Results for "Alan R. Duffy"

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Low-mass galaxy formation and the ionizing photon budget during reionizationMay 29 2014Jul 20 2014We use high-resolution simulations of cosmological volumes to model galaxy formation at high-redshift, with the goal of studying the photon budget for reionization. We demonstrate that galaxy formation models that include a strong, thermally coupled supernovae ... More
Model dispersion with PRISM; an alternative to MCMC for rapid analysis of modelsJan 25 2019We have built PRISM, a "Probabilistic Regression Instrument for Simulating Models". PRISM uses the Bayes linear approach and history matching to construct an approximation ('emulator') of any given model, by combining limited model evaluations with advanced ... More
Galaxy redshift surveys selected by neutral hydrogen using FASTJul 16 2007Apr 15 2008We discuss the possibility of performing a substantial spectroscopic galaxy redshift survey selected via the 21cm emission from neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope (FAST) to be built in China. We consider issues ... More
The accretion history of dark matter halos III: A physical model for the concentration-mass relationFeb 02 2015Aug 03 2015We present a semi-analytic, physically motivated model for dark matter halo concentration as a function of halo mass and redshift. The semi-analytic model combines an analytic model for the halo mass accretion history (MAH), based on extended Press Schechter ... More
The accretion history of dark matter halos II: The connections with the mass power spectrum and the density profileJan 19 2015Aug 03 2015We explore the relation between the structure and mass accretion histories of dark matter halos using a suite of cosmological simulations. We confirm that the formation time, defined as the time when the virial mass of the main progenitor equals the mass ... More
Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling and star formation in dwarf galaxies at high redshiftFeb 12 2018We study dwarf galaxy formation at high redshift ($z\ge5$) using a suite of high-resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling and star formation in this work by isolating the relevant ... More
Impact of baryon physics on dark matter structures: a detailed simulation study of halo density profilesJan 20 2010Mar 09 2010The back-reaction of baryons on the dark matter halo density profile is of great interest, not least because it is an important systematic uncertainty when attempting to detect the dark matter. Here, we draw on a large suite of high resolution cosmological ... More
Dark ages reionization & galaxy formation simulation XII: Bubbles at dawnApr 18 2017Jul 21 2017Direct detection of regions of ionized hydrogen (HII) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, ... More
Dark-ages Reionization and Galaxy Formation Simulation - XIII. AGN quenching of high-redshift star formation in ZF-COSMOS-20115Apr 11 2017Aug 25 2017Massive quiescent galaxies (MQGs) are thought to have formed stars rapidly at early times followed by a long period of quiescence. The recent discovery of a MQG, ZF-COSMOS-20115 at $z\sim4$, only 1.5 Gyr after the big bang, places new constraints on galaxy ... More
Modelling neutral hydrogen in galaxies using cosmological hydrodynamical simulationsJul 19 2011Sep 29 2011The characterisation of the atomic and molecular hydrogen content of high-redshift galaxies is a major observational challenge that will be addressed over the coming years with a new generation of radio telescopes. We investigate this important issue ... More
Guessing random additive noise decoding with soft detection symbol reliability information (SGRAND)Feb 11 2019Assuming hard detection from an additive noise channel, we recently introduced two new channel decoding algorithms that can be used with any code-book construction. For uniform sources using arbitrary code-books, Guessing Random Additive Noise Decoding ... More
Dark-ages reionization and galaxy formation simulation XI: Clustering and halo masses of high redshift galaxiesMar 15 2017Sep 15 2017We investigate the clustering properties of Lyman-break galaxies (LBGs) at $z\sim6$ - $8$. Using the semi-analytical model {\scshape Meraxes} constructed as part of the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulation ... More
