Results for "Matthew J. Graham"

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The Art of Data ScienceJun 16 2011To flourish in the new data-intensive environment of 21st century science, we need to evolve new skills. These can be expressed in terms of the systemized framework that formed the basis of mediaeval education - the trivium (logic, grammar, and rhetoric) ... More
Software search is not a science, even among scientistsMay 08 2016When they seek software for a task, how do people go about finding it? Past research found that searching the Web, asking colleagues, and reading papers have been the predominant approaches---but is it still true today, given the popularity of Facebook, ... More
Software search is not a science, even among scientists: A survey of how scientists and engineers find softwareMay 08 2016May 28 2018Improved software discovery is a prerequisite for greater software reuse: after all, if someone cannot find software for a particular task, they cannot reuse it. Understanding people's approaches and preferences when they look for software could help ... More
Marked Smooth MoviesJul 17 2014We present a marked analogue of Carter and Saito's smooth movie theorem. To accomplish this we define markings for a surface embedded in 4-space. Our definition of marking was chosen to coincide with the markings that arise in link Floer homology. In ... More
Movie Moves for Knotted Surfaces with MarkingsJul 17 2014Jan 03 2018We present a marked analogue of Carter and Saito's movie theorem. Our definition of marking was chosen to coincide with the markings that arise in link Floer homology. In order to deal with complications arising from certain isotopies, we define three ... More
Grid MoviesMar 07 2013Jul 18 2014We present a grid diagram analogue of Carter, Rieger and Saito's smooth movie theorem. Specifically, we give definitions for grid movies, grid movie isotopies and present a definition of grid planar isotopy as a particular subset of the grid diagram moves: ... More
Asymptotically exact inference in differentiable generative modelsMay 25 2016Mar 02 2017Many generative models can be expressed as a differentiable function of random inputs drawn from some simple probability density. This framework includes both deep generative architectures such as Variational Autoencoders and a large class of procedurally ... More
Continuously tempered Hamiltonian Monte CarloApr 11 2017Hamiltonian Monte Carlo (HMC) is a powerful Markov chain Monte Carlo (MCMC) method for performing approximate inference in complex probabilistic models of continuous variables. In common with many MCMC methods, however, the standard HMC approach performs ... More
Chern-Gauss-Bonnet formula for singular Yamabe metrics in dimension fourFeb 05 2019We derive a formula of Chern-Gauss-Bonnet type for the Euler characteristic of a four dimensional manifold-with-boundary in terms of the geometry of the Loewner-Nirenberg singular Yamabe metric in a prescribed conformal class. The formula involves the ... More
A Sample of Field EllipticalsNov 27 2003Using well-defined selection criteria applied to the LEDA galaxy catalogue we have constructed a sample of elliptical galaxies that can be taken to lie in the field. Such criteria can easily be applied to theoretical simulations for direct comparison ... More
Astro2020: Molecular Masers as Probes of the Dynamic Atmospheres of Dying StarsMar 13 2019More than half of the dust and heavy element enrichment in galaxies originates from the winds and outflows of evolved, low-to-intermediate mass stars on the asymptotic giant branch (AGB). However, numerous details of the physics of late-stage stellar ... More
Error Analysis and Uncertainty Quantification for the Heterogeneous Transport Equation in Slab GeometryMar 28 2019We present an analysis of multilevel Monte Carlo techniques for the forward problem of uncertainty quantification for the radiative transport equation, when the coefficients ({\em cross-sections}) are heterogenous random fields. To do this, we first give ... More
Modern Monte Carlo Variants for Uncertainty Quantification in Neutron TransportFeb 12 2017Oct 17 2017We describe modern variants of Monte Carlo methods for Uncertainty Quantification (UQ) of the Neutron Transport Equation, when it is approximated by the discrete ordinates method with diamond differencing. We focus on the mono-energetic 1D slab geometry ... More
A new assessment of the completeness of quasar surveys: implications for the luminosity functionOct 02 1998We apply a simple statistical method (Derenzo & Hildebrand 1969) to estimating the completeness of quasar surveys. It requires that an area has been covered by two or more, preferably different, selection techniques. We use three suitable data sets with ... More
