Migrants'' dreams and planners'' nightmares: International labour migration in the Arab world and the growth of two sets of cities

"The author investigates how trends in international labour migration in the Arab world have been paralleled by new directions in migration research....[She] seeks to evaluate why the urban impact of international migration is so great and outlines the considerable potential which exists for pursuing research on this aspect of urban development."     

矿化垃圾浸出液对植物发芽与幼苗生长的影响研究

选择青岛市太原路垃圾填埋场和即墨市灵山填埋场填埋龄约10~12年的矿化垃圾,制备浸出液,通过测定玉米和小麦两种植物的萌发率、萌根数、根长和芽长这4项指标,研究了矿化垃圾浸出液对两种植物种子发芽和幼苗生长的影响,为矿化垃圾的后续处理和利用提供理论基础.研究结果表明,填埋龄在10~12年的垃圾浸出液会对植物的萌发和生长产生抑制作用,但稀释之后会有不同程度的促进;同时,不同植物对浸出液毒性的敏感程度不同,同一植物的根和芽对浸出液的毒性敏感程度也不同;植物发芽和生长受浸出液中各种物质的综合影响.     

混凝土工程植生伪装的研究现状

本研究从植生混凝土、填充料和植物选择3个方面考察了国内外混凝土工程植生的研究现状,总结了混凝土工程伪装研究中可能涉及的试验方法和测试标准;对混凝土工程植生伪装中的植生混凝土系统、填充料系统和植物系统的关系进行了初步的分析;对混凝土工程植生伪装研究可能出现的问题作了初步的总结.     

Artificial recharge of groundwater through sprinkling infiltration: Impacts on forest soil and the nutrient status and growth of Scots pine

We studied the chemical changes in forest soil and the effects on Scots pine trees caused by continuous sprinkling infiltration over a period of two years, followed by a recovery period of two years. Infiltration increased the water input onto the forest soil by a factor of approximately 1000. After one year of infiltration, the pH of the organic layer had risen from about 4.0 to 6.7. The NH₄-N concentration in the organic layer increased, most probably due to the NH₄ ions in the infiltration water, as the net N mineralization rate did not increase. Sprinkling infiltration initiated nitrification in the mineral soil. Macronutrient concentrations generally increased in the organic layer and mineral soil. An exception, however, was the concentration of extractable phosphorus, which decreased strongly during the infiltration period and did not show a recovery within two years. The NO₃-N and K concentrations had reverted back to their initial level during the two-year recovery period, while the concentrations of Ca, Mg and NH₄-N were still elevated. Nutrient concentrations in the pine needles increased on the infiltrated plots. However, the needle P concentration increased, despite the decrease in plant-available P in the soil. Despite the increase in the nutrient status, there were some visible signs of chlorosis in the current-year needles after two years of infiltration. The radial growth of the pines more than doubled on the infiltrated plots, which suggests that the very large increase in the water input onto the forest floor had no adverse effect on the functioning of the trees. However, a monitoring period of four years is not sufficient for detecting potential long term detrimental effects on forest trees.     

燃煤电厂软土层地基预处理方案和施工探究

本文阐述了预处理的重要性,揭示了当前施工中存在的问题,并对软土层地基处理提出了具体的方案。     

基于生长空间限定与并行搜索的模拟植物生长算法的空间结构优化方法

为弥补传统设计理念和优化方法的不足,促进空间结构的发展与创新,结合前沿优化理论,依据模拟植物生长算法(PGSA)的基本原理,提出基于生长空间限定与并行搜索的模拟植物生长算法(GSL&PS-PGSA),并与空间结构优化相结合,建立了基于GSL&PS-PGSA的空间结构优化方法.给出了相应的结构优化流程,并采用MATLAB...     

水分迁移引起的季节性冰冻路基病害及防治措施

详细分析了水分迁移对路基病害的影响,揭示了冻胀、翻浆、融沉病害的机理,并在综合考虑影响水分迁移的多种因素的条件下,提出了防治路基病害发生的措施,以结合新材料、新工艺及施工时的实际条件,综合运用各种防治措施更好地解决季冻区路基的病害问题。     

Plant growth simulation algorithm based on double growth point parallel growth mechanism and its structural optimization

针对模拟植物生长算法(PGSA)系列算法中存在的搜索路径相对单一、搜索覆盖面不够广等问题，结合复杂结构优化问题中设计变量多、存在多个局部最优解、算法难以自动终止等特点，基于PGSA的基本原理和植物的实际生长规律，提出一种新的算法机制——双生长点并行生长机制，并与基于生长空间限定与并行搜索(GSL&PS-PGSA)算法相融合。通过典型数学及空间桁架结构算例进行了验证，结果表明：双生长点并行生长机制增加了寻优搜索路径，拓宽了搜索覆盖面，降低了陷入局部最优解的概率，并为算法提供更为有效的终止机制，从而具有更加显著的优化效率及全局搜索能力；与序列两级算法、蚁群算法等常用优化方法相比，融入双生长点并行生长机制的GSL&PS-PGSA进一步提升了算法的优化求解能力，在结构优化问题中表现出良好的适应性及有效性。     

