Results for "Abhay Shah"

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3-D Surface Segmentation Meets Conditional Random FieldsJun 11 2019Automated surface segmentation is important and challenging in many medical image analysis applications. Recent deep learning based methods have been developed for various object segmentation tasks. Most of them are a classification based approach, e.g. ... More
Gravitational-wave flux for a particle orbiting a Kerr black hole to 20th post-Newtonian order: a numerical approachMar 11 2014May 24 2014In this article we present the post-Newtonian (pN) coefficients of the energy flux (and angular momentum flux) at infinity and event horizon for a particle in circular, equatorial orbits about a Kerr black hole (of mass $M$ and spin-parameter $a$) up ... More
iResum: a new paradigm for resumming gravitational wave amplitudesJun 01 2016Sep 28 2016We introduce a new, resummed, analytical form of the post-Newtonian (PN), factorized, multipolar amplitude corrections $f_{\ell m}$ of the effective-one-body (EOB) gravitational waveform of spinning, nonprecessing, circularized, coalescing black hole ... More
Linear-in-mass-ratio contribution to spin precession and tidal invariants in Schwarzschild spacetime at very high post-Newtonian orderMar 09 2015Apr 02 2015Using black hole perturbation theory and arbitrary-precision computer algebra, we obtain the post-Newtonian (pN) expansions of the linear-in-mass-ratio corrections to the spin-precession angle and tidal invariants for a particle in circular orbit around ... More
Self-force from reconstructed metric perturbations: numerical implementation in Schwarzschild spacetimeOct 11 2014Aug 07 2015We present a first numerical implementation of a new scheme by Pound et al. that enables the calculation of the gravitational self-force in Kerr spacetime from a reconstructed metric-perturbation in a radiation gauge. The numerical task of the metric ... More
The Last 50 Years of General Relativity and Gravitation: From GR3 to GR20 Warsaw ConferencesDec 22 2013Jan 24 2014This article has a dual purpose: i) to provide a flavor of the scientific highlights of the landmark conference, GR3, held in July 1962 at Jablonna, near Warsaw; and, ii) to present a bird's eye view of the tremendous advances that have occurred over ... More
Time in Fundamental PhysicsDec 21 2013The first three sections of this article contain a broad brush summary of the profound changes in the notion of time in fundamental physics that were brought about by three revolutions: the foundations of mechanics distilled by Newton in his Principia, ... More
Vote Aggregation as a Clustering ProblemNov 16 2016An important way to make large training sets is to gather noisy labels from crowds of non experts. We propose a method to aggregate noisy labels collected from a crowd of workers or annotators. Eliciting labels is important in tasks such as judging web ... More
Approximating Wisdom of Crowds using K-RBMsNov 16 2016Nov 17 2016An important way to make large training sets is to gather noisy labels from crowds of non experts. We propose a method to aggregate noisy labels collected from a crowd of workers or annotators. Eliciting labels is important in tasks such as judging web ... More
Reanalyzing variable directionality of gene expression in transgenerational epigenetic inheritanceJun 28 2016A previous report claimed no evidence of transgenerational epigenetic inheritance in a mouse model of in utero environmental exposure, based on the observation that gene expression changes observed in the germ cells of G1 and G2 male fetus were not in ... More
Simultaneous Multiple Surface Segmentation Using Deep LearningMay 19 2017The task of automatically segmenting 3-D surfaces representing boundaries of objects is important for quantitative analysis of volumetric images, and plays a vital role in biomedical image analysis. Recently, graph-based methods with a global optimization ... More
Optimal Multi-Object Segmentation with Novel Gradient Vector Flow Based Shape PriorsMay 22 2017Shape priors have been widely utilized in medical image segmentation to improve segmentation accuracy and robustness. A major way to encode such a prior shape model is to use a mesh representation, which is prone to causing self-intersection or mesh folding. ... More
