Membranes constant

At the opposite extreme is the example of amiodarone. The log octanol partition coefficient is 7.8 [162], whereas the membrane constant is reported as 6.0 [429], surprisingly, almost two orders of magnitude smaller (8 = —1.8). 

Plotting the reciprocals of membrane constant(pure water permeability) against time elasped as shown in Fig. 3, a much more straight line can be obtained for each operating pressure 2000, 1500,1000 and 600 psi. But during the initial period of the operation of less than seven to three hours, the reciprocal values increase steeply untill they reach the straight lines. 

Toray s data are plotted as the reciprocal of membrane constants against time elasped like Fig. U. The first generation of Toray module tested at the laboratory might have some defect In the membrane backing material. After 6000 hours in operation, they exchanged half of the modules for the second generation chlorine resistant. The second had been improved about twice in its resistance against flux decline. 

Figure 16. Decrease of separation (or increase of solute permeabilities) of seawater reverse osmosis desalination at several concentration levels of NaOCl. Initial membrane constants pure water permeability constant = 97.0 nmol m Pa s and the solute permeability constant for NaCl = 0.9 X 10 cm s . Operational conditions k = 7.(97 X 10 cm s Ap = 6.0 MPa, and T = 25°C.

The initial membrane constants and the operating conditions were almost same as those assumed for the calculation of this graph. The concentration of chlorine in the feed had been controlled minimum 1.2 mg/l or about 2.3 mg/1 as NaOCl. 

The obtained values of the membrane constant LpAx are considered to contain an uncertainty of 20%, mostly due to the uncertainty of 15% in the measurement of Ax by a dial micrometer. 

Set the supply to deliver 0.75-1.0 mA/cm2 membrane constant current for 1 h, and turn the supply on. The voltage will start between 5 and 10 V but will gradually rise throughout the course of the run. 

Lr Membrane constant for solute transport by diffusion (m/s) Lp Membrane hydraulic permeability (mol m 2s-1bar-1)... 

Rm did not correlate with the intrinsic activity of agonists for their ability to attenuate adenylate cyclase stimulation (36).In that system, only the ratio of K./K appeared to correlate with the intrinsic activity ofLthe alpha-adrenergic agonists. Here, in anterior pituitary membranes constant proportions of both receptor states were evidenced but ratios of 30-200 were found for K./Km for a series of dopaminergic agonists despite the fact that these agonists all appear to display full intrinsic activity in their ability to inhibit prolactin secretion from pituitary cells. 

The ratio of complexed and uncomplexed receptor molecules can be fixed by the concentration of lipophilic anionic sites in the membrane. When, for monovalent primary ions, the concentration of lipophilic anionic groups is approximately 50mol% with respect to the concentration of receptor, the ratio of complexed to free ionophore will be close to unity and consequently 5, Under these circumstances, the association equilibrium acts as an effective ion buffer system which keeps the activity of the free ion involved in the equilibrium in the membrane constant. The consequence is that changes of the activity of that particular ion in solution will not cause changes of activity of that ion in the membrane phase but will... 

The membrane constant a is the permeability divided by the membrane thickness evaluated at the reference pressure. The physical significance of a is that it represents the proportionality constant between flux and pressure drop at the reference pressure. The parameter b indicates the extent to which Poiseuille flow contributes to the permeability and lies between 0 and 1. Equation 19.30 is know as Knudsen-Poiseuille model, where is the dimensionless pressure defined as Pavg/ ref. the Pref is chosen in such a way that P becomes close to unity for the range of application of the equation. If a different pressure is assumed, Equation 19.30 may be modified retaining its original form, but having different values for the parameters a and b with the reference pressure as a new P close to unity. In such a case the new parameters a and b can be written as [59]... 

