Emergence and persistence of communities in coevolutionary networks

We investigate the emergence and persistence of communities through a recently proposed mechanism of adaptive rewiring in coevolutionary networks. We characterize the topological structures arising in a coevolutionary network subject to an adaptive rewiring process and a node dynamics given by a simple voterlike rule. We find that, for some values of the parameters describing the adaptive rewiring process, a community structure emerges on a connected network. We show that the emergence of communities is associated to a decrease in the number of active links in the system, i.e. links that connect two nodes in different states. The lifetime of the community structure state scales exponentially with the size of the system. Additionally, we find that a small noise in the node dynamics can sustain a diversity of states and a community structure in time in a finite size system. Thus, large system size and/or local noise can explain the persistence of communities and diversity in many real systems.Comment: 6 pages, 5 figures, Accepted in EPL (2014

STECF Evaluation of Fishing Effort Regimes in European Waters - Part 2 (STECF-13-21)

STECF notes that it has extensively addressed the ToR regarding the requested fishing effort regime evaluations in the 1. Eastern and Western Baltic, 2. the Kattegat, 3. the Skagerrak, North Sea, European waters in ICES Div.2 and the Eastern Channel, 4. to the West of Scotland, 5. Irish Sea, 6. Celtic Sea, 7. Atlantic waters off the Iberian Peninsula, 8. Western Channel, 9. Western Waters and Deep Sea 10. and the Bay of Biscay, i.e. updated estimates of trends in fishing effort, landings and discards by species, CPUE and LPUE by fisheries and species, and partial fishing mortalities for effort regulated and non-regulated fisheries by Member States. Few ToR could not be accomplished due to time constraints and/or data deficiencies. It is noted that compilations of fisheries specific data by fishing effort management regime and Member State are provided as electronic appendixes and can be downloaded at http://stecf.jrc.ec.europa.eu/web/stecf/ewg1313 in order to facilitate transparent dissemination of the information and further use. Due to the complexity of the fisheries information provided, interested users are advised to consult the data quality notes and data notations provided in the present report.JRC.G.4-Maritime affair

The anatomy of urban social networks and its implications in the searchability problem

The appearance of large geolocated communication datasets has recently increased our understanding of how social networks relate to their physical space. However, many recurrently reported properties, such as the spatial clustering of network communities, have not yet been systematically tested at different scales. In this work we analyze the social network structure of over 25 million phone users from three countries at three different scales: country, provinces and cities. We consistently find that this last urban scenario presents significant differences to common knowledge about social networks. First, the emergence of a giant component in the network seems to be controlled by whether or not the network spans over the entire urban border, almost independently of the population or geographic extension of the city. Second, urban communities are much less geographically clustered than expected. These two findings shed new light on the widely-studied searchability in self-organized networks. By exhaustive simulation of decentralized search strategies we conclude that urban networks are searchable not through geographical proximity as their country-wide counterparts, but through an homophily-driven community structure

Aplicación de O- y N- radicales a la química de carbohidratos

Se demuestra la utilidad de la reacción de AIH en la síntesis cíclicos 2,7-dioxabiciclo[2.2.1] heptano, 6,8-dioxabiciclo[3.2.1]octano, 8-oxa-6-azabiciclo[3.2.1]octano, 7-oxa-2-azabiciclo[2.2.1]heptano, 2,9-dioxabiciclo[3.3.1]nonano y 7a-metoxihexahidro-2H-furo[3,2-b]pirano. Los productos obtenidos son interesantes como potenciales sintones quiroles en la síntesis de moléculas más complejas. Como se puede observar, la reacción también puede ser útil para la oxidación selectiva de carbonos específicos en carbohidratos, siendo un procedimiento muy suave para la síntesis de ulosas protegidas, las cuales no son fácilmente accesibles por otros métodos. Se ha desarrollado una teoría que explica razonablemente el mecanismo de la reacción, con el objetivo de poder predecir con anticipación lo que ocurrirá en otros ejemplos no ensayados, haciendo uso de herramientas fácilmente accesibles como son los programas de mecánica molecular. La suavidad de las condiciones de reacción nos permite trabajar con sustratos que poseen una gran variedad de grupos funcionales, tales como ésters, carbonatos, dobles enlaces, O-bencilos, isopropilidenos, nitrilos,etc. Se ha descrito por primera vez la formacón de N-radicales a partir de carbamatos, siendo éstos los grupos protectores más usados en síntesis orgánica para el grupo amino, que junto al uso de fenil y bencilfosforamidas nos abre muchas posibilidades para posteriores transformaciones de los sintones obtenidos. Se ha demostrado que se puede tener control en la regioselectividad del proceso, con el uso de diferentes grupos protectores muy comunes en la química de los carbohidratos. En el capítulo 4 hemos demostrado la posibilidad de modificar una unidad de azúcar desde la otra unidad en un disacárido D-Glc-a1--->4-D-Glc. El compuesto L-Ido-B1-->4-D-Glc puede ser de interés en la química de los análogos de la heparina, ya que la unidad L-Iduronic-B1-->4-D-Glc es un fragmento presente en este polisacárido. Actualmente, la síntesis de compuestos con esqueletos de a-L-idosa y ácido a-L-idurónico es un área de investigación muy activa. Nosotros creemos que estas condiciones de reacción de AIH, muy suaves, pueden ser extendidas a otros disacáridos a1-->4 y presumiblemente a otros diferentes que presenten las condiciones antes mencionadas. Un aspecto a resaltar es que la reacción puede realizarse en condiciones oxidativas y reductivas, dándonos un control sintético adicional sobre la evolución del radical generado en C5

