On constant-sign solutions of a system of discrete equations

We consider the following system of discrete equations $$u_i (k) = \sum\limits_{\ell = 0}^N {g_i (k,\ell )fi(\ell ,u_1 (\ell )} ,u_2 (\ell ), \cdots ,u_n (\ell )), k \in \{ 0,1, \cdots ,T\} ,$$ 1≤i≤n whereT≥N>0, 1≤i≤n. Existence criteria for single, double and multiple constant-sign solutions of the system are established. To illustrate the generality of the results obtained, we include applications to several well known boundary value problems. The above system is also extended to that on {0, 1,…} $$u_i (k) = \sum\limits_{\ell = 0}^\infty {g_i (k,\ell )fi(\ell ,u_1 (\ell )} ,u_2 (\ell ), \cdots ,u_n (\ell )), k \in \{ 0,1, \cdots \} ,1 \leqslant i \leqslant n$$ for which the existence of constant-sign solutions is investigated.     

Positive solutions for a system of nonlinear singular Hammerstein integral equations via nonnegative matrices and applications

We are concerned with the existence and multiplicity of positive solutions for the system of nonlinear singular Hammerstein integral equations $$u_i(t)=\int_a^bk_i(t,s)g_i(s)f_i(s,u_1(s),\ldots,u_n(s)) {\rm d} s,\quad i=1,2,\ldots,n.$$ We use fixed point index theory to establish our main results based on a priori estimates achieved by utilizing nonnegative matrices. As applications, the main results are applied to establish the existence and multiplicity of positive solutions for an elliptic system in an annulus.     

Positive solutions of BVPs for third-order discrete nonlinear difference systems

This paper is concerned with the following system $$\Delta ^3u_i(k)+f_i(k,u_1(k),u_2(k),\ldots,u_n(k))=0,\quad{}k\in [0,T],\ i=1,2,\ldots,n,$$ with the Dirichlet boundary condition $$u_i(0)=u_i(1)=u_i(T+3)=0,\quad{}i=1,2,\ldots,n.$$ Some results are obtained for the existence, multiplicity and nonexistence of positive solutions to the above system by using nonlinear alternative of Leray-Schauder type, Krasnosel’skii’s fixed point theorem in a cone and Leggett-Williams fixed point theorem. In particular, it proves that the above system has N positive solutions under suitable conditions, where N is an arbitrary integer.     

Constant-Sign Periodic and Almost Periodic Solutions for a System of Integral Equations

We consider the following system of integral equations $${u_{i}(t)=\int\nolimits_{I} g_{i}(t, s)f(s, u_{1}(s), u_{2}(s), \cdots, u_{n}(s))ds, \quad t \in I, \ 1 \leq i\leq n}$$ where I is an interval of $\mathbb{R}$ . Our aim is to establish criteria such that the above system has a constant-sign periodic and almost periodic solution (u ₁, u ₂,…,u _n ) when I is an infinite interval of $\mathbb{R}$ , and a constant-sign periodic solution when I is a finite interval of $\mathbb{R}$ . The above problem is also extended to that on $\mathbb{R}$ $$u_{i} {\left( t \right)} = {\int_\mathbb{R} {g_{i} {\left( {t,s} \right)}f_{i} {\left( {s,u_{1} {\left( s \right)},u_{2} {\left( s \right)}, \cdots ,u_{n} {\left( s \right)}} \right)}ds\quad t \in \mathbb{R},\quad 1 \leqslant i \leqslant n.} }$$      

Transformations z(t) = L(t)y(ϕ(t)) of ordinary differential equations

The paper describes the general form of an ordinary differential equation of an order n + 1 (n ≥ 1) which allows a nontrivial global transformation consisting of the change of the independent variable and of a nonvanishing factor. A result given by J. Aczél is generalized. A functional equation of the form $f\left( {s,w_{00} \upsilon _0 ,...,\sum\limits_{j = 0}^n {w_{nj\upsilon _j } } } \right) = \sum\limits_{j = 0}^n {w_{n + 1j\upsilon j} + w_{n + 1n + 1} f\left( {x,\upsilon ,\upsilon _1 ,...,\upsilon _n } \right),}$ where $w_{n + 10} = h\left( {s,x,x_1 ,u,u_1 ,...,u_n } \right),w_{n + 11} = g\left( {s,x,x_1 ,...,x_n ,u,u_1 ,...,u_n } \right){\text{ and }}w_{ij} = a_{ij} \left( {x_i ,...,x_{i - j + 1} ,u,u_1 ,...,u_{i - j} } \right)$ for the given functions a _ij is solved on $\mathbb{R},u \ne {\text{0}}$ .     

