Difference systems of sets (DSSs) are combinatorial structures introduced by Levenshtein, which are a generalization of cyclic difference sets and arise in connection with code synchronization. In this paper, we describe four direct constructions of optimal DSSs from finite projective geometries and present a recursive construction of DSSs by extending the known construction. As a consequence, new infinite families of optimal DSSs can be obtained.
The large-scale multi-objective optimization problem is characterized by a large decision space. How to design an efficient optimization algorithm that can search a large decision space and find the global optimum in the objective space is a very challenging problem at present. In order to solve this problem, this paper proposes a sampling strategy based on direction vectors, which takes into account both convergence and diversity. First, select some excellent individuals who are close to the ideal point based on the reference vector. Secondly, construct a three-way search direction vector using the boundary point and an additional center point, and execute a directional sampling strategy called the convergence-related sampling strategy to improve the convergence of the algorithm. After, the direction vector is constructed among excellent individuals and executes a directional sampling strategy called the diversity-related sampling strategy to maintain the diversity of the population. Finally, the adjustment strategy of the reference vector in the Reference Vector Guidance Algorithm (RVEA) is adopted to adjust the reference vector. Numerical experiments are performed on large-scale multi-objective benchmark problem sets with 500, 1000, and 2000 decision variables and compared with the state-of-the-art algorithms. Experimental results show that the algorithm proposed in this paper is effective and can obtain solutions that are significantly better than those of the compared algorithms.
The accuracy of the kinematic model is affected by the error of geometric parameters caused by the machining and assembly of the robot, causing decline of the accuracy of the motion control and the odometry. In order to improve the motion accuracy of the omnidirectional mobile robot（OMR）, a step-by-step calibration method is proposed for an omnidirectional mobile robot based on decoupled powered caster wheels（DPCW）.This method simplifies the kinematic matrix by limiting the input of motion in joint space. Then the least squares method is used to obtain actual values of kinematic parameters. As a result, the precision of the kinematic model is improved. The experimental platform for the OMR based on DPCW is built, and the calibration algorithm is verified by simulation and experiment. The results show that the accuracies of both velocity control and odometry are significantly improved in three degrees of freedom in the plane, which proves the effectiveness of the calibration algorithm.
Task allocation is one of the key issues in multi-mobile robot scheduling system. The existing methods tend to focus on improving the efficiency of task assignment without considering the task execution time, ignoring the overall task completion efficiency and the computational cost. In addition, they usually adopt a centralized control architecture, which requires the robot to be in a stable and reliable communication environment. In order to solve the above problems, a distributed auction mechanism-based dynamic task assignment algorithm for multiple mobile robots is proposed. The method adopts a distributed control method for robot groups, shares and dynamically updates task sets with each other, bids for tasks using a distributed auction mechanism, adds a link to adjust the task execution order, and considers the overall task completion efficiency. Finally, a simulation environment with multiple robots and obstacles is built under Linux system and relevant experiments are conducted. The experimental results show that the algorithm has higher allocation efficiency than the linear and mixed integer solving algorithms CLP and CBC, and has stability. Comparing with the Deep Reinforcement Learning（DQN） and Vacancy Chain（VC） algorithms, the execution efficiency remains stable while the movement cost is significantly reduced by 55%, which achieves a balance between the efficiency and cost in operation. This study, as believed, can be put to the real-world applications with promising outlook.
The current study is to determine the safety of inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines in patients with skin allergies and egg intolerance but lacking laboratory evidence of egg allergy. This retrospective study included adults with skin allergies but lacking laboratory evidence of egg allergy who received two doses of the SARS-CoV-2 vaccines. Local and systemic reactions for 7 days following each vaccine dose were recorded during telephone interviews. 122 participants with skin allergies (mean age, 30±9.47 years) were enrolled. Egg-intolerant individuals had more anaphylactic reactions after receiving the vaccine than did egg-tolerant individuals (39.78％vs.17.24％, P<0.05). A higher titer of egg sIgG4 was associated with the increased risk of allergic responses after receiving the vaccine (P for trend=0.008). Unusual pain and new or worsened skin rashes were common reactions, especially after the first dose. After adjustments, egg-intolerance was correlated with a higher risk of unusual pain (P=0.044, adjusted odds ratio (aOR): 5.061, 95％ confidence interval (CI): 1.047-24.457) and new or worsened skin rashes (P=0.041, aOR: 9.109, 95％CI: 1.098-75.563) after the first injection. The results supported the overall safety of inactivated SAR-CoV-2 vaccines. Egg intolerance increased the risk of allergic reactions in adults with skin allergies but lacking laboratory evidence of egg allergy within 7 days of receiving the inactivated vaccine. These reactions were more frequent after the first dose and were positively associated with egg serum concentration.
