Catálogo de publicaciones - revistas

<jats:title>A radical route to soot</jats:title> <jats:p> The chemical origin of soot is a persistent puzzle. It is clear that small hydrocarbon fragments formed in flames must aggregate into larger particles, but the initial driving force for aggregation remains a mystery. Johansson <jats:italic>et al.</jats:italic> combined theory and mass spectrometry to suggest a solution based on resonance-stabilized radicals (see the Perspective by Thomson and Mitra). Aromatics such as cyclopentadiene have a characteristically weak C–H bond because their cleavage produces radicals with extended spans of π-electron conjugation. Clusters thus build up through successive coupling reactions that extend conjugation in stabilized radicals of larger and larger size. </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="6406" page="997" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat3417">997</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6406" page="978" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aau5941">978</jats:related-article> </jats:p>

<jats:title>Two-step energy transfer in space plasma</jats:title> <jats:p> Plasmas are ionized gases that contain negative electrons, positive ions, and electromagnetic fields. These constituents can oscillate in position over time, carrying energy as plasma waves. In principle, such waves could transfer energy between two different ion populations. Kitamura <jats:italic>et al.</jats:italic> analyzed data from the Magnetospheric Multiscale mission, a group of four spacecraft that are flying in tight formation through Earth's magnetosphere. They discovered an event in which energy was transferred from hydrogen ions to plasma waves and then from the waves to helium ions. This energy transfer process is likely to occur in many other plasma environments. </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="6406" page="1000" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aap8730">1000</jats:related-article> </jats:p>

<jats:title>All-optical deep learning</jats:title> <jats:p> Deep learning uses multilayered artificial neural networks to learn digitally from large datasets. It then performs advanced identification and classification tasks. To date, these multilayered neural networks have been implemented on a computer. Lin <jats:italic>et al.</jats:italic> demonstrate all-optical machine learning that uses passive optical components that can be patterned and fabricated with 3D-printing. Their hardware approach comprises stacked layers of diffractive optical elements analogous to an artificial neural network that can be trained to execute complex functions at the speed of light. </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="6406" page="1004" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat8084">1004</jats:related-article> </jats:p>

<jats:title>The makings of permeable membranes</jats:title> <jats:p> A challenge in making membranes is finding ways to control the pore structure during the fabrication process or through postfabrication treatment. The deposition of a zeolitic imidazolate framework material called ZIF-8 onto an alumina support gives a dense, impermeable material. However, when Ma <jats:italic>et al.</jats:italic> exposed this material to vapors of 2-methylimidazole, it transformed into a porous material able to separate propylene from propane. </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="6406" page="1008" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat4123">1008</jats:related-article> </jats:p>

<jats:title>Selectively exciting desorption</jats:title> <jats:p> Reactions of molecules adsorbed on surfaces can be induced by injecting electrons from the tip of a scanning tunneling microscope. Rusimova <jats:italic>et al.</jats:italic> show that for the tip-induced desorption of toluene molecules from a silicon surface, two activation channels exist: One is invariant, but the other depends on the height of the tip above the surface. When the tip is very close to the molecule, it can quench the excitation. The decreased lifetime, in turn, decreases the desorption probability. </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="6406" page="1012" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat9688">1012</jats:related-article> </jats:p>

<jats:title>Molecular gas ejected from a distant galaxy</jats:title> <jats:p> Galaxies grow by forming stars from cold molecular gas. The rate at which they do so is limited by various feedback processes (such as supernovae or stellar winds) that heat and/or eject gas from the host galaxy. Spilker <jats:italic>et al.</jats:italic> used submillimeter observations to discover an outflow of molecular gas from a galaxy in the early Universe, a period of vigorous star formation. Modeling the outflow revealed that the mass of gas being ejected is similar to that being turned into stars. The results will help determine how quickly galaxies formed after the Big Bang. </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="6406" page="1016" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aap8900">1016</jats:related-article> </jats:p>

<jats:title>More energy, more rain</jats:title> <jats:p> Energy generation by wind and solar farms could reduce carbon emissions and thus mitigate anthropogenic climate change. But is this its only benefit? Li <jats:italic>et al.</jats:italic> conducted experiments using a climate model to show that the installation of large-scale wind and solar power generation facilities in the Sahara could cause more local rainfall, particularly in the neighboring Sahel region. This effect, caused by a combination of increased surface drag and reduced albedo, could increase coverage by vegetation, creating a positive feedback that would further increase rainfall. </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="6406" page="1019" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aar5629">1019</jats:related-article> </jats:p>

<jats:title>Learning where and when</jats:title> <jats:p> Large ungulate migrations occur across continents and inspire curiosity about how these animals know when to leave and where to go. Jesmer <jats:italic>et al.</jats:italic> took advantage of regional extinctions and reintroductions of several North American ungulate species to determine the role of learning in migrations (see the Perspective by Festa-Bianchet). Reintroduced populations of bighorn sheep and moose did not migrate as historical herds had. However, after several decades, newly established herds were better able to track the emergence of vegetation in the environment and were increasingly migratory. Thus, newly introduced animals learned about their environment and shared the information through social exchange. </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="6406" page="1023" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat0985">1023</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6406" page="972" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aau6835">972</jats:related-article> </jats:p>

<jats:title>Flexible growth and immune responses in rice</jats:title> <jats:p> Plants that are fighting microbial pathogens often divert resources that could be used for growth into the immune response. For crops, this translates into lower yield when plant immunity is activated. Wang <jats:italic>et al.</jats:italic> show that, in rice, reversible phosphorylation of a key transcription factor allows the plant to defend against fungal attack when needed but then, within days, reallocate resources back to growth (see the Perspective by Greene and Dong). Thus, both pathogen defense and crop yield can be sustained. </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="6406" page="1026" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat7675">1026</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6406" page="976" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aau9065">976</jats:related-article> </jats:p>

<jats:title>Bouncer keeps fertilization specific</jats:title> <jats:p> Fertilization needs to be highly efficient while remaining species-specific. However, despite decades of research, it is still unclear how these two requirements are met. Herberg <jats:italic>et al.</jats:italic> report the discovery of the Ly6/uPAR-type protein Bouncer as a species-specific fertilization factor in zebrafish (see the Perspective by Lehmann). Bouncer localizes to the egg membrane and is required for sperm entry. Remarkably, expression of Bouncer from another fish species (medaka) in zebrafish allowed for cross-species fertilization. </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="6406" page="1029" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat7113">1029</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6406" page="974" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aau8356">974</jats:related-article> </jats:p>