Results for "G. Metcalfe"

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Decay estimates for variable coefficient wave equations in exterior domainsJun 20 2008Aug 28 2009In this article we consider variable coefficient, time dependent wave equations in exterior domains. We prove localized energy estimates if the domain is star-shaped and global in time Strichartz estimates if the domain is strictly convex.
The Strauss conjecture on asymptotically flat space-timesMay 07 2016Sep 04 2017By assuming a certain localized energy estimate, we prove the existence portion of the Strauss conjecture on asymptotically flat manifolds, possibly exterior to a compact domain, when the spatial dimension is 3 or 4. In particular, this result applies ... More
The ^12C(alpha,gamma)^16O Nuclear Reaction Rate from Asteroseismology of the DBV White Dwarf CBS 114Aug 12 2002We have identified seven independent pulsation modes in the helium-atmosphere variable (DBV) white dwarf star CBS 114, based on 65 hours of time-resolved CCD photometry from the 0.75-m telescope at SAAO. We interpret these pulsations as non-radial g-modes ... More
Exact Unification and AdmissibilityAug 18 2015Sep 25 2015A new hierarchy of "exact" unification types is introduced, motivated by the study of admissible rules for equational classes and non-classical logics. In this setting, unifiers of identities in an equational class are preordered, not by instantiation, ... More
Paraproducts in One and Several ParametersFeb 16 2005Aug 09 2005For multiparameter bilinear paraproduct operators $B$ we prove the estimate $$ B: L^p X L^q --> L^r, 1<p,q\le{}\infty. $$ Here, $1/p+1/q=1/r$ and special attention is paid to the case of $0<r<1$. (Note that the families of multiparameter paraproducts ... More
Sequent and Hypersequent Calculi for Abelian and Lukasiewicz LogicsNov 18 2002We present two embeddings of infinite-valued Lukasiewicz logic L into Meyer and Slaney's abelian logic A, the logic of lattice-ordered abelian groups. We give new analytic proof systems for A and use the embeddings to derive corresponding systems for ... More
Local energy decay for scalar fields on time dependent non-trapping backgroundsMar 23 2017We consider local energy decay estimates for solutions to scalar wave equations on nontrapping asymptotically flat space-times. Our goals are two-fold. First we consider the stationary case, where we can provide a full spectral characterization of local ... More
GAIA Cepheid parallaxes and 'Local Hole' relieve $H_0$ tensionOct 05 2018Jan 16 2019There is an $\approx9\pm2.5$\% tension between the value of Hubble's Constant, $H_0=67.4\pm0.5$km\,s$^{-1}$Mpc$^{-1}$, implied by the {\it Planck} microwave background power spectrum and that given by the distance scale of $H_0=73.4\pm1.7$km\,s$^{-1}$Mpc$^{-1}$. ... More
Uniform Interpolation and Compact CongruencesApr 12 2019Uniform interpolation properties are defined for equational consequence in a variety of algebras and related to properties of compact congruences on first the free and then the finitely presented algebras of the variety. It is also shown, following related ... More
The asteroseismological potential of the pulsating DB white dwarf stars CBS 114 and PG 1456+103May 27 2002We have acquired 65 h of single-site time-resolved CCD photometry of the pulsating DB white dwarf star CBS 114 and 62 h of two-site high-speed CCD photometry of another DBV, PG 1456+103. The pulsation spectrum of PG 1456+103 is complicated and variable ... More
Chaotic Advection at the Pore Scale: Mechanisms, Upscaling and Implications for Macroscopic TransportFeb 17 2016The macroscopic spreading and mixing of solute plumes in saturated porous media is ultimately controlled by processes operating at the pore scale. Whilst the conventional picture of pore-scale mechanical dispersion and molecular diffusion leading to persistent ... More
The Mathematics of Market TimingDec 13 2017Market timing is an investment technique that tries to continuously switch investment into assets forecast to have better returns. What is the likelihood of having a successful market timing strategy? With an emphasis on modeling simplicity, I calculate ... More
Universality properties of Gelfand-Tsetlin patternsMay 06 2011Nov 12 2011A standard Gelfand-Tsetlin pattern of depth $n$ is a configuration of particles in $\{1,...,n\} \times \R$. For each $r \in \{1,...,n\}$, $\{r\} \times \R$ is referred to as the $r^\text{th}$ level of the pattern. A standard Gelfand-Tsetlin pattern has ... More
Global Strichartz Estimates for Solutions to the Wave Equation Exterior to a Convex ObstacleOct 15 2002Jul 20 2004In this paper, we show that certain local Strichartz estimates for solutions of the wave equation exterior to a convex obstacle can be extended to estimates that are global in both space and time. This extends the work that was done previously by H. Smith ... More
