Results for "Jack W. Silverstein"

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Eigenvalues of Large Sample Covariance Matrices of Spiked Population ModelsAug 12 2004We consider a spiked population model, proposed by Johnstone, whose population eigenvalues are all unit except for a few fixed eigenvalues. The question is to determine how the sample eigenvalues depend on the non-unit population ones when both sample ... More
Singular values of large non-central random matricesFeb 08 2018We study largest singular values of large random matrices, each with mean of a fixed rank $K$. Our main result is a limit theorem as the number of rows and columns approach infinity, while their ratio approaches a positive constant. It provides a decomposition ... More
Fundamental limit of sample generalized eigenvalue based detection of signals in noise using relatively few signal-bearing and noise-only samplesFeb 25 2009The detection problem in statistical signal processing can be succinctly formulated: Given m (possibly) signal bearing, n-dimensional signal-plus-noise snapshot vectors (samples) and N statistically independent n-dimensional noise-only snapshot vectors, ... More
On the signal-to-interference ratio of CDMA systems in wireless communicationsFeb 28 2007Let $\{s_{ij}:i,j=1,2,...\}$ consist of i.i.d. random variables in $\mathbb{C}$ with $\mathsf{E}s_{11}=0$, $\mathsf{E}|s_{11}|^2=1$. For each positive integer $N$, let $\mathbf{s}_k={\mathbf{s}}_k(N)=(s_{1k},s_{2k},...,s_{Nk})^T$, $1\leq k\leq K$, with ... More
A CLT for Information-theoretic statistics of Non-centered Gram random matricesJul 01 2011In this article, we study the fluctuations of the random variable: $$ {\mathcal I}_n(\rho) = \frac 1N \log\det(\Sigma_n \Sigma_n^* + \rho I_N),\quad (\rho>0) $$ where $\Sigma_n= n^{-1/2} D_n^{1/2} X_n\tilde D_n^{1/2} +A_n$, as the dimensions of the matrices ... More
Gaussian fluctuations for non-Hermitian random matrix ensemblesFeb 18 2005Feb 28 2007Consider an ensemble of $N\times N$ non-Hermitian matrices in which all entries are independent identically distributed complex random variables of mean zero and absolute mean-square one. If the entry distributions also possess bounded densities and finite ... More
A Deterministic Equivalent for the Analysis of Correlated MIMO Multiple Access ChannelsJun 19 2009Oct 24 2010In this article, novel deterministic equivalents for the Stieltjes transform and the Shannon transform of a class of large dimensional random matrices are provided. These results are used to characterise the ergodic rate region of multiple antenna multiple ... More
The Random Matrix Regime of Maronna's M-estimator with elliptically distributed samplesNov 27 2013This article demonstrates that the robust scatter matrix estimator $\hat{C}_N\in {\mathbb C}^{N\times N}$ of a multivariate elliptical population $x_1,\ldots,x_n\in {\mathbb C}^N$ originally proposed by Maronna in 1976, and defined as the solution (when ... More
A note on the CLT of the LSS for sample covariance matrix from a spiked population modelApr 23 2013Jul 05 2013In this note, we establish an asymptotic expansion for the centering parameter appearing in the central limit theorems for linear spectral statistic of large-dimensional sample covariance matrices when the population has a spiked covariance structure. ... More
Separation of the largest eigenvalues in eigenanalysis of genotype data from discrete subpopulationsJan 18 2013We present a mathematical model, and the corresponding mathematical analysis, that justifies and quantifies the use of principal component analysis of biallelic genetic marker data for a set of individuals to detect the number of subpopulations represented ... More
Robust Estimates of Covariance Matrices in the Large Dimensional RegimeApr 24 2012Apr 14 2014This article studies the limiting behavior of a class of robust population covariance matrix estimators, originally due to Maronna in 1976, in the regime where both the number of available samples and the population size grow large. Using tools from random ... More
