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Showing papers on "Shock wave published in 2002"


Book
31 Mar 2002
TL;DR: In this paper, the authors discuss the physics of gas dynamics and classical theory of shock waves, including thermal radiation and radiant heat exchange in a medium, and some self-similar processes in gas dynamics.
Abstract: : Contents: Elements of gas dynamics and classical theory of shock waves; thermal radiation and radiant heat exchange in a medium; thermodynamic properties of gases at high temperatures; shock tubes; absorption and emission of radiation in gases at high temperatures; speed of relaxation processes in gases; structure of front of shock waves in gases; physico-chemical kinetics in hydrodynamic processes; light phenomena in shock waves and during strong explosion in air; thermal waves; shock waves in solids; certain self-similar processes in gas dynamics.

3,685 citations


Journal ArticleDOI
TL;DR: In this article, the authors give a complete description of all possible spectra under those assumptions and find that there are five possible regimes, depending on the ordering of the break frequencies, and calculate more accurate expressions for the value of these break frequencies and describe the shape of the spectral breaks around them.
Abstract: Gamma-ray burst afterglows are well described by synchrotron emission from relativistic blast waves expanding into an external medium. The blast wave is believed to amplify the magnetic field and accelerate the electrons into a power-law distribution of energies promptly behind the shock. These electrons then cool both adiabatically and by emitting synchrotron and inverse Compton radiation. The resulting spectra are known to consist of several power-law segments, which smoothly join at certain break frequencies. Here, we give a complete description of all possible spectra under those assumptions and find that there are five possible regimes, depending on the ordering of the break frequencies. The flux density is calculated by integrating over all of the contributions to a given photon arrival time from all of the shocked region using the Blandford & McKee solution. This allows us to calculate more accurate expressions for the value of these break frequencies and describe the shape of the spectral breaks around them. This also provides the shape of breaks in the light curves caused by the passage of a break frequency through the observed band. These new, more exact, estimates are different from more simple calculations by typically a factor of a few, and they describe some new regimes that were previously ignored.

573 citations


Journal ArticleDOI
31 May 2002-Science
TL;DR: Multimillion-atom molecular-dynamics simulations are used to investigate the shock-induced phase transformation of solid iron, finding that the dynamics and orientation of the developing close-packed grains depend on the shock strength and especially on the crystallographic shock direction.
Abstract: Multimillion-atom molecular-dynamics simulations are used to investigate the shock-induced phase transformation of solid iron. Above a critical shock strength, many small close-packed grains nucleate in the shock-compressed body-centered cubic crystal growing on a picosecond time scale to form larger, energetically favored grains. A split two-wave shock structure is observed immediately above this threshold, with an elastic precursor ahead of the lagging transformation wave. For even higher shock strengths, a single, overdriven wave is obtained. The dynamics and orientation of the developing close-packed grains depend on the shock strength and especially on the crystallographic shock direction. Orientational relations between the unshocked and shocked regions are similar to those found for the temperature-driven martensitic transformation in iron and its alloys.

413 citations


Journal ArticleDOI
TL;DR: In this article, a model for the thermal processing of particles in shock waves typical of the solar nebula is presented, and the model is applied to the melting and cooling of chondrules.
Abstract: We present a model for the thermal processing of particles in shock waves typical of the solar nebula. This shock model improves on existing models in that the dissociation and recombination of H2 and the evaporation of particles are accounted for in their effects on the mass, momentum and energy fluxes. Also, besides thermal exchange with the gas and gas-drag heating, particles can be heated by absorbing the thermal radiation emitted by other particles. The flow of radiation is calculated using the equations of radiative transfer in a slab geometry. We compute the thermal histories of particles as they encounter and pass through the shock. We apply this shock model to the melting and cooling of chondrules in the solar nebula. We constrain the combinations of shock speed and gas density needed for chondrules to reach melting temperatures, and show that these are consistent with shock waves generated by gravitational instabilities in the protoplanetary disk. After their melting, cooling rates of chondrules in the range 10-1000 K h^(-1) are naturally reproduced by the shock model. Chondrules are kept warm by the reservoir of hot shocked gas, which cools only as fast as the dust grains and chondrules themselves can radiate away the gas's energy. We predict a positive correlation between the concentration of chondrules in a region and the cooling rates of chondrules in that region. This correlation is supported by the unusually high frequency of (rapidly cooled) barred chondrules among compound chondrules, which must have collided preferentially in regions of high chondrule density. We discuss these and other compelling consistencies between the meteoritic record and the shock wave model of chondrule formation.

