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Results for "David A. Forsyth"

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Big but Imperceptible Adversarial Perturbations via Semantic ManipulationApr 12 2019Machine learning, especially deep learning, is widely applied to a range of applications including computer vision, robotics and natural language processing. However, it has been shown that machine learning models are vulnerable to adversarial examples, ... More
Weakly chained matrices, policy iteration, and impulse controlOct 13 2015Mar 26 2016This work is motivated by numerical solutions to Hamilton-Jacobi-Bellman quasi-variational inequalities (HJBQVIs) associated with combined stochastic and impulse control problems. In particular, we consider (i) direct control, (ii) penalized, and (iii) ... More
The existence of optimal bang-bang controls for GMxB contractsFeb 19 2015Nov 04 2015A large collection of financial contracts offering guaranteed minimum benefits are often posed as control problems, in which at any point in the solution domain, a control is able to take any one of an uncountable number of values from the admissible ... More
Weakly chained matrices, policy iteration, and impulse controlOct 13 2015Sep 24 2017This work is motivated by numerical solutions to Hamilton-Jacobi-Bellman quasi-variational inequalities (HJBQVIs) associated with combined stochastic and impulse control problems. In particular, we consider (i) direct control, (ii) penalized, and (iii) ... More
CDVAE: Co-embedding Deep Variational Auto Encoder for Conditional Variational GenerationDec 01 2016Problems such as predicting an optical flow field (Y) for an image (X) are ambiguous: many very distinct solutions are good. Representing this ambiguity requires building a conditional model P(Y|X) of the prediction, conditioned on the image. It is hard ... More
Detecting Anomalous Faces with 'No Peeking' AutoencodersFeb 15 2018Detecting anomalous faces has important applications. For example, a system might tell when a train driver is incapacitated by a medical event, and assist in adopting a safe recovery strategy. These applications are demanding, because they require accurate ... More
Swapout: Learning an ensemble of deep architecturesMay 20 2016We describe Swapout, a new stochastic training method, that outperforms ResNets of identical network structure yielding impressive results on CIFAR-10 and CIFAR-100. Swapout samples from a rich set of architectures including dropout, stochastic depth ... More
Dense domains, symmetric operators and spectral triplesJun 07 2013This article is about erroneous attempts to weaken the standard definition of unbounded Kasparov module (or spectral triple). We present counterexamples to claims in the literature that Fredholm modules can be obtained from these weaker variations of ... More
An Approximate Shading Model with Detail Decomposition for Object RelightingApr 20 2018We present an object relighting system that allows an artist to select an object from an image and insert it into a target scene. Through simple interactions, the system can adjust illumination on the inserted object so that it appears naturally in the ... More
Learning Diverse Image ColorizationDec 06 2016Colorization is an ambiguous problem, with multiple viable colorizations for a single grey-level image. However, previous methods only produce the single most probable colorization. Our goal is to model the diversity intrinsic to the problem of colorization ... More
Authoring image decompositions with generative modelsDec 05 2016We show how to extend traditional intrinsic image decompositions to incorporate further layers above albedo and shading. It is hard to obtain data to learn a multi-layer decomposition. Instead, we can learn to decompose an image into layers that are "like ... More
A Visual Representation for Editing Face ImagesDec 02 2016We propose a new approach for editing face images, which enables numerous exciting applications including face relighting, makeup transfer and face detail editing. Our face edits are based on a visual representation, which includes geometry, face segmentation, ... More
Rotation Blurring: Use of Artificial Blurring to Reduce Cybersickness in Virtual Reality First Person ShootersOct 06 2017Users of Virtual Reality (VR) systems often experience vection, the perception of self-motion in the absence of any physical movement. While vection helps to improve presence in VR, it often leads to a form of motion sickness called cybersickness. Cybersickness ... More
Quantitative Evaluation of Style TransferMar 31 2018Style transfer methods produce a transferred image which is a rendering of a content image in the manner of a style image. There is a rich literature of variant methods. However, evaluation procedures are qualitative, mostly involving user studies. We ... More
Distinct differences in the nanoscale behaviors of the twist-bend liquid crystal phase of a flexible linear trimer and homologous dimerOct 02 2017Feb 19 2018We synthesized the liquid crystal dimer and trimer members of a series of flexible linear oligomers and characterized their microscopic and nanoscopic properties using resonant soft x-ray scattering and a number of other experimental techniques. On the ... More
