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<jats:p> Direct evidence is presented for a conformational switch in 16 <jats:italic>S</jats:italic> ribosomal RNA (rRNA) that affects tRNA binding to the ribosome and decoding of messenger RNA (mRNA). These data support the hypothesis that dynamic changes in rRNA structure occur during translation. The switch involves two alternating base-paired arrangements apparently facilitated by ribosomal proteins S5 and S12, and produces significant changes in the rRNA structure. Chemical probing shows reciprocal enhancements or protections at sites in 16 <jats:italic>S</jats:italic> rRNA that are at or very near sites that were previously crosslinked to mRNA. These data indicate that the switch affects codon-anticodon arrangement and proper selection of tRNA at the ribosomal A site, and that the switch is a fundamental mechanism in all ribosomes. </jats:p>

<jats:p>The motions between the Somalian, Antarctic, and Australian plates—the three plates believed to meet at the Rodrigues triple junction in the Indian Ocean—are inconsistent with the assumption that all three plates are rigid. The discrepancy is best explained if the Australian plate contains two component plates. Thus, the traditionally defined Indo-Australian plate consists of three component plates and multiple diffuse plate boundaries. The pattern of present deformation indicates that the boundaries between the three component plates are two unconnected zones accommodating divergence and a larger zone, which we interpret as three diffuse convergent plate boundaries and a diffuse triple junction.</jats:p>

<jats:p>A method for the prediction of the interactions within complex reaction networks from experimentally measured time series of the concentration of the species composing the system has been tested experimentally on the first few steps of the glycolytic pathway. The reconstituted reaction system, containing eight enzymes and 14 metabolic intermediates, was kept away from equilibrium in a continuous-flow, stirred-tank reactor. Input concentrations of adenosine monophosphate and citrate were externally varied over time, and their concentrations in the reactor and the response of eight other species were measured. Multidimensional scaling analysis and heuristic algorithms applied to two-species time-lagged correlation functions derived from the time series yielded a diagram from which the interactions among all of the species could be deduced. The diagram predicts essential features of the known reaction network in regard to chemical reactions and interactions among the measured species. The approach is applicable to many complex reaction systems.</jats:p>

<jats:p> Laser incremental heating of sanidine from the pumice deposited by the Plinian eruption of Vesuvius in 79 A.D. yielded a <jats:sup>40</jats:sup> Ar/ <jats:sup>39</jats:sup> Ar isochron age of 1925 ± 94 years ago. Close agreement with the Gregorian calendar–based age of 1918 years ago demonstrates that the <jats:sup>40</jats:sup> Ar/ <jats:sup>39</jats:sup> Ar method can be reliably extended into the temporal range of recorded history. Excess <jats:sup>40</jats:sup> Ar is present in the sanidine in concentrations that would cause significant errors if ignored in dating Holocene samples. </jats:p>

<jats:p>The isotopic composition of zirconium in silicon carbide grains from the Murchison meteorite was measured by resonant ionization mass spectrometry of laser-ablated neutral atoms. These grains are condensates from the atmospheres of red giant stars that existed before the formation of our sun and solar system, and they contain records of nucleosynthesis in these stars. The r-process–dominated isotope zirconium-96 was depleted by more than a factor of 2 compared with the s-process–dominated isotopes zirconium-90, zirconium-91, zirconium-92, and zirconium-94, in agreement with expectations for neutron capture nucleosynthesis in asymptotic giant branch stars.</jats:p>

<jats:p> Time-resolved Kerr reflectivity of two-dimensional electron gases in II-VI semiconductors provides a direct measure of electron spin precession and relaxation over a temperature range from 4 to 300 kelvin. The introduction of <jats:italic>n</jats:italic> -type dopants increases the electronic spin lifetimes several orders of magnitude relative to insulating counterparts, a trend that is also observed in doped bulk semiconductors. Because the electronic spin polarization in these systems survives for nanoseconds, far longer than the electron-hole recombination lifetime, this technique reveals thousands of spin precession cycles of 15 gigahertz per tesla within an electron gas. Remarkably, these spin beats are only weakly temperature dependent and persist to room temperature. </jats:p>