Optimal Performance in Tracking Stochastic Signal Under Disturbance Rejection

The analysis method of optimal tracking performance is proposed for multiple‐input multiple‐output (MIMO) linear time‐invariant (LTI) systems under disturbance rejection. An H₂ criterion of the error signal between the output of the plant and the reference signal is used as a measure for the tracking performance. Spectral factorization is applied to obtain the optimal solution of the system tracking error. The explicit expressions are derived for this minimal tracking error with respect to random reference signals under disturbance rejection. It is shown that the nonminimum phase zeros, the zero direction, the unstable poles, the pole direction of a given plant, statistical characteristics of the reference input signal, and disturbance signal have a negative effect on a feedback system's ability to reduce the system error with disturbance rejection. The results show that the optimal tracking performance will further be damaged because of disturbance rejection. Some typical examples are given to illustrate the theoretical results.     

方柱体镦粗的两个新力学模型

在对平板间镦粗圆柱体的研究［１，２，３］基础上，进一步对普通平板间的方柱体镦粗，进行了工程力学的分析，提出了二个新力学模型，并进行了实验验证。这为形成新的拔长理论［４，６］奠定了力学基础。     

Crystallographic structure- and texture-dependent fracture behavior of polycrystalline lead zirconate titanate ceramics

Journal of Electroceramics - The effect of crystallographic structure and texture on the fracture behavior of lead zirconate titanate (PZT) ceramics was investigated. PZT ceramics with Zr/Ti ratio...     

焊接热源有效利用率的测试计算法

给出实际热输入值是正确求解焊接热弹塑性问题和焊接残余应力与变形问题的前提;因而,准确地确定热源有效利用率η,在焊接力学的发展中是一个急待解决的命题。本文推荐采用的“测试计算法”提供了一个能够准确、简捷地求得η值的新途径。引入被焊材料的熔化潜热系数后,给出了线热源加热焊缝金属至熔化温度(处于液态)时的实际热有效利用率ηt 的表达式。在四种不同类型的薄板材料上进行了钨极氩弧焊试验,测试计算结果与理论值相符合。理论推导与试验结果均证明,形成焊缝所需要的线能量的无量纲数值等于焊缝金属熔化热有效利用率ηt 的倒数。文中给出的焊接规范参数选择原则也适用于符合线热源条件的其它熔焊热源。η值不但与焊接工艺方法、规范参数有关,而且也随被焊材料的热物理特性不同而异。     

基于粒子群算法的移动机器人全局最优路径规划*

以栅格法和粒子群算法为基础,提出了一种新的机器人实时全局最优路径规划方法.该方法包括采用栅格法对环境进行建模和直接运用粒子群算法在环境模型中搜索全局最优路径.在计算机上进行了仿真,仿真结果证明了该方法的可行性和有效性.     

Correction to: Bismuth Yttrium Oxide (Bi3YO6), A New Electrode Material For Asymmetric Aqueous Supercapacitors

Journal of Inorganic and Organometallic Polymers and Materials - The original version of this article unfortunately contained mistakes. In line 9 of the abstract, 5% should read as 2%. The...     

Design and Achievement of Metallurgical Bonding of Mg/Al Interface Prepared by Liquid–Liquid Compound Casting via a Co-deposited Cu–Ni Alloy Coating

The metallurgical bonding of Mg/Al bimetal by liquid–liquid compound casting was realized via co-deposition Cu–Ni alloy coating. The metallurgical layer of the Mg/Al bimetal consisted of Cu solid solution, Cu₂Mg and (Al0.7Cu1.3) Mg, Mg solid solution, Al₃Ni₂, and Mg₂Cu. Vickers hardness of the interface was between 149.9 and 209 HV, which was significantly lower than those of Al–Mg intermetallic compounds. The formation mechanism of the interface was attributed to interdiffusion among AZ91D, A356, and Cu–Ni alloy coating.

     

硬脆材料专用ELID磨削液的研制

本文在已有新型通用ELID磨削液(HDMY-20型)的基础上，根据硬脆材料的磨削特点和ELID磨削过程中磨削液的电解修锐生膜缓蚀作用、结合通用ELID磨削液的研制经验．通过增添表面活性剂、稳定剂、防锈剂、油性极压剂和调整无机盐等成分的比例关系．优化出适合硬脆材料ELID磨削最佳状态的专用ELID磨削液。应用此磨削液磨削硬质合金表面粗糙度可达Ra0．007μm比通用型磨削液磨削的硬质合金Ra值降低了0．005μm。     

Mg-Sr牺牲阳极显微组织和电化学性能的研究

研究了Mg-Sr牺牲阳极的显微组织和电化学性能的特征.结果表明,Mg-Sr牺牲阳极的晶粒尺寸随Sr含量的增加而减小;当Sr质量分数为0.19%时,电流效率达到58.56%,开路电位达到-1.735 VSCE;Sr的质量分数再增加,Mg-Sr阳极的电流效率降低,开路电位正移.研究认为,Sr的质量分数为0.19%时,晶界析出的Mg17Sr2相（弱阴极相）和α-Mg基体（阳极相）组成电偶对,阻碍了阳极晶间腐蚀,减少了晶粒大块脱落, 且Sr能够和Mg、Fe形成弱阴极性化合物降低Fe的危害,电流效率升高,同时晶粒细化,晶界面积变大,杂质相分布更均匀,开路电位负移;Sr含量大于0.19%时,过量的Mg17Sr2相作为阴极相加大了阳极的自腐蚀,电流效率下降,开路电位正移.     

气-电纺PHB引导组织再生膜的仿生矿化研究

实验将PHB通过气流-高压静电纺丝制成无纺膜，利用扫描电镜（SEM）、X射线衍射（XRD）对其形态和结构进行表征。在体外研究中，分别将无纺膜样本浸入37℃1．5倍仿生体液（SBF）中3、7、14、28d后对其表面形态和结构进行表征。结果表明，气电纺PHB无纺膜由超细纤维交织而成，纤维之间有多孔形成；通过气流一静电纺丝之后，PHB的结晶度及晶体的有序度降低；PHB膜在SBF中浸泡3天之后就有矿化结晶在纤维的表面形成，随着浸泡时间的增长，矿化结晶的数目增加，结晶度也随之增高，XRD及FTIR表明形成的结晶为含有碳酸根的磷灰石晶体。