Results for "Dylan Rees"

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Quantized Photocurrents in the Chiral Multifold Fermion System RhSiFeb 08 2019The rapid pace of discovery of new classes of Weyl semimetals is driving a search for properties that derive from their unique bandstructure topology. One of the most striking of the predicted properties is the quantized circular photogalvanic effect ... More
The parameter capturemap for V_3Jan 19 2012This is a study of the Wittner capture construction for critically finite quadratic rational maps for which one critical point is periodic, and the second critical point is in the backward orbit of the first. This construction gives a way of describing ... More
Multiple equivalent matings with the aeroplane polynomialDec 07 2008Jun 05 2009We produce arbitrarily large equivalence classes of matings with the aeroplane polynomial. These are obtained by a slight generalisation of the technique of proof of a similar result for Wittner captures.
Persistent Markov partitions and hyperbolic components of rational mapsAug 03 2016Markov partitions persisting in a neighbourhood of hyperbolic components of rational maps were constructed under the condition that closures of Fatou components are disjoint in \cite{R1}. Given such a partition, we characterize all nearby hyperbolic components ... More
Persistent Markov partitions for rational mapsJun 26 2013Sep 30 2016A construction is given of Markov partitions for some rational maps, which persist over regions of parameter space, not confined to single hyperbolic components. The set on which the Markov partition exists, and its boundary, are analysed.
The Ending Laminations Theorem direct from Teichmuller geodesicsApr 01 2004Jul 18 2007A proof of the Ending Laminations Theorem is given, using Teichmuller geodesics directly.
A Fundamental Domain for V_3Apr 02 2009Mar 19 2010We describe a fundamental domain for the punctured Riemann surface $V_{3,m}$ which parametrises (up to M\"obius conjugacy) the set of quadratic rational maps with numbered critical points, such that the first critical point has period three, and such ... More
A connected string of long thick and dominantsSep 18 2012We prove that every Teichmuller geodesic of a finite type surface contains a string of intersecting long, thick and dominant segments, such that the distance between consecutive segments is bounded. This is key to obtaining some results about Teichmuller ... More
Field evolution of magnons in $α$-RuCl$_3$ by high-resolution polarized terahertz spectroscopyJun 03 2018Oct 05 2018The Kitaev quantum spin liquid (KSL) is a theoretically predicted state of matter whose fractionalized quasiparticles are distinct from bosonic magnons, the fundamental excitation in ordered magnets. The layered honeycomb antiferromagnet $\alpha$-RuCl$_3$ ... More
Non-perturbative Treatments of the Bosonic String and the Axion with Cosmological ImplicationsJun 28 2012This paper is about the use of a novel, exact functional quantization method as applied to two commonly studied actions in theoretical physics. The functional method in question has its roots in the exact renormalisation group flow techniques pioneered ... More
Second Order Backward Stochastic Differential Equations under Monotonicity ConditionJan 03 2012Apr 11 2014In a recent paper, Soner, Touzi and Zhang [20] have introduced a notion of second order backward stochastic differential equations (2BSDEs for short), which are naturally linked to a class of fully non-linear PDEs. They proved existence and uniqueness ... More
Greedy bases in rank 2 generalized cluster algebrasSep 10 2013In this note we extend the notion of greedy bases developed by Lee, Li, and Zelevinsky to rank two generalized cluster algebras, i.e. binomial exchange relations are replaced by polynomial exchange relations. In the process we give a combinatorial construction ... More
A Curvature Flow and Applications to an Isoperimetric InequalityOct 19 2016Long time existence and convergence to a circle is proved for radial graph solutions to a mean curvature type curve flow in warped product surfaces (under a weak assumption on the warp potential of the surface). This curvature flow preserves the area ... More
Quantum Cluster CharactersSep 29 2011Aug 13 2012Let $\FF$ be a finite field and $(Q,\bfd)$ an acyclic valued quiver with associated exchange matrix $\tilde{B}$. We follow Hubery's approach \cite{hub1} to prove our main conjecture of \cite{rupel}: the quantum cluster character gives a bijection from ... More
The Fully Quantized Axion and Dark EnergyDec 17 2012This letter reviews the exact evolution equation for the axion effective potential with the axion scale factor f and phenomenological consequences of the flat effective potential solution are discussed. It is shown that the corresponding vacuum energy ... More
Proof of the Kontsevich Non-Commutative Cluster Positivity ConjectureJan 17 2012Feb 01 2012We extend the Lee-Schiffler Dyck path model to give a proof of the Kontsevich non-commutative cluster positivity conjecture with unequal parameters.