Dark-ages Reionization and Galaxy Formation Simulation - X. The small contribution of quasars to reionizationMar 15 2017Sep 26 2017Motivated by recent measurements of the number density of faint AGN at high redshift, we investigate the contribution of quasars to reionization by tracking the growth of central supermassive black holes in an update of the Meraxes semi-analytic model. ... More
The Theoretical Astrophysical Observatory: Cloud-Based Mock Galaxy CataloguesMar 20 2014Jan 22 2016We introduce the Theoretical Astrophysical Observatory (TAO), an online virtual laboratory that houses mock observations of galaxy survey data. Such mocks have become an integral part of the modern analysis pipeline. However, building them requires an ... More
Dark-ages reionization & galaxy formation simulation VI: The origins and fate of the highest known redshift galaxyMay 25 2016Using Hubble data, including new grism spectra, Oesch et al. (2016) recently identified GN-z11, a $M_\textrm{UV}$=-21.1 galaxy at $z$=11.1 (just 400 Myr after the Big Bang). With an estimated stellar mass of $\sim$10$^9$M$_\odot$, this galaxy is surprisingly ... More
Dark-ages reionization and galaxy formation simulation - IX. Economics of reionizing galaxiesMay 20 2017Jun 19 2017Using a series of high-resolution hydrodynamical simulations we show that during the rapid growth of high-redshift (z > 5) galaxies, reserves of molecular gas are consumed over a time-scale of 300Myr, almost independent of feedback scheme. We find that ... More
Dark-ages reionization & galaxy formation simulation V: morphology and statistical signatures of reionizationDec 02 2015Aug 15 2016We use the Dark-ages, Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) framework to investigate the effect of galaxy-formation physics on the morphology and statistics of ionized hydrogen (HII) regions during the Epoch ... More
Dark-ages reionization and galaxy formation simulation - III. Modelling galaxy formation and the epoch of reionizationDec 02 2015Aug 18 2016We introduce Meraxes, a new, purpose-built semi-analytic galaxy formation model designed for studying galaxy growth during reionization. Meraxes is the first model of its type to include a temporally and spatially coupled treatment of reionization and ... More
Dark-ages reionization & galaxy formation simulation IV: UV luminosity functions of high-redshift galaxiesDec 02 2015Apr 27 2016In this paper we present calculations of the UV luminosity function from the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) project, which combines N-body, semi-analytic and semi-numerical modelling designed ... More
Dark-ages Reionization & Galaxy Formation Simulation I: The dynamical lives of high redshift galaxiesDec 02 2015Mar 21 2016We present the Dark-ages Reionization and Galaxy-formation Observables from Numerical Simulations (DRAGONS) program and Tiamat, the collisionless N-body simulation program upon which DRAGONS is built. The primary trait distinguishing Tiamat from other ... More
Dark-ages Reionization & Galaxy Formation Simulation VIII. Suppressed growth of dark matter halos during the Epoch of ReionizationJan 13 2017Feb 21 2017We investigate how the hydrostatic suppression of baryonic accretion affects the growth rate of dark matter halos during the Epoch of Reionization. By comparing halo properties in a simplistic hydrodynamic simulation in which gas only cools adiabatically, ... More
Dark-ages reionization and galaxy formation simulation--VII. The sizes of high-redshift galaxiesAug 02 2016Nov 08 2016We investigate high-redshift galaxy sizes using a semi-analytic model constructed for the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulation project. Our fiducial model, including strong feedback from supernovae and photoionization ... More
Dark-ages Reionization & Galaxy Formation Simulation II: Spin and concentration parameters for dark matter haloes during the Epoch of ReionizationDec 02 2015We use high resolution N-Body simulations to study the concentration and spin parameters of dark matter haloes in the mass range $10^8\, {\rm M}_{\odot}\, h^{-1} < {\rm M} < 10^{11}\, {\rm M}_{\odot}\, h^{-1}$ and redshifts $5{<}z{<}10$, corresponding ... More
