Catálogo de publicaciones - revistas

<jats:title>Entanglement On Cue</jats:title> <jats:p> Quantum entanglement between particles lies at the core of quantum mechanics. For practical applications such as long-distance quantum communications, cryptography, and quantum networks, entanglement must be heralded. That is, a signal flags the existence of the entangled state so that it can be manipulated and transferred. <jats:bold> Hofmann <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="72" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1221856">72</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6090" page="40" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224202"> <jats:bold>Volz and Rauschenbeutel</jats:bold> </jats:related-article> ) excited trapped single atoms in different laboratory rooms 20 meters apart and were able to show that manipulation, interference, and detection of the photons from the excited atoms could signal when the atoms are entangled. The extent of the observed entanglement may be sufficient to start to probe fundamental questions relating to the entanglement process and thus address the foundations of quantum mechanics. </jats:p>

<jats:title>Mr. Cool</jats:title> <jats:p> Laser cooling of atoms relies on the presence of electronic transitions of specific structure, making it practical for a limited number of atomic species at relatively low densities. Alternative methods include those involving optical cavities, where atom-cavity interaction enables cooling without the need for resonant transitions. <jats:bold> Wolke <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="75" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1219166">75</jats:related-article> ) present such a cooling scheme that was used to heat and then cool a Bose-Einstein condensate of Rb atoms. The method should be applicable to hotter samples where a sequence of laser pulses of different frequencies would need to be used. </jats:p>

<jats:title>Indirect Injection</jats:title> <jats:p> Aerosols in the stratosphere, especially submicron-hydrated sulfuric acid droplets, are an important factor influencing climate variability. Stratospheric sulfate aerosols can form from sulfur dioxide that has been transported from the underlying troposphere. Large volcanic eruptions can inject sulfur dioxide and other material into the stratosphere, but smaller volcanoes have been thought not to be energetic enough to do so. <jats:bold> Bourassa <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="78" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1219371">78</jats:related-article> ) used satellite data to show that sulfur dioxide from the 2011 eruption of the Nabro stratovolcano in Eritrea was lofted into the stratosphere by deep convection associated with the Asian summer monsoon. </jats:p>

<jats:title>A Long Collapse</jats:title> <jats:p> Coral reefs are threatened by global warming and ocean acidification, and so it is important to understand better how and why environmental changes have affected them in the past. <jats:bold> Toth <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="81" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1221168">81</jats:related-article> ) present a 6000-year-long record of coral reefs off the coast of Panama, Central America. The reefs effectively stopped growing for approximately 2600 years, beginning around 4000 years ago. This collapse of the coral reef system was probably caused by increased variability of ENSO, the El Nino–Southern Oscillation. If the strength or frequency of ENSO were to increase, the viability of these and other reef systems in the Pacific could be put further at risk. </jats:p>

<jats:title>Twin Tales of Two Toxins</jats:title> <jats:p> The luminescent bacterium, <jats:italic>Photorhabdus luminescens</jats:italic> , is carried in the gut of an insect-parasitic nematode as a stealth weapon. By using an allele swapping technique, <jats:bold> Somvanshi <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="88" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1216641">88</jats:related-article> ) investigated the promoter-switching mechanism that flips the bacterium from the almost dormant M forms, which stick to the adult nematode's posterior gut, into the motile, luminous P forms, which are armed with the toxic virulence factors needed to overcome the insect prey of the nematode. Similar switches may operate in bacteria that flip between harmless commensals and lethal pathogens. The bio-control agent <jats:italic>Bacillus thuringiensis</jats:italic> also kills insects by means of a crystal toxin, which allows the bacteria to penetrate the host gut and access nutrients. Release of nutrients also allows bacterial cheats that do not make toxin, to grow and outcompete the toxin-producing colonizers. In field experiments, <jats:bold> Raymond <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="85" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1218196">85</jats:related-article> ) found that, consequently, the bacterial population becomes less virulent. Because these type of virulence factors are secreted from the cell and are widespread in pathogens, such social interactions may affect the fitness and constrain the virulence of many toxin-producing bacteria. </jats:p>

