Dur previous volume 14 was devoted to an exposition of the topics of sensitivity analysis and uncertainty theory with its development and application in nuclear reactor physics at the heart of the discussion. In this volume, we return to our customary format as a selection of topics of current interest, authored by those working in the field. These topics range from the theoretical underpinnings of the (linear) Boltzmann transport equation to a resume of our ex­ pectations in what still may be thought of as twenty-first century technology, the world's fusion reactor program. In the first article of this volume, we have Protopop­ escu's analysis of the structure of the Boltzmann equation and its solutions for energy and space-dependent problems of an eigenvalue nature. There long has been a curious "folk history" effect in this area~ Wigner and Weinberg could de­ scribe it as "what was generally known was generally untrue". This account of the Boltzmann equation surely will show that a rigorous basis for our expectations of certain solutions can be well-founded on analysis. Ely Gelbard's review of the methods of determining diffusion-type parameters in complex geometries where simple diffusion theory would be welcome has required just as much rigor to determine how such modeling can be made accurate, although to a more immediate and practical purpose. The two articles can be seen as interesting contrasts, facets of the same underlying problem showing apparently different aspects of the same central core.

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Eigenvalue Problems for the Boltzmann Operator in Various Formulations.- I. Introduction.- II. The Role of Eigenvalues.- III. Various Forms of the Boltzmann Equation.- IV. Isotropic Scattering.- V. Pseudomodes and True "Shadowed" Modes.- VI. Anisotropic Scattering.- VII. Conclusions.- Acknowledgements.- References.- The Definition and Computation of Average Neutron Lifetimes.- Abstract.- I. Introduction.- II. Definitions.- III. Analysis.- IV. Specific Cases.- V. Approximate Expressions for Neutron Lifetimes.- VI. Summary.- References.- Nonlinear Nuclear Stochastic Theory.- Abstract.- I. Introduction.- II. Nonlinear Stochastic Phenomena in Nuclear Reactors.- III. Theoretical Treatment of Nonlinear Stochastic Effects.- IV. Concluding Remarks.- References.- Appendix I. Kummers's Confluent Hypergeornetric Function.- Appendix II. Nonlinear Transformation of Stochastic Variables.- Fusion Reactor Development: A Review.- Abstract.- I. Introduction.- II. Tokamaks.- III. Technology.- IV. Tokamak Reactor Studies.- V. Alternate Confinement Concepts.- VI. Commercialization Timetable.- References.- Streaming in Lattices.- I. Introduction.- II. Definition of Diffusion Coefficients.- III. Monte Carlo Computation of Diffusion Coefficients.- IV. Testing of Homogenized Diffusion Coefficients.- References.- Contributors.