Catálogo de publicaciones - revistas

<jats:p>Full-stress flow models for ice sheets promise improved projections of sea-level change.</jats:p>

<jats:p>How much diversity is needed to maintain the productivity of ecosystems?</jats:p>

<jats:p>Naturally blond hair in Solomon Islanders maps to a missense mutation in a gene associated with pigmentation.</jats:p>

<jats:title>Giant Spin Hall</jats:title> <jats:p> One of the primary challenges in the field of spin-electronics, which exploits the electron's spin rather than its charge, is to create strong currents of electrons with polarized spins. One way to do this is to use a ferromagnet as a polarizer, a principle used in magnetic tunnel junctions; however, these devices suffer from reliability problems. An alternative is the spin Hall effect, where running a charge current through a material generates a spin current in the transverse direction, but the efficiency of this process tends to be small. <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="555" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218197">555</jats:related-article> ) now show that the spin Hall effect in Tantalum in its high-resistance β phase generates spin currents strong enough to induce switching of the magnetization of an adjacent ferromagnet; at the same time, Ta does not cause energy dissipation in the ferromagnet. These properties allowed efficient and reliable operation of a prototype three-terminal device. </jats:p>

<jats:title>Going to Ground</jats:title> <jats:p> Frustrated systems, in which the geometry of the crystal lattice stands in the way of achieving an energetic minimum on all lattice sites simultaneously, have the potential to remain disordered down to the lowest temperatures. Numerous experimental efforts to find a material with a truly fluctuating ground state have failed because ordering often sets in at a finite temperature owing to symmetry breaking. <jats:bold> Nakatsuji <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="559" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1212154">559</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="6081" page="547" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1221364">Balents</jats:related-article> </jats:bold> ) identify the compound Ba <jats:sub>3</jats:sub> CuSb <jats:sub>2</jats:sub> O <jats:sub>9</jats:sub> as a promising candidate for this state; the Cu-Sb dipoles reside on a hexagonal structure, forming fluctuating spin singlets. Multiple lines of evidence suggest that the material does not order down to the millikelvin temperature range, remaining magnetically isotropic. </jats:p>

<jats:title>Uneven Gap</jats:title> <jats:p> Electron pairs that are responsible for the phenomenon of superconductivity can only be broken by investing a finite amount of energy, called the energy gap. The size of the gap may depend on the position on the Fermi surface; in cuprates, the gap completely disappears at certain points. What happens in the pnictide superconductors is still a subject of debate, not least because there appear to be differences between the different pnictide families. <jats:bold> Allan <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="563" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218726">563</jats:related-article> ) used scanning tunneling spectroscopy to study the compound LiFeAs. The gap was mapped on three of the five bands on which the Fermi surface resides and was found to be anisotropic in momentum space. </jats:p>

<jats:title>Magnetic Reconnection</jats:title> <jats:p> Magnetic reconnection (MR) has been observed in the magnetospheres of planets with an intrinsic magnetic field, such as Earth, Mercury, Jupiter, and Saturn. MR is a universal plasma process that occurs in regions of strong magnetic shear and converts magnetic energy into kinetic energy. On Earth, MR is responsible for magnetic storms and auroral events. Using data from the European Space Agency Venus Express spacecraft, <jats:bold> Zhang <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="567" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1217013">567</jats:related-article> , published online 5 April; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6081" page="548" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1221805">Slavin</jats:related-article> </jats:bold> ) present surprising evidence for MR in the magnetosphere of Venus, which is a nonmagnetized body. </jats:p>

<jats:title>Martian Veins</jats:title> <jats:p> After more than 7 years of traveling across the Meridiani Planum region of Mars, the Mars Exploration rover Opportunity reached the Endeavour Crater, a 22-km-impact crater made of materials older than those previously investigated by the rover. <jats:bold> Squyres <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="570" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1220476">570</jats:related-article> ) present a comprehensive analysis of the rim of this crater. Localized zinc enrichments that provide evidence for hydrothermal alteration and gypsum-rich veins that were precipitated from liquid water at a relatively low temperature provide a compelling case for aqueous alteration processes in this area at ancient times. </jats:p>

<jats:title>Not So Fast</jats:title> <jats:p> Recent observations of some of Greenland's outlet glaciers have shown large and rapid increases in the speeds at which their ice has streamed to the sea. Simple projections of ice loss and sea level rise, based only on these increases, result in alarmingly high values and correspondingly great public concern. In order to provide a more comprehensive and detailed picture of this type of ice sheet mass loss, <jats:bold> Moon <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="576" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219985">576</jats:related-article> ; see the cover) compiled a decade-long record of ice stream velocity measurements for nearly all of Greenland's major outlet glaciers. The pattern of flow variability around the ice sheet was both spatially and temporally complex, with clear differences between marine- and land-terminating types, as well as between regions. Furthermore, the integrated velocity of all of the outlet glaciers measured was considerably less than the upper bounds that have been proposed on the basis of a few rapidly accelerating locations, implying that sea level rise over the next century may be less than the 2 meters that have been suggested. </jats:p>

<jats:title>Small But Perfectly Formed</jats:title> <jats:p> The imaginal discs of <jats:italic>Drosophila</jats:italic> represent defined larval tissues that give rise to the subsequent adult appendages. These tissues regenerate in response to damage. When the imaginal discs are injured or show tumor growth, they signal to the rest of the larval animal to slow down growth and delay morphogenesis. <jats:bold> Garelli <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="579" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1216735">579</jats:related-article> ) and <jats:bold> Colombani <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="582" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1216689">582</jats:related-article> ) now show that an insulin-like peptide, termed Dilp8, is secreted into the hemolymph (insect “blood”) and participates in the communication between growing organs and the endocrine system to adjust the growth program and maturation time. This collaboration ensures that adults attain the normal size and maintain appropriate proportions and symmetry. </jats:p>