Peridynamics simulations of geomaterial fragmentation by impulse loads

In this work, we have developed nonlinear peridynamics models of drained and saturated geomaterials, and applied them to simulations of dynamic fragmentation and ejecta formation due to impulse loads. First, we have re‐phrased and re‐interpreted the non‐local state‐based peridynamics formulation to connect the non‐local integral operator with the local differential operator. Second, we have implemented the Drucker–Prager plasticity model in state‐based peridynamics at finite strain. A peridynamics version of the Hughes and Winget algorithm is derived for the constitutive update. Third, we have developed a peridynamics U‐p formulation for saturated geomaterials. Fourth, numerical simulations have been carried out to verify the proposed peridynamics formulations in the simulation of geomaterial fragmentation induced by impulse loads. Comparisons of analytical and numerical results indicate that the peridynamics model has the ability to both match traditional continuum compression examples, as well as simulate complex geomaterial fragmentation processes resulting from impulse loads. Copyright © 2015 John Wiley & Sons, Ltd.     

CO2 absorption of sandy soil induced by rainfall pulses in a desert ecosystem

Soil CO₂ flux is strongly influenced by precipitation in many ecosystem types, yet knowledge of the effects of precipitation on soil CO₂ flux in semi‐arid desert ecosystems remains insufficient, particularly for sandy soils. To address this, we investigated the response of sandy soil CO₂ flux to rainfall pulses in a desert ecosystem in northern China during August–September 2011. Significant changes (P < 0.05) were found in diel patterns of soil CO₂ flux induced by small (2.1 mm), moderate (12.4 mm) and large (19.7 mm) precipitation events. Further analysis indicated that rainfall pulses modified the response of soil CO₂ flux to soil temperature, including hysteresis between soil CO₂ flux and soil temperature, with F_s higher when T_s was increasing than when T_s was decreasing, and the linear relationship between them. Moreover, our results showed that rainfall could result in absorption of atmospheric CO₂ by soil, possibly owing to mass flow of CO₂ induced by a gradient of gas pressure between atmosphere and soil. After each precipitation event, soil CO₂ flux recovered exponentially to pre‐rainfall levels with time, with the recovery times exhibiting a positive correlation with precipitation amount. On the basis of the amounts of precipitation that occurred at our site during the measurement period (August–September), the accumulated rain‐induced carbon absorption evaluated for rainy days was 1.068 g C m^?2; this corresponds approximately to 0.5–2.1% of the net primary production of a typical desert ecosystem. Thus, our results suggest that rainfall pulses can strongly influence carbon fluxes in desert ecosystems. Copyright © 2014 John Wiley & Sons, Ltd.     

"旅游地理信息系统"非标准答案考试改革初探

非标准答案课程考试的探索旨在以改革驱动创新、健全能力与知识考核并重的多元化学业考核,以学生发展为中心,通过推动课堂改革促进教育改革,在注重课程学习过程性考核的基础上,力求过程性考核和期末考核题目不拘一格,考试题目采取灵活多样的方式,综合评价学生各方面能力,重点考察学生应用知识、建构知识的能力,强化多角度思维和跨学科思维的能力.本文对"旅游地理信息系统"的课程内容、教学模式、试题形式进行了改革,引导学生自发地对课程产生兴趣,考试题目不拘一格,采取科学、有效的方式对学生综合能力方面进行评估,改变学生"高分低能"的现状,培养学生自学能力、应用能力和创新实践能力.     

青海卡尔却卡铜多金属矿床地球化学特征与成矿物质来源

为了解卡尔却卡铜多金属矿床的物质来源, 探讨其成岩、成矿机制, 通过现场调查, 结合矿床地质成矿条件, 对矿区典型的岩浆岩、围岩及矿石进行了主量元素、微量元素分析及S、Pb同位素分析.结果表明: 矿区岩体属中酸性岩, 为高钾钙碱性系列岩石, 源于深部, 上侵时受地壳混染, 具同源特征.不同地质体稀土配分曲线均为右倾轻稀土富集型, 岩浆岩、矽卡岩和矿石为同一成矿系统.微量元素地球化学显示矿区花岗岩产于火山弧环境.矿石硫同位素δ34S_CDT值为4.4×10-3~11.0×10-3, 处于岩浆硫跟围岩混合硫范围内, 成矿物质具多源性.矿石铅同位素Th/U值范围为3.46~3.69, μ值为9.46~9.52, 均低于9.58, 介于地壳与原始地幔值之间, 反应矿石铅具深源铅和壳源铅特征.铅同位素特征参数示踪、构造模式示踪和Δβ-Δγ图解示踪的结果表明: 铅来源与岩浆作用有关, 以壳源铅为主并混合少量深源地幔铅.总结矿床地球化学特征表明成矿物质主要来源于岩浆, 少量来源于周围地层.矿区岩体成矿演化过程复杂, 在岩体中形成斑岩型铜、钼矿化, 在与碳酸盐岩接触带形成矽卡岩型铅、锌矿化, 及至后期热液作用形成中低温热液脉型金矿化, 是一个多因复成矿床.      

