Catálogo de publicaciones - revistas

<jats:title>Assessing Biodiversity Declines</jats:title> <jats:p> Understanding human impact on biodiversity depends on sound quantitative projection. <jats:bold> Pereira <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="1496" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1196624">1496</jats:related-article> , published online 26 October) review quantitative scenarios that have been developed for four main areas of concern: species extinctions, species abundances and community structure, habitat loss and degradation, and shifts in the distribution of species and biomes. Declines in biodiversity are projected for the whole of the 21st century in all scenarios, but with a wide range of variation. <jats:bold> Hoffmann <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="1503" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194442">1503</jats:related-article> , published online 26 October) draw on the results of five decades' worth of data collection, managed by the International Union for Conservation of Nature Species Survival Commission. A comprehensive synthesis of the conservation status of the world's vertebrates, based on an analysis of 25,780 species (approximately half of total vertebrate diversity), is presented: Approximately 20% of all vertebrate species are at risk of extinction in the wild, and 11% of threatened birds and 17% of threatened mammals have moved closer to extinction over time. Despite these trends, overall declines would have been significantly worse in the absence of conservation actions. </jats:p>

<jats:p>Three types of temporally linked slow earthquakes may limit nearby buildup of stress.</jats:p>

<jats:title>Assessing Biodiversity Declines</jats:title> <jats:p> Understanding human impact on biodiversity depends on sound quantitative projection. <jats:bold> Pereira <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="1496" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1196624">1496</jats:related-article> , published online 26 October) review quantitative scenarios that have been developed for four main areas of concern: species extinctions, species abundances and community structure, habitat loss and degradation, and shifts in the distribution of species and biomes. Declines in biodiversity are projected for the whole of the 21st century in all scenarios, but with a wide range of variation. <jats:bold> Hoffmann <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="1503" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194442">1503</jats:related-article> , published online 26 October) draw on the results of five decades' worth of data collection, managed by the International Union for Conservation of Nature Species Survival Commission. A comprehensive synthesis of the conservation status of the world's vertebrates, based on an analysis of 25,780 species (approximately half of total vertebrate diversity), is presented: Approximately 20% of all vertebrate species are at risk of extinction in the wild, and 11% of threatened birds and 17% of threatened mammals have moved closer to extinction over time. Despite these trends, overall declines would have been significantly worse in the absence of conservation actions. </jats:p>

<jats:title>Making a Point with Metamaterials</jats:title> <jats:p> A long-predicted electromagnetic excitation, the toroidal moment (or anapole), is associated with toroidal shape and current flow within a structure and has been implicated in nuclear and particle physics. This distinct family of electromagnetic excitations has not been observed directly because they are masked by much stronger electric and magnetic multipoles. <jats:bold> Kaelberer <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="1510" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1197172">1510</jats:related-article> , published online 4 November) have developed a metamaterial structure based on stacked loops of inverted split-ring resonators (“metamolecules”) whose response under excitation is consistent with the existence of a toroidal moment. The metamaterial is designed so that both the electric and magnetic dipole moments induced by an incident electromagnetic wave are suppressed, while the toroidal response is isolated and resonantly enhanced to a detectable level. </jats:p>

<jats:title>Supersolidity in a Spin</jats:title> <jats:p> Observing superfluid flow in a solid is a counterintuitive finding that has been accomplished by freezing <jats:sup>4</jats:sup> He inside a torsional oscillator and monitoring the oscillating period as the temperature is lowered: A reduction in the oscillating period will be observed at the supersolid transition when the mass of the superfluid decouples from the oscillator and the remaining normal component of the solid. However, extraneous classical effects can also cause this reduction, and so, to confirm supersolid formation, <jats:bold> Choi <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="1512" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1196409">1512</jats:related-article> , published online 18 November) performed a slightly different measurement. Rotation was superimposed onto the oscillating motion, and the period and the shear modulus of the system were measured simultaneously. These two quantities exhibited very different responses to the rotation speed, suggesting that supersolidity (rather than classical effects that would also affect the shear modulus) is indeed at the root of the previously observed change in the oscillating period. </jats:p>

