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The binary companion mass ratio distribution: an imprint of the star formation process?Apr 10 2013We explore the effects of dynamical evolution in dense clusters on the companion mass ratio distribution (CMRD) of binary stars. Binary systems are destroyed by interactions with other stars in the cluster, lowering the total binary fraction and significantly ... More

CO(1-0) in z>2 Quasar Host Galaxies: No Evidence for Extended Molecular Gas ReservoirsJun 13 2011We report the detection of CO(1-0) emission in the strongly lensed high-redshift quasars IRAS F10214+4724 (z=2.286), the Cloverleaf (z=2.558), RX J0911+0551 (z=2.796), SMM J04135+10277 (z=2.846), and MG 0751+2716 (z=3.200), using the Expanded Very Large ... More

Tori in symplectic 4-manifoldsNov 19 2003Sep 29 2004We study the question of how many embedded symplectic or Lagrangian tori can represent the same homology class in a simply connected symplectic 4-manifold.

Surgery on Nullhomologous ToriNov 18 2011Nov 28 2011By studying the example of smooth structures on CP^2#3(-CP^2) we illustrate how surgery on a single embedded nullhomologous torus can be utilized to change the symplectic structure, the Seiberg-Witten invariant, and hence the smooth structure on a 4-manifold. ... More

Invariants for Lagrangian toriApr 25 2003Jul 09 2004We define an simple invariant of an embedded nullhomologous Lagrangian torus and use this invariant to show that many symplectic 4-manifolds have infinitely many pairwise symplectically inequivalent nullhomologous Lagrangian tori. We further show that ... More

GREENBURST: a commensal fast radio burst search back-end for the Green Bank TelescopeMar 13 2019We describe the design and deployment of GREENBURST, a commensal Fast Radio Burst (FRB) search system at the Green Bank Telescope. GREENBURST uses the dedicated L-band receiver tap to search over the 960$-$1920 MHz frequency range for pulses with dispersion ... More

Exotic group actions on simply connected smooth 4-manifoldsFeb 05 2009Sep 17 2009We produce infinite families of exotic actions of finite cyclic groups on simply connected smooth 4-manifolds with nontrivial Seiberg-Witten invariants.

Rational surfaces and symplectic 4-manifolds with one basic classFeb 19 2002May 26 2002We present constructions of simply connected symplectic 4-manifolds which have (up to sign) one basic class and which fill up the geographical region between the half-Noether and Noether lines.

On The Origin of HI in Galaxies: Photodissociation and the ``Schmidt Law'' for Global Star FormationMay 13 2002Young stars in the disks of galaxies produce HI from their parent H2 clouds by photodissociation. This process is widespread in late-type galaxies, and follows the distribution of Far-UV photons produced primarily by B-type stars. An estimate of the amount ... More

Station-Keeping Requirements for Constellations of Free-Flying Collectors Used for Astronomical Imaging in SpaceJul 02 2007The accuracy requirements on station-keeping for constellations of free-flying collectors coupled as (future) imaging arrays in space for astrophysics applications are examined. The basic imaging element of these arrays is the two-element interferometer. ... More

Photodissociation and the Morphology of HI in GalaxiesJun 30 2004Young massive stars produce Far-UV photons which dissociate the molecular gas on the surfaces of their parent molecular clouds. Of the many dissociation products which result from this ``back-reaction'', atomic hydrogen \HI is one of the easiest to observe ... More

On The Origin Of HI In Galaxies: The Sizes and Masses of HI Photodissociation RegionsMar 06 2002Young stars in the disks of galaxies produce HI from their parent H2 clouds by photodissociation. This paper describes the observational evidence for and the morphology of such HI. Simple estimates of the amount of dissociated gas lead to the startling ... More

A quantum theory of distance along a curveFeb 13 2014Apr 16 2014We present a quantum theory of distances along a curve, based on a linear line element that is equal to the operator square root of the quadratic metric of Riemannian geometry. Since the linear line element is an operator, we treat it according to the ... More

