Catálogo de publicaciones - revistas

<jats:title>Freed from a rocky embrace</jats:title> <jats:p> Nitrogen availability is a central controller of terrestrial plant growth and, thereby, of the carbon cycle and global climate change. It has been widely assumed that the atmosphere is the main source of terrestrial nitrogen input. Surprisingly, Houlton <jats:italic>et al.</jats:italic> now show that bedrock is just as large a nitrogen source across major sectors of the global terrestrial environment. They used three diverse and largely independent assessments of the nitrogen mobility and reactivity of rocks in the surface environment. These approaches yielded convergent estimates pointing to the equal importance of the atmosphere and bedrock as nitrogen sources. </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="6384" page="58" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aan4399">58</jats:related-article> </jats:p>

<jats:title>Beyond fractional quantum Hall</jats:title> <jats:p> Unlike most electronic topological phenomena, the fractional quantum Hall effect requires correlations among electrons. Spanton <jats:italic>et al.</jats:italic> describe a class of related but even more unusual states, the fractional Chern insulators (see the Perspective by Repellin and Regnault). They observed these states in samples of bilayer graphene, where one of the graphene layers was misaligned by a small angle with respect to an adjoining layer of hexagonal boron nitride. The misalignment created a superlattice potential and topologically nontrivial bands, which had a fractional filling, thanks to strong electronic interactions. The findings expand the class of correlated topological states, which have been predicted to harbor exotic excitations. </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="6384" page="62" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aan8458">62</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6384" page="31" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar5675">31</jats:related-article> </jats:p>

<jats:title>Light relaxes hybrid perovskites</jats:title> <jats:p> Ion migration in organic-inorganic perovskite solar cells limits device stability and performance. Tsai <jats:italic>et al.</jats:italic> found that a cesium-doped lead triiodide perovskite with mixed organic cations underwent a uniform lattice expansion after 180 min of exposure at 1 sun of illumination. This structural change reduced the energy barriers for charge carriers at the contacts of solar cells. The resulting increase in power conversion efficiency from 18.5 to 20.5% was maintained for more than 1500 hours of illumination. </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="6384" page="67" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aap8671">67</jats:related-article> </jats:p>

<jats:title>Double rings made with heme</jats:title> <jats:p> Cyclic organic structures with adjacent three-carbon rings—bicyclobutanes—are useful starting materials for chemical and materials synthesis owing to their extreme ring strain. Constructing these molecules is a challenging task for organic chemists, especially if a single stereoisomer is desired. Chen <jats:italic>et al.</jats:italic> engineered a heme-containing enzyme to catalyze sequential carbene insertion reactions using an alkyne substrate. Starting with an enzyme that could only catalyze a single carbene insertion, a series of mutations led to variants that catalyzed efficient, stereoselective production of bicyclobutanes. By using a less reactive alkyne substrate and screening more variants with active site mutations, the authors found enzymes that stop at either enantiomer of the intermediate cyclopropene. </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="6384" page="71" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar4239">71</jats:related-article> </jats:p>

<jats:title>A sulfur matchmaker for fluorous coupling</jats:title> <jats:p> Fluorination is a burgeoning technique for fine-tuning the properties of pharmaceutical compounds. Unfortunately, the cross-coupling reactions widely used to make carbon-carbon bonds in drug research can be tripped up by fluorine substituents. Merchant <jats:italic>et al.</jats:italic> report a class of easily prepared, solid sulfone compounds that engage in nickel-catalyzed coupling of their fluoroalkyl groups with aryl zinc reagents. These sulfones considerably simplify the synthetic routes to fluorinated analogs that would previously have required multistep strategies focused strictly on the fluorination protocol. </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="6384" page="75" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar7335">75</jats:related-article> </jats:p>

<jats:title>Embryonic hints of adult diversity</jats:title> <jats:p> The adult brain contains dozens of different types of interneurons that control and refine neuronal circuits. Mi <jats:italic>et al.</jats:italic> used single-cell transcriptomics to investigate when these subtypes emerge during interneuron development in the mouse. Transcriptomes of embryonic interneurons showed similarities to adult classes of differentiated interneurons, thus dividing the immature embryonic interneurons themselves into classes. Nearly a dozen classes of embryonic neurons could be identified soon after their last mitosis by transcriptomic similarity with known classes of adult cortical interneurons. Thus, the fate of embryonic interneurons can be read in their transcriptomes well before the neurons migrate and reach their final sites of differentiation and circuit integration. </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="6384" page="81" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar6821">81</jats:related-article> </jats:p>