在溶剂热条件下,以 4,4'-磺酰基二苯甲酸(H2SDBA)为配体与硝酸铕构建出具有荧光性质的稀土有机框架[Eu2(SDBA)3(H2O)4].NMP(NMP=N-甲基吡咯烷酮),并对其进行粉末 X 射线衍射、荧光光谱、紫外吸收光谱等手段表征.X 射线单晶衍射分析结果显示该材料具有三维结构.Eu-MOFs具有良好的荧光性能,能够在水中同时实现对维生素B4和阿奇霉素的高灵敏及高选择的荧光淬灭检测.
基于浙江省第六、七次人口普查数据,使用探索性空间数据分析和空间计量模型分析2010-2020 年浙江省县域尺度人口老龄化的空间格局演变及其驱动机制.研究结果发现:(1)浙江省人口老龄化程度整体加深,老龄化空间格局由"团带式"转变为"团点式",各县级单元之间老龄化存在正向空间相关性,其中低-低集聚区主要分散分布在西南部,零星分布于北部和东部,高-高集聚区主要分布在西部地区,且范围有所增大;(2)以出生率和死亡率为主的人口变化因素是影响浙江省老龄化空间格局的直接原因,教育水平、医疗资源和经济水平等地区社会经济发展差异是根本原因.因此,浙江省应从完善基础设施、优化人口政策等方面应对老龄化社会.
排水管网过流能力对于评估其运行状况至关重要,现有的在线流量监测成本普遍偏高.本研究基于排水性能图谱提出了一种利用监测多个检查井液位以推求管网动态流量的新方法,并应用于宁波某典型片区污水管网水力分析与模拟计算,结果与暴雨洪水管理模型模拟输出数据进行对比,表明流量监测结果最大误差不超过 5%,间接推导得到水深结果最大误差不超过 8%.基于排水性能图谱对影响该排水管网系统最大过流能力的瓶颈管段进行了诊断分析,并提出描述管道内水流充满度的新参数,以反映排水管网的负载情况.基于排水性能图谱对排水管道系统进行非恒定流演算,其中节点流量演算结果的最大相对误差为 5%,节点水深演算结果的最大相对误差为 6%,表明该方法具有较高准确性和效率.
模壁粗糙度对微注塑成型的充模过程有着十分重要的作用,本文从微尺度流中塑料熔体的可压缩性充模模型出发,对模具内壁粗糙度进行了讨论和简化,并通过连续性方程、动量守恒方程和能量守恒方程给出了考虑模具表面粗糙度的充模控制方程,采用有限元/有限差分法来求解充模中的压力、温度等,采用修正的 Cross-WLF 模型表征熔融塑料材料的非牛顿行为流变特性.通过数值模拟,分析了模壁粗糙度对充模流动的影响,并设计一系列实验,考察各种工艺参数情况下模壁粗糙度对充模流动的影响.模拟和实验结果表明:型腔厚度越小,模壁粗糙度对充模流动的影响越显著;熔体温度越低,模壁粗糙度对充模流动的影响越显著;注射速率对模具表面粗糙度效应影响较小.
聚丙烯腈的合成一直是高分子合成和特种高分子材料领域的研究热点.稀土金属苄基配合物(2,5-Me2C4H2CH2CH2NC6H5)Ln(CH2C6H4NMe2-o)2(Ln=Sc,La)、(C5Me5)Sc(CH2C6H4NMe2-o)2、(2,5-Me2C4H2NSiMe2NC6H5)Sc(CH2C6H4NMe2-o)2和Ln(CH2C6H4NMe2-o)3(Ln=Sc,Y,La,Lu)可以作为单组分催化剂引发丙烯腈聚合.通过改变辅助配体、聚合溶剂、金属离子以及聚合温度等条件,探究了稀土金属苄基配合物催化丙烯腈聚合的活性及选择性.结果表明,这些稀土金属配合物对丙烯腈聚合表现出很高的催化活性,得到了高分子量的无规聚丙烯腈.辅助配体、溶剂、聚合温度和中心金属半径对所得聚合物的微观结构没有太大影响.
