Results for "Warren R. Brown"

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The Binary Fraction of Low Mass White DwarfsJan 26 2011We describe spectroscopic observations of 21 low-mass (<0.45 M_sun) white dwarfs (WDs) from the Palomar-Green Survey obtained over four years. We use both radial velocities and infrared photometry to identify binary systems, and find that the fraction ... More
Gaia and the Galactic Center Origin of Hypervelocity StarsMay 10 2018Aug 17 2018We use new Gaia measurements to explore the origin of the highest velocity stars in the Hypervelocity Star Survey. The measurements reveal a clear pattern in the B-type stars. Halo stars dominate the sample at speeds about 100 km/s below Galactic escape ... More
Nearby high-speed stars in Gaia DR2Aug 08 2018Oct 18 2018We investigate the nature of nearby (10-15 kpc) high-speed stars in the Gaia DR2 archive identified on the basis of parallax, proper motion and radial velocity. Together with a consideration of their kinematic, orbital, and photometric properties, we ... More
Accurate Masses for the Primary and Secondary in the Eclipsing White Dwarf Binary NLTT 11748Aug 05 2010We measure the radial velocity curve of the eclipsing detached white dwarf binary NLTT 11748. The primary exhibits velocity variations with a semi-amplitude of 273 km/s and an orbital period of 5.641 hr. We do not detect any spectral features from the ... More
The DECam Minute Cadence Survey II: 49 Variables but No Planetary Transits of a White DwarfFeb 11 2019We present minute cadence photometry of 31732 point sources observed in one 3 $deg^{2}$ DECam pointing centred at RA = 09:03:02 and Dec = -04:35:00 over eight consecutive half-nights. We use these data to search for eclipse-like events consistent with ... More
The Runaway Binary LP 400-22 is Leaving the GalaxyJul 11 2013We present optical spectroscopy, astrometry, radio, and X-ray observations of the runaway binary LP 400-22. We refine the orbital parameters of the system based on our new radial velocity observations. Our parallax data indicate that LP 400-22 is significantly ... More
Astro2020 Decadal Science White Paper: Gravitational Wave Survey of Galactic Ultra Compact BinariesMar 13 2019Ultra-compact binaries (UCBs) are systems containing compact or degenerate stars with orbital periods less than one hour. Tens of millions of UCBs are predicted to exist within theGalaxy emitting gravitational waves (GWs) at mHz frequencies. Combining ... More
A quantitative spectral analysis of 14 hypervelocity stars from the MMT surveyJun 22 2018Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The tidal disruption of a binary system by the supermassive black hole in the Galactic center is widely assumed to be their ejection mechanism. To test the hypothesis of an origin ... More
Discovery of an ultramassive pulsating white dwarfJun 17 2013We announce the discovery of the most massive pulsating hydrogen-atmosphere (DA) white dwarf (WD) ever discovered, GD 518. Model atmosphere fits to the optical spectrum of this star show it is a 12,030 +/- 210 K WD with a log(g) = 9.08 +/- 0.06, which ... More
Least Squares Policy Iteration with Instrumental Variables vs. Direct Policy Search: Comparison Against Optimal Benchmarks Using Energy StorageJan 04 2014This paper studies approximate policy iteration (API) methods which use least-squares Bellman error minimization for policy evaluation. We address several of its enhancements, namely, Bellman error minimization using instrumental variables, least-squares ... More
Hypervelocity Stars and the Galactic CenterNov 04 2008A summary of the current knowledge on hypervelocity stars (HVSs). HVSs are fascinating because their properties are linked to Sgr A* and the stellar environment of the Galactic Center. Observing the distribution of HVSs can address: 1) the nature of the ... More
Statistical analysis of the spatial distribution of operons in the transcriptional regulation network of Escherichia coliOct 23 2003We have performed a statistical analysis of the spatial distribution of operons in the transcriptional regulation network of Escherichia coli. The analysis reveals that operons that regulate each other and operons that are coregulated tend to lie next ... More
Introspection LearningFeb 27 2019Traditional reinforcement learning agents learn from experience, past or present, gained through interaction with their environment. Our approach synthesizes experience, without requiring an agent to interact with their environment, by asking the policy ... More
Rational Points on the Intersection of Three QuadricsOct 05 2015This paper proves the Hasse principle and weak approximation for varieties defined by the smooth intersection of three quadratics in at least 19 variables, over arbitrary number fields.
