3,836 research outputs found
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
The resonance spectrum of the cusp map in the space of analytic functions
We prove that the Frobenius--Perron operator of the cusp map
, (which is an approximation of the
Poincar\'e section of the Lorenz attractor) has no analytic eigenfunctions
corresponding to eigenvalues different from 0 and 1. We also prove that for any
the spectrum of in the Hardy space in the disk
\{z\in\C:|z-q|<1+q\} is the union of the segment and some finite or
countably infinite set of isolated eigenvalues of finite multiplicity.Comment: Submitted to JMP; The description of the spectrum in some Hardy
spaces is adde
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
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