Some Effects of Galaxy Structure and Dynamics on the Fundamental PlaneJan 07 1997We examine the effects on the Fundamental Plane (FP) of structural departures from an R^{1/4} galaxy light profile. We also explore the use of volumetric as well as projected galaxy parameters. We fit the Sersic R^{1/n} law to the V-band light profiles ... More
IVOA Recommendation: Web Services Basic Profile Version 1.0Oct 03 2011This document describes rules to take into account when implementing SOAP-based web services. It explains also how to check conformance to these rules. It can be read as a "Guideline to VO Web Service Interoperability" or a "How to provide interoperable ... More
Dynamics of Stochastic Epidemics on Heterogeneous NetworksApr 17 2013Epidemic models currently play a central role in our attempts to understand and control infectious diseases. Here, we derive a model for the diffusion limit of stochastic susceptible-infectious-removed (SIR) epidemic dynamics on a heterogeneous network. ... More
Opportunities in Time-Domain Extragalactic Astrophysics with the NASA Near-Earth Object Camera (NEOCam)Apr 12 2019This White Pape motivates the time domain extragalactic science case for the NASA Near-Earth Object Camera (NEOCam). NEOCam is a NASA Planetary mission whose goal is to discover and characterize asteroids and comets, to assess the hazard to Earth from ... More
Detection of quasars in the time domainDec 21 2016The time domain is the emerging forefront of astronomical research with new facilities and instruments providing unprecedented amounts of data on the temporal behavior of astrophysical populations. Dealing with the size and complexity of this requires ... More
Pseudo-Marginal Slice SamplingOct 10 2015May 24 2016Markov chain Monte Carlo (MCMC) methods asymptotically sample from complex probability distributions. The pseudo-marginal MCMC framework only requires an unbiased estimator of the unnormalized probability distribution function to construct a Markov chain. ... More
Using conditional entropy to identify periodicityJun 27 2013Jul 03 2013This paper presents a new period finding method based on conditional entropy that is both efficient and accurate. We demonstrate its applicability on simulated and real data. We find that it has comparable performance to other information-based techniques ... More
Asymptotically exact inference in likelihood-free modelsMay 25 2016Oct 12 2016Many generative models can be expressed as a differentiable function of random inputs drawn from some simple probability density. This framework includes both deep generative architectures such as Variational Autoencoders and a large class of 'likelihood-free' ... More
Machine-assisted discovery of relationships in astronomyFeb 20 2013High-volume feature-rich data sets are becoming the bread-and-butter of 21st century astronomy but present significant challenges to scientific discovery. In particular, identifying scientifically significant relationships between sets of parameters is ... More
Searching for the scale of homogeneityApr 07 1998May 11 1998We introduce a statistical quantity, known as the $K$ function, related to the integral of the two--point correlation function. It gives us straightforward information about the scale where clustering dominates and the scale at which homogeneity is reached. ... More
Environments of Strong / Ultrastrong, Ultraviolet Fe II Emitting QuasarsApr 27 2013May 22 2013We have investigated the strength of ultraviolet Fe II emission from quasars within the environments of Large Quasar Groups (LQGs) in comparison with quasars elsewhere, for 1.1 <= <z_LQG> <= 1.7, using the DR7QSO catalogue of the Sloan Digital Sky Survey. ... More
Data challenges of time domain astronomyAug 13 2012Astronomy has been at the forefront of the development of the techniques and methodologies of data intensive science for over a decade with large sky surveys and distributed efforts such as the Virtual Observatory. However, it faces a new data deluge ... More
Infrared single-pixel imaging utilising microscanningNov 09 2015Since the invention of digital cameras there has been a concerted drive towards detector arrays with higher spatial resolution. Microscanning is a technique that provides a final higher resolution image by combining multiple images of a lower resolution. ... More
Multi-region relaxed magnetohydrodynamics with anisotropy and flowMay 01 2014We present an extension of the multi-region relaxed magnetohydrodynamics (MRxMHD) equilibrium model that includes pressure anisotropy and general plasma flows. This anisotropic extension to our previous isotropic model is motivated by Sun and Finn's model ... More
Responding to the Event DelugeJun 01 2012We present the VOEventNet infrastructure for large-scale rapid follow-up of astronomical events, including selection, annotation, machine intelligence, and coordination of observations. The VOEvent standard is central to this vision, with distributed ... More
