Time Variation Of Density Research Articles

Electron Bulk Surface Density Variability in Ionosphere during Quiet Days at Low Latitudes

This work deals with electron surface density time variation in ionosphere region. The study uses international reference ionosphere (IRI) model for investigation. Total Electron Content (TEC) parameter is carried out at different levels in the F2-layer of ionosphere. The study takes place at Ouagadougou station (12,4°N and 358,5°E), in West Africa. Quiet time periods of solar cycle 22 are considered. This study considers only the maximum and minimum phases of solar cycle 22. The five quietest days of the characteristic months in each season are used in the study. Seasonal time profiles of ionosphere parameters highlight relation between Total Electron Content (TEC) and Height of F2-layer (hmF2) in ionosphere region. The results found in this study correlate closely with parameters behavior previously found in other works.

Simulation of the compaction dynamics of Cu + Al2O3 powder mixture under impulse hot pressing

The compaction dynamics of Cu + Al 2 O 3 powder mixture under impulse hot pressing is simulated using a third-order dynamic system. The computer simulation has established the time dependence of the force induced by mechanical interaction between the impact machine and a heated porous blank, time variation in density, and root-mean-square strain rates and stresses in the matrix that forms the porous body. The phase trajectory of dynamic system from the beginning of compaction to the elastic recoil of the hammer block characterizes impact dynamics. The mechanical-thermal effect induced by bulk viscous flow and manifested itself as an increase in temperature of the porous body is determined. It is established that the shear viscosity of the porous body matrix shows a stronger dependence upon the initial impact velocity in comparison with the heating temperature. The activation energy of the matrix viscous flow is equal to 0.266 eV.

CFD simulation of homogenization in large-scale crude oil storage tanks

The homogenization time of two layers of crude oils obtained from different reservoirs in 19 000 m 3 floating roof storage tank is predicted using computational fluid dynamics (CFD). The tank equipped with a side-entry 0.65 m marine-type mixer. An in-house CFD code using Multiple Frame of Reference (MFR) and the renormalization group version (RNG) of k– ε turbulent model has been employed. The fluid region has been divided to 580 484 number of control volumes. The time variation of density at three sampling points in the tank has been compared with corresponding points in the model. The results show a good agreement.

Variation of the Density Observed during the Pressure-Induced Phase Transition of a Single Crystal of RbCl

Pressure dependence of the density of a large-size single crystal of RbCl was observed cyclicly up to 860 MPa at 294 K and 383 K. The hysteresis loop observed in the second cycle was overlapped with that in the first cycle. While clicking sound accompanying the discontinuous increase in density was produced in the forward transition both in the first and second cycles, no sound was detected in the reverse one. The time variations of density at constant pressure were observed, where the density was nearly constant in the forward transition at 294 K, whereas steady decrease was observed in the reverse transition. Separate mechanisms are proposed, that is the Martensite transition in the forward transition, and the nucleation and its growth in the reverse one. At higher temperatures the nucleation and its growth in the forward transition are also proposed.

Computer Controlled Rotational Molding of Liquid Silicone Polymer

Abstract Rotational molding in two axes has the advantage of producing hollow products. Previously, the inherent difficulty was in the production of objects with uniform thickness since the speed of the two primary axes are fixed and cannot be varied independently to take into account the changes in material properties such as its density and viscosity. With the advent of computers, it is now possible to control the thickness of the object accurately. This is made possible by creating an intelligent software which takes in the viscosity and density time variation of the polymer and using the flat plate withdrawal theory, computes the new speed for each axis. The relationship between rotational molding parameters and polymeric material properties for a solvent – silicone rubber system to produce a hand prosthesis is illustrated in this paper.

Molecular dynamics study on the liquid structures of BaB2O4 just after melting

Molecular dynamics simulations have been carried out with respect to the structural features of BaB 2 0 4 liquids prepared from the a and /3 phases. The simulated interference functions of each liquid are in fairly good agreement with recent experimental results. There were found several noticeable features in simulated liquids with regard to the time variations of density and structures. Memories of the original crystal structures are found in the liquid from the/3 phase with respect to the periodicity of the atomic configuration of (3030), but such a feature is less evident in the liquid from the a phase. A difference between the two liquids is also noticed in the ring structure formed by B-O bonding, in that the number of (-B-O-)5 rings increases only in the liquid obtained from the/3 phase.

Study of recombination — Processes in a late stage of a spark discharge

In this work the recombination processes in the stage of a decay of a spark discharge,burning in air under atmospheric pressure. have been examined. The time variation of density of ionized particles was described by the model of radiative — collisional plasma decay. Effective recombination coefficient was gained from the measured time dependence of the electron density, determined from the Stark spectral line widths.