Cosmological Numerical Simulations of Radio Relics in Galaxy Clusters: Insights for Future ObservationsJan 18 2011The acceleration of electrons at shock fronts is thought to be responsible for radio relics, extended radio features in the vicinity of merging galaxy clusters. By combining high resolution Adaptive Mesh Refinement Hydro/N-body cosmological simulations ... More
Resonance fluorescence in a band gap material: Direct numerical simulation of non-Markovian evolutionAug 23 2000A numerical method of calculating the non-Markovian evolution of a driven atom radiating into a structured continuum is developed. The formal solution for the atomic reduced density matrix is written as a Markovian algorithm by introducing a set of additional, ... More
Eigen-Inference for Energy Estimation of Multiple SourcesJan 22 2010Oct 24 2010In this paper, a new method is introduced to blindly estimate the transmit power of multiple signal sources in multi-antenna fading channels, when the number of sensing devices and the number of available samples are sufficiently large compared to the ... More
Global U(1) R-Symmetry And Conformal Invariance Of (0,2) ModelsMar 08 1994We derive a condition under which (0,2) linear sigma models possess a ``left-moving'' conformal stress tensor in $\bq$ cohomology (i.e. which leaves invariant the ``right-moving'' ground states) even away from their critical points. At the classical level ... More
4d Conformal Field Theories and Strings on OrbifoldsFeb 25 1998Mar 16 1998We propose correspondences between 4d quantum field theories with N=2,1,0 (super)conformal invariance and Type IIB string theory on various orbifolds. We argue using the spacetime string theory, and check using the beta functions (exactly for N=2,1 and ... More
Chirality Changing Phase Transitions in 4d String VacuaApr 25 1997May 12 1997We provide evidence that some four-dimensional N=1 string vacua with different numbers of generations are connected through phase transitions. The transitions involve going through a point in moduli space where there is a nontrivial fixed point governing ... More
On Vanishing Two Loop Cosmological Constants in Nonsupersymmetric StringsOct 16 1998It has recently been suggested that in certain special nonsupersymmetric type II string compactifications, at least the first two perturbative contributions to the cosmological constant $\Lambda$ vanish. Support for perturbative vanishing beyond 1-loop ... More
Singularities, Gauge Dynamics, and Nonperturbative Superpotentials in String TheoryAug 29 1996Aug 30 1996We describe a class of 4d N=1 compactifications of the $SO(32)$ heterotic/type I string theory which are destabilized by nonperturbatively generated superpotentials. In the type I description, the destabilizing superpotential is generated by a one instanton ... More
Galaxy Clusters at the Edge: Temperature, Entropy, and Gas Dynamics at the Virial RadiusApr 20 2010Recently, Suzaku has produced temperature and entropy profiles, along with profiles of gas density, gas fraction, and mass, for multiple galaxy clusters out to ~r_200 (~= virial radius). In this paper, we compare these novel X-ray observations with results ... More
Dark Ages Radio Explorer Mission: Probing the Cosmic DawnDec 05 2014The period between the creation of the cosmic microwave background at a redshift of ~1000 and the formation of the first stars and black holes that re-ionize the intergalactic medium at redshifts of 10-20 is currently unobservable. The baryonic component ... More
Astrophysics Conducted by the Lunar University Network for Astrophysics Research (LUNAR) and the Center for Lunar Origins (CLOE)Sep 11 2012[Abridged] The Moon is a unique platform from and on which to conduct astrophysical measurements. The Lunar University Network for Astrophysics Research (LUNAR) and the Center for Lunar Origins and Evolution (CLOE) teams within the NASA Lunar Science ... More
Graphs with three eigenvalues and second largest eigenvalue at most 1Jun 08 2015We classify the connected graphs with precisely three distinct eigenvalues and second largest eigenvalue at most 1.
