ESR study of free radicals in UHMW-PE fiber irradiated by gamma rays

ESR spectra of the trapped radicals in an ultra-high molecular weight polyethylene (UHMW-PE) fiber irradiated by gamma rays showed well-resolved hyperfine splitting at room temperature since the c-axis of the crystallites is aligned with the fiber direction and the radicals are trapped in crystallites. The alkyl radical (?CH₂?^?CH?CH₂?) was the major product after irradiation in vacuum and in air at room temperature. Some of the alkyl radicals converted to allyl radicals (?CH₂?^?CH?CH=CH?) and polyenyl radicals (?CH₂?^?CH?(CH=CH)_n?CH₂?) during storage in vacuum. Upon storage in air atmosphere, the alkyl radicals decayed by reaction with oxygen. Of particular interest is the very slow decay rate of the alkyl radical trapped in UHMW-PE fiber, the half-life is 26 days in vacuum, and 13 days in air at room temperature, which is about 1/30 and 1/100 of that reported for high density polyethylene (HDPE), respectively. The extremely long lifetime of the alkyl radical is supposed to be caused by the large size of crystallites in UHMW-PE fiber. The rate of radical decay was accelerated by annealing at elevated temperature.     

中国散裂中子源大功率可编程脉冲电源设计

在中国散裂中子源大功率可编程脉冲电源设计中,主回路采用绝缘栅双极型晶体管(IGBT)H桥串并联拓扑,错相工作方式,利用IGBT功率放大的特性,实现了电源高功率(60 MW)、高频率(1.843 2MHz)、高压(3.319 kV)和大电流(18 kA)的要求,并通过电源反馈控制系统,实现了电源的快速响应时间,使电源跟踪精度达到1.5%,满足指标要求。在电源研制中,解决了IGBT高压、大电流的均压和均流问题;由于IGBT工作在开关状态,为了消除谐波,利用多重化技术,得到了光滑的输出脉冲电流曲线;采用电流互感器的并联,实现了输出大电流的检测;电源的反馈控制策略采用比例和前馈运算,实现了电源输出波形对给定波形的快速跟踪。     

Lattice vibrations and optical properties of wurtzite InN in the reststrahlen region

The lattice vibrations and optical properties of wurtzite InN are studied by the first-principle calculations based on the density functional theory. The phonon spectra of lattice vibration are calculated under the Generalized-Gradient Approximation (GGA). The optical properties are investigated based on the phonon spectra. The phonon dispersion curve and the phonon density of state are calculated and compared with the existing experimental data. The calculation indicates that InN has a metal-like behavior. Our calculation shows that the fundamental vibration is therefore infrared active in wurtzite structure semiconductors.     

利用激光诱导荧光技术研究Ca(1S0)与氯代乙烷的反应

The internal state distributions of nascent CaCl formed in the reactions Ca + (1,1) and (1,2) C_2H_4Cl_2、(1,1,2) C_2H_2Cl_3, (1,1,2,2) C_2H_2Cl_4 have been studied by means of the laser induced fluorescence (LIF) in the beam-gas apparatus. The results showed that the vibrational distributions of the CaCl products from Ca+ (1, 1) C_2H_4Cl_2. (1,1,2,2) C_2H_2Cl_4 are similar to vibrational distributions of the CaCl products from Ca + CH_2Cl_2、CHCl_3, respectively. However, the vibrational distribution of the CaCl product from Ca+(1,1,2) C_2H_3Cl_3 is equivalent to the combination of that from Ca+(1,2) C_2H_4Cl_2 and Ca+(1,1,2,2) C_2H_2Cl_4. No LIF signal has been found in the reaction Ca+(1,1) C_2H_4Cl_2.     

