Review:Layer⁃Number Controllable Preparation of High⁃Quality Graphene for Wide Applications

Graphene, a well-known two-dimensional(2 D) material, has sparked broad enthusiasm in both scientific and industrial communities in these years, due to its exceptional electrical, thermal, mechanical, and versatile properties. However, many properties and applications of graphene are layer-number dependent. The preparation of high-quality graphene with controlled layer numbers is full of challenge, since the layer number varies much with the synthesis routes and relevant experimental conditions. Hence, there is an urgent need to improve the layer-number controllability of graphene preparation. Generally, graphene can be prepared by two complementary approaches: "top-down" and "bottom-up". Since they have their own advantages, the recent advances in the layer-number tunable preparation of high-quality graphene are separately studied from the two aspects in this review, especially those dedicated to single parameter. Some effective strategies are discussed in detail, mainly including 1) supercritical-CO2 assisted sonication, electrochemical exfoliation of graphite intercalation compounds, and layer-by-layer thinning with plasma or laser, for "top-down" graphene;2) chemical vapor deposition(CVD) on dual-metal substrate, ion-implantation CVD, layer-by-layer CVD, plasma-enhanced CVD, layered-double-hydroxides template-assisted CVD;and 3) graphite-enclosure assisted epitaxial growth and pulsed-magnetron-sputtering assisted physical vapor deposition for "bottom-up" graphene on various substrates. In addition, the respective advantages of graphene with different layer numbers in properties and applications are also presented. Finally, the contribution concludes with some important perspectives on the remained challenges and future perspectives.

Using modified Soil Conservation Service curve number method to simulate the role of forest in flood control in the upper reach of the Tingjiang River in China

To improve flood control efficiency and increase urban resilience to flooding,the impacts of forest type change on flood control in the upper reach of the Tingjiang River(URTR) were evaluated by a modified model based on the Soil Conservation Service curve number(SCS-CN) method. Parameters of the model were selected and determined according to the comprehensive analysis of model evaluation indexes. The first simulation of forest reconstruction scenario,namely a coniferous forest covering 59.35km^2 is replaced by a broad-leaved forest showed no significant impact on the flood reduction in the URTR. The second simulation was added with 61.75km^2 bamboo forest replaced by broad-leaved forest,the reduction of flood peak discharge and flood volume could be improved significantly. Specifically,flood peak discharge of 10-year return period event was reduced to 7-year event,and the reduction rate of small flood was 21%-28%. Moreover,the flood volume was reduced by 9%-14% and 18%-35% for moderate floods and small floods,respectively. The resultssuggest that the bamboo forest reconstruction is an effective control solution for small to moderate flood in the URTR,the effect of forest conversion on flood volume is increasingly reduced as the rainfall amount increases to more extreme magnitude. Using a hydrological model with scenarios analysis is an effective simulation approach in investigating the relationship between forest type change and flood control. This method would provide reliable support for flood control and disaster mitigation in mountainous cities.

Preliminary prediction of the control reproduction number of COVID-19 in Shaanxi Province,China

Objectives Firstly,according to the characteristics of COVID-19 epidemic and the control measures of the government of Shaanxi Province,a general population epidemic model is es-tablished.Then,the control reproduction number of general population epidemic model is obtained.Based on the epidemic model of general population,the epidemic model of general population and college population is further established,and the control reproduction number is also obtained.Methods For the established epidemic model,firstly,the expression of the control reproduc-tion number is obtained by using the next generation matrix.Secondly,the real-time reported data of COVID-19 in Shaanxi Province is used to fit the epidemic model,and the parameters in the model are estimated by least square method and MCMC.Thirdly,the Latin hypercube sampling method and partial rank correlation coefficient(PRCC)are adopted to analyze the sensitivity of the model.Conclusions The control reproduction number remained at 3 from January 23 to January 31,then gradually decreased from 3 to slightly greater than 0.2 by using the real-time reports on the number of COVID-19 infected cases from Health Committee of Shaanxi Province in China.In order to further control the spread of the epidemic,the following measures can be taken:(i)reducing infection by wearing masks,paying attention to personal hygiene and limiting travel;(i)improving isolation of suspected patients and treatment of symptomatic individuals.In particular,the epidemic model of the collge population and the general population is estab-lished,and the control reproduction number is given,which will provide theoretical basis for the prevention and control of the epidemic in the colleges.

