Results for "Robert Kozma"

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Reinforced random walkAug 01 2012A survey of reinforced random walk, with emphasis on the linear case.
Minimum Average Distance TriangulationsDec 08 2011Jun 20 2012We study the problem of finding a triangulation T of a planar point set S such as to minimize the expected distance between two points x and y chosen uniformly at random from S. By distance we mean the length of the shortest path between x and y along ... More
Locally Connected Spiking Neural Networks for Unsupervised Feature LearningApr 12 2019In recent years, Spiking Neural Networks (SNNs) have demonstrated great successes in completing various Machine Learning tasks. We introduce a method for learning image features by \textit{locally connected layers} in SNNs using spike-timing-dependent ... More
New Lower Bound for the Optimal Ball Packing Density in Hyperbolic 4-spaceJan 23 2014Aug 22 2014In this paper we consider ball packings in $4$-dimensional hyperbolic space. We show that it is possible to exceed the conjectured $4$-dimensional realizable packing density upper bound due to L. Fejes T\'oth (Regular Figures, 1964). We give seven examples ... More
Structure and Visualization of Optimal Horoball Packings in $3$-dimensional Hyperbolic SpaceJan 14 2016Four packings of hyperbolic 3-space are known to yield the optimal packing density of $0.85328\dots$. They are realized in the regular tetrahedral and cubic Coxeter honeycombs with Schl\"afli symbols $\{3,3,6 \}$ and $\{4,3,6\}$. These honeycombs are ... More
New Horoball Packing Density Lower Bound in Hyperbolic 5-spaceSep 13 2018We describe the optimal horoball packings of asymptotic Koszul type Coxeter simplex tilings of $5$-dimensional hyperbolic space where the symmetries of the packings are generated by Coxeter groups. We find that the optimal horoball packing density of ... More
Optimally Dense Packings for Fully Asymptotic Coxeter Tilings by Horoballs of Different TypesJul 05 2010Jul 12 2012The goal of this paper to determine the optimal horoball packing arrangements and their densities for all four fully asymptotic Coxeter tilings (Coxeter honeycombs) in hyperbolic 3-space $\mathbb{H}^3$. Centers of horoballs are required to lie at vertices ... More
A note about critical percolation on finite graphsSep 24 2009Nov 16 2009In this note we study the geometry of the largest component C_1 of critical percolation on a finite graph G which satisfies the finite triangle condition, defined by Borgs et al. There it is shown that this component is of size n^{2/3}, and here we show ... More
Late Spectral Evolution of SN 1987A: II. Line EmissionDec 17 1997Using the temperature and ionization calculated in our previous paper, we model the spectral evolution of SN 1987A. The IR-catastrophe is seen in the metal lines as a transition from thermal to non-thermal excitation, most clearly in the [O I] 6300, 6364 ... More
Thermodynamic Model of Criticality in the Cortex Based On EEG/ECOG DataJun 06 2012Criticality in the cortex emerges from the seemingly random interaction of microscopic components and produces higher cognitive functions at mesoscopic and macroscopic scales. Random graphs and percolation theory provide natural means to de- scribe critical ... More
Irreducible polynomials of bounded heightOct 14 2017The goal of this paper is to prove that a random polynomial with i.i.d. random coefficients taking values uniformly in $\{1,\ldots, 210\}$ is irreducible with probability tending to $1$ as the degree tends to infinity. Moreover, we prove that the Galois ... More
STDP Learning of Image Patches with Convolutional Spiking Neural NetworksAug 24 2018Spiking neural networks are motivated from principles of neural systems and may possess unexplored advantages in the context of machine learning. A class of \textit{convolutional spiking neural networks} is introduced, trained to detect image features ... More
