Alex Grasas | EADA - Academia.edu (original) (raw)

Papers by Alex Grasas

Vox sanguinis, 2015

Recent studies suggest that transfusion of old red blood cell (RBC)s, mainly those close to the 4... more Recent studies suggest that transfusion of old red blood cell (RBC)s, mainly those close to the 42-day maximum shelf life (MSL), is associated with increased morbi-mortality. Although there is no formal proof supporting a causal relationship, the precautionary principle asks for corrective interventions whenever they do not bring about other risks or unjustified costs. Here, we investigated the feasibility of reducing the MSL. A trace simulation model was used to analyse the repercussions of several MSLs on a large regional blood system. The baseline model was fed with real input and output data from years 2009 to 2010 and validated against real inventory data. Shortage and outdate rates and inventory levels for each blood group were derived assuming 42-, 35-, 28-, 21- and 14-day MSLs, as well as several distribution rules and supply shocks (periods without blood collections). The model shows that MSL could be reduced to 28-35 days without major increases in the shortage or outdate ...

Se presenta una herramienta multimedia para la práctica de la toma de decisiones en los estudiant... more Se presenta una herramienta multimedia para la práctica de la toma de decisiones en los estudiantes de asignaturas sobre la organización de la producción. El juego consiste en simular el funcionamiento en el ámbito productivo que produce zumos y los distribuye. El jugador debe actuar como jefe de producción y tomar decisiones: programación de la producción, realización de pedidos de materiales de aprovisionamiento y gestión de la distribución de productos acabados. El objetivo del juego es alcanzar unos beneficios máximos y a su vez obtener un grado de satisfacción de los clientes lo más elevado posible.

Production and Operations Management, 2014

To understand whether retailers should consider consumer returns when merchandising, we study how... more To understand whether retailers should consider consumer returns when merchandising, we study how the optimal assortment of a retailer is influenced by its return policy. The retailer selects its assortment from an exogenous set of horizontally differentiated products. Consumers make purchase and keep/return decisions in nested multinomial logit fashion. Our main finding is that the optimal assortment has a distinct structure for relatively strict return policies: It is optimal to offer a mix of the most popular and most eccentric products when the refund amount is sufficiently low, which can be viewed as a form of risk sharing between the retailer and consumers. In contrast, if the refund is sufficiently high, or when returns are disallowed, optimal assortment is composed of only the most popular products (a common finding in the literature). We provide preliminary empirical evidence for one of the key drivers of our results: more eccentric products have higher probability of return -conditional on purchase. In light of our analytical findings and managerial insights, we conclude that retailers should take returns into account when merchandising.

This work focuses on the Total Weighted Tardiness Job-Shop Scheduling Problem. In this problem, e... more This work focuses on the Total Weighted Tardiness Job-Shop Scheduling Problem. In this problem, each job consists of a set of tasks that must be processed on a given set of machines for uninterrupted and predetermined time. Each job has a due date and a penalty associated with the delay in completion time. The objective is to minimize the total weighted tardiness. We propose an heuristic method based on Iterated Local Search (ILS) metaheuristic, designated as TWTJSSP-ILS. The method applies GRASP to obtain an initial solution, combining a random choice technique with the longest processing time. In the refinement stage of the ILS method, a Variable Neighborhood Descent (VND) procedure is applied as the as local search step. We present a computational experiment applying this method to the benchmark instances taken from the literature. The initial results lead to high quality solutions.

The International Journal of Logistics Management

Purpose -The aim of this paper is to present a problem-based learning (PBL) activity that uses a ... more Purpose -The aim of this paper is to present a problem-based learning (PBL) activity that uses a decision support system (DSS) to teach one of the most fundamental topics in distribution planning: vehicle routing.

International Series in Operations Research & Management Science, 2009

Should retailers take product returns into account when choosing their assortments? And, when doi... more Should retailers take product returns into account when choosing their assortments? And, when doing so, should they consider assortment selection as a popularity contest -by carrying products that they think will be popular among consumers? Or, is there ever a case for carrying eccentric products -those that are least likely to be purchased by a typical consumer? In search of answers to these questions, we explore in this chapter the interactions between product assortment, return policy, and pricing decisions of a retailer. We consider a category of horizontally differentiated products delivered in two alternative supply modes: make-to-order (MTO) and make-to-stock (MTS). In the MTO mode, products are supplied after demand materializes, whereas in the MTS mode, the retailer stocks products prior to the selling season. Underlying our demand model, consumer choice behavior follows a nested multinomial logit model, with the first stage involving a product choice, and the second stage involving a keep-or-return decision. We show that the structure of the optimal assortment strongly depends on both the return policy, which we parameterize by refund fraction (percentage of price refunded upon return) and the supply mode (MTO vs. MTS). For relatively strict return policies with a sufficiently low refund fraction, it is optimal for the retailer to offer most eccentric products in the MTO mode, and a mix of most popular and most eccentric products in the MTS mode. For relatively lenient return policies, on the other hand, conventional thinking applies: the retailer selects most popular products. We also

