Spatial patterns and driving mechanisms of mid‐Holocene hydroclimate in western North America          下载免费PDF全文

Nicholas Wayne Hermann  Jessica Leigh Oster  Daniel Enrique Ibarra 《第四纪科学杂志》2018,33(4):421-434

  相似文献   

Implementation of a coupled plastic damage distinct lattice spring model for dynamic crack propagation in geomaterials          下载免费PDF全文

Chao Jiang  Gao‐Feng Zhao 《国际地质力学数值与分析法杂志》2018,42(4):674-693

This paper studies dynamic crack propagation by employing the distinct lattice spring model (DLSM) and 3‐dimensional (3D) printing technique. A damage‐plasticity model was developed and implemented in a 2D DLSM. Applicability of the damage‐plasticity DLSM was verified against analytical elastic solutions and experimental results for crack propagation. As a physical analogy, dynamic fracturing tests were conducted on 3D printed specimens using the split Hopkinson pressure bar. The dynamic stress intensity factors were recorded, and crack paths were captured by a high‐speed camera. A parametric study was conducted to find the influences of the parameters on cracking behaviors, including initial and peak fracture toughness, crack speed, and crack patterns. Finally, selection of parameters for the damage‐plasticity model was determined through the comparison of numerical predictions and the experimentally observed cracking features.  相似文献   

弧形海岸裂流的数值模拟研究   总被引：3，自引：0，他引：3  

汪鸿  朱首贤  李训强  张文静  聂屿 《海洋学报(英文版)》2018,37(3):21-30

弧形海岸波浪产生的裂流严重危害人类活动，但是目前对其特征缺乏充分认识。本文对Haller物理模型实验和三亚大东海的数值模拟表明FUNWAVE模式具有较好的裂流模拟能力。基于该模式进行了多种弧形海岸条件的裂流数值模拟，给出裂流的一些特征：（1）海岸弯曲度增大，裂流增强；（2）海岸坡度对裂流有比较大的影响，太陡或太平缓的海岸不利于形成裂流；（3）海岸尺寸减小，裂流减弱；（4）波高和波周期增大，裂流增强，但是对于某些海岸而言，0.4m波高可能就存在危害比较大的裂流。  相似文献   

Sharks caught in the KwaZulu-Natal bather protection programme,South Africa. 14. The smooth hammerhead shark Sphyrna zygaena (Linnaeus)     

ML Dicken  H Winker  MJ Smale  G Cliff 《African Journal of Marine Science》2018,40(2):157-174

The current study provides long-term catch-rate, biological and feeding data for smooth hammerhead sharks, Sphyrna zygaena, caught in South Africa’s KwaZulu-Natal bather protection programme. In total, 2 512 S. zygaena were caught in net installations between 1978 and 2014, and 72 S. zygaena were caught on drumlines between 2007 and 2014. There was no significant log-linear year trend in the net catch rate over time (slope = 0.0054, t = 1.808, p = 0.07). However, there was a significant temporal increase in mean size of the captured sharks (slope = 0.0012, t = 3.502, p < 0.001). A quasi-Poisson generalised additive mixed model showed that increasing latitude, winter months, colder sea temperatures and the deployment of drumlines all had a significant positive effect on the catch rate of sharks in nets. The size frequency of the catch was unimodal, with significantly more females caught in the nets and more males on the drumlines. The majority (93.1%) of all sharks caught were immature and measured between 80 and 120 cm precaudal length. Teleosts and cephalopods dominated the sharks’ diet in terms of all dietary indices. The prey species consumed indicate that immature S. zygaena are feeding primarily within the pelagic zone of shallow coastal habitats.  相似文献   

基于"山西2015速度模型"的定位方法对比研究     

殷伟伟  宋秀青  李自红  朱元清 《大地测量与地球动力学》2018,38(5):469-472

为了确定山西台网基于“山西2015速度模型”的相对固定的定位方法，选择2010~2016年最大空隙角小于45°、参与定位台站数大于40的103个地震事件，分别采用单纯形法、Hypo2000、Hyposat结合PTD等3种方法重新测定。结果显示，单纯形法和Hyposat结合PTD测定的残差以及网缘地震的震中距两方面均优于Hypo2000；在震源深度方面，Hyposat结合PTD的结果较为可信。综合分析认为，基于“山西2015速度模型”定位地震时，山西台网应固定使用Hyposat结合PTD的方法。  相似文献   

Assessment of alternative adsorption models and global sensitivity analysis to characterize hexavalent chromium loss from soil to surface runoff          下载免费PDF全文

Chuan‐An Xia  Juxiu Tong  Bill X. Hu  Xiujie Wu  Alberto Guadagnini 《水文研究》2018,32(20):3140-3157

We investigate our ability to assess transfer of hexavalent chromium, Cr(VI), from the soil to surface runoff by considering the effect of coupling diverse adsorption models with a two‐layer solute transfer model. Our analyses are grounded on a set of two experiments associated with soils characterized by diverse particle size distributions. Our study is motivated by the observation that Cr(VI) is receiving much attention for the assessment of environmental risks due to its high solubility, mobility, and toxicological significance. Adsorption of Cr(VI) is considered to be at equilibrium in the mixing layer under our experimental conditions. Four adsorption models, that is, the Langmuir, Freundlich, Temkin, and linear models, constitute our set of alternative (competing) mathematical formulations. Experimental results reveal that the soil samples characterized by the finest grain sizes are associated with the highest release of Cr(VI) to runoff. We compare the relative abilities of the four models to interpret experimental results through maximum likelihood model calibration and four model identification criteria (i.e., the Akaike information criteria [AIC and AIC_C] and the Bayesian and Kashyap information criteria). Our study results enable us to rank the tested models on the basis of a set of posterior weights assigned to each of them. A classical variance‐based global sensitivity analysis is then performed to assess the relative importance of the uncertain parameters associated with each of the models considered, within subregions of the parameter space. In this context, the modelling strategy resulting from coupling the Langmuir isotherm with a two‐layer solute transfer model is then evaluated as the most skilful for the overall interpretation of both sets of experiments. Our results document that (a) the depth of the mixing layer is the most influential factor for all models tested, with the exception of the Freundlich isotherm, and (b) the total sensitivity of the adsorption parameters varies in time, with a trend to increase as time progresses for all of the models. These results suggest that adsorption has a significant effect on the uncertainty associated with the release of Cr(VI) from the soil to the surface runoff component.  相似文献   

