We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and accretion ...

We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and accretion ...

A possible accretion model associated with the ionization instability of quasar disks is proposed to

A possible accretion model associated with the ionization instability of quasar disks is proposed to

Gas accreting onto T Tauri stars should form shocks that are susceptible to the classical radiative shock instability. The instability should give rise to strong periodic modulation in the X-ray emission from the shock-heated plasma. Time series analysis of soft X-rays thought to arise predominantly in an accretion ...

The global nonlinear time-dependent evolution of the inertial-acoustic mode instability in accretion

We present three-dimensional simulations on a new mechanism for the detonation of a sub-Chandrasekhar CO white dwarf in a dynamically unstable system where the secondary is either a pure He white dwarf or a He/CO hybrid. For dynamically unstable systems where the accretion stream directly impacts the surface of the primary, the final tens of orbits can ...

Whether an efficient collisonless temperature equilibration mechanism exists for a two-temperature ion-electron plasma, with Ti>Te, is important for understanding astrophysical phenomena such as radiatively inefficient accretion flows and relativistic collisionless shocks in GRBs. Here we study whether the two-stream and Weibel ...

Whether an efficient collisonless temperature equilibration mechanism exists for a two-temperature ion-electron plasma, with Ti> Te, is important for understanding astrophysical phenomena such as radiatively inefficient accretion flows and relativistic collisionless shocks in Gamma-ray bursts. Here we study whether the two-stream and Weibel ...

A possible accretion model associated with the ionization instability of quasar disks is proposed to

We consider the consequences of magnetic buoyancy and the magnetic shearing instability (MSI) on the

Electromagnetic streaming instabilities of multicomponent collisional magnetized accretion disks are studied. Sufficiently ionized regions of the disk are explored where there is strong collisional coupling of neutral atoms with both ions and dust grains simultaneously. The steady state is investigated in detail and the azimuthal and ...

With the discovery that Alfven waves can be strongly unstable in a magnetized accretion disk, it can be expected to explain the turbulence necessary to drive accretion in these disks. The instability of non-axisymmetric Alfven waves is studied using analy...

... Saturation of the Relativistic Two-Stream Instability by Electron Trapping. ... Abstract : The single-wave weak cold relativistic two-stream instability has ...

Context. High resolution X-ray observations of classical T Tauri stars (CTTSs) show a soft X-ray excess due to high density plasma (ne = 1011-113 cm-3). This emission has been attributed to shock-heated accreting material impacting onto the stellar surface. Aims: We investigate the observability of the shock-heated accreting material in the X-ray band as ...

Steady state and time dependent calculations of a model for accretion instability are presented, in which matter accumulates in a cold torus and then undergoes a thermal instability causing the matter to heat and flow down onto the central star. The model...

Context. Plasma accreting onto classical T Tauri stars (CTTS) is believed to impact the stellar surface at free-fall velocities, generating a shock. Current time-dependent models describing accretion shocks in CTTSs are one-dimensional, assuming that the plasma moves and transports energy only along magnetic field lines (? ? 1). Aims: We investigate the ...

... Title : THE WAVE BASIS FOR ONSET OF INSTABILITIES IN ION- NEUTRALIZED ELECTRON STREAMS IN DRIFT TUBES,. ...

Theoretical interest in astrophysical disks with counterrotating components of stars and/or gas has been stimulated by recently discovered counterrotating spiral and S0 galaxies. A variety of physical processes can occur in counterrotating disks. We have shown that a strong two-stream instability can occur for one armed (m = 1) tightly-wrapped spiral waves ...

We study electromagnetic streaming instabilities in thermal viscous regions of rotating astrophysical objects, such as protostellar and protoplanetary magnetized accretion disks, molecular clouds, their cores, and elephant trunks. The obtained results can also be applied to any regions of interstellar medium, where different ...

We study electromagnetic streaming instabilities in thermal viscous regions of rotating astrophysical objects, such as protostellar and protoplanetary magnetized accretion disks, molecular clouds, their cores, and elephant trunks. The obtained results can also be applied to any regions of interstellar medium, where different ...

A general theory for instabilities of multicomponent warm magnetized accretion disks is developed using Maxwell's equations and the equations of motion and continuity for each disk component. The compressibility, anisotropic thermal pressure, and collisions of the charged species with neutrals are taken into account. The thermal effects are ...

A general theory for instabilities of multicomponent warm magnetized accretion disks is developed using Maxwell's equations and the equations of motion and continuity for each disk component. The compressibility, anisotropic thermal pressure, and collisions of the charged species with neutrals are taken into account. The thermal effects are involved ...

The transport of angular momentum in the outward direction is the fundamental requirement for accretion to proceed in an accretion disk. This objective can be achieved if the accretion flow is turbulent. Instabilities are one of the sources for the turbulence. We study a differentially rotating compressive flow in ...

The report deals with the question of whether mass accretion on a star can cause pulsational instability by itself. The principal result is a formula for the effect of accretion on the growth (or decay) rate of a radial pulsation mode. Application of this...

The influence of accretion disk instabilities on the UV fluxes of Seyfert 1 galaxies was studied. The observed characteristic timescales of variability are consistent with the interpretation that most of the UV radiation originates in an accretion disk, a...

This presentation describes the behavior of matter in environments with extreme magnetic and gravitational fields, explains the instability/stability of accretion disks in certain systems, and discusses how emergent radiation affects accretion flow. Magne...

We present a series of simulations of turbulent stratified protostellar discs with the goal of characterizing the settling of dust throughout a minimum-mass solar nebula. We compare the evolution of both compact spherical grains, as well as highly fractal grains. Our simulations use a shearing-box formulation to study the evolution of dust grains locally within the disc, and collectively our ...