Global existence for semilinear wave equations exterior to nontrapping obstaclesOct 16 2002Feb 21 2003In this paper, we show global existence, in spatial dimensions greater than or equal to four, for semilinear wave equations with quadratic nonlinearities exterior to a nontrapping obstacle. This extends the previous work of Shibata-Tsutsumi and Hayashi. ... More
Asteroseismic Signatures of Stellar Magnetic Activity CyclesApr 12 2007Observations of stellar activity cycles provide an opportunity to study magnetic dynamos under many different physical conditions. Space-based asteroseismology missions will soon yield useful constraints on the interior conditions that nurture such magnetic ... More
Limits on surface gravities of Kepler planet-candidate host stars from non-detection of solar-like oscillationsJan 24 2014We present a novel method for estimating lower-limit surface gravities log g of Kepler targets whose data do not allow the detection of solar-like oscillations. The method is tested using an ensemble of solar-type stars observed in the context of the ... More
Ages and fundamental properties of Kepler exoplanet host stars from asteroseismologyApr 29 2015Jun 24 2015We present a study of 33 {\it Kepler} planet-candidate host stars for which asteroseismic observations have sufficiently high signal-to-noise ratio to allow extraction of individual pulsation frequencies. We implement a new Bayesian scheme that is flexible ... More
The Local Hole in the Galaxy Distribution: New Optical EvidenceFeb 17 2003We present a new CCD survey of galaxies within the N and S strips of the 2dFGRS areas. We use the new CCD data to check the photographic photometry scales of the 2dFGRS, APMBGC, APM-Stromlo Redshift Survey, Durham-UKST (DUKST) survey, Millenium Galaxy ... More
A ring galaxy at z=1 lensed by the cluster Abell 370Jan 11 1999Jan 26 1999We present a study of a very peculiar object found in the field of the cluster-lens Abell 370. This object displays, in HST imaging, a spectacular morphology comparable to nearby ring-galaxies. From spectroscopic observations at the CFHT, we measured ... More
The Local Hole in the Galaxy Distribution: Evidence from 2MASSFeb 17 2003Using the bright galaxy counts from the 2 Micron All Sky Survey (2MASS) second incremental release, two techniques for probing large-scale structure at distances of ~150 h-1 Mpc are investigated. First, we study the counts from two sets of six 5 degree ... More
An asteroseismic test of diffusion theory in white dwarfsFeb 07 2005The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens ... More
Activity Cycles of Southern Asteroseismic TargetsSep 29 2009The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle periods is thought to reflect differences in the rotational properties and ... More
The Pan-STARRS1 Medium-Deep Survey: The role of galaxy group environment in the star formation rate versus stellar mass relation and quiescent fraction out to $z \sim 0.8$Dec 17 2013Using a large sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey, we present the specific star formation rate (SSFR) - stellar mass (M*) relation, as well as the quiescent fraction versus M* relation in different environments. ... More
The shell game: a panoramic view of FornaxJul 23 2015We present a panoramic study of the Fornax dwarf spheroidal galaxy, using data obtained as part of the VLT Survey Telescope (VST) ATLAS Survey. The data presented here -- a subset of the full survey -- uniformly cover a region of 25 square degrees centred ... More
White Dwarf Asteroseismology and the ^12C(alpha,gamma)^16O RateMar 03 2003Due to a new global analysis method, it is now possible to measure the internal composition of pulsating white dwarf stars, even with relatively simple theoretical models. The precise internal mixture of carbon and oxygen is the largest single source ... More
Almost global existence for quasilinear wave equations in waveguides with Neumann boundary conditionsSep 14 2005In this paper, we prove almost global existence of solutions to certain quasilinear wave equations with quadratic nonlinearities in infinite homogeneous waveguides with Neumann boundary conditions. We use a Galerkin method to expand the Laplacian of the ... More
HD 49933: A laboratory for magnetic activity cyclesOct 03 2011Seismic analyses of the CoRoT target HD 49933 have revealed a magnetic cycle. Further insight reveals that frequency shifts of oscillation modes vary as a function of frequency, following a similar pattern to that found in the Sun. In this preliminary ... More
Test beam measurement of ams H35 HV-CMOS capacitively coupled pixel sensor prototypes with high-resistivity substrateDec 22 2017Dec 03 2018In the context of the studies of the ATLAS High Luminosity LHC programme, radiation tolerant pixel detectors in CMOS technologies are investigated. To evaluate the effects of substrate resistivity on CMOS sensor performance, the H35DEMO demonstrator, ... More
