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At least 1,063 records · Page 59

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NASA NTRS1987

Search for dark companions of K and M giants - Preliminary results for Alpha Boo

Preliminary results are presented for Alpha Boo, encompassing selected measurements during the period from January 1979 to June 1984. Four groups of data are chosen, each group taken within an interval of up to 1.5 months, and examined the internal consistency of each set to look for short term trends. The radial velocity was found to be very consistent with a standard deviation of about + or - 50 m/s within time scales of hours, days, and weeks. No significant radial velocity changes over these periods were detected. This suggests that the stellar surface activity is confined to the level of uncertainty. Because of this consistency it was possible to take the means of the radial velocity measurements within each group and compare them to look for possible long term changes. Variations of the radial velocity of about 200 m/s were found over the span of a few years, significant at the 6 to 8 sigma level.

Heyer, I.↗

NASA NTRS1987

Stability and refrigeration of magnet cryosystems near 1.8 K using the thermomechanical effect

Magnet cryosystem options utilizing the thermomechanical effect of He II and the mechano-caloric effect for refrigeration (referred to as vortex refrigeration) are examined. The performance of the existing He II magnet refrigeration system is briefly reviewed, with attention given to superleak properties, vortex shedding, heat input, and thermodynamic cycle. It is concluded that the possibilities of magnet heat leak use for energetics and stability improvements are promising when He II is selected as magnet coolant.

Frederking, T. H. K.↗

NASA NTRS1989

Comment on 'Observations of Low-Latitude Electron Precipitation' by R. Lieu, J. Watermann, K. Wilhelm, J. J. Quenby, and W. I. Axford

Observations made by an electron spectrometer aboard Spacelab 1 and presented by Lieu et al. (1988) are examined critically. The precipitation of electrons in the energy range of 0.1-12.5 keV was measured on December 6 and 7, 1983. Data for 16 passes near 240 km altitude, between + and - 30 deg geographic latitude, outside the South Atlantic Anomaly were included. It is argued that there is no geophysical confirmation of the large electron fluxes reported by Lieu et al. In their response, Lieu et al. discuss the sampling bias in the Spacelab 1 data and the magnetic shielding deficiencies of the calibration facility below about 500 eV.

Rassoul, H. K.↗

NASA NTRS1990

Experiment K-6-10. Effects of zero gravity on myofibril protein content and isomyosin distribution in rodent skeletal muscle

The purpose of this experiment was to investigate the effects of 12 days of zero gravity (0G) exposure (Cosmos 1887 Biosputnik) on the enzymatic properties, protein content, and isomyosin distribution of the myofibril fraction of the slow-twitch vastus intermedius (VI) and the fast-twitch vastus lateralis (VL) muscles of adult male rats. Measurements were obtained on three experimental groups (n=5 each group) designated as flight-group (FG), vivarium-control (VC), and synchronous-control (SC). Body weight of the FG was significantly lower than the two control groups (p less than 0.05). Compared to the two control groups, VI weight was lower by 23 percent (p less than 0.10); whereas no such reduction was observed for the VL muscle. Myofibril yields (mg protein/g of muscle) in the VI were 35 percent lower in the FG compared to the controls (p less than 0.05); whereas, no such pattern was apparent for the VL muscle. When myofibril yields were expressed on a muscle basis (mg/g x muscle weight), the loss of myofibril protein was more exaggerated and suggests that myofibril protein degradation is an early event in the muscle atrophy response to 0G. Analysis of myosin isoforms indicated that slow-myosin was the primary isoform lost in the calculated degradation of total myosin. No evidence of loss of the fast isomyosins was apparent for either muscle following space flight. Myofibril ATPase activity of the VI was increased in the FG compared to controls, which is consistent with the observation of preferential slow-myosin degradation. These data suggest that muscles containing a high percent of slow-twitch fibers undergo greater degrees of myofibril protein degradation than do muscles containing predominantly fast-twitch fibers in response to a relatively short period of 0G exposure, and the primary target appears to be the slow-myosin molecule.

Baldwin, K.↗

NASA NTRS1990

Experiment K-6-13. Morphological and biochemical examination of heart tissue. Part 1: Effects of microgravity on the myocardial fine structure of rats flown on Cosmos 1887. Ultrastructure studies. Part 2: Cellular distribution of cyclic ampdependent protein kinase regulatory subunits in heart muscle of rats flown on Cosmos 1887

The left ventricle of hearts from rats flown on the Cosmos 1887 biosatellite for 12.5 days was compared to the same tissue of synchronous and vivarium control animals maintained in a ground based laboratory. The volume density of the mitochondria in the myocardium of the space-flown animals was statistically less (p equal less than 0.01) than that of the synchronous or vivarium control rats. Exposure to microgravity resulted in a certain degree of myocardial degeneration manifested in mitochondrial changes and accumulation of myeloid bodies. Generalized myofibrillar edema was also observed.

Philpott, D. E.↗

NASA NTRS1990

Experiment K-6-16. Morphological examination of rat testes. The effect of Cosmos 1887 flight on spermatogonial population and testosterone level in rat testes

Testes from rats flown on Cosmos 1887 for twelve and a half days were compared to basal control, synchronous control and vivarium maintained rats. When the mean weights of flight testes, normalized for weight/100 gms, were compared to the vivarium controls they were 6.7 percent lighter. Although the flight testes were lighter than the synchronous, the difference is not significant. Counts of spermatogonial cells from 5 animals in each group revealed a 4 percent decrease in flight compared to vivarium controls. In both cases the t-Test significance was less than 0.02. The serum testosterone levels of all animals (flight, synchronous and vivarium) were significantly below the basal controls.

Philpott, D. E.↗

NASA NTRS1990

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.

Phillips, R. W.↗

NASA NTRS1990

Detection of trace helium in G104 - 27, a 26,000 K DA white dwarf

The detection of the He I 4471 A feature in the moderately hot DA white dwarf G104 - 27 places this star within the rather sparse class of DAB white dwarfs. It does not appear possible, on the basis of the present data, to distinguish between a stratified and a homogeneously mixed atmosphere. While a stratified structure would be natural for a DA white dwarf, G104 - 27 resides near the red edge of the DB gap, in a region where DA stars could transform into DB stars through convective mixing in the underlying He envelope and thereby destroy envelope stratification. Both atmospheres are consistent with the existing soft X-ray flux limit for this star.

Holberg, J. B.↗

NASA NTRS1991

The PSR 2127+12 as an indicator of a massive blac k hole in the core of globular cluster M 15

The 110-millisecond pulsar PSR 2127+12 in the core of the globular cluster M15 is distinguished by having a negative period derivative P approximately equals -2 x 10(exp -17). This value cannot be provided by acceleration in the mean gravitational potential of the core. A flyby of a star approximately equal to 300 AU away could explain the P observed, but the probability of such an event is small, approximately equal to 10(exp -13). We suggest that the pulsar motion is governed by the presence of a moderately massive (approximately equals 2 divided by 3 x 10(exp 4) solar mass) black hole in the clusters center. The idea is further supported by an observed post-collapse morphology of the M15 core.

Postnov, K. A.↗

NASA NTRS1932