Where's My Drink? Enabling Peripheral Real World Interactions While Using HMDsFeb 16 2015Head Mounted Displays (HMDs) allow users to experience virtual reality with a great level of immersion. However, even simple physical tasks like drinking a beverage can be difficult and awkward while in a virtual reality experience. We explore mixed reality ... More
Learning Diverse Image ColorizationDec 06 2016Apr 27 2017Colorization is an ambiguous problem, with multiple viable colorizations for a single grey-level image. However, previous methods only produce the single most probable colorization. Our goal is to model the diversity intrinsic to the problem of colorization ... More
Max-Sliced Wasserstein Distance and its use for GANsApr 11 2019Generative adversarial nets (GANs) and variational auto-encoders have significantly improved our distribution modeling capabilities, showing promise for dataset augmentation, image-to-image translation and feature learning. However, to model high-dimensional ... More
Piecewise Constant Policy Approximations to Hamilton-Jacobi-Bellman EquationsMar 19 2015Jan 20 2016An advantageous feature of piecewise constant policy timestepping for Hamilton-Jacobi-Bellman (HJB) equations is that different linear approximation schemes, and indeed different meshes, can be used for the resulting linear equations for different control ... More
Factorisation of equivariant spectral triples in unbounded KK-theoryMay 12 2015We provide sufficient conditions to factorise an equivariant spectral triple as a Kasparov product of unbounded classes constructed from the group action on the algebra and from the fixed point spectral triple. Our results are for the action of compact ... More
A new technique for determining Substorm Onsets and Phases from Indices of the Electrojet (SOPHIE)Jun 07 2016We present a new quantitative technique that determines the times and durations of substorm expansion and recovery phases and possible growth phases based on percentiles of the rate of change of auroral electrojet indices. By being able to prescribe different ... More
Dawn-dusk asymmetries in the coupled solar wind-magnetosphere-ionosphere system: a reviewJan 17 2017Dawn-dusk asymmetries are ubiquitous features of the coupled solar-wind-magnetosphere-ionosphere system. During the last decades, increasing availability of satellite and ground-based measurements has made it possible to study these phenomena in more ... More
Itinerant Antiferromagnetism in FeGe_2Oct 01 1996FeGe_2, and lightly doped compounds based on it, have a Fermi surface driven instability which drive them into an incommensurate spin density wave state. Studies of the temperature and magnetic field dependence of the resistivity have been used to determine ... More
Measured Aperture-Array Noise Temperature of the Mark II Phased Array Feed for ASKAPSep 18 2015Nov 06 2015We have measured the aperture-array noise temperature of the first Mk. II phased array feed that CSIRO has built for the Australian Square Kilometre Array Pathfinder telescope. As an aperture array, the Mk. II phased array feed achieves a beam equivalent ... More
Establishing, versus Maintaining, Brain Function: A Neuro-computational Model of Cortical Reorganization after Injury to the Immature BrainDec 22 2011The effect of age at injury on outcome after acquired brain injury (ABI) has been the subject of much debate. Many argue that young brains are relatively tolerant of injury. A contrasting viewpoint due to Hebb argues that greater system integrity may ... More
Interplanetary Coronal Mass Ejections observed by MESSENGER and Venus ExpressNov 24 2015Interplanetary coronal mass ejections (ICMEs) observed by the MESSENGER (MES) and Venus Express (VEX) spacecraft have been catalogued and analysed. The ICMEs were identified by a relatively smooth rotation of the magnetic field direction consistent with ... More
Metacommutation as a Group Action on the Projective Line over $\mathbf{F}_\mathbf{p}$Mar 21 2015Cohn and Kumar showed the quadratic character of $q$ modulo $p$ gives the sign of the permutation of Hurwitz primes of norm $p$ induced by the Hurwitz primes of norm $q$ under metacommutation. We demonstrate that these permutations are equivalent to those ... More
Remarks on Privileged WordsNov 28 2013We discuss the notion of privileged word, recently introduced by Peltomaki. A word w is privileged if it is of length <=1, or has a privileged border that occurs exactly twice in w. We prove the following results: (1) if w^k is privileged for some k >=1, ... More
Measured Sensitivity of the First Mark II Phased Array Feed on an ASKAP AntennaSep 02 2015This paper presents the measured sensitivity of CSIRO's first Mk. II phased array feed (PAF) on an ASKAP antenna. The Mk. II achieves a minimum system-temperature-over-efficiency $T_\mathrm{sys}/\eta$ of 78 K at 1.23 GHz and is 95 K or better from 835 ... More
