Searching Arxiv, refresh for possibly better results.

Results for "Ira Thorpe"

total 455took 0.14s
LISA long-arm interferometryNov 16 2009The Laser Interferometer Space Antenna (LISA) will observe gravitational radiation in the milliHertz band by measuring picometer-level fluctuations in the distance between drag-free proof masses over baselines of approximately five million kilometers. ... More
Gravitational-wave parameter estimation with gaps in LISA: a Bayesian data augmentation methodJul 10 2019By listening to gravity in the low frequency band, between 0.1 mHz and 1 Hz, the future space-based gravitational-wave observatory LISA will be able to detect tens of thousands of astrophysical sources from cosmic dawn to the present. The detection and ... More
Arm-Locking with the GRACE Follow-On Laser Ranging InterferometerOct 09 2015Arm-locking is a technique for stabilizing the frequency of a laser in an inter-spacecraft interferometer by using the spacecraft separation as the frequency reference. A candidate technique for future space-based gravitational wave detectors such as ... More
Time Domain Simulations of Arm Locking in LISAFeb 26 2011Apr 27 2011Arm locking is a technique that has been proposed for reducing laser frequency fluctuations in the Laser Interferometer Space Antenna (LISA), a gravitational-wave observatory sensitive in the milliHertz frequency band. Arm locking takes advantage of the ... More
Comparison of Atom Interferometers and Light Interferometers as Space-Based Gravitational Wave DetectorsJan 26 2012We consider a class of proposed gravitational wave detectors based on multiple atomic interferometers separated by large baselines and referenced by common laser systems. We compute the sensitivity limits of these detectors due to intrinsic phase noise ... More
Detection and Characterization of Micrometeoroids with LISA PathfinderOct 21 2015Oct 30 2015The Solar System contains a population of dust and small particles originating from asteroids, comets, and other bodies. These particles have been studied using a number of techniques ranging from in-situ satellite detectors to analysis of lunar microcraters ... More
Wave-ray algorithms for Helmholtz equations with variable wave numbers: a one-dimensional implementation of two-dimensional ideasDec 10 2013The subject of this paper is multigrid solvers for Helmholtz operators with large wave numbers. Algorithms presented here are variations of the wave-ray solver which is modified to allow efficient solutions for operators with constant, continuous, and ... More
Shifted Laplacian based multigrid preconditioners for solving indefinite Helmholtz equationsDec 10 2013Shifted Laplacian multigrid preconditioner has become a tool du jour for solving highly indefinite Helmholtz equations. The idea is to add a complex damping to the original Helmholtz operator and then apply a multigrid processing to the resulting operator ... More
The Maximal Graph Dirichlet Problem in Semi-Euclidean SpacesDec 19 2011The maximal graph Dirichlet problem asks whether there exists a spacelike graph, in a semi-Euclidean space, with a given boundary and with mean curvature everywhere zero. We prove the existence of solutions to this problem under certain assumptions on ... More
Analysis of $p$-Laplacian Regularization in Semi-Supervised LearningJul 19 2017Oct 15 2017We investigate a family of regression problems in a semi-supervised setting. The task is to assign real-valued labels to a set of $n$ sample points, provided a small training subset of $N$ labeled points. A goal of semi-supervised learning is to take ... More
Asymptotic Analysis of the Ginzburg-Landau Functional on Point CloudsApr 17 2016The Ginzburg-Landau functional is a phase transition model which is suitable for clustering or classification type problems. We study the asymptotics of a sequence of Ginzburg-Landau functionals with anisotropic interaction potentials on point clouds ... More
Data series subtraction with unknown and unmodeled background noiseApr 18 2014Aug 04 2014LISA Pathfinder (LPF), ESA's precursor mission to a gravitational wave observatory, will measure the degree to which two test-masses can be put into free-fall, aiming to demonstrate a residual relative acceleration with a power spectral density (PSD) ... More
Impact of mergers on LISA parameter estimation for nonspinning black hole binariesNov 05 2009Apr 15 2010We investigate the precision with which the parameters describing the characteristics and location of nonspinning black hole binaries can be measured with the Laser Interferometer Space Antenna (LISA). By using complete waveforms including the inspiral, ... More
Sky localization of complete inspiral-merger-ringdown signals for nonspinning massive black hole binariesApr 29 2011We investigate the capability of LISA to measure the sky position of equal-mass, nonspinning black hole binaries, combining for the first time the entire inspiral-merger-ringdown signal, the effect of the LISA orbits, and the complete three-channel LISA ... More
A vanishing theorem for operators in Fock spaceJul 22 2011We consider the bosonic Fock space over the Hilbert space of transversal vector fields in three dimensions. This space carries a canonical representation of the group of rotations. For a certain class of operators in Fock space we show that rotation invariance ... More