364 citations


Journal ArticleDOI
TL;DR: In this article, the relativistic rotational supernova core collapse in axisymmetry has been studied and the gravity radiation emitted by such an event has been computed using hydrodynamic simulations.
Abstract: We have performed hydrodynamic simulations of relativistic rotational supernova core collapse in axisymmetry and have computed the gravitational radiation emitted by such an event. The Einstein equations are formulated using the confor- mally flat metric approximation, and the corresponding hydrodynamic equations are written as a first-order flux-conservative hyperbolic system. Details of the methodology and of the numerical code have been given in an accompanying paper. We have simulated the evolution of 26 models in both Newtonian and relativistic gravity. The initial configurations are dierentially rotat- ing relativistic 4=3-polytropes in equilibrium which have a central density of 10 10 gc m 3 . Collapse is initiated by decreasing the adiabatic index to some prescribed fixed value. The equation of state consists of a polytropic and a thermal part for a more realis- tic treatment of shock waves. Any microphysics like electron capture and neutrino transport is neglected. Our simulations show that the three dierent types of rotational supernova core collapse and gravitational waveforms identified in previous Newtonian simulations (regular collapse, multiple bounce collapse, and rapid collapse) are also present in relativistic gravity. However, ro- tational core collapse with multiple bounces is only possible in a much narrower parameter range in relativistic gravity. The relativistic models cover almost the same range of gravitational wave amplitudes (4 10 21 h TT 3 10 20 for a source at a distance of 10 kpc) and frequencies (60 Hz 1000 Hz) as the corresponding Newtonian ones. Averaged over all models, the total energy radiated in the form of gravitational waves is 8:2 10 8 Mc 2 in the relativistic case, and 3:6 10 8 Mc 2 in the Newtonian case. For all collapse models that are of the same type in both Newtonian and relativistic gravity, the gravitational wave signal is of lower amplitude. If the collapse type changes, either weaker or stronger signals are found in the relativistic case. For a given model, relativistic gravity can cause a large increase of the characteristic signal frequency of up to a factor of five, which may have important consequences for the signal detection. Our study implies that the prospects for detection of gravita- tional wave signals from axisymmetric supernova rotational core collapse do not improve when taking into account relativistic gravity. The gravitational wave signals obtained in our study are within the sensitivity range of the first generation laser interfer- ometer detectors if the source is located within the Local Group. An online catalogue containing the gravitational wave signal amplitudes and spectra of all our models is available at the URL http://www.mpa-garching.mpg.de/Hydro/hydro.html.

299 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the relationship between upstream turbulent boundary-layer properties and the unsteady separation shock behavior in a Mach 5 unswept compression ramp interaction and found that a fuller velocity is associated with increased resistance to separation to the boundary layer and, hence, causes downstream shock motion.
Abstract: Particle image velocimetry and high-frequency response wall pressure measurements have been used to investigate the relationship between upstream turbulent boundary-layer properties and the unsteady separation shock behavior in a Mach 5 unswept compression ramp interaction No correlation is found between variations in the incoming boundary-layer thickness and the separation shock foot position, as has been suggested in earlier work However, themean velocity proe le, conditioned on theseparation shock foot position, exhibits a subtly fullershape when the shock is downstream than when it is upstream More signie cantly, a clear correlation is observed between positivestreamwisevelocity e uctuations in thelowerthird of the upstream boundary layer and downstream shock motions, and vice versa The strongest correlations are found for velocity e uctuations with frequencies of about4‐10 kHz, which is signie cantly lowerthan the frequencies that characterize the large-scale structures in the boundary layer (40 kHz), although spatial limitations in the transducer array may limit the instrument sensitivity to this lower range These results are qualitatively consistent with the simple physical principle that a fuller velocity proe le imparts increased resistance to separation to the boundary layer and, hence, causes downstream shock motion, whereas a less-full velocity proe le is associated with lower resistance to separation and, hence, upstream shock motion