Motion stability and control of supercavitating vehicle with variable cavitation number

Cavitation number and speed are capable of variation during the motion of supercavitating vehicle underwater, for example, under the condition of accelerated motion stage and external disturbance. The dynamic model and control challenge associated with the longitudinal motion of supereavitating vehicle with variable cavitation number and speed have been explored. Based on the principle of cavity expansion independence the properties of cavity and the influence on planning force of body were researched. Calculation formula of efficiency of the fin was presented. Nonlinear dynamics model of variable cavitation number and speed supercavitating vehicle was established. Stabilities of the open-loop systems of different situations were analyzed. The simulations results of open-loop systems show that it is necessary to design a control method to control a supereavitating vehicle. A gain schedule controller with guaranteed H∞ performance was designed to stabilize the dive-plane dynamics of supercavitating vehicle under changing conditions.

基于DCS-惯性权重组合的柔性机械臂运动轨迹控制系统研究

为了有效调控机械臂运动幅度,避免柔性机械臂实际运动轨迹与目标轨迹发生较大的偏差,设计一种基于分散控制系统(DCS)-惯性权重组合的柔性机械臂运动轨迹控制系统,它是一个集合了计算机、通信、显示和控制的计算机系统,该系统由过程控制和过程监控。通过DCS算法控制监测对象行为幅度并计算柔性机械臂惯性权重,利用DCS-惯性权重组合求解素数控制指标的具体数值,实现了对柔性机械臂运动轨迹控制系统的软件设计。实验结果表明,DCS-惯性权重组合算法作用下的机械臂末端坐标在横轴、纵轴、空间轴方向上的运动幅值均可以被控制在10个单位长度之内,并且在0.52 s内进入机械臂运动轨迹最佳控制状态,运动轨迹差值最大仅为0.01 rad,验证了该系统具备可行性和有效性。

Control of Vortex Shedding at Moderate Reynolds Numbers

The suppression method of vortex shedding from a circular cylinder has been studied experimentally in the Reynolds number range from 300 to 1600. The test is performed in a water channel. The model cylinder is 1 cm in diameter and 38 cm in length. A row of small rods of 0.18 cm in diameter and 1.5 cm in length are perpendicularly connected to the surface of the model cylinder and distributed along the meridian, The distance between the neighboring rods and the angle of attack of the rods can be changed so that the suppression effect on vortex shedding can be adjusted. The results show that vortex shedding can be suppressed effectively if the distance between the neighboring rods is smaller than 3 times and the cylinder diameter and the angle of attack is in the range of 30degreesless than or equal tobeta<90&DEG;.

Control of mean and fluctuating forces on a circular cylinder at high Reynolds numbers

A narrow strip is used to control mean and fluctuating forces on a circular cylinder at Reynolds numbers from 2.0 ×10^4 to 1.0 ×^ 10^5. The axes of the strip and cylinder are parallel. The control parameters are strip width ratio and strip position characterized by angle of attack and distance from the cylinder. Wind tunnel tests show that the vortex shedding from both sides of the cylinder can be suppressed, and mean drag and fluctuating lift on the cylinder can be reduced if the strip is installed in an effective zone downstream of the cylinder. A phenomenon of mono-side vortex shedding is found. The strip-induced local changes of velocity profiles in the near wake of the cylinder are measured, and the relation between base suction and peak value in the power spectrum of fluctuating lift is studied. The control mechanism is then discussed from different points of view.

Q-Learning-Based Inter-Networking Mobile Number Portability Congestion Control Mechanism

Inter-networking Mobile Number Portability(MNP) is an important way to promote the development of new telecom services.For the congestion that always occurs on the MNP query nodes,this paper proposes a Q-learning-based inter-networking mobile number portability congestion control mechanism,taking the node queue delay and query service stability as the control targets,based on the optimal decision which is made over mobile user number portability query through self-adaptive connection admission control.The simulation and analysis show that,compared with tail-drop,random early detection and other mechanisms,this mechanism realizes a smoother and more regular queue size when the load is relatively light;and maintains a relatively low and stable queue size with relatively small loss when the load is relatively heavy,thus improving QoS and increasing network throughput at lower cost.

