Catálogo de publicaciones - revistas

<jats:title>Small Is Beautiful</jats:title> <jats:p> Shrinking the size of lasers is attractive because it generally leads to a reduction in power requirements, an increase in switching speed, and possibly a cleaner output. <jats:bold> Walther <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="1495" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1183167">1495</jats:related-article> ) combined patterned electronic components (inductor and capacitor) and an active gain material to develop a submillimeter laser that emits in the microwave regime at low temperature. The use of established patterning techniques and tunable superlattice structures offer the prospect of shrinking the size still further, as well as providing a route to designer laser output for high-speed information transport and optical processing. </jats:p>

<jats:title>Messy Mountain Meandering</jats:title> <jats:p> Predicting the influence of climate on landscapes is sometimes straightforward; for example, river deposits might grow with increased rainfall because erosion rates and sediment transport increase. However, long-term tectonic processes complicate the geomorphic signatures of more gradual climate-related phenomena that reconfigure landscapes. By correlating a decades-long record of typhoon rainfall in Japan with digital elevation models, <jats:bold> Stark <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="1497" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184406">1497</jats:related-article> ) show that climate directly influences the extent of river meandering. When expanded to a larger region of the western North Pacific, this analysis revealed a strong climatic imprint on the landscape of humid mountainous areas. The region-wide analysis also revealed that underlying bedrock strength, as opposed to tectonic uplift, acts as a secondary control. </jats:p>

<jats:title>Partial View</jats:title> <jats:p> Skilled billiard players can easily predict how spinning of one ball will affect the trajectory of the second ball it strikes in a collision. In principle, quantum mechanics can be used to predict the analogous impact of the angular momentum of reagents on the outcome of a chemical reaction. In practice, however, observation of most chemical reactions—even in the confines of a molecular beam apparatus—encompasses a vast number of collisions over multiple angular momentum distributions. <jats:bold> Dong <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="1501" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1185694">1501</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="5972" page="1460" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1187822">Althorpe</jats:related-article> </jats:bold> ) have honed their spectroscopic resolution sufficiently to distinguish the impact of subtle angular momentum variations on the reactivity of fluorine with hydrogen atoms. Their data agree with theory and reveal oscillating peaks in reaction probability, termed partial wave resonances. </jats:p>

<jats:title>At Sixes and Sevens</jats:title> <jats:p> Molecular synthesis and macroscopic aggregation have often been regarded as entirely separate processes. From the researcher's standpoint, once reagents have been mixed, synthesis is largely passive, whereas processes such as crystallization can be more actively manipulated. <jats:bold> Carnall <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="1502" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1182767">1502</jats:related-article> ) characterized an unusual system in which the formation of aggregated cyclic macromolecules (macrocycles) from small peptide-based building blocks was governed by intimately interdependent factors ranging from the scale of covalent bond formation all the way to micron scale fiber growth. As the macrocycles stacked against one another to form the fibers, they remained loosely bonded enough internally to incorporate or expel individual building blocks. Varying the type of mechanical force applied to the growing fibers (either through shaking or stirring the solution), alternately favored formation of either 6-membered or 7-membered covalent macrocycles. </jats:p>

<jats:title>Sperm Wars</jats:title> <jats:p> Some female insects mate on only one day of their life, but then they may mate with multiple males and store the sperm, sometimes for years. But as the mates compete for mates, so their sperm compete for ova, and competition between ejaculates can result in the destruction of sperm inside multiply mated females. But females need to select the sperm they want and to maintain stores of viable sperm to ensure a lifetime's fertility. <jats:bold> Den Boer <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="1506" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184709">1506</jats:related-article> ) compared species of bees and ants with queens that either mate once or mate multiple times, and found that sperm competition has driven the evolution of compounds in the male accessory gland that protect a male's own sperm while damaging another male's sperm. To counteract the male effect, queens produce compounds that mitigate sperm destruction and maximize the number of her offspring. </jats:p>

