Results for "Aris Karastergiou"

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The frequency dependence of scattering imprints on pulsar observationsJul 18 2016Aug 22 2016Observations of pulsars across the radio spectrum are revealing a dependence of the characteristic scattering time ($\tau$) on frequency, which is more complex than the simple power law with a theoretically predicted power law index. In this paper we ... More
Goonhilly SparklersOct 18 2011Flux monitoring of compact radio quasars has revealed dramatic radio-wave lensing events which challenge our understanding of the interstellar medium. However, the data on these events remain very sparse. Here we consider how the Goonhilly radio astronomical ... More
The Period-Width relationship for radio pulsars revisitedFeb 06 2019In the standard picture of radio pulsars, the radio emission arises from a set of open magnetic field lines, the extent of which is primarily determined by the pulsar's spin period, P, and the emission height. We have used a database of parameters from ... More
Observations of transients and pulsars with LOFAR international stations and the ARTEMIS backendOct 16 2012Oct 30 2012The LOw Frequency ARray - LOFAR - is a new radio interferometer designed with emphasis on flexible digital hardware instead of mechanical solutions. The array elements, so-called stations, are located in the Netherlands and in neighbouring countries. ... More
Pulsar braking and the P-Pdot diagramFeb 13 2017The location of radio pulsars in the period-period derivative (P-Pdot) plane has been a key diagnostic tool since the early days of pulsar astronomy. Of particular importance is how pulsars evolve through the P-Pdot diagram with time. Here we show that ... More
An investigation of the absolute circular polarization in radio pulsarsMay 07 2004In most pulsars, the circularly polarized component, Stokes $V$, is weak in the average pulse profiles. By forming the average profile of $|V|$ from single pulses we can distinguish between pulsars where $V$ is weak in the individual pulses and those ... More
Observations of transients and pulsars with LOFAR international stationsJul 02 2012The LOw FRequency ARray - LOFAR is a new radio telescope that is moving the science of radio pulsars and transients into a new phase. Its design places emphasis on digital hardware and flexible software instead of mechanical solutions. LOFAR observes ... More
Verifying and Reporting Fast Radio BurstsAug 23 2018Fast Radio Bursts (FRBs) are a class of short-duration transients at radio wavelengths with inferred astrophysical origin. The prototypical FRB is a broadband signal that occurs over the extent of the receiver frequency range, is narrow in time, and is ... More
Simultaneous radio and X-ray observations of PSR B0611+22Jul 26 2016We report results from simultaneous radio and X-ray observations of PSR B0611+22 which is known to exhibit bursting in its single-pulse emission. The pulse phase of the bursts vary with radio frequency. The bursts are correlated in 327/150~MHz datasets ... More
High frequency observations of southern pulsarsApr 19 2006We present polarization data for 32 mainly southern pulsars at 8.4 GHz. The observations show that the polarization fraction is low in most pulsars at this frequency except for the young, energetic pulsars which continue to show polarization fractions ... More
Linking Long- and Short-Term Emission Variability in PulsarsApr 24 2019It is now known that the emission from radio pulsars can vary over a wide range of timescales, from fractions of seconds to decades. However, it is not yet known if long- and short-term emission variability are caused by the same physical processes. A ... More
New pulsar rotation measures and the Galactic magnetic fieldMar 05 2008We measured a sample of 150 pulsar Rotation Measures (RMs) using the 20-cm receiver of the Parkes 64-m radio telescope. 46 of the pulsars in our sample have not had their RM values previously published, whereas 104 pulsar RMs have been revised. We used ... More
Multi-frequency integrated profiles of pulsarsApr 24 2008We have observed a total of 67 pulsars at five frequencies ranging from 243 to 3100 MHz. Observations at the lower frequencies were made at the Giant Metre Wave Telescope in India and those at higher frequencies at the Parkes Telescope in Australia. We ... More
