Results for "Mateusz Koren"

total 592took 0.12s
Volume reduction in large-N lattice gauge theories [with adjoint fermions]Dec 18 2013This work covers volume reduction in quantum field theories on a lattice at large $N$ (number of colors), as first described by Eguchi and Kawai in 1982. The volume reduction (or volume independence) means that the theory defined on an arbitrarily small ... More
SU(3) Yang Mills theory at small distances and fine latticesNov 06 2017We investigate the SU(3) Yang Mills theory at small gradient flow time and at short distances. Lattice spacings down to $a=0.015$ fm are simulated with open boundary conditions to allow topology to flow in and out. We study the behaviour of the action ... More
Screening in two-dimensional gauge theoriesDec 03 2012We analyze the problem of screening in 1+1 dimensional gauge theories. Using QED2 as a warm-up for the non-abelian models we show the mechanism of the string breaking, in particular the vanishing overlap of the Wilson loops to the broken-string ground ... More
Preliminary study of two-dimensional SU(N) Yang-Mills theory with adjoint matter by Hybrid Monte Carlo approachNov 20 2011Two-dimensional non-abelian quantum field models provide a useful laboratory for analytic and numerical investigations of quantum theories with gauge symmetry. They can exhibit various features, such as charge confinement, which are known from D=4 theories ... More
Magnetoresistance and gating effects in ultrathin NbN-$\rm Bi_2Se_3$ bilayersJun 29 2015Ultrathin $\rm Bi_2Se_3$-NbN bilayers comprise a simple proximity system of a topological insulator and an s-wave superconductor for studying gating effects on topological superconductors. Here we report on 3 nm thick NbN layers of weakly connected superconducting ... More
Proximity effects at the interface of a superconductor and a topological insulator in NbN - Bi_2Se_3 thin film bilayersSep 10 2014In a search for a simple proximity system of a topological insulator and a superconductor for studying the role of surface versus bulk effects by gating, we report here on a first step toward this goal, namely the choice of such a system and its characterization. ... More
Strongly suppressed superconducting proximity effect and ferromagnetism in trilayers of $\rm Bi_2Se_3$ / $\rm SrRuO_3$ / underdoped $\rm YBa_2Cu_3O_x$: A possible new platform for Majorana nano-electronicsFeb 11 2018Feb 15 2018We report properties of topological insulator - ferromagnet - superconductor trilayers comprised of thin films of 20 nm thick $\rm Bi_2Se_3$ on 10 nm $\rm SrRuO_3$ on 30 nm $\rm YBa_2Cu_3O_x$. As deposited trilayers are underdoped and have a superconductive ... More
Wilson loops with arbitrary chargesNov 24 2014We discuss how to implement, in lattice gauge theories, external charges which are not commensurate with an elementary gauge coupling. It is shown that an arbitrary, real power of a standard Wilson loop (or Polyakov line) can be defined and consistently ... More
Large-N reduction with two adjoint Dirac fermionsNov 04 2011We study the single site SU(N) lattice gauge theory with N_f=2 adjoint Wilson fermions for values of N up to 53. We determine the phase diagram of the theory as a function of the hopping parameter kappa and the inverse 't Hooft coupling b, searching for ... More
Large-N reduction in QCD with two adjoint Dirac fermionsJun 27 2011May 01 2012We use lattice simulations to study the single-site version of SU(N) lattice gauge theory with two flavors of Wilson-Dirac fermions in the adjoint representation, a theory whose large volume correspondent is expected to be conformal or nearly conformal. ... More
Proximity effects and pair currents in cuprate junctionsNov 16 2016Proximity effects and pair currents were measured in epitaxial trilayer \textit{c-axis} junctions comprise of a $PrBa_2Cu_3O_{7-\delta}$ barrier sandwiched in between an overdoped $Y_{0.94}Ca_{0.06}Ba_2Cu_3O_{7-\delta}$ and underdoped $YBa_2Cu_{2.7}Co_{0.3}O_y$ ... More
On non-trivial spectra of trivial gauge theoriesOct 24 2012Apr 10 2013In this Letter we point out that the analytic solution of the two dimensional U(1) gauge theory, on a finite lattice, reveals in the continuum limit the renowned Manton's spectrum of topological electric fluxes together with their effective hamiltonian ... More
