Compelled to do the right thing

We use a model of opinion formation to study the consequences of some mechanisms attempting to enforce the right behaviour in a society. We start from a model where the possible choices are not equivalent (such is the case when the agents decide to comply or not with a law) and where an imitation mechanism allow the agents to change their behaviour based on the influence of a group of partners. In addition, we consider the existence of two social constraints: a) an external authority, called monitor, that imposes the correct behaviour with infinite persuasion and b) an educated group of agents that act upon their fellows but never change their own opinion, i.e., they exhibit infinite adamancy. We determine the minimum number of monitors to induce an effective change in the behaviour of the social group, and the size of the educated group that produces the same effect. Also, we compare the results for the cases of random social interactions and agents placed on a network. We have verified that a small number of monitors are enough to change the behaviour of the society. This also happens with a relatively small educated group in the case of random interactions.Comment: 8 pages, 9 figures, submitted to EPJ

Oxygen vacancies in strained SrTiO3_{3} thin films: formation enthalpy and manipulation

We report the enthalpy of oxygen vacancy formation in thin films of electron-doped SrTiO$_{3}$, under different degrees of epitaxial stress. We demonstrate that both compressive and tensile strain decrease this energy at a very similar rate, and promote the formation of stable doubly ionized oxygen vacancies. Moreover, we also show that unintentional cationic vacancies introduced under typical growth conditions, produce a characteristic rotation pattern of TiO$_6$ octahedra. The local concentration of oxygen vacancies can be modulated by an electric field with an AFM tip, changing not only the local electrical potential, but also producing a non-volatile mechanical response whose sign (up/down) can be reversed by the electric field.Comment: Physical Review B (accepted for publication

Detection of spatially structured scattering polarization of Sr i 4607.3 Å with the Fast Solar Polarimeter

Context. Scattering polarization in the Sr I 4607.3 Å line observed with high resolution is an important diagnostic of the Sun's atmosphere and magnetism at small spatial scales. Investigating the scattering polarization altered by the Hanle effect is key to constraining the role of small-scale magnetic activity in solar atmospheric activity and energy balance. At present, spatially resolved observations of this diagnostic are rare and have not been reported as close to the disk center as for μ = 0.6. Aims. Our aim is to measure the scattering polarization in the Sr I line at μ = 0.6 and to identify the spatial fluctuations with a statistical approach. Methods. Using the Fast Solar Polarimeter (FSP) mounted on the TESOS filtergraph at the German Vacuum Tower Telescope (VTT) in Tenerife, Spain, we measured both the spatially resolved full Stokes parameters of the Sr I line at μ = 0.6 and the center-to-limb variation of the spatially averaged Stokes parameters. Results. We find that the center-to-limb variation of the scattering polarization in the Sr I line measured with FSP is consistent with previous measurements. A statistical analysis of Stokes Q/I (i.e., the linear polarization component parallel to the solar limb), sampled with 0.16″ pixel-1 in the line core of Sr I reveals that the signal strength is inversely correlated with the intensity in the continuum. We find stronger linear polarimetric signals corresponding to dark areas in the Stokes I continuum image (intergranular lanes). In contrast, independent measurements at μ = 0.3 show a positive correlation of Q/I with respect to the continuum intensity. We estimate that the subregion diameter responsible for the excess Q/I signal is on the order of 0.5″-1″. Conclusions. The presented observations and the statistical analysis of Q/I signals at μ = 0.6 complement reported scattering polarization observations as well as simulations. The FSP has proven to be a suitable instrument to measure spatially resolved scattering polarization signals. In the future, a systematic center-to-limb series of observations with subgranular spatial resolution and increased polarimetric sensitivity (<10-3) compared to that in the present study is needed in order to investigate the change in trend with μ that the comparison of our results with the literature suggests.Fil: Zeuner, F.. Universität Göttingen; Alemania. Institut für Sonnensystemforschung; AlemaniaFil: Feller, A.. Institut für Sonnensystemforschung; AlemaniaFil: Iglesias, Francisco Andres. Institut für Sonnensystemforschung; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Solanki, S.K.. Institut für Sonnensystemforschung; Alemania. Kyung Hee University; Corea del Su

Measuring satisfaction in societies with opinion leaders and mediators

An opinion leader-follower model (OLF) is a two-action collective decision-making model for societies, in which three kinds of actors are considered:Preprin