Cet article examine la relation entre le secteur dans lequel les individus travaillent et le niveau de leur profession, d’une part, et, d’autre part, le rapport qu’ils entretiennent avec les médias, y compris Internet, selon qu’ils en disposent ou non dans leur foyer et en fonction des usages qu’ils en font. Il se penche aussi sur l’identité sociale, en mettant diverses manifestations en relation avec la manière dont les individus vivent leur rapport aux médias. Il remet en question l’hypothèse d’une forte association entre le niveau professionnel et le rapport aux médias. Il met en évidence des phénomènes complexes d’homogénéisation et de différenciation sociales. Les données proviennent d’un échantillon de travailleurs du nord-ouest de l’Ontario qui ont répondu à un questionnaire centré sur le rapport aux médias.

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A multi-domain homogenization method is proposed and developed in this thesis based on a two-scale technique. The method is capable of analyzing composite structures with several periodic distributions by partitioning the entire domain of the composite into substructures making use of the classical homogenization theory following a first-order standard continuum mechanics formulation. The need to develop the multi-domain homogenization method arose because current homogenization methods are based on the assumption that the entire domain of the composite is represented by one periodic or quasi-periodic distribution. However, in some cases the structure or composite may be formed by more than one type of periodic domain distribution, making the existing homogenization techniques not suitable to analyze this type of cases in which more than one recurrent configuration appears. The theoretical principles used in the multi-domain homogenization method were applied to assemble a computational tool based on two nested boundary value problems represented by a finite element code in two scales: a) one global scale, which treats the composite as an homogeneous material and deals with the boundary conditions, the loads applied and the different periodic (or quasi-periodic) subdomains that may exist in the composite; and b) one local scale, which obtains the homogenized response of the representative volume element or unit cell, that deals with the geometry distribution and with the material properties of the constituents. The method is based on the local periodicity hypothesis arising from the periodicity of the internal structure of the composite. The numerical implementation of the restrictions on the displacements and forces corresponding to the degrees of freedom of the domain's boundary derived from the periodicity was performed by means of the Lagrange multipliers method. The formulation included a method to compute the homogenized non-linear tangent constitutive tensor once the threshold of nonlinearity of any of the unit cells has been surpassed. The procedure is based in performing a numerical derivation applying a perturbation technique. The tangent constitutive tensor is computed for each load increment and for each iteration of the analysis once the structure has entered in the non-linear range. The perturbation method was applied at the global and local scales in order to analyze the performance of the method at both scales. A simple average method of the constitutive tensors of the elements of the cell was also explored for comparison purposes. A parallelization process was implemented on the multi-domain homogenization method in order to speed-up the computational process due to the huge computational cost that the nested incremental-iterative solution embraces. The effect of softening in two-scale homogenization was investigated following a smeared cracked approach. Mesh objectivity was discussed first within the classical one-scale FE formulation and then the concepts exposed were extrapolated into the two-scale homogenization framework. The importance of the element characteristic length in a multi-scale analysis was highlighted in the computation of the specific dissipated energy when strain-softening occurs. Various examples were presented to evaluate and explore the capabilities of the computational approach developed in this research. Several aspects were studied, such as analyzing different composite arrangements that include different types of materials, composites that present softening after the yield point is reached (e.g. damage and plasticity) and composites with zones that present high strain gradients. The examples were carried out in composites with one and with several periodic domains using different unit cell configurations. The examples are compared to benchmark solutions obtained with the classical one-scale FE method. / En esta tesis se propone y desarrolla un método de homogeneización multi-dominio basado en una técnica en dos escalas. El método es capaz de analizar estructuras de materiales compuestos con varias distribuciones periódicas dentro de un mismo continuo mediante la partición de todo el dominio del material compuesto en subestructuras utilizando la teoría clásica de homogeneización a través de una formulación estándar de mecánica de medios continuos de primer orden. La necesidad de desarrollar este método multi-dominio surgió porque los métodos actuales de homogeneización se basan en el supuesto de que todo el dominio del material está representado por solo una distribución periódica o cuasi-periódica. Sin embargo, en algunos casos, la estructura puede estar formada por más de un tipo de distribución de dominio periódico. Los principios teóricos desarrollados en el método de homogeneización multi-dominio se aplicaron para ensamblar una herramienta computacional basada en dos problemas de valores de contorno anidados, los cuales son representados por un código de elementos finitos (FE) en dos escalas: a) una escala global, que trata el material compuesto como un material homogéneo. Esta escala se ocupa de las condiciones de contorno, las cargas aplicadas y los diferentes subdominios periódicos (o cuasi-periódicos) que puedan existir en el material compuesto; y b) una escala local, que obtiene la respuesta homogenizada de un volumen representativo o celda unitaria. Esta escala se ocupa de la geometría, y de la distribución espacial de los constituyentes del compuesto así como de sus propiedades constitutivas. El método se basa en la hipótesis de periodicidad local derivada de la periodicidad de la estructura interna del material. La implementación numérica de las restricciones de los desplazamientos y las fuerzas derivadas de la periodicidad se realizaron por medio del método de multiplicadores de Lagrange. La formulación incluye un método para calcular el tensor constitutivo tangente no-lineal homogeneizado una vez que el umbral de la no-linealidad de cualquiera de las celdas unitarias ha sido superado. El procedimiento se basa en llevar a cabo una derivación numérica aplicando una técnica de perturbación. El tensor constitutivo tangente se calcula para cada incremento de carga y para cada iteración del análisis una vez que la estructura ha entrado en el rango no-lineal. El método de perturbación se aplicó tanto en la escala global como en la local con el fin de analizar la efectividad del método en ambas escalas. Se lleva a cabo un proceso de paralelización en el método con el fin de acelerar el proceso de cómputo debido al enorme coste computacional que requiere la solución iterativa incremental anidada. Se investiga el efecto de ablandamiento por deformación en el material usando el método de homogeneización en dos escalas a través de un enfoque de fractura discreta. Se estudió la objetividad en el mallado dentro de la formulación clásica de FE en una escala y luego los conceptos expuestos se extrapolaron en el marco de la homogeneización de dos escalas. Se enfatiza la importancia de la longitud característica del elemento en un análisis multi-escala en el cálculo de la energía específica disipada cuando se produce el efecto de ablandamiento. Se presentan varios ejemplos para evaluar la propuesta computacional desarrollada en esta investigación. Se estudiaron diferentes configuraciones de compuestos que incluyen diferentes tipos de materiales, así como compuestos que presentan ablandamiento después de que el punto de fluencia del material se alcanza (usando daño y plasticidad) y compuestos con zonas que presentan altos gradientes de deformación. Los ejemplos se llevaron a cabo en materiales compuestos con uno y con varios dominios periódicos utilizando diferentes configuraciones de células unitarias. Los ejemplos se comparan con soluciones de referencia obtenidas con el método clásico de elementos finitos en una escala.