249 citations



Journal ArticleDOI
TL;DR: In this article, the authors applied a band splitting procedure to 18 metric type II bursts with the fundamental band starting frequencies up to 270 MHz and showed that the split can be used to evaluate the density jump at the shock front and to estimate the shock Mach number, which in combination with the shock speed inferred from the frequency drift provides an estimate of the Alfven velocity and the magnetic field.
Abstract: Type II radio bursts recorded in the metric wavelength range are excited by MHD shocks traveling through the solar corona. They often expose the fundamental and harmonic emission band, both frequently being split in two parallel lanes that show a similar frequency drift and intensity behaviour. Our previous paper showed that band-splitting of such characteristics is a consequence of the plasma emission from the upstream and downstream shock regions. Consequently, the split can be used to evaluate the density jump at the shock front and to estimate the shock Mach number, which in combination with the shock speed inferred from the frequency drift provides an estimate of the Alfven velocity and the magnetic field in the ambient plasma. In this paper such a procedure is applied to 18 metric type II bursts with the fundamental band starting frequencies up to 270 MHz. The obtained values show a minimum of the Alfven velocity at the heliocentric distance R 2 amounting tovA 400-500 km s 1 . It then increases achieving a local maximum ofvA 450-700 km s 1 at R 2:5. The implications regarding the process of formation and decay of MHD shocks in the corona are discussed. The coronal magnetic field in the range 1:3< R< 3 decreases as R 3 to R 4 ,o rH 1:5 to H 2 if expressed as a function of the height. The results are compared with other estimates of the coronal magnetic field in the range 1 < R < 10. Combined data show that below H < 0: 3t he magnetic field is dominated by active region fields, whereas above H= 1 it becomes radial, behaving roughly as B= 2 R 2 with a plausible value of B 5n T at 1a .u.

196 citations


Journal ArticleDOI
TL;DR: A model for a moderately deep underwater explosion bubble is developed that integrates the shock wave and oscillation phases of the motion and agreement between these histories and experimental data is found to be substantially better than that produced by previous models.
Abstract: A model for a moderately deep underwater explosion bubble is developed that integrates the shock wave and oscillation phases of the motion. A hyperacoustic relationship is formulated that relates bubble volume acceleration to far-field pressure profile during the shock-wave phase, thereby providing initial conditions for the subsequent oscillation phase. For the latter, equations for bubble-surface response are derived that include wave effects in both the external liquid and the internal gas. The equations are then specialized to the case of a spherical bubble, and bubble-surface displacement histories are calculated for dilational and translational motion. Agreement between these histories and experimental data is found to be substantially better than that produced by previous models.

183 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the fluid dynamics of high-speed (500 m/s) small size (200 μm in diameter) droplet impact on a rigid substrate.
Abstract: We are investigating the fluid dynamics of high-speed (500 m/s) small size (200 μm in diameter) droplet impact on a rigid substrate. Utilizing a high-resolution axisymmetric solver for the Euler equations, we show that the compressibility of the liquid medium plays a dominant role in the evolution of the phenomenon. Compression of the liquid in a zone defined by a shock wave envelope, very high velocity lateral jetting, and expansion waves in the bulk of the medium are the most important mechanisms identified, simulated, and discussed. Comparisons of computationally obtained jetting inception times with analytic results show that agreement improves significantly if the radial motion of liquid in the compressed area is taken into account.

179 citations


Journal ArticleDOI
TL;DR: In this article, the suprathermal electron acceleration mechanism in a perpendicular magnetosonic shock wave in a high Mach number regime was studied by using a particle-in-cell simulation, and it was shown that the electrons are likely to be trapped by solitary waves and during the trapping phase they can be effectively accelerated by the shock motional/convection electric field.
Abstract: We study the suprathermal electron acceleration mechanism in a perpendicular magnetosonic shock wave in a high Mach number regime by using a particle-in-cell simulation. We find that shock surfing/surfatron acceleration producing suprathermal electrons occurs in the shock transition region, where a series of large-amplitude electrostatic solitary waves (ESWs) are excited by Buneman instability under the interaction between the reflected ions and the incoming electrons. It is shown that the electrons are likely to be trapped by ESWs, and during the trapping phase they can be effectively accelerated by the shock motional/convection electric field. We discuss that suprathermal electrons can be accelerated up to mic2(v0/c), where mic2 is the ion rest mass energy and v0 is the shock upstream flow velocity. Furthermore, some of these suprathermal electrons may be effectively trapped for an infinitely long time when the Alfven Mach number MA exceeds several tens, and they are accelerated up to the shock potential energy determined by the global shock size.

