Mössbauer studies of the superconducting cobalt/nickel-doped BaFe2As2. Whither go the injected electron(s)?

Mössbauer studies of cobalt- and nickel-doped BaFe(2)As(2) show that the s-electron density at the (57)Fe nuclei, as measured by the isomer shift, is the same as that for the parent BaFe(2)As(2). Apparently, the electron population of the d shell, which shields the s-electron density at the nuclei, remains unchanged. We invoke the involvement of p-orbital hybridization with the d orbital in Fe-As bonding. Furthermore, the shrinkage of the lattice on substitution enhances the As-As sp hybridization, providing a path for the migration of additional electrons. The proposed mechanism is consistent with Hall coefficient and thermoelectric effect measurements.

A mathematical model of weight change with adaptation.

As obesity and its related health problems grow around the world, efforts to control and manage weight is increasing in importance. It is well known that altering and maintaining weight is problematic and this has led to specific studies trying to determine the cause of the difficulty. Recent research has identified that the body reacts to forced weight change by adapting individual total energy expenditure. Key factors are an adaptation of resting metabolic rate, non-exercise activity thermogenesis and dietary induced thermogenesis. We develop a differential equation model based on the first law of thermodynamics that incorporates all three adjustments along with natural age related reduction of the resting metabolic rate. Forward time simulations of the model compare well with mean data in both overfeeding and calorie restriction studies.

Modeling bubbles and droplets in magnetic fluids.

We develop, test and apply a volume of fluid (VOF) type code for the direct numerical simulation of two-fluid configurations of magnetic fluids with dynamic interfaces. Equilibrium magnetization and linear magnetic material are assumed and uniform imposed magnetic fields are considered, although extensions to nonlinear materials and to fields with spatio-temporal variability are possible. Models are computed for configurations of bubbles of non-magnetic fluid rising in ferrofluid and droplets of ferrofluid falling through non-magnetic fluid. Bubbles and droplets exhibit similar changes of shape in the presence of vertical fields, due to a combination of elongation along the field lines and the fluid dynamics of ordinary rising or falling at small Bond number. Bubbles become more prolate than droplets under the same parameters and are accordingly found to break up more readily than droplets in stronger fields. Indirect effects are observed, such as the change in rise time and the consequent changes in the flow due to increased Reynolds number.

Mathematical modeling of biowall reactors for in-situ groundwater treatment.

In this paper we develop a comprehensive model for the remediation of contaminated groundwater in a passive, in-ground reactor, generally known as a biowall. The model is based on our understanding of the component transport and biokinetic processes that occur as water passes through a bed of inert particles on which a biofilm containing active microbial degraders, typically aerobic bacteria, is developing. We give a detailed derivation of the model based on accepted engineering formulations that account for the mass transport of the contaminant (substrate) to the surface of the biofilm, its diffusion into the biofilm to the proximity of a microbe, and its subsequent destruction within that degrader. The model has been solved numerically and incorporated in a robust computer code. Based on representative input values, the results of varying key parameters in the model are presented. The relation between biofilm growth and biowall performance is explored, revealing that the amount of biomass and its distribution within the biowall are key parameters affecting contaminant removal.