The Onion Approach

5 The Onion Approach. - In addition to the usual hybrid methodology described above, Morokuma et al. have taken a slightly different onion approach to combining calculations at different levels of theory. In the 

More sophisticated examples of such expressions are used in Pople s Gl, G2 and G3 theories.162-164 In the onion approaches, the calculated structure of the lower level is used as a constraint upon the higher level of theory. The breaking of covalent bonds between the model and the real system is treated by replacing the corresponding atom in the real system with a hydrogen atom in the model system, much like the link atom method. The coordinates of the new 

6 Applications. - The following is a by no means exhaustive selection of some the interesting results obtained in the last couple of years using hybrid QM/MM methods. 

---

All too often safety and health (and environmental) considerations are left to the final stages of the design. Returning to the hierarchy of design illustrated by the onion diagram in Fig. 1.6, such considerations would add another layer in the diagram outside the utilities layer. This approach leaves much to be desired. 

S - Alky Icy steines, while not cleaved by the onion enzymes, inhibit the cleavage of the sulfoxides (27, 42) in a partially competitive manner —1/v does not increase hnearly with inhibitor concentration but approaches a maximum (42). The eflFect has not been explained. Other amino acids, including L-cysteine itself, did not inhibit the onion enzyme although L-cysteine did inhibit the garlic enzyme (40). 

A number of experimental chemical process synthesis procedures have been developed with a hierarchical architecture based on both the hierarchical structure of the chemical innovation process and the physical property hierarchy. Examples include PIP (Kirkwood et al, 1988) and BALTAZAR (Mahalec and Motard, 1977). This hierarchical approach is also evident in the Pinch Technology Onion Diagram (Linnhoff and Ahmad, 1983). The hierarchical approach is also the foundation for the two early textbooks on process synthesis methodology (Rudd et al, 1973 Douglas, 1988). 

Thus, the process-improvement approach to the safety of the medication-use cycle goes beyond the celebrated cases and first stories to scientifically investigate the system as a whole. Data on near-misses and uncelebrated errors should be analyzed to find hidden flaws and strengths, and to better understand the dynamics of our medication-use system. Scientific investigation of the whole cycle— peeling away the layers of the onion—will reveal latent points of failure and facilitate a redesign that substantially reduces the occurrence of harmful outcomes. 

In short, the traditional design approach adopts a sequential design approach. In contrast, the process integration methodology for process design takes a different approach in that process design aspects in the inner part of the onion diagram are... 

Synthesis of carbon onions through heat treatment of soot by de Heer and Ugarte represented the first approach in producing carbon onions in macroscopic quantities. This is an important requirement for many further characterization steps and for any potential applications of this material. These carbon onions consist of hollow carbon onions, with between 2 and 8 graphitic shells, and their production in macroscopic quantities by this experimental approach enabled their examination by ultraviolet-visible (UV-Vis) and Raman spectroscopy. It was proposed that carbon onions could be a possible carrier of the 2175 A interstellar absorption bump. ° Raman spectra of this material revealed pronounced differences to other graphitic materials. ... 

Spectra of Titan s north polar limb, shown in Fig. 8.4.1, were obtained by the Voyager 1 spectrometer (IRIS). The continuum between gaseous emission features is due mainly to a stratospheric aerosol, although tropospheric emission also contributes to the spectmm shown in the lower panel. Because each field of view extends over several scale heights, it is necessary to convolve Eq. (8.3.9) with the field of view the onion peeling approach is not practical. Instead, the equation is solved directly, varying the aerosol parameters until the spectral continua are fit simultaneously for a given model. 

In the organic sector, the non-chemical approach also has effects on traits concerning product quality, such as long-term storability without chemical sprouting inhibitors for onions... 

De Melo, P.E. 2003. The root systems of onion and Allium fistulosum in the context of organic farming a breeding approach. PhD thesis, Wageningen University, the Netherlands. 

---