Time-varying formation tracking for high-order multi-agent systems with switching topologies and a leader of bounded unknown input

Time-varying formation tracking problems for high-order multi-agent systems with switching topologies are investigated. Different from the previous work, the states of the followers form a predefined time-varying formation while tracking the state of the leader with bounded unknown control input. Besides, the communication topology can be switching, and the dynamics of each agent can have nonlinearities. Firstly, a nonlinear time-varying formation tracking control protocol is presented which is constructed using only local neighboring information. Secondly, an algorithm with four steps is proposed to design the time-varying formation tracking protocol, where the time-varying formation tracking feasibility condition is introduced. Thirdly, by using the Lyapunov theory, the stability of the proposed algorithm is proven. It is proved that the high-order multi-agent system with switching topologies achieves the time-varying formation tracking if the feasibility condition holds and the dwell time is larger than a positive constant. Finally, a numerical example with six followers and one leader is given to demonstrate the effectiveness of the obtained results.     

Network-based leader-following formation control of second-order autonomous unmanned systems

This article investigates two kinds of leader-following formation control problems of second-order autonomous unmanned systems under directed topology, that are, the cases with constant velocity and time-varying velocity for the leader. First, the kinematical equation of autonomous unmanned systems is established according to some real scenarios. Second, by assuming the velocity of the leader is constant, a sufficient condition ensuring the formation control of autonomous unmanned systems is derived and some control parameters are suitably designed. Third, it is assumed that the velocity of leader is time-varying, and the formation controller with two parts is designed. The first part is intended to form the desired formation of all followers and the second part aims to reach the consensus of velocity. Some simulation examples are finally presented to verify the effectiveness of the obtained theoretical results.     

A cyclic pursuit framework for networked mobile agents based on vector field approach

This paper proposes a pursuit formation control scheme for a network of double-integrator mobile agents based on a vector field approach. In a leaderless architecture, each agent pursues another one via a cyclic topology to achieve a regular polygon formation. On the other hand, the agents are exposed to a rotational vector field such that they rotate around the vector field centroid, while they keep the regular polygon formation. The main problem of existing approaches in the literature for cyclic pursuit of double-integrator multiagent systems is that under those approaches, the swarm angular velocity and centroid are not controllable based on missions and agents capabilities. However, by employing the proposed vector field approach in this paper, while keeping a regular polygon formation, the swarm angular velocity and centroid can be determined arbitrary. The obtained results can be extended to achieve elliptical formations with cyclic pursuit as well. Simulation results for a team of eight mobile agents verify the accuracy of the proposed control scheme.     

Practical time-varying output formation tracking for high-order multi-agent systems with collision avoidance,obstacle dodging and connectivity maintenance

Practical time-varying output formation tracking problems with collision avoidance, obstacle dodging and connectivity maintenance for high-order multi-agent systems are investigated, and the practical time-varying output formation tracking error is controlled within an arbitrarily small bound. The outputs of followers are designed to track the output of the leader with unknown control input while retaining the predefined time-varying formation. Uncertainties are considered in the dynamics of the followers and the leader. Firstly, distributed extended state observers are developed to estimate the uncertainties and the leader’s unknown control input. A strategy of obstacle dodging is given by designing an ideal secure position for the followers which are in the threatened area of the obstacles. By constructing collision avoidance, obstacle dodging and connectivity maintenance artificial potential functions, corresponding negative gradient terms are calculated to achieve the safety guarantee. Secondly, a practical time-varying output formation tracking protocol is proposed by using distributed extended state observers and the negative gradient terms. Additionally, an approach is presented to determine the gain parameters in the protocol. The stability of the closed-loop multi-agent system with the protocol is analyzed by using Lyapunov stability theory. Finally, a simulation experiment is provided to illustrate the effectiveness of the obtained methods.     

基于扎根理论的网络用户信息茧房形成机制的质性研究

[目的/意义]为了厘清网络用户信息茧房的形成机制和运行机理,预防群体极化的社会现象的出现,从信息的视角,促进社会的和谐发展。[方法/过程]通过深度访谈的形式,获得原始访谈资料,运用扎根理论的方法,对访谈文本进行编码处理,结合信息生态理论,得到网络用户信息茧房形成机制的研究模型。[结果/结论]研究结果显示,信息人因素、信息因素、信息技术因素和信息环境因素是网络用户信息茧房形成过程中重要的影响因素。最后从预防信息茧房形成的视角,提出了提高网络用户信息素养、优化信息技术和改善信息环境的对策和建议。     

