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Profiling Astronomical Objects Using Unsupervised Learning Approach

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Computers, Materials & Continua 2023年第1期74卷 1641-1655页

作者： Theerapat Sangpetch Tossapon Boongoen Natthakan Iam-On Center of Excellence in AI and Emerging Technologies School of Information TechnologyMae Fah Luang UniversityChiang Rai57100Thailand Department of Computer science Aberystwyth UniversityAberystwythCeredigionUK

Attempts to determine characters of astronomical objects have been one of major and vibrant activities in both astronomy and data science *** of a manual inspection,various automated systems are invented to satisfy the need,including the classification of light curve profiles.A specific Kaggle competition,namely Photometric LSST Astronomical Time-Series Classification Challenge(PLAsTiCC),is launched to gather new ideas of tackling the abovementioned task using the data set collected from the Large Synoptic Survey Telescope(LSST)*** all proposed methods fall into the supervised family with a common aim to categorize each object into one of pre-defined *** this challenge focuses on developing a predictive model that is robust to classifying unseen data,those previous attempts similarly encounter the lack of discriminate features,since distribution of training and actual test datasets are largely *** a result,well-known classification algorithms prove to be sub-optimal,while more complicated feature extraction techniques may help to slightly boost the predictive *** such a burden,this research is set to explore an unsupervised alternative to the difficult quest,where common classifiers fail to reach the 50%accuracy mark.A clustering technique is exploited to transform the space of training data,from which a more accurate classifier can be *** addition to a single clustering framework that provides a comparable accuracy to the front runners of supervised learning,a multiple-clustering alternative is also introduced with improved *** fact,it is able to yield a higher accuracy rate of 58.32%from 51.36%that is obtained using a simple *** this difficult problem,it is rather good considering for those achieved by well-known models like support vector machine(SVM)with 51.80%and Naive Bayes(NB)with only 2.92%.

关键词： Astronomy sky survey light curve data classification data clustering

Internal Magnetic Configuration Measured by ECE Imaging on EAST Tokamak

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Plasma science and Technology 2013年第12期15卷 1189-1193页

作者：徐明闻一之谢锦林俞昌旋高炳西徐小圆刘万东胡立群孙有文钱金平万宝年 CAS Key Laboratory of Plasma Physics University of Science and Technology of China Institute of Plasma Physics Chinese Academy of Sciences

ECE imaging （electron cyclotron emission imaging） is an important diagnostic which can give 2D imaging of temperature fluctuation in the core of tokamak. A method based on ECE imaging is introduced which can give the information of the position of magnetic axis and the structure of internal magnetic surface for EAST tokamak. The EFIT equilibrium reconstruction is not reliable due to the absence of important core diagnostic at the initial phase for EAST, so the information given by ECE imaging could help to improve the accuracy of EFIT equilibrium reconstruction.

关键词： MHD instability internal magnetic configuration ECE imaging

Collecting volunteered geographic information from the Global Navigation Satellite System(GNSS):experiences from the CAMALIOT project

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International Journal of Digital Earth 2023年第1期16卷 2818-2841页

作者： Linda See Benedikt Soja Grzegorz Klopotek Tobias Sturn Rudi Weinacker Santosh Karanam Ivelina Georgieva Yuanxin Pan Laura Crocetti Markus Rothacher Vicente Navarro Steffen Fritz Ian McCallum Novel Data Ecosystems for Sustainability Research Group International Institute for Applied Systems Analysis(IIASA)LaxenburgAustria Institute of Geodesy and Photogrammetry ETH ZurichZurichSwitzerland Navigation science office European Space Agency(ESA)MadridSpain

Raw observations(carrier-phase and code observations)from the Global Navigation Satellite System(GNSS)can now be accessed from Android mobile phones(Version 7.0 onwards).This paves the way for GNSS data to be utilized for low-cost precise positioning or in ionospheric or tropospheric *** paper presents results from data collection campaigns using the CAMALIOT mobile *** the frst campaign,116.3 billion measurements from 11,828 mobile devices were collected from all *** participation decreased during the second campaign,data are still being collected *** this contribution,we demonstrate the potential of volunteered geographic information(VGl)from mobile phones to fill data gaps in geodetic station networks that collect GNSS data,*** Brazil,but also how the data can provide a denser set of observations than current networks in countries across *** also show that mobile phones capable of dual-frequency reception,which is an emerging technology that can provide a richer source of GNSS data,are contributing in a substantial ***,we present the results from a survey of participants to indicate that participation is diverse in terms of backgrounds and geography,where the dominant motivation for participation is to contribute to scientific research.

