GUM and six sigma approaches positioned as deterministic tools in quality target engineering

In order to improve the quality and logistics of care, health care organizations should deal with uncertainty of demand and supply, inflexibility of the health care organization and its capacity and organizational complexity. What is needed is integrated process management and standardization to improve quality and safety of care, patient logistics and working conditions of staff. This paper tries to fuse (and in that way better understand) the concept of six sigma with the guide to the expression of uncertainty in measurement in relation to the concept of target engineering.Presented at the 9th Conference on Quality in the Spotlight, 18–19 March 2004, Antwerp, Belgium.     

Critical Points in a Crystal and Procrystal

The critical points in the model electron density distributions of LiF, NaF, NaCl, and MgO crystals, constructed from accurate X-ray diffraction data, are determined. For LiF and MgO they are compared with those obtained from a Hartree–Fock electron density calculation. Both experiment and theory show the same type of critical points on the bond lines. The topological features in areas between structural units, where the electron density is low and near-uniform, turn out to be model dependent and cannot be established well with the data available. Topological analysis of procrystals (hypothetical systems consisting of spherical atoms or ions placed on the same sites as atoms in real crystal) show that (3, –1) critical points, usually connected with bonding interaction, are observed on interatomic lines in these nonbonded systems as well.     

Implicit solvent models: Combining an analytical formulation of continuum electrostatics with simple models of the hydrophobic effect

The recent development of approximate analytical formulations of continuum electrostatics opens the possibility of efficient and accurate implicit solvent models for biomolecular simulations. One such formulation (ACE, Schaefer & Karplus, J. Phys. Chem., 1996, 100:1578) is used to compute the electrostatic contribution to solvation and conformational free energies of a set of small solutes and three proteins. Results are compared to finite-difference solutions of the Poisson equation (FDPB) and explicit solvent simulations and experimental data where available. Small molecule solvation free energies agree with FDPB within 1–1.5 kcal/mol, which is comparable to differences in FDPB due to different surface treatments or different force field parameterizations. Side chain conformation free energies of aspartate and asparagine are in qualitative agreement with explicit solvent simulations, while 74 conformations of a surface loop in the protein Ras are accurately ranked compared to FDPB. Preliminary results for solvation free energies of small alkane and polar solutes suggest that a recent Gaussian model could be used in combination with analytical continuum electrostatics to treat nonpolar interactions. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 322–335, 1999     

Prelude to molecular dynamics: Topography-driven gaussian charge models

A new strategy to develop Gaussian charge models (GCMs) for molecules like ammonia, water, ethene, hydrogen sulfide, formaldehyde and benzene is presented. These molecular models comprising of positive point charges and negative Gaussian charge distributions (GCDs), which represent nuclei and continuous electron charge distribution, are found to correctly represent the ab initio Molecular Electrostatic Potential (MESP) and reproduce its essential topographical features of corresponding molecules. The models use optimized parameters: positive charges at nuclei, negative charges on GCDs, Gaussian exponent and centers. The Potential Energy Surface (PES) of water dimer has been explored using water GCMs. A good agreement has been found between PES obtained using GCMs and wave function. The Gaussian models correctly predict structure of benzene-water complex. It is thus recommended to use GCMs for molecular dynamic simulations.     

FSGO point charge models—Their accuracy and extension to higher gaessians

An FSGO model of ethane demonstrates how currently used point charge models can give the wrong sign for the potential. The Hall point charge potential on the other hand is asymptotically accurate.An extension of the Hall point charge model to higher Gaussians is demonstrated. This extended model potential is shown to be of comparable accuracy to that of the spherical Gaussian model.     

Intermolecular interaction coefficients using point charge models

Values of the two-body interaction coefficientsC6 andd4 between like species, as well as the three-body term 3, are obtained from point charge model formulae. Lewis set results may be compared with atomically centered wave-function values as well as results obtained using an experimental point charge model. Generally results are in good agreement with experiment and when theoretical values differ wildly from experiment they may be normalized using theoretical and experimental static polarizability values.     

Point charge models for LiH,CH4, and H2O

Point charge models for LiH. CH₄, and H₂O are presented. The models preserve the correct total charge and dipole moment of the molecules. Relations between spherical Gaussian wave function values and point charge model values of a variety of one-electron molecular properties are derived. The errors inherent in some of the point charge model values are of two types: those which may be large but are easily evaluated and those which are small and diminish rapidly as the distance from the molecule increases. The models are shown to be a reliable means of calculating one-electron properties and possible uses of the models are suggested.