Performance of capillary columns for high-temperature gas chromatography

The developments in stationary-phase synthesis and capillary column technology have opened new perspectives in the analysis of high-molecular-weight compounds (600 daltons) and thermolabile organic compounds by high-temperature-high-resolution gas chromatography. This branch of high-resolution gas chromatography deals with analysis performed up to 390 degrees C oven temperature (with some applications going up to 420 degrees C and even a few applications to 450 degrees C maximum). The technique has been applied to many different fields of science (e.g., organic geochemistry, environmental chemistry, archeology, and natural product research). Apolar and medium-polar gum phases can now be operated at temperatures from 400 to 480 degrees C, but these higher temperatures are seldom used because of the thermostability of the material used to make the capillary tubing. This paper shows the performance of nine commercial high-temperature columns when used in routine applications.     

Large Eddy and Reynolds-Averaged Navier - Stokes Simulations of Turbulent Flow Over an Airfoil

A Large Eddy Simulation (LES) of turbulent flow over an airfoil near stall is performed. Results of the LES are compared with those of Reynolds-Averaged Navier-Stokes (RANS) simulations using two well-known turbulence models, namely the Baldwin-Lomax model and the Spalart-Allmaras model. The subgrid scale model used for the LES is the filtered structure function model. All simulations are performed using the same structured multi-block code. In order to reduce the CPU time, an implicit time stepping method is used for the LES. The purpose of this study is to show the possibilities and limitations of LES of complex flows associated with aeronautical applications using state of the art simulation techniques. Typical flow features are captured by the LES such as the adverse-pressure gradient and flow retardation. Visualization of instantaneous flow fields shows the typical streaky structures in the near-wall region.     

Theory and experiments on elastic band gaps

We study elastic band gaps in nonhomogeneous periodic finite media. The finite-difference time-domain method is used for the first time in the field of elastic band-gap materials. It is used to interpret experimental data for two-dimensional systems consisting of cylinders of fluids (Hg, air, and oil) inserted periodically in a finite slab of aluminum host. The method provides good convergence, can be applied to realistic finite composite slabs, even to composites with a huge contrast in the elastic parameters of their components, and describes well the experiments.     

Recurrence properties of sequences of integers

In order to study the recurrence of sequences of integers, we investigate their L2-exactness and Θ-Hartman property (Θ being a set of rational numbers). Two classes of sequences of integers are well studied, which are return times relative to a weakly mixing system and Bernoulli random sequences.