM) to fit a model that probabilistically ... More
A Structured Variational Autoencoder for Contextual Morphological InflectionJun 10 2018Statistical morphological inflectors are typically trained on fully supervised, type-level data. One remaining open research question is the following: How can we effectively exploit raw, token-level data to improve their performance? To this end, we ... More
Quantum oscillations in the parent magnetic phase of an iron arsenide high temperature superconductorJun 30 2008Nov 17 2008We report quantum oscillation measurements in SrFe2As2 - which is an antiferromagnetic parent of the iron-arsenide family of superconductors - known to become superconducting under doping and the application of pressure. The magnetic field and temperature ... More
Properties of Hubbard models with degenerate localized single particle eigenstatesFeb 14 2012Apr 19 2012We consider the repulsive Hubbard model on a class of lattices or graphs for which there is a large degeneracy of the single particle ground states and where the projector onto the space of single particle ground states is highly reducible. This means ... More
Quantum oscillations from nodal bilayer magnetic breakdown in the underdoped high temperature superconductor YBa2Cu3O6+xMay 11 2012We report quantum oscillations in underdoped YBa2Cu3O6.56 over a significantly large range in magnetic field extending from 24 to 101 T, enabling three well-spaced low frequencies at 440 T, 532 T, and 620 T to be clearly resolved. We show that a small ... More
Spin-order driven Fermi surface revealed by quantum oscillations in an underdoped high Tc superconductorJul 17 2009We use quantum oscillation measurements to distinguish between spin and orbital components of the lowest energy quasiparticle excitations in YBa2Cu3O6.54, each of which couple differently to a magnetic field. Our measurements reveal the phase of the observed ... More
Noise induced stability in fluctuating, bistable potentialsDec 14 1999The over-damped motion of a Brownian particle in an asymmetric, bistable, fluctuating potential shows noise induced stability: For intermediate fluctuation rates the mean occupancy of minima with an energy above the absolute minimum is enhanced. The model ... More
Stability of Ferromagnetism in Hubbard models with degenerate single-particle ground statesOct 25 1999A Hubbard model with a N_d-fold degenerate single-particle ground state has ferromagnetic ground states if the number of electrons is less or equal to N_d. It is shown rigorously that the local stability of ferromagnetism in such a model implies global ... More
Similarity renormalization of the electron--phonon couplingSep 06 1996Dec 17 1996We study the problem of the phonon-induced electron-electron interaction in a solid. Starting with a Hamiltonian that contains an electron-phonon interaction, we perform a similarity renormalization transformation to calculate an effective Hamiltonian. ... More
Calculating critical temperatures of superconductivity from a renormalized HamiltonianSep 16 1997It is shown that one can obtain quantitatively accurate values for the superconducting critical temperature within a Hamiltonian framework. This is possible if one uses a renormalized Hamiltonian that contains an attractive electron-electron interaction ... More
Stability of Ferromagnetism in Hubbard models on two-dimensional line graphsSep 06 2006Apr 03 2012It is well known that the Hubbard model on a line graph has a flat band and ferromagnetic ground states in a certain density range. We show that for a Hubbard model on a line graph of a planar bipartite graph the ferromagnetic ground state is stable if ... More
Elements for Response Time Statistics in ERP Transaction SystemsApr 16 2004May 16 2005We present some measurements and ideas for response time statistics in ERP systems. It is shown that the response time distribution of a given transaction in a given system is generically a log-normal distribution or, in some situations, a sum of two ... More
Ferromagnetism in single-band Hubbard models with a partially flat bandApr 19 1999A Hubbard model with a single, partially flat band has ferromagnetic ground states. It is shown that local stability of ferromagnetism implies its global stability in such a model: The model has only ferromagnetic ground states if there are no single ... More
Analysis of energetic models for rate-independent materialsMay 01 2003We consider rate-independent models which are defined via two functionals: the time-dependent energy-storage functional $\calI:[0,T]\ti X\to [0,\infty]$ and the dissipation distance $\calD:X\ti X\to[0,\infty]$. A function $z:[0,T]\to X$ is called a solution ... More
