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Analysis of Maxwell’s Equations. Cosmic Magnetism 被引量:3
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作者 Vladimir S. Netchitailo 《Journal of High Energy Physics, Gravitation and Cosmology》 2018年第1期1-7,共7页
According to Hypersphere World-Universe Model, dark matter particles DIRACs are magnetic dipoles consisting of two Dirac’s monopoles. We conclude that DIRACs are the subject of Maxwell’s equations. So-called “auxil... According to Hypersphere World-Universe Model, dark matter particles DIRACs are magnetic dipoles consisting of two Dirac’s monopoles. We conclude that DIRACs are the subject of Maxwell’s equations. So-called “auxiliary” magnetic field intensity H is indeed current density of magnetic dipoles. The developed approach to magnetic field can explain a wealth of discovered phenomena in Cosmic Magnetism: a dark magnetic field, the large-scale structure of the Milky Way’s magnetic field, and other magnetic phenomena which are only partly related to objects visible in other spectral ranges. 展开更多
关键词 HYPERSPHERE World-Universe Model Maxwell’s equations Dirac’s Monopole MAGNETIC Dipole MAGNETIC FIELD Intensity MAGNETIC DIPOLES Current Density COSMIC MAGNETISM Dark MAGNETIC FIELD
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Hidden Properties of Mathematical Physics Equations. Double Solutions. The Realization of Integrable Structures. Emergence of Physical Structures and Observable Formations
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作者 L. I. Petrova 《Journal of Applied Mathematics and Physics》 2020年第7期1255-1262,共8页
With the help of skew-symmetric differential forms the hidden properties of the mathematical physics equations are revealed. It is shown that the equations of mathematical physics can describe the emergence of various... With the help of skew-symmetric differential forms the hidden properties of the mathematical physics equations are revealed. It is shown that the equations of mathematical physics can describe the emergence of various structures and formations such as waves, vortices, turbulent pulsations and others. Such properties of the mathematical physics equations, which are hidden (they appear only in the process of solving these equations), depend on the consistency of derivatives in partial differential equations and on the consistency of equations, if the equations of mathematical physics are a set of equations. This is due to the integrability of mathematical physics equations. It is shown that the equations of mathematical physics can have double solutions, namely, the solutions on the original coordinate space and the solutions on integrable structures that are realized discretely (due to any degrees of freedom). The transition from the solutions of the first type to one of the second type describes discrete transitions and the processes of origin of various structures and observable formations. Only mathematical physics equations, on what no additional conditions such as the integrability conditions are imposed, can possess such properties. The results of the present paper were obtained with the help of skew-symmetric differential forms. 展开更多
关键词 Integrability of Mathematical Physics equations Double Solutions Integrable Structures Discrete Transitions Skew-Symmetric Differential Forms
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McKean-Vlasov Backward Stochastic Differential Equations with Weak Monotonicity Coefficients
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作者 FU Zongkui FEI Dandan GUO Shanshan 《应用数学》 北大核心 2026年第1期98-107,共10页
This paper deals with Mckean-Vlasov backward stochastic differential equations with weak monotonicity coefficients.We first establish the existence and uniqueness of solutions to Mckean-Vlasov backward stochastic diff... This paper deals with Mckean-Vlasov backward stochastic differential equations with weak monotonicity coefficients.We first establish the existence and uniqueness of solutions to Mckean-Vlasov backward stochastic differential equations.Then we obtain a comparison theorem in one-dimensional situation. 展开更多
关键词 McKean-Vlasov backward stochastic differential equation Weak monotonicity condition Comparison theorem
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DEEP NEURAL NETWORKS COMBINING MULTI-TASK LEARNING FOR SOLVING DELAY INTEGRO-DIFFERENTIAL EQUATIONS 被引量:1
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作者 WANG Chen-yao SHI Feng 《数学杂志》 2025年第1期13-38,共26页
