利用光变曲线估计猎鹰九号火箭末级的旋转状态研究     

苏向泽  汤儒峰  李荣旺  李语强 《天文研究与技术》2021,(2):203-212

光度观测是地基观测空间目标的主要手段之一,利用光度信息能够估计空间目标的相关特征信息。为了更好地了解空间目标的旋转状态,选取具有代表性的猎鹰九号火箭末级作为研究对象,由其光变信息研究旋转状态。首先利用云南天文台1.2 m光学望远镜获取猎鹰九号火箭末级的光度数据,再对目标星等进行斜距归一化,得到目标光变信息并分析目标星等随时间变化的曲线,估计大致的旋转周期,再由相位离散最小化方法计算会合周期。根据太阳、目标和测站之间的位置关系、惯性主轴指向、旋转轴指向、初始相位等因素,采用姿态旋转矩阵计算理论星等,利用最小二乘原则确定惯性主轴方向及初相角度、旋转轴指向。最后给出了猎鹰九号火箭末级的旋转周期、会合周期以及旋转轴指向等参数,为后续开展其他空间目标光度信息研究提供参考。  相似文献   

A two-layer model for studying 2D dissolved pollutant runoff over impermeable surfaces     

Taotao Zhang  Yang Xiao  Dongfang Liang  Hongwu Tang  Junzeng Xu  Saiyu Yuan  Nairu Wang  Bin Luan 《水文研究》2021,35(5):e14152

Dissolved pollutants in stormwater are a main contributor to water pollution in urban environments. However, many existing transport models are semi-empirical and only consider one-dimensional flows, which limit their predictive capacity. Combining the shallow water and the advection–diffusion equations, a two-dimensional physically based model is developed for dissolved pollutant transport by adopting the concept of a ‘control layer’. A series of laboratory experiments has been conducted to validate the proposed model, taking into account the effects of buildings and intermittent rainfalls. The predictions are found to be in good agreement with experimental observations, which supports the assumption that the depth of the control layer is constant. Based on the validated model, a parametric study is conducted, focusing on the characteristics of the pollutant distribution and transport rate over the depth. The hyetograph, including the intensity, duration and intermittency, of rainfall event has a significant influence on the pollutant transport rates. The depth of the control layer, rainfall intensity, surface roughness and area length are dominant factors that affect the dissolved pollutant transport. Finally, several perspectives of the new pollutant transport model are discussed. This study contributes to an in-depth understanding of the dissolved pollutant transport processes on impermeable surfaces and urban stormwater management.  相似文献   

Investigation of inner-basin variation: Impact of large reservoirs on water regimes of downstream water bodies     

Xue Dai  Zhongbo Yu  Guishan Yang  Chong-Yu Xu  Rongrong Wan 《水文研究》2021,35(5):e14241

Large dams and reservoirs alter not only the natural flow regimes of streams and rivers but also their flooding cycles and flood magnitudes. Although the effect of dams and reservoirs has been reported for some vulnerable locations, the understanding of the inner-basin variation with respect to the effects remains limited. In this study, we analyse the Three Gorges Dam (TGD) built on the Changjiang mainstream (Yangtze River) to investigate the dam effect variations in the system of interconnected water bodies located downstream. We investigated the effect of flow alterations along the downstream river network using discharge time series at different gauging stations. The river–lake interactions (referring to the interactions between the Changjiang mainstream and its tributary lakes i.e. the Dongting and Poyang lakes) and their roles in modifying the TGD effect intensity were also investigated in the large-scale river–lake system. The results show that the water storage of the tributary lakes decreased after the activation of the TGD. Severe droughts occurred in the lakes, weakening their ability to recharge the Changjiang mainstream. As a consequence, the effect of the TGD on the Changjiang flow increase during the dry season diminished quickly downstream of the dam, whereas its impact on the flow decrease during the wet season gradually exacerbated along the mainstream, especially at sites located downstream of the lake outlets. Therefore, when assessing dam-induced hydrological changes, special attention should be paid to the changes in the storage of tributary lakes and the associated effects in the mainstream. This is of high importance for managing the water resource trade-offs between different water bodies in dam-affected riverine systems.  相似文献   