城市雨污混合制管道中的沉积物会导致管道腐蚀、排水效率降低,甚至管道堵塞,影响城市正常运转.在各种清洁方法中,使用产生冲刷波的冲刷装置已被广泛认为是一种有效和经济的解决方案.本文使用 Flow-3D 软件进行了一系列数值模拟计算,通过与文献中的实验进行水动力和泥沙冲刷对比,验证了该软件中泥沙冲淤模型的正确性,在此基础上利用该模型研究了 3种简化的自动冲刷装置对管道沉积物的清淤效率.结果表明,半开口阀门高度对冲刷效率存在直接影响,阀门相对高度设置为 0.2 时冲刷效率最高.在 3 种阀门冲刷作用下,沉积层形态各异,冲刷效率也存在差异.开口阀门、倾倒式阀门、半开口阀门在冲刷下沉积床形态分别呈现直线形、V形和U形.半开口阀门条件下,清除全部沉积物所需的冲刷时间比开口阀门少30%.与开口阀门和倾倒式阀门相比,半开口阀门可分别节约 75%和26%的水.
建立高效液相色谱-串联质谱法测定果汁中恩镰孢菌素和白僵菌素检测方法.样品用V(乙腈):V(水):V(甲酸)混合液(79:20:1)提取,QuEChERS填料包(4g无水MgSO4、0.5 g无水CH3COONa和 0.5 g NaCl)盐析,100 mg C18净化,经过液相色谱柱分离,2 mmol·L-1 乙酸铵水溶液-甲醇为流动相梯度洗脱,由 ESI 源扫描,多反应监测模式,基质外标法定量分析.该方法中,恩镰孢菌素A(ENA)、恩镰孢菌素 B(ENB)和白僵菌素(BEA)在 0.1～200 μg·L-1 以及恩镰孢菌素 A1(ENA1)和恩镰孢菌素B1(ENB1)在 1～200 μg·L-1 范围内线性关系良好,且线性相关系数(R2)均大于 0.9989,相对标准偏差范围为 1.7%～11.7%.3 个不同加标浓度的添加回收率为 88.0%～114.1%,样品检测限为 1.5µg·kg-1,样品定量限为 5µg·kg-1.本文建立的方法简单、高效、准确,满足果汁中恩镰孢菌素和白僵菌素污染筛查需求.
座椅是汽车内饰件中质量较重的一部分,座椅骨架的轻量化设计可以有效地降低座椅整体质量,提高汽车整体性能.本文利用 CATIA 软件对某乘用车前排座椅骨架进行几何建模,建立座椅骨架的有限元模型,并基于国家标准 GB 15083-2006 对座椅骨架模型进行有限元分析.然后利用相对密度法的拓扑优化模型对座椅骨架进行轻量化设计,以体积约束下的最小结构柔度为优化目标,通过 ABAQUS 软件中的 TOSCA 模块对座椅骨架进行拓扑优化,将优化后的座椅骨架结构在ABAQUS中进行静力学分析.结果显示,在满足座椅结构强度和刚度的情况下,座椅骨架减轻了0.584 kg,减重约4%,实现了座椅轻量化的效果.
跟腱病是对复杂、多方面病理跟腱的总称,在临床中突出的特征表现是跟腱及腱周组织的肿胀、疼痛和跟腱功能受限.跟腱作为人体最大、最强壮的肌腱,是踝关节跖屈的主要力量,跟腱病的发生会严重影响患者的生活质量.目前对于跟腱病治疗多以保守治疗为主,而伴随着组织工程和再生医学的发展,其中富血小板血浆(Platelet-Rich Plasma,PRP)与肌腱干细胞(Tendon Stem Cells,TSCs)治疗肌腱相关疾病成为近期研究的热点.本文回顾了与PRP和TSCs治疗跟腱病相关的研究,对PRP和TSCs治疗跟腱病的进展作一综述.
为解决航空涡轮轴成形难、制造流程长、材料利用率低等问题,提出了一种穿轧一体化成形工艺,运用多辊系斜轧技术,在外表面加工上克服阶梯状大断面收缩率的制造难题,在内孔加工上实现由减材制造到等材制造的转变.采用Simufact有限元软件对镍基高温合金GH4169涡轮轴坯的成形过程进行数值模拟,分析其成形过程中轧件金属流动以及应力应变场、力能参数的变化规律,验证了新工艺的可行性.
