Differential Equations Of Mixed Type Research Articles

Well-posedness of the Tricomi Problem for the Multidimensional Lavrent'ev-Bitsadze Equation

Numerous applications in physics and engineering involve models with partial differential equations of mixed type. The theory of boundary-value problems for such equations in two dimensions has been well studied. However, the key problem of well-posedness of mixed problems for such equations in multidimensional bounded domains remains currently unsolved. This paper establishes a mixed domain in which the solution of the Tricomi problem for the multidimensional Lavrent'ev-Bitsadze equation has a unique classical solution.

Oscillatory behavior of solutions of second-order non-linear differential equations with mixed non-linear neutral terms

This study primarily seeks to expand upon these developments by encompassing neutral differential equations of mixed type, incorporating both delay and advanced terms, particularly in the case of the canonical operator. The presented results are derived from the application of the comparison method, Riccati transformation, and integral averaging technique. These methodologies lead to substantial improvements and extensions of existing results found in the literature. Additionally, illustrative examples are provided to demonstrate the practical implications of the developed criteria.

Oscillation criteria for mixed neutral differential equations

<abstract><p>In this study, we aim to contribute to the increasing interest in functional differential equations by obtaining new theorems for the oscillation of second-order neutral differential equations of mixed type in a non-canonical form. The results obtained here improve and extend those reported in the literature. The applicability of the results is illustrated by several examples.</p></abstract>

Morawetz’s contributions to the mathematical theory of transonic flows, shock waves, and partial differential equations of mixed type

This article is a survey of Cathleen Morawetz’s contributions to the mathematical theory of transonic flows, shock waves, and partial differential equations of mixed elliptic-hyperbolic type. The main focus is on Morawetz’s fundamental work on the nonexistence of continuous transonic flows past profiles, Morawetz’s program regarding the construction of global steady weak transonic flow solutions past profiles via compensated compactness, and a potential theory for regular and Mach reflection of a shock at a wedge. The profound impact of Morawetz’s work on recent developments and breakthroughs in these research directions and related areas in pure and applied mathematics are also discussed.

Adapting PINN Models of Physical Entities to Dynamical Data

This article examines the possibilities of adapting approximate solutions of boundary value problems for differential equations using physics-informed neural networks (PINNs) to changes in data about the physical entity being modelled. Two types of models are considered: PINN and parametric PINN (PPINN). The former is constructed for a fixed parameter of the problem, while the latter includes the parameter for the number of input variables. The models are tested on three problems. The first problem involves modelling the bending of a cantilever rod under varying loads. The second task is a non-stationary problem of a thermal explosion in the plane-parallel case. The initial model is constructed based on an ordinary differential equation, while the modelling object satisfies a partial differential equation. The third task is to solve a partial differential equation of mixed type depending on time. In all cases, the initial models are adapted to the corresponding pseudo-measurements generated based on changing equations. A series of experiments are carried out for each problem with different functions of a parameter that reflects the character of changes in the object. A comparative analysis of the quality of the PINN and PPINN models and their resistance to data changes has been conducted for the first time in this study.

Partial Differential Equations of Mixed Type – Analysis and Applications

Partial Differential Equations of Mixed Type – Analysis and Applications

Rigorous verification of Hopf bifurcations in functional differential equations of mixed type

We propose a rigorously validated numerical method to prove the existence of Hopf bifurcations in functional differential equations of mixed type. The eigenvalue transversality and steady state conditions are verified using the Newton–Kantorovich theorem. The non-resonance condition and simplicity of the critical eigenvalues are verified by either computing a pair of generalized Morse indices of the step map, or by applying the argument principle to the characteristic equation and a suitable contour in the complex plane, computing the contour integral using the equivalence with a winding number. As a first application and test problem, we prove the existence of Hopf bifurcations in the Lasota–Wazewska–Czyzewska model and a pair of two such coupled equations. We then use our method to prove the existence of periodic traveling waves in the Fisher equation with nonlocal reaction. These periodic traveling waves are solutions of an ill-posed functional differential equation of mixed type.

