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arXiv 2022年

作者： Xie, Hui Zhai, Chuanlei Liu, Li Yong, Heng Institute of Applied Physics and Computational Mathematics Beijing100094 China

In this paper, a new weighted first-order formulation is proposed for solving the anisotropic diffusion equations with deep neural networks. For many numerical schemes, the accurate approximation of anisotropic heat flux is crucial for the overall accuracy. In this work, the heat flux is firstly decomposed into two components along the two eigenvectors of the diffusion tensor, thus the anisotropic heat flux approximation is converted into the approximation of two isotropic components. Moreover, to handle the possible jump of the diffusion tensor across the interface, the weighted first-order formulation is obtained by multiplying this first-order formulation by a weighted function. By the decaying property of the weighted function, the weighted first-order formulation is always well-defined in the pointwise way. Finally, the weighted first-order formulation is solved with deep neural network approximation. Compared to the neural network approximation with the original second-order elliptic formulation, the proposed method can significantly improve the accuracy, especially for the discontinuous anisotropic diffusion problems. Copyright © 2022, The Authors. All rights reserved.

关键词： Heat flux

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Neural Canonical Transformations for Quantum Anharmonic Solids of Lithium

arXiv

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arXiv 2024年

作者： Zhang, Qi Wang, Xiaoyang Shi, Rong Ren, Xinguo Wang, Han Wang, Lei Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing100190 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Fenghao East Road 2 Beijing100094 China CAS Key Laboratory of Quantum Information University of Science and Technology of China Anhui Hefei230026 China HEDPS CAPT College of Engineering Peking University Beijing100871 China

Lithium is a typical quantum solid, characterized by cubic structures at ambient pressure. As the pressure increases, it forms more complex structures and undergoes a metal-to-semiconductor transformation, complicating theoretical and experimental analyses. We employ the neural canonical transformation approach, an ab initio variational method based on probabilistic generative models, to investigate the quantum anharmonic effects in lithium solids at finite temperatures. This approach combines a normalizing flow for phonon excited-state wave functions with a probabilistic model for the occupation of energy levels, optimized jointly to minimize the free energy. Our results indicate that quantum anharmonicity lowers the bcc-fcc transition temperature compared to classical molecular dynamics predictions. At high pressures, the predicted fractional coordinates of lithium atoms in the cI16 structure show good quantitative agreement with experimental observations. Finally, contrary to previous beliefs, we find that the poor metallic oC88 structure is stabilized by the potential energy surface obtained via high-accuracy electronic structure calculations, rather than thermal or quantum nuclear effects. Copyright © 2024, The Authors. All rights reserved.

关键词： Excited states

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Discontinuity Computing with physics-Informed Neural Network

TechRxiv

引用

TechRxiv 2022年

作者： Liu, Li Liu, Shengping Yong, Heng Xiong, Fansheng Yu, Tengchao Institute of Applied Physics and Computational Mathematics Beijing100094 China

How to simulate shock waves and other discontinuities is a long history topic. As a new and booming method, the physics-informed neural network (PINN) is still weak in calculating shock waves than traditional shock-capturing methods. In this paper, we propose a ‘retreat in order to advance’ way to improve the shock capturing ability of PINN by using a weighted equations (WE) method with PINN. The primary strategy of the method is to weaken the expression of the network in high compressible regions by adding a local positive and compression-dependent weight into governing equations at each interior point. With this strategy, the network will focus on training smooth parts of the solutions. Then automatically affected by the compressible property near shock waves, a sharp discontinuity appears with the wrong inside-shock-points ‘compressed’ into well-trained smooth regions just like passive particles. In this paper, we study one-dimensional and two-dimensional Euler equations. And illustrated by the comparisons with high-order classical WENO-Z method in numerical examples, the proposed method can significantly improve the discontinuity computing ability. © 2022, CC BY.

关键词： Euler equations

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LMA Detection Via Circumferential Spatial Information Learning with Hall Sensor Array for Steel Wire Ropes

LMA Detection Via Circumferential Spatial Information Learni...