Journal ArticleDOI
TL;DR: In this paper, the authors presented detailed three-dimensional magneto-hydrodynamical simulations of the passage of a radio plasma cocoon filled with turbulent magnetic fields through a shock wave.
Abstract: ABSTRA C T In several merging clusters of galaxies so-called cluster radio relics have been observed. These are extended radio sources which do not seem to be associated with any radio galaxies. Two competing physical mechanisms to accelerate the radio-emitting electrons have been proposed: (i) diffusive shock acceleration and (ii) adiabatic compression of fossil radio plasma by merger shock waves. Here the second scenario is investigated. We present detailed three-dimensional magneto-hydrodynamical simulations of the passage of a radio plasma cocoon filled with turbulent magnetic fields through a shock wave. Taking into account synchrotron, inverse Compton and adiabatic energy losses and gains, we evolved the relativistic electron population to produce synthetic polarization radio maps. On contact with the shock wave the radio cocoons are first compressed and finally torn into filamentary structures, as is observed in several cluster radio relics. In the synthetic radio maps the electric polarization vectors are mostly perpendicular to the filamentary radio structures. If the magnetic field inside the cocoon is not too strong, the initially spherical radio cocoon is transformed into a torus after the passage of the shock wave. Very recent, high-resolution radio maps of cluster radio relics seem to exhibit such toroidal geometries in some cases. This supports the hypothesis that cluster radio relics are fossil radio cocoons that have been revived by a shock wave. For a late-stage relic the ratio of its global diameter to the filament diameter should correlate with the shock strength. Finally, we argue that the total radio polarization of a radio relic should be well correlated with the three-dimensional orientation of the shock wave that produced the relic.

Journal ArticleDOI
TL;DR: In this paper, the contribution of cosmic gamma-ray background from cosmic-ray ions and electrons accelerated at intergalactic shocks associated with cosmological structure formation was investigated numerically, and it was shown that the kinetic energy of accretion flows in the low-redshift inter-galactic medium is thermalized primarily through moderately strong shocks, which allow for an efficient conversion of shock ram pressure into cosmicray pressure.
Abstract: We investigate numerically the contribution to the cosmic gamma-ray background from cosmic-ray ions and electrons accelerated at intergalactic shocks associated with cosmological structure formation. We show that the kinetic energy of accretion flows in the low-redshift intergalactic medium is thermalized primarily through moderately strong shocks, which allow for an efficient conversion of shock ram pressure into cosmic-ray pressure. Cosmic rays accelerated at these shocks produce a diffuse gamma-ray flux which is dominated by inverse Compton emission from electrons scattering off cosmic microwave background photons. Decay of neutral π mesons generated in p-p inelastic collisions of the ionic cosmic-ray component with the thermal gas contribute about 30 per cent of the computed emission. Based on experimental upper limits on the photon flux above 100 MeV from nearby clusters we constrain the efficiency of conversion of shock ram pressure into relativistic CR electrons to ≤ 1 per cent. Thus, we find that cosmic rays of cosmological origin can generate an overall significant fraction of order 20 per cent and no more than 30 per cent of the measured gamma-ray background.

