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Results for "Benjamin J. Walker"

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Identifying flagella from videomicroscopy: exploiting a conserved morphologyAug 03 2018Ubiquitous in eukaryotic microorganisms, the flagellum is a well-studied and highly-functional organelle that is well-known to be responsible for motility in a variety of organisms. Pertinent to multiple areas of active scientific interest is the understanding ... More
A new basis for filament simulation in three dimensionsJul 10 2019Jul 11 2019Simulations of slender inextensible filaments in a viscous fluid are often plagued by numerical stiffness. Recent coarse-graining studies have reduced the computational requirements of such systems, though have thus far been limited to the motion of planar ... More
Filament mechanics in a half-space via regularised Stokeslet segmentsApr 02 2019We present a generalisation of efficient numerical frameworks for modelling fluid-filament interactions via the discretisation of a recently-developed, non-local integral equation formulation to incorporate regularised Stokeslets with half-space boundary ... More
Collective excitation profiles and the dynamics of photonic condensatesSep 24 2018Photonic condensates are complex systems exhibiting phase transitions due to the interaction with their molecular environment. Given the macroscopic number of molecules that form a reservoir of excitations, numerical simulations are expensive, even for ... More
Filament mechanics in a half-space via regularised Stokeslet segmentsApr 02 2019Apr 09 2019We present a generalisation of efficient numerical frameworks for modelling fluid-filament interactions via the discretisation of a recently-developed, non-local integral equation formulation to incorporate regularised Stokeslets with half-space boundary ... More
The pairwise hydrodynamic interactions of synchronized spermatozoaJun 01 2019The journey of mammalian spermatozoa in nature is well-known to be reliant on their individual motility. Often swimming in crowded microenvironments, the progress of any single swimmer is likely dependent on their interactions with other nearby swimmers. ... More
A new basis for filament simulation in three dimensionsJul 10 2019Simulations of slender inextensible filaments in a viscous fluid are often plagued by numerical stiffness. Recent coarse-graining studies have reduced the computational requirements of such systems, though have thus far been limited to the motion of planar ... More
Inferring Information Flow in Spike-train Data Sets using a Trial-Shuffle MethodFeb 17 2018Oct 25 2018Understanding information processing in the brain requires the ability to determine the functional connectivity between the different regions of the brain. We present a method using transfer entropy to extract this flow of information between brain regions ... More
Boundary behaviours of Leishmania mexicana: a hydrodynamic simulation studyJun 01 2018Nov 16 2018It is well established that the parasites of the genus Leishmania exhibit complex surface interactions with the sandfly vector midgut epithelium, but no prior study has considered the details of their hydrodynamics. Here, the boundary behaviours of motile ... More
Non-critical slowing down of photonic condensationSep 24 2018We investigate the response of a photonic gas interacting with a reservoir of pumped dye-molecules to quenches in the pump power. In addition to the expected dramatic critical slowing down of the equilibration time around phase transitions we find extremely ... More
Bose-Einstein condensation of photons from the thermodynamic limit to small photon numbersJun 29 2017Photons can come to thermal equilibrium at room temperature by scattering multiple times from a fluorescent dye. By confining the light and dye in a microcavity, a minimum energy is set and the photons can then show Bose-Einstein condensation. We present ... More
Driven-dissipative Bose-Einstein condensation of just a few photonsNov 29 2017Coherence and correlations are defining features of quantum condensates. These condensates are inherently multimode phenomena and in the macroscopic limit it becomes extremely difficult to resolve populations of individual modes and correlations among ... More
