Catálogo de publicaciones - revistas

<jats:title>Merging Coma</jats:title> <jats:p> Galaxy clusters grow through mergers and accretion of matter to become the largest gravitationally bound structures in the universe. <jats:bold> Sanders <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="6152" page="1365" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1238334">1365</jats:related-article> ) report long, high-resolution observations with NASA's Chandra X-ray Observatory that probe hot, ionized gas at the core of the Coma cluster—one of the nearest and best-studied galaxy clusters. The data reveal several large-scale, filament-shaped x-ray brightness enhancements, which provide insight into the cluster's merging history. </jats:p>

<jats:title>Dissipating Static</jats:title> <jats:p> The accumulation of a static charge on polymers and other insulators often causes little more than a slight annoyance but it can lead to the destruction of sensitive electrical equipment. Thus, approaches are required that prevent and dissipate static electricity through improved electrical conductivity, or that ensure complete discharge before a contact with a key piece of equipment. <jats:bold> Baytekin <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="6152" page="1368" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241326">1368</jats:related-article> ) show that surface charges will colocalize with radicals on the surface of a polymer, and that the addition of free radical scavengers causes a discharge of the surface as the charges are removed. The approach was used successfully to produce coatings that protected electronic circuits from damage caused by electrostatic discharge. </jats:p>

<jats:title>Polymer Dynamics</jats:title> <jats:p> While free surfaces should allow polymer chains to move faster than in the bulk, the presence of a substrate might slow down the motion if there is an attraction between the two. <jats:bold> Tress <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="6152" page="1371" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1238950">1371</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="6152" page="1351" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1244110">Russell</jats:related-article> </jats:bold> ) used dielectric spectroscopy to study “polymer islands” deposited on a substrate from dilute solution, where some islands contained just a few or only one polymer chain. The confinement of the polymer chain to small-surface geometries had virtually no influence on the dynamics of the polymers, aside from the segments in direct contact with the substrate. </jats:p>

<jats:title>The Pull of Phosphorus</jats:title> <jats:p> Lewis acidity is primarily associated with compounds like boranes that lack a full complement of electrons in their coordination sphere and therefore attract electron donors (Lewis bases) to fill the gap. <jats:bold> Caputo <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="6152" page="1374" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241764">1374</jats:related-article> ; see the Perspective by <jats:related-article issue="6152" page="" related-article-type="in-this-issue" vol="341"> <jats:bold>Gabbaï</jats:bold> </jats:related-article> ) now show that a class of 4-coordinate phosphonium salts can act as surprisingly potent Lewis acids, despite their electronic saturation. The phosphorus cations, bearing fluorine and fluorinated aromatic substituents, can sever an alkyl carbon-fluorine bond by pulling away its fluoride—a process rendered catalytic through the use of a silane acceptor. </jats:p>

<jats:title>Delineating Deep Faults</jats:title> <jats:p> Most large, damaging earthquakes initiate in Earth's crust where friction and brittle fracture control the release of energy. Strong earthquakes can occur in the mantle too, but their rupture dynamics are difficult to determine because higher temperatures and pressures play a more important role. <jats:bold> Ye <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="6152" page="1380" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242032">1380</jats:related-article> ) analyzed seismic <jats:italic>P</jats:italic> waves generated by the 2013 <jats:italic>M</jats:italic> <jats:sub>w</jats:sub> 8.3 Sea of Okhotsk earthquake—the largest deep earthquake recorded to date—and its associated aftershocks. The earthquake ruptured along a fault over 180-kilometer-long and structural heterogeneity resulted in a massive release of stress from the subducting slab. In a set of complementary laboratory deformation experiments, <jats:bold> Schubnel <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="6152" page="1377" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240206">1377</jats:related-article> ) simulated the nucleation of acoustic emission events that resemble deep earthquakes. These events are caused by an instantaneous phase transition from olivine to spinel, which would occur at the same depth and result in large stress releases observed for other deep earthquakes. </jats:p>

