DEM resolution dependencies of terrain attributes across a landscape     

Y. Deng  J. P. Wilson  B. O. Bauer 《International journal of geographical information science》2013,27(2):187-213

This paper documents resolution dependencies in terrain analysis and describes how they vary across landform location. Six terrain attributes were evaluated as a function of DEM resolution—slope, plan curvature, profile curvature, north–south slope orientation, east–west slope orientation, and topographic wetness index. The research highlights the effect of varying spatial resolution through a spatial sampling/resampling scheme while maintaining sets of indexed sample points at various resolutions. Tested sample points therefore coincide exactly between two directly compared resolutions in terms of their location and elevation value. An unsupervised landform classification procedure based on statistical clustering algorithms was employed to define landform classes in a reproducible manner. Correlation and regression analyses identified sensitive and consistent responses for each attribute as resolution was changed, although the tested terrain attributes responded in characteristically different ways. These responses displayed distinguishable patterns among various landform classes, a conclusion that was further verified by a series of two‐sample, two‐tailed t‐tests.  相似文献   

Reinforcement effects of ground treatment with dynamic compaction replacement in cold and saline soil regions     

Yu Zhang  JianKun Liu  JianHong Fang  AnHua Xu 《寒旱区科学》2013,5(4):0440-0443

The mechanical property of saline soils varies with moisture and climate in the cold and salt lake region of Qinghai-Tibet Plateau, which influences project construction. In order to improve foundation reinforcement effect of the Qarhan–Golmud Highway, Qinghai Province, China, dynamic compaction replacement (DCR) composite foundation was applied in saline soils. A field experiment was conducted in this area, where strength and working mechanism of pier-soil and deformation modulus of the composite foundation was analyzed after reinforcement. This paper presents methods for determining the coefficient on the bearing capacity evaluation and deformation modulus of composite foundation with DCR. Reinforcement case of DCR is highly effective in saline soils of the salt lake regions, which helps the migration of water and salt in saline soils.  相似文献   

ENVIRONMENTS OF AEOLIAN DEPOSITION IN SOUTH-CENTRAL NEBRASKA DURING THE LAST GLACIAL MAXIMUM     

Zhao-Dong Feng  William C. Johnson  Robert F. Diffendal Jr. 《自然地理学》2013,34(3):249-261

The Peoria Loess of south-central Nebraska, deposited approximately during the Last Glacial Maximum, can be subdivided into three zones: an upper laminated loess and a lower massive loess, separated by a dark gley zone in which bison bones and spruce charcoal are found. The lower Peoria unit is characterized by high organic matter content, relatively high bulk density, and common root channels. The upper Peoria unit has rhythmic patterns of two orders: strongly gleyed and weakly gleyed zones alternating in couplets about 2–5 m thick, and coarse- and fine-grained laminae of second order, about 2–4 mm thick. The strongly gleyed zones are relatively low in magnetic susceptibility and contain lenses with abundant fossil plant debris. They may have formed in active zones on top of permafrost during relatively cold and probably moist intervals, with magnetic susceptibility secondarily lowered in the redox environment. Magnetic susceptibility also indicates the possible existence of first-order rhythmic patterns in the lower massive loess. Each of the ten susceptibility oscillations within Peoria Loess has a mean duration of about 1000 years, assuming that the loess was deposited between approximately 20,000–22,000 and 10,000–10,500 yr BP. The second-order laminae, close to the expected mean annual accumulation rate of Peoria Loess, may be due to seasonal variation in wind intensity or to secondary grain sorting of niveoeolian deposits. [Key words: Peoria Loess, dust, Great Plains, Last Glacial Maximum.]  相似文献   

生物活动对海床沉积物工程地质特征改造研究   总被引：4，自引：1，他引：3  

贾永刚  周其健  马德翠 《工程地质学报》2005,13(1):49-56

底栖穴居动物是河口潮滩生态系统的重要组成部分,它对沉积物的二次改造作用非常重要。本文以黄河三角洲钓 口区潮滩为研究对象,研究了不同生物密度对沉积物工程地质特征的改造,包括滩面形态、沉积物强度、以及沉积物颗粒大小 的改变。在此基础上探讨了生物活动与滩面凹坑,沉积物强度非均匀性以及研究区浮泥之间的关系。  相似文献   

Foreshock cavities and internal foreshock boundaries     

Laurence Billingham  Steven J. Schwartz 《Planetary and Space Science》2011,59(7):456-467

We present two case studies of cluster encounters with foreshock cavities. For one event, we are able, for the first time, to accurately relate the observation of a foreshock cavity to the measured position of the bow shock. This allows us to compute the shock angle, a vital parameter in models of foreshock cavity formation, with greater confidence than any previous study. This cavity appears to be elongated along the magnetic field and we use the multispacecraft nature of the Cluster mission to constrain its field-parallel and -perpendicular extent. We show that this event is embedded within a region of field-aligned ion beams. This is the first time a foreshock cavity has been shown to be surrounded by foreshock ion beams. A second foreshock cavity is associated with a small rotation in the interplanetary magnetic field (IMF). We show that this event appears on the boundary between an interval when the spacecraft were inside the ion foreshock, and an excursion upstream. This is the first report of a foreshock cavity observed during the traversal of the global foreshock. This second event has some features expected from the new Sibeck et al. (2008) model of cavities as brief encounters with a spatial boundary in the global foreshock.  相似文献   

