Problems Of Mathematical Physics Research Articles

Cauchy problem for the biharmonic equation in an unbounded region

The article studies the continuation of the solution of the Cauchy problem for the biharmonic equation in the domain G from its known values on the smooth part S of the boundary дG. The considered problem belongs to the problems of mathematical physics, in which there is no continuous dependence of solutions on the initial data. It is assumed that the solution to the problem exists and is continuously differentiable in a closed domain with exactly given Cauchy data. For this case, an explicit formula for the continuation of the solution is established.

Alternative Transient and Steady State Analysis of Some Gaver’s Parallel Systems

This paper presents one of the most interesting generalizations of Gaver’s basic two-unit parallel system sustained by a cold standby unit and attended by a repairman with multiple vacations. The system was studied using the supplementary variables technique, like many other similar semi-Markov systems. D.P. Gaver, Jr. was the first to apply this method for constructing and studying reliability models, and since then it has been then widely used by other researchers to study various reliability problems. As a result, non-classical boundary value problem of mathematical physics with nonlocal boundary conditions has been obtained. Until now, a solution to this problem was obtained in terms of Laplace transforms. Naturally, the most significant part of the problem is a system of partial differential equations (Kolmogorov forward equations). In this study, we demonstrate that Kolmogorov equations are redundant and we can solve the problem by avoiding the necessity of using them. We present here a novel, purely probabilistic approach. The results are formulated as rigorous mathematical statements, offering a significant simplification in the reliability analysis of stochastic systems. Our findings show that this novel approach can be applied to study both semi-Markov and some non semi-Markov models where the supplementary variables technique is used.

USING OPERATOR INEQUALITIES IN STABILITY RESEARCH OF DIFFERENCE SCHEMES FOR NONLINEAR BOUNDARY PROBLEMS WITH NONLINEARITY OF UNLIMITED GROWTH

The article develops the theory of stability of linear operator schemes for operator inequalities and nonlinear nonstationary initial-boundary value problems of mathematical physics with nonlinearities of unlimited growth. Based on sufficient conditions for the stability of A.A. Samarsky’s two-layer and three-layer difference schemes, the corresponding a priori estimates for operator inequalities are obtained under the condition of the criticality of the difference schemes under consideration, i.e. when the difference solution and its first time derivative are non-negative at all nodes of the grid region. The results obtained are applied to the analysis of the stability of difference schemes that approximate the Fisher and Klein-Gordon equation with a nonlinear right-hand side.

XXVIII International Conference on Integrable Systems and Quantum Symmetries (ISQS-28)

Abstract The XXVIII International Conference on Integrable Systems and Quantum Symmetries (ISQS-28), was organized by the Department of Mathematics, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University Prague. It belongs to a successful series of conferences held at the Czech Technical University which began in 1992, and it is devoted to problems of mathematical physics and in particular to the theory of integrable systems, quantum groups and quantum symmetries. This year the Conference attracted around 95 scientists from all over the world. 47 papers of plenary lectures and contributions presented at ISQS-28, are published in the present issue of the Journal of Physics: Conference Series. List of Conference board and Local organizing committee are available in this Pdf.

Computational study of thin films made from the ferroelectric materials with Paul Painlevé approach and expansion and variational methods

In this paper, the thin-film ferroelectric material equation which enables a propagation of solitary polarization in thin-film ferroelectric materials, and it also can be described using the nonlinear evolution equations. Ferroelectrics are dielectric materials explain wave propagation nonlinear behaviors. Thin films made from the ferroelectric materials are used in various modern electronics devices. The Paul-Painlevé approach is adopted for the first time to solve these nonlinear thin-film equation analytically. To investigate the characterizations of new waves, the solitary wave dynamics of the thin-film ferroelectric material equation are obtained using the standard \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ an (\\phi /2)$$\\end{document}-expansion technique and generalized G-expansion method. The bright and periodic solutions are obtained by semi-inverse variational principle scheme. Many alternative responses are achieved utilizing various formulaes; each of these solutions is shown by a distinct graph. The validity of such methods and solutions are demonstrated by assessing how well the relevant techniques and solutions match up. Three novel analytical and numerical techniques provide new, dependable approaches for determining and estimating responses. The effect of the free variables on the behavior of reached solutions to a few of graphs on the exact solutions is also explored depending upon the nature of nonlinearities. The simulations, which are exhibited in both two-dimensional (2D) and three-dimensional (3D), depict the behavior of a solitary solution in both the natural and digital worlds. These findings demonstrate that this strategy is the most effective way to solve nonlinear mathematical physics problems.