Exponential dichotomies for nonlocal differential operators with infinite range interactions

We show that functional differential equations of mixed type (MFDEs) with infinite range discrete and/or continuous interactions admit exponential dichotomies, building on the Fredholm theory developed by Faye and Scheel for such systems. For the half line, we refine the earlier approach by Hupkes and Verduyn Lunel. For the full line, we construct these splittings by generalizing the finite-range results obtained by Mallet-Paret and Verduyn Lunel. The finite dimensional space that is ‘missed’ by these splittings can be characterized using the Hale inner product, but the resulting degeneracy issues raise subtle questions that are much harder to resolve than in the finite-range case. Indeed, there is no direct analogue for the standard ‘atomicity’ condition that is typically used to rule out degeneracies, since it explicitly references the smallest and largest shifts.We construct alternative criteria that exploit finer information on the structure of the MFDE. Our results are optimal when the coefficients are cyclic with respect to appropriate shift semigroups or when the standard positivity conditions typically associated to comparison principles are satisfied. We illustrate these results with explicit examples and counter-examples that involve the Nagumo equation.

An Oscillation Test for Solutions of Second-Order Neutral Differential Equations of Mixed Type

It is easy to notice the great recent development in the oscillation theory of neutral differential equations. The primary aim of this work is to extend this development to neutral differential equations of mixed type (including both delay and advanced terms). In this work, we consider the second-order non-canonical neutral differential equations of mixed type and establish a new single-condition criterion for the oscillation of all solutions. By using a different approach and many techniques, we obtain improved oscillation criteria that are easy to apply on different models of equations.

Inverse Boundary Value Problem for a Fractional Differential Equations of Mixed Type with Integral Redefinition Conditions

In this paper, we consider an inverse boundary value problem for a mixed type partial differential equation with Hilfer operator of fractional integro-differentiation in a positive rectangular domain and with spectral parameter in a negative rectangular domain. The differential equation depends from another positive parameter in mixed derivatives. With respect to first variable this equation is a fractional-order nonhomogeneous differential equation in the positive part of the considering segment, and with respect to second variable is a second-order differential equation with spectral parameter in the negative part of this segment. Using the Fourier series method, the solutions of direct and inverse boundary value problems are constructed in the form of a Fourier series. Theorems on the existence and uniqueness of the problem are proved for regular values of the spectral parameter. It is proved the stability of the solution with respect to redefinition functions, and with respect to parameter given in mixed derivatives. For irregular values of the spectral parameter, an infinite number of solutions in the form of a Fourier series are constructed.

NONLOCAL PROBLEM FOR A MIXED TYPE FOURTH-ORDER DIFFERENTIAL EQUATION WITH HILFER FRACTIONAL OPERATOR

In this paper, we consider a non-self-adjoint boundary value problem for a fourth-order differential equation of mixed type with Hilfer operator of fractional integro-differentiation in a positive rectangular domain and with spectral parameter in a negative rectangular domain. The mixed type differential equation under consideration is a fourth order differential equation with respect to the second variable. Regarding the first variable, this equation is a fractional differential equation in the positive part of the segment, and is a second-order differential equation with spectral parameter in the negative part of this segment. A rational method of solving a nonlocal problem with respect to the Hilfer operator is proposed. Using the spectral method of separation of variables, the solution of the problem is constructed in the form of Fourier series. Theorems on the existence and uniqueness of the problem are proved for regular values of the spectral parameter. For sufficiently large positive integers in unique determination of the integration constants in solving countable systems of differential equations, the problem of small denominators arises. Therefore, to justify the unique solvability of this problem, it is necessary to show the existence of values of the spectral parameter such that the quantity we need is separated from zero for sufficiently large \(n\). For irregular values of the spectral parameter, an infinite number of solutions in the form of Fourier series are constructed. Illustrative examples are provided.

Boundary Value Problem for Weak Nonlinear Partial Differential Equations of Mixed Type with Fractional Hilfer Operator

In this paper, we consider a boundary value problem for a nonlinear partial differential equation of mixed type with Hilfer operator of fractional integro-differentiation in a positive rectangular domain and with spectral parameter in a negative rectangular domain. With respect to the first variable, this equation is a nonlinear fractional differential equation in the positive part of the considering segment and is a second-order nonlinear differential equation with spectral parameter in the negative part of this segment. Using the Fourier series method, the solutions of nonlinear boundary value problems are constructed in the form of a Fourier series. Theorems on the existence and uniqueness of the classical solution of the problem are proved for regular values of the spectral parameter. For irregular values of the spectral parameter, an infinite number of solutions of the mixed equation in the form of a Fourier series are constructed.

