Efficient methods of discharge measurements in rivers and streams based on the probability concept     

Chao‐Lin Chiu  Shih‐Meng Hsu  Ning‐Chien Tung 《水文研究》2005,19(20):3935-3946

Regularities exist in fluid flows and can be represented by a set of constants. These constants are functions of the parameter of a probability distribution that exhibits resilience and stability under various flow conditions. Together, these regularities form a network and interact with each other, such that if one is known then the others can be determined from it. The regularities and their network explain the various fluid‐flow phenomena and can be used in analysis of rivers and streams. For example, they can be used as the basis to develop simple and efficient methods of discharge measurements as presented herein, which only require velocity sampling at a single point on a water surface or a few points on a single vertical. Because of their simplicity and the short time requirement, these methods can be easily automated for collecting discharge data in unsteady, high flows that are badly needed for real‐time flow forecasting and design of flood control structures, and for advancing the fundamental, scientific knowledge in hydrology. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

风沙流中跃移沙粒冲击速度和角度联合概率分布风洞实验     

肖锋军  董治宝  郭烈锦  王跃社  李德标 《中国沙漠》2020,40(3):127-134

近地表跃移沙粒速度和角度概率分布是连接风沙运动宏观研究和微观研究的桥梁，对沙粒跃移轨迹和输沙率分布有很大影响。但是，目前跃移沙粒冲击速度概率分布和角度概率分布之间的关系还不明确。使用相位多普勒粒子分析仪（PDPA）测量了风洞沙床面1 mm高度处的跃移沙粒速度，通过分析各冲击速度对应的冲击角度的概率分布研究了沙粒冲击速度和角度的联合概率分布。结果表明：沙粒冲击速度概率分布可用对数正态函数描述，冲击角度概率分布可用指数函数描述；各冲击速度对应的冲击角度都符合指数函数分布，且其衰减速度随冲击速度增加而加快。这表明，冲击速度概率分布和冲击角度概率分布之间具有很强的相关性。最后分别给出了沙粒冲击速度和角度的独立假设概率分布和条件联合概率分布。  相似文献   

2003-2017年北京市地表热力景观时空分异特征及演变规律   总被引：6，自引：3，他引：6  

乔治  黄宁钰  徐新良  孙宗耀  吴晨  杨俊 《地理学报》2019,74(3):475-489

利用2003-2017年MODIS地表温度数据,分别从数量、形状和结构角度揭示北京市不同季相和昼夜间地表热力景观时空分异特征,并进一步通过热力等级变化图谱及质心迁移轨迹揭示城市热力景观空间演变规律,探究热力景观等级转换生态过程。结论如下：① 城市地表热力景观季节和昼夜空间特征差异显著;② 中温区在城市热环境中占主导地位。白天中温区是最不稳定的热力景观等级;夜间次低温区和次高温区不稳定性增加;③ 地表热力景观等级变化以稳定型占主,反复变化型和前期变化型次之。地表热力景观等级通常呈现逐级递增或递减规律,山区呈现逐级降温趋势,北部城郊—山地交错地带表现出次低温和中温的反复转向,南部地区有一定的升温趋势;④ 2003-2017年高温区面积增大且质心向城市中心集中,低温区质心向城市外围扩散。生态涵养发展区对北京市地表热力景观质心迁移贡献率最高。热力景观时空分异特征及演变规律可为有效缓解城市热岛效应提供管理决策支持。  相似文献   

White dwarf + red dwarf binary systems and the period gap of cataclysmic variables     

N. F. Vojkhanskaja 《Astrophysics》2007,50(3):351-361

Cataclysmic variables (CV) and pre-cataclysmic binaries (PCB) are discussed. The main difference between them (accretion or its absence) is shown to be a consequence of the evolutionary process and the properties of their progenitors. Both types of system have a bimodal distribution of their periods, but the extrema are in counterphase. Luminosity-effective temperature diagrams for the primary components are used to show that both systems have approximately the same age, which conflicts with the notion of PCBs as precursors of CVs. Calculations of the maximum distance between components for which the system remains stable show that CVs have passed this limit, while PCBs maintain their stability during this evolution. It is suggested that, after ejecting a common shell, future CVs immediately become semi-detached systems. It this is so, then there must be cataclysmic variables which are the central stars of planetary nebulae. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 427–439 (August 2007).  相似文献   

华北地块北缘金矿预测   总被引：4，自引：1，他引：3  

李钟山  范继璋 《吉林大学学报(地球科学版)》2004,34(2):292-296

对华北地块北缘的金矿进行了成因分类,共分为3大类7亚类.利用地质体单元法对3大金矿类型进行了单元划分,共划分出214个单元.在综合信息成矿理论的指导下,对本区的岩浆重熔热液型金矿、岩浆同熔热液型金矿床以及火山-次火山热液型金矿床分别采用特征分析,对矿产资源的产出位置进行了估计,采用成矿概率估计对各单元的成矿可能性进行分级,共预测出24个最有远景的工作区.  相似文献   