In the accretion disk around a black hole or a neutron star, the radiative viscosity will much exceed the viscosity of the fully ionized gas. The Reynolds number, depending strongly on the accretion rate, will reach a minimum in the zone where the bulk of the energy is released. Thermal instability will set in, altering the local ...

The electrical equilibrium of a satellite at high altitudes, representing the balance between emission and accretion of charge at the satellite surface, requires for its existence the stability of the potential and charge distributions throughout the space surrounding the satellite. The stability of equilibrium states of geometrically simple satellites illuminated by solar ...

Motivated by recent simulations of galaxy formation in which protogalaxies acquire their baryonic content through cold accretion, we study the gravitational fragmentation of cold streams flowing into a typical first galaxy. We use a one-zone hydrodynamical model to examine the thermal evolution of the gas flowing into a 108 M sun dark matter halo at ...

The current status of the physics of accretion disks in close binary stars is reviewed, with an emphasis on the hydrodynamic overreflection instability, which is a factor leading to the accretion disk turbulence. The estimated turbulent viscosity coefficients are in good agreement with observations and explain the high angular momentum ...

Apr 12, 2011 ... The characteristics of a particular planetary system depend upon the ... planets are formed from dynamic instabilities in accretion disks. ...

The instability of the flow along the accretion line in the two-dimensional Bondi-Hoyle-Lyttleton type accretion flow is studied. By means of numerical simulations, the nonlinear regime of the instability is explored, thus extending a previous work that dealt with the linear regime using the WKB approximation. In ...

We consider the problem of the flow produced by the accretion of gas from a rotating cloud onto a point gravitational source. It is shown that, for a cloud initially in uniform rotation, the effect of accretion is to produce a Taylor column in the cloud parallel to the rotation axis. Only gas within the column is accreted; the gas ...

It is shown that the basic nonlinear effect associated with the oscillating two-stream instability is a downshift of the natural frequencies of electron plasma waves. As a result, conversion of this instability to a decay instability can take place. (Auth...

Stars form by the flow of matter through an accretion disk. An efficient mechanism of angular momentum transport is required to drive this flow. The magneto rotational instability (MRI) is the leading candidate (along with self-gravity in the early stages of growth) to drive turbulent momentum transport in disks. I will briefly summarize the current status ...

We present a simple theoretical framework for massive galaxies at high redshift, where the main assembly and star formation occurred, and report on the first cosmological simulations that reveal clumpy disks consistent with our analysis. The evolution is governed by the interplay between smooth and clumpy cold streams, disk instability, and bulge ...

... goal of understanding the development and nature of turbulence generated from a source of free streaming energy within a collisionless plasma. ...

We present simulations of the nonlinear evolution of streaming instabilities in protoplanetary disks. The two components of the disk, gas treated with grid hydrodynamics and solids treated as superparticles, are mutually coupled by drag forces. We find that the initially laminar equilibrium flow spontaneously develops into turbulence in our unstratified ...

planet :: smoking gun : caught in the actsmoking gun : caught in the act Most simulations of disk-planetDisk Instability vsvs. Core Accretion. Core Accretion Formed planet : forming planet ::Formed planet : formingMost simulations of disk-planet interactions start with fully-formed planetinteractions start with fully

Steady state and time dependent calculations of a model for accretion instability are presented, in which matter accumulates in a cold torus and then undergoes a thermal instability causing the matter to heat and flow down onto the central star. The model is compared to the observations of dwarf novae and certain examples of both hard ...

A linear theory is developed for thermal convective instability in radiating gas dominated by radiation pressure. Analysis demonstrates how the magnetic field and differential rotation will affect the onset of thermal convection in the interior of a black hole accretion disk.

The evolution of thick accretion tori around black holes was investigated. Using three-dimensional computer models, it is shown that isentropic, pressure supported tori with constant specific angular momentum (Omega = r sup - 2) are unstable. Nonaxisymmet...

We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It produces tall, thin tongues of plasma that penetrate the ...

In this paper, we study electromagnetic streaming instabilities in the thermal viscous regions of rotating astrophysical objects, such as magnetized accretion discs, molecular clouds, their cores and elephant trunks. The results obtained can also be applied to any regions of interstellar medium, where different equilibrium velocities ...

Pinch-point instability analysis is used to study the effects of finite temperature on the time-asymptotic pulse shapes of electrostatic and electromagnetic two-stream instabilities. Their absolute or convective instability nature is established over the entire regime from instability threshold ...

Motivated by recent simulations of galaxy formation in which protogalaxies acquire their baryonic content through cold accretion, we study the gravitational fragmentation of cold streams flowing into a typical first galaxy. We use a one-zone hydrodynamical model to examine the thermal evolution of the gas flowing into a 10{sup 8} M{sub sun} dark matter ...

Supercomputer simulations have been used in conjunction with analytic studies to investigate the central issue of astrophysical accretion-disk dynamics: the nature of the angular momentum transport. Simulations provide the means to investigate and experiment with candidate mechanisms, including global hydrodynamic instabilities, spiral shock waves, and ...

... Descriptors : *DEBRIS, *ENVIRONMENTAL IMPACT, *STREAMS, STABILITY, MORPHOLOGY, GEOMORPHOLOGY, INSTABILITY, CHANNELS ...

Reasons that could produce two-stream instability in pulsar plasma are discussed. It is noted that if the outflow of electron-positron plasma from the pulsar vicinity is stationary, this instability either is stabilized, or its growth rate is so low that ...

We consider the effects of a weak ambient magnetic field on the oscillating two stream and parametric decay instabilities, with particular emphasis on the dependence on the angular variation of the instability thresholds and growth rates on the magnetic f...

We present analytical and numerical work which indicates that during ionospheric heating with high-powered hf radio waves, the oscillating two-stream instability may dominate the parametric decay instability. The oscillating two-stream instability saturat...

