y using the perturbation method,the instabilities of thin accretion disks with viscosity and magnetic field were studied both analytically and numerically.The instability criterions were obtained for four special cases.It has been found that the pulsational instability exists both in pure viscous disks and pure magnetized disks.When viscosity and magnetic field are both considered in a disk,there are two kinds of instabilities.One is pulsational and the other one is monotonic.The former one most probably exists in the inner region of disk while the latter one has physical meaning only to the s...
