Flow distribution and mass removal in floating treatment wetlands arranged in series and spanning the channel width

Floating treatment wetlands (FTWs) use plants’ roots for water quality improvement. The plants are supported by a buoyant structure deployed at the water surface. The roots form a porous zone beneath the structure and remove pollutants carried in suspension through filtering, absorption and uptake. This paper used CFD simulation to model FTWs arranged in series and spanning the channel width and to study the effects of root length and spacing between FTWs on flow distribution and mass removal. The root zone was modelled as a porous media, and removal was computed using first-order decay, for which a range of removal constants was tested. Longer roots increased the reactive volume of the root zone, which increased the fraction of pollutant inflow entering the FTWs. Increasing the distance between FTWs allowed greater mixing between water that went through and beneath the upstream FTW. This increased the concentration entering each FTW, which enhanced mass removal per FTW. However, a larger distance between FTWs reduced the number of FTWs in the channel, reducing the reactive volume. In the tradeoff between mixing and reactive volume, the reactive volume was more important, such that total removal in the channel increased with longer roots and more units of FTW (shorter gap distance). However, removing the gap entirely was detrimental, as FTWs in series removed more mass than a continuous FTW of same volume. This study points to two design recommendations for FTWs in series. First, if resources for building FTWs are not limiting, but the channel length is, it is preferable to prioritize higher reactive volume (shorter gap distance) to achieve maximum removal per channel length. Second, if resources for FTWs are limiting, but channel length is not, it is better to place the FTWs with a longer gap distance, preferably along enough to allow mixing over the full depth between FTWs, as this will achieve maximum removal per FTW.     

分布式多元随机动态场景生成及快速精准场景降维算法

高比例新能源及多源耦合是电力系统发展的重要特征,这也为系统稳定经济运行提出了新挑战。该文以园区型多能系统为对象,研究了分布式多元随机动态场景分析,从多时空角度有效量化不确定因素给系统造成的影响,可为系统灵活重构、多维度协同运行与决策提供有力模型与场景支撑。首先由预测误差驱动拟合多元功率预测误差概率分布,全面反映随机功率出力信息,提高模型泛化性;以时序相关范围参数为数据驱动关联变量,高效动态控制波动强度;最终场景生成利用逆变换映射思想保证置信度。然后针对典型场景提取,提出一种综合递归聚类思想的多段嵌套削减算法,结合改进Wasserstein距离指标,兼具准确、时效、稳定方面的优势。最后由对比实验论证该方法的前沿有效性。     

Efficiency evaluation of healthcare services in China based on stochastic multicriteria acceptability analysis and directional distance function

Evaluating the efficiency of healthcare services accurately can help in analyzing the rationality of inputs and outputs in such services. Considering the consistency and equity of assessment criteria, this study conducts the stochastic multicriteria acceptability analysis (SMAA-2) with a directional distance function to evaluate the efficiency of healthcare services in 31 provincial administrative regions of mainland China, as observed in 2018. We use SMAA-DDF to explore all the projection directions to the efficient frontier instead of a certain projection direction. We measure the maximum and average efficiencies for each of the 31 provincial healthcare services. Our empirical findings show that only seven provinces achieve optimal healthcare service efficiency; the eastern area performed the best, followed by the central, western, and northeast areas. Furthermore, the path along the projection directions is provided to help inefficient provinces improve their efficiency and obtain the best possible positions.     

不同距离应变片测定Ⅰ型动态应力强度因子对比试验研究

基于线弹性断裂力学理论，采用应变片法开展了冲击动荷载作用下的三点弯曲试验，探讨距扩展裂纹不同距离的应变片测定Ⅰ型应力强度因子的差异。当应变片与扩展裂纹成特定锐角和钝角时，采用与裂纹扩展速度和应变片的位置相关的二项式表征裂纹尖端附近应变场，并结合理论解析和试验实测的应变与裂纹扩展时间曲线，推导得到了应力强度因子计算公式。同时，采用动焦散线试验对比分析应变片法测定的动态应力强度因子值。结果表明，应变片在裂纹尖端附近合理区域内，测定的裂纹尖端动态应力强度因子值与动焦散线试验结果吻合较好;明确了不同距离对测定Ⅰ型裂纹应力强度因子的影响，随着应变片粘贴距离变大，测定的动态应力强度因子值与动焦散线法相差增大。研究结果为进一步应用应变片法研究岩石类材料的断裂性能提供了试验基础。     

