具有初荷载的钢筋混凝土梁桥粘贴碳纤维布加固试验研究

通过对五片实桥模型T型梁粘贴不同数量、不同受力阶段碳纤维片材的破坏试验,研究了碳纤维布数量和二次受力对钢筋混凝土T型梁抗弯承载能力的影响,对梁的裂缝、挠度、刚度等做了调查分析,讨论了粘贴碳纤维布对正常使用状态的影响,提出了粘贴碳纤维布加固钢筋混凝土简支T型梁的抗弯承载力计算方法,针对不同破坏形态讨论了不同的计算方法并予以一定简化。与试验结果比较表明该方法准确有效。     

阿苯达唑在石墨烯与[Bupy]PF_6复合修饰碳糊电极上的电化学性质及电分析方法研究

目的:本文研究了阿苯达唑(ABZ)在石墨烯与离子液体(N-丁基吡啶六氟磷酸盐)复合修饰碳糊电极上的电催化氧化及电化学性质,建立了阿苯达唑的电化学定量检测方法。方法:循环伏安法(CV法),计时库仑法(CC法)、计时电流法(CA),方波伏安法(SWV)。结果:ABZ在GR-[Bupy]PF6/CPE上具有良好的电化学行为,而且ABZ在此电极上的电化学氧化是一受扩散控制的不可逆电极反应过程,并用SWV法测的ABZ氧化峰电流(Ip)与其浓度在9.0×10~(-7)~2.0×10~(-4)mol·L~(-1)范围内呈良好的线性关系,线性回归方程为Ip(μA)=4.804+198.522c(10~(-3)mol·L~(-1)),R=0.9987,检测限(S/N=3)为1.4×10-8 mol·L-1。结论:GR-[Bupy]PF6/CPE对ABZ的电化学氧化具有良好的催化作用,该方法可用于对市售的ABZ片剂中ABZ含量进行电化学定量测定,且检测限低,检测范围宽。     

低空多径环境下雷达目标检测性能研究

针对低空多径环境下不同体制雷达目标检测性能展开研究,通过优化配置雷达阵元达到多径环境下的最优检测性能。建立低空多径环境下雷达接收信号模型,引入多径功率传播因子,将经典的Swerling目标起伏模型推广应用于低空多径环境,采用特征函数法推导低空多径环境下不同体制雷达的检测概率。仿真研究了多径功率传播因子对检测性能的影响,比较不同体制雷达的检测性能,结果表明多输入单输出雷达兼具相控阵雷达和多输入多输出雷达的优点,在多径环境下具有稳定的检测性能。     

Formation kinetics of polyoxymethylene dimethyl ethers from methylal and trioxane with little water

Polyoxymethylene dimethyl ethers(CH_3-O-(CH_2 O)n-CH_3, PODE_n, n1) can be added to diesel to reduce air pollution caused by incomplete combustion. Driven by this need, a cost-effective and efficient synthetic route is presented and investigated by this work for the production of PODEn, which are formed from methylal and trioxane with low water content(10 %(mass)) over HZSM-5 catalyst in a batch slurry autoclave at the temperature from 353.15 K to 393.15 K. The reaction rate laws including the PODEnand byproducts of polyoxymethylene hemiformals(HF_n), polyoxymethylene glycols(MG), methanol(Me OH) and methyl formate(MF) are developed. The rate constants of propagation step(k_6) and depolymerization step(k_(-6)) are assumed independent on polymerization degree of PODE_n. The rate of reaction is proportional to the content of the catalyst(W_(cat)) for the catalytic reaction within the scope of the study. All kinetic parameters were estimated by combining genetic algorithm and least square regression to fit experimental data well. This work is valuable for process optimization and reactor design.     

CFRP圆形胞元蜂窝芯层面外剪切模量

为了减少卫星的热变形,将碳纤维增强树脂基复合材料（CFRP）材料圆管周期排布获得新型圆形胞元蜂窝芯层。考虑无论是Ressiner理论还是商业有限元软件ABAQUS,层合板计算热变形时,芯层的面外剪切模量均很重要,因此对CFRP圆形胞元蜂窝芯层的面外剪切进行了研究。分别从应力与应变的角度基于能量等效原理求出圆形胞元蜂窝芯层的面外剪切模量公式。以T300/环氧材料的工程常见铺层为例,比较基于ABAQUS软件计算所得剪切模量仿真解与公式计算所得理论解,其最大误差仅为10.4%,证实公式对于CFRP材料的适用性。同时用（±45°）₂铺层的T300/环氧芯层完成双剪试验,试验结果与理论结果误差为24.1%,与前人研究的铝蜂窝面外剪切模量理论解与试验解的误差相近。最后通过仿真手段证实,24.1%的误差对整体夹层结构影响较小,说明公式具有良好的工程应用价值。为以后CFRP圆形胞元蜂窝芯层的设计提供重要基础。     

Dynamic output feedback robust MPC for LPV systems subject to input saturation and bounded disturbance

For linear parameter varying (LPV) systems with unknown scheduling parameters and bounded disturbance, a synthesis approach of dynamic output feedback robust model predictive control (OFRMPC) with input saturation is investigated. By pre-specifying partial controller parameters, a main optimization problem is solved by convex optimization to reduce the on-line computational burden. The main optimization problem guarantees that the estimated state and estimation error converge within the corresponding invariant sets such that recursive feasibility and robust stability are guaranteed. The consideration of input saturation in the main optimization problem improves the control performance. Two numerical examples are given to illustrate the effectiveness of the approach.     