生态地貌学研究体系及其功能提升探讨     

申元村  程维明 《地理研究》2019,38(2):348-356

地球表层是人类生存的家园,地表形态直接或间接影响人类生活、生产和社会经济活动。地貌学和生态学是与人类关系密切的学科。自然实体与人文实体都依附于地表,研究生态与地貌关系的科学便统称为生态地貌学,直接影响人类生存选址、生存保障、生产方向、产业布局、交通、城乡建设等,因此,生态地貌学是保障人类生存与社会经济可持续协调发展的基础性与应用性极强的学科,是国家实现生态文明战略的基础性学科。生态地貌学研究生态与地貌两者相互作用形成的生态地貌综合实体,学科体系包含地貌基础学科、生态基础学科及其相互作用形成的生态地貌学科。生态地貌学科下又包含生态地貌区划学、生态地貌类型学、生态地貌资源学、生态地貌岩态学、生态地貌遥感与GIS技术、生态地貌管理与规划等分支学科,是目前仍然属于探索性的学科。生态地貌结构可表达为：由地貌与生物成分、类型、区域组合、数量构成及其空间排列组合方式。从生态地貌结构理论出发,对其功能进行系统梳理,主要可以归纳为区域结构、类型结构、资源结构、岩态结构等多种类型。不同结构类型具有不同的功能,主要功能有提升中国自然地理区划质量与空间定位功能、生态评估与生态设计功能、土地利用评估与利用结构调整功能、地质地貌灾害成因和防灾减灾对策功能等。故该研究意在实现生态地貌功能间协调、高效可持续,通过对各功能进行整合,形成功能体系,并从调控管理上提出了提升功能能力的设计路径。  相似文献   

利用稳定同位素(15N)示踪技术研究浮游藻类氮素吸收速率特征     

韩菲尔  赵中华  李大鹏  张路 《海洋与湖沼》2019,50(4):811-821

浮游藻类对溶解态氮的吸收同化是湖泊氮生物循环和水体富营养化发生机制探讨的关键环节。本文通过~(15)N稳定同位素添加实验以铜绿微囊藻(Microcystis aeruginosa)、海链藻(Thalassiosira sp.)、卡德藻(Tetraselmis sp.)、剧毒卡尔藻(Karlodinium veneficum)以及盐水隐藻(Rhodomonas salina)为研究对象,从浮游藻类氮素吸收时间、营养盐基质以及藻种差异三个方面研究五种藻类对铵氮(NH_4~+-N)、硝氮(NO_3~--N)、尿素氮(Urea-N)三种形态氮的吸收特征。研究发现:(1)浮游藻类对三种形态氮的吸收均在1h时吸收速率最高,其氮素吸收过程为快速吸收。(2)浮游藻类优先吸收还原态氮,其中NH_4~+-N吸收速率最高,当培养周期为1d和4d时浮游藻类对NH_4~+-N吸收速率的均值分别为4.05和4.15μmol/(L·h);浮游藻类对Urea-N吸收相对偏好系数为25.18—713.42,表现出对小分子溶解态有机氮的特定偏好性。(3)不同藻种对氮素吸收具有不同特征,其中,剧毒卡尔藻对三种形态氮的吸收速率均为最高,而铜绿微囊藻的吸收速率均为最低;不同藻种不同培养时间氮素吸收速率差异与浮游藻类生长周期等特性有关。不同浮游藻类对不同形态氮素表现出吸收特异性,对水体氮负荷和浮游藻类水华优势种形成将产生重要影响。  相似文献   

An Automatic Method for Detecting Transients and Variable Sources in AST3 Survey Based on Image Subtraction and Random Forest     

《Chinese Astronomy and Astrophysics》2020,44(1):41-60

AST3-2 (the second Antarctic Survey Telescope) is located in Antarctic Dome A, the loftiest ice dome on the Antarctic Plateau. It produces a huge amount of observational data which require a more efficient data reduction program to be developed. Also the data transmission in Antarctica is much difficult, thus it is necessary to perform data reduction and detect variable and transient sources remotely and automatically in Antarctica, but this attempt is restricted by the unsatisfactory performance of the low power consumption computer in Antarctica. For realizing this purpose, to develop a new method based on the existing image subtraction method and random forest algorithm, taking the AST3-2 2016 dataset as the test sample, becomes an alternative choice. This method performs image subtraction on the dataset, then applies the principle component analysis to extract the features of residual images. Random forest is used as a machine learning classifier, and in the test a recall rate of 97% is resulted for the positive sample. Our work has verified the feasibility and accuracy of this method, and finally found out a batch of candidates for variable stars in the AST3-2 2016 dataset.  相似文献   

