Results for "Christian Johnson"

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Oxygen and Sodium Abundances in M13 (NGC 6205) Giants: Linking Globular Cluster Formation Scenarios, Deep Mixing, and Post-RGB EvolutionJul 08 2012We present O, Na, and Fe abundances, as well as radial velocities, for 113 red giant branch (RGB) and asymptotic giant branch (AGB) stars in the globular cluster M13. The abundances and velocities are based on spectra obtained with the WIYN-Hydra spectrograph, ... More
Chemical Abundances for 855 Giants in the Globular Cluster Omega Centauri (NGC 5139)Aug 12 2010We present elemental abundances for 855 red giant branch (RGB) stars in the globular cluster Omega Centauri (w Cen) from spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. The sample includes nearly all RGB stars brighter ... More
From Exoplanets to Quasars: Detection of Potential Damped Lyman Alpha Absorbing Galaxies Using Angular Differential ImagingSep 01 2016The advantages of angular differential imaging (ADI) has been previously untested in imaging the host galaxies of damped Lyman alpha (DLA) systems. In this pilot study, we present the first application of ADI to directly imaging the host galaxy of the ... More
On the impossible NGC 4372 V1 and V2: an extended AGB to the [Fe/H] = -2.2 clusterOct 30 2012The asymptotic giant branch (AGB) of the globular cluster NGC 4372 appears to extend to unexpectedly high luminosities. We show, on the basis of proper motions and spatial distribution, that the extended AGB is indeed a likely part of the cluster. We ... More
Fe and Al Abundances for 180 Red Giants in the Globular Cluster Omega Centauri (NGC 5139)Apr 16 2008We present radial velocities, Fe, and Al abundances for 180 red giant branch (RGB) stars in the Galactic globular cluster Omega Centauri ($\omega$ Cen). The majority of our data lie in the range 11.0$<$V$<$13.5, which covers the RGB from about 1 mag. ... More
Empirical determination of the integrated red giant and horizontal branch stellar mass loss in omega CentauriJun 06 2011We herein determine the average integrated mass loss from stars stars belonging to the dominant metal-poor population ([Fe/H] ~ --1.7) of the Galactic globular cluster omega Centauri (NGC 5139) during their red giant and horizontal branch evolution. Masses ... More
Chemical Analysis of Five Red Giants in the Globular Cluster M10 (NGC 6254)Aug 18 2008We have determined Al, $\alpha$, Fe-peak, and neutron capture elemental abundances for five red giant branch (RGB) stars in the Galactic globular cluster M10. Abundances were determined using equivalent width analyses of moderate resolution (R$\sim$15,000) ... More
The Chemical Composition of Red Giant Branch Stars in the Galactic Globular Clusters NGC 6342 and NGC 6366Jun 27 2016We present radial velocities and chemical abundances for red giant branch stars in the Galactic bulge globular clusters NGC 6342 and NGC 6366. The velocities and abundances are based on measurements of high resolution (R > 20,000) spectra obtained with ... More
Light Element Discontinuities Suggest an Early Termination of Star Formation in the Globular Cluster NGC 6402 (M14)Mar 05 2019NGC 6402 is among the most massive globular clusters in the Galaxy, but little is known about its detailed chemical composition. Therefore, we obtained radial velocities and/or chemical abundances of 11 elements for 41 red giant branch cluster members ... More
Light, Alpha, and Fe-Peak Element Abundances in the Galactic BulgeJul 08 2014We present radial velocities and chemical abundances of O, Na, Mg, Al, Si, Ca, Cr, Fe, Co, Ni, and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near (l,b)=(+5.25,-3.02) and (0,-12). The (+5.25,-3.02) field also includes ... More
Constraints on the Formation of the Galactic Bulge from Na, Al, and Heavy Element Abundances in Plaut's FieldFeb 20 2012We report chemical abundances of Na, Al, Zr, La, Nd, and Eu for 39 red giant branch (RGB) stars and 23 potential inner disk red clump stars located in Plaut-s low extinction window. We also measure lithium for a super Li-rich RGB star. The abundances ... More
Chemical Abundances of Red Giant Stars in the Globular Cluster M107 (NGC 6171)Aug 25 2011We present chemical abundances of Al and several Fe-Peak and neutron-capture elements for 13 red giant branch stars in the Galactic globular cluster NGC 6171 (M107). The abundances were determined using equivalent width and spectrum synthesis analyses ... More
