Local kinetic interpretation of entropy production through reversed diffusion

Thermodynamic Langevin equations

The physical significance of the stochastic processes associated to the generalized Gibbs ensembles is scrutinized here with special attention to the thermodynamic fluctuations of small systems. Differently from the so-called stochastic thermodynamics, which starts from stochastic versions of the first and second law of thermodynamics and associates thermodynamic quantities to microscopic variables, here we consider stochastic variability directly in the macroscopic variables. By recognizing the potential structure of the Gibbs ensembles, when expressed as a function of the potential entropy generation, we obtain exact nonlinear thermodynamic Langevin equations (TLEs) for macroscopic variables, with drift expressed in terms of entropic forces. The analysis of the canonical ensemble for an ideal monoatomic gas and the related TLEs show that introducing currents leads to nonequilibrium heat transfer conditions with interesting bounds on entropy production but with no obvious thermodynamic limit. For a colloidal particle under constant force, the TLEs for macroscopic variables are different from those for the microscopic position, typically used in stochastic thermodynamics; while TLEs are consistent with the fundamental equation obtained from the Hamiltonian, stochastic thermodynamics requires isothermal conditions and entropy proportional to position.

Fluctuation theorem and extended thermodynamics of turbulence

Turbulent flows are out-of-equilibrium because the energy supply at large scales and its dissipation by viscosity at small scales create a net transfer of energy among all scales. This energy cascade is modelled by approximating the spectral energy balance with a nonlinear Fokker-Planck equation consistent with accepted phenomenological theories of turbulence. The steady-state contributions of the drift and diffusion in the corresponding Langevin equation, combined with the killing term associated with the dissipation, induce a stochastic energy transfer across wavenumbers. The fluctuation theorem is shown to describe the scale-wise statistics of forward and backward energy transfer and their connection to irreversibility and entropy production. The ensuing turbulence entropy is used to formulate an extended turbulence thermodynamics.

Sodium/calcium exchanger is involved in apoptosis induced by H2S in tumor cells through decreased levels of intracellular pH

We explored possibility that sodium/calcium exchanger 1 (NCX1) is involved in pH modulation and apoptosis induction in GYY4137 treated cells. We have shown that although 10 days treatment with GYY4137 did not significantly decreased volume of tumors induced by colorectal cancer DLD1 cells in nude mice, it already induced apoptosis in these tumors. Treatment of DLD1 and ovarian cancer A2780 cells with GYY4137 resulted in intracellular acidification in a concentration-dependent manner. We observed increased mRNA and protein expression of both, NCX1 and sodium/hydrogen exchanger 1 (NHE1) in DLD1-induced tumors from GYY4137-treated mice. NCX1 was coupled with NHE1 in A2780 and DLD1 cells and this complex partially disintegrated after GYY4137 treatment. We proposed that intracellular acidification is due to uncoupling of NCX1/NHE1 complex rather than blocking of the reverse mode of NCX1, probably due to internalization of NHE1. Results might contribute to understanding molecular mechanism of H₂S-induced apoptosis in tumor cells.