A method of building a log structure using naturally-shaped logs is provided. A heat pipe body has a closed loop flow path. The ratio of the total contacting area of the first bumps to that of the second bumps is between 0. The recombinant microorganisms obtained by manipulating the metabolic flux of microorganisms are able to selectively produce butanol with high efficiency, and thus are useful as microorganisms for producing industrial solvents and transportation fuels.