The Southern Vilnius Photometric System. IV. The E Regions Standard Stars

This paper is the fourth in a series on the extension of the Vilnius photometric system to the southern hemisphere. Observations were made of 60 stars in the Harvard Standard E regions to increase a set of standard stars.Comment: 6 pages, TeX, requires 2 macros (baltic2.tex, baltic4.tex) included no figures, to be published in Baltic Astronomy, Vol 6, pp1-6 (1997

Gapless finite-TT theory of collective modes of a trapped gas

We present predictions for the frequencies of collective modes of trapped Bose-condensed $^{87}$Rb atoms at finite temperature. Our treatment includes a self-consistent treatment of the mean-field from finite-$T$ excitations and the anomolous average. This is the first gapless calculation of this type for a trapped Bose-Einstein condensed gas. The corrections quantitatively account for the downward shift in the $m=2$ excitation frequencies observed in recent experiments as the critical temperature is approached.Comment: 4 pages Latex and 2 postscript figure

Effects of temperature upon the collapse of a Bose-Einstein condensate in a gas with attractive interactions

We present a study of the effects of temperature upon the excitation frequencies of a Bose-Einstein condensate formed within a dilute gas with a weak attractive effective interaction between the atoms. We use the self-consistent Hartree-Fock Bogoliubov treatment within the Popov approximation and compare our results to previous zero temperature and Hartree-Fock calculations The metastability of the condensate is monitored by means of the $l=0$ excitation frequency. As the number of atoms in the condensate is increased, with $T$ held constant, this frequency goes to zero, signalling a phase transition to a dense collapsed state. The critical number for collapse is found to decrease as a function of temperature, the rate of decrease being greater than that obtained in previous Hartree-Fock calculations.Comment: 4 pages LaTeX, 3 eps figures. To appear as a letter in J. Phys.

Recoverin Regulates Light-dependent Phosphodiesterase Activity in Retinal Rods

The Ca2+-binding protein recoverin may regulate visual transduction in retinal rods and cones, but its functional role and mechanism of action remain controversial. We compared the photoresponses of rods from control mice and from mice in which the recoverin gene was knocked out. Our analysis indicates that Ca2+-recoverin prolongs the dark-adapted flash response and increases the rod's sensitivity to dim steady light. Knockout rods had faster Ca2+ dynamics, indicating that recoverin is a significant Ca2+ buffer in the outer segment, but incorporation of exogenous buffer did not restore wild-type behavior. We infer that Ca2+-recoverin potentiates light-triggered phosphodiesterase activity, probably by effectively prolonging the catalytic activity of photoexcited rhodopsin

Gas Purity effect on GEM Performance in He and Ne at Low Temperatures

The performance of Gas Electron Multipliers (GEMs) in gaseous He, Ne, He+H2 and Ne+H2 was studied at temperatures in the range of 3-293 K. This paper reports on previously published measurements and additional studies on the effects of the purity of the gases in which the GEM performance is evaluated. In He, at temperatures between 77 and 293 K, triple-GEM structures operate at rather high gains, exceeding 1000. There is an indication that this high gain is achieved through the Penning effect as a result of impurities in the gas. At lower temperatures the gain-voltage characteristics are significantly modified probably due to the freeze-out of these impurities. Double-GEM and single-GEM structures can operate down to 3 K at gains reaching only several tens at a gas density of about 0.5 g/l; at higher densities the maximum gain drops further. In Ne, the maximum gain also drops at cryogenic temperatures. The gain drop in Ne at low temperatures can be re-established in Penning mixtures of Ne+H2: very high gains, exceeding 104, have been obtained in these mixtures at 30-77 K, at a density of 9.2 g/l which corresponds to saturated Ne vapor density at 27 K. The addition of small amounts of H2 in He also re-establishes large GEM gains above 30 K but no gain was observed in He+H2 at 4 K and a density of 1.7 g/l (corresponding to roughly one-tenth of the saturated vapor density). These studies are, in part, being pursued in the development of two-phase He and Ne detectors for solar neutrino detection.Comment: 4 pages, 7 figure

Internal Vortex Structure of a Trapped Spinor Bose-Einstein Condensate

The internal vortex structure of a trapped spin-1 Bose-Einstein condensate is investigated. It is shown that it has a variety of configurations depending on, in particular, the ratio of the relevant scattering lengths and the total magnetization.Comment: replacement; minor grammatical corrections but with additional figure