Search for Physics Beyond the Standard Model

We survey some recent ideas and progress in looking for particle physics beyond the Standard Model, connected by the theme of Supersymmetry (SUSY). We review the success of SUSY-GUT models, the expected experimental signatures and present limits on SUSY partner particles, and Higgs phenomenology in the minimal SUSY model.Comment: Standard Latex file. 18 pages without figures. (Calls to postscript figure files blocked out. Full 32 page version with 37 in-text figures available via regular mail.) MAD/PH/75

The atomistic structure and energy of nascent dislocation loops

An harmonic lattice theory is used, in conjunction with Mura's theory of eigendistorsions, to study the structure and energetics of nascent dislocation loops in face-centred-cubic (FCC) crystals. An analytical expression for the activation energies of such loops is derived. The results obtained herein indicate that thermal activation of small dislocation loops is possible at high stress levels such as those found in the vicinity of a crack tip. The implications of these results in understanding phenomena such as the brittle-ductile transition are discussed

Experiment K-6-17. Structural changes and cell turnover in the rats small intestine induced by spaceflight

The purpose of this project was to test the hypothesis that the generalized, whole body decrease in synthetic activity associated with microgravity conditions of space flight as evidenced by negative nitrogen balance and muscle atrophy (Nicogossian and Parker, 1982; Oganov, 1981), as well as inhibited lymphocyte proliferation (Bechler and Cogoli, 1986), would be evident in cells characterized by a rapid rate of turnover. As a model, researchers chose to study the turnover of mucosal cells lining the jejunum of the small intestine, since these cells are among the most rapidly proliferating in the body. Under normal conditions, epithelial cells that line the small intestine are continually produced in the crypts of Lieberkuhn. These cells migrate out of the crypts onto intestinal villi, are progressively pushed up the villus as new crypt cells are formed, and ultimately reach the tip of villi where they are then descquamated. In rats, the entire process, from initial proliferation in crypts to desquamation, takes approximately 2 days (Cairnie et al., 1965; Lipkin, 1973). In this study, researchers determined the mitotic index for mucosal cells lining the proximal, middle, and distal regions of the jejunum in rats from three treatment groups (synchronous control, vivarium control and flight), and measured the depth of the crypts of Lieberkuhn and the length of villi present in each of the three jejunal regions sampled

Quasicontinuum Models of Interfacial Structure and Deformation

Microscopic models of the interaction between grain boundaries (GBs) and both dislocations and cracks are of importance in understanding the role of microstructure in altering the mechanical properties of a material. A recently developed mixed atomistic and continuum method is extended to examine the interaction between GBs, dislocations and cracks. These calculations elucidate plausible microscopic mechanisms for these defect interactions and allow for the quantitative evaluation of critical parameters such as the stress to nucleate a dislocation at a step on a GB and the force needed to induce GB migration.Comment: RevTex, 4 pages, 4 figure

Delta Effects in Pion-Nucleon Scattering and the Strength of the Two-Pion-Exchange Three-Nucleon Interaction

We consider the relationship between P-wave pi-N scattering and the strength of the P-wave two-pion-exchange three-nucleon interaction (TPE3NI). We explain why effective theories that do not contain the delta resonance as an explicit degree of freedom tend to overestimate the strength of the TPE3NI. The overestimation can be remedied by higher-order terms in these ``delta-less'' theories, but such terms are not yet included in state-of-the-art chiral EFT calculations of the nuclear force. This suggests that these calculations can only predict the strength of the TPE3NI to an accuracy of +/-25%.Comment: 13 pages, 2 figures, uses eps