Comparison of heuristics for flowtime minimisation in permutation flowshops

In this paper, we address the problem of sequencing jobs in a permutation flow shop with the objective of minimising the sum of completion times or flowtime. This objective is considered to be relevant and meaningful for today's dynamic production environment, and therefore it has attracted the attention of researchers during the last years. As a result, a number of different types of heuristics have recently been developed, each one claiming to be the best for the problem. However, some of these heuristics have been independently developed and only partial comparisons among them exist. Consequently, there are no conclusive results on their relative performance. Besides, some of these types of heuristics are of a different nature and could be combined in order to obtain composite heuristics. In this paper, we first classify and conduct an extensive comparison among the existing heuristics. Secondly, based on the results of the experiments, we suggest two new composite heuristics for the problem. The subsequent computational experience shows these two heuristics to be efficient for the problem under consideration

Revisión de los sistemas de control de la producción basados en tarjetas

Los sistemas de control de la producción han sido clasificados tradicionalmente en dos grandes grupos: sistemas push y sistemas pull. Sin embargo algunos autores han demostrado que sistemas considerado habitualmente de tipo pull contienen características de tipo push y viceversa [1]. En el presente trabajo nos centramos en los sistemas de control de la producción basados en tarjetas, tradicionalmente considerados de tipo pull. Desde el original Kanban hasta nuestros días han surgido gran cantidad de sistemas controlados por tarjetas. Muchos autores han partido de sistemas existentes modificando algunas características de éstos, e incluso existen varias versiones sobre el funcionamiento de un mismo sistema. El objeto de este trabajo es realizar una revisión y clasificación sobre los distintos mecanismos en los sistemas de control de la producción basados en tarjetas, con el objeto de clarificar el funcionamiento de cada unos de ellos y poder explorar otros sistemas en futuras líneas de investigación.Ministerio de Ciencia y Tecnología DPI2001-311

La internacionalización de la empresa como generadora de capacidades organizacionales: una aplicación empírica al sector de la alimentación

La internacionalización de las empresas se ha considerado tradicionalmente una magnífica herramienta para el aumento de sus ventas, la disminución de sus riesgos, la disminución de sus costes o, en general el aumento de su rentabilidad. Más recientemente, algunos trabajos han comenzado a plantear la posibilidad de que la internacionalización también afecte positivamente a las capacidades organizacionales internas de la empresa. Por ello, nos planteamos como objetivo de este trabajo analizar en qué medida la internacionalización de la empresa permite a la misma desarrollar su capacidad de innovar. Para conseguir tal objetivo tomaremos como muestra 155 empresas españolas del sector de la alimentación. Los resultados de este trabajo muestran que no todas las dimensiones relacionadas con la internacionalización afectan de forma positiva a la obtención de capacidad de innovación por parte de la empresa. Concretamente, el número de zonas geográficas internacionales en las que actúa la empresa, el número de años que lleva exportando y el grado de satisfacción de los directivos en relación al conocimiento adquirido en la internacionalización afectan de forma positiva a la capacidad de innovación de la empresa. Estos resultados ponen de manifiesto que son precisamente la diversidad de conocimientos adquiridos como consecuencia de la internacionalización los que repercuten de forma positiva en la capacidad de innovación de la compañía. Del mismo modo, los resultados muestran la existencia de una relación positiva entre el nivel de satisfacción en relación al conocimiento derivado de la actividad de exportación y su capacidad para innovar, resaltando la importancia de las percepciones de los directivos a la hora de implementar los conocimientos adquiridos. Sin embargo, otras dimensiones relacionadas con la internacionalización como su propensión exportadora o el índice de entropía de los mercados internacionales no afectan a la capacidad innovadora de la compañía. El estudio realizado tiene implicaciones prácticas tanto para los directivos de las empresas, como para las instituciones encargadas de promocionar las exportaciones. Dado que la innovación ha demostrado ser fundamental a la hora de afrontar el entorno competitivo actual, las empresas han de ser conscientes de que la realización de políticas de internacionalización diversificadas no sólo les permitirá diversificar el riesgo asumido, sino que también influirá favorablemente sobre el desarrollo de su capacidad de innovación. Del mismo modo, las instituciones que promueven la internacionalización deberán poner en marcha medidas de apoyo que favorezcan la diversificación internacional de las empresas ya que esto redundará positivamente en la mejora de la competitividad de dichas empresas.The internationalization of firms has been traditionally considered a powerful tool to increase their sales, diminish their risks, reduce their costs or in a general way, improve their performance. Recently, some works have started to raise whether internationalization also has a positive influence on the internal capabilities of firms. For this reason, the aim of this work is to analyze how the internationalization of firms enables them to develop innovation capability. To achieve this objective we use a sample of 155 Spanish firms in the food sector. The results of this work show that not all the dimensions of internationalization have a positive influence on the generation of innovation capability for the firm. Specifically, only the number of international geographic areas where firms act, the number of years that firms have been exporting and the satisfaction of managers with the knowledge that is acquired in internationalization have a positive influence on the innovation capability of firms. These results show that the diverse knowledge which is acquired by the firm through internationalization allows the generation of innovation capability for the firm. In the same way, the results show that there is a positive relationship between the level of satisfaction of managers with the knowledge that is acquired through the export activity and the innovation capability of the firm. This result shows the importance of the perception of managers to apply the knowledge which is acquired through internationalization toward the generation of innovation within the firm. However, other dimensions of internationalization, such as, the export tendency or the entropy rate in international markets, haven´t any influence on innovation capability of the firm. This work has some practical implications both for managers as well as for institutions that promote exportations. Taking into account that innovation has shown to be essential to face the current competitive environment, firms have to notice that diversify internationalization policy will not only allow to diversify the risk, but also have a positive influence on innovation capability of the firm. In the same way, institutions that promote exports should undertake supported measures which promote international diversification since this will improve the competitiveness of these firms

