Two analyses pertaining to shock waves in a radiating gas are presented. The first study investigates the influence of an isothermal accretion shock on a spherical accretion flow. An 'isothermal shock' is the combination of a regular shock and a postshock...

Sep 27, 2002 ... Accretion Disk Simulation ... Instead, the graphic shows spiral shock waves in a three dimensional simulation of an accretion disk -- material ...

Shock recovery experiments in the 25 to 45 GPa range on antigorite serpentine determine the amount of shock-induced loss of structural water as a function of shock pressure. Infrared absorption spectra of shock recovered samples demonstrate systematic changes in the amount of structural water and molecular, surface ...

A general mechanism is presented for generating pressure-driven winds that are intrinsically bipolar from objects undergoing disk accretion. The energy librated in a boundary layer shock as the disk matter impacts the central object is shown to be sufficient to eject a fraction ..beta..approx.10/sup -2/ to 10/sup -3/ of the accreted ...

A two dimensional numerical model forming two spiral shock fronts in accretion flow in close binary star system is presented. The position of these shocks is discussed. In the model, the position of the second shock front depends on the relation between t...

We are developing GenASiS (General Astrophysical Simulation System) to study the explosion mechanism of core-collapse supernovae. The current version of GenASiS is suitable for large scale simulations and includes a mature implementation of magnetohydrodynamics as well as a general Poisson solver. As a science application of the code, we explore the capacity of the stationary ...

We consider time-dependent accretion onto magnetized white dwarfs. A detailed description of a numerical method of solution to the hydrodynamical equations is given. The postshock flow is cooled by optically thin bremsstrahlung and is thermally unstable. As a result the shock height undergoes periodic oscillations. We consider the properties of this ...

Spherically accreting black holes may sustain strong collisionless shocks, downstream of which the fluid approximation is not valid. The proton-electron Coulomb exchange provides for the downstream matter diffusion into the hole. Energy conversion efficiencies upward of 10-30% are obtained, with most of the luminosity in hard x-rays and ..gamma..-rays. The ...

We formulate and solve the equations governing the transonic behaviour of a general relativistic black-hole accretion disc with non-zero advection velocity. We demonstrate that a relativistic Rankine Hugoniot shock may form leading to the formation of accretion powered outflow. We show that the critical points of transonic discs ...

We develop and discuss global accretion solutions for viscous advection-dominated accretion flow (ADAF) disks containing centrifugally supported isothermal shock waves. The fact that such shocks can exist at all in ADAF disks is a new result. Interestingly, we find that isothermal shocks can ...

A model of the X-ray radiation emitted from the accretion column of a compact object in AM Herculis binaries, using Monte Carlo methods is presented. The accretion column in the model has cylindrical symmetry. Above a shocked region in the column there is...

A previous report that 22 Vul is a zeta Aur--type eclipsing binary is supported by our discovery of evidence for an accretion shock cone in 22 Vul similar to those found in zeta Aurigae and 32 Cygni.

The nonlinear evolution of the Parker instability in accretion disks and galactic gas disks is studied by using a two-dimensional magnetohydrodynamic (MHD) code. The gas layer is assumed to be located at some distance from a point mass which is the origin of gravity. The magnetic fields are assumed to be parallel to the disk plane in magnetostatic equilibrium. The sound and ...

X-ray emitting MHD accretion shocks in classical T Tauri stars. Case for moderate to high plasma-? values

The known properties of water and ice over a wide range of pressures and temperatures are applied to

We present an analytical description of the energetics of the population of cosmic accretion shocks, for a concordance cosmology. We calculate how the shock-processed accretion power and mass current are distributed among different shock Mach numbers, and how they evolve with cosmic time. We ...

We present an analytical description of the energetics of the population of cosmic accretion shocks, for a concordance cosmology (?m+??=1). We calculate how the shock-processed accretion power and mass current are distributed among different shock Mach numbers and how they evolve with cosmic ...

We present a linear stability analysis of a planar radiative shock with cooling function ..lambda..proportionalT/sup ..cap alpha../. We investigate an oscillatory instability similar to that found in numerical calculations of accretion onto degenerate dwarfs by Langer, Chanmugam, and Shaviv. Our analysis shows that multiple modes of oscillations are ...

This paper discusses the solutions for stationary, axisymmetric, transonic, adiabatic flows with polytropic, rotating fluid configurations of small transverse thickness in an arbitrarily chosen potential. Special attention is paid to the formation of the standing shocks in the case of black hole accretion and winds. The possibility of three types of ...

A general numerical scheme is presented that allows a variety of analyses of an arbitrary set of hydrodynamic equations: a search for steady states; stability of steady states; nonlinear integration; search for specified nonlinear solutions; stability of nonlinear solutions. The scheme is an extension of the ''Henyey'' relaxation method and is especially useful ...

The polarized radiation from accretion shocks with a three-dimensional structure are calculated for the first time. It is shown that, because of inhomogeneities along the flow lines, accretion columns with a uniform accretion rate across the column can also produce flat optical/IR spectra as has been noted ...