The Thin-Wall Approximation in Vacuum Decay: a LemmaNov 21 2017Nov 26 2018The 'thin-wall approximation' gives a simple estimate of the decay rate of an unstable quantum field. Unfortunately, the approximation is uncontrolled. In this paper I show that there are actually two different thin-wall approximations and that they bracket ... More
HyperinflationMay 08 2017Jan 01 2019A model of cosmological inflation is proposed in which field space is a hyperbolic plane. The inflaton never slow-rolls, and instead orbits the bottom of the potential, buoyed by a centrifugal force. Though initial velocities redshift away during inflation, ... More
A Factor Stochastic Volatility Model with Markov-Switching Panic RegimesMar 05 2019The use of factor stochastic volatility models requires choosing the number of latent factors used to describe the dynamics of the financial returns process; however, empirical evidence suggests that the number and makeup of pertinent factors is time-varying ... More
Tensile Strength and the Mining of Black HolesJul 13 2012There are a number of important thought experiments that involve raising and lowering boxes full of radiation in the vicinity of black hole horizons. This paper looks at the limitations placed on these thought experiments by the null energy condition, ... More
Brane tunneling and virtual brane-antibrane pairsSep 24 2007Sep 24 2017We survey barrier penetration by quantum tunneling for four cases: nonrelativistic point particles, scalar fields, relativistic point particles, and DBI branes. We examine two novel features that arise for DBI brane tunneling: the rate can sometimes increase ... More
A Serendipitous Pulsar Discovery in a Search for a Companion to a Low-Mass White DwarfJun 15 2018We report the discovery of a previously unidentified pulsar as part of a radio campaign to identify neutron star companions to low-mass white dwarfs (LMWDs) using the Robert C.\ Byrd Green Bank Telescope (GBT). PSR J0802-0955, which is coincident with ... More
Schwinger pair production at nonzero temperatures or in compact directionsDec 17 2015Jan 27 2019Electric fields may decay by quantum tunneling: as calculated by Schwinger, an electron-positron pair may be summoned from the vacuum. In this paper I calculate the pair-production rate at nonzero temperatures. I find that at high temperatures the decay ... More
The decay of hot KK spaceAug 25 2014Apr 30 2015The non-perturbative instabilities of hot Kaluza-Klein spacetime are investigated. In addition to the known instability of hot space (the nucleation of 4D black holes) and the known instability of KK space (the nucleation of bubbles of nothing by quantum ... More
Boom and Bust Inflation: a Graceful Exit via Compact Extra DimensionsJul 03 2008A model of inflation is proposed in which compact extra dimensions allow a graceful exit without recourse to flat potentials or super-Planckian field values. Though bubbles of true vacuum are too sparse to uniformly reheat the Universe by colliding with ... More
Galois theory and a new homotopy double groupoid of a map of spacesAug 27 2002The authors have used generalised Galois Theory to construct a homotopy double groupoid of a surjective fibration of Kan simplicial sets. Here we apply this to construct a new homotopy double groupoid of a map of spaces, which includes constructions by ... More
Bounds for the Cubic Weyl SumMay 12 2009It is shown, subject to the abc-conjecture, that \[\sum_{n\le N}\exp(2\pi i\alpha n^3)\ll_{\epsilon,\alpha}N^{5/7+\epsilon}\] for any $\epsilon>0$ and any quadratic irrational $\alpha$.
