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Primordial non-Gaussianity from LAMOST surveys

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Research in Astronomy and Astrophysics 2010年第2期10卷 107-115页

作者： Yah Gong Xin Wang Zheng Zheng xue-lei chen National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Graduate University of Chinese Academy of Sciences Beijing 100049 China Institute for Advanced Study Einstein Drive Princeton NJ 08540 USA Center of High Energy Physics Peking University Beijing 100871 China Kavli Institute for Theoretical Physics China CAS Beijing 100190 China

The primordial non-Gaussianity （PNG） in the matter density perturbation is a very powerful probe of the physics of the very early Universe. The local PNG can induce a distinct scale-dependent bias on the large scale structure distribution of galaxies and quasars, which could be used for constraining it. We study the detection limits of PNG from the surveys of the LAMOST telescope. The cases of the main galaxy survey, the luminous red galaxy （LRG） survey, and the quasar survey of dif- ferent magnitude limits are considered. We find that the Mainl sample （i.e. the main galaxy survey which is one magnitude deeper than the SDSS main galaxy survey, or r 〈 18.8） could only provide a very weak constraint on PNG. For the Main2 sample （r 〈 19.8） and the LRG survey, the 2or （95.5%） limits on the PNG parameter fNL are ｜ fNL｜〈 145 and ｜ fNL｜〈 114 respectively, which are comparable to the current limit from cosmic microwave background （CMB） data. The quasar survey could provide a much more stringent constraint, and we find that the 2a limit for ｜fNL｜ is between 50 and 103, depending on the magnitude limit of the survey. With Planck-like priors on cosmological parameters, the quasar survey with g 〈 21.65 would improve the constraint to I fNLI 〈 43 （2or）. We also discuss the possibility of further tightening the constraint by using the relative bias method proposed by Seljak.

关键词： cosmology: large scale structure

Cosmological constraint on Brans-Dicke Model

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Research in Astronomy and Astrophysics 2015年第12期15卷 2151-2163页

作者： Ji-Xia Li Feng-Quan Wu Yi-Chao Li Yan Gong xue-lei chen National Astronomical Observatories Chinese Academy of Sciences University of Chinese Academy of Sciences Center of High Energy Physics Peking University

We combine new Cosmic Microwave Background （CMB） data from Planck with Baryon Acoustic Oscillation （BAO） data to constrain the Brans-Dicke （BD） the- ory, in which the gravitational constant G evolves with time. Observations of type Ia supernovae （SNela） provide another important set of cosmological data, as they may be regarded as standard candles after some empirical corrections. However, in theories that include modified gravity like the BD theory, there is some risk and complication when using the SNIa data because their luminosity may depend on G. In this paper, we assume a power law relation between the SNIa luminosity and G, but treat the power index as a free parameter. We then test whether the differ- ence in distances measured with SNIa data and BAO data can be reduced in such a model. We also constrain the BD theory and cosmological parameters by making a global fit with the CMB, BAO and SNIa data set. For the CMB＋BAO＋SNIa data set, we find 0.08 × 10-2 〈 ζ 〈 0.33 ×10-2 at the 68% confidence level （CL） and -0.01 × 10-2 〈 ζ〈 0.43 × 10-2 at the 95% CL, where ζ is related to the BD parameter w by ζ = In（1 ＋ 1/w）.

关键词： cosmology: supernovae -- Brans-Dicke -- standard-candle -- BAO

On fitting the full spectrum of luminous red galaxies by using ULySS and STARLIGHT

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Research in Astronomy and Astrophysics 2013年第9期13卷 1025-1040页

作者： Gao-Chao Liu You-Jun Lu xue-lei chen Wei Du Yong-Heng Zhao Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences University of Chinese Academy of Sciences College of Science China Three Gorges University Center for High Energy Physics Peking University

We select a sample of quiescent luminous red galaxies （LRGs） from the Sloan Digital Sky Survey Data Release 7 with a high signal-to-noise ratio （S/N） to study the consistency of fitting the full spectrum by using different packages, mainly, ULySS and STARLIGHT. The spectrum of each galaxy in the sample is fitted by the full spectrum fitting packages ULySS and STARLIGHT. We find：（1） for spec- tra with higher S/Ns, the ages of stellar populations obtained from ULySS are slightly older than those from STARLIGHT, and metallicities derived from ULySS are slightly richer than those from STARLIGHT. In general, both packages can give roughly con- sistent fitting results. （2） For low S/N spectra, it is possible that the fitting by ULySS can become trapped at some local minimum in the parameter space during execution and thus may give unreliable results, but STARLIGHT can still give reliable results. Based on the fitting results of LRGs, we further analyze their star formation history and the relation between their age and velocity dispersion, and find that they agree well with conclusions from previous works.

