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arXiv 2025年

作者： Lai, Huilin Lin, Chuandong Li, Demei Yang, Tao Gan, Yanbiao Lian, Lingyan Xu, Aiguo Fujian Normal University Fuzhou350117 China Sino-French Institute of Nuclear Engineering and Technology Sun Yat-sen University Zhuhai519082 China Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power Engineering Tsinghua University Beijing100084 China Hebei Key Laboratory of Trans-Media Aerial Underwater Vehicle School of Liberal Arts and Sciences North China Institute of Aerospace Engineering Langfang065000 China National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009-26 Beijing100088 China National Key Laboratory of Shock Wave and Detonation Physics Mianyang621999 China HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing100871 China State Key Laboratory of Explosion Science and Safety Protection Beijing Institute of Technology Beijing100081 China

The Richtmyer–Meshkov (RM) instability occurs when a perturbed interface between two fluids undergoes impulsive acceleration due to a shock wave. In this paper, a numerical investigation of the RM instability during the reshock process is conducted using the two-component discrete Boltzmann method. The influence of reflection distance on the RM instability, including both hydrodynamic and thermodynamic non-equilibrium effects, is explored in detail. The interaction time between the reflected shock wave and the material interface varies with different reflection distances. Larger reflection distances lead to a longer evolution time of the material interface before reshock, resulting in more complex effects on the interface deformation, the mixing extent of the fluid system, and non-equilibrium behaviors after reshock. Additionally, while the reflection distance has a minimal impact on mixing entropy before the secondary impact, a significant difference emerges after the secondary impact. This suggests that the secondary impact enhances the evolution of the RM instability. Furthermore, non-equilibrium behaviors or quantities exhibit complex dynamics due to the influence of the transmitted shock wave, transverse waves, rarefaction waves, material interfaces, and dissipation/diffusion processes. Copyright © 2025, The Authors. All rights reserved.

关键词： Shock waves

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Supersonic flow kinetics: Mesoscale structures, thermodynamic nonequilibrium effects and entropy production mechanisms

arXiv

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arXiv 2025年

作者： Gan, Yanbiao Zhuang, Zhaowen Yang, Bin Xu, Aiguo Zhang, Dejia Chen, Feng Song, Jiahui Wu, Yanhong Hebei Key Laboratory of Trans-Media Aerial Underwater Vehicle North China Institute of Aerospace Engineering Langfang065000 China School of Energy and Safety Engineering Tianjin Chengjian University Tianjin300384 China National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009-26 Beijing100088 China National Key Laboratory of Shock Wave and Detonation Physics Mianyang621999 China HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing100871 China State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology Beijing100081 China School of Physical Science and Technology Guangxi University Nanning530004 China School of Aeronautics Shan Dong Jiaotong University Jinan250357 China School of Aerospace Engineering Beijing Institute of Technology Beijing100081 China

Supersonic flow is a typical nonlinear, nonequilibrium, multiscale, and complex phenomenon. Compared to scenarios described by Navier-Stokes (NS) theory, mesoscale behavior in supersonic flow exhibits greater discreteness and a higher degree of nonequilibrium. Meanwhile, the entropy production mechanism, which involves compression efficiency and the ability to perform external work, is a significant focus in supersonic flow fields. As the degree of discrete/nonequilibrium effects increases, the study of entropy production based on NS theory may need reevaluation and appropriate revision. To address these issues, this paper develops and applies the discrete Boltzmann modeling and analysis method/model (DBM), based on kinetic and mean-field theories, to simulate, and analyze these phenomena. The study provides the following results: A Burnett-level DBM suitable for supersonic flow is constructed based on the Shakhov-BGK model. Higher-order analytical expressions for typical thermodynamic nonequilibrium effects are derived, providing a constitutive basis for improving traditional macroscopic hydrodynamics modeling. Criteria for evaluating the validity of DBM are established by comparing numerical and analytical solutions of nonequilibrium effects. The multiscale DBM is used to investigate discrete/nonequilibrium characteristics and entropy production mechanisms in shock regular reflection. The findings include: (a) Compared to the NS-level DBM, the Burnett-level DBM offers more accurate representations of viscous stress and heat flux, i.e., more precise dissipative mechanisms, ensures non-negativity of entropy production in accordance with the second law of thermodynamics, and exhibits better numerical stability. (b) Near the interfaces of incident and reflected shock waves, strong nonequilibrium driving forces lead to prominent nonequilibrium effects. By monitoring the timing and location of peak nonequilibrium quantities, the evolution characteristics of incident and

