Modern pollen assemblages from surface lake sediments and their environmental implications on the southwestern Tibetan Plateau

The relationships amongst modern pollen assemblages, vegetation, climate and human activity are the basis for reconstructing palaeoenvironmental changes using pollen records. It is important to determine these relationships at regional scales due to the development of vegetation under different climatic conditions and human activities. In this paper, we report on an analysis of modern pollen assemblages of 31 surface lake samples from 31 lakes (one sample per lake) on the southwestern Tibetan Plateau where the knowledge of modern pollen and their relationships with vegetation, climate and human activities is insufficient. The region includes five vegetation zones: sub‐alpine shrub steppe, alpine steppe, alpine meadow and steppe ecotone, mountain desert and alpine desert. The lakes span a wide range of mean annual precipitation (50–500 mm) and mean annual temperature (?8 to 6 °C). Modern pollen assemblages from our samples mainly consist of herb taxa (Artemisia, Cyperaceae, Poaceae, Chenopodiaceae, etc.) and some tree taxa (Pinus, Fagaceae, Alnus, etc.). The results indicate that modern pollen assemblages are able to reflect the main vegetation distribution. Redundancy analysis for the main pollen types and environmental variables shows that precipitation is the leading factor that influences the pollen distribution in the study area with the first axis capturing 13.7% of the variance in the pollen data set. The Artemisia/Chenopodiaceae ratio is valid for separating the desert component (<2) from the steppe and other vegetation zones (>2) but is unable to distinguish moisture variations. The Artemisia/Cyperaceae ratio is able to identify meadows (<1) and steppes (>1) and can be used as a moisture index on the southwestern Tibetan Plateau. Our results show that an appropriate range is needed for a modern pollen data set in order to perform pollen‐based quantitative climate reconstructions in one region. It is essential to perform modern studies before using pollen ratios to reconstruct palaeovegetation and palaeoclimate at a regional scale.     

可变尺度区域拟合模型的侧扫声纳分割方法

为解决现有侧扫声纳图像目标分割准确度不高的问题,提出一种联合最大熵去噪和可变尺度区域拟合模型的侧扫声纳图像分割方法。首先,计算图像一维熵,基于最大熵原则对侧扫图像进行降噪处理,提高图像质量,并根据峰值信噪比评判降噪效果;然后基于可变尺度区域拟合模型,采用高斯核函数对分割活动轮廓进行约束,分割降噪后的侧扫声纳图像。通过对含有不同目标物的侧扫声纳图像进行分割实验,验证了联合最大熵去噪和可变尺度区域拟合模型的有效性。     

一种基于迁移学习的栅格型图表自动分类方法

图表自动分类是实现图表内容解译及信息提取的前提.基于Inception V3模型,采用迁移学习的方法,对图表自动分类方法进行了研究,提出了对5类栅格图表进行自动分类的模型.通过与传统的图表自动分类方法的对比试验,测试了在不同学习率参数下模型的分类效果,给出了针对结构化特征的指数衰减学习率的数学表达式.结果表明:采用迁移...     

地震作用下立式储液罐罐壁"象足"变形仿真分析

基于ANSYS软件建立了考虑液体晃动和罐底提离立式储液罐有限元模型,分别进行了水平地震和竖向地震作用下罐壁"象足"变形分析.分析表明:立式储液罐罐壁"象足"变形主要是由罐壁纵向压应力超过临界应力而产生的局部屈曲破坏,并非强度破坏.因罐底提离导致的罐底与基础反复撞击加大了作用在罐壁上的应力,使罐壁底部"象足"变形不断发展,最终导致罐壁撕裂.在完全相同地震加速度作用下,水平地震作用比竖向地震作用罐壁更早更容易进入屈曲状态,产生"象足"变形.     

