Results for "Grant M. Kennedy"

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Empty gaps? Depleting annular regions in debris discs by secular resonance with a two-planet systemJun 22 2018We investigate the evolution on secular time-scales of a radially extended debris disc under the influence of a system of two coplanar planets interior to the disc, showing that the secular resonances of the system can produce a depleted region in the ... More
Planet formation around stars of various masses: Hot super-EarthsApr 15 2008We consider trends resulting from two formation mechanisms for short-period super-Earths: planet-planet scattering and migration. We model scenarios where these planets originate near the snow line in ``cold finger'' circumstellar disks. Low-mass planet-planet ... More
Transiting exocomets detected in broadband light by TESS in the $β$ Pictoris systemMar 26 2019May 31 2019We search for signs of falling evaporating bodies (FEBs, also known as exocomets) in photometric time series obtained for $\beta$ Pictoris after fitting and removing its $\delta$ Scuti type pulsation frequencies. Using photometric data obtained by the ... More
Planet formation around low mass stars: the moving snow line and super-EarthsSep 06 2006We develop a semi-analytic model for planet formation during the pre-main sequence contraction phase of a low mass star. During this evolution, the stellar magnetosphere maintains a fixed ratio between the inner disk radius and the stellar radius. As ... More
Infrared colours and inferred masses of metal-poor giant stars in the Kepler fieldMay 30 2018Intrinsically luminous giant stars in the Milky Way are the only potential volume-complete tracers of the distant disk, bulge, and halo. The chemical abundances of metal-poor giants also reflect the compositions of the earliest star-forming regions, providing ... More
A Gap in the Mass Distribution for Warm Neptune and Terrestrial PlanetsJun 27 2019Structure in the planet distribution provides an insight into the processes that shape the formation and evolution of planets. The Kepler mission has led to an abundance of statistical discoveries in regards to planetary radius, but the number of observed ... More
A statistically significant lack of debris discs in medium separation binary systemsJul 10 2019Jul 11 2019We compile a sample of 341 binary and multiple star systems with the aim of searching for and characterising Kuiper belt-like debris discs. The sample is assembled by combining several smaller samples studied in previously published work with targets ... More
Spatially Resolved Images of Dust Belt(s) Around the Planet-hosting Subgiant Kappa CrBFeb 27 2013Mar 08 2013We present Herschel spatially resolved images of the debris disc orbiting the subgiant Kappa CrB. Not only are these the first resolved images of a debris disc orbiting a subgiant, but Kappa CrB is a rare example of an intermediate mass star where a detailed ... More
Effects of disc asymmetries on astrometric measurements - Can they mimic planets?May 16 2016Astrometry covers a parameter space that cannot be reached by RV or transit methods to detect terrestrial planets on wide orbits. In addition, high accuracy astrometric measurements are necessary to measure the inclination of the planet's orbits. Here ... More
The wavelength dependence of interstellar polarization in the Local Hot BubbleDec 02 2018The properties of dust in the interstellar medium (ISM) nearest the Sun are poorly understood because the low column densities of dust toward nearby stars induce little photometric reddening, rendering the grains largely undetectable. Stellar polarimetry ... More
Bott-Kitaev Periodic Table and the Diagonal MapDec 15 2014Building on the 10-way symmetry classification of disordered fermions, the authors have recently given a homotopy-theoretic proof of Kitaev's "Periodic Table" for topological insulators and superconductors. The present paper offers an introduction to ... More
Nature or nurture of coplanar Tatooines: the aligned circumbinary Kuiper belt analogue around HD 131511Dec 01 2014A key discovery of the Kepler mission is of the circumbinary planets known as "Tatooines", which appear to be well aligned with their host stars' orbits. Whether this alignment is due to initially coplanar circumbinary planet-forming discs (i.e. nature), ... More
Circumbinary, not transitional: On the spiral arms, cavity, shadows, fast radial flows, streamers and horseshoe in the HD142527 discMar 07 2018We present 3D hydrodynamical models of the HD142527 protoplanetary disc, a bright and well studied disc that shows spirals and shadows in scattered light around a 100 au gas cavity, a large horseshoe dust structure in mm continuum emission, together with ... More
