Results for "A. Lazarian"

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Mapping of the structure of the galactic magnetic field with velocity gradients: Test using star light polarizationMay 25 2018We apply Velocity Channel Gradients (VChGs) and Reduced Velocity Centroids Gradients (RVCGs) to Hi data (the LAB survey) and get the plane of the sky component of the magnetic field as a function of the relative velocity. Assuming a galactic rotation ... More
Grain Alignment, Polarization and Magnetic FieldsAug 02 2006Aligned non-spherical dust particles polarize starlight passing through the dust cloud. They also emit polarized far infrared and sub-mm radiation. Substantial progress in understanding of grain alignment theory makes the interpretation of the polarized ... More
Paramagnetic alignment of thermally rotating dustFeb 16 1997Paramagnetic alignment of thermally rotating oblate dust grains is studied analytically for finite ratios of grain to gas temperatures. For such ratios, the alignment of angular momentum J in respect to the grain axis of maximal inertia is only partial. ... More
Davis-Greenstein alignment of non-spherical grainsMay 07 1995Paramagnetic alignment of non-spherical dust grains rotating at thermal velocities is studied. The analytical solution is found for the alignment measure of oblate grains. Perturbative approach is used for solving the problem. It is shown that even the ... More
Heat Transfer and Reconnection Diffusion in Turbulent Magnetized PlasmasAug 10 2011Feb 08 2012It is well known that magnetic fields constrain motions of charged particles, impeding the diffusion of charged particles perpendicular to magnetic field direction. This modification of transport processes is of vital importance for a wide variety of ... More
Obtaining Spectra of Turbulent Velocity from ObservationsNov 06 2008We discuss a long-standing problem of how turbulence can be studied using observations of Doppler broadened emission and absorption lines. The focus of the present review is on two new techniques, the Velocity-Channel Analysis (VCA), which makes use of ... More
Grain Alignment and CMB Polarization StudiesNov 06 2008Polarized microwave emission from dust is an important foreground that may contaminate polarized CMB studies unless carefully accounted for. Modeling of polarization from dust requires a quantitative understanding of grain alignment. I review the current ... More
Magnetic Fields via Polarimetry: Progress of Grain Alignment TheoryAug 28 2002Most astrophysical systems, e.g. stellar winds, the diffuse interstellar medium, molecular clouds, are magnetized with magnetic fields that influence almost all of their properties. One of the most informative techniques of magnetic field studies is based ... More
Theoretical approaches to particle propagation and acceleration in turbulent intergalactic mediumAug 02 2006Intercluster medium is expected to be turbulent with turbulence being superAlfvenic at large scales. Magnetic fields substantially modify the turbulent cascade when the turbulence reaches the scales at which the fluctuation velocity gets less than the ... More
SINS of Viscosity Damped TurbulenceAug 02 2006Oct 26 2006The problems with explaining the Small Ionized and Neutral Structures (SINS) appealing to turbulence stem from inefficiency of the Kolmogorov cascade in creating large fluctuations at sufficiently small scales. However, other types of cascades are possible. ... More
Obtaining Statistics of Turbulent Velocity from Astrophysical Spectral Line DataAug 10 2004Turbulence is a crucial component of dynamics of astrophysical fluids dynamics, including those of ISM, clusters of galaxies and circumstellar regions. Doppler shifted spectral lines provide a unique source of information on turbulent velocities. We discuss ... More
Enhancement and suppression of heat transfer by MHD turbulenceAug 02 2006Aug 03 2006We study of the effect of turbulence on heat transfer within magnetized plasmas for energy injection velocities both larger and smaller that the Alfven speed. We find that in the latter regime the heat transfer is partially suppressed, while in the former ... More
Polarized Microwave Radiation from DustDec 30 2000Observations of cosmic microwave background in the range 10-90 GHz have revealed an anomalous foreground component well correlated with 12 \mum, 60 \mum and 100 \mum emission from interstellar dust. As the recent cross-correlation analysis of WHAM H\alpha ... More
Power of Turbulent Reconnection: Star Formation, Acceleration of Cosmic Rays, Heat Transfer, Flares and Gamma Ray BurstsDec 14 2011Turbulence is ubiquitous in astrophysical fluids. Therefore it is necessary to study magnetic reconnection in turbulent environments. The model of fast turbulent reconnection proposed in Lazarian & Vishniac 1999 has been successfully tested numerically ... More