Exact UnificationOct 21 2014A new hierarchy of "exact" unification types is introduced, motivated by the study of admissibility for equational classes and non-classical logics. In this setting, unifiers of identities in an equational class are preordered, not by instantiation, but ... More
Crowdfunding Astronomy Research with Google SkyFeb 25 2015Nov 20 2015For nearly four years, NASA's Kepler space telescope searched for planets like Earth around more than 150,000 stars similar to the Sun. In 2008 with in-kind support from several technology companies, our non-profit organization established the Pale Blue ... More
Asteroseismology and the Solar-Stellar ConnectionAug 22 2008Oct 14 2008In March 2009, NASA will launch the Kepler satellite -- a mission designed to discover habitable Earth-like planets around distant Sun-like stars. The method that Kepler will use to detect distant worlds will only reveal the size of the planet relative ... More
A deeper understanding of white dwarf interiorsAug 09 2005A detailed record of the physical processes that operate during post-main-sequence evolution is contained in the internal chemical structure of white dwarfs. Global pulsations allow us to probe the stellar interior through asteroseismology, revealing ... More
Genetic-Algorithm-based Light Curve Optimization Applied to Observations of the W UMa star BH CasJan 21 1999May 21 1999I have developed a procedure utilizing a Genetic-Algorithm-based optimization scheme to fit the observed light curves of an eclipsing binary star with a model produced by the Wilson-Devinney code. The principal advantages of this approach are the global ... More
The Rise and Citation Impact of astro-ph in Major JournalsMar 23 2005The rise in the use of the arXiv preprint server (astro-ph) over the past decade has led to a major shift in the way astronomical research is disseminated. Schwarz & Kennicutt (2004) recently found that Astrophysical Journal papers posted to astro-ph ... More
Lessons for Asteroseismology from White Dwarf StarsJan 19 2005The interpretation of pulsation data for Sun-like stars is currently facing challenges quite similar to those faced by white dwarf modelers ten years ago. The observational requirements for uninterrupted long-term monitoring are beginning to be satisfied ... More
Discovery of a 1.6-year Magnetic Activity Cycle in the Exoplanet Host Star iota HorologiiSep 27 2010Oct 01 2010The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle periods is thought to reflect differences in the rotational properties and ... More
Asteroseismic Signatures of Magnetic Activity Variations in Solar-type StarsSep 09 2013Observations of magnetic activity cycles in other stars provide a broader context for our understanding of the 11-year sunspot cycle. The discovery of short activity cycles in a few stars, and the recognition of analogous variability in the Sun, suggest ... More
The Citation Impact of Digital Preprint Archives for Solar Physics PapersJul 05 2006Oct 16 2006Papers that are posted to a digital preprint archive are typically cited twice as often as papers that are not posted. This has been demonstrated for papers published in a wide variety of journals, and in many different subfields of astronomy. Most astronomers ... More - Establishing a permanent endowment for the Whole Earth TelescopeAug 08 2002White Dwarf Research Corporation is a 501(c)(3) non-profit organization dedicated to scientific research and public education on topics relevant to white dwarf stars. It was founded in 1999 in Austin, Texas to help fulfill the need for an alternative ... More
White Dwarf Seismology and the ^{12}C(alpha,gamma)^{16}O RateAug 01 2002Recent determinations of the internal composition and structure of two helium-atmosphere variable white dwarf stars, GD 358 and CBS 114, have led to conflicting implied rates for the ^{12}C(alpha,gamma)^{16}O reaction. If we assume that both stars were ... More
Asteroseismology for the MassesAug 31 2000For many years, astronomers interested in white dwarf stars have promised that the study of these relatively simple compact objects would ultimately lead to useful information about the physics under extreme conditions of temperature and pressure. We ... More
Towards a Proof Theory of Gödel Modal LogicsMay 06 2011May 14 2011Analytic proof calculi are introduced for box and diamond fragments of basic modal fuzzy logics that combine the Kripke semantics of modal logic K with the many-valued semantics of G\"odel logic. The calculi are used to establish completeness and complexity ... More