Beneficial influence of Hf and Zr additions to Nb4at.%Ta on the vortex pinning of Nb$_{3}$Sn with and without an O sourceNov 21 2018Here we show that addition of Hf to Nb4Ta can significantly improve the high field performance of Nb$_{3}$Sn, making it suitable for dipole magnets for Future Circular Collider (FCC). A big challenge for the FCC is that a realistic production target for ... More
Measuring the Black Hole Spin in Sgr A*May 11 2001The polarized mm/sub-mm radiation from Sgr A* is apparently produced by a Keplerian structure whose peak emission occurs within several Schwarzschild radii (r_S=2GM/c^2) of the black hole. The Chandra X-ray counterpart, if confirmed, is presumably the ... More
Driven-dissipative, non-equilibrium Bose-Einstein condensation of just a few photonsNov 29 2017May 15 2018Coherence is a defining feature of quantum condensates. These condensates are inherently multimode phenomena and in the macroscopic limit it becomes extremely difficult to resolve populations of individual modes and the coherence between them. In this ... More
Propagation Speed of Longitudinally Oscillating Gravitational and Electrical FieldsJun 27 1997Jul 28 1997The near-field Lienard-Wiechert potential solution of a longitudinally oscillating electrical field produced by an oscillating charge is presented, and the results are compared to the R. P. Feynman multipole far-field solution. The results indicate that ... More
Quantum corrections to the Larmor radiation formula in scalar electrodynamicsAug 19 2009We use the semi-classical approximation in perturbative scalar quantum electrodynamics to calculate the quantum correction to the Larmor radiation formula to first order in Planck's constant in the non-relativistic approximation, choosing the initial ... More
Classical and quantum radiation reaction in conformally flat spacetimeMar 10 2009May 29 2009We investigate the physics of a charged scalar particle moving in conformally flat spacetime with the conformal factor depending only on time in the framework of quantum electrodynamics (QED). In particular, we show that the radiation-reaction force derived ... More
NNLO QCD Corrections to Jet Production in Charged Current Deep Inelastic ScatteringJul 06 2018The production of jets in charged current deep inelastic scattering (CC DIS) constitutes a class of observables that can be used to simultaneously test perturbative predictions for the strong and the electroweak sectors of the Standard Model. We compute ... More
A Partial Homogenization Result for Nonconvex Viscous Hamilton-Jacobi EquationsFeb 21 2014We provide a general result concerning the homogenization of nonconvex viscous Hamilton-Jacobi equations in the stationary, ergodic setting. In particular, we show that homogenization occurs for a non-empty set of points within every level set of the ... More
Symmetric subgroup orbit closures on flag varieties: Their equivariant geometry, combinatorics, and connections with degeneracy lociJan 20 2012Jun 29 2012We give explicit formulas for torus-equivariant fundamental classes of closed $K$-orbits on the flag variety $G/B$ when $G$ is one of the classical groups $SL(n,\C)$, $SO(n,\C)$, or $Sp(2n,\C)$, and $K$ is a symmetric subgroup of $G$. We describe parametrizations ... More
Analytical solutions for nonlinear plasma waves with time-varying complex frequencyMay 07 2019May 17 2019Bernstein-Kruskal-Greene (or BGK) modes are ubiquitous nonlinear solutions for the 1D electrostatic Vlasov equation, with the particle distribution function $f$ given as a function of the particle energy. Here, we consider other solutions $f = f[\epsilon]$ ... More
Fast post-hoc method for updating moments of large datasetsDec 21 2018Moments of large datasets utilise the mean of the dataset; consequently, updating the dataset traditionally requires one to update the mean, which then requires one to recalculate the moment. This means that metrics such as the standard deviation, $R^2$ ... More
