共查询到20条相似文献，搜索用时 234 毫秒
1.
M. J. Grosskopf R. P. Drake C. C. Kuranz A. R. Miles J. F. Hansen T. Plewa N. Hearn D. Arnett J. C. Wheeler 《Astrophysics and Space Science》2009,322(1-4):57-63
The National Ignition Facility (NIF) will soon provide experiments with far more than ten times the energy than has been previously available on laser facilities. In the context of supernova-relevant hydrodynamics, this will enable experiments in which hydrodynamic instabilities develop from multiple, coupled interfaces in a diverging explosion. This paper discusses the design of such blast-wave-driven explosions in which the relative masses of the layers are scaled to those within the star. It reports scaling simulations with CALE to model the global dynamics of such an experiment. CALE is a hybrid, Arbitrary Lagrangian-Eulerian code. The simulations probed the instability growth and multi-interface interactions in mass-scaled systems using different materials. The simulations assist in the target design process and in developing an experiment that can be diagnosed. 相似文献
2.
S. P. Regan T. C. Sangster D. D. Meyerhofer K. Anderson R. Betti T. R. Boehly T. J. B. Collins R. S. Craxton J. A. Delettrez R. Epstein O. V. Gotchev V. Yu. Glebov V. N. Goncharov D. R. Harding P. A. Jaanimagi J. P. Knauer S. J. Loucks L. D. Lund J. A. Marozas F. J. Marshall R. L. Mccrory P. W. Mckenty S. F. B. Morse P. B. Radha W. Seka S. Skupsky H. Sawada V. A. Smalyuk J. M. Soures C. Stoeckl B. Yaakobi J. A. Frenje C. K. Li R. D. Petrasso F. H. SÉguin 《Astrophysics and Space Science》2005,298(1-2):227-233
3.
P. A. Rosen J. M. Foster M. J. Taylor P. A. Keiter C. C. Smith J. R. Finke M. Gunderson T. S. Perry 《Astrophysics and Space Science》2007,307(1-3):213-217
Clumpiness of the interstellar medium may play an important role in the transfer of infrared continuum radiation in star forming
regions (Boisse, 1990). For example, in homogeneous models, C II emission should be confined to the cloud edge (Viala, 1986).
However, in star formation regions (such as M17SW, M17 and W51), it is observed to extend deep into the molecular cloud (Stutzki
et al., 1988; Keene et al., 1985). One plausible interpretation of these observations is that, due to their clumpiness, the
clouds are penetrated by UV radiation far deeper than expected from simple homogeneous models.
The interaction of H II regions around young massive stars with a clumpy medium is another area of interest. Molecular clouds
are well established to be clumpy on length scales down to the limits of observational resolution. Clumps can act as localized
reservoirs of gas which can be injected into the surroundings by photoionization and/or hydrodynamic ablation (Dyson et al.,
1995; Mathis et al., 1998).
The calculation of radiation transport in hot, clumpy materials is a challenging problem. Approximate, statistical treatments
of this problem have been developed by several workers, but their application has not been tested in detail. We describe laboratory
experiments, using the Omega laser to test modelling of radiation transport through clumpy media in the form of inhomogeneous
plasmas. 相似文献
4.
简要介绍了赖曼α森林的各种模型，宇宙流体力学模拟成功地再现了赖曼α森林的大部分观测结果，并使人们认识到：产生赖曼α森林的吸收体实际上是星系际介质中延伸的过密区，这种密度起伏是宇宙结构形成过程的自然结果。赖曼α森林己成为宇宙学研究的有力工具。 相似文献
5.
S. Sublett J. P. Knauer I. V. Igumenshchev A. Frank D. D. Meyerhofer 《Astrophysics and Space Science》2007,307(1-3):47-50
A double-pulse laser drive is used to create episodic supersonic plasma jets that propagate into a low density ambient medium.
These are among the first laser experiments to generate pulsed outflow. The temporal laser-intensity profile consists of two
1-ns square pulses separated by 9.6 ns. The laser is focused on a truncated conical plug made of medium Z material inserted into a high-Z washer. Unloading material from the plug is collimated within the cylindrical washer hole, then propagates into the low-Z foam medium. The resulting jet is denser than the ambient medium. Double-pulse jet evolution is compared to that driven by
a single laser pulse. The total drive energy is the same for both jets, as if a source with fixed energy generated a jet from
either one or two bursts. Radiographs taken at 100 ns show that a single-pulse jet was broader than the double-pulse jet,
as predicted by hydrodynamic simulations. Since the initial shock creating the jet is stronger when all the energy arrives
in a single pulse, the jet material impacts the ambient medium with higher initial velocity. Detailed comparisons between
single- and double-pulsed jet rheology and shock structure are presented. 2-D hydrodynamic simulations are compared to the
experimental radiographs.