A novel multiscale approach is introduced for determining the thermal conductivity of polymer nanocomposites (PNCs) reinforced with single-walled carbon nanotubes (SWCNTs), which accounts for their intrinsic uncertainties associated with dispersion, distribution, and morphology. Heterogeneities in PNCs on nanoscale are identified and quantified in a statistical sense, for the calculation of effective local properties. A finite element method computes the overall macroscale properties of PNCs in conjunction with the Monte Carlo simulations. This Monte Carlo Finite Element Approach (MCFEA) allows for acquiring the randomness in spatial distribution of the nanotubes throughout the composite. Furthermore, the proposed MCFEA utilizes the nanotube content, orientation, aspect ratio and diameter inferred from their statistical information. Local SWCNT volume or weight fractions are assigned to the finite elements (FEs), based on various spatial probability distributions. Multi-phase homogenization techniques are applied to each FE to calculate the local thermal conductivities. Then, the Monte Carlo simulations provide the statistics on the overall thermal conductivity of the PNCs. Subsequently, dispersion characteristics of the nanotubes are assessed by incorporating nanotube agglomerates. In this regard, a multi-phase homogenization method is developed for enhanced accuracy and effectiveness. The effect of the nanotube orientation in a polymer is studied for the cases where the SWCNTs are randomly oriented as well as longitudinally aligned. The influence of voids existing in the polymer is investigated on the thermal conductivity, to capture the uncertainties in PNCs more extensively. Further, a unique damage evaluation model is proposed to assess the degradation of PNCs when subjected to thermal cycling. The growth in void content is represented with a Weibull-based equation, to quantify the deterioration of the thermal and mechanical properties of PNCs under thermal fatigue. In addition, the MCFEA considers the interface resistance of the carbon nanotubes as one of the key factors in the thermal conductivity of nanocomposites. Parametric studies are performed comprehensively. The numerical results obtained are compared with available analytical techniques at hand and with the data from pertinent independent experimental studies. It is found that the proposed MCFEA is capable of estimating the thermal conductivity with good accuracy.

