Finite-time control for nonlinear spacecraft attitude based on terminal sliding mode technique

In this paper, a fast terminal sliding mode control (FTSMC) scheme with double closed loops is proposed for the spacecraft attitude control. The FTSMC laws are included both in an inner control loop and an outer control loop. Firstly, a fast terminal sliding surface (FTSS) is constructed, which can drive the inner loop tracking-error and the outer loop tracking-error on the FTSS to converge to zero in finite time. Secondly, FTSMC strategy is designed by using Lyaponov's method for ensuring the occurrence of the sliding motion in finite time, which can hold the character of fast transient response and improve the tracking accuracy. It is proved that FTSMC can guarantee the convergence of tracking-error in both approaching and sliding mode surface. Finally, simulation results demonstrate the effectiveness of the proposed control scheme.     

摩擦阻尼器支撑刚度对结构耗能特征的影响

根据双板型摩擦阻尼器的结构特点,分析了该摩擦阻尼器的工作特性,建立了使用该摩擦阻尼器的结构动力方程,并从实际结构各层摩擦阻尼器的支撑刚度出发,计算讨论了由摩擦阻尼器支撑刚度与结构层间刚度关系的不同导致的摩擦阻尼器耗能特性的差异,由此得出摩擦阻尼器的支撑刚度与结构层间刚度之间的关系对结构响应的影响,探讨了摩擦阻尼器支撑刚度与结构层间刚度之间的关系对实际结构各层摩擦阻尼器滞回特性和地震时程响应的影响,提出如何改变摩擦阻尼器的支撑刚度以使各层摩擦阻尼器耗能特性最佳的解决方案。     

基于二阶滑模观测器的永磁同步电机无位置传感器控制

为了准确估计永磁同步电机的转子位置与速度,提出一种二阶滑模观测器.该观测器在传统线性滑模面基础上引入了混合非奇异终端滑模面,避免了常规滑模观测器由于低通滤波所产生的相位滞后问题,同时可以提高转子位置与速度的估算精度.为了保证观测器的稳定并抑制滑模固有的抖振现象,设计了滑模控制律.最后,采用具有锁相功能的转子位置与速度跟踪算法从观测的反电动势中解调出转子位置和速度信息.仿真和实验证明了所提观测器的正确性.     

Macrofabrication with Digital Materials: Robotic Assembly

Rapid-prototyping processes are being extended to increasingly large scales, including 3D printing from gantries, and robotic arms for cutting, milling and winding. These all use designs that are digital, but materials that are not: they are continuously deposited or removed. Neil Gershenfeld, Matthew Carney, Benjamin Jenett, Sam Calisch and Spencer Wilson of the MIT Center for Bits and Atoms explore the implications of the use of digital materials, reversibly assembled from a discrete set of parts with a discrete set of relative positions and orientations, for applications on scales ranging from aerostructures to geoprinting. Here, they discuss the production of the parts, the modelling of structures made with them, and their automated assembly.     

Probing the Substrate Requirements of the In Vitro Geranylation Activity of Selenouridine Synthase (SelU)

Natural RNA modifications diversify the structures and functions of existing nucleic acid building blocks. Geranyl is one of the most hydrophobic groups recently identified in bacterial tRNAs. Selenouridine synthase (SelU, also called mnmH) is an enzyme with a dual activity which catalyzes selenation and geranylation in tRNAs containing 2-thiouridine using selenophosphate or geranyl-pyrophosphate as cofactors. In this study, we explored the in vitro geranylation process of tRNA anticodon stem loops (ASL) mediated by SelU and showed that the geranylation activity was abolished when U₃₅ was mutated to A₃₅ (ASL-tRNA^Lys_(s2U)UU to ASL-tRNA^Ile_(s2U)AU). By examining the SelU cofactor geranyl-pyrophosphate (gePP) and its analogues, we found that only the geranyl group, but not dimethylallyl- and farnesyl-pyrophosphate with either shorter or longer terpene chains, could be incorporated into ASL. The degree of tRNA geranylation in the end-point analysis for SelU follows the order of ASL^Lys_(s2UUU) ASL^Gln_(s2UUG)>ASL^Glu_(s2UUC). These findings suggest a putative mechanism for substrate discrimination by SelU and reveal key factors that might influence its enzymatic activity. Given that SelU plays an important role in bacterial translation systems, inhibiting this enzyme and targeting its geranylation and selenation pathways could be exploited as a promising strategy to develop SelU-based antibiotics.     

基于适应型Petri网的多环电陬方向保护简单回路拓扑分析

为了减少复杂环网方向保护整定计算中有向简单回路形成的复杂性。对双回线支路进行处理．使得简单回路计算规模得到预先缩小。考察网络实时拓扑分析的动态特性。运用适应型Petfi网推理系统拓扑结构．将复杂系统的网络分解为若干基本分析单元。描述了一个由保护开关状态变化引起网络关联节点变迁的离散事件动态过程。通过对电网节点支路关联信息进行推理．得到约简有向简单回路矩阵。通过实际算例仿真．建立模型，分析该方法的拓扑机理。计算结果与传统算法一致．验证所提方法的有效性，得出该方法计算准确、过程简便且易于实现的结论。