利用水生植物氮同位素作为人为氮输入太湖的生物指标

富营养化是一个全球性的环境问题,需要更准确地评估人为氮输入对水生生态系统的影响.而初级生产者的N同位素已成为一个有用的生物指标.本研究通过测定太湖和太湖周围湖荡水生植物的δ15N,与水体中的环境因子做GAM分析,结果表明δ15N与水体中的铵态氮、正磷酸盐、总氮都有很显著的相关性,而这主要是由于植物在吸收和同化过程中有较大的同位素效应.水生植物的氮同位素值与氮的有效性和植物对氮的需求有关.当氮浓度有限时,植物对氮的需求变大并且减少了15N的分馏,水生植物则有较高的同位素值,而高氮浓度下,氮的可用性超过植物对氮的需求,15N分馏增大则氮同位素值较低.无锡地区和吴江地区湖荡水生植物同位素值有显著的差异性,无锡地区湖荡湿地富营养化最严重,所以水生植物的δ15N值比吴江地区高.总体来说,水生植物氮同位素可以作为评价生态系统人为氮输入影响的一个有效且简单的生物指标.     

长周期地震动输入下大型建筑剪力墙振动台试验

为优化处于长周期地震动输入下的大型建筑剪力墙结构,进行了振动台试验。分析普通地震动与长周期地震动波的区别,证明了长周期地震波具有显著长周期分量的特性。将某一高层酒店剪力墙作为研究案例,设计模拟实验台的构建流程与传感器布局,将建筑模型缩尺比例设置为1∶10。选择CA波、RG波、EL波作为实验用地震波,从位移与结构周期、层间剪力与位移比、易损性以及损失评估等方面对大型建筑剪力墙的抗震性能进行了评估。振动台试验结果表明,在位移相同的情况下,长周期地震波下的建筑极限承载力最小;在经历CA波、RG波、EL波后,模型的自振周期均发生变化,而EL波作用下模型的自振周期始终比基本周期略长;不同地震波下,X、Y向层间剪力变化基本趋于一致;CA波、EL波作用下,X向位移比较为接近,而剪力墙Y向上位移比在三种地震波作用下具有较大差异性;在长周期地震波作用下,大型建筑剪力墙损伤最为严重。     

多维地震激励下曲线梁桥简化模型及最不利输入方向研究

曲线梁桥只有在某一特定方向输入地震动时,结构某点或某截面的内力(或应力)才能达到最大值,需要沿多个可能方向输入计算才能确定地震动最不利输入方向。根据隔震曲线梁桥受力特点,将桥梁上部结构和桥墩简化均具有两个水平自由度和一个围绕质量中心轴扭转自由度的堆积质量模型,建立双质点六自由度简化分析模型,通过求解曲线梁桥的动力学方程研究结构的动力特性和地震动行为。算例表明,双质点模型计算结果与传统的有限元模型基本一致,且计算方法简单,可以考虑各种敏感因素的影响,借助编程更适合提出规律性的设计方法。进而在双质点模型基础上应用MATLAB编程探讨多维地震作用下曲线梁桥地震波最不利输入方向的问题,针对不同参数的隔震曲线梁桥,改变相关参数后只需运行一次就可以实现最不利输入角度的确定,可为有限元法最不利地震波输入方向的确定提供参考,并大大减少多个方向输入试算的工作量。     

颗粒物质力学及其在工程地质领域中的应用初探

由碎散物质组成的地质体失稳流滑大变形所致的地质灾害严重影响国民经济发展和人民生命财产安全,绝大多数造成此类地质灾害的对象属于颗粒物质,而地质灾害与颗粒物质力学的交叉融合一直以来都是软物质物理学和工程地质科研工作者的努力方向之一.颗粒物质是由大量离散颗粒组成的复杂无序体系,其力学特性极为复杂,根据颗粒的运动状态可以表现出...     

