Computer calculations of phase diagrams

The thermodynamic route of establishing phase diagrams is a relatively recent activity, considering that till about the fifties most phase diagrams were determined by the measurement of certain physical property or quantitative microscopy using light optics or x-ray diffraction. The thermodynamic formalism used by Kaufman and Bernstein is explained and illustrated with examples of the development of hypothetical binary phase diagrams. The calculation of ternary phase diagrams can begin with the binary phase diagram data as a first approximation. However, to calculate a reasonably accurate ternary phase diagram a certain amount of ternary solution data is necessary. Various empirical equations have been proposed in the literature to express ternary thermodynamic data. Calculation of simple ternary isothermal sections is illustrated with the examples of Mo-V-W and Cd-Sn-Pb systems. The numerical techniques which involve the differentiation of thermodynamic parameters with respect to composition get more involved with the number of components becoming 3 or more. A simpler approach has been applied recently to find the minimum position on the Gibbs free energy surface.     

Radiation sensitivity of successively irradiated generations of Tribolium castaneum (Herbst) (Coleoptera,Tenebrionidae), and Sitophilus oryzae (L.) (Coleoptera,Curculionidae)

Four populations of Tribolium castaneum (Herbst) and of Sitophilus oryzae (L.) were treated with 0 (control), 0·5, 1 or 2 krad of gamma radiation for 7 and 5 successive generations, respectively, and the adults from the subsequent unirradiated generation of each population were checked for fecundity. Groups of 6th generation T. castaneum and S. oryzae adults from each population were tested for resistance to acute radiation by exposure to doses of 16 and 50 krad followed by a check for mortality.No evidence of increased resistance to acute radiation exposures was found. Irradiated T. castaneum populations did not show significant decreases in mean survival time, but some significant decreases in life-span of irradiated S. oryzae populations were found.Fecundity of the 8th generation 0·5 krad T. castaneum was greater than that of the control population, but 1- and 2-krad populations did not show any difference in fecundity. Fecundity of the 6th generation S. oryzae population was not significantly different from that of the control, but 1- and 2-krad populations had significantly reduced fecundities. The test results indicated that possible accidental exposure of some insects to substerilizing doses during commercial radiation disinfestation is unlikely to bring about the development of radiation-resistant insect populations.     

On the dynamics of framed structures

The paper presents a comparison between the eigen-values of a structure obtained using the distributed mass-stiffness technique proposed by the author[l] and those obtained using a static stiffness matrix coupled with a mass matrix both of them based on the same shape function (consistent mass matrix). The paper also includes some suggestions for improving the results obtained using the latter method.     

Electron spin resonance linewidths of Cr3+ in magnesium oxide

Electron spin resonance linewidths of Cr³⁺ in single crystal MgO at 9 GHz and 35 GHz were examined experimentally and theoretically for a range of Cr³⁺ concentrations. In contrast to the behaviour expected from dipolar broadening the experimental peak-to-peak linewidth for the 1/2 to–1/2 transition, which had a value of about 0.5 mT at 293 K, was independent of both polar angle and concentration over the range from 800 p.p.m. Cr to 15 100 p.p.m. Cr. The calculated dipolar linewidths exceeded those observed by factors of over one hundred; the ratio of momentsM ₄ ^1/2 /M ₂ ^1/2 derived from the experimental data lay between 1.33 and 1.39 and the lineshapes were markedly Lorentzian. The data suggested that Cr³⁺ entered the lattice substitutionally, occupying magnesium sites, that the linewidths were determined by exchange narrowing over the whole concentration range examined and that the exchange energy, whose values lay between 4 GHz and 100 GHz, varied linearly with concentration.     

On the dynamics of plates using a beam-analog

The paper describes a beam-analog element which simulates both the static and dynamic behaviour of plates, with or without in-plane forces, using the same routine program. Typical examples of plate dynamics are used to demonstrate the accuracy and convergency of the anolog.     

Medium effects in hydrochloric acid solutions containing phosphoric acid at 25°C

The emf of the cell Pt, H₂ | HCl(m), phosphoric acid (M) | AgCl, Ag was measured at 25°C at various concentrations of HCl and phosphoric acid. The standard potential of the cell decreases with increase in phosphoric acid concentration. Values of the activity coefficient of HCl and medium effects are calculated. A comparison with the previously studied succinic, maleic and tartaric acid systems is given. The results are interpreted on the basis of the effect of the solutes on the structure of liquid water.