Catálogo de publicaciones - revistas

<jats:p>Caterpillars masquerading as twigs are misidentified by chick predators as inanimate objects, rather than remaining undetected.</jats:p>

<jats:title>Dendrites Shape Interneuron Firing</jats:title> <jats:p> Basket cells, a group of fast-spiking inhibitory interneurons, play an important part in the function of neuronal networks. The mechanisms underlying the high temporal precision and short latency of basket cell activity are unclear. <jats:bold> Hu <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="52" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177876">52</jats:related-article> , published online 3 December) investigated dendrite functions in fast-spiking hippocampal basket cells and found that action potentials are initiated in the axon and propagate back into the dendrites without activity dependence but with strongly reduced amplitude. This is very different from what has been observed previously in widely investigated pyramidal cell dendrites, probably due to the high potassium to sodium conductance ratios in the dendrites of the interneurons. These dendritic mechanisms can explain the high-frequency firing and precise timing of basket cells seen in network activity in vivo. </jats:p>

<jats:title>We Are Stardust</jats:title> <jats:p> Supernovae form as the result of stellar explosions and are classified according to the properties of their spectra. <jats:bold> Poznanski <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="58" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1181709">58</jats:related-article> , published online 5 November) present a peculiar supernova that is characterized by extremely fast temporal evolution and unusual spectroscopic features, such that it defies classification. SN2002bj appears to be a member of a new class of supernovae, possibly formed by a helium detonation on a white dwarf ejecting a small envelope of material. </jats:p>

<jats:title>Activating Stubborn Dopants</jats:title> <jats:p> Many applications of semiconductor light-emitting diodes and lasers, such as reading optical disks, benefit from shorter wavelengths, but this requires materials with larger energy gaps between their valance and conduction bands. The electronic conductivity of these materials often has to be increased by doping with impurity atoms. However, in nitride materials, such as GaN and AlGaN, hole doping with acceptor atoms such as Mg is ineffective at room temperature. <jats:bold> Simon <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="60" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1183226">60</jats:related-article> ) grew a gradient of AlGaN on the surface of GaN and found that the polarization of the layer could field-ionize the acceptor dopants efficiently at room temperature. The heterostructure was used successfully in a light-emitting diode that emits in the ultraviolet. </jats:p>

<jats:title>Carbon Nanotube Bridge for DNA Transport</jats:title> <jats:p> The nanoporosity of carbon nanotubes has been exploited in the control of molecular transport—for example, in creating membranes. <jats:bold> Liu <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="64" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1181799">64</jats:related-article> ) fabricated devices in which one single-walled carbon nanotube connects two fluid reservoirs. In some of these devices, apparently those in which the nanotube is metallic, the ionic conductivity is anomalously higher than that expected from the bulk resistivity of the electrolyte. This high conductivity was exploited for the transport of single-stranded DNA, which was accompanied by large but transient increases in the ion current. </jats:p>

<jats:title>Metal in the Middle</jats:title> <jats:p> Biphasic reaction mixtures allow the isolation of sensitive products, which can form in one solvent and then shift rapidly into another, protected from side reactions and interfering by-products. However, ensuring that catalysts remain in the proper phase can be challenging, and surfactants added to induce efficient mixing often prove difficult to separate from the product stream. <jats:bold> Crossley <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="68" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1180769">68</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="5961" page="41" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184556">Cole-Hamilton</jats:related-article> </jats:bold> ) tackle these issues by preparing easily recoverable amphiphilic nanoparticles that simultaneously stabilize aqueous-organic emulsions and catalyze organic reactions. The particles combine hydrophobic nanotubes with hydrophilic oxides, causing them to accumulate at water-hydrocarbon interfaces. Depositing palladium on specific portions of the particles' surfaces thus localizes the metal in one or both phases, facilitating hydrogenation of several compounds of interest in biofuel refining. </jats:p>

<jats:title>A Hidden Template</jats:title> <jats:p> The entropic challenge inherent in forming a ring-shaped molecule generally increases considerably with the size of the ring. Assuming that a linear precursor must bind its ends together, extending its length diminishes the likelihood of the opposite ends approaching one another. In the absence of an external force, how then can a family of molybdenum oxide rings, several nanometers in diameter (quite large at the molecular scale), self-assemble? <jats:bold> Miras <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="72" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1181735">72</jats:related-article> , 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="5961" page="38" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184533">Whitmire</jats:related-article> </jats:bold> ) have now uncovered an internal template guiding the process. By carefully controlling conditions in a flow reactor, they were able to halt the assembly process partway through and characterize a smaller molybdenum oxide core cluster, around which the larger ring was forming. Ejection of this template then yielded the hollow finished product. </jats:p>

<jats:title>The Depths of the Changes</jats:title> <jats:p> Over the course of the past glacial cycle, there have been two major types of rapid, large climate warming events: shorter-lived warm intervals lasting on the order of 1000 years and the last glacial-interglacial transition. Although both involved dramatic changes in large-scale ocean circulation, the extent to which those changes were similar is unclear. <jats:bold> Roberts <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="75" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1178068">75</jats:related-article> ) analyzed the neodymium isotopic composition of the Fe-Mn oxide coatings of planktonic foraminifera and reconstructed patterns of Atlantic Ocean circulation during Heinrich event 1, a rapid global climate fluctuation about 14,000 years ago involving the destruction of Northern Hemisphere ice shelves and the last deglaciation. While both the source of deep water and the whole-ocean overturning rate shifted rapidly and synchronously during the last deglacial transition, only upper ocean circulation strength was affected during Heinrich event 1. </jats:p>

<jats:title>Toward $1000 Genomes</jats:title> <jats:p> The ability to generate human genome sequence data that is complete, accurate, and inexpensive is a necessary prerequisite to perform genome-wide disease association studies. <jats:bold> Drmanac <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="78" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1181498">78</jats:related-article> , published online 5 November) present a technique advancing toward this goal. The method uses Type IIS endonucleases to incorporate short oligonucleotides within a set of randomly sheared circularized DNA. DNA polymerase then generates concatenated copies of the circular oligonucleotides leading to formation of compact but very long oligonucleotides which are then sequenced by ligation. The relatively low cost of this technology, which shows a low error rate, advances sequencing closer to the goal of the $1000 genome. </jats:p>

<jats:title>Bacterial Compartmentalization</jats:title> <jats:p> In diverse bacteria, reactions that involve toxic or volatile metabolites are carried out by enzymes inside proteinaceous microcompartments. <jats:bold> Tanaka <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="81" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179513">81</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="5961" page="42" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184318"> <jats:bold>Kang and Douglas</jats:bold> </jats:related-article> </jats:bold> ) now report high-resolution crystal structures for four homologous proteins that are constituents of the shell that sequesters the metabolism of ethanolamine in bacteria. While the structures have similar overall folds, they have distinctive structural features that provide insight into how they build the shell and participate in microcompartment function. </jats:p>