Strain balanced quantum posts

Quantum posts are assembled by epitaxial growth of closely spaced quantum dot layers, modulating the composition of a semiconductor alloy, typically InGaAs. In contrast with most self-assembled nanostructures, the height of quantum posts can be controlled with nanometer precision, up to a maximum value limited by the accumulated stress due to the lattice mismatch. Here we present a strain compensation technique based on the controlled incorporation of phosphorous, which substantially increases the maximum attainable quantum post height. The luminescence from the resulting nanostructures presents giant linear polarization anisotropy.Comment: Submitted to Applied Physics Letters (7th March 2011). 4 pages, 4 figure

Análisis exergético de escenarios integrados de producción de etanol y otros productos a partir de la caña de azúcar

Se realiza el análisis exergético de seis escenarios parala producción conjunta de alcohol y otros productos derivados de la caña de azúcar, con el objetivo de identificar y localizar las principales fuentes generadoras de irreversibilidades en estos esquemas. En los esquemas integrados se considera la caña de azúcar como materia prima principal para la generación de productos y coproductos. Los seis escenarios de integración evaluados incluyen la producción de azúcar, alcohol de primera y segunda generación y coproductos tales como: furfural y lignina, la obtención de levadura torula y la recuperacióndel CO2. Se realizaron los balances de masa y energía para cada proceso, determinando los flujos de las corrientes que intervienen en el análisis exergético. Para el análisis exergético el esquema integrado fue dividido en diez subsistemas. Los subsistemas extracción de jugo, cristalización y cocción, fermentación y destilación resultaron los mayores generadores de pérdidas exergéticas. Para los primeros cinco escenarios la eficiencia exergética total se encuentra entre 71-80% y para el escenario de tiempo de no zafra en un 59%

Effect of SiC on the oxidation behavior of a Carbon-Carbon composite

Se prepararon dos materiales compuestos, CC y CC-SiC, mediante ciclos de infiltración líquida de brea-carbonización, el porcentaje en peso de SiC requerido fue determinado a través de TGA. Las estructuras morfológicas de los compuestos CC y CC-SiC se evaluaron mediante PLM y SEM. Las pérdidas de masa en llama de oxiacetileno se observaron en ambos compuestos durante 5, 10 y 15 minutos, respectivamente. Los valores de peso de los materiales CC y CC-SiC decrecieron con un mayor tiempo de exposición a la llama; se indujeron cambios morfológicos durante la exposición a la llama. El exceso de carbono en la matriz se oxidó formando CO, y se emitieron sustancias volátiles, generando una estructura porosa en los compuestos. Sin embargo, para el compuesto CCSiC, se conservó la integridad del refuerzo, verificando el efecto del SiC en el comportamiento de los compuestos a altas temperaturas.Abstract: Two composite materials, CC and CC-SiC, were prepared by liquid pitch infiltration-carbonization cycles; required SiC weight percentage was determined by TGA. Morphological structures of CC and CC-SiC composites were evaluated using PLM and SEM. Weight loss at oxy-acetylene flame was observed on both composites during 5, 10 and 15 minutes, respectively. CC and CC-SiC weight values decreased with the increasing of flame exposure time; morphological changes were induced during flame exposure. Excessive carbon on the matrix was oxidized forming CO, and volatile substances were released, generating a porous structure on the composites. However, for CC-SiC composite, the reinforcement integrity was remained, verifying the effect of SiC on the composites behavior at high temperatures

Chiral symmetry breaking and effective lagrangians for softly broken supersymmetric QCD

We study supersymmetric QCD with N_f<N_c in the limit of small supersymmetry-breaking masses and smaller quark masses using the weak-coupling Kahler potential. We calculate the full spectrum of this theory, which manifests a chiral symmetry breaking pattern similar to that caused by the strong interactions of the standard model. We derive the chiral effective lagrangian for the pion degrees of freedom, and discuss the behavior in the formal limit of large squark and gluino masses and for large N_c. We show that the resulting scalings of the pion decay constant and pion masses in these limits differ from those expected in ordinary nonsupersymmetric QCD. Although there is no weak coupling expansion with N_f=N_c, we extend our results to this case by constructing a superfield quantum modified constraint in the presence of supersymmetry breaking.Comment: 16 pages, LaTe

Heavy metal pollution in drinking water - a global risk for human health: A review

Water resources in the world have been profoundly influenced over the last years by human activities, whereby the world is currently facing critical water supply and drinking water quality problems. In many parts of the world heavy metal (HM) concentrations in drinking water are higher than some international guideline values. Discussing about the HM pollution in drinking water, the incorporation of them into the food chain, and their implications as a global risk for the human health, are the objectives of this review. It is known that there are million people with chronic HM poisoning which has become a worldwide public health issue, while 1.6 million children die each year from diseases for which contaminated drinking water is a leading cause. There is also evidence of HM in drinking water that are responsible for causing adverse effect on human health through food chain contamination. A global effort to offering affordable and healthy drinking water most to be launched throughout the world, while various laws and regulations to protect and improve the utilization of drinking water resources should be updated or created throughout the world, including the low income countries; otherwise, the problem of HM-polluted drinking water will be growing because demand for drinking water is still growing such as this problem will become even more pressing in the future. Finally, notwithstanding, additional researches are necessaries about the correlation between HM concentration in drinking water and human diseases, while the development of robust, cheap and sustainable technologies to improve the drinking water quality is necessary.Key words: Groundwater, aquifer, water quality, water pollution, microorganism, water supply, microbial communities, food chain, disease