The Complexity of Reasoning for Fragments of Default Logic

Default logic was introduced by Reiter in 1980. In 1992, Gottlob classified the complexity of the extension existence problem for propositional default logic as \SigmaPtwo-complete, and the complexity of the credulous and skeptical reasoning problem as SigmaP2-complete, resp. PiP2-complete. Additionally, he investigated restrictions on the default rules, i.e., semi-normal default rules. Selman made in 1992 a similar approach with disjunction-free and unary default rules. In this paper we systematically restrict the set of allowed propositional connectives. We give a complete complexity classification for all sets of Boolean functions in the meaning of Post's lattice for all three common decision problems for propositional default logic. We show that the complexity is a hexachotomy (SigmaP2-, DeltaP2-, NP-, P-, NL-complete, trivial) for the extension existence problem, while for the credulous and skeptical reasoning problem we obtain similar classifications without trivial cases.Comment: Corrected versio

Resonance approximation and charge loading/unloading in adiabatic quantum pumping

Quantum pumping through mesoscopic quantum dots is known to be enhanced by resonant transmission. The pumped charge is close to an integer number of electrons when the pumping contour surrounds a resonance, but the transmission remains small on the contour. For non-interacting electrons, we give a quantitative account of the detailed exchange of electrons between the dot and the leads (to the electron reservoirs) during a pumping cycle. Near isolated distinct resonances, we use approximate Breit-Wigner expressions for the dot's Green function to discuss the loading/unloading picture of the pumping: the fractional charge exchanged between the dot and each lead through a single resonance point is related to the relative couplings of the dot and the leads at this resonance. If each resonance point along the pumping contour is dominated by the coupling to a single lead (which also implies a very small transmission), then the crossing of each such resonance results in a single electron exchange between the dot and that lead, ending up with a net quantized charge. When the resonance approximation is valid, the fractional charges can also be extracted from the peaks of the transmissions between the various leads.Comment: 10 pages, 4 figure

Analysis and Reuse of Plots Using Similarity and Analogy

Abstract: A plot is a partially ordered set of events. Plot analysis is a relevant source of knowledge about the agents behavior when accessing data stored in the database. It relies on logical logs which register the actions of individual agents. This paper proposes techniques to analyze and reuse plots based on the concepts of similarity and analogy, borrowed from cognitive science and linguistics. The concept of similarity is applied to organize plots as a library, and to explore the reuse of plots in the same domain. By contrast, the concept of analogy helps reuse plots across different domains. The techniques proposed in this paper find applications in areas such as computer games and emergency response information systems, as well as some traditional business applications

Un capítulo recuperado en la historia de la Universidad de Barcelona: el programa de cursos para el año 1936-1937

Podeu consultar el document original sobre el que es basa el treball en català a: http://hdl.handle.net/2445/33756 i en castellà a: http://hdl.handle.net/2445/33755Afortunadamente, en los últimos años la bibliografia sobre la historia de la Universidad de Barcelona (y en especial del periodo de la autonomía universitaria, la guerra civil y la posguerra) se ha ido enriqueciendo con importantes aportaciones, cubriendo asi un área fundamental para comprender nuestro presente y poder encarar mejor nuestro futuro. Estos estudios establecen análisis de conjunto absolutamente necesarios para empezar a desbrozar el terreno, pero son necesarias también investigaciones parciales, más concretas, que vayan arrojando luz sobre aspectos poco conocidos o que todavía permanecen por estudiar en nuestros archivos

Designing Security Requirements Models through Planning

The quest for designing secure and trusted software has led to refined Software Engineering methodologies that rely on tools to support the design process. Automated reasoning mechanisms for requirements and software verification are by now a well-accepted part of the design process, and model driven architectures support the automation of the refinement process. We claim that we can further push the envelope towards the automatic exploration and selection among design alternatives and show that this is concretely possible for Secure Tropos, a requirements engineering methodology that addresses security and trust concerns. In Secure Tropos, a design consists of a network of actors (agents, positions or roles) with delegation/permission dependencies among them. Accordingly, the generation of design alternatives can be accomplished by a planner which is given as input a set of actors and goals and generates alternative multiagent plans to fulfill all given goals.We validate our claim with a case study using a state-of-the-art planner

Magnetic anisotropy and magnetization reversal of La0.67Sr0.33MnO3 thin films on SrTiO3(110)

The magnetic behavior of La 0.67 Sr 0.33 MnO 3 (LSMO) filmsgrown on SrTiO 3 (110) substrates was studied. In-plane uniaxial magnetic anisotropy with the easy axis aligned with the [001] lattice direction was observed, together with an out-of-plane component. This is explained by the crystal structure of the films, which shows a tilt of the (001) planes. This tilt creates a long body diagonal which forces the easy axis out-of-plane and results in magnetic domain formation. The domain size is estimated at 500 nm. The switching behavior of the magnetization is well described by a two-phase model which takes both coherent rotation and domain wall motion into account. These results are of importance for the application of LSMO in tunnel magnetoresistance devices, where the (110) orientation is preferred because of the reduction in the dead layer in this directio