Fermi surface of CeIn3 above the Neel critical fieldJun 16 2007We report measurements of the de Haas-van Alphen effect in CeIn3 in magnetic fields extending to ~90 T, well above the Ne'el critical field of Hc ~61 T. The unreconstructed Fermi surface a-sheet is observed in the high magnetic field polarized paramagnetic ... More
Experimental observation of Frohlich superconductivity in high magnetic fieldsMar 08 2001Apr 05 2001Resistivity and irreversible magnetisation data taken within the high-magnetic-field CDWx phase of the quasi-two-dimensional organic metal alpha-(BEDT-TTF)2KHg(SCN)4 are shown to be consistent with a field-induced inhomogeneous superconducting phase. ... More
Quantum oscillations in antiferromagnetic CaFe2As2 on the brink of superconductivityFeb 09 2009We report quantum oscillation measurements on CaFe2As2 under strong magnetic fields- recently reported to become superconducting under pressures of as little as a kilobar. The largest observed carrier pocket occupies less than 0.05 % of the paramagnetic ... More
Improved Energy-Momentum Currents in Metric-Affine SpacetimeOct 15 1992In Minkowski spacetime it is well-known that the canonical energy-momentum current is involved in the construction of the globally conserved currents of energy-momentum and total angular momentum. For the construction of conserved currents corresponding ... More
A photonic bandgap resonator to facilitate GHz frequency conductivity experiments in pulsed magnetic fieldsJun 19 2006We describe instrumentation designed to perform millimeter-wave conductivity measurements in pulsed high magnetic fields at low temperatures. The main component of this system is an entirely non-metallic microwave resonator. The resonator utilizes periodic ... More
Direct observation of multiple spin zeroes in the underdoped high temperature superconductor YBa2Cu3O6+xMar 22 2011We report the direct observation of multiple `spin zeroes' in angle-dependent magnetic quantum oscillations measured up to 85T in YBa2Cu3O6+x, at which the amplitude falls to a deep minimum accompanied by a phase inversion of the measured quantum oscillations, ... More
Metal-insulator quantum critical point beneath the high Tc superconducting domeOct 13 2009An enduring question in correlated systems concerns whether superconductivity is favoured at a quantum critical point (QCP) characterised by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high Tc cuprates ... More
Compensated electron and hole pockets in an underdoped high Tc superconductorJan 27 2010Apr 28 2010We report quantum oscillations in the underdoped high Tc YBCO over a wide range in magnetic field 28<B<85 T corresponding to ~12 oscillations, enabling the Fermi surface topology to be mapped to high resolution. As earlier reported by Sebastian et al., ... More
The CoNLL--SIGMORPHON 2018 Shared Task: Universal Morphological ReinflectionOct 16 2018Oct 18 2018The CoNLL--SIGMORPHON 2018 shared task on supervised learning of morphological generation featured data sets from 103 typologically diverse languages. Apart from extending the number of languages involved in earlier supervised tasks of generating inflected ... More
UniMorph 2.0: Universal MorphologyOct 25 2018The Universal Morphology UniMorph project is a collaborative effort to improve how NLP handles complex morphology across the world's languages. The project releases annotated morphological data using a universal tagset, the UniMorph schema. Each inflected ... More
Einsteinian gravity from a topological actionJul 23 2007Sep 10 2007The curvature-squared model of gravity, in the affine form proposed by Weyl and Yang, is deduced from a topological action in 4D. More specifically, we start from the Pontrjagin (or Euler) invariant. Using the BRST antifield formalism with a double duality ... More
Equilibrium Correlation Functions of the Spin-Boson Model with Sub-Ohmic BathJul 17 2002Sep 30 2002The spin-boson model is studied by means of flow equations for Hamiltonians. Our truncation scheme includes all coupling terms which are linear in the bosonic operators. Starting with the canonical generator $\eta_c=[H_0,H]$ with $H_0$ resembling the ... More
Bose-Hubbard model on two-dimensional line graphsDec 01 2011Apr 15 2012We construct a basis for the many-particle ground states of the positive hopping Bose-Hubbard model on line graphs of finite 2-connected planar bipartite graphs at sufficiently low filling factors. The particles in these states are localized on non-intersecting ... More