On one minimal hyperbolic Gellerstedt operator with internal degeneracy

The minimal operators generated by overdetermined boundary value problems for differential equations are extremely important in the description of regular boundary value problems for differential equations, and are also widely used in the study of local properties of solutions. The study of overdetermined boundary value problems is closely related to the theory of correct restrictions and extensions and the construction of minimal differential operators. In addition, for inverse problems of mathematical physics arising from applications, when determining unknown data, it is necessary to study problems with overdetermined boundary conditions, including minimal operators, which is reflected in the study of problems, including for hyperbolic equations and systems arising in physics, geophysics, seismic tomography, medicine and many other practical areas. Thus, the study of minimal operators is of both theoretical and applied interest. In this paper, a criterion for the invertibility of the minimal hyperbolic Gellerstedt operator with internal degeneracy is established. The proof is based on the Gellerstedt potential, properties of solutions to the Goursat problem, and properties of special functions. It should be noted that the Gellerstedt differential operator has numerous applications in transonic gas dynamics, the theory of infinitesimal surface bends, the instantaneous theory of shells with curvature of variable sign, magnetodynamics and hydrodynamics, and the conditions of invertibility of minimal operators imposed on the right side of the initial equation are widely used in the study of the so-called source problem, which arises in a variety of applications inverse problems of mathematical physics.

Martínez–Kaabar Fractal–Fractional Laplace Transformation with Applications to Integral Equations

This paper addresses the extension of Martinez–Kaabar (MK) fractal–fractional calculus (for simplicity, in this research work, it is referred to as MK calculus) to the field of integral transformations, with applications to some solutions to integral equations. A new notion of Laplace transformation, named MK Laplace transformation, is proposed, which incorporates the MK α,γ-integral operator into classical Laplace transformation. Laplace transformation is very applicable in mathematical physics problems, especially symmetrical problems in physics, which are frequently seen in quantum mechanics. Symmetrical systems and properties can be helpful in applications of Laplace transformations, which can help in providing an effective computational tool for solving such problems. The main properties and results of this transformation are discussed. In addition, the MK Laplace transformation method is constructed and applied to the non-integer-order first- and second-kind Volterra integral equations, which exhibit a fractal effect. Finally, the MK Abel integral equation’s solution is also investigated via this technique.

Mathematical Models for Removal of Pharmaceutical Pollutants in Rehabilitated Treatment Plants

This paper aims to investigate appropriate mathematical models devoted to the optimization of some cleaning processes related to pharmaceutical contaminant removal. In our recent works, we found the rehabilitation of the existing cleaning plants as a viable solution for the removal of this type of micropollutants from waters by introducing efficient techniques such as adsorption on granulated active carbon filters and micro-, nano-, or ultrafiltration. To have these processes under better control and to assure the transfer from small- to large-scale treatment stations, specific mathematical models are necessary. Starting from Navier–Stokes equations and imposing proper boundary conditions, some mathematical physics problems are obtained for which adequate solving methods via variational methods and surjectivity results are proposed. The importance of these solution characterizations consists in their continuation in adequate numerical methods and the possibility to visualize the result by using a CFD program.

Structure-preserving methods for Marcus stochastic Hamiltonian systems with additive Lévy noise

A general structure-preserving method is proposed for a class of Marcus stochastic Hamiltonian systems driven by additive Lévy noise. The convergence of the symplectic Euler scheme for this systems is investigated by Generalized Milstein Theorem. Realizable numerical implementation of this scheme is also provided in details. Numerical experiments are presented to illustrate the effectiveness and superiority of the proposed scheme. Applications of the method to solve two mathematical physical problems are provided.

Mathematical model for heat transfer during underground coal gasification process

Purpose. To develop a mathematical model of the “coal-gas” medium heat transfer during underground coal gasification to predict the combustion face advance velocity and the duration of gasification column mining. Methodology. To detect the temperature fields in the coal seam and gas, depending on the displacement length of the phase transition boundary, a boundary-value problem of mathematical physics has been developed. To solve this boundary-value problem, Boltzmann transformations, as well as methods for solving ordinary differential equations, are used. Newton-Raphson method, which has quadratic convergence, is used to find the roots of the transcendental equation. Findings. Tendencies in the formation of mathematical models when studying temperature fields around an underground gasifier have been analyzed, with highlighting their disadvantages. A mathematical model of heat transfer during underground gasification has been developed, taking into account the phase transition boundaries of the “coal-gas” medium. A computational experiment was conducted to determine the temperature of the phase transition boundary based on the length of the gasification column and the duration of the process. Originality. A mathematical model for heat transfer during coal gasification in the form of a boundary-value problem of mathematical physics, which consists of parabolic heat-transfer equations, the Stefan condition at the phase transition boundary, and the Dirichlet boundary conditions, has been constructed. As a result of solving the boundary-value problem, a self-similar solution has been obtained for the distribution of the coal seam and gas temperature fields, as well as the position of the phase transition boundary depending on the gasification duration and on the medium density, thermal conductivity coefficients, specific heat capacity of gas and coal, specific calorific value and temperature of coal combustion, initial coal temperature and constant temperature of the gasification process. The conducted analysis of numerical calculations provides a deeper understanding of the dynamics of underground coal gasification process and makes necessary corrections to achieve the maximum process efficiency. Practical value. A methodology for determining the displacement length of the phase transition boundary of the “coal-gas” medium has been developed, taking into account the change in the combustion face temperature along the gasification zone length depending on the duration of this process. Application of the methodology makes it possible to predict the time of mining the gasified coal column for drawing up a calendar plan for mining operations.

