提高曲面近似展开精度的方法与实现

通过对不可展曲面近似展开精度的研究，提出了根据曲面曲率的大小对曲面自动进行网格划分，通过对综合展开误差数据场进行数据拟合来选取最优展开基点，基于空间曲面与其展开图间近似的等距变换关系进行展开样形的误差矫正等3种方法，这几种方法的实现在不同程度上有效地减小了曲面的近似展开误差，提高了曲面的近似展开精度。     

黄河下游稳定主槽之节点整治

稳定主槽是当前黄河下游河道治理的关键。窄深河槽具有很强的泄洪能力与输沙能力,是主槽整治追求的目标。黄河下游均是顺直微弯河道,河道水流最基本的主导机理是沿着阻力最小的方向流动,走直路、走近路,主槽整治设计流路应以顺直为上策。当前有必要对微弯整治方案进行再认识,实现对其否定之否定的提高。控制性弯道整治、对口丁坝整治、节点整治都属于双岸整治的范畴,对双岸整治的方向应予肯定。今后的整治应从微弯整治向节点整治发展,逐步过渡到以节点整治为主,最终达到稳定河势流路、高效排洪输沙之目的。     

Polymer-Modified Bitumen Using Ethylene Terpolymers

Polymer modified bitumen (PMB) is used in various construction applications, especially in motorways. The aim of this study is to improve features of 60/70 penetration grade, modified bitumen used on highways. Increasing the sensitivity to temperature and oxidation resistance are very important points for the modified bitumen. This condition was provided by reacting the carboxylic acid groups in asphaltene with the reactive ethylene terpolymer to form ester. Reactive ethylene terpolymer (RETP) and ethylene terpolymer (ETP) manufactured by DuPont USA were used as additives in this study. Infrared Spectrophotometer (IR) graphics and optical pictures of the modified bitumen have been examined. It has been observed that the softening point has increased on the other hand, the penetration and ductility values have decreased according to the test results.     

Necessary optimality conditions in a nonsmooth control problem with variable structure

An optimal control problem with nonsmooth performance criterion described by a system of ordinary differential equations is considered. Necessary first-order optimality conditions are obtained.     

Evaluation of a proper controller performance for maximum-power point tracking of a stand-alone PV system

In this paper the implementation of a suggested stand-alone PV system, for maximum-power point tracking (MPPT), is carried out. Also, this paper presents a comparative study, through experimental work, between the conventional PI controller and the fuzzy logic controller (FLC) under different atmospheric conditions. The implemented system with both the PI controller and the FLC gives a good maximum-power operation of the PV array, but the tracking capability for different optimum operating points is better and faster for the case of using the FLC compared to the case of using the PI controller.     

微型构造表征技术在八面河油田的应用

通过对八面河油田井网密集区及井网稀疏的欠开发区的微构造研究,探讨了微构造表征技术。首先在储层多层次逐级对比的基础上,建立主力油层对比关系;密集井网条件下,则利用钻井资料编制油层顶底微型构造图;对于欠开发地区,通过人机联作自动追踪成图技术,输出2m等值线间隔构造图,建立微构造模型。以微构造模型为基础进行潜力评价,部署关键井寻找优质储量或进行开发动态调整。应用该项技术在八面河油田滚动发现了角15块等断鼻翼部局部高点,增加石油地质储量488×10~4t。     

复合内衬在燃油加热炉中的应用

对导热油加热炉炉壁温度升高的原因进行了分析,介绍了新型复合内衬的特点,并对其技术特点、施工工艺及应用效果进行了简单阐述。     

Survey of switching techniques in high-speed networks and their performance

One of the most promising approaches for high speed networks for integrated service applications is fast packet switching, or ATM (asynchronous transfer mode). ATM can be characterized by very high speed transmission links and simple, hard-wired protocols within a network. To match the transmission speed of the network links, and to minimize the overhead due to the processing of network protocols, the switching of cells is done in hardware switching fabrics in ATM networks. A number of designs have been proposed for implementing ATM switches. Although many differences exist among the proposals, the vast majority of them are based on self-routeing multistage interconnection networks. This is because of the desirable features of multi-stage interconnection networks such as self-routeing capability and suitability for VLSI implementation. Existing ATM switch architectures can be classified into two major classes: blocking switches, where blockings of cells may occur within a switch when more than one cell contends for the same internal link, and non-blocking switches, where no internal blocking occurs. A large number of techniques have also been proposed to improve the performance of blocking and non-blocking switches. In this paper, we present an extensive survey of the existing proposals for ATM switch architectures, focusing on their performance issues.     

A high-capacity broadband packet switch architecture based on a multilink approach

Broadband packet networks based on asynchronous transfer mode (ATM) are expected to provide a wide range of services, including motion video, voice, data and image. When these networks become prevalent, some applications such as motion video and high-speed LAN interconnections will place a very large bit rate requirement on the channels. Currently, the physical layer supported by the synchronous optical network (SONET) allows the transmission of up to 2.4 Gbit/s with the OC-48 optical interface. However, it is not feasible for the electronic packet switch to route packets at this rate on a single link. In this paper we present a design of a broadband packet switch that uses multiple links in parallel to realize a high-speed channel. This implementation permits the switch to operate at the lower link rate, which can be at 150 Mbit/s, while having the ability to support a virtual circuit at a higher rate (up to 2.4 Gbit/s). The main contribution of the design is that packet sequence on a channel is still maintained even though packets are allowed to use any of the links belonging to the same channel. Besides allowing the switch to function at a slower rate than the transmission channel rate, the implementation of the multilinks benefits from statistical multiplexing gain. Analytical results show the performance advantages of multilink design with respect to delay, throughput and packet loss probability.     

Rheology in Processing of in Situ Composites of Polypropylene and Low Melting Poing Metals

The low melting point metallic tin powder or alloy of tin and lead was blended with polypropy-lene. A kind of in situ composite has been prepared. The variations of torque were studied when the composites were mixed in Haake torque rheogeniometer. By way of capillary extrusion, effects upon rheology of the in situ com-posites of the low melting point metals (LMPM) and coupling agent for their different variety and content, were investigated. From flow curves, the results indicate that in situ composites mixed with the LMPM are a kind of pseudoplastic fluid. If the LMPM were melted, the higher the content of the LMPM , the lower apparent viscosity of composites. Meanwhile, when the coupling agent is added into composites, the viscosity of composite will go up first and drop then. This shows that the LMPM have a promoter flow action on the polypropylene.