Relationship-based access control: its expression and enforcement through hybrid logic

Access control policy is typically de ned in terms of attributes, but in many applications it is more natural to de- ne permissions in terms of relationships that resources, systems, and contexts may enjoy. The paradigm of relationshipbased access control has been proposed to address this issue, and modal logic has been used as a technical foundation. We argue here that hybrid logic { a natural and wellestablished extension of modal logic { addresses limitations in the ability of modal logic to express certain relationships. Also, hybrid logic has advantages in the ability to e ciently compute policy decisions relative to a relationship graph. We identify a fragment of hybrid logic to be used for expressing relationship-based access-control policies, show that this fragment supports important policy idioms, and study its expressiveness. We also capture the previously studied notion of relational policies in a static type system. Finally, we point out that use of our hybrid logic removes an exponential penalty in existing attempts of specifying complex relationships such as \at least three friends"

High volume ergonomic simulation of chairs

To understand what makes a chair comfortable or practical we need to test a large number of chairs, both good and bad. Due to the numbers involved we cannot achieve this with physical testing. Instead we use simpli ed ergonomic simulations. The sim- ulations presented here produce pressure maps within the range given the literature, along with several other measures of comfort and practicality. This was done sub- stantially faster than examples in the literature, permitting collection of thousands of results

Heavy Schistosomiasis Associated With Poor Short-Term Memory and Slower Reaction Times in Tanzania Schoolchildren

Cross-sectional studies of the relationship between helminth infection and cognitive function can be informative in ways that treatment studies cannot. However, interpretation of results of many previous studies has been complicated by the failure to control for many potentially confounding variables.We gave Tanzanian schoolchildren aged 9±14 a battery of 11 cognitive and three educational tests and\ud assessed their level of helminth infection. We also took measurements of an extensive range of potentially confounding or mediating factors such as socioeconomic and educational factors, anthropometric and other biomedical measures. A total of 272 children were moderately or heavily\ud infected with Schistosoma haematobium, hookworm or both helminth species and 117 were uninfected with either species. Multiple regression analyses, controlling for all confounding and mediating variables, revealed that children with a heavy S. haematobium infection had signi®cantly lower scores than uninfected children on two tests of verbal short-term memory and two reaction time tasks. In one of\ud these tests the effect was greatest for children with poor nutritional status. There was no association between infection and educational achievement, nor between moderate infection with either species of helminth and performance on the cognitive tests. We conclude that children with heavy worm burdens and poor nutritional status are most likely to suffer cognitive impairment, and the domains of verbal\ud short-term memory and speed of information processing are those most likely to be affected