关键词： Citizen science crowdsourcing volunteered geographicinformation(VGl) global navigation satellite system(GNSS) mobile apps Earth observation

Linear gyrokinetic simulations of reversed shear Alfvén eigenmodes and ion temperature gradient modes in DIII-D tokamak

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Plasma science and Technology 2021年第1期23卷 32-38页

作者： Hongyu WANG Pengfei LIU Zhihong LIN Wenlu ZHANG fusion Simulation Center Peking UniversityBeijing 100871People’s Republic of China Department of Physics and Astronomy University of CaliforniaIrvineCA 92697United States of America Institute of Physics Chinese Academy of SciencesBeijing 100190People’s Republic of China

Global linear gyrokinetic simulations using realistic DIII-D tokamak geometry and plasma profiles find co-existence of unstable reversed shear Alfvén eigenmodes(RSAE)with low toroidal mode number n and electromagnetic ion temperature gradient(ITG)instabilities with higher toroidal mode number *** intermediate n?=?[10,12],RSAE and ITG co-exist and overlap weakly in the radial domain with similar growth rates but different real *** RSAE and ITG growth rates decrease less than 5%when compressible magnetic perturbations are neglected in the *** ITG growth rates increase less than 7%when fast ions are not included in the ***,the effects of trapped electrons on the RSAE are negligible.

关键词： fast ions gyrokinetic simulation reversed shear Alfvén eigenmodes microturbulence

Gyrokinetic simulations of nonlinear interactions between magnetic islands and microturbulence

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Plasma science and Technology 2019年第11期21卷 7-16页

作者： Kaisheng FANG Jian BAO Zhihong LIN fusion Simulation Center Peking UniversityBeijing 100871People’s Republic of China Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190People’s Republic of China University of Chinese Academy of sciences Beijing 100049People’s Republic of China Department of Physics and Astronomy University of CaliforniaIrvineCA 92697United States of America

A conservative scheme of kinetic electrons for gyrokinetic simulations in the presence of magnetic islands has been implemented and verified in the gyrokinetic toroidal code, where zonal and nonzonal components of all perturbed quantities are solved together. Using this new conservative scheme, linear simulation of kinetic ballooning mode has been successfully benchmarked with the electromagnetic hybrid model. Simulations of nonlinear interactions between magnetic islands and the ion temperature gradient(ITG) mode in a tokamak show that the islands rotate at the electron diamagnetic drift velocity. The linear ITG structure shifts from the island O-point toward the X-point due to the pressure flattening effect inside the islands, and the nonlinear ITG structure peaks along the magnetic island separatrix because of the increased pressure gradient there.

关键词： gyrokinetic simulations magnetic islands microturbulence

Trajectory sampling and finite-size effects in first-principles stopping power calculations

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npj Computational Materials 2023年第1期9卷 238-246页

作者： Alina Kononov Thomas W.Hentschel Stephanie B.Hansen Andrew D.Baczewski Center for Computing Research Sandia National LaboratoriesAlbuquerqueNMUSA School of Applied&Engineering Physics Cornell UniversityIthacaNYUSA Pulsed Power sciences Center Sandia National LaboratoriesAlbuquerqueNMUSA

Real-time time-dependent density functional theory(TDDFT)is presently the most accurate available method for computing electronic stopping powers from first ***,obtaining application-relevant results often involves either costly averages over multiple calculations or ad hoc selection of a representative ion *** consider a broadly applicable,quantitative metric for evaluating and optimizing trajectories in this *** methodology enables rigorous analysis of the failure modes of various common trajectory choices in crystalline *** randomly selecting trajectories is common practice in stopping power calculations in solids,we show that nearly 30%of random trajectories in an FCC aluminum crystal will not representatively sample the material over the time and length scales feasibly simulated with TDDFT,and unrepresentative choices incur errors of up to 60%.We also show that finite-size effects depend on ion trajectory via“ouroboros”effects beyond the prevailing plasmon-based interpretation,and we propose a cost-reducing scheme to obtain converged results even when expensive core-electron contributions preclude large *** work helps to mitigate poorly controlled approximations in first-principles stopping power calculations,allowing 1–2 order of magnitude cost reductions for obtaining representatively averaged and converged results.

