The Brownian motion of colloidal particles in quasi-two-dimensional (q2D) confinement displays a distinct kinetic character from that in bulk. Here we experimentally report dynamic coupling motion of Brownian particles in a relatively long process (∼100 h), which displays a quasi-equilibrium state in the q2D system. In the quasi-equilibrium state, the q2D confinement results in the coupling of particle motions, which slowly damps the motion and interaction of particles until the final equilibrium state is reached. The process of approaching the equilibrium is a random relaxation of a many-body interaction system of Brownian particles. As the relaxation proceeds for ∼100 h, the system reaches the equilibrium state in which the energy gained by the particles from the stochastic collision in the whole system is counteracted by the dissipative energy resulting from the collision. The relaxation time of this stochastic q2D system is 17.7 h. The theory is developed to explain coupling motions of Brownian particles in q2D confinement.

<p>The aim of the study presented in this dissertation was to investigate a new method of improving the ductility of masonry shear walls by means of confinement. This proprietary method, referred to as Self-Reinforced Concrete Block (SR Block) employs a previously untried technique of molding lateral confining devices into concrete block. This internal reinforcement provides lateral confinement to the enclosed volume of block and grout material. The resulting triaxial state of compressive stress under axial load allows the confined material to maintain high compressive capacity while undergoing high axial compressive strains. The results from a proof-of-concept program indicated improved plasticity due to the presence of the confining devices within the block. Despite spalling of the unconfined portions of the block at high strains, the SR Block specimens retained load carrying capacities in excess of the peak capacity of similar unreinforced/unconfined block prisms at strains beyond 2% with no visible damage to the confining devices or to the confined material. Further to this proof-of-concept study, an experimental program was undertaken involving additional prism tests as well as testing of shear walls constructed with the SR Block. This program proved the efficacy of a second confining device design in enabling prisms to retain compressive load capacity to strains over six times larger than that of standard grouted masonry. Additionally, the results of the shear wall program indicated that these desirable characteristics were effective in a wall configuration and led to significant increases in the displacement ductility of the walls when compared to similar, unconfined walls. The data presented is expected to serve as a basis for future testing and acceptance of SR Block as a method of increasing the compressive strain capacity of reinforced masonry in order to improve the ductility of masonry shear walls as a lateral force resisting system.</p> / Master of Applied Science (MASc)

This paper presents the behaviour and design of axially loaded concrete filled stainless steel circular and square hollow sections. The experimental investigation was conducted using different concrete cube strengths varied from 30 to 100 MPa. The column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with existing design methods for composite carbon steel sections ¿ Eurocode 4 and ACI. It was found that existing design guidance for carbon steel may generally be safely applied to concrete filled stainless steel tubes, though it tends to be over-conservative. A continuous strength method is proposed and it is found to provide the most accurate and consistent prediction of the axial capacity of the composite concrete filled stainless steel hollow sections due largely to the more precise assessment of the contribution of the stainless steel tube to the composite resistance.

no / This paper investigates the axial compressive behaviour of short concrete-filled elliptical steel columns using the ABAQUS/Standard solver, and a new confined concrete stress-stain model for the concrete-filled elliptical steel hollow section is proposed. The accuracy of the simulation and the concrete stress-strain model was verified experimentally. The stub columns tested consist of 150 × 75 elliptical hollow sections (EHSs) with three different wall thicknesses (4 mm, 5 mm and 6.3 mm) and concrete grades C30, C60 and C100. The compressive behaviour, which includes the ultimate load capacity, load versus end-shortening relationship and failure modes, were obtained from the numerical models and compared against the experimental results, and good agreements were obtained. This indicated that the proposed model could be used to predict the compressive characteristics of short concrete-filled elliptical steel columns.