Closed String Tachyons, AdS/CFT, and Large N QCDMar 26 2001Apr 06 2001We find that tachyonic orbifold examples of AdS/CFT have corresponding instabilities at small radius, and can decay to more generic gauge theories. We do this by computing a destabilizing Coleman-Weinberg effective potential for twisted operators of the ... More
Large-density field theory, viscosity, and "$2k_F$" singularities from string dualsMar 05 2012Mar 15 2012We analyze systems where an effective large-N expansion arises naturally in gauge theories without a large number of colors: a sufficiently large charge density alone can produce a perturbative string ('tHooft) expansion. One example is simply the well-known ... More
Double Ionisation in R-Matrix Theory Using a 2-electron Outer RegionJul 03 2015We have developed a two-electron outer region for use within R-matrix theory to describe double ionisation processes. The capability of this method is demonstrated for single-photon double ionisation of He in the photon energy region between 80 eV to ... More
Probing spacetime foam with extragalactic sourcesAug 29 2005Dec 30 2005Due to quantum fluctuations, spacetime is probably ``foamy'' on very small scales. We propose to detect this texture of spacetime foam by looking for core-halo structures in the images of distant quasars. We find that the Very Large Telescope interferometer ... More
Probing Planck-scale Physics with Extragalactic Sources?Feb 18 2003May 26 2003At Planck-scale, spacetime is "foamy" due to quantum fluctuations predicted by quantum gravity. Here we consider the possibility of using spacetime foam-induced phase incoherence of light from distant galaxies and gamma-ray bursters to probe Planck-scale ... More
Searching For the Physical Drivers of Eigenvector 1: Influence of Black Hole Mass and Eddington RatioJul 21 2003[Abridged] We compute the virial mass of the central black hole (M) and the luminosity-to-mass (L/M) ratio of ~ 300 low-z quasars and luminous Seyfert 1 nuclei. We analyze: (1) whether radio-quiet and radio-loud objects show systematic differences in ... More
Don't Panic! Closed String Tachyons in ALE SpacetimesAug 10 2001Sep 07 2001We consider closed string tachyons localized at the fixed points of noncompact nonsupersymmetric orbifolds. We argue that tachyon condensation drives these orbifolds to flat space or supersymmetric ALE spaces. The decay proceeds via an expanding shell ... More
Self-tuning flat domain walls in 5d gravity and string theoryJan 31 2000We present Poincare invariant domain wall (``3-brane'') solutions to some 5-dimensional effective theories which can arise naturally in string theory. In particular, we find theories where Poincare invariant solutions exist for arbitrary values of the ... More
Cosmological Shocks in Adaptive Mesh Refinement Simulations and the Acceleration of Cosmic RaysJun 09 2008Aug 21 2008We present new results characterizing cosmological shocks within adaptive mesh refinement N-Body/hydrodynamic simulations that are used to predict non-thermal components of large-scale structure. This represents the first study of shocks using adaptive ... More
Vacuum Energy Cancellation in a Non-supersymmetric StringJul 10 1998Dec 21 1998We present a nonsupersymmetric orbifold of type II string theory and show that it has vanishing cosmological constant at the one and two loop level. We argue heuristically that the cancellation persists at higher loops.
New N=1 Superconformal Field Theories in Four Dimensions from D-brane ProbesOct 27 1996We present several new examples of nontrivial 4d N=1 superconformal field theories. Some of these theories exhibit exotic global symmetries, including non-simply laced groups (such as $F_4$). They are obtained by studying threebrane probes in F-theory ... More
Tate cohomology of circle actions as a Heisenberg groupFeb 16 2001Sep 13 2001We study the Madsen-Tillman spectrum \CP^\infty_{-1} as a quotient of the Mahowald pro-object \CP^\infty_{-\infty}, which is closely related to the Tate cohomology of circle actions. That theory has an associated symplectic structure, whose symmetries ... More
Projective Model Structures for Exact CategoriesMar 21 2016In this article we provide sufficient conditions on weakly idempotent complete exact categories $E$ which admit an abelian embedding, such that various categories of chain complexes in $E$ are equipped with projective model structures. In particular we ... More
P-adic Line Integrals and Cauchy's TheoremsMay 20 2016Jun 16 2016Working in the p-adic analog of the complex numbers, we'll define a line integral on a small arc of a circle. This allows new versions of the Residue Theorem, the Cauchy-Goursat Theorem on discs with and without holes, Cauchy's Integral Formula and the ... More
Moduli of Singular CurvesNov 28 2010The purpose of this note is to prove that there is an algebraic stack U parameterizing all curves. The curves that appear in the algebraic stack U are allowed to be arbitrarily singular, non-reduced, disconnected, and reducible. We also prove the boundedness ... More
Weak semiprojectivity for purely infinite C*-algebrasJun 18 2002Apr 13 2005We prove that a simple, separable, nuclear, purely infinite classifiable $C^*$-algebra is weakly semiprojective if and only if its $K$-groups are direct sums of cyclic groups.
