演化参数反演方法

给出了一类基于演化计算的演化参数反演方法,此类方法既可以给定参数的函数类,用遗传算法（Genetic Algorithms）来反演参数的最优估计值,也可以不指定函数类形式,用遗传程序设计（Genetic Programming）的方法反演出最优的函数模型,使参数反演实现客观化、自动化.由此建立反演系统后,在使用过程中可以根据最新获得的数据对模型中的物理参数作适时校准,一旦发现预报误差较大,就利用演化算法及时修正方程中的参数以改进预报.运用该方法于椭圆边值问题的物理参数反演的数值模拟,证实了此方法的有效性,为物理模型参数的反演提供了一种崭新的实用方法.     

保参数方向的形状可调过渡曲线与曲面

针对保参数方向构造过渡曲线曲面方法的不足, 构造了任意参数曲线曲面间既保持参数方向又具有形状可调性的C¹与C²连续过渡曲线曲面。首先,基于2类带1个自由参数的调配函数,分别构造满足C¹与C²连续的过渡曲线,并讨论基于能量优化模型的最佳过渡曲线构造问题;然后,将所提出的方法推广到过渡曲面的构造。 实例结果表明,2被过渡曲线曲面为任意参数曲线曲面时,利用该方法构造的过渡曲线曲面不仅与2被过渡曲线曲面的参数方向保持一致,而且可利用所带的自由参数对其形状进行调整。通过能量优化模型确定自由参数的取值,可获得尽可能光顺的过渡曲线曲面。 所提方法弥补了保参数方向构造过渡曲线曲面方法的不足,是一种实用的过渡曲线曲面构造方法。     

基于移相法的光学玻璃应力等倾角全场数字化测量

提出了一种用四步移相法实现光学玻璃应力等倾角全场数字化测量的方法。用数码相机拍摄椭圆偏振光场转过不同角度时的四幅出射光强图像,根据移相法的原理计算出在0°～90°范围内的等倾角β。通过对具有典型应力分布的光学玻璃进行实验验证表明,计算结果与实际情况相符。     

螺旋轴流式多相泵流动参数设计值探讨

本文在对螺旋轴流式多相泵高速试验的基础上,通过三级多相泵输送性能情况来分析动态参数进口冲角、相对液流角和比转速在设计时对增压单元参数的影响,从而改进增压单元的设计,使多相泵能具有更好的输送性能。     

A simple model to extract hyperfine interaction distributions from Mössbauer spectra

The general problem of finding a distribution in hyperfine interaction parameters from experimental Mössbauer spectra is outlined. Existing methods may lack flexibility to be easily applicable to simple problems. A line shape for hyperfine parameter distributions is given, which is based on linear segments in the probability function. This method is applied in the analysis of samples containing iron in a silicate glass.     

基于三维成像技术的四轮定位参数建模方法

鉴于现有四轮定位仪参数求取方法误差大、参数项目少、对测量环境要求高等不足,提出了一种基于三维成像技术的四轮定位参数建模方法;该方法通过双摄像机对目标板拍摄获得的图像信息,应用空间向量方法,求取车体运动状态下的轮轴信息,动态建立四轮定位参数测量模型,解决测量平面的动态建立、测量平台的补偿等问题;经过零标定平台测试,当车轮旋转在18~22°时,定位参数求取方法正确有效,通过实车对比测量验证,平均误差小于0.07°。     

Collective bounce-off phenomenon in139La+Ag(Br) reaction at 1.1 A GeV energy

Out of a total statistics of 896¹³⁹La+Ag(Br) interactions, 128 interactions having multiplicity of target fragments (Z⩾1)⩾8 and projectile fragments (Z⩾2)⩾4 have been selected. They correspond to quasi-peripheral interactions. Azimuthal angle correlation between sources of target fragments (TFs) and projectile fragments (PFs) shows the existence of bounce-off effect. Using data of La+Ag(Br) and⁸⁴Kr+Ag(Br) reactions it is shown that individual helium [Z=2, PFs] and heavier fragment [Z⩾3, PFs] show different emission characteristics. Further, a two prong correlation functionT(Φ _ij ) plotted for heavier fragments and helium fragments separately, indicates the possibility of existence of different physical conditions. This observation is supported by the different momentum widths of helium fragments and heavier fragments. From the momentum width data of Kr+Ag(Br) reactions normalized density comes out to be ≈4.7. Using quasi-elastic kinematics for the bounce-off nuclei, the excitation energy has been computed from the experimental data of flow angles. The strength of bounce-off seems to decrease with the increase of excitation energy or temperature.     

Langevin dynamic simulation of hysteresis in a field-swept Landau potential

Numerical simulations are done of Langevin dynamics for a uniform-orderparameter, field-swept Landau model,= –|a/2|m ²+|b/4|m ⁴–mh(t) , to study hysteresis effects. The field is swept at a constant rateh(t)=h(0)+ht. The stochastic jump values of the field {h_J from an initially prepared metastable minimumm(0) are recorded, on passage to a global minimum m(). The results are: (a) The mean jump¯h _J(h) increases (hysteresis loop widens) with h, confirming a previous theoretical criterion based on rate competition between field-sweep and inverse mean first-passage time (FPT); (b) The broad jump distribution(h _J,h) is related to intrinsically large FPT fluctuations ( ²–²)/ ² O(1), and can be quantitatively understood. Possible experimental tests of the ideas are indicated.     

On the mechanism of the N,N‐dimethyl amination of Grignard reagents: a kinetic study

A direct kinetic study is reported for the electrophilic amination of substituted phenylmagnesium bromides with N,N‐dimethyl O‐(mesitylenesulfonyl)hydroxylamine in THF. Rate data, Hammett relationship, and activation entropy are consistent with a S_N2 displacement involving the attack of carbanions to sp³N in the amination reagent (AR). Copyright © 2007 John Wiley & Sons, Ltd.     

Improved surface morphology of flow-modulated MOVPE grown AIN on sapphire using thin medium-temperature AIN buffer layer

High-temperature (HT) AIN films were grown on (0 0 0 1) sapphire by low-pressure flow-modulated (FM) metal organic vapor phase epitaxy (MOVPE) with and without inserting a thin medium-temperature (MT) AIN layer. To suppress parasitic reactions between the sources of trimethylaluminum (TMA) and ammonia (NH₃), TMA and NH₃ was introduced to the reactor of MOVPE by alternating supply way. Surface morphology and crystalline quality were characterized by a scanning electronic microscopy (SEM), atomic force microscopy (AFM) and X-ray rocking curve (XRC) measurements of (0 0 0 2) and (10-12) diffractions. The AFM and SEM measurements indicated that the thin MT-AIN layer had a strong influence on the surface morphology of the HT-AIN films. The surface morphology became quite smooth by inserting the thin MT-AIN layer and surface RMS roughness values were 0.84 nm and 13.4 nm for the HT-AIN films with and without inserting the thin MT-AIN buffer layer, respectively. By etching the samples in aqueous KOH solution, it was found that the polarity of AIN films was different, the HT-AIN film with the thin MT-AIN layer could not be etched, indicating that the film had an Al-polar surface; however, the film without the MT-AIN layer was etched, which was explained that that film had a N- or mixed-polar surface. The mechanism for the origin of the different polarity of HT-AIN with and without the thin MT-AIN layer was proposed and discussed in detail.