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Two Nonmonotone Proximal Gradient Methods for Nonsmooth Optimization over the Stiefel Manifold

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Acta Mathematicae Applicatae Sinica 2024年

作者： Jin-chao ZHANG Juan GAO Ya-kui HUANG Xin-wei LIU School of Artificial Intelligence Hebei University of Technology Institute of Mathematics Hebei University of Technology

We propose two nonmonotone retraction-based proximal gradient methods for solving a class of nonconvex nonsmooth optimization problems over the Stiefel manifold. The proposed methods are equipped with the descent direction obtained by a proximal mapping restricted in tangent space of the manifold and the BarzilaiBorwein stepsizes determined by two recent iteration points and the corresponding descent directions. By employing, respectively, the Grippo-Lampariello-Lucidi nonmonotone line search strategy and the Dai-Fletcher nonmonotone line search strategy, our proposed methods are proved to be globally convergent. Analysis on the iteration complexity of NPGL for obtaining an?-stationary solution is provided. Numerical results on the sparse principle component analysis problems demonstrate the efficiency of our methods.

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Analyses of Political Crisis Impact on Tourism: A Panel Counterfactual Approach with Internet Search Index

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Journal of Systems science & Complexity 2024年第4期37卷 1581-1603页

作者： HUANG Bai SUN Yuying YANG Boyu School of Statistics and Mathematics Central University of Finance & Economics Academy of Mathematics and Systems science Chinese Academy of Sciences Center for Forecasting science Chinese Academy of Sciences School of Economics and Management University of Chinese Academy of Sciences

Existing research has shown that political crisis events can directly impact the tourism industry. However, the current methods suffer from potential changes of unobserved variables, which poses challenges for a reliable evaluation of the political crisis impacts. This paper proposes a panel counterfactual approach with Internet search index, which can quantitatively capture the change of crisis impacts across time and disentangle the effect of the event of interest from the rest. It also provides a tool to examine potential channels through which the crisis may affect tourist outflows.This research empirically applies the framework to analyze the THAAD event on tourist flows from the Chinese Mainland to South Korea. Findings highlight the strong and negative short-term impact of the political crisis on the tourists' intentions to visit a place. This paper provides essential evidence to help decision-makers improve the management of the tourism crisis.

关键词： Composite search index counterfactual analysis political crisis search query data tourism demand

Improved error estimates for a modified exponential Euler method for the semilinear stochastic heat equation with rough initial data

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science china Mathematics 2024年

作者： Xinping Gui Buyang Li Jilu Wang Beijing Computational science Research Center Department of Applied Mathematics The Hong Kong Polytechnic University School of science Harbin Institute of Technology

A class of stochastic Besov spaces BpL2(Ω;H~α(O)), 1≤ p ≤∞ and α ∈ [-2, 2], is introduced to characterize the regularity of the noise in the semilinear stochastic heat equation du-△udt = f(u)dt + d W(t),under the following conditions for some α ∈(0, 1]:‖(∫t)0e~(-(t-s)A)dW(S)‖_(L2(Ω;L2(O)))≤Cta/2and ‖(∫t)0e~(-(t-s)A)dW(S)‖_(B~∞L2(Ω;H~α(O)))≤C The conditions above are shown to be satisfied by both trace-class noises(with α = 1) and one-dimensional space-time white noises(with α =1/2). The latter would fail to satisfy the conditions with α =1/2 if the stochastic Besov norm ∥·∥_(B~∞L2(Ω;H~α(O)))is replaced by the classical Sobolev norm ∥·∥_(L2(Ω;H~α(O))), and this often causes reduction of the convergence order in the numerical analysis of the semilinear stochastic heat equation. In this paper, the convergence of a modified exponential Euler method, with a spectral method for spatial discretization,is proved to have order α in both the time and space for possibly nonsmooth initial data in L4(Ω;H~β(O)) withβ >-1, by utilizing the real interpolation properties of the stochastic Besov spaces and a class of locally refined stepsizes to resolve the singularity of the solution at t = 0.

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Structural transition, electric transport, and electronic structures in the compressed trilayer nickelate LaNiO

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science china(Physics,Mechanics & Astronomy) 2024年

作者： Jingyuan Li Cuiqun Chen Chaoxin Huang Yifeng Han Mengwu Huo Xing Huang Peiyue Ma Zhengyang Qiu Junfeng Chen Xunwu Hu Lan Chen Tao Xie Bing Shen Hualei Sun Daoxin Yao Meng Wang Center for Materials of the Universe School of Molecular Sciences Arizona State University Center for Neutron science and Technology Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices School of Physics Sun Yat-sen University School of sciences Sun Yat-sen University

