A volatile semiconductor memory includes a self-test controller detecting a defect of a memory cell, and an address storage storing a defective address indicating an address of a defective memory cell, and a refresh adjust circuit setting a refresh cycle of a memory cell designated by the defective address to be shorter than a refresh cycle of a normal memory cell. to obtain a temporarily sintered first body, impregnating the resulted temporarily sintered first body with a phenol resin as a carbon source, temporarily sintering the resulted carbon source-impregnated temporarily sintered first body in one of a vacuum atmosphere or inert gas atmosphere at 900 to 1400\xb0 C. Specifically, the present invention provides for the production of PMR-type polyimides having 2,2-disubstituted biaryls in the polymer backbone. Each user device is equipped with a supervising program that ensures, by use of the tag and other information, that no software instance will be used on the device in a manner infringing on the vendor, distributor, or software owner’s rights. Linear movement of the first ends of the first and second pivot arms results in linear movement of the first shutter and the second shutter.