Raising and Lowering operators of spin-weighted spheroidal harmonicsMar 09 2015Jun 03 2016In this paper we generalize the spin-raising and lowering operators of spin-weighted spherical harmonics to linear-in-$\gamma$ spin-weighted spheroidal harmonics where $\gamma$ is an additional parameter present in the second order ordinary differential ... More
Observables of a test-mass along an inclined orbit in a post-Newtonian approximated Kerr spacetime to leading-order-quadratic-in-spinMar 27 2013Jun 17 2013The orbital motion is derived for a non-spinning test-mass in the relativistic, gravitational field of a rotationally deformed body not restricted to the equatorial plane or spherical orbit. The gravitational field of the central body is represented by ... More
Dynamical Black Holes: Approach to the Final StateJun 24 2013Sep 27 2013Since black holes can be formed through widely varying processes, the horizon structure is highly complicated in the dynamical phase. Nonetheless, as numerical simulations show, the final state appears to be universal, well described by the Kerr geometry. ... More
Metric perturbations produced by eccentric equatorial orbits around a Kerr black holeJun 15 2015Aug 17 2016We present the first numerical calculation of the (local) metric perturbation produced by a small compact object moving on an eccentric equatorial geodesic around a Kerr black hole, accurate to first order in the mass ratio. The procedure starts by first ... More
Optimal Surface Segmentation with Convex Priors in Irregularly Sampled SpaceNov 09 2016Feb 14 2019Optimal surface segmentation is a state-of-the-art method used for segmentation of multiple globally optimal surfaces in volumetric datasets. The method is widely used in numerous medical image segmentation applications. However, nodes in the graph based ... More
Truth Serums for Massively Crowdsourced Evaluation TasksJul 25 2015Sep 06 2016A major challenge in crowdsourcing evaluation tasks like labeling objects, grading assignments in online courses, etc., is that of eliciting truthful responses from agents in the absence of verifiability. In this paper, we propose new reward mechanisms ... More
EMRI corrections to the angular velocity and redshift factor of a mass in circular orbit about a Kerr black holeJul 24 2012Sep 26 2012This is the first of two papers on computing the self-force in a radiation gauge for a particle moving in circular, equatorial orbit about a Kerr black hole. In the EMRI (extreme-mass-ratio inspiral) framework, with mode-sum renormalization, we compute ... More
Optimal Multiple Surface Segmentation with Convex Priors in Irregularly Sampled SpaceNov 09 2016Optimal surface segmentation is widely used in numerous medical image segmentation applications. However, nodes in the graph based optimal surface segmentation method typically encode uniformly distributed orthogonal voxels of the volume. Thus the segmentation ... More
Truth Serums for Massively Crowdsourced Evaluation TasksJul 25 2015Nov 08 2016A major challenge in crowdsourcing evaluation tasks like labeling objects, grading assignments in online courses, etc., is that of eliciting truthful responses from agents in the absence of verifiability. In this paper, we propose new reward mechanisms ... More
Stabilizing Adversarial Nets With Prediction MethodsMay 20 2017Feb 08 2018Adversarial neural networks solve many important problems in data science, but are notoriously difficult to train. These difficulties come from the fact that optimal weights for adversarial nets correspond to saddle points, and not minimizers, of the ... More
Loop quantum cosmology and slow roll inflationDec 21 2009Oct 02 2010In loop quantum cosmology (LQC) the big bang is replaced by a quantum bounce which is followed by a robust phase of super-inflation. Rather than growing unboundedly in the past, the Hubble parameter \emph{vanishes} at the bounce and attains a \emph{finite ... More
Action and Hamiltonians in higher dimensional general relativity: First order frameworkAug 14 2008We consider $d>4$-dimensional space-times which are asymptotically flat at spatial infinity and show that, in the first order framework, the action principle is well-defined \emph{without the need of infinite counter terms.} It naturally leads to a covariant ... More