Quantitative Theory of Grain Alignment: Probing Grain Environment and Grain CompositionMar 05 2009While the problem of grain alignment was posed more than 60 years ago the quantitative model of grain alignment that can account for the observed polarization arising from aligned grains has been formulated only recently. The quantitative predictions ... More
Grain Alignment by Radiative TorquesDec 03 2008Grain alignment is a notoriously difficult problem, that is extremely rich in underlying physics. The long history of attempts theoretical handling of the problem resulted in rather sceptical approach to the theory on the part of some polarimetry practitioners. ... More
Tracing Magnetic Fields with Aligned GrainsJul 05 2007Jul 05 2007Magnetic fields play a crucial role in various astrophysical processes, including star formation, accretion of matter, transport processes (e.g., transport of heat), and cosmic rays. One of the easiest ways to determine the magnetic field direction is ... More
Astrophysical Implications of Turbulent Reconnection: from cosmic rays to star formationMay 28 2005Turbulent reconnection allows fast magnetic reconnection of astrophysical magnetic fields. This entails numerous astrophysical implications and opens new ways to approach long standing problems. I briefly discuss a model of turbulent reconnection within ... More
Intermittency of Magnetohydrodynamic Turbulence: Astrophysical PerspectiveAug 02 2006Intermittency is an essential property of astrophysical fluids, which demonstrate an extended inertial range. As intermittency violates self-similarity of motions, it gets impossible to naively extrapolate the properties of fluid obtained computationally ... More
Turbulence Statistics from Spectral Line ObservationsMay 28 2005Turbulence is a crucial component of dynamics of astrophysical fluids dynamics, including those of ISM, clusters of galaxies and circumstellar regions. Doppler shifted spectral lines provide a unique source of information on turbulent velocities. We discuss ... More
Grain Alignment in Molecular CloudsNov 17 2003One of the most informative techniques of studying magnetic fields in molecular clouds is based on the use of starlight polarization and polarized emission arising from aligned dust. How reliable the interpretation of the polarization maps in terms of ... More
Turbulence in Atomic HydrogenApr 02 1998Understanding the properties of interstellar turbulence is a great intellectual challenge and the urge to solve this problem is partially motivated by a necessity to explain the star formation mystery. This review deals with a recently suggested inversion ... More
Alignment of suprathermally rotating grainsAug 15 1995It is shown, that mechanical alignment can be efficient for suprathermally rotating grains, provided that they drift with supersonic velocities. Such a drift should be widely spread due to both Alfv\'{e}nic waves and ambipolar diffusion. Moreover, if ... More
Mechanical alignment of suprathermally rotating grainsMay 01 1995It is shown that mechanical alignment of grains can be efficient for grains rotating suprathermally, i.e. with kinetic energy substantially exceeding $k$ (the Boltzmann constant) over any temperature in the system. The paper studies suprathermal rotation ... More
Damping of Alfven waves by Turbulence and its Consequences: from Cosmic-Rays Streaming to Launching WindsJul 06 2016This paper considers turbulent damping of Alfven waves in magnetized plasmas. We identify two cases of damping, one related to damping of cosmic rays streaming instability, the other related to damping of Alfven waves emitted by a macroscopic wave source, ... More
Reconnection Diffusion, Star Formation and Numerical SimulationsApr 10 2013We consider fast magnetic reconnection that takes place within turbulent magnetic flux and show that the process results in diffusion of magnetic fields and matter, which we term reconnection diffusion. The process of reconnection diffusion is based on ... More
Fast Reconnection and Reconnection Diffusion: Implications for Star FormationNov 03 2011Feb 05 2012Fast reconnection of magnetic field in turbulent fluids allows magnetic field to change its topology and connections. As a result, the traditional concept of magnetic fields being frozen into the plasma is no longer applicable. The diffusion of plasmas ... More
Turbulence Spectra from Doppler-shifted Spectral LinesOct 26 2006Turbulence is a key element of the dynamics of astrophysical fluids, including those of interstellar medium, clusters of galaxies and circumstellar regions. Turbulent motions induce Doppler shifts of observable emission and absorption lines. In the review ... More
Statistics of Turbulence from Spectral-Line Data CubesJan 01 2000Emission in spectral lines can provide unique information on interstellar turbulence. Doppler shifts due to supersonic motions contain information on turbulent velocity field which is otherwise difficult to measure. However, the problem of separation ... More
