Catálogo de publicaciones - revistas

<jats:title>Resonant systems with high bandwidth</jats:title><jats:p>The performance of an active system, whether it is optical, electrical, or mechanical, is often described by its quality (<jats:italic>Q</jats:italic>) factor. Typically, one learns the rule that the higher the<jats:italic>Q</jats:italic>factor, the sharper the resonance—that is, the bandwidth of the device is reduced. Tsakmakidis<jats:italic>et al.</jats:italic>show that this is indeed the case, but only for symmetric systems. However, for the case of asymmetric (or nonreciprocal) systems, the rule need not be obeyed. They show theoretically that the more asymmetric a system with high<jats:italic>Q</jats:italic>is, the wider the bandwidth can be. The effect raises the prospect of designing high-<jats:italic>Q</jats:italic>devices operating over large bandwidths.</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="6344" page="1260" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aam6662">1260</jats:related-article></jats:p>

<jats:title>Quantum effects in ambient conditions</jats:title> <jats:p> Quantum back action—the “reaction” of a quantum mechanical object to being measured—is normally observed at cryogenic temperatures, where it is easier to distinguish from thermal motion. Purdy <jats:italic>et al.</jats:italic> managed to tease out the effects of quantum back action at room temperature by using a mechanical oscillator and probing it with light (see the Perspective by Harris). The fluctuations of the force produced by the light probe caused correlated changes to the motion of the oscillator and the properties of the transmitted light. These correlations revealed the effects of the back action, which allows the system to be used as a quantum thermometer. </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="6344" page="1265" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aag1407">1265</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6344" page="1232" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aan0400">1232</jats:related-article> </jats:p>

<jats:title>Understanding the formation of spicules</jats:title> <jats:p> Spicules are small jets lasting a few minutes that form in the solar atmosphere and propel hot plasma upward from the visible surface. The underlying physics of spicules is not well understood. Martínez-Sykora <jats:italic>et al.</jats:italic> developed radiation-magnetohydrodynamic simulations that can spontaneously produce numerous spicules with properties that match observations. Interactions between large-scale magnetic fields and the plasma, such as ambipolar diffusion, drive the formation process and subsequent evolution. Understanding how spicules form will help assess how much they heat the solar corona and how they relate to other solar phenomena. </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="6344" page="1269" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aah5412">1269</jats:related-article> </jats:p>

<jats:title>Trifluoromethylation via broken C-F bonds</jats:title> <jats:p> Trifluoromethyl substituents are widely used in pharmaceutical research to tune the properties of drug candidates. Generally, they are introduced intact through the formation of carbon-carbon bonds. Levin <jats:italic>et al.</jats:italic> discovered an unusual alternative mechanism, in which borane abstracts fluoride from the CF <jats:sub>3</jats:sub> group in a gold complex. The activated CF <jats:sub>2</jats:sub> fragment can then bond to a wide variety of other carbon substituents added to the same gold center. Return of the fluoride liberates a trifluoromethylated compound from the metal. This mechanism could be useful for the introduction of radioactive fluoride substituents for positron emission tomography applications. </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="6344" page="1272" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aan1411">1272</jats:related-article> </jats:p>

<jats:title>Sulfur's balancing act in cytochrome c</jats:title> <jats:p> Cytochrome c enzymes have two distinct functions that depend on the position of a methionine residue. When the sulfur in the methionine side chain coordinates with iron in the enzyme's active site, the protein is optimized for electron transfer; otherwise, it is poised for peroxidase activity. Mara <jats:italic>et al.</jats:italic> used ultrafast x-ray absorption and emission spectroscopy to probe the energetics of this Fe-S bond (see the Perspective by Bren and Raven). By breaking the bond transiently with light and then timing its reformation, they determined that the surrounding protein environment boosts the bond strength by 4 kilocalories per mole—just enough to toggle between each functional state at a practical rate. </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="6344" page="1276" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aam6203">1276</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6344" page="1236" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aan5587">1236</jats:related-article> </jats:p>

