Results for "Sean P. Matt"

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New Calculations of Stellar Wind TorquesSep 26 2008Using numerical simulations of magnetized stellar winds, we carry out a parameter study to find the dependence of the stellar wind torque on observable parameters. We find that the power-law dependencies of the torque on parameters is significantly different ... More
The Effect of Magnetic Variability on Stellar Angular Momentum Loss I: The Solar Wind Torque During Sunspot Cycles 23 & 24Jul 31 2018Aug 23 2018The rotational evolution of cool stars is governed by magnetised stellar winds which slow the stellar rotation during their main sequence lifetimes. Magnetic variability is commonly observed in Sun-like stars, and the changing strength and topology of ... More
The Enigmatic HH 255Nov 26 2002To gain insight into the nature of the peculiar Herbig-Haro object HH 255 (also called Burnham's nebula), we use previously published observations to derive information about the emission line fluxes as a function of position within HH 255 and compare ... More
The Nature of Stellar Winds in the Star-Disk InteractionJul 02 2007Stellar winds may be important for angular momentum transport from accreting T Tauri stars, but the nature of these winds is still not well-constrained. We present some simulation results for hypothetical, hot (~1e6 K) coronal winds from T Tauri stars, ... More
Understanding the Spins of Young StarsJan 23 2007We review the theoretical efforts to understand why pre-main-sequence stars spin much more slowly than expected. The first idea put forward was that massive stellar winds may remove substantial angular momentum. Since then, it has become clear that the ... More
Does Disk Locking Solve the Stellar Angular Momentum Problem?Mar 26 2004May 21 2004We critically examine the theory of disk locking, which assumes that the angular momentum deposited on an accreting protostar is exactly removed by torques carried along magnetic field lines connecting the star to the disk. In this letter, we consider ... More
Spin Evolution of Accreting Young Stars. I. Effect of Magnetic Star-Disk CouplingMay 05 2010We present a model for the rotational evolution of a young, solar mass star interacting with an accretion disk. The model incorporates a description of the angular momentum transfer between the star and disk due to a magnetic connection, and includes ... More
Convection and Differential Rotation Properties of G & K Stars Computed with the ASH CodeNov 23 2011The stellar luminosity and depth of the convective envelope vary rapidly with mass for G- and K-type main sequence stars. In order to understand how these properties influence the convective turbulence, differential rotation, and meridional circulation, ... More
Accretion-Powered Stellar Winds II: Numerical Solutions for Stellar Wind TorquesJan 02 2008Jan 18 2008[Abridged] In order to explain the slow rotation observed in a large fraction of accreting pre-main-sequence stars (CTTSs), we explore the role of stellar winds in torquing down the stars. For this mechanism to be effective, the stellar winds need to ... More
Spin Evolution of Accreting Young Stars. II. Effect of Accretion-Powered Stellar WindsNov 28 2011We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a ... More
From solar to stellar corona: the role of wind, rotation and magnetismSep 23 2015Observations of surface magnetic fields are now within reach for many stellar types thanks to the development of Zeeman-Doppler Imaging. These observations are extremely useful for constraining rotational evolution models of stars, as well as for characterizing ... More
The Last Hurrah: PPN Formation by a Magnetic ExplosionAug 29 2003Aug 29 2003We discuss a mechanism by which a giant star can expel its envelope in an outburst, leaving its core exposed. The outburst is powered by rotational kinetic energy of the core, transferred to the envelope via the twisting of magnetic fields. We show that, ... More
Modelling the Corona of HD 189733 in 3DNov 10 2014The braking of main sequence stars originates mainly from their stellar wind. The efficiency of this angular momentum extraction depends on the rotation rate of the star, the acceleration profile of the wind and the coronal magnetic field. The derivation ... More
On the diversity of magnetic interactions in close-in star-planet systemsSep 18 2014Magnetic interactions between close-in planets and their host star can play an important role in the secular orbital evolution of the planets, as well as the rotational evolution of their host. As long as the planet orbits inside the Alfv\'en surface ... More
