Results for "Jeremy S. Perkins"

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VERITAS Observations of the Coma Cluster of GalaxiesOct 01 2008Clusters of galaxies are one of the few prominent classes of objects predicted to emit gamma rays not yet detected by satellites like EGRET or ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs). The detection of Very High Energy (VHE, E > 100 ... More
Casimir Interactions between Magnetic Flux Tubes in a Dense LatticeJul 28 2014Feb 18 2015We use the worldline numerics technique to study a cylindrically symmetric model of magnetic flux tubes in a dense lattice and the non-local Casimir forces acting between regions of magnetic flux. Within a superconductor the magnetic field is constrained ... More
Statistical ages and the cooling rate of X-ray dim isolated neutron starsMay 04 2013Aug 12 2013The cooling theory of neutron stars is corroborated by its comparison with observations of thermally emitting isolated neutron stars and accreting neutron stars in binary systems. An important ingredient for such an analysis is the age of the object, ... More
What is the nature of RX J0720.4-3125?Jan 06 1998RX J0720.4-3125 has recently been identified as a pulsating soft X-ray source in the ROSAT all-sky survey with a period of 8.391 s. Its spectrum is well characterized by a black-body with a temperature of $8 \times 10^5$ K. We propose that the radiation ... More
The Thermal Evolution of Ultramagnetized Neutron StarsOct 21 1997Using recently calculated analytic and numerical models for the thermal structure of ultramagnetized neutron stars, we estimate the effects that ultrastrong magnetic fields $B \ge 10^{14}$ G have on the thermal evolution of a neutron star. Understanding ... More
An Analytic Form for the Effective Lagrangian of QED and its Application to Pair Production and Photon SplittingJul 15 1996We derive an analytic form for the Heisenberg-Euler Lagrangian in the limit where the component of the electric field parallel to the magnetic field is small. We expand these analytic functions to all orders in the field strength ($F_{\mu\nu}F^{\mu\nu}$) ... More
A QED Model for the Origin of Bursts from SGRs and AXPsDec 23 2003Aug 31 2004We propose a model to account for the bursts from soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) in which quantum electrodynamics (QED) plays a vital role. In our theory, that we term ``fast-mode breakdown,'' magnetohydrodynamic (MHD) ... More
RCW 103 -- Revisiting a cooling neutron starMay 07 1998Recent observations of the compact source embedded within the supernova remnant RCW 103 rekindle interest in the origin of this object's emission. We contrast several models in which neutron-star cooling powers RCW 103. Specifically, either the presence ... More
Nonlinear Electromagnetic Waves in Magnetosphere of a MagnetarFeb 15 2010Nov 10 2010We compute electromagnetic wave propagation through the magnetosphere of a magnetar. The magnetosphere is modeled as the QED vacuum and a cold, strongly magnetized plasma. The background field and electromagnetic waves are treated nonperturbatively and ... More
Fermipy: An open-source Python package for analysis of Fermi-LAT DataJul 29 2017Fermipy is an open-source python framework that facilitates analysis of data collected by the Fermi Large Area Telescope (LAT). Fermipy is built on the Fermi Science Tools, the publicly available software suite provided by NASA for the LAT mission. Fermipy ... More
Bulk measurement of copper and sodium content in CuIn(0.7)Ga(0.3)Se(2) (CIGS) solar cells with nanosecond pulse length laser induced breakdown spectroscopy (LIBS)Jan 07 2013In this work, we show that laser induced breakdown spectroscopy (LIBS) with a nanosecond pulse laser can be used to measure the copper and sodium content of CuIn(0.7)Ga(0.3)Se(2) (CIGS) thin film solar cells on molybdenum. This method has four significant ... More
Implicit scaffolding in interactive simulations: Design strategies to support multiple educational goalsJun 27 2013Jan 23 2014We build on theoretical foundations of tool-mediated learning, tool design, and human computer interaction to develop a framework for implicit scaffolding in learning environments. Implicit scaffolding employs affordances, constraints, cueing, and feedback ... More
