菲律宾海北部19cal.kaBP以来表层海水温度变化

对菲律宾海北部E-2岩心柱(29.62°N、131.14°E,水深3 877m)进行了浮游有孔虫δ18 O分析、AMS14 C测年以及U3k7表层海水温度(U3k7-SST)的测试。结果表明,E-2岩心记录了约19cal.kaBP以来U3k7-SST变化过程,其末次冰消期整体变化过程与北大西洋高纬地区相似,记录了Heinrich 1(H1)、Blling/Allerd(B/A)和Younger Dryas(YD)等快速气候事件,同时也识别出发生于19.4～19.2和18.5～18.0cal.kaBP的2次变冷事件,说明了研究区与北大西洋气候存在遥相关;在B/A和YD阶段中发现的百年尺度气候波动及变化过程,可能反映了热带过程对研究区域的影响;E-2岩心柱末次冰消期变暖存在阶段性,其变暖时间开始于19.4cal.kaBP,而大幅升温阶段则从15.3cal.kaBP开始。     

Simultaneous optical and radar observations of poleward moving auroral forms under different IMF conditions

Using high temporal resolution optical data obtained from three-wavelength all-sky imagers at Chinese Yellow River Station in the Arctic, together with the EISCAT Svalbard radar （ESR） and SuperDARN radars, we investigated the dayside pole- ward moving auroral forms （PMAFs） and the associated plasma features in the polar ionosphere under difibrent interplanetary magnetic field （1MF） conditions, between 0900 and 1010 UT on 22 December 2003. Simultaneous optical and ESR observations revealed that all PMAFs were clearly associated with pulsed particle precipitations. During northward IMF, particles can precipi- tate into lower altitudes and reach the ionospheric E-region, and there is a reverse convection cell associated with these PMAFs. This cell is one of the typical signatures of the dayside high-latitude （lobe） reconnection in the polar ionosphere. These results indicate that the PMAFs were associated with the high-latitude reconnection. During southward IMF, the PMAFs show larger lati- tudinal motion, indicating a longer mean lifetime, and the associated ionospheric features indicate that the PMAFs were generated by the dayside low-latitude reconnection.     

壤塘县大骨节病病区环境中硒的分布特征

大骨节病是一种地方性骨关节病,主要分布于环境低硒地区。目前,我国大部分地区大骨节病病情已经得到控制,病情相对活跃而严重的区域主要集中于青藏高原地区。四川省壤塘县地处青藏高原东南缘,大骨节病遍布全县各村且最低患病率不低于13.28%。本文选择不同病区采集了耕作土壤(0~20cm)、青稞、糌粑和饮用水等样品,并分析了样品含硒量与大骨节病病情的关系。结果表明：壤塘县大骨节病病区环境含硒水平很低,特别是病情比较严重的村子其环境含硒水平更低。耕作土壤和青稞籽粒含硒水平依次为中病区>重病区>极重病区。受制作过程中添加物的影响糌粑含硒水平为中病区>重病区≈极重病区。虽然不同饮水类型硒的水平存在差异,但是,极重病区饮用水中含硒量也低于中病区和重病区。大骨节病与当地环境因素特别是主要粮食和食物含硒量的关系非常密切。在低硒环境条件下,由于饮水仅对人体硒的摄入起辅助性的作用,因此,调节和改善环境低硒地带居民的膳食结构,增加外源性高硒食物的输入,减少人体对低硒环境因素的依赖性,将会对大骨节病的防治具有重要的意义。     

A Modified Soil Moisture Model for Two‐Layer Soil

There can be marked variations in soil hydraulic properties in a soil vertical profile from the soil surface to the base of the root zone. Many existing two‐layer soil moisture (TLSM) models cannot well describe typical stratified soil profiles. A modified TLSM model is presented in this study. The modified model results and those from two existing models are compared with field observations. The modified TLSM model had the best agreement with the field observations. In both the surface layer and the root zone layer, the root mean square errors of soil moisture estimated by the modified model were smaller than those for the other models. The parameters in the modified TLSM model are relatively easy to determine. The modified TLSM model offers clear advantages over current TLSM models.     