Large-N reduction with adjoint Wilson fermionsDec 03 2012We analyze the large-N behavior of SU(N) lattice gauge theories with adjoint fermions by studying volume-reduced models, as pioneered by Eguchi and Kawai. We perform simulations on a single-site lattice for Nf = 1 and Nf = 2 Wilson Dirac fermions with ... More
HQET form factors for $B_s\to K\ellν$ decays beyond leading orderNov 03 2017Nov 25 2017We compute semi-leptonic $B_s$ decay form factors using Heavy Quark Effective Theory on the lattice. To obtain good control of the $1/m_b$ expansion, one has to take into account not only the leading static order but also the terms arising at $O(1/m_b)$: ... More
Glueball masses in 2+1 dimensional SU(N) gauge theories with twisted boundary conditionsNov 19 2014Nov 26 2014We analyze 2+1 dimensional Yang-Mills theory regularized on a lattice with twisted boundary conditions in the spatial directions. In previous work it was shown that the observables in the non-zero electric flux sectors obey the so-called $x$-scaling, ... More
The spectrum of 2+1 dimensional Yang-Mills theory on a twisted spatial torusJul 10 2018Aug 07 2018We compute and analyse the low-lying spectrum of 2+1 dimensional $SU(N)$ Yang-Mills theory on a spatial torus of size $l\times l$ with twisted boundary conditions. This paper extends our previous work \cite{Perez:2013dra}. In that paper we studied the ... More
Interface effects in d-wave superconductor-ferromagnet junctionsJun 01 2010Oct 07 2010Measurements of the differential conductance spectra of YBa2Cu3O7-SrRuO3 and YBa2Cu3O7-La0.67Ca_0.33MnO3 ramp-type junctions along the node and anti-node directions are reported. The results are consistent with a crossed Andreev reflection effect only ... More
Zero energy bound states in tunneling conductance spectra at the interface of an s-wave superconductor and a topological insulator in NbN-$Bi_2Se_3$-Au thin film junctionsJul 23 2012Oct 11 2012Measurements of conductance spectra in a superconductor - topological insulator - normal metal thin film junctions of NbN-$\rm Bi_2Se_3$-Au are reported. Junctions with ex-situ and in-situ prepared $\rm NbN-Bi_2Se_3$ interfaces were studied. At low temperatures, ... More
Observation of two Andreev-like energy scales in $La_{2-x}Sr_{x}CuO_4$ superconductor/normal-metal/superconductor junctionsJan 06 2011Conductance spectra measurements of highly transparent ramp-type junctions made of superconducting $La_{2-x}Sr_{x}CuO_4$ electrodes and non superconducting $La_{1.65}Sr_{0.35}CuO_4$ barrier are reported. At low temperatures below $T_c$, these junctions ... More
The Computational Power of Optimization in Online LearningApr 08 2015Jan 27 2016We consider the fundamental problem of prediction with expert advice where the experts are "optimizable": there is a black-box optimization oracle that can be used to compute, in constant time, the leading expert in retrospect at any point in time. In ... More
Optimal Algorithms for Ridge and Lasso Regression with Partially Observed AttributesAug 23 2011Nov 27 2012We consider the most common variants of linear regression, including Ridge, Lasso and Support-vector regression, in a setting where the learner is allowed to observe only a fixed number of attributes of each example at training time. We present simple ... More
Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of $La_{1.9}Sr_{0.1}CuO_4$ - $La_{0.67}Ca_{0.33}MnO_3$ - $La_{1.9}Sr_{0.1}CuO_4$Jul 05 2011Transport and Conductance spectra measurements of ramp-type junctions made of cuprate superconducting $La_{1.9}Sr_{0.1}CuO_4$ electrodes and a manganite ferromagnetic $La_{0.67}Ca_{0.33}MnO_3$ barrier are reported. At low temperatures below $T_c$, the ... More
Signature of a crossed Andreev reflection effect (CARE) in the magnetic response of YBCO junctions with the itinerant ferromagnet SrRuO_3Aug 31 2005Magnetic properties of SFS and SF ramp-type junctions with $YBa_2Cu_3O_{7-\delta}$ (YBCO) electrodes (S), and the itinerant ferromagnet $SrRuO_3$ (SRO - F), were investigated. We looked for a crossed Andreev reflection effect (CARE) in which an electron ... More
