Mesoscopic Model for Diffusion-Influenced Reaction Dynamics

A hybrid mesoscopic multi-particle collision model is used to study diffusion-influenced reaction kinetics. The mesoscopic particle dynamics conserves mass, momentum and energy so that hydrodynamic effects are fully taken into account. Reactive and non-reactive interactions with catalytic solute particles are described by full molecular dynamics. Results are presented for large-scale, three-dimensional simulations to study the influence of diffusion on the rate constants of the A+CB+C reaction. In the limit of a dilute solution of catalytic C particles, the simulation results are compared with diffusion equation approaches for both the irreversible and reversible reaction cases. Simulation results for systems where the volume fraction of catalytic spheres is high are also presented, and collective interactions among reactions on catalytic spheres that introduce volume fraction dependence in the rate constants are studied.Comment: 9 pages, 5 figure

Damping and clustering into crowded environment of catalytic chemical oscillators

A system formed by a crowded environment of catalytic obstacles and complex oscillatory chemical reactions is inquired. The obstacles are static spheres of equal radius, which are placed in a random way. The chemical reactions are carried out in a fluid following a multiparticle collision scheme where the mass, energy and local momentum are conserved. Firstly, it is explored how the presence of catalytic obstacles changes the oscillatory dynamics from a limit cycle to a fix point reached after a damping. The damping is characterized by the decay constant, which grows linearly with volume fraction for low values of the mesoscale collision time and the catalytic reaction constant. Additionally, it is shown that, although the distribution of obstacles is random, there are regions in the system where the catalytic chemical reactions are favored. This entails that in average the radius of gyrations of catalytic chemical reaction does not match with the radius of gyration of obstacles, that is, clusters of reactions emerge on the catalytic obstacles, even when the diffusion is significant.Comment: 8 pages, 7 figure

Desarrollo de modelos de tráfico en GALATEA.

A pesar de que lo vivimos a diario, el traco vehicular es un fenomeno que no esta todava totalmente comprendido. Hay muchas dicultades para su estudio, pero hoy en da ya tenemos suciente informacion estadstica y capacidad de calculo para comenzar a desarrollar modelos realistas y detallados de traco vehicular. En este trabajo implementamos algunos modelos de traco, que se pueden utilizar como prototipo, para extender el sistema de modelos de demostracion de la plataforma de simulacion Galatea, desarrollada en el Centro de Simulacion y Modelos de Universidad de Los los Andes. Se implementaron tres tipos de modelos microscopicos de traco vehicular: con automatas celulares, con mapas acoplados y con los sistemas de ecuaciones diferenciales ordinarias; para cada uno de ellos se estudiaron tres situaciones diferentes: una situacion base de un carril unidireccional, la incorporacion de vehculos al carril y un semaforo en el carril.Despite that we live everyday, the trac of vehicles is a not yet compleatly understood phenomenon. There are many diculties for its study, but nowadays we already have enought statistical information and capacity of calculation to begin to develop realistic and detailed models of vehicles trac. In this work some models of trac are implemented, the ones that can be used as prototype, in order to extend the set of demoinstration models of the simulation platform Galatea, developed in Centro de Simulacion y Modelos of Universidad de Los Andes. Three types of microscopic models of trac of vehicles were implemented: with cellular automatas, with coupled maps and with systems of ordinary dierential equations; for each of them three dierent settings are studied: a base setting of a unidirectional lane, the incorporation of vehicles to the lane and a trac light on the lane

Simulación por autómatas celulares de las conformaciones espaciales de polielectrolitos

Hemos llevado a cabo simulaciones del tipo Autómata Celular para un modelo de un polielectrolito en dilución infinita, para reproducir de manera cualitativa sus propiedades conformacionales. Nuestros resultados predicen las llamadas estructuras de collar de perlas, las cuales se comparan bien con simulaciones de Dinámica Molecular más elaboradas y costosas.Cellular automata simulation of the spatial conformations of polyelectrolytes

Estructuras jerarquicas inducidas por estimulo externo en redes dinamicas coevolutivas

