Results for "Philip J. T. Woodburn"

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Effects of mechanical processing and annealing on optical coherence properties of Er$^{3+}$:LiNbO$_3$ powdersJan 20 2017Optical coherence lifetimes and decoherence processes in erbium-doped lithium niobate (Er$^{3+}$:LiNbO$_3$) crystalline powders are investigated for materials that underwent different mechanical and thermal treatments. Several complimentary methods are ... More
Electron Spin Coherences in Rare-Earth Optically Excited States for Microwave to Optical Quantum TransducersFeb 09 2018Efficient and reversible optical to microwave coherent transducers are required to enable entanglement transfer between superconducting qubits and light for quantum networks. Rare-earth-doped crystals that possess narrow optical and spin transitions are ... More
Modification of relaxation dynamics in Tb$^{3+}$:Y$_3$Al$_5$O$_{12}$ nanopowdersNov 07 2017Mar 01 2018Nanostructured rare-earth-ion doped materials are increasingly being investigated for on-chip implementations of quantum information processing protocols as well as commercial applications such as fluorescent lighting. However, achieving high-quality ... More
Effects of fabrication methods on spin relaxation and crystallite quality in Tm-doped Y$_2$Al$_5$O$_{12}$ powders studied using spectral hole burningSep 25 2015Apr 27 2016High-quality rare-earth-ion (REI) doped materials are a prerequisite for many applications such as quantum memories, ultra-high-resolution optical spectrum analyzers and information processing. Compared to bulk materials, REI doped powders offer low-cost ... More
Electron Spin Coherences in Rare-Earth Optically Excited States for Microwave to Optical Quantum TransducersFeb 09 2018Feb 16 2018Efficient and reversible optical to microwave coherent transducers are required to enable entanglement transfer between superconducting qubits and light for quantum networks. Rare-earth-doped crystals that possess narrow optical and spin transitions are ... More
Characterization of ${}^{171}Yb^{3+}\!:\! YVO_4$ for photonic quantum technologiesMay 03 2018Rare-earth ions in crystals are a proven solid-state platform for quantum technologies in the ensemble regime and attractive for new opportunities at the single ion level. Among the trivalent rare earths, ${}^{171}\mathrm{Yb}^{3+}$ is unique in that it ... More
An Algorithmic Proof of Suslin's Stability Theorem over Polynomial RingsMay 10 1994Let $k$ be a field. Then Gaussian elimination over $k$ and the Euclidean division algorithm for the univariate polynomial ring $k[x]$ allow us to write any matrix in $SL_n(k)$ or $SL_n(k[x])$, $n\geq 2$, as a product of elementary matrices. Suslin's stability ... More
The Heated Core of the Radio-Quiet Galaxy Cluster A644May 19 2005We present an analysis of a Chandra ACIS-I observation of the massive galaxy cluster A644. This cluster was previously classified as a cooling flow, but no radio emission has been detected from its cD galaxy. Outside the core (R ~75 kpc ~0.03R_vir) the ... More
Paving Spin-Wave Fibers in Magnonic Nanocircuits Using Spin-Orbit TorqueJan 14 2017Recent studies have revealed that domain walls in magnetic nanostructures can serve as compact, energy-efficient spin-wave waveguides for building magnonic devices that are considered promising candidates for overcoming the challenges and bottlenecks ... More
Combining Mathematical Morphology and the Hilbert Transform for Fully Automatic Nuclei Detection in Fluorescence MicroscopyApr 10 2019Accurate and reliable nuclei identification is an essential part of quantification in microscopy. A range of mathematical and machine learning approaches are used but all methods have limitations. Such limitations include sensitivity to user parameters ... More
Dramatic Raman Gain Suppression in the Vicinity of the Zero Dispersion Point in Gas-Filled Hollow-Core Photonic Crystal FiberAug 26 2015In 1964 Bloembergen and Shen predicted that Raman gain could be suppressed if the rates of phonon creation and annihilation (by inelastic scattering) exactly balance. This is only possible if the momentum required for each process is identical, i.e., ... More
Scalar oscillatory integrals in smooth spaces of homogeneous typeMay 25 2012We consider a generalization of the notion of spaces of homogeneous type, inspired by recent work of Street [21] on the multi-parameter Carnot-Caratheodory geometry, which imbues such spaces with differentiability structure. The setting allows one to ... More
