The other frontiers of science

Frontiers of science are usually considered as those areas where the boundares of human knowledge are being pushed most vigorousl into the unknown. These are the intemal frontiers. But no less important are the external frontiers. Those bordering on the federal govermment, on education, on private industry and on intemational affairs and the developing world are among the most critical and demanding. Some of the outstanding problems facing science, and scientists in these extemal interactions, are discussed within the context of our changing national and international priorities.     

Orthopyroxene exsolution in augite: a two-step, diffusion-transformation process

Orthopyroxene lamellae exsolved from augite on (100) are shown to grow by a two-step process involving (i) the diffusion of calcium and (magnesium, iron) to form clinohypersthene and (ii) the inversion of clinohypersthene to orthopyroxene, probably by glide twinning. If complete inversion is prevented by cooling or steep concentration gradients, the two-step process produces orthopyroxene with narrow margins of clinohypersthene. Measured elemental concentration gradients at (100) lamellar interfaces support this mechanism.     

Conservation and duplication of isozymes in plants

Many enzymes in plants have isozymes because the same catalytic reaction is often present in several subcellular compartments, most frequently the plastids and the cytosol. The number and subcellular locations of the isozymes appear to be highly conserved in plant evolution. However, gene duplication in diploid species and the addition of genomes in polyploid species have increased the number of isozymes.     

Primary sulfates in atmospheric sulfates: estimation by oxygen isotope ratio measurements

The relative amounts of primary and secondary sulfates in atmospheric aerosols and precipitation can be estimated from measurements of the stable oxygen isotope ratios. The oxygen-18 content of sulfates formed in power plant stack gases before emission into the atmosphere is significantly higher than that of sulfates formed from sulfur dioxide after emission. Results show that 20 to 30 percent of the sulfates in rain and snow at Argonne, Illinois, are of primary origin.