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排序方式: 共有300条查询结果,搜索用时 296 毫秒
91.
Pryor WR Rymer AM Mitchell DG Hill TW Young DT Saur J Jones GH Jacobsen S Cowley SW Mauk BH Coates AJ Gustin J Grodent D Gérard JC Lamy L Nichols JD Krimigis SM Esposito LW Dougherty MK Jouchoux AJ Stewart AI McClintock WE Holsclaw GM Ajello JM Colwell JE Hendrix AR Crary FJ Clarke JT Zhou X 《Nature》2011,472(7343):331-333
Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity. 相似文献
92.
Skarnes WC Rosen B West AP Koutsourakis M Bushell W Iyer V Mujica AO Thomas M Harrow J Cox T Jackson D Severin J Biggs P Fu J Nefedov M de Jong PJ Stewart AF Bradley A 《Nature》2011,474(7351):337-342
Gene targeting in embryonic stem cells has become the principal technology for manipulation of the mouse genome, offering unrivalled accuracy in allele design and access to conditional mutagenesis. To bring these advantages to the wider research community, large-scale mouse knockout programmes are producing a permanent resource of targeted mutations in all protein-coding genes. Here we report the establishment of a high-throughput gene-targeting pipeline for the generation of reporter-tagged, conditional alleles. Computational allele design, 96-well modular vector construction and high-efficiency gene-targeting strategies have been combined to mutate genes on an unprecedented scale. So far, more than 12,000 vectors and 9,000 conditional targeted alleles have been produced in highly germline-competent C57BL/6N embryonic stem cells. High-throughput genome engineering highlighted by this study is broadly applicable to rat and human stem cells and provides a foundation for future genome-wide efforts aimed at deciphering the function of all genes encoded by the mammalian genome. 相似文献
93.
Crystal structure of 15-mer DNA duplex containing unpaired bases 总被引:4,自引:0,他引:4
Errors during DNA replication or repair can lead to the presence of unpaired or inserted bases in the double helix, as well as to mismatched base pairs. So far only structures of the latter type have been characterized by X-ray crystallography. We report here a 3-A crystal structure of DNA 15-mer d(CGCGAAATTTACGCG), which forms a duplex with two unpaired adenine residues looped outside the B-type helix. This arrangement is in disagreement with the nuclear magnetic resonance spectroscopy results for the same 15-mer in solution, indicating polymorphic nature of the structure adopted by this sequence. 相似文献
94.
95.
Instability of the Trypanosoma brucei rhodesiense metacyclic variable antigen repertoire 总被引:1,自引:0,他引:1
Trypanosoma brucei rhodesiense undergoes antigenic variation in its mammalian host by changing the glycoprotein composing its surface coat. Trypanosome clones which have the same repertoire of variable antigen types (VATs) are said to belong to the same serodeme. Tsetse flies infected with a particular serodeme extrude infective metacyclic trypanosomes which express only a restricted part of this repertoire. As the only known acquired immunity in African trypanosomiasis is VAT-specific this limitation of metacyclic VAT (M-VAT) repertoire could be important in devising a vaccine. This possibility of immunoprophylaxis could depend, however, on whether or not the M-VAT repertoire is conserved over long periods of repeated cyclical transmission and between epidemics. Studies reported here on isolates made from an East African focus of sleeping sickness over a 20-yr period suggest substantial changes in the M-VATs expressed during this time. Furthermore, we have detected change in expression of 3 M-VATs during sequential tsetse transmission of a clone in the laboratory indicating a possible instability in the organization of M-VAT genes. 相似文献
96.
97.
Vasorelaxant properties of the endothelium-derived relaxing factor more closely resemble S-nitrosocysteine than nitric oxide 总被引:75,自引:0,他引:75
Studies of cultured bovine aortic endothelial cells using quantitative chemiluminescence techniques have shown that the amount of nitric oxide released under basal conditions, or in response to either bradykinin or the calcium ionophore A23187 is insufficient to account for the vasorelaxant activities of the endothelium-derived relaxing factor (EDRF) derived from the same source. This observation contradicts previous suggestions that nitric oxide and EDRF are the same compound, but may be explained if EDRF is a compound that contains nitric oxide within its structure but is a much more potent vasodilator than nitric oxide. Such a molecule could be one of several nitrosothiols which may yield nitric oxide after a one-electron reduction. The present experiments were carried out to test the possibility that the biological activities of the endothelium-derived relaxing factor might more closely resemble those of one of these compounds, S-nitrosocysteine, than nitric oxide. Nitric oxide release from cultured bovine aortic endothelial cells was detected by chemiluminescence and bioassay experiments compared the vasodilator potencies of nitric oxide, S-nitrosocysteine, and EDRF. The results suggest that EDRF is much more likely to be a nitrosylated compound such as a nitrosothiol than authentic nitric oxide. 相似文献
98.
Cumulative Sum techniques are widely used in quality control and model monitoring. A single-sided cusum may be regarded essentially as a sequence of sequential tests which, in many cases, such as those for the Exponential Family, is equivalent to a Sequence of Sequential Probability Ratio Tests. The relationship between cusums and Bayesian decisions is difficult to establish using conventional methods. An alternative approach is proposed which not only reveals a relation but also offers a very simple formulation of the decision process involved in model monitoring. This is first illustrated for a Normal mean and then extended to other important practical cases including Dynamic Models. For V-mask cusum graphs a particular feature is the interpretation of the distance of the V vertex from the latest plotted point in terms of the prior precision as measured in ‘equivalent’ observations. 相似文献
99.
A genome-wide association study of nonsynonymous SNPs identifies a type 1 diabetes locus in the interferon-induced helicase (IFIH1) region 总被引:1,自引:0,他引:1
Smyth DJ Cooper JD Bailey R Field S Burren O Smink LJ Guja C Ionescu-Tirgoviste C Widmer B Dunger DB Savage DA Walker NM Clayton DG Todd JA 《Nature genetics》2006,38(6):617-619
In this study we report convincing statistical support for a sixth type 1 diabetes (T1D) locus in the innate immunity viral RNA receptor gene region IFIH1 (also known as mda-5 or Helicard) on chromosome 2q24.3. We found the association in an interim analysis of a genome-wide nonsynonymous SNP (nsSNP) scan, and we validated it in a case-control collection and replicated it in an independent family collection. In 4,253 cases, 5,842 controls and 2,134 parent-child trio genotypes, the risk ratio for the minor allele of the nsSNP rs1990760 A --> G (A946T) was 0.86 (95% confidence interval = 0.82-0.90) at P = 1.42 x 10(-10). 相似文献
100.