Results for "Michelle Chalupnik"

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Measuring Electromagnetic and Gravitational Responses of Photonic Landau LevelsFeb 13 2018The topology of an object describes global properties that are insensitive to local perturbations. Classic examples include string knots and the genus (number of handles) of a surface: no manipulation of a closed string short of cutting it changes its ... More
Moduli spaces for families of rational maps on P^1Feb 11 2009Feb 15 2009Let phi: P^1 --> P^1 be a rational map defined over a field K. We construct the moduli space M_d(N) parameterizing conjugacy classes of degree-d maps with a point of formal period N and present an algebraic proof that M_2(N) is geometrically irreducible ... More
Detecting essential surfaces as intersections in the character varietySep 15 2016We describe a family of hyperbolic knots whose character variety contain exactly two distinct components of characters of irreducible representations. The intersection points between the components carry rich topological information. In particular, these ... More
Dynamics on the PSL(2,C)-character variety of a twisted I-bundleMar 17 2011Let M be a twisted interval bundle over a nonorientable hyperbolizable surface. Let X(M) be the PSL(2,C)-character variety of \pi_1(M). We examine the dynamics of the action of Out(\pi_1(M)) on X(M), and in particular, we find an open set on which the ... More
Dynamics on the PSL(2,C)-character variety of a compression bodyJul 02 2013Let M be a nontrivial compression body without toroidal boundary components. We study the dynamics of the group of outer automorphisms of the fundamental group of M on the PSL(2,C)-character variety of M.
Annotation Enrichment Analysis: An Alternative Method for Evaluating the Functional Properties of Gene SetsAug 20 2012May 03 2013Gene annotation databases (compendiums maintained by the scientific community that describe the biological functions performed by individual genes) are commonly used to evaluate the functional properties of experimentally derived gene sets. Overlap statistics, ... More
The norm of the Euler classSep 13 2010We prove that the norm of the Euler class E for flat vector bundles is $2^{-n}$ (in even dimension $n$, since it vanishes in odd dimension). This shows that the Sullivan--Smillie bound considered by Gromov and Ivanov--Turaev is sharp. We construct a new ... More
Sum list coloring, the sum choice number, and sc-greedy graphsMay 08 2013Let G=(V,E) be a graph and let f be a function that assigns list sizes to the vertices of G. It is said that G is f-choosable if for every assignment of lists of colors to the vertices of G for which the list sizes agree with f, there exists a proper ... More
The absence of phase transition for the classical XY-model on Sierpinski pyramid with fractal dimension D=2Aug 27 2010For the spin models with continuous symmetry on regular lattices and finite range of interactions the lower critical dimension is d=2. In two dimensions the classical XY-model displays Berezinskii-Kosterlitz-Thouless transition associated with unbinding ... More
Milnor-Wood inequalities for productsJan 01 2012We prove Milnor-Wood inequalities for local products of manifolds. As a consequence, we establish the generalized Chern Conjecture for products $M\times \Sigma^k$ for any product of a manifold $M$ with a product of $k$ copies of a surface $\Sigma$ for ... More
Tailoring Native Defects in LiFePO4: Insights from First-Principles CalculationsMay 17 2011We report first-principles density-functional theory studies of native point defects and defect complexes in olivine-type LiFePO4, a promising candidate for rechargeable Li-ion battery electrodes. The defects are characterized by their formation energies ... More
On a recursive construction of circular paths and the search for $π$ on the integer lattice $\mathbb{Z}^2$Feb 04 2016Digital circles not only play an important role in various technological settings, but also provide a lively playground for more fundamental number-theoretical questions. In this paper, we present a new recursive algorithm for the construction of digital ... More
Separable-stable representations of a compression bodyNov 06 2013Let M be a hyperbolizable, nontrivial compression body without toroidal boundary components. In this paper, we characterize which discrete and faithful representations of the fundamental group of M into PSL(2,C) are separable-stable. The set of separable-stable ... More
Finding New Order in Biological Functions from the Network Structure of Gene AnnotationsSep 28 2012May 03 2013The Gene Ontology (GO) provides biologists with a controlled terminology that describes how genes are associated with functions and how functional terms are related to each other. These term-term relationships encode how scientists conceive the organization ... More
The field of definition for dynamical systems on P^NSep 26 2013Let Hom^N_d be the set of morphisms of degree d from P^N to itself. For f an element of PGL_{N+1}, let phi^f represent the conjugation action f^{-1} phi f. Let M^N_d = Hom_d^N/PGL_{N+1} be the moduli space of degree d morphisms of P^N. A field of definition ... More
Network Coding: Is zero error always possible?Feb 15 2011Oct 02 2011In this work we study zero vs. epsilon-error capacity in network coding instances. For multicast network coding it is well known that all rates that can be delivered with arbitrarily small error probability can also be delivered with zero error probability; ... More
Explicit Descriptions of Quadratic Maps on $\pp^1$ defined over a field $K$Apr 15 2010Jul 30 2010We describe an explicit parameter space for the set of all quadratic rational maps on $\pp^1$ defined over a field $K$, up to conjugacy over $K$.
