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Results for "R. O. Brown"

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Covering groups of non-connected topological groups revisitedSep 02 2000Dec 18 2006In general a universal covering of a non connected topological group need not admit a topological group structure such that the covering map is a morphism of topological groups. This result is due to R.L. Taylor (1953). We generalise this result and relate ... More
Local subgroupoids II: Examples and propertiesAug 22 2000Aug 29 2000The notion of local subgroupoid as a generalisation of a local equivalence relation was defined in a previous paper by the first two authors. Here we use the notion of star path connectivity for a Lie groupoid to give an important new class of examples, ... More
Solar Flare X-ray Source Motion as a Response to Electron Spectral HardeningMay 07 2013Context: Solar flare hard X-rays (HXRs) are thought to be produced by nonthermal coronal electrons stopping in the chromosphere, or remaining trapped in the corona. The collisional thick target model (CTTM) predicts that sources produced by harder power-law ... More
Impact of modulation on CMB B-mode polarization experimentsSep 24 2008May 26 2009We investigate the impact of both slow and fast polarization modulation strategies on the science return of upcoming ground-based experiments aimed at measuring the B-mode polarization of the CMB. Using simulations of the Clover experiment, we compare ... More
Modelling the observable behaviour of SXP 5.05Apr 12 2019SXP 5.05 is a Be/X-ray binary with a neutron star companion located in the Small Magellanic Cloud. It was first detected in 2013, and later that year, SXP 5.05 underwent a massive optical and X-ray outburst. This outburst dwarfs any other optical event ... More
Massive Double White Dwarfs and the AM CVn BirthrateJun 02 2016We present Chandra and Swift X-ray observations of four extremely low-mass (ELM) white dwarfs with massive companions. We place stringent limits on X-ray emission from all four systems, indicating that neutron star companions are extremely unlikely and ... More
Simulating the X-ray luminosity of Be X-ray binaries: the case for black holes versus neutron starsApr 16 2018There are over 100 Be stars that are known to have neutron star companions but only one such system with a black hole. Previous theoretical work suggests this is not due to their formation but due to differences in X-ray luminosity. It has also been proposed ... More
Category Theory and Higher Dimensional Algebra: potential descriptive tools in neuroscienceJun 13 2003Feb 10 2008We explain the notion of colimit in category theory as a potential tool for describing structures and their communication, and the notion of higher dimensional algebra as a potential yoga for dealing with processes and processes of processes.
The theory of the rise of sap in trees: some historical and conceptual remarksApr 11 2014The ability of trees to suck water from roots to leaves, sometimes to heights of over a hundred meters, is remarkable given the absence of any mechanical pump. This study deals with a number of issues, of both an historical and conceptual nature, in the ... More
The Cubic Case of Vinogradov's Mean Value Theorem --- A Simplified Approach to Wooley's "Efficient Congruencing"Dec 10 2015This is an expository paper, giving a simplified proof of the cubic case of the main conjecture for Vinogradov's mean value theorem.
Energy protection arguments fail in the interaction pictureMay 16 2007Jul 27 2007Spin Hamiltonians with degenerate ground states are one potential system for the storage of quantum information at low temperatures. Trapped ions can be used to simulate the dynamics of these Hamiltonians, but the coherence-preserving properties will ... More
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
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.
Convexity bounds for L-functionsSep 10 2008We give a sharp convexity estimate for L-functions which have a functional equation and an Euler product.
