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Statistical properties of radio flux densities of solar flares

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Research in Astronomy and Astrophysics 2020年第11期20卷 239-251页

作者： Lu Wang Si-Ming Liu Zong-Jun Ning Purple Mountain Observatory Nanjing 210000China Key Laboratory of Dark Matter and Space Astronomy Nanjing 210000China University of Science and Technology of China Heifei 100049China

Short timescale flux variations are closely related to the energy release process of magnetic reconnection during solar *** light curves at 1,2,3.75,9.4,and 17 GHz of 209 flares observed by the Nobeyama Radio Polarimeter from 2000 to 2010 are analyzed with a running smooth *** find that the impulsive component(with a variation timescale shorter than 1 s)of 1 GHz emission of most flares peaks at a few tens of solar flux unit and lasts for about 1 minute and the impulsive component of 2 GHz emission lasts a shorter period and peaks at a lower flux level,while at the three high frequency channels the occurrence frequency of flares increases with the decrease of the flux density up to the noise level of the corresponding ***,the gradual components of these emissions have similar duration and peak flux density *** also derive the power spectrum on different timescales and a normalized wavelet analysis is used to confirm features on short *** a time resolution of 0.1 s,more than^60%of these radio light curves show significant flux variation on 1 s or shorter time *** fraction increases with the decrease of frequency and reaches^100%at 1 GHz,implying that short timescale processes are universal in solar *** also study the correlation between the impulsive radio flux densities and soft X-ray fluxes obtained with the GOES satellites and find that more than 65%of the flares with an impulsive component have their impulsive radio emission reach a peak value ahead of the soft X-ray fluxes and this fraction increases with the radio frequency.

关键词： methods data analysis Sun flares Sun radio radiation

Network reconstructions with partially available data

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Frontiers of physics 2017年第3期12卷 117-123页

作者： Chaoyang Zhang Yang Chen Gang Hu Departraent of Physics Ningbo University Ningbo 315211 China School of Sciences Beijing University of Posts and Telecommunications Beijing 100876 China Department-of-Physics Beijing- Normal University Beijing 100875 China

Many practical systems in natural and social sciences can be described by dynamical networks. Day by day we have measured and accumulated huge amounts of data from these networks, which can be used by us to further our understanding of the world. The structures of the networks producing these data are often unknown. Consequently, understanding the structures of these networks from available data turns to be one of the central issues in interdisciplinary fields, which is called the network recon- struction problem. In this paper, we considered problems of network reconstructions using partially available data and some situations where data availabilities are not sufficient for conventional network reconstructions. Furthermore, we proposed to infer subnetwork with data of the subnetwork available only and other nodes of the entire network hidden; to depict group-group interactions in networks with averages of groups of node variables available; and to perform network reconstructions with known data of node variables only when networks are driven by both unknown internal fast-varying noises and unknown external slowly-varying signals. All these situations are expected to be common in practical systems and the methods and results may be useful for real world applications.

关键词： network reconstruction dynamics data analysis

Periodicity of the solar radius revisited by using empirical mode decomposition and the Lomb–Scargle method

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Research in Astronomy and Astrophysics 2015年第6期15卷 879-888页

作者： Zhi-Ning Qu Wen Feng Hong-Fei Liang Yunnan Observatories Chinese Academy of Sciences University of Chinese Academy of Sciences Key Laboratory of Solar Activity National Astronomical Observatories CAS Department of Physics School of Science Sichuan University of Science & Engineering Research Center of analysis and Measurement Kunming University of Science and Technology Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University) Ministry of Education Department of Physics Yunnan Normal University

Using the Hilbert-Huang transform and the Lomb-Scargle method, we investigate periodicities in the daily solar radius data during the time interval from February 1978 to October 1999 derived from Caleru Observatory. The following prominent periods are found：（1） the rotation cycle signal; （2） several mid-term periods including 122, 162.9 and 225 days, annual-variation periodicities （319 and 359 days）, quasi-triennial oscillations （3.46 and 3.94 years）; （3） the 11-year Schwabe cycle, which is in anti-phase with solar activity. This result indicates that the strong magnetic field associated with the Sun has a greater inhibitive effect on the radius variation.

