Results for "Colin P. Folsom"

total 120032took 0.14s
Fingerprints of giant planets in the photospheres of Herbig starsSep 09 2015Around 2% of all A stars have photospheres depleted in refractory elements. This is hypothesized to arise from a preferential accretion of gas rather than dust, but the specific processes and the origin of the material -- circum- or interstellar -- are ... More
Age dependence of wind properties for solar type stars: a 3d studySep 21 2016Dec 16 2016Young and rapidly rotating stars are known for intense, dynamo generated magnetic fields. Spectropolarimetric observations of those stars in precisely aged clusters are key input for gyrochronology and magnetochronology. We use ZDI maps of several young ... More
From solar to stellar corona: the role of wind, rotation and magnetismSep 23 2015Observations of surface magnetic fields are now within reach for many stellar types thanks to the development of Zeeman-Doppler Imaging. These observations are extremely useful for constraining rotational evolution models of stars, as well as for characterizing ... More
The magnetic fields of intermediate-mass T Tauri stars : I. Magnetic detections and fundamental stellar parametersOct 30 2018Context. The origin of the fossil magnetic fields detected in 5 to 10% of intermediate-mass main sequence stars is still highly debated. Aims. We want to bring observational constraints to a large population of intermediate-mass pre-main sequence (PMS) ... More
Do the close binaries HD 22128 and HD 56495 contain Ap or Am stars?Jun 12 2013HD 22128 and HD 56495 are both double-lined spectroscopic binary systems with short orbital periods, which have been proposed to host magnetic Ap stars. Ap stars in short period binary systems are very rare, and may provide insight into the origin of ... More
Estimating magnetic filling factors from Zeeman-Doppler magnetogramsMar 13 2019Low-mass stars are known to have magnetic fields that are believed to be of dynamo origin. Two complementary techniques are principally used to characterise them. Zeeman-Doppler imaging (ZDI) can determine the geometry of the large-scale magnetic field ... More
Almost harmonic Maass forms and Kac-Wakimoto charactersDec 20 2011Mar 03 2013We resolve a question of Kac, and explain the automorphic properties of characters due to Kac-Wakimoto pertaining to sl(m|n)^ highest weight modules, for n \geq 1. We prove that the Kac-Wakimoto characters are essentially holomorphic parts of certain ... More
Candidate Ap stars in close binary systemsNov 07 2013Short period binary systems containing magnetic Ap stars are anomalously rare. This apparent anomaly may provide insight into the origin of the magnetic fields in theses stars. As an early investigation of this, we observed three close binary systems ... More
Age dependence of wind properties for solar type stars: a 3d studySep 21 2016Young and rapidly rotating stars are known for intense, dynamo generated magnetic fields. Spectropolarimetric observations of those stars in precisely aged clusters are key input for gyrochronology and magnetochronology. We use ZDI maps of several young ... More
On the Structure of Dark Matter Halos at the Damping Scale of the Power Spectrum with and without Relict VelocitiesSep 25 2007We report a series of high-resolution cosmological N-body simulations designed to explore the formation and properties of dark matter halos with masses close to the damping scale of the primordial power spectrum of density fluctuations. We further investigate ... More
Entropy Production in Collisionless Systems. III. Results from SimulationsMar 24 2015The equilibria formed by the self-gravitating, collisionless collapse of simple initial conditions have been investigated for decades. We present the results of our attempts to describe the equilibria formed in $N$-body simulations using thermodynamically-motivated ... More
Non-separability of the Gelfand space of measure algebrasMar 18 2016Jun 27 2016We prove that there exists uncountably many pairwise disjoint open subsets of the Gelfand space of the measure algebra on any locally compact non-discrete abelian group which shows that this space is not separable (in fact, we prove this assertion for ... More
The Evolving Magnetic Topology of $τ$ BoötisApr 08 2016We present six epochs of spectropolarimetric observations of the hot-Jupiter-hosting star $\tau$ Bo\"otis that extend the exceptional previous multi-year data set of its large-scale magnetic field. Our results confirm that the large-scale magnetic field ... More