Decay of eigenfunctions of elliptic PDE'sJun 28 2013We study exponential decay of eigenfunctions of self-adjoint higher order elliptic operators on $\R^d$. We show that the possible critical decay rates are determined algebraically. In addition we show absence of super-exponentially decaying eigenfunctions ... More
On the Signature of Short Distance Scale in the Cosmic Microwave BackgroundMar 12 2002We discuss the signature of the scale of short distance physics in the Cosmic Microwave Background. In addition to effects which depend on the ratio of Hubble scale H during inflation to the energy scale M of the short distance physics, there can be effects ... More
Mother Moose: Generating Extra Dimensions from Simple Groups at Large NSep 21 2001Oct 03 2001We show that there exists a correspondence between four dimensional gauge theories with simple groups and higher dimensional gauge theories at large N. As an example, we show that a four dimensional {N}=2 supersymmetric SU(N) gauge theory, on the Higgs ... More
Spin-perpendicular kicks from evanescent binaries formed in the aftermath of rotational core-collapse and the nature of the observed bimodal distribution of pulsar peculiar velocitiesFeb 17 2003If rotating core collapse leads to the formation of a proto-neutron star binary in super-close orbit, then the lighter star, propelled toward the minimum stable mass, explodes. The neutron star (or black hole) that remains acquires a spin-perpendicular ... More
Symmetric inclusion-exclusionMay 12 2005Jul 24 2005One form of the inclusion-exclusion principle asserts that if A and B are functions of finite sets then A(S) is the sum of B(T) over all subsets T of S if and only if B(S) is the sum of (-1)^|S-T| A(T) over all subsets T of S. If we replace B(S) with ... More
Reciprocals of exponential polynomials and permutation enumerationJul 24 2018May 02 2019We show that the reciprocal of a partial sum with 2m terms of the alternating exponential series is the exponential generating function for permutations in which every increasing run has length congruent to 0 or 1 modulo 2m. More generally we study polynomials ... More
On the Schur function expansion of a symmetric quasi-symmetric functionMar 25 2018Egge, Loehr, and Warrington proved a formula for the Schur function expansion of a symmetric function in terms of its expansion in fundamental quasi-symmetric functions. Their formula involves the coefficients of a modified inverse Kostka matrix. Recently ... More
Analyticity estimates for the Navier-Stokes equationsJul 24 2009We study spatial analyticity properties of solutions of the Navier-Stokes equations and obtain new growth rate estimates for the analyticity radius. We also study stability properties of strong global solutions of the Navier-Stokes equations with data ... More
Realizing holonomic constraints in classical and quantum mechanicsSep 07 1999Nov 02 2000We consider the problem of constraining a particle to a submanifold Sigma of configuration space using a sequence of increasing potentials. We compare the classical and quantum versions of this procedure. This leads to new results in both cases: an unbounded ... More
Scale dependence of the CMB power spectrum in small field models of inflation with a high tensor to scalar ratioJul 13 2016We study scale dependence of the cosmic microwave background (CMB) power spectrum in a class of small, single-field models of inflation which lead to a high value of the tensor to scalar ratio. The inflaton potentials that we consider are degree 5 polynomials, ... More
Oscillations of Bose-Einstein condensates with vortex lattices. II. Finite temperaturesJun 10 2003Apr 27 2004We derive the finite temperature oscillation modes of a harmonically confined Bose-Einstein condensed gas undergoing rigid body rotation supported by a vortex lattice in the condensate. The hydrodynamic modes separate into two classes corresponding to ... More
Runup of tsunami waves in U-shaped baysMay 10 2010The problem of tsunami wave shoaling and runup in U-shaped bays (such as fjords) and underwater canyons is studied in the framework of shallow water theory. The wave shoaling in bays, when the depth varies smoothly along the channel axis, is studied with ... More
Ground States in the Spin Boson ModelMar 30 2010Aug 27 2010We prove that the Hamiltonian of the model describing a spin which is linearly coupled to a field of relativistic and massless bosons, also known as the spin-boson model, admits a ground state for small values of the coupling constant lambda. We show ... More
Cosmological Constraints on Tachyon MatterMay 01 2002Jun 27 2002We examine whether tachyon matter is a viable candidate for the cosmological dark matter. First, we demonstrate that in order for the density of tachyon matter to have an acceptable value today, the magnitude of the tachyon potential energy at the onset ... More
Factorization, Power Corrections, and the Pion Form FactorJan 27 2003Aug 05 2004This letter is an investigation of the pion form factor utilizing recently developed effective field theory techniques. The primary results reported are: Both the transition and electromagnetic form factors are corrected at order $\Lambda/Q$. However, ... More
