Pyrolysis of vinyl and vinylidene fluoride polymers: Influence of prior γ-irradiation

Quantitative comparisons were made between the rates of thermal volatilization of several fluoropolymers before and after exposure to γ-radiation. The effects of γ-irradiation on poly(vinyl fluoride) and poly(vinylidene fluoride) were also investigated by swelling and sol-gel ratios. With both polymers as well as with polytrifluoroethylene, crosslinks occur predominantly, though there is an appreciable number of scissions. The rates of volatilization and char formation were enhanced by γ-radiation, whereas the previously studied polytrifluoroethylene did not produce more char upon irradiation, although radiation did accelerate its volatilization. It is believed that in polytrifluoroethylene the enhanced rates of volatilization occur by a different mechanism than in the case of the vinyl and vinylidene fluoride polymers.     

X-ray determination of the mean amplitudes of vibration and debye temperatures of some rare earth monochalcogenides

The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe).     

Euclidean ramsey theorems. I

The general Ramsey problem can be described as follows: Let A and B be two sets, and R a subset of A × B. For a?A denote by R(a) the set {b?B | (a, b) ?R}. R is called r-Ramsey if for any r-part partition of B there is some a?A with R(a) in one part. We investigate questions of whether or not certain R are r-Ramsey where B is a Euclidean space and R is defined geometrically.     

Size effect in the magnetic field dependence of nonequilibrium electron tunneling

The electron bottleneck in normal metal-insulator-metal tunnel junctions due to nonequilibrium effects has been investigated in the presence of a magnetic field. The observed results are due to a new geometrical size effect and are explained in an extension of our nonequilibrium theory.     

Atomgewichte

Ohne Zusammenfassung     

Which rational numbers are binding numbers?

The concept of the binding number of a graph was introduced by Woodall in 1973. in this paper we characterize the set F_n of all pairs (a, b) of integers such that there is a graph G with n vertices and binding number a/b that has a realizing set of b vertices.