大气作用下膨胀土地基的水分迁移与胀缩变形分析

运用土体渗流和蒸发理论,建立了大气-非饱和土相互作用模型;以现场观测的气象数据作为边界条件,进行了地基土中水分迁移的数值模拟,得到了大气作用下地基土体含水量的动态分布规律.计算结果表明,地基土中含水量变化幅度随深度增加而递减,3.5m深度以下土体的体积含水量基本不变,从而确定了南宁地区膨胀土地基的大气影响层深度为3.5...     

大型渡槽结构动力学研究进展

大型渡槽是灌区生命线工程中的关键性建筑物,其在地震及风载作用下的安全性已是渡槽建设的瓶劲,也是国内外研究的热点。渡槽结构的抗震、减震和抗风技术的核心是渡槽结构动力学的问题,而渡槽结构动力学系属流固耦合(FSI)系统的动力学范畴。在已有研究的基础上,首先对渡槽结构FSI系统模型的研究进行了总结和评述;然后简述了渡槽结构动力特性和响应的求解技术以及抗震、隔震、减震与抗风技术的研究概况;最后总结了渡槽结构动力学的研究进展,提出了该学科进一步研究的内容和方法。     

抗生素与三唑类杀菌剂混合物对羊角月牙藻的长期毒性相互作用研究

地表水中抗生素与农药的混合暴露及其潜在生态与健康风险受到广泛关注。然而,目前关于抗生素与农药混合毒性研究大多仅考虑急性毒性,缺乏其长期毒性相互作用的研究。以较为广泛使用的2种抗生素土霉素(OXY)、环丙沙星(CIP)和1种三唑类杀菌剂农药戊唑醇(TCZ)及其二元混合物为研究对象,以生态系统中初级生产者绿藻(羊角月牙藻)为受试生物,研究目标混合物在暴露时间为96、120、144和168 h的长期毒性相互作用。结果表明,单一物质及其混合物随暴露时间延长而毒性增大;同一暴露时间点的单一污染物毒性大小顺序为OXYTCZCIP;混合物毒性相互作用与浓度、混合物组分和暴露时间三者密切相关;混合体系的拮抗作用均出现在高浓度区域,而中、低浓度区域呈协同作用或加和作用; OXY-CIP与CIPTCZ混合体系的协同作用随着暴露时间延长而协同作用逐渐增大。研究结果对水环境中抗生素与农药复合污染生态风险评估具有重要的现实意义。     

膨胀土地基中大比例模型桩浸水试验研究

通过对埋设在膨胀土地基中的一试桩的长时间浸水试验观测，模拟了自然降雨气候条件下单桩位移、沿桩身轴力、侧摩阻力分布、地基胀缩及其时间变化等基桩一系列工作性状和桩-土共同作用规律。试验结果显示：桩顶位移呈现出先下沉后回升并最后趋于稳定的3阶段特征；桩身全长受拉，轴力沿桩身分布呈“波峰”形态。基桩的最大轴力位于桩的中下部，轴力峰值历经由小到大的过程；中性点在浸水过程中，其位置有从桩下部上移的现象；桩侧摩阻力与桩端阻力荷载分担比随时间呈现出先减小后增大并渐趋稳定的3阶段特征。研究结果对膨胀土地基中的桩基设计和施工提供了理论依据。     

覆水场地地震反应分析

随着各种海洋结构物的兴建,覆水场地的地震反应逐渐成为研究热点。基于任意拉格朗日-欧拉描述,推导时变区域上的流体运动方程,给出流场、结构的接触条件和流场网格运动控制方法。对于平坦覆水场地,水平向地震动作用下,根据Couette流理论证明该类场地流体作用可以忽略;竖向地震动激励下,横向均匀场地可以通过动水压力公式准确考虑流体作用,横向非均匀场地则需要通过流固耦合方法考虑流体作用,以海底隧道为例加以说明。对于起伏场地,天然起伏场地在地震动激励下的动力反应具有明显的流固耦合特征,以三角形起伏场地为算例;结构物的兴建造成的人工起伏场地同样需要考虑流固耦合效应,以某沉管隧道在水平向地震动激励下的动力反应为算例,并根据结果初步提出该类结构物流固耦合分析的简化计算方法。     

Physicochemical interaction and its influence on deep bed filtration process

The capillary model was used to analyze the hydraulic conditions in the deep bed filtration process. The physicochemical interaction forces between the filter media and suspended particles and their influence on deep bed filtration process were also studied theoretically. Through the comparison of the hydraulic and physicochemical forces, the key influencing factors on the filtration process were proposed and investigated. Pilot study of the microflocculation deep bed filtration was carried out in the No. 9 Potable Water Treatment Plant of Beijing, and the experimental results of hydraulic head loss, particle distribution and entrapment were presented. The theoretical prediction was reasonably consistent with the experimental results under different conditions, which indicated that the regulation and control of micro-flocculation and deep bed filtration could be realized by the evaluation of the physicochemical interactions. Further theoretical and experimental research should be carried out to investigate the interaction mechanism and its application in the deep bed filtration and other cases.     

