Feeding prolonged times between

Only the first type of neurotransmitter release mediates the fast point-to-point synaptic transmission process at classical synapses (sometimes referred to as wiring transmission). All of the other types of neurotransmitter release effect one or another form of volume transmission whereby the neurotransmitter signal acts diffusely over more prolonged time periods (Agnati et al., 1995). Of these volume transmitter pathways, the time constants and volumes involved differ considerably. For example, diffusible neurotransmitters such as nitric oxide act relatively briefly in a localized manner, whereas at least some neuropeptides act on the whole brain, and can additionally act outside of it (i.e., function as hormones). There is an overlap between wiring and volume neurotransmission in that all classical neurotransmitters act as wiring transmitters via ionotropic receptors, and also act as volume transmitters via G-protein-coupled receptors. Moreover, neuromodulators in turn feed back onto classical synaptic transmission. 

Increasing the pressure in the reaction zone increases the residence time by increasing the density of the hydrocarbon phase. This dense-phase hydrocarbon keeps the heavy polymer or tar washed off the catalyst and prolongs catalyst life. The optimum pressure depends upon the composition of the feed stock. Pressures of between 400 and 1000 p.s.i. are normally considered best for commercial operation. 

Even more advantageous is the fact that with the concentration of the feed mixture increasing, the distance between the fronts of the two components under separation noticeably increases. This corresponds to an increase in the separation selectivity, which further enhances the productivity of the process. An analogous phenomenon was first observed by Nelson and Kraus [116] in 1958 in the separation of concentrated solutions of LiCl from HCl on the anion-exchange resin Dowex-lxlO. The prolonged retention of HCl at increasing LiCl concentration was explained at that time by the authors as due to a drop of the activity coefficient of HCl in the resin phase (which, obviously, was not a correct explanation). 

Considerations of process simplicity as well as economy suggest that the waste heat produced by the fuel cell (about 0.25 kW per kW of net electrical DC output) should be fed back to thermally decompose the raw coal feed. This requires that the cell produce sufficient heat at a sufficiently high temperature to effect thermal decomposition within a time span that is short compared with that of electrochemical conversion. Fig. 8 (after Howard, 1981) reproduces data underlying Dryden s correlation (Dryden, 1957) for many British and American coal seams and shows the extent of decomposition (relative to that at prolonged pyrolysis at 1000°C) as a function of temperature and time. The reference to 1000 C is useful, as the yields observed at this temperature approach those of higher temperature asymptote. Also in Fig. 8 is the data from Anthony et al. (1975) taken after various exposure intervals between 0.1 and 14400 s, showing that devolatilization is 90% complete in the range of 5-20 s. 

---