The assessment and planning of non-inferiority trials for retention of effect hypotheses - towards a general approachDec 21 2009The objective of this paper is to develop statistical methodology for planning and evaluating three-armed non-inferiority trials for general retention of effect hypotheses, where the endpoint of interest may follow any (regular) parametric distribution ... More
Flow equations for the Anderson HamiltonianMay 12 1994May 13 1994Using a continuous unitary transformation recently proposed by Wegner \cite{Wegner} together with an approximation that neglects irrelevant contributions, we obtain flow equations for Hamiltonians. These flow equations yield a diagonal or almost diagonal ... More
Posterior Consistency for Bayesian Inverse Problems through Stability and Regression ResultsFeb 17 2013Jul 16 2013In the Bayesian approach, the a priori knowledge about the input of a mathematical model is described via a probability measure. The joint distribution of the unknown input and the data is then conditioned, using Bayes' formula, giving rise to the posterior ... More
A note on ferromagnetism in the Hubbard model on the complete graphJun 17 1996Recently there have appeared some papers which discuss the existence of ferromagnetism in the Hubbard model defined on the complete graph. At least for the special electron number N_e=N-1, where N denotes the number of sites in the lattice, the existence ... More
Quantum Oscillations in the Underdoped Cuprate YBa2Cu4O8Jun 30 2007Feb 04 2008We report the observation of quantum oscillations in the underdoped cuprate superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed magnetic fields up to 85T. There is a clear signal, periodic in inverse field, with frequency 660+/-15T ... More
A dynamical trichotomy for structured populations experiencing positive density-dependence in stochastic environmentsJan 29 2017Positive density-dependence occurs when individuals experience increased survivorship, growth, or reproduction with increased population densities. Mechanisms leading to these positive relationships include mate limitation, saturating predation risk, ... More
Dimension-Independent MCMC Sampling for Inverse Problems with Non-Gaussian PriorsFeb 09 2013Oct 22 2014The computational complexity of MCMC methods for the exploration of complex probability measures is a challenging and important problem. A challenge of particular importance arises in Bayesian inverse problems where the target distribution may be supported ... More
Persistence for stochastic difference equations: A mini-reviewSep 27 2011Understanding under what conditions populations, whether they be plants, animals, or viral particles, persist is an issue of theoretical and practical importance in population biology. Both biotic interactions and environmental fluctuations are key factors ... More
On gravitational interactions between two bodiesSep 03 2014Sep 13 2015Many physicists, following Einstein, believe that the ultimate aim of theoretical physics is to find a unified theory of all interactions which would not depend on any free dimensionless constant, i.e., a dimensionless constant that is only empirically ... More
Chaotic self-similar wave maps coupled to gravityOct 08 2003Oct 08 2003We continue our studies of spherically symmetric self-similar solutions in the SU(2) sigma model coupled to gravity. For some values of the coupling constant we present numerical evidence for the chaotic solution and the fractal threshold behavior. We ... More
Coexistence in the face of uncertaintyDec 12 2015Sep 23 2016Over the past century, nonlinear difference and differential equations have been used to understand conditions for species coexistence. However, these models fail to account for random fluctuations due to demographic and environmental stochasticity which ... More
Universal Distribution of Would-be Topological Zero Modes in Coupled Chiral SystemsSep 14 2016We consider two quenched, chiral ensembles which are coupled in such a way that a combined chiral symmetry is preserved. The coupling also links the topology of the two systems such that the number of exact zero modes in the coupled system equals the ... More
Flow equations for Hamiltonians: Contrasting different approaches by using a numerically solvable modelSep 27 2002Jan 30 2003To contrast different generators for flow equations for Hamiltonians and to discuss the dependence of physical quantities on unitarily equivalent, but effectively different initial Hamiltonians, a numerically solvable model is considered which is structurally ... More
Quasi-two-dimensional organic superconductors: a reviewFeb 25 2002We present a review of quasi-two-dimensional organic superconductors. These systems exhibit many interesting phenomena, including reduced dimensionality, strong electron-electron and electron-phonon interactions and the proximity of antiferromagnetism, ... More
