Catálogo de publicaciones - revistas

<jats:title>A Complicated Scaffold, Simply</jats:title> <jats:p> Materials with tailored pore structures can be useful as catalysis supports and for lightweight materials. When preparing medical scaffolds, restrictive preparation conditions have to be met, which can prohibit multistep preparation procedures. <jats:bold> Sai <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="530" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1238159">530</jats:related-article> ) describe a method for making porous polymers containing both relatively large (several microns) interconnecting pores and a second population of ∼ tens of nanometer pores. The process exploits spinodal decomposition of a block copolymer blended with small-molecule additives and requires a simple washing step with water, methanol, or ethanol. </jats:p>

<jats:title>Keeping Electrolytes in Porous Electrodes</jats:title> <jats:p> Electrochemical capacitors (ECs) can rapidly charge and discharge, but generally store less energy per unit volume than batteries. One approach for improving on the EC electrodes made from porous carbon materials is to use materials such as chemically converted graphene (CCG, or reduced graphene oxide), in which intrinsic corrugation of the sheets should maintain high surface areas. In many cases, however, these materials do not pack into compact electrodes, and any ECs containing them have low energy densities. <jats:bold> Yang <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="534" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239089">534</jats:related-article> ) now show that capillary compression of gels of CCG containing both a volatile and nonvolatile electrolyte produced electrodes with a high packing density. The intersheet spacing creates a continuous ion network and leads to high energy densities in prototype ECs. </jats:p>

<jats:title>Doppler Effect with a Twist</jats:title> <jats:p> The Doppler shift is a familiar and well-understood effect in acoustics. Radar guns use the same effect to determine the speed of moving vehicles. Applied to a rotating object side-on, however, a linear Doppler effect would register no movement. Using twisted light, whereby photons are imprinted with a given amount of optical angular momentum, <jats:bold> Lavery <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="537" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239936">537</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="464" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242097">Marrucci</jats:related-article> </jats:bold> ) detected rotation with an analogous angular Doppler shift, which may be useful for remote sensing and observational astronomy. </jats:p>

<jats:title>Isothermal Water Splitting</jats:title> <jats:p> Solar concentrators can create extremely high temperatures that can drive chemical reactions, including the thermal splitting of water to provide hydrogen. A metal oxide catalyst is needed that is usually cycled between hotter conditions where it is reduced and cooler conditions where it is reoxidized by water. This cycling can limit catalyst lifetime, which can be costly. <jats:bold> Muhich <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="540" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239454">540</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="470" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241311">Roeb and Sattler</jats:related-article> </jats:bold> ) developed an approach that allowed the redox cycle to be driven isothermally, using pressure swings. </jats:p>

<jats:title>Hot and Bothered</jats:title> <jats:p> One of the most uncertain aspects of energy production at geothermal fields is the potential for the induction of earthquakes from extraction of hot fluids and injection of wastewater back into the subsurface. <jats:bold>Brodsky and Lajoie</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="543" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239213">543</jats:related-article> , published online 11 July) compared the historical rates of seismicity—after correcting for the occurrence of aftershocks—to operational parameters at the Salton Sea Geothermal Field in southern California. The net volume of fluid extracted and injected was correlated with recent seismicity. However, since the 1980s, when the first plant came online, the rate of earthquakes induced with additional increments of volume injected has decreased. </jats:p>

<jats:title>Coding Reward Versus Punishment</jats:title> <jats:p> Reinforcement learning is driven by reward prediction error, and a very influential theory has proposed that dopamine neurons provide this signal to teach value to the brain. Although this is called a reward prediction error, it has been assumed to also represent aversiveness. Thus, it was thought that the dopamine signal could be sufficient for learning total value. <jats:bold>Fiorillo</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="546" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1238699">546</jats:related-article> ) found that dopamine alone was not sufficient to encode value, implying that there must be an analogous signal for aversiveness. </jats:p>