Bootstrap percolation on a random graph coupled with a latticeJul 29 2015Nov 12 2015In this paper a random graph model $G_{\mathbb{Z}^2_N,p_d}$ is introduced, which is a combination of fixed torus grid edges in $(\mathbb{Z}/N \mathbb{Z})^2$ and some additional random ones. The random edges are called long, and the probability of having ... More
Complete stability analysis of a heuristic ADP control designAug 15 2013Jul 28 2015This paper provides new stability results for Action-Dependent Heuristic Dynamic Programming (ADHDP), using a control algorithm that iteratively improves an internal model of the external world in the autonomous system based on its continuous interaction ... More
The 44Ti-powered spectrum of SN 1987AMar 18 2011May 25 2011SN 1987A provides a unique opportunity to study the evolution of a supernova from explosion into very late phases. Due to the rich chemical structure, the multitude of physical process involved, and extensive radiative transfer effects, detailed modeling ... More
Upper bounds on the percolation correlation lengthFeb 08 2019We study the size of the near-critical window for Bernoulli percolation on $\mathbb Z^d$. More precisely, we use a quantitative Grimmett-Marstrand theorem to prove that the correlation length, both below and above criticality, is bounded from above by ... More
Improved robustness of reinforcement learning policies upon conversion to spiking neuronal network platforms applied to ATARI gamesMar 26 2019Various implementations of Deep Reinforcement Learning (RL) demonstrated excellent performance on tasks that can be solved by trained policy, but they are not without drawbacks. Deep RL suffers from high sensitivity to noisy and missing input and adversarial ... More
Unsupervised Learning with Self-Organizing Spiking Neural NetworksJul 24 2018We present a system comprising a hybridization of self-organized map (SOM) properties with spiking neural networks (SNNs) that retain many of the features of SOMs. Networks are trained in an unsupervised manner to learn a self-organized lattice of filters ... More
BindsNET: A machine learning-oriented spiking neural networks library in PythonJun 04 2018Dec 10 2018The development of spiking neural network simulation software is a critical component enabling the modeling of neural systems and the development of biologically inspired algorithms. Existing software frameworks support a wide range of neural functionality, ... More
Faster and simpler algorithms for finding large patterns in permutationsFeb 23 2019Apr 16 2019Permutation patterns and pattern avoidance have been intensively studied in combinatorics and computer science, going back at least to the seminal work of Knuth on stack-sorting (1968). Perhaps the most natural algorithmic question in this area is deciding ... More
Bessel Functions in Mass Action. Modeling of Memories and RemembrancesJun 14 2015Data from experimental observations of a class of neurological processes (Freeman K-sets) present functional distribution reproducing Bessel function behavior. We model such processes with couples of damped/amplified oscillators which provide time dependent ... More
Faster and simpler algorithms for finding large patterns in permutationsFeb 23 2019Permutation patterns and pattern avoidance have been intensively studied in combinatorics and computer science, going back at least to the seminal work of Knuth on stack-sorting (1968). Perhaps the most natural algorithmic question in this area is deciding ... More
Percolation, Perimetry, PlanaritySep 10 2005Apr 11 2006Let G be a planar graph with polynomial growth and isoperimetric dimension bigger than 1. Then the critical p for Bernoulli percolation on G satisfies p<1.