Science with an ngVLA: Debris disk structure and compositionOct 15 2018Debris disks, comprised of planetsimal belts and the dust and gas produced by their mutual collisions, are the longest-lived phase of circumstellar disks. Typically much fainter in emission than protoplanetary disks, debris disks can be found in associations ... More
Stellar Multiplicity and Debris Disks: An Unbiased SampleMar 04 2015Circumstellar dust disks have been observed around many nearby stars. However, many stars are part of binary or multiple stellar systems. A natural question arises regarding the presence and properties of such disks in systems with more than one star. ... More
Warm exo-Zodi from cool exo-Kuiper belts: the significance of P-R drag and the inference of intervening planetsMar 04 2015Poynting-Robertson drag has been considered an ineffective mechanism for delivering dust to regions interior to the cool Kuiper belt analogues seen around other Sun-like stars. This conclusion is however based on the very large contrast in dust optical ... More
Curved Tails in Polymerization-Based Bacterial MotilityMay 15 2001The curved actin ``comet-tail'' of the bacterium Listeria monocytogenes is a visually striking signature of actin polymerization-based motility. Similar actin tails are associated with Shigella flexneri, spotted-fever Rickettsiae, the Vaccinia virus, ... More
Accelerating Fermionic Molecular DynamicsSep 21 2004Sep 22 2004We consider how to accelerate fermionic molecular dynamics algorithms by introducing n pseudofermion fields coupled with the nth root of the fermionic kernel. This reduces the maximum pseudofermionic force, and thus allows a larger molecular dynamics ... More
The REASONS Survey: Resolved Millimeter Observations of a Large Debris Disk Around the Nearby F Star HD 170773Jun 20 2019Debris disks are extrasolar analogs to our own Kuiper Belt and they are detected around at least 17% of nearby Sun-like stars. The morphology and dynamics of a disk encode information about its history, as well as that of any exoplanets within the system. ... More
The bright end of the exo-Zodi luminosity function: Disk evolution and implications for exo-Earth detectabilityMay 28 2013Jun 09 2013We present the first characterisation of the 12um warm dust ("exo-Zodi") luminosity function around Sun-like stars, focussing on the dustiest systems that can be identified by WISE. We detect six new warm dust candidates, five of which have unknown ages. ... More
Exo-zodi modelling for the Large Binocular Telescope InterferometerDec 01 2014Habitable zone dust levels are a key unknown that must be understood to ensure the success of future space missions to image Earth analogues around nearby stars. Current detection limits are several orders of magnitude above the level of the Solar System's ... More
Collisional Evolution of Irregular Satellite Swarms: Detectable Dust around Solar System and Extrasolar PlanetsNov 22 2010Since the 1980's it has been becoming increasingly clear that the Solar System's irregular satellites are collisionally evolved. We derive a general model for the collisional evolution of an irregular satellite swarm and apply it to the Solar System and ... More
ISPY - NaCo Imaging Survey for Planets around Young stars - Discovery of an M dwarf in the gap between HD 193571 and its debris ringJun 04 2019Context. The interaction between low-mass companions and the debris discs they reside in is still not fully understood. A debris disc can evolve due to self-stirring, a process in which planetesimals can excite their neighbours to the point of destructive ... More
Stellar Mass Dependent Disk DispersalJan 17 2009We use published optical spectral and IR excess data from nine young clusters and associations to study the stellar mass dependent dispersal of circumstellar disks. All clusters older than ~3 Myr show a decrease in disk fraction with increasing stellar ... More
Planet formation around stars of various masses: The snow line and the frequency of giant planetsOct 04 2007We use a semi-analytic circumstellar disk model that considers movement of the snow line through evolution of accretion and the central star to investigate how gas giant frequency changes with stellar mass. The snow line distance changes weakly with stellar ... More