Adhesion of Sol-Gel-Derived Organic-Inorganic Hybrid Coatings on Polyester

Inorganic coatings, including metal-oxide coatings, provide polymer surfaces with excellent abrasion and wear resistance, and protection against environmental degradation. However, one drawback associated with the incorporation of such ceramic coatings to polymeric materials is the adhesion characteristic at the ceramic-polymer interface. In this paper, two strategies for adhesion enhancement of ceramic coatings on polymer substrates were proposed: (1) formation of chemical bonds through surface condensation reactions, and (2) development of interlocked ceramic and polymeric networks through diffusion of alkoxide precursors. The current research has focused on the adhesion of sol-gel-derived organic-inorganic hybrid coatings on polyester by forming chemical bonds between the polymer substrate and the hybrid coatings, as well as developing interlocked polymeric and inorganic networks at the interface. Contact angle, wettability tests, and chemicalanalysis were done to verify the effectiveness of the adhesion of organic-inorganic hybrid coatings on polyester substrates. In addition, dry and wet thermal cycling tests were done to analyze the adhesion behavior of the hybrid coatings on polyester, followed by microscopy examination. It was found that although both approaches resulted in excellent adhesion of hybrid coatings on polyester, adhesion with interlocked ceramic and polymeric networks was far better than that with chemical bonds in the presence of water at elevated temperatures.     

Template-Based Growth of Oxide Nanorod Arrays by Centrifugation

This paper reports template-based growth of nanorod arrays by combination of sol–gel processing and centrifugation. The technical concept is simple and straightforward; centrifugation force drives the sol nanoclusters into the pores of the template, filling the pores completely to form nanorods. However, simulation reveals the formation of nanorods inside pores is more complex; centrifugation force is insufficient to overcome the energy barrier that prevents agglomeration of two nanoclusters. Thermal fluctuation and solvent evaporation upon drying are considered to be the forces leading to the eventual agglomeration of concentrated nanoclusters inside template pores. Dense nanorods with 200 nm diameter and 10 m length were readily obtained from polymeric SiO₂, colloidal SiO₂, TiO₂ and PZT sols after heat treatment.     

碱土金属与卤代有机小分子的反应激发函数

反应截面与初始相对平动能的相互关系一反应激发函数,是分子反应动力学研究的一个重要方面,自Bernstein等人＊于1971年对反应K＋Cll3I、KI＋Cll3进行研究后,这方面的实验研究一直较为活跃,也有一些简单模型或统计模型对实验结果进行讨论［’－‘］．到目前为止,这方面的实验研克主要集中于碱金属与卤素分子、卤化氢、卤代有机小分子的反应,碱土金属与卤代有机小分子反应的激发函数研究还未见任何报导,本文在交叉分子束反应条件下,利用激光诱导荧光（LIF）和时间飞渡（TOF）方法测量了下列十四个反应的激发函数：1实验利用超声…     

Rotational reorientation dynamics of Rhodamine 700 in different excited states

The rotational reorientation dynamics of rhodamine 700 (LD700) in the first (S₁) and the fifth (S₅) excited state in three aprotic polar solvents have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP TD) spectroscopy. In both excited states, the overall rotational relaxation of LD700 occurs on a time scale of 40-230 ps depending on the solvent, and a quantitative analysis of this time constant has been performed using the Stokes-Einstein-Debye (SED) hydrodynamic theory combined with the extended charge distribution model developed by Alavi and Waldeck. The experimentally measured reorientation times for LD700 in S₅ are smaller than those in S₁, which is in accord with the predictions by the SED theory. In addition, for LD700 in S₅, a rapid initial decrease on the time scale less than 0.5 ps has been found. According to our analysis, this fast component may account for the rapid internal conversion from S₅ to S₁, and the rate of internal conversion was found to be sensitive to the solvent polarity.     

关于B运输问题的两点注记

用实例说明 B运输问题和传统运输问题解的区别 .给出了 B运输问题一个定理的证明 ,从而使 B运输问题的有关理论更加完善     

压电薄板屈曲有限元分析及DKQ单元

在机电耦合本构方程基础上,利用Hamilton原理推导了压电薄板屈曲分析的有限元特征方程和机电耦合的内力计算公式,在有限元实现中选择了基于Kirchhoff薄板假定的四边形薄板单元（DKQ单元）,并给出该单元的几何刚度阵及其数值积分方法。在大型通用有限元分析和优化设计软件系统JIFEX中实现了该方法。给出的数值验证了DKQ单元在屈曲分析和压电薄板静力分析中具有较高精度和收敛性,通过机械荷载和电荷载联合作用下的临界荷载计算,表明压电耦合效应能够影响结构的稳定性,可以通过改变外加电压对结构稳定性进行控制。