Gauss Linking Number and Electro-magnetic Uncertainty PrincipleJan 24 1997It is shown that there is a precise sense in which the Heisenberg uncertainty between fluxes of electric and magnetic fields through finite surfaces is given by (one-half $\hbar$ times) the Gauss linking number of the loops that bound these surfaces. ... More
Photon inner product and the Gauss linking numberAug 06 1996It is shown that there is an interesting interplay between self-duality, loop representation and knots invariants in the quantum theory of Maxwell fields in Minkowski space-time. Specifically, in the loop representation based on self-dual connections, ... More
Rate Constrained Random Access over a Fading ChannelAug 22 2009In this paper, we consider uplink transmissions involving multiple users communicating with a base station over a fading channel. We assume that the base station does not coordinate the transmissions of the users and hence the users employ random access ... More
Asymptotic Capacity of Wireless Ad Hoc Networks with Realistic Links under a Honey Comb TopologyNov 10 2007Oct 05 2010We consider the effects of Rayleigh fading and lognormal shadowing in the physical interference model for all the successful transmissions of traffic across the network. New bounds are derived for the capacity of a given random ad hoc wireless network ... More
Quantum Gravity in the Sky: Interplay between fundamental theory and observationsAug 15 2016Nov 12 2016Observational missions have provided us with a reliable model of the evolution of the universe starting from the last scattering surface all the way to future infinity. Furthermore given a specific model of inflation, using quantum field theory on curved ... More
Probability of Inflation in Loop Quantum CosmologyMar 12 2011Inflationary models of the early universe provide a natural mechanism for the formation of large scale structure. This success brings to forefront the question of naturalness: Does a sufficiently long slow roll inflation occur generically or does it require ... More
Relation between polymer and Fock excitationsJul 11 2001Aug 16 2001To bridge the gap between background independent, non-perturbative quantum gravity and low energy physics described by perturbative field theory in Minkowski space-time, Minkowskian Fock states are located, analyzed and used in the background independent ... More
Generalization of Strongly Clean RingsMar 14 2012In this paper, strongly clean ring defined by W. K. Nicholson in 1999 has been generalized to n-strongly clean, {\Sigma}-strongly clean and with the help of example it has been shown that there exists a ring, which is n-strongly clean and {\Sigma}-strongly ... More
A Truth Serum for Large-Scale EvaluationsJul 25 2015Feb 16 2018A major challenge in obtaining large-scale evaluations, e.g., product or service reviews on online platforms, labeling images, grading in online courses, etc., is that of eliciting honest responses from agents in the absence of verifiability. We propose ... More
Finding high-order analytic post-Newtonian parameters from a high-precision numerical self-force calculationDec 06 2013Mar 11 2014We present a novel analytic extraction of high-order post-Newtonian (pN) parameters that govern quasi-circular binary systems. Coefficients in the pN expansion of the energy of a binary system can be found from corresponding coefficients in an extreme-mass-ratio ... More
Experimental mathematics meets gravitational self-forceMar 09 2015Jul 27 2015It is now possible to compute linear in mass-ratio terms in the post-Newtonian (PN) expansion for compact binaries to very high orders using black hole perturbation theory applied to various invariants. For instance, a computation of the redshift invariant ... More
Quantum Gravity in the Sky: Interplay between fundamental theory and observationsAug 15 2016Observational missions have provided us with a reliable model of the evolution of the universe starting from the last scattering surface all the way to future infinity. Furthermore given a specific model of inflation, using quantum field theory on curved ... More
