To provide a process for producing a polyester ether poly- or mono-ol having a narrow molecular weight distribution, which is obtained by copolymerizing an initiator having hydroxyl groups with a cyclic ester compound and an alkylene oxide. The hydrophobic layer may have properties such as high contact angle \u03b8. The method uses a knowledge base that contains disease models exhibiting clinical data. An element body has a cavity portion located so as to cover the whole of the discharge inducing portion when viewed in the stack direction from the coil side. The catheter has a catheter body and a tip electrode with a shell wall and a hollow cavity.