Astro2020: Unlocking the Secrets of Late-Stage Stellar Evolution and Mass Loss through Radio Wavelength ImagingMar 13 2019During the late phases of evolution, low-to-intermediate mass stars like our Sun undergo periods of extensive mass loss, returning up to 80% of their initial mass to the interstellar medium. This mass loss profoundly affects the stellar evolutionary history, ... More
Panoramic Views of the Cygnus LoopMay 01 1998We present a complete atlas of the Cygnus Loop supernova remnant in the light of [O III] (5007), H alpha, and [S II] (6717, 6731). Despite its shell-like appearance, the Cygnus Loop is not a current example of a Sedov-Taylor blast wave. Rather, the optical ... More
Large groups in the Chile-UK quasar surveyOct 24 1997The Chile-UK quasar survey, a new-generation 140 deg^2 UVX survey to B = 20, is now \sim 25 per cent complete. The catalogue currently contains 319 quasars and 93 emission line galaxies. Using the minimal-spanning tree method, we have independently confirmed ... More
Two close Large Quasar Groups of size ~ 350 Mpc at z ~ 1.2Aug 31 2011The Clowes & Campusano (1991) Large Quasar Group (LQG) at <z> = 1.28 has been re-examined using the quasar data from the DR7QSO catalogue of the Sloan Digital Sky Survey. In the 1991 discovery, the LQG impinged on the northern, southern and eastern limits ... More
The VAO Transient FacilityNov 09 2011The time domain community wants robust and reliable tools to enable production of and subscription to community-endorsed event notification packets (VOEvent). The VAO Transient Facility (VTF) is being designed to be the premier brokering service for the ... More
Nonminimally coupled topological-defect boson stars: Static solutionsDec 07 2015We consider spherically symmetric static composite structures consisting of a boson star and a global monopole, minimally or non-minimally coupled to the general relativistic gravitational field. In the non-minimally coupled case, Marunovic and Murkovic ... More
A comparison of period finding algorithmsJul 08 2013This paper presents a comparison of popular period finding algorithms applied to the light curves of variable stars from the Catalina Real-time Transient Survey (CRTS), MACHO and ASAS data sets. We analyze the accuracy of the methods against magnitude, ... More
Understanding extreme quasar optical variability with CRTS: I. Major AGN flaresJun 09 2017There is a large degree of variety in the optical variability of quasars and it is unclear whether this is all attributable to a single (set of) physical mechanism(s). We present the results of a systematic search for major flares in AGN in the Catalina ... More
A novel variability-based method for quasar selection: evidence for a rest frame ~54 day characteristic timescaleDec 31 2013We compare quasar selection techniques based on their optical variability using data from the Catalina Real-time Transient Survey (CRTS). We introduce a new technique based on Slepian wavelet variance (SWV) that shows comparable or better performance ... More
A targeted spectral interpolation algorithm for the detection of continuous gravitational wavesMar 01 2016We present an improved method of targeting continuous gravitationalwave signals in data from the LIGO and Virgo detectors with a higher efficiency than the time-domain Bayesian pipeline used in many previous searches. Our spectral interpolation algorithm, ... More
Modeling Grasp Motor Imagery through Deep Conditional Generative ModelsJan 11 2017Grasping is a complex process involving knowledge of the object, the surroundings, and of oneself. While humans are able to integrate and process all of the sensory information required for performing this task, equipping machines with this capability ... More
An Integrated Simulator and Dataset that Combines Grasping and Vision for Deep LearningFeb 07 2017Apr 17 2017Deep learning is an established framework for learning hierarchical data representations. While compute power is in abundance, one of the main challenges in applying this framework to robotic grasping has been obtaining the amount of data needed to learn ... More
IVOA Recommendation: VOSpace specification Version 1.15Oct 03 2011VOSpace is the IVOA interface to distributed storage. This version extends the existing VOSpace 1.0 (SOAP-based) specification to support containers, links between individual VOSpace instances, third party APIs, and a find mechanism. Note, however, that ... More
CARMA CO(J = 2 - 1) Observations of the Circumstellar Envelope of BetelgeuseJun 19 2012We report radio interferometric observations of the 12C16O 1.3 mm J = 2-1 emission line in the circumstellar envelope of the M supergiant Alpha Ori and have detected and separated both the S1 and S2 flow components for the first time. Observations were ... More
Intervening Mg II absorption systems from the SDSS DR12 quasar spectraAug 17 2016Sep 14 2016We present the catalogue of the Mg II absorption systems detected at a high significance level using an automated search algorithm in the spectra of quasars from the twelfth data release of the Sloan Digital Sky Survey. A total of 266,433 background quasars ... More
