青藏高原东南缘高山湖泊藻类响应气候变化和大气沉降的长期特征     

朱云  陈光杰  孔令阳  李静  陈小林  李平  马欠  周起  黄林培  任雁 《湖泊科学》2023,35(6):2155-2169

高山湖泊远离人类活动直接影响,通常具有面积小、寡营养、食物网单一等特点,对气候变化和营养输入具有较高的敏感性。我国青藏高原东南缘地区氮沉降通量较高、增温幅度显著,已有研究显示该地区可能受湖泊类型、流域特征等影响存在差异性的湖泊响应模式。本研究选择该区域位于树线以下、具有不同水深的3个小型湖泊(盖公错纳、沃迪错、碧沽天池)开展沉积物调查和对比研究,通过钻孔样品测年、理化特征和藻类(硅藻群落、藻类色素)等多指标分析,结合区域气候定量重建和氮沉降等数据收集,评价了过去300年来藻类演替模式的异同特征及湖泊水深的调节作用。结果显示,3个湖泊中硅藻的优势物种与群落组成差异明显。深水型湖泊盖公错纳(最大水深39.4 m)的硅藻群落以浮游种为主(占比达82%),优势种为眼斑小环藻(Pantocsekiolla ocellata)、科曼小环藻(Pantocsekiella comensis);深水型湖泊沃迪错(最大水深20.7 m)的硅藻群落中浮游种和底栖种约各占50%,优势种为眼斑小环藻(Pantocsekiella ocellata)、连结脆杆藻(Saurosira construens);浅水湖...  相似文献   

低周反复荷载下Q460钢材框架柱抗震性能分析     

刘宽  马煜东  黄娇  刘笑笑  苏佶智 《震灾防御技术》2019,14(3):535-554

为了进一步完善Q460钢材在抗震设计规范中相关限值的要求,本文利用有限元软件ABAQUS,以轴压比、翼缘宽厚比、腹板高厚比和壁板宽厚比为变量,建立了共48根“工”字型框架柱和“箱”型框架柱,分析了其抗震性能。结果表明:翼缘宽厚比对框架柱的能量耗散系数影响较小;能量耗散系数随轴压比、腹板高厚比（“工”字型）和壁板宽厚比（“箱”型）增大而明显减小;框架柱的极限承载力随轴压比的减小及壁板宽厚比和翼缘宽厚比的增大而逐渐增大,当腹板高厚比接近规范限值时,承载力下降趋势明显增大。与采用Q235钢材的框架柱相比,Q460钢材框架柱的延性较小,仅为2左右;当采用Q460钢材时,“工”字型框架柱的极限位移角限值建议取为0.03,“箱”型框架柱的极限位移角限值建议取为0.032。规范中对翼缘宽厚比限值的规定偏于保守,其值最大可取至9。无论是“工”字型框架柱还是“箱”型框架柱,其腹板高厚比均不宜过大。Q460钢材框架柱的刚度退化率随轴压比的增大而增强,且翼缘宽厚比越大,腹板高厚比越小,柱的初始刚度越大,刚度退化程度越明显。  相似文献   

Experimental seismic behavior of squat shear walls with precast concrete hollow moulds     

Han  Wenlong  Zhao  Zuozhou  Qian  Jiaru  Zhang  Yingbao  Ma  Tao 《地震工程与工程振动(英文版)》2019,18(4):871-886

This study proposes an innovative precast shear wall system, called an EVE precast hollow shear wall structure (EVE-PHSW). Precast panels in EVE-PHSW are simultaneously precast with vertical and horizontal holes. Noncontact lap splices of rebars are used in vertical joints connecting adjacent precast panels for automated prefabrication and easy in situ erection. The seismic behavior of EVE walls was examined through a series of tests on six wall specimens with aspect ratios of 1.0∼1.3. Test results showed that EVE wall specimens with inside cast-in situ concrete achieved the desired “strong bending and weak shear” and failed in shear mode. Common main diagonal cracks and brittle shear failure in squat cast-in situ walls were prevented. Inside cast-in situ concrete could significantly improve the shear strength and stiffness of EVE walls. The details of boundary elements (cast-in situ or prefabricated) and vertical joints (contiguous or spaced) had little effect on the global behavior of EVE walls. Noncontact lap splices in vertical joints could enable EVE walls to exhibit stable load-carrying capacity through extensive deformations. Evaluation on design codes revealed that both JGJ 3-2010 and ACI 318-14 provide conservative estimation of shear strength of EVE walls, and EVE walls achieved shear strength reserves comparative to cast-in situ walls. The recommended effective stiffness for cast-in situ walls in ASCE 41–17 appeared to be appropriate for EVE walls.

