Flow improvements, with cells

Anfolini et al. [161] also compared SAB and Vulcan XC-72 as possible candidates in MPLs, but in this case they used carbon cloth DLs with two MPLs. From their results, it was concluded that the Vulcan XC-72 gave slightly higher electrocatalytic activity for fhe ORR. On the other hand, MPLs near the FF that used SAB had better performance. Thus, it was suggested that for improved fuel cell performance af high pressures (around 3 atm), the ideal cathode MPL compositions would use the Vulcan XC-72 in the MPL next to the CL and SAB in the MPL next to the flow fields. 

The limitations of the application of conventional detergents mentioned above can be circumvented by replacing this approach with cell membrane permeabilization by microwave heating. Improved detection of intracellular antigens can be obtained with microwave heating used in combination with flow cytometry. This approach yields histogram patterns that show clear discrimination between intact cells and cell debris (Fig. 9.5). 

Fig. 9.5. Efficiency and speed of sorting are affected by the flow rate of cells. At high flow rates, more desired cells are lost, but the speed of collecting these desired cells increases until the loss of efficiency becomes greater than the increase in speed. Highspeed sorting, with more drops per second, increases the efficiency and decreases the time required to obtain the desired number of cells. The model from which these graphs were generated was derived by Robert Hoffman for these data, a three-drop sort envelope was used, 1% of the cells were sorted, and the electronic dead time was set at 6 ps. If one drop is sorted with each sort decision (instead of three), the theoretical efficiency of the sorting improves considerably (as does the rate of collecting the sorted cells).

The carrier-gas flow rate influences both the sensitivity and resolution of the method affecting the steady-state arsenic concentration in the atomizer cell and the rate of utilization. The effect on sensitivity of varying carrier-gas flow rate is demonstrated in Figure 2. The peak height for As(III) or As(V), methyl and dimethylarsenic decreased with increasing flow rate whereas instrument stability and resolution improved with increasing gas flow rates. The optimum flow rate is 150 ml min" F... 

A novel feature of the technique is that the cells are maintained in a vertical orientation with the various interfaces horizontal during the entire experiment. This scheme represents a significant improvement over the previous method where the cells were vertical during the initial contacting process but where rotation to the horizontal position was required for observation with a conventional microscope (4). Although much useful information was obtained from the earlier technique, the inevitable flow associated with oil overriding the aqueous phase after rotation obscured some features of intermediate phase development and precluded measurement of the rates of growth of these phases. 

Lipophilic metabolites tend to accumulate within the production host. If in addition the metabolite is colored or fluorescing, a carotenoid for instance, flow cytometry-based cell sorting protocols are suited to isolate individuals with improved production traits out of a mutagenized population, even if they are present at very low frequency. Value compounds typically produced with B. subtilis production hosts, such as water-soluble vitamins, purine nucleosides, ribose, or proteins, are secreted and accumulate in the culture medium. Screening of improved production strains for such metabolites requires clonal cultivation of the members of the mutagenized population in compartmentalized reactors and individual analyses of the culture supernatants in each of the reactors. 

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