A Production–Inventory Model for a Push–Pull Manufacturing System with Capacity and Service Level Constraints

We study a hybrid push–pull production system with a two‐stage manufacturing process, which builds and stocks tested components for just‐in‐time configuration of the final product when a specific customer order is received. The first production stage (fabrication) is a push process where parts are replenished, tested, and assembled into components according to product‐level build plans. The component inventory is kept in stock ready for the final assembly of the end products. The second production stage (fulfillment) is a pull‐based assemble‐to‐order process where the final assembly process is initiated when a customer order is received and no finished goods inventory is kept for end products. One important planning issue is to find the right trade‐off between capacity utilization and inventory cost reduction that strives to meet the quarter‐end peak demand. We present a nonlinear optimization model to minimize the total inventory cost subject to the service level constraints and the production capacity constraints. This results in a convex program with linear constraints. An efficient algorithm using decomposition is developed for solving the nonlinear optimization problem. Numerical results are presented to show the performance improvements achieved by the optimized solutions along with managerial insights provided.     

Ignorance as an under-identified social problem

This paper examines the persistence and intensification of ignorance in the ostensible knowledge society. Given the ubiquity of ignorance, it focuses on research and observations dealing with functional knowledge deficits that challenge the ideal of the well-informed citizen. These developments are traced back to the contradictory dynamics of the knowledge society, specifically information explosions in the knowledge economy and the resultant knowledge-ignorance paradox. The theoretical unfolding of this paradox in terms of entry and speech barriers suggests that pockets of observed public knowledge - rather than ignorance - are exceptional and require specific explanation. While ignorance among individuals, as well as experts and organizations, is a serious social problem with potentially deadly consequences, ignorance remains relatively unrecognized since it has major liabilities as a marketable issue. The conclusion points to the importance of future research on the cultural and institutional production of ignorance.     

社会经济地位与老年健康——基于(CGSS)2013数据的实证分析

借助中国综合社会调查(CGSS)2013年的截面数据,选取3 108个60岁及以上老年人样本,采用有序Probit模型,从自评健康、心理健康和生理健康三个维度,考察反映老年人社会经济地位的诸多因素对其健康的影响。实证结果表明:较高的社会经济地位对老年人健康有明显的提升作用。城镇老年人的健康状况明显好于农村,但农村老年人更为广泛的社会网络对其精神支持的影响较城镇老年人更大。具有党员身份的老年人与其心理健康呈显著正向关系,老年人的健康状况也会随受教育程度的提高而改善,主观阶层认同较高的老年人的健康水平也相对较高。从人口学特征来看,老年男性的健康状况比女性要好,有配偶的老年人精神状态更加乐观。就政策含义而言,当下应针对老年群体的异质性给予更多关注,积极提升老年人的生命质量和生活质量,共同营造一个"健康老龄化"的社会。     

Inference in Arch and Garch Models with Heavy–Tailed Errors

ARCH and GARCH models directly address the dependency of conditional second moments, and have proved particularly valuable in modelling processes where a relatively large degree of fluctuation is present. These include financial time series, which can be particularly heavy tailed. However, little is known about properties of ARCH or GARCH models in the heavy–tailed setting, and no methods are available for approximating the distributions of parameter estimators there. In this paper we show that, for heavy–tailed errors, the asymptotic distributions of quasi–maximum likelihood parameter estimators in ARCH and GARCH models are nonnormal, and are particularly difficult to estimate directly using standard parametric methods. Standard bootstrap methods also fail to produce consistent estimators. To overcome these problems we develop percentile–t, subsample bootstrap approximations to estimator distributions. Studentizing is employed to approximate scale, and the subsample bootstrap is used to estimate shape. The good performance of this approach is demonstrated both theoretically and numerically.     

Liquidity in Asset Markets With Search Frictions

We develop a search‐theoretic model of financial intermediation in an over‐the‐counter market and study how trading frictions affect the distribution of asset holdings and standard measures of liquidity. A distinctive feature of our theory is that it allows for unrestricted asset holdings, so market participants can accommodate trading frictions by adjusting their asset positions. We show that these individual responses of asset demands constitute a fundamental feature of illiquid markets: they are a key determinant of trade volume, bid–ask spreads, and trading delays—the dimensions of market liquidity that search‐based theories seek to explain.     

The Ex Ante Incentive Compatible Core in the Absence of Wealth Effects

In a differential information economy with quasi–linear utilities, monetary transfers facilitate the fulfillment of incentive compatibility constraints: the associated ex ante core is generically nonempty. However, we exhibit a well–behaved exchange economy in which this core is empty, even if goods are allocated through random mechanisms.