Normalization conventions for Newton's constant and the Planck scale in arbitrary spacetime dimensionSep 17 2006We calculate, in d spacetime dimensions, the relationship between the coefficient 1/K^2 of the Einstein-Hilbert term in the action of general relativity and the coefficient G_N of the force law that results from the Newtonian limit of general relativity. ... More
Large deviation asymptotics and control variates for simulating large functionsMar 14 2006Consider the normalized partial sums of a real-valued function $F$ of a Markov chain, \[\phi_n:=n^{-1}\sum_{k=0}^{n-1}F(\Phi(k)),\qquad n\ge1.\] The chain $\{\Phi(k):k\ge0\}$ takes values in a general state space $\mathsf {X}$, with transition kernel ... More
Computable exponential bounds for screened estimation and simulationDec 01 2006Aug 22 2008Suppose the expectation $E(F(X))$ is to be estimated by the empirical averages of the values of $F$ on independent and identically distributed samples $\{X_i\}$. A sampling rule called the "screened" estimator is introduced, and its performance is studied. ... More
Spatial Small Worlds: New Geographic Patterns for an Information EconomyOct 17 2003Networks are structures that pervade many natural and man-made phenomena. Recent findings have characterized many networks as not random structures, but as efficent complex formations. Current research has examined complex networks as largely non-spatial ... More
Relationship between Hawking Radiation and Gravitational AnomaliesFeb 15 2005Aug 23 2005We show that in order to avoid a breakdown of general covariance at the quantum level the total flux in each outgoing partial wave of a quantum field in a black hole background must be equal to that of a (1+1)-dimensional blackbody at the Hawking temperature. ... More
Factor graph fragmentization of expectation propagationJan 16 2018Expectation propagation is a general approach to fast approximate inference for graphical models. The existing literature treats models separately when it comes to deriving and coding expectation propagation inference algorithms. This comes at the cost ... More
Outflows, Bubbles, and the Role of the Radio Jet: Direct Evidence for AGN Feedback at z~2Oct 15 2008To accommodate the seemingly "anti-hierarchical" properties of galaxies near the upper end of the mass function within our hierarchical paradigm, current models of galaxy evolution postulate a phase of vigorous AGN feedback at high redshift, which effectively ... More
Real-time semiparametric regressionSep 17 2012Feb 06 2013We develop algorithms for performing semiparametric regression analysis in real time, with data processed as it is collected and made immediately available via modern telecommunications technologies. Our definition of semiparametric regression is quite ... More
The crater function approach to ion-induced nanoscale pattern formation: Craters for flat surfaces are insufficientMar 08 2014In the crater function approach to the erosion of a solid surface by a broad ion beam, the average crater produced by the impact of an ion is used to compute the constant coefficients in the continuum equation of motion for the surface. We extend the ... More
Differential TD Learning for Value Function ApproximationApr 06 2016Dec 23 2018Value functions arise as a component of algorithms as well as performance metrics in statistics and engineering applications. Computation of the associated Bellman equations is numerically challenging in all but a few special cases. A popular approximation ... 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
OFFl models: novel schema for dynamical modeling of biological systemsApr 06 2016Jun 08 2016Flow diagrams are a common tool used to help build and interpret models of dynamical systems, often in biological contexts such as consumer-resource models and similar compartmental models. Typically, their usage is intuitive and informal. Here, we present ... More
Impure AdS/CFTJan 11 2008Feb 14 2008We study momentum relaxation due to dilute, weak impurities in a strongly coupled CFT, a truncation of the M2 brane theory. Using the AdS/CFT correspondence, we compute the relaxation time scale as a function of the background magnetic field B and charge ... More
Regarding the `Hole Argument' and the `Problem of Time'Dec 06 2015The canonical formalism of general relativity affords a particularly interesting characterisation of the infamous hole argument. It also provides a natural formalism in which to relate the hole argument to the problem of time in classical and quantum ... More
