Uniform payoff security and Nash equilibrium in metric games

We introduce a condition, uniform payoff security, for games with separable metric strategy spaces and payoffs bounded and measurable in players' strategies. We show that if any such metric game G is uniformly payoff secure, then its mixed extension G is payoff secure. We also establish that if a uniformly payoff secure metric game G has compact strategy spaces, and if its mixed extension G has reciprocally upper semicontinuous payoffs, then G has a Nash equilibrium in mixed strategies. We provide several economic examples of metric games satisfying uniform payoff security.Uniform payoff security, Nash equilibrium, discontinuous games, mixed extension.

Sound ranking algorithms for XML search

Ranking algorithms for XML should reflect the actual combined content and structure constraints of queries, while at the same time producing equal rankings for queries that are semantically equal. Ranking algorithms that produce different rankings for queries that are semantically equal are easily detected by tests on large databases: We call such algorithms not sound. We report the behavior of different approaches to ranking content-and-structure queries on pairs of queries for which we expect equal ranking results from the query semantics. We show that most of these approaches are not sound. Of the remaining approaches, only 3 adhere to the W3C XQuery Full-Text standard

Learning Approach, Thinking Style and Critical Inquiry: The Online Community

The study examined if a thematically designed online introductory psychology course set in a cooperative and collaborative learning environment led to deeper learning. Using the revised two-factor Study Process Questionnaire (R-SPQ-2F; Biggs, Kember & Leung, 2001), the study predicted peer and teacher guided asynchronous dialogue would lead to increasing students’ self-perceptions of deeper learning approaches (DA) and higher levels of thinking. Individual thinking style (ITS; Sternberg & Wagner, 1992) was presumed to be an important mediator on both student pre- and post-DA scores. It was also hypothesized that thinking styles would influence student perceptions towards participating in a learning community, as measured by the Classroom Community Scale (CCS; Rovai, 2002). Contrary to the hypotheses, thinking styles didn’t predict either pre- or post DA nor end of semester CCS scores. The two main hypotheses, premised on Vygotsky’s theory of social constructivism and post Vygotskian thinking on conceptual learning, demonstrated mixed results. The expected increase in self perceptions of deep learning and a predictive relationship between DA and CCS to reflect this contextualized learning were not found. While post DA scores weren’t significantly correlated with CCS, CCS was correlated with students’ perceptions of which types of discussions guided their learning. Qualitative evidence from the online dialogue demonstrated deeper, conceptual and applied understanding than students’ self-reports. What requires further study is whether students develop an explicit metacognitive understanding of how cooperative discussions aren’t an added burden, but rather, a means of constructing a deeper meaning and approach to learning

Thermal histories of the samples of two KOSI comet nucleus simulation experiments

Temperatures recorded during two KOSI comet nucleus simulation experiments strongly suggest that heat transport by vapor flow into the interior of the sample is very important. Two comet nucleus simulation experiments have been done by the KOSI team in a big space simulator. The thermal evolution of the sample during insolation and the results of simplified thermal evolution calculations are discussed. The observed thermal histories cannot be explained by a simple model with heat transferred by heat conduction at a constant conductivity, so a coupled heat and mass transfer problem was considered. The porous ice matrix was assumed to have a constant thermal conductivity and to be in thermal equilibrium with vapor in the pores, the internal pressure being the vapor pressure. The vapor was modelled as an ideal gas because, at the temperatures relevant to the problem, the mean free path length of the vapor molecules is large in comparison with the pore dimensions. The heat capacity at constant volume per unit mass of the two phase mixture was also assumed constant. The vapor was allowed to flow and transfer heat in response to an internal pressure gradient

Improved adhesive for cryogenic applications cures at room temperature

Adhesive cured at room temperature provides an effective adhesive bond over the range from room temperature down to the temperature of liquid hydrogen. The adhesive consists of one part of 200-mesh powdered nylon filler to two parts of an epoxy-polyamine resin