Atomic structure and electronic band structure are fundamental properties for understanding the mechanism of superconductivity. Motivated by the discovery of pressure-induced high-temperature superconductivity at 80 K in the bilayer Ruddlesden-Popper nickelate La3Ni2O7, the atomic structure and electronic band structure of the trilayer nickelate La4Ni3O10under pressure up to 44.3 GPa are investigated. A structural transition from the monoclinic P21/a space group to the tetragonal I4/mmm around 12.6-13.4 GPa is identified, accompanied by a drop of resistance below 7 K. Density functional theory calculations suggest that the bonding state of Ni 3dz2orbital rises and crosses the Fermi level at high pressures, which may give rise to possible superconductivity observed in resistance under pressure in La4Ni3O10. The trilayer nickelate La4Ni3O10shows some similarities with the bilayer La3Ni2O7and has unique properties, providing a new platform to investigate the underlying mechanism of superconductivity in nickelates.

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Mechanism of field-like torque in spin-orbit torque switching of perpendicular magnetic tunnel junction

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science china(Physics,Mechanics & Astronomy) 2022年第10期65卷 109-114页

作者： Yudong Zhuo Wenlong Cai Daoqian Zhu Hongchao Zhang Ao Du Kaihua Cao Jialiang Yin Yan Huang Kewen Shi Weisheng Zhao Fert Beijing Institute MIIT Key Laboratory of SpintronicsSchool of Integrated Circuit Science and EngineeringBeihang UniversityBeijing 100191China Beihang-Goertek Joint Microelectronics Institute Qingdao Research InstituteBeihang UniversityQingdao 266000China

The current-induced spin-orbit torque(SOT) is one of the most promising ways for high speed and low power spintronics devices. However, the mechanism of SOT driven magnetization reversal, especially the role of the field-like torque(FLT), is still unclear. Here, we report the observed promotion and suppression of switching by FLT, which depends on the relative direction of FLT and spin polarization. Our results reveal that the FLT could modulate the switching speed and power consumption by affecting the work done by the damping-like torque, and leads two different reversal dynamical paths during the switching.Furthermore, the origin of incubation time in SOT induced switching is clarified simultaneously.

关键词： spin-orbit torque field-like torque magnetization reversal magnetic tunnel junction

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Realization of Oriented and Nanoporous Bismuth Chalcogenide Layers via Topochemical Heteroepitaxy for Flexible Gas Sensors

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Research 2022年第4期2022卷 211-221页

作者： Zhiwei Wang Jie Dai Jian Wang Xinzhe Li Chengjie Pei Yanlei Liu Jiaxu Yan Lin Wang Shaozhou Li Hai Li Xiaoshan Wang Xiao Huang Wei Huang Institute of Advanced Materials(IAM) Nanjing Tech University(NanjingTech)30 South Puzhu RoadNanjing 211816China Frontiers science Center for Flexible Electronics Xi'an Institute of Flexible Electronics(IFE)and Xi'an Institute of Biomedical Materials EngineeringNorthwestern Polytechnical University127 West Youyi RoadXi'an 710072China Key Laboratory for Organic Electronic e Information Displays(KLOEID)and Jiangsu Key Laboratory for Biosensors Institute of Advanced Materials(IAM)Nanjing University of Posts and Telecommunications9 Wenyuan RoadNanjing 210023China

Most van der Waals two-dimensional(2D)materials without surface dangling bonds show limited surface activities except for their edge sites.Ultrathin Bi_(2)Se_(3),a topological insulator that behaves metal-like under ambient conditions,has been overlooked on its surface activities.Herein,through a topochemical conversion process,ultrathin nanoporous Bi_(2)Se_(3) layers were epitaxially deposited on BiOCl nanos.eets with strong electronic coupling,leading to hybrid electronic states with further bandgap narrowing.Such oriented nanoporous Bi_(2)Se_(3) layers possessed largely exposed active edge sites,along with improved surface roughness and film forming ability even on inkjet-printed flexible electrodes.Superior room-temperature NO_(2) sensing performance was achieved compared to other 2D materials under bent conditions.Our work demonstrates that creating nanos.ale features in 2D materials through topochemical heteroepitaxy is promising to achieve both favorable electronic properties and surface activity toward practical applications.

