An effective method for improving diffraction performance of magnetostatic backward volume wave-based magneto-optic Bragg cells by using an appropriately tilted bias magnetic field in YIG film plane

The universal magneto-optic (MO) coupled-mode equations for magnetostatic waves (MSWs) and guided optical waves (GOWs) under arbitrarily tilted bias magnetic fields are presented for the first time and, as an example, applied to the noncollinear Stokes interaction between the incident TE₀-mode light and magnetostatic backward volume wave (MSBVW) excited by single-element microstrip line transducer in yttrium–iron–garnet (YIG) film. Our calculation indicates that, for the case of magnetization parallel to the MSBVW propagation direction, the diffraction efficiency (DE) is equal to the mode-conversion efficiency of the diffracted lights (MCDE) and the calculated curve of relative DE for the MSBVW-based MO Bragg cell in pure YIG waveguide is in good agreement with the experimental data. In contrast, the diffraction performance can be greatly improved by optimizing the bias magnetic field and the DE gain can be increased by 6.3 dB in the tangentially magnetized film. The angular dependences of the DE and the corresponding Bragg angle upon the magnetization direction are also discussed in the paper.     

二元合金微观偏析的相场法数值模拟

使用耦合溶质场的相场模拟研究了Ni-Cu二元合金枝晶生长过程中固相溶质扩散系数D_s 对枝晶形貌和微观偏析等的影响.计算结果表明，随着D_s的减少，固液界 面前沿溶质扩散层越薄，枝晶生长越有利，枝晶尖端生长的速度越大，侧向分支越发达；D< sub>s越小，固相中溶质成分的波动越强烈，随着D_s的增大，固相中溶质 成分的波动相应减小；溶质微观偏析程度随D_s的增大而减小. 关键词： 相场方法 微观偏析 固相扩散系数 数值模拟     

Copolymerization of N‐vinylcaprolactam and glycidyl methacrylate: Reactivity ratio and composition control

Free‐radical copolymerizations of N‐vinylcaprolactam (VCL) and glycidyl methacrylate (GMA) were investigated to synthesize temperature‐responsive reactive copolymers with minimized compositional heterogeneity. The average copolymer composition was determined by Fourier transform infrared and nuclear magnetic resonance techniques. The reactivity ratios for VCL and GMA were found to be 0.0365 ± 0.0009 and 6.44 ± 0.36 by the Fineman–Ross method and 0.039 ± 0.006 and 6.75 ± 0.29 by the Kelen–Tudos method, respectively. When prepared by batch polymerization, VCL–GMA copolymers had a highly heterogeneous composition and fractions of different solubilities in water. The use of a gradual feeding technique, which included the sequential addition of more reactive GMA monomer into the reaction, yielded copolymers with much more homogeneous composition. The produced copolymers with 0.9 and 0.11 fractional GMA contents preserved their temperature‐responsive properties and precipitated from aqueous solutions when the temperature exceeded 31 °C. The GMA units in the VCL–GMA copolymers were capable of reacting with amino end‐functionalized poly(ethylene oxide) at room temperature to produce poly(N‐vinylcaprolactam)–poly(ethylene oxide) graft copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 183–191, 2006     

The energy exchange and the optimum length of the sample tube of opfirl

The energy exchange between the pumping laser and FIR signal in the optically pumped FIR laser (OPFIRL) system was studied. The iteration method has been used to calculate the power density of the pumping and FIR signals at any point along the optical axis of the sample tube. It was found that the power density of the FIR signal did not always increase along the length of the laser tube. There was a maximum FIR power density at the appropriate point in the sample tube. If the distance of maximum power point from the entrance of the OPFIRL tube was taken as the length of sample tube Z_opt, the maximum FIR laser output should be obtained. This was the optimum length of OPFIRL tube. The value of Z_opt was closely related to the parameter of OPFIRL such as the pumping power density, the pumping detuning and the frequency of the FIR laser. The energy-exchange and the maximum output of the fir laser were calculated under the ideal condition.     

半导体激光泵浦预激光锁模调Q固体激光器研究

报道半导体激光侧面泵浦预激光锁模调Ｑ的Ｎｄ：ＹＡＧ固体板条激光器，预激光锁模调Ｑ的激光脉冲宽度为３６ｐｓ，调Ｑ包纤各心的锁模单脉冲能量超过７μＪ，相应的峰值功率达２００ｋＷ。     

Interval parameter perturbation method for evaluating the bounds on natural frequencies of structures with interval parameters

For structural parameters with uncertainties, interval mathematics can, in the case where the probabilistic distribution density of uncertain variables is unavailable, deal with the influence of uncertainties in structural parameters on the response of structures. In order to evaluate the region containing natural frequencies of structures with interval parameters, the interval parameter perturbation method is presented in this paper. The advantage of the present method is its computational efficiency in evaluating the region containing natural frequencies. A numerical example is used to illustrate the efficiency of the method proposed. The project is supported by National Youth Natural Science Foundation of China and National Outstanding Youth Science Foundation of China.