基于双生长点并行生长机制的模拟植物生长算法及其结构优化

针对模拟植物生长算法(PGSA)系列算法中存在的搜索路径相对单一、搜索覆盖面不够广等问题,结合复杂结构优化问题中设计变量多、存在多个局部最优解、算法难以自动终止等特点,基于PGSA的基本原理和植物的实际生长规律,提出一种新的算法机制——双生长点并行生长机制,并与基于生长空间限定与并行搜索(GSL&PS-PGSA)算法相融合。通过典型数学及空间桁架结构算例进行了验证,结果表明：双生长点并行生长机制增加了寻优搜索路径,拓宽了搜索覆盖面,降低了陷入局部最优解的概率,并为算法提供更为有效的终止机制,从而具有更加显著的优化效率及全局搜索能力;与序列两级算法、蚁群算法等常用优化方法相比,融入双生长点并行生长机制的GSL&PS-PGSA进一步提升了算法的优化求解能力,在结构优化问题中表现出良好的适应性及有效性。     

Internal migration and educational outcomes in Italy: Evidence from a cohort of youths

This paper analyses the educational outcomes and the human capital accumulation of a cohort of youths, focusing on their family origin. Using a unique survey of a Northern Italian province traditionally interested by large internal migration inflows especially from the South, we find that migrants' children have a higher probability of early dropout, especially in the case of males. This evidence calls into question the integration of internal migrants, for whom education plays a crucial role, even in a period in which foreign immigration seems to be of major concern.     

模拟植物生长算法的改进策略及桁架结构优化研究

模拟植物生长算法(PGSA)是一种以植物向光性机理(形态素浓度理论)为启发准则的新型智能优化算法。对PGSA的基本原理进行了分析，指出并证实了该优化算法的局限性。在此基础上，提出了两种新的算法改进策略：形态素浓度计算的精英策略及智能变步长策略。前者通过在生长过程中快速剔除劣质生长点以提高算法的优化效率，后者通过不断变化步长以减少算法搜索时间。通过算例验证了所提出的改进策略可有效提高优化效率及解决算法缺乏终止判断机制的问题。最后采用改进PGSA和PGSA对典型桁架进行优化计算，结果表明改进PGSA的优化效率明显高于PGSA，在结构优化问题中具有较好的适用性。     

废弃煤矸石山治理中提高植被成活率及生长量技术方法研究

文章以房山区大安山乡西苑一队煤矿治理区为研究对象,对区域基础资料及勘查资料进行分析评价,研究区部分区域的树木栽植条件较差、成活率较低。经过对区域限制性因素分析,提出两种提高植被成活率及生长量的技术方法,分别是具有保水保肥能力的节水系统和添加椰糠及保水剂等材料的植生袋种植系统。     

穿越膨胀土地层隧道施工塌方成因分析

依托某膨胀土隧道工程,总结了隧道施工过程中发生的大变形及塌方的原因,并开展了膨胀土隧道围岩土体试验,研究了膨胀土隧道塌方的影响因素,结果表明:膨胀土体的含水率、干密度、液性指数和塑性指数是评价膨胀土围岩的重要指标,对膨胀土体的膨胀潜势影响较大。     

Relatedness through experience: On the importance of collected worker experiences for plant performance

We demonstrate that multiple cognitive dimensions exist between employees in knowledge intensive business services (KIBS) and that these dimensions interact in their influence on plant performance. Knowledge and cognitive distance are measured as formal knowledge and industry experience. Pooled OLS regressions with year, industry, and region‐fixed effects are used to estimate the impact on plant performance. The results suggest that the commonly found negative impact of similarity in formal knowledge on plant performance may be reduced by high human capital ratios or high levels of similarity in experience. Moreover, the organizational structures associated with single‐plant and multi‐plant firms, generate different plant performance outcomes of knowledge variety.     

细粒迁移及组构变化对黏土渗透性影响的试验研究

为进一步探究水化学环境下土体渗透性的变化规律及作用机理,对饱和重塑压实黏土样在不同水化学条件及渗流路径下进行了一系列变水头渗透试验,分析了不同浓度的NaCl溶液在不同渗流路径下对饱和黏土渗透性的影响。结果表明：不同干密度试样的渗透性随浓度增加展现出较大的差异,干密度为1.40 g/cm³时,渗透系数呈先升后降,而干密度为1.50 g/cm³时,渗透系数不断降低;逆转渗流方向,试样渗透系数发生突变;孔隙盐溶液浓度周期性变化,试样渗透性不可逆。基于核磁共振（NMR）分析技术,测试了土体内部孔隙结构分布随孔隙盐溶液浓度的变化。最后基于上述试验结果从细粒迁移产生的孔隙堵塞效应和组构改变引起的孔隙封闭效应两个方面,解释了孔隙盐溶液浓度变化对黏土渗透性的影响。     

蓄热过程中非饱和土壤热湿迁移特性的数值研究

基于多孔介质传热传质理论,建立了在蓄热过程中关于非饱和土壤热湿迁移的数学模型,采用控制容积法,利用Matlab软件对模型进行了数值求解,得到了基本的传热传质机理及温湿度场间的关联性,为优化地下蓄/放热系统提供参考依据。