Japhet Sebastian Law

MPS with multiple freeze fences in multi-product multi-level MRP systems

In the current severe competitive marketplace, customers are now expecting better quality, price and service, and demanding higher flexibility. To survive in this highly demanding and competitive manufacturing environment, many manufacturers are forced to improve flexibility in their manufacturing management systems. Traditionally, manufacturers use a single freeze fence in their master production schedule (MPS). Within the single freeze fence, even if a more accurate sales forecast is available, no schedule change is allowed. This paper introduces a new approach to improve MPS flexibility by imposing a freeze fence on each item in the bill of materials (BOM). This new approach allows schedule changes within certain periods of the traditional single freeze fence subject to the availability of component supply. It allows manufacturers to react more quickly to market trends. When applying multiple freeze fences, allocating limited component supply is required. In this study, a mathematical model for allocat...

Standardization of the Chinese Personality Assessment Inventory: The prototype standardization method and its rationale

Methods and techniques for the standardization of the Chinese Personality Assessment Inventory (CPAI) are reviewed and discussed. Based on the idea of the UT transformation (Tellegen & Ben‐Porath, 1992), a general method called prototype standardization is applied to the clinical scales as well as the personality scales of the CPAI. The rationale of the prototype standardization method is explained. Some variations of the basic methodology are suggested and applied to the CPAI. It is demonstrated that the prototype standardization of the CPAI yields desirable psychometric properties such as percentile comparability across scales and preservation of the correlation structures of the scales, even for the personality scales of the CPAI that do not have a homogeneous distributional shape. We conclude that prototype standardization is a useful method for standardizing all kinds of personality inventories consisting of a large number of scales.

Economic Contribution to Hong Kong of the Aviation Sector: A Value-Added Approach

The emergence of air transport has greatly facilitated long-distance travel and the exchange of goods. The industry also contributes substantially to the economy. Our study measures the benefits that the aviation industry has brought to the Hong Kong economy using the value-added (VA) approach. We find that air transport itself and services that are incidental to the sector (direct benefits) contributed about 2.54 percent of gross domestic product (GDP) at factor cost (at current prices) in 2003, while trade services and the tourism industry (indirect benefits) contributed 4.48 percent. Hence, the total benefit brought by the aviation industry was 7.02 percent of GDP at factor cost (at current prices) in 2003. This demonstrates that the industry is a major component of the Hong Kong economy, and our findings should aid in understanding the effects of recent changes in aviation policies, which have altered the business environment of the aviation market.

Estimating Technical Efficiencies of Airports in the Greater China: Stochastic Output Distance Function Method vs. Data Envelopment Analysis Method

In this paper, we study the technical efficiencies of Chinese airportsby using multi-output stochastic output distance function analysis. The benefits of this approach are as follows: 1) It allows multiple-output and multiple-input analysis to be conducted in just one equation. However, in single-output production frontier analysis, two stages of empirical estimation are required.; 2) The estimated values of output distance are in fact the technical efficiency scores. We compare and contrast the estimated technical efficiencies computed based on the stochastic output distance function method with those computed based on DEA method. In terms of the ranking of efficiency scores, we conclude that both methods are consistent with each other.

Measuring the Efficiency of Ariports in China with the DEA and Endogenous-Weight TFP Methods.

The study of Chinese airport efficiency has been largely neglected, despite the Chinese civil aviation industrys recent impressive growth. The authors used the Data Envelopment Analysis and Endogenous-Weight Total Factor Productivity methods to study Chinese airport operational efficiency at 41 facilities, including regional airports, regional hubs, and international hubs. The studys empirical results show that among Chinese airports there is a statistically significant operational efficiency variation, and that strongly increasing returns to scale are exhibited by most Chinese airports, especially relatively efficient ones. Accordingly, a significant widening of the efficiency gap between Chinese airports may occur if investment is focused solely on efficient airports. A policy may need to be devised by the Civil Aviation Administration of China, therefore, not only to improve the operational efficiency of major airports, but also to maintain balanced regional airport development nationwide.

