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C. Vermeer M. M. W. Ulrich 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(12):139-142
The rapid loss of bone mass is one of the serious problems which have to be solved before long-lasting manned spaceflights may be considered. In this paper we describe investigations in which we have checked whether the bone loss in astronauts as well as in osteoporotic patients may be related to abnormalities in a recently discovered calcium-binding protein, named osteocalcin. It was observed that in all subjects of a limited number of osteoporotic patients, the amount of calcium-binding groups (Gla-residues) in the circulating osteocalcin was substantially reduced. The Gla-content could be normalized, however, by the oral administration of vitamin K (1 mg/day). We also analyzed the Gla-content of plasma-osteocalcin from 4 astronauts before and after the D-1 mission. The amount of Gla-residues was reduced by more than 50% in the post-flight samples. It seems probable, that an increased vitamin K-intake by the astronauts will correct the observed abnormality, but whether this will lead to a decrease of the microgravity-induced bone-loss remains to be seen. 相似文献
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We discuss the various problems occurring when trying to fix a geoid or geopotential model using sea level observations sampled
during a limited time span from a bounded geographical domain. Such problems are on the one hand aliasing and spectral leakage,
and on the other, the non-conservation of matter over only part of the world ocean.
In the light of these issues we discuss whether it is sensible to include in a definition of the global geoid the radially
symmetric part of either the mean sea level field itself, or its linear or nonlinear time dependence, arriving at a negative
conclusion.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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