eLoran系统新型信号波形设计及其性能评估          下载免费PDF全文

李婉清  刘中伟  李实锋  叶清琳 《全球定位系统》2020,45(2):13-20

增强型罗兰导航系统(eLoran)作为全球卫星导航系统(GNSS)的备份系统,是国家定位导航授时(PNT)安全的重要基础设施.针对目前标准eLoran信号存在易受交叉干扰、天波干扰,通信数据传输速率低等的问题,本文基于标准罗兰信号体制提出了两种波形改进方法(衰减函数法与对称波形法)并对新型波形进行性能评估.实验结果表明,两种方法能够有效缩短波形持续时间,加速后沿波形下降,减小发射机功耗.对称波形法能够大幅减小波形持续时间,但缩短波形持续时间也将改变原信号波形的频谱特性,利用衰减函数法可以最大程度保证信号的频谱性能.综合分析可知,新型波形能够有效利用时域资源,空余的时间可用于增加传输信号,进而提高数据调制技术的性能.  相似文献   

A case study on Landscape Component Niche based on Landscape Pattern Indices: Yanchi,Ningxia Province,China     

XiaoNing Zhang  XueLu Liu  Ghanney Philip  XiaoDan Li  QuanXi Wang  YaNan Xu  TingTing Hui 《寒旱区科学》2020,(1):22-33

Yanchi County is located in the agro-pastoral ecotone and belongs to the ecologically fragile area of Northwest China.It is important to study the evolution of landscape pattern to curb its environmental degradation.In order to intuitively show how the landscape pattern of the study area changes over time,Landsat Thematic Mappers(TM)and Landsat Operational Land Imager(OLI)data of 1991,2000,2010 and 2017 were used.This paper attempts to apply niche theories and methods into landscape ecology,and constructs a niche model of landscape components by using"n-dimentional hypervolume niche theory"and landscape pattern indices.By evaluating the spatial and temporal evolution of niche from the perspective of two-dimensional space to reflect the changes of landscape pattern in the study area over the past 26 years,new theories and methods were introduced for the characterization of landscape pattern.The results indicate that:1)The larger the attribute and dominance value of landscape components,the higher the ecological niche and the stronger the control effect on the overall landscape.2)The ecological niche of each landscape component was significantly different,just as its control effect on the overall landscape.3)The dynamic change of the ecological niche of each landscape component was different,with grassland,unused land and arable land always in a high dominant position,although the ecological niche of construction land and water area was always low.In general,the introduction of niche theory into the landscape ecology provided a new method to study the changes in regional landscape pattern.  相似文献   

陡立矿山岩壁治理中的飘台稳定性分析          下载免费PDF全文

王腾飞  王蒙 《探矿工程》2020,47(10):61-66

随着国家和社会的发展，人们对生态环境越发重视。在经济发展的过程中，因采矿而遗留下了大量的废弃矿坑，这些矿坑的治理迫在眉睫。飘台作为一种治理高陡光滑岩壁的有效方法，在实际工程中被大量使用，然而对飘台稳定性的分析大多停留在简单的公式上。本文设计了一种适用于陡立矿山岩壁治理的砼制飘台结构，提炼了计算飘台稳定性的公式并结合FLAC3D数值模拟软件，对飘台的稳定性进行了分析。研究结果表明，此砼制飘台比较适用于陡立矿山岩壁的治理。  相似文献   

基于ArcGIS的土壤稳定性评估——以张飞庙景区为例     

赵保睿  匡明星  王均浩  覃莹莹 《北京测绘》2020,(2):229-232

近年来山体滑坡以及泥石流等自然灾害事故频发,为能够减少灾害的影响,需要对特定区域的土壤稳定性进行调查或评估。传统对于土壤稳定性的评估一般是采用实地调查的方法,这种方法不仅效率低,而且对事故多发地段对于调查人员的安全影响较大。因此论文利用ArcGIS软件,根据DEM数据以及地区矢量图,通过计算坡度或坡向等方法对云阳县张飞庙景区进行土壤稳定性评估。运用该方法能够快速得到张飞庙景区土壤稳定性情况,确定不稳定区域范围,具有较强的实效性和实用性。  相似文献   

BDS卫星差分码偏差稳定性分析及其短期预报     

梅登奎  闻德保 《大地测量与地球动力学》2020,40(7):746-750

利用MGEX(multi-GNSS experiment)发布的BDS卫星差分码偏差(differential code bias, DCB)产品，比较分析不同太阳活动水平下BDS卫星DCB产品的稳定性变化特性，并采用差分自回归移动平均(auto-regressive integrated moving average, ARIMA)时间序列预测模型，实现不同太阳活动水平下BDS卫星DCB的短期预报。结果表明，在太阳活动高年，BDS卫星DCB日解值稳定度、月稳定性均明显低于太阳活动低年，且不同卫星星座类型的BDS卫星DCB稳定性也存在差异；ARIMA时间序列预报结果与MGEX发布值符合程度较好，优于多项式拟合法预测结果。  相似文献   

基于组合权重与灰色关联度分析法的地铁深基坑开挖稳定性评价     

郎秋玲  王伟  高成梁 《吉林大学学报(地球科学版)》2020,50(6):1823-1832

伴随着城市的快速发展，地铁深基坑工程越来越多。在开挖过程中如何对其稳定性进行评价，是当前需要重点关注的问题。以成都地铁十七号线凤溪站深基坑支护开挖工程为依托，利用层次分析确定的主观权重与利用熵值法确定的客观权重计算获得组合权重，并与灰色关联度分析法相结合，通过现场数据采集并进行综合评判，客观评价地铁深基坑开挖的稳定性。结果表明，各监测项目对基坑稳定性的重要程度从大到小依次为桩顶水平位移（0.29）、地表沉降（0.24）、建筑物沉降（0.19）、桩顶沉降（0.18）、内支撑轴力（0.10），基坑稳定性综合评判结果等级为"非常好"。所建立的评价模型可为类似地铁深基坑开挖稳定性评价提供新的方法。  相似文献   