Search for gamma-ray emission from $p$-wave dark matter annihilation in the Galactic CenterApr 12 2019Indirect searches for dark matter through Standard Model products of its annihilation generally assume a cross-section which is dominated by a term independent of velocity ($s$-wave annihilation). However, in many DM models an $s$-wave annihilation cross-section ... More
Alpha Enhancement and the Metallicity Distribution Function of Plaut's WindowMar 10 2011We present Fe, Si, and Ca abundances for 61 giants in Plaut's Window (l=-1,b=-8.5) and Fe abundances for an additional 31 giants in a second, nearby field (l=0,b=-8) derived from high resolution (R~25,000) spectra obtained with the Blanco 4m telescope ... More
A Large Sample Study of Red Giants in the Globular Cluster Omega Centauri (NGC 5139)Apr 22 2009We present abundances of several light, alpha, Fe-peak, and neutron-capture elements for 66 red giant branch (RGB) stars in the Galactic globular cluster Omega Centauri. Our observations lie in the range 12.0<V<13.5 and focus on the intermediate and metal-rich ... More
Light and Heavy Element Abundance Variations in the Outer Halo Globular Cluster NGC 6229Aug 31 2017NGC 6229 is a relatively massive outer halo globular cluster that is primarily known for exhibiting a peculiar bimodal horizontal branch morphology. Given the paucity of spectroscopic data on this cluster, we present a detailed chemical composition analysis ... More
Multiple populations in Omega Centauri: a cluster analysis of spectroscopic dataMay 27 2011Omega Cen is composed of several stellar populations. Their history might allow us to reconstruct the evolution of this complex object. We performed a statistical cluster analysis on the large data set provided by Johnson and Pilachowski (2010). Stars ... More
Insights from the Outskirts: Chemical and Dynamical Properties in the outer Parts of the Fornax Dwarf Spheroidal GalaxyAug 24 2014We present radial velocities and [Fe/H] abundances for 340 stars in the Fornax dwarf spheroidal from R~16,000 spectra. The targets have been obtained in the outer parts of the galaxy, a region which has been poorly studied before. Our sample shows a wide ... More
Detailed Abundances for a Large Sample of Giant Stars in the Globular Cluster 47 Tucanae (NGC 104)Nov 06 201347 Tuc is an ideal target to study chemical evolution and GC formation in massive more metal-rich GCs since is the closest, massive GC. We present chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu in 164 red giant branch (RGB) stars in ... More
Light-Element Abundances of Giant Stars in the Globular Cluster M71 (NGC 6838)Jan 13 2015Aluminum is the heaviest light element displaying large star--to--star variations in Galactic globular clusters (GCs). This element may provide additional insight into the origin of the multiple populations now known to be a common place in GCs, and also ... More
Light Element Chemistry and the Double Red Giant Branch in the Galactic Globular Cluster NGC 288Jun 19 2014The globular cluster NGC 288 was previously reported to exhibit two distinct red giant branches (RGBs) in the narrow-band Calcium (HK) and Str\"omgren b and y band passes. In order to investigate this phenomenon further, we obtained moderate resolution ... More
The Chemical/Dynamical Evolution of the Galactic BulgeApr 08 2019The last decade has seen apparent dramatic progress in large spectroscopic datasets aimed at the study of the Galactic bulge. We consider remaining problems that appear to be intractable with the existing data, including important issues such as whether ... More
Metallicity Distribution Functions, Radial Velocities, and Alpha Element Abundances in Three Off-Axis Bulge FieldsFeb 15 2013We present radial velocities and chemical abundance ratios of [Fe/H], [O/Fe], [Si/Fe], and [Ca/Fe] for 264 red giant branch (RGB) stars in three Galactic bulge off-axis fields located near (l,b)=(-5.5,-7), (-4,-9), and (+8.5,+9). The results are based ... More
A Spectroscopic Analysis of the Galactic Globular Cluster NGC 6273 (M19)Jul 02 2015A combined effort utilizing spectroscopy and photometry has revealed the existence of a new globular cluster class. These "anomalous" clusters, which we refer to as "iron-complex" clusters, are differentiated from normal clusters by exhibiting large (>0.10 ... More