An entropic gradient structure for Lindblad equations and GENERIC for quantum systems coupled to macroscopic modelsSep 19 2016We show that all Lindblad operators (i.e. generators of quantum semigroups) on a finite-dimensional Hilbert space satisfying the detailed balance condition with respect to the thermal equilibrium state can be written as a gradient system with respect ... More
Hard-core bosons in flat band systems above the critical densityApr 12 2017Aug 17 2017We investigate the behaviour of hard-core bosons in one- and two-dimensional flat band systems, the chequerboard and the kagom\'e lattice and one-dimensional analogues thereof. The one dimensional systems have an exact local reflection symmetry which ... More
Interacting bosons in two-dimensional flat band systemsMay 14 2015Jul 07 2015The Hubbard model of bosons on two dimensional lattices with a lowest flat band is discussed. In these systems there is a critical density, where the ground state is known exactly and can be represented as a charge density wave. Above this critical filling, ... More
Convergence results for a coarsening model using global linearizationSep 17 2002We study a coarsening model describing the dynamics of interfaces in the one-dimensional Allen-Cahn equation. Given a partition of the real line into intervals of length greater than one, the model consists in constantly eliminating the shortest interval ... More
Flow Equations for the Henon-Heiles HamiltonianSep 29 1998The Henon-Heiles Hamiltonian was introduced in 1964 as a mathematical model to describe the chaotic motion of stars in a galaxy. By canonically transforming the classical Hamiltonian to a Birkhoff-Gustavson normalform Delos and Swimm obtained a discrete ... More
Diffusive Mixing of Stable States in the Ginzburg-Landau EquationJan 27 1998For the time-dependent Ginzburg-Landau equation on the real line, we construct solutions which converge, as $x \to \pm\infty$, to periodic stationary states with different wave-numbers $\eta_\pm$. These solutions are stable with respect to small perturbations, ... More
Noise induced transport at zero temperatureNov 06 1997We consider a particle in the over-damped regime at zero temperature under the influence of a sawtooth potential and of a noisy force, which is correlated in time. A current occurs, even if the mean of the noisy force vanishes. We calculate the stationary ... More
Diagonalization of system plus environment HamiltoniansJan 17 1997A new approach to dissipative quantum systems modelled by a system plus environment Hamiltonian is presented. Using a continuous sequence of infinitesimal unitary transformations the small quantum system is decoupled from its thermodynamically large environment. ... More
Anomalies and gravityMay 16 2006Anomalies in Yang-Mills type gauge theories of gravity are reviewed. Particular attention is paid to the relation between the Dirac spin, the axial current j_5 and the non-covariant gauge spin C. Using diagrammatic techniques, we show that only generalizations ... More
Geometric properties of cones with applications on the Hellinger-Kantorovich space, and a new distance on the space of probability measuresDec 05 2017May 18 2018We study general geometric properties of cone spaces, and we apply them on the Hellinger--Kantorovich space $(\mathcal{M}(X),\mathsf{H\hspace{-0.25em} K}_{\alpha,\beta}).$ We exploit a two-parameter scaling property of the Hellinger-Kantorovich metric ... More
Linearized plasticity is the evolutionary Γ-limit of finite plasticityNov 04 2011We provide a rigorous justification of the classical linearization approach in plasticity. By taking the small-deformations limit, we prove via \Gamma-convergence for rate-independent processes that energetic solutions of the quasi-static finite-strain ... More
Thermoviscoelasticity in Kelvin-Voigt rheology at large strainsMar 26 2019The frame-indifferent thermodynamically-consistent model of thermoviscoelasticity at large strain is formulated in the reference configuration with using the concept of the second-grade nonsimple materials. We focus on physically correct viscous stresses ... More
On the existence of global-in-time weak solutions and scaling laws for Kolmogorov's two-equation model of turbulenceJan 06 2018Oct 15 2018This paper is concerned with Kolmogorov's two-equation model for the free turbulence in three dimensions. We first discuss scaling laws for slightly more general two-equation models to highlight the special role of the model devised by Kolmogorov in 1942. ... More