Two-dimensional (2D) nanoscale confinement effects on poly(ε-caprolactone) (PCL) crystallization were probed through crystallization studies of PCL-b-poly(tert-butyl acrylate) (PCL-b-PtBA) copolymers, PCL with bulky tri-tert-butyl ester endgroups (PCL triesters), PCL with triacid end groups (PCL triacids), and magnetic nanoparticles stabilized by PCL triacid (PCL MNPs) at the air/water (A/W) interface. Thermodynamic analyses of surface pressure-area per monomer (Π−A)) isotherms for the Langmuir films at the A/W interface showed that PCL-b-PtBA copolymers, PCL triheads and PCL MNPs all formed homogenous monolayers below the dynamic collapse pressure of PCL, Π_C ~11 mN•m⁻¹. For compression past the collapse point, the PCL monolayers underwent a phase transition to three-dimensional (3D) crystals and the nanoscale confinements impacted the PCL crystalline morphologies. Studies of PCL-b-PtBA copolymers revealed that the morphologies of the LB-films became smaller and transitioned to dendrites with defects, stripes and finally nano-scale cylindrical features as the block length of PtBA increased. For the case of PCL triester, irregularly shaped crystals formed at the A/W interface and this was attributed to the accumulation of bulky tert-butyl ester groups around the crystal growth fronts. In contrast, regular, nearly round-shaped lamellar crystals were obtained for PCL triacids. These morphological differences between PCL triacids and PCL triesters were molar mass dependent and attributed to differences in dipole density and the submersion of carboxylic acid groups in the subphase. Nonetheless, enhanced uniformity for PCL triacid crystals was not retained once the polymers were tethered to the spherical surface of a PCL MNP. Instead, the PCL MNPs exhibited small irregularly shaped crystals. This nano-scale confinement effect on the surface morphology at the A/W interface was also molar mass dependent. For the small molar mass PCL MNPs, two layers of collapsed nanoparticles were observed. In a later chapter, studies of polyethylene glycol (PEG) surfactant adsorption onto phospholipid bilayers through quartz crystal microbalance with dissipation monitoring (QCM-D) measurements revealed a strong dependence of the adsorption and desorption kinetics on hydrophobic tail group structure. PEG surfactants with a single linear alkyl tail inserted and saturated the bilayer surface quickly and the surfactants had relatively fast desorption rates. In contrast, PEG lipids, including dioleoyl PEG lipids and cholesterol PEGs, demonstrated slower adsorption and desorption kinetics. The interactions of Pluronics and Nonoxynol surfactants with phospholipid bilayers were also studied. Pluronics showed no apparent affinity for the phospholipid bilayer, while the Nonoxynol surfactants damaged the lipid bilayers as PEG chain length decreased. / Ph. D.

This master thesis deals with the optimal initial perturbation problem for a 1D unsteady self-similar ablation flow in an inertial confinement fusion context. The physical modelling consists of the compressible Euler equations with nonlinear heat conduction. The base flow and linear 3D perturbations are computed using a multidomain Chebyshev collocation method. Longitudinal optimal initial perturbations are computed by means of a non-modal analysis method for stationary perturbation evolution operators (Schmid, 2001 &amp; 2007) after transformation of the time-dependent perturbation problem. Results of optimal gain and initial perturbation differ significantly from those produced by a non-stationary direct-adjoint method (Varillon, 2019). This discrepancy is analyzed to be a consequence of a diagonalization failure of the discrete perturbation evolution operator.

Proton exchange membrane fuel cells typically consist of stacks of membrane electrode assemblies sandwiched between bipolar plates, effectively combining the individual cells in series to achieve the desired voltage levels. Elastomeric gaskets are commonly used between each cell to insure that the reactant gases are isolated; any failure of a fuel cell gasket can cause the reactants to mix, which may lead to failure of the fuel cell. An investigation of the durability of these fuel cell seals was performed by using accelerated characterization methods. A hydrocarbon sealant was tested in five different environments to simulate fuel cell conditions. Viscoelastic properties of these seals were analyzed using momentary and relaxation compressive stress tests. Material properties such as secant modulus at 100% strain, tensile strength, and strain at failure were determined using dog-bone samples aged at several different imposed strains and aging times in environments of interest. Tearing energy was evaluated using trouser test samples tested under different rates and temperatures after various environmental aging conditions. Additionally, tearing tests were conducted on samples tested in liquid environment. A viscoelastic and mechanical property characterization of these elastomeric seals under accelerated aging conditions could help understand the behavior and predict durability in the presence of mechanical and environmental loading. Additionally, the effects of confinement have been evaluated for a bonded joint with varying thickness along the bonded direction. The Dreaming project is a glass art project in Fredrick, MD which incorporates such a varying thickness joint where thermal expansion of the adhesive has caused the glass adherend to break and debonding of the sealant. To examine this joint design, finite element analysis has been used to determine the effects of thermal expansion on such a complex geometry. Nine different test geometries have been evaluated to determine the effect of confinement coupled with thermal expansion on joint design with an elastomeric adhesive. Once evaluated, design changes were performed to try to reduce the loading while maintaining the general joint design. Results of this analysis can be used to determine the effects of confinement on a complex elastomeric joint. / Master of Science