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基于微型无人机摄影技术的微构造信息提取研究——以博-阿断裂乌苏通沟东岸为例     

马建  黄帅堂  吴国栋 《中国地震》2019,35(3):550-557

利用微型无人机摄影测量技术,获取了博-阿断裂在乌苏通沟东岸的高精度地形、地貌数据,解译DEM数据,并结合野外调查工作,明确了断裂在乌苏通沟东岸冲洪积扇上19.3～31.1m的水平位错。分析获取的陡坎剖面,且对比陡坎两侧地貌的剥蚀程度,认为陡坎形成后受到后期水流的侵蚀,部分陡坎的高度在一定程度上被放大,断裂的实际垂直位错在0.7m左右。通过实例展示了无人机摄影技术在活动构造研究中的巨大潜力以及在微构造信息提取中的独特优势。  相似文献   

内蒙古中部地区形变主要干扰的时频响应特征分析     

张小艳  熊峰  王旭东  赵星  刘永梅  刘芳 《中国地震》2019,35(4):718-725

选取内蒙古中部地区定点形变观测中受降雨、大风、气压干扰以及地震波影响的典型数据,采用S变换,对该地区形变观测中4种主要干扰信号的时频响应特征进行分析与讨论。结果表明,降雨干扰信号主要集中在低频区域,其频率先增大后减小;大风干扰表现为高频干扰,时频域能量强度与观测曲线受风扰影响变化幅度成正比;气压干扰信号的优势频率分布在低频段内;地震波影响中VP垂直摆和JCZ地震计记录的地震波较为相似,但VP垂直摆记录的频段要小于JCZ地震计,VP垂直摆主要记录的是低频地震波。同时,4种干扰信号的时频域频率、能量强度随时间变化趋势与数据观测时域变化趋势相一致。  相似文献   

基于贝叶斯定理的地震危险性概率预测研究     

邓世广  周龙泉  马亚伟  臧阳  王月  韩颜颜 《中国地震》2019,35(1):1-13

由于地震孕育过程的复杂性和观测技术的局限性,不同地震观测资料表现出异常变化与后续较大地震的对应关系存在不确定性,因此对预测意见进行概率表达是一种科学恰当的做法。本文基于泊松分布的危险区背景地震概率预测和单项预测方法(包括测震、流体、形变、电磁等学科)的历史预测效能,采用贝叶斯定理计算得到单项预测方法的短期或年度地震危险概率预测结果,进而采用综合概率方法,给出基于多种单项预测方法的短期或年度地震危险概率预测结果。短期概率预测初步结果表明,2018年2～9月,中国大陆72%的5级以上地震都位于相对高概率预测区域。  相似文献   

Seasonal variability of the carbon export in the central South China Sea     

Ma  Wentao  Xiu  Peng  Chai  Fei  Li  Hongliang 《Ocean Dynamics》2019,69(8):955-966

Ocean Dynamics - The South China Sea (SCS) is strongly influenced by the East Asian monsoon system with seasonal reversal. Measurements from a 7-year continuous sediment trap located in the central...  相似文献   

Devonian integrative stratigraphy and timescale of China     

Qie  Wenkun  Ma  Xueping  Xu  Honghe  Qiao  Li  Liang  Kun  Guo  Wen  Song  Junjun  Chen  Bo  Lu  Jianfeng 《中国科学:地球科学(英文版)》2019,62(1):112-134

The Global Boundary Stratotype Sections and Points(GSSPs) for the bases of all seven international Devonian stages have been formally defined and ratified by IUGS till 1996, and nowadays, the main tasks for Devonian stratigraphers include further subdivision of these standard stages, strictly constrained absolute ages for the boundaries, and precise neritic-pelagic and marine-terrestrial correlations using multidisciplinary stratigraphy methods. Establishment of high-resolution Devonian integrative stratigraphy framework and timescale of China would play an important role in improving regional and international correlation, facilitating the recognition of important stratigraphic levels in different paleogeographic settings, and understanding the evolution pattern of biota, paleoclimate and paleoenvironment during this critical interval. Based on well-studied bio-and chronostratigraphy of Devonian in South China and adjacent areas, in combination with recent achievements in carbon isotope stratigraphy, event stratigraphy and radioactive isotope ages, this paper briefly summarize the research history and current status of Devonian chronostratigraphy of China, and for the first time introduce Devonian integrative stratigraphy framework of China.Up to date, few studies have been conducted on the astronomical cyclostratigraphy and high-resolution radioactive isotope dating in Devonian of China, which should be our main focuses in the near future.  相似文献   

Ordovician integrative stratigraphy and timescale of China     

Zhang  Yuandong  Zhan  Renbin  Zhen  Yongyi  Wang  Zhihao  Yuan  Wenwei  Fang  Xiang  Ma  Xuan  Zhang  Junpeng 《中国科学:地球科学(英文版)》2019,62(1):61-88

