共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
A. C. Calder 《Astrophysics and Space Science》2005,298(1-2):25-32
The growing field of Laboratory Astrophysics seeks to study the extreme environments found in many astrophysical events in
the controlled setting of a laboratory. In addition to the opportunity to perform basic research into the nature and properties
of materials in astrophysical environments, laboratory astrophysics experiments serve beautifully for validating calculations
performed by simulation codes designed to model astrophysical phenomena. I present results from our ongoing validation effort
for FLASH, a parallel adaptive-mesh hydrodynamics code for the compressible, reactive flows of astrophysical environments.
The first test case is a laser-driven shock propagating though a multilayer target introducing Rayleigh–Taylor and Richtmyer–Meshkov
fluid instabilities at the material interfaces. The second is an accelerating fluid interface that is subject to the Rayleigh–Taylor
instability. We found good agreement between simulations and experiment for the multilayer target case, but disagreement between
experiment and simulation in the Rayleigh–Taylor case. I discuss our findings and possible reasons for the disagreement. 相似文献
3.
Shimon M. Asida Eli Livne Josef Stein Lior Metzker 《Astrophysics and Space Science》2005,298(1-2):363-367
The growth rate of the turbulent mixing zone, which develops from random perturbations under Rayleigh–Taylor instability,
has been studied using the 3D version of the hydrodynamical code VULCAN. Previous studies show large differences between the
α parameter of different codes. In its Eulerian mode VULCAN/3D employs Van–Leer scheme for the advection of all variables,
and can also use interface tracking for multi-phase flows. Simulations using parallel version of VULCAN/3D give α of about
0.06, a value which agrees very well with experiments and some other simulations. 相似文献
4.
J. O. Kane A. Mizuta M. W. Pound B. A. Remington D. D. Ryutov 《Astrophysics and Space Science》2005,298(1-2):261-265
Our ongoing investigation of how ‘Pillars’ and other structure form in molecular clouds irradiated by ultraviolet (UV) stars
has revealed that the Rayleigh–Taylor instability is strongly suppressed by recombination in the photoevaporated outflow,
that clumps and filaments may be key, that the evolution of structure is well-modeled by compressible hydrodynamics, and that
directionality of the UV radiation may have significant effects. We discuss a generic, flexible set of laboratory experiments
that can test these results. 相似文献
5.
We study analytically the Rayleigh–Taylor instability in expanding supernova gas shell. The instability appears at the inner
shell surface accelerated by blowing pulsar wind. The most dangerous perturbations correspond to wavelengths comparable to
the shell thickness. We analyze the fragility of the supernova remnant shell in function of the initial perturbation amplitude
and the shell thickness. 相似文献
6.
A. D. Edens R. G. Adams P. K. Rambo I. C. Smith J. L. Porter T. Ditmire 《Astrophysics and Space Science》2007,307(1-3):127-130
We have performed a series of experiments examining the properties of high Mach number blast waves. Experiments were conducted
on the Z-Beamlet laser at Sandia National Laboratories. We created blast waves in the laboratory by using ∼1000 J laser pulses
to illuminate millimeter scale solid targets immersed in gas. Our experiments studied the validity of theories forwarded by
Ryu and Vishniac (1987, 1991) and Vishniac (1983) to explain the dynamics of perturbations on astrophysical blast waves. These
experiments consisted of a systematic scan of the decay rates of perturbations of known primary mode number induced on the
surface of blast waves by means of a regularly spaced wire array. The amplitude of the induced perturbations relative to the
radius of the blast wave was tracked and fit to a power law in time. Measurements were taken for a number of different mode
numbers in a mixed gas consisting of 7.5 Torr xenon and 2.5 Torr nitrogen and the results are compared to theoretical predictions.
It is found that two of the three mode numbers imply one polytropic index while the third case, which is the most complicated
for several reasons, implies a higher polytropic index. 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.