Embeddings of quotient division algebras of rings of differential operatorsNov 13 2014Let $k$ be an algebraically closed field of characteristic zero, let $X$ and $Y$ be smooth irreducible algebraic curves over $k$, and let $D(X)$ and $D(Y)$ denote respectively the quotient division rings of the ring of differential operators of $X$ and ... More
The Surface Magnetic Activity of the Weak-Line T Tauri Stars TWA 9A and V1095 ScoJul 20 2018We present a detailed analysis of high-resolution spectropolarimetric observations of the weak-line T Tauri stars (wTTSs) TWA 9A and V1095 Sco as part of a wider sur- vey of magnetic properties and activity in weak-line T Tauri stars, called MaTYSSE (Magnetic ... More
The Solar Wind in Time II: 3D stellar wind structure and radio emissionNov 13 2018In this work, we simulate the evolution of the solar wind along its main sequence lifetime and compute its thermal radio emission. To study the evolution of the solar wind, we use a sample of solar mass stars at different ages. All these stars have observationally-reconstructed ... More
Mixed finite elements for global tide models with nonlinear dampingJun 05 2017We study mixed finite element methods for the rotating shallow water equations with linearized momentum terms but nonlinear drag. By means of an equivalent second-order formulation, we prove long-time stability of the system without energy accumulation. ... More
Stellar magnetism: empirical trends with age and rotationApr 10 2014We investigate how the observed large-scale surface magnetic fields of low-mass stars (~0.1 -- 2 Msun), reconstructed through Zeeman-Doppler imaging (ZDI), vary with age t, rotation and X-ray emission. Our sample consists of 104 magnetic maps of 73 stars, ... More
Shear-induced fractures and three-dimensional motions in an organogelMar 31 2009The flow behavior of a viscoelastic organogel is investigated using ultrasonic velocimetry combined with rheometry. Our gel presents a decreasing flow curve, i.e., the measured stress decreases as a function of the applied shear rate. Strikingly, we note ... More
Orbital advection with magnetohydrodynamics and vector potentialAug 16 2017Sep 03 2017Orbital advection is a significant bottleneck in disk simulations, and a particularly tricky one when used in connection with magnetohydrodynamics. We have developed an orbital advection algorithm suitable for the induction equation with magnetic potential. ... More
Image registration and super resolution from first principlesSep 14 2018Feb 19 2019Image registration is the inference of transformations relating noisy and distorted images. It is fundamental in computer vision, experimental physics, and medical imaging. Many algorithms and analyses exist for inferring shift, rotation, and nonlinear ... More
Magnetic field and wind of Kappa Ceti: towards the planetary habitability of the young Sun when life arose on EarthMar 12 2016We report magnetic field measurements for Kappa1~Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic ... More
Quantum Clock Synchronization Based on Shared Prior EntanglementApr 27 2000Jun 30 2000We demonstrate that two spatially separated parties (Alice and Bob) can utilize shared prior quantum entanglement, and classical communications, to establish a synchronized pair of atomic clocks. In contrast to classical synchronization schemes, the accuracy ... More
Migrating super-Earths in low-viscosity discs: unveiling the roles of feedback, vortices, and laminar accretion flowsNov 30 2018Jan 13 2019We present the highest resolution study to date of super-Earths migrating in inviscid and low-viscosity discs, motivated by the connection to laminar, wind-driven models of protoplanetary discs. Our models unveil the critical role of vortices in determining ... More
Tutorial models of the climate and habitability of Proxima Centauri b: a thin atmosphere is sufficient to distribute heat given low stellar fluxAug 25 2016Proxima Centauri b, an Earth-size planet in the habitable zone of our nearest stellar neighbour, has just been discovered. A theoretical framework of synchronously rotating planets, in which the risk of a runaway greenhouse on the sunlight side and atmospheric ... More
Number and Luminosity Evolution of Interacting Galaxies as a Natural explanation for the Galaxy CountsMay 23 1995A newly developed isochrone synthesis algorithm for the photometric evolution of galaxies is described. Two initial mass functions, IMFs, in particular, the recent IMF determined by Kroupa, Tout, and Gilmore, three photometric transformations, and a 1-Gyr-burst ... More
A univalent universe in finite order arithmeticDec 21 2014Jan 10 2015Homotopy Type Theory with a univalent universe $\,\mathcal{U}_0$ is interpreted at the strength of finite order arithmetic. We eliminate Grothendieck universes, avoid the axiom of replacement, and bound all uses of separation.
