Results for "B. D. G. Chandran"

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Radio-wave propagation through a medium containing electron-density fluctuations described by an anisotropic Goldreich-Sridhar spectrumFeb 13 2002We study the propagation of radio waves through a medium possessing density fluctuations that are elongated along the ambient magnetic field and described by an anisotropic Goldreich-Sridhar power spectrum. We derive general formulas for the wave phase ... More
Alfven Wave Turbulence and Perpendicular Ion Temperatures in Coronal HolesJun 17 2010Low-frequency Alfven-wave turbulence causes ion trajectories to become chaotic, or "stochastic," when the turbulence amplitude is sufficiently large. Stochastic orbits enable ions to absorb energy from the turbulence, increasing the perpendicular ion ... More
A review of the theory of incompressible MHD turbulenceNov 13 2003May 17 2004This brief invited review provides an introduction to key ideas in the theory of incompressible magnetohydrodynamic (MHD) turbulence.
Convection in galaxy-cluster plasmas driven by active galactic nuclei and cosmic-ray buoyancyJul 18 2004Dec 20 2004Turbulent heating may play an important role in galaxy-cluster plasmas, but if turbulent heating is to balance radiative cooling in a quasi-steady state, some mechanism must set the turbulent velocity to the required value. This paper explores one possible ... More
Strong Anisotropic MHD Turbulence with Cross HelicityJan 31 2008This paper proposes a new phenomenology for strong incompressible MHD turbulence with nonzero cross helicity. This phenomenology is then developed into a quantitative Fokker-Planck model that describes the time evolution of the anisotropic power spectra ... More
Particle acceleration by slow modes in strong compressible MHD turbulence, with application to solar flaresNov 13 2003Energetic particles that undergo strong pitch-angle scattering and diffuse through a plasma containing strong compressible MHD turbulence undergo diffusion in momentum space with diffusion coefficient Dp. In this paper, the contribution of slow modes ... More
AGN-driven convection in galaxy-cluster plasmasJun 04 2005This paper describes how active galactic nuclei can heat galaxy-cluster plasmas by driving convection in the intracluster medium. A model is proposed in which a central supermassive black hole accretes intracluster plasma at the Bondi rate and powers ... More
Weakly Turbulent MHD Waves in Compressible Low-Beta PlasmasOct 30 2008In this Letter, weak turbulence theory is used to investigate interactions among Alfven waves and fast and slow magnetosonic waves in collisionless low-beta plasmas. The wave kinetic equations are derived from the equations of magnetohydrodynamics, and ... More
The importance of anisotropic interstellar turbulence and molecular-cloud magnetic mirrors for galactic cosmic-ray propagationOct 04 2000Recent studies suggest that when magnetohydrodynamic (MHD) turbulence is excited by stirring a plasma at large scales, the cascade of energy from large to small scales is anisotropic, in the sense that small-scale fluctuations satisfy the inequality k_parallel ... More
Parametric Instability, Inverse Cascade, and the $1/f$ Range of Solar-Wind TurbulenceDec 26 2017In this paper, weak turbulence theory is used to investigate the nonlinear evolution of the parametric instability in 3D low-$\beta$ plasmas at wavelengths much greater than the ion inertial length under the assumption that slow magnetosonic waves are ... More
Weak compressible magnetohydrodynamic turbulence in the solar coronaNov 21 2005This Letter presents a calculation of the power spectra of weakly turbulent Alfven waves and fast magnetosonic waves ("fast waves") in low-beta plasmas. It is shown that three-wave interactions transfer energy to high-frequency fast waves and, to a lesser ... More
Rayleigh-Taylor stability of a strong vertical magnetic field at the Galactic center confined by a disk threaded with horizontal magnetic fieldSep 12 2000Feb 13 2002Observations of narrow radio-emitting filaments near the Galactic center have been interpreted in previous studies as evidence of a pervasive vertical (i.e. perpendicular to the Galactic plane) milliGauss magnetic field in the central 150 pc of the Galaxy. ... More
