Imperfect Imitation Can Enhance Cooperation

The promotion of cooperation on spatial lattices is an important issue in evolutionary game theory. This effect clearly depends on the update rule: it diminishes with stochastic imitative rules whereas it increases with unconditional imitation. To study the transition between both regimes, we propose a new evolutionary rule, which stochastically combines unconditional imitation with another imitative rule. We find that, surprinsingly, in many social dilemmas this rule yields higher cooperative levels than any of the two original ones. This nontrivial effect occurs because the basic rules induce a separation of timescales in the microscopic processes at cluster interfaces. The result is robust in the space of 2x2 symmetric games, on regular lattices and on scale-free networks.Comment: 4 pages, 4 figure

Super-roughening as a disorder-dominated flat phase

We study the phenomenon of super-roughening found on surfaces growing on disordered substrates. We consider a one-dimensional version of the problem for which the pure, ordered model exhibits a roughening phase transition. Extensive numerical simulations combined with analytical approximations indicate that super-roughening is a regime of asymptotically flat surfaces with non-trivial, rough short-scale features arising from the competition between surface tension and disorder. Based on this evidence and on previous simulations of the two-dimensional Random sine-Gordon model [Sanchez et al., Phys. Rev. E 62, 3219 (2000)], we argue that this scenario is general and explains equally well the hitherto poorly understood two-dimensional case.Comment: 7 pages, 4 figures. Accepted for publication in Europhysics Letter

A theorem on the absence of phase transitions in one-dimensional growth models with onsite periodic potentials

We rigorously prove that a wide class of one-dimensional growth models with onsite periodic potential, such as the discrete sine-Gordon model, have no phase transition at any temperature $T>0$. The proof relies on the spectral analysis of the transfer operator associated to the models. We show that this operator is Hilbert-Schmidt and that its maximum eigenvalue is an analytic function of temperature.Comment: 6 pages, no figures, submitted to J Phys A: Math Ge

Utilidad de los archivos de prensa en el estudio de inestabilidades de ladera en Asturias (NO de España)

[ResumenLa aplicación de los archivos de prensa al estudio de inestabilidades de ladera en Asturias plantea diversas limitaciones metodológicas. Entre ellas destacan la baja frecuencia de noticias referentes a inestabilidades, la recogida prácticamente exclusiva de aquellas que afectan a infraestructuras y la ausencia de una toma de datos de carácter científico. Sin embargo, el análisis de la información de 209 noticias pertenecientes al período 1980-94 ha puesto de manifiesto su utilidad en diversos aspectos, como la ubicación global de las inestabilidades de ladera en la Cuenca Carbonífera Central, y la valoración de su impacto sobre infraestructuras. Es destacable asimismo la posibilidad que ofrece este tipo de archivos como regis·tro cronológico de inestabilidades, lo que ha permitido establecer una aproximación a la relación temporal entre los eventos de precipitación e inestabilidad.[Abstract] The application of newspaper archives to the study of slope instabilities in Asturias has several methodological limitations. Sorne of them are the low frequency of news refering to slope instability and the publication of only those affecting people and infrastructures without a scientifical data collection. Nevertheless, the analysis of the information about 209 news in the period 198094 has evidenced its utility in showing the spatiallocation of instabilities in the Central Coal Basin, and giving an approach to its impact over infrastructures. It is also worth to point out the possibility of using these archives as chronological instability records. This has allowed the establishment of an approach to the temporal relationships between rainfal1 and instability events for the studied interval

