A fast-settling frequency-presetting PLL frequency synthesizer with process variation compensation and spur reduction

This paper proposes a fast-settling frequency-presetting PLL frequency synthesizer. A mixed-signal VCO and a digital processor are developed to accurately preset the frequency of VCO and greatly reduce the settling time. An auxiliary tuning loop is introduced in order to reduce reference spur caused by leakage current. The digital processor can automatically compensate presetting frequency variation with process and temperature, and control the operation of the auxiliary tuning loop. A 1.2 GHz integer-N synthesizer with 1 MHz reference input Was implemented in a 0.18μm process. The measured results demonstrate that the typical settling time of the synthesizer is less than 3μs,and the phase noise is -108 dBc/Hz@1MHz.The reference spur is -52 dBc.

指标约简中Gear算法的实现

基于组件的建模有时会产生高指标的微分代数方程(DAE),不能直接求解,需要进行指标约简。Gear方法是一个经典的指标约简方法,对Gear方法从理论上进行了说明和分析。对于一类具有特殊结构的DAE,提出了Gear方法实现中的优化策略,以降低指标约简后得到的方程规模。把优化后的实现与未优化的实现进行了比对,实验结果表明,优化过的实现方法针对这类特殊的问题确实达到了更好的约简效果。

带压电陶瓷片梁的力学分析和二类变量广义变分原理

对于采用贴有压电陶瓷片作为作动元件的智能结构，在进行自适应控制时，往往要分析压电陶瓷片所引起的结构中的应力、应变和位移。对于带有压电陶瓷片梁的力学分析，文献中大多采用Euler-Bernoulli模型，即不考虑梁中的剪力，且假定梁沿厚度方向满足直法线假定。考虑到压电陶瓷片对梁的作用主要是通过粘贴层以剪力的形式传递到梁上，梁截面上的剪应力和剪应变一般很大，其影响不能忽略。本文采用Hellinger-Reissner二类变分广义余能原理，导出考虑梁截面上剪应力和剪应变影响的方程式，其中采用吉尔法求解非齐次常微分方程组。并将求得的解与相同条件的有限元解进行比较。结果证明该方法很有效。本文还对二类广义变分法进行了一般的讨论，发现，在使用二类广义变分法求解时，随着应力和位移所取项数的增加，结果有时反而变坏。并对二类广义变分法的使用提出了一些建议。

MDT三维工具集在齿轮造型与分析中的应用

通过MDT三维工具集方便地实现了直齿轮的造型，重点说明了用基于特征造型的方法在MDT环境下实现斜齿轮造型的详细过程，并用MDT的有限元分析功能对齿轮的受力善进行了分析。整个过程在MDT的集成环境下完成，对齿轮的工程设计具有较高的实用价值。

Population status, threats and conservation of the Yangtze finless porpoise

The Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) is currently limited to the middle and lower reaches of the Yangtze River from Yichang to Shanghai, China, and the adjoining Poyang and Dongting Lakes. Its population size has decreased remarkably during the last several decades due to the heavy impact of human activities, including overfishing of prey species, water development projects that cause attendant habitat loss and degradation, water pollution, and accidental deaths caused by harmful fishing gear and collisions with motorized vessels. It was estimated that the number of remaining individuals was down to approximately 1800 in 2006, a number that is decreasing at a rate as high as 5% per year. Three conservation measures - in situ and ex situ conservation and captive breeding have been applied to the protection of this unique porpoise since the early 1990s. Seven natural and two "semi-natural" reserves have so far been established. Since 1996, a small group of finless porpoises has been successfully reared in a facility at the Institute of Hydrobiology of the Chinese Academy of Sciences; three babies were born in captivity on July 5, 2005, June 2, 2007 and July 5, 2008. These are the first freshwater cetaceans ever born in captivity in the world. Several groups of these porpoises caught in the main stream of the Yangtze River, or rescued, have been introduced into the Tian'e-Zhou Semi-natural Reserve since 1990. These efforts have proven that, not only can these animals survive in the area, they are also to reproduce naturally and successfully. More than 30 calves had been born in the reserve since then, with one to three born each year. Taking deaths and transfers into account, there were approximately 30 individuals living in the reserve as of the end of 2007. Among eight mature females captured in April 2008, five were confirmed pregnant. This effort represents the first successful attempt at off-site protection of a cetacean species in the world, and establishes a solid base for conservation of the Yangtze finless porpoise. A lesson must be drawn from the tragedy of Chinese River Dolphin (Lipotes vexillifer), which has already been declared likely extinct. Strong, effective and appropriate protective measures must be carried out quickly to prevent the Yangtze finless porpoise from becoming a second Chinese River Dolphin, and save the biodiversity of the Yangtze River as a whole.

