| 1. |
- Zhang, Ge, et al.
(författare)
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Dual β-oxidation pathway and transcription factor engineering for methyl ketones production in Saccharomyces cerevisiae
- 2022
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Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 73, s. 225-234
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Tidskriftsartikel (refereegranskat)abstract
- Methyl ketones (MK) are highly valuable fatty acid derivatives with broad applications. Microbes based biosynthesis represents an alternative route for production of these usually fossil based chemicals. In this study, we reported metabolic engineering of Saccharomyces cerevisiae to produce MK, including 2-nonanone, 2-undecanone, 2-tridecanone and 2-pentadecanone. Besides enhancing inherent peroxisomal fatty acids β-oxidation cycle, a novel heterologous cytosolic fatty acids β-oxidation pathway was constructed, and this resulted in an increased production of MK by 2-fold. To increase carbon fluxes to methyl ketones, the supply of precursors was enhanced by engineering lipid metabolism, including improving the intracellular biosynthesis of acyl-CoAs, weakening the consumption of acyl-CoAs for lipids storage, and reinforcing activation of free fatty acids to acyl-CoAs. Hereby the titer of MK was improved by 7-fold, reaching 143.72 mg/L. Finally, transcription factor engineering was employed to increase the biosynthesis of methyl ketones and it was found that overexpression of ADR1 can mimic the oleate activated biogenesis and proliferation of peroxisomes, which resulted in a further increased production of MK by 28%. With these modifications and optimization, up to 845 mg/L total MK were produced from glucose in fed-batch fermentation, which is the highest titer of methyl ketones reported produced by fungi.
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| 2. |
- Zhang, Qinhong, et al.
(författare)
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Optimal ordering and pricing decisions for a company issuing product-specific gift cards
- 2018
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Ingår i: Omega. - : Elsevier. - 0305-0483 .- 1873-5274. ; 74, s. 92-102
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate gift card's influence on retailers’ ordering decisions and analyse the benefits of issuing product-specific gift cards. We propose an optimal ordering model for retailers’ decision problems with gift cards being issued. We also solve the problem with the analytical forms of optimal order quantities and expected profits. By comparing the results with the classical newsvendor problem, we classify the benefits of issuing gift cards into three categories: (1) the demand stimulating; (2) the pre-payment, and (3) the non-redemption. We step further to explore a retailer's problem on how to determine the optimal discount for gift cards, which is characterized by a joint optimal policy on the ordering quantity and the discount. We derive the optimal condition on this joint policy. Numerical examples are conducted to illustrate the model results and analyse the influences of parameters. A sample average approximation method is also been introduced to solve the optimization model.
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| 3. |
- Liu, Biyu, et al.
(författare)
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A min–max solution to optimise planned lead time in a remanufacturing system
- 2019
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Ingår i: International Transactions in Operational Research. - : John Wiley & Sons. - 0969-6016 .- 1475-3995. ; 26:2, s. 485-506
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Tidskriftsartikel (refereegranskat)abstract
- Determining a rational planned lead time (PLT) is a critical and difficult problem in production planning, especially for a remanufacturing system. This paper considers an optimisation problem of the PLT in a make-to-order remanufacturing system to coordinate disassembly–remanufacturing–reassembly and to improve performance. This optimisation model is designed to determine the PLT that minimises the inventory holding and shortage costs. Given the unknown distribution of remanufacturing time but with known first and second moments, this model is solved by a min–max approach, which can capture distributions with the same first and second moments. How the PLT and total cost are affected by yield rate with different first and second moments, unit holding cost, unit shortage cost and purchasing lead time are also investigated through numerical examples in this paper. The results of this study are shown to be consistent with practice and can be a support to decision-making in production planning and scheduling for remanufacturing.
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| 4. |
- Liu, Biyu, et al.