Variational study of the antiferromagnetic insulating phase of V2O3 based on Nth order Muffin-Tin-OrbitalsApr 17 2009Motivated by recent results of $N$th order muffin-tin orbital (NMTO) implementation of the density functional theory (DFT), we re-examine low-temperature ground-state properties of the anti-ferromagnetic insulating phase of vanadium sesquioxide V$_2$O$_3$. ... More
An effective spin-orbital Hamiltonian for the double perovskite Sr$_2$FeW O$_6$: Derivation of the phase diagramFeb 14 2003We formulate a superexchange theory of insulating double-perovskite compounds such as Sr$_2$FeWO$_6$. An effective spin-orbital Hamiltonian is derived in the strong coupling limit of Hubbard model for d-electrons on Fe and W ions. The relevant degrees ... More
Lichnerowicz Modes and Black Hole Families in Ricci Quadratic GravityApr 18 2017A new branch of black hole solutions occurs along with the standard Schwarzschild branch in $n$-dimensional extensions of general relativity including terms quadratic in the Ricci tensor. The standard and new branches cross at a point determined by a ... More
Spherically Symmetric Solutions in Higher-Derivative GravityJul 31 2015Dec 19 2015Extensions of Einstein gravity with quadratic curvature terms in the action arise in most effective theories of quantised gravity, including string theory. This article explores the set of static, spherically symmetric and asymptotically flat solutions ... More
Black Holes in Higher-Derivative GravityFeb 03 2015Apr 14 2015Extensions of Einstein gravity with higher-order derivative terms arise in string theory and other effective theories, as well as being of interest in their own right. In this paper we study static black-hole solutions in the example of Einstein gravity ... More
Potential for modulation of the hydrophobic effect inside chaperoninsFeb 05 2008Despite the spontaneity of some in vitro protein folding reactions, native folding in vivo often requires the participation of barrel-shaped multimeric complexes known as chaperonins. Although it has long been known that chaperonin substrates fold upon ... More
QED and the High Polarization of the Thermal Radiation from Neutron StarsMar 05 2002May 16 2002The thermal emission of strongly magnetized neutron-star atmospheres is thought to be highly polarized. However, because of the different orientations of the magnetic field over the surface of the neutron star (NS), it is commonly assumed that the net ... More
The Influence of Triaxial Halos on Collisionless Galactic DisksSep 09 2002Sep 11 2002We investigate the effect of rotating, triaxial halos on disk galaxies through an extensive set of numerical N-body simulations. Our simulations use a rigid potential field for the halos and bulges and collisionless particles for the disks. The triaxiality ... More
Cosmic Rays from Pulsars and MagnetarsMay 06 2010We compare the expected abundance of cosmic-ray electrons and positrons from pulsars and magnetars. We assume that the distribution of infant pulsars and magnetars follows that of high-mass stars in the Milky Way and that the production rate of cosmic ... More
Polarization Evolution in Strong Magnetic FieldsSep 20 1999Extremely strong magnetic fields change the vacuum index of refraction. Although this polarization dependent effect is small for typical neutron stars, it is large enough to decouple the polarization states of photons traveling within the field. The photon ... More
Uncertainty Propagation in Deep Neural Networks Using Extended Kalman FilteringSep 17 2018Extended Kalman Filtering (EKF) can be used to propagate and quantify input uncertainty through a Deep Neural Network (DNN) assuming mild hypotheses on the input distribution. This methodology yields results comparable to existing methods of uncertainty ... More
Supermassive black holes at high redshiftsMar 14 2019MeV blazars are the most luminous persistent sources in the Universe and emit most of their energy in the MeV band. These objects display very large jet powers and accretion luminosities and are known to host black holes with a mass often exceeding $10^9 ... More
cltorch: a Hardware-Agnostic Backend for the Torch Deep Neural Network Library, Based on OpenCLJun 15 2016This paper presents cltorch, a hardware-agnostic backend for the Torch neural network framework. cltorch enables training of deep neural networks on GPUs from diverse hardware vendors, including AMD, NVIDIA, and Intel. cltorch contains sufficient implementation ... More
