Jérôme Vicente

An image processing technique for automatically detecting forest fire

In this paper we present an automatic system for early smoke source detection through the real time processing of landscape images. The first part describes the segmentation technique we use to extract persistent dynamical envelopes of pixels into the images. We describe the temporal algorithm at the pixel level (filtering) and the spatial analysis to bring together connected pixels into the same envelopes (object labeling). The second part deals with the method we use to discriminate the various natural phenomena that may cause such envelopes. We describe the image sequence analysis we developed to discriminate distant smokes from other phenomena, by extracting the transitory and complex motions into little pre-processed envelopes. We present then our main criterion for smoke recognition based on the analysis of the smoke plumes velocity.

Environmental exposure to TiO2 nanomaterials incorporated in building material.

Nanomaterials are increasingly being used to improve the properties and functions of common building materials. A new type of self-cleaning cement incorporating TiO2 nanomaterials (TiO2-NMs) with photocatalytic properties is now marketed. This promising cement might provide air pollution-reducing properties but its environmental impact must be validated. During cement use and aging, an altered surface layer is formed that exhibits increased porosity. The surface layer thickness alteration and porosity increase with the cement degradation rate. The hardened cement paste leaching behavior has been fully documented, but the fate of incorporated TiO2-NMs and their state during/after potential release is currently unknown. In this study, photocatalytic cement pastes with increasing initial porosity were leached at a lab-scale to produce a range of degradation rates concerning the altered layer porosity and thickness. No dissolved Ti was released during leaching, only particulate TiO2-NM release was detected. The extent of release from this batch test simulating accelerated worst-case scenario was limited and ranged from 18.7xa0±xa02.1 to 33.5xa0±xa05.1xa0mg of Ti/m2 of cement after 168xa0h of leaching. TiO2-NMs released into neutral aquatic media (simulate pH of surface water) were not associated or coated by cement minerals. The TiO2-NM release mechanism is suspected to start from freeing of TiO2-NMs in the altered layer pore network due to partial cement paste dissolution followed by diffusion into the bulk pore solution to the surface. The extent of TiO2-NM release was not solely related to the cement degradation rate.

Influence of pore and strut shape on open cell metal foam bulk properties

The thermo-physical behavior of open-celled metal foams depends on their microscopic structure. An ideal periodic isotropic structure of tetrakaidecahedron shape i.e. Kelvin cell is studied. We have proposed an analytical model in order to obtain geometrical parameters correctly as they have substantial influence on thermal and hydraulic phenomena, where strut geometry is of prime importance. Various relationships between different geometrical parameters and porosities are presented. Consequently, empirical correlations are proposed to determine permeability and inertia coefficient using Ergun like model for computing pressure drop.

Towards the development of simple methods for determining normal absorptances of open-cell foams based on opaque materials

The knowledge of the normal spectral absorptances of open-cell foams used as volumetric solar receivers is required to finely compute their thermal efficiencies. For this purpose, absorptances of a set of virtual open-cell foams of varying porosities, beforehand generated by using a numerical generator, are computed thanks to a ray tracing code. This work details the contribution of the intrinsic optical properties of the solid phase to the normal spectral absorptance of open-cell foams, through the statistical analysis of both the path and the events undergone by a ray, which is permitted by the ray tracing code. This study allows us to propose a robust and linear relationship that links the normal spectral absorptance to the porosity and the intrinsic optical properties of the solid phase, which is considered as optically thick.

μCT-Based Analysis of the Solid Phase in Foams: Cell Wall Corrugation and other Microscopic Features.

This work presents a series of three-dimensional computational methods with the objective of analyzing and quantifying some important structural characteristics in a collection of low-density polyolefin-based foams. First, the solid phase tortuosity, local thickness, and surface curvature, have been determined over the solid phase of the foam. These parameters were used to quantify the presence of wrinkles located at the cell walls of the foams under study. In addition, a novel segmentation technique has been applied to the continuous solid phase. This novel method allows performing a separate analysis of the constituting elements of this phase, that is, cell struts and cell walls. The methodology is based on a solid classification algorithm and evaluates the local topological dissimilarities existing between these elements. Thanks to this method it was possible to perform a separate analysis of curvature, local thickness, and corrugation ratio in the solid constituents that reveals additional differences that were not detected in the first analysis of the continuous structure. The methods developed in this work are applicable to other types of porous materials in fields such as geoscience or biomedicine.

PREDICTION OF THERMAL RADIATIVE PROPERTIES IN POROUS MEDIA: A MONTE-CARLO RAY TRACING METHOD

Knowledge of the thermal radiative properties of materials involved in industrial systems is crucial for dealing with energy balance. The evolution of computer performances opens today new perspectives in the development of predictive code aiming to accurately compute the radiative properties of a given industrial material from its 3D numerical image. In the other hand, predictive approaches appear insightful when experimental measurements cannot be easily performed (high pressure, high temperature, corrosive atmosphere, irradiative exposure...). In this work, a numerical tool has been implemented to reproduce the normal spectral emittance of porous media that can be measured by infrared emittance spectroscopy (300uf0ae3000 K). The code takes into account the chemical composition and the 3D numerical image of the heated sample. In particular, x-ray μ-tomography is used to provide such images. Then, from the analysis of the sample texture, a Monte Carlo ray tracing scheme is applied for the retrieval of the radiative properties. In this work, we discuss of this procedure and its use for the characterization of aluminium foam (ERG Al 20).