Catálogo de publicaciones - revistas

<jats:p>The information technology industry is focusing on approaches to hot-water cooling for the design of energy-efficient data centers.</jats:p>

<jats:p>Despite advances made in composite materials, metals remain irreplaceable in many important applications.</jats:p>

<jats:title>Eat Less, Live Long</jats:title> <jats:p> Studies in several model organisms have shown that dietary restriction without malnutrition, or manipulation of nutrient-sensing pathways through mutations or drugs, can increase life span and reduce age-related disease. <jats:bold> Fontana <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="321" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1172539" xlink:type="simple">321</jats:related-article> ) review the ways in which nutrient-sensing pathways are central to aging. Studies of yeast, worms, rodents, and primates show that these pathways are conserved during evolution. Although data on the effects of dietary restriction in primates are very limited, in humans, the protective effects of dietary restriction against cancer, cardiovascular disease, and diabetes must be judged against potentially negative long-term effects. More work is needed to determine whether dietary restriction and the modulation of anti-aging pathways through drugs can extend life span and reduce pathologies in humans. </jats:p>

<jats:title>Deadly Diced DNA</jats:title> <jats:p> Mammalian cells undergoing programmed cell death, or apoptosis, destroy DNA with the deoxyribonuclease known as DFF40. Cells of the worm <jats:italic>Caenorhabditis elegans</jats:italic> also undergo cell death but they do so without a DFF40 enzyme. <jats:bold> Nakagawa <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="327" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1182374">327</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="5976" page="314" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189245"> <jats:bold>Liu and Paroo</jats:bold> </jats:related-article> </jats:bold> ; see the cover) searched for other nucleases that might be involved in worm apoptosis by systematically depleting nucleases with interfering RNA. They found the ribonuclease Dicer, known for its role in sequence-specific silencing of gene expression, was cleaved by a protease that changed Dicer's catalytic activity. The remaining C-terminal fragment switched from being a ribonuclease to a deoxyribonuclease. Thus, caspase activation leads to DNA degradation in the worm as well. </jats:p>

<jats:title>Cluster Within Virgo</jats:title> <jats:p> Globular clusters are gravitationally bound systems within galaxies containing hundreds of thousands of stars. Using data from the Sloan Digital Sky Survey of the thousands of galaxies that constitute the Virgo cluster, <jats:bold> Lee <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="334" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1186496">334</jats:related-article> , published online 11 March) fulfilled a prediction made almost 60 years ago and found globular clusters outside galaxies. In Virgo the clusters are found far from the center and are concentrated in several substructures much larger than galaxies. Possibly they were stripped off from low-mass dwarf galaxies, and potentially trace the dark matter distribution within the Virgo cluster. </jats:p>

<jats:title>Hidden Under the Carpet</jats:title> <jats:p> Transformation optics, combined with the ability to fabricate structures with complex refractive index profiles, allow materials to be formed with fascinating optical properties, such as cloaks where both the object and the cloak concealing the object are rendered invisible. To date, the cloaks have been restricted to two dimensions, which limits realistic applications. Based on a photonic crystal structure with a polymer filling the empty space, <jats:bold> Ergin <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="337" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1186351">337</jats:related-article> , published online 18 March) have designed, fabricated, and realized a three-dimensional cloak operating at optical wavelengths. </jats:p>

<jats:title>Aromatic Lead</jats:title> <jats:p> The bond stabilization, or aromaticity, observed in cyclic carbon molecules, such as benzene, relies on delocalization of electrons around the ring. Although electron distributions in heavier elements can complicate this arrangement, <jats:bold> Saito <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="339" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1183648">339</jats:related-article> ) show that even lead, one of the heaviest metals, is able to participate in an otherwise carbon-based aromatic network. In an analog of the well-studied cyclopentadienyl anion, one carbon atom was replaced with lead, and the framework stabilized by appending phenyl groups to the other four carbons. Crystallography revealed a planar structure, which together with spectroscopic data and theoretical calculations confirmed the aromatic character of the product. </jats:p>

<jats:title>Bulking Up Water Oxidation</jats:title> <jats:p> Storing solar energy by water oxidation, in a process akin to photosynthesis, is a promising approach for building a renewable energy infrastructure. Unfortunately, many of the most active synthetic catalysts for this process fall prey to degradation by the generated oxygen. <jats:bold> Yin <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="342" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1185372">342</jats:related-article> , published online 11 March; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5976" page="315" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187721">Hurst</jats:related-article> </jats:bold> ) used bulky polyoxometalate ligands to protect a catalytic cobalt center from this fate. The full complex was easily prepared by mixing proper ratios of inexpensive tungsten, cobalt, and phosphate salts in boiling water. After isolating and redissolving the catalyst in slightly basic aqueous solution, rapid oxygen generation was observed with a ruthenium-based oxidant. </jats:p>

<jats:title>One B, One O</jats:title> <jats:p> Boron has a tendency to share electrons with multiple different atoms, hence exhibiting a rich cluster chemistry, in contrast to the more traditional two-center, two-electron bonds prevailing in the compounds of most other light elements. <jats:bold> Braunschweig <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="345" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1186028">345</jats:related-article> ) have coaxed boron into a more confined setting and made a boron analog of carbon monoxide as a triply bonded BO anion that was stabilized by coordination to a platinum center. The product formed easily in room temperature solution from a precursor substituted with a silyl group on the oxygen and a bromide on the boron and exhibited surprising stability toward heating and photolysis. The BO anion is a fundamental binary material, isoelectronic with CO, CN-, and NO+, which have been the key binary ligands in organometallic and coordination chemistry for more than 50 years. </jats:p>

<jats:title>Less Old Martian Meteorite</jats:title> <jats:p> The oldest Martian meteorite known, ALH84001, was thought to be a remnant of primordial martian crust formed during solidification of an early magma ocean. Using isotope data, <jats:bold> Lapen <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="347" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1185395">347</jats:related-article> ) revised the crystallization age of this meteorite from 4.51 billion years to 4.09 billion years ago, meaning that this rock cannot be a fragment of primordial crust that escaped the period of intense bombardment that occurred between 4.25 and 4.10 billion years ago. The revised age also suggests that magmatism was ongoing in Mars for a large part of its history and that ALH84001 was actually formed during the heavy bombardment period, just before the martian core dynamo stopped and the planetary magnetic field was lost. </jats:p>