Synthesis,structural analysis,and self-assembly of phenylene ethynylene oligomers and their ?F, ?CF3, and ?CH3 substituted derivatives

Oligomers consisting of aromatic building blocks separated by alkynyl units were synthesized by Sonogashira cross-coupling of aryl halides with terminal acetylenes. Strong electron acceptors such as  F and  CF₃ and weak electron donors like  CH₃ were placed as substituents on one of the benzene rings. Acetyl-protected sulfhydryl groups were attached to one end of these molecules to promote their self-organization on gold surfaces. The electron-transport properties of such self-assembled monolayers (SAMs) are highly sensitive to the local order of the molecules in the solid state. Single crystals were analyzed by X-ray diffraction experiments that revealed structural details that could lead to a better understanding of the electron-transport properties. The unsymmetrical substitution of the aromatic rings by electron-active groups in the ortho-, meta-, or para positions resulted in changes of such molecular parameters as bonding and torsion angles and planarity. These parameters, in turn, can affect the angle of the molecular attachment to a gold substrate and the density of the resulting SAMs. Patterned SAMs of some of these molecules and comparison alkane thiols were obtained on gold by microcontact printing or flooding. The SAM thickness was determined by spectroscopic ellipsometry. Surface potential differences between adjacent SAMs or between SAMs and the gold substrate were measured by scanning surface potential microscopy under ambient conditions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 541–550, 2004     

A description of nitrogen-nitrogen bond in terms of charge distributions

A theoretical analysis of properties of the shared interactions between two neighbouring nitrogen atoms in a variety of compounds is presented, based on properties of charge distributions derived from 6-31 ⁺⁺G^** wave functions. Bond is characterized in terms of its bond order, bond ellipticity and the quantity of Laplacian of ρ at the bond critical point. The difference between the bond path angle and the corresponding geometrical angle provides a measure of the degree of relaxation for the charge density away from the geometrical constraints imposed by the nuclear framework. Comparisons have been made between the nitrogen-containing compounds and isoelectronic hydrocarbons. Values of the NN bond energies, based on the properties of NN bond interatomic surface, are determined in three schemes.     

On Strongly Interacting Internal Solitary Waves

The Cauchy problem and global well-posedness for a mathematical model of the strong interaction of two-dimensional, long, internal gravity waves propogating on neighboring pycnoclines in a stratified fluid have been studied by Bona, Ponce, Saut, Tom, and others. We show that global well-posedness occurs even when the initial data is rough.     

Neutron activation analysis of wear products in a Diesel engine fueled with coal-oil slurries

The technique described is a stable tracer method and has the advantage of eliminating the use of radioactive engine components during the wear tests. The results obtained clearly show that the use of these slurries comprising pulverized coal and fuel oil is not acceptable due to excessive wear rates.     

Partition theorems for subspaces of vector spaces

The principal result of this paper provides a nearly complete answer to the following question. For which cardinal numbers $\text{t}$, $\text{m}$, $\text{n}$, $\text{q}$ and $\text{r}$ is it true that whenever the $\text{t}$-dimensional subspaces of an $\text{n}$-dimensional vector space V over a field of $\text{q}$ elements are partitioned into $\text{r}$ classes, there must be some $\text{m}$-dimensional subspace of V, all of whose $\text{t}$-dimensional subspaces lie in the same class? This question is answered completely if $\text{r}$ ≤ $\text{N}$₀. The contributions of this paper are in the form of negative answers, since it turns out that all affirmative answers (which we have) were already known or easily deducible from known results.