基于前导码重传辅助控制的mMTC动态随机接入

为解决海量机器类通信(mMTC,massive machine type communications)场景下,机器类通信设备(MTCD,machine type communication device)采用传统随机接入方案时,往往出现网络严重拥塞,导致大量MTCD无法成功接入网络问题,提出了一种基于前导码重传辅助的动态接入类别限制(PRT-ACB,preamble retransmission access class barring)方案。利用MTCD的前导码重传次数,将每个随机接入机会(RAO,random access opportunity)中尝试发起接入的MTCD划分为高、低优先级,结合每个RAO中负载数估计模型,分别为其设定随每个RAO中的接入负载动态变化的高、低优先级限制因子和可用前导码池,使更多MTCD能在未达到最大前导码传输次数前成功接入网络。仿真结果表明,所提方案能有效提升MTCD的接入成功概率,降低MTCD接入网络所需时延。所提方案可以作为缓解海量通信设备同时接入网络造成拥塞的一种解决方案。

计及静态电压稳定约束的最少发电机优化调度方法

电压稳定控制中的控制数量多,且紧急状态时要求控制措施快速响应。构建一种以最少发电机调整数量为目标的优化调度数学模型,该模型为包含离散变量和连续变量的非线性混合整数规划问题,为快速获得高质量的可行解,提出一种由快速筛选和模型转化组成的阶段式求解方法。利用负荷裕度对发电机有功出力的灵敏度快速筛选出可提高负荷裕度的发电机集合,缩小离散变量的搜索范围;将原问题转化为混合整数线性规划子问题以及非线性规划子问题进行交替求解,得到需要调整的发电机数量及其出力。通过IEEE 118和IEEE 300节点系统进行测试,结果表明所提控制模型和求解方法可有效提高电力系统负荷裕度,减少可行解中包含的发电机调整数量,与分支定界法的对比验证了所提求解方法的快速性和有效性。

拓扑优化相变热沉在不同重力场的性能

为强化相变热沉的性能,基于带惩罚的固体各向同性材料(SIMP)法对山梨糖醇相变热沉进行传热拓扑优化设计。对拓扑优化的相变热沉(Ⅰ)和直肋式的相变热沉(Ⅱ)进行定常重力(0~20g)和周期性重力条件的数值模拟研究。利用无量纲数对比二者的热性能,研究结果表明:热沉Ⅰ的吸热和均热性能优于热沉Ⅱ;在相同重力环境下,以80℃为目标,热沉Ⅰ温控时间比热沉Ⅱ平均多26.8%;微低重力下热沉内部近乎导热,略逊于常规重力下热性能;超重力强化的自然对流可以显著提升热沉性能,10g条件相比常规重力的温控时间增加8.94%,而相同Ra^(*)下,周期性重力对热沉Ⅰ的性能有抑制作用。研究结果对飞行器载相变热沉的地面细化设计有一定指导意义。

基于内生转换模型的养猪场生物安全防控效果研究

为了解我国养猪场生物安全防控水平,评估生物安全防控效果,本文基于全国12省723份养猪场调研数据,构建评价体系量化样本养猪场生物安全防控水平,分析养猪场生物安全预防、控制和各个环节的防控现状,并利用内生转换模型纠正样本选择偏差导致的内生性问题,考察生物安全水平对养猪场生猪病死数量的影响。结果表明:我国养猪场已逐步开展生物安全防控但整体水平不高,部分环节表现较差,优劣两极化明显;生物安全水平提高能显著降低养猪场病死猪数量,根据平均处理效应计算可知若生物安全由低水平向高水平转变,养猪场生猪病死数量会减少15.147~100.209头,生猪病死率降低1.125%~2.732%。本研究验证了养猪场生物安全防控具有避免生猪病死的显著效果。

眼镜镜片尖边轮廓的五轴数控加工

为了改善和优化眼镜镜片的加工流程,避免镜片尖边加工过程中刀轴矢量变化剧烈、影响工件表面的加工质量,提出了一种基于UG NX的五轴数控加工路径。利用智能镜框扫描仪对镜框边缘进行扫描,获得镜框凹槽点云数据文件,编写相应程序对符合眼镜片加工标准的OMA文件中的球坐标数据进行坐标及格式转换等处理。基于NURBS曲线拟合算法,实现刀路轨迹的连续性并保证拟合曲线的精度。设计和建立一种控制刀轴矢量平滑变化的刀轴驱动约束方法,依靠曲线驱动刀轴及镜片曲面法向量约束刀轴使刀头平滑进给,并将刀轨文件经过后处理转换为NC文件。最后,对加工后的镜片进行误差测量,结果表明,通过点云数据拟合刀路曲线的方法提高了加工面的精确度和光滑性,有效缩减了加工流程,提高了加工效率。

