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   

Temporal and Spatial Dynamics Analysis of Grassland Ecosystem Pressure in Kazakhstan     

WEN Xin  YAN Huimin  XIE Xiaoping  DU Wengpeng  LAI Chenxi  ZHEN Lin 《资源与生态学报(英文版)》2019,10(6):667-675

Affected by climate change and policy factors, Kazakhstan is the country with the most severe ecological degradation and grassland conflicts in Central Asia. Therefore, studying the state of grassland carrying resources in Kazakhstan is particularly important for understanding the responses of grassland ecosystems to climate change and human activities. Based on Kazakhstan's remote sensing data and animal husbandry statistics, this study analyzes the patterns of changes in grassland ecosystems in Kazakhstan based on the supply and consumption of these ecosystems. The results show that: 1) From 2003 to 2017, the number of livestock raised in Kazakhstan showed a trend of sustained and steady growth. Due to freezing damage, the scale of livestock farming decreased in 2011, but a spatial difference in the livestock farming structure was not obvious. 2) The fluctuation of grassland supply in Kazakhstan has increased, while the consumption due to animal husbandry has also continued to increase, resulting in an increasing pressure on the grassland carrying capacity. 3) Between 2003 and 2017, the overall grassland carrying status of Kazakhstan have been abundant, but the grassland carrying pressure index has shown a steadily increasing trend, the grassland carrying pressure is growing, and it is mainly determined by grassland productivity. The greater pressure in lower Kyzylorda state, the southern Kazakhstan state of the cultivated land and the northern Kazakhstan state has gradually expanded to include the agro-pastoral zone and the semi-desert zone.  相似文献   

Locality Attributes and Networks Serving to Reveal Amazonian Urbanization beyond the Cities     

Ana Paula Dal'Asta  Silvana Amaral 《Geographical review》2019,109(2):199-223

Beyond the Amazonian cities, distinct spatial units arranged in networks compose an extended urban space, usually invisible to government agencies and public polities. This article empirically reveals this space by studying the localities’ characteristics and connections. In southwestern Pará, Brazil, 236 communities were sampled using field expeditions. Variables related to the locality organization, history, health and education services, urban infrastructure, and land use were explored in a fuzzy cluster analysis. Local production and consumption flows were considered in the locality network analysis. The fuzzy analysis allowed identifying a hierarchy of localities for which the geographical location influences the spatial distribution patterns of five groups. On the other hand, consumption and production networks identified different locality's articulations, with persistent dependence on cities. These results characterize extensive urbanization at the local level and highlights the participation of the local populations configuring the Amazonian territory.  相似文献   

贵州安龙县耕地土壤几种有效态与对应全量、pH值、有机质的相关分析          下载免费PDF全文

鲍大忠  游桂芝  袁盛博 《贵州地质》2020,37(4):546-550

为了掌握快速路瓶颈路段异质交通流的演变规律，以缓解交通拥堵，本文以快速路上匝道瓶颈路段为研究对象，构建了考虑安全距离的改进NaSch上匝道模型，利用数值仿真，对不同场景交通流演化过程进行系统性研究。仿真结果显示：在不同条件下，异质交通流中自动驾驶车辆比例的增加对瓶颈路段交通运营状态影响结果各异。在自由流阶段，自动驾驶车辆比例的增加对快速路瓶颈路段运营通行能力的增加无显著影响，自动驾驶车辆比例取0.9时，瓶颈路段运营通行能力反而降低了2.48%；在交通拥堵状态下，当异质交通流中自动驾驶车辆比例达到0.7及以上时，才有助于交通拥堵的消散，且其临界值随交通拥堵状态程度的提高而增大；当交通密度达到100 veh/km以上时，自动驾驶车辆比例的增加无法实质性改善瓶颈路段交通拥堵状态。研究结果可为异质交通流环境下的快速路上匝道瓶颈路段的治堵策略提供理论依据。  相似文献   

Formation of Carbon-Enhanced Metal-Poor RR Lyrae Stars     

《Chinese Astronomy and Astrophysics》2020,44(1):61-69

Carbon-enhanced metal-poor (CEMP) stars are considered to be related to the first generation of stars, and responsible for the chemical evolution of the early Galaxy. More than half of them are in binaries, and could be explained by the binary evolution, but the formation channel of them is still not fully understood. Among the hundreds of CEMP stars, there are nine CEMP RR Lyrae stars identified, and at least seven of which are very likely not binaries. The usual binary star evolution channel is difficult to produce such a single star, particularly that of carbon enrichment. One way in which such a single star might be produced is the merger of a helium white dwarf with a Hertzsprung gap (HG) star. We use a stellar evolution program to calculate the models of the merger remnants, and find that the models can reproduce the observed distribution of these CEMP single RR Lyrae stars in terms of surface temperature, gravity, and carbon abundance. Hence, it is extremely possible that the helium white dwarf and HG star merger model is one of the formation channels of the metal-poor carbon-rich RR Lyrae stars.  相似文献   

Local meteoric water lines describe extratropical precipitation     

Devin F. Smith  Elsa Saelens  Deborah L. Leslie  Anne E. Carey 《水文研究》2021,35(2):e14059

