Catálogo de publicaciones - revistas

<jats:p>Posttranscriptional regulation plays a substantial role in controlling the mammalian circadian clockwork.</jats:p>

<jats:p>New process chemistries will be needed to replace petroleum with abundant natural gas as the most economical feedstock for fuels and chemicals.</jats:p>

<jats:p>Inborn errors of metabolism underlying some cases of autism present possibilities for prevention and treatment.</jats:p>

<jats:title>All Change</jats:title> <jats:p> Research on early warning signals for critical transitions in complex systems such as ecosystems, climate, and global finance systems recently has been gathering pace. At the same time, studies on complex networks are starting to reveal which architecture may cause systems to be vulnerable to systemic collapse. <jats:bold> Scheffer <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="344" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225244">344</jats:related-article> ) review how previously isolated lines of work can be connected, conclude that many critical transitions (such as escape from the poverty trap) can have positive outcomes, and highlight how the new approaches to sensing fragility can help to detect both risks and opportunities for desired change. </jats:p>

<jats:title>Transcription Around the Clock</jats:title> <jats:p> The biological clock that controls daily rhythms in mammalian physiology and behavior is thought to be regulated in large part by transcriptional events (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6105" page="338" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1230008"> <jats:bold>Doherty and Kay</jats:bold> </jats:related-article> ). <jats:bold> Koike <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="349" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226339">349</jats:related-article> ; published online 30 August) produced a comprehensive analysis of these transcriptional events across the entire mouse liver genome over a 24-hour period. Only ∼22% of cycling messenger RNA transcripts were driven by de novo transcription, suggesting that posttranscriptional events also play an important regulatory role in the mammalian clock. Biological timing in organisms can also respond to rhythmic cues from the environment. <jats:bold> Morf <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="379" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1217726">379</jats:related-article> , published online 23 August) explored how one such cue, cycles in ambient temperature, influence circadian timing in mammalian cells. Cold-inducible RNA–binding protein (CIRP) accumulates when body temperature is low. A systematic search for binding partners of CIRP identified RNA encoding core components of the circadian clock. Loss of CIRP decreased the amplitude of circadian gene expression and cells lacking CIRP adapted more quickly to temperature cycles. </jats:p>

<jats:title>Black Hole Close-Up</jats:title> <jats:p> M87 is a giant elliptical galaxy about 55 million light-years away. Accretion of matter onto its central massive black hole is thought to power its relativistic jet. To probe structures on scales similar to that of the black hole's event horizon, <jats:bold> Doeleman <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="355" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224768">355</jats:related-article> , published online 27 September) observed the relativistic jet in M87 at a wavelength of 1.3 mm using the Event Horizon Telescope, a special purpose, very-long-baseline interferometry array consisting of four radio telescopes located in Arizona, California, and Hawaii. The analysis suggests that the accretion disk that powers the jet orbits in the same direction as the spin of the black hole. </jats:p>

<jats:title>Beyond Quantum Dots</jats:title> <jats:p> Semiconducting colloidal nanoparticles—quantum dots—are of interest for their unusual properties. One current challenge is the controlled assembly of colloidal particles into larger structures, such as two-dimensional lattices on a substrate, or three-dimensional superparticles. <jats:bold> Wang <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="358" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224221">358</jats:related-article> ) present a two-step self-assembly of CdSe/CdS semiconductor nanorods to form mesoscopic colloidal superparticles. The particles show well-defined super-crystalline domains with dimensions ranging from hundreds of nanometers to several microns, and with the particle morphology controlled by the number of constituent rods. Films of the needle-shaped superparticles were able to act as polarizing light-emitting diodes. </jats:p>

<jats:title>A Twist of Light</jats:title> <jats:p> The angular momentum of photons can be used to encode and transmit information. <jats:bold> Cai <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="363" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226528">363</jats:related-article> ) developed a method for generating and emitting controllable orbital angular momentum states of light from a reconfigurable and scalable silicon photonic chip. Using micro-ring resonators embedded with angular gratings allowed the imprinting of optical angular momentum on the light propagating in the whispering gallery modes of the resonator. The method may enable large-scale integration of optical vortex emitters on complementary metal-oxide–semiconductor-compatible silicon chips. </jats:p>

<jats:title>Too-Hot Times</jats:title><jats:p>Climate warming has been invoked as a factor contributing to widespread extinction events, acting as a trigger or amplifier for more proximal causes, such as marine anoxia.<jats:bold>Sun<jats:italic>et al.</jats:italic></jats:bold>(p.<jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="366" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224126">366</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="6105" page="336" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1228998">Bottjer</jats:related-article></jats:bold>) present evidence that exceptionally high temperatures themselves may have caused some extinctions during the end-Permian. A rapid temperature rise coincided with a general absence of ichthyofauna in equatorial regions, as well as an absence of many species of marine mammals and calcareous algae, consistent with thermal influences on the marine low latitudes. Sea surface temperatures approached 40°C, which suggests that land temperatures likely fluctuated to even higher values that suppressed terrestrial equatorial plant and animal abundance during most of the Early Triassic.</jats:p>

<jats:title>Dating Carbon</jats:title> <jats:p> Radiocarbon dating is the best way to determine the age of samples that contain carbon and that are younger than ∼50,000 years, the limit of precision for the method. There are several factors that complicate such age determinations, however, some of the most important of which include variability of the <jats:sup>14</jats:sup> C production in the atmosphere (which affects organic samples whose radiocarbon inventories are derived from atmospheric CO <jats:sub>2</jats:sub> ), surface ocean reservoir effects (which affect marine samples that acquire their radiocarbon signatures from seawater), and variable dead carbon fraction effects (which affect speleothems that derive their carbon from groundwaters). <jats:bold> Bronk Ramsey <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="370" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226660">370</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="6105" page="337" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1228653">Reimer</jats:related-article> </jats:bold> ) avoid the need to make such assumptions, reporting the <jats:sup>14</jats:sup> C results of sediments from Lake Suigetsu, Japan. Analysis of terrestrial plant macrofossils in annually layered datable sediments yielded a direct record of atmospheric radiocarbon for the entire measurable interval up to 52.8 thousand years ago. </jats:p>