Braids, trees, and operadsSep 13 2001The space of unordered configurations of distinct points in the plane is aspherical, with Artin's braid group as its fundamental group. Remarkably enough, the space of ordered configurations of distinct points on the real projective line, modulo projective ... More
New Dimensions for Wound Strings: The Modular Transformation of Geometry to TopologyDec 13 2006Jan 03 2007We show, using a theorem of Milnor and Margulis, that string theory on compact negatively curved spaces grows new effective dimensions as the space shrinks, generalizing and contextualizing the results in hep-th/0510044. Milnor's theorem relates negative ... More
Bounds on curved domain walls in 5d gravityFeb 15 2000Feb 17 2000We discuss maximally symmetric curved deformations of the flat domain wall solutions of five-dimensional dilaton gravity that appeared in a recent approach to the cosmological constant problem. By analyzing the bulk field configurations and the boundary ... More
The Markov approximation for the atomic output couplerOct 30 1998The regions of validity of the Markov approximation for the coupling of atoms out of an atomic trap are determined. We consider radio-frequency output coupling in the presence of gravity and collisional repulsion, and Raman output coupling. The Markov ... More
CIV 1549 as an Eigenvector 1 Parameter for Active Galactic NucleiMay 14 2007[Abridged] We have been exploring a spectroscopic unification for all known types of broad line emitting AGN. The 4D Eigenvector 1 (4DE1) parameter space shows promise as a unification capable of organizing quasar diversity on a sequence primarily governed ... More
How Much Can We Learn From A Merging Cold Front Cluster? : Insights From X-ray Temperature and Radio Maps of Abell 3667Aug 21 2014The galaxy cluster Abell 3667 is an ideal laboratory to study the plasma processes in the intracluster medium (ICM). High resolution Chandra X-ray observations show a cold front in Abell 3667. At radio wavelengths, Abell 3667 reveals a double radio-relic ... More
Categories of orbit types for proper Lie groupoidsMay 17 2014It is widely understood that the quotient space of a topological group action can have a complicated combinatorial structure, indexed somehow by the sotropy groups of the action, but how best to record this structure seems unclear. This sketch defines ... More
Abelian varieties and the Kervaire invariantMay 03 2011Notes from a talk at the April 2011 ICMS (Edinburgh) conference on the recent solution of the Kervaire invariant problem. This is an entirely expository account, emphasizing connections with the theory of topological automorphic forms.
Restrictions of Steiner bundles and divisors on the Hilbert scheme of points in the planeFeb 28 2011Mar 01 2012The Hilbert scheme of n points in the projective plane parameterizes degree n zero-dimensional subschemes of the projective plane. We examine the dual cones of effective divisors and moving curves on the Hilbert scheme. By studying interpolation, restriction, ... More
Generalizing the GAGA PrincipleJan 26 2011Jan 27 2011This paper generalizes the fundamental GAGA results of Serre cite{MR0082175} in three ways---to the non-separated setting, to stacks, and to families. As an application of these results, we show that analytic compactifications of $\mathcal{M}_{g,n}$ possessing ... More
Graph-Based Models for Kirchberg AlgebrasApr 14 2005We give a construction of Kirchberg algebras from graphs. By using product graphs in the construction we are able to provide models for general (UCT) Kirchberg algebras while maintaining the explicit generators and relations of the underlying graphs.
