Nonsmooth stabilization of a class of nonlinear cascaded systems

A global nonsmooth stabilization scheme is presented for a class of nonlinear cascaded systems with uncontrollable linearization. A stepwise constructive control methodology is proposed for the driving subsystem by using the adding a power integrator technique. Under suitable conditions and based on homogeneous properties, it is proved that the stabilization of the driving subsystem implies the stabilization of the overall cascaded system. Due to the versatility of the adding a power integrator technique and homogeneous properties, the proposed controller not only can be used to stabilize the cascaded system asymptotically, but also is able to lead to an interesting result of finite-time stabilization under appropriate conditions.     

Optimal control of unknown nonaffine nonlinear discrete-time systems based on adaptive dynamic programming

An intelligent-optimal control scheme for unknown nonaffine nonlinear discrete-time systems with discount factor in the cost function is developed in this paper. The iterative adaptive dynamic programming algorithm is introduced to solve the optimal control problem with convergence analysis. Then, the implementation of the iterative algorithm via globalized dual heuristic programming technique is presented by using three neural networks, which will approximate at each iteration the cost function, the control law, and the unknown nonlinear system, respectively. In addition, two simulation examples are provided to verify the effectiveness of the developed optimal control approach.     

Eigenvalue Modeling and Cross-Correlation Analysisfor 6.0-6.4 GHz MIMO Channel

In Multiple-Input Multiple-Output （MIMO） system, the number of positive channel matrix eigenvalues ~s directly related to system performance. In order to characterize and model channel matrix eigenvalues, channel measurements at 6. 0 -6. 4GHz by using 4 ~ 4 MIMO structure were conducted in a typical classroom environment. Based on measured data, the eigenvalues were modeled as Log-Normal distributed random variables and parameterized. Furthermore, Cross-Correlation （CC） coefficients of eigenvalues were estimated. The measurement results show that, under both Light-Of-Sight （LOS） and Non- Light-Of-Sight （NLOS） scenarios, eigenvalues are highly de-correlatod so that CC can be ignored for eigenvalue model.     

J-积分在镀层基体平面压痕边界开裂中的应用

当二维平端刚性压头作用在镀层基体的表面时,在镀层材料的表面形成一个平面压痕,同时在压痕的边界处将诱生奇异应力场和K-控制区。与裂纹问题类似,该应力场的平面压痕应力强度因子是描述奇异应力场应力集中程度的唯一参量。本文将利用守恒积分,讨论镀层基体平面压痕守恒积分的主要特征,同时给出镀层基体平面压痕应力强度因子的远场积分计算方法。     

基于ANSYS和FLUENT的内燃灶进排气管设计

针对传统燃气灶和吸油烟机存在的诸多弊端,本文基于ANSYS和FLUENT给出了内燃灶的结构原理,建立了内燃灶进排气管结构模型,并对进气管和排气管内的气体进行流场和温度场的仿真分析,仿真结果表明,在两个管内部的形状突变处和靠近进气口处,气体处于紊流状态,在管内靠近出气口处是比较稳定的层流状态。这种层流状态有利于气体流通,但不利于排气管内部高温气体与外部进行热交换,大量的热通过排气管排出室外,不利于废气余热再利用;同时,经分析,理论废气温度与实验数据存在较大的偏差,可见排气管中废气温度的变化与原理样机实验结果中废气温度的变化相吻合。该研究对废气余热利用和内燃灶功能的实现具有重要作用。     

A review of heavy-duty legged robots

Heavy-duty legged robots have been regarded as one of the important developments in the field of legged robots because of their high payload-total mass ratio, terrain adaptability, and multitasking. The problems associated with the development and use of heavy-duty legged robots have motivated researchers to conduct many important studies, covering topics related to the mechanical structure, force distribution, control strategy, energy efficiency, etc. Overall, heavy-duty legged robots have three main characteristics: greater body masses, larger body sizes, and higher payload-total mass ratios. Thus, various heavy-duty legged robots and their performances are reviewed here. This review presents the current developments with regard to heavy-duty legged robots. Also, the main characteristics of high-performance heavy-duty legged robots are determined and conclusions are drawn. Furthermore, the current research of key techniques of heavy-duty legged robots, including the mechanical structure, force distribution, control method, and power source, is described. To assess the transportation capacity of heavy-duty legged robots, performance evaluation parameters are proposed. Finally, problems that need further research are addressed.     

