Émissions de carbone dans un modèle de production-stocks multi-echelon avec prise en compte des contraintes de délai

Colloque avec actes et comité de lecture. internationale.International audienceNous développons un modèle mathématique d'optimisation qui intègre les émissions de carbone dans un modèle gestion production-stock multi-échelon sous des contraintes de délai. Le modèle proposé capte l’impact de certaines décisions logistiques sur les émissions carbone. Nous nous intéressons principalement aux décisions suivantes : production des produits finis et intermédiaire, approvisionnement chez des fournisseurs internes et externes, positionnement des stocks des différents produits (fini et intermédiaires) aux différents niveaux de la chaîne logistique. Nous considérons deux types de réglementation environnementale: (1) taxe sur les émissions et (2) seuil infranchissable d'émissions carbone. Nous utilisons le modèle pour réaliser un ensemble d’expérimentations et fournir une série d’implications managériales

Study of Client Reject Policies under Lead-Time and Price Dependent Demand

Delivery lead-time has become a factor of competitiveness for companies and an important criterion of purchase for the customers today. Thus, in order to increase their profit, companies must not focus only on price but also need to quote the right delivery lead time to their customers. Some authors to find a way in quoting the right delivery lead-time while considering an M/M/1 system. In M/M/1, all customers are accepted. This can lead to longer lead times in the queue. Firms can react by quoting longer lead times in order to cope with this situation. However, this leads to lower demand and revenue. Starting from this observation, we investigate in this paper whether a customer rejection policy can be more beneficial for the firm than an all-customers’ acceptance policy. Indeed, our idea is based on the fact that rejecting some customers might help to quote shorter lead time for the accepted customers, which might lead to higher demand and profit. We model this rejection policy based on an M/M/1/K system. We analytically determine the optimal firm’s policy (optimal price and quoted lead time) in case of M/M/1/1 system. Then, we compare the optimal firm’s profit under M/M/1/1 with the optimal profit obtained by M/M/1. Two situations are considered: a system without holding and penalty costs and a system where these costs are included

Government strategies to secure the supply of medical products in pandemic times

We investigate how to secure reliable access to personal protective equipment (PPE) in pandemics, which are characterized by random occurrences and durations, at the lowest expected cost. The policymaker\u27s strategy is based on a mix of (1) holding ready-to-use strategic stockpile that is acquired at regular price but incurs a holding cost, (2) building partnership with PPE manufacturers to relocate offshore production locally, which guarantees some local supply but requires offering subsidies, and (3) buying PPE from the spot market, which is characterized by long supply lead times and high prices. We model the problem as a Stackelberg game between a policymaker (leader) and a manufacturer (follower). The policymaker decides the PPE stockpile, the subsidy offered to the local manufacturer, and the quantity to buy from the spot market. The manufacturer determines whether to move production onshore. We determine the optimal strategy for each player and study the effect of spot market conditions and pandemic characteristics. Analytical results show that attracting local manufacturers is less costly for the government when the variability of pandemic duration increases. While it is sub-optimal to rely only on the strategic stockpile, holding some stockpile may be necessary even when the PPE can be obtained from the spot market as soon as the pandemic starts. Results reveal policymaker\u27s preference for subsidizing onshore production in the following cases: products with low spot prices (counter-intuitively), spot market with long supply lead time, less frequent pandemics, and shorter pandemics

Modélisation par des processus stochastiques de l'intensité et du spectre des atomes dans un plasma.

L'étude des propriétés radiatives des plasmas est un outil important pour réaliser le diagnostic des plasmas. Cette thèse analyse les modélisations de diagnostic utilisant une approche stochastique. La méthode consiste à modéliser un paramètre plasma fluctuant avec une évolution par paliers séparés par des sauts instantanés. Le paramètre plasma est échantillonné selon une fonction de densité de probabilité (PDF), et son évolution est gouvernée par une distribution de probabilités de temps d'attente (WTD), qui est liée à la fonction d'autocorrélation du paramètre plasma considéré. Après une partie théorique présentant les bases de notre modèle stochastique, nous nous intéressons dans une seconde partie à l'application de ce dernier à la cinétique des populations atomiques dans un plasma turbulent et à l'élargissement Stark des raies de l'hydrogène.Nous étudions d'une part l'effet des fluctuations de la température sur les abondances ioniques du carbone dans des conditions des tokamaks, et à un système atomique simplifié des raies de Balmer afin de préparer un diagnostic de la turbulence. Nos résultats montrent que les fluctuations modifient les populations atomiques des systèmes étudiés. Nous intéressons aux profils Stark des raies de Lyman de l'hydrogène pour une seconde application dans un plasma supposé à l'équilibre thermodynamique. Dans ce cas, c'est le microchamp électrique de la composante ionique du plasma qui est modélisé par un processus stochastique. La particularité de cette étude est qu'elle explore pour des températures de l'ordre de l'eV, le régime intermédiaire entre l'approximation statique à haute densité, et l'approximation d'impact à faible densité.The study of radiative properties of the plasmas (spectra and line intensities) is an important tool for achieving the diagnostic of plasmas. This thesis analyses diagnostic modeling using a stochastic approach. The method consists in modeling a fluctuating plasma parameter by a stepwise constant evolution separated by instantaneous jumps. The plasma parameter is sampled according to a probability density function (PDF), and its evolution is governed by a waiting time (WTD) which is related to the autocorrelation function of the considered plasma parameter. After presenting the theoretical foundations of our stochastic model, we are interested in a second part to the application of the latter for the kinetics of atomic populations in a turbulent plasma and to the Stark broadening of hydrogen line shapes. We apply our model to study the effect of temperature fluctuations on the ion abundances of carbon in conditions that may be encountered in thermonuclear fusion machines (tokamaks) and to a simplified atomic system of Balmer lines, with the aim of preparing a turbulence diagnostic based on line ratios. Our results and show that retaining fluctuations modifies the atomic populations of the system studied.We focus our interest on Stark profiles in a plasma assumed to be in thermodynamic equilibrium for our second application. In this case, it is the electric plasma microfield which is modeled by a stochastic process. The distinctive feature of this study is that it explores, for temperatures of the order of the eV, the intermediate regime between the static approximation at high density, and the impact approximation at low density

An optimization model for the design of global multi-echelon supply chains under lead time contraints

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Integration of the profit-split treansfer pricing method in the design of global supply chains with a focus on offshoring context

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Integration of delivery lead time constraints and inventory replenishment conditions in supply chain models

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A capacitated multi-echelon inventory placement model under lead time constraints

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Inventory placement in multi-echelon supply chains with delivery lead time constraints

Manufacturing and Service Operations Management Society (MSOM)International audienc