Sharif Digital Repository

Decentralized supply chain management is found to be significantly relevant in today’s competitive markets. Production and distribution planning is posed as an important optimization problem in supply chain networks. Here, we propose a multi-period decentralized supply chain network model with uncertainty. The imprecision related to uncertain parameters like demand and price of the final product is appropriated with stochastic and fuzzy numbers. We provide mathematical formulation of the problem as a bi-level mixed integer linear programming model. Due to problem’s convolution, a structure to solve is developed that incorporates a novel heuristic algorithm based on Kth-best algorithm, fuzzy... 

Supply chain management has gained much interest from researchers and practitioners in recent years. Proposing practical models that efficiently address different aspects of the supply chain is a difficult challenge. This research investigates an integrated production-distribution supply chain problem. The developed model incorporates parties with a specified number of processes to obtain raw materials from the suppliers in order to convert them to semi and final products. These products are then distributed through warehouses to end-distributors having uncertain demands. This uncertainty is captured as a dynamic stochastic data process during the planning horizon and is modeled into a... 

Decentralized supply chain management is found to be significantly relevant in today’s competitive markets. Production and distribution planning is posed as an important optimization problem in supply chain networks. Here, we propose a multi-period decentralized supply chain network model with uncertainty. The imprecision related to uncertain parameters like demand and price of the final product is appropriated with stochastic and fuzzy numbers. We provide mathematical formulation of the problem as a bi-level mixed integer linear programming model. Due to problem’s convolution, a structure to solve is developed that incorporates a novel heuristic algorithm based on Kth-best algorithm, fuzzy... 

An aggregate production–distribution (P-D) planning generates an aggregate plan for regular time, overtime, outsourcing, hiring, and firing that takes into account distributing, inventory holding, backordering, and machine capacity for a definite planning horizon. A large number of P-D problems require decisions to be made in the presence of uncertainty. Previous research on this topic mainly utilized either stochastic programming or fuzzy programming to cope with the uncertainty. This may lead into huge challenges for supply chain managers that use non-robust P-D planning in uncertain environments. Moreover, there has been little discussion about robust optimization approach in aggregate... 

The FT reaction involves the conversion of syngas which is derived from natural gas or coal to different kinds of products according to the operating conditions and the type of the catalyst. In other words, it is a practical way to convert solid fuel (coal) and natural gas to various hydrocarbons (C1-C60) and oxygenates such as alkanes, alkenes etc. The main products of the reaction are naphtha and gasoline. This paper deals with developing a proper product distribution model for FT process using the appropriate kinetic model, optimizing the respective rate constants while applying them in product distribution equations. The results revealed only 8.09% deviations from the olefin experimental... 

Nowadays, diversion of products distribution from authorised channels to the gray markets is one of the main challenges of manufacturers. Suppose an international supplier distributes the products in several countries with different prices. In parallel importation, there are unauthorised distributers who supply products with a lower price and import them to a higher price market. The problem of parallel importation considering a manufacturer and a competitor is analysed using the game theory approach in this article. We investigate the pricing strategy for manufacturers and the effect of unauthorised distributer on price, market share and profit. We also investigate the performance of... 

A kinetic model based on a mechanistic approach was developed for thermal hydrocracking of a paraffinic feedstock. The hydrocarbon feed was described as a mixture of representative molecules based on structural group analysis (SGA) where information from elemental analysis, H1, and C13-NMR of the feed were used to obtain the average concentration of various structural groups from which representative molecules were constructed. The behavior of the feedstock under reaction conditions was described in terms of the reaction of the individual molecules. The reaction of each of the representative molecules and the corresponding product distribution was based on free radical mechanisms. The... 

Catalytic decomposition of the ethyl mercaptan over an H-ZSM-5 zeolite in a newly designed microreactor was undertaken in this study. A numerically developed distributor possessing superior flow distribution was amended to 24 parallel microchannels with 64 mm length, 700 μm width, and 600 μm depth. Ethyl mercaptan complete conversion required 350 °C through the developed microreactor while in a conventional fixed-bed-reactor 400 °C was needed. Higher selectivity towards the main products of this decomposition (hydrogen sulfide and ethylene) were observed in this microreactor in comparison to that of a fixed-bed-reactor. In addition, lower selectivity towards formation of byproducts was... 