Simulating the Ising Model with a Deep Convolutional Generative Adversarial NetworkOct 13 2017The deep learning framework is witnessing expansive growth into diverse applications such as biological systems, human cognition, robotics, and the social sciences, thanks to its immense ability to extract essential features from complicated systems. ... 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
Circumstellar Dust Disks in Taurus-Auriga: The Submillimeter PerspectiveJun 08 2005We present a sensitive, multiwavelength submillimeter continuum survey of 153 young stellar objects in the Taurus-Auriga star formation region. The submillimeter detection rate is 61% to a completeness limit of ~10 mJy (3-sigma) at 850 microns. The inferred ... More
Submillimeter Array Observations of Disks in the SR 24 Multiple Star SystemNov 05 2004We present high-resolution aperture synthesis images from the Submillimeter Array of the 225 GHz (1.3 mm) continuum and CO J=2-1 line emission from the disks around components of the hierarchical triple system SR 24, located in the Ophiuchus star-forming ... More
The Dust Properties of Eight Debris Disk Candidates as Determined by Submillimeter PhotometrySep 05 2006The nature of far-infrared dust emission toward main sequence stars, whether interstellar or circumstellar, can be deduced from submillimeter photometry. We present JCMT/SCUBA flux measurements at 850 microns toward 8 stars with large photospheric excesses ... More
Submillimeter studies of circumstellar disks in Taurus and OrionNov 19 2005We highlight two recent studies of circumstellar disks in the Taurus and Orion star forming regions. Using the JCMT and CSO, we measure disk fluxes in Taurus over a wide range of submillimeter wavelengths and determine the frequency dependence of the ... More
Strategies for the preparation of large cluster states using non-deterministic gatesJan 12 2007The cluster state model for quantum computation has paved the way for schemes that allow scalable quantum computing, even when using non-deterministic quantum gates. Here the initial step is to prepare a large entangled state using non-deterministic gates. ... More
Estimating magnetic filling factors from Zeeman-Doppler magnetogramsMar 13 2019Low-mass stars are known to have magnetic fields that are believed to be of dynamo origin. Two complementary techniques are principally used to characterise them. Zeeman-Doppler imaging (ZDI) can determine the geometry of the large-scale magnetic field ... More
The Effect of Combined Magnetic Geometries on Thermally Driven Winds II: Dipolar, Quadrupolar and Octupolar TopologiesJan 23 2018During the lifetime of sun-like or low mass stars a significant amount of angular momentum is removed through magnetised stellar winds. This process is often assumed to be governed by the dipolar component of the magnetic field. However, observed magnetic ... More
Effect of the stellar spin history on the tidal evolution of close-in planetsJul 09 2012We investigate how the evolution of the stellar spin rate affects, and is affected by, planets in close orbits, via star-planet tidal interactions. To do this, we used a standard equilibrium tidal model to compute the orbital evolution of single planets ... More
X-Ray Emitting Ejecta of Supernova Remnant N132DNov 20 2007The brightest supernova remnant in the Magellanic Clouds, N132D, belongs to the rare class of oxygen-rich remnants, about a dozen objects that show optical emission from pure heavy-element ejecta. They originate in explosions of massive stars that produce ... More
The luminosity function of Ly-alpha emitters at 2.3 < z < 4.6 from integral-field spectroscopyFeb 21 2005We have used VIsible MultiObject Spectrograph Integral-Field Unit (VIMOS-IFU) observations centred on a radio galaxy at z=2.9 to search for Ly-alpha emitters within a comoving volume of ~ 10^4 Mpc^3. We find 14 Ly-alpha emitters with flux > 1.4 x 10^-20 ... More
Numerical aspects of 3D stellar windsOct 13 2014This paper explores and compares the pitfalls of modelling the three-dimensional wind of a spherical star with a cartesian grid. Several numerical methods are compared, using either uniform and stretched grid or adaptative mesh refinement (AMR). An additional ... More
The hard X-ray view of the low-luminosity blazar in the radio galaxy NGC6251Aug 05 2003Aug 06 2003We present results from a BeppoSAX (July 2001) observation of the FRI radio galaxy NGC6251, together with a re-analysis of archival ASCA (October 1994) and Chandra (September 2000) data. The weak detection above 10 keV and the lack of iron fluorescent ... More