The Differences Between Consecutive Smooth NumbersAug 08 2018We show that large gaps between smooth numbers are infrequent. The key new tool is a novel mean value bound for a special type of Dirichlet polynomial.
Zeros of Pairs of Quadratic FormsApr 14 2013We prove the Hasse principle and weak approximation for varieties defined over number fields by the nonsingular intersection of pairs of quadratic forms in 8 variables. The argument develops work of Colliot-Thelene, Sansuc and Swinnerton-Dyer, and centres ... More
A Note on the Chevalley--Warning TheoremsSep 20 2010Sep 23 2016Let $f_1,\...,f_r$ be polynomials in $n$ variables over a finite field $F$ of cardinality $q$ and characteristic $p$. Let $f_i$ have total degree $d_i$ and define $d=d_1+\...+d_r$. Write $Z$ for the set of common zeros of the $f_i$, over the field $F$. ... More
Stellar Collisions and the Interior Structure of Blue StragglersJul 19 2001Nov 02 2001Collisions of main sequence stars occur frequently in dense star clusters. In open and globular clusters, these collisions produce merger remnants that may be observed as blue stragglers. Detailed theoretical models of this process require lengthy hydrodynamic ... More
Spatial isomorphisms of algebras of truncated Toeplitz operatorsNov 03 2010Apr 05 2011We examine when two maximal abelian algebras in the truncated Toeplitz operators are spatially isomorphic. This builds upon recent work of N. Sedlock, who obtained a complete description of the maximal algebras of truncated Toeplitz operators.
Saturation in the Nuclear Matter ProblemOct 12 1992Once density-dependent meson masses are introduced into the nuclear many-body problem, conventional mechanisms for saturation no longer operate. We suggest that a loop correction, essentially the introduction of the axial vector coupling $g_A(\rho,k)$ ... More
Comparison of a quantum error correction threshold for exact and approximate errorsDec 31 2014Jan 05 2015Classical simulations of noisy stabilizer circuits are often used to estimate the threshold of a quantum error-correcting code. Physical noise sources are efficiently approximated by random insertions of Pauli operators. For a single qubit, more accurate ... More
Small Steps and Giant Leaps in the LandscapeApr 22 2010Oct 21 2010For landscapes of field theory vacua, we identify an effect that can greatly enhance the decay rates to wildly distant minima--so much so that such transitions may dominate over transitions to near neighbors. We exhibit these 'giant leaps' in both a toy ... More
Chromospheric Evaporation in an M1.8 Flare Observed by the Extreme-ultraviolet Imaging Spectrometer on HinodeDec 17 2012We discuss observations of chromospheric evaporation for a complex flare that occurred on 9 March 2012 near 03:30 UT obtained from the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. This was a multiple event with a strong energy ... More
Evidence for Steady Heating: Observations of an Active Region Core with Hinode and TRACEOct 02 2009Jan 14 2010Previous observations have not been able to exclude the possibility that high temperature active region loops are actually composed of many small scale threads that are in various stages of heating and cooling and only appear to be in equilibrium. With ... More
On 'Nothing'Nov 01 2011May 16 2012Nothing---the absence of spacetime---can be either an endpoint of tunneling, as in the bubble of nothing, or a starting point for tunneling, as in the quantum creation of a universe. We argue that these two tunnelings can be treated within a unified framework, ... More
Bubbles of Nothing and the Fastest Decay in the LandscapeOct 25 2010Sep 23 2011The rate and manner of vacuum decay are calculated in an explicit flux compactification, including all thick-wall and gravitational effects. For landscapes built of many units of a single flux, the fastest decay is usually to discharge just one unit. ... More
The inverse resonance problem for perturbations of algebro-geometric potentialsJun 02 2003We prove that a compactly supported perturbation of a rational or simply periodic algebro-geometric potential of the one-dimensional Schr\"odinger equation on the half line is uniquely determined by the location of its Dirichlet eigenvalues and resonances. ... More
Stability and Spectrum of Compactifications on Product ManifoldsOct 23 2013Dec 23 2014We study the spectrum and perturbative stability of Freund-Rubin compactifications on $M_p \times M_{Nq}$, where $M_{Nq}$ is itself a product of $N$ $q$-dimensional Einstein manifolds. The higher-dimensional action has a cosmological term $\Lambda$ and ... More
Populating the Whole LandscapeJul 31 2011Feb 19 2012Every de Sitter vacuum can transition to every other de Sitter vacuum despite any obstacle, despite intervening anti-de Sitter sinks, despite not being connected by an instanton. Eternal inflation populates the whole landscape.