Deep neural networks(DNNs)are effective in solving both forward and inverse problems for nonlinear partial differential equations(PDEs).However,conventional DNNs are not effective in handling problems such as delay di... Deep neural networks(DNNs)are effective in solving both forward and inverse problems for nonlinear partial differential equations(PDEs).However,conventional DNNs are not effective in handling problems such as delay differential equations(DDEs)and delay integrodifferential equations(DIDEs)with constant delays,primarily due to their low regularity at delayinduced breaking points.In this paper,a DNN method that combines multi-task learning(MTL)which is proposed to solve both the forward and inverse problems of DIDEs.The core idea of this approach is to divide the original equation into multiple tasks based on the delay,using auxiliary outputs to represent the integral terms,followed by the use of MTL to seamlessly incorporate the properties at the breaking points into the loss function.Furthermore,given the increased training dificulty associated with multiple tasks and outputs,we employ a sequential training scheme to reduce training complexity and provide reference solutions for subsequent tasks.This approach significantly enhances the approximation accuracy of solving DIDEs with DNNs,as demonstrated by comparisons with traditional DNN methods.We validate the effectiveness of this method through several numerical experiments,test various parameter sharing structures in MTL and compare the testing results of these structures.Finally,this method is implemented to solve the inverse problem of nonlinear DIDE and the results show that the unknown parameters of DIDE can be discovered with sparse or noisy data. 展开更多
关键词 Delay integro-differential equation Multi-task learning parameter sharing structure deep neural network sequential training scheme
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Numerical Methods for Boundary Value Problems in Variable Coefficient Ordinary Differential Equations 被引量:1
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作者 ZHAO Ting-ting CAI Wei-yun 《Chinese Quarterly Journal of Mathematics》 2025年第3期295-303,共9页
In order to solve the problem of the variable coefficient ordinary differen-tial equation on the bounded domain,the Lagrange interpolation method is used to approximate the exact solution of the equation,and the error... In order to solve the problem of the variable coefficient ordinary differen-tial equation on the bounded domain,the Lagrange interpolation method is used to approximate the exact solution of the equation,and the error between the numerical solution and the exact solution is obtained,and then compared with the error formed by the difference method,it is concluded that the Lagrange interpolation method is more effective in solving the variable coefficient ordinary differential equation. 展开更多
关键词 Variable coefficient ordinary differential equations Lagrange interpolation Difference methods
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Two Second-Order Ecient Numerical Schemes for the Boussinesq Equations
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作者 LIU Fang WANG Danxia ZHANG Jianwen 《应用数学》 北大核心 2025年第1期114-129,共16页
In this paper,we construct two fully decoupled,second-order semi-discrete numerical schemes for the Boussinesq equations based on the scalar auxiliary variable(SAV)approach.By introducing a scalar auxiliary variable,t... In this paper,we construct two fully decoupled,second-order semi-discrete numerical schemes for the Boussinesq equations based on the scalar auxiliary variable(SAV)approach.By introducing a scalar auxiliary variable,the original Boussinesq system is transformed into an equivalent one.Then we discretize it using the second-order backward di erentiation formula(BDF2)and Crank-Nicolson(CN)to obtain two second-order time-advanced schemes.In both numerical schemes,a pressure-correction method is employed to decouple the velocity and pressure.These two schemes possess the desired property that they can be fully decoupled with satisfying unconditional stability.We rigorously prove both the unconditional stability and unique solvability of the discrete schemes.Furthermore,we provide detailed implementations of the decoupling procedures.Finally,various 2D numerical simulations are performed to verify the accuracy and energy stability of the proposed schemes. 展开更多
关键词 Scalar auxiliary variable approach Pressure-correction method Fully decoupled Unconditional stability Boussinesq equations
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Normalized Solutions of Nonlinear Choquard Equations with Nonconstant Potential
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作者 LI Nan XU Liping 《应用数学》 北大核心 2025年第1期14-29,共16页
In this paper,we mainly focus on a type of nonlinear Choquard equations with nonconstant potential.Under appropriate hypotheses on potential function and nonlinear terms,we prove that the above Choquard equation with ... In this paper,we mainly focus on a type of nonlinear Choquard equations with nonconstant potential.Under appropriate hypotheses on potential function and nonlinear terms,we prove that the above Choquard equation with prescribed 2-norm has some normalized solutions by introducing variational methods. 展开更多