Linear Regression with Limited ObservationJun 18 2012We consider the most common variants of linear regression, including Ridge, Lasso and Support-vector regression, in a setting where the learner is allowed to observe only a fixed number of attributes of each example at training time. We present simple ... More
A Linear-Time Algorithm for Trust Region ProblemsJan 27 2014We consider the fundamental problem of maximizing a general quadratic function over an ellipsoidal domain, also known as the trust region problem. We give the first provable linear-time (in the number of non-zero entries of the input) algorithm for approximately ... More
Pairing and the phase diagram of the normal coherence length $ξ_N(T,x)$ above $T_c$ of $La_{2-x}Sr_xCuO_4$ thin films probed by the Josephson effectNov 10 2013Apr 30 2014Critical currents $I_c$ were measured in Superconducting - normal - superconducting SNS c-axis junctions, where S was optimally doped $YBa_2Cu_3O_{7-\delta}$ below $T_c$ (90 K) and N was $La_{2-x}Sr_xCuO_4$ above its $T_c$ ($<$25 K) but in the pseudogap ... More
Conventional proximity effect in bilayers of superconducting underdoped $La_{1.88}Sr_{0.12}CuO_4$ islands coated with non superconducting overdoped $La_{1.65}Sr_{0.35}CuO_4$Apr 13 2009Following a recent study by our group in which a large $T_c$ enhancement was reported in bilayers of the non-superconducting $La_{1.65}Sr_{0.35}CuO_4$ and superconducting $La_{1.88}Sr_{0.12}CuO_4$ films [Phys. Rev. Lett. \textbf{101}, 057005 (2008)], ... More
Nighttime Light, Superlinear Growth, and Economic Inequalities at the Country LevelOct 30 2018Research has highlighted relationships between size and scaled growth across a large variety of biological and social organisms, ranging from bacteria, through animals and plants, to cities an companies. Yet, heretofore, identifying a similar relationship ... More
Investigating Bimodal Clustering in Human MobilityNov 03 2009We apply a simple clustering algorithm to a large dataset of cellular telecommunication records, reducing the complexity of mobile phone users' full trajectories and allowing for simple statistics to characterize their properties. For the case of two ... More
On the Empirical Importance of the Conditional Skewness Assumption in Modelling the Relationship Between Risk and ReturnDec 26 2007May 06 2008The main goal of this paper is an application of Bayesian inference in testing the relation between risk and return on the financial instruments. On the basis of the Intertemporal CAPM model we built a general sampling model suitable in analysing such ... More
Finite phylogenetic complexity of $Z_p$ and invariants for $Z_3$Aug 17 2015Aug 20 2016We study phylogenetic complexity of finite abelian groups - an invariant introduced by Sturmfels and Sullivant. The invariant is hard to compute - so far it was only known for $Z_2$, in which case it equals $2$. We prove that phylogenetic complexity of ... More
Spectral analysis of subordinate Brownian motions in half-lineJun 02 2010Oct 22 2011We study one-dimensional Levy processes with Levy-Khintchine exponent psi(xi^2), where psi is a complete Bernstein function. These processes are subordinate Brownian motions corresponding to subordinators, whose Levy measure has completely monotone density; ... More
Observation of two distinct pairs fluctuation lifetimes and supercurrents in the pseudogap regime of cuprate junctionsSep 06 2016Pairs fluctuation supercurrents and inverse lifetimes were measured on epitaxial c-axis junctions of the cuprates in the pseudogap regime, with a $PrBa_2Cu_3O_{7-\delta}$ barrier sandwiched in between two $YBa_2Cu_3O_{7-\delta}$ or doped $YBa_2Cu_3O_y$ ... More
Nearly irreducibility of polynomials and the Newton diagramsMay 06 2019Let f be a polynomial in two complex variables. We say that f is nearly irreducible if any two nonconstant polynomial factors of f have a common zero. In the paper we give a criterion of nearly irreducibility for a given polynomial f in terms of its Newton ... More
