Assigning Orders to Suppliers with Linear Piecewise Concave Costs

Purpose: Once a set of suppliers has been determined, according to criteria of quality, price and reliability, among others, there remains the problem of assigning orders to the selected suppliers, in order to cover the needs at the lowest cost. We consider the case in which the needs of a component for a set of plants should be covered by suppliers with linear piecewise concave cost functions, a lower bound on the order size for the non-zero deliveries and a capacity constraint. The purpose is to design procedures for solving this problem. Design/methodology/approach: With the aim of providing practical tools to solve the problem of assigning orders to suppliers with linear piecewise concave costs, two mixed integer linear programs are proposed. Findings: The two MILP models are compared through an extensive computational experiment. This shows that both models, with a slight advantage for one of them, can be solved within a very short time, even when the dimensions of the instance largely exceed those that can occur in real cases. Originality/value: The paper proposes novel models that can be used to solve the problem to optimality in reasonable times and with standard optimization software.Peer Reviewe

Planificación del tiempo de trabajo con jornada anualizada: clasificación de problemas.

Se propone una clasificación de los problemas de planificación del tiempo de trabajo con jornada anualizada y con una serie de restricciones que deben respetarse

La jornada anualizada como medio para hacer frente a las variaciones de la demanda.

Se presenta la anualización de la jornada laboral (distribución irregular de la jornada laboral a lo largo del año, sometida a diversas restricciones), como fuente de flexibilidad de los recursoshumanos, para hacer frente a las variaciones en la cantida

LETRIS: Staffing service systems by means of simulation

Purpose: This paper introduces a procedure for solving the staffing problem in a service system (i.e., determining the number of servers for each staffing period). Design/methodology: The proposed algorithm combines the use of queueing theory to find an initial solution with the use of simulation to adjust the number of servers to meet previously specified target non-delay probabilities. The basic idea of the simulation phase of the procedure is to successively fix the number of servers from the first staffing period to the last, without backtracking. Findings: Under the assumptions that the number of servers is not upper-bounded and there are no abandonments and, therefore, no retrials, the procedure converges in a finite number of iterations, regardless of the distributions of arrivals and services, and requires a reasonable amount of computing time. Originality / value: The new procedure proposed in this paper is a systematic, robust way to find a good solution to a relevant problem in the field of service management and it is very easy to implement using no more than commonly accessible tools.Peer Reviewe

A MILP model for the teacher assignment problem considering teachers’ preferences

The Teacher Assignment Problem is part of the University Timetabling Problem and involves assigning teachers to courses, taking their preferences into consideration. This is a complex problem, usually solved by means of heuristic algorithms. In this paper a Mixed Integer Linear Programing model is developed to balance teachers’ teaching load (first optimization criterion), while maximizing teachers’ preferences for courses according to their category (second optimization criterion). The model is used to solve the teachers-courses assignment in the Department of Management at the School of Industrial Engineering of Barcelona, in the Universitat Politècnica de Catalunya. Results are discussed regarding the importance given to the optimization criteria. Moreover, to test the model's performance a computational experiment is carried out using randomly generated instances based on real patterns. Results show that the model is proven to be suitable for many situations (number of teachers-courses and weight of the criteria), being useful for departments with similar requests.Peer ReviewedPostprint (author's final draft

A variable neighborhood search algorithm for the constrained task allocation problem

A Variable Neighborhood Search algorithm is proposed for solving a task allocation problem whose main characteristics are: (i) each task requires a certain amount of resources and each processor has a finite capacity to be search between task it is assigned; (ii) the cost of solutions includes fixed cost when using processors, assigning cost and communication cost between task assigned to different processors. A computational experiment shows that the algorithm is satisfactory in terms of time and solution qualit

A proposal for a green supply chain strategy

Purpose: The purpose of this paper is to establish a set of steps for helping companies to create a Green Supply Chain Strategy based on the reduction of their carbon footprint. The aim is to put forward a simple guideline that companies can follow and guide them in achieving their carbon emission targets, as well as obtaining attractive supply chain savings. Design/methodology/approach: Based on a literature review and benchmarking this paper proposes a methodology based on three pillars: 1) Corporate Carbon Strategy; 2) Carbon emission roadmap; and 3) Implementation and tracking. Analytic Hierarchy Process (AHP) techniques were used in order to create a green strategy and support the decision-making processes to select the most interesting alternatives for carbon emission reduction and supply chain savings. The supply chain of a metallurgical company is used to illustrate the case study where the proposed methodology is used. The criteria used for the carbon alternatives selection was based on three factors: 1) the supply chain cost of the alternative; 2) carbon emission impact in terms of CO2 tonnes; and 3) marketing effect. Findings: The paper identifies some specific steps for developing a Green Supply Chain Strategy. The case study developed, demonstrates the importance of following a proper methodology based on a set of steps, it also demonstrates that some alternatives focus on improving the supply chain, such as the facilities location, can also improve the key performance indicator related with carbon emission. Originality/value: The study provides guidance for manufacturing companies in implementing their Green Supply Chain Strategy.Peer ReviewedPostprint (author's final draft

