Results for "Sean P. Matt"

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Magnetic braking of Sun-like and low-mass stars: Dependence on coronal temperatureOct 03 2017Sun-like and low-mass stars possess high temperature coronae and lose mass in the form of stellar winds, driven by thermal pressure and complex magnetohydrodynamic processes. These magnetized outflows probably do not significantly affect the star's structural ... More
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 Combined Magnetic Geometries on Thermally Driven Winds II: Dipolar, Quadrupolar and Octupolar TopologiesJan 23 2018Mar 21 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
The Effect of Combined Magnetic Geometries on Thermally Driven Winds I: Interaction of Dipolar and Quadrupolar FieldsJul 13 2017Cool stars with outer convective envelopes are observed to have magnetic fields with a variety of geometries, which on large scales are dominated by a combination of the lowest order fields such as the dipole, quadrupole and octupole modes. Magnetised ... More
The Effect of Magnetic Variability on Stellar Angular Momentum Loss II: The Sun, 61 Cygni A, $ε$ Eridani, $ξ$ Bootis A and $τ$ Bootis AMar 23 2019The magnetic fields of low-mass stars are observed to be variable on decadal timescales, ranging in behaviour from cyclic to stochastic. The changing strength and geometry of the magnetic field should modify the efficiency of angular momentum loss by ... 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
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
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
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
The Mass-Dependence of Angular Momentum Evolution in Sun-Like StarsDec 15 2014To better understand the observed distributions of rotation rate and magnetic activity of sun-like and low-mass stars, we derive a physically motivated scaling for the dependence of the stellar-wind torque on Rossby number. The torque also contains an ... 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
Coronal Mass Ejections and Angular Momentum Loss in Young StarsFeb 28 2014In our own solar system, the necessity of understanding space weather is readily evident. Fortunately for Earth, our nearest stellar neighbor is relatively quiet, exhibiting activity levels several orders of magnitude lower than young, solar-type stars. ... More
Mass loss in pre-main sequence stars via coronal mass ejections and implications for angular momentum lossSep 28 2012We develop an empirical model to estimate mass-loss rates via coronal mass ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method estimates the CME mass-loss rate from the observed energies of PMS X-ray flares, using our empirically ... 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
Physical Conditions of Accreting Gas in T Tauri Star SystemsJul 10 2008We present results from a low resolution (R~300) near-infrared spectroscopic variability survey of actively accreting T Tauri stars (TTS) in the Taurus-Auriga star forming region. Paschen and Brackett series H I recombination lines were detected in 73 ... 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
On differential rotation and overshooting in solar-like starsFeb 21 2017We seek to characterize how the change of global rotation rate influences the overall dynamics and large scale flows arising in the convective envelopes of stars covering stellar spectral types from early G to late K. We do so through numerical simulations ... 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
Geometric Ergodicity and the Spectral Gap of Non-Reversible Markov ChainsJun 29 2009We argue that the spectral theory of non-reversible Markov chains may often be more effectively cast within the framework of the naturally associated weighted-$L_\infty$ space $L_\infty^V$, instead of the usual Hilbert space $L_2=L_2(\pi)$, where $\pi$ ... More
Random-Time, State-Dependent Stochastic Drift for Markov Chains and Application to Stochastic Stabilization Over Erasure ChannelsOct 22 2010May 17 2012It is known that state-dependent, multi-step Lyapunov bounds lead to greatly simplified verification theorems for stability for large classes of Markov chain models. This is one component of the "fluid model" approach to stability of stochastic networks. ... 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
Evolving pulsation of the slowly rotating magnetic beta Cep star xi 1 CMaDec 07 2017We report BRITE-Constellation photometry of the beta Cep pulsator xi 1 CMa. Analysis of these data reveals a single pulsation period of 0.2095781(3) d, along with its first and second harmonics. We find no evidence for any other frequencies, limiting ... More
The influence of the magnetic topology on the braking of sun-like starsOct 31 2014Stellar winds are thought to be the main process responsible for the spin down of main-sequence stars. The extraction of angular momentum by a magnetized wind has been studied for decades, leading to several formulations for the resulting torque. However, ... More
The effect of magnetic topology on thermally-driven winds: towards a general formulation of the braking lawOct 31 2014Nov 27 2014Stellar winds are thought to be the main process responsible for the spin down of main-sequence stars. The extraction of angular momentum by a magnetized wind has been studied for decades, leading to several formulations for the resulting torque. However, ... 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
Quantum gravity without Lorentz invarianceMay 18 2009Oct 13 2009There has been a significant surge of interest in Horava's model for 3+1 dimensional quantum gravity, this model being based on anisotropic scaling at a z=3 Lifshitz point. Horava's model, and its variants, show dramatically improved ultra-violet behaviour ... More
Solutions to Sparse Multilevel Matrix ProblemsMar 07 2019We define and solve classes of sparse matrix problems that arise in multilevel modeling and data analysis. The classes are indexed by the number of nested units, with two-level problems corresponding to the common situation in which data on level 1 units ... More