Exploring the Chemical Composition and Double Horizontal Branch of the Bulge Globular Cluster NGC 6569Jan 31 2018Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge ... More
Evidence for a chemical enrichment coupling of globular clusters and field stars in the Fornax dSphOct 13 2015The globular cluster H4, located in the center of the Fornax dwarf spheroidal galaxy, is crucial for understanding the formation and chemical evolution of star clusters in low-mass galactic environments. H4 is peculiar because the cluster is significantly ... More
NGC 7789: An Open Cluster Case StudyFeb 09 2015We have obtained high-resolution spectra of 32 giants in the open cluster NGC 7789 using the Wisconsin-Indiana-Yale-NOAO Hydra spectrograph. We explore differences in atmospheric parameters and elemental abundances caused by the use of the linelist developed ... More
The metal-poor Knee in the Fornax Dwarf Spheroidal GalaxyFeb 25 2014We present alpha-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal galaxy (dSph), obtained with VLT/GIRAFFE (R~16,000). Due to the large fraction of metal-poor stars in our sample, ... More
Chemical Complexity in the Eu-enhanced Monometallic Globular Cluster NGC 5986May 30 2017NGC 5986 is a poorly studied but relatively massive Galactic globular cluster that shares several physical and morphological characteristics with "iron-complex" clusters known to exhibit significant metallicity and heavy element dispersions. In order ... More
Lattice-Mediated Magnetic Order Melting in TbMnO3Jan 13 2018Recent ultrafast magnetic-sensitive measurements [Phys. Rev. B 92, 184429 (2015) and Phys. Rev. B 96, 184414 (2017)] have revealed a delayed melting of the long-range cycloid spin-order in TbMnO$_3$ following photoexcitation across the fundamental Mott-Hubbard ... More
X-ray line coincidence photopumping in a solar flareNov 21 2017Line coincidence photopumping is a process where the electrons of an atomic or molecular species are radiatively excited through the absorption of line emission from another species at a coincident wavelength. There are many instances of line coincidence ... More
A Chemical Composition Survey of the Iron-Complex Globular Cluster NGC 6273 (M 19)Nov 17 2016Recent observations have shown that a growing number of the most massive Galactic globular clusters contain multiple populations of stars with different [Fe/H] and neutron-capture element abundances. NGC 6273 has only recently been recognized as a member ... More
Direct characterisation of tuneable few-femtosecond dispersive-wave pulses in the deep UVOct 31 2018Dispersive wave emission (DWE) in gas-filled hollow-core dielectric waveguides is a promising source of tuneable coherent and broadband radiation, but so far the generation of few-femtosecond pulses using this technique has not been demonstrated. Using ... More
Crater 2: An Extremely Cold Dark Matter HaloDec 19 2016We present results from MMT/Hectochelle spectroscopy of red giant candidate stars along the line of sight to the recently-discovered Galactic satellite Crater 2. Modelling the joint distribution of stellar positions, velocities and metallicities as a ... More
Separating the conjoined red clump in the Galactic Bulge: Kinematics and AbundancesApr 01 2011Apr 05 2011We have used the AAOMEGA spectrograph to obtain R $\sim 1500$ spectra of 714 stars that are members of two red clumps in the Plaut Window Galactic bulge field $(l,b)=0^{\circ},-8^{\circ}$. We discern no difference between the clump populations based on ... More
Radial velocities of RR Lyrae stars in and around NGC 6441Feb 26 2018Detailed elemental abundance patterns of metal-poor ([Fe/H] ~ -1~dex) stars in the Galactic bulge indicate that a number of them are consistent with globular cluster (GC) stars and may be former members of dissolved GCs. This would indicate that a few ... More
Low-resolution Spectroscopy for the Globular Clusters with Signs of Supernova Enrichment: M22, NGC 1851 and NGC 288Dec 04 2014There is increasing evidence for the presence of multiple red giant branches (RGBs) in the color-magnitude diagrams of massive globular clusters (GCs). In order to investigate the origin of this split on the RGB, we have performed new narrow-band Ca photometry ... More
