Dr. Koga's group introduced a new approach to the thermodynamic studies of aqueous solutions. They devised methods of measuring various thermodynamic quantities differentially. These methods allow them to experimentally evaluate the intermolecular interaction, the key quantity in the so-called "many-body problem. The group has started applying this new methodology to aqueous solutions of biopolymers. As a recognition of his contribution to solution thermodynamics, he was awarded the Society Award by The Japan Society of Calorimetry and Thermal Analysis in 2006. In 2011, he obtained for the first time in the world a fourth derivative of Gibbs energy and named it "Acceleration of the effect of solute on entropy-volume cross fluctuation density."