Capillarity and Evaporation Exacerbated Seepage Losses from Unlined Channels

Steady, essentially two-dimensional, tension-saturated seepage from a flat-bottomed soil channel in an arid environment is studied analytically. Physically, the action of capillary spreading, evaporative drive to the atmosphere both from the near-channel banks and capillary fringe boundary, Darcian resistance of the matrix and gravity are juxtaposed and result in trifurcation of infiltrated water into deep percolation and semi-infinite evaporation “wings” with two hinge points on the soil surface and two dividing streamlines. Mathematically, free boundary problem is solved by conformal mappings and the Polubarinova-Kochina boundary-value problem method. The dependence of deep percolation losses and evaporative return flow on the channel width, conductivity, static capillary rise height, and intensity of evaporation is found.     

LNN Blind Multi-user Detection Algorithm for Multi-path-fading CDMA Channels

A blind multi-user detection algorithm （BMUD） which is suitable for multi-path-fading Channels based on Lagrange neural network （LNN） is proposed. Based on the minimum output energy （MOE） criterion, the blind detection algorithm is formulated as a constrained optimization problem inherently and is then resolved efficiently using the neural network . Compared with the previous RLS（recursive least squares ）-MOE blind detection algorithm or for multi-path channel, the BMUD based on LNN has better performances： lower computational complexity, faster convergence speed and capability in the multi-path-fading channel. The bit error rate （BER） and signal-to-interference-and-noise ratio （SINR） performances of the detection algorithm in multi-path channel are close to that in single path channel.     

基于VxWorks操作系统的双下行信道CMTS的研制

随着网络多媒体业务的不断发展,现有CMTS的数据传输能力已不能满足用户的大数据量传输业务,为解决这一问题,设计开发了支持双下行信道的CMTS,对其研制过程中的主要技术问题进行了分析,给出了基于嵌入式操作系统VxWorks的双下行信道CMTS的实现方法.     

Web crippling of cold-formed unlipped channels with flanges restrained

The paper describes a series of web crippling tests on cold-formed unlipped channels with flanges restrained (fastened) as well as channels with flanges unrestrained (unfastened). The tests were performed under end and interior two-flange loading conditions specified in the North American Specification and Australian/New Zealand Standard for cold-formed steel structures, namely end-two-flange and interior-two-flange loading conditions. The concentrated load was applied by a bearing plate at the top flange of the channels, and the reaction force applied by an identical bearing plate at the bottom flange of the channels. The bearing plates acted across the full flange widths of the channels. The flanges of the channels were either bolted to one or two bearing plates for the specimens with flanges restrained. The web crippling test strengths are compared with the design strengths obtained using the North American Specification, Australian/New Zealand Standard and American Iron and Steel Institute Specification for cold-formed steel structures. It is shown that the design strengths predicted by the North American Specification using the unfastened design rules are generally conservative, but unconservatively predicted using the fastened design rules, even when the flanges of the specimens were restrained. The design strengths predicted by the Australian/New Zealand Standard and American Iron and Steel Institute Specification are unconservative.     

Serviceability and ultimate limit states of channels under compression and bi-axial bending

As the demand for light-weight steel constructions continues on the rise, efficient and accurate design procedures become extremely essential. A good understanding and knowledge of the structural performance is a fundamental step to achieve this target. The paper examines the behavior of channel members subjected to compression and bi-axial bending. A modeling strategy is first presented for non-linear analysis of channels under this combined loading arrangement. The interaction between serviceability and ultimate limit states is then highlighted. Cost-effective design spaces are shown for channels under this loading that can be used in practice to achieve economical light-weight designs. Several strategies are also presented that tackle common design challenges encountered in practice. The paper offers to practitioners and steel fabricators procedures that can be used to optimize the channel size under this general loading combination.     

Numerical and Experimental Verification of the Polymer Electrolyte Fuel Cell Performances Enhanced by Under‐Rib Convection

Understanding the current density distributions in polymer electrolyte fuel cells (PEFCs) is crucial for designing cell components, such as the flow field of bipolar plates. A new serpentine flow field equipped with sub‐channels and by‐passes (SFFSB) was numerically and experimentally confirmed to enhance the reactant transport rates and liquid removal efficiency compared with a conventional advanced serpentine flow field (CASFF). Consequently, the maximum current and the power densities of the SFFSB were increased due to the promotion of under‐rib convection. In this study, current density distributions are measured under transient conditions to verify the PEFC performances enhanced by under‐rib convection. The current density distributions of the SFFSB are compared with those of the CASFF. The results show that the SFFSB has a higher local current density and a more uniform distribution than the CASFF, therefore, the PEFC performances with the new flow field of SFFSB is enhanced by the better current density distributions.     

整车道路模拟与道路试验关联研究

24通道道路模拟机能最大程度地复现路面对整车的激励,能真实、快速地暴露出大部分整车可靠性问题,它已成为整车可靠性开发重要的手段之一。为探讨整车道路模拟和道路试验的关联程度,进行了道路载荷谱采集和台架迭代,将试验场载荷和台架响应,从时域和频域多个角度进行对比分析,并与路试发生的故障进行对标分析,结果表明:24通道台架试验与路试具有非常高的关联度,在项目前期开发中,可替代路试以缩短试验开发周期。     

Vulnerability-Based Risk Assessment for Stream Instability at Bridges

The Federal Highway Administration recommends that stream stability analyses at bridges over water begin with a Level 1 assessment. Following this assessment of the physical condition of the stream in the vicinity of the bridge, the user must determine whether or not the relative risk is low. If it is low, then no action is needed. If the risk is greater than low, then a Level 2 analysis is recommended; however, no method is given for determining the risk. In this paper, the relative risk of unsatisfactory conditions at bridge foundations is assessed as a simple function of vulnerability and criticality. Vulnerability is based on a stream stability assessment and data from the National Bridge Inventory (NBI). Criticality is determined indirectly as a function of the bridge serviceability and cost by using data extracted from the NBI. Relative risk is then qualitatively determined by combining vulnerability and criticality. Three examples in central Pennsylvania are provided in which the relative level of risk is used to determine the need for a Level 2 analysis.     

Photoshop常用抠图工具比较

抠图是Photoshop软件应用中最基本的功能之一,本文介绍了抠图的概念,分析比较了实际工作中常用的几种抠图方法以及它们各自的特点。     

基于Web模式的配电前置机参数设置

基于Web模式进行参数设置的方式解决了目前前置机参数设置所存在的问题,这种方式提供了一个Web服务器守护程序,任何一台远程联网的计算机在任何时候都可以跟Web服务器提出连接请求,Web服务器根据连接请求返回Web面,用户在Web面上进行参数设置后把数据提交给Web服务器以后远程重启前置机的相应程序,所做的参数设置使在前置机中生效。其通用性和可移植性比以往采用的设置方式有了较大的提高。