基于最小二乘支持向量机算法的高层建筑结构的强震抗毁性估计模型

采用现有的估计模型对混凝土建筑结构的抗毁性进行估计时,存在估计精度低、耗时长等问题。为此,提出一种基于最小二乘支持向量机的强震作用下混凝土高层建筑结构的抗毁性估计模型。该模型采用最小二乘支持向量机对混凝土结构强震损伤程度相关数据的训练样本进行训练,创建混凝土结构抗毁性估计模型;为了减少可能存在的模型误差,采用KLASSO调参模型对结构抗毁性估计模型中的参数进行调节和优化,得出可靠、稳定的强震作用下混凝土高层建筑结构抗毁性估计模型。仿真实验证明,该模型估计精度相对较高,可节省估计用时,为更好地提升建筑行业的安全检测工作效率提供很好的依据。     

Performance of High Speed Railway Subgrade Strengthened by Long-Short Piles—Part I: Experimental Results

Geotechnical and Geological Engineering - The Yinxi Railway is located in the western region of China. As a high speed railway line connecting Yinchuan-Xi'an, it is of great significance for...     

新疆东部托勒库勒湖流域表土花粉初步分析

研究现代表土花粉谱与植被及气候的关系对正确解译地层花粉所指示的植被演化历史以及生态环境具有重要意义.本文首次选取新疆东部托勒库勒湖盆地开展现代表土花粉与植被关系的分析.结果发现各个植被带的花粉组合与其主要植物成分具有良好的对应关系.湖泊表层样品的花粉组合是区域植被组成的综合反映;莎草科花粉主要出现在草甸中;禾本科是湖边草原中重要的花粉类型,该科花粉呈现出明显的低代表性;藜科和蒿属是荒漠草原植被中两种最主要的花粉类型;白刺属主要出现在低洼平坦的湖边,该属植物的分布与水源有着密切的关系;在采自砾漠的样品中,菊科、麻黄属成为两种最主要的花粉类型,这对解释地质时期该湖地层中两种花粉组合所指示的植被演化和生态意义具有重要作用.     

Effects of fracture grouting with sodium hydroxide during electro-osmosis on clay

ABSTRACT

Electro-osmosis is a foundation treatment method for clay that is not widely used because of its nonuniform consolidation effect and high cost. To overcome these limitations, this study investigates fracture grouting. To determine the optimal grouting method, anode grouting, polyurethane grouting, and fracture grouting were first compared in one-dimensional electro-osmosis consolidation tests using self-made model boxes under an equal electric potential gradient, and then different solution concentrations were tested. By comparing the current, drainage rate, and coefficient of energy consumption during the electro-osmosis process, as well as moisture content, electrical conductivity, and shear strength after the tests, the moisture and shear strength of clay after electro-osmosis were found to be significantly improved by adding chemical reagents at the fracture. In addition, the optimum concentration of fracture grouting was determined to be 1.5%, and the shear strength after testing of clay that had been treated with sodium hydroxide was found to be higher than that of the control group. However, the effects of fracture grouting in the early stage were clearer than the effects of fracture grouting at later stages.     

徐淮地区煤矿井筒破裂原因初探

本用震源力学理论和方法研究了徐淮地区从１９７０年以来构造应力场的方向和强度的时空变化过程。结果表明：以唐山地震为分界线，本区的应力场Ｐ轴取向由震前平均６１．８°变为震后平均７７．７°。如果将本区以宿北断裂为界分为南区和北区两个部分，则北区的Ｐ轴取向从６８．１°变７１．２°，而南区的Ｐ轴取向由６２．５°变到８３．６°，南区的变化明显于北区。     

A high-resolution late Pleistocene record of pollen vegetation and climate change from Jingning, NW China

During the late Pleistocene, a number of climatic fluctuations such as the Heinrich events were recorded in the climatic proxies in the Loess Plateau and in North China[1―7]. Most of these records were based on geophysical and geochemical evidence[1―4]. Therefore, more biologic evidence is necessary for explaining the regional ecosystems in response to climatic change in the Loess Plateau during this period since pollen re-cords in other areas presented strong evidence to cli-matic fluctu…