Resumo. Este trabalho tem seu foco no problema de roteamento de veículos (PRV) com frota heterogê... more Resumo. Este trabalho tem seu foco no problema de roteamento de veículos (PRV) com frota heterogênea e múltiplas viagens. Dada a natureza combinatória do problema, que praticamente inviabiliza a utilização exclusiva de métodos de programação matemática, dito exatos, a solução de casos reais normalmente é feita por meio de métodos heurísticos. Os problemas reais de roteamento de veículos envolvem a utilização de diferentes tipos de caminhões e, em alguns casos, suporte para múltiplas rotas. Como contribuição para esse campo de pesquisa, descreve-se neste trabalho um algoritmo, inspirado na heurística Iterated Local Search, aplicado a um problema real de roteamento de veículos, considerando uma frota heterogênea e múltiplas viagens opcionais. O estudo de caso é baseado em um conjunto de instâncias de uma empresa europeia de grande porte, envolvendo aproximadamente 400 clientes. Resultados computacionais comprovam a eficiência do algoritmo proposto, mostrando-se capaz de reduzir os gastos da empresa em até 51100,00 euros. PALAVRAS-CHAVE: Roteamento de Veículos com Frota Heterogênea, Múltiplas Viagens, Aplicações Reais e Iterated Local Search. Abstract. This paper has its focus on the vehicle routing problem (VRP) with heterogeneous fleet multiple trips. Given the combinatorial nature of the problem, which practically precludes the exclusive use of mathematical programming methods, said exact, solution of real cases is typically done through heuristic methods. The real vehicle routing problems involve the use of different types of trucks and ,in some cases, support for multiple routes. As a contribution to this field of research, this paper describes an algorithm inspired on the Iterated Local Search heuristic applied on a real-life case problem, considering a heterogeneous fleet with optional multiple trips. The case study is based on a set of instances provided by a large European company, involving approximately 400 stores. Computational results show the effectiveness of the proposed algorithm, being able to reduce company expenses by up to 51100,00 EUR.

Journal of Simulation, 2014

Iterated Local Search (ILS) is one of the most popular single-solution-based metaheuristics. ILS ... more Iterated Local Search (ILS) is one of the most popular single-solution-based metaheuristics. ILS is recognized by many authors as a relatively simple yet efficient framework able to deal with complex combinatorial optimization problems (COPs). ILS-based algorithms have been successfully applied to provide near-optimal solutions to different COPs in logistics, transportation, production, etc. However, ILS is designed to solve COPs under deterministic scenarios. In some real-life applications where uncertainty is present, the deterministic assumption makes the model less accurate since it does not reflect the real stochastic nature of the system. This paper presents the SimILS framework that extends ILS by integrating simulation to be able to cope with Stochastic COPs in a natural way. The paper also describes several tested applications that illustrate the main concepts behind SimILS and give rise to a new brand of ILS-based algorithms.

OR Insight, 2013

In this article we present a Vehicle Routing Problem (VRP) faced by a large distribution company ... more In this article we present a Vehicle Routing Problem (VRP) faced by a large distribution company in the Northeast of Spain. The company distributes products from its central facilities to a chain of around 400 stores all over the country. One of the peculiarities of the VRP of this company -which is common among real-life VRPs -is the presence of a heterogeneous fleet where vehicles with different capacities can make multiple trips during a single day. This variant of the problem, which we refer as Heterogeneous Fleet and Multi-trip VRP, has been barely studied in the literature. To solve the problem, we use an algorithm based on the wellknown savings heuristic with a biased-randomization effect and three local search operations. Our approach is simple to implement as it needs few parameters and no fine-tuning processes, which are usually cumbersome and require experts' involvement. We obtain savings of around 12 per cent in transportation costs, which represent around h30 000 saved per week.

BMC Health Services Research, 2014

Background: Blood samples are usually collected daily from different collection points, such hosp... more Background: Blood samples are usually collected daily from different collection points, such hospitals and health centers, and transported to a core laboratory for testing. This paper presents a project to improve the collection routes of two of the largest clinical laboratories in Spain. These routes must be designed in a cost-efficient manner while satisfying two important constraints: (i) two-hour time windows between collection and delivery, and (ii) vehicle capacity.

papers.ssrn.com

... We provide empirical evidence for one of the key drivers of our results: more eccentric produ... more ... We provide empirical evidence for one of the key drivers of our results: more eccentric products have higher probability of return (conditional on purchase). Moreover, we ... Assortment Selection in Retailing assortment is usually thought of as strategic and more marketing related. ...

... (US), Yankee Candle, includes a collection of customized jar candles in their online catalog.... more ... (US), Yankee Candle, includes a collection of customized jar candles in their online catalog. Customers can choose their favorite fragrance and label design along with its accompanying set of adornments. ... For example, Lands' End and Yankee Candle allow returns ...