The Bulge Radial Velocity Assay (BRAVA): II. Complete Sample and Data ReleaseDec 08 2011We present new radial velocity measurements from the Bulge Radial Velocity Assay (BRAVA), a large scale spectroscopic survey of M-type giants in the Galactic bulge/bar region. The sample of ~4500 new radial velocities, mostly in the region -10 deg < l ... More
Statistical Mechanics of Amplifying ApparatusFeb 08 2005We implement Feynman's suggestion that the only missing notion needed for the puzzle of Quantum Measurement is the statistical mechanics of amplifying apparatus. We define a thermodynamic limit of quantum amplifiers which is a classically describable ... More
Hurwitz numbers, ribbon graphs, and tropicalizationMar 06 2013Double Hurwitz numbers have at least four equivalent definitions. Most naturally, they count covers of the Riemann sphere by genus g curves with certain specified ramification data. This is classically equivalent to counting certain collections of permutations. ... More
The effect of alternative tree representations on tree bank grammarsNov 20 1997Nov 21 1997The performance of PCFGs estimated from tree banks is sensitive to the particular way in which linguistic constructions are represented as trees in the tree bank. This paper presents a theoretical analysis of the effect of different tree representations ... More
Horizontal Heegaard splittings of Seifert fibered spacesFeb 06 2008We show that if an orientable Seifert fibered space $M$ with an orientable genus $g$ base space admits a strongly irreducible horizontal Heegaard splitting then there is a one-to-one correspondence between isotopy classes of strongly irreducible horizontal ... More
Neural Style Representations and the Large-Scale Classification of Artistic StyleNov 16 2016The artistic style of a painting is a subtle aesthetic judgment used by art historians for grouping and classifying artwork. The recently introduced `neural-style' algorithm substantially succeeds in merging the perceived artistic style of one image or ... More
Deep, Skinny Neural Networks are not Universal ApproximatorsSep 30 2018In order to choose a neural network architecture that will be effective for a particular modeling problem, one must understand the limitations imposed by each of the potential options. These limitations are typically described in terms of information ... More
Topological graph clustering with thin positionJun 04 2012A clustering algorithm partitions a set of data points into smaller sets (clusters) such that each subset is more tightly packed than the whole. Many approaches to clustering translate the vector data into a graph with edges reflecting a distance or similarity ... More
Heegaard splittings and the pants complexSep 28 2005Apr 17 2009We define integral measures of complexity for Heegaard splittings based on the graph dual to the curve complex and on the pants complex defined by Hatcher and Thurston. As the Heegaard splitting is stabilized, the sequence of complexities turns out to ... More
A pathological o-minimal quotientApr 11 2014We give an example of a definable quotient in an o-minimal structure which cannot be eliminated over any set of parameters, giving a negative answer to a question of Eleftheriou, Peterzil, and Ramakrishnan. Equivalently, there is an o-minimal structure ... More
Combinatorial Game Theory, Well-Tempered Scoring Games, and a Knot GameJul 25 2011We begin by reviewing and proving the basic facts of combinatorial game theory. We then consider scoring games (also known as Milnor games or positional games), focusing on the "fixed-length" games for which all sequences of play terminate after the same ... More
On dp-minimal fieldsJul 09 2015We classify dp-minimal pure fields up to elementary equivalence. Most are equivalent to Hahn series fields $K((t^\Gamma))$ where $\Gamma$ satisfies some divisibility conditions and $K$ is $\mathbb{F}_p^{alg}$ or a local field of characteristic zero. We ... More
Heegaard splittings and open booksOct 10 2011We show that if the monodromy of an open book decomposition has sufficiently high displacement distance, acting on the loop and arc complex for a page, then it is the unique minimal Euler characteristic open book for the manifold. In particular, we show ... More
Mapping class groups of Heegaard splittings of surface bundlesJan 12 2012Apr 06 2012Every surface bundle with genus $g$ fiber has a canonical Heegaard splitting of genus $2g+1$. We classify the mapping class groups of such Heegaard splittings in the case when the surface bundle has a sufficiently complicated monodromy map.