<jats:title>Diversity Gradients</jats:title> <jats:p> Latitudinal gradients in species abundance, with relatively few occurring at the poles and many at the equator, are well known for macroorganisms. It is a matter of controversy, fueled by a lack of observational data, whether such gradients also occur among microorganisms. <jats:bold> Barton <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="1509" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184961">1509</jats:related-article> , published online 25 February) have built on a global marine circulation model to predict the dynamics of phytoplankton populations. In silico, they obtain patterns of latitudinal gradation for plankton that are interspersed with hotspots of amplified diversity, which point to plausible natural explanations for the phenomenon that can be tested in the future by systematic metagenomic surveys. </jats:p>

<jats:title>Oceanic Nitrogen Fixation</jats:title> <jats:p> Nitrogen fixation in the oceans is important in sustaining global marine productivity and balances carbon dioxide export to the deep ocean. It was previously believed that marine nitrogen fixation was due to a single genus of filamentous cyanobacteria, <jats:italic>Trichodesmium</jats:italic> . The recent discovery of unicellular open-ocean cyanobacteria has raised the question of how they contribute to global ocean nitrogen fixation and how they compare in distribution and activity to <jats:italic>Trichodesmium</jats:italic> . Using data collected from the southwest Pacific Ocean, <jats:bold> Moisander <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="1512" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1185468">1512</jats:related-article> , published online 25 February) show that the unicellular nitrogen-fixing cyanobacteria (UCYN-A and <jats:italic>Crocosphaera watsonii</jats:italic> ) have distinct ecophysiologies and distinct oceanic distributions from each other, and from <jats:italic>Trichodesmium</jats:italic> . These data can be incorporated into models to retune estimates of the global rates of oceanic nitrogen fixation and carbon sequestration. </jats:p>

<jats:title>Puberty Impairs Plasticity</jats:title> <jats:p> While the existence of a period of reduced learning coinciding with the onset of puberty in mice is well characterized, the underlying cellular and molecular mechanisms remain unclear. <jats:bold> Shen <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="1515" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184245">1515</jats:related-article> ) assessed the role of specific γ-aminobutyric acid type A (GABA <jats:sub>A</jats:sub> ) receptors for restricting hippocampal plasticity during puberty. At puberty, but not in adults or the very young, GABA receptors containing the α4 and δ subunits were targeted perisynaptically to excitatory synapses, shunting the depolarizing current necessary for <jats:italic>N</jats:italic> -methyl- <jats:sc>d</jats:sc> -aspartate (NMDA) receptor activation. As a consequence, signal transmission was affected and spatial learning reduced. </jats:p>

<jats:title>Dancing with AMPARs</jats:title> <jats:p> A type of transmembrane receptor for glutamate, known as AMPAR, mediates most of the fast excitatory transmission in the mammalian central nervous system. Their function is regulated by the composition of their subunits, posttranslational modifications, and protein-protein interactions. Recently, several proteins that interact with AMPARs have been identified that affect their subcellular localization, synaptic stabilization, and kinetics. Using proteomic analysis, immunohistochemistry, and electrophysiology, <jats:bold> von Engelhardt <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="1518" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184178">1518</jats:related-article> , published online 25 February; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5972" page="1463" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1187920">Farrant and Cull-Candy</jats:related-article> </jats:bold> ) identified a protein, CKAMP44, which modulates postsynaptic AMPA receptor gating, deactivation, and desentization. </jats:p>

<jats:title>Cycle Entrainment</jats:title> <jats:p> Cells manage many cyclic processes that must coordinate with each other for best cellular performance. <jats:bold> Yang <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="1522" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1181759">1522</jats:related-article> ) present a general theoretical framework that quantitatively describes coupled cyclic processes and then apply this to the interaction between the circadian and cell-division cycles in single cyanobacteria. Simultaneously tracking individual cell divisions and circadian phases and fitting the data with the model suggest that cell-cycle progression slows down dramatically during a specific circadian interval, whereas cell-cycle progression is independent of the cell-cycle phase. </jats:p>