往事值得回首

<正> 这20年是文献检索课从无到有,由小而大的一段发展历程。这当中的一些事,今天回想起来仍然很有意思,谨就记忆所及,略述一二。 两条经验 改革开放的号角,催动了各项事业蓬勃发展,用户信息需求也随之迅速增长。但是,他们当中大部分人的利用信息能力与其需求颇不相称,这是当时一个甚为突出的矛盾。身临生产、科研第一线的用户,急切地要求补上这一课。从长远看,培养大学生的这方面能力尤为迫切。解决这一问题,于深化个人治学,于发展生产科研,都有其一定的意义。     

State and unknown input estimations for discrete-time switched linear systems with average dwell time

In this paper, the problem of state and unknown input estimations for a class of discrete-time switched linear systems with average dwell time switching is investigated. First, a proportional integral observer with an exponential H_∞ performance is constructed to estimate the system state and unknown input simultaneously. Second, both of the observability and the stability of the estimation error system are analyzed, then the derivation of the observer gain matrices is transformed into the calculation of linear matrix inequalities. Third, the obtained results are extended to the systems with output disturbances. Finally, two simulation examples are provided to show the validity and effectiveness of the proposed methods.     

Fault-tolerant control for a class of linear interconnected hyperbolic systems by boundary feedback

This paper considers a fault-tolerant control problem for a class of interconnected linear hyperbolic partial differential equation systems. Both subsystem faults and coupling faults are considered. Firstly, the well-posedness of the faulty system is analyzed by using semigroup theory. Secondly, for the fault-free case, a stabilizing boundary feedback control based on small-gain theorem is proposed. Consequently, in the presence of faults, fault recoverability conditions are established that maintain the stability of the faulty systems. The fault-tolerant control strategies are also provided. A heat exchanger example is taken to illustrate the effectiveness and practicality of the proposed methods.     

Novel integral sliding mode control for small-scale unmanned helicopters

Integral sliding mode (ISM) control which consists of a nominal control and a sliding-mode motion control, provides a nice framework for high tracking performance and good disturbance reduction. Our work develops ISM to attenuate the adverse effect of mismatched perturbations. By properly choosing sliding-manifold surface, the elimination of disturbances on control outputs enables to be achieved. Additionally, the chattering of sliding-mode control part is attenuated based on second-order sliding mode idea. Then, the proposed novel ISM control scheme is applied to address trajectory tracking problem for helicopters under perturbations. Approximated input-output linearization is implemented, such that the obtained linearized model is suitable for applying the proposed ism control. The stability of the closed-loop system for helicopter and its convergence to zeros of tracking errors are demonstrated by Lyapunov theory analysis. Several comparison simulations illustrate the effectiveness and superiority of the proposed methods.     

Dynamics of a stochastic multigroup SIQR epidemic model with standard incidence rates

In this paper, we consider a stochastic multigroup SIQR epidemic model with standard incidence rates. By using the stochastic Lyapunov function method, we establish sufficient conditions for the existence of a stationary distribution of the positive solutions to the model. Then we establish sufficient conditions for extinction of the diseases. A stationary distribution means that all the individuals can be coexistent and persistent in the long term. Finally, some examples and numerical simulations are introduced to illustrate our theoretical results.     

我国高校创新效率及环境分析:价值类型视角

经济价值和社会价值是高校创新价值的两大重要体现,随着利他性的高校创新活动在经济发展和提升区域创新能力中的重要性日益突显,高校创新的价值本源--社会价值正成为创新型国家建设的关键。然而,现有研究主要关注高校创新的经济价值效率而缺乏对社会价值效率的深入关切。文章基于经济价值和社会价值视角,运用DF-DEA模型测算高校创新经济价值和社会价值效率,并对效率动态演进过程和效率变化趋势进行分析,最后使用面板Tobit模型对高校创新效率的影响因素进行了剖析。研究表明：2011-2015年我国省域高校创新经济价值效率较高但波动较大,社会价值效率相对较低但较稳定;使用核密度估计进一步分析发现：样本期内高校创新经济价值效率和社会价值效率均呈显著“单峰”分布,但经济价值效率有改善趋势,社会价值效率则有恶化趋势;使用面板Tobit模型对创新环境分析后发现：经济优势、区位优势、政府扶持力度、基础设施状况对高校创新效率具有较显著影响。     

2019年夏季全国气候趋势展望

2019年春夏季,赤道中东太平洋将维持弱-中等强度厄尔尼诺（El Niño）。中国科学院大气物理研究所的全国气候趋势预测结果表明,预计2019年汛期（6—8月）,长江中下游以南大部分地区降水偏多,其中江南地区偏多2—5成,可能发生局地洪涝灾害;新疆北部、东北北部、四川东部和陕西南部等地降水正常略偏多。我国其他大部分地区降水正常略偏少,其中河套地区降水偏少2—5成。预计2019年登陆台风数正常略偏多。     

基于贝叶斯网络的组织创新影响机制研究

组织创新影响机制中各变量具有不确定性与动态性等特点,可以尝试进行贝叶斯网络分析。根据贝叶斯网络的基本原理,构建了基于贝叶斯网络的组织创新影响机制模型,并对复杂贝叶斯网络计算问题的简化问题进行了探讨。实例应用表明,该方法克服了其他传统分析方法局限于线性、静态分析的缺点,较为准确地反映了组织创新影响机制各变量间的动态关系。     

基于词频分析的CSSCI中知识共享的热点研究

利用CiteSpaceⅡ以“知识共享”和“知识转移”为关键词从CSSCI数据库检索1998-2011 年的1388 条数据 为基础,通过共词分析和共现分析等发现,刘益等是知识共享研究发文数量较多的学者,西安交通大学等是知识共享 领域发文数量较多的机构单位;Nonaka 等是知识共享领域较有影响的学者。通过关键词的共现网络发现,“图书馆”、“知 识共享机制”、“知识网络”等是知识共享领域研究的热点。在研究热点的知识基础中,Nonaka的《组织知识创造的动态 理论》、Cohen的《吸收能力：基于学习与创新的新视角》等是十分重要的经典文献。