Differential Equations Of Elliptic Type Research Articles

Computing enhancement of the nonlinear SPN approximations of radiative heat transfer in participating material

Anisotropic mesh adaptation is an efficient procedure for controlling the output error of finite element simulations, particularly when used for three-dimensional problems. In this paper, we present an enhanced computational algorithm based on an anisotropic mesh adaptation for nonlinear SPN approximations of radiative heat transfer in both two- and three-dimensional enclosures. Using an asymptotic analysis for the optical scale in the radiative transfer, the integro-differential equation is replaced by a series of partial differential equations of elliptic type. The nonlinear coupling between the heat transfer and radiation in the SPN equations does not depend on the direction ordinates. In an anisotropic participating media, internal boundary layers with different magnitudes occur for each direction and developing an efficient numerical algorithm to accurately resolve them is a challenging task. In the present study, we propose an adaptive finite element method using an efficient hierarchical error estimator. A second-order scheme is used for the time integration and a Newton-type solver is implemented for the fully coupled nonlinear system. The proposed method has the potential to use large timesteps in the simulations for radiative heat transfer in anisotropic media at high temperatures. To demonstrate the viability of the method, several examples are presented for two- and three-dimensional problems. The numerical results confirm the capability of the proposed method to efficiently solve the nonlinear SPN approximations of radiative transfer in anisotropic media.

On an elliptic chemotaxis system with flux limitation and subcritical signal production

In this article we study the existence of solutions of a system of partial differential equations of elliptic type, describing the distribution of a biological species “u” and the density of a chemical stimulus “ψ” in a bounded domain Ω of RN. The equation for u includes a chemotaxis term with nonlinear flux limitation which depends on the exponent p>1.The equation for u is given by −div(M(x)∇u)+u=−χdiv(u|∇ψ|p−2∇ψ)+f(x),where ψ presents a subcritical production term uθ and satisfies the equation −div(M(x)∇ψ)+ψ=uθ.The matrix of coefficients, M, is a known, symmetric and positive defined with coefficients mij∈C1(Ω¯),χ is a given real constant, f is a non-negative function belonging to Lm(Ω), m>max{1,N2}. The production term exponent, θ, is assumed to be positive and fulfills one of the following constrains 1<p<NθNθ−1,1<Nθor max{N,p}<θ+1θ for θ>0.The problem is completed with Dirichlet boundary conditions for u and ψ. The main result of the article includes the existence of positive solutions in H01(Ω)∩L∞(Ω).

On approximation of functions from the class $L^{\psi}_{\beta, 1}$ by the Abel-Poisson integrals in the integral metric

In the paper, we investigate an asymptotic behavior of the sharp upper bounds in the integral metric of deviations of the Abel-Poisson integrals from functions from the class $L^{\psi}_{\beta, 1}$. The Abel-Poisson integrals are solutions of the partial differential equations of elliptic type with corresponding boundary conditions, and they play an important role in applied problems. The approximative properties of the Abel-Poisson integrals on different classes of differentiable functions were studied in a number of papers. Nevertheless, a problem on the respective approximation on the classes $L^{\psi}_{\beta,1}$ in the metric of the space $L$ remained unsolved. We managed to obtain the estimates for the values of approximation of $(\psi, \beta)$-differentiable functions from the unit ball of the space $L$ by the Abel-Poisson integrals. In some cases, we also write down asymptotic equalities for these quantities, that is we solve the Kolmogorov-Nikol'skii problem for the the Abel-Poisson integrals on the classes $L^{\psi}_{\beta,1}$ in the integral metric.

Differential Equations of Elliptic Type with Variable Operators and Homogeneous Robin Boundary Value Condition in UMD Spaces

Differential Equations of Elliptic Type with Variable Operators and Homogeneous Robin Boundary Value Condition in UMD Spaces

The Continuous Classical Boundary Optimal Control of Triple Nonlinear Elliptic Partial Differential Equations with State Constraints

Our aim in this work is to study the classical continuous boundary control vector problem for triple nonlinear partial differential equations of elliptic type involving a Neumann boundary control. At first, we prove that the triple nonlinear partial differential equations of elliptic type with a given classical continuous boundary control vector have a unique "state" solution vector, by using the Minty-Browder Theorem. In addition, we prove the existence of a classical continuous boundary optimal control vector ruled by the triple nonlinear partial differential equations of elliptic type with equality and inequality constraints. We study the existence of the unique solution for the triple adjoint equations related with the triple state equations.&#x0D; The Fréchet derivative is obtained. Finally we prove the theorems of both the necessary and sufficient conditions for optimality of the triple nonlinear partial differential equations of elliptic type through the Kuhn-Tucker-Lagrange's Multipliers theorem with equality and inequality constraints.

