Overlapping Zones

Inspection of the last three equations shows that nc is multiplicative 

Thus an approximate rule emerges for comparing ID and 2D peak capacities the single-dimensional peak capacities multiply together to yield the 2D peak capacity. This rule illustrates the enormous separation power of 2D (more generally, multidimensional) forms of separation. 

Ideally, the component zones or peaks emerging from a separation process should be well isolated from one another. With isolation, each peak s center of gravity can be precisely located and used to establish or confirm the identity of the component forming the peak. The peak area or peak height can be accurately measured and used as a source of information on the amount of the component. Also, the peak contents can be collected in pure form and subjected to additional tests (such as mass spectroscopy) in order to confirm the identity of the component without risk of interference. 

Unfortunately, the ideal separation, producing only well-isolated peaks, is rarely found in practice. This is particularly so with complex multicomponent mixtures. Very often there is not sufficient space along the separation coordinate (that is, there is not sufficient peak capacity) to isolate all components. However, even in circumstances in which the peak capacity is adequate to handle all components (i.e., when nc exceeds the number of components), the components tend not to oblige rather than filling the 

If peak overlap occurs, there is a loss in the quality of analytical information relative to that derived from isolated peaks. The extent of the loss depends on the extent of overlap. For slight overlap, one may simply lose information at the level of a few percent on the quantity of the components in the sample. With strong overlap, particularly between small peaks and large peaks, the small peak may be totally obscured even its existence may be in doubt. 

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J. C. Giddings, Steady-state, two-dimensional and overlapping zones , in Unified Separation Science, John Wiley Sons, New York, Ch. 6, pp. 112-140 (1991). 

In actual in-situ coal gasification, numerous processes, i.e. oxidation, reduction, thermal cracking and a variety of catalytic as well as non-catalytic reactions, occur in overlapping zones, and to explore the chemistry of these reactions as single or consecutive unit processes is virtually impossible. It is, however, feasible to study the individual reactions under controlled conditions by simulating in-situ gasification in the laboratory. 

For circular tubes, the experimental data set consisted of a total of 603 points. Of these, 77 points lie in the intermittent regime, 448 in the disperse/annular/mist flow regime, and the remaining 78 data points are in the overlap zone between these two regimes. Pressure drop models for these regimes are described below. 

A comparison of the measured pressure drops and those calculated using the intermittent and annular/disperse-wave/mist flow models is shown in Figure 11 for each tube considered. In the overlap zone (Figure 7), the flow exhibits both the adjoining mechanisms (intermittent and annular/disperse-wave/mist flow). Therefore, for calculating the pressure drops in the overlap zones in Figure 11, the four-point interpolation scheme described above in connection with the transition between laminar and turbulent data was applied to the pressure drops calculated using the intermittent and annular/disperse-wave/mist flow models. This combined model for the... 

If the compound does not have an ultraviolet spectrum— it should be noted that the ultraviolet spectra need not be different, although it is convenient if they are because this allows one to detect overlapping zones— infrared or nuclear magnetic-resonance spectroscopy could be used. In many cases, however, the solution would have to be treated in some way in order to make it appropriate for use with these types of spectrometers. Finally, in the absence of other methods, each fraction could be evaporated and weighed. If this procedure is followed, it is... 

Fig. 10. Strike projections of Fault 1, viewed from the downthrown (west) side vertical exaggeration x5. (a) Juxtaposition plot. Upthrown Brent zones are shown with coloured fill (see legend) downthrown zones are shown in black outline, labelled at each end of the fault. Footwall hydrocarbon contacts are shown in black, hangingwall contacts in blue, (b) SGR for the area of Brent-Brent overlap. Upthrown zones outlined in blue, downthrown zones in black contacts as in (a). SGR is colour-coded in the ranges 0-15%, 15-20%, 20-30% and >30%. Note the area of slightly lower SGR on the upper part of the overlap zone this is the critical area for fault seal.

The display of SGR on the fault surface (Fig. 10b) uses the shale fractions observed in the adjacent wells. Since the fault displacements are generally greater than the zone thicknesses, the calculated SGR values are relatively homogeneous. However, a significant point is the area of lower values (in yellow, <20%) near the upper part of the reservoir overlap zone. This represents the critical area for fault seal calibration. 

Childs, C., Watterson, J. and Walsh, J.J. 1995. Fault overlap zones within developing normal fault systems. J. Geol. Soc. London, 152 535-549. 

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