The generalized Chern conjecture for manifolds that are locally a product of surfacesFeb 09 2009May 23 2009We consider closed manifolds that admit a metric locally isometric to a product of symmetric planes. For such manifolds, we prove that the Euler characteristic is an obstruction to the existence of flat structures, confirming an old conjecture proved ... More
Milnor-Wood inequalities for manifolds locally isometric to a product of hyperbolic planesApr 12 2008This note describes sharp Milnor--Wood inequalities for the Euler number of flat oriented vector bundles over closed Riemannian manifolds locally isometric to products of hyperbolic planes. One consequence is that such manifolds do not admit an affine ... More
Galois theory of quadratic rational functionsJan 23 2011May 04 2012For a number field K with absolute Galois group G_K, we consider the action of G_K on the infinite tree of preimages of a point in K under a degree-two rational function phi, with particular attention to the case when phi commutes with a non-trivial Mobius ... More
The simplicial volume of closed manifolds covered by H^2 x H^2Mar 20 2007Sep 13 2007We compute the value of the simplicial volume for closed, oriented Riemannian manifolds covered by $\mathbb{H}^{2}\times\mathbb{H}^{2}$ explicitly, thus in particular for products of closed hyperbolic surfaces. This gives the first exact value of a nonvanishing ... More
Penalty approximation for non smooth constraints in vibroimpactApr 10 2000We examine the penalty approximation of the free motion of a material point in an angular domain; we choose an over-damped penalty, and we prove that if the first impact point is not at the vertex, then, the limit of the approximation exists and is described ... More
On the use of analytic expressions for the voltage distribution to analyze intracellular recordingsFeb 09 2006Different analytic expressions for the membrane potential distribution of membranes subject to synaptic noise have been proposed, and can be very helpful to analyze experimental data. However, all of these expressions are either approximations or limit ... More
Cyclic sieving and rational Catalan theoryOct 28 2015Let $a < b$ be coprime positive integers. Armstrong, Rhoades, and Williams defined a set $\mathsf{NC}(a,b)$ of `rational noncrossing partitions', which form a subset of the ordinary noncrossing partitions of $\{1, 2, \dots, b-1\}$. Confirming a conjecture ... More
A tree metric using structure and length to capture distinct phylogenetic signalsJul 18 2015Sep 11 2015Phylogenetic trees are a central tool in understanding evolution. They are typically inferred from sequence data, and capture evolutionary relationships through time. It is essential to be able to compare trees from different data sources (e.g. several ... More
Effective Field Theory for Bound State ReflectionJun 27 2012Jan 17 2013Elastic quantum bound-state reflection from a hard-wall boundary provides direct information regarding the structure and compressibility of quantum bound states. We discuss elastic quantum bound-state reflection and derive a general theory for elastic ... More
Small generators of cocompact arithmetic Fuchsian groupsMar 02 2016In the study of Fuchsian groups, it is a nontrivial problem to determine a set of generators. Using a dynamical approach we construct for any cocompact arithmetic Fuchsian group a fundamental region in $\mathbf{SL}_2(\mathbb{R})$ from which we determine ... More
A Greedy Double Swap Heuristic for Nurse SchedulingMay 10 2012One of the key challenges of nurse scheduling problem (NSP) is the number of constraints placed on preparing the timetable, both from the regulatory requirements as well as the patients' demand for the appropriate nursing care specialists. In addition, ... More
Exponential growth rates of free and amalgamated productsSep 18 2012We prove that there is a gap between $\sqrt{2}$ and $(1+\sqrt{5})/2$ for the exponential growth rate of free products $G=A*B$ not isomorphic to the infinite dihedral group. For amalgamated products $G=A*_C B$ with $([A:C]-1)([B:C]-1)\geq2$, we show that ... More
Pi Visits ManhattanJul 31 2017Is it possible to draw a circle in Manhattan, using only its discrete network of streets and boulevards? In this study, we will explore the construction and properties of circular paths on an integer lattice, a discrete space where the distance between ... More
Virtual Windshields: Merging Reality and Digital Content to Improve the Driving ExperienceMay 05 2014In recent years, the use of the automobile as the primary mode of transportation has been increasing and driving has become an important part of daily life. Driving is a multi-sensory experience as drivers rely on their senses to provide them with important ... More