A family of effective structure-preserving schemes with second-order accuracy for the undamped sine–Gordon equation

In this paper, a family of linear structure-preserving (energy conservation) schemes with second-order accuracy in the time direction is developed to numerically solve the undamped sine–Gordon equation. To be specific, first, transformation of the undamped sine–Gordon system into an equivalent new system is made by introducing an improved scalar auxiliary variable (SAV), and generalization of the conservative Crank–Nicolson scheme is made by applying a non-negative family parameter ϑ to discretize time-dependent variables at the time step (n+ϑ) instead of just (n+1∕2), thereby to establish a family of second-order conservative semi-discrete schemes. Further, based on the advantages of the improved SAV method, not only does the newly introduced scalar auxiliary variable be uncoupled with the original variables at the discrete level, it also requires the family of approximations, at each time step, no more efforts than the solution of a second-order linear differential equation of elliptic type with constant coefficients, making the computational cost of this method only half of the original one, which thus is particularly effective. Finally, several numerical experiments are presented to demonstrate the efficiency, stability, accuracy and energy conservation of the family of schemes developed herein.

О приближении функций класса Зигмунда бигармоническими интегралами Пуассона

Работа посвящена изучению поведения верхнего предела отклонения функций класса Зигмунда от их бигармонических интегралов Пуассона. Исследования в данном направлении проводились и проводятся систематически как отечественными, так и зарубежными учеными. Большинство полученных результатов относится к оценке отклонений функций того или иного класса от операторов, построенных с помощью треугольных методов суммирования рядов Фурье (Фейера, Валле Пуссена, Рисса, Рогозинского, Стеклова, Фавара и др.). Что касается результатов относительно линейных методов суммирования рядов Фурье, заданных с помощью множества функций натурального аргумента (Абеля-Пуассона, Гаусса-Вейерштрасса, бигармонического и трехгармонического интегралов Пуассона), то здесь успехи менее заметны. Возможно, это связано с тем, что упомянутые выше линейные методы суммирования рядов Фурье являются решениями соответствующих интегрально-дифференциальных уравнений эллиптического типа и поэтому требуют более трудоемких вычислений с целью получения для них определенных оценок, пригодных для их непосредственное использование в прикладных целях. Исследования, проведенные в данной работе, относятся к изучению апроксимативных характеристик линейных положительных операторов типа Пуассона на классах функций Зигмунда. Согласно хорошо известным результатам П.П. Коровкина именно эти положительные линейные операторы осуществляют наилучшее асимптотическое приближение функций класса Зигмунда. Таким образом, полученная в данной работе оценка отклонения функций класса Зигмунда от их бигармонических интегралов Пуассона (наименее исследованных и наиболее востребованных среди всех линейных положительных операторов) актуальна с точки зрения прикладной математики.

О ПРИБЛИЖЕНИИ ФУНКЦИЙ ИНТЕГРАЛАМИ ГАУССА–ВЕЙЕРШТРАССА

Рассматривая разные схемы и алгоритмы игровых задач динамики, исследователи часто сталкиваются с решением дифференциальных уравнений в частных производных. Особое место среди последних занимают так называемые уравнения эллиптического типа (согласно соответствующей классификации), с помощью которых наиболее полно и качественно можно описать естественные и социальные процессы. Кроме того, математический аппарат дифференциальных уравнений в част-ных производных эллиптического типа позволяет проникать в среду детерминированных явлений и предсказывать их будущее. В то же время одним из самых важных понятий прикладной математики является понятие модуля непрерывности. Термин «модуль непрерывности» и его определение был введен Анри Лебегом в начале прошлого века с целью изучения разнообразных свойств непрерывных функций. Используя понятие модуля непрерывности и его свойства, можно исследовать принадлежность изучаемого объекта к определенному классу функций: Гельдера, Липшица, Зигмунда и т.д. Это, несомненно, позволяет наиболее эффективно осуществлять приближение функций различного рода операторами. В данной работе на примере интеграла Гаусса-Вейерштрасса, как решение соответствующего дифференциального уравнения эллиптического типа, исследуется его скорость сходимости в терминах модуля непрерывности второго порядка к функции, по которой он фактически был построен. А именно, были изучены предельные свойства интеграла Гаусса-Вейерштрасса, как линейного положительного оператора, осуществляющего свое наилучшее приближение на функциях класса Зигмунда. Полученные в данной статье результаты в дальнейшем могут использоваться при решении многих задач прикладной математики.