Compatibility of the Large Quasar Groups with the Concordance Cosmological ModelMar 10 2016Jun 22 2016We study the compatibility of large quasar groups with the concordance cosmological model. Large Quasar Groups are very large spatial associations of quasars in the cosmic web, with sizes of 50-250h^-1 Mpc. In particular, the largest large quasar group ... More
Intervening Mg II absorption systems from the SDSS DR12 quasar spectraAug 17 2016Oct 03 2016We present the catalogue of the Mg II absorption systems detected at a high significance level using an automated search algorithm in the spectra of quasars from the twelfth data release of the Sloan Digital Sky Survey. A total of 266,433 background quasars ... More
A structure in the early universe at z ~ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmologyNov 27 2012A Large Quasar Group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume^1/3) ~ 500 Mpc (proper size, present epoch), longest dimension ~ ... More
Supersymmetric Homogeneous Quantum Cosmologies Coupled to a Scalar FieldJun 14 1993Recent work on $N=2$ supersymmetric Bianchi type IX cosmologies coupled to a scalar field is extended to a general treatment of homogeneous quantum cosmologies with explicitely solvable momentum constraints, i.e. Bianchi types I, II, VII, VIII besides ... More
Non-commutative crepant resolutions: scenes from categorical geometryMar 28 2011Aug 19 2011Non-commutative crepant resolutions are algebraic objects defined by Van den Bergh to realize an equivalence of derived categories in birational geometry. They are motivated by tilting theory, the McKay correspondence, and the minimal model program, and ... More
Total Galaxy Magnitudes and Effective Radii from Petrosian Magnitudes and RadiiApr 13 2005Jun 26 2005Petrosian magnitudes were designed to help with the difficult task of determining a galaxy's total light. Although these magnitudes (taken here as the flux within 2R_P, with the inverted Petrosian index 1/eta(R_P)=0.2) can represent most of an object's ... More
Single-pixel 3D imaging with time-based depth resolutionMar 02 2016Time-of-flight three dimensional imaging is an important tool for many applications, such as object recognition and remote sensing. Unlike conventional imaging approach using pixelated detector array, single-pixel imaging based on projected patterns, ... More
Endomorphism rings of finite global dimensionMay 16 2005For a commutative local ring $R$, consider (noncommutative) $R$-algebras $\Lambda$ of the form $\Lambda = End_R(M)$ where $M$ is a reflexive $R$-module with nonzero free direct summand. Such algebras $\Lambda$ of finite global dimension can be viewed ... More
Derived equivalence classification of m-cluster tilted algebras of type AJul 24 2008We use the maximal faces of the $m$-cluster complex of type A to describe the m-cluster tilted algebras of type A as quivers with relations. We then classify connected components of m-cluster tilted algebras of type A up to derived equivalence using tilting ... More
A possible close supermassive black-hole binary in a quasar with optical periodicityJan 07 2015Quasars have long been known to be variable sources at all wavelengths. Their optical variability is stochastic, can be due to a variety of physical mechanisms, and is well-described statistically in terms of a damped random walk model. The recent availability ... More
The Zwicky Transient Facility Alert Distribution SystemFeb 06 2019The Zwicky Transient Facility (ZTF) survey generates real-time alerts for optical transients, variables, and moving objects discovered in its wide-field survey. We describe the ZTF alert stream distribution and processing (filtering) system. The system ... More
Connecting the time domain community with the Virtual Astronomical ObservatoryJun 18 2012The time domain has been identified as one of the most important areas of astronomical research for the next decade. The Virtual Observatory is in the vanguard with dedicated tools and services that enable and facilitate the discovery, dissemination and ... More
Local rings of bounded Cohen-Macaulay typeNov 26 2002Apr 22 2003Let (R,m,k) be a local Cohen-Macaulay (CM) ring of dimension one. It is known that R has finite CM type if and only if R is reduced and has bounded CM type. Here we study the one-dimensional rings of bounded but infinite CM type. We will classify these ... More
Infrared Time Lags for the Periodic Quasar PG 1302-102Nov 04 2015The optical light curve of the quasar PG 1302-102 at $z = 0.278$ shows a strong, smooth 5.2 yr periodic signal, detectable over a period of $\sim 20$ yr. Although the interpretation of this phenomenon is still uncertain, the most plausible mechanisms ... More