On anti-Ramsey numbers for complete bipartite graphs and the Turan functionAug 25 2011Nov 18 2015Given two graphs $G$ and $H$ with $H\subseteq G$ we consider the anti-Ramsey function $AR(G,H)$ which is the maximum number of colors in any edge-coloring of $G$ so that every copy of $H$ receives the same color on at least one pair of edges. The classical ... More
On a Conjecture of ThomassenOct 18 2014Jun 10 2015In 1989, Thomassen asked whether there is an integer-valued function f(k) such that every f(k)-connected graph admits a spanning, bipartite $k$-connected subgraph. In this paper we take a first, humble approach, showing the conjecture is true up to a ... More
Obstructions to ShellabilityJul 07 1997We consider a simplicial complex generaliztion of a result of Billera and Meyers that every nonshellable poset contains the smallest nonshellable poset as an induced subposet. We prove that every nonshellable $2$-dimensional simplicial complex contains ... More
Surface bundles over surfaces: new inequalities between signature, simplicial volume and Euler characteristicMay 10 2016We present three new inequalities tying the signature, the simplicial volume and the Euler characteristic of surface bundles over surfaces. Two of them are true for any surface bundle, while the third holds on a specific family of surface bundles, namely ... More
On the Capacity Advantage of a Single BitJul 24 2016In this work we study the capacity advantage achieved by adding a single bit of communication -- not a link of capacity 1 but a single bit over all time -- to a memoryless network. Specifically, we present a memoryless network in which adding a single ... More
On Zero-Error Source Coding with FeedbackJan 14 2010We consider the problem of zero error source coding with limited feedback when side information is present at the receiver. First, we derive an achievable rate region for arbitrary joint distributions on the source and the side information. When all source ... More
The bounded cohomology of SL_2 over local fields and S-integersSep 16 2016It is proved that the continuous bounded cohomology of SL_2(k) vanishes in all positive degrees whenever k is a non-Archimedean local field. This holds more generally for boundary-transitive groups of tree automorphisms and implies low degree vanishing ... More
Periodic points in towers of finite fields for polynomials associated to algebraic groupsJan 25 2013We find the limiting proportion of periodic points in towers of finite fields for polynomial maps associated to algebraic groups, namely pure power maps z^d and Chebyshev polynomials.
A Flexible Mixed Integer Programming framework for Nurse SchedulingOct 12 2012In this paper, a nurse-scheduling model is developed using mixed integer programming model. It is deployed to a general care ward to replace and automate the current manual approach for scheduling. The developed model differs from other similar studies ... More
Intelligent Search Heuristics for Cost Based SchedulingOct 04 2012Nurse scheduling is a difficult optimization problem with multiple constraints. There is extensive research in the literature solving the problem using meta-heuristics approaches. In this paper, we will investigate an intelligent search heuristics that ... More
On the Separation of Lossy Source-Network Coding and Channel Coding in Wireline NetworksMay 02 2010This paper proves the separation between source-network coding and channel coding in networks of noisy, discrete, memoryless channels. We show that the set of achievable distortion matrices in delivering a family of dependent sources across such a network ... More
Minimal exponential growth rates of metabelian Baumslag-Solitar groups and lamplighter groupsJun 11 2015We prove that for any prime $p\geq 3$ the minimal exponential growth rate of the Baumslag-Solitar group $BS(1,p)$ and the lamplighter group $\mathcal{L}_p=(\mathbb{Z}/p\mathbb{Z})\wr \mathbb{Z}$ are equal. We also show that for $p=2$ this claim is not ... More
On the Product Representation of Number Sequences, with Application to the Fibonacci FamilyAug 25 2015We investigate general properties of number sequences which allow explicit representation in terms of products. We find that such sequences form whole families of number sequences sharing similar recursive identities. Restricting to the cosine of fractional ... More
Reflections on trisection genusSep 13 2018The Heegaard genus of a 3-manifold, as well as the growth of Heegaard genus in its finite sheeted cover spaces, has extensively been studied in terms of algebraic, geometric and topological properties of the 3-manifold. This note shows that analogous ... More