Pointwise a posteriori error bounds for blow-up in the semilinear heat equationFeb 21 2018This work is concerned with the development of a space-time adaptive numerical method, based on a rigorous a posteriori error bound, for the semilinear heat equation with a general local Lipschitz reaction term whose solution may blow-up in finite time. ... More
The lifespan for 3-dimensional quasilinear wave equations in exterior domainsApr 20 2012This article focuses on long-time existence for quasilinear wave equations with small initial data in exterior domains. The nonlinearity is permitted to fully depend on the solution at the quadratic level, rather than just the first and second derivatives ... More
Universal edge fluctuations of discrete interlaced particle systemsJan 30 2017Jul 02 2018We impose the uniform probability measure on the set of all discrete Gelfand-Tsetlin patterns of depth $n$ with the particles on row $n$ in deterministic positions. These systems equivalently describe a broad class of random tilings models, and are closely ... More
Admissibility in Finitely Generated QuasivarietiesMay 15 2013Jun 23 2013Checking the admissibility of quasiequations in a finitely generated (i.e., generated by a finite set of finite algebras) quasivariety Q amounts to checking validity in a suitable finite free algebra of the quasivariety, and is therefore decidable. However, ... More
The Production Rate and Employment of Ph.D. AstronomersDec 17 2007Dec 19 2007In an effort to encourage self-regulation of the astronomy job market, I examine the supply of, and demand for, astronomers over time. On the supply side, I document the production rate of Ph.D. astronomers from 1970 to 2006 using the UMI Dissertation ... More
Computational AsteroseismologyJun 29 2001Jul 10 2001White dwarf asteroseismology offers the opportunity to probe the structure and composition of stellar objects governed by relatively simple physical principles. The observational requirements of asteroseismology have been addressed by the development ... More
The Future of Computational AsteroseismologyNov 14 2006The history of stellar seismology suggests that observation and theory often take turns advancing our understanding. The recent tripling of the sample of pulsating white dwarfs generated by the Sloan Digital Sky Survey represents a giant leap on the observational ... More
Elastic waves in exterior domains, Part II: Global existence with a null structureMay 04 2006In this article, we prove that solutions to a problem in nonlinear elasticity corresponding to small initial displacements exist globally in the exterior of a nontrapping obstacle. The medium is assumed to be homogeneous, isotropic, and hyperelastic, ... More
Asymptotic geometry of discrete interlaced patterns: Part IDec 20 2014Jul 23 2015A discrete Gelfand-Tsetlin pattern is a configuration of particles in Z^2. The particles are arranged in a finite number of consecutive rows, numbered from the bottom. There is one particle on the first row, two particles on the second row, three particles ... More
Global parametrices and dispersive estimates for variable coefficient wave equationsJul 09 2007Aug 28 2009In this article we consider variable coefficient, time-dependent wave equations. Using phase space methods we construct outgoing parametrices and prove Strichartz-type estimates globally in time. This is done in the context of C^2 metrics which satisfy ... More
The Consequences of assuming m=0 for Global Model-fittingAug 05 2002Aug 06 2002A recent re-analysis of Whole Earth Telescope observations of GD 358 obtained in 1990 suggests that asteroseismology of additional DBV white dwarfs can lead to independent constraints on the important, but poorly determined, ^{12}C(alpha,gamma)^{16}O ... More
An Asteroseismic Test of Diffusion TheorySep 14 2005The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG 1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens ... More
Seismic Inference using Genetic AlgorithmsAug 15 2002A flood of reliable seismic data will soon arrive. The migration to larger telescopes on the ground may free up 4-m class instruments for multi-site campaigns, and several forthcoming satellite missions promise to yield nearly uninterrupted long-term ... More
The Strauss conjecture on asymptotically flat space-timesMay 07 2016By assuming a certain localized energy estimate, we prove the existence portion of the Strauss conjecture on asymptotically flat manifolds, possibly exterior to a compact domain, when the spatial dimension is 3 or 4. In particular, this result applies ... More
Asymptotic Geometry of Discrete Interlaced Patterns: Part IIJul 02 2015Sep 23 2015We study the boundary of the liquid region $\mathcal{L}$ in large random lozenge tiling models defined by uniform random interlacing particle systems with general initial configuration, which lies on the line $(x,1)$, $x\in\mathbb{R}\equiv \partial \mathbb{H}$. ... More
