The structure of direct-current microdischarges is investigated using a detailed two-dimensional multi-species continuum model. Microdischarges are directcurrent discharges that operate at a relatively high pressure of about 100 Torr and geometric dimensions in the 10-100 micrometer range. Our motivation for the study of microdischarges comes from a potential application of these devices in microthrusters for small satellite propulsion. The Micro Plasma Thruster (MPT) concept consists of a direct-current microdischarge in a geometry comprising a constant area flow section followed by a diverging exit nozzle. A detailed description of the plasma dynamics inside the MPT including power deposition, ionization, coupling of the plasma phenomena with high-speed flow, and propulsion system performance is reported in this study. A two-dimensional model is developed as part of this study. The model consists of a plasma module coupled to a flow module and is solved on a hybrid unstructured mesh framework. The plasma module provides a self-consistent, multispecies, multi-temperature description of the microdischarge phenomena while the flow module provides a description of the low Reynolds number compressible flow through the system. The plasma module solves conservation equations for plasma species continuity and electron energy, and Poisson’s equation for the self-consistent electric field. The flow module solves mass, bulk gas momentum and energy equations. The coupling of energy from the electrostatic field to the plasma species is modeled by the Joule heating term which appears in the electron and heavy species energy equations. Discretization of the Joule heating term on unstructured meshes requires special attention. We propose a new robust method for the numerical discretization of the Joule heating term on such meshes using a cell-centered, finite volume approach. A prototypical microhollow cathode discharge (MHCD) is studied to guide and validate the modeling effort for theMPT. Computational results for the impedance characteristics as well as electrodynamic and chemical features of the discharge are reported and compared to experimental results. At low current (< 0.1 mA), the plasma activity is localized inside the cylindrical hollow region of the discharge operating in the so-called “abnormal regime”. For larger currents, the discharge expands over the outer flat surface of the cathode and operates in the “normal regime”. Transient relaxation oscillations are predicted in the plasma properties for intermediate discharge currents ranging from 0.1 mA to 0.3 mA; a phenomenon that is reported in experiments. The MPT, in its present configuration, is found to operate as an electrothermal, rather than as an electrostatic thruster. A significant increase in specific impulse, compared to the cold gas micronozzle, is obtained from the power deposition into the expanding gas. For a discharge voltage of 750 V, a power input of 650 mW, and an argon mass flow rate of 5 sccm, the specific impulse of the device is increased by a factor of 1.5 to a value of 74 s. The microdischarge remains mostly confined inside the micronozzle and operates in an abnormal regime. Gas heating, primarily due to ion Joule heating, is found to have a strong influence on the overall discharge behavior. The study provides crucial understanding to aid in the design of direct-current microdischarge based thrusters. / text

In this thesis, we have investigated some interesting dynamical problems in microstructural continuum using Eringen's polar theory. These problems are pertaining to surface waves in a microstretch plate, Stoneley waves at an interface between two different microstretch half-spaces, surface waves in a micropolar cylindrical borehole filled with micropolar fluid, reflection and transmission of elastic waves at a liquid/solid half-space and reflection of elastic waves from a micropolar mixture porous half-space.

