Catálogo de publicaciones - revistas

<jats:title>The Galaxy Center in X-rays</jats:title> <jats:p> At the center of our Galaxy there is a black hole 4-million-fold more massive than the Sun. <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" issue="6149" page="981" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240755">981</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="6149" page="964" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1243115">Schnittman</jats:related-article> </jats:bold> ) report x-ray data on the accretion flow around this supermassive black hole, revealing how it interacts with its surroundings. The data rule out the possibility that the quiescent (that is, flare-free) x-rays observed are produced by coronal emission from a population of stars at the center of the Galaxy and also rule out the possibility that there is a pure radiatively inefficient accretion flow with no outflows. </jats:p>

<jats:title>Hydrogel Stretch</jats:title><jats:p>A range of stretchable, conductive materials can be made either by making an electrical conductor more stretchable or by adding an electrical conductor to a stretchable material.<jats:bold>Keplinger<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="6149" page="984" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240228">984</jats:related-article>; see the Perspective by<jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6149" page="968" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1243314">Rogers</jats:related-article>) have added to the possibilities of an alternative stretchable ionic conductor based on a hydrogel material used to make deformable devices that are fully transparent to light over the visible spectrum and that can withstand high voltages and high frequencies.</jats:p>

<jats:title>Oxide Chemistry Below the Surface</jats:title> <jats:p> Although metal oxides, such as titanium dioxide (TiO <jats:sub>2</jats:sub> ), are used for catalytic oxidation reactions and photocatalysis, the O <jats:sub>2</jats:sub> does not react directly with substrates. Vacancies in the surface region of the TiO <jats:sub>2</jats:sub> rutile phase can transfer a negative charge to adsorbed O <jats:sub>2</jats:sub> to create more reactive species. By contrast, in anatase—the phase associated with nanoscale TiO <jats:sub>2</jats:sub> particles—subsurface vacancies form. <jats:bold> Setvin <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="6149" page="988" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239879">988</jats:related-article> ) used a scanning tunneling microscopy tip to pull these vacancies to the surface in a niobiumdoped anatase crystal and followed the transformation of adsorbed O <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> into a peroxo species and a bridging O <jats:sub>2</jats:sub> dimer. </jats:p>

<jats:title>Local Acceleration</jats:title> <jats:p> How the electrons trapped in Earth-encircling Van Allen radiation belts get accelerated has been debated since their discovery in 1958. <jats:bold> Reeves <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="6149" page="991" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1237743">991</jats:related-article> , published online 25 July) used data from the Van Allen Radiation Belt Storm Probes, launched by NASA on 30 August 2012, to discover that radiation belt electrons are accelerated locally by wave-particle interactions, rather than by radial transport from regions of weaker to stronger magnetic fields. </jats:p>

<jats:title>A Uranian Trojan</jats:title> <jats:p> Bodies that share their orbit with that of a planet and that trail or lead the planet by 60° are called Trojans. Based on data from the Canada-France-Hawaii Telescope, <jats:bold> Alexandersen <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="6149" page="994" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1238072">994</jats:related-article> ) have found an object shadowing Uranus that is predicted to remain a Trojan for at least 700,000 years and to stay in co-orbital motion for around one million years before escaping. </jats:p>

<jats:title>Ice Lubricant</jats:title> <jats:p> The Greenland and Antarctic ice sheets both possess hydrological systems that allow water accumulating from the melting of surface ice to be transported to the base of the ice sheet. If that water, when it reaches the ice-bedrock interface, is distributed over large areas, it will lubricate rapid ice sheet flow toward the sea. <jats:bold> Bamber <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="6149" page="997" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239794">997</jats:related-article> ) report the existence of a large, 750-km-long subglacial canyon in northern Greenland, which may act as a channel for the transport of basal meltwater to the margin of the ice sheet and thus influence overall ice sheet dynamics. </jats:p>

<jats:title>Follow the Leader</jats:title> <jats:p> How birds migrate between wintering and breeding grounds, often over thousands of kilometers through difficult conditions, remains mysterious. The recovery of North American Whooping Cranes by release of captive-reared birds trained to migrate by following aircraft provided an opportunity for <jats:bold> Mueller <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="6149" page="999" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1237139">999</jats:related-article> ; see the cover) to analyze 8 years of data for individual birds. The presence of older birds within a group of migrating cranes significantly decreased the deviations the flock took from a straight line migration path. The lack of evidence for a genetic component indicates that social learning dominates any innate capacity in developing migratory behavior. </jats:p>

<jats:title>Egg WAVE1</jats:title> <jats:p> Eggs not only activate sperm nuclei for normal development but also reprogram transplanted somatic nuclei. In addition to its well-established cytoplasmic role in actin organization, <jats:bold> Miyamoto <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="6149" page="1002" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240376">1002</jats:related-article> ) discovered that the Wiskott-Aldrich syndrome protein family member 1 in oocytes cooperates with transcriptional machineries in the nucleus to activate previously silenced genes. </jats:p>

<jats:title>Pluripotency Control</jats:title> <jats:p> The transcription factors Pou5f1/Oct4, Sox2, and Nanog play central roles in pluripotency control in mammalian embryonic stem (ES) cells. The evolution of the pluripotency regulatory network and its roles during early development of nonmammalian vertebrates is unknown. <jats:bold> Leichsenring <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="6149" page="1005" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242527">1005</jats:related-article> , published online 15 August) show that in zebrafish embryos, Pou5f1 controls priming and transcriptional activation of the first zygotically expressed genes. This mechanism for transition from the transcriptionally silent cleavage stage to the transcriptionally active blastula stage may have evolved to control the prolonged cell pluripotency state in mammalian early development and ES cells, establishing a link between zygotic gene activation and pluripotency control. </jats:p>

<jats:title>Cilium Conundrum</jats:title> <jats:p> The cilium has emerged as the antenna of eukaryotic cells, having numerous functions in sensory reception and developmental signaling. Several disorders, such as polycystic kidney disease, are the result of compromised cilia structure. <jats:bold> Bhogaraju <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="6149" page="1009" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240985">1009</jats:related-article> ) elucidate how the intraflagellar transport machinery recognizes tubulin, a ciliary cargo that is integral to cilium maintenance and formation and is constantly turned over at the cilium tip. </jats:p>