Adaptive networks: coevolution of disease and topology

Adaptive networks have been recently introduced in the context of disease propagation on complex networks. They account for the mutual interaction between the network topology and the states of the nodes. Until now, existing models have been analyzed using low-complexity analytic formalisms, revealing nevertheless some novel dynamical features. However, current methods have failed to reproduce with accuracy the simultaneous time evolution of the disease and the underlying network topology. In the framework of the adaptive SIS model of Gross et al. [Phys. Rev. Lett. 96, 208701 (2006)], we introduce an improved compartmental formalism able to handle this coevolutionary task successfully. With this approach, we analyze the interplay and outcomes of both dynamical elements, process and structure, on adaptive networks featuring different degree distributions at the initial stage.Comment: 11 pages, 8 figures, 1 appendix. To be published in Physical Review

Exact solution of bond percolation on small arbitrary graphs

We introduce a set of iterative equations that exactly solves the size distribution of components on small arbitrary graphs after the random removal of edges. We also demonstrate how these equations can be used to predict the distribution of the node partitions (i.e., the constrained distribution of the size of each component) in undirected graphs. Besides opening the way to the theoretical prediction of percolation on arbitrary graphs of large but finite size, we show how our results find application in graph theory, epidemiology, percolation and fragmentation theory.Comment: 5 pages and 3 figure

Modeling the dynamical interaction between epidemics on overlay networks

Epidemics seldom occur as isolated phenomena. Typically, two or more viral agents spread within the same host population and may interact dynamically with each other. We present a general model where two viral agents interact via an immunity mechanism as they propagate simultaneously on two networks connecting the same set of nodes. Exploiting a correspondence between the propagation dynamics and a dynamical process performing progressive network generation, we develop an analytic approach that accurately captures the dynamical interaction between epidemics on overlay networks. The formalism allows for overlay networks with arbitrary joint degree distribution and overlap. To illustrate the versatility of our approach, we consider a hypothetical delayed intervention scenario in which an immunizing agent is disseminated in a host population to hinder the propagation of an undesirable agent (e.g. the spread of preventive information in the context of an emerging infectious disease).Comment: Accepted for publication in Phys. Rev. E. 15 pages, 7 figure

Comportement du béton de chanvre en compression simple et cisaillement

International audience Dans la littérature, la plupart des mélanges chaux/chanvre étudiés montrent un comportement fragile et une très faible résistance mécanique. Les formulations sont généralement riches en liant et légèrement compactées. Jusqu'à présent, ce matériau n'est pas considéré comme un matériau porteur et est principalement utilisé comme isolant de remplissage, combiné avec des composants de structure en bois, en béton ou en maçonnerie. Le présent travail est une étude expérimentale du comportement du béton de chanvre à la compression et au cisaillement, afin d'évaluer la capacité porteuse et au contreventement de ce matériau bio-sourcé, tout en assurant de bonnes qualités d'isolation thermique. Deux séries de tests sont effectuées. Le premier est un test de compression uniaxiale dans chaque direction pour caractériser l'anisotropie mécanique du matériau. Le second permet de caractériser le comportement au cisaillement de différentes configurations de la composition. Les expériences réalisées montrent une ductilité élevée de ce matériau en cisaillement, ce qui confirme les résultats de la littérature sur les structures de paroi. Ces résultats sont très prometteurs, notamment pour des applications parasismiques.</p

Understanding the Behavior of Sulfidic Colloids in the Presence of Metals

Riverton, Wyoming was host to a former uranium and vanadium ore processing plant, which operated from 1958 to 1963. The milling operations at the site contaminated the surface and shallow groundwater. The area became a Department of Energy (DOE) legacy site, where the U.S. Nuclear Regulatory Commission approved the DOE’s natural flushing compliance strategy. Up until the flooding in 2010, the natural flushing compliance strategy was going underway as expected. Sampling after the flood revealed a significant increase in contaminant concentration. New updated models need to be developed to help understand the situation at Riverton, for which this laboratory experiment is conducted. We want to understand the behavior of sulfidic colloids in the groundwater to the presence of metals. At the lab of Stanford’s Green Earth Sciences Building, samples of Riverton groundwater solution and 0.1 M NaCl water solution were place under different parameters. These parameters were: different Ferrihydrite and Sulfur ratios (0.05, 0.1, 0.5, and 2), the duration of agitation (3h, 9h, 24h, 48h, 3d, 5d, 10d, and 14d), and the metals used (Uranium, Zinc, Copper, Nickel, and Molybdenum). The generation of sulfidic colloids is closely monitored throughout the progression of the experiment, which will give insight to their behavior

