arXiv subjects

Ivan Latella

Publications and source records attributed to Ivan Latella.

At least 19 recordsLinked to original sources

arXiv2026

Ising Models of Cooperativity in Muscle Contraction

Regulation of contraction in striated muscle is controlled by a dual mechanism involving both thin filaments containing actin and thick filaments containing myosin. The thin filament is activated by calcium ions binding to troponin, leading to tropomyosin azimuthal displacement which allows the activation of a regulatory unit (composed of one troponin, one tropomyosin and seven actin monomers) that exposes the actin sites for interaction with the myosin motors. Motor attachment to actin contributes to spreading activation within and beyond a regulatory unit along the thin filament through a cooperative mechanism. We introduce a one-dimensional Ising model to elucidate the mechanism of cooperativity in thin filament activation in relation to the force generated by the attached myosin motor. The model characterizes thin filament activation and cooperativity using only two parameters: one related to calcium concentration and the other to the force exerted by the attached myosin motor, which is modulated by temperature. At any force, the model is able to determine the extent of actin-myosin interactions on a correlation length ranging from two to seven actin monomers in addition to the seven actin monomers of the regulatory unit. Our theoretical predictions are successfully tested on experimental data, and our tests also include the condition of hindered filament activation by the use of the specific drug Omecamtiv Mecarbil (OM). According to our model, the effect of OM results in an anti-cooperativity mechanism accounting for the experimental data.

cond-mat.stat-mech↗

arXiv2025

Free-energy REconstruction from Stable Clusters (FRESC): A new method to evaluate nucleation barriers from simulation

We present a simulation technique to evaluate the most important quantity for nucleation processes: the nucleation barrier, i.e. the free energy of formation of the critical cluster. The method is based on stabilizing a small cluster by simulating it in the NVT ensemble and using the thermodynamics of small systems to convert the properties of this stable cluster into the Gibbs free energy of formation of the critical cluster. We demonstrate this approach using condensation in a Lennard-Jones truncated and shifted fluid as an example, showing an excellent agreement with previous Umbrella Sampling simulations. The method is straightforward to implement, computationally inexpensive, requires only a small number of particles comparable to the critical cluster size, does not rely on the use of Classical Nucleation Theory, and does not require any cluster definition or reaction coordinate. All of these advantages hold the promise of opening the door to simulate nucleation processes in complex molecules of atmospheric, chemical or pharmaceutical interest that cannot be easily simulated with current techniques.

cond-mat.stat-mech↗

arXiv2025

Feynman paradox induced by vacuum and thermal fluctuations

A charged particle initially at rest in an external magnetic field starts to rotate when the magnetic field is switched off. This is a variant of the Feynman disc paradox, where the conservation of angular momentum is seemingly violated. The paradox is understood by realizing that angular momentum is initially stored in the electromagnetic field and is transferred to the particle when the magnetic field is removed. In a classical description, no rotation occurs if the particle is uncharged, as the initial angular momentum is zero in this case. We show that electromagnetic fluctuations in thermal equilibrium can induce a quantum analog of the Feynman paradox, where a nonreciprocal particle without charge starts to rotate when the source of nonreciprocity is removed. This paradox is due to persistent energy fluxes arising in nonreciprocal systems at equilibrium, leading to angular momentum stored in the electromagnetic field. We demonstrate that the contribution of vacuum fluctuations to persistent energy fluxes dominate over thermal fluctuations at finite temperature, so vacuum fluctuations dominate the equilibrium angular momentum as well. Observation of the induced motion would thus provide a means of detecting persistent energy fluxes and offer further evidence for the physical reality of vacuum fluctuations.

cond-mat.mes-hall↗

arXiv2025

On persistent energy currents at equilibrium in non-reciprocal systems

We investigate the properties of the mean Poynting vector in global thermal equilibrium, which can be non-zero in non-reciprocal electromagnetic systems. Using dyadic Green's functions and the fluctuation-dissipation theorem, we provide a general proof that the mean Poynting vector is divergence-free under equilibrium conditions. Relying on this proof, we explicitly demonstrate that for systems where a normal mode expansion of the Green's function is applicable, the divergence of the equilibrium mean Poynting vector vanishes. As concrete examples, we also examine the equilibrium mean Poynting vector near a planar non-reciprocal substrate and in configurations involving an arbitrary number of dipolar non-reciprocal objects in free space. Finally, we argue that the so-called persistent heat current, while present in equilibrium, cannot be detected through out-of-equilibrium heat transfer measurements.

cond-mat.mes-hall↗

arXiv2024

Radiative Corbino effect in nonreciprocal many-body systems

When a magnetic field is applied in the perpendicular direction to a metallic disk under the action of a radial bias voltage, a tangential electric current superimposes to the radial current due to the presence of the Lorentz force which acts on electrons. Here we introduce a thermal analog of this Corbino effect in many-body systems made of nonreciprocal bodies which interact by exchanging photons in near-field regime. In systems out of thermal equilibrium with a radial temperature gradient, we demonstrate that the Poynting field in the Corbino geometry is bent in presence of an external magnetic field, giving rise to a tangential heat flux. This thermomagnetic effect could find applications in the field of thermal management and energy conversion at nanoscale.

cond-mat.mes-hall↗

arXiv2023

Splitting of temperature distributions due to dual-channel photon heat exchange in many-body systems

We investigate the radiative heat transfer and spatial distributions of stationary temperatures in periodic many-body systems composed of alternating slabs of two different materials. We show that temperature distributions exhibit an alternating spatial pattern and split into two distinct components, with each component corresponding to one of the two materials. Spatial temperature variations following the periodicity of the structure can be attributed to a dual-channel photon heat exchange through a long-range coupling of electromagnetic modes supported by bodies of the same material. We also analyze the thermal relaxation of the temperatures in the system to verify potential applications in dynamical situations. The results reveal that tunable nonmonotonic temperature variations can be also designed and utilized at a transient mode. The dual-channel mechanism to control temperature distributions proposed in the present work may pave new avenues for prospective applications in nano devices, especially for thermal photon-driven logic circuitry and thermal management.

