MIXED ASSEMBLY AND DISASSEMBLY OPERATIONS FOR REMANUFACTURING

In this paper we consider the problem of designing a mixed assembly‐disassembly line for remanufacturing. That is, parts from the disassembly and repair of used products can be used to build “new” products. This is a problem common to many OEM remanufacturers, such as Xerox or Kodak. We study two main configurations, under the assumption that the disassembly sequence is exactly the reverse of the assembly sequence. Under a parallel configuration, there exist two separate dedicated lines, one for assembly and one for disassembly, which are decoupled by buffers—from both disassembly operations, which have preference, as well as parts from an outside, perfectly reliable supplier. Under a mixed configuration, the same station is used for both disassembly and assembly of a specific part. The problem is studied using GI/G/c networks, as well as simulation. Due to a loss of pooling, we conclude that the parallel configuration outperforms the mixed line only when the variability of both arrivals and processing time are significantly higher for disassembly and remanufacturing than for assembly. Via a simulation, we explore the impact of having advanced yield information for the remanufacturing parts. We find that advanced yield information generally improves flow times; however, there are some instances where it lengthens flow times.     

Choice of Estimators Based on Different Observations: Modified AIC and LCV Criteria

Abstract. It is quite common in epidemiology that we wish to assess the quality of estimators on a particular set of information, whereas the estimators may use a larger set of information. Two examples are studied: the first occurs when we construct a model for an event which happens if a continuous variable is above a certain threshold. We can compare estimators based on the observation of only the event or on the whole continuous variable. The other example is that of predicting the survival based only on survival information or using in addition information on a disease. We develop modified Akaike information criterion (AIC) and Likelihood cross‐validation (LCV) criteria to compare estimators in this non‐standard situation. We show that a normalized difference of AIC has a bias equal to o ( n ^{? 1} ) if the estimators are based on well‐specified models; a normalized difference of LCV always has a bias equal to o ( n ^{? 1} ). A simulation study shows that both criteria work well, although the normalized difference of LCV tends to be better and is more robust. Moreover in the case of well‐specified models the difference of risks boils down to the difference of statistical risks which can be rather precisely estimated. For ‘compatible’ models the difference of risks is often the main term but there can also be a difference of mis‐specification risks.     

HEDONIC IMPUTATION AND THE PRICE INDEX PROBLEM: AN APPLICATION TO HOUSING

In this study, we show how use of the hedonic imputation method complicates the price index problem. In addition to the usual choice between formulas such as Fisher and Törnqvist, the fact that index compilers have some discretion over which prices are imputed implies that it is necessary to choose as well between different varieties of each formula. The functional form of the hedonic model must also be taken into account. We illustrate the importance of these issues in a housing context using house price data for three regions in Sydney over a 3‐yr period. (JEL C43, E31, O47, R31)     

MAINTAINING COLLECTIVE IDENTITY IN A HOSTILE ENVIRONMENT: CONFRONTING NEGATIVE PUBLIC PERCEPTION AND FACTIONAL DIVISIONS WITHIN THE SKINHEAD SUBCULTURE

Previous examinations of skinhead groups have limited their attention to racist elements within the subculture. But skinheads are a far more heterogeneous group than earlier studies indicate. This diversity has put skinhead factions at odds with each other, and has challenged mainstream conceptions about the skinhead movement. In this paper, we document how traditional skinheads maintain their unique collective identity in the midst of subcultural conflict and hostile stereotypes perpetuated by mainstream society. The study employs both primary and secondary sources to examine collective identity among traditional skinheads. Culture and ideology play an important role in counteracting negative stereotypes and solidifying traditional skinhead identity. Through culture and politics traditional skinheads establish collective identity and promote their nonracist beliefs. By focusing on nonracist and antiracist factions we expand the current literature on the skinhead subculture. The results illustrate that skinhead groups are diverse. Traditional factions see racism as an abomination of original skinhead culture, and as a result, many groups have taken action to confront their racist skinhead counterparts.     

REPUTATION AND EARNINGS: THE ROLES OF QUALITY AND QUANTITY IN ACADEME

We examine the determinants of professional reputation. Does quantity of exposures raise reputation independent of quality? Does quality of the most important exposure have extra effects on reputation? In a very large sample of academic economists, there is little evidence that a scholar's most influential work provides any extra enhancement of reputation. Quality rankings matter more than absolute quality. Quantity has a zero or even negative effect on proxies for reputation. Data on salaries, however, show positive effects of quantity independent of quality. We test explanations for the differences between the determinants of reputation and salary. (JEL L14, J31)     

THE USE OF COLLATERAL TO ENFORCE DEBT CONTRACTS

This paper analyzes the enforcement of debt contracts by treating the adherence to a contract as a matter of choice. Many commonly observed features of debt contracts, including the widespread use of collateral, are shown to be market responses to the costs of enforcing contracts. The characteristics of the collateral asset, including its marketability and expectations regarding its future price are shown to have important effects on the payments schedule of the debt. Since default is treated as a choice variable I am able to demonstrate the effects of macroeconomic fluctuations on default rates and lending decisions. Thus the analysis provides a basis for modeling the multiplier phenomena associated with the collapse of lending markets during severe depressions.     

Les facteurs sociaux liés au degré d'information de la population du Saguenay‐Lac‐Saint‐Jean à propos des maladies héréditaires et des services disponibles*

The past few years have seen significant advances in medical genetics. These advances have in turn given rise to several important clinical applications that have targeted populations with specific historical and demogenetic characteristics. One such population lives in the Saguenay‐Lac‐Saint‐Jean region of Quebec. One might think that this population is reasonably well informed of the situation. But their knowledge of population‐specific genetic pathologies and of the services available to them happens to vary considerably from one social group to another. This article presents the results of a quantitative study aimed at determining the factors that contribute to the acquisition of such knowledge in this population. Depuis quelques années, nous assistons à d'importantes avancées en génétique médicale. Celles‐ci induisent un développement sans précèdent de nouvelles applications cliniques qui interpellent certaines populations dont les caractéristiques historiques et démogénétiques font qu'elles sont davantage concernées. C'est le cas, notamment de la population du Saguenay‐Lac‐Saint‐Jean (Québec). On pourrait penser que cette population s'avère, dans l'ensemble, largement sensibilisée mais il appert que le niveau d'information sur les génopathies régionales et les services offerts varie considérablement d'un groupe social à l'autre. Le présent article livre les résultats d'une enquête quantitative visant à connaître les facteurs qui favorisent l'acquisition de telles connaissances dans cette population.     

The Effects of Branching on Item Nonresponse

The analysis of responses to a large sample survey instrumentindicates that branching instructions significantly increasethe rate of item nonresponse for items immediately followingthe branch. While older respondents did have a higher incidenceof item nonresponse, none of six other factors (education, gender,distance to next question, number of previous branches, futurebehavior, or nature of response) hypothesized to affect itemnonresponse were significantly related to the rate of nonresponse.