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This paper is concerned with the coupling of two models for the
propagation of particles in scattering media. The first model is a
linear transport equation of Boltzmann type posed in the phase space
(position and velocity). It accurately describes the physics but is
very expensive to solve. The second model is a diffusion equation
posed in the physical space. It is only valid in areas of high
scattering, weak absorption, and smooth physical coefficients, but
its numerical solution is...
This paper deals with the diffusion limit of a kinetic equation where the collisions are modeled by a Lorentz type operator. The main aim is to construct a discrete scheme to approximate this equation which gives for any value of the Knudsen number, and in particular at the diffusive limit, the right discrete diffusion equation with the same value of the diffusion coefficient as in the continuous case. We are also naturally interested with a discretization which can be used with few velocity discretization...
This paper deals with the diffusion limit of a kinetic equation where the
collisions are modeled by a Lorentz type operator. The main aim is to construct a
discrete scheme to approximate this equation which gives for any value of the
Knudsen number, and in particular at the diffusive limit, the right discrete
diffusion equation with the same value of the diffusion coefficient as in the
continuous case. We are also naturally interested with a discretization which
can be used with few velocity discretization...
We consider the spatially inhomogeneous Bekker-Döring infinite-dimensional kinetic system describing the evolution of coagulating and fragmenting particles under the influence of convection and diffusion. The simultaneous consideration of opposite coagulating and fragmenting processes causes many additional difficulties in the investigation of spatially inhomogeneous problems, where the space variable changes differently for distinct particle sizes. To overcome these difficulties, we use a modified...
Nonequilibrium collective motion is ubiquitous in nature and often results in a rich collection of intriguing phenomena, such as the formation of shocks or patterns, subdiffusive kinetics, traffic jams, and nonequilibrium phase transitions. These stochastic many-body features characterize transport processes in biology, soft condensed matter and, possibly, also in nanoscience. Inspired by these applications, a wide class of lattice-gas models has recently been considered. Building on the celebrated...
We investigate the diffusion limit for general conservative Boltzmann equations with oscillating coefficients. Oscillations have a frequency of the same order as the inverse of the mean free path, and the coefficients may depend on both slow and fast variables. Passing to the limit, we are led to an effective drift-diffusion equation. We also describe the diffusive behaviour when the equilibrium function has a non-vanishing flux.
We investigate the diffusion limit for general conservative Boltzmann equations with oscillating coefficients.
Oscillations have a frequency of the same order as the inverse of the mean free path, and the coefficients may depend on both slow
and fast variables. Passing to the limit, we are led to an effective drift-diffusion equation.
We also describe the diffusive behaviour when the equilibrium function has a non-vanishing flux.
An overview of recent results pertaining to the hydrodynamic description (both Newtonian
and non-Newtonian) of granular gases described by the Boltzmann equation for inelastic
Maxwell models is presented. The use of this mathematical model allows us to get exact
results for different problems. First, the Navier–Stokes constitutive equations with
explicit expressions for the corresponding transport coefficients are derived by applying
the Chapman–Enskog...
We study an inverse problem for photon transport in an interstellar cloud. In particular, we evaluate the position of a localized source , inside a nebula (for example, a star). We assume that the photon transport phenomenon is one-dimensional. Since a nebula moves slowly in time, the number of photons inside the cloud changes slowly in time. For this reason, we consider the so-called quasi-static approximation to the exact solution . By using semigroup theory, we prove existence and uniqueness...
In this paper, we review recent developments on the derivation and properties of macroscopic models of collective motion and self-organization. The starting point is a model of self-propelled particles interacting with its neighbors through alignment. We successively derive a mean-field model and its hydrodynamic limit. The resulting macroscopic model is the Self-Organized Hydrodynamics (SOH). We review the available existence results and known properties of the SOH model and discuss it in view...
In this paper, we propose a mathematical model for flow and transport processes of diluted solutions in domains separated by a leaky semipermeable membrane. We formulate transmission conditions for the flow and the solute concentration across the membrane which take into account the property of the membrane to partly reject the solute, the accumulation of rejected solute at the membrane, and the influence of the solute concentration on the volume flow, known as osmotic effect. The model is solved...
A solid dispersion is a dosage form in which an active ingredient (a drug) is mixed with at least one inert solid component. The purpose of the inert component is usually to improve the bioavailability of the drug. In particular, the inert component is frequently chosen to improve the dissolution rate of a drug that is poorly soluble in water. The construction of reliable mathematical models that accurately describe the dissolution of solid dispersions would clearly assist with their rational design....
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