Catálogo de publicaciones - revistas

<jats:p>An iterative method that estimates both sequence alignments and phylogenies leads to improved phylogenetic trees for large data sets.</jats:p>

<jats:title>Expanding Flatland</jats:title> <jats:p> Since its discovery and isolation some 5 years ago, research on graphene has exploded. The sheets of carbon atoms, just one atom thick, exhibit a vast array of properties—mechanical, optical, and electrical—that make it an ideal test bed to probe fundamental problems in physics, as well as lending itself to a wide portfolio of applications. <jats:bold>Geim</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1530" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1158877">1530</jats:related-article> ), the discoverer of this remarkable material, reviews recent advances and discusses what other developments may be in store for this material. </jats:p>

<jats:p>Giant ostracode sperm date back at least 100 million years ago.</jats:p>

<jats:title>Sensorin Reporter</jats:title> <jats:p> Long-term memory and synaptic plasticity require changes in gene expression and yet can occur in a synapse-specific manner. Messenger RNA (mRNA) localization and regulated translation at synapses have been proposed as mechanisms for spatially restricting gene expression during transcription-dependent, synapse-specific forms of neuronal plasticity. In the sea slug <jats:italic>Aplysia</jats:italic> , which is a frequently used model system for studying learning and memory, sensorin is a sensory cell–specific peptide neurotransmitter. The mRNA encoding sensorin localizes to distal sensory neurites and further concentrates at sites of synaptic contact between sensory and motor neurons. <jats:bold> Wang <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="1536" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1173205">1536</jats:related-article> , published online 14 May; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1527" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1176484">Korte</jats:related-article> </jats:bold> ) demonstrate, using translational reporters of sensorin mRNA expressed in individual cultured <jats:italic>Aplysia</jats:italic> sensory and motor neurons, that local translation occurs at synapses during transcription-dependent, learning-related forms of synaptic plasticity. </jats:p>

<jats:title>Star Gazing</jats:title> <jats:p> Seismology of stars provides a unique insight into physical mechanisms taking place in their interior. Like the Sun, some stars have low-amplitude pulsations that are excited by turbulent convection in their outer layers. <jats:bold> Belkacem <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="1540" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171913">1540</jats:related-article> ), using data gathered by the CoRoT satellite, report on low-amplitude, solar-like oscillations in a massive star that undergoes radial pulsations as a result of expanding and contracting layers in its interior. The finding opens the possibility of probing the interiors of this type of massive star, which can be the progenitors of supernovae. </jats:p>

<jats:title>Reaping Gain from Decay</jats:title> <jats:p> In photovoltaic devices, absorbed light excites electrons into a conduction band and thereby initiates electric current flow. Unfortunately, if the energy of the incident photons exceeds the threshold for this excitation (the bandgap), the excess tends to be wasted. Initially, a photon bearing several multiples of the bandgap energy may correspondingly promote several electrons, but before these can begin to travel through a circuit, most of them drop back down to the immobile state, transferring their packet of energy to a lone remaining carrier in a process termed “Auger decay.” <jats:bold> Sukhovatkin <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="1542" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1173812">1542</jats:related-article> ) show that a photoconductive device design can actually leverage the Auger decay process to improve sensitivity in ultraviolet detection. Their detector, a thin film assembled from lead sulfide quantum dots, improves its response by up to a factor of four when the incident light frequency rises to several multiples of the bandgap. </jats:p>

<jats:title>Minimally Acidic</jats:title> <jats:p> Acidity is usually construed in the context of a bulk liquid solvent: billions of trillions of molecules such as HCl, added to hundreds of billions of trillions of water molecules. What happens under sparser conditions, for example, in atmospheric or interstellar environments, when a single HCl molecule might interact with just three or four water molecules? <jats:bold> Gutberlet <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="1545" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171753">1545</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1522" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175387">Zwier</jats:related-article> </jats:bold> ) explored this question using theoretical simulations together with vibrational spectroscopy in ultracold helium droplets that effectively isolated small aqueous HCl clusters. HCl remained intact upon solvation by one, two, or three water molecules. Dissociation into an ion pair, as occurs in bulk water, required the approach of a fourth water molecule and was facilitated by the geometry of the existing (H <jats:sub>2</jats:sub> O) <jats:sub>3</jats:sub> cluster. </jats:p>

<jats:title>2 Be or Not 2 Be?</jats:title> <jats:p> The beryllium dimer is a rather simple-looking compound, bridging two atoms of the fourth-lightest element. Yet it has long posed a frustrating challenge to theorists, because, to a first approximation, chemical bonding models suggest that it should not exist. In recent decades, calculations of ever-increasing sophistication have offered rationales for the two atoms' puzzling mutual attraction. Now <jats:bold> Merritt <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="1548" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174326">1548</jats:related-article> , published online 21 May; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1526" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175751">Bernath</jats:related-article> </jats:bold> ) have used high-resolution spectroscopy to assemble, at last, a full experimental potential energy function describing the ground electronic state of Be <jats:sub>2</jats:sub> . The curve is unusually shallow at long bond lengths, deviating from the contour of more traditional molecular Morse potentials, and provides a detailed basis of comparison for future theoretical bonding frameworks. </jats:p>

<jats:title>A Change in the Air?</jats:title> <jats:p> Between around 1.2 million and 500,000 years ago, Earth's glacial cycle changed from one with a period of roughly 40,000 years to one with a period of about 100,000 years. Although there has been much speculation about why this transition may have occurred, no potential explanation seemed more likely than that it was caused by decreasing concentrations of atmospheric CO <jats:sub>2</jats:sub> . <jats:bold> Hönisch <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="1551" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171477">1551</jats:related-article> ) present a record of atmospheric <jats:italic>p</jats:italic> CO <jats:sub>2</jats:sub> for the past 2.1 million years, derived from the boron isotopic composition of planktonic foraminifera, and show that the amount of CO <jats:sub>2</jats:sub> in the atmosphere has remained relatively constant over that period. While <jats:italic>p</jats:italic> CO <jats:sub>2</jats:sub> was approximately 30 ppm higher before the start of the mid-Pleistocene transition than after the transition, atmospheric CO <jats:sub>2</jats:sub> did not decrease gradually as would be expected were it to be the driver of the transition. </jats:p>

<jats:title>Extinction Distinction</jats:title> <jats:p> The Triassic-Jurassic extinction approximately 200 million years ago is one of the five major extinctions in Earth's history. It has been primarily recognized through the loss of marine species, as well as the subsequent emergence of dinosaurs, but its pace, both on land and in sea, has been unclear. <jats:bold> McElwain <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="1554" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171706">1554</jats:related-article> ) now provide evidence from the plant fossil record from rocks in East Greenland. The total number of taxa and the number of common taxa decreased across the extinction boundary. The decrease was fairly abrupt and seemed to coincide with a period with increased atmospheric CO <jats:sub>2</jats:sub> levels. </jats:p>