On removing one point from a compact spaceApr 15 2005If B is a compact space and B\{pt} is Lindelof then B^k\{pt} is star-Linedlof for every cardinality k. If B\{pt} is compact then B^k\{pt} is discretely star-Lindelof. In particular, this gives new examples of Tychonoff discretely star-Lindelof spaces ... More
Random homeomorphisms and Fourier expansions - the pointwise behaviorNov 02 2005Let phi be a Dubins-Freedman random homeomorphism on [0,1] derived from the base measure uniform on the vertical line x=1/2, and let f be a periodic function satisfying that |f(x)-f(0)| = o(1/log log log 1/x). Then the Fourier expansion of f composed ... More
Effective medium approximation of ellipsometric response from random surface roughness simulated by finite-element methodFeb 26 2019We used numerical simulations based on the finite element method (FEM) to calculate both the amplitude and phase information of the scattered electric field from random rough surfaces, which can be directly compared to ellipsometric measurements and effective ... More
Percolation of finite clusters and infinite surfacesMar 07 2013Oct 16 2013Two related issues are explored for bond percolation on the d-dimensional cubic lattice (with d > 2) and its dual plaquette process. Firstly, for what values of the parameter p does the complement of the infinite open cluster possess an infinite component? ... More
Hamiltonicity below Dirac's conditionFeb 05 2019Dirac's theorem (1952) is a classical result of graph theory, stating that an $n$-vertex graph ($n \geq 3$) is Hamiltonian if every vertex has degree at least $n/2$. Both the value $n/2$ and the requirement for every vertex to have high degree are necessary ... More
Modeling supernova emission at late timesMar 26 1999We compare model calculations with observations of supernovae at late times to infer the time evolution of temperature, ionization and line emission. Here we mainly report on our results from our modeling of SN 1987A. We discuss the oxygen mass from the ... More
Maximum Scatter TSP in Doubling MetricsDec 09 2015Jun 28 2016We study the problem of finding a tour of $n$ points in which every edge is long. More precisely, we wish to find a tour that visits every point exactly once, maximizing the length of the shortest edge in the tour. The problem is known as Maximum Scatter ... More
Continuous vs discrete spins in the hyperbolic planeSep 28 2016Oct 17 2016We study the $O(n)$ model on planar hyperbolic cocompact lattices, with free boundary conditions. We observe that the pair correlations decay exponentially with distance, for all temperatures, if and only if $n>1$.
A null series with small anti-analytic partOct 19 2005We show that it is possible for a square integrable function on the circle, which is a sum of an almost everywhere convergent series of exponentials with positive frequencies, to not belong to the Hardy space. A consequence in the uniqueness theory is ... More
Is PLA large?Oct 06 2005Oct 18 2005We examine the class of functions representable by an analytic sum (by which we mean a trigonometric sum involving only positive frequencies) converging almost everywhere. We show that it is dense but that it is first category and has zero Wiener measure. ... More
Combining Riesz bases in $R^d$Jan 21 2015We prove that every finite union of rectangles in $R^d$ admits a Riesz basis of exponentials.
Streaming Algorithms for Partitioning Integer SequencesApr 07 2014Jul 07 2014We study the problem of partitioning integer sequences in the one-pass data streaming model. Given is an input stream of integers $X \in \{0, 1, \dots, m \}^n$ of length $n$ with maximum element $m$, and a parameter $p$. The goal is to output the positions ... More
Lower bound for the escape probability in the Lorentz Mirror Model on the latticeNov 28 2013We show that in the Lorentz mirror model, at any density of mirrors, the probability of a particle starting at the origin to reach distance n is at least 1/(2n+1).
One cannot hear the winding numberDec 07 2006We construct an example of two continuous maps f and g of the circle to itself with the same absolute value of the Fourier transform but with different winding numbers, answering a question of Brezis.
Central limit theorem for random walks in divergence-free random drift field: "H-minus-one" sufficesNov 15 2014We prove central limit theorem under diffusive scaling for the displacement of a random walk on ${\mathbb Z}^d$ in stationary divergence-free random drift field, under the ${\mathcal H}_{-1}$-condition imposed on the drift field. The condition is equivalent ... More
Singular distributions and symmetry of the spectrumJan 12 2013This is a survey of the "Fourier symmetry" of measures and distributions on the circle in relation with the size of their support. Mostly it is based on our paper arxiv:1004.3631 and a talk given by the second author in the 2012 Abel symposium.
Singular distributions, dimension of support, and symmetry of Fourier transformApr 21 2010Jan 25 2011We study the "Fourier symmetry" of measures and distributions on the circle, in relation with the size of their supports. The main results of this paper are: (1) A one-side extension of Frostman's theorem, which connects the rate of decay of Fourier transform ... More
Combining Riesz basesOct 23 2012Apr 15 2014We show that any finite union of intervals supports a Riesz basis of exponentials
Consensus formation on coevolving networks: groups' formation and structureJan 31 2008We study the effect of adaptivity on a social model of opinion dynamics and consensus formation. We analyze how the adaptivity of the network of contacts between agents to the underlying social dynamics affects the size and topological properties of groups ... More
Random Menshov spectraOct 20 2005We show that a spectrum of frequencies obtained by a random perturbation of the integers allows one to represent any measurable function on R by an almost everywhere converging sum of harmonics almost surely.
