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When two or more (groups of) researchers independently investigating the same domain arrive at the same result, a multiple discovery occurs. The pervasiveness of multiple discoveries in science suggests the intuition that they are in some sense inevitable—that one should view them as results that force themselves upon us, so to speak. We argue that, despite the intuitive force of such an “inevitabilist insight,” one should reject it. More specifically, we distinguish two facets of the insight and argue that: (a) the profusion of multiple discoveries in scientific practice does not support the inevitabilist side of the inevitability/contingency of science controversy; and (b) the crucial role of background knowledge in scientific inquiry complicates the attempt to interpret the pervasiveness of multiple discoveries in realist terms. 相似文献
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Caffau E Bonifacio P François P Sbordone L Monaco L Spite M Spite F Ludwig HG Cayrel R Zaggia S Hammer F Randich S Molaro P Hill V 《Nature》2011,477(7362):67-69
The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as 'metallicity'. A number of very metal-poor stars has been found, some of which have a low iron abundance but are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with Z?1.5?×?10(-5), it has been suggested that low-mass stars cannot form from the primitive interstellar medium until it has been enriched above a critical value of Z, estimated to lie in the range 1.5?×?10(-8) to 1.5?×?10(-6) (ref. 8), although competing theories claiming the contrary do exist. (We use 'low-mass' here to mean a stellar mass of less than 0.8 solar masses, the stars that survive to the present day.) Here we report the chemical composition of a star in the Galactic halo with a very low Z (≤?6.9?×?10(-7), which is 4.5?×?10(-5) times that of the Sun) and a chemical pattern typical of classical extremely metal-poor stars--that is, without enrichment of carbon, nitrogen and oxygen. This shows that low-mass stars can be formed at very low metallicity, that is, below the critical value of Z. Lithium is not detected, suggesting a low-metallicity extension of the previously observed trend in lithium depletion. Such lithium depletion implies that the stellar material must have experienced temperatures above two million kelvin in its history, given that this is necessary to destroy lithium. 相似文献
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Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life grow by accreting gas from the surrounding material. But for stars approximately 10 times more massive than the Sun (approximately 10M(o)), the powerful stellar radiation is expected to inhibit accretion and thus limit the growth of their mass. Clearly, stars with masses >10M(o) exist, so there must be a way for them to form. The problem may be solved by non-spherical accretion, which allows some of the stellar photons to escape along the symmetry axis where the density is lower. The recent detection of rotating disks and toroids around very young massive stars has lent support to the idea that high-mass ( > 8M(o)) stars could form in this way. Here we report observations of an ammonia line towards a high-mass star forming region. We conclude that the gas is falling inwards towards a very young star of approximately 20M(o), in line with theoretical predictions of non-spherical accretion. 相似文献
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L. Baschieri M. Negri F. de Luca L. Sereno L. Cramarossa 《Cellular and molecular life sciences : CMLS》1962,18(3):144-146
Riassunto Gli autori hanno ottenuto in conigli un siero anti-TSH usando come antigene ormone bovino. Questo siero inibisce il TSH endogeno di ratti nutriti con dieta di Remington e trattati con tiouracile, impedendo cosi la formazione della iperplasia tiroidea. È stato anche osservato che il trattamento con siero anti-TSH mantiene normale il rapporto MIT/DIT cancellando le salienti alterazioni indotte dal trattamento con tiouracile. 相似文献
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QI XueBin YANG Su ZHENG HongKun WANG YinQiu LIAO ChengHong LIU Ying CHEN XiaoHua SHI Hong YU xiaoJing Alice A. LIN Luca L. CAVALLI-SFORZA WANG Jun SU Bing 《科学通报(英文版)》2007,52(3):324-335
To understand the genetic basis that underlies the phenotypic divergence between human and non- human primates, we screened a total of 7176 protein-coding genes expressed in the human brain and compared them with the chimpanzee orthologs to identify genes that show evidence of rapid evolution in the human lineage. Our results showed that the nonsynonymous/synonymous substitution (Ka/Ks) ratio for genes expressed in the brain of human and chimpanzee is 0.3854, suggesting that the brain-expressed genes are under functional constraint. The X-linked human brain-expressed genes evolved more rapidly than autosomal ones. We further dissected the molecular evolutionary patterns of 34 candidate genes by sequencing representative primate species to identify lineage-specific adaptive evolution. Fifteen out of the 34 candidate genes showed evidence of positive Darwinian selection in human and/or chimpanzee lineages. These genes are predicted to play diverse functional roles in em- bryonic development, spermatogenesis and male fertility, signal transduction, sensory nociception, and neural function. This study together with others demonstrated the usefulness and power of phy- logenetic comparison of multiple closely related species in detecting lineage-specific adaptive evolu- tion, and the identification of the positively selected brain-expressed genes may add new knowledge to the understanding of molecular mechanism of human origin. 相似文献
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Mossé YP Laudenslager M Longo L Cole KA Wood A Attiyeh EF Laquaglia MJ Sennett R Lynch JE Perri P Laureys G Speleman F Kim C Hou C Hakonarson H Torkamani A Schork NJ Brodeur GM Tonini GP Rappaport E Devoto M Maris JM 《Nature》2008,455(7215):930-935
Neuroblastoma is a childhood cancer that can be inherited, but the genetic aetiology is largely unknown. Here we show that germline mutations in the anaplastic lymphoma kinase (ALK) gene explain most hereditary neuroblastomas, and that activating mutations can also be somatically acquired. We first identified a significant linkage signal at chromosome bands 2p23-24 using a whole-genome scan in neuroblastoma pedigrees. Resequencing of regional candidate genes identified three separate germline missense mutations in the tyrosine kinase domain of ALK that segregated with the disease in eight separate families. Resequencing in 194 high-risk neuroblastoma samples showed somatically acquired mutations in the tyrosine kinase domain in 12.4% of samples. Nine of the ten mutations map to critical regions of the kinase domain and were predicted, with high probability, to be oncogenic drivers. Mutations resulted in constitutive phosphorylation, and targeted knockdown of ALK messenger RNA resulted in profound inhibition of growth in all cell lines harbouring mutant or amplified ALK, as well as in two out of six wild-type cell lines for ALK. Our results demonstrate that heritable mutations of ALK are the main cause of familial neuroblastoma, and that germline or acquired activation of this cell-surface kinase is a tractable therapeutic target for this lethal paediatric malignancy. 相似文献