An image forming apparatus includes a transfer belt unit configured to be detachable from a housing. IPDA having a cistrans isomer ratio in the range from 6337 to 6634 can be obtained in any desired cistrans isomer ratio, irrespective of temperature, by reacting IPDA with H2 and NH3 in the presence of a hydrogenation catalyst. The user sends an invitation to one or more members or non-members. The vertically separated resonators are supported by standoffs that are fabricated on the substrate, or on a resonator.