Journal ArticleDOI
TL;DR: In this paper, a planar laser-induced fluorescence (PLIF) visualization is used to investigate the Richtmyer-Meshkov instability generated by two incident shock strengths (M s = 1.11 and 1.21).
Abstract: Investigations of the Richtmyer–Meshkov instability carried out in shock tubes have traditionally used membranes to separate the two gases. The use of membranes, in addition to introducing other experimental difficulties, impedes the use of advanced visualization techniques such as planar laser-induced fluorescence (PLIF). Jones & Jacobs (1997) recently developed a new technique by which a perturbed, membrane-free gas–gas interface can be created in a shock tube. The gases enter the shock tube from opposite ends and exit through two small slots on opposite sides of the test section, forming a stagnation point flow at the interface location. A gentle rocking motion of the shock tube then provides the initial perturbation in the form of a standing wave. The original investigation using this technique utilized dense fog seeding for visualization, which allowed large-scale effects to be observed, but was incapable of resolving smaller-scale features. PLIF visualization is used in the present study to investigate the instability generated by two incident shock strengths ( M s = 1.11 and 1.21), yielding very clear digital images of the flow. Early-time growth rate measurements obtained from these experiments are found to be in excellent agreement with incompressible linear stability theory (appropriately adjusted for a diffuse interface). Very good agreement is also found between the late-time amplitude measurements and the nonlinear models of Zhang & Sohn (1997) and Sadot et al . (1998). Comparison of images from the M s = 1.11 and 1.21 sequences reveals a significant increase in the amount of turbulent mixing in the higher-Mach-number experiments, suggesting that a mixing transition has occurred.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the nonlinear whistler critical Mach number corresponds to the transition between stationary and non-stationary dynamical behavior of the shock wave and that the transition to the nonstationarity of the wave front structure is always accompanied by the disappearance of the whistler wave train within the shock front.
Abstract: Whistler waves are an intrinsic feature of the oblique quasiperpendicular collisionless shock waves. For supercritical shock waves, the ramp region, where an abrupt increase of the magnetic field occurs, can be treated as a nonlinear whistler wave of large amplitude. In addition, oblique shock waves can possess a linear whistler precursor. There exist two critical Mach numbers related to the whistler components of the shock wave, the first is known as a whistler critical Mach number and the second can be referred to as a nonlinear whistler critical Mach number. When the whistler critical Much number is exceeded, a stationary linear wave train cannot stand ahead of the ramp. Above the nonlinear whistler critical Mach number, the stationary nonlinear wave train cannot exist anymore within the shock front. This happens when the nonlinear wave steepening cannot be balanced by the effects of the dispersion and dissipation. In this case nonlinear wave train becomes unstable with respect to overturning. In the present paper it is shown that the nonlinear whistler critical Mach number corresponds to the transition between stationary and nonstationary dynamical behavior of the shock wave. The results of the computer simulations making use of the 1D full particle electromagnetic code demonstrate that the transition to the nonstationarity of the shock front structure is always accompanied by the disappearance of the whistler wave train within the shock front. Using the two-fluid MHD equations, the structure of nonlinear whistler waves in plasmas with finite beta is investigated and the nonlinear whistler critical Mach number is determined. It is suggested a new more general proof of the criteria for small amplitude linear precursor or wake wave trains to exist.

Journal ArticleDOI
15 Feb 2002-Science
TL;DR: Synchrotron x-radiography and a fast x-ray detector were used to record the time evolution of the transient fuel sprays from a high-pressure injector and revealed the complex nature of the spray hydrodynamics.
Abstract: Synchrotron x-radiography and a fast x-ray detector were used to record the time evolution of the transient fuel sprays from a high-pressure injector. A succession of 5.1-microsecond radiographs captured the propagation of the spray-induced shock waves in a gaseous medium and revealed the complex nature of the spray hydrodynamics. The monochromatic x-radiographs also allow quantitative analysis of the shock waves that has been difficult if not impossible with optical imaging. Under injection conditions similar to those found in operating engines, the fuel jets can exceed supersonic speeds and result in gaseous shock waves.

Journal ArticleDOI
TL;DR: In this article, a model with full coupling between micro-and macroscale motion is developed for compressible multiphase mixtures, and the equations of motion and the coupling microstructural equation (an analogue of the Rayleigh-Lamb equation) are obtained by using the Hamilton principle of stationary action.