Fractional Poincare and logarithmic Sobolev inequalities for measure spacesMay 25 2012We prove generalizations of the Poincare and logarithmic Sobolev inequalities corresponding to the case of fractional derivatives in measure spaces with only a minimal amount of geometric structure. The class of such spaces includes (but is not limited ... More
$L^p$-improving estimates for averages on polynomial curvesDec 13 2008In the combinatorial method proving of $L^p$-improving estimates for averages along curves pioneered by Christ (IMRN, 1998), it is desirable to estimate the average modulus (with respect to some uniform measure on a set) of a polynomial-like function ... More
Rank and regularity for averages over submanifoldsFeb 04 2008This paper establishes endpoint $L^p-L^q$ and Sobolev mapping properties of Radon-like operators which satisfy a homogeneity condition (similar to semiquasihomogeneity) and a condition on the rank of a matrix related to rotational curvature. For highly ... More
Fourier extension for extremal quadratic submanifoldsFeb 15 2016Feb 16 2016This note establishes the full range of $L^p$--$L^q$ Fourier extension estimates for the model $n$-dimensional quadratic submanifold in ${\mathbb R}^{n(n+3)/2}$ parametrized by $\gamma(x_1,\ldots,x_n) := (x_1,\ldots,x_n, (x_i x_j)_{1 \leq i \leq j \leq ... More
Generalized curvature for certain Radon-like operators of intermediate dimensionSep 09 2016This paper establishes $L^p$-improving estimates for a variety of Radon-like transforms which integrate functions over submanifolds of intermediate dimension. In each case, the results rely on a unique notion of curvature which relates to, but is distinct ... More
Uniform estimates for cubic oscillatory integralsJul 17 2007Jul 19 2007This paper establishes the optimal decay rate for scalar oscillatory integrals in $n$ variables which satisfy a nondegeneracy condition on the third derivatives. The estimates proved are stable under small linear perturbations, as encountered when computing ... More
Uniform sublevel Radon-like inequalitiesOct 04 2010This paper is concerned with establishing uniform weighted $L^p$-$L^q$ estimates for a class of operators generalizing both Radon-like operators and sublevel set operators. Such estimates are shown to hold under general circumstances whenever a scalar ... More
On multilinear determinant functionalsNov 06 2009This paper considers the problem of $L^p$-estimates for a certain multilinear functional involving integration against a kernel with the structure of a determinant. Examples of such objects are ubiquitous in the study of Fourier restriction and geometric ... More
Uniform geometric estimates for sublevel setsSep 04 2009This paper reconsiders the uniform sublevel set estimates of Carbery, Christ, and Wright (1999) and Phong, Stein, and Sturm (2001) from a geometric perspective. This perspective leads one to consider a natural collection of homogeneous, nonlinear differential ... More
$L^p$-nondegenerate Radon-like operators with vanishing rotational curvatureAug 06 2013We consider the $L^p \rightarrow L^q$ mapping properties of a model family of Radon-like operators integrating functions over n-dimensional submanifolds of ${\mathbb R}^{2n}$. It is shown that nonvanishing rotational curvature is never generic when $n ... More
Sharp $L^p$-$L^q$ estimates for generalized $k$-plane transformsJan 04 2007In this paper, optimal $L^p-L^q$ estimates are obtained for operators which average functions over polynomial submanifolds, generalizing the $k$-plane transform. An important advance over previous work is that full $L^p-L^q$ estimates are obtained by ... More
Damping oscillatory integrals by the Hessian determinant via SchrödingerNov 17 2014We consider the question of when it is possible to force a degenerate scalar oscillatory integral to decay as fast as a nondegenerate one by restricting the support to the region where the Hessian determinant of the phase is bounded below. We show in ... More
A Collisional Origin to Earth's Non-chondritic Composition?Oct 13 2014Several lines of evidence indicate a non-chondritic composition for Bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142Nd/144Nd and low Mg/Fe ratios, might be explained ... More
