Back-feeding element

Screw elements and kneading blocks can also be designed so that their feeding effect acts against the material flow direction, however. These are known as back-feeding elements . They are also always filled completely and create a pressure drop. 

Figure 7.8 Back-pressure length in relation to the length of the back-feeding element for a right/left combination of elements of the same type...

The last element necessary for the construction of a universal computer is a simple time delay, i.e. a circuit primitive whose output at time t-fl equals the input at time t and which allows us to feed outputs back into gates as inputs. 

Ion exchange (IX) is a very useful technique for the concentration, the purification and the separation of chemically similar metallic elements present in an aqueous solution. In its most popular form of application, the metal-bearing aqueous solution is passed through a bed of solid organic resin in a particulate form wherein the sorption of the metal ions on the resin takes place by ion-exchange reactions. The pregnant resin is washed free of the entrapped feed solution and then brought into contact with an eluant of suitable composition and volume so that the resin releases the metal ions back to the eluant. The ratio of the volume of the feed and that of the eluant determines the extent of concentration that can be achieved. Purification and separation are achievable if the resin is selective or specific with respect to the metal ions of interest in comparison to impurity ions. 

For example, in the adjacency matrix of Fig. 14 we can start with the first row and trace a path from/j to fs because there is a nonzero element in row 1 and column 5. Then the path is traced from fs back to /t because of the nonzero element in row 5, column 7, yielding the loop /1-/5-/1. After this loop has been found, each path traced from the vertices in this loop will yeild a loop. We can return to the last equation found in the loop, /5, and trace a path from/5 to another equation that feeds it,/3. The path is then continued from /3 to the first equation that feeds it, /2, and from f2 back to /3. Thus the loop f3-f2-f3 has been found. We return to the last equation found, /2, and see that no other equation feeds it, in which case we must return to the equation found just previous to/2, namely f3. Now/3 is fed by f4 and a new path can be traced to obtain a loop f3-j4-f5-f3. Steward continues this procedure until all of the feeds to each equation have been exhausted, but it is not obvious when this situation occurs except if a tree is drawn of the paths. For a large block, drawing a tree may not prove to be especially feasible. 

These discussions of course can be an additional input to the creative process. This process does not stop with the generation of an original idea that is often the least of it. The major elements of creativity, in management as in other spheres, are in the realization of the idea in practice - in the actual change that is brought about. The process of implementation feeds back to the conception. 

Stretford plants have been in operation for 30 years. There are hundreds of such plants worldwide, used in a variety of sulfur removal operations (Dalrymple 1989). In a Stretford process, the hydrogen sulfide in the feed gas stream is absorbed and oxidized to elemental sulfur in aqueous phase, using pentavalent vanadium which is subsequently reduced from a pentavalent form to a tetravalent form. Later in the process, the vanadium is re-oxidized back again, using anthraquinone disulfonic acid (ADA) as a catalyst, and the elemental sulfur is floated to the surface of the solution and removed. 

As described in Figure 3.7, TRU separation is performed by implementing the DIDPA process on pretreated PUREX raffinates. A front-end denitration step by formic acid is thus required to reduce the nitric acid concentration of the feed down to 0.5 M to allow the TRU elements to be extracted by the cation exchanger di-fvo-dccyl-phosphoric acid (DIDPA). This preliminary step, however, induces the precipitation of Mo and Zr (and thus the potential carrying of Pu), which requires filtration steps. The TRU and Ln(III) elements are coextracted by a solvent composed of the dimerized DIDPA and TBP, dissolved at 0.5 and 0.1 M, respectively, in n-dodecane. The An(III) + Ln(III) fraction is back-extracted into a concentrated 4 M nitric acid solution, whereas Np and Pu are selectively stripped by oxalic acid. 

The processing elements are typically arranged in layers one of the most commonly used arrangements is known as a back propagation, feed forward network as shown in Figure 7.8. In this network there is a layer of neurons for the input, one unit for each physicochemical descriptor. These neurons do no processing, but simply act as distributors of their inputs (the values of the variables for each compound) to the neurons in the next layer, the hidden layer. The input layer also includes a bias neuron that has a constant output of 1 and serves as a scaling device to ensure... 

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