花岗岩成因研究的若干问题

花岗岩是大陆地壳的重要组成,是地质学研究的重要课题.本文对当前花岗岩研究中的几个重要问题进行了讨论,内容包括：（1）花岗岩的成因分类,（2）花岗岩浆起源的温度与压力条件,（3）结晶分异作用与花岗岩成分变化,（4）花岗岩成因与壳幔演化,（5）花岗岩形成的构造环境等.通过分析认为,高分异花岗岩成因类型的确定是比较困难的,在有些情况甚至不可能准确分类.花岗岩的锆饱和温度和锆石钛温度计可对花岗岩浆形成的温度提供重要信息,但花岗岩浆起源的压力条件确定相对困难.花岗岩主要形成于俯冲带或碰撞造山带后造山的拉张构造背景中,在这两种情况下,挥发份和热的加入可使地壳发生部分熔融而形成花岗岩.本文还对我国近年来花岗岩研究的进展情况做了概要性叙述,并就我国东部中生代花岗岩研究的近期突破问题进行了分析.     

A Direct Method for Model Reduction of Discrete systems

A new method for the model reduction of linear discrete stable systems in Z-transfer functions is presented. First, a set of parameters is defined, whose values uniquely determine the given system. Then an always stable reduced approximant is obtained by neglecting the parameters which do not contribute significantly in the formation of the system's responses. The proposed method slightly modified also preserves, in the reduced model, the rank of the given system. Formulae are provided to select the reduced order.     

在线商品虚假评论形成路径研究

以淘宝为例,通过对43万条评论语料进行分析以及乔装淘宝店主获取的事实数据,从在线商品虚假评论实际解决需要出发,为在线商品虚假评论界定了新的含义,归纳了在线商品虚假评论的影响,最后全面分析了由在线评论者、在线销售商家、在线商品交易平台、虚假评论中介四大主体所组成体系中在线商品虚假评论的六大形成路径、形成动因及特点.本文对下一步的在线商品虚假评论识别技术等相关研究有极强的理论和实践指导意义.     

异戊二烯二聚钠系催化剂的制备与研究

在恒温－磁力搅拌实验装置上考察了金属钠负载在不同载体AI2O3分子筛、稀土氧化物（CeO2、La2O3、Sm2O3)和MgO上，在添加剂DIPA／TEA的作用下对异戊二烯二聚的影响，发现酸性载体不利于二聚的形成；稀土氧化物作载体，虽有同类萜类化合物的结构获得，但产率较低；而负载在碱土金属氧化物上，其中碱土中的MgO表现出较好的二聚结果，这也许是与MgO的晶粒细化及载体碱性密切相关，它更有利于金属钠的负载及分散，以提供更多的有效活性中心数目。     

Perforation of Nonlocal Visco- Plastic Plates by a Cylindrical Projectile

This paper is concerned with the analysis of the problem of dynamic perforation of visco-plastic plates by a cylindrical projectile, leading to a failure of the plate by a plug formation. Assuming the behavior of the plate material is nonlocal visco-plastic, the classical theory of visco-plasticity for Bingham solids is generalized to take the non-local effects into consideration. The target plate being thin, it is assumed that only the contributions of vertical shearing stress need be taken into account. The effect of the impact is represented by a uniform velocity distribution over a circular region of the plate surface. The expressions of velocity, strain rate and shear stress are obtained and some particular cases are discussed. Some numerical results concerning stress distributions are also included.     

应用型高校材料成型设备课程教学模式的改革与探讨

本文结合材料成型设备课程的特点和本课程教学的现状,从调整课程教学内容、改革教学方法以及加强实践能力培养等三个方面,提出了本课程教学模式的改革措施,取得了一定的成效,为同类专业课程的教学改革提供了依据。     

应用型高校材料成型设备课程教学模式的改革与探讨

本文结合材料成型设备课程的特点和本课程教学的现状,从调整课程教学内容、改革教学方法以及加强实践能力培养等三个方面,提出了本课程教学模式的改革措施,取得了一定的成效,为同类专业课程的教学改革提供了依据。     

建筑信息模型(BIM)生态系统的形成动因分析

建筑信息模型（BIM）将信息技术应用到建筑业,其中涉及的技术、流程、政策和组织网络等要素构成了复杂的BIM生态系统,共同影响着建筑信息化的发展。基于生态系统理论和建筑产业背景,本文首先通过类比分析构建了BIM生态系统的理论模型;其次,从信息、信息人、信息环境3个角度探讨了BIM平台的介入对工程项目产生的影响;在分析BIM生态系统理论模型的基础上,根据BIM生态系统的起源,并结合企业分工与协作、环境变化等驱动条件,探讨了BIM生态系统形成的动因;最后构建了BIM生态系统的研究框架,该框架考虑了BIM生态系统的形成、架构、运转和演化等四个方面,分别提出了针对这四个方面的研究理论、研究内容、研究方法及其预期结果,以期为后续研究提供可能的研究思路。     