多通道比相仪TSCMMS测量性能分析     

李雨薇  刘娅  李孝辉 《时间频率学报》2011,34(1)

为了研究美国Symmetricom公司的多通道比相仪TSC MMS(multi-channel measurement system)(它是一种基于双混频时差测量原理的相位测量设备)的测量性能以及进一步探索改进其测量性能的方法,搭建了TSC MMS设备的性能测试平台,测量了TSC MMS的本底噪声。本底噪声的测量结果与该设备制造商发布的2.5×10-13(10 MHz)处于同一水平。另外,对影响测量结果的具体原因进行了分析。  相似文献   

基于中美抗震设计规范的双向水平地震效应组合方法的有效性评估          下载免费PDF全文

王健泽  戴靠山 《世界地震工程》2022,38(1):001-10

在地震来临时,一般假设建筑结构同时受到两个正交水平方向分量与一个竖向分量的地震动作用。双向水平地震效应组合方法用于估计两个正交水平分量地震动同时作用时结构的内力效应。本文主要对我国与美国抗震设计规范中规定使用的平方和开平方根（SRSS）方法与百分比组合方法的有效性进行了评估。首先,对比了我国与美国规范在考虑双向水平地震效应时的适用情况及相关规定上的异同。以一4层中心支撑-框架结构为工程案例,考虑两国规范在适用情况上的规定,设置了三个结构布置方案。对三个结构布置方案建立有限元模型,选取22组地震动,开展了动力时程分析。提出了针对SRSS方法与百分比组合方法的评估指标,基于时程分析结果,发展了双向水平地震效应组合的概率性评估方法。评估结果表明:SRSS方法与百分比组合方法用于平面扭转不规则结构的设计较为保守。在简化组合规则的适用条件上,美国规范对平面扭转不规则结构不进行考虑有一定的合理性。建议我国规范对中心支撑-框架结构中含双向受压柱的设计要求考虑双向水平地震效应组合。  相似文献   

基于背景信息的MODIS林火自动提取算法     

缪婷婷  沈润平 《测绘科学》2013,38(5):49-50,60

本文在火点提取算法中加入了背景信息,减少了伪火点,提高了火点提取算法的准确性和可靠性。通过选取江西省武宁县为实验区,应用MODIS数据进行了火点的提取,实现了从数据的处理到火点的自动提取。经实验验证后,发现改进后的算法火点提取精度较高,能很好地满足林火监测要求。  相似文献   

面向矿产行业的GIS卓越工程师培养模式研究     

吴浩  孙久运  花向红  池秀文  袁艳斌  黄解军 《测绘科学》2013,38(5):185-187

针对现有GIS专业培养方案难以适应社会发展需求的问题,本文以国家"卓越工程师教育培养计划"为契机,依托我校矿物资源工程优势学科的矿产行业背景,对GIS专业的实践教学计划与内容进行改革,探索了校内特色专业实验室、校外典型行业实践基地和双师制行业实践的3种教学模式,构建出培养具备高素质矿产行业背景GIS卓越工程师培养的"四四"实践教学平台。并在开放式矿业教学平台的支持下,研究了"学习—实践—研究—创新—再学习"为主线的实践教学方法,达到提升GIS专业学生行业应用能力的目的。  相似文献   

2012年5月28日河北省唐山4.8级地震   总被引：5，自引：1，他引：4  

张跃刚  王玉珍  尹宝军  王想  马栋  张子广  乔子云  王晓山 《中国地震》2013,29(2):219-229

2012年5月28日河北省唐山市古冶区与滦县交界发生4.8级地震,地震宏观震中位于古冶区的王辇庄乡.震中烈度为V度,地震发生在NE走向的唐山断裂带附近.地震没有造成人员伤亡和经济损失.震源机制解P轴方位为SEE,T轴方位为SSW,接近水平,这与华北构造应力场的NE-NEE方向不一致.唐山4.8级地震是1976年唐山7.8级地震晚期余震的正常起伏,2004年以来唐山老震区的ML4.0以上地震呈现了很好的准周期性.唐山4.8级地震前地震活动性和测震学参数存在背景性异常,从不同角度反映了老震区地震活动平静、起伏的阶段性特征.前兆异常以中短期异常为主,其中地下流体异常、电磁异常表现更为突出.此次地震虽然震级不高,但无论是地震活动性还是前兆方面都出现了一定数量的异常.异常既有趋势性的,也有短临的,配套性很好.  相似文献