Quality assurance frameworks.

We present a new quantum mechanical model to introduce Pauli repulsion interaction between a molecular solute and the surrounding solvent in the framework of the Polarizable Continuum Model. The new expression is derived in a way to allow naturally for a position-dependent solvent density. This development makes it possible to employ the derived expression for the calculation of molecular properties at the interface between two different dielectrics. The new formulation has been tested on the azide anion (N3-) for which we have calculated the solvation energy, the dipole moment, and the static polarizability at the interface as a function of the ion position. The calculations have been carried out for different ion-surface orientations, and the results have also been compared with the parallel electrostatic-only solvation model.

Models, Theoretical↗

PubMed2006

A novel assessment tool for reusability of wastes.

This paper presents a new assessment method, which is able to determine the practicality of opportunities to reuse wastes. In this study, the term--reuse has much wider concepts than simply recycling to a process. In other words, reuse in this case can include recycling, utilisation as a raw material for other processes, and particularly transformation of the waste to low or preferably high value added products. Preliminary opportunities for the reuse of a waste can be generated by various methods such as brainstorming, desk research, consultation with industrial and academic contacts, and the like. In this work, each preliminary solution is then assessed according to three different categories--technical, economic, and environmental and regulatory, in order to determine the viability for reuse. The responses of nine collaborating companies to questionnaires pertaining to the three categories were used to set up feasible boundaries of each category in terms of the reuse of their wastes. Based on the replies, lower bounds for each category were determined, and then the preliminary solutions generated were ranked. The approach was applied to several industrial examples. The ranking of the high-dimensional information was aided by visual representation on a parallel coordinate graphic plot. Although the selection or rejection of an opportunity was highly dependent on the boundaries obtained, the approach proposed could provide a useful guideline to decision-makers for selection/rejection of the reuse opportunities available.

Models, Theoretical↗

PubMed2006

Simulation of solute transport across low-permeability barrier walls.

Low-permeability, non-reactive barrier walls are often used to contain contaminants in an aquifer. Rates of solute transport through such barriers are typically many orders of magnitude slower than rates through the aquifer. Nevertheless, the success of remedial actions may be sensitive to these low rates of transport. Two numerical simulation methods for representing low-permeability barriers in a finite-difference groundwater-flow and transport model were tested. In the first method, the hydraulic properties of the barrier were represented directly on grid cells and in the second method, the intercell hydraulic-conductance values were adjusted to approximate the reduction in horizontal flow, allowing use of a coarser and computationally efficient grid. The alternative methods were tested and evaluated on the basis of hypothetical test problems and a field case involving tetrachloroethylene (PCE) contamination at a Superfund site in New Hampshire. For all cases, advective transport across the barrier was negligible, but preexisting numerical approaches to calculate dispersion yielded dispersive fluxes that were greater than expected. A transport model (MODFLOW-GWT) was modified to (1) allow different dispersive and diffusive properties to be assigned to the barrier than the adjacent aquifer and (2) more accurately calculate dispersion from concentration gradients and solute fluxes near barriers. The new approach yields reasonable and accurate concentrations for the test cases.

Models, Theoretical↗