Catálogo de publicaciones - revistas

<jats:title>Probed But Not Perturbed</jats:title> <jats:p> The processing and manipulation of quantum information holds great promise in terms of outperforming classical computers and secure communication. However, quantum information is delicate, and even reading the information is a destructive and probabilistic process requiring a number of measurements to home in on the information stored as a quantum state. For the nitrogen vacancy in diamond, <jats:bold> Neumann <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="542" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1189075">542</jats:related-article> , published online 1 July) show that these limitations can be eliminated. A measurement protocol was designed and implemented where the spin state of the nuclear spin of the vacancy could be mapped onto and read out from the surrounding electronic spins in a single-shot measurement nondestructively. </jats:p>

<jats:title>Straining Graphene's Electronic States</jats:title> <jats:p> The conduction electrons in graphene, single sheets of graphite, can have very high mobilities. Under the influence of an applied magnetic field, a series of energy steps, or Landau levels, can be observed that correspond to the conduction electrons traveling in cyclotron orbits. Recent theoretical work has indicated that if graphene layers are strained, the strain field creates a pseudomagnetic field that should also lead to observable Landau levels. <jats:bold> Levy <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="544" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1191700">544</jats:related-article> ) used scanning tunneling microscopy to probe the energy levels of graphene grown on a platinum surface, which forms highly strained “nanobubbles.” The strain is equivalent to applying very high magnetic fields (in excess of 300 tesla). Thus, the electronic properties of graphene can indeed be modified using applied strain. </jats:p>

<jats:title>From Superfluid to Mott Insulator</jats:title> <jats:p> One of the most attractive characteristics of cold atomic gases in optical lattices is their ability to simulate condensed-matter systems. The results of these quantum simulations are usually averaged over the atomic ensemble, or course-grained over several lattice sites. Now, <jats:bold> Bakr <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="547" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192368">547</jats:related-article> , published online 17 June; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5991" page="523" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1193401">DeMarco</jats:related-article> </jats:bold> ) provide a single lattice site view onto the transition of a Bose gas of Rb-87 from the superfluid to the Mott-insulating state. Characteristic concentric shells of uniform number density were observed deep in the Mott insulator regime, and probing the local quantum dynamics revealed unexpectedly short time scales. The low-defect Mott structures identified may provide a starting point for quantum magnetism experiments. </jats:p>

<jats:title>Manufacturing Nanomaterials</jats:title> <jats:p> The exploration of many materials at the nanoscale has revealed properties that only emerge when working at these small dimensions. For device manufacture, materials need to be deposited or assembled in specific patterns. <jats:bold> Schliehe <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="550" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1188035">550</jats:related-article> ; see the cover) show the oriented attachment of lead sulfide nanocrystals into two-dimensional sheets. The packing is driven by the choice of solvents that influence the interactions between the nanocrystals. The nanocrystals have excellent photoconductive properties and were incorporated into a photodetector without any additional chemical processing. </jats:p>

<jats:title>Tilting Toward Reaction</jats:title> <jats:p> Collisions between molecules and metal surfaces underlie many of the catalytic pathways that transform natural feedstocks into fuels and commodity chemical compounds. One such reaction, in which nickel strips hydrogen from methane, depends on whether the methyl C-H bonds are vibrating just before the molecule strikes the surface. <jats:bold> Yoder <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="553" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1191751">553</jats:related-article> ) now delve deeper into this system. By aligning incoming molecular samples using polarized infrared light, they show that the hydrocarbon reacts most readily when it is vibrating parallel, rather than perpendicular, to the surface. </jats:p>

<jats:title>Sinking in Slowly</jats:title> <jats:p> As the Arctic warms and its sea ice continues to melt, more of the ocean surface will be exposed, creating the potential for greater uptake of carbon dioxide from the atmosphere. <jats:bold> Cai <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="556" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1189338">556</jats:related-article> , published online 22 July) present results from a series of Arctic Ocean transects that show that the amount of CO <jats:sub>2</jats:sub> in the surface waters has increased greatly recently. This will act as a barrier to future CO <jats:sub>2</jats:sub> uptake and suggests that the Arctic Ocean will not become the large CO <jats:sub>2</jats:sub> sink that some have predicted. </jats:p>

<jats:title>Toward Alkane Synthesis</jats:title> <jats:p> Alkanes are major components of fossil fuels, and synthesis of alkanes remains a challenge in the conversion of renewable raw materials to fuels. Even though diverse organisms synthesize alkanes, synthesis pathways have remained elusive. Now <jats:bold> Schirmer <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="559" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1187936">559</jats:related-article> ) describe an alkane biosynthesis pathway in cyanobacteria that converts intermediates of fatty acid metabolism to alkanes and alkenes. Heterologous expression of the biosynthetic genes resulted in production of alkanes in <jats:italic>Escherichia coli</jats:italic> . This pathway is likely to be a valuable tool in the production of biofuels. </jats:p>

<jats:title>Epithelial Cleft Formation</jats:title> <jats:p> The internal architecture of many embryonic organs is established by repetitive branching of epithelia. Epithelial clefts and outgrowths generate this internal branching of glands and other organs. <jats:bold> Onodera <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="562" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1191880">562</jats:related-article> ) identify a gene, <jats:italic>Btbd7</jats:italic> , as a regulator of epithelial dynamics and cleft formation, linking the extracellular matrix with morphogenesis. <jats:italic>Btbd7</jats:italic> is induced by a matrix protein at sites of cleft progression and induces a transcription factor and suppresses cell adhesion. The resulting local cell separation and motility contribute to transient tissue gaps that contribute to clefts that help form branched organs. </jats:p>

<jats:title>Building the Heart</jats:title> <jats:p> The multichambered heart of birds and mammals develops through addition of second heart field (SHF)–derived precursor cells to a primary heart tube. <jats:bold> Stolfi <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="565" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1190181">565</jats:related-article> ) show that, in the simple chordate <jats:italic>Ciona intestinalis</jats:italic> , the heart and atrial siphon muscle (ASM) precursors arise from common progenitors following asymmetric cell divisions and that the transcription factor COE (Collier/Olf1/EBF) is involved in this fate choice. The ASM precursors express molecular markers of the vertebrate pharyngeal mesoderm that gives rise to the SHF and lower jaw muscles, suggesting that the origins of both can be traced back to the last common ancestor of tunicates and vertebrates. </jats:p>

<jats:title>Another Cell Culprit in Prostate Cancer</jats:title> <jats:p> A recent controversial hypothesis about the cellular origins of human cancer, the so-called “cancer stem cell hypothesis,” has fueled interest in identifying the specific cell types that give rise to common epithelial cancers. A single, well-defined cell of origin could, in principle, lead to more effective targeted therapies. Based on histological evidence and/or studies of mouse tumors, luminal cells are believed to be the cell of origin in prostate cancer. Now, using functional assays of cells derived from benign human prostate tissue, <jats:bold> Goldstein <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="568" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1189992">568</jats:related-article> ) find that a different cell type, basal cells, can give rise in mice to prostate tumors that closely resemble human prostate tumors. Thus, the cellular origin of prostate cancer may be more complex than anticipated. </jats:p>