Catálogo de publicaciones - revistas

<jats:title>Taking carbon out of the ammonial recipe</jats:title> <jats:p> The reaction used to make ammonia for synthetic fertilizer requires hydrogen. Nowadays, that hydrogen is stripped from methane, creating CO <jats:sub>2</jats:sub> as a by-product. Licht <jats:italic>et al.</jats:italic> demonstrate a relatively efficient electrochemical process in which water and nitrogen react directly to form ammonia. The approach removes the need for an independent hydrogen generation step. The process takes place in molten hydroxide salt and requires a nanostructured iron oxide–derived catalyst. Although the catalyst suspension is currently only stable for a few hours, the protocol points to a way to produce ammonia from purely renewable resources. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="637" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1254234">637</jats:related-article> </jats:p>

<jats:title>Working out how to pack benzene in silico</jats:title> <jats:p> Many organic compounds crystallize in several different energetically similar packing arrangements, or polymorphs. This complicates processes such as drug formulation that rely on reproducible crystallization. Yang <jats:italic>et al.</jats:italic> have now achieved the long-standing goal of calculating a crystal packing arrangement from first principles to an accuracy that can distinguish polymorphs (see the Perspective by Price). They used benzene as a prototypical test case and applied quantum chemical methods that improve estimates of multibody interactions. The results bode well for future applications of theory to optimization of crystallization protocols. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="640" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1254419">640</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="619" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1257250">619</jats:related-article> </jats:p>

<jats:title>Folding robots and metamaterials</jats:title> <jats:p> The same principles used to make origami art can make self-assembling robots and tunable metamaterials—artificial materials engineered to have properties that may not be found in nature (see the Perspective by You). Felton <jats:italic>et al.</jats:italic> made complex self-folding robots from flat templates. Such robots could potentially be sent through a collapsed building or tunnels and then assemble themselves autonomously into their final functional form. Silverberg <jats:italic>et al.</jats:italic> created a mechanical metamaterial that was folded into a tessellated pattern of unit cells. These cells reversibly switched between soft and stiff states, causing large, controllable changes to the way the material responded to being squashed. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="644" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1252610">644</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="647" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1252876">647</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="623" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1257841">623</jats:related-article> </jats:p>

<jats:title>Folding robots and metamaterials</jats:title> <jats:p> The same principles used to make origami art can make self-assembling robots and tunable metamaterials—artificial materials engineered to have properties that may not be found in nature (see the Perspective by You). Felton <jats:italic>et al.</jats:italic> made complex self-folding robots from flat templates. Such robots could potentially be sent through a collapsed building or tunnels and then assemble themselves autonomously into their final functional form. Silverberg <jats:italic>et al.</jats:italic> created a mechanical metamaterial that was folded into a tessellated pattern of unit cells. These cells reversibly switched between soft and stiff states, causing large, controllable changes to the way the material responded to being squashed. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="644" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1252610">644</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="647" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1252876">647</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="623" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1257841">623</jats:related-article> </jats:p>

<jats:title>Relocating a heavy-metal factory</jats:title> <jats:p> We can learn about the solar system's past by measuring heavy radioactive isotopes in meteorites—the extraterrestrial equivalent of carbon dating on Earth. Elements heavier than iron are mainly synthesized in supernovae or asymptotic giant branch (AGB) stars. Knowing exactly which element is produced where, is key to dating the solar system. Lugaro <jats:italic>et al.</jats:italic> found that AGB stars generated more of a nuclide called <jats:sup>182</jats:sup> Hf than previously thought (see the Perspective by Bizzarro). Its abundance indicates that it was produced about 30 million years before the Sun's formation. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="650" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1253338">650</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="620" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1257083">620</jats:related-article> </jats:p>

<jats:title>Seeing magnetism on an atomic level</jats:title> <jats:p> Electrons tunneling from the magnetized tip of a scanning tunneling microscope into the surface of a material can reveal the material's magnetic structure. Although researchers have used the technique on simple nanostructures, they've had trouble preparing the tip in just the right way to visualize the magnetic order in more exotic materials. Enayat <jats:italic>et al.</jats:italic> used a tip with a magnetic cluster on its apex to reveal patterns of magnetic ordering in the material Fe <jats:sub>1+y</jats:sub> Te, which becomes superconducting by substituting Te with Se atoms. The researchers prepared the tip by simply picking up atoms from the surface of the material. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6197" page="653" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1251682">653</jats:related-article> </jats:p>