舵叶固定式液压球形关节运动学及性能分析

针对球面运动机构驱动方式问题,提出了一种新型的二自由度液压驱动球面运动关节机构,该机构利用超全周转动马达及舵叶摆动马达作为驱动,采用了滑轨支撑框架位置测量系统,可以实现超全周转动;给出了两驱动马达各自的油路设计方案,在机构的不同部位采取了合理的密封方法;由机构的工作原理推导了正逆运动学方程及速度雅可比矩阵,得出了机构的奇异位形;分析了机构的灵巧度性能指标,通过仿真得到了机构性能较优时的工作空间.该球形关节机构具有结构紧凑、运动精度高、负载大、并且能够实现全方位输出的特点.     

本科秘书学概论教材建设探析

当前秘书学概论教材存在诸多不足。只有从端正教材编写态度、正确认识秘书学概论课程的地位和作用、明确学生就业实际出发,通过加强社会、学校、学生调研,统筹规划秘书学概论教学内容．创新教材叙述模式,加强教材多样化、立体化建设等途径,才能提高教材质量。     

A simple model to predict solar radiation under clear sky conditions

Solar radiation is one of the major factors that dominate the thermal behaviors of aerostats in the daytime and the primary energy source of high altitude long endurance aerostats. Therefore, it is necessary to propose an accurate model to predict the solar irradiances. A comprehensive review of the well-known solar radiation models is conducted to help develop the new model. Based on the analysis of the existing models and the available radiation data, the extensive computer tests of the regression and optimization are conducted, from which the new solar radiation model for direct and diffuse irradiances under clear sky conditions is proposed. The new model has excellent prediction accuracy. The coefficient of determination for direct radiation is 0.992, with the root mean square error (RMSE) of 16.9 W/m² and the mean absolute error (MAE) of 2.2%. The coefficient of determination for diffuse radiation is 0.86, with RMSE = 8.7 W/m² and MAE = 9.9%. Comparisons with the well-known existing models show that the new model is much more accurate than the best existing ones.     

The application of micro-CT in monitoring bone alterations in tail-suspended rats in vivo

Osteopenia is a pathological process that affects human skeletal health not only on earth but also in long-time spaceflight. Micro-computed tomography (micro-CT) is a nondestructive method for assessing both bone quantity and bone quality. To investigate the characteristics of micro-CT on evaluating the microgravity-induced osteopenia (e.g. early detection time and the sensitive parameters), the bone loss process of tail-suspended rats was monitored by micro-CT in this study. 8-Week-old female Sprague Dawley rats were divided into two groups: tail suspension (TS) and control (CON). Volumetric bone mineral density (vBMD) and microstructure of the femur and tibia were evaluated in vivo by micro-CT at 0, 7, 14, 22 days. Biomechanical properties of the femur and tibia were determined by three-point bending test. The ash weight of bone was also investigated. The results showed that (1) bone loss in the proximal tibia appeared earlier than in the distal femur. (2) On day 7, the percent bone volume (BV/TV) of the tibia 15.44% decreased significantly, and the trabecular separation (Tb.Sp) 30.29% increased significantly in TS group, both of which were detected earlier than other parameters. (3) Biomechanical properties (e.g. femur, −22.4% maximum load and −23.75% Young’s modulus vs. CON) and ash weight of the femur and tibia decreased significantly in the TS group in comparison to CON group. (4) vBMD of the femur and tibia were clearly related to bone ash and dry weight (r = 0.75–0.87, p < 0.05). (5) BV/TV of both femur and tibia were clearly related to maximum load and Young’s modulus (r = 0.66–0.87, p < 0.05). Similarly, trabecular vBMD and BV/TV of the femur and tibia were clearly related to Young’s modulus (r = 0.73–0.89, p < 0.05). These indicated that BV/TV and Tb.Sp were more sensitive than other parameters for evaluating bone loss induced by tail suspension, moreover, trabecular vBMD and other parameters might be used to evaluate bone strength. Therefore, micro-CT is a reliable and sensitive method for predicting unloading-induced bone loss in small animals.     

