Catálogo de publicaciones - revistas

<jats:title> Honing in on HONO <jats:sub>2</jats:sub> </jats:title> <jats:p> Modeling air pollution requires knowledge of all the interrelated reactions occurring in the atmosphere. Among the most significant is the formation of nitric acid (HONO <jats:sub>2</jats:sub> ) from OH and NO <jats:sub>2</jats:sub> radicals. One sticking point in the study of this reaction has been the uncertainty in how often radicals link through an O-O rather than an O-N bond. <jats:bold> Mollner <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="646" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193030">646</jats:related-article> ) measured the partitioning coefficient, as well as the overall consumption rate of the radicals, with an array of highly sensitive spectroscopic techniques in the laboratory. The measurements yielded a well-defined rate constant for nitric acid formation, which was applied to the prediction of ozone levels in atmospheric simulations of the Los Angeles basin. </jats:p>

<jats:title>Designing Carbon Dioxide Traps</jats:title> <jats:p> One widely discussed means of stemming the rise in atmospheric carbon dioxide concentration is to capture the gas prior to its emission and then bury it. The materials currently known to best adsorb CO <jats:sub>2</jats:sub> for this purpose tend to involve amine groups; however, the precise molecular details of adsorption often remain murky, and rational improvement of sorbent properties by structural modification has been challenging. <jats:bold> Vaidhyanathan <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="650" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194237">650</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="6004" page="595" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1198066">Lastoskie</jats:related-article> </jats:bold> ) have crystallographically resolved the binding motifs of CO <jats:sub>2</jats:sub> in an amine-bearing metal-organic framework solid. Accompanying theoretical simulations matched the experimental observations. </jats:p>

<jats:title>Closing in on Extraterrestrial Earths</jats:title> <jats:p> With close to 500 extrasolar planets discovered to date, researchers are starting to estimate the occurrence of low-mass planets to help our understanding of how planets form and evolve. Based on observations of 166 nearby stars with the Keck Telescope, <jats:bold> Howard <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="653" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194854">653</jats:related-article> ) report the occurrence of short-period planets around Sun-like stars as a function of planet mass. Planet formation models predicted that planet occurrence would increase with decreasing mass, such that satellites with masses similar to that of Neptune, and less, would be more common than gas-giant planets like Jupiter. Contrary to predictions, there is no dearth of planets with masses 5 to 30 times that of Earth, implying that the models may need revision. Nevertheless, observations suggest that 23% of Sun-like stars may be orbited by a close-in, terrestrial mass planet. </jats:p>

<jats:title>Gallium Nitride Grown on Graphene</jats:title> <jats:p> Nitride semiconductor materials used in light-emitting diodes and lasers are usually grown on single-crystal sapphire substrates with intermediate buffer layers. Instead, <jats:bold> Chung <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="655" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195403">655</jats:related-article> ) used graphene as a substrate for gallium nitride growth and found that nucleation of the gallium nitride layers was enhanced by first depositing zinc oxide, which grew as vertical nanowalls on the graphene. The gallium nitride layers displayed strong photo- and electroluminescence and, even better, the layers could be transferred to flexible substrates such as plastic. </jats:p>

<jats:title>Lost Details</jats:title> <jats:p> Changes in ocean circulation are commonly inferred by differences between the distribution of carbon isotopes in the past and now, but making such comparisons neglects the fact that modern fossil fuel burning has modified the carbon isotopic composition of the ocean. This in turn obscures details about recent mass movement of water. <jats:bold>Olsen and Ninnemann</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="658" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193769">658</jats:related-article> ) correct for this effect in the North Atlantic and show that the natural distribution of carbon isotopes has more detail and is clearly related to water mass distributions. The results change some important ideas about glacial-interglacial ocean variations within the context of modern climate variability. </jats:p>