On the Non-Uniqueness of Solutions to the Average Cost HJB for Controlled Diffusions with Near-Monotone CostsSep 21 2013We present a theorem for verification of optimality of controlled diffusions under the average cost criterion with near-monotone running cost, without invoking any blanket stability assumptions. The implications of this result to the policy iteration ... More
Gapped spin Hamiltonian motivated by quantum teleportationOct 07 2014We construct a Hamiltonian whose ground state encodes a time-independent emulation of quan- tum teleportation. We calculate properties of the Hamiltonian, using exact diagonalization and a mean-field theory, and argue that it has a gap. The system exhibits ... More
Fault-tolerant, Universal Adiabatic Quantum ComputationMar 30 2014Quantum computation has revolutionary potential for speeding computational tasks such as factoring and simulating quantum systems, but the task of constructing a quantum computer is daunting. Adiabatic quantum computation and other ``hands-off" approaches ... More
Evidence for Line Broadening by Electron Scattering in the Broad Line Region of NGC 4395Jan 30 2006A high quality Keck spectrum of the Halpha line in NGC 4395 reveals symmetric exponential wings, fv\propto e^{-v/sigma}, with sigma~500km/s. The wings extend out to >2500km/s from the line core, and down to a flux density of <10^-3 of the peak flux density. ... More
Lyman $α$ Absorption as a Sensitive Probe of the H I Column in Cooling FlowsSep 24 1996X-ray spectra of a significant fraction of cooling flow (CF) clusters of galaxies indicate the presence of a large column of ``cold'' absorbing gas. The physical nature of the absorbing medium remains a mystery. Searches for H I absorption using the 21 ... More
The Ionizing Continuum of QuasarsOct 15 1998The ionizing continuum shape of quasars is generally not directly observable, but indirect arguments, based on photoionization models and thin accretion disk models suggest that it should peak in the extreme UV, and drop steeply into the soft X-ray regime. ... More
Grothendieck groups of categories of abelian varietiesJan 13 2017We compute the Grothendieck group of the category of abelian varieties over an algebraically closed field $k$. We also compute the Grothendieck group of the category of $A$-isotypic abelian varieties, for any simple abelian variety $A$, assuming $k$ has ... More
L^p change of variables inequalities on manifoldsApr 02 2010Nov 28 2011We prove two-sided inequalities for the $L^p$-norm of a pushforward or pullback (with respect to an orientation-preserving diffeomorphism) on oriented volume and Riemannian manifolds. For a function or density on a volume manifold, these bounds depend ... More
A counterexample to a nonlinear version of the Krein-Rutman theorem by R. MahadevanFeb 13 2018In this short note we present a simple counterexample to a nonlinear version of the Krein-Rutman theorem reported in [Nonlinear Anal. 11 (2007), 3084-3090]. Correct versions of this theorem, and related results for superadditive maps are also presented. ... More
"The Waters I am Entering No One yet Has Crossed": Alexander Friedman and the Origins of Modern CosmologyFeb 06 2013Ninety years ago, in 1922, Alexander Friedman (1888-1925) demonstrated for the first time that the General Relativity equations admit non-static solutions and thus the Universe may expand, contract, collapse, and even be born. The fundamental equations ... More
Discovery of Hubble's Law: an Example of Type III ErrorMar 24 2014Recently much attention has been paid to the discovery of Hubble's law: the linear relation between the rate of recession of the distant galaxies and distance to them. Though we now mention several names associated with this law instead of one, the motivation ... More
Mimicking Time Evolution within a Quantum Ground State: Ground-State Quantum Computation, Cloning, and TeleportationDec 09 2003Ground-state quantum computers mimic quantum mechanical time evolution within the amplitudes of a time-independent quantum state. We explore the principles that constrain this mimicking. A no-cloning argument is found to impose strong restrictions. It ... More
Some Comments related to AGN Radio LoudnessDec 16 2003Dec 24 2003The bimodality of the AGN radio loudness distribution, and the relation of radio loudness and black hole mass were recently disputed. A closer look at the existing data suggests possible resolutions of these disputes, as further described below.