In the absence of accretion torques, a pulsar in a binary system will spin down due to electromagnetic dipole radiation and the spin-down power will drive a wind of relativistic electron-positron pairs. Winds from pulsars with short periods will prevent any subsequent accretion but may be confined by the companion star atmosphere, wind or magnetosphere to ...

In the absence of accretion torques, a pulsar in a binary system will spin down due to electromagnetic dipole radiation, and the spin-down power will drive a wind of relativistic electron-position pairs. Winds from pulsars with short periods will prevent any subsequent accretion but may be confined by the companion star atmosphere, wind, or magnetosphere ...

We propose a new CFD method modified from the Direct Simulation Monte Carlo method (DSMC). The DSMC is modified to handle continuum flows by setting the mean free path of molecules to a fixed, constant value, which is on the order of a cell size ? x. By doing so, we quickly reach equilibrium. We call our scheme 'Molecular hydrodynamics' (MH). We test our MH scheme with three typical examples: the ...

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 ...

... Title : APPLICATION OF RESULTS FROM SHOCK TUBE EXPERIMENTS ON RADIATION IN AIR TO OBSERVED TRAJECTORIES AND ...

We present a model of accretion disk where the disk luminosity is entirely due to the reprocessing of hard radiation impinging on the disk. The hard radiation itself is emitted by a hot point source above the disk, that could be physically realized by a strong shock terminating an aborted jet. This hot source contains ultrarelativistic leptons scattering ...

Shock degassing was a major factor in releasing the gases present in planetesimals while the earth was in its accretion phase. The atmosphere was formed as the earth grew, and it was of the oxidizing type. As much as 30--45% may have been contributed on the earth by shock degassing, and no less than 25--40% on Venus, but ...

This paper presents global solutions of adiabatic accretion flows with isothermal shocks in Kerr black hole geometry. It is known that, in the previously studied cases, where the flow including the shock is either entirely adiabatic or entirely isothermal, there can be no more than one stable shock solution, and ...

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 ...

Mass accretion onto (proto-)stars at high accretion rates \\dot{M}_* > 10^{-4} M_{&sun;} yr^{-1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk accretion. We consider a ...

Solid recovery impact-induced volatile loss experiments on the Murchison C2M meteorite indicate that

Solid recovery impact-induced volatile loss experiments on the Murchison C2M meteorite indicate that

UCDs with bright radio emission show radio bursts. ? Electron Cyclotron Maser ... Diagnostic for accretion shock: high-density (~ 1012 cm-3) ...

of stalled accretion shock. - Convection in the gain region, low l ? (Herant, Benz & Colgate 1992) ... hydrostatic equilibrium. (Chandrasekhar 1961) ...

Jul 20, 2011 ... (bremsstrahlung, cyclotron, blackbody) from accretion mound in shock. ... Cyclotron Resonant Scattering Features CRSFs ("Cyclotron Lines") ...

L is the maximal distance, which the proton can cover during the cluster age. Cluster mass. Mass of gas shell between. accretion shock and virial radius: ...

Equations of radiative transfer in fixed matter are shown to verify, under hypothesis frequently verified in applications, accretiveness properties and maximum principle. A criterium of time step for the standard explicit scheme, then for an algorithm der...

All the major viable acceleration mechanisms suggested so far in order to explain the energy of the gamma-rays observed from Cygnus X-3 are critically reviewed. It is argued that Cyg X-3 must be an accretion-fed strong X-ray binary with negligible orbital eccentricity and cannot contain a young active pulsar. It is shown that, for reasonable assumptions, the ...

In the non viscous fluid dynamics, Smooth Particle Hydrodynamics (SPH), as a free Lagrangian, �shock capturing� method adopts either an artificial viscosity contribution or an appropriate Riemann solver technique. An explicit or an implicit dissipation, introduced in such techniques, is necessary to solve the Euler equations to solve flow discontinuities (the Riemann ...

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 astrophysical importance of the new class of theoretical models for accretion disks concentrating mainly on the applications to active galactic nuclei are discussed. The slim accretion disks model describes several important astrophysical processes wh...

Derivations are made for the mass and the mass-turnover time scale of an accretion disk as a function of the accretion rate, the observed disk radius, the non-viscous disk radius, and two parameters. These parameters depend on the effectiveness of viscosity and tidal angular momentum loss. Application is made to DQ Herculis.

The properties of cyclotron emission from accretion shocks in AM Herculis binaries are studied which

We study the standing dissipative and non-dissipative shocks and the isentropic compression waves systematically in the thin, rotating, adiabatic astrophysical flows, such as accretion or winds, near the black holes and the neutron stars. The flow is assu...

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 ...

Previous work on axisymmetric shock solutions in hybrid model flows is extended to the case when the shocks are nonaxisymmetric. The properties of the sonic surface as well as the shocks are characterized analytically. The shocks are assumed to be self-similar, and the flow everywhere is assumed to be in ...

We use 2D numerical simulations to study the linear response of the stalled accretion shock during the first few hundred milliseconds after core bounce in core-collapse supernovae. We use these simulations to measure the growth rate and frequency of the Spherical Accretion Shock Instability, or SASI. These ...

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 ...

... Accession Number : ADD455301. Title : MULTIFUNCTIONAL CERAMICS FOR THERMAL SHOCK APPLICATIONS. Corporate Author : ...

