Numerical studies on zinc oxide synthesis via physical vapor transport

This project examined the transport phenomena in the synthesis of ZnO by physical vapor transport. In the numerical simulations Zn and O2 were treated as diluted species transported in nitrogen. The modes of transport were investigated and the velocity, temperature and concentration profiles in the reactor under reaction conditions elucidated. Also a parametric examination was conducted to determine the effect of physical variables on the flow. It was found that in open reaction conditions at high pressures convective transport dominates, while lower pressures lead to diffusive dominance and significant mass transport resistance. The linear temperature profile assumption was validated; further it was found that thermal expansion is insignificant, hence free convection can be neglected

Magnetoresistance in multilayer fullerene spin valves : a first-principles study

Carbon-based molecular semiconductors are explored for application in spintronics because their small spin-orbit coupling promises long spin life times. We calculate the electronic transport from first principles through spin valves comprising bi- and tri-layers of the fullerene molecules C60 and C70, sandwiched between two Fe electrodes. The spin polarization of the current, and the magnetoresistance depend sensitively on the interactions at the interfaces between the molecules and the metal surfaces. They are much less affected by the thickness of the molecular layers. A high current polarization (CP > 90%) and magnetoresistance (MR > 100%) at small bias can be attained using C70 layers. In contrast, the current polarization and the magnetoresistance at small bias are vanishingly small for C60 layers. Exploiting a generalized Julli`ere model we can trace the differences in spin-dependent transport between C60 and C70 layers to differences between the molecule-metal interface states. These states also allow one to interpret the current polarization and the magnetoresistance as a function of the applied bias voltage

HARVESTING HELIUM-3 FROM THE MOON

The world is approaching an energy crisis, and it is critical to focus on an alternate long term energy source. Given the current urge to explore space and expand humanity's outreach, harvesting the energetically rich Helium-3 from the Moon's surface is an ideal, yet challenging, objective which is amply motivated by current energy economic realities. He-3 can be used in a nuclear fusion reactor to generate enormous energy outputs with negligible waste. In this project, we study the scientific breakthroughs required in space and fusion technologies to successfully harvest He-3 from the Moon. Additionally, a multitude of interests expressed on a global scale in lunar He-3 are examined and assessed based on a legal space framework, and socio-economic political scenarios are developed that would result from the aforementioned space venture

Recursos Hídricos: Conceptos básicos y estudios de caso en Iberoamérica

El agua como fuente de vida y en el desempeño de sus funciones: sociales, ambientales, económicas y culturales, condiciona el desarrollo de una región, nación o continente, pues, la concentración urbana, el incremento de la superficie de riego para la producción de alimentos y la creciente contaminación someten a los recursos hídricos a una fuerte presión que no es posible soportar, originando situaciones de crisis. Así, mientras encuentran localidades la satisfacción de las necesidades en agua de sus habitantes representa un esfuerzo cotidiano, en otras, el desperdicio es una práctica generalizada pero inadmisible. Sin duda alguna en el mediano y largo plazo la tendencia actual en el uso de agua es simplemente insostenible. No es posible sufragar permanentemente el costo económico, social ay ambiental de abastecer a las grandes urbes con escurrimientos superficiales importados desde enormes distancias, de agotar los acuíferos de alterar la calidad de las agua rebasando límites de renovación económicamente factibles. Tampoco es posible enfrentar el problema del agua como si la disponibilidad del recurso fuera ilimitada y gratuita..