On the rate of convergence to stationarity of the M/M/N queue in the Halfin-Whitt regimeMar 10 2010Sep 09 2013We prove several results about the rate of convergence to stationarity, that is, the spectral gap, for the M/M/n queue in the Halfin-Whitt regime. We identify the limiting rate of convergence to steady-state, and discover an asymptotic phase transition ... More
Steady-state $\mathit{GI}/\mathit{GI}/\mathit{n}$ queue in the Halfin-Whitt regimeMar 09 2011Dec 03 2013We consider the FCFS $\mathit{GI}/\mathit{GI}/n$ queue in the so-called Halfin-Whitt heavy traffic regime. We prove that under minor technical conditions the associated sequence of steady-state queue length distributions, normalized by $n^{1/2}$, is tight. ... More
Acceleration of Solar Wind Ions by Nearby Interplanetary Shocks: Comparison of Monte Carlo Simulations with Ulysses ObservationsOct 02 1996The most stringent test of theoretical models of the first-order Fermi mechanism at collisionless astrophysical shocks is a comparison of the theoretical predictions with observational data on particle populations. Such comparisons have yielded good agreement ... More
Boundaries, spectral triples and K-homologyJul 25 2016This paper extends the notion of a spectral triple to a relative spectral triple, an unbounded analogue of a relative Fredholm module for an ideal $J\triangleleft A$. Examples include manifolds with boundary, manifolds with conical singularities, dimension ... More
Non-Negative Networks Against Adversarial AttacksJun 15 2018Jan 03 2019Adversarial attacks against neural networks are a problem of considerable importance, for which effective defenses are not yet readily available. We make progress toward this problem by showing that non-negative weight constraints can be used to improve ... More
Multi-point shock and flux rope analysis of multiple interplanetary coronal mass ejections around 2010 August 1 in the inner heliosphereSep 13 2012We present multi-point in situ observations of a complex sequence of coronal mass ejections (CMEs) which may serve as a benchmark event for numerical and empirical space weather prediction models. On 2010 August 1, instruments on various space missions ... More
Stochastic gradient variational Bayes for gamma approximating distributionsSep 04 2015While stochastic variational inference is relatively well known for scaling inference in Bayesian probabilistic models, related methods also offer ways to circumnavigate the approximation of analytically intractable expectations. The key challenge in ... More
Comments on D-brane Dynamics Near NS5-BranesAug 10 2004Sep 16 2004We study the properties of a D-brane in the presence of $k$ NS5 branes. The Dirac-Born-Infeld action describing the dynamics of this D-brane is very similar to that of a non-BPS D-brane in ten dimensions. As the D-brane approaches the fivebranes, its ... More
A Chandra and XMM View of the Mass & Metals in Galaxy Groups and ClustersOct 28 2002X-ray observations with Chandra and XMM are providing valuable new measurements of the baryonic and dark matter content of groups and clusters. Masses of cD clusters obtained from X-ray and gravitational lensing studies generally show good agreement, ... More
X-Ray Evidence for Multiphase Hot Gas with Nearly Solar Fe Abundances in the Brightest Groups of GalaxiesMar 18 1999Aug 27 1999We analyze the ASCA spectra accumulated within ~100 kpc radii of 12 of the brightest groups of galaxies. Upon fitting isothermal models (1T) jointly to the ASCA SIS and GIS spectra we obtain fits for most groups that are of poor or at best marginal quality ... More
On The Origin of Radio Halos in Galaxy ClustersApr 11 2001May 15 2001Previously it has been recognized that radio halos in galaxy clusters are preferentially associated with merging systems as indicated by substructure in the X-ray images and temperature maps. Since, however, many clusters without radio halos also possess ... More
Renormalization Group Flows from Gravity in Anti-de Sitter Space versus Black Hole No-Hair TheoremsMar 06 2000Apr 10 2000Black hole no-hair theorems are proven using inequalities that govern the radial dependence of spherically symmetric configurations of matter fields. In this paper, we analyze the analogous inequalities for geometries dual to renormalization group flows ... More
Constraints on Higher Derivative Operators in the Matrix Theory Effective LagrangianOct 12 1998Oct 13 1998The consistency of Matrix theory with supergravity requires that in the large N_c limit terms of order v^4 in the SU(N_c) Matrix effective potential are not renormalized beyond one loop in perturbation theory. For SU(2) gauge group, the required non-renormalization ... More
Alternating Subgroups of Exceptional Groups of Lie TypeSep 02 2015Jun 07 2016In this paper we examine embeddings of alternating groups and symmetric groups into almost simple groups of exceptional type. In particular, we prove that unless the alternating or symmetric group has degree 6 or 7, there is no maximal subgroup of any ... More
