共查询到20条相似文献，搜索用时 15 毫秒
1.
C. C. Kuranz R. P. Drake T. L. Donajowski K. K. Dannenberg M. Grosskopf D. J. Kremer C. Krauland D. C. Marion H. F. Robey B. A. Remington J. F. Hansen B. E. Blue J. Knauer T. Plewa N. Hearn 《Astrophysics and Space Science》2007,307(1-3):115-119
We present data from recent high-energy-density laboratory experiments designed to explore the Rayleigh–Taylor instability
under conditions relevant to supernovae. The Omega laser is used to create a blast wave structure that is similar to that
of the explosion phase of a core-collapse supernova. An unstable interface is shocked and then decelerated by the planar blast
wave, producing Rayleigh–Taylor growth. Recent experiments were performed using dual, side-on, x-ray radiography to observe
a 3D “egg crate” mode and an imposed, longer-wavelength, sinusoidal mode as a seed perturbation. This paper explores the method
of data analysis and accurately estimating the position of important features in the data. 相似文献
2.
In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh–Taylor (RT), Richtmyer–Meshkov (RM),
and Kelvin–Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale
velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly shocked interface whose
evolution is a scaled version of the unstable hydrogen–helium interface in core-collapse supernovae such as SN 1987A. The
ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting
transition to turbulence on supernovae observables that remain as yet unexplained.
This paper represents a summary of recent results from a computational study of unstable systems driven by high Mach number
shock and blast waves. For planar multimode systems, compressibility effects preclude the emergence of a regime of self-similar
instability growth independent of the initial conditions (ICs) by allowing for memory of the initial conditions to be retained
in the mix-width at all times. With higher-dimensional blast waves, divergence restores the properties necessary for establishment
of the self-similar state, but achieving it requires very high initial characteristic mode number and high Mach number for
the incident blast wave. Initial conditions predicted by some recent stellar calculations are incompatible with self-similarity. 相似文献
3.
4.
We have investigated the nonlinear interaction between a 3D kinetic Alfvén wave (KAW) and an ion acoustic wave (IAW) in solar wind plasmas. A set of dimensionless equations was developed that describes the pump KAW perturbed by a low-frequency ion acoustic wave. The dependence of the growth rate of the modulational instability on the perturbation wave number was studied. We simulated numerically the dynamical equation of KAW with a pseudo-spectral method, taking ponderomotive nonlinearity into account. The 3D KAW itself propagates in the form of a vortex beam in a magnetised plasma, which manifests the presence of orbital angular momentum of the wave eigenmodes. We discuss the evolution of these vortex structures. Our results reveal that the Kolmogorov scaling is followed by a steeper scaling of power spectra, which is consistent with the solar wind observations by the Cluster spacecraft. We discuss the relevance of our investigation for solar wind plasmas. 相似文献
5.
Using the 2D numerical simulation we have studied the nonlinear evolution of kinetic Alfvén wave (KAW) in intermediate β plasmas (β?m e /m i ?1). The coupled equations of kinetic Alfvén wave (KAW) and ion acoustic wave (IAW) have been studied with different initial conditions using (1) periodic perturbation, (2) Gaussian perturbation and (3) random perturbation. We have studied the effect of initial conditions on the filament formation and on the turbulent scaling laws. The scale size of the localized structures is also obtained under different conditions. 相似文献
6.
The blast wave produced by an explosion of wire under the influence of a magnetic field has been studied in this paper. Conductivity of the gas is assumed to be infinite. Numerical integration has been performed using the Runge-Kutta method and the distribution of flow variables behind the shock wave is shown graphically. 相似文献
7.
A. D. Edens T. Ditmire J. F. Hansen M. J. Edwards R. G. Adams P. Rambo L. Ruggles I. C. Smith J. L. Porter 《Astrophysics and Space Science》2005,298(1-2):39-47
We have performed two sets of experiments looking at laser-driven radiating blast waves. In the first set of experiments the
effect of a drive laser’s passage through a background gas on the hydrodynamical evolution of blast waves was examined. The
laser’s passage heated a channel in the gas, creating a region where a portion of the blast wave front had an increased velocity,
leading to the formation of a bump-like protrusion on the blast wave. The second set of experiments involved the use of regularly
spaced wire arrays used to induce perturbations on a blast wave surface. The decay of these perturbations as a function of
time was measured for various wave number perturbations and found to be in good agreement with theoretical predictions. 相似文献
8.
