Agronomic, economic and ecological aspects of the papaya (Carica papaya) production in Tabasco, Mexico

The cultivation of papaya is important in the tropic because it provides source of income to the farmer within a short time. Statistical data were obtained from farmers located in the Chontalpa, Rios and Centro-Sierra regions; the size of the survey was 67 farmers. The study shows the results of the farmers’ problem in a drastic reduction of their productivity because of the virosis and low prices in commercialization. The farmers were classified into three levels of technology, “low”, “middle” and “high”. The first one covers 88% of the farmers in seasonal conditions in contrast with the high technology that concentrates 4.5% in irrigation conditions. According to the technology used, the fertilizer shows more yields. Economically, the high technology had an internal tax return of 0.43 in comparison with the low technology of 0.25, which means that the investment is recovered with different yields. However, the use of high technology makes the system more competitive. Key words

Grain Sorting Effects on Geochemical Characteristics of Sulfide Mine Tailings: a Case Study

The geochemical evolution of a sulfide mine tailings impoundment in SW Spain was studied. The impoundment was selected because of its small size and its tailings deposition system with a simple discharge point. The objective of this study was to test the hypothesis that mineral segregation associated to hydraulic sorting has significant effects on the geochemical characteristics and the long term weathering. Tailings samples were collected along depth profiles in three sampling points (proximal, central and distal to the point of discharge), and characterized by color, grain size, pH, acid-base account and chemical elements concentration, with the help of routine XRD analysis. Three vertical zones were identified: an upper oxidized zone, a transition intermediate zone, and an unoxidized zone. The analytical results indicate a segregation pattern in the unoxidized tailings based on differences in size and density of tailings grains. Near the discharge point, tailings were coarser and rich in pyrite, whereas the proportion of silicates increased from proximal to distal points. This results in a clear zoning which has consequences on geochemical and mineralogical evolution under weathering, showing substantial differences in the depth of the oxidation front, the acid generation and neutralization capacity, the formation of Fe secondary phases (jarosite) and the total content of the sulfide-related elements (Fe, As, Zn, Cu, Pb and Cd). The results of the study can serve to improve the theoretical bases for the development of conceptual models for predicting environmental impacts associated with sulfide tailings impoundments. Recently, the impoundment has been covered with a soil cover. This fact offers the possibility of new research on its evolution under new conditions

Evaluation of Surface Residual Stresses in Friction Stir Welds Due to Laser and Shot Peening

The effects of laser, and shot peening on the residual stresses in Friction Stir Welds (FSW) has been investigated. The surface residual stresses were measured at five different locations across the weld in order to produce an adequate residual stress profile. The residual stresses before and after sectioning the coupon from the welded plate were also measured, and the effect of coupon size on the residual stress relaxation was determined and characterized. Measurements indicate that residual stresses were not uniform along the welded plate, and large variation in stress magnitude could be exhibited at various locations along the FSW plate. Sectioning resulted in significant residual stress relaxation in the longitudinal direction attributed to the large change in dimensions in this direction. Overall, Laser and shot peening resulted in a significant reduction in tensile residual stresses at the surface of the specimens

Modelización gravimétrica 2D de la fosa de l'Empordà (NE de la Península Ibérica)

A gravimetric study of the Empordà Basin has been developed in this paper. Seismic reflection profiles and boreholes have furnished valuable data in order to build gravity models. The aim of this paper is the 2D modelling of the Empordà basin, and the calculation of neogene sediment thickness. 2D gravity profiles have been calculated parallel to the principal seismic lines

Influencia de la longitud de la biela en la eficiencia y biomecánica del pedaleo submáximo

El principal objetivo de este estudio es analizar el efecto de pequeños cambios en la longitud de la biela en el gasto energético y la técnica de pedaleo submáximo. Participaron 12 ciclistas de fondo en carretera bien entrenados, que realizaron pruebas de pedaleo a tres potencias con cadencia estable, utilizando tres longitudes de biela (en orden aleatorio). Sus bicicletas fueron exactamente reproducidas en un ergómetro que medía el torque ejercido sobre la biela izquierda y derecha de forma independiente. Simultáneamente se registró cinemática 2D de la pierna derecha y el gasto energético al pedalear (eficiencia gruesa). Los resultados muestran que los cambios en la longitud de la biela no tuvieron efecto en la eficiencia gruesa, pero sí en las variables biomecánicas. Una biela de mayor longitud provocó una pérdida de eficiencia mecánica y un aumento en la flexión y el rango de movimiento de la cadera y la rodilla, sin cambios en el tobillo. Aunque estos cambios no fueron lo suficientemente importantes para alterar la eficiencia gruesa, sí que podrían tener implicaciones negativas a largo plazo (peor técnica de pedaleo y riesgo de lesión). En conclusión, el efecto de pequeños cambios en la longitud de la biela, que serían asumibles por ciclistas de competición, producen alteraciones en la biomecánica de pedaleo, pero no en su eficiencia gruesa. Futuros estudios deben abordar los efectos a largo plazo de estos cambios.The main purpose of this study was to analyze the effects of small changes in crank length on gross efficiency and pedaling technique during submaximal cycling. Twelve well-trained road cyclists participated. They pedaled at three power outputs and steady cadence with three crank lengths (in a randomized order). Their bicycles were exactly reproduced on an ergometer where crank torque of the left and right legs were independently registered. 2D kinematic of the right leg and energy cost (gross efficiency) were recorded. The results showed that changes in crank length had no effect on the gross efficiency, but had effect on the biomechanical variables. A longer crank caused a decreased in mechanical efficiency and an increase in the flexion and range of movement of the hip and the knee, without changes in the ankle. These alterations were not significant enough to alter the gross efficiency, but they could have negative long-term implications (worse pedaling technique and possible injuries). In conclusion, the small changes in crank arm length which are feasible for competitive cyclists affected cycling biomechanics, but not gross efficiency. Future studies should study long-term effects of these changes.Peer Reviewe