Design and implementation methodology based on Petri net formalism of flexible manufacturing systems control

This paper presents an aided design methodology of flexible manufacturing system control with a view to industrial implementation. The approach considered through a modelling phase, the a validation phase by simulation and finally a distributed implementation phase. In the modelling phase, based on the Petri net formalism, we demonstrate the hierarchical aspect which separates the part flow control and the product resource control. In addition, we emphasize generic aspects which allow us to use an object-oriented approach. These aspects and the set of modelled objects are directly used in the simulation and production phases after an automatic translation in an implementation language (ADA in our case). In consequence, the distributed location for those two phases is well facilitated from the viewpoint of the approach used.     

MOONLIGHTING OVER THE BUSINESS CYCLE

Using data from the 1979 National Longitudinal Survey of Youth, we examine the cyclicality of moonlighting by gender. We estimate a random-effects Tobit model of moonlighting among working men and women and find that while male moonlighting behavior does not fluctuate significantly with the business cycle, female moonlighting does. The cyclicality of female moonlighting has, nonetheless, varied over the course of the past 35 yr. Female moonlighting seemed to behave countercyclically during much of the 1980s and early 1990s, confirming the popular media belief that moonlighting is more likely to occur during periods of economic distress. Yet, this countercyclical behavior disappears during the 1993–1999 period to become procyclical by the early twentieth century. The recent procyclicality of female moonlighting supports the idea that female workers respond to a need for "just-in-time" employment following the economic upturn of the mid- to late 1990s. ( JEL J2, E32)     

Is More Truly Merrier?: Mentoring and the Practice of Law

Cet article examine deux questions sur le mentorat. D'abord, qui est le plus susceptible de bénéficier de services de mentorat au cours de sa carrière? Ensuite, comment le mentorat influence‐t‐il les carrières des professionnels? En utilisant une enquête longitudinale sur des avocats, les auteures évaluent l'incidence des postes et des aspirations en début de carrière sur les chances de bénéficier de services de mentorat. Elles mesurent les bénéfices du mentorat au moyen des récompenses de carrière intrinsèques et extrinsèques, pour découvrir que le contexte organisationnel et les attributs individuels constituent d'importants prédicteurs de qui bénéficiera de mentorat. Les professionnels ayant de multiples mentors se sont avérés les grands gagnants, en ce qu'ils obtiennent des récompenses de carrière plus importantes et plus diversifiées que ceux n'ayant pas de mentor. This paper addresses two questions regarding mentoring: First, who is most likely to receive mentorship during their career? And second, how does mentorship shape the careers of professionals? Using a longitudinal survey of lawyers, we evaluate the impact of early career positions and aspirations on the chances for mentorship. We assess the benefits of mentorship across extrinsic and intrinsic career rewards. We find organizational context and individual attributes are important predictors of who receives mentorship. Professionals with multiple mentors were the big winners in that they obtain greater and more diverse career rewards over those with one or no mentors.     

Simulation of right and left truncated gamma distributions by mixtures

We study the properties of truncated gamma distributions and we derive simulation algorithms which dominate the standard algorithms for these distributions. For the right truncated gamma distribution, an optimal accept–reject algorithm is based on the fact that its density can be expressed as an infinite mixture of beta distribution. For integer values of the parameters, the density of the left truncated distributions can be rewritten as a mixture which can be easily generated. We give an optimal accept–reject algorithm for the other values of the parameter. We compare the efficiency of our algorithm with the previous method and show the improvement in terms of minimum acceptance probability. The algorithm proposed here has an acceptance probability which is superior to e/4.     

Work Hard,Play Hard?: A Comparison of Male and Female Lawyers' Time in Paid and Unpaid Work and Participation in Leisure Activities

Les auteures tentent de déterminer le temps que les professionnels, hommes et femmes, passent à effectuer du travail rémunéré ou non, et la façon dont cela influe sur leur participation à différentes activités de loisirs. Elles se fondent sur des données provenant d'avocats professant dans différents milieux juridiques. Elles constatent que les hommes rapportent consacrer plus de temps au travail rémunéré et aux loisirs, alors que les femmes accordent plus de temps aux travaux ménagers ainsi qu'aux soins des enfants. Les résultats semblent démontrer que les occasions dans l'ensemble plus importantes de loisirs chez les hommes comparées à celles des femmes seraient attribuables à des relations inattendues entre la participation des hommes aux travaux domestiques et aux soins des enfants, et leurs activités de loisirs. Les auteures présentent différentes explications à ces résultats. There has been a considerable amount of research that documents how women and men spend their time in different work and home tasks. We examine how much time professional women and men spend in paid and unpaid work and how this relates to their participation in different leisure activities. We also explore whether time in paid and unpaid work has gender‐specific effects on leisure participation. In examining these issues, we rely on data from lawyers working in different legal settings. Our results show that, as hypothesized, men report more time in paid work and leisure whereas women devote more time to housework and childcare. An unexpected finding is that the time men spend in housework or childcare is either unrelated or positively related to their leisure participation. These results suggest that men's greater overall opportunities for leisure compared with women's appear to stem from the unanticipated relationships between men's involvement in housework and childcare and their leisure activities. We raise several possible explanations for these findings.     

A Non‐Parametric Estimator of the Spectral Density of a Continuous‐Time Gaussian Process Observed at Random Times

Abstract. In numerous applications data are observed at random times and an estimated graph of the spectral density may be relevant for characterizing and explaining phenomena. By using a wavelet analysis, one derives a non‐parametric estimator of the spectral density of a Gaussian process with stationary increments (or a stationary Gaussian process) from the observation of one path at random discrete times. For every positive frequency, this estimator is proved to satisfy a central limit theorem with a convergence rate depending on the roughness of the process and the moment of random durations between successive observations. In the case of stationary Gaussian processes, one can compare this estimator with estimators based on the empirical periodogram. Both estimators reach the same optimal rate of convergence, but the estimator based on wavelet analysis converges for a different class of random times. Simulation examples and an application to biological data are also provided.     

On the Validity of the Bootstrap in Non‐Parametric Functional Regression

Abstract. We consider the functional non‐parametric regression model Y= r( χ )+?, where the response Y is univariate, χ is a functional covariate (i.e. valued in some infinite‐dimensional space), and the error ? satisfies E(? | χ ) = 0. For this model, the pointwise asymptotic normality of a kernel estimator of r (·) has been proved in the literature. To use this result for building pointwise confidence intervals for r (·), the asymptotic variance and bias of need to be estimated. However, the functional covariate setting makes this task very hard. To circumvent the estimation of these quantities, we propose to use a bootstrap procedure to approximate the distribution of . Both a naive and a wild bootstrap procedure are studied, and their asymptotic validity is proved. The obtained consistency results are discussed from a practical point of view via a simulation study. Finally, the wild bootstrap procedure is applied to a food industry quality problem to compute pointwise confidence intervals.     

Regularized Posteriors in Linear Ill‐Posed Inverse Problems

Abstract. We study the Bayesian solution of a linear inverse problem in a separable Hilbert space setting with Gaussian prior and noise distribution. Our contribution is to propose a new Bayes estimator which is a linear and continuous estimator on the whole space and is stronger than the mean of the exact Gaussian posterior distribution which is only defined as a measurable linear transformation. Our estimator is the mean of a slightly modified posterior distribution called regularized posterior distribution. Frequentist consistency of our estimator and of the regularized posterior distribution is proved. A Monte Carlo study and an application to real data confirm good small‐sample properties of our procedure.