Hypoxémie et inflammation systémique après ischémie cérébrale aiguë chez le rat Wistar

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal

Finite Element Modeling Of The Hygroscopic Warping Of Medium Density Fiberboard

The objective of this study was to develop a three-dimensional finite element model of the hygromechanical deformation of medium density fiberboard (MDF) panels with various vertical density profiles subjected to moisture adsorption on one face. The theoretical model was based on three sets of equations: 1) three-dimensional equations of unsteady-state moisture diffusion, 2) three-dimensional equations of mechanical equilibrium, and 3) Hooke's law for plane isotropy, which takes into account shrinkage and swelling through the panel thickness. The finite element model was applied to six panels with various density profiles. For both the simulations and the experiments, the warping was caused by moisture adsorption from one of the faces of 560-mm x 560-mm x 12-mm MDF panels while the other surface and the edges were sealed. Physical and mechanical characteristics defined as a function of density and moisture content were used as model inputs. The model made it possible to capture the rapid initial development of maximum warp and its following decrease as moisture content equalized through panel thickness; the effect of the density profile on the level of warp caused by moisture adsorption; and warp fluctuations resulting from changes in the ambient relative humidity, and from the hysteresis in the expansion coefficient between adsorption and desorption. To validate the model, the warp development of laboratory MDF panels was compared to simulation results. The agreement between calculated and actual panel warping confirmed that the model could successfully be used to simulate moisture movement in MDF and the resulting warp, and to help in the optimization of panel vertical density profiles aiming at better stability of form in MDF panels. For the typical experimental cases, it was observed that there was a strong effect of panel density profile on the levels of warp and its dynamics. The levels of warp increased with average panel density. The panels with sharper density profile developed stronger warp compared to panels with an even profile. When the density profile was skewed towards one of the surfaces, the panel developed positive or negative warp and did not return to the original flat form

Linear Expansion And Thickness Swell Of Mdf As A Function Of Panel Density And Sorption State

Experiments were conducted using ASTM standard methods to determine the medium density fiberboard (MDF) expansion properties and swelling characteristics as a function of panel density and sorption state. Specimens without density profile were produced by removing the surface layers of laboratory MDF panels. The results from the trials showed that for laboratory MDF, linear expansion is homogenous in panel plane. When specimen density increased, linear expansion, linear expansion coefficient, thickness shrinkage coefficient, linear contraction, and linear contraction coefficient increased. Thickness swell was higher than thickness shrinkage at any density level. Thickness swell coefficient was higher than thickness shrinkage coefficient for low density levels. The values of linear contraction and linear contraction coefficient (in desorption) were higher than the values of linear expansion and linear expansion coefficient (in adsorption). The values on thickness swell and thickness shrinkage were much higher than the values of linear expansion and linear expansion and linear contraction at any density level. The effect of density on linear expansion, linear expansion coefficient and linear contraction coefficient was significantly stronger than the effect of density on thickness swell, thickness swell coefficient and thickness shrinkage

Numerical Prediction of Engineered Wood Flooring Deformation

Dimensional stability is of primary importance in the use of layered wood composites such as engineered wood flooring. It is largely due to the physical and mechanical properties and moisture content changes of each layer. Therefore, the non-homogeneous adsorption or desorption of moisture by the composite may induce its deformation, thus decreasing product value. The objective of this study was to develop a finite element model of the hygromechanical cupping in layered wood composite flooring. The model is based on two sets of equations: 1) the three-dimensional equations of unsteady-state moisture diffusion, and 2) the three-dimensional equations of elasticity including the orthotropic Hooke's law, which takes into account the shrinkage and swelling of each layer. The proposed model was used to predict the deformation of an engineered wood flooring strip following desorption by the top surface. The model was solved by the finite element method, and the calculated cupping was validated against experimental data. The results show that the proposed model can be successfully used to simulate the non-homogeneous moisture movement and the resulting cupping deformation in layered wood composites such as engineered wood flooring strips. For both predicted and measured deformation, roughly 80% of the cupping deformation appears after 3 days of conditioning. The low water vapor diffusion coefficient of the urea-formaldehyde film used between the surface and core layers of the strip plays a key role in the deformation process. After 42 days of conditioning, the model results overestimated the experimental results by 12% but were within one standard deviation of the experimental results. The model presented in this study appears to be a useful tool for product design purposes

Wood I-Joist Model Sensitivity to Oriented Strandboard Web Mechanical Properties

Research on wood I-joist design has often used laboratory testing, but simulation using the finite element method (FEM) offers advantages, including the possibility to separately study different joist components. The objective of this project was to perform a sensitivity analysis using FEM to determine which oriented strandboard (OSB) properties have higher impact on I-joist shear strain and deflection. OSB mechanical properties were changed from 50 to 200% of the reference value to determine their impact on web shear strain and I-joist deflection. The model was primarily sensitive to in-plane web shear stiffness, which changed I-joist deflection up to 23%. The model was also sensitive to the web tensile modulus of elasticity parallel and perpendicular to joist length and, to a lesser extent, to web shear stiffness. These properties changed I-joist deflection up to 2 and 1%, respectively. These findings will be used to plan future work to experimentally determine sensitive OSB web properties required to develop a finite element model of the mechanical behavior of wood I-joists

On the integration of Dantzig-Wolfe and Fenchel decompositions via directional normalizations

The strengthening of linear relaxations and bounds of mixed integer linear programs has been an active research topic for decades. Enumeration-based methods for integer programming like linear programming-based branch-and-bound exploit strong dual bounds to fathom unpromising regions of the feasible space. In this paper, we consider the strengthening of linear programs via a composite of Dantzig-Wolfe and Fenchel decompositions. We provide geometric interpretations of these two classical methods. Motivated by these geometric interpretations, we introduce a novel approach for solving Fenchel sub-problems and introduce a novel decomposition combining Dantzig-Wolfe and Fenchel decompositions in an original manner. We carry out an extensive computational campaign assessing the performance of the novel decomposition on the unsplittable flow problem. Very promising results are obtained when the new approach is compared to classical decomposition methods

The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.Comment: Published in the ESO Messenge