Catálogo de publicaciones - revistas

<jats:p>Tying cytoskeletal motors together on a DNA rope reveals how opposing motors compete to determine the direction of cargo transport.</jats:p>

<jats:title>Ocean Monarchs</jats:title> <jats:p> It is hard to grasp that the unseen microorganisms of the oceans are the most productive on the planet, at orders of magnitude greater than sharks and whales or even terrestrial forests. The plankton is thus a major contributor to the geochemical cycles that are currently under pressure from climate change. <jats:bold>Stocker</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="628" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1208929">628</jats:related-article> ) reviews the state of knowledge of the web of myriad ephemeral microenvironments within the ocean's bulk and how microorganisms respond to the ever-shifting chemical spectrum. To this end, <jats:bold>Taylor and Stocker</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="675" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1219417">675</jats:related-article> ) report experiments on the effects of turbulence on nutrient uptake by chemotactic marine bacteria. They propose that turbulence favors motile bacteria that adopt an optimal foraging strategy, which trades off the relative high cost of motility to gain the benefits of plumes of nutrients by zipping between them at optimized speeds. Scaled up, such apparently “micro” behavior will influence the rate of remineralization of dissolved organic matter and in turn will feed into global patterns of geochemical cycling. </jats:p>

<jats:title>Delaying Quantum Choice</jats:title> <jats:p> Photons can display wavelike or particle-like behavior, depending on the experimental technique used to measure them. Understanding this duality lies at the heart of quantum mechanics. In two reports, <jats:bold> Peruzzo <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="634" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226719">634</jats:related-article> ) and <jats:bold> Kaiser <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="637" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226755">637</jats:related-article> ; see the Perspective on both papers by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6107" page="621" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1229825">Lloyd</jats:related-article> </jats:bold> ) perform an entangled version of John Wheeler's delayed-choice gedanken experiment, in which the choice of detection can be changed after a photon passes through a double-slit to avoid the measurement process affecting the state of the photon. The original proposal allowed the wave and particle nature of light to be interchanged after the light had entered the interferometer. By contrast in this study, entanglement allowed the wave and particle nature to be interchanged after the light was detected and revealed the quantum nature of the photon, for example, it displays wave- and particle-like behavior simultaneously. </jats:p>

<jats:title>Delaying Quantum Choice</jats:title> <jats:p> Photons can display wavelike or particle-like behavior, depending on the experimental technique used to measure them. Understanding this duality lies at the heart of quantum mechanics. In two reports, <jats:bold> Peruzzo <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="634" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226719">634</jats:related-article> ) and <jats:bold> Kaiser <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="637" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226755">637</jats:related-article> ; see the Perspective on both papers by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6107" page="621" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1229825">Lloyd</jats:related-article> </jats:bold> ) perform an entangled version of John Wheeler's delayed-choice gedanken experiment, in which the choice of detection can be changed after a photon passes through a double-slit to avoid the measurement process affecting the state of the photon. The original proposal allowed the wave and particle nature of light to be interchanged after the light had entered the interferometer. By contrast in this study, entanglement allowed the wave and particle nature to be interchanged after the light was detected and revealed the quantum nature of the photon, for example, it displays wave- and particle-like behavior simultaneously. </jats:p>

<jats:title>Twist and Entangle</jats:title> <jats:p> Entanglement is a key feature in quantum information science and plays an important role in various applications of quantum mechanics. <jats:bold> Fickler <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="640" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1227193">640</jats:related-article> ) present a method for converting the polarization state of photons into information encoded into spatial modes of a single photon. From this, superposition states and entangled photons with very high orbital angular momentum quantum numbers were generated. </jats:p>

<jats:title>Perovskite Photovoltaics</jats:title> <jats:p> For many types of low-cost solar cells, including those using dye-sensitized titania, performance is limited by low open-circuit voltages. <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="643" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1228604">643</jats:related-article> , published online 4 October; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6107" page="625" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1230283"> <jats:bold>Norris and Aydil</jats:bold> </jats:related-article> ) have developed a solid-state cell in which structured films of titania or alumina nanoparticles are solution coated with a lead-halide perovskite layer that acts as the absorber and n-type photoactive layer. These particles are coated with a spirobifluorene organic-hole conductor in a solar cell with transparent oxide and metal contacts. For the alumina particles, power conversion efficiencies of up to 10.9% were obtained. </jats:p>

<jats:title>Ullman Upgrade</jats:title> <jats:p> Precious metals may dominate contemporary catalysis, but the early development of synthetic organic chemistry relied on more abundant elements—a strategy that chemists are returning to now for the sake of sustainability. Copper-mediated coupling of aryl halides with amines was reported by Ullman more than a century ago and remains in use today for the synthesis of certain organic compounds. However, the reaction generally requires high temperature to proceed efficiently. <jats:bold> Creutz <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="647" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226458">647</jats:related-article> ) have developed a photochemical variant that uses copper and reacts at room temperature or below, apparently by a radical mechanism. </jats:p>

<jats:title>Dating the First Solids</jats:title> <jats:p> The solar system's first solids: calcium-aluminum–rich inclusions and chondrules are found in meteorites and provide a direct record of the dynamics of the solar protoplanetary disk that led to the formation of the solar system. Previous results indicate that chondrules formed 1 to 2 million years after the inclusions—an age difference that has been used in constructing models of chondrule formation. Based on uranium- and lead-isotope measurements of a collection of these primitive materials, <jats:bold> Connelly <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="651" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226919">651</jats:related-article> ) show that chondrules in fact started to form at the same time as the inclusions, 4.567 billion years ago, and that their formation took about 3 million years. </jats:p>

<jats:title>Chloroplast Rescued by Ubiquitin</jats:title> <jats:p> The ubiquitin proteasome system is important in the regulation of many nucleocytosolic processes. However, its regulatory reach was not thought to extend to the chloroplast. Using a forward-genetic screen in <jats:italic>Arabidopsis</jats:italic> , <jats:bold> Ling <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="655" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225053">655</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="6107" page="622" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1230658">Kessler</jats:related-article> </jats:bold> ) identified a ubiquitin E3 ligase, termed SP1, embedded in the chloroplast outer envelope membrane. SP1 was found to target components of the chloroplast protein import machinery for degradation by the ubiquitin proteasome and was important for changes in chloroplast biogenesis. </jats:p>

<jats:title>Necrophilic Bandit Fungi</jats:title> <jats:p> The immune systems that plants use to defend against pathogens normally deflect attack. However, <jats:bold> Lorang <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="659" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226743">659</jats:related-article> , published online 18 October) have identified a rearguard susceptibility that a necrotrophic fungus exploits. The fungal toxin victorin interacts with the defense protein LOV1 in <jats:italic>Arabidopsis</jats:italic> and activates it, but the result, counterintuitively, is that the plant succumbs to the disease rather than fighting it off. What seems to be happening is that victorin targets a thioredoxin that regulates the systemic acquired resistance pathway. That interaction triggers activity of LOV1, which in turn incites cell death. The invading fungus then benefits from the ready access to dead cells. </jats:p>