The present study of the two-stream instability in stellar disks with counterrotating components of stars and/or gas is stimulated by recently discovered counterrotating spiral and S0 galaxies. Strong linear two-stream instability of tightly wrapped spiral waves is found for one- and two-armed waves with the ...

We study the two-dimensional, time-dependent MHD of radiation-driven winds from luminous accretion disks initially threaded by a purely axial magnetic field. The radiation force is mediated primarily by spectral lines. We use ideal MHD to compute the evolution of Keplerian disks, varying the magnetic field strengths and the luminosity of the disk, the central ...

A plasma instability which may lead to the thermal coupling of ions and electrons in two-temperature

Icing; Swept wings; Ice scallop formations; Lobster tails; Cross flow vortices; Cross flow instability; Swept wing ice accretions. NUMBER OF PAGES: ...

Nov 19, 2004 ... In this scenario the plasma instabilities that can occur during the accretion process (Rayleigh-Taylor, Kelvin-Helmoltz, ...

Mar 7, 2000 ... Accretion-Ejection Instability and QPO in Black-hole binaries ... RXTE Study of the Cyclotron Resonance Scattering Feature in Her X-1 ...

Icing; Swept wings; Ice scallop formations; Lobster tails; Cross flow vortices; Cross flow instability; Swept wing ice accretions. NUMBER OF PAGES: ...

Highly nonstationary accretion onto a magnetized neutron star from a surrounding accretion disc is considered. Nonstationary accretion has been considered before in terms of droplets or rain or as a necessary consequence of instabilities in the accretion column flow. Here, the extreme of very ...

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without magnetic a field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge separation is required ...

Context: The interstellar medium contains warm clouds that are embedded in a hot dilute gas produced by supernovae. Because both gas phases are in contact, an interface forms where mass and energy are exchanged. Whether heat conduction leads to evaporation of these clouds or whether condensation dominates has been analytically derived. Both phases behave differently dynamically so that their ...

A general discussion of modulational instabilities in plasmas is given. The basic mechanism is a four wave interaction and examples include the langmuir modulational instability, the oscillating two-stream instability and the filamentation of laser light ...

The existence of a new instability mechanism of a current-carrying plasma which, for a sufficiently long system, may occur after saturation of the two-stream instability is shown. The instability is due to combined asymmetry and nonuniformity of the elect...

The stability of magnetic fields within the accretion disks is examined, including the effects of magnetic buoyancy. Rayleigh-Taylor, and Kelvin-Helmholtz instabilities. The purpose of the study is to examine the efficacy of turbulent accretion (..cap alpha..-) disk models which depend upon ''magnetic ...

Non-linear Kelvin-Helmholtz instability, of two parallel horizontal streams of inviscid incompressible fluids under the action of gravity, is studied theoretically. The lower stream is denser and there is surface tension between the streams. Some progress...

Accretion describes the process by which matter in an astrophysical disk falls onto a central massive object. Accretion disks are present in many astrophysical situations including binary star systems, young stellar objects, and near black holes at the center of galaxies. Measurements from observations of these disks have shown that viscous processes are ...

During the initial stages of planet formation in circumstellar gas disks, dust grains collide and build up larger and larger bodies. How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem: boulders are expected to stick together poorly, and to spiral into the protostar in a few hundred orbits owing to a 'headwind' from the slower rotating ...

The electromagnetic dynamics of multicomponent collisional magnetized accretion disks is considered. The sufficiently ionized regions of the disk are explored where there is the strong collisional coupling of neutrals with ions and dust grains simultaneously. The stationary state is investigated in detail and the azimuthal and radial velocities of species are found. It is ...

The thermal instability of accretion disk is thought to play an important role in the activity of low-mass X-ray binaries (LMXBs). It should also appear when a (quasi)persistent LMXB like KS 1731-260 goes into its low state. In our interpretation, the irradiation of the donor during the main outburst lead to an increase of the mass transfer rate ?tr, which ...

A dusty plasma cloud in space has a gravitational instability which allows star formation even orders of magnitude below the Jeans limit for gravitational collapse. This instability leads to a stellesimal accretion which is analogous to the planetesimal a...

Differentially rotating disks are subject to the axisymmetric instability for perfectly conducting plasma in the presence of poloidal magnetic fields. For nonaxisymmetric perturbations, the authors find localized unstable eigenmodes whose eigenfunction is...

. There is a class of dynamos where the field is caused by a velocity field which, in turn, is driven by the generated magnetic field. Numerical threedimensional simulations of this type of process are reviewed. This process is here discussed in connection with accretion discs, but we point out that similar mechanisms have also been suggested in the context of solar and ...

It is shown that an ionized disk in a vertical magnetic field (e.g., the dipole field of the central object for an accretion or planetary disk) is subject to spiral instabilities of low azimuthal wavenumber, driven by differential rotation. The amplification is due to the Swing mechanism already known for the spiral instability of ...

This paper presents analytical solutions, which describe the effect of time-variable net recharge (net accretion to water table) and bank storage in alluvial aquifers on the sustenance of stream flows during storm and inter-storm events. The solutions relate the stream discharge,...

This study presents a theoretical approach to analyze the influence of kappa distributed streaming ions and magnetized electrons on the plasma wave propagation in the presence of dust by employing two-potential theory. In particular, analytical expressions under certain conditions are derived for various modes of propagation comprising of kinetic Alfven wave ...

If you fall into a real astronomical black hole (choosing a supermassive black hole, to make sure that the tidal forces do not get you first), then you will probably meet your fate not at a central singularity, but rather in the exponentially growing, relativistic counter-streaming instability at the inner horizon first pointed out by Poisson & Israel ...