Geometric Tate-Swan cohomology of equivariant spectraOct 15 2012Nov 21 2012We sketch a quick and dirty geometric approach to the Tate-Swan cohomology of equivariant spectra, illustrating it with conjectural applications to Atiyah-Segal $K$-theory of circle actions, and a possible geometric model for the topological cyclic homology ... More
Moonshine elements in elliptic cohomologyDec 06 2007This is a historical talk about the recent confluence of two lines of research in equivariant elliptic cohomology, one concerned with connected Lie groups, the other with the finite case. These themes come together in (what seems to me remarkable) work ... More
Largeness of LERF and 1-relator groupsMar 26 2008We consider largeness of groups given by a presentation of deficiency 1, where the group is respectively free-by-cyclic, LERF or 1-relator. We give the first examples of (finitely generated free)-by-(infinite cyclic) word hyperbolic groups which are large, ... More
Techniques for classifying nonnegatively curved left-invariant metrics on compact Lie groupsAug 14 2006We provide techniques for studying the nonnegatively curved left-invariant metrics on a compact Lie group. For "straight" paths of left-invariant metrics starting at bi-invariant metrics and ending at nonnegatively curved metrics, we deduce a nonnegativity ... More
Complex orientations for THH of some perfectoid fieldsAug 16 2016Oct 14 2016This sketch argues that work of Hesselholt [8] on the topological Hochschild homology of $\Cp$ extends, using work of Scholze [15, 23] on flat descent, to define complex orientations for a version of topological Hochschild homology for rings of integers ... More
Complex orientations for THH of some perfectoid fieldsAug 16 2016Oct 02 2016This sketch argues that work of Hesselholt [8] on the topological Hochschild homology of $\Cp$ extends, using work of Scholze [15, 23] on flat descent, to define complex orientations for a version of topological Hochschild homology for rings of integers ... More
A theory of base motivesAug 21 2009A category of correspondences based on Waldhausen A-theory has interesting analogies, in the context of differential topology, to categories of mixed Tate motives studied in arithmetic geometry. In particular, the Hopf object S \wedge_A S (regarding A(*) ... More
Complex cobordism and algebraic topologyJul 21 2007This is a historical survey, beginning where Atiyah and Sullivan leave off...
On the canonical formula of C. Levi-StraussJun 10 2003Jun 11 2003The anthropologist Claude LeviStrauss has formulated a theory of the structure of myths using a formalism borrowed from mathematics, which has been difficult to interpret, and is somewhat controversial. Nevertheless, LeviStrauss's old school chum Andre ... More
On gauge theories of massJan 06 2010May 22 2010Mass as broken conformal symmetry: the graviton makes better sense as a Goldstone boson associated to the dilaton, than vice versa. The discussion of the Yamabe problem for the interior Schwarzschild solution [\S 4.2.4] has been sharpened in this revision. ... More
An Euler system for characters over an imaginary biquadratic fieldNov 17 2016Given a pair of modular forms with complex multiplication by distinct imaginary quadratic fields, the four dimensional Galois representation associated to their Rankin--Selberg convolution is induced from a character over an imaginary biquadratic field ... More
Local fields and extraordinary K-theoryJul 17 2012Jul 23 2012We describe integral lifts K(L), indexed by local fields L of degree n = [L:\Q_p], of the extraordinary cohomology theories K(n), and apply the generalized character theory of Hopkins, Kuhn and Ravenel to identify K(L)(BG) \otimes \Q$, for a finite group ... More
A remark on Hopkins' chromatic splitting conjectureJun 12 2014Mar 29 2015Ravenel proved the remarkable fact that the $K$-theoretic localization $L_K S^0$ of the sphere spectrum has $\mathbb{Q}/\mathbb{Z}$ as homotopy group in dimension -2. Mike Hopkins' chromatic splitting conjecture implies more generally that there are $3^{n-1}$ ... More
HKR characters and higher twisted sectorsAug 29 2002May 26 2004This is the writeup of an expository talk. It is intended as an introduction to the work of Hopkins, Kuhn, and Ravenel on generalized group characters, which seems to fit very well with the theory of what physicists call higher twisted sectors in the ... More
Quantum generalized cohomologyJul 11 1998We construct a ring structure on complex cobordism tensored with the rationals, which is related to the usual ring structure as quantum cohomology is related to ordinary cohomology. The resulting object defines a generalized two- dimensional topological ... More