Six easy roads to the Planck scaleJan 08 2010We give six arguments that the Planck scale should be viewed as a fundamental minimum or boundary for the classical concept of spacetime, beyond which quantum effects cannot be neglected and the basic nature of spacetime must be reconsidered. The arguments ... More

Galaxy MorphologyFeb 02 2011Galaxy morphology is a product of how galaxies formed, how they interacted with their environment, how they were influenced by internal perturbations, AGN, and dark matter, and of their varied star formation histories. This article reviews the phenomenology ... More

Will we ever classify simply-connected smooth 4-manifolds?Feb 08 2005Feb 25 2005These notes are adapted from two talks given at the 2004 Clay Institute Summer School on Floer homology, gauge theory, and low dimensional topology at the Alfred Renyi Institute. We will quickly review what we do and do not know about the existence and ... More

Cold Molecular Gas, PDRs, and the Origin of HI in GalaxiesMar 01 2001In the currently-accepted model for star formation out of the interstellar gas in galaxies, the basic construction material is assumed to be large clouds of atomic hydrogen (HI). These clouds are thought to form higher-density complexes of gas and dust, ... More

Some mixed character sum identities of KatzJul 20 2016Apr 30 2017A conjecture connected with quantum physics led N. Katz to discover some amazing mixed character sum identities over a field of $q$ elements, where $q$ is a power of a prime $p>3$. His proof required deep algebro-geometric techniques, and he expressed ... More

Towards Benchmarking Scene Background InitializationJun 12 2015Given a set of images of a scene taken at different times, the availability of an initial background model that describes the scene without foreground objects is the prerequisite for a wide range of applications, ranging from video surveillance to computational ... More

A Metric Approach to Elastic ReformationsJul 17 2012Jul 28 2013We study a variational framework to compare shapes, modeled as Radon measures on R^N, in order to quantify how they differ from isometric copies. To this purpose we discuss some notions of weak deformations termed reformations as well as integral functionals ... More

The fundamental groupoid of the quotient of a Hausdorff space by a discontinuous action of a discrete group is the orbit groupoid of the induced actionDec 19 2002The main result is that the fundamental groupoid of the orbit space of a discontinuous action of a discrete group on a Hausdorff space which admits a universal cover is the orbit groupoid of the fundamental groupoid of the space. We also describe work ... More

Secular Evolution and the Morphological Transformation of Cluster and Field GalaxiesOct 20 2006Deep surveys conducted during the past decades have shown that galaxies in the distant universe are generally of more irregular shapes, and are disky in appearance and in their star formation rate, compared to galaxies in similar environments in the nearby ... More

Crowded-Field Astrometry with SIM PlanetQuest. II. An Improved Instrument ModelMay 29 2008In a previous paper we described a method of estimating the single-measurement bias to be expected in astrometric observations of targets in crowded fields with the future Space Interferometry Mission (SIM). That study was based on a simplified model ... More

Galaxy Secular Mass Flow Rate Determination Using the Potential-Density Phase Shift Approach: Application to Six Nearby Spiral GalaxiesAug 22 2016Using the potential-density phase shift approach developed by the present authors in earlier publications, we estimate the magnitude of radial mass accretion/excretion rates across the disks of six nearby spiral galaxies having a range of Hubble types. ... More

Measuring Time of Flight Using Satellite-Based ClocksOct 12 2011Nov 18 2011Considering the OPERA neutrino-velocity measurement from the point of view of a GPS satellite we find that the detector at Gran Sasso has a velocity component in the order of $10^{-5}c$ towards the neutrino emission location at CERN. On GPS-receivers ... More

Crowded-Field Astrometry with the Space Interferometry Mission - I. Estimating the Single-Measurement Astrometric Bias Arising from ConfusionOct 23 2007Oct 25 2007The accuracy of position measurements on stellar targets with the future Space Interferometry Mission (SIM) will be limited not only by photon noise and by the properties of the instrument (design, stability, etc.) and the overall measurement program ... More