Equilibrium roughening transition in a 1D modified sine-Gordon model

We present a modified version of the one-dimensional sine-Gordon that exhibits a thermodynamic, roughening phase transition, in analogy with the 2D usual sine-Gordon model. The model is suited to study the crystalline growth over an impenetrable substrate and to describe the wetting transition of a liquid that forms layers. We use the transfer integral technique to write down the pseudo-Schr\"odinger equation for the model, which allows to obtain some analytical insight, and to compute numerically the free energy from the exact transfer operator. We compare the results with Monte Carlo simulations of the model, finding a perfect agreement between both procedures. We thus establish that the model shows a phase transition between a low temperature flat phase and a high temperature rough one. The fact that the model is one dimensional and that it has a true phase transition makes it an ideal framework for further studies of roughening phase transitions.Comment: 11 pages, 13 figures. Accepted for publication in Physical Review

Utilización de freidora doméstica entre universitarios madrileños. Aceptación de alimentos congelados fritos en aceite de oliva virgen extra, girasol y girasol alto oleico

The goal of this study was to get information about the use of domestic fryers, type of oil used for frying, kind of food fried in it, and number of frying until rejection of oil. To this aim, a preliminary survey was performed in 50 persons belonging to the Madrid University to know which kind of food and oils they used for frying. None of them used other oils for frying than olive or sunflower oils. Afterwards, another survey was performed between 250 university students, belonging to the Madrid University, in which homes the domestic fryer was used. Information was obtained about kind of oil used, food usually fried, and frying number when the oil used in successive frying was discarded. Most of them employed olive oil and used the same oil 11-20 times, and about the half of them fried only one type of food in the same oil. The most frequent food fried were potatoes, frozen pre-fried potatoes and fish. Fresh foods were preferentially fried in pans while the frozen pre-cooked ones were fried without any priority. Taking into account results of the second survey, 20 frying of frozen foods in extra virgin olive oil, sunflower oil and high oleic acid sunflower oil were performed using domestic fryers. With the aim to analyse the effect of oil used on fried croquette palatability, identifying and punctuation triangular tests were used. The effect of the frying modality (with and without oil reposition) and type of oil used on croquette acceptability were also tested. Croquettes were well accepted obtaining an average score of 6.8 in a scale range from 1 to 10. The organoleptic quality of this food did not change with the number of frying. Nevertheless, the panel was able to identify croquettes fried in sunflower oil from the 6th frying. Croquettes fried in oils with a frequent replenishment obtain a higher organoleptic score than those fried without oil replenishment. Then it should be considered the convenience to perform frying with a frequent replenishment with unused oil.La finalidad del estudio fue obtener información sobre el uso de freidoras domésticas, tipo de aceite utilizado para freír, alimentos que se fríen y número de frituras tras el que se elimina el aceite. Para ello se realizó una encuesta preliminar en 50 personas pertenecientes a la Universidad Complutense de Madrid para conocer qué tipo de aceite y qué alimentos se emplean en fritura doméstica. Ninguna de ellas usaba un aceite diferente del de oliva o girasol. Con estos datos se realizó otra encuesta entre 250 universitarios en cuyos hogares se empleaba freidora acerca del aceite empleado, los alimentos que se fríen más habitualmente y el número de fritura tras el que se desecha el aceite usado. Los resultados señalan que en los hogares de estos universitarios, el aceite más utilizado para freír es el de oliva. La mayoría de ellos usa el aceite de 11 a 20 veces y aproximadamente la mitad de los encuestados fríen sólo un tipo de alimento en el mismo aceite. Los alimentos que se fríen con más frecuencia en sartén eran las patatas, las patatas prefritas congeladas y el pescado, observándose una preferencia al uso de la sartén respecto al de la freidora para los alimentos frescos, mientras que no había preferencias respecto a los precocinados. Teniendo en cuenta los resultados de la segunda encuesta se realizaron un total de 20 frituras de alimentos congelados en freidoras domésticas en aceite de oliva virgen extra, girasol y girasol con alto contenido en ácido oleico. Las croquetas fritas se valoraron mediante cata, realizándose pruebas triangulares de identificación y de puntuación con la finalidad de estudiar el efecto del aceite empleado en su fritura. También se evaluó la calidad organoléptica global de las croquetas fritas en función de la modalidad de fritura (con o sin adición de aceite sin usar) y del tipo de aceite. La aceptación de las croquetas fue bastante buena, con una puntuación de 6,8 sobre una escala de 1-10. No se encontró una influencia del número de frituras en la valoración de la calidad organoléptica de las mismas. El panel de catadores únicamente encontró diferencias significativas entre el aceite de girasol y el de oliva virgen extra, pero sólo para las croquetas provenientes de la 6ª fritura. La aceptación de las croquetas fritas en las freidoras donde se mantuvo el nivel inicial de aceite fue superior a la de las obtenidas en frituras sin reponer las pérdidas de aceite, señalando la conveniencia de freír adicionando frecuentemente aceite sin usar