NRQCD: A Critical ReviewNov 08 1999Nov 09 1999In this talk I review some recent applications of NRQCD. I first discuss the unquenched NRQCD lattice extractions of the strong coupling constant, paying particular attention to the recent advances in reducing systematic errors. I then discuss the progress ... More
Hadro-Production of Quarkonia in Fixed Target ExperimentsSep 06 1996In this talk I review the recent progress made in the calculations of quarkonia production in fixed target experiments. NRQCD organizes the calculations in a systematic expansion in $\alpha_s$ and $v$, the relative velocity between the heavy quarks. Within ... More
Can we trust the relationship between resonance poles and lifetimes?Nov 11 2015We show that the shape resonances induced by a one dimensional well of delta functions disappear as soon as a small constant electric field is applied. In particular, in any compact subset below the positive real axis there are no resonances if the non-zero ... More
The Generating Function of Ternary Trees and Continued FractionsMay 11 2005Michael Somos conjectured a relation between Hankel determinants whose entries $\frac 1{2n+1}\binom{3n}n$ count ternary trees and the number of certain plane partitions and alternating sign matrices. Tamm evaluated these determinants by showing that the ... More
Ring Correlations in Random NetworksJul 22 2016We examine the correlations between rings in random network glasses in two dimensions as a function of their separation. Initially, we use the topological separation (measured by the number of intervening rings), but this lead to pseudo-long-range correlations ... More
Canaries in a Coal Mine: Using Globular Clusters to Place Limits on Massive Black Holes in the Galactic HaloNov 23 1998We explore the possibility that massive black holes comprise a significant fraction of the dark matter of our galaxy by studying the dissolution of galactic globular clusters bombarded by them. In our simulations, we evolve the clusters along a sequence ... More
Partition Functions on the Euclidean Plane with Compact Boundaries in Conformal and Non-Conformal TheoriesNov 02 2011In this letter we calculate the exact partition function for free bosons on the plane with lacunae. First the partition function for a plane with two spherical holes is calculated by matching exactly for the infinite set of Wilson coefficients in an effective ... More
Smoothness and analyticity of perturbation expansions in QEDJul 06 2010Sep 04 2010We consider the ground state of an atom in the framework of non-relativistic qed. We assume that the ultraviolet cutoff is of the order of the Rydberg energy and that the atomic Hamiltonian has a non-degenerate ground state. We show that the ground state ... More
Gravitational Anderson LocalizationNov 30 2012We present a higher dimensional model where gravity is bound to a brane due to Anderson localization. The extra dimensions are taken to be a disordered crystal of branes, with randomly distributed tensions of order the fundamental scale. Such geometries ... More
Toroidal Magnetic Fields in Type II Superconducting Neutron StarsMay 15 2007Nov 01 2007We determine constraints on the form of axisymmetric toroidal magnetic fields dictated by hydrostatic balance in a type II superconducting neutron star with a barotropic equation of state. Using Lagrangian perturbation theory, we find the quadrupolar ... More
Reciprocals of exponential polynomials and permutation enumerationJul 24 2018We show that the reciprocal of a partial sum with 2m terms of the alternating exponential series is the exponential generating function for permutations in which every increasing run has length congruent to 0 or 1 modulo 2m. More generally we study polynomials ... More
Small field models with gravitational wave signature supported by CMB dataJul 13 2016May 24 2018We study scale dependence of the cosmic microwave background (CMB) power spectrum in a class of small, single-field models of inflation which lead to a high value of the tensor to scalar ratio. The inflaton potentials that we consider are degree 5 polynomials, ... More
Separated by an Un-common Language: Towards Judgment Language Informed Vector Space ModelingAug 01 2015Dec 06 2015A common evaluation practice in the vector space models (VSMs) literature is to measure the models' ability to predict human judgments about lexical semantic relations between word pairs. Most existing evaluation sets, however, consist of scores collected ... More
Counting tanglegrams with speciesSep 13 2015Sep 15 2015A tanglegram is a diagram, used in biology to compare phylogenetic trees, consisting of two binary trees together with a matching of their leaves. Unlabeled tanglegrams were recently counted by Billey, Konvalinka, and Matsen. Using the theory of combinatorial ... More
A historical survey of P-partitionsJun 10 2015We give a historical survey of the theory P-partitions, starting with MacMahon's work, describing Richard Stanley's contributions and his related work, and continuing with more recent developments.