Investigation on mechanism of polymer filling in high-aspect-ratio trenches for through-silicon-via (TSV) application

Vacuum-assisted spin-coating is an effective polymer filling technology for sidewall insulating of through-silicon-via (TSV). This paper investigated the flow mechanism of the vacuum-assisted polymer filling process based on experiments and numerical simulation, and studied the effect of vacuum pressure, viscosity of polymer and aspect-ratio of trench on the filling performance. A 2D axisymmetric model, consisting of polymer partially filled into the trench and void at the bottom of trench, was developed for the computational fluid dynamics (CFD) simulation. The simulation results indicate that the vacuum-assisted polymer filling process goes through four stages, including bubble formation, bubble burst, air elimination and polymer re-filling. Moreover, the simulation results suggest that the pressure significantly affects the bubble formation and the polymer re-filling procedure, and the polymer viscosity and the trench aspect-ratio influence the duration of air elimination.     

地铁专用间接蒸发冷却器布水方式优化

为了解决常规间接蒸发冷却器由于表面水膜均匀性、完整性差而导致换热效率低的问题,提出了两侧旋转布水间接蒸发冷却器,进行了3种布置方式下的换热性能实验,运用正交实验对影响换热器性能的因素进行研究,研究表明:开孔正对气流方向时换热器换热性能最佳,且旋转布水装置存在最佳转速76 r/min,喷水量、空气流速、冷却水流量、冷却水进口温度的增加使换热器的换热量增大,喷水温度、空气温度的升高使换热器的换热量减少,其中冷却水进口温度的改变对换热性能的影响最为显著,温度由35℃上升到39℃时,换热量提高37.62％,单位面积换热量为1.14 kW,该换热器可安装于地下车站排风坑道内,可有效地解决地铁站冷却塔安装位置难题.     

北京地区能源消费碳排放演变的多因素动态冲击分析

本文研究了北京地区经济规模、交通运输量、产业集聚与能源消费碳排放之间的关系。通过协整检验发现,四者之间存在长期的均衡关系;利用脉冲响应函数和方差分解分析发现,能源消费碳排放对自身的冲击响应最大;其次是产业集聚对于节能减排具有重要作用;交通运输量在短期内对于碳排放的增加具有促进作用,改善交通运输条件是短期内节能减排的重要措施;经济规模的变化对于能源消费碳排放的冲击较小,其对能源消费的依赖性逐渐减弱,经济增长已发生结构性转变。     

Effect of curing regime on the distribution of Al3+ coordination in hardened cement pastes

The effect of curing regime on the distribution of Al³⁺ coordination in hardened cement pastes within 28 d were investigated by ²⁹Si and ²⁷Al magic angle spinning (MAS) nuclear magnetic resonance(NMR) with deconvolution technique. The results indicate that the tetrahedral coordination Al³⁺ incorporated in C-S-H structure mainly originate from the Al³⁺ incorporated in the alite and belite phases in the Portland cement. The curing regime of constant temperature of 20 °C is beneficial to the octahedral coordination Al³⁺ transforming to tetrahedral coordination Al³⁺ incorporated in C-S-H structure. However, at curing regime of variable temperature, the temperature rising process is more advantageous to the transformation from ettringite to monosulphate, substitution of Al³⁺ for Si⁴⁺ in the C-S-H structure and the formation of the third aluminate hydrate (TAH) than that at constant temperature of 20 °C. The high temperature of 60 °C in the holding temperature process promotes the decomposition of ettringite, and enhances the consumption of the Al³⁺ incorporated in C-S-H phases and the Al³⁺ in TAH for the monosulphate forming. The temperature decreasing promotes the transformation from monosulphate to ettringite, and increases the consumption of the Al³⁺ incorporated in C-S-H phases, and then increases the quantity of the TAH.