ISPY -- NaCo Imaging Survey for Planets around Young stars. Discovery of an M dwarf in the gap between HD 193571 and its debris ringJun 04 2019Jun 14 2019Context. The interaction between low-mass companions and the debris discs they reside in is still not fully understood. A debris disc can evolve due to self-stirring, a process in which planetesimals can excite their neighbours to the point of destructive ... More
Do Two Temperature Debris Disks Have Multiple Belts?Aug 18 2014We present a study of debris disks whose spectra are well modelled by dust emission at two different temperatures. These disks are typically assumed to be a sign of multiple belts, which in only a few cases have been confirmed via high resolution observations. ... More
Young tableaux and the Steenrod algebraMar 28 2009The purpose of this paper is to forge a direct link between the hit problem for the action of the Steenrod algebra A on the polynomial algebra P(n)=F_2[x_1,...,x_n], over the field F_2 of two elements, and semistandard Young tableaux as they apply to ... More
Stimulated transitions due to arbitrary, Fourier decomposed, perturbing HamiltoniansOct 07 2015Apr 04 2016An external, time-dependent perturbing potential acting upon a quantum system can lead to transitions between its eigenstates which oscillate in time. In this paper we present an approximate analytic solution for the temporal evolution of the system in ... More
Force Gradient IntegratorsOct 15 2009We present initial results of the use of Force Gradient integrators for lattice field theories. These promise to give significant performance improvements, especially for light fermions and large lattices. Our results show that this is indeed the case, ... More
Tuning HMC using Poisson bracketsOct 07 2008We discuss how the integrators used for the Hybrid Monte Carlo (HMC) algorithm not only approximately conserve some Hamiltonian $H$ but exactly conserve a nearby shadow Hamiltonian (\tilde H), and how the difference $\Delta H \equiv \tilde H - H $ may ... More
Analytical aspects of isospectral drumsMay 08 2013We reexamine the proofs of isospectrality of the counterexample domains to Kac' question `Can one hear the shape of a drum?' from an analytical viewpoint. We reformulate isospectrality in a more abstract setting as the existence of a similarity transform ... More
Constraining the presence of giant planets in two-belt debris disk systems with VLT/SPHERE direct imaging and dynamical argumentsJul 03 2018Jul 11 2018Giant, wide-separation planets often lie in the gap between multiple, distinct rings of circumstellar debris: this is the case for the HR\,8799 and HD\,95086 systems, and even the solar system where the Asteroid and Kuiper belts enclose the four gas and ... More
Discovery of a low-mass companion inside the debris ring surrounding the F5V star HD206893Dec 01 2016Dec 06 2016Uncovering the ingredients and the architecture of planetary systems is a very active field of research that has fuelled many new theories on giant planet formation, migration, composition, and interaction with the circumstellar environment. We aim at ... More
Essential normality and the decomposability of homogeneous submodulesFeb 08 2012Feb 21 2013We establish the essential normality of a large new class of homogeneous submodules of the finite rank d-shift Hilbert module. The main idea is a notion of essential decomposability that determines when an arbitrary submodule can be decomposed into the ... More
Imaged sub-stellar companions: not as eccentric as they appear? The effect of an unseen inner mass on derived orbitsOct 28 2013Increasing numbers of sub-stellar companions are now being discovered via direct imaging. Orbital elements for some of these objects have been derived using star--companion astrometry, and several of these appear to have eccentricities significantly greater ... More
Topological Hopf-Chern Insulators and the Hopf SuperconductorApr 11 2016We introduce new three-dimensional topological phases of two-band models using the Pontryagin-Thom construction. In symmetry class A these are the infinitely many Hopf-Chern topological insulators, which are hybrids of layered Chern insulators and the ... More
Conformal invariance of the loop-erased percolation explorerJun 29 2018Sep 28 2018We consider critical percolation on the triangular lattice in a bounded simply connected domain with boundary conditions that force an interface between two prescribed boundary points. We say the interface forms a "near-loop" when it comes within one ... More
Five steps in the evolution from protoplanetary to debris diskDec 17 2014The protoplanetary disks of Herbig Ae stars eventually dissipate leaving a tenuous debris disk comprised of planetesimals and dust, as well as possibly gas and planets. This paper uses the properties of 10-20Myr A star debris disks to consider the protoplanetary ... More