Information inequalities and a dependent Central Limit TheoremOct 03 2008We adapt arguments concerning information-theoretic convergence in the Central Limit Theorem to the case of dependent random variables under Rosenblatt mixing conditions. The key is to work with random variables perturbed by the addition of a normal random ... More
A Central Limit Theorem for non-overlapping return timesJun 09 2005Define the non-overlapping return time of a random process to be the number of blocks that we wait before a particular block reappears. We prove a Central Limit Theorem based on these return times. This result has applications to entropy estimation, and ... More
A multi-variate generating function for the Weyl Dimension FormulaMar 13 2014We present a closed form for a multi-variate generating function for the dimensions of the irreducible representations of a semisimple, simply connected linear algebraic group over $\mathbb{C}$ whose highest weights lie in a finitely generated lattice ... More
Theoretical properties of Cook's PFC dimension reduction algorithm for linear regressionJun 25 2008Sep 18 2008We analyse the properties of the Principal Fitted Components (PFC) algorithm proposed by Cook. We derive theoretical properties of the resulting estimators, including sufficient conditions under which they are $\sqrt{n}$-consistent, and explain some of ... More
Calculating isotopy classes of Heegaard splittingsApr 26 2010Jul 10 2011We show that given a partially flat angled ideal triangulation for a 3-manifold $M$ with boundary (as defined by Lackenby), there is an algorithm to produce a list of Heegaard splittings for $M$ such that below a given genus $g$, each isotopy class appears ... More
Morita Theory For Derived Categories: A Bicategorical PerspectiveMay 23 2008Jun 03 2008We present a bicategorical perspective on derived Morita theory for rings, DG algebras, and spectra. This perspective draws a connection between Morita theory and the bicategorical Yoneda Lemma, yielding a conceptual unification of Morita theory in derived ... More
VC density and dp rankAug 22 2011Aug 25 2011We derive that dpR(n) \leq dens(n) \leq dpR(n)+1, where dens(n) is the supremum of the VC density of all formulas in n parameters, and dpR(n) is the maximum depth of an ICT pattern in n variables. Consequently, strong dependence is equivalent to finite ... More
An upper bound on common stabilizations of Heegaard splittingsJul 11 2011We show that for any two Heegaard splittings of genus $p$ and $q$ for the same closed 3-manifold, there is a common stabilization of genus at most 3/2 p + 2q - 1. One may compare this to recent examples of Heegaard splittings whose smallest common stabilizations ... More
Partial results on dp-finite fieldsMar 27 2019We prove that NIP valued fields of positive characteristic are henselian. Furthermore, we partially generalize the known results on dp-minimal fields to dp-finite fields. We prove a dichotomy: if K is a sufficiently saturated dp-finite expansion of a ... More
Differential-Dunkl Operators and Nonstandard Solutions to the Classical Yang-Baxter EquationSep 19 2013For every pair of positive coprime integers, m and n, with m<n, there is an associated generalized Cremmer-Gervais r-matrix r_{m,n} for the Lie algebra sl_n which provides a nonstandard quasitriangular solution to the classical Yang-Baxter equation. We ... More
Locally unknotted spines of Heegaard splittingsNov 03 2004Nov 28 2005We show that under reasonable conditions, the spines of the handlebodies of a strongly irreducible Heegaard splitting will intersect a closed ball in a graph which is isotopic into the boundary of the ball. This is in some sense a generalization of the ... More
