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

Disturbance and investment: developmental responses of tropical lotic midges to repeated tube destruction in the juvenile stages

1. Investment in silken tubes may give tubicolous chironomid larvae more to lose than non-tube building taxa when physical disturbances or the actions of other organisms induce dispersal. In this study, two chironomid species from flood-prone Australian tropical streams were subjected to repeated experimental destruction of their larval and pupal tubes in laboratory experiments, with life-history parameter responses recorded.\ud \ud 2. When subjected to the tube destruction treatments, Echinocladius martini (Orthocladiinae), whose larvae construct branched loose silken tubes in fast flow, showed no reduction in survivorship to adult, whereas Polypedilum australotropicus (Chironominae), which builds compact tightly woven tubes incorporating detrital material within pool leaf packs, showed reduced survivorship of about 25%.\ud \ud 3. For both species, tube destruction reduced pupal duration, regardless of whether destruction occurred in the larval stage only, or in both the larval and pupal stages. This may be a response to the risks of exposure outside tubes in nature, particularly for pupae, which are incapable of spinning silk.\ud \ud 4. Tube destruction caused little or no reduction in adult size, longevity, or female fecundity (oocyte number) for either species, but oocyte development and size was retarded in E. martini females, reflecting the energetic and nutritive costs of the tube destruction treatments.\ud \ud 5. Contrasts in the responses of the two species reflect differences in tube-building behaviour and in situ habitat use. These results demonstrate that tube loss can affect the fitness of individual chironomids, though both species proved generally resilient, which may reflect their long-term exposure to variable tropical lotic conditions