Adaptive discontinuous Galerkin methods for nonlinear parabolic problemsApr 10 2015This work is devoted to the study of a posteriori error estimation and adaptivity in parabolic problems with a particular focus on spatial discontinuous Galerkin (dG) discretisations. We begin by deriving an a posteriori error estimator for a linear non-stationary ... More
Global existence for systems of quasilinear wave equations in (1+4)-dimensionsDec 31 2018H\"ormander proved global existence of solutions for sufficiently small initial data for scalar wave equations in $(1+4)-$dimensions of the form $\Box u = Q(u, u', u'')$ where $Q$ vanishes to second order and $(\partial_u^2 Q)(0,0,0)=0$. Without the latter ... More
Coherence in Modal LogicFeb 07 2019A variety is said to be coherent if the finitely generated subalgebras of its finitely presented members are also finitely presented. In a recent paper by the authors it was shown that coherence forms a key ingredient of the uniform deductive interpolation ... More
Uniform interpolation and coherenceMar 24 2018A variety V is said to be coherent if any finitely generated subalgebra of a finitely presented member of V is finitely presented. It is shown here that V is coherent if and only if it satisfies a restricted form of uniform deductive interpolation: that ... More
Global existence for a coupled wave system related to the Strauss conjectureJan 19 2017A coupled system of semilinear wave equations is considered, and a small data global existence result related to the Strauss conjecture is proved. Previous results have shown that one of the powers may be reduced below the critical power for the Strauss ... More
Sharp local smoothing for manifolds with smooth inflection transmissionMar 13 2013We consider a family of spherically symmetric, asymptotically Euclidean manifolds with two trapped sets, one which is unstable and one which is semi-stable. The phase space structure is that of an inflection transmission set. We prove a sharp local smoothing ... More
Localized energy estimates for wave equations on high dimensional Schwarzschild space-timesAug 27 2010Sep 30 2010The localized energy estimate for the wave equation is known to be a fairly robust measure of dispersion. Recent analogs on the $(1+3)$-dimensional Schwarzschild space-time have played a key role in a number of subsequent results, including a proof of ... More
Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomyMay 28 2010Herschel was launched on 14 May 2009, and is now an operational ESA space observatory offering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55-671 {\mu}m. Herschel carries a 3.5 metre diameter passively ... More
Kepler Asteroseismology Program: Introduction and First ResultsDec 31 2009Asteroseismology involves probing the interiors of stars and quantifying their global properties, such as radius and age, through observationsof normal modes of oscillation. The technical requirements for conducting asteroseismology include ultra-high ... More
Hydrogen-Poor Superluminous Supernovae from the Pan-STARRS1 Medium Deep SurveyAug 04 2017Jan 12 2018We present light curves and classification spectra of 17 hydrogen-poor superluminous supernovae (SLSNe) from the Pan-STARRS1 Medium Deep Survey (PS1 MDS). Our sample contains all objects from the PS1 MDS sample with spectroscopic classification that are ... More
The Orbital and Absolute Magnitude Distributions of Main Belt AsteroidsJan 05 1998Mar 16 1998We have developed a model-independent analytical method for debiasing the four-dimensional (a,e,i,H) distribution obtained in any asteroid observation program and have applied the technique to results obtained with the 0.9m Spacewatch Telescope. From ... More
Hyperbolic trapped rays and global existence of quasilinear wave equationsJan 24 2003Sep 25 2003We prove global existence for quasilinear wave equations outside of a wide class of obstacles. The obstacles may contain trapped hyperbolic rays as long as there is local exponential energy decay for the associated linear wave equation. Thus, we can handle ... More
Deep ISOCAM Observations of Abell 2218Mar 13 1998We report on the mid-infrared imaging at 5, 7, 10 and 15 microns of the galaxy cluster Abell 2218 obtained with the ISOCAM instrument onboard ESA's Infrared Space Observatory (ISO), as part of an on-going program to image gravitational arcs and arclets ... More
Admissibility via Natural DualitiesJan 25 2015It is shown that admissible clauses and quasi-identities of quasivarieties generated by a single finite algebra, or equivalently, the quasiequational and universal theories of their free algebras on countably infinitely many generators, may be characterized ... More
Gamma-ray bursts and X-ray melting of material to form chondrules and planetsJul 15 2004Chondrules are millimeter sized objects of spherical to irregular shape that constitute the major component of chondritic meteorites that originate in the region between Mars and Jupiter and which fall to Earth. They appear to have solidified rapidly ... More
