Variational approach to the closure problem of turbulence theory

A new method is proposed to solve the closure problem of turbulence theory and to drive the Kolmogorov law in an Eulerian framework. Instead of using complex Fourier components of velocity field as modal parameters, a complete set of independent real parameters and dynamic equations are worked out to describe the dynamic states of a turbulence. Classical statistical mechanics is used to study the statistical behavior of the turbulence. An approximate stationary solution of the Liouville equation is obtained by a perturbation method based on a Langevin-Fokker-Planck (LFP) model. The dynamic damping coefficient eta of the LFP model is treated as an optimum control parameter to minimize the error of the perturbation solution; this leads to a convergent integral equation for eta to replace the divergent response equation of Kraichnan's direct-interaction (DI) approximation, thereby solving the closure problem without appealing to a Lagrangian formulation. The Kolmogorov constant Ko is evaluated numerically, obtaining Ko = 1.2, which is compatible with the experimental data given by Gibson and Schwartz, (1963).

凤眼莲根区异养细菌的群落特征与异养活性的研究

本文研究了凤眼莲根区(根际与根面)异养细菌的群落特征与异养活性。从根区分离出24株优势菌,经鉴定有10个属。其中以气单胞菌属、微球菌属、假单胞菌属、土壤杆菌属和芽孢杆菌属为主要菌属。细菌总数:根际>根面>水体。异养活性以氧化葡萄糖的速率计算。在30℃和pH7.0的条件下。根区菌群都显示较高的活性,且按下列顺序增强:老根区菌群>幼根区菌群>枯根区菌群;而根面菌群活性均大于根际菌群。但在10℃和pH5.0、8.6时,其活性明显地受到抑制。

单晶硅中铒点缺陷及Er-O复合缺陷电子结构的EHMO计算

本文采用集团模型和推广的Hucket分子轨道理论(EHMO)计算c-Si中Er点缺陷及Er-O复合缺陷的原子构型及电子结构。计算结果符合实验及一些文献的第一性原理计算结果,解释了Er有c-Si中的发光特性。

关于国家自然科学基金生物力学学科优先资助领域的思考

<正>作为我国基础研究最重要的资助机构之一,国家自然科学基金委员会自成立伊始即大力扶持生物力学新兴学科发展、培养和造就生物力学专业人才、推动生物力学研究基地建设,成绩斐然。在科学发展至二十一世纪的今天,针对国际生物力学领域及相关学科发展动态、国家中长期科技发展规划、以及生物力学学科

内蒙古岱海DH99a岩芯沉积物碳含量变化与湖区全新世气候变迁

Daihai Lake, a graben-type closed lake, lies ca. 10 km east of Liangcheng County, Inner Mongolia, north-central China. For its location at the transition of semi-humid and semi-arid areas, and in the north edge of the East Asian monsoon, the lake is sensitive to changes in climate and environment. Based on analyses of total inorganic carbon (TIC), total organic carbon (TOC) and the ratio of total organic carbon to total nitrogen (C/N ratio) of DH99a core sediments recovered in the central part of Daihai Lake, the data suggest Holocene climatic history of the lake region is reconstructed. In this paper, the TIC and TOC contents of the lake sediments are closely related to climate changes. 1) Changes in TIC content of the lake sediments is closely related to climate, which directly reflect changes of temperature in the lake region, i.e., higher TIC content is linked with warmer temperature and stronger evaporation; 2) Changes in TOC and C/N ratio reflect the regional precipitation, i.e., relatively higher TOC content and C/N ratio indicate higher rainfall which results in stronger river flow and more organic matter entering into the lake. Data of the TIC content, TOC content and C/N ratio of DH99a core sediments suggest that climatic history of the Daihai Lake region is characterized by 4 stages. During the interval of ca. 11200-7500 a BP, higher TIC content, relatively lower TOC content and C/N ratio value indicate a warmer and slight dry condition over the lake area. From ca. 7500 to 4500 a BP, high values of TIC content, with an increase in TOC content and C/N ratio suggest the climate was warm and humid. Changes of TIC content, TOC content show that both temperature and precipitation displayed obvious fluctuations during the period, i.e., slightly cool and humid ca. 7500-6700 a BP, warm and moist ca. 6700-5300a BP, mild and comparatively humid ca. 5300-4500a BP. Between ca. 4500 and 2900 a BP, TIC content and TOC content decreased gradually while fluctuating, C/N ratio displayed a decreasing trend. These data imply that the climate generally became cooler and drier than the preceding period. The lowest values of TIC content, TOC content and C/N ratio during the interval of ca. 2900-0 a BP, demonstrate that the climate was severe, and became cool and dry. However the relative higher values of TIC content, TOC content and C/N ratio between ca. 1700 and 1300 a BP may denote an increase both in temperature and in precipitation. Data of TIC content, TOC content and C/N ratio in Daihai DH99a core sediments indicate that the warm period was asynchronous with the humid time, the warm interval began in ca. 11200 a BP, and ended in ca. 2900 a BP. The humid period was ca. 7500-2900 a BP. During ca. 7500^500 a BP, the climate was warm and humid, which was the climatic optimum of the Holocene Epoch in the Daihai Lake region. Data of TIC content, TOC content and C/N ratio in Daihai DH99a core sediments imply that the Holocene climate was unstable, the fluctuating events happened occasionally. Such as the cold and dry climate in ca. 4400-4200a BP, the warm and humid climatic condition in the period between ca.1700 and 1300a BP.

Ag/SiO2: A novel catalyst with high activity and selectivity for hydrogenation of chloronitrobenzenes

Ag/SiO2 prepared by an in situ reduction method are found, for the first time, to be highly effective and recyclable catalysts for the selective hydrogenation of a range of chloronitrobenzes to their corresponding chloroanilines, which are of great potential as industrially viable and cheap novel catalysts for the production of chloroanilines.