arXiv subjects

Judith Vancostenoble

Publications and source records attributed to Judith Vancostenoble.

6 recordsLinked to original sources

arXiv2026

Comparison principles and long time behavior for a diffusive Energy Balance Model with vertical resolution

We study a two-layer one-dimensional energy balance model, which allows for vertical energy exchanges between a surface layer and the atmosphere, as well as meridional energy transport across latitudes via a diffusion law. The evolution equations of the surface temperature and the atmospheric temperature are coupled by exchange of infrared radiation as well as other non-radiative energy exchanges. The energy enters the system as solar radiation, which is partially absorbed and partially reflected by the two layers. The system is then composed of two degenerate parabolic equations coupled by nonlinear terms, the growth of these terms being crucial for the choice of the functional setting. An essential parameter is the absorptivity of the atmosphere, denoted $\varepsilon _a$, whose value depends critically on greenhouse gases. We prove that blow up in finite time occurs if $\varepsilon _a >2$, while global existence of solutions and the existence of a global attractor hold when $\varepsilon _a \in (0,2)$. Proofs are based on comparison principles that derive from the cooperative structure of the problem, and that provide invariant rectangles for smooth initial conditions, and on regularity properties.

math.AP↗

arXiv2023

Analysis of a two-layer energy balance model: long time behaviour and greenhouse effect

We study a two-layer energy balance model, that allows for vertical exchanges between a surface layer and the atmosphere. The evolution equations of the surface temperature and the atmospheric temperature are coupled by the emission of infrared radiation by one level, that emission being captured by the other layer, and the effect of all non radiative vertical exchanges of energy. Therefore, an essential parameter is the absorptivity of the atmosphere, denoted $ε_a$. The value of $ε_a$ depends critically on greenhouse gases: increasing concentrations of $CO_2$ and $CH_4$ lead to a more opaque atmosphere with higher values of $ε_a$. First we prove that global existence of solutions of the system holds if and only if $ε_a \in (0, 2)$, and blow up in finite time occurs if $ε_a > 2$. (Note that the physical range of values for $ε_a$ is $(0, 1]$.) Next, we explain the long time dynamics for $ε_a \in (0, 2)$, and we prove that all solutions converge to some equilibrium point. Finally, motivated by the physical context, we study the dependence of the equilibrium points with respect to the involved parameters, and we prove in particular that the surface temperature increases with respect to $ε_a$. This is the key mathematical manifestation of the greenhouse effect.

math.AP↗

arXiv2020

Existence and cost of boundary controls for a degenerate/singular parabolic equation

In this paper, we consider the following degenerate/singular parabolic equation $$ u_t -(x^αu_{x})_x - \fracμ{x^{2-α}} u =0, \qquad x\in (0,1), \ t \in (0,T), $$ where $0\leq α<1$ and $μ\leq (1-α)^2/4$ are two real parameters. We prove the boundary null controllability by means of a $H^1(0,T)$ control acting either at $x=1$ or at the point of degeneracy and singularity $x=0$. Besides we give sharp estimates of the cost of controllability in both cases in terms of the parameters $α$ and $μ$. The proofs are based on the classical moment method by Fattorini and Russell and on recent results on biorthogonal sequences.

math.AP↗

arXiv2018

The cost of controlling strongly degenerate parabolic equations

We consider the typical one-dimensional strongly degenerate parabolic operator $Pu= u_t - (x^αu_x)_x$ with $0<x<\ell$ and $α\in(0,2)$, controlled either by a boundary control acting at $x=\ell$, or by a locally distributed control. Our main goal is to study the dependence of the so-called controllability cost needed to drive an initial condition to rest with respect to the degeneracy parameter $α$. We prove that the control cost blows up with an explicit exponential rate, as $e^{C/((2-α)^2 T)}$, when $α\to 2^-$ and/or $T\to 0^+$. Our analysis builds on earlier results and methods (based on functional analysis and complex analysis techniques) developed by several authors such as Fattorini-Russel, Seidman, Güichal, Tenenbaum-Tucsnak and Lissy for the classical heat equation. In particular, we use the moment method and related constructions of suitable biorthogonal families, as well as new fine properties of the Bessel functions $J_ν$ of large order $ν$ (obtained by ordinary differential equations techniques).

math.OC↗

arXiv2017

Precise estimates for biorthogonal families under asymptotic gap conditions

A classical and useful way to study controllability problems is the moment method developed by Fattorini-Russell, based on the construction of suitable biorthogonal families. Several recent problems exhibit the same behaviour: the eigenvalues of the problem satisfy a uniform but rather 'bad' gap condition, and a rather 'good' but only asymptotic one. The goal of this work is to obtain general and precise upper and lower bounds for biorthogonal families under these two gap conditions, and so to measure the influence of the 'bad' gap condition and the good influence of the 'good' asymptotic one. To achieve our goals, we extend some of the general results of Fattorini-Russell concerning biorthogonal families, using complex analysis techniques developed by Seidman, Güichal, Tenenbaum-Tucsnak, and Lissy.

math.OC↗

arXiv2015

The cost of controlling degenerate parabolic equations by boundary controls

We consider the one-dimensional degenerate parabolic equation $$ u_t - (x^αu_x)_x =0 \qquad x\in(0,1),\ t \in (0,T) ,$$ controlled by a boundary force acting at the degeneracy point $x=0$. First we study the reachable targets at some given time $T$ using $H^1$ controls, extending the moment method developed by Fattorini and Russell to this class of degenerate equations. Then we investigate the controllability cost to drive an initial condition to rest, deriving optimal bounds with respect to $α$ and deducing that the cost blows up as $α\to 1^-$.

math.OC↗