C. C. Kuranz R. P. Drake M. J. Grosskopf H. F. Robey B. A. Remington J. F. Hansen B. E. Blue J. Knauer 《Astrophysics and Space Science》2009,322(1-4):49-55
This paper discusses high-energy-density laboratory astrophysics experiments exploring the Rayleigh-Taylor instability under conditions similar to the blast wave driven, outermost layer in a core-collapse supernova. The planar blast wave is created in an experimental target using the Omega laser. The blast wave crosses an unstable interface with a seed perturbation machined onto it. The perturbation consists of a 3D “egg crate” pattern and, in some cases, an additional longer wavelength mode is added to this 3D, single-mode pattern. The main diagnostic of this experiment is x-ray radiography. This paper explores an image processing technique to improve the identification and characterization of structure in the radiographic data. 相似文献
9.
Douglas O. ReVelle 《Earth, Moon, and Planets》2008,102(1-4):345-356
We have developed a new approach to modeling the acoustic-gravity wave (AGW) radiation from bolide sources. This first effort
involves entry modeling of bolide sources that have available satellite data through procedures developed in ReVelle (Earth
Moon Planets 95, 441–476, 2004a; in: A. Milani, G. Valsecchi, D. Vokrouhlicky (eds) NEO Fireball Diversity: Energetics-based Entry Modeling and Analysis Techniques, Near-earth Objects: Our Celestial Neighbors
(IAU S236), 2007b). Results from the entry modeling are directly coupled to AGW production through line source blast wave theory for the initial
wave amplitude and period at (at 10 blast wave radii and perpendicular to the trajectory). The second effort involves the prediction of the formation
and or dominance of the propagation of the atmospheric Lamb, edge-wave composite mode in a viscous fluid (Pierce, J. Acoust.
Soc. Amer. 35, 1798–1807, 1963) as a function of the source energy, horizontal range and source altitude using the Lamb wave frequency that was deduced
directly during the entry modeling and that is used as a surrogate for the source energy. We have also determined that Lamb
wave production by bolides at close range decreases dramatically as either the source energy decreases or the source altitude
increases. Finally using procedures in Gill (Atmospheric-Ocean Dynamics, 1982) and in Tolstoy (Wave Propagation, 1973), we have analyzed two simple dispersion relationships and have calculated the expected dispersion for the Lamb edge-wave
mode and for the excited, propagating internal acoustic waves. Finally, we have used the above formalism to fully evaluate
these techniques for four large bolides, namely: the Tunguska bolide of June 30, 1908; the Revelstoke bolide of March 31,
1965; the Crete bolide of June 6, 2002 and the Antarctic bolide of September 3, 2004. Due to page limitations, we will only
present results in detail for the Revelstoke bolide. 相似文献
10.
Alastair S. Moore James Lazarus Matthias Hohenberger Joseph S. Robinson Edward T. Gumbrell Mike Dunne Roland A. Smith 《Astrophysics and Space Science》2007,307(1-3):139-145
We describe experiments that investigate the capability of an experimental platform, based on laser-driven blast waves created
in a medium of atomic clusters, to produce results that can be scaled to astrophysical situations. Quantitative electron density
profiles were obtained for blast waves produced in hydrogen, argon, krypton and xenon through the interaction of a high intensity
(I ≈ 1017 Wcm−2), sub-ps laser pulse. From this we estimate the local post-shock temperature, compressibility, shock strength and adiabatic
index for each gas. Direct comparisons between blast wave structures for consistent relative gas densities were achieved through
careful gas jet parameter control. From these we investigate the applicability of different radiative and Sedov-Taylor self-similar
solutions, and therefore the (ρ,T) phase space that we can currently access. 相似文献
11.