ModelWizard: Toward Interactive Model ConstructionApr 15 2016Data scientists engage in model construction to discover machine learning models that well explain a dataset, in terms of predictiveness, understandability and generalization across domains. Questions such as "what if we model common cause Z" and "what ... More
On Quantum Analogue of The Caldero-Chapoton FormulaMar 12 2010Apr 24 2010Let $Q$ be any invertible valued quiver without oriented cycles. We study connections between the category of valued representations of $Q$ and expansions of cluster variables in terms of the initial cluster in quantum cluster algebras. We show that an ... More
Weighted Power Counting and Perturbative UnitarityDec 10 2010Feb 28 2011We consider the relationship between renormalizability and unitarity at a Lifshitz point in d dimensions. We test tree unitarity for theories containing only scalars and fermions, and for pure gauge theory. In both cases, we find the requirement of weighted ... More
Why is the CMB fluctuation level 10^{-5}?Sep 08 1997Dec 12 1997We explore the qualitative changes that would occur if the amplitude Q ~ 10^{-5} of cosmological density fluctuations were different. If is less than about 10^{-6}, the cosmological objects that form would have so low virial temperatures that they may ... More
Holographic renormalization for irrelevant operators and multi-trace countertermsFeb 10 2011We investigate the structure of holographic renormalization in the presence of sources for irrelevant operators. By working perturbatively in the sources we avoid issues related to the non-renormalizability of the dual field theory. We find new classes ... More
Using administrative data to improve the estimation of immigration to local areas in EnglandMar 03 2009Aug 24 2009International migration is now a significant driver of population change across Europe but the methods available to estimate its true impact upon sub-national areas remain inconsistent, constrained by inadequate systems of measurement and data capture. ... More
Irrelevant deformations and the holographic Callan-Symanzik equationMay 26 2011We discuss the systematics of obtaining the Callan-Symanzik equation within the framework of the gauge/gravity dualities. We present a completely general formula which in particular takes into account the new holographic renormalization results of arXiv:1102.2239. ... More
Omega from Velocities in VoidsAug 23 1993We propose a method for deriving a dynamical lower bound on $\Omega$ from diverging flows in low-density regions, based on the fact that large outflows are not expected in a low-$\Omega$ universe. The velocities are assumed to be induced by gravity from ... More
Counting Hyperbolic ComponentsMar 31 2010Apr 11 2012We give formulas for the numbers of type II and type IV hyperbolic components in the space of quadratic rational maps, for all fixed periods of attractive cycles.
Correlation functions for Schrödinger backgroundsJun 27 2012We work out the holographic dictionary for the three-dimensional Schr\"odinger spacetimes. The first step in our analysis involves the correct identification of the dual sources from the radial expansion of the bulk fields, which turns out to be surprisingly ... More
Real-time gauge/gravity duality and ingoing boundary conditionsFeb 24 2009In arXiv:0805.0150 [hep-th] and arXiv:0812.2909 [hep-th] a general prescription was presented for the computation of real-time correlation functions using the gauge/gravity duality. I apply this prescription to the specific case of retarded thermal correlation ... More
Contracting theory with competitive interacting agentsMay 25 2016In a framework close to the one developed by Holmstr\"om and Milgrom [44], we study the optimal contracting scheme between a Principal and several Agents. Each hired Agent is in charge of one project, and can make efforts towards managing his own project, ... More
Laminations from the symplectic doubleOct 11 2014Jun 24 2016Let $S$ be a compact oriented surface with boundary together with finitely many marked points on the boundary, and let $S^\circ$ be the same surface equipped with the opposite orientation. We consider the double $S_\mathcal{D}$ obtained by gluing the ... More
Normality of different orders for Cantor series expansionsJul 25 2016Let $S \subseteq \mathbb{N}$ have the property that for each $k \in S$ the set $(S - k) \cap \mathbb{N} \setminus S$ has asymptotic density $0$. We prove that there exists a basic sequence $Q$ where the set of numbers $Q$-normal of all orders in $S$ but ... More