关键词 Nonlinear Choquard equation Potential function Variational method Normalized solution
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Optimizing mesophase pitch spinning using melt spinning process equations and the fiber structure produced
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作者 SUN Xiang GONG Rui-fu LU Yong-gen 《新型炭材料(中英文)》 北大核心 2025年第6期1347-1361,共15页
Mesophase pitch carbon fibers have an ultra-high modulus and thermal conductivity that are unmatched by other carbon fibers,making it irreplaceable in many fields.However,due to the high temperature dependence of the ... Mesophase pitch carbon fibers have an ultra-high modulus and thermal conductivity that are unmatched by other carbon fibers,making it irreplaceable in many fields.However,due to the high temperature dependence of the viscosity of the melted pitch and the poor mechanical properties of pitch fibers,it is difficult to reduce the fiber diameter when using continuous spinning.We used the Mathworks Matlab software to optimize the mesophase pitch melt spinning model and to simulate the effects of spinning temperature,mass flow rate,winder speed,and quenching air temperature near the spinneret on the maximum shear rate during drawing.Simulation results demonstrate that applying gradient cooling to the melt upon exiting the spinneret significantly reduces the maximum shear rate and extends the drawing zone,thereby promoting the spinning stability and helping reduce the fiber diameter.In the experiment,instead of quenching in air,we applied gradient cooling to the melt,whose temperature decreased according to the equation Ta=298+278exp(−11.4z),where Ta is the final air temperature in Kelvin,and z is the distance from the spinneret in meters.It was found the gradient cooling greatly improved the draw-down ratio,reducing the average diameter of the pitch fibers from 20.8 to 13.1μm,along with improved process stability.The experimental results are in excellent agreement with the predictions.At the same time,the tensile strength of the 1150°C carbonized fibers increased from 0.6 to 1.1 GPa.Although the degree of orientation of the fibers decreased slightly,the tight bonding between microcrystals,the suppression of splitting,and the smaller diameter improved the mechanical properties of carbon fibers.This study provides an effective method for reducing the fiber diameter while improving continuity. 展开更多
关键词 Mesophase pitch Melt spinning equations SPINNABILITY Carbon fiber STRUCTURE
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Smoluchowski-Kramers Approximation for Stochastic Differential Equations under Discretization
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作者 Li Ge 《应用概率统计》 北大核心 2025年第4期622-635,共14页
This paper studies the Smoluchowski–Kramers approximation for a discrete-time dynamical system modeled as the motion of a particle in a force field.We show that the approximation holds for the drift-implicit Euler–M... This paper studies the Smoluchowski–Kramers approximation for a discrete-time dynamical system modeled as the motion of a particle in a force field.We show that the approximation holds for the drift-implicit Euler–Maruyama discretization and derive its convergence rate.In particular,the solution of the discretized system converges to the solution of the first-order limit equation in the mean-square sense,and this convergence is independent of the order in which the mass parameterμand the step size h tend to zero. 展开更多
关键词 stochastic differential equations Smoluchowski-Kramers approximation driftimplicit Euler-Maruyama scheme convergence rate
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A class of quasilinear equations with-1 powers
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作者 ZHANG Heng SUN Yijing 《中国科学院大学学报(中英文)》 北大核心 2025年第1期13-19,共7页
This paper deals with quasilinear elliptic equations of singular growth like-Δu-uΔ(u^(2))=a(x)u^(-1).We establish the existence of positive solutions for general a(x)∈L^(p)(Ω),p>2,whereΩis a bounded domain inℝ... This paper deals with quasilinear elliptic equations of singular growth like-Δu-uΔ(u^(2))=a(x)u^(-1).We establish the existence of positive solutions for general a(x)∈L^(p)(Ω),p>2,whereΩis a bounded domain inℝ^(N)with N≥1. 展开更多
关键词 quasilinear singular equation -1 power elliptic equation
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Two Efficient Numerical Algorithms for the Thermally Coupled Incompressible MHD Equations
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作者 LIAO Mingliang WANG Danxia 《应用数学》 北大核心 2025年第4期932-951,共20页
