A non-linear degenerate equation for direct aggregation and traveling wave dynamics

The gregarious behavior of individuals of populations is an important factor in avoiding predators or for reproduction. Here, by using a random biased walk approach, we build a model which, after a transformation, takes the general form [u_{t}=[D(u)u_{x}]_{x}+g(u)] . The model involves a density-dependent non-linear diffusion coefficient [D] whose sign changes as the population density [u] increases. For negative values of [D] aggregation occurs, while dispersion occurs for positive values of [D] . We deal with a family of degenerate negative diffusion equations with logistic-like growth rate [g] . We study the one-dimensional traveling wave dynamics for these equations and illustrate our results with a couple of examples. A discussion of the ill-posedness of the partial differential equation problem is included

SRec, software de animación de la recursividad

SRec es una aplicación que permite la generación automatizada de animaciones de programas basados en la recursividad. Ofrece una gran variedad de facilidades educativas como cargar y guardar animaciones ya generadas, configuración de la información que se muestra en cada momento y una interfaz muy intuitiva. Mitiga el esfuerzo de elaboración de animaciones para los profesores y ayuda a analizar los algoritmos recursivos a los alumnos. Los resultados obtenidos de su utilización en las clases indican una gran aceptación por parte de los alumnos y una mejora en sus evaluaciones académicas.Peer Reviewe

Analysis of air flow past and through the 2415-3S airfoil for an unmanned aerial vehicle with internal propulsion system

This paper deals with the prediction of velocity fields on the 2415-3S airfoil which will be used for an unmanned aerial vehicle with internal propulsion system and in this way analyze the air flow through an internal duct of the airfoil using computational fluid dynamics. The main objective is to evaluate the effect of the internal air flow past the airfoil and how this affects the aerodynamic performance by means of lift and drag forces. For this purpose, three different designs of the internal duct were studied; starting from the base 2415-3S airfoil developed in previous investigation, basing on the hypothesis of decreasing the flow separation produced when the propulsive airflow merges the external flow, and in this way obtaining the best configuration. For that purpose, an exhaustive study of the mesh sensitivity was performed. It was used a non-structured mesh since the computational domain is three-dimensional and complex. The selected mesh contains approximately 12.5 million elements. Both the computational domain and the numerical solution were made with commercial CAD and CFD software, respectively. Air, incompressible and steady was analyzed. The boundary conditions are in concordance with experimental setup in the AF 6109 wind tunnel. The k-e model is utilized to describe the turbulent flow process as followed in references. Results allowed obtaining velocity contours as well as lift and drag coefficients and also the location of separation and reattachment regions in some cases for zero degrees of angle of attack on the internal and external surfaces of the airfoil. Finally, the selection of the configuration with the best aerodynamic performance was made, selecting the option without curved baffles

Effect of ambient temperature on machine tool compensation functions

Volumetric verification is increasing daily its relevance. However, as it is based on mathematical compensation, it does not model only the influence of the machine tool's geometric error to verify, but the total error of the data. Among all error sources, thermal variations due to changes in environmental conditions strongly affect MT position accuracy. This paper studies how verification changes affect compensation functions based on a modification of machine tool kinematic model and a generator of synthetic data. It takes into consideration the influence of the measurement noise on verification too. Moreover, the paper also studies how differences between verification and working conditions affect the accuracy of MT compensation functions. To do that, a brief explanation of the developed algorithm is presented

Stochastic reserving with a stacked model based on a hybridized Artificial Neural Network

Currently, legal requirements demand that insurance companies increase their emphasis on monitoring the risks linked to the underwriting and asset management activities. Regarding underwriting risks, the main uncertainties that insurers must manage are related to the premium sufficiency to cover future claims and the adequacy of the current reserves to pay outstanding claims. Both risks are calibrated using stochastic models due to their nature. This paper introduces a reserving model based on a set of machine learning techniques such as Gradient Boosting, Random Forest and Artificial Neural Networks. These algorithms and other widely used reserving models are stacked to predict the shape of the runoff. To compute the deviation around a former prediction, a log-normal approach is combined with the suggested model. The empirical results demonstrate that the proposed methodology can be used to improve the performance of the traditional reserving techniques based on Bayesian statistics and a Chain Ladder, leading to a more accurate assessment of the reserving risk

Specific enzyme detection following isoelectric focusing as a complimentary tool for the differentiation of related Gadoid fish species

5 páginas, 4 figurasThe presence of specific enzymes in the sarcoplasmic protein fraction of eight gadoid fish species has been investigated following isoelectric focusing (IEF) in the 3.5–9.5 pH range. Lactate dehydrogenase (LDH) and glycerol-3-phosphate-dehydrogenase (G-3-PD) allowed the differentiation of most of the gadoids tested, even in the case of closely related species belonging to the genus Merluccius. Investigation of arginine kinase and creatine kinase afforded non-specific enzyme patterns in the species tested. Adenylate kinase and malate dehydrogenase did not give specific or reproducible enzyme patterns. Analysis of LDH and G-3-PD activities in commercial IEF gels was shown to be a reliable and reproducible technique for distinguishing closely related Merluccius spp. and other gadoid fish speciesThe authors thank the financial support of CICYT (Project ALI95-0053)Peer reviewe

The sustainabibility of the Cuban Creole Black pig in the integral development of the mountain areas

Cuban Creole pig present excellent possibilities under the official program of complete development of Cuban Mountain areas. His role consist in their utilisation as a father breed in the environmental management system (CIAL), but also in their pure breeding in those areas named porcine protected areas. Here we describe the main zootechnique objectives of the Cuban Creole pig under the sustainable development.El Cerdo Criollo Cubano presenta unas excelentes posibilidades dentro del programa de desarrollo integral de la montaña por su utilización como línea padre en los sistemas de cría intensiva al aire libre (CIAL) o bien en los sistemas de cría en pureza denominados cotos porcinos. Se plantean los principales objetivos zootécnicos en el cerdo criollo dentro del desarrollo sostenible