赛跑运动的牛顿力学分析

本文介绍一种用牛顿力学研究赛跑运动的物理模型,给出两种情形下跑步时间的最优化结果.这一结果与优秀运动员的实际比赛成绩很好地相符.     

从立方抛物线谈起(1)--余弦型振动,椭圆余弦型振动与双曲线型非周期运动

从立方抛物线的特性谈起 ,用较初浅的方法 ,借助于雅可比椭圆函数求椭圆方程的解来说明一大类一维保守系统的余弦振动、椭圆余弦型振动与双曲线型非周期运动 .并以杜芬振子、单摆、倒摆、转动圆环上的小环运动为典型实例作了详细讨论     

Hierarchical structures in a turbulent pipe flow

A hierarchical structure (HS) analysis (β-test and γ-test) is applied to a fully developed turbulent pipe flow. Velocity signals are measured at two cross sections in the pipe and at a series of radial locations from the pipe wall. Particular attention is paid to the variation of turbulent statistics at wall units 10<y⁺<3000. It is shown that at all locations the velocity fluctuations satisfy the She–Leveque hierarchical symmetry (Phys. Rev. Lett. 72 (1994) 336). The measured HS parameters, β and γ, are interpreted in terms of the variation of fluid structures. Intense anisotropic fluid structures generated near the wall appear to be more singular than the most intermittent structures in isotropic turbulence and appear to be more outstanding compared to the background fluctuations; this yields a more intermittent velocity signal with smaller γ and β. As turbulence migrates into the logarithmic region, small-scale motions are generated by an energy cascade and large-scale organized structures emerge which are also less singular than the most intermittent structures of isotropic turbulence. At the center, turbulence is nearly isotropic, and β and γ are close to the 1994 She–Leveque predictions. A transition is observed from the logarithmic region to the center in which γ drops and the large-scale organized structures break down. We speculate that it is due to the growing eddy viscosity effects of widely spread turbulent fluctuations in a similar way as in the breakdown of the Taylor vortices in a turbulent Couette–Taylor flow at high Reynolds numbers.     

变加速动力学与舒适性问题

用变加速动力学的急动度(加加速度)概念,分析了车辆、电梯的乘座舒适性与高层钢结构建筑的风振舒适性问题.     

Iodine catalyzed efficient synthesis of symmetrical diaryl sulfoxides from arenes and thionyl chloride under solvent-free conditions

Synthesis of symmetrical diaryl sulfoxides from arenes and thionyl chloride in the presence of a catalytic amount of iodine at room temperature under solvent-free conditions is described.Mild reaction conditions,easy workup,high yield,and easily available catalyst are important features of this method.     

流通池介质交换差示脉冲阳极溶出伏安法用于多元素重叠峰的分离及其同时测定

本文用流通池介质交换差示脉冲阳极溶出伏安法在盐酸介质中富集,而以碳酸钠-碳酸氢钠缓冲溶液为溶出介质,有效地分离了酸性介质中Cu(Ⅱ)、Sb(Ⅲ)、Pb(Ⅱ)、Tl(Ⅰ)、Cd(Ⅱ)、In(Ⅲ)的重叠溶出峰,实现了多离子的同时测定。     

一种利用质谱信息进行结构特征鉴定的模式识别方法

本文提出了分段式离子系列谱编码方法,实验证明具有很好的结构表征能力。本程序主要是以模式识别技术为基础,实现了对未知物谱图的KNN分类,进而得到未知物的主要结构特征。这个程序应用于有机化合物的分类,取得了满意的结果。     

Photocatalytic degradation of methylene blue on Fe3+-doped TiO2 nanoparticles under visible light irradiation

Fe³⁺-doped TiO₂ composite nanoparticles with different doping amounts were successfully synthesized using sol-gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultravioletvisible spectroscopy (UV-Vis) diffuse reflectance spectra (DRS). The photocatalytic degradation of methylene blue was used as a model reaction to evaluate the photocatalytic activity of Fe³⁺/TiO₂ nanoparticles under visible light irradiation. The influence of doping amount of Fe³⁺ (ω: 0.00%–3.00%) on photocatalytic activities of TiO₂ was investigated. Results show that the size of Fe³⁺/TiO₂ particles decreases with the increase of the amount of Fe³⁺ and their absorption spectra are broaden and absorption intensities are also increased. Doping Fe³⁺ can control the conversion of TiO₂ from anatase to rutile. The doping amount of Fe³⁺ remarkably affects the activity of the catalyst, and the optimum efficiency occurs at about the doping amount of 0.3%. The appropriate doping of Fe³⁺ can markedly increase the catalytic activity of TiO₂ under visible light irradiation. __________ Translated from Journal of Northwest Normal University (Natural Science), 2006, 42(6): 55–56 [译自: 西北师范大学学报(自然科学版)]     

A new isoprenyl phenyl ether compound from mangrove fungus

A new isoprenyl phenyl ether, 3-hydroxy-4-(3-methylbut-2-enyloxy)benzoic acid methyl ester (1), together with 4-hydroxybenzoic acid (2), 2-hydroxy-6-methylbenzoic acid (3), and 4-hydroxy-3-methoxybenzoic acid (4) were isolated from Mangrove fungus (No. B60) from the South China Sea. The structures of the compounds were established on the basis of NMR spectroscopic and mass spectrometric data. In the preliminary bioassay, compound 1 exhibited antibacterial and antifungal activities. Compound 1 also inhibited cytotoxicity to the hepG2 cell line with an IC₅₀ value of 10.0 μg/mL. Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 313–314, July–August, 2007.