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341.
湍流多尺度相干结构间歇性的PIV实验研究 总被引:1,自引:0,他引:1
利用粒子成像测速(PIV)系统测量了湍流边界层中流向速度平面,并对湍流多尺度相干结构统计特性进行了实验研究.利用连续子波变换,计算了不同尺度、不同法向位置的子波系数概率密度函数.结果发现缓冲区有着更强的间歇性.利用子波系数量化湍流间歇性的方法,应用推广的自相似律(ESS),计算了子波系数结构函数的标度指数.研究表明:当多尺度相干结构被提取出后,利用子波系数计算的ESS标度律就符合科尔莫戈罗夫提出的线性标度律,验证了多尺度相干结构是湍流边界层产生奇异标度律的原因.此外,利用PIV系统测量的数据,给出了流向平面内的以子波系数表达的能量分布.这种方法有利于进一步对多尺度相干结构在空间平面内的辨识与特性进行研究. 相似文献
342.
I claim that one way thought experiments contribute to scientific progress is by increasing scientific understanding. Understanding does not have a currently accepted characterization in the philosophical literature, but I argue that we already have ways to test for it. For instance, current pedagogical practice often requires that students demonstrate being in either or both of the following two states: 1) Having grasped the meaning of some relevant theory, concept, law or model, 2) Being able to apply that theory, concept, law or model fruitfully to new instances. Three thought experiments are presented which have been important historically in helping us pass these tests, and two others that cause us to fail. Then I use this operationalization of understanding to clarify the relationships between scientific thought experiments, the understanding they produce, and the progress they enable. I conclude that while no specific instance of understanding (thus conceived) is necessary for scientific progress, understanding in general is. 相似文献
343.
Glycogen synthase kinase 3β and Alzheimer’s disease: pathophysiological and therapeutic significance 总被引:3,自引:0,他引:3
Balaraman Y Limaye AR Levey AI Srinivasan S 《Cellular and molecular life sciences : CMLS》2006,63(11):1226-1235
Alzheimer’s disease (AD) is a neurodegenerative disorder associated with cognitive and behavioral dysfunction and is the leading
cause of dementia in the elderly. Several studies have implicated molecular and cellular signaling cascades involving the
serine-threonine kinase, glycogen synthase kinase β(GSK-3β) in the pathogenesis of AD. GSK-3β may play an important role in
the formation of neurofibrillary tangles and senile plaques, the two classical pathological hallmarks of AD. In this review,
we discuss the interaction between GSK-3β and several key molecules involved in AD, including the presenilins, amyloid precursor
protein, tau, and β-amyloid. We identify the signal transduction pathways involved in the pathogenesis of AD, including Wnt,
Notch, and the PI3 kinase/Akt pathway. These may be potential therapeutic targets in AD.
Received 19 December 2005; received after revision 24 January 2006; accepted 6 February 2006 相似文献
344.
Muñoz U Bartolomé F Esteras N Bermejo-Pareja F Martín-Requero A 《Cellular and molecular life sciences : CMLS》2008,65(21):3507-3519
It has been proposed that neuroinflammation, among other factors, may trigger an aberrant neuronal cell cycle re-entry leading
to neuronal death. Cell cycle disturbances are also detectable in peripheral cells from Alzheimer’s disease (AD) patients.
We previously reported that the anti-inflammatory 15- deoxy-Δ12,14-prostaglandin J
2 (15d-PGJ
2) increased the cellular content of the cyclin-dependent kinase inhibitor p27, in lymphoblasts from AD patients. This work
aimed at elucidating the mechanisms of 15d-PGJ
2-induced p27 accumulation. Phosphorylation, half-life, and the nucleo-cytoplasmic traffic of p27 protein were altered by 15d-PGJ2
by mechanisms dependent on PI3K/Akt activity. 15d-PGJ
2 prevents the calmodulin-dependent Akt overactivation in AD lymphoblasts by blocking its binding to the 85-kDa regulatory
subunit of PI3K. These effects of 15d-PGJ
2 were not mimicked by 9,10-dihydro-15-deoxy-Δ12,14- prostaglandin J
2, suggesting that 15d-PGJ
2 acts independently of peroxisome proliferator-activated receptor γ activation and that the α,β-unsaturated carbonyl group
in the cyclopentenone ring of 15d-PGJ
2 is a requisite for the observed effects.
Received 14 July 2008; received after revision 2 September 2008; accepted 12 September 2008 相似文献
345.
拓扑优化在单缸机缸体轻量化设计中的应用 总被引:5,自引:0,他引:5
为将三维拓扑优化技术应用于发动机气缸体轻量化设计中,对采用变密度拓扑优化方法的拓扑优化技术进行了研究.以缸体上施加最大爆发压力工况为边界条件,以缸体总柔度最小化为优化目标,以缸体重量为约束条件,对缸体进行拓扑优化.拓扑优化后的结构考虑加工、装配等因素,进行合理的重新建模后,分析了最大爆发压力工况和最大侧向力工况的气缸体应力分布,两种工况下优化后的缸体最大应力比原气缸体降低,应力分布更加均匀.结构优化方法用于缸体的等强度轻量化设计中,很容易确定缸体的最佳形状,并能减少重复设计验证的次数。 相似文献
346.
在应力代数模型基础上引入密度状态方程建立了变密度的各向异性湍浮力射流模型,并给出了浮力系数的简单计算式.对存在密度差的射流进行了数值计算,所得轨迹线与实验结果吻合良好.应用有限体积法对流动环境中不同喷角二维立面射流流场特性进行了数值分析,对涡心及分离点位置与喷角关系的结果分析表明喷角为90°时回流区域最大.提出了面积湍动能kA概念,以此分析了流体间的掺混强度与喷角间的关系,结果表明喷角为90°时最有利于射流水体与环境水体间的掺混. 相似文献
347.
接种密度对Vero细胞在微载体表面生长的影响 总被引:4,自引:0,他引:4
研究了接种密度对Vero细胞在微载体表面生长行为的影响,发现培养过程中所获得的细胞最高密度随接种密度的增加而有所提高,当细胞的表面接种密度高于1.0×10^5cells/mgMC时,因贴壁后细胞扩展受到限制而不利于进入对数生长期。就整个Vero细胞培养过程,适宜的表面接种密度为3×10^-4-7×10^4cells/mgMC,此时可以获得较高的比生长速率和细胞增殖倍数。 相似文献
348.
349.
2017年2月21日,国际著名数理经济学家、1972年度诺贝尔(Nobel)经济学奖获得者阿罗(K.J.Arrow)于美国辞世。谨作此文,以纪念他在社会选择理论,特别是其中将有关数学应用于研究经济学领域发现的"阿罗不可能性定理"作出的重大贡献。 相似文献
350.
The impact of parameter and model uncertainty on market risk predictions from GARCH‐type models
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We study the effect of parameter and model uncertainty on the left‐tail of predictive densities and in particular on VaR forecasts. To this end, we evaluate the predictive performance of several GARCH‐type models estimated via Bayesian and maximum likelihood techniques. In addition to individual models, several combination methods are considered, such as Bayesian model averaging and (censored) optimal pooling for linear, log or beta linear pools. Daily returns for a set of stock market indexes are predicted over about 13 years from the early 2000s. We find that Bayesian predictive densities improve the VaR backtest at the 1% risk level for single models and for linear and log pools. We also find that the robust VaR backtest exhibited by linear and log pools is better than the backtest of single models at the 5% risk level. Finally, the equally weighted linear pool of Bayesian predictives tends to be the best VaR forecaster in a set of 42 forecasting techniques. 相似文献