Improved effective estimates of Pólya's Theorem for quadratic formsApr 08 2018Apr 14 2018Following de Loera and Santos, the P\'olya exponent of a $n$-ary real form (i.e. a homogeneous polynomial in $n$ variables with real coefficients) $f$ is the infimum of the upward closed set of nonnegative integers $m$ such that $(x_1 + \cdots + x_n)^m ... More
Flexible Toggles and Symmetric Invertible Asynchronous Elementary Cellular AutomataNov 22 2015May 24 2018A sequential dynamical system (SDS) consists of a graph $G$ with vertices $v_1,v_2,\ldots,v_n$, a state set $A$, a collection of "vertex functions" $\{f_{v_i}\}_{i=1}^n$, and a permutation $\pi\in S_n$ that specifies how to compose these functions to ... More
Counting 3-Stack-Sortable PermutationsMar 21 2019May 07 2019We prove a "Decomposition Lemma" that allows us to count preimages of certain sets of permutations under West's stack-sorting map $s$. As a first application, we give a new proof of Zeilberger's formula for the number of 2-stack-sortable permutations ... More
Triple Crossing Number of Knots and LinksJul 31 2012Sep 04 2012A triple crossing is a crossing in a projection of a knot or link that has three strands of the knot passing straight through it. A triple crossing projection is a projection such that all of the crossings are triple crossings. We prove that every knot ... More
A new paradigm for the universeNov 03 2003Jan 25 2012A new paradigm for the universe is presented in which the universe is far older than current estimates and there is no big bang.
Connected Components of Complex Divisor FunctionsNov 12 2017May 04 2018For any complex number $c$, define the divisor function $\sigma_c\colon\mathbb N\to\mathbb C$ by $\displaystyle\sigma_c(n)=\sum_{d\mid n}d^c$. Let $\overline{\sigma_c(\mathbb N)}$ denote the topological closure of the range of $\sigma_c$. Extending previous ... More
Postorder PreimagesApr 06 2016Jun 02 2018Given a set $Y$ of decreasing plane trees and a permutation $\pi$, how many trees in $Y$ have $\pi$ as their postorder? Using combinatorial and geometric constructions, we provide a method for answering this question for certain sets $Y$ and all permutations ... More
A new paradigm for the universeNov 03 2003Dec 21 2017This book provides a completely new approach to understanding the universe. The main idea is that the principal objects in the universe form a spectrum unified by the presence of a massive or hypermassive black hole. These objects are variously called ... More
Lens rigidity for manifolds with hyperbolic trapped setDec 04 2014Dec 21 2015For a Riemannian manifold $(M,g)$ with strictly convex boundary $\partial M$, the lens data consists in the set of lengths of geodesics $\gamma$ with endpoints on $\partial M$, together with their endpoints $(x_-,x_+)\in \partial M\times \partial M$ and ... More
Connectivity for bridge-alterable graph classesNov 13 2013Mar 01 2016A collection of graphs is called bridge-alterable if, for each graph G with a bridge e, G is in the class if and only if G-e is. For example the class of forests is bridge-alterable. For a random forest $F_n$ sampled uniformly from the set of forests ... More
The Harish-Chandra integralJun 28 2018This paper introduces Harish-Chandra's integral formula for compact, connected, semisimple Lie groups. It is intended for mathematicians and physicists who are familiar with the basics of Lie groups and Lie algebras but who may not be specialists in representation ... More
Anti-Power Prefixes of the Thue-Morse WordJul 20 2016Oct 08 2016Recently, Fici, Restivo, Silva, and Zamboni defined a $k$-anti-power to be a word of the form $w_1w_2\cdots w_k$, where $w_1,w_2,\ldots,w_k$ are distinct words of the same length. They defined $AP(x,k)$ to be the set of all positive integers $m$ such ... More
Stack-Sorting Preimages of Permutation ClassesSep 10 2018Feb 11 2019We extend and generalize many of the enumerative results concerning West's stack-sorting map $s$. First, we prove a useful theorem that allows one to efficiently compute $|s^{-1}(\pi)|$ for any permutation $\pi$, answering a question of Bousquet-M\'elou. ... More