A Bayesian method for detecting stellar flaresJun 06 2014Sep 30 2014We present a Bayesian-odds-ratio-based algorithm for detecting stellar flares in light curve data. We assume flares are described by a model in which there is a rapid rise with a half-Gaussian profile, followed by an exponential decay. Our signal model ... More
Invisible widths of heavy mesonsSep 12 2018We revisit calculations of invisible widths of heavy mesons in the standard model, which serve as benchmarks for the studies of production of light, long-lived neutral particles in heavy meson decays. We challenge the common assumption that in the standard ... More
Constraining the orbits of sub-stellar companions imaged over short orbital arcsFeb 06 2015Imaging a star's companion at multiple epochs over a short orbital arc provides only four of the six coordinates required for a unique orbital solution. Probability distributions of possible solutions are commonly generated by Monte Carlo (MCMC) analysis, ... More
Towards Chemical Constraints on Hot Jupiter MigrationAug 15 2014The origin of hot Jupiters -- gas giant exoplanets orbiting very close to their host stars -- is a long-standing puzzle. Planet formation theories suggest that such planets are unlikely to have formed in-situ but instead may have formed at large orbital ... More
A transiting exocomet detected in broadband light by TESS in the $β$ Pictoris systemMar 26 2019We search for signs of falling evaporating bodies (FEBs, also known as exocomets) in photometric time series obtained for $\beta$ Pictoris after fitting and removing its $\delta$ Scuti type pulsation frequencies. Using photometric data obtained by the ... More
Shaping HR8799's outer dust belt with an unseen planetJan 19 2018HR8799 is a benchmark system for direct imaging studies. It hosts two debris belts, which lie internally and externally to four giant planets. This paper considers how the four known planets and a possible fifth planet, interact with the external population ... More
Damage Spreading During Domain GrowthApr 07 1994We study damage spreading in models of two-dimensional systems undergoing first order phase transitions. We consider several models from the same non-conserved order parameter universality class, and find unexpected differences between them. An exact ... More
Practical Analysis of Codebook Design and Frequency Offset Estimation for Virtual-MIMO SystemsFeb 07 2013A virtual multiple-input multiple-output (MIMO) wireless system using the receiver-side cooperation with the compress-and-forward (CF) protocol, is an alternative to a point-to-point MIMO system, when a single receiver is not equipped with multiple antennas. ... More
The heavy quark potential in QCD with 2 flavors of dynamical quarksJan 20 1994We compute the heavy quark potential on configurations generated by the HEMCGC collaboration with dynamical staggered fermions at $6/g^2 = 5.6$ and with dynamical Wilson fermions at $6/g^2 = 5.3$. The computations are done on $16^3 \times 32$ lattices, ... More
The Dirichlet-to-Neumann operator via hidden compactnessMay 03 2013We show that to each symmetric elliptic operator of the form \[ \mathcal{A} = - \sum \partial_k \, a_{kl} \, \partial_l + c \] on a bounded Lipschitz domain $\Omega \subset \mathbb{R}^d$ one can associate a self-adjoint Dirichlet-to-Neumann operator on ... More
SONS: The JCMT legacy survey of debris discs in the submillimetreJun 05 2017Debris discs are evidence of the ongoing destructive collisions between planetesimals, and their presence around stars also suggests that planets exist in these systems. In this paper, we present submillimetre images of the thermal emission from debris ... More
Roche Lobe Underfilling of the Secondary Star in PSR J102347.6+003841?Jul 28 2015PSR J102347.6+003841 is a radio pulsar system with a spin period of 1.69 ms and an orbital period of 4.75 hours. Uniquely, it undergoes periods of transient accretion from its companion star: it occupies an important position in the evolutionary track ... More
Large low-temperature magnetoresistance in SrFe2As2 single crystalsOct 22 2013We present the first report on a large low-temperature magnetoresistance (MR) of more than 1600% in a SrFe2As2 single crystal and 1300% in a low-energy Ca ion-implanted SrFe2As2 single crystal that occurs before the emergence of crystallographic strain-induced ... More
Topological Complexity and non-immersions of real projective spaceDec 07 2009Apr 14 2011This article has been withdrawn due to an error in a proof of the main result.
