Membrane flow and differentiation

The concepts of membrane flow and differentiation were first emphasized by Morre and his associates (Grove et al., 1968 Morre et al., 1974). By the term "membrane flow," these investigators mean the actual process of physical transference of membranes from one cellular organelle to another. "Membrane differentiation" refers to a change in... 

The observations recorded for intestinal epithelial cells during fat absorption (Friedman and Cardell, 1972a, 1977) would tend to support a hypothesis of membrane flow and differentiation similar to that out-... 

The problem of endomembrane origins is considerably simplified by the presence of a eukaryotic nucleus. Once a cell derived an eukaryotic nucleus with a nuclear envelope, other endomembrane components (endoplasmic reticulum, Golgi apparatus, lysosomes, etc.) were likely acquired in a manner not unlike their present-day derivations (i.e., formation by processes of membrane flow and membrane differentiation (Table II) beginning with endoplasmic reticulum-like extensions of the nuclear envelope (Table 1)). 

A precise ordering of events in the evolution of the eukaryotic cell is not possible. It is difficult to exclude even a fully independent origin of one or each of the individual cell components with eventual amalgamation into an interdependent system. What I present is a hypothesis to explain how plasma membranes and other endomembrane components are renewed during cell division and maintained at other times by processes of membrane biogenesis, flow, and differentiation along clearly defined subcellular developmental... 

In order to develop a theory of membrane recycling, rather than flow and differentiation, it is worthwhile to review briefly the experimental evidence favoring this alternate explanation of membrane utilization. 

Flow injection analysis (FIA) (Ruzicka and Hansen), since 1975 In continuous flow, stopped flow or with merging zones (FIA scanning or intermittent pumping) Adapted voltammetric electrodes Membranes for Partial dialysis Membrane amperometry (Clark) Differential techniques (Donnan) Computerization, including microprocessors Special measuring requirements in plant control (to avoid voltage leakage, etc., Section 5.5)... 

Membranes. Apart from the role of membranes180 in ISEs, there are at least three important applications of membranes as measurement aids in flow analysis. viz., as diffusion membranes in (1) (partial) dialysis and in (2a) membrane amperometry (MEAM) and (2b) membrane voltammetry (MEVA), and as Donnan membranes in (3) differential ionic chromatography. 

Mod i f 1 ed Mjymbrajne Viscometer Foi- the pulsed system a coil of tubing (the injection loop) was placed after the prefilter and liefore the membrane holder as shown in Figure P. Directional valves at each end of the loop controlled the flow path. Solvent or solution could be pumped directly to the UV to establish baseline absorbance or for calibration. To make P measurements the flow was directed through the membrane and then into the differential UV spectrophotometer. The flow could also be brought to the upstream portion of tlie membrane holder and then to the UV detector in an effort to measure the concentration at the membrane surface. 

The purpose of this paper is to describe steady flow of water and transport of solutes across single and series arrays of arbitrary numbers of membranes. Differential forms of the flow and transport equations are used as the point of departure and from these the incremental forms are derived. This theory allows one to state concisely some general properties of series arrays of membranes, with regard to nonlinearity, polarity, and changes of the ordering of individual membranes. This study is motivated by the problems of flow of water and transport of solutes in clay soils [1] and of simultaneous uptake of water and solutes by plant roots [2], Some of the conclusions are generalizations of results obtained earlier for special cases see [3] for a detailed evaluation of the literature. 

Low-differential-pressure membrane modules can be considered a subset of low-fouling membranes. These low-differential-pressure membrane modules typically have a thicker feed spacer. Instead of the standard 28-mil thick spacer, these low-differential-pressure membranes have 31- or 34-mil thick spacers. There is less resistance to flow through the feed channels, resulting in lower pressure drops through the membrane modules. Furthermore, the feed channels will not plug as quickly with suspended solids, foulants, or scale. Examples of low-differential-pressure membrane modules are the FilmTec BW30-400-34i (with a 34-mil feed spacer) and the Hydranautics CPA3-LD (with a 31-mil feed spacer). 

Normalized salt passage is generally not used as the primary indicator of when to clean membranes. This is because normalized product flow and/or differential pressure drop (see below) will usually indicate problems with the membranes before product quality becomes an issue. However, normalized salt passage should be used in conjunction... 

Data, particularly normalized data, is evaluated to determine the nature of the loss in membrane performance (see Chapter 11.3 for a complete discussion on data normalization). Normalized permeate flow, salt rejection, and differential pressure should be evaluated to determine trends in performance. 

The pilot plant is equipped with two gauges one at the membrane entrance and the other at the exit. The plant is also equipped with two flowmeters one located at the entrance to the membranes to record the pumped flow and the other in the permeate stream to measure the discharge flow. The plant has a control panel, for starting and stopping the process and for controlling the blower and pump that feeds the bioreactor. The control panel can be set to automatic and the level inside the reactor is kept constant by means of the differential control. 

The volumetric flow rate at which a gas permeates a membrane is called the flux Ui) and it is related to membrane thickness (/), permeability OP,), and differential pressure (AP) as shown in Equation 8.1,... 

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