关键词： chemical bonds roughness

Achieving geometric convergence for distributed optimization with Barzilai-Borwein step sizes

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science china(Information sciences) 2022年第4期65卷 280-281页

作者： Juan GAO Xin-Wei LIU Yu-Hong DAI Yakui HUANG Peng YANG School of Artificial Intelligence Hebei University of Technology Institute of Mathematics Hebei University of Technology LSEC Academy of Mathematics and Systems Science Chinese Academy of Sciences School of Mathematical sciences University of Chinese Academy of Sciences

Dear editor,We consider distributed optimization, which can be formulated to minimize the average of all local objective functions:■where each local function f;:■ is L;-smooth and μ;-strongly convex and known only ... 详细信息

关键词： distributed optimization multi-agent network Barzilai-Borwein step sizes optimization algorithms convergence rate

Associations of muscle mass,strength,and quality with all-cause mortality in china:a population-based cohort study

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Chinese Medical Journal 2022年第11期135卷 1358-1368页

作者： Man Wu Yuxia Wei Jun Lv Yu Guo Pei Pei Jiachen Li Huaidong Du Ling Yang Yiping Chen Xiaohui Sun Hua Zhang Junshi Chen Zhengming Chen Canqing Yu Liming Li 无 Department of Epidemiology and Biostatistics School of Public HealthPeking UniversityBeijing 100191China Key Laboratory of Molecular Cardiovascular sciences Ministry of EducationPeking UniversityBeijing 100191China Peking University Center for Public Health and Epidemic Preparedness&Responses Beijing 100191China national Coordinating Center of china Kadoorie Biobank Chinese Academy of Medical SciencesBeijing 102308China Medical Research Council Population Health Research Unit the University of OxfordOxford OX37LFUK Clinical Trial Service Unit and Epidemiological Studies Unit(CTSU) Nuffield Department of Population HealthUniversity of OxfordOxford OX37LFUK NCDs Prevention and Control Department Qingdao CDCQingdaoShandong 266033China NHC Key Laboratory of Food Safety Risk Assessment China National Center for Food Safety Risk AssessmentBeijing 100022China. on behalf of the china Kadoorie Biobank Collaborative Group

Background It remains unclear about the association of muscle mass,strength,and quality with death in the general Chinese population of diverse economical and geographical backgrounds.The present study aimed to comprehensively examine such associations across different regions in china.Methods Based on the china Kadoorie Biobank study,the present study included 23,290 participants who were aged 38 to 88 years and had no prevalent cardiovascular diseases or cancer.Muscle mass and grip strength were measured using calibrated instruments.Arm muscle quality was defined as the ratio of grip strength to arm muscle mass.Low muscle mass,grip strength,and arm muscle quality were defined as the sex-specific lowest quintiles of muscle mass index,grip strength,and arm muscle quality,respectively.Cox proportional hazards models yielded hazard ratios(HRs)and 95%confidence intervals(CIs)for risks of all-cause mortality in relation to muscle mass,strength,and quality.Results During a median follow-up of 3.98 years,739 participants died.The HR(95%CI)of all-cause mortality risk was 1.28(1.08–1.51)for low appendicular muscle mass index,1.38(1.16–1.62)for low total muscle mass index,1.68(1.41–2.00)for low grip strength,and 1.41(1.20–1.66)for low arm muscle quality in models adjusted for sociodemographic characteristics,lifestyle factors,and medical histories.Conclusion Low muscle mass,grip strength,and arm muscle quality are all associated with short-term increased risks of mortality,indicating the importance of maintaining normal muscle mass,strength,and quality for general Chinese adults.

关键词： Muscle All-cause mortality Chinese Prospective Muscle mass Muscle strength Muscle quality

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Organic matter pore characteristics of over-mature marine black shale: a comparison of organic fractions with different densities

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Frontiers of Earth science 2023年第1期17卷 310-321页

作者： Shitan NING Peng XIA Niuniu ZOU Yi ZHONG Yin YU Yuliang MOU Ke WANG College of Resources and Environmental Engineering Guizhou UniversityGuiyang 500025China Key Laboratory of Karst Georesources and Environment Ministry of Education Guizhou UniversityGuiyang 500025China School of Geosciences China University of PetroleumQingdao 266580China

Organic matter pores are considered to be the most important type of pore for preserving hydrocarbon gases in shale gas reservoirs.The organic matter in each over-mature marine shale sample was separated into two organic fractions with densities of greater than and less than 1.25 g/cm^(3),and then their molecular compositions and pore characteristics were quantitatively evaluated using solid state 13C-nuclear magnetic resonance(NMR)and gas(N2 and CO_(2))adsorption analyses,respectively.The results revealed that aromatic carbon is the dominant molecular composition of the over-mature organic matter in the Lower Cambrian Niutitang shale.During the over-mature stage,the organic fractions with densities of greater than and less than 1.25 g/cm^(3) have no significant differences in molecular composition.The organic fractions with densities of greater than and less than 1.25 g/cm^(3) do have significant differences in their organic pore characteristics.In contrast to the high density organic fraction,the low density fraction contained abundant micropores and lacked mesopores and macropores.The organic pore structures of the different occurrence states of organic matter were significantly different.The C/O of organic matter in different occurrence states are obviously different,which proves that the organic pore structure is closely related to both the occurrence state and density of the organic matter.However,these relationships are still unclear and require further study.

关键词： pore characteristics organic matter black shale Early Cambrian Yangtze Block