On self-intersection invariantsNov 14 2011Aug 09 2012We prove that the Hatcher-Quinn and Wall invariants of a self-transverse immersion $f\co N^n\imm M^{2n}$ coincide. That is, we construct an isomorphism between their target groups which carries one onto the other. We also employ methods of normal bordism ... More
Symmetrized topological complexityMar 21 2017We present upper and lower bounds for symmetrized topological complexity $TC^\Sigma(X)$ in the sense of Basabe-Gonz\'alez-Rudyak-Tamaki. The upper bound comes from equivariant obstruction theory, and the lower bounds from the cohomology of the symmetric ... More
Topological complexity, fibrations and symmetryApr 14 2011Sep 26 2011We show how locally smooth actions of compact Lie groups on a manifold $X$ can be used to obtain new upper bounds for the topological complexity $\TC(X)$, in the sense of Farber. We also obtain new bounds for the topological complexity of finitely generated ... More
Topological complexity of motion planning and Massey productsSep 14 2007Jan 15 2008We employ Massey products to find sharper lower bounds for the Schwarz genus of a fibration than those previously known. In particular we give examples of non-formal spaces $X$ for which the topological complexity $\TC(X)$ (defined to be the genus of ... More
The Nakayama automorphism of a self-injective preprojective algebraJun 27 2019We give a simple proof, using Auslander-Reiten theory, that the preprojective algebra of a basic hereditary algebra of finite representation type is Frobenius. We then describe its Nakayama automorphism, which is induced by the Nakayama functor on the ... More
Equitable Candy SharingDec 08 2015Children, sitting in a circle, each have a nonnegative number of candies in front of them. A whistle is blown and each child with more than one candy passes one candy to the left and one to the right. The sharing process is repeated until a fixed state ... More
Derived autoequivalences from periodic algebrasJun 14 2011Feb 18 2013We present a construction of autoequivalences of derived categories of symmetric algebras based on projective modules with periodic endomorphism algebras. This construction generalises autoequivalences previously constructed by Rouquier-Zimmermann and ... More
Emergence of Quantum Phase-Slip Behaviour in Superconducting NbN Nanowires: DC Electrical Transport and Fabrication TechnologiesJun 20 2018Superconducting nanowires undergoing quantum phase-slips have potential for impact in electronic devices, with a high-accuracy quantum current standard among a possible toolbox of novel components. A key element of developing such technologies is to understand ... More
On the Milnor fiber boundary of a quasi-ordinary surfaceNov 02 2018We give a recursive formula, expressed in terms of the characteristic tuples, for the Betti numbers of the boundary of the Milnor fiber of an irreducible quasi-ordinary surface. The singular locus of the surface consists of two components, and for each ... More
A sharp eigenvalue bound for quantum graphs in terms of their diameterJul 21 2018We establish a sharp lower bound on the first non-trivial eigenvalue of the Laplacian on a metric graph equipped with natural (i.e., continuity and Kirchhoff) vertex conditions in terms of the diameter and the total length of the graph. This extends a ... More
Searching for Saturn's Dust Swarm: Limits on the size distribution of Irregular Satellites from km to micron sizesJul 11 2011We describe a search for dust created in collisions between the Saturnian irregular satellites using archival \emph{Spitzer} MIPS observations. Although we detected a degree scale Saturn-centric excess that might be attributed to an irregular satellite ... More
ALMA observations of the narrow HR 4796A debris ringJan 16 2018The young A0V star HR 4796A is host to a bright and narrow ring of dust, thought to originate in collisions between planetesimals within a belt analogous to the Solar System's Edgeworth-Kuiper belt. Here we present high spatial resolution 880$\mu$m continuum ... More
