Chaotic gas bubble oscillations in a viscoelastic fluid

Regular and chaotic radial oscillations of an acoustically driven gas bubble in a viscoelastic fluid have been theoretically analyzed. For parameter values usually found in diagnostic ultrasound period-doubling routes to chaos have been identified. Thresholds values of the external pressure amplitude for a first bifurcation in terms of the elasticity and the shear viscosity of the host fluid have also been evaluated. Les oscillations radiales, régulières ou chaotiques, d’une bulle de gaz au sein d’un fluide viscoélastique et soumise à l’action d’un champ acoustique sont analysées théoriquement. Pour des valeurs des paramètres qui sont normalement rencontrées dans le diagnostic médical, des chemins vers le chaos par doublement de la période ont été identifiés. Les valeurs limites pour la première bifurcation en fonction de l’élasticité et de la viscosité du fluide, ont été aussi déterminées

Nonlinear response to ultrasound of encapsulated microbubbles

The acoustic backscatter of encapsulated gas-filled microbubbles immersed in a weak compressible liquid and irradiated by ultrasound fields of moderate to high pressure amplitudes is investigated theoretically. The problem is formulated by considering, for the viscoelastic shell of finite thickness, an isotropic hyperelastic neo-Hookean model for the elastic contribution in addition to a Newtonian viscous component. First and second harmonic scattering cross-sections have been evaluated and the quantitative influence of the driving pressure amplitude on the harmonic resonance frequencies for different initial equilibrium bubble sizes and for different encapsulating physical properties has been determined. Conditions for optimal second harmonic imaging have been also investigated and some regions in the parameters space where the second harmonic intensity is dominant over the fundamental have been identified. Results have been obtained for albumin, lipid and polymer encapsulating shells, respectively

Dynamics of gas bubbles encapsulated by a viscoelastic fluid shell under acoustic fields

The dynamics of a gas-filled microbubble encapsulated by a viscoelastic fluid shell immersed in a Newtonian liquid and subject to an external pressure field is theoretically studied. The problem is formulated by considering a nonlinear Oldroyd type constitutive equation to model the rheological behavior of the fluid shell. Heat and mass transfer across the surface bubble have been neglected but radiation losses due to the compressibility of the surrounding liquid have been taken into account. Bubble collapse under sudden increase of the external pressure as well as nonlinear radial oscillations under ultrasound fields are investigated. The numerical results obtained show that the elasticity of the fluid coating intensifies oscillatory collapse and produces a strong increase of the amplitudes of radial oscillations which may become chaotic even for moderate driving pressure amplitudes. The role played by the elongational viscosity has also been analyzed and its influence on both, bubble collapse and radial oscillations, has been recognized. According to the theoretical predictions provided in the present work, a microbubble coated by a viscoelastic fluid shell is an oscillating system that, under acoustic driving, may experience volume oscillations of large amplitude, being, however, more stable than a free bubble. Thus, it could be expected that such a system may have a suitable behavior as an echogenic agent

Teaching Nash Equilibrium and Strategy Dominance: A Classroom Experiment on the Beauty Contest

The aim of this investigation is to display how the use of classroom experiments may be a good pedagogical tool to teach the Nash equilibrium (NE) concept. The basic game for our purposes is a repeated version of the Beauty Contest Game (BCG), a simple guessing game whose repetition lets students react to other players’ choices and to converge iteratively to the equilibrium solution. We performed this experiment with undergraduate students without any previous knowledge about game theory. After four rounds, we observed in all groups a clear decreasing tendency in the average chosen number. So, our findings prove that, by playing a repeated BCG, students quickly learn how to reach the NE solution.Classroom Experiments, Beauty Contest Game, Teaching, Nash Equilibrium.

Characterization and Classification of Collaborative Tools

Traditionally, collaboration has been a means for organizations to do their work. However, the context in which they do this work is changing, especially in regards to where the work is done, how the work is organized, who does the work, and with this the characteristics of collaboration. Software development is no exception; it is itself a collaborative effort that is likewise affected by these changes. In the context of both open source software development projects and communities and organizations that develop corporate products, more and more developers need to communicate and liaise with colleagues in geographically distant places about the software product they are conceiving, designing, building, testing, debugging, deploying and maintaining. Thus, work teams face sizeable collaborative challenges, for which they have need of tools that they can use to communicate and coordinate their Work efficiently

Accurate ab initio determination of magnetic interactions and hopping integrals in La2-xSrxCuO4 systems

