Catálogo de publicaciones - revistas

<jats:title>All Together Now</jats:title> <jats:p> An atom, when excited, will typically decay with a characteristic decay time. An ensemble of atoms, collectively coupled together with just one of the atoms excited will conspire to decay much faster than the single atom case. This enhancement of light-matter interaction is known as superradiance. <jats:bold> Röhlsberger <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="1248" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187770">1248</jats:related-article> , published online 13 May; see the cover; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5983" page="1239" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1190737">Scully and Svidzinsky</jats:related-article> </jats:bold> ) present the realization of an artificial superradiant system comprising resonant iron atoms embedded in a semiconductor cavity and excited by synchrotron radiation and report the signature collective Lamb shift expected from the cooperative interaction and enhanced decay rate. The availability of such a controlled system to look closer at this effect should shed light on its role in natural and complex light-harvesting systems, and possibly allow the production of more efficient solar cells. </jats:p>

<jats:title>Selectively Spun</jats:title> <jats:p> Biaryl compounds, in which two phenyl rings are linked by a single bond, exhibit an interesting sort of chirality, termed atropisomerism. If bulky substituents block the mutual rotation of the rings about the linking bond, then two isomers can be isolated that differ only in the direction one ring has swiveled away from the plane of the other. This feature is useful in ligand design for asymmetric catalysis and also appears in a number of polycyclic natural products. However, selective synthesis of a single isomer is difficult. <jats:bold> Gustafson <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="1251" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188403">1251</jats:related-article> ) now show that a simple tripeptide derivative acts as an efficient catalyst for this purpose, trapping a freely rotating precursor in one orientation through selective bromination; the large bromine substituents then inhibit further swiveling. </jats:p>

<jats:title>Not So Random Walk</jats:title> <jats:p> In rotaxanes, a molecular ring can shuttle back and forth between docking sites along an axle. <jats:bold> Panman <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="1255" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187967">1255</jats:related-article> ) traced the intricacies of this shuttling motion using vibrational spectroscopy. The kinetics were dominated by the slow scission of hydrogen bonds tying the ring to its starting site. Varying the length of the axle allowed the extraction of relative rates for forward and backward motion once the ring was free: Somewhat surprisingly, forward motion toward the destination site was slightly hindered relative to regression toward the starting place. </jats:p>

<jats:title> The Weakness of HO <jats:sub>3</jats:sub> </jats:title> <jats:p> OH radicals play a critical role in the chemistry of Earth's atmosphere. Understanding atmospheric reaction networks thus requires an accurate knowledge of OH sources and sinks. One vexing question has been whether or not a significant pool of OH binds temporarily with oxygen to form HO <jats:sub>3</jats:sub> . <jats:bold> Le Picard <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="1258" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1184459">1258</jats:related-article> ) have succeeded in measuring the equilibrium constant for this reaction using sensitive fluorescent tracking of OH in a laboratory apparatus. This measurement was then used to quantify the strength of the O <jats:sub>2</jats:sub> –OH bond, which was found to be too weak for the complexation to play a major role in the atmosphere. </jats:p>

<jats:title>Down the Drain</jats:title> <jats:p> A pervasive cooling event affected much of the Northern Hemisphere approximately 9300 years ago. This event was accompanied by changes in ocean circulation in the North Atlantic, forced presumably by a large injection of fresh water produced by melting of the Laurentide Ice Sheet, but the source, magnitude, and routing of the meltwater remain unknown. <jats:bold> Yu <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="1262" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187860">1262</jats:related-article> , published online 29 April) present evidence that the trigger for this cooling episode was an outburst flood from Lake Superior. Reconstructing lake-level changes in the Superior basin suggests that a rapid fall of lake level of about 45 meters occurred 9300 years ago, possibly due to the sudden failure of a drift dam. Rapid drainage through the North Bay–Ottawa River–St. Lawrence River valleys into the North Atlantic should have been sufficient to disturb ocean circulation in line with the geologic record. </jats:p>