<jats:title>Fragile Tin Oxide Electrodes</jats:title> <jats:p> While tin oxide has a high energy density, and would thus make an attractive anode material for a Li-ion battery, it undergoes significant volume changes when Li is intercalated. The large strains cause cracking, pulverization, and a resultant loss of electrical conduction. <jats:bold> Huang <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="1515" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195628">1515</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="6010" page="1485" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1198591">Chiang</jats:related-article> </jats:bold> ) used in situ transmission electron microscopy on a single tin oxide nanowire to identify the physical changes that occur during intercalation and observed a moving cloud of dislocations that separated the reacted and unreacted sections. Upon completion of the electrochemical charging, the nanowire showed up to 90% elongation and a 35% increase in diameter. </jats:p>

<jats:title>Mechanical Transparency</jats:title> <jats:p> In atomic gases and other solid-state systems with appropriate energy levels, manipulation of the optical properties can be induced with a control pulse, allowing the system to transmit light of specific wavelengths that would otherwise have been absorbed. <jats:bold> Weis <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="1520" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195596">1520</jats:related-article> , published online 11 November) now report electromagnetically induced transparency in an optomechanical system whereby the coupling of a cavity to a light pulse is used to control the transmission of light through the cavity. This approach may help to allow the engineering of light storage and routing on an optical chip. </jats:p>

<jats:title>Positive Message</jats:title> <jats:p> Climate warming affects both cloud number and cloud properties, which in turn affect warming itself, creating a cloud-climate feedback that complicates predictions of the amount of warming caused by increasing concentrations of atmospheric carbon dioxide. This feedback has generally been considered to be positive, but so far we have only a qualitative idea of the effect. <jats:bold>Dessler</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1523" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1192546">1523</jats:related-article> ; see the news story by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6010" page="1465" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.330.6010.1465">Kerr</jats:related-article> </jats:bold> ) estimated the magnitude of the feedback by analyzing 10 years of satellite data on the flux of radiation through the top of the atmosphere. As expected, the feedback is positive and within the canonical range of estimates of how much warming will occur for a doubling of atmospheric CO <jats:sub>2</jats:sub> : 2°C to 4.5°C. </jats:p>

<jats:title>For the Love of Iron</jats:title> <jats:p> Iron-loving elements such as Re, Os, Ir, Pt, Rh, Pd, and Au must have been delivered to the upper mantle of Earth, Mars, and the Moon after formation of the planetary cores, because, before that, these elements tended to bond with the core's metallic iron, stripping them from the planetary upper layers. Using Monte Carlo models, <jats:bold> Bottke <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="1527" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1196874">1527</jats:related-article> ) show that the relative abundances of iron-loving elements on Earth, Mars, and the Moon can be explained if most of the impacting planetesimals that delivered the elements had sizes extending up to several thousand kilometers. In these circumstances, most of the iron-loving elements would arrive in a small number of random impacts, the most massive of which hit Earth but not the Moon. Some of these impacts may also have altered Earth's obliquity, produced the Moon's orbital inclination, and delivered water to the Moon's mantle. </jats:p>

<jats:title>All in the Mind</jats:title> <jats:p> Pavlov's experiments, in which dogs salivate in anticipation of food, mirror our own imagined experience; that is, thinking about the future consumption of chocolate enhances our desire for it and our motivation to obtain it. After several bites, however, our appetite usually wanes and the offer of a second bar is less appealing than the first. <jats:bold> Morewedge <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="1530" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195701">1530</jats:related-article> ) show that the decrease in hedonic response can also be induced by having imagined eating the first bar of chocolate. In comparisons of subjects asked to imagine the repetitive consumption of candy or cheese, they observed a specific drop in the amount consumed when subjects were actually offered the previously imagined foods to eat. </jats:p>