<jats:title>Ancient Innovations</jats:title> <jats:p> Pressure flaking is a method of forming points, grooves, and notches on stone tools in which a tool is pressed up against another stone, instead of striking it. It has been thought to be a fairly recent innovation, arising in the Upper Paleolithic 20,000 or so years ago. <jats:bold> Mourre <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="659" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195550">659</jats:related-article> ), show that tools from Blombos Cave, dating to about 75,000 years ago, have grooves and patterns resembling production by heat treatment followed by pressure flaking. Replication experiments were performed using similar source material followed by microscopic study of the tools. Despite the evidence for an early innovation, it seems that pressure flaking was not used widely elsewhere until much later; thus, such early innovations may have been sporadic ephemeral. </jats:p>

<jats:title>Self-Recognition and Survival</jats:title> <jats:p> Soay sheep are a remnant of an ancient breed of sheep that, although intensively studied for many years, live unmanaged on the remote Scottish island of St. Kilda. Life is harsh on the island, and the numbers of sheep show cycles of winter population crashes and high exposure to infection. <jats:bold> Graham <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="662" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194878">662</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="6004" page="602" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1198303">Martin and Coon</jats:related-article> </jats:bold> ) measured levels of self-reactive antibodies in the sheep called antinuclear antibodies (ANA). Having high ANA levels was a heritable trait that reflected generally high levels of immunoglobulin in individuals and of specific antibodies to parasitic worms. Female sheep with high levels of ANAs survived better during crash years, but had fewer births. If these sheep did reproduce, although the lambs tended to be small, they tended to have higher rates of early survival. Thus, maintaining high antibody levels apparently reflected investment in immunity and greater survival, but doing so was also associated with reduced reproductive success. </jats:p>

<jats:title>Innate Innit?</jats:title> <jats:p> Innate lymphocytes (ILCs) are a recently described population of immune cells that produce cytokines like those associated with T helper cells, but lack the recombined antigen receptors characteristic of T cells. Again, like some T helper cell lineages, a proportion of ILCs express the transcription factor RORγt. These include lymphoid tissue inducer (LTi) cells required for fetal lymphoid tissue organogenesis and a population of natural killer (NK)–like cells that function in gut immune responses. <jats:bold> Sawa <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="665" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194597">665</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="6004" page="594" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1198298">Veldhoen and Withers</jats:related-article> </jats:bold> ) wondered whether the RORγt-expressing ILCs all develop from the same progenitor population. Indeed, they found a fetal liver progenitor that gave rise to several phenotypically distinct populations. However, the LTi cells were not progenitors for the NK-like cells. It seems the trajectory of different ILC populations is developmentally regulated, and postnatally ILCs are favored that play a role in intestinal defense before the gut is fully colonized by intestinal microbiota. </jats:p>

<jats:title>Small Is Attractive</jats:title> <jats:p> The optic tectum of zebrafish larvae is required for the detection, tracking, and capture of small, highly motile prey. <jats:bold> Del Bene <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="669" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1192949">669</jats:related-article> ) applied a combination of optical, genetic, and pharmacological tools to investigate how neural circuits in the optic tectum filter out low-frequency visual information. Most tectal neurons were tuned to respond selectively to small, moving objects in the fish's visual environment and responded very poorly to large stimuli. This spatial filtering mechanism depended on the activity of a small population of GABAergic, inhibitory interneurons at the tectal surface. Inactivation or destruction of these interneurons removed the size selectivity of deeper neurons and the zebrafish lost their ability to catch prey. </jats:p>

<jats:title>Ribosome Assembly Pathway</jats:title> <jats:p> The bacterial ribosome is made up of two subunits (50 <jats:italic>S</jats:italic> and 30 <jats:italic>S</jats:italic> ) that together comprise 55 proteins and three large ribosomal RNAs. Both subunits self-assemble from their components in vitro, and hence, <jats:bold> Mulder <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="673" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193220">673</jats:related-article> ) were able to use a derivation of time-resolved electron microscopy to monitor assembly of the 30 <jats:italic>S</jats:italic> subunit. This approach identified 14 distinct assembly intermediates and allowed characterization of the population, conformation, and protein composition of the intermediates along the assembly pathway. </jats:p>