A Character Formula for the Category ÕNov 05 2007Jul 14 2008One may construct, for any function on the integers, an irreducible module of level zero for affine sl(2), using the values of the function as structure constants. The modules constructed using exponential-polynomial functions realise the irreducible ... More
Schubert calculus of Richardson varieties stable under spherical Levi subgroupsSep 04 2012Feb 13 2013We observe that the expansion in the basis of Schubert cycles for $H^*(G/B)$ of the class of a Richardson variety stable under a spherical Levi subgroup is described by a theorem of Brion. Using this observation, along with a combinatorial model of the ... More
Maximum elastic deformations of compact stars with exotic equations of stateMar 17 2005Nov 15 2005I make the first estimates of maximum elastic quadrupole deformations sustainable by alternatives to conventional neutron stars. Solid strange quark stars might sustain maximum ellipticities (dimensionless quadrupoles) up to a few times $10^{-4}$ rather ... More
Kernel Phase and Kernel Amplitude in Fizeau ImagingSep 01 2016Kernel phase interferometry is an approach to high angular resolution imaging which enhances the performance of speckle imaging with adaptive optics. Kernel phases are self-calibrating observables that generalize the idea of closure phases from non-redundant ... More
A Liouville Property for Isotropic Diffusions in Random EnvironmentJun 05 2014We obtain a Liouville property for stationary diffusions in random environment which are small, isotropic perturbations of Brownian motion in spacial dimension greater than two. Precisely, we prove that, on a subset of full probability, the constant functions ... More
On The Existence of an Invariant Measure for Isotropic Diffusions in Random EnvironmentApr 21 2014The results of this paper build upon those first obtained by Sznitman and Zeitouni in [11]. We establish, for spacial dimensions greater than two, the existence of a unique invariant measure for isotropic diffusions in random environment which are small ... More
Exit Laws of Isotropic Diffusions in Random Environment from Large DomainsJan 23 2016This paper studies, in dimensions greater than two, stationary diffusion processes in random environment which are small, isotropic perturbations of Brownian motion satisfying a finite range dependence. Such processes were first considered in the continuous ... More
Macroscopic Symmetry Group Describes Josephson Tunneling in Twinned CrystalsAug 28 1996A macroscopic symmetry group describing the superconducting state of an orthorhombically twinned crystal of YBCO is introduced. This macroscopic symmetry group is different for different symmetries of twin boundaries. Josephson tunneling experiments performed ... More
U(2)-chiral symmetries of supersymmetric QED3Mar 14 1997Jun 23 1997Supersymmetry is studied in 2+1 dimensions. In addition to the multiplets corresponding to those in 3+1 dimensions the Clifford algebra allows an extra set. When the extra chiral multiplet is included, formulating supersymmetric QED3 in the manner of ... More
A High Accuracy Stochastic Estimation of a Nonlinear Deterministic ModelNov 12 2015In this paper, an approach to estimating a nonlinear deterministic model is presented. We introduce a stochastic model with extremely small variances so that the deterministic and stochastic models are essentially indistinguishable from each other. This ... More
GL(p) x GL(q)-orbit closures on the flag variety and Schubert structure constants for (p,q)-pairsSep 02 2011Sep 05 2012We give positive combinatorial descriptions of Schubert structure constants $c_{u,v}^w$ for the full flag variety in type $A_{n-1}$ when $u$ and $v$ form what we refer to as a "$(p,q)$-pair" ($p+q=n$). The key observation is that a certain subset of the ... More
Some conjectures regarding certain Schubert structure constants in Lie types B and DFeb 13 2013I give the details of some conjectures regarding Schubert calculus in Lie types B and D. Specifically, I conjecture rules for Schubert structure constants $c_{u,v}^w$ when $X_{w_0u}^v$ is a Richardson variety stable under the spherical Levi subgroup $\C^* ... More
