稳定高质量光参量啁啾脉冲放大系统优化设计

要实现光参量啁啾脉冲放大（OPCPA）系统稳定、高质量输出,需要同时对光参量放大和泵浦光倍频这两个非线性过程进行优化设计。在光参量放大系统优化设计中,建立了描述光参量放大过程的多种简化物理模型;通过模拟泵浦光和信号光口径匹配关系,分析了放大信号光空间两维对称性并提出了优化方法;建立了非线性晶体最佳长度确定及调谐方法,以实现信号光输出高稳定性。在泵浦光倍频系统优化设计过程中,提出应用位相失配法实现稳定倍频输出,研究表明这种方法不仅能实现倍频光能量起伏抖动远远小于基频光能量的起伏抖动,而且能减小泵浦光近场调制度和时间波形调制,极大地改善输出倍频光光束质量,进而提高OPCPA系统输出信号光质量。     

Numerical simulation based on two-directional freeze and thaw algorithm for thermal diffusion model

Freeze-thaw processes significantly modulate hydraulic and thermal characteristics of soil. The changes in the frost and thaw fronts (FTFs) affect the water and energy cycles between the land surface and the atmosphere. Thus, the frozen soil comprising permafrost and seasonally frozen soil has important effects on the land surface hydrology in cold regions. In this study, a two-directional freeze and thaw algorithm is incorporated into a thermal diffusion equation for simulating FTFs. A local adaptive variable-grid method is used to discretize the model. Sensitivity tests demonstrate that the method is stable and FTFs can be tracked continuously. The FTFs and soil temperature at the Qinghai-Tibet Plateau D66 site are simulated hourly from September 1, 1997 to September 22, 1998. The results show that the incorporated model performs much better in the soil temperature simulation than the original thermal diffusion equation, showing potential applications of the method in land-surface process modeling.     

The design of adaptive sigma-delta A/D converter

The signal to noise ratio （SNR） of conventional sigma delta analog to digital converter （∑△ADC） reduces with input signal strength. The existing concept of adaptive quantization is applied to the design of ∑△ADC to improve SNR with high dynamic range. An adaptive algorithm and its circuit implementation is proposed. Because of the error due to the circuit implementation, an error self-calibration circuit is also designed. Simulation results indicate that SNR can he nearly independent of the signal strength.     

Substituent effects in the zinc(II) coordination chemistry of isomeric pyridylpyrazole ligands

Abstract

Pyrazoles with unsymmetric substitution are useful ligands in coordination chemistry, but are under-developed due to synthetic challenges in accessing the pure isomers. We have prepared four new structurally related N-(2-pyridyl)-3,5-dialkylpyrazole ligands, L1–L4, and probed their coordination chemistry in the crystalline phase and in solution to elucidate a relationship between steric influence of the alkyl substituents, the stability of the subsequent metal complexes, and their crystal packing influences. We find that L1 and L2, bearing linear or branched alkyl substituents, show similar stabilities and crystal packing motifs featuring π···π and C-H···Cl interactions in the crystalline complexes 1 and 2, respectively. The cyclohexyl-fused species L3 and L4 vary both in the solution stability of complexes 3 and 4, respectively, and in their crystal packing. Complex [ZnCl₂(L3)] (3) is a mononuclear complex similar to 1 and 2, albeit with π···π interactions disallowed by the bulk of the cyclohexyl ring. Reaction of isomeric L4 with ZnCl₂ gives two polymorphic complexes, 4α and 4β, of the form [Zn₂Cl₂(μ₂-Cl)₂(L4)₂], varying only in their long-range packing modes. These results show the importance of understanding the steric influences in substituted pyridylpyrazoles, which determine both stability in solution and speciation in the crystalline phase.     

基于舒适性的软土地区公路行驶质量评价方法

针对软土地基公路工后沉降大、分布范围广,现有国际平整度指数IRI评价方法存在很大局限性的问题,提出了基于行车舒适性的软土地区公路行驶质量评价方法.首先采用五自由度1/2车辆模型,计算比较了道路纵面线形拟合方法和数据间距对车辆振动加速度计算结果的影响,获得了车辆振动的加权加速度均方根值;根据ISO2631振动舒适性标准提出评价司乘人员的舒适性DCI和RQI计算公式及参数取值;结合软土地基及非软土地基两种路段沉降情况,比较了本文方法与国际平整度指数IRI方法评价结果的区别.分析发现,在非软土地基公路,本文方法与IRI方法评价结果接近;而在软土地基公路,两者的结果差异较大,本文方法更加符合工程师的直观感觉.     

电路元件的映射理论（1）—基本变量的映射

本文提出了理想电路元件的映射理论，阐明了电路元件的一系列新概念和新定义，提出了研究电路问题的“网络观”和“端口观”。根据电路元件的映射理论，着重研究了电路基本变量的映射。     

流动图象的自动识别和分析

本文应用数字图象处理技术，判读流场示综粒子迹线照片．从而给出瞬时二维流场速度分布，为了保证足够的信息量，即迹线条款，图象处理技术中除必须有自动识别单条迹线位置、大小、方向的能力外，还必须有判别出多条迹线粘连的能力，最后由流场速度分布可以得到流函数等其它物理量。     

动态电路故障诊断的理论和算法

本文研究具有动态元件的模拟电路的故障诊断理论和方法，在作用提出的故障诊断方程的基础上，基于一种新的雅可比矩阵计算方法和迭代算法，把一般性的故障诊断理论引伸到动态模拟电路的领域。     

增量网络理论与网络的故障定位

本文提出了包括若干定理的增量网络理论，并以此理论来处理模拟电路故障诊断的定位问题．当代集成电路的重要特征是含有各种受控电源．本文着重研究含有受控源的模拟电路故障诊断，并得出了相应的结论．     

模拟电路故障诊断的一种方程及其可解性

本文提出了一种故障诊断的非线性方程，该方法能对模拟电路内部故障与电路外部端口测量值建立映射关系。