What Can We Learn from the Smallest AGN?Feb 21 2007Quite a few things. In particular, reverberation mapping of NGC 4395, the lowest luminosity type 1 Active Galactic Nucleus (AGN, L_bol~10^40 erg/s) revealed a size of only ~1 light hour for the C IV broad line region (BLR), which is by far the smallest ... More
Another look at Black Hole SpinsMar 21 2019Do black holes rotate, and if yes, how fast? This question is fundamental and has broad implications, but still remains open. There are significant observational challenges in current spin determinations, and future facilities offer prospects for precision ... More
Where do statistical models come from? Revisiting the problem of specificationOct 27 2006R. A. Fisher founded modern statistical inference in 1922 and identified its fundamental problems to be: specification, estimation and distribution. Since then the problem of statistical model specification has received scant attention in the statistics ... More
Quadratic twists of abelian varieties with real multiplicationOct 11 2017Jan 09 2018Let $F$ be a totally real number field and $A/F$ a principally polarized abelian variety with real multiplication by the ring of integers $\mathcal{O}$ of a totally real field. Assuming $A$ admits an $\mathcal{O}$-linear 3-isogeny over $F$, we prove that ... More
Some new results on sample path optimality in ergodic control of diffusionsMay 12 2016We present some new results on sample path optimality for the ergodic control problem of a class of non-degenerate diffusions controlled through the drift. The hypothesis most often used in the literature to ensure the existence of an a.s.\ sample path ... More
Quantum vortex tunneling: Microscopic theory and application to d-wave superconductorsJul 25 2001Sep 26 2003We present a microscopic approach to the quantum tunneling of vortices. The formalism characterizes the rate at which a many-body superconducting state with a vortex in one location makes a transition to a second many-body superconducting state with a ... More
On The Linearity of The Black Hole - Bulge Mass Relation in Active and in Nearby GalaxiesJan 23 2001Analysis of PG quasar observations suggests a nonlinear relation between the black hole mass, M_BH, and the bulge mass, M_bulge, although a linear relation, as proposed for nearby galaxies, cannot be ruled out. New M_BH values for nearby galaxies from ... More
On Quasar Masses and Quasar Host GalaxiesJul 27 1998The mass of massive black holes in quasar cores can be deduced using the typical velocities of Hb-emitting clouds in the Broad Line Region (BLR) and the size of this region. However, this estimate depends on various assumptions and is susceptible to large ... More
Revisiting Simpson's Paradox: a statistical misspecification perspectiveMay 07 2016May 13 2016The primary objective of this paper is to revisit Simpson's paradox using a statistical misspecification perspective. It is argued that the reversal of statistical associations is sometimes spurious, stemming from invalid probabilistic assumptions imposed ... More
Revisiting the Neyman-Scott model: an Inconsistent MLE or an Ill-defined Model?Jan 26 2013The Neyman and Scott (1948) model is widely used to demonstrate a serious weakness of the Maximum Likelihood (ML) method: it can give rise to inconsistent estimators. The primary objective of this paper is to revisit this example with a view to demonstrate ... More
Inner Market as a "Black Box"Jun 20 2001Each market has its singular characteristic. Its inner structure is directly responsible for the observed distributions of returns though this fact is widely overlooked. Big orders lead to doubling the tails. The behavior of a market maker with many or ... More
FZZ ScatteringJun 08 2006Nov 03 2006We study the duality between the two dimensional black hole and the sine-Liouville conformal field theories via exact operator quantization of a classical scattering problem. The ideas are first illustrated in Liouville theory, which is dual to itself ... More
Liouville theory without an actionJan 26 2006Jun 08 2006We show that the crossing symmetry of the four-point function in the Liouville conformal field theory on the sphere contains more information than what was hitherto considered. Under certain assumptions, it provides the special structure constants that ... More