关键词： Supersonic flow

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Cause of Extreme Heavy and Persistent Rainfall over Yangtze River in Summer 2020

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Advances in Atmospheric sciences 2021年第12期38卷 1994-2009页

作者： Xiao PAN Tim LI Ying SUN Zhiwei ZHU Key Laboratory of Meteorological Disaster Ministry of Education(KLME)/Joint International Research Laboratory of Climate and Environment Change(ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters(CIC-FEMD)Nanjing University of Information Science and TechnologyNanjing 210044China International Pacific Research Center and Department of Atmospheric Sciences School of Ocean and Earth Science and TechnologyUniversity of Hawaii at ManoaHonoluluHawaii 96822USA National Climate Center Beijing 100081China State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China

Record-breaking heavy and persistent precipitation occurred over the Yangtze River Valley(YRV)in June-July(JJ)*** observational data analysis has indicated that the strong and persistent rainfall arose from the confluence of southerly wind anomalies to the south associated with an extremely strong anomalous anticyclone over the western North Pacific(WNPAC)and northeasterly anomalies to the north associated with a high-pressure anomaly over Northeast Asia.A further observational and modeling study has shown that the extremely strong WNPAC was caused by both La Niña-like SST anomaly(SSTA)forcing in the equatorial Pacific and warm SSTA forcing in the tropical Indian Ocean(IO).Different from conventional central Pacific(CP)El Niños that decay slowly,a CP El Niño in early 2020 decayed quickly and became a La Niña by early *** quick transition had a critical impact on the ***,an unusually large area of SST warming occurred in the tropical IO because a moderate interannual SSTA over the IO associated with the CP El Niño was superposed by an interdecadal/long-term trend *** sensitivity experiments have demonstrated that both the heating anomaly in the IO and the heating anomaly in the tropical Pacific contributed to the formation and maintenance of the *** persistent high-pressure anomaly in Northeast Asia was part of a stationary Rossby wave train in the midlatitudes,driven by combined heating anomalies over India,the tropical eastern Pacific,and the tropical Atlantic.

关键词： Yangtze River floods anomalous anticyclone over the western North Pacific CP and EP El Niño Indian Ocean warming La Niña Rossby wave train

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Subspace method based on neural networks for eigenvalue problems

arXiv

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arXiv 2024年

作者： Dai, Xiaoying Fan, Yunying Sheng, Zhiqiang LSEC Institute of Computational Mathematics and Scientific/Engineering Computing Academy of Mathematics and Systems Science Chinese Academy of Sciences Beijing100190 China School of Mathematical Sciences University of Chinese Academy of Sciences Beijing100049 China National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing100871 China

With the rapid development of machine learning, numerical discretization methods based on deep neural networks have been widely used in many fields, especially in solving high-dimensional problems where traditional methods face bottlenecks. However, for low-dimensional problems, existing machine learning methods are not as accurate and efficient as traditional methods. In this paper, we propose a subspace method based on neural networks for eigenvalue problems with high accuracy and low cost. Our basic idea is to use neural network based basis functions to span a subspace, then calculate the parameters of the neural network based basis functions through appropriate training, and finally calculate the Galerkin projection of the eigenvalue problem onto the subspace and obtain an approximate solution. In addition, we reduce the dimension of the subspace by applying some dimensionality reduction technique, which can improve the accuracy of the approximate solution in further. numerical experiments show that we can obtain approximate eigenvalues with accuracy of 10−11 but with less then 400 epochs, which is significantly superior to other existing neural network based *** Codes 65N25, 65L15, 68T07 Copyright © 2024, The Authors. All rights reserved.

