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A thermodynamically complete multi-phase equation of state for dense and porous metals at wide ranges of temperature and pressure

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Chinese physics B 2025年第3期34卷 499-504页

作者： Yanhong Zhao Li-Fang Wang Qili Zhang Le Zhang Hongzhou Song Xingyu Gao Bo Sun Haifeng Liu Haifeng Song National Key Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100094China

A thermodynamically complete multi-phase equation of state(EOS)applicable to both dense and porous metals at wide ranges of temperature and pressure is constructed.A standard three-term decomposition of the Helmholtz free energy as a function of specific volume and temperature is presented,where the cold component models both compression and expansion states,the thermal ion component introduces the Debye approximation and melting entropy,and the thermal electron component employs the Thomas-Fermi-Kirzhnits(TFK)*** porosity of materials is considered by introducing the dynamic porosity coefficientαand the constitutive P-αrelation,connecting the thermodynamic properties between dense and porous systems,allowing for an accurate description of the volume decrease caused by void collapse while maintaining the quasi-static thermodynamic properties of porous systems identical to the dense *** models enable the EOS applicable and robust at wide ranges of temperature,pressure and porosity.A systematic evaluation of the new EOS is conducted with aluminum(Al)as an example.300 K isotherm,shock Hugoniot,as well as melting curves of both dense and porous Al are calculated,which shows great agreements with experimental data and validates the effectiveness of the models and the accuracy of ***,it is for the first time Hugoniot P-σcurves up to 10~6 GPa and shock melting behaviors of porous Al are derived from analytical EOS models,which predict much lower compression limit and shock melting temperatures than those of dense Al.

关键词： equation of state multi-phase model porous metal

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LONG TIME EXISTENCE FOR THE NON-ISENTROPIC SLIGHTLY COMPRESSIBLE FLUID MODEL OF KORTEWEG TYPE

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Acta Mathematica Scientia 2025年第2期45卷 416-445页

作者： Qiangchang JU Jianjun XU Institute of Applied Physics and Computational Mathematics Beijing 100088China

We investigate the long time existence of strong solutions to the initial value problem for the three-dimensional non-isentropic compressible Navier-Stokes-Korteweg *** the conditions of slight density and temperature variations,we verify that the full compressible Navier-Stokes-Korteweg equations admit a unique strong solution as long as the solution of the limiting system exists,when the Mach number is sufficiently ***,we deduce the uniform convergence of strong solutions for the compressible system toward those for the corresponding incompressible system on the time interval in which the solution exists.

关键词： non-isentropic compressible Navier-Stokes-Korteweg equations low Mach num-ber limit long time existence strong solution

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Effect of order–disorder transition on thermodynamic and electronic properties of σ and χ phases in W–Re alloy: the first-principles calculation

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Tungsten 2025年第1期7卷 195-213页

作者： Zhi-Peng Zhu Dian Jia William Yi Wang Jun-Lei Yin Xing-Yu Gao Shu-Feng Yang Hai-Feng Song Jin-Shan Li State Key Laboratory of Solidification Processing Northwestern Polytechnical University Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics School of Metallurgical and Ecological Engineering University of Science and Technology Beijing

The Tungsten-Rhenium(W-Re) alloys,celebrated for their high melting point,strength at elevated temperatures,electrical resistivity,and radiation resistance,have been widely utilized in high-temperature components,aerospace,electronics,and nuclear *** constituents of the topologically close-packed(TCP) phases,the sigma phase(σ) and chi phase(χ) formed within W-Re alloys wield considerable influence on the mechanical properties and the stability of the *** calculations were utilized in the present work to explore the structural,thermodynamic,and electronic properties of both ordered and disordered configurations within the σ and χ phases,culminating in a systematic elucidation of the higher phase stability exhibited by the ordered *** is found that the bulk modulus of these two phases is directly proportional to the concentration of Re in the alloy,while the equilibrium volume is inversely *** thermodynamic parameters of the σ and χ phases are calculated via the mean-field potential *** similar trends observed in the isobaric heat capacity,enthalpy increment,and entropy change curves for these two phases suggest they possess comparable thermodynamic *** is noteworthy that the contribution of ionic vibrations predominantly affects the isobaric heat capacity,while the contribution of thermal electronic excitations increases linearly with *** the structure and thermodynamic properties of TCP phases in W-Re alloys at low temperatures has profound significance for optimizing material performance,microstructures features,establishing theoretical foundations,and predicting material behavior.

