围压作用下自振空化射流脉动特性实验研究

就围压下自振空化射流动压力特性进行了实验研究,其实验结果表明：在围压作用下,自振空化射流脉动幅度存在最优喷距,并且最优喷距随围压的增大而增大;在压降一定情况下,脉动幅度随围压的增加而减小;在围压和压降一定时,自振空化射流的最大冲击压力明显高于普通连续射流;自振空化射流的脉动频率,基本不随围压、压降和喷距的变化而变化,在本实验条件下,基本保持在１．３８ＫＨｚ 左右     

A STOCHASTIC DYNAMIC PROGRAMMING MODEL FOR THE OPTIMUM OPERATION OF A MULTI-PURPOSE RESERVOIR1

ABSTRACT: The main objective of this paper is to present a stockastic dynamic programming model useful in determining the optimal operating policy of a single multipurpose surface reservoir. It is the unreliability of forecasting the amount of future streamflow which makes the problem of a reservoir operation a stochastic process. In this paper the stochastic nature of the streamflow is taken into account by considering the correlation between the streamflows of each pair of consecutive time intervals. This interdependence is used to calculate the probability of transition from a given state and stage to its succeeding ones. A dynamic programming model with a physical equation and a stochastic recursive equation is developed to find the optimum operational policy. For illustrative purposes, the model is applied to a real surface water reservoir system.     

高等级公路车速管理研究

高等级公路交通事故中约 1/ 3与车速直接相关。为保证高等级公路行车安全 ,车速管理非常必要。从我国高等级公路管理现状出发 ,根据对我国高等级公路车辆实际运行特征和运行车速的实地调查 ,笔者对高等级公路车速限制的设定、发布及实施进行了研究 ,提出了应根据公路、交通、气象、历史事故数据等条件动态确定限制车速的概念 ,并就高等级公路车速管理的实施进行了探讨 ,重点强调了道路设计和交通安全文化建设在实施车速管理中的重要性。     

矿井外因火灾计算机控制及有待解决的若干问题

针对矿井外因火灾,评价了计算机技术在矿井火灾防治应用中的研究现状,阐述了发展矿井火灾计算机控制技术的重要意义及其应用前景。同时,指出了进一步发展矿井火灾计算机控制技术中有待解决的问题     

移动Ad hoc网络路由协议的安全性分析与对策

移动Ad hoc网络是一种自组织、多跳的无线网络,由于其独特性能使移动Adhoc网络面临着比现有网络具有更大的安全挑战,其中路由安全对该网络的安全性起着关键性的作用。在介绍移动Ad hoc网络主要路由协议及其特点的基础上,笔者深入研究了移动Ad hoc网络路由协议中存在的黑洞、拒绝服务等安全漏洞;详细分析了几种主要的Ad hoc路由协议的安全性增强方案;根据不同路由协议的特点,分别提出了利用单向散列链改进距离矢量路由协议安全性的两种方案;分析了一种用于改善源路由协议安全性的方案的可行性。最后,指出了移动Ad hoc网络路由协议安全性问题的进一步改进和研究方向。     

Modeling the Influence of Dynamic Zoning of Forest Harvesting on Ecological Succession in a Northern Hardwoods Landscape