Coupling and exponential ergodicity for stochastic differential equations driven by Lévy processesSep 29 2015Oct 28 2015We present a novel idea for a coupling of solutions of stochastic differential equations driven by L\'{e}vy noise, inspired by some results from the optimal transportation theory. Then we use this coupling to obtain exponential contractivity of the semigroups ... More
Characterizing compact families via the Laplace transformMay 13 2019In 1985, Robert L. Pego characterized compact families in $L^2(\reals)$ in terms of the Fourier transform. It took nearly 30 years to realize that Pego's result can be proved in a wider setting of locally compact abelian groups (works of G\'orka and Kostrzewa). ... More
Reflected BSDEs with general filtration and two completely separated barriersNov 21 2016We consider reflected backward stochastic differential equations, with two barriers, defined on probability spaces equipped with filtration satisfying only the usual assumptions of right continuity and completeness. As for barriers we assume that there ... More
Constructive degree bounds for group-based modelsJul 04 2012Jun 04 2013Group-based models arise in algebraic statistics while studying evolution processes. They are represented by embedded toric algebraic varieties. Both from the theoretical and applied point of view one is interested in determining the ideals defining the ... More
Systems of BSDEs with oblique reflection and related optimal switching problemsDec 14 2017Oct 03 2018We consider systems of backward stochastic differential equations with c\`adl\`ag upper barrier $U$ and oblique reflection from below driven by an increasing continuous function $H$. Our equations are defined on general probability spaces with a filtration ... More
Continuum limit of the leading order HQET form factor in $B_s \to K\ellν$ decaysJan 17 2016Jun 02 2016We discuss the computation of form factors for semi-leptonic decays of $\rm B$-, $\rm B_s$- mesons in lattice QCD. Considering in particular the example of the static $\rm B_s$ form factors we demonstrate that after non-perturbative renormalization the ... More
Exact Pollard-like internal water wavesDec 01 2018In this paper we construct a new solution which represents Pollard-like three-dimensional nonlinear geophysical internal water waves. The Pollard-like solution includes the effects of the rotation of Earth and describes the internal water wave which exists ... More
Reflected BSDEs with general filtration and two completely separated barriersNov 21 2016Oct 31 2018We consider reflected backward stochastic differential equations, with two barriers, defined on probability spaces equipped with filtration satisfying only the usual assumptions of right continuity and completeness. As for barriers we assume that there ... More
Extraction of bare Form Factors for $\mathrm B_\mathrm s \to \mathrm K \ell ν$ Decays in non-perturbative HQETMar 14 2019We discuss the extraction of the ground state $\langle \mathrm{K} ({\bf p})|V_\mu(0)|\mathrm{B} ({\bf 0})\rangle$ matrix elements from Euclidean lattice correlation functions. The emphasis is on the elimination of excited state contributions. Two typical ... More
A mimetic spectral element solver for the Grad-Shafranov equationDec 18 2015Apr 07 2016In this work we present a robust and accurate arbitrary order solver for the fixed-boundary plasma equilibria in toroidally axisymmetric geometries. To achieve this we apply the mimetic spectral element formulation presented in [56] to the solution of ... More
Exploring the Nonlinear Cloud and Rain EquationAug 24 2016Jan 10 2017Marine stratocumulus cloud decks are regarded as the reflectors of the climate system, returning back to space a significant part of the income solar radiation, thus cooling the atmosphere. Such clouds can exist in two stable modes, open and closed cells, ... More
Critical current measurements in superconductor - ferromagnet - superconductor junctions of $YBa_2Cu_3O_y$-$SrRuO_3$-$YBa_2Cu_3O_y$: No evidence for a dominant proximity induced triplet superconductivity in the ferromagnetic barrierJul 05 2011Transport measurements in ramp-type junctions of $YBa_2Cu_3O_y-SrRuO_3-YBa_2Cu_3O_y$ with $T_c$ values of either 80-90 K or 60-70 K are reported. In both type of junctions but without a barrier ("shorts"), the supercurrent densities at 4.2 K reached 7.5 ... More