Current density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. II. Furo-furan Isomers

Magnetic susceptibility and nuclear magnetic shielding at the nuclei of bis-heteropentalenes formed by two furan units ([2,3-b], [3,2-b], [3,4-b], and [3,4-c] isomers) have been computed by several approximated techniques and a large Gaussian basis set to achieve near Hartree–Fock estimates. Ab initio models of the ring currents induced by a magnetic field normal to the molecular plane were obtained for the three isomeric systems of higher symmetry, showing that the π electrons give rise to intense diamagnetic circulation. The π currents are responsible for enhanced magnetic anisotropy and strong out-of-plane proton deshielding. The theoretical findings are used to build up a “diatropicity matrix” for two fused five-membered heterocyclic [email protected] ; [email protected]

Stability of the personal relationship networks in a longitudinal study of middle school students

The personal network of relationships is structured in circles of friendships, that go from the most intense relationships to the least intense ones. While this is a well established result, little is known about the stability of those circles and their evolution in time. To shed light on this issue, we study the temporal evolution of friendships among teenagers during two consecutive academic years by means of a survey administered on five occasions. We show that the first two circles, best friends and friends, can be clearly observed in the survey but also that being in one or the other leads to more or less stable relationships. We find that being in the same class is one of the key drivers of friendship evolution. We also observe an almost constant degree of reciprocity in the relationships, around 60%, a percentage influenced both by being in the same class and by gender homophily. Not only do our results confirm the mounting evidence supporting the circle structure of human social networks, but they also show that these structures persist in time despite the turnover of individual relationships -- a fact that may prove particularly useful for understanding the social environment in middle schools.Comment: 10 pages, 7 figures, requires wlscirep.cls, jabbrv.sty, jabbrv-ltwa-all.ldf, and jabbrv-ltwa-en.ldf (included

Gender differences in cooperation: experimental evidence on high school students

The emergence of cooperation among unrelated human subjects is a long-standing conundrum that has been amply studied both theoretically and experimentally. Within the question, a less explored issue relates to the gender dependence of cooperation, which can be traced back to Darwin, who stated that "women are less selfish but men are more competitive". Indeed, gender has been shown to be relevant in several game theoretical paradigms of social cooperativeness, including prisoner's dilemma, snowdrift and ultimatum/dictator games, but there is no consensus as to which gender is more cooperative. We here contribute to this literature by analyzing the role of gender in a repeated Prisoners' Dilemma played by Spanish high-school students in both a square lattice and a heterogeneous network. While the experiment was conducted to shed light on the influence of networks on the emergence of cooperation, we benefit from the availability of a large dataset of more 1200 participants. We applied different standard econometric techniques to this dataset, including Ordinary Least Squares and Linear Probability models including random effects. All our analyses indicate that being male is negatively associated with the level of cooperation, this association being statistically significant at standard levels. We also obtain a gender difference in the level of cooperation when we control for the unobserved heterogeneity of individuals, which indicates that the gender gap in cooperation favoring female students is present after netting out this effect from other socio-demographics factors not controlled for in the experiment, and from gender differences in risk, social and competitive preferences.This paper has benefited from the funding from the Spanish Ministry of Education and Science (Projects ECO2012-34828, RESINEE and PRODIEVO). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript