No abstract

No abstract

A symmetry rule for predicting molecular shapes which is based on the second-order Jahn-Teller effect has been applied to the predictions of bond distortions in a number of nonalternant hydrocarbons in their ground and electronically excited states. In spite of the very crude approximation that only the lowest-lying excited state plays a dominant role in determining the energetically most favorable nuclear displacement, a fairly clear-cut criterion for molecular-symmetry reduction was obtained. The actual types of the most soft bond distortions, determined by examining the two-center components of transition densities, are in good agreement with the results of variable bond-length SCF MO calculations and available experimental results. The problem of symmetry reductions possible in large cyclic polyenes C4n+2H4n+2 is briefly discussed.

No abstract

No abstract

No abstract

A heat transfer and flow visualization experiment was conducted with a one-fifth scale model simulating a dry shielded canister (DSC) with 24 PWR spent fuel assemblies in order to elucidate the heat transfer characteristics and the velocity distribution for natural convection inside a DSC filled with air or water at atmospheric pressure. It was found that the average heat transfer coefficients were proportional to the onefourth power of the Rayleigh number despite the complicated geometry inside the DSC. Flow patterns inside the DSC were visualized clearly through a digital image processing system. The velocity distributions inside the DSC were obtained quantitatively from the Particle Tracking Velocimetry. In comparison with the results of a two-dimentional thermal hydraulic analysis, computed flow patterns were similar to the experimental results and the computational temperature distributions on the sleeve surfaces agreed well with the experiments within S%, except at the top point of the center gap. It was also found that the difference in the heat transfer coefficient was within 25% for air as the working fluid, while a satisfactory agreement was not obtained when water was the working fluid.

No abstract