关键词： galaxies: evolution -- galaxies: formation -- galaxies: stellar content

Semi-numerical simulation of reionization with semi-analytical modeling of galaxy formation

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Research in Astronomy and Astrophysics 2013年第4期13卷 373-386页

作者： Jie Zhou Qi Guo Gao-Chao Liu Bin Yue Yi-Dong Xu xue-lei chen National Astronomical Observatories Chinese Academy of Sciences College of Science China Three Gorges University Center of High Energy Physics Peking University

In a semi-numerical model of reionization, the evolution of ionization fraction is approximately simulated by the criterion of ionizing photon to baryon ratio. We incorporate a semi-analytical model of galaxy formation based on the Millennium II N-body simulation into the semi-numerical modeling of reionization. The semianalytical model is used to predict the production of ionizing photons, then we use the semi-numerical method to model the reionization process. Such an approach allows more detailed modeling of the reionization, and also connects observations of galaxies at low and high redshifts to the reionization history. The galaxy formation model we use was designed to match the low-z observations, and it also fits the high redshift luminosity function reasonably well, but its prediction about star formation falls below the observed value, and we find that it also underpredicts the stellar ionizing photon production rate, hence the reionization cannot be completed at z ~ 6. We also consider simple modifications of the model with more top heavy initial mass functions, which can allow the reionization to occur at earlier epochs. The incorporation of the semi-analytical model may also affect the topology of the HI regions during the epoch of reionization, and the neutral regions produced by our simulations with the semi-analytical model, which appeared less poriferous than the simple halo-based models.

关键词： cosmology reionization - galaxies formation

Radio frequency interference detection based on the AC-UNet model

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Research in Astronomy and Astrophysics 2021年第5期21卷 168-178页

作者： Rui-Qing Yan Cong Dai Wei Liu Ji-Xia Li Si-Ying chen Xian-Chuan Yu Shi-Fan Zuo xue-lei chen College of Information Science and Technology Beijing Normal UniversityBeijing 100875China National Laboratory of Pattern Recognition Institute of AutomationChinese Academy of SciencesBeijing 100190China National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China

Radio frequency interference(RFI)is a serious issue in radio *** paper proposes a U-Net network model with atrous convolution to detect *** the ability of convolutional neural networks to extract image features of RFI,and learning RFI distribution patterns,the detection model of the RFI is *** use observational data containing real RFIs obtained by the Tianlai telescope to train the model so that the model can detect *** the probability of a data point being RFI pixel by pixel,and set a *** the same time the dropout layer was added to avoid overfitting *** the predicted probability of a data point exceeds the threshold,it is considered that there is RFI,and if the predicted probability of a data point does not exceed the threshold,then it is considered that there is no RFI,so that the part of the image with RFI is *** results show that this approach can achieve satisfactory accuracy in the detection of radio observation images with a small amount of RFI.

关键词： methods:data analysis techniques:image processing methods:observational

Spatial Prediction of Heavy Metal Pollution for Soils in Peri-Urban Beijing, China Based on Fuzzy Set Theory

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Pedosphere 2006年第5期16卷 545-554页

作者： TAN Man-Zhi XU Fang-Ming chen Jie ZHANG xue-lei chen Jing-Zhong State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 （China） Graduate school of the Chinese Academy of Sciences Beijing 100039 chengdu University of Technology Chengdu 610059 （China） Nanjing Station of Soil and Fertilizer Nanjing 210036 （China）

Fuzzy classification combined with spatial prediction was used to assess the state of soil pollution in the peri-urban Beijing area. Total concentrations of As, Cr, Cd, Hg, and Pb were determined in 220 topsoil samples （0-20 cm） collected using a grid design in a study area of 2 600 kin2. Heavy metal concentrations were grouped into three classes according to the optimum number of classes and fuzziness exponent using the fuzzy comean （FCM） algorithm. Membership values were interpolated using ordinary kriging. The polluted soils of the study area induced by the measured heavy metals were concentrated in the northwest corner and eastern part, especially the southeastern part close to the urban zone, whereas the soils free of pollution were mainly distributed in the southwestern part. The soils with potential risk of heavy metal pollution were located in isolated spots mainly in the northern part and southeastern corner of the study region. The FCM algorithm combined with geostatistical techniques, as compared to conventional single geostatistical kriging methods, could produce a prediction with a quantitative uncertainty evaluation and higher reliability. Successful prediction of soil pollution achieved with FCM algorithm in this study indicated that fuzzy set theory had great potential for use in other areas of soil science.