The GBT Gain Curve at High FrequencyOct 31 2018Recent measurements at Q-band (43 GHz) have verified the improved performance of the GBT provided by the updated gravity model that was deployed in the fall of 2014. The measured gain curve is indistinguishable from 1.0 over an elevation range from 15 ... More

Transport Problems and Disintegration MapsJul 17 2012By disintegration of transport plans it is introduced the notion of transport class. This allows to consider the Monge problem as a particular case of the Kantorovich transport problem, once a transport class is fixed. The transport problem constrained ... More

OH as an Alternate Tracer for Molecular Gas: Excitation Temperatures of the OH 18-cm Main Lines in W5Mar 26 2018We present excitation temperatures $T_{ex}$ for the OH 18-cm main lines at 1665 and 1667 MHz measured directly in front of the W5 star-forming region, using observations from the Green Bank Telescope and the Very Large Array. We find unequivocally that ... More

BVRI Photometry of the Classic Type II-P Supernova 2017eaw in NGC 6946: Day 3 to Day 594May 08 2019Broadband $BVRI$ light curves of SN 2017eaw in NGC 6946 reveal the classic elements of a Type II-P supernova. The observations were begun on 16 May 2017 (UT), approximately 1 day after the discovery was announced, and the photometric monitoring was carried ... More

Discovery of a strong spiral magnetic field crossing the inner pseudoring of NGC 4736Mar 04 2008We report the discovery of a coherent magnetic spiral structure within the nearby ringed Sab galaxy NGC 4736. High sensitivity radio polarimetric data obtained with the VLA at 8.46GHz and 4.86GHz show a distinct ring of total radio emission precisely ... More

Superdense Coding Interleaved with Forward Error CorrectionJan 23 2016Apr 13 2016Superdense coding promises increased classical capacity and communication security but this advantage may be undermined by noise in the quantum channel. We present a numerical study of how forward error correction (FEC) applied to the encoded classical ... More

Saturn's upper atmosphere during the Voyager era: Reanalysis and modeling of the UVS occultationsAug 08 2014The Voyager 1 and 2 Ultraviolet Spectrometer (UVS) solar and stellar occultation dataset represents one of the primary, pre-Cassini sources of information that we have on the neutral upper atmosphere of Saturn. Despite its importance, however, the full ... More

Radio & Optical Interferometry: Basic Observing Techniques and Data AnalysisJan 13 2012Astronomers usually need the highest angular resolution possible, but the blurring effect of diffraction imposes a fundamental limit on the image quality from any single telescope. Interferometry allows light collected at widely-separated telescopes to ... More

Forbidden Subgraphs for Chorded PancyclicitySep 20 2017We call a graph $G$ pancyclic if it contains at least one cycle of every possible length $m$, for $3\le m\le |V(G)|$. In this paper, we define a new property called chorded pancyclicity. We explore forbidden subgraphs in claw-free graphs sufficient to ... More

Cold Molecular Gas as a Possible Component of Dark Matter in the Outer Parts of Disk GalaxiesMar 16 2004In the last few years new evidence has been presented for the presence of ongoing massive star formation in the outer HI disks of galaxies. These discoveries strongly suggest that precursor molecular gas must also be present in some physical state which ... More

The Production of HI in Photodissociation Regions and A Comparison with CO(1-0) EmissionFeb 16 2004The gas at the surfaces of molecular clouds in galaxies is heated and dissociated by photons from young stars both near and far. HI resulting from the dissociation of molecular hydrogen H2 emits hyperfine line emission at 21 cm, and warmed CO emits dipole ... More

Set-theoretical solutions of the pentagon equation on groupsFeb 12 2019Let $M$ be a set. A set-theoretical solution of the pentagon equation on $M$ is a map $s:M\times M\longrightarrow M\times M$ such that \begin{equation*} s_{23}\, s_{13}\, s_{12}=s_{12}\, s_{23}, \end{equation*} where $s_{12}=s\times id_M$, $s_{23}=id_M ... More

