Catálogo de publicaciones - revistas

<jats:p>An atomic force microscope equipped with a functionalized tip can map out the electronic and structural properties of individual chemical bonds.</jats:p>

<jats:p>A physicist who helped to found radio astronomy and build one of the largest radio telescopes in the world.</jats:p>

<jats:title>Killer Eradication</jats:title> <jats:p> Rinderpest is the second disease to be eradicated globally after smallpox. <jats:bold> Mariner <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="1309" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223805">1309</jats:related-article> ) review the technical and social challenges that were overcome during the course of eradication. Key achievements were the development of a thermostable vaccine, the recruitment of the pastoralists themselves for training and administration of vaccine, and complete vaccination coverage, despite occasionally hazardous environmental and political conditions. Although these achievements offer important lessons for future human and animal health programs, institutional memories are surprisingly short-lived, and it is important to document these lessons for the next eradication campaign. </jats:p>

<jats:p>Killer whale mothers continue to help their adult male offspring to survive long after ceasing reproduction.</jats:p>

<jats:title>An Eight-Noded Monster</jats:title> <jats:p> In superconductors, electrons are bound into pairs, and the exact form of that pairing and the resulting energy gap can vary, depending on the details of the electron-electron interaction and the band structure of the material. The energy gaps of the recently discovered iron-based superconductors exhibit a variety of pairing functions. KFe <jats:sub>2</jats:sub> As <jats:sub>2</jats:sub> has been suggested to have a <jats:italic>d</jats:italic> -wave gap, similar to cuprate superconductors. <jats:bold> Okazaki <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="1314" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1222793">1314</jats:related-article> ) use laser-based angle-resolved photoemission spectroscopy (ARPES) to map out the superconducting gap on three Fermi surfaces (FS) of the compound. They find a different gap structure on each, with the middle FS gap vanishing at eight distinct positions (nodes). It appears that the gap respects the tetragonal symmetry of the crystal, indicating (although the details may vary) the all iron-based superconductors have an extended <jats:italic>s</jats:italic> -wave–symmetric pairing—a finding that will help understanding of unconventional superconductivity. </jats:p>

<jats:title>Prethermalization</jats:title> <jats:p> When a physical system is subjected to a rapid change of conditions (for example, a gas of atoms is allowed to occupy a volume twice the size of the original container), it quickly achieves a new temperature (thermalizes) through collisions. However, in some quantum systems many conserved variables inhibit thermalization; understanding the phases the systems go through in the slowing process is of great interest to cosmologists and physicists. <jats:bold> Gring <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="1318" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224953">1318</jats:related-article> , published online 31 August) separate an ultracold one-dimensional gas of bosonic atoms into two nearly identical halves, and follow how local differences in phase between the halves evolve in time by examining their interference. Initially, the local phases are almost identical, but a rapid decoherence ensues, followed by a very slow further decay. The authors analyze the relative state reached after the initial fast decay and find that it can be described by an equilibrium function with an effective temperature several times less than the initial temperature. Because this cannot be the final state of the system, the authors term the initial process prethermalization. </jats:p>

<jats:title>Fluorine's Smooth Introduction</jats:title> <jats:p> Carbon-fluorine bonds are emerging as increasingly versatile constituents of drugs, agrochemicals, and positron emission tomography tracers. Elemental F <jats:sub>2</jats:sub> gas is in principle an efficient reagent for their preparation, but its extreme reactivity requires special handling precautions. Substantial research has therefore focused on promoting selective reactivity of more conveniently handled fluoride ion salts. <jats:bold> Liu <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="1322" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1222327">1322</jats:related-article> ) present a manganese catalyst that transfers fluoride to a range of hydrocarbons in conjunction with a hypervalent iodine-based oxidant. Mechanistic studies implicate a manganese difluoride intermediate that reacts with alkyl radicals generated by a preceding manganese oxo. </jats:p>

<jats:title>Visualizing Bond Order</jats:title> <jats:p> Bond lengths in conjugated molecules closely reflect individual bond order and are usually determined by diffraction methods. It is valuable to know bond order for rationalizing aromaticity, and reactivity and for chemical structure determination. <jats:bold> Gross <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="1326" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1225621">1326</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="6100" page="1305" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227726">Perez</jats:related-article> </jats:bold> and the cover) differentiated the bond orders in individual molecules in the fullerene C <jats:sub>60</jats:sub> and in polyaromatic hydrocarbons by imaging with noncontact atomic force microscopy (AFM). The molecules were adsorbed onto a copper surface, and the AFM tip was decorated with a CO molecule, which was used to measure tip frequency shifts above the bonds and their apparent lengths. Multiple bonds appeared brighter in the images because of stronger Pauli repulsion, and their shorter length was amplified by bending of the CO at the tip apex. </jats:p>

<jats:title>Cooling Year-Round</jats:title> <jats:p> Ice cores from Greenland show that several abrupt cooling events occurred during the last glacial period and early Holocene—two of the most dramatic being the Younger Dryas [which lasted from around 12.9 to 11.7 thousand years ago (ka)] and 8.2-ka event (which began around 8200 years ago and lasted for ∼150 years). Wintertime temperatures in Greenland during the Younger Dryas seem to have been relatively lower than summertime temperatures although it is not clear if the 8.2-ka event experienced the same pattern of seasonal cooling. <jats:bold> Young <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="1330" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1222759">1330</jats:related-article> ) report observations of the positions of the leading edge of the Laurentide Ice Sheet and mountain glaciers on Baffin Island during the 8.2-ka event and find that mountain glaciers were larger than their predecessors during the Younger Dryas. It seems that cooling during the 8.2-ka event was more evenly distributed across the seasons than it was during that earlier cold period. </jats:p>

<jats:title>It's the Pits</jats:title> <jats:p> Cellular shape is tied to the cytoskeleton, with specialized regions of the plasma membrane attracting or repelling microtubules, a process mediated by the microtubule binding protein MIDD1. In plants, individual xylem cells are peppered with open pits that facilitate fluid transport and so <jats:bold>Oda and Fukuda</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1333" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1222597">1333</jats:related-article> ) studied ROP “Rho family guanosine triphosphatases of plants” proteins from xylem cells to investigate how pits develop. Formation of the pits seems to depend on MIDD1 to destabilize the microtubules at that point. A cascade of ROP proteins establishes the point at which MIDD1 functions, and reverse inhibition of one of the ROP proteins keeps the pit formation focused on a point. </jats:p>