A New $k$-th Derivative Estimate for Exponential Sums via Vinogradov's Mean ValueJan 18 2016Mar 07 2016We give a slight refinement to the process by which estimates for exponential sums are extracted from bounds for Vinogradov's mean value. Coupling this with the recent works of Wooley, and of Bourgain, Demeter and Guth, providing optimal bounds for the ... 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
Homotopies and automorphisms of crossed modules of groupoidsAug 16 2000Dec 10 2001We give a detailed description of the structure of the actor 2-crossed module related to the automorphisms of a crossed module of groupoids. This generalises work of Brown and Gilbert for the case of crossed modules of groups, and part of this is needed ... More
Artin's Conjecture on Zeros of $p$-Adic FormsFeb 19 2010This is an exposition of work on Artin's Conjecture on the zeros of $p$-adic forms. A variety of lines of attack are described, going back to 1945. However there is particular emphasis on recent developments concerning quartic forms on the one hand, and ... More
Sums and Differences of Three k-th PowersJun 26 2008Let k>2 be a fixed integer exponent and let \theta > 9/10. We show that a positive integer N can be represented as a non-trivial sum or difference of 3 k-th powers, using integers of size at most B, in O(B^{\theta}N^{1/10}) ways, providing that N << B^{3/13}. ... More
Assessing the association between trends in a biomarker and risk of event with an application in pediatric HIV/AIDSOct 09 2009We present a new joint longitudinal and survival model aimed at estimating the association between the risk of an event and the change in and history of a biomarker that is repeatedly measured over time. We use cubic B-splines models for the longitudinal ... More
Zeros of p-adic formsMay 05 2008Sep 14 2009A variant of Brauer's induction method is developed. It is shown that quartic p-adic forms with at least 9127 variables have non-trivial zeros, for every p. For odd p considerably fewer variables are needed. There are also subsidiary new results concerning ... More
Square-free values of $n^2+1$Oct 29 2010May 09 2012We show that there is a positive constant $c_0$ such that \[\sum_{n\le x}\mu^2(n^2+1)c_0x+O_{\varepsilon}(x^{7/12+\varepsilon})\] for any fixed $\varepsilon>0$. This improves a result of Estermann [3] from 1931, in which the error term had an exponent ... More
Floydian trajectories for stationary systems: a modification for bound statesFeb 20 2001Dec 16 2001The Floydian trajectory method of quantum mechanics and the appearance of microstates of the Schr\"{o}dinger equation are reviewed and contrasted with the Bohm interpretation of quantum mechanics. The kinematic equation of Floydian trajectories is analysed ... More
Iteration of Quadratic Polynomials Over Finite FieldsJan 10 2017Jan 17 2017For a finite field of odd cardinality $q$, we show that the sequence of iterates of $aX^2+c$, starting at $0$, always recurs after $O(q/\log\log q)$ steps. For $X^2+1$ the same is true for any starting value. We suggest that the traditional "Birthday ... More
Brane tunneling and virtual brane-antibrane pairsSep 24 2007We 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
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
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
$p$-adic Zeros of Systems of Quadratic FormsJan 04 2012This survey describes work on the number of variables required to ensure that a system of r quadratic forms over the p-adics has a non-trivial common zero.
Powerfree Values of PolynomialsMar 10 2011For irreducible integer polynomials $f(n)=n^d+c$ we prove an asymptotic formula for the number of $k$-th power free values taken by $f(n)$, for $n$ running up to $x$, subject to the condition $k\ge (5d+3)/9$. This improves earlier results in which the ... More
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.
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
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
The quantum potential: the breakdown of classical symplectic symmetry and the energy of localisation and dispersionMar 06 1997Feb 05 2002The composition of the quantum potential and its role in the breakdown of classical symplectic symmetry in quantum mechanics is investigated. General expressions are derived for the quantum potential in both configuration space and momentum space representations. ... More
Small Solutions of Quadratic Congruences, and Character Sums with Binary Quadratic FormsNov 18 2014Let $Q(x,y,z)$ be an integral quadratic form with determinant coprime to some modulus $q$. We show that $q\mid Q$ for some non-zero integer vector $(x,y,z)$ of length $O(q^{5/8+\varepsilon})$, for any fixed $\varepsilon>0$. Without the coprimality condition ... More
Schwinger pair production at nonzero temperatures or in compact directionsDec 17 2015Electric 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
Zero Zeros After All These (20) YearsSep 27 1999We celebrate two birthdays connected with the radiation zero phenomenon. First, a striking dip in the theoretical angular distributions of radiative weak-boson production was discovered twenty years ago. The key experimental interest is that this will ... 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 $\alpha$.
Pair Correlation for Fractional Parts of $αn^2$Apr 04 2009We construct real numbers $\alpha$ for which the pair correlation function \[N^{-1}#\{m<n\le N:||\alpha m^2-\alpha n^2||\le XN^{-1}\}\] tends to $X$ as $N$ grows. Moreover we show for any "Diophantine" $\alpha$ that the pair correlation function is $X+O(X^{7/8})+O((\log ... More
Fractional Moments of Dirichlet $L$-FunctionsOct 12 2009Let $k$ be a positive real number, and let $M_k(q)$ be the sum of $|L(\tfrac12,\chi)|^{2k}$ over all non-principal characters to a given modulus $q$. We prove that $M_k(q)\ll_k \phi(q)(\log q)^{k^2}$ whenever $k$ is the reciprocal $n^{-1}$ of a positive ... More
Zeros of Systems of ${\mathfrak p}$-adic Quadratic FormsOct 07 2008Apr 24 2009It is shown that a system of $r$ quadratic forms over a ${\mathfrak p}$-adic field has a non-trivial common zero as soon as the number of variables exceeds $4r$, providing that the residue class field has cardinality at least $(2r)^r$.