A 1.1 to 1.9 GHz SETI Survey of the Kepler Field: I. A Search for Narrow-band Emission from Select TargetsFeb 04 2013We present a targeted search for narrow-band (< 5 Hz) drifting sinusoidal radio emission from 86 stars in the Kepler field hosting confirmed or candidate exoplanets. Radio emission less than 5 Hz in spectral extent is currently known to only arise from ... More

Diffuse HI Disks in Isolated GalaxiesJun 15 2007In order to investigate the contribution of diffuse components to their total HI emission, we have obtained high precision HI line flux densities with the 100m Green Bank Telescope for a sample of 100 isolated spiral and irregular galaxies which we have ... More

Reconstructing Galaxy Histories from Globular ClustersJan 19 2004Nearly a century after the true nature of galaxies as distant "island universes" was established, their origin and evolution remain great unsolved problems of modern astrophysics. One of the most promising ways to investigate galaxy formation is to study ... More

Babcock Redux: An Ammendment of Babcock's Schematic of the Sun's Magnetic CycleJun 16 2016We amend Babcock's original scenario for the global dynamo process that sustains the Sun's 22-year magnetic cycle. The amended scenario fits post-Babcock observed features of the magnetic activity cycle and convection zone, and is based on ideas of Spruit ... More

The minimal representation of the conformal group and classic solutions to the wave equationJan 15 2009We give a uniform realization of the minimal representation of a double cover of the conformal group SO(2,n+1)_0 in the kernel of the wave operator on flat Minkowski space as a positive energy representation H^+ for n even and odd. Using this realization, ... More

The Structure of Dark Molecular Gas in the Galaxy - I: A Pilot Survey for 18-cm OH Emission Towards $l \approx 105^°, b \approx +1^°$Feb 02 2015We report the first results from a survey for 1665, 1667, and 1720 MHz OH emission over a small region of the Outer Galaxy centered at $l \approx 105.0\deg , b \approx +1.0\deg$ . This sparse, high-sensitivity survey ($\Delta Ta \approx \Delta Tmb \approx ... More

Crossed complexes, and free crossed resolutions for amalgamated sums and HNN-extensions of groupsJul 03 2002The category of crossed complexes gives an algebraic model of CW-complexes and cellular maps. Free crossed resolutions of groups contain information on a presentation of the group as well as higher homological information. We relate this to the problem ... More

Stochastic domain decomposition for time dependent adaptive mesh generationApr 01 2015The efficient generation of meshes is an important component in the numerical solution of problems in physics and engineering. Of interest are situations where global mesh quality and a tight coupling to the solution of the physical partial differential ... More

An Effective Photon Momentum in a Dielectric Medium: A Relativistic ApproachNov 24 2017Jan 15 2018We use a relativistic argument to define an effective photon that travels through a transparent (non-absorbing) nondispersive dielectric medium of index of refraction $n$. If $p$ is the momentum of the photon in a vacuum, then the momentum of an effective ... More

Method for characterizing bulk recombination using photoinduced absorptionMar 17 2017The influence of reaction order and trap-assisted recombination on continuous-wave photoinduced absorption measurements is clarified through analytical calculations and numerical simulations. The results reveal the characteristic influence of different ... More

Texture features for the reproduction of the perceptual organization of soundMay 15 2017Human categorization of sound seems predominantly based on sound source properties. To estimate these source properties we propose a novel sound analysis method, which separates sound into different sonic textures: tones, pulses, and broadband noises. ... More

Dependence of nuclear spin singlet lifetimes on RF spin-locking powerJan 06 2012We measure the lifetime of long-lived nuclear spin singlet states as a function of the strength of the RF spin-locking field and present a simple theoretical model that agrees well with our measurements, including the low-RF-power regime. We also measure ... More