A robust but disordered collapsed-volume phase in a cerium alloy under the application of pulsed magnetic fieldsSep 27 2011We report synchrotron x-ray powder diffraction measurements of Ce0.8La0.1Th0.1 subject to pulsed magnetic fields as high as 28 Tesla. This alloy is known to exhibit a continuous volume collapse on cooling at ambient pressure, which is a modification of ... More
Bulk single crystal growth of the theoretically predicted magnetic Weyl semimetals $R$AlGe ($R$ = Pr, Ce)Jun 27 2019We explore two methods for single crystal growth of the theoretically proposed magnetic Weyl semimetals $R$AlGe ($R$ = Pr,Ce), which prove that a floating zone technique, being both crucible- and flux-free, is crucial to obtain perfectly stoichiometric ... More
High magnetic field-induced insulating phase in an organic conductorSep 25 2002We report electrical transport, skin depth, and magnetocaloric measurements in the tau-series of organic conductors at very high magnetic fields. Above 36 T these materials show a magnetic field induced first order phase transition from a metallic to ... More
Anisotropic Magnetoresistance in Ga$_{1-x}$Mn$_x$AsFeb 27 2002We have measured the magnetoresistance in a series of Ga$_{1-x}$Mn$_x$As samples with 0.033$\le x \le$ 0.053 for three mutually orthogonal orientations of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in these materials is negative ... More
Theory of the Anderson impurity model: The Schrieffer--Wolff transformation re--examinedOct 25 1995We apply the method of infinitesimal unitary transformations recently introduced by Wegner to the Anderson single impurity model. It is demonstrated that this method provides a good approximation scheme for all values of the on-site interaction $U$, it ... More
Entropy Trees and Range-Minimum Queries In Optimal Average-Case SpaceMar 06 2019The range-minimum query (RMQ) problem is a fundamental data structuring task with numerous applications. Despite the fact that succinct solutions with worst-case optimal $2n+o(n)$ bits of space and constant query time are known, it has been unknown whether ... More
Persistence in fluctuating environments for interacting structured populationsApr 06 2013Nov 02 2013Individuals within any species exhibit differences in size, developmental state, or spatial location. These differences coupled with environmental fluctuations in demographic rates can have subtle effects on population persistence and species coexistence. ... More
Robust permanence for ecological equations with internal and external feedbacksDec 20 2016Species experience both internal feedbacks with endogenous factors such as trait evolution and external feedbacks with exogenous factors such as weather. These feedbacks can play an important role in determining whether populations persist or communities ... More
Thermal activation between Landau levels in the organic superconductor $β''$-(BEDT-TTF)$_{2}$SF$_{5}$CH$_{2}$CF$_{2}$SO$_{3}$May 02 2001We show that Shubnikov-de Haas oscillations in the interlayer resistivity of the organic superconductor $\beta''$-(BEDT-TTF)$_{2}$SF$_{5}$ CH$_{2}$CF$_{2}$SO$_{3}$ become very pronounced in magnetic fields $\sim$~60~T. The conductivity minima exhibit ... More
Robust permanence for interacting structured populationsMay 22 2010The dynamics of interacting structured populations can be modeled by $\frac{dx_i}{dt}= A_i (x)x_i$ where $x_i\in \R^{n_i}$, $x=(x_1,\dots,x_k)$, and $A_i(x)$ are matrices with non-negative off-diagonal entries. These models are permanent if there exists ... More
Persistence and extinction for stochastic ecological models with internal and external variablesAug 23 2018Mar 26 2019The dynamics of species' densities depend both on internal and external variables. Internal variables include frequencies of individuals exhibiting different phenotypes or living in different spatial locations. External variables include abiotic factors ... More
Recognizing recurrent neural networks (rRNN): Bayesian inference for recurrent neural networksJan 20 2012Recurrent neural networks (RNNs) are widely used in computational neuroscience and machine learning applications. In an RNN, each neuron computes its output as a nonlinear function of its integrated input. While the importance of RNNs, especially as models ... More
Einstein clusters as models of inhomogeneous spacetimesDec 28 2018We study the effect of small-scale inhomogeneities for Einstein clusters. We construct a spherically symmetric stationary spacetime with small-scale radial inhomogeneities and propose the Gedankenexperiment. An hypothetical observer at the center constructs, ... More
On standing waves in general relativityJan 29 2019We propose a covariant definition of standing gravitational waves in general relativity.
