陕西关中地区生态弹性计量模型与测算

关中地区是关中-天水经济区的主要部分,生态环境面临来自社会经济、自然环境等方面的压力,研究关中地区的生态弹性及其影响因素具有重要意义.通过GIS和RS技术,运用生态弹性度计算模型,测算了2000-2015年15 a间陕西省关中地区的生态弹性度,分析了市区间生态弹性度和生态弹性动态度的时空特征;探讨了土地利用变化和植被净初级生产力对生态弹性度的影响.研究结果表明：关中地区生态弹性度总体在4~8,从2000年的4.17~7.67升至2015年的5.94~7.52,总体呈上升趋势,生态环境有所改善.区域生态弹性受土地利用方式和NPP的影响,其中林地对区域生态弹性的提高影响最大,草地、耕地次之.通过植树造林增加建成区植被覆盖面积,有益于改善区域生态环境,提高区域生态弹性度.     

关于克劳修斯方法对可逆和不可逆过程(循环)的处理

介绍了克劳修斯方法对可逆和不可逆过程(循环)的处理,提出了处理不可逆过程的方法,论证了处理方法与克劳修斯方程的一致性,论述了克劳修斯方法的实质和意义;简单介绍了熵的另一个导出方法,比较了两种方法对绝热过程的处理,指出克劳修斯方法存在一个假设条件.     

Constrained regulation of continuous Petri nets

This paper deals with constrained regulation of continuous Petri nets under the so-called infinite servers semantics. Our aim is to design feedback gains that permit us to reach both desired stationary marking vector and desired asymptotic firing rate vector. The proposed approach takes into account constraints on the control, the marking of the Petri net, and the stability of the closed-loop system. The existence of a solution is first expressed geometrically, in terms of the inclusion of two polyhedral sets. They are reformulated algebraically as linear matrix inequalities, which provides an effective way to calculate feedback gains answering the problem. Finally, an application to an assembly production system is given.     

基于资金现值约束的双目标项目组合选择模型研究

近年来,项目组合选择问题已引起人们越来越多的关注,如何从众多项目中选择合适项目以满足企业长期发展战略已成为企业面临的重要问题。因此,本文在考虑项目可打断的基础上构建了一个净现值和效用并存的双目标项目组合选择模型,同时把模型中的资金约束转变为资金现值约束,并通过理论给予证明,使模型得以简化。最后,通过实际算例进行分析。结果表明:基于双目标的项目组合选择模型比单一目标更加符合企业长期发展战略,该模型也为投资决策者进行项目组合选择提供了较完善的理论依据。     

航天器多总线系统网信息仿真系统设计

针对航天器系统网多组1553B与串行总线通信的应用情况,设计了一种航天器多总线系统网信息仿真系统;系统采用三层网络的数据系统架构,使用C语言与CVI混合编程以多线程机制模拟遥测遥控数据的采集、处理、显示及存储,具有人机界面友好,可靠性、实时性高及成本低的特点;试验结果表明,该系统功能及性能完全满足航天器系统网信息仿真要求,有效支撑了航天器系统网的总体设计,大幅度降低了研发周期。     

不同算法原子电荷下的~1J_(CH)理论计算

用一种计算直接键连原子核自旋耦合常数的半经验公式,结合量子化学计算得到的32种有机分子稳定几何构型的7种不同算法下的原子电荷,探究原子电荷算法的不同对1JCH理论计算的影响,拟合出基于7种原子电荷的耦合常数计算公式,并利用拟合公式对5种分子进行了检验.计算结果表明拟合的32种分子及检验的5种分子的耦合常数的计算值均与实验值较好的符合,拟合得到的基于7种原子电荷的计算公式均可以对其他分子体系的耦合常数进行预测.另外,计算结果同样显示原子电荷算法的不同对1JCH理论计算值有一定的影响却不显著,其中基于电荷均衡方法电荷(QEq)得出的耦合常数计算值与实验值的偏差较其它6种原子电荷的小,结果更可靠.     

Performance safety enforcement in stochastic event graphs against boost and slow attacks

This paper studies a performance safety enforcing problem in stochastic event graphs, a subclass of stochastic Petri net models. We assume that an intruder can attack part of the transitions to increase/decrease their firing rate such that the performance of the system violates a given safety interval. The difficulty in solving this problem is that the capability of the intruder, i.e., the number of transitions that can be simultaneously attacked, is limited. The control aim is to find a protecting policy such that the performance of the protected plant is guaranteed to be in a given safety interval. We show that this problem can be formulated as a two-player game between the intruder and the operator of the plant. By using mixed integer linear programming technique, we develop a heuristic method to compute a protecting policy that is locally optimal.     

A procedure for the static analysis of cable structures following elastic catenary theory

The paper proposes an unitary strategy for the static analysis of general cable nets under conservative loads. A form-finding is first performed in order to initialize the successive non linear analysis. The numerical procedures carried on in both steps, form finding and structural analysis of the net, employ a three dimensional elastic catenary element. Equilibrium conditions at internal nodes and kinematic compatibility at the end nodes of each cable are used to derive the global equations of the net. When the pre-stresses are high and the topology of the net is involved, an accurate initializing solution is essential for the convergence of the successive numeric non linear structural analysis (performed by Newton method). The numerical applications highlight the capability of the proposed procedure to solve three dimensional problems with taut and slack cables, out of plane distributed forces (modeling wind loads), point loads along the cables. The contemporary presence of cables and compression truss elements is also considered testing the effectiveness of the method in the analysis of tensegrity structures.     

Numerical simulation of the interaction between flow and flexible nets

A numerical approach is proposed to simulate the interaction between flow and flexible nets in steady current. The numerical approach is based on the joint use of the porous-media model and the lumped-mass model. The configuration of flexible nets can be simulated using the lumped-mass model and the flow field around fishing nets can be simulated using the porous-media model. Using an appropriate iterative scheme, the fluid–structure interaction problem can be solved and the steady flow field around flexible nets can be obtained. In order to validate the numerical models, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. Using the proposed numerical approach, this paper presents the flow field around a single flexible net and two flexible nets with a spacing distance. Both the configuration of the flexible nets and the flow velocity results are in accordance with those of the corresponding physical model tests.     

基于Geo/Geo/1(E,SV)排队系统的均衡止步策略

基于单重休假Geo/Geo/1排队系统,研究顾客的均衡止步策略,首次将休假服务机制引入到离散时间排队经济学模型中. 顾客基于“收入--支出”结构,自主决定去留. 利用拟生灭过程理论,运用差分方程求解技巧,对系统进行了稳态分析,得到了顾客的平均逗留时间;进而构造适当的函数,给出了寻找均衡止步策略的具体方法并证明之;而后分析了在均衡策略下, 系统的稳态行为和社会收益;最后通过数值实验讨论了系统参数对均衡行为的影响.