Searching for Synergism Among Combinations of Drugs of Abuse and the Use of Isobolographic AnalysisFeb 21 2012It is well known that individuals who abuse drugs usually use more than one substance. Toxic consequences of single and multiple drug use are well documented in the Treatment Episodes Data Set that lists combinations that result in hospital admissions. ... More

Ionized Gas in the Smith CloudAug 12 2009We present Wisconsin H-Alpha Mapper observations of ionized gas in the Smith Cloud, a high velocity cloud which Lockman et al. have recently suggested is interacting with the Galactic disk. Our H-alpha map shows the brightest H-alpha emission, 0.43 \pm ... More

A terrestrial search for dark contents of the vacuum, such as dark energy, using atom interferometryJan 28 2011We describe the theory and first experimental work on our concept for searching on earth for the presence of dark content of the vacuum (DCV) using atom interferometry. Specifically, we have in mind any DCV that has not yet been detected on a laboratory ... More

Scaling Exponents of Rough Surfaces Generated by the Domany-Kinzel Cellular AutomatonSep 24 2001The critical behavior at the frozen/active transition in the Domany-Kinzel stochastic cellular automaton (DKCA) is studied {\it via} a surface growth process in (1+1) dimensions. At criticality, this process presents a kinetic roughening transition; we ... More

Anomalous H_2CO Absorption Towards the Galactic Anticenter: A Blind Search for Dense Molecular CloudsJul 27 2006We have carried out a blind search in the general direction of the Galactic Anticenter for absorption of the Cosmic Microwave Background (CMB) radiation near 4.83 GHz by molecular clouds containing gaseous ortho-formaldehyde (H_2CO). The observations ... More

The Opacity of Nearby Galaxies from Counts of Background Galaxies: II. Limits of the Synthetic Field MethodDec 03 2002Recently, we have developed and calibrated the Synthetic Field Method (SFM) to derive the total extinction through disk galaxies. The method is based on the number counts and colors of distant background field galaxies that can be seen through the foreground ... More

Schur positivity of skew Schur function differences and applications to ribbons and Schubert classesJun 22 2007Dec 14 2007Some new relations on skew Schur function differences are established both combinatorially using Sch\"utzenberger's jeu de taquin, and algebraically using Jacobi-Trudi determinants. These relations lead to the conclusion that certain differences of skew ... More

Ionized Gas in the Smith CloudJan 06 2009We present WHAM observations of Halpha, [N II], and [S II] in the Smith Cloud. A map of Halpha emission from the cloud shows ionized gas coincident with the brightest H I emission, but nearly-as-bright Halpha in some regions with faint H I. The ionized ... More

Preparation of Nuclear Spin Singlet States using Spin-Lock Induced CrossingJul 02 2013We introduce a broadly applicable technique to create nuclear spin singlet states in organic molecules and other many-atom systems. We employ a novel pulse sequence to produce a spin-lock induced crossing (SLIC) of the spin singlet and triplet energy ... More

Revisiting the critical behavior of nonequilibrium models in Short-time Monte Carlo SimulationsApr 02 2004We analyze two alternative methods for determining the exponent $z$ of the contact process (CP) and Domany-Kinzel (DK) cellular automaton in Monte Carlo Simulations. One method employs mixed initial conditions, as proposed for magnetic models [Phys. Lett. ... More

Sandpiles with height restrictionsMar 27 2002We study stochastic sandpile models with a height restriction in one and two dimensions. A site can topple if it has a height of two, as in Manna's model, but, in contrast to previously studied sandpiles, here the height (or number of particles per site), ... More

A Point Source Excess in Abell 1185: Intergalactic Globular Clusters?Jan 08 2003Deep imaging with WFPC2 and the Hubble Space Telescope has been used to search for a population of intergalactic globular clusters (GCs) belonging to Abell 1185, a richness I cluster at cz = 9800 km/s. The field is noteworthy in that it contains no bright ... More

