A bill of materials-based approach for end-of-life decision making in design for the environment

Re-use, recycling or remanufacturing of products and components are good alternatives for reducing the environmental problems resulting from the huge amounts of waste currently arriving at landfills. A new approach is proposed in this paper for enhancing these alternatives from the earliest stages of product design. Given the product structure (obtained from its bill of materials (BOM)) and the joining and geometrical relationships among the components (obtained from the three-dimensional, computer-aided design representation), a model is proposed that will determine the EOL (EOL) strategy, i.e. the depth of disassembly inside the structure and the final end (re-use, recycle, remanufacture or disposal) for each disassembled part leading to the highest profit. A scatter search (SS) metaheuristic is used to determine the disassembly cost at each level of the BOM. The model presents a number of major improvements with respect to previous research. It addresses the problems of simultaneously determining both the best EOL strategy and the disassembly sequence, as well as allowing removal of components not only over the two or three Cartesian axes and affording the possibility of modifying the encountered strategy in a further step so as to fulfil other business criteria (such as disassembly time, resources availability or maximum waste generation rate).     

Assessing supply chain robustness to links failure

Supply chain networks need to respond efficiently to operation disruptions, as one of their aims is to guarantee the on time delivery of products. Hence, robustness has become one of the important issues to consider when designing supply networks. There are alternative ways to measure what robustness means in this context. In this paper, we propose a new metric based on the effect on service level of the collapse of active transportation links. Numerical experiments are carried out to understand how different design factors affect robustness. Robustness under a targeted attack is compared with robustness to random failures. Results show that flow complexity (i.e. the number of potential transportation links between supply network nodes) is the most influential factor affecting supply network and its robustness, as well as the service level that can be maintained after disruptions. Thus, diversification both in supply sources and transportation routes seems to be key to robustness.     

Complex network analysis of keywords co-occurrence in the recent efficiency analysis literature

Scientometrics - A network analysis (NA) of keyword co-occurrences for a broad collection of Data envelopment analysis (DEA) papers in the period 2008–2017 is carried out. The raw keywords...     

Diagnosis of learner dropout based on learning styles for online distance learning

The amount of data generated by computer systems in Online Distance Learning (ODL) contains rich information. One example of this information we define as the Learner Learning Trail (LLT), which is the sequence of interactions between the students and the virtual environment. Another example is the Learner Learning Style (LLS), which is associated with the student behavior and choices during the learning process. This information can be used to identify learner behavior and learning style. We perceived, after the study of related literature, that the research field of learner diagnosis for ODL does not apply the conjoint use of LLT and LLS. In this article, we propose a model capable of integrating data generated from the behavior of students in ODL with cognitive aspects of them, such as their Learning Styles, by crossing LLT with LLS. We also propose the CPAD method (Collect, Preprocessing, Analysis, Diagnosis), which is implemented by collecting the raw data regarding learning activities, preprocessing the data into structured time sequences, analyzing the sequences regarding the learning styles and using this analysis to diagnose the learner behavior. We selected the dropout to investigate, once the dropout rate in ODL is a real problem in universities around the world. In addition, the dropout is a student decision which can be associated with previous students behaviors. We performed a study with 202 learners to evaluate if learning styles are capable of explaining aspects of the student behavior. The results suggest that Sequential/Global learning style dimension is more capable of explaining the dropout than the other dimensions. Also, we performed four classification experiments to verify how the dimensions of Felder-Silverman Learning Style Model influence the learner diagnosis. We perceived that the Sequential/Global dimension could provide a higher accuracy average with lower variation independently of the diagnosis technique.     

Bicriteria Optimization Model for Locating Maritime Container Depots: Application to the Port of Valencia

Since the location of container depots has an impact on maritime logistics costs, the container depot location problem is usually treated as a cost minimization problem. But the location of the container depots also has a serious environmental impact, given the heavy traffic load inherent to these operations and the setting up and maintenance of the depots. In this paper a bicriteria optimization model for designing a network of depots in a hinterland is proposed and its application to the Port of Valencia, Spain is reported. The two objectives considered are (1) the total cost of the network and (2) the environmental impact of the container depots and the transport operations associated with them. An Analytic Hierarchy Process (AHP) has been used to determine the environmental impact of each depot, and the ε-constraint method to obtain the optimal Pareto set of the problem. The results clearly show that trade-offs are possible between both objective functions and that, for our case study, the proposed approach can obtain solutions that are more cost-effective and have lower environmental impacts than those currently existing.     

A GRASP approach for the extended car sequencing problem

This paper presents a solution procedure for a new variant of the Car Sequencing Problem (CSP) based on the GRASP metaheuristic. In this variant, called xCSP (extended CSP), the aim is to satisfy the hard constraints of the CSP while scheduling the maximum possible number of cars with specific options at specific times of the day in order to satisfy other production requirements. Additional constraint ratios are likewise considered that force at least a minimum specific number of consecutive options. An extension of the CSP is formalized in this paper and computational results are presented using available on-line instances that verify the good performance of a GRASP procedure defined for the xCSP.     

An efficient GRASP algorithm for disassembly sequence planning

One of the steps in a reverse supply chain is to disassemble the recovered products. The design of such disassembly operations is more complex than that of classical assembly lines. A new GRASP algorithm is presented in this paper for solving Disassembly Sequence Planning, i.e. the determination of the sequence for disassembling component parts. The problem has a combinatorial structure and a large number of constraints. Moreover, checking the feasibility of each solution element is time consuming. The proposed approach is successfully tested against previous best known solutions for a set of public benchmark problems.     

The resistance to detachment of dairy strains of Listeria monocytogenes from stainless steel by shear stress is related to the fluid dynamic characteristics of the location of isolation

Strains of Listeria monocytogenes isolated from artisanal Portuguese cheese-making dairies were divided into two categories on the basis of the locations from which they were isolated: strains from dynamic locations were those that were habitually exposed to flowing liquids during the process of cheese-making, whereas those from static locations were rarely, if ever, exposed to the shear stresses generated by liquid flows. The strength of attachment to stainless steel discs of all of these strains was obtained using a radial flow chamber. Initial attachment strengths to stainless steel (after a 0.5 h contact time) of L. monocytogenes strains were greater for the 5 isolates from surfaces exposed to flow (dynamic isolates) than for most (3 out of 4) of those that were not (static isolates). After a 24 h contact time, attachment strength of all isolates reached similar levels. These results suggest that strains having high initial attachment strength are more likely to persist on surfaces exposed to flow than strains having low initial attachment strength. The numerical values of shear forces obtained could prove useful in the rational design of cleaning and decontamination procedures in food processing facilities.     

A scatter search approach to the optimum disassembly sequence problem

One of the most difficult problems faced by OR researchers in the reverse logistics field consists in determining an efficient disassembly sequence for a product at its end of life. In this paper, a scatter search (SS) metaheuristic is presented aiming to deal with the optimum disassembly sequence problem for the case of complex products with sequence-dependent disassembly costs, and assuming that only one component can be released at each time. The algorithm was tested over a set of 48 products consisting of 25, 50, 75 and 100 right-angled parallelepiped components, connected by different kinds of joints. A feasible disassembly sequence, consisting on the reverse of the assembly sequence, is always usable. Comparing by using some statistical analysis the costs of the sequence proposed by the SS algorithm with those corresponding to the reverse order, efficiency of the metaheuristic is shown up.