Most likely paths to error when estimating the mean of a reflected random walkJun 24 2009Jun 25 2010It is known that simulation of the mean position of a Reflected Random Walk (RRW) $\{W_n\}$ exhibits non-standard behavior, even for light-tailed increment distributions with negative drift. The Large Deviation Principle (LDP) holds for deviations below ... More
Guesswork, large deviations and Shannon entropyMay 18 2012Jun 21 2012How hard is it guess a password? Massey showed that that the Shannon entropy of the distribution from which the password is selected is a lower bound on the expected number of guesses, but one which is not tight in general. In a series of subsequent papers ... More
Tail asymptotics for busy periodsDec 08 2011Mar 10 2012The busy period for a queue is cast as the area swept under the random walk until it first returns to zero, $B$. Encompassing non-i.i.d. increments, the large-deviations asymptotics of $B$ is addressed, under the assumption that the increments satisfy ... More
Estimating large deviation rate functionsNov 07 2015Establishing a Large Deviation Principle (LDP) proves to be a powerful result for a vast number of stochastic models in many application areas of probability theory. The key object of an LDP is the large deviations rate function, from which probabilistic ... More
Estimating Loynes' exponentOct 28 2009Loynes' distribution, which characterizes the one dimensional marginal of the stationary solution to Lindley's recursion, possesses an ultimately exponential tail for a large class of increment processes. If one can observe increments but does not know ... More
Probing the nature of dark energy through galaxy redshift surveys with radio telescopesMay 29 2014Galaxy redshift surveys using optical telescopes have, in combination with other cosmological probes, enabled precision measurements of the nature of dark energy. We show that radio telescopes are rapidly becoming competitive with optical facilities in ... More
The physics driving the cosmic star formation historySep 28 2009Nov 24 2009We investigate the physics driving the cosmic star formation (SF) history using the more than fifty large, cosmological, hydrodynamical simulations that together comprise the OverWhelmingly Large Simulations (OWLS) project. We systematically vary the ... More
Inferring average generation via division-linked labelingJun 07 2015For proliferating cells subject to both division and death, how can one estimate the average generation number of the living population without continuous observation or a division-diluting dye? In this paper we provide a method for cell systems such ... More
Decentralised Learning MACs for Collision-free Access in WLANsSep 22 2010Mar 02 2011By combining the features of CSMA and TDMA, fully decentralised WLAN MAC schemes have recently been proposed that converge to collision-free schedules. In this paper we describe a MAC with optimal long-run throughput that is almost decentralised. We then ... More
Inferring average generation via division-linked labelingJun 07 2015Apr 27 2017For proliferating cells subject to both division and death, how can one estimate the average generation number of the living population without continuous observation or a division-diluting dye? In this paper we provide a method for cell systems such ... More
Sample Path Properties of the Average Generation of a Bellman-Harris ProcessJul 18 2018Motivated by a recently proposed design for a DNA coded randomised algorithm that enables inference of the average generation of a collection of cells descendent from a common progenitor, here we establish strong convergence properties for the average ... More
Decentralized Constraint SatisfactionMar 02 2011Oct 09 2012We show that several important resource allocation problems in wireless networks fit within the common framework of Constraint Satisfaction Problems (CSPs). Inspired by the requirements of these applications, where variables are located at distinct network ... More
Measuring Visual Complexity of Cluster-Based VisualizationsFeb 23 2013Handling visual complexity is a challenging problem in visualization owing to the subjectiveness of its definition and the difficulty in devising generalizable quantitative metrics. In this paper we address this challenge by measuring the visual complexity ... More