Journal ArticleDOI
TL;DR: In this paper, a propagating disturbance in the solar corona observed in emission in soft X-ray images from the Yohkoh Soft Xray Telescope (SXT) was reported.
Abstract: We report observations of a propagating disturbance in the solar corona observed in emission in soft X-ray images from the Yohkoh Soft X-ray Telescope (SXT). The disturbance was associated with a flare which began at about 09:04 UT on 1997 November 03. This flare was associated with a type II radio burst observed at decimetric-dekametric wavelengths by the Astrophysikalisches Institut Potsdam Radio Spectrograph. H α data from Kanzelhohe Solar Observatory show that a Moreton wave was associated with this event. Moreover, Solar and Heliospheric Observatory Extreme Ultraviolet Imaging Telescope (EIT) 195 A data show an `EIT wave' associated with this event. Extrapolations of the leading edge of the propagating soft X-ray disturbance show a close association with both of these wave features. The soft X-ray disturbance is observed to travel with a speed of about 546 km s -1 . Using Nancay Radioheliograph data we directly determine the source locations of the type II radio burst. These are found to be located close to the soft X-ray disturbance and show motions consistent with the soft X-ray motions. These results lead us to conclude that the “SXT wave” is the coronal counterpart of a Moreton wave, analogous to EIT waves, i.e., it is the first confirmed direct observation of a solar coronal shock wave in X-rays.

Journal ArticleDOI
Thierry Foglizzo1
TL;DR: In this paper, the linear stability of isothermal Bondi accretion with a shock is studied analytically in the asymptotic limit of high incident Mach numberM 1. The growth rate of non-radial perturbations l= 1 is higher by a factorM 2=3 1, and is therefore intermediate between the advection and acoustic frequencies.
Abstract: The linear stability of isothermal Bondi accretion with a shock is studied analytically in the asymptotic limit of high incident Mach numberM1. The flow is unstable with respect to radial perturbations as expected by Nakayama (1993), due to post-shock acceleration. Its growth-time scales like the advection time from the shock rsh to the sonic point rson. The growth rate of non-radial perturbations l= 1 is higher by a factorM 2=3 1 , and is therefore intermediate between the advection and acoustic frequencies. Besides these instabilities based on post-shock acceleration, our study revealed another generic mechanism based on the cycle of acoustic and vortical perturbations between the shock and the sonic radius, independently of the sign of post- shock acceleration. The vortical-acoustic instability is fundamentally non-radial. It is fed by the ecient excitation of vorticity waves by the isothermal shock perturbed by acoustic waves. The growth rate exceeds the advection frequency by a factor logM1. Unstable modes cover a wide range of frequencies from the fundamental acoustic frequencyc=rsh up to a cut-o c=rson associated with the sonic radius. The highest growth rate is reached for l= 1 modes near the cut-o. The additional cycle of acoustic waves between the shock and the sonic radius is responsible for variations of the growth rate by a factor up to 3 depending on its phase relative to the vortical-acoustic cycle. The instability also exists, with a similar growth rate, below the fundamental acoustic frequency down to the advection frequency, as vorticity waves are eciently coupled to the region of pseudosound. These results open new perspectives to address the stability of shocked accretion flows.

Journal ArticleDOI
TL;DR: In this paper, the nonlinear propagation of the dust ion-acoustic waves has been investigated accounting for the charge fluctuation dynamics of stationary dust grains in an unmagnetized dusty plasma.
Abstract: The nonlinear propagation of the dust ion-acoustic waves has been investigated accounting for the charge fluctuation dynamics of stationary dust grains in an unmagnetized dusty plasma. The Korteweg-de Vries equation, as well as the Korteweg-de Vries-Burgers equation, are derived by employing the reductive perturbation method. It has been shown that dust charge fluctuations produce a dissipation which is responsible for shock waves. Conditions for the formation of dust ion-acoustic solitary and shock waves as well as their properties are clearly explained. The implications of our investigations to both space and laboratory dusty plasmas are discussed.

Journal ArticleDOI
TL;DR: In this paper, a shock-capturing numerical scheme for the one-dimensional Savage-Hutter theory of granular flow is employed to describe the phenomenon of supercritical flow merging into a region of subcritical flow.

Journal ArticleDOI
01 Aug 2002-Icarus
TL;DR: In this article, the authors present numerical simulations of the thermal and dynamical histories of chondrules and their precursors during passage of an adiabatic shock wave through a particle-gas suspension in a minimum-mass solar nebula.

