23 Febbraio, 2009 15:00

A numerical model for the hydrostatic equations of atmospheric motion using mimetic finite differences on spherical triangular grids.

Dr.ssa Hui Wan, Max Planck Institut fuer Meteorologie, Hamburg

Aula Seminari F. Saleri VI Piano

abstract

abstract

Atmospheric general circulation models (AGCMs) are important tools for atmospheric research, climate modelling and numerical weather forecast.
At the base of an AGCM is the numerical solution of the partial differential equations governing the atmospheric motions. In recent years, quasi-uniform triangular grids on the sphere and mimetic finite-difference methods have gained popularity due to their suitability for the massively parallel computing and for achieving important conservation properties in the numerical model.
The ICON project, initiated in 2001 by the Max Planck Institute for Meteorology and the German Weather Service aims at developing new climate and weather forecasting models using spherical triangular grids.
As the first step, the horizontal grids and mimetic differencing operators were defined and a 2D shallow water model was developed by Bonaventura et al.
Since 2006, further development has been carried out to extend the 2D model a 3D hydrostatic atmospheric circulation model.

In this talk the 3D hydrostatic model will be described, and the properties of the numerical schemes used therein will be discussed.
The performance of the new model will be demonstrated by selected idealized experiments. The numerical results show that the new model can successfully simulate important mechanisms of the large-scale atmospheric dynamics.
Good numerical stability is observed in both deterministic tests and an idealized climate simulation. The new model thus forms a good basis for a full AGCM.

18 Febbraio, 2009 15:00

Seminari FDS

Labirinti e matematica: da Versailles alla topologia

F. Peiretti

Laboratorio Didattico FDS

Atmospheric general circulation models (AGCMs) are important tools for atmospheric research, climate modelling and numerical weather forecast.
At the base of an AGCM is the numerical solution of the partial differential equations governing the atmospheric motions. In recent years, quasi-uniform triangular grids on the sphere and mimetic finite-difference methods have gained popularity due to their suitability for the massively parallel computing and for achieving important conservation properties in the numerical model.
The ICON project, initiated in 2001 by the Max Planck Institute for Meteorology and the German Weather Service aims at developing new climate and weather forecasting models using spherical triangular grids.
As the first step, the horizontal grids and mimetic differencing operators were defined and a 2D shallow water model was developed by Bonaventura et al.
Since 2006, further development has been carried out to extend the 2D model a 3D hydrostatic atmospheric circulation model.

In this talk the 3D hydrostatic model will be described, and the properties of the numerical schemes used therein will be discussed.
The performance of the new model will be demonstrated by selected idealized experiments. The numerical results show that the new model can successfully simulate important mechanisms of the large-scale atmospheric dynamics.
Good numerical stability is observed in both deterministic tests and an idealized climate simulation. The new model thus forms a good basis for a full AGCM.

18 Febbraio, 2009 15:30

Sezione di Calcolo delle Variazioni ed Equazioni Differenziali

Regolarità degli attrattori globali

Vittorino Pata, Politecnico di Milano

Atmospheric general circulation models (AGCMs) are important tools for atmospheric research, climate modelling and numerical weather forecast.
At the base of an AGCM is the numerical solution of the partial differential equations governing the atmospheric motions. In recent years, quasi-uniform triangular grids on the sphere and mimetic finite-difference methods have gained popularity due to their suitability for the massively parallel computing and for achieving important conservation properties in the numerical model.
The ICON project, initiated in 2001 by the Max Planck Institute for Meteorology and the German Weather Service aims at developing new climate and weather forecasting models using spherical triangular grids.
As the first step, the horizontal grids and mimetic differencing operators were defined and a 2D shallow water model was developed by Bonaventura et al.
Since 2006, further development has been carried out to extend the 2D model a 3D hydrostatic atmospheric circulation model.

In this talk the 3D hydrostatic model will be described, and the properties of the numerical schemes used therein will be discussed.
The performance of the new model will be demonstrated by selected idealized experiments. The numerical results show that the new model can successfully simulate important mechanisms of the large-scale atmospheric dynamics.
Good numerical stability is observed in both deterministic tests and an idealized climate simulation. The new model thus forms a good basis for a full AGCM.

16 Febbraio, 2009 11:00

Sezione di Calcolo delle Variazioni ed Equazioni Differenziali

On the motion of a rigid body in a Navier-Stokes liquid under the action of a time-periodic driving mechanism

Prof. Giovanni Paolo Galdi, University of Pittsburgh

Aula Seminari F. SALERI VI piano

abstract

abstract

This talk is devoted to the mathematical investigation of the motion of a rigid body in an infinite Navier-Stokes liquid, under the action of a time-periodic driving mechanism. This latter can be, for example, a time-periodic force acting along a given constant direction, or time-periodic boundary data.

The main objective is to find conditions under which the body is propelled by the driving mechanism, namely, conditions that ensure that the body can cover a given trajectory in a finite time interval.

10 Febbraio, 2009 

Sezione di Geometria, Algebra e loro applicazioni

Slowly Synchronizing Automata with Zero and Incomplete Sets

Elena V. Pribavkina, Ural State University - Ekaterinburg - Russia

Aula seminari III piano

abstract

abstract

Using combinatorial properties of incomplete sets in a free monoid we construct a series of $n$-state deterministic automata with zero whose shortest synchronizing word has length
$\frac{n^2}4+\frac{n}2-1$.