Solvability of nonlinear systems including (γ, δ)-comparison pairs

Let $\gamma ,\delta \in \mathbb{R}^n $ with $\gamma _j ,\delta _j \in \{ 0,1\} $ . A comparison pair for a system of equations f_i(u₁,…,u_n)=0 (i=1,…,n) is a pair of vectors $v,w \in \mathbb{R}^n ,v \leqslant w$ , such that $$\begin{array}{*{20}c} {\gamma _i f_i (u_1 , \ldots ,u_{i - 1} ,v_i ,u_i + 1, \ldots ,u_n ) \leqslant 0,} \\ {\delta _i f_i (u_1 , \ldots ,u_{i - 1} ,w_i ,u_i + 1, \ldots ,u_n ) \geqslant 0} \\ \end{array} $$ for $\gamma _j u_j \geqslant v_j ,\delta _j u_j \leqslant w_j (j = 1, \ldots ,n)$ . The presence of comparison pairs enables one to essentially weaken the assumptions of the existence theorem. Bibliography: 1 title.     

Strong convergence theorems for a Mann-type iterative scheme for a family of Lipschitzian mappings

In the paper, we obtain the existence of triple positive solutions for the following second order three-point boundary value problem, $$\left\{\begin{array}{l}(\phi_p(u'))'(t)+q(t)f(u(t),u'(t),(Tu)(t),(Su)(t))=0,\quad 0\leq t\leq1,\\[4pt]u'(0)=\beta u'(\eta),\qquad u(1)=g(u'(1)),\end{array}\right.$$ where $\phi_{p}(s)=|s|^{p-2}s,p>1,\beta\in[0,1),\eta\in(0,\frac{1}{2}]$ , T and S are all linear operators, g(t) is continuous.     

Multiple solutions of weakly-coupled systems with p-laplacian operators

We prove a multiplicity result for weakly-coupled systems with p-laplacian operators of the form $$(\phi_{pi}(u_{i}^{\prime}))^{\prime}+gi(u_i)=h_i(t,u,u^\prime),\qquad t\ \in \ (0,1),\qquad$$ Neumann boundary conditions are assumed and the nonlinearity is supposed to be superlinear asymmetric. We use a topological degree method based on a continuation theorem and on the performance of a time-map technique for the unperturbed case.     

Global existence of small radially symmetric solutions to quadratic nonlinear wave equations in an exterior domain

We study the initial boundary value problem for the nonlinear wave equation: (*) $$\left\{ \begin{gathered} \partial _t^2 u - (\partial _r^2 + \frac{{n - 1}}{r}\partial _r )u = F(\partial _t u,\partial _t^2 u),t \in \mathbb{R}^ + ,R< r< \infty , \hfill \\ u(0,r) = \in _0 u_0 (r),\partial _t u(0,r) = \in _0 u_1 (r),R< r< \infty , \hfill \\ u(t,R) = 0,t \in \mathbb{R}^ + , \hfill \\ \end{gathered} \right.$$ wheren=4,5,u ₀,u ₁ are real valued functions and ∈₀ is a sufficiently small positive constant. In this paper we shall show small solutions to (*) exist globally in time under the condition that the nonlinear termF:?²→? is quadratic with respect to ? _t u and ? _t ² u.     

