Direct conversion of methane to higher hydrocarbons via an oxygen free,low-temperature route

The direct conversion of methane to higher hydrocarbons over a silica-supported Ru catalyst has been investigated via an oxygen free, two-step route. The reaction consists of decomposition of methane over a 3% silica-supp orted Ru catalyst at temperatures between 400 and 800 K to produce surface carbonaceous species followed by rehydrogenation of these species to higher hydrocarbons at of 368 K. It was found that the Ru/SiO₂ catalyst exhibits a trend similar to that for single-crystal Ru catalysts. However, the temperature at which a maximum in ethane selectivity occurs shifts toward a higher temperature. It was also found that the ethane yield can be optimized by changing the surface carbon coverage. Under optimum conditions a net ethane yield of about 13–15% has been realized. For this two-step reaction sequence, only a few reaction cycles could be operated without intermediate high temperature rehydrogenation and without significant loss in ethane yield. This is attributed to large amounts of inactive carbon that could not be hydrogenated at 368 K. Higher methane partial pressures were found to be desirable for this reaction. The activity of the catalyst could also be maintained at total pressures up to 10 atm.     

The Effect of Temperature on the Strength of Adhesively-Bonded Composite-Aluminium Joints

Different materials have different coefficients of thermal expansion, which is a measure of the change in length for a given change in temperature. When different materials are combined structurally, as in a bonded joint, a temperature change leads to stresses being set up. These stresses are present even in an unloaded joint which has been cured at say 150°C and cooled to room temperature. Further stresses result from operations at even lower temperatures.

In addition to temperature-induced stresses, account also has to be taken of changes in adhesive properties. Low temperatures cause the adhesive to become more brittle (reduced strain to failure), while high temperatures cause the adhesive to become more ductile, but make it less strong and more liable to creep.

Theoretical predictions are made of the strength of a series of aluminium/CFRP joints using three different adhesives at 20°C and 55°C. Various failure criteria are used to show good correlation with experimental results.     

重庆市发展长江水源热泵的水源概况分析

为了解重庆段长江水作为热泵冷热源的概况,对重庆段长江水温的横断面变化和时间变化进行了实测分析,并对江水的水质和水位变化进行了分析,得到长江水温在整个横断面基本恒定,而江水的夏季月平均温度在22~25℃,冬季月平均温度在11~16℃,水温日变化幅度不超过0.5℃。是一种具有良好品质的稳定的冷热源。而长江水作为水源热泵的冷热源,主要解决的水质问题是泥沙和悬浮物,在三峡库区形成后水位变化可达到30 m,因此取水方式可考虑采用浮船取水方式。     

Experimental study on temperature stress calculation and temperature control optimization of concrete based on early age parameters

Temperature control curve is the key to achieving temperature control and crack prevention of high concrete dam during construction,and its rationality depends on the accurate measurement of temperature stress.With the simulation testing machine for the temperature stress,in the present study,we carried out the deformation process tests of concrete under three temperature curves：convex,straight and concave.Besides,we not only measured the early-age elastic modulus,creep parameters and stress process,but also proposed the preferred type.The results show that at early age,higher temperature always leads to greater elastic modulus and smaller creep.However,the traditional indoor experiments have underestimated the elastic modulus and creep development at early age,which makes the calculated value of temperature stress too small,thus increasing the cracking risk.In this study,the stress values of the three curves calculated based on the strain and early-age parameters are in good agreement with the temperature stress measured by the temperature stress testing machine,which verifies the method accuracy.When the temperature changes along the concave curve,the law of stress development is in consistent with that of strength.Under this condition,the stress fluctuation is small and the crack prevention safety of the concave type is higher,so the concave type is better.The test results provide a reliable basis and support for temperature control curve design and optimization of concrete dams.     

Fixed‐time synchronization for complex‐valued BAM neural networks with time delays

In this paper, the fixed‐time synchronization for complex‐valued bidirectional associative memory (BAM) neural networks with time delays is studied. Based on the fixed‐time stability, the Lyapunov functional method and some inequality techniques, a new criterion is presented to guarantee that the addressed systems achieve synchronization in fixed time and a more accurate estimation independent of the initial conditions is given for the settling time. Meanwhile, a new nonlinear delayed controller different from the existing ones is designed. In the end, two numerical examples are provided to illustrate the effectiveness of the obtained result.     