... Descriptors : *MILITARY PERSONNEL, *GENES, *WOUNDS AND INJURIES, *TRAUMATIC SHOCK, *HEMORRHAGIC SHOCK, *DEATH ...

Spiral shocks have been discovered in hot accretion disks in dwarf novae during outbursts, using Doppler maps of HeI and Balmer emission lines. Here, we present the eclipse light curves of these lines and we simulate the parameters that affect dilution of the spiral shock light by the ambient symmetric disk emission. Taking into ...

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 ...

Recent high spectral resolution X-ray observations of some CTTSs show the presence of high density plasma (ne=10^{11}-10^{13} cm^{-3}) at temperature T=2-3 MK. This plasma is likely heated up by an accretion shock on the star surface. We investigate this issue by an accurate modelling of the impact of an accretion stream onto the ...

Young T Tauri stars exhibit strong solar-type magnetic activity, with extremely high temperature coronae and energetic flares. In a few systems discovered with Chandra and XMM-Newton there is also evidence for X-ray emission produced by shocks associated with magnetically channeled accretion. A recent 489 ksec Chandra HETG/ACIS-S observation of the ...

We discuss results of 2D and 3D numerical simulations of gas accretion processes in binary stars of the T Tau type. Analysis of the obtained flow structure shows that in such systems following gas dynamic details are formed: inner gap, circumstellar disks, bow shocks before components, and gaseous ``bridge'' between the components. It is shown that the bow ...

Results of two-dimensional gas dynamic computations of gas flow in symbiotic stars are presented, with radiation cooling of gas in the forming accretion disk taken into consideration. As computations show, radiation cooling does not change qualitatively the picture of the flow in the vicinity of the accreting star. The structure of the ...

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 ...

High resolution X-ray spectroscopy of accreting young stars is providing new insights into the physical conditions of the shocked plasma. While young stars exhibit exceedingly active coronae (>10 MK) with highly energetic flares, the relatively low temperature ( 3 MK), high density (>1012 cm-3) accretion ...

A deep (489 ks) Chandra High Energy Transmission Grating spectrum of the classical T Tauri star TW Hydrae shows a new type of coronal structure that is produced by the accretion process. In the standard model for a stellar dipole, the magnetic field truncates the disk and channels the accreting material onto the star. The He-like diagnostic lines of Ne IX ...

... Accession Number : ADA342636. Title : The Applicability of Scaling Laws to Underwater Shock Tests. Corporate Author ...

... Title : Shock Induced Chemistry: Application and Development of Ultrafast Nonlinear Probes of the Energy Dynamics of Molecules in Solids. ...

A generic expectation for gas accreted by high-mass haloes is that it is shock-heated to the virial temperature of the halo. In low-mass haloes, or at high redshift, however, the gas cooling rate is sufficiently rapid that an accretion shock is unlikely to form close to the virial radius. Instead, the ...

Adaptive spatial domains are currently used in smooth particle hydrodynamics (SPH) with the aim of performing better spatial interpolations, mainly for expanding or shock gas dynamics. In this work, we propose an SPH interpolating kernel reformulation, also suitable for treating free edge (FE) boundaries in the computational domain. Application to both ...

Three-dimensional numerical simulations of gas dynamics are used to study the flow pattern in a close binary system after it has reached the steady-state accretion regime. The special attention is paid to physics of accretion disks in binary systems and, particularly, the waves in disks. It is shown that in systems with stationary ...

It is believed that protostellar accretion disks are formed from nearly ballistic infall of molecular matter in rotating core collapse. Collisions of this infalling matter leads to formation of strong supersonic shocks, which if they cool rapidly, result in accumulation of that material in a thin structure in the equatorial plane. Here, we investigate the ...

We explore self-similar hydrodynamic evolution of central voids embedded in an isothermal gas of spherical symmetry under the self-gravity. More specifically, we study voids expanding at constant radial speeds in an isothermal gas and construct all types of possible void solutions without or with shocks in surrounding envelopes. We examine properties of void boundaries and ...

In physically inviscid fluid dynamics, `shock-capturing' methods adopt either an artificial viscosity contribution or an appropriate Riemann-solver algorithm. These techniques are necessary to solve the strictly hyperbolic Euler equations if flow discontinuities (the Riemann problem) are to be solved. A necessary dissipation is normally used in such cases. An explicit ...

An approximation theory of the acceleration of particles in low-density shear flows is developed and is applied to a number of astrophysical flows including accretion disks, radial accretion, and convective turbulence. In the disk application, the theory suggests a mechanism by which the bulk of the accretion power ...

Solution for a stationary spherically symmetric accretion of the relativistic perfect fluid with an equation of state p(rho) onto the Schwarzschild black hole is presented. This solution is a generalization of Michel solution and applicable to the problem of dark energy accretion. It is shown that accretion of ...

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 ...

The rotation period of classical T Tauri stars (CTTS) represents a longstanding puzzle. While young low-mass stars show a wide range of rotation periods, many CTTS are slow rotators, spinning at a small fraction of breakup, and their rotation period does not seem to shorten, despite the fact that they are actively accreting and contracting. Matt & Pudritz proposed that the ...