A breakpoint detection error function for segmentation model selection and evaluationSep 01 2015We consider the multiple breakpoint detection problem, which is concerned with detecting the locations of several distinct changes in a one-dimensional noisy data series. We propose the breakpointError, a function that can be used to evaluate estimated ... More
An Adaptive Data Representation for Robust Point-Set Registration and MergingNov 13 2015This paper presents a framework for rigid point-set registration and merging using a robust continuous data representation. Our point-set representation is constructed by training a one-class support vector machine with a Gaussian radial basis function ... More
Cluster algebras and triangulated surfaces. Part II: Lambda lengthsOct 20 2012For any cluster algebra whose underlying combinatorial data can be encoded by a bordered surface with marked points, we construct a geometric realization in terms of suitable decorated Teichmueller space of the surface. On the geometric side, this requires ... More
Short-time existence for some higher-order geometric flowsOct 20 2010We establish short-time existence and regularity for higher-order flows generated by a class of polynomial natural tensors that, after an adjustment by the Lie derivative of the metric with respect to a suitable vector field, have strongly parabolic linearizations. ... More
Symplectic groupoids for cluster manifoldsJul 10 2018We construct symplectic groupoids integrating log-canonical Poisson structures on cluster varieties of type $\mathcal{A}$ and $\mathcal{X}$ over both the real and complex numbers. Extensions of these groupoids to the completions of the cluster varieties ... More
Normality preserving operations for Cantor series expansions and associated fractals part IJul 03 2014Jul 08 2014It is well known that rational multiplication preserves normality in base $b$. We study related normality preserving operations for the $Q$-Cantor series expansions. In particular, we show that while integer multiplication preserves $Q$-distribution normality, ... More
Unexpected distribution phenomenon resulting from Cantor series expansionsMar 12 2014Mar 07 2015We explore in depth the number theoretic and statistical properties of certain sets of numbers arising from their Cantor series expansions. As a direct consequence of our main theorem we deduce numerous new results as well as strengthen known ones.
On the Existence of Finite Type Link Homotopy InvariantsOct 21 2000We show that for links with at most 5 components, the only finite type homotopy invariants are products of the linking numbers. In contrast, we show that for links with at least 9 components, there must exist finite type homotopy invariants which are ... More
The cluster symplectic double and moduli spaces of local systemsSep 04 2015We prove a conjecture of Fock and Goncharov which provides a birational equivalence of a cluster variety called the cluster symplectic double and a certain moduli space of local systems associated to a surface.
Quantum cluster characters of Hall algebrasAug 13 2013Nov 28 2014The aim of the present paper is to introduce a generalized quantum cluster character, which assigns to each object V of a finitary Abelian category C over a finite field FF_q and any sequence ii of simple objects in C the element X_{V,ii} of the corresponding ... More
Wheeling: A diagrammatic analogue of the Duflo isomorphismJun 11 2000We construct and prove a diagrammatic version of the Duflo isomorphism between the invariant subalgebra of the symmetric algebra of a Lie algebra and the center of the universal enveloping algebra. This version implies the original for metrized Lie algebras ... More
Second Order Backward Stochastic Differential Equations with Quadratic GrowthJan 03 2012Apr 11 2014We extend the wellposedness results for second order backward stochastic differential equations introduced by Soner, Touzi and Zhang \cite{stz} to the case of a bounded terminal condition and a generator with quadratic growth in the $z$ variable. More ... More
Grid Diagrams, Braids, and Contact GeometryDec 19 2008Feb 16 2009We use grid diagrams to present a unified picture of braids, Legendrian knots, and transverse knots.