Generalized effective description of loop quantum cosmologySep 29 2015Oct 15 2015The effective description of loop quantum cosmology (LQC) has proved to be a convenient platform to study phenomenological implications of the quantum bounce that resolves the classical big-bang singularity. Originally, this description was derived using ... More
Quantum geometry and the Schwarzschild singularitySep 18 2005In homogeneous cosmologies, quantum geometry effects lead to a resolution of the classical singularity without having to invoke special boundary conditions at the singularity or introduce ad-hoc elements such as unphysical matter. The same effects are ... More
Black hole evaporation: A paradigmApr 07 2005Jul 01 2005A paradigm describing black hole evaporation in non-perturbative quantum gravity is developed by combining two sets of detailed results: i) resolution of the Schwarzschild singularity using quantum geometry methods; and ii) time-evolution of black holes ... More
Quantum Theory of Gravity I: Area OperatorsFeb 23 1996Aug 23 1996A new functional calculus, developed recently for a fully non-perturbative treatment of quantum gravity, is used to begin a systematic construction of a quantum theory of geometry. Regulated operators corresponding to areas of 2-surfaces are introduced ... More
Completeness of Wilson loop functionals on the moduli space of $SL(2,C)$ and $SU(1,1)$-connectionsApr 30 1993The structure of the moduli spaces $\M := \A/\G$ of (all, not just flat) $SL(2,C)$ and $SU(1,1)$ connections on a n-manifold is analysed. For any topology on the corresponding spaces $\A$ of all connections which satisfies the weak requirement of compatibility ... More
DAiSEE: Towards User Engagement Recognition in the WildSep 07 2016Nov 16 2016Recognizing user engagement plays an important role in several contemporary vision applications including advertising, healthcare, and e-learning. However, the lack of any publicly available dataset to address this problem severely limits the development ... More
Asymptotically Anti-de Sitter Space-times: Conserved QuantitiesNov 29 1999Asymptotically anti-de Sitter space-times are considered in a general dimension $d\ge 4$. As one might expect, the boundary conditions at infinity ensure that the asymptotic symmetry group is the anti-de Sitter group (although there is an interesting ... More
Compressible ModulesMar 13 2012The main purpose of this paper is to study under what condition compressible modules are critically compressible. A sufficient condition for the injective hull of a critically compressible module to be critically compressible is also provided. Furthermore ... More
A Loop Representation for the Quantum Maxwell FieldFeb 19 1992Quantization of the free Maxwell field in Minkowski space is carried out using a loop representation and shown to be equivalent to the standard Fock quantization. Because it is based on coherent state methods, this framework may be useful in quantum optics. ... More
Non-minimal couplings, quantum geometry and black hole entropyMay 21 2003Aug 20 2003The black hole entropy calculation for type I isolated horizons, based on loop quantum gravity, is extended to include non-minimally coupled scalar fields. Although the non-minimal coupling significantly modifies quantum geometry, the highly non-trivial ... More
Loop Quantum Cosmology: A Status ReportAug 03 2011Aug 22 2011The goal of this article is to provide an overview of the current state of the art in loop quantum cosmology for three sets of audiences: young researchers interested in entering this area; the quantum gravity community in general; and, cosmologists who ... More
Nanoplasmonic Tweezers Visualize Protein p53 Suppressing Unzipping of Single DNA-HairpinsMar 16 2014Here we report on the use of double-nanohole (DNH) optical tweezers as a label-free and free-solution single-molecule probe for protein-DNA interactions. Using this approach, we demonstrate the unzipping of individual 10 base pair DNA-hairpins, and quantify ... More
Initial conditions for cosmological perturbationsOct 28 2016Penrose proposed that the big bang singularity should be constrained by requiring that the Weyl curvature vanishes there. The idea behind this past hypothesis is attractive because it constrains the initial conditions for the universe in geometric terms ... More