A scenario optimisation procedure to plan annualised working hours under demand uncertainty

Annualising working hours (i.e., the possibility of irregularly distributing the total number of working hours over the course of a year) enables to adapt production capacity to fluctuations in demand. The demand, which is an essential data for an optimal planning of work time, usually depends on several and complex factors. Often, tit is not possible to obtain a reliable prediction of the demand or it is no realistic to consider that can be adjusted to a probability distribution. In some cases, it is possible to determine a set of demand scenarios. Each one with a related probability. In this work we present a multistage stochastic optimization model which provides a robust solution (i.e., feasible for any possible scenario) and minimises the expected total capacity shortag

Asia-Pacific zoos in the 21st century : stakeholder perceptions of the roles and functions of zoos : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Environmental Management at Massey University, New Zealand

The advent of the anthropocene accentuates the transformation of ecosystems on a global scale. This study responds to these concerns by assessing the role and function of 21st century zoos in general and the Asia-Pacific zoos in particular. The lack of information on key zoo stakeholders (visitors, staff members, corporate sponsors and zoo associates) is significant in the Asia-Pacific region, particularly in Asia, where there are complexities that may stem from cultural and societal differences. Furthermore, current literature is predominantly based upon Western research and case studies, which rarely take into account the complexities and differences of Asia. This research considers the diversity of the Asia-Pacific region by examining the perceptions and attitudes of the four groups of key stakeholders. Zoos in six countries across the Asia-Pacific were visited over a period of six months to March 2013 in order to assess the diversity of the study region. A literature survey and meta-analysis of 138 zoo-based publications was employed to create a matrix table of themes, stakeholders, and research outcomes. These results were used to design survey instruments directed at stakeholder groups as well as provide a framework against which the results of this study can be compared and contrasted. Quantitative analysis such as Principal Component Analysis, Spearman’s Rho and Kruskal-Wallis H test were used to analyse the results. The face-to-face and computer-based instruments were augmented with the use of a reflective diary and personal work experience to triangulate and validate the research results. The results show that individual zoos across the world are facing similar challenges. Differences in educational backgrounds and socio-cultural norms within the Asia- Pacific region are reflected in stakeholders’ experiences, perceptions, and evaluations of zoos. The results show that there are many differences amongst Asia-Pacific zoo practices, visitor satisfaction, and stakeholder participation and these differences would make it extremely difficult to coordinate activities at a regional level to give them a single voice with a single agenda

Evaluating the impact of strategic personnel policies using a MILP model: the public university case

Purpose: The main purpose of the paper is to evaluate the impact of diverse personnel policies around personnel promotion in the design of the strategic staff plan for a public university. The strategic staff planning consists in the determination of the size and composition of the workforce for an organization. Design/methodology/approach: The staff planning is solved using a Mixed Integer Linear Programming (MILP) model. The MILP model represents the organizational structure of the university, the personnel categories and capacity decisions, the demand requirements, the required service level and budget restrictions. All these aspects are translated into a set of data, as well as the parameters and constraints building up the mathematical model for optimization. The required data for the model is adopted from a Spanish public university. Findings: The development of appropriate policies for personnel promotion can effectively reduce the number of dismissals while proposing a transition towards different preferable workforce structures in the university. Research limitations/implications: The long term staff plan for the university is solved by the MILP model considering a time horizon of 8 years. For this time horizon, the required input data is derived from current data of the university. Different scenarios are proposed considering different temporal trends for input data, such as in demand and admissible promotional ratios for workers. Originality/value: The literature review reports a lack of formalized procedures for staff planning in universities taking into account, at the same time, the regulations on hiring, dismissals, promotions and the workforce heterogeneity, all considered to optimize workforce size and composition addressing not only an economic criteria, but also the required workforce expertise and the quality in the service offered. This paper adopts a formalized procedure developed by the authors in previous works, and exploits it to assess the impact of various personnel policies in the staff planning for a particular university case, and this is the principal contribution of the paper.Postprint (published version