# Seminário Matemática Aplicada e Análise Numérica

## Sessões anteriores

### 21/02/2019, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Nedjem Eddine Ramdani, *Université de Banta 2, Argélia*

### Solving integral and integro-diﬀerential equations using Collocation and Wavelets methods

The main objective of this work is to study some classes of integral and integro-diﬀerential equations with regular and singular kernels. We introduce a wavelets method to solve a new class of Fredholm integral equations of the second kind with non symmetric kernel; we also apply a collocation method based on the airfoil polynomial to numerically solve an integro-diﬀerential equation of second order with Cauchy kernel.

### 31/01/2019, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Rodrigo G. Serrão, *Instituto Superior Técnico*

### Numerical simulations of Stokes flow in 3D using the MFS

In this work we present the method of fundamental solutions (MFS) in several contexts. We start with a more intuitive example and then we extend it to vectorial PDE's. We present the density results that justify our approach and then we use the MFS to solve the Stokes system in 2D and 3D. We deal with non-trivial domains and with different types of boundary conditions, namely the mixed Dirichlet-Neumann conditions. We will present several simulations that show the strengths of the method and some of the numerical difficulties found.

(Joint work with C. J. S. Alves and A. L. Silvestre)

### 24/01/2019, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Erida Gjini, *Instituto Gulbenkian de Ciência*

### Modeling microbial interactions, dynamics and interventions: from data to processes

Controlling the evolution and spread of antimicrobial resistance is a major global health priority. While the discovery of new antibiotics does not follow the rate at which new resistances develop, a more rational use of available drugs remains critical. In my work, I explore the role of host immunity in infection dynamics and control, hence as an important piece in the puzzle of antibiotic resistance management.

I will present two studies from my research on microbial dynamics, addressing processes that occur at the within- and between-host level.

The first study examines antibiotic resistance and treatment optimization for bacterial infections, quantifying the crucial role of host immune defenses at the single host level.

The second study presents a multi-strain epidemiological model applied to pneumococcus data before and after vaccination.

This framework allows for retrospective inference of strain interactions in co-colonization and vaccine efficacy parameters, and can be useful for comparative analyses across different immunized populations.

### 29/11/2018, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Tomas Bodnar, *Czech Technical University in Prague*

### Suitable Far-field Boundary Conditions for Wall-bounded Stratified Flows

This talk presents an alternative boundary conditions setup for the numerical simulations of stable stratified flow. The focus of the tested computational setup is on the pressure boundary conditions on the artificial boundaries of the computational domain. The simple three dimensional test case deals with the steady flow of an incompressible, variable density fluid over a low smooth model hill. The Boussinesq approximation model is solved by an in-house developed high-resolution numerical code, based on compact finite-difference discretization in space and Strong Stability Preserving Runge-Kutta method for (pseudo-) time stepping.

*This is a joint work with Philippe Fraunie, University of Toulon, France.*

### 14/11/2018, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Luís Bandeira, *Universidade de Évora*

### Necessary and sufficient conditions for existence of minimizers for vector problems in the Calculus of Variations

We report our work about the main necessary and sufficient conditions for weak lower semi-continuity of integral functionals in vector Calculus of Variations.

In particular we provide tools to investigate rank-one convexity of functions defined on $2\times 2$-matrices. Furthermore, we explore some consequences and examples.

We also explore the quasiconvexity condition in the case where the integrand of an integral functional is a fourth-degree homogeneous polynomial.

### 22/09/2017, 15:30 — 16:30 — Sala P3.10, Pavilhão de Matemática

Raúl Manásevich, *Universidad de Chile*

### Systems of Quasilinear Elliptic Equations with Weights

### 26/04/2017, 15:30 — 16:30 — Sala P3.10, Pavilhão de Matemática

Luisa Fermo, *Univ. de Cagliari*

### A numerical approach for non linear partial differential equations of integrable type

### 23/03/2017, 14:30 — 15:30 — Sala P3.10, Pavilhão de Matemática

Nilson C. Roberty, *Universidade Federal do Rio de Janeiro*

### Reconstruction of PDE coefficients with overprescripton of Cauchy data at the boundary

Frequently incomplete information about coefficients in partial differential equations is compensated by overprescribed Cauchy data on the boundary.

We analyse this kind of boundary value problems in an elliptic system in Lipschitz domains. Main techniques are variational formulation, boundary integral equations and the Calderon projector. To estimate those coefficients we propose a variational formulation based on internal discrepancy observed in the mixed boundary value problem, obtained by splitting the overprescribed Cauchy data. Some numerical experiments are presented.