On Stability and Convergence of the Finite Difference Methods for the Nonlinear Pseudo-Parabolic System

In this paper, we deal with the finite difference method for the initial boundary value problem of the nonlinear pseudo-parabolic system $(-1)^Mu_t+A(x,t,u,u_x,\cdots,u_x 2M-1)u_x2M_t=F(x,t,u,u_x,\cdots,u_x 2M)$,$u_xk(o,t)=\psi_{0k}(t), u_xk(L,t)=\psi_{1k}(t),k=0,1,\cdots,M-1,u(x,0)=\phi (x)$ in the rectangular domain $D=[0\leq X\leq L,0\leq t\leq T]$, where $u(x,t)=(u_1(x,t),u_2(x,t),\cdots,u_m(x,t)),\phi (x),\psi_{0k}(t),\psi_{1k}(t),F(x,t,u,u_x,\cdots,u_x 2M)$ are $m$-dimensional vector functions, and $A(x,t,u,u_x,\cdots,u_x2M-1)$ is an $m\times m$ positive definite matrix. The existence and uniqueness of solution for the finite difference system are proved by fixed-point theory. Stability, convergence and error estimates are derived.     

Three solutions of constant sign for a system of discrete equations

We consider the following system of discrete equations

Linear Approximation and Asymptotic Expansion of Solutions in Many Small Parameters for a Nonlinear Kirchhoff Wave Equation with Mixed Nonhomogeneous Conditions

In this paper, we consider the following nonlinear Kirchhoff wave equation

$\left\{\begin{array}{l}u_{tt}-\frac{\partial }{\partial x}(\mu (u,\Vert u_{x}\Vert ^{2})u_{x})=f(x,t,u,u_{x},u_{t}),\quad 0

(1)

where \(\widetilde{u}_{0}\), \(\widetilde{u}_{1}\), μ, f, g are given functions and \(\Vert u_{x}\Vert ^{2}=\int_{0}^{1}u_{x}^{2}(x,t)dx.\) To the problem (1), we associate a linear recursive scheme for which the existence of a local and unique weak solution is proved by applying the Faedo–Galerkin method and the weak compact method. In particular, motivated by the asymptotic expansion of a weak solution in only one, two or three small parameters in the researches before now, an asymptotic expansion of a weak solution in many small parameters appeared on both sides of (1)₁ is studied.

     

Extinction profile of the logarithmic diffusion equation

Let ${N \geq 3}$ and u be the solution of u _t = Δ log u in ${\mathbb{R}^N \times (0, T)}$ with initial value u ₀ satisfying ${B_{k_1}(x, 0) \leq u_{0} \leq B_{k_2}(x, 0)}$ for some constants k ₁ > k ₂ > 0 where ${B_k(x, t) = 2(N - 2)(T - t)_{+}^{N/(N - 2)}/(k + (T - t)_{+}^{2/(N - 2)}|x|^{2})}$ is the Barenblatt solution for the equation and ${u_0 - B_{k_0} \in L^{1}(\mathbb{R}^{N})}$ for some constant k ₀ > 0 if ${N \geq 4}$ . We give a new different proof on the uniform convergence and ${L^1(\mathbb{R}^N)}$ convergence of the rescaled function ${\tilde{u}(x, s) = (T - t)^{-N/(N - 2)}u(x/(T - t)^{-1/(N - 2)}, t), s = -{\rm log}(T - t)}$ , on ${\mathbb{R}^N}$ to the rescaled Barenblatt solution ${\tilde{B}_{k_0}(x) = 2(N - 2)/(k_0 + |x|^{2})}$ for some k ₀ > 0 as ${s \rightarrow \infty}$ . When ${N \geq 4, 0 \leq u_0(x) \leq B_{k_0}(x, 0)}$ in ${\mathbb{R}^N}$ , and ${|u_0(x) - B_{k_0}(x, 0)| \leq f \in L^{1}(\mathbb{R}^{N})}$ for some constant k ₀ > 0 and some radially symmetric function f, we also prove uniform convergence and convergence in some weighted L ¹ space in ${\mathbb{R}^N}$ of the rescaled solution ${\tilde{u}(x, s)}$ to ${\tilde{B}_{k_0}(x)}$ as ${s \rightarrow \infty}$ .     

