Catálogo de publicaciones - revistas

<jats:p>Counts of impact craters provide age for a region on Mars close to the landing site of rover Curiosity.</jats:p>

<jats:title>Go with the Flow</jats:title> <jats:p> Effective absorption or filtration can be achieved by having a material with multiple levels of porosity, so that the main flow can occur in the larger channels, while smaller passageways can be used to sequester a secondary material. It can be difficult to make these materials because the pores need to be different sizes, but still fully connected to each other. <jats:bold> Zhang <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="1684" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1221111">1684</jats:related-article> ) show that a hierarchical zeolite can be made through a simple process using a single structure-directing agent that causes repetitive branching. This leads to a material with improved transport and catalytic properties. </jats:p>

<jats:title>Spinning Backwards</jats:title> <jats:p> When atoms and molecules collide, the energy embedded in the reaction products gets distributed among translations, vibrations, and rotations. Decades of meticulous experiments have mapped out the quantum mechanical rules underlying this distribution process, particularly in simple systems comprising just three light atoms. Now, <jats:bold> Jankunas <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="1687" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1221329">1687</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6089" page="1650" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1223680"> <jats:bold> Yang <jats:italic>et al.</jats:italic> </jats:bold> </jats:related-article> ) describe a previously unappreciated wrinkle in the elementary reaction of an H atom with deuterium. Typically, products with low vibrational and rotational excitation tend to scatter backwards from the collision, whereas the spinning products scatter sideways. Above a certain vibrational threshold, however, spinning HD products were observed to scatter backwards. </jats:p>

<jats:title>The Sedimentary Life of Earthquakes</jats:title> <jats:p> Estimating the hazards associated with possible large earthquakes depends largely on evidence of prior seismic activity. The relatively new global seismic networks installed to monitor earthquakes, however, have only captured the very recent history of fault zones that can remain active for thousands of years. To understand the recurrence of large earthquakes along the Alpine Fault in New Zealand, <jats:bold> Berryman <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="1690" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218959">1690</jats:related-article> ) looked to the sediments near an old creek for evidence of surface ruptures and vertical offset. Along this fault segment, 24 large earthquakes seem to have occurred over the last 6000 years, resulting in a recurrence interval of ∼329 years. The activity is more regular than other similar strike-slip faults, such as the San Andreas Fault in California. </jats:p>

<jats:title>Early Burrowers</jats:title> <jats:p> Direct fossil evidence of animals from Ediacaran period—the time in Earth's history just before extensive animal diversification in the Cambrian—is scant. However, the remains of animal activity in sediment, which remain intact through geologic time can provide clues about animal behavior and evolution. <jats:bold> Pecoits <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="1693" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1216295">1693</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="6089" page="1646" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1223848">Droser and Gehling</jats:related-article> </jats:bold> ) found a suite of fossil animal burrows in sedimentary rocks in Uruguay. Radiometric dating places the age of the structures at ∼585 million years old, coinciding with the likely emergence of stem-group bilaterians. The complex morphologies of the fossil burrows suggest that these animals actively grazed and had the ability to burrow deep within sediments. </jats:p>

<jats:title>Pots and Crocks</jats:title> <jats:p> The invention of pottery allowed for more secure storage of food than was provided by baskets or hide pouches, and the vessels could also be used in cooking. The earliest pottery has been thought to have appeared in China and Japan ∼18,000 years ago, several thousands of years before the advent of agriculture. <jats:bold> Wu <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="1696" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218643">1696</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="6089" page="1644" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1224119">Shelach</jats:related-article> </jats:bold> ) have now dated broken pieces of pottery from a cave in China, the earliest of which date to ∼20,000 years ago, the time of the Last Glacial Maximum. Scorch marks on many pieces imply that the pottery was used in cooking. </jats:p>

<jats:title>Seeing in the Dark</jats:title> <jats:p> Elephantnose fish are known to use electrosensing to navigate their murky freshwater environment. However, unlike some other animals from dark environments, they have retained their eyes and some dependence on vision. While most vertebrate vision optimizes either photon catch (for increased light capture) or visual acuity, <jats:bold> Kreysing <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="1700" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218072">1700</jats:related-article> ) show that the unique structures of the grouped retinae found in the eyes of this species matches rod and cone sensitivity, which allows for the simultaneous use of both types of photoreceptors over a large range of dim light intensities. </jats:p>

<jats:title>Alkaloid Synthetic Pathway</jats:title> <jats:p> Noscapine, a nonaddictive alkaloid found in the opium poppy, can be used as a cough suppressant and a tubulin-binding antitumor agent. <jats:bold> Winzer <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="1704" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1220757">1704</jats:related-article> , published online 31 May; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6089" page="1648" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1225473">DellaPenna and O'Connor</jats:related-article> </jats:bold> ) found that a cluster of 10 genes were key to the production of noscapine. Poppies homozygous for this gene cluster produced high levels of noscapine, heterozygous poppies produced low levels of noscapine, and those poppies lacking the gene cluster produced no noscapine. Silencing individual genes in turn and analyzing the accumulation of intermediate metabolites allowed the biosynthetic pathway of noscapine to be elucidated. </jats:p>

<jats:title>Plant Hormone Modulators</jats:title> <jats:p> The activity and stability of several plant hormones is modulated by conjugation with various amino acids and their derivatives. <jats:bold> Westfall <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="1708" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1221863">1708</jats:related-article> , published online 24 May) solved the crystal structures for two acyl acid amido synthetases from <jats:italic>Arabidopsis</jats:italic> . The findings suggest how the enzymes might discriminate between apolar and acidic amino acids and lend insight into the reaction chemistries that add functional diversity to hormone signaling pathways. </jats:p>

<jats:title>Pretty or Sweet</jats:title> <jats:p> The grocery-store tomato that looks beautiful but tastes like tart cardboard arises from selection processes favoring phenotypes that make commercial production more reliable. Significant in that selection process was a mutation that reduced the mottled color variations of unripe green tomatoes, leaving them a uniform, pale, green. <jats:bold> Powell <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="1711" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1222218">1711</jats:related-article> ) analyzed the molecular biology of the mutation. The <jats:italic>uniform ripening</jats:italic> mutation turns out to disable a transcription factor called <jats:italic>Golden 2-like</jats:italic> ( <jats:italic>GLK2</jats:italic> ). <jats:italic>GLK2</jats:italic> expression increases the fruit's photosynthetic capacity, resulting in higher sugar content. </jats:p>