arXiv subjects

Marzia Bisi

Publications and source records attributed to Marzia Bisi.

14 recordsLinked to original sources

arXiv2026

Action potential dynamics on heterogenous neural networks: from kinetic to macroscopic equations

In the context of multi-agent systems of binary interacting particles, a kinetic model for action potential dynamics on a neural network is proposed, accounting for heterogeneity in the neuron-to-neuron connections, as well as in the brain structure. Two levels of description are coupled: in a single area, pairwise neuron interactions for the exchange of membrane potential are statistically described; among different areas, a graph description of the brain network topology is included. Equilibria of the kinetic and macroscopic settings are determined and numerical simulations of the system dynamics are performed with the aim of studying the influence of the network heterogeneities on the membrane potential propagation and synchronization.

physics.bio-ph↗

arXiv2026

Kinetic modeling of knowledge and wealth dynamics in national and global markets

We propose a kinetic model to describe the dynamical evolution of wealth and knowledge in national and global markets, starting from a microscopic description of individual interactions. The model is built upon interaction rules that account for a strong interdependence between the microscopic variables, influencing agents' trading and saving propensities, knowledge acquisition, and the stochastic market effects. We begin with a domestic market scenario and extend the framework to international trade, incorporating the possibility of individual transfers between different countries. The dynamics of the system are described through Boltzmann-type equations, which allow for a detailed study of the evolution of the agent distribution in each country. In this context, we study the evolution of macroscopic quantities of the system, focusing on the number density of individuals, and the mean wealth and knowledge of each population, and we discuss these results in relation to existing models in the literature. Finally, under a quasi-invariant trading limit, we derive simplified Fokker-Planck type equations that reveal some emergent behaviors of the system, including the formation of Pareto tails in the long-term wealth and knowledge distributions.

physics.soc-ph↗

arXiv2026

Derivation from kinetic theory and 2-D pattern analysis of chemotaxis models for Multiple Sclerosis

In this paper, a class of reaction-diffusion equations for Multiple Sclerosis is presented. These models are derived by means of a diffusive limit starting from a proper kinetic description, taking account of the underlying microscopic interactions among cells. At the macroscopic level, we discuss the necessary conditions for Turing instability phenomena and the formation of two-dimensional patterns, whose shape and stability are investigated by means of a weakly nonlinear analysis. Some numerical simulations, confirming and extending theoretical results, are proposed for a specific scenario.

q-bio.QM↗

arXiv2026

Reaction-diffusion systems from kinetic models for bacterial communities on a leaf surface

Many mathematical models for biological phenomena, such as the spread of diseases, are based on reaction-diffusion equations for densities of interacting cell populations. We present a consistent derivation of reaction-diffusion equations from systems of suitably rescaled kinetic Boltzmann equations for distribution functions of cell populations interacting in a host medium. We show at first that the classical diffusive limit of kinetic equations leads to linear diffusion terms only. Then, we show possible strategies in order to obtain, from the kinetic level, macroscopic systems with nonlinear diffusion and also with cross-diffusion effects. The derivation from a kinetic description has the advantage of relating reaction and diffusion coefficients to the microscopic parameters of the interactions. We present an application of our approach to the study of the evolution of different bacterial populations on a leaf surface. Turing instability properties of the relevant macroscopic systems are investigated by analytical methods and numerical tools, with particular emphasis on pattern formation for varying parameters in two-dimensional space domains.

math.AP↗

arXiv2025

A space-dependent Boltzmann-BGK model for gas mixtures and its hydrodynamic limits

We present a hybrid Boltzmann-BGK model for inert mixtures, where each kind of binary interaction may be described by a classical Boltzmann integral or by a suitable relaxation-type operator. We allow also the possibility of changing the option Boltzmann/BGK operator according to the space position. We prove that this model guarantees conservations of species masses, global momentum and energy, as well as the entropy dissipation, leading to the expected Maxwellian equilibria with all species sharing the same mean velocity and the same temperature. We investigate then such mixed kinetic equations in three different hydrodynamic limits: the classical collision dominated regime, a situation with dominant intra-species collisions, and a mixture with heavy and light particles leading to a kinetic-fluid description.

math-ph↗

arXiv2025

On the modelling of polyatomic molecules in kinetic theory

This communication is both a pedagogical note for understanding polyatomic modelling in kinetic theory and a ''cheat sheet'' for a series of corresponding concepts and formulas. We explain, detail and relate three possible approaches for modelling the polyatomic internal structure, that are: the internal states approach, well suited for physical modelling and general proofs, the internal energy levels approach, useful for analytic studies and corresponding to the common models of the literature, and the internal energy quantiles approach, less known while being a powerful tool for particle-based numerical simulations such as Direct Simulation Monte-Carlo (DSMC). This note may in particular be useful in the study of non-polytropic gases.

math.AP↗

arXiv2024

Microscopic models for the large-scale spread of SARS-CoV-2 virus: A Statistical Mechanics approach

In this work, we derive a system of Boltzmann-type equations to describe the spread of SARS-CoV-2 virus at the microscopic scale, that is by modeling the human-to-human mechanisms of transmission. To this end, we consider two populations, characterized by specific distribution functions, made up of individuals without symptoms (population $1$) and infected people with symptoms (population $2$). The Boltzmann operators model the interactions between individuals within the same population and among different populations with a probability of transition from one to the other due to contagion or, vice versa, to recovery. In addition, the influence of innate and adaptive immune systems is taken into account. Then, starting from the Boltzmann microscopic description we derive a set of evolution equations for the size and mean state of each population considered. Mathematical properties of such macroscopic equations, as equilibria and their stability, are investigated and some numerical simulations are performed in order to analyze the ability of our model to reproduce the characteristic features of Covid-19.

