Lowland rainforest response to hydrological changes during the last 1500 years in Gabon, Western Equatorial Africa     

Alfred Ngomanda  Dominique Jolly  Ilhem Bentaleb  Alex Chepstow-Lusty  M'voubou Makaya  Jean Maley  Michel Fontugne  Richard Oslisly  Nicaise Rabenkogo 《Quaternary Research》2007,67(3):411-425

Pollen and δ¹³C_TOM data obtained from two contrasting lake sequences (Lakes Kamalété and Nguène), located 200 km apart in the lowland rainforest of Gabon, provide complementary local and regional 1500-yr records of high resolution (15–30 yr) vegetation change. A combination of aquatic, semi-aquatic and terrestrial pollen showed in both records that the tropical rainforest increased during periods of high rainfall and decreased during drought intervals. The strong fluctuations of water balance at decadal scale during the “Medieval Warm Period” ( 1100–800 cal yr BP) coincided with a noticeable increase in shade-intolerant taxa, indicating recurring rainforest canopy disturbance. The δ¹³C_TOM signal showed high-amplitude variations in both records, which positively correlates with the rainforest dynamics and local vegetation changes. The similar trends in both the pollen and the δ¹³C_TOM signals between these sites demonstrate the regional broadly synchronous timing of shifting hydrological conditions. The largely positive co-variation between strong fluctuations of hydrological conditions and changes in rainforest structure and composition indicate that regional climatic change is probably the driving force for major rainforest dynamics in Gabon. Any significant anthropogenic impact on vegetation has not been clearly identified, and this issue still needs to be resolved independently by obtaining detailed archeological records across the interval 1400–800 BP, which currently seem to be extremely rare or not easily available.  相似文献   

基于LSTM的震后通信数据异常检测分析     

王晓湘  刘洞天  刘南江  丁一  姜立新 《中国地震》2022,38(2):270-279

震后通信数据会发生异常变化,通过对通信数据异常进行分析,有助于提供有效的灾情数据以及更好地了解震后产生的影响,进而有效地为抗震救灾提供辅助支持。本文基于LSTM对震后的通信数据异常进行分析,研究内容主要包括通信数据流预处理、基于LSTM的异常检测模型以及数据分布变化检测模型。结果表明,本文模型能够对通信数据的异常变化进行识别,为后续的灾情分析提供数据。  相似文献   

中国玛珥湖及其研究意义   总被引：4，自引：2，他引：2  

储国强  刘嘉麒 《岩石学报》2018,34(1):4-12

随着全球变化研究的深入,科学家们认识到古气候变化除轨道尺度的冰期/间冰期旋回之外还存在年代际-千年尺度的高频变化和突变事件。要认知这些变化,古气候记录的时间分辨率要达到"年-年代际"。因此,寻求时间跨度长、连续性好、信息丰富的高分辨率记录是过去全球变化研究面临的主要任务之一。玛珥湖为火山射汽喷发形成的封闭湖泊,由于其独特的形成机制及水文背景,使其能够提供数万年乃至几十万年连续稳定的沉积记录,是高分辨率古气候、古环境变化研究的重要对象。中国玛珥湖得天独厚,从热带到寒温带均有分布,为系统研究中国不同气候区各种时间尺度古气候变化规律提供了理想材料。本文基于中国玛珥湖的分布及沉积特征,探讨玛珥湖沉积记录能够为古全球变化研究做出怎样的贡献,解决什么科学问题,具体包括以下三个方面的内容:(1)在轨道尺度上,精确定位现代气候在地质历史中的位置是未来最具挑战性的科学问题之一。我国热带地区玛珥湖沉积物跨越了至少4个冰期-间冰期旋回,能够为理解冰期驱动机制、下一次冰期来临、高低纬关联等关键科学问题提供多学科数据;(2)千年尺度古气候变化,其成因可能源于不同的动力学机制,是气候系统对各种外部和内部驱动因子响应的结果,因此千年震荡可能存在明显的时空差异。集成不同气候带的玛珥湖沉积记录将为理解千年震荡规律及其驱动因子做出贡献;(3)年-年代际气候变化是预测未来气候变化的基础,PAGES、IPCC以及PAGES-Asia 2K均将过去2千年来气候变化作为预测未来几十年至百年尺度上重大全球变化的背景,并为此构建全球数据体系,玛珥湖沉积特别是纹层沉积记录能够填补某些地区高分辨率数据的空白。  相似文献   

应用改进的ICP算法检测工业封头表面变形     

王春林  郑德华  孟敏  谢波 《测绘与空间地理信息》2015,(1):209-211

由于工业封头变形使得采集到的两期点云重心不一致,受点云重心变化的干扰,传统ICP算法出现局部收敛的情况,本文提出了一种基于点对间欧氏距离计算点云加权重心的ICP改进算法。该方法通过给不同距离的点对赋予权值,变形区域的点对距离较大,赋予的权值相对小,有效地消除了变形区域的点云对重心位置的影响。实验结果表明,该方法大大提高了ICP算法的精准性,有效消除重心变化的影响,从而可以准确地检测出工业封头变形区域。  相似文献   