From gauge transformations to topology computation in quantum lattice gas automataMay 17 2001The evolution of a quantum lattice gas automaton (LGA) for a single charged particle is invariant under multiplication of the wave function by a global phase. Requiring invariance under the corresponding local gauge transformations determines the rule ... More
Scale decoherence in inhomogeneous potentialsMay 14 1998Finite precision measurement factors the Hilbert space of a quantum system into a tensor product $H_{coarse} \otimes H_{fine}$. This is mathematically equivalent to the partition into system and environment which forms the arena for decoherence, so we ... More
Quantum lattice gases and their invariantsMar 16 1997The one particle sector of the simplest one dimensional quantum lattice gas automaton has been observed to simulate both the (relativistic) Dirac and (nonrelativistic) Schroedinger equations, in different continuum limits. By analyzing the discrete analogues ... More
Growth-Algorithm Model of Leaf ShapeApr 25 2010The innumerable shapes of plant leaves present a challenge to the explanatory power of biophysical theory. A model is needed that can produce these shapes with a small set of parameters. This paper presents a simple model of leaf shape based on a growth ... More
Control-based continuation: bifurcation and stability analysis for physical experimentsJun 12 2015Dec 22 2015Control-based continuation is technique for tracking the solutions and bifurcations of nonlinear experiments. The basic idea is to apply the method of numerical continuation to a feedback-controlled physical experiment. Since in an experiment it is not ... More
Towards Patterns for Heaps and Imperative LambdasOct 19 2015In functional programming, point-free relation calculi have been fruitful for general theories of program construction, but for specific applications pointwise expressions can be more convenient and comprehensible. In imperative programming, refinement ... More
The Hausdorff dimension of a class of random self-similar fractal treesOct 22 2012In this article a collection of random self-similar fractal dendrites is constructed, and their Hausdorff dimension is calculated. Previous results determining this quantity for random self-similar structures have relied on geometrical properties of an ... More
Random walk on the range of random walkOct 23 2012We study the random walk $X$ on the range of a simple random walk on $\mathbb{Z}^d$ in dimensions $d\geq 4$. When $d\geq 5$ we establish quenched and annealed scaling limits for the process $X$, which show that the intersections of the original simple ... More
Well-posed two-point initial-boundary value problems with arbitrary boundary conditionsApr 29 2011Sep 26 2011We study initial-boundary value problems for linear evolution equations of arbitrary spatial order, subject to arbitrary linear boundary conditions and posed on a rectangular 1-space, 1-time domain. We give a new characterisation of the boundary conditions ... More
Review of the Solar Array TelescopesAug 11 2006For several years the only experiments sensitive to astrophysical gamma rays with energies beyond the reach of EGRET but below that of the Cherenkov imaging telescopes have been the "solar tower" detectors. They use >2000 m2 mirror areas to sample the ... More
On Conjugacy of Maximal Subalgebras of Solvable Lie AlgebrasOct 17 2011The purpose of this paper is to consider when two maximal subalgebras of a finite-dimensional solvable Lie algebra $L$ are conjugate, and to investigate their intersection.
Solvable Complemented Lie AlgebrasApr 19 2011In this paper a characterisation is given of solvable complemented Lie algebras. They decompose as a direct sum of abelian subalgebras and their ideals relate nicely to this decomposition. The class of such algebras is shown to be a formation whose residual ... More
The index complex of a maximal subalgebra of a Lie algebraJun 29 2010Let M be a maximal subalgebra of the Lie algebra L. A subalgebra C of L is said to be a completion for M if C is not contained in M but every proper subalgebra of C that is an ideal of L is contained in M. The set I(M) of all completions of M is called ... More
Second-order Markov random fields for independent sets on the infinite Cayley treeJan 09 2013Jun 18 2015Recently, there has been significant interest in understanding the properties of Markov random fields (M.r.f.) defined on the independent sets of sparse graphs. When these M.r.f. are restricted to pairwise interactions (i.e. hardcore model), much progress ... More
On the steady-state probability of delay and large negative deviations for the $GI/GI/n$ queue in the Halfin-Whitt regimeJun 30 2013Aug 31 2016We consider the FCFS $GI/GI/n$ queue in the Halfin-Whitt heavy traffic regime, and prove bounds for the steady-state probability of delay (s.s.p.d.) for generally distributed processing times. We prove that there exist $\epsilon_1, \epsilon_2 > 0$, depending ... More
Equations of Parametric Surfaces via SyzygiesOct 11 2000Feb 22 2001The revised version has two additional references and a shorter proof of Proposition 5.7. This version also makes numerous small changes and has an appendix containing a proof of the degree formula for a parametrized surface.
