Flash photolysis electron spin resonance and CIDEP studies of radicals derived from nitrogen heterocyclics. II. The photophysics and photochemistry of the methylpyrazines

Application of the CIDEP phenomenon is extended to the identification of the specific triplet energy levels which react to produce radicals in pyrazine and its methyl derivatives. Advantage is taken of the proximity of ³nπ and ³ππ states in which the opposite signs of the zero-field coupling constants cause triplet mechanism polarization of opposite phase in the derived radicals. The electronic natures of the radicals observed parallel those of the triplet states from which they are formed.     

Effect of ortho‐methylation on a bis(4‐cyanatocumyl)benezene low‐dielectric resin

A synthesis procedure for and characterization of a tetra‐ortho‐methyl substituted three‐ringed cyanate ester monomer, 4,4′‐[1,3‐phenylenebis(1‐methylethylidene)]bis[2,6‐dimethyl]phenylcyanato, and the corresponding cured resin are described with comparative characterization of the resin analogue without the ortho‐methyl substitutents. The othro‐methylation lowered the dielectric from 2.64 to 2.59 at 1 GHz and from 2.64 to 2.48 GHz at 15 GHz, whereas the tan δ was not significantly affected. Other physical properties also affected included a 40 °C decrease in the glass‐transition temperature, an increase in the thermal‐expansion coefficients, and a reduction in thermogravimetric stability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 60–67, 2003     

Ordered clusters and dynamical states of particles in a vibrated fluid

Fluid-mediated interactions between particles in a vibrating fluid lead to both long range attraction and short range repulsion. The resulting patterns include hexagonally ordered microcrystallites, time-periodic structures, and chaotic fluctuating patterns with complex dynamics. A model based on streaming flow gives a good quantitative account of the attractive part of the interaction.     

Prediction of stress in a linear viscoelastic solid strained while cooling

A simplethermoelastic method is proposed, and justified, for predicting stresses arising during cooling of a linearviscoelastic solid. It is equivalent to representing the material by an array of spring-switch thermoelastic elements. The final stress resulting from an increment of strain is calculated using isochronal modulus data applying to the temperature at which the strain was applied, modified to accommodate temperature dependence of the limiting moduli. The method is exact for a material whose relaxation times and limiting moduli scale uniformly with change in temperature, with time-temperature shift factora _T obeying the Arrhenius equation, cooled such that reciprocal absolute temperature is linear in time. For other cooling sequences it is useful as an approximation. In particular, it assists the computational prediction of stresses arising during cooling in polymer processes.     

Über einige Derivate von [2,2]-Paracyclophan mit physiologischer Aktivität

Zusammenfassung Die Synthese von 4-Dialkylaminoacetyl-[2,2]-paracyclophanen, der entsprechenden Aminoalkohole, von 1-(2-N,N-Diäthylamino-äthoxy)-1-(4-[2,2]-paracyclophan), und 4-([2,2]-Paracyclophanyl)-penicillin wird beschrieben. Eine biologische Auswertung zeigt, daß die Eigenschaften dieser Substanzen, im Vergleich zu denen analoger bekannter Benzolderivate, qualitativ den Erwartungen entsprechen.

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The synthesis of 4-dialkylaminoacetyl-[2,2]-paracyclophane derivatives and of the corresponding amino alcohols is described, as well as that of 4-([2,2]paracyclophanyl)-penicillin. Evaluation of these compounds demonstrated that their biological properties are qualitatively like those of analogous known benzene derivatives.

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Herrn Professor Dr.Hermann Bretschneider zum 60. Geburtstag in Freundschaft gewidmet.

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This study was supported, in part, by a Grant, NB-01445, from the Institute of Neurological Diseases and Blindness, National Institutes of Health, U. S. Public Health Service.     

Atoll decompositions of graphs

An island decomposition of a graph G consists of a set of vertex-disjoint paths which cover the vertex set of G. If the endpoints of the paths are mutually nonadjacent, then we have an atoll decomposition. We characterize graphs requiring two paths in an island decomposition yet having no atoll decomposition. Results are given relating atoll decompositions to cutpoints and Hamiltonian blocks.