The Monte Carlo method has been applied to calculate the solubilities (gas-solid equilibria) of high-boiling compounds (aromatic compounds, higher alcohols, and higher fatty acids) in supercritical fluids. Supercritical fluids were treated as single site molecules, and high-boiling compounds were treated as multisite molecules. The solubilities of aromatic isomers in supercritical carbon dioxide can be quantitatively distinguished by a group contribution site model without any binary interaction parameters. The structures of supercritical carbon dioxide around aromatic isomers are found to be different because of the screen effect of the substituents. The radial distribution functions of supercritical fluids and mean-square end-to-end separations for chain molecules have been reported as fundamental knowledge of the microstructure of chain molecules in the supercritical fluid phase.
After an overview of the formulation of hydrocodes applied to the numerical simulation of the shock and pressure waves in solid, liquid and gas phases of materials, several examples of hypervelocity impact and explosion analyses are shown and discussed partly as compared with corresponding experimental results.
In powder forming processes, the behaviour of powders during compaction, such as the mechanisms of density increase, density distribution, evolution of anisotropy, the shape of compacts in isostatic compaction, etc. significantly influence the quality of the products, dimensional and geometrical accuracy and material consumption. Further, the compacts that have been compacted at room temperature are subject to a sintering process; they undergo dimensional and geometrical change during the process; these are affected by the previous compaction process and density distribution. In recent years, the demand has been increasing for accuracy in the dimensions and shapes of products. Simulation of compaction behaviour of powders is, thus, of great importance for near net shape production. To simulate the behaviours of powders or granular materials, there are two approaches: one is to treat the powder based on continuum mechanics, and the other is to observe the movement of individual particles. In this article, we shall overview the state of the art regarding both types of simulation.
A computational-physics approach to design and prediction of hypothetical BCN heterodiamonds is reviewed. A probable heterodiamond BC2N structure that can be obtained from the compression of graphitic BC2N at low temperature is proposed using first-principles calculations. The structure, which has a large bulk modulus comparable to that of diamond as well as a wide band gap, can also be synthesized from a superlattice of graphite and hexagonal BN monolayers, suggesting that we could design a variety of polytypes.
A stress distribution of pressure media in a high pressure apparatus, the flat belt type, was estimated by the rigid plastic method. Since it was so difficult to estimate the stress distribution of that primarily, because of the complicated inner structure of the pressure media, we tried to estimate stress distribution in a diamond anvil cell that had a simple structure. Various kinds of pressure media, copper, pyrophyllite and salt, were used to study the effect of friction factors. The estimated stress distribution of copper in a diamond anvil cell was quite similar to the observed one, when the friction factor was supposed to be a constant at any inner pressure. On the other hand, the estimated stress distribution of pyrophyllite became equal to the observed one, when the friction factor was supposed to be proportional to the 3rd power of an inner pressure. Finally, the estimated stress distribution of the pressure media in the high pressure apparatus could be equal to the observed one using the supposition of the friction factor being proportional to the 3rd power of an inner pressure.
In this report, a technique of single-crystal X-ray diffraction measurements under high pressures, using a diamond-anvil-cell with helium gas as an inert and hydrostatic pressure-transmitting medium, is introduced. The technique has been applied to three-dimensional halogen-bridged mixed-valence gold complexes, Cs2AuIAuIIIX6 (X=Cl, I) to investigate the mixed-valence state and the crystal structure under high pressures up to 18 GPa and 7. 5 GPa, respectively. The pressure dependences of the unit cell parameters indicate that structural phase transitions occur from tetragonal to cubic at 12. 5 GPa for the Cl-bridged complex, and from tetragonal to monoclinic at 6. 0 GPa for the I-bridged complex. The Cl-bridged complex in the higher pressure phase has a space group, Pm3m and the cubic Perovskite-type structure.
Singlet oxygen, lO2 (lΔg), which is the lowest electronically excited state of the oxygen molecule, is quenched by various compounds. In this article, the pressure effects on the physical quenching of lO2 (lΔg) by solvent molecules and amines, and also on the chemical reactions of lO2 (lΔg) with furans and tetramethylethylene (TME) (ene reaction) in liquid solution are reviewed. For these systems, the quenching mechanism is described.
Biocalorimetry is one of the powerful and convenient tools to evaluate microbial activities under high pressure. The method is mainly based on the fact that the heat evolved is strictly proportional to the metabolic activity, and the magnitude of calorimetric signal is employed as an index to express the biological activities. This method was adopted in order to investigate the thermotolerance of heat- and pressure-shocked yeast. The effects of non-reducing disaccharide trehalose on the stress response of yeast were also studied by a colony counting method and calorimetry. The biostimulation effect of a He-Ne laser was used for the recovery of yeast activity under high pressure up to 100 MPa. At 50 MPa and 30°C, the growth of unirradiated yeasts was inhibited entirely, however, the viable cell numbers of irradiated ones were increased and the rate of the increase in number of viable cells corresponded to that of the inrradiated ones at 0. 1 MPa.
The paper presents the results of experiments for determination of response of spherical shells having load-bearing layer from fiber glass under radially symmetrical inner explosive loading. We carried out assessment of dynamic strength of two shell types with diameter of 500 mm, which differed in the scheme of fiber glass layer coiling. It was demonstrated that a shell with more even thickness (of 15-20 mm) of load-bearing fiber glass layer has significant advantage. Such a sheath has approximately twofold reserve of strength during explosion of a charge equal in energy to 1. 4 kg of trinitrotoluene in its geometrical center. It has been found that transition from one-axial strains, which are realized under explosive loading of a cylindrical shell, to two-axial strains, when spherical shells are used, does not change the value of limiting strains of fiber glass (on the destruction threshold). This value is determined by limiting strains of a glass thread. It is equal to 4-5 %. Tested spherical shells from fiber glass reinforced by steel layer allow to obtain record high value of the explosion-proofness property, i. e. relation between the high-explosive charge mass, where explosion of this high-explosive charge is confined inside of the sheath cavity, and mass of this shell. It is equal to 3-6 %.