Some Effects of Galaxy Collisions in a Cluster ICMOct 20 2003We present preliminary results of numerical modeling of the combined effects of ICM stripping and galaxy collisions on galaxies in clusters. We use the Hydra adaptive mesh, P3M + SPH code of Couchman et al. (1995). Generally, the formation of extended ... More
A disintegrating minor planet transiting a white dwarfOct 21 2015White dwarfs are the end state of most stars, including the Sun, after they exhaust their nuclear fuel. Between 1/4 and 1/2 of white dwarfs have elements heavier than helium in their atmospheres, even though these elements should rapidly settle into the ... More
A Spitzer Search for Substellar Companions to Low Mass White DwarfsNov 04 2009The formation scenarios for single low-mass (M < 0.45 Msol) white dwarfs include enhanced mass loss from a metal-rich progenitor star or a common envelope phase of a solar-like star with a close-in massive planet or a brown dwarf. Both scenarios suggest ... More
The Identification of RR Lyrae and Delta Scuti Stars from Variable GALEX Ultraviolet SourcesAug 04 2014We identify the RR Lyrae and delta Scuti (DSCT) stars in three catalogs of GALEX variable sources. The NUV amplitude of RR Lyrae stars is about twice that in V-band, so we find a larger percentage of low amplitude variables than catalogs such as Abbas ... More
The BHB stars in the Survey Fields of Rodgers et al. (1993): New Observations and Comparisons with other Recent SurveysMar 07 2011We study blue horizontal branch (BHB) and RR Lyrae stars in the Rogers et al. (1993a) fields and compare their velocity and density distributions with other surveys in the same part of the sky. Photometric data are given for 176 early-type stars in the ... More
Low-Amplitude Variables: Distinguishing RR Lyrae stars from Eclipsing BinariesMar 18 2010It is not easy to identify and classify low-amplitude variables, but it is important that the classification is done correctly. We use photometry and spectroscopy to classify low-amplitude variables in a 246 deg^2 part of the Akerlof et al. (2002) field. ... More
Handling Leakage with Subsystem CodesMar 10 2019Leakage is a particularly damaging error that occurs when a qubit state falls out of its two-level computational subspace. Compared to independent depolarizing noise, leaked qubits may produce many more configurations of harmful correlated errors during ... More
Conformal Mapping of Circular Quadrilaterals and Weierstrass Elliptic FunctionsDec 16 2010Numerical and theoretical aspects of conformal mappings from a disk to a circular-arc quadrilateral, symmetric with respect to the coordinate axes, are developed. The problem of relating the accessory parameters (prevertices together with coefficients ... More
Dynamics and Endogeny for recursive processes on treesJun 02 2005We consider stochastic processes indexed by the vertices of an infinite binary tree having a simple recursive structure. The value at any vertex is some fixed function of the values at the two daughter vertices together with some independent innovation. ... More
On free-group algorithms that sandwich a subgroup between free-product factorsJun 17 2013Let $F$ be a finite-rank free group and $H$ be a finite-rank subgroup of $F$. We discuss proofs of two algorithms that sandwich $H$ between an upper-layer free-product factor of $F$ that contains $H$ and a lower-layer free-product factor of $F$ that is ... More
An improved proof of the Almost Stability TheoremNov 02 2018In 1989, Dicks and Dunwoody proved the Almost Stability Theorem, which has among its corollaries the Stallings-Swan theorem that groups of cohomological dimension one are free. In this article, we use a nestedness result of Bergman, Bowditch, and Dunwoody ... More
Sticky Particles and Stochastic FlowsSep 24 2014Gaw\c{e}dzki and Horvai have studied a model for the motion of particles carried in a turbulent fluid and shown that in a limiting regime with low levels of viscosity and molecular diffusivity, pairs of particles exhibit the phenomena of stickiness when ... More
A Bernstein result and counterexample for entire solutions to Donaldson's equationMar 23 2015We show that convex entire solutions to Donaldson's equation are quadratic, using a result of Weiyong He. We also exhibit entire solutions to the Donaldson equation that are not of the form discussed by He. In the process we discover some non-trivial ... More
Simultaneous equal sums of three powersSep 07 2005Using a recent result of Salberger, we establish the paucity of non-trivial positive integer solutions to a certain system of diagonal Diophantine equations.