DAE系统中两类指标约简修正算法的研究与实现

为了应对设计复杂产品的需求，研究者们提出了一些面向对象、基于组件的建模语言，比如说Modelica 语言。Modelica语言建模中采用了分治的思想，将大型的系统划分成一系列小型组件，极大程度地提高了模型复用性，简化了建模的过程。 Modelica语言构建的模型往往会被转化成一个DAE方程组。在一些情况中，这个DAE是指标数大于1的高指标问题。由于目前对高指标问题不存在通用的求解器，为了求解这类问题，通常的方法是先对问题进行指标约简。 指标约简有两类主流的方法，一类基于微分指标，如Gear算法；另一类基于结构指标，如Pantelides和哑导方法。Gear方法是解决一般高指标问题最为经典的方法，对它的研究和深入分析意义重大。在本文的第一部分，作者提出了一种Gear方法的修正实现。实验结果表明，对于一类特殊结构的DAE，修正实现比起经典实现做了更少的微分，最终得到了规模更小的方程组。 本文另一部分工作集中在对结构指标修正的方面。相比Gear算法，基于结构指标的指标约简算法是一类快速算法，但是并非百分之百有效。在少数情况下，当微分指标与结构指标不一致时，这类方法会失效。为了提高结构指标的适用性，必须首先消除这种不一致性。因此，作者深入分析了处理这一问题的组合松弛型算法，并做出了相应的实现。利用组合松弛型算法，作者进一步对几个Modelica模型导出的DAE方程组进行了处理。实验结果表明，作者所实现的算法解决了微分指标与结构指标不一致的问题。

A study on water film in saturated sand

Water film can serve as a sliding surface and cause landslides on gentle slopes. The development of "water film" in saturated sand is analyzed numerically and theoretically based on a quasi-three-phase model. It is shown that stable water films initiate and grow if the choking state (where the fluid velocity decreases to near zero) remains steady in a liquefied sand column. Discontinuity can occur in pore water velocity, grain velocity and pore pressure after the initiation of a water film. However, the discontinuity and water film can disappear once the choking state is changed. The key to the formation of water film is the choking in the sand column caused by eroded fine grains.

地下滴灌埋管深度对冬小麦根冠生长及水分利用效率的影响

在试验室内 ,进行了地下滴灌埋管深度对不同生育时期冬小麦根系生长和地上部分生长影响的试验研究。结果表明 :2 0 cm和 4 0 cm埋管深度的水分分布特征 ,在生育早期抑制地上部分营养生长 ,促进冬小麦蹲苗 ;而中后期则促进生殖生长 ,产量和水分利用效率较高。不考虑犁底层影响时 ,在重壤土上 4 0 cm是冬小麦进行地下滴灌的较好埋深

一种轮足复合式爬壁机器人机构建模与分析

基于行星轮系运动及双足真空吸附原理,提出了一种新型爬壁机器人机构,介绍了机构的构型及结构特点,推导了运动学方程,分析了沿直线行走、平面旋转和跨越交叉壁面三种运动模式.仿真结果表明该机构具有移动速度快、运动灵活、跨越交叉壁面能力强等特点.

基于SolidWorks斜齿轮、蜗轮三维建模的研究

详细阐述利用VB6.0进行SolidWorks二次开发的关键技术,论述斜齿轮的三维参数化建模系统开发的具体过程,对比了不同建模方法的特点,提出齿轮三维建模误差分析的两种方法,为模型应用提供了理论指导,同时对该研究方法的拓展性应用举出实例,给出用VB开发SolidWorks一般方法。

基于加速度传感器反馈控制的谐波驱动系统的研究

在机器人驱动中经常采用谐波传动。但谐波减速器的柔性、非线性摩擦、随速度波动、低阻尼等因素会给负载端带来振动 ,导致工作端的轨迹跟踪精度不高。为了抑制其振动 ,实现高精度轨迹跟踪控制 ,提出利用加速度传感器反馈控制来抑制负载端的振动、力矩干扰和动力学效应 ,提高其响应性能。理论分析和实验结果证实了提出方法的可行性。