Fully dissipative relativistic lattice Boltzmann method in two dimensions

In this paper, we develop and characterize the fully dissipative Lattice Boltzmann method for ultra-relativistic fluids in two dimensions using three equilibrium distribution functions: Maxwell-J\"uttner, Fermi-Dirac and Bose-Einstein. Our results stem from the expansion of these distribution functions up to fifth order in relativistic polynomials. We also obtain new Gaussian quadratures for square lattices that preserve the spatial resolution. Our models are validated with the Riemann problem and the limitations of lower order expansions to calculate higher order moments are shown. The kinematic viscosity and the thermal conductivity are numerically obtained using the Taylor-Green vortex and the Fourier flow respectively and these transport coefficients are compared with the theoretical prediction from Grad's theory. In order to compare different expansion orders, we analyze the temperature and heat flux fields on the time evolution of a hot spot

Abundance patterns in early-type galaxies: is there a 'knee' in the [Fe/H] vs. [alpha/Fe] relation?

Early-type galaxies (ETGs) are known to be enhanced in alpha elements, in accordance with their old ages and short formation timescales. In this contribution we aim to resolve the enrichment histories of ETGs. This means we study the abundance of Fe ([Fe/H]) and the alpha-element groups ([alpha/Fe]) separately for stars older than 9.5 Gyr ([Fe/H]o, [alpha/Fe]o) and for stars between 1.5 and 9.5 Gyr ([Fe/H]i, [alpha/Fe]i). Through extensive simulation we show that we can indeed recover the enrichment history per galaxy. We then analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS selected to be ETGs. We separate out those galaxies for which the abundance of iron in stars grows throughout the lifetime of the galaxy, i.e. in which [Fe/H]o < [Fe/H]i. We confirm earlier work where the [Fe/H] and [alpha/Fe] parameters are correlated with the mass and velocity dispersion of ETGs. We emphasize that the strongest relation is between [alpha/Fe] and age. This relation falls into two regimes, one with a steep slope for old galaxies and one with a shallow slope for younger ETGs. The vast majority of ETGs in our sample do not show the 'knee' in the plot of [Fe/H] vs. [alpha/Fe] commonly observed in local group galaxies. This implies that for the vast majority of ETGs, the stars younger than 9.5 Gyrs are likely to have been accreted or formed from accreted gas. The properties of the intermediate-age stars in accretion-dominated ETGs indicate that mass growth through late (minor) mergers in ETGs is dominated by galaxies with low [Fe/H] and low [alpha/Fe]. The method of reconstructing the stellar enrichment histories of ETGs introduced in this paper promises to constrain the star formation and mass assembly histories of large samples of galaxies in a unique way.Comment: 22 pages, 25 figures, accepted for publication by A&

Quantitative measures of crowd patterns in agent-based models of street protests

In this work we describe the introduction of quantitative measures of emergent crowd patterns in an existing Agent-Based model (ABM) of street protests with multiple actors (police, protester and ‘media’ agents). The model was applied to a scenario of a police force defending a government building which protesters seek to invade. The improved model provided a coherent ‘narrative’ of the simulations and highlighted the realistic and unrealistic aspects of the agents’ interactions. Two new types of police agents – ‘defensive’ and ‘offensive’ – were introduced, leading to a realistic model representation of police cordons defending a site or charging to disperse clusters of violent protesters. The new quantitative measures provided information on cluster size and orientation of clusters of violent protesters, as well as police coverage and protester breaching of the defensive perimeter, together with the time history of the bursts of localized fights and arrests. It was shown how the quantitative measures of the emergent properties can be used for both parameterization and validation of the model.info:eu-repo/semantics/acceptedVersio