OUTFLOWS FROM DYNAMO-ACTIVE PROTOSTELLAR ACCRETION DISCS BRIGITTA VON REKOWSKI1 , AXEL BRANDENBURG2, Newcastle, UK Abstract. An axisymmetric model of a cool, dynamo-active accretion disc is applied by the disc dynamo driven by the magneto-rotational instability and some form of outflow is indeed seen

Recent observational data has shown that the Algol-type binary system RS Vul possesses an accretion disk tilted out of the orbital plane. Magnetic effects in the surface of the donor star could produce a nontrivial effect in the flow of the accretion stream as it travels through the L1 Lagrange point. Such a deflection could introduce ...

A review of work on plasma models primarily involving unstable situations is presented. Double stream instabilities are observed in which two cold streams of electrons pass through each other and through a fixed neutralizing background. Current instabilities are observed in which an electron current is ...

Massive stars produce so much light that the radiation pressure they exert on the gas and dust around them is stronger than their gravitational attraction, a condition that has long been expected to prevent them from growing by accretion. We present three-dimensional radiation-hydrodynamic simulations of the collapse of a massive prestellar core and find that radiation ...

The nonlinear evolution and spatial propagation of the thermal instability in accretion disks in galactic nuclei are investigated. Integrations of the vertical structure of the disks are described for different alpha prescriptions, and the thermal stability is examined. Global time-dependent calculations of the unstable disks are performed which show that ...

The radial-azimuthal instability of a hot two-temperature accretion disc with advection is analyzed. After obtaining the dispersion equation, we find that advection and viscous force have an influence on the stability of acoustic modes, but not on the stability of thermal and viscous modes. We also find azimuthal perturbations to affect the stability of ...

We report experimental observation of an instability in a Couette-Taylor flow of a polymer fluid in a thin gap between two coaxially rotating cylinders in a regime where their angular velocity decreases with the radius while the specific angular momentum increases with the radius. In the considered regime, neither the inertial Rayleigh instability nor the ...

We report experimental observation of an instability in a Couette-Taylor flow of a polymer fluid in a thin gap between two coaxially rotating cylinders in a regime where their angular velocity decreases with the radius while the specific angular momentum increases with the radius. In the considered regime, neither the inertial Rayleigh instability nor the ...

... is solved numerically and the results show there is no instability for omega sub b ... sub b tau, the fastest-growing modes have a growth rate of omega ...

instability, two-streaming, Weibel instabilities) created in the shock are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic ...

Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible ...

... by diamagnetic streaming) or the drift dissipative instability. jThe gravitational instability due to magnetic field curvature is ...

... compressible mix- * ing layers is also considered. Page 53. 0 28 4.1 Free Stream Conditions 0 The instability characteristics of compressible mixing ...

Bounds are placed on the growth rates of dynamical instability in shear flows in accretion discs and tori. Ft is shown that the critical layer lies in the flow even when the boundaries are free for flows in accretion discs, cylinders and isentropic, constant angular momentum tori (for which the relativistic effects are also ...

The effect of rapid accretion on a moderate-mass stellar model is studied. The surface boundary condition is examined for two modes of accretion - disk and direct impact. It is found that the effective temperature must be increased for disk accretion but not for direct-impact accretion. In the latter mode the ...

By analyzing the fourth-order dispersion relation, the influence of coupled radial and azimuthal perturbations on the stability of a radiation-pressure-dominated accretion disk is investigated. If the azimuthal perturbations are considered, we find that the stability properties of disk are different from that in purely radial perturbation case. For a standard alpha disk model, ...

The Magellanic Stream (MS) is the nearest example of a gaseous trail formed by interacting galaxies. While the substantial gas masses in these kinds of circumgalactic structures are postulated to represent important sources of fuel for future star formation, the mechanisms whereby this material might be accreted back into galaxies remain unclear. Recent ...

Bolometric luminosities and black hole (BH) masses are estimated by various methods for a sample of young radio galaxies with known ages. We find that the ages are positively correlated with the bolometric luminosities in these young radio galaxies. This positive correlation is consistent with the theoretical prediction based on the radiation pressure instability of ...

We describe in detail our two-dimensional, axisymmetric computer code for calculating fully relativistic ideal gas hydrodynamics around a Kerr black hole. This code is being used to study fully dynamic inviscid fluid accretion onto black holes, as well as the evolution and developement of nonlinear instabilities in pressure-supported ...

Jun 1, 2010 ... The black holes are surrounded and nourished by disks of gas and dust, called accretion disks. Powerful jets stream out from below and above ...

resolved spectra of the accretion disk and gas stream of the nova-like variable UX Ursae Majoris." Mon. Notices Roy. Astron. Soc. 298, 1079. ...

A Search for Terrestrial Planets. A Fundamental NASA Mission Goal: ... To place our Solar System in context with other planetary systems ..... Interacting binaries, accretion disks and streams, cataclysmic variables and novae ...

... from a bipolar jet that has formed near the point where material streaming from star 2 interacts with the accretion disk around star 1 (Harmanec et al. ...

Image of the Day Gallery. n this artist's conception, a galaxy accretes mass from rapid, narrow streams of cold. Back to Gallery ...

May 2, 2007 ... Results: V407 Vul proposed to be a double degenerate Algol (i.e., non-magnetic white dwarf accreting via direct stream impact). ...

Jan 2, 2003 ... Results: V407 Vul proposed to be a double degenerate Algol (i.e., non-magnetic white dwarf accreting via direct stream impact). ...

Oct 28, 2004... large swirling streams of hot gas that spiral toward the black hole as a fast moving incandescent whirlpool known as an accretion disk. ...