The Dirichlet Problem for Harmonic Functions on Compact SetsApr 30 2010Jan 21 2011For any compact set $K\subset \mathbb{R}^n$ we develop the theory of Jensen measures and subharmonic peak points, which form the set $\mathcal{O}_K$, to study the Dirichlet problem on $K$. Initially we consider the space $h(K)$ of functions on $K$ which ... More
VERITAS Telescope 1 Relocation: Details and ImprovementsDec 18 2009The first VERITAS telescope was installed in 2002-2003 at the Fred Lawrence Whipple Observatory and was originally operated as a prototype instrument. Subsequently the decision was made to locate the full array at the same site, resulting in an asymmetric ... More
Relaxation time of the global order parameter on multiplex networks: the role of interlayer coupling in Kuramoto oscillatorsAug 06 2017This work considers the timescales associated with the global order parameter and the interlayer synchronization of coupled Kuramoto oscillators on multiplexes. For the two-layer multiplexes with initially high degree of synchronization in each layer, ... More
Doniach diagram for ordered, disordered and underscreened Kondo latticesAug 28 2007The Doniach's diagram has been originally proposed to describe the competition between the local Kondo effect and the intersite RKKY interactions in cerium compounds. Here we discuss the extension of this diagram to different variations of Kondo lattice ... More
Two-Component Fokker-Planck Models for the Evolution of Isolated Globular ClustersNov 11 1997Two-component (normal and degenerate stars) models are the simplest realization of clusters with a mass spectrum because high mass stars evolve quickly into degenerates, while low mass stars remain on the main-sequence for the age of the universe. Here ... More
Magnetic Lensing near Ultramagnetized Neutron StarsJan 27 1999Extremely strong magnetic fields change the vacuum index of refraction. This induces a lensing effect that is not unlike the lensing phenomenon in strong gravitational fields. The main difference between the two is the polarization dependency of the magnetic ... More
CHAM: action recognition using convolutional hierarchical attention modelMay 09 2017May 19 2017Recently, the soft attention mechanism, which was originally proposed in language processing, has been applied in computer vision tasks like image captioning. This paper presents improvements to the soft attention model by combining a convolutional LSTM ... More
Hierarchical Multi-scale Attention Networks for Action RecognitionAug 25 2017Aug 28 2017Recurrent Neural Networks (RNNs) have been widely used in natural language processing and computer vision. Among them, the Hierarchical Multi-scale RNN (HM-RNN), a kind of multi-scale hierarchical RNN proposed recently, can learn the hierarchical temporal ... More
Free Semidefinite Representation of Matrix Power FunctionsMay 18 2013Oct 09 2014Consider the matrix power function X^p defined over the cone of positive definite matrices S^{n}_{++}. It is known that X^p is convex over S^{n}_{++} if p is in [-1,0] or [1,2] and X^p is concave over S^{n}_{++} if p is in [0,1]. We show that the hypograph ... More
Non-additivity of van der Waals forces on liquid surfacesApr 18 2016Apr 19 2016We present an approach for modeling nanoscale wetting and dewetting of liquid surfaces that exploits recently developed, sophisticated techniques for computing van der Waals (vdW) or (more generally) Casimir forces in arbitrary geometries. We solve the ... More
Topological and algebraic pullback functorsMay 14 2012We give algebraic equivalents for certain desirable properties of pullback functors on categories of coverings and group sets, namely nullity zero, essential injectivity, and essential surjectivity. Nullity zero turns out to be equivalent to the notion ... More
Cantor set arithmeticNov 23 2017Every element $u$ of $[0,1]$ can be written in the form $u=x^2y$, where $x,y$ are elements of the Cantor set $C$. In particular, every real number between zero and one is the product of three elements of the Cantor set. On the other hand the set of real ... More
The dimension of the boundary of super-Brownian motionNov 09 2017We show that the Hausdorff dimension of the boundary of $d$-dimensional super-Brownian motion is $0$, if $d=1$, $4-2\sqrt2$, if $d=2$, and $(9-\sqrt{17})/2$, if $d=3$.