某装备天线伺服系统算法研究

论文根据某装备伺服系统实际应用情况,考虑其实时跟踪目标特点,采用了快速最优算法+模糊PID算法相结合的控制策略,有效确保了天线的实时稳定运转。通过实验测试,采用快速最优算法+模糊PID算法的控制策略,天线稳定运行,全系统具有良好的动静态特性。

不同土壤封闭除草剂对南方大豆玉米带状复合种植地的防草效果

为解决南方大豆玉米带状间作复合种植杂草难以防治的问题,选用土壤封闭除草剂单剂、复配剂及土壤封闭除草剂单剂+草甘膦异丙胺盐等共8种,开展了复合种植生育中期及后期土壤封闭除草剂对杂草的株防效和鲜重防效研究。结果表明:土壤封闭除草剂复配剂平均效果好于单剂;鲜重防效高于株防效;随着生育进程的推进,株防效和鲜重防效随之降低,株防效降低幅度大于鲜重防效;药后97 d,土壤封闭除草剂鲜重防效依次为精异丙甲草胺+草甘膦异丙胺盐>噻磺·乙草胺>异丙甲草胺>精异丙甲草胺>二甲戊灵>扑·乙>乙草胺,防效分别为84.8%、83.04%、81.52%、80.11%、78.36%、77.35%、67.54%,均可作为湖南及南方大豆玉米带状间作复合种植土壤封闭除草剂使用;唑嘧磺草胺在南方作为土壤封闭除草剂仍需进一步研究。

气浮电动缸功率匹配分析与控制算法设计

针对承担重载的电驱机构存在运行功率大、机械结构易磨损等问题,论文介绍了一种气浮电动的联合驱动方案,首先分析了气浮电动缸的工作原理及电、气驱动力和功率匹配情况,然后把电动系统功率作为预测变量,以降低电动系统功率为目的,设计了气动系统模型预测控制(MPC)算法。仿真结果显示,应用MPC算法后的气动系统分担了较大驱动力,降低电动系统功率效果显著。

Optimality of Distributed Control for <i>n ×n</i>Hyperbolic Systems with an Infinite Number of Variables

In this paper, we study the existence of solutions for 2l order (n × n) cooperative systems governed by Dirichlet and Neumann problems involving hyperbolic operators with an infinite number of variables and with variable coefficients. The necessary and sufficient conditions for optimality of the distributed control with constraints are obtained and the set of inequalities that defining the optimal control of these systems are also obtained.

具有媒体播报效应的埃博拉传染病模型的动力学分析

该文依据埃博拉的传播机制,构建一类具有媒体播报效应及有限医疗资源环境下的SIRDM传染病模型,计算模型的控制再生数,证明了无病平衡点的存在性、全局稳定性以及地方病平衡点的存在唯一性.然后对控制再生数进行敏感性分析,最后进行数值模拟以探究医疗资源及媒体播报对于疾病的影响,结果表明适量增加医疗资源和媒体播报量会降低疾病的暴发规模,从而能有效地防控疫情.

一类具有疫苗接种和环境传播的新型冠状病毒肺炎模型的动力学分析

依据传染病动力学的数学建模方法和新型冠状病毒肺炎(COVID-19)的传播机理,综合考虑疫苗接种及环境中的病毒载量对COVID-19传播的影响,建立了一类SEIARW传染病模型。首先,计算了模型的控制再生数,并证明了在控制再生数大于1时,模型存在唯一的地方病平衡点。然后,通过构造Lyapunov函数证明了无病平衡点和地方病平衡点的全局稳定性。最后,绘制出了控制再生数随其参数的变化曲线图,并拟合了2022年11月20日至12月5日期间北京显性感染者的疫情数据。数值模拟结果表明:提高疫苗接种率及疫苗效力能够降低疫情暴发的最终规模,并且加强环境中病毒的消杀能够有效减少潜伏期感染者、显性感染者和隐性感染者的人数。同时,应因地制宜地制定科学的防控策略,避免过度消毒损害人体健康和污染环境。

基于变论域模糊自抗扰的PMSM控制研究

为提高永磁同步电机伺服系统抗负载能力和速度控制的精度,提出一种变论域模糊自抗扰控制策略。变论域模糊控制对自抗扰控制参数进行在线优化调整,提升线性自抗扰控制器自调节能力。在Matlab/Simulink平台进行仿真实验,结果表明,基于变论域模糊自抗扰控制算法,与传统比例微分控制策略相比,具有更好的系统动、静态响应性能,且对负载扰动具有更强的鲁棒性。