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排序方式: 共有125条查询结果,搜索用时 15 毫秒
31.
Fynbo JP Watson D Thöne CC Sollerman J Bloom JS Davis TM Hjorth J Jakobsson P Jørgensen UG Graham JF Fruchter AS Bersier D Kewley L Cassan A Cerón JM Foley S Gorosabel J Hinse TC Horne KD Jensen BL Klose S Kocevski D Marquette JB Perley D Ramirez-Ruiz E Stritzinger MD Vreeswijk PM Wijers RA Woller KG Xu D Zub M 《Nature》2006,444(7122):1047-1049
It is now accepted that long-duration gamma-ray bursts (GRBs) are produced during the collapse of a massive star. The standard 'collapsar' model predicts that a broad-lined and luminous type Ic core-collapse supernova accompanies every long-duration GRB. This association has been confirmed in observations of several nearby GRBs. Here we report that GRB 060505 (ref. 10) and GRB 060614 (ref. 11) were not accompanied by supernova emission down to limits hundreds of times fainter than the archetypal supernova SN 1998bw that accompanied GRB 980425, and fainter than any type Ic supernova ever observed. Multi-band observations of the early afterglows, as well as spectroscopy of the host galaxies, exclude the possibility of significant dust obscuration and show that the bursts originated in actively star-forming regions. The absence of a supernova to such deep limits is qualitatively different from all previous nearby long-duration GRBs and suggests a new phenomenological type of massive stellar death. 相似文献
32.
Systematic distortions in world fisheries catch trends. 总被引:22,自引:0,他引:22
Over 75% of the world marine fisheries catch (over 80 million tonnes per year) is sold on international markets, in contrast to other food commodities (such as rice). At present, only one institution, the Food and Agriculture Organization of the United Nations (FAO) maintains global fisheries statistics. As an intergovernmental organization, however, FAO must generally rely on the statistics provided by member countries, even if it is doubtful that these correspond to reality. Here we show that misreporting by countries with large fisheries, combined with the large and widely fluctuating catch of species such as the Peruvian anchoveta, can cause globally spurious trends. Such trends influence unwise investment decisions by firms in the fishing sector and by banks, and prevent the effective management of international fisheries. 相似文献
33.
34.
Mayer K Schüller C Wambutt R Murphy G Volckaert G Pohl T Düsterhöft A Stiekema W Entian KD Terryn N Harris B Ansorge W Brandt P Grivell L Rieger M Weichselgartner M de Simone V Obermaier B Mache R Müller M Kreis M Delseny M Puigdomenech P Watson M Schmidtheini T Reichert B Portatelle D Perez-Alonso M Boutry M Bancroft I Vos P Hoheisel J Zimmermann W Wedler H Ridley P Langham SA McCullagh B Bilham L Robben J Van der Schueren J Grymonprez B Chuang YJ Vandenbussche F Braeken M Weltjens I Voet M 《Nature》1999,402(6763):769-777
The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins. 相似文献
35.
A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization 总被引:63,自引:0,他引:63
Boyd PW Watson AJ Law CS Abraham ER Trull T Murdoch R Bakker DC Bowie AR Buesseler KO Chang H Charette M Croot P Downing K Frew R Gall M Hadfield M Hall J Harvey M Jameson G LaRoche J Liddicoat M Ling R Maldonado MT McKay RM Nodder S Pickmere S Pridmore R Rintoul S Safi K Sutton P Strzepek R Tanneberger K Turner S Waite A Zeldis J 《Nature》2000,407(6805):695-702
Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the 'iron hypothesis'. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction. 相似文献
36.
