Catálogo de publicaciones - revistas

<jats:title>Forcing the East Asian summer monsoon</jats:title> <jats:p> What factors have controlled the intensity of the East Asian summer monsoon over the recent geological past? To answer this key question requires a robust proxy for rainfall amounts. Beck <jats:italic>et al.</jats:italic> measured the beryllium isotopic content of loess from China, from which they reconstructed a 550,000-year-long record of rainfall. Rainfall correlated with orbital precession and global variations in ice volume. This finding suggests that the monsoon is governed by low-latitude interhemispheric gradients in solar radiation levels, rather than by high-northern-latitude solar radiation levels as previously suggested. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="877" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aam5825">877</jats:related-article> </jats:p>

<jats:title>Evolution of the brain</jats:title> <jats:p> Just how related are reptilian and mammalian brains? Tosches <jats:italic>et al.</jats:italic> used single-cell transcriptomics to study turtle, lizard, mouse, and human brain samples. They assessed how the mammalian six-layered cortex might be derived from the reptilian three-layered cortex. Despite a lack of correspondence between layers, mammalian astrocytes and adult neural stem cells shared evolutionary origins. General classes of interneuron types were represented across the evolutionary span, although subtypes were species-specific. Pieces of the much-folded mammalian hippocampus were represented as adjacent fields in the reptile brains. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="881" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar4237">881</jats:related-article> </jats:p>

<jats:title>Reduction can make cobalt act precious</jats:title> <jats:p> Enzymes rely on abundant metals such as iron and nickel to manipulate hydrogen. Chemists, on the other hand, have largely had to rely on precious metals such as platinum and rhodium for the task. Friedfeld <jats:italic>et al.</jats:italic> now report a simple trick to make cobalt act more like rhodium. Reduction of Co(II) to Co(I) by zinc reinforced binding of phosphine ligands to the metal to facilitate its use in asymmetric hydrogenation of alkenes. The cobalt catalysts tolerated alcohol solvents, unlike their rhodium congeners, and could be applied to a 200-gram-scale reduction at 0.08% loading. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="888" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar6117">888</jats:related-article> </jats:p>

<jats:title>Tracking the spin-valley current</jats:title> <jats:p> Taking advantage of the electron's spin and valley degrees of freedom requires a method for generating currents of carriers that have a particular spin or come from a particular valley in the electronic structure. Jin <jats:italic>et al.</jats:italic> used a heterostructure made out of adjacent layers of WSe <jats:sub>2</jats:sub> and WS <jats:sub>2</jats:sub> to create a spin-valley diffusion current without applying an external electric field. Instead, they used circularly polarized laser light to initiate the diffusion and a second laser pulse to image the propagation of the carriers. With long lifetimes and diffusion lengths, the method may be of practical use in future valleytronic devices. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="893" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao3503">893</jats:related-article> </jats:p>

<jats:title>A longer exciton pathway</jats:title> <jats:p> Organic semiconductors typically exhibit exciton diffusion lengths on the order of tens of nanometers. Jin <jats:italic>et al.</jats:italic> prepared nanofibers from block polymers consisting of emissive polyfluorene cores surrounded by coronas of polyethylene glycol and polythiophene (see the Perspective by Holmes). Excitons generated in the polyfluorene cannot enter the polyethylene glycol layer and so diffuse more than 200 nm. This distance can be tuned by varying the length of the polyethylene glycol—a feature that could potentially be exploited in the development of organic devices such as photovoltaics. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="897" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar8104">897</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="854" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aat6009">854</jats:related-article> </jats:p>

<jats:title>Lighting the way to molecules, one by one</jats:title> <jats:p> When chemists run reactions, what they are really doing is mixing up an enormous number of reacting partners and then hoping that they collide productively. It is possible to manipulate atoms more deliberately with a scanning tunneling microscope tip, but the process is then confined to a surface. Liu <jats:italic>et al.</jats:italic> directly manipulated individual atoms with light to form single molecules in isolation (see the Perspective by Narevicius). They used optical tweezers of two different colors to selectively steer ultracold sodium (Na) and cesium (Cs) atoms together. A subsequent optical excitation formed NaCs. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="900" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar7797">900</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="855" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aat7917">855</jats:related-article> </jats:p>

<jats:title>Poking a semiconductor</jats:title> <jats:p> Noncentrosymmetric crystal structure can lead to a peculiar kind of charge separation under illumination called the bulk photovoltaic (BPV) effect. Solar cells made of such materials, however, typically have low efficiency. Yang <jats:italic>et al.</jats:italic> expanded the class of materials capable of exhibiting the BPV effect by making ordinarily centrosymmetric materials, such as SrTiO <jats:sub>3</jats:sub> and TiO <jats:sub>2</jats:sub> , lose their inversion symmetry. The authors accomplished this by applying a point force on the surface of the material. This induced a strain gradient and the loss of inversion symmetry, resulting in large photovoltaic currents under illumination. The mechanism, dubbed the flexo-photovoltaic effect, is expected to apply to most semiconductors. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="904" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aan3256">904</jats:related-article> </jats:p>

<jats:p>Between bacteria and phages, increasing phage diversity accelerates arms races with the host and leads to increased bacterial divergence.</jats:p>

<jats:p>GPS tagging reveals leaders and followers among migrating white storks.</jats:p>

<jats:title>Using bugs in the gut to detect blood</jats:title> <jats:p> Bacteria are environmentally resilient and can be engineered to sense various biomolecules. Mimee <jats:italic>et al.</jats:italic> combined biosensor bacteria with a miniaturized wireless readout capsule to produce a minimally invasive device capable of in vivo biosensing in harsh, difficult-to-access environments (see the Perspective by Gibson and Burgell). The device successfully measured gastrointestinal bleeding in pigs. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="915" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aas9315">915</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6391" page="856" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aat8658">856</jats:related-article> </jats:p>