XIN-RONG ZHANG, PHD, is Professor in the Department of Energy and Resources Engineering at Peking University in China. His contribution to this area includes not only the fundamentals, such as flow and heat transfer of supercritical CO2; but also applications, designs of commercial and industrial CO2 heat pumps, novel CO2 refrigeration cycle using solid-gas flow, and solar powered CO2 cogeneration system. He teaches a graduate course called “CO2 Refrigeration and Heat Pumps” at Peking University. HIROSHI YAMAGUCHI, PHD, is Professor in the Department of Mechanical Engineering at Doshisha University in Japan. He received his doctorate from the University of Manchester Institute of Science and Technology in the United Kingdom in 1982. His research focus is on fluid engineering, solar energy conversion, ultra-low temperature refrigeration, and magnetic fluids.