引用

2024 Academic Conference of China Instrument and Control Society, ACCIS 2024

作者： Huang, Yicheng Liu, Zhiliang Yang, Leilei Ren, Liyuan Glasgow Collage University of Electronic Science and Technology of China Chengdu China School of Mechanical and Electrical Engineering University of Electronic Science and Technology of China Chengdu China Institute of Applied Physics and Computational Mathematics Beijing China

ISBN: (纸本)9798350350326

In the industrial sector, steel wire ropes (SWR) are crucial for traction. Early damage such as wear can lead to further loss of metallic cross-sectional area (LMA) of SWR. In existing studies, LMA-type defects are mainly measured using PCB coils, which sense the overall change of magnetic flux will ignore the information of the circumferential distribution of magnetic flux, resulting in insufficient detection accuracy. To address these issues, this paper utilizes spatial information from Hall sensors and an improved CNN network to extract LMArelated cross-sectional loss characteristics. This approach enhances the utilization of the circumferential information obtained by Hall sensors and achieves excellent quantitative detection results. Experimental validation shows that even under complex conditions, the average error rate for LMA detection is below 0.1%. Therefore, this paper proposes a highaccuracy and noise-resistant LMA detection method based on Hall sensors. © 2024 IEEE.

关键词： Circumferential Spatial Information Hall Sensor Array Improved CNN Loss of Metal Cross-Sectional Area Steel Wire Ropes

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Continuum-discretized coupled-channels calculations for Li6 fusion reactions with closed channels

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Physical Review C 2023年第6期107卷 064610-064610页

作者： Wendi Chen D. Y. Pang Hairui Guo Ye Tao Weili Sun Yangjun Ying School of Physics Beihang University Beijing 100191 People's Republic of China Institute of Applied Physics and Computational Mathematics Beijing 100094 People's Republic of China

Fusion reactions induced by the weakly bound nucleus Li6 with targets Si28, Ni64, Sm144, and Bi209 at energies around the Coulomb barrier are investigated within a three-body model where Li6 is described with an α+d cluster model. The total fusion (TF) cross sections are calculated with the continuum-discretized coupled-channels (CDCC) method and the complete fusion (CF) cross sections are extracted through the sum-rule model. The calculations demonstrate that (i) for the TF cross-section calculations, the continuum states up to 40 MeV are found to be necessary, which corresponds to the inclusion of closed channels for light and medium mass targets, such as Si28, Co59, and Sm144; (ii) the converged CDCC results for TF cross section at energies above the Coulomb barrier are almost the same as single-channel results in which the continuum coupling effect is neglected; and (iii) the continuum coupling strongly influences partial-wave fusion cross sections and the closed channels play a significant role in the improvement of the description of the CF cross sections at energies below the Coulomb barrier for the Li6+Si28, Co59, and Sm144 systems.

关键词： Nuclear fusion Nuclear reactions Optical, coupled-channel & distorted wave models

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Caustic effects on high-order harmonic generation in graphene

arXiv

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arXiv 2023年

作者： Dong, Fulong Xia, Qinzhi Liu, Jie Graduate School China Academy of Engineering Physics Beijing100193 China Institute of Applied Physics and Computational Mathematics Beijing100088 China

We employ the two-band density-matrix equations and time-dependent density functional theory to calculate high-order harmonic generation (HOHG) in graphene under a femtosecond laser irradiation. Our investigation uncovers a striking harmonic enhancement structure (HES) within a specific energy range of the HOHG spectrum. In this regime, we find the convergence of multiple interband electron-hole recombination trajectories, leading to the zero determinant of the Hessian matrix of the semiclassical action. This trajectory convergence exhibits the characteristics akin to the focusing behavior of light rays, commonly known as caustic effects. In contrast to atom situation, where caustic effects are confined to a narrow energy regime around the HOHG cut-off energy and the enhancement due to caustic trajectory convergence is less apparent, the two-dimensional nature of graphene results in a broad energy region for HOHG enhancement that the caustic trajectories can even dominate the entire interband harmonic generation regime. The magnitude of enhancement is significant and can be estimated to be on the order of ∼ N2/3, with N representing the harmonic order, according to the catastrophe theory. These mechanisms have broad applicability and hold significant implications for other two-dimensional materials, as well as bulk materials, providing crucial insights into the understanding of HOHG phenomena in diverse material systems. Copyright © 2023, The Authors. All rights reserved.