<jats:title>Twin Tales of Two Toxins</jats:title> <jats:p> The luminescent bacterium, <jats:italic>Photorhabdus luminescens</jats:italic> , is carried in the gut of an insect-parasitic nematode as a stealth weapon. By using an allele swapping technique, <jats:bold> Somvanshi <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="88" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1216641">88</jats:related-article> ) investigated the promoter-switching mechanism that flips the bacterium from the almost dormant M forms, which stick to the adult nematode's posterior gut, into the motile, luminous P forms, which are armed with the toxic virulence factors needed to overcome the insect prey of the nematode. Similar switches may operate in bacteria that flip between harmless commensals and lethal pathogens. The bio-control agent <jats:italic>Bacillus thuringiensis</jats:italic> also kills insects by means of a crystal toxin, which allows the bacteria to penetrate the host gut and access nutrients. Release of nutrients also allows bacterial cheats that do not make toxin, to grow and outcompete the toxin-producing colonizers. In field experiments, <jats:bold> Raymond <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="85" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1218196">85</jats:related-article> ) found that, consequently, the bacterial population becomes less virulent. Because these type of virulence factors are secreted from the cell and are widespread in pathogens, such social interactions may affect the fitness and constrain the virulence of many toxin-producing bacteria. </jats:p>

<jats:title>Letting Pyruvate In</jats:title> <jats:p> Transport of pyruvate is an important event in metabolism whereby the pyruvate formed in glycolysis is transported into mitochondria to feed into the tricarboxylic acid cycle (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6090" page="41" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1225601"> <jats:bold>Murphy and Divakaruni</jats:bold> </jats:related-article> ). Two groups have now identified proteins that are components of the mitochondrial pyruvate transporter. <jats:bold> Bricker <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="96" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1218099">96</jats:related-article> , published online 24 May) found that the proteins mitochondrial pyruvate carrier 1 and 2 (MPC1 and MPC2) are required for full pyruvate transport in yeast and <jats:italic>Drosophila</jats:italic> cells and that humans with mutations in MPC1 have metabolic defects consistent with loss of the transporter. <jats:bold> Herzig <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="93" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1218530">93</jats:related-article> , published online 24 May) identified the same proteins as components of the carrier in yeast. Furthermore, expression of the mouse proteins in bacteria conferred increased transport of pyruvate into bacterial cells. </jats:p>

<jats:title>Letting Pyruvate In</jats:title> <jats:p> Transport of pyruvate is an important event in metabolism whereby the pyruvate formed in glycolysis is transported into mitochondria to feed into the tricarboxylic acid cycle (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6090" page="41" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1225601"> <jats:bold>Murphy and Divakaruni</jats:bold> </jats:related-article> ). Two groups have now identified proteins that are components of the mitochondrial pyruvate transporter. <jats:bold> Bricker <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="96" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1218099">96</jats:related-article> , published online 24 May) found that the proteins mitochondrial pyruvate carrier 1 and 2 (MPC1 and MPC2) are required for full pyruvate transport in yeast and <jats:italic>Drosophila</jats:italic> cells and that humans with mutations in MPC1 have metabolic defects consistent with loss of the transporter. <jats:bold> Herzig <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="93" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1218530">93</jats:related-article> , published online 24 May) identified the same proteins as components of the carrier in yeast. Furthermore, expression of the mouse proteins in bacteria conferred increased transport of pyruvate into bacterial cells. </jats:p>

<jats:title>A Deep Look Into Our Genes</jats:title> <jats:p> Recent debates have focused on the degree of genetic variation and its impact upon health at the genomic level in humans (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6090" page="39" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224528"> <jats:bold>Casals and Bertranpetit</jats:bold> </jats:related-article> ). <jats:bold> Tennessen <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="64" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1219240">64</jats:related-article> , published online 17 May), looking at all of the protein-coding genes in the human genome, and <jats:bold> Nelson <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="100" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1217876">100</jats:related-article> , published online 17 May), looking at genes that encode drug targets, address this question through deep sequencing efforts on samples from multiple individuals. The findings suggest that most human variation is rare, not shared between populations, and that rare variants are likely to play a role in human health. </jats:p>

<jats:title>Cancer Gene Islands</jats:title> <jats:p> Human tumors are riddled with genomic alterations that rearrange, remove, amplify, or otherwise disrupt a wide spectrum of genes, and a key challenge is identifying which of these alterations are causally involved in tumorigenesis. The role of recurrent hemizygous focal deletions is especially puzzling because these deletions preferentially affect certain chromosomal regions and result in the loss of one copy of a whole cluster of adjacent genes. <jats:bold> Solimini <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="104" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1219580">104</jats:related-article> , published online 24 May; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6090" page="47" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224806">Greenman</jats:related-article> </jats:bold> ) found that these deletions span genomic regions that are enriched in genes that negatively regulate cell proliferation. The cumulative reduction in dosage and tumor suppressive function of the genes within these “cancer gene islands” may represent a critical factor driving tumor growth. </jats:p>