Extremely low frequency (ELF)/Very low frequency (VLF) hiss is whistler mode wave that interacts with energetic electrons
in the magnetosphere. The characteristics features of ELF/VLF hiss observed at low latitude ground station Jammu (Geomag.
lat. 22°16′ N, L=1.17) are reported. It is observed that most of hiss events first propagate in ducted mode along higher L-values (L = 4–5), after reaching lower edge of ionosphere excite the Earth-ionosphere waveguide and propagate towards equator to be
received at low-latitude station Jammu. To understand the generation mechanism of ELF/VLF hiss, incoherent Cerenkov radiated
power from the low-latitude and mid-latitude plasmasphere are evaluated. Considering this estimated power as an input for
wave amplification through wave–particle interaction, the growth rate and amplification factor is evaluated which is too small
to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of
ELF/VLF hiss. 相似文献
12.
In this paper we determined the wave mode of subsecond pulses (SSP). We used data on pulses with a degree of polarization
over 30%, with the sources located at −60 to +60 deg from the central meridian, for the period 2000–2002. The superposition
of SSRT radio maps and MDI magnetograms has shown that radio SSP sources are typically located near the polarity inversion
line of the active region magnetic field. Such an arrangement indicates that SSP sources are located at the tops of magnetic
loops. The ordinary mode of electromagnetic radiation is recorded in SSP sources located from the inversion line by no less
than about 10 arc sec. 相似文献
13.
Photoelectric observations of the RS CVn type non-eclipsing binary UX Arietis obtained at Nizamiah Observatory during the
observing seasons of 1975–76, 1981–82 and 1982–83 are presented. The light curve of UX Ari showed a distortion wave with an
amplitude inV varying from 0.02 mag during 1975–76 to 0.15 mag during 1982–83. An analysis of the available data shows that the light maximum
is almost constant. It is also evident that the light-curve minimum decreases as the wave amplitude increases. The constant
light at maximum,V = 6.51 ± 0.03 indicates the unspotted photospheric brightness. It is also suggested that the variation in meanV brightness is mainly due to spot activity and not due to intrinsic variation. 相似文献
14.
We study the fundamental modes of radiation hydrodynamic waves arising from one-dimensional small-amplitude initial fluctuations
with wave number k in a radiating and scattering grey medium using the Eddington approximation. The dispersion relation analyzed is the same
as that of Paper I (Kaneko et al., 2000), but is solved as a quintic in angular frequency ω while a quadratic in k
2 in Paper I. Numerical results reveal that wave patterns of five solutions are distinguished into three types of the radiation-dominated
and type 1 and type 2 matter-dominated cases. The following wave modes appear in our problem: radiation wave, conservative
radiation wave, entropy wave, Newtonian-cooling wave, opacity-damped and cooling-damped waves, constant-volume and constant-pressure
diffusion modes, adiabatic sound wave, cooling-damped and drag–force-damped isothermal sound waves, isentropic radiation-acoustic
wave, and gap mode. The radiation-dominated case is characterized by the gap between the isothermal sound and isentropic radiation-acoustic
speeds within which there is not any acoustic wave propagating with real phase speed. One of the differences between type
1 and type 2 matter-dominated cases is the connectivity of the constant-volume diffusion mode, which originates from the radiative
mode in the former case, while from the Newtonian-cooling wave in the latter case. Analytic solutions are derived for all
wave modes to discuss their physical significance. The criterion, which distinguishes between radiation-dominated and type
1 matter-dominated cases, is given by Γ0 = 9, where Γ0 = C
p
(tot)/C
V
(tot) is the ratio of total specific heats at constant pressure and constant volume. Waves in a scattering grey medium are also
analyzed, which provides us some hints for the effects of energy and momentum exchange between matter and radiation. 相似文献
15.
We report on the first production of “tailored” blast waves in cluster media using a 1 ps laser pulse focused to 2×1016 W/cm2. This new technique allows cylindrical blast waves to be produced with a strong axial modulation of variable spatial frequency,
as a seed for instability growth. Energy deposition is modified by changing the cluster density whilst keeping the atomic
density of the target constant. Electron density maps show the production of strongly modulated blast waves and the development
of a thin shell structure in H at late times, and the trajectories show blast waves forming in H, and Ar. In Xe, a blast wave
does not form on the timescales studied. Analysis of astrophysical similarity parameters suggests that a hydrodynamically
similar situation is created in H, and that further evolution would create a regime where radiative effects may be influential
in Ar and Xe. 相似文献
16.