<jats:title>Delineating Deep Faults</jats:title> <jats:p> Most large, damaging earthquakes initiate in Earth's crust where friction and brittle fracture control the release of energy. Strong earthquakes can occur in the mantle too, but their rupture dynamics are difficult to determine because higher temperatures and pressures play a more important role. <jats:bold> Ye <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="6152" page="1380" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242032">1380</jats:related-article> ) analyzed seismic <jats:italic>P</jats:italic> waves generated by the 2013 <jats:italic>M</jats:italic> <jats:sub>w</jats:sub> 8.3 Sea of Okhotsk earthquake—the largest deep earthquake recorded to date—and its associated aftershocks. The earthquake ruptured along a fault over 180-kilometer-long and structural heterogeneity resulted in a massive release of stress from the subducting slab. In a set of complementary laboratory deformation experiments, <jats:bold> Schubnel <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="6152" page="1377" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1240206">1377</jats:related-article> ) simulated the nucleation of acoustic emission events that resemble deep earthquakes. These events are caused by an instantaneous phase transition from olivine to spinel, which would occur at the same depth and result in large stress releases observed for other deep earthquakes. </jats:p>

<jats:title>Stealth Nod Factor Recognition</jats:title> <jats:p> Legumes' symbiotic interaction with nitrogen fixing bacteria supplies the plant with nitrogen. Many important crop plants, however, cannot establish these symbioses and, thus, agriculture depends on externally applied fertilizers. Surprisingly, <jats:bold> Liang <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="6152" page="1384" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242736">1384</jats:related-article> , published online 5 September) found that several nonleguminous plants, including <jats:italic>Arabidopsis</jats:italic> , tomato, and corn, were able to respond to the same Nod factors that initiate the microbial symbiosis in soybean. </jats:p>

<jats:title>CCR5-Maraviroc Structure</jats:title> <jats:p> The chemokine receptor CCR5, a G protein–coupled receptor best known as a co-receptor during HIV-1 infection, is important in a variety of physiological processes. <jats:bold> Tan <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="6152" page="1387" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241475">1387</jats:related-article> , published online 12 September; see the Perspective by <jats:bold> <jats:related-article issue="6152" page="" related-article-type="in-this-issue" vol="341">Klasse</jats:related-article> </jats:bold> ) now report the high-resolution crystal structure of CCR5 bound to the HIV-1 entry inhibitor, Maraviroc. The structure suggests that Maraviroc acts as a noncompetitive inhibitor by binding to a region of CCR5 that is distinct from the binding site of HIV-1 and chemokines. Comparison of the structure of CCR5 with the other HIV-1 co-receptor, the chemokine receptor CXCR4, provides insight into the co-receptor selectivity of the virus. </jats:p>

<jats:title>Alarm Bells</jats:title> <jats:p> The presence of DNA in the cytosol of mammalian cells is a danger signal, indicating, for example, that a DNA-containing virus has infected the cell. This signal triggers an innate immune response, which involves the expression of type I interferons, and is critical for antiviral immunity and responses to DNA vaccines. Cyclic GMP-AMP synthase (cGAS) was recently identified as a sensor of cytosolic DNA. <jats:bold> Li <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="6152" page="1390" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1244040">1390</jats:related-article> , published online 29 August) now use knockout mice to provide genetic evidence that, in multiple cell types, cGAS is the primary DNA sensor required for the type I interferon response in vivo. </jats:p>

<jats:title>Pain and Dependence</jats:title> <jats:p> The properties and functions of µ-opioid receptors have been studied intensively with respect to the binding of endogenous or exogenous ligands. However, much less is known about the constitutive, ligand-independent, activation of opioid receptors. Working in mice, <jats:bold> Corder <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="6152" page="1394" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239403">1394</jats:related-article> ) observed the prolonged constitutive activation of µ-opioid receptors in the spinal dorsal horn after transient peripheral inflammation. The results suggest that constitutive activation of µ-opioid receptors depresses nociception—the perception of pain—for long periods of time and induces cellular and physical dependence on endogenous opioid signaling. </jats:p>