We discuss the fueling of the central black hole in active galactic nuclei (AGN) in the framework of a clumpy accretion flow. Shocks between elements (clumps) forming the accretion flow are at the origin of the observed radiation. We expect a cascade of shocks, with optically thick shocks ...

Context. Radiative shocks play a dominant role in star formation. The accretion shocks on first and second Larson cores involve radiative processes and are thus characteristic of radiative shocks. Aims: In this study, we explore the formation of the first Larson core and characterize the radiative and dynamical ...

A deep (489 ks) Chandra High Energy Transmission Grating spectrum of the classical T Tauri star TW Hydrae shows a new type of coronal structure that is produced by the accretion process. In the standard model for a stellar dipole, the magnetic field truncates the disk and channels the accreting material onto the star. The He-like diagnostic lines of Ne IX ...

There are lines of evidence which relate bounds on the primordial water content of the Earth's mantle to a magma ocean and the accompanying Earth accretion process. We assume initially (before a magma ocean could form) that as the Earth accreted, it grew from volatile- (H2O, CO2, NH3, CH4, SO2, plus noble) gas-rich planetesimals, which ...

One of the standard methods for characterizing mechanical shock is by means of the shock spectrum. The principal application of the shock spectrum in aerospace technology is to permit component shock test specifications to be generated, independent of spe...

Mass accretion onto (proto-)stars at high accretion rates M-dot{sub *}> 10{sup -4} M{sub sun} yr{sup -1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk accretion. We ...

Even under idealized conditions of spherical infall, the shock wave generated in the canonical core-collapse model for Type II supernovae does not remain spherical. We examine the inherent asymmetry of the stalled shock wave in core-collapse supernovae using an idealized model of a standing accretion shock. We show ...

Various papers on shock waves are presented. The general topics addressed include: shock wave structure, propagation, and interaction; shock wave reflection, diffraction, refraction, and focusing; shock waves in condensed matter; shock waves in dusty gases and multiphase media; hypersonic flows ...

Five AM Herculis binary systems show an optical QPO that is known to be associated with magentically channeled polar cap accretion. Hard X-ray QPOs are predicted by the time-depndent hydrodynamic models. We propose to search selected AM Her systems for polar cap X-ray QPOs using the XTE PCA. Because of its large collecting area, the PCA is the only instrument that can do this ...

A model for the 0.3-1.2 Hz optical quasi-periodic oscillations (QPOs) observed in a number of AM Her-type binary systems has been developed. It is suggested that the observed optical modulation is the result of shock oscillations induced by nonsteady accretion flows. It is shown that time-dependent models of radiative shock waves in ...

Results of shock recovery experiments carried out on antigorite serpentine Mg3Si2O5(OH)4 are reported. The main objective of the present study is the determination of critical shock pressures for partial and complete dehydration of serpentine under shock loading. It is pointed out that serpentine and serpentine-like layer silicates are ...

Archival IUE observations of 31 Cygni at phases at which its sister Zeta Aurigae systems exhibit evidence of an accretion wake are discussed. The absence of absorption in Mg II can be explained by the phase at the specific times of observation. The detection of high-velocity absorption due to C IV but not N V implies a shock temperature lower than that of ...

As the dense molecular cloud that was the precursor of our Solar System was collapsing to form a protosun and the surrounding solar-nebula accretion disk, infalling interstellar grains were heated much more effectively by radiation from the forming protosun than by radiation from the disk's accretion shock. Accordingly, we have ...

As the dense molecular cloud that was the precursor of our Solar System was collapsing to form a protosun and the surrounding solar-nebula accretion disk, infalling interstellar grains were heated much more effectively by radiation from the forming protosun than by radiation from the disk's accretion shock. Accordingly, we have ...

resolve the internal structure of the shocked shell-ISM matter, which will leave its imprint on the GRB shell and shocked ISM regions. We found that the propagating 2D ultrarelativistic shell does not accrete medium, producing a relativistic shock-dominated evolu- tion. As the shell sweeps up the matter

We study the rate at which gas accretes on to galaxies and haloes and investigate whether the accreted gas was shocked to high temperatures before reaching a galaxy. For this purpose, we use a suite of large cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations project, which uses a modified version of the ...

A detailed survey is presented of shock tube experiments, theoretical developments, and applications

Papers are presented on the applications of shock-wave technology to the study of hydrodynamics, the

... lution of oblique shock waves ,-ccording to the method given in NASA TR R-63. I iv ... 16 APPLICATION TO OBLIQUE SHOCK WAVES 18 SUMMARY ...

Methods and equipment used for obtaining shock wave data, the compilation of shock wave data, and uses of these data are described. (LCL)

Previously derived formulation for the evaluation of thermal shock of ceramic materials is reviewed and evaluated in terms of materials properties and aerospace requirements. In the attempt to improve resistance to thermal shock, developmental approaches ...

The gravitational accretion of gas onto a compact star moving supersonically through a uniform ambient medium is dynamically unstable in the restricted case of two-dimensional planar geometry (a cylindrical star). Numerical simulations in 3D (e.g., the series of papers by Ruffert) show some hint of instability, but not the dramatic flip-flop seen in 2D planar simulations. We ...