Positive cosmological constant in loop quantum cosmologyDec 01 2011The k=0 Friedmann Lemaitre Robertson Walker model with a positive cosmological constant and a massless scalar field is analyzed in detail. If one uses the scalar field as relational time, new features arise already in the Hamiltonian framework of classical ... More
Laws Governing Isolated Horizons: Inclusion of Dilaton CouplingsOct 20 1999Dec 24 1999Mechanics of non-rotating black holes was recently generalized by replacing the static event horizons used in standard treatments with `isolated horizons.' This framework is extended to incorporate dilaton couplings. Since there can be gravitational and ... More
Loop quantum cosmology: From pre-inflationary dynamics to observationsApr 28 2015Sep 30 2015The Planck collaboration has provided us rich information about the early universe, and a host of new observational missions will soon shed further light on the `anomalies' that appear to exist on the largest angular scales. From a quantum gravity perspective, ... More
The Overview Chapter in Loop Quantum Gravity: The First 30 YearsMar 21 2017This is the introductory Chapter in the monograph Loop Quantum Gravity: The First 30 Years, edited by the authors, that was just published in the series "100 Years of General Relativity. The 8 invited Chapters that follow provide fresh perspectives on ... More
On Finding a Subset of Healthy Individuals from a Large PopulationJul 31 2013Feb 28 2016In this paper, we derive mutual information based upper and lower bounds on the number of nonadaptive group tests required to identify a given number of "non defective" items from a large population containing a small number of "defective" items. We show ... More
Radiative and non-radiative effects of a substrate on localized plasmon resonance of particlesApr 20 2012Experiments have shown strong effects of some substrates on the localized plasmons of metallic nano particles but they are inconclusive on the affecting parameters. Here we have used Discrete Dipole Approximation in conjunction with Sommerfeld integral ... More
Inelastic X-ray Scattering by Electronic Excitations in Solids at High PressureDec 02 2008Sep 09 2009Investigating electronic structure and excitations under extreme conditions gives access to a rich variety of phenomena. High pressure typically induces behavior such as magnetic collapse and the insulator-metal transition in 3d transition metals compounds, ... More
Instability, finite amplitude pulsation and mass-loss in models of massive OB-type starsFeb 05 2018Variability and mass-loss are common phenomena in massive OB-type stars. It is argued that they are caused by violent strange mode instabilities identified in corresponding stellar models. We present a systematic linear stability analysis with respect ... More
The Discussion on Hulls of Cyclic Codes over the Ring $\Re =\Z_4+v\Z_4$, $v^2=v$Apr 07 2019For odd length $n$, the cyclic codes construction over $\Re= \Z_4[v]/ \langle v^2-v \rangle$ is provided. The hulls of cyclic codes over $\Re$ are studied. The average $2$-dimension $E(n)$ of the hulls of cyclic codes over $\Re$ is also conferred. Among ... More
Construction of cyclic DNA codes over the Ring $\Z_4[u]/\langle u^2-1 \rangle $ Based on the deletion distanceMar 13 2016In this paper, we develop the theory for constructing DNA cyclic codes of odd length over $R=\Z_4[u]/\langle u^2-1 \rangle$ based on the deletion distance. Firstly, we relate DNA pairs with a special 16 elements of ring $R$. Cyclic codes of odd length ... More
Path Gain Algebraic Formulation for the Scalar Linear Network Coding ProblemJul 08 2008Jun 19 2010In the algebraic view, the solution to a network coding problem is seen as a variety specified by a system of polynomial equations typically derived by using edge-to-edge gains as variables. The output from each sink is equated to its demand to obtain ... More
A class of cyclic Codes Over the Ring $\Z_4[u]/<u^2>$ and its Gray imageJul 17 2015Cyclic codes over R have been introduced recently. In this paper, we study the cyclic codes over R and their $\Z_2$ image. Making use of algebraic structure, we find the some good $\Z_2$ codes of length 28.
