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An experimental study was undertaken to examine two phenomena associated with a jet issuing from a forward-facing circular cylinder (with a length to outer radius ratio of 6.8) into a counterflow: (1) the effect of the counterflow on the internal velocity profile near the injector exit, and (2) the combined jet and counterflow influence on the external surface boundary layer profiles. Wind tunnel experiments, utilizing hot-wire anemometry, were conducted at very low jet-to-counterflow velocity ratios between 0 and 0.41 and Reynolds numbers based on cylinder outer diameter of 2.6×104 and 5.2×104. It was found that the flow at the internal location was negligibly affected by the counterflow, with the profiles exhibiting typical turbulent pipe flow behavior. However, close to the injector exit plane, the counter-flow accelerated the exiting jet in an annular region adjacent to the cylinder inner wall, creating a high velocity region which reversed direction upon exiting. The exit flow reversal around the lip of the cylinder was manifested downstream as an addition of momentum to the flow field. Boundary layer measurements were taken at seven streamwise locations along the upper surface of the cylinder. A dimensionless parameter constructed from both a traditional flat plate turbulent boundary layer scaling and a geometric curvature ratio was used to plot all data, which collapsed to a single curve at all locations in the absence of a jet, while in the presence of the jet, the only differences in the profiles were close to the surface. Independently of jet-to-counterflow velocity ratio, the boundary layer on the cylinder was seen to grow in the streamwise direction at a rate proportional to x25 rather than x45 as occurs with a turbulent boundary layer on a flat plate, even though the boundary layer height to curvature ratio was relatively low (≈ 1), and hence would have been expected to approximate flat plate behavior.

The photobiscyclization reaction of N-azomethine pyridinium derivatives was investigated and the final and intermediate photoproducts were isolated. The first step of the reaction involves dihydro intermediate self-trapping by a 1,5-sigmatropic proton shift.

The photophysics and photochemistry of N-amino-substituted pyridinium salts were investigated. Electron transfer from the amino group to the pyridinium ring takes place in the singlet excited state. The fluorescence quenching and photoreactivity of these compounds is conditioned by this process. Irradiation of N-aminopyridinium salts in solution leads to novel fused heterocycles or to triphenylpyridine, depending on the concentration of the initial compound. Free radical intermediates are involved in the photoreaction.

Les proprietes d'absorption et d'emission electroniques sont resumees et expliquees en fonction de la structure moleculaire des cations pyridinium - ont ete vus, en particulier, les processus photochimiques des sels (accent mis sur la cyclisation et l'effet, sur le mecanisme et la cinetique, des variations structurelles) ainsi que les processus photophysiques montrant un schema reactionnel general faisant intervenir une excitation et des relaxations photo-induites