Log-Convexity of Rate Region in 802.11e WLANsFeb 22 2011In this paper we establish the log-convexity of the rate region in 802.11 WLANs. This generalises previous results for Aloha networks and has immediate implications for optimisation based approaches to the analysis and design of 802.11 wireless networks. ... More
A Classification of Real Indecomposable Solvable Lie Algebras of Small Dimension with Codimension One NilradicalsNov 24 2013This thesis was concerned with classifying the real indecomposable solvable Lie algebras with codimension one nilradicals of dimensions two through seven. This thesis was organized into three chapters. In the first, we described the necessary concepts ... More
Mapping Properties of Quadrature Domains in Several Complex VariablesOct 24 2016We make use of the Bergman kernel function to study quadrature domains for square-integrable holomorphic functions of several variables. Emphasis is given to generalizing biholomorphic mapping properties of planar quadrature domains to the several-dimensional ... More
Time-Symmetric Initial Data for Multi-Body Solutions in Three DimensionsNov 18 1995Feb 02 1996Time-symmetric initial data for two-body solutions in three dimensional anti-deSitter gravity are found. The spatial geometry has constant negative curvature and is constructed as a quotient of two-dimensional hyperbolic space. Apparent horizons correspond ... More
Poisson-Boltzmann Theory of Charged Colloids: Limits of the Cell Model for Salty SuspensionsApr 24 2010Thermodynamic properties of charge-stabilised colloidal suspensions are commonly modeled by implementing the mean-field Poisson-Boltzmann (PB) theory within a cell model. This approach models a bulk system by a single macroion, together with counterions ... More
The Gribov Legacy, Gauge Theories and the Physical S-MatrixJul 29 2015Reggeon unitarity and non-abelian gauge field copies are focussed on as two Gribov discoveries that, it is suggested, may ultimately be seen as the most significant and that could, in the far distant future, form the cornerstones of his legacy. The crucial ... More
Past, Present, and Future Multi-Regge TheoryMar 18 2014The connection of the unitary Critical Pomeron to QUD - a unique massless, infra-red fixed-point, left-handed SU(5) field theory that might provide an unconventional underlying unification for the Standard Model, is discussed in the context of developments ... More
The Potential Importance of Low Luminosity and High Energy at the LHCOct 24 2013Low luminosity runs at higher LHC energy could provide definitive evidence for an electroweak scale sextet quark sector of QCD that produces electroweak symmetry breaking and dark matter within the bound-state S-Matrix of QUD - a massless, weak coupling, ... More
The Nightmare Scenario and the Origin of the Standard Model. "We Got it Wrong ...How did we misread the signals? ... What to Do?"Jun 05 2014It is thought that the emergence of the "nightmare scenario" at the LHC could be a serious crisis for particle physics that could require radical new concepts and even a major paradigm change. A root cause may have been exaggeration of the significance ... More
Charge Renormalization, Effective Interactions, and Thermodynamics of Deionized Colloidal SuspensionsSep 22 2008Thermodynamic properties of charge-stabilised colloidal suspensions depend sensitively on the effective charge of the macroions, which can be substantially lower than the bare charge in the case of strong counterion-macroion association. A theory of charge ... More
Phase Separation in Charge-Stabilized Colloidal Suspensions: Influence of Nonlinear ScreeningMay 03 2006The phase behavior of charge-stabilized colloidal suspensions is modeled by a combination of response theory for electrostatic interparticle interactions and variational theory for free energies. Integrating out degrees of freedom of the microions (counterions, ... More
Rate of Adaptive Evolution under Blending InheritanceApr 01 2015Jan 28 2016In a population of size N, adaptive evolution is 2N times faster under Mendelian inheritance than under the 19th-century theory of blending inheritance.