Convergence and Rates for Fixed-Interval Multiple-Track Smoothing Using $k$-Means Type OptimizationJun 08 2015May 04 2016We address the task of estimating multiple trajectories from unlabelled data. This problem arises in many settings, one could think of the construction of maps of transport networks from passive observation of travellers, or the reconstruction of the ... More
Weak Convergence of General Smoothing SplinesJun 28 2015Establishing the convergence of splines can be cast as a variational problem which is amenable to a $\Gamma$-convergence approach. We consider the case in which the regularization coefficient scales with the number of observations, $n$, as $\lambda_n=n^{-p}$. ... More
Deep Limits of Residual Neural NetworksOct 28 2018Neural networks have been very successful in many applications however we often lack a theoretical understanding of what the neural networks are actually learning. This problem emerges when trying to generalise to new data sets. The contribution of this ... More
Pointwise Convergence in Probability of General Smoothing SplinesJun 28 2015Mar 11 2017Establishing the convergence of splines can be cast as a variational problem which is amenable to a $\Gamma$-convergence approach. We consider the case in which the regularization coefficient scales with the number of observations, $n$, as $\lambda_n=n^{-p}$. ... More
Regularization Learning Networks: Deep Learning for Tabular DatasetsMay 16 2018Oct 23 2018Despite their impressive performance, Deep Neural Networks (DNNs) typically underperform Gradient Boosting Trees (GBTs) on many tabular-dataset learning tasks. We propose that applying a different regularization coefficient to each weight might boost ... More
Small field models of inflation that predict a tensor-to-scalar ratio $r=0.03$Mar 28 2019Future observations of the cosmic microwave background (CMB) polarization are expected to set an improved upper bound on the tensor-to-scalar ratio of $r\lesssim 0.03$. Recently, we showed that small field models of inflation can produce a significant ... More
Likelihood analysis of small field polynomial models of inflation yielding a high Tensor-to-Scalar ratioJan 22 2018Apr 03 2019Inflationary potentials, with Planckian field excursions, described by a 6th degree polynomial are studied. We solve the Mukhanov-Sasaki equations exactly and employ a probabilistic approach as well as multinomial fitting to analyse the results. We identify ... More
Resonances in the one dimensional Stark effect in the limit of small fieldJul 07 2019We discuss the resonances of Hamiltonians with constant electric field in one dimension in the limit of small field. These resonances occur near the real axis, near zeros of the analytic continuation of a reflection coefficient for potential scattering, ... More
Lagrange InversionSep 20 2016We give a survey of the Lagrange inversion formula, including different versions and proofs, with applications to combinatorial and formal power series identities.
