Albert Corominas

The aim of this article is to provide elements to answer the question of how and when the situation the situation of depletion of a non-renewable, non-durable resource would be reached. To this end, a nonlinear programming model is used under the assumption that the resource is in the hands of a monopolist who knows the corresponding demand functions and is trying to maximize the present value of their net income. General properties of optimal extractive policies and corresponding prices are established, and the cases of negative exponential and linear demand functions are analyzed. The study shows that it is not possible to determine a pattern of optimal policy that is valid for all scenarios, since such a policy depends on the initial availability of the resource, the demand functions, the costs, the interest rate and the duration of the planning horizon adopted by the monopolist.

Purpose: We consider the long-term survival of the newsvendor's supply chain (SC). In this regard, the main contribution of this paper is to identify and analyze two risks that threaten it, both derived from the random nature of the demand, which is inherent in the definition of the newsvendor problem (NVP). These are the risk of a decrease in demand due to unsatisfied demands because of the lack of stock and the risk of bankruptcy of the vendor due to insufficient monetary inflows.Design/methodology/approach: We present a mathematical model of the newsvendor's supply chain with three components: the Producer (P), the Vendor (V) and the Consumers (C). The model takes into account the relation between the components of the SC, the income and operative costs of P and V and the initial funds of V. We solve the model considering several assumptions related with the cost, the initial funds and the demand of C. Findings: We identify and analyze two risks that threat the continuity of the newsvendor’s supply chain in the long term. The first comes from the decreasing in the demand derived from the low level of service that can result from optimizing the joint income of P and V without considering a level of service constraint, which is an essential characteristic of any system of inventory management and has deserved little attention in the literature on the NVP. In fact, an unacceptable low level of service is hardly compatible with the assumption that the law of the demand does not change throughout the time. The second risk is that of V’s bankruptcy due to insufficient monetary inflows, what can happen even if the expected value of V's daily net income is positive. Indicators are proposed to measure these risks and procedures to calculate them.Practical implications: First, in the design of the Supply Chain, under conditions similar to that of the NVP, the decision maker must compare the options of resort or not to V, considering the consequences on income and risk. Second, the objective of coordinating the SC, understood as the maximization of the joint income of P and V, has the limitation of not taking into account that the consumers, which are also part of the SC, can leave it when they deem that the service is unsatisfactory. Third, P must be aware, when setting the parameters of the SC, that its decisions determine those of V and their consequences; therefore, P must take into consideration the economic survival of V, in order to avoid disruptions in the SC and the negative consequences they imply for P itself.Originality/value: Our approach is different from the most usual, which is focused on the criteria and the optimization procedures of the vendor. Instead, we consider the whole SC, including one essential component of it, namely, the consumers.

The problem dealt with in this paper is that of optimizing the path of the extraction rate (and, consequently, the price) for the monopolistic owner of the primary sources of a totally or partially durable non-renewable resource (such as precious metals or gemstones) in a continuous-time frame, assuming that there is an upper bound on the extraction rate and with an interest rate equal to zero. The durability of the resource implies that, unlike the case of non-durable resources, at any time there is a stock of already-used amounts of the resource that are still potentially reusable, in addition to the resource available in the ground for extraction. The problem is addressed using the Maximum Principle of Pontryagin in the framework of optimal control theory, which allows identifying the patterns that the optimal policies can adopt. In this framework, the Hamiltonian is linear in the control input, which implies a bang-bang control policy governed by a switching surface. There is an underlying geometry to the problem that determines the solutions. It is characterized by the switching surface, its time derivative, the intersection point (if any) and the bang-bang trajectories through this point.

The COVID-19 pandemic has caused a general shortage of personal protection products and therapeutic devices, which has highlighted the need for each country to have its own production resources and not depend solely on imports. Given the time that elapses between the onset of an epidemic and its detection, as well as the time required to activate production and the lead time of purchasing operations, it is necessary to have a permanent reserve, which we call shield stock, in order to immediately meet the demand for equipment at the beginning and throughout the course of the epidemic. This situation is analysed in order to identify the most relevant decisions in the scenario described, formulate a cost optimisation model and develop procedures to find the most economical combination of shield stock, domestic production capacity and imports to guarantee the immediate satisfaction of demand and the restoration of the shield stock after the epidemic, as a preventative measure. The procedure is illustrated with a specific pattern of the spread of the epidemic and some numerical examples.

Purpose: This paper, devoted to the selection of strategic sourcing options as a part of the supply chain design, aims to provide supply chain designers with guidelines for selecting the best strategic sourcing option for each item (i.e., products, modules, parts and services).Design/methodology/approach: The study is based on a review of the literature on sourcing options, buyer-supplier relationships, factors and criteria to select a sourcing strategy as well as the authors experience in this field.Findings: We propose a multi-step process by considering the three dimensions of the strategic sourcing options (who and how many will make the item; in cases of outsourcing, the kind of relationship between buyer and supplier(s); and where the item is to be made) together with the characteristics of the context, demand and product, and the relevant criteria to evaluate them.Originality/value: The main contributions are the review of the factors and criteria for selecting the best strategic sourcing option for each item (i.e., products, modules, parts and services) as well as the guidelines provided for each step of the process.

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.

Based on the analysis of the pertinent literature, we propose a framework to serve as a guide in designing a distribution network as a component of a supply chain (SC). It consists of three steps that are common to goods and services SCs: position of the decoupling point, structure of the network, and product delivery. For each step, we take into account the peculiarities of both goods and services separately in order to establish a list of available options and evaluate their suitability in relation to the relevant factors that characterise the products and the markets.

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