Jérôme Coville (INRAE, Avignon)

Talk title & abstract: TBA

Jorge Estrada Hernández (Universidad de la Habana)

Modelling sterile mosquito releases in a heterogeneous 2D terrain

Abstract: The Sterile Insect Technique consists of the breeding and release of a large number of sterilized males into the wild mosquito population, which increases the probability that a female mosquito will mate with a sterile male, thus leaving no offspring and leading to the population's decline over time. I will present a reaction-diffusion PDE system that models the use of the SIT in a mosquito population that inhabits a heterogeneous 2D terrain, where the heterogeneity of the terrain is modeled by having a space-dependent diffusion coefficient. I will perform numerical simulations to gain an idea of the behavior of the solutions for the introduced sterile males and the wild mosquito population. The ultimate goal is to use this information to obtain rigorous results that extend the results  proven in [1] and [2], which guarantee the success of the SIT and the prevention of the reinfestation by mosquitos outside the release zone, for a large enough sterile male release, given certain conditions that link the amount of the sterile male release and the size of the release zone.

[1] L. Almeida, J. Estrada, N. Vauchelet, "The sterile insect technique used as a barrier control against
reinfestation", 2022, in: Optimization and Control for Partial Differential Equations, De Gruyter, pp.
91-112, ISBN: 9783110695984, doi: https://doi.org/10.1515/9783110695984-005

[2] L. Almeida, J. Estrada, N. Vauchelet, "Wave blocking in a bistable system by local introduction of a species :
Application to sterile insect techniques on mosquitoes populations", 2022, in: Mathematical Modelling of Natural Phenomena,
vol.17, doi: https://doi.org/10.1051/mmnp/2022026

Karina Garcia-Martinez (Center of Molecular Immunology)

Talk title & abstract: TBA

Sophie Hecht (CNRS & LJLL - Sorbonne Université)

Talk title & abstract: TBA

Victoria Hernández Mederos (Instituto de Cibernética, Matemática y Física)

Isogeometric approach to the study of focused ultrasound induced heating in biological tissues

Ultrasound medical treatments are non-invasive, repeatable, and non-toxic methods that can be used to treat muscle, bone, and skin tissue. Focused ultrasound systems for medical therapy must be carefully designed, implemented, and applied toavoid tissue damage. In this talk we discuss a study of the heating of a biological tissue induced by the ultrasonic pulse emitted by a curved transducer. The thermal diffusion effect of the ultrasound is computed solving Helmholtz and Pennes partial differential equations. Isogeometric analysis (IgA) is proposed as an effective tool to compute the acoustic pressure field, solution of Helmholtz equation. In combination with the method of lines, IgA is also used to compute the temperature field, solution of Pennes bioheat equation. Numerical experiments are performed with a biological tissue composed of three layers: skin, fat and muscle and a fixed value of the frequency of the pulse, in order to determine the intensity at which ultrasound effectively stimulates the tissues while avoiding tissue injury, according to the time-temperature combinations recommended in the literature.

Florence Hubert (Aix-Marseille Université)

 Growth Fragmentations Models

Growth fragmentation models are often used in structured population dynamics to model, for example, cell division and polymerization. The classical form of the equation is:

∂ₜρ(t,x) + ∂ₓ(g(x)ρ(t,x)) = -B(x)ρ(t,x) + ∫ₓ^∞ B(y)k(y,x)ρ(t,y) dy, t > 0, x > 0
ρ(t,0) = 0, t > 0
ρ(0,x) = ρ⁰(x), x > 0

The well-posedness of a globally defined solution to this equation as well as its asymptotic behaviour has been widely studied. We will first give some contexts where this model is used. We will then recall the main results (see Gabriel et al. 2021, Perthame). We will also propose extensions of such equations in the context of metastasis spreading and microtubule dynamical instabilities. We will highlight the properties of these models and the remaining challenges.

References

J. A. Cañizo, P. Gabriel, and H. Yoldaş. Spectral gap for the growth-fragmentation equation via Harris's theorem. SIAM J. Math. Anal., Vol.53, No.5, pp.5185-5214, (2021).

N. Hartung, S. Mollard, D. Barbolosi, A. Benabdallah, G. Chapuisat, G. Henry, S. Giacometti, A. Iliadis, J. Ciccolini, C. Faivre, F. Hubert. Mathematical Modeling of tumor growth and metastatic spreading: validation in tumor-bearing mice, Cancer Research 74, p. 6397-6407, 2014.

