Biological and Medical Experiments on the Space Shuttle, 1981 - 1985

This volume is the first in a planned series of reports intended to provide a comprehensive record of all the biological and medical experiments and samples flown on the Space Shuttle. Experiments described have been conducted over a five-year period, beginning with the first plant studies conducted on STS-2 in November 1981, and extending through STS 61-C, the last mission to fly before the tragic Challenger accident of January 1986. Experiments were sponsored within NASA not only by the Life Sciences Division of the Office of Space Science and Applications, but also by the Shuttle Student Involvement Program (SSIP) and the Get Away Special (GAS) Program. Independent medical studies were conducted as well on the Shuttle crew under the auspices of the Space Biomedical Research Institute at Johnson Space Center. In addition, cooperative agreements between NASA and foreign government agencies led to a number of independent experiments and also paved the way for the joint US/ESA Spacelab 1 mission and the German (DFVLR) Spacelab D-1. Experiments included: (1) medically oriented studies of the crew aimed at identifying, preventing, or treating health problems due to space travel; (2) projects to study morphological, physiological, or behavioral effects of microgravity on animals and plants; (3) studies of the effects of microgravity on cells and tissues; and (4) radiation experiments monitoring the spacecraft environment with chemical or biological dosimeters or testing radiation effects on simple organisms and seeds

A Comprehensive Spectroscopic Analysis of DB White Dwarfs

We present a detailed analysis of 108 helium-line (DB) white dwarfs based on model atmosphere fits to high signal-to-noise optical spectroscopy. We derive a mean mass of 0.67 Mo for our sample, with a dispersion of only 0.09 Mo. White dwarfs also showing hydrogen lines, the DBA stars, comprise 44% of our sample, and their mass distribution appears similar to that of DB stars. As in our previous investigation, we find no evidence for the existence of low-mass (M < 0.5 Mo) DB white dwarfs. We derive a luminosity function based on a subset of DB white dwarfs identified in the Palomar-Green survey. We show that 20% of all white dwarfs in the temperature range of interest are DB stars, although the fraction drops to half this value above Teff ~ 20,000 K. We also show that the persistence of DB stars with no hydrogen features at low temperatures is difficult to reconcile with a scenario involving accretion from the interstellar medium, often invoked to account for the observed hydrogen abundances in DBA stars. We present evidence for the existence of two different evolutionary channels that produce DB white dwarfs: the standard model where DA stars are transformed into DB stars through the convective dilution of a thin hydrogen layer, and a second channel where DB stars retain a helium-atmosphere throughout their evolution. We finally demonstrate that the instability strip of pulsating V777 Her white dwarfs contains no nonvariables, if the hydrogen content of these stars is properly accounted for.Comment: 74 pages including 30 figures, accepted for publication in the Astrophysical Journa

On the formation of hot DQ white dwarfs

We present the first full evolutionary calculations aimed at exploring the origin of hot DQ white dwarfs. These calculations consistently cover the whole evolution from the born-again stage to the white dwarf cooling track. Our calculations provide strong support to the diffusive/convective-mixing picture for the formation of hot DQs. We find that the hot DQ stage is a short-lived stage and that the range of effective temperatures where hot DQ stars are found can be accounted for by different masses of residual helium and/or different initial stellar masses. In the frame of this scenario, a correlation between the effective temperature and the surface carbon abundance in DQs should be expected, with the largest carbon abundances expected in the hottest DQs. From our calculations, we suggest that most of the hot DQs could be the cooler descendants of some PG1159 stars characterized by He-rich envelopes markedly smaller than those predicted by the standard theory of stellar evolution. At least for one hot DQ, the high-gravity white dwarf SDSS J142625.70+575218.4, an evolutionary link between this star and the massive PG1159 star H1504+65 is plausible.Comment: 4 pages, 2 figures. To be published in The Astrophysical Journal Letter

Quantum ballistic experiment on antihydrogen fall

We study an interferometric approach to measure gravitational mass of antihydrogen. The method consists of preparing a coherent superposition of antihydrogen quantum state localized near a material surface in the gravitational field of the Earth, and then observing the time distribution of annihilation events followed after the free fall of an initially prepared superposition from a given height to the detector plate. We show that a corresponding time distribution is related to the momentum distribution in the initial state that allows its precise measurement. This approach is combined with a method of production of a coherent superposition of gravitational states by inducing a resonant transition using oscillating gradient magnetic field. We estimate an accuracy of measuring the gravitational mass of antihydrogen atom which could be deduced from such a measurement.Comment: arXiv admin note: text overlap with arXiv:1403.478

Casimir-Polder shifts on quantum levitation states

An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Casimir-Polder interaction, which holds it against gravity and leads to quantum levitation states. We analyze this system by using a Liouville transformation of the Schr\"odinger equation and a Langer coordinate adapted to problems with a classical turning point. Reflection on the Casimir-Polder attractive well is replaced by reflection on a repulsive wall and the problem is then viewed as an ultracold atom trapped inside a cavity with gravity and Casimir-Polder potentials acting respectively as top and bottom mirrors. We calculate numerically Casimir-Polder shifts of the energies of the cavity resonances and propose a new approximate treatment which is precise enough to discuss spectroscopy experiments aiming at tests of the weak equivalence principle on antihydrogen. We also discuss the lifetimes by calculating complex energies associated with cavity resonances.Comment: Accepted in PR

Le nouveau droit du mariage-une revolution a Froid...ses origines jusnaturalistes-ses principes axiologiques

«11 faut par ailleurs dépasser le mentalité selon laquelle l'honneur de la femme vient devantage du travail a l'exterieur que de 1 'activité familiale» 56