Stable water isotopes δ¹⁸O and δ²H are used to investigate precipitation trends and storm dynamics to advance knowledge of precipitation patterns in a warming world. Herein, δ¹⁸O and δ²H were used to determine the relationship between extratropical cyclonic precipitation and local meteoric water lines (LMWLs) in the eastern Ohio Valley and the eastern United States. Precipitation volume weighted and unweighted central Ohio LMWLs, created with samples collected during 2012–2018, showed that temperature had the greatest effect on precipitation isotopic composition. HYSPLIT back trajectory modelling showed that precipitation was primarily derived from a mid-continental moisture source. Remnants of major hurricanes were collected as extratropical precipitation during the 2012–2018 sampling period in central Ohio. Extratropical precipitation samples were not significantly different from the samples that created the central Ohio LMWL. Six additional LMWLs were derived from United States Geological Survey (USGS) Atmospheric Integrated Research Monitoring Network (AIRMoN) samples collected in Pennsylvania, Delaware, Tennessee, Vermont, New Hampshire, and Oxford, Ohio. Meteoric water lines describing published samples from Superstorm Sandy, plotted with these AIRMoN LMWLs, showed isotopic composition of Superstorm Sandy precipitation was commonly more depleted than the average isotopic composition at the mid-latitude locations. Meteoric water lines describing the Superstorm Sandy precipitation were not significantly different in slope from LMWLs generated within 300 km of the USGS AIRMoN site. This finding, which was observed across the eastern Ohio Valley and eastern United States, demonstrated a consistent precipitation δ²H–δ¹⁸O relationship for extratropical cyclonic and non-cyclonic events. This work also facilitates the analysis of storm development based on the relationship between extratropical event signature and the LMWL. Analysis of extratropical precipitation in relation to LMWLs along storm tracks allows for stronger development of precipitation models and understanding of which climatic and atmospheric factors determine the isotopic composition of precipitation.  相似文献   

Evaluation of the temporal variations of groundwater storage and its interactions with climatic variables using GRACE data and hydrological models: A study from Turkey     

Behnam Khorrami  Orhan Gunduz 《水文研究》2021,35(3):e14076

Monitoring of the fluctuations of groundwater storage is particularly important in arid and semi-arid regions where water scarcity brings about various challenges. Remote sensing data and techniques play a preponderant role in developing solutions to environmental problems. The launch of Gravity Recovery and Climate Experiment (GRACE) satellites has eased the remote monitoring and evaluation of groundwater resources with an unprecedented precision over large scales. Within the scope of the current study, the latest release (RL06) of GRACE mass concentrations (Mascons) from Jet Propulsion Laboratory (JPL) dataset as well as Global Land Data Assimilation System (GLDAS) models of Noah and Catchment Land Surface Model (CLSM) were used to provide Groundwater Storage Anomalies (GWSA) over Turkey. The temporal interactions of the estimated GWSA with the climatic variables of precipitation and temperature (derived from the reanalysis datasets of CHELSA [Climatologies at High resolution for the Earth's Land Surface Areas] and FLDAS [the Famine Early Warning Systems Network Land Data Assimilation System], respectively) were investigated statistically. The results suggest that there is a descending trend (from 2003 to 2016) for Terrestrial Water Storage Anomalies (TWSA) and GWSA over Turkey with a total loss of 11 and 6 cm of water, respectively. The statistical analysis results also indicate that the monthly variations of GWSA over Turkey are highly correlated with precipitation and temperature at 2-month lag. The analysis of the climatology (long-term) values of monthly GWSA, precipitation and temperature also revealed high agreement between the variables.  相似文献   

基态位涡径向分布对浅水涡旋系统演变的影响分析Part Ⅱ:扰动发展和结构变化          下载免费PDF全文

刘爽  钟玮  刘宇迪 《地球物理学报》2018,61(9):3592-3606

本文在基态位涡（Potential Vorticity，PV）径向分布和基态涡旋强度对热带气旋（Tropical Cyclone，TC）类涡旋系统稳定性特征影响的研究基础上，结合理想试验和数值模拟诊断分析基态PV径向分布对扰动增长和系统结构变化的影响.基于线性正压浅水模型，设计三种典型基态PV中空结构下基态涡旋强度对系统稳定性影响的敏感性试验.结果表明：基态涡旋的强度主要影响稳定性的强弱，强度越强，不稳定增长率越大，而基态PV径向分布对系统最不稳定波动性质起着决定作用.分析不同波数下扰动的发展及不同波数间扰动的相互作用可知，对于宽且实的PV环，系统稳定性主要取决于低波数不稳定，且最不稳定波数扰动的发展具有明显的优势地位；对于窄且空的PV环，系统稳定性主要取决于高波数不稳定，且多个高波数下增长最快模态的不稳定增长率值十分接近.利用模态线性叠加法讨论扰动增长对系统结构变化的影响表明：最不稳定波数的扰动发展对系统结构变化有关键影响，而多个波数的扰动不稳定增长相当时，不同波数的扰动发生相互作用从而影响系统结构变化.最后，利用实际个例模拟资料分析基态PV径向分布及其变化对TC结构和强度的影响表明：TC内核区出现的多边形眼墙结构与当前时刻基态PV径向分布所决定的最不稳定波数有很好的对应关系，同时基态PV径向分布变化所反映出的系统动力稳定性强弱与TC强度发展阶段具有很好的相关性.  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   

一种旋转塑性势面模型及非关联塑性流动法则     

徐日庆  蒋佳琪  冯苏阳  鞠露莹 《岩土力学》2020,41(5):1474-1482

为了较好地描述软土塑性应变发展规律，提出了一种改进的塑性流动模型。该模型采用了与屈服函数形式相同，但具有一定倾角 的塑性势函数。土体在变形过程中，塑性流动方向会依赖于塑性势面的旋转而变化，直至达到破坏状态。通过对常规三轴试验结果的分析可以发现：在剪切过程中，塑性势面旋转角的初值 与终值 较为稳定，不受围压变化影响。在此试验观察基础上，引入了归一化的旋转角参数 以及描述土体应力状态的参数 ，在采用蛋形势函数的情况下二者具有良好的分段线性关系。利用该关系，建立了改进的塑性流动法则，只需要2个额外的模型参数。对所提出的塑性流动模型进行了验证，计算结果表明该模型能较好地反映塑性应变的变化趋势。  相似文献