Markov chain approach to anomalous diffusion on Newman-Watts networksJan 31 2019Feb 26 2019A Markov chain (MC) formalism is used to investigate the mean-square displacement (MSD) of a random walker on Newman-Watts (NW) networks. It leads to a precise analysis of the conditions for the emergence of anomalous sub- or super-diffusive regimes in ... More
Aspects of classical backgrounds and scattering for affine Toda theory on a half-lineSep 23 1999In this paper we study various aspects of classical solutions to the affine Toda equations on a half-line with integrable boundary conditions. We begin by finding conditions that the theory has a stable vacuum by finding a Bogomolny bound on the energy, ... More
Probing Screening and the Graviton Mass with Gravitational WavesNov 06 2018Gravitational waves can probe fundamental physics, leading to new constraints on the mass of the graviton. Previous tests, however, have neglected the effect of screening, which is typically present in modified theories that predict a non-zero graviton ... More
Super-conducting critical fields and anisotropy of a MgB2 single crystalMay 02 2002May 07 2002Despite the intense activity in the year since the discovery of superconductivity in MgB2, key parameters, in particular the upper and lower critical fields Hc2 and Hc1 and their anisotropies, are not well-established, largely because of the difficulty ... More
Raman scattering in a Heisenberg {\boldmath $S=1/2$} antiferromagnet on the triangular latticeMar 02 2008We investigate two-magnon Raman scattering from the $S=1/2$ Heisenberg antiferromagnet on the triangular lattice, considering both the effect of renormalization of the one-magnon spectrum by 1/S corrections and final-state magnon-magnon interactions. ... More
Convex and subharmonic functions on graphsApr 01 2013We explore the relationship between convex and subharmonic functions on discrete sets. Our principal concern is to determine the setting in which a convex function is necessarily subharmonic. We initially consider the primary notions of convexity on graphs ... More
Extinction for two parabolic stochastic PDE's on the latticeMar 16 1999Dec 31 2001It is well known that, starting with finite mass, the super-Brownian motion dies out in finite time. The goal of this article is to show that with some additional work, one can prove finite time die-out for two types of systems of stochastic differential ... More
A lower bound for $p_c$ in range-$R$ bond percolation in two and three dimensionsMar 14 2016We use the connection between bond percolation and SIR epidemics to establish lower bounds for the critical percolation probability in $2$ and $3$ dimensions as the range becomes large. The bound agrees with the conjectured asymptotics for the long range ... More
Diffusion in jammed particle packsJul 31 2015Using random walk simulations we explore diffusive transport through monodisperse sphere packings over a range of packing fractions, $\phi$, in the vicinity of the jamming transition at $\phi_{c}$. Various diffusion properties are computed over several ... More
Cherenkov and Jansky: Our Understanding of AGN at the Highest EnergiesJun 21 2012Misaligned blazars have been the subject of some of the most successful radio and gamma-ray multiwavelength campaigns. These campaigns have included many of the major ground and space based gamma-ray telescopes and span decades of energy. Even though ... More
Unbounded derived categories and the finitistic dimension conjectureApr 25 2018We consider the question of whether the injective modules generate the unbounded derived category of a ring as a triangulated category with arbitrary coproducts. We give an example of a non-Noetherian commutative ring where they don't, but prove that ... More
On the Geometric Interpretation of the Complex Fourier Transforms of a Class of Exponential FunctionsJan 21 2009A class of complex Fourier Transforms of exponential functions which have all their zeros on the real line is explored from a geometric perspective. These transforms belong to the Laguerre - Polya class, and it is proved that all the zeros are simple. ... More
Stability and bifurcation of equilibria for the axisymmetric averaged mean curvature flowNov 08 2012Nov 09 2012We study the averaged mean curvature flow, also called the volume preserving mean curvature flow, in the particular setting of axisymmetric surfaces embedded in R^3 satisfying periodic boundary conditions. We establish analytic well--posedness of the ... More
Generalized covering space theoriesAug 20 2015In this paper, we unify various approaches to generalized covering space theory by introducing a categorical framework in which coverings are defined purely in terms of unique lifting properties. For each category $\mathcal{C}$ of path-connected spaces ... More
Quadratic forms representing all odd positive integersNov 03 2011Nov 06 2013We consider the problem of classifying all positive-definite integer-valued quadratic forms that represent all positive odd integers. Kaplansky considered this problem for ternary forms, giving a list of 23 candidates, and proving that 19 of those represent ... More
