Coupled thermogravimetry/photometry for polymer ignition studies

Evaluation of the ignition properties of a polymeric system is difficult due to the large number of properties that must be measured and correlated. This problem is complicated by the fact that these properties are often measured using different test under widely varying conditions. We have developed an attachment for a commercial thermogravimetric analyzer that detects ignition and measures smoke generation. Since thermogravimetry provides information concerning the char yield and the decomposition kinetics, four important measures of polymer ignition are thus simultaneously obtained. The use of this apparatus is illustrated on polymeric systems.     

Structural and Mechanical Properties of Polybutadiene-Urethane Elastomer

A series of polyurethanes based on hydroxyl-terminated polybutadiene (HTPBD) and cured with Bis-(-hydroxy ethyl)-terephthalate (BHET) have been synthesized. Mechanical, microscopic and kinetic studies were carried out to elucidate the structure-property relationships from the view point of phase separation. We studied the effects of the polymerization method, varying the hard to soft segment ratio and changing the hard-segment domain structure on the properties of the subject materials. Dynamic mechanical responses showed that the Tg of the soft-segment at ?60°C was independent of the hard-segment content, which indicates that the copolymers were well phase separated. A higher hard-segment content brought about a slight increase in the modulus, a moderate increase in the tensile strength and a decrease in the ultimate elongation. The size of the hard-segment domain, as estimated from electron micrographs, ranged from 60A to 100A. It was observed that a higher content of hard-segments causes an increase in the hard-segment domain size. In addition, a general survey of the reaction rate indicated that BHET is less reactive with diphenyl methyl diisocyanate (MDI) than with HTPBD.     

A comparison between pp and pp diffractive peaks at and beyond ISR energies

Although a substantial difference between pp differential cross section at ISR energies and $\text{p}\text{p}$ differential cross section at SPS energy has been reported, we demonstrate that both differential cross sections, at least up to |t| ～ 1.2 GeV², can be satisfactory accounted for within the usual eikonal model in which the diffractive component is crossing even. Thus at a given ultra high energy, there is no suggestive evidence for a difference between pp and $\text{p}\text{p}$ diffractive peaks.     

Nitrosation of alkenes by nitric oxide: Crystal structures of bis-(1-nitroso-2-nitro-cyclohexane) and bis-(1-nitroso-2-nitro-1-phenylethane)

The reaction of nitric oxide with alkenes has been studied. Crystal structures have been established by X-ray diffraction studies for bis-(1-nitroso-2-     

Cluster molecular orbitals and an orbital symmetry view of solid phase transitions in perovskites

The molecular orbitals, normalization constants and energies of the M₈(O_h), M₄(T_d) and M₆(O_h) clusters are derived and tabulated through the d-atomic orbitals. A vector method, adapted to computer application, is devised to compute s, p and d overlap between variously oriented orbitals at atoms that do not have co-directional local axes. Mixing of σ, π and δ orbitals to give the same irreducible representation is also included. As illustrations, the orbitals of Sr₈, La₈, TiO₆ and AlO₆ clusters are computed by the Mulliken—Wolfsberg and Helmholz approximations. During solid phase transitions in the perovskite structures of SrTiO₃ and LaAlO₃, the TiO₆ octahedron rotates about the C₄ axis whereas the AlO₆ octahedron rotates about the C₃ axis. This difference is explained qualitatively in terms of the relative symmetries of the cluster HOMOs and LUMOs using the second-order Jahn—Teller effect. Allusions are made to the application of this cluster symmetry approach to other systems.     

The first exit time and ruin time for a risk process with reserve-dependent income

This paper investigates the first exit time and the ruin time of a risk reserve process with reserve-dependent income under the assumption that the claims arrive as a Poisson process. We show that the Laplace transform of the distribution of the first exit time from an interval satisfies an integro-differential equation. The exact solution for the classical model and for the Embrechts–Schmidli model are derived.