Ensemble filter techniques for intermittent data assimilation - a surveyAug 31 2012This survey paper is written with the intention of giving a mathematical introduction to filtering techniques for intermittent data assimilation, and to survey some recent advances in the field. The paper is divided into three parts. The first part introduces ... More
Evolutionarily induced alternative states and coexistence in systems with apparent competitionApr 03 2015Predators often consume multiple prey and by mutually subsidizing a shared predator, the prey may reciprocally harm each other. When predation levels are high, this apparent competition can culminate in a prey species being displaced. Coupling quantitative ... More
Solving First Order Autonomous Algebraic Ordinary Differential Equations by PlacesMar 13 2018Nov 14 2018Given a first-order autonomous algebraic ordinary differential equation, we present a method for computing formal power series solutions by means of places. We provide an algorithm for computing a full characterization of possible initial values, classified ... More
Pre-Hausdorff SpacesMar 07 2008This paper introduces three separation conditions for topological spaces, called T_{0,1}, T_{0,2} ("pre-Hausdorff"), and T_{1,2}. These conditions generalize the classical T_(1) and T_(2) separation axioms, and they have advantages over them topologically ... More
Avoided Valence Transition in a Plutonium SuperconductorSep 14 2014Some of the most remarkable phenomena---and greatest theoretical challenges---in condensed matter physics arise when $d$ or $f$ electrons are neither fully localized around their host nuclei, nor fully itinerant. This localized/itinerant "duality" underlies ... More
Gravitational Goldstone fields from affine gauge theoryJul 27 2000In order to facilitate the application of standard renormalization techniques, gravitation should be decribed, if possible, in pure connection formalism, as a Yang-Mills theory of a certain spacetime group, say the Poincare or the affine group. This embodies ... More
Comment on: Topological Invariants, instantons, and the chiral anomaly on spaces with torsionApr 27 1999Apr 28 1999In Riemann-Cartan spacetimes with torsion only its axial covector piece $A$ couples to massive Dirac fields. Using renormalization group arguments, we show that besides the familiar Riemannian term only the Pontrjagin type four-form $dA\wedge dA$ does ... More
2D XY Behavior observed in quasi-2D quantum Heisenberg antiferromagnetsMar 13 2009The magnetic properties of a new family of molecular-based quasi-two dimension $S=1/2$ Heisenberg antiferromagnets are reported. Three compounds, ($Cu(pz)_2(ClO_4)_2$, $Cu(pz)_2(BF_4)_2$, and $[Cu(pz)_2(NO_3)](PF_6)$) contain similar planes of Cu$^{2+}$ ... More
Cyclotron and combined phonon-assisted resonances in double-well heterostructure In$_{0.65}$Ga$_{0.35}$As/In$_{0.52}$Al$_{0.48}$As at megagauss magnetic fieldsJun 20 2018Sep 25 2018Experiments on resonances of conduction electrons in InGaAs/InAlAs double quantum wells at megagauss magnetic fields in the Faraday geometry are reported. We observe new cyclotron resonances assisted by emission of InAs-like and GaAs-like optic phonons ... More
TOPICAL REVIEW: General relativistic boson starsJan 01 2008There is accumulating evidence that (fundamental) scalar fields may exist in Nature. The gravitational collapse of such a boson cloud would lead to a boson star (BS) as a new type of a compact object. Similarly as for white dwarfs and neutron stars, there ... More
An existence result and evolutionary $Γ$-convergence for perturbed gradient systemsJan 16 2018The initial-value problem for the perturbed gradient flow \[ B(t,u(t)) \in \partial\Psi_{u(t)}(u'(t))+\partial \mathcal E_t(u(t)) \text{ for a.a. } t\in (0,T),\qquad u(0)=u_0 \] with a perturbation $B$ in a Banach space $V$ is investigated, where the ... More
Magnetic susceptibility of the normal-superconducting transition in high-purity single-crystal alpha-uraniumAug 26 2002We report complex ac magnetic susceptibility measurements of a superconducting transition in very high-quality single-crystal alpha-uranium using microfabricated coplanar magnetometers. We identify an onset of superconductivity at T~0.7 K in both the ... More
On Lossless Feedback Delay NetworksJun 24 2016Lossless Feedback Delay Networks (FDNs) are commonly used as a design prototype for artificial reverberation algorithms. The lossless property is dependent on the feedback matrix, which connects the output of a set of delays to their inputs, and the lengths ... More
A practical approach to the sensitivity analysis for kinetic Monte Carlo simulation of heterogeneous catalysisNov 22 2016Lattice kinetic Monte Carlo simulations have become a vital tool for predictive quality atomistic understanding of complex surface chemical reaction kinetics over a wide range of reaction conditions. In order to expand their practical value in terms of ... More
