Membranes Nitrogen data

For membranes with pore diameters smaller than 3.5 nm, the nitrogen adsorption/desorption method based on the widely used BET theory ean be employed. This measurement technique, however, is good only for pore diameters ranging from 1.5 nm to 100 nm ( = 0.1 micron). Typical data from this method are split into two portions adsorption and desorption. The nitrogen desorption curve is usually used to describe the pore size distribution and corresponds better to the mercury intrusion curve. Given in Figure... 

It is important to describe the preparation of these samples, which were annealed at high temperature in dry nitrogen gas and then rapidly quenched in liquid nitrogen. Because they were thereby rendered amorphous, there was no scattering due to the PTFE-like crystallinity that would complicate the data interpretation. Membranes were boiled in NiCL solutions and then soaked in H2O, D2O, and H2O/ D2O = 50 50 solutions. Due to the elimination of crystallinity from the melt-quench pretreatment, these samples were considerably hydrated at 41 vol %. 

To verify the membrane integrity prior to attempting separations, pure gas permeation rates for nitrogen and helium were determined and compared to the vendor s data supplied with the membrane. Figure 4 and Table V verify the vendor s data reasonably well for the only membrane which survived shipment and startup. The agreement of the nitrogen values is particularly indicative of the membrane s integrity. 

Table n shows the changes in the composition of the bacterial substance which occur when 100 mg. of log cells at the depletion point grow into valine cells (if that is the limiting amino acid), or into threonine cells if threonine is limited. The amounts formed from 100 mg. at the point of depletion average 145 mg. in the case of valine and 190 mg. in the case of threonine. The determination of wall substance by mechanical disruption and the determination of membrane substance by lipide analysis have been outlined. The other data are obtained by way of conventional procedures DNA (deoxyribonucleic acid) by diphenylamine, and completely independently by thymine RNA (ribonucleic acid) by ultraviolet extinction and cytoplasmic protein from nitrogen determinations corrected for the nitrogen content of the other components. 

Figure 9.11 Net pressure difference in the counterdiffusion of N2 and CjH4. Symbols show the experimental data of Waldmann and Schmitt [11] drawn line show simulation with the binary friction model. Highest pressure on the nitrogen side. The DGM predicts no pressure difference (from Kerkhof [5]). Reprinted from Chemical Engineering Journal, 64, PJ.A.M. Kerkhof, A modified Maxwell-Stefan model for transport through inert membranes the binary friction model, 319-344,1996, with kind permission from Elsevier Science S.A., RO. Box 564,1001 Lausanne, Switzerland.

Uptake capacity is dependent on the number and eiEciency of membrane transport proteins. It is not really known how the numbers of transporters (e.g. ammonium or nitrate) per cell varies as a function of physiological state, or how the kinetics of transport may be a function of the protein structure of the transporters themselves. Some studies indicate that the number of transporters per cell increase with nitrogen limitation, but kinetic data suggests otherwise and that transporter numbers are more or less constant as a function of growth rate under N limitation... 

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