### 16/02/2017, 14:30 — 15:30 — Sala P3.10, Pavilhão de Matemática

Ezio Venturino, *Universitá de Torino*

### Models for sustainable biodiesel production

Several countries have already begun to invest in alternative energies due to smaller and smaller fossil fuel resources. In particular, for biodiesel production the Jatropha curcas appears to be a possible resource, in that it thrives even in harsh and very dry conditions. From its seeds a relevant quantity of oil can be extracted, for production of high grade biodiesel fuel.

But this plant is subject to parasitism from a mosaic virus, the Begomovirus, that is carried by white-flies Bemisia tabaci. The talk is centered on the investigation of two models for the fight of this plant infection.

In the case of large plantations we investigate the optimal insecticide spraying policy. Here the most relevant parameters of the ecosystem appear to be the infection transmission rate from vectors to plants and the vector mortality. The results indicate that spraying should be administered only after 10 days of the epidemics insurgence, relentlessly continued for about three months, after which disease eradication is obtained, [2].

At the small scale instead, we consider possible production by individuals, that cultivate this plant in small plots that would be otherwise be left wild and unproductive, [1]. We consider the effects of media campaigns that keep people aware of this plant disease, and indicate means for fighting it. The model shows that awareness campaigns should be implemented rather intensively, in order to effectively reduce or completely eradicate the infection.

**References**

[1] Priti Kumar Roy, Fahad Al Basir, Ezio Venturino (2017) Effects of Awareness Program for Controlling Mosaic Disease in Jatropha curcas Plantations, to appear in MMAS.

[2] Ezio Venturino, Priti Kumar Roy, Fahad Al Basir, Abhirup Datta (2016) A model for the control of the Mosaic Virus disease in *Jatropha Curcas* plantations, to appear in Energy, Ecology and Environment, doi:10.1007/s40974-016-0033-8.

*(work in collaboration with Fahad Al Basir and Priti K. Roy, Javadpur University, India)*

### 09/02/2017, 14:30 — 15:30 — Sala P3.10, Pavilhão de Matemática

K. R. Rajagopal, *Texas A&M University*

### A hierarchy of models for the flow of fluids through porous solids

The celebrated equations due to Fick and Darcy are approximations that can be obtained systematically on the basis of numerous assumptions within the context of Mixture Theory; these equations however not having been developed in such a manner by Fick or Darcy. Relaxing the assumptions made in deriving these equations via mixture theory, selectively, leads to a hierarchy of mathematical models and it can be shown that popular models due to Forchheimer, Brinkman, Biot and many others can be obtained via appropriate approximations to the equations governing the flow of interacting continua. It is shown that a variety of other generalizations are possible in addition to those that are currently in favor, and these might be appropriate for describing numerous interesting technological applications.

### 19/01/2017, 14:30 — 15:30 — Sala P3.10, Pavilhão de Matemática

Gabriele Inglese, *CNR - Ist. Applic. Calcolo (Firenze, Italy)*

### Perturbative methods in thermal imaging

I will discuss shortly three different inverse problems in the field of thermal nondestructive testing. In all cases we have a thin metallic plate $\Omega_0$ whose top boundary $S_{top}$ is not accessible while we are able to operate on the opposite surface $S_{bot}$.

We heat the specimen by applying a heat flux of density $\phi$ on $S_{bot}$ and measure a sequence of temperature maps.

Problem 1. Recover a perturbation of the heat transfer coefficient on $S_{top}$. [Inglese, Olmi - 2017]

Problem 2. Recover a surface damage on the inaccessible side $S_{top}$. [Inglese, Olmi - in progress]

Problem 3. Recover a nonlinear heat transfer coefficient on $S_{top}$. [Clarelli, Inglese - 2016]

### 14/12/2016, 14:30 — 15:30 — Sala Q4.6, Torre Sul

Azzeddine Bellour, *Ecole Normale Supérieure de Constantine (Algeria)*

### Two cubic spline methods for solving Fredholm integral equations

In this lecture, we propose two methods based on the use of natural and quasi cubic spline interpolations for approximating the solution of the second kind Fredholm integral equations.

Convergence analysis is established. Some numerical examples are given to show the validity of the presented methods.

