Catálogo de publicaciones - revistas

<jats:p>The Philae lander provides a unique opportunity to investigate the internal structure of a comet nucleus, providing information about its formation and evolution in the early solar system. We present Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) measurements of the interior of Comet 67P/Churyumov-Gerasimenko. From the propagation time and form of the signals, the upper part of the “head” of 67P is fairly homogeneous on a spatial scale of tens of meters. CONSERT also reduced the size of the uncertainty of Philae’s final landing site down to approximately 21 by 34 square meters. The average permittivity is about 1.27, suggesting that this region has a volumetric dust/ice ratio of 0.4 to 2.6 and a porosity of 75 to 85%. The dust component may be comparable to that of carbonaceous chondrites.</jats:p>

<jats:title>Growing crystals by attaching particles</jats:title> <jats:p> Crystals grow in a number a ways, including pathways involving the assembly of other particles and multi-ion complexes. De Yoreo <jats:italic>et al.</jats:italic> review the mounting evidence for these nonclassical pathways from new observational and computational techniques, and the thermodynamic basis for these growth mechanisms. Developing predictive models for these crystal growth and nucleation pathways will improve materials synthesis strategies. These approaches will also improve fundamental understanding of natural processes such as biomineralization and trace element cycling in aquatic ecosystems. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aaa6760">10.1126/science.aaa6760</jats:related-article> </jats:p>

<jats:p>The Philae lander, part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko, was delivered to the cometary surface in November 2014. Here we report the precise circumstances of the multiple landings of Philae, including the bouncing trajectory and rebound parameters, based on engineering data in conjunction with operational instrument data. These data also provide information on the mechanical properties (strength and layering) of the comet surface. The first touchdown site, Agilkia, appears to have a granular soft surface (with a compressive strength of 1 kilopascal) at least ~20 cm thick, possibly on top of a more rigid layer. The final landing site, Abydos, has a hard surface.</jats:p>

<jats:title>Tumor suppressor p53 linked to immune function</jats:title> <jats:p> We thought we knew all we needed to about the tumor suppressor p53. However, Yoon <jats:italic>et al.</jats:italic> now describe a previously unrecognized function of p53 (see the Perspective by Zitvogel and Kroemer). p53 induces expression of the gene encoding DD1α, a receptor-like transmembrane protein of the immunoglobulin superfamily. In conditions of stress, p53 activation can lead to cell death. p53-induced expression of DD1α also promotes the clearance of dead cells by promoting engulfment by macrophages. Furthermore, expression of DD1α on T cells inhibits T cell function. Thus, p53 offers protection from inflammatory disease caused by the accumulation of apoptotic cells, and its suppression of T cells might help cancer cells to escape immune detection. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.1261669">10.1126/science.1261669</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6247" page="476" related-article-type="in-this-issue" vol="349" xlink:href="10.1126/science.aac8475">476</jats:related-article> </jats:p>

<jats:p> The surface and subsurface of comets preserve material from the formation of the solar system. The properties of cometary material thus provide insight into the physical and chemical conditions during their formation. We present mass spectra taken by the Ptolemy instrument 20 minutes after the initial touchdown of the Philae lander on the surface of comet 67P/Churyumov-Gerasimenko. Regular mass distributions indicate the presence of a sequence of compounds with additional -CH <jats:sub>2</jats:sub> - and -O- groups (mass/charge ratios 14 and 16, respectively). Similarities with the detected coma species of comet Halley suggest the presence of a radiation-induced polymer at the surface. Ptolemy measurements also indicate an apparent absence of aromatic compounds such as benzene, a lack of sulfur-bearing species, and very low concentrations of nitrogenous material. </jats:p>

<jats:p>On 20 July 2015, the United States reopened its embassy in Havana, Cuba, after more than 50 years, creating a spirit of engagement between the two Cold War adversaries. This is a welcome addition to the 285 U.S. embassies and consulates in 190 other countries and should encourage Cuban and American scientists to practice “science diplomacy.” Sadly, however, U.S. diplomacy has rarely paid enough attention to science. Given that science and technology (S&amp;T) capabilities affect diplomatic agendas on a global scale, the powerful S&amp;T base of the United States must be better linked to its foreign policy goals.</jats:p>

<jats:p>A roundup of weekly science policy and related news.</jats:p>

<jats:p>Philae has fallen silent after fragmentary messages.</jats:p>

<jats:p>Technique could revolutionize tracking of individual cells.</jats:p>