q-bio.PE↗

arXiv2023

A chemotaxis reaction-diffusion model for Multiple Sclerosis with Allee effect

In this paper, we study a modification of the mathematical model describing inflammation and demyelination patterns in the brain caused by Multiple Sclerosis proposed in [Lombardo et al. (2017), Journal of Mathematical Biology, 75, 373--417]. In particular, we hypothesize a minimal amount of macrophages to be able to start and sustain the inflammatory response. Thus, the model function for macrophage activation includes an Allee effect. We investigate the emergence of Turing patterns by combining linearised and weakly nonlinear analysis, bifurcation diagrams and numerical simulations, focusing on the comparison with the previous model.

math.AP↗

arXiv2023

Kinetic models for systems of interacting agents with multiple microscopic states

We propose and investigate general kinetic models %of Boltzmann type with transition probabilities that can describe the simultaneous change of multiple microscopic states of the interacting agents. These models can be applied to many problems in socio-economic sciences, where individuals may change both their compartment and their characteristic kinetic variable, as for instance kinetic models for epidemics or for international trade with possible transfers of agents. Mathematical properties of our kinetic model are proved, as existence and uniqueness of a solution for the Cauchy problem in suitable Wasserstein spaces. The quasi-invariant asymptotic regime, leading to simpler kinetic Fokker-Planck-type equations, is investigated and commented on in comparison with other existing models. Some numerical tests are performed in order to show time evolution of distribution functions and of meaningful macroscopic fields, even in case of non-constant interaction probabilities.

math-ph↗

arXiv2023

A general framework for the kinetic modeling of polyatomic gases

A general framework for the kinetic modelling of non-relativistic polyatomic gases is proposed,where each particle is characterized both by its velocity and by its internal state, and the Boltzmann collisionoperator involves suitably weighted integrals over the space of internal energies. The description of the internalstructure of a molecule is kept highly general, and this allows classical and semi-classical models, such asthe monoatomic gas description, the continuous internal energy structure, and the description with discreteinternal energy levels, to fit our framework. We prove the H-Theorem for the proposed kinetic equation ofBoltzmann type in this general setting, and characterize the equilibrium Maxwellian distribution and thethermodynamic number of degrees of freedom. Euler equations are derived, as zero-order approximation in asuitable asymptotic expansion. In addition, within this general framework it is possible to build up new models,highly desirable for physical applications, where rotation and vibration are precisely described. Examples ofmodels for the Hydrogen Fluoride gas are presented.

math-ph↗

arXiv2017

From the simple reacting sphere kinetic model to the reaction-diffusion system of Maxwell-Stefan type

In this paper we perform a formal asymptotic analysis on a kinetic model for reactive mixtures in order to derive a reaction-diffusion system of Maxwell-Stefan type. More specifically, we start from the kinetic model of simple reacting spheres for a quaternary mixture of monatomic ideal gases that undergoes a reversible chemical reaction of bimolecular type. Then, we consider a scaling describing a physical situation in which mechanical collisions play a dominant role in the evolution process, while chemical reactions are slow, and compute explicitly the production terms associated to the concentration and momentum balance equations for each species in the reactive mixture. Finally, we prove that, under isothermal assumptions, the limit equations for the scaled kinetic model is the reaction diffusion system of Maxwell-Stefan type.

physics.flu-dyn↗

arXiv2015

Entropy dissipation estimates for the linear Boltzmann operator

We prove a linear inequality between the entropy and entropy dissipation functionals for the linear Boltzmann operator (with a Maxwellian equilibrium background). This provides a positive answer to the analogue of Cercignani's conjecture for this linear collision operator. Our result covers the physically relevant case of hard-spheres interactions as well as Maxwellian kernels, both with and without a cut-off assumption. For Maxwellian kernels, the proof of the inequality is surprisingly simple and relies on a general estimate of the entropy of the gain operator due to Matthes and Toscani (2012) and Villani (1998). For more general kernels, the proof relies on a comparison principle. Finally, we also show that in the grazing collision limit our results allow to recover known logarithmic Sobolev inequalities.

math.AP↗

arXiv2011

Uniqueness in the weakly inelastic regime of the equilibrium state of the inelastic Boltzmann equation driven by a particle bath

We consider the spatially homogeneous Boltzmann equation for inelastic hard-spheres (with constant restitution coefficient $α\in (0,1)$) under the thermalization induced by a host medium with a fixed Maxwellian distribution. We prove uniqueness of the stationary solution (with given mass) in the weakly inelastic regime; i.e., for any inelasticity parameter $α\in (α_0,1)$, with some constructive $α_0 \in [0, 1)$. Our analysis is based on a perturbative argument which uses the knowledge of the stationary solution in the elastic limit and quantitative estimates of the convergence of stationary solutions as the inelasticity parameter goes to 1. In order to achieve this we give an accurate spectral analysis of the associated linearized collision operator in the elastic limit. Several qualitative properties of this unique steady state $F_α$ are also derived; in particular, we prove that $F_α$ is bounded from above and from below by two explicit universal (i.e. independent of $α$) Maxwellian distributions.

math.AP↗

arXiv2008

Equilibrium Solution to the Inelastic Boltzmann Equation Driven by a Particles Thermal Bath

We show the existence of smooth stationary solutions for the inelastic Boltzmann equation under the thermalization induced by a host-medium with a fixed distribution. This is achieved by controlling the Lp-norms, the moments and the regularity of the solutions for the Cauchy problem together with arguments related to a dynamical proof for the existence of stationary states.

math.AP↗