Search results for "operations research"

A Multi objective inventory model for short food supply chains

2017

Over the past 50 years, vertically integrated multinationals dominated global food markets by providing huge product diversity at low prices. Such systems are characterized by long supply chains capable of achieving high cost efficiencies resulting from the use of cheap raw materials, high chemical inputs, industrial shelf-life extension processes, economies of scale and mechanization. This dominant position on the market, however, has been achieved at a heavy cost on the global environment, generated by massive food wastage, and by a steady supply of fossil fuels. For such reasons, global supply chains are considered unsustainable and new food systems are being promoted in order to replace…

Stopover strategies in birds: a review of methods for estimating stopover length

1999

This study categorizes and reviews methods used to estimate stopover length in migratory birds. Stopover length is an important variable in analysing migration strategies. The analysis of the stopover pattern of migratory birds typically attempts to investigate variability in the number of stopovers and in the length of time spent at stopover sites in relation to species, age, sex and body condition. Although the number of capture-recapture studies analysing stopover length has increased substantially, most are analysed using the simple last-first capture method which gives biased estimates. The use of mathematical models to calculate stopover length is uncommon. Most researchers assume hom…

Brief Introduction to Probability Distributions

2014

There is a great deal of uncertainty in any project. That is, data is seldom absolutely reliable and exact, since there is never certainty about duration of tasks, price variations, effect on the environment, etc., to say nothing about those aspects which are external to the project and for which the project developer has no control, such as weather conditions, demand, stock fluctuations, inflation, supplier’s delays, etc. It is believed that many projects are not completed in time and finish with cost overrun, because in their preparation, data is taken as unquestionable, and then actual conditions show that it is not precisely the case. For this reason the uncertainty aspect has to be con…

A Fuzzy Chance-constraint Programming Model for a Home Health Care Routing Problem with Fuzzy Demand

2017

An Adaptive Alternating Direction Method of Multipliers

2021

AbstractThe alternating direction method of multipliers (ADMM) is a powerful splitting algorithm for linearly constrained convex optimization problems. In view of its popularity and applicability, a growing attention is drawn toward the ADMM in nonconvex settings. Recent studies of minimization problems for nonconvex functions include various combinations of assumptions on the objective function including, in particular, a Lipschitz gradient assumption. We consider the case where the objective is the sum of a strongly convex function and a weakly convex function. To this end, we present and study an adaptive version of the ADMM which incorporates generalized notions of convexity and penalty…

Constrained control of a nonlinear two point boundary value problem, I

1994

In this paper we consider an optimal control problem for a nonlinear second order ordinary differential equation with integral constraints. A necessary optimality condition in form of the Pontryagin minimum principle is derived. The proof is based on McShane-variations of the optimal control, a thorough study of their behaviour in dependence of some denning parameters, a generalized Green formula for second order ordinary differential equations with measurable coefficients and certain tools of convex analysis.

Reconfiguration: a key to handle exceptions and performance deteriorations in manufacturing operations

2005

During a manufacturing operation, exceptions may occur dynamically and unpredictably. Their occurrence may lead to the degradation of system performance or, in the worst case scenario may interrupt the production process by causing errors in the schedule plan. This paper classifies three families of exceptions: (1) out-of-order events such as machine breakdowns, (2) operational out-of-ordinary events such as rush orders and (3) deteriorations of manufacturing resource performance such as reductions of machines' utilization. In all cases, in order to maintain an adequate level of system performance, it is necessary to detect exceptions, to diagnose them quickly and to recover them by taking …

Understanding the Health Disaster: Research Design for the Response to the 2014 West African Ebola Outbreak

2015

International audience; The 2014 Ebola outbreak in West Africa is the largest ever in history, affecting multiple countries and to this date, the World Health Organization has registered more than 6,500 deaths attributed to Ebola. The challenges arising from this outbreak to responders worldwide do not follow the standard characterisation or response patterns of natural sudden onset vs. conflict disasters. Rather, it is a medical emergency, which is intertwined with multiple challenges in the sectors decision-making, coordination, logistics and information management. In this paper, we present our research framework, which is based on desk research and initial interviews with responders. Th…

Leadership and employees’ perceived safety behaviours in a nuclear power plant: A structural equation model

2011

Leadership is considered an essential element in guaranteeing the safe running of organizations. The purpose of the present study is to find out how leader behaviours influence employees' safety behaviours (perceived safety behaviours) in the nuclear field. In an attempt to answer this question, the authors of this research have considered the way this influence is exercised, taking into consideration some important factors like safety culture and safety climate. To achieve this, the empowerment leadership model, based on a behavioural approach to leadership, was used. The sample was made up of 566 employees from a Spanish nuclear power plant. The results indicated that when safety culture …

Multinationality, foreignness and institutional distance in the relation between R&D and productivity

2012

Abstract This paper empirically examines to what extent being foreign and part of a multinational affects the endogenous relation between R&D and productivity. Our findings indicate that multinationals obtain in general higher R&D returns. Also, there is a negative foreignness effect in that domestic-owned multinationals outperform foreign subsidiaries. However, these effects are somehow moderated by the institutional distance between the home and host countries. These results, obtained for a panel of UK firms, are largely consistent with a set of hypotheses derived from the institutional and international business theories.