APPLICATION OF FUNCTIONAL RELATIONS TO MODELING BY MEANS OF DIFFERENTIAL EQUATIONS

Modeling by means of differential equations is considered in the paper. Their solutions are constructed on the base of functional relations connecting values of a solution of the equation in different points (infinite or finite set of values). For examples, even, odd and periodical solutions, Vallée-Poussin’s assertion, Lagrange interpolation polynomial, Hermite interpolation polynomial, spline-functions for ordinary differential equations, Asgeirsson’s identity and its generalizations for partial differential equations of hyperbolic type, “mean value” for partial differential equations of elliptic type are considered. Also, if an equation is close to one of considered types then an assertion is to be fulfilled approximately. Some estimations are found for such examples. An application of such relations to investigate some problems of interpolation and extrapolation is demonstrated.

Lucid characterization of unsteady heat conduction in large, square crossbars and cubes subject to uniform surface heat flux by way of “quasi–steady” Helmholtz equations

The technical paper addresses unsteady heat conduction in large, square crossbars and cubes heated continually with uniformly surface heat flux. The uniform surface heat flux is customarily provided by electrical, radiative and pool fire heating in engineering applications. This type of heating fall under the category of non-homogeneous Neumann boundary conditions. The existing traditional method for solving the unsteady, heat conduction equation in two and three dimensions with constant thermo-physical properties and subject to non-homogeneous uniform heat flux boundary conditions is the principle of superposition of partial solutions of simpler unsteady, heat conduction equations. For the latter, the exact, analytical temperature distributions are customarily expressed by infinite series regardless of the solution method. For the numerical evaluation of spatio-temporal temperatures, the main inconvenience of the infinite series lies in the poor convergence when the time is small. To prevent the impeding obstacle, the Transversal Method Of Lines (TMOL) is implemented in this work to transform the unsteady, two- and three-dimensional heat conduction equations into degraded “quasi steady”, two- and three-dimensional heat conduction equations, namely the homogeneous Helmhotz equations. Thereby, the exact, analytical solutions of the converted partial differential equations of elliptic type and homogeneous were determined by the standard method of separation of variables. The resulting approximate, semi-analytical two- and three-dimensional temperature distributions for large, square crossbars and cubes do not contain elaborate infinite series. Instead, the temperature disdtributions contain hyperbolic functions elucidating worthy compactness and superb quality, regardless of the time, either “small time”, “moderate time” or “large time”.

Asymptotics of the Solution to the Boundary-Value Problems with Non Smooth Coefficient

The first boundary-value problem for a linear inhomogeneous second-order partial differential equation of elliptic type with two independent variables in a ring is investigated in the case when the potential is a non smooth function. Using the modified method of boundary functions, a uniform asymptotic expansion of the solution of the Dirichlet problem is constructed. The maximum principle is used to obtain an estimate for the remainder term of the asymptotic expansion. The resulting series is asymptotic in the sense of Erdey.

New Results on Elliptic Equations with Nonlocal Boundary Coefficient-Operator Conditions in UMD Spaces: Noncommutative Cases

This paper is devoted to the abstract study of operational second-order differential equations of elliptic type with nonregular coefficient-operator boundary conditions in a non-commutative framework. The study is performed when the second member f belongs to $$L^{p}(0,1;X)$$, with general $$p\in ]1,+\infty [$$, X being a UMD Banach space. We give some new results by using semigroups and interpolation theory. Existence, uniqueness and optimal regularity of the classical and semi-classical solution are proved. This paper improves naturally the ones studied in the commutative case by Hammou et al. (Mediterr J Math, 1669–1683, 2015).