Menshov representation spectraOct 28 2005A Menshov spectrum is a subset of the integers that is sufficient for representing every measurable function as an almost-everywhere converging trigonometric (non-Fourier) sum. In this language the celebrated "Menshov representation theorem" states that ... More
Every exponential group supports a positive harmonic functionOct 31 2017May 20 2018We prove that all groups of exponential growth support non-constant positive harmonic functions. In fact, out results hold in the more general case of strongly connected, finitely supported Markov chains invariant under some transitive group of automorphisms ... More
SN 1998bw at late phasesJun 28 2000We present observations of the peculiar supernova SN 1998bw, which was probably associated with GRB 980425. The photometric and spectroscopic evolution is monitored up to 500 days past explosion. We also present modeling based on spherically symmetric, ... More
Maximal smoothness of the anti-analytic part of a trigonometric null seriesOct 19 2005We proved recently math.CA/0510403 that the anti-analytic part of a trigonometric series, converging to zero almost everywhere, may be square integrable on the circle. Here we prove that it can even be infinitely differentiable, and we characterize precisely ... More
Representation of non periodic functions by trigonometric series with almost integer frequenciesDec 02 2005Inspired by Menshov's representation theorem, we prove that there exists a sequence of frequecies such that any measurable (complex valued) function on R can be represented as a sum of almost everywhere convergent trigonometric series with these frequencies. ... More
Loop-erased random walk on a torus in dimensions 4 and aboveAug 31 2003Sharp estimates for the length of loop erased random walk between two vertices on the [n]^d -torus, d > 4, are established. The mean length is order n^{d/2} . In dimension 4 we have only an upper bound.
Nonamenable Liouville GraphsOct 16 2010Add to each level of binary tree edges to make the induced graph on the level a uniform expander. It is shown that such a graph admits no non-constant bounded harmonic functions.
Binary search trees and rectangulationsMar 26 2016We revisit the classical problem of searching in a binary search tree (BST) using rotations, and present novel connections of this problem to a number of geometric and combinatorial structures. In particular, we show that the execution trace of a BST ... More
On common roots of random Bernoulli polynomialsSep 11 2011We prove that with high probability, d+1 random Bernoulli polynomials in d variables of degree n (n goes to infinity) do not possess a common root.
Divisibility and Laws in Finite Simple GroupsMar 10 2014May 20 2014We provide new bounds for the divisibility function of the free group F_2 and construct short laws for the symmetric groups Sym(n). The construction is random and relies on the classification of the finite simple groups. We also give bounds on the length ... More
Groups with minimal harmonic functions as small as you likeMay 24 2016For any order of growth $f(n)=o(\log n)$ we construct a finitely-generated group $G$ and a set of generators $S$ such that the Cayley graph of $G$ with respect to $S$ supports a harmonic function with growth $f$ but does not support any harmonic function ... More
Exponential Riesz bases, discrepancy of irrational rotations and BMOSep 11 2010Mar 13 2011We study the basis property of systems of exponentials with frequencies belonging to 'simple quasicrystals'. We show that a diophantine condition is necessary and sufficient for such a system to be a Riesz basis in L^2 on a finite union of intervals. ... More
Uniqueness of percolation on products with ZMay 13 2011Jul 28 2012We show that there exists a connected graph G with subexponential volume growth such that critical percolation on the product of G with the line has infinitely many infinite clusters. We also give some conditions under which this cannot occur.
Analytic representation of functions and a new quasi-analyticity thresholdJun 14 2004Apr 27 2007We characterize precisely the possible rate of decay of the anti-analytic half of a trigonometric series converging to zero almost everywhere.