A systematic search for close supermassive black hole binaries in the Catalina Real-Time Transient SurveyJul 27 2015Hierarchical assembly models predict a population of supermassive black hole (SMBH) binaries. These are not resolvable by direct imaging but may be detectable via periodic variability (or nanohertz frequency gravitational waves). Following our detection ... More
The Signature of Primordial Grain Growth in the Polarized Light of the AU Mic Debris DiskSep 12 2006We have used the Hubble Space Telescope/ACS coronagraph to make polarization maps of the AU Mic debris disk. The fractional linear polarization rises monotonically from about 0.05 to 0.4 between 20 and 80 AU. The polarization is perpendicular to the disk, ... More
IVOA Recommendation: IVOA Support InterfacesOct 26 2011This document describes the minimum interface that a (SOAP- or REST-based) web service requires to participate in the IVOA. Note that this is not required of standard VO services developed prior to this specification, although uptake is strongly encouraged ... More
Hypersurfaces of bounded Cohen--Macaulay typeAug 10 2002Apr 22 2003Let R = k[[x_0,...,x_d]]/(f), where k is a field and f is a non-zero non-unit of the formal power series ring k[[x_0,...,x_d]]. We investigate the question of which rings of this form have bounded Cohen--Macaulay type, that is, have a bound on the multiplicities ... More
Brauer-Thrall theory for maximal Cohen-Macaulay modulesNov 14 2012The Brauer-Thrall Conjectures, now theorems, were originally stated for finitely generated modules over a finite-dimensional $\sk$-algebra. They say, roughly speaking, that infinite representation type implies the existence of lots of indecomposable modules ... More
Vertices of high degree in the preferential attachment treeDec 26 2010Jan 29 2012We study the basic preferential attachment process, which generates a sequence of random trees, each obtained from the previous one by introducing a new vertex and joining it to one existing vertex, chosen with probability proportional to its degree. ... More
Instrumental and Observational Artifacts in Quiet Sun Magnetic Flux Cance llation FunctionsSep 27 2012Under the assumption that the photospheric quiet-Sun magnetic field is turbulent, the cancellation function has previously been used to estimate the true, resolution-independent mean, unsigned vertical flux $<|B_z|>_{\mathrm{true}}$. We show that the ... More
The Population Genetic Signature of Polygenic Local AdaptationJul 29 2013Feb 06 2014Adaptation in response to selection on polygenic phenotypes may occur via subtle allele frequencies shifts at many loci. Current population genomic techniques are not well posed to identify such signals. In the past decade, detailed knowledge about the ... More
Wild hypersurfacesAug 14 2010Mar 08 2011Complete hypersurfaces of dimension at least 2 and multiplicity at least 4 have wild Cohen-Macaulay type.
Adaptive foveated single-pixel imaging with dynamic super-samplingJul 27 2016As an alternative to conventional multi-pixel cameras, single-pixel cameras enable images to be recorded using a single detector that measures the correlations between the scene and a set of patterns. However, to fully sample a scene in this way requires ... More
Revealing the Two `Horns' of Taurus with GAIA DR2Apr 15 2019In this Letter we investigate the spatial properties of sources from the GAIA catalogue previously identified as being members of the Taurus star forming region and which appear in the Spitzer catalogue. We study an area of sky of 10x15 deg, centred on ... More
Using the VO to Study the Time DomainJan 03 2012Just as the astronomical "Time Domain" is a catch-phrase for a diverse group of different science objectives involving time-varying phenomena in all astrophysical regimes from the solar system to cosmological scales, so the "Virtual Observatory" is a ... More
IVOA Recommendation: IVOA Credential Delegation Protocol Version 1.0Oct 03 2011The credential delegation protocol allows a client program to delegate a user's credentials to a service such that that service may make requests of other services in the name of that user. The protocol defines a REST service that works alongside other ... More
IVOA Recommendation: IVOA Single-Sign-On Profile: Authentication Mechanisms Version 1.01Oct 03 2011Approved client-server authentication mechanisms are described for the IVOA single-sign-on profile: digital signatures (for SOAP services); TLS with passwords (for user sign-on points); TLS with client certificates (for everything else). Normative rules ... More
Extended stellar kinematics of elliptical galaxies in the Fornax clusterJun 25 1998We present extended stellar kinematics for a sample of 13 elliptical galaxies in the Fornax cluster. Major-axis velocity dispersion profiles (VDPs) and rotation curves (RCs) are given for 12 of the galaxies. A major feature of this data is the spatial ... More