Notice the Room: Q 4.6

### 02/12/2016, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Léonard Monsaingeon, *Université de Lorraine, Nancy (France)*

### Numerical investigation of the free boundary regularity for a degenerate advection-diffusion problem

In this talk I will describe the free boundary regularity of the traveling wave solutions to a degenerate advection-diffusion problem of Porous Medium type, whose existence was proved in a previous work with A. Novikov (PennState Univ, USA) and J.-M. Roquejoffre (IMT Toulouse, France). I will set up a finite-difference scheme allowing to compute approximate solutions and capture the free boundaries, and will carry out a numerical investigation of their regularity. Based on some nondegeneracy assumptions supported by solid numerical evidence, I will show the Lipschitz regularity of the free boundaries. Simulations indicate that this regularity is optimal, and the free boundaries seem to develop Lipschitz corners at least for some values of the nonlinear diffusion exponent. I will also discuss the existence of corners in the more analytical framework of viscosity solutions to certain periodic Hamilton-Jacobi equations, whose validity will be again supported by numerical evidence.

### 24/11/2016, 14:00 — 15:00 — Sala P3.10, Pavilhão de Matemática

Liviu Marin, *University of Bucharest (Romania)*

### An MFS-fading regularization approach to inverse BVPs in two-dimensional linear elasticity.

We investigate the numerical reconstruction of the missing displacements (Dirichlet data) and tractions (Neumann data) on an inaccessible part of the boundary in the case of a linear isotropic elastic material from the knowledge of over-prescribed noisy measurements taken on the remaining accessible boundary part. This inverse problem is solved using the fading regularization method, originally proposed by Cimetière et al. (2000, 2001) for the Laplace equation, in conjunction with a meshless method, namelythe method of fundamental solutions (MFS). The stabilization of the numerical method proposed herein is achieved by stopping the iterative procedure according to Morozov's discrepancy principle.

This is a joint work with Franck Delvare (University of Caen) and Alain Cimetière (University of Poitiers).

### 11/11/2016, 17:10 — 18:10 — Sala P3.10, Pavilhão de Matemática

Adélia Sequeira, *Dep. Matemática - CEMAT - Instituto Superior Técnico*

### Aplicações da Matemática a Simulações do Sistema Cardiovascular

Divulgação do trabalho desenvolvido no departamento de matemática do IST, relativo à modelação do sistema cardiovascular.

(Dirigido a alunos do 12º ano da Escola Secundária Seomara da Costa Primo, a frequentar o curso de Ciência e Tecnologia.)

Em colaboração com Jorge Tiago (CEMAT-IST).

### 12/05/2016, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Marília Pires, *Departamento de Matemática, CIMA, Universidade de Évora*

### The Traceless Oldroyd viscoelastic model

In the traceless Oldroyd viscoelastic model, the viscoelastic extra stress tensor is decomposed into its traceless (deviatoric) and spherical parts, leading to a reformulation of the classical Oldroyd model. The equivalence of the two models is established comparing model predictions for simple test cases. The new model is validated using several 2D benchmark problems. The structure and behaviour of the new model are discussed and the future use of the new model in envisioned, both on the theoretical and numerical perspectives.

Work in collaboration with T. Bodnár.

#### References

Bodnár, T., Pires, M. and Janela, J. (2014). Blood Flow Simulation Using Traceless Variant of Johnson-Segalman Viscoelastic Model. *Mathematical Modelling of Natural Phenomena* 9,(6), 117-141.

### 31/03/2016, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Kathleen Curran, *University College Dublin*

### FibReGen: Modelling Myofibre Regeneration

In young individuals, myofibres are capable of altering their profile in response to perturbation, but plasticity of ageing skeletal muscle is less clearly understood. The age-related loss of muscle mass in sarcopenia is mediated by a reduction in the total number of myofibres, a decrease in size of fast-twitch myosin heavy chain fibres and altered morphology. These maladaptations create negative metabolic and functional implications that impede healthy ageing.

Despite modern advances, Duchenne muscular dystrophy (DMD) remains fatal and incurable. Muscle is extensively replaced by adipose tissue, and heart failure often results. We propose to model for the molecular pathogenesis centred around the increased susceptibility of glycolytic fibres to degeneration in DMD and connect the histological findings of hypercontracted fibres, segmental necrosis and grouped necrosis to glycolytic fibres and investigate recent evidence from animal models suggesting that oxidative fibre type switching may ameliorate the effects of the disease.