On simple zeros of the Riemann zeta-functionFeb 20 2013We show that at least 19/27 of the zeros of the Riemann zeta-function are simple, assuming the Riemann Hypothesis (RH). This was previously established by Conrey, Ghosh and Gonek [Proc. London Math. Soc. 76 (1998), 497--522] under the additional assumption ... More
A note on the fourth moment of Dirichlet L-functionsMar 24 2009We prove an asymptotic formula for the fourth power mean of Dirichlet L-functions averaged over primitive characters to modulus q and over t\in [0,T] which is particularly effective when q \ge T. In this range the correct order of magnitude was not previously ... More
Edge modes and non local conductance in graphene superlatticesJul 04 2017Oct 25 2017We study the existence of edge modes in gapped Moir\'e superlattices in graphene monolayer ribbons. We find that the superlattice bands acquire finite Chern numbers, which lead to a Valley Hall Effect. The presence of dispersive edge modes is confirmed ... More
Medium Modifications of Charm and Charmonium in High-Energy Heavy-Ion CollisionsMar 18 2004The production of charmonia in heavy-ion collisions is investigated within a kinetic theory framework simultaneously accounting for dissociation and regeneration processes in both quark-gluon plasma (QGP) and hadron-gas phases of the reaction. In-medium ... More
Forms in many variables and differing degreesMar 24 2014Feb 02 2015We generalise Birch's seminal work on forms in many variables to handle a system of forms in which the degrees need not all be the same. This allows us to prove the Hasse principle, weak approximation, and the Manin-Peyre conjecture for a smooth and geometrically ... More
Thermal derivation of the Coleman-De Luccia tunneling prescriptionJun 12 2007Sep 01 2007We derive the rate for transitions between de Sitter vacua by treating the field theory on the static patch as a thermal system. This reproduces the Coleman-De Luccia formalism for calculating the rate, but leads to a modified interpretation of the bounce ... More
Quantum Complexity and Negative CurvatureAug 08 2016As time passes, once simple quantum states tend to become more complex. For strongly coupled k-local Hamiltonians, this growth of computational complexity has been conjectured to follow a distinctive and universal pattern. In this paper we show that the ... More
Minimal Free Resolutions of $2\times n$ Domino TilingsAug 23 2017We introduce a squarefree monomial ideal associated to the set of domino tilings of a $2\times n$ rectangle and proceed to study the associated minimal free resolution. In this paper, we use results of Dalili and Kummini to show that the Betti numbers ... More
Direct measurement of Bacon-Shor code stabilizersApr 03 2018A Bacon-Shor code is a subsystem quantum error-correcting code on an $L \times L$ lattice where the $2(L-1)$ weight-$2L$ stabilizers are usually inferred from the measurements of $(L-1)^2$ weight-2 gauge operators. Here we show that the stabilizers can ... More
Density of rational points on a quadric bundle in $\mathbb{P}^3\times \mathbb{P}^3$May 27 2018An asymptotic formula is established for the number of rational points of bounded anticanonical height which lie on a certain Zariski dense subset of the biprojective hypersurface $x_1y_1^2+\dots+x_4y_4^2=0$ in $\mathbb{P}^3\times\mathbb{P}^3$. This confirms ... More
Estimates for the $L^q$-mixed problem in $C^{1,1}$-domainsFeb 23 2019We consider the $L^q$-mixed problem in domains in ${\bf R}^n$ with $C^ {1,1}$-boundary. We assume that the boundary between the sets where we specify Neumann and Dirichlet data is Lipschitz. With these assumptions, we show that we may solve the $L^q$-mixed ... More