Phenomenologically viable Lorentz-violating quantum gravityApr 28 2009Jun 26 2009Horava's "Lifschitz point gravity" has many desirable features, but in its original incarnation one is forced to accept a non-zero cosmological constant of the wrong sign to be compatible with observation. We develop an extension of Horava's model that ... 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
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
Ohm's Law at strong coupling: S duality and the cyclotron resonanceJun 22 2007Oct 18 2007We calculate the electrical and thermal conductivities and the thermoelectric coefficient of a class of strongly interacting 2+1 dimensional conformal field theories with anti-de Sitter space duals. We obtain these transport coefficients as a function ... More
Predicting Effective Control Parameters for Differential Evolution using Cluster Analysis of Objective Function FeaturesJun 25 2018A methodology is introduced which uses three simple objective function features to predict effective control parameters for differential evolution. This is achieved using cluster analysis techniques to classify objective functions using these features. ... More
Complete Intersection Hom Injective DimensionSep 13 2018We introduce and investigate a new injective version of the complete intersection dimension of Avramov, Gasharov, and Peeva. It is like the complete intersection injective dimension of Sahandi, Sharif, and Yassemi in that it is built using quasi-deformations. ... More
Rationally inattentive control of Markov processesFeb 12 2015Feb 23 2016The article poses a general model for optimal control subject to information constraints, motivated in part by recent work of Sims and others on information-constrained decision-making by economic agents. In the average-cost optimal control framework, ... More
Evaluating the role of data quality when sharing information in hierarchical multi-stock assessment models, with an application to Dover SoleApr 10 2018Oct 20 2018An emerging approach to data-limited fisheries stock assessment uses hierarchical multi-stock assessment models to group stocks together, sharing information from data-rich to data-poor stocks. In this paper, we simulate data-rich and data-poor fishery ... 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
Approximating exponential family models (not single distributions) with a two-network architectureMar 18 2019Recently much attention has been paid to deep generative models, since they have been used to great success for variational inference, generation of complex data types, and more. In most all of these settings, the goal has been to find a particular member ... 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
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
Fastest Convergence for Q-learningJul 12 2017Mar 21 2018The Zap Q-learning algorithm introduced in this paper is an improvement of Watkins' original algorithm and recent competitors in several respects. It is a matrix-gain algorithm designed so that its asymptotic variance is optimal. Moreover, an ODE analysis ... More
Superpositions of the cosmological constant allow for singularity resolution and unitary evolution in quantum cosmologyJan 17 2018Aug 14 2018A novel approach to quantization is shown to allow for superpositions of the cosmological constant in isotropic and homogeneous mini-superspace models. Generic solutions featuring such superpositions display unitary evolution and resolution of the classical ... More
Bouncing Unitary Cosmology II: Mini-Superspace PhenomenologyJan 17 2018Dec 14 2018A companion paper provides a proposal for cosmic singularity resolution based upon general features of a bouncing unitary cosmological model in the mini-superspace approximation. This paper analyses novel phenomenology that can be identified within particular ... More
Bouncing Unitary Cosmology I: Mini-Superspace General SolutionJan 17 2018Dec 14 2018We offer a new proposal for cosmic singularity resolution based upon a quantum cosmology with a unitary bounce. This proposal is illustrated via a novel quantization of a mini-superspace model in which there can be superpositions of the cosmological constant. ... 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
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
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
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
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
Streamlined Computing for Variational Inference with Higher Level Random EffectsMar 07 2019We derive and present explicit algorithms to facilitate streamlined computing for variational inference for models containing higher level random effects. Existing literature, such as Lee and Wand (2016), is such that streamlined variational inference ... 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
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
The Evolution of K* and the Halo Occupation Distribution since z=1.5: Observations vs. SimulationsSep 26 2011Oct 27 2011We study the evolution of the K-band luminosity function (LF) and the Halo Occupation Distribution (HOD) using Subaru observations of 15 X-ray clusters at z=0.8-1.5 and compare the results with mock clusters (0<z<1.3) extracted from the Millennium Simulation ... 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
Duality for Nonlinear Filtering: What is the Lagrangian for Nonlinear Filtering?Mar 27 2019Duality between estimation and optimal control is a problem of rich historical significance. The first duality principle appears in the seminar paper of Kalman-Bucy where the problem of minimum variance estimation is shown to be dual to a linear quadratic ... 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
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
Inhomogeneous Structures in Holographic Superfluids: I. Dark SolitonsNov 10 2009We begin an investigation of inhomogeneous structures in holographic superfluids. As a first example, we study domain wall like defects in the 3+1 dimensional Einstein-Maxwell-Higgs theory, which was developed as a dual model for a holographic superconductor. ... More