physics.optics↗

arXiv2023

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.

cond-mat.stat-mech↗

arXiv2022

Modified Thirring model beyond the excluded-volume approximation

Long-range interacting systems may exhibit ensemble inequivalence and can possibly attain equilibrium states under completely open conditions, for which energy, volume and number of particles simultaneously fluctuate. Here we consider a modified version of the Thirring model for self-gravitating systems with attractive and repulsive long-range interactions in which particles are treated as hard spheres in dimension d=1,2,3. Equilibrium states of the model are studied under completely open conditions, in the unconstrained ensemble, by means of both Monte Carlo simulations and analytical methods and are compared with the corresponding states at fixed number of particles, in the isothermal-isobaric ensemble. Our theoretical description is performed for an arbitrary local equation of state, which allows us to examine the system beyond the excluded-volume approximation. The simulations confirm the theoretical prediction of the possible occurrence of first-order phase transitions in the unconstrained ensemble. This work contributes to the understanding of long-range interacting systems exchanging heat, work and matter with the environment.

cond-mat.stat-mech↗

arXiv2021

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.

physics.class-ph↗

arXiv2021

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.

cond-mat.mes-hall↗

arXiv2021

Monte Carlo simulations in the unconstrained ensemble

The unconstrained ensemble describes completely open systems whose control parameters are chemical potential, pressure, and temperature. For macroscopic systems with short-range interactions, thermodynamics prevents the simultaneous use of these intensive variables as control parameters, because they are not independent and cannot account for the system size. When the range of the interactions is comparable with the size of the system, however, these variables are not truly intensive and may become independent, so equilibrium states defined by the values of these parameters may exist. Here, we derive a Monte Carlo algorithm for the unconstrained ensemble and show that simulations can be performed using chemical potential, pressure, and temperature as control parameters. We illustrate the algorithm by applying it to physical systems where either the system has long-range interactions or is confined by external conditions. The method opens up a new avenue for the simulation of completely open systems exchanging heat, work, and matter with the environment.

cond-mat.stat-mech↗

arXiv2021

Graphene-based autonomous pyroelectric system for near-field energy conversion

In the close vicinity of a hot solid, at distances smaller than the thermal wavelength, a strong electromagnetic energy density exists because of the presence of evanescent field. Here we explore the possibility to harvest this energy using graphene-based pyroelectric conversion devices made with an active layer encapsulated between two graphene field-effect transistors (GFETs) deposited on the source and on the cold sink. By tuning the bias voltage applied to the gates of these transistors, the thermal state and the spontaneous polarization of the active layer can be controlled at kHz frequencies. We demonstrate that the power density generated by these conversion systems can reach 1300 W/m^2 using pyroelectric Ericsson cycles, a value which surpasses the current production capacity of near-field thermophotovoltaic conversion devices by more than five orders of magnitude with low grade heat sources (T<500 K) and small temperature differences (DT~100 K).

cond-mat.mes-hall↗

arXiv2019

Saturation of radiative heat transfer due to many-body thermalization

Radiative heat transfer between two bodies saturates at very short separation distances due to the nonlocal optical response of the materials. In this work, we show that the presence of radiative interactions with a third body or external bath can also induce a saturation of the heat transfer, even at separation distances for which the optical response of the materials is purely local. We demonstrate that this saturation mechanism is a direct consequence of a thermalization process resulting from many-body interactions in the system. This effect could have an important impact in the field of nanoscale thermal management of complex systems and in the interpretation of measured signals in thermal metrology at the nanoscale.

cond-mat.mes-hall↗

arXiv2019

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-isobaric ensembles. By comparing the thermodynamic phase diagram in the unconstrained case with that obtained in the isothermal-isobaric 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.

cond-mat.stat-mech↗

arXiv2018

Concavity, Response Functions and Replica Energy

In nonadditive systems, like small systems or like long-range interacting systems even in the thermodynamic limit, ensemble inequivalence can be related to the occurrence of negative response functions, this in turn being connected with anomalous concavity properties of the thermodynamic potentials associated to the various ensembles. We show how the type and number of negative response functions depend on which of the quantities E, V and N (energy, volume and number of particles) are constrained in the ensemble. In particular, we consider the unconstrained ensemble in which E, V and N fluctuate, physically meaningful only for nonadditive systems. In fact, its partition function is associated to the replica energy, a thermodynamic function that identically vanishes when additivity holds, but that contains relevant information in nonadditive systems.

cond-mat.stat-mech↗

arXiv2018

Dynamical response of a radiative thermal transistor based on suspended insulator-metal transition membranes

We investigate the dynamical control of the heat flux exchanged in near-field regime between a membrane made with a phase-change material and a substrate when the temperature of the membrane is tuned around its critical value. We show that in interaction with an external source of thermal radiation, this system is multistable and behaves as a thermal transistor, being able to dynamically modulate and even amplify super-Planckian heat fluxes. This behavior could be used to dynamically control heat fluxes exchanged at the nanoscale in systems out of thermal equilibrium and to process thermal information employing suspended membranes.

cond-mat.mes-hall↗

arXiv2018

Nonequilibrium Phenomena in Confined Systems

Keywords: nonequilibirum phenomena; diffusion in confined systems; dynamics and relaxation in confined systems; entropic transport in confined systems; ion and polymer translocation; forces induced by fluctuations; confined active mater; macromolecular crowding.

cond-mat.stat-mech↗

arXiv2018

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.

physics.optics↗