Scattering of energetic particles by anisotropic magnetohydrodynamic turbulence with a Goldreich-Sridhar power spectrumAug 30 2000Nov 03 2000Scattering rates for a Goldreich-Sridhar (GS) spectrum of anisotropic, incompressible, magnetohydrodynamic turbulence are calculated in the quasilinear approximation. Because the small-scale fluctuations are constrained to have wave vectors nearly perpendicular ... More
Refined critical balance in strong Alfvenic turbulenceJun 21 2014Aug 24 2015We present numerical evidence that in strong Alfvenic turbulence, the critical balance principle---equality of the nonlinear decorrelation and linear propagation times---is scale invariant, in the sense that the probability distribution of the ratio of ... More
Observational Test of Stochastic Heating in Low-$β$ Fast Solar Wind StreamsJul 14 2013Spacecraft measurements show that protons undergo substantial perpendicular heating during their transit from the Sun to the outer heliosphere. In this paper, we use {\em Helios~2} measurements to investigate whether stochastic heating by low-frequency ... More
Evolution of The Proton Velocity Distribution due to Stochastic Heating in the Near-Sun Solar WindFeb 16 2016We investigate how the proton distribution function evolves when the protons undergo stochastic heating by strong, low-frequency, Alfv\'en-wave turbulence under the assumption that $\beta$ is small. We apply our analysis to protons undergoing stochastic ... More
Scale dependent alignment between velocity and magnetic field fluctuations in the solar wind and comparisons to Boldyrev's phenomenological theoryJan 25 2009Feb 07 2009(Abridged abstract) A theory of incompressible MHD turbulence recently developed by Boldyrev predicts the existence of a scale dependent angle of alignment between velocity and magnetic field fluctuations that is proportional to the lengthscale of the ... More
Stochastic Heating, Differential Flow, and the Alpha-to-Proton Temperature Ratio in the Solar WindJul 30 2013We extend previous theories of stochastic ion heating to account for the motion of ions along the magnetic field. We derive an analytic expression for the ion-to-proton perpendicular temperature ratio in the solar wind for any ion species, assuming that ... More
The Dispersion Relations and Instability Thresholds of Oblique Plasma Modes in the Presence of an Ion BeamDec 20 2012Jan 29 2013An ion beam can destabilize Alfv\'en/ion-cyclotron waves and magnetosonic/whistler waves if the beam speed is sufficiently large. Numerical solutions of the hot-plasma dispersion relation have previously shown that the minimum beam speed required to excite ... More
Stochastic relativistic shock-surfing accelerationJul 30 2004Aug 03 2004We study relativistic particles undergoing surfing acceleration at perpendicular shocks. We assume that particles undergo diffusion in the component of momentum perpendicular to the shock plane due to moderate fluctuations in the shock electric and magnetic ... More
Direct Numerical Simulations of Reflection-Driven, Reduced MHD Turbulence from the Sun to the Alfven Critical PointAug 19 2013Sep 09 2013We present direct numerical simulations of inhomogeneous reduced magnetohydrodynamic (RMHD) turbulence between the Sun and the Alfv\'en critical point. These are the first such simulations that take into account the solar-wind outflow velocity and the ... More
Parker/buoyancy instabilities with anisotropic thermal conduction, cosmic rays, and arbitrary magnetic field strengthSep 03 2008We report the results of a local stability analysis for a magnetized, gravitationally stratified plasma containing cosmic rays. We account for cosmic-ray diffusion and thermal conduction parallel to the magnetic field and allow beta to take any value, ... More
Convection and AGN Feedback in Clusters of GalaxiesJul 16 2007Aug 20 2007A number of studies have shown that the convective stability criterion for the intracluster medium (ICM) is very different from the Schwarzchild criterion due to the effects of anisotropic thermal conduction and cosmic rays. Building on these studies, ... More
Alfven Wave Reflection and Turbulent Heating in the Solar Wind from 1 Solar Radius to 1 AU: an Analytical TreatmentNov 05 2009We study the propagation, reflection, and turbulent dissipation of Alfven waves in coronal holes and the solar wind. We start with the Heinemann-Olbert equations, which describe non-compressive magnetohydrodynamic fluctuations in an inhomogeneous medium ... More
