Catálogo de publicaciones - revistas

<jats:title>Early Separation</jats:title> <jats:p> In photovoltaic devices, electrons excited by the absorption of light must travel across a junction, while the positively charged “holes” they leave behind effectively migrate in the opposite direction. If the electrons and holes do not separate efficiently, they can recombine and fail to produce any appreciable current. <jats:bold> Gélinas <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="6170" page="512" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246249">512</jats:related-article> , published online 12 December; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6170" page="492" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249230"> <jats:bold>Bredas</jats:bold> </jats:related-article> ) studied this separation process by ultrafast optical absorption spectroscopy in thiophene-derived donor-fullerene acceptor systems common in organic photovoltaics and report a rate significantly faster than simple charge diffusion would suggest. The results implicate a coherent charge delocalization process, likely to involve fullerene π-electron states. </jats:p>

<jats:title>Acoustically Isolated</jats:title> <jats:p> The control of sound transmission is desirable in a number of circumstances from noise suppression to imaging technologies. <jats:bold> Fleury <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="6170" page="516" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246957">516</jats:related-article> ; see the cover; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6170" page="495" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249616">Cummer</jats:related-article> </jats:bold> ) studied a subwavelength acoustic meta-atom consisting of a resonant ring cavity biased by an internally circulating fluid. The direction of rotational flow of the fluid (air) changed the resonant properties of the ring cavity, allowing the propagation of sound waves within the cavity to be controlled. With several ports connected to the cavity, sound could be directed to a certain port while isolating transmission in another. </jats:p>

<jats:title>Disorderly Flow</jats:title> <jats:p> Lithium batteries are becoming ever more important in society. While their application used to be confined to portable electronics, they are now becoming the enabling technology for electric vehicles and grid storage for renewables. Generally, the flow of lithium ions into and out of battery electrodes is thought to require ordered materials. <jats:bold> Lee <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="6170" page="519" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246432">519</jats:related-article> , published online 9 January) used a combination of experimental work and computations to identify disordered electrode materials with high Li diffusion. The improved energy density properties could be attributed to compositions with excess lithium beyond the stoichiometric limit, leading to intermixing between the lithium and transition metal sublattices and the formation of a percolation network providing specific lithium transport pathways. </jats:p>

<jats:title>Melting Moments</jats:title> <jats:p> The boundary between Earth's core and mantle defines where the iron-rich liquid outer core meets the more chemically heterogeneous solid lower mantle and is marked by a sharp thermal gradient of nearly 1500 kelvin. The precise relationship between temperature and melting of the lowermost mantle constrains the structure and heat flow across the core-mantle boundary. In order to identify trace amounts of liquid as melting initiates, <jats:bold> Nomura <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="6170" page="522" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248186">522</jats:related-article> , published online 16 January) performed x-ray microtomographic imaging of rocks of a primitive mantle composition that had been subjected to high pressures and temperatures in a diamond anvil cell. The experimentally determined maximum melting point of 3570 kelvin suggests that some phases typically thought to lose stability in the lowermost mantle, such as MgSiO <jats:sub>3</jats:sub> -rich post-perovskite, may be more widely distributed than expected. </jats:p>

<jats:title>Coordinating the Clock</jats:title> <jats:p> In flies, the mechanosensory chordotonal organs help to coordinate the effects of temperature on circadian cycles. <jats:bold> Simoni <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="6170" page="525" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1245710">525</jats:related-article> ) provide a mechanism by which mechanosensory input is processed to help to synchronize the biological clock in <jats:italic>Drosophila melanogaster</jats:italic> . The chordotonal organs, which have similarities to the mammalian ear, were also required for sensation of a vibration stimulus and its effects on the endogenous brain clock. The chordotonal organs, present in the joints of the limbs, provide neuronal signals that allow the animal to sense its position or posture—and thus might mediate feedback of a range of behaviors onto the endogenous biological clock. </jats:p>

<jats:title>Big MACs</jats:title> <jats:p> Tubeworms are important marine benthic species that encrust rocks and contribute to fouling of man-made objects, such as ships' hulls and drilling well heads. Like most marine invertebrates, the larval stages of tubeworms are free-swimming, but the cues for larval settlement and the triggers for metamorphosis are mysterious. <jats:bold> Shikuma <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="6170" page="529" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246794">529</jats:related-article> , published online 9 January) experimented on larval settlement by the tubeworm, <jats:italic>Hydroides elegans</jats:italic> , which needs to associate with a biofilm-forming bacterium, <jats:italic>Pseudoalteromonas luteoviolacea</jats:italic> , before settlement can occur. The bacterium was found to express metamorphosis-associated contractile structures (MACs) in large and structurally elaborate arrays that allow the tubeworm larvae to develop. </jats:p>