Sedimentary Organic Carbon Mineralization and Its Contribution to the Marine Carbon Cycle in the Marginal Seas

Continental margin sediments are important ocean carbon repository, and the internal carbon cycle is mainly driven by the mineralization processes of sedimentary organic matter. Most organic carbon is transformed to Dissolved Inorganic Carbon (DIC) by mineralization processes after being delivered to continental margin sediments, and DIC from pore water diffuses into the upper water column and participates in the ocean carbon cycle. At the same time, some DIC combines ions such as Ca²⁺ and Mg²⁺ and precipitates as authigenic carbonate minerals so that carbon is stored in the deposits. Based on the biogeochemical study of the mechanism and efficiency of organic matter burial, we discussed the interaction among sulfate reduction, methanogenesis and anaerobic oxidation of methane, and the effect of organic mineralization on the formation of authigenic carbonate. By reviewing the above-mentioned aspects, we can obtain a better understanding of the role of continental margin sediments in the global carbon cycling budgets as well as its climate and environmental effects.     

降雨入渗条件下自嵌式挡土墙倒塌机理分析

某高校自嵌式挡土墙在暴雨入渗后多处发生坍塌,破坏形式主要表现为与挡土砌块相连的土工格栅被拉断,自嵌式挡土砌块及临近土体局部坍塌,但挡土墙后土体基本保持稳定。基于饱和-非饱和土渗流理论,分析降雨入渗情况下墙后土负孔隙水压力的分布,基于Fredlund双变量强度准则采用极限平衡法计算挡土墙稳定,结果表明:降雨入渗后回填土区域负孔隙水压力明显降低且分布较均匀,整体稳定满足要求。为分析局部坍塌原因,现场取样试验得出降雨前后墙后土体总应力强度进行有限元分析,结果表明:砌筑过程中土工格栅在自嵌式挡土砌块与砾石交界处会产生弯折,降雨入渗对土体的软化增大了格栅弯折程度及内力,在弯折段土工格栅处于复合受力状态,复合受力状态下土工格栅的抗拉强度远小于其极限抗拉强度,是导致与挡土砌块相连处格栅被拉断及临近土体局部坍塌的主要原因,设计时应特别引起重视。     

黄土层中深基坑预应力锚索试验研究

在深基坑预应力锚索现场试验基础上,通过实测数据分析,提出在特定黄土地层中,当锚索锚固段长度设置合理时,其锚固段极限黏结强度标准值可高于现行规范推荐值。从试验锚索的不同荷载位移曲线,显现出预应力锚索在黄土地层中和其他黏性土地层中基本一致的受荷服役工况和荷载传递变化情况,试验曲线直观清晰地反映了每级张拉荷载下锚索的工作状态,并通过试验数据得到了相关拟合式。最后从试验数据反算锚索刚度并与现行规范推荐计算公式进行比较,得到一些有益结论。研究成果可以为黄土地区深基坑预应力锚索的设计、施工等提供参考。     

基于改进广义卡尔曼滤波的结构损伤识别方法

针对传统的广义卡尔曼滤波算法不能有效地追踪结构刚度的变化情况,本文以传统卡尔曼滤波理论为基础,得到了基于衰减记忆的广义卡尔曼滤波算法公式,利用该算法对所得到的地震响应信号进行分析,提取结构的特性,辨识结构的参数,并从中判断结构损伤发生的时刻、位置及程度,改善了广义卡尔曼滤波的效果。衰减记忆的广义卡尔曼滤波算法只能够判断出结构参数变化的时间并且容易出现振荡,因此采用了一种新的自适应追踪技术,用一个自适应因子矩阵代替了原有的遗忘因子,这种技术可以有效追踪结构参数变化的时间、位置和大小,从而能够在线识别出结构的损伤。     

北京城区周边地区湿地重建与恢复可行性研究

对北京温地演化规律进行了总结,通过对北京城区周边地区湿地现状的调查研究,分析了20世纪50年代以来湿地消失的主要原因,结合对已经恢复成功的典型湿地的剖析,提出了湿地重建与恢复的3处目标区域,并从中选取一处目标涅地作为例子,着重从地质地貌与水源的角度,论证其重建与恢复可行性。