The superluminous supernova PS1-11ap: bridging the gap between low and high redshiftOct 16 2013Oct 18 2013We present optical photometric and spectroscopic coverage of the superluminous supernova (SLSN) PS1-11ap, discovered with the Pan-STARRS1 Medium Deep Survey at z = 0.524. This intrinsically blue transient rose slowly to reach a peak magnitude of M_u = ... More
Global existence of null-form wave equations in exterior domainsNov 16 2006We provide a proof of global existence of solutions to quasilinear wave equations satisfying the null condition in certain exterior domains. In particular, our proof does not require estimation of the fundamental solution for the free wave equation. We ... More
Global existence for Dirichlet-wave equations with quadratic nonlinearties in high dimensionsApr 22 2004Apr 08 2005We prove global existence of solutions to quasilinear wave equations with quadratic nonlinearities exterior to nontrapping obstacles in spatial dimensions four and higher. This generalizes a result of Shibata and Tsutsumi in spatial dimensions greater ... More
Precision distances to dwarf galaxies and globular clusters from Pan-STARRS1 3$π$ RR LyraeNov 27 2018We present new spatial models and distance estimates for globular clusters (GC) and dwarf spheroidals (dSphs) orbiting our Galaxy based on RR Lyrae (RRab) stars in the Pan-STARRS1 (PS1) 3$\pi$ survey. Using the PS1 sample of RRab stars from Sesar et al. ... More
Constraints of a pulsation frequency on stellar parameters in the eclipsing spectroscopic binary system: V577 OphNov 12 2010We present a preliminary spectroscopic analysis of the binary system V577Oph, observed during the summer of 2007 on the 2.6m NOT telescope on La Palma. We have obtained time series spectroscopic observations, which show clear binary motion as well as ... More
The complementary roles of interferometry and asteroseismology in determining the mass of solar-type starsFeb 09 2007How important is an independent diameter measurement for the determination of stellar parameters of solar-type stars? When coupled with seismic observables, how well can we determine the stellar mass? If we can determine the radius of the star to between ... More
Stellar Structure Modeling using a Parallel Genetic Algorithm for Objective Global OptimizationAug 16 2002Nov 22 2002Genetic algorithms are a class of heuristic search techniques that apply basic evolutionary operators in a computational setting. We have designed a fully parallel and distributed hardware/software implementation of the generalized optimization subroutine ... More
Global existence for high dimensional quasilinear wave equations exterior to star-shaped obstaclesOct 02 2009We study long time existence for high dimensional quasilinear wave equations exterior to star-shaped obstacles. In particular, we obtain exterior domain analogs of the four dimensional results of H\"ormander where the nonlinearity is permitted to depend ... More
Sounding stellar cycles with Kepler - III. Comparative analysis of chromospheric, photometric and asteroseismic variabilityFeb 06 2019Mar 13 2019By combining ground-based spectrographic observations of variability in the chromospheric emission from Sun-like stars with the variability seen in their eigenmode frequencies, it is possible to relate the changes observed at the surfaces of these stars ... More
XMM-Newton (cross)-calibrationJul 13 2004ESA's large X-ray space observatory XMM-Newton is in its fifth year of operations. We give a general overview of the status of calibration of the five X-ray instruments and the Optical Monitor. A main point of interest in the last year became the cross-calibration ... More
An ISOCAM Mid-IR Survey through Gravitationally Lensing Galaxy ClustersOct 18 1999We present imaging results and source counts from a deep ISOCAM cosmological survey at 15 microns, through gravitationally lensing galaxy clusters. We take advantage of the cluster gravitational amplification to increase the sensitivity of our survey. ... More
Sounding stellar cycles with Kepler - III. Comparative analysis of chromospheric, photometric and asteroseismic variabilityFeb 06 2019By combining ground-based spectrographic observations of variability in the chromospheric emission from Sun-like stars with the variability seen in their eigenmode frequencies, it is possible to relate the changes observed at the surfaces of these stars ... More
The Structure and Stellar Content of the Outer Disks of Galaxies: A New View from the Pan-STARRS1 Medium Deep SurveyDec 10 2014We present the results of an analysis of Pan-STARRS1 Medium Deep Survey multi-band (g,r,i,z,y) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. We use population synthesis ... More
