Mechanism of isotope exchange reaction between methane and deuterium

The rate of CH₄ disappearance in a shock-heated CH₄:D₂:Ar = 9.70:9.86:80.44 mixture was monitored by coincidence absorption of the 2948 cm^?1 He-Ne laser line over the shockfront temperature range of 1900–2300K. Comparison with CH₄ pyrolysis results by means of computer simulations suggested that atom and free radical chains are responsible for the homogeneous D/H exchange reaction on CH₄. Additional simulations for the experimental conditions of previous single-pulse shock tube experiments led to the recognition of a high sensitivity of the exchange rate to trace amounts of hydrocarbon impurity and to the dissociation rate of CH₄.     

Synthesis of cyclic beta-amino acid esters from methionine, allylglycine, and serine

Here we report a versatile ring-closing metathesis-based approach to 5-, 6-, and 7-membered cyclic beta-amino esters starting with simple and readily available building blocks-methionine, allylglycine, and serine-where the nature of the amino acid determines the size of the carbocyclic ring.     

Considerations in the preparation of biological and environmental reference materials for use in the study of the chemical speciation of trace elements

Summary The role that information on chemical speciation can play in the selection of reference materials for the analysis of biological and environmental samples is reviewed. Some considerations that might go into the preparation of materials designed for chemical speciation studies are explored. Individual steps in the preparation of lyophilized serum and urine reference materials are examined in relation to changes that could occur in the chemical speciation of trace elements.     

Smart structures—The relevance of fiber optics

The concept of the smart structure integrates structural engineering, sensing, control systems, and actuation to provide a mechanical assembly that is capable of responding to its environment and/or loading conditions. The realization of the smart structure requires integration of skills in a variety of scientific and engineering disciplines ranging from mechanical engineering through materials science into signal processing, data analysis, sensing, and actuation. The sensing technology must have a number of key features of which the ability to take distributed measurements of various parameters throughout the structure is paramount. Therefore, fiber optics technology promises to have a significant role to play in the evolution of the smart structures concept. This article analyzes this role in detail, presents an assessment of the current state of the art in fiber optic technology related to smart structures, and presents a scenario for future developments.     

Infrared spectra,vibrational assignment,normal coordinate analysis and thermodynamic functions of tetracyanomethane

The infrared spectrum of tetracyanomethane in acetonitrile solution has been recorded and the full set of fundamental frequencies assigned. A normal coordinate analysis has been carried out and the values of the calculated force constants are compared with those of related molecules. Some thermodynamic functions have also been computed.     

Finite common coverings of pairs of regular graphs

The graph G is a covering of the graph H if there exists a (projection) map p from the vertex set of G to the vertex set of H which induces a one-to-one correspondence between the vertices adjacent to v in G and the vertices adjacent to p(v) in H, for every vertex v of G. We show that for any two finite regular graphs G and H of the same degree, there exists a finite graph K that is simultaneously a covering both of G and H. The proof uses only Hall's theorem on 1-factors in regular bipartite graphs.