Physiological and genetic response of olive leaves to water stress and recovery: implications of mesophyll conductance and genetic expression of aquaporins and carbonic anhydrase

8 páginas, 2 figuras, 18 referencias.-- XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on CLIMWATER 2010: Horticultural Use of Water in a Changing Climate. Lisboa, Portugal.Drought is considered to be the main environmental factor limiting photo-synthesis (AN) and, consequently, plant growth and yield worldwide. During photosynthesis, the pathway of CO2 from the atmosphere to the site of carboxylation in the chloroplast stroma has two main components: stomatal (gs) and mesophyll (gm) conductances. Both are finite and dynamic, responding to many abiotic factors, therefore reducing CO2 concentration. However, little is known about gm regulation in the short term, where a possible role of aquaporins (AQP) and carbonic anhydrase (CA) has been proposed. Five-year-old olive trees growing in 50 L pots were used to evaluate the acclimation and recovery of AN to drought and subsequent re-watering. Control trees were well-irrigated, while in stressed trees irrigation was withheld for 13 days and then resumed. We made a simultaneous analysis of the genetic expression of two AQP, OePIP1.1 and OePIP2.1, and of CA, on the one hand, and leaf water status, leaf gas exchange and shoot hydraulic conductivity on the other. This is the first time that genetic expression in olive is related to main physiological variables. Two days after withholding irrigation (a.w.i.), the gs and gm values in Stress tress were lower than in Control trees. This limited photosynthesis. Leaf water status decreased from day 4 a.w.i. Midday leaf water potential dropped from -1.2 on the day before withholding irrigation to -6.0 MPa on day 9 a.w.i. CA expression decreased during drought and there was a peak on OePIP1.1 expression on day 4 a.w.i. Leaf water status recovered in ca. 36 h after resuming irrigation. Both gm and AN did not fully recover until 46 days after rewatering. Stomatal conductance, however, did not recover in that period, probably because of an irreversible loss of shoot hydraulic conductivity. Both OePIP1.1 and OePIP2.1 peaked 36 h after rewatering. We found significant correlations between gm and both OePIP2.1 and CA expression.This work was partly supported by grants for projects AGL2005-00220/AGR and AGL-2009-11310.Peer Reviewe

Flapless implant surgery: a review of the literature and 3 case reports

Since the 1970s, modern Implantology is based on a concept of surgery with flap elevation. Gradually, several clinical trials demonstrated that a mid-crestal incision gives similar success rates compared to those obtained using the classical protocol. However, over the past decade in medicine it has been established the concept of minimally invasive surgery, consisting in taking advantage of advancements experienced in diagnostic techniques and specific surgical instruments, to perform surgical procedures infringing as less damage as possible to the patient The present work aims to produce a thorough review of the literature published on the field of Implantology with flapless surgery, to determine the current scientific evidence of the technique, along with illustrating the results with different clinical cases. After presenting the clinical cases, and the review of literature, we can say that flapless surgeries should be restricted to well-selected cases in which a proper clinical and radiological planning has been made. Patients treated with anticoagulant drugs or medically compromised equally can get benefitted by this minimal invasion technique

About the impact of the materials properties in the catastrophic degradation of high power GaAs based laser

Producción CientíficaThe catastrophic degradation of high power lasers depends on both external factors, associated with the technological processes followed to fabricate the laser, and also on intrinsic aspects related to the materials forming the laser structure, more specifically the active zone composed by the QW, guide layers and claddings. The materials properties: optical, thermal and mechanical, play a paramount role in the degradation of the laser. We analyse here how these properties have an impact on the mechanisms responsible for the catastrophic degradation.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. Project VA293U13 and VA081U16 (003))Ministerio de Economía, Industria y Competitividad (Proyect ENE2014-56069-C4-4-R

Thermomechanical degradation of single and multiple quantum well AlGaAs/GaAs laser diodes

The catastrophic degradation of laser diodeswith active zones comprising either single (SQW) or multiple quantum wells (MQW) has been analysed via finite elementmethods. This analysis is based on a physical model that explicitly considers the thermal and mechanical properties of the diode laser structure and the relevant size effects associated with the small thickness of the active layers of the device. The reduced thermal conductivities and the thermal barriers at the interfaces result in a significant local heating process which is accentuated as more quantum wells form the active part of the device. Therefore, in the design of high power devices, the SQW configuration would be more appropriate than the MQW alternative.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref VA293U13 and VA081U16 (003)Ministerio de Economía, Industria y Competitividad (ENE2014-56069-C4-4-R