Radiative heat shuttling

We demonstrate the existence of a shuttling effect for the radiative heat flux exchanged between two bodies separated by a vacuum gap when the chemical potential of photons or the temperature difference is modulated. We show that this modulation typically gives rise to a supplementary flux which superimposes to the flux produced by the mean gradient, enhancing the heat exchange. When the system displays a negative differential thermal resistance, however, the radiative shuttling contributes to insulate the two bodies from each other. These results pave the way for a novel strategy for an active management of radiative heat exchanges in nonequilibrium systems

Lifetime of locally stable states near a phase transition in the Thirring model

We study the lifetime of locally stable states in the Thirring model, which describes a system of particles whose interactions are long-range. The model exhibits first-order phase transitions in the canonical ensemble and, therefore, a free energy barrier separates two free energy minima. The energy of the system diffuses as a result of thermal fluctuations and we show that its dynamics can be described by means of a Fokker-Planck equation. Considering an initial state where the energy takes the value corresponding to one of the minima of the free energy, we can define the lifetime of the initial state as the mean first-passage time for the system to reach the top of the free energy barrier between the minima. We use an analytical formula for the mean first-passage time which is based on the knowledge of the exact free energy of the model, even at a finite number of particles. This formula shows that the lifetime of locally stable states increases exponentially in the number of particles, which is a typical feature of systems with long-range interactions. We also perform Monte Carlo simulations in the canonical ensemble in order to obtain the probability distribution of the first-passage time, which turns out to be exponential in time in a long time limit. The numerically obtained mean first-passage time agrees with the theoretical prediction. Combining theory and simulations, our work provides a new insight in the study of metastability in many-body systems with long-range interactions.Comment: minor changes, version accepted for publicatio

Ingegnerizzazione e ottimizzazione del flusso di produzione di un componente per impianti a gas nel settore automotive

This thesis work, born by the internship realized in the manufacturing enterprise Hallite Italia S.r.l, it was composed during the advanced prototyping phase of a special rod seal to be installed in the pressure adaptor utilized for Volkswagen motors and the object was that of a process flow engineering with improvement of efficacy and efficiency. After an initial phase on product data collecting trough the prototyping batch realization, on customer requirements and AS - IS production process analysis, studies are conducted on product/process/system performance improvement, achieving the TO – BE process definition. This is also proved by following batch realization in qualitative and quantitative terms, according to customer orders. Moreover, new optimization solution are proposed both in an immediate instant of serial production launch and in a future instant for utilization of new technologies

Radiative thermal rectification in many-body systems

Radiative thermal diodes based on two-element structures rectify heat flows thanks to a temperature dependence of material optical properties. The heat transport asymmetry through these systems, however, remains weak without a significant change in material properties with the temperature. Here we explore the heat transport in three-element radiative systems and demonstrate that a strong asymmetry in the thermal conductance can appear because of many-body interactions, without any dependence of optical properties on the temperature. The analysis of transport in three-body systems made with polar dielectrics and metallic layers reveals that rectification coefficients exceeding 50% can be achieved in the near-field regime with temperature differences of about 200 K. This work paves the way for compact devices to rectify near-field radiative heat fluxes over a broad temperature range and could have important applications in the domain of nanoscale thermal management

Nonequilibrium Phenomena in Confined Systems

Confined 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 on Statistical Mechanics, devoted to "Nonequilibrium phenomena in confined systems". The conference took 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 than 60 international scientists in the areas of physics, chemistry, and biology working on confined systems in 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 confined systems and Casimir effect; Confined active matter; Macromolecular crowding; and Energy conversion in confinement

Phase transitions in the unconstrained ensemble

The unconstrained ensemble describes completely open systems in which energy, volume and number of particles fluctuate. Here we show that not only equilibrium states can exist in this ensemble, but also that completely open systems can undergo first-order phase transitions. This is shown by studying a modified version of the Thirring model with attractive and repulsive interactions and with particles of finite size. The model exhibits first-order phase transitions in the unconstrained ensemble, at variance with the analogous model with point-like particles. While unconstrained and grand canonical ensembles are equivalent for this model, we found inequivalence between the unconstrained and isothermal\u2013isobaric ensembles. By comparing the thermodynamic phase diagram in the unconstrained case with that obtained in the isothermal\u2013isobaric ensemble, we show that phase transitions under completely open conditions for this model are different from those in which the number of particles is fixed, highlighting the inequivalence of ensembles

Smart thermal management with near-field thermal radiation

When two objects at different temperatures are separated by a vacuum gap they can exchange heat by radiation only. At large separation distances (far-field regime), the amount of transferred heat flux is limited by Stefan-Boltzmann's law (blackbody limit). In contrast, at subwavelength distances (near-field regime), this limit can be exceeded by orders of magnitude thanks to the contributions of evanescent waves. This article reviews the recent progress on the passive and active control of near-field radiative heat exchange in two- and many-body systems