(författare)
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Optimal Operational Decision Making of Manufacturers and Authorized Remanufacturers with Patent Licensing under Carbon Cap-and-Trade Regulations
- 2020
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Ingår i: Complexity. - : Hindawi Publishing Corporation. - 1076-2787 .- 1099-0526. ; 2020
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Tidskriftsartikel (refereegranskat)abstract
- Constrained by production capacity and the pressure to reduce emissions, many original equipment manufacturers (OEMs) authorize third-party remanufacturers (TPRs) to remanufacture patented products. We investigate the operational decisions of OEMs and authorized TPRs under carbon cap-and-trade regulations in a two-echelon supply chain. We first formulate an operational decision model for OEMs before a TPR enters. Then, for the cases of centralized and decentralized decision making, we formulate an operational decision-making model for the TPR and, subsequently, establish one for the OEM after the TPR enters. We further analyze the effects of carbon emissions cap, trading price of carbon permits, yield rate, and consumer willingness to pay (WTP) on optimal decisions. Our results indicate: whether TPRs accept authorization remanufacturing depending on the ratio of carbon emissions cap to carbon emissions for producing per remanufactured product; royalty rate is negatively affected by trading price of carbon permits and per remanufactured product’ carbon emissions other than that for per new product, and can offset the threat caused by TPRs; the implementation of carbon cap-and-trade regulations causes OEMs to charge TPRs lower royalty rate; centralized decision making increases the total profit of the supply chain and delivers superior environmental benefits. As yield rate and WTP increase, the total profit increases, increasingly sensitive to WTP.
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| 5. |
- Segerstedt, Anders, et al.
(författare)
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Order quantities in a production line : influences on production output and lead-time
- 2020
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This article tests the effect of different order quantities and setup times and its dependence of maximum Work-in-Process (WIP). The main studied supply chain consists of five linked machines with a fixed setup time for every batch in every machine, and stochastic operation times for every item in the batch. Additionally three linked machines with a clear bottleneck are studied. Production management can only control maximum WIP and not average WIP. Average WIP is a consequence of released work, variations, capacity and maximum WIP. A number of test cases are made where the number of units in the machines and the buffer areas are restricted. Previous studies have shown the dominance of CONWIP over Kanban, so only situations where maximum WIP is restricted in the total production line is studied. – The results show that increased maximum WIP leads to longer average lead-time but also that its coefficient of variation increases, independent of setup time and order quantity. A literature review confirms our assumption and opinion that large variations in lead-times are worse than long lead-times. A smaller order quantity leads to a lower production rate if not the setup time is decreased proportionally. A reduction of the order quantity can also increase the lead-time and its variation. A decrease of the order quantity requires a reduction of maximum WIP to implement its advantages. Therefore, reducing order quantities but still use the same parameters in in the companies’ computer system for material- and production control will prevent improvements. It is always favourable to reduce setup times and/or variation in operation times.
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| 6. |
- Zhang, Qinhong, et al.
(författare)
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Returnable packaging management in automotive parts logistics: dedicated mode and shared mode
- 2015
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Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273 .- 1873-7579. ; 168, s. 234-244
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Tidskriftsartikel (refereegranskat)abstract
- We compare two different modes, i.e., dedicated mode and shared mode, used in packaging management in automotive parts logistics. In dedicated mode, every parts supplier uses his own packaging; while in shared mode, packages can be shared among the suppliers. For each mode, we calculate the total costs consisting of transportation cost and inventory holding cost, and prove that the total costs, the transportation cost and the inventory holding cost are all smaller under shared mode. We further illustrate the factors that influence the cost savings of shared mode, i.e., the total cost of dedicated mode minus that of shared mode. In particular, the cost savings are proved to be negatively related to the number of package categories, and are positively related to: (1) the demand gap of packages between areas, i.e., sum of the volume difference of every kind of packages that transported in and out of one area; (2) the failed ratio factor of the returned packages, i.e., the ratio of the packages that cannot be returned to the supplier because of broken, pilferage, misplace, etc.; and (3) the time savings of short distance transportation, i.e., the transportation time consumed between areas minus the transportation time within one area. Finally, numerical examples show that the cost savings can be considerable, and the number of package categories is the most important influence factor.
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| 7. |
- Zhang, Qinhong, et al.
(författare)
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Supply Chain Coordination with Trade Credit and Quantity Discount Incorporating Default Risk
- 2014
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Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273 .- 1873-7579. ; 153, s. 352-360
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Tidskriftsartikel (refereegranskat)abstract
- We explore the issue of supply chain coordination by considering trade credit and its risk. It shows that, in a retailer-manufacturer system, the manufacturer may deliver less than the retailer's order quantity when the payment is delayed, and the manufacturer's risk aversion makes this result hold in a wider range. These findings are different from the common sense believed in the retailer-manufacturer coordination literature, which suggests the manufacturer to entice the retailer to enlarge the lot size. The manufacturer's decision of decreasing the order quantity prevents the supply chain from operating in the optimal situation. In order to coordinate supply chain, we propose a modified quantity discount based on both order quantity and advance payment which means the manufacturer offers quantity discount if the retailer pays part of the payment in advance and enlarges her order quantity. The ranges of advance payment ratio and the quantity discount are derived. Numerical examples are used to demonstrate the conclusions.
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