Common features and different trajectories of land cover changes in six Western Mediterranean urban regions     

《Applied geography (Sevenoaks, England)》2015

Land use and land cover change (LULCC) dynamics have been particularly strong in the Mediterranean region, due to its historical development and to agro-pedoclimatic conditions favorable to human settlement. This area has undergone in the 1950s and the 1980s intense urbanization processes that has followed different trajectories. Urban expansion commonly occurs at the expense of agricultural land, leading to the fragmentation of natural areas and conflicts over access to land resources. These dynamics mainly concern the fringe between urban and agricultural land, e.g. the peri-urban areas usually included within functional urban regions. Here, to identify common features of LULCC in Western Mediterranean urban regions, we investigated two main features: direct changes due to urbanization and indirect changes affecting non-artificial land uses. We compared LULCC dynamics in 6 case studies from the north and south of the Western Mediterranean region: the urban regions of Montpellier and Avignon (France), Pisa (Italy), Madrid (Spain), Meknes (Morocco), and Constantine (Algeria), using a 30-year multitemporal spatial analysis (1980–2010). Two series of Landsat TM images were acquired for each case study and land cover data were analyzed both for dynamics and for land patterns, using landscape and class metrics. We found no significant north-south differences in LULCC dynamics between the investigated Western Mediterranean urban regions. Differences are more pronounced between small–medium cities and large metropolitan areas in type of urban diffusion, which is more sprawled in small–medium cities and more compact in large metropolitan areas. Rather, differences occur in LULCC not directly affected by urbanization, since in Northern Mediterranean urban regions afforestation and abandonment of agricultural areas are prevalent and closer to the urban areas, whereas transformation of natural areas into agricultural ones occurs mainly in Southern Mediterranean urban regions at a similar distance from urban areas than it happens for afforested or abandoned areas. In attempting for the first time to assess LULCC in these Mediterranean urban regions, we provide a preliminary comprehensive analysis that can contribute to the active LULCC research in the Mediterranean basin and that can be easily applied to other Mediterranean urban regions.  相似文献   

The Asian Development Bank and the production of poverty: Neoliberalism,technocratic modernization and land dispossession in the Greater Mekong Subregion          下载免费PDF全文

Kearrin Sims 《Singapore journal of tropical geography》2015,36(1):112-126

In 1992 the Asian Development Bank coordinated a meeting between government representatives from China, Cambodia, Laos, Myanmar, Thailand and Vietnam to discuss regional economic integration. From that meeting the Greater Mekong Subregion was formed to promote peace and prosperity within the Mekong countries. Yet, despite more than more than USD 14 billion being spent on facilitating trade, development and infrastructural ties between these nations, poverty remains widespread. This article provides a critical analysis of the Asian Development Bank and its approach to development and poverty alleviation within the Greater Mekong Subregion. It suggests that the institution's technocratic neoliberal development ideology provides a discursive legitimation to processes of displacement and dispossession that has seen the production of new forms of poverty. To make this argument, the article draws on an ethnographic study of the local‐scale implications of forced resettlement at the Luang Prabang Airport. It conducts an analysis of how the Asian Development Bank defines and measures poverty, and critiques the institution's resettlement guidelines for the airport project.  相似文献   

过去2000年亚洲气候变化(PAGES-Asia2k)集成研究进展及展望   总被引：2，自引：0，他引：2  

葛全胜  郑景云  郝志新 《地理学报》2015,70(3)

介绍了国际过去全球变化研究计划(PAGES)过去2000年气候变化研究网络的设立背景、研究目的及亚洲在其中的独特性;总结了过去2000年亚洲气候变化(PAGES-Asia2k)集成研究的主要进展及中国的贡献,分析了当前在亚洲区域开展该项研究的主要问题及难点,并对未来研究进行了展望。亚洲历史悠久,高分辨率的代用资料丰富,是开展过去2000年气候变化研究的理想区域,但目前尚处于起步阶段。已有进展表明:在过去1200年中,亚洲830-1220年相对温暖,1340-1880年明显寒冷,20世纪则快速增暖;但亚洲气候类型多、变化过程复杂、区域差异大。因此,发展气候序列重建的新技术方法,提高重建序列的时、空分辨率、空间覆盖度和重建结果的精度,建立亚洲过去2000年气候代用资料数据库,集成重建过去2000年区域温度变化序列及干湿变化空间型,进而开展区域气候变化驱动机制与气候变化影响及适应研究,是该计划下一步的研究重点。  相似文献   