First Antineutrino Oscillation Results from T2KMay 05 2016As limits improve on the neutrino mixing angles and mass-squared differences, the focus of T2K has shifted towards studying antineutrino oscillation. This will give an insight into CP violation (if P($\bar{\nu}_{\mu} \rightarrow \bar{\nu}_{e}) \neq \mbox{P}(\nu_{\mu} ... More
Results and Prospects from T2KJul 12 2016As measurements of the neutrino oscillation parameters improve it is becoming more interesting to study antineutrino oscillations, to investigate CP and CPT violation in the lepton sector and nonstandard matter effects. We present the most recent T2K ... More
Detection of Cosmic-Ray Ensembles with CREDONov 26 2018One of the main objectives of cosmic-ray studies are precise measurements of energy and chemical composition of particles with extreme energies. Large and sophisticated detectors are used to find events seen as showers starting in the Earth's atmosphere ... More
Buoyancy-driven inflow to a relic cold core: the gas belt in radio galaxy 3C 386Apr 20 2016We report measurements from an XMM-Newton observation of the low-excitation radio galaxy 3C 386. The study focusses on an X-ray-emitting gas belt, which lies between and orthogonal to the radio lobes of 3C 386 and has a mean temperature of $0.94\pm0.05$ ... More
Colloids, polymers, and needles: Demixing phase behaviorOct 04 2001We consider a ternary mixture of hard colloidal spheres, ideal polymer spheres, and rigid vanishingly thin needles, which model stretched polymers or colloidal rods. For this model we develop a geometry-based density functional theory, apply it to bulk ... More
Ion Density Deviations in Polyelectrolyte Microcapsules: Influence on BiosensorsOct 24 2014Polyelectrolyte microcapsules loaded with fluorescent dyes have been proposed as biosensors to monitor local pH and ionic strength for diagnostic purposes. In the case of charged microcapsules, however, the local electric field can cause deviations of ... More
Phase Separation of Charge-Stabilized Colloids: A Gibbs Ensemble Monte Carlo Simulation StudyNov 03 2006Apr 20 2007Fluid phase behavior of charge-stabilized colloidal suspensions is explored by applying a new variant of the Gibbs ensemble Monte Carlo simulation method to a coarse-grained one-component model with implicit microions and solvent. The simulations take ... More
RKKY interaction between extended magnetic defect lines in grapheneJun 03 2014Of fundamental interest in the field of spintronics is the mechanism of indirect exchange coupling between magnetic impurities embedded in metallic hosts. A range of physical features, such as magnetotransport and overall magnetic moment formation, are ... More
Guessing a password over a wireless channel (on the effect of noise non-uniformity)Nov 05 2013Nov 26 2013A string is sent over a noisy channel that erases some of its characters. Knowing the statistical properties of the string's source and which characters were erased, a listener that is equipped with an ability to test the veracity of a string, one string ... More
Brute force searching, the typical set and GuessworkJan 27 2013May 13 2013Consider the situation where a word is chosen probabilistically from a finite list. If an attacker knows the list and can inquire about each word in turn, then selecting the word via the uniform distribution maximizes the attacker's difficulty, its Guesswork, ... More
The Mechanical Design for the Darht-II Downstream Beam Transport LineAug 14 2000This paper describes the mechanical design of the downstream beam transport line for the second axis of the Dual Axis Radiographic Hydrodynamic Test (DARHT II) Facility. The DARHT-II project is a collaboration between LANL, LBNL and LLNL. DARHT II is ... More
Non-adiabatic loading of a Bose-Einstein condensate into the ground state of an optical latticeMay 09 2003Oct 23 2003We present a scheme for rapid loading of a Bose-Einstein condensate into a single Bloch state of a weak optical lattice at a quasi-momentum of q = hbar k. Rabi cycling of a Bose condensate between momentum states is modified by a phase shift applied to ... More
Strain-Modified RKKY Interaction in Carbon NanotubesMay 12 2015For low-dimensional metallic structures, such as nanotubes, the exchange coupling between localized magnetic dopants is predicted to decay slowly with separation. The long-range character of this interaction plays a significant role in determining the ... More