K-orbit closures on G/B as universal degeneracy loci for flagged vector bundles splitting as direct sumsJan 08 2013Oct 07 2015We use equivariant localization and divided difference operators to determine formulas for the torus-equivariant fundamental cohomology classes of $K$-orbit closures on the flag variety $G/B$ for various symmetric pairs $(G,K)$. In type $A$, we realize ... More
K-orbits on G/B and Schubert constants for pairs of signed shuffles in types C and DSep 12 2011Jun 28 2012We give positive descriptions for certain Schubert structure constants $c_{u,v}^w$ for the full flag variety in Lie types $C$ and $D$. This is accomplished by first observing that a number of the $K=GL(n,\C)$-orbit closures on these flag varieties coincide ... More
Deep slitless infrared spectroscopic surveys with HST/WFC3Sep 06 2012HST is commonly thought of as an optical-IR imaging or UV-spectroscopy observatory. However, the advent of WFC3-IR made it possible to do slitless infrared spectroscopic surveys over an area significant for galaxy evolution studies (~0.15 deg^2). Slitless ... More
Analytical solutions for nonlinear plasma waves with time-varying complex frequencyMay 07 2019We analytically examine the time evolution of plasma waves with time-varying complex frequency $\gamma - i \omega$ in the linear and nonlinear phases. Using a Laplace-like decomposition of the electric potential, we give allowed solutions for the time-varying ... More
The Status of the MicroBooNE ExperimentOct 07 2011The MicroBooNE experiment is an upcoming liquid argon TPC experiment which will pursue a program of short baseline neutrino physics in the Fermilab Booster Neutrino Beam, starting in early 2014. I give a description of the experiment and review the current ... More
A fault-tolerant non-Clifford gate for the surface code in two dimensionsMar 27 2019Magic-state distillation, used to perform non-Clifford gates, consumes an overwhelming majority of the resources of a surface code architecture for universal quantum computing. Here we show how to perform a fault-tolerant non-Clifford gate with the surface ... More
Matroids and Geometric Invariant Theory of torus actions on flag spacesNov 24 2005Feb 14 2006We apply a theorem of Gel'fand, Goresky, MacPherson, and Serganova about matroid polytopes to study semistability of partial flags relative to a T-linearized ample line bundle of a flag space F = SL(n)/P where T is a maximal torus in SL(n) and P is a ... More
Stochastic Homogenization of Monotone Systems of Viscous Hamilton-Jacobi Equations with Convex NonlinearitiesMay 08 2012We consider the homogenization of monotone systems of viscous Hamilton-Jacobi equations with convex nonlinearities set in the stationary, ergodic setting. The primary focus of this paper is on collapsing systems which, as the microscopic scale tends to ... More
Imaginary highest-weight representation theory and symmetric functionsFeb 28 2007Affine Lie algebras admit non-classical highest-weight theories through alternative partitions of the root system. Although significant inroads have been made, much of the classical machinery is inapplicable in this broader context, and some fundamental ... More
Josephson tunneling in high-$T_c$ superconductorsApr 01 1996This article describes the Josephson tunneling from time-reversal symmetry-breaking states and compares it with that from time-reversal invariant states for both twinned and untwinned crystals and for both $c$-axis and basal-plane currents, in a model ... More
Nonperturbative Vertices in Supersymmetric Quantum ElectrodynamicsApr 21 1999We derive the complete set of supersymmetric Ward identities involving only two- and three- point proper vertices in supersymmetric QED. We also present the most general form of the proper vertices consistent with both the supersymmetric and U(1) gauge ... More
Generic Connectivity-Based CGRA Mapping via Integer Linear ProgrammingJan 30 2019Coarse-grained reconfigurable architectures (CGRAs) are programmable logic devices with large coarse-grained ALU-like logic blocks, and multi-bit datapath-style routing. CGRAs often have relatively restricted data routing networks, so they attract CAD ... More
