Catálogo de publicaciones - revistas

<jats:p>Transporters that import chloride ions in exchange for the export of protons control the function of intracellular vesicles in mammalian cells.</jats:p>

<jats:p>An ammonium iodide salt can perform selective organic oxidation reactions and replace more toxic metal catalysts.</jats:p>

<jats:p>A better understanding of how aerosols form in the atmosphere could greatly improve climate models.</jats:p>

<jats:title>Mind the Gap</jats:title> <jats:p> The symmetry of the pairing gap is one of the most important properties of a superconductor. Whereas conventional superconductors such as lead have a gap that is uniform in momentum space, the enigmatic cuprates have point nodes and a characteristic <jats:italic>d</jats:italic> -wave symmetry. The heavy fermion compound UPt <jats:sub>3</jats:sub> has long been known to exhibit unconventional pairing. Now, <jats:bold> Strand <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="1368" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187943">1368</jats:related-article> ) have measured the momentum space dependence of UPt <jats:sub>3</jats:sub> 's superconducting gap as a function of temperature. A real gap with line nodes was observed to develop first; then, at a lower critical temperature, a complex component appeared, with the total gap expected to become fully uniform at absolute zero. </jats:p>

<jats:title>Spin Control Through Molecular Stretching</jats:title> <jats:p> Molecules with high symmetry, such as metal complexes with several equivalent ligands, can, in principle, have this symmetry broken by stresses that lengthen bonds in one direction. <jats:bold> Parks <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="1370" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1186874">1370</jats:related-article> ; see the Perspective by <jats:bold>Jarillo-Herrero</jats:bold> ) placed cobalt complexes in a break-junction contact and then applied a mechanical force to slowly open the contact. Low-temperature measurement of differential conductance revealed a splitting of the Kondo peak at zero-applied voltage into two features, which occurred by breaking the degeneracy of <jats:italic>S</jats:italic> = 1 triplet states. This assignment of the spin state was confirmed by the evolution of splitting with magnetic field and by comparison to theory for a case where the conduction electrons only partially screen the spin states. </jats:p>

<jats:title>Writing Conductive Lines with Hot Tips</jats:title> <jats:p> The interface within devices between conductors, semiconductors, and insulators is usually created by stacking patterned layers of different materials. For flexible electronics, it can be advantageous to avoid this architectural constraint. Graphene oxide, formed by chemical exfoliation of graphite, can be reduced to a more conductive form using chemical reductants. <jats:bold> Wei <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="1373" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188119">1373</jats:related-article> ) now show that layers of graphene oxide can also be reduced using a hot atomic force microscope tip to create materials comparable to those of organic conductors. This process can create patterned regions (down to 12 nanometers in width) that differ in conductivity by up to four orders of magnitude. </jats:p>

<jats:title>Eye for an I</jats:title> <jats:p> Oxidative catalysis is largely the domain of transition metals, whether iron in an enzyme, or rarer palladium in a synthetic system. These metals can efficiently shuttle between oxidation states, easing the transfer of hydrogen and oxygen atoms between hydrocarbons and oxidants. <jats:bold> Uyanik <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="1376" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188217">1376</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5984" page="1365" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1191408">French</jats:related-article> ) now show that iodine can take the place of the metal to catalytically activate peroxide during the formation of benzofuran derivatives. Pairing iodide anions with chiral ammonium cations allowed the generation of stereoselectivity at levels similar to those seen with metal complexes bearing chiral ligands. </jats:p>

<jats:title>Warm-Blooded Reptiles?</jats:title> <jats:p> Existing reptiles are not thought to be endothermic, but what about extinct species? Three large extinct swimming reptiles, the ichthyosaurs, plesiosaurs, and mosasaurs, were active predators in the Mesozoic oceans. <jats:bold> Bernard <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="1379" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187443">1379</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="5984" page="1361" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1191409">Motani</jats:related-article> </jats:bold> ) investigated their metabolism by analyzing the oxygen isotopes in their teeth, compared with fish in deposits from a variety of ocean environments. The data imply that the ichthyosaurs and plesiosaurs, which were both pursuit predators, probably controlled their own temperature. The data for the mosasaurs, which are thought to have hunted by ambush, are more equivocal. </jats:p>

<jats:title>Towering Figures</jats:title> <jats:p> The Tibetan plateau and adjacent mountain ranges are the source areas of the five major rivers of Asia. Climate change promises to affect both precipitation patterns and glacial melting in the region, which could have marked impacts on river flows and on associated agriculture. <jats:bold> Immerzeel <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="1382" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1183188">1382</jats:related-article> ) analyzed the relative importance of glacial meltwater and rainfall in the region in order to determine how the rivers depend on different sources of water, and how the river basins may be affected by climate change. Climate change is likely to affect water availability in the river basins in substantial but diverse ways, which may threaten the food security of tens of millions of people. </jats:p>

<jats:title>Reconsidering Recurrence</jats:title> <jats:p> The very long times between major earthquakes on known susceptible faults make estimating a long-term recurrence interval difficult. Deep, low-frequency earthquakes happen much more frequently and thus provide a natural setting for studying earthquake occurrence. <jats:bold>Shelly</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1385" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189741">1385</jats:related-article> ) examined the timing of over 900 tiny earthquakes along a well-studied portion of the San Andreas Fault during a span of 8.5 years. The recurrence intervals between these microearthquakes, which roughly occurred on 3- and 6-day cycles, were sensitive to larger nearby events. For example, following the Parkfield earthquake in 2004, the 3-day cycle shortened and the 6-day cycle disappeared. If large-earthquake recurrence intervals are similarly variable over time, it will be extremely difficult to predict future damaging earthquakes from a short historical record. </jats:p>