A flexible framework for defeasible logics

Logics for knowledge representation suffer from over-specialization: while each logic may provide an ideal representation formalism for some problems, it is less than optimal for others. A solution to this problem is to choose from several logics and, when necessary, combine the representations. In general, such an approach results in a very difficult problem of combination. However, if we can choose the logics from a uniform framework then the problem of combining them is greatly simplified. In this paper, we develop such a framework for defeasible logics. It supports all defeasible logics that satisfy a strong negation principle. We use logic meta-programs as the basis for the framework.Comment: Proceedings of 8th International Workshop on Non-Monotonic Reasoning, April 9-11, 2000, Breckenridge, Colorad

Black-Hole Solutions with Scalar Hair in Einstein-Scalar-Gauss-Bonnet Theories

In the context of the Einstein-scalar-Gauss-Bonnet theory, with a general coupling function between the scalar field and the quadratic Gauss-Bonnet term, we investigate the existence of regular black-hole solutions with scalar hair. Based on a previous theoretical analysis, that studied the evasion of the old and novel no-hair theorems, we consider a variety of forms for the coupling function (exponential, even and odd polynomial, inverse polynomial, and logarithmic) that, in conjunction with the profile of the scalar field, satisfy a basic constraint. Our numerical analysis then always leads to families of regular, asymptotically-flat black-hole solutions with non-trivial scalar hair. The solution for the scalar field and the profile of the corresponding energy-momentum tensor, depending on the value of the coupling constant, may exhibit a non-monotonic behaviour, an unusual feature that highlights the limitations of the existing no-hair theorems. We also determine and study in detail the scalar charge, horizon area and entropy of our solutions.Comment: PdfLatex file, 29 Pages, 18 figures, the analysis was extended to study the scalar charge, horizon area and entropy of our solutions, comments added, typos corrected, version to appear in Physical Review

Representation results for defeasible logic

The importance of transformations and normal forms in logic programming, and generally in computer science, is well documented. This paper investigates transformations and normal forms in the context of Defeasible Logic, a simple but efficient formalism for nonmonotonic reasoning based on rules and priorities. The transformations described in this paper have two main benefits: on one hand they can be used as a theoretical tool that leads to a deeper understanding of the formalism, and on the other hand they have been used in the development of an efficient implementation of defeasible logic.Comment: 30 pages, 1 figur

Quantum Zeno and anti-Zeno effects in the Friedrichs model

We analyze the short-time behavior of the survival probability in the frame of the Friedrichs model for different formfactors. We have shown that this probability is not necessary analytic at the time origin. The time when the quantum Zeno effect could be observed is found to be much smaller than usually estimated. We have also studied the anti-Zeno era and have estimated its duration.Comment: References added. Appendix B shortened. Discussions extende

An investigation into the epistemologies assumed by English language secondary education teachers in Greece and their impact on English language learners' collaborative construction of learning in web 2.0. settings: An exploratory case study

This study explores the emerging epistemologies of EFL language teachers in the context of Edmodo digital platform which is a web 2.0. tool in secondary education in Greece and the impact of these epistemologies on EFL students’ collaborative learning. In this thesis, a general picture of the current situation is depicted based on data obtained from the EFL teachers’ and students’ questionnaires, interviews and participant observations. The main goal of this thesis is to propose an alternative look to English language teaching which occurs with the incorporation of web 2.0. tools mainly as a means of urging EFL students to discover peers’-based learning. The findings indicate that the epistemologies assumed by the EFL teachers affect their teaching practices that are employed by them. It also reflects the conscious effort of the English language practitioners to move away from an autocratic, know it all stance, and focus on the learners as experts and legitimate holders of their reality. This entails a closer inspection of the learner-based reality which is best captured within the boundaries of Edmodo digital platform- based community whereby issues of immediate interests to the learners are accessed and analysed. There seems to be a desire on the part of the EFL teachers to forge an establishment of a learning community with the same concerns and a common goal. Also there seems to be a partial transformation of the role of the EFL practitioners to catalyse the reflection process, to contextualize matters of concerns and to forge a learning community in order to reach a consensual meaning that is gauged to their learners’ immediate needs. The findings raise implications for Language Learning Educational Policy in Greece, as well as the EFL teachers themselves

Critical Fluctuations at RHIC

On the basis of universal scaling properties, we claim that in Au+Au collisions at RHIC, the QCD critical point is within reach. The signal turns out to be an extended plateau of net baryons in rapidity with approximate height of the net-baryon rapidity density approximately 15 and a strong intermittency pattern with index s_2=1/6 in rapidity fluctuations. A window also exists, to reach the critical point at the SPS, especially in Si+Si collisions at maximal energy.Comment: 8 pages, 3 figure