Investigation of the existence of hybrid stars using Nambu-Jona-Lasinio models

We investigate the hadron-quark phase transition inside neutron stars and obtain mass-radius relations for hybrid stars. The equation of state for the quark phase using the standard NJL model is too soft leading to an unstable star and suggesting a modification of the NJL model by introducing a momentum cutoff dependent on the chemical potential. However, even in this approach, the instability remains. In order to remedy the instability we suggest the introduction of a vector coupling in the NJL model, which makes the EoS stiffer, reducing the instability. We conclude that the possible existence of quark matter inside the stars require high densities, leading to very compact stars.Comment: 4 pages, 2 figures; prepared for IV International Workshop on Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, 4-8 Oct 200

Network influence effects in agent-based modelling of civil violence

In this paper we describe an agent-based model of civil violence with network influence effects. We considered two different networks, ‘family’ and ‘news’, as a simplified representation of multiple-context influences, to study their individual and joint impact on the size and timing of violence bursts, the perceived legitimacy, and the system’s long term behaviour. It was found that network influences do not change either the system’s long term behaviour or the periodicity of the rebellion peaks, but increase the size of violence bursts, particularly for the case of strong ‘news impact’. For certain combinations of network influences, initial legitimacy, and legitimacy feedback formulation, the solutions showed a very complicated behaviour with unpredictable alternations between long periods of calm and turmoil.info:eu-repo/semantics/acceptedVersio

Ensuring successful introduction of Wolbachia in natural populations of Aedes aegypti by means of feedback control

The control of the spread of dengue fever by introduction of the intracellular parasitic bacterium Wolbachia in populations of the vector Aedes aegypti, is presently one of the most promising tools for eliminating dengue, in the absence of an efficient vaccine. The success of this operation requires locally careful planning to determine the adequate number of individuals carrying the Wolbachia parasite that need to be introduced into the natural population. The introduced mosquitoes are expected to eventually replace the Wolbachia-free population and guarantee permanent protection against the transmission of dengue to human. In this study, we propose and analyze a model describing the fundamental aspects of the competition between mosquitoes carrying Wolbachia and mosquitoes free of the parasite. We then use feedback control techniques to devise an introduction protocol which is proved to guarantee that the population converges to a stable equilibrium where the totality of mosquitoes carry Wolbachia.Comment: 24 pages, 5 figure

Agent-Based modeling of protests and violent confrontation: A micro-situational, multi-player, contextual rule-based approach

We propose an innovative Agent-Based model of street protests with multiple actors: police agents, three types of protesters (“hardcore”, “hangers- on” and “passers-by”), and “media” agents that seek to witness and publish episodes and situations of violence. Agents have multiple goals and action selection is performed using a “personality” vector together with context rules that provide adaptation. Protesters turn active or violent according to the threshold rule proposed by Epstein, and police agents arrest violent protesters within their move range if they have sufficient backup. The model was applied to a scenario where policemen defend a government building from protesters and described several emergent crowd patterns in real protests, such as clustering of violent and active protesters and formation of a confrontation line moving back and forth with localized fights. Violent behavior was restricted to the initially more aggressive protesters and did not propagate to the bulk of the crowd.info:eu-repo/semantics/acceptedVersio

Agent-based modeling of social conflict, civil violence and revolution: State-of-the-art-review and further prospects

In this paper, we present a state-of-the-art review of Agent-based models (ABM) for simulation of social conflict phenomena, such as peaceful or violent street protests, civil violence and revolution. First, a simplified characterization of social conflict phenomena as emergent properties of a complex system is presented, together with a description of their macro and micro levels and the scales of the emergent properties. Then, existing ABM for simulation of crowd dynamics, civil violence and revolution are analyzed and compared, using a framework that considers their purpose/scope, environment representation, agent types and their architecture, the scales of the emergent properties, the qualitative and quantitative understanding of the phenomena provided by the results obtained from the models. We discuss the strengths and limitations of the existing models, as well as the promising lines of research for filling the gaps between the state-of-the-art models and real phenomena. This review is part of a work in progress on the assembling and dynamics of protests and civil violence, involving both simulation of the assembling process and the protest dynamics, as well as data collection in real protest events, and provides hints and guidelines for future developments.info:eu-repo/semantics/publishedVersio