Shrub Communities and Environmental Variables Responsible for Species Distribution Patterns in an Alpine Zone of the Qilian Mountains,Northwest China

Understanding the factors that drive variation in species distribution is a central theme of ecological research. Although several studies focused on alpine vegetation, few efforts have been made to identify the environmental factors that are responsible for the variations in species composition and richness of alpine shrublands using numericalmethods. In the present study, we investigated vegetation and associated environmental variables from 45 sample plots in the middle Qilian Mountains of the northwestern China to classify different community types and to elucidate the speciesenvironment relationships. We also estimated the relative contributions of topography and site conditions to spatial distribution patterns of the shrub communities using the variation partitioning. The results showed that four shrub community types were identified and striking differences in floristic composition were found among them. Species composition greatly depended on elevation, slope,shrub cover, soil p H and organic carbon. The important determinants of species richness were soil bulk density and slope. No significant differences in species richness were detected among the community types. Topography and site conditions had almost equal effects on compositional variation. Nonetheless,a large amount of the variation in species composition remained unexplained.     

Shale Oil Occurrence and Reservoir Characteristics of the Qijia-Gulong Depression in Songliao Basin

<正>1 Introduction The technology breakthrough in the exploration of shale gas and tight oil has greatly extended the global fossil fuel resources(Jia et al.,2012;Zou et al.,2012;Qiu et al.,2013).Although shale oil has been the global hot topic in the study of unconventional resources,there are varied definitions with respect to shale oil by different researchers.     

不同应力水平下结构性黏土动力特性试验研究

对天津滨海地区典型结构性软黏土进行了压缩试验和不同固结应力下的循环三轴试验。结果表明:结构性软黏土的静力变形特性以先期固结应力和结构屈服应力为分界点可分为3个阶段;不同固结应力下的动应变-振次关系曲线上存在着一个临界动应力比,且该值随着围压的增大而降低;孔隙水压力的变化以结构屈服应力为转折点呈现出不同的变化规律;当振动频率为2Hz时固结应力的改变对轴向动应变的影响不明显。     

各向异性介质中大地电磁正演研究综述

在地球物理资料处理解释中,各向异性现象是一个无法忽视的重要因素.各向异性介质中大地电磁(MT)的正演数值模拟计算一直是国内外电磁感应领域研究的前沿课题.文中简要介绍了正演数值模拟计算的发展历程和几种主要的研究方法,探讨了未来各向异性介质中大地电磁正演研究方向、需要解决的难点和面临的挑战.     

基于统计学与专家系统的测井相自动识别

通过测井相来研究沉积微相的平面展布是油藏描述研究工作的重要手段,尤其是针对油藏开发后期密集井网区的沉积微提精细研究尤为重要.在测井相自动识别的研究中,目前主要采用神经网络和Bayes准则判别分析等方法,但这些方法过于依赖数学模型而忽略了地质专家的判相经验,常导致识别结果准确率较低.本文从研究区沉积环境以及岩性特点出发,...     

机车荷载下多年冻土区桥梁桩基振动响应特征

为研究多年冻土区机车振动荷载作用下桥梁桩基的动力响应特征,选取了多年冻土区清水河特大桥的两个桥梁桩基进行现场强震动测试．对测试数据进行加速度响应及傅里叶谱响应分析,得出桥梁桩基的振动响应衰减规律及振动能量的分布规律．在此基础上,结合有限元结构分析软件,运用瞬态动力分析法,选取一个测试桩为实例进行二维动力响应的数值计算,...     

疏勒河中下游胡杨林土壤水盐空间变化与影响

基于河西走廊疏勒河中下游绿洲天然胡杨林下8个采样点720个土壤样品和6.8524 hm2的7个样方,应用统计学及相邻格子法等研究了胡杨林土壤水盐的空间变化特征及其影响。结果表明:研究区土壤含水量随深度而增加,土壤全盐量变化与之相反,两者在80 cm土层之上变化剧烈,之下变化平缓;土壤水盐含量变异差异明显,均属于中强度变异。各层土壤水盐含量存在着自中游向下游水分减少、盐分增加、表层聚盐加重的显著空间分布规律。研究区胡杨林生长受到土壤水盐胁迫,种群结构残缺;下游胡杨林分偏老,稀疏矮小,已明显衰退。长此下去,下游胡杨林将因快速衰退演替而全部死亡。     

菲律宾蛤仔（Ruditapes philippinarum）海洋橙品系两个世代的杂交与近交效应

于2009年8月以菲律宾蛤仔海洋橙品系的全同胞子一代和子二代上选10%的个体作为亲本,通过建立近交组合（F22、F33）、杂交组合（F23、F32）和设置对照组（C22、C33）,研究了两个近交世代的杂交效应及近交效应,以提高菲律宾蛤仔海洋橙品系的表型性状。结果表明,杂交使幼虫和稚贝的生长性状得到了部分改良,但存活性状...     

东北地区水稻冷害气候风险度和经济脆弱度及其分区研究

应用历年气象、水稻产量资料和冷害指标,分析东北地区水稻低温冷害发生的温度条件、气候频率和风险概率,建立了水稻冷害气候风险度模式,将东北地区分成高、偏高、中等、较低和低风险5级水稻冷害气候风险度区.在气候风险性分析的基础上,考虑各地水稻冷害减产率、总产量和面积比例等经济损失因素,建立水稻生产对低温冷害反应的经济脆弱度模式...     

山东省曹县黄河故道石英砂矿调查

黄河多沙善淤,黄河故道赋存大量的石英砂资源,运用地质手段对这些资源进行科学合理的评估,探索其利用远景,为其开发提供依据具现实意义。调查工作投入了区域地质调查、物探直流电测深、钻探、取样分析等技术手段,初步查明曹县境内黄河故道石英砂的品质、分布范围、赋存条件,黄河故道地形、地貌、地质等条件,石英砂的持有量及开发利用前景。