Main active faults and seismic activity along the Yangtze River Economic Belt: Based on remote sensing geological survey     

《China Geology》2020,3(2):314-338

The Yangtze River Economic Belt (YREB) spans three terrain steps in China and features diverse topography that is characterized by significant differences in geological structure and present-day crustal deformation. Active faults and seismic activity are important geological factors for the planning and development of the YREB. In this paper, the spatial distribution and activity of 165 active faults that exist along the YREB have been compiled from previous findings, using both remote-sensing data and geological survey results. The crustal stability of seven particularly noteworthy typical active fault zones and their potential effects on the crustal stability of the urban agglomerations are analyzed. The main active fault zones in the western YREB, together with the neighboring regional active faults, make up an arc fault block region comprising primarily of Sichuan-Yunnan and a “Sichuan-Yunnan arc rotational-shear active tectonic system” strong deformation region that features rotation, shear and extensional deformation. The active faults in the central-eastern YREB, with seven NE-NNE and seven NW-NWW active faults (the “7-longitudinal, 7-horizontal” pattern), macroscopically make up a “chessboard tectonic system” medium-weak deformation region in the geomechanical tectonic system. They are also the main geological constraints for the crustal stability of the YREB.  相似文献   

Photometric Follow-up Transit (Primary Eclipse) Observations of WASP-43 b and TrES-3b and A Study on Their Transit Timing Variations     

Sun Zhao  Ji Jiang-hui  Dong Yao 《Chinese Astronomy and Astrophysics》2018,42(1):101-128

Two photometric follow-up transit (primary eclipse) observations on WASP-43 b and four observations on TrES-3 b are performed using the Xuyi Near-Earth Object Survey Telescope. After differential photometry and light curve analysis, the physical parameters of the two systems are obtained and are in good match with the literature. Combining with transit data from a lot of literature, the residuals (O ? C) of transit observations of both systems are fitted with the linear and quadratic functions. With the linear fitting, the periods and transit timing variations (TTVs) of the planets are obtained, and no obvious periodic TTV signal is found in both systems after an analysis. The maximum mass of a perturbing planet located at the 1:2 mean motion resonance (MMR) for WASP-43 b and TrES-3 b is estimated to be 1.826 and 1.504 Earth mass, respectively. By quadratic fitting, it is confirmed that WASP-43 b may have a long-term TTV which means an orbital decay. The decay rate is shown to be P? = (?0.005248 ± 0.001714) s·yr^?1, and compared with the previous results. Based on this, the lower limit of the stellar tidal quality parameter of WASP-43 is calculated to be ${Q^{\prime }}_{*}\ge 1.5\times {10}^5$, and the remaining lifetimes of the planets are presented for the different ${Q^{\prime }}_{*}$ values of the two systems, correspondingly.  相似文献   

基于连岛沙坝原理设计的海滩排水管头地貌稳定性研究     

董标  蔡锋  金保明  刘建辉  雷刚 《海洋工程》2018,36(1):128-137

海滩排水管建设对海滩环境影响较大。以厦门会展中心连岛沙坝式排水管头工程影响海滩演变为例,研究连岛沙坝式海滩排水管头对海滩地形稳定性和沉积的影响。1)通过对研究区连岛沙坝式管头附近海滩10条剖面进行分析,研究管头附近海滩滩肩宽度、滩面坡度和单宽留存沙量等剖面形态变化特征。测量数据分析表明,无管头保护滩面高程降低,滩面坡度总体变陡,滩肩蚀退严重;受管头保护滩面高程上升,坡度变缓,滩肩宽度略有减小,剖面单宽沙量留存比例大于1。2)2012-2016年多期岸线及管头边界线变化结果表明,工程施工后,排水管身始终被沙体覆盖,一年后部分管头被沙体覆盖,最终管头被覆盖率稳定在70%以上。3)会展管头附近海滩潮上带和高潮带沉积物自北向南运移,低潮带则相反;潮上带和中潮带上部沉积物从管头所在"连岛沙坝"向两侧海滩输移,而低潮带和中潮带下部输移方向相反。沉积物粒径由岸向海逐渐变粗,越靠近管头,沉积物粒径呈变细趋势。最后讨论了引起管头局部海滩地形地貌变化的主要因素。  相似文献   

气举反循环钻进井壁稳定及适用性探讨          下载免费PDF全文

郑伯乐  郑秀华  段晨阳  叶宏宇 《探矿工程》2020,47(6):13-18

气举反循环工艺具有钻进效率高、携带岩屑能力强、防漏效果好以及钻头寿命长等优点，同时还可以提高流体矿产的产能。但是一般认为气举反循环钻进抽吸作用会产生负压，不利于井壁稳定，不宜在松散地层应用。本文通过计算气举反循环钻进环空水力参数，并从环空压力以及冲洗液流态、流速等方面探讨研究气举反循环钻进中井壁稳定及其适用性，指出通过选取合适的钻具组合以及调节冲洗液性能，可使气举反循环工艺对不同地层的适应性更广。  相似文献