中美在南亚地缘影响力的时空演变及机制   总被引：17，自引：1，他引：16  

王淑芳  葛岳静  刘玉立 《地理学报》2015,70(6)

南亚是中美两国重要的地缘战略区,无论是对中国海上运输的安全和西部边疆的稳定,还是对美国实施"亚太再平衡"战略,都有着十分重要的作用。如何解析中美在南亚地缘影响力的变化及演变机制,是需要解决的关键科学问题。结合地理学、国际关系学和政治学研究视角,采用数学建模方法,构建国家地缘影响力的指标体系和模型,选取南亚为研究区域,探讨中美在南亚地缘影响力的时空演变,探寻地缘影响力演变的影响因素以及驱动机制。结果表明:1近10年,中美在南亚的地缘影响力在小幅波动中呈逐年上升趋势。从增幅比率看,中国在南亚地缘影响力的增速要比美国快。2国家地缘影响力演变是一个缓慢过程。2003-2012年间,中美在南亚国家和地区的地缘影响力变化幅度不大。3硬实力、软实力、相互依赖力和摩擦力是地缘影响力演变的主要影响因素。其中,硬实力和软实力是主导因素,起拉力作用;相互依赖力是辅助因素,起推力作用;而摩擦力是弱化因素,起反向力作用。4中美在南亚地缘影响力演变的驱动力包括地缘区位、地缘政治、地缘经济和地缘文化。地缘区位是国家地缘影响力演变的制约力,地缘政治是主导力,地缘经济是驱动力,地缘文化是辐射力。5国家硬实力不等于地缘影响力,国家硬实力强并不能代表其对外的地缘影响力就高,两者是非线性关系。硬实力虽起主导作用,但不能决定地缘影响力变化的强度和速度。  相似文献   

The response of Caragana microphylla seedlings to water table changes in Horqin Sandy Land, China     

YunHua M  TongHui Zhang  XinPing Liu  Wei Mao  XiangFei Yue 《寒旱区科学》2015,7(1):0088-0093

This paper focuses on the growth response of Caragana microphylla seedlings to changes of artificially controlled water table in Horqin Sandy Land, China. Monitoring results of soil water content shows that soil moisture is closely correlated to groundwater depths. Soil volumetric water increased rapidly when close to water sources and finally stabilized in a saturated state. The soil moisture trend of CK(control) increased gradually at 0–50 cm of soil depth then decreased to 4% below 50 cm soil depth. C. microphylla can adapt to different soil environments by changes in ecological and physiological characteristics. By comparing the ecological characteristics of C. microphylla seedlings at various water tables, we found that a shallow water table of 40 cm depth inhibited seedling growth because of weak ecological characteristics. A groundwater depth of 120 cm was more advantageous for plant height and canopy growth of C. microphylla seedlings. During the first two years, the most suitable water depth for root biomass was 120 cm, and 180 cm for root length. The growth of vertical roots is positively correlated with groundwater depth, and root thickness is the determinate factor for root biomass while the fine root is the determinate factor for root length. A thick root would grow much more in a natural drought environment while access to ground water promotes the growth of fine roots.  相似文献   

西南三江义敦岛弧南端地壳抬升历史及资源评价意义   总被引：5，自引：0，他引：5  

刘学龙  李文昌  张娜 《地质学报》2015,89(2):289-304

云南格咱岛弧成矿带是西南"三江"(怒江、澜沧江、金沙江)多岛弧盆系中一个重要的地质构造单元,位于甘孜—理塘结合带西侧德格—中甸陆块的东缘,印支期义敦岛弧带南端。它始于晚三叠世甘孜—理塘洋壳的向西俯冲,燕山期经历了陆内汇聚和造山后伸展作用阶段,喜山期受青藏高原碰撞隆起效应的影响,本区表现为强烈的逆冲-推覆构造和大规模走滑平移活动。区内岩浆活动强烈,成矿地质条件优越,是近年来新发现的重要铜多金属成矿带,其中以印支期产出于普朗复式岩体的斑岩型铜矿床最为典型。本文通过格咱岛弧岩浆岩带主要成矿斑岩体的磷灰石裂变径迹热年代学的研究表明,裂变径迹年龄分布于12~68Ma,均小于成岩成矿时代,区内主要成矿斑岩体的剥蚀速率为0.046~0.236mm/a,剥蚀程度约为1473~2904m。通过岩体的剥蚀程度与铜多金属矿床的形成深度来分析,各成矿岩体的剥蚀深度基本上小于侵位深度,这对矿床形成后的保存情况较为有利。根据区内主要斑岩型矿床剥蚀资源量的定量计算,将矿床剥蚀情况划分为3个数量级:I级为矿床轻度剥蚀、Ⅱ级为矿床中等剥蚀、Ⅲ级为矿床严重剥蚀,为该区斑岩成矿系统资源潜力评价和深部找矿提供了理论依据。  相似文献