We consider the motion of a point mass in a one-dimensional viscous compressible barotropic fluid. The fluid--point mass system is governed by the barotropic compressible Navier--Stokes equations and Newton's equation of motion. Our main result concerns the long time behavior of the fluid and the point mass; it gives pointwise convergence estimates of the density and the velocity of the fluid to their equilibrium values. As a corollary, it shows that the fluid velocity $U(x,t)$ and the point mass velocity $V(t)=U(h(t)\pm 0,t)$, where $h(t)$ is the location of the point mass, decay differently as $||U(\cdot,t)||_{L^{\infty}(\mathbb{R}\backslash \{ h(t) \})}\approx t^{-1/2}$ and $|V(t)|\lesssim t^{-3/2}$. This discrepancy between the decay rates of $||U(\cdot,t)||_{L^{\infty}(\mathbb{R}\backslash \{ h(t) \})}$ and $|V(t)|=|U(h(t)\pm 0,t)|$ is due to the hyperbolic-parabolic nature of the problem: The fluid velocity decays slower on the characteristics $x=\pm ct$, where $c$ is the speed o 查看全文>>