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Results for "Sebastian J. Mielke"

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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
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
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
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
Effective rate equations for the over-damped motion in fluctuating potentialsApr 18 2001We discuss physical and mathematical aspects of the over-damped motion of a Brownian particle in fluctuating potentials. It is shown that such a system can be described quantitatively by fluctuating rates if the potential fluctuations are slow compared ... More
Flow equations for band--matricesMar 16 1998Continuous unitary transformations can be used to diagonalize or approximately diagonalize a given Hamiltonian. In the last four years, this method has been applied to a variety of models of condensed matter physics and field theory. With a new generator ... 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
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
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
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
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
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
An entropic gradient structure for Lindblad equations and GENERIC for quantum systems coupled to macroscopic modelsSep 19 2016Oct 13 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
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
On light propagation in Swiss-Cheese cosmologiesDec 23 2010Mar 26 2011We study the effect of inhomogeneities on light propagation. The Sachs equations are solved numerically in the Swiss-Cheese models with inhomogeneities modelled by the Lemaitre-Tolman solutions. Our results imply that, within the models we study, inhomogeneities ... 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
Stable causality of Black SaturnsFeb 19 2011We prove that the Black Saturns are stably causal on the closure of the domain of outer communications.
When do factors promoting balanced selection also promote population persistence? A demographic perspective on Gillespie's SAS-CFF modelFeb 09 2019Classical stochasticity demography predicts that environmental stochasticity reduces population growth rates and, thereby, can increase extinction risk. In contrast, the SAS-CFF model demonstrates that environmental stochasticity can promote genetic diversity. ... 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
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
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
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
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
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
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
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
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
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
Quasi-stationary distributions for randomly perturbed dynamical systemsJan 18 2011Apr 15 2014We analyze quasi-stationary distributions $\{\mu^{\varepsilon}\}_{\varepsilon>0}$ of a family of Markov chains $\{X^{\varepsilon}\}_{\varepsilon>0}$ that are random perturbations of a bounded, continuous map $F:M\to M$, where $M$ is a closed subset of ... 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
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
Low temperature equilibrium correlation functions in dissipative quantum systemsJul 23 1996Oct 24 1996We introduce a new theoretical approach to dissipative quantum systems. By means of a continuous sequence of infinitesimal unitary transformations, we decouple the small quantum system that one is interested in from its thermodynamically large environment. ... 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
The Brain Uses Reliability of Stimulus Information when Making Perceptual DecisionsSep 07 2015In simple perceptual decisions the brain has to identify a stimulus based on noisy sensory samples from the stimulus. Basic statistical considerations state that the reliability of the stimulus information, i.e., the amount of noise in the samples, should ... 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
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
Chiral Anomaly in Contorted SpacetimesApr 18 1997The Dirac equation in Riemann-Cartan spacetimes with torsion is reconsidered. As is well-known, only the axial covector torsion $A$, a one-form, couples to massive Dirac fields. Using diagrammatic techniques, we show that besides the familiar Riemannian ... More
Alignment Dynamics of Single-Walled Carbon Nanotubes in Pulsed Ultrahigh Magnetic FieldsAug 15 2008We have measured the dynamic alignment properties of single-walled carbon nanotube (SWNT) suspensions in pulsed high magnetic fields through linear dichroism spectroscopy. Millisecond-duration pulsed high magnetic fields up to 56 T as well as microsecond-duration ... 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
Extended event driven molecular dynamics for simulating dense granular matterDec 21 2010A new numerical method is presented to efficiently simulate the inelastic hard sphere (IHS) model for granular media, when fluid and frozen regions coexist in the presence of gravity. The IHS model is extended by allowing particles to change their dynamics ... 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
State and Parameter Estimation from Observed Signal IncrementsMar 26 2019May 01 2019The success of the ensemble Kalman filter has triggered a strong interest in expanding its scope beyond classical state estimation problems. In this paper, we focus on continuous-time data assimilation where the model and measurement errors are correlated ... More
Evolution as a coexistence mechanism: Does genetic architecture matter?Sep 19 2016Jun 12 2017Species sharing a prey or a predator species may go extinct due to exploitative or apparent competition. We examine whether evolution of the shared species acts as a coexistence mechanism and to what extent the answer depends on the genetic architecture ... 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
Stable causality of the Pomeransky-Senkov black holesOct 01 2010We show stable causality of the Pomeransky-Senkov black rings.
