Large Eddy Simulation of a Turbulent Nonpremixed Jet Flame Using a Finite-Rate Chemistry Model

Large eddy simulation (LES) is conducted of a turbulent piloted nonpremixed methane jet flame. This flame has been studied experimentally at Sandia National Laboratories. The subgrid scale (SGS) closure in LES is based on the scalar filtered mass density function (SFMDF) methodology. The SFMDF is essentially the mass weighted probability density function (PDF) of the SGS scalar quantities. The SFMDF is obtained from an exact transport equation which provides a closed form for the chemical reaction effects. The unclosed terms in this equation are modeled by a set of stochastic differential equations (SDEs). The SDEs are solved by a hybrid finite-difference/Lagrangian Monte Carlo procedure. This flame exhibits little local extinction. In previous work, the instantaneous flame composition was related to the mixture fraction based on the flamelet model at low strain rates. In the present work, this assumption is relaxed, and a direct solver is employed for finite-rate chemistry. The results via this method agree favorably with those obtained experimentally. The end result is an accurate and affordable method for the LES of realistic turbulent flames

Studies of the evolution of the x ray emission of clusters of galaxies

The x ray luminosity function of clusters of galaxies was determined at different cosmic epoches using data from the Einstein Observatory Extended Medium Survey. The sample consisted of 67 x ray selected clusters that were grouped into three redshift shells. Evolution was detected in the x ray properties of clusters. The present volume density of high luminosity clusters was found to be greater than it was in the past. This result is the first convincing evidence for evolution in the x ray properties of clusters. Investigations into the constraints provided by these data on various Cold Dark Matter models are underway

Environmental Resource Management in Borderlands: Evolution from Competing Interests to Common Aversions

Great enthusiasm is attached to the emergence of cross-border regions (CBRs) as a new institutional arrangement for dealing with local cross-border environmental resource management and other issues that remain too distant from national capitals and/or too expensive to be addressed in the traditional topocraticmanner requiring instead local adhocratic methods. This study briefly discusses the perceived value of CBRs and necessary and sufficient conditions for the successful and sustainable development of such places. Then, assuming that necessary conditions can be met, the study investigates an intriguing hypothesis concerning the catalyzing of sustainable consensus for cross-border resource management based on a game theoretical approach that employs the use of dilemma of common aversion rather than the more traditional dilemma of competing common interests. Using this lens to investigate a series of events on the Pacific northwestern Canadian-American border in a part of the Fraser Lowland, we look for evidence of the emergence of an active and sustainable CBR to address local trans-border resource management issues. Although our micro-level scale fails to conclusively demonstrate such evidence, it does demonstrate the value of using this approach and suggests a number of avenues for further research

The growth of a Super Stable Heap : an experimental and numerical study

We report experimental and numerical results on the growth of a super stable heap (SSH). Such a regime appears for flows in a thin channel and for high flow rate : the flow occurs atop a nearly static heap whose angle is stabilized by the flowing layer at its top and the side wall friction. The growth of the static heap is investigated in this paper. A theoretical analysis inspired by the BRCE formalism predicts the evolution of the growth process, which is confirmed by both experiments and numerical simulations. The model allows us to link the characteristic time of the growth to the exchange rate between the "moving" and "static" grains. We show that this rate is proportional to the height of the flowing layer even for thick flows. The study of upstream traveling waves sheds new light on the BCRE model

‘School Streets’ and the Adaptation of London’s State-Led Tactical Urbanism During Covid-19

During the Covid-19 pandemic, London rapidly expanded its scheme of temporary School Streets closures. This represented an acceleration of pre-existing tendencies in the city towards using the methods of ‘Tactical Urbanism.’ Through a document review and a series of interviews with practitioners, this case study explores the varied ways in which different levels of government acted ‘tactically’ in the implementation London’s Covid-19 School Streets. It also considers the way this example of a state-led scheme intersects with debates around the concept of Tactical Urbanism and its increasing adoption by local and municipal governments