Catálogo de publicaciones - revistas

<jats:title>Weighing the neutron against the proton</jats:title> <jats:p> Elementary science textbooks often state that protons have the same mass as neutrons. This is not far from the truth—the neutron is about 0.14% heavier (and less stable) than the proton. The precise value is important, because if the mass difference were bigger or smaller, the world as we know it would likely not exist. Borsanyi <jats:italic>et al.</jats:italic> calculated the mass difference to high precision using a sophisticated approach that took into account the various forces that exist within a nucleon. The calculations reveal how finely tuned our universe needs to be. </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="6229" page="1452" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.1257050">1452</jats:related-article> </jats:p>

<jats:title>Atoms behaving in an orderly manner</jats:title> <jats:p> In physics, interactions between components of a system can cause it to become more orderly in an attempt to minimize energy. Such ordered phases appear, for example, in magnetic systems. Schauss <jats:italic>et al</jats:italic> . simulated these phenomena using a collection of neutral atoms at low temperatures. By shining laser light on the atoms, the authors brought some of them into a high energy state called the Rydberg state. By carefully varying the experimental parameters, they coaxed these Rydberg atoms into patterns reminiscent of crystal lattices in rod- and disk-shaped atomic samples. </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="6229" page="1455" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.1258351">1455</jats:related-article> </jats:p>

<jats:title>A place where stars are more predictable</jats:title> <jats:p> Astrophysicists use reference objects of known brightness to determine distances. For example, type Ia supernova (SN Ia) always reach nearly the same peak brightness. This is because they explode when the progenitor white dwarf exceeds its supportable mass threshold. Kelly <jats:italic>et al.</jats:italic> find that a particular subset of SN Ia—those in environments with high ultraviolet surface brightness and star-formation density—can calibrate distances even more tightly. It seems that only one or two intrinsic parameters may drive the apparent relationship between luminosity, color, and fading with time. </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="6229" page="1459" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.1261475">1459</jats:related-article> </jats:p>

<jats:title>Uncloaking the influence of the invisible actor</jats:title> <jats:p> The idea of dark matter enjoys popular support, but two major concerns persist: the so-called Standard Model excludes it, and it cannot be directly detected by any telescope. For now, astronomers can only observe dark matter's influence indirectly, such as when watching unseen creatures perturb the surface of a pond. Harvey <jats:italic>et al.</jats:italic> observed 72 galaxy collisions to compare the resulting centers of mass for the gas and stars (from direct observations) and for the dark matter (by inference). Based on these offsets, dark matter is clearly present. </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="6229" page="1462" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.1261381">1462</jats:related-article> </jats:p>

<jats:title>Build the builders before the brain</jats:title> <jats:p> Humans are much smarter than mice—key to this is the relative thickness of the human brain's neocortex. Florio <jats:italic>et al.</jats:italic> combed through genes expressed in the progenitor cells that build the neocortex and zeroed in on one gene found in humans but not in mice. The gene, which seems to differentiate humans from chimpanzees, drives proliferation of the key progenitor cells. Mice expressing this human gene during development built more elaborate brains. </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="6229" page="1465" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.aaa1975">1465</jats:related-article> </jats:p>

<jats:title>Trypanosomes reveal tricky tricks in vivo</jats:title> <jats:p> The sleeping sickness parasite, <jats:italic>Trypanosoma brucei</jats:italic> , is covered with variant surface glyco proteins (VSGs) recognized by the host's immune system. The parasite uses a repertoire of 2000 VSG genes to switch between different surface variants, continually evading the host's defensive responses. Classic experiments showed that one variant succeeded another, causing waves of infection; however, infection in animals shows different behavior. Mugnier <jats:italic>et al.</jats:italic> discovered that several VSGs are expressed simultaneously and that the repertoire for variation is amplified even more by recombination between the genes to make mosaic VSGs. </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="6229" page="1470" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.aaa4502">1470</jats:related-article> </jats:p>

<jats:title>Building a biogeochemical battery</jats:title> <jats:p> Iron acts as both a source and sink of electrons for microorganisms in the environment. Some anaerobic bacteria use oxidized Fe(III) as an electron acceptor, whereas phototrophic bacteria can use reduced Fe(II) as an electron donor. Byrne <jats:italic>et al.</jats:italic> show that the iron-bearing mineral magnetite, which contains both Fe(II) and Fe(III), can serve as both an electron acceptor and donor. Cocultures of iron-reducing and iron-oxidizing bacteria exposed to simulated day/night cycles or changes in organic matter altered the ratio of Fe(II) to Fe(III) in magnetite particles. </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="6229" page="1473" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.aaa4834">1473</jats:related-article> </jats:p>

<jats:title>Exciting nerve cells deep inside the brain</jats:title> <jats:p> Current techniques to stimulate regions inside the brain need a permanently implanted wire or an optical fiber. Working in mice, Chen <jats:italic>et al.</jats:italic> developed a method to overcome this problem (see the Perspective by Temel and Jahanshahi). They introduced heat-sensitive capsaicin receptors into nerve cells and then injected magnetic nanoparticles into specific brain regions. The nanoparticles could be heated by external alternating magnetic fields, which activated the ion channel–expressing neurons. Thus, cellular signaling deep inside the brain can be controlled remotely without permanent implants. </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="6229" page="1477" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.1261821">1477</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6229" page="1418" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.aaa9610">1418</jats:related-article> </jats:p>

<jats:title>Abuse from generation to generation?</jats:title> <jats:p> Parents who were abused as children are thought more likely to abuse their own children. Widom <jats:italic>et al.</jats:italic> compared reports from parents, from children, and from child protective service agency records gathered on the same families and on matched controls. They observed different findings depending on which information they used. Increases in sexual abuse and neglect relative to controls were reported by children of abuse victims. However, much of the believed transmission of abuse and neglect between generations could be ascribed to surveillance or detection bias targeted at parents with childhood histories of abuse or neglect. </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="6229" page="1480" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.1259917">1480</jats:related-article> </jats:p>

<jats:title>An explosive way to fuse membranes</jats:title> <jats:p> The molecular machine that promotes membrane fusion during intracellular transport involves a number of so-called SNARE proteins. Ryu <jats:italic>et al.</jats:italic> describe the molecular mechanism by which two proteins —NSF and α-SNAP—disassemble SNARE complexes. A combination of single-molecule techniques resolved intermediate steps of the reaction. Surprisingly, unlike previously assumed, NSF did not unwind SNARE complexes processively. Instead, built-up tension was released in a single burst to “tear” the SNARE complex apart in a one-step global unfolding reaction. </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="6229" page="1485" related-article-type="in-this-issue" vol="347" xlink:href="10.1126/science.aaa5267">1485</jats:related-article> </jats:p>