On cyclic self-orthogonal codes over ZpmJul 11 2015The purpose of this paper is to study the cyclic self orthogonal codes over $\mathbb{Z}_{p^m}$. After providing the generator polynomial of cyclic self orthogonal codes over $\mathbb{Z}_{p^m}$, we give the necessary and sufficient condition for the existence ... More
Biconvex Relaxation for Semidefinite Programming in Computer VisionMay 31 2016Aug 08 2016Semidefinite programming is an indispensable tool in computer vision, but general-purpose solvers for semidefinite programs are often too slow and memory intensive for large-scale problems. We propose a general framework to approximately solve large-scale ... More
Gravitational Self-force in a Radiation GaugeApr 13 2010Oct 22 2014In this, the first of two companion papers, we present a method for finding the gravitational self-force in a modified radiation gauge for a particle moving on a geodesic in a Schwarzschild or Kerr spacetime. An extension of an earlier result by Wald ... More
Conservative, gravitational self-force for a particle in circular orbit around a Schwarzschild black hole in a Radiation GaugeSep 24 2010Mar 07 2011This is the second of two companion papers on computing the self-force in a radiation gauge; more precisely, the method uses a radiation gauge for the radiative part of the metric perturbation, together with an arbitrarily chosen gauge for the parts of ... More
Self-force as a cosmic censor in the Kerr overspinning problemAug 17 2015It is known that a near-extremal Kerr black hole can be spun up beyond its extremal limit by capturing a test particle. Here we show that overspinning is always averted once back-reaction from the particle's own gravity is properly taken into account. ... More
Genetic Algorithm for a class of Knapsack ProblemsFeb 15 2019The 0/1 knapsack problem is weakly NP-hard in that there exist pseudo-polynomial time algorithms based on dynamic programming that can solve it exactly. There are also the core branch and bound algorithms that can solve large randomly generated instances ... More
Standardization in the UV with Astrosat and its issues related to star cluster studiesOct 07 2018The Ultra-Violet Imaging Telescope (UVIT) is one of the payloads in Astrosat, the first Indian Space Observatory. The UVIT instrument has two 375 mm telescopes: one for the far-ultraviolet (FUV) channel (1300-1800 A), and the other for the near-ultraviolet ... More
Orbits of Distal Actions on Locally Compact GroupsOct 27 2010We discuss properties of orbits of (semi)group actions on locally compact groups G. In particular, we show that if a compactly generated locally compact abelian group acts distally on G then the closure of each of its orbits is a minimal closed invariant ... More
Quasi-abelian hearts of twin cotorsion pairs on triangulated categoriesJul 14 2018Jun 23 2019We prove that, under a mild assumption, the heart H of a twin cotorsion pair ((S,T),(U,V)) on a triangulated category C is a quasi-abelian category. If C is also Krull-Schmidt and T=U, we show that the heart of the cotorsion pair (S,T) is equivalent to ... More
Gauge-invariant perturbations of Schwarzschild spacetimeNov 24 2016We study perturbations of Schwarzschild spacetime in a coordinate-free, covariant form. The GHP formulation, having the advantage of not only being covariant but also tetrad-rotation invariant, is used to write down the previously known odd- and even-parity ... More
Estimation from Pairwise Comparisons: Sharp Minimax Bounds with Topology DependenceMay 06 2015Data in the form of pairwise comparisons arises in many domains, including preference elicitation, sporting competitions, and peer grading among others. We consider parametric ordinal models for such pairwise comparison data involving a latent vector ... More
When is it Better to Compare than to Score?Jun 25 2014When eliciting judgements from humans for an unknown quantity, one often has the choice of making direct-scoring (cardinal) or comparative (ordinal) measurements. In this paper we study the relative merits of either choice, providing empirical and theoretical ... More
Expansive Automorphisms on Locally Compact GroupsDec 04 2018We show that any connected locally compact group which admits an expansive automorphism is nilpotent. We also show that for any locally compact group $G$, $\alpha\in {\rm Aut}(G)$ is expansive if and only if for any $\alpha$-invariant closed subgroup ... More