The transfer of wave energy to plasma energy is a very crucial issue in coronal holes and helmet streamer regions. Mixed mode
Alfvén waves, also known as kinetic Alfvén wave (KAW) can play an important role in the energization of the plasma particles
because of their potential ability to heat and accelerate the plasma particles via Landau damping. This paper presents an
investigation of the growth of a Gaussian perturbation on a non-uniform kinetic Alfvén wave having Gaussian wave front. The
effect of the nonlinear coupling between the main KAW and the perturbation has been studied. The dynamical equations for the
field of the main KAW and the perturbation have been established and their semi-analytical solution has been obtained in the
low (β≪ me/mi≪ 1) and the high (β≫ me/mi≪ 1) β cases. The critical field of the main KAW and the perturbation has been evaluated. Nonlinear evolution of the main
KAW and the perturbation into the filamentary structures and its dependence on various parameters of the solar wind and the
solar corona have been investigated in detail. These filamentary structures can act as a source for the particle acceleration
by wave particle interaction because the KAWs are mixed modes and Landau damping is possible. Especially, in the solar corona,
the low β and the high β cases could correspond to the coronal holes and the helmet streamer. The presence of the primary
and the secondary filaments of the perturbation may change the spectrum of the Alfvénic turbulence in the solar wind. 相似文献
9.
In this paper we examine the wave properties of a hot plasma living in a Schwarzschild magnetosphere. The 3+1 GRMHD perturbation
equations are formulated for this scenario. These equations are Fourier analyzed and then solved numerically to obtain the
dispersion relations for a non-rotating, rotating non-magnetized and rotating magnetized plasma. The wave vector is evaluated,
which is used to calculate the refractive index. These quantities are shown in graphs which are helpful to discuss the dispersive
properties of the medium near the event horizon. 相似文献
10.
E. V. Polyachenko 《Astronomy Letters》2013,39(2):72-82
Several mechanisms of bar mode formation in stellar galactic disks, including the Toomre swing amplification mechanism and modal approaches, are considered. Using the well-known Kuzmin-Toomre stellar disk model as an example, it has been shown through numerical simulations that the stellar bar results from the development of an unstable normal mode. The pattern speed and the spiral wave growth rate found from a numerical experiment agree well with the linear perturbation theory. The nonlinear evolution of the bar is traced. The possible role of growing transient spirals in the formation of bars is discussed. 相似文献
11.
The propagation of magnetoacoustic waves in the neighbourhood of a 2D null point is investigated for both β=0 and β ≠ 0 plasmas. Previous work has shown that the Alfvén speed, here v A ∝r, plays a vital role in such systems and so a natural choice is to switch to polar coordinates. For β=0 plasma, we derive an analytical solution for the behaviour of the fast magnetoacoustic wave in terms of the Klein–Gordon equation. We also solve the system with a semi-analytical WKB approximation which shows that the β=0 wave focuses on the null and contracts around it but, due to exponential decay, never reaches the null in a finite time. For the β ≠ 0 plasma, we solve the system numerically and find the behaviour to be similar to that of the β=0 system at large radii, but completely different close to the null. We show that for an initially cylindrically-symmetric fast magnetoacoustic wave perturbation, there is a decrease in wave speed along the separatrices and so the perturbation starts to take on a quasi-diamond shape; with the corners located along the separatrices. This is due to the growth in pressure gradients that reach a maximum along the separatrices, which in turn reduces the acceleration of the fast wave along the separatrices leading to a deformation of the wave morphology. 相似文献
12.
