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Xsophe, a Computer Simulation Software Suite for the Analysis of Electron Paramagnetic Resonance Spectra -[45 refs.]. -(GRIF-FIN, M.; MUYS, A.; NOBLE, C.; WANG, D.; ELDERSHAW, C.; GATES, K. E.; BURRAGE, K.; HANSON, G. R.; Mol. Phys. Rep. 26 (1999) 60-84; Dep.

The application of the Nesbet algorithm to the full iterative solution of the two-dimensional master equation for thermal unimolecular reactions is presented. This leads to an efficient algorithm for computing thermal rate coefficients in the falloff regime for reactions such as simple fission dissociations, radical-radical recombinations, and ion-molecule reactions wherein microcanonical dissociation rate coefficients are sensitive to both the vibrational energy and the angular momentum of the excited species.

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The large deflection theory of circular cross-section elastic rods is used to consider the writhing of long straight rods subjected to tension and torque, such as undersea cables, and to closed loops with inserted twist, such as DNA supercoils.The writhed shape of the long straight rod under tension and torque is easily generated by twisting a piece of string with the fingers and consists of three separate parts: a balanced-ply region, a free end loop, and two tail regions. The solution for the rod shape in each of the regions is found. The results are then joined together to ensure continuity of the position and tangent vectors of the strand centreline through the introduction of point forces and moments at the points where the strands enter and exit the balanced ply. The results of the model are consistent with simple experiments on long braided rope.The writhed shape of the closed loop with twist inserted between the ends prior to closure is modelled as a balanced ply joined to two end loops. The analysis combines the mechanics solution with the conservation of topological link to provide a simple formula which quantitatively predicts the approximate shape and helix angle of the supercoil. The results are in good agreement with simple experiments on rope and with available data on DNA supercoils.

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An RRKM/master equation model is constructed for the isomerization of cyclopropene. It is shown how the dense matrix of the master equation operator can be reduced to a banded form by a combination of diffusion equation approximation and equation rearrangement. The lowest eigenvalues and eigenvectors of the master equation, which are sufficient for simulation purposes, are rapidly found using shift and invert Lanczos based methods.