E-voting in EstoniaJun 28 2016Estonia has one of the most established e-voting systems in the world. Internet voting - remote e-voting using the voter's own equipment - was piloted in 2005 with the first real elections using e-voting being conducted the same year and has been in use ... More
Companion cluster algebras to a generalized cluster algebraApr 25 2015We study the $c$-vectors, $g$-vectors, and $F$-polynomials for generalized cluster algebras satisfying a normalization condition and a power condition recovering classical recursions and separation of additions formulas. We establish a relationship between ... More
Cell Decompositions for Rank Two Quiver GrassmanniansMar 18 2018We prove that all quiver Grassmannians for exceptional representations of a generalized Kronecker quiver admit a cell decomposition. In the process, we introduce a class of regular representations which arise as quotients of consecutive preprojective ... More
The Earliest Luminous Sources and the Damping Wing of the Gunn-Peterson TroughJun 20 2000Aug 18 2000Recent observations of high-redshift galaxies and quasars indicate that the hydrogen component of the intergalactic medium (IGM) must have been reionized at some redshift z>6. Prior to complete reionization, sources of ultraviolet radiation will be seen ... More
Optical and Long Wavelength Afterglow from Gamma-Ray BurstsJun 06 1996We discuss the evolution of cosmological gamma-ray burst remnants, consisting of the cooling and expanding fireball ejecta together with any swept-up external matter, after the gamma-ray event. We show that significant optical emission is predicted which ... More
GRB 990123: Reverse and Internal Shock Flashes and Late AfterglowFeb 25 1999The prompt $(t \siml 0.16$ days) light curve and initial 9-th magnitude optical flash from GRB 990123 can be attributed to a reverse external shock, or possibly to internal shocks. We discuss the time decay laws and spectral slopes expected under various ... More
Rapid growth of high redshift black holesJun 02 2005Jul 26 2005We discuss a model for the early assembly of supermassive black holes (SMBHs) at the center of galaxies that trace their hierarchical build-up far up in the dark halo `merger tree'. Motivated by the observations of luminous quasars around redshift z=6 ... More
Some closure results for C-approximable groupsJan 08 2016Oct 14 2016We investigate closure results for C-approximable groups, for certain classes C of groups with invariant length functions. In particular we prove, each time for certain (but not necessarily the same) classes C that (i) the direct product of two C-approximable ... More
Quasars at z=6: the survival of the fittestJul 05 2006The Sloan Digital Sky survey detected luminous quasars at very high redshift, z>6. Follow-up observations indicated that at least some of these quasars are powered by supermassive black holes (SMBHs) with masses in excess of billion solar masses. SMBHs, ... More
Massive Black Holes as Population III RemnantsJan 13 2001Mar 09 2001Recent numerical simulations of the fragmentation of primordial molecular clouds in hierarchical cosmogonies have suggested that the very first stars (the so-called Population III) may have been rather massive. Here we point out that a numerous population ... More
Dissipative Photosphere Models of Gamma-ray Bursts and X-ray FlashesDec 31 2004Apr 08 2005We consider dissipative effects occurring in the optically thick inner parts of the relativistic outflows producing gamma-ray bursts and X-ray flashes, emphasizing specially the Comptonization of the thermal radiation flux that is advected from the base ... More
Refreshed Shocks and Afterglow Longevity in GRBDec 18 1997We consider fireball models where the ejecta have a range of bulk Lorentz factors, so that the inner (lower $\Gamma$) parts may carry most of the mass, or even most of the energy. The outer shock and contact discontinuity decelerate as the fireball sweeps ... More
Capture of stellar--mass compact objects by massive black holes in galactic cuspsAug 14 1996A significant fraction of the stellar population in the cusp around central black holes of galaxies consists of compact remnants of evolved stars, such as white dwarfs, neutron stars and stellar mass black holes. We estimate the rate of capture of compact ... More
Normal equivalencies for eventually periodic basic sequencesAug 26 2014W. M. Schmidt, A. D. Pollington, and F. Schweiger have studied when normality with respect to one expansion is equivalent to normality with respect to another expansion. Following in their footsteps, we show that when $Q$ is an eventually periodic basic ... More
