The problem of determining optimal tolls established on a subset of arcs in a multicommodity capacitated transportation network is presented. The problem is formulated as a bilevel optimization problem where the upper level consists of an administrator who establishes tolls in some arcs of a network, while the lower level is represented by a group of users who travel along the shortest paths with respect to the travel cost. The objective is not only to increase the tolls, but also to maintain an optimal flow on the arcs of the network in order to maximize the leader's profit. If the leader sets very high toll values, the followers will be discouraged from using the tolled arcs, so the profit obtained from that decision is not going to be convenient for the leader. A methodology to solve this problem using optimization software at the lower level and the metaheuristic Scatter Search at the upper level is proposed.

This is a summary of the author's PhD thesis supervised by Jose Luis González-Velarde (Tecnológico de Monterrey, Mexico) and Belarmino Adenso-Díaz (Universidad de Oviedo, Spain) and defended on October 11, 2010 at the Tecnológico de Monterrey. The thesis is written in English and is available from the author upon request. This research focuses on Reverse Logistics. Its main objective is to develop mathematical programming models and algorithms to optimize emerging Waste of Electric and Electronic Equipment (WEEE) collection systems. The thesis begins with an overview of the WEEE collection process and identifies key strategic decision areas which impact the performance of a collection system. It specifically identifies three closely interrelated problems within the logistics-manufacturing interface: network design, vehicle routing and cellular manufacturing (disassembly). Even though there is plenty of published literature on each of these individual problems, this research bridges a gap in existing literature on vehicle routing and cellular disassembly systems. The research aims to provide efficient solution approaches to optimize WEEE collection systems, therefore it uses real-world data and case studies (when possible) to test the proposed solution procedures. Computational results using real data show that the proposed methods outperform real existing approaches to reverse logistics.

Este artículo presenta un resumen de la tesis doctoral del autor, la cual fue supervisada por José Luis González-Velarde (Tecnológico de Monterrey, México) y Belarmino Adenso-Díaz (Universidad de Oviedo, España) y defendida el 11 de Octubre de 2010 en el Tecnológico de Monterrey. La tesis está escrita en inglés y disponible sobre petición directa al autor. Esta investigación se enfoca en el estudio de la logística inversa. Su principal objetivo consiste en desarrollar modelos de programación matemática y algoritmos para optimizar los emergentes sistemas de recolección de Residuos de Aparatos Eléctricos y Electrónicos (RAEE). La tesis comienza con una descripción general del proceso de recolección de RAEE, e identifica las principales áreas de decisión que impactan el rendimiento de los sistemas de recolección. De forma específica se identifican tres problemas altamente interrelacionados dentro de la interfaz logística-producción-manufactura: diseño de redes, ruteo de vehículos y manufactura (desensamble) celular. Aun cuando existe una plenitud de literatura publicada sobre cada uno de estos temas, esta investigación llena un vacío en la literatura de ruteo de vehículos y manufactura celular. La investigación tiene por meta proporcionar enfoques de solución eficientes para optimizar los sistemas de recolección de RAEE, por ello utiliza datos reales y casos de estudio para probar los procedimientos de solución propuestos. Los resultados computacionales muestran que los métodos sobresalen respecto a los enfoques actuales en logística inversa.

OBJETIVO: Estudar a importância clínica da determinação eletrofisiológica da presença de bloqueio bidirecional na condução pelo istmo localizado entre a veia cava inferior e o anel da valva tricúspide (VCI - AT), após a ablação do flutter atrial tipo I (FL) com radiofreqüência (RF). MÉTODOS: Quarenta pacientes consecutivos (idade média 51±11 anos) com FL foram submetidos a ablação do istmo VCI-AT com RF. Em 30 pacientes (GI), o sucesso foi avaliado pela interrupção e não reindução do FL com estimulação atrial programada. Nos últimos 10 pacientes foi avaliada também a condução bidirecional pelo istmo, com cateteres posicionados na sua entrada e saída e em cada lado da linha de bloqueio. O bloqueio foi considerado bidirecional quando ocorrido nos dois sentidos e unidirecional quando ocorrido em um só sentido. RESULTADOS: Vinte e seis (86%) pacientes do GI e 10 (100%) do GII tiveram sucesso imediato (p= 0,5558). Durante o seguimento, 7 (30%) de 23 pacientes do GI e 3 (30%) de 9 do GII tiveram recorrência de FL (p= NS). Os três pacientes do GII que apresentaram recorrência tinham bloqueio unidirecional, enquanto os seis casos sem recorrência tinham bloqueio bidirecional (p=0,012). CONCLUSÃO: A demonstração de bloqueio bidirecional no istmo VCI-AT, obtida imediatamente após a ablação do FL com RF, relaciona-se a menor índice de recorrência clínica, devendo ser o critério preferencial para término do procedimento.

PURPOSE: To determine the clinical importance of a bi-directional line of block demonstration in the inferior vena cava-tricuspid annulus isthmus as an end-point for radiofrequency (RF) atrial flutter (FL) ablation. METHODS: Forty consecutive patients (51±11 years) with type I FL were divided in 2 groups: GI (30 patients) anatomic, non-electrophysiologic isthmus ablation technique (interruption and non-induction FL criteria); and GII (10 patients) anatomic with electrophysiologic evaluation of bi-directional isthmus conduction. The isthmus activation was analyzed before and after anatomic RF ablation with a cateter exploring each side of the line of block, depending on the conduction evaluation (anterograde or retrograde). RESULTS: FL was interrupted and not reinduced in 26/30 (86.6%) GI patients and in 10 (100%) GII patients (p= 0.5558). During follow-up FL recurred in 30% of the patients in both groups. In GII, 6 patients with bi-directional block remained assymptomatic, whereas 3 patients with unidirectional block presented recurrence (p= 0.012). CONCLUSION: Electrophysiologic demonstration of bi-directional line of block in the isthmus is related to long-term success and should be the criterion for interruption of type I atrial FL RF ablation.