Turbulence and angular momentum transport in a global accretion disk simulationMay 11 1998The global development of magnetohydrodynamic turbulence in an accretion disk is studied within a simplified disk model that omits vertical stratification. Starting with a weak vertical seed field, a saturated state is obtained after a few tens of orbits ... More
Massive planet migration: Theoretical predictions and comparison with observationsMay 21 2007Jul 25 2007We quantify the utility of large radial velocity surveys for constraining theoretical models of Type II migration and protoplanetary disk physics. We describe a theoretical model for the expected radial distribution of extrasolar planets that combines ... More
Magnetic activity in accretion disc boundary layersOct 30 2001We use three dimensional magnetohydrodynamic simulations to study the structure of the boundary layer between an accretion disc and a non-rotating, unmagnetized star. Under the assumption that cooling is efficient, we obtain a narrow but highly variable ... More
Dynamics of Protoplanetary DisksNov 05 2010Aug 23 2011Protoplanetary disks are quasi-steady structures whose evolution and dispersal determine the environment for planet formation. I review the theory of protoplanetary disk evolution and its connection to observations. Substantial progress has been made ... More
Collisional stripping of planetary crustsDec 07 2017Geochemical studies of planetary accretion and evolution have invoked various degrees of collisional erosion to explain differences in bulk composition between planets and chondrites. Here we undertake a full, dynamical evaluation of 'crustal stripping' ... More
Physical processes in protoplanetary disksSep 21 2015This review introduces physical processes in protoplanetary disks relevant to accretion and the initial stages of planet formation. After reprising the elementary theory of disk structure and evolution, I discuss the gas-phase physics of angular momentum ... More
Ab initio simulations of accretion disc boundary layersOct 10 2001I discuss the results of simplified three dimensional magnetohydrodynamic simulations of the boundary layer between a disc and a non-rotating, unmagnetized star. Strong magnetic fields, possibly approaching equipartition with the thermal energy, occur ... More
Eccentricity of masing disks in Active Galactic NucleiFeb 11 2008Observations of Keplerian disks of masers in NCG 4258 and other Seyfert galaxies can be used to obtain geometric distance estimates and derive the Hubble constant. The ultimate precision of such measurements could be limited by uncertainties in the disk ... More
A reduced efficiency of terrestrial planet formation following giant planet migrationNov 21 2002Substantial orbital migration of massive planets may occur in most extrasolar planetary systems. Since migration is likely to occur after a significant fraction of the dust has been locked up into planetesimals, ubiquitous migration could reduce the probability ... More
Suppression of giant planet formation in stellar clustersJul 04 2000Sep 02 2000Photoevaporation driven by the ultraviolet radiation from massive stars severely limits the lifetime of protoplanetary discs around stars formed within stellar clusters. I investigate the resulting influence of clustered environments on the probability ... More
The stream-disk interactionJul 31 1997I review theoretical aspects of the interaction between the accretion stream and the disk in interacting binary systems, concentrating on recent hydrodynamic calculations. At low accretion rates, cooling is expected to be efficient, and the interaction ... More
Thin Elements and Commutative Shells in Cubical omega-categoriesAug 23 2004The relationships between thin elements, commutative shells and connections in cubical omega-categories are explored by a method which does not involve the use of pasting theory or nerves of omega-categories (both of which were previously needed for this ... More
Theory of disk accretion onto supermassive black holesMay 10 2004Accretion onto supermassive black holes produces both the dramatic phenomena associated with active galactic nuclei and the underwhelming displays seen in the Galactic Center and most other nearby galaxies. I review selected aspects of the current theoretical ... More