<jats:title>Modification Without Enzymes</jats:title> <jats:p> Control of metabolic enzymes and regulation of many other biological processes is mediated in large part by binding of small molecules to proteins or through enzymatically medimediated covalent posttranslational modification of proteins. <jats:bold>Moellering and Cravatt</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="549" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1238327">549</jats:related-article> ) wondered whether another scenario might occur in which reactive intermediates in a metabolic pathway might specifically react with and modify particular amino acids in proteins to produce regulatory changes without the need for catalysis by another enzyme. A particularly reactive intermediate formed during glycolysis, 1,3-bisphosphoglycerate, could nonenzymatically modify specific lysines in proteins, providing a means by which accumulation of metabolic intermediates could provide regulatory feedback to balance or control flux through various pathways. Proteomic analysis showed that the 3-phosphoglyceryl-lysine formed when certain lysine residues interacted with 1,3-bisphosphoglycerate produced naturally in cells and was particularly common in proteins that function in glycolysis. Such modification decreased activity of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. </jats:p>

<jats:title>As the Worm Squirms</jats:title> <jats:p> Restoration of oxygen supply to cells that have been deprived of oxygen actually causes further damage to cells and tissues. Such responses, known as reperfusion injury, contribute to the deadly effects of heart attacks and strokes in humans. Lack of oxygen is sensed directly by a prolyl hydroxylase known as EGL-9 in worms and EGLN2 in mammals. Inhibition of EGL-9 can reduce damage caused by reperfusion of tissues with oxygen, but how such beneficial effects are mediated is not clear. <jats:bold> Ma <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="554" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1235753">554</jats:related-article> , published online 27 June) used a genetic screen in the nematode <jats:italic>Caenorhabditis elegans</jats:italic> , which has a behavioral response to reoxygenation in which the animals increase their movement, to find factors that interact with EGL-9. They identified the cytochrome p450 oxygenase CYP-13A12 as such a factor. Some cytochrome p450 enzymes act on polyunsaturated fatty acids to make cellular signaling molecules known as eicosanoids. The effects of CYP-13A23 were mediated by eicosanoids. Because the regulatory pathways involved appear to be evolutionarily conserved, the results may aid understanding and management of reperfusion injury in humans. </jats:p>

<jats:title>Simple Signals?</jats:title> <jats:p> Cells process information about themselves and their surroundings through biochemical signaling pathways. <jats:bold> Uda <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="558" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1234511">558</jats:related-article> 8) used a recently developed cytometric method to quantitate signaling through biochemical pathways in individual rat pheochromocytoma cells responding to growth factors. The signaling pathways studied provided about 1 bit of information, or only enough for a binary (on or off) decision. In spite of the simplicity, the results showed interactions between pathways with shared components. In some cases, information carried between inputs and intermediate outputs was less than that between the input and more “downstream” outputs, indicating that information was carried through multiple paths. Similarly, in the presence of pharmacological inhibitors of one pathway, others were able to compensate to allow robust transfer of information. Thus, in spite of noise and variation in signal intensities in individual cells, robust transfer of information from the growth factors was achieved. </jats:p>

<jats:title>Examining Y</jats:title> <jats:p> The evolution of human populations has long been studied with unique sequences from the nonrecombining, male-specific Y chromosome (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="465" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242899">Cann</jats:related-article> </jats:bold> ). <jats:bold> Poznik <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="562" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1237619">562</jats:related-article> ) examined 9.9 Mb of the Y chromosome from 69 men from nine globally divergent populations—identifying population and individual specific sequence variants that elucidate the evolution of the Y chromosome. Sequencing of maternally inherited mitochondrial DNA allowed comparison between the relative rates of evolution, which suggested that the coalescence, or origin, of the human Y chromosome and mitochondria both occurred approximately 120 thousand years ago. <jats:bold> Francalacci <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6145" page="565" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1237947">565</jats:related-article> ) investigated the sequence divergence of 1204 Y chromosomes that were sampled within the isolated and genetically informative Sardinian population. The sequence analyses, along with archaeological records, were used to calibrate and increase the resolution of the human phylogenetic tree. </jats:p>