Kinematics and Dynamics of Young Star Clusters with TMTSep 26 2018Oct 12 2018Star clusters are evolving n-body systems. We discuss the early dynamics of star clusters, the process of primordial mass segregation and clustering observed in certain young clusters. We discuss how the dynamics coupled with stellar evolution of a cluster ... More
Smooth phase transition of energy equilibration in a springy Sinai billiardSep 17 2018Statistical equilibration of energies in a slow-fast system is a fundamental open problem in physics. In a recent paper, it was shown that the equilibration rate in a springy billiard can remain strictly positive in the limit of vanishing mass ratio (of ... More
Hölder continuity of bounded, weak solutions of a variational system in the critical caseSep 14 2016Let $\Omega\subset\mathbb{R}^{2}$ be a bounded, Lipschitz domain. We consider bounded, weak solutions ($u\in W^{1, 2}\cap L^{\infty}(\Omega;\mathbb{R}^N)$) of the vector-valued, Euler-Lagrange system: \text{div } \big( A(x, u)Du\big)=g(x, u, Du)\quad\text{in ... More
On 3-dimensional asymptotically harmonic manifolds with minimal horospheresAug 22 2011May 21 2013Let $(M,g)$ be a complete, simply connected Riemannian manifold of dimension 3 without conjugate points. We show that $M$ is a flat manifold, provided $M$ is asymptotically harmonic of constant $h = 0$.
Interpolating PeriodsMay 13 2013We study the interpolation of Hodge-Tate and de Rham periods in families of Galois representations. Given a Galois representation on a coherent locally free sheaf over a reduced rigid space and a bounded range of weights, we obtain a stratification of ... More
Security Landscape for RoboticsApr 05 2019In this paper, the current state of security in robotics is described to be in need of review. When we consider safety mechanisms implemented in an Internet-connected robot, the requirement of safety becomes a crucial security requirement. Upon review ... More
Asymptotic predictions using short-time data in oscillating billiardsMay 20 2010Particle motion in a smoothly oscillating non-integrable billiard is known to result in unbounded energy growth. Though the asymptotic energy growth rate of an ensemble of particles in an oscillating chaotic billiard is known to be quadratic, there are ... More
H^o type Riemannian metrics on the space of planar curvesOct 10 2005Michor and Mumford have shown that the distances between planar curves in the simplest metric (not involving derivatives) are identically zero. We consider two conformally equivalent metrics for which the distances between curves are nontrivial. We show ... More
Parametrized higher category theory and higher algebra: Exposé II - Indexed homotopy limits and colimitsSep 16 2018We develop foundations for the category theory of $\infty$-categories parametrized by a base $\infty$-category. Our main contribution is a theory of indexed homotopy limits and colimits, which specializes to a theory of $G$-colimits for $G$ a finite group ... More
Expansive Automorphisms on Locally Compact GroupsDec 04 2018Feb 20 2019We show that any connected locally compact group which admits an expansive automorphism is nilpotent. We also show that for any locally compact group $G$, $\alpha\in {\rm Aut}(G)$ is expansive if and only if for any $\alpha$-invariant closed subgroup ... More
Big Data and the Internet of ThingsMar 24 2015Advances in sensing and computing capabilities are making it possible to embed increasing computing power in small devices. This has enabled the sensing devices not just to passively capture data at very high resolution but also to take sophisticated ... More
The Open Universe and Data-driven AstronomyOct 08 2018Activities related to access to astronomical facilities and data could offer an effective, entry-level path for outreach and astronomy education. The Government of Italy proposed the Open Universe initiative that was adopted by the United Nations Office ... More
Quasi-abelian hearts of twin cotorsion pairs on triangulated categoriesJul 14 2018We prove that, under a mild assumption, the heart H of a twin cotorsion pair ((S,T),(U,V)) on a triangulated category C is a quasi-abelian category. If C is also Krull-Schmidt and T=U, we show that the heart of the cotorsion pair (S,T) is equivalent to ... More
