Magneto-optical Cotton—Mouton effect of molecular oxygen. A comparison

Measurements of the magneto-optical Cotton—Mouton effect at 632.8 nm of O₂(³Σ) over a range of temperature (≈299–464 K) and pressure (up to 613 kPa) are reported and analysed. The study enables a useful comparison to be made of data obtained under different conditions by the two groups that have undertaken systematic measurements of this effect. Agreement between the experimental results and also the derived molecular properties is found to be satisfactory.     

Reduction of Entrained Hydroxy Species in Ormosil Films for Integrated Optics

Organically modified silicates (ormosils) have been viewed as possible materials for optical signal processing devices for communications networks. One significant problem obstructing their use in this application is the absorption of infrared light by hydroxy species (present for example in silanol groups (SiOH) and water) around the communications wavelengths (1310 and 1550 nm). We have investigated several ormosil compositions, synthesised via an aqueous sol-gel method, to determine if residual hydroxy groups can be removed more effectively via reducing the connectivity of the material by increasing the number of organic groups (such as Si—CH₃). Furthermore, we have investigated the effect of different inert atmospheres on the drying process. It was found that reducing the connectivity does promote the removal of hydroxy absorption, mainly via the condensation of residual silanol groups, but also by removal of residual water, depending on the other precursors in the system. It was also found that the drying atmosphere used (nitrogen or helium) had no effect on the drying process.     

Second harmonic generation and polar order in thin films of polyesters

A series of optically active main chain polyesters were synthesized by high temperature polycondensation from biphenolic azo chromophores with azobenzene-4,4'-dicarbonylchloride and 1,4:3,6-dianhydro-D-sorbitol ([!]_D²⁵=+42.5°). The second harmonic generation of the polyesters is studied in thin films. The polar order in films is determined from the UV-visible absorption spectra. The variation in SHG intensity with chiral monomer concentration is explained as a function of polar order. The polymers with chiral units showed good second harmonic efficiency. The intensity of second harmonic light (532 nm) increased with angle of incidence and indicated the polar order in the plane of the film. The SH signal also showed good temporal stability.     

On the local structure of doubly laced crystals

Let g be a Lie algebra all of whose regular subalgebras of rank 2 are type A₁×A₁, A₂, or C₂, and let B be a crystal graph corresponding to a representation of g. We explicitly describe the local structure of B, confirming a conjecture of Stembridge.     

The harmonic consistency index for the analytic hierarchy process

A new consistency measure, the harmonic consistency index, is obtained for any positive reciprocal matrix in the analytic hierarchy process. We show how this index varies with changes in any matrix element. A tight upper bound is provided for this new consistency measure when the entries of matrix are at most 9, as is often recommended. Using simulation, the harmonic consistency index is shown to give numerical values similar to the standard consistency index but it is easier to compute and interpret. In addition, new properties of the column sums of reciprocal matrices are obtained.     

Completely Simple Semigroups,Lie Algebras,and the Road Coloring Problem

Consider a semigroup generated by matrices associated with an edge-coloring of a strongly connected, aperiodic digraph. We call the semigroup Lie-solvable if the Lie algebra generated by its elements is solvable. We show that if the semigroup is Lie-solvable then its kernel is a right group. Next, we study the Lie algebra generated by the kernel. Lie algebras generated by two idempotents are analyzed in detail. We find that these have homomorphic images that are generalized quaternion algebras. We show that if the kernel is not a direct product, then the Lie algebra generated by the kernel is not solvable by describing the structure of these algebras. Finally, we discuss an infinite class of examples that are shown to always produce strongly connected aperiodic digraphs having kernels that are not right groups.     

Epimerization, diastereoselectivity and hemilability in dicationic chiral ruthenium complexes with bidentate (PS) bisphosphine monosulfide ligands

The binding of heterobidentate P^∧S ligands introduces metal-centered chirality to the planar chiral parent complex Ru(η⁶:η¹-NMe₂C₆H₄C₆H₄PCy₂)Cl₂. Observed diastereomeric ratios for the kinetic product vary dramatically depending upon ring size of the chelate formed with the P^∧S ligand. The complexes epimerize very slowly to thermodynamic product ratios that are substantially different from the kinetic product ratios.