关键词： First-principles calculations Phase stability Thermodynamic properties W-Re alloy TCP phases

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Phonon-mediated superconductivity in orthorhombic XS(X=Nb,Ta or W)

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Chinese physics B 2025年第2期34卷 419-423页

作者： Guo-Hua Liu Kai-Yue Jiang Yi Wan Shu-Xiang Qiao Jin-Han Tan Na Jiao Ping Zhang Hong-Yan Lu School of Physics and Physical Engineering Qufu Normal UniversityQufu 273165China Institute of Applied Physics and Computational Mathematics Beijing 100088China

The unique three-dimensional orthorhombic NbS(o-NbS)compound synthesized in 1969 has recently been experimentally confirmed to be a superconductor[***.B 108174517(2023)].However,there is currently no theoretical research on its superconducting *** this work,we investigate the superconducting properties of o-Nb S from first-principles *** on the Eliashberg equation,it is found that the superconductivity mainly originates from the coupling between the electrons of Nb-4d orbitals and the vibrations of Nb atoms in the low-frequency region and those of S atoms in the high-frequency region.A superconducting transition temperature(T_c)of 10.7 K is obtained,which is close to the experimental value and higher than most transition metal chalcogenides(TMCs).The calculated thermodynamic properties in the superconducting state,such as specific heat,energy gap,isotope coefficient,etc.,also indicate that o-NbS is a conventional phonon-mediated *** results are consistent with recent experimental reports and provide a good understanding of the superconducting mechanism of o-Nb ***,the TMCs of o-TaS and o-WS are also investigated;these belong to the same and neighboring groups of Nb,and we find that o-TaS and o-WS are also phonon-mediated superconductors with T_c of 8.9 K and 7.2 K,respectively.

关键词： first-principles calculations phonon-mediated superconductivity orthorhombic transition metal chalcogenides

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The global existence and low Mach number limit for full Navier-Stokes equations around the Couette flow in a finite channel

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Science China mathematics 2025年

作者： Tuowei Chen Qiangchang Ju Institute of Applied Physics and Computational Mathematics

In this paper, we study the global existence and low Mach number limit of strong solutions to the2-D full compressible Navier-Stokes equations around the Couette flow in a horizontally periodic layer with non-slip and isothermal boundary conditions. It is shown that the Couette flow is asymptotically stable for sufficiently small initial perturbations, provided that the Reynolds number, Mach number and temperature difference between the top and the lower walls are small. For the case where both the top and the lower walls maintain the same temperature, we further prove that such global strong solutions converge to a steady solution of the incompressible Navier-Stokes equations as the Mach number goes to zero.

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MSene: A large family of two-dimensional transition metal sulfides with MXene structure

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Physical Review B 2025年第4期111卷 L041404-L041404页

作者： Shu-Xiang Qiao Yu-Lin Han Na Jiao Meng-Meng Zheng Hong-Yan Lu Ping Zhang School of Physics and Physical Engineering Qufu Normal University Qufu 273165 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China

In this Letter, we theoretically report a large family of two-dimensional (2D) transition metal sulfides M2S with a MXene structure in the 2H and 1T phases, which we refer to as MSene. Twenty-four out of fifty-eight MSenes are proved to be stable. Notably, this family includes twelve superconducting (SC) materials, seven SC topological metals (SCTMs), four charge density wave (CDW) materials, and five magnetic materials including one ferromagnetic (FM) and four A-type antiferromagnetic (AFM) materials. For example, 2H−Mo2S is a SCTM which exhibits a SC critical temperature (Tc) of 10.2 K and nontrivial topological properties; 1T−Hf2S is a CDW material with the CDW originating from electron-phonon coupling. The CDW can be suppressed by compressive strain, leading to the emergence of superconductivity; 2H−Cr2S and 1T−Mn2S show FM and A-type AFM properties, respectively. Thus, the large family we predicted shows rich physical properties and significantly expands the repertoire of 2D materials. It serves as a platform for investigating the competition or coexistence of multiple orders such as SC, CDW, FM, AFM, and topological orders in 2D materials.

关键词： Ferromagnetic materials

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The High-Order Variable-Coefficient Explicit-Implicit-Null Method for Diffusion and Dispersion Equations

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应用数学与计算数学学报 2025年第1期7卷 115-150页

作者： Meiqi Tan Juan Cheng Chi-Wang Shu Graduate School China Academy of Engineering PhysicsBeijing 100088China Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China HEDPS Center for Applied Physics and TechnologyCollege of EngineeringPeking UniversityBeijing 100871China Division of Applied Mathematics Brown UniversityProvidenceRI 02912USA

For the high-order diffusion and dispersion equations,the general practice of the explicit-implicit-null(EIN)method is to add and subtract an appropriately large linear highest derivative term with a constant coefficient at one side of the equation,and then apply the standard implicit-explicit method to the equivalent *** call this approach the con-stant-coefficient EIN method in this paper and hereafter denote it by"CC-EIN".To reduce the error in the CC-EIN method,the variable-coefficient explicit-implicit-null(VC-EIN)method,which is obtained by adding and subtracting a linear highest derivative term with a variable coefficient,is proposed and studied in this *** with the local discon-tinuous Galerkin(LDG)spatial discretization,the VC-EIN method is shown to be uncon-ditionally stable and can achieve high order of accuracy for both one-dimensional and two-dimensional quasi-linear and nonlinear *** addition,although the computational cost slightly increases,the VC-EIN method can obtain more accurate results than the CC-EIN method,if the diffusion coefficient or the dispersion coefficient has a few high and narrow bumps and the bumps only account for a small part of the whole computational domain.

