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51.
Mullighan CG Miller CB Radtke I Phillips LA Dalton J Ma J White D Hughes TP Le Beau MM Pui CH Relling MV Shurtleff SA Downing JR 《Nature》2008,453(7191):110-114
52.
Domingues CM Church JA White NJ Gleckler PJ Wijffels SE Barker PM Dunn JR 《Nature》2008,453(7198):1090-1093
Changes in the climate system's energy budget are predominantly revealed in ocean temperatures and the associated thermal expansion contribution to sea-level rise. Climate models, however, do not reproduce the large decadal variability in globally averaged ocean heat content inferred from the sparse observational database, even when volcanic and other variable climate forcings are included. The sum of the observed contributions has also not adequately explained the overall multi-decadal rise. Here we report improved estimates of near-global ocean heat content and thermal expansion for the upper 300 m and 700 m of the ocean for 1950-2003, using statistical techniques that allow for sparse data coverage and applying recent corrections to reduce systematic biases in the most common ocean temperature observations. Our ocean warming and thermal expansion trends for 1961-2003 are about 50 per cent larger than earlier estimates but about 40 per cent smaller for 1993-2003, which is consistent with the recognition that previously estimated rates for the 1990s had a positive bias as a result of instrumental errors. On average, the decadal variability of the climate models with volcanic forcing now agrees approximately with the observations, but the modelled multi-decadal trends are smaller than observed. We add our observational estimate of upper-ocean thermal expansion to other contributions to sea-level rise and find that the sum of contributions from 1961 to 2003 is about 1.5 +/- 0.4 mm yr(-1), in good agreement with our updated estimate of near-global mean sea-level rise (using techniques established in earlier studies) of 1.6 +/- 0.2 mm yr(-1). 相似文献
53.
Bedding TR Mosser B Huber D Montalbán J Beck P Christensen-Dalsgaard J Elsworth YP García RA Miglio A Stello D White TR De Ridder J Hekker S Aerts C Barban C Belkacem K Broomhall AM Brown TM Buzasi DL Carrier F Chaplin WJ Di Mauro MP Dupret MA Frandsen S Gilliland RL Goupil MJ Jenkins JM Kallinger T Kawaler S Kjeldsen H Mathur S Noels A Aguirre VS Ventura P 《Nature》2011,471(7340):608-611
Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes. Progress is hampered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies. Here we report observations of gravity-mode period spacings in red giants that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained by the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly ~ 50 seconds) and those that are also burning helium (period spacing ~ 100 to 300 seconds). 相似文献
54.
Identification of the genes orchestrating neurogenesis would greatly enhance our understanding of this process. Genes have been identified that specify neuron type (for example cut and numb in Drosophila and mec-3 in Caenorhabditis elegans) and process guidance (for example, unc-5, unc-6 and unc-40 in C. elegans and the fas-1 gene of Drosophila). We sought genes defining synaptic specificity by identifying mutations that alter synaptic connectivity in the motor circuitry in the nematode C. elegans. We used electron microscopy of serial sections to reconstruct the ventral nerve-cords of uncoordinated (unc) mutants that have distinctive locomotory choreographies. Here we describe the phenotype of mutations in the unc-4 gene in which a locomotory defect is correlated with specific changes in synaptic input to a subset of the excitatory VA motor neurons, normally used in reverse locomotion. The circuitry alterations do not arise because of the inaccessibility of the appropriate synaptic partners, but are a consequence of changes in synaptic specificity. The VA motor neurons with altered synaptic inputs are all lineal sisters of VB motor neurons; the VA motor neurons without VB sisters have essentially the same synaptic inputs as in wild-type animals. The normal function of the wild-type allele of unc-4 may thus be to invoke the appropriate synaptic specificities to VA motor neurons produced in particular developmental contexts. 相似文献
55.
R T White D Damm J Miller K Spratt J Schilling S Hawgood B Benson B Cordell 《Nature》1985,317(6035):361-363
Pulmonary surfactant is a phospholipid-protein complex which serves to lower the surface tension at the air-liquid interface in the alveoli of the mammalian lung and is essential for normal respiration. Inadequate levels of surfactant at birth, a frequent situation in premature infants, results in respiratory failure. In all species examined, surfactant is composed primarily of dipalmitoylphosphatidylcholine and two major protein species of relative molecular mass (Mr) 32,000 (32K) and 10K (refs 2-5). Reconstitution in vitro of purified 32K pulmonary surfactant apoprotein (PSAP) with synthetic lipids forms a lipoprotein complex that lowers surface tension by spreading to create a thin interfacial film. Here we describe the cloning of the human PSAP gene and complementary DNA, and discuss features of the unusual encoded protein. 相似文献
56.
