Catálogo de publicaciones - revistas

<jats:title>Fabricating Quartz</jats:title> <jats:p> Quartz is used industrially as an abrasive, as an inert glassy material, or for high-quality crystals in microelectronics. It is also valued for its piezoelectronic properties. However, it is hard to grow quartz as a patterned material or to integrate it into nanostructured devices. <jats:bold> Carretero-Genevrier <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="6134" page="827" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1232968">827</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="6134" page="818" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1236752">Brinker and Clem</jats:related-article> </jats:bold> ) have developed a method for preparing oriented epitaxial thin films of polycrystalline α-quartz on single-crystal silicon substrates using ambient pressure and temperatures below 1000°C. Different processing conditions can be used to fabricate quartz films with a variety of pore sizes or as a dense nonporous α-quartz film. </jats:p>

<jats:title>Falling Out</jats:title> <jats:p> During simple precipitation, molecules fall out of solution from locations of highest concentration and, consequently, the shape of the precipitate will be dictated by its crystallization thermodynamics. <jats:bold> Noorduin <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="6134" page="832" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1234621">832</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="6134" page="822" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1238619">Vlieg</jats:related-article> </jats:bold> ) designed micrometer-scale structures by varying the reaction conditions for silica and carbonate precipitation in which precipitation changes the local concentration and acidity to alter the next stage of precipitation, thus controlling whether the solid phase grows toward or away from the bulk solution. The result is the ability to design and generate a variety of complex structures by simple reaction-diffusion processes. </jats:p>

<jats:title>Stress Inside Out</jats:title> <jats:p> In Gram-negative bacteria, the integrity of the outer membrane is crucial for survival and is an important aspect of resistance to antibiotics. The biogenesis of the major components lipopolysaccharide (LPS) and outer-membrane protein (OMP) of the outer membrane begins in the cytoplasmic compartment, involves export across the inner membrane and transport through the periplasm, and finally requires active insertion into the outer membrane by specialized assembly machines. <jats:bold> Lima <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="6134" page="837" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1235358">837</jats:related-article> ) supply results for a model in which serious defects in LPS biogenesis also create problems for OMP biogenesis, thereby producing the two signals needed to activate the σ <jats:sup>E</jats:sup> stress response pathway. </jats:p>

<jats:title>Confined Helium</jats:title> <jats:p> Helium-3 ( <jats:sup>3</jats:sup> He) has superfluid phases closely related to topological insulators and topological superconductors. In geometrical confinement, <jats:sup>3</jats:sup> He is expected to support exotic excitations, but its phase diagram is largely unknown, as such measurements are experimentally challenging. <jats:bold> Levitin <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="6134" page="841" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1233621">841</jats:related-article> ) confine <jats:sup>3</jats:sup> He in a slab geometry of defined height and use nuclear magnetic resonance as a probe. As predicted by theory, the authors find that the confinement stabilizes some of the superfluid phases across a larger portion of the phase diagram with respect to the bulk and potentially provides a testbed for topological superfluidity. </jats:p>

<jats:title>Cheap Pix</jats:title> <jats:p> Three-dimensional (3D) images can be captured by, for example, holographic imaging or stereoimaging techniques. To avoid using expensive optical components that are limited to specialized bands of wavelengths, <jats:bold> Sun <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="6134" page="844" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1234454">844</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="6134" page="821" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1238415">Faccio and Leach</jats:related-article> </jats:bold> ) projected pulses of randomly textured light onto an object. They were able to reconstruct an image of the 3D object by detecting the reflected light with several photodetectors without any need for lenses. The patterned light beams can thus in principle be substituted for light sources of any wavelength. </jats:p>

<jats:title>Modules of Desire</jats:title> <jats:p> Using computational methods to design materials with specific properties has found some limited success. <jats:bold> Dyer <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="6134" page="847" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1226558">847</jats:related-article> , published online 11 April) have devised a method, based on extended module materials assembly, that combines chemical intuition and <jats:italic>ab initio</jats:italic> calculations starting from fragments or modules of structure types that show the desired functionality. The method was tested by identifying materials suitable for a solid oxide fuel cell cathode. </jats:p>

<jats:title>Melting Away</jats:title> <jats:p> We assume the Greenland and Antarctica ice sheets are the main drivers of global sea-level rise, but how large is the contribution from other sources of glacial ice? <jats:bold> Gardner <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="6134" page="852" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1234532">852</jats:related-article> ) synthesize data from glacialogical inventories to find that glaciers in the Arctic, Canada, Alaska, coastal Greenland, the southern Andes, and high-mountain Asia contribute approximately as much melt water as the ice sheets themselves: 260 billion tons per year between 2003 and 2009, accounting for about 30% of the observed sea-level rise during that period. </jats:p>

<jats:title>EZ Inhibition</jats:title> <jats:p> Missense mutations in the core constituents of the genome packaging material, chromatin, have been implicated in several of human cancers. Nucleosomes are made up of histones, and a mutation of lysine 27 (K27) to methionine in the N-terminal tail of histone variants H3.3 and H3.1 has been identified in various pediatric gliomas. <jats:bold> Lewis <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="6134" page="857" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1232245">857</jats:related-article> , published online 28 March; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6134" page="823" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1239223">Morgan and Shilatifard</jats:related-article> </jats:bold> ) show that the polycomb enzyme complex, which can epigenetically modify K27 by addition of a methyl group—and which is often a silencing signal—is itself potently inhibited by replacement of the H3.3/3.1 K27 by methionine. The inhibition of the EZH2 subunit causes an overall reduction of K27 methylation. Methionine mutants of other methylated lysine residues in histone H3 cause similar reductions in methylation levels of the cognate lysine, altering the epigenetic profiles of such cancer cells. </jats:p>

<jats:title>Surprise Attack</jats:title> <jats:p> Humans conduct the largest ecological experiment ever by continually moving species between continents. For example, the harlequin ladybird beetle, native to Asia, has become highly invasive in many regions after being introduced for biological control, but we do not understand why this species should so readily outcompete native ladybirds. <jats:bold> Vilcinskas <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="6134" page="862" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1234032">862</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="6134" page="816" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1238998">Reynolds</jats:related-article> </jats:bold> ) show that harlequin beetles have parasitic microsporidia within their hemolymph, which are fatal to other ladybird beetles that prey on harlequin beetle eggs and larvae. Harlequin beetles thus have an innate advantage over species that are otherwise equivalent in their abilities, but this sort of competitive advantage can be hard to spot. </jats:p>

<jats:title>Nuclear Actin in Action</jats:title> <jats:p> Actin polymerization is essential for structures in mammalian cells. Although actin filament network structures are observed in the cytoplasm and at the plasma membrane, monomeric actin is also seen in the nucleus. <jats:bold> Baarlink <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="6134" page="864" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1235038">864</jats:related-article> , published online 4 April) directly visualized a distinct and dynamic actin network within the nucleus in living cells. The network spanned the entire nucleus and appeared to be enriched along the nuclear cortex. Transient formation of a nuclear actin network may be induced by the transcriptional serum response. </jats:p>