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Interlocked stresses in cartilage 总被引:2,自引:0,他引:2
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Walter F Decarli R Carilli C Bertoldi F Cox P Da Cunha E Daddi E Dickinson M Downes D Elbaz D Ellis R Hodge J Neri R Riechers DA Weiss A Bell E Dannerbauer H Krips M Krumholz M Lentati L Maiolino R Menten K Rix HW Robertson B Spinrad H Stark DP Stern D 《Nature》2012,486(7402):233-236
The Hubble Deep Field provides one of the deepest multiwavelength views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time. An early map of the Hubble Deep Field at a wavelength of 850?micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF?850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass. Here we report a redshift of z = 5.183 for HDF?850.1, from a millimetre-wave molecular line scan. This places HDF?850.1 in a galaxy overdensity at z?≈?5.2, corresponding to a cosmic age of only 1.1?billion years after the Big Bang. This redshift is significantly higher than earlier estimates and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3?×?10(11) solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive. 相似文献
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A potential animal model for Lesch-Nyhan syndrome through introduction of HPRT mutations into mice 总被引:17,自引:0,他引:17
The human Lesch-Nyhan syndrome is a rare neurological and behavioural disorder, affecting only males, which is caused by an inherited deficiency in the level of activity of the purine salvage enzyme hypoxanthine-guanosine phosphoribosyl transferase (HPRT). How the resulting alterations in purine metabolism lead to the severe symptoms characteristic of Lesch-Nyhan patients is still not understood. No mutations at the Hprt locus leading to loss of activity have been described in laboratory animals. To derive an animal model for the Lesch-Nyhan syndrome, we have used cultured mouse embryonic stem cells, mutagenized by retroviral insertion and selected for loss of HPRT activity, to construct chimaeric mice. Two clonal lines carrying different mutant Hprt alleles have given rise to germ cells in chimaeras, allowing the derivation of strains of mutant mice having the same biochemical defect as Lesch-Nyhan patients. Male mice carrying the mutant alleles are viable and analysis of their cells shows a total lack of HPRT activity. 相似文献
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The taxonomic group Prochlorales (Lewin 1977) Burger-Wiersma, Stal and Mur 1989 was established to accommodate a set of prokaryotic oxygenic phototrophs which, like plant, green algal and euglenoid chloroplasts, contain chlorophyll b instead of phycobiliproteins. Prochlorophytes were originally proposed (with concomitant scepticism) to be a monophyletic group sharing a common ancestry with these 'green' chloroplasts. Results from molecular sequence phylogenies, however, have suggested that Prochlorothrix hollandica is not on a lineage that leads to plastids. Our results from 16S ribosomal RNA sequence comparisons, which include new sequences from the marine picoplankter Prochlorococcus marinus and the Lissoclinum patella symbiont Prochloron sp., indicate that prochlorophytes are polyphyletic within the cyanobacterial radiation, and suggest that none of the known species is specifically related to chloroplasts. This implies that the three prochlorophytes and the green chloroplast ancestor acquired chlorophyll b and its associated structural proteins in convergent evolutionary events. We report further that the 16S rRNA gene sequence from Prochlorococcus is very similar to those of open ocean Synechococcus strains (marine cluster A), and to a family of 16S rRNA genes shotgun-cloned from plankton in the north Atlantic and Pacific Oceans. 相似文献