Mapping the circumnuclear matter of NGC1068 in X-raysOct 11 1999An-energy dependent variation of the X-ray emission from the archetypical "Compton-thick'' Seyfert 2 galaxy NGC1068 has been observed between two BeppoSAX observations, performed one year apart. This variation (at the 2.6 sigma level) is highest in the ... More
Quantum simulation with ions in micro-fabricated Penning trapsDec 17 2018Feb 12 2019We propose the use of 2-dimensional Penning trap arrays as a scalable platform for quantum simulation and quantum computing with trapped ions. Using realistic experimental parameters, we show that large arrays of micro-structured electrodes defining static ... More
Actuation of Micro-Optomechanical Systems Via Cavity-Enhanced Optical Dipole ForcesFeb 26 2007Apr 30 2007We demonstrate a new type of optomechanical system employing a movable, micron-scale waveguide evanescently-coupled to a high-Q optical microresonator. Micron-scale displacements of the waveguide are observed for milliwatt(mW)-level optical input powers. ... More
Magnetic games between a planet and its host star: the key role of topologyNov 09 2015Magnetic interactions between a star and a close-in planet are postulated to be a source of enhanced emissions and to play a role in the secular evolution of the orbital system. Close-in planets generally orbit in the sub-alfv\'enic region of the stellar ... More
Measurement of the intracluster light at z ~ 1Jun 20 2012A significant fraction of the total photospheric light in nearby galaxy clusters is thought to be contained within the diffuse intracluster light (ICL), which extends 100s of kpc from cluster cores. The study of the ICL can reveal details of the evolutionary ... More
Gravitational anomalies: a recipe for Hawking radiationMay 16 2007Mar 27 2008We explore the method of Robinson and Wilczek for deriving the Hawking temperature of a black hole. In this method, the Hawking radiation restores general covariance in an effective theory of near-horizon physics which otherwise exhibits a gravitational ... More
A universal Dirac operator and noncommutative spin bundles over fuzzy complex projective spacesNov 08 2007Sep 15 2008We present a universal Dirac operator for noncommutative spin and spin^c bundles over fuzzy complex projective spaces. We give an explicit construction of these bundles, which are described in terms of finite dimensional matrices, calculate the spectrum ... More
Controlling Complex Networks with Compensatory PerturbationsMay 18 2011The response of complex networks to perturbations is of utmost importance in areas as diverse as ecosystem management, emergency response, and cell reprogramming. A fundamental property of networks is that the perturbation of one node can affect other ... More
Building an AdS/CFT superconductorMar 22 2008We show that a simple gravitational theory can provide a holographically dual description of a superconductor. There is a critical temperature, below which a charged condensate forms via a second order phase transition and the (DC) conductivity becomes ... More
Holographic SuperconductorsOct 09 2008It has been shown that a gravitational dual to a superconductor can be obtained by coupling anti-de Sitter gravity to a Maxwell field and charged scalar. We review our earlier analysis of this theory and extend it in two directions. First, we consider ... More
Simulating Turbulence-aided Neutrino-driven Core-collapse Supernova Explosions in One DimensionFeb 04 2019The core-collapse supernova (CCSN) mechanism is fundamentally three-dimensional with instabilities, convection, and turbulence playing crucial roles in aiding neutrino-driven explosions. Simulations of CCNSe including accurate treatments of neutrino transport ... More
Gain function approximation in the Feedback Particle FilterFeb 19 2019This paper is concerned with numerical algorithms for the problem of gain function approximation in the feedback particle filter. The exact gain function is the solution of a Poisson equation involving a probability-weighted Laplacian. The numerical problem ... More
Accelerator-Oriented Algorithm Transformation for Temporal Data MiningMay 13 2009Temporal data mining algorithms are becoming increasingly important in many application domains including computational neuroscience, especially the analysis of spike train data. While application scientists have been able to readily gather multi-neuronal ... More
$Ψ$-Epistemic Quantum Cosmology?Jun 23 2016This paper provides a prospectus for a new way of thinking about the wavefunction of the universe: a $\Psi$-epistemic quantum cosmology. We present a proposal that, if successfully implemented, would resolve the cosmological measurement problem and simultaneously ... More