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
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
Corrigendum --- Quadratic Class Numbers Divisible by 3Sep 23 2010An error in the author's paper (Functiones et Approximatio, 37 . pp. 203-211) is corrected.
Comparing Zeeman qubits to hyperfine qubits in the context of the surface code: $^{174}$Yb$^{+}$ and $^{171}$Yb$^{+}$Mar 07 2018Apr 16 2018Many systems used for quantum computing possess additional states beyond those defining the qubit. Leakage out of the qubit subspace must be considered when designing quantum error correction codes. Here we consider trapped ion qubits manipulated by Raman ... More
Magnetic phase diagram of cubic perovskites SrMn_1-xFe_xO_3Feb 11 2003We combine the results of magnetic and transport measurements with Mossbauer spectroscopy and room-temperature diffraction data to construct the magnetic phase diagram of the new family of cubic perovskite manganites SrMn_1-xFe_xO_3. We have found antiferromagnetic ... More
The ELM Survey. IV. 24 White Dwarf Merger SystemsMar 30 2012We present new radial velocity and X-ray observations of extremely low-mass (ELM, 0.2 Msol) white dwarf candidates in the Sloan Digital Sky Survey (SDSS) Data Release 7 area. We identify seven new binary systems with 1-18 h orbital periods. Five of the ... More
Two-Pion Exchange Interaction Between Constituent QuarksFeb 11 1999May 11 1999The two-pion exchange interaction between constituent quarks is shown to enhance the effect of the the isospin dependent spin-spin component of the one-pion exchange interaction, and to cancel out its tensor component. It therefore provides a partial ... More
Nucleon Resonance Transition Couplings to Vector MesonsMay 17 2000Recent heavy ion experiments indicate modifications of the $\rho-$meson mass in medium. In the CERES experiments $\rho-$mesons are produced at $\sim$ normal nuclear matter density, where hadrons are more appropriate constituents than quarks. A collective ... More
Clarifying possible misconceptions in the foundations of general relativityDec 31 2015Mar 18 2016We discuss what we take to be three possible misconceptions in the foundations of general relativity, relating to: (a) the interpretation of the weak equivalence principle and the relationship between gravity and inertia; (b) the connection between gravitational ... More
Minkowski space-time: a glorious non-entityMar 17 2004Einstein distinguished between ``principle'' and ``constructive'' theories in physics, and although he thought the latter were more explanatory than the former, he regarded his 1905 formulation of special relativity theory as a principle theory. Some ... More
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
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
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
Redshifts for 2410 Galaxies in the Century Survey RegionSep 06 2001The `Century Survey' strip covers 102 square degrees within the limits 8.5h \leq \alpha_{1950} \leq 16.5h, 29.0 degrees \leq \delta_{1950} \leq 30.0 degrees. The strip passes through the Corona Borealis supercluster and the outer region of the Coma cluster. ... More
Simple applications of Noether's first theorem in quantum mechanics and electromagnetismFeb 09 2003Internal global symmetries exist for the free non-relativistic Schr\"{o}dinger particle, whose associated Noether charges--the space integrals of the wavefunction and the wavefunction multiplied by the spatial coordinate--are exhibited. Analogous symmetries ... More
Topological Subsystem Codes From Graphs and HypergraphsJul 02 2012Topological subsystem codes were proposed by Bombin based on 3-face-colorable cubic graphs. Suchara, Bravyi and Terhal generalized this construction and proposed a method to construct topological subsystem codes using 3-valent hypergraphs that satisfy ... More
The Case of the Disappearing InstantonJun 02 2011Instantons are tunneling solutions that connect two vacua, and under a small change in the potential, instantons sometimes disappear. We classify these disappearances as smooth (decay rate goes to 0 at disappearance) or abrupt (decay rate not equal to ... More
The Second Law of Quantum ComplexityJan 04 2017Dec 05 2018We give arguments for the existence of a thermodynamics of quantum complexity that includes a "Second Law of Complexity". To guide us, we derive a correspondence between the computational (circuit) complexity of a quantum system of $K$ qubits, and the ... More
Giant Leaps and Minimal Branes in Multi-Dimensional Flux LandscapesOct 25 2010Sep 14 2011There is a standard story about decay in multi-dimensional flux landscapes: that from any state, the fastest decay is to take a small step, discharging one flux unit at a time; that fluxes with the same coupling constant are interchangeable; and that ... More
Einstein, the reality of space, and the action-reaction principleJun 20 2013Einstein regarded as one of the triumphs of his 1915 theory of gravity --- the general theory of relativity --- that it vindicated the action--reaction principle, while Newtonian mechanics as well as his 1905 special theory of relativity supposedly violated ... More
Solving the measurement problem: de Broglie-Bohm loses out to EverettMar 12 2004The quantum theory of de Broglie and Bohm solves the measurement problem, but the hypothetical corpuscles play no role in the argument. The solution finds a more natural home in the Everett interpretation.