Compositional evolution during rocky protoplanet accretionSep 24 2015The Earth appears non-chondritic in its abundances of refractory lithophile elements, posing a significant problem for our understanding of its formation and evolution. It has been suggested that this non-chondritic composition may be explained by collisional ... More
Integrating design synthesis and assembly of structured objects in a visual design languageMar 21 2004Computer Aided Design systems provide tools for building and manipulating models of solid objects. Some also provide access to programming languages so that parametrised designs can be expressed. There is a sharp distinction, therefore, between building ... More
Parametric Bilinear Generalized Approximate Message PassingAug 30 2015Dec 11 2015We propose a scheme to estimate the parameters $b_i$ and $c_j$ of the bilinear form $z_m=\sum_{i,j} b_i z_m^{(i,j)} c_j$ from noisy measurements $\{y_m\}_{m=1}^M$, where $y_m$ and $z_m$ are related through an arbitrary likelihood function and $z_m^{(i,j)}$ ... More
Warkworth 12m VLBI Station: WARK12M - 2014Feb 01 2015The Warkworth Radio Astronomical Observatory is operated by the Institute for Radio Astronomy and Space Research (IRASR), AUT University, Auckland, New Zealand. Here we review the characteristics of the VLBI station facilities and report on a number of ... More
Low-Mass X-ray Binaries and Globular Clusters in Early-Type Galaxies. II. Globular Cluster Candidates and their Mass-Metallicity RelationSep 03 2008We present an astrometry and photometry catalogue of globular cluster (GC) candidates detected with HST WFPC2 in a sample of 19 early-type galaxies, appropriate for comparison to the low-mass X-ray binary (LMXB) populations observed with Chandra. In a ... More
Lecture notes on the formation and early evolution of planetary systemsJan 16 2007Aug 26 2014These notes provide an introduction to the theory of the formation and early evolution of planetary systems. Topics covered include the structure, evolution and dispersal of protoplanetary disks; the formation of planetesimals, terrestrial and gas giant ... More
EXor outbursts from disk amplification of stellar magnetic cyclesDec 05 2016EXor outbursts - moderate-amplitude disk accretion events observed in Class I and Class II protostellar sources - have time scales and amplitudes that are consistent with the viscous accumulation and release of gas in the inner disk near the dead zone ... More
The Mass Distribution and Assembly of the Milky Way from the Properties of the Magellanic CloudsNov 09 2010Nov 22 2011We present a new measurement of the mass of the Milky Way (MW) based on observed properties of its largest satellite galaxies, the Magellanic Clouds (MCs), and an assumed prior of a {\Lambda}CDM universe. The large, high-resolution Bolshoi cosmological ... More
Broadband-tunable LP$_{01}$ mode frequency shifting by Raman coherence waves in H$_2$-filled hollow-core PCFJun 08 2015When a laser pump beam of sufficient intensity is incident on a Raman-active medium such as hydrogen gas, a strong Stokes signal, red-shifted by the Raman transition frequency {\Omega}$_R$, is generated. This is accompanied by the creation of a "coherence ... More
Characterizing the Cool KOIs VIII. Parameters of the Planets Orbiting Kepler's Coolest DwarfsMar 03 2015The coolest dwarf stars targeted by the Kepler Mission constitute a relatively small but scientifically valuable subset of the Kepler target stars, and provide a high-fidelity and nearby sample of transiting planetary systems. Using archival Kepler data ... More
Feedback-Driven Evolution of the Far-Infrared Spectral Energy Distributions of Luminous and Ultraluminous Infrared GalaxiesMay 25 2006Jan 22 2007We calculate infrared spectral energy distributions (SEDs) from simulations of major galaxy mergers and study the effect of AGN and starburst driven feedback on the evolution of the SED as a function of time. We use a self-consistent three-dimensional ... More
Explaining the variability of WD 1145+017 with simulations of asteroid tidal disruptionOct 21 2016Post-main-sequence planetary science has been galvanised by the striking variability, depth and shape of the photometric transit curves due to objects orbiting white dwarf WD 1145+017, a star which also hosts a dusty debris disc and circumstellar gas, ... More