Toward Collaborative Information Seeking (CIS)Aug 05 2009It is natural for humans to collaborate while dealing with complex problems. In this article I consider this process of collaboration in the context of information seeking. The study and discussion presented here are driven by two dissatisfactions: (1) ... More
Geometry of Asymptotically harmonic manifolds with minimal horospheresMar 01 2017Feb 19 2018$(M^n,g)$ be a complete Riemannian manifold without conjugate points. In this paper, we show that if $M$ is also simply connected, then $M$ is flat, provided that $M$ is also asymptotically harmonic manifold with minimal horospheres (AHM). The (first ... More
The pre-inflationary dynamics of loop quantum cosmology: Confronting quantum gravity with observationsFeb 01 2013Apr 08 2013Using techniques from loop quantum gravity, the standard theory of cosmological perturbations was recently generalized to encompass the Planck era. We now apply this framework to explore pre-inflationary dynamics. The framework enables us to isolate and ... More
The Approximate Capacity of the Many-to-One and One-to-Many Gaussian Interference ChannelsSep 21 2008Recently, Etkin, Tse, and Wang found the capacity region of the two-user Gaussian interference channel to within one bit/s/Hz. A natural goal is to apply this approach to the Gaussian interference channel with an arbitrary number of users. We make progress ... More
A Hamiltonian Formulation of the BKL ConjectureFeb 17 2011Mar 12 2011The Belinskii, Khalatnikov and Lifshitz conjecture \cite{bkl1} posits that on approach to a space-like singularity in general relativity the dynamics are well approximated by `ignoring spatial derivatives in favor of time derivatives.' In \cite{ahs1} ... More
On High Spatial Reuse Link Scheduling in STDMA Wireless Ad Hoc NetworksJan 02 2007Graph-based algorithms for point-to-point link scheduling in Spatial reuse Time Division Multiple Access (STDMA) wireless ad hoc networks often result in a significant number of transmissions having low Signal to Interference and Noise density Ratio (SINR) ... More
Multi-Player Multi-Armed Bandit Based Resource Allocation for D2D CommunicationsDec 12 2018Device-to-device (D2D) communications is expected to play a significant role in increasing the system capacity of the fifth generation (5G) wireless networks. To accomplish this, efficient power and resource allocation algorithms need to be devised for ... More
Minisuperspaces: Observables and QuantizationFeb 21 1993A canonical transformation is performed on the phase space of a number of homogeneous cosmologies to simplify the form of the scalar (or, Hamiltonian) constraint. Using the new canonical coordinates, it is then easy to obtain explicit expressions of Dirac ... More
Behavior of Einstein-Rosen Waves at Null InfinityAug 16 1996The asymptotic behavior of Einstein-Rosen waves at null infinity in 4 dimensions is investigated in {\it all} directions by exploiting the relation between the 4-dimensional space-time and the 3-dimensional symmetry reduction thereof. Somewhat surprisingly, ... More
Quantum gravity, shadow states, and quantum mechanicsJul 26 2002Nov 20 2002A program was recently initiated to bridge the gap between the Planck scale physics described by loop quantum gravity and the familiar low energy world. We illustrate the conceptual problems and their solutions through a toy model: quantum mechanics of ... More
An Extension of the Quantum Theory of Cosmological Perturbations to the Planck EraNov 06 2012Jan 16 2013Cosmological perturbations are generally described by quantum fields on (curved but) classical space-times. While this strategy has a large domain of validity, it can not be justified in the quantum gravity era where curvature and matter densities are ... More
Perturbations in loop quantum cosmologyApr 05 2012The era of precision cosmology has allowed us to accurately determine many important cosmological parameters, in particular via the CMB. Confronting Loop Quantum Cosmology with these observations provides us with a powerful test of the theory. For this ... More
On Coretractable ModuleMay 31 2015The main aim of this paper is to discuss the structure of coretractble and mono-coretractble modules. We have provided the characterizations of coretractable modules in terms of Kasch ring, CS modules, mono-coretractble modules, projective modules, epi ... More