Poset Topology: Tools and ApplicationsFeb 10 2006Feb 11 2006These lecture notes for the IAS/Park City Graduate Summer School in Geometric Combinatorics (July 2004) provide an overview of poset topology. These notes include introductory material, as well as recent developments and open problems. Some of the topics ... More
Bringing the Internet to Schools: US and EU policiesSep 24 2001The Internet is changing rapidly the way people around the world communicate, learn, and work. Yet the tremendous benefits of the Internet are not shared equally by all. One way to close the gap of the "digital divide" is to ensure Internet access to ... More
A Survey of the Trends in Facial and Expression Recognition Databases and MethodsNov 07 2015Dec 05 2015Automated facial identification and facial expression recognition have been topics of active research over the past few decades. Facial and expression recognition find applications in human-computer interfaces, subject tracking, real-time security surveillance ... More
Random 4-regular graphs have claw-decompositions asymptotically almost surelyOct 04 2016In 2006, Barat and Thomassen conjectured that the edges of every planar 4-regular 4-edge connected graph can be decomposed into claws. Shortly afterward, Lai constructed a counterexample to this conjecture. Using the small subgraph conditioning method ... More
Optical Spectroscopy of GX 339-4 - Paper I: Orbital ModulationFeb 12 2003Optical spectroscopic observations of GX 339-4 were carried out between 1998 May (X-ray high state) and 1999 May (X-ray low state) over 7 epochs. The equivalent width of Halpha increased during the high state then decreased during the low state. The equivalent ... More
How quantum bound states bounce and the structure it revealsAug 30 2010Mar 01 2011We investigate how quantum bound states bounce from a hard surface. Our analysis has applications to ab initio calculations of nuclear structure and elastic deformation, energy levels of excitons in semiconductor quantum dots and wells, and cold atomic ... More
Separation of source-network coding and channel coding in wireline networksOct 17 2011Dec 18 2012In this paper we prove the separation of source-network coding and channel coding in wireline networks. For the purposes of this work, a wireline network is any network of independent, memoryless, point-to-point, finite-alphabet channels used to transmit ... More
Statistical Implications of the Revenue Transfer Methodology in the Affordable Care ActMar 03 2017Jun 07 2018The Affordable Care Act (ACA) includes a permanent revenue transfer methodology which provides financial incentives to health insurance plans that have higher than average actuarial risk. In this paper, we derive some statistical implications of the revenue ... More
A numerical scheme for impact problemsOct 04 1999We consider a mechanical system with impact and n degrees of freedom, written in generalized coordinates. The system is not necessarily Lagrangian. The representative point of the system must remain inside a set of constraints K; the boundary of K is ... More
Top homology of hypergraph matching complexes, $p$-cycle complexes and Quillen complexes of symmetric groupsAug 22 2008We investigate the representation of a symmetric group $S_n$ on the homology of its Quillen complex at a prime $p$. For homology groups in small codimension, we derive an explicit formula for this representation in terms of the representations of symmetric ... More
From Poset Topology to $q$-Eulerian Polynomials to Stanley's Chromatic Symmetric FunctionsMay 13 2015In recent years we have worked on a project involving poset topology, various analogues of Eulerian polynomials, and a refinement of Richard Stanley's chromatic symmetric function. Here we discuss how Stanley's ideas and results have influenced and inspired ... More
A Harris process to model stochastic volatilityMay 17 2016We present a tractable non-independent increment process which provides a high modeling flexibility. The process lies on an extension of the so-called Harris chains to continuous time being stationary and Feller. We exhibit constructions, properties, ... More
Simulations of Glitches in Isolated PulsarsMay 25 2001Many radio pulsars exhibit glitches wherein the star's spin rate increases fractionally by $\sim 10^{-10} - 10^{-6}$. Glitches are ascribed to variable coupling between the neutron star crust and its superfluid interior. With the aim of distinguishing ... More
Eulerian quasisymmetric functions and poset topologyMay 15 2008We introduce a family of quasisymmetric functions called {\em Eulerian quasisymmetric functions}, which have the property of specializing to enumerators for the joint distribution of the permutation statistics, major index and excedance number on permutations ... More