Unitary Cayley Graphs of Dedekind Domain QuotientsDec 09 2014Mar 26 2017If $X$ is a commutative ring with unity, then the unitary Cayley graph of $X$, denoted $G_X$, is defined to be the graph whose vertex set is $X$ and whose edge set is $\{\{a,b\}\colon a-b\in X^\times\}$. When $R$ is a Dedekind domain and $I$ is an ideal ... More
Absence of resonance near the critical line on asymptotically hyperbolic spacesJun 24 2004Sep 02 2005As a consequence of a result of Cardoso and Vodev, we show that the resolvent of the Laplacian on asymptotically hyperbolic manifolds is analytic in an exponential neighbourhood of the critical line. The case of non-trapping metrics with constant curvature ... More
Cabling Conjecture for Small Bridge NumberJul 06 2015Let $k\subset S^3$ be a nontrivial knot. The Cabling Conjecture of Francisco Gonz\'alez-Acu\~na and Hamish Short posits that $\pi$-Dehn surgery on $k$ produces a reducible manifold if and only if $k$ is a $(p,q)$-cable knot and the surgery slope $\pi$ ... More
Polyurethane TogglesApr 09 2019We consider the involutions known as "toggles," which have been used to give simplified proofs of the fundamental properties of the promotion and evacuation maps. We transfer these involutions so that they generate a group $\mathscr P_n$ that acts on ... More
Motzkin Intervals and Valid Hook ConfigurationsApr 23 2019We define a new natural partial order on Motzkin paths that serves as an intermediate step between two previously-studied partial orders. We provide a bijection between valid hook configurations of $312$-avoiding permutations and intervals in these new ... More
Nonlinear waves in stratified Taylor--Couette flow. Part 2. Buoyancy fluxSep 09 2016This paper is the second part of a two-fold study of mixing, i.e. the formation of layers and upwelling of buoyancy, in axially stratified Taylor--Couette flow, with fixed outer cylinder. In a first paper, we showed that the dynamics of the flow was dominated ... More
Slingshot prominence evolution for a solar-like starFeb 20 2019Although the present-day Sun rotates too slowly to exhibit centrifugally-supported 'slingshot prominences', at some time during its past it may have formed these clouds of cool gas and ejected them into the interplanetary medium. We determine the time ... More
Visualizing probabilistic models: Intensive Principal Component AnalysisOct 05 2018May 10 2019Unsupervised learning makes manifest the underlying structure of data without curated training and specific problem definitions. However, the inference of relationships between data points is frustrated by the `curse of dimensionality' in high-dimensions. ... More
On the Use of ArXiv as a DatasetApr 30 2019The arXiv has collected 1.5 million pre-print articles over 28 years, hosting literature from scientific fields including Physics, Mathematics, and Computer Science. Each pre-print features text, figures, authors, citations, categories, and other metadata. ... More
The generalised Fitting subgroup of a profinite groupApr 02 2009The generalised Fitting subgroup of a finite group is the group generated by all subnormal subgroups that are either nilpotent or quasisimple. The importance of this subgroup in finite group theory stems from the fact that it always contains its own centraliser, ... More
Random graphs from a weighted minor-closed classOct 09 2012There has been much recent interest in random graphs sampled uniformly from the n-vertex graphs in a suitable minor-closed class, such as the class of all planar graphs. Here we use combinatorial and probabilistic methods to investigate a more general ... More
Connectivity for random graphs from a weighted bridge-addable classMar 15 2012Aug 01 2012There has been much recent interest in random graphs sampled uniformly from the n-vertex graphs in a suitable structured class, such as the class of all planar graphs. Here we consider a general 'bridge-addable' class of graphs - if a graph is in the ... More