Formation of OB Associations in GalaxiesMay 04 2007We consider the formation of OB associations from two perspectives: (a) the fractional gas consumption in star formation,epsilon, per dynamical time scale t_dyn in a galaxy, and (b) the origin of the so-called Kennicutt-Schmidt law that the rate of star ... More

Spectral and structural stability properties of charged particle dynamics in coupled latticesApr 16 2015It has been realized in recent years that coupled focusing lattices in accelerators and storage rings have significant advantages over conventional uncoupled focusing lattices, especially for high-intensity charged particle beams. A theoretical framework ... More

On the exhaustive generation of convex permutominoesOct 16 2008A permutomino of size n is a polyomino determined by a pair of permutations of size n+1, such that they differ in each position. In this paper, after recalling some enumerative results about permutominoes, we give a first algorithm for the exhaustive ... More

A new variational approach to linearization of traction problems in elasticityNov 26 2018A new energy functional for pure traction problems in elasticity has been deduced in [23] as the variational limit of nonlinear elastic energy functional for a material body subject to an equilibrated force field: a sort of Gamma limit with respect to ... More

Euler's optimal profile problemApr 15 2019We study an old variational problem formulated by Euler as Proposition 53 of his `Scientia Navalis' by means of the direct method of the calculus of variations. Precisely, through relaxation arguments, we prove the existence of minimizers. We fully investigate ... More

$N$-player games and mean-field games with smooth dependence on past absorptionsFeb 07 2019Mean-field games with absorption is a class of games, that have been introduced in Campi and Fischer [7] and that can be viewed as natural limits of symmetric stochastic differential games with a large number of players who, interacting through a mean-field, ... More

The Discovery of a New Massive Molecular Gas Component Associated with the Submillimeter Galaxy SMM J02399-0136May 18 2018We present CO(1-0), CO(3-2), and CO(7-6) observations using the Green Bank Telescope (GBT) and the Atacama Large Millimeter Array (ALMA) of the z=2.8 sub-millimeter galaxy SMM J02399-0136. This was the first submillimeter-selected galaxy discovered and ... More

On the Continuing Formation of the Andromeda Galaxy: Detection of HI Clouds in the M31 HaloNov 25 2003Green Bank Telescope (GBT) 21cm observations have revealed a faint, yet extensive HI cloud population surrounding the Andromeda Galaxy (M31). The newfound objects are likely analogs to the high-velocity HI clouds (HVCs) seen around the Milky Way. At least ... More

A note on evolutionary stochastic portfolio optimization and probabilistic constraintsJan 29 2010In this note, we extend an evolutionary stochastic portfolio optimization framework to include probabilistic constraints. Both the stochastic programming-based modeling environment as well as the evolutionary optimization environment are ideally suited ... More

Exact sequences of fibrations of crossed complexes, homotopy classification of maps, and nonabelian extensions of groupsFeb 29 2008Jun 25 2008The classifying space of a crossed complex generalises the construction of Eilenberg-Mac Lane spaces. We show how the theory of fibrations of crossed complexes allows the analysis of homotopy classes of maps from a free crossed complex to such a classifying ... More

J. L. Doob: Foundations of stochastic processes and probabilistic potential theorySep 23 2009During the three decades from 1930 to 1960 J. L. Doob was, with the possible exception of Kolmogorov, the man most responsible for the transformation of the study of probability to a mathematical discipline. His accomplishments were recognized by both ... More

A new higher homotopy groupoid: the fundamental globular omega-groupoid of a filtered spaceFeb 22 2007We use the n-globe with its skeletal filtration to define the fundamental globular omega--groupoid of a filtered space; the proofs use an analogous fundamental cubical omega--groupoid due to the author and Philip Higgins. This method also relates the ... More

Nonabelian Algebraic TopologyJul 15 2004Jul 27 2004This talk gave a sketch of the contents and background to a book with the title `Nonabelian algebraic topology' being written under support of a Leverhulme Emeritus Fellowship (2002-2004) by the speaker and Rafael Sivera (Valencia). The aim is to give ... More

Towards non commutative algebraic topologyMay 12 2003This is a slightly edited version of the transparencies for a seminar at UCL, May 7, 2003. It is intended to give a quick view of background, ideas, and some calculations, in the applicatioon of some non commutative methods to algebraic topology.