Thermal conduction and particle transport in strong MHD turbulence, with application to galaxy-cluster plasmasMar 11 2003Oct 16 2003We investigate field-line separation in strong MHD turbulence analytically and with direct numerical simulations. We find that in the static-magnetic-field approximation the thermal conductivity in galaxy clusters is reduced by a factor of about 5-10 ... More
Acceleration of energetic particles by large-scale compressible magnetohydrodynamic turbulenceNov 13 2003Fast particles diffusing along magnetic field lines in a turbulent plasma can diffuse through and then return to the same eddy many times before the eddy is randomized in the turbulent flow. This leads to an enhancement of particle acceleration by large-scale ... More
Stochastic Acceleration of Electrons by Fast Magnetosonic Waves in Solar Flares: the Effects of Anisotropy in Velocity andWavenumber SpaceJun 03 2014We develop a model for stochastic acceleration of electrons in solar flares. As in several previous models, the electrons are accelerated by turbulent fast magnetosonic waves ("fast waves") via transit-time-damping (TTD) interactions. (In TTD interactions, ... More
Turbulence and Mixing in the Intracluster MediumSep 01 2009The intracluster medium (ICM) is stably stratified in the hydrodynamic sense with the entropy $s$ increasing outwards. However, thermal conduction along magnetic field lines fundamentally changes the stability of the ICM, leading to the "heat-flux buoyancy ... More
Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal ConductionJan 30 2009Using a linear stability analysis and two and three-dimensional nonlinear simulations, we study the physics of buoyancy instabilities in a combined thermal and relativistic (cosmic ray) plasma, motivated by the application to clusters of galaxies. We ... More
The divergence of neighboring magnetic field lines and fast-particle diffusion in strong magnetohydrodynamic turbulence, with application to thermal conduction in galaxy clustersMar 11 2003Nov 06 2003We investigate field-line separation in strong MHD turbulence using direct numerical simulations. We find that in the static-magnetic-field approximation the thermal conductivity in galaxy clusters is reduced by a factor of about 50 relative to the Spitzer ... More
Magnetohydrodynamic Slow Mode with Drifting He$^{++}$: Implications for Coronal Seismology and the Solar WindApr 17 2014The MHD slow mode wave has application to coronal seismology, MHD turbulence, and the solar wind where it can be produced by parametric instabilities. We consider analytically how a drifting ion species (e.g. He$^{++}$) affects the linear slow mode wave ... More
Intermittency and Alignment in Strong RMHD TurbulenceMar 25 2014We develop an analytic model of intermittent, three-dimensional, strong, reduced magnetohydrodynamic turbulence with zero cross helicity. We take the fluctuation amplitudes to have a log-Poisson distribution and incorporate into the model a new phenomenology ... More
Instabilities Driven by the Drift and Temperature Anisotropy of Alpha Particles in the Solar WindJul 07 2013Aug 06 2013We investigate the conditions under which parallel-propagating Alfv\'en/ion-cyclotron (A/IC) waves and fast-magnetosonic/whistler (FM/W) waves are driven unstable by the differential flow and temperature anisotropy of alpha particles in the solar wind. ... More
Measures of Three-Dimensional Anisotropy and Intermittency in Strong Alfvénic TurbulenceDec 04 2015We measure the local anisotropy of numerically simulated strong Alfv\'enic turbulence with respect to two local, physically relevant directions: along the local mean magnetic field and along the local direction of one of the fluctuating Elsasser fields. ... More
Collisionless Isotropization of the Solar Wind by Compressive Fluctuations and Plasma InstabilitiesMay 23 2016Compressive fluctuations are a minor yet significant component of astrophysical plasma turbulence. In the solar wind, compressive slow-mode fluctuations lead to changes in $\beta_{\parallel \mathrm p}\equiv 8\pi n_{\mathrm p}k_{\mathrm B}T_{\parallel ... More
A Modified Version of Taylor's Hypothesis for Solar Probe Plus ObservationsDec 11 2014Feb 18 2015The Solar Probe Plus (SPP) spacecraft will explore the near-Sun environment, reaching heliocentric distances less than $10 R_{\odot}$. Near Earth, spacecraft measurements of fluctuating velocities and magnetic fields taken in the time domain are translated ... More
Constraining Low-Frequency Alfvenic Turbulence in the Solar Wind Using Density Fluctuation MeasurementsAug 05 2009One proposed mechanism for heating the solar wind, from close to the sun to beyond 10 AU, invokes low-frequency, oblique, Alfven-wave turbulence. Because small-scale oblique Alfven waves (kinetic Alfven waves) are compressive, the measured density fluctuations ... More
