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.

On the Mechanism of Gamma-Ray Burst Afterglows

Abstract: The standard model of afterglow production by the forward shock wave is not supported by recent observations. We propose a model in which the forward shock is invisible and afterglow is emitted by a long-lived reverse shock in the burst ejecta. It explains observed optical and X-ray light curves, including the plateau at 103-104 s with a peculiar chromatic break, and the second break that was previously associated with a beaming angle of the explosion. The plateau forms following a temporary drop of the reverse-shock pressure much below the forward-shock pressure. A simplest formalism that can describe such blast waves is the "mechanical" model; we use it in our calculations.

Two-dimensional measurement of density, velocity, and temperature in turbulent high-speed air flows by UV Rayleigh scattering

Abstract: Instantaneous cross-sectional images of turbulent air flows with densities on the order of one atmosphere or less can be obtained in a straightforward manner using far ultraviolet Rayleigh scattering. These images give quantitative values for the air density and show the details of turbulent structure, shock structure, and shock wave/boundary layer interactions. Two-dimensional spatial correlations taken from multiple images give the shape and extent of average turbulent structure as well as the coupling between turbulent structure and other flow features. This technique may be extended to observe velocity fields by either double pulsing the illumination source or by using a narrow linewidth atomic or molecular filter window in front of the detector array. The latter approach also yields temperature. Used in conjunction with flow marking techniques such as RELIEF, coupling between turbulent structure and velocity fluctuations can also be determined. These diagnostic techniques can be extended to combusting flows to observe instantaneous structure, mixing, flame front location, and velocity fields.

Dynamical feedback of self‐generated magnetic fields in cosmic ray modified shocks

Abstract: We present a semi-analytical kinetic calculation of the process of non-linear diffusive shock acceleration (NLDSA) which includes magnetic field amplification due to cosmic ray induced streaming instability, the dynamical reaction of the amplified magnetic field and the possible effects of turbulent heating. This kinetic calculation allows us to show that the net effect of the amplified magnetic field is to enhance the maximum momentum of accelerated particles while reducing the concavity of the spectra, with respect to the standard predictions of NLDSA. This is mainly due to the dynamical reaction of the amplified field on the shock, which smoothens the shock precursor. The total compression factors which are obtained for parameters typical of supernova remnants are R{sub tot} {approx} 7-10, in good agreement with the values inferred from observations. The strength of the magnetic field produced through excitation of streaming instability is found in good agreement with the values inferred for several remnants if the thickness of the X-ray rims are interpreted as due to severe synchrotron losses of high energy electrons. We also discuss the relative role of turbulent heating and magnetic dynamical reaction in smoothening the shock precursor.

Temporal evolution of the shock wave and hot core air in laser induced plasma

Abstract: The temporal evolution of electric breakdown in air at atmospheric pressure by Nd:yttrium–aluminum–garnet Q-switched nanosecond laser pulses was studied from the nanosecond to the millisecond time scale by shadowgraphy and interferometry techniques. The results were modeled with a gasdynamic code with good agreement. It was possible to simultaneously model the whole evolution of the plasma, the shock wave, and the hot core air. The shock wave velocity was determined to be ⩾60 km s−1 at 20 ns. The plasma temperature was found to reach about 1.7×104 K at 1 μs and the hot core air temperature was determined to be <103 K at 100 μs. This letter presents an experimental work that extends the study of laser induced plasmas to millisecond time scales.

Effects of Laser Induced Shock Waves on Metals

Abstract: A high-energy, pulsed laser beam combined with suitable transparent overlays occn generate pressure pulses of up to 6 to 10 GPa on the surface of a metal. The propogation of these pressure pulses into the metal in the form of a shock wave produces changes in the materials micro structure and properties similar to those produced by shock waves caused in other ways. This paper reviews the mechanism of shock wave formation, calculations for predicting the pressure pulse shape and amplitude, in-depth microstructural changes and the property changes observed in metals. These property changes include increases in hardness, tensile strength and fatigue life. The increases in fatigue life appear to result from significant residual surface stresses introduced by the shock process.