<jats:title>The Middle Stone Age in Africa</jats:title> <jats:p> The Olorgesailie basin in the southern Kenya rift valley contains sediments dating back to 1.2 million years ago, preserving a long archaeological record of human activity and environmental conditions. Three papers present the oldest East African evidence of the Middle Stone Age (MSA) and elucidate the system of technology and behavior associated with the origin of <jats:italic>Homo sapiens</jats:italic> . Potts <jats:italic>et al.</jats:italic> present evidence for the demise of Acheulean technology that preceded the MSA and describe variations in late Acheulean hominin behavior that anticipate MSA characteristics. The transition to the MSA was accompanied by turnover of large mammals and large-scale landscape change. Brooks <jats:italic>et al.</jats:italic> establish that ∼320,000 to 305,000 years ago, the populations in eastern Africa underwent a technological shift upon procurement of distantly sourced obsidian for toolmaking, indicating the early development of social exchange. Deino <jats:italic>et al.</jats:italic> provide the chronological underpinning for these discoveries. </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="6384" page="86" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2200">86</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6384" page="90" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2646">90</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6384" page="95" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2216">95</jats:related-article> </jats:p>

<jats:title>The Middle Stone Age in Africa</jats:title> <jats:p> The Olorgesailie basin in the southern Kenya rift valley contains sediments dating back to 1.2 million years ago, preserving a long archaeological record of human activity and environmental conditions. Three papers present the oldest East African evidence of the Middle Stone Age (MSA) and elucidate the system of technology and behavior associated with the origin of <jats:italic>Homo sapiens</jats:italic> . Potts <jats:italic>et al.</jats:italic> present evidence for the demise of Acheulean technology that preceded the MSA and describe variations in late Acheulean hominin behavior that anticipate MSA characteristics. The transition to the MSA was accompanied by turnover of large mammals and large-scale landscape change. Brooks <jats:italic>et al.</jats:italic> establish that ∼320,000 to 305,000 years ago, the populations in eastern Africa underwent a technological shift upon procurement of distantly sourced obsidian for toolmaking, indicating the early development of social exchange. Deino <jats:italic>et al.</jats:italic> provide the chronological underpinning for these discoveries. </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="6384" page="86" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2200">86</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6384" page="90" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2646">90</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6384" page="95" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2216">95</jats:related-article> </jats:p>

<jats:title>The Middle Stone Age in Africa</jats:title> <jats:p> The Olorgesailie basin in the southern Kenya rift valley contains sediments dating back to 1.2 million years ago, preserving a long archaeological record of human activity and environmental conditions. Three papers present the oldest East African evidence of the Middle Stone Age (MSA) and elucidate the system of technology and behavior associated with the origin of <jats:italic>Homo sapiens</jats:italic> . Potts <jats:italic>et al.</jats:italic> present evidence for the demise of Acheulean technology that preceded the MSA and describe variations in late Acheulean hominin behavior that anticipate MSA characteristics. The transition to the MSA was accompanied by turnover of large mammals and large-scale landscape change. Brooks <jats:italic>et al.</jats:italic> establish that ∼320,000 to 305,000 years ago, the populations in eastern Africa underwent a technological shift upon procurement of distantly sourced obsidian for toolmaking, indicating the early development of social exchange. Deino <jats:italic>et al.</jats:italic> provide the chronological underpinning for these discoveries. </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="6384" page="86" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2200">86</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6384" page="90" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2646">90</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6384" page="95" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aao2216">95</jats:related-article> </jats:p>

<jats:title>Staging quiescent cells</jats:title> <jats:p> Tissue-specific stem cells either divide or wait in a quiescent state until needed by the body. Quiescent stem cells have been thought to reside in the G <jats:sub>0</jats:sub> stage before activating to reenter the cell cycle. However, Otsuki and Brand now show that most quiescent stem cells in the <jats:italic>Drosophila</jats:italic> brain are arrested in G <jats:sub>2</jats:sub> . Cells in the two phases display differences; for example, G <jats:sub>2</jats:sub> stem cells awaken more quickly than G <jats:sub>0</jats:sub> stem cells, with the conserved pseudokinase Tribbles playing a regulatory role. Elucidating the different pathways and mechanisms underlying quiescence could help to inform regenerative drug design. </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="6384" page="99" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aan8795">99</jats:related-article> </jats:p>