Comparison of methods for numerical calculation of continuum dampingFeb 26 2014Continuum resonance damping is an important factor in determining the stability of certain global modes in fusion plasmas. A number of analytic and numerical approaches have been developed to compute this damping, particularly in the case of the toroidicity-induced ... More
The Absolute Rate of LGRB FormationNov 04 2015We estimate the LGRB progenitor rate using our recent work on the effects of environmental metallically on LGRB formation in concert with SNe statistics via an approach patterned loosely off the Drake equation. Beginning with the cosmic star-formation ... More
Two theorems about maximal Cohen--Macaulay modulesApr 09 2004This paper contains two theorems concerning the theory of maximal Cohen--Macaulay modules. The first theorem proves that certain Ext groups between maximal Cohen--Macaulay modules $M$ and $N$ must have finite length, provided only finitely many isomorphism ... More
Brightest Cluster Galaxy Profile ShapesMar 04 1996We model the surface brightness profiles of a sample of 119 Abell Brightest Cluster Galaxies (BCG), finding a generalised deVaucouleurs R^{1/n} law, where n is a free parameter, to be appropriate. Departures from the R^{1/4} law are shown to be a real ... More
Ultraviolet Fe II Emission in Fainter Quasars: Luminosity Dependences, and the Influence of EnvironmentsApr 28 2016We investigate the strength of ultraviolet Fe II emission in fainter quasars compared with brighter quasars for 1.0 <= z <= 1.8, using the SDSS (Sloan Digital Sky Survey) DR7QSO catalogue and spectra of Schneider et al., and the SFQS (SDSS Faint Quasar ... More
The importance of jet bending in gamma-ray AGN - revisitedJan 23 2014Feb 04 2014We investigate the hypothesis that {\gamma}-ray-quiet AGN have a larger tendency for jet bending than {\gamma}-ray-loud AGN, revisiting the analysis of Tingay, Murphy & Edwards (1998). We perform a statistical analysis using a large sample of 351 radio-loud ... More
Characteristics of Correlated Photon Pairs Generated in Ultra-compact Silicon Slow-light Photonic Crystal WaveguidesNov 16 2011We report the characterization of correlated photon pairs generated in dispersion-engineered silicon slow-light photonic crystal waveguides pumped by picosecond pulses. We found that taking advantage of the 15 nm flat-band slow-light window (vg ~ c/30) ... More
Extreme Variability in a Broad Absorption Line QuasarApr 12 2017CRTS J084133.15+200525.8 is an optically bright quasar at z=2.345 that has shown extreme spectral variability over the past decade. Photometrically, the source had a visual magnitude of V~17.3 between 2002 and 2008. Then, over the following five years, ... More
Feature Selection Strategies for Classifying High Dimensional Astronomical Data SetsOct 08 2013The amount of collected data in many scientific fields is increasing, all of them requiring a common task: extract knowledge from massive, multi parametric data sets, as rapidly and efficiently possible. This is especially true in astronomy where synoptic ... More
Gravitational leptogenesis, C, CP and strong equivalenceNov 13 2014The origin of matter-antimatter asymmetry is one of the most important outstanding problems at the interface of particle physics and cosmology. Gravitational leptogenesis (baryogenesis) provides a possible mechanism through explicit couplings of spacetime ... More
On the full automorphism group of a Hamiltonian cycle system of odd orderJan 28 2015It is shown that a necessary condition for an abstract group G to be the full automorphism group of a Hamiltonian cycle system is that G has odd order or it is either binary, or the affine linear group AGL(1; p) with p prime. We show that this condition ... More
Retardation effects in induced atomic dipole-dipole interactionsOct 18 2016We present mean-field calculations of azimuthally averaged retarded dipole-dipole interactions in a Bose-Einstein condensate induced by a laser, at both long and short wavelengths. Our calculations demonstrate that dipole-dipole interactions become significantly ... More
Factoring the Adjoint and Maximal Cohen--Macaulay Modules over the Generic DeterminantMay 15 2005Apr 17 2006A question of Bergman asks whether the adjoint of the generic square matrix over a field can be factored nontrivially as a product of square matrices. We show that such factorizations indeed exist over any coefficient ring when the matrix has even size. ... More
The Metal Aversion of LGRBsNov 29 2012Aug 21 2013Recently, it has been suggested that the metallicity aversion of long-duration gamma-ray bursts (LGRBs) is not intrinsic to their formation, but rather a consequence of the anti-correlation between star-formation and metallicity seen in the general galaxy ... More
The adjoint of an even size matrix factorsAug 31 2004We show that the adjoint matrix of a generic square matrix of even size can be factored nontrivially, answering a question of G. Bergman. This note is a preliminary report on work in progress.