Reciprocals of exponential polynomials and permutation enumerationJul 24 2018May 17 2019We show that the reciprocal of a partial sum with 2m terms of the alternating exponential series is the exponential generating function for permutations in which every increasing run has length congruent to 0 or 1 modulo 2m. More generally we study polynomials ... More
A short proof of the Deutsch-Sagan congruence for connected non crossing graphsMar 29 2014We give a short proof, using Lagrange inversion, of a congruence modulo 3 for the number of connected noncrossing graphs on n vertices that was conjectured by Emeric Deutsch and Bruce Sagan. A more complicated proof had been given earlier by S.-P. Eu, ... More
Cavity-enhanced direct frequency comb spectroscopyMar 31 2008Cavity-enhanced direct frequency comb spectroscopy combines broad spectral bandwidth, high spectral resolution, precise frequency calibration, and ultrahigh detection sensitivity, all in one experimental platform based on an optical frequency comb interacting ... More
Micrometeoroid Events in LISA PathfinderMay 07 2019The zodiacal dust complex, a population of dust and small particles that pervades the Solar System, provides important insight into the formation and dynamics of planets, comets, asteroids, and other bodies. Here we present a new set of data obtained ... More
The limit as p -> infinity of the Hilbert-Kunz multiplicity of sum(x_i^(d_i))Jul 12 2010Let p be a prime. The Hilbert-Kunz multiplicity, mu, of the element sum(x_i^(d_i)) of (Z/p)[x_1,..., x_s] depends on p in a complicated way. We calculate the limit of mu as p -> infinity. In particular when each d_i is 2 we show that the limit is 1 + ... More
Enumeration of tilings of diamonds and hexagons with defectsOct 23 1998We show how to count tilings of Aztec diamonds and hexagons with defects using determinants. In several cases these determinants can be evaluated in closed form. In particular, we obtain solutions to problems 1, 2, and 10 in James Propp's list of problems ... More
Symmetry Realization via a Dynamical Inverse Higgs MechanismDec 21 2017Apr 13 2018The Ward identities associated with spontaneously broken symmetries can be saturated by Goldstone bosons. However, when space-time symmetries are broken, the number of Goldstone bosons necessary to non-linearly realize the symmetry can be less than the ... More
Epidemic Extinction Paths in Complex NetworksApr 27 2017We study the extinction of long-lived epidemics on finite complex networks induced by intrinsic noise. Applying analytical techniques to the stochastic Susceptible-Infected-Susceptible model, we predict the distribution of large fluctuations, the most ... More
Large order fluctuations, switching, and control in complex networksJul 19 2017We propose an analytical technique to study large fluctuations and switching from internal noise in complex networks. Using order-disorder kinetics as a generic example, we construct and analyze the most probable, or optimal path of fluctuations from ... More
Effective Field Theory and Matching in Non-Relativistic Gauge TheoriesMar 11 1997Oct 15 1997The effective Lagrangian and power counting rules for non-relativistic gauge theories are derived via an expansion in $1/c$. It is shown that the $1/c$ expansion leads to an effective field theory which incorporates a multipole expansion. Failure to use ... More
A triple lacunary generating function for Hermite polynomialsMar 04 2004Jul 22 2005Some of the classical orthogonal polynomials such as Hermite, Laguerre, Charlier, etc. have been shown to be the generating polynomials for certain combinatorial objects. These combinatorial interpretations are used to prove new identities and generating ... More
Classical Space-Times from the S MatrixApr 26 2013We show that classical space-times can be derived directly from the S-matrix for a theory of massive particles coupled to a massless spin two particle. As an explicit example we derive the Schwarzchild space-time as a series in $G_N$. At no point of the ... More
Spherical Gravitational Collapse of Annihilating Dark Matter and the Minimum Mass of CDM Black HolesMay 25 2005Spherical gravitational collapse of a cold gas of annihilating particles involves a competition between the free-fall rate $\propto\sqrt{\rho}$ and the (s-wave) annihilation rate $\propto\rho$. Thus, there is a critical density $\rhoann$ above which annihilation ... More
Symmetry Obstruction to Fermi Liquid Behavior in the Unitary LimitDec 21 2017Apr 19 2018We show that a Fermi gas, in three dimensions, at temperatures above the superconducting phase transition but below the Fermi temperature, can not be described by Fermi Liquid Theory (FLT) in the unitary limit where the scattering length diverges. The ... More
A refinement of Cayley's formula for treesJul 24 2005A proper vertex of a rooted tree with totally ordered vertices is a vertex that is less than all its proper descendants. We count several kinds of labeled rooted trees and forests by the number of proper vertices. Our results are all expressed in terms ... More