This thesis is a blend of neutron transport theory and numerical analysis. We start with the study of the problem of the Mika/Case eigenexpansion used in the solution process of the homogeneous one-speed Boltzmann neutron transport equation with anisotropic scattering for plane symmetry. The anisotropic scattering is expressed as a finite Legendre series in which the coefficients are the ``scattering coefficients'. This eigenexpansion consists of a discrete spectrum of eigenvalues with its corresponding eigenfunctions and the continuous spectrum [-1,+1] with its corresponding eigendistributions. In the general case where the anisotropic scattering can be of any (finite) order, multiple discrete eigenvalues exist and these have to be located to have the complete spectrum. We have devised a stable and robust method that locates all these discrete eigenvalues. The method is a two-step process: first the number of discrete eigenvalues is calculated and this is followed by the calculation of the discrete eigenvalues themselves, now being able to count them down and make sure none are forgotten. During our numerical experiments, we came across what we called near-singular eigenvalues: discrete eigenvalues that are located extremely close to the continuum and hence lead to near-singular behaviour in the eigenfunction. Our solution method has been adapted and allows for the automatic detection of such a near-singular eigenvalue. For the elements of the continuous spectrum [-1,+1], there is no non-zero function satisfying the associated eigenequation but there is a non-zero distribution that does satisfy it. It is not feasible to compute a distribution as such but one can evaluate integrals in which this distribution appears. The continuum part of the eigenexpansion can hence only be characterised by its (angular) moments. Accurate and fast numerical quadrature is needed to evaluate these integrals. Several quadrature methods have been evaluated on a representative test function. The eigenexpansion was proved to be orthogonal and complete and hence can be used to represent the infinite medium Green's function. The latter is the building block of the Boundary Sources Method, an integral solution method for the neutron transport equation. Using angular and angular/spatial moments of the Green's function, it is possible to solve with high accuracy slab problems. We have written a one-dimensional slab code implementing this Boundary Sources Method allowing for media with arbitrary order anisotropic scattering. Our results are very good and the code can be considered as a benchmark code for others. As a final application, we have used our code to study the discrete spectrum of a well-known scattering kernel in radiative transfer, the Henyey-Greenstein kernel. This kernel has one free parameter which is used to fit the kernel to experimental data. Since the kernel is a continuous function, a finite Legendre approximation needs to be adopted. Depending on the free parameter, the approximation order and the number of secondaries per collision, the number of discrete eigenvalues ranges from two to thirty and even more. Bounds for the minimum approximation order are derived for different requirements on the approximation: non-negativity, an absolute and relative error tolerance.

No description available.

In this thesis I used a sample of radio galaxies with 1.4GHz radio luminosity, S1.4 > 10mJy, with the aim of finding high-redshift radio galaxies in the Lockman Hole, ELAIS-N1, ELAISN2, XMM-LSS and CDFS using near-infrared data from the Spitzer Space Telescope, and in the VIMOS4/SSA22 field using near-infrared data from the UKIRT Infrared Deep Sky Survey Deep Extragalactic Survey (UKIDSS-DXS). I used these near-infrared data to filter out low redshift (z < 2) radio galaxies by only including sources with either a very faint identification or non-detection in the K−band or at 3.6μm. I then applied a radio selection criteria based on the compactness of the radio structure in the FIRST survey, to ensure that it was possible to correctly associate a near-infrared identification if detected. Using these filtering critera I reduced the sample from 498 to 220, and I obtained spectroscopic observations for 46 of these. I successfully measured redshifts for 22 of these. Four of these sources were found to have redshifts at z > 3, thus proving the efficiency of the selection. Using these spectroscopically identified sources I investigated the correlation between radio luminosity and Lyα emission line luminosity and showed that these radio sources lie on the same correlations as their more radio-luminous counterparts, suggesting that accretion rate on to the central supermassive black hole determines the power of the AGN, both in terms of photoionizing radiation and radio power. I also investigated the near infrared properties of the host galaxy for these sources. Studying the 3.6μm magnitude versus redshift, I found that many of the radio galaxies in our sample lie on a similar relation as other powerful radio sources studied by different methods, although in my selection there is a bias to the fainter end of the distribution, likely due to the selection bias that I impose. The selection criteria has led us to report on the discovery of the highest redshift radio galaxy ever found, however the robustness of the redshift should be confirmed by follow up spectroscopy as the source has KAB magnitude of ∼ 20.7 which is in an area of the K − z diagram which makes it consistent with both z∼ 1 (in the case of [Oii]) and z ∼ 5 (in the case of Lyα). Finally I determined the number density of high-redshift sources in my sample at different epochs and show that the SKADS simulation is consistent with our observed radio galaxy sample. Using this knowledge I go on to predict the number of sources for current and future near-infrared surveys, where the future appears very bright for this kind of work.