A closely linked genetic marker for cystic fibrosis 总被引:8,自引:0,他引:8
R White S Woodward M Leppert P O'Connell M Hoff J Herbst J M Lalouel M Dean G Vande Woude 《Nature》1985,318(6044):382-384
Cystic fibrosis is a recessive genetic disorder, characterized clinically by chronic obstructive lung disease, pancreatic insufficiency and elevated sweat electrolytes; affected individuals rarely live past their early twenties. Cystic fibrosis is also one of the most common genetic diseases in the northern European population. The frequency of carriers of mutant alleles in some populations is estimated to be as high as 1 in 20, carrying a concomitant burden of about one affected child in 1,500 births. Because little is known of the essential biochemical defect caused by the mutant gene, a genetic linkage approach based on arbitrary genetic markers and family studies is indicated to determine the chromosomal location of the cystic fibrosis (CF) gene. We have now obtained evidence for tight linkage between the CF locus and a DNA sequence polymorphism at the met oncogene locus. This evidence, combined with the physical localization data for the met locus presented in the accompanying paper, places the CF locus in the middle third of the long arm of chromosome 7, probably between bands q21 and q31. 相似文献
57.
The helical repeat of double-stranded DNA varies as a function of catenation and supercoiling 总被引:8,自引:0,他引:8
DNA in the cell is intertwined at several levels: one polynucleotide strand wraps helically around its complement and the double helix is in turn coiled in space. The higher-order intertwining most often takes the form of supercoiling of the helix axis, but can also be observed as the wrapping of one DNA duplex around another, as in catenation. We have investigated the relationship between intertwining at these three levels, the double helix, supercoiling, and catenation, using an approach that relies on comparative measurements of DNA linking numbers by gel electrophoresis. The method determines both the handedness of DNA catenanes and the change in helical repeat that accompanies catenation-induced supercoiling. For multiply-linked catenated rings of 3.5 kilobase pairs (kb), we conclude that the double helix unwinds by two-thirds of a turn for every right-handed supercoil involved in linking the two circles. Altering the geometry of the catenanes by linking rings of dissimilar size changes the effect of catenation on helical and superhelical parameters. Our experiments used intact DNA rings, but we note that linear DNA molecules, by virtue of their subdivision into closed loops or domains in vivo, can intertwine in the same ways. 相似文献
58.
Hedin P. A. Jenkins J. N. Collum D. H. White W. H. Parrott W. L. MacGown M. W. 《Cellular and molecular life sciences : CMLS》1983,39(7):799-801
Summary Cyanidin-3--glucoside was shown to be an important factor of resistance in cottonGossypium hirsutum L. leaves to the tobacco budwormHeliothis virescens (Fab.). This provides a potential basis for achieving insect resistance in non-glanded cotton and other crops infested byHeliothis.In cooperation with the Mississippi Agriculture and Forestry Experiment Station, Mississippi State. Mention of a trademark, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable. 相似文献
59.
Irs-2 coordinates Igf-1 receptor-mediated beta-cell development and peripheral insulin signalling. 总被引:14,自引:0,他引:14
Insulin receptor substrates (Irs proteins) mediate the pleiotropic effects of insulin and Igf-1 (insulin-like growth factor-1), including regulation of glucose homeostasis and cell growth and survival. We intercrossed mice heterozygous for two null alleles (Irs1+/- and Irs2+/-) and investigated growth and glucose metabolism in mice with viable genotypes. Our experiments revealed that Irs-1 and Irs-2 are critical for embryonic and post-natal growth, with Irs-1 having the predominant role. By contrast, both Irs-1 and Irs-2 function in peripheral carbohydrate metabolism, but Irs-2 has the major role in beta-cell development and compensation for peripheral insulin resistance. To establish a role for the Igf-1 receptor in beta-cells, we intercrossed mice heterozygous for null alleles of Igf1r and Irs2. Our results reveal that Igf-1 receptors promote beta-cell development and survival through the Irs-2 signalling pathway. Thus, Irs-2 integrates the effects of insulin in peripheral target tissues with Igf-1 in pancreatic beta-cells to maintain glucose homeostasis. 相似文献
60.
Vestrand WT Wren JA Wozniak PR Aptekar R Golentskii S Pal'shin V Sakamoto T White RR Evans S Casperson D Fenimore E 《Nature》2006,442(7099):172-175
The taxonomy of optical emission detected during the critical first few minutes after the onset of a gamma-ray burst (GRB) defines two broad classes: prompt optical emission correlated with prompt gamma-ray emission, and early optical afterglow emission uncorrelated with the gamma-ray emission. The standard theoretical interpretation attributes prompt emission to internal shocks in the ultra-relativistic outflow generated by the internal engine; early afterglow emission is attributed to shocks generated by interaction with the surrounding medium. Here we report on observations of a bright GRB that, for the first time, clearly show the temporal relationship and relative strength of the two optical components. The observations indicate that early afterglow emission can be understood as reverberation of the energy input measured by prompt emission. Measurements of the early afterglow reverberations therefore probe the structure of the environment around the burst, whereas the subsequent response to late-time impulsive energy releases reveals how earlier flaring episodes have altered the jet and environment parameters. Many GRBs are generated by the death of massive stars that were born and died before the Universe was ten per cent of its current age, so GRB afterglow reverberations provide clues about the environments around some of the first stars. 相似文献