大孔隙对径流过程影响的研究进展          下载免费PDF全文

吕海深 《水文》2020,40(1):13-17

大孔隙流是土壤优先流的一种,在植被发育区土壤大孔隙比较常见,对径流形成过程产生重要的影响。介绍了大孔隙流的研究方法,系统总结了近50年植被发育区土壤大孔隙对降雨入渗过程及径流形成过程的影响:从水分入渗的角度,大孔隙可以加快降雨入渗过程;由土壤大孔隙流与山坡产流的关系,大孔隙促进了边坡雨水的运动进而引起了快速产流;世界范围内的研究都表明土壤管流或大孔隙流是径流组分重要贡献者。  相似文献   

Hydrologic separation and their contributions to N loss in an agricultural catchment in hilly red soil region   总被引：1，自引：0，他引：1  

Wang  Yaji  Gao  Lei  Peng  Xinhua 《中国科学:地球科学(英文版)》2019,62(11):1730-1743

The impacts of hydrological processes on N loss is of great value to understand the N transport at catchment scale,which is far from clear. Rainfall, soil water, groundwater and stream water and their N concentrations were monitored from March 2017 to February 2018 in Sunjia agricultural catchment of the red soil critical zone. Objectives of this study were:(1) to determine the dynamics of N concentration of different waters and their N loads;(2) to assess their contributions to N load of streamflow in the paddy and upland mixed agricultural catchment. Our results showed that the N concentrations of soil water(4.8 mg L~(-1)) and groundwater(6.0 mg L~(-1)) were the highest, approximately 2 to 5 times higher than those of stream water(2.7 mg L~(-1)), rain water(1.7 mg L~(-1)) and irrigation water(1.2 mg L~(-1)). The N net loss of the catchment(38.2 kg ha~(-1) yr~(-1))accounted for 15% of the total fertilizer N input. Rainy season(April–June) was a high-risk period of N loss, contributing to more than one third of the total annual loss amount. Using end-member mixing analysis model(EMMA), we found groundwater(whose discharge accounted for 25% of the catchment streamflow) was an important source for the N loss in the agricultural catchment. Even in this catchment with coexisting upland and paddy field ecosystems, identified end-members could be used to predict the N load well(R~20.87, p0.001). These results can deepen our understanding of the relationship between hydrological process and N transport in the red soil critical zone and are also helpful to improve the water and fertilizer management in subtropical agricultural catchment.  相似文献   

基于引文分析法的“点-轴系统”理论研究述评     

李满春  姚梦汝  汪侠  刘小强  陈焱明 《地理科学进展》2019,38(2):164-174

论文采用引文分析法,对陆大道院士所著《关于“点-轴”空间结构系统的形成机理分析》一文的349篇引文进行分析,从引文数量、引文作者、发文期刊、研究案例地、学科领域、研究主题、引用动机7个方面,探究“点-轴系统”理论的研究现状。结果表明：自2002年以来,“点-轴系统”理论的引文数量整体呈上升趋势,研究主题聚焦于区域经济和旅游发展;研究案例地以省级和市级中观尺度为主,多为单一型研究区,主要集中在西北丝绸之路经济带、东北辽宁经济圈、西南藏滇川渝、东部长三角四大热点区域;引文质量普遍较高,并且具有多学科交叉应用的特点,但批判性思考和创造性提升相对较少。基于此,论文从拓展研究和实践应用2个角度对“点-轴系统”理论未来发展进行了展望,以期为相关研究提供参考。  相似文献   

Precise Determination of Astronomical Azimuth by the Hour Angle Method of Multiple Meridian Stars     

《Chinese Astronomy and Astrophysics》2020,44(4):536-548

  相似文献