A computational analysis of lower bounds for big bucket production planning problems

In this paper, we analyze a variety of approaches to obtain lower bounds for multi-level production planning problems with big bucket capacities, i.e., problems in which multiple items compete for the same resources. We give an extensive survey of both known and new methods, and also establish relationships between some of these methods that, to our knowledge, have not been presented before. As will be highlighted, understanding the substructures of difficult problems provide crucial insights on why these problems are hard to solve, and this is addressed by a thorough analysis in the paper. We conclude with computational results on a variety of widely used test sets, and a discussion of future research

La sperimentazione MIFORCALUn modello formativo per il contesto culturale allargato

I processi di mondializzazione attraverso logiche di cooperazione trasnazionale così come dei flussi migratori espontanei, rivoluzionano completamente il setting accademico e di aula; fenomeno coadiuvato dallo sviluppo del web sociale come spazio di apprendimento informale e di comunicazioni fluide. Il suddetto cambiamento sociale, tecnologico e culturale plasma processi di internazionalizzazione educativa; nel livello dell’istruzione superiore, in particolare, esiste un profondo interesse per la promozione degli stessi, generando diversi tipi di esperienze dentro le quali può essere inquadrato il Progetto MIFORCAL. Una visione critica di tali dinamiche indica il rischio dell’implementazione di logiche egemoniche che orientano la costruzione del curriculum (classificazione di saperi potenzialmente insegnabili) ed i tipi di dispositivi pedagogici che da tale costruzione ne deriva, come compartimenti rigidi, generatori di logiche di esclusione e di colonialismo accademico (Mc Laren, 1996). Il progetto MIFORCAL ha esplorato nella sua prima fase un modello curricolare e pedagogico contra-egemone, puntando alla equa partecipazione di ogni stakeholder nella costruzione ed accesso alla conoscenza. In questo scenario si produce la prima ipotesi formativa verso la maggiore inclusione educativa: il modello si muove in un contesto formativo che può essere denominato “contesto culturale allargato” (Raffaghelli, 2008; 2009). E cioè, considerando la Teoria dell’Attività di 3za generazione ed il concetto di knotworking (Engestrom, 1987, 1999), possiamo concepire tale contesto formativo come ambito nel quale la cultura insegnata è decostruita, esplorata criticamente e ricostruita a partire dal particolare riferimento a “finestre” di espansione della conoscenza apportate dai soggetti in situazione di apprendimento e collaborazione a trama di rete (Engestrom, 2009), nella ricerca della generazione di un modello formativo equilibrato dal punto di vista discorsivo, semantico e per tanto eco-sociale (Lemke, 2005). L’ipotesi alla base è che tale modello può portare verso la giustizia pedagogica e curricolare (Connel, 1993, Raffaghelli, 2009). In questo articolo vengono descritti ed analizzate criticamente le caratteristiche del modello formativo MIFORCAL, attraverso la presentazione di esempi di costituzione del modello e pratiche pedagogiche nel contesto culturale allargato, in tanto che spazio di prassi pedagogica trasformativ

LS-LIB: A Library of tools for Solving Production Planning Problems

Much progress has been made in recent years in solving certain classes of production planning problems using mixed integer programming. One of the major challenges is how to make this expertise available and easy to use to the non-specialist and to the practitioners. Here we describe a modeling approach and tool LS-LIB, and report on computational results. LS-LIB is a library of primitives to declare procedures/subroutines/global constraints in a high-level modeling language that we believe offers an interesting partial answer to this challenge. LS-LIB provides routines for problem reformulation, cut generation, and heuristics to find good feasible solutions quickly. The user must provide an initial formulation of his problem in the modeling language MOSEL. Then using his knowledge of the problem he must first classify each product or sku according to a simple three field scheme: [production type, capacity type, variant] proposed recently. Then it is a simple matter to use the global constraints of LS-LIB by adding a few lines to his initial MOSEL formulation to get a tightened formulation and/or call the appropriate cut separation routines. The heuristic procedures are called in a similar fashion. We illustrate the use of LS-LIB on an intractable two-level problem, and a hard multi-level problem

On Modelling Approaches for Planning and Scheduling in Food Processing Industry

We consider developments in lot-sizing and scheduling, particularly relevant for problem settings arising in food processing industry. Food processing industry (FPI) reveals several specific characteristics which make integrated production planning and scheduling a challenge. First of all, setups are usually sequence-dependent and may include the so-called non-triangular setup conditions. Secondly, planning problems in FPI have to deal with product decay due to deterioration of inventory. We give an overview of lot-sizing and scheduling models, and assess their suitability for addressing sequence-dependent setups, non-triangular setups and product decay. We show that a trend exists towards so-called big bucket models. However, the advantage of these approaches may become a major obstacle in addressing the identified characteristics in FPI

Mapping autism risk loci using genetic linkage and chromosomal rearrangements

Autism spectrum disorders (ASDs) are common, heritable neurodevelopmental conditions. The genetic architecture of ASDs is complex, requiring large samples to overcome heterogeneity. Here we broaden coverage and sample size relative to other studies of ASDs by using Affymetrix 10K SNP arrays and 1,168 families with at least two affected individuals, performing the largest linkage scan to date while also analyzing copy number variation in these families. Linkage and copy number variation analyses implicate chromosome 11p12-p13 and neurexins, respectively, among other candidate loci. Neurexins team with previously implicated neuroligins for glutamatergic synaptogenesis, highlighting glutamate-related genes as promising candidates for contributing to ASDs. © 2007 Nature Publishing Group