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The fundamental localization phases in quasiperiodic systems: A unified framework and exact results

arXiv

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arXiv 2025年

作者： Zhou, Xin-Chi Yao, Bing-Chen Wang, Yongjian Wang, Yucheng Wei, Yudong Zhou, Qi Liu, Xiong-Jun International Center for Quantum Materials School of Physics Peking University Beijing100871 China Hefei National Laboratory Hefei230088 China School of Mathematics and Statistics Nanjing University of Science and Technology Nanjing210094 China Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China International Quantum Academy Shenzhen518048 China Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Chern Institute of Mathematics and LPMC Nankai University Tianjin300071 China

The disordered quantum systems host three types of quantum states, the extended, localized, and critical, which bring up various distinct fundamental phases, including the pure phases and coexisting ones with mobility edges. The quantum phases involving critical states are of particular importance, but are less understood compared with the other ones, and the different phases have been separately studied in different quasiperiodic models. Here we propose a unified framework based on a spinful quasiperiodic system which unifies the realizations of all the fundamental Anderson phases, with the exact and universal results being obtained for these distinct phases. Through the duality transformation and renormalization group method, we show that the pure phases are obtained when the (emergent) chiral symmetry preserves in the proposed spin-1/2 quasiperiodic model, which provides a criterion for the emergence of the pure phases or the coexisting ones with mobility edges. Further, we uncover a new universal mechanism for the critical states that the emergence of such states is protected by the generalized incommensurate matrix element zeros in the spinful quasiperiodic model, as a novel generalization of the quasiperiodic hopping zeros in the spinless systems. We also show with the Avila’s global theory the criteria of exact solvability for the present unified quasiperiodic system, with which we identify several new quasiperiodic models derived from the spinful system hosting exactly solvable Anderson phases. In particular, we reach a single model that hosts all the seven fundamental phases of Anderson localization. Finally, an experimental scheme is proposed to realize these models using quasiperiodic optical Raman lattices. This study establishes a unified theoretical framework which enables an in-depth exploration of the broad classes of all fundamental localization phases in quasiperiodic systems, and offers key insights for constructing their exactly solvable models w

关键词： numerical models

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Accelerating relaxation through Liouvillian exceptional point

arXiv

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arXiv 2023年

作者： Zhou, Yan-Li Yu, Xiao-Die Wu, Chun-Wang Li, Xie-Qian Zhang, Jie Li, Weibin Chen, Ping-Xing Institute for Quantum Science and Technology College of Science National University of Defense Technology Changsha410073 China Hunan Key Laboratory of Mechanism and Technology of Quantum Information Changsha410073 China Hefei National Laboratory Anhui Hefei230088 China College of Science National University of Defense Technology Changsha410073 China School of Physics and Astronomy Centre for the Mathematics and Theoretical Physics of Quantum Non-Equilibrium Systems University of Nottingham NottinghamNG7 2RD United Kingdom

We investigate speeding up of relaxation of Markovian open quantum systems with the Liouvillian exceptional point (LEP), where the slowest decay mode degenerate with a faster decay mode. The degeneracy significantly increases the gap of the Liouvillian operator, which determines the timescale of such systems in converging to stationarity, and hence accelerates the relaxation process. We explore an experimentally relevant three level atomic system, whose eigenmatrices and eigenspectra are obtained completely analytically. This allows us to gain insights in the LEP and examine respective dynamics with details. We illustrate that the gap can be further widened through Floquet engineering, which further accelerates the relaxation process. Finally, we extend this approach to analyze laser cooling of trapped ions, where vibrations (phonons) couple to the electronic states. An optimal cooling condition is obtained analytically, which agrees with both existing experiments and numerical simulations. Our study provides analytical insights in understanding LEP, as well as in controlling and optimizing dissipative dynamics of atoms and trapped ions. Copyright © 2023, The Authors. All rights reserved.