Coevolutionary immune system dynamics driving pathogen speciationAug 06 2013Aug 04 2014We introduce and analyze a within-host dynamical model of the coevolution between rapidly mutating pathogens and the adaptive immune response. Pathogen mutation and a homeostatic constraint on lymphocytes both play a role in allowing the development of ... More
Differential Temporal Difference LearningDec 28 2018Value functions derived from Markov decision processes arise as a central component of algorithms as well as performance metrics in many statistics and engineering applications of machine learning techniques. Computation of the solution to the associated ... More
A Dynamical AdS/Yang-Mills ModelJan 18 2018The Anti-de Sitter Space/Conformal Field Theory (AdS/CFT) correspondence has provided new and useful insights into the non-perturbative regime of strongly coupled gauge theories. We construct a class of models meant to mimic Yang-Mills theory using the ... More
Distributed computation of equilibria in misspecified convex stochastic Nash gamesAug 25 2013Oct 11 2015The distributed computation of Nash equilibria is assuming growing relevance in engineering where such problems emerge in the context of distributed control. Accordingly, we consider static stochastic convex games complicated by a parametric misspecification, ... More
Stability of exact force-free electrodynamic solutions and scattering from spacetime curvatureJan 22 2015Jul 31 2015Recently, a family of exact force-free electrodynamic (FFE) solutions was given by Brennan, Gralla and Jacobson, which generalizes earlier solutions by Michel, Menon and Dermer, and other authors. These solutions have been proposed as useful models for ... More
Analysis of non-processive molecular motor transport using renewal reward theoryNov 13 2017Sep 27 2018We propose and analyze a mathematical model of cargo transport by non-processive molecular motors. In our model, the motors change states by random discrete events (corresponding to stepping and binding/unbinding), while the cargo position follows a stochastic ... More
A Search for Star-Disk Interaction Among the Strongest X-ray Flaring Stars in the Orion Nebula ClusterMay 12 2010The Chandra Orion Ultradeep Project observed hundreds of young, low-mass stars undergoing highly energetic X-ray flare events. The 32 most powerful cases have been modeled with the result that the magnetic structures responsible for these flares can be ... More
Modeling magnetized star-planet interactions: boundary conditions effectsNov 15 2013We model the magnetized interaction between a star and a close-in planet (SPMIs), using global, magnetohydrodynamic numerical simulations. In this proceedings, we study the effects of the numerical boundary conditions at the stellar surface, where the ... More
Surprises from a deep ASCA spectrum of a Broad Absorption Line Quasar PHL 5200Feb 18 2001We present a deep ($\sim$85 ksec) ASCA observation of the prototype Broad Absorption Line Quasar (BALQSO) PHL 5200. This is the best X-ray spectrum of a BALQSO yet. We find that (1) the source is not intrinsically X-ray weak, (2) the line of sight absorption ... More
Simultaneous Production of Disk and Lobes: A Single-Wind MHD Model for the Eta Carinae NebulaAug 02 2004Aug 05 2004The luminous blue variable Eta Carinae is surrounded by a complex and highly structured nebula of ejected material. The best-studied and axisymmetric components of this outflow consist of bipolar lobes (the ``homunculus'') and an equatorial ``skirt.'' ... More
Tunnel One, Fibered LinksDec 15 2010Let K be a tunnel number one, fibered link in S^3, with fiber F, and unknotting tunnel $\tau$. We show that $\tau$ can be isotoped to lie in F.
An Enhanced Decomposition Theorem for Knots with Symmetry InformationNov 10 2014Nov 13 2014We present an enhanced prime decomposition theorem for knots that gives the isotopy classes of composite knots that can be constructed from a given list of prime factors (allowing for the mirroring and orientation reversing for each factor). Underlying ... More
Billiards in L-shaped tables with barriersMay 23 2007We compute the volumes of the eigenform loci in the moduli space of genus two Abelian differentials. From this, we obtain asymptotic formulas for counting closed billiards paths in certain L-shaped polygons with barriers.
Convergence of the parabolic complex Monge-Ampère equation on compact Hermitian manifoldsSep 29 2010Oct 12 2011We prove $C^\infty$ convergence for suitably normalized solutions of the parabolic complex Monge-Amp\`ere equation on compact Hermitian manifolds. This provides a parabolic proof of a recent result of Tosatti and Weinkove.
