基于不同强度等级混凝土的动力学特性研究

基于TAW-2000D电液伺服岩石三轴仪和直径75 mm的霍普金森压杆试验装置,得到了C25,C35和C45混凝土在静、动载荷作用下的应力-应变曲线,探讨了混凝土强度等级、动态峰值强度、峰值应变和应变率之间的变化规律。结果表明:混凝土准静态应力-应变曲线和动态应力-应变曲线在形态上存在明显差异,动态应力-应变曲线的峰值点随应变率的增大向右上方移动,线弹性阶段各曲线斜率变化不明显;动态峰值应力、动态弹性模量和峰值应变均存在不同程度的率相关性,并且混凝土材料的应变率敏感性随其强度等级的提高而增强;混凝土C45的各力学指标对应变率的敏感性最强,C35次之,C25的应变率敏感性最弱;推导了应变率与强度等级和冲击速率之间的经验公式,三者之间存在非线性变化规律。     

Teams as boundaries: How intra‐team and inter‐team brokerage influence network changes in knowledge‐seeking networks

What role does an ego's brokerage location—within a team (intra‐team) or outside the team (inter‐team)—play in the evolution of an instrumental knowledge‐seeking network in terms of both proximal (i.e., within the team) and distal (i.e., outside the team) tie formation and tie decay? We address this question by drawing on literature about social networks, brokerage, and teams. We use temporally separated data from 302 students embedded in 97 teams to test our hypotheses about the impacts of intra‐team and inter‐team brokerage on proximal and distal network evolution, specifically on four network changes in knowledge‐seeking networks: proximal tie formation, proximal tie decay, distal tie formation, and distal tie decay. We find that these four changes depend on individual network brokerage location even after controlling for personality and task characteristics. Specifically, inter‐team brokers change their networks both within and outside their teams, whereas intra‐team brokers curtail their network changes. We argue that these opposite effects occur because inter‐team brokers have greater autonomy than intra‐team brokers. This study adds to the ongoing dialog about network evolution in social network literature and to the conversations about brokerage and its location in the context of team‐based work.     

On the subjective experience and correlates of downtime at work: A mixed‐method examination

In the current paper, we studied downtime at work. Downtime represents a unique aspect of work time, as employees have low workload and more discretion about their activities but are still paid to be at work. Despite its prevalence and potentially significant implications for productivity and well‐being, the experience of downtime has not been a focus in the literature. To study this phenomenon, we first used a qualitative method involving 15 focus groups. Results from 95 employees showed that downtime is distinct from formal breaks and withdrawal behavior and is generally a negative subjective experience. Categories of antecedents of experience and downtime activities were classified. Next, to further explore the phenomenon, and based on Study 1 and relevant literature, we proposed several hypotheses and tested them using an experience sampling method. Results from 86 employees (across 5 workdays and 689 data points) indicated that the amount of downtime was negatively related to day level job satisfaction, job performance, and subjective health. The duration of relaxation activities during downtime mitigated the negative effects of downtime on fatigue. The effects of enjoyment level of the activities, job autonomy, work engagement, and boredom proneness were also examined. Implications, limitations, and future research are discussed.     

不同来源重金属在土壤中的形态分布差异

试验表明：不同来源的Ｐｂ、Ｚｎ和Ｃｄ复合污染物在土壤中的形态分布有明显的差异，在废矿水和尾矿砂污染的土壤中，Ｐｂ、Ｚｎ和Ｃｄ主要以残渣态存在，而添加土壤中的Ｐｂ主要以弱专性吸附态和有机结合态存在，Ｚｎ和Ｃｄ主要以交换态存在，大豆苗对添加土壤中Ｐｂ、Ｚｎ和Ｃｄ的富集能力较强，而对废矿水污染和尾矿砂污染土壤中Ｐｂ、Ｚｎ和Ｃｄ的富集能力相对较弱。     

水体颗粒物以及土壤对有机物吸附常数的测定

本文介绍了用批量平衡测定水体悬浮颗粒物以及土壤对有机物吸附常数的测定方法，并给出实例和方法的注意事项。     

应用系统动力学原理制定小流域经济建设决策

本文应用系统动力学原理，就太平沟小流域资源的开发利用进行了系统分析，绘制了ＳＤ模型流程图，编制了ＳＤ模型程序，经微机模拟仿真，确定了“综合型”发展为该流域资源开发利用方向，为该类型区小而域经济建设及两高一优农业发展提供了科学依据和方法。     

遥感与GIS支持下的城市绿地信息提取方法研究--以深圳市为例

城市绿地作为城市结构中的自然生产力主体，在城市系统中起着重要作用。传统的城市绿地调查多采用人工普查并结合统计学方法进行城市绿地调查，需要投入大量的人力和资金，但得到的数据精度和现时性都较差，而采用高分辨率遥感卫星数据与地理信息系统相结合的方法，可以达到对城市绿地遥感数据的快速特征提取和准确的空间统计分析。文章采用基于遥感和GIS相结合的方法，并以深圳市为例，进行了城市绿地特征提取方法的研究和应用分析。     

丘陵地区农牧渔生态系统的研究

经四年研究，本文提出了适宜丘陵地区的作物－猪－鱼复合生态系统模型。在该系统中，淡水鱼的养殖以半精养方式最佳。本文还讨论了半精养方式的混养结构、水质管理和饵料组合等配套技术。     

珠江广州河段底泥中汞铜铅的污染及其与有机质硫化物积累的关系

珠江广州河段底泥中有机质、硫化物和重金属汞、铜、铅的污染监测结果表明：各种污染物的含量范围分别为有机质２０．８—７４．４ｇ／ｋｇ，硫化物２８．７—５３８ｍｇ／ｋｇ，汞０．０７－０．７４ｍｇ／ｋｇ，铜２０．９—１０１ｍｇ／ｋｇ，铅１４．２—９１７ｍｇ／ｋｇ；它们在沿程各断面的分布表现为上游往中游递增，而中游向下游递减，基本上以猎德、广纸和黄沙三个断面的污染最严重；各种污染物的污染程度顺序是硫化物＞汞＞铜＞铅。相关分析表明：汞、铜与有机质和硫化物的相关关系均达到极显著水平。说明随着底泥中有机质和硫化物积累的增加，汞、铜的富集量相应增加，污染加重。     

安徽省长江以北地区土壤水溶性氟含量及分布特征

采集安徽省长江以北地区有代表性土壤样品３４７个，测定了其水溶性氟含量。结果表明，土壤水溶性氟含量范围０３８～１２６９ｍｇ／ｋｇ，平均为２３８ｍｇ／ｋｇ。地区分布是南低北高，以淮北宿州和阜阳地区为最高，平均含量在３ｍｇ／ｋｇ以上。主要土壤类型土壤水溶性氟含量顺序是砂姜黑土、潮土＞黄棕壤、紫色土＞水稻土＞石灰土、粗骨土。不同母质土壤水溶性氟含量顺序是古黄土性河湖相沉积物＞黄泛冲积物＞紫色砂岩＞下蜀黄土＞石灰岩＞酸性结晶岩风化物＞河流冲积物。土壤水溶性氟含量与土壤ｐＨ呈正相关。ｐＨ高的黄泛冲积物和古黄土性河湖相沉积物母质土壤含水溶性氟多，该土壤地区发生氟中毒可能性较大。