In this chapter, starting with a brief review of the research history and current status in the studies of the Ordovician chronostratigraphy in China, the subdivision of the Ordovician System, definition and recognition of its series and stage boundaries, and possible stratigraphic gaps are discussed in details in order to establish a multidisciplinary stratigraphic correlation through an integrated approach including lithostratigraphy, biostratigraphy, radiometric dating, chemostratigraphy and magnetostratigraphy. Being internationally accepted, the Ordovician System is now subdivided into three series and seven stages, in ascending order, Lower(Tremadocian, Floian), Middle(Dapingian, Darriwilian) and Upper series(Sandbian, Katian,Hirnantian). Three of the seven "Golden Spikes" defining the bases of the Ordovician stages, which were established in 1997–2007, are located in China. As a regionally applied chronostratigraphy, the Ordovician System was subdivided in China into Lower(Xinchangian, Yiyangian), Middle(Dapingian, Darriwilian) and Upper series(Neichiashanian, Chientangkiangian,Hirnantian). This scheme agrees largely with the standard international classification, which can actually be directly applied to China, except for some special circumstances where the Neichiashanian and Chientangkiangian stages of the Upper Ordovician are used. Based on the new studies in recent years and distinctions and differences recognized in the development of the Ordovician System in the constituent terranes of China, a new framework for correlation among the major Chinese palaeoplates or terranes, e.g. South China, North China(including Tarim and Qaidam) and Xizang(Tibet)-western Yunnan, has been established. However, it has been recognized herein that uncertainties still remain on defining the base of the Tremadocian,Dapingian and Katian, and on the correlation between different mega-facies. More specifically, for the Tremadocian, the precise correlation of its base will depend on the better-defined conodont taxonomy, while for the Dapingian and Katian, on the correlation between different mega-facies. It is worthwhile to note that the chemostratigraphic studies of the Ordovician System in China produced the carbonate δ13 C curves for the Darriwilian(Middle Ordovician) and Katian(Upper Ordovician), which show significant differences from the composite global curve. Record of the Ordovician isotopic dating is relatively rare in China, with only three reliable ages from zircons that are all from the upper Katian to Hirnantian of the Upper Ordovician.Abundant bentonite beds in the Upper Ordovician of South China will also provide unique opportunities to advance the isotopic dating and related researches. Studies on the Ordovician magnetostratigraphy need to be significantly enhanced in China, as currently all the available results are restricted to the Lower Ordovician of North China, although they can be correlated with those known from other parts of the world. The analysis of the durational unevenness of the seven stages in the Ordovician supports the possibility to further subdivide the long-durational Tremadocian, Darriwilian and Katian stages, each into two substages.  相似文献   

湖泊沉积物中磷酸盐氧同位素前处理方法对比   总被引：2，自引：1，他引：1  

张秀梅  王亚蕊  马书占  陈向超  冯慕华 《湖泊科学》2017,29(2):512-520

磷酸盐氧同位素(δ~(18)OP)是一种有效的磷源示踪方式.由于湖泊沉积物的组成十分复杂,必须对样品进行除碳处理和纯化处理.本文对目前应用较为广泛的几种前处理方法进行比较,包括NaClO处理和H_2O_2处理等除有机碳方法,以及Blake法和Mc Laughlin法等纯化方法,以期获得适用于湖泊沉积物磷酸盐氧同位素的前处理方法.结果表明:(1)NaClO处理可以保证较高的无机磷提取效率,同时能有效地减少无机磷提取液中有机质含量,且对不同形态磷的破坏较小;H2O2对有机质的去除效果不稳定,且处理后样品磷形态之间发生转化,显著增加了提取的无机磷浓度.(2)Blake法和Mc Laughlin法分别采用磷钼酸铵(APM)+磷酸铵镁(MAP)沉淀和Ce PO4沉淀对样品进行纯化.在纯化处理湖泊沉积物过程中,Blake法优于Mc Laughlin法,主要体现为有机质去除率高,并且磷的回收率较为稳定.(3)经Blake法纯化丹麦Nordborg湖沉积物样品得到的Ag_3PO_4中C、N含量低于Mc Laughlin法且重现性好.本文结合NaClO法与Blake法的优点,建立了一种适合湖泊沉积物的磷酸盐氧同位素前处理方法:首先用2.5%NaClO对沉积物样品进行除碳预处理,然后对磷酸盐提取液依次通过氢氧化镁共沉淀(MAGIC)、APM+MAP沉淀、阳离子交换树脂处理,最后生成Ag3PO4沉淀.  相似文献