Catálogo de publicaciones - revistas

<jats:p>Pathogens and bacteria that normally live in the gut induce different immune responses.</jats:p>

<jats:p>Games, information, and discussions with scientists bring neuroscience knowledge to all hands.</jats:p>

<jats:p> A monthly roundup of recent news and projects of <jats:italic>Science</jats:italic> 's publisher, the American Association for the Advancement of Science. </jats:p>

<jats:title>Warming Up</jats:title> <jats:p> For the past half-million years, our planet has passed through a cycle of glaciation and deglaciation every 100,000 years or so. Each of these cycles consists of a long and irregular period of cooling and ice sheet growth, followed by a termination—a period of rapid warming and ice sheet decay—that precedes a relatively short warm interval. But what causes glacial terminations? <jats:bold> Denton <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="1652" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1184119">1652</jats:related-article> ) review the field and propose a chain of events that may explain the hows and whys of Earth's emergence from the last glacial period. Pulling together many threads from both hemispheres suggests a unified causal chain involving ice sheet volume, solar radiation energy, atmospheric carbon dioxide concentrations, sea ice, and prevailing wind patterns. </jats:p>

<jats:p>Plant root growth is modified in the presence of within-species competition and uneven local resource distributions.</jats:p>

<jats:title>Defining Time-Zero</jats:title> <jats:p> When a high-energy photon hits an atom and is absorbed, the result can be the excitation and emission of an electron. This photoemission, or photoelectric effect, is generally assumed to occur instantaneously, and represents the definition of “time-zero” in clocking such ultrafast events. <jats:bold> Schultze <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="1658" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189401">1658</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="5986" page="1645" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1191842"> <jats:bold>van der Hart</jats:bold> </jats:related-article> </jats:bold> ) use ultrafast spectroscopy, with light pulses on the time scale of several tens of attoseconds, to test this assumption directly. They excite neon atoms with 100 eV photons and find that there is a small (20-attosecond) time delay between the emission of electrons from the 2 <jats:italic>s</jats:italic> and 2 <jats:italic>p</jats:italic> orbitals of the atoms. These results should have implications in modeling electron dynamics occurring on ultrafast time scales. </jats:p>

<jats:title>Just Breathe</jats:title> <jats:p> Design of artificial systems that mimic in vivo organs could provide a better alternative for understanding mechanisms underlying physiological responses than current cell-based models or animal tests. <jats:bold> Huh <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="1662" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188302">1662</jats:related-article> ) have created a tissue-tissue interface of human-cultured epithelial cells and endothelial cells together, with extracellular matrix in a device that models the alveolar-capillary interface of the human lung. The device mimicked physiological organ-level functions, including pathogen-induced inflammatory responses and responses to cytokine exposure. Breathing-type movements affected acute pulmonary cell toxicity and proinflammatory activity of widely used nanoparticulates. </jats:p>

<jats:title>Temporal Tomography</jats:title> <jats:p> Tomography is a widely used technique for visualizing three-dimensional objects by algorithmic reconstruction from multiple two-dimensional images from distinct vantage points. However, its application has largely been restricted to static imaging. <jats:bold>Kwon and Zewail</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1668" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1190470">1668</jats:related-article> ) have now adapted an ultrafast electron microscope to perform tomography with subpicosecond resolution. The method relies on systematically varying the tilt angle of the sample with respect to the incoming electron beam, and enabled assembly of a detailed frame-by-frame record of the response of a curled carbon nanotube to sudden heating. </jats:p>

<jats:title>Dancing in the Light</jats:title> <jats:p> Nearly 200 years ago, the botanist Robert Brown noted that pollen particles floating on a liquid displayed a random motion, jittering under the microscope as if the particles were alive. In 1905, Albert Einstein described this Brownian motion in terms of statistical thermodynamics. Now, <jats:bold> Li <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="1673" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189403">1673</jats:related-article> , published online 20 May) use a single, optically trapped silica bead to probe the dynamics of Brownian motion, measuring the predicted instantaneous velocity of the particle and verifying the short-time-scale behavior predicted a century ago. As well as testing fundamental principles of physics, the technique also has practical implications for cooling particles to ultralow temperatures. </jats:p>

<jats:title>Tangle-Free Polymer Dynamics</jats:title> <jats:p> The dynamics of polymer chains at interfaces will differ from the dynamics in the bulk. While hard interfaces generally cause chain motions to slow down, at free surfaces the dynamics should generally speed up. A consequence is that for thin polymer films, there should be a reduction in the glass transition temperature ( <jats:italic>T</jats:italic> <jats:sub>g</jats:sub> ), but a wide range of effects have been seen in different polymeric materials. Now, <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="1676" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1184394">1676</jats:related-article> ) show that for short, unentangled polystyrene polymers, there is a direct correlation between the viscosity and the glass transition temperature, and that the reduction in <jats:italic>T</jats:italic> <jats:sub>g</jats:sub> is due to a surface mobile layer that dominates the behavior as the films decrease in thickness. </jats:p>