10 Febbraio, 2009 15:30

Sezione di Geometria, Algebra e loro applicazioni

Constitutive Modeling of Biodegradable Polymers for Application in Endovascular Stents

Dott. Joao Soares, Mox

Aula Seminari F. SALERI VI piano

abstract

abstract

Balloon angioplasty followed by stent implantation has been of great benefit in coronary applications, whereas in peripheral applications, success rates remain low. Analysis of healing patterns in successful deployments shows that six months after implantation the artery has reorganized itself and there is no purpose for the stent to remain, potentially provoking inflammation and foreign body reaction. Thus, a fully absorbable stent that fulfills the mission and steps away is of great benefit.

Biodegradable polymers have a widespread usage in the biomedical field, such as sutures, scaffolds and implants. Aliphatic polyesters (the main class of biodegradable polymers used in biomedical applications) degrade by random scission due to passive hydrolysis which results in molecular weight reduction, loss of strength, and ultimately, loss of mass. A constitutive model involving degradation and its impact on mechanical properties was developed through an extension of a material which response depends on the history of the motion and on a scalar parameter reflecting the local extent of
degradation. The material properties decrease with degradation and a rate equation describing the chain scission process confers characteristics of stress relaxation, creep and hysteresis. These phenomena arise due to the entropy-producing nature of degradation
and are markedly different from their viscoelastic counterparts.

4 Febbraio, 2009 15:00

Seminari FDS

Approccio termodinamico ad alcuni problemi astronomici

U. Bielli

Laboratorio Didattico FDS

Balloon angioplasty followed by stent implantation has been of great benefit in coronary applications, whereas in peripheral applications, success rates remain low. Analysis of healing patterns in successful deployments shows that six months after implantation the artery has reorganized itself and there is no purpose for the stent to remain, potentially provoking inflammation and foreign body reaction. Thus, a fully absorbable stent that fulfills the mission and steps away is of great benefit.

Biodegradable polymers have a widespread usage in the biomedical field, such as sutures, scaffolds and implants. Aliphatic polyesters (the main class of biodegradable polymers used in biomedical applications) degrade by random scission due to passive hydrolysis which results in molecular weight reduction, loss of strength, and ultimately, loss of mass. A constitutive model involving degradation and its impact on mechanical properties was developed through an extension of a material which response depends on the history of the motion and on a scalar parameter reflecting the local extent of
degradation. The material properties decrease with degradation and a rate equation describing the chain scission process confers characteristics of stress relaxation, creep and hysteresis. These phenomena arise due to the entropy-producing nature of degradation
and are markedly different from their viscoelastic counterparts.

3 Febbraio, 2009 11:00

Sezione di Probabilità e Statistica Matematica

Perche' un setting Markoviano per equazioni di tipo Volterra?

prof. Stefano Bonaccorsi, Universita di Trento

aula seminari III piano

abstract

abstract

Lo sforzo necessario per tradurre una equazione di Volterra con rumore stocastico in forma di equazione di evoluzione stocastica non e' banale. A prima vista puo' non sembrare neppure giustificato, in quanto la buona positura dell'equazione si ottiene piu' facilmente in altre vie.
Tuttavia, lo sforzo si rivela proficuo se possiamo usare il fatto che la soluzione dell'equazione di evoluzione e' un processo Markoviano: per studiare l'esistenza di misure invarianti per l'equazione di partenza, la convergenza delle soluzioni oppure per applicare le tecniche di controllo e ottimizzazione note per le EDS e trovare risultati di controllo ottimo per equazioni integrali stocastiche.

30 Gennaio, 2009 11:30

Sezione di Probabilità e Statistica Matematica

Text mining e testi biomedici: una ricerca sulla continuità dell'informazione

dott.Stefano Ballerio, Politecnico di Milano

Aula Seminari MOX - VI piano

abstract

abstract

Il text mining e la knowledge discovery sono strumenti necessari per fronteggiare il rischio di information overflow che deriva dall'aumento continuo della letteratura biomedica pubblicata. La presentazione introduce al text mining e illustra un'operazione di text mining condotta su un corpus di 413 lettere di dimissione di pazienti con problemi di scompenso cardiaco. La ricerca è stata condotta presso l'Ospedale Uboldo di Cernusco sul Naviglio (Azienda Ospedaliera di Melegnano). Scopo della ricerca era valutare il contenuto informativo delle lettere in riferimento allo standard ACC 3.2 di Joint Commission International. Il text mining quindi è stato usato come metodo per valutare la continuità dell'informazione come parte della continuità assistenziale.

29 Gennaio, 2009 10:00

Sezione di Probabilità e Statistica Matematica

A monotonic algorithm for solving nonlinear optimal control problems

Prof. Gabriel Turinici, Universite Dauphine Paris

Aula Seminari VII Piano Dip. di Matematica

abstract

abstract

Initially introduced in the framework of quantum control, the so-called monotonic algorithms have shown excellent numerical results when dealing with various bilinear optimal control problems.

This talk introduces the historical origins and presents a unified formulation of such procedures and the intrinsic assumptions they require. In this framework, we prove the feasibility of the general algorithm. Finally, we explain how these assumptions can be relaxed.