The Myth of Unity: The Contra War, 1980–1990

This research focuses on the anti-Sandinista forces popularly known as the contras who operated in Nicaragua from 1980 to 1990, in particular the Fuerza Democrática Nicaragüense (FDN), the Alianza Revolucionaria Democrática (ARDE), and the two main Atlantic Coast contra groups: MISURA (Miskito Sumu and Rama Indians of the Atlantic Coast) and MISURASATA (Miskito, Sumu, Rama, Sandinista Aslatakanta [Working Together]). This thesis looks at the different ways these contra groups viewed their conflict and explained it to national and international audiences, as well as to those within the anti-Sandinista movement. Because there was such heterogeneity within the contra movement, a comparative look at the different groups that composed it is essential. While there were similar strains of thought among the most prominent contra groups, goals were articulated differently from one group to another, and these varied narratives serve as a basis to explain how they became obstacles to unity among the contra groups, and how these differences were finally reconciled into the larger, more-unified anti-Sandinista effort

Mach-Zehnder Interferometric device for spin filtering in a GaAs/AlGaAs electron gas

A spin filtering device using quantum spin interference is theoretically proposed in a GaAs/AlGaAs electron gas that has both Rashba and Dresselhaus spin-orbit couplings. The device achieves polarized electron currents by separating spin up and spin down components without a magnetic field gradient. We find two broad spin filtering regimes, one where the interferometer has symmetrical arms, where a small magnetic flux is needed to achieve spin separation, and the other with asymmetric arms where the change in path length renders an extra phase emulating the effects of a magnetic field. We identify operating points for the device where optimal electron polarization is achieved within value ranges found in a 2D electron gas. Both device setups apply for arbitrary incoming electron polarization and operate at broad energy ranges within the incoming electron band

A new non-linear RANS model with enhanced near-wall treatment of turbulence anisotropy

A new ω-based non-linear eddy-viscosity model is proposed. It was developed based on the original k−ω model and formulated using a quadratic stress-strain relation for the Reynolds stress tensor, with an added realisability condition. For enhanced treatment of near-wall turbulence anisotropy, a formulation that scales only with the turbulent Reynolds number is proposed for the first time. The new model has been implemented in the open-source Computational Fluid Dynamics (CFD) package OpenFOAM and validated against plane channel flow, a zero-pressure-gradient flat plate, and a U-bend curved channel configuration. To further assess the performance of the model for more complex geometries, it has been tested on configurations relevant to automotive applications. Overall, the new model outperforms the standard k−ω model. For example, on a curved channel, improved predictions for the minimum pressure and maximum skin friction of approximately 50% are obtained. Improved predictions are also obtained for quantities of practical engineering relevance, such as the pressure distribution along the wall of a sudden expansion diffuser, a configuration used to inform the design of automotive exhaust systems. This demonstrates that the proposed model has important practical applications for internal flows where anisotropic turbulence effects dominate