Multilinear generating functions for Charlier polynomialsJun 08 2009Charlier configurations provide a combinatorial model for Charlier polynomials. We use this model to give a combinatorial proof of a multilinear generating function for Charlier polynomials. As special cases of the multilinear generating function, we ... More
Counting permutations by alternating descentsAug 08 2014We find the exponential generating function for permutations with all valleys even and all peaks odd, and use it to determine the asymptotics for its coefficients, answering a question posed by Liviu Nicolaescu. The generating function can be expressed ... More
Epidemic extinction and control in heterogeneous networksApr 25 2016Jun 14 2016We consider epidemic extinction in finite networks with broad variation in local connectivity. Generalizing the theory of large fluctuations to random networks with a given degree distribution, we are able to predict the most probable, or optimal, paths ... More
Non-equilibrium effects in steady relativistic $e^+e^-γ$ windsMay 11 1998We consider an ultra-relativistic wind consisting of electron-positron pairs and photons with the principal goal of finding the asymptotic Lorentz factor $\gamma_{\infty}$ for zero baryon number. The wind is assumed to originate at radius $r_i$ where ... More
Application of Maximum Entropy Deconvolution to $γ$-ray SkymapsAug 25 2015Skymaps measured with imaging atmospheric Cherenkov telescopes (IACTs) represent the real source distribution convolved with the point spread function of the observing instrument. Current IACTs have an angular resolution in the order of 0.1$^\circ$ which ... More
Rare slips in fluctuating synchronized oscillator networksMay 24 2018Jul 25 2018We study rare phase slips due to noise in synchronized Kuramoto oscillator networks. In the small-noise limit, we demonstrate that slips occur via large fluctuations to saddle phase-locked states. For tree topologies, slips appear between subgraphs that ... More
Delay Induced Instabilities in Self-Propelling SwarmsDec 18 2007Feb 25 2008We consider a general model of self-propelling particles interacting through a pairwise attractive force in the presence of noise and communication time delay. Previous work by Erdmann, et al. [Phys. Rev. E {\bf 71}, 051904 (2205)] has shown that a large ... More
The Dynamics of Interacting SwarmsMar 22 2018Swarms are self-organized dynamical coupled agents which evolve from simple rules of communication. They are ubiquitous in nature, and be- coming more prominent in defense applications. Here we report on a preliminary study of swarm collisions for a swarm ... More
A Short Proof of the Zeilberger-Bressoud $q$-Dyson TheoremDec 17 2004Feb 22 2005We give a formal Laurent series proof of Andrews's $q$-Dyson Conjecture, first proved by Zeilberger and Bressoud.
Shuffle-compatible permutation statisticsJun 02 2017May 13 2018Since the early work of Richard Stanley, it has been observed that several permutation statistics have a remarkable property with respect to shuffles of permutations. We formalize this notion of a shuffle-compatible permutation statistic and introduce ... More
Predicting unobserved exposures from seasonal epidemic dataSep 10 2013We consider a stochastic Susceptible-Exposed-Infected-Recovered (SEIR) epidemiological model with a contact rate that fluctuates seasonally. Through the use of a nonlinear, stochastic projection, we are able to analytically determine the lower dimensional ... More
Escape Rates in a Stochastic Environment with Multiple ScalesSep 08 2008Jul 02 2009We consider a stochastic environment with two time scales and outline a general theory that compares two methods to reduce the dimension of the original system. The first method involves the computation of the underlying deterministic center manifold ... More
A Collective Motion Algorithm for Tracking Time-Dependent BoundariesOct 07 2005We present a numerical method that allows a formation of communicating agents to target the boundary of a time dependent concentration by following a time dependent concentration gradient. The algorithm motivated by \cite{MB, BKM}, allows the agents to ... More
A Combinatorial Interpretation of The Numbers $6(2n)! /n! (n+2)!$Jan 22 2004Aug 06 2004It is well known that the numbers $(2m)! (2n)!/m! n! (m+n)!$ are integers, but in general there is no known combinatorial interpretation for them. When $m=0$ these numbers are the middle binomial coefficients $\binom{2n}{n}$, and when $m=1$ they are twice ... More
Algorithms for 3D rigidity analysis and a first order percolation transitionFeb 27 2007A fast computer algorithm, the pebble game, has been used successfully to study rigidity percolation on 2D elastic networks, as well as on a special class of 3D networks, the bond-bending networks. Application of the pebble game approach to general 3D ... More
Annual modulation in the scattering of J1819+3845: peculiar plasma velocity and anisotropyMar 10 2003We present two years of monitoring observations of the extremely variable quasar J1819+3845. We observe large yearly changes in the timescale of the variations (from ~ 1 hour to ~ 10 hours at 5GHz). This annual effect can only be explained if the variations ... More