Fertility NumbersSep 11 2018A nonnegative integer is called a fertility number if it is equal to the number of preimages of a permutation under West's stack-sorting map. We prove structural results concerning permutations, allowing us to deduce information about the set of fertility ... More
On Arithmetic Functions Related to Iterates of the Schemmel Totient FunctionsJun 17 2015We begin by introducing an interesting class of functions, known as the Schemmel totient functions, that generalizes the Euler totient function. For each Schemmel totient function $L_m$, we define two new functions, denoted $R_m$ and $H_m$, that arise ... More
Enumerating Cliques in Direct Product GraphsJul 17 2017Nov 19 2018The unitary Cayley graph of $\mathbb Z/n\mathbb Z$, denoted $G_{\mathbb Z/n\mathbb Z}$, is the graph with vertices $0,1,\ldots,$ $n-1$ in which two vertices are adjacent if and only if their difference is relatively prime to $n$. These graphs are central ... More
A new proof of Harish-Chandra's integral formulaDec 11 2017Jul 02 2018We present a new proof of Harish-Chandra's formula $$\Pi(h_1) \Pi(h_2) \int_G e^{\langle \mathrm{Ad}_g h_1, h_2 \rangle} dg = \frac{ [ \! [ \Pi, \Pi ] \!] }{|W|} \sum_{w \in W} \epsilon(w) e^{\langle w(h_1),h_2 \rangle},$$ where $G$ is a compact, connected, ... More
Meromorphic properties of the resolvent on asymptotically hyperbolic manifoldsNov 24 2003Mar 29 2004We show that the resolvent of the Laplacian on asymptotically hyperbolic spaces extends meromorphically with finite rank poles to the complex plane if and only if the metric is `even' (in a sense). If it is not even, there exist some cases where the resolvent ... More
Lower Bounds in the Preprocessing and Query Phases of Routing AlgorithmsJan 18 2015Sep 07 2015In the last decade, there has been a substantial amount of research in finding routing algorithms designed specifically to run on real-world graphs. In 2010, Abraham et al. showed upper bounds on the query time in terms of a graph's highway dimension ... More
Catalan Intervals and Uniquely Sorted PermutationsApr 04 2019For each positive integer $k$, we consider five well-studied posets defined on the set of Dyck paths of semilength $k$. We establish bijections between uniquely sorted permutations that avoid various patterns and intervals in these posets. We end with ... More
The probability that the number of points on the Jacobian of a genus 2 curve is primeJan 25 2011Sep 30 2011In 2000, Galbraith and McKee heuristically derived a formula that estimates the probability that a randomly chosen elliptic curve over a fixed finite prime field has a prime number of rational points. We show how their heuristics can be generalized to ... More
A search for Vega-like fields in OB starsOct 10 2014Very weak magnetic fields (with a longitudinal component below 1 Gauss) have recently been discovered in the A star Vega as well as in a few Am stars. According to fossil field scenarios, such weak fields should also exist in more massive stars. In the ... More
Why are some A stars magnetic, while most are not?Dec 21 2007A small fraction of intermediate-mass main sequence (A and B type) stars have strong, organised magnetic fields. The large majority of such stars, however, show no evidence for magnetic fields, even when observed with very high precision. In this paper ... More
The connection between stellar activity cycles and magnetic field topologyOct 12 2016Zeeman Doppler imaging has successfully mapped the large-scale magnetic fields of stars over a large range of spectral types, rotation periods and ages. When observed over multiple epochs, some stars show polarity reversals in their global magnetic fields. ... More
The energy budget of stellar magnetic fieldsAug 06 2015Spectropolarimetric observations have been used to map stellar magnetic fields, many of which display strong bands of azimuthal fields that are toroidal. A number of explanations have been proposed to explain how such fields might be generated though ... More
