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   

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

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2003-2016年北极净初级生产力时空变化     

李海丽  柯长青  朱庆辉  舒苏 《海洋学报(英文版)》2019,38(8):111-121

The area of Arctic sea ice has dramatically decreased, and the length of the open water season has increased;these patterns have been observed by satellite remote sensing since the 1970 s. In this paper, we calculate the net primary productivity(NPP, calculated by carbon) from 2003 to 2016 based on sea ice concentration products,chlorophyll a(Chl a) concentration, photosynthetically active radiation(PAR), sea surface temperature(SST), and sunshine duration data. We then analyse the spatiotemporal changes in the Chl a concentration and NPP and further investigate the relations among NPP, the open water area, and the length of the open water season. The results indicate that(1) the Chl a concentration increased by 0.025 mg/m~3 per year;(2) the NPP increased by 4.29 mg/(m~2·d) per year, reaching a maximum of 525.74 mg/(m~2·d) in 2016; and(3) the Arctic open water area increased by 57.23×10~3 km~2/a, with a growth rate of 1.53 d/a for the length of the open water season. The annual NPP was significantly positively related to the open water area, the length of the open water season and the SST.The daily NPP was also found to have a lag correlation with the open water area, with a lag time of two months.With global warming, NPP has maintained an increasing trend, with the most significant increase occurring in the Kara Sea. In summary, this study provides a macroscopic understanding of the distribution of phytoplankton in the Arctic, which is valuable information for the evaluation and management of marine ecological environments.  相似文献   

Research on the Methods of Performance Monitoring and Evaluation for Active Hydrogen Maserstwo     

《Chinese Astronomy and Astrophysics》2019,43(2):292-304

Active hydrogen maser is the main frequency standard for establishing and maintaining the time scale. It has the characteristics of high short-term stability and low phase noise. At present, it plays an increasingly important role in the international atomic time (TAI) and various local time scales. Firstly, in combination with the internal state parameters of an active hydrogen maser, the correlation between the internal state parameters and the comparison data of a hydrogen maser is analyzed, and a method for the performance monitoring of a hydrogen maser is proposed. Secondly, according to the characteristics of hydrogen maser performance, a method for evaluating the performance of a hydrogen maser is given. The hydrogen maser performance includes mainly two aspects, namely the frequency stability and predictability. The performances of two types of active hydrogen masers (CH1-75 and MHM-2010) are evaluated by this method. The correlation analysis of the atomic clock state parameters and comparison data shows that the state parameter monitoring can effectively predict the variation of the hydrogen maser performance. The evaluation results of atomic clock frequency stability and predictability show that the atomic clock with a higher medium-and-long term frequency stability has a better predictability. There are two methods for the predictability evaluation, one is based on the data published by BIPM (Bureau International des Poids et Measures), and another one is based on the quadratic model. Both methods are consistent with the weights published by BIPM. Therefore, the two methods can be used as a quantitative method to evaluate the predictability of a hydrogen maser.  相似文献   

Research on Parallel Algorithms for uv-faceting Imaging     

《Chinese Astronomy and Astrophysics》2019,43(3):424-443

The uv-faceting imaging is one of the widely used large field of view imaging technologies, and will be adopted for the data processing of the low-frequency array in the first stage of the Square Kilometre Array (SKA1). Due to the scale of the raw data of SKA1 is unprecedentedly large, the efficiency of data processing directly using the original uv-faceting imaging will be very low. Therefore, a uv-faceting imaging algorithm based on the MPI (Message Passing Interface)+OpenMP (Open Multi-Processing) and a uv-faceting imaging algorithm based on the MPI+CUDA (Compute Unified Device Architecture) are proposed. The most time-consuming data reading and gridding in the algorithm are optimized in parallel. The verification results show that the results of the proposed two algorithms are basically consistent with that obtained by the current mainstream data processing software CASA (Common Astronomy Software Applications), which indicates that the proposed two algorithms are basically correct. Further analysis of the accuracy and total running time shows that the MPI+CUDA method is better than the MPI+OpenMP method in both the correctness rate and running speed. The performance test results show that the proposed algorithms are effective and have certain extensibility.  相似文献   

Classification of yearly extreme precipitation events and associated flood risk in the Yangtze-Huaihe River Valley     