Optical CagesJul 16 2018Dec 06 2018We examine array of metal-mesh frameworks for their wide-band absorption. These take the form of quasi-crystal optical cages. An array of cages tends to focus the incoming radiation within each framework. An array of cage-within-cage funnels the radiation ... More
K-orbit closures on G/B as universal degeneracy loci for flagged vector bundles with symmetric or skew-symmetric bilinear formJun 28 2012Feb 13 2013We use equivariant localization and divided difference operators to determine formulas for the torus-equivariant fundamental cohomology classes of $K$-orbit closures on the flag variety $G/B$, where $G = GL(n,\C)$, and where $K$ is one of the symmetric ... More
The Bruhat order on clansOct 07 2015Oct 08 2015We give an explicit description of the closure containment order (or "Bruhat order") on the set of orbits of GL_p \times GL_q on the flag variety GL_{p+q}/B, relative to the parametrization of the orbits by combinatorial objects called "clans". This leads ... More
The dark matter density problem in massive disk galaxiesOct 22 2003I discuss measurements of disk mass from non-circular streaming motions of gas in the barred galaxies NGC 3095 and NGC 4123. In these galaxies with strong shocks and non-circular motions, the inner regions must be disk-dominated to reproduce the shocks. ... More
Representations of Truncated Current Lie AlgebrasJun 20 2007Oct 16 2007Let g denote a Lie algebra, and let T(g) denote the tensor product of g with a ring of truncated polynomials. The Lie algebra T(g) is called a truncated current Lie algebra. The highest-weight representation theory of T(g) is developed, and a reducibility ... More
Highest-Weight Theory for Truncated Current Lie AlgebrasMay 09 2007Let g denote a Lie algebra over a field of characteristic zero, and let T(g) denote the tensor product of g with a ring of truncated polynomials. The Lie algebra T(g) is called a truncated current Lie algebra, or in the special case when g is finite-dimensional ... More
On the Exit Time and Stochastic Homogenization of Isotropic Diffusions in Large DomainsFeb 28 2016Stochastic homogenization is achieved for a class of elliptic and parabolic equations describing the lifetime, in large domains, of stationary diffusion processes in random environment which are small, statistically isotropic perturbations of Brownian ... More
Flipping SU(5) out of TroubleMay 30 2002Minimal supersymmetric SU(5) GUTs are being squeezed by the recent values of alpha_s, sin^2 theta_W, the lower limit on the lifetime for p to nubar K decay, and other experimental data. We show how the minimal flipped SU(5) GUT survives these perils, ... More
Dense Atom Clouds in a Holographic Atom TrapNov 08 2002We demonstrate the production of high density cold atom samples (2e14 atoms/cc) in a simple optical lattice formed with YAG light that is diffracted from a holographic phase plate. A loading protocol is described that results in 10,000 atoms per lattice ... More
Chiral Symmetry in Supersymmetric Three Dimensional Quantum ElectrodynamicsJan 17 1999Mar 17 1999We describe the investigation of spontaneous mass-generation and chiral symmetry breaking in supersymmetric QED3 using numerical solutions of the Dyson-Schwinger equation together with the CJT effective action and supersymmetric Ward identities. We find ... More
The Discrete and Continuous Painleve VI Hierarchy and the Garnier SystemsJan 25 2000We present a general scheme to derive higher-order members of the Painleve VI (PVI) hierarchy of ODE's as well as their difference analogues. The derivation is based on a discrete structure that sits on the background of the PVI equation and that consists ... More
Monomial Valuations, Cusp Singularities, and Continued FractionsNov 25 2013Aug 12 2014This paper explores the relationship between real valued monomial valuations on $k(x,y)$, the resolution of cusp singularities, and continued fractions. It is shown that up to equivalence there is a one to one correspondence between real valued monomial ... More
Size of the group IVA iron meteorite core: Constraints from the age and composition of MuonionalustaJun 13 2011The group IVA fractionally crystallized iron meteorites display a diverse range of metallographic cooling rates. These have been attributed to their formation in a metallic core, approximately 150 km in radius, that cooled to crystallization in the absence ... More