Properties of the Bare Nucleus of Comet 96P/Machholz 1Mar 21 2019Apr 10 2019We observed comet 96P/Machholz 1 on a total of 9 nights before and after perihelion during its 2017/2018 apparition. Both its unusually small perihelion distance and the observed fragmentation during multiple apparitions make 96P an object of great interest. ... More
Comet 322P/SOHO 1: An asteroid with the smallest perihelion distance?Apr 26 2016We observed comet 322P/SOHO 1 (P/1999 R1) from the ground and with the Spitzer Space Telescope when it was between 2.2 and 1.2 AU from the Sun. These are the first observations of any SOHO-discovered periodic comet by a non-solar observatory, and allow ... More
Poset Pattern-Avoidance Problems Posed by YakoubovAug 13 2016Feb 21 2017Extending the work of Yakoubov, we enumerate the linear extensions of comb posets that avoid certain length-$3$ patterns. We resolve many of Yakoubov's open problems and prove both of the conjectures from her paper.
Invariant distributions and X-ray transform for Anosov flowsAug 20 2014Dec 21 2015For Anosov flows preserving a smooth measure on a closed manifold $\mathcal{M}$, we define a natural self-adjoint operator $\Pi$ which maps into the space of invariant distributions in $\cap_{u<0} H^{u}(\mathcal{M})$ and whose kernel is made of coboundaries ... More
The finiteness theorem for invariants of a finite group (translation of Emmy Noether's "Der Endlichkeitsatz der Invarianten endlicher Gruppen")Mar 22 2015A translation of Emmy Noether's paper "Der Endlichkeitsatz der Invarianten endlicher Gruppen" (Mathematische Annalen, vol. 77, 1920, pages 89--92). In Noether's words, the paper gives "an entirely elementary finiteness proof---using only the theory of ... More
Fertility, Strong Fertility, and Postorder Wilf EquivalenceApr 05 2019We introduce "fertility Wilf equivalence," "strong fertility Wilf equivalence," and "postorder Wilf equivalence," three variants of Wilf equivalence for permutation classes that formalize some phenomena that have appeared in the study of West's stack-sorting ... More
Descents in $t$-Sorted PermutationsApr 04 2019Let $s$ denote West's stack-sorting map. A permutation is called $t-\textit{sorted}$ if it is of the form $s^t(\mu)$ for some permutation $\mu$. We prove that the maximum number of descents that a $t$-sorted permutation of length $n$ can have is $\left\lfloor\frac{n-t}{2}\right\rfloor$. ... More
Proofs of Conjectures about Pattern-Avoiding Linear ExtensionsMay 07 2019After fixing a canonical ordering (or labeling) of the elements of a finite poset, one can associate each linear extension of the poset with a permutation. Some recent papers consider specific families of posets and ask how many linear extensions give ... More
Enumeration of Stack-Sorting Preimages via a Decomposition LemmaApr 04 2019We give three applications of a recently-proven "Decomposition Lemma," which allows one to count preimages of certain sets of permutations under West's stack-sorting map $s$. We first enumerate the permutation class $s^{-1}(\text{Av}(231,321))=\text{Av}(2341,3241,45231)$, ... More
Measurement of air fluorescence light yield induced by an electromagnetic showerMar 09 2007Oct 20 2008For most of the Ultra-High-Energy-Cosmic-Ray (UHECR) experiments and projects (HiRes, AUGER, TA, JEM-EUSO, TUS,...), the detection technique of Extensive Air Showers is based, at least, on the measurement of the air-fluorescence-induced signal. The knowledge ... More
Measurement of air and nitrogen fluorescence light yields induced by electron beam for UHECR experimentsDec 04 2006Most of the Ultra High Energy Cosmic Ray (UHECR) experiments and projects (HiRes, AUGER, TA, EUSO, TUS,...) use air fluorescence to detect and measure extensive air showers (EAS). The precise knowledge of the Fluorescence Light Yield (FLY) is of paramount ... More
Sensitivity analysis for the average treatment effect in paired observational studiesSep 07 2016A method for conducting a sensitivity analysis for the average treatment effect in a paired observational study is presented. It is shown that, in the limit, the power of a sensitivity analysis for the average treatment effect under a constant treatment ... More