Cubical abelian groups with connections are equivalent to chain complexesDec 11 2002The theorem of the title is deduced from the equivalence between crossed complexes and cubical $\omega$-groupoids with connections proved by the authors in 1981. In fact we prove the equivalence of five categories defined internally to an additive category ... More
Study of Oxygen Diffusion and Clustering in Silicon using an Empirical Interatomic PotentialApr 25 1995The diffusion path and diffusivity of oxygen in crystalline silicon are computed using an empirical interatomic potential which was recently developed for modelling the interactions between oxygen and silicon atoms. The diffusion path is determined by ... More
Development and Evaluation of a Quantum Interactive Learning Tutorial on Larmor Precession Of SpinFeb 16 2016We conducted research on student difficulties and developed and evaluated a quantum interactive learning tutorial (QuILT) on Larmor precession of spin to help students learn about time-dependence of expectation values in quantum mechanics. The QuILT builds ... 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
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
Magnetothermodynamics: measuring the equations of state of a compressible magnetized plasmaNov 16 2018Magnetothermodynamics (MTD) is the study of compression and expansion of magnetized plasma with an eye towards identifying equations of state for magneto-inertial fusion experiments. We present recent results from SSX experiments on the thermodynamics ... More
The origin of the spacetime metric: Bell's `Lorentzian pedagogy' and its significance in general relativityAug 17 1999Oct 19 1999The purpose of this paper is to evaluate the `Lorentzian pedagogy' defended by J.S. Bell in his essay ``How to teach special relativity'', and to explore its consistency with Einstein's thinking from 1905 to 1952. Some remarks are also made in this context ... More
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
Comment on "Phase-Shift Analysis of NN Scattering Below 160 Mev: Indication of a Strong Tensor Force"Dec 01 1993In his recent publication of a NN phase shift analysis below 160 MeV, Henneck reports relatively large values for the mixing parameter $\epsilon_1$. Based on these results, Henneck suggests that the strength of the $\rho$-meson tensor coupling to the ... 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.
The Complexity Geometry of a Single QubitMar 29 2019The computational complexity of a quantum state quantifies how hard it is to make. `Complexity geometry', first proposed by Nielsen, is an approach to defining computational complexity using the tools of differential geometry. Here we demonstrate many ... More
Split-off dimer defects on the Si(001)2x1 surfaceMay 05 2003Dimer vacancy (DV) defect complexes in the Si(001)2x1 surface were investigated using high-resolution scanning tunneling microscopy and first principles calculations. We find that under low bias filled-state tunneling conditions, isolated 'split-off' ... More
Far-Ultraviolet to Near-Infrared Spectroscopy of A Nearby Hydrogen Poor Superluminous Supernova Gaia16apdNov 09 2016We report the first maximum-light far-Ultraviolet to near-infrared spectra (1000A - 1.62um, rest) of a H-poor superluminous supernova, Gaia16apd. At z=0.1018, it is one of the closest and the UV brightest such events, with 17.4 (AB) magnitude in Swift ... More
Observation and characterization of laser-driven Phase Space Electron HolesAug 31 2009The direct observation and full characterization of a Phase Space Electron Hole (EH) generated by laser-matter interaction is presented. This structure has been detected via proton radiography during the interaction between an intense laser pulse (t=1ns ... More
Far-Ultraviolet to Near-Infrared Spectroscopy of A Nearby Hydrogen Poor Superluminous Supernova Gaia16apdNov 09 2016Apr 17 2017We report the first maximum-light far-Ultraviolet to near-infrared spectra (1000A - 1.62um, rest) of a H-poor superluminous supernova, Gaia16apd. At z=0.1018, it is one of the closest and the UV brightest such events, with 17.4 (AB) magnitude in Swift ... More