关键词： Trapped ions

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A New Formation Mechanism of Counterstreaming Mass Flows in Filaments and the Doppler Bullseye Pattern in Prominences

arXiv

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arXiv 2025年

作者： Zhou, Chengrui Shen, Yuandeng Xia, Chun Liu, Dongxu Tang, Zehao Yao, Surui Yunnan Observatories Chinese Academy of Sciences Kunming650216 China School of Aerospace Harbin Institute of Technology Shenzhen518055 China Shenzhen Key Laboratory of Numerical Prediction for Space Storm Harbin Institute of Technology Shenzhen518055 China State Key Laboratory of Solar Activity and Space Weather National Space Science Center Chinese Academy of Sciences Beijing100190 China School of Physics and Astronomy Yunnan University Kunming650500 China University of Chinese Academy of Sciences Beijing100049 China

The eruption of solar prominences can eject substantial mass and magnetic field into interplanetary space and cause geomagnetic storms. However, various questions about prominences and their eruption mechanism remain unclear. In particular, what causes the intriguing Doppler bullseye pattern in prominences has not yet been solved, despite some preliminary studies proposing that they are probably associated with counterstreaming mass flows. Previous studies are mainly based on single-angle and short timescale observations, making it difficult to determine the physical origin of Doppler bullseye patterns in prominences. Here, taking advantage of stereoscopic observations taken by the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory and a three-dimensional numerical simulation, we investigate the origin of prominence Doppler bullseye pattern by tracing a long-lived transequatorial filament/prominence from July 23 to August 4, 2012. We find that repeated coronal jets at one end of the prominence can launch the Doppler bullseye pattern. It is evidenced in our observations and simulation that during the forward traveling of jet plasma along the helical magnetic field structure of the prominence, part of the ejecting plasma can not pass through the apex of the prominence due to the insufficient kinetic energy and therefore forms a backward-moving mass flow along the same or neighboring magnetic field lines. This process finally forms counterstreaming mass flows in on-disk filaments. When the on-disk filament rotates to the solar limb to be a prominence, the counterstreaming mass flows are naturally observed as a Doppler bullseye pattern. Copyright © 2025, The Authors. All rights reserved.

关键词： Plasma magnetohydrodynamic waves

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南大洋增暖及其气候影响

引用

science Bulletin 2023年第9期68卷 946-960,M0004页

作者：蔡文炬高立宝罗义勇李熙晨郑小童张学斌程旭华贾凡 Ariaan Purich Agus Santoso 杜岩 David MHolland 石佳睿项宝强谢尚平 Frontiers Science Center for Deep Ocean Multispheres and Earth System and Key Laboratory of Physical Oceanography Ocean University of ChinaQingdao 266100China Laboratory for Ocean and Climate Dynamics Pilot National Laboratory for Marine Science and TechnologyQingdao 266237China Center for Southern Hemisphere Oceans Research Commonwealth Scientific and Industrial Research Organisation(CSIRO)Oceans and AtmosphereHobart 7004Australia First Institute of Oceanography and Key Laboratory of Marine Science and Numerical Modeling Ministry of Natural ResourcesQingdao 266061China Laboratory for Regional Oceanography and Numerical Modeling Pilot National Laboratory for Marine Science and TechnologyQingdao 266237China Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029China College of Oceanography Hohai UniversityNanjing 210098China Key Laboratory of Ocean Circulation and Waves Institute of OceanologyChinese Academy of SciencesQingdao 266071China Climate Change Research Centre University of New South WalesSydney 2052Australia Australian Research Council Centre of Excellence for Climate Extremes University of New South WalesSydney 2052Australia State Key Laboratory of Tropical Oceanography South China Sea Institute of OceanologyChinese Academy of SciencesGuangzhou 510301China Southern Marine Science and Engineering Guangdong Laboratory Guangzhou 511458China Courant Institute of Mathematical Sciences New York UniversityNew York NY 10012USA Woods Hole Oceanographic Institution Woods Hole MA 02543USA NOAA/Geophysical Fluid Dynamics Laboratory Princeton NJ 08540USA University Corporation for Atmospheric Research Boulder CO 80307USA Scripps Institution of Oceanography University of California San DiegoLa Jolla CA 92093USA