Herschel Observations of Debris Discs Orbiting Planet-hosting SubgiantsNov 12 2013Debris discs are commonly detected orbiting main-sequence stars, yet little is known regarding their fate as the star evolves to become a giant. Recent observations of radial velocity detected planets orbiting giant stars highlight this population and ... More
Spectral conditions on Lie and Jordan algebras of compact operatorsMar 31 2008We investigate the properties of bounded operators which satisfy a certain spectral additivity condition, and use our results to study Lie and Jordan algebras of compact operators. We prove that these algebras have nontrivial invariant subspaces when ... More
Closed nodal surfaces for simply connected domains in higher dimensionsSep 08 2010We give an example of a domain in dimension $N \geq 3$, homeomorphic to a ball and with analytic boundary, for which the second eigenvalue of the Dirichlet Laplacian has an eigenfunction with a closed nodal surface. The domain is constructed via a sequence ... More
A Simple Proof of the BPH TheoremDec 10 1996A new formalism is given for the renormalization of quantum field theories to all orders of perturbation theory, in which there are manifestly no overlapping divergences. We prove the BPH theorem in this formalism, and show how the local subtractions ... More
Some remarks on the isoperimetric problem for the higher eigenvalues of the Robin and Wentzell LaplaciansOct 20 2009We consider the problem of minimising the $k$th eigenvalue, $k \geq 2$, of the ($p$-)Laplacian with Robin boundary conditions with respect to all domains in $\mathbb{R}^N$ of given volume $M$. When $k=2$, we prove that the second eigenvalue of the $p$-Laplacian ... More
On the Milnor fiber boundary of a quasi-ordinary surfaceNov 02 2018Jun 15 2019We give a recursive formula, expressed in terms of the characteristic tuples, for the Betti numbers of the boundary of the Milnor fiber of an irreducible quasi-ordinary surface. The singular locus of the surface consists of two components, and for each ... More
Know your population and know your model: Using model-based regression and poststratification to generalize findings beyond the observed sampleJun 26 2019Psychology is all about interactions, and this has deep implications for inference from non-representative samples. For the goal of estimating average treatment effects, we propose to fit a model allowing treatment to interact with background variables ... More
Essential normality, essential norms and hyperrigiditySep 15 2013Jun 01 2014Let $S = (S_1, \ldots, S_d)$ denote the compression of the $d$-shift to the complement of a homogeneous ideal $I$ of $\mathbb{C}[z_1, \ldots, z_d]$. Arveson conjectured that $S$ is essentially normal. In this paper, we establish new results supporting ... More
Recursive Formulas for the Characteristic Numbers of Rational Plane CurvesApr 28 1996We derive recursive equations for the characteristic numbers of rational nodal plane curves with at most one cusp, subject to point conditions, tangent conditions and flag conditions, developing techniques akin to quantum cohomology on a moduli space ... More
The nodal line of the second eigenfunction of the Robin Laplacian in $\mathbb{R}^2$ can be closedSep 24 2010We construct a multiply connected domain in $\mathbb{R}^2$ for which the second eigenfunction of the Laplacian with Robin boundary conditions has an interior nodal line. In the process, we adapt a bound of Donnelly-Fefferman type to obtain a uniform estimate ... More
Boundaries of reduced C*-algebras of discrete groupsMay 17 2014Oct 09 2014For a discrete group G, we consider the minimal C*-subalgebra of $\ell^\infty(G)$ that arises as the image of a unital positive G-equivariant projection. This algebra always exists and is unique up to isomorphism. It is trivial if and only if G is amenable. ... More
