Adaptive Control of a Production-Inventory Model with Uncertain Deterioration Rate

This paper studied a continuous-time model of a production maintenance system in which a manufacturing firm produces a single product selling some and stocking the remaining. The problem of adaptive control of a production-maintenance system with unknown deterioration has been presented. Using Liapunov technique, the production rate and updating rule of deterioration rate are derived as non-linear functions of inventory level perturbation. Numerical analysis for the system has been presented for a set of parameter values and demand rate.

Ordering Cost Depletion in Inventory Policy with Imperfect Products and Backorder Rebate

This study presents an inventory model for imperfect products with depletion in ordering costs and constant lead time where the price discount in the backorder is permitted.The imperfect products are refused or modified or if they reached to the customer,returned and thus some extra costs are experienced.Lately some of the researchers explicitly present on the significant association between size of lot and quality imperfection.In practical situations,the unsatisfied demands increase the period of lead time and decrease the backorders.To control customers'problems and losses,the supplier provides a price discount in backorders during shortages.Also,an order’s policies may result in including some imperfect products in arrival lots.A discount on price may be offered by the supplier on the out-of-stock products to manage the backorder problems.The study aims to develop a model with imperfect products by permitting the price discount in backorders,and the cost of ordering is considered a decision variable.First,it is assumed that the demand for lead time is followed by a normal distribution and then stops it and assumed that the first two moments of demand for lead time are known.Further,the minimax distribution method is used to solve this model,and a separate algorithm is designed.In this study,two models are discussed with and without a normally distributed rate of demand.The current study verified with the help of some numerical examples over various model parameters.

An Inventory Model of Production with Level Dependent Demand Allowing Few Defective Items

This paper considers a model regarding the products with finite life which allows defective items in reproduction and causes a small amount of decay. The market demand is assumed to be level dependent linear type. The model has also considered the constant production rate which stops after a desired level of inventories and that is the highest level of it. Due to the market demand, defective item and product’s decay, the inventory reduces to the zero level where again the production cycle starts. With a numerical search procedure, the proof of the proposed model has been shown. The objective of the proposed model is to find out the total optimum inventory cost, optimum ordering cost and optimum ordering cycle.

A Time Dependent Inventory Model for Exponential Demand Rate with Constant Production Where Shelf-Life of the Product Is Finite

In this paper a time dependent inventory model is developed on the basis of constant production rate and market demands which are exponentially decreasing. It advances in quest of total average optimum cost considering those products which have finite shelf-life. The model also considers the small amount of decay. Without having any sort of backlogs, production starts. Reaching at the desired level of inventories, it stops production. After that due to demands along with the deterioration of the items it initiates its depletion and after certain periods the inventory gets zero. The decay of the products is level dependent. The objective of this paper is to find out the optimum inventory cost and optimum time cycle. The model has also been justified with proving the convex property and by giving a numerical example.

A Production Inventory Model of Constant Production Rate and Demand of Level Dependent Linear Trend

The proposed model considers the products with finite shelf-life which causes a small amount of decay. The market demand is assumed to be level dependent and in a linear form. The model has also considered the constant production rate which stops attaining a desired level of inventories and that is the highest level of inventories. Production starts with a buffer stock and without any sort of backlogs. Due to the market demand and product’s decay, the inventory reduces to the level of buffer stock where again the production cycle starts. With a numerical search procedure the proof of the proposed model has been shown. The objective of the model is to obtain the total average optimum inventory cost and optimum ordering cycle.

中国内地省级无意产生的五氯苯和六氯苯多源大气排放清单

基于技术分类方法构建了动态排放因子数据库,再采用排放因子法,自下而上构建了1960~2019年中国内地省级无意产生的五氯苯和六氯苯的多源大气排放清单,并探究其时空分布特征.研究结果显示,五氯苯的最大排放源是含氯化学品生产,而六氯苯的最大排放源则是金属冶炼;五氯苯和六氯苯的排放密度均表现为东部地区高于西部地区的特征.从1960~2019年,五氯苯和六氯苯的排放量从1277.9,81.2kg分别上升至11862.3,439.7kg,但排放强度(单位GDP的排放量)却从869.3,55.2g/亿元分别下降至12.0,0.4g/亿元.

