Magnetic field induced entropy change and magnetoelasticity in Ni-Mn-Ga alloys

The magnetocaloric effect that originates from the martensitic transition in the ferromagnetic Ni-Mn-Gashape-memory alloy is studied. We show that this effect is controlled by the magnetostructural coupling at boththe martensitic variant and magnetic domain length scales. A large entropy change induced by moderatemagnetic fields is obtained for alloys in which the magnetic moment of the two structural phases is not verydifferent. We also show that this entropy change is not associated with the entropy difference between themartensitic and the parent phase arising from the change in the crystallographic structure which has beenfound to be independent of the magnetic field within this range of fields.

Quantum critical effects in mean-field glassy systems

We consider the effects of quantum fluctuations in mean-field quantum spin-glass models with pairwise interactions. We examine the nature of the quantum glass transition at zero temperature in a transverse field. In models (such as the random orthogonal model) where the classical phase transition is discontinuous an analysis using the static approximation reveals that the transition becomes continuous at zero temperature.

Asymmetric Little spin-Glass model

We study the static properties of the Little model with asymmetric couplings. We show that the thermodynamics of this model coincides with that of the Sherrington-Kirkpatrick model, and we compute the main finite-size corrections to the difference of the free energy between these two models and to some clarifying order parameters. Our results agree with numerical simulations. Numerical results are presented for the symmetric Little model, which show that the same conclusions are also valid in this case.

Evidence of aging in spin glass mean-field models

We study numerically the out-of-equilibrium dynamics of the hypercubic cell spin glass in high dimensionalities. We obtain evidence of aging effects qualitatively similar both to experiments and to simulations of low-dimensional models. This suggests that the Sherrington-Kirkpatrick model as well as other mean-field finite connectivity lattices can be used to study these effects analytically.

Evidence of a critical time in constrained Kinetic Ising models

We study the relaxational dynamics of the one-spin facilitated Ising model introduced by Fredrickson and Andersen. We show the existence of a critical time which separates an initial regime in which the relaxation is exponentially fast and aging is absent from a regime in which relaxation becomes slow and aging effects are present. The presence of this fast exponential process and its associated critical time is in agreement with some recent experimental results on fragile glasses.

Republicanismo: el lugar de la virtud

No hay caracterización del republicanismo que no mencione la virtud cívica. Sin embargo, no siempre es clara la ubicación de la virtud en el entramado de la filosofía política republicana. Tomaré como punto de partida la reflexión de Rawls. Su temor es que la defensa de lo que la democracia necesita, la virtud cívica, ponga en peligro la libertad. Es lo que llamaré el «problema (de Rawls) con la virtud». Un problema que, a su parecer, compromete seriamente al republicanismo. Por mi parte, intentaré mostrar que, en realidad, se trata de un problema del liberalismo que apunta directamente a una bien conocida tensión entre los derechos y la democracia, cuya única «solución liberal» pasa por atrincherar los derechos «frente a la democracia», excluyendo el compromiso ciudadano. En la segunda parte mostraré que el problema es real, pero que no afecta a todos los republicanismos y argumentaré que «el problema de Rawls» afecta, fundamentalmente, a aquel republicanismo que hace de la «realización ciudadana» su objetivo, que busca, por así decir, maximizar la virtud. No sucede lo mismo con aquel otro que otorga a la virtud un carácter instrumental. En la parte final precisaré esa idea de republicanismo que otorga tanto a la virtud como a la democracia un papel instrumental en lo que realmente importa: la libertad.

Higiene sociologica

"Por un giro analítico en sociología" es algo más que una defensa de la sociología analítica. Es, entre otras cosas, un diagnóstico del estado de la disciplina. Un diagnóstico que, aunque cauteloso en las formas, resulta bastante pesimista, incluso sombrío, en su fondo, al menos en lo que atañe a la sociología de más relumbrón:"la ocurrencia, el chispazo momentáneo, la metáfora aparentemente brillante que no contribuye al análisis riguroso de los problemas del mundo actual en cuanto se apaga su brillo, o la producción alegre de etiquetas lingüísticas o conceptuales se han convertido, en demasiados casos, en el rasgo más señalado y públicamente visible del quehacer sociológico"

Roman amphora trade across the Straits of Gibraltar: An ancient 'anti-economic practice'?

Summary. Olive oil and fish products from the south of Hispania and North Africa played an important role in the Roman economy. The authors call attention to the asymmetrical distribution of archaeological data available on this subject, in particular the location of amphora kilns, and try to give an explanation, based on the evolution of European archaeology in the twentieth century.