The Turbulent Heating Rate in Strong MHD Turbulence with Nonzero Cross HelicityMay 20 2009Different results for the cascade power in strong, incompressible MHD turbulence with nonzero cross helicity appear in the literature. In this paper, we discuss the conditions under which these different results are valid. We define z+ to be the rms amplitude ... More
Collisionless Isotropization of the Solar-Wind Protons by Compressive Fluctuations and Plasma InstabilitiesMay 23 2016Nov 02 2016Compressive fluctuations are a minor yet significant component of astrophysical plasma turbulence. In the solar wind, long-wavelength compressive slow-mode fluctuations lead to changes in $\beta_{\parallel \mathrm p}\equiv 8\pi n_{\mathrm p}k_{\mathrm ... More
Stochastic proton heating by kinetic-Alfvén-wave turbulence in moderately high-$β$ plasmasNov 21 2018Stochastic heating refers to an increase in the average magnetic moment of charged particles interacting with electromagnetic fluctuations whose frequencies are smaller than the particles' cyclotron frequencies. This type of heating arises when the amplitude ... More
The Coronal Physics Investigator (CPI) Experiment for ISS: A New Vision for Understanding Solar Wind AccelerationApr 19 2011In February 2011 we proposed a NASA Explorer Mission of Opportunity program to develop and operate a large-aperture ultraviolet coronagraph spectrometer called the Coronal Physics Investigator (CPI) as an attached International Space Station (ISS) payload. ... More
Incorporating Kinetic Physics into a Two-Fluid Solar-Wind Model with Temperature Anisotropy and Low-Frequency Alfven-Wave TurbulenceOct 13 2011Nov 29 2011We develop a 1D solar-wind model that includes separate energy equations for the electrons and protons, proton temperature anisotropy, collisional and collisionless heat flux, and an analytical treatment of low-frequency, reflection-driven, Alfven-wave ... More
On the Conservation of Cross Helicity and Wave Action in Solar-Wind Models with Non-WKB Alfven Wave ReflectionSep 03 2015The interaction between Alfven-wave turbulence and the background solar wind affects the cross helicity in two ways. Non-WKB reflection converts outward-propagating Alfven waves into inward-propagating Alfven waves and vice versa, and the turbulence transfers ... More
Perpendicular Ion Heating by Reduced Magnetohydrodynamic TurbulenceSep 03 2013Sep 04 2013Recent theoretical studies argue that the rate of stochastic ion heating in low-frequency Alfv\'en-wave turbulence is given by $Q_\perp = c_1 [(\delta u)^3 /\rho] \exp(-c_2/\epsilon)$, where $\delta u$ is the rms turbulent velocity at the scale of the ... More
Limits on Alpha Particle Temperature Anisotropy and Differential Flow from Kinetic Instabilities: Solar Wind ObservationsSep 16 2013Sep 19 2013Previous studies have shown that the observed temperature anisotropies of protons and alpha particles in the solar wind are constrained by theoretical thresholds for pressure-anisotropy-driven instabilities such as the Alfv\'en/ion-cyclotron (A/IC) and ... More
The Efficiency of Second-Order Fermi Acceleration by Weakly Compressible MHD TurbulenceJun 28 2013Aug 23 2013We investigate the effects of pitch-angle scattering on the efficiency of particle heating and acceleration by MHD turbulence using phenomenological estimates and simulations of non-relativistic test particles interacting with strong, subsonic MHD turbulence. ... More
Spectral tensor networks for many-body localizationOct 02 2014Subsystems of strongly disordered, interacting quantum systems can fail to thermalize because of the phenomenon of many-body localization (MBL). In this article, we explore a tensor network description of the eigenspectra of such systems. Specifically, ... More
Deceleration of Alpha Particles in the Solar Wind by Instabilities and the Rotational Force: Implications for Heating, Azimuthal Flow, and the Parker Spiral Magnetic FieldNov 17 2014Jun 16 2015Protons and alpha particles in the fast solar wind are only weakly collisional and exhibit a number of non-equilibrium features, including relative drifts between particle species. Two non-collisional mechanisms have been proposed for limiting differential ... More