重庆多历时极值降水的概率型优选及应用     

王颖  刘晓冉  程炳岩  孙佳 《气象科学》2020,40(4):560-568

基于重庆34个国家气象站1981—2016年5 min,24 h至3 d的过程最大雨量共18个年极值降水序列,利用线性矩法计算6种常用概率分布函数的模型参数,通过备选最优模型筛选法客观选取各站各历时极值降水的最优概率模型,并将优选结果应用于重庆不同历时百年重现期降水的计算。结果表明:模型优选方法得到的重庆各站不同历时极值降水的最优线型略有差异,广义极值分布占比最大,三参数Weibull分布次之,三参数对数正态分布第三,皮尔逊Ⅲ型和Gumbel分布相当,指数分布最差。最优线型计算的重庆不同历时百年重现期降水的空间分布大值区由短历时的点状分布向长历时的片状分布转变,渝东北的大值中心受地形影响不断向北移动。基于线性矩法的概率模型参数估计及客观的线型优选过程具有较强的可操作性和适应性,可应用于其他工程气象参数的推算中。  相似文献   

Mapping spatio-temporal flood inundation dynamics at large river basin scale using time-series flow data and MODIS imagery     

《International Journal of Applied Earth Observation and Geoinformation》2014

Flood inundation is crucial to the survival and prosperity of flora and fauna communities in floodplain and wetland ecosystems. This study tried to map flood inundation characteristics in the Murray-Darling Basin, Australia, utilizing hydrological and remotely sensed data. It integrated river flow time series and Moderate Resolution Imaging Spectroradiometer (MODIS) images to map inundation dynamics over the study area on both temporal and spatial dimensions. Flow data were analyzed to derive flow peaks and Annual Exceedance Probabilities (AEPs) using the annual flood series method. The peaks were linked with MODIS images for inundation detection. Ten annual maximum inundation maps were generated for water years 2001–2010, which were then overlaid to derive an inundation frequency map. AEPs were also combined with the annual maximum inundation maps to derive an inundation probability map. The resultant maps revealed spatial and temporal patterns of flood inundation in the basin, which will benefit ecological and environmental studies when considering response of floodplain and wetland ecosystems to flood inundation.  相似文献   

城市地铁变形监测数据处理     

杨国东  詹福雷 《东北测绘》2014,(2):6-8,11

为确保地铁施工安全进行变形监测是非常重要的手段,而变形监测的最终目的是预测,即对观测物的未来形态进行预报和分析。时间序列的原理是找出事物随时间变化的规律,从而对数据变化趋势做出正确的分析和预报。本文通过对时间序列的研究对长春地铁繁荣路站的变形监测数据进行了分析和预报。  相似文献   

Image relaxation matching based on feature points for DSM generation   总被引：1，自引：0，他引：1  

ZHENGShunyi ZHANGZuxun ZHANGJianqing 《地球空间信息科学学报》2004,7(4):243-248

In photogrammetry and remote sensing, image matching is a basic and crucial process for automatic DEM generation. In this paper we presented a image relaxation matching method based on feature points. This method can be considered as an extention of regular grid point based matching. It avoids the shortcome of grid point based matching. For example, with this method, we can avoid low or even no texture area where errors frequently appear in cross correlaton matching. In the mean while, it makes full use of some mature techniques such as probability relaxation, image pyramid and the like which have already been successfully used in grid point matching process. Application of the technique to DEM generaton in different regions proved that it is more reasonable and reliable.  相似文献   

Species richness,diversity and density of understory vegetation along disturbance gradients in the Himalayan conifer forest     

Kesang WANGCHUK  András DARABANT  Prem Bahadur RAI  Maria WURZINGER  Werner ZOLLITSCH  Georg GRATZER 《山地科学学报》2014,11(5):1182-1191

We investigated whether species richness, diversity and density of understory herbaceous plants differed along logging(gap) and grazing(primarily by cattle) disturbance gradients, and sought to identify drivers of richness, diversity and density of understory vegetation of logged sites. A factorial experiment was conducted in the mixed conifer forest of Gidakom in Western Bhutan. Levels of the logging treatment included small(0.15 – 0.24 ha), medium(0.25 – 0.35 ha) and large(0.36 – 1.31 ha) gaps. The grazing treatment included grazed(primarily by cattle) and ungrazed(where herbivores were excluded by a fence) plots nested within each gap. Data were collected from 12 gaps(4 replicates at each level of logging) using the point intercept method. Shannon Weaver Diversity and Margalef's indices were used to estimate species diversity and describe species richness, respectively. Soil samples were analyzed for pH and nutrients. The interaction effect of logging and grazing was significant(p≤0.001) only on species diversity. Relative to ungrazed areas, species diversity was significantly higher(0.01≤p≤0.05) in medium grazed gaps. Under grazed conditions, soil P was negatively correlated with gap size and species diversity. While species diversity was positivelycorrelated(0.01≤p≤0.05) with soil N in grazed plots species richness was positively correlated(0.001≤p≤0.01) with soil N in ungrazed plots. Relative density of Yushania microphylla and Carex nubigena were higher under ungrazed conditions. Our study suggests that the combined effect of cattle grazing and logging results in higher species diversity of understory vegetation in medium and grazed gaps in mixed conifer forests of Bhutan,whereas increase or decrease in relative density of major species is determined primarily by the independent effects of grazing and logging. From management perspective, forest managers must refrain from creating large gaps to avoid loss of nutrients(mainly P and N), which may eventually affect tree regeneration. Managers intending to maintain understory vegetation diversity must consider the combined effects of grazing and logging, ensuring low to moderate grazing pressure.  相似文献