北京山区泥石流灾害临界雨量研究

目前北京山区泥石流灾害的临界雨量研究方法主要是基于统计资料的临界雨量阈值判别法,该方法没有包含泥石流形成地区的地质背景条件与形成机理的信息,因此在推广上存在难度。本文从松散物质失稳引发泥石流的机理出发,推导了松散物质失稳时的雨量计算公式,该公式可用于计算不同流域内泥石流沟道的松散物质起动的临界雨量。将该公式与常规的临界雨量阈值判别公式相结合,能够提高北京地区泥石流灾害预报预警的准确度。     

天山乌鲁木齐河源1号冰川东支能量-物质平衡模拟研究

基于天山乌鲁木齐河源1号冰川东支海拔4025 m处自动气象站的观测数据和同期物质平衡花杆观测数据,采用COSIMA模型,对该冰川东支2018年消融期单点能量-物质平衡进行了模拟.结果显示:物质平衡模拟值为(-0.67±0.03)m w.e.,与实测值有非常好的一致性,相关系数达0.96.造成冰川消融的能量来源于净短波辐...     

Pyrite Formation in Organic-rich Clay, Calcitic and Coal-Forming Environments

The early diagenetic characteristics of pyrite formation processes in a Miocene freshwater sequence of mixed sediments （coal fragments in clays, sandstones or shales） alternating with continuous brown coal layers was investigated. Based on abundant minerals, the following main sedimentary environments were distinguished： the illite-montmorillonitic （I-M）, calcitic （Ct） and coal-forming environment （CL）. For these hydrogeochemically differing environments the effects of limiting factors on the pyrite formation process （availability of sulphate and Fe, amount of organic matter and participation of organic sulphur） were assessed by correlation analysis. Significant differences in the effects of these limiting factors in the particular environments were observed. These differences were explained taking in account the different oxidative activity, Fe-complex and surface complex forming properties of humic substances in dependence of pH of environment and the abundance of sorptionally active clay minerals. In environments having a relatively low pH and containing clay minerals （I-M- and CL-environments） the oxidative activity of humic substances （Hs） on pyrite precursors was greatly prevented however pyrite formation depended on reactive Fe availability as the consequence of complex formation. On the contrary, in environments with a relatively high pH, as it was the calcitic, the oxidative activity of Hs was greatly enhanced, thus oxidizing the sulfur precursors of pyrite. The oxidation degree of organic matter was probably also a consequence of the differing activity of the humic electron-acceptors.     

A Study of Chromium Adsorption on Natural Goethite Biomineralized with Iron Bacteria

Goethite, especially biogenic goethite, has high specific surface area and great capacity for the adsorption of many contaminants including metal ions and organic chelates. Chromium is a redox actively toxic metal ion that exists as either Cr^Ⅲ or Cr^Ⅵ in nature, and as such it is essential to understand its behavior of adsorption on natural goethite mineralized by iron bacteria, as Gallionella and Leptothrix in water body. The adsorption of Cr^3＋ and Cr^Ⅵ on naturally biomineralized goethite is studied in this paper. The results show that both Langmuir and Freundlich adsorption isothermal models are able to accurately describe the adsorption of these two ions. Investigation of SEM/EDS, TEM/EDS indicates that the two ions do not adsorb homogeneously on goethite owing to the different microstructures of goethite, and that the microspherical goethite has a greater adsorption capacity for chromium ions than the helical one. XPS data show that redox reaction of chromium on the surface of biomineralized goethite takes place in the adsorption of both Cr^3＋ and Cr^Ⅵ. The CrvI adsorbed on biogoethite is much easier to transform into CrIII than the oxidization of Cr^Ⅲ on the bio-goethite.     

基于空时显著性的日冕物质抛射检测

日冕物质抛射(Coronal Mass Ejection, CME)是一种剧烈的太阳爆发现象, 它会对行星际空间造成严重扰动, 进而影响人类生产、生活. 基于CME的时空显著性, 将显著性检测方法引入到CME检测中, 利用结构化矩阵分解SOHO (Solar and Heliospheric Observatory)的大角度光谱日冕仪(Large Angle and Spectrometric Coronagraph Experiment, LASCO) C2的日冕图像对应的特征矩阵, 从中恢复出稀疏部分获得显著前景. 然后考虑CME运动时产生的时间显著性, 从而去除非CME结构(如冕流), 得到最终检测结果. 实验表明, 以人工目录协调数据分析中心(Coordinated Data Analysis Workshop, CDAW)检测结果为基准时, 所提方法不仅在检测CME数量上比计算机辅助跟踪软件包(Computer Aided CME Tracking Software package, CACTus)和太阳爆发事件检测系统(Solar Eruptive Event Detection System, SEEDS)有优势, 还在CME中心角度和张角宽度等特征物理参数测量上比CACTus和SEEDS更接近CDAW目录参考值.