A mathematical treatment of bank monitoring incentivesFeb 09 2012Apr 04 2015In this paper, we take up the analysis of a principal/agent model with moral hazard introduced in [17], with optimal contracting between competitive investors and an impatient bank monitoring a pool of long-term loans subject to Markovian contagion. We ... More
A duality map for the quantum symplectic doubleMay 05 2016This paper is a continuation of the author's work with Kim (arXiv:1509.01567), which provided a natural $q$-deformation of Fock and Goncharov's canonical basis for the coordinate ring of a cluster variety associated to a punctured surface. Here we consider ... More
Moral hazard under ambiguityOct 26 2015Oct 24 2016In this paper, we extend the Holmstro\"om and Milgrom problem [47] by adding uncertainty about the volatility of the output for both the Agent and the Principal. We study more precisely the impact of the "Nature" playing against the Agent and the Principal ... More
Integral Expressions for the Vassiliev Knot InvariantsJan 25 1999Jan 26 1999It has been folklore for several years in the knot theory community that certain integrals on configuration space, originally motivated by perturbation theory for the Chern-Simons field theory, converge and yield knot invariants. This was proposed independently ... More
The geometry of cluster varieties from surfacesJun 24 2016Cluster varieties are geometric objects that have recently found applications in several areas of mathematics and mathematical physics. This thesis studies the geometry of a large class of cluster varieties associated to compact oriented surfaces with ... More
Weak approximation of second-order BSDEsOct 04 2013Sep 09 2015We study the weak approximation of the second-order backward SDEs (2BSDEs), when the continuous driving martingales are approximated by discrete time martingales. We establish a convergence result for a class of 2BSDEs, using both robustness properties ... More
A positive characterization of rational mapsDec 13 2016When is a topological branched self-cover of the sphere equivalent to a rational map on CP^1? William Thurston gave one answer in 1982, giving a negative criterion (an obstruction to a map being rational). We give a complementary, positive criterion: ... More
Classical and quantum chaos in a circular billiard with a straight cutJul 09 1998We study classical and quantum dynamics of a particle in a circular billiard with a straight cut. This system can be integrable, nonintegrable with soft chaos, or nonintegrable with hard chaos, as we vary the size of the cut. We use a quantum web to show ... More
Steep Slopes and Preferred Breaks in GRB Spectra: the Role of Photospheres and ComptonizationAug 11 1999Oct 27 1999The role of a photospheric component and of pair breakdown is examined in the internal shock model of gamma-ray bursts. We discuss some of the mechanisms by which they would produce anomalously steep low energy slopes, X-ray excesses and preferred energy ... More
Gamma-Ray Bursts: Multiwaveband Spectral Predictions for Blast Wave ModelsSep 09 1993In almost any scenario for 'cosmological' gamma-ray bursts (and in many models where they originate in our own Galaxy), the initial energy density is so large that the resulting relativistic plasma expands with $v\sim c$ producing a blast wave ahead of ... More
Iron K-alpha Emission from a Decaying Magnetar Model of Gamma-Ray BurstsOct 13 2000The recent report of X-ray Fe features in the afterglow of the gamma-ray burst GRB 991216 may provide important clues for identifying the nature of its progenitor and constraining the burst mechanism. We argue that the strong line emission can be attributed ... More
Multi-GeV Neutrinos from Internal Dissipation in GRB FireballsJul 07 2000Sub-photospheric internal shocks and transverse differences of the bulk Lorentz factor in relativistic fireball models of GRB lead to neutron diffusion relative to protons, resulting in inelastic nuclear collisions. This produces significant fluxes of ... More
Delayed Gev Emission from Cosmological Gamma-Ray Bursts : Impact of a Relativistic Wind on External MatterApr 22 1994Sudden collapse of a compact object, or coalescence of a compact binary, can generate an unsteady relativistic wind that lasts for a few seconds. The wind is likely to carry a high magnetic field; and its Lorentz factor depends on the extent to which ... More
Consistent Anisotropic Repulsions for Simple MoleculesDec 01 2000We extract atom-atom potentials from the effective spherical potentials that suc cessfully model Hugoniot experiments on molecular fluids, e.g., $O_2$ and $N_2$. In the case of $O_2$ the resulting potentials compare very well with the atom-atom potentials ... More
Massive Black Holes: formation and evolutionJan 17 2007Supermassive black holes are nowadays believed to reside in most local galaxies. Observations have revealed us vast information on the population of local and distant black holes, but the detailed physical properties of these dark massive objects are ... More
