Catálogo de publicaciones - revistas

<jats:p>A sinuous receptor links cAMP signaling to myelin formation by Schwann cells in the vertebrate nervous system.</jats:p>

<jats:title>Assessing the Arctic</jats:title> <jats:p> The Arctic is experiencing some of the most rapid climate change currently under way across the globe, but consequent ecological responses have not been widely reported. At the close of the Fourth International Polar Year, <jats:bold> Post <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="1355" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173113">1355</jats:related-article> ) review observations on ecological impacts in this sensitive region. The widespread changes occurring in terrestrial, freshwater, and marine systems, presage changes at lower latitudes that will affect natural resources, food production, and future climate buffering. </jats:p>

<jats:p>Dyed flax fibers from 30,000 years ago show that humans in the Caucasus were making colored twine at that time.</jats:p>

<jats:title>Mapping Out an Entropic Landscape</jats:title> <jats:p> Quantum critical points are continuous phase transitions occurring near absolute zero displaying interesting properties that may have valuable applications. Experimental thermodynamic information on quantum critical systems is sparse, partly because the better known systems are tuned using hydrostatic pressure, and thermodynamic measurements are difficult to perform under such conditions. <jats:bold> Rost <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="1360" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176627">1360</jats:related-article> , published online 6 August 2009; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5946" page="1348" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1179046">Fisk</jats:related-article> </jats:bold> ) built and calibrated bespoke apparatus for a thermodynamic study of strontium ruthenate using a magnetic field as the tuning parameter. The specific heat and magnetocaloric measuremements were combined to map an “entropy landscape” of the quantum criticality and phase formation. This technique should offer a way to probe other materials to reveal unusual properties, such as novel metallic states and superconductivity. </jats:p>

<jats:title>A Lower Tunnel</jats:title> <jats:p> Among the peculiarities inherent in quantum mechanics is the ability of particles to tunnel through barriers that they lack the energy to surmount classically, as happens during radioactive decay. Strong laser fields can liberate electrons in this way from atoms and molecules. <jats:bold> Akagi <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="1364" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175253">1364</jats:related-article> ) elegantly confirm that tunneling is not limited to the highest-energy electrons in a system by mapping the energy and momentum of both the ejected electron and positive ion produced when an intense laser pulse impinges on hydrogen chloride. When the molecule adopts specific orientations relative to the laser field, tunneling occurs from lower-lying states, as well as the highest-energy occupied orbital. This raises the possibility of tunneling microscopy capable of imaging the electronic structure of single molecules. </jats:p>

<jats:title>Efficient Carbon Nanotube Photodiodes</jats:title> <jats:p> A single photon absorbed in a single-walled carbon nanotube device can generate multiple unbound particles carrying an electric charge. <jats:bold> Gabor <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="1367" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176112">1367</jats:related-article> ) report that in such a device at low temperatures, excitation with light of increasing energy leads to well-defined stepwise increases in current. Interestingly, because of the unique band structure of carbon nanotubes, this behavior is analogous to particle-antiparticle creation commonly observed in high-energy particle physics. These observations point to the promise of investigations in other nanoscale carbon systems, such as graphene, and could lead to numerous applications, including highly sensitive photon detection and ultra-efficient photovoltaics. </jats:p>

<jats:title>Himalayan-Tibetan Underplate</jats:title> <jats:p> The Himalayas formed from the collision of India with Eurasia beginning about 50 million years ago, but the fate and position of the subducted Indian crust was not well defined until the Hi-CLIMB seismic experiment was initiated. The centerpiece of the project is an 800-kilometer-long, closely spaced, linear array of broadband seismographs, extending from the Ganges lowland, across the Himalayas, and onto the central Tibetan plateau. <jats:bold> Nábělek <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="1371" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1167719">1371</jats:related-article> ) present images of the crust and upper mantle of the Southern Tibetan plateau underthrust northward by the Indian plate, in which they trace the base of the Indian plate to 31°N. The character of the crust-mantle interface in this region suggests that the Indian crust is at least partly decoupled from the mantle beneath. </jats:p>

<jats:title>Cycling Around</jats:title> <jats:p> Water vapor is the most important greenhouse gas, and clouds are one of the most important components of climate, but the global hydrological cycle is still poorly-enough understood that the atmospheric cycling of water and cloud formation are inadequately represented in global climate models. As the transformation from liquid into vapor tends to deplete water of the isotope deuterium, <jats:bold> Frankenburg <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="1374" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173791">1374</jats:related-article> ) were able to use satellite measurements of global “heavy” water abundances to provide a deeper understanding of atmospheric water dynamics. </jats:p>

<jats:title>Blowing Away Coal</jats:title> <jats:p> China is the world's largest carbon dioxide producer and the world's second-largest producer of electrical power, 80% of which it generates by burning coal. An affordable, carbon-free source of electrical power generation would thus constitute an important way for China to reduce its CO <jats:sub>2</jats:sub> emissions and other environmental impacts of fossil-fuel burning. <jats:bold> McElroy <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="1378" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175706">1378</jats:related-article> , see the cover) show that there is enough wind in China to generate electricity to supply the nation's entire projected demand for 2030 (about twice what is used now) at reasonable prices per kilowatt-hour. </jats:p>

<jats:title>It's a Gas</jats:title> <jats:p> Many antibiotics, including beta-lactams, aminoglycosides, and quinolones, kill bacteria (at least in part) by oxidative stress. <jats:bold> Gusarov <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="1380" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175439">1380</jats:related-article> ) show that nitric oxide (NO) produced by bacterial NO synthases (bNOS) protects bacteria, including <jats:italic>Staphylococcus aureus</jats:italic> and <jats:italic>Bacillus anthracis</jats:italic> , against toxic agents they may encounter in the soil or in host organisms. Thus, bNOS activity is specifically induced in response to antibiotics and, in turn, activates the expression of another key antioxidant enzyme: superoxide dismutase. Hence, NO-mediated antibiotic resistance not only operates by direct chemical modification of toxic molecules, but also alleviates oxidative stress caused by naturally occurring antibiotics. </jats:p>