The photo-oxidation of EPDM rubber: Part III—Mechanistic aspects and stabilization

The kinetics of the photo-oxidation of crude EPDM rubber has been studied in order to propose a mechanism for the sequence of reactions which occurs during the photo-degradation process. The presence of the unsaturation markedly affects the kinetics of the photo-oxidation of EPDM in comparison with that of EPM. We have also studied the stabilization effect of a hindered amine and a hindered phenol on EPDM and compared this with crude EPM rubber. These stabilizers showed poor efficiency, which is explained by the presence of impurities which act as sensitizers for the degradation of the crude rubber.     

Sugar cane bagasse lignin as stabilizer for rubbers: Part III—Styrene/butadiene rubber and natural rubber

The stabilizing effect of a natural antioxidant, sugar cane bagasse-lignin, on the photo-chemical, thermal and environmental degradation of styrene/butadiene rubber and of natural rubber has been studied. For natural rubber the stabilizer was investigated in various concentrations in the pure form and for styrene/butadiene rubber it was also studied in substitution for a hindered phenol in a commercially used formulation which includes a p-phenylenediamine. For the photo-degradation of natural rubber, stabilization becomes appreciable only above a stabilizer concentration of 5·0% whilst in thermal degradation a concentration of 1·0% is sufficient to increase the induction period by a factor of 3 in relation to pure rubber. For styrene/butadiene rubber the same effect occurs; a concentration of 2·0% increases the induction period for photo-degradation by a factor of 1·5 whilst 1·0% increases the induction period for thermodegradation by a factor of 26 in relation to the pure unstabilized rubber. Substitution of the hindered phenol by lignin in the commercial formulation increases the induction period for the thermal degradation by a factor of 6 in relation to the commercial sample. In the environmental ageing experiments the influence of the lower photo-stabilizing effect predominated over the strong thermostabilizing activity of the lignin for both rubbers.     

Sensible improvements induced by ionic liquids in the reaction of modified carbasugars with bases for the building of constrained carbanucleosides

Starting from racemic 4-hydroxy-4-methyl-2-cyclopentenone, a family of enantiopure carbanucleosides locked in the northern conformation has been synthesized. The use of ionic liquids was determinant in the last step resulting in a tangible increase of the yields and dramatic reduction of reaction times and volumes of organic solvents. To our knowledge, this is the first example of the use of ionic liquids in the coupling of carbasugars with heterocyclic bases.     

A convergence result for a vibro-impact problem with a general inertia operator

Nonlinear Dynamics - We consider a mechanical system with a finite number of degrees of freedom and non-trivial inertia matrix, submitted to a single perfect unilateral constraint. We assume that...     

Comparison of mean distance in superposed networks

In this paper, we consider the problem of the superposition of two networks in the structure of local telecommunication networks: the physical one, determined by the ways of the means of communication, and the interconnection one. We compare the mean-distance of the graphs associated to these two networks.     

2-nerves for bicategories

We describe a Cat-valued nerve of bicategories, which associates to every bicategory a simplicial object in Cat, called the 2-nerve. This becomes the object part of a 2-functor N : NHom → [Δ^op,Cat], where NHom is a 2-category whose objects are bicategories and whose 1-cells are normal homomorphisms of bicategories. The 2-functor N is fully faithful and has a left biadjoint, and we characterize its image. The 2-nerve of a bicategory is always a weak 2-category in the sense of Tamsamani, and we show that NHom is biequivalent to a certain 2-category whose objects are Tamsamani weak 2-categories. The hospitality of Macquarie University and the support of the Australian Research Council are gratefully acknowledged by S. Lack. The support of the Australian Research Council is gratefully acknowledged by S. Paoli.     

Magnetic field dependence of the specific heat of heavily doped n-type silicon

The low temperature specific heat of an n-type phosphorous doped silicon sample containing 5 × 10¹⁸ charge carriers/cm³ in zero magnetic field and in a magnetic field of 28.5 kGauss has been measured. Within the experimental accuracy of the experiments no magnetic contribution to the specific heat has been detected. This result is discussed in the light of recent E.S.R. experiments on the same impurity banded silicon sample.