Artin groups of large type are shortlex automatic with regular geodesicsMar 31 2010We prove that any Artin group of large type is shortlex automatic with respect to its standard generating set, and that the set of all geodesic words over the same generating set satisfies the Falsification by Fellow-Traveller Property (FFTP) and hence ... More
Winding numbers and SU(2)-representations of knot groupsJun 07 2007Given an abelian group $A$ and a Lie group $G$, we construct a bilinear pairing from $A\times\pi_1({\mathcal R})$ to $\pi_1(G)$, where $\mathcal R$ is a subvariety of the variety of representations $A\to G$. In the case where $A$ is the peripheral subgroup ... More
Relativistic SpringsMay 13 2012May 15 2012Here we develop a model for the relativistic spring. We examine the effects of revising the simple harmonic oscillator to include relativistic momentum and a delayed force law. These corrections alter two of the most significant features of the simple ... More
GOGMA: Globally-Optimal Gaussian Mixture AlignmentMar 01 2016Gaussian mixture alignment is a family of approaches that are frequently used for robustly solving the point-set registration problem. However, since they use local optimisation, they are susceptible to local minima and can only guarantee local optimality. ... More
Elastic GraphsJul 01 2016An elastic graph is a graph with an elasticity associated to each edge, which may be viewed as a network made out of ideal rubber bands. The rubber bands may be stretched on a target space, giving an elastic energy. We characterize when a homotopy class ... More
Control Function Instrumental Variable Estimation of Nonlinear Causal Effect ModelsFeb 02 2016The instrumental variable method consistently estimates the effect of a treatment when there is unmeasured confounding and a valid instrumental variable. A valid instrumental variable is a variable that is independent of unmeasured confounders and affects ... More
Mediation Analysis Without Sequential Ignorability: Using Baseline Covariates Interacted with Random Assignment as Instrumental VariablesSep 06 2011Dec 31 2012In randomized trials, researchers are often interested in mediation analysis to understand how a treatment works, in particular how much of a treatment's effect is mediated by an intermediated variable and how much the treatment directly affects the outcome ... More
Uniqueness for Some Higher-Order Geometric FlowsJul 16 2014We show that solutions to certain higher-order intrinsic geometric flows on a compact manifold, including some flows generated by the ambient obstruction tensor, are unique. With the goal of providing a complete self-contained proof, details surrounding ... More
Reprocessing of radiation by multi-phase gas in Low Luminosity Accretion FlowsJul 24 1998We discuss the role that magnetic fields in low luminosity accretion flows can play in creating and maintaining a multi-phase medium, and show that small magnetically-confined clouds or filaments of dense cold gas can dramatically reprocess the `primary' ... More
Gamma-Ray BurstsJan 13 2014Gamma-ray bursts are the most luminous explosions in the Universe. They appear connected to supernova remnants from massive stars or the merger of their remnants, and their brightness makes them temporarily detectable out to the larges distances yet explored ... More
Gamma-ray bursts as X-ray depth-gauges of the UniverseMay 07 2003May 31 2003We discuss the X-ray flux of gamma-ray burst afterglows at redshifts in the range 3-30, including the effects of the intergalactic He II absorption. We point out that strong X-ray lines may form locally in burst afterglows starting minutes after the trigger. ... More
Poynting Jets from Black Holes and Cosmological Gamma-Ray BurstsSep 07 1996Mar 20 1997We discuss the properties of magnetically dominated jet-like outflows from stellar mass black holes surrounded by debris tori resulting from neutron star disruption. These jets may have narrow cores (along the rotation axis) which are almost free of baryons ... More
GeV Emission from Collisional Magnetized Gamma Ray BurstsApr 26 2011Magnetic fields may play a dominant role in gamma-ray bursts, and recent observations by the Fermi satellite indicate that GeV radiation, when detected, arrives delayed by seconds from the onset of the MeV component. Motivated by this, we discuss a magnetically ... More
Collapsar Jets, Bubbles and Fe LinesApr 25 2001Jun 20 2001In the collapsar scenario, gamma ray bursts are caused by relativistic jets expelled along the rotation axis of a collapsing stellar core. We discuss how the structure and time-dependence of such jets depends on the stellar envelope and central engine ... More