PACS: 52.30.−q 41.75.Jv 42.62.−b 42.68.Sq 47.40.−x 47.56.+r 相似文献
6.
X. Ribeyre P. Nicolaï S. Galera V. T. Tikhonchuk 《Astrophysics and Space Science》2009,322(1-4):85-90
Supersonic plasma jets are ubiquitous in astrophysics. Our study focus on the jets emanated from Herbig-Haro (HH) objects. They have velocities of a few hundred km/s and are extending over the distances more than a parsec. Interaction of the jets with surrounding matter produces two specific structures in the jet head: the bow shock and the Mach disk. The radiative cooling of these shocks affects strongly the jet dynamics. A tool to understand the physics of these jets is the laboratory experiment. A supersonic jet interaction with surrounding plasma was studied on the PALS laser facility. A collimated high-Z plasma jet with a velocity exceeding 400 km/s was generated and propagated over a few millimeters length. Here we report on study the effect of radiative cooling on the head jet structure with a 2D radiative hydrodynamic code. The simulation results demonstrated the scalability of the experimental observations to the HH jets. 相似文献
7.
In the traditional axisymmetric models of the 11-year solar cycle, oscillations of the magnetic fields appear in the background of nonoscillating (over time scale considered) turbulent velocity fields and differential rotation. In this paper, an alternative approach is developed: The excitation of magnetic oscillations with the 22-year period is the consequence of hydrodynamic oscillations with the 11-year period. In the excitation of hydrodynamic oscillations, two processes taking place in high latitudes near the interface between the convective and radiative zones play a key role. One is forcing of the westerly zonal flow, the conditions for which are due to deformation of the interfacial surface. The other process is the excitation of a shear instability of zonal flow as a consequence of a strong radial gradient of angular velocity. The development of a shear instability at some stage brings about the disruption of the forcing of differential rotation. In the first (hydrodynamic) part of the paper, the dynamics of axisymmetric flows near the bottom of the convection zone is numerically simulated. Forcing of differential rotation having velocity shear in latitude and the existence of solutions in the form of torsional waves with the 11-year oscillation period are shown. In the second part the dynamics of the magnetic field is studied. The most pronounced peculiarities of the solutions are the existence of forced oscillations with the 22-year period and the drift of the toroidal magnetic field component from the mid latitudes to the equator. In high and low latitudes after cycle maximum, the toroidal component is of opposite sign in accordance with observations. In the third part, the transport of momentum from the bottom of the convection zone to the outer surface by virtue of diffusivity is considered. The existence of some sources of differential rotation in the convection zone is not implied. A qualitative correspondence of the differential rotation profile in the bulk of the convection zone and on its outer surface to experimental data is shown. The time correspondence between torsional and magnetic oscillations is also in accordance with observations. 相似文献
8.
An experimental technique to measure crater growth is presented whereby a high speed video captures profiles of a crater forming after impact obtained using a vertical laser sheet centered on the impact point. Unlike previous so called “quarter-space experiments,” where projectiles were launched along a transparent Plexiglas sheet so that growth of half a crater could be viewed, the use of the laser sheet permits viewing changes in crater shape without any physical interference to the cratering process. This technique indicates that for low velocity impacts (<300 m/s) into 220 μm glass beads that are without cohesion and where the projectile is not disrupted, craters initially grow somewhat proportionally, but that later their depths remain essentially constant while their diameters continue to expand. In addition, these experiments indicate that as the impact velocity increases, the rate of growth and the transient depth to diameter ratio at the end of ejecta excavation decreases. These last two observations are probably due to the large time of penetration of the projectile, which becomes a significant fraction of the time of crater formation. This is contrary to the expectations for the scaling rules, which assumes a point source. Very high curtain angles (>45°) are also seen, and could be due to the low friction angle of the target. Significant crater modification, which is rarely seen in “quarter-space experiments,” is also observed and appears to be controlled by the dynamic angle of repose of the target. These latter observations indicate that differences in target friction angles may need to be considered when determining near rim ejecta-mass distributions and large-scale crater modification processes on the planets. 相似文献
9.
