Walk-regular divisible design graphs

A divisible design graph (DDG for short) is a graph whose adjacency matrix is the incidence matrix of a divisible design. DDGs were introduced by Kharaghani, Meulenberg and the second author as a generalization of $(v,k,\lambda )$ -graphs. It turns out that most (but not all) of the known examples of DDGs are walk-regular. In this paper we present an easy criterion for this to happen. In several cases walk-regularity is forced by the parameters of the DDG; then known conditions for walk-regularity lead to nonexistence results for DDGs. In addition, we construct some new DDGs, and check old and new constructions for walk-regularity. In doing so, we present and use special properties in case the classes have size two. All feasible parameter sets for DDGs on at most $27$ vertices are examined. Existence is established in all but one case, and existence of a walk-regular DDG in all cases.     

Quantum molecular dynamics study of the Su-Schrieffer-Heeger model

A quantum molecular dynamics technique is presented to compute the static and dynamic properties of a system of fermions coupled to classical degrees of freedom. The method is employed to investigate the properties of the Su-Schrieffer-Heeger model, an electron-phonon model which is often used to describe the electronic properties of conjugated polymers. The Su-Schrieffer-Heeger model is shown to exhibit a metal-insulator transition away from half-filling. In the metallic phase the electron transport is collective and shows the features characteristic of Fröhlich conductivity. Our simulation data for the optical absorption at room-temperature are in good agreement with experiment.     

β-Fluorinated proline derivatives: potential transition state inhibitors for proline selective serine dipeptidases

Three new types of β-fluorinated proline derivatives were synthesized as potential transition state inhibitors for proline selective serine dipeptidases. The fluorophosponate derived from protected proline was tested as a Wadsworth-Horner-Emmons reagent for the synthesis of fluoro-olefin-containing pseudodipeptides.     

Self-dual, not self-polar

The smallest number of points of an incidence structure which is self-dual but not self-polar is 7. For non-binary structures (where a “point” may occur more than once in a “block”) the number is 6.     

Quasi-symmetric designs related to the triangular graph

LetT _m be the adjacency matrix of the triangular graph. We will give conditions for a linear combination ofT _m, I andJ to be decomposable. This leads to Bruck-Ryser-Chowla like conditions for, what we call, triangular designs. These are quasi-symmetric designs whose block graph is the complement of the triangular graph. For these designs our conditions turn out to be stronger than the known non-existence results for quasi-symmetric designs.     

Liquid chromatographic assay for the protease inhibitor atazanavir in plasma

Atazanavir is the most recently introduced protease inhibitor for the suppression of the anti-human immunodeficiency virus. A sensitive and selective reversed-phase liquid chromatographic assay for this drug in human plasma has been developed and validated. Atazanavir was isolated from a 500 microL plasma sample using liquid-liquid extraction with dichloromethane. After evaporation and reconstitution of the extract the sample was analysed using liquid chromatography and ultraviolet detection at 280 nm. In the evaluated concentration range (44-4395 ng/mL atazanavir), intra-day precisions were < or =7% and inter-day precisions were < or =14%. Accuracies between 96 and 106% were found. The lower limit of quantification was 44 ng/mL with an intra-day precision of 7%, an inter-day precision of 14% and an accuracy of 87%. There was no interference from 32 tested potentially co-administrated drugs and metabolites. The usefulness of the assay was demonstrated for samples obtained from an HIV-infected patient treated with atazanavir.