Subprime Solutions of the Classical Yang-Baxter EquationDec 19 2017Sep 26 2018We introduce a new family of classical $r$-matrices for the Lie algebra $\mathfrak{sl}_n$ that lies in the Zariski boundary of the Belavin-Drinfeld space ${\mathcal M}$ of quasi-triangular solutions to the classical Yang-Baxter equation. In this setting ... More
One-sided and two-sided Heegaard splittingsDec 02 2011We define a notion of Hempel distance for one-sided Heegaard splittings and show that the existence of alternate surfaces restricts distance for one-sided splittings in a manner similar to Hartshorn's and Scharlemann-Tomova's results for two-sided splittings. ... More
The Number of Group Homomorphisms from $D_m$ into $D_n$Jan 11 2012Feb 22 2012Counting homomorphisms between cyclic groups is a common exercise in a first course in abstract algebra. A similar problem, accessible at the same level, is to count the number of group homomorphisms from a dihedral group of order $2m$ into a dihedral ... More
Determining the Nature of the Extended HI Structure Around LITTLE THINGS Dwarf Galaxy NGC 1569Apr 04 2013This work presents an extended, neutral Hydrogen emission map around Magellanic-type dwarf irregular galaxy (dIm) NGC 1569. In the Spring of 2010, the Robert C. Byrd Green Bank Telescope (GBT) was used to map a 9 degree x 2 degree region in HI line emission ... More
Joint and conditional estimation of tagging and parsing modelsMay 07 2001This paper compares two different ways of estimating statistical language models. Many statistical NLP tagging and parsing models are estimated by maximizing the (joint) likelihood of the fully-observed training data. However, since these applications ... More
Type-driven semantic interpretation and feature dependencies in R-LFGNov 21 1997Once one has enriched LFG's formal machinery with the linear logic mechanisms needed for semantic interpretation as proposed by Dalrymple et. al., it is natural to ask whether these make any existing components of LFG redundant. As Dalrymple and her colleagues ... More
Memoization of Top Down ParsingApr 25 1995This paper discusses the relationship between memoized top-down recognizers and chart parsers. It presents a version of memoization suitable for continuation-passing style programs. When applied to a simple formalization of a top-down recognizer it yields ... More
The Knotting-Unknotting Game played on Sums of Rational ShadowsJul 13 2011Jul 22 2011We consider the recently introduced knotting-unknotting game, in which two players take turns resolving crossings in a knot diagram which initially is missing all its crossing information. Once the knot is fully resolved, the winner is decided by whether ... More
Some new maximum VC classesSep 08 2013Set systems of finite VC dimension are frequently used in applications relating to machine learning theory and statistics. Two simple types of VC classes which have been widely studied are the maximum classes (those which are extremal with respect to ... More
Cremmer-Gervais r-matrices and the Cherednik Algebras of type GL2Oct 28 2009We give an intepretation of the Cremmer-Gervais r-matrices for sl(n) in terms of actions of elements in the rational and trigonometric Cherednik algebras of type GL2 on certain subspaces of their polynomial representations. This is used to compute the ... More
On the proof of elimination of imaginaries in algebraically closed valued fieldsJun 13 2014We give a simplified proof of elimination of imaginaries (in the geometric sorts) in ACVF, based on ideas of Hrushovski. This proof manages to avoid many of the technical issues which arose in the original proof by Haskell, Hrushovski, and Macpherson. ... More
Maximum VC familiesJun 01 2011Jun 02 2011Maximum VC classes which are stable in the sense of model theory are characterized.