Journal ArticleDOI
TL;DR: In this article, three traveling disturbances recorded in the absorption line of Helium I at 10830 A (HeI), analogous to HαMoreton waves, are analyzed and the morphology and kinematics of the wavefronts are described in detail.
Abstract: Three traveling disturbances recorded in the absorption line of Helium I at 10830 A (HeI), analogous to HαMoreton waves, are analyzed. The morphology and kinematics of the wavefronts are described in detail. The HeI wave appears as an expanding arc of increased absorption roughly corresponding to the Hα disturbance, although not as sharply defined. HeI perturbations consist of a relatively uniform diffuse component and a patchy one that appears as enhanced absorption in HeI mottles. It leads the Hα front by some 20 Mm and can be followed to considerably larger distances than in Hα observations. Behind the front stationary areas of reduced HeI absorption develop, resembling EUV coronal dimming. The observed HeI as well as the Hα disturbances show a deceleration of the order of 100-1000 ms −2 . Moreover, in the event where Hα ,H eI, and EUV wavefronts are observed, all of them follow closely related kinematical curves, indicating that they are a consequence of a common disturbance. The analysis of spatial perturbation profiles indicates that HeI disturbances consist of a forerunner and a main dip,the latterbeing cospatial withthe Hαdisturbance. The properties and behavior of the wavefronts can be comprehended as a consequence of a fast-mode MHD coronal shock whose front is weakly inclined to the solar surface. The Hα disturbance and the main HeI dip are a consequence of the pressure jump in the corona behind the shock front. The HeI forerunner might be caused by thermal conduction from the oblique shock segments ahead of the shock-chromosphere intersection, or by electron beams accelerated in the quasi-perpendicular section of the shock.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the effect of the transverse magnetic induction on the velocities of rovibrational transitions of H2 emitted from C-type shock waves propagating in molecular gas.
Abstract: We report calculations of the intensities of rovibrational transitions of H2 emitted from C-type shock waves propagating in molecular gas. Attention was paid to the thermal balance of the gas and to the rates of collisional dissociation and ionization of H2. We found that the maximum shock speeds which can be attained, prior to the collisional dissociation of H2 (which results in a sonic point in the flow and hence a J-type shock wave), can be much higher than had previously been believed. Thus, adopting the `standard' scaling of the transverse magnetic induction with the gas density, B(muG)=[nH(cm-3)]1/2, we established that the maximum shock speed increased from 20-30kms-1 at high pre-shock densities (nH>=106cm-3) to 70-80kms-1 at low densities (nH<=104cm-3). The critical shock speed, vcrit, also increases significantly with the transverse magnetic induction, B, at a given pre-shock gas density, nH. By way of an application of these results, we demonstrate that a two-component model, comprising shock waves with velocities vs=60 and 40kms-1, reproduces the column densities of H2 observed by ISO-SWS up to the highest level (possibly) detected, v=0, J=27, which lies 42515K above the ground state. We found no necessity to invoke mechanisms other than thermal collisional excitation in the gas phase; but the v=1 vibrational band remains less completely thermalized than is indicated by the observations. Fine structure transitions of atoms and ions were also considered. The intensity of the [SiI] 68.5mum transition, observed by Gry et al. using ISO-LWS, is satisfactorily reproduced by the same model and may also originate in OMC-1, rather than Orion-KL as originally believed. The transitions of [FeII] and [SI] observed by Rosenthal et al. may also arise in the shock-heated gas.

Journal ArticleDOI
TL;DR: Slowing the rate of shock wave administration during shock wave lithotripsy significantly improves the efficiency of stone fragmentation in vivo.

Journal ArticleDOI
TL;DR: It is demonstrated that shock wave lithotripsy damage to the kidney is reduced when cavitation is suppressed, and this finding supports the idea that cavitation has a prominent role inshock wave lithOTripsy trauma.