An "Analytic" Version of Menshov's Representation TheoremDec 01 2005Every measurable function f on the circle can be represented as a sum of harmonics with positive spectrum, converging in measure. For convergence almost everywhere this is not true. We discuss several other subsets of Z for which one might get a Menshov ... More
Perturbing PLAFeb 24 2012We proved earlier that every measurable function on the circle, after a uniformly small perturbation, can be written as a power series (i.e. a series of exponentials with positive frequencies), which converges almost everywhere. Here we show that this ... More
Stochastic Growth in a Small WorldMay 01 2003We considered the Edwards-Wilkinson model on a small-world network. We studied the finite-size behavior of the surface width by performing exact numerical diagonalization for the underlying coupling matrix. We found that the spectrum exhibits a gap or ... More
Arm exponents in high dimensional percolationNov 04 2009We study the probability that the origin is connected to the sphere of radius r (an arm event) in critical percolation in high dimensions, namely when the dimension d is large enough or when d>6 and the lattice is sufficiently spread out. We prove that ... More
The Alexander-Orbach conjecture holds in high dimensionsJun 09 2008Nov 16 2009We examine the incipient infinite cluster (IIC) of critical percolation in regimes where mean-field behavior has been established, namely when the dimension d is large enough or when d>6 and the lattice is sufficiently spread out. We find that random ... More
The probability of long cycles in interchange processesSep 20 2010May 25 2012We examine the number of cycles of length k in a permutation, as a function on the symmetric group. We write it explicitly as a combination of characters of irreducible representations. This allows to study formation of long cycles in the interchange ... More
Finsler connection for general Lagrangian systemsAug 11 2014Feb 24 2016We give a Finsler non-linear connection by a new simplified definition for not only regular case but also singular case. In regular case, it corresponds to non-linear connection part of Berwald's connection, but our connection is expressed not in line ... More
I knew I should have taken that left turn at AlbuquerqueAug 25 2010May 02 2011We study the Laplacian-infinity path as an extreme case of the Laplacian-alpha random walk. Although, in the finite alpha case, there is reason to believe that the process converges to SLE, we show that this is not the case when alpha is infinite. In ... More
Shattering, Graph Orientations, and ConnectivityNov 06 2012We present a connection between two seemingly disparate fields: VC-theory and graph theory. This connection yields natural correspondences between fundamental concepts in VC-theory, such as shattering and VC-dimension, and well-studied concepts of graph ... More
Radioactivities and nucleosynthesis in SN 1987ADec 17 2001The nucleosynthesis and production of radioactive elements in SN 1987A are reviewed. Different methods for estimating the masses of 56Ni, 57Ni, and 44Ti are discussed, and we conclude that broad band photometry in combination with time-dependent models ... More
Late Spectral Evolution of SN 1987A: I. Temperature and IonizationDec 17 1997The temperature and ionization of SN 1987A is modeled between 200 and 2000 days in its nebular phase, using a time-dependent model. We include all important elements, as well as the primary composition zones in the supernova. The energy input is provided ... More
Groups with minimal harmonic functions as small as you like (With an appendix by Nicolas Matte Bon)May 24 2016Feb 05 2017For any order of growth $f(n)=o(\log n)$ we construct a finitely-generated group $G$ and a set of generators $S$ such that the Cayley graph of $G$ with respect to $S$ supports a harmonic function with growth $f$ but does not support any harmonic function ... More
Counting batsApr 10 2013We demonstrate an algorithm that reconstructs the number of walkers in an unknown graph from observations of their returns to a fixed point.
A Resistance Bound via an Isoperimetric InequalityDec 23 2002Jun 09 2012An isoperimetric upper bound on the resistance is given. As a corollary we resolve two problems, regarding mean commute time on finite graphs and resistance on percolation clusters. Further conjectures are presented.