Se investiga una red coevolutiva de mapas acoplados, sujetos a un forzamiento, como un modelo simple de un sistem adptativo de neuronas expuestas a un estmulo externo. Coevolucion signica que la dinamica de los mapas produ cambios en la estructura de conectividad de la red, haciendo que la topologa del sistema tambien vare en el tiemp lo cual a su vez afecta la dinamica local. La dinamica local es de tipo oscilatoria y caotica, descrita por el ma del crculo. Se estudia la in uencia de los parametros del sistema, tales como la intensidad del estmulo extern en la formacion de estructuras y se caracteriza el comportamiento dinamico colectivo y las propiedades topologic de la red emergente. Los resultados muestran que existen rangos de valores de la intensidad del estmulo para cuales surgen estructuras jerarquicas en la red. Adicionalmente, se encuentra que el estmulo externo induce may estructura en la red cuando los estados de los mapas estan menos sincronizados. Nuestro trabajo ilustra el potenc que tiene la aplicacion de los modelos de mapas acoplados en el estudio de coevolucion en sistemas complejos.We investigate a coevolving network of coupled maps subject to a forcing as a simple model for an adaptive syste of system of neurons recibing an external estimulus. Coevolution means that the dynamics of the maps modies t connectivity structure of the underlying network, and that this structure in turn aects the dynamics, both varyi in time. The local dynamics is chaotic and described by the circle map. The in uence of the intensity of the estern stimulus on the dynamical collective behavior and the topological properties of the network are studied. It is sho that there are ranges of the intensity of the stimulus for which hierarchical structures arise in the network. addition, it is found that the stimulus induces more structure when the states of the maps are less synchroniz Our work illustrates the potential of coupled map models for studying coevolution in complex systems

Galatea: una historia de modelado y simulación

Galatea es una plataforma libre de codigo abierto para simulación de sistemas multi-agente que incorpora estrategias de simulación bien conocidas con la que cualquier modelista o simulista puede ensayar esas estrategias en problemas de simulacion de sistemas complejos. La historia de Galatea comienza mucho antes que se planteara formalmente el proyecto con ese nombre. En 1993, nuestro muy joven Centro de Simulacion y Modelos, CeSiMo, propone un proyecto para explorar la reimplementacion de la plataforma de simulacion Glider sobre una plataforma orientada a objetos dando origen a un prototipo experimental. El problema del cambio estructural, inspirado por investigaciones en economa, se haba convertido entonces en uno de los objetivos de investigacion fundamentales del CeSiMo y vendra a dictar tambien la pauta para Galatea. La nocion de agente hizo su aparicion en algunos reportes internos en los que se enfatizaba su importancia para modelar sistemas complejos como una economa nacional. En 1998 se planteo la posibilidad de integrar Glider con herramientas de inteligencia articial para modelar agentes. En el 2000, un proyecto vendra a combinar aquel prototipo de 1993, con una teora de agentes basada en logica computacional que se planeaba integrar en una nueva teora de simulacion de sistemas multi-agentes. All nacio Galatea. El logro fundamental para el proyecto, sin embargo, llegara con las aplicaciones. En 2004, Galatea fue incorporada al banco de pruebas de un proyecto en biocomplejidad. Las lecciones aprendidas desde entonces, los aportes particulares del proyecto, as como los desaciertos y caminos futuros, son discutidos en este documento.Galatea is free and open source software for multi-agent, DEVS simulations. The platform integrates well-known, and some experimental simulation strategies to allow any modelist or simulist to use them to solve problems involving simulations of complex systems. The history of Galatea precedes its naming. In 1993, our beginning Centre for Simulation and Modelling, CeSiMo, started a project to migrate the simulation system Glider to a object-oriented platform leading to a functional prototype. The problem of Structural Change, identied by the economists, had become a research objective for CeSiMo and it also did for Galatea. The notion of agent appeared in some internal reports amid the insistence upon its importance as an abstract tool to model systems as complex as a national economy. In 1998, there was a proposal to integrate Glider with some Articial Intelligence developments to model agents. In 2000, that proposal became a project objective to combine the 1993 prototype with the agent modelling proposal to produce a multi-agent simulation theory that serve as the specication of a new simulation platform. At that time, Galatea was born. However, the real achievements started to be obtained in 2004, when Galatea was considered, among other tools, as a test-bed for a biocomplexity international project. The lessons learnt ever since, other achievements, strategic mistakes and future developments are discussed in this paper