Variants on Andrica's conjecture with and without the Riemann hypothesisApr 07 2018Nov 28 2018The gap between what we can explicitly prove regarding the distribution of primes and what we suspect regarding the distribution of primes is enormous. It is (reasonably) well-known that the Riemann hypothesis is not sufficient to prove Andrica's conjecture: ... More
General Relativity effects and line emissionOct 07 2006General Relativity effects (gravitational redshift, light bending, ...) strongly modify the characteristics of the lines emitted close to the Black Hole in Active Galactic Nuclei and Galactic Black Hole systems. These effects are reviewed and illustrated, ... More
The X-ray view of highly obscured AGNJul 31 2001The properties of Compton-thick AGN are reviewed, with particular emphasis on BeppoSAX hard X-ray observations. I also discuss evidence for the presence of Compton-thick, circumnuclear matter in unobscured AGN, and I briefly introduce the HELLAS2XMM 5-10 ... More
New graceful diameter-6 trees by transfersFeb 22 2014Jun 28 2015Given a graph $G$, a labeling of $G$ is an injective function $f:V(G)\rightarrow\mathbb{Z}_{\ge 0}$. Under the labeling $f$, the label of a vertex $v$ is $f(v)$, and the induced label of an edge $uv$ is $|f(u) - f(v)|$. The labeling $f$ is graceful if ... More
Flows on Bidirected GraphsOct 31 2013The study of nowhere-zero flows began with a key observation of Tutte that in planar graphs, nowhere-zero k-flows are dual to k-colourings (in the form of k-tensions). Tutte conjectured that every graph without a cut-edge has a nowhere-zero 5-flow. Seymour ... More
Strong version of Andrica's conjectureDec 06 2018Feb 19 2019A strong version of Andrica's conjecture can be formulated as follows: Except for $p_n\in\{3,7,13,23,31,113\}$, that is $n\in\{2,4,6,9,11,30\}$, one has \[ \sqrt{p_{n+1}}-\sqrt{p_n} < {1\over2}. \] While a proof is far out of reach I shall show that this ... More
$\ell^{2}$-torsion of free-by-cyclic groupsSep 30 2015Dec 14 2016We provide an upper bound on the $\ell^{2}$-torsion of a free-by-cyclic group, $-\rho^{(2)}(\mathbb{F} \rtimes_{\Phi} \mathbb{Z})$, in terms of a relative train-track representative for $\Phi \in \mathrm{Aut}(\mathbb{F})$. Our result shares features with ... More
Numerical investigation into the injection-locking phenomena of gain switched lasers for optical frequency comb generationMar 26 2015We present detailed numerical simulations of the laser dynamics that describe optical frequency comb formation by injection-locking a gain-switched laser. The typical rate equations for semiconductor lasers including stochastic carrier recombination and ... More
LoCuSS: Pre-processing in galaxy groups falling into massive galaxy clusters at z=0.2Oct 11 2017We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have been identified via their X-ray emission in the infall regions ... More
On the Distribution of Witnesses in the Miller-Rabin TestAug 25 2016We show that the set of normalized Miller-Rabin witnesses becomes equidistributed in the unit interval. This will be done by exhibiting cancellation in certain exponential sums.
Dark matter in dwarf galaxiesJan 19 2017Although the cusp-core controversy for dwarf galaxies is seen as a problem, I argue that the cored central profiles can be explained by flattened cusps because they suffer from conflicting measurements and poor statistics and because there is a large ... More
Deformation spaces of G-trees and automorphisms of Baumslag-Solitar groupsFeb 20 2007Mar 25 2008We construct an invariant deformation retract of a deformation space of G-trees. We show that this complex is finite dimensional in certain cases and provide an example that is not finite dimensional. Using this complex we compute the automorphism group ... More
Exterior products of 0-cyclesApr 05 2005We study the exterior product on 0-cycles modulo rational equivalence, and prove some nonvanishing results. The main tools used are higher cycle- and Abel-Jacobi- classes developed in articles of J. Lewis and the author. A theorem of Rosenschon-Saito ... More
Quadrant Marked Mesh Patterns and the r-Stirling NumbersDec 01 2014Dec 18 2014Marked mesh patterns are a very general type of permutation pattern. We examine a particular marked mesh pattern originally defined by Kitaev and Remmel, and show that its generating function is described by the $r$-Stirling numbers. We examine some ramifications ... More
Primes and the Lambert W functionNov 11 2013Feb 03 2017The Lambert W function, implicitly defined by W(x) exp{W(x)}=x, is a "new" special function that has recently been the subject of an extended upsurge in interest and applications. In this note, I point out that the Lambert W function can also be used ... More