新质生产力赋能产业链供应链韧性提升研究——来自上市公司的经验证据

新质生产力以提升全要素生产率为核心,以颠覆式创新为主导不断推动产业变革。在大国博弈的时代背景下,文章通过供需关系匹配、供需关系维持以及供应质量提升三个维度对产业链供应链韧性的内涵与机制进行理论分析。通过2009—2022年中国上市公司高度细化的“上游企业—下游企业—年份”数据集,实证检验了新质生产力对产业链供应链韧性的影响。研究发现,新质生产力显著促进供需关系匹配、供需关系维持以及供应质量提升,进而提升产业链供应链韧性,该结论在经过内生性问题处理以及一系列稳健性检验后依然成立。机制检验结果表明,新质生产力通过降低协调沟通成本与运输库存成本提升产业链供应链韧性。此外,新质生产力对产业链供应链韧性的提升效果存在明显差异,在大型供应商、国有供应商以及高市场化地区样本中,新质生产力的促进作用更明显。研究结论为新质生产力提升产业链供应链韧性提供了经验支持,为加快产业链供应链韧性与安全水平提供了政策启示。

随机情景下MTS/MTO串联生产系统库存控制策略

该研究探讨供应链库存控制策略及生产协同重要性。将备货型生产(make-to-stock, MTS)与按订单生产(make-to-order, MTO)两级串联模式应用于高效响应性供应链的生产与库存联合控制问题并刻画其最优策略。针对订单到达服从泊松过程和生产时间服从指数分布情形,通过马尔科夫过程转移速率一致化技术建立起马尔科夫决策过程模型并得到相应贝尔曼最优方程。基于最优费用函数结构性质,将最优生产与库存控制策略刻画为依赖系统状态的基本库存策略。随后,将模型拓展到批量生产情形。数值算例验证了最优策略单调结构性质,给出不同情境下的最优策略绩效。同时将最优策略与两种常见策略进行比较。基础情境下,容限策略偏离最优7.36%,短视策略偏离最优25.73%。其他情境下,最优策略都明显优于另两种策略。

工业锅炉产品碳足迹评估方法研究

产品碳足迹评估以工业锅炉为对象,基于生命周期视角,确定工业锅炉的系统边界、功能单位及取舍原则,将工业锅炉生命周期分为原材料获取阶段、生产阶段、使用阶段及处置回收阶段,进行清单数据收集与分析,建立各阶段的碳足迹计算方法。以某锅炉制造厂的燃气蒸汽锅炉为例,对其生命周期各阶段的碳排放进行计算和分析,结果表明:在其生命周期的各个阶段中,使用阶段的碳排放在总排放中具有最大贡献,占比超过99%。通过敏感性分析,发现燃料使用敏感度最高,其次是电力和原材料;运用蒙特卡洛方法进行不确定度分析,确定并量化输入数据产生的不确定性,优化清单数据收集方案,从而更加真实地反映产品生命周期碳排放量。

生鲜农产品在连锁超市的横向补给问题研究

随着经济的发展,消费者对生鲜农产品的需求逐步提升,生鲜农产品在各大连锁超市的销售比例逐渐上升,但由于消费者对于生鲜农产品的需求难以准确预测,超市存在生鲜农产品库存过剩或短缺的现象。文章将连锁超市的所有加盟店视为一个系统,通过建立横向补货的库存总成本模型和运输模型,寻求补货过程中使整个系统的库存成本最低的补货方案,从而提高整个系统的利润率。

石化产品碳足迹种类规则标准化研究

碳足迹作为评价产品或服务生命周期碳排放的重要方法已得到了广泛应用,但由于现有国际标准原则性较强,需要针对不同行业进行标准化处理。产品种类规则是对一种或多种产品种类进行碳足迹评价所必须满足的一套具体的规则、要求和指南,制定《碳足迹产品种类规则石化产品》行业标准对推动石化产品碳足迹评价的标准化和一致性具有重要意义。该文从石化产业链、国民经济行业分类、化学工业的专业范畴等角度,提出了涵盖石油炼制、基本有机原料、有机化工品和高分合成材料在内的石化产品描述,阐述了制定该产品种类规则的功能单位、系统边界、分配规则、生命周期阶段定义等内容的相关思考。