Eulerian quasisymmetric functionsDec 03 2008Aug 21 2010We introduce a family of quasisymmetric functions called {\em Eulerian quasisymmetric functions}, which specialize to enumerators for the joint distribution of the permutation statistics, major index and excedance number on permutations of fixed cycle ... More
Superfluid Friction and Late-time Thermal Evolution of Neutron StarsOct 27 1998The recent temperature measurements of the two older isolated neutron stars PSR 1929+10 and PSR 0950+08 (ages of $3\times 10^6$ and $2\times 10^7$ yr, respectively) indicate that these objects are heated. A promising candidate heat source is friction ... More
q-Eulerian Polynomials: Excedance Number and Major indexAug 11 2006In this research announcement we present a new q-analog of a classical formula for the exponential generating function of the Eulerian polynomials. The Eulerian polynomials enumerate permutations according to their number of descents or their number of ... More
Defect chemistry in layered transition-metal oxides from screened hybrid density functional calculationsDec 16 2014We report a comprehensive first-principles study of the thermodynamics and transport of intrinsic point defects in layered oxide cathode materials LiMO$_2$ (M=Co, Ni), using density-functional theory and the Heyd-Scuseria-Ernzerhof screened hybrid functional. ... More
Persistent Homology of Geospatial Data: A Case Study with VotingJan 29 2019A crucial step in the analysis of persistent homology is transformation of data into a simplicial complex. Modern packages for persistent homology often construct Vietoris--Rips or other distance-based simplicial complexes on point clouds because they ... More
Electromechanical control of quantum emitters in nanophotonic devicesJan 25 2019Photon-mediated coupling between distant matter qubits may enable secure communication over long distances, the implementation of distributed quantum computing schemes, and the exploration of new regimes of many-body quantum dynamics. Nanophotonic devices ... More
Geometrically constructed bases for homology of partition lattices of types A, B and DJan 02 2004We use the theory of hyperplane arrangements to construct natural bases for the homology of partition lattices of types A, B and D. This extends and explains the "splitting basis" for the homology of the partition lattice given in [Wa96], thus answering ... More
A classification of degree $2$ semi-stable rational maps $\mathbb{P}^2\to\mathbb{P}^2$ with large finite dynamical automorphism groupJul 19 2016Let $K$ be an algebraically closed field of characteristic $0$. In this paper we classify the $\text{PGL}_3(K)$-conjugacy classes of semi-stable dominant degree $2$ rational maps $f:{\mathbb P}^2_K\dashrightarrow{\mathbb P}^2_K$ whose automorphism group ... More
Evolution, its Fractional Extension and GeneralizationDec 29 1999The evolution of a quantity, described by a function of space and time, relates the first derivative in time of this function to a spatial operator applied to the function. The initial value of the function at time $t=0$ is given. The fractional extension ... More
Poset homology of Rees products, and $q$-Eulerian polynomialsDec 03 2008The notion of Rees product of posets was introduced by Bj\"orner and Welker, where they study connections between poset topology and commutative algebra. Bj\"orner and Welker conjectured and Jonsson proved that the dimension of the top homology of the ... More
Vulnerability of linear systems against sensor attacks--a system's security indexFeb 21 2016The `security index' of a discrete-time LTI system under sensor attacks is introduced as a quantitative measure on the security of an observable system. We derive ideas from error control coding theory to provide sufficient conditions for attack detection ... More
Gamma-positivity of variations of Eulerian polynomialsFeb 22 2017Jun 12 2018An identity of Chung, Graham and Knuth involving binomial coefficients and Eulerian numbers motivates our study of a class of polynomials that we call binomial-Eulerian polynomials. These polynomials share several properties with the Eulerian polynomials. ... More
On enumerators of Smirnov words by descents and cyclic descentsJan 06 2019A Smirnov word is a word over the positive integers in which adjacent letters must be different. A symmetric function enumerating these words by descent number arose in the work of Shareshian and the second named author on $q$-Eulerian polynomials, where ... More
Chromatic quasisymmetric functions and Hessenberg varietiesJun 21 2011Jul 06 2012We discuss three distinct topics of independent interest; one in enumerative combinatorics, one in symmetric function theory, and one in algebraic geometry. The topic in enumerative combinatorics concerns a q-analog of a generalization of the Eulerian ... More
