Catálogo de publicaciones - revistas

<jats:p>A newly discovered messenger system between muscle and fat tissue may explain the systemic benefits of exercise.</jats:p>

<jats:p>The growth and coalescence of platinum nanocrystals held in a pocket created by graphene sheets is followed at atomic resolution in an electron microscope.</jats:p>

<jats:p>Bacterial speciation is driven by interplay between natural selection, genetic linkage, and lateral gene transfer.</jats:p>

<jats:p>Standardized criteria will help to reliably distinguish marks made by hominid tools from feeding traces of other animals.</jats:p>

<jats:title>Some Sort of Species</jats:title> <jats:p> Certain populations of bacteria are known to show ecological differentiation, but how this happens has remained controversial. <jats:bold> Shapiro <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="48" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218198">48</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="6077" page="45" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219241">Papke and Gogarten</jats:related-article> </jats:bold> ) examined whole-genome sequences from ecologically divergent <jats:italic>Vibrio</jats:italic> populations and found that genes and genome regions containing so-called “eco-SNPs” (single-nuleotide polymorphisms) have swept through populations. These regions differentiate the bacteria genetically, apparently according to the type of substratum on which they live. Subsequently, tight genotypic clusters may have emerged as a result of preferential recombination occurring within particular habitats. Although specialization into different habitats may reduce gene flow between bacterial populations, the bacteria will always remain open to taking up DNA from other populations and so they cannot be said to be species in the eukaryotic sense. </jats:p>

<jats:title>All Set for Majoranas</jats:title> <jats:p> When put in the proximity of a superconductor, topological insulators (TIs) are expected to support Majorana fermions, exotic particles that are their own antiparticles. For this to be realized, the interface between the TI and superconductor layers has to be atomically sharp but electronically transparent. <jats:bold> Wang <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="52" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1216466">52</jats:related-article> , published online 15 March) fabricated this heterostructure by growing a film of the TI material Bi <jats:sub>2</jats:sub> Se <jats:sub>3</jats:sub> on the superconductor NbSe <jats:sub>2</jats:sub> covered with a Bi bilayer. Scanning tunneling spectroscopy revealed a superconducting gap on the TI surface of the heterostructure with varying thickness of the Bi <jats:sub>2</jats:sub> Se <jats:sub>3</jats:sub> film. This coexistence of superconductivity and topological order should now allow observation of exotic phenomena such as Majorana fermions. </jats:p>

<jats:title>Here, There, Everywhere</jats:title> <jats:p> Random walks are a powerful mathematical method that can be used to simulate certain processes in biology, chemistry, or even the stock market. They present a statistical method for mapping the possible routes that processes can take. Quantum walks are expected to be able to probe multiple paths simultaneously. Quantum walks have been demonstrated for one-dimensional, or straight-line, walks. Now, <jats:bold> Schreiber <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="55" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218448">55</jats:related-article> , published online 8 March) demonstrate an optical system that can simulate quantum walks over a two-dimensional system, thereby providing the capability of describing much more complex processes. </jats:p>

<jats:title>Changing Polarization with Applied Stress</jats:title> <jats:p> The direction of electric polarization in ferroelectric materials can be switched with an applied field, but mechanical stresses can also couple to the polarization, forming the basis for piezoelectric effects. In principle, it should be possible to change the polarization of a ferroelectric material mechanically through stress gradients. <jats:bold> Lu <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="59" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218693">59</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="6077" page="41" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1220827">Gregg</jats:related-article> </jats:bold> ) demonstrate such switching for nanoscale-sized regions created by the stress induced with an atomic force microscope. The substrates are single-crystalline barium titanate films that have a vertically aligned dipole moment created by compressive stresses in the film. This approach may lead to memory devices in which bits are written mechanically but read electrically. </jats:p>

<jats:title>Liquid Nanocrystals</jats:title> <jats:p> In high-resolution transmission electron microscopy, grid materials are used to support solid samples while providing a means for preventing a build-up of static charge. Liquids are difficult to study at the same atomic resolution and require encapsulation to prevent excess sample movement, sample damage, or evaporation. Materials that have been used for liquid cells, like silicon nitride or silicon oxide, need thick layers and have poor electron transmittance at the thicknesses required because they contain high atomic number elements. <jats:bold> Yuk <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="61" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1217654">61</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="6077" page="44" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219835">Colliex</jats:related-article> </jats:bold> ) show that liquids can be encapsulated in graphene sheets, and through this technique, they studied the formation of platinum nanocrystals with atomic resolution. The crystals could be tracked as they selectively coalesced, modified their shape, and formed surface facets. </jats:p>

<jats:title>Copper-Bottomed Crust</jats:title> <jats:p> The formation of volcanic arc chains near subduction zones brings large amounts of magma from the upper mantle to the crust, contributing to the formation of island chains in the ocean and adding material to continents. Over time, arc magmas also contribute indirectly to the composition of the oceans and atmosphere through outgassing and weathering of volcanic minerals; however, it is unclear what determines the oxidized nature of arc magmas themselves. <jats:bold> Lee <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="64" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1217313">64</jats:related-article> ) measured Cu contents in a range of arc-derived volcanic rocks as a proxy for arc magma redox states. An overall depletion of Cu, which is sensitive to reduced sulfur contents, in global continental crust suggests that there is a hidden reservoir of copper-rich sulfides deep in Earth's interior. </jats:p>