Hierarchical inversion‐based output tracking control for uncertain autonomous underwater vehicles using extended Kalman filter

In this study, a hierarchical inversion‐based output tracking controller (HIOTC) is developed for an autonomous underwater vehicle (AUV) subject to random uncertainties (e.g., current disturbances, unmodeled dynamics, and parameter variations) and noises (e.g., process and measurement noises). The proposed HIOTC respectively utilizes a combination of feedforward and feedback controls in a hierarchical structure based on the kinematic and dynamic models of the system. Moreover, to obtain uncontaminated or unavailable states for implementing the proposed control law, the extended Kalman filter (EKF) is employed to estimate the system states. Then, the position outputs, orientation, and velocity of the AUV are reached with guaranteed asymptotic stability. The robustness of the proposed HIOTC is verified through injection of random uncertainties into the system model. The closed‐loop stability of the proposed individual subsystems is respectively guaranteed to have uniformly ultimately bounded (UUB) performance based on the Lyapunov stability criteria. In addition, the asymptotic tracking of the overall system is demonstrated using Barbalat's lemma. Finally, the feasibility and effectiveness of the proposed control scheme are evaluated through computer simulations and it is shown that the overall system achieves good asymptotic tracking performance.     

基于区块链的侦查机器人实时避障与航线控制

为弥补侦查机器人行进灵活性不足的缺陷,降低无故运动碰撞事件的发生几率,提出基于区块链的侦查机器人实时避障与航线控制算法;利用超声信号处理电路,提取可供直接应用的侦查运动节点,联合已完成配置的MoveIt避障程序,实现对侦查机器人的实时避障运动规划;在此基础上,设置LQR控制器,在控制机器人侦查航速的同时,建立必要运动操纵方程,完成对侦查机器人的运动航线控制,提升与运动设备元件相关的行进灵活性;完善P2P网络平台,以待交互的运动数据作为处理支持条件,将所有侦查信息封装至同一区块组织中,完成基于区块链的避障控制原理研究,实现侦查机器人实时避障与航线控制算法的搭建;对比实验结果表明,应用基于区块链的控制算法后,C-Space参数极值超过8.0,RRT灵敏度也提升至75%,实现了对侦查机器人的灵活性行进控制,有效抑制了无故运动碰撞事件的出现。     

改进Otsu算法的镀锌板表面缺陷检测方法

针对镀锌板在生产工艺和传输过程中对镀锌板表面造成缺陷的问题;文章应用了基于Otsu算法的镀锌板表面缺陷检测系统,由数字光源控制器、高速CCD相机、同步触发器和编码器等硬件设备共同连接组成,采集到镀锌板表面的图像,然后将图像传输给基于Otsu算法的图像处理系统;改进优化了Ostu算法,在一维直方图求解最佳截距阈值,利用该阈值和二维信息完成图像的分割,提高了图像的抗噪能力;使用分块检验所发初步判定镀锌板表面缺陷,再逐个排查确认缺陷区域,对缺陷特征进行分类并保存在缺陷数据库中,同时发出预警;实验结果显示文章研究的检测系统对镀锌板表面缺陷检出率最高可高达98％,检测出缺陷镀锌板的数量最多,系统的检测精度高.     

基于物联网实验室环境远程监测系统的研究

实验室环境对电子仪器及设备的使用安全和寿命以及实验室消防安全有着非常重大的影响,传统实验室环境监控需要安排人员进行24 h值班和巡检,人力投入和安装布线成本非常高;针对上述问题,采用高性能低功耗离子式烟雾传感器NIS-07和温湿度复合传感器DTH11进行环境数据的采集,采用无线网络模块完成数据的传输,并通过微处理器将采集的数据上传服务器,同时采用基于BP神经网络PID控制算法实现在线动态温湿度调控;服务器端使用Tomcat web服务器,采用MySQL数据库进行数据存储,并通过Java编程语言实现传感器数据的存储、分析、处理以及客户端数据的更新;客户端通过Web网页或APP对实验室环境进行实时监控,从而实现精确和高效的实验室环境远程集中管理.     

小型无人机发动机温度监控系统设计

为了实时监控小型油动无人机的发动机工作温度,设计开发了基于K型热电偶的4路温度监控系统;该系统采用模拟开关CD4052作通道切换,选通的热电偶信号经放大调理,由STM32F103控制器片上A/D采集,经DS18B20数字温度传感器作冷端补偿,最终以Modbus RTU协议将温度值发送到485总线上;经调试校准,该温度监控系统在蚊子直升机MZ202型发动机正常工作温度范围内与原机温度仪表相差±3℃,数据刷新率大于2 Hz,且工作稳定抗干扰能力较强,为发动机调校提供了可靠的依据,有效地保障了发动机安全稳定运行;该温度监控系统也可用于Rotax582,Rotax912/914等小型活塞航空发动机缸头及排气温度的采集与监控。