Flamelet LES of a swirl-stabilized multi-stream pulverized coal burner in air and oxy-fuel atmospheres with pollutant formation

A large-eddy simulation of a swirl-stabilized multi-stream laboratory-scale pulverized coal burner designed specifically for oxy-fuel investigation is conducted using a three-mixture-fraction flamelet model, in which both NO_x and SO_x emissions are considered. The simulation results are compared to those in an air atmosphere and the available experimental data. The flame structures and pollutant formation mechanisms are analyzed in detail. The results show that the oxy-coal flame is narrower in the radial direction compared to the air-coal flame. Further, the particle clustering phenomenon can be observed in the oxy-fuel atmosphere. The distributions of the thermo-chemical quantities in different conditions are significantly different. For pollutant formation, the results show that NO is mainly formed around the quarl zone in an oxy-fuel atmosphere, while a large amount of NO is formed in the far downstream region in an air atmosphere. Although the instantaneous distributions of SO_x are qualitatively similar in different conditions, they are quantitatively different due to the different oxygen partial pressure in the air and oxy-fuel atmospheres.     

Diffusive stability for periodic metric graphs

We consider a nonlinear diffusion equation on an infinite periodic metric graph. We prove that the terms which are irrelevant w.r.t. linear diffusion on the real line are irrelevant w.r.t. linear diffusion on the periodic metric graph, too. The proof is based on L¹‐ estimates combined with Bloch wave analysis for periodic metric graphs.     

Facile synthesis of phenyl-rich functional siloxanes from simple silanes

Phenyl-rich silicone polymers are used for their excellent thermal properties and high refractive indices. Traditional syntheses of these polymers utilize cationic or anionic equilibration, which limits the molecular weights that can be achieved due, in part, to the coproduction of cyclic monomers that must be removed. Kinetically controlled processes may reduce the impact of these limitations, but require high temperatures, alkyllithium initiators and an inert atmosphere; precise structures are difficult to access. The Piers-Rubinsztajn reaction, combined with hydrolysis, allows the synthesis of highly ordered, Si-H terminated, phenyl-rich silicone homo- and copolymers comprised of phenylmethyl, diphenyl and, dimethylsilicone monomers. The processes are mild and permit a high level of structural control, including alternating copolymers with different levels of phenyl content (Ph/Si = 0.3–1.5) with molecular weights up to ~100 kDa. Yet higher molecular weights could be achieved—M_n up to 300 kDa—when phenyl-rich siloxanes were incorporated into block copolymers with dimethylsilicones (Ph/Si = 0.4). Unlike kinetic processes in which cyclic byproducts are formed by redistribution or backbiting (particularly at high conversion), in this process cyclics form near the onset of the reaction and only with low molecular weight starting materials (< 4 siloxane units).     

Investigation of acceptance simulated annealing — A simplified approach to adaptive cooling schedules

Simulated annealing is the classic physical optimization algorithm, which has been applied to a large variety of problems for many years. Over time, several adaptive mechanisms for decreasing the temperature and thus controlling the acceptance of deteriorations have been developed, based on the measurement of the mean value and the variance of the energy. Here we propose a new simplified approach in which we consider the probability of accepting deteriorations as the main control parameter and derive the temperature by averaging over the last few deteriorations stored in a memory. We present results for the traveling salesman problem and demonstrate, how the amount of data retained influences both the cooling schedule and the quality of the results.     

TDPAC studies of the iron–molybdenum cofactor in nitrogenase

The uptake and the processing of molybdenum in nitrogen fixing bacteria was studied applying the TDPAC-technique with radioactive ⁹⁹Mo. The observation of the nuclear quadrupole frequencies allowed a ‘finger-printing’ of the characteristic binding states in three bacteria species. The measurements have been carried out with intact cells and with the isolated proteins. In one bacterium a molybdenum storage protein was identified. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chaotic actions of topological semigroups

In this paper we propose and explore a general notion of chaos in the abstract context of continuous actions of topological semigroups and show that any chaotic action on a Hausdorff uniform space is sensitive to initial conditions.     

Coherent Vortex Simulation of weakly compressible turbulent mixing layers using adaptive multiresolution methods

An adaptive mulitresolution method based on a second-order finite volume discretization is presented for solving the three-dimensional compressible Navier–Stokes equations in Cartesian geometry. The explicit time discretization is of second-order and for flux evaluation a 2–4 Mac Cormack scheme is used. Coherent Vortex Simulations (CVS) are performed by decomposing the flow variables into coherent and incoherent contributions. The coherent part is computed deterministically on a locally refined grid using the adaptive multiresolution method while the influence of the incoherent part is neglected to model turbulent dissipation. The computational efficiency of this approach in terms of memory and CPU time compression is illustrated for turbulent mixing layers in the weakly compressible regime and for Reynolds numbers based on the mixing layer thickness between 50 and 200. Comparisons with direct numerical simulations allow to assess the precision and efficiency of CVS.