Recommender Systems for the Conference Paper Assignment ProblemJun 22 2009Conference paper assignment, i.e., the task of assigning paper submissions to reviewers, presents multi-faceted issues for recommender systems research. Besides the traditional goal of predicting `who likes what?', a conference management system must ... More
Aerosol Effect on the Mobility of Cloud DropletsJul 02 2015Oct 19 2015Cloud droplet mobility is referred to here as a measure of the droplets ability to move with ambient air. We claim that an important part of the aerosol effect on convective clouds is driven by changes in droplet mobility. We show that the mass-weighted ... More
Exploring strong-field deviations from general relativity via gravitational wavesApr 08 2019Two new observational windows have been opened to strong gravitational physics: gravitational waves, and very long baseline interferometry. This suggests observational searches for new phenomena in this regime, and in particular for those necessary to ... More
Magnetoresistance of Junctions made of Underdoped YBCO Separated by a Ga-doped YBCO BarrierFeb 10 2005We report magnetoresistance measurements of ramp type superconductor-normal-superconductor (SNS) junctions. The junctions consist of underdoped $YBa_{2}Cu_{3}O_y$ (YBCO) electrodes separated by a barrier of $YBa_{2}Cu_{2.6}Ga_{0.4}O_y$. We observe a large ... More
An adaptive minimum spanning tree multi-element method for uncertainty quantification of smooth and discontinuous responsesMar 19 2018A novel approach for non-intrusive uncertainty propagation is proposed. Our approach overcomes the limitation of many traditional methods, such as generalised polynomial chaos methods, which may lack sufficient accuracy when the quantity of interest depends ... More
Efficiency of pair formation in a model societyMay 08 2006Aug 10 2006In a recent paper a set of differential equations was proposed to describe a social process, where pairs of partners emerge in a community. The choice was performed on a basis of attractive resources and of random initial preferences. An efficiency of ... More
The role of dry mergers for the formation and evolution of brightest cluster galaxiesFeb 02 2009Using a resimulation technique, we perform high-resolution cosmological simulations of dry mergers in a massive galaxy cluster identified in the Millennium Run. Our initial conditions include well resolved compound galaxy models consisting of dark matter ... More
Boundary Harnack Inequality for alpha-harmonic functions on the Sierpiński triangleJul 04 2009We prove an uniform boundary Harnack inequality for nonnegative functions harmonic with respect to $\alpha$-stable process on the Sierpi{\'n}ski triangle, where $\alpha \in (0, 1)$. Our result requires no regularity assumptions on the domain of harmonicity. ... More
Spectral analysis of stable processes on the positive half-lineSep 22 2015We study the spectral expansion of the semigroup of a general stable process killed on the first exit from the positive half-line. Starting with the Wiener-Hopf factorization we obtain the q-resolvent density for the killed process, from which we derive ... More
Obstructions to combinatorial formulas for plethysmJul 25 2015Feb 26 2016Motivated by questions of Mulmuley and Stanley we investigate quasi-polynomials arising in formulas for plethysm. We demonstrate, on the examples of $S^3(S^k)$ and $S^k(S^3)$, that these need not be counting functions of inhomogeneous polytopes of dimension ... More
Data-Driven Segmentation of Post-mortem Iris ImagesJul 11 2018This paper presents a method for segmenting iris images obtained from the deceased subjects, by training a deep convolutional neural network (DCNN) designed for the purpose of semantic segmentation. Post-mortem iris recognition has recently emerged as ... More
Effective constructions in plethysms and Weintraub's conjectureJul 24 2012We give a short proof of Weintraub's conjecture by constructing explicit highest weight vectors in the symmetric power of an even exterior power.