关键词： Diffusion equation Dispersion equation Stability Explicit-implicit-null(EIN)time discretization Local discontinuous Galerkin(LDG)method

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A low Mach number asymptotic analysis of dissipation-reducing methods for curing shock instability

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applied mathematics and Mechanics(English Edition) 2025年第4期46卷 723-744页

作者： Hongping GUO Xun WANG Zhijun SHEN National Key Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsBeijing100088China Faculty of Mathematics Baotou Teachers’CollegeBaotouInner Mongolia Autonomous Region014030China School of Mathematical Sciences Peking UniversityBeijing100871China PKU-Changsha Institute for Computing and Digital Economy Changsha410205China Center for Applied Physics and Technology Peking UniversityBeijing100871China

We are intrigued by the issues of shock instability,with a particular emphasis on numerical schemes that address the carbuncle phenomenon by reducing dissipation rather than increasing *** a specific class of planar flow fields where the transverse direction exhibits vanishing but non-zero velocity components,such as a disturbed onedimensional(1D)steady shock wave,we conduct a formal asymptotic analysis for the Euler system and associated numerical *** analysis aims to illustrate the discrepancies among various low-dissipative numerical ***,a numerical stability analysis of steady shock is undertaken to identify the key factors underlying shock-stable *** verify the stability mechanism,a consistent,low-dissipation,and shock-stable HLLC-type Riemann solver is presented.

关键词： Riemann solver numerical shock instability low Mach number HLLC

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Research on Multimodal Brain Tumor Segmentation Algorithm Based on Feature Decoupling and Information Bottleneck Theory

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Computers, Materials & Continua 2025年第2期82卷 3281-3307页

作者： Xuemei Yang Yuting Zhou Shiqi Liu Junping Yin China Academy of Engineering Physics Graduate SchoolBeijing100193China Shanghai Zhangjiang Institute of Mathematics Biomedical LaboratoryShanghai201203China Institute of Applied Physics and Computational Mathematics Tang Chuang CentreBeijing100094China

Aiming at the problems of information loss and the relationship between features and target tasks in multimodal medical image segmentation, a multimodal medical image segmentation algorithm based on feature decoupling and information bottleneck theory is proposed in this paper. Based on the reversible network, the bottom-up learning method for different modal information is constructed, which enhances the features’ expression ability and the network’s learning ability. The feature fusion module is designed to balance multi-directional information flow. To retain the information relevant to the target task to the maximum extent and suppress the information irrelevant to the target task, the feature decoupling module is designed to ensure a strong correlation between the feature and the target task. A loss function based on information bottleneck theory was intended to improve information quality and remove redundant information. Based on BraTs2021, BraTs2023-MET and ANNLIB datasets, the proposed algorithm is analyzed qualitatively and quantitatively in this paper. In the quantitative experiment, the Dice coefficient of the proposed algorithm was increased by 0.110 on average compared with other methods, and the HD95 was decreased by 28.568 on average compared with other methods. In qualitative analysis, the proposed algorithm can effectively segment the incoherent region between the lesion and the lesion boundary and achieve accurate segmentation of the lesion.

关键词： Image fusion image segmentation deep learning

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Hörmander oscillatory integral operators:A revisit

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Science China mathematics 2025年第4期68卷 873-890页

作者： Chuanwei Gao Zhong Gao Changxing Miao School of Mathematical Sciences Capital Normal UniversityBeijing 100048China Institute of Applied Physics and Computational Mathematics Beijing 100088China

In this paper,we present new proofs for both the sharp Lp estimate and the decoupling theorem for the Hörmander oscillatory integral *** sharp Lp estimate was previously obtained by Stein(1986)and Bourgain and Guth(2011)via the TT^(*) and multilinear methods,*** provide a unified proof based on the bilinear method for both odd and even *** strategy is inspired by Barron’s work(2022)on the restriction *** decoupling theorem for the Hörmander oscillatory integral operator can be obtained by the approach in Beltran et al.(2020),where the key observation can be roughly formulated as follows:in a physical space of sufficiently small scale,the variable setting can be essentially viewed as *** contrast,we reprove the decoupling theorem for the Hörmander oscillatory integral operator through the Pramanik-Seeger approximation approach(Pramanik and Seeger(2007)).Both proofs rely on a scale-dependent induction argument,which can be used to deal with perturbation terms in the phase function.

关键词： Hormander oscillatory integral operators bilinear method decoupling inequality induction argument Broad-Narrow analysis

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