Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Investigations to improve and assess the accuracy of computational fluid dynamic based explosion models

A summary is given of part of the CEC co-sponsored project MERGE (Modelling and Experimental Research into Gas Explosions). The objective of this part of the project was to provide improved Computational Fluid Dynamic explosion models with the potential for use in hazard assessments. Five organisations with substantial experience in both theoretical and experimental explosion modelling contributed to this model assessment study; British Gas, Christian Michelsen Institute, Imperial College, Telemark Technological Research and Development Centre and TNO Prins Maurits Laboratory. The theoretical and numerical basis of the models are described. Results are given of a comparison exercise of model predictions against calculations which were chosen to test the accuracy of the various physical sub-models embodied within the overall explosion model. The development phase of the study is also described in which further extensions to the models were made to provide the best achievable agreement with small- and medium-scale experiments also conducted as part of the project. The models were finally used to simulate large-scale explosion experiments prior to the experiments being conducted. The overall capabilities of the models are reviewed and areas of uncertainty in the physics highlighted. A summary is given of part of the CEC co-sponsored project MERGE (Modelling and Experimental Research into Gas Explosions). The objective of this part of the project was to provide improved Computational Fluid Dynamic explosion models with the potential for use in hazard assessments. Five organisations with substantial experience in both theoretical and experimental explosion modelling contributed to this model assessment study; British Gas, Christian Michelsen Institute, Imperial College, Telemark Technological Research and Development Centre and TNO Prins Maurits Laboratory. The theoretical and numerical basis of the models are described. Results are given of a comparison exercise of model predictions against calculations which were chosen to test the accuracy of the various physical sub-models embodied within the overall explosion model. The development phase of the study is also described in which further extensions to the models were made to provide the best achievable agreement with small-and medium-scale experiments also conducted as part of the project. The models were finally used to simulate large-scale explosion experiments prior to the experiments being conducted. The overall capabilities of the models are reviewed and areas of uncertainty in the physics highlighted

GasTurbnLab: a multidisciplinary problem solving environment for gas turbine engine design on a network of nonhomogeneous machines

Gas turbine engines are very complex (with 20-40,000 parts) and have extreme operating conditions. The important physical phenomena take place on scales from 10-100 microns to meters. A complete and accurate dynamic simulation of an entire engine is enormously demanding. Designing a complex system, like a gas turbine engine, will require fast, accurate simulations of computational models from multiple engineering disciplines along with sophisticated optimization techniques to help guide the design process. In this paper, we describe the architecture of an agent-based software framework for the simulation of various aspects of a gas turbine engine, utilizing a "network" of collaborating numerical objects through a set of interfaces among the engine parts. Moreover, we present its implementation using the Grasshopper agent middleware and provide simulation results that show the feasibility of the computational paradigm implemented. (C) 2002 Published by Elsevier Science B.V