Backward SDEs and infinite horizon stochastic optimal control

We study an optimal control problem on infinite horizon for a controlled stochastic differential equation driven by Brownian motion, with a discounted reward functional. The equation may have memory or delay effects in the coefficients, both with respect to state and control, and the noise can be degenerate. We prove that the value, i.e. the supremum of the reward functional over all admissible controls, can be represented by the solution of an associated backward stochastic differential equation (BSDE) driven by the Brownian motion and an auxiliary independent Poisson process and having a sign constraint on jumps. In the Markovian case when the coefficients depend only on the present values of the state and the control, we prove that the BSDE can be used to construct the solution, in the sense of viscosity theory, to the corresponding Hamilton-Jacobi-Bellman partial differential equation of elliptic type on the whole space, so that it provides us with a Feynman-Kac representation in this fully nonlinear context. The method of proof consists in showing that the value of the original problem is the same as the value of an auxiliary optimal control problem (called randomized), where the control process is replaced by a fixed pure jump process and maximization is taken over a class of absolutely continuous changes of measures which affect the stochastic intensity of the jump process but leave the law of the driving Brownian motion unchanged.

Формирование моделей радиолокационных изображений в виде стохастических дифференциальных уравнений для распознавания космических объектов

The resource problems of the traditional use of detailed radar images for reliable recognition of space objects are shown. The urgent task of forming a new type of model of radar images of space objects to determine the signs of their recognition is posed. Corresponding mathematical models of such images based on stochastic differential equations of elliptic type are presented. The adequacy of the developed models to the real radar images of a space object was assessed. It is established that for the description of radar images of space objects the most suitable is a modified model in the form of a mixed derivative of an elliptical model. To test the hypothesis about the possibility of using the radar image model when constructing descriptive recognition signs, an experiment was conducted to distinguish four different types of space objects. The experimental results showed the possibility of using a mixed derivative of the elliptical model to determine signs of recognition of space objects.

Geometric grid network and third-order compact scheme for solving nonlinear variable coefficients 3D elliptic PDEs

By using nonuniform (geometric) grid network, a new high-order finite-difference compact scheme has been obtained for the numerical solution of three-space dimensions partial differential equations of elliptic type. Single cell discretization to the elliptic equation makes it easier to compute and exhibit stability of the numerical solutions. The monotone and irreducible property of the Jacobian matrix to the system of difference equations analyses the converging behavior of the numerical solution values. As an experiment, applications of the compact scheme to Schrödinger equations, sine-Gordon equations, elliptic Allen–Cahn equation and Poisson’s equation have been presented with root mean squared errors of exact and approximate solution values. The results corroborate the reliability and efficiency of the scheme.

Local properties of certain solutions of differential equations of elliptic type

Local properties of certain solutions of differential equations of elliptic type

Some properties of zeros of solutions of second-order linear partial differential equations of elliptic type

Some properties of zeros of solutions of second-order linear partial differential equations of elliptic type

Uniqueness theorem for linear elliptic equation of the second order with constant coefficients

The interior uniqueness theorem for analytic functions was generalized by M. B. Balk to the case of polyanalytic functions of order n. He proved that if the zeros of a polyanalytic function have an accumulation point of order n, then this function is identically zero. In this paper the interior uniqueness theorem is generalized to the solution to a linear homogeneous second order differential equation of elliptic type with constant coefficients.

Numerical solution of optimization problems for semi-linear elliptic equations with discontinuous coefficients and solutions

In this work we consider optimization problems for processes described by semi-linear partial differential equations of elliptic type with discontinuous coefficients and solutions (with imperfect contact matching conditions), with controls involved in the coefficients. Finite difference approximations of optimization problems are constructed. For the numerical implementation of finite optimization problems differentiability and Lipshitz-continuity of the grid functional of the approximating grid problems are proved. An iterative method for solving boundary value problems of contact for PDEs of elliptic type with discontinuous coefficients and solutions is developed and validated. The convergence of the iterative process is investigated. And the convergence rate of iterations (with calculated constants) is estimated.

Nonlocal General Boundary Value Problems of Elliptic Type in L p Cases

This paper is devoted to the study of operational second-order differential equations of elliptic type with nonregular coefficient-operator boundary conditions. In the framework of UMD spaces, we give some new results by using semi-groups and interpolation theory. We define two types of solutions: semi-strict and strict solutions. We then characterizes the existence and uniqueness of such solutions.