Nonlocal pure spin current injection via quantum pumping and crossed Andreev reflectionFeb 24 2005Jul 12 2005A pure spin current injector is proposed based on adiabatic pumping and crossed normal/Andreev reflection. The device consists of a three-terminal ferromagnet-superconductor-semiconductor system in which the injection of a pure spin current is into the ... More
Quantum spin pumping with adiabatically modulated magnetic barrier'sMar 29 2003Dec 09 2003A quantum pump device involving magnetic barriers produced by the deposition of ferro magnetic stripes on hetero-structure's is investigated. The device for dc- transport does not provide spin-polarized currents, but in the adiabatic regime, when one ... More
The discriminant and oscillation lengths for contact and Legendrian isotopiesMay 09 2012Jul 19 2013We define an integer-valued non-degenerate bi-invariant metric (the discriminant metric) on the universal cover of the identity component of the contactomorphism group of any contact manifold. This metric has a very simple geometric definition, based ... More
A partial answer to the Demyanov-Ryabova conjectureFeb 01 2017Sep 06 2017In this work we are interested in the Demyanov--Ryabova conjecture for a finite family of polytopes. The conjecture asserts that after a finite number of iterations (successive dualizations), either a 1-cycle or a 2-cycle eventually comes up. In this ... More
On the Kodaira dimension of maximal ordersNov 30 2016Jun 23 2017Let ${k}$ be an algebraically closed field of characteristic zero and let ${K}$ be a field finitely generated over ${k}$. Let $\Sigma$ be a central simple ${K}$-algebra, $X$ a normal projective model of ${K}$ and $\Lambda$ a sheaf of maximal $\mathcal{O}_X$-orders ... More
On nodal Enriques surfaces and quartic double solidsDec 16 2010We consider the class of singular double coverings $X \to \PP^3$ ramified in the degeneration locus $D$ of a family of 2-dimensional quadrics. These are precisely the quartic double solids constructed by Artin and Mumford as examples of unirational but ... More
Homological behavior of idempotent subalgebras and Ext algebrasMar 25 2017Oct 11 2017Let $A$ be a (left and right) Noetherian ring that is semiperfect. Let $e$ be an idempotent of $A$ and consider the ring $\Gamma:=(1-e)A(1-e)$ and the semi-simple right $A$-module $S_e : = eA/e{\rm rad}A$. In this paper, we investigate the relationship ... More
Transforming the content, pedagogy and structure of an introductory physics course for life sciences majorsSep 15 2017In this paper, we describe how we transformed our large-enrollment introductory physics sequence for life-science students to a Lecture/Studio format and aligned the physics concepts with authentic biological applications. We have reformed the pedagogy ... More
Lenses as an Atom-Photon Interface: A Semiclassical ModelDec 03 2010Strong interaction between the light field and an atom is often achieved with cavities. Recent experiments have used a different configuration: a propagating light field is strongly focused using a system of lenses, the atom being supposed to sit at the ... More
A classification of spanning surfaces for alternating linksMay 24 2012A classification of spanning surfaces for alternating links is provided up to genus, orientability, and a new invariant that we call aggregate slope. That is, given an alternating link, we determine all possible combinations of genus, orientability, and ... More
Phototactic Clustering of Swimming Micro-organisms in a Turbulent Velocity FieldFeb 05 2008We study the distribution of swimming micro-organisms advected by a model turbulent flow and attracted towards a localised light source through phototaxis. It is shown that particles aggregate along a dynamical attractor with fractal measure whose dimension ... More
Low dimensional orders of finite representation typeMay 23 2018In this paper, we study noncommutative surface singularities arising from orders. The singularities we study are mild in the sense that they have finite representation type or, equivalently, are log terminal in the sense of the Mori minimal model program ... More
