This is a study of a type of fluid dynamics dominated by a "one-body" dissipation mechanism expected to be relevant for an assembly of particles whose mean free paths are comparable to or larger than the size of the system. Two simple dissipation formulae are derived, one relevant for the process of nuclear fission and the other for nuclear collisions. The resulting predictions, free of adjustable parameters, are compared quantitatively with measured fission-fragment kinetic * This work was done with partial support from the U. S. Energy Research and Development Administration.

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Relating seismic anisotropy to mantle flow requires detailed understanding of the development and evolution of olivine crystallographic preferred orientation (CPO). Recent experimental and field studies have shown that olivine CPO evolution depends strongly on the integrated deformation history, which may lead to differences in how the corresponding seismic anisotropy should be interpreted. In this study, two widely used numerical models for CPO evolution-D-Rex and VPSC-are evaluated to further examine the effect of deformation history on olivine texture and seismic anisotropy. Building on previous experimental work, models are initiated with several different CPOs to simulate unique deformation histories. Significantly, models initiated with a preexisting CPO evolve differently than the CPOs generated without preexisting texture. Moreover, the CPO in each model evolves differently as a function of strain. Numerical simulations are compared to laboratory experiments by Boneh and Skemer (2014). In general, the D-Rex and VPSC models are able to reproduce the experimentally observed CPOs, although the models significantly over-estimate the strength of the CPO and in some instances produce different CPO from what is observed experimentally. Based on comparison with experiments, recommended parameters for D-Rex are: M* 5 10, k* 5 5, and v 5 0.3, and for VPSC: a 5 10-100. Numerical modeling confirms that CPO evolution in olivine is highly sensitive to the details of the initial CPO, even at strains greater than 2. These observations imply that there is a long transient interval of CPO realignment which must be considered carefully in the modeling or interpretation of seismic anisotropy in complex tectonic settings.

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Calculated angular and energy distributions of the a particles in long-range a-particle fission are presented. The distributions were obtained from calculated a-particle trajectories based on a three-point-charge model for the scissioning nucleus. The calculation is two dimensional, and spontaneous fission (no preferred direction) is assumed. This reduces the number of free variables of the system to seven (except for the mass ratio). The system is thus parametrized in terms of the following initial dynamical variables: the initial distance between the fission fragments, the initial position of the a particle (not restricted to the fission axis), and the initial momenta of the a particle and one of the fragments. Reasonably good agreement with the experimental distributions is obtained. The calculations support the view that the scission point moves closer to the light fragment as the mass ratio increases. They also support the assumption that at the moment of scission the fission fragments have already attained a substantial part of their final velocity.

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