Gold alignment & internal dissipationFeb 16 1997The measures of mechanical alignment were obtained for both prolate and oblate grains when their temperature is comparable with grain kinetic energy devided by k, the Boltzmann constant. For such grains, the alignment of angular momentum, J, with the ... More
Paramagnetic alignment of fractal grainsAug 23 1994Paramagnetic alignment of fractal suprathermally rotating grains is discussed. It is shown that if the concentration of H$_{2}$formation sites is low and resurfacing is active, fractal structure of grains enhances their alignment. Studying the influence ... More
The Velocity Centroids Gradients for Absorbing MediaMar 08 2017We explore the application of the Velocity Gradient Technique, new way to trace magnetic fields in the plane of the sky, to an absorbing media for the case of $^{13}$CO~2-1 emission. Using MHD turbulence simulations, we calculate the velocity gradient ... More
Diagnostics of turbulence properties through Velocity Gradient Amplitudes: Theory and ObservationsJan 31 2018Based on the properties of magneto-hydrodynamic (MHD) turbulence, the recent development of the Velocity Gradient Technique (VGT) allows observers to trace magnetic field directions using spectroscopic information. In this paper, we explore how the amplitudes ... More
Structure of Stationary Strong Imbalanced TurbulenceApr 16 2009Jul 16 2009In this paper we systematically study the spectrum and structure of incompressible MHD turbulence by means of high resolution direct numerical simulations. We considered both balanced and imbalanced (cross-helical) cases and simulated sub-Alfvenic as ... More
Turbulence Spectra from Doppler-broadened Spectral Lines: Tests of the Velocity Channel Analysis and Velocity Coordinate Spectrum TechniquesNov 05 2008Nov 07 2008Turbulent motions induce Doppler shifts of observable emission and absorption lines motivating studies of turbulence using precision spectroscopy. We provide the numerical testing of the two most promising techniques, Velocity Channel Analysis (VCA) and ... More
Extending Big Power Law in the Sky with Turbulence Spectra from WHAM dataMay 27 2009Feb 11 2010We use the data of Wisconsin H$\alpha$ Mapper (WHAM) to test the hypothesis of whether the amplitudes and spectrum of density fluctuations measured by WHAM can be matched to the data obtained for interstellar scintillations and scattering. To do this, ... More
Statistics of Centroids of VelocityJan 13 2009We review the use of velocity centroids statistics to recover information of interstellar turbulence from observations. Velocity centroids have been used for a long time now to retrieve information about the scaling properties of the turbulent velocity ... More
Velocity coordinate spectrum: geometrical aspects of observationsNov 15 2006Jan 31 2007We analyze a technique of obtaining turbulence power spectrum using spectral line data along the velocity coordinate, which we refer to as Velocity Coordinate Spectrum (VCS). We formalize geometrical aspects of observation through a single factor, "geometric ... More
Statistics of Velocity from Spectral Data: Modified Velocity CentroidsApr 01 2003Jun 10 2003We address the problem of studying interstellar turbulence using spectral line data. We find a criterion when the velocity centroids may provide trustworthy velocity statistics. To enhance the scope of centroids applications, we construct a measure that ... More
Astrophysical hydromagnetic turbulenceJul 21 2013Recent progress in astrophysical hydromagnetic turbulence is being reviewed. The physical ideas behind the now widely accepted Goldreich--Sridhar model and its extension to compressible magnetohydrodynamic turbulence are introduced. Implications for cosmic ... More
Turbulence Spectra from Spectral Lines: Tests of the Velocity Channel Analysis and Velocity Coordinate Spectrum TechniquesNov 15 2006Jan 31 2007Turbulence is a key element of the dynamics of astrophysical fluids, including those of interstellar medium, clusters of galaxies and circumstellar regions. Turbulent motions induce Doppler shifts of observable emission and absorption lines and this motivates ... More
Tsallis statistics as a tool for studying interstellar turbulenceMay 15 2009Dec 09 2009We used magnetohydrodynamic (MHD) simulations of interstellar turbulence to study the probability distribution functions (PDFs) of increments of density, velocity, and magnetic field. We found that the PDFs are well described by a Tsallis distribution, ... More
Strong Imbalanced TurbulenceSep 05 2007Jul 07 2008We consider stationary, forced, imbalanced, or cross-helical MHD Alfvenic turbulence where the waves traveling in one direction have higher amplitudes than the opposite waves. This paper is dedicated to so-called strong turbulence, which cannot be treated ... More
