Delta: An object-oriented finite element code architecture for massively parallel computers

Delta is an object-oriented code architecture based on the finite element method which enables simulation of a wide range of engineering mechanics problems in a parallel processing environment. Written in C{sup ++}, Delta is a natural framework for algorithm development and for research involving coupling of mechanics from different Engineering Science disciplines. To enhance flexibility and encourage code reuse, the architecture provides a clean separation of the major aspects of finite element programming. Spatial discretization, temporal discretization, and the solution of linear and nonlinear systems of equations are each implemented separately, independent from the governing field equations. Other attractive features of the Delta architecture include support for constitutive models with internal variables, reusable ``matrix-free`` equation solvers, and support for region-to-region variations in the governing equations and the active degrees of freedom. A demonstration code built from the Delta architecture has been used in two-dimensional and three-dimensional simulations involving dynamic and quasi-static solid mechanics, transient and steady heat transport, and flow in porous media

Interactions Among Fire, Insects and Pathogens in Coniferous Forests of the Interior Western United States and Canada

1 Natural and recurring disturbances caused by fire, native forest insects and pathogens have interacted for millennia to create and maintain forests dominated by seral or pioneering species of conifers in the interior regions of the western United States and Canada. 2 Changes in fire suppression and other factors in the last century have altered the species composition and increased the density of trees in many western forests, leading to concomitant changes in how these three disturbance agents interact. 3 Two- and three-way interactions are reviewed that involve fire, insects and pathogens in these forests, including fire-induced pathogen infection and insect attack, the effects of tree mortality from insects and diseases on fuel accumulation, and efforts to model these interactions. 4 The emerging concern is highlighted regarding how the amount and distribution of bark beetle-caused tree mortality will be affected by large-scale restoration of these fire-adapted forest ecosystems via prescribed fire. 5 The effects of fire on soil insects and pathogens, and on biodiversity of ground-dwelling arthropods, are examined. 6 The effects of fire suppression on forest susceptibility to insects and pathogens, are discussed, as is the use of prescribed fire to control forest pests

Is income inequality a determinant of population health? Part 1:A systematic review

This article reviews 98 aggregate and multilevel studies examining the associations between income inequality and health. Overall, there seems to be little support for the idea that income inequality is a major, generalizable determinant of population health differences within or between rich countries. Income inequality may, however, directly influence some health outcomes, such as homicide in some contexts. The strongest evidence for direct health effects is among states in the United States, but even that is somewhat mixed. Despite little support for a direct effect of income inequality on health per se, reducing income inequality by raising the incomes of the most disadvantaged will improve their health, help reduce health inequalities, and generally improve population health