Метод R-функцій для розв’язання задачі масообміну циліндричного тіла з твірною у вигляді кривої Ламе з в’язкою нестисливою рідиною

The problem of stationary mass exchange of a cylindrical body with viscous incompressible fluid flow is reduced to solving the equation for concentration with the corresponding boundary conditions on the surface of the body and at infinity. Applying the constructive apparatus of the R-functions theory allows us to accurately take into account the geometry of the domain, as well as the boundary conditions together with the condition at infinity. The R-function method was proposed by V. L. Rvachev, Ukraine National Academy of Sciences academician. For boundary value problems of mathematical physics, this method allows constructing the so-called structure of the solution of the boundary value problem, i.e. a bundle of functions that accurately takes into account all boundary conditions of the problem and depends on some uncertain components. The choice of these uncertain components is performed in such a way as to satisfy (in a certain sense) the equation of the problem. For this, one can use standard numerical methods of mathematical physics (the Ritz method, the Galerkin method, the least squares method, collocations method, etc.). It should be noted that the geometry of the region is taken into account exactly, i.e. in particular, there is no replacement of curvilinear sections of the boundary with polygonal lines inscribed in them, as it is done, for example, in the finite element method. The purpose of this article is to apply the R-functions method to the problem of mass exchange of a cylindrical body formed by the Lame curve, with a viscous incompressible fluid flowing around it. To achieve this goal, a complete structure of the solution of a linear boundary value problem for concentration is constructed by the R-functions theory methods, and a numerical algorithm based on the Galerkin method for approximating indefinite components in the problem structure is used. The degree of rigor and the conditions for using the considered equations of fluid motion are not considered in the work; these equations are considered as mathematical models subject to numerical algorithmization

Solution of Inverse Photoacoustic Problem for Semiconductors via Phase Neural Network

The inverse photoacoustic problem is an ill-posed mathematical physics problem. There are many methods of solving the inverse photoacoustic problem, from parameter reduction to the development of complex regularization algorithms. The idea of this work is that semiconductor physical properties are determined from phase characteristic measurements because phase measurements are more sensitive than amplitude measurements. To solve the inverse photoacoustic problem, the thermoelastic properties and thickness of the sample are estimated using a neural network approach. The neural network was trained on a large database of photoacoustic phases calculated from a theoretical Si n-type model in the range of 20 Hz to 20 kHz, to which random Gaussian noise was applied. It is shown that in solving the inverse photoacoustic problem, high accuracy and precision can be achieved by applying phase measurement and neural network approaches. This study showed that a multi-parameter inverse problem can be solved using phase networks.

The overdetermined Cauchy problem for the hyperbolic Gellerstedt equation

Abstract Overdetermined boundary value problems and the minimal operators generated by them are extremely important in the description of regular boundary value problems for differential equations, and are also widely used in the study of local properties of solutions. In addition, for inverse problems of mathematical physics arising from applications, when determining unknown data, it is necessary to study problems with overdetermined boundary conditions, which is reflected in the study of problems, including for hyperbolic equations and systems, arising in physics, geophysics, seismic tomography, geoelectrics, electrodynamics, medicine, ecology, economics and many other practical areas. Thus, the study of overdetermined boundary value problems is of both theoretical and applied interest. In this paper, a criterion for the regular solvability of the overdetermined Cauchy problem for the Gellerstedt equation and the minimal differential operator generated by it in a hyperbolic domain is established, as which both the case of a characteristic triangle and the case of a more general domain with fairly general assumptions about the boundary of the domain are considered. Due to overdetermined boundary conditions, the problem under consideration will be ill-posed in the general case, therefore, for its regular solvability, additional conditions must be imposed on the initial data. In other words, we have considered the inverse problem: to determine what requirements the initial data of the problem, in particular the right part of the Gellerstedt equation, should meet, in question, so that the overdetermined Cauchy problem is regularly solvable. The proof is based on the Gellerstedt potential, the properties of solutions of the Goursat problem in the characteristic triangle, and the properties of special functions.

