90,352 research outputs found

    Demand uncertainty and lot sizing in manufacturing systems: the effects of forecasting errors and mis-specification

    Get PDF
    This paper proposes a methodology for examining the effect of demand uncertainty and forecast error on lot sizing methods, unit costs and customer service levels in MRP type manufacturing systems. A number of cost structures were considered which depend on the expected time between orders. A simple two-level MRP system where the product is manufactured for stock was then simulated. Stochastic demand for the final product was generated by two commonly occurring processes and with different variances. Various lot sizing rules were then used to determine the amount of product made and the amount of materials bought in. The results confirm earlier research that the behaviour of lot sizing rules is quite different when there is uncertainty in demand compared to the situation of perfect foresight of demand. The best lot sizing rules for the deterministic situation are the worst whenever there is uncertainty in demand. In addition the choice of lot sizing rule between ‘good’ rules such as the EOQ turns out to be relatively less important in reducing unit cost compared to improving forecasting accuracy whatever the cost structure. The effect of demand uncertainty on unit cost for a given service level increases exponentially as the uncertainty in the demand data increases. The paper also shows how the value of improved forecasting can be analysed by examining the effects of different sizes of forecast error in addition to demand uncertainty. In those manufacturing problems with high forecast error variance, improved forecast accuracy should lead to substantial percentage improvements in unit costs

    High quality exports and consumers’ trust: a development perspective

    Get PDF
    We analyze the impact of the effectiveness of internal regulation for the development of internal and export markets for credence goods, particularly for a developing country which is an exporter (or a potential exporter). In the model, since goods of actual different quality can be sold as high quality goods, expected quality is a function of consumers’ beliefs about the effectiveness of regulation. Foreign consumers, who cannot observe foreign regulation as closely as domestic ones, may partly base their expectations on the level of development of the exporting country. Low effectiveness, negative stereotype and low consumers’ trust may cause a failure in the market for high quality, and there may be a trap of underdevelopment and no high quality exports. The main policy implications are that increasing the effectiveness of regulation improves export prospects; standard setting and enforcement by external actors, such as supermarkets, or NGOs in the case of certain niche markets, is likely to be beneficial

    Dampening variability by using smoothing replenishment rules.

    Get PDF
    A major cause of supply chain deficiencies is the bullwhip effect which can be substantial even over a single echelon. This effect refers to the tendency of the variance of the replenishment orders to increase as it moves up a supply chain. Supply chain managers experience this variance amplification in both inventory levels and replenishment orders. As a result, companies face shortages or bloated inventories, run-away transportation and warehousing costs and major production adjustment costs. In this article we analyse a major cause of the bullwhip effect and suggest a remedy. We focus on a smoothing replenishment rule that is able to reduce the bullwhip effect across a single echelon. In general, dampening variability in orders may have a negative impact on customer service due to inventory variance increases. We therefore quantify the variance of the net stock and compute the required safety stock as a function of the smoothing required. Our analysis shows that bullwhip can be satisfactorily managed without unduly increasing stock levels to maintain target fill rates.Bullwhip effect; Companies; Cost; Costs; Impact; Inventory; Managers; Order; Replenishment rule; Rules; Safety stock; Supply chain; Supply chain management; Variability; Variance; Variance reduction;

    Measuring the variability in supply chains with the peakedness

    Get PDF
    This paper introduces a novel way to measure the variability of order flows in supply chains, the peakedness. The peakedness can be used to measure the variability assuming the order flow is a general point pro- cess. We show basic properties of the peakedness, and demonstrate its computation from real-time continuous demand processes, and cumulative demand collected at fixed time intervals as well. We also show that the peakedness can be used to characterize demand, forecast, and inventory variables, to effectively manage the variability. Our results hold for both single stage and multistage inventory systems, and can further be extended to a tree-structured supply chain with a single supplier and multiple retailers. Furthermore, the peakedness can be applied to study traditional inventory problems such as quantifying bullwhip effects and determining safety stock levels. Finally, a numerical study based on real life Belgian supermarket data verifies the effectiveness of the peakedness for measuring the order flow variability, as well as estimating the bullwhip effects.variability, peakedness, supply chain

    Coordination of Foliar and Wood Anatomical Traits Contributes to Tropical Tree Distributions and Productivity along the Malay-Thai Peninsula

    Get PDF
    Drought is a critical factor in plant species distributions. Much research points to its relevance even in moist tropical regions. Recent studies have begun to elucidate mechanisms underlying the distributions of tropical tree species with respect to drought; however, how such desiccation tolerance mechanisms correspond with the coordination of hydraulic and photosynthetic traits in determining species distributions with respect to rainfall seasonality deserves attention. In the present study, we used a common garden approach to quantify inherent differences in wood anatomical and foliar physiological traits in 21 tropical tree species with either widespread (occupying both seasonal and aseasonal climates) or southern (restricted to aseasonal forests) distributions with respect to rainfall seasonality. Use of congeneric species pairs and phylogenetically independent contrast analyses allowed examination of this question in a phylogenetic framework. Widespread species opted for wood traits that provide biomechanical support and prevent xylem cavitation and showed associated reductions in canopy productivity and consequently growth rates compared with southern species. These data support the hypothesis that species having broader distributions with respect to climatic variability will be characterized by traits conducive to abiotic stress tolerance. This study highlights the importance of the well-established performance vs. stress tolerance trade-off as a contributor to species distributions at larger scales

    South African Farmers’ Perceptions of the Benefits and Costs of Complying with EUREPGAP to Export Fresh Citrus to the European Union (EU)

    Get PDF
    A representative stratified random sample of 100 South African farmers from across all production regions that export fresh citrus to the EU were surveyed during 2007-2008 to document their perceptions of the benefits and costs of complying with EUREPGAP standards on citrus exports. Principal Component Analysis identified six broad dimensions of internal benefits as improved operating/technical performance; regulations compliance and intra-business benefits; gains in competitiveness; regulations compliance and new market access; benefits from existing markets; and to overcome non-tariff barriers to entry. Two further dimensions of supply chain benefits identified by PCA were improved business working relationship and product quality benefits, and improved cooperation and contractual benefits. The sampled growers thus perceive operational, technical, safety, management, monetary, marketing and supply chain benefits from certification. The major costs of implementing EUREPGAP certification related to initial investment costs and the recurrent annual costs of compliance. The respondents, on average, spent R70510 on initial compliance costs, mainly for infrastructure, additional buildings and employees training. Some 60% of respondents spent less than 1% of annual farm turnover on initial compliance costs, while most of the respondents (84%) spent less than 1% of annual farm turnover on recurrent costs of compliance. Growers that owned a pack-house had statistically significantly higher initial and annual costs of compliance. The intra- and inter-firm benefits and costs of compliance identified by these results indicate factors that policymakers, and the Citrus Growers’ Association of Southern Africa, can focus on to improve the competitiveness of SA fresh citrus exports to the EU.South African fresh citrus exports, European Union, perceived benefits and costs, EUREPGAP compliance, Farm Management,
    • 

    corecore