<jats:title>Eggs Well Done</jats:title> <jats:p> Germ cells can endure extensive DNA damage during their development. Programmed meiotic double-strand breaks (DSBs) are essential for proper segregation of chromosomes to oocytes and sperm. However, incomplete DSB repair by recombination activates a checkpoint that triggers cell death. Exogenous DNA damage is also lethal to oocytes via a highly sensitive checkpoint. <jats:bold> Bolcun-Filas <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="6170" page="533" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1247671">533</jats:related-article> ) show that the CHK2 kinase is a key component of both checkpoints in mouse oocytes. Deletion of <jats:italic>Chk2</jats:italic> restored fertility to females that would otherwise be sterile because of a meiotic recombination mutation or radiation exposure. </jats:p>

<jats:title>Battle of the Sexes</jats:title> <jats:p> In many species, males compete with one another to propagate their own DNA, often to the detriment of females (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6170" page="491" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1250174">Promislow and Kaeberlein</jats:related-article> ). <jats:bold>Shi and Murphy</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6170" page="536" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1242958">536</jats:related-article> , published online 19 December) discovered that mating in <jats:italic>Caenorhabditis</jats:italic> species causes mothers to shrink and die soon after they have ceased producing progeny. Males appear to hijack the longevity and stress resistance pathways normally employed by the mothers to slow reproduction and somatic aging in times of stress. <jats:bold> Maures <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="6170" page="541" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1244160">541</jats:related-article> , published online 29 November) explored why the presence of abundant mating-competent males causes a decrease in the life span of nematodes of the opposite sex and found that a secreted substance, possibly a pheromone, reproduced the effect of the males when transferred in the culture medium. Detection of pheromones from a female fruit fly is enough to cause changes in metabolism, reduce resistance to starvation, and shorten the life span of male flies. <jats:bold> Gendron <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="6170" page="544" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1243339">544</jats:related-article> , published online 29 November) report that the signals from the female appear to be recognized by sensory receptors on the legs of male flies. </jats:p>

<jats:title>Battle of the Sexes</jats:title> <jats:p> In many species, males compete with one another to propagate their own DNA, often to the detriment of females (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6170" page="491" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1250174">Promislow and Kaeberlein</jats:related-article> ). <jats:bold>Shi and Murphy</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6170" page="536" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1242958">536</jats:related-article> , published online 19 December) discovered that mating in <jats:italic>Caenorhabditis</jats:italic> species causes mothers to shrink and die soon after they have ceased producing progeny. Males appear to hijack the longevity and stress resistance pathways normally employed by the mothers to slow reproduction and somatic aging in times of stress. <jats:bold> Maures <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="6170" page="541" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1244160">541</jats:related-article> , published online 29 November) explored why the presence of abundant mating-competent males causes a decrease in the life span of nematodes of the opposite sex and found that a secreted substance, possibly a pheromone, reproduced the effect of the males when transferred in the culture medium. Detection of pheromones from a female fruit fly is enough to cause changes in metabolism, reduce resistance to starvation, and shorten the life span of male flies. <jats:bold> Gendron <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="6170" page="544" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1243339">544</jats:related-article> , published online 29 November) report that the signals from the female appear to be recognized by sensory receptors on the legs of male flies. </jats:p>

<jats:title>Battle of the Sexes</jats:title> <jats:p> In many species, males compete with one another to propagate their own DNA, often to the detriment of females (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6170" page="491" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1250174">Promislow and Kaeberlein</jats:related-article> ). <jats:bold>Shi and Murphy</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6170" page="536" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1242958">536</jats:related-article> , published online 19 December) discovered that mating in <jats:italic>Caenorhabditis</jats:italic> species causes mothers to shrink and die soon after they have ceased producing progeny. Males appear to hijack the longevity and stress resistance pathways normally employed by the mothers to slow reproduction and somatic aging in times of stress. <jats:bold> Maures <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="6170" page="541" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1244160">541</jats:related-article> , published online 29 November) explored why the presence of abundant mating-competent males causes a decrease in the life span of nematodes of the opposite sex and found that a secreted substance, possibly a pheromone, reproduced the effect of the males when transferred in the culture medium. Detection of pheromones from a female fruit fly is enough to cause changes in metabolism, reduce resistance to starvation, and shorten the life span of male flies. <jats:bold> Gendron <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="6170" page="544" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1243339">544</jats:related-article> , published online 29 November) report that the signals from the female appear to be recognized by sensory receptors on the legs of male flies. </jats:p>