Steady state, spherically symmetric solutions of the cosmic-ray transport equation describing the acceleration of energetic particles in galactic accretion flows onto neutron stars, black holes, white dwarfs, and protostars are studied. The results indicate that astrophysical accretion flows can be partitioned into distinct classes depending upon whether ...

... rebound Polythioethcr Elastomer Dynamic mechanical analysis Polyether Damping Shock Thermal analysis 20. ABSTRACT ...

... that detonation waves may be substituted for air shock waves when the incident loading is important and that applications are generally limited to ...

The theory of diffusive shock acceleration and its application in interplanetary space are reviewed.

Techniques for the quantitative determination of shock position in supersonic flows using direct and

... of Grout and Concrete as Shock Impedance Matching Materials for Geologic Formations. ... environment in the same manner as the in situ formation. ...

... Descriptors : *MATHEMATICAL MODELS, *DAMAGE, *SHOCK ... TENSION, DAMAGE TOLERANCE, FAILURE(MECHANICS), SHOCK ...

... Accession Number : AD0079595. Title : A MACH-ZEHNDER INTERFEROMETER FOR SHOCK TUBE APPLICATIONS. Corporate ...

We find a self-consistent solution for the outflow rate from an accretion disc around a black hole. The centrifugal pressure dominated shock in a transonic accretion flow can act as a Compton cloud by emitting radiation in the form of hard X-rays. It is also the base of an outflow where considerable matter is ejected. We modify the ...

We present a study of cooling in radiative shocks simulated with smoothed particle hydrodynamics and adaptive mesh refinement codes. We obtain a similarity solution for a shock-tube problem in the presence of radiative cooling, and test how well the solution is reproduced in GADGET and FLASH. Shock broadening governed by the details of ...

We present a study of cooling in radiative shocks simulated with smoothed particle hydrodynamics and adaptive mesh refinement codes. We obtain a similarity solution for a shock-tube problem in the presence of radiative cooling, and test how well the solution is reproduced in GADGET and FLASH. Shock broadening governed by the details of ...

We present all the solutions for stationary, axially symmetric, transonic, adiabatic flows with polytropic, rotating fluid configurations of small transverse thickness, in an arbitrarily chosen potential. Special attention is paid to the formation of the ...

The role of impact vaporization acting during the formation of the Jovian and Saturnian satellites is examined in an attempt to explain the observed density in terms of composition of these rock and ice objects. A hypothesis is examined which states that ...

A model for a class of quasars and active galactic nuclei is described in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. These protons ...

is in vertical hydrostatic equilibrium or free fall. Hence we conclude that the original Shakura is in vertical hydrostatic equilibrium near the horizon or in free fall. The fact that the original Shakura to provide ideal environments for the shock accel- eration of relativistic particles that can escape to power

We investigate the Green's function energy/space distribution of the relativistic particles accelerated in viscous, advection-dominated accretion disks containing standing, centrifugally-supported shock waves. The dynamical structure of the accreting gas is described using a new model for viscous, shocked disks ...

A model for a class of quasars and active galactic nuclei is proposed in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. It is suggested...

Impact-induced devolatilization of porous serpentine was investigated, using two independent experimental methods, the gas recovery and the solid recovery method, each yielding nearly identical results. For shock pressures near incipient devolatilization,...

When a simple model for the relationship between the density-temperature fluctuation correlation and mean values is used, we determine that the rate of change of turbulent intensity can influence directly the accretion rate of droplets. We find, experimen...

Results of an IUE study of the N V lines in detached binary systems, including evidence for a reverse P-Cygni profile in zeta Aur and 22 Vul are presented. Differences in observable parameters among the systems are examined, and it is suggested how the ph...

Fuel Supply. IR (VLT) image of central ~ pc. Chandra image of central ~ 3 pc. Genzel et al. Baganoff et al. Hot x-ray emitting gas produced via shocked ...

We review the various theories which have been proposed along the years to explain the origin of the stellar initial mass function. We pay particular attention to four models, namely the competitive accretion and the theories based respectively on stopped accretion, MHD shocks and turbulent dispersion. In each case, we derive the main ...

We formulate the general problem of perturbing a (non--self-gravitating) perfect fluid potential flow in an arbitrary background gravitational field. We then specialize to the case of perturbing stationary, spherical accretion onto a Schwarzschild black hole and derive the following stability results: (i) no unstable normal modes exist which extend outside the sound horizon of ...

In October 1980, during its low-luminosity state, spectrograms of the novalike star TT Ari were obtained with the 6-m telescope. Between phases 0.5 and 0.6 of the 3/sup h/12/sup m/ orbital period the radial velocities jump abruptly, perhaps because the line of sight crosses a conical shock generated by accretion in this binary system.

It is demonstrated that oblique whistlers may be effective in coupling and energizing plasma populations during accretion flow onto massive central objects such as black holes. These plasma collective modes could be excited by inverse ion-populations in p...

Sep 10, 2008 ... Intro/Motivation. Ray-Tracing. Disk/Corona Model. Results. Applications. X-Ray Polarization from Accreting Black Holes. Jeremy Schnittman ...