Aims: We apply Floquet analysis to study the dynamical stability of two-dimensional axisymmetric Keplerian flows distorted by an m = 2 epicyclic periodic forcing term, representing a tidal perturbation in a thin accretion disk (AD) of a cataclysmic variable (CV). This tidal mode is responsible for the disk truncation mechanism. Methods: Floquet analysis reveals, with a ...

Context. High resolution X-ray spectroscopy has revealed soft X-rays from high density plasma in classical T Tauri stars (CTTSs), probably arising from the accretion shock region. However, the mass accretion rates derived from the X-ray observations are consistently lower than those derived from UV/optical/NIR studies. Aims: We aim to test the hypothesis ...

We investigate the launching and stability of extragalactic jets through magnetohydrodynamic simulations of jet evolution. In these simulations, a small scale equilibrium magnetic corona is twisted by a differentially rotating accretion disk. Two-dimensional calculations show the formation of a collimated outflow. This outflow is divided into two regions by the Alfv�n ...

... Accession Number : AD0697363. Title : UHF-PLASMA INTERACTION--THE TWO-STREAM INSTABILITY OF A current-CARRYING PLASMA,. ...

Page 1. UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP012496 TITLE: Two-Stream ...

Particle in cell plasma simulation technique has been used to study the effect of the ion two-stream

The ion distribution function in a thermal barrier is modeled by counter streaming Maxwellian distribution. Its stability with respect to parallel propagating electrostatic and electromagnetic modes is investigated both analytically and numerically. It is...

The integrated growth rate of various relativistic beam/plasma instabilities in a weakly varying plasma density gradient is calculated using a WKB-like approximation. It is proven that such an assumption can be made in fast ignition scenario conditions. The formalism is applied to the two-stream, the filamentation, and the ...

This thesis addresses the issue, 'Which approach to instabilities - temporal, spatial or pulse theory - is the most appropriate model for the Gulf Stream.' I also address the question of how the observations might be compared to theory. This thesis consis...

For counter-streaming ion currents along a uniform magnetic field, a purely growing instability exists with a growth rate as high as 16 times the ion gyrofrequency. When the streaming ions are only 1 percent of the stationary ions, the growth rate is stil...

This document identifies and provides design guidelines for bridge scour and stream instability countermeasures that have been implemented by various State departments of transportation (DOTs) in the United States. Countermeasure experience, selection, an...

This document identifies and provides design guidelines for bridge scour and stream instability countermeasures that have been implemented by various State departments of transportation (DOTs) in the United States. Countermeasure experience, selection, an...

High resolution infrared spectroscopy is a very valuable tool for the study of the formation of low mass and very low mass stars. At the stage in which these objects are already visible, they still undergo strong mass accretion and mass loss processes. Many of the features observed on these stars can be explained by the magnetospheric accretion model, in ...

The effect of thermal anisotropies on the Drummond-Rosenbluth two-stream ion cyclotron instability were investigated. The properties of the instability were found to be dependent on the ratio of parallel electron temperature to perpendicular ion temperatu...

We investigate a new mechanism, the two-energy-stream cyclotron instability, for fast ions (e.g., fusion products) to drive electrostatic waves and to slow down. The instability comes from a relativistic effect, which dominates conventional phase overtaki...

One possible mechanism for giant planet formation is disk instability in which the planet is formed as a result of gravitational instability in the protoplanetary disk surrounding the young star. The final composition and core mass of the planet will depend on the planet's mass, environment, and the planetesimal accretion efficiency. ...

We derive the evolution equations describing a thin axisymmetric disk of gas and stars with an arbitrary rotation curve that is kept in a state of marginal gravitational instability and energy equilibrium due to the balance between energy released by accretion and energy lost due to decay of turbulence. Rather than adopting a parameterized ? prescription, ...

We study the stability of disc accretion in the recurrent nova RS Ophiuchi. We construct a one-dimensional time-dependent model of the binary-disc system, which includes viscous heating and radiative cooling and a self-consistent treatment of the binary potential. We find that the extended accretion disc in this system is always unstable to the ...

The shape of the Alfven surface separating the magnetosphere of a neutron star from the stream of accreting plasma and the velocity and scattering optical depth of the gas layer flowing along the Alfven surface are calculated. Calculations are made both for spherically symmetrical fall of the gas and for disk accretion. It is shown ...

... E. ; Thompson,James R. ; Sloan,Millard L. ... DENSITY, TURBULENCE, THERMONUCLEAR REACTIONS, MAGNETOHYDRODYNAMICS, STABILITY ...

... propagating at an oblique angle with ... Thus, the magnetic field has a ... COUPLING(INTERACTION), MAGNETIC FIELDS, STABILITY, PARAMETRIC ...

... TRANSFER, TRAPPING(CHARGED PARTICLES), ELECTRON BEAMS, FREE STREAM, INSTABILITY, RELATIVITY THEORY, CYCLOTRONS. ...

The two-stream instability in a periodic structure is analyzed through use of the kinematic approximation for quasistatic waves. (AIP).

... Observations and Numerical Simulations of Inertia�Gravity Waves and Shearing Instabilities in the Vicinity of a Jet Stream ...

... Title : Observations and Numerical Simulations of Inertia-Gravity Waves and Shearing Instabilities in the Vicinity of a Jet Stream. ...

... The NMI equations for two streams is the same as though were separately present; and the dispersion relation for longitudinal oscillations of beams ...

... following mechanisms which are relevant to the generation of radio noise receive special attention: Cerenkov radiation, two-stream instability, and ...

... one at a time into the diode and are ... under the influence of their own electric fields and that ... For streams of finite cross section, circular or rectangular ...

... in typical plasmas; Collisions and transport; Ionospheric parameters; Electrostatic streaming instabilities; CTR; Dimensionless numbers of fluid ...