On the First Passage Time and Leapover Properties of Levy MotionsNov 27 2006We investigate two coupled properties of Levy stable random motions: The first passage times (FPTs) and the first passage leapovers (FPLs). While, in general, the FPT problem has been studied quite extensively, the FPL problem has hardly attracted any ... More
Correlation of tunneling spectra with surface nano-morphology and doping in thin YBa2Cu3O7-delta filmsMar 28 2001Tunneling spectra measured on thin epitaxial YBa2Cu3O7-delta films are found to exhibit strong spatial variations, showing U and V-shaped gaps as well as zero bias conductance peaks typical of a d-wave superconductor. A full correspondence is found between ... More
Measurement of the vortex mass in a superconducting filmSep 11 2011We have combined high resolution magneto-optical imaging with an ultra-fast heating/cooling technique to measure the movement of individual vortices in a superconducting film. The motion took place while the film was heated close to $T_c$, where pinning ... More
Observation of a common symmetry for the pseudogap and the superconducting order parameter near the surface of underdoped YBCOJun 24 2003Measurements of the angular dependence of conductance spectra in the a-b plane of underdoped YBCO junctions are reported. At zero magnetic field the superconducting gap shows a |d+is|-like symmetry. Application of a magnetic field strongly suppresses ... More
Observation of Magnetic Flux Generated Spontaneously During a Rapid Quench of Superconducting FilmsApr 16 2003We report observations of spontaneous formation of magnetic flux lines during a rapid quench of YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ films through T$_{c}$. This effect is predicted according to the Kibble-Zurek mechanism of creation of topological defects ... More
Chasing Ghosts: Competing with Stateful PoliciesJul 29 2014We consider sequential decision making in a setting where regret is measured with respect to a set of stateful reference policies, and feedback is limited to observing the rewards of the actions performed (the so called "bandit" setting). If either the ... More
Learning Linear-Quadratic Regulators Efficiently with only $\sqrt{T}$ RegretFeb 17 2019Feb 23 2019We present the first computationally-efficient algorithm with $\widetilde O(\sqrt{T})$ regret for learning in Linear Quadratic Control systems with unknown dynamics. By that, we resolve an open question of Abbasi-Yadkori and Szepesv\'ari (2011) and Dean, ... More
Incentivizing the Dynamic Workforce: Learning Contracts in the Gig-EconomyNov 16 2018In principal-agent models, a principal offers a contract to an agent to perform a certain task. The agent exerts a level of effort that maximizes her utility. The principal is oblivious to the agent's chosen level of effort, and conditions her wage only ... More
Tight Bounds for Bandit Combinatorial OptimizationFeb 24 2017We revisit the study of optimal regret rates in bandit combinatorial optimization---a fundamental framework for sequential decision making under uncertainty that abstracts numerous combinatorial prediction problems. We prove that the attainable regret ... More
Online Learning with Feedback Graphs Without the GraphsMay 23 2016We study an online learning framework introduced by Mannor and Shamir (2011) in which the feedback is specified by a graph, in a setting where the graph may vary from round to round and is \emph{never fully revealed} to the learner. We show a large gap ... More
The poset of rational conesJun 07 2016Jun 14 2016We introduce a natural partial order on the set Cones(d) of rational cones in R^d. The poset NPol(d-1) of normal polytopes in R^{d-1} embeds into Cones(d) via the homogenization map. Informally Cones(d) can be thought of as a minimal smooth extension ... More
Potential kernels, probabilities of hitting a ball, harmonic functions and the boundary Harnack inequality for unimodal Lévy processesNov 30 2016In the first part of this article, we prove two-sided estimates of hitting probabilities of balls, the potential kernel and the Green function for a ball for general isotropic unimodal L\'evy processes. Our bounds are sharp under the absence of the Gaussian ... More
On the toric ideal of a matroidFeb 21 2013Mar 30 2014Describing minimal generating set of a toric ideal is a well-studied and difficult problem. In 1980 White conjectured that the toric ideal associated to a matroid is equal to the ideal generated by quadratic binomials corresponding to symmetric exchanges. ... More
Plethysm and lattice point countingAug 25 2014Aug 12 2015We apply lattice point counting methods to compute the multiplicities in the plethysm of $GL(n)$. Our approach gives insight into the asymptotic growth of the plethysm and makes the problem amenable to computer algebra. We prove an old conjecture of Howe ... More
Extension technique for complete Bernstein functions of the Laplace operatorJul 08 2017We discuss representation of certain functions of the Laplace operator $\Delta$ as Dirichlet-to-Neumann maps for appropriate elliptic operators in half-space. A classical result identifies $(-\Delta)^{1/2}$, the square root of the $d$-dimensional Laplace ... More
Models of Positive TruthDec 01 2017This paper is a follow-up to "Models of PT${}^-$ with internal induction for total formulae." We give a strenghtening of the main result on the semantical non-conservativity of the theory of PT${}^-$ with internal induction for total formulae (PT${}^- ... More
Models of Weak Theories of TruthDec 01 2017In the following paper we propose a model-theoretical way of comparing the "strength" of various truth theories which are conservative over PA. Let $\mathfrak{Th}$ denote the class of models of PA which admit an expansion to a model of theory Th. We show ... More
Finite phylogenetic complexity and combinatorics of tablesJun 23 2016Sep 07 2016We prove that the phylogenetic complexity -- an invariant introduced by Sturmfels and Sullivant -- of any finite abelian group is finite.