The investigations of advection-dominated accretion flows (ADAFs), with emphasis on applications to X-ray binaries containing black holes and neutron stars is presented. This work is now being recognized as the standard paradigm for understanding the vari...

This article reviews the physics of advection-dominated accretion flows (ADAFs) and describes applications to several black hole X-ray binaries and galactic nulcei. The possibility of using ADAFs to explore the event horizons of black holes is highlighted.

Recent observations show that the measured rates of star formation in the early universe are insufficient to produce re-ionization, and therefore, another source of ionizing photons is required. In this Letter, we examine the possibility that these can be supplied by the fast accretion shocks formed around the cores of the most massive haloes (10.5

Recent observations show that the measured rates of star formation in the early universe are insufficient to produce re-ionization, and therefore, another source of ionizing photons is required. In this Letter, we examine the possibility that these can be supplied by the fast accretion shocks formed around the cores of the most massive haloes (10.5

The intergalactic gas in groups and clusters of galaxies bears the indelible stamp of galaxy formation. We present a comparison between observations and simple theoretical models indicating that radiative cooling governs the entropy scale that sets the core radius of the intracluster medium. Entropy measured at the radius 0.1r200 scales as T2/3, in accord with cooling threshold models for the ...

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 accretion disks. In ...

Shocks in advective flows around black holes have become es- sential ingredients in explaining wide variety of observed features. We first analytically study the properties of shocks in the special case when viscosity and other dissipative processes are negligible. We compare our analytical re- sults with those obtained numerically. The agreement is ...

We study the nonlinear evolution of the Rossby wave instability in thin disks using global two-dimensional hydrodynamic simulations. The detailed linear theory of this nonaxisymmetric instability was developed earlier by Lovelace et al. and Li et al., who found that the instability can be excited when there is an extremum in the radial profile of an entropy-modified version of potential vorticity. ...

... 62 Bedford, Massachusetts ON THE APPLICATION OF THE THEORY OF LOCKING MEDIA TO GROUND SHOCK PHENOMENA I by ...

... Accession Number : AD0408649. Title : ON THE APPLICATION OF THE THEORY OF LOCKING MEDIA TO GROUND SHOCK PHENOMENA. ...

... Title : APPLICATION OF THERMAL ANALYSIS TO THE SEMICONDUCTOR PLASTIC PACKAGE THERMAL SHOCK TESTING RELIABILITY. ...

... Accession Number : AD0608030. Title : APPLICATION OF THE MECHANICAL IMPEDANCE CONCEPT TO SHOCK AND VIBRATION TESTING. ...

This article summarizes the processes of high-energy emission in young stellar objects. Stars of spectral type A and B are called Herbig Ae/Be (HAeBe) stars in this stage, all later spectral types are termed classical T Tauri stars (CTTS). Both types are studied by high-resolution X-ray and UV spectroscopy and modeling. Three mechanisms contribute to the high-energy emission from CTTS: 1) CTTS ...

Context. The soft X-ray emission from high density plasma observed in several CTTS is usually associated with the accretion process. However, it is still unclear whether this high density "cool" plasma is heated in the accretion shock, or if it is coronal plasma fed or modified by the accretion process. Aims: We ...

We present X-ray spectral analysis of the accreting young star TW Hydrae from a 489 ks observation using the Chandra High Energy Transmission Grating. The spectrum provides a rich set of diagnostics for electron temperature Te , electron density Ne , hydrogen column density NH , relative elemental abundances, and velocities, and reveals its source in three distinct regions of ...

We present X-ray spectral analysis of the accreting young star TW Hydrae from a 489 ks observation using the Chandra High Energy Transmission Grating. The spectrum provides a rich set of diagnostics for electron temperature T{sub e} , electron density N{sub e} , hydrogen column density N{sub H} , relative elemental abundances, and velocities, and reveals its source in three ...

The relativistic accretion rate of dark matter by a black hole is revisited. Under the assumption that the phase space density indicator, Q={rho}{sub {infinity}}/{sigma}{sub {infinity}}{sup 3}, remains constant during the inflow, the derived accretion rate can be higher up to 5 orders of magnitude than the classical accretion formula, ...

We use time-dependent, two-dimensional hydrodynamic simulations including a passive magnetic field to quantify the amplification of progenitor magnetic fields by the strong shear created by the non-axisymmetric mode of the spherical accretion shock instability. During the linear growth phase of the instability, the total magnetic field energy scales with ...

Context: High spectral resolution X-ray observations of classical T Tauri stars (CTTSs) demonstrate the presence of plasma at temperature T� 2-3� 106 K and density n_e� 1011-1013 cm-3, which are unobserved in non-accreting stars. Stationary models suggest that this emission is due to shock-heated accreting material, but do not ...

The equations describing the transport of suprathermal charged particles, electromagnetic radiation and neutrinos across accretion flows onto compact objects are solved analytically, the effects of shocks in the flow being included. These solutions are used in discussing three illustrative astrophysical examples: acceleration of cosmic rays, generation of ...

