Polarized Lambdas in the Current Fragmentation Region

Data on the nucleon spin structure suggests that the $u$ (and $d$) quark distributions in the $\Lambda$ hyperon may be polarized. If this correlation carries over into fragmentation, then the study of polarized $\Lambda$'s in the current fragmentation region of deep inelastic lepton scattering will be a sensitive probe of nucleon spin structure. $\Lambda$ production by polarized electrons from unpolarized targets can search for this correlation. If it is signficant, $\Lambda$ production by unpolarized electrons from longitudinally and transversely polarized targets can probe the $u$-quark helicity and transversity distributions in the nucleon. We review what is known about quark polarization in the $\Lambda$, summarize electroproduction of polarized $\Lambda$s, and estimate the sensitivity to quark polarizations in the nucleon. We also describe polarization phenomena associated with vector meson electroproduction that can be observed in the same experimental regime.Comment: Revised manuscript corrects minor errors and typos. Revised figure with proper labels. 12 pages, revtex, one ps figure, BoxedEPS.tex macros include

SPIN - Progress and Prospects

I review the progress in fundamental spin physics over the past several years and the prospects for the future. The progress is striking and the prospects are excellent.Comment: A Talk Presented at SPIN2000, October 30, 2000; 21 pages, 13 figures, using aiproc.sty, BoxedEPS macros; email correspondence to [email protected]

Comment on the relation between the nonadiabatic coupling and the complex intersection of potential energy curves

Simple relations are discussed that provide a correspondence between the complex intersection of two potential surfaces and the nonadiabatic coupling matrix element between those surfaces. These are key quantities in semiclassical and quantum mechanical theories of collision induced electronic transitions. Within the two state approximation, the complex intersection is shown to be directly related to the location and magnitude of the peak in the nonadiabatic coupling. Two cases are considered: the avoided crossing between two potential surfaces; and the spin orbit interaction due to a P-2 halogen atom. Comparisons are made between the results of the two-state model and the results of ab initio quantum chemical calculations

Solar Tests of Aperture Plate Materials for Solar Thermal Dish Collectors

If a malfunction occurs in a solar thermal point-focus distributed receiver power plant while a concentrator is pointed at the Sun, motion of the concentrator may stop. As the Sun moves relative to the Earth, the spot of concentrated sunlight then slowly walks off the receiver aperture, across the receiver face plate, and perhaps across adjacent portions of the concentrator. Intense local heating by the concentrated sunlight may damage or destroy these parts. The behavior of various materials under conditions simulating walk-off of a parabolic dish solar collector were evaluated. Each test consisted of exposure to concentrated sunlight at a peak flux density of about 7000 kW/square meter for 15 minutes. Types of materials tested included graphite, silicon carbide, silica, various silicates, alumina, zirconia, aluminum, copper, steel, and polytetrafluoroethylene. The only material that neither cracked nor melted was grade G-90 graphite. Grade CS graphite, a lower cost commercial grade, cracked half-way across, but did not fall apart. Both of these grades are medium-grain extruded graphites. A graphite cloth (graphitized polyacrylonitrile) showed fair performance when tested as a single thin ply; it might be useful as a multi-ply assembly. High purity slipcast silica showed some promise also