Toshihiko Kadono Rei Niimi Kyoko Okudaira Sunao Hasegawa Makoto Tabata Akira Tsuchiyama 《Icarus》2012,221(2):587-592
In order to understand the penetration process of projectiles into lower-density targets, we carry out hypervelocity impact experiments using low-density (60 mg cm?3) aerogel targets and various types of projectiles, and observe the track formation process in the targets using a high-speed camera. A carrot shaped track, a bulbous, and a “hybrid” one consisting of bulbous and thin parts, are formed. The results of the high-speed camera observations reveal the similarity and differences on the temporal evolution of the penetration depth and maximum diameter of these tracks. At very early stages of an impact, independent of projectile type, the temporal penetration depth is described by hydrodynamic models for the original projectiles. Afterward, when the breakup of projectiles does not occur, intact projectiles continue to penetrate the aerogels. In the case of the breakup of projectiles, the track expands with a velocity of about a sound velocity of the aerogel at final stages. If there are large fragments, they penetrate deeper and the tracks become a hybrid type. The penetration of the large fragments is described by hydrodynamic models. Based on these results, we discuss the excavation near the impact point by shock waves. 相似文献
10.
D. Dravins 《Astronomische Nachrichten》2010,331(5):535-540
High‐fidelity spectroscopy presents challenges for both observations and in designing instruments. High‐resolution and high‐accuracy spectra are required for verifying hydrodynamic stellar atmospheres and for resolving intergalactic absorption‐line structures in quasars. Even with great photon fluxes from large telescopes with matching spectrometers, precise measurements of line profiles and wavelength positions encounter various physical, observational, and instrumental limits. The analysis may be limited by astrophysical and telluric blends, lack of suitable lines, imprecise laboratory wavelengths, or instrumental imperfections. To some extent, such limits can be pushed by forming averages over many similar spectral lines, thus averaging away small random blends and wavelength errors. In situations where theoretical predictions of lineshapes and shifts can be accurately made (e.g., hydrodynamic models of solar‐type stars), the consistency between noisy observations and theoretical predictions may be verified; however this is not feasible for, e.g., the complex of intergalactic metal lines in spectra of distant quasars, where the primary data must come from observations. To more fully resolve lineshapes and interpret wavelength shifts in stars and quasars alike, spectral resolutions on order R = 300 000 or more are required; a level that is becoming (but is not yet) available. A grand challenge remains to design efficient spectrometers with resolutions approaching R = 1 000 000 for the forthcoming generation of extremely large telescopes (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
激光驱动亥姆霍兹电容线圈靶的磁重联实验已经提出并进行了多年.当实验中的金属板被强激光照射时产生自由电子,这些自由电子的运动在连接两金属板的两个平行线圈中产生电流,由两个平行线圈内部电流产生的磁场之间随即发生重联.该实验不同于其他直接由Biermann电池效应所产生高β(等离子体热压与磁压的比值)环境下的磁重联实验.对该类实验进行了3维磁流体动力学数值模拟,首次展示了亥姆霍兹电容器线圈靶如何驱动磁重联的过程.数值模拟结果清楚地表明,磁重联的出流等离子体在线圈周围发生与实验结果相一致的堆积现象.线圈电流产生的磁场可高达100 T,使得磁重联区域周围的等离子体β值达到10^-2.与实验室结果进行比较,数值模拟重复了实验展示的大多数特征,可有助于深入认识和理解实验结果背后的物理学原理. 相似文献
12.
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
13.
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
14.
Since their formation in the outflows of evolved stars, materials suffer in space deep chemical and physical modifications. Most abundant elements (C, N, O, Mg, Si, S and Fe) are present in dust as refractory chemical species. Among them silicates are one of the main constituents. Spectroscopic observations in various astronomical environments have shown that magnesium rich silicates are present both in amorphous and in crystalline form. An accurate interpretation of these observations requires studies on the formation of silicate dust in the atmospheres of giant stars and their evolution in the interstellar medium until their inclusion in protoplanetary disks.Many theoretical works have described the chemical and physical evolution of solids in space and their link to observable optical properties. Laboratory studies of cosmic dust analogues are needed to investigate these processes experimentally.In this work, experiments aimed at simulating the formation of silicates in space are presented. In particular, the laser ablation technique is used to produce amorphous silicates with various Si-Mg-Fe content. The analysis of their thermal evolution is presented. 相似文献
15.
16.
C. Michaut E. Falize C. Cavet S. Bouquet M. Koenig T. Vinci A. Reighard R. P. Drake 《Astrophysics and Space Science》2009,322(1-4):77-84
Radiative shocks (RS) occur in astrophysical systems and in high-energy density laboratory experiments. Aided by three dimensionless parameters, we propose a classification of RS into four types, integrating previous work that has focused independently on optical depth and on Mach number. Specific terms, such as a cooling function, a radiative flux, or radiative energy and pressure must be added to the Euler equations in order to model these various kinds of shocks. We examine how these terms correspond to the radiative classification regimes. In astrophysics, observed RS arise generally in optically thin material. Thus, radiation escapes without interaction with the surrounding gas, except perhaps to ionize it, and the energy loss in such shocks can be modeled by a cooling function Λ. In this case only the post-shock region is structured by the radiation cooling. We found the analytical solution for hydrodynamic equations including Λ∝ ρ ε P ζ x θ for arbitrary values of ε, ζ, θ. This is a completely new result. An application of this calculation for the accretion shock in cataclysmic variables of polar type is given in astrophysical terms. We also draw a parallel between RS experiments performed using the LULI2000 laser facility, in France and the Omega laser Facility, in USA. RS developed in these laboratories are more or less optically thick. These high-Mach number RS present a radiative precursor. 相似文献
17.