Multi-user guesswork and brute force securityMay 20 2014Oct 24 2015The Guesswork problem was originally motivated by a desire to quantify computational security for single user systems. Leveraging recent results from its analysis, we extend the remit and utility of the framework to the quantification of the computational ... More
Site-specific recombinatorics: in situ cellular barcoding with the Cre Lox systemFeb 05 2016Feb 28 2016Cellular barcoding is a significant, recently developed, biotechnology tool that enables the familial identification of progeny of individual cells in vivo. Most existing approaches rely on ex vivo viral transduction of cells with barcodes, followed by ... More
RKKY interaction between adsorbed magnetic impurities in graphene: symmetry and strain effectsJul 04 2013The growing interest in carbon-based spintronics has stimulated a number of recent theoretical studies on the RKKY interaction in graphene, with the aim of determining the most energetically favourable alignments between embedded magnetic moments. The ... More
Strain-induced modulation of magnetic interactions in grapheneJul 12 2012Nov 20 2012The ease with which the physical properties of graphene can be tuned suggests a wide range of possible applications. Recently, strain engineering of these properties has been of particular interest. Possible spintronic applications of magnetically doped ... More
Ion Density Deviations in Semipermeable Ionic MicrocapsulesJul 07 2015By implementing the nonlinear Poisson-Boltzmann theory in a cell model, we theoretically investigate the influence of polyelectrolye gel permeability on ion densities and pH deviations inside the cavities of ionic microcapsules. Our calculations show ... More
Charge Renormalization, Thermodynamics, and Structure of Deionized Colloidal SuspensionsDec 10 2008In charge-stabilized colloidal suspensions, highly charged macroions, dressed by strongly correlated counterions, carry an effective charge that can be substantially reduced (renormalized) from the bare charge. Interactions between dressed macroions are ... More
Effective Electrostatic Interactions in Solutions of Polyelectrolyte Stars with Rigid Rodlike ArmsOct 25 2005In solutions of star-branched polyelectrolytes, electrostatic interactions between charged arms on neighboring stars can compete with intra-star interactions and rotational entropy to induce anisotropy in the orientational distribution of arms. For model ... More
Color--Sextet Quark Condensation in QCDJan 12 1993We suggest that the sextet color condensation model is not only the simplest and most attractive scheme to modify the standard model but also may already have some ``experimental" support. The crucial test may be to observe a short-- lived axion--like ... More
Demixing of colloid-polymer mixtures in poor solventsApr 15 2002The influence of poor solvent quality on fluid demixing of a model mixture of colloids and nonadsorbing polymers is investigated using density functional theory. The colloidal particles are modelled as hard spheres and the polymer coils as effective interpenetrating ... More
Effective Electrostatic Interactions in Suspensions of Polyelectrolyte Brush-Coated ColloidsSep 15 2004Effective electrostatic interactions between colloidal particles, coated with polyelectrolyte brushes and suspended in an electrolyte solvent, are described via linear response theory. The inner cores of the macroions are modeled as hard spheres, the ... More
Swelling, Structure, and Phase Stability of Compressible MicrogelsOct 17 2016Microgels are soft colloidal particles that, when dispersed in a solvent, swell and deswell in response to changes in environmental conditions, such as temperature, concentration, and $p$H. Using Monte Carlo simulation, we model bulk suspensions of microgels ... More
Crowding of Polymer Coils and Demixing in Nanoparticle-Polymer MixturesJun 24 2011The Asakura-Oosawa-Vrij (AOV) model of colloid-polymer mixtures idealizes nonadsorbing polymers as effective spheres that are fixed in size and impenetrable to hard particles. Real polymer coils, however, are intrinsically polydisperse in size (radius ... More
Counterion-Induced Swelling of Ionic MicrogelsOct 04 2016Ionic microgel particles, when dispersed in a solvent, swell to equilibrium sizes that are governed by a balance between electrostatic and elastic forces. Tuning of particle size by varying external stimuli, such as $p$H, salt concentration, and temperature, ... More