The interactions of plasmas with non-thermal electron populations can result in instabilities that are of importance in a number of applications and phenomena. Such instabilities include the anomalous Doppler instability that may occur in magnetic confinement fusion, the two-stream instability ...

Gravitational instability plays an important role in driving gas accretion in massive protostellar discs. Particularly strong is the global gravitational instability which arises when the disc mass is of order 0.1 of the mass of the central star and has a characteristic spatial scale much greater than the disc's vertical scaleheight. ...

Young stars can produce X-rays by different mechanisms: Coronal activity, accretion shocks and shocks in outflows. We propose to observe two targets within one field-of-view (FOV): SU Aur is accreting mass from a disk and shows violent coronal activity. We will study the time evolution of stellar flares on time scales from seconds to minutes using the high ...

An extension of the theory of the two-stream plasma ion wave instability and an application of the theory to the physics of the ionosphere are discussed. The effect of a magnetic field and also the effect of collisions with neutral particles are included in the theory. Qualitative and quantitative predictions of the theory are in agreement with ...

Many galaxy clusters pose a 'cooling-flow problem', where the observed X-ray emission from their cores is not accompanied by enough cold gas or star formation. A continuous energy source is required to balance the cooling rate over the whole core volume. We address the feasibility of a gravitational heating mechanism, utilizing the gravitational energy released by the gas that ...

Using N-body simulations of the interaction between an accreting satellite and M31, we have successfully reproduced observed distribution of the Andromeda stellar stream. We predict the spatial distribution of the metal in the progenitor dwarf galaxy by the comparison with the recent observations and the simulations.

Stars form by the flow of matter through an accretion disk. Inside these disks, solids particles suspended in the gas grow to form terrestrial planets and giant planet cores. I will review the physical processes of early planet growth, with an emphasis on the strong aerodynamic coupling between gas and dust (as well as larger solids). Turbulence in the gas disk is a crucial ...

Gas giant planets have been detected in orbit around an increasing number of nearby stars. Two theories have been advanced for the formation of such planets: core accretion and disk instability. Core accretion, the generally accepted mechanism, requires several million years or more to form a gas giant planet in a protoplanetary disk ...

Recently, Ida et al. made an N-body simulation of lunar accretion from a protolunar disk formed by a giant impact. One of their important conclusions is that the accretion time of the Moon is as short as one month. Such rapid accretion is a necessary consequence of the high surface density of a lunar mass disk ...

By employing a quantum hydrodynamic model for bounded three-component quantum plasmas, two kinds of streaming instabilities due to ion-streaming and dust-streaming are studied. For this purpose, the dispersion relation for the bounded wave in quantum electron-ion-dust plasmas is obtained by carrying out a normal ...

An effort is made to observationally constrain accretion disks on the basis of light curves from the eclipsing cataclysmic variable UX Ursae Majoris, reconstructing the spectral energy distribution across the face of an accretion disk. The spectral resolution obtained suffices to reveal not only the radial dependence of absorption and emission line ...

UV spectra of the magnetic accretor AO Psc show absorption features for half the binary orbit. The absorption is unlike the wind-formed features often seen in similar stars. Instead, we attribute it to a fraction of the stream that overflows the impact with the accretion disk. Rapid velocity variations can be explained by changes in the trajectory of the ...

We investigate the properties and evolution of accretion tori formed after the coalescence of two compact objects. At these extreme densities and temperatures, the accreting torus is cooled mainly by neutrino emission produced primarily by electron and positron capture on nucleons (?-reactions). We solve for the disk structure and its time evolution by ...

The final stage of terrestrial planet formation is known as the giant impact stage where protoplanets collide with one another to form planets. So far this stage has been mainly investigated by N-body simulations with an assumption of perfect accretion in which all collisions lead to accretion. However, this assumption breaks for collisions with high ...

Hot intracluster gas associated with clusters of galaxies can cool and accrete into stationary or slowly moving giant galaxies near the cluster center. Enhanced soft X-ray emission and faint extranucler optical emission lines observed in M87 (in the Virgo cluster) and NGC 1275 (in the Perseus cluster) strongly suggest that this process is occurring. In both cases, however, the ...

Star-forming disc galaxies such as the Milky Way need to accrete >~1 Msolar of gas each year to sustain their star formation. This gas accretion is likely to come from the cooling of the hot corona, however it is still not clear how this process can take place. We present simulations supporting the idea that this cooling and the subsequent ...

During the aggregation of amoebae of the cellular slime mould Dictyostelium, the interaction of chemical waves of the signaling molecule cAMP with cAMP-directed cell movement causes the breakup of a uniform cell layer into branching patterns of cell streams. Recent numerical and experimental investigations emphasize the pivotal role of the cell-density dependence of the ...

It is shown by theory and computer simulations that streaming electrons confined by a surface picket-fence magnetic field (periodic array of magnetic cusps) are subject to a two-stream instability between the electrons trapped by the surface cusp fields and the streaming electrons. This phenomenon is discussed, and ...

In two previous publications, we have demonstrated that stationary rotation of magnetized plasma about a compact central object permits an enormous number of different MHD instabilities, with the well-known magneto-rotational instability as just one of them. We here concentrate on the new instabilities found that are driven by ...

Stability properties of two-stream instability of two hollow electron beams are investigated. The equilibrium configuration consists of two intense relativistic hollow electron beams propagating through a grounded conducting cylinder. Analysis of the longitudinal two-stream instability is carried out within the ...

Channel instability is manifested as lateral bank erosion, progressive degradation of the streambed, or natural scour and fill of the streambed. Lateral stability is related to stream type, and four major stream types having different stability characteri...

... this once-clay-bottomed stream now has an abrasive benthic layer of sand that moves continuously, even ... this once-clay-bottomed stream now has an abrasive benthic layer of sand that moves continuously,...

