Materials fiables i tècniques robustes (original) (raw)
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Marco de evaluación para cocinas solares de pequeña dimensión
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Este documento presenta un marco de evaluación para las cocinas solares con base en tres parámetros: eficiencia energética, facilidad de uso y accesibilidad económica. Cada parámetro evalúa diversos indicadores cuantificables: a) eficiencia energética: potencia de cocción estándar, tiempo de calentamiento, el rendimiento térmico; b) facilidad de uso: la masa en relación al área del colector, orientaciones por hora y capacidad de carga de la olla y; c) accesibilidad económica: el coste por vatio generado y la durabilidad del reflector y/o acumulador térmico. A cada indicador se le asigna una escala máxima y mínima de la evaluación y los datos obtenidos de estos indicadores se integran en un gráfico radial. La suma de los indicadores constituye el aspecto que debe compararse, pero el gráfico también nos permite interpretar las fortalezas y debilidades descritas. Este marco no se puede analizar una sola cocina solar, ya que es una herramienta comparativa que requiere dos o más disposit...
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Revista Mexicana De Ciencias Pecuarias, 2012
Physiological and productive response of feedlot steers with an open space cooling system in an arid, dry climate RESÚMEN Con objeto de evaluar el efecto de un sistema de enfriamiento a espacio abierto sobre la ganancia de peso, frecuencia de respiración y niveles sanguíneos de triiodotironina (T 3 ) y tiroxina (T 4 ) durante el verano, 60 novillos Holstein fueron asignados aleatoriamente a un grupo testigo con únicamente sombra y un segundo grupo con sombra, más enfriamiento. Durante el experimento se registró un Índice de temperatura-humedad máximo que oscilo entre 82 a 88. El sistema de enfriamiento colocado a 8 m a partir de la sombra, consistió de una hélice de 2.4 m de diámetro produciendo 1,416 m 3 /min de aire con una rotación de 90° y un flujo de agua de 12 L/min. El peso corporal y los niveles de hormonas fueron registrados cada dos semanas, mientras la frecuencia de respiración 1400) en dos ocasiones por semana. Los datos fueron analizados con un diseño de mediciones repetidas, incluyendo el peso inicial como covariable. La ganancia de peso fue mayor (P<0.05) en el grupo con enfriamiento (1.43±0.091 kg/animal/día) que en el testigo (1.25±0.091 kg/animal/día). La frecuencia respiratoria expresada en respiraciones por minuto difirió (P<0.01) entre el grupo testigo (111±0.74) y enfriamiento (94±0.74). El grupo con enfriamiento obtuvo mayores (P<0.05) niveles de T 3 (1.7±0.042 ng/ml) en comparación al testigo (1.5±0.042 ng/ml); sin embargo, los niveles de T 4 fueron similares entre el enfriamiento (79.3±1.82 ng/ml) y el testigo (78.2±1.82 ng/ml). El enfriamiento artificial puede ser una alternativa para incrementar la eficiencia productiva y el confort de novillos Holstein en verano. ABSTRACT Evaluation of the effects of an open space cooling system on weight gain, respiration rate and serum thyroid hormone (T 3 and T 4 ) levels in feedlot steers was done using 60 Holstein steers (344 kg) allotted randomly in two treatments: a control with only shade in the corral (n=30); and a cooling with an open space cooling system (n=30). Daily maximum temperature-humidity index (THI) ranged from 82 to 88 during the 12-week study period. The open space cooling system consisted of a fan with 2.4 m diameter blade that displaced 1,416 m 3 of air per minute and had a 90º oscillation range, and sprinklers. The fan was installed at 8 m distance on the south side of the shade. Water discharge was 12 L per minute over a 7 h period. Body weight and thyroid hormone levels were measured every two weeks and respiration rate twice a week (1400). Data were analyzed by repeated measures, including initial weight as a covariate. Daily weight gain was different (P<0.05) between the cooling treatment (1.43±0.091 kg/d) and the control treatment (1.25±0.091 kg/d). Respiration rate was lower (P<0.05) in steers in the cooling treatment (94±0.74 breaths per minute) than in those in the control treatment (111±0.74 breaths per minute). Levels of T 3 were higher (P<0.05) in the cooling treatment (1.7±0.042) than in the control (1.5±0.042). Levels of T 4 were similar between the cooling (79.3±1.82 ng/ml) and control (78.2±1.82 ng/ml) treatments. Use of this cooling system improved production performance and comfort in feedlot Holstein steers in a hot, dry climate.