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AlGaN/GaN HEMTs on silicon substrates have been fabricated and their static and small-signal RF characteristics investigated. The AlGaN/GaN material structures were grown on (111) p-Si by LP-MOVPE. Devices exhibit a saturation current of 0.91 A/mm, a good pinchoff and a peak extrinsic transconductance of 122 mS/mm. A unity current gain frequency of 12.5 GHz and max = 0.83 were obtained. The highest saturation current reported so far, static output characteristics of up to 20 V and breakdown voltage at pinchoff higher than 40 V demonstrate that the devices are capable of handling 16 W/mm static heat dissipation

The effect of the additive non ionic polyacrylamide (PAM), was studied at the laboratory level, as refining crystalline grain in the copper electrorefining. Experiments were performed 24 h of electrolysis, using an electrolyte of copper sulphate acid, with 0.5 to 10 mgl-1 polyacrylamide at 55 °C and a current density of 260 Am-2. The effectiveness of these organic additives in copper electrorefining was determined by directly measuring the surface roughness of the copper deposit and contrasted with the results of other instrumental techniques (SEM and metallographic analysis). The results of the analysis SEM, metallographic analysis and measurement of the surface roughness of the copper deposit, show that to concentrations as low as 0.5 mgl-1 of this additive is manifested its property of tuner of grain. However, in the range of 7 to 10 mgl-1 of polyacrylamide, it reaches an optimum size of grain for the deposit of copper in the cathodes. El efecto del aditivo poliacrilamida no iónica (PAM), se estudió a nivel de laboratorio, como afinador de grano cristalino en el refino electrolítico del cobre. Se realizaron experimentos de electrólisis de 24 h, utilizando un electrolito de sulfato de cobre ácido, con 0,5 a 10 mgl-1 de poliacrilamida, a 55 °C y una densidad de corriente de 260 Am-2. La efectividad de este aditivo orgánico en la refinación electrolítica del cobre fue determinada mediante la medida de la rugosidad de la superficie del depósito de cobre y contrastada con los resultados de otras técnicas instrumentales (MEB y análisis metalográfico). Los resultados obtenidos del análisis MEB, análisis metalográfico y medición de la rugosidad superficial del depósito de cobre, muestran que a concentraciones tan bajas como 0,5 mgl-1 de este aditivo, se manifiesta su propiedad de afinador de grano. Sin embargo, en el rango de 7 a 10 mgl-1 de poliacrilamida, se alcanza un tamaño de grano óptimo para el depósito de cobre en el cátodo.

The biological value of three phosphate feeds and the tissue concentration of some potentially toxic elements were assessed using two raw rock tricalcium phosphates (RRPA and RRPC ), a dicalcium dehydrated phosphate (DPB) and two levels of available P (0.40 and 0.45%), in a 3x2 factorial arrangement of treatments, with one to twenty-one day old broiler chicks. There were no interactions (p > 0.05) for the variables measured. DPB was associated, without statistical significance, with faster growth rate and better feed conversion efficiency. DPB had also the highest biological value of the three phosphates. It also presented the highest (p < 0.05) tibia ash and the greatest (p < 0.05) breaking strength. The dietary supplementation of RRPA and RRPC incorporated levels of vanadium (V) in the diets which are considered toxic for poultry. The concentration of V in the kidneys was higher in birds fed RRPC as compared to RRPA and DPB. Based on these and on previous results, the use of raw rock tricalcium phosphates as the only inorganic P supplement in poultry diets is not recommended., Se realizó un estudio tendiente a comparar las respuestas productivas y las concentraciones tisulares de algunos elementos minerales potencialmente tóxicos, cuando pollos broiler machos se alimentaron durante los primeros 21 días de vida con dietas suplementadas con fosfatos rocosos crudos (tricálcicos) o con un fosfato dicálcico monohidratado tratado químicamente. Además, el diseño consideró el empleo de dos niveles de inclusión dietaria de P disponible: 0.40 y 0.45%. Los pollos que recibieron la suplementación de P con fosfato dicálcico mostraron una tendencia a obtener una mayor velocidad de crecimiento y una mejor eficiencia de conversión alimenticia. Así mismo, lograron un valor biológico mayor que el obtenido por las aves alimentadas con los fosfatos tricálcicos rocosos crudos (p>0.05). Los pollos alimentados con el producto tratado químicamente, lograron mineralizar mejor sus tibias, las que a su vez presentaron mayor resistencia a la fractura, que las de pollos suplementados con los otros fosfatos (p