Growth of Nd:GdVO4 Single Crystal and its Laser Output at 1062 nm,1342 nm

A new liquid‐phase method synthesizing Nd:GdVO₄ polycrystalline materials was introduced. High optical quality Nd:GdVO₄ single crystals have been successfully grown by the Czochralski method. The effective segregation coefficients of Nd ion in Nd:GdVO₄ crystal have been measured and discussed. Laser outputs at 1.06 μm and at 1.34 μm were achieved when Nd:GdVO₄ crystal samples of 0.52 at% Nd concentration were pumped by a high‐power LD. A maximum output of 14.5 W at 1.06 μm has been obtained when the pump power is to 26 W, giving the slope efficiency of 63%. It is reported the first time that up to 4.64 W power laser at 1.34 μm has been achieved with optical conversion efficiency of 31.4% and slope efficiency of 32.9%.     

基于小波-Galerkin方法的结构随机动力响应功率谱的确定

在最近发展的周期广义谐和小波PGHW(Periodic Generalized Harmonic Wavelet)的基础上,通过小波-Galerkin方法推导得到了线性单自由度结构的随机动力响应功率谱密度。在此过程中,利用PGHW的解析形式及其在频域内的特殊性:(1)推导得出了PGHW的联系系数(Connection Coefficient)的解析形式;(2)基于PGHW及其联系系数,利用小波-Galerkin方法推导得到了线性单自由度系统在确定性激励下的响应;(3)得到了在具有演变功率谱的随机动力激励下单自由度线性振子的随机响应功率谱解答。数值算例表明,无论是确定性响应解答,还是随机动力响应的功率谱密度,小波-Galerkin法的计算结果均能较好地吻合数值解。     

一类不确定双线性系统的状态反馈Robust控制*

本文针对一类含不确定性的双线性系统设计了一种线性状态反馈控制.在一定的条件下,利用改进的李雅普诺夫第二方法关于稳定性的理论,证明了系统的稳定性.并给出例子说明.     

带电粒子光学系统优化问题的研究

对带电粒子光学系统的优化过程进行了研究,提出将象差的优化与透镜场形的优化分离开来。在象差的优化中考虑含光学参数的隐式约束条件。该优化过程只需做简单的积分运算,因此不必花费时间计算电磁场。在透镜场形的优化中,其优化模型与一般电磁系统的优化完全一样,因而可以采用已经研究的很多的电磁场的优化方法来优化透镜的场形。计算了两个优化的实例。     

Free‐Radical Propagation Rate Coefficients via n‐Pulse Periodic Polymerization

Aspects of applying n‐pulse periodic initiation in pulsed laser polymerization/size‐exclusion chromatography (PLP/SEC) experiments are studied via simulation of molecular weight distributions (MWDs). In n‐pulse periodic PLP/SEC, sequences of n laser pulses at successive time intervals Δt₁ up to Δt_n are periodically applied. With the dark time intervals being suitably chosen, n‐modal MWDs with n well separated peaks occur. The n‐pulse periodic PLP/SEC method has the potential for providing accurate propagation rate coefficients, k_p. Among several measures for k_p, the differences in molecular weights at the MWD peak positions yield the best estimate of k_p under conditions of medium and high pulse laser‐induced free‐radical concentration. Deducing k_p from n dark time intervals (corresponding to n regions of free‐radical chain length) within one experiment at otherwise identical PLP/SEC conditions allows addressing in more detail a potential chain‐length dependence of k_p. Simulations are compared with experimental data for 2‐pulse periodic polymerization of methyl methacrylate.

Measured MWD (solid line) and associated first derivative curve (dotted line) for a 2‐pulse periodic bulk polymerization experiment of MMA at 20 °C.     

Dynamics of Bond‐Fluctuation Model Chains in Good and Theta Solvents

The dynamic Monte Carlo algorithm is employed to explore the dynamics of flexible linear chains. The chains are represented by the bond‐fluctuation model with and without attractions between non‐bonded units placed at close distances. This mimics the behavior of real chains in the good and poorer solvents. We obtain the chain sizes, diffusion coefficients, Rouse modes, and their relaxation times. We also evaluate the time correlation function of the end‐to‐end vector at different concentrations. Subsequently, we compare the dependence of the simulation results on chain length, solvent quality, concentration, and mode order with the corresponding theoretical predictions. We observe a retardation of diffusion for non‐dilute systems close to the theta state. This retardation is too high to be exclusively attributed to the increase of global friction and can be caused by temporary adherence of the chains to transient clusters.     

类镍金离子的双电子复合速率系数

 在自旋轨道劈裂阵模型下, 理论计算在0.02keV≤T≤10keV范围内,类镍金Au⁵¹⁺的3d⁹nln''l''(n''=4,5,6; l''=s,p,d,f)双电子复合速率系数,并分析了影响双电子复合速率系数的主要因素。     

Stress in transversely isotropic half-space with typical loads acting on its surface

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Use of experiment and an inverse method to study interface heat transfer during solidification in the investment casting process

A technique to determine the thermal boundary conditions existing during the solidification of metallic alloys in the investment casting process is presented. Quantitative information about these conditions is needed so that numerical models of heat transfer in this process produce accurate results. In particular, the variation of the boundary conditions both spatially and temporally must be known. The method used involves the application of a new inverse heat conduction method to thermal data recorded during laboratory experiments of aluminium alloy solidification in investment casting shell moulds. The resultant heat transfer coefficient for the alloy/mould interface is calculated. An experimental programme to determine requisite mould thermal properties was also undertaken. It was observed that there is significant variation of the alloy/mould heat transfer coefficient during solidification. It is found to be highly dependent on the alloy type and on the vertical position below the initial free surface of the liquid metal. The aluminium casting alloys used in this study were 413, A356, 319 (Aluminum Association designations), and commercially pure aluminium. These alloys have significantly different freezing ranges. In particular, it was found that alloys with a high freezing range solidify with rates of heat transfer to the mould which are very sensitive to metallostatic head.     

Positron Emission Tomography and Random Coefficients Regression

We further explore the relation between random coefficients regression (RCR) and computerized tomography. Recently, Beran et al. (1996, Ann. Statist., 24, 2569–2592) explored this connection to derive an estimation method for the non-parametric RCR problem which is closely related to image reconstruction methods in X-ray computerized tomography. In this paper we emphasize the close connection of the RCR problem with positron emission tomography (PET). Specifically, we show that the RCR problem can be viewed as an idealized (continuous) version of a PET experiment, by demonstrating that the nonparametric likelihood of the RCR problem is equivalent to that of a specific PET experiment. Consequently, methods independently developed for either of the two problems can be adapted from one problem to the other. To demonstrate the close relation between the two problems we use the estimation method of Beran, Feuerverger and Hall for image reconstruction in PET.