Partitioning array

Light sensitive material is electrically partitioned into 0 2-t> array of pixels (each pixel is a 3-D volume)... 

Figure 5. Simplified schematic of the 2-D array of pixels in a focal plane array. The thin wafer of light sensitive material is partitioned into a two-dimensional array of pixels that collect the electric charge produced by the light. Each pixel is a three-dimensional volume that is defined by electric fields within the light sensitive material.

In conclusion, the inclined U-Pa and U-Th arrays appear to have some time significance because their interpretation as simply the result of recent mixing with a fluid containing Th and Pa as well as U requires fluid partition coefficients for Th and Pa well in excess of those observed experimentally. The corollary is that that there must be a decoupling between Ra-Th and Th-U disequilibria. A further possibility is a combination of the two end-member models discussed above into one in which some Th and Pa addition by fluids is followed by some in-growth due to ageing. In this case (discussed further below) the age inferred from the U-Th and U-Pa arrays is necessarily less straight forward to interpret. 

Following the publication of the first example of fluorous biphase catalysis by Horvath and Rabai in 1994 [1], the immediate focus was to develop catalysts that would exhibit very biased partition coefficients with respect to fluorous and organic solvents. Such liquids are normally immiscible at room temperature. This was done by attaching ponytails of the formula (CH2)m(CF2) -iCF3 (abbreviated (CH2)mRf )> including arrays emanating from silicon atoms [2]. Catalysis was then effected at elevated temperatures, where fluorous and organic solvents are commonly miscible, with prod-uct/catalysis separation at the low-temperature two-phase limit. 

The nature of combinatorial chemistry can present a considerable challenge because these libraries are generally produced as arrays of compounds and it is often inconvenient to synthesize individual compounds in order to achieve an optimal design. Two methods have been described that attempt to select optimal subset of reagents from a virtual library that has been partitioned into favorable and unfavorable compounds by some method of filtering. The PLUMS algorithm [97] was designed to simultaneously optimize the size of the library based on effectiveness and efEciency . 

It is interesting to note that various QSAR/QSPR models from an array of methods can be very different in both complexity and predictivity. For example, a simple QSPR equation with three parameters can predict logP within one unit of measured values (43) while a complex hybrid mixture discriminant analysis-random forest model with 31 computed descriptors can only predict the volume of distribution of drugs in humans within about twofolds of experimental values (44). The volume of distribution is a more complex property than partition coefficient. The former is a physiological property and has a much higher uncertainty in its experimental measurements while logP is a much simpler physicochemical property and can be measured more accurately. These and other factors can dictate whether a good predictive model can be built. 

To use Equation 20.6 to calculate the fractional concentration change resulting from a diffusion process, one partitions the medium (the solution) into an as yet unspecified number of volume elements of thickness Ax and requires that f(x,t) be uniform within each element. In the simplest case, these elements would form a linear array originating at a planar surface (the electrode) of area A located at x = 0. Therefore, the volume of each element will be A Ax, as represented in Figure 20.1. Each element may be assigned a serial number, J, as indicated in this figure, so that any distance x is given as... 

As indicated earlier, Equation 20.8 is applied successively to each element in the array of volume elements to simulate material transfer during the interval At. To define a At unit, one must select some known time (tk) in the physical experiment and partition that known time into L equal intervals for the purpose of the simulation. Thus... 

Zanzucchi, P. J., Cherukuri, S. C., McBride, S. E., Etching to form cross-over, non-intersecting channel networks for use in partitioned microelectronic and fluidic device arrays for clinical diagnostics and chemical synthesis, US 5681484, David Sarnoff Research Center, Princeton, NJ, 1995. 

---