Calculation of turbulent fluid flow and heat transfer in ducts by a full Reynolds stress model

A computational method has been developed to predict the turbulent Reynolds stresses and turbulent heat fluxes in ducts by different turbulence models. The turbulent Reynolds stresses and other turbulent flow quantities are predicted with a full Reynolds stress model (RSM). The turbulent heat fluxes are modelled by a SED concept, the GGDH and the WET methods. Two wall functions are used, one for the velocity field and one for the temperature field. All the models are implemented for an arbitrary three‐dimensional channel. Fully developed condition is achieved by imposing cyclic boundary conditions in the main flow direction. The numerical approach is based on the finite volume technique with a non‐staggered grid arrangement. The pressure–velocity coupling is handled by using the SIMPLEC‐algorithm. The convective terms are treated by the van Leer scheme while the diffusive terms are handled by the central‐difference scheme. The hybrid scheme is used for solving the ε equation. The secondary flow generation using the RSM model is compared with a non‐linear k–ε model (non‐linear eddy viscosity model). The overall comparison between the models is presented in terms of the friction factor and Nusselt number. Copyright © 2003 John Wiley & Sons, Ltd.     

Trace metal determinations in estuarine waters by electrothermal atomic absorption spectrometry after extraction of dithiocarbamate complexes into freon

Cadmium, copper, iron, lead, nickel and zinc are determined. The dithiocarbamate complexes of the metals are extracted into Freon-TF and back-extracted into dilute nitric acid solution. Portions of the back-extracts are injected into a graphite furnace. The method gives complete separation from the matrix irrespective of salinity. It is therefore useful throughout the full salinity range of an estuary, 0–35‰.The effect of high iron concentrations on the extraction is eliminated by using a mixed acetate buffercomplexing agent solution.     

Spectrum of lattice gauge theories with fermions from a 1/d expansion at strong coupling

We study the strong coupling limit of U(N) or SU(N) gauge theories with fermions on a lattice. The integration over the gauge and fermion degrees of freedom is performed by analytic methods, leading to a partition function in terms of localized meson and baryon fields. A method for deriving a systematic expansion in the inverse of the space-time dimension of the corresponding Green functions is developed. It is applied to the study of spontaneous breakdown of chiral symmetry, which occurs for any U(N) or SU(N) theory with fermions in the fundamental representation. Meson and baryon spectra are then computed, and found to be in close agreement with those obtained by numerical methods at finite coupling. The pion decay constant is estimated.     

Transition moment directions of some important in-plane vibrations of uracil,thymine and cytosine. A fixed partial charge model calculation

Transition moment directions for the double-bond region vibrations of uracil, thymine and cytosine are calculated using the fixed partial charge model approximation. The coupling between the two carbonyl bonds and the carbon—carbon double bond in uracil and thymine is sensitive to the choice of the corresponding stretching force constants. The transition moment directions are correspondingly changed, thus, in principle, enabling the quantitative determination of coupling between the vibrations from linear dichroism measurements.     

Determination of ammonia in air and aqueous samples with a gas-sensitive semiconductor capacitor

The properties of a new type of ammonia gas-sensitive semiconductor capacitor are described. The sensor is based on a palladium MOS field-effect capacitor with a thin layer (3 nm) of iridium surrounding the palladium gate. The lower limit of detection for ammonia in air is 1 ppm (0.59 mg kg^?1). The analytical characteristics and temperature-dependence of the sensor in measurements of ammonia in air are evaluated. Ammonia in aqueous solutions is determined by the use of a continuous flow system utilizing a gaspermeable membrane in combination with the sensor. The calibration plot of the voltage drop of the capacitor vs. ammonia concentration in 150-μl samples is linear in the concentration range 0.2 × 10^?6–5 × 10^?5 M. Ammonia is determined in rain and river water as well as in whole blood and blood serum; 15 samples per hour can be assayed. Analytical recovery studies and the selectivity properties of the system are described and discussed. Finally, the properties of the flow-through system in continuous monitoring are described.     

Die Anzahl von Lösungen gewisser diophantischer Gleichungen

Ohne Zusammenfassung     

Zur Axiomatik endlicher Gruppen

Ohne Zusammenfassung