Intrinsic Instrumental Polarization and High-Precision Pulsar TimingJul 24 2015Radio telescopes are used to accurately measure the time of arrival (ToA) of radio pulses in pulsar timing experiments that target mostly millisecond pulsars (MSPs) due to their high rotational stability. This allows for detailed study of MSPs and forms ... More
Real-time, fast radio transient searches with GPU de-dispersionJul 13 2011The identification, and subsequent discovery, of fast radio transients through blind-search surveys requires a large amount of processing power, in worst cases scaling as $\mathcal{O}(N^3)$. For this reason, survey data are generally processed offline, ... More
A transient component in the pulse profile of PSR J0738-4042Mar 11 2011One of the tenets of the radio pulsar observational picture is that the integrated pulse profiles are constant with time. This assumption underpins much of the fantastic science made possible via pulsar timing. Over the past few years, however, this assumption ... More
GREENBURST: a commensal fast radio burst search back-end for the Green Bank TelescopeMar 13 2019We describe the design and deployment of GREENBURST, a commensal Fast Radio Burst (FRB) search system at the Green Bank Telescope. GREENBURST uses the dedicated L-band receiver tap to search over the 960$-$1920 MHz frequency range for pulses with dispersion ... More
Unitarity of supersymmetric SL(2,R)/U(1) and no-ghost theorem for fermionic strings in AdS(3) x NJan 16 2003Feb 16 2003The unitarity of the NS supersymmetric coset SL(2,R)/U(1) is studied for the discrete representations. The results are applied to the proof of the no-ghost theorem for fermionic strings in AdS(3) x N in the NS sector. A no-ghost theorem is proved for ... More
Critically damped quantum searchOct 02 2008Although measurement and unitary processes can accomplish any quantum evolution in principle, thinking in terms of dissipation and damping can be powerful. We propose a modification of Grover's algorithm in which the idea of damping plays a natural role. ... More
Variational Monte Carlo for Interacting Electrons in Quantum DotsMay 03 2005We use a variational Monte Carlo algorithm to solve the electronic structure of two-dimensional semiconductor quantum dots in external magnetic field. We present accurate many-body wave functions for the system in various magnetic field regimes. We show ... More
Discrete Hamilton-Pontryagin mechanics and generating functions on Lie groupoidsMay 27 2009Jan 19 2010We present a discrete analog of the recently introduced Hamilton-Pontryagin variational principle in Lagrangian mechanics. This unifies two, previously disparate approaches to discrete Lagrangian mechanics: either using the discrete Lagrangian to define ... More
Banach space projections and Petrov-Galerkin estimatesJul 16 2013Nov 03 2015We sharpen the classic a priori error estimate of Babuska for Petrov-Galerkin methods on a Banach space. In particular, we do so by (i) introducing a new constant, called the Banach-Mazur constant, to describe the geometry of a normed vector space; (ii) ... More
A GPU implementation of the Correlation Technique for Real-time Fourier Domain Pulsar Acceleration SearchesApr 15 2018The study of binary pulsars enables tests of general relativity. Orbital motion in binary systems causes the apparent pulsar spin frequency to drift, reducing the sensitivity of periodicity searches. Acceleration searches are methods that account for ... More
Correlated emission and spin-down variability in radio pulsarsMar 07 2018The recent revelation that there are correlated period derivative and pulse shape changes in pulsars has dramatically changed our understanding of timing noise as well as the relationship between the radio emission and the properties of the magnetosphere ... More
A Note on the Viability of Gaseous Ionization in Active Galaxies by Fast ShocksFeb 12 1998Observational evidence suggest that shocks may affect the spatial and velocity distributions of gas in the NLR/ENLR of some active galaxies. It thus seemed plausible that shocks may also energize the NLR. The observed emission line ratios strongly favor ... More
What is the Broad Line Region?Dec 16 2003What is the Broad Line Region (BLR) made of? What determines its location? Why is it sometimes missing? What controls its properties? Some recent results and new approaches which may shed light on these issues are briefly described.