Maximal Decay Inequalities for Trilinear oscillatory integrals of convolution typeNov 17 2015In this paper we prove sharp $L^\infty$-$L^\infty$-$L^\infty$ decay for certain trilinear oscillatory integral forms of convolution type on $\mathbb R^2$. These estimates imply earlier $L^2$-$L^2$-$L^2$ results obtained by the second author as well as ... More
X-ray Emission from Hot Gas in Galaxy MergersApr 06 2005Jul 13 2006We examine X-ray emission produced from hot gas during collisions and mergers of disk galaxies. To study this process, we employ simulations that incorporate cosmologically motivated disk-galaxy models and include the effects of radiative cooling, star ... More
An Evolutionary Model For Submillimeter GalaxiesOct 29 2006[abridged]We calculate multi-wavelength spectral energy distributions (SEDs) (spanning optical to millimeter wavelengths) from simulations of major galaxy mergers with black hole feedback which produce submillimeter bright galaxies (SMGs), using a self-consistent ... More
The Self-Regulated Growth of Supermassive Black HolesApr 17 2008Jul 02 2008We present a series of simulations of the self--regulated growth of supermassive black holes (SMBHs) in galaxies via three different fueling mechanisms: major mergers, minor mergers, and disk instabilities. The SMBHs in all three scenarios follow the ... More
Spatial and Temporal Stability of Airglow Measured in the Meinel Band Window at 1191.3 nmOct 26 2015We report on the temporal and spatial fluctuations in the atmospheric brightness in the narrow band between Meinel emission lines at 1191.3 nm using an R=320 near-infrared instrument. We present the instrument design and implementation, followed by a ... More
Online adaptive basis refinement and compression for reduced-order modelsFeb 27 2019In many applications, projection-based reduced-order models (ROMs) have demonstrated the ability to provide rapid approximate solutions to high-fidelity full-order models (FOMs). However, there is no a priori assurance that these approximate solutions ... More
An operator van der Corput estimate arising from oscillatory Riemann-Hilbert problemsAug 06 2013We study an operator analogue of the classical problem of finding the rate of decay of an oscillatory integral on the real line. This particular problem arose in the analysis of oscillatory Riemann-Hilbert problems associated with partial differential ... More
Order from chaos: Observation of large-scale flow from turbulence in a two-dimensional superfluidJan 22 2018Mar 14 2018Interacting systems driven far from equilibrium tend to evolve to steady states exhibiting large-scale structure and order. In two-dimensional turbulent flow the seemingly random swirling motion of a fluid can evolve towards persistent large-scale vortices. ... More
A Theoretical and Empirical Comparison of the Temporal Exponential Random Graph Model and the Stochastic Actor-Oriented ModelJun 22 2015May 03 2016The temporal exponential random graph model (TERGM) and the stochastic actor-oriented model (SAOM, e.g., SIENA) are popular models for longitudinal network analysis. We compare these models theoretically, via simulation, and through a real-data example ... More
Entropic Elasticity of Twist-Storing PolymersNov 30 1997Jun 03 1998We investigate the statistical mechanics of a torsionally constrained polymer. The polymer is modeled as a fluctuating rod with bend stiffness A kT and twist stiffness C kT. In such a model, thermal bend fluctuations couple geometrically to an applied ... More
The Blandford-Znajek mechanism and emission from isolated accreting black holesJul 21 1999In the presence of a magnetic field, rotational energy can be extracted from black holes via the Blandford-Znajek mechanism. We use self-similar advection dominated accretion (ADAF) models to estimate the efficiency of this mechanism for black holes accreting ... More
Warped discs and the directional stability of jets in Active Galactic NucleiDec 01 1998Jun 27 1999Warped accretion discs in Active Galactic Nuclei (AGN) exert a torque on the black hole that tends to align the rotation axis with the angular momentum of the outer disc. We compute the magnitude of this torque by solving numerically for the steady state ... More
Metriplectic formalism: friction and much moreJun 04 2017The metriplectic formalism couples Poisson brackets of the Hamiltonian description with metric brackets for describing systems with both Hamiltonian and dissipative components. The construction builds in asymptotic convergence to a preselected equilibrium ... More
