The critical velocity of mode-I fracture in a non-linear lattice in the absence of viscosity

The high-velocity regime of mode-I fracture is interesting, especially because of the instability of the steady-state propagating crack to a more complex dynamics (such as micro-branching). In this article, we study mode-I fracture in a non-linear lattice in the absence of a viscous force. In earlier study, we had studied the effects of the bond potential parameters, including Kelvin viscous force, on the macroscopic behavior of the crack, including the high velocity regime instability. Recently, a new study has appeared using a very similar non-linear force but claiming quite different results. In this article, we seek to discover an explanation of these differences. We find that they do not result from the viscosity present in our previous study. At least part of the differences are attributable, rather, to the very wide system used in the recent study, which leads to long transients and a failure to probe the steady-state behavior. Our results confirm our previously claimed lack of agreement with the Yoffe prediction for the critical velocity of a steady-state crack, and neither do they match the predictions of Gao’s model.     

Rearrangement of 3-Acyl Derivatives of L-Ascorbic Acid

Abstract

Evidence of rearrangement of 3-acyl derivatives of ascorbic acid to 2-acyl derivatives has been found for carbon and phosphorus acyl groups. The observations are consistent with intramolecular rearrangement through a cyclic intermediate in which the acyl group is bonded to both the 2- and 3-oxygen atoms of ascorbic acid. A rate of rearrangement has been measured for the 3-diphenylphosphinate ester. Calculated results indicate an increase in negative atomic charge at O-2 in the 3-acyl esters but a decrease in the charge of O-3 in the 2-acyl esters.     

Verhalten der Chroms?ure und der Uebermangans?ure gegen die niederen Oxydationsstufen des Eisens, Arsens und Antimons

Ohne Zusammenfassung     

A study of cole diagrams of some alkali halide relaxation maxima appearing at temperatures above 100°C

Relaxation maxima occurring at a frequency of 1 kHz above 100°C in pure LiF, KCl, NaCl and CaCl₂-doped NaCl were investigated and an interesting fact, the dependence of the relaxational loss angle as well as the resp. dielectric constant on the sample thickness, was found and discussed.     

Einen Apparat zur fractionirten Destillation unter vermindertem Druck

Ohne Zusammenfassung