Total pressure

About: Total pressure is a research topic. Over the lifetime, 5199 publications have been published within this topic receiving 66658 citations.

A method of measuring the pressure produced in the detonation of high explosives or by the impact of bullets

Abstract: If a rifle bullet be fired against the end of a cylindrical steel rod, or some gun-cotton be detonated in its neighbourhood, a wave of pressure is transmitted along the rod with the velocity of sound. If the pressure in different sections of the rod be plotted at any instant of time, the abscissae being distances along the rod, then at a later time the same curve shifted through a distance proportional to the time will represent the then distribution of pressure. Also the same curve represents the relation between of the pressure across any section of the rod and the time, the scale of time being approximately 2 inches for 10 -5 seconds. In particular it represents the relation between the total pressure applied to the end of the rod and the time, and the length of the curve represents the total duration of the blow. If the rod be divided at a point a few inches from the far end, the opposed surfaces of the cut being in firm contact and carefully faced, the wave of pressure travels practically unchanged through the joint. At the free end it is reflected as a wave of tension, and the pressure at any section is then to be obtained by adding the effects of the pressure wave and the tension wave. At the joint the pressure continues to act until the head of the reflected tension wave arrives there. If the tail of the pressure wave has then passed the joint the end-piece flies off, having trapped within it the whole of the momentum of the blow, and the rest of the rod is left completely at rest. The length of end-piece which is just sufficient completely to stop the rod is half the length of the pressure wave, and the duration of the blow is twice the time taken by the pressure wave to travel the length of the end-piece. Further, it is easy to see, as is proved in detail in the paper, that the momentum trapped in quite short end-pieces will be equal to the maximum pressure multiplied by twice the time taken by the wave in traversing the end-piece. Thus by experimenting with different lengths of end-pieces and determining the momentum with which each flies off the rod as- the result of the blow it is possible to measure both the duration of the blow and the maximum pressure developed by it. This is the basis of the experimental method described in the paper. A steel rod is hung up as a ballistic pendulum, and the piece is held on to the end by magnetic attraction.

Variation of the Oxidation Rate of Silicon Carbide with Water‐Vapor Pressure

Abstract: Chemically vapor deposited silicon carbide (CVD SiC) was oxidized at temperatures of 1000°-1400°C in H2O/O2 gas mixtures with compositions of 10-90 vol% water vapor at a total pressure of 1 atm. Additional experiments were conducted in H2O/argon mixtures at a temperature of 1100°C. Experiments were designed to minimize impurity and volatility effects, so that only intrinsic water-vapor effects were observed. The oxidation kinetics increased as the water-vapor content increased. The parabolic oxidation rates in the range of 10-90 vol% water vapor (the balance being oxygen) were approximately one order of magnitude higher than the rates that were observed in dry oxygen for temperatures of 1200°-1400°C. The power-law dependence of the parabolic oxidation rate on the partial pressure of water vapor at all temperatures of the study indicated that the molecular species was not the sole rate-limiting oxidant. The determination of an activation energy for diffusion was complicated by variations in the oxidation mechanism and oxide-scale morphology with the partial pressure of water vapor and the temperature.

Alkali Element Chemistry in Cool Dwarf Atmospheres

Abstract: The equilibrium thermochemistry of the alkali elements in cool dwarf atmospheres is investigated as part of a comprehensive set of chemical equilibrium calculations. The abundances of all important gases and the condensation temperatures of all initial condensates for Li, Na, K, Rb, and Cs are calculated as a function of pressure and temperature. Also discussed is the chemistry of refractory elements such as Al, Ca, Cr, Fe, Mg, Si, Ti, and V. The calculation of the alkali element and refractory element chemistry can help to constrain pressure and temperature conditions in dwarf atmospheres. A relative temperature scale is developed and compared to recent observations of the alkali elements in late-type dwarfs and brown dwarfs, such as the DENIS objects and Gliese 229B. The calculations show (1) Atomic Li gas abundances are expected to be lower than the bulk Li abundance because LiOH gas (at high total pressure) or LiCl gas (at low total pressure) form in very cool objects. Observations of only monatomic Li are therefore not a good test for the substellar nature of very cool objects. (2) The observations of atomic Cs in Gliese 229B can be understood by considering the distribution of Cs between atomic Cs and CsCl gases. (3) Liquid condensates, which may form solutions with complex compositions, form at higher pressures, and need to be considered in further atmospheric structure and opacity modeling.

Radiation-Dominated Disks are Thermally Stable

Abstract: When the accretion rate is more than a small fraction of Eddington, the inner regions of accretion disks around black holes are expected to be radiation dominated. However, in the α-model, these regions are also expected to be thermally unstable. In this paper, we report two three-dimensional radiation magnetohydrodynamic simulations of a vertically stratified shearing box in which the ratio of radiation to gas pressure is ~10, and yet no thermal runaway occurs over a timespan 40 cooling times. Where the time-averaged dissipation rate is greater than the critical dissipation rate that creates hydrostatic equilibrium by diffusive radiation flux, the time-averaged radiation flux is held to the critical value, with the excess dissipated energy transported by radiative advection. Although the stress and total pressure are well correlated as predicted by the α-model, we show that stress fluctuations precede pressure fluctuations, contrary to the usual supposition that the pressure controls the saturation level of the magnetic energy. This fact explains the thermal stability. Using a simple toy model, we show that independently generated magnetic fluctuations can drive radiation pressure fluctuations, creating a correlation between the two while maintaining thermal stability.