Madeup: A Mobile Development Environment for Programming 3-D ModelsSep 27 2013Constructionism is a learning theory that states that we learn more when we construct tangible objects. In the process of building and presenting our work, we make concrete the abstract mental models we've formed, see where they breakdown through the ... More
Azumaya Objects in Triangulated BicategoriesMay 26 2010Apr 26 2013We introduce the notion of Azumaya object in general homotopy-theoretic settings. We give a self-contained account of Azumaya objects and Brauer groups in bicategorical contexts, generalizing the Brauer group of a commutative ring. We go on to describe ... More
A conditional Entropy Power Inequality for dependent variablesNov 02 2001We provide a condition under which a version of Shannon's Entropy Power Inequality will hold for dependent variables. We provide information inequalities extending those found in the independent case.
Absence of Observed Unspeakably Large Black Holes Tells Us the Curvature of SpaceApr 30 2015Using black-hole arguments with widely accepted premises, we show that it is extremely improbable that space is Euclidean, and that it is unspeakably improbable that space is hyperbolic. Independently, using an argument which makes no appeal to black ... More
Circular Planar Resistor Networks with Nonlinear and Signed ConductorsMar 19 2012We consider the inverse boundary value problem in the case of discrete electrical networks containing nonlinear (non-ohmic) resistors. Generalizing work of Curtis, Ingerman, Morrow, Colin de Verdiere, Gitler, and Vertigan, we characterize the circular ... More
Eigenvalue fluctuations for random regular graphsJun 26 2014One of the major themes of random matrix theory is that many asymptotic properties of traditionally studied distributions of random matrices are universal. We probe the edges of universality by studying the spectral properties of random regular graphs. ... More
Exchangeable pairs, switchings, and random regular graphsDec 04 2011Feb 17 2015We consider the distribution of cycle counts in a random regular graph, which is closely linked to the graph's spectral properties. We broaden the asymptotic regime in which the cycle counts are known to be approximately Poisson, and we give an explicit ... More
Non-uniqueness of high distance Heegaard splittingsAug 21 2013Kevin Hartshorn showed that if a three-dimensional manifold $M$ admits a Heegaard surface $\Sigma$ with Hempel distance $d$ then every incompressible surface in $M$ has genus at least $\frac{d}{2}$. Scharlemann-Tomova generalized this, proving that in ... More
Entropy and a generalisation of `Poincare's Observation'Jan 29 2002Consider a sphere of radius root(n) in n dimensions, and consider X, a random variable uniformly distributed on its surface. Poincare's Observation states that for large n, the distribution of the first k coordinates of X is close in total variation distance ... More
No elliptic islands for the universal area-preserving mapDec 10 2010Jun 02 2011A renormalization approach has been used in \cite{EKW1} and \cite{EKW2} to prove the existence of a \textit{universal area-preserving map}, a map with hyperbolic orbits of all binary periods. The existence of a horseshoe, with positive Hausdorff dimension, ... More
Convergence of the Poincare ConstantJun 21 2002The Poincare constant R(Y) of a random variable Y relates the L2 norm of a function g and its derivative g'. Since R(Y) - Var(Y) is positive, with equality if and only if Y is normal, it can be seen as a distance from the normal distribution. In this ... More
Dp-rank and forbidden configurationsAug 31 2011Nov 07 2011A theory $T$ is shown to have an ICT pattern of depth $k$ in variables $\xbar$ iff it interprets some $k$-maximum VC class in $|\xbar|$ parameters.
Amalgamated Products of Ore and Quadratic Extensions of RingsMar 07 2012We study the ideal theory of amalgamated products of Ore and quadratic extensions over a base ring R. We prove an analogue of the Hilbert Basis theorem for an amalgamated product Q of quadratic extensions and determine conditions for when the one-sided ... More
Mapping class groups of once-stabilized Heegaard splittingsAug 26 2011Apr 26 2013We show that if a Heegaard splitting is the result of stabilizing a high distance Heegaard splitting exactly once then its mapping class group is finitely generated.
