In this paper two similar models for the maintenance of a production-inventory system are considered. In both models, an input generating installation supplies a buffer with a raw material and a production unit pulls the raw material from the buffer. The installation in the first model and the production unit in the second model deteriorate stochastically over time and the problem of their opti...

Introduction: The Failure Mode and Effects Analysis (FMEA), first of all, identifies dangerous modes in a process and, then, provides proper control measures that are required to reduce the level of risk. This study aims to investigate the risk level before and after the implementation of control measures in an edible oil factory. Methods: This cross-sectional study was conducted in an edibl...

We propose a mathematical model which considers the series-type product structure with n−1 predecessors. Our objective is to obtain the optimal production functions, in the planning horizon [0,T ], based on the assumptions (1) that the cost of production unit is a linear function of production quantity in a time unit, (2) that sales of finished goods occur at the end of planning horizon, and (3...

Conventional learning curves relating unit cost to measures of production experience are estimated for 221 specialty chemicals produced by a Fortune 500 company. Detailed records on cost and R&D coupled with insights from company personnel are used to explain the variation across products in the rate of cost reduction. Products that exhibited the strongest relationship between unit cost and mea...

This paper proposes a multiobjective, mixed-integer nonlinear programming (MINLP) model for the superstructure optimization of hydrocarbon biorefineries via gasification pathway under economic and environmental criteria. The proposed hydrocarbon biorefinery superstructure includes a number of major processing stages, such as drying of the cellulosic biomass feedstocks, air separation unit, gasi...

polygalacturonase production under different shear stress environments by aspergillus sp. was studied. it was found that the rate of enzyme production in the stirred tank fermentor decreased with increasing the stirrer speed in the range 300-750 rpm. on the other hand, in a split cylinder air-lift fermentor, the rate of polygalacturonase production slightly increased with increasing in air rate...