Dark Solitons in Holographic SuperfluidsJun 29 2009Nov 10 2009We construct dark soliton solutions in a holographic model of a relativistic superfluid. We study the length scales associated with the condensate and the charge density depletion, and find that the two scales differ by a non-trivial function of the chemical ... More
ManifoldOptim: An R Interface to the ROPTLIB Library for Riemannian Manifold OptimizationDec 12 2016Dec 25 2016Manifold optimization appears in a wide variety of computational problems in the applied sciences. In recent statistical methodologies such as sufficient dimension reduction and regression envelopes, estimation relies on the optimization of likelihood ... More
Are commercially implemented adaptive cruise control systems string stable?May 06 2019In this article, we assess the string stability of seven 2018 model year adaptive cruise control (ACC) equipped vehicles that are widely available in the US market. Seven distinct vehicle models from two different vehicle makes are analyzed using data ... 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
The Rotation of the halo of NGC 6822 from the radial velocities of carbon starsMay 18 2016Using spectra taken with the AAOmega spectrograph, we measure the radial velocities of over 100 stars, many of which are intermediate age carbon stars, in the direction of the dwarf irregular galaxy NGC 6822. Kinematic analysis suggests that the carbon ... 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
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
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
Distributed computation of equilibria in misspecified convex stochastic Nash gamesAug 25 2013Oct 14 2017The distributed computation of Nash equilibria is assuming growing relevance in engineering where such problems emerge in the context of distributed control. Accordingly, we present schemes for computing equilibria of two classes of static stochastic ... More
Solitons as Probes of the Structure of Holographic SuperfluidsDec 01 2010Detailed features of solitons in holographic superfluids are discussed. Using solitons as probes, we study the behavior of holographic superfluids by varying the scaling dimension of the condensing operator, and build a comparison to the BEC-BCS comparison ... 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
What is the Lagrangian for Nonlinear Filtering?Mar 27 2019Apr 04 2019Duality between estimation and optimal control is a problem of rich historical significance. The first duality principle appears in the seminal paper of Kalman-Bucy, where the problem of minimum variance estimation is shown to be dual to a linear quadratic ... More
Zap Q-Learning for Optimal Stopping Time ProblemsApr 25 2019May 01 2019We propose a novel reinforcement learning algorithm that approximates solutions to the problem of discounted optimal stopping in an irreducible, uniformly ergodic Markov chain evolving on a compact subset of $\mathbb R^n$. A dynamic programming approach ... 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
Inhomogeneous Structures in Holographic Superfluids: II. VorticesDec 22 2009Jan 19 2010We study vortex solutions in a holographic model of Herzog, Hartnoll, and Horowitz, with a vanishing external magnetic field on the boundary, as is appropriate for vortices in a superfluid. We study relevant length scales related to the vortices and how ... More
Zap~Q-Learning for Optimal Stopping Time ProblemsApr 25 2019We propose a novel reinforcement learning algorithm that approximates solutions to the problem of discounted optimal stopping in an irreducible, uniformly ergodic Markov chain evolving on a compact subset of $\mathbb R^n$. A dynamic programming approach ... 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.
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.
A Call for Clarity in Reporting BLEU ScoresApr 23 2018Sep 12 2018The field of machine translation faces an under-recognized problem because of inconsistency in the reporting of scores from its dominant metric. Although people refer to "the" BLEU score, BLEU is in fact a parameterized metric whose values can vary wildly ... More
Noncommutative deformation theory, the derived quotient, and DG singularity categoriesOct 23 2018Nov 28 2018We show that Braun-Chuang-Lazarev's derived quotient prorepresents a naturally defined noncommutative derived deformation functor. Given a noncommutative partial resolution of a Gorenstein algebra, we show that the associated derived quotient controls ... More
Chaplygin gas in decelerating DGP gravityApr 21 2008Explanations to the accelerated expansion of the Universe are usually sought either in modifications of Einstein gravity or in new forms of energy density. An example of modified gravity is the braneworld Dvali-Gabadadze-Porrati (DGP) model which is characterized ... More
DefunT: A Tool for Automating Termination Proofs by Using the Community Books (Extended Abstract)Oct 10 2018We present a tool that automates termination proofs for recursive definitions by mining existing termination theorems.
Verifying the Firoozbakht, Nicholson, and Farhadian conjectures up to the 81st maximal prime gapMar 31 2019The Firoozbakht, Nicholoson, and Farhadian conjectures can be phrased in terms of increasingly powerful conjectured bounds on the prime gaps $g_n := p_{n+1}-p_n$. \[ g_n \leq p_n \left(p_n^{1/n} -1 \right)\qquad\qquad\qquad (n \geq 1; \; Firoozbakht). ... More
A formula for the Selmer group of a rational three-isogenyJun 10 1999A formula is given for the dimension of the Selmer group of the rational three-isogeny of elliptic curves of the form y^2=x^3+a(x-b)^2. The formula is in terms of the three-ranks of the quadratic number fields Q(\sqrt{a}) and Q(\sqrt{-3a}) and various ... More
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
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
Verifying the Firoozbakht, Nicholson, and Farhadian conjectures up to the 81st maximal prime gapMar 31 2019Apr 08 2019The Firoozbakht, Nicholoson, and Farhadian conjectures can be phrased in terms of increasingly powerful conjectured bounds on the prime gaps $g_n := p_{n+1}-p_n$. \[ g_n \leq p_n \left(p_n^{1/n} -1 \right)\qquad\qquad\qquad (n \geq 1; \; Firoozbakht). ... More