Secondary emission equilibria

This is because the total secondary emission yield a (number of secondary electrons created per incident electron) varies with beam energy so that charge equilibrium (a equal to 1) is created, regardless of the material analysed, for a low voltage of approximately 1 to 2 kV (Fig. 7.8). Beyond this voltage level, the number ofmeident electrons exceeds the number of electrons emitted and, in the case of an insulating material, these electrons accumulate in the impact zone and make observation impossible. 

Lead and sulphur are derived from the fuel and there is a complex equilibrium dependent upon temperatures and gas composition controlling the absorption/desorption of these poisons. In the case of lead, extended trials have demonstrated the feasibility (ref. 20) of successful operation of oxidation catalysts on leaded fuel. However, it has been noted that in the decade since introduction of lead-free fuel in the USA, residual lead levels have fallen dramatically. In that market, where leaded and unleaded fuels are both available, incidents of poisoning reflect contamination of distribution equipment or deliberate misfuelling (refs. 21,22). Sulphur may also be derived from lube oil but its impact in the sense of poisoning is low on PGM catalysts. Interaction with catalyst components can, however, influence secondary/unregulated emissions of... 

As shown in Figure 9-2. important regions of a flame include the primary combustion zone, the interzonal region, and the secondary combustion zone. The appearance and relative size of these regions vary considerably with the fuel-to-oxidant ratio as well as with the type of fuel and oxidant. The primary combustion zone in a hydrocarbon flame is recognizable by its blue luminescence arising from the band emission of C-, CH, and other radicals. Thermal equilibrium is usually not achieved in this region, and it is, therefore, rarely used for flame spectroscopy. 

This basic picture of organic aerosol was relatively well developed by the end of the 1990s. Chemical transport models were fed by inventories for POA emissions from a wide array of sources, and those emissions were treated in a variety of microphysics modules as effectively non-volatile and often chemically inert particles [19, 20]. SOA models evolved from relatively primitive treatments that simply converted a fixed fraction of VOC emissions into equally non-volatile secondary material (for example 12% of monoterpene emissions) to more sophisticated two-product representations that treated the equilibrium partitioning of surrogate species based on smog-chamber experiments [21-23]. Even today some global-scale models represent SOA as a fixed non-volatile fraction of VOC emissions [24, 25]. 

Local Thermal Equilibrium (LTE) A model describing secondary ion emission... 

When the dc discharge is first ignited at a constant pressure and voltage, there is a decrease in cathode current with time. This is due to removing the oxides, which have a high secondary electron emission coefficient, from the cathode surface, and heating of the gas, which reduces its atomic/molecular density. The plasma is not in equilibrium until the discharge current becomes constant. 

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