On Black Hole Masses and Radio Loudness in AGNSep 13 2000The distribution of radio to optical fluxes in AGN is bimodal. The physical origin for this bimodality is not understood. In this Letter I describe observational evidence, based on the Boroson & Green PG quasar sample, that the radio loudness bimodality ... More
On fixed-gap adiabatic quantum computationFeb 04 2010Jan 21 2014Quantum computation has revolutionary potential for speeding algorithms and for simulating quantum systems such as molecules. We report here a quantum computer design that performs universal quantum computation within a single non-degenerate ground state ... More
BRST Quantization of String Theory in AdS(3)Apr 28 2003Aug 21 2003We study the BRST quantization of bosonic and NSR strings propagating in AdS(3) x N backgrounds. The no-ghost theorem is proved using the Frenkel-Garland-Zuckerman method. Regular and spectrally-flowed representations of affine SL(2,R) appear on an equal ... More
ALFABURST: A realtime fast radio burst monitor for the Arecibo telescopeNov 13 2015Fast radio bursts (FRBs) constitute an emerging class of fast radio transient whose origin continues to be a mystery. Realizing the importance of increasing coverage of the search parameter space, we have designed, built, and deployed a realtime monitor ... More
Commissioning of ALFABURST: initial tests and resultsFeb 13 2016Fast Radio Bursts (FRBs) are apparently one-time, relatively bright radio pulses that have been observed in recent years. The origin of FRBs is currently unknown and many instruments are being built to detect more of these bursts to better characterize ... More
Nonlinear coupling of nano mechanical resonators to Josephson quantum circuitsMay 01 2006We propose a technique to couple the position operator of a nano mechanical resonator to a SQUID device by modulating its magnetic flux bias. By tuning the magnetic field properly, either linear or quadratic couplings can be realized, with a discretely ... More
Hadronic Production of TeV Gamma Ray Flares from BlazarsOct 30 1996Jan 13 1997We propose that TeV $\gamma$-ray emission from blazars is produced by collisions near the line of sight of high energy jet protons with gas targets (``clouds'') from the broad emission-line region (BLR). Intense TeV $\gamma$-ray flares (GRFs) are produced ... More
Infinite Horizon Average Optimality of the N-network Queueing Model in the Halfin-Whitt RegimeFeb 10 2016Sep 30 2016We study the infinite horizon optimal control problem for N-network queueing systems, which consist of two customer classes and two server pools, under average (ergodic) criteria in the Halfin-Whitt regime. We consider three control objectives: 1) minimizing ... More
Trace formulae for Schrödinger operators with complex-valued potentials on cubic latticesSep 30 2016We consider Schr\"odinger operators with complex decaying potentials on the lattice. Using some classical results from Complex Analysis we obtain some trace formulae and using them estimate globally all zeros of the Fredholm determinant in terms of the ... More
On the negative spectrum of two-dimensional Schrödinger operators with radial potentialsAug 04 2011Dec 21 2011For a two-dimensional Schr\"odinger operator $H_{\alpha V}=-\Delta-\alpha V$ with the radial potential $V(x)=F(|x|), F(r)\ge 0$, we study the behavior of the number $N_-(H_{\alpha V})$ of its negative eigenvalues, as the coupling parameter $\alpha$ tends ... More
Radiative corrections to the Higgs boson decay rate $Γ(H\rightarrow ZZ)$ in the minimal supersymmetric modelJun 26 1992We consider radiative corrections to the decay rate $\Gamma(H\rightarrow ZZ)$ of the heavy {\it CP}-even Higgs boson of the minimal supersymmetric model to two $Z$ bosons. We perform a one loop Feynman diagram calculation in the on-mass-shell renormalization ... More
Metal enrichment by radiation pressure in active galactic nucleus outflows -- theory and observationsJul 30 2012Outflows from active galactic nuclei may be produced by absorption of continuum radiation by UV resonance lines of abundant metal ions, as observed in broad absorption line quasars (BALQs). The radiation pressure exerted on the metal ions is coupled to ... More