Experimental results and simulations of imploding fusion concepts have identified the Rayleigh-Taylor (RT) instability as one of the largest inhibitors to achieving fusion. Understanding the origin and development of the RT instability will allow for the development of mitigating measures to dampen the instability growth, thus improving the chance that fusion concepts such as inertial confinement fusion (ICF) are successful. A study of 1D and 2D simulations are presented for investigating RT instability growth in deceleration stage of imploding geometries. Two cases of laser-driven implosion geometry, Cartesian and cylindrical, are used to study late stage deceleration-phase RT instability development on the interior surface of imploding targets. FLASH's hydrodynamic (HD) and magnetohydrodynamic (MHD) modeling capabilities are used for different laser and target parameters in order to study the RT instability and the impact of externally applied magnetic fields on their evolution. Several simulation regimes have been identified that provide novel insight into the impact that a seeded magnetic field can have on RT instability growth and the conditions under which magnetic field stabilization of the RT instability is observable. Finally, future work and recommendations are made. / Master of Science / The direction for the future of renewable energy is uncertain at this time; however, it is known that the future of human energy consumption must be green in order to be sustainable. Fusion energy presents an opportunity for an unlimited clean renewable energy source that has yet to be realized. Fusion is achieved only by overcoming the earthly limitations presented by trying to replicate conditions at the interior of stellar structures. The pressures, temperature, and densities seen in the interior of stars are not easily reproduced, and thus human technology must be developed to reach these difficult stellar conditions in order to harvest fusion energy. There are two main branches of developmental technology geared towards achieving the difficult conditions controlled nuclear fusion presents, magnetic confinement fusion (MCF) and inertial confinement fusion (ICF)[17]. Yet in both approaches barriers exist which have thwarted the efforts toward reaching fusion ignition which must be addressed through scientific discovery. Successfully reaching ignition is only the first step in the ultimate pursuit of a self sustaining fusion reactor. This work will focus on the experimental ICF configuration, and on one such inhibitor toward achieving ignition, the Rayleigh-Taylor (RT) instability. The RT instability develops on the surfaces of the fusion fuel capsules, targets, and causes nonuniform compression of the target. This nonuniform compression of the target leads to lower pressures and densities through the material mixing of fusion fuel and the capsule shell, which ultimately leads to challenges with reaching fusion ignition. The work presented here was performed utilizing the University of Chicago's FLASH code, which is a state-of-the-art open source radiation magneto-hydrodynamic (MHD) code used for plasma and astrophysics computational modeling [11]. Simulations of the RT instability are performed using FLASH in planar and cylindrical geometries to explore fundamental Rayleigh-Taylor instability evolution for these two different geometries. These geometries provide easier access for experimental diagnostics to probe RT dynamics. Additionally, the impact of externally applied magnetic fields are explored in an effort to examine if and how the detrimental instability can be controlled.

