Rarefaction

About: Rarefaction is a research topic. Over the lifetime, 1852 publications have been published within this topic receiving 26943 citations.

Influence of the shock-induced α-ε transition in Fe on its post-shock substructure evolution and mechanical behavior

Abstract: The effect of shock-prestraining high-purity Fe, above and below the 13 GPa phase transition, on post-shock compressive stress-strain behavior and substructure evolution is presented. The degree of shock hardening in Fe is higher for shock strength above the transition than below it. The substructure also displayed more deformation twinning for shocks above the phase transition than below. The shock hardening in Fe varied with propagation distance. Modeling shock propagation in Fe revealed that for the geometry used, the transition wave was overtaken and quenched by the rarefaction release explaining the gradient in shock hardening.

Melting phenomenon in laser-induced shock waves.

Abstract: The melting fraction in laser-induced shock waves in aluminum was estimated as a function of the shock pressure. The results show that partial melting can begin during the relaxation of a shock pressure of 680 kbar. It is also suggested that for very short laser pulses (femtoseconds) a supercooling phenomenon may occur without melting during the rarefaction wave.

Why Syrovatskii's mechanism of dynamic dissipation of magnetic fields does not work.

Abstract: Syrovatskii's mechanism of ‘dynamic dissipation of magnetic field’ is reinvestigated. In order to have this kind of ‘dynamic dissipation’ at a neutral line the ratio of current density to particle density must exceed a certain critical value. For conditions in the solar atmosphere near sunspots, this value can only be reached by a mechanism which produces a very large compression of the magnetic field as well as an extreme rarefaction of the density. Syrovatskii claims that his mechanism provides both these features. His enormous field compression, however, can only be obtained if one neglects the restoring Lorentz force (e.g. in Syrovatskii's model the compressed field near the neutral line is about one order of magnitude larger than the field of the sunspots which generates it). The second effect, i.e. the large plasma rarefaction around the neutral line, also is not real. This rarefaction is due to the particular flow field of Syrovatskii's model which allows for a free reconnection of the field lines across the neutral line; the magnetic field is treated like a vacuum field, the effects of the field accumulation near the neutral line being neglected. The aim of the present paper is to show how more realistic models modify Syrovatskii's results. Our numerical calculations lead to a maximum current to density ratio which is a factor of 106 smaller than the one obtained by Syrovatskii. Therefore one has to conclude that in the solar atmosphere one cannot produce in the way described by Syrovatskii the configurations which are necessary for ‘dynamic dissipation’.

On the Similarity Character of an Unsteady Rarefaction Wave in a Gas-Vapour Mixture with Condensation

Abstract: The self-similar solution of an unsteady rarefaction wave in a gas-vapour mixture with condensation is investigated. If the onset of condensation occurs at the saturation point, the rarefaction wave is divided into two zones, separated by a uniform region. If condensation is delayed until a fixed critical saturation ratio X c > 1 is reached, a condensation discontinuity of the expansion type is part of the solution. Numerical simulation, using a simple relaxation model, indicates that time has to proceed over more then two decades of characteristic times of condensation before the self-similar solution can be recognized. Experimental results on heterogeneous nucleation and condensation caused by an unsteady rarefaction wave in a mixture of water vapour, nitrogen gas and chromium-oxide nuclei are presented. The results are fairly well described by the numerical relaxation model. No plateau formation could be observed.