Investigating the impact of organizational climate,motivational drivers,and empowering leadership on knowledge sharing

This paper presents a research model aimed to investigate the impact of organizational climate, motivational drivers, and empowering leadership on behavioral intention formation in knowledge sharing. A research model has been developed by integrating several knowledge management studies having in-focus behavioral intention formation in knowledge sharing. The hypotheses are tested on data collected from 873 employees from public and private sector organizations from Serbia’s province of Vojvodina, using partial least square structural modeling technique and SmartPLS software. Findings suggest that organizational climate with prominent dimensions of fairness, innovativeness and affiliation, empowering leadership, sense of self-worth, and altruism significantly influence individuals’ knowledge-sharing attitude, intention, and behavior thus confirming the theory of reasoned action. Results obtained in this research expand and deepen findings reported in previous studies and enable a comprehensive framework for understanding the influence of some organizational variables on employees’ tendencies to be engaged in knowledge sharing.     

跨组织知识网边界锁定及编码机理

利用边界锁定技术对知识网进行研究。通过对跨组对织知识边界及形成机理的分析,得出知识网结构模型,在知识边界锁定的基础上,利用编码技术,初步研究跨组织知识网编码方法,从而为实现基于Internet的跨组织知识共享及协同工作准备了技术基础,同时也为大规模的科学知识研究层次化、权限化、模块化、集成化、信息化以及科学研究的一致性和动态更新及维护提供方法。     

资源开发对资源型经济的影响机制分析

为分析资源型经济运行机制,通过建立资源型地区内生增长模型,考察了资源型经济的要素流动机制和路径选择特征,结果表明:在要素配置水平低下的情况下,依赖资源开发不仅会直接阻碍长期中的经济增长,还能通过其他社会经济变量的间接作用弱化经济增长;并通过计量模型进行了实证检验。实现资源型经济良性运行,需要完善要素配置环境,通过相关政策规范资源型地区的经济行为,建设可递进的资本形成机制。     

基于演化博弈的上下游企业产业共生形成模式选择

产业共生是提高工业废弃物利用效率的主要方法之一。针对产业共生形成模式的选择问题,以演化博弈为主要方法构建了产业共生演化博弈模型。该模型以实现社会总经济效益最大化为目标,从治理主体和驱动模式两个角度出发,提出了产业共生形成的四种情景模式。在此基础上,通过计算得出可以实现产业共生的九个参数情形及其对应的产业共生实现概率。研究表明:第一,在给定参数的情形下,可以根据该模型进行上下游企业工业废弃物治理的形成模式选择;第二,无论治理主体是上游企业还是下游企业,政府与市场在机制选择中的替换作用并没有明确的边界;第三,当治理主体为下游企业时,仅靠市场作用很难实现上下游企业的合作。在此基础上,提出了相关政策建议,为政府和企业决策提供理论支持。     

关键词检索特性的计量学分析

利用文献计量学方法,对关键词检索文献出现的数量上特征,通过列表进行分析,得出关键词检索具有专指性、结合性与层次性以及层次性分离的特性,形成对关键词检索的认识,对标引与检索文献以及日后的研究具有积极意义。     

人工合成岩矿石频谱参数对比及其找矿意义研究

在实验室对人工合成的岩、矿石标本进行了复电阻率特性测量,利用标本的复电阻率振幅频谱曲线反演求得其Cole-Cole模型参数,讨论了各标本的Cole-Cole模型参数的异同,得出了可以通过标本的4个模型参数(ρ0、m、τ、c)区分良导电、高极化率岩、矿石,达到区分矿与非矿的目的的结论,为在有干扰地层(黄铁矿、炭质层等)的地区开展物探电法找矿工作提供了试验依据。     

Event-triggered time-varying formation control for general linear multi-agent systems

This paper investigates event-triggered formation control problems for general linear multi-agent systems. The time-varying formation this paper studied can be described by a bounded piecewise differentiable vector-valued function. Firstly, a time-varying formation control protocol based on event-triggered scheme is constructed by the states of the neighboring agents. Each agent broadcasts its state information to neighbor nodes if the triggering condition is satisfied, and the communication load is decreased significantly. Then, an algorithm consisting of three steps is proposed to design the event-triggered formation control protocol. Moreover, it is proven that under the designed event-triggered formation protocol, the multi-agent systems can achieve the desired time-varying formation which belongs to the feasible formation set with the bounded formation error and the closed systems do not exhibit Zeno behavior. Finally, simulation results are given to demonstrate the effectiveness of the theoretical analysis.