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.     

高气压反射式高能电子衍射仪监控脉冲激光外延氧化物薄膜

在超高真空分子束外延（MBE）生长技术中，反射式高能电子衍射仪（RHEED）能实时显示半导体和金属外延生长过程，给出薄膜表面结构和平整度的信息，成为MBE必备的原位表面分 析仪.为了研究氧化物薄膜如高温超导（YBa₂Cu₃O₇） 、铁电薄膜（Sr_1-xBa_x TiO₃）及它们的同质和异质外延结构的生长机理，获得高质量的符合各种应用 需要的氧化 物多层薄膜结构，在常规的制备氧化 关键词： 高温超导薄膜 RHEED     

Crystal Structure of Adduct 2-Phenyl-imidazo [ 4,5-f ] 1,10-phenanthroline Methanol

The structure of the title adduct comprises a phenanthroline derivative 2-phenyl-imidazo[4,5-f]1,10-phenanthroline and a methanol.The composition of the crystalline adduct was characterized as C19H12N4.CH3OH.It belongs to orthorhombic system,space group Pna21 with a=1.3693(4)nm,b=2.2988(7)nm,c=0.51338(15)nm,V=1.6160(8)nm^3.Z=4,and final R1=0.0423.wR2=0.1012 .Crystal structure shows that all the 19 carbon atoms and 4 nitrogen atoms are coplanar.The bond length data indicated that a very extensive conjugation system was formed.This conjugation makes the compound being a potentially excellent energy transformer used for luminescent materials.     

Speciation Analysis of Inorganic Tin (Sn(II)/Sn(IV)) by Graphite Furnace Atomic Absorption Spectrometry Following Ion-Exchange Separation

A new method based on anion exchange resin separation and graphite furnace atomic absorption spectrometry (GFAAS) detection is proposed for the determination of inorganic tin species. The result showed that Sn(IV) was quantitatively retained on the resin when [HCl] = 9.0 mol · L⁻¹, but Sn(II) could not be adsorbed on the resin under the same condition. Thus, a separation of Sn(II) and Sn(IV) has been realized. When the concentration of NaOH solution was between 2.0–7.0 mol · L⁻¹, Sn(IV) that adsorbed on the resin could be eluated from the resin completely. Meanwhile, under the atmosphere and the nitrogen states, the translation between Sn(II) and Sn(IV) was investigated. Under the optimal conditions, the detection limit of Sn(IV) is 0.40 μg · L⁻¹ with RSD of 2.3% (n = 5, c = 2.0 μg · L⁻¹). The proposed method was applied to the speciation analysis of tin in different water samples and the recovery of total Sn was in the range of 98.7–101.7%. In order to verify the accuracy of the method, a certified reference water sample was analyzed and the results obtained were in good agreement with the certified value.     

牛顿第二定律实验中的误差分析

本文是通过对加速度的实验值和理论值进行比较和分析，给出误差的合理范围。     

PuN基态分子势能函数与热力学函数的理论计算

在Pu的相对论有效原子实势近似和N原子 6 - 311G 全电子基函数下 ,用密度泛函B3LYP方法计算得到PuN分子基态X6Σ+ 的结构与势能函数、力常数与光谱数据 .同时计算得到PuN(g)分子在 2 98K时的标准生成热力学函数ΔfH0 、ΔS0 和ΔfG0 ,分别为 - 4 87.2 39kJ/mol、95 .345J/molK和 - 5 15 .6 6 6 1kJ/mol.     

ALGEBRAIC INDEPENDENCE OF CERTAIN NUMBERS OVER A FIELD OF FINITE TRANSCENDENCE TYPE

The transcendental degree of certain numbers concerned with the exponential funotion over a field of finite transcendence type is considered.     

离子注入诱导量子阱界面混合效应的光致荧光谱研究

采用多元芯片方法获得了一系列不同离子注入剂量的GaAsAlGaAs非对称耦合量子阱单元,通过光致荧光谱测量,研究了单纯的离子注入导致的界面混合效应.荧光光谱行为与有效质量理论计算研究表明,Al原子在异质结界面的扩散在离子注入过程中已基本完成,而热退火作用主要是去除无辐射复合中心. 关键词： 量子阱 离子注入 光致荧光谱 界面混合     

碰壁分子的平均速率和平均能量

本文对气体系统内的碰壁分子的平均速率和平均能量为会么会大于系统内分子的平均速率和平均能量进行了定性解释，并求出了这两类不同平均值之间的一般关系，最后针对经典理想气体算出了定量结构。     

Cycle control functions and the number of limit cycles

The cycle control function is defined and used to estimate the number of limit cycles for some planar autonomous systems. Some sufficient conditions for the existence of no or at most one limit cycle are given.