Mixtures of Charged Colloid and Neutral Polymer: Influence of Electrostatic Interactions on Demixing and Interfacial TensionMay 10 2005The equilibrium phase behavior of a binary mixture of charged colloids and neutral, non-adsorbing polymers is studied within free-volume theory. A model mixture of charged hard-sphere macroions and ideal, coarse-grained, effective-sphere polymers is mapped ... More
Experimental investigation of early-time diffusion in the quantum kicked rotor using a Bose-Einstein condensateJan 19 2004May 31 2004We report the experimental observation of resonances in the early-time momentum diffusion rates for the atom-optical delta-kicked rotor. In this work a Bose-Einstein condensate provides a source of ultra-cold atoms with an ultra-narow initial momentum ... More
A Variation on Chip-Firing: the diffusion gameSep 19 2016We introduce a natural variant of the parallel chip-firing game, called the diffusion game. Chips are initially assigned to vertices of a graph. At every step, all vertices simultaneously send one chip to each neighbour with fewer chips. Although the ... More
Bounds on inferenceOct 05 2013Lower bounds for the average probability of error of estimating a hidden variable X given an observation of a correlated random variable Y, and Fano's inequality in particular, play a central role in information theory. In this paper, we present a lower ... More
Anomalous Transport and Particle Acceleration at ShocksSep 11 1995The theory of first order Fermi acceleration at shocks assumes that particles diffuse due to scattering off slow-moving magnetic irregularities. However, cosmic rays are closely tied to magnetic field lines, and the transport process, particularly across ... More
Cosmological surveys with the Australian Square Kilometre Array PathfinderMar 21 2011Apr 12 2012This is a design study into the capabilities of the Australian Square Kilometre Array Pathfinder in performing a full-sky low redshift neutral hydrogen survey, termed WALLABY, and the potential cosmological constraints one can attain from measurement ... More
Giant Radio Galaxies: I. Intergalactic BarometersMar 20 2013We present new wideband radio observations with the Australia Telescope Compact Array of a sample of 12 giant radio galaxies. The radio observations are part of a larger radio-optical study aimed at relating the radio structures with the ambient medium ... More
Particle-acceleration timescales in TeV blazar flaresNov 21 2008Dec 01 2008Observations of minute-scale flares in TeV Blazars place constraints on particle acceleration mechanisms in those objects. The implications for a variety of radiation mechanisms have been addressed in the literature; in this paper we compare four different ... More
Radiative losses and cut-offs of energetic particles at relativistic shocksApr 02 2007We investigate the acceleration and simultaneous radiative losses of electrons in the vicinity of relativistic shocks. Particles undergo pitch angle diffusion, gaining energy as they cross the shock by the Fermi mechanism and also emitting synchrotron ... More
Specific Heat of the 2D Hubbard ModelDec 13 1996Dec 16 1996Quantum Monte Carlo results for the specific heat c of the two dimensional Hubbard model are presented. At half-filling it was observed that $c \sim T^2$ at very low temperatures. Two distinct features were also identified: a low temperature peak related ... More
Hole Pockets in the Doped 2D Hubbard ModelJul 07 1994The electronic momentum distribution ${\rm n({\bf k})}$ of the two dimensional Hubbard model is studied for different values of the coupling ${\rm U/t}$, electronic density ${\rm \langle n \rangle}$, and temperature, using quantum Monte Carlo techniques. ... More
Indications of a Metallic Antiferromagnetic Phase in the 2 Dimensional $U-t-t'$ ModelApr 29 1996Oct 14 1996We present mean-field and quantum Monte Carlo results that suggest the existence of an itinerant antiferromagnetic ground state in the half-filled $U-t-t'$ model in two dimensions. In particular, working at $t'/t=-0.2$ we found that antiferromagnetic ... More
Uniformly Valid Inference in Nonparametric Predictive RegressionSep 16 2015Dec 29 2017A significant problem in predictive regression concerns the invalidity of conventional OLS-based tests, when the regressor is highly persistent. Recent work has suggested that, in contrast, nonparametric regression-based inferences are free of this problem. ... More