关键词： Sun activity -- Sun solar radius -- Sun photosphere -- Sun data analysis

Improved astrometry of space debris with image restoration

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Research in Astronomy and Astrophysics 2014年第8期14卷 992-1000页

作者： Rong-Yu Sun Chang-Yin Zhao Key Laboratory of Space Object and Debris Observation Chinese Academy of Sciences Purple Mountain Observatory Chinese Academy of Sciences

In order to implement an observing strategy, image degradation that occurs during optical observation of space debris is ineluctable and has distinct characteris- tics. Image restoration is presented as a way to remove the influence of degradation in CCD images of space debris, based on assumed PSF models with the same F-WHM as images of the object. In the process of image restoration, the maximum entropy method is adopted. The results of reduction using observed raw CCD images indi- cate that the precision in estimating positions of objects is improved and the effects of degradation are reduced. Improving the astrometry of space debris using image restoration is effective and feasible.

关键词： techniques image processing -- space vehicles -- astrometry -- methods data analysis

A Study on Non-coplanar Baseline Effects for Mingantu Spectral Radioheliograph

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Research in Astronomy and Astrophysics 2022年第10期22卷 111-118页

作者： Qiu-Ping Yang Feng Wang Hui Deng Ying Mei Wei Wang Yunnan Observatories Chinese Academy of SciencesKunming 650216China Faculty of Information Engineering and Automation Kunming University of Science and TechnologyKunming 650500China University of Chinese Academy of Sciences Beijing 100049China Center of Astrophysics Guangzhou UniversityGuangzhou 510006China National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China

As a dedicated solar radioheliograph,the MingantU SpEctral RadioHeliograph(MUSER)has a maximum baseline of more than 3000 m and a frequency range of 400 MHz–15 *** to the classical radio interferometry theory,the non-coplanar baseline effect(i.e.,w-term effect)would be considered and calibrated for such a radio ***,little previous literature made the qualitative or quantitative analyses on w-term effects of solar radioheliograph *** study proposes a complete quantitative analysis of w-term effects for the *** a brief introduction of the MUSER,we systematically investigate the baseline variations over a year and analyze the corresponding variations of *** further studied the effects of the w-term in the imaging for the specified extended source,i.e.,the *** discussed the possible effects of the w-term,such as image distortion and so *** simulated results show that the w-term is an essential and unavoidable issue for solar radio imaging with high spatial resolution.

关键词： instrumentation interferometers-Sun radio radiation-methods data analysis

Identification of the Original Tectonic Setting for Oceanic Andesite Using Discrimination Diagrams:An Approach Based on Global Geochemical data Synthesis

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Journal of Earth Science 2022年第3期33卷 696-705页

作者： Xinyu Liu Qi Zhang Chengli Zhang State Key Laboratory of Continental Dynamics Department of GeologyNorthwest UniversityXi'an 710069China Institute of Geology and Geophysics Chinese Academy of SciencesBeijing 100029China

Systematical analyses of data from GEOROC and PetDB database show that large amount of Cenozoic andesites occurred in the various oceanic environments such as mid-oceanic ridge,plumerelated island and oceanic *** this study,we employed the geochemical data of 351 mid-ocean ridge andesites(MORA),2539 plume-related andesites(PRA)and 3488 oceanic arc andesites(OAA)from the database to discuss the relationship between andesite tectonic settings and their geochemical features,thereby making an attempt to construct tectonic discrimination *** on the data-driven pattern,all available elements were employed to derive logratios for the possible coordinates,and the overlap-rate calculation was adopted to evaluate the discrimination effect of more than 330000 prospective ***,four tectonic discrimination diagrams have been successfully established to identify MORA,PRA and OAA,which can be utilized to identify the original settings of andesite with an age range from Cenozoic to Archean a certain *** these diagrams,PRA is mainly distinguished by high LREE/HREE ratio due to enriched mantle ***,OAA is mainly characterized by high LILE/HFSE ratio,which reveals that fluids derived from subducted slab play an important role in forming oceanic arc ***,the petrogenesis of andesites is closely related to their tectonic ***,it should be noted that those andesites formed in both continental and oceanic environments cannot be effectively distinguished using these *** strongly recommend integrating the discrimination diagrams result with other geological information to reach a comprehensive interpretation of evolution history with those ancient *** paper presents a case study which suggests that data-driven method is a powerful tool for solving geological problems in this’big data’era.