Radio scintillation of gamma-ray-burst afterglowsJun 09 1997Stars twinkle to the eye through atmospheric turbulence, but planets, because of their larger angular size, do not. Similarly, scintillation due to the local interstellar medium will modulate the radio flux of gamma-ray-burst afterglows and may permit ... More
Betting on Quantum ObjectsJul 20 2017Jul 28 2017Dutch book arguments have been applied to beliefs about the outcomes of measurements of quantum systems, but not to beliefs about quantum objects prior to measurement. In this paper, we prove a quantum version of the probabilists' Dutch book theorem that ... More
Probabilism for Stochastic TheoriesSep 09 2018I defend an analog of probabilism that characterizes rationally coherent estimates for chances. Specifically, I demonstrate the following accuracy-dominance result for stochastic theories in the C*-algebraic framework: supposing an assignment of chance ... More
The intermediate age population of the Galactic haloMar 13 2019We have learned recently that the inner halo of the Milky Way contains a kinematically coherent component (Gaia-Enceladus) from a significant merger 10 Gyrs ago. By contrast the inner halo (defined to exclude the Magellanic Stream) contains no similar ... More
The MERger-event Gamma-Ray (MERGR) TelescopeNov 09 2017We describe the MERger-event Gamma-Ray (MERGR) Telescope intended for deployment by ~2021. MERGR will cover from 20 keV to 2 MeV with a wide field of view (6 sr) using nineteen gamma-ray detectors arranged on a section of a sphere. The telescope will ... More
The Derived Marsden-Weinstein Quotient is SymplecticMay 29 2012Let $(X,\omega_X)$ be a derived scheme with a 0-symplectic form and suppose there is a Hamiltonian $G$-action with a moment map for $G$ a reductive group. We prove, under no further assumptions, that symplectic reduction along any coadjoint orbit in the ... More
An infinite-temperature limit for a quantum scattering processJan 04 2008Dec 12 2008We study a quantum dynamical semigroup driven by a Lindblad generator with a deterministic Schr\"odinger part and a noisy Poission-timed scattering part. The dynamics describes the evolution of a test particle in $\R^{n}$, $n=1,2,3$, immersed in a gas, ... More
A limit theorem to a time-fractional diffusionOct 04 2011Feb 12 2013We prove a limit theorem for an integral functional of a Markov process. The Markovian dynamics is characterized by a linear Boltzmann equation modeling a one-dimensional test particle of mass $\lambda^{-1}\gg 1$ in an external periodic potential and ... More
A completely integrable system on $G_2$ coadjoint orbitsMay 05 2016May 23 2016We construct a Gelfand-Zeitlin system on a one-parameter family of $G_2$ coadjoint orbits that are multiplicity-free Hamiltonian $SU(3)$-spaces. Using this system we prove a lower bound for the Gromov width of these orbits. This lower bound agrees with ... More
Next Generation Deep 2 micron SurveySep 18 2012There is a major opportunity for the KDUST 2.5m telescope to carry out the next generation IR survey. A resolution of 0.2 arcsec is obtainable from Dome A over a wide field. This opens a unique discovery space during the 2015-2025 decade. A next generation ... More
A far-from-CMC existence result for the constraint equations on manifolds with ends of cylindrical typeJun 03 2013Jul 25 2013We extend the study of the vacuum Einstein constraint equations on manifolds with ends of cylindrical type initiated by Chru\'sciel and Mazzeo by finding a class of solutions to the fully coupled system on such manifolds. We show that given a Yamabe positive ... More
On identities involving the sixth order mock theta functionsNov 13 2009Nov 16 2009We present q-series proofs of four identities involving sixth order mock theta functions from Ramanujan's lost notebook. We also show how Ramanujan's identities can be used to give a quick proof of four sixth order identities of Berndt and Chan.
Measuring the impact of input data on energy consumption of softwareNov 10 2014The amount of energy consumed during the execution of software, and the ability to predict future consumption, is an important factor in the design of embedded electronic systems. In this technical report I examine factors in the execution of software ... More
A cocomplete but not complete abelian categoryMay 27 2018An example of a cocomplete abelian category that is not complete is constructed.
Uniform distribution and algorithmic randomnessMar 19 2012Jul 14 2012A seminal theorem due to Weyl states that if (a_n) is any sequence of distinct integers, then, for almost every real number x, the sequence (a_n x) is uniformly distributed modulo one. In particular, for almost every x in the unit interval, the sequence ... More
Proximity inductive dimension and Brouwer dimension agree on compact Hausdorff spacesMar 04 2019In this paper we show that the proximity inductive dimension defined by Isbell agrees with the Brouwer dimension originally described by Brouwer on the class of compact Hausdorff spaces. Consequently, Fedorchuk's example of a compact Hausdorff space whose ... More