During a campaign of optical observations at high latitude, a bi-dimensional study of the wave structure of the OH layer has been performed in December 1981 from Sodankyla (Finland). This site is one of the three stations of the EISCAT ionosphere sounding system. It has been found that a wave field covering an area of 1 million km2 may extend to latitudes as high as 70°N. The OH wave structure shows many similarities with noctilucent clouds. The fairly large horizontal wavelength, of the order of 40 km cannot easily be explained by a wave motion at an interface. The observed wave structure seems to be a result of the propagation of an internal gravity wave in the 80–100 km region. This wave structure was often recorded during the same time as an active aurora was present. As a result, it appears that the perturbation might be correlated with particle precipitations at auroral latitudes. 相似文献
13.
James Etherington Witold Maciejewski 《Monthly notices of the Royal Astronomical Society》2006,367(3):1003-1010
If supermassive black holes in centres of galaxies form by merging of black hole remnants of massive Population III stars, then there should be a few black holes of mass one or two orders of magnitude smaller than that of the central ones, orbiting around the centre of a typical galaxy. These black holes constitute a weak perturbation in the gravitational potential, which can generate wave phenomena in gas within a disc close to the centre of the galaxy. Here, we show that a single orbiting black hole generates a three-arm spiral pattern in the central gaseous disc. The density excess in the spiral arms in the disc reaches values of 3–12 per cent when the orbiting black hole is about 10 times less massive than the central black hole. Therefore, the observed density pattern in gas can be used as a signature in detecting the most massive orbiting black holes. 相似文献
14.
T. P. Downes † P. Duffy S. S. Komissarov 《Monthly notices of the Royal Astronomical Society》2002,332(1):144-154
Relativistic shocks can accelerate particles by the first-order Fermi mechanism; the particles then emit synchrotron emission in the post-shock gas. This process is of particular interest in the models used for the afterglow of gamma-ray bursts. In this paper we use recent results in the theory of particle acceleration at highly relativistic shocks to model the synchrotron emission in an evolving, inhomogeneous and highly relativistic flow. We have developed a numerical code that integrates the relativistic Euler equations for fluid dynamics with a general equation of state, together with a simple transport equation for the accelerated particles. We present tests of this code and, in addition, we use it to study the gamma-ray burst afterglow predicted by the fireball model, along with the hydrodynamics of a spherically-symmetric relativistic blast wave.
We find that, while broadly speaking the behaviour of the emission is similar to that already predicted with semi-analytic approaches, the detailed behaviour is somewhat different. The 'breaks' in the synchrotron spectrum behave differently with time, and the spectrum above the final break is harder than had previously been expected. These effects are due to the incorporation of the geometry of the (spherical) blast wave, along with relativistic beaming and adiabatic cooling of the energetic particles leading to a mix, in the observed spectrum, between recently injected 'uncooled' particles and the older 'cooled' population in different parts of the evolving, inhomogeneous flow. 相似文献
We find that, while broadly speaking the behaviour of the emission is similar to that already predicted with semi-analytic approaches, the detailed behaviour is somewhat different. The 'breaks' in the synchrotron spectrum behave differently with time, and the spectrum above the final break is harder than had previously been expected. These effects are due to the incorporation of the geometry of the (spherical) blast wave, along with relativistic beaming and adiabatic cooling of the energetic particles leading to a mix, in the observed spectrum, between recently injected 'uncooled' particles and the older 'cooled' population in different parts of the evolving, inhomogeneous flow. 相似文献
15.
本文在细环近似和共转半么位移不为零的条件下，考虑吸积环中非轴对称动力学不稳定性的线性扰动过程，采用数值计算方法求得不稳定性的线性增长率和共转半径位移随波数的变化关系，发现线性增长率受共转半径不为零的影响较小，而共转半径位移项随波数的色散关系与线性Ｋｄｖ方程的色散关系相同，说明窄吸收环在动力学不稳定性数值模拟中出现的“行星状解”很可能是类似于Ｋｄｖ方程中的孤子解。 相似文献
16.