Asteroseismic modelling of the solar-type subgiant star $β$ HydriDec 17 2010Comparing models and data of pulsating stars is a powerful way to understand the stellar structure better.\beta Hyi is an evolved solar-type pulsator with mixed modes in its frequency spectrum, making it very interesting for asteroseismic studies.The ... More
Kepler White Paper: Asteroseismology of Solar-Like Oscillators in a 2-Wheel MissionSep 03 2013We comment on the potential for continuing asteroseismology of solar-type and red-giant stars in a 2-wheel Kepler Mission. Our main conclusion is that by targeting stars in the ecliptic it should be possible to perform high-quality asteroseismology, as ... More
Asteroseismology of Solar-type Stars with Kepler I: Data AnalysisMay 04 2010Jul 19 2010We report on the first asteroseismic analysis of solar-type stars observed by Kepler. Observations of three G-type stars, made at one-minute cadence during the first 33.5d of science operations, reveal high signal-to-noise solar-like oscillation spectra ... More
An Asteroid Belt Interpretation for the Timing Variations of the Millisecond Pulsar B1937+21Jan 28 2013Pulsar timing observations have revealed companions to neutron stars that include other neutron stars, white dwarfs, main-sequence stars, and planets. We demonstrate that the correlated and apparently stochastic residual times of arrival from the millisecond ... More
The VLT LBG Redshift Survey - III. The clustering and dynamics of Lyman-break galaxies at z ~ 3Apr 16 2012Apr 09 2013We present a catalogue of 2135 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z ~ 3 galaxies in wide fields centred on background quasi-stellar objects. We have used deep optical imaging to select galaxies via the ... More
ISO's Contribution to the Study of Clusters of GalaxiesJun 17 2005Aug 22 2005Starting with nearby galaxy clusters like Virgo and Coma, and continuing out to the furthest galaxy clusters for which ISO results have yet been published ($z=0.56$), we discuss the development of knowledge of the infrared and associated physical properties ... More
The Impact of Gaia DR1 on Asteroseismic Inferences from KeplerJan 30 2017The Kepler mission has been fantastic for asteroseismology of solar-type stars, but the targets are typically quite distant. As a consequence, the reliability of asteroseismic modeling has been limited by the precision of additional constraints from high-resolution ... More
$hp$-Adaptive Galerkin Time Stepping Methods for Nonlinear Initial Value ProblemsDec 20 2016This work is concerned with the derivation of an a posteriori error estimator for Galerkin approximations to nonlinear initial value problems with an emphasis on finite-time existence in the context of blow-up. The stucture of the derived estimator leads ... More
Wave packet parametrices for evolutions governed by PDO's with rough symbolsNov 09 2006Sep 27 2010In this note, we consider wave packet parametrices for Schrodinger-like evolution equations. Under an integrability condition along the flow, we prove that the flow is then globally well-defined and bilipschitz. Under an additional smallness assumption, ... More
Galaxy and Mass Assembly (GAMA): Projected Galaxy ClusteringSep 07 2015We measure the projected 2-point correlation function of galaxies in the 180 deg$^2$ equatorial regions of the GAMA II survey, for four different redshift slices between z = 0.0 and z=0.5. To do this we further develop the Cole (2011) method of producing ... More
Asteroseismology of Solar-type stars with Kepler II: Stellar ModelingJun 29 2010Observations from the Kepler satellite were recently published for three bright G-type stars, which were monitored during the first 33.5d of science operations. One of these stars, KIC 11026764, exhibits a characteristic pattern of oscillation frequencies ... More
New H-band Galaxy Number Counts: A Large Local Hole in the Galaxy Distribution?Sep 29 2005We examine H-band number counts determined using new photometry over 0.30 sq.deg. to H=19, as well as H<14 counts from 2MASS. First, we examine 2MASS counts extracted for the 4000 sq.deg. APM survey area and find a deficiency of 25% at H=13, in line with ... More
Asteroseismic constraints on diffusion in WD envelopesJan 20 2011The asteroseismic analysis of white dwarfs allows us to peer below their photospheres and determine their internal structure. At ~ 28,000 K EC20058-5234 is the hottest known pulsating helium atmosphere white dwarf. As such, it constitutes an important ... More
Asteroseismic Signatures of Small Convective CoresMay 21 2007We present an analytical study of the effect of small convective cores on the oscillations of solar-like pulsators. Based on an asymptotic analysis of the wave equation near the center of the star, we derive an expression for the perturbations to the ... More