Double groupoids, matched pairs and then matched triplesApr 08 2011In this note we show that the known relation between double groupoids and matched pairs of groups may be extended, or seems to extend, to the triple case. The references give some other occurrences of double groupoids.

M Dwarf Exoplanet Surface Density Distribution: A Log-Normal Fit from 0.07-400 AUJul 17 2017We fit a log-normal function to the M dwarf orbital surface density distribution of gas giant planets, over the mass range 1-10 times that of Jupiter, from 0.07-400 AU. We use a Markov Chain Monte Carlo approach to explore the likelihoods of various parameter ... More

Nonlinear waves in adhesive stringsMar 24 2016We study a 1D semilinear wave equation modeling the dynamic of an elastic string interacting with a rigid substrate through an adhesive layer. The constitutive law of the adhesive material is assumed elastic up to a finite critical state, beyond such ... More

Egocentric Hand Track and Object-based Human Action RecognitionMay 02 2019Egocentric vision is an emerging field of computer vision that is characterized by the acquisition of images and video from the first person perspective. In this paper we address the challenge of egocentric human action recognition by utilizing the presence ... More

Supernova Detection in IceCube: Status and FutureFeb 08 2013The IceCube detector, located at the South Pole, is discussed as a detector for core collapse supernovae. The large flux of $\bar{\nu}_{e}$ from a Galactic supernova gives rise to Cherenkov light from positrons and electrons created in neutrino interactions ... More

Duality theory for Markov processes: Part 1Feb 11 2010This is the first part of a possible monograph on the duality of Markov processes. It contains a proof of Fitzsimmons' existence theorem of a moderate Markov dual process relative to an excessive measure, m, together with the necessary preliminary material. ... More

Moore hyperrectangles on a space form a strict cubical omega-categorySep 11 2009Sep 21 2009A question of Jack Morava is answered by generalising the notion of Moore paths to that of Moore hyperrectangles, so obtaining a strict cubical omega-category. This also has the structure of connections in the sense of Brown and Higgins, but cancellation ... More

Possible connections between whiskered categories and groupoids, many object Leibniz algebras, automorphism structures and local-to-global questionsAug 13 2007Jul 28 2010We define the notion of whiskered categories and groupoids, showing that whiskered groupoids have a commutator theory. So also do whiskered $R$-categories, thus answering questions of what might be `commutative versions' of these theories. We relate these ... More

Crossed modules and the homotopy 2-type of a free loop spaceMar 29 2010May 23 2010The question was asked by Niranjan Ramachandran: how to describe the fundamental groupoid of LX, the free loop space of a space X? We give an answer by assuming X to be the classifying space of a crossed module over a group, and then describe completely ... More

Modelling and Computing Homotopy Types: IOct 24 2016Feb 03 2017The aim of this article is to explain a philosophy for applying higher dimensional Seifert-van Kampen Theorems, and how the use of groupoids and strict higher groupoids resolves some foundational anomalies in algebraic topology at the border between homology ... More

Covering morphisms of groupoids, derived modules and a 1-dimensional Relative Hurewicz TheoremDec 13 2010Mar 19 2017We fill a lacuna in the literature by giving a version in dimension 1 of the Relative Hurewicz Theorem, and relate this to abelianisations of groupoids, covering spaces and covering morphisms of groupoids, and Crowell's notion of derived modules.

Three themes in the work of Charles Ehresmann: Local-to-global; Groupoids; Higher dimensionsFeb 22 2006Mar 04 2006This paper illustrates the themes of the title in terms of: van Kampen type theorems for the fundamental groupoid; holonomy and monodromy groupoids; and higher homotopy groupoids. Interaction with work of the writer is explored.

