Ivan Latella

Heat Engine Driven by Photon Tunneling in Many-Body Systems

Near-field heat engines are devices that convert the evanescent thermal field supported by a primary source into usable mechanical energy. By analyzing the thermodynamic performance of three-body near-field heat engines, we demonstrate that the power they supply can be substantially larger than that of two-body systems, showing their strong potential for energy harvesting. Theoretical limits for energy and entropy fluxes in three-body systems are discussed and compared with their corresponding two-body counterparts. Such considerations confirm that the thermodynamic availability in energy-conversion processes driven by three-body photon tunneling can exceed the thermodynamic availability in two-body systems.

Near-field thermodynamics: Useful work, efficiency, and energy harvesting

We show that the maximum work that can be obtained from the thermal radiation emitted between two planar sources in the near-field regime is much larger than that corresponding to the blackbody limit. This quantity, as well as an upper bound, for the efficiency of the process is computed from the formulation of thermodynamics in the near-field regime. The case when the difference of temperatures of the hot source and the environment is small, relevant for energy harvesting, is studied in detail. We also show that thermal radiation energy conversion can be more efficient in the near-field regime. These results open new possibilities for the design of energy converters that can be used to harvest energy from sources of moderate temperature at the nanoscale.

Long-range interacting systems in the unconstrained ensemble

Completely open systems can exchange heat, work, and matter with the environment. While energy, volume, and number of particles fluctuate under completely open conditions, the equilibrium states of the system, if they exist, can be specified using the temperature, pressure, and chemical potential as control parameters. The unconstrained ensemble is the statistical ensemble describing completely open systems and the replica energy is the appropriate free energy for these control parameters from which the thermodynamics must be derived. It turns out that macroscopic systems with short-range interactions cannot attain equilibrium configurations in the unconstrained ensemble, since temperature, pressure, and chemical potential cannot be taken as a set of independent variables in this case. In contrast, we show that systems with long-range interactions can reach states of thermodynamic equilibrium in the unconstrained ensemble. To illustrate this fact, we consider a modification of the Thirring model and compare the unconstrained ensemble with the canonical and grand-canonical ones: The more the ensemble is constrained by fixing the volume or number of particles, the larger the space of parameters defining the equilibrium configurations.

Radiative heat transfer and nonequilibrium Casimir-Lifshitz force in many-body systems with planar geometry

A general theory of photon-mediated energy and momentum transfer in N-body planar systems out of thermal equilibrium is introduced. It is based on the combination of the scattering theory and the fluctuational electrodynamics approach in many-body systems. By making a Landauer-like formulation of the heat transfer problem, explicit formulas for the energy transmission coefficients between two distinct slabs as well as the self-coupling coefficients are derived and expressed in terms of the reflection and transmission coefficients of the single bodies. We also show how to calculate local equilibrium temperatures in such systems. An analogous formulation is introduced to quantify momentum transfer coefficients describing Casimir-Lifshitz forces out of thermal equilibrium. Forces at thermal equilibrium are readily obtained as a particular case. As an illustration of this general theoretical framework, we show on three-body systems how the presence of a fourth slab can impact equilibrium temperatures in heat-transfer problems and equilibrium positions resulting from the forces acting on the system.

Local thermodynamics and the generalized Gibbs-Duhem equation in systems with long-range interactions.

The local thermodynamics of a system with long-range interactions in d dimensions is studied using the mean-field approximation. Long-range interactions are introduced through pair interaction potentials that decay as a power law in the interparticle distance. We compute the local entropy, Helmholtz free energy, and grand potential per particle in the microcanonical, canonical, and grand canonical ensembles, respectively. From the local entropy per particle we obtain the local equation of state of the system by using the condition of local thermodynamic equilibrium. This local equation of state has the form of the ideal gas equation of state, but with the density depending on the potential characterizing long-range interactions. By volume integration of the relation between the different thermodynamic potentials at the local level, we find the corresponding equation satisfied by the potentials at the global level. It is shown that the potential energy enters as a thermodynamic variable that modifies the global thermodynamic potentials. As a result, we find a generalized Gibbs-Duhem equation that relates the potential energy to the temperature, pressure, and chemical potential. For the marginal case where the power of the decaying interaction potential is equal to the dimension of the space, the usual Gibbs-Duhem equation is recovered. As examples of the application of this equation, we consider spatially uniform interaction potentials and the self-gravitating gas. We also point out a close relationship with the thermodynamics of small systems.

