Push-pull concept

The flow ratio method was first suggested for use in designing receptor hoods and then it was suggested for design of push-pull systems. The concept of the method is described as follows. 

Using fundamentally the same concepts as those embodied in the push-pull system, ALZA scientists along with those at Merck have commercialized... 

The concept of captodative substitution implies the simultaneous action of a captor (acceptor) and a donor substituent on a molecule. Furthermore, in the definition of Viehe et al. (1979), which was given for free radicals, both substituents are bonded to the same or to two vinylogous carbon atoms, i.e. 1,1- and 1,3-substitution, and so forth is considered. One might, however, also include 1,2-, 1,4-,. .. disubstitution, a situation which is more often referred to as push-pull substitution. Before discussing captodative substituent effects it might be helpful to analyse the terms capto and dative in more detail. 

Bridge mediation mechanisms in heterogeneous outer sphere electrochemical reactions has also been theoretically treated using the pull—push and push-pull mechanistic concepts [84]. Schmidt [85] has considered theoretically homogeneous inner sphere bridge electron transfer reactions without atom or ion transfer. Bridge mediation in electron transfer reactions may also involve simultaneous atom or ion transfer. Heyrovsky [86] invoked mediation of electron transfer by formation of bridges to explain the enhancement of the rate of electroreduction of indium (III) ions in the presence of specifically adsorbed halide ions on mercury. 

OROS Push-Pull system. After the introduction of commercial products based on EOP technology in the early 1980s, numerous attempts were made to apply the osmotic concept to a broader range of drugs. Since the elementary osmotic pump is limited to the delivery of relatively soluble drugs with solubilities greater than about 2 to 10 wt%, depending on dose, other modifications were necessary to expand the utility of the EOP... 

Design concept straight push pull, rising stem, with triple rotating plugs... 

The transistor impedances within the amplifier may be measured by removing the transistor after matching circuit adjustments are made for best specified performance and connecting the impedance measuring instrument, such as a network analyzer, to the input and output connections left open by the transistor. Figure 7.57 illustrates the same concept as that presented in Fig. 7.53(a) for the Class B amplifier except that the latter is for a push-pull configuration and the former is for the single ended. 

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