Development of Air Transport Industry in the Asia‐Pacific Region

The volume of air passengers and cargo in the Asia-Pacific region has grown significantly over the past decade due to the strong impetus of economic growth as well as trade and economic integration at both the regional and global levels. Although public funds have been the main source of financing for airports in most parts of the region, governments have increasingly resorted to privatization or are seriously considering it as a form of private sector participation enabling new airports to be built or existing airports to be upgraded. The present paper provides a brief survey of airport privatization in the Asia-Pacific region, discusses the relevant issues, and introduces the following five papers published in this special section on the air transport industry in the Asia-Pacific region.

The impact of using multiple freeze fences on costs in MRP systems

There are two approaches to managing freeze fences when planning master production schedule (MPS) in material requirements planning (MRP) systems--namely, single freeze fence and multiple freeze fences. The approach of using a single freeze fence gives no schedule change flexibility within the freeze fence, while the multiple freeze fences approach allows a schedule change within a semi-frozen interval. The concept of multiple freeze fences was introduced by Yeung et al. (1999). However, little research has been done to evaluate the performance of multiple freeze fences. This research is the first study in examining the cost impact of using multiple freeze fences in multi-product, multi-level MRP systems. The influences of environmental factors and cost factors on the total system cost when using multiple freeze fences and a single freeze fence are evaluated. The results of this research show that multiple freeze fences outperform single freeze fence in almost all environments when total inventory holding cost is of major concern. In terms of total shortage cost, multiple freeze fences also perform better in a high commonality product structure. This research also found that, in many environments, the total system costs can be lowered by using multiple freeze fences to shorten the frozen interval, which contradicts previous findings that it is more economical to have a frozen interval to cover the cumulative lead time. The result provides an insight into situations in which manufacturers should consider using multiple freeze fences to improve their flexibility in this dynamic, highly demanding and competitive marketplace.

Comments on ‘Deficient EOQ-independent lot-sizing heuristics’

Cheng and Siu (1989) argued that previous economic order quantity (EOQ) related heuristics are inherently flawed, and proposed two lot-sizing heuristics that are relatively tree from EOQ considerations (EOQ-independent). Based on their computational study, it was concluded that EOQ-independent heuristics performed ‘amazingly well’ compared to optimal solutions generated by the Wagner-Whilin algorithm. This comment is a critique of the premise under which the Cheng and Siu study was conducted, illustrates the inadequacy of the test data and errors in the computational results, and compares the performance of their heuristics with two EOQ-based heuristics. It is concluded that the EOQ-independent heuristics of Cheng and Siu are far inferior to existing heuristics in the literature.

Regional development and airport productivity in China

This chapter studies the technical efficiencies of Chinese airports by using a meta-frontier production function model which accounts for airports in different regions accessing different technologies. Our empirical results show that the technical efficiency scores of airports and provincial output in the coastal region are higher than their counterparts in the inland region. However, the technical efficiency scores of airports and provincial output in inland region are steadily increasing while the counterparts of airports and provincial output in coastal region are slowly declining. In addition, our analysis of provincial efficiency changes shows that airport productivity has a positive and statistically significant effect on the technical changes of provincial output. Our results partially confirm the success of the government policy of promoting airport construction and development in the western inland region.

Non-cost-based lot-sizing heuristics: a comment on Cheng

Abstract In a recent article, Cheng [1] argued that previous economic orde quantity (EOQ) related heuristics are inherently flawed, and proposed two lot- sizing heuristics which are non-cost-based (cost data ignored in determining lot-sizes) and relatively free from EOQ considerations. Based on a computational study, it was concluded that non-cost-based heuristics“can be quite effective for lot-sizing decisons” [1, p.95] as compared to optimal solutions generated by the Wagner-Whitin algorithm [2]. This comment critiques the premise under which the Cheng study was conducted, illustrates the inadequacy of the test data and errors in the computational results, and compares the performance of the proposed heuristics to two EOQ-based heuristics. It is concluded that the non-cost-based heuristics proposed in Cheng [1] are naive and arbitary in nature, and that their computational performance is far inferior to existing heuristics in the literature.