On Solutions to Cournot-Nash Equilibria Equations on the SphereMar 28 2013We discuss equations associated to Cournot-Nash Equilibria as put forward recently by Blanchet and Carlier. These equations are related to an optimal transport problem in which the source measure is known, but the target measure is part of the problem. ... More
On slow escaping and non-escaping points of quasimeromorphic mappingsMar 21 2019We show that for any quasimeromorphic mapping with an essential singularity at infinity, there exist points whose iterates tend to infinity arbitrarily slowly. This extends a result by Nicks for quasiregular mappings, and Rippon and Stallard for transcendental ... More
Non-polynomial entire solutions to $σ_{k}$ equationsMar 23 2015Apr 03 2015For $2k \leq n+1$, we exhibit non-polynomial solutions to the Hessian equation \[ \sigma_{k}(D^{2}u)=1 \] on all of $\mathbb{R}^{n}.$
A McLean Theorem for the moduli space of Lie solutions to mass transport equationsJun 07 2010Aug 24 2010On compact manifolds which are not simply connected, we prove the existence of "fake" solutions to the optimal transportion problem. These maps preserve volume and arise as the exponential of a closed 1 form, hence appear geometrically like optimal transport ... More
Splitting: Tanaka's SDE revisitedNov 16 1999The weak solution of Tanaka's SDE is not a function of the driving Brownian motion, and therefore it has no Wiener chaos expansion. However in some sense explained here it has a generalised chaos expansion involving infinite products of stochastic differentials ... More
Qatar-2: A K dwarf orbited by a transiting hot Jupiter and a more massive companion in an outer orbitOct 26 2011We report the discovery and initial characterization of Qatar-2b, a hot Jupiter transiting a V = 13.3 mag K dwarf in a circular orbit with a short period, P_ b = 1.34 days. The mass and radius of Qatar-2b are M_p = 2.49 M_j and R_p = 1.14 R_j, respectively. ... More
On the iteration of quasimeromorphic mappingsMay 01 2018May 03 2018The Fatou-Julia theory for rational functions has been extended both to transcendental meromorphic functions and more recently to several different types of quasiregular mappings in higher dimensions. We extend the iterative theory to quasimeromorphic ... More
Quadratic polynomials represented by norm formsSep 01 2011The Hasse principle and weak approximation is established for equations of the shape P(t)=N(x_1,x_2,x_3,x_4), where P is an irreducible quadratic polynomial in one variable and N is a norm form associated to a quartic extension of the rationals containing ... More
Webs of type QDec 29 2017We introduce web supercategories of type Q. We describe the structure of these categories and show they have a symmetric braiding. The main result of the paper shows these diagrammatically defined monoidal supercategories provide combinatorial models ... More
Automated behavioural fingerprinting of C. elegans mutantsJan 06 2013Rapid advances in genetics, genomics, and imaging have given insight into the molecular and cellular basis of behaviour in a variety of model organisms with unprecedented detail and scope. It is increasingly routine to isolate behavioural mutants, clone ... More
Zariski topologies on stratified spectra of quantum algebrasNov 01 2013A framework is developed to describe the Zariski topologies on the prime and primitive spectra of a quantum algebra $A$ in terms of the (known) topologies on strata of these spaces and maps between the collections of closed sets of different strata. A ... More
Almost prime triples and Chen's TheoremApr 02 2015Oct 05 2015We show that there are infinitely many primes $p$ such that not only does $p + 2$ have at most two prime factors, but $p + 6$ also has a bounded number of prime divisors. This refines the well known result of Chen.
