Membrane system performance correlations

The transport properties of a semi-permeable membrane are determined by the perme-abdity of the membrane and by a driving force both of which impact energy requirements. The flux of the solvent is direcdy proportional to the applied pressure and is given by the equation at constant temperature  

The viability of a membrane process for potable water production depends on the energy consumption. The power input reflects the pressure energy required to pump water molecules through a size/charge selective membrane and is expressed as SEC in kWh/m of product water. The foUowing relationships are used to calculate energy consumption  

Membrane performance correlations are given below. For additional correlations refer to Section 2.4.7. 

The performance of RO and NF membrane processes is typicaUy determined by two key parameters, recovery and rejection, defined as foUows  

The net driving pressure, NDP, across a RO/NF membrane is estimated from  

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Equilibrium properties are surprisingly accurately predicted by molecular-level SCF calculations. MC simulations help us to understand why the SCF theory works so well for these densely packed layers. In effect, the high density screens the correlations for chain packing and chain conformation effects to such a large extent that the properties of a single chain in an external field are rather accurate. Cooperative fluctuations, such as undulations, are not included in the SCF approach. Also, undulations cannot easily develop in an MD box. To see undulations, one needs to perform molecularly realistic simulations on very large membrane systems, which are extremely expensive in terms of computation time. 

Early studies on the effects of marijuana on the immune system attributed these to the ability of THC to perturb cellular membranes since it was highly lipophilic. However, it was soon recognized that THC also exhibited specificity of action at the physiological and pharmacological levels as well as in distribution in organs and cells. Studies performed on various rodents demonstrated that THC produced a characteristic tetrad of behavioral effects that consists of catalepsy, antinociception, hypothermia, and hypomobility (see Wiley and Martin 2003). These centrally mediated effects could be elicited following intravenous, intrathecal, and intraperitoneal administration. Furthermore, use of radiolabeled THC in hybridization studies revealed a distribution of binding in rodent brain slices that was consistent with that attributed to areas in the brain that correlated with specified behavioral activities. 

With the difficulties associated with accurate estimation of permeability based only on physicochemical properties, a variety of methods of measuring permeability have been developed and used, among which are (l)cul-tured monolayer cell systems, such as Caco-2 or MDCK ( 2 diffusion cell systems that use small sections of intestinal mucosa between two chambers (3) in situ intestinal perfusion experiments performed in anesthetized animals such as rats and (4)intestinal perfusion studies performed in humans (40,54-62). All of these methods offer opportunities to study transport of drug across biological membranes under well-controlledconditions. Caco-2 mono-layer systems in particular have become increasingly commonly used in recent years and human intestinal perfusion methods are also becoming more commonly available. Correlations between Caco-2 permeability and absorption in humans have been developed in several laboratories (63-72). As shown in Fig. 

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