On certain decompositions of solvable Lie algebrasDec 04 2012May 03 2013The author has previously shown that solvable Lie A-algebras and complemented solvable Lie algebras decompose as a vector space direct sum of abelian subalgebras, and their ideals relate nicely to this decomposition. However, neither of these classes ... More
Simple Modules for Groups with Abelian Sylow 2-Subgroups are AlgebraicJan 17 2008May 18 2008Let G be a finite group and let p be a prime. A module for G over a field of characteristic p is called algebraic if it satisfies a polynomial, with addition and multiplication given by direct sum and tensor product. In some sense, having this property ... More
The Schwinger model on $S^1$: Hamiltonian formulation, vacuum and anomalyJun 18 2012We present a Hamiltonian formulation of the Schwinger model on the circle in Coulomb gauge as a semi-bounded self-adjoint operator which is invariant under the modular group ${\cal M}=\Z$ of large gauge transformations. There is a nontrivial action of ... More
Perverse Equivalences and Broué's Conjecture II: The Cyclic CaseJun 30 2012We study Brou\'e's abelian defect group conjecture for groups of Lie type using the recent theory of perverse equivalences and Deligne--Lusztig varieties. Our approach is to analyze the perverse equivalence induced by certain Deligne--Lusztig varieties ... More
Fundamental Limit to Linear One-Dimensional Slow Light StructuresOct 18 2007Using a new general approach to limits in optical structures that counts orthogonal waves generated by scattering, we derive an upper limit to the number of bits of delay possible in one-dimensional slow light structures that are based on linear optical ... More
The $(2,p)$-generation of sporadic simple groupsJul 07 2015In this short note we prove that, if $p$ is an odd prime dividing the order of a sporadic simple group, then with the exception of four groups for $p=3$, all sporadic simple groups are generated by an involution and an element of order $p$.
Rare and Forbidden Decays of D MesonsMay 14 2001We summarize the results of two recent searches for flavor-changing neutral current, lepton-flavor violating, and lepton-number violating decays of D+, Ds, and D0 mesons (and their antiparticles) into modes containing muons and electrons. Using data from ... More
Scaling limits for simple random walks on random ordered graph treesOct 22 2012Oct 23 2012Consider a family of random ordered graph trees $(T_n)_{n\geq 1}$, where $T_n$ has $n$ vertices. It has previously been established that if the associated search-depth processes converge to the normalised Brownian excursion when rescaled appropriately ... More
Heat kernel fluctuations for a resistance form with non-uniform volume growthOct 22 2012In this article, we consider the problem of estimating the heat kernel on measure-metric spaces equipped with a resistance form. Such spaces admit a corresponding resistance metric that reflects the conductivity properties of the set. In this situation, ... More
Toric ResiduesOct 19 1994In ${\bf C}^{n+1}$, one can show that the residue of $n+1$ homogeneous forms of the same degree equals the integral of a certain $(n,n)$ form over ${\bf P}^n$. Furthermore, the Jacobian of the forms has nonzero residue equal to a certain intersection ... More
On n-maximal subalgebras of Lie algebrasFeb 10 2015A chain $S_0 < S_1 < \ldots < S_n = L$ is a {\em maximal chain} if each $S_i$ is a maximal subalgebra of $S_{i+1}$. The subalgebra $S_0$ in such a series is called an {\em $n$-maximal} subalgebra. There are many interesting results concerning the question ... More
On the Lengths of Certain Chains of Subalgebras in Lie AlgebrasDec 10 2011May 07 2013In this paper we study the lengths of certain chains of subalgebras of a Lie algebra L: namely, a chief series, a maximal chain of minimal length, a chain of maximal length in which each subalgebra is modular in L, and a chain of maximal length in which ... More
Supplements to maximal subalgebras of Lie algebrasJul 28 2010For a Lie algebra $L$ and a subalgebra $M$ of $L$ we say that a subalgebra $U$ of $L$ is a {\em supplement} to $M$ in $L$ if $L = M + U$. We investigate those Lie algebras all of whose maximal subalgebras have abelian supplements, those that have nilpotent ... More
On maximal subalgebras of Lie algebras containing Engel subalgebrasApr 28 2010Relationships between certain properties of maximal subalgebras of a Lie algebra $L$ and the structure of $L$ itself have been studied by a number of authors. Amongst the maximal subalgebras, however, some exert a greater influence on particular results ... More