O contínuo mediático atmosférico é um ponto de partida, uma abertura na busca por compreensão de um fenômeno do mundo contemporâneo que se inicia com as multidões, os públicos, as massas e as maiorias. O contínuo mediático atmosférico é esse novo campo de batalha do mundo atual onde querem ocupar, e nele permanecer, o Estado, o mercado, as maiorias. O contínuo mediático atmosférico é constituído por quatro elementos: 1. O campo das ideias, valores e crenças; 2. A esfera pública; 3. As massas e 4. Os grandes meios de comunicação, com a finalidade de: 4.1 Atuar no imaginário, produzir fascinação e glamour e 4.2 Cooptar as massas para as causas políticas e outros ativismos. A esse novo momento, a esse novo campo de batalha constituído, onde se procura a tudo conectar, tudo energizar, tudo transformar em um medium de comunicação, damos o nome de contínuo mediático atmosférico. Essa nova situação provocada pelo contínuo mediático atmosférico nos faz pensar e problematizar o presente. / The atmospheric mediatic continuum is a starting point, a breaking through the search for understanding of a phenomenon of the contemporary world that begins with the crowds, the public, the masses and the majorities. The atmospheric mediatic continuum is this new battleground of the present world which wants to occupy, and remain in it, the State, the market, the majorities. The atmospheric mediatic continuum consists of four elements: 1. The field of ideas, values and beliefs; 2. The public sphere; 3. The masses; and 4. The major media. This last one, with the purpose of: 4.1 Acting on the imaginary, producing fascination and glamor; and 4.2 Co-opting the masses for political causes and other activism. To this new moment, to this new battleground constituted, where everything is sought to connect, to energize, to transform into a medium of communication, we call the atmospheric mediatic continuum. This new situation provoked by the atmospheric mediatic continuum leads us to think and problematize the present.

In this thesis, we studied three small subjects in the realm of continuum mechanics: imbibition in fluid mechanics, beam and rod buckling in solid mechanics and shell buckling at the solid-liquid interface. In chapter 2, we examined the radial imbibition into a homogenous semi-infinite porous media from a point source with infinite liquid supply. We proved that in the absence of gravity (or in the regime while gravity is negligible compared to surface tension), the shape of the wet area is a hemisphere, and the radius of the wet area evolves as a function with respect to time. This new law with respect to time has been verified by Finite Element Method simulation in software COMSOL and a series of experiments using packed glass microsphere as the porous media. We also found that even though the imbibition slows down, the flow rate through the point source remains constant. This new result for three dimensional radial imbibition complements the classic Lucas-Washburn law in one dimension and two dimensional radial imbibition in one plane. In chapter 3, we studied the elastic beam/rod buckling under lateral constraints in two dimension as well as in three dimension. For the two dimensional case with unique boundary conditions at both ends, the buckled beam can be divided into segments with alternate curved section and straight section. The curved section can be solved by the Euler beam equation. The straight sections, however, are key to the transition between different buckling modes, and the redistributed length of straight sections sets the upper limit and lower limit for the transition. We compared our theoretical model of varying straight sections with Finite Element Method simulation in software ABAQUS, and good agreements are found. We then attempted to employ this model as an explanation with qualitative feasibility for the crawling snake in horizontal plane between parallel walls, which shows unique shape like square wave. For the three dimensional buckling beam/rod confined in cylindrical constraints, three stages are found for the buckling and post buckling processes: initial two dimensional shape, three dimensional spiral/helix shape and final foldup/alpha shape. We characterized the shape at each stage, and then we calculated the transition points between the three stages using geometrical arguments for energy arguments. The theoretical analysis for three dimensional beam/rod are also complemented with Finite Element Method simulations from ABAQUS. In chapter 4, we investigated the buckling shape of solid shell filled with liquid core in two dimension and three dimension. A material model for liquid is first described that can be readily incorporated in the framework of solid mechanics. We then applied this material model in two dimensional and three dimensional Finite Element Method simulation using software ABAQUS. For the two dimensional liquid core solid shell model, a linear analysis is first performed to identify that ellipse corresponds to lowest order of buckling with smallest elastic energy. Finite Element Method simulation is then performed to determine the nonlinear post-buckling process. We discovered that two dimensional liquid core solid shell structures converge to peanut shape eventually while the evolution process is determined by two dimensionless parameters Kτ/μ and ρR^2/μτ. Amorphous shape exists before final peanut shape for certain models with specific Kτ/μ and ρR^2/μτ. The two dimensional peanut shape is also verified with Lattice Boltzmann simulations. For the three dimensional liquid core solid shell model, the post buckling shape is studied from Finite Element Method simulations in ABAQUS. Depending on the strain loading rate, the deformations show distinctive patterns. Large loading rate induces herringbone pattern on the surface of solid shell which resembles solid core solid shell structure, while small loading rate induces major concave pattern which resemble empty solid shell structure. For both two dimensional and three dimensional liquid core system, small scale ordered deformation pattern can be generated by increasing the shear stress in liquid core. In the final chapter, we summarized the discoveries in the dissertation with highlights on the role that geometry plays in all of the three subjects. Recommendations for future studies are also discussed.

