Biomedical subjects

Reginald W Smith

Publications and source records attributed to Reginald W Smith.

3 recordsLinked to original sources

PubMed2002

The influence of gravity on the precise measurement of solute diffusion coefficients in dilute liquid metals and metalloids.

It is now well known that the diffusion coefficient (D) measured in a laboratory in low earth orbit (LEO) is less than the corresponding value measured in a terrestrial laboratory. However, all LEO laboratories are subject to transient accelerations (g-jitter) superimposed on the steady reduced gravity environment of the space platform. In measurements of the diffusion coefficients for dilute binary alloys of Pb-(Ag, Au,Sb), Sb-(Ga,In), Bi-(Ag,Au,Sb), Sn-(Au,Sb), Al-(Fe, Ni,Si), and In-Sb in which g-jitter was suppressed, it was found that D proportional to T (temperature) if g-jitter was suppressed, rather than D proportional to T(2) as observed by earlier workers with g-jitter present. Furthermore, when a forced g-jitter was applied to a diffusion couple, the value measured for D increased. The significance of these results is reviewed in the light of recent work in which ab initio molecular dynamics simulations predicted a D proportional to T relationship.

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PubMed2002

ATEN: a new high temperature materials processing facility for the international space station.

Since the beginning of microgravity materials research, studies of diffusion in liquids have been performed as the typical research that efficiently uses the microgravity environment. Successful experiments in microgravity have demonstrated the ability of the Canadian Microgravity Program (QUEST I, QUELDs I and II) to make significant contributions to this field of international microgravity research. Recently, Millenium Biologix was selected to develop and build the advanced thermal environment facility (ATEN) for the International Space Station. The design of this new processing facility builds on the considerable experience gained in designing and building the QUELD II furnace and developing sealed samples for use on board a manned space platform. The system requirements for ATEN are presented, along with preliminary test data from a prototype furnace.

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PubMed2002

Gravity-induced anomalies in interphase spacing reported for binary eutectics.

It has been reasoned that desirable microstructural refinement in binary eutectics could result from freezing in reduced-gravity. It is recognized that the interphase spacing in a binary eutectic is controlled by solute transport and that, on Earth, buoyancy-driven convection may enhance this. Hence, it has been presumed that the interphase spacing ought to decrease when a eutectic alloy is frozen under conditions of much-reduced gravity, where such buoyancy effects would be largely absent. The result of such speculation has been that many workers have frozen various eutectics under reduced gravity and have reported that, although some eutectics became finer, others showed no change, and some even became coarser. This reported varied behavior will be reviewed in the light of long term studies by the author at Queen's University, including recent microgravity studies in which samples of two eutectic alloy systems, MnBi-Bi and MnSb-Sb, were frozen under very stable conditions and showed no change in interphase spacing.

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