A globally convergent algorithm for transportation continuous network design problem

The continuous network design problem (CNDP) is characterized by a bilevel programming model, in which the upper level problem is generally to minimize the total system cost under limited expenditure, while at the lower level the network users make choices with regard to route conditions following the user equilibrium principle. In this paper, the bilevel programming model for CNDP is transformed into a single level convex programming problem by virtue of an optimal-value function tool and the relationship between System Optimum (SO) and User Equilibrium (UE). By exploring the inherent nature of the CNDP, the optimal-value function for the lower level user equilibrium problem is proved to be continuously differentiable and its derivative in link capacity enhancement can be obtained efficiently by implementing user equilibrium assignment subroutine. However, the reaction (or response) function between the upper and lower level problem is implicit and its gradient is difficult to obtain. Although, here we approximately express the gradient with the difference concept at each iteration, based on the method of successive averages (MSA), we propose a globally convergent algorithm to solve the single level convex programming problem. Comparing with widely used heuristic algorithms, such as sensitivity analysis based (SAB) method, the proposed algorithm needs not strong hypothesis conditions and complex computation for the inverse matrix. Finally, a numerical example is presented to compare the proposed method with some existing algorithms.     

Three-dimensional stability analysis of the dam foundation at Baise

It is usually difficult to determine the actual safety factors of rock masses in an ordinary two-dimensional stability analysis if the safety factors of the different cross sections in the rock mass vary significantly. In addition to the actual slope, arch dam abutment, and the actual foundation of a high building, another example is that the different cross sections of the foundation in the monolith of a gravity dam vary significantly, just like the condition at the overflow dam in the Baise project. A three-dimensional stability analysis method based on the upper-bound theorem was employed to solve this problem. The parameters used in the analysis were obtained from geomechanics tests, as well as continuity simulations of the randomly distributed joints. Two failure patterns against sliding are analyzed. One pattern is the foundation slide along deep-seated planes which were determined by calculations. The other pattern is the foundation slide along the planes across the bottom of the high steps in the foundation pit. The results indicate that a special overflow dam monolith can be considered to be safe in case of considering the three dimensional effect. However, a key wall with a depth of 5m must be constructed at the upper side of this monolith in order to ensure the safety of the foundation. Translated from Chinese Journal of Rock Mechanics and Engineering, 2006, 25(3): 533–538 [译自: 岩土力学与工程学报]     

俄罗斯圣彼得堡防潮工程建设的若干历史经验

本文系统介绍了俄罗斯圣彼得堡防潮工程规划的发展过程、工程的布置、组成以及工程的设计和当前施工的进展情况.圣彼得堡防潮工程是圣彼得堡城市建设的重要保障,在各个历史时期均得到了俄罗斯各级政府的高度重视.工程的规划、设计和施工建设过程反映了俄罗斯人对防潮管理、人水和谐相处和工程建设中对环境保护认识的发展过程.对圣彼得堡防潮工程建设经验的分析、总结,将对我国水利工作者和位于河口地区的城市防潮和防洪建设与管理起到积极的借鉴作用.     

Effect of Magnetic Interaction on Thermally Activated Reversal in a Magnet With a Distribution of Energy Barriers

The time dependence of magnetization is usually expressed as M(t)=M₀-SInt [see Proc. Phys. Soc. 62, 562 (1949)] for magnetic viscosity experiments. Considering magnetic interaction during the thermal activation process, a form as M(t)=M₀-SIn(t+t₀) is deduced. The dipolar interaction and exchange coupling in a magnet can lead to positive and nonpositive t₀, respectively. In the experiments of the magnetic viscosity for nanocrystalline Pr₂Fe₁₄B ribbons, the existence of positive t₀ is confirmed.     

