Catálogo de publicaciones - revistas

<jats:title>Optical Angular Selection</jats:title> <jats:p> A monochromatic electromagnetic plane wave is typically characterized by three properties: its frequency, its polarization, and its propagation direction. While the selection of light signals based on the first two properties has been studied in depth, selection based on direction is relatively unexplored but equally important. <jats:bold> Shen <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6178" page="1499" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249799">1499</jats:related-article> ) demonstrate a simple approach that provides narrow-angle selectivity over a broad range of wavelengths using heterostructured photonic crystals that act as a mirror for all but a narrow range of viewing angles where the crystals are transparent. Such angular selection should find a number of applications in, for example, high efficiency solar energy conversion, privacy protection systems, or high signal-to-noise detectors. </jats:p>

<jats:title>Hydrologic Thermostat</jats:title> <jats:p> When the silicate-rich rocks and minerals in Earth's interior are uplifted and exposed to Earth's surface, they dissolve. On a geologic time scale, this chemical weathering process ultimately creates a sink for CO <jats:sub>2</jats:sub> , thereby influencing global temperatures. <jats:bold>Maher and Chamberlain</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6178" page="1502" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1250770">1502</jats:related-article> , published online 13 March) developed a theoretical framework for understanding the fundamental relationship between weathering, tectonics, and the geological carbon cycle. The analysis suggests that temperature plays less of a role in regulating chemical weathering—which is dependent on the balance of tectonic uplift and erosion—than runoff on continents and the time that silicate minerals are exposed to fluids. Plateaus in weathering fluxes with increasing runoff or temperature allows for the stabilization of atmospheric CO <jats:sub>2</jats:sub> despite high rates of uplift or erosion. </jats:p>

<jats:title>From Drips to Tubes</jats:title> <jats:p> In the evolutionary transition from aquatic to terrestrial habitats, plants acquired internal systems to transport water and provide structural support. <jats:bold> Xu <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6178" page="1505" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248417">1505</jats:related-article> , published online 20 March) studied a family of genes and the cells they control to better understand the innovations required to adapt to dry land. In <jats:italic>Arabidopsis</jats:italic> , specific transcription factors regulate development of xylem—the plant tissue that transports water. The moss <jats:italic>Physcomitrella patens</jats:italic> has similar genes, which regulate development of hydroids and stereids, cells specialized in water transport and structural support. The similarity in the genes and their functions suggests the evolutionary origins of land-plant vascular systems. </jats:p>

<jats:title>Move and Countermove</jats:title> <jats:p> Receptors on plant cell surfaces are tuned to recognize molecular patterns associated with pathogenic bacteria. <jats:bold> Macho <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6178" page="1509" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248849">1509</jats:related-article> ; published online 13 March) found that activation of one of these receptors in <jats:italic>Arabidopsis</jats:italic> results in phosphorylation of a specific tyrosine residue, which in turn triggers the plant's immune response to the phytopathogen <jats:italic>Pseudomonas syringae. P. syringae</jats:italic> counters by secreting a specifically targeted phosphatase, thus stalling the plant's immune response. </jats:p>

<jats:title>Keeping Germ Cells Special</jats:title> <jats:p> Germ cells separate from the somatic lineage during early metazoan development. <jats:bold> Eun <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6178" page="1513" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246514">1513</jats:related-article> ) found that <jats:italic>Drosophila</jats:italic> germ cells lose their identity and turn on somatic cell–specific marker expression in adult testes when a Polycomb group component E(z) is inactivated in somatic cells. However, only early-stage germ cells, including germline stem cells, retain this plasticity. Thus, one role for somatic cells in male gonads is to antagonize somatic identity in germ cells. </jats:p>

<jats:title>Circadian Rhythms</jats:title> <jats:p> Circadian rhythms in the fruit fly <jats:italic>Drosophila</jats:italic> are driven by neurons in the brain. <jats:bold>Yao and Shafer</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6178" page="1516" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1251285">1516</jats:related-article> ) analyzed different sets of neurons that can drive circadian rhythms. Manipulating the period of each set of neurons separately revealed that when the various clock signals were fairly consistent, the fly showed a robust circadian rhythm. But when the various clock signals were seriously out of sync with one another, the fly was oblivious to the day-night cycle. </jats:p>

<jats:title>Monitoring Migration</jats:title> <jats:p> Migrant “stock” data—the number of people living in a country other than the one in which they were born—are frequently used to understand contemporary trends in international migration, but the data are severely limited. <jats:bold>Abel and Sander</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6178" page="1520" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248676">1520</jats:related-article> ) present a set of global bilateral migration flows estimated from sequential stock data in 5-year intervals. The percentage of the world population moving over 5-year periods has not shown dramatic changes between 1995 and 2010. People from individual African countries tended to move within the continent, whereas people from Europe tended to move to very diverse locations. </jats:p>

<jats:p> On this week's show: a look back at the race for the <jats:italic>BRCA1</jats:italic> gene, 20 years later and a roundup from our daily news site. </jats:p>

<jats:p>The ultimate aim of most scientific research is the creation of therapies that will cure or extend the life of patients. In recent years, though, the flow of new drugs in the development pipeline seems to have slowed, despite increased R&amp;D budgets and the concerted efforts of researchers. The reasons for this are hotly debated, including the suggestion that the "easy" targets have already been found, or that increasing regulatory demands are stifling progress. Another possibility is that, as a result of the proliferation of technologies intended to enable drug discovery, the basic biological questions are being overlooked or ignored. Technological development in high throughput target identification, screening, library synthesis, and validation have their place, but they are essentially just tools, and a clear understanding of the underlying biology is paramount. This webinar will take a critical look at what role technology plays in helping researchers understand molecular pathways and characterize signaling cascades, to better predict the efficacy, and potential toxicity, of new drugs.</jats:p>

<jats:p>A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.</jats:p>