Robust RHC for wheeled vehicles with bounded disturbances

The robust receding horizon control (RHC) synthesis approach is developed in this paper, for the simultaneous tracking and regulation problem (STRP) of wheeled vehicles with bounded disturbances. Considering the bounded disturbances, we firstly provide a robust positively invariant (RPI) set and associated feedback controller for the perturbed vehicles, which contribute to the foundation of the robust RHC synthesis approach. Then, by extending the tube‐based approach introduced in the article of Mayne et al (robust model predictive control of constrained linear systems with bounded disturbances in Automatica, 2005, vol. 41) to the STRP of wheeled vehicles, we employ the designed RPI set to determine the robust tube and terminal state region, and further construct a nominal optimal control problem. The actual control input is implemented by correcting the solved nominal input with the designed feedback controller. Following the contributed properties of the developed RPI set and extended tube‐based approach, a robust RHC algorithm is finally proposed with the guarantees of recursive feasibility and robust convergence, which can also be adapted for real‐time implementation. Additionally, due to the elaborate control design, the effect of disturbances can be completely nullified to achieve better tracking performance. The effectiveness and advantage of the proposed approach are illustrated by two simulation examples.     

An efficient design for fast memory registration in RDMA

Remote Direct Memory Access (RDMA) improves network bandwidth and reduces latency by eliminating unnecessary copies from network interface card to application buffers, but the communication buffer management to reduce memory registration and deregistration cost is a significant challenge to be addressed. Previous studies use pin-down cache and batched deregistration, but only simple LRU is used as a replacement algorithm to manage cache space. In this paper, we evaluate the cost of memory registration in both user and kernel spaces. Based on our analysis, we reduce the overhead of communication buffer management in two aspects simultaneously: utilize a Memory Registration Region Cache (MRRC), and optimize the RDMA communication process of clients and servers with Fast RDMA Read and Write Process (FRRWP). MRRC manages memory in terms of memory region, and replaces old memory regions according to both their sizes and recency. FRRWP overlaps memory registrations between a client and a server, and allows applications to submit RDMA write operations without being blocked by message synchronization. We compare the performance of MRRC and FRRWP with traditional RDMA operations. The results show that our new design improves the total cost of memory registrations and overall communication latency by up to 70%.     

扩散热阻对FR4/AlN复合材料导热性能的影响

首先,将AlN陶瓷表面金属化后分别切割成10 mm×10 mm×1.0mm、12 mm×12 mm×1.0 mm及15 mm×15 mm×1.0mm的方块,嵌入环氧树脂中制备成FR4/AlN复合材料;然后,利用SMT工艺将同款LED灯珠与上述内置三种不同尺寸AlN的复合基板材料组装成LED模组;最后,利用结温测试仪与半导体制冷温控台对三种LED模组分别进行了结温测试.同时,结合热仿真手段对复合材料水平面的温度分布情况进行了模拟研究.结果表明:上述三种尺寸陶瓷片对应LED的结温分别为96.95、92.94与91.81℃.热仿真结果显示,陶瓷片尺寸通过界面热阻对扩散热阻产生影响,增大陶瓷片尺寸有助于降低扩散热阻,进而改善FR4/AlN复合材料的整体散热性能.     

Research on the fabricating quality optimization of the overhanging surface in SLM process

Overhanging surface is inherent geometric restraint during selective laser melting (SLM), which is suitable for various complex parts fabrication. In order to improve the fabricating quality of overhanging surface, a series of experiments were designed to investigate the effects of inclined angle, scanning speed, laser power, accumulated residual stress, and scanning vector length on overhanging surface fabrication. Analysis found that overhanging surface would warp easier when the inclined angle and the scanning speed became smaller and the warping trend will be larger as the laser power became larger. The relationships of laser power, scanning speed, and the critical inclined angle were mutual restraint, that is, larger inclined angle will be designed when the laser power becomes larger and scanning speed gets smaller, or vice versa: the selection of the fabricating parameters will be determined by established inclined angle of the overhanging surface. More serious warp would happen as the processing layers increased as a result of residual stress accumulation, and it was found that longer scanning vector were more helpful to stress accumulation, leading to more serious warp than shorter vector. At last, two effective methods were adopted to optimize overhanging surface fabrication, including adjusting part orientation to improve the inclined angle at the key position, and controlling regional parameters to reduce energy input. Above two ways were adopted to manufacture complex parts with typical overhanging surface, the results proved that adjusting part orientation and controlling regional parameters were effective ways to improve the fabricating quality of overhanging surface. In this study, the basis for building overhanging surface by SLM was provided from the view of process and design, and the preliminary solutions were proposed to manufacture complex metal parts with lower risk.