Prevalencia de Trypanosoma vivax en bovinos de Villavicencio por pruebas parasitológicas directas y por inmunofluorescencia indirecta.

Para determinar la prevalencia de tripanosomiasis bovina en Villavicencio, Colombia, empleando la técnica indirecta de anticuerpos fluorescentes, a manera de comparación se utilizaron los métodos parasitológicos directos. Se examinaron 500 bovinos mayores de un año en 50 fincas escogidas al azar. Se encontraron 47 reactores positivos o una prevalencia real entre 6.8 y 9.4 por ciento, utilizando la prueba de inmunofluorescencia indirecta. No se encontraron animales positivos al emplear los métodos parasitológicos directos (preparación en fresco, frotis delgado, gota gruesa, centrifugación en tubo capilar o técnica de Woo). Lo anterior indica la ausencia de correlación entre los procedimientos utilizados. Se comprueba que los métodos parasitológicos directos son solo de ayuda en los casos que cursan con parasitemias detectables. Se puede afirmar que el Tripanosoma vivax es endémico en esta región tropical de Colombia, destacándose la importancia de la tripanosomiasis como enfermedad inmunodepresora y los posibles efectos que puede tener sobre los programas de vacunación que se realicen en los bovinos de esta zona. Los reactores positivos pueden ser reservorios potenciales de tripanosomas, los cuales podrían transmitirse dada la presencia de algunos insectos vectoresGanado de leche-Ganadería lech

Iron Particle Size Effects for Direct Production of Lower Olefins from Synthesis Gas

The Fischer–Tropsch synthesis of lower olefins (FTO) is an alternative process for the production of key chemical building blocks from non-petroleum-based sources such as natural gas, coal, or biomass. The influence of the iron carbide particle size of promoted and unpromoted carbon nanofiber supported catalysts on the conversion of synthesis gas has been investigated at 340–350 °C, H₂/CO = 1, and pressures of 1 and 20 bar. The surface-specific activity (apparent TOF) based on the initial activity of unpromoted catalysts at 1 bar increased 6–8-fold when the average iron carbide size decreased from 7 to 2 nm, while methane and lower olefins selectivity were not affected. The same decrease in particle size for catalysts promoted by Na plus S resulted at 20 bar in a 2-fold increase of the apparent TOF based on initial activity which was mainly caused by a higher yield of methane for the smallest particles. Presumably, methane formation takes place at highly active low coordination sites residing at corners and edges, which are more abundant on small iron carbide particles. Lower olefins are produced at promoted (stepped) terrace sites that are available and active, quite independent of size. These results demonstrate that the iron carbide particle size plays a crucial role in the design of active and selective FTO catalysts

Iron Particle Size Effects for Direct Production of Lower Olefins from Synthesis Gas

The Fischer–Tropsch synthesis of lower olefins (FTO) is an alternative process for the production of key chemical building blocks from non-petroleum-based sources such as natural gas, coal, or biomass. The influence of the iron carbide particle size of promoted and unpromoted carbon nanofiber supported catalysts on the conversion of synthesis gas has been investigated at 340–350 °C, H2/CO = 1, and pressures of 1 and 20 bar. The surface-specific activity (apparent TOF) based on the initial activity of unpromoted catalysts at 1 bar increased 6–8-fold when the average iron carbide size decreased from 7 to 2 nm, while methane and lower olefins selectivity were not affected. The same decrease in particle size for catalysts promoted by Na plus S resulted at 20 bar in a 2-fold increase of the apparent TOF based on initial activity which was mainly caused by a higher yield of methane for the smallest particles. Presumably, methane formation takes place at highly active low coordination sites residing at corners and edges, which are more abundant on small iron carbide particles. Lower olefins are produced at promoted (stepped) terrace sites that are available and active, quite independent of size. These results demonstrate that the iron carbide particle size plays a crucial role in the design of active and selective FTO catalysts