Cubical abelian groups with connections are equivalent to chain complexesDec 11 2002The theorem of the title is deduced from the equivalence between crossed complexes and cubical $\omega$-groupoids with connections proved by the authors in 1981. In fact we prove the equivalence of five categories defined internally to an additive category ... More
Exotic Baker and wandering domains for Ahlfors islands mapsAug 10 2010Let X be a Riemann surface of genus at most 1, i.e. X is the Riemann sphere or a torus. We construct a variety of examples of analytic functions g:W->X, where W is an arbitrary subdomain of X, that satisfy Epstein's "Ahlfors islands condition". In particular, ... More
Black hole formation via hypercritical accretion during common envelope evolutionJun 02 1999Neutron stars inspiralling into a stellar envelope can accrete at rates vastly exceeding the Eddington limit if the flow develops pressures high enough to allow neutrinos to radiate the released gravitational energy. It has been suggested that this hypercritical ... More
Lense-Thirring precession of accretion disks around compact objectsFeb 19 1999Jun 27 1999Misaligned accretion disks surrounding rotating compact objects experience a torque due to the Lense-Thirring effect, which leads to precession of the inner disk. It has been suggested that this effect could be responsible for some low frequency Quasi-Periodic ... More
Influence of massive planet scattering on nascent terrestrial planetsJan 17 2005In most extrasolar planetary systems, the present orbits of known giant planets admit the existence of stable terrestrial planets. Those same giant planets, however, have typically eccentric orbits that hint at violent early dynamics less benign for low ... More
The Dynamics of Two Massive Planets on Inclined OrbitsJun 30 2004The significant orbital eccentricities of most giant extrasolar planets may have their origin in the gravitational dynamics of initially unstable multiple planet systems. In this work, we explore the dynamics of two close planets on inclined orbits through ... More
Epi-two-dimensional flow and generalized enstrophyApr 08 2016The conservation of the enstrophy ($L^2$ norm of the vorticity $\omega$) plays an essential role in the physics and mathematics of two-dimensional (2D) Euler fluids. Generalizing to compressible ideal (inviscid and barotropic) fluids, the generalized ... More
Dynamically-Stabilized Pores in Bilayer MembranesOct 08 1996May 14 1997Zhelev and Needham have recently created large, quasi-stable pores in artificial lipid bilayer vesicles [Biochim. Biophys. Acta 1147 (1993) 89]. Initially created by electroporation, the pores remain open for up to several seconds before quickly snapping ... More
Time Delay CosmographyMay 17 2016Gravitational time delays, observed in strong lens systems where the variable background source is multiply-imaged by a massive galaxy in the foreground, provide direct measurements of cosmological distance that are very complementary to other cosmographic ... More
Stability Boundaries and Sufficient Stability Conditions for Stably Stratified, Monotonic Shear FlowsDec 03 2015Jan 28 2016Linear stability of inviscid, parallel, and stably stratified shear flow is studied under the assumption of smooth strictly monotonic profiles of shear flow and density, so that the local Richardson number is positive everywhere. The marginally unstable ... More
A birth and growth of a collimated molecular jet from an AGB starSep 25 2003With the VLBA, we have observed water masers associated with the OH/IR star, W43A, which trace a birth and growth of a molecular jet. The water masers exhibit the collimated distribution (1700 AU: 20 AU) and fast motions (+/-150 km/s). The maser distribution ... More
Negative absolute temperatures of vortices in a two-dimensional superfluidJan 22 2018We have observed negative absolute temperature configuration of vortices in a 2D superfluid atomic gas of Rb atoms confined in a circular-shaped, flat-bottom potential. We create the vortex configurations by sweeping a linear array of optical barriers ... More
Torsional Directed Walks, Entropic Elasticity, and DNA Twist StiffnessAug 21 1997DNA and other biopolymers differ from classical polymers due to their torsional stiffness. This property changes the statistical character of their conformations under tension from a classical random walk to a problem we call the `torsional directed walk'. ... More
