Wiener Index of Hexagonal Systems

The Wiener index W is the sum of distances between all pairs of vertices of a (connected) graph. Hexagonal systems (HS's) are a special type of plane graphs in which all faces are bounded by hexagons. These provide a graph representation of benzenoid hydrocarbons and thus find applications in chemistry. The paper outlines the results known for W of the HS: method for computation of W, expressions relating W with the structure of the respective HS, results on HS's extremal w.r.t. W, and on integers that cannot be the W-values of HS's. A few open problems are mentioned. The chemical applications of the results presented are explained in detail.     

Peculiar Features of Reaction of 2-tert-Butoxy-5,6-benzo-1,3,2-dioxaphosphinin-4-one with Chloral. Steric Structure of 2-Chloro-3-trichloromethyl-6,7-benzo-1,4,2λ5-dioxaphopshepin-5-one 2-Oxide

The reaction of 2-tert-butoxy-5,6-benzo-1,3,2-dioxaphosphinin-4-one with chloral involves expansion of the six-membered heteroring to form 2-hydroxy-3-trichloromethyl-6,7-benzo-1,4,2⁵-dioxaphosphepin-5-one 2-oxide as a single diastereomer. The product was chlorinated with thionyl chloride to obtain (RS,SR)-2-chloro-3-trichloromethyl-6,7-benzo-1,4,2⁵-dioxaphosphepin-5-one 2-oxide.     

Wavelet processing of topographic high dynamic range images

For a 6H-SiC single crystal, experimental results of the digital processing of topographic images with various dynamic ranges are given. In this case, wavelet analysis was used. The images were obtained by x-ray topography based on the Borrmann effect and were presented in 8-, 16-, and 32-bit formats. It is shown that, on eliminating the experimental contrast granularity, 32-bit images turn out to be more convenient for decoding and contain more useful information about structure defects of a single crystal under study as compared to the 8- and 16-bit images. The wavelet analysis efficiency increases considerably for the digital processing of separate topogram fragments and depends on the choice of the region and the size of the reference image.     

Molecular visualization of conformation-triggered flow instability

A new type of flow fingering instability was observed in monolayer-thick polymer films as they spread on a solid substrate. Tracing the movement of individual molecules by atomic force microscopy enabled us to follow the development of the flow instability on the molecular level and to understand the underlying physical mechanism. The fingering instability was observed to be triggered by conformational changes of brushlike macromolecules in response to the pressure gradient driving the flow.     

Adsorption of polyelectrolytes at an oppositely charged surface

We develop a scaling theory of polyelectrolyte adsorption at an oppositely charged surface. At low surface charge densities, the thickness of the adsorbed layer is determined by the balance between electrostatic attraction to the charged surface and chain entropy. At high surface charge densities, it is determined by the balance between electrostatic attraction and short-range monomer-monomer repulsion. These different stabilizing mechanisms result in the nonmonotonic dependence of the layer thickness on the surface charge density.     

Synthesis of substituted 1-thia-3-aza-λ<Superscript>5</Superscript>-phosphacyclohex-2-ene

The addition of dimethylamine to O-phenyl 2-chloropropylisothiocyanatophosphonate afforded the six-membered cyclic product, viz., 1-thia-3-aza-4⁵-phosphacyclohex-2-ene.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1657–1659, August, 2004.