Topological Entanglement Entropy and HolographyMay 13 2008May 30 2008We study the entanglement entropy in confining theories with gravity duals using the holographic prescription of Ryu and Takayanagi. The entanglement entropy between a region and its complement is proportional to the minimal area of a bulk hypersurface ... More
Tides Alone Cannot Explain Kepler Planets Close to 2:1 MMRAug 19 2015A number of Kepler planet pairs lie just wide of first-order mean motion resonances (MMRs). Tides have been frequently proposed to explain these pileups, but it is still an ongoing discussion. We contribute to this discussion by calculating an optimistic ... More
High-field magnetoresistance revealing scattering mechanisms in grapheneMay 02 2012Sep 13 2012We show that the type of charge carrier scattering significantly affects the high-field magnetoresistance of graphene nanoribbons. This effect has potential to be used in identifying the scattering mechanisms in graphene. The results also provide an explanation ... More
Exact diagonalization of the Hubbard model on graphics processing unitsApr 16 2012Jun 19 2012We solve the Hubbard model with the exact diagonalization method on a graphics processing unit (GPU). We benchmark our GPU program against a sequential CPU code by using the Lanczos algorithm to solve the ground state energy in two cases: a one-dimensional ... More
Control of a two-electron quantum ring with an external magnetic fieldFeb 04 2010We investigate the use of external time-dependent magnetic field for the control of the quantum states in a two-electron quantum ring. The hyperfine interaction of the confined electrons with surrounding nuclei couples the singlet state with the three ... More
Charge dynamics in two-electron quantum dotsMay 19 2010We investigate charge dynamics in a two-electron double quantum dot. The quantum dot is manipulated by using a time-dependent external voltage that induces charge oscillations between the dots. We study the dependence of the charge dynamics on the external ... More
Ground-state of two-dimensional finite electron systems in the Quantum Hall regimeMar 09 2005May 20 2005We study electronic structures of quasi-two-dimensional finite electron systems in high magnetic fields. The solutions in the fractional quantum Hall regime are interpreted as quantum liquids of electrons and off-electron vortices. The ground states are ... More
A Gross-Kohnen-Zagier formula for Heegner-Drinfeld cyclesJul 01 2017Let $F$ be the field of rational functions on a smooth projective curve over a finite field, and let $\pi$ be an unramified cuspidal automorphic representation for $\mathrm{PGL}_2$ over $F$. We prove a variant of the formula of Yun and Zhang relating ... More
The modal logic of $σ$-centered forcing and related forcing classesJan 18 2017We consider the modality "$\varphi$ is true in every $\sigma$-centered forcing extension", denoted $\square\varphi$ and its dual "$\varphi$ is true in some $\sigma$-centered forcing extension", denoted $\lozenge\varphi$, (where $\varphi$ is a statement ... More
Brane Inflation and Moduli Stabilization on Twisted ToriOct 24 2013Aug 08 2015We consider supergravity compactifications on 6-dimensional twisted tori, which are 5-torus fibrations of the circle. The motion of branes on such manifolds can lead to power-law potentials at low energy, that may be useful for inflation. We classify ... More
Infinite Horizon Average Optimality of the N-network Queueing Model in the Halfin-Whitt RegimeFeb 10 2016Aug 28 2017We study the infinite horizon optimal control problem for N-network queueing systems, which consist of two customer classes and two server pools, under average (ergodic) criteria in the Halfin-Whitt regime. We consider three control objectives: 1) minimizing ... More
Large Deviations for Partition Functions of Directed Polymers and Some Other Models in an IID FieldApr 27 2007Consider the partition function of a directed polymer in an IID field. We assume that both tails of the negative and the positive part of the field are at least as light as exponential. It is a well-known fact that the free energy of the polymer is equal ... More
Geodesics in a Graph of Perfect MatchingsJun 15 2013Sep 09 2014This paper studies geodesics in the graph $\mathscr{P}_{m}$, which has all perfect matchings in $K_{2m}$ as vertices with two perfect matchings connected by an edge if their symmetric difference is a cycle of length four. The diameter of $\mathscr{P}_{m}$, ... More