Network analyses of 4D genome datasets automate detection of community-scale gene structure and plasticitySep 18 2018Oct 01 2018Chromosome conformation capture and Hi-C technologies provide gene-gene proximity datasets of stationary cells, revealing chromosome territories, topologically associating domains, and chromosome topology. Imaging of tagged DNA sequences in live cells ... 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
From Declarative Languages to Declarative Processing in Computer GamesSep 09 2009Recent work has shown that we can dramatically improve the performance of computer games and simulations through declarative processing: Character AI can be written in an imperative scripting language which is then compiled to relational algebra and executed ... More
Synthesizing Symmetric LensesOct 26 2018Jun 25 2019Lenses are programs that can be run both "front to back" and "back to front," allowing updates to either their source or their target data to be transferred in both directions. Lenses have been extensively studied, extended, and applied. Recent work has ... More
Emulating satellite drag from large simulation experimentsDec 01 2017Mar 07 2019Obtaining accurate estimates of satellite drag coefficients in low Earth orbit is a crucial component in positioning and collision avoidance. Simulators can produce accurate estimates, but their computational expense is much too large for real-time application. ... More
Synthesizing Bijective LensesOct 09 2017Bidirectional transformations between different data representations occur frequently in modern software systems. They appear as serializers and deserializers, as database views and view updaters, and more. Manually building bidirectional transformations---by ... More
Transient crosslinking kinetics optimize gene cluster interactionsSep 18 2018May 21 2019Our understanding of how chromosomes structurally organize and dynamically interact has been revolutionized through the lens of long-chain polymer physics. Major protein contributors to chromosome structure and dynamics are condensin and cohesin that ... More
Synthesizing Symmetric LensesOct 26 2018Lenses are programs that can be run both "front to back" and "back to front," allowing data and updates to be transformed in two directions. Since their introduction, lenses have been extensively studied and applied. Recent work has also demonstrated ... More
Emulating satellite drag from large simulation experimentsDec 01 2017Jun 22 2019Obtaining accurate estimates of satellite drag coefficients in low Earth orbit is a crucial component in positioning and collision avoidance. Simulators can produce accurate estimates, but their computational expense is much too large for real-time application. ... More
A note on triangulations of sum setsNov 03 2013For finite sets A and B in the plane, we write A+B to denote the set of sums of the elements of A and B. In addition, we write tr(A) to denote the common number of triangles in any triangulation of the convex hull of A using the points of A as vertices. ... More
Combinatorial results on (1,2,1,2)-avoiding $GL(p,\mathbb{C}) \times GL(q,\mathbb{C})$-orbit closures on $GL(p+q, \mathbb{C})/B$Mar 03 2014Using recent results of the second author which explicitly identify the "$(1,2,1,2)$-avoiding" $GL(p,\mathbb{C}) \times GL(q,\mathbb{C})$-orbit closures on the flag manifold $GL(p+q,\mathbb{C})/B$ as certain Richardson varieties, we give combinatorial ... More
Non-radiative decay and stability of $N$-heterocyclic carbene iridium(III) complexesMar 08 2018Devices based on deep-blue emitting iridium (III) complexes with N-heterocyclic carbene (NHC) ligands have recently been shown to give excellent performance as phosphorescent organic light-emitting diodes (PHOLEDs). To facilitate the design of even better ... More
Discussion of "Statistical Modeling of Spatial Extremes" by A. C. Davison, S. A. Padoan and M. RibatetAug 17 2012Discussion of "Statistical Modeling of Spatial Extremes" by A. C. Davison, S. A. Padoan and M. Ribatet [arXiv:1208.3378].