<jats:title>Optimum human input</jats:title> <jats:p> Exoskeletons can be used to augment human abilities—for example, to lift very heavy loads or to provide greater endurance. For each user, though, a device will need to be adjusted for optimum effect, which can be time-consuming. Zhang <jats:italic>et al.</jats:italic> show that the human can be included in the optimization process, with real-time adaptation of an ankle exoskeleton (see the Perspective by Malcolm <jats:italic>et al.</jats:italic> ). By using indirect calorimetry to measure metabolic rates, the authors were able to adjust the torque provided by the device while users were walking, running, and carrying a load. </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="6344" page="1280" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aal5054">1280</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6344" page="1230" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aan5367">1230</jats:related-article> </jats:p>

<jats:title>Packaging without nucleosomes</jats:title> <jats:p> The fundamental compaction of DNA in chromosomes is thought to start with the wrapping of DNA around nucleosomes, but is nucleosome wrapping required for the condensation of mitotic chromosomes? Shintomi <jats:italic>et al.</jats:italic> combined <jats:italic>Xenopus</jats:italic> egg extracts and mouse sperm nuclei and found that chromosome-like structures could be assembled in the near-complete absence of nucleosomes (see the Perspective by Kakui and Uhlmann). These “nucleosome-depleted” chromosomes were composed of condensin-enriched discrete axes and poorly organized chromatin loops. This finding challenges the textbook view of mitotic chromosome organization. </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="6344" page="1284" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aam9702">1284</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6344" page="1233" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aan8090">1233</jats:related-article> </jats:p>

<jats:title>PKA-activation mechanism revised</jats:title> <jats:p> Many hormone receptors stimulate production of cyclic AMP (adenosine monophosphate), which activates PKA (protein kinase A). The textbook view suggests that activation releases the catalytic subunit of the enzyme from its complex with the regulatory subunit. Smith <jats:italic>et al.</jats:italic> closely monitored activation of PKA in cultured human cells and found that dissociation of the holoenzyme was not necessary for activation. The kinase, which binds anchoring proteins that localize it in the cell, appears to be restricted to acting within about 200 Å of such anchoring proteins. Thus, PKA activity is more precisely targeted within the cell than previously anticipated. </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="6344" page="1288" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aaj1669">1288</jats:related-article> </jats:p>

<jats:title>How to make a protein-based nanocontainer</jats:title> <jats:p> Bacterial microcompartments are to bacteria what membrane-bound organelles are to eukaryotic cells. They are specialized subcellular compartments for colocalizing enzymes to enhance reaction rates, protect sensitive proteins, and sequester toxic intermediates. Sutter <jats:italic>et al.</jats:italic> determined the atomic-resolution structure of a complete 6.5-megadalton bacterial microcompartment shell. The shell is composed of hundreds of copies of five distinct proteins that form hexamers, pentamers, and three types of trimers. The assembly principles revealed by the structure provide the basis to rationally manipulate self-assembly in native and engineered systems and could help, for example, in the design of subcellular nanoreactors. </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="6344" page="1293" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aan3289">1293</jats:related-article> </jats:p>

<jats:p> The traditional techniques of standard microscopy and flow cytometry have been the stalwart of cell analysis for many years. But times have changed—scientific breakthroughs, grant applications, and publications wait for no one—and there are now a host of new technologies that complement these traditional modalities. With the advent of automation and high-throughput technologies, researchers no longer need to spend hours in a darkroom to capture a simple fluorescent image, painstakingly measuring cell parameters one cell at a time, or risk losing precious samples due to mechanical issues. Our panelists will explain how applying the latest cutting-edge technologies, such as high-content analysis and superresolution microscopy, as well as other advances in flow cytometry and microscopy, can lead to new discoveries while saving time and making your lab more efficient and productive. <jats:list list-type="bullet"> <jats:list-item> <jats:p> <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.sciencemag.org/custom-publishing/webinars/cell-analysis-time-change">View the Webinar</jats:ext-link> </jats:p> </jats:list-item> </jats:list> </jats:p>