关键词： continuous classification fuzzy c-means heavy metal soil pollution spatial prediction

Palladium-Catalyzed[4+2]and[6+2]Dipolar Cycloadditions for the Construction of Benzo[d]isothiazole 1,1-Dioxide Fused 1,3-Oxazinanes and 1,3-Oxazocanes

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Chinese Journal of Chemistry 2024年第8期42卷 829-834页

作者： lei chen Hongling Xie Yu xue Zhengyu Han Jianwei Sun Hai Huang Jiangsu Key Laboratory of Advanced Catalytic Materials&Technology School of Petrochemical EngineeringChangzhou UniversityChangzhouJiangsu213164 China Department of Chemistry The Hong Kong University of Science and TechnologyClear Water BayKowloonHong Kong SARChina

Comprehensive Summary,The Pd-catalyzed dipolar cycloaddition represents a significant synthetic strategy for the construction of useful heterocyclic *** study developed the dipolar[4+2]and[6+2]cycloaddition reactions of benzo[d]isothiazole 1,1-dioxides(BDs)leading to the synthesis of BD-fused 1,3-oxazinane and 1,3-oxazocane derivatives,*** particular,the synthesis of BD-fused 1,3-oxazinanes demonstrated regio-and enantioselective characteristics,resulting in products with good yields,enantioselectivity and regioselectivity(if applicable).Furthermore,the[6+2]cycloaddition reaction developed in this work represented the first strategy for the synthesis of medium-sized ring compounds based on BDs.

关键词： Cycloaddition 1,3-Oxazinanes 1,3-Oxazocanes Medium-ring compounds Stereochemistry N-Heterocycles Sulfonamides Enantioselectivity Asymmetricsynthesis

Effect of Reclamation on the Groundwater-Lake Water Interaction in chen Lake

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Journal of Earth Science 2024年第3期35卷 1083-1086页

作者： Kun lei Teng Ma Liuzhu chen Zhenxing Li Yu chen School of Environmental Studies State Key Laboratory of Biogeology and Environmental GeologyChina University of GeosciencesWuhan 430078China

0 INTRODUCTION To relieve the short supply of suitable land for residing,cultivating,and commerce,it is accepted to reclaim land from lakes,river estuaries,and coastal regions in many countries(Mancini et al.,2020).The large-scale reclamation activities have an irreversible effect on the mico-geomorphology and hydrodynamic system of seasonally flooded areas(Zhang et al.,2019;Yu et al.,2018).For example,coastal regions reclaimed extended the groundwater flow paths,as well as created groundwater level rise,resulting in water-logging in the reclaimed area(Hu et al.,2008).Similar changes in groundwater flow systems may alter groundwater-lake water interactions,and it can ultimately affect the water cycle in the lake ***,such detailed studies are presently *** addition,natural exchanges between the lake and groundwater systems can be strongly affected by physical hydrological processes(Javadzadeh et al.,2020),chemical properties(Kamtchueng et al.,2015),and bioto behavior(Hancock et al.,2005).

关键词： groundwater coastal logging

Comprehensive analysis and mitigation strategies for safety issues of sodium-ion batteries

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Rare Metals 2024年第4期43卷 1343-1349页

作者： Tao Wei Xiao-Ling Xian Shi-xue Dou Wei chen Shu-lei Chou Institute for Carbon Neutralization College of Chemistry and Materials EngineeringWenzhou UniversityWenzhou325035China Wenzhou Key Laboratory of Sodium-Ion Batteries Wenzhou University Technology Innovation Institute for Carbon NeutralizationWenzhou325035China Zhejiang Key Laboratory of Carbon Materials College of Chemistry and Materials EngineeringWenzhou UniversityWenzhou325035China Institute for Superconducting and Electronic Materials Australian Institute for Innovative MaterialsUniversity of WollongongInnovation CampusWollongongNSW2522Australia

Sodium-ion batteries show great potential as an alternative energy storage system,but safety concerns remain a major hurdle to their mass *** paper analyzes the key factors and mechanisms leading to safety issues,including thermal runaway,sodium dendrite,internal short circuits,and gas *** promising solutions are proposed,such as high-safety electrode materials in the cathode and anode,high-safety electrolytes,and external battery management *** in also we emphasize the importance of selecting appropriate analysis methods and developing reliable failure models while suggesting advanced machine learning tools for *** a comprehensive approach,this study offers valuable recommendations to optimize materials and solutions for improving the safety of sodium-ion batteries.

关键词： Sodium-ion batteries Safety issues Thermal runaway Sodium dendrites