An interstellar cloud suddenly overrun by a supernova blast wave experiences a very rapid increase in boundary pressure. A shock wave propagates into the cloud. As a preliminary investigation, the propagation of spherical shock waves in an adiabatic medium is studied numerically. 相似文献
17.
X. Ribeyre L. Hallo V. T. Tikhonchuk S. Bouquet J. Sanz 《Astrophysics and Space Science》2007,307(1-3):169-172
The Rayleigh-Taylor instability (RTI) plays an important role in the dynamics of several astronomical objects, in particular,
in the supernovae (SN) evolution. In the present paper we examine the dynamics of a shell (representing a type II SN remnant)
blown-up by a wind emitted by a central pulsar. The shell is accelerated by the pulsar wind and its inner surface experiences
the RTI. We develop an analytical approach by using a specific transformation into the coordinate frame co-moving with the
SN ejecta. We first derive a non-stationary spherically symmetric solution describing an expansion of a gas shell under the
pressure of a central source (pulsar). Then, we analyze its 3D stability with respect to a small perturbation on the inner
shell surface. The dispersion relation is derived in the co-moving reference frame. The growth rate of the perturbation is
found and its temporal evolution is discussed. We compare our result with the previous published studies and apply it to the
Crab nebula evolution. 相似文献
18.
The nonlinear properties of solitary waves structure in a hot magnetized dusty plasma consisting of a negatively charged,
extremely massive hot dust fluid, positively charged hot ion fluid and vortex-like distributed electrons, are reported. A
modified Korteweg de Vries equation (mKdV) which admits a solitary wave solution for small but finite amplitude is derived
using a reductive perturbation theory. The modifications in the amplitude and width of the solitary wave structures due to
the inclusion of an external magnetic field and dust and ions temperature are investigated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
This is an examination of the gravitational instability of the major large-scale perturbation modes for a fixed value of the
azimuthal wave number m = 1 in nonlinearly nonstationary disk models with isotropic and anisotropic velocity diagrams for
the purpose of explaining the displacement of the nucleus away from the geometric center (lopsidedness) in spiral galaxies.
Nonstationary analogs of the dispersion relations for these perturbation modes are obtained. Critical diagrams of the initial
virial ratio are constructed from the rotation parameters for the models in each case. A comparative analysis is made of the
instability growth rates for the major horizontal perturbation modes in terms of two models, and it is found that, on the
average, the instability growth rate for the m = 1 mode with a radial wave number N = 3 almost always has a clear advantage
relative to the other modes. An analysis of these results shows that if the initial total kinetic energy in an isotropic model
is no more than 12.4% of the initial potential energy, then, regardless of the value of the rotation parameter Ω, an instability
of the radial motions always occurs and causes the nucleus to shift away from the geometrical center. This instability is
aperiodic when Ω = 0 and is oscillatory when Ω ≠ 0 . For the anisotropic model, this kind of structure involving the nucleus
develops when the initial total kinetic energy in the model is no more than 30.6% of the initial potential energy. 相似文献
20.
Orhan Dönmez 《Astrophysics and Space Science》2006,305(2):187-196
In this paper, perturbations of an accretion disk by a star orbiting around a black hole are studied. We report on a numerical experiment, which has been carried out by using a parallel-machine code originally developed by Dönmez (2004). An initially steady state accretion disk near a non-rotating (Schwarzschild) black hole interacts with a “star”, modeled as an initially circular region of increased density. Part of the disk is affected by the interaction. In some cases, a gap develops and shock wave propagates through the disk. We follow the evolution for order of one dynamical period and we show how the non-axisymetric density perturbation further evolves and moves downwards where the material of the disk and the star become eventually accreted onto the central body. When the star perturbs the steady state accretion disk, the disk around the black hole is destroyed by the effect of perturbation. The perturbed accretion disk creates a shock wave during the evolution and it loses angular momentum when the gas hits on the shock waves. Colliding gas with the shock wave is the one of the basic mechanism of emitting the X-rays in the accretion disk. The series of supernovae occurring in the inner disk could entirely destroy the disk in that region which leaves a more massive black hole behind, at the center of galaxies. 相似文献