火电仿真技术研究

在电力行业中，计算机仿真一直是不可缺少的工具，它在减少损失、节约经费、提高效率、确保安全经济运行等方面发挥了巨大作用。主要介绍了计算机仿真技术在660MW火电站中的具体应用情况。以邯峰发电厂^#1机为对象，采用STAR-90仿真支撑系统，建立起660MW火电机组1：1仿真机，并在机组投产前建成，取得了良好的培训效果。论述了火电站仿真机未来的发展趋势，包括开发高精度机理性仿真数学模型以及真实的DCS仿真模型、进行性能计算与故障诊断、应用于热工人员培训及机组调试等。     

紫外写入光纤光栅用特种光纤的研究

本文详细地介绍了如何加强用于制做紫外写入光纤光栅所需的特种光纤的高光敏性、温度不敏感性以及对包层模的高度抑制性等。     

基于内容图像检索中的优化鉴别特征

为了提高基于内容图像检索系统的检索速度和准确率,提出一种融合两类线性鉴别分析的方法来提取低维的优化鉴别特征.首先把多类问题转换为多个两类问题,对每个两类问题进行线性鉴别分析,得到鉴别向量;所有的鉴别向量组成鉴别变换矩阵,对图像特征进行投影变换得到鉴别特征;最后用变换后的鉴别特征进行图像检索或分类,得到准确率更高的结果.该方法中鉴别特征空间的维数与类别数相等.与多种特征优化方法进行比较的实验结果表明,采用文中方法可以显著地提高图像检索和图像分类的性能.     

无线传感器网络中一种基于移动Sink的数据收集算法

针对移动无线传感器网络设计一种不依赖于节点地理位置的基于移动汇聚节点(Sink)的数据收集算法(Mobile Sink-based Data Gathering,MSDG)。该算法解决了无线传感器网络中多跳路由通信时出现能量空洞的"热点"问题。Sink沿途以最近的固定节点作为根节点动态构建路由树。簇内移动节点感知的数据经簇头进行数据融合计算,然后将融合后的数据沿路由树反向逐跳转发给Sink。仿真结果表明,MSDG在节点的平均能耗和网络生存时间等方面的性能远超过LEACH、ACE-L等数据收集协议。     

关于饱和软土地基堤坝边坡稳定分析总应力法的讨论

在饱和的软土地基上修筑堤坝,由于孔隙水压力不易准确测定,需采用“φ=0”的总应力法进行稳定分析。这一做法在国外已明确纳入设计规范,在国内工程界较少受到重视,导致过高地估计了安全系数。本文首先系统地回顾了临界状态土力学中的伏斯列夫强度理论,在理论上阐述了饱和软土地基快速填筑时采用总应力法的原因,同时引用了Bishop和Bjerrum、美国联邦公路局、美国陆军工程师团与我国水电水利工程边坡设计规范的相关条文,确认在饱和软土地基采用总应力法进行稳定分析的合理性。以花敖泡土石坝和拉哇水电站围堰为工程实例,分别采用对土的固结不排水剪的两种做法开展稳定性分析,结果表明,直接将土的固结不排水剪强度指标ccu与φcu作为填筑后的强度参数,将严重高估其安全系数。因此建议正在修订的碾压式土石坝与边坡设计规范增加相应条文,并期望引起工程界对这一问题的重视。     

磷酸镁水泥制备试验研究

基于水工建筑物的应急抢险与快速修补加固处理的需要,运用常规的水泥凝结时间、强度等基本性能试验,研究各材料组成对磷酸镁水泥性能的影响,确定磷酸镁水泥配方,并对不同粒径砂土的磷酸镁水泥砂浆水胶比、养护条件、强度等进行了试验研究。结果表明,硼砂是磷酸镁水泥的有效缓凝剂;氧化镁细度对水泥性能有明显影响,氧化镁越细水泥早期强度越高,但细度过细凝结时间将难以满足施工要求;磷酸镁水泥配方为:P/M值1∶3,硼砂掺量10%,氧化镁细度宜为195 m~2/kg左右;磷酸镁水泥砂浆抗压强度与胶水比具有线性相关性,与龄期呈对数关系;水中养护与标准养护相比,抗压强度降低约6%～27%,磷酸盐水泥在长期水下环境中的适用性需论证。研究成果可为水工建筑物的应急抢险与快速修补加固处理提供参考和依据。