A statistically significant lack of debris discs in medium separation binary systemsJul 10 2019We compile a sample of 341 binary and multiple star systems with the aim of searching for and characterising Kuiper belt-like debris discs. The sample is assembled by combining several smaller samples studied in previously published work with targets ... More
Using ACIS on the Chandra X-ray Observatory as a particle radiation monitorJul 23 2010The Advanced CCD Imaging Spectrometer (ACIS) is one of two focal-plane instruments on the Chandra X-ray Observatory. During initial radiation-belt passes, the exposed ACIS suffered significant radiation damage from trapped soft protons scattering off ... More
$^{75}$As NMR study of overdoped CeFeAsO$_{0.8}$F$_{0.2}$Dec 05 2012We report the results from a $^{75}$As NMR study on the overdoped iron pnictide superconductor, CeFeAsO$_{0.8}$F$_{0.2}$. Two peaks are observed in the NMR spectra for temperatures as high as 100 K, which is above the superconducting transition temperature ... More
Distribution of electrons and holes in cuprate superconductors as determined from $^{17}$O and $^{63}$Cu nuclear magnetic resonanceMar 25 2014The distribution of electrons and holes in the CuO$_2$ plane of the high-temperature superconducting cuprates is determined with nuclear magnetic resonance through the quadrupole splittings of $^{17}$O and $^{63}$Cu. Based on new data for single crystals ... More
An automated search for transiting exocometsNov 07 2018This paper discusses an algorithm for detecting single transits in photometric time-series data. Specifically, we aim to identify asymmetric transits with ingress that is more rapid than egress, as expected for cometary bodies with a significant tail. ... More
JILA SrI Optical Lattice Clock with Uncertainty of $2.0 \times 10^{-18}$Jun 14 2019We report on an improved systematic evaluation of the JILA SrI optical lattice clock, achieving a nearly identical systematic uncertainty compared to the previous strontium accuracy record set by the JILA SrII optical lattice clock (OLC) at $2.1 \times ... More
Active metamaterials with negative static electric susceptibilityApr 20 2017Apr 30 2019Well-established textbook arguments suggest that static electric susceptibility must be positive in "all bodies" [1]. However, it has been pointed out that media that are not in thermodynamic equilibrium are not necessarily subject to this restriction; ... More
Exocometary ScienceApr 04 2019Evidence for exocomets, icy bodies in extrasolar planetary systems, has rapidly increased over the past decade. Volatiles are detected through the gas that exocomets release as they collide and grind down within their natal belts, or as they sublimate ... More
Discovery of New Dipper Stars with K2: A Window into the Inner Disk Region of T Tauri StarsFeb 01 2018In recent years a new class of Young Stellar Object has been defined, referred to as dippers, where large transient drops in flux are observed. These dips are too large to be attributed to stellar variability, last from hours to days and can reduce the ... More
Dipper disks not inclined towards edge-on orbitsJul 11 2016Sep 11 2017The so-called "dipper" stars host circumstellar disks and have optical and infrared light curves that exhibit quasi-periodic or aperiodic dimming events consistent with extinction by transiting dusty structures orbiting in the inner disk. Most of the ... More
Metal-Poor Stars Observed with the Magellan Telescope II. Discovery of Four Stars with [Fe/H] < -3.5Nov 22 2013We report on the discovery of seven low-metallicity stars selected from the Hamburg/ESO Survey, six of which are extremely metal-poor ([Fe/H]<-3.0), with four having [Fe/H]<-3.5. Chemical abundances or upper limits are derived for these stars based on ... More
On functional equations leading to exact solutions for standing internal wavesNov 25 2014The Dirichlet problem for the wave equation is a classical example of a problem which is not well-posed. Nevertheless, it has been used to model internal waves oscillating sinusoidally in time, in various situations, standing internal waves amongst them. ... More