S. Honoré, F. Hubert, M. Tournus, D. White. A growth-fragmentation approach for modeling microtubule dynamic instability, Bulletin of Mathematical Biology, 81, p. 722–758 (2019).

B. Perthame. Transport equations in biology, Springer.

Alejandro Lage Castellanos (Universidad de la Habana) 

Inference of hidden processes in first waves of COVID in Cuba

I'll discuss two researches carried in our group at the early onset of COVID in Cuba. They both deal with the possibility of inferring what lies behind the surface of the public data of new cases.

First I'll discuss the inference of the number of undetected cases in Cuba's first waves of COVID. This research, published in Revista Cubana de Matematica, https://arxiv.org/pdf/2008.03332, was inspired by some similar work done in France (L. Roques[1]). The idea is Not to fix SIR models to the public data of cases. Instead, understand that such reports are a stochastic sample from the real epidemic, that evolves as SIR but is not detected. So, we fit two models, one stochastic for the detection process and one mechanistic for the underlying epidemic, to match the public data.

Second, I'll discuss how to treat the  contact tracing of cases in an epidemic as a cascade process. Cuba's public report of cases separated the primary from secondary cases. Notably, there was a much higher number of secondary cases than primary cases. We built a cascade model of contact tracing to try to fit this data and understand the efficiency of the Cuban health system in detecting cases. This approach is similar to results from the group of Ferguson in the early 2000's, and somehow is a rediscovery of their results.

 

King-Yeung (Adrian) Lam (Ohio State University)

Control formulation for a road-field population dynamics model

Berestycki, Roquejoffre, and Rossi introduced a reaction-diffusion system for populations that have a distinguished ‘road’ on which they move quickly but do not reproduce.  The goal is to understand invasion behavior (fronts).  This model has attracted enormous interest in the decade since it was introduced, with a nearly complete picture in the case of a straight road.  In this talk, I will discuss a joint work with Adrian Lam in which we provide an optimal control perspective on this problem.  This gives a natural interpretation of the front in terms of balancing speed on the road and growth in the field, and it lets us easily deduce that ‘bent’ line case, which was previously not well-understood, is a simple consequence of the straight line case and some elementary geometry. 

Cinzia Soresina (University of Trento)

Derivation of cross-diffusion models in population dynamics: dichotomy, time-scales, and fast-reaction

In population dynamics, cross-diffusion describes the influence of one species on the diffusion of another. A benchmark problem is the cross-diffusion SKT model, proposed in the context of competing species to account for stable inhomogeneous steady states exhibiting spatial segregation. Even though the reaction part does not present the activator-inhibitor structure, the cross-diffusion terms are the key ingredient for the appearance of spatial patterns [1]. From the modelling perspective, cross-diffusion terms naturally appear in the fast-reaction limit of a ``microscopic'' model (in terms of time scales) presenting only standard diffusion and fast-reaction terms, thus incorporating processes occurring on different time scales [4]. In this talk, recent applications of this approach will be presented, e.g., predator-prey [2] and mutualistic interactions, plant dynamics with autotoxicity effects [3], and epidemiology.

[1] Breden, M., Kuehn, C., Soresina, C. (2021). On the influence of cross-diffusion in pattern formation. Journal of Computational Dynamics 8(2):213--240.
https://doi.org/10.3934/jcd.2021010

[2] Desvillettes, L., Soresina, C. (2019) Non-triangular cross-diffusion systems with predator-prey reaction terms. Ricerche di Matematica 68(1):295--314.
https://doi.org/10.1007/s11587-018-0403-y

[3] Giannino, F., Iuorio, A., Soresina,  C. (in preparation). The effect of auto-toxicity in plant-growth dynamics: a cross-diffusion model.

[4] Kuehn, C., Soresina, C. (2020). Numerical continuation for a fast-reaction system and its cross-diffusion limit. SN Partial Differential Equations and Applications 1:7.
https://doi.org/10.1007/s42985-020-0008-7

Ariane Trescases (CNRS & Institut de Mathématiques de Toulouse)

A viscous multi-tissue model for vertebrate embryo growth

During elongation of the vertebrate embryo, live imaging reveals cellular turbulence in the embryonic tissues. We propose a 2D mechanical model for tissue growth during embryo elongation, which recovers these turbulent movements and addresses the question of the mechanism of segregation between tissues. Having (formally) determined the incompressible limit, we study the qualitative behavior at the limit and discuss a ghost effect, then deduce new biological hypotheses.