The nature of magnetic interactions and electron transfer processes in La22xSrxCuO4 systems are studied, by means of an ab initio embedded cluster model approach, using a difference dedicated configuration interaction ~DDCI! procedure. For the undoped system, the crucial role played by the ligand to metal charge transfer ~LMCT! configurations in the magnetic process makes necessary the use of an enlarged DDCI space, which explicitly takes account of the relaxation of these LMCT configurations. This procedure allows us to approach the experimental magnetic coupling constant value. In hole-doped systems, the value obtained for the electron transfer integral, t, is of 0.54–0.57 eV. The extra hole, characterized from the nature and occupation of differential natural orbitals, has a strong p character ~approximately 50%! and is essentially localized in CuO2 planes. These results are in agreement with the experimental evidence about these kinds of compounds. Neither the value of t nor the nature of the extra hole are seriously affected by the optimization of the orbitals used in the CI expansion. This suggests that a t – J effective Hamiltonian is an adequate model to study the electronic properties of these system

Optimal Microgrid Topology Design and Siting of Distributed Generation Sources Using a Multi-Objective Substrate Layer Coral Reefs Optimization Algorithm

n this work, a problem of optimal placement of renewable generation and topology design for a Microgrid (MG) is tackled. The problem consists of determining the MG nodes where renewable energy generators must be optimally located and also the optimization of the MG topology design, i.e., deciding which nodes should be connected and deciding the lines’ optimal cross-sectional areas (CSA). For this purpose, a multi-objective optimization with two conflicting objectives has been used, utilizing the cost of the lines, C, higher as the lines’ CSA increases, and the MG energy losses, E, lower as the lines’ CSA increases. To characterize generators and loads connected to the nodes, on-site monitored annual energy generation and consumption profiles have been considered. Optimization has been carried out by using a novel multi-objective algorithm, the Multi-objective Substrate Layers Coral Reefs Optimization algorithm (Mo-SL-CRO). The performance of the proposed approach has been tested in a realistic simulation of a MG with 12 nodes, considering photovoltaic generators and micro-wind turbines as renewable energy generators, as well as the consumption loads from different commercial and industrial sites. We show that the proposed Mo-SL-CRO is able to solve the problem providing good solutions, better than other well-known multi-objective optimization techniques, such as NSGA-II or multi-objective Harmony Search algorithm.This research was partially funded by Ministerio de Economía, Industria y Competitividad, project number TIN2017-85887-C2-1-P and TIN2017-85887-C2-2-P, and by the Comunidad Autónoma de Madrid, project number S2013ICE-2933_02

Communication, coordination and competition in the beauty contest game: eleven classroom experiments

Este trabajo ha sido publicado en Central European Journal of Operations Research 12(4): 369-287 (2004).This paper introduces some new features in the standard experimental design of the beauty contest in order to allow communication among participants. With that aim, we use the mode instead of the mean and non-rival payoffs. This design encourages students to communicate their guessed number, with a higher probability if subjects know the 0 Nash equilibrium. The lack of communication can only be explained by subjects endowed with competitive other-regarding preferences. Experiments are run in 11 classrooms ranging from 11 to 60 students in size. Participants are given at least one week to submit their guesses and a questionnaire explaining their choice. Results indicate that: i) communication induces coordination in the responses, ii) communication does not guarantee any improvement in the average reasoning level, iii) there exist significative differences according to classroom size and duration of degree.We gratefully acknowledge the financial support from the University of Jaén R+D program (# 20210/148)

A social and emotional model for obtaining believable emergent behaviors

Proceeding of: 13th International Conference, AIMSA 2008, Varna, Bulgaria, September 4-6, 2008This paper attempts to define an emotional model for virtual agents that behave autonomously in social worlds. We adopt shallow modeling based on the decomposition of the emotional state in two qualities: valence (pleasantness or hedonic value) and arousal (bodily activation) and, also, for the agent personality based on the five factors model (openness, conscientiousness, extroversion, agreeableness and neuroticism). The proposed model aims to endow agents with a satisfactory emotional state achieved through the social actions, i.e. the development of social abilities. Psychology characterizes these social abilities for: using the language as a tool (verbal and nonverbal communication), being learned, producing reciprocal reward among the individuals involved in the communication and for depending on the individual features. We have implemented our model in the framework of a computer game, AI-live, to show its validity.Publicad

Memoria histórica o recuperación:¿qué podemos hacer ante un libro consumido por el fuego?

El Palacio Arzobispal de Valencia alberga parte de un libro litúrgico de gran formato que tras sufrir los estragos del fuego durante la guerra civil española, se ha convertido en testimonio bibliográfico único de un capítulo de la Historia de esta institución valenciana. Su estado de conservación es lamentable: consiste en un bloque compacto de pergamino deforme cuyo interior es totalmente inaccesible. Tras iniciar la investigación con un estudio interdisciplinar previo, con esta comunicación se pretenden dar a conocer las distintas posibilidades de intervención y abrir a debate los criterios más oportunos para su conservación y/o recuperación