Scaling laws and diffuse locality of balanced and imbalanced MHD turbulenceFeb 11 2010May 03 2010The search of ways to generalize the theory of strong MHD turbulence for the case of non-zero cross-helicity (or energy imbalance) has attracted considerable interest recently. In our earlier publications we performed three-dimensional numerical simulations ... More
MHD Turbulence: Properties of Alfven, Slow and Fast ModesMay 29 2005We summarise basic properties of MHD turbulence. First, MHD turbulence is not so messy as it is believed. In fact, the notion of strong non-linear coupling of compressible and incompressible motions along MHD cascade is not tenable. Alfven, slow and fast ... More
Turbulence Effects at Small ScalesOct 26 2006It is most natural to assume that mysterious Small Ionized and Neutral Structures (SINS) indiffuse ISM arise from turbulence. There are two obvious problem with such an explanation, however. First of all, it is generally believed that at the small scales ... More
Velocity centroids as tracers of the turbulent velocity statisticsJan 28 2004May 28 2005We use the results of magnetohydrodynamic (MHD) simulations to emulate spectroscopic observations and use maps of centroids to study their statistics. In order to assess under which circumstances the scaling properties of the velocity field can be retrieved ... More
Cosmic Ray transport in MHD turbulence: large and small scale interactionsDec 01 2011Dec 05 2011Cosmic ray (CR) transport and acceleration is essential for many astrophysical problems, e.g., CMB foreground, ionization of molecular clouds and all high energy phenomena. Recent advances in MHD turbulence call for revisions in the paradigm of cosmic ... More
Magnetic reconnection as the cause of cosmic ray excess from the heliospheric tailAug 11 2010The observation of a broad excess of sub-TeV cosmic rays compatible with the direction of the heliospheric tail (Nagashima et al. 1998) and the discovery of two significant localized excess regions of multi-TeV cosmic rays by the MILAGRO collaboration ... More
Cosmic Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic FieldOct 15 2007Oct 23 2007We consider the propagation of cosmic rays in turbulent magnetic fields. We use the models of magnetohydrodynamic turbulence that were tested in numerical simulations, in which the turbulence is injected on large scale and cascades to small scales. Our ... More
Polarization from aligned atoms as a diagnostics of circumstellar, AGN and interstellar magnetic fields: II. Atoms with Hyperfine StructureNov 09 2006Dec 13 2006We show that atomic alignment presents a reliable way to study topology of astrophysical magnetic fields. The effect of atomic alignment arises from modulation of the relative population of the sublevels of atomic ground state pumped by anisotropic radiation ... More
Cosmic ray transport in MHD turbulenceDec 23 2007Numerical simulations shed light onto earlier not trackable problem of magnetohydrodynamic (MHD) turbulence. They allowed to test the predictions of different models and choose the correct ones. Inevitably, this progress calls for revisions in the picture ... More
Cosmic Ray Scattering by Compressible Magnetohydrodynamic TurbulenceNov 17 2003Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call for substantial revisions in the picture of cosmic ray transport. In this paper we use recently obtained scaling laws for MHD modes to calculate the scattering frequency for ... More
Microwave Emission from Aligned DustJul 01 2003Polarized microwave emission from dust is an important foreground that may contaminate polarized CMB studies unless carefully accounted for. We discuss potential difficulties associated with this foreground, namely, the existence of different grain populations ... More
MHD Turbulence as a Foreground for CMB StudiesMay 17 2002Measurements of intensity and polarization of diffuse Galactic synchrotron emission as well as starlight polarization reveal power law spectra of fluctuations. We show that these fluctuations can arise from magnetohydrodynamic (MHD) turbulence in the ... More
Imbalanced Relativistic Force-Free Magnetohydrodynamic TurbulenceDec 20 2013When magnetic energy density is much larger than that of matter, as in pulsar/black hole magnetospheres, the medium becomes force-free and we need relativity to describe it. As in non-relativistic magnetohydrodynamics (MHD), Alfv\'enic MHD turbulence ... More
Magnetic Reconnection in Turbulent Plasmas and Gamma Ray BurstsFeb 13 2013We discuss how the model of magnetic reconnection in the presence of turbulence proposed inLazarian & Vishniac 1999 makes the reconnection rate independent either of resistivity or microscopic plasma effects, but determined entirely by the magnetic field ... More