The Santa Fe Light Cone Simulation Project: II. The Prospects for Direct Detection of the WHIM with SZE SurveysMar 18 2009Detection of the Warm-Hot Intergalactic Medium (WHIM) using Sunyaev-Zeldovich effect (SZE) surveys is an intriguing possibility, and one that may allow observers to quantify the amount of "missing baryons" in the WHIM phase. We estimate the necessary ... More
On the Origin of Cool Core Galaxy Clusters: Comparing X-Ray Observations with Numerical SimulationsMar 24 2009To better constrain models of cool core galaxy cluster formation, we have used X-ray observations taken from the Chandra and ROSAT archives to examine the properties of cool core and non-cool core clusters, especially beyond the cluster cores. We produced ... More
Biregular graphs with three eigenvaluesDec 22 2014Apr 12 2016We consider nonregular graphs having precisely three distinct eigenvalues. The focus is mainly on the case of graphs having two distinct valencies and our results include constructions of new examples, structure theorems, valency constraints, and a classification ... More
The Design of EzWindows: A Graphics API for an Introductory Programming CourseOct 03 1998Teaching object-oriented programming in an introductory programming course poses considerable challenges to the instructor. An often advocated approach to meeting this challenge is the use of a simple, object-oriented graphics library. We have developed ... More
Spacetime Emergence and General Covariance TransmutationJun 01 2012Dec 20 2012Spacetime emergence refers to the notion that classical spacetime "emerges" as an approximate macroscopic entity from a non-spatio-temporal structure present in a more complete theory of interacting fundamental constituents. In this article, we propose ... More
Topological gravity in Minkowski spaceJul 07 2004May 22 2006The two-category with three-manifolds as objects, h-cobordisms as morphisms, and diffeomorphisms of these as two-morphisms, is extremely rich; from the point of view of classical physics it defines a nontrivial topological model for general relativity. ... More
The tangent bundle of an almost-complex free loopspaceSep 13 2001Apr 06 2003The main construction of this paper contains a serious error, and I am withdrawing it. I owe Andrew Stacey and Ralph Cohen thanks for seeing the problem; in particular, Stacey has shown that the projections constructed in \S 3.1 will fail in general to ... More
Homotopy-theoretically enriched categories of noncommutative motivesFeb 15 2014Mar 22 2015Waldhausen's $K$-theory of the sphere spectrum (closely related to the algebraic $K$-theory of the integers) is a naturally augmented $S^0$-algebra, and so has a Koszul dual. Classic work of Deligne and Goncharov implies an identification of the rationalization ... More
Complex orientations for THH of some perfectoid fieldsAug 16 2016This sketch argues that work of Hesselholt [8] on the topological Hochschild homology of $\Cp$ extends, using work of Scholze [15, 23] on flat descent, to define complex orientations for a version of topological Hochschild homology for rings of integers ... More
A functorial approach to the C*-algebras of a graphFeb 27 2001Oct 05 2001A functor from the category of directed trees with inclusions to the category of commutative C*-algebras with injective *-homomorphisms is constructed. This is used to define a functor from the category of directed graphs with inclusions to the category ... More
Birational geometry of moduli spaces of sheaves and Bridgeland stabilityJun 08 2016Jun 23 2016Moduli spaces of sheaves and Hilbert schemes of points have experienced a recent resurgence in interest in the past several years, due largely to new techniques arising from Bridgeland stability conditions and derived category methods. In particular, ... More
Effective divisors on the Hilbert scheme of points in the plane and interpolation for stable bundlesOct 24 2012Oct 29 2013We compute the cone of effective divisors on the Hilbert scheme of points in the projective plane. We show the sections of many stable vector bundles satisfy a natural interpolation condition, and that these bundles always give rise to the edge of the ... More
An algebraic analog of the Virasoro groupSep 13 2001The group of diffeomorphisms of a circle is not an infinite-dimensional algebraic group, though in many ways it behaves as if it were. Here we construct an algebraic model for this object, and discuss some of its representations, which appear in the Kontsevich-Witten ... More
Topological gravity in dimensions two and fourAug 01 1999Recent work by physicists on gravity in two dimensions has a natural generalization to four dimensions, formulated in terms of an analogue of Segal's category [defined for the study of conformal field theory].