Ca-Al rich Inclusions (CAIs) commonly have a Al-26/Al-27 ratio of 5 x 10-5, but this ratio is smaller in chondrules; a few CAI chondrule time intervals in the range 2-6 m.y. exist, and there are many more cases in which numbers in this range are lower limits. Circumstellar gaseous disks about young stellar objects progressively disappear at ages of 3-10 m.y. The commonality of the Al-26/Al-27 ...

The mass assembly of galaxies leaves various imprints on their surroundings, such as shells, streams and tidal tails. The frequency and properties of these fine structures depend on the mechanism driving the mass assembly: e.g. a monolithic collapse, rapid cold-gas accretion followed by violent disk instabilities, minor mergers or ...

We describe local shearing box simulations of turbulence driven by the magnetorotational instability (MRI) in a collisionless plasma. Collisionless effects may be important in radiatively inefficient accretion flows, such as near the black hole in the Gal...

Mar 11, 2008 ... Discovery of Cyclotron Resonance Features in the Soft Gamma Repeater SGR .... Accretion-ejection instability and QPO in black-hole binaries. ...

to affect the flo~v. 111 the limit of snlal] values of the Nlach ..... tllc mass accretion rate. 'J'he solution of tllc polytropic clisc is illdcpcrlclent ...

This program has led to a series of papers being written and published in the Astrophysical Journal. Together these papers try to explain major parts of the LINER and low luminosity AGN puzzle. One paper ('Accretion Disk Instabilities, Cold Dark Matter Mo...

Mar 1, 2011 ... Considerable interest exists in the accretion rate for condensates in nonequilibrium flow with icing ... from crossed light beam correlations and electric probes. ... interpreted using a boundary layer model of contact surface flow ... instability is probably responsible for the observed phenomenon. ...

The nonaxisymmetric stability of self-gravitating, geometrically thick accretion disks has been studied for protostellar systems having a wide range of disk-to-central object mass ratios. Global eigenmodes with four distinctly different characters were id...

The collisional origin of the Moon is considered. The angular momentum of the Earth-Moon system is less than sufficient to spin the Earth to rotational instability. Nevertheless the mass of the body striking a tangential blow to the protoearth, imparting the angular momentum of the Earth-Moon system to the protoearth is examined.

The model involves a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay...

Aug 30, 1997 ... On the Relevance of the R-Mode Instability for Accreting Neutron Stars ..... BeppoSAX Observation of 4U 1907+09: Detection of a Cyclotron ...

We revisit, via a very simplified set of equations, a linear streaming instability (technically an overstability), which is present in, and potentially important for, dusty protoplanetary discs. The goal is a better understanding of the physical origin of such instabilities, which are notoriously subtle. Rotational dynamics seem to be ...

We revisit, via a very simplified set of equations, a linear streaming instability (technically an overstability), which is present in, and potentially important for, dusty protoplanetary discs. The goal is a better understanding of the physical origin of such instabilities, which are notoriously subtle. Rotational dynamics seem to be ...

In fast ignition inertial fusion intense relativistic electron beams, generated by the ignition laser, propagate into the dense plasma where the energy is deposited. The beam undergoes a number of instabilities. In particular the two stream and Weibel instabilities have been identified as important in the evolution and absorption of ...

The limit-cycle thermal instability model for accretion disks is used to study the soft X-ray transient A0620-00. Thermal instability in geometrically thin, Keplerian alpha-model disks is reviewed. The observational constraints on A0620-00 are presented and the parameters chosen for the model are discussed. It is found that, with the ...

The effects of radial advection and thermal diffusion were considered in investigating the linear stability of an optically thin, two-temperature accretion disk. If the disk has very little advection, we prove that the thermal instability exists when the disk is geometrically thin. However, it disappears in a geometrically slim disk if the thermal ...

New instabilities in multicomponent cold magnetized accretion disks are found using not the magnetohydrodynamics (MHD) framework but the equations of motion and continuity for each disk component and Maxwell's equations, where the magnetic field perturbations are substituted by the electric field perturbations. The stationary velocities of ...

A protoearth accretion stage configuration consisting of an undifferentiated solid core, an intermediate metal-melt layer, and an outer silicate-melt layer, is presently taken as the initial state in an investigation of Rayleigh-Taylor instability-induced core formation. The Ida et al. (to be published) quantitative results on the ...

Differential rotation occurs in conducting flows in accretion disks and planetary cores. In such systems, the magnetorotational instability can arise from coupling Lorentz and centrifugal forces to cause large radial angular momentum fluxes. We present the first experimental observation of the magnetorotational instability. Our system ...

This study is devoted to the experimental analysis of the stratorotational instability (SRI). This instability affects the classical cylindrical Couette flow when the fluid is stably stratified in the axial direction. In agreement with recent theoretical and numerical analyses, we describe for the first time in detail the destabilization of the stratified ...

The viscous model for accretion disks encounters difficulties both in providing a source of viscosity and in removing angular momentum from the disk outer edges where it is transported by the viscous stress. This paper investigates radiative tides as an alternative mechanism for accretion in disks in mass-transfer binary systems. We consider the process in ...

We have constructed vertically integrated, steady state convective models of accretion disks to explore the mechanism of instability in dwarf novae. The models and observations of dwarf novae suggest a picture in which transferred matter piles up in an optically thin torus. The torus eventually becomes optically thick and the resulting convective structure ...

Vertically integrated, steady state convective models of accretion disks have been constructed to explore the mechanism of instability in dwarf novae. The models and observations of dwarf novae suggest a picture in which transferred matter piles up in an optically thin torus. The torus eventually becomes optically thick, and the resulting convective ...