Statistics of Reconnection-Driven TurbulenceNov 11 2016Feb 06 2017Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Within the standard Sweet-Parker model, this process would be too slow to explain observations (e.g. solar flares). In reality, the process must be ubiquitous ... More
Turbulence, Reconnection and Cosmic Rays in Galaxy ClustersAug 10 2011Recent years have been marked by substantial changes in our understanding of magnetic turbulence and magnetic reconnection, which, in its turn induced better understanding of cosmic ray diffusion and acceleration. Current models of magnetized turbulence ... More
Line-of-sight statistical methods for turbulent medium: VCS for emission and absorption linesJan 30 2009We present an overview of the Velocity Coordinate Spectrum (VCS), a new technique for studying astrophysical turbulence that utilizes the line-of-sight statistics of Doppler-broadened spectral lines. We consider the retrieval of turbulence spectra from ... More
Aspects of Density Fluctuations in Compressible MHD TurbulenceJul 26 2007We study scaling relations of compressible isothermal strongly magnetized turbulence using numerical simulations with resolution 512$^3$. We find a good correspondence of our results with the Fleck (1996) model of compressible hydrodynamic turbulence. ... More
Cosmic ray transport in MHD turbulenceMay 28 2005Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call for revisions in the picture of cosmic ray transport. In this paper we use recently obtained scaling laws for MHD modes to obtain the scattering frequency for cosmic rays. We ... More
Grain Alignment by Radiation in Dark Clouds and CoresMay 28 2005We study alignment of grains by radiative torques. We found steep rise of radiative torque efficiency as grain size increases. This allows larger grains that are known to exist within molecular clouds to be aligned by the attenuated and reddened interstellar ... More
Velocity Modification of Power Spectrum from Absorbing MediumMay 24 2004Quantitative description of the statistics of intensity fluctuations within spectral line data cubes introduced in our earlier work is extended to the absorbing media. A possibility of extracting 3D velocity and density statistics from both integrated ... More
Polarized Foreground Emission from Dust: Grain Alignment and MHD TurbulenceNov 02 2002Aligned grains present a foreground for cosmic microwave emission studies. We review basic physical processes involved in grain alignment and discuss the niches for different alignment mechanisms. We show that mechanisms which were favored for decades ... More
Turbulent Cooling Flows in Molecular CloudsNov 03 1998We propose that inward, subsonic flows arise from the local dissipation of turbulent motions in molecular clouds. Such "turbulent cooling flows" may account for recent observations of spatially extended inward motions towards dense cores. These pressure-driven ... More
Occlusion Effects and the Distribution of Interstellar Cloud Sizes and MassesAug 15 1995The frequency distributions of sizes of ``clouds" and ``clumps" within clouds are significantly flatter for extinction surveys than for CO spectral line surveys, even for comparable size ranges. A possible explanation is the blocking of extinction clouds ... More
Spinning Dust Emission from Wobbling Grains: Important Physical Effects and ImplicationsOct 31 2012We review major progress on the modeling of electric dipole emission from rapidly spinning tiny dust grains, including polycyclic aromatic hydrocarbons (PAHs). We begin by summarizing the original model of spinning dust proposed by Draine and Lazarian ... More
Acceleration of Small Dust Grains due to Charge FluctuationsDec 15 2011Dec 22 2011We consider the acceleration of very small dust grains including Polycyclic Aromatic Hydrocarbons (PAHs) arising from the electrostatic interactions of dust grains that have charge fluctuations in time due to charging events. We simulate the charge fluctuations ... More
Alignment of Dust with Magnetic Inclusions: Radiative Torques and Superparamagnetic Barnett and Nuclear RelaxationJan 01 2008Jan 03 2008We consider grains with superparamagnetic inclusions and report two new condensed matter effects that can enhance the internal relaxation of the energy of a wobbling grain, namely, superparamagnetic Barnett relaxation, as well as, an increase of frequencies ... More
Alignment of Dust by Radiative Torque: Recent DevelopmentsDec 31 2008Alignment of dust by radiative torques (RATs) has proven to be the most promising mechanism to explain alignment in various astrophysical environments, from comet atmospheres to accretion disks, molecular clouds, and diffuse interstellar gas. We discuss ... More