Resonant Interactions Between Protons and Oblique Alfvén/Ion-Cyclotron WavesDec 28 2009Resonant interactions between ions and Alfv\'en/ion-cyclotron (A/IC) waves may play an important role in the heating and acceleration of the fast solar wind. Although such interactions have been studied extensively for "parallel" waves, whose wave vectors ... More
Hybrid-Kinetic Simulations of Ion Heating in Alfvénic TurbulenceJan 30 2019We present three-dimensional, hybrid-kinetic numerical simulations of driven Alfv\'{e}n-wave turbulence of relevance to the collisionless near-Earth solar wind. Special attention is paid to the spectral transition that occurs near the ion-Larmor scale ... More
Acceleration of Relativistic Electrons by MHD Turbulence: Implications for Non-thermal Emission from Black Hole Accretion DisksMar 12 2014Jul 27 2014We use analytic estimates and numerical simulations of test particles interacting with magnetohydrodynamic (MHD) turbulence to show that subsonic MHD turbulence produces efficient second-order Fermi acceleration of relativistic particles. This acceleration ... More
Resonance Broadening and Heating of Charged Particles in Magnetohydrodynamic TurbulenceApr 01 2012Sep 06 2012The heating, acceleration, and pitch-angle scattering of charged particles by MHD turbulence are important in a wide range of astrophysical environments, including the solar wind, accreting black holes, and galaxy clusters. We simulate the interaction ... More
A Parallel-Propagating Alfvénic Ion-Beam Instability in the High-Beta Solar WindJun 11 2013Jul 18 2013We investigate the conditions under which parallel-propagating Alfv\'en/ion-cyclotron waves are driven unstable by an isotropic ($T_{\perp \alpha} = T_{\parallel\alpha}$) population of alpha particles drifting parallel to the magnetic field at an average ... More
Perpendicular Ion Heating by Low-Frequency Alfven-Wave Turbulence in the Solar WindJan 13 2010We consider ion heating by turbulent Alfven waves (AWs) and kinetic Alfven waves (KAWs) with perpendicular wavelengths comparable to the ion gyroradius and frequencies smaller than the ion cyclotron frequency. When the turbulence amplitude exceeds a certain ... More
Bounds On Isoperimetric Values of TreesJan 21 2007Jan 09 2008Let G = (V,E) be a finite, simple and undirected graph. For $S \subseteq V$, let $\delta(S,G) = \{(u,v) \in E : u \in S \mbox {and} v \in V-S \}$ be the edge boundary of $S$. Given an integer $i$, $1 \leq i \leq | V |$, let the edge isoperimetric value ... More
When is an area law not an area law?Nov 10 2015Entanglement entropy is typically proportional to area, but sometimes it acquires an additional logarithmic pre-factor. We offer some intuitive explanations for these facts.
Practical and theoretical improvements for bipartite matching using the pseudoflow algorithmMay 09 2011We show that the pseudoflow algorithm for maximum flow is particularly efficient for the bipartite matching problem both in theory and in practice. We develop several implementations of the pseudoflow algorithm for bipartite matching, and compare them ... More
[Plasma 2020 Decadal] Multipoint Measurements of the Solar Wind: A Proposed Advance for Studying Magnetized TurbulenceMar 13 2019A multi-institutional, multi-national science team will soon submit a NASA proposal to build a constellation of spacecraft to fly into the near-Earth solar wind in a swarm spanning a multitude of scales in order to obtain critically needed measurements ... More
Interplay between intermittency and dissipation in collisionless plasma turbulenceJul 24 2018We study the damping of collisionless Alfv\'enic turbulence by two mechanisms: stochastic heating (whose efficiency depends on the local turbulence amplitude $\delta z_\lambda$) and linear Landau damping (whose efficiency is independent of $\delta z_\lambda$), ... More
Dynamic transition in driven vortices across the peak effect in superconductorsMar 16 2003We study the zero-temperature dynamic transition from the disordered flow to an ordered flow state in driven vortices in type-II superconductors. The transition current $I_{p}$ is marked by a sharp kink in the $V(I)$ characteristic with a concomitant ... More
Bulk-Edge Correspondence in the Entanglement SpectraFeb 10 2011Li and Haldane conjectured and numerically substantiated that the entanglement spectrum of the reduced density matrix of ground-states of time-reversal breaking topological phases (fractional quantum Hall states) contains information about the counting ... More
