Thermodynamics of the quasi-static growth of Griffith cracks

Restrictions on the quasi-static extension, or healing, of Griffith cracks are developed in the framework of irreversible thermodynamics. It is emphasized that thermodynamics requires that (G ? 2γ)ι ? 0, where ι is crack speed, G the Irwin energy release rate, and 2γ the work of reversible separation of the surfaces to be fractured. Implications for ‘lattice trapping’ models of cracks and for thermally-activated crack motion are discussed, as are the effects on crack growth and healing of a surface-reactive environment, in which case γ must be given a definition appropriate to adsorption-altered surface properties.     

Oscillatory disruptions in the Alcator C tokamak

Periodic disruptions were observed which persisted for as long as 400 ms during plasma discharges. Soft X-ray emissions, T_e, n_e, impurity radiation and plasma position showed the pulsations. The abrupt collapse in X-ray signal (1–2 ms; period ∽10 ms) encompassed a large fraction of the plasma cross section. Plasma conditions associated with the onset of this pattern are examined.     

Elastic scattering of electrons by hydrogen molecules at intermediate energies

Several quantum mechanical calculations of differential cross sections for elastic scattering of electrons by H₂ are compared with the recent experiments by Williams.     

Ab initio studies of the structures and force fields of ketenimine and related molecules

Theoretical equilibrium geometries for ketenimine, aminoacetylene and ethynol have been obtained using the MP3/6-31G** ab initio method. Empirical scaling factors have been introduced to estimate the rotational constants A_o, B_o and C_o. In addition the complete harmonic force fields for ketenimine, ketene and diazomethane have been computed, normal coordinate analyses have been performed and the quartic centrifugal distortion constants estimated.     

A study of the reaction K−p→Λπ+π− at c.m. energies in the range 1.65 to 1.72 GeV

Results are presented of a study of the reaction K^?p→Λπ⁺π^? in the c.m. energy region of 1.65 to 1.72 GeV. Dalitz plots indicate that the reaction proceeds primarily through the intermediate states Σ^?(1385)π⁺ and Σ^?(1385)π⁺, but the resonance bands intersect inside the kinematic ellipse and a simple quasi-two-body interpretation is not possible. Legendre coefficients are presented for the angular distributions of the Λπ⁺ and Λπ^? sub-systems in the overall c.m. frame. Analogous coefficients as suggested by Deler and Valladas, which describe the angular distribution of the final three-body state are also presented.