Dynamic zoning (systematic alteration in the spatial and temporal allocation of even-aged forest management practices) has been proposed as a means to change the spatial pattern of timber harvest across a landscape to maximize forest interior habitat while holding timber harvest levels constant. Simulation studies have established that dynamic zoning strategies produce larger tracts of interior, closed canopy forest, thus increasing the value of these landscapes for interior-dependent wildlife. We used the simulation model LANDIS to examine how the implementation of a dynamic zoning strategy would change trajectories of ecological succession in the Great Divide Ranger District of the Chequamegon–Nicolet National Forest in northern Wisconsin over 500 years. The components of dynamic zoning strategies (number of zones in a scenario and the length of the hiatus between successive entries into zones) and their interaction had highly significant impacts on patterns of forest succession. Dynamic zoning scenarios with more zones and shorter hiatus lengths increased the average amount of the forest dominated by early successional aspen (Populus sp.). Dynamic zoning scenarios with two zones produced more late successional mature northern hardwoods than scenarios with four zones. Dynamic zoning scenarios with very short (30 years) or very long (120 years) hiatus lengths resulted in more late successional mature northern hardwoods than scenarios with intermediate hiatus lengths (60 and 90 years). However, none of the dynamic scenarios produced as much late successional mature northern hardwoods as the static alternative. Furthermore, the amounts of all habitat types in all dynamic zoning scenarios fluctuated greatly in time and space relative to static alternatives, which could negatively impact wildlife species that require a stable amount of habitat above some minimum critical threshold. Indeed, implementing dynamic zoning scenarios of different designs would have both positive and negative effects on wildlife species and for other objectives of forest management.     

铁路安全管理综合评价的一种新方法

针对铁路安全管理的现状 ,从实际应用角度出发 ,笔者提出了一种新的综合评价方法———动态集成综合分析评价法。该方法能把铁路安全管理定性与定量信息、历史事故信息与管理现状信息、安全管理措施与专家咨询意见有机地结合起来 ,构成一种动态目标评价体系 ,从而对铁路安全管理的多个方面进行综合评判 ,因此 ,能客观地反映了铁路安全管理的现状。     

龙口市海水入侵动态系统分析与防治对策

海水入侵已成为全球普遍关注的地下水环境问题,它不仅严重地威胁着人类淡水资源,而且破坏生态环境平衡,制约着社会经济可持续发展。以山东省龙口市为靶区,通过分析研究衡量海水入侵重要因子－氯离子浓度时空分布规律及其影响因素,探索海水入侵动态系统规律,提出防治海水入侵的措施和对策。     

Carrousel氧化沟单个表曝机流态的模型试验和分析比较

对仅安装1个倒伞形表面曝气机(简称表曝机)的Carrousel氧化沟模型进行了水力学测定,通过颗粒动态分析仪(PDA)系统分析流出和流入表曝机一侧的液体流动速度、沉降速度,以及固体含量分布.结果表明,流出表曝机一侧,距表曝机较近的x轴位置流速较大;沉降速度沿y轴有个转折点,位于沟壁与挡板的中间;远离单个表曝机,固体含量逐渐增大.并将单个表曝机的测量结果与氧化沟内安装2个表曝机的流动试验进行比较,发现2个表曝机所产生的流场与单个表曝机产生的流场差别较大,且2个表曝机所产生的流场更稳定.      

Does industrial waste taxation contribute to reduction of landfilled waste? Dynamic panel analysis considering industrial waste category in Japan

Waste taxes, such as landfill and incineration taxes, have emerged as a popular option in developed countries to promote the 3Rs (reduce, reuse, and recycle). However, few studies have examined the effectiveness of waste taxes. In addition, quite a few studies have considered both dynamic relationships among dependent variables and unobserved individual heterogeneity among the jurisdictions. If dependent variables are persistent, omitted variables cause a bias, or common characteristics exist across the jurisdictions that have introduced waste taxes, the standard fixed effects model may lead to biased estimation results and misunderstood causal relationships. In addition, most existing studies have examined waste in terms of total amounts rather than by categories. Even if significant reductions in total waste amounts are not observed, some reduction within each category may, nevertheless, become evident.Therefore, this study analyzes the effects of industrial waste taxation on quantities of waste in landfill in Japan by applying the bias-corrected least-squares dummy variable (LSDVC) estimators; the general method of moments (difference GMM); and the system GMM. In addition, the study investigates effect differences attributable to industrial waste categories and taxation types. This paper shows that industrial waste taxes in Japan have minimal, significant effects on the reduction of final disposal amounts thus far, considering dynamic relationships and waste categories.