The authors suggest that a rotating massive black hole (105Msun) located at an inactive galaxy may convert its host into a transient active phase by capturing and disrupting a star. During this period, a transient accretion disk is formed and a strong transient magnetic field can be produced in the inner boundary of the accretion disk. A large amount of ...

We examine the stability of a standing shock wave within a spherical accretion flow onto a gravitating star, in the context of core-collapse supernova explosions. Our focus is on the effect of nuclear dissociation below the shock on the linear growth, and nonlinear saturation, of nonradial oscillations of the ...

We examine the stability of a standing shock wave within a spherical accretion flow onto a gravitating star, in the context of core-collapse supernova explosions. Our focus is on the effect of nuclear dissociation below the shock on the linear growth, and nonlinear saturation, of nonradial oscillations of the ...

The explosion of a supernova forms because of the collapse to a neutron star. In addition an explosion requires that a region of relatively high entropy be in contact with the neutron star and persisting for a relatively protracted period of time. The high entropy region ensures that the maximum temperature in contact with the neutron star and in hydrostatic equilibrium is less than some maximum. ...

The method of determining shock and detonation wave pressures is described. The experimental set-up and the experiments carried out are reviewed. The method appears to be applicable for the measurement of shock and detonation wave pressures greater than a...

Some formulas useful in the analysis and application of ground shock information with a view either to estimating the safety of an existing structure against ground shocks or to designing economically a supponting structure which ' will protect the main structure against ground shocks are reported. ...

The shock-loading of natural materials by an impact, such as a comet or meteorite, can result in the formation of modified and altered phases in the target rock. In order to characterize the resulting material and to evaluate the extent of shock modificat...

We propose to obtain a Chandra/HETGS spectrum of IM Lup with an exposure of 150 ks. IM Lup is the only known X-ray bright transition object between the classical T Tauri star phase and the weak-lined T Tauri phase. IM Lup shows an IR excess, but its Halpha equivalent width is small, indicating very low accretion rates. The Chandra spectrum will provide important information on ...

Classical T Tauri stars are pre-main-sequence objects that undergo simultaneous accretion, wind outflow, and coronal X-ray emission. The impact of plasma on the stellar surface from magnetospheric accretion streams is likely to be a dominant source of energy and momentum in the upper atmospheres of these stars. This paper presents a set of models for the ...

The displacement method for estimating shock position in a shock-capturing compressible hydrodynamics code is introduced. Common estimates use simulation data within the captured shock, but the displacement method uses data behind the shock, making the estimate consistent with and as reliable as estimates of ...

Jetting can occur during oblique impacts of water ice bodies at relative velocities at low as {approximately}500 m s{sup {minus}1}, because of the low Hugoniot elastic limit and high compressibility of ice compared to rock. In jetted ice, incipient melting, complete melting, and incipient vaporization occur, upon release to low pressure, at impact velocities of 1.3, 2.0, and 2.7 km s{sup ...

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 ...

The mixing necessary to explain the Fe'' line widths and possibly the observed red shifts of 1987A is explained in terms of large scale, entropy conserving, up and down flows (calculated with a smooth particle 2-D code) taking place between the neutron star and the explosion shock wave due to the gravity and neutrino deposition. Depending upon conditions of ...

The mixing necessary to explain the ``Fe`` line widths and possibly the observed red shifts of 1987A is explained in terms of large scale, entropy conserving, up and down flows (calculated with a smooth particle 2-D code) taking place between the neutron star and the explosion shock wave due to the gravity and neutrino deposition. Depending upon conditions of entropy and mass ...

... for Research Development Test and Evaluation (RDT&E) data. ... Title : Application of the Explosive Test to Evaluate Shock Properties of High Yield ...

A method is proposed for restoring the structure of the accretion disk in a binary system from analysis of eclipse curves. Application of the method to the x-ray binary HZ Herculis yields the distribution of brightness and color temperatures over the optical accretion disk associated with the neutron star. The luminosity, mean ...

The direct simulation Monte Carlo (DSMC) method, originally developed to treat rarefied gas dynamical problems, is modified to calculate continum gas flows. We do this by fixing the mean free path of simulated molecules in such a way that the continum properties of the fluid are maintained everywhere. We extend the scheme to take into account internal degrees of freedom, allowing us to treat ...

Recovered samples from shock recovery experiments on single crystal calcite were subjected to thermogravimetric analysis to determine the amount of post-shock CO2, the decarbonization interval and the activation energy, for the removal of remaining CO2 in shock-loaded calcite. Comparison of post-shock CO2 with that ...

Recovered samples from shock recovery experiments on single crystal calcite were subjected to thermogravimetric analysis to determine the amount of post-shock CO2, the decarbonization interval and the activation energy, for the removal of remaining CO2 in shock-loaded calcite. Comparison of post-shock CO2 with that ...

of the shock in an accretion column; Sacco et al. (2008a) improved those results by per- forming 1-D time variability. Assuming optically thin emission, Sacco et al. (2008a) showed that, even for low with that predicted on the basis of the HD shock model of (Sacco et al. 2008a). 2. Targets We selected the two CTTS MP

Matter accreting onto black holes suffers a standing or oscillating shock wave in much of the parameter space. The post-shock region is hot, puffed up and reprocesses soft photons from a Keplerian disc to produce the characteristic hard tail of the spectrum of accretion discs. The post-shock ...