Determining Tropical HypersurfacesSep 18 2015Sep 23 2016We consider the question of when points in tropical affine space uniquely determine a tropical hypersurface. We introduce a notion of multiplicity of points so that this question may be meaningful even if some of the points coincide. We give a geometric/combinatorial ... More
Duck Traps: Two-dimensional Critical Manifolds in Planar SystemsAug 30 2018Nov 05 2018In this work we consider two-dimensional critical manifolds in planar fast-slow systems near fold and so-called canard (=`duck') points. These higher-dimension, and lower-codimension, situation is directly motivated by the case of hysteresis operators ... More
Thermal Quantum Fields without Cut-offs in 1+1 Space-time DimensionsMar 26 2004We construct interacting quantum fields in 1+1 dimensional Minkowski space, representing neutral scalar bosons at positive temperature. Our work is based on prior work by Klein and Landau and Hoegh-Krohn
Thermal Quantum Fields with Spatially Cut-off Interactions in 1+1 Space-time DimensionsJul 25 2003We construct interacting quantum fields in 1+1 space-time dimensions, representing charged or neutral scalar bosons at positive temperature and zero chemical potential. Our work is based on prior work by Klein and Landau and Hoegh-Krohn. Generalized path ... More
Differential Characters and Geometric ChainsMar 26 2013Apr 09 2013We study Cheeger-Simons differential characters and provide geometric descriptions of the ring structure and of the fiber integration map. The uniqueness of differential cohomology (up to unique natural transformation) is proved by deriving an explicit ... More
Distances and large deviations in the spatial preferential attachment modelSep 26 2018Sep 27 2018We investigate two asymptotic properties of a spatial preferential-attachment model introduced by E. Jacob and P. M\"orters (2013). First, in a regime of strong linear reinforcement, we show that typical distances are at most of doubly-logarithmic order. ... More
Retired A Stars and Their Companions. III. Comparing the Mass-Period Distributions of Planets Around A-Type Stars and Sun-Like StarsDec 02 2009We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass subgiants (1.5 < M*/Msun < 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type ... More
The 2-degree Field Lensing Survey: photometric redshifts from a large new training sample to r<19.5Dec 01 2016We present a new training set for estimating empirical photometric redshifts of galaxies, which was created as part of the 2dFLenS project. This training set is located in a 700 sq deg area of the KiDS South field and is randomly selected and nearly complete ... More
Galaxy and Quasar Fueling Caught in the Act from the Intragroup to the Interstellar MediumNov 26 2018We report the discovery of six spatially extended (10-100 kpc) line-emitting nebulae in the z=0.57 galaxy group hosting PKS0405-123, one of the most luminous quasars at z<1. The discovery is enabled by the Multi Unit Spectroscopic Explorer (MUSE) and ... More
LSST Cadence Optimization White Paper: The Definitive Map of the Galactic bulgeDec 20 2018We recommend configuring the LSST coverage of the inner Galactic plane to allow the production of the definitive age/metallicity map of the Galactic bulge from LSST data, matched to external surveys where appropriate. This will allow the formation history ... More
AGB Sodium Abundances in the Globular Cluster 47 Tucanae (NGC 104)Dec 12 2014A recent analysis comparing the [Na/Fe] distributions of red giant branch (RGB) and asymptotic giant branch (AGB) stars in the Galactic globular cluster NGC 6752 found that the ratio of Na-poor to Na-rich stars changes from 30:70 on the RGB to 100:0 on ... More
The origin of accreted stellar halo populations in the Milky Way using APOGEE, $\textit{Gaia}$, and the EAGLE simulationsAug 02 2018Oct 30 2018Recent work indicates that the nearby Galactic halo is dominated by the debris from a major accretion event. We confirm that result from an analysis of APOGEE-DR14 element abundances and $\textit{Gaia}$-DR2 kinematics of halo stars. We show that $\sim$2/3 ... More