Shock wave

About: Shock wave is a research topic. Over the lifetime, 36184 publications have been published within this topic receiving 635848 citations. The topic is also known as: Shock waves & shockwave.

Origin of Coronal Shock Waves

Abstract: The basic idea of the paper is to present transparently and confront two different views on the origin of large-scale coronal shock waves, one favoring coronal mass ejections (CMEs), and the other one preferring flares. For this purpose, we first review the empirical aspects of the relationship between CMEs, flares, and shocks (as manifested by radio type II bursts and Moreton waves). Then, various physical mechanisms capable of launching MHD shocks are presented. In particular, we describe the shock wave formation caused by a three-dimensional piston, driven either by the CME expansion or by a flare-associated pressure pulse. Bearing in mind this theoretical framework, the observational characteristics of CMEs and flares are revisited to specify advantages and drawbacks of the two shock formation scenarios. Finally, we emphasize the need to document clear examples of flare-ignited large-scale waves to give insight on the relative importance of flare and CME generation mechanisms for type II bursts/Moreton waves.

Shock initiation of solid explosives

Abstract: Initiation phenomena in solid explosives produced by strong shock waves are described. Shock pressures in the explosive are between 20 and 200 kbar. It is demonstrated that in the usual case the shock wave travels not as an inert shock, but as a shock to which the explosive contributes energy, probably from reaction at voids and defects. This slightly reacting shock travels at increasing velocity for some distance, typically 1 cm in the experiments described, and then in a travel of perhaps 0.01 cm becomes full detonation, moving at full velocity. The increase to full detonation velocity occurs without overshoot. Experiments demonstrating the variation of sensitivity to shock with density, grain size, and other properties are discussed. The explosives studied are cyclotol B, TNT, plastic‐bonded HMX, and nitromethane‐carborundum mixtures.

Cavitation clouds created by shock scattering from bubbles during histotripsy.

Abstract: Histotripsy is a therapy that focuses short-duration, high-amplitude pulses of ultrasound to incite a localized cavitation cloud that mechanically breaks down tissue. To investigate the mechanism of cloud formation, high-speed photography was used to observe clouds generated during single histotripsy pulses. Pulses of 5−20 cycles duration were applied to a transparent tissue phantom by a 1-MHz spherically focused transducer. Clouds initiated from single cavitation bubbles that formed during the initial cycles of the pulse, and grew along the acoustic axis opposite the propagation direction. Based on these observations, we hypothesized that clouds form as a result of large negative pressure generated by the backscattering of shockwaves from a single bubble. The positive-pressure phase of the wave inverts upon scattering and superimposes on the incident negative-pressure phase to create this negative pressure and cavitation. The process repeats with each cycle of the incident wave, and the bubble cloud elongates toward the transducer. Finite-amplitude propagation distorts the incident wave such that the peak-positive pressure is much greater than the peak-negative pressure, which exaggerates the effect. The hypothesis was tested with two modified incident waves that maintained negative pressure but reduced the positive pressure amplitude. These waves suppressed cloud formation which supported the hypothesis.

The physics of dissipational galaxy formation.

Abstract: A number of arguments lead one to consider the possibility that the first massive galaxies were formed after redshift 10 The formation of galaxies at small redshifts can only have occurred if the formation process was dissipative This paper is concerned with one theory of dissipative galaxy formation: the theory which arises from the supposition that a protogalactic cloud would not have fragmented very extensively during the first phase of its infall and thus that the collapse of the cloud would be halted by the formation of shock fronts around a caustic surface Detailed calculations of the formation and evolution of these shock fronts yield values for the physical conditions of the protogalactic gas and the rate of radiation of galactic binding energy by such shocks The adiabaticity or isothermality of these shock fronts is found to be dependent on the characteristic infall velocity and the surface density associated with the shock front but not on the shape of the initial density profile perpendicular to the incipient shock surfaces Protogalaxies which recollapsed at high z are more likely to have generated isothermal shocks than ones which collapsed at low z It is found that this binding energy release could makemore » collapsing protogalactic clouds very high surface brightness objects It appears that there is a scale radius approx30 kpc associated with the collapse of the most massive galaxies and that it may be possible to explain the original inability of the material of galactic disks to fragment in terms of this scale radius A similar theory of the origin of Magellanic irregulars, low surface brightness spheroidals, and dwarf ellipticals is suggested« less