Electronic structure of the high and low pressure polymorphs of MgSiN$_{2}$May 02 2016We have performed density functional calculations on the group II-IV nitride MgSiN$_{2}$. At a pressure of about 20~GPa the ground state wurtzite derived MgSiN$_{2}$ structure (LP-MgSiN$_{2}$) transforms into a rock-salt derived structure (HP-MgSiN$_{2}$) ... More
Solitary waves and conservation laws for highly nonlinear wave equations modeling granular chainsJul 16 2015Jan 11 2016Nonlinear fourth-order wave equations modeling the long wavelength behavior of compression pulses in one-dimensional homogeneous granular chains with weak and strong initial pre-compression are considered. As a main result, the exact solitary wave solution ... More
A finite mixture model approach to regression under covariate misclassificationNov 28 2016This paper considers the problem of mismeasured categorical covariates in the context of regression modeling; if unaccounted for, such misclassification is known to result in misestimation of model parameters. Here, we exploit the fact that explicitly ... More
First-principles studies of the effects of impurities on the ionic and electronic conduction in LiFePO$_{4}$Jan 19 2012Olivine-type LiFePO$_{4}$ is widely considered as a candidate for Li-ion battery electrodes, yet its applicability in the pristine state is limited due to poor ionic and electronic conduction. Doping can be employed to enhance the material's electrical ... More
On the Homogenized Linial Arrangement: Intersection Lattice and Genocchi NumbersNov 16 2018Hetyei recently introduced the homogenized Linial arrangement and showed that its number of regions is equal to a median Genocchi number, which enumerates a class of permutations called Dumont derangements. Hetyei makes use of a a well-known formula of ... More
Pruning Bayesian Networks for Efficient ComputationMar 27 2013This paper analyzes the circumstances under which Bayesian networks can be pruned in order to reduce computational complexity without altering the computation for variables of interest. Given a problem instance which consists of a query and evidence for ... More
The Thual-Fauve pulse: skew stabilizationSep 15 1999It is possible to choose the parameters of a real quintic Ginzburg-Landau equation so that it possesses localized pulse-like solutions; Thual and Fauve have observed numerically that these pulses are stabilized by perturbations destroying the gradient ... More
Unimodality of Eulerian quasisymmetric functionsJan 24 2011We prove two conjectures of Shareshian and Wachs about Eulerian quasisymmetric functions and polynomials. The first states that the cycle type Eulerian quasisymmetric function $Q_{\lambda,j}$ is Schur-positive, and moreover that the sequence $Q_{\lambda,j}$ ... More
Chromatic quasisymmetric functionsMay 19 2014Mar 29 2016We introduce a quasisymmetric refinement of Stanley's chromatic symmetric function. We derive refinements of both Gasharov's Schur-basis expansion of the chromatic symmetric function and Chow's expansion in Gessel's basis of fundamental quasisymmetric ... More
Counterexamples Related to Rotations of Shadows of Convex BodiesMay 21 2015We construct examples of two convex bodies $K,L$ in $\mathbb{R}^n$, such that every projection of $K$ onto a $(n-1)$-dimensional subspace can be rotated to be contained in the corresponding projection of $L$, but $K$ itself cannot be rotated to be contained ... More
Torsion in the Matching Complex and Chessboard ComplexSep 03 2004Topological properties of the matching complex were first studied by Bouc in connection with Quillen complexes, and topological properties of the chessboard complex were first studied by Garst in connection with Tits coset complexes. Bj\"orner, Lov\'asz, ... More
On Sequentially Cohen-Macaulay Complexes and PosetsFeb 26 2007The classes of sequentially Cohen-Macaulay and sequentially homotopy Cohen-Macaulay complexes and posets are studied. First, some different versions of the definitions are discussed and the homotopy type is determined. Second, it is shown how various ... More
Ionized Gas in the First 10 Kiloparsecs of the Interstellar Galactic Halo: Metal Ion FractionsSep 20 2012We present direct measures of the ionization fractions of several sulfur ions in the Galactic warm ionized medium (WIM). We obtained high resolution ultraviolet absorption line spectroscopy of post-asymptotic giant branch stars in the the globular clusters ... More