The shear behavior of a specimen made of reinforced concrete is complex. The resisting mechanisms are affected by different factors such as section form, slimness of the specimen, longitudinal and transversal reinforcement arrangement, adhesion between concrete and steel, among others. Addition of steel fibers to the concrete improves the ductility as well as the tensile behavior; providing good control during the cracking process. Fibers also enhance the shear behavior of structural elements, increasing ultimate resistance and ductility. Push-off tests had been used to study the mechanisms of concrete shear transfer. Shear strength of the specimen depends on the contribution of both concrete and reinforcement. Aggregate interlock has a significant contribution to the concrete shear capacity. In the last decades new kinds of concrete have been developed for industrial use, such as high strength concrete (HSC), self-compacting concrete (SCC) or fiber reinforced concrete (FRC), among others. In these new materials aggregate interlock phenomenon may be different when compared to conventional concrete (CC). There is a lack of information in literature about the mechanisms of shear transfer in fiber reinforced concrete elements. / Echegaray Oviedo, JA. (2014). Upgrading the push-off test to analyze the contribution of steel fiber on shear transfer mechanisms [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/43723

Thèse ou mémoire avec insertion d'articles / Les futurs parents et les parents de jeunes enfants ont été particulièrement touchés par les restrictions gouvernementales liées à la COVID-19 comme l'annulation des cours prénataux en présentiel, les confinements et la fermeture des services de garde. Le stress périnatal et parental peut entraîner des conséquences délétères sur la santé des parents et le développement des enfants. Il est donc important de comprendre dans quelle mesure la pandémie a pu affecter la santé mentale de ces parents. Le but de ce mémoire était d'évaluer les effets de la crise pandémique sur la santé mentale de ces parents au Québec. Pour ce faire, nous avons regroupé deux initiatives, réalisées pendant la pandémie, portant sur de futurs parents d'un premier enfant (PASS-COVID) et de parents d'au moins un jeune enfant (MAVIPAN). Les objectifs étaient (i) de déterminer les effets du premier confinement de la crise sur l'évolution d'indicateurs de santé mentale (détresse, anxiété et dépression) auprès de futurs et nouveaux parents nullipares (cohorte PASS-COVID) et (ii) d'estimer la progression de l'état de santé mentale (dépression, anxiété, stress et bien-être) de parents de jeunes enfants durant les 18 premiers mois de la crise (cohorte MAVIPAN).Un total de 862 participants (862 femmes, âge moyen de 29 ans) a été inclus pour les analyses PASS-COVID et 113 participants (102 femmes, âge moyen de 36 ans) pour les analyses MAVIPAN. Des modèles linéaires (mixtes et à mesures répétées) avec des ajustements pour variables confondantes ont été réalisés. Nous avons trouvé des résultats statistiquement significatifs pour la dépression et l'anxiété chez les futurs parents et pour la dépression et le bien-être chez les parents de jeunes enfants. Cependant, les différences étant faibles, cela suggère que les résultats ne sont pas cliniquement significatifs. Ainsi, nous n'avons pas détecté d'effets de la pandémie sur la santé mentale parentale / Future parents and parents of young children have been particularly affected by the COVID-19 pandemic's restrictive measures, such as cancellation of in-person group prenatal education sessions, lockdowns, and closing of schools and daycares. Perinatal and parental stress can have harmful consequences for parents' mental health and children's development; it is therefore important to understand to what extent the pandemic may have affected the mental health of future parents and parents of young children. The aim of this thesis was to evaluate the impact of the COVID-19 pandemic on the mental health of future parents and parents of young children in the Province of Quebec. To do so, we brought together two separate initiatives, carried out during the pandemic, involving future parents of a first child (PASS-COVID) and parents of at least one young child (MAVIPAN). Specifically, our objectives were (i) to determine the impact of the first COVID-19 lockdown on the evolution of perinatal mental health (distress, anxiety and depression) (PASSCOVID cohort) and (ii) to estimate the evolution of mental health (depression, anxiety, stress and mental wellbeing) of parents of young children during the first 18 months of the COVID-19 pandemic (MAVIPAN cohort). A total of 862 participants (862 women, mean age of 29 years old) have been included in the PASS-COVID analysis, and 113 participants (102 women, mean age of 36 years old) for the MAVIPAN analysis. Linear models (mixed and repeated measures) adjusting for potential cofounders were performed. We found statistically significant results for depression and anxiety in future parents, and for depression and mental well-being in parents of young children. However, the differences in scores being very small, this suggests that the results are not clinically significant. Thus, we did not find any impact of the pandemic on parental mental health for these two populations.