Boson Stars: Alternatives to primordial black holes?Jan 20 2000The present surge for the astrophysical relevance of boson stars stems from the speculative possibility that these compact objects could provide a considerable fraction of the non-baryonic part of dark matter within the halo of galaxies. For a very light ... More
Variational convergence of gradient flows and rate-independent evolutions in metric spacesJul 11 2012We study the asymptotic behaviour of families of gradient flows in a general metric setting, when the metric-dissipation potentials degenerate in the limit to a dissipation with linear growth. We present a general variational definition of BV solutions ... More
Nonsmooth analysis of doubly nonlinear evolution equationsMay 21 2011In this paper we analyze a broad class of abstract doubly nonlinear evolution equations in Banach spaces, driven by nonsmooth and nonconvex energies. We provide some general sufficient conditions, on the dissipation potential and the energy functional,for ... More
High-frequency averaging in semi-classical Hartree-type equationsSep 30 2009Dec 08 2009We investigate the asymptotic behavior of solutions to semi-classical Schroedinger equations with nonlinearities of Hartree type. For a weakly nonlinear scaling, we show the validity of an asymptotic superposition principle for slowly modulated highly ... More
Conformal and projection diagrams in LaTeXMay 09 2013In general relativity, the causal structure of space-time may sometimes be depicted by conformal Carter-Penrose diagrams or a recent extension of these - the projection diagrams. The introduction of conformal diagrams in the sixties was one of the progenitors ... More
Existence and convergence of Puiseux series solutions for first order autonomous differential equationsAug 24 2019Given an algebraic first order autonomous ordinary differential equation F(y,y')=0, we prove that every formal Puiseux series solution of F(y,y')=0, expanded around any finite point or at infinity, is convergent. The proof is constructive and we provide ... More
Evolution of unconditional dispersal in periodic environmentsJul 29 2010Organisms modulate their fitness in heterogeneous environments by dispersing. Prior work shows that there is selection against "unconditional" dispersal in spatially heterogeneous environments. "Unconditional" means individuals disperse at a rate independent ... More
What Kind of Language Is Hard to Language-Model?Jun 11 2019How language-agnostic are current state-of-the-art NLP tools? Are there some types of language that are easier to model with current methods? In prior work (Cotterell et al., 2018) we attempted to address this question for language modeling, and observed ... More
The remapped particle-mesh advection schemeJul 26 2006We describe the remapped particle-mesh method, a new mass-conserving method for solving the density equation which is suitable for combining with semi-Lagrangian methods for compressible flow applied to numerical weather prediction. In addition to the ... More
Generalized Urn Models of Evolutionary ProcessesJul 08 2004Generalized Polya urn models can describe the dynamics of finite populations of interacting genotypes. Three basic questions these models can address are: Under what conditions does a population exhibit growth? On the event of growth, at what rate does ... More
Invasion speeds for structured populations in fluctuating environmentsJun 12 2010We live in a time where climate models predict future increases in environmental variability and biological invasions are becoming increasingly frequent. A key to developing effective responses to biological invasions in increasingly variable environments ... More
A graph partition problemAug 02 2014Given a graph $G$ on $n$ vertices, for which $m$ is it possible to partition the edge set of the $m$-fold complete graph $mK_n$ into copies of $G$? We show that there is an integer $m_0$, which we call the \emph{partition modulus of $G$}, such that the ... More
Scarcity of finite orbits for rational functions over a number fieldNov 09 2017Let $\phi$ be a an endomorphism of degree $d\geq{2}$ of the projective line, defined over a number field $K$. Let $S$ be a finite set of places of $K$, including the archimedean places, such that $\phi$ has good reduction outside of $S$. The article presents ... More
Evolution as a coexistence mechanism: Does genetic architecture matter?Sep 19 2016Species sharing a prey or a predator species may go extinct due to exploitative or apparent competition. We examined whether evolution of the shared species acts as a coexistence mechanism and to what extent the answer depends on the genetic architecture ... More
Spatial heterogeneity promotes coexistence of rock-paper-scissor metacommunitiesJul 02 2012The rock-paper-scissor game -- which is characterized by three strategies R,P,S, satisfying the non-transitive relations S excludes P, P excludes R, and R excludes S -- serves as a simple prototype for studying more complex non-transitive systems. For ... More