Propagation rules of shock waves in confined space under different initial pressure environments

In this paper, an initial pressure adjustable explosion vessel was developed, and the effect of negative pressure, positive pressure (0.2–1.8 atm) different initial ambient pressure on the explosive shock wave generated by the explosion of explosives was studied. The relationships between the specific impulse, shock wave velocity, the amount of explosive gas products and the ambient pressure were analyzed for different initial pressure environments. It was found that: the overpressure of the blast shock wave decreases with the initial ambient pressure of the explosion, and there exists a negative pressure environment with a dramatic pressure decrease near 0.6 atm, defined as the super-sensitive negative pressure P_cr. The propagation velocity of an explosive wave increases with a decrease in the ambient pressure, and the propagation velocity at a pressure of 1.8 atm is four times less than the velocity at a pressure of 0.2 atm. The production of explosive gas products did not change. The greater the initial pressure of the environment where the explosive is located, the smaller the ratio of the gas generated by the explosion to the initial force gas in the explosion vessel is, and the greater the impact on the propagation of shock waves is. The maximum attenuation of the first specific impulse i₁ is 72.97% and the maximum attenuation of the second specific impulse i₂ is 72.39%. The experiments provide reference data for high-altitude military confrontation, high-altitude weapons and ammunition development, and deep-earth protection engineering.

Biogenesis of plasma lipoproteins in rat hepatoma McA-RH7777: importance of diffusion-mediated events during cell growth

Cultured McA-RH7777 rat hepatoma cells actively synthesize and secrete plasma lipoproteins. However, synthesis of [14C]triglyceride declines monotonically throughout the early growth period and remains low in postconfluent cultures; and net secretion of [14C]triglyceride is 10-fold more efficient in logarithmically growing cultures than in postconfluent cultures. Secretion of apolipoproteins associated with very low density and low density lipoproteins is selectively reduced in postconfluent cultures. The temporal reductions in [14C]triglyceride production are related more strongly to increasing cell concentration (cells/cm3 medium) than to increasing cell density (cells/cm2 growth surface). We have allowed cells to grow either retained within small circular corrals or unrestricted in culture dishes. When seeded at equal density (10(4) cells/cm2) but at one-fifth the cell concentration, corralled cells synthesize twice as much [14C]triglyceride per cell after 2 and 4 d, and are 10 times as efficient in [14C]triglyceride secretion by 6 d of growth, as noncorralled cells. When seeded at equal cell concentration (10(5) cells/dish) but at 5 times the cell density, corralled cells are only 20% less efficient at [14C]triglyceride synthesis and secretion than noncorralled cells. Conditioned medium depresses synthesis and secretion efficiency of [14C]triglyceride. Orotic acid exposure also inhibits synthesis of [14C]triglyceride and secretion of certain [35S]apolipoproteins in early cultures, but it has no significant effect on late cultures. We conclude that diffusion-mediated events are important regulators of triglyceride and apolipoprotein production in growing rat hepatoma cells, but that events associated with formation of cell-to-cell contacts play a minor role in regulation of plasma lipoprotein biogenesis.