In this work,we construct two efficient fully decoupled,linear,unconditionally stable numerical algorithms for the thermally coupled incompressible magnetohydrodynamic equations.Firstly,in order to obtain the desired ... In this work,we construct two efficient fully decoupled,linear,unconditionally stable numerical algorithms for the thermally coupled incompressible magnetohydrodynamic equations.Firstly,in order to obtain the desired algorithm,we introduce a scalar auxiliary variable(SAV)to get a new equivalent system.Secondly,by combining the pressure-correction method and the explicit-implicit method,we perform semi-discrete numerical algorithms of first and second order,respectively.Then,we prove that the obtained algorithms follow an unconditionally stable law in energy,and we provide a detailed implementation process,which we only need to solve a series of linear differential equations with constant coefficients at each time step.More importantly,with some powerful analysis,we give the order of convergence of the errors.Finally,to illustrate theoretical results,some numerical experiments are given. 展开更多
关键词 Magnetohydrodynamic equation Fully decoupled Unconditionally stability Scalar auxiliary variable Error analysis
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Investigating Solutions in Nonlinear Evolution Equations:A Focus on Local Existence in Mixed Types
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作者 NAFFISA Toureche Trouba FAN Long ABDELGHANI Dahou 《应用数学》 北大核心 2025年第3期691-702,共12页
With the urgent need to resolve complex behaviors in nonlinear evolution equations,this study makes a contribution by establishing the local existence of solutions for Cauchy problems associated with equations of mixe... With the urgent need to resolve complex behaviors in nonlinear evolution equations,this study makes a contribution by establishing the local existence of solutions for Cauchy problems associated with equations of mixed types.Our primary contribution is the establishment of solution existence,illuminating the dynamics of these complex equations.To tackle this challenging problem,we construct an approximate solution sequence and apply the contraction mapping principle to rigorously prove local solution existence.Our results significantly advance the understanding of nonlinear evolution equations of mixed types.Furthermore,they provide a versatile,powerful approach for tackling analogous challenges across physics,engineering,and applied mathematics,making this work a valuable reference for researchers in these fields. 展开更多
关键词 Nonlinear evolution equation Contraction mapping principle Sobolev space Dissipative system
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Methods for Exact Solutions of Nonlinear Ordinary Differential Equations
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作者 Robert CONTE Micheline MUSETTE +1 位作者 Tuen Wai NG WU Chengfa 《数学进展》 北大核心 2025年第2期379-389,共11页
In order to find closed form solutions of nonintegrable nonlinear ordinary differential equations,numerous tricks have been proposed.The goal of this short review is to explain how a theorem of Eremenko on meromorphic... In order to find closed form solutions of nonintegrable nonlinear ordinary differential equations,numerous tricks have been proposed.The goal of this short review is to explain how a theorem of Eremenko on meromorphic solutions of some nonlinear ODEs together with some classical,19th-century results,can be turned into algorithms(thus avoiding ad hoc assumptions)which provide all(as opposed to some)solutions in a precise class.To illustrate these methods,we present some new such exact solutions,physically relevant. 展开更多
关键词 elliptic solution complex Ginzburg-Landau equation Closed-form solution Nevanlinna theory
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A New Class of Efficient Schemes for the Cahn-Hilliard-Navier-Stokes Equations
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作者 WANG Lijing WANG Danxia ZHANG Jianwen 《应用数学》 北大核心 2025年第3期607-624,共18页
In this paper,we construct a new class of efficient and high-order schemes for the Cahn-Hilliard-Navier-Stokes equations with periodic boundary conditions.These schemes are based on two types of scalar auxiliary varia... In this paper,we construct a new class of efficient and high-order schemes for the Cahn-Hilliard-Navier-Stokes equations with periodic boundary conditions.These schemes are based on two types of scalar auxiliary variable approaches.By using a new pressure correction method,the accuracy of the pressure has been greatly improved.Furthermore,one only needs to solve a series of fully decoupled linear equations with constant coefficients at each time step.In addition,we prove the unconditional energy stability of the schemes,rigorously.Finally,plenty of numerical simulations are carried out to verify the convergence rates,stability,and effectiveness of the proposed schemes numerically. 展开更多
关键词 Cahn-Hilliard-Navier-Stokes equation Scalar auxiliary variable Pressurecorrection Unconditional energy stability
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Symmetric Periodic Solution of Linear Periodic Matrix Equations via BCR Algorithm
