Catálogo de publicaciones - revistas

<jats:title>Vibrating in a Crowd</jats:title> <jats:p> High-vacuum molecular beam studies can probe the roles of specific vibrations and rotations on molecular reactivity with remarkably fine resolution. <jats:bold> Glowacki <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="1066" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224106">1066</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="6098" page="1046" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227528">Tyndall</jats:related-article> </jats:bold> ) now show, through a combination of spectroscopy and theoretical modeling, that oxidation of acetylene under effectively atmospheric conditions proceeds in part through vibrationally excited intermediates prior to collisional randomization. </jats:p>

<jats:title>Pretend Wires</jats:title> <jats:p> Cold atomic gases have been successfully used to simulate solid-state phenomena such as quantum criticality. However, simulating mesoscopic electronic transport like that realized in quantum wires is challenging. <jats:bold> Brantut <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="1069" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223175">1069</jats:related-article> , published online 2 August) connected two reservoirs of fermionic <jats:sup>6</jats:sup> Li atoms (simulating electrons) with a narrow channel (simulating a wire), created a nonequilibrium situation by applying a magnetic field gradient, and observed the flow through the channel. When the mean-free path of the atoms exceeded the length of the channel, the atomic density in the channel was constant in the central region and only changed at the ends, indicating the presence of contact resistance. The opposite diffusive regime created by imposing a disordered laser potential produced a uniformly varying density inside the channel. </jats:p>

<jats:title>Boundaries on Plasmonic Excitations</jats:title> <jats:p> The localization of optical fields within a metal nanostructure can achieve strengths that are orders of magnitude greater than that of the incident field. This focusing and enhancement of the optical field maybe useful in sensing, nonlinear optics, and optical scattering applications. In probing the properties of metallic nanoparticles, <jats:bold> Ciracì <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="1072" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224823">1072</jats:related-article> ; see the cover) show that the enhancement is limited by the electronic response of the metal, which has implications for the ultimate performance of nanophotonic systems. </jats:p>

<jats:title>Salty Origins of Fresh Water</jats:title> <jats:p> Cloud droplets above the Amazonian rain forest form mostly around organic aerosols, but the source of the aerosols has been a mystery. <jats:bold> Pöhlker <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="1075" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223264">1075</jats:related-article> ) report that particles rich in potassium salts emitted by Amazonian vegetation can act as the seeds for the growth of organic aerosol particles that function as condensation nuclei for water droplets. These specks of biogenic salts provide a surface for the condensation of low- or semi-volatile organic compounds formed by the atmospheric oxidation of isoprene and terpenes, molecules produced in great abundance by many kinds of Amazonian plants. </jats:p>

<jats:title>Dark Forcing</jats:title> <jats:p> Soot, or black carbon, is a ubiquitous atmospheric pollutant whose warming effect might be second only to carbon dioxide. When black carbon is emitted, it combines with other aerosols to form heterogeneous mixtures. Models have predicted that internal mixing of black carbon with other materials can double the amount of radiation absorbed. <jats:bold> Cappa <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="1078" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223447">1078</jats:related-article> ) report that in situ measurements of the enhancement of radiation absorption by these mixed black carbon–containing particles in the atmosphere show a much smaller effect. Thus, many climate models may be overestimating the amount of warming caused by black carbon emissions. </jats:p>

<jats:title>Natural Selection at Work</jats:title> <jats:p> Catching the evolution of a novel function and determining its selective parameters in nature remains an extremely difficult task. <jats:bold> Prasad <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="1081" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1221636">1081</jats:related-article> ) have undertaken this quest documenting the molecular basis of a natural allelic polymorphism and its effects on herbivory and survival in the <jats:italic>Arabidopsis</jats:italic> relative, <jats:italic>Boechera stricta</jats:italic> , living in the Rocky Mountains. </jats:p>

<jats:title>A Fungal Culprit to Carbon Loss</jats:title> <jats:p> In some ecosystems, such as in the layer of soil containing plant roots, fungi, and bacteria, increased levels of CO <jats:sub>2</jats:sub> should stimulate more efficient aboveground photosynthesis, which in turn should promote increased sequestration of organic carbon in soil through the protective action of arbuscular mycorrhizal fungi. However, in a series of field and microcosm experiments performed under elevated levels of CO <jats:sub>2</jats:sub> thought to be consistent with future emissions scenarios, <jats:bold> Cheng <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="1084" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224304">1084</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="6098" page="1049" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227303">Kowalchuk</jats:related-article> </jats:bold> ) observed that these fungi actually promote degradation of soil organic carbon, releasing more CO <jats:sub>2</jats:sub> in the process. </jats:p>

<jats:title>Curls Beget More Curls</jats:title> <jats:p> Cucumber tendrils reach up to find an attachment, and then coil to shorten and drag the plant up toward the sunlight. <jats:bold> Gerbode <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="1087" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223304">1087</jats:related-article> ) analyzed the biomechanics of cucumber tendril coiling. The process depends on a thin layer of cells within the tendril that becomes lignified during the coiling process. A construct of pre-strained silicon sheets, fabric ribbon, and copper wire reproduced the coiling functions in abiotic materials. Physical and mathematical models explained the peculiar response by which the cucumber tendril initially overwinds when pulled further. </jats:p>

<jats:title>Epithelial Defense Force</jats:title> <jats:p> The nature of the cells that maintain and heal the epithelium lining the esophagus has been controversial. <jats:bold> Doupé <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="1091" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1218835">1091</jats:related-article> , published online 19 July; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6098" page="1051" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227506">Kushner</jats:related-article> </jats:bold> ) show that, unlike many other tissues, mouse esophagus is devoid of slow cycling stem cells. Instead, the epithelium is maintained and repaired by a single population of proliferating cells that can switch rapidly from homeostatic behavior into “repair mode” in the vicinity of a wound. </jats:p>

<jats:title>Modulating the Clock</jats:title> <jats:p> Because of the close association of the circadian clock with a wide range of physiological processes, identification of clock-modulating small molecules may prove useful for the treatment of circadian-related disorders, which include circadian sleep disorders, cardiovascular disease, cancer, and metabolic disease. <jats:bold> Hirota <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="1094" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223710">1094</jats:related-article> , published online 12 July) screened for chemical compounds that affected the period of the circadian clock in a human osteosarcoma cell line. A carbazole derivative named KL001 appeared to act by inhibiting proteolytic degradation of the cryptochrome proteins, which in turn caused a lengthening of the circadian period. KL001 also inhibited glucagon-induced gluconeogenesis in primary cultures of mouse hepatocytes. </jats:p>