I want to know the physical interpretation of the term $$\int\limits\_0^\infty {g(s){\psi \_{xx}}(x,t - s)ds}$$ in some equation. This term is called infinite memory and the function $g$ is called relaxation function. What is the difference between this term and the same term replacing $\infty $ by $t$? This term can be found in Temoshinko system or Von Karman system. Is there any relation between this term and viscoelasticity ? Thanks.