UBV photometry of HR 1099 obtained during the 1979-80 and 1980-81 observing seasons is presented. An analysis of the available
data shows that the brightness at the light curve maximum increases as the wave amplitude increases, while the brightness
at the light minimum remains almost the same. In terms of the starspot model it implies that there is always a hemisphere
of the active component that is nearly ’saturated’ with spots and that spots occupy a larger fraction of the stellar surface
when the wave amplitude is smaller. The continuous migration attributed to the photometric wave by various authors is far
from certain. The amplitude of the wave has a sharp rise followed by slow decay with a period around 5–6 yr. It is found that
the two-spot model proposed by Dorren and Guinan (1982) is inadequate to describe all the observed photometric peculiarities
of HR 1099. 相似文献
17.
P. A. Sturrock 《Solar physics》2008,252(1):1-18
Time – frequency analysis of data from the GALLEX and GNO solar neutrino experiments shows that some features in power-spectrum
analyses of those datasets are due to aliasing (a result of the fact that run durations tend to be small multiples of one
week). Displays formed from the published GALLEX data show a sharp discontinuity that we attribute to some systematic effect.
We therefore normalize data for each of the four experiments in the GALLEX series and concatenate the resulting normalized
data. This step effectively removes the presumed systematic effect. To help understand the effect of aliasing, we form time – frequency
displays of the two principal modulations found in the data, at 11.87 year−1 and at 13.63 year−1. We also form time – frequency displays of datasets formed by subtracting these modulations from the actual (normalized)
data. The results suggest that the true principal modulation is that at 11.87 year−1. Comparison with helioseismology data suggests that modulation may be occurring in the core, perhaps resulting from inhomogeneities
and fluctuations in the nuclear-burning process, and that the sidereal rotation rate of the core is 12.87 year−1, or 408 nHz. 相似文献
18.
The results of a nonlinear wave theory of spiral structure that we have developed are compared with observational data on
the galaxies M81, M51, UGC 2259, and NGC 3883, which are characterized by different types of rotation curves.
Translated from Astrofizika, Vol. 43, No. 2, pp. 211–218, April–June, 2000. 相似文献
19.
In this paper, we study self-similar solutions, and their linear stability as well, describing the flow within a spherical
shell with finite thickness, expanding according to a power law of time, t
q
, where q>0. The shell propagates in a medium with initially uniform density and it is bounded by a strong shock wave at its outer
border while the inner face is submitted to a time-dependent uniform pressure. For q=2/5, the well-known Sedov–Taylor solution is recovered. In addition, although both accelerated and decelerated shells can
be unstable against dynamic perturbations, they exhibit highly different behaviors. Finally, the dispersion relation derived
earlier by Vishniac (Vishniac, E.T. in Astrophys. J. 274:152, 1983) for an infinitely thin shell is obtained in the limit of an isothermal shock wave. 相似文献
20.
C. C. Kuranz R. P. Drake K. K. Dannenberg P. J. Susalla D. J. Kremer T. Boehly J. Knauer 《Astrophysics and Space Science》2005,298(1-2):267-271
Hydrodynamic experiments have become a very active area within High Energy Density Laboratory Astrophysics. In such experiments,
preheat of an interior surface due to heating prior to shock arrival can alter the initial conditions for further evolution
and can change the nature of the experiment (Olson et al., 2003). Unfortunately, preheat cannot typically be detected without
undertaking dedicated experiments for this purpose. We have designed such experiments, relevant to hydrodynamic instability
experiments using Omega Laser at intensities of ~1015 W/cm2. Simulations using the HYADES code suggest that radiative preheat alone causes the interface to move approximately 2 μm before
the blast wave reaches it. Hot-electron preheat could cause much larger motions. These experiments will use VISAR to examine
the motion of an aluminum sample layer at the rear interface of a standard hydrodynamic target during the period before the
shock reaches it (Allen and Burton, 1993). 相似文献