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排序方式: 共有266条查询结果,搜索用时 31 毫秒
61.
62.
Woosuk Park 《Foundations of Science》2012,17(4):321-337
One of the most pressing issues in understanding abduction is whether it is an instinct or an inference. For many commentators find it paradoxical that new ideas are products of an instinct and products of an inference at the same time. Fortunately, Lorenzo Magnani’s recent discussion of animal abduction sheds light on both instinctual and inferential character of Peircean abduction. But, exactly for what reasons are Peirce and Magnani so convinced that animal abduction can provide us with a novel perspective? Inspired by Peirce’s and Magnani’s discussions of animal abduction, I propose to compare Peirce’s and Magnani’s views of animal abduction with the estimative power of non-human animals and humans, which was one of the internal senses in medieval psychology. 相似文献
63.
The use of microring resonators to assist in the evanescent field coupling between dissimilar waveguides is proposed and analyzed. Theoretical analysis based on the coupled mode theory and nu-merical example show that complete cross power transfers can be obtained near the microring resonances. Applications of the device include power dividers, low-power thermo-optic or electro-optic switches, and modulators. 相似文献
64.
Most proteins that participate in cellular signalling networks contain modular protein-interaction domains. Multiple versions of such domains are present within a given organism: the yeast proteome, for example, contains 27 different Src homology 3 (SH3) domains. This raises the potential problem of cross-reaction. It is generally thought that isolated domain-ligand pairs lack sufficient information to encode biologically unique interactions, and that specificity is instead encoded by the context in which the interaction pairs are presented. Here we show that an isolated peptide ligand from the yeast protein Pbs2 recognizes its biological partner, the SH3 domain from Sho1, with near-absolute specificity--no other SH3 domain present in the yeast genome cross-reacts with the Pbs2 peptide, in vivo or in vitro. Such high specificity, however, is not observed in a set of non-yeast SH3 domains, and Pbs2 motif variants that cross-react with other SH3 domains confer a fitness defect, indicating that the Pbs2 motif might have been optimized to minimize interaction with competing domains specifically found in yeast. System-wide negative selection is a subtle but powerful evolutionary mechanism to optimize specificity within an interaction network composed of overlapping recognition elements. 相似文献
65.
Bmi-1 is required for maintenance of adult self-renewing haematopoietic stem cells 总被引:119,自引:0,他引:119
Park IK Qian D Kiel M Becker MW Pihalja M Weissman IL Morrison SJ Clarke MF 《Nature》2003,423(6937):302-305
66.
Sung BJ Hwang KY Jeon YH Lee JI Heo YS Kim JH Moon J Yoon JM Hyun YL Kim E Eum SJ Park SY Lee JO Lee TG Ro S Cho JM 《Nature》2003,425(6953):98-102
Phosphodiesterases (PDEs) are a superfamily of enzymes that degrade the intracellular second messengers cyclic AMP and cyclic GMP. As essential regulators of cyclic nucleotide signalling with diverse physiological functions, PDEs are drug targets for the treatment of various diseases, including heart failure, depression, asthma, inflammation and erectile dysfunction. Of the 12 PDE gene families, cGMP-specific PDE5 carries out the principal cGMP-hydrolysing activity in human corpus cavernosum tissue. It is well known as the target of sildenafil citrate (Viagra) and other similar drugs for the treatment of erectile dysfunction. Despite the pressing need to develop selective PDE inhibitors as therapeutic drugs, only the cAMP-specific PDE4 structures are currently available. Here we present the three-dimensional structures of the catalytic domain (residues 537-860) of human PDE5 complexed with the three drug molecules sildenafil, tadalafil (Cialis) and vardenafil (Levitra). These structures will provide opportunities to design potent and selective PDE inhibitors with improved pharmacological profiles. 相似文献
67.
科氏力对高速旋转汽轮机叶片动态特性的影响 总被引:4,自引:1,他引:4
采用解析的方法,建立了高速旋转汽轮机叶片中科氏力和科氏动应力的计算模型。该模型克服了以往在叶片动态特性分析时难以考虑科氏力影响的问题,导出了科氏动应力和非稳态气流动应力比值的计算公式以及科氏力和离心力比值的计算公式,并进行了实例分析.计算结果表明,科氏力对叶片轴向振动和扭转振动的固有频率没有影响,对切向振动的影响很小,可以忽略不计;科氏力所产生的动应力不到非稳态气流动应力的1%。 相似文献
68.
1 Results One dimensional (1D) nanostructures such as nanowires,nanotubes,nanorods and nanoribbons have been extensively investigated for a wide range of applications[1].Here,we present the synthesis,characterization and technological applications of several 1D nanostructures including SnO2 nanowires,CuO nanoribbons,CdSe nanowires and In2O3 nanowires.SnO2 nanowires were synthesized by thermal evaporation combined with a self-catalyzed growth procedure.Scanning electron microscopy (SEM) observation shows... 相似文献
69.
p53 mutant mice that display early ageing-associated phenotypes. 总被引:56,自引:0,他引:56
Stuart D Tyner Sundaresan Venkatachalam Jene Choi Stephen Jones Nader Ghebranious Herbert Igelmann Xiongbin Lu Gabrielle Soron Benjamin Cooper Cory Brayton Sang Hee Park Timothy Thompson Gerard Karsenty Allan Bradley Lawrence A Donehower 《Nature》2002,415(6867):45-53
The p53 tumour suppressor is activated by numerous stressors to induce apoptosis, cell cycle arrest, or senescence. To study the biological effects of altered p53 function, we generated mice with a deletion mutation in the first six exons of the p53 gene that express a truncated RNA capable of encoding a carboxy-terminal p53 fragment. This mutation confers phenotypes consistent with activated p53 rather than inactivated p53. Mutant (p53+/m) mice exhibit enhanced resistance to spontaneous tumours compared with wild-type (p53+/+) littermates. As p53+/m mice age, they display an early onset of phenotypes associated with ageing. These include reduced longevity, osteoporosis, generalized organ atrophy and a diminished stress tolerance. A second line of transgenic mice containing a temperature-sensitive mutant allele of p53 also exhibits early ageing phenotypes. These data suggest that p53 has a role in regulating organismal ageing. 相似文献
70.
Beum‐Jo Park 《Journal of forecasting》2002,21(5):381-393
Since volatility is perceived as an explicit measure of risk, financial economists have long been concerned with accurate measures and forecasts of future volatility and, undoubtedly, the Generalized Autoregressive Conditional Heteroscedasticity (GARCH) model has been widely used for doing so. It appears, however, from some empirical studies that the GARCH model tends to provide poor volatility forecasts in the presence of additive outliers. To overcome the forecasting limitation, this paper proposes a robust GARCH model (RGARCH) using least absolute deviation estimation and introduces a valuable estimation method from a practical point of view. Extensive Monte Carlo experiments substantiate our conjectures. As the magnitude of the outliers increases, the one‐step‐ahead forecasting performance of the RGARCH model has a more significant improvement in two forecast evaluation criteria over both the standard GARCH and random walk models. Strong evidence in favour of the RGARCH model over other competitive models is based on empirical application. By using a sample of two daily exchange rate series, we find that the out‐of‐sample volatility forecasts of the RGARCH model are apparently superior to those of other competitive models. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献