We give existence theorems for weak and strong solutions with trichotomy of the nonlinear differential equation $$\dot{x}\left(t\right)=ℒ\left(t\right)x\left(t\right)+f(t,x\left(t\right)),t\in ℝ\left(\mathrm{P}\right)$$ where $\left\{ℒ\right(t):t\in ℝ\}$ is a family of linear operators from a Banach space $E$ into itself and $f:ℝ\times E\to E$. By $L\left(E\right)$ we denote the space of linear operators from $E$ into itself. Furthermore, for $a<b$ and $d>0$, we let $C\left(\right[-d,0],E)$ be the Banach space of continuous functions from $[-d,0]$ into $E$ and $f^d:[a,b]\times C([-d,0],E)\to E$. Let $\widehat{ℒ}:[a,b]\to L\left(E\right)$ be a strongly measurable and Bochner integrable operator on $[a,b]$ and for $t\in [a,b]$ define ${\tau }_{t}x\left(s\right)=x(t+s)$ for each $s\in [-d,0]$. We prove that, under certain conditions,...

We develop the existence theory for sequential fractional differential equations involving Liouville-Caputo fractional derivative equipped with anti-periodic type (non-separated) and nonlocal integral boundary conditions. Several existence criteria depending on the nonlinearity involved in the problems are presented by means of a variety of tools of the fixed point theory. The applicability of the results is shown with the aid of examples. Our results are not only new in the given configuration...

The existence of single and multiple nonnegative solutions for singular positone boundary value problems to the delay one-dimensional p-Laplacian is discussed. Throughout our nonlinearity f(·,y) may be singular at y = 0.

In this paper we establish the existence of single and multiple solutions to the positone discrete Dirichlet boundary value problem $$\left\{\begin{array}{c}\Delta \left[\phi \right(\Delta u(t-1)\left)\right]+q\left(t\right)f(t,u(t\left)\right)=0,t\in \{1,2,\cdots ,T\}\hfill \\ u\left(0\right)=u(T+1)=0,\hfill \end{array}\right.$$ where $\phi \left(s\right)={\left|s\right|}^{p-2}s$, $p>1$ and our nonlinear term $f(t,u)$ may be singular at $u=0$.

This paper studies the existence of solutions to the singular boundary value problem $$\left\}\begin{array}{c}-u^{\text{'}\text{'}}=g(t,u)+h(t,u),t\in (0,1),u\left(0\right)=0=u\left(1\right),\hfill \end{array}\right.$$ where $g(0,1)\times (0,\infty )\to ℝ$ and $h(0,1)\times [0,\infty )\to [0,\infty )$ are continuous. So our nonlinearity may be singular at $t=0,1$ and $u=0$ and, moreover, may change sign. The approach is based on an approximation method together with the theory of upper and lower solutions.