基于F-范数的不确定性平差模型的解算方法     

鲁铁定  朱国红 《大地测量与地球动力学》2018,38(6):557-561

为提高基于F-范数的不确定性平差模型的解算效率，给出直接迭代算法进行参数估计。该算法无需SVD，解算过程简单且易于编程计算，同时给出迭代不收敛时的SVD-解方程算法。二元线性拟合及沉降观测AR模型的算例结果表明，这2种算法正确可行，与SVD-迭代算法具有等价性。当迭代收敛时，宜使用直接迭代算法，收敛速度更快，解算效率更高；当迭代不收敛时，可釆用SVD-解方程算法。  相似文献   

呼和浩特市生境质量对城市用地扩展的时空响应          下载免费PDF全文

冯琰玮  甄江红  马晨阳 《干旱区地理》2020,43(4):1014-1022

以呼和浩特市为研究区,采用梯度分析法,结合InVEST模型,在评价研究区近27 a城市用地扩展及生境质量演变的基础上,运用双变量空间自相关剖析生境质量对城市用地扩展的时空响应。结果表明：（1） 研究时段内,城市扩展表现为核心区的低密度扩张及外围区的多点扩散,紧凑度不断下降,城市结构不稳定,扩展模式不尽合理。（2） 生境平均值从0.49下降到0.44,质量等级跌至较差水平。低等级生境主要呈圈层向南部、东南部扩散,与建设用地扩展方向基本一致。（3） 建设用地扩展强度与生境质量变化空间分布呈负相关关系,核心外围区的建设用地扩展始终为变化最强烈的地带,生境质量退化也最为剧烈。（4） 斑块密度不断上升,特别是建设用地斑块的增加使得城市景观格局愈发破碎。  相似文献   

基于 SRP 概念模型的祁连山地区生态脆弱性评价   总被引：1，自引：0，他引：1       下载免费PDF全文

刘佳茹  赵军  沈思民  赵彦军 《干旱区地理》2020,43(6):1573-1582

基于生态敏感性-生态恢复力-生态压力度（SRP）概念模型，从地形、气候、植被和社会经济 因子选取 8 个评价指标，利用遥感和 GIS 技术，采用主成分分析方法求取权重，对祁连山地区启动 水源涵养区生态环境保护和综合治理规划研究前后近 10 a 的生态脆弱性程度进行系统、定量地评 估，旨在揭示生态脆弱性的分布特征、时空演变及动因，为区域生态保护、资源利用和可持续发展 提供参考。结果表明：（1）从研究区生态脆弱性分布来看，祁连山地区主要以轻度和重度脆弱为 主，脆弱性程度从西北向东南地区逐渐减弱，西北地区植被覆盖度小，海拔高，生态环境较为恶劣 是导致脆弱性程度较高的原因；（2）祁连山地区 3 期生态脆弱程度呈逐渐下降趋势，综合指数分别 为 3.307、3.118 和 3.103；2005 年 生 态 脆 弱 性 较 高 ，极 度 脆 弱 面 积 为 28 610 km²，2010 年 下 降 为 11 723 km²，2015 年降低为 6 174 km²，极度脆弱面积逐渐减少；（3）从祁连山地区生态脆弱性演变动 因来看，8 个指标对生态脆弱性影响均较为显著，但在不同的时间影响程度各不相同，2005—2015 年 3 期数据中对生态脆弱性影响最大的均为植被指数，降水次之，地形因子影响最小。总体来看， 近年来祁连山地区生态脆弱性程度有所降低，但仍然需要加强保护力度，促进生态环境可持续 发展。  相似文献   

科尔沁湿草甸参考作物蒸散发模拟分析     

李霞  刘廷玺  段利民  王冠丽  童新  周亚军  杨晓君 《中国沙漠》2020,40(2):134-143

为探明气候变化下干旱半干旱地区湿草甸参考作物蒸散发(ET₀)影响因子,使用FAO 56 P-M模型对科尔沁湿草甸ET₀进行模拟,利用涡度相关系统对模型的适用性进行评价,并通过通径分析及指标敏感性分析对ET₀的影响因子进行辨识。结果表明:(1)小时尺度模拟精度最高,日尺度次之,月尺度较差,小时尺度上晴、阴、雨3种天气条件下模拟效果不同,晴天最优,阴雨天较差。(2)ET₀年内变化呈单峰曲线状,生长季明显高于非生长季,集中在3—10月,占全年89.79%。生长季典型晴天ET₀逐小时分布特征遵循倒“U”单峰型变化规律。(3)通径分析结果显示,对ET₀的通径系数以及对回归方程估测可靠程度E的总贡献均表现为VPD(饱和水汽压差) > T_min(最低气温) > R_n(冠层表面净辐射)>u₂(2 m高度风速),即VPD为影响ET₀最重要的因子;指标敏感性分析中,在去除VPD后引起的E变化最大,说明ET₀对VPD的变化最为敏感,其次为u₂、T_min和R_n。  相似文献