Predictions for the correlation between giant and terrestrial extrasolar planets in dynamically evolved systemsApr 04 2006The large eccentricities of many giant extrasolar planets may represent the endpoint of gravitational scattering in initially more crowded systems. If so, the early evolution of the giant planets is likely to be more restrictive of terrestrial planet ... More
Accretion during the merger of supermassive black holesJan 18 2002We study the evolution of disk accretion during the merger of supermassive black hole binaries in galactic nuclei. In hierarchical galaxy formation models, the most common binaries are likely to arise from minor galactic mergers, and have unequal mass ... More
Hydrodynamics of the stream-disk impact in interacting binariesSep 04 1997We use hydrodynamic simulations to provide quantitative estimates of the effects of the impact of the accretion stream on disks in interacting binaries. For low accretion rates, efficient radiative cooling of the hotspot region can occur, and the primary ... More
Eccentricity of supermassive black hole binaries coalescing from gas rich mergersAug 23 2005Angular momentum loss to circumbinary gas provides a possible mechanism for overcoming the `last parsec' problem and allowing the most massive black hole binaries formed from galactic mergers to coalesce. Here, we show that if gas disks also catalyze ... More
On the nature of the peculiar superthin galaxy UGC 12281Jan 12 2012UGC 12281 has been classified as having a pure disk and being a low surface brightness galaxy (LSBG), thus being an obvious member of the so-called superthin galaxies. At the same time it represents an extremely untypical type of LSBG due to its remarkable ... More
The Better Half of Selling SeparatelyDec 24 2017Oct 26 2018Separate selling of two independent goods is shown to yield at least 62% of the optimal revenue, and at least 73% when the goods satisfy the Myerson regularity condition. This improves the 50% result of Hart and Nisan (2017, originally circulated in 2012). ... More
Computing the Invariant Measure and the Lyapunov Exponent for One-Dimensional Maps using a Measure-Preserving Polynomial BasisNov 25 2011We consider a generalisation of Ulam's method for approximating invariant densities of one-dimensional chaotic maps. Rather than use piecewise constant polynomials to approximate the density, we use polynomials of degree n which are defined by the requirement ... More
Gravitationally lensed quasars and supernovae in future wide-field optical imaging surveysJan 13 2010Mar 08 2010Cadenced optical imaging surveys in the next decade will be capable of detecting time-varying galaxy-scale strong gravitational lenses in large numbers, increasing the size of the statistically well-defined samples of multiply-imaged quasars by two orders ... More
Hydrodynamic outcomes of planet scattering in transitional discsAug 26 2011A significant fraction of unstable multiple planet systems likely scatter during the transitional disc phase as gas damping becomes ineffectual. Using an ensemble of FARGO hydrodynamic simulations and MERCURY n-body integrations, we directly follow planet-disc ... More
Mode signature and stability for a Hamiltonian model of electron temperature gradient turbulenceSep 30 2010Stability properties and mode signature for equilibria of a model of electron temperature gradient (ETG) driven turbulence are investigated by Hamiltonian techniques. After deriving the infinite families of Casimir invariants, associated with the noncanonical ... More
Geometric derivation of the quantum speed limitMar 25 2010The Mandelstam-Tamm and Margolus-Levitin inequalities play an important role in the study of quantum mechanical processes in Nature, since they provide general limits on the speed of dynamical evolution. However, to date there has been only one derivation ... More
Common Envelope Evolution on a Moving MeshApr 19 2019We outline the methodology of simulating common envelope evolution (CEE) with the moving-mesh code MANGA. We extend MANGA to include multiple time-steps. This provides substantial speedups for problems with large dynamic range. We describe the implementation ... More