Non-normal very ample polytopes - constructions and examplesJun 16 2014Jul 30 2014We present a method of constructing non-normal very ample polytopes as a segmental fibration of unimodular graph polytopes. In many cases we explicitly compute their invariants - Hilbert function, Ehrhart polynomial, gap vector. In particular, we answer ... More
Almost Periodically Correlated Time Series in Business Fluctuations AnalysisApr 21 2012We propose a non-standard subsampling procedure to make formal statistical inference about the business cycle, one of the most important unobserved feature characterising fluctuations of economic growth. We show that some characteristics of business cycle ... More
Hangable GraphsDec 24 2015Let $G=(V_G,E_G)$ be a connected graph. The distance $d_G(u,v)$ between vertices $u$ and $v$ in $G$ is the length of a shortest $u-v$ path in $G$. The eccentricity of a vertex $v$ in $G$ is the integer $e_G(v)= \max\{ d_G(v,u) \colon u\in V_G\}$. The ... More
Secants of minuscule and cominuscule minimal orbitsJan 09 2014We study the geometry of the secant and tangential variety of a cominuscule and minuscule variety, e.g. a Grassmannian or a spinor variety. Using methods inspired by statistics we provide an explicit local isomorphism with a product of an affine space ... More
Multiple positive solutions of parabolic systems with nonlinear, nonlocal initial conditionsJul 28 2014Aug 05 2016In this paper we study the existence, localization and multiplicity of positive solutions for parabolic systems with nonlocal initial conditions. In order to do this, we extend an abstract theory that was recently developed by the authors jointly with ... More
Obstructions to combinatorial formulas for plethysmJul 25 2015Feb 09 2018Motivated by questions of Mulmuley and Stanley we investigate quasi-polynomials arising in formulas for plethysm. We demonstrate, on the examples of $S^3(S^k)$ and $S^k(S^3)$, that these need not be counting functions of inhomogeneous polytopes of dimension ... More
Potential kernels, probabilities of hitting a ball, harmonic functions and the boundary Harnack inequality for unimodal Lévy processesNov 30 2016Mar 29 2017In the first part of this article, we prove two-sided estimates of hitting probabilities of balls, the potential kernel and the Green function for a ball for general isotropic unimodal L\'evy processes. Our bounds are sharp under the absence of the Gaussian ... More
Ab initio and phenomenological studies of the static response of neutron matterAug 11 2016We investigate the problem of periodically modulated strongly interacting neutron matter. We carry out ab initio non-perturbative auxiliary-field diffusion Monte Carlo calculations using an external sinusoidal potential in addition to phenomenological ... More
Transportation inequalities for non-globally dissipative SDEs with jumps via Malliavin calculus and couplingOct 21 2016By using the mirror coupling for solutions of SDEs driven by pure jump L\'evy processes, we extend some transportation and concentration inequalities, which were previously known only in the case where the coefficients in the equation satisfy a global ... More
Minimal Hermite-type eigenbasis of the discrete Fourier transformJun 27 2017There exist many ways to build an orthonormal basis of $\mathbb{R}^N$, consisting of the eigenvectors of the discrete Fourier transform (DFT). In this paper we show that there is only one such orthonormal eigenbasis of the DFT that is optimal in the sense ... More
On the $l^p$-norm of the discrete Hilbert transformSep 21 2017Oct 18 2017Using a representation of the discrete Hilbert transform in terms of martingales arising from Doob $h$-processes, we prove that its $l^p$-norm, $1<p<\infty$, is bounded above by the $L^p$-norm of the continuous Hilbert transform. Together with the already ... More
The poset of rational conesJun 07 2016Jun 13 2017We introduce a natural partial order on the set Cones(d) of rational cones in R^d. The poset NPol(d-1) of normal polytopes in R^{d-1} embeds into Cones(d) via the homogenization map. The order in Cones(d) is conjecturally the inclusion order. We prove ... More