A nonlinear third order multi-point boundary value problem in the resonance case

In this paper, we discuss the following third order ordinary differential equation $$x^{\prime\prime\prime}(t)=f(t,x(t),x^{\prime}(t),x^{\prime\prime}(t))+e(t),\quad t\in (0,1)$$ with the multi-point boundary conditions $$x^{\prime}(0)=\alpha x^{\prime}(\xi),\qquad x^{\prime\prime}(0)=0,\qquad x(1)=\sum^{m-2}_{j=1}\beta_{j}x(\eta_{j})$$ where β _j (1≤j≤m?2), α∈R, 0<η ₁<η ₂<???<η _m?2<1, 0<ξ<1. When the β _j ’s have no same sign, some existence results are given for the nonlinear problems at resonance case. An example is provided in this paper.     

Asymptotic behavior of eigenvalues for two-parameter perturbed elliptic Sine-Gordon type equations

We consider two types of the perturbed elliptic Sine-Gordon type equations on an interval $$\pm u^{\prime \prime}(t)+\lambda \ {\rm sin}\ u(t)=\mu f(u(t)),\ u(t)>0\ t\in I: =(-T,T),\ u(\pm T)=0,$$ where λ, μ > 0 are parameters and T > 0 is a constant. We shall establish asymptotic formulas for variational eigenvalues by using variational methods.     

Regularity for solutions to anisotropic obstacle problems

For Ω a bounded subset of R n,n 2,ψ any function in Ω with values in R∪{±∞}andθ∈W1,(q i)(Ω),let K(q i)ψ,θ(Ω)={v∈W1,(q i)(Ω):vψ,a.e.and v-θ∈W1,(q i)0(Ω}.This paper deals with solutions to K(q i)ψ,θ-obstacle problems for the A-harmonic equation-divA(x,u(x),u(x))=-divf(x)as well as the integral functional I(u;Ω)=Ωf(x,u(x),u(x))dx.Local regularity and local boundedness results are obtained under some coercive and controllable growth conditions on the operator A and some growth conditions on the integrand f.     

On oscillation of solutions of second-order systems of deviated differentaial equations

Sufficient conditions are found for the oscillation of proper solutions of the system of differential equations $$\begin{array}{*{20}c} {u'_1 (t) = f_1 (t,u_1 (\tau _1 (t)),...,u_1 (\tau _m (t)),u_2 (\sigma _1 (t)),...,u_2 (\sigma _m (t))),} \\ {u'_2 (t) = f_2 (t,u_1 (\tau _1 (t)),...,u_1 (\tau _m (t)),u_2 (\sigma _1 (t)),...,u_2 (\sigma _m (t))),} \\ \end{array}$$ wheref _i: R₊×R^2m→R (i=1,2) satisfy the local Carathéodory conditions andσ _i , τ _i :R ₊ →R (i=1,...,m) are continuous functions such that $\sigma _i (t) \leqslant t for t \in R_ + ,\mathop {\lim }\limits_{t \to + \infty } \sigma _i (t) = + \infty ,\mathop {\lim }\limits_{t \to + \infty } \tau _i (t) = + \infty (i = 1,...,m)$      

Constant-Sign Solutions for Systems of Fredholm and Volterra Integral Equations: The Singular Case

We consider the system of Fredholm integral equations

On the discrepancy function in arbitrary dimension, close to L 1

Let A _N to be N points in the unit cube in dimension d, and consider the discrepancy function $$ D_N (\vec x): = \sharp \left( {\mathcal{A}_N \cap \left[ {\vec 0,\vec x} \right)} \right) - N\left| {\left[ {\vec 0,\vec x} \right)} \right| $$ Here, $$ \vec x = \left( {\vec x,...,x_d } \right),\left[ {0,\vec x} \right) = \prod\limits_{t = 1}^d {\left[ {0,x_t } \right),} $$ and $ \left| {\left[ {0,\vec x} \right)} \right| $ denotes the Lebesgue measure of the rectangle. We show that necessarily $$ \left\| {D_N } \right\|_{L^1 (log L)^{(d - 2)/2} } \gtrsim \left( {log N} \right)^{\left( {d - 1} \right)/2} . $$ In dimension d = 2, the ‘log L’ term has power zero, which corresponds to a Theorem due to [11]. The power on log L in dimension d ≥ 3 appears to be new, and supports a well-known conjecture on the L ¹ norm of D _N . Comments on the discrepancy function in Hardy space also support the conjecture.