碳基集流体具有质量轻、耐腐蚀等优点,但在锂电池应用中存在与金属极耳难以用传统焊接方式进行有效连接的共性问题,为此本文旨在发展两者的创新连接方案,以解决碳基集流体的应用难题,提出了3种可能的连接方式.通过分析对比不同连接方式的导电性能、力学性能以及在软包电池中的应用效果,来判定碳基集流体与金属极耳的连接有效性,最终优选出双层极耳连接作为最佳连接方式,并进一步采用正交实验对双层极耳连接进行了工艺参数优化.结果表明,提出的创新连接方式能够提供优良的导电接触和连接强度,确保碳基集流体在锂电池中的正常应用.
模具在现代工业生产中有着重要地位,而增材制造技术出现和产业化应用为模具行业带来了变革.本文对目前模具行业应用较多的增材制造技术,包括喷射粘结成形、选择性激光烧结、选择性激光融化和光固化成形进行了原理简述.同时,根据增材制造技术在模具行业的2 个典型应用方向(模具快速原型制造和高性能模具零件制造),分析了增材制造技术在其中的具体应用方法,并对国内外相关研究成果进行了综述,总结出增材制造技术在模具行业进行批量化应用所需要解决的关键问题是:如何通过对原材料、工艺和设备的研究来提高增材制造技术相比于传统制造技术的性价比.最后对增材制造技术在模具行业的未来发展进行了展望.
针对直边蜂窝结构进行优化,提出了一种S形曲边蜂窝结构.基于激光选区熔化增材制造技术,以GP1不锈钢为基材,制备了直边和曲边蜂窝结构,实验结合有限元计算模拟研究曲边蜂窝结构的力学响应、变形模式和吸能特性,并讨论了加载应变速率和相对密度的影响规律.结果表明:(1)S形曲边蜂窝结构的载荷—位移曲线出现2次平台区,其原因是S形曲边蜂窝结构出现从六角变形模式向四角变形模式的转变;(2)在相同体积条件下,相比直边蜂窝结构,S形曲边蜂窝结构的吸收总能量和吸能有效率均得到一定提升;(3)随着加载应变速率增大,S形曲边蜂窝结构二次平台载荷均增大,第2次平台载荷对加载应变速率更为敏感,同时还发现加载应变速率不影响S形曲边蜂窝结构的变形模式;(4)随着相对密度的增加,S形曲边蜂窝结构二次平台载荷均呈线性增长,压实临界位移量减小.
随着港口产业转型升级,港口城市的内城港区作为交通枢纽的传统功能被削弱,其空间转型和新空间生产一直是社会和学界关注点.以马赛内城港区空间更新为例,基于空间生产理论的权力与资本视角构建港口城市空间转型的定性分析框架,结合熵权TOPSIS、效能累加模型以及多元回归等方法,定量分析其空间更新效果和驱动因素.结果表明:(1)马赛通过设施更新、文化营造等关键措施实现空间更新;1995 年至 2020 年空间更新水平总体提高,在用地面积、城市设施、就业和投资指标方面有所差异.子系统的空间生产总体效率从 1995 年起稳步提升,但由于空间保护效率增长缓慢,制约了空间更新综合效率的提高.(2)不同尺度的权力和资本主体共同驱动马赛从工业贸易空间到旅游休闲空间的转型.马赛港城空间体现了空间实践、空间表征和表征空间的三元辩证融合.此案例研究旨在为我国一些历史港城在"海上丝绸之路"倡议中探讨老港区更新效能和驱动机制等方面提供启发.
水泥土渗透特性对滨海软土地区植入式排水桩排水固结效果影响显著.本文首先开展水泥土抽排水固结试验,研究水泥土渗透系数随时间变化的性质;然后假定水泥土为竖井地基涂抹区,建立涂抹区渗透系数随时间呈指数衰减的固结方程,得到真空负压下竖井固结解析解.在此基础上,分析水泥土固化影响因子θ、涂抹区径长rs和涂抹区的初始渗透系数ks0对软土地基固结性状的影响.结果表明:水泥土固化作用对固结速率影响显著,水泥土的渗透性对桩周土体的固结效果起着控制作用;随着θ 变大,桩侧土体固结效果逐渐减弱;rs越小,ks0越大,桩周土体固结速率越快.