关键词： size prevailing selecting

Ab initio study of H and He migrations in β-phase Sc,Y,and Er hydrides

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Chinese Physics B 2012年第5期21卷 464-472页

作者：陈汝承杨莉代云雅朱自强彭述明龙兴贵高飞祖小涛 Department of Applied Physics University of Electronic Science and Technology of China Pacific Northwest National Laboratory P.O.Box 999Richland WA 99352USA Institute of Nuclear Physics and Chemistry China Academy of Engineering Physics

Ab initio calculations based on the density functional theory have been performed to investigate the migrations of hydrogen（H） and helium（He） atoms in β-phase scandium（Sc）,yttrium（Y）,and erbium（Er） hydrides with three different ratios of H to *** results show that the migration mechanisms of H and He atoms mainly depend on the crystal structures of hydrides,but their energy barriers are affected by the host-lattice in metal *** formation energies of octahedral-occupancy H（H oct） and tetrahedral vacancy（V tet） pairs are almost the same（about 1.2 eV）.It is of interest to note that the migration barriers of H increase with increasing host-lattice atomic *** addition,the results show that the favorable migration mechanism of He depends slightly on the V tet in the Sc hydride,but strongly on that in the Y and Er hydrides,which may account for different behaviours of initial He release from ScT2 and ErT2.

关键词： hydrogen helium metal hydride ab initio calculation

Effect of Hyper-Resistivity on Nonlinear Tearing Modes

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Chinese Physics Letters 2018年第6期35卷 37-40页

作者： Wen Yang Ding Li Xue-qiao Xu Institute of Physics Chinese Academy of Sciences Beijing 100190 University of Chinese Academy of sciences Beijing 100049 Lawrence Livermore National Laboratory Livermore California 94550 USA

We analytically investigate nonlinear tearing modes with the anomalous electron viscosity or,as it is normally called,*** contrast to the flux average method used by previous work,we employ the standard singular perturbation technique and a quasilinear method to obtain the time evolution equation of tearing *** result that the magnetic flux grows with time in a scaling as t^（2/3）demonstrates that nonlinear tearing modes with the hyper-resistivity effect alone have a weaker dependence on time than that of the corresponding resistive case.

关键词： Effect of Hyper-Resistivity on Nonlinear Tearing Modes

Magnetic probe diagnostics of nonlinear standing waves and bulk ohmic electron power absorption in capacitive discharges

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Plasma science and Technology 2021年第11期23卷 74-83页

作者： Kai ZHAO Yongxin LIU Quanzhi ZHANG Demetre J ECONOMOU Younian WANG Key Laboratory of Materials Modification by Laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024People's Republic of China Plasma Processing Laboratory William A.Brookshire Department of Chemical and Biomolecular EngineeringUniversity of HoustonHoustonTexas 77204-4004United States of America

It is recognized that standing wave effects appearing in large-area,very-high-frequency capacitively coupled plasma(CCP)reactors cause center-high plasma *** a high-frequency magnetic probe,we present a direct experimental diagnostic of the nonlinear standing waves and bulk ohmic electron power absorption dynamics in low pressure CCP discharges for different driving frequencies of 13.56,30,and 60 *** design,principle,calibration,and validation of the probe are described in *** structures of the harmonics of the magnetic field,determined by the magnetic probe,were used to calculate the distributions of the harmonic current and the corresponding ohmic electron power deposition,providing insights into the behavior of nonlinear *** a low driving frequency,i.e.13.56 MHz,no remarkable nonlinear standing waves were identified and the bulk ohmic electron power absorption was observed to be *** harmonic magnetic field/current was found to increase dramatically with the driving frequency,due to decreased sheath reactance and more remarkable nonlinear standing waves at a higher driving frequency,leading to the enhancements of the ohmic heating and the plasma density in the bulk,specifically at the electrode *** a high driving frequency,i.e.60 MHz,the high-order harmonic current density and the corresponding ohmic electron power absorption exhibited a similar node structure,with the main peak on axis,and one or more minor peaks between the electrode center and the edge,contributing to the center-high profile of the plasma density.

关键词： capacitively coupled plasmas magnetic probe nonlinear standing waves ohmic heating