Machine learning reveals the influences of grain morphology on grain crushing strength

Acta Geotechnica - Grain morphology has significant impacts on the mechanical behaviors of granular materials. However, its influences on grain breakage are still poorly understood due to the...     

青海某地第三系红色碎屑岩层中金异常特征及成因探讨

对青海某地第三系红色碎屑岩层中的金异常特征进行了综述,指出金异常主要存在于第三系中段岩层中,异常在水系沉积物中强度最大,并认为金异常由次生富集作用形成.     

Dust supply from river floodplains: the case of the lower Huang He (Yellow River) recorded in a loess–palaeosol sequence from the Mangshan Plateau

The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd.     

Environmental magnetic studies of sediment cores from Gonghai Lake: implications for monsoon evolution in North China during the late glacial and Holocene

Environmental magnetic studies were conducted on a 9.42-m-long sediment core from Gonghai Lake, North China. Radiocarbon dating indicates that the record spans the last 15,000 cal year BP. The principal magnetic mineral in the sediments is pseudo-single domain magnetite of detrital origin with minimal post-depositional alteration. Although the variations in the concentration of detrital magnetic minerals and their grain size throughout the core reflect inputs from both soil erosion and eolian dust, it is shown that their climatic and environmental significance changes with time. In the lowermost part of the core, ~15,000–11,500 cal year BP, the magnetic minerals were supplied mainly by bedrock erosion, soil erosion and dust input when climate ameliorated after the cold and dusty last glacial maximum. The increasing magnetic susceptibility (χ) in this interval may indicate a combination of changes in the lake environment together with catchment-surface stabilization and a decreasing proportion of dust input. In the central part of the core, ~11,500–1,000 cal year BP, the detrital magnetic minerals mainly originated from dust inputs from outside the catchment when the lake catchment was covered by forest, and catchment-derived sediment supply (and thus the lake sediment accumulation rate) were minimal. The generally low concentration of magnetic minerals in this part of the core reflects the highest degree of soil stability and the strongest summer monsoon during the Holocene. In the uppermost part of the core, the last ~1,000 years, detrital magnetic minerals mainly originated from erosion of catchment soils when the vegetation cover was sparse and the sediment accumulation rates were high. Within this part of the core the high magnetic susceptibility reflects strong pedogenesis in the lake catchment, and thus a strong summer monsoon. This scenario is similar to that recorded in loess profiles. Overall, the results document three main stages of summer monsoon history with abrupt shifts from one stage to another: an increasing and variable summer monsoon during the last deglacial, a generally strong summer monsoon in the early and middle Holocene and a weak summer monsoon in the late Holocene. The results also suggest that different interpretational models may need to be applied to lake sediment magnetic mineral assemblages corresponding to different stages of environmental evolution.     

塔里木盆地塔中北坡奥陶系微生物碳酸盐岩储层形成机制与评价

微生物岩储层是当前的研究热点之一.通过对塔中北坡微生物岩样品的岩芯以及铸体薄片的观察,发现研究区域的微生物岩储层以裂缝-孔隙型储层为主.对其进行全直径孔渗性检测发现,微生物岩储层具有较好的天然气储集物性.通过对微生物岩的形成机制及特点的分析,结合应力敏感实验和成像测井资料,总结出微生物岩储集空间发育的优势因素.原生白云石的生成可以促进方解石的溶解,而塔中北坡微生物岩发生早成岩岩溶作用,部分地区叠加晚期深成热液改造,提高了储集物性;有机质含量较丰富不仅可以在埋藏成岩阶段生成有机酸造成溶蚀,还能够降低微生物岩的极限强度从而容易在构造作用下发生断裂形成裂缝,因此塔中北坡微生物岩储集空间主要以次生作用为主.通过岩石压缩系数的测定,得出微生物岩的抗压实能力一般,但藻屑骨架对藻孔的保护有利,抗压实能力最强的是受到热液作用而硅化的微生物岩,其次是白云石化微生物岩.     

