21 Ottobre, 2009 11:30

Numerical modeling and optimization of fluid and thermal systems

Timo Karvinen, Tampere University of Technology, Department of Mechanics and Design, Finland

Aula Seminari F. Saleri VI Piano MOX- Dipartimento di Matematica, Politecnico di Milano

abstract

abstract

This presentation gives an overview on some of the research of numerical modeling and optimization of fluid and thermal systems conducted at Tampere University of Technology. The topics covered in the presentation are the fluid-structure interaction in the paper making process, multi-objective shape optimization of sewers, thermo-elastic modeling of grinding process, and optimization of heat transfer fins.

20 Ottobre, 2009 12:00

Image processing based on partial differential equations

Xue Cheng Tai, Depart of Math, University of Bergen Norway and Division of Mathematical Sciences SPMS, Nanyang Tech

Aula Seminari F. Saleri VI Piano MOX- Dipartimento di Matematica, Politecnico di Milano

abstract

abstract

In this talk, we will highlight some of the research we have done in the group
for image processing based on partial differential equations.

First, we will introduce a method which is called a "Piecewise Constant Level Set Method (PCLSM)". This method is proposed for tracing boundaries of closed regions with applications in computer vision, image processing and shape optimization. We will point out a relationship between PCLSM, phase field models and traditional level set idea. We then show some theoretical results for the discretized problems. It seems that some properties valid for the discretized problem is not correct for the continuous model. Traditional gradient decent algorithms can be used to solve the discretized problems. However, they are slow and may get stuck at local minimizers. We then try to construct a special graph and show the solution can be obtained by finding a minimum cut on the constructed graph through some combinatorial minimization algorithms. The numerical efficiency is greatly improved.

In the end, some new geometrical models for image processing will be discussed. We try to use some special nonlinear PDEs related to higher order derivatives for image restoration and inpainting.

19 Ottobre, 2009 17:30

A color sensitive pixel with tunable spectral responsivities

Federico Zaraga, Politecnico di Milano - Dipartimento di Elettronica e Informazione

Aula Seminari F. Saleri VI Piano MOX- Dipartimento di Matematica, Politecnico di Milano

abstract

abstract

A recently proposed pixel device relies on the wavelength dependence of the Silicon absorption
coefficient for color sensing without color filters. A suitable transverse electric field configuration, in the depleted region beneath the pixel surface of this device (TFD), makes it possible to collect at different superficial contacts the carriers generated at different depth from the surface. With three or more junctions the color information can be reconstructed. With respect to a conventional color sensitive pixel sensor based on Color Filter Arrays (CFA), in a TFD pixel sensor each single pixel is by itself color sensitive and therefore no subsequent demosaicking algorithms are needed to interpolate the colors.

A unique characteristic of this new device is the capability of fine spectral responses tunability,
which can be obtained by simply changing the voltage configuration of the superficial junctions (and thus the carriers collection paths), without affecting the overall quantum efficiency. This feature allows to change the sensor native color space and to adjusting it to the scene. In the presentation it will be shown how the spectral responses tunability can be exploited to perform a White Balance operation, to compensate for the illuminant spectrum prior to image acquisition. Further applications may include filter tuning to reduce color error, filter optimization and adaptation of the camera to the scene.

16 Ottobre, 2009 14:00

Sezione di Geometria, Algebra e loro applicazioni

Non deterministic finite automata

Boris Melnikov, Togliatti State University

Aula seminari Mox F.Saleri

A recently proposed pixel device relies on the wavelength dependence of the Silicon absorption
coefficient for color sensing without color filters. A suitable transverse electric field configuration, in the depleted region beneath the pixel surface of this device (TFD), makes it possible to collect at different superficial contacts the carriers generated at different depth from the surface. With three or more junctions the color information can be reconstructed. With respect to a conventional color sensitive pixel sensor based on Color Filter Arrays (CFA), in a TFD pixel sensor each single pixel is by itself color sensitive and therefore no subsequent demosaicking algorithms are needed to interpolate the colors.

A unique characteristic of this new device is the capability of fine spectral responses tunability,
which can be obtained by simply changing the voltage configuration of the superficial junctions (and thus the carriers collection paths), without affecting the overall quantum efficiency. This feature allows to change the sensor native color space and to adjusting it to the scene. In the presentation it will be shown how the spectral responses tunability can be exploited to perform a White Balance operation, to compensate for the illuminant spectrum prior to image acquisition. Further applications may include filter tuning to reduce color error, filter optimization and adaptation of the camera to the scene.

14 Ottobre, 2009 15:15

Seminari FDS

TEORIA DEI GIOCHI: dall'astrazione alla realtà

Roberto Lucchetti, Dipartimento di Matematica - Politecnico di Milano

Aula Consiglio del Dipartimento di Matematica (VII piano)

A recently proposed pixel device relies on the wavelength dependence of the Silicon absorption
coefficient for color sensing without color filters. A suitable transverse electric field configuration, in the depleted region beneath the pixel surface of this device (TFD), makes it possible to collect at different superficial contacts the carriers generated at different depth from the surface. With three or more junctions the color information can be reconstructed. With respect to a conventional color sensitive pixel sensor based on Color Filter Arrays (CFA), in a TFD pixel sensor each single pixel is by itself color sensitive and therefore no subsequent demosaicking algorithms are needed to interpolate the colors.