Hydrocracking is one of the most versatile petroleum refining processes for production of valuable products including gasoline, gas oil, and jet fuel. In this paper, a five-parameter continuous lumping model was used for kinetic modeling of hydrocracking of vacuum gas oil (VGO). The model parameters were estimated from industrial data obtained from a fixed bed reactor operating at an average temperature of 400°C and residence time of 0.3 h. Product distributions were obtained in terms of the weight fraction of various boiling point cuts. The model parameters were estimated using the Nelder-Mead optimization procedure and were correlated with temperature. Comparison of experimental and... 

The effects of i-butane addition to methanol in MTP reaction were investigated over an in-house prepared HZSM-5 catalyst. It was observed that, propylene yield would be enhanced when i-butane fed to the reactor along with methanol. The rising growth of the propylene yield continued to peak on till the balance in thermal condition established. Similar trends have been observed when water was added to the mixture. The effect of WHSV with fixed water composition on product distribution was also studied. The optimum point where the highest amount of propylene yielded was shown to be high depended upon the temperature and residence time  

A collaborative supply chain seeks to coordinate its members to produce and distribute products along the chain for minimum overall costs to satisfy customer demand. An integrated multi-period, multi-product and multi-stage supply chain model is developed. A collaborative supply chain grid (CSCG) system gathers necessary information on operations and resources from members of the supply chain. It then guides the members on ordering decisions for a minimum overall cost, while continuously re-directing them as new data becomes available. An actual CSCG system has been implemented in a collaborative auto industry with diverse and dynamic membership, yielding an approximately 26% reduction in... 

Co(salen)-type [where salen = di-(salicylal)-ethylenediimine] complexes were shown to be efficient catalysts in the oxidation of 2-phenylpropane (cumene) by dioxygen primarily to 2-phenyl-2-propanol (cumyl alcohol), 2-phe-nylpropene (a-methylstyrene), and 1-phenylethanone (acetophenone) applying 1H NMR spectroscopy and gas chromatography-mass spectrometry (GC-MS). The effect of substitution on the ligand was also monitored in both oxygen-absorption and the catalytic reaction. Based on these results, the trend observed for the production of a-methylstyrene and cumyl alcohol were parallel to dioxygen uptake by the catalyst in neat cumene, while acetophenone productions obeyed a non-linear... 

The present study deals with the feasibility of a microfluidic microbial electrolysis cell (MEC) as an efficient biohydrogen generator for medical usage for the first time. The evaluation of nickel in microfluidic MEC as an alternative for conventional electrodes indicates successful performance in the improvement of bioenergy production. The maximum biohydrogen production rate and produced power density of 2.2 μW cm−2 and 1.4 μl H2 μl substrate−1 day−1 were obtained, respectively. It is considered a promising technology for medical usage due to the following factors: significant biohydrogen generation, low consumption of expensive materials, simple construction, and utilization of human... 

Mononuclear nonheme iron containing systems are versatile and vital oxidants of substrate hydroxylation reactions in many biosystems, whereby the rate constant of hydroxylation correlates with the strength of the C-H bond that is broken in the process. The thermodynamic reason behind these correlations, however, has never been established. In this work results of a series of density functional theory calculations of substrate hydroxylation by a mononuclear nonheme iron(IV)-oxo oxidant with a 2 His/ 1Asp structural motif analogous to aketoglutarate dependent dioxygenases are presented. The calculations show that these oxidants are very efficient and able to hydroxylate strong C-H bonds,... 

The catalytic activity of highvalent iron-oxo active species of heme enzymes is known to be dependent on the nature of the axial ligand trans to the iron-oxo group. In a similar fashion, experimental studies on iron-oxo porphyrin biomimetic systems have shown a significant axial ligand effect on ethylbenzene hydroxylation, with an axial acetonitrile ligand leading to phenyl hydroxylation products and an axial chloride anion giving predominantly benzyl hydroxylation products. To elucidate the fundamental factors that distinguish this regioselectivity reversal in iron-oxo porphyrin catalysis, we have performed a series of density functional theory calculations on the hydroxylation of...