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
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
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
Interaction of modulated pulses in the nonlinear Schroedinger equation with periodic potentialMay 01 2007We consider a cubic nonlinear Schroedinger equation with periodic potential. In a semiclassical scaling the nonlinear interaction of modulated pulses concentrated in one or several Bloch bands is studied. The notion of closed mode systems is introduced ... More
Modeling solutions with jumps for rate-independent systems on metric spacesJul 04 2008Rate-independent systems allow for solutions with jumps that need additional modeling. Here we suggest a formulation that arises as limit of viscous regularization of the solutions in the extended state space. Hence, our parametrized metric solutions ... More
A gradient system with a wiggly energy and relaxed EDP-convergenceJan 13 2018If gradient systems depend on a microstructure, we want to derive a macroscopic gradient structure describing the effective behavior of the microscopic effects. We introduce a notion of evolutionary Gamma-convergence that relates the microscopic energy ... More
Accurate effective Hamiltonians via unitary flow in Floquet spaceApr 12 2013Oct 22 2013We present a systematic construction of effective Hamiltonians of periodically driven quantum systems. Because of an equivalence between the time dependence of a Hamiltonian and an interaction in its Floquet operator, flow equations, that permit to decouple ... More
Eigenvalues of the Stewart-Lyth equation for inflation with a blue spectrumJun 24 2000By using the rather stringent nonlinear second order slow-roll approximation, we reconsider the nonlinear second order Abel equation of Stewart and Lyth. We determine a new blue eigenvalue spectrum. Some of the discrete values of the spectral index $n_s$ ... More
A New Method of Generating Exact Inflationary SolutionsJul 27 1994The mechanism of the initial inflation of the universe is based on gravitationally coupled scalar fields $\phi$. Various scenarios are distinguished by the choice of an {\it effective self--interaction potential} $U(\phi)$ which simulates a {\it temporarily} ... More
Boson Stars: Early History and Recent ProspectsJan 19 1998Boson stars are descendants of the so-called geons of Wheeler, except that they are built from scalar particles instead of electromagnetic fields. If scalar fields exist in nature, such localized configurations kept together by their self-generated gravitational ... More
A rate-independent model for the isothermal quasi-static evolution of shape-memory materialsAug 31 2007This note addresses a three-dimensional model for isothermal stress-induced transformation in shape-memory polycrystalline materials. We treat the problem within the framework of the energetic formulation of rate-independent processes and investigate ... More
Universal Broadening of Zero Modes: A General Framework and IdentificationFeb 05 2019May 14 2019We consider the smallest eigenvalues of perturbed Hermitian operators with zero modes, either topological or system specific. To leading order for small generic perturbation we show that the corresponding eigenvalues broaden to a Gaussian random matrix ... More
BV solutions and viscosity approximations of rate-independent systemsOct 18 2009In the nonconvex case solutions of rate-independent systems may develop jumps as a function of time. To model such jumps, we adopt the philosophy that rate independence should be considered as limit of systems with smaller and smaller viscosity. For the ... More
Global existence results for viscoplasticity at finite strainSep 28 2016We study a model for rate-dependent gradient plasticity at finite strain based on the multiplicative decomposition of the strain tensor, and investigate the existence of global-in-time solutions to the related PDE system. We reveal its underlying structure ... More
Circular-Polarization Dependent Cyclotron Resonance in Large-Area Graphene in Ultrahigh Magnetic FieldsOct 20 2011Jan 14 2012Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 um, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular-polarization dependent studies ... More
Pressure Evolution of a Field Induced Fermi Surface Reconstruction and of the Neel Critical Field in CeIn3Mar 30 2009We report high-pressure skin depth measurements on the heavy fermion material CeIn3 in magnetic fields up to 64 T using a self-resonant tank circuit based on a tunnel diode oscillator. At ambient pressure, an anomaly in the skin depth is seen at 45 T. ... More
