Catálogo de publicaciones - revistas

<jats:title>Electron Breakdown</jats:title> <jats:p> An electron possesses charge and spin. In general, these properties are confined to the electron. However, in strongly interacting many-body electronic systems, such as one-dimensional wires, it has long been theorized that the charge and spin should separate. There have been tantalizing glimpses of this separation experimentally, but questions remain. <jats:bold> Jompol <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="597" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1171769">597</jats:related-article> ) looked at the tunneling current between an array of one-dimensional wires and a two-dimensional electron gas and argue that the results reveal a clear signature of spin-charge separation. </jats:p>

<jats:title>Genesis of Binary Stars</jats:title> <jats:p> Numerical simulations of collapsing clouds of primordial gas indicate that the first luminous objects to form in the universe were isolated massive stars. <jats:bold> Turk <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="601" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173540">601</jats:related-article> , published online 9 July) now show that it is possible for single primordial clouds to break up into two dense cores. Three-dimensional calculations, which follow the evolution of primordial gas (composed of hydrogen and helium, with traces of deuterium and lithium) and dark matter starting from realistic, cosmological initial conditions, suggest that these cores may evolve to form binary star systems. </jats:p>

<jats:title>Tracing Mantle Oxidation</jats:title> <jats:p> The chemical composition of the Earth's mantle varies with tectonic setting. For example, basaltic melts near subduction zones are more oxidized than magma near divergent plate boundaries. <jats:bold>Kelley and Cottrell</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="605" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174156">605</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="5940" page="545" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176882">Hirschmann</jats:related-article> </jats:bold> ) examined melts formed in different tectonic environments, using highly sensitive synchrotron-based analytical methods. The oxidation state of Fe increased with water content and mobile trace elements concentrations. Thus, fluids released from wet subducting plates drive mantle oxidation above subduction zones, which may help to explain the spatial differences in oxygen fugacity of the mantle. </jats:p>

<jats:title>Expanding Sulfonylurea Mechanisms</jats:title> <jats:p> Sulfonylureas are important drugs used for treatment of diabetes that act through adenosine triphosphate–sensitive potassium channels to promote secretion of insulin from the pancreas. <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="607" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1172256">607</jats:related-article> ) present another mechanism by which the beneficial effects of sulfonylureas may also be obtained. Sulfonylureas were identified in a screen for substances that modify the activity of Epac2, a guanine nucleotide exchange factor for the small guanosine triphosphatase Rap1. Mice lacking Epac2 were less responsive to sulfonylureas, which may suggest that Epac2 would be a useful target for development of drugs for treatment of diabetes. </jats:p>

<jats:title>Young and Flexible</jats:title> <jats:p> How an infant learns to understand and speak a language remains a deep scientific mystery even though millions of kids accomplish these feats each year. Furthermore, this learning capacity is apparently not even taxed to its utmost; children who grow up in bilingual families learn two languages just as rapidly as those who learn only one. <jats:bold>Kovács and Mehler</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="611" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173947">611</jats:related-article> , published online 9 July) have assessed the cognitive flexibility of preverbal 1-year-old children raised in monolingual versus bilingual households and find that the bilingual group displays an impressive facility in handling inconsistent, language-like, inputs. That is, the kids exposed to two distinct languages since birth were able to associate two distinct syllabic structures—AAB and ABA—with looking leftward and rightward, whereas the monolinguals could only do so only with the simpler AAB structure. </jats:p>

<jats:title>Monitoring Monocyte Reservoirs</jats:title> <jats:p> Monocytes are cells of the immune system that are recruited to sites of tissue injury and inflammation where they help to resolve the infection and are important for tissue repair. The bone marrow and blood are believed to be the primary reservoirs from which monocytes are mobilized after injury. <jats:bold> Swirski <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="612" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175202">612</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="5940" page="549" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178329">Jia and Pamer</jats:related-article> </jats:bold> ) now demonstrate that the spleen also serves as a critical reservoir of monocytes that are recruited during ischemic myocardial injury. Monocytes in the spleen are very similar in phenotype to blood-derived monocytes and are mobilized to the injured heart, where they represent a large fraction of the total monocytes that are recruited. The chemoattractant, angiotensin II, is required for optimal monocyte mobilization from the spleen and emigration into injured tissue. </jats:p>

<jats:title>Maintaining Mutual Ignorance</jats:title> <jats:p> Our gut is colonized by trillions of bacteria that do not activate the immune system because of careful compartmentalization. Such compartmentalization means that our immune system is “ignorant” of these microbes and thus it has been proposed that loss of compartmentalization might result in an immune response to the colonizing bacteria. Microorganisms are sensed by cells that express pattern recognition receptors, such as Toll-like receptors, which recognize patterns specific to those microbes. <jats:bold> Slack <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="617" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1172747">617</jats:related-article> ) show that Toll-like receptor–dependent signaling is required to maintain compartmentalization of bacteria to the gut of mice. In the absence of Toll-dependent signaling, intestinal bacteria disseminated throughout the body and the mice mounted a high-titer antibody response against them. This antibody response was of great functional importance because, despite the loss of systemic ignorance to intestinal microbes, the mice were tolerant of the bacteria. Thus, in the absence of innate immunity, the adaptive immune system can compensate so that host and bacterial mutualism can be maintained. </jats:p>

<jats:title>Brain Rewiring After Stress</jats:title> <jats:p> Chronic stress, mainly through the release of corticosteroids, affects executive behavior through sequential structural modulation of brain networks. Stress-induced deficits in spatial reference, working memory, and behavioral flexibility are associated with synaptic and dendritic reorganization in both the hippocampus and the medial prefrontal cortex. However, the effects of chronic stress on action selection strategies are unclear. <jats:bold> Dias-Ferreira <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="621" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1171203">621</jats:related-article> ) examined whether chronic stress affects the ability of animals to select the appropriate actions based on the consequences of their choice, and found that rats exposed to chronic unpredictable stress rapidly shift toward using habitual strategies. The shift in behavioral strategies observed in chronically stressed animals corresponded to dramatic and divergent changes in connectivity in the associative and sensorimotor corticostriatal circuits underlying these behaviors. </jats:p>

<jats:title>Gradual Unpacking</jats:title> <jats:p> Eukaryotic DNA is packaged onto nucleosomes, which form the main constituent of chromatin. This packaging material presents a barrier to accessing the genome by the various machineries that need to deal with the DNA: replication, recombination, repair, and transcription complexes, for example. <jats:bold> Hodges <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="626" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1172926">626</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="5940" page="547" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1177311">Otterstrom and van Oijen</jats:related-article> </jats:bold> ) use single-molecule techniques to analyze how a yeast RNA polymerase II ternary elongation complex copes when it encounters a single nucleosome directly in its path. The polymerase does not actively peel the DNA from the nucleosome's surface but, instead, waits patiently until the DNA fluctuates off the nucleosome and then advances, increment by increment, until the nucleosome is destabilized. Under certain conditions the destabilized nucleosome, rather than being lost entirely from the DNA, can be passed back to the DNA behind the polymerase. </jats:p>

<jats:p>The show includes assessing ecological restoration, rethinking graduate student funding, science in Venezuela, and more.</jats:p>