Model reduction for molecular diffusion in nanoporous media

Porous materials are widely used for applications in gas storage and separation. The diffusive properties of a variety of gases in porous media can be modeled using molecular dynamics simulations that can be computationally demanding depending on the pore geometry, complexity and amount of gas adsorbed. We explore a dimensionality reduction approach for estimating the self-diffusion coefficient of gases in simple pores using Langevin dynamics, such that the three-dimensional (3D) atomistic interactions that determine the diffusion properties of realistic systems can be reduced to an effective one-dimensional (1D) diffusion problem along the pore axis. We demonstrate the approach by modeling the transport of nitrogen molecules in single-walled carbon nanotubes of different radii, showing that 1D Langevin models can be parametrized with a few single-particle 3D atomistic simulations. The reduced 1D model predicts accurate diffusion coefficients over a broad range of temperatures and gas densities. Our work paves the way for studying the diffusion process of more general porous materials as zeolites or metal-organics frameworks with effective models of reduced complexity.Comment: 8 pages, 6 figure

A PGD-based multiscale formulation for non-linear solid mechanics under small deformations

Model reduction techniques have became an attractive and a promising field to be applied in multiscale methods. The main objective of this work is to formulate a multiscale procedure for non-linear problems based on parametrized microscale models. The novelty of this work relies in the implementation of the model reduction technique known as Proper Generalized Decomposition for solving the high dimensional parametrized problem resulting from the microscale model. The multiscale framework here proposed is formulated to non-linear problems, specifically to material non-linearities, where material response is governed by a strain dependent evolution law. Two strategies to deal with this kind of problem under small deformations are detailed in this work. Both strategies based on parametrized microscale models solved by PGD have been applied to a problem with a rate-dependent isotropic damage model. First, a procedure where the problem is solved by uncoupling the equilibrium equation to the state variable expression has been explored. In order, to alleviate the parametrized microscale problem, a second strategy for problems with material non-linearity has been proposed, incorporating a parametrized microscale problem at each macroscale increment (FE-PGD). The basis of those procedures are described and compared, highlighting the solution accuracy and computer time consumption in comparison to a traditional finite element analysis

General coevolution of topology and dynamics in networks

We present a general framework for the study of coevolution in dynamical systems. This phenomenon consists of the coexistence of two dynamical processes on networks of interacting elements: node state change and rewiring of links between nodes. The process of rewiring is described in terms of two basic actions: disconnection and reconnection between nodes, both based on a mechanism of comparison of their states. We assume that the process of rewiring and node state change occur with probabilities Pr and Pc respectively, independent of each other. The collective behavior of a coevolutionary system can be characterized on the space of parameters (Pr, Pc). As an application, for a voterlike node dynamics we find that reconnections between nodes with similar states lead to network fragmentation. The critical boundaries for the onset of fragmentation in networks with different properties are calculated on this space. We show that coevolution models correspond to curves on this space describing functional relations between Pr and Pc. The occurrence of a one-large-domain phase and a fragmented phase in the network is predicted for diverse models, and agreement is found with some earlier results. The collective behavior of system is also characterized on the space of parameters for the disconnection and reconnection actions. In a region of this space, we find a behavior where different node states can coexist for very long times on one large, connected network.Comment: 6 pages, 6 figure

First case of isolation of Nocardia wallacei reported in Mexico

AbstractNocardia species are aerobic, Gram-positive bacteria with branched filaments reported as opportunistic microorganisms associated with infectious diseases of the skin. We report the isolation of N. wallacei in Mexico from a 43-year-old man, an HIV-positive construction worker who sought care for difficulty breathing and abundant sputum