Turbulent dynamo in a conducting fluid and partially ionized gasAug 18 2016By following the Kazantsev theory and taking into account both microscopic and turbulent diffusion of magnetic fields, we develop a unified treatment of the kinematic and nonlinear stages of turbulent dynamo, and study the dynamo process for a full range ... More
Stochastic reacceleration of relativistic electrons by turbulent reconnection: a mechanism for cluster-scale radio emission ?Mar 01 2016In this paper we investigate a situation where relativistic particles are reaccelerated diffusing across regions of reconnection and magnetic dynamo in super-Alfvenic, incompressible large-scale turbulence. We present an exploratory study of this mechanism ... More
Particle reacceleration by compressible turbulence in galaxy clusters: effects of reduced mean free pathNov 04 2010Direct evidence for in situ particle acceleration mechanisms in the inter-galactic-medium (IGM) is provided by the diffuse Mpc--scale synchrotron emissions observed from galaxy clusters. It has been proposed that MHD turbulence, generated during cluster-cluster ... More
Magnetic Field Measurement with Ground State AlignmentFeb 13 2013Observational studies of magnetic fields are crucial. We introduce a process "ground state alignment" as a new way to determine the magnetic field direction in diffuse medium. The alignment is due to anisotropic radiation impinging on the atom/ion. The ... More
Anisotropy of TeV Cosmic Rays and the Outer Heliospheric BoundariesNov 13 2011Oct 29 2012Cosmic rays in the energy range from about 10's GeV to several 100's TeV are observed on Earth with an energy-dependent anisotropy of order 0.01-0.1%, and a consistent topology that appears to significantly change at higher energy. The nearest and most ... More
The Anisotropy of Electron MHD TurbulenceJun 25 2004We present numerical studies of 3-dimensional electron magnetohydrodynamic (EMHD) turbulence. We investigate cascade timescale and anisotropy of freely decaying strong EMHD turbulence with zero electron skin depth. Cascade time scales with $k^{-4/3}$. ... More
Angular Spectra of Polarized Galactic ForegroundsJun 09 2003It is believed that magnetic field lines are twisted and bend by turbulent motions in the Galaxy. Therefore, both Galactic synchrotron emission and thermal emission from dust reflects statistics of Galactic turbulence. Our simple model of Galactic turbulence, ... More
Generation of Compressible Modes in MHD TurbulenceJan 23 2003Astrophysical turbulence is magnetohydrodynamic (MHD) in its nature. We discuss fundamental properties of MHD turbulence. In particular, we discuss the generation of compressible MHD waves by Alfvenic turbulence and show that this process is inefficient. ... More
Dust Motions Driven by MHD TurbulenceMay 17 2002We discuss the relative grain motions due to MHD turbulence in interstellar medium. It has been known for decades that turbulent drag is an efficient way to induce grain relative motions. However, earlier treatments disregarded magnetic field and used ... More
Thermal Flipping and Thermal Trapping -- New Elements in Dust Grain DynamicsJan 19 1999Since the classical work by Purcell (1979) it has been generally accepted that most interstellar grains rotate suprathermally. Suprathermally rotating grains would be nearly perfectly aligned with the magnetic field by paramagnetic dissipation if not ... More
Polarized Microwave Emission from DustNov 12 2001Polarized emission from dust is an important foreground that can hinder the progress in polarized CMB studies unless carefully accounted for. We discuss potential difficulties associated with the dust foreground, namely, the existence of different grain ... More
Inelastic Dissipation in Wobbling Asteroids and CometsNov 03 1998Dec 06 2001Asteroids and comets dissipate energy when they rotate about the axis different from the axis of the maximal moment of inertia. We show that the most efficient internal relaxation happens at the double frequency of body's tumbling. Therefore the earlier ... More
Magnetic Properties of Dust Grains, Effect of Precession and Radiative Torque AlignmentOct 25 2018We revisit the process of grain alignment by Radiative Torques (RATs) and focus on constraining magnetic susceptibility of grains via observations. We discuss the possibility of observational testing of the magnetic properties of grains as the alignment ... More
The Column Density Variance-Sonic Mach Number RelationshipMay 16 2012Jun 22 2012Although there are a wealth of column density tracers for both the molecular and diffuse interstellar medium, there are very few observational studies investigating the relationship between the density variance ($\sigma^2$) and the sonic Mach number (${\cal ... More
Cosmic Rays and Stochastic Magnetic Reconnection in the HeliotailMay 16 2012Galactic cosmic rays are believed to be generated by diffusive shock acceleration processes in Supernova Remnants, and the arrival direction is likely determined by the distribution of their sources throughout the Galaxy, in particular by the nearest ... More