Méthode de Mahler, transcendance et relations linéaires : aspects effectifsOct 28 2016This note deals with some effective results in Mahler's method. In a recent work, we used a theorem of Philippon to show that given a Mahler function $f(z)$ in ${\bf k}\{z\}$, where ${\bf k}$ denotes a number field, and an algebraic number $\alpha$ in ... More
Radiative forcings for 28 potential Archean greenhouse gasesSep 05 2014Despite reduced insolation in the late Archean, evidence suggests a warm climate which was likely sustained by a stronger greenhouse effect, the so-called Faint Young Sun Problem (FYSP). CO2 and CH4 are generally thought to be the mainstays of this enhanced ... More
Efficient glueball simulations on anisotropic latticesApr 22 1997Monte Carlo results for the low-lying glueball spectrum using an improved, anisotropic action are presented. Ten simulations at lattice spacings ranging from 0.2 to 0.4 fm and two different anisotropies have been performed in order demonstrate the advantages ... More
On interchanging the states of a pair of quditsNov 10 2008The qubit SWAP gate has been shown to be an integral component of quantum circuitry design. It permutes the states of two qubits and allows for the storage quantum information, teleportation of atomic or ionic states, and is a fundamental element in the ... More
Recognition of unipolar and generalised split graphsApr 04 2016A graph is unipolar if it can be partitioned into a clique and a disjoint union of cliques, and a graph is a generalised split graph if it or its complement is unipolar. A unipolar partition of a graph can be used to find efficiently the clique number, ... More
Random Perfect GraphsApr 04 2016Sep 05 2017We investigate the asymptotic structure of a random perfect graph $P_n$ sampled uniformly from the perfect graphs on vertex set $\{1,\ldots,n\}$. Our approach is based on the result of Pr\"omel and Steger that almost all perfect graphs are generalised ... More
Hamilton cycles, minimum degree and bipartite holesApr 04 2016Apr 19 2016We present a tight extremal threshold for the existence of Hamilton cycles in graphs with large minimum degree and without a large ``bipartite hole`` (two disjoint sets of vertices with no edges between them). This result extends Dirac's classical theorem, ... More
Resolvent at low energy and Riesz transform for Schroedinger operators on asymptotically conic manifolds. IIMar 12 2007Let $(M^\circ, g)$ be an asymptotically conic manifold, in the sense that $M^\circ$ compactifies to a manifold with boundary $M$ in such a way that $g$ becomes a scattering metric on $M$. A special case of particular interest is that of asymptotically ... More
An extension of the Duistermaat-Singer Theorem to the semi-classical Weyl algebraFeb 18 2009Motivated by many recent works (by L. Charles, V. Guillemin, T. Paul, J. Sj\"ostrand, A. Uribe, S. Vu Ngoc, S. Zelditch and others) on the semi-classical Birkhoff normal forms, we investigate the structure of the group of automorphisms of the graded semi-classical ... More
Finite Implication AlgebrasFeb 01 2009We consider several distinct characterizations of finite implication algebras. One of these leads to a new characterization of Boolean polymatroids.
Wave 0-Trace and length spectrum on convex co-compact hyperbolic manifoldsJun 09 2006Apr 30 2012For quotients of the $n+1$-dimensional hyperbolic space by a convex co-compact group $\Gamma$, we obtain a formula relating the renormalized trace of the wave operator with the resonances of the Laplacian and some conformal invariants of the boundary, ... More
The marked length spectrum of Anosov manifoldsJun 11 2018Oct 23 2018In all dimensions, we prove that the marked length spectrum of a Riemannian manifold $(M,g)$ with Anosov geodesic flow and non-positive curvature locally determines the metric in the sense that two close enough metrics with the same marked length spectrum ... More