Formulating the two-body problem of classical relativistic electrodynamics in terms of action at a distance and using retarded potential, the equations of one-dimensional motion are functional differential equations of the retarded type. For this kind of equations, in general it is not enough to specify instantaneous data to specify unique trajectories. Nevertheless, Driver (1969) has shown that under special conditions for these electrodynamic equations, there exists an unique solution for this...

The asymptotic properties of solutions of the equation $u^{\text{'}\text{'}\text{'}}\left(t\right)=p_1\left(t\right)u\left({\tau }_1\left(t\right)\right)+p_2\left(t\right)u^{\text{'}}\left({\tau }_2\left(t\right)\right)$, are investigated where $p_i:[a,+\infty [\to R(i=1,2)$ are locally summable functions, ${\tau }_i:[a,+\infty [\to R(i=1,2)$ measurable ones and ${\tau }_i\left(t\right)\ge t(i=1,2)$. In particular, it is proved that if $p_1\left(t\right)\le 0$, $p_2^2\left(t\right)\le \alpha \left(t\right)\left|p_1\left(t\right)\right|$, $${\int }_a^{+\infty }{[{\tau }_1\left(t\right)-t]}^2{p}_1\left(t\right)dt<+\infty \text{and}{\int }_a^{+\infty }\alpha \left(t\right)dt<+\infty ,$$ then each solution with the first derivative vanishing at infinity is of the Kneser type and a set of all such solutions forms a one-dimensional linear space.

On the segment $I=[a,b]$ consider the problem $$u^{\text{'}}\left(t\right)=f\left(u\right)\left(t\right),u\left(a\right)=c,$$ where $fC(I,ℝ)\to L(I,ℝ)$ is a continuous, in general nonlinear operator satisfying Carathéodory condition, and $c\in ℝ$. The effective sufficient conditions guaranteeing the solvability and unique solvability of the considered problem are established. Examples verifying the optimality of obtained results are given, as well.

The main goal of the paper is to formulate some new properties of the Ishlinskii hysteresis operator $F$, which characterizes e.g. the relation between the deformation and the stress in a non-perfectly elastic (elastico-plastic) material. We introduce two energy functionals and derive the energy inequalities. As an example we investigate the equation $u^{\text{'}\text{'}}+F\left(u\right)=0$ describing the motion of a mass point at the extremity of an elastico-plastic spring.

We prove several results on lower bounds for the periods of periodic solutions of some classes of functional-differential equations in Hilbert and Banach spaces and difference inclusions in Hilbert spaces.