青藏高原第四纪冰川作用及其气候响应的讨论

关于青藏高原和周边山地第四纪冰川作用及其气候响应存在不同观点.一些学者认为老冰期主要发生在氧同位素奇数阶段;MIS 3和早全新世存在规模较大的冰川前进;南亚季风对青藏高原冰川作用起主导作用(水汽驱动).另一些学者则认为青藏高原冰川作用主要对应于氧同位素偶数阶段;冰川发育是构造隆升-冰期气候耦合的产物(低温驱动).本文基于现有的陆地生成宇宙核素(TCN)和光释光(OSL)等年代结果总结了不同时间尺度和不同类型冰川波动与气候变化历史的对比,并对几个关键的争议问题做了讨论.结果表明,在不同类型冰川区和不同时间尺度下,冰川作用在湿润期和低温期都有可能发生,但总体上主要与低温相对应.青藏高原冰川对气温的响应似乎更为敏感.MIS 3冰进规模较大可能是降水较多结合冷期(或冷事件)降温所致,显示了印度季风降水和气温波动对高原冰川的共同作用.早全新世冰进也与印度季风和北半球冷事件关系密切.目前的测年数据还没有推翻“冰期发生在氧同位素偶数阶段”这种传统认识.当前急需更多精确的数字定年工作,以不断更新对青藏高原冰期时代及其气候响应机制的了解.     

一个长生命期准静止中尺度对流系统的观测特征及其持续的环境条件

2010年5月31日至6月1日华南特大暴雨过程经历了三次集中降水期,共有4次MCS（Mesoscale Convective Systems）演变过程,其中一个TL/AS MCS（Training Line/Adjoining Stratiform Mesoscale Convective System,邻接层状单向发展的中尺度对流系统）在广西壮族自治区中部准静止地维持了10多个小时,导致了多个观测站出现极端强降水。用观测资料和数值模拟结果重点探讨了该TL/AS MCS的观测特征及其发展持续的环境条件。结果表明,准静止TL/AS MCS发展在一个高空强辐散、低空气旋性汇合环流的天气尺度环境中,TL/AS MCS维持期间热力环境特征表现为对流层中低层持续高湿近饱和态、偏中性层结、合适的对流有效位能和极小的对流抑制能量。在对流层中低层,低空急流的加强发展维持与对流层中层相对弱的环境风形成了风垂直切变随高度呈现强逆转,近地层风垂直切变垂直于对流线的分量大,而在中层风垂直切变平行于对流线的分量占绝对优势,风切变特征可能是TL/AS MCS 准静止的原因;低空急流和中层环流的相互作用、对流层动力和热力条件有利于强上升运动的长时间维持与发展,不断触发新对流从而组织成一个长生命期准静止的TL/AS MCS     

Geocomputation over the Emerging Heterogeneous Computing Infrastructure

Emerging computer architectures and systems that combine multi‐core CPUs and accelerator technologies, like many‐core Graphic Processing Units (GPUs) and Intel's Many Integrated Core (MIC) coprocessors, would provide substantial computing power for many time‐consuming spatial‐temporal computation and applications. Although a distributed computing environment is suitable for large‐scale geospatial computation, emerging advanced computing infrastructure remains unexplored in GIScience applications. This article introduces three categories of geospatial applications by effectively exploiting clusters of CPUs, GPUs and MICs for comparative analysis. Within these three benchmark tests, the GPU clusters exemplify advantages in the use case of embarrassingly parallelism. For spatial computation that has light communication between the computing nodes, GPU clusters present a similar performance to that of the MIC clusters when large data is applied. For applications that have intensive data communication between the computing nodes, MIC clusters could display better performance than GPU clusters. This conclusion will be beneficial to the future endeavors of the GIScience community to deploy the emerging heterogeneous computing infrastructure efficiently to achieve high or better performance spatial computation over big data.     

基于格点场的江西省气象和水文降水资料对比分析

应用反距离权重插值法,将2019年4—6月江西省气象部门自动气象站和水利部门自动雨量站逐小时降水观测数据,分别转换为分辨率为0.05°×0.05°格点降水资料,以对比分析两种观测系统降水资料的相关性、误差及其时空变化规律。结果表明：1） 气象、水文降水量格点场具有显著相关关系,其中中度及以上相关的格点数占总数的99.54%;两者的平均相关系数为0.93,平均均方根误差为0.56 mm/h,绝对误差为0.13 mm/h,误差为-0.01 mm/h;气象与水文降水总量平均差异在-4%左右。2） 出现零星或短时降水时,气象、水文小时降水量格点场相关性差异较大;而出现系统性降水过程时,两者表现为高度相关。逐时格点平均降水量,在系统性降水的初期和结束期气象类高于水文类,而持续期水文类高于气象类,两者差异在-6%—6%以内。3） 气象、水文降水资料在时间和空间分布上具有较好的一致性,对两者的融合应用可以明显提高站点密度,站网分布更合理,能更准确地反映过程降水的时空变化。     

2009年秋末山西大暴雪天气过程分析

利用高空、地面和卫星云图资料,对2009年11月9-12日山西出现的有气象记录以来最强的一场大暴雪天气过程进行综合分析.结果表明:高空强盛的西南气流和低层东北气流以及地面回流为暴雪过程提供了有利的流场配置,500hPa阶梯槽和700hPa切变线是主要影响系统,低空急流的持续及水汽的辐合为这次暴雪提供了充足的水汽,卫星云...