Planck 2013 results. XX. Cosmology from Sunyaev-Zeldovich cluster counts

We present constraints on cosmological parameters using number counts as a function of redshift for a sub-sample of 189 galaxy clusters from the Planck SZ (PSZ) catalogue. The PSZ is selected through the signature of the Sunyaev--Zeldovich (SZ) effect, and the sub-sample used here has a signal-to-noise threshold of seven, with each object confirmed as a cluster and all but one with a redshift estimate. We discuss the completeness of the sample and our construction of a likelihood analysis. Using a relation between mass $M$ and SZ signal $Y$ calibrated to X-ray measurements, we derive constraints on the power spectrum amplitude $\sigma_8$ and matter density parameter $\Omega_{\mathrm{m}}$ in a flat $\Lambda$CDM model. We test the robustness of our estimates and find that possible biases in the $Y$--$M$ relation and the halo mass function are larger than the statistical uncertainties from the cluster sample. Assuming the X-ray determined mass to be biased low relative to the true mass by between zero and 30%, motivated by comparison of the observed mass scaling relations to those from a set of numerical simulations, we find that $\sigma_8=0.75\pm 0.03$, $\Omega_{\mathrm{m}}=0.29\pm 0.02$, and $\sigma_8(\Omega_{\mathrm{m}}/0.27)^{0.3} = 0.764 \pm 0.025$. The value of $\sigma_8$ is degenerate with the mass bias; if the latter is fixed to a value of 20% we find $\sigma_8(\Omega_{\mathrm{m}}/0.27)^{0.3}=0.78\pm 0.01$ and a tighter one-dimensional range $\sigma_8=0.77\pm 0.02$. We find that the larger values of $\sigma_8$ and $\Omega_{\mathrm{m}}$ preferred by Planck's measurements of the primary CMB anisotropies can be accommodated by a mass bias of about 40%. Alternatively, consistency with the primary CMB constraints can be achieved by inclusion of processes that suppress power on small scales relative to the $\Lambda$CDM model, such as a component of massive neutrinos (abridged).Comment: 20 pages, accepted for publication by A&

Planck 2015 results. XXVII. The second Planck catalogue of Sunyaev-Zeldovich sources

We present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest systematic all-sky surveyof galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data sets, and is the first SZ-selected cluster survey containing >103 confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that the estimates of the SZ strength parameter Y5R500are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical, and X-ray data sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under-luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac

A novel multi-frequency technique for the detection of point sources in Cosmic Microwave Background maps

In this work we address the problem of simultaneous multi-frequency detection of extragalactic point sources in maps of the Cosmic Microwave Background. We apply a new linear filtering technique, the so called `matched matrix filters', that incorporates full spatial information, including the cross-correlation among channels, without making any a priori assumption about the spectral behaviour of the sources. A substantial reduction of the background is achieved thanks to the optimal combination of filtered maps. We describe in detail the new technique and we apply it to the detection/estimation of radio sources in realistic all-sky Planck simulations at 30, 44, 70 and 100 GHz. Then we compare the results with the mono-frequential approach based on the standard matched filter, in terms of reliability, completeness and flux accuracy of the resulting point source catalogs. The new filters outperform the standard matched filters for all these indexes at 30, 44 and 70 GHz, whereas at 100 GHz both kind of filters have a similar performance. We find a noticeable increment of the number of true detections for a fixed reliability level. In particular, for a 95% reliability we practically double the number of detections at 30, 44 and 70 GHz.Comment: 12 pages, 10 figures, submitted to MNRA