Coupling and exponential ergodicity for stochastic differential equations driven by Lévy processesSep 29 2015Apr 29 2017We present a novel idea for a coupling of solutions of stochastic differential equations driven by L\'{e}vy noise, inspired by some results from the optimal transportation theory. Then we use this coupling to obtain exponential contractivity of the semigroups ... More
Spectral analysis of stable processes on the positive half-lineSep 22 2015Jan 02 2018We study the spectral expansion of the semigroup of a general stable process killed on the first exit from the positive half-line. Starting with the Wiener-Hopf factorization we obtain the q-resolvent density for the killed process, from which we derive ... More
Quantum vortex tunneling in $YBa_2Cu_3O_{7-δ}$ thin filmsJul 17 2007Cuprate films offer a unique opportunity to observe vortex tunneling effects, due to their unusually low superfluid density and short coherence length. Here, we measure the magnetoresistance (\textit{MR}) due to vortex motion of a long meander line of ... More
Appearance of spontaneous macroscopic magnetization at the superconducting transition of YBCOJan 05 2000Jan 25 2000We report the observation of a weak spontaneous magnetic field appearing at the transition temperature of $\rm YBa_2Cu_3O_{7-\delta}$ into the superconducting state. The effect is observed in 14 out of 15 epitaxial films grown on different substrates ... More
Oracle-Based Robust Optimization via Online LearningFeb 25 2014Robust optimization is a common framework in optimization under uncertainty when the problem parameters are not known, but it is rather known that the parameters belong to some given uncertainty set. In the robust optimization framework the problem solved ... More
Long range proximity effect in La2/3Ca1/3MnO3 (LCMO)/(100)YBa2Cu3O7-delta (YBCO) ferromagnet/superconductor bilayers: Evidence for induced triplet superconductivity in the ferromagnetOct 03 2010Scanning tunneling spectroscopy measurements conducted on epitaxially grown bilayers of half-metallic ferromagnetic La2/3Ca1/3MnO3 (LCMO) on superconducting (SC) (100)YBa2Cu3O7-delta (YBCO) reveal long-range penetration of superconducting order into the ... More
Anomalous proximity effect in gold coated (110) $YBa_2Cu_3O_{7-δ}$ films: Penetration of the Andreev bound statesAug 28 2004Aug 31 2004Scanning tunneling spectroscopy of (110) $YBa_2Cu_3O_{7-\delta}/Au$ bi-layers reveal a proximity effect markedly different from the conventional one. While proximity-induced mini-gaps rarely appear in the Au layer, the Andreev bound states clearly penetrate ... More
Online Learning with Composite Loss FunctionsMay 18 2014We study a new class of online learning problems where each of the online algorithm's actions is assigned an adversarial value, and the loss of the algorithm at each step is a known and deterministic function of the values assigned to its recent actions. ... More
Evidence for Induced Magnetization in Superconductor-Ferromagnet Hetero-structures: a Scanning Tunnelling Spectroscopy StudyFeb 24 2009We performed scanning tunneling spectroscopy of c-axis oriented YBCO films on top of which ferromagnetic SRO islands were grown epitaxially in-situ. When measured on the ferromagnetic islands, the density of states exhibits small gap-like features consistent ... More
Penetration of Andreev bound states into the ferromagnet in a SrRuO$_{3}$/(110)YBa$_2$Cu$_3$O$_{7-δ}$ bilayer: a scanning tunneling spectroscopy studyJun 28 2007Scanning tunneling spectroscopy of thin epitaxial $SrRuO_{3}/(110)YBa_2Cu_3O_{7-\delta}$ ferromagnet/superconductor bilayers, reveal a clear penetration of the Andreev bound states into the ferromagnetic layer. The penetration is manifested in the density ... More
Signature of proximity induced triplet superconductivity in junctions made of the doped topological insulator $\rm Bi_2Se_3$ and the s-wave superconductor NbNMar 04 2013Oct 07 2013Thin film junctions and bilayers of the doped topological insulator $\rm Bi_2Se_3$ and the s-wave superconductor NbN were found to exhibit conductance spectra with prominent zero bias and coherence peaks. Various tunneling models with different pair potentials ... More
Distributed Exploration in Multi-Armed BanditsNov 04 2013We study exploration in Multi-Armed Bandits in a setting where $k$ players collaborate in order to identify an $\epsilon$-optimal arm. Our motivation comes from recent employment of bandit algorithms in computationally intensive, large-scale applications. ... More