On realizing homology classes by maps of restricted complexityNov 01 2011Jul 13 2012We show that in every codimension greater than one there exists a mod 2 homology class in some closed manifold (of sufficiently high dimension) which cannot be realized by an immersion of closed manifolds. The proof gives explicit obstructions (in terms ... More
Robot motion planning, weights of cohomology classes, and cohomology operationsJun 17 2007Jul 07 2007The complexity of algorithms solving the motion planning problem is measured by a homotopy invariant TC(X) of the configuration space X of the system. Previously known lower bounds for TC(X) use the structure of the cohomology algebra of X. In this paper ... More
Isotopy and homeomorphism of closed surface braidsMar 05 2019Apr 29 2019The closure of a braid in a closed orientable surface $\Sigma$ is a link in $\Sigma\times S^1$. We classify such closed surface braids up to isotopy and homeomorphism (with a small indeterminacy for isotopy of closed sphere braids), in terms of the algebra ... More
Kuiper Belt-Like Hot and Cold Populations of Planetesimal Inclinations in the $β$ Pictoris Belt Revealed by ALMAFeb 11 2019The inclination distribution of the Kuiper belt provides unique constraints on its origin and dynamical evolution, motivating vertically resolved observations of extrasolar planetesimal belts. We present ALMA observations of millimeter emission in the ... More
ALMA Observations of the Debris Disk of Solar Analogue Tau CetiJul 08 2016We present 1.3 mm observations of the Sun-like star $\tau$ Ceti with the Atacama Large Millimeter/submillimeter Array (ALMA) that probe angular scales of $\sim1$'' (4 AU). This first interferometric image of the $\tau$ Ceti system, which hosts both a ... More
Summation formula inequalities for eigenvalues of the perturbed harmonic oscillatorMay 06 2016We derive explicit inequalities for sums of eigenvalues of one-dimensional Schr\"{o}dinger operators on the whole line. In the case of the perturbed harmonic oscillator, these bounds converge to the corresponding trace formula in the limit as the number ... More
Cartan Prolongation of a Family of Curves Acquiring a NodeOct 08 2017Apr 07 2018Using the monster/Semple tower construction, we study the structure of the Cartan prolongation of the family $x_1x_2 = t$ of plane curves with nodal central member.
Tangential Quantum Cohomology of Arbitrary OrderNov 29 2006Jul 23 2007J. Kock has previously defined a tangency quantum product on formal power series with coefficients in the cohomology ring of any smooth projective variety, and thus a ring that generalizes the quantum cohomology ring. We further generalize Kock's construction ... More
Isometric tuples are hyperreflexiveJun 25 2012An $n$-tuple of operators $(V_1,...,V_n)$ acting on a Hilbert space $H$ is said to be isometric if the row operator $(V_1,...,V_n) : H^n \to H$ is an isometry. We prove that every isometric $n$-tuple is hyperreflexive, in the sense of Arveson. For $n ... More
Discussion of "Data-driven confounder selection via Markov and Bayesian networks" by Jenny HäggströmOct 31 2017In this discussion we consider why it is important to estimate causal effect parameters well even they are not identified, propose a partially identified approach for causal inference in the presence of colliders, point out an under-appreciated advantage ... More
IR-excesses around nearby Lambda Boo stars are caused by debris disks rather than ISM bow wavesNov 18 2015Lambda Boo stars are predominately A-type stars with solar abundant C, N, O, and S, but up to 2 dex underabundances of refractory elements. The stars' unusual surface abundances could be due to a selective accretion of volatile gas over dust. It has been ... More
Physics of reverse annealing in high-resistivity Chandra ACIS CCDsJul 10 2008After launch, the Advanced CCD Imaging Spectrometer (ACIS), a focal plane instrument on the Chandra X-ray Observatory, suffered radiation damage from exposure to soft protons during passages through the Earth's radiation belts. An effect of the damage ... More