Haldane Statistics in the Finite Size Entanglement Spectra of Laughlin StatesSep 21 2010Oct 04 2011We conjecture that the counting of the levels in the orbital entanglement spectra (OES) of finite-sized Laughlin Fractional Quantum Hall (FQH) droplets at filling $\nu=1/m$ is described by the Haldane statistics of particles in a box of finite size. This ... More
Ultraviolet Coronagraph Spectroscopy: A Key Capability for Understanding the Physics of Solar Wind AccelerationNov 10 2010Understanding the physical processes responsible for accelerating the solar wind requires detailed measurements of the collisionless plasma in the extended solar corona. Some key clues about these processes have come from instruments that combine the ... More
Metastability and uniqueness of vortex states at depinningApr 02 2002Apr 16 2004We present results from numerical simulations of transport of vortices in the zero-field cooled (ZFC) and the field-cooled (FC) state of a type-II superconductor. In the absence of an applied current $I$, we find that the FC state has a lower defect density ... More
The eigenstate thermalization hypothesis in constrained Hilbert spaces: a case study in non-Abelian anyon chainsJul 01 2016Many phases of matter, including superconductors, fractional quantum Hall fluids and spin liquids, are described by gauge theories with constrained Hilbert spaces. However, thermalization and the applicability of quantum statistical mechanics has primarily ... More
Domain regime in two-dimensional disordered vortex matterFeb 17 2004A detailed numerical study of the real space configuration of vortices in disordered superconductors using 2D London-Langevin model is presented. The magnetic field $B$ is varied between 0 and $B_{c2}$ for various pinning strengths $\Delta$. For weak ... More
The quasi-periodic quantum Ising transition in 1DJan 22 2018Unlike random potentials, quasi-periodic modulation can induce localisation-delocalisation transitions in one dimension. In this article, we analyse the implications of this for symmetry breaking in the quasi-periodically modulated quantum Ising chain. ... More
Real-Space Entanglement Spectrum of Quantum Hall StatesNov 11 2011Mar 15 2012We investigate the entanglement spectra arising from sharp real-space partitions of the system for quantum Hall states. These partitions differ from the previously utilized orbital and particle partitions and reveal complementary aspects of the physics ... More
Characterization of a qubit Hamiltonian using adaptive measurements in a fixed basisFeb 17 2011Nov 23 2011We investigate schemes for Hamiltonian parameter estimation of a two-level system using repeated measurements in a fixed basis. The simplest (Fourier based) schemes yield an estimate with a mean square error (MSE) that decreases at best as a power law ... More
Universal corner entanglement of Dirac fermions and gapless bosons from the continuum to the latticeJun 09 2016A quantum critical (QC) fluid exhibits universal subleading corrections to the area law of its entanglement entropies. In two dimensions when the partition involves a corner of angle $\theta$, the subleading term is logarithmic with coefficient $a_\alpha(\theta)$ ... More
MHD wave modes resolved in fine-scale chromospheric magnetic structuresMay 05 2015Within the last decade, due to significant improvements in the spatial and temporal resolution of chromospheric data, magnetohydrodynamic (MHD) wave studies in this fascinating region of the Sun's atmosphere have risen to the forefront of solar physics ... More
The Linear BaryonOct 19 1999We describe classical orbits and quantum states of a three particle system which is weakly chaotic. The quantum energies of the lowest 48 states which are invariant under permutations are given both in various approximations and to high accuracy. The ... More
Dynamic Partitioning of Physical Memory Among Virtual Machines, ASMI:Architectural Support for Memory IsolationMar 10 2015Cloud computing relies on secure and efficient virtualization. Software level security solutions compromise the performance of virtual machines (VMs), as a large amount of computational power would be utilized for running the security modules. Moreover, ... More
Numerical simulations of buoyancy instabilities in galaxy cluster plasmas with cosmic rays and anisotropic thermal conductionSep 02 2008In clusters of galaxies, the specific entropy of intracluster plasma increases outwards. Nevertheless, a number of recent studies have shown that the intracluster medium is subject to buoyancy instabilities due to the effects of cosmic rays and anisotropic ... More