As alternatives to partial differential equations (PDEs), nonlocal continuum models given in integral forms avoid the explicit use of conventional spatial derivatives and allow solutions to exhibit desired singular behavior. As an application, peridynamic models are reformulations of classical continuum mechanics that allow a natural treatment of discontinuities by replacing spatial derivatives of stress tensor with integrals of force density functions. The thesis is concerned about the mathematical perspective of nonlocal modeling and local-nonlocal coupling for fracture mechanics both theoretically and numerically. To this end, the thesis studies nonlocal diffusion models associated with ``Neumann-type'' constraints (or ``traction conditions'' in mechanics), a nonlinear peridynamic model for fracture mechanics with bond-breaking rules, and a multi-scale model with local-nonlocal coupling. In the computational studies, it is of practical interest to develop robust numerical schemes not only for the numerical solution of nonlocal models, but also for the evaluation of suitably defined derivatives of solutions. This leads to a posteriori nonlocal stress analysis for structure mechanical models.

La technologie de fabrication additive a été identifiée comme l'une des innovations numériques majeures qui a révolutionné non seulement le domaine de l'industrie, mais aussi celui de la construction. D'un point de vue de recherche, la fabrication additive reste un sujet d’actualité. C’est un procédé automatisé de dépôt de matériaux couche par couche afin d'imprimer des maisons ou des structures de petites dimensions pour un montage sur site. Dans la fabrication additive, l'étape de dépôt des matériaux est généralement suivie d'une étape de contrôle de la qualité d'impression. Cependant, le contrôle de qualité des objets imprimés ayant des surfaces funiculaires est parfois complexe à réaliser avec des robots rigides, ne pouvant atteindre des zones mortes. Dans cette thèse, un manipulateur souple et hyper-redondant a été modélisé et commandé cinématiquement, placé comme un effecteur d'un manipulateur rigide et mobile, afin d'effectuer une inspection des structures imprimées par des techniques de la fabrication additive. En effet, les manipulateurs souples peuvent fléchir et du coup suivre la forme géométrique de surfaces funiculaires. Ainsi, une approche hybride a été proposée pour modéliser la cinématique du robot souple et hyper-redondant, combinant une approche analytique pour la génération des équations cinématiques et une méthode qualitative à base des réseaux de neurones pour la résolution de ces dernières. Les performances de l'approche proposée sont validées à travers des expériences réalisées sur le robot "compact bionic handling arm" (cbha). / Additive manufacturing technology has been identified as one of the major digital innovations that has revolutionized not only industry, but also building. From a research point of view, additive manufacturing remains a very relevant topic. It is an automated process for depositing materials layer by layer to print houses or small structures for on-site assembly. In additive manufacturing processes, the deposition of materials is generally followed by a printing quality control step. However, the geometry of structures printed with funicular surfaces is sometimes complex, as robots with rigid structures cannot reach certain areas of the structure to be inspected. In this thesis, a flexible and highly redundant manipulator equipped with a camera is attached to the end-effector of a mobile manipulator robot for the quality inspection process of the printed structures. Indeed, soft manipulators can bend along their surounded 3D objects; and this inherent flexibility makes them suitable for navigation in crowded environments. As the number of controlled actuators is greater than the dimension of the workspace, this thesis can be summarized as a trajectory tracking of hyper-redundant robots. In this thesis, a hybrid approach that combines the advantages of model-based approaches and learning-based approaches is developed to model and solve the kinematics of soft and hyper-redundant manipulators. The principle is to develop mathematical models with reasonable assumptions, and to improve their accuracy through learning processes. The performance of the proposed approach is validated by performing a series of simulations and experiments applied to the compact bionic handling arm (cbha) robot.

