Hemaspaandra et al. [1] proved that, for m > 0 and 0 < i < k 1: if i DIFFm( p k) is closed under complementation, then DIFFm( p k) = coDIFFm( p k). This sharply asymmetric result fails to apply to the case in which the hypothesis is weakened by allowing the i to be replaced by any class in its di erence hierarchy. We so extend the result by proving that, for s;m > 0 and 0 < i < k 1: if DIFFs( p...

This paper considers the propagation of waves on the edge of a stratospheric polar vortex, represented by a three-dimensional patch of uniform potential vorticity in a compressible quasigeostrophic system. Waves are initialized by perturbing the vortex from axisymmetry in the center of the vortex, and their subsequent upward and downward propagation is measured in terms of a nonlinear, pseudomo...

A problem that often arises in using abstraction is the generation of abstract states, called spurious states, that are—in the abstract space—reachable from some abstract image of a state s, but which have no corresponding state in the original space reachable from s. Spurious states can have a negative effect on pattern database sizes and heuristic quality. We formally define a property—the do...

Previous research has demonstrated abstract concepts associated with spatial location (e.g., God in the Heavens) could direct visual attention upward or downward, because thinking about the abstract concepts activates the corresponding vertical perceptual symbols. For self-concept, there are similar metaphors (e.g., "I am above others"). However, whether thinking about the self can induce visua...

In this paper we identify modal logics of some bimodal Kripke frames corresponding to geometrical structures. Each of these frames is a set of ‘geometrical’ objects with some natural accessibility relation plus the universal relation. For these logics we present finite axiom systems and prove completeness. We also show that all these logics have the finite model property and are PSPACE-complete...

Cognitive assessment in a clinical setting is generally made by pencil-and-paper tests, while computer-based tests enable the measurement and the extraction of additional performance indexes. Previous studies have demonstrated that in a research context exploration deficits occur also in patients without evidence of unilateral neglect at pencil-and-paper tests. The objective of this study is to...

Although the literature has identified both a self-enhancement and a self-improvement function of counterfactual thinking, most evidence points to situations in which the self-improvement function predominates. The current research spotlights a set of factors that increase the role of self-enhancement in counterfactual thinking. Threatening experiences such as chronic illness (Study 1) and the ...