The Unbounded Benefit of Encoder Cooperation for the $k$-user MACJan 22 2016Sep 30 2016Cooperation strategies allow communication devices to work together to improve network capacity. Consider a network consisting of a $k$-user multiple access channel (MAC) and a node that is connected to all $k$ encoders via rate-limited bidirectional ... More
The Multivariate Covering Lemma and its ConverseAug 13 2015Jan 21 2016The multivariate covering lemma states that given a collection of $k$ codebooks, each of sufficiently large cardinality and independently generated according to one of the marginals of a joint distribution, one can always choose one codeword from each ... More
Superfast solution of Toeplitz systems based on syzygy reductionJan 24 2013We present a new superfast algorithm for solving Toeplitz systems. This algorithm is based on a relation between the solution of such problems and syzygies of polynomials or moving lines. We show an explicit connection between the generators of a Toeplitz ... More
Detecting Functional Communities in Complex NetworksNov 14 2009Mar 02 2012We consider an alternate definition of community structure that is functionally motivated. We define network community structure-based on the function the network system is intended to perform. In particular, as a specific example of this approach, we ... More
Uniform bounds for pre-periodic points in families of twistsApr 19 2012May 08 2012Let phi be a morphism of projective N-space defined over a number field K. We prove that there is a bound B depending only on phi such that every twist of phi has no more than B K-rational preperiodic points. (This result is analagous to a result of Silverman ... More
Does nitrate deposition following astrophysical ionizing radiation events pose an additional threat to amphibians?Apr 22 2008Jun 27 2008It is known that amphibians are especially susceptible to the combination of heightened UVB radiation and increased nitrate concentrations. Various astrophysical events have been suggested as sources of ionizing radiation that could pose a threat to life ... More
Amalgam Anosov representationsNov 09 2014Nov 23 2015Let $\Gamma$ be a one-ended, torsion-free hyperbolic group and let $G$ be a semisimple Lie group with finite center. Using the canonical JSJ splitting due to Sela, we define amalgam Anosov representations of $\Gamma$ into $G$ and prove that they form ... More
Adiabatic projection method for scattering and reactions on the latticeSep 10 2013Nov 15 2013We demonstrate and test the adiabatic projection method, a general new framework for calculating scattering and reactions on the lattice. The method is based upon calculating a low-energy effective theory for clusters which becomes exact in the limit ... More
MgII absorption systems and their neighbouring galaxies from a background subtraction techniqueNov 17 2008We estimate the absolute magnitude distribution of galaxies which lie within about a Mpc of Mg II absorption systems. The absorption systems themselves lie along 1880 lines of sight to QSOs from the Sloan Digital Sky Survey Data Release 3, have rest equivalent ... More
Eulerian quasisymmetric functions and cyclic sievingSep 17 2009It is shown that a refined version of a q-analogue of the Eulerian numbers together with the action, by conjugation, of the subgroup of the symmetric group $S_n$ generated by the $n$-cycle $(1,2,...,n)$ on the set of permutations of fixed cycle type and ... More
Reconstructing the Star Knowledge of Aboriginal TasmaniansOct 10 2016The canopy of stars is a central presence in the daily and spiritual lives of Aboriginal Tasmanians. With the arrival of European colonists, Tasmanian astronomical knowledge and traditions were interrupted and dispersed. Fragments can be found scattered ... More
Determination of $Λ_{\overline{\textrm{MS}}}^{(n_f=2)}$ and analytic parameterization of the static quark-antiquark potentialApr 29 2018Nov 29 2018While lattice QCD allows for reliable results at small momentum transfers (large quark separations), perturbative QCD is restricted to large momentum transfers (small quark separations). The latter is determined up to a reference momentum scale $\Lambda$, ... More
Amalgam Anosov representationsNov 09 2014Aug 15 2017Let $\Gamma$ be a one-ended, torsion-free hyperbolic group and let $G$ be a semisimple Lie group with finite center. Using the canonical JSJ splitting due to Sela, we define amalgam Anosov representations of $\Gamma$ into $G$ and prove that they form ... More
Computational landscape of user behavior on social mediaJan 25 2019With the increasing abundance of 'digital footprints' left by human interactions in online environments, e.g., social media and app use, the ability to model complex human behavior has become increasingly possible. Many approaches have been proposed, ... More