Acyclic Edge coloring of Planar GraphsAug 16 2009An $acyclic$ edge coloring of a graph is a proper edge coloring such that there are no bichromatic cycles. The \emph{acyclic chromatic index} of a graph is the minimum number k such that there is an acyclic edge coloring using k colors and is denoted ... More
Rainbow Colouring of Split and Threshold GraphsMay 08 2012A rainbow colouring of a connected graph is a colouring of the edges of the graph, such that every pair of vertices is connected by at least one path in which no two edges are coloured the same. Such a colouring using minimum possible number of colours ... More
The compact central source in the RX J0852-4622 supernova remnantAug 08 2001The central region of the recently discovered supernova remnant RX J0852.0-4622 was observed with the ACIS detector aboard the Chandra X-ray Observatory. We found only one relatively bright source, about 4' north of the SNR center, with a flux of $\sim ... More
On the magnetic field through the Upper Centaurs-Lupus Super bubble, in the vicinity of the Southern CoalsackDec 15 2010The Southern Coalsack is located in the interior of the Upper Centaurus-Lupus (UCL) super bubble and shows many traits that point to a much more energetic environment than might be expected from a dark, starless molecular cloud. A hot, X-ray emitting, ... More
Sustained resonance: a binary system perturbed by gravitational radiationNov 30 1999The general phenomena associated with sustained resonance are studied in this paper in connection with relativistic binary pulsars. We represent such a system by two point masses in a Keplerian binary system that evolves via gravitational radiation damping ... More
Chaos in the Kepler SystemJun 26 1998The long-term dynamical evolution of a Keplerian binary orbit due to the emission and absorption of gravitational radiation is investigated. This work extends our previous results on transient chaos in the planar case to the three dimensional Kepler system. ... More
A repulsive atomic gas in a harmonic trap on the border of itinerant ferromagnetismJul 21 2009Oct 19 2009Alongside superfluidity, itinerant (Stoner) ferromagnetism remains one of the most well-characterized phases of correlated Fermi systems. A recent experiment has reported the first evidence for novel phase behavior on the repulsive side of the Feshbach ... More
HI and Star Formation Properties of Massive Galaxies: First Results from the GALEX Arecibo SDSS SurveyJan 11 2010The GALEX Arecibo SDSS Survey (GASS) is an ambitious program designed to investigate the cold gas properties of massive galaxies, a challenging population for HI studies. Using the Arecibo radio telescope, GASS is gathering high-quality HI-line spectra ... More
The GALEX Arecibo SDSS Survey (GASS)Mar 29 2008The GALEX Arecibo SDSS Survey (GASS) is a large targeted survey that started at Arecibo in March 2008. GASS is designed to measure the neutral hydrogen content of ~1000 massive galaxies (with stellar mass Mstar > 10^10 Msun) at redshift 0.025<z<0.05, ... More
Cascading on extragalactic background lightApr 30 2007High-energy gamma-rays propagating in the intergalactic medium can interact with background infrared photons to produce e+e- pairs, resulting in the absorption of the intrinsic gamma-ray spectrum. TeV observations of the distant blazar 1ES 1101-232 were ... More
Galactic fundamental mode RR Lyrae stars. Period - amplitude diagram, metallicities and distributionJun 12 2009Aug 19 2009We have analysed 1455 fundamental mode RR Lyrae stars of the Galactic field, using the All Sky Automated Survey (ASAS) data. The sample covers 75% of the sky and contains objects in the close neighbourhood of the Sun, within 4 kpc distance. Unlike in ... More
M_1 - M* Correlation in Galaxy ClustersJul 15 1994Photographic F band photometry of a sample of 36 Abell clusters has been used to study the relation between the magnitude $M_1$ of the brightest cluster member and the Schechter function parameter $M^*$. Clusters appear segregated in the $M_1$-$M^*$ plane ... More
Low symmetry phases in piezoelectric systems: PZN-xPT single crystal and powderSep 28 2001In this review we address some of the experimental challenges found in the x-ray diffraction characterization of the low-symmetry phases recently discovered in the PZT, PZN-PT and PMN-PT piezoelectric systems around their morphotropic phase boundaries. ... More