Water column gradients beneath the summer ice of a High Arctic freshwater lake as indicators of sensitivity to climate change

Ice cover persists throughout summer over many lakes at extreme polar latitudes but is likely to become increasingly rare with ongoing climate change. Here we addressed the question of how summer ice-cover affects the underlying water column of Ward Hunt Lake, a freshwater lake in the Canadian High Arctic, with attention to its vertical gradients in limnological properties that would be disrupted by ice loss. Profiling in the deepest part of the lake under thick mid-summer ice revealed a high degree of vertical structure, with gradients in temperature, conductivity and dissolved gases. Dissolved oxygen, nitrous oxide, carbon dioxide and methane rose with depth to concentrations well above air-equilibrium, with oxygen values at >150% saturation in a mid water column layer of potential convective mixing. Fatty acid signatures of the seston also varied with depth. Benthic microbial mats were the dominant phototrophs, growing under a dim green light regime controlled by the ice cover, water itself and weakly colored dissolved organic matter that was mostly autochthonous in origin. In this and other polar lakes, future loss of mid-summer ice will completely change many water column properties and benthic light conditions, resulting in a markedly different ecosystem regime

Creación de un entorno virtual en Houdini con animaciones y simulaciones controladas por audio

El proyecto trata sobre la creación de un entorno virtual en el que se van a producir animaciones y simulaciones 3D, haciendo uso del software de Houdini, y de la creación de una canción en Cakewalk que controle el funcionamiento de los efectos. Una parte importante del proyecto se basa en mostrar la eficacia de producir dichas animaciones y simulaciones disponiendo del archivo original de la música, ya que con este archivo se podrían exportar diferentes pistas, instrumentos o sonidos de la propia canción producida. Poder optar a obtener archivos separados por grupos de instrumentos o sonidos es una gran ventaja, porque posibilita gestionar el procesamiento del audio dentro de Houdini y su resultado estético final. Esto se debe a que en una canción, no todos los sonidos e instrumentos tienen la misma intensidad. Clasificarlos por grupos en función de su rango dinámico y aplicarlos en diferentes animaciones mediante un proceso de gestión del audio facilita que el resultado pueda ajustarse de manera mucho más precisa. Además, esta práctica mejora el resultado final, ya que se facilita la distinción de los diferentes instrumentos y sonidos de manera visual. Finalmente, en este proyecto se propone crear un vídeo final de alta calidad como resultado de la ejecución de los efectos y la música en el que se va a enseñar el aspecto que podría tener un entorno virtual con elementos que reaccionan al audi

Propagation dynamics on networks featuring complex topologies

Analytical description of propagation phenomena on random networks has flourished in recent years, yet more complex systems have mainly been studied through numerical means. In this paper, a mean-field description is used to coherently couple the dynamics of the network elements (nodes, vertices, individuals...) on the one hand and their recurrent topological patterns (subgraphs, groups...) on the other hand. In a SIS model of epidemic spread on social networks with community structure, this approach yields a set of ODEs for the time evolution of the system, as well as analytical solutions for the epidemic threshold and equilibria. The results obtained are in good agreement with numerical simulations and reproduce random networks behavior in the appropriate limits which highlights the influence of topology on the processes. Finally, it is demonstrated that our model predicts higher epidemic thresholds for clustered structures than for equivalent random topologies in the case of networks with zero degree correlation.Comment: 10 pages, 5 figures, 1 Appendix. Published in Phys. Rev. E (mistakes in the PRE version are corrected here