A spin-wave frequency doubler by domain wall oscillationFeb 13 2009We present a new mechanism for spin-wave excitation using a pinned domain wall which is forced to oscillate at its eigenfrequency and radiates spin waves. The domain wall acts as a frequency doubler, as the excited spin waves have twice the frequency ... More
Multilevel Monte Carlo for Reliability TheorySep 01 2016As the size of engineered systems grows, problems in reliability theory can become computationally challenging, often due to the combinatorial growth in the cut sets. In this paper we demonstrate how Multilevel Monte Carlo (MLMC) - a simulation approach ... More
Note on A. Barbour's paper on Stein's method for diffusion approximationsFeb 10 2017Apr 15 2017In (Barbour, 1990) foundations for diffusion approximation via Stein's method are laid. This paper has been cited more than 130 times and is a cornerstone in the area of Stein's method. A semigroup argument is used therein to solve a Stein equation for ... 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
The Electromagnetic Green's Function for Layered Topological InsulatorsSep 10 2015The dyadic Green's function of the inhomogeneous vector Helmholtz equation describes the field pattern of a single frequency point source. It appears in the mathematical description of many areas of electromagnetism and optics including both classical ... More
Dramatic Raman Gain Suppression in the Vicinity of the Zero Dispersion Point in Gas-Filled Hollow-Core Photonic Crystal FiberAug 26 2015In 1964 Bloembergen and Shen predicted that Raman gain could be suppressed if the rates of phonon creation and annihilation (by inelastic scattering) exactly balance. This is only possible if the momentum required for each process is identical, i.e., ... More
On smoothness of Black SaturnsJul 21 2010We prove smoothness of the domain of outer communications (d.o.c.) of the Black Saturn solutions of Elvang and Figueras. We show that the metric on the d.o.c. extends smoothly across two disjoint event horizons with topology R x S^3 and R x S^1 x S^2. ... More
A New Parareal Algorithm for Problems with Discontinuous SourcesMar 14 2018The Parareal algorithm allows to solve evolution problems exploiting parallelization in time. Its convergence and stability have been proved under the assumption of regular (smooth) inputs. We present and analyze here a new Parareal algorithm for ordinary ... More
Persistence in fluctuating environmentsMay 14 2010Understanding under what conditions interacting populations, whether they be plants, animals, or viral particles, coexist is a question of theoretical and practical importance in population biology. Both biotic interactions and environmental fluctuations ... More
Space-time diagrammaticsNov 07 2012Jan 20 2013We introduce a new class of two-dimensional diagrams, the \emph{projection diagrams}, as a tool to visualize the global structure of space-times. We construct the diagrams for several metrics of interest, including the Kerr-Newman - (anti) de Sitter family, ... More
An iterative technique for bounding derivatives of solutions of Stein equationsOct 09 2015Oct 20 2017We introduce a simple iterative technique for bounding derivatives of solutions of Stein equations $Lf=h-\mathbb{E}h(Z)$, where $L$ is a linear differential operator and $Z$ is the limit random variable. Given bounds on just the solutions or certain lower ... More
PIE: A Domain-Specific Language for Interactive Software Development PipelinesMar 27 2018Apr 19 2018Context. Software development pipelines are used for automating essential parts of software engineering processes, such as build automation and continuous integration testing. In particular, interactive pipelines, which process events in a live environment ... More
Robust permanence for ecological mapsMar 16 2016We consider ecological difference equations of the form $X_{t+1}^i =X_t^i A_i(X_t)$ where $X_t^i$ is a vector of densities corresponding to the subpopulations of species $i$ (e.g. subpopulations of different ages or living in different patches), $X_t=(X_t^1,X_t^2,\dots,X_t^m)$ ... More
Multipole solutions in metric--affine gravityApr 23 1998Above Planck energies, the spacetime might become non--Riemannian, as it is known fron string theory and inflation. Then geometries arise in which nonmetricity and torsion appear as field strengths, side by side with curvature. By gauging the affine group, ... More
Inflation, bifurcations of nonlinear curvature Lagrangians and dark energyApr 09 2007A possible equivalence of scalar dark matter, the inflaton, and modified gravity is analyzed. After a conformal mapping, the dependence of the effective Lagrangian on the curvature is not only singular but also bifurcates into several almost Einsteinian ... More