Infinite Horizon Risk-Sensitive Control of Diffusions Without Any Blanket Stability AssumptionsJan 03 2016Nov 04 2016We consider the infinite horizon risk-sensitive problem for nondegenerate diffusions with a compact action space, and controlled through the drift. We only impose a structural assumption on the running cost function, namely near-monotonicity, and show ... More
Exact Hamiltonian Monte Carlo for Truncated Multivariate GaussiansAug 20 2012Jun 05 2013We present a Hamiltonian Monte Carlo algorithm to sample from multivariate Gaussian distributions in which the target space is constrained by linear and quadratic inequalities or products thereof. The Hamiltonian equations of motion can be integrated ... More
Exact chiral ring of AdS(3)/CFT(2)Mar 02 2007Jun 05 2007We carry out an exact worldsheet computation of tree level three-point correlators of chiral operators in string theory on AdS(3) x S^3 x T^4 with NS-NS flux. We present a simple representation for the string chiral operators in the coordinate basis of ... More
Infinite Horizon Average Optimality of the N-network Queueing Model in the Halfin-Whitt RegimeFeb 10 2016We study the infinite horizon optimal control problem for N-network queueing systems, which consist of two customer classes and two server pools, under average (ergodic) criteria in the Halfin-Whitt regime. We consider three control objectives: 1) minimizing ... More
Efficiently decoding strings from their shinglesApr 15 2012Determining whether an unordered collection of overlapping substrings (called shingles) can be uniquely decoded into a consistent string is a problem that lies within the foundation of a broad assortment of disciplines ranging from networking and information ... More
Type 1 AGN at low zMar 22 2012We present the emission properties of a sample of 3,579 type 1 AGN, selected based on the detection of broad H-alpha emission. The sample covers the range of black hole mass 10^6<M_BH/M_Sun<10^9.5 and luminosity in Eddington units 10^-3 < L/L_Edd < 1. ... More
The Mass of a Spin Vortex in a Bose-Einstein CondensateFeb 20 2009Mar 07 2009In contrast to charge vortices in a superfluid, spin vortices in a ferromagnetic condensate move inertially (if the condensate has zero magnetization along an axis). The mass of spin vortices depends on the spin-dependent interactions, and can be measured ... More
Radiative Corrections to Neutralino and Chargino Masses in the Minimal Supersymmetric ModelDec 08 1993Dec 09 1993We determine the neutralino and chargino masses in the MSSM at one-loop. We perform a Feynman diagram calculation in the on-shell renormalization scheme, including quark/squark and lepton/slepton loops. We find generically the corrections are of order ... More
What controls the [O III] 5007 line strength in AGN?Jan 20 2005Feb 22 2005AGN display an extreme range in the narrow emission line equivalent widths. Specifically, in the PG quasar sample the equivalent width of the narrow [O III] 5007 line has a range of >300, while the broad Hb line, for example, has a range of 10 only. The ... More
What controls the C IV line profile in active galactic nuclei?Sep 08 2004The high ionization lines in active galactic nuclei (AGN), such as C IV, tend to be blueshifted with respect to the lower ionization lines, such as H beta, and often show a strong blue excess asymmetry not seen in the low ionization lines. There is accumulating ... More
What is the Origin of the Baldwin Effect in the BLR and the NLR?Dec 16 2003Dec 24 2003The origin of the luminosity dependence of the strength of broad and narrow emission lines in AGN (i.e. the Baldwin effect) is not firmly established yet. We explore this question using the Boroson & Green sample of the 87 z<=0.5 PG quasars. UV spectra ... More
A Faster FPTAS for the Subset-Sums Ratio ProblemMar 27 2018The Subset-Sums Ratio problem (SSR) is an optimization problem in which, given a set of integers, the goal is to find two subsets such that the ratio of their sums is as close to 1 as possible. In this paper we develop a new FPTAS for the SSR problem ... More
Berezin--Li--Yau inequalities on domains on the sphereDec 28 2017We prove Berezin--Li--Yau inequalities for the Dirichlet and Neumann eigenvalues on domains on the sphere $\mathbb{S}^{d-1}$. The case of $\mathbb{S}^{2}$ is treated in greater detail, including the vector Dirichlet Laplacian and the Stokes operator.