Spectral Features from Ultrarelativistic Ions in Gamma-Ray Bursts?Apr 13 1998Jun 11 1998Gamma ray burst outflows may entrain small blobs or filaments of dense, highly ionized metal rich material. Such inhomogeneities, accelerated by the flow to Lorentz factors in the range 10-100, could have a significant coverage factor, and give rise to ... More
Unsteady Outflow Models for Cosmological Gamma-Ray BurstsApr 18 1994The 'event' that triggers a gamma ray burst cannot last for more than a few seconds. This is, however, long compared with the dynamical timescale of a compact stellar-mass object ($\sim 10^{-3}$ seconds). Energy is assumed to be released as an outflow ... More
Quasars and Galaxy FormationJan 04 1998The formation of massive black holes may precede the epoch that characterises the peak of galaxy formation, as characterized by the star formation history in luminous galaxies. Hence protogalactic star formation may be profoundly affected by quasar-like ... More
Accelerating Fast Fourier Transforms Using Hadoop and CUDAJul 25 2014There has been considerable research into improving Fast Fourier Transform (FFT) performance through parallelization and optimization for specialized hardware. However, even with those advancements, processing of very large files, over 1TB in size, still ... More
Alignment of the Angular Momentum Vectors of Planetary Nebulae in the Galactic BulgeJul 22 2013We use high-resolution H {\alpha} images of 130 planetary nebulae (PNe) to investigate whether there is a preferred orientation for PNe within the Galactic Bulge. The orientations of the full sample have an uniform distribution. However, at a significance ... More
Generalising some results about right-angled Artin groups to graph products of groupsOct 12 2011Oct 25 2011We prove three results about the graph product $G=\G(\Gamma;G_v, v \in V(\Gamma))$ of groups $G_v$ over a graph $\Gamma$. The first result generalises a result of Servatius, Droms and Servatius, proved by them for right-angled Artin groups; we prove a ... More
Population III Gamma Ray BurstsApr 12 2010We discuss a model of Poynting-dominated gamma-ray bursts from the collapse of very massive first generation (pop. III) stars. From redshifts of order 20, the resulting relativistic jets would radiate in the hard X-ray range around 50 keV and above, followed ... More
The Edge of a Gamma Ray Burst AfterglowJun 12 1998Jul 16 1998We discuss the formation of spectral features in the decelerating ejecta of gamma-ray bursts, including the possible effect of inhomogeneities. These should lead to blueshifted and broadened absorption edges and resonant features, especially from H and ... More
The generalised word problem for subgroups of hyperbolic groupsMay 10 2015Nov 03 2015We prove that the generalised word problem of a finitely generated subgroup of a finitely generated virtually free group is context-free, that a hyperbolic group must be virtually free if it has a torsion-free quasiconvex subgroup of infinite index with ... More
An Axisymmetric Object-Based Search for a Flat Compact DimensionMar 24 2005Sep 25 2005A method is presented to search for a hypertorus symmetry axis by the alignment of distant objects. This offers greater sensitivity than previously proposed object-based methods that rely on accurate true distances. When applied to the catalog of objects ... More
PeakSegJoint: fast supervised peak detection via joint segmentation of multiple count data samplesJun 03 2015Joint peak detection is a central problem when comparing samples in genomic data analysis, but current algorithms for this task are unsupervised and limited to at most 2 sample types. We propose PeakSegJoint, a new constrained maximum likelihood segmentation ... More
On the Geometry of Adversarial ExamplesNov 01 2018Dec 11 2018Adversarial examples are a pervasive phenomenon of machine learning models where seemingly imperceptible perturbations to the input lead to misclassifications for otherwise statistically accurate models. We propose a geometric framework, drawing on tools ... More
Searchlight-based multi-voxel pattern analysis of fMRI by cross-validated MANOVAJan 16 2014Feb 07 2014Multi-voxel pattern analysis (MVPA) is a fruitful and increasingly popular complement to traditional univariate methods of analyzing neuroimaging data. We propose to replace the standard 'decoding' approach to searchlight-based MVPA, measuring the performance ... More
Radio-frequency impedance measurements using a tunnel-diode oscillator (TDO) techniqueApr 01 1999A resonant method based on a tunnel-diode oscillator (TDO) for precision measurements of relative impedance changes in materials, is described. The system consists of an effective self-resonant LC-tank circuit driven by a forward-biased tunnel diode operating ... More