Static Potential and Local Color Fields in Unquenched Three-Dimensional Lattice QCD

String breaking by dynamical quarks in (2+1)-d lattice QCD is demonstrated in this project, by measuring the static potential and the local color-electric field strength between a heavy quark and antiquark pair at large separations. Simulations are done for unquenched SU(2) color with two flavors of staggered quarks. An improved gluon action is used which allows simulations to be done on coarse lattices, providing an extremely efficient means to access the quark separations and propagation times at which string breaking occurs. The static quark potential is extracted using only Wilson loop operators and hence no valence quarks are present in the trial states. Results give unambiguous evidence for string breaking as the static quark potential completely saturates at twice the heavy-light meson mass at large separations. It is also shown that the local color-electric field strength between the quark pair tends toward vacuum values at large separations. Implications of these results for unquenched simulations of QCD in 4-d are drawn.Comment: 3 pages, contribution to Lattice 2002 proceedings (Confinement

On the screening of the potential between adjoint sources in QCD3QCD_3

We calculate the potential between adjoint sources in $SU(2)$ pure gauge theory in three dimensions. We investigate whether the potential saturates at large separations due to the creation of a pair of gluelumps, colour-singlet states formed when glue binds to an adjoint source.Comment: 3 pages, uuencoded Z-compressed postscript file, contribution to Lattice '9

A new specification of generalized linear models for categorical data

Regression models for categorical data are specified in heterogeneous ways. We propose to unify the specification of such models. This allows us to define the family of reference models for nominal data. We introduce the notion of reversible models for ordinal data that distinguishes adjacent and cumulative models from sequential ones. The combination of the proposed specification with the definition of reference and reversible models and various invariance properties leads to a new view of regression models for categorical data.Comment: 31 pages, 13 figure

Costs and Benefits of Preventing Workplace Accidents : Going from a Mechanical to a Manual Handling System

This paper provides a cost-benefit analysis of the passage from a mechanical to a manual handling system that took place at the beginning of the 1990s at a warehouse of the Société des Alcools du Québec in Montreal. In particular, this change was aimed at reducing workplace accidents among packers. After evaluating the costs of the program, we present a rigorous econometric analysis to assess how many accidents have been prevented by the change so as to compute the direct and indirects costs avoided as a result of such accident reduction. We show that the demechanization of the handling system has indeed been profitable for the firm. Les auteurs de cet article ont effectué l'analyse coûts-avantages du passage d'un système de manutention mécanisé à un système manuel mis en oeuvre en 1990 dans un entrepôt de la Société des Alcools du Québec situé à Montréal. Après avoir estimé les coûts du programme, ils ont conduit une analyse économétrique rigoureuse pour déterminer le nombre d'accidents évités grâce à ce changement. Ils ont pu ainsi calculer les coûts directs et indirects qui n'auront pas à être subis à cause de la réduction du nombre des accidents. Ils en concluent que le changement a été rentable pour l'entreprise.

Partitioned conditional generalized linear models for categorical data

In categorical data analysis, several regression models have been proposed for hierarchically-structured response variables, e.g. the nested logit model. But they have been formally defined for only two or three levels in the hierarchy. Here, we introduce the class of partitioned conditional generalized linear models (PCGLMs) defined for any numbers of levels. The hierarchical structure of these models is fully specified by a partition tree of categories. Using the genericity of the (r,F,Z) specification, the PCGLM can handle nominal, ordinal but also partially-ordered response variables.Comment: 25 pages, 13 figure