Palomar-QUEST: A case study in designing sky surveys in the VO eraFeb 25 2004The advent of wide-area multicolour synoptic sky surveys is leading to data sets unprecedented in size, complexity and data throughput. VO technology offers a way to exploit these to the full but requires changes in design philosophy. The Palomar-QUEST ... More
Causality, Renormalizability and Ultra-High Energy Gravitational ScatteringJan 26 2016The amplitude A(s,t) for ultra-high energy scattering can be found in the leading eikonal approximation by considering propagation in an Aichelburg-Sexl gravitational shockwave background. Loop corrections in the QFT describing the scattered particles ... More
Centres of Hecke algebras: the Dipper-James conjectureMar 14 2006May 15 2006In this paper we prove the Dipper-James conjecture that the centre of the Iwahori-Hecke algebra of type A is the set of symmetric polynomials in the Jucys-Murphy operators.
A Mid-IR Selected Changing-Look Quasar and Physical Scenarios for Abrupt AGN FadingMay 17 2018We report a new changing-look quasar, WISE~J105203.55+151929.5 at $z=0.303$, found by identifying highly mid-IR variable quasars in the WISE/NEOWISE data stream. Compared to multi-epoch mid-IR photometry of a large sample of SDSS-confirmed quasars, WISE ... More
Causality and Micro-Causality in Curved SpacetimeJul 16 2007Sep 20 2007We consider how causality and micro-causality are realised in QED in curved spacetime. The photon propagator is found to exhibit novel non-analytic behaviour due to vacuum polarization, which invalidates the Kramers-Kronig dispersion relation and calls ... More
`Superluminal' Photon Propagation in QED in Curved Spacetime is Dispersive and CausalJun 07 2010It is now well-known that vacuum polarisation in QED can lead to superluminal low-frequency phase velocities for photons propagating in curved spacetimes. In a series of papers, we have shown that this quantum phenomenon is dispersive and have calculated ... More
The Effect of Gravitational Tidal Forces on Vacuum Polarization: How to Undress a PhotonJun 01 2010Jun 14 2010The effect of gravitational tidal forces on photon propagation in curved spacetime is investigated. It is found that the imaginary part of the local refractive index Im n(u;w) may be negative as well as positive, corresponding to a local amplification ... More
The Refractive Index of Curved Spacetime: the Fate of Causality in QEDJul 16 2007Oct 29 2007It has been known for a long time that vacuum polarization in QED leads to a superluminal low-frequency phase velocity for light propagating in curved spacetime. Assuming the validity of the Kramers-Kronig dispersion relation, this would imply a superluminal ... More
Diffuson-driven Ultralow Thermal Conductivity in Amorphous Nb2O5 Thin FilmsJul 15 2018Niobium pentoxide (Nb2O5) has been extensively reported for applications of electrochemical energy storage, memristors, solar cells, light emitting diodes (LEDs), and electrochromic devices. The thermal properties of Nb2O5 play a critical role in device ... More
DeepStreaks: identifying fast-moving objects in the Zwicky Transient Facility data with deep learningApr 11 2019We present DeepStreaks, a convolutional-neural-network, deep-learning system designed to efficiently identify streaking fast-moving near-Earth objects that are detected in the data of the Zwicky Transient Facility (ZTF), a wide-field, time-domain survey ... More
A new physical interpretation of optical and infrared variability in quasarsMay 17 2018Sep 27 2018Changing-look quasars are a recently identified class of active galaxies in which the strong UV continuum and/or broad optical hydrogen emission lines associated with unobscured quasars either appear or disappear on timescales of months to years. The ... More
Observational Constraints on Planet Nine: Cassini Range ObservationsApr 12 2016We significantly constrain the sky position, distance, and mass of a possible additional, distant planet in the solar system by examining its influence on the distance between Earth and the Cassini Spacecraft. Our preferred region is approximately centered ... More