Primes values of $a^2 + p^4$Apr 02 2015Nov 24 2015We prove an asymptotic formula for the number of primes of the shape $a^2 +p^4$, thereby refining the well known work of Friedlander and Iwaniec. Along the way, we prove a result on equidistribution of primes up to $x$, in which the moduli may be almost ... More
Integers Represented as a Sum of Primes and Powers of TwoJan 30 2002Apr 02 2002It is shown that every sufficiently large even integer is a sum of two primes and exactly 13 powers of 2. Under the Generalized Rieman Hypothesis one can replace 13 by 7. Unlike previous work on this problem, the proof avoids numerical calculations with ... More
Dyson's Brownian motions, intertwining and interlacingSep 30 2005A family of reflected Brownian motions is used to construct Dyson's process of non-colliding Brownian motions. A number of explicit formulae are given, including one for the distribution of a family of coalescing Brownian motions.
A stochastic flow arising in the study of local timesMay 10 2004A stochastic flow of homeomorphisms of the real line previously studied by Bass and Burdzy is shown to arise in describing a Brownian motion conditional on knowing its local times on hitting a fixed level. This makes it possible to connect Ray-Knight ... More
In-Medium Effects on Charmonium Production in Heavy-Ion CollisionsJun 09 2003Oct 09 2003Charmonium production in heavy-ion collisions is investigated within a kinetic theory framework incorporating in-medium properties of open- and hidden-charm states in line with recent QCD lattice calculations. A continuously decreasing open-charm threshold ... More
Flux Compactifications on $(S_2)^N$Jan 28 2014We investigate a simple extra-dimensional model and its four-dimensional vacua. This model has a two-form flux and a positive cosmological constant, and the extra dimensions are compactified as the product of $N$ two-spheres. The theory is an interesting ... More
Compactifying de Sitter Naturally Selects a Small Cosmological ConstantNov 11 2013Nov 29 2014We study compactifications of $D$-dimensional de Sitter space with a $q$-form flux down to $D-Nq$ dimensions. We show that for $(N-1)(q-1)\geq 2$ there are double-exponentially or even infinitely many compact de Sitter vacua, and that their effective ... More
Hinode/Extreme-Ultraviolet Imaging Spectrometer Observations of the Temperature Structure of the Quiet CoronaMay 22 2009Oct 28 2009We present a Differential Emission Measure (DEM) analysis of the quiet solar corona on disk using data obtained by the Extreme-ultraviolet Imaging Spectrometer (EIS) on {\it Hinode}. We show that the expected quiet Sun DEM distribution can be recovered ... More
Truncated Toeplitz Operators: Spatial Isomorphism, Unitary Equivalence, and SimilarityJul 15 2009Oct 02 2009A truncated Toeplitz operator is the compression $A_{\phi}:\K_{\Theta} \to \K_{\Theta}$ of a Toeplitz operator $T_{\phi}:H^2\to H^2$ to a model space $\K_{\Theta} := H^2 \ominus \Theta H^2$. For $\Theta$ inner, let $\T_{\Theta}$ denote the set of all ... More
The Clustering of Massive HalosJun 28 2006Oct 24 2006The clustering properties of dark matter halos are a firm prediction of modern theories of structure formation. We use two large volume, high-resolution N-body simulations to study how the correlation function of massive dark matter halos depends upon ... More
Drivers of HI Turbulence in Dwarf GalaxiesJun 10 2013Neutral hydrogen (HI) velocity dispersions are believed to be set by turbulence in the interstellar medium (ISM). Although turbulence is widely believed to be driven by star formation (SF), recent studies have shown that this driving mechanism may not ... More