Concerning thermal tides on hot JupitersJan 21 2009By analogy with a mechanism proposed by Gold and Soter to explain the retrograde rotation of Venus, Arras and Socrates suggest that thermal tides may excite hot jovian exoplanets into nonsynchronous rotation, and perhaps also noncircular orbits. It is ... More
Weighing the "Heaviest" Polya UrnFeb 13 2014Jun 29 2014In the classical Polya urn problem, one begins with $d$ bins, each containing one ball. Additional balls arrive one at a time, and the probability that an arriving ball is placed in a given bin is proportional to $m^\gamma$, where $m$ is the number of ... More
Integers represented by positive-definite quadratic forms and Petersson inner productsFeb 09 2018Let $Q$ be a positive-definite quaternary quadratic form with integer coefficients. We study the problem of giving bounds on the largest positive integer $n$ that is locally represented by $Q$ but not represented. Assuming that $n$ is relatively prime ... More
Compressed words and automorphisms in fully residually free groupsAug 05 2009Oct 21 2009We show that the compressed word problem in a finitely-generated fully residually free group (F -group) is decidable in polynomial time, and use the result to show that the word problem in the automorphism group of such a group is decidable in polynomial ... More
Topological Monodromy of an Integrable Heisenberg Spin ChainNov 25 2014Jul 31 2015We investigate topological properties of a completely integrable system on $S^2\times S^2 \times S^2$ which was recently shown to have a Lagrangian fiber diffeomorphic to $\mathbb{R} P^3$ not displaceable by a Hamiltonian isotopy [Oakley J., Ph.D. Thesis, ... More
A Discretized Fourier Orthogonal Expansion in Orthogonal Polynomials on a CylinderJun 12 2009We study the convergence of a discretized Fourier orthogonal expansion in orthogonal polynomials on $B^2 \times [-1,1]$, where $B^2$ is the closed unit disk in $\RR^2$. The discretized expansion uses a finite set of Radon projections and provides an algorithm ... More
Inside-out Galaxy FormationOct 29 1997Mar 01 1999Current theories of galaxy formation have tended to focus on hierarchical structure formation, which is the most likely scenario for cosmological models with lots of power at small scales (e.g. standard cold dark matter). Models with little small scale ... More
Felix de Roy: a life of variable starsNov 28 2010Apr 22 2011Felix de Roy (1883-1942), an internationality recognised amateur astronomer, made significant contributions to variable star research. As an active observer, he made some 91,000 visual estimates of a number of different variable stars. A Belgian national, ... More
The fundamental group as a topological groupSep 21 2010Feb 26 2012This paper is devoted to the study of a natural group topology on the fundamental group which remembers local properties of spaces forgotten by covering space theory and weak homotopy type. It is known that viewing the fundamental group as the quotient ... More
Work Issues in Software EngineeringMar 11 2013Using data from a web-based survey of software developers, the author attempts to determine root causes of "death march" projects and excessive work hours in the software industry in relation to company practices and management. Special emphasis is placed ... More
Open subgroups of free topological groupsSep 25 2012Feb 01 2013The theory of covering spaces is often used to prove the Nielsen-Schreier theorem, which states that every subgroup of a free group is free. We apply the more general theory of semicovering spaces to obtain analogous subgroup theorems for topological ... More
High Speed Interconnects and Parallel Software Libraries: Enabling Technologies for the NVOSep 08 2000The NVOs core data mining and archive federation activities are heavily dependent on the underlying data pipeline software necessary to translate the raw data into scientifically relevant source detections. The data pipeline software dictates: the raw ... More
Arthur Neville Brown: schoolmaster and variable star observerSep 18 2012Sep 27 2012Arthur Neville Brown, MA, FRAS (1864-1934) was a prolific variable star observer and served for many years as Secretary of the BAA Variable Star Section. This paper discusses Brown's life and career, both as a variable star enthusiast and as a dedicated ... More
Ernest Elliott Markwick: variable stars and military campaignsSep 20 2011Colonel E.E. Markwick, CB, CBE, FRAS (1853 - 1925) pursued a distinguished career in the British Army, serving in Great Britain and other parts of the Empire and rising to the rank of Colonel. He was an original member of the BAA and went on to become ... More
A priori bounds for some infinitely renormalizable quadratics: I. Bounded primitive combinatoricsSep 01 2006Sep 06 2006We prove the a priori bounds for infinitely renormalizable quadratic polynomials of bounded primitive type. This implies the local connectivity of the Mandelbrot set at the corresponding points.