C*-algebras for categories of paths asociated to the Baumslag-Solitar groupsNov 29 2011Nov 15 2012In this paper we describe the C*-algebras associated to the Baumslag-Solitar groups with the ordering defined by the usual presentations. These are Morita equivalent to the crossed product C*-algebras obtained by letting the group act on its directed ... More
Semiprojectivity for certain purely infinite C*-algebrasFeb 28 2001Jun 18 2002It is proved that classifiable simple separable nuclear purely infinite C*-algebras having finitely generated K-theory and torsion-free K_1 are semiprojective. This is accomplished by exhibiting these algebras as C*-algebras of infinite directed graphs. ... More
Techniques for Profile Binning and Analysis of Eigenvector Composite Spectra: Comparing Hbeta and MgII 2800 as Virial EstimatorsOct 16 2013We review the basic techniques for extracting information about quasar structure and kinematics from the broad emission lines in quasars. We consider which lines can most effectively serve as virial estimators of black hole mass. At low redshift the Balmer ... More
Structural Signatures of Vitrification in Hard Core FluidsAug 18 2003Computer simulations of hard spheres and disks are used to estimate the most probable cavity size, $\xi_{\rm cavity}$, and a ``rattle'' size, $\xi_{\rm rattle}$, over which a particle can translate holding all other particles fixed. Both of these measures ... More
Effects Of The Ionosphere On Ground-Based Detection Of The Global 21 CM Signal From The Cosmic Dawn And The Dark AgesSep 01 2014Mar 09 2016Detection of the global HI 21 cm signal from Cosmic Dawn and Epoch of Reionization is the key science driver for several ongoing ground-based and future ground/space-based experiments. The crucial spectral features in the global 21 cm signal (turning ... More
Decapitating TadpolesSep 26 2002Dec 09 2002We propose that perturbative quantum field theory and string theory can be consistently modified in the infrared to eliminate, in a radiatively stable manner, tadpole instabilities that arise after supersymmetry breaking. This is achieved by deforming ... More
Learning Dynamic Feature Selection for Fast Sequential PredictionMay 22 2015We present paired learning and inference algorithms for significantly reducing computation and increasing speed of the vector dot products in the classifiers that are at the heart of many NLP components. This is accomplished by partitioning the features ... More
Detection of the Circumstellar Disk Associated with 2MASS J0820-8003 in the eta Cha ClusterMar 14 2012The Nearby Young Moving Groups (NYMGs) of stars are ideal for the study of evolution circumstellar disks in which planets may form because their ages range from a few Myr to about 100 Myr, about the same as the interval over which planets are thought ... More
On The Road To More Realistic Galaxy Cluster Simulations: The Effects of Radiative Cooling and Thermal Feedback Prescriptions on the Observational Properties of Simulated Galaxy ClustersNov 13 2012Flux limited X-ray surveys of galaxy clusters show that clusters come in two roughly equally proportioned varieties: "cool core" clusters (CCs) and non-"cool core" clusters (NCCs). In previous work, we have demonstrated using cosmological $N$-body + Eulerian ... More
The Santa Fe Light Cone Simulation Project: I. Confusion and the WHIM in Upcoming Sunyaev-Zel'dovich Effect SurveysApr 19 2007Aug 29 2007We present the first results from a new generation of simulated large sky coverage (~100 square degrees) Sunyaev-Zeldovich effect (SZE) cluster surveys using the cosmological adaptive mesh refinement N-body/hydro code Enzo. We have simulated a very large ... More
