The covariance structure of sequential forecasts obtained by regression analysis

A method is presented for evaluating the covariance matrix of a set of sequential forecasts obtained by regression analysis. The matrix can be used to derive the relation between the variance of the forecasts on the one hand, and the lead times between the forecasting time and the time at which the forecasted variables are realized, on the other hand. The determination of this relation is important whenever the optimal frequency of forecasting must be determined.     

《抱朴子外篇》的用典考

《抱朴子外篇》中用典的数量庞大.从典源出处看,葛洪引用较多的当数儒家经典和道家著作《庄子》,体现出其儒道兼修的精神世界.根据引用内容的不同,可将《抱朴子外篇》中的用典分为引言和引事两大类.引言大多出自《易》、《诗经》、《论语》等儒家经典,可以使观点更加有力,让人更易信服.引事则多取自史书,往往在引用历史故事时对其进行高度概括,用己言叙古事,且看不出任何雕琢的痕迹.《抱朴子外篇》使用典故的手法多样,有正用、反用、活用等,有时还对原有典故进行改编.     

大气中痕量镉、铅的测定

本文提出在0．05mol／LKCI－0．02mol／LHNO3－0．0025mol／L（CH2）5N4－3×10（－5）mol／LHgCl2体系中，采用微分脉冲阳极溶出伏安技术测定大气中痕量镉、铅，该方法灵敏度高，检测下限达5．0×10（-11）ug／ml（即0．05ppb），样品回收率均在95－105％范围内，十次平行测定结果的相对标准偏差不大于5％。     

Lead factory operationalisation and challenges

Abstract

This paper deepens the understanding of the lead factory concept by examining how the lead factory role is operationalised and what challenges are associated with it. The research is based on an explorative case study of eight Swedish lead factories in the manufacturing industry. The empirical findings suggest that the understanding of the lead factory concept should be extended as it is not restricted to one type of set-up. The findings show a spectrum ranging from an entire manufacturing plant, parts of a plant, to a virtual plant considered to be the lead factory. The research also shows a broad range of challenges experienced by lead factories. Several of these are related to and originate from unclear role, responsibility and mandate of the lead factory. The lack of dedicated resources for lead factory activities, specifically long-term development and difficulties in measuring the benefits of the role, were other challenges faced.     

Derivation of a Target Level of Lead in Soil at Residential Sites Corresponding to a De Minimis Contribution to Blood Lead Concentration1

Inability to define either a clear toxicologic threshold or a stochastic all-or-nothing (cancer-type) response model for the noncarcinogenic effects of lead (Pb) in young children has posed difficulties for derivation of risk-based target levels of Pb in residential soil. Approaches based on empirical relationships between Pb levels in blood (PbB) and Pb in soil suffer from inability to specify the numerous variables which mediate between these two quantities. Approaches based on achieving a toxicologically de minimis target PbB level (e.g., 10 μg/dl) are subject to large uncertainty in estimating the distribution of existing PbB levels in a specific exposed population and in estimating the relative contribution from nonsoil sources of Pb. The multisource contribution to the distribution of PbB makes this approach unsuited for determination of a target Pb level in a single medium. An alternative approach is presented based on achieving a de minimis contribution to PbB (ΔPbB) from soil. Contributions to Pb exposure from outdoor soil and indoor soil-derived dust (ISDD) are modeled and appropriate values are suggested for input parameters. This analysis predicts that chronic exposure of young children to 200 μg Pb/g (ppm) in residential soil will result in a ΔPbB of 2 μg Pb/dl blood. This concentration of Pb in soil may provide an appropriate target level for residential soil when other significant sources of Pb exposure are present. In other cases, this approach can be used to predict a soil concentration of Pb corresponding to an appropriate non-de minimisΔPbB.     

Inventory record inaccuracy – The impact of structural complexity and lead time variability

This article presents a rigorous prospective analysis of the impact of Inventory Record Inaccuracy (IRI) on complex multi-echelon Supply Chains (SCs). Specifically, key operational factors (i.e., the magnitude of the error, frequency of the inventory audits and lead time variability) and SC structure are systematically assessed. We find that the detrimental effects of IRI are exacerbated by the structural complexity of the SC and lead time variability. Furthermore, we show how the efficacy of countermeasure strategies may vary depending on SC configuration and operational conditions. These results allow us to provide interesting managerial recommendations to guarantee investment in prevention and correction strategies.     

Centralized versus Decentralized Competition for Price and Lead‐Time Sensitive Demand

We study two firms that compete on price and lead‐time decisions in a common market. We explore the impact of decentralizing these decisions, as made by the marketing and production departments, respectively, with either marketing or production as the leader. We compare scenarios in which none, one, or both of the firms are decentralized to see whether decentralization can be the equilibrium strategy. We find that under intense price competition, with intensity characterized by the underlying parameters of market demand, firms may suffer from a decentralized structure, particularly under high flexibility induced by high capacity, where revenue‐based sales incentives motivate sales/marketing to make aggressive price cuts that often erode profit margins. In contrast, under intense lead‐time competition, a decentralized strategy with marketing as the leader can not only result in significantly higher profits, but also be the equilibrium strategy. Moreover, decentralization may no longer lead to lower prices or longer lead‐times if the production department chooses capacity along with lead‐time.      

Decision support for lead time and demand variability reduction

Companies undertaking operations improvement in supply chains face many alternatives. This work seeks to assist practitioners to prioritize improvement actions by developing analytical expressions for the marginal values of three parameters – (i) lead time mean, (ii) lead time variance, and (iii) demand variance – which measure the marginal cost of an incremental change in a parameter. The relative effectiveness of reducing lead time mean versus lead time variance is captured by the ratio of the marginal value of lead time mean to that of lead time variance. We find that this ratio strongly depends on whether the lead time mean and variance are independent or correlated. We illustrate the application of the results with a numerical example from an industrial setting. The insights can help managers determine the optimal investment decision to modify demand and supply characteristics in their supply chain, e.g., by switching suppliers, factory layout, or investing in information systems.     

Lead time adjustment through scrap management

In a discrete parts manufacturing environment, it is necessary to compensate for the decreasing planned batch size resulting from production of scrap (defectives) in the production line, by increasing the planned production volume. This calls for a revision in the initially computed manufacturing lead time (MLT). A survey of the literature reveals that although issues related to product quantity regeneration have been studied in detail, little has been done to assess the impact on manufacturing lead times. This paper discusses the impact of scrap on manufacturing lead time in a shop with an intermittent-flow, bath-oriented, discrete-parts manufacturing environment, producing make-to-stock items.     

Justice Sector Reform in Afghanistan: From a ‘Lead Nation’ Approach to a ‘Mixed Ownership’ Regime?

The article describes the policy-making structure which governs the reform of justice in Afghanistan. It is characterized by an evolution from a bilateral to a multilateral approach, aimed at increasing the Afghan ownership. However, observing the system ‘from within’, it seems currently ruled by a mixed regime, being still deeply influenced by external inputs. As a consequence, the final outcome of the process remains uncertain.