排序方式: 共有63条查询结果,搜索用时 15 毫秒
31.
Sicardy B Bellucci A Gendron E Lacombe F Lacour S Lecacheux J Lellouch E Renner S Pau S Roques F Widemann T Colas F Vachier F Martins RV Ageorges N Hainaut O Marco O Beisker W Hummel E Feinstein C Levato H Maury A Frappa E Gaillard B Lavayssière M Di Sora M Mallia F Masi G Behrend R Carrier F Mousis O Rousselot P Alvarez-Candal A Lazzaro D Veiga C Andrei AH Assafin M da Silva Neto DN Jacques C Pimentel E Weaver D Lecampion JF Doncel F Momiyama T Tancredi G 《Nature》2006,439(7072):52-54
Pluto and its satellite, Charon (discovered in 1978; ref. 1), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities. Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius, which was later refined to 601.5 km (ref. 4). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, R(C) = 603.6 +/- 1.4 km (1sigma), and a density of rho = 1.71 +/- 0.08 g cm(-3). This occultation also provides upper limits of 110 and 15 (3sigma) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere. 相似文献
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Mira MT Alcaïs A Van Thuc N Thai VH Huong NT Ba NN Verner A Hudson TJ Abel L Schurr E 《Nature genetics》2003,33(3):412-415
Leprosy, a chronic infectious disease caused by Mycobacterium leprae, affects an estimated 700,000 persons each year. Clinically, leprosy can be categorized as paucibacillary or multibacillary disease. These clinical forms develop in persons that are intrinsically susceptible to leprosy per se, that is, leprosy independent of its specific clinical manifestation. We report here on a genome-wide search for loci controlling susceptibility to leprosy per se in a panel of 86 families including 205 siblings affected with leprosy from Southern Vietnam. Using model-free linkage analysis, we found significant evidence for a susceptibility gene on chromosome region 6q25 (maximum likelihood binomial (MLB) lod score 4.31; P = 5 x 10(-6)). We confirmed this by family-based association analysis in an independent panel of 208 Vietnamese leprosy simplex families. Of seven microsatellite markers underlying the linkage peak, alleles of two markers (D6S1035 and D6S305) showed strong evidence for association with leprosy (P = 6.7 x 10(-4) and P = 5.9 x 10(-5), respectively). 相似文献
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A conserved RNA-binding protein controls germline stem cells in Caenorhabditis elegans 总被引:9,自引:0,他引:9
Crittenden SL Bernstein DS Bachorik JL Thompson BE Gallegos M Petcherski AG Moulder G Barstead R Wickens M Kimble J 《Nature》2002,417(6889):660-663
Germline stem cells are defined by their unique ability to generate more of themselves as well as differentiated gametes. The molecular mechanisms controlling the decision between self-renewal and differentiation are central unsolved problems in developmental biology with potentially broad medical implications. In Caenorhabditis elegans, germline stem cells are controlled by the somatic distal tip cell. FBF-1 and FBF-2, two nearly identical proteins, which together are called FBF ('fem-3 mRNA binding factor'), were originally discovered as regulators of germline sex determination. Here we report that FBF also controls germline stem cells: in an fbf-1 fbf-2 double mutant, germline proliferation is initially normal, but stem cells are not maintained. We suggest that FBF controls germline stem cells, at least in part, by repressing gld-1, which itself promotes commitment to the meiotic cell cycle. FBF belongs to the PUF family ('Pumilio and FBF') of RNA-binding proteins. Pumilio controls germline stem cells in Drosophila females, and, in lower eukaryotes, PUF proteins promote continued mitoses. We suggest that regulation by PUF proteins may be an ancient and widespread mechanism for control of stem cells. 相似文献
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量子色动力学(QCD)自创立至今只有约30年的历史,QCD在解释基本粒子的高能实验以及强子的结构与静态性质方面取得了惊人的成就,已被公认作为基本粒子强相互作用的基本理论。有关QCD理论的教科书和专著已不少。但都内容庞杂、篇幅巨大,有些过多侧重于微扰QCD的介绍。作者撰写本书的目的:一个是为力求简明,另一个就是强调QCD的非微扰方面。非微扰QCD问题至今仍是粒子物理理论家甚感棘手的难题,也是量子规范场理论研究领域中最活跃的前沿课题之一。 相似文献
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Mira MT Alcaïs A Nguyen VT Moraes MO Di Flumeri C Vu HT Mai CP Nguyen TH Nguyen NB Pham XK Sarno EN Alter A Montpetit A Moraes ME Moraes JR Doré C Gallant CJ Lepage P Verner A Van De Vosse E Hudson TJ Abel L Schurr E 《Nature》2004,427(6975):636-640