A model of acceleration of Anomalous Cosmic Rays by Reconnection in the HeliosheathMay 08 2009Jul 17 2009We discuss a model of cosmic ray acceleration that accounts for the observations of anomalous cosmic rays by Voyager 1 and 2. The model appeals to fast magnetic reconnection rather than shocks as the driver of acceleration. The ultimate source of energy ... More
Simulations of Electron Magnetohydrodynamic TurbulenceApr 03 2009Jun 16 2009We present numerical simulations of electron magnetohydrodynamic (EMHD) and electron reduced MHD (ERMHD) turbulence. Comparing scaling relations, we find that both EMHD and ERMHD turbulence show similar spectra and anisotropy. We develop new techniques ... More
Ground-state alignment of atoms and ions: New Diagnostics of Astrophysical Magnetic field in diffuse mediumJun 23 2008We discuss a new technique of studying magnetic fields in diffuse astrophysical media, e.g. interstellar and intergalactic gas/plasma. This technique is based on the angular momentum alignment of atoms and ions in their ground or metastable states. As ... More
Studying Turbulence using Doppler-broadened lines: Velocity Coordinate SpectrumNov 09 2005Jul 28 2006We discuss a new technique for studying astrophysical turbulence that utilizes the statistics of Doppler-broadened spectral lines. The technique relates the power Velocity Coordinate Spectrum (VCS), i.e. the spectrum of fluctuations measured along the ... More
Particle Acceleration by MHD TurbulenceSep 14 2005Oct 21 2005Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call for revisions in the picture of particle acceleration. We make use of the recently established scaling of slow and fast MHD modes in strong and weak MHD turbulence to provide ... More
Statistics of turbulence via polarimetry: alignment of grains and atomsMay 29 2005Most astrophysical fluids are turbulent and magnetized. Fluctuations of polarization provide a promising way to study astrophysical magnetic turbulence. We discuss polarization that arises from grains and atoms aligned in respect to magnetic field, describe ... More
Optical polarization from aligned atoms as a new diagnostic of Astrophysical magnetic fieldsDec 08 2004Feb 03 2005Population of levels of the hyperfine and fine split ground state of an atom is affected by radiative transitions induced by anisotropic radiation flux. Such aligned atoms precess in the external magnetic field and this affects properties of polarized ... More
Alignment of Dust in Molecular CloudsAug 10 2004Polarimetry is one of the most informative techniques of studying magnetic fields in molecular clouds. How reliable the interpretation of the polarization maps in terms of magnetic fields is the issue that the grain alignment theory addresses. We show ... More
Translational Velocities and Rotational Rates of Interstellar Dust GrainsNov 17 2003Interstellar dust grains exhibit complex dynamics which is essential for understanding many key interstellar processes that involve dust, including grain alignment, grain growth, grain shattering etc. Grain rotational and translational motions are affected ... More
Grain Acceleration by MHD Turbulence: Gyroresonance MechanismJan 01 2003Jun 12 2003We discuss a new mechanism of dust acceleration that acts in a turbulent magnetized medium. The magnetohydrodynamic (MHD) turbulence includes both fluid motions and magnetic fluctuations. We show that while the fluid motions bring about grain motions ... More
Scattering of Cosmic Rays by Magnetohydrodynamic Interstellar TurbulenceMay 17 2002Nov 22 2002Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call for substantial revisions in our understanding of cosmic ray transport. In this paper we use gyroresonance recently obtained scaling laws for MHD modes to calculate the scattering ... More
Compressible MHD Turbulence: Mode Coupling, Anisotropies and ScalingsDec 06 2002Dec 08 2002Compressible turbulence, especially the magnetized version of it, traditionally has a bad reputation with researchers. However, recent progress in theoretical understanding of incompressible MHD as well as that in computational capabilities enabled researchers ... More
Velocity and density spectra of the Small Magellanic CloudFeb 11 2001This paper reports results on the statistical analysis of HI turbulence in the Small Magellanic Cloud (SMC). We use 21 cm channel maps, obtained with the Australia Telescope Compact Array and the Parkes telescope, and analyze the spectrum of observed ... More
Velocity Modification of HI Power SpectrumJan 19 1999Jan 11 2000The distribution of atomic hydrogen in the Galactic plane is usually mapped using the Doppler shift of 21cm emission line. We calculate the emission spectrum in velocity slices of data (channel maps) and derive its dependence on the statistics of HI velocity ... More