The microarcsecond quasar J1819+3845Dec 08 2000We present new WSRT observations of the micro-arcsecond quasar J1819+3845. All short term variations are attributed to interstellar scintillation of a source which is at most 30 micro-arcseconds in diameter. The timescale of the modulations changes over ... More
The discovery of a microarcsecond quasar: J1819+3845Dec 10 1999Dec 13 1999We report on the discovery of a source which exhibits over 300% amplitude changes in radio flux density on the period of hours. This source, J1819+3845, is the most extremely variable extragalactic source known in the radio sky. We believe these properties ... More
Interstellar scintillation as the origin of rapid radio variability in the quasar J1819+3845Jan 04 2002Quasars shine brightly due to the liberation of gravitational energy as matter falls onto a supermassive black hole in the centre of a galaxy. Variations in the radiation received from active galactic nuclei (AGN) are studied at all wavelengths, revealing ... More
Coding static natural images using spiking event times: do neurons cooperate?Nov 01 2006To understand possible strategies of temporal spike coding in the central nervous system, we study functional neuromimetic models of visual processing for static images. We will first present the retinal model which was introduced by Van Rullen and Thorpe ... More
Geographical Security Questions for Fallback AuthenticationJul 01 2019Fallback authentication is the backup authentication method used when the primary authentication method (e.g., passwords, fingerprints, etc.) fails. Currently, widely-deployed fallback authentication methods (e.g., security questions, email resets, and ... More
Hierarchical Rigidity from Pair Distance FluctuationsMar 19 2007Mar 26 2007Often, experiments, observations or simulations generate large numbers of snapshots of the configurations of complex many-particle systems. It is important to find methods of extracting useful information from these ensembles of snapshots in order to ... More
Flat radio-spectrum galaxies and BLLacs: Part I: core propertiesAug 22 2000This paper concerns the relationship of BLLacs and flat spectrum weak emission-line galaxies. We compare the weak emission-line galaxies and the BLLacs in a sample of 57 flat spectrum objects (Marcha et al. 1996), using high-frequency radio and non-thermal ... More
Renormalization group treatment of rigidity percolationJul 25 2011Renormalization group calculations are used to give exact solutions for rigidity percolation on hierarchical lattices. Algebraic scaling transformations for a simple example in two dimensions produce a transition of second order, with an unstable critical ... More
The Laser Interferometer Space Antenna: Unveiling the Millihertz Gravitational Wave SkyJul 15 2019The first terrestrial gravitational wave interferometers have dramatically underscored the scientific value of observing the Universe through an entirely different window, and of folding this new channel of information with traditional astronomical data ... More
Effective Field Theory of 2D van Hove SingularitiesJan 13 2016We study the effective field theory of 2D fermions with a short-range interaction in the presence of a van Hove singularity. We find that there are additional divergences associated with the singularity that necessitate regularization beyond the usual ... More
An Effective Field Theory for Forward Scattering and Factorization ViolationJan 15 2016Aug 03 2016Starting with QCD, we derive an effective field theory description for forward scattering and factorization violation as part of the soft-collinear effective field theory (SCET) for high energy scattering. These phenomena are mediated by long distance ... More
Effective Field Theory of 2D van Hove SingularitiesJan 13 2016Apr 06 2018We study the effective field theory of 2D fermions with a short-range interaction in the presence of a van Hove singularity. We find that there are additional divergences associated with the singularity that necessitate regularization beyond the usual ... More
On the construction of composite Wannier functionsJun 24 2015Mar 09 2016We give a constructive proof for the existence of an $N$-dimensional Bloch basis which is both smooth (real analytic) and periodic with respect to its $d$-dimensional quasi-momenta, when $1\leq d\leq 2$ and $N\geq 1$. The constructed Bloch basis is conjugation ... More
Structure Function Sum rules for Systems with Large Scattering LengthsDec 29 2010Apr 13 2011We use a dispersion relation in conjunction with the operator product expansion (OPE) to derive model independent sum rules for the dynamic structure functions of systems with large scattering lengths. We present an explicit sum rule for the structure ... More
SAMBLASTER: fast duplicate marking and structural variant read extractionMar 28 2014Motivation: Illumina DNA sequencing is now the predominant source of raw genomic data, and data volumes are growing rapidly. Bioinformatic analysis pipelines are having trouble keeping pace. A common bottleneck in such pipelines is the requirement to ... More