Voltage-clamping techniques, which hold the electrical potential across the neuronal membrane constant, while still allowing for the transmural flux of ions, have provided detailed analyses of the rates at which various ions cross the membrane and the kinetics of ion channel activation and inactivation. Specific information about a given anion or cation can be obtained by altering the ionic composition of the bathing medium (Hodgkin and Huxley, 1952 also see Aidley, 1971). 

For FRAP of the membrane, use a freehand drawing tool to create the ROl. This allows you to create the appropriate ROl when there are significant curves along the cell perimeter. However, to maintain consistency, you should maintain the maximum width along the membrane constant at 4.5 pm and the average depth below and above the membrane between 1 and 1.5 pm depending on how much the cell moved before bleaching. 

The aCSF mimics the extracellular environment of neurons and provides the necessary ingredients that allow neurons to survive m vitro for at least several hours. Because metabolic processes and the maintenance of the ionic gradient across the cell membrane constantly consume ATP, glucose and oxygen must be supplied to generate energy. 

The drop in flux can be shown quantitatively by the drop in the value of the membrane constant, A. For a perfectly semi-permeable membrane with feed-side mixing or flow conditions such that the boundary layer is insignificant. 

Jdif and convective, diffusive and migration fluxes, Eq. (114) generalized volume flow. Table 7 constant of Henry s adsorption isotherm proportionality constant in AdSV, Eq. (110) proportionality constant in ASV, Eq. (108) heterogeneous rate constant, Eq. (3) standard heterogeneous rate constant at E , Eq. (3) membrane constant in the oxygen sensor, Eq. (16) surface reaction rate constant linear dimension of the electrode system, Eq. (117) number of microband electrodes, Eq. (21) the flow rate of mercury in DC polarography, Eq. (22)... 

Figure VII 10 demonstrates that on increasing the feed concentration, but keeping the mass transfer coefficient and the concentration at the membrane constant, the value of the limiting flux, Joo, decreases. On the other hand, increases when the mass transfer coefficient k is increased at constant feed concentrations.

Other fatty acids varied to a lesser extent. The accumulation of unsaturated fatty acids occurs with an increase in chain length which would mantain the fluidity of the membrane constant, suggesting that these variations in fatty acid composition do not contribute significantly to the observed changes in Ca transport during muscle development in vivo. This is supported by the lack of changes in passive Ca permeability observed in sarcoplasmic reticulum membranes isolated from developing embryos and chicks (Martonosi, 1975). 

Solution We will employ equation (7.2.43) under the assumptions of a highly rejecting membrane, constant AP, ku, A,... 

The membrane is treated as the same simple system as described above (Figure 1). We assume, besides the electroneutrality inside the membrane (constant field hypothesis), a continuity of the electrical potential ip from the bulk of the surrounding medium to the center of the cell. We are compelled, therefore, to assume that the potential at the outer Helmholtz plane, which is induced by the effective surface charge (dissociated functional groups or strongly adsorbed ions) is screened to a major extent by counterion-site pairing in the Nernst layer. We consider the three classes of transferable chemical species quoted in the introduction. Among the species not directly involved in chemical reactions, the calculation takes into account an anion (Cl ), two monovalent cations (K, Na+) and two divalent cations (Mg2+, Ca ). As for the species involved in chemical reactions, we assume that they do not interact inside the membrane (independent channels). However, their flux balance must take into account the chemical reactions in both lateral phases. We handle only here two types of equilibria the water dissociation and the first dissociation of the carbonic acid. The three flux balances of the five chemical species which are interconnected by the conditions for the equilibria are as follows ... 

Example 13.2 Northrop and Anson examined the diffusion of HCl in water by means of a diaphragm cell fitted with a porous aluminum membrane this membrane separated pure water from 0.1 HCl. Over a period of 30 min, the amount of acid that diffused through the membrane was equivalent to 0.26 cm of 0.1HCl. What is the value of the membrane constant L/Al It is known that D12 equals 2.14 x 10 cm /sec. Assume that cj and cj remain unchanged over the course of the experiment. 

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