Leprosy is caused by Mycobacterium leprae and affects about 700,000 individuals each year. It has long been thought that leprosy has a strong genetic component, and recently we mapped a leprosy susceptibility locus to chromosome 6 region q25-q26 (ref. 3). Here we investigate this region further by using a systematic association scan of the chromosomal interval most likely to harbour this leprosy susceptibility locus. In 197 Vietnamese families we found a significant association between leprosy and 17 markers located in a block of approx. 80 kilobases overlapping the 5' regulatory region shared by the Parkinson's disease gene PARK2 and the co-regulated gene PACRG. Possession of as few as two of the 17 risk alleles was highly predictive of leprosy. This was confirmed in a sample of 975 unrelated leprosy cases and controls from Brazil in whom the same alleles were strongly associated with leprosy. Variants in the regulatory region shared by PARK2 and PACRG therefore act as common risk factors for leprosy. 相似文献
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Solid-state cavity quantum electrodynamics (QED) systems offer a robust and scalable platform for quantum optics experiments and the development of quantum information processing devices. In particular, systems based on photonic crystal nanocavities and semiconductor quantum dots have seen rapid progress. Recent experiments have allowed the observation of weak and strong coupling regimes of interaction between the photonic crystal cavity and a single quantum dot in photoluminescence. In the weak coupling regime, the quantum dot radiative lifetime is modified; in the strong coupling regime, the coupled quantum dot also modifies the cavity spectrum. Several proposals for scalable quantum information networks and quantum computation rely on direct probing of the cavity-quantum dot coupling, by means of resonant light scattering from strongly or weakly coupled quantum dots. Such experiments have recently been performed in atomic systems and superconducting circuit QED systems, but not in solid-state quantum dot-cavity QED systems. Here we present experimental evidence that this interaction can be probed in solid-state systems, and show that, as expected from theory, the quantum dot strongly modifies the cavity transmission and reflection spectra. We show that when the quantum dot is coupled to the cavity, photons that are resonant with its transition are prohibited from entering the cavity. We observe this effect as the quantum dot is tuned through the cavity and the coupling strength between them changes. At high intensity of the probe beam, we observe rapid saturation of the transmission dip. These measurements provide both a method for probing the cavity-quantum dot system and a step towards the realization of quantum devices based on coherent light scattering and large optical nonlinearities from quantum dots in photonic crystal cavities. 相似文献
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Variant of transcription factor 7-like 2 (TCF7L2) gene confers risk of type 2 diabetes 总被引:1,自引:0,他引:1
Grant SF Thorleifsson G Reynisdottir I Benediktsson R Manolescu A Sainz J Helgason A Stefansson H Emilsson V Helgadottir A Styrkarsdottir U Magnusson KP Walters GB Palsdottir E Jonsdottir T Gudmundsdottir T Gylfason A Saemundsdottir J Wilensky RL Reilly MP Rader DJ Bagger Y Christiansen C Gudnason V Sigurdsson G Thorsteinsdottir U Gulcher JR Kong A Stefansson K 《Nature genetics》2006,38(3):320-323
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Sulem P Gudbjartsson DF Stacey SN Helgason A Rafnar T Magnusson KP Manolescu A Karason A Palsson A Thorleifsson G Jakobsdottir M Steinberg S Pálsson S Jonasson F Sigurgeirsson B Thorisdottir K Ragnarsson R Benediktsdottir KR Aben KK Kiemeney LA Olafsson JH Gulcher J Kong A Thorsteinsdottir U Stefansson K 《Nature genetics》2007,39(12):1443-1452
Hair, skin and eye colors are highly heritable and visible traits in humans. We carried out a genome-wide association scan for variants associated with hair and eye pigmentation, skin sensitivity to sun and freckling among 2,986 Icelanders. We then tested the most closely associated SNPs from six regions--four not previously implicated in the normal variation of human pigmentation--and replicated their association in a second sample of 2,718 Icelanders and a sample of 1,214 Dutch. The SNPs from all six regions met the criteria for genome-wide significance. A variant in SLC24A4 is associated with eye and hair color, a variant near KITLG is associated with hair color, two coding variants in TYR are associated with eye color and freckles, and a variant on 6p25.3 is associated with freckles. The fifth region provided refinements to a previously reported association in OCA2, and the sixth encompasses previously described variants in MC1R. 相似文献