Well-posedness and conditioning of 3rd and higher order two-point initial-boundary value problemsDec 21 2012We discuss initial-boundary value problems of arbitrary spatial order subject to arbitrary boundary conditions. We formalise the concept of the conditioning of such a problem and show that it represents a necessary criterion for well-posedness. The other ... More
Oxygen Absorption in M87: Evidence for a Warm+Hot ISMAug 25 2000Aug 26 2000We present a re-analysis of the ROSAT PSPC data within the central 100 kpc of M87 to search for intrinsic oxygen absorption similar to that recently measured in several galaxies and groups. Using a spatial-spectral deprojection analysis we find the strongest ... More
An XMM-Newton Observation of NGC 1399 Reveals Two Phases of Hot Gas and Super-Solar Abundances in the Central RegionsJun 24 2002We present an initial analysis of a new XMM observation of NGC 1399, the central elliptical galaxy of the Fornax group. Spectral fitting of the spatially resolved spectral data of the EPIC MOS and pn CCDs reveals that a two-temperature model (2T) of the ... More
X-Ray Observations of Cluster Mergers: Cluster Morphologies and Their ImplicationsJun 04 2001X-ray observations have played a key role in the study of substructure and merging in galaxy clusters. I review the evidence for cluster substructure and mergers obtained from X-ray observations with satellites that operated before Chandra and XMM. Different ... More
Warm Absorbing Gas in Cooling FlowsAug 30 2000We summarize the discovery of oxygen absorption and warm (10^5-10^6 K) gas in cooling flows. Special attention is given to new results for M87 for which we find the strongest evidence to date for ionized oxygen absorption in these systems. We briefly ... More
Randomization Does Not Justify Logistic RegressionAug 28 2008The logit model is often used to analyze experimental data. However, randomization does not justify the model, so the usual estimators can be inconsistent. A consistent estimator is proposed. Neyman's non-parametric setup is used as a benchmark. In this ... More
Intro To Logarithms After The MeltdownDec 06 2009Mar 02 2010This work is an attempt to 'reconstruct' logarithms in the hypothetical case that mankind has suffered a catastrophe through which all repositories of (mathematical as well as other) knowledge are lost, with the exception of simple arithmetic operations. ... More
Pinning-induced pn junction formation in low-bandgap two-dimensional semiconducting systemsSep 01 2015A model is presented for $pn$ junction formation near metal-semiconductor contacts in two-dimensional semiconducting systems such as graphene. Carrier type switching occurs in a region near the metal-semiconductor junction when energy band bending leads ... More
Some comments on embedding inflation in the AdS/CFT correspondenceOct 18 2007The anti-de Sitter space/conformal field theory correspondence (AdS/CFT) can potentially provide a complete formulation of string theory on a landscape of stable and metastable vacua that naturally give rise to eternal inflation. As a model for this process, ... More
Yes, semiclassical zero temperature black holes existNov 14 2000In a recent paper (gr-qc/0002007), Anderson, Hiscock and Taylor claimed that "in all physically realistic cases, macroscopic zero temperature black hole solutions do not exist." We show this conclusion was reached on the basis of an incorrect calculation. ... More
Unitarity Relations in c=1 Liouville TheoryApr 24 1992We consider the S-matrix of c=1 Liouville theory with vanishing cosmological constant. We examine some of the constraints imposed by unitarity. These completely determine (N,2) amplitudes at tree level in terms of the (N,1) amplitudes when the plus tachyon ... More
q-Deformed de Sitter/Conformal Field Theory CorrespondenceJul 21 2004Aug 16 2004Unitary principal series representations of the conformal group appear in the dS/CFT correspondence. These are infinite dimensional irreducible representations, without highest weights. In earlier work of Guijosa and the author it was shown for the case ... More
Heterotic Matrix String TheoryApr 06 1997Apr 14 1997M-theory suggests the large N limit of the matrix description of a collection of N Type IA D-particles should provide a nonperturbative formulation of heterotic string theory. In this paper states in the matrix theory corresponding to fundamental heterotic ... More