关键词： andesite oceanic arc plume-related island mid-oceanic ridge tectonic discrimination diagrams geochemical data data analysis big data

New open cluster candidates discovered in the XSTPS-GAC survey

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Research in Astronomy and Astrophysics 2018年第3期18卷 77-90页

作者： Jin-Cheng Guo Hua-Wei Zhang Hui-Hua Zhang Xiao-Wei Liu Hai-Bo Yuan Yang Huang Song Wang Li Chen Hai-Bin Zhao Ji-Feng Liu Bing-Qiu Chen Mao-Sheng Xiang Zhi-Jia Tian Zhi-Ying Huo Chun Wang Department of Astronomy Peking University Kavli Institute for Astronomy and Astrophysics Peking University Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences South-Western Institute for Astronomy Research Yunnan University Department of Astronomy Beijing Normal University Shanghai Astronomical Observatory Chinese Academy of Sciences Purple Mountain Observatory Chinese Academy of Sciences

The Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center（XSTPS-GAC）is a photometric sky survey that covers nearly 6000 deg^2 towards the Galactic Anti-center（GAC） in the g,r,i bands. Half of its survey field is located on the Galactic Anti-center disk,which makes XSTPSGAC highly suitable to search for new open clusters in the GAC region. In this paper,we report new open cluster candidates discovered in this survey,as well as properties of these open cluster candidates,such as age,distance and reddening,derived by isochrone fitting in the color-magnitude diagram（CMD）.These open cluster candidates are stellar density peaks detected in the star density maps by applying the method from Koposov et al. Each candidate is inspected in terms of its true color image composed from three XSTPS-GAC band images. Then its CMD is checked,in order to identify whether the central region stars have a clear isochrone-like trend differing from background stars. The parameters derived from isochrone fitting for these candidates are mainly based on three band photometry of ***,when these new candidates are able to be seen clearly in 2 MASS data,their parameters are also derived based on the 2 MASS（J-H,J） CMD. There are a total of 320 known open clusters rediscovered and 24 new open cluster candidates discovered in this work. Furthermore,the parameters of these new candidates,as well as another 11 previously known open clusters,are properly determined for the first time.

关键词： open clusters and associations general - Galaxy structure - methods data analysis

AI Enlightens Wireless Communication: Analyses and Solutions for DMRS Channel Estimation

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China Communications 2023年第5期20卷 275-287页

作者： Bule Sun Zhiqin Wang Ang Yang Xiaofeng Liu Shi Jin Peng Sun Rakesh Tamrakar Dajie Jiang Vivo Mobile Communication Co. Ltd.Beijing 100015China China Academy of Information and Communications Technology Beijing 100191China National Mobile Communications Research Laboratory Southeast UniversityNanjing 211189China

In this paper,a systematic description of the artificial intelligence(AI)-based channel estimation track of the 2nd Wireless Communication AI Competition(WAIC)is provided,which is hosted by IMT-2020(5G)Promotion Group 5G+AIWork ***,the system model of demodulation reference signal(DMRS)based channel estimation problem and its corresponding dataset are *** the potential approaches for enhancing the performance of AI based channel estimation are discussed from the viewpoints of data analysis,pre-processing,key components and backbone network *** last,the final competition results composed of different solutions are *** is expected that the AI-based channel estimation track of the 2nd WAIC could provide insightful guidance for both the academia and industry.

关键词： MIMO DMRS channel estimation AI data analysis preprocessing model design

Application of an Error Statistics Estimation Method to the PSAS Forecast Error Covariance Model

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Advances in Atmospheric Sciences 2006年第1期23卷 33-44页

作者： Runhua YANG Jing GUO Lars Peter RIISHФJGAARD Science Systems and Applications Inc. Lanham USA Science Applications International Corporation Beltsville USA Joint Center for Earth Systems Technology/UMBC Baltimore USA Global Modeling and Assimilation Office NASA Goddard Space Flight Center Greenbelt USA

In atmospheric data assimilation systems, the forecast error covariance model is an important component. However, the paralneters required by a forecast error covariance model are difficult to obtain due to the absence of the truth. This study applies an error statistics estimation method to the Pfiysical-space Statistical analysis System （PSAS） height-wind forecast error covariance model. This method consists of two components： the first component computes the error statistics by using the National Meteorological Center （NMC） method, which is a lagged-forecast difference approach, within the framework of the PSAS height-wind forecast error covariance model; the second obtains a calibration formula to rescale the error standard deviations provided by the NMC method. The calibration is against the error statistics estimated by using a maximum-likelihood estimation （MLE） with rawindsonde height observed-minus-forecast residuals. A complete set of formulas for estimating the error statistics and for the calibration is applied to a one-month-long dataset generated by a general circulation model of the Global Model and Assimilation Office （GMAO）, NASA. There is a clear constant relationship between the error statistics estimates of the NMC-method and MLE. The final product provides a full set of 6-hour error statistics required by the PSAS height-wind forecast error covariance model over the globe. The features of these error statistics are examined and discussed.

关键词： forecast error statistics estimation data analysis forecast error covariance model