Sigma concept

Justiniano JM, Gopalaswamy V. Six Sigma for Medical Device Design. 1st ed. Boca Raton, FL CRC Press Inc., 2004. First book available on applying Six-Sigma concepts to medical device design and development. 

The so-caUed Sigma concept has been widely used in the field of centrifugal sedimentation ever since its first development by Ambler in 1952. It is a simplified relation between the machine performance in terms of X50, total volumetric flow rate Q and an index of the centrifuge size E. The cut size X50 is represented by its terminal settling velocity Vg in the given liquid under gravity so that from Stokes law (using equation 7.5b for the definition of K)... 

There is however one major shortcoming of the Sigma concept the cut size is insufficient as a criterion of separation efficiency because different total efficiencies can be obtained at a given cut size, if the size distribution of the feed particles differs. Murkes recognized this but suggested a method which assumes a certain form of the feed distribution function, thus introducing an unnecessary limitation. 

Figure 21.7 The Six Sigma Concept (Montgomery and Runger, 2007). Top No shift in the mean. Bottom 1.5a shift.

R. D. McDowaH, ed., Faboratory Information Management Systems Concepts, Integration andimplementation. Sigma Press, New York, 1987, p. 12. 

Sxx is the sum of squares of the residuals, r, that are obtained when the average value Xmean is subtracted from each observation a ,. Xmean is the best estimate for the true mean fj.. When discussing theoretical concepts or when the standard deviation is precisely known, a small Greek sigma, a, is used in all other cases, the estimate Sx appears instead. 

DFTB has been combined with various force field programs, including CHARMM [49], Amber [50, 51], SIGMA [52], TINKER [34] and GROMACS (to be published). All these combined methods have used the same strategy for the interface with respect to the treatment of bonding interactions at the interface and non-bonded Coulomb and van der Waals (vdW) terms. The concepts will not be reviewed in detail here, for this purpose we would like to refer to an excellent and extensive recent review [4],... 

Finally, we briefly compare the NBO donor-acceptor picture of geminal delocalization with Dewar s sigma-aromaticity concept and the associated pi-complex... 

ICH Q8 also discusses the concept of QbD, which has its roots in the early quality and Six Sigma for manufacturing work of Juran and colleagues. ... 

The anomeric effect in terms of a stabilizing effect can be illustrated by the concept of "double-bond - no-bond resonance" (14, 15) shown by the resonance structures 4 and 2 or by the equivalent modern view (16, 17) that this electronic delocalization is due to the overlap of an electron pair orbital of an oxygen atom with the antibonding orbital of a C —OR sigma bond (12). 

One approach that QA would use to assure itself that a given process (step) is under control is the effort associated with the concept of process capability. Ekvall and Juran [15] defined the concept as the measured inherent reproducibility of the product turned out by the process. The statistical definition of process capability is that all the measured values fall within a 6-sigma range (i.e., range of the minimum to maximum limits). The information is used to show that the process is under control over a period of time as well as determine whether there is any drifting or abnormal behavior from time to time. Process validation is a QA tool in this case because its data will be used as the origin for the data curve developed for the process capability concept. 

In contrast to these concepts above obtained from numerous ab-initio molecular orbital calculations (usually from small radicals, e. g. H, F, H3C or HOCH2 to fluoroalkenes), some semi-empirical calculation on more longer halogenated radicals were performed by Rozhkov et al. [333, 334] and Xu et al. [335]. The former team determined equilibrium geometries and electronic properties of perfluoroalkyl halogenides and showed that fluorine atoms in vinyl position strongly stabilise all the sigma molecular orbital. 

Many CQI models exist. Examples of specific models include the plan, do, check, and act (PDCA) model and the find, organize, clarify, understand, select, plan, do, check, and act (FOCUS-PDCA) model and six sigma (Lazarus and Butler, 2001 Lazarus and Stamps, 2002). Most models include elements that reflect the following core concepts (1) plan, (2) design, (3) measure, (4) assess, and (5) improve (Coe, 1998a). 

Another company culture that many corporations are adopting or have adopted is the concept behind Six Sigma (Chowdury, 2001). Six Sigma represents a statistical measure and a management philosophy that gives people well-defined roles and a clear structure to their tasks. 

We start with some biographical notes on Erich Huckel, in the context of which we also mention the merits of Otto Schmidt, the inventor of the free-electron model. The basic assumptions behind the HMO (Huckel Molecular Orbital) model are discussed, and those aspects of this model are reviewed that make it still a powerful tool in Theoretical Chemistry. We ask whether HMO should be regarded as semiempirical or parameter-free. We present closed solutions for special classes of molecules, review the important concept of alternant hydrocarbons and point out how useful perturbation theory within the HMO model is. We then come to bond alternation and the question whether the pi or the sigma bonds are responsible for bond delocalization in benzene and related molecules. Mobius hydrocarbons and diamagnetic ring currents are other topics. We come to optimistic conclusions as to the further role of the HMO model, not as an approximation for the solution of the Schrodinger equation, but as a way towards the understanding of some aspects of the Chemical Bond. 

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