In this paper we illustrate a compositional method for modeling the concurrent execution of working processes in flexible manufacturing systems (FMS) through a special class of Petri Nets that we call S 'PI?. In essence, this class is built from state machines sharing a set of places modeling the availability of system resources. The analysis of S ' P R leads us to characterize deadlock situations in terms of a zero marking for some structural objects called siphons. In order to prevent the system from deadlocks, we propose a policy for resource allocation based on the addition of new places to the net imposing restrictions that prevent the presence of unmarked siphons (direct cause of deadlocks). Finally, we present the application of this technique to a realistic FMS case.
This paper presents some results from a survey carried out in 2004 among 223 olive tree farmers from mountainous areas in the Spanish Southern provinces of Granada and Jaén regarding the adoption of soil conservation and management practices. Olive tree groves in mountainous areas are subject to a high risk of soil erosion and incur a higher cost of soil conservation. This results in greater difficulty to comply with the requirements of the new single payment scheme (cross-compliance) and to benefit from agri-environmental schemes. The main objectives of this study are to analyze the current adoption level of soil conservation practices in this area and to address which socioeconomic and institutional factors determine such adoption. Three probit models are estimated. Dependent variables are three different soil conservation practices, namely tillage following contour lines, maintenance of terraces with stonewalls, and non-tillage with weedicides. Results show a significant increase in the adoption of several soil conservation measures in the last 15 years, especially of non-tillage practices. Some factors positively related with the adoption of soil conservation practices are farm profitability, the presence of young farmers, and continuity of the farming activity by relatives and the use of family labour.Additional key words: olive trees, probit models, socioeconomic factors, soil erosion, technology adoption.
ResumenAdopción de prácticas de conservación de suelos en olivar: el caso de las zonas de montaña del sur de EspañaEste artículo presenta resultados de una encuesta realizada en 2004 a 223 olivicultores de zonas de montaña en las provincias españolas de Granada y Jaén sobre la adopción de prácticas de manejo y conservación de suelos. El olivar en zonas de montaña presenta un elevado riesgo de erosión de los suelos, y los agricultores deben de incurrir en elevados costes para su conservación. Esto supone una mayor dificultad para cumplir las nuevas exigencias ambientales que permiten cobrar el pago único por explotación (condicionalidad) o participar en los programas agro-ambientales. En este trabajo se analizó el nivel actual de adopción de prácticas de conservación de suelos en esta zona, así como aquellos factores socioeconómicos e institucionales que determinan dicha adopción. Para ello se estiman tres modelos probit de adopción, cuyas variables dependientes son las principales prácticas de conservación de suelos que se llevan a cabo en la zona: laboreo siguiendo las curvas de nivel, mantenimiento de terrazas y muretes de piedra y no laboreo con uso de herbicidas. Los resultados muestran un incremento significativo durante los últimos 15 años del número de agricultores que realizan diversas prácticas de conservación de suelos, especialmente no laboreo. Algunos factores que aparecen positivamente relacionados con la adopción de prácticas de conservación de suelos son la rentabilidad de la explotación, la presencia de jóvenes agricultores, la continuidad de la actividad agraria por parte de fami...
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