Modeling and Analysis of Effective Ways for Improving the Reliability of Second-hand Products Sold with Warranty

Often, customers are uncertain about the performance and durability of the used/second-hand products. The warranties play an important role in reassuring the buyer. Offering the warranty implies that the dealer incurs additional costs to service any claims made by the customers. Reducing warranty costs is an issue of great interest to dealers. One way of improving the reliability and reducing the warranty servicing cost for second-hand items is through actions such as overhaul and upgrade which are carried out by the dealer or a third party. Improving actions allow the dealer to offer better warranty terms and to sell the item at a higher price. This paper deals with two effective approaches (virtual age approach and screening test approach) to decide on the reliability improvement strategies for second-hand products sold under various warranty policies (failure-free, rebate warranty, and a combination of free replacement and lump sum). A numerical example illustrates that from a dealer’s point of view, it is beneficial to carry out an improvement action only if the reduction in the warranty servicing cost is greater than the extra cost incurred due to this improvement action

Диалог. 2012. № 002

Our understanding of the role of freshwaters in the global carbon cycle is being revised, but there is still a lack of data, especially for the cycling of methane, in rivers and streams. Unravelling the role of methanotrophy is key to determining the fate of methane in rivers. Here we focus on the carbon conversion efficiency (CCE) of methanotrophy, that is, how much organic carbon is produced per mole of CH4 oxidised, and how this is influenced by variation in methanotroph communities. First, we show that the CCE of riverbed methanotrophs is consistently high (~50%) across a wide range of methane concentrations (~10–7000 nM) and despite a 10-fold span in the rate of methane oxidation. Then, we show that this high conversion efficiency is largely conserved (50%± confidence interval 44–56%) across pronounced variation in the key functional gene (70 operational taxonomic units (OTUs)), particulate methane monooxygenase (pmoA), and marked shifts in the abundance of Type I and Type II methanotrophs in eight replicate chalk streams. These data may suggest a degree of functional redundancy within the variable methanotroph community inhabiting these streams and that some of the variation in pmoA may reflect a suite of enzymes of different methane affinities which enables such a large range of methane concentrations to be oxidised. The latter, coupled to their high CCE, enables the methanotrophs to sustain net production throughout the year, regardless of the marked temporal and spatial changes that occur in methane