Fuzzy Hashing as Perturbation-Consistent Adversarial Kernel EmbeddingDec 17 2018Measuring the similarity of two files is an important task in malware analysis, with fuzzy hash functions being a popular approach. Traditional fuzzy hash functions are data agnostic: they do not learn from a particular dataset how to determine similarity; ... More
Capacitative coupling of singlet-triplet qubits in different inter-qubit geometriesApr 22 2014In the singlet-triplet qubit architecture, the two-qubit interactions required in universal quantum computing can be implemented by capacitative coupling, by exploiting the charge distribution differences of the singlet and triplet states. The efficiency ... More
New Bounds on the Minimum Density of a Vertex Identifying Code for the Infinite Hexagonal GridOct 05 2011For a graph, $G$, and a vertex $v \in V(G)$, let $N[v]$ be the set of vertices adjacent to and including $v$. A set $D \subseteq V(G)$ is a vertex identifying code if for any two distinct vertices $v_1, v_2 \in V(G)$, the vertex sets $N[v_1] \cap D$ and ... More
Stochastic programs without duality gaps for objectives without a lower boundAug 22 2014This paper studies parameterized stochastic optimization problems in finite discrete time that arise in many applications in operations research and mathematical finance. We prove the existence of solutions and the absence of a duality gap under conditions ... More
Maximum principles for the relativistic heat equationJul 17 2015The classical heat equation is incompatible with relativity, since the strong maximum principle allows for disturbances to propagate instantaneously. Some authors have proposed limiting the propagation speed by adding a linear hyperbolic correction term, ... More
Semilinear mixed problems on Hilbert complexes and their numerical approximationOct 29 2010Aug 09 2011Arnold, Falk, and Winther recently showed [Bull. Amer. Math. Soc. 47 (2010), 281-354] that linear, mixed variational problems, and their numerical approximation by mixed finite element methods, can be studied using the powerful, abstract language of Hilbert ... More
Infinite horizon risk-sensitive control of diffusions without any blanket stability assumptionsJan 03 2016Aug 16 2017We consider the infinite horizon risk-sensitive problem for nondegenerate diffusions with a compact action space, and controlled through the drift. We only impose a structural assumption on the running cost function, namely near-monotonicity, and show ... More
Linear structure of functions with maximal Clarke subdifferentialSep 03 2018It is hereby established that the set of Lipschitz functions $f:\mathcal{U}\rightarrow \mathbb{R}$ ($\mathcal{U}$ nonempty open subset of $\ell_{d}^{1}$) with maximal Clarke subdifferential contains a linear subspace of uncountable dimension (in particular, ... More
Eigenvalue bounds of mixed Steklov problemsDec 03 2017Sep 06 2018We study bounds on the Riesz means of the mixed Steklov-Neumann and Steklov-Dirichlet eigenvalue problem on a bounded domain $\Omega$ in $\mathbb{R}^n$. The Steklov-Neumann eigenvalue problem is also called the sloshing problem. We obtain two-term asymptotically ... More
A variational formula for risk-sensitive control of diffusions in $\mathbb{R}^d$Oct 02 2018We address the variational problem for the generalized principal eigenvalue on $\mathbb{R}^d$ of linear and semi-linear elliptic operators associated with nondegenerate diffusions controlled through the drift. We establish the Collatz-Wielandt formula ... More