Extrasolar planetary dynamics with a generalized planar Laplace-Lagrange secular theoryMar 05 2007The dynamical evolution of nearly half of the known extrasolar planets in multiple-planet systems may be dominated by secular perturbations. The commonly high eccentricities of the planetary orbits calls into question the utility of the traditional Laplace-Lagrange ... More
Migration of extrasolar planets to large orbital radiiOct 06 2003Observations of structure in circumstellar debris discs provide circumstantial evidence for the presence of massive planets at large (several tens of au) orbital radii, where the timescale for planet formation via core accretion is prohibitively long. ... More
The fundamental groupoid of the quotient of a Hausdorff space by a discontinuous action of a discrete group is the orbit groupoid of the induced actionDec 19 2002The main result is that the fundamental groupoid of the orbit space of a discontinuous action of a discrete group on a Hausdorff space which admits a universal cover is the orbit groupoid of the fundamental groupoid of the space. We also describe work ... More
The inverse-Compton ghost HDF 130 and the giant radio galaxy 6C 0905+3955: matching an analytic model for double radio source evolutionJul 05 2011We present new GMRT observations of HDF 130, an inverse-Compton (IC) ghost of a giant radio source that is no longer being powered by jets. We compare the properties of HDF 130 with the new and important constraint of the upper limit of the radio flux ... More
Submillimetre galaxies in a hierarchical universe: number counts, redshift distribution, and implications for the IMFSep 11 2012Oct 15 2012High-redshift submillimetre galaxies (SMGs) are some of the most rapidly star-forming galaxies in the Universe. Historically, galaxy formation models have had difficulty explaining the observed number counts of SMGs. We combine a semi-empirical model ... More
Do sub-millimeter galaxy number counts provide evidence for a top-heavy IMF?Aug 26 2010Aug 30 2010Theoretical models have had difficulty matching the observed number density of sub-millimeter galaxies (SMGs), causing some authors (e.g., Baugh et al. 2005) to suggest that SMGs provide evidence for a top-heavy initial mass function (IMF). To test this ... More
A Business Zone Recommender System Based on Facebook and Urban Planning DataNov 21 2016We present ZoneRec---a zone recommendation system for physical businesses in an urban city, which uses both public business data from Facebook and urban planning data. The system consists of machine learning algorithms that take in a business' metadata ... More
Kinematic Structure of Merger RemnantsJul 19 2006We use numerical simulations to study the kinematic structure of remnants formed from mergers of equal-mass disk galaxies. In particular, we show that remnants of dissipational mergers, which include the radiative cooling of gas, star formation, feedback ... More
Large-scale Star Formation Triggering in the Low-mass Arp 82 System: A Nearby Example of Galaxy Downsizing Based on UV/Optical/Mid-IR ImagingOct 13 2006As part of our Spitzer Spirals, Bridges, and Tails project to help understand the effects of galaxy interactions on star formation, we analyze GALEX ultraviolet, SARA optical, and Spitzer infrared images of the interacting galaxy pair Arp 82 (NGC 2535/6) ... More
Inferring habitat quality and habitat selection using static site occupancy modelsJul 18 2016When evaluating the ecological value of land use within a landscape, investigators typically rely on measures of habitat selection and habitat quality. Traditional measures of habitat selection and habitat quality require data from resource intensive ... More
Using Numerical Simulations to Gain Insight into the Structure of SuperbubblesJan 21 1999Recent high resolution observations of Galactic superbubbles have motivated us to re-examine several classes of superbubble models. We compare three classes of hydrodynamic models (the Kompaneets approximation, the thin shell model, and numerical simulations) ... More
Estimation of Apollo lunar dust transport using optical extinction measurementsFeb 28 2015A technique to estimate mass erosion rate of surface soil during landing of the Apollo Lunar Module (LM) and total mass ejected due to the rocket plume interaction is proposed and tested. The erosion rate is proportional to the product of the second moment ... More