Cycle structure of the interchange process and representation theoryMay 21 2012Consider the process of random transpositions on the complete graph. We use representation theory to give an exact, simple formula for the expected number of cycles of size k at time t, in terms of an incomplete Beta function. Using this we show that ... More
Consensus formation on adaptive networksJul 30 2007The structure of a network can significantly influence the properties of the dynamical processes which take place on them. While many studies have been devoted to this influence, much less attention has been devoted to the interplay and feedback mechanisms ... More
Ordering the representations of S_n using the interchange processMar 08 2010Jul 21 2011Inspired by Aldous' conjecture for the spectral gap of the interchange process and its recent resolution by Caputo, Liggett and Richthammer, we define an associated order on the irreducible representations of S_n. Aldous' conjecture is equivalent to certain ... More
On the gaps between zeros of trigonometric polynomialsJan 02 2006We show that for every finite symetric set S of integer vectors, every real trigonometric polynomial on the d dimensional torus with spectrum in S has a zero in every closed ball of diameter D, where D is the sum over S of 1 over 4 times the L2 norm of ... More
Central Limit Theorem for Random Walks in Doubly Stochastic Random Environment: $\mathcal{H}_{-1}$ SufficesFeb 22 2017We prove a central limit theorem under diffusive scaling for the displacement of a random walk on ${\mathbb Z}^d$ in stationary and ergodic doubly stochastic random environment, under the $\mathcal{H}_{-1}$-condition imposed on the drift field. The condition ... More
Three-dimensional modeling of Type Ia supernovae - The power of late time spectraApr 14 2005Late time synthetic spectra of Type Ia supernovae, based on three-dimensional deflagration models, are presented. We mainly focus on one model,"c3_3d_256_10s", for which the hydrodynamics (Roepke 2005) and nucleosynthesis (Travaglio et al. 2004) was calculated ... More
Is a bivariate polynomial with plus minus 1 coefficients irreducible? Very likely!Feb 21 2016Apr 19 2016We prove that a random bivariate polynomial with plus minus 1 coefficients is irreducible with high probability.
Hydrogen and helium in the spectra of Type Ia supernovaeJul 15 2013We present predictions for hydrogen and helium emission line luminosities from circumstellar matter around Type Ia supernovae (SNe Ia) using time dependent photoionization modeling. ESO/VLT optical echelle spectra of the SN Ia 2000cx were taken before ... More
On the hyperplane conjecture for random convex setsDec 18 2006Let N > n, and denote by K the convex hull of N independent standard gaussian random vectors in an n-dimensional Euclidean space. We prove that with high probability, the isotropic constant of K is bounded by a universal constant. Thus we verify the hyperplane ... More
Hubble Space Telescope and Ground-Based Observations of SN 1993J and SN 1998S: CNO Processing in the ProgenitorsSep 17 2004Ground-based and Hubble Space Telescope observations are presented for SN 1993J and SN 1998S. SN 1998S shows strong, relatively narrow circumstellar emission lines of N III-V and C III-IV, as well as broad lines from the ejecta. Both the broad ultraviolet ... More
The late-time light curve of the Type Ia supernova 2000cxSep 14 2004We have conducted a systematic and comprehensive monitoring programme of the Type Ia supernova 2000cx at late phases using the VLT and HST. The VLT observations cover phases 360 to 480 days past maximum brightness and include photometry in the BVRIJH ... More
The Toom Interface Via CouplingJan 20 2015Sep 19 2016We consider a one dimensional interacting particle system which describes the effective interface dynamics of the two dimensional Toom model at low temperature and noise. We prove a number of basic properties of this model. First we consider the dynamics ... More
Random walks with $k$-wise independent incrementsMay 31 2004We construct examples of a random walk with pairwise-independent steps which is almost-surely bounded, and for any $m$ and $k$ a random walk with $k$-wise independent steps which has no stationary distribution modulo $m$.
