Distance mapping technique

More objective procedures in series design are clustering methods in multidimensional parameter space substituents from different clusters are selected for synthesis (chapter 3) [50, 154, 403]. As this approach cannot automatically avoid collinearity or multicollinearity, several different standard sets of aromatic substituents have been proposed e.g. [652, 653]). A distance mapping technique may be used to select further substituents on the basis of a nj ximum distance to the substituents which already are included [652]. A modification [654] of this approach uses the determinant of the parameter correlation matrix as the criterion for substituent selection. 

Usually the 3-D structure of the enzyme/receptor is not known. In this case, receptor mapping techniques such as CoMFA and conformational analysis techniques such as systematic search and distance geometry are applied to a series of active and inactive structures to obtain a pharmacophore model for use in 3-D database searching. 

Some discontinuities may be identified by a conventional two-dimensional ultrasonic technique, from which the well-known C-scan image is the most popular. The C-scan technique is relatively easy to implement and the results from several NDE studies have been very encouraging [1]. In the case of cylindrical specimens, a circular C-scan image is convenient to show discontinuity information. The circular C-scan image shows the peak amplitude of a back-scattered pulse received in the circular array. The axial scan direction is shown as a function of transducer position in the circular array. The circular C-scan image serves also as an initial step for choosing circular B-scan profiles. The latter provides a mapping between distance to the discontinuity and transducer position in the circular array. 

However, the spatial resolution of AES is mueh greater than that of XPS and ean approaeh approximately 25 nm. This makes AES a powerful technique for constructing high-resolution maps showing the distribution of chemical species across a surface. Because of the small analysis area, it is an easy matter to combine AES with inert gas sputtering to construct depth profiles showing the distribution of chemical species as a function of distance away from the surface and into the bulk of the solid. Quantitative analysis can be done using sensitivity factors and an equation similar to Eq. 17. 

All considerations for measurements of single spot Raman spectra also hold for mapping because the measuring technique is essentially identical. The spatial resolution in a map depends also on the distance between the single points and can be altered from map to map. By increasing the distance, the spatial resolution... 

Fleischer, R. L. and A. Mogro-Campero, Mapping of Integrated Radon Emanation for Detection of Long-Distance Migration of Gases Within the Earth Techniques and Principles,. 1. Geophvs. Res. 83(B7) 3539-3549 (1977). 

AFM is based on the detection of very small (of the order of nano newtons) forces between a sharp tip and atoms on a surface (Figure 2.31 (b-d)). The tip is scanned across the surface at subnanometer distances, and the deflections due to attraction or repulsion by the underlying atoms detected. The technique produces atomic scale maps of the surface. 

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