Catálogo de publicaciones - revistas

<jats:p>“Investigating Microbial Diversity on Arabia Mountain,” the IBI Prize–winning module, allows students to explore microbial diversity by DNA isolation and sequencing.</jats:p>

<jats:p> “Genetic Analysis of Adaptation to Osmotic Stress in <jats:italic>Salmonella</jats:italic> ,” the IBI Prize–winning module, uses mutant isolation and DNA sequencing to engage students in bacterial genetics and evolution. </jats:p>

<jats:p> A monthly roundup of recent news and projects of <jats:italic>Science</jats:italic> 's publisher, the American Association for the Advancement of Science. </jats:p>

<jats:p>An engineered microbe transforms carbon dioxide into a prospective liquid fuel in tandem with electrical power rather than light.</jats:p>

<jats:title>Chiral Ice</jats:title> <jats:p> Water ice, even at the lowest temperatures, is not completely “frozen”—its lattice structure allows for multiple equivalent ground states and it thus retains finite entropy even at absolute zero. Equivalent structures are realized in frustrated magnets called spin ices, where spins interact ferromagnetically, and in the even more exotic artificial spin ices, which are fabricated arrays of nanoscale magnets. <jats:bold> Branford <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1597" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1211379">1597</jats:related-article> ) studied the transport behavior of an artificial spin ice with a honeycomb geometry during upward and downward sweeps of an external magnetic field, which revealed a field-asymmetric peak when the magnetic field was applied parallel to the current and the voltage was measured transversely. Micromagnetic simulations suggest that the asymmetric response is a result of the loops of opposite handedness forming at the edges of the sample, resulting in an overall chirality of the transport response. </jats:p>

<jats:title>Electrons Beat Phonons</jats:title> <jats:p> The phenomenon of superconductivity, in which a material suddenly (below a certain transition temperature <jats:italic> T <jats:sub>c</jats:sub> </jats:italic> ) becomes a perfect conductor with zero electrical resistance, can be roughly explained in terms of Bose-Einstein condensation of pairs of electrons. In conventional superconductors, the formation of these so-called Cooper pairs is mediated by lattice deformations (phonons), but this mechanism is insufficient to explain the high <jats:italic> T <jats:sub>c</jats:sub> </jats:italic> of cuprate superconductors. Other mechanisms, such as magnetic fluctuations, have been proposed which originate with the electrons themselves rather than the lattice. <jats:bold> Dal Conte <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1600" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1216765">1600</jats:related-article> ) used time-resolved optical spectroscopy of an optimally doped cuprate to show that the temporal evolution of the reflectivity is consistent with the electronic contribution being dominant and is able to account for the high <jats:italic> T <jats:sub>c</jats:sub> </jats:italic> by itself. </jats:p>

<jats:p>The spin of a nitrogen vacancy defect in diamond is used to sense the motion a magnetized microresonator.</jats:p>

<jats:title>An Iron Separator</jats:title> <jats:p> Petroleum processing initially yields a mixture of saturated and unsaturated hydrocarbons—the feedstocks for fuels, plastics, pharmaceuticals, and a wide range of other commercial products. At present, distillation is the primary means of separating the components of this mixture. A sorbent or membrane-based approach to separation could reap substantial energy savings. <jats:bold> Bloch <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1606" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1217544">1606</jats:related-article> ) found that an iron-based metal organic framework material shows promise for very efficient sorption-based separation of ethane and ethylene, propane and propylene, and several other light hydrocarbon mixtures. Neutron diffraction directly revealed the binding motifs at the iron centers that selectively pinned down the olefins while the saturated hydrocarbons passed by. </jats:p>

<jats:title>A Better Date</jats:title> <jats:p> Uranium-lead (U-Pb) dating, which is one of the most commonly used methods of radiometric dating for old terrestrial materials, operates by comparing the ratio of trace levels of U with its nuclear decay product Pb. This dating method, and the similar Pb-Pb method, assumes that the ratio between the two most common U isotopes ( <jats:sup>238</jats:sup> U and <jats:sup>235</jats:sup> U) is constant. By accurately measuring the <jats:sup>238</jats:sup> U/ <jats:sup>235</jats:sup> U ratio in a suite of minerals representing a range of tectonic environments, <jats:bold> Hiess <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1610" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215507">1610</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6076" page="1585" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1220333">Stirling</jats:related-article> </jats:bold> ) demonstrate that this ratio is more variable than was previously thought. The variability does not reflect any systematic bias with time, location, or temperature—suggesting that ideally <jats:sup>238</jats:sup> U/ <jats:sup>235</jats:sup> U should be determined for every sample to calculate ages. In the absence of such data, a revised <jats:sup>238</jats:sup> U/ <jats:sup>235</jats:sup> U ratio for zircon minerals could significantly modify previous age estimates using U-Pb and Pb-Pb dating techniques. </jats:p>

<jats:title>A New Lease on Half-Life</jats:title> <jats:p> Radiometric dating relies on measuring the abundance of long-lived radionuclides relative to the abundance of their radiogenic decay products—a process determined by the original radionuclide's half-life. For primordial radionuclides that decay slowly, such as <jats:sup>146</jats:sup> Sm decaying to <jats:sup>142</jats:sup> Nd, this method provides the timing of some of the earliest processes in solar system history. Using accelerator mass spectrometry, <jats:bold> Kinoshita <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1614" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215510">1614</jats:related-article> ) provide a revised estimate for the <jats:sup>146</jats:sup> Sm half-life of ∼68.7 million years, which is 30% shorter than the previously accepted value. This shorter half-life suggests that reductions need to be made in the estimated ages for differentiation of Earth's mantle and the solidification of the Moon's magma ocean and for other more recent processes. </jats:p>