A unique characteristic of this new device is the capability of fine spectral responses tunability,
which can be obtained by simply changing the voltage configuration of the superficial junctions (and thus the carriers collection paths), without affecting the overall quantum efficiency. This feature allows to change the sensor native color space and to adjusting it to the scene. In the presentation it will be shown how the spectral responses tunability can be exploited to perform a White Balance operation, to compensate for the illuminant spectrum prior to image acquisition. Further applications may include filter tuning to reduce color error, filter optimization and adaptation of the camera to the scene.

13 Ottobre, 2009 15:30

Seminari FDS

Checkpointing e Algorithm 799: implementazione e parallelizzazione

Cristiano Padrin, Mox-Dipartimento di Matematica, Politecnico di Milano

Aula Seminari F. Saleri VI Piano MOX- Dipartimento di Matematica, Politecnico di Milano

abstract

abstract

Il checkpointing è un metodo utilizzato per ottenere delle ricostruzioni inverse di fenomeni fisici tempo-dipendenti sfruttando
pochi parametri. In particolare, dal 2000, uno dei programmi più importanti e più usati per l attuazione di tale metodo è il cosidetto Algorithm 799, sviluppato da Griewank.
In questo seminario, dopo una breve presentazione del metodo, verrà presentato un nuovo modo per implementareAlgorithm 799, e brevemente verrà accennato a come lo si possa parallelizzare.

12 Ottobre, 2009 17:30

Seminario Matematico e Fisico di Milano

Spectral method in Hamiltonian PDE

Wei-Min Wang, Université Paris-Sud

Dipartimento di Matematica, Universita di Milano

abstract

abstract

We discuss some recent development in Hamiltonian PDE. The Hamiltonians here are typically non convex and moreover in infinite dimensions. This new approach is local. It eliminates the convexity condition and is natural for PDE.

12 Ottobre, 2009 15:30

Seminario Matematico e Fisico di Milano

Modello delle acque basse, soluzioni vicino all equilibrio e schemi ben bilanciati

Gabriella Puppo,  Dipartimento di Matematica, Politecnico di Torino

Aula Seminari F. Saleri VI Piano MOX- Dipartimento di Matematica, Politecnico di Milano

abstract

abstract

In questo seminario considereremo il classico modello delle shallow water e alcune varianti. Questo lavoro e il frutto di collaborazioni con Sebastian Noelle dell RWTH di Aachen, che aveva lo scopo di studiare l effetto delle correnti sulle onde al largo della costa nord della Norvegia, e il gruppo di Carlos Pares dell Universita di Malaga, interessato soprattutto alle correnti che si sviluppano nello stretto di Gibilterra per effetto delle maree.
Studieremo alcuni problemi legati alla modellizzazione di questi fenomeni e alcuni problemi dovuti alla discretizzazione numerica dei modelli risultanti.
In particolare, ci concentreremo sulla soluzione numerica di problemi vicini all equilibrio, quando la soluzione numerica puo produrre oscillazioni spurie dello stesso ordine di grandezza delle fluttuazioni dall equilibrio che si vogliono studiare. Per ovviare a questo inconveniente sono stati introdotti gli schemi ben bilanciati, che mantengono in maniera esatta, a livello discreto, alcune soluzioni di equilibrio. In questo lavoro, descriveremo schemi ben bilanciati di alto ordine per lunghi tempi di integrazione e schemi ben bilanciati per alcuni problemi non conservativi, legati al modello delle acque basse.

5 Ottobre, 2009 15:30

Seminario Matematico e Fisico di Milano

BLOOD-FLOW MODELLING AND SIMULATIONS ALONG AND TROUGH A BRAIDED MULTI-LAYER METALLIC STENT

Vuk Milisic, Wolfgang Pauli Institute (WPI) Vienna

Aula Seminari F. Saleri VI Piano MOX- Dipartimento di Matematica, Politecnico di Milano

abstract

abstract

Using tools from asymptotic analysis for elliptic equations, we study in this work the hemodynamics in a stented artery connected either to a collateral artery or to an aneurysmal sac.
The blood flow is driven by a pressure drop. Our aim is to characterize the flow-rate and the pressure in the contiguous zone to the main artery: using boundary layer theory we construct a homogenized first order approximation with respect to epsilon, the size of the stent s wires.
In the collateral artery this gives the flow-rate. In the case of the aneurysm, it shows that:
i) the zeroth order term of the pressure in the sac equals the averaged pressure along the stent in the main artery,
ii) the presence of the stent inverses the rotation of the vortex.
We prove rigorously that our asymptotic approximation is first order accurate with respect to epsilon. We derive also new averaged implicit interface conditions that our approximation formally satisfies, generalizing our analysis to other possible geometrical configurations.
In the last part we provide numerical results that illustrate and validate the theoretical approach.

PS.:
For further details, please refer to the link.

2 Ottobre, 2009 15:00

Seminario Matematico e Fisico di Milano

On De Giorgi Conjecture and Beyond

Jun-Cheng Wei, The Chinese University of Hong Kong

TBA

abstract

abstract

Thirty years old, the famous Italian mathematician De Giorgi asked if entire solutions to certain nonlinear PDEs in the whole space are indeed ODE solutions, provided certain monotonicity assumption is assumed.
This conjecture has attracted lots of studies. In this talk, I will discuss the status of this conjecture, its extensions, and moreover the intricate connections between differential geometry and nonlinear PDE.