Smart random walkers: the cost of knowing the path

In this work we study the problem of targeting signals in networks using entropy information measurements to quantify the cost of targeting. We introduce a penalization rule that imposes a restriction to the long paths and therefore focus the signal to the target. By this scheme we go continuously from fully random walkers to walkers biased to the target. We found that the optimal degree of penalization is mainly determined by the topology of the network. By analyzing several examples, we have found that a small amount of penalization reduces considerably the typical walk length, and from this we conclude that a network can be efficiently navigated with restricted information.Comment: 9 pages, 11 figure

Análisis de la capacidad de soporte sísmica de fundaciones superficiales

Indexación: Web of Science; Scielo.In the context of engineering practice, the problem of the seismic bearing capacity of shallow foundations has been solved indirectly, either due an increase of the static allowable soil pressures related to the probability of occurrence of the design earthquake or by adopting an equivalent pseudo-static approach. However, during last decades, a series of analytical methods that directly address the problem from the seismic point of view has been developed. This paper presents a parametric comparative analysis of different methods for estimating seismic bearing capacity of shallow strip foundations. Analytical methods, developed in the framework of both limit equilibrium and limit analysis theories, and also simplified design procedures typically used in practice were considered. The results obtained show an important decrease of the bearing foundation capacity with increasing of the maximum earthquake acceleration, which highlights the need to obtain a measure of the reliability associated with both calculation methods and safety factors commonly used for seismic design.En el contexto de la práctica ingenieril, el problema de la capacidad de soporte sísmica de fundaciones superficiales generalmente ha sido resuelto, de modo indirecto, ya sea considerando un incremento en las tensiones admisibles estáticas del suelo, asociado a la probabilidad de ocurrencia de un cierto evento sísmico de diseño, o bien adoptando un enfoque de tipo pseudoestático equivalente. Sin embargo, durante las últimas décadas se han desarrollado una serie de métodos analíticos que abordan directamente el problema desde el punto de vista sísmico. Este artículo presenta un análisis comparativo de tipo paramétrico entre diferentes métodos para estimar la capacidad de soporte sísmica de fundaciones superficiales corridas. Se consideraron métodos analíticos, desarrollados en el contexto de las teorías de equilibrio límite y análisis límite, y también procedimientos de diseño simplificados típicamente utilizados en la práctica. Los resultados obtenidos muestran un importante deterioro de la capacidad de soporte de la fundación en la medida que la aceleración máxima del sismo aumenta, lo cual pone de manifiesto la necesidad de establecer una medida de la confiabilidad asociada a los métodos de cálculo y factores de seguridad comúnmente usados para diseño sísmico.http://ref.scielo.org/kp4j8

The flow field in the slender combustion chambers of solid propellant rockets

We analyse the near inviscid flow field generated in a slender non-axisymmetric cylindrical cavity by the gasification and combustion reactions of a surrounding solid propellant grain. These reactions are confined to a thin layer adjacent to the surface of the solid propellant, so that the flow is non-reacting in most of the cavity, and of the same form as the flow in slender ducts due to fluid injection through lateral porous walls. The non-reacting flow can be described in terms of self-similar solutions of the Navier -Stokes equations that we calculate numerically for star-shaped grain configurations, with Reynolds numbers only moderately large for the flow to remain laminar and steady. The self-similar flows for non-axisymmetric configurations show strong axial vortices that we analyze using the Euler simplified form of the flow equations for large Reynolds numbers, and the general solution of the Burgers equation for strained vortices that describes their viscous cores; a logarithmic singularity could then be encountered at their center line