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Sunflower detonation  [PDF]
A. Kasimov,S. Korneev
Physics , 2012,
Abstract: In this fluid dynamic video we present simulations of converging two-dimensional detonation in a radially expanding supersonic flow of ideal reactive gas. The detonation is found to be unstable and leads to formation of characteristic cellular patterns. Without any obstacles in the flow, the detonation keeps expanding radially. To retain the wave within a bounded region, we place a number of rigid obstacles in the flow so that the detonation shock stands some distance toward the center from the obstacles. This leads to generation of reflected shock waves from the obstacles which help the detonation wave to remain at a finite distance from the source. The cellular structure of detonation creates beautiful patterns of shock waves and contact discontinuities within and after the reaction zone. The patterns often resemble a sunflower, hence the name of "sunflower detonation".
Spallation caused by the diffusion and agglomeration of vacancies in ductile metals  [PDF]
Yuanjie Huang
Physics , 2013,
Abstract: In this work, the spallation processes in the ductile metals are systematically discussed in theory. By employing the phase transition theory and non-equilibrium transport theory, the spallation processes of ductile metals under dynamic loading may be mainly determined by the diffusion and agglomeration of generated vacancies. And through the theoretical analysis on the dynamic spallation processes, it is found that (1)the spallation critical behaviors exist; (2)both the damage evolution rate and the void growth velocity in the spallation planes are monitored by the grain sizes, the tensile strain rate and the temperature of the metal after shocking, i.e., a larger grain size and tensile strain rate and higher temperature will cause a larger damage evolution rate and void growth velocity; (3)there exists the characteristic size for the voids and the characteristic stress on the void boundary, which are dependent of vacancy excitation energy and the average volume occupied by the metal atom; (4)both the stress and temperature close to the void are high and may cause the melting, and they decrease quickly as the distance away from the void increases; (5)the plastic zone surrounding the formed voids is obtained and found to be governed by the characteristic stress; (6)the void growth in the spallation processes may arise from the agglomeration of vacancies rather than the emitting of dislocations. Most of the theoretical results are novel and obtained first. And they are found to be in agreement with the experimental results and the simulated results.
Deflagration to Detonation  [PDF]
A. M. Khokhlov
Physics , 1999,
Abstract: Thermonuclear explosions of Type Ia supernovae (SNIa) involve turbulent deflagrations, detonations, and possibly a deflagration-to-detonation transition. A phenomenological delayed detonation model of SNIa successfully explains many observational properties of SNIa including monochromatic light curves, spectra, brightness - decline and color - decline relations. Observed variations among SNia are explained as a result of varying nickel mass synthesised in an explosion of a Chandrasekhar mass C/O white dwarf. Based on theoretical models of SNIa, the value of the Hubble constant H_o \simeq 67km/s/Mpc was determined without the use of secondary distance indicators. The cause for the nickel mass variations in SNIa is still debated. It may be a variation of the initial C/O ratio in a supernova progenitor, rotation, or other effects.
Sweeping by a tame process  [PDF]
Aris Daniilidis,Dmitriy Drusvyatskiy
Mathematics , 2014,
Abstract: We show that any semi-algebraic sweeping process admits piecewise absolutely continuous solutions, and any such bounded trajectory must have finite length. Analogous results hold more generally for sweeping processes definable in o-minimal structures. This extends previous work on (sub)gradient dynamical systems beyond monotone sweeping sets.
Technology of Porous Tantalum Production  [PDF]
Yu. Zh. Tuleushev, V. N. Volodin, Е. А. Zhakanbaev, V. N. Lisitsin, A. A. Migunova, A. S. Suleymenova
World Journal of Nano Science and Engineering (WJNSE) , 2016, DOI: 10.4236/wjnse.2016.62006
Abstract: Ion-plasma sputtering and codeposition of ultrafine Ta and Cd particles on a moving substrate were used to prepare the solid solutions, in particular, the alloys with up to 66.2 at.% Cd in the form of coatings. In vacuum heat treatment cadmium evaporates at 700°C from cadmium based solid solutions resulting in formation of a porous tantalum with a highly developed surface. The prepared tantalum-based materials assume the technological application of the investigation results.
Equation of state of HE detonation products  [cached]
Nadykto B.A.
EPJ Web of Conferences , 2011, DOI: 10.1051/epjconf/20101000008
Abstract: Computational analysis of steady-state HE detonation parameters is possible if one knows the equation of state of detonation products and thermal energy released at the Jouget point during detonation. There are a number of equations of state of HE detonation products that result from different assumptions concerning detonated material conditions. The paper considers one more version of the equation of state for HE detonation products.
A Spallation Model for 44Ti production in Core Collapse Supernovae  [PDF]
Amir Ouyed,Rachid Ouyed,Denis Leahy,Prashanth Jaikumar
Physics , 2012,
Abstract: Current cc-SN models predict overproduction of 44Ti compared to observations. We present a model for an alternative channel where a cc-SN explosion is followed by a neutron star detonation (Quark Nova or QN), resulting in a spallation reaction of SN ejecta that produces 44Ti. We can achieve a 44Ti production of ~ 10^-4 Msun with our model under the right time delay between the QN and the SN. Our model also produces unique signals not found in standard, cc-SN nucleosynthesis models. Some of these unique signals include a significantly large production of 7Be and 22Na. We discuss some of these signals by analyzing the late time light curve and gamma spectroscopy of our model.
On probabilistic aspects in the dynamic degradation of ductile materials  [PDF]
Herve Trumel,Francois Hild,Gilles Roy,Yves-Patrick Pellegrini,Christophe Denoual
Physics , 2009, DOI: 10.1016/j.jmps.2009.07.001
Abstract: Dynamic loadings produce high stress waves leading to the spallation of ductile materials such as aluminum, copper, magnesium or tantalum. The main mechanism used herein to explain the change of the number of cavities with the stress rate is nucleation inhibition, as induced by the growth of already nucleated cavities. The dependence of the spall strength and critical time with the loading rate is investigated in the framework of a probabilistic model. The present approach, which explains previous experimental findings on the strain-rate dependence of the spall strength, is applied to analyze experimental data on tantalum.
Refinement of the equation of state of tantalum  [PDF]
Agnes Dewaele,Paul Loubeyre,Mohamed Mezouar
Physics , 2004, DOI: 10.1103/PhysRevB.69.092106
Abstract: The volume of tantalum versus pressure has been accurately measured up to 101 GPa by single-crystal x-ray diffraction, with helium as pressure transmitting medium. Slight deviation from previous static determinations is observed. Discrepancy with reduced shock-wave and ultrasonic data supports recent doubts about the calibration of the ruby pressure scale. Finally, first principle calculations of the literature show a positive curvature in $P(V)$ relative to the experimental data, even with a modified pressure scale.
Marek Woliński,Piotr Wolański
Bulletin of the Institute of Heat Engineering , 1986,
Abstract: The paper presents results of studies of influence of relatively large chemically inert particles dispersed in a gaseous mixture on transition to detonation processes and on detonation combustion.It has been found out that these particles cause acceleration of transition from deflagration to detonation, and reduce the detonation velocity.A physical model of the transition to detonation and propagation of the detonation under such conditions has been presented. Also mathematical model allowing determination of velocity of the detonation wave has been proposed.
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