Uncomputably noisy ergodic limitsMay 03 2011Oct 31 2011V'yugin has shown that there are a computable shift-invariant measure on Cantor space and a simple function f such that there is no computable bound on the rate of convergence of the ergodic averages A_n f. Here it is shown that in fact one can construct ... More
Minimally Ramified Deformations when $\ell \neq p$Jul 27 2018Let $p$ and $\ell$ be distinct primes, and $\rho$ be an orthogonal or symplectic representation of the absolute Galois group of an $\ell$-adic field over a finite field of characteristic $p$. We define and study a liftable deformation condition of lifts ... More
Explicit bounds for sums of squaresMay 24 2011For an even integer $k$, let $r_{2k}(n)$ be the number of representations of $n$ as a sum of $2k$ squares. The quantity $r_{2k}(n)$ is appoximated by the classical singular series $\rho_{2k}(n) \asymp n^{k-1}$. Deligne's bound on the Fourier coefficients ... More
Lost in Math? A review of 'Lost in Math: How Beauty Leads Physics Astray', by Sabine HossenfelderFeb 09 2019This is a review of Hossenfelder's book, 'Lost in Math: How Beauty Leads Physics Astray'. The book gives a breezy exposition of the present situation in fundamental physics, and raises important questions: both about the content of the physics, and the ... More
Spin systems on Bethe latticesAug 10 2018In an extremely influential paper Mezard and Parisi put forward an analytic but non-rigorous approach called the cavity method for studying spin systems on the Bethe lattice, i.e., the random $d$-regular graph [Eur. Phys. J. B 20 (2001) 217--233]. Their ... More
First order magnetic transition in CeFe$_2$ alloys: Phase-coexistence and metastabilityDec 15 2003First order ferromagnetic (FM) to antiferromagnetic (AFM) phase transition in doped-CeFe$_2$ alloys is studied with micro-Hall probe technique. Clear visual evidence of magnetic phase-coexistence on micrometer scales and the evolution of this phase-coexistence ... More
Testing randomness with photonsDec 06 2013Generating and characterising randomness is fundamentally important in both classical and quantum information science. Here we report the experimental demonstration of ensembles of pseudorandom optical processes comprising what are known as t-designs. ... More
Chandra observations of Cygnus OB2Mar 03 2011Cygnus OB2 is the nearest example of a massive star forming region, containing over 50 O-type stars and hundreds of B-type stars. We have analyzed two Chandra pointings in Cyg OB2, detecting ~1700 X-ray sources, of which ~1450 are thought to be members ... More
Multi-robot Dubins Coverage with Autonomous Surface VehiclesAug 07 2018In large scale coverage operations, such as marine exploration or aerial monitoring, single robot approaches are not ideal, as they may take too long to cover a large area. In such scenarios, multi-robot approaches are preferable. Furthermore, several ... More
Image Captioning Based on a Hierarchical Attention Mechanism and Policy Gradient OptimizationNov 13 2018Jan 11 2019Automatically generating the descriptions of an image, i.e., image captioning, is an important and fundamental topic in artificial intelligence, which bridges the gap between computer vision and natural language processing. Based on the successful deep ... More
Traffic scene recognition based on deep cnn and vlad spatial pyramidsJul 24 2017Traffic scene recognition is an important and challenging issue in Intelligent Transportation Systems (ITS). Recently, Convolutional Neural Network (CNN) models have achieved great success in many applications, including scene classification. The remarkable ... More
The Age of the Directly-Imaged Planet Host Star $κ$ Andromedae Determined From Interferometric ObservationsApr 07 2016$\kappa$ Andromedae, an early type star that hosts a directly imaged low mass companion, is expected to be oblate due to its rapid rotational velocity ($v\sin i$ = $\sim$162 $\mathrm{km~s^{-1}}$). We observed the star with the CHARA Array's optical beam ... More
Stochastic Activation Pruning for Robust Adversarial DefenseMar 05 2018Neural networks are known to be vulnerable to adversarial examples. Carefully chosen perturbations to real images, while imperceptible to humans, induce misclassification and threaten the reliability of deep learning systems in the wild. To guard against ... More
Evolution of Internal Granular Structure at the Flow-Arrest TransitionMar 02 2019The evolution of the internal granular structure in shear-arrested and shear-flowing states of granular materials is characterized using fabric tensors as descriptors of the internal contact and force networks. When a dilute system of frictional grains ... More
Void Statistics in Large Galaxy Redshift Surveys: Does Halo Occupation of Field Galaxies Depend on Environment?Jul 23 2007We use measurements of the projected galaxy correlation function w_p and galaxy void statistics to test whether the galaxy content of halos of fixed mass is systematically different in low density environments. We present new measurements of the void ... More
The Central X-Ray Point Source in Cassiopeia AJan 04 2000Sep 10 2000The spectacular first light observation by the Chandra X-Ray Observatory revealed an X-ray point source near the center of the 300 yr old Cas A supernova remnant. We present an analysis of the public X-ray spectral and timing data. No coherent pulsations ... More