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181.
Aurélien Royer Christophe Lécuyer Sophie Montuire Gilles Escarguel François Fourel Alan Mann Bruno Maureille 《Quaternary Research》2013
The middle Paleolithic stratigraphic sequence of Les Pradelles (Charente, France) spans from the end of Marine Isotope Stage (MIS) 4 until the middle of MIS 3. Micromammal remains are present in all the stratigraphic levels, offering a rare opportunity to address the questions of both environmental and climatic fluctuations throughout this period. Climate modes were studied through the taphonomy, biodiversity and oxygen isotope compositions of phosphate (δ18Op) from 66 samples of rodent tooth enamel. The δ18Op values from the lower sedimentary levels provide summer mean air temperatures of 19 ± 2°C (level 2/1) and of 16 ± 2°C (levels 2A, 2B and 4A). Within the middle of sequence (level 4B), a paleobiodiversity change can be identified with an increase of Dicrostonyx torquatus, which is associated with the largest amplitude in δ18Op values and the highest maximal δ18Op values. At the top of the sequence (level 5-2), a biodiversity change is observed with the increase of Microtus arvalis, but without any change in δ18Op values. The association of cold rodent species with unexpected high and large amplitudes in the δ18Op values of their teeth, possibly indicative of aridity, suggests their deposition during a Heinrich event. 相似文献
182.
短基线GPS控制网双差整周模糊的直接解算方法(DC,D irect Calcu lation算法)可以避开"周跳的探测与修复"和"整周模糊度的搜索固定",是一种新的整周模糊度解算方法。在基线坐标满足一定条件的情况下,可以保证解算的L1,-1和L-3,4双差整周模糊度的浮点解与整数解之间的偏差小于0.5周,由浮点解直接四舍五入,进而可以直接解算L1双差整周模糊度。本文用自编软件解算了实测数据,验证了本文方法的实用性,并可获得与商用软件TGO精度相当的基线。 相似文献
183.
184.
Transhumant pastoralism is an important activity in southern Morocco. Migration pattern of transhumant pastoralists can be affected by physical factors (e.g. droughts and diseases) or socioeconomic factors (e.g. schooling options for children and migration costs). We studied the spatio-temporal rangeland usage of the three tribes Ait Mgoun, Ait Zekri, and Ait Toumert in the south-central Atlas region with a two-fold approach. First, we tracked the migration movements of one representative transhumant herd using the Advanced Research and Global Observation Satellite (ARGOS) collars, which record coordinates from satellite signals. Second, we interviewed herders to obtain information about general grazing practices of the respective tribe and to gain more direct information on motivations underlying decisions. For each tribe we observed small-, medium- and large-scale movements. We found that the most important drivers of migration decisions were seasonal fodder availability and weather conditions in combination with herd-specific risk and cost assessment, as well as personal factors. In conclusion, general migration patterns vary in time, both between and within the tribes, but according to a regulatory framework. Moreover, it appears that both the customary rules and its flexible adaptation to physical constraints are generally beneficial in terms of conservation of the arid and semiarid rangeland resources. 相似文献
185.
地球物理成像解释的一个重要问题是,地震波传播时其本身受到地质体中小尺度非均匀性的影响,对该问题的研究具有重要的意义且备受关注. 据此,本文首先从统计意义上的表示形式来描述小尺度非均匀性,给出一种拓展了小尺度非均匀性择优取向的随机介质建模新方法,重点阐述了建模过程中对误差处理的重要性. 其次讨论了地震波在水平层状介质中传播时的长波长理论,并指出对该理论的适用条件进行研究的重要意义.且还基于1D随机层状介质,从局部各向异性因子曲线的角度对长波长理论进行了研究,并讨论了密度及泊松比扰动对曲线形态的影响. 最后,从对1D和2D随机介质进行数值模拟的角度重点研究长波长理论不能满足的情况下地震记录的特点,为了便于对比分析,文中也计算了1D随机介质在不同平均化长度下,通过长波长理论得到的等效介质的理论走时(走时的计算是在弱各向异性假设条件下完成的),并给出有指导意义的结论. 相似文献
186.
锰矿是中国大宗紧缺战略性矿产, 在现代工业中具有广泛用途。近年来锰资源的战略地位急剧提升, 锰资源勘查也日益受到重视。确定Mn元素在中国的浓度和分布对寻找新的锰矿床和缓解锰资源短缺至关重要。依托中国地球化学基准计划采集3392个汇水域沉积物样品数据, 首次提供了中国深层土壤Mn地球化学背景和异常空间分布数据。全国汇水域沉积物深层样品Mn的平均含量为610 mg/kg, 背景值为574 mg/kg。依据全国汇水域沉积物深层样品地球化学数据, 以85%累积频率为异常下限, 共圈定出31个Mn地球化学异常, 归为15个地球化学省。根据Mn异常空间分布, 结合地质背景和矿床分布, 提出8处异常具有进一步寻找锰矿的远景区。 相似文献
187.
Small island developing states (or SIDS) are exposed to a large number of natural hazards and many characteristics of small
island developing states make them particularly vulnerable to the impacts of natural hazards. In spite of this acknowledged vulnerability, there are relatively few studies which focus
on the impacts of natural hazards in these countries. This paper presents a review of our current state of knowledge of impacts
in small island developing states and highlights a number of research needs. Central to these is the need to integrate natural
hazards research within a sustainable development context and the need to exploit existing procedures such as government coordinated
disaster impact assessments to generate a detailed understanding of natural hazards impacts. 相似文献
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189.
Jonathan M. Abell Paul van Dam-Bates Deniz Özkundakci David P. Hamilton 《新西兰海洋与淡水研究杂志》2020,54(4):636-657
ABSTRACT Knowledge of trophic status is fundamental to understanding the condition and function of lake ecosystems. We developed regression models to predict chlorophyll a concentrations (chl a) in New Zealand lakes for reference and current states, based on an existing dataset of total nitrogen (TN) and total phosphorus (TP) concentrations for 1031 lakes. Models were then developed to predict Secchi depth based on chl a and a sediment resuspension term applicable to shallow lakes. Estimates of all four Trophic Level Index (TLI) variables (chl a, TN, TP and Secchi depth) were analysed to estimate reference and current state TLI for the nationally representative sample of 1031 lakes. There was a trend of eutrophication between reference and current states, with systematic differences among lake geomorphic types. Mean chl a increased 3.5-fold (2.42?mg?m?3 vs. 8.32?mg?m?3) and mean Secchi depth decreased (indicating lower clarity) by approximately one-third (9.62?m vs. 6.48?m) between reference and current states. On average, TLI increased by 0.67, with the TLI increase >1 in approximately one-third (31%) of lakes. This study informs the status of lake ecosystems in NZ and provides benchmarks to guide management and assessment. 相似文献
190.