Thesis advisor: Udayan Mohanty / The high surface area and atomic-level tunability offered by nanoparticles has defined their promise as heterogeneous catalysts. While initial studies began with nanoparticles of a single metal assuming thermodynamic shapes, modern work has focused on using nanoparticle composition and geometry to optimize nanocatalysts for a wide variety of reactions. Further optimization of these refined nanocatalysts remains difficult, however, as the factors that determine catalytic activity are intertwined and a fundamental understanding of each remains elusive. In this work, precise synthetic methods are used to tune a number of factors, including composition, strain, metal-to-metal charge transfer, atomic order, and surface faceting, and understand their impact on catalysis. The first chapter focuses on current achievements and challenges in the synthesis of intermetallic nanocatalysts, which offer long-range order that allows for total control of surface structure. A particular focus is given to the impact of the synthetic approach on the activity of the resulting nanoparticles. In the second chapter, multilayered Pd-(Ni-Pt)x nanoparticles serve as a controlled arena for the study of metallic mixing and order formation on the nanoscale. The third chapter controls the shell thickness of Au@PdPt core-alloyed shell nanoparticles on a nanometer scale to isolate strain at the nanoparticle surface. In the fourth chapter, the synthetic approaches of chapters two and three are applied to catalysis. In totality, the work presented here represents a brick in the foundation of understanding and exploiting structure-function relationships on the nanoscale, with an eye toward the rational design of tailored nanocatalysts. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / In this paper, a three-dimensional numerical solution for the bending study of laminated composite doubly-curved shells is presented. The partial differential equations are solved analytically by the Navier summation for the midsurface variables; this method is only valid for shells with constant curvature where boundary conditions are considered simply supported. The partial differential equations present different coefficients, which depend on the thickness coordinates. A semi-analytical solution and the so-called Differential Quadrature Method are used to calculate an approximated derivative of a certain function by a weighted summation of the function evaluated in a certain grin domain. Each layer is discretized by a grid point distribution such as: Chebyshev-Gauss-Lobatto, Legendre, Ding and Uniform. As part of the formulation, the inter-laminar continuity conditions of displacements and transverse shear stresses between the interfaces of two layers are imposed. The proper traction conditions at the top and bottom of the shell due to applied transverse loadings are also considered. The present results are compared with other 3D solutions available in the literature, classical 2D models, Layer-wise models, etc. Comparison of the results show that the present formulation correctly predicts through-the-thickness distributions for stresses and displacements while maintaining a low computational cost. / Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica

The industrial demand for high strength-to-weight ratio materials is increasing due to the need for high performance components. Epoxy polymers, although often used in fiber-reinforced polymeric composites, have an inherent low toughness that further decreases with decreasing temperatures. Second-phase additives have been effective in increasing the toughness of epoxies at room temperature; however, the mechanisms at low temperatures are still not understood. In this study, the deformation mechanisms of a DGEBA epoxy modified with MX960 core-shell rubber (CSR) particles were investigated under quasi-static tensile and impact loads at room temperature (RT) and liquid nitrogen (LN2) temperature. Overall, the CSR had little effect on the tensile properties at RT and LN2 temperature. The impact strength decreased from neat to 3 wt% but increased from neat to 5 wt% at RT and LN2 temperature, with a higher impact strength at RT at all CSR loadings. The CSR particles debonded in front of the crack tip, inducing voids into the matrix. It was found that an increase in shear deformation and void growth likely accounted for the higher impact strength at 5 wt% CSR loading at RT while the thermal stress fields due to the coefficient of thermal expansion mismatch between rubber and epoxy and an increase in secondary cracking is likely responsible for the higher impact strength at 5 wt% tested at LN2 temperature. While a large toughening effect was not seen in this study, the mechanisms analyzed herein will likely be of use for further material investigations at cryogenic temperatures.

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This investigation was concerned with developing a procedure for using nonexpendable pattern materials in ceramic shell piece molds. Literature relating to this study indicated that nonexpendable materials, used in whole ceramic shell molds, had been limited to frozen mercury.

The deformation capacity of typical buckling-restrained braced frames (BRBFs) is limited by the rotation capacity of connecting regions. The rotation capacity of the connection region is limited by fracture of the gusset welds and yielding in the beams and columns. A different connection detail with beam-splices outside the gusset has been shown to increase connection rotation capacity when compared to typical connections, in a few component tests. This study expands upon the performed component tests, by analyzing the beam splice connection at the system level under directional dynamic loads. Finite element analysis and dynamic loads are used to analyze two 3-story frames having different connection configurations. The first frame has typical BRBF gusset connections, while the second frame has BRBF gusset connections with beam splices. The two frames are dynamically loaded using a recorded earthquake ground acceleration applied at three directions, relative to the frames, and the performance of each frame is compared. Results indicate that the connections with beam splices effectively prevent large moments from accumulating in the connection regions, reducing gusset stresses. In addition, the use of beam splices more uniformly distributes the brace load into the beams and columns, and has little effect on in and out-of-plane story drift.

Precipitation polymerization is a unique method that produces narrow-disperse, uniform polymer particles with clean surfaces. In this research, internally structured poly(divinylbenzene-co-chloromethylstyrene) polymer microspheres were prepared by thermal imprinting precipitation polymerization. The influence of thermal profiles and the monomer/crosslinker feed ratio on the resulting core-shell microspheres were explored by optical and transmission electron microscopy, and potential route to extend this technique to other polymer system was discussed. Further surface functionalization of this type of particles was demonstrated by substitution of chlorine with cysteine, a good and hydrophilic nucleophile. Narrow-disperse, hydrophilic particles may in future serve as components of synthetic extracellular matrices used in exploring cell-matrix interactions in a 3D context. / Thesis / Master of Science (MSc)

<p> Even with a good fit to nucleon-nucleon scattering data, there is considerable freedom in the off-energy-shell behaviour of the nuclear reaction matrix because of (1) the unavailability of the elastic scattering data in the high energy region and (2) the assumptions about the non-locality of the interaction. We have investigated off-energy shell behaviour by developing 'super' soft core potentials and several pairs of phase shift equivalent separable, local and momentum dependent potentials. Nuclear matter calculations were done using these potentials in order to study the sensitivity of the binding energy to the differences in the off-energy-shell behaviour. The effective range formula has been extended to the off-energy-shell case.</p> / Thesis / Doctor of Philosophy (PhD)