Example unit-selection systems

Here we review a few well-known nnit-selection systems to give a feeling of how they use the various components described in this chapter to effect full synthesis. 

Advanced Telecommunications Research (ATR) in Kyoto has played a particularly central role in the development of nnit selection. It was there that Yoshinori Sagisaka 

Partly because of its institutional nature, where visiting researchers would come for a few months to a few years and then leave to work for another organisation, ATR spawned a whole family tree of synthesis systems, including the Festival work at Edinburgh University [49] and the AT T Next Gen system [42], [104], which in turn spawned many other commercial systems. In fact, it is probably true to say that the only major unit-selection systems that are not in some way associated with ATR are those of Laureate and Donovan (see below). 

AT T NextGen The NextGen system developed by AT T labs directly used components from CHATR, and so is included in the ATR family [42], [104]. The AT T group, however, made significant improvements to all aspects of the system, for example in search issues [291] and the perceptual design of the cost functions 

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Other applications of supported liquid membranes have been related to metal speciation. For example, recently a system for chromium speciation has been developed based on the selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two SLM units connected in series. Aliquat 336 and DEHPA were used respectively as carriers for the two species and graphite furnace atomic absorption spectrometry used for final metal determination. With this process, it was possible to determine chromium in its different oxidation states [103]. 

In the early 1970s, Union Oil developed and patented a chromatographic system based on the principle of a simulated moving bed (SMB) [6-8]. A schematic of a SMB unit is shown in Figure 1.4. Streams of the mobile phase (the desorbent ) and of the feed to separate are continuously injected into the column while streams of the less retained (the raffinate ) and the more retained components (the extract ) are continuously withdrawn, all at constant flow rates. The rotary valves switch periodically the positions in the columns where these streams enter or exit. The operation of SMB imits is discussed in detail in Chapter 17. Manufacturing facilities have been built and are operated for the fractionation of various petroleiun distillates, for example, the selective separation of p-xylene, o-xylene and ethylbenzene from the C7-C8 aromatic fraction of light petroleum reformates, the separation of olefins from paraffins in feed mixtures of hydrocarbons having 10 to 14... 

M.A. Serageldin, The Unit Operation System for Measuring Plant Envirornnental Performance (with selected examples), NTIS PB98-124399INZ, November 1996. 

Iditional importance is that the vibrational modes are dependent upon the reciprocal e vector k. As with calculations of the electronic structure of periodic lattices these cal-ions are usually performed by selecting a suitable set of points from within the Brillouin. For periodic solids it is necessary to take this periodicity into account the effect on the id-derivative matrix is that each element x] needs to be multiplied by the phase factor k-r y). A phonon dispersion curve indicates how the phonon frequencies vary over tlie luin zone, an example being shown in Figure 5.37. The phonon density of states is ariation in the number of frequencies as a function of frequency. A purely transverse ition is one where the displacement of the atoms is perpendicular to the direction of on of the wave in a pmely longitudinal vibration tlie atomic displacements are in the ition of the wave motion. Such motions can be observed in simple systems (e.g. those contain just one or two atoms per unit cell) but for general three-dimensional lattices of the vibrations are a mixture of transverse and longitudinal motions, the exceptions... 

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