<jats:title>The Past Looks Hazy</jats:title> <jats:p> During the first couple of billion years of Earth's history, the Sun is thought to have been 30% less luminous than today, yet the surface of the planet was warm enough to prevent glacier formation and for early life to become established. Why were temperatures so high, despite the lower flux of solar energy? <jats:bold>Wolf and Toon</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1266" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1183260">1266</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="5983" page="1238" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189196">Chyba</jats:related-article> </jats:bold> ) propose that the presence of a photochemical haze with a fractal size distribution was the reason. Such a haze, unlike one composed of spherical particles assumed in previous models, could have been opaque enough to block ultraviolet radiation that would have hindered or prevented life from arising, but transparent enough in the shorter wavelengths to keep the atmosphere warm. </jats:p>

<jats:title>Insects in the Wild</jats:title> <jats:p> Insects are of fundamental importance to terrestrial ecosystems and provide laboratory model systems for the study of physiology and genetics. Studies examining how natural and sexual selection operate to drive evolution in wild populations have often neglected invertebrates, resulting in a chasm between our understandings of how things work in the lab versus the natural environment. <jats:bold> Rodríguez-Muñoz <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="1269" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188102">1269</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="5983" journal-id-type="" page="1237" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1191036">Zuk</jats:related-article> </jats:bold> ) bridge this gap by comprehensively monitoring the life histories, behavior, and reproductive success of an entire population of field crickets. Adding genetic data allowed evaluation of how behavior impacts reproductive success and confirmed that male reproductive success varies more than that of females. </jats:p>

<jats:title>Influenza Escape Tricks</jats:title> <jats:p> Tamiflu, or oseltamivir, has been extensively stockpiled by several governments in anticipation of a dangerous influenza pandemic. So far, its large-scale use has not been required, but, despite this, resistance has emerged in seasonal strains mediated by a single point mutation of histidine to tyrosine in the 274 residue (H274Y) of neuraminidase. When the resistant virus was first discovered in 1998, it grew poorly, but by 2008 the virus was reinvigorated and the mutation had spread worldwide in seasonal influenza. So what happened that improved viral fitness so radically? <jats:bold> Bloom <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="1272" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187816">1272</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="5983" page="1243" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1190994">Holmes</jats:related-article> </jats:bold> ) show that the H274Y mutation hinders the folding of the neuraminidase enzyme. In the more vigorous recent oseltamivir-resistant isolates, other mutations compensate for the deleterious effect of H274Y and restore fitness to the virus. </jats:p>

<jats:title>Seeing REDD</jats:title> <jats:p> Reducing emissions from deforestation and degradation (REDD) has become a key economic mechanism in the global strategy to reduce the rate of anthropogenic climate change. For Brazilian Amazonia, <jats:bold>Aragão and Shimabukuro</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1275" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1186925">1275</jats:related-article> ) point out that the efficacy of REDD could depend not only on avoiding deforestation but also on tackling fire usage. A satellite-based time-series of Amazonian deforestation rates and fire incidence suggests an increased trend in fire incidence across most of the region, despite the overall decrease in deforestation rates. The survey also suggests that the introduction of managed agriculture, instead of traditional slash-and-burn land use in already deforested areas, may promote a reduction of in fire incidence in the Amazon. </jats:p>

<jats:title>Germline Quality Control</jats:title> <jats:p> The p53 tumor suppressor protein plays a key role in protecting organisms from aberrant cancer cells. But during evolution, animals would rarely, if ever, have lived long enough to develop cancer and so need such a function of p53. What, then, were the original functions for which p53 was selected? <jats:bold> Lu <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="1278" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1185640">1278</jats:related-article> ) observed a pulse of p53 activation during <jats:italic>Drosophila</jats:italic> development in the female germ line. In cancer, p53 is activated in response to DNA damage. Similarly, in this study, breaks in DNA that occur normally during meiosis also caused p53 activation. In animals in which resolution of DNA breaks during crossing over was inhibited, activation of p53 was prolonged; furthermore, when p53 was also lacking oogenesis was abnormal. Exactly how activation of p53 contributes to the process of chromosome recombination during meiosis remains unclear, but it may provide quality control, only allowing survival of gametes that possess intact DNA. </jats:p>