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作者 MA Changfeng XIE Yajun 《数学进展》 北大核心 2025年第4期881-890,共10页
Analysis and design of linear periodic control systems are closely related to the periodic matrix equations.The biconjugate residual method(BCR for short)have been introduced by Vespucci and Broyden for efficiently so... Analysis and design of linear periodic control systems are closely related to the periodic matrix equations.The biconjugate residual method(BCR for short)have been introduced by Vespucci and Broyden for efficiently solving linear systems Aα=b.The objective of this paper is to provide one new iterative algorithm based on BCR method to find the symmetric periodic solutions of linear periodic matrix equations.This kind of periodic matrix equations has not been dealt with yet.This iterative method is guaranteed to converge in a finite number of steps in the absence of round-off errors.Some numerical results are performed to illustrate the efficiency and feasibility of new method. 展开更多
关键词 periodic matrix equation biconjugate residual method symmetric periodic solution convergence analysis
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Transportation Cost-information Inequalities for Stochastic Heat Equations Driven by Fractional Noise
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作者 ZHANG Bin YAO Zhigang LIU Junfeng 《数学进展》 北大核心 2025年第1期212-224,共13页
In this paper,we prove the transportation cost-information inequalities on the space of continuous paths with respect to the L~2-metric and the uniform metric for the law of the mild solution to the stochastic heat eq... In this paper,we prove the transportation cost-information inequalities on the space of continuous paths with respect to the L~2-metric and the uniform metric for the law of the mild solution to the stochastic heat equation defined on[0,T]×[0,1]driven by double-parameter fractional noise. 展开更多
关键词 transportation cost-information inequality stochastic heat equation fractional noise
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Normalized Positive Ground State Solutions for Nonhomogeneous Kirchhoff Equations
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作者 ZHANG Xiaocang XU Liping 《应用数学》 北大核心 2025年第3期711-720,共10页
This article studies a class of nonlinear Kirchhoff equations with exponential critical growth,trapping potential,and perturbation.Under appropriate assumptions about f and h,the article obtained the existence of norm... This article studies a class of nonlinear Kirchhoff equations with exponential critical growth,trapping potential,and perturbation.Under appropriate assumptions about f and h,the article obtained the existence of normalized positive solutions for this equation via the Trudinger-Moser inequality and variational methods.Moreover,these solutions are also ground state solutions.Additionally,the article also characterized the asymptotic behavior of solutions.The results of this article expand the research of relevant literature. 展开更多
关键词 Normalized positive ground state solution Nonhomogeneous Kirchhoff equation Variational method Exponential critical growth Trapping potential
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On Linear Equations with Three Prime Variables in Arithmetic Progressions
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作者 KONG Yafang 《数学进展》 北大核心 2025年第6期1233-1242,共10页
Let a_(1),a_(2),a_(3)be nonzero integers with gcd(a_(1),a_(2),a_(3))=1,and let k be any positive integer,K=max[3,|a_(1)|,|a_(2)|,|a_(3)|,k].Suppose that l_(1),l_(2),l_(3)are integers each coprime to k.Suppose further ... Let a_(1),a_(2),a_(3)be nonzero integers with gcd(a_(1),a_(2),a_(3))=1,and let k be any positive integer,K=max[3,|a_(1)|,|a_(2)|,|a_(3)|,k].Suppose that l_(1),l_(2),l_(3)are integers each coprime to k.Suppose further that b is any integer satisfying some necessary congruent conditions.The solvability of linear equation a_(1)p_(1)+a_(2)p_(2)+a_(3)p_(3)=b(p_(j)=l_(j)(mod k),1≤j≤3)with prime variables pi,p_(2),ps is investigated.It is proved that if ai,a_(2),a_(3)are all positive,then the above equation is solvable whenever b≥K^(25);if a,a_(2),a_(3)are not all of the same sign,then the above equation has a solution p_(1),p_(2),p_(3)satisfying max(p_(1),p_(2),p_(3))≤3|b|+K^(25). 展开更多
关键词 ternary linear equation small prime solution arithmetic progression
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Analytic Smoothing Effect of Cauchy Problem for a Class of Kolmogorov-Fokker-Planck Equations
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作者 CAO Xiaodong XU Chaojiang XU Yan 《数学进展》 北大核心 2025年第5期1015-1030,共16页
We study the Cauchy problem of the Kolmogorov-Fokker-Planck equations and show that the solution enjoys an analytic smoothing effect with L?initial datum for positive time.
关键词 Kolmogorov-Fokker-Planck equation analytic smoothing effect
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