Catálogo de publicaciones - revistas

<jats:p>Oscillations in the synthesis and release of a chemical signal synchronize the behavioral response of a cell population.</jats:p>

<jats:title>Astronomical Inflation</jats:title> <jats:p> In astronomy, according to the theory of inflation, the universe underwent a period of extremely accelerated expansion when it was only a fraction of a second old. This process made the universe flat, isotropic, and homogeneous, and it explains how quantum mechanical seeds developed into the large-scale structure we observe today. The theory also predicts that gravitational waves were produced during the early inflationary phase. Alternative theories either predict no gravitational waves or waves with different properties. <jats:bold> Krauss <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="989" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1179541">989</jats:related-article> ) review how primordial gravitational waves could provide information on the physics shortly after the Big Bang and how they could be detected indirectly through their imprint on the cosmic microwave background radiation—relic radiation from the Big Bang released when the universe became transparent to electromagnetic radiation. </jats:p>

<jats:p>Mutation of a small noncoding RNA drives adaptive evolution in a social bacterium.</jats:p>

<jats:title>News from the Inner Tube of Life</jats:title> <jats:p> A major initiative by the U.S. National Institutes of Health to sequence 900 genomes of microorganisms that live on the surfaces and orifices of the human body has established standardized protocols and methods for such large-scale reference sequencing. By combining previously accumulated data with new data, <jats:bold> Nelson <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="994" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1183605">994</jats:related-article> ) present an initial analysis of 178 bacterial genomes. The sampling so far barely scratches the surface of the microbial diversity found on humans, but the work provides an important baseline for future analyses. </jats:p>

<jats:title>More Crossings for Graphene</jats:title> <jats:p> Graphene, which consists of single sheets of graphite, has a number of distinctive electronic properties, including a conical structure that leads to a “Dirac point” where the valence and conduction band intersect at a zero-energy point. <jats:bold> Bostwick <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="999" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1186489">999</jats:related-article> ) used angle-resolved photoemission spectroscopy to study graphene that was doped with alkali atoms and suspended from its substrate. They observed features associated with plasmarons, which arise from the interaction of the charge carriers with plasmons, the density oscillations of the electron gas. The Dirac crossing now becomes three crossings: one that involves charge bands, one involving plasmarons, and one involving the interaction between the two. </jats:p>

<jats:title>Wet Twists and Turns</jats:title> <jats:p> When salts dissolve in water, their constituent positively and negatively charged ions are pulled apart and surrounded by shells of H <jats:sub>2</jats:sub> O molecules (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5981" page="985" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1190093">Skinner</jats:related-article> </jats:bold> ). <jats:bold> Ji <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="1003" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187707">1003</jats:related-article> ) looked closely at the motion in these shells, using a type of vibrational spectroscopy sensitive to both the orientation and to the neighbors of the targeted molecules. In agreement with recent theoretical predictions, the individual water molecules shifted orientation between an anion and the surrounding liquid in sudden discrete steps, rather than by making smooth incremental rotations. <jats:bold> Tielrooij <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="1006" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1183512">1006</jats:related-article> ) compared the relative impacts of cations and anions on the rigidity of the wider water network, using spectroscopic techniques sensitive to the role of each ion. Certain cation/anion combinations, such as magnesium sulfate, appeared to act together to restrict water motion beyond the boundaries of individual shells. </jats:p>

<jats:title>Wet Twists and Turns</jats:title> <jats:p> When salts dissolve in water, their constituent positively and negatively charged ions are pulled apart and surrounded by shells of H <jats:sub>2</jats:sub> O molecules (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5981" page="985" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1190093">Skinner</jats:related-article> </jats:bold> ). <jats:bold> Ji <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="1003" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187707">1003</jats:related-article> ) looked closely at the motion in these shells, using a type of vibrational spectroscopy sensitive to both the orientation and to the neighbors of the targeted molecules. In agreement with recent theoretical predictions, the individual water molecules shifted orientation between an anion and the surrounding liquid in sudden discrete steps, rather than by making smooth incremental rotations. <jats:bold> Tielrooij <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="1006" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1183512">1006</jats:related-article> ) compared the relative impacts of cations and anions on the rigidity of the wider water network, using spectroscopic techniques sensitive to the role of each ion. Certain cation/anion combinations, such as magnesium sulfate, appeared to act together to restrict water motion beyond the boundaries of individual shells. </jats:p>

<jats:title>Janus Drug Delivery Vehicle</jats:title> <jats:p> Efficient drug delivery vehicles need to be produced in a limited size range and with uniform size distribution. The self-assembly of traditional small-molecule and polymeric amphiphiles has led to the production of micelles, liposomes, polymeric micelles, and polymersomes for use in drug delivery applications. Now, <jats:bold> Percec <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="1009" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1185547">1009</jats:related-article> ) describe the self-assembly of Janus-type (i.e., two-headed) dendrimers to produce monodisperse supramolecular constructs, termed “dendrimersomes,” and other complex architectures. The structures, which showed long-term stability as well as very narrow size distributions, were easily produced by the injection of an ethanolic solution of the dendrimer into water. The dendrimersomes could be loaded with the anticancer drug doxorubicin and exhibited controlled drug release with changing pH. </jats:p>

<jats:title>Clearing Up the Inner Core</jats:title> <jats:p> The behavior of Earth's core controls the planet's heat budget and magnetic field, yet its structure remains enigmatic. For instance, the seismic properties of the solid inner core suggest hemispherical structural asymmetry, but questions remain as to how these variations arose (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5981" page="982" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1190506">Buffett</jats:related-article> </jats:bold> ). <jats:bold> Monnereau <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="1014" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1186212">1014</jats:related-article> , published online 15 April) modeled grain sizes of crystalline iron—the predicted dominant mineral phase in the core—and found that a slow translational motion eastward may trigger melting in the Eastern Hemisphere and solidification in the Western Hemisphere, creating a lopsided core. <jats:bold> Deuss <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="1018" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188596">1018</jats:related-article> , published online 15 April) examined the normal-mode seismic structure of the inner core, collected from 90 large earthquakes, which reveal not just simple hemispherical variations, but more nuanced regional structures. The overlap of the seismic data with Earth's magnetic field suggests that directionally dependent crystal alignment in the inner core formed during the solidification of the core or as a consequence of strong forces exerted by magnetism. </jats:p>

<jats:title>Clearing Up the Inner Core</jats:title> <jats:p> The behavior of Earth's core controls the planet's heat budget and magnetic field, yet its structure remains enigmatic. For instance, the seismic properties of the solid inner core suggest hemispherical structural asymmetry, but questions remain as to how these variations arose (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5981" page="982" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1190506">Buffett</jats:related-article> </jats:bold> ). <jats:bold> Monnereau <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="1014" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1186212">1014</jats:related-article> , published online 15 April) modeled grain sizes of crystalline iron—the predicted dominant mineral phase in the core—and found that a slow translational motion eastward may trigger melting in the Eastern Hemisphere and solidification in the Western Hemisphere, creating a lopsided core. <jats:bold> Deuss <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="1018" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188596">1018</jats:related-article> , published online 15 April) examined the normal-mode seismic structure of the inner core, collected from 90 large earthquakes, which reveal not just simple hemispherical variations, but more nuanced regional structures. The overlap of the seismic data with Earth's magnetic field suggests that directionally dependent crystal alignment in the inner core formed during the solidification of the core or as a consequence of strong forces exerted by magnetism. </jats:p>