Efficiency of cyclic devices working with non-Boltzmannian fluids:   challenging the second principle of thermodynamics
  According to classical Boltzmannian thermodynamics, the efficiency of a cyclic machine is strictly lower than one. Such a result is a straightforward consequence of the second principle of thermodynamics. Recent advances in the study of the thermodynamics of long-range interacting system report however on a rather intricate zoology of peculiar behaviors, which are occasionally in contrast with customarily accepted scenarios, dueling with intuition and common sense. In this paper, a thermodynamical cycle is assembled for an ideal device working with non-Boltzmaniann long-range fluid and operating in contact with two thermal reservoirs. The system is analytically shown to violate the second principle of thermodynamics, a phenomenon that ultimately relates to the existence of regions with negative kinetic specific heat, in the canonical ensemble for the system under scrutiny. We argue that the validity of the second principle of thermodynamics can be possibly restored, by revisiting the definition of canonical ensemble, as well as the Fourier law of heat transport, and consequently relaxing the constraint on the maximal efficiency as imposed by the Carnot theorem. 
Duccio Fanelli, Giovanni De Ninno, Alessio Turchi
cond-mat.stat-mech