Methane bursts as a trigger for intermittent lake-forming climates on post-Noachian Mars

Lakes existed on Mars later than 3.6 billion years ago, according to sedimentary evidence for deltaic deposition. The observed fluviolacustrine deposits suggest that individual lake-forming climates persisted for at least several thousand years (assuming dilute flow). But the lake watersheds’ little-weathered soils indicate a largely dry climate history, with intermittent runoff events. Here we show that these observational constraints, although inconsistent with many previously proposed triggers for lake-forming climates, are consistent with a methane burst scenario. In this scenario, chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize methane clathrate. Using numerical simulations, we find that outgassed methane can build up to atmospheric levels sufficient for lake-forming climates, if methane clathrate initially occupies more than 4% of the total volume in which it is thermodynamically stable. Such occupancy fractions are consistent with methane production by water–rock reactions due to hydrothermal circulation on early Mars. We further estimate that photochemical destruction of atmospheric methane curtails the duration of individual lake-forming climates to less than a million years, consistent with observations. We conclude that methane bursts represent a potential pathway for intermittent excursions to a warm, wet climate state on early Mars

Managing the environmental externalities of traffic logistics: the issue of emissions

Companies are increasingly being held accountable for the life-cycle impact of their products and services. Transportation is frequently a major component of this life-cycle impact. Hence, to reduce total environmental impact, logistics managers will have to become more sophisticated in their understanding of how they can reduce the environmental impact of their transportation operations, without negatively affecting the cost or effectiveness of these operations. In line with this mandate, we quantify the dynamic impact of road vehicles on the environment. In most emission models, a constant speed is used depending only on the specific road type. Using such a model will lead to an underestimation of the effective emissions. It turns out that the differences with a more realistic dynamic assessment model are significant. The analysis here suggests that the policy consequences of these differences for both public sector managers and private companies are potentially quite important

Supplier managed inventory in the OEM supply chain:The impact of relationship types on total costs and cost distribution

\u3cp\u3eWe investigate the impact of four variants of supplier managed inventory on total costs and cost distribution in a capital goods supply chain consisting of a parts supplier who delivers parts to an original equipment manufacturer's assembly plant. The four supplier managed inventory variants differ in the components of inventory costs that the supplier has to carry. The performance of the supplier managed inventory relationships is benchmarked with the situation where the assembly plant manages the inventories. Interesting managerial insights follow from this comparison.\u3c/p\u3

An on-time delivery improvement model for manufacturing organisations

The purpose of this research was to develop an on-time delivery (OTD) improvement model for make-to-order (MTO) manufacturing organisations, based on: (i) a business process model combining product development and customer order management processes; and (ii) an integrated database with basic data, transaction data and functional applications, for broader planning within manufacturing organisations. The business process model, as part of the overall model, was designed using event-driven process chain (EPC) methodology and incorporated both capacity and material requirements planning functionalities for estimating on-time delivery dates and times. The database associated with the model defines all the data including both basic and transaction data; and links with required functions from sales to service and field return. These functions integrate through the database, using basic data and generate various transaction data including sales orders with an accurate promised date, based not only on the available stock but also on procurement and distribution times of any raw materials from external sources. The proposed model was then implemented in a selected manufacturing organisation. A systematic investigation was carried out to find the major causes of OTD problems of that manufacturer, with a view to implementing and validating the proposed model. After implementing the model average OTD was increased from 10% to 65% in about 12 months of operation

Incubation of methamphetamine but not heroin craving after voluntary abstinence in male and female rats

We recently introduced an animal model of incubation of methamphetamine craving after choice-based voluntary abstinence in male rats. Here we studied the generality of this phenomenon to (1) female rats, and (2) male and female rats with a history of heroin self-administration. We first trained rats to self-administer palatable food pellets for 6 days (6 h per day) for either methamphetamine (0.1 mg/kg/infusion) or heroin (0.1 mg/kg/infusion) for 12 days (6 h/day). We then assessed relapse to drug seeking under extinction conditions after 1 and 21 abstinence days. Between tests, the rats underwent either voluntary abstinence (achieved via a discrete choice procedure between drug and palatable food; 20 trials/day) or home-cage forced abstinence. We found no sex differences in methamphetamine self-administration or in the strong preference for the palatable food over methamphetamine during the choice-based voluntary abstinence. In both sexes, methamphetamine seeking in the relapse tests was higher after 21 days of either voluntary or forced abstinence than after 1 day (incubation of methamphetamine craving). We also found no sex differences in heroin self-administration or the strong preference for the palatable food over heroin during the choice-based voluntary abstinence. However, male and female rats with a history of heroin self-administration showed incubation of heroin craving after forced but not voluntary abstinence. Our results show that incubation of methamphetamine craving after voluntary abstinence generalizes to female rats. Unexpectedly, prolonged voluntary abstinence prevented the emergence of incubation of heroin craving in both sexes