We present temporal and spectral characteristics of X-ray flares observed from six late-type G–K active dwarfs (V368 Cep, XI Boo, IM Vir, V471 Tau, CC Eri and EP Eri) using data from observations with the XMM–Newton observatory. All the stars were found to be flaring frequently and altogether a total of 17 flares were detected above the 'quiescent' state X-ray emission which varied from 0.5 to 8.3 × 1029 erg s−1 . The largest flare was observed in a low-activity dwarf XI Boo with a decay time of 10 ks and ratio of peak flare luminosity to 'quiescent' state luminosity of 2. We have studied the spectral changes during the flares by using colour–colour diagram and by detailed spectral analysis during the temporal evolution of the flares. The exponential decay of the X-ray light curves, and time evolution of the plasma temperature and emission measure are similar to those observed in compact solar flares. We have derived the semiloop lengths of flares based on the hydrodynamic flare model. The size of the flaring loops is found to be less than the stellar radius. The hydrodynamic flare decay analysis indicates the presence of sustained heating during the decay of most flares. 相似文献
18.
V. V. Zharkova 《Solar physics》2008,251(1-2):641-663
In this paper the mechanisms responsible for observational features associated with sunquakes induced by different classes of solar flares are compared. The role of high-energy particle beams via Coulomb and Ohmic heating of the ambient plasma and nonthermal excitation and ionization is explored for different beam parameters at various atmospheric depths. On the one hand, only hard electron beams with high-energy fluxes are found producing extensive nonthermal hydrogen ionization, four orders of magnitude higher than in the quiet atmosphere. This excess ionization leads to the white-light flares associated with the seismic emission appearing simultaneously with hard X-ray emission and, consequently, to a strong increase of Ni-line emission observed as the seismic emission measured with the holographic technique. On the other hand, the ambient plasma hydrodynamic response to heating by such beam electrons forms hydrodynamic shocks just below the transition region, in the upper chromosphere, and they travel with supersonic velocity for up to five minutes before reaching the photosphere. These hydrodynamic responses caused by the beam electrons are maximized in the lower chromosphere for moderate electron beams because of their smaller Ohmic losses in the upper atmosphere compared to those for higher-energy electron beams whose bulk energy is deposited in the transition region. These shocks caused by electron beams can explain the observations of seismic emission by time?–?distance (TD) diagrams and the holographic method in M- and C-class flares, whereas to account for the quakes in X-class flares, high-energy quasi-thermal protons or power-law proton beams either by themselves or blended with electron beams are the most likely agents. Nonthermal ionization and excitation of lower atmospheric levels during the beam injection followed by thermo-conductive heating after the beam is stopped can contribute to the seismic signatures observed with the holographic technique caused by strong nonthermal ionization and back-warming heating occurring in the shock while it loses its energy by optically-thick radiation in the photospheric lines and continua. 相似文献
19.
Astronomy Letters - Our study of the photometric and spectroscopic observations of SN 1987A based on the hydrodynamic modeling of its bolometric light curve and nonstationary hydrogen kinetics and... 相似文献
20.
Despite great advances in observations and modelling, the problem of solar and stellar heating still remains one of the most challenging problems of space physics. To find a definite answer to what sort of mechanisms act to heat the plasma to a few million degrees requires a collaborative effort of small scales observations, large capacity numerical modelling and complicated theoretical approaches. A unique theory should incorporate aspects such as the generation of energy, its transport and dissipation. Up to now, the first two problems are rather clarified. However, the modality of transfer of magnetic or kinetic energy into heat is a question still awaiting for an answer. In the present paper we review the various popular heating mechanisms put forward in the existing extensive literature. The heating processes are, somewhat arbitrarily, classified as hydrodynamic, magnetohydrodynamic or kinetic based on the characteristics of the model medium. These mechanisms are further divided based on the time scales of the ultimate dissipation involved (i.e. AC and DC heating, turbulent heating). In particular, special attention is paid to discuss shock dissipation, mode coupling, resonant absorption, phase mixing, and, reconnection. Finally, we briefly review the various heating mechanisms proposed to heat other stars. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献