The effect of magmatic activity on hydrothermal venting along the superfast-spreading East pacific rise

A survey of hydrothermal activity along the superfast-spreading (approximately 150 millimeters per year) East Pacific Rise shows that hydrothermal plumes overlay approximately 60 percent of the ridge crest between 13 degrees 50' and 18 degrees 40'S, a plume abundance nearly twice that known from any other rige portion of comparable length. Plumes were most abundant where the axial cross section is inflated and an axial magma chamber is present. Plumes with high ratios of volatile ((3)He, CH(4), and H(2)S) to nonvolatile (Mn and Fe) species marked where hydrothermal circulation has been perturbed by recent magmatic activity. The high proportion of volatile-rich plumes observed implies that such episodes are more frequent here than on slower spreading ridges.     

Phyllotaxis and the fibonacci series

The principal conclusion is that Fibonacci phyllotaxis follows as a mathematical necessity from the combination of an expanding apex and a suitable spacing mechanism for positioning new leaves. I have considered an inhibitory spacing mechanism at some length, as it is a plausible candidate. However, the same treatment would apply equally well to depletion of, or competition for, a compound by developing leaves, and could no doubt accommodate other ingredients. The mathematical principles involved are clear when it is assumed that only two leaves (the contacts) position a new leaf. There is some experimental evidence for this assumption. Nonetheless, it is not a precondition for Fibonacci phyllotaxis, since a computer model shows that this pattern is generated even when many leaves contribute to inhibition at a given point. Indeed, the Fibonacci pattern seems to be a robust and stable mathematical phenomenon, a finding which goes some way to explaining its widespread occurrence throughout the plant kingdom.     

Multiplex spectroscopy: determining the transition moments and absolute concentrations of molecular species

A procedure is described that uses two spectroscopic techniques, absorption and infrared degenerate four-wave mixing, in tandem (multiplex) to measure the transition dipole moments and absolute concentrations of molecular species in situ. The method is demonstrated by the measurement of the relative transition moments and concentrations of two dissimilar sample gas components, hydrogen chloride and nitrogen dioxide, but is applicable to a wide variety of molecules and, thus, can provide new information for transient molecular species. Further, difficulties in obtaining quantitative information through techniques such as laser-induced fluorescence, coherent anti-Stokes Raman scattering, and degenerate four-wave mixing spectroscopies can be overcome when a multiplex approach is used.     

Developmentally regulated piRNA clusters implicate MILI in transposon control

Nearly half of the mammalian genome is composed of repeated sequences. In Drosophila, Piwi proteins exert control over transposons. However, mammalian Piwi proteins, MIWI and MILI, partner with Piwi-interacting RNAs (piRNAs) that are depleted of repeat sequences, which raises questions about a role for mammalian Piwi's in transposon control. A search for murine small RNAs that might program Piwi proteins for transposon suppression revealed developmentally regulated piRNA loci, some of which resemble transposon master control loci of Drosophila. We also find evidence of an adaptive amplification loop in which MILI catalyzes the formation of piRNA 5' ends. Mili mutants derepress LINE-1 (L1) and intracisternal A particle and lose DNA methylation of L1 elements, demonstrating an evolutionarily conserved role for PIWI proteins in transposon suppression.     

Implications for Geophysics of the Precise Measurement of the Earth's Rotation

A radio interferometer could yield an error on the order of 10(-9) second at the semidiurnal frequency. With errors of this magnitude, yearly changes in the rate at which the earth's rotation is slowing down could be determined. The proposed interferometer could also yield significant improvements in the determination of the Love number k and its variation with frequency, and in the changes in angular momentum of the atmosphere for periods greater than 1 week.     

Analysis of hydrothermal vent-associated symbionts by ribosomal RNA sequences

Ribosomal RNA (rRNA) sequences were used to establish the phylogenetic affiliations of symbioses in which prokaryotes appear to confer sulfur-based chemoautotrophy on their invertebrate hosts. Two submarine hydrothermal vent animals, the vestimentiferan tube worm Riftia pachyptila and the clam Calyptogena magnifica, and a tidal-flat bivalve, Solemya velum, were inspected. 5S rRNA's were extracted from symbiont-bearing tissues, separated into unique forms, and their nucleotide sequences determined and related to other 5S rRNA's in a phylogenetic tree analysis. The prokaryotic symbionts are related to one another and affiliated with the same narrow phylogenetic grouping as Escherichia coli and Pseudomonas aeruginosa. The sequence comparisons suggest that Riftia is more closely related to the bivalves than their current taxonomic status would suggest.