Analysis and Comparison for Fusion Algorithms of Time Transfer     

WANG Wei-xiong  DONG Shao-wu  WU Wen-jun  GUO Dong  ZHANG Jian 《Chinese Astronomy and Astrophysics》2021,45(2):224-235

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豫西南泥湖地区辉长岩地球化学特征及其与成矿关系          下载免费PDF全文

刘辉 《山东国土资源》2018,34(3)

豫西南泥湖钼矿集区是以花岗斑岩体为中心的钼多金属矿床系列,区内出露大面积加里东期变辉长岩和燕山期辉长岩。通过分析区内辉长岩的岩石学、年代学、地球化学和成矿元素等方面特征,研究其在成岩成矿过程中的作用。区内加里东期变辉长岩和燕山期辉长岩成矿元素总稀土含量低,稀土元素球粒陨石标准化曲线右倾平缓,具有明显的Eu,Tm元素的异常;同比世界基性岩,自晚元古代上地幔主要成矿元素(除钨元素以外)基本没有明显的富集,主成矿元素钼含量呈明显的亏损,预示燕山期成矿花岗质岩浆没有从上地幔获得主要成矿物质。初步认为大规模的钼多金属成矿带的形成与基性岩浆的底垫作用相关,基性岩浆的底垫作用为下地壳部分熔融形成岩浆房提供了热源。  相似文献   

Towards Regional Synergy: Reconciling Rangeland Ecological Functioning with Forage Production of Cultivated Pasture     

SHI Peili  ZHANG Xianzhou 《资源与生态学报(英文版)》2020,11(3):247-252

Animal husbandry and crop farming are specialized for development in separate areas on the Tibetan Plateau. Such a pattern of isolation has led to current concerns of rangeland and farming system degradation due to intensive land use. The crop-livestock integration, however, has been proven to increase food and feed productivity thorough niche complementarity, and is thereby especially effective for promoting ecosystem resilience. Regional synergy has emerged as an integrated approach to reconcile rangeland livestock with forage crop production. It moves beyond the specialized sectors of animal husbandry and intensive agriculture to coordinate them through regional coupling. Therefore, crop-livestock integration (CLI) has been suggested as one of the effective solutions to forage deficit and livestock production in grazing systems. But it is imperative that CLI moves forward from the farm level to the regional scale, in order to secure regional synergism during agro-pastoral development. The national key R & D program, Technology and Demonstration of Recovery and Restoration of Degraded Alpine Ecosystems on the Tibetan Plateau, aims to solve the problems of alpine grassland degradation by building up a grass-based animal husbandry technology system that includes synergizing forage production and ecological functioning, reconciling the relationship between ecology, forage production and animal husbandry, and achieving the win-win goals of curbing grassland degradation and changing the development mode of animal husbandry. It is imperative to call for regional synergy through integrating ecological functioning with ecosystem services, given the alarming threat of rangeland degradation on the Tibetan Plateau. The series of papers in this issue, together with those published previously, provide a collection of rangeland ecology and management studies in an effort to ensure the sustainable use and management of the alpine ecosystems.  相似文献   

资源三号和天绘一号卫星影像无控联合平差精度分析     

郑义  张宏伟  杜晓  张俊辉  周琦  林尚纬  陈利军 《测绘通报》2020,(7):10

近年来国产卫星传感器类型日益丰富，使用自主可控的国产卫星影像进行生产和研究的需求越来越大，多源国产卫星影像联合平差的精度分析显得尤为重要。本文针对在立体测图生产中，资源三号卫星影像在时相较旧、噪声较大、云覆盖和摄影漏洞等特殊困难的条件下，利用天绘一号卫星影像进行补漏生产的情况，最终分析并验证了两者无控联合平差的可行性和成果精度。  相似文献   

盾构隧道下穿管道施工引起的管-土相互作用研究     

可文海  管凌霄  刘东海  邓建林  李科  徐长节 《岩土力学》2020,41(1):221-228

采用Loganathan公式研究了盾构隧道下穿管道施工引起的地下管道处土体竖向位移，利用考虑土中剪力传递的Pasternak模型模拟管-土相互作用，运用修正Vlasov模型中的迭代流程计算出Pasternak模型的关键参数——弹性系数k与剪切系数gs。将计算结果与已有文献结果及工程监测数据进行对比，深入分析了迭代求解k、gs值的Pasternak模型与传统模型的计算差异，并进一步研究了土中剪力、管道与隧道的夹角、土体弹性模量及隧道半径的变化对管-土相互作用的影响。研究结果表明：迭代求解的k、gs值能提升Pasternak模型的精确度；土中剪力对管道竖向位移计算值的影响可达15.3%；随着管道与隧道夹角的减小，管道的竖向位移增大、弯矩减小；土体弹性模量与隧道半径的增大均会增加管道的竖向位移和弯矩。  相似文献   