Computing Homotopy Types Using Crossed N-Cubes of GroupsSep 14 2001Aug 13 2006The aim of this paper is to explain how, through the work of a number of people, some algebraic structures related to groupoids have yielded algebraic descriptions of homotopy n-types. Further, these descriptions are explicit, and in some cases completely ... More

On point processes in multitarget trackingMar 08 2016Mar 02 2018The finite-set statistics (FISST) approach to multitarget tracking was introduced in the mid-1990s. Its current extended form dates from 2001. In 2008, an "elementary" alternative to FISST was proposed, based on "finite point processes" rather than RFS's. ... More

An Evolutionary Optimization Approach to Risk Parity Portfolio SelectionNov 27 2014Jan 19 2015In this paper we present an evolutionary optimization approach to solve the risk parity portfolio selection problem. While there exist convex optimization approaches to solve this problem when long-only portfolios are considered, the optimization problem ... More

Beyond the Imry-Ma Length: Scaling Behavior in the 3D Random Field $XY$ ModelDec 13 2018We have performed studies of the 3D random field $XY$ model on $L \times L \times L$ simple cubic lattices with periodic boundary conditions, with a random field strength of $h_r$ = 1.875, for $L =$ 64, 96 and 128, using a parallelized Monte Carlo algorithm. ... More

Continuously variable spreading exponents in the absorbing Nagel-Schreckenberg modelJun 19 2018I study the critical behavior of a traffic model with an absorbing state. The model is a variant of the Nagel-Schreckenberg (NS) model, in which drivers do not decelerate if their speed is smaller than their headway, the number of empty sites between ... More

Percentile rank scores are congruous indicators of relative performance, or aren't they?Aug 09 2011Percentile ranks and the I3 indicator were introduced by Bornmann, Leydesdorff, Mutz and Opthof. These two notions are based on the concept of percentiles (or quantiles) for discrete data. As several definitions for these notions exist we propose one ... More

Embeddability of Arrangements of Pseudocircles into the SphereAug 17 2005An arrangement of pseudocircles is a finite set of oriented closed Jordan curves each two of which cross each other in exactly two points. To describe the combinatorial structure of arrangements on closed orientable surfaces, in (Linhart, Ortner 2004) ... More

Groupoids, the Phragmen-Brouwer Property and the Jordan Curve TheoremJul 09 2006We publicise a proof of the Jordan Curve Theorem which relates it to the Phragmen-Brouwer Property, and whose proof uses the van Kampen theorem for the fundamental groupoid on a set of base points.

Crossed complexes and homotopy groupoids as non commutative tools for higher dimensional local-to-global problemsDec 19 2002Oct 10 2008We outline the main features of the definitions and applications of crossed complexes and cubical $\omega$-groupoids with connections. These give forms of higher homotopy groupoids, and new views of basic algebraic topology and the cohomology of groups, ... More

Measuring the Sizes, Shapes, Surface Features and Rotations of Solar System Objects with InterferometryFeb 03 2011We consider the application of interferometry to measuring the sizes and shapes of small bodies in the solar system that cannot be spatially resolved by today's single-dish telescopes. Assuming ellipsoidal shapes, our results indicate that interferometers ... More

Solid-State Thermal Energy Storage Using Reversible Martensitic TransformationsJan 21 2019The identification and use of reversible Martensitic transformations, typically described as shape memory transformations, as a new class of solid-solid phase change material is experimentally demonstrated here for the first time. To prove this claim, ... More

Physics of Solar Neutron Production: Questionable Detection of Neutrons from the 2007 December 31 FlareJul 14 2010May 05 2011Spacecraft observations in the inner heliosphere offer the first opportunity to measure 1-10 MeV solar neutrons. We discuss the physics of low-energy neutron production in solar flares and show that, even at interacting-particle energies of 2 MeV/nucleon, ... More