Manufacturing flow line systems: a review of models and analytical results

The most important models and results of the manufacturing flow line literature are described. These include the major classes of models (asynchronous, synchronous, and continuous); the major features (blocking, processing times, failures and repairs); the major properties (conservation of flow, flow rate-idle time, reversibility, and others); and the relationships among different models. Exact and approximate methods for obtaining quantitative measures of performance are also reviewed. The exact methods are appropriate for small systems. The approximate methods, which are the only means available for large systems, are generally based on decomposition, and make use of the exact methods for small systems. Extensions are briefly discussed. Directions for future research are suggested.National Science Foundation (U.S.) (Grant DDM-8914277

Aquaporin-2: COOH terminus is necessary but not sufficient for routing to the apical membrane.

Item does not contain fulltextRenal regulation of mammalian water homeostasis is mediated by the aquaporin-1 (AQP1) water channel, which is expressed in the apical and basolateral membranes of proximal tubules and descending limbs of Henle, and aquaporin-2 (AQP2), which is redistributed from intracellular vesicles to the apical membrane (AM) of collecting duct cells with vasopressin. In transfected Madin-Darby canine kidney cells, AQP1 and AQP2 are regulated similarly, which indicates that routing elements reside in their primary sequences. We studied the role of the AQP2 COOH terminus in apical routing and AQP2 shuttling. An AQP1 chimera (AQP1 with an AQP2 tail: AQP1/2-N220) was located only in the AM independent of forskolin treatment. Forskolin increased the apical expression of AQP1 and AQP1/2-N220 less than twofold; that of AQP2 increased more than fourfold with concomitant changes in osmotic water permeabilities. The dimeric AQP2 tail coupled to placental alkaline phosphatase (AQP2-Plap) was retained in intracellular vesicles different from those of homotetrameric wild-type AQP2; the same protein without the AQP2 tail (TMR-Plap) was only expressed in the AM. The study shows that the AQP2 COOH tail is necessary but not sufficient for routing to the AM and suggests that other parts of AQP2 are needed for AQP2 accumulation in intracellular vesicles