Continued Neutron Star Crust Cooling of the 11 Hz X-Ray Pulsar in Terzan 5: A Challenge to Heating and Cooling Models?Jun 10 2013Aug 23 2013The transient neutron star low-mass X-ray binary and 11 Hz X-ray pulsar IGR J17480-2446 in the globular cluster Terzan 5 exhibited an 11-week accretion outburst in 2010. Chandra observations performed within five months after the end of the outburst revealed ... 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
Numerical Conformal Mapping to One-Tooth Gear-Shaped Domains and ApplicationsMar 03 2015We study conformal mappings from the unit disk (or a rectangle) to one-tooth gear-shaped planar domains from the point of view of the Schwarzian derivative, with emphasis on numerical considerations. Applications are given to evaluation of a singular ... More
Gears, Pregears and Related DomainsMar 03 2015We study conformal mappings from the unit disk to one-toothed gear-shaped planar domains from the point of view of the Schwarzian derivative. Gear-shaped (or "gearlike") domains fit into a more general category of domains we call "pregears" (images of ... 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
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
GT strengths and electron-capture rates for pf-shell nuclei of relevance for late stellar evolutionApr 09 2012This paper presents a systematic evaluation of the ability of theoretical models to reproduce experimental Gamow-Teller transition strength distributions measured via (n,p)-type charge-exchange reactions at intermediate beam energies. The focus is on ... More
Asteroseismic Investigation of Known Planet Hosts in the Kepler FieldDec 30 2009In addition to its great potential for characterizing extra-solar planetary systems the Kepler mission is providing unique data on stellar oscillations. A key aspect of Kepler asteroseismology is the application to solar-like oscillations of main-sequence ... More
Magnetic-field induced effects on the electric polarization in RMnO3 (R = Dy, Gd)Feb 23 2009Feb 24 2009X-ray resonant magnetic scattering studies of rare earth magnetic ordering were performed on perovskite manganites RMnO3 (R = Dy, Gd) in an applied magnetic field. The data reveal that the field-induced three-fold polarization enhancement for H || a (H ... More
Capturing the Fire: Flame Energetics and Neutronizaton for Type Ia Supernova SimulationsNov 01 2006We develop and calibrate a realistic model flame for hydrodynamical simulations of deflagrations in white dwarf (Type Ia) supernovae. Our flame model builds on the advection-diffusion-reaction model of Khokhlov and includes electron screening and Coulomb ... 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
The MUSCLES Treasury Survey III: X-ray to Infrared Spectra of 11 M and K Stars Hosting PlanetsApr 16 2016We present a catalog of panchromatic spectral energy distributions (SEDs) for 7 M and 4 K dwarf stars that span X-ray to infrared wavelengths (5 {\AA} - 5.5 {\mu}m). These SEDs are composites of Chandra or XMM-Newton data from 5 - ~50 {\AA}, a plasma ... More
Found: The Progenitors of AM CVn and Supernovae .IaOct 23 2013We present optical and X-ray observations of two tidally distorted, extremely low-mass white dwarfs (WDs) with massive companions. There is no evidence of neutron stars in our Chandra and XMM observations of these objects. SDSS J075141.18$-$014120.9 (J0751) ... More
Simultaneous Integer Values of Pairs of Quadratic FormsSep 26 2013We prove that a pair of integral quadratic forms in 5 or more variables will simultaneously represent "almost all" pairs of integers that satisfy the necessary local conditions, provided that the forms satisfy a suitable nonsingularity condition. In particular ... 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
Galilean non-invariance of geometric phaseOct 06 1996It is shown that geometric phase in non-relativistic quantum mechanics is not Galilean invariant.
Peak into the Past - An Archaeo-Astronomy Summer SchoolSep 28 2010Mar 23 2011Our landscape has been shaped by man throughout the millennia. It still contains many clues to how it was used in the past giving us insights into ancient cultures and their everyday life. Our summer school uses archaeology and astronomy as a focus for ... More