基于奇异摄动法的水下机器人串-并联PID控制

针对串级PID控制应用于水下机器人位置、姿态控制时出现的收敛速度慢、抗扰动能力差等问题,提出一种基于奇异摄动法的串-并联PID控制方法.使用时标分解法得到水下机器人的快慢子系统模型,根据奇异摄动法设计串-并联PID控制.以自主设计的水下机器人为基础,使用最小二乘法测定水动力参数.通过仿真与实验证明串-并联PID控制具有...     

重粒子碰撞对霍尔推力器通道等离子体影响数值研究

为了研究重粒子碰撞对霍尔推力器通道等离子体影响,采用PIC/MCC/DSMC混合法对放电通道工作过程进行数值仿真研究。建立放电通道二维数值仿真模型,模型中对重粒子碰撞进行重点考虑。估算了通道内各粒子碰撞下的平均自由程,并针对重粒子碰撞单一变量开展了2个仿真模型计算,并对结果进行了对比分析及验证。结果表明:重粒子碰撞对通道内离子数密度分布影响较大,主要表现为离子数密度分布在电离区更为均匀,离子数密度峰值下降6.9%;离子轴向速度影响较小,出口处离子轴向平均速度下降1.3%。与实验结果对比验证,重粒子碰撞因素使仿真结果与测试值之间误差由9.0%缩小到7.3%。     

GPS scintillation and TEC gradients at equatorial latitudes in April 2006

We use observations of ionospheric scintillation at equatorial latitudes from two GPS receivers specially modified for recording, at a sampling rate of 50 Hz, the phase and the amplitude of the L1 signal and the Total Electron Content (TEC) from L1 and L2. The receivers, called GISTM (GPS Ionospheric Scintillation and TEC Monitor), are located in Vietnam (Hue, 16.4°N, 107.6°E; Hoc Mon, 10.9°N, 106.6°E). These experimental observations are analysed together with the tomographic reconstruction of the ionosphere produced by the Multi-Instrument Data Analysis System (MIDAS) for investigating the moderate geomagnetic storm which occurred on early April 2006, under low solar activity. The synergic adoption of the ionospheric imaging and of the GISTM measurements supports the identification of the scale-sizes of the ionospheric irregularities causing scintillations and helps the interpretation of the physical mechanisms generating or inhibiting the appearance of the equatorial F layer irregularities. In particular, our study attributes to the turning of the IMF (Interplanetary Magnetic Field) between northward and southward direction an important role in the inhibition of the generation of spread F irregularities resulting in a lack of scintillation enhancement in the post-sunset hours.     

Ariane 5 flight environments

This paper presents a status of the ARIANE 5 launch vehicle dynamic environments after the 5 first flights. It concerns mainly the low frequency vibrations, the acoustic and the shocks that the payloads experience and the related external excitations. The flight measurement plan is described. The results show that the frequencies are well characterized and the levels are low pointing out margins with regard to the specifications Furthermore, one describe the efficiency of attenuation solutions implemented to reduce the payload environments.     

企业HR管理的e化发展

企业的竞争实际上就是人才的竞争。信息技术为人力资源管理提供了发展的动力。电子人才资源，即eHR，是一种全新的人力资源管理模式，实际上指的是人力资源管理信息化的全面解决方案，是对传统HRMS在技术上与理念上的延伸，使HR部门从琐碎的行政事务中解脱，从而扮演一个战略性的角色，这一角色所经营的是企业最重要的资产：人才。     

CNES—the way forward: A new strategic plan

This article is based on the French space centre's (CNES) new strategic plan, which marks a shift in strategy. Guided in particular by changed political circumstances and the growing maturity of the space industry, the agency plans to renegotiate its relationships in all major sectors. While the inevitability of European integration and hence cooperation is acknowledged, there is a firm commitment to ensuring that French national and foreign policy is well served.     

Immunolocalization of an annexin-like protein in corn.

Although calcium has been proposed to be an important regulatory element in plant gravitropic growth, as yet no specific function of Ca2+ in growth regulation has been discovered. Our recent studies on a Ca(2+)-binding protein in pea seedlings called p35 indicate that it is a member of the annexin family of proteins and may play a key role in growth regulation through its function in delivering polysaccharides needed for wall construction. We previously reported the isolation of p35 from pea plumules and the production of polyclonal antibodies to it. Immunolocalizaton analyses of p35 in pea tissues revealed high levels of staining in secretory cell types such as developing vascular cells and outer root cap cells. To test how general was the occurrence and distribution of this annexin-like protein in plant cells we initiated an analysis of annexins in the monocot corn using immunological techniques. Our results indicate the immunochemical properties and localization of corn annexins are very similar to those reported for pea. They are consistent with the postulate that annexins may play a general role in the regulation of the secretion of wall polysaccharides needed for growth, and thus could be an important target of calcium action during gravitropic growth.