Bound States of Type I' D-particles and Enhanced Gauge SymmetryJan 31 1997Feb 10 1997Duality between the E_8 x E_8 heterotic string and Type I' theory predicts a tower of D(irichlet)-particle bound states corresponding to perturbative heterotic string states. In the limit of infinite Type I' coupling, some of these bound states become ... More
The Planckian Conspiracy: String Theory and the Black Hole Information ParadoxMay 12 1995It has been argued that the consistency of quantum theory with black hole physics requires nonlocality not present in ordinary effective field theory. We examine the extent to which such nonlocal effects show up in the perturbative S-matrix of string ... More
Quantum mechanics of lattice gas automata. I. One particle plane waves and potentialsNov 05 1996Classical lattice gas automata effectively simulate physical processes such as diffusion and fluid flow (in certain parameter regimes) despite their simplicity at the microscale. Motivated by current interest in quantum computation we recently defined ... More
From quantum cellular automata to quantum lattice gasesApr 04 1996Nov 13 1996A natural architecture for nanoscale quantum computation is that of a quantum cellular automaton. Motivated by this observation, in this paper we begin an investigation of exactly unitary cellular automata. After proving that there can be no nontrivial, ... More
Quantum mechanics of lattice gas automata. II. Boundary conditions and other inhomogeneitiesDec 23 1997We continue our analysis of the physics of quantum lattice gas automata (QLGA). Previous work has been restricted to periodic or infinite lattices; simulation of more realistic physical situations requires finite sizes and non-periodic boundary conditions. ... More
The Unusually High Halo Concentration of the Fossil Group NGC 6482: Evidence for Weak Adiabatic ContractionNov 25 2016We revisit the massive isolated elliptical galaxy / fossil group NGC 6482 for which previous X-ray studies of a modest Chandra observation obtained a very uncertain, but also possibly very high, halo concentration. We present new measurements of the hot ... More
On minimal non-elementary Lie algebrasFeb 05 2013The class of minimal non-elementary Lie algebras over a field F are studied. These are classified when F is algebraically closed and of characteristic different from 2,3. The solvable algebras in this class are also characterised over any perfect field. ... More
Conic degeneration and the determinant of the LaplacianAug 09 2012Oct 01 2013We investigate the behavior of various spectral invariants, particularly the determinant of the Laplacian, on a family of smooth Riemannian manifolds which undergo conic degeneration; that is, which converge in a particular way to a manifold with a conical ... More
Ore extensions and Poisson algebrasDec 17 2012For a derivation d of a commutative Noetherian complex algebra A, a homeomorphism is established between the prime spectrum of the Ore extension A[z;d] and the Poisson prime spectrum of the polynomial algebra A[z] endowed with the Poisson bracket such ... More
Solvable Lie A-algebrasApr 06 2009Sep 30 2009A finite-dimensional Lie algebra $L$ over a field $F$ is called an $A$-algebra if all of its nilpotent subalgebras are abelian. This is analogous to the concept of an $A$-group: a finite group with the property that all of its Sylow subgroups are abelian. ... More
Symmetric Group Character Degrees and Hook NumbersSep 06 2007In this article we prove the following result: that for any two natural numbers k and j, and for all sufficiently large symmetric groups Sym(n), there are k disjoint sets of j irreducible characters of Sym(n), such that each set consists of characters ... More
Control of Fusion and Solubility in Fusion SystemsOct 05 2009In this article, we consider the control of fusion in fusion systems, proving three previously known, non-trivial results in a new, largely elementary way. We then reprove a result of Aschbacher, that the product of two strongly closed subgroups is strongly ... More
Complex zero strip decreasing operatorsJan 01 2014Jan 29 2015In this paper we study the effect of linear differential operators coming from the Laguerre-Polya class that act on functions in the extended Laguerre-Polya class with zeros in a horizontal strip in the complex plane. These operator decrease the size ... More
Moduli of continuity of local times of random walks on graphs in terms of the resistance metricMay 12 2014Mar 09 2015In this article, universal concentration estimates are established for the local times of random walks on weighted graphs in terms of the resistance metric. As a particular application of these, a modulus of continuity for local times is provided in the ... More