Nonequilibrium Phenomena in Confined Systems

nonequilibirum phenomena; diffusion in confined systems; dynamics and relaxationin confined systems; entropic transport in confined systems; ion and polymer translocation; forcesinduced by fluctuations; confined active mater; macromolecular crowdingConfined systems exhibit a large variety of nonequilibrium phenomena. In this special issue,we have collected a limited number of papers that were presented during the XXV Sitges Conference onStatistical Mechanics, devoted to “Nonequilibrium phenomena in confined systems”. The conferencetook place in Barcelona from the 6th until the 10th of June 2016 (http://www.ffn.ub.es/~sitges25/),was organized by G. Franzese, I. Latella, D. Reguera, and J.M. Rubi, and gathered more than60 international scientists in the areas of physics, chemistry, and biology working on confined systemsin topics like: Diffusion and entropic transport in confined systems; Ion and polymer translocation;Phase transitions and chemical reactions in confined media; Forces induced by fluctuations in confinedsystems and Casimir effect; Confined active matter; Macromolecular crowding; and Energy conversionin confinement.In the first contribution to this special issue [1], by P. Malgaretti, I. Pagonabarraga and J.M. Rubi,the authors focus on how local forces in heterogeneous media modify Brownian motion and leadto deviations in the Gaussian probability distribution of displacements typical of thermal motion.Their results can be used to detect local forces and to characterize relevant properties of the host medium.Crowding is another source of heterogeneous local forces. In their contribution, P.M. Blanco,M. Via, J.L. Garces, S. Madurga, and F. Mas analyze protein diffusion in crowded media [2].They use dextran macromolecules as obstacles and propose a model based on effective radiiaccounting for macromolecular compression induced by crowding. They adopt a Brownian dynamicscomputational model to calculate the diffusion coefficient and the anomalous diffusion exponent.They compare their results with experiments, emphasizing the effects of varying volume fraction andhydrodynamic interactions.The search for the origin of life motivates the study performed by D. Niether and S. Wiegand [3]about the accumulation process of formamide in hydrothermal pores. The authors consider a heuristicapproach and show that the combination of thermophoresis and convection in hydrothermalpores leads to an accumulation of formamide that depends on the geometry of the system andambient conditions. A sufficiently high concentration of formamide could allow the synthesis ofprebiotic molecules.Smaller bio-pores are considered by M. Aguilella-Arzo, M. Queralt-Martin, M.-L. Lopez,and A. Alcaraz that in their contribution [4] address fluctuation-driven transport of ions in nanopores.The authors study the bacterial channel OmpF under conditions similar to those met in vivo. They use

Phase transitions in Thirring's model

In his pioneering work on negative specific heat, Walter Thirring in\-tro\-duced a model that is solvable in the microcanonical ensemble. Here, we give a complete description of the phase-diagram of this model in both the microcanonical and the canonical ensemble, highlighting the main features of ensemble inequivalence. In both ensembles, we find a line of first-order phase transitions which ends in a critical point. However, neither the line nor the point have the same location in the phase-diagram of the two ensembles. We also show that the microcanonical and canonical critical points can be analytically related to each other using a Landau expansion of entropy and free energy, respectively, in analogy with what has been done in [O. Cohen, D. Mukamel, J. Stat. Mech., P12017 (2012)]. Examples of systems with certain symmetries restricting the Landau expansion have been considered in this reference, while no such restrictions are present in Thirrings model. This leads to a phase diagram that can be seen as a prototype for what happens in systems of particles with kinematic degrees of freedom dominated by long-range interactions.

Near-field thermodynamics and nanoscale energy harvesting

We study the thermodynamics of near-field thermal radiation between two identical polar media at different temperatures. As an application, we consider an idealized energy harvesting process from sources at near room temperature at the nanoscale. We compute the maximum work flux that can be extracted from the radiation in the near-field regime and compare it with the corresponding maximum work flux in the blackbody regime. This work flux is considerably higher in the near-field regime. For materials that support surface phonon polaritons, explicit expressions for the work flux and an upper bound for the efficiency as functions of the surface wave frequency are obtained.