Induction period of a two-component aerosol of liquid oxidizer and propellant

The problem of self-ignition of a two-component aerosol consisting of uniformly mixed drops of an oxidizer and a propellant reacting in the gas phase is considered. The process of self-ignition of such an aerosol is divided into two stages: vaporization of aerosol components and subsequent chemical heating of the mixture. An approximate analytical formula is derived, for the period of self-ignition of a two-component aerosol. This formula takes into account the differences in thermophysical characteristics of aerosol liquids, mass concentrations, sizes of the drops of aerosol components, and the difference between the initial temperature of these drops and the initial temperature of the gas phase. The calculation results for the self-ignition period obtained using this analytical formula and the results of numerical solution of the problem in the zero-dimensional formulation coincide within 20% in a wide range of the governing parameters of the problem. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 15–21, November–December 1999.     

An Electrophysiological Comparison of Voltage-Gated Proton Channels,Other Ion Channels,and Other Proton Channels

Voltage-gated proton selective channels occupy an ill-defined region between “normal” ion channels and a variety of proton-conducting pathways inside proteins, including, but not limited to, membrane-bound proteins. Voltage-gated H⁺ channels closely resemble other voltage-gated ion channels in their voltage- and time-dependent gating, but differ in their extreme selectivity, their miniscule single-channel conductance, and the high activation enthalpy for conduction. Furthermore, in contrast with the “multiple occupancy” hypothesized to account for aspects of permeation through other ion channels, it seems unlikely that H⁺ channels can be occupied by more than one proton at a time. Voltage-gated H⁺ channels functionally resemble other proton-conducting pathways in proteins, but until their structure has been determined, this similarity will remain speculative. The present restriction to functional measurements is less of a handicap than might be expected—the history of ion channel research shows that deductions based on electrophysiological measurements often closely predict the eventually determined structure. Existing evidence supports the idea that protons permeate the membrane through voltage-gated H⁺ channels by hopping across a hydrogen-bonded chain that consists of at least some amino acid side groups in addition to water molecules.     

Processing of short fiber reinforced polypropylene. II: Statistical study of the effects of processing conditions on the impact strength

Within the general objective of analyzing and modeling the processability of polypropylene and of its short fiber composites, a statistical analysis of the relationship between processing conditions and final properties has been performed applying modern experimental design concepts. In order to gather the largest amount of information with a manageable quantity of experiments, Taguchi methods were used for the design of injection molding tests and for the analysis of experimental fiber orientation and impact strength results. Two levels of each variable of interest were selected, and the results of the analysis not only show which of the processing variables are predominant but also show that interactions between variables must be taken into account. The approach presented here offers a viable route to the scaling-up of the injection molding process through the reduction of the number of variables in the prediction of the processing behavior of semicrystalline polymers and of their composites.     

Mass transfer between a liquid and an array of discs in a cylindrical container. Part I: Pumped flow or rotation alone

This paper deals with average mass transfer between a liquid and both sides of discs arranged as baffles in a cylindrical container. The case of pumped flow alone through the stationary arrangement is first considered; the radial flow between the pairs of stationary discs is divergent and convergent successively. In other experiments, there is no pumped flow, but the discs are rotated between the stationary annular discs. The mass transfer coefficients are measured electrochemically for different geometrical and hydrodynamic conditions and the results are empirically correlated. The behaviour of corresponding surfaces involving a convergent or a divergent radial flow is discussed.     

FTIR study of thermal cyclization processes in the synthesis of polyetherimidazopyrrolones

An FTIR method was used to investigate the thermal cyclization process in synthesis of polyetherimidazopyrrolones from dietherdianhydrides and 3,3′-diaminobenzidine. It was concluded that the highest degree of cyclization to imidazopyrrolone structure is observed in the case of polymer with bisphenol A group having electron-donating character after dynamic heating, though for the all polyether-imides investigated even at 320°C cyclization are not complete.     

Advances in calculating thermally induced stresses in nonlinear viscoelastic materials

Temperature change can build up tensile stresses into thermoplastic materials, if their thermal expansion is hindered. This paper describes how to calculate those stresses. Because thermoplastic materials are time dependent with respect to temperature and strain, a nonlinear viscoelastic material model is necessary for the prediction of thermal stresses. This paper presents a numerical model that is able to predict thermally induced stresses in dependency on the load history. The calibration as well as the numerical procedures are described. The model is evaluated with a semicrystalline high density polyethylene (HDPE). Finally, a simulation of a screwed joint reveals the importance of this modeling for a more effective use of thermoplastics in the future.     

Flow induced deformation of dual-phase continuity in polymer blends and alloys. Part I

A hypothesis for formation of bi-continuous phase structures in immiscible polymer blends is proposed. It is based on the observation that a critical volume fraction φ_cr for the dual continuity of phases may be calculated considering the geometry of the dispersed phase. The knowledge of the form of discrete domains at the volume fractions φ < φ_cr and the probability that two close neighbor domains will form a strongly fused connection are sufficient to calculate φ_cr. Furthermore, it can be predicted that φ_cr should increase with stabilization of the interface. A comparative study showed that an addition of block copolymer may narrow the volume fraction range where bi-continuous phase structures are formed. Both annealing in the molten state and shearing history influence the measured φ_cr for the formation of bi-continuous phase structure in amorphous immiscible polymer blends.     

Studying the mechanism of the interaction between silicon nitride, oxygen, and nitrogen in heating and the processes of defect formation in Si3N4 — gas systems

The method of precision thermal massometry is used to study the interaction between silicon nitride, oxygen, and nitrogen in nonisothermal heating at 300 -1300 K and a partial gas pressure of 19,998.3 Pa (150 Torr). The behavior of Si₃N₄ heated in forevacuum is studied. A special computer analysis of the experimentally obtained dependencies has provided kinetic equations for analyzing and determining the mechanisms of these processes and computing their activation energy. The experimental data are used for creating a hypothesis that the nitrogen sublattice of Si₃N₄ is dispersed before the beginning of its interaction with oxygen and nitrogen.     

High-strength ceramics from Zr02

Specimens of powder fabricated by codeposition of zirconium and yttrium nitrates with the using special dry ing techniques and regranulation by the method of hot isostatic pressing have been tested in air allowing for the laws of compaction of granulated powder at a final firing temperature of about 1500°C. The resulting ma terial had the following properties: a density p = 5.91 g/cm (98% of the theoretical value), an ultimate bend ing strength a = 1100 MPa, and a crack resistance K = 19.5 MPa . rn A set of the specimens was sub jected to hot isostatic pressing after natural sintering and exhibited the following properties: p = 6.08 g/cm = 1400 MPa, K = 17.5 MPa · m^1/2.     

New silicate-based powders for fire protection of thermoplastics

A new, intumescent powdered silicate additive for plastics (polyethylene and polyvinyl chloride) has been investigated that gives improved flame retardancy. Cone calorimeter evaluations of the compounds of polymer/powder show reduction in peak rate of heat release, total heat release, and rate of mass loss. The effects of various polymer/powder ratios and powder particle sizes on the fire protection performance are shown. The morphology of this powder and the polymer/powder compounds before and after combustion is observed. A fire-protection mechanism is discussed that suggests the importance of an interpenetrating char structure.