Catálogo de publicaciones - revistas

<jats:title>Relativity Comes Down to Earth</jats:title> <jats:p> Over a century ago, Einstein presented the theory of relativity—where space and time are no longer fixed concepts, but are relative to an observer and their frame of reference. Tests of relativity have usually been confined to space-based measurements and/or with objects with velocities approaching the speed of light. Time-dilation and length-contraction have been confirmed and are used in satellite communication and global positioning systems. Using the precision of state-of-the-art optical clocks, <jats:bold> Chou <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="1630" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192720">1630</jats:related-article> ) have confirmed that relativistic effects can now be measured at speeds attained by 100 meters sprinters (10 m/s) and gravitational effects due to just one meter height difference. </jats:p>

<jats:title>Substituting Salt for Cerium Oxide</jats:title> <jats:p> The water-gas shift reaction converts carbon monoxide and water to hydrogen and carbon dioxide. Catalysts that operate at lower temperatures will be useful in fuel cells. Nanoparticles of platinum adsorbed on reducible oxides, such as ceria, can stabilize catalytically active Ptoxygen species. <jats:bold> Zhai <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="1633" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192449">1633</jats:related-article> ) now show that, when alkali atoms are added, atomically dispersed Pt can be an active catalyst for the water-gas shift reaction at ∼100°C, even on simple oxides such as alumina and silica. </jats:p>

<jats:title>Extending the Capability of Supercapacitors</jats:title> <jats:p> Supercapacitors have porous electrodes that can store more charge per volume in electrical double layers than conventional parallel plate capacitors. However, the porous electrodes cause poor performance in filter circuits that eliminate residual alternating current ripple from rectified direct current. <jats:bold> Miller <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="1637" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1194372">1637</jats:related-article> ) fabricated electrodes with a high surface area for ionic adsorption by growing graphene sheets in the vertical direction off a metal surface. Such capacitors may be able to perform the same filtering tasks as conventional capacitors but take up less space. </jats:p>

<jats:title>Slippery When Squeezed</jats:title> <jats:p> The behavior of seismic waves as they pass through Earth's interior depends on the physical properties of major mineral phases at depth. If such minerals are anisotropic—that is, they influence seismic waves preferentially depending on crystallographic orientation—interpreting the structure of a region becomes more challenging. In the lowermost mantle, near the boundary with the outer core, deformation of MgSiO <jats:sub>3</jats:sub> post-perovskite may affect anisotropy. <jats:bold> Miyagi <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="1639" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192465">1639</jats:related-article> ) solved previous experimental limitations to show that, when squeezed at high pressures, MgSiO <jats:sub>3</jats:sub> post-perovskite weakens and breaks along its (001) lattice plane. When modeled, this deformation pattern produces anisotropic structures that are consistent with seismic data collected from this region. </jats:p>

<jats:title>Return of the Florida Panther</jats:title> <jats:p> The Florida panther is an endangered lineage that has been the target of extensive human management to maintain genetic diversity within a small population. Now, <jats:bold> Johnson <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="1641" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192891">1641</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="5999" page="1606" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1196738">Packer</jats:related-article> </jats:bold> ) provide comprehensive genetic and demographic analyses of a project to rescue the Florida panther from inbreeding, low genetic diversity, inbreeding depression, and demographic stochasticity by outcrossing it to Texas pumas. The genetics and reproductive fitness traits of different panther populations and their crosses reveal the benefits of outcrossing on survival, genetic diversity, male reproductive characteristics, and population demography. </jats:p>

<jats:title>Nervous Disposition</jats:title> <jats:p> Organ development requires the differentiation and coordination of nerves and blood vessels with multiple cell types. The peripheral parasympathetic nervous system innervates many organs during embryogenesis; however, the function of this interaction during organogenesis is unclear. By exploiting the close association during development of the parasympathetic ganglion with the mouse embryonic salivary gland epithelium, <jats:bold> Knox <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="1645" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192046">1645</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="5999" page="1610" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1196016">Rock and Hogan</jats:related-article> </jats:bold> ) found that neuronal innervation preserves an epithelial progenitor cell population via muscarinic receptor and epidermal growth factor receptor signaling. These progenitor cells are then maintained in the adult salivary gland. A similar system was observed in the developing prostate gland. Peripheral innervation is thus necessary for organogenesis and may also be involved in organ repair or regeneration. </jats:p>

<jats:title>Too Close for Comfort</jats:title> <jats:p> Pheromones are often used for sexual communications in animals, but they can also serve as a measure of population density. Now, <jats:bold> Yamada <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="1647" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192020">1647</jats:related-article> ) have found that population density in the nematode worm <jats:italic>Caenorhabditis elegans</jats:italic> regulates plasticity of olfactory behavior, in which attraction to an odorant decreases after prolonged exposure. Using two rounds of genetic screens, a peptide named SNET-1 and a homolog of a mammalian transmembrane peptidase neprilysin were found to mediate pheromonal regulation. This regulation of olfactory behavior may serve to coordinate the behavior of individual animals in relation to the status of the whole population. </jats:p>

<jats:title>Addition by Contraction</jats:title> <jats:p> Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common hereditary neuromuscular disorders in Western populations, affecting about 1 in 20,000 people. In most patients, the disorder is associated with contraction of a D4Z4 microsatellite repeat array on chromosome 4q, but this contraction can also occur in the absence of disease, so the underlying genetic mechanisms have remained elusive. <jats:bold> Lemmers <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="1650" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1189044">1650</jats:related-article> , published online 19 August; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5999" page="1607" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1195984">Mahadevan</jats:related-article> </jats:bold> ) now show that FSHD patients carry sequence variants that create a canonical polyadenylation signal for transcripts derived from <jats:italic>DUX4</jats:italic> , a homeobox gene straddling the last D4Z4 repeat unit and the adjacent sequence. Addition of poly(A) stabilizes the <jats:italic>DUX4</jats:italic> transcript, which is likely to be a contributing factor in the disease. </jats:p>

<jats:title>Enzymes for Sunscreen Synthesis</jats:title> <jats:p> Many fungi, cyanobacteria, algae, and other marine organisms can biosynthesize small molecules termed mycosporine and mycosporine-like amino acids (MAAs) that, among other functions, protect them from harmful UV exposure. A formulation containing MAAs is used as a sunscreen in skin care and cosmetic products. <jats:bold>Balskus and Walsh</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1653" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1193637">1653</jats:related-article> , published online 2 September) have now identified the gene cluster in a cyanobacterium that is responsible for MAA production. They expressed the cluster in <jats:italic>Escherichia coli</jats:italic> and characterized the four biosynthetic enzymes bio chemically. Two are adenosine triphosphate.dependent peptide bond.forming enzymes that catalyze imine bond formation through unusual mechanisms. </jats:p>

<jats:title>Invariant in the Face of Change</jats:title> <jats:p> The number of copies of a gene network in a cell, or network dosage, is altered in a variety of situations, including switching between haploid and diploid states, and during cell cycle progression. Combining experimental and computational approaches, <jats:bold> Acar <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="1656" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1190544">1656</jats:related-article> ) explore how the activity of a gene network can be invariant despite alterations in network dosage. A two-component genetic circuit with elements of opposite regulatory activity (that is, an activator and an inhibitor) was revealed as a minimal requirement. Specific network topologies and a 1-to-1 interaction stoichiometry between the activating and inhibiting agents also represented essential elements for network-dosage compensation. </jats:p>