Optimal control of the service rate of an exponential queuing network using Markov decision theory

An exponential queuing network of two service stations is considered. The service rate at each station can either be fast or slow. A policy in which the service rate to be used at each station is specified as a function of the state of the system is investigated in order to minimize a given objective cost function. Howard's policy space algorithm is used to characterize the form of the optimal policy. Results show that the optimal policy is a simply connected one and of montone structure.     

MATHEMATICAL MODELING of TRANSIENT HEAT and MASS TRANSPORT IN A BAKING BISCUIT

Drying behavior of a single baking biscuit was modeled using unsteady state, anisotropic, two dimensional, simultaneous heat and mass balances. Solutions of these equations agreed well with the experimentally determined temperature and the moisture data. Modeling revealed that in the outer sections of the baking biscuit conduction and diffusion were the dominant heat and mass transfer mechanisms, respectively. In the central section of the biscuit the gas cells cracked with the increased vapor pressure and the upward volume expansion, then air/vapor enclaves were formed among the horizontal dough layers in the radial direction. the dominant heat and mass transfer mechanisms in the central section of the biscuit were convection. Presence of two different regime zones in a baking biscuit may have important consequences concerning the strength of the commercial products against crumbling during marketing and consumption.     

EFFECT OF HIGH PRESSURE ON LACTOCOCCAL BACTERIOPHAGES

Four different host-specific lactococcal bacteriophages were subjected to high hydrostatic pressure and heat treatments. Pressure treatments were done at room temperature at 300 and 350 MPa for 5–40 min. Complete inactivation of bacteriophages was observed starting at 350 MPa for 20-min treatment at room temperature. The effect of heat on the bacteriophages was analyzed by heat treatment at 71.7C for predetermined lengths of time (1–5 min). Decrease in bacteriophage number was observed after 3 min of heat treatment at 71.7C. Pressure treatment at 350 MPa/5 min and heat treatment at 71.7C/3 min were both found to be effective for the inactivation of lactococcal bacteriophages. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis indicated that protein profiles of pressure-treated (350 MPa, 25 min) bacteriophages were altered.

PRACTICAL APPLICATIONS

Bacteriophages are still a problem for the production of fermented dairy products, as there has not been a process to eliminate them completely from the fermentation environment. Processes such as pasteurization are not adequate to eliminate bacteriophages. However, new food preservation methods have been developed, one of which is high hydrostatic pressure (HHP) processing. HHP has potential application for the inactivation of viruses. Here, we demonstrate the application of HHP to inactivate the bacteriophages of dairy starter culture Lactococcus in comparison with heat treatment.     

QUALITY CONTROL CHARTS FOR STORAGE OF EGGS

Modified Shewhart charts were constructed with weight loss, Haugh units and yolk index for storage of untreated, soda lime, water glass or oil coated and thermostabilized eggs. The data obtained showed differences between the treatments, and control charts derived therefrom illustrate maintenance within limits of the inevitable quality loss which accompanies storage of eggs. Knowledge of the trends make it possible to readjust the storage conditions to prolong the period before violation of acceptable limits comes into play.