The Spread of Cooperative Strategies on Grids with Random Asynchronous UpdatingOct 19 2016The Prisoner's Dilemma Process on a graph $G$ is an iterative process where each vertex, with a fixed strategy (\emph{cooperate} or \emph{defect}), plays the game with each of its neighbours. At the end of a round each vertex may change its strategy to ... More
Uniform Inference in Nonparametric Predictive Regression, and a Unified Limit Theory for Spatial Density EstimationSep 16 2015Nov 14 2015A significant problem in predictive regression concerns the invalidity of standard OLS-based inferences when the regressor is highly persistent. Recent work on nonparametric methods has suggested that inference based on these may remain valid in this ... More
The Simple Chromatic Number of $(m,n)$-Mixed GraphsSep 12 2018An $(m,n)$-mixed graph generalizes the notions of oriented graphs and edge-coloured graphs to a graph object with $m$ arc types and $n$ edge types. A simple colouring of such a graph is a non-trivial homomorphism to a reflexive target. We find that simple ... More
Uniform convergence rates over maximal domains in structural nonparametric cointegrating regressionMay 07 2015This paper presents uniform convergence rates for kernel regression estimators, in the setting of a structural nonlinear cointegrating regression model. We generalise the existing literature in three ways. First, the domain to which these rates apply ... More
Charge Exchange Losses and Stochastic Acceleration in the Solar WindSep 05 2016Stochastic acceleration of particles under a pressure balance condition can accommodate the universal $p^{-5}$ spectra observed under many different conditions in the inner heliosphere. In this model, in order to avoid an infinite build up of particle ... More
The Spread of Cooperative Strategies on Grids with Random Asynchronous UpdatingOct 19 2016Oct 24 2016The Prisoner's Dilemma Process on a graph $G$ is an iterative process where each vertex, with a fixed strategy (\emph{cooperate} or \emph{defect}), plays the game with each of its neighbours. At the end of a round each vertex may change its strategy to ... More
Chromatic Polynomials of Oriented GraphsOct 12 2018Dec 20 2018The oriented chromatic polynomial of a oriented graph outputs the number of oriented $k$-colourings for any input $k$. We fully classify those oriented graphs for which the oriented graph has the same chromatic polynomial as the underlying simple graph, ... More
Observation of low frequency spin dynamics in INVAR Fe$_{65}$Ni$_{35}$Mar 10 2016Jun 02 2016We present ferromagnetic neutron spin echo measurements and muon spin relaxation ($\mu$SR) measurements of the spin dynamics in the ordered phase of the metallic alloy INVAR Fe$_{65}$Ni$_{35}$. Both techniques display evidence of slow spin dynamics in ... More
The impact of baryons on the spins and shapes of dark matter haloesJul 19 2012Jan 21 2013We use numerical simulations to investigate how the statistical properties of dark matter (DM) haloes are affected by the baryonic processes associated with galaxy formation. We focus on how these processes influence the spin and shape of a large number ... More
Hiding Symbols and Functions: New Metrics and Constructions for Information-Theoretic SecurityMar 30 2015We present information-theoretic definitions and results for analyzing symmetric-key encryption schemes beyond the perfect secrecy regime, i.e. when perfect secrecy is not attained. We adopt two lines of analysis, one based on lossless source coding, ... More
Lists that are smaller than their parts: A coding approach to tunable secrecyOct 08 2012We present a new information-theoretic definition and associated results, based on list decoding in a source coding setting. We begin by presenting list-source codes, which naturally map a key length (entropy) to list size. We then show that such codes ... More
Temperature dependence of the spin and orbital magnetization density in $Sm_{1-x}Gd_{x} Al_{2}$ around the spin-orbital compensation pointJan 14 2002Jan 18 2002Non-resonant ferromagnetic x-ray diffraction has been used to separate the spin and orbital contribution to the magnetization density of the proposed zero-moment ferromagnet $Sm_{0.982}Gd_{0.018} Al_{2}$. The alignment of the spin and orbital moments ... More
Kinks and Time MachinesMay 02 1994May 09 1994We show that it is not possible to smooth out the metric on the Deutsch-Politzer time machine to obtain an everywhere non-singular asymptotically flat Lorentzian metric.