This paper investigates how Latin America and its cultures are represented in textbooks on Spanish as a foreign language. The study aims at investigating how much attention and of what type is dedicated to Latin America in the investigated material, whether the textbooks contribute to giving a varied and nuanced image of the Spanish-American cultures and how this relates to the educational goal of promoting an intercultural competence.A qualitative method of analysis has been applied in order to carry out the analysis of three textbooks for intermediate levels of language studies: Caminando 3, Alegria and De acuerdo.The results of the investigation show that the investigated textbooks mostly present a simplified, ethnocentric, homogenized and sometimes postcolonial image of the Spanish-American cultures. Texts where the culture constitutes the context and not the subject can promote a process of identification and consequently an intercultural competence.The study’s main conclusions show that Spanish-American cultures are underrepresented in the investigated material and that a non-native perspective dominates in the majority of the texts. This combined with the lack of variety and profundity, may have consequences for the promotion of an intercultural competence and for teachers’ work with textbooks and cultural content.

This work investigates the application of homogenization techniques to the dynamic analysis of periodic solids, with emphasis on lattice structures. The presented analysis is conducted both through a Fourier-based technique and through an alternative approach involving Taylor series expansions directly performed in the spatial domain in conjunction with a finite element formulation of the lattice unit cell. The challenge of increasing the accuracy and the range of applicability of the existing homogenization methods is addressed with various techniques. Among them, a multi-cell homogenization is introduced to extend the region of good approximation of the methods to include the short wavelength limit. The continuous partial differential equations resulting from the homogenization process are also used to estimate equivalent mechanical properties of lattices with various internal configurations. In particular, a detailed investigation is conducted on the in-plane behavior of hexagonal and re-entrant honeycombs, for which both static properties and wave propagation characteristics are retrieved by applying the proposed techniques. The analysis of wave propagation in homogenized media is furthermore investigated by means of the bridging scales method to address the problem of modelling travelling waves in homogenized media with localized discontinuities. This multi-scale approach reduces the computational cost associated with a detailed finite element analysis conducted over the entire domain and yields considerable savings in CPU time. The combined use of homogenization and bridging method is suggested as a powerful tool for fast and accurate wave simulation and its potentials for NDE applications are discussed.

The overall goal of the present research is to provide a computationally based methodology to realize the projected extraordinary properties of Carbon Nanotube (CNT)- reinforced composites and polymeric nanofibers for engineering applications. The discovery of carbon nanotubes (CNT) and its derivatives has led to considerable study both experimentally and computationally as carbon based materials are ideally suited for molecular level building blocks for nanoscale systems. Research in nanomechanics is currently focused on the utilization of CNTs as reinforcements in polymer matrices as CNTs have a very high modulus and are extremely light weight. The nanometer dimension of a CNT and its interaction with a polymer chain requires a study involving the coupling of the length scales. This length scale coupling requires analysis in the molecular and higher order levels. The atomistic interactions of the nanotube are studied using molecular dynamic simulations. The elastic properties of neat nanotube as well as doped nanotube are estimated first. The stability of the nanotube under various conditions is also dealt with in this dissertation. The changes in the elastic stiffness of a nanotube when it is embedded in a composite system are also considered. This type of a study is very unique as it gives information on the effect of surrounding materials on the core nanotube. Various configurations of nanotubes and nanocomposites are analyzed in this dissertation. Polymeric nanofibers are an important component in tissue engineering; however, these nanofibers are found to have a complex internal structure. A computational strategy is developed for the first time in this work, where a combined multiscale approach for the estimation of the elastic properties of nanofibers was carried out. This was achieved by using information from the molecular simulations, micromechanical analysis, and subsequently the continuum chain model, which was developed for rope systems. The continuum chain model is modified using properties of the constituent materials in the mesoscale. The results are found to show excellent correlation with experimental measurements. Finally, the entire atomistic to mesoscale analysis was coupled into the macroscale by mathematical homogenization techniques. Two-scale mathematical homogenization, called asymptotic expansion homogenization (AEH), was used for the estimation of the overall effective properties of the systems being analyzed. This work is unique for the formulation of spectral/hp based higher-order finite element methods with AEH. Various nanocomposite and nanofibrous structures are analyzed using this formulation. In summary, in this dissertation the mechanical characteristics of nanotube based composite systems and polymeric nanofibrous systems are analyzed by a seamless integration of processes at different scales.