双渠道供应链下易腐品的库存和定价决策

以现实易腐产品供应链为背景,研究单一零售商和单一供应商组成的双渠道供应链模型,即供应商可通过直接在线渠道和间接零售渠道销售易腐产品,除了产品数量下降外,产品质量也会随着时间的推移而下降,同时,产品质量的下降会影响零售渠道的需求率。分别建立集中式和分散式两类模型,并提出相应算法求解最佳价格、订购频率和订购周期等。结果显示,分散式的供应链不仅会侵蚀两家公司的利润,并且产品的浪费率也较高。通过采用收入分享和二部定价法的方式能够协调供应链,减少供应链的总浪费率。同时,随着产品劣化率的提高,两家公司会更倾向于进行供应链协调,协调合同对零售商利润的提升更为显著。在模型扩展部分考虑直接渠道的交货时间,结果表明,分散式模型的供应商会投入更多资金以缩短交货时间。

生产能力约束下易逝品动态批量决策研究

针对易逝品在生产能力有限的情况下的决策问题,首先通过构建包含生产成本和库存持有成本在内的成本最小化模型,分析了生产成本和库存持有成本为一般化的单调递增凹函数的最优动态批量决策和相互影响。然后通过求解模型得出了最优解的结构特性,并设计出前向动态规划算法以及分析了无投机性成本结构的特殊情形。研究发现:在生产计划中,不同周期生产的产品库存应按照先进先出的原则满足各周期需求;若任意周期的需求都不大于生产能力,则著名的零库存性质在时间依赖的库存损失率及库存持有成本和生产能力双重约束下仍然成立。

Mushroom Production as an Alternative for Rural Development in a Forested Mountainous Area

Wild mushrooms are recognized as important non-wood forest products in mountainous ecosystems, but their real potential for generating rural economies has not been fully evaluated due to the difficulties in obtaining reliable productivity data, minimizing their true potential as contributor to rural economies. Mushroom yield models based on large data series from Pinus forest ecosystems in the region of Catalonia(Spain), combined with data from the Spanish National Forest Inventory allow us to estimate the potential mushroom productivity by forest ecosystems. The results of 24,500 tons/yr of mushrooms of which 16,300 tons are classified as edible and 7,900 tons are commonly marketed demonstrate the importance of mushroom productions in Catalonian pine forests, mostly located in mountainous areas where the development of agricultural activities is limited. Economic mushroom value is estimated at 48 million € for the edible mushroom and 32 million € for those corresponding to marketable yields, confirming the potential of this non-wood forest product. These production results and corresponding economic values provide a basis for the incorporation of wild mushrooms as significant non-wood forest products in the development of forest policies in mountainous areas.

Development of a Tool Cost Optimization Model for Stochastic Demand of Machined Products

Cutting tool management in manufacturing firms constitutes an essential element in production cost optimization. In order to optimize the cutting tool stock level while concurrently minimizing production costs, a cost optimization model which considers machining parameters is required. This inclusive modeling consideration is a major step towards achieving effectiveness of cutting tool management policy in manufacturing systems with stochastic driven policies for tool demand. This paper presents a cost optimization model for cutting tools whose utilization level is assumed to be optimized in respect of the machining parameters. The proposed cost model in this research incorporated the effects of diversified machining costs ranging from operational through machining, shortage, holding, material and ordering costs. The machining of parts was assumed to be a single cutting operation. Holt-Winters forecasting technique was used to create a stochastic demand dataset for a test scenario in the production of a high-end automotive part. Some numerical examples used to validate the developed model were implemented to illustrate the optimal machining and tool inventory conditions. Furthermore, a sensitivity analysis was carried out to study the influence of varying production parameters such as: machine uptime, demand and cutting parameters on the overall production cost. The results showed that a desired low level of tool storage and holding costs were obtained at the optimal stock levels. The machining uptime had a significant influence on the total cost while tool life and cutting feed rate were both identified as the most influential cutting variables on the total cost. Furthermore, the cutting speed rate had a marginal effect on both costs and tool life. Other cost variables such as shortage and tool costs had significantly low effect on the overall cost. The output trend showed that the feed rate is the most significant cutting parameter in the machining operation, hence influencing the cost the most. Also, machine uptime and demand significantly influenced the total production cost.