近距离煤层上行开采围岩应力演化特征分析

基于潘一东煤矿地质概况及原始地应力测试数据，采用相似模拟与数值模拟相结合的方法，分析了近距离煤层上行开采过程中两煤层采场超前支承压力变化规律和覆岩裂隙发育特征。结果表明:下保护层开采弱化了覆岩关键层的承载能力，采空区后方形成的覆岩断裂线对上覆被保护层基本顶初次垮落步距具有一定影响；下保护层采场超前支承压力峰值呈线性增长趋势，而被保护层采场超前支承压力峰值受保护层采动影响呈增大—稳定—减小的趋势，工作面推进距离达到1/2“见方”及“见方”时，悬顶岩梁会发生大面积垮落失稳，应注重采场动力灾害防治工作。     

人工假顶工艺在近距离过巷掘进的应用

为了保证近距离煤层巷道掘进施工安全,提高过巷段顶板稳定性,对2112巷过830轨道巷期间采取人工假顶的方法进行近距离顶板维护工艺。实际应用表明,该工艺有效保证了近距离巷道掘进顶板稳定性,保证了巷道施工安全,取得了显著成效。     

高压直流接地极对埋地管道的电流干扰及人身安全距离

高压直流输电系统的直流接地极在运行初期或发生故障和检修时,会产生瞬间大电流,给附近埋地油气管道设施及操作人员带来极大的安全隐患。为了保障埋地管道附近人员的安全,对高压直流接地极对埋地管道的电流干扰及人身安全距离(以下简称安全距离)进行了研究。首先利用数值模拟技术建立了埋地管道受电磁干扰的模型,进而利用该模型计算了不同土壤电阻率、管线长度、管道防腐层、接地极入地电流、管道尺寸等情况下,高压直流接地极对埋地管道杂散电流干扰的安全距离,并分析了上述条件对高压直流接地极干扰程度的影响规律。研究结果表明:①管线长度对高压直流接地极干扰程度的影响较大,管线越长,安全距离越大,但当管线长度达到或超过600 km时,安全距离则基本不变;②管线涂层对高压直流接地极干扰程度的影响较大,随着涂层面电阻率的增加,安全距离逐渐增大;③对于多层土壤结构,可将最大的单层电阻率作为整体电阻率,其计算得到的安全距离最大,评价结果也更为保守。结论认为,利用计算结果得到的4类长度管线的安全距离图谱,可供高压直流接地极及管线设计时参考,并且可以作为拟建高压直流接地极或埋地管线安全距离选取的依据。     

Study on estimating electric potential in space between parallel electrodes

We have been studying on estimating distribution of permittivity between measurement electrodes using capacitance and electric potential. Two arc electrodes were separated by long distance and there electrodes were surrounded by additional electrodes respectively. In past research work, we carried out numerical electric analysis for calculating the capacitance and electric potential using Finite Element Method (FEM) and compared with experimental and numerical results. The capacitance values were almost agreed with experimental and numerical results. However, the electric potential values were different between experimental and numerical results in conventional studies. In this paper, we proposed an equivalent circuit including the stray capacity and measurement method for capacitance, the electric potential in space between long distance electrodes was estimated.     

数据驱动的地铁车门微小故障智能诊断方法

车门控制系统是地铁车辆中最重要的子系统之一,其机电部件紧密耦合且存在频繁往复运动,易受环境和乘客干扰,故障率居高不下。为准确检测诊断地铁车门早期故障,本文提出一种大数据驱动的车门故障特征优选方法和基于随机森林(RF)的智能诊断方法。首先,从地铁运营公司累积的大量车门运行状态数据中,提取门扇位置、驱动电机转速和电流信号的多阶段时域特征指标,构建车门运行状态的特征向量;然后,应用距离评估准则,优选对故障敏感度高且对干扰鲁棒性强的车门状态特征,降低特征维度,减少冗余、无关特征的干扰;以优选后的车门状态特征作为RF网络的输入,故障标签作为输出,建立智能故障诊断模型,实现车门系统不同微小故障状态的自动识别。在杭州地铁4号线台架车门上的应用结果表明,所提方法能准确提取早期故障的微弱特征,故障分类模型精度高,故障诊断准确率优于现有其他方法。     

基于数据挖掘的开源电子资源访问行为统计模型

为了解决当前图书馆资源个性化推荐过程中存在推荐的准确率、召回率以及效率较低的问题,采用二维距离模型构建用户社区模型,用于描述访问用户与图书馆开源电子资源之间的关系,并对互联网用户需求和访问行为进行模糊规则推理.依据互联网用户属性和图书馆资源访问需求属性之间的模糊规则,建立图书馆开源电子资源访问行为统计模型,并利用该模型向用户提供个性化推荐服务.仿真结果表明,所建模型的推荐召回率高达98. 4%,推荐准确率为99. 2%,运行时间小于0. 04 s.所建模型能够为互联网用户提供准确、高效地图书馆资源个性化推荐服务.