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Two Earth-sized planets orbiting Kepler-20 总被引:1,自引:0,他引:1
Fressin F Torres G Rowe JF Charbonneau D Rogers LA Ballard S Batalha NM Borucki WJ Bryson ST Buchhave LA Ciardi DR Désert JM Dressing CD Fabrycky DC Ford EB Gautier TN Henze CE Holman MJ Howard A Howell SB Jenkins JM Koch DG Latham DW Lissauer JJ Marcy GW Quinn SN Ragozzine D Sasselov DD Seager S Barclay T Mullally F Seader SE Still M Twicken JD Thompson SE Uddin K 《Nature》2012,482(7384):195-198
Since the discovery of the first extrasolar giant planets around Sun-like stars, evolving observational capabilities have brought us closer to the detection of true Earth analogues. The size of an exoplanet can be determined when it periodically passes in front of (transits) its parent star, causing a decrease in starlight proportional to its radius. The smallest exoplanet hitherto discovered has a radius 1.42 times that of the Earth's radius (R(⊕)), and hence has 2.9 times its volume. Here we report the discovery of two planets, one Earth-sized (1.03R(⊕)) and the other smaller than the Earth (0.87R(⊕)), orbiting the star Kepler-20, which is already known to host three other, larger, transiting planets. The gravitational pull of the new planets on the parent star is too small to measure with current instrumentation. We apply a statistical method to show that the likelihood of the planetary interpretation of the transit signals is more than three orders of magnitude larger than that of the alternative hypothesis that the signals result from an eclipsing binary star. Theoretical considerations imply that these planets are rocky, with a composition of iron and silicate. The outer planet could have developed a thick water vapour atmosphere. 相似文献
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Agrawal A Lingappa J Leppla SH Agrawal S Jabbar A Quinn C Pulendran B 《Nature》2003,424(6946):329-334
Anthrax poses a clear and present danger as an agent of biological terrorism. Infection with Bacillus anthracis, the causative agent of anthrax, if untreated can result in rampant bacteraemia, multisystem dysfunction and death. Anthrax lethal toxin (LT) is a critical virulence factor of B. anthracis, which occurs as a complex of protective antigen and lethal factor. Here we demonstrate that LT severely impairs the function of dendritic cells--which are pivotal to the establishment of immunity against pathogens--and host immune responses by disrupting the mitogen-activated protein (MAP) kinase intracellular signalling network. Dendritic cells exposed to LT and then stimulated with lipopolysaccharide do not upregulate co-stimulatory molecules, secrete greatly diminished amounts of proinflammatory cytokines, and do not effectively stimulate antigen-specific T cells in vivo. Furthermore, injections of LT induce a profound impairment of antigen-specific T- and B-cell immunity. These data suggest a role for LT in suppressing host immunity during B. anthracis infections, and represent an immune evasion strategy, where a microbe targets MAP kinases in dendritic cells to disarm the immune response. 相似文献
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Christina Prell Klaus Hubacek Claire Quinn Mark Reed 《Systemic Practice and Action Research》2008,21(6):443-458
Environmental applications of social network analysis (SNA) are just beginning to emerge, and so far have focussed on understanding
the characteristics of social networks that increase the likelihood of collective action and successful natural resource management.
We move beyond this discussion to demonstrate how knowledge gained from analysing the social networks of stakeholders can
be harnessed for selecting stakeholders, and further, how these analyses can be influenced by the expressed wishes and concerns
of stakeholders. Although we began our SNA using concepts derived from the resource-management literature, stakeholder involvement
in the interpretation of the results led to the use of SNA techniques that had not previously been applied in the context
of resource management. We thus re-analysed our data and modified our selection of research participants. Re-analysis led
to the selection of research participants who (1) had unique positions in the network, thus occupying non-redundant communication
roles in the network, (2) came from different stakeholder categories and (3) were relatively well-connected to others and
tended to broker across different segments of the network. By combining insights from researchers and stakeholders in this
way, it was possible to use SNA in an innovative and sensitive way to better meet the needs of the stakeholders and the research
project.
相似文献
Christina PrellEmail: |
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Villeda SA Luo J Mosher KI Zou B Britschgi M Bieri G Stan TM Fainberg N Ding Z Eggel A Lucin KM Czirr E Park JS Couillard-Després S Aigner L Li G Peskind ER Kaye JA Quinn JF Galasko DR Xie XS Rando TA Wyss-Coray T 《Nature》2011,477(7362):90-94
In the central nervous system, ageing results in a precipitous decline in adult neural stem/progenitor cells and neurogenesis, with concomitant impairments in cognitive functions. Interestingly, such impairments can be ameliorated through systemic perturbations such as exercise. Here, using heterochronic parabiosis we show that blood-borne factors present in the systemic milieu can inhibit or promote adult neurogenesis in an age-dependent fashion in mice. Accordingly, exposing a young mouse to an old systemic environment or to plasma from old mice decreased synaptic plasticity, and impaired contextual fear conditioning and spatial learning and memory. We identify chemokines--including CCL11 (also known as eotaxin)--the plasma levels of which correlate with reduced neurogenesis in heterochronic parabionts and aged mice, and the levels of which are increased in the plasma and cerebrospinal fluid of healthy ageing humans. Lastly, increasing peripheral CCL11 chemokine levels in vivo in young mice decreased adult neurogenesis and impaired learning and memory. Together our data indicate that the decline in neurogenesis and cognitive impairments observed during ageing can be in part attributed to changes in blood-borne factors. 相似文献
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R. P. Gregson J. F. Marwood R. J. Quinn 《Cellular and molecular life sciences : CMLS》1981,37(9):930-931
Summary 5-Hydroxytryptamine (5-HT) and hypoxanthine were isolated chromatographically from the holothurianPentacter crassa. This study was initiated as a result of the observed hypotensive activity of aP. crassa extract. This activity was also encountered in extracts of the holothuriansThelenota ananus andStichopus chloronatus and can be attributed to 5-HT. 相似文献
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