过去几十年南大洋在南极平流层臭氧消耗和大气二氧化碳浓度增加的共同作用下大幅增暖,显著影响着南极冰架和冰盖的融化、海平面上升、南北半球的降水分配以及热带海洋和大气环流等,引发了深远的气候效应.全球变暖背景下南大洋西风表现... 详细信息

过去几十年南大洋在南极平流层臭氧消耗和大气二氧化碳浓度增加的共同作用下大幅增暖,显著影响着南极冰架和冰盖的融化、海平面上升、南北半球的降水分配以及热带海洋和大气环流等,引发了深远的气候效应.全球变暖背景下南大洋西风表现为极向加强,同时进入南大洋的热辐射和淡水通量持续增加,由此上翻的海水可吸收更多的热量和碳,经由更强的平均流向北输送,更多地在45°S附近海域下沉并存储.当前对南大洋增暖背后诸多复杂的物理过程仍缺乏足够的理解,比如来自冰架、冰盖及海洋涡旋的作用、热带-极地相互作用、南大洋本身对全球变暖的响应等,尤其是有限的观测数据和较低分辨率的模式无法准确呈现快速变化的物理现象和机理.因此,南大洋的未来增暖存在很大的不确定性且可能长期持续,但近期的进展为深入认知南大洋增暖及其气候影响奠定了坚实的基础.

关键词：平流层臭氧南大洋物理现象物理过程全球变暖热带海洋南北半球低分辨率

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An Ultra Wideband FSS Operating at Ka Band 5

An Ultra Wideband FSS Operating at Ka Band

引用

5th IEEE International Conference on Computational Electromagnetics, ICCEM 2019

作者： Xu, Yinfang Zhang, Shengjun National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing Institute of Space Long March Vehicle Beijing China

ISBN: (纸本)9781538671115

An Ultra Wideband frequency selective surface (FSS) with forth-order bandpass responses operating at Ka band is proposed in the paper. To improve the performance of the FSS especially in angular stability, the coupling of capacitive surface and inductive surface is employed to realize the miniaturization of the structural unit around 0.26λ. Furthermore, to enhance the passband and to suppress sharply the bandstop edge of the FSS, a multi-layer FSS structure is adopted to form a forth-order filter. In addition, the FSS working at the Ka band frequency with a low-profile broadband and a high rejection stopband is designed. The proposed FSS can provide sharp frequency selectivity and stable frequency responses as functions of angle and polarization of incidence of the EM wave. Principles of operation, detailed design, and simulated results of the fabricated prototypes are presented and discussed in this paper. © 2019 IEEE.

关键词： Frequency selective surfaces

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An Improved Adaptive Pulse Compression Algorithm Based on Linear Frequency Modulation Signal

An Improved Adaptive Pulse Compression Algorithm Based on Li...

引用

2019 IEEE International Conference on Signal, Information and Data Processing, ICSIDP 2019

作者： Bai, Jinliang Qin, Peng Li, Hu Zhang, Ran Zhang, Xinyu National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing Institute of Space Long March Vehicle Beijing China

ISBN: (纸本)9781728123455

In this paper, the radar signal is optimized based on the pulse compression repair (PCR) algorithm, which mainly reduces the computational amount to makes it more advantageous to achieve. The main idea is to implement PCR in a parallel way. The method of implementing parallelism is well known, that is, the signal is segmented, and different segmentation methods can be adopted according to different signal models. In this paper, the chirp signal is mainly processed by decimation and segmentation, and some intrinsic benefits of the performance and computational balance of the proposed method are discussed. © 2019 IEEE.

关键词： Frequency modulation

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