El presumpte racionalisme de Ramon Llull

Abstract not availabl

La doctrina del Maestro Ramon Llull sobre la demostración de los dogmas, juzgada a la luz de la Historia y de la teología

Abstract not availabl

Dissociation of high-pressure solid molecular hydrogen: Quantum Monte Carlo and anharmonic vibrational study

A theoretical study is reported of the molecular-to-atomic transition in solid hydrogen at high pressure. We use the diffusion quantum Monte Carlo method to calculate the static lattice energies of the competing phases and a density-functional-theory-based vibrational self-consistent field method to calculate anharmonic vibrational properties. We find a small but significant contribution to the vibrational energy from anharmonicity. A transition from the molecular Cmca-12 direct to the atomic I4_1/amd phase is found at 374 GPa. The vibrational contribution lowers the transition pressure by 91 GPa. The dissociation pressure is not very sensitive to the isotopic composition. Our results suggest that quantum melting occurs at finite temperature.Comment: Accepted for publication by Phys. Rev. Let

Antiferroelectric Topological Insulators in Orthorhombic AMgBi Compounds (A=Li, Na, K).

We introduce antiferroelectric topological insulators as a new class of functional materials in which an electric field can be used to control topological order and induce topological phase transitions. Using first principles methods, we predict that several alkali-MgBi orthorhombic members of an ABC family of compounds are antiferroelectric topological insulators. We also show that epitaxial strain and hydrostatic pressure can be used to tune the topological order and the band gap of these ABC compounds. Antiferroelectric topological insulators could enable precise control of topology using electric fields, enhancing the applicability of topological materials in electronics and spintronics

On the integrability of Wilson loops in AdS_5 x S^5: Some periodic ansatze

Wilson loops are calculated within the AdS/CFT correspondence by finding a classical solution to the string equations of motion in AdS_5 x S^5 and evaluating its action. An important fact is that this sigma-model used to evaluate the Wilson loops is integrable, a feature that has gained relevance through the study of spinning strings carrying large quantum numbers and spin-chains. We apply the same techniques used to solve the equations for spinning strings to find the minimal surfaces describing a wide class of Wilson loops. We focus on different cases with periodic boundary conditions on the AdS_5 and S^5 factors and find a rich array of solutions. We examine the different phases that appear in the problem and comment on the applicability of integrability to the general problem.Comment: LaTex, 49 pages, 8 figure

La cultura talayótica una sociedad de la edad del hierro en la periferia de la colonización fenicia

En el presente trabajo se razona una crítica sobre las bases cronológicas en las que se venían fundamentando los orígenes de la cultura talayótica balear. A partir de ello se acepta un nuevo marco cronológico que ya se había venido postulando en los últimos años por diferentes equipos de investigación. La sincronía que se observa entre los inicios y primer desarrollo de la cultura talayótica, la llegada del hierro a las islas, así como los cambios sustanciales que se observan en las redes de intercambio ultramarino en el Mediterráneo central y occidental, que pasan a estar monopolizadas por los comerciantes fenicios, permite sugerir que también la cristalización y primera evolución de la sociedad talayótica se inserta en este contexto geohistórico, con sus evidentes y conocidas peculiaridades. Señalando, no obstante, que las causas últimas de los orígenes son endógenas y se venían gestando algún tiempo antes en el seno de las comunidades isleñas del Bronce Naviforme. Se propone igualmente una secuencia de modelos de intecambio entre los agentes que controlan las navegaciones el comercio a larga distancia, los fenicios, y púnicos ebusitanos después, y las comunidades talayóticas de Mallorca y Menorca. No se abordan en el presente escrito asuntos relacionados con la tipología y función de la arquitectura ciclópea turriforme, ni otros relacionados con la cultura material cuyo conocimiento ha sido actualizado, renovado y difundido en la literatura arqueológica de los últimos años.The Talayotic culture. An Iron Age society in the periphery of the phoenician colonization. The present study explains a critique about the chronological bases on which the origins of the Talayotic culture of the Balearic Islands have been grounded. From this, a new chronological framework is accepted, which has already been postulated by various research teams in recent years. The synchronicity that is seen between the Talayotic culture’s beginnings and its initial development, and the arrival of iron on the islands, as well as the substantial changes seen in the network of overseas trade in the Central and Western Mediterranean, which came to be monopolised by Phoenician merchants, permits us to suggest that the crystallisation and evolution of the Talayotic society, with its clear and well-known peculiarities, are also included within this geohistoric context. Indications of the Talayotic culture’s ultimate causes, however, point to endogenous origins and a period of prior gestation in the midst of Balearic communities of the Naviform Bronze Period. A sequence is also proposed for the models of trade among the agents that controlled long-distance maritime commerce, that is, among the Phoenicians, the Punic peoples of Ibiza afterwards, and the Talayotic communities of Majorca and Minorca. Not touched upon in the present paper are matters related to the typology and function of Cyclopean turriform architecture, nor those related to the material culture whose understanding has been re-assessed, up dated, and disseminated in the archaeological literature of recent years

Goedel's Universe in a Supertube Shroud

We demonstrate that certain supersymmetric Goedel-like universe solutions of supergravity are not solutions of string theory. This is achieved by realizing that supertubes are BPS states in these spaces, and under certain conditions, when wrapping closed timelike curves, some world-volume modes develop negative kinetic terms. Since these universes are homogeneous, this instability takes place everywhere in space-time. We also construct a family of supergravity solutions which locally look like the Goedel universe inside a domain wall made out of supertubes, but have very different asymptotic structure. One can adjust the volume inside the domain wall so there will be no closed timelike curves, and then those spaces seem like perfectly good string backgrounds.Comment: 4 pages, revtex double column. v2: corrected the metric outside the domain wal