Naval Reactors Physics Handbook. Volume 3: The Physics of Intermediate Spectrum Reactors

The present volume has been prepared for persons with some knowledge of the physics of nuclear reactors. It is intended to make available the accumulated physics experience of the Knolls Atomic Power Laboratory in its work on intermediate spectrum reactors. Only those portions have been selected which were deemed to be most useful and significant to other physicists concerned with the problems of reactor design. The volume is divided into four parts which are more or less independent of one another. Part 1 (Chaps. 2--9), Investigation of Reactor Characteristics by Critical Assemblies, reflects the importance of the properties of critical assemblies and of the techniques for obtaining experimental information about such assemblies. Part 2 (Chaps. 10--20), Reactivity Effects Associated with Reactor Operation, details the use of both critical assemblies and reactor theory to make and test predictions of the manner in which the reactivity of an intermediate power reactor will vary during operation. Part 3 (Chaps. 21--26), Heat Generation and Nuclear Materials Problems, considers how reactor heat generation is spread out in space and time, and what nuclear effects result from the presence of beryllium or sodium in the reactor. Part 4 (Chaps. 27--38), Reactor Kinetics and Temperature Coefficients, relates to the transient or near-transient behavior of intermediate reactors

Least squares fit of thermal data for fissile nuclei

Since our previous paper was written, we have learned of one new set of measurements that would have been included had we known of it: Gwin, Spencer and Ingle's measurement of the nu-prompt ratios of the four fissile materials with respect to /sup 252/Cf. Their recently published paper reports revised final results for /sup 233/U, /sup 235/U and /sup 239/Pu and includes a measurement on anti nu/sub p/(241)/anti nu/sub p/(252) that was not attempted previously. In some of the fitted results reported here, we have replaced their earlier 1978/1981 values by the final 1984 set. The replacement has appreciable effect on some of the parameters. Another revised value that we have used here is Axton's 1984 revision (3.7509 +- 0.0107) of his 1982 /sup 252/Cf anti nu/sub p/ value (3.744 +- 0.021). The effect of including the revised result is not appreciable. Thermal constants for /sup 233/U, /sup 235/U, /sup 239/Pu, and /sup 241/Pu are given. 11 references. (WHK

An Analysis of Pharmaceutical Experience with Decades of Rat Carcinogenicity Testing: Support for a Proposal to Modify Current Regulatory Guidelines

Data collected from 182 marketed and nonmarketed pharmaceuticals demonstrate that there is little value gained in conducting a rat two-year carcinogenicity study for compounds that lack: (1) histopathologic risk factors for rat neoplasia in chronic toxicology studies, (2) evidence of hormonal perturbation, and (3) positive genetic toxicology results. Using a single positive result among these three criteria as a test for outcome in the two-year study, fifty-two of sixty-six rat tumorigens were correctly identified, yielding 79% test sensitivity. When all three criteria were negative, sixty-two of seventy-six pharmaceuticals (82%) were correctly predicted to be rat noncarcinogens. The fourteen rat false negatives had two-year study findings of questionable human relevance. Applying these criteria to eighty-six additional chemicals identified by the International Agency for Research on Cancer as likely human carcinogens and to drugs withdrawn from the market for carcinogenicity concerns confirmed their sensitivity for predicting rat carcinogenicity outcome. These analyses support a proposal to refine regulatory criteria for conducting a two-year rat study to be based on assessment of histopathologic findings from a rat six-month study, evidence of hormonal perturbation, genetic toxicology results, and the findings of a six-month transgenic mouse carcinogenicity study. This proposed decision paradigm has the potential to eliminate over 40% of rat two-year testing on new pharmaceuticals without compromise to patient safet

Actin-based dynamics during spermatogenesis and its significance*

Actin can be found in all kinds of eukaryotic cells, maintaining their shapes and motilities, while its dynamics in sperm cells is understood less than their nonmuscle somatic cell counterparts. Spermatogenesis is a complicated process, resulting in the production of mature sperm from primordial germ cell. Significant structural and biochemical changes take place in the seminiferous epithelium of the adult testis during spermatogenesis. It was proved that all mammalian sperm contain actin, and that F-actin may play an important role during spermatogenesis, especially in nuclear shaping. Recently a new model for sperm head elongation based on the acrosome-acroplaxome-manchette complex has been proposed. In Drosophila, F-actin assembly is supposed to be very crucial during individualization. In this mini-review, we provide an overview of the structure, function, and regulation characteristics of actin cytoskeleton, and a summary of the current status of research of actin-based structure and movement is also provided, with emphasis on the role of actins in sperm head shaping during spermiogenesis and the cell junction dynamics in the testis. Research of the Sertoli ectoplasmic specialization is in the spotlight, which is a testis-specific actin-based junction very important for the movement of germ cells across the epithelium. Study of the molecular architecture and the regulating mechanism of the Sertoli ectoplasmic specialization has become an intriguing field. All this may lead to a new strategy for male infertility and, at the same time, a novel idea may result in devising much safer contraception with high efficiency. It is hoped that the advances listed in this review would give developmental and morphological researchers a favorable investigating outline and could help to enlarge the view of new strategies and models for actin dynamics during spermatogenesis