Identification of key factors governing chemistry in groundwater near the water course recharged by reclaimed water at Miyun County, Northern China

Reclaimed water was successfully used to recover the dry Chaobai River in Northern China, but groundwater may be polluted. To ensure groundwater protection, it is therefore critical to identify the governing factors of groundwater chemistry. Samples of reclaimed water, river and groundwater were collected monthly at Chaobai River from January to September in 2010. Fifteen water parameters were analyzed. Two kinds of reclaimed water were different in type (Na-Ca-Mg-Cl-HCO3 or Na-Ca-Cl-HCO3 ) and concentration of nitrogen. The ionic concentration and type in river were similar to reclaimed water. Some shallow wells near the river bed had the same type (Na-Ca-Mg-Cl-HCO3 ) and high concentration as reclaimed water, but others were consistent with the deep wells (Ca-Mg-HCO3 ). Using cluster analysis, the 9 months were divided into two periods (dry and wet seasons), and all samples were grouped into several spatial clusters, indicating different controlling mechanisms. Principal component analysis and conventional ionic plots showed that calcium, magnesium and bicarbonate were controlled by water-rock interaction in all deep and some shallow wells. This included the dissolution of calcite and carbonate weathering. Sodium, potassium, chloride and sulfate in river and some shallow wells recharged by river were governed by evaporation crystallization and mixing of reclaimed water. But groundwater chemistry was not controlled by precipitation. During the infiltration of reclaimed water, cation exchange took place between (sodium, potassium) and (calcium, magnesium). Nitrification and denitrification both happened in most shallow groundwater, but only denitrification in deep groundwater.     

On the parameterization of the roughness length for the air-sea interface in free convection

The roughness length at the air-sea interface during free convection (z_0fc) is mainly related to the convective velocity (w_*) rather than the friction velocity (u_*). The parameterization of z_0fc with w _* ² /g as proposed by Abdella and DAlessio in 2003 is evaluated. It is shown that their proposed formula is consistent with field measurements. In order to avoid self-correlation by using u_*, a new parameterization of w_* with wind speed (U_z) at height z and stability parameter (z/L, where L is the buoyancy length) is proposed. This new formula for w_* is in agreement with an independent field result.     

Reproductive Success of Captive-Bred Steelhead Trout in the Wild: Evaluation of Three Hatchery Programs in the Hood River

Abstract:  Population supplementation programs that release captive-bred offspring into the wild to boost the size of endangered populations are now in place for many species. The use of hatcheries for supplementing salmonid populations has become particularly popular. Nevertheless, whether such programs actually increase the size of wild populations remains unclear, and predictions that supplementation fish drag down the fitness of wild fish remain untested. To address these issues, we performed DNA-based parentage analyses on almost complete samples of anadromous steelhead ( Oncorhynchus mykiss ) in the Hood River in Oregon (U.S.A.). Steelhead from a supplementation hatchery (reared in a supplementation hatchery and then allowed to spawn naturally in the wild) had reproductive success indistinguishable from that of wild fish. In contrast, fish from a traditional hatchery (nonlocal origin, multiple generations in hatcheries) breeding in the same river showed significantly lower fitness than wild fish. In addition, crosses between wild fish and supplementation fish were as reproductively successful as those between wild parents. Thus, there was no sign that supplementation fish drag down the fitness of wild fish by breeding with them for a single generation. On the other hand, crosses between hatchery fish of either type (traditional or supplementation) were less fit than expected, suggesting a possible interaction effect. These are the first data to show that a supplementation program with native brood stock can provide a single-generation boost to the size of a natural steelhead population without obvious short-term fitness costs. The long-term effects of population supplementation remain untested.     

中国交通运输碳排放强度时空交互特征及跃迁机制

采取多种空间分析的方法,对2002～2020年交通运输业碳排放强度的时空交互特征进行剖析,通过得到的时空跃迁类型与面板分位数模型进行嵌套来探究其跃迁机制,最后根据不同的跃迁机制引入地理探测器模型来考察影响交通运输业碳排放强度的不同因素之间的交互作用效应.结果表明: ①中国30个省区的交通运输业碳排放强度整体呈波动下降态势,在空间上的聚集水平也相对稳定.②ESTDA的时空交互特征表明,西北地区和周边邻接空间单位的关系不稳定,变化和波动较大.而东部沿海城市等经济发达地区已经形成了成熟的交通运输网络,因此局部空间格局也相对稳定,但仍有部分地区存在时空竞争性.③交通运输业碳排放强度时空跃迁可分为4类驱动或制约模式（人口-经济-城镇化制约模式;人口-经济-城镇化-设施制约模式;技术-消费-产业驱动模式和技术-产业-规制驱动模式）.大部分省份受低分位制约和高分位驱动两种模式的影响,仅有少部分省份受高分位制约和低分位驱动的作用影响,且绝大多数属于西北或西南地区.④根据得出的交通运输业碳排放强度跃迁机制进一步引入地理探测器模型,注重多因子的协调发展,加强区域间协同治理.