Eshelby-type inclusion problems of an infinite or a finite homogeneous isotropic elastic body containing an arbitrary-shape inclusion prescribed with an eigenstrain and an eigenstrain gradient are analytically solved. The solutions are based on a simplified strain gradient elasticity theory (SSGET) that includes one material length scale parameter in addition to two classical elastic constants. For the infinite-domain inclusion problem, the Eshelby tensor is derived in a general form by using the Green’s function in the SSGET. This Eshelby tensor captures the inclusion size effect and recovers the classical Eshelby tensor when the strain gradient effect is ignored. By applying the general form, the explicit expressions of the Eshelby tensor for the special cases of a spherical inclusion, a cylindrical inclusion of infinite length and an ellipsoidal inclusion are obtained. Also, the volume average of the new Eshelby tensor over the inclusion in each case is analytically derived. It is quantitatively shown that the new Eshelby tensor and its average can explain the inclusion size effect, unlike its counterpart based on classical elasticity. To solve the finite-domain inclusion problem, an extended Betti’s reciprocal theorem and an extended Somigliana’s identity based on the SSGET are proposed and utilized. The solution for the disturbed displacement field incorporates the boundary effect and recovers that for the infinite-domain inclusion problem. The problem of a spherical inclusion embedded concentrically in a finite spherical body is analytically solved by applying the general solution, with the Eshelby tensor and its volume average obtained in closed forms. It is demonstrated through numerical results that the newly obtained Eshelby tensor can capture the inclusion size and boundary effects, unlike existing ones. Finally, a homogenization method is developed to predict the effective elastic properties of a heterogeneous material using the SSGET. An effective elastic stiffness tensor is analytically derived for the heterogeneous material by applying the Mori-Tanaka and Eshelby’s equivalent inclusion methods. This tensor depends on the inhomogeneity size, unlike what is predicted by existing homogenization methods based on classical elasticity. Numerical results for a two-phase composite reveal that the composite becomes stiffer when the inhomogeneities get smaller.

Conventional three dimensional structural analysis methods prove to be expensive for the preliminary design of wind turbine blades. However, wind turbine blades are large slender members with complex cross sections. They can be accurately modeled using beam models. The accuracy in the predictions of the structural behavior using beam models depends on the accuracy in the prediction of their effective section properties. Several techniques were proposed in the literature for predicting the effective section properties. Most of these existing techniques have limitations because of the assumptions made in their approaches. Two generalized beam theories, Generalized Timoshenko and Generalized Euler-Bernoulli, for the static analysis based on the principles of the simple 1D-theories are developed here. Homogenization based on the strain energy equivalence principle is employed to predict the effective properties for these generalized beam theories. Two efficient methods, Quasi-3D and Unit Cell, are developed which can accurately predict the 3D deformations in beams under the six fundamental deformation modes: extension, two shears, torsion and two flexures. These methods help in predicting the effective properties using the homogenization technique. Also they can recover the detailed 3D deformations from the predictions of 1D beam analysis. The developed tools can analyze two types of slender members 1) slender members with invariant geometric features along the length and 2) slender members with periodically varying geometric features along the length. Several configurations were analyzed for the effective section properties and the predictions were validated using the expensive 3D analysis, strength of materials and Variational Asymptotic Beam Section Analysis (VABS). The predictions from the new tools showed excellent agreement with full 3D analysis. The predictions from the strength of materials showed disagreement in shear and torsional properties. Explanations for the same are provided recalling the assumptions made in the strength of materials approach.

In this dissertation we develop and analyze numerical method to solve general elliptic boundary value problems with many scales. The numerical method presented is intended to capture the small scales effect on the large scale solution without resolving the small scale details, which is done through the construction of a multiscale map. The multiscale method is more effective when the coarse element size is larger than the small scale length. To guarantee a numerical conservation, a finite volume element method is used to construct the global problem. Analysis of the multiscale method is separately done for cases of linear and nonlinear coefficients. For linear coefficients, the multiscale finite volume element method is viewed as a perturbation of multiscale finite element method. The analysis uses substantially the existing finite element results and techniques. The multiscale method for nonlinear coefficients will be analyzed in the finite element sense. A class of correctors corresponding to the multiscale method will be discussed. In turn, the analysis will rely on approximation properties of this correctors. Several numerical experiments verifying the theoretical results will be given. Finally we will present several applications of the multiscale method in the flow in porous media. Problems that we will consider are multiphase immiscible flow, multicomponent miscible flow, and soil infiltration in saturated/unsaturated flow.