Multiple Wavelength Extinction Technique for Particle Characterization in Dense Particle Clouds

In utilizing the advantages of extinction measurements in micron and especially submicron particle characterization, the properties of a multiple wavelength extinction technique have been the subject of extended theoretical studies. Furthermore, an experimental set-up was designed which provides high flexibility owing to its modular design. The performance of the technique described is demonstrated by a large variety of applications in aerosol and combustion research and in large-scale industrial systems. It was found to be a reliable tool in characterizing dense particulate systems.     

Essentially optimal explicit Runge–Kutta methods with application to hyperbolic–parabolic equations

Optimal explicit Runge–Kutta methods consider more stages in order to include a particular spectrum in their stability domain and thus reduce time-step restrictions. This idea, so far used mostly for real-line spectra, is generalized to more general spectra in the form of a thin region. In thin regions the eigenvalues may extend away from the real axis into the imaginary plane. We give a direct characterization of optimal stability polynomials containing a maximal thin region and calculate these polynomials for various cases. Semi-discretizations of hyperbolic–parabolic equations are a relevant application which exhibit a thin region spectrum. As a model, linear, scalar advection–diffusion is investigated. The second-order-stabilized explicit Runge–Kutta methods derived from the stability polynomials are applied to advection–diffusion and compressible, viscous fluid dynamics in numerical experiments. Due to the stabilization the time step can be controlled solely from the hyperbolic CFL condition even in the presence of viscous fluxes.