Noel Edwards Catriona M. H. Anderson Nichola J. Conlon Andrew K. Watson Rebecca J. Hall Timothy R. Cheek T. Martin Embley David T. Thwaites 《Cellular and molecular life sciences : CMLS》2018,75(5):921-938
Amino acid transporters are essential components of prokaryote and eukaryote cells, possess distinct physiological functions, and differ markedly in substrate specificity. Amino acid transporters can be both drug targets and drug transporters (bioavailability, targeting) with many monogenic disorders resulting from dysfunctional membrane transport. The largest collection of amino acid transporters (including the mammalian SLC6, SLC7, SLC32, SLC36, and SLC38 families), across all kingdoms of life, is within the Amino acid-Polyamine-organoCation (APC) superfamily. The LeuT-fold is a paradigm structure for APC superfamily amino acid transporters and carriers of sugars, neurotransmitters, electrolytes, osmolytes, vitamins, micronutrients, signalling molecules, and organic and fatty acids. Each transporter is specific for a unique sub-set of solutes, specificity being determined by how well a substrate fits into each binding pocket. However, the molecular basis of substrate selectivity remains, by and large, elusive. Using an integrated computational and experimental approach, we demonstrate that a single position within the LeuT-fold can play a crucial role in determining substrate specificity in mammalian and arthropod amino acid transporters within the APC superfamily. Systematic mutation of the amino acid residue occupying the equivalent position to LeuT V104 titrates binding pocket space resulting in dramatic changes in substrate selectivity in exemplar APC amino acid transporters including PAT2 (SLC36A2) and SNAT5 (SLC38A5). Our work demonstrates how a single residue/site within an archetypal structural motif can alter substrate affinity and selectivity within this important superfamily of diverse membrane transporters. 相似文献
37.
Fox DB Frail DA Price PA Kulkarni SR Berger E Piran T Soderberg AM Cenko SB Cameron PB Gal-Yam A Kasliwal MM Moon DS Harrison FA Nakar E Schmidt BP Penprase B Chevalier RA Kumar P Roth K Watson D Lee BL Shectman S Phillips MM Roth M McCarthy PJ Rauch M Cowie L Peterson BA Rich J Kawai N Aoki K Kosugi G Totani T Park HS MacFadyen A Hurley KC 《Nature》2005,437(7060):845-850
The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs) centres on the origin of the short-hard class of bursts, which are suspected on theoretical grounds to result from the coalescence of neutron-star or black-hole binary systems. Numerous searches for the afterglows of short-hard bursts have been made, galvanized by the revolution in our understanding of long-duration GRBs that followed the discovery in 1997 of their broadband (X-ray, optical and radio) afterglow emission. Here we present the discovery of the X-ray afterglow of a short-hard burst, GRB 050709, whose accurate position allows us to associate it unambiguously with a star-forming galaxy at redshift z = 0.160, and whose optical lightcurve definitively excludes a supernova association. Together with results from three other recent short-hard bursts, this suggests that short-hard bursts release much less energy than the long-duration GRBs. Models requiring young stellar populations, such as magnetars and collapsars, are ruled out, while coalescing degenerate binaries remain the most promising progenitor candidates. 相似文献
38.
What's in a virus name? 总被引:3,自引:0,他引:3
39.
E. L. Watson I. A. Siegel M. R. Robinovitch 《Cellular and molecular life sciences : CMLS》1974,30(8):876-877
Zusammenfassung Membranen sekretorischer Granula wurden von der Ohrspeicheldrüse (Parotis) der Ratte isoliert und auf Kalzium-ATPase-Aktivität (Ca2+-ATPase) untersucht und postuliert, dass die gefundene Ca2+-ATPase eine Rolle in der Aufnahme und Abgabe von Kalzium in sekretorischen Granula spielt. 相似文献
40.
Frequent somatic mutations in PTEN and TP53 are mutually exclusive in the stroma of breast carcinomas 总被引:19,自引:0,他引:19
We have recently shown that loss of heterozygosity of specific markers, including those at 10q23, 17p13-p15 and 16q24, can occur in the stromal and epithelial compartments of primary invasive breast carcinomas. Here, we demonstrate high frequencies of somatic mutations in TP53 (encoding tumor protein p53) and PTEN (encoding phosphate and tensin homolog) in breast neoplastic epithelium and stroma. Mutations in TP53 and PTEN are mutually exclusive in either compartment. In contrast, mutations in WFDC1 (16q24, encoding WAP four-disulfide core domain 1) occur with low frequency in the stroma. 相似文献