A hardware model database is identified which stores a graph-based common representation of a hardware design that includes hardware module nodes each representative of a unique module of the hardware design and associated with one or more instances of the unique module. As a result, without using Cr plating, it is possible to provide an electric soldering iron having an excellent resistance to oxidation under high temperature environment and a high heat conductivity. Also disclosed are diagnostic methods for detecting a mutation in the TNF-gamma-alpha and TNF-gamma-beta nucleic acid sequences or overexperession of the TNF-gamma-alpha and TNF-gamma-beta polypeptides.