降水检验方案变化对降水检验评估效果的影响分析

为了实现对中尺度模式降水预报产品的合理化统计检验,在我国现有观测系统条件下,研究了24小时加密降水观测实况对降水统计检验评分的影响。过去的标准检验系统观测站为400站,分为9个区,目前业务试运行的加密检验系统采用的观测站为2510站,分为33个区。同时对国外常用的统计检验量ETS评分进行了初步的研究。通过对2005年7—8月我国近年来引进或自主发展的T213L31、HLAFS25、MM5、MESO-GRAPES60km和30km模式,WRF20km模式,以及日本及德国的全球模式的降水预报产品的统计学检验,主要得到如下结论:(1)加密检验系统和标准检验系统在站点分布和分区形式上有较大的差别,新旧检验系统对各模式和预报员全国降水预报的评估结论在大雨以下各级降水评估方面差别不大,结论基本相似,除中雨预报外,加密系统的TS评分均略低于标准检验的结果。暴雨以上评分的差别较大,其中部分模式的两个检验系统的预报偏差差别很大,说明暴雨以上的天气系统多为中小尺度系统,其发生的频率在加密系统中的反映可能更合理一些。(2)新的检验量ETS,对于全国这样较大的检验分区而言,大雨以下各级降水评分在量值上要小于TS评分,暴雨以上则比较接近,但其在多模式对比检验中所得的排序结论与TS和技巧评分相近,部分小雨空报较多的模式的评分有较大差别。(3)无论是加密检验,还是标准检验,各级降水检验中表现最好的模式是相同的。(4)分区相同、预报种类不同时,加密检验与标准检验的差别不同。对T213模式而言,两者在暴雨和大暴雨的预报偏差上的差别更显著一些,部分分区检验结论相反。而对预报员的预报而言,差别并不显著,检验结论一致。     

东北振兴以来吉林省区域经济差异的时空演变研究

基于吉林省2003~2015年间地区生产总值和人均地区生产总值数据,以市域、县域两个尺度单元为研究对象,采用人口加权变异系数、基尼系数、泰尔指数等统计分析方法,对吉林省东北振兴战略实施以来的13 a内,区域经济差异的时空演变进行定量分析,并运用泰尔指数的分解方法,探讨了吉林省区域经济差异的空间格局。结果发现：① 吉林省区域经济总体差异、市域差异、县域差异均呈逐年下降趋势。② 通过差异贡献率显示：县域差异是区域总体差异变化的主导力量,长春市域的内部差异远高于其他市域,但有逐年减小的趋势,长吉两地的二元结构仍然突出,是全省区域经济差异产生的主要来源,主导着全省区域经济差异走向;③ 从2003~2015年来看,全省经济增长速度较快的地区主要还是集中在“三核一带”;④吉林省经济差异主要是由资源禀赋、产业结构、极化效应和政策导向等多种因素综合作用的结果。     

厄尔尼诺与亚洲季风对港澳地区降雨影响

分析研究了香港1853～1997年（145年）、澳门1901～1997年（97年）的月和年降雨量的一些特征。主要结论是：（1）香港、澳门年降雨量存在准2～6年的周期振荡，澳门年降雨量有很强的长期趋势，香港年降雨量无明显趋势；（2）香港、澳门年内雨量的峰值出现在西南季风期（6月和8月），而谷值在东北季风期（12月）；（3）EI Nino事件年，香港、澳门年降雨量距平百分率多为正，降雨偏多。在La Nila事件年，香港、澳门年降雨量距平百分率多为负，降雨偏少。     

1958-2016年呼伦贝尔草原新巴尔虎右旗气温和降水变化特征

气候变化是影响草原区植被与环境状况的重要因素。利用呼伦贝尔草原新巴尔虎右旗1958-2016年的气温和降水数据资料,采用线性倾向估计法、累积距平分析法、M-K检验法和Morlet小波分析等方法,从不同时间序列上,对该地区近59年的气候变化趋势、极端气候以及突变现象进行分析。结果表明：年平均气温以0.354℃/10a的速率上升,上升趋势显著;四季平均气温均呈现增温趋势,其中春季增温趋势最大;1985-1986年发生了由低温到高温的突变;研究区年平均气温存在11 a的强显著周期。研究区年降水量整体以8.68 mm/10a的速率呈下降趋势,变化趋势不显著;降水集中在夏季（6-8月）,占全年降水量的72.9%,7月降水量最大,有效降水日数最多;1961-1962年和1981-1982年降水发生突变;极端降水指标中日最大降水量、连续5 d最大降水量、强降水量、极强降水量、强降水比率、连续无雨日数、零降水量日数均呈现递减趋势,仅降水强度呈递增趋势,变化趋势均不显著;Morlet小波分析表明研究区年降水量存在52 a的强显著周期。新巴尔虎右旗近59 a气候总体呈现干旱化趋势。