Catálogo de publicaciones - revistas

<jats:title>Stable molecular switches</jats:title> <jats:p> Many single-molecule current switches have been reported, but most show poor stability because of weak contacts to metal electrodes. Jia <jats:italic>et al.</jats:italic> covalently bonded a diarylethene molecule to graphene electrodes and achieved stable photoswitching at room temperature (see the Perspective by Frisbie). The incorporation of short bridging alkyl chains between the molecule and graphene decoupled their pielectron systems and allowed fast conversion of the open and closed ring states. </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="6292" page="1443" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf6298">1443</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6292" page="1394" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aag0827">1394</jats:related-article> </jats:p>

<jats:title>Organic solar cells tuned by blending</jats:title> <jats:p> Electrical engineers can finetune the energetics of rigid photovoltaics and transistors by blending different semiconducting materials. However, it's hard to apply this tuning protocol to the flexible class of carbon-based semiconductors. Schwarze <jats:italic>et al.</jats:italic> now show that continuous band energy tuning is indeed possible by varying the blend ratios of certain organic phthalocyanines and their fluorinated or chlorinated derivatives (see the Perspective by Ueno). They demonstrated the effect, which they attribute to quadrupolar interactions, in model solar cells. </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="6292" page="1446" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf0590">1446</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6292" page="1395" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf8937">1395</jats:related-article> </jats:p>

<jats:title>Chiral molecule discovered in space</jats:title> <jats:p> A chiral molecule is one that has two forms that are mirror images of each other: enantiomers. Biological systems overwhelmingly use one enantiomer over another, and some meteorites show an excess of one type. The two forms are almost identical chemically, so how this excess first arose is unknown. McGuire <jats:italic>et al.</jats:italic> used radio astronomy to detect the first known chiral molecule in space: propylene oxide. The work raises the prospect of measuring the enantiomer excess in various astronomical objects, including regions where planets are being formed, to discover how and why the excess first appeared. </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="6292" page="1449" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aae0328">1449</jats:related-article> </jats:p>

<jats:title>A future for boreal forests</jats:title><jats:p>Conservation under climate change presents the challenge of predicting where will be suitable for particular organisms and ecological communities in the future. D'Orangeville<jats:italic>et al.</jats:italic>assess the probable future range for boreal forests in eastern North America, which are expected to be subject to large temperature increases in their natural range. Using tree-ring data from many thousands of forest stands, they delineate the geographical extent of the region where tree growth responds favorably to higher temperatures and where the forest should persist at least until 2070.</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="6292" page="1452" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf4951">1452</jats:related-article></jats:p>

<jats:title>China's national ecosystem assessment</jats:title> <jats:p> China recently completed its first National Ecosystem Assessment covering the period 2000–2010. Ouyang <jats:italic>et al.</jats:italic> present the main findings of the assessment. Investment in the restoration and preservation of natural capital has resulted in improvements at the national level in most of the major ecosystem services measured. In particular, food production, carbon sequestration, and soil retention showed strong gains; on the other hand, habitat provision for biodiversity showed a gradual decline. Regional differences remain nonetheless, and there are serious environmental challenges still to be met in areas such as air quality and the wider global footprint of raw material imports. </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="6292" page="1455" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf2295">1455</jats:related-article> </jats:p>

<jats:title>Tackling the advance of online threats</jats:title> <jats:p> Online support for adversarial groups such as Islamic State (ISIS) can turn local into global threats and attract new recruits and funding. Johnson <jats:italic>et al.</jats:italic> analyzed data collected on ISIS-related websites involving 108,086 individual followers between 1 January 1 and 31 August 2015. They developed a statistical model aimed at identifying behavioral patterns among online supporters of ISIS and used this information to predict the onset of major violent events. Sudden escalation in the number of ISIS-supporting ad hoc web groups (“aggregates”) preceded the onset of violence in a way that would not have been detected by looking at social media references to ISIS alone. The model suggests how the development and evolution of such aggregates can be blocked. </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="6292" page="1459" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf0675">1459</jats:related-article> </jats:p>

<jats:title>Coding abstract concepts in the brain</jats:title> <jats:p> Grid cells are thought to provide the neuronal code that underlies spatial knowledge in the brain. Grid cells have mostly been studied in the context of path integration. However, recent theoretical studies have suggested that they may have a broader role in the organization of general knowledge. Constantinescu <jats:italic>et al.</jats:italic> investigated whether the neural representation of concepts follows a structure similar to the representation of space in the entorhinal cortex. Several brain regions, including the entorhinal cortex and the ventromedial prefrontal cortex, showed gridlike neural representation of conceptual space. </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="6292" page="1464" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf0941">1464</jats:related-article> </jats:p>

<jats:title>Punishment doesn't work in cocaine addicts</jats:title> <jats:p> Addiction is extremely difficult to treat, particularly cocaine use disorder. Animal experiments have led to the concept of drug addiction as abnormal goal-directed learning and habit formation. Ersche <jats:italic>et al.</jats:italic> found that overtraining with positive reinforcement such as rewards made cocaine-addicted patients less sensitive to the outcome of their actions. In contrast, overtraining on a punishment paradigm had no effect. Thus, habits may determine the behavior of cocaine users. </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="6292" page="1468" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf3700">1468</jats:related-article> </jats:p>

<jats:title>Tracking stem cell fate in time and space</jats:title> <jats:p> After injury and during homeostasis, tissues rely on the balance of cell loss and renewal. Rompolas <jats:italic>et al.</jats:italic> visualized individual stem cells over their lifetime in the epidermis of live mice. Tracking stem cells over multiple generations revealed that tissue homeostasis in the mouse epidermis is not maintained by asymmetric cell division as previously thought, but through the coordination of sibling cell fate and lifetimes. Furthermore, differentiating stem cells reused the existing spatial organization of the epidermis. </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="6292" page="1471" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf7012">1471</jats:related-article> </jats:p>

<jats:title> A fluorescent sensor for NAD <jats:sup>+</jats:sup> in living cells </jats:title> <jats:p> Roles of cellular nicotinamide adenine dinucleotide (NAD <jats:sup>+</jats:sup> ) in metabolism, aging, and disease have garnered much interest, but methods have been lacking to measure the amounts of NAD <jats:sup>+</jats:sup> in living cells. Cambronne <jats:italic>et al.</jats:italic> developed a genetically encoded biosensor that can be used to monitor concentrations of free NAD <jats:sup>+</jats:sup> in various compartments of a cell (see the Perspective by Guarente). Such concentrations of NAD <jats:sup>+</jats:sup> appear to be important in regulating the activity of NAD <jats:sup>+</jats:sup> -consuming enzymes such as sirtuins and ADP-ribosyltransferases. The authors used the sensor to demonstrate that NAD <jats:sup>+</jats:sup> concentrations in mitochondria of cultured human cells can be controlled by multiple mechanisms. </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="6292" page="1474" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aad5168">1474</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6292" page="1396" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aag1718">1396</jats:related-article> </jats:p>