多星近距离绕飞观测任务姿轨耦合控制研究

针对多星近距离绕飞观测任务,建立了相对姿态轨道动力学模型,分别考虑了在椭圆、空间圆绕飞轨道上观测卫星的两种期望三角形编队构型,以观测卫星视线始终指向目标为期望姿态,采用基于四元数和角速度误差反馈的比例 微分控制律以及一种改进的基于人工势场法的制导方法相结合,对相对姿态及轨道进行控制。仿真结果表明：在控制律的作用下,绕飞过程中各观测卫星均能够有效地跟踪期望相对姿态和期望相对轨道;在空间圆绕飞轨道构型中,各观测卫星从初始同一位置出发后,在任意时刻3颗观测卫星构成的编队构型始终为正三角形,且正三角形的边长从零逐渐增大,最终等于期望正三角形构型的边长。     

An attempt to inverse the ionospheric sporadic-E layer critical frequency based on the COSMIC radio occultation data

Ionospheric sporadic E layer refers to localized thin irregularity with enhanced plasma density appearing in the height range of ionospheric E layer (～90–130?km). The much higher electron density in the sporadic E layer than the background ionosphere would cause sudden TEC enhancement in the occultation TEC profile. A wavelet decomposition and reconstruction method is applied to extract the TEC fluctuation in this paper, and then $S_{\text{max}}$ index is defined to represent the intensity of the sudden TEC enhancement. $S_{\text{max}}$ index is compared with sporadic E critical frequency ($\mathit{foEs}$) observed by the ionosonde. The results show a well linear correlation between them with mean correlation coefficient about 0.7. Thus, an empirical linear model is established to inverse the $\mathit{foEs}$. The monthly/hourly mean values and global distribution of sporadic E intensity and occurrence ratio are calculated using this method based on the COSMIC occultation data from 2007 to 2011. The statistical analysis results indicate that it is feasible to inverse the $\mathit{foEs}$ based on the occultation TEC profile data and the inversion results can be applied to the long-term global variations of sporadic E investigations.     

转动惯量存在不确定性的挠性航天器动态自适应滑模姿态控制

针对存在转动惯量不确定性和外部干扰的挠性航天器,首先构造了一个部分状态观测器估计挠性模态,然后设计自适应律对转动惯量不确定性和外部干扰组成的函数的上界进行估计。最后,在设计的观测器和自适应律的基础上,建立了挠性航天器的基于部分状态观测器的自适应滑模姿态稳定控制律。采用Lyapunov方法证明了在挠性航天器存在转动惯量不确定性和外部干扰时, 所设计的自适应滑模姿态控制律能使闭环航天器姿态系统稳定。最后, 通过数值仿真例子验证了所提出方法的有效性。     

基于夏氏最小二乘的轨道控制力系数辨识

在航天器轨道捕获、轨道维持和空间目标碰撞规避中都需要进行航天器轨道机动。针对航天器轨道机动过程中推力器的推力系数为装订常数,没有根据在轨工作实际进行优化而导致出现较大误差的情况,对控制力拟合系数进行辨识,作为修正控制参数以补偿轨道控制误差的依据,提高轨道控制精度。统计分析在轨管理的典型航天器平台及其发动机的轨道控制历史数据,分析轨道控制理论和在轨控制数据拟合建立轨道控制经验模型,用当前可测量的系统输入和输出预测系统输出的未来演变,得到不同工作情况下实际轨道控制误差与控制参数及其他主要影响因素之间关系的经验公式,为轨道控制策略决策提供参考。选取轨道半长轴控制量300m以上和300m以下的两类近地卫星,对其轨道控制历史数据进行分析,经实际数据测试,采用夏氏法进行推力系数拟合后预测的速度变化量精度较高。该种计算方法利用了轨道控制历史数据,计算方法简单,提高了轨道控制速度增量的预测精度,对轨道控制实施具有参考意义。     

基于UDP的端对端通讯的原理及实现

通过探索网络地址转换设备在进行UDP (User Datagram Protocol) 端口映射所存在的临时时间窗口,论述了使用UDP穿透网络地址转换设备的原理.引入检测及握手服务器及其所实现的数据包反射服务,来检测动态映射的端口信息以及网络地址转换设备在进行端口映射的特性.探讨了不同类型的网络地址转换设备对这种实现的影响,给出了检测过程以及建立端对端通讯过程的具体流程.这种实现可被广泛应用在IP语音、实时视频、文件共享以及分布式计算等应用中.     

基于CCD和超声的物体位姿检测方法及精度分析

介绍了用单个CCD摄像机和超声传感器相结合检测物体位姿的方法.首先由CCD摄像机采集一幅图像,获取物体上目标点在图像坐标系中的理想坐标,并由此确定该点投影矢量(连接物体点和对应图像点的直线)的方向;然后控制机器人运动,使超声传感器的z轴与求得的投影矢量重合;最后用超声传感器测出投影矢量的长度,确定目标点在摄像机坐标系中的坐标.分析了影响检测精度的主要因素,具体研究了超声传感器的安装参数对检测精度的影响规律,进行了仿真分析.该方法可以有效地降低图像处理所带来的巨大数据量,避开双目视觉中的图像匹配问题,快捷、精确检测物体的位姿.