Maximum gravitational-wave energy emissible in magnetar flaresFeb 16 2011Recent searches of gravitational-wave (GW) data raise the question of what maximum GW energies could be emitted during gamma-ray flares of highly magnetized neutron stars (magnetars). The highest energies (\sim 10^{49} erg) predicted so far come from ... More
Dynamical locality of the free Maxwell fieldMar 27 2014May 09 2014We consider the non-interacting source-free Maxwell field, described both in terms of the vector potential and the field strength. Starting from the classical field theory on contractible globally hyperbolic spacetimes, we extend the classical field theory ... More
Skip-gram word embeddings in hyperbolic spaceAug 30 2018Embeddings of tree-like graphs in hyperbolic space were recently shown to surpass their Euclidean counterparts in performance by a large margin. Inspired by these results, we present an algorithm for learning word embeddings in hyperbolic space from free ... More
Universal fault-tolerant measurement-based quantum computationNov 28 2018Certain physical systems that one might consider for fault-tolerant quantum computing where qubits do not readily interact, for instance photons, are better suited for measurement-based quantum-computational protocols. We develop a framework to map fault-tolerant ... More
Equilibrium states for products of flows and the mixing properties of rank 1 geodesic flowsJun 21 2019Jun 27 2019Equilibrium states for geodesic flows over closed rank 1 manifolds were studied recently by Burns, Climenhaga, Fisher and Thompson. For sufficiently regular potentials, it was shown that if the singular set does not carry full pressure then the equilibrium ... More
Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+Nov 29 2011Observations of H3+ in the Galactic diffuse interstellar medium (ISM) have led to various surprising results, including the conclusion that the cosmic-ray ionization rate (zeta_2) is about 1 order of magnitude larger than previously thought. The present ... More
Exact Matrix Completion via Convex OptimizationMay 29 2008We consider a problem of considerable practical interest: the recovery of a data matrix from a sampling of its entries. Suppose that we observe m entries selected uniformly at random from a matrix M. Can we complete the matrix and recover the entries ... More
Equilibrium states for products of flows and the mixing properties of rank 1 geodesic flowsJun 21 2019Equilibrium states for geodesic flows over closed rank 1 manifolds were studied recently by Burns, Climenhaga, Fisher and Thompson. For sufficiently regular potentials, it was shown that if the singular set does not carry full pressure then the equilibrium ... More
Pulsar TeV Halos Explain the TeV Excess Observed by MilagroJul 06 2017Milagro observations have found bright, diffuse TeV emission concentrated along the galactic plane of the Milky Way. The intensity and spectrum of this emission is difficult to explain with current models where gamma-ray production is dominated by hadronic ... More
Skip-gram word embeddings in hyperbolic spaceAug 30 2018May 27 2019Recent work has demonstrated that embeddings of tree-like graphs in hyperbolic space surpass their Euclidean counterparts in performance by a large margin. Inspired by these results and scale-free structure in the word co-occurrence graph, we present ... More
Topology and metastability in the lattice Skyrme modelAug 02 2000We offer the Skyrme model on a lattice as an effective field theory - fully quantized - of baryon-meson interactions at temperatures below the chiral phase transition. We define a local topological density that involves the volumes of tetrahedra in the ... More
Polynomials for GL_p x GL_q orbit closures in the flag varietyAug 12 2013Mar 04 2014The subgroup K=GL_p x GL_q of GL_{p+q} acts on the (complex) flag variety GL_{p+q}/B with finitely many orbits. We introduce a family of polynomials that specializes to representatives for cohomology classes of the orbit closures in the Borel model. We ... More
The Complexity of Reasoning with FODD and GFODDJul 05 2014Feb 20 2015Recent work introduced Generalized First Order Decision Diagrams (GFODD) as a knowledge representation that is useful in mechanizing decision theoretic planning in relational domains. GFODDs generalize function-free first order logic and include numerical ... More
Entropy and mixing for amenable group actionsMay 01 2000For \Gamma a countable amenable group consider those actions of \Gamma as measure-preserving transformations of a standard probability space, written as {T_\gamma}_{\gamma \in \Gamma} acting on (X,{\cal F}, \mu). We say {T_\gamma}_{\gamma\in\Gamma} has ... More