Reversal of current blockade through multiple trap correlationsJan 15 2009Current noise in electronic devices usually arises from uncorrelated charging events, with individual transitions resolved only at low temperatures. However, in 1-D nanotube-based transistors, we have observed random telegraph signal (RTS) with unprecedented ... More
Trapped InflationFeb 06 2009Feb 24 2009We analyze a distinctive mechanism for inflation in which particle production slows down a scalar field on a steep potential, and show how it descends from angular moduli in string compactifications. The analysis of density perturbations -- taking into ... More
Controlled non-Fermi liquids from spacetime dependent couplingsFeb 24 2014We construct perturbatively controlled non-Fermi liquids in 3+1 spacetime dimensions, using mild power-law translation breaking interactions. Our mechanism balances the leading tree level effects from such gradients against quantum effects from the interaction ... More
Micromanaging de Sitter holographyMay 28 2010We develop tools to engineer de Sitter vacua with semi-holographic duals, using elliptic fibrations and orientifolds to uplift Freund-Rubin compactifications with CFT duals. The dual brane construction is compact and constitutes a microscopic realization ... More
Unitarity bounds and RG flows in time dependent quantum field theoryMar 08 2012We generalize unitarity bounds on operator dimensions in conformal field theory to field theories with spacetime dependent couplings. Below the energy scale of spacetime variation of the couplings, their evolution can strongly affect the physics, effectively ... More
A Lunar L2-Farside Exploration and Science Mission Concept with the Orion Multi-Purpose Crew Vehicle and a Teleoperated Lander/RoverNov 14 2012A novel concept is presented in this paper for a human mission to the lunar L2 (Lagrange) point that would be a proving ground for future exploration missions to deep space while also overseeing scientifically important investigations. In an L2 halo orbit ... More
Year 3 LUNAR Annual Report to the NASA Lunar Science InstituteMar 04 2012Apr 17 2012The Lunar University Network for Astrophysics Research (LUNAR) is a team of researchers and students at leading universities, NASA centers, and federal research laboratories undertaking investigations aimed at using the Moon as a platform for space science. ... More
The Frequent Paucity of Trivial StringsOct 23 2013May 07 2014A 1976 theorem of Chaitin can be used to show that arbitrarily dense sets of lengths n have a paucity of trivial strings (only a bounded number of strings of length n having trivially low plain Kolmogorov complexities). We use the probabilistic method ... More
Cardinality bounds involving the skew-$λ$ Lindelöf degree and its variantsJul 23 2015We introduce a modified closing-off argument that results in several improved bounds for the cardinalities of Hausdorff and Urysohn spaces. These bounds involve the cardinal invariant $skL(X,\lambda)$, the skew-$\lambda$ Lindel\"of degree of a space $X$, ... More
On the Algebraic K-theory of MonoidsSep 16 2010Let $A$ be a not necessarily commutative monoid with zero such that projective $A$-acts are free. This paper shows that the algebraic K-groups of $A$ can be defined using the +-construction and the Q-construction. It is shown that these two constructions ... More
The distribution of $H_{8}$-extensions of quadratic fieldsNov 17 2016We compute all the moments of a normalization of the function which counts unramified $H_{8}$-extensions of quadratic fields, where $H_{8}$ is the quaternion group of order 8, and show that the values of this function determine a constant distribution. ... More