In a dynamic pressure bearing, when a step portion is formed on the inner peripheral surface of a sleeve and radial dynamic pressure grooves are formed on the inner peripheral surface of the step portion, the width in the axial direction of the dynamic pressure grooves is set to be slightly smaller than the width in the axial direction of the step portion. The mono-diameter wellbore casing is formed by plastically deforming and radially expanding a first tubular member within a wellbore. The manganite is perovskite-type manganese oxides with the general formula RE1-xAExMnOy, where RE is a rare earth ion and AE is an alkaline-earth ion, with x in the range between 0. In one class of embodiments, this is done by introducing a vertical gradation in the density of fixed electrostatic charge, or in the background doping of the drift region, or both.