Comparison of Radionuclide’s Inventories and Activities With Slightly Enriched Uranium and Plutonium Fuel in CANDU Reactors

In these studies the isotopic inventories and corresponding activities of important nuclides for different fuel cycles of a CANDU reactor have been compared. The calculations have been performed using the computer code WIMSD4. The isotopic inventories and activities have been calculated versus the fuel burn-up for the natural UO2 fuel, 1.2% enriched UO2 fuel and for the 0.45% PuO2-UO2 fuel. It is found that 1.2% enriched uranium fuel has the lowest activity as compared to other two fuel cycles and vice versa for the 0.45% PuO2-UO2 fuel.

Models for Ordering Multiple Products Subject to Multiple Constraints, Quantity and Freight Discounts

One of the most important responsibilities of a supply chain manager is to decide “how much” (or “many”) of inventory items to order and how to transport them. This paper presents four mixed-integer linear programming models to help supply chain managers make these decisions for multiple products subject to multiple constraints when suppliers offer quantity discounts and shippers offer freight discounts. Each model deals with one of the possible combinations of all-units, incremental quantity discounts, all-weight and incremental freight discounts. The models are based on a piecewise linear approximation of the number of orders function. They allow any number of linear constraints and determine if independent or common (fixed) cycle ordering has a lower total cost. Results of computational experiments on an example problem are also presented.

考虑疫情风险与双重时效性的生鲜品供应中断库存控制策略研究

为解决重大疫情引发的供应中断导致生鲜品库存水平振荡,在市场需求随机变化的情形下,建立一个由供应商、配送中心和零售商组成的三级生鲜供应链库存系统,考虑由疫情引起的三种风险情景,引入系统动力学模型对零售商动态库存系统运营进行仿真分析。研究发现:受疫情风险传导系数和变质率两个序参量影响,供应链库存呈现振荡趋势;通过确定不同供应中断时长下的疫情风险情景提出优化保鲜投入策略、安全库存策略、以及共享库存联合提前转运策略有效降低零售端库存水平振荡并使其呈现渐稳趋势,实现产品在交付过程中的双重时效性,达到供需匹配,缓解疫情风险带来的影响,为相关零售企业提供决策支持。

乳制品企业存货管理问题研究——以H乳业有限公司为例

存货作为企业流动资产的重要组成部分,良好的存货管理能够维持企业的供、产、销有序进行,并为其带来资金流入。食品加工制造业企业,尤其是保质期较短且质量要求严格的乳制品企业,加强存货管理是提高企业营业利润的关键。本研究通过收集整理H企业2017-2020年原料采购、存货管理等相关数据,发现该企业存在原料采购不合理、库存管理不善、产品积压损耗较大等问题。对此,本文提出了改良仓库结构、采用ABC模式进行存货精细化管理、通过最佳经济订货模型计算采购量并进行精准销售预测等改进策略,以期降低企业的存货管理成本,提高企业存货周转率和经济效益。

生产速率可调整时现货型生产系统的最优生产决策研究

本文针对现货型生产系统,研究其生产速率可调整情况下的最优库存决策问题。生产系统有高速率、低速率生产或者暂停生产这三种生产状况。本文以长期折扣利润最大化为目标,研究其最优生产决策。假设需求过程为泊松过程,生产时间间隔服从指数分布。本文首先将该问题抽象为连续时间下的马氏决策过程,并构建无穷周期下的折扣生产利润最大化为目标的HJB方程。其次,进一步对模型结构性质进行分析,最终获得使利润最大化的动态库存控制决策,即:当库存量大于高存储点时,系统停止生产;当库存量小于低存储点时,系统以高速率生产;当库存量介于两个存储点之间时,则以低速率生产。最后,在最优策略分析的基础上进行模型算例分析。