SYNDIOSPECIFIC POLYMERIZATION OF STYRENE WITH MULTI-NUCLEAR TITANIUM COMPLEXES

Two multi-nuclear titanium complexes [Ti(η5-Cp*)Cl(μ-O)]3 (1) and [(η5-Cp*TiCl)(μ-O)2(η5-Cp*Ti)2(μ-O)(μ-O)2]2Ti (Cp* = C5Me5) (2) have been investigated as the precatalysts for syndiospecific polymerization of styrene. In the presence of modified methylaluminoxane (MMAO) as a cocatalyst, complexes 1 and 2 display much higher catalytic activities towards styrene polymerization, and produce the higher molecular weight polystyrenes with higher syndiotacticities and melting temperatures (Tm) than the mother complex Cp*TiCl3 does when the polymerization temperature is above 70℃and the Al/Ti molar ratio is in the low range especially.     

Comparison of Different Crucible Materials for the Growth of AlN Crystals

Choice of crucible material is a key issue during the growth of AlN crystal. The stabilities at high temperature and life-spans of boron nitride (BN) crucible,tantalum (Ta) crucible and tungsten (W) crucible were compared. Tantalum crucible behaved worse at high temperature and life-span was shortened as compared with the other two crucible materials. It was very crisp and easy to crack. In contrast,self-seeded AlN crystals with different morphologies could be obtained at different high temperatures using BN crucible. The boron nitride crucible was stable below 2200 ℃,above which it would decompose. Thus it was unsuitable for the bulky AlN crystal growth. Tungsten crucible could endure the temperatures higher than 2200℃. Unfortunately we could only get AlN polycrystallines using tungsten crucible. After 50～100 hours’ run,the crucible was destroyed completely due to the multiple deep cracks. XRD results of destroyed tungsten crucible indicated that the main phases are tungsten carbide and tungsten nitride.     

共振条件下载波包络相位效应对阈上电离谱的影响

本文通过求解三维含时薛定谔方程, 从理论上研究了共振条件下氢原子的光电子能谱与角分布随着激光脉冲载波包络相位(CEP)的变化规律. 研究结果表明: 在共振位置附近, 光电子能谱的强度与CEP有强烈的依赖关系; 进一步对各个分波的分析, 可以确定共振电离初态的角量子数. 此外, 利用光电子的角分布信息, 可以对多周期激光脉冲的初始相位信息进行高精度探测. 关键词： 阈上电离 超短脉冲 载波包络相位     

阈上电离过程中光电子角分布的精细结构

应用非微扰散射理论并考虑自发辐射 ,研究了阈上电离过程中光电子的角分布。由于自发辐射的影响 ,电子的角分布具有精细结构 ,成功地解释了Nandor等人的实验观测。     

铝原子激发态近阈限光电离截面测量

本文利用激光烧蚀、激光泵浦-探测、共振增强多光子电离和飞行时间质谱相结合的实验技术,根据离子产额和电离激光能量的关系,获取铝原子激发态的光电离截面;并研究了光电离截面与电离富余能的依赖关系.电离富余能0-2.98 e V内光电离截面值范围为15.6±1.7 Mb-2.3±0.9 Mb,激发态的寿命为17.6±1.8,16.9±1.7 ns.在光电离截面的测量中,总的均方根误差上限约为17%.     

A note on Sobolev orthogonality for Laguerre matrix polynomials

Let {Ln(A,λ)(x)}n≥0 be the sequence of monic Laguerre matrix polynomials defined on [0, ∞) by Ln(A,λ)(x)=n!/(-λ)n∑nk=0(-λ)κ/k!(n-1)! (A I)n[(A I)k]-1 xk,where A ∈ Cr×r. It is known that {Ln(A,λ)(x)}n≥0 is orthogonal with respect to a matrix moment functional when A satisfies the spectral condition that Re(z) ＞ - 1 for every z ∈σ(A).In this note we show that forA such that σ(A) does not contain negative integers, the Laguerre matrix polynomials Ln(A,λ) (x) are orthogonal with respect to a non-diagonal SobolevLaguerre matrix moment functional, which extends two cases: the above matrix case and the known scalar case.     

Excitation and ionization of positronium by 50–100 fs laser pulses

The interaction between Ps and a strong laser pulse of short duration is studied. Substantial population is deposited in excited states under few photon excitation. The possible usefulness as a source of excited Ps to spectroscopy and the formation of antihydrogen is discussed. Finally, photoelectron energy spectra are calculated. This revised version was published online in August 2006 with corrections to the Cover Date.     

A new lower bound of the Hausdorff measure of the Sierpinski gasket

For the Sierpinski gasket, by using a sort of cover consisting of special regular hexagons, we define a new measure that is equivalent to the Hausdorff measure and obtain a lower bound of this measure. Moreover, the following lower bound of the Hausdroff measure of the Sierpinski gasket has been achieved H^s（S）≥0.670432,where S denotes the Sierpinski gasket, s = dimn（S） = log23, and H^s（S） denotes the s-dimensional Hausdorff measure of S. The above result improves that developed in .     

强光场中氦原子的ATI谱

提出了一个新的处理强光中基态氦原子阈上电离谱的解析模型。由这个模型算得的基态氦原子阈上电离谱同最近的实验结果作了比较。同时简单地讨论了现在的模型对先前的模型的改进。     

Thermal degradation of polyether-urethanes: 5. Polyether-urethanes prepared from methylene bis(4-phenylisocyanate) and high molecular weight poly(ethylene glycols) and the effect of ammonium polyphosphate

Polyurethanes prepared by reaction of methylene bis(4-phenylisocyanate) with poly(ethylene glycols) with molecular weights of approximately 1000 and 1500 have been degraded thermally, alone and in the presence of ammonium polyphosphate (APP). Degradation has been carried out at temperatures up to 500°C and the volatile products and structural changes in the residue analysed in detail. From these data, comprehensive mechanisms have been deduced and discussed and the differences in absence and presence of APP emphasised.A brief general discussion of this and previous work on polyetherurethanes (PEU) is presented, which illustrates in particular the effect of the length of the polyether segment on the degradation reaction.