Standing accretion shocks (SAS) arise when the expansion of a shock front stalls and can no longer sustain its development. The aim of our study is to identify feasible conditions and parameters for an experimental system that is able to capture the essential physics processes required for SAS development. Analytic methods and ...

We perform axisymmetric simulations of the magnetorotational collapse of very massive stars in full general relativity. Our simulations are applicable to the collapse of supermassive stars with masses M > or approx. 10{sup 3}M{sub {center_dot}} and to very massive Population III stars. We model our initial configurations by n=3 polytropes, uniformly rotating near the ...

We discuss a special case of formation of axisymmetric shocks in the accretion flow of ideal gas on to a Schwarzschild black hole: when the total energy of the flow is negative. The result of our analysis enlarges the parameter space for which these steady shocks are exhibited in the accretion of gas rotating ...

We study the accretion processes on a black hole by a numerical simulation. We use a grid-based finite difference code for this purpose. We scan the parameter space spanned by the specific energy and the angular momentum and compare the time-dependent solutions with those obtained from theoretical considerations. We found several important results. (a) The time-dependent flow ...

A theory of shocks dominated by radiation energy flux in optically mixed thin-upstream thick-downstream systems, in which the temperature immediately ahead and some short distance behind the shock front are equilibrated by radiation transport, is presented. This theory is applied to determine properties of the normal and oblique radiative ...

We present a general procedure to solve the General Relativistic Hydrodynamical (GRH) equations with Adaptive-Mesh Refinement (AMR) and model of an accretion disk around a black hole. To do this, the GRH equations are written in a conservative form to exploit their hyperbolic character. The numerical solutions of the general relativistic hydrodynamic equations is done by High ...

The paper sets forth the important aspects of the application of the electrodynamic shaker for carrying out shock pulse testing, giving attention to the shock pulse time-history and the shock spectrum. Basic pulse theory is reviewed, and a technique of pulse equalization using digital control is described. The ...

Classical T Tauri stars undergo magnetospheric accretion, power outflows, and possess the physical and chemical conditions in their disks to give rise to planet formation. Existing high resolution FUV spectra verify that this spectral region offers unique diagnostics of these processes, which have the potential to significantly advance our understanding of the interaction of a ...

Experimental rates of dehydration of shocked and unshocked serpentine were determined using a differential scanning calorimetric technique. Dehydration rates in shocked serpentine are enhanced by orders of magnitude over corresponding rates in unshocked material, even though the impact experiments were carried out under conditions that inhibited direct ...

Mar 1, 2011 ... Sagittae are discussed with reference to the similarity between WZ Sge and dwarf novae and the applicability of accretion disk models. ...

May 13, 1999 ... Astro-tomography also has applications over timescales longer or ... optical and IR reprocessing off the accretion disc and companion star. ...

We reported the results of the time-dependent simulations of large amplitude oscillations of advective, viscous, sub-Keplerian disks with a proper trement of angular momentum transfer in one-dimensional, quasi-spherical transonic accretion flow around a non-rotating black hole using the Lagrangian Total Variation Diminising (TVD) and a remap routine.Our code has a ...

We investigate the effects of neutrino heating and alpha-particle recombination on the hydrodynamics of core-collapse supernovae. Our focus is on the nonlinear dynamics of the shock wave that forms in the collapse and the assembly of positive energy material below it. To this end, we perform time-dependent hydrodynamic simulations with FLASH2.5 in spherical and axial symmetry. ...

A stalled spherical accretion shock, such as that arising in core-collapse supernovae, is unstable to non-spherical perturbations. In three dimensions, this Standing Accretion Shock Instability can develop spiral modes that spin-up the protoneutron star. Here, we study these non-axisymmetric modes by combining ...

Young stellar objects exhibit X-ray emission throughout their evolution. The emission above about 1 keV is primarily produced from coronal structures and flares, indicating that magnetic activity is present from early on. For stars that are still actively accreting, X-ray accretion signatures of accretion are only distinguishable at ...

We present a model for high-energy emission sources generated by a standing magnetohydrodynamical (MHD) shock in a black hole magnetosphere. The black hole magnetosphere would be constructed around a black hole with an accretion disk, where a global magnetic field could be originated by currents in the accretion disk and its corona. ...

RS Ophiuchi is a recurrent nova system that experiences outbursts every ~20 years, implying accretion at a high rate onto a massive white dwarf. However, previous X-ray observations of the system in quiescence have detected only faint emission that is difficult to reconcile with the high accretion rate (>2 � 10�8 M sun yr�1) predicted by nova ...

... increased strength of portland cement concrete in routine production, shock reduction applications of lightweight vermiculite concrete, reduction of ...

... TIME PROFILES IN SHOCK WAVES AND THE APPLICATION OF THIS METHOD TO THE OXIDATION OF CARBON MONOXIDE. ...

... The piezoelectric polymer is formed into a ... Patent applications, *Hydrophones, *Shock resistance ... Piezoelectric materials, *Polymers, Polyvinylidenes ...