Loop Amplitudes in an Extended Gravity TheoryNov 15 2017Feb 27 2018We extend the $S$-matrix of gravity by the addition of the minimal three-point amplitude or equivalently adding $R^3$ terms to the Lagrangian. We demonstrate how Unitarity can be used to simply examine the renormalisability of this theory and determine ... More
Spin glass in semiconducting KFe$_{1.05}$Ag$_{0.88}$Te$_{2}$ single crystalsApr 20 2016We report discovery of KFe$_{1.05}$Ag$_{0.88}$Te$_{2}$ single crystals with semiconducting spin glass ground state. Composition and structure analysis suggest nearly stoichiometric I4/mmm space group but allow for the existence of vacancies, absent in ... More
Irreversible thermodynamics of creep in crystalline solidsJul 26 2013We develop an irreversible thermodynamics framework for the description of creep deformation in crystalline solids by mechanisms that involve vacancy diffusion and lattice site generation and annihilation. The material undergoing the creep deformation ... More
High Spatial Resolution Observations of Loops in the Solar CoronaMay 10 2013Jul 17 2013Understanding how the solar corona is structured is of fundamental importance to determining how the Sun's upper atmosphere is heated to high temperatures. Recent spectroscopic studies have suggested that an instrument with a spatial resolution of 200km ... More
On difference graphs and the local dimension of posetsMar 23 2018The dimension of a partially-ordered set (poset), introduced by Dushnik and Miller (1941), has been studied extensively in the literature. Recently, Ueckerdt (2016) proposed a variation called local dimension which makes use of partial linear extensions. ... More
Measurement of the Electric Form Factor of the Neutron at Q^2=0.5 and 1.0 (GeV/c)^2Aug 20 2003Feb 02 2004The electric form factor of the neutron was determined from measurements of the \vec{d}(\vec{e},e' n)p reaction for quasielastic kinematics. Polarized electrons were scattered off a polarized deuterated ammonia target in which the deuteron polarization ... More
Invariance-like results for Nonautonomous Switched SystemsSep 19 2016Aug 29 2017This paper generalizes the Lasalle-Yoshizawa Theorem to switched nonsmooth systems. Filippov and Krasovskii regularizations of a switched system are shown to be contained within the convex hull of the Filippov and Krasovskii regularizations of the subsystems, ... More
Diagrammar in an Extended Theory of GravityFeb 27 2017Mar 24 2017We show how the $S$-matrix of an extended theory of gravity defined by its three-point amplitudes can be constructed by demanding factorisation. The resultant $S$-matrix has tree amplitudes obeying the same soft singularity theorems as Einstein gravity ... More
Variability of Hypervelocity StarsFeb 07 2013We present time-series photometry of 11 hypervelocity stars (HVSs) to constrain their nature. Known HVSs are mostly late-B spectral type objects that may be either main-sequence (MS) or evolved blue horizontal branch (BHB) stars. Fortunately, MS stars ... More
MMT Hypervelocity Star SurveyAug 19 2008Sep 15 2008We describe a new survey for unbound hypervelocity stars (HVSs), stars traveling with such extreme velocities that dynamical ejection from a massive black hole (MBH) is their most likely origin. We investigate the possible contribution of unbound runaway ... More
Dusty WDs in the $WISE$ All Sky Survey $\cap$ SDSSFeb 19 2014A recent cross-correlation between the SDSS DR7 White Dwarf Catalog with the Wide-Field Infrared Survey Explorer ($WISE$) all-sky photometry at 3.4, 4.6, 12, and 22 microns performed by Debes et al. (2011) resulted in the discovery of 52 candidate dusty ... More
The Lowest Mass White DwarfNov 15 2006Feb 13 2007Extremely low mass white dwarfs are very rare objects likely formed in compact binary systems. We present MMT optical spectroscopy of 42 low mass white dwarf candidates serendipitously discovered in a survey for hypervelocity B-type stars. One of these ... More