关键词： Graphene

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A practical PINN framework for multi-scale problems with multi-magnitude loss terms

arXiv

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arXiv 2023年

作者： Wang, Yong Yao, Yanzhong Guo, Jiawei Gao, Zhiming Institute of Applied Physics and Computational Mathematics Beijing100088 China Graduate School China Academy of Engineering Physics Beijing100088 China

For multi-scale problems, the conventional physics-informed neural networks (PINNs) face some challenges in obtaining available predictions. In this paper, based on PINNs, we propose a practical deep learning framework for multi-scale problems by reconstructing the loss function and associating it with special neural network architectures. New PINN methods derived from the improved PINN framework differ from the conventional PINN method mainly in two aspects. First, the new methods use a novel loss function by modifying the standard loss function through a (grouping) regularization strategy. The regularization strategy implements a different power operation on each loss term so that all loss terms composing the loss function are of approximately the same order of magnitude, which makes all loss terms be optimized synchronously during the optimization process. Second, for the multi-frequency or high-frequency problems, in addition to using the modified loss function, new methods upgrade the neural network architecture from the common fully-connected neural network to special network architectures such as the Fourier feature architecture given in Ref. [1] and the integrated architecture developed by us. The combination of the above two techniques leads to a significant improvement in the computational accuracy of multi-scale problems. Several challenging numerical examples demonstrate the effectiveness of the proposed methods. The proposed methods not only significantly outperform the conventional PINN method in terms of computational efficiency and computational accuracy, but also compare favorably with the state-of-the-art methods in the recent literature. The improved PINN framework facilitates better application of PINNs to multiscale problems. The data and code accompanying this paper are available at https://***/wangyong1301108/MMPINN. Copyright © 2023, The Authors. All rights reserved.

关键词： Deep learning

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Suppression of auto-resonant stimulated Brillouin scattering in supersonic flowing plasmas by different forms of incident lasers

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Chinese physics B 2020年第9期29卷 364-368页

作者： S S Ban Q Wang Z J Liu C Y Zheng X T He HEDPS Center for Applied Physics and TechnologySchool of PhysicsPeking UniversityBeijing 100871China Institute of Applied Physics and Computational Mathematics Beijing 100094China

In supersonic flowing plasmas,the auto-resonant behavior of ion acoustic waves driven by stimulated Brillouin backscattering is self-consistently investigated.A nature of absolute instability appears in the evolution of the stimulated Brillouin *** adopting certain form of incident lights combined by two perpendicular linear polarization lasers or polarization rotation lasers,the absolute instability is suppressed *** suppression of auto-resonant stimulated Brillouin scattering is verified with the fully kinetic Vlasov code.

关键词： inertial confinement fusion laser plasma interaction stimulated Brillouin scattering fully kinetic simulation

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Phase Effects of Long-Wavelength Rayleigh–Taylor Instability on the Thin Shell

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Chinese physics Letters 2020年第2期37卷 35-38页

作者： Zhi-Yuan Li Li-Feng Wang Jun-Feng Wu Wen-Hua Ye Institute of Applied Physics and Computational Mathematics Beijing 100094 Center for Applied Physics and Technology HEDPSand College of EngineeringPeking UniversityBeijing 100871

Taking the long-wavelength Rayleigh-Taylor instability(RTI) on the thin shell of inertial confinement fusion as the research object,a linear analytical model is presented to study the phase effects that are caused by the phase difference of single-mode perturbations on the two *** accuracy is tested by numerical *** analyzing the characteristic of this model,it is found that the phase difference does not change the basic RTI structure(only one spike and one bubble in a period).However,the symmetry of the spike and bubble is destroyed,which has non-expected influences on the convergent motion of ICF ***,the phenomenon that the distance between spikes and bubbles along the vertical direction of acceleration differs by π is *** is also shown that when the phase difference is large,the temporal evolution of the RTI is more serious and the thin target is easier to tend to break.

关键词： Effects bubble Rayleigh

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Unified Variational Approach Description of Ground-State Phases of the Two-Dimensional Electron Gas

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Physical Review Letters 2024年第26期133卷 266504-266504页

作者： Conor Smith Yixiao Chen (陈一潇) Ryan Levy Yubo Yang (杨煜波) Miguel A. Morales Shiwei Zhang Center for Computational Quantum Physics Flatiron Institute New York New York 10010 USA Department of Electrical and Computer Engineering University of New Mexico Albuquerque New Mexico 87131 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

The two-dimensional electron gas (2DEG) is a fundamental model, which is drawing increasing interest because of recent advances in experimental and theoretical studies of 2D materials. Current understanding of the ground state of the 2DEG relies on quantum Monte Carlo calculations, based on variational comparisons of different Ansätze for different phases. We use a single variational ansatz, a general backflow-type wave function using a message-passing neural quantum state architecture, for a unified description across the entire density range. The variational optimization consistently leads to lower ground-state energies than previous best results. Transition into a Wigner crystal (WC) phase occurs automatically at rs=37±1, a density lower than currently believed. Between the liquid and WC phases, the same ansatz and variational search strongly suggest the existence of intermediate states in a broad range of densities, with enhanced short-range nematic spin correlations.

关键词： Wave functions

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