Density Estimates for the Solutions of Backward Stochastic Differential Equations Driven by Gaussian Processes

The aim of this paper is twofold. Firstly, we derive upper and lower non-Gaussian bounds for the densities of the marginal laws of the solutions to backward stochastic differential equations (BSDEs) driven by fractional Brownian motions. Our arguments consist of utilizing a relationship between fractional BSDEs and quasilinear partial differential equations of mixed type, together with the profound Nourdin-Viens formula. In the linear case, upper and lower Gaussian bounds for the densities and the tail probabilities of solutions are obtained with simple arguments by their explicit expressions in terms of the quasi-conditional expectation. Secondly, we are concerned with Gaussian estimates for the densities of a BSDE driven by a Gaussian process in the manner that the solution can be established via an auxiliary BSDE driven by a Brownian motion. Using the transfer theorem we succeed in deriving Gaussian estimates for the solutions.

Nonlocal boundary value problems for the second order mixed type differential equation

Nonlocal boundary value problems for the second order mixed type differential equation

Nonlinear stability of pulse solutions for the discrete FitzHugh-Nagumo equation with infinite-range interactions

We establish the existence and nonlinear stability of travelling pulse solutions for the discrete FitzHugh-Nagumo equation with infinite-range interactions close to the continuum limit. For the verification of the spectral properties, we need to study a functional differential equation of mixed type (MFDE) with unbounded shifts. We avoid the use of exponential dichotomies and phase spaces, by building on a technique developed by Bates, Chen and Chmaj for the discrete Nagumo equation. This allows us to transfer several crucial Fredholm properties from the PDE setting to our discrete setting.

On the Asymptotic Behavior of Solutions of Neutral Mixed Type Differential Equations

In this study, the asymptotic behavior for solutions of neutral mixed type differential equation has been investigated, where some necessary and sufficient conditions are obtained to guarantee the convergence of all solutions of $$\begin{aligned} x^{\prime }(t)+a(t)x^{\prime }(\tau (t))+\sum _{i=1}^{k}b_{i}(t)x(\sigma _{i}(t))+\sum _{j=1}^{l}c_{j}(t)x(r_{j}(t))=0 \end{aligned}$$ to zero. An example is given to illustrate our main results.

Some New Oscillatory Behavior of Certain Third-Order Nonlinear Neutral Differential Equations of Mixed Type

By applying Riccati substitution techniques triply, we establish some new oscillation and asymptotic nature of solutions to the third-order nonlinear differential equations with mixed neutral type. We present many theorems and related examples in order to illustrate and substantiate the main theory.

Existence of solutions for a mixed type differential equation with state-dependence

In this paper we study a general n-dimensional mixed type differential equation with state dependence. Many known works give the existence of solutions with the so-called Return Condition. In this paper, without requiring the Return Condition, we prove a non-local existence of solutions by using a technique of compactification and the dependence of the maximum of functions on the size of their domains. We apply our result to differential equations with iterates.

Об одной спектральной задаче для системы дифференциальных уравнений смешанного типа

Изучаются спектральные характеристики дифференциального оператора, порожденного граничной задачей для линейной системы дифференциальных уравнений в частных производных смешанного типа. Простейшим примером классической системы уравнений в частных производных, попадающих в поле нашего рассмотрения, может служить система уравнений смешанного типа: $$D_tu_1-\mathopsign(t)D_xu_2-\varepsilon u_2=f_1, \quad D_tu_2+D_xu_1+\varepsilon u_1=f_2,$$ эллиптическая при $t>0$ и гиперболическая при $t<0$.

Nonlocal problem for a third order partial differential equation of mixed type with an integral two-space-variables condition

Nonlocal problem for a third order partial differential equation of mixed type with an integral two-space-variables condition