Modeling fracture in geomaterials is essential to the understanding of many physical phenomenon which may posses natural hazards e.g. landslides, faults and iceberg calving or man-made processes e.g. hydraulic fracture and excavations. Continuum Damage Mechanics (CDM) models the crack as a solid region with a degraded stiffness. This continuum definition of cracks in CDM allows more feasible coupling with other forms of material non-linearity and eliminates the need to track complicated crack geometry. Using CDM to analyze fracture for the modeling of fracture in geomaterials encounters several challenges e.g.: 1) the need to model the multiple physical processes occurring in geomaterials, typically: coupled fluid flow and solid deformation, 2) the need to consider non-local damage and transport in order to capture the underlying long range interactions and achieve mesh-independent finite element solutions and 3) the elevated computational cost associated with non-linear mixed finite element formulations. The research presented in this thesis aims at improving the CDM formulations for modeling fracture geomaterials. This research can be divided into three main parts. The first is the introduction of a novel non-local damage transport formulation for modeling fracture in poroelastic media. The mathematical basis of the formulation are derived from thermodynamic equilibrium that considers non-local processes and homogenization principles. The non-local damage transport model leads to two additional regularization equations, one for non-local damage and the other for non-local transport which is reduced to non-local permeability. We consider two options for the implementation of the derived non-local transport damage model. The first option is the four-field formulation which extends the (u/P) formulation widely used in poroelasticity to include the non-local damage and transport phenomena. The second option is the three-field formulation, which is based on the coupling of the regularization equations under the assumptions of similar damage and permeability length scales and similar driving local stress/strain for the evolution of the damage and permeability. The three-field formulation is computationally cheaper but it degrades the physical modeling capabilities of the model. For each of these formulations, a non-linear mixed-finite element solution is developed and the Jacobian matrix is derived analytically. The developed formulations are used in the analysis of hydraulic fracture and consolidation examples. In the second part, a novel approach for CDM modeling of hydraulic fracture of glaciers is pretended. The presence of water-filled crevasses is known to increase the penetration depth of crevasses and this has been hypothesized to play an important role controlling iceberg calving rate. Here, we develop a continuum damage-based poro-mechanics formulation that enables the simulation of water-filled basal and/or surface crevasse propagation. The formulation incorporates a scalar isotropic damage variable into a Maxwell-type viscoelastic constitutive model for glacial ice and the effect of the water pressure on fracture propagation using the concept of effective solid stress. We illustrate the model by simulating quasi-static hydro-fracture in idealized rectangular slabs of ice in contact with the ocean. Our results indicate that water-filled basal crevasses only propagate when the water pressure is sufficiently large and that the interaction between simultaneously propagating water-filled surface and basal crevasses can have a mutually positive influence leading to deeper crevasse propagation which can critically affect glacial stability. In the third part, we propose a coupled Boundary Element Method (BEM) and Finite Element Method (FEM) for modeling localized damage growth in structures. BEM offers the flexibility of modeling large domains efficiently while the nonlinear damage growth is accurately accounted by a local FEM mesh. An integral-type nonlocal continuum damage mechanics with adapting FEM mesh is used to model multiple damage zones and follow their propagation in the structure. Strong form coupling, BEM hosted, is achieved using Lagrange multipliers. Since the non-linearity is isolated in the FEM part of the system of equations, the system size is reduced using Schur complement approach, then, the solution is obtained by a monolithic Newton method that is used to solve both domains simultaneously. The method is applied to multiple fractures growth benchmark problems and shows good agreement with the literature.