Catálogo de publicaciones - revistas

<jats:p>Mechanical systems acting as electronic quantum dots can be tuned at the level of single electrons.</jats:p>

<jats:p>What do Antarctic ice core records really record?</jats:p>

<jats:p> A monthly roundup of recent news and projects of <jats:italic>Science</jats:italic> 's publisher, the American Association for the Advancement of Science. </jats:p>

<jats:title>Toward New Scaffolds</jats:title> <jats:p> Most existing antibiotics are derived from a small number of core molecular structures or scaffolds. As more and more pathogens emerge that are resistant to existing antibiotics, <jats:bold>Fischbach and Walsh</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1089" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176667">1089</jats:related-article> ) review why renewed efforts must be made to find not only new antibiotics but new scaffolds. Approaches in the areas of natural products, synthesis, and target-based discovery are all yielding promising antibiotics candidates. The battle against resistance should also involve researching narrow-spectrum antibiotics and using combination therapies to extend the usefulness of drugs with high intrinsic resistance rates. </jats:p>

<jats:p>A gene thought to defend plants against infectious bacterial pathogens also supplies defense against a parasitic plant.</jats:p>

<jats:title>Adapting Coat Color</jats:title> <jats:p> Simple phenotypic changes can often be the target of selection—for example, variations in coat color that provide protection against detection by predators. <jats:bold> Linnen <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="1095" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175826">1095</jats:related-article> ) explore the underlying molecular mechanisms behind the production of pale deer mice living on the light-colored Nebraska Sand Hills. The mice that live on the sand are significantly lighter in color than conspecifics living nearby on darker soils. This lighter color was found to be due to de novo changes at the Agouti coat color locus. Thus, rapid adaptive change does not always rely on preexisting genetic variation. </jats:p>

<jats:title>Mind the Pseudogap</jats:title> <jats:p> Below the transition temperature, an energy gap opens in superconductors, which effectively protects the superconducting phase. Above the transition temperature, the gap closes, creating excitations and a loss of superconductivity. In the high-temperature superconducting cuprates, however, the gap persists above the transition temperature. Understanding the electronic structure of this pseudogap region is important in understanding the mechanism of superconductivity in the cuprates. <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" page="1099" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176369">1099</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="5944" page="1080" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178841">Norman</jats:related-article> </jats:bold> ) use high-resolution, temperature-dependent scanning tunneling microscopy to reveal that the pseudogap regime is an incoherent (or phase-disordered) d-wave superconductor. </jats:p>

<jats:title>Tuning Carbon Nanotube Resonances</jats:title> <jats:p> Nanoscale resonators can be used in sensing and for processing mechanical signals. Single-walled carbon nanotubes have potential design advantages as resonators in that their oscillatory motion could be coupled to electron transport (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5944" page="1084" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178574">Hone and Deshpande</jats:related-article> </jats:bold> ). <jats:bold> Steele <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="1103" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176076">1103</jats:related-article> , published online 23 July) and <jats:bold> Lassagne <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="1107" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174290">1107</jats:related-article> , published online 23 July) report that the resonance frequency of a suspended single-walled carbon nanotube can be excited when operated as a single-electron transistor at low temperatures. Electrostatic forces are set up when the carbon nanotubes charge and discharge. The resonance frequency depends on applied voltages, and the coupling is strong enough to drive the mechanical motion into the nonlinear response regime. Differences in the responses of the devices in the two studies reflect in part the different quality factors of the resonators and different cryogenic temperatures. </jats:p>

<jats:title>Tuning Carbon Nanotube Resonances</jats:title> <jats:p> Nanoscale resonators can be used in sensing and for processing mechanical signals. Single-walled carbon nanotubes have potential design advantages as resonators in that their oscillatory motion could be coupled to electron transport (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5944" page="1084" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178574">Hone and Deshpande</jats:related-article> </jats:bold> ). <jats:bold> Steele <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="1103" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176076">1103</jats:related-article> , published online 23 July) and <jats:bold> Lassagne <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="1107" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174290">1107</jats:related-article> , published online 23 July) report that the resonance frequency of a suspended single-walled carbon nanotube can be excited when operated as a single-electron transistor at low temperatures. Electrostatic forces are set up when the carbon nanotubes charge and discharge. The resonance frequency depends on applied voltages, and the coupling is strong enough to drive the mechanical motion into the nonlinear response regime. Differences in the responses of the devices in the two studies reflect in part the different quality factors of the resonators and different cryogenic temperatures. </jats:p>

<jats:title>Atomic Imaging Within Adsorbed Molecules</jats:title> <jats:p> Scanning tunneling microscopy provides atomic resolution images of surfaces and adsorbed atoms, but imaging atoms within an organic molecule adsorbed on a surface is difficult because contrast is lacking in the states that determine the tunneling current. Atomic force microscopy should be able to resolve atoms through changes in short-range chemical forces, but resolution is lost if the scanning tip undergoes modifications or if it moves the molecule. <jats:bold> Gross <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="1110" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176210">1110</jats:related-article> ) show that in situ functionalization of the tip—for example, with CO—can dramatically improve the resolution of images of pentacene molecules adsorbed on conducting surfaces, like copper, and nonconductors, like NaCl. </jats:p>