Obscured AGN: the hidden side of the X-ray UniverseMay 11 2002Most Active Galactic Nuclei (AGN) are `obscured', i.e. the nucleus is hiding behind a screen of absorbing material. The advantage of having the nucleus obscured is to make easier the observations of those emission components which originate in circumnuclear ... More
The Structure of Critical Product SetsJan 01 2013Sep 07 2013Let $G$ be a multiplicative group, let $A,B \subseteq G$ be finite and nonempty, and define the product set $AB = {ab \mid $a \in A$ and $b \in B$}$. Two fundamental problems in combinatorial number theory are to find lower bounds on $|AB|$, and then ... More
Integral-field studies of the high-redshift UniverseMar 09 2006We present results from a new method of exploring the distant Universe. We use 3-D spectroscopy to sample a large cosmological volume at a time when the Universe was less than 3 billion years old to investigate the evolution of star-formation activity. ... More
The graphic nature of the symmetric groupMay 21 2013Aug 07 2013We investigate a remarkable class of exponential sums which are derived from the symmetric groups and which display a diverse array of visually appealing features. Our interest in these expressions stems not only from their astounding visual properties, ... More
The trail of water and the delivery of volatiles to habitable planetsMar 15 2019Water is fundamental to our understanding of the evolution of planetary systems and the delivery of volatiles to the surfaces of potentially habitable planets. Yet, we currently have essentially no facilities capable of observing this key species comprehensively. ... More
Representations of Rank Two Affine Hecke Algebras at Roots of UnityApr 26 2011In this paper, we will fully describe the representations of the crystallographic rank two affine Hecke algebras using elementary methods, for all possible values of q. The focus is on the case when q is a root of unity of small order.
The X-ray spectrum of Compton-thick Seyfert 2 GalaxiesNov 29 1996Current ideas on the X-ray spectrum of Compton-thick Seyfert 2 galaxies are reviewed, and a brief description of the four presently known sources belonging to this class are given.
Prospects for Probing Triple Gauge-boson Couplings at the LHCJun 17 2005In these proceedings I explore one aspect of gauge-boson physics at the LHC - Triple Gauge-boson Couplings (TGCs) in $WZ$ and Wgamma production. Methods for extracting confidence limits on anomalous TGCs are assessed, while accounting for the effects ... More
Incorporating next-to-leading order matrix elements for hadronic diboson production in showering event generatorsMar 15 2001A method for incorporating information from next-to-leading order QCD matrix elements for hadronic diboson production into showering event generators is presented. In the hard central region (high jet transverse momentum) where perturbative QCD is reliable, ... More
Euler characteristics of Teichmüller curves in genus twoNov 14 2006We calculate the Euler characteristics of all of the Teichmuller curves in the moduli space of genus two Riemann surfaces which are generated by holomorphic one-forms with a single double zero. These curves can all be embedded in Hilbert modular surfaces ... More
Optimized quasisymmetric stellarators are consistent with the Garren-Boozer constructionFeb 05 2019Most quasisymmetric stellarators to date have been designed by numerically optimizing the plasma boundary shape to minimize symmetry-breaking Fourier modes of the magnetic field strength $B$. At high aspect ratio, a faster approach is to directly construct ... More
Higher Abel-Jacobi maps for 0-cyclesApr 05 2005Mar 13 2006Starting from the candidate Bloch-Beilinson filtration on Chow groups of 0-cycles constructed by J. Lewis, we develop and describe geometrically a series of Hodge-theoretic invariants defined on the graded pieces. Explicit formulas (in terms of currents ... More
When does a right-angled Artin group split over $\mathbb{Z}$?Mar 07 2014Aug 01 2014We show that a right-angled Artin group, defined by a graph $\Gamma$ that has at least three vertices, does not split over an infinite cyclic subgroup if and only if $\Gamma$ is biconnected. Further, we compute JSJ--decompositions of 1--ended right-angled ... More
Motivic irrationality proofsAug 13 2017We exhibit geometric conditions on a family of toric hypersurfaces under which the value of a canonical normal function at a point of maximal unipotent monodromy is irrational.
XMM-Newton observation of the bright Seyfert 1 galaxy, MCG+8-11-11Sep 01 2005We report on the XMM-Newton observation of the bright Seyfert 1 galaxy, MCG+8-11-11. Data from the EPIC/p-n camera, the Reflection Gratings Spectrometers (RGS) and the Optical Monitor (OM) have been analyzed. The p-n spectrum is well fitted by a power ... More