Catálogo de publicaciones - revistas

<jats:title>The Cuprate Pseudogap</jats:title> <jats:p> The properties of copper-oxide superconductors are changed by chemical doping, but, if doping is suboptimal, the transition temperature <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> drops. Conversely, the so-called pseudogap, a depression in the density of states around the Fermi level that may or may not be related to superconductivity, gains strength. The cuprate YBa <jats:sub>2</jats:sub> Cu <jats:sub>3</jats:sub> O <jats:sub>6+x</jats:sub> shows a charge density order that grows as <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> is approached from both low and high temperatures. <jats:bold> Hayward <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1336" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246310">1336</jats:related-article> ) have developed a model in which classical fluctuations of a six-component order parameter, encompassing both superconducting and charge orders, reproduce the characteristic concave temperature dependence of the x-ray scattering intensity and thus provide a framework for the understanding of the pseudogap regime. </jats:p>

<jats:title>Giving Electrocatalysts an Edge</jats:title> <jats:p> Platinum (Pt) is an excellent catalyst for the oxygen-reduction reaction (ORR) in fuel cells and electrolyzers, but it is too expensive and scarce for widespread deployment, even when dispersed as Pt nanoparticles on carbon electrode supports (Pt/C). Alternatively, <jats:bold> Chen <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1339" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249061">1339</jats:related-article> , published online 27 February; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1319" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1251865">Greer</jats:related-article> </jats:bold> ) made highly active ORR catalysts by dissolving away the interior of rhombic dodecahedral PtNi <jats:sub>3</jats:sub> nanocrystals to leave Pt-rich Pt <jats:sub>3</jats:sub> Ni edges. These nanoframe catalysts are durable—remaining active after 10,000 rounds of voltage cycling—and are far more active than Pt/C. </jats:p>

<jats:title>Sourcing Martian Meteorites</jats:title> <jats:p> There are nearly 150 recognized martian meteorites, but where exactly they came from on Mars is not known. <jats:bold> Werner <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1343" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1247282">1343</jats:related-article> , published online 6 March) present evidence that the &lt;5 million-year-old Mojave impact crater on Mars is the single ejection site of one type of martian meteorites: the shergottites. The Mojave crater formed on an ancient terrain on Mars, and so the shergottites represent old martian crustal material. </jats:p>

<jats:title>Productive Dustiness</jats:title> <jats:p> The idea that biological productivity in the surface ocean is limited by a lack of available iron has been widely accepted, but it has been difficult to show that this effect might have operated in the geological past. <jats:bold> Martínez-García <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1347" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246848">1347</jats:related-article> ) investigated the isotopic composition of foraminifera-bound nitrogen in samples from an Ocean Drilling Project sediment core and found millennial-scale changes in nitrate consumption correlated with fluxes in the iron burial and productivity proxies over the past 160,000 years. Hence, in the Southern Ocean the biological pump was strengthened when dust fluxes were high, which explains a significant part of the difference in atmospheric CO <jats:sub>2</jats:sub> concentrations observed to occur across glacial cycles. </jats:p>

<jats:title>Predation Favors Parasitism</jats:title> <jats:p> Parasitism in birds often results in ejection or starvation of the host's nestlings. Consequently, many host bird species have evolved protective behavior such as mobbing and parasite egg rejection. Curiously, some host species show no parasite avoidance behaviors; for example, the crow <jats:italic>Corvus corone corone</jats:italic> tolerates cuckoo chicks among its own brood. In a long-term study, <jats:bold> Canestrari <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1350" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249008">1350</jats:related-article> ) found that crow nests containing a cuckoo chick had lower rates of predation because the parasite's chicks secrete a noxious repellent substance. Overall, in years of high predation pressure, the presence of cuckoos improves the crow's breeding success, but when there are fewer predators around, parasitism reduces crow fitness. </jats:p>

<jats:title>Coordinated Hair Growth</jats:title> <jats:p> Wnt/β-catenin signaling is a key pathway that plays a conserved role in regulating stem cell function during adult tissue regeneration. Using time-lapse imaging of live mice, <jats:bold> Deschene <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1353" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248373">1353</jats:related-article> ) show that genetic activation of β-catenin within hair follicle stem cells generates axes of hair growth by coordinated cell divisions and cell movements, even when the normal niches—the dermal papillae—are laser-ablated. Activated β-catenin enhances Wnt ligand secretion, and these ligands can then activate Wnt signaling in adjacent cells that do not have activated β-catenin, indicating how activated stem cells could influence neighboring cells during normal growth and in cancer. </jats:p>

<jats:title>Life and Cell Death</jats:title> <jats:p> Trying to protect animals from one form of cell death may lead to death by another. Two protein kinases, known as RIPK1 and RIPK3 promote signaling that leads to cell death by necroptosis. However, <jats:bold> Newton <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1357" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249361">1357</jats:related-article> , published online 20 February; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1322" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1252526">Zhang and Chan</jats:related-article> </jats:bold> ) found that inhibition of RIPK3 was not always beneficial. Instead, mice expressing a form of RIPK3 with no catalytic activity died from increased apoptotic cell death, but animals lacking the RIPK3 protein entirely, did not die perhaps because RIPK3 restrains apoptosis mediated by caspase-8 by an independent mechanism. </jats:p>

<jats:title>Transcripts Visualized in Situ</jats:title> <jats:p> Despite advances, current methods for single-cell sequencing are unable to resolve transcript location within the cell, so <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" issue="6177" page="1360" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1250212">1360</jats:related-article> , published online 27 February) developed a method of fluorescent in situ RNA sequencing (FISSEQ) that works in vivo to show messenger RNA localization within cells. The method amplifies complementary DNA targets by rolling circle amplification, and then in situ cross-linking locks amplicons to produce ample, highly localized templates for three-dimensional sequencing. The technique was tested in fibroblasts to reveal the differences between individual cells during wound repair. </jats:p>

<jats:title>Translocation in Injury</jats:title> <jats:p> The translocator protein TSPO is essential for the import of cholesterol and porphyrins into mitochondria. TSPO expression increases in areas of brain injury and during neuroinflammation and, thus, has diagnostic and therapeutic implications. <jats:bold> Jaremko <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1363" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248725">1363</jats:related-article> ) used nuclear magnetic resonance spectroscopy to determine the high-resolution structure of the 18- kilodalton mammalian TSPO with the ligand PK11195, which stabilized the structure and resolved the conformation as a tight bundle of five helices. </jats:p>

<jats:title>Serial Mutation</jats:title> <jats:p> Mutations that affect gene function and, ultimately, the phenotype of an organism are grist to the mill of evolution. While examining the genetic basis for a stable polymorphism observed in bacteria during a long-term mutation experiment, <jats:bold> Plucain <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6177" page="1366" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248688">1366</jats:related-article> , published online 6 March) identified three specific, successive mutational events exhibiting synergistic epistatic and frequency-dependent interactions that enabled one lineage to invade the other and to be maintained. Thus, a series of specific mutations conferred the invasion phenotype and allowed the use of novel resources only when all mutations were present. </jats:p>