菲与纳米银对胶州湾表层沉积物反硝化作用的复合毒性效应评价     

孙鹏飞  白洁  李岿然  白晓岩  田延昭  赵阳国 《中国海洋大学学报(自然科学版)》2020,(1):104-114

多环芳烃(PAHs)与纳米材料污染已对沉积物生态系统和人类生存环境构成严重威胁,其复合污染的毒性效应环境危害可能更大。为了深入探讨PAHs与纳米材料对近岸表层沉积物反硝化作用的复合毒性效应,本文选取位于胶州湾(JZB)的大沽河河口区(DRE)E站和湾内S站,分别以菲和纳米银代表PAHs和纳米材料,通过测定不同剂量单一及复合污染下沉积物反硝化潜势(PDA)的变化,结合浓度相加模型(CA)、独立作用模型(IA)和中效/联合指数等效图法(CI)三种复合毒性评价方法,评价菲和纳米银对沉积物反硝化潜势的复合毒性效应,并对评价方法进行了优选。结果表明,两种污染物浓度越高,对研究区域反硝化潜势的抑制作用越大。菲、纳米银单一及复合作用下对河口区沉积物反硝化潜势的EC50值分别为44.62、112.49和64.86 mg·kg-1,对湾内分别为61.79、147.05和96.18 mg·kg-1。菲单一作用对反硝化潜势的抑制效应强于纳米银,但复合污染的抑制效应更强。两种污染物对河口区的沉积物反硝化潜势抑制效应强于湾内,可能与河口区具有较高Eh和沉积物颗粒度及较低的pH、盐度和有机质含量有关。三种毒性效应评价方法的结果表明,菲和纳米银的复合污染对2个站位反硝化潜势的毒性效应均为协同作用,且对大沽河河口区的协同作用更强。此外,CI法对复合效应的预测结果比CA和IA法更为接近实际观测值,且CI不需要考虑污染物作用模式的限制,因此认为CI法更适用于评价混合污染对沉积物反硝化作用复合影响的效果。本研究结果表明,菲和纳米银会增强彼此对反硝化菌及反硝化功能的毒性效应,由此推断,PAHs和纳米材料在环境中同时存在时比其单独存在对沉积环境的危害更大。  相似文献   

不同法截面子午线椭球衔接的研究及应用          下载免费PDF全文

李复才  姚德新 《全球定位系统》2020,45(1):88-92

为了满足高速铁路线路控制网的投影长度变形值不大于10 mm／km的要求,将长线工程线路分成多段并建立各自的法截面子午线椭球．针对相邻法截面子午线椭球的衔接问题,提出交点法线重合的方法,实现椭球变换之后交点位置的一致性,解决线路的衔接问题,从而大大加强法截面子午线椭球理论在工程线路弯曲性、复杂性及长度的适用性．   相似文献   

波浪溢流作用下海堤内坡高性能加筋草皮护坡防侵蚀特征研究     

潘毅  张同鑫  周子骏  陈永平 《海洋工程》2019,37(1):29-36

基于1∶1的大型水槽试验结果,分析了波浪溢流过程中位于海堤内坡的高性能加筋草皮护面的侵蚀特征。试验观察表明试验期间有一定土壤的损失,但护坡无明显的破坏;土面高度测量表明,当土壤流失发展到一定深度后,如果水动力强度变化不大,侵蚀趋于逐渐停止,这种现象称为侵蚀上限;结合试验现象对侵蚀上限进行了初步解释,并讨论了侵蚀上限达到前的侵蚀速率特征;植株密度监测表明,试验期间的草茎密度基本不变,草叶密度在开始几次试验期间持续减小,而后达到一个稳定值,这对于海堤的可持续防护有重要意义。研究成果能够为波浪溢流期间海堤内坡防御的相关研究和工程措施提供参考依据。  相似文献   

无人机倾斜摄影支持下的1∶500高精度三维测图方案及应用     

赵小阳  孙松梅 《测绘通报》2019,(7):87-91

研发了一种适合于大范围1∶500的无人机测图方案，围绕平面和高程点位中误差在5 cm以内这一核心目标，从无人机的平台稳定性、空中精准定位飞控、空三与三维建模及模型与影像结合的多视角测图等方面进行了设计。在广州马沥村的应用表明，本文研究的无人机倾斜摄影方案可以满足1∶500高精度的三维测图，并具有较高的效率。  相似文献   

Conditional statistics of Reynolds shear stress in flow over 2D dunes in the presence of surface waves          下载免费PDF全文

Satya P. Ojha 《水文研究》2014,28(18):4829-4842

This study presents the analysis of the velocity fluctuations to describe the conditional statistics of Reynolds shear stress in flow over two‐dimensional dunes in the presence of surface waves of varying frequency. The flow velocity measurements over the dunes are made using a 16‐MHz 3D acoustic Doppler velocimeter. The joint probability distributions of the normalized stream‐wise and vertical velocity fluctuations at different vertical locations are calculated in the trough region of a selected dune in quasi‐steady region of the flow. Third‐order moments of the stream‐wise and vertical velocity components over one dune length are also calculated throughout the flow depth for understanding the effect of surface waves on relative contributions to the Reynolds shear stress due to the four quadrant events. The structure of instantaneous Reynolds stresses is analysed using quadrant analysis technique. It has been shown that the contributions of second and fourth quadrant events to the Reynolds shear stress increase with increase in the frequency of surface waves. In fact, the largest contribution to turbulent stresses comes from the second quadrant. The cumulant discard method is applied to describe the statistical properties of the covariance term u′w′. Conditional statistics and conditional sampling are used to compare the experimental and theoretical relative contributions to the Reynolds shear stress from the four quadrant events. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献