Early physiological changes often start at the cellular or fascicular level, which is beyond the capabilities of conventional MRI. Histology, requiring invasive biopsies, is necessary to assess early treatment and training effects. Diffusion tensor imaging (DTI) provides a sensitive noninvasive readout of early physiological changes in tissue microstructure. DTI can also be applied for in vivo quantification and 3D visualisation of the macroscopic muscle fibre architecture.

The aim of FibReGen is to develop subject-specific and patient-specific computational models of skeletal and cardiac muscle entirely from MRI data. These computational models will integrate anatomical, functional, metabolic and mechanical data, and will characterise fibre type proportion and interconversion in a wide-ranging spectrum of subjects including elite athletes, those with age-related sarcopenia and patients with DMD.

Financial support:

### 17/03/2016, 14:30 — 15:30 — Sala P3.10, Pavilhão de Matemática

Cristiana Silva, *CIDMA - Universidade de Aveiro*

### Optimal control of epidemiological models

We apply optimal control theory to a Tuberculosis (TB) and a TB-HIV/AIDS co-infection models. The models are given by systems of ordinary differential equations.

For the TB model, optimal control strategies are proposed to minimize the number of active infectious and persistent latent individuals, as well as the cost of interventions. A cost-effectiveness analysis is done, to compare the application of each one of the control measures, separately or in combination.

We introduce delays in the TB model, representing the time delay on the diagnosis and commencement of treatment of individuals with active TB infection. The stability of the disease free and endemic equilibriums is investigated for any time delay. Corresponding optimal control problems, with time delays in both state and control variables, are formulated and studied.

We propose a model for TB-HIV/AIDS coinfection transmission dynamics. We analyze separately the HIV-only, TB-only and TB-HIV/AIDS models. The respective basic reproduction numbers are computed, equilibria and stability are studied. Optimal control theory is applied to the TB-HIV/AIDS model and optimal treatment strategies for co-infected individuals with HIV and TB are derived. Numerical simulations to the optimal control problem show that non intuitive measures can lead to the reduction of the number of individuals with active TB and AIDS.

### 16/12/2015, 16:00 — 17:00 — Sala P4.35, Pavilhão de Matemática

Annie Raoult, *Université Paris Descartes, France*

### Effective behavior of lattices with angular interactions

Angular interactions are of primary importance in mechanical trusses that they stabilize as well as in atomistic lattices, see Allinger and Tersoff-Brenner potentials. Graphenes are nowadays the best known example of hexagonal lattices. We will concentrate on the behavior of 2d-lattices undergoing deformations in the 3d-space, where major difficulties are already present when seeking for an equivalent behavior. We will give an example where homogenization is not required in the formulation of an equivalent continuous problem. We will show that for hexagonal lattices, on the contrary, homogenization is required even when only bond energy is taken into account. When angular interactions are added, we characterize the equivalent behavior by an alternate method. We will discuss the practical interest of the representation formulas.

### 16/07/2015, 15:00 — 16:00 — Sala P3.10, Pavilhão de Matemática

Nuno Lopes, *Instituto Superior de Engenharia de Lisboa*

### Analytical and Numerical Methods of the type FEM-C/D for Improved Boussinesq Models

In this talk, some analytical and numerical models are developed for the generation and propagation of surface water waves. These problems are solved using asymptotic and numerical methods. Regarding the numerical methods, we consider the continuous and continuous/discontinuous Galerkin finite element methods (FEM-C/D) with penalty terms. In the first problem, the model of Zhao et al. (2004) is extended in order to include some effects like dissipation and absorption of the energy of the surface water waves. We show that this model is robust with respect to the instabilities related to steep bottom gradients of the bathymetry. A new class of nonlinear Boussinesq-type systems is derived in the second problem. A CFL type condition is obtained for the linearized problem with constant bathymetry. The consistency of the dispersion relation as well as the good stability properties of this model are verified. From the numerical tests, we can conclude that the proposed numerical model is appropriate to model surface water waves. In the third problem, a class of Korteweg, de Vries–Benjamin, Bona and Mahony (KdV-BBM) type equations is deduced. The Nwogu’s parameter is determined in order to optimise the velocity potential of the linearized KdV-BBM model. Moreover, a numerical analysis of the proposed model is performed. We conclude that the KdV-BBM model is less prone to instabilities than the KdV model. Finally, a new Boussinesq-type differential equation of sixth-order to model bidirectional waves is derived and exact travelling wave solutions are obtained. A new analytical travelling wave solution is found. This is a joint work with P. J. S. Pereira and L. Trabucho.

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