Gradient-type Approaches to Inverse and Ill-Posed Problems of Mathematical Physics

Gradient-type Approaches to Inverse and Ill-Posed Problems of Mathematical Physics

Asymptotic Criticality of the Navier–Stokes Regularity Problem

The problem of global-in-time regularity for the 3D Navier-Stokes equations, i.e., the question of whether a smooth flow can exhibit spontaneous formation of singularities, is a fundamental open problem in mathematical physics. Due to the super-criticality of the equations, the problem has been super-critical in the sense that there has been a ‘scaling gap’ between any regularity criterion and the corresponding a priori bound (regardless of the functional setup utilized). The purpose of this work is to present a mathematical framework-based on a suitably defined ‘scale of sparseness’ of the super-level sets of the positive and negative parts of the components of the higher-order spatial derivatives of the velocity field—in which the scaling gap between the regularity class and the corresponding a priori bound vanishes as the order of the derivative goes to infinity.

A novel study of analytical solutions of some important nonlinear fractional differential equations in fluid dynamics

The space-time fractional Burger-like equation and the space-time coupled Boussinesq equation with conformable derivative, both of which are significant in fluid dynamics, are investigated in this work using the improved [Formula: see text] method. The process works effectively and produces soliton solutions. The method was successfully and consistently implemented with Maple, a symbolic computing tool. The solutions also contain a few of graphics. Numerous novel exact solutions to these equations, distinct from those found earlier with the proposed approach, have been provided. The study’s findings add to the body of knowledge by offering insightful justifications for various types of nonlinear systems. The results demonstrated the value of the proposed method as a mathematical tool and the ease, dependability, and speed increases that result from carrying out these tasks using a symbolic computing program. Notably, it applies to many nonlinear evolution problems in mathematical physics.

Parabolic Boundary-Value Problems of Mathematical Physics in a Piecewise Homogeneous Wedge-Shaped Hollow Cylinder

Parabolic Boundary-Value Problems of Mathematical Physics in a Piecewise Homogeneous Wedge-Shaped Hollow Cylinder

Bessel equation and functions in computer mathematics system

The relevance of technical issues of solving problems of mathematical physics is growing every year. The development of computer technologies leads to the use of modern methods for their solution. The application of analytical computing systems is considered as an effective method, which contributes to their productive implementation. The article deals with finding a general solution of the Bessel equation and equations leading to it in the Maple program, graphs of functions are plotted

Singular backward stochastic Volterra integral equations in infinite dimensional spaces

In this paper, the notion of singular backward stochastic Volterra integral equations (singular BSVIEs for short) in infinite dimensional space is introduced, and the corresponding well-posedness is carefully established. A class of singularity conditions are proposed, which not only cover that of fractional kernel, Volterra Heston model kernel, completely monotone kernels, to mention a few, but also happen to be used in the forward stochastic Volterra integral with new conclusions arising. Motivated by mathematical physics problem such as the viscoelasticity/thermoviscoelasticity of materials, heat conduction in materials with memory, optimal control problems of abstract stochastic Volterra integral equations (including fractional stochastic evolution equations and stochastic evolutionary integral equations) are presented. At last, our BSVIEs are surprisingly used in maximum principle of controlled stochastic delay evolution equations. One advantage of this new standpoint is that the final cost functional can naturally depend on the past state.

Innovative coupling of s-stage one-step and spectral methods for non-smooth solutions of nonlinear problems

The behavior of nonlinear dynamical systems arising in mathematical physics through numerical tools is a challenging task for researchers. In this context, an efficient semi-spectral method is proposed and applied to observe the robust solutions for the mathematical physics problems. Firstly, the space variable is approximated by the Vieta-Lucas polynomials and then the s-stage one-step method is applied to discretize the temporal variable which transfers the problem in the form Cn+1=Cn+Δtϕ(x,t,Cn,F(un)). Novel operational matrices of integer order are developed to replace the spatial derivative terms presented in the discussed problem. Related theorems are included in the study to validate the approach mathematically. The proposed semi-spectral schemes convert the considered nonlinear problem to a system of linear algebraic equations which is easier to tackle. We also accomplish an investigation on the error bound and convergence to confirm the mathematical formulation of the computational algorithm. To show the accuracy and effectiveness of the suggested computational method numerous test problems, such as the advection-diffusion problem, generalized Burger-Huxley, sine-Gordon, and modified KdV–Burgers’ equations are considered. An inclusive comparative examination demonstrates the currently suggested computational method in terms of credibility, accuracy, and reliability. Moreover, the coupling of the spectral method with the fourth-order Runge-Kutta method seems outstanding to handle the nonlinear problem to examine the precise smooth and non-smooth solutions of physical problems. The computational order of convergence (COC) is computed numerically through numerous simulations of the proposed schemes. It is found that the proposed schemes are in exponential order of convergence in the spatial direction and the COC in the temporal direction validates the studies in the literature.