Efficiency of a wide-area survey in achieving short- and long-term warning for small impactorsOct 18 2011Feb 10 2012We consider a network of telescopes capable of scanning all the observable sky each night and targeting Near-Earth objects (NEOs) in the size range of the Tunguska-like asteroids, from 160 m down to 10 m. We measure the performance of this telescope network ... More
Network Synchronization in a Noisy Environment with Time Delays: Fundamental Limits and Trade-OffsMay 19 2010Aug 06 2010We study the effects of nonzero time delays in stochastic synchronization problems with linear couplings in an arbitrary network. Using the known exact threshold value from the theory of differential equations with delays, we provide the synchronizability ... More
Dynamics of a FitzHugh-Nagumo system subjected to autocorrelated noiseOct 08 2008We analyze the dynamics of the FitzHugh-Nagumo (FHN) model in the presence of colored noise and a periodic signal. Two cases are considered: (i) the dynamics of the membrane potential is affected by the noise, (ii) the slow dynamics of the recovery variable ... More
Compact Symmetric Objects as Radio Flux Density CalibratorsMay 31 2001We present results from the first intensive monitoring campaign of a sample of Compact Symmetric Objects (CSOs). We observed seven CSOs at 8.5 GHz over a period of eight months, with an average spacing between observations of 2.7 days. Our results show ... More
Low-temperature phases in Pb(Zr0.52Ti0.48)O3: A neutron powder diffraction studyAug 09 2004A neutron powder diffraction study has been carried out on Pb(Zr0.52Ti0.48)O3 in order to resolve an ongoing controversy about the nature of the low-temperature structure of this strongly-piezoelectric and technologically-important material. The results ... More
Energy loss in perturbative QCDFeb 18 2000Apr 17 2000We review the properties of energetic parton propagation in hot or cold QCD matter, as obtained in recent works. Advances in understanding the energy loss - collisional and radiative - are summarized, with emphasis on the latter: it features very interesting ... More
Dynamical Hartree-Fock-Bogoliubov Theory of Vortices in Bose-Einstein Condensates at Finite TemperatureDec 08 2010Sep 22 2011We present a method utilizing the continuity equation for the condensate density to make predictions of the precessional frequency of single off-axis vortices and of vortex arrays in Bose-Einstein condensates at finite temperature. We also present an ... More
Role of Noise in a Market Model with Stochastic VolatilityOct 06 2005Oct 09 2006We study a generalization of the Heston model, which consists of two coupled stochastic differential equations, one for the stock price and the other one for the volatility. We consider a cubic nonlinearity in the first equation and a correlation between ... More
A Pressure Anomaly for HII Regions in Irregular GalaxiesMay 08 2000The pressures of giant HII regions in 6 dwarf Irregular galaxies are a factor of ~10 larger than the average pressures of the corresponding galaxy disks, obtained from the stellar and gaseous column densities. Either the visible HII regions in these dwarfs ... More
Epochs of Maximum Light and Bolometric Light Curves of Type Ia SupernovaeMay 25 2000We present empirical fits to the UBVRI light curves of type Ia supernovae. These fits are used to objectively evaluate light curve parameters. We find that the relative times of maximum light in the filter passbands are very similar for most objects. ... More
Consistency of the Chiral Pion-Pion Scattering Amplitudes with Axiomatic ConstraintsOct 17 1994The pion-pion scattering amplitudes provided by second-order chiral perturbation theory are confronted with known rigorous constraints derived from the axioms of quantum field theory. We mainly test constraints restricting the $\pi^0$-$\pi^0$ $S$- and ... More
Low Energy Sum Rules For Pion-Pion Scattering and Threshold ParametersOct 09 1995We derive a set of sum rules for threshold parameters of pion-pion scattering whose dispersion integrals are rapidly convergent and are dominated by S- and P-waves absorptive parts. Stringent constraints on some threshold parameters are obtained.
Universality of the Anderson transition with the quasiperiodic kicked rotorApr 15 2009Feb 23 2011We report a numerical analysis of the Anderson transition in a quantum-chaotic system, the quasiperiodic kicked rotor with three incommensurate frequencies. It is shown that this dynamical system exhibits the same critical phenomena as the truly random ... More