Zhiqing Xie  Yin Du  Yan Zeng  Qian Miao 《中国科学:地球科学(英文版)》2018,61(9):1341-1356

Fifty cases of regional yearly extreme precipitation events(RYEPEs)were identified over the Yangtze-Huaihe River Valley(YHRV)during 1979–2016 applying the statistical percentile method.There were five types of RYEPEs,namely Yangtze Meiyu(YM-RYEPE),Huaihe Meiyu(HM-RYEPE),southwest-northeast-oriented Meiyu(SWNE-RYEPE)and typhoon I and II(TC-RYEPE)types of RYEPEs.Potential vorticity diagnosis showed that propagation trajectories of the RYEPEs along the Western Pacific Subtropical High and its steering flow were concentrated over the southern YHRV.As a result,the strongest and most frequently RYEPEs events,about 16–21 cases with average rainfall above 100 mm,occurred in the southern YHRV,particularly in the Nanjing metropolitan area.There have been 14 cases of flood-inducing RYEPEs since 1979,with the submerged area exceeding 120 km~2as simulated by the Flood Area hydraulic model,comprising six HM-RYEPEs,five YM-RYEPEs,two TC-RYEPEs,and one SWNE-RYEPE.The combination of evolving RYEPEs and rapid expansion of urban agglomeration is most likely to change the flood risk distribution over the Nanjing metropolitan area in the future.In the RCP6.0(RCP8.5)scenario,the built-up area increases at a rate of about 10.41 km~2(10 yr)~(-1)(24.67 km~2(10 yr)~(-1))from 2010 to 2100,and the area of high flood risk correspondingly increases from 3.86 km~2(3.86 km~2)to 9.00 km~2(13.51 km~2).Areas of high flood risk are mainly located at Chishan Lake in Jurong,Lukou International Airport in Nanjing,Dongshan in Jiangning District,Lishui District and other low-lying areas.The accurate simulation of flood scenarios can help reduce losses due to torrential flooding and improve early warnings,evacuation planning and risk analysis.More attention should be paid to the projected high flood risk because of the concentrated population,industrial zones and social wealth throughout the Nanjing metropolitan area.  相似文献   

Hydrologic implications of the isotopic kinetic fractionation of open-water evaporation     

Wei Xiao  Yufei Qian  Xuhui Lee  Wei Wang  Mi Zhang  Xuefa Wen  Shoudong Liu  Yongbo Hu  Chengyu Xie  Zhen Zhang  Xuesong Zhang  Xiaoyan Zhao  Fucun Zhang 《中国科学:地球科学(英文版)》2018,61(10):1523-1532

The kinetic fractionation of open-water evaporation against the stable water isotope H_2 ~(18)O is an important mechanism underlying many hydrologic studies that use ~(18)O as an isotopic tracer. A recent in-situ measurement of the isotopic water vapor flux over a lake indicates that the kinetic effect is much weaker(kinetic factor 6.2‰) than assumed previously(kinetic factor14.2‰) by lake isotopic budget studies. This study investigates the implications of the weak kinetic effect for studies of deuterium excess-humidity relationships, regional moisture recycling, and global evapotranspiration partitioning. The results indicate that the low kinetic factor is consistent with the deuterium excess-humidity relationships observed over open oceans.The moisture recycling rate in the Great Lakes region derived from the isotopic tracer method with the low kinetic factor is a much better agreement with those from atmospheric modeling studies than if the default kinetic factor of 14.2‰ is used. The ratio of transpiration to evapotranspiration at global scale decreases from 84±9%(with the default kinetic factor) to 76±19%(with the low kinetic factor), the latter of which is in slightly better agreement with other non-isotopic partitioning results.  相似文献   

多种海洋开发类型的综合效益评估     

高升  徐敏  刘佰琼  曹广喜  赵林 《海洋通报》2018,(1):17-24

随着海洋开发活动的不断加剧,各海洋开发类型综合效益的评估与分析对维持海洋社会经济与海洋生态环境的可持续发展具有重大意义,不同海洋开发活动带来不同的社会、经济效益,也产生了海洋资源的损耗,影响了海洋环境和海洋生态服务功能。根据江苏省海洋资源开发活动特点,筛选出江苏海岸带资源开发中常见的4种典型的开发利用类型,选取了能够突出反映海洋开发活动综合效益的经济效益指标、社会效益指标、资源损耗指标、环境成本指标构建海洋开发类型综合效益评估体系。基于层次分析法与熵权法组合权重,运用综合效益指数评价模型分别计算了单一指标效益值、准则层效益值、各研究案例效益值、各用海类型效益值并对以上研究数据之间的相互关系进行了深入分析,探求各用海类型综合效益评估值的关键影响因素。通过实证研究发现4种海洋开发类型的综合效益评估值均介于0.4~0.6之间,处于一般的综合效益状态,综合效益从高到底依次排序:临港工业用海类型为0.551 3、海上风电用海类型为0.492 4、排污倾倒用海类型为0.441、围海养殖用海类型为0.434 3。海洋开发类型综合效益的评估对及时调整海洋开发对策,缓和海洋开发与海洋生态环境的矛盾具有积极意义。  相似文献   

Estimating the properties of weathered bedrock and pilerock interaction from the geological strength index     

Chun-mei Zhou  Wei Shao  Kun-long Yin  Zong-ji Yang 《山地科学学报》2018,15(8):1757-1776

The effect of variable rock mass properties on pile-rock interaction poses a great challenge to the design of stabilizing piles and numerical analysis of pile-rock interaction. The paper presents a novel method to estimate the properties of weathered bedrock, which can be applied to routine design of landslide-stabilizing piles for collivial landslides. The Ercengyan landslide located in the Three Gorges Reservoir, China, is the area of interest for this study. A geological investigation and triaxial tests were conducted to estimate the basic parameters, including Geological Strength Index(GSI), uniaxial compressive strength σ_(ci) and Hoek-Brown constant m_i of intact bedrock in the study area. Hoek-Brown criterion was used to estimate mechanical properties of the weathered rock, including elastic modulus E_m, cohesion c, friction angle Φ, and normal ultimate lateral resistance p_(max). A parametric study was performed to evaluate the effect of parameterizations of GSI, σ_(ci) and m_i on the bedrock properties and p-y curves. The estimated rock mass properties were used with PLAXIS 2D software to simulate pile-rock interaction. Effect of GSI on stress at the pile-rock interface and in the rock, pile bending moment, pile shear force, and p-y curve were analysed.  相似文献