Kinetics and mechanism of polymerization of methyl methacrylate initiated by stibonium ylide

Homopolymerization of methyl methacrylate (MMA) was carried out in the presence of triphenylstibonium 1,2,3,4-tetraphenyl-cyclopentadienylide as an initiator in dioxane at 65°C±0·l°C. The system follows non-ideal radical kinetics (R _p ∝ [M]^1·4 [I]^0·44 @#@) due to primary radical termination as well as degradative chain-transfer reaction. The overall activation energy and average value ofk ₂ ^p /k _t were 64 kJmol⁻¹ and 0.173 × 10⁻³ 1 mol⁻¹ s⁻¹ respectively     

HCHO-(DL-苹果酸)-BrO-3-Mn2+-H2SO4体系化学振荡反应动力学研究

研究了HCHO参与下的(DL-苹果酸)-BrO-3-Mn2+-H2SO4化学振荡反应体系的非线性动力学行为,考察了该体系中各反应物的初始浓度范围及主要影响因素. 结果表明,在5.0×10-5～1.0×10-2 mol·L-1范围内, HCHO对振荡反应的诱导期和周期有较大影响,且HCHO浓度的对数lnc(HCHO)与诱导期倒数的对数ln(1/tin)及周期倒数的对数ln(1/tp)均存在线性关系. 诱导期和周期的表观活化参数分别为70.87,55.71 kJ·mol-1. 另外还对HCHO参与下的可能振荡反应机理进行了探讨.     

A projection method for solving incompressible viscous flows on domains with moving boundaries

In this paper, a projection method is presented for solving the flow problems in domains with moving boundaries. In order to track the movement of the domain boundaries, arbitrary‐Lagrangian–Eulerian (ALE) co‐ordinates are used. The unsteady incompressible Navier–Stokes equations on the ALE co‐ordinates are solved by using a projection method developed in this paper. This projection method is based on the Bell's Godunov‐projection method. However, substantial changes are made so that this algorithm is capable of solving the ALE form of incompressible Navier–Stokes equations. Multi‐block structured grids are used to discretize the flow domains. The grid velocity is not explicitly computed; instead the volume change is used to account for the effect of grid movement. A new method is also proposed to compute the freestream capturing metrics so that the geometric conservation law (GCL) can be satisfied exactly in this algorithm. This projection method is also parallelized so that the state of the art high performance computers can be used to match the computation cost associated with the moving grid calculations. Several test cases are solved to verify the performance of this moving‐grid projection method. Copyright © 2004 John Wiley Sons, Ltd.     

Phase Measurement Algorithm in Wavelength Scanned Fizeau Interferometer

Wavelength scanned interferometry allows the simultaneous measurement of top surface shape and optical thickness variation of a transparent object consisting of several parallel surfaces. Interference signals from these surfaces can be separated in frequency space, and their phases are detected by discrete Fourier analysis. However, these signal frequencies are shifted from the detection frequency by the refractive index dispersion of the object and a nonlinearity of the wavelength scanning. The Fourier analysis is sensitive to the detuning of the signal frequency and suffers from the multiple-beam interference noise. Conventional error-compensating algorithms cannot be applied to an object consisting of more than three reflecting surfaces. We derive a new 2N-1 sample error-compensating algorithm, which allows the phase detection of any order of harmonic frequency among the interference signals. The new algorithm suppresses the effect of signal frequency detuning as well as the multiple-beam interference noise and can be applied to the measurement of complex objects consisting of more than three reflecting surfaces.     

旋转带电体磁矩计算的若干法则与算例

本文在文献 [1]、[2 ]等的基础上给出关于旋转带电体的磁矩计算的若干法则 ,均以定理形式表达 ,并列表枚举其相关算例     

Kinetics and mechanism of free-surface vaporization of zinc, cadmium and mercury oxides analyzed by the third-law method

On the basis of critical comparison of experimental and theoretical values of the E parameter and investigation of the retardation effect of oxygen on the evaporation rate of ZnO, CdO and HgO, it was concluded that the dissociative evaporation of ZnO and HgO proceeds with releasing of atomic oxygen (O) as a primary product of decomposition. By contrast, the mechanism of dissociative evaporation of CdO corresponds to the equilibrium reaction with releasing of molecular oxygen (O₂) as a primary product of decomposition. As was shown, this difference in mechanisms is not related with interatomic OO distances in these oxides. From the analysis of crystal structure for 12 different oxides, which evaporate with releasing of atomic oxygen, and for 13 compounds, which evaporate with releasing of molecular oxygen, it was revealed that the first mechanism is observed for all oxides with the cubic crystal structure. It was proposed that a decisive role in this difference belongs to a local symmetry in the position of O atoms.     

机械结构因素对光电跟踪伺服系统性能的影响

为克服机械结构因素对光电跟踪伺服系统性能的不良影响,分析了转动惯量、结构谐振频率、摩擦力矩等伺服机械结构因素与伺服系统性能的关系,包括分析转动惯量与伺服系统性能的关系、结构谐振频率与伺服系统性能的关系、摩擦力矩与伺服系统性能的关系,探讨了消除或减小机械谐振的措施.该分析方法可应用于设计和制造响应速度快、跟踪精度高的光电跟踪伺服系统.     

CO（ a）+ NO（X）传能体系中的新传能通道

在相对碰撞平动能为 0 .0 5eV的分子束实验条件下 ,研究了亚稳态CO(a) +NO(X)的E E传能通道 .通过测量和分析交碰区的传能发射光谱 ,在 780和 860nm处观测到了NO(b -a)跃迁Ogawa带的△v =+ 4和△v =+ 3序的发射光谱 .从而首次在实验上直接证实了传能过程中第四通道的存在 (CO (a) +NO(X)→CO (X) +NO(b) ) .这一通道的发现解释了前人测量到的在CO(a)与NO(X)碰撞传能过程中CO(a)的猝灭速率远大于NO(A ,B)生成速率的实验结果 ,并进一步证实了这一“经典”E E传能体系为电子交换机理的传能观点     

Formation of metallic NbSe2 nanotubes and nanofibers

We succeed in synthesizing NbSe₂ nanotubes along with nanofibers by chemical vapor transportation. They are stable crystalline systems and can be synthesized reproducibly in a nearly equilibrium reacting process. We have investigated these nanosize structures of NbSe₂ by transmission electron microscopy and electron diffraction. Both of the structures have a similar size of 100–200 nm in diameter. While nanotubes consist of rolled-up NbSe₂ layers, nanofibers are a pile of thin flat layers. We propose a mechanism of the formation of NbSe₂ nanotubes and nanofibers on the basis of deseleniditive transition from a NbSe₃ fiber-shaped crystal. We also measured electrical resistance of the nanofibers with conductive atomic force microscopy and demonstrated that the material show metallic behavior at room temperature.     

掺Perylene的PVK薄膜荧光谱及发光机理

用高荧光效率的有机染料芘(perylene)掺杂聚乙烯咔唑(PVK),其荧光光谱与芘的发射光谱基本一致,而且亮度比纯芘发光提高十多倍,说明发光主要来自芘分子,并在PVK和perylene之间存在十分有效的能量传递或电荷转移过程,荧光谱强度随掺杂浓度的变化关系说明存在一个最佳的掺杂浓度比.分析PVK和perylene之间可能发生的能量转移过程,认为从PVK到perylene这种能量转移与实验不符;分析PVK和perylene薄膜的光致发光过程,认为从(PVK+)→(perylene+)和从(PVK-)→(p