A balanced excited random walkSep 03 2010The following random process on $\Z^4$ is studied. At first visit to a site, the two first coordinates perform a (2-dimensional) simple random walk step. At further visits, it is the last two coordinates which perform a simple random walk step. We prove ... More
Supercritical self-avoiding walks are space-fillingOct 13 2011Sep 25 2012We consider random self-avoiding walks between two points on the boundary of a finite subdomain of Z^d (the probability of a self-avoiding trajectory gamma is proportional to mu^{-length(gamma)}). We show that the random trajectory becomes space-filling ... More
On the connectivity of the Poisson process on fractalsApr 11 2006For a measure mu supported on a compact connected subset of a Euclidean space which satisfies a uniform d-dimensional decay of the volume of balls we show that the maximal edge in the minimum spanning tree of n indepndent samples from mu is, with high ... More
Why did Supernova 1054 shine at late times?Dec 15 2000The Crab nebula is the remnant of supernova 1054 (SN 1054). The progenitor of this supernova has, based on nucleosynthesis arguments, been modeled as an 8-10 solar mass star. Here we point out that the observations of the late light curve of SN 1054, ... More
Testing the Collective Properties of Small-World Networks through Roughness ScalingSep 08 2003Motivated by a fundamental synchronization problem in scalable parallel computing and by a recent criterion for ``mean-field'' synchronizability in interacting systems, we study the Edwards-Wilkinson model on two variations of a small-worldnetwork. In ... More
Diffusion Processes on Small-World Networks with Distance-Dependent Random-LinksApr 19 2007Jun 15 2007We considered diffusion-driven processes on small-world networks with distance-dependent random links. The study of diffusion on such networks is motivated by transport on randomly folded polymer chains, synchronization problems in task-completion networks, ... More
Diffusion Processes on Power-Law Small-World NetworksJan 20 2005May 20 2005We consider diffusion processes on power-law small-world networks in different dimensions. In one dimension, we find a rich phase diagram, with different transient and recurrent phases, including a critical line with continuously varying exponents. The ... More
Who's talking first? Consensus or lack thereof in coevolving opinion formation modelsNov 08 2007We investigate different opinion formation models on adaptive network topologies. Depending on the dynamical process, rewiring can either (i) lead to the elimination of interactions between agents in different states, and accelerate the convergence to ... More
The minimal spanning tree and the upper box dimensionNov 26 2003Nov 30 2003We show that the alpha-weight of an MST over n points in a metric space with upper box dimension d has a bound independent of n if alpha is smaller than d and does not have one if alpha is larger than d.
Effective Lifetimes of $B_s$ Decays and their Constraints on the $B_s^0$-$\bar B_s^0$ Mixing ParametersSep 23 2011Measurements of the effective lifetimes of $B_s$-meson decays, which only require untagged rate analyses, allow us to probe the width difference $\Delta\Gamma_s$ and the CP-violating phase $\phi_s$ of $B^0_s$-$\bar B^0_s$ mixing. We point out that the ... More
A Fresh Look at B_{s,d} -> pi pi, pi K, K K DecaysDec 03 2010Using updated measurements and SU(3)-breaking form factors, we have a detailed look at the B_d -> pi^+ pi^-, B_s -> K^+ K^- and B_d -> pi^\mp K^\pm, B_s -> pi^\pm K^\mp systems. The corresponding decays are related to each other by the U-spin symmetry ... More
A Flow-aware MAC Protocol for a Passive Optical Metropolitan Area NetworkFeb 17 2011The paper introduces an original MAC protocol for a passive optical metropolitan area network using time-domain wavelength interleaved networking (TWIN)% as proposed recently by Bell Labs . Optical channels are shared under the distributed control of ... More
c-axis Josephson Tunneling in Twinned YBCO CrystalsJul 02 1999Jan 13 2000Josephson tunneling between YBCO and Pb with the current flowing along the c-axis of the YBCO is persumed to come from an s-wave component of the superconductivity of the YBCO. Experiments on multi-twin samples are not entirely consistent with this hypothesis. ... More
Theory of Josephson tunneling along the c-axis of YBCOMar 10 1998The existence of Josephson tunneling has been demonstrated between YBa$_2$Cu$_3$O$_{7-\delta}$ and Pb with the current flowing along the c-axis of YBa$_2$Cu$_3$O$_{7-\delta}$. This is presumed to come from an s-wave component of the superconductivity ... More
Physical states of Bianchi type IX quantum cosmologies described by the Chern-Simons functionalMar 18 1996A class of exact solutions of the Wheeler-DeWitt equation for diagonal Bianchi type IX cosmologies with cosmological constant is derived in the metric representation. This class consists of all the ``topological solutions'' which are associated with the ... More
Excited random walk against a wallSep 21 2005Oct 27 2006We analyze random walk in the upper half of a three dimensional lattice which goes down whenever it encounters a new vertex, a.k.a. excited random walk. We show that it is recurrent with an expected number of returns of square-root log n.