It's a theoretical study. Like the image showing, the curved piston move in container and need energy for that. In the same time, another piston move up and recover energy. The pressure inside container is always the same (need to control speed of pistons, but there is a pressure). No gravity here. Like one piston is curved it seems pressure on curved piston is reduced and atoms of helium has a up force in the same time. So, the image is false ? where ?