Journal ArticleDOI
TL;DR: Using an existing expression for the state-to-state rotational transition rate coefficients, which is derived from the experimental data taken at temperatures equal to or below 1500 K, the master equation for rotational states is integrated with time for N 2.
Abstract: Using an existing expression for the state-to-state rotational transition rate coefficients, which is derived from the experimental data taken at temperatures equal to or below 1500 K, the master equation for rotational states is integrated with time for N 2 . The postshock temperature considered is from 400 to 128,000 K. From the numerical solutions of the master equation, the effective collision numbers and characteristic relaxation times are determined

Journal ArticleDOI
TL;DR: In this paper, the stability of hypersonic boundary layers over a compression corner is investigated numerically using a high-order, weighted, essentially nonoscillatory shockcapturing scheme.
Abstract: The stability of hypersonic boundary layers over a compression corner is investigated numerically. To compute the shock and the interaction of the shock with the instability waves, the simulation solves the three-dimensional Navier-Stokes equations using a high-order, weighted, essentially nonoscillatory shock-capturing scheme. After computing the mean flowfield, the procedure then superimposes two-dimensional unsteady disturbances at the inflow and computes the evolution of these disturbances in downstream direction. Because of the interaction of the shock with the boundary layer, a separation bubble forms at the corner, and two compression waves form near the separation and reattachment points. These compression waves merge farther away from the boundary layer to form a shock

Journal ArticleDOI
TL;DR: In this article, the ejecta particle size distributions for shocked Al and Sn metals were measured using an in-line Fraunhofer holography technique, and the size of the ejected particles was then measured using the size distribution method.
Abstract: When a shock wave interacts at a metal vacuum interface “ejected particulates” (ejecta) can be emitted from the surface. The mass, size, shape, and velocity of the ejecta varies depending on the initial shock conditions and the material properties of the metal sample. To understand this phenomena, experiments have been conducted at the Pegasus Pulsed Power Facility located at Los Alamos National Laboratory. For the experiments reported in this article, the facility is used to implode a cylinder to a velocity of 3.4 mm/μs. When this cylinder impacts a smaller diameter target cylinder, shock pressures of 30 and 40 GPa can be obtained in Al and Sn metals, respectively. Ejecta formation proceeds as the shock wave in the metal sample interacts at the metal vacuum interface. The size of the ejected particles is then measured using an in-line Fraunhofer holography technique. In this report, ejecta particle size distributions will be presented for shocked Al and Sn metals. The measured particle size distributions...

Journal ArticleDOI
TL;DR: In this article, the authors show that the ejecta decelerates at R < Rload, producing a lot of soft radiation, and the light curve of soft emission peaks at tpeak ≈ 40(1 + z)E(Γej/100)-2 s.
Abstract: Gamma-ray bursts (GRBs) are emitted by relativistic ejecta from powerful cosmic explosions. Their light curves suggest that the γ-ray emission occurs at early stages of the ejecta expansion, well before it decelerates in the ambient medium. If so, the launched γ-ray front must overtake the ejecta and sweep the ambient medium outward. As a result, a gap is opened between the ejecta and the medium that surfs the radiation front ahead. Effectively, the ejecta moves in a cavity until it reaches a radius Rgap ≈ 1016E cm, where E is the isotropic energy of the GRB. At R = Rgap the gap is closed and a blast wave forms and collects the medium swept by radiation. Further development of the blast wave is strongly affected by the leading radiation front: the front plays the role of a precursor where the medium is loaded with e± pairs and preaccelerated. It impacts the emission from the blast at R < Rload = 5Rgap (the early afterglow). A spectacular observational effect results: GRB afterglows should start in optical/UV and evolve fast (less than minutes) to a normal X-ray afterglow. The early optical emission observed in GRB 990123 may be explained in this way. The impact of the front is especially strong if the ambient medium is a wind from a massive progenitor of the GRB. In this case three phenomena are predicted. (1) The ejecta decelerates at R < Rload, producing a lot of soft radiation. (2) The light curve of soft emission peaks at tpeak ≈ 40(1 + z)E(Γej/100)-2 s, where Γej is the Lorentz factor of the ejecta. Given measured redshift z and tpeak, one finds Γej. (3) The GRB acquires a spectral break at 5-50 MeV because harder photons are absorbed by radiation scattered in the wind. A measurement of the break position will determine the wind density.