Limit cycles for cubic systems with a symmetry of order 4 and without in nite critical points

"Vegeu el resum a l'inici del document del fitxer adjunt."

Repeated games played in a network

Delayed perfect monitoring in an infinitely repeated discounted game is modelled by letting the players form a connected and undirected network. Players observe their immediate neighbors' behavior only, but communicate over time the repeated game's history truthfully throughout the network. The Folk Theorem extends to this setup, although for a range of discount factors strictly below 1, the set of sequential equilibria and the corresponding payoff set may be reduced. A general class of games is analyzed without imposing restrictions on the dimensionality of the payoff space. This and the bilateral communication structure allow for limited results under strategic communication only. As a by-product this model produces a network result; namely, the level of cooperation in this setup depends on the network's diameter, and not on its clustering coefficient as in other models.

Chat seguro

L'objectiu d'aquest projecte ha estat elaborar una aplicació, un sistema xat o missatgeria instantània, que implementés tècniques criptogràfiques per a l'intercanvi segur d'informació punt per punt.

Monitoring procedures in environmental geochemistry and compositional data analysis theory

First discussion on compositional data analysis is attributable to Karl Pearson, in 1897. However, notwithstanding the recent developments on algebraic structure of the simplex, more than twenty years after Aitchison’s idea of log-transformations of closed data, scientific literature is again full of statistical treatments of this type of data by using traditional methodologies. This is particularly true in environmental geochemistry where besides the problem of the closure, the spatial structure (dependence) of the data have to be considered. In this work we propose the use of log-contrast values, obtained by asimplicial principal component analysis, as LQGLFDWRUV of given environmental conditions. The investigation of the log-constrast frequency distributions allows pointing out the statistical laws able togenerate the values and to govern their variability. The changes, if compared, for example, with the mean values of the random variables assumed as models, or other reference parameters, allow definingmonitors to be used to assess the extent of possible environmental contamination. Case study on running and ground waters from Chiavenna Valley (Northern Italy) by using Na+, K+, Ca2+, Mg2+, HCO3-, SO4 2- and Cl- concentrations will be illustrated

An axiomatization of the prekernel of nontransferable utility games

We characterize the prekernel of NTU games by means of consistency,converse consistency, and five axioms of the Nash type on bilateral problems.The intersection of the prekernel and the core is also characterized with thesame axioms over the class of games where the core is nonempty.

Les restes humanes del jaciment epipaleolític de la Balma de Guilanyà (Navés, Solsonès)

Les restes humanes deIs períodes epipaleolític i mesolític estan pobrament representades a la Península Iberica, tot i que existeixen dos jaciments mesolítics excepcional s a Muge, Portugal (Moita do Sebastiao i Cabe~o da Arruda), amb uns 67 individus, i un altre de recentment excavat a Oliva (El Collado, Valencia), on s'han trobat uns 15 individus. EIs primers estan datats entre 7.240 i 6.300 a.P. (Ferreira 1994: 664-674), mentre que el darrer té una datació de 7.640-7.570 a.P (Aparicio 1989). Ambdós jaciments es troben en zones properes a estuaris de rius o a la costa, la qual cosa permetia 1'explotació intensiva de recursos marins molt variats. Aquest tipus d' economia condicionava un tipus de vida força sedentaria i a més a més, va permetre un increment en la densitat de població, que hauria tingut lloc probablement entre el 8.000-7.000 a.e. (Ferreira 1994: 664-674). A Catalunya, s'han excavat fins ara pocs jaciments importants d'aquests periodes (Martín y Vaquer 1995: 35-73), tots d'ells en zones d'interior i corresponents presumiblement a grups petits de caçadors-recol·lectors, força diferents dels posteriors assentaments humans més grans com Muge i Oliva. De tots aquests jaciments, només a la Balma de Guilanya (Naves, Solsones) s'han trobat restes humanes que es puguin atribuir sense cap mena de dubte als nivells epipaleolítics.

Predictions of the MCMI-III personality disorders from NEO-PI-R domains and facets: Comparison between American and Spanish samples

Este estudio ex post facto analiza las relaciones entre las dimensiones y facetas del NEO-PI-R y los 14 trastornos de personalidad del MCMI-III en una muestra no clínica española (N = 674). Se exploran las diferencias y similitudes con los resul- tados de Dyce y O’Connor en una muestra americana con los mismos instrumentos. Como se esperaba, los análisis factoriales de facetas reteniendo cinco factores mostraron un modelo de relaciones muy similar entre ambas muestras, con un coeficiente de la congruencia total de 0,92, y coeficientes de congruencia de factor aceptables, salvo para el factor Apertura (0,68). En consonancia con las predicciones de Widiger y Widiger et al. los porcentajes de correlaciones significativas estaban alrededor de 60% en ambas muestras, y la mayoría coincidían. El análisis de regresión múltiple con dimensiones también reveló un gran parecido entre los resultados americanos y españoles, Neuroticismo fue el predictor más relacionado con los trastornos de personalidad. Se encontraron diferencias en las regresiones por facetas, aunque la varianza explicada fue prácticamente la misma que en las dimensiones. Se discute la validez transcultural y el valor predictivo del NEO-PI-R sobre los trastornos de personalidad del MCMI-III, junto con las ventajas relativas de las facetas sobre las dimensiones.

Personality and job stress: a comparison of direct effects on parenting

The impact of personality and job characteristics on parental rearing styles was compared in 353 employees. Hypotheses concerning the relationships between personality and job variables were formulated in accordance with findings in past research and the Belsky’s model (1984). Structural equation nested models showed that Aggression-hostility, Sociability and job Demand were predictive of Rejection and Emotional Warmth parenting styles, providing support for some of the hypothesized relationships. The findings suggest a well-balanced association of personality variables with both parenting styles: Aggression-Hostility was positively related to Rejection and negatively to Emotional Warmth, whereas Sociability was positively related to Emotional Warmth and negatively related to Rejection. Personality dimensions explained a higher amount of variance in observed parenting styles. However, a model that considered both, personality and job dimensions as antecedent variables of parenting was the best representation of observed data, as both systems play a role in the prediction of parenting behavior.