Asymptotic Phase for Stochastic OscillatorsNov 06 2014Jan 18 2015Oscillations and noise are ubiquitous in physical and biological systems. When oscillations arise from a deterministic limit cycle, entrainment and synchronization may be analyzed in terms of the asymptotic phase function. In the presence of noise, the ... More
Testing two nuclear physics approximations used in the standard leaky box model for the spallogenic production of LiBeBFeb 05 2003The spallative production rates of Lithium, Beryllium and Boron (LiBeB) are a necessary component in any calculation of the evolution of these nuclei in the Galaxy. Previous calculations of these rates relied on two assumptions relating to the nuclear ... More
Characterizing a Dramatic $ΔV\sim-9$ Flare on an Ultracool Dwarf Found by the ASAS-SN SurveyOct 16 2013Nov 21 2013We analyze a $\Delta V\sim-9$ magnitude flare on the newly identified M8 dwarf SDSS J022116.84+194020.4 (hereafter SDSSJ0221) detected as part of the All-Sky Automated Survey for Supernovae (ASAS-SN). Using infrared and optical spectra, we confirm that ... More
The Spallagenic Production Rates of Lithium, Beryllium and BoronAug 04 2000We calculate the production rates of Li6, Li7, Be9, B10 and B11 via spallation of Carbon, Nitrogen and Oxygen nuclei by protons and alpha-particles and by alpha-alpha fusion reactions. We include recent measurements of the cross sections of alpha-alpha ... More
Transforming a large introductory lab course: impacts on views about experimental physicsJul 11 2018Laboratory courses are key components of most undergraduate physics programs. Lab courses often aim to achieve the following learning outcomes: developing students' experimental skills, engaging students in authentic scientific practices, reinforcing ... More
The Importance of Metric Learning for Robotic Vision: Open Set Recognition and Active LearningFeb 27 2019State-of-the-art deep neural network recognition systems are designed for a static and closed world. It is usually assumed that the distribution at test time will be the same as the distribution during training. As a result, classifiers are forced to ... More
Phase descriptions of a multidimensional Ornstein-Uhlenbeck processMay 24 2019Stochastic oscillators play a prominent role in different fields of science. Their simplified description in terms of a phase has been advocated by different authors using distinct phase definitions in the stochastic case. One notion of phase that we ... More
Polynomials for symmetric orbit closures in the flag varietyOct 27 2013Sep 30 2014In [Wyser-Yong '13] we introduced polynomial representatives of cohomology classes of orbit closures in the flag variety, for the symmetric pair $(GL_{p+q}, GL_p \times GL_q)$. We present analogous results for the remaining symmetric pairs of the form ... More
Mechanism Design for Subadditive Agents via an Ex-Ante RelaxationMar 11 2016Aug 09 2016We consider the problem of maximizing revenue for a monopolist offering multiple items to multiple heterogeneous buyers. We develop a simple mechanism that obtains a constant factor approximation under the assumption that the buyers' values are additive ... More
On the Good-$λ$ inequality for nonlinear potentialsMay 31 2011This note concerns an extension of the good-$\lambda$ inequality for fractional integrals, due to B. Muckenhoupt and R. Wheeden. The classical result is refined in two aspects. Firstly, general nonlinear potentials are considered; and secondly, the constant ... More
Pure quasifree states of the Dirac field from the fermionic projectorAug 07 2014Sep 26 2014We consider the quantised free Dirac field on oriented and globally hyperbolic ultrastatic slab spacetimes with compact spatial section and demonstrate how a gauge invariant, pure and quasifree state on the C*-completion of the self-dual CAR-algebra can ... More
A Lagrangian stochastic model of a volcanic eruption columnApr 06 2018We develop a Lagrangian stochastic model (LSM) of a volcanic plume in which the mean flow is provided by an integral plume model of the eruption column and fluctuations in the vertical velocity are modelled by a suitably constructed stochastic differential ... More
Random Walks on Hypergraphs with Edge-Dependent Vertex WeightsMay 20 2019Hypergraphs are used in machine learning to model higher-order relationships in data. While spectral methods for graphs are well-established, spectral theory for hypergraphs remains an active area of research. In this paper, we use random walks to develop ... More