X-rays from young stellar objects can influence the physical properties of their surroundings. A particularly interesting example is the ionization of the accretion disk by hard X-rays at distances of the order of 1 AU or more. The authors show that X-rays induce a layered ionization structure in which the outer layer is sufficiently ionized to permit the Balbus-Hawley ...

A series of processes in the solar nebula transforms infallen interstellar grains into planets. Somewhat surprisingly, samples of planetary material from the very first stages of this processing and aggregration were preserved, and are accessible for study in the terrestrial laboratory. These are the chondritic meteoroids, which passed the last 4.5 Gyr safely stored in asteroids. Thermal ...

The abundances of the chemical elements observed at the surface of metal-poor stars are not always representative of their initial values. During stellar evolution, various physical processes modify their internal composition. In this short paper, in honor of George W. Preston, I remind the importance of atomic diffusion, and the possible effects of accretion processes which ...

Local hydromagnetic simulations of accretion-disc turbulence currently provide the most convincing evidence that the origin of turbulence in discs could be the Balbus-Hawley magnetorotational instability. The main results of such calculations are highlighted with particular emphasis on the generation of large-scale magnetic fields. Comparison with ...

: accretion, accretion disks -- instabilities -- X�rays: stars -- stars: novae, cataclysmic variables 1. Introduction VY Scl stars are a subclass of nova�like, cataclysmic variables which are bright most of the time for VY Scl (see Table 2). 4. Discussion 4.1. Comparison between VY Scl stars and dwarf novae Not much

A final report is given of two research projects dealing with magnetic fields of neutron stars. These are the modulation of thermal x-rays from cooling neutron stars and plasma instabilities in neutron star accretion columns. (DWL)

A final report is given of two research projects dealing with magnetic fields of neutron stars. These are the modulation of thermal x-rays from cooling neutron stars and plasma instabilities in neutron star accretion columns. (ERA citation 12:044375)

Although the magnetorotational instability (MRI) has been widely accepted as a powerful accretion mechanism in magnetized accretion disks, it has not been realized in the laboratory. The possibility of studying MRI in a rotating liquid-metal annulus (Couette flow) is explored by local and global stability analysis and ...

We study the gravitational instability (GI) of small solids in a gas disk as a mechanism to form planetesimals. Dissipation from gas drag introduces secular GI, which proceeds even when standard GI criteria for a critical density or Toomre's Q predict stability. We include the stabilizing effects of turbulent diffusion, which suppresses small-scale GI. The radially wide rings ...

We apply an eclipse mapping technique using `genetically modified fire-flies' to the eclipse light curves of HU Aqr and EP Dra. The technique makes as few assumptions as possible about the location of accretion stream material, allowing the emission to be located anywhere within the Roche lobe of the white dwarf. We model two consecutive eclipses in the ...

We apply an eclipse mapping technique using `genetically modified fireflies' to the eclipse light curves of HU Aqr and EP Dra. The technique makes as few assumptions as possible about the location of accretion stream material, allowing the emission to be located anywhere within the Roche lobe of the white dwarf. We model two consecutive eclipses in the ...

A two fluid stability analysis of an inhomogeneous solar wind plasma leads to a prediction of possible instabilities in both Alfven and magnetoacoustic waves driven by local velocity gradients. A detailed study, based on Pioneer 6 magnetic and plasma data relative to several high-speed streams in the solar wind, on the direction of propagation of the ...

We revisit the flip-flop instability of two-dimensional planar accretion using high-fidelity numerical simulations. By starting from an initially steady-state axisymmetric solution, we are able to follow the growth of this overstability from small amplitudes. In the small-amplitude limit, before any transient accretion disk is formed, ...

Primordial matter mainly consists of hydrogen and helium with a small amount of lithium. Taking into account contributions to the opacity from hydrogen and helium only has been assumed to be sufficient so far. Lithium, however, influences the opacity indirectly through a change in chemical equilibrium due to absorption of atomic lithium and lithium hydride. The differences reach two orders of ...

About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In particular, we investigate the ...

We discuss the dynamics of the accretion flow onto a black hole driven by Poynting flux in a simplified model of a two-dimensional accretion disk. In this simplified model, the condition of the stationary accretion flow is found to impose a nontrivial constraint on the magnetic field configuration. The effect of the magnetic field on ...

We study the effect of radiative feedback on accretion onto intermediate-mass black holes (IMBHs) using the hydrodynamical code ZEUS-MP with a radiative transfer algorithm. In this paper, the first of a series, we assume accretion from a uniformly dense gas with zero angular momentum and extremely low metallicity. Our one-dimensional (1D) and 2D ...

OAK-B135 We consider an accretion flow model originally proposed by Bisnovatyi-Kogan and Ruzmaikin (1974), which has been confirmed in recent 3D MHD simulations. In this model, the accreting gas drags in a strong poloidal magnetic field to the center such that the accumulated field disrupts the axisymmetric accretion flow at a ...

This paper studies the production of high-energy gamma radiation (E-gamma about 100 MeV) in the vicinity of a black hole through the collisions of accreting protons on the stable orbits. A spherical accretion with a small rate is considered as a fully computable example. If the accretion rate is about 0.001 of the critical rate, ...

Galactic nuclei should contain a cluster of stars and compact objects in the vicinity of the central supermassive black hole due to stellar evolution, minor mergers and gravitational dynamical friction. By analogy with protoplanetary migration, nuclear cluster objects (NCOs) can migrate in the accretion discs that power active galactic nuclei (AGN) by exchanging angular ...

This thesis describes in detail a two-dimensional, axisymmetric computer code for calculating fully relativistic ideal gas hydrodynamics around a Kerr black hole. The aim is to study fully dynamic inviscid fluid accretion onto black holes, as well as to study the evolution and development of nonlinear instabilities in pressure supported ...