The orienteering problem: A hybrid control Formulation

In the last years, a growing number of challenging applications in navigation, logistics, and tourism were modeled as orienteering problems. This problem has been proposed in relation to a sport race where certain control points must be visited in a minimal time. In a certain kind of these competitions, the choice of the number and the order for the control points are left to the competitor. We propose an original approach to solve the orienteering problem based on hybrid control. The continuous state of the system contains information about the navigation toward the next control point. In contrast, the discrete state keeps track of the already visited ones. The control problem is solved using non-standard dynamical programming techniques

Effectiveness of occupational safety and health training for migrant farmworkers: a scoping review

Objectives: Migrant farmworkers report higher rates of work-related illnesses, injuries and fatalities compared with local workers. Language and cultural barriers represent a relevant source of risk, which can be reduced by means of targeted training interventions. However, very little evidence is available about the effectiveness of Occupational Safety and Health (OSH) training programmes addressing migrant farmworkers. Study design: We carried out a scoping review. Methods: Currently available literature about the effectiveness of OSH training for migrant farmworkers--in terms of improvements in at least one of the following: safety knowledge, behaviours, attitudes and beliefs and health outcomes--was searched from four databases: PubMed, PsycINFO, Scopus and Web of Science. The screening was performed independently by two authors, and any disagreement was resolved through discussion until consensus was achieved. Once the articles eligible for inclusion were selected, the objectives, design, sample and setting, interventions and findings of each study were recorded. No quality assessment tool for publications considered by this study has been used because a scoping review does not aim for critical appraisal. Results: Twenty-nine publications met the inclusion criteria. Of these, nine cross-sectional studies discussed the effectiveness of training activities in terms of whether participating in any programme had or did not have a significant effect on the dependent variables, when training was considered along with other sociodemographic factors. In the majority of these studies, training appeared to have low or no effect on the dependent variables considered. Twenty mainly within-subject experimental studies addressed the effectiveness of specific training methods, reporting significant improvements especially for interventions based on a participatory approach. Conclusions: Training could greatly contribute to an effective attainment of OSH information, but the present review shows that more evidence is needed to guide the future development of effective training activities

Conveying safety messages on agricultural machinery: The comprehension of safety pictorials in a group of migrant farmworkers in Italy

The comprehension of safety signs affixed to agricultural machinery is fundamental to warning users about the residual risks which cannot be eliminated with machinery design and the adoption of protections. This is particularly relevant for the migrant workforce, which may encounter some language barriers with written safety communication. The present study aimed to investigate the comprehension of safety signs affixed to agricultural machinery in a group of migrants from both European and non-European countries employed in Italian agriculture. Thirty-seven migrant farmworkers (12 Indians, 17 Pakistanis, and eight Romanians) were individually interviewed to test the comprehension of four safety signs referring to the main causes of fatal and non-fatal injuries caused by interactions with farm machinery. Romanians obtained the highest comprehension performance (68.8% of correct answers), followed by Indians (35.4%), with Pakistanis being last (32.4%). The nationality and the previous experience as a farmworker significantly affected the comprehension of safety signs. The results pointed out the importance of adequately training migrants on the meaning of safety signs. Beside this, the study suggests a redesign of the signs, considering some signs' features to enhance pictorials' cross-cultural comprehension

Bandwagon effect in mean-field games

This paper provides a mean-field game theoretic model of the bandwagon effect in social networks. The latter phenomenon can be observed whenever individuals tend to align their own opinions to a mainstream opinion. The contribution is three-fold. First, we provide a mean-field games framework that describes the opinion propagation under local interaction. Second, we establish mean-field equilibrium strategies in the case where the mainstream opinion is stationary. Such strategies are shown to have a threshold structure. Third, we study conditions under which a given opinion distribution is stationary if agents implement optimal non-idle and threshold strategies. © 2013 IEEE

Opinion dynamics and stubbornness through mean-field games

This paper provides a mean field game theoretic interpretation of opinion dynamics and stubbornness. The model describes a crowd-seeking homogeneous population of agents, under the influence of one stubborn agent. The game takes on the form of two partial differential equations, the Hamilton-Jacobi-Bellman equation and the Kolmogorov- Fokker-Planck equation for the individual optimal response and the population evolution, respectively. For the game of interest, we establish a mean field equilibrium where all agents reach "-consensus in a neighborhood of the stubborn agent's opinion. ©2013 IEEE

Mean-Field Games and Dynamic Demand Management in Power Grids

This paper applies mean-field game theory to dynamic demand management. For a large population of electrical heating or cooling appliances (called agents), we provide a mean-field game that guarantees desynchronization of the agents thus improving the power network resilience. Second, for the game at hand, we exhibit a mean-field equilibrium, where each agent adopts a bang-bang switching control with threshold placed at a nominal temperature. At equilibrium, through an opportune design of the terminal penalty, the switching control regulates the mean temperature (computed over the population) and the mains frequency around the nominal value. To overcome Zeno phenomena we also adjust the bang-bang control by introducing a thermostat. Third, we show that the equilibrium is stable in the sense that all agents' states, initially at different values, converge to the equilibrium value or remain confined within a given interval for an opportune initial distribution. © 2013 Springer Science+Business Media New York

A hybrid control framework for an optimal visiting problem

The optimal visiting problem is the optimization of a trajectory that has to touch or pass as close as possible to a collection of target points. The problem does not verify the dynamic programming principle, and it needs a specific formulation to keep track of the visited target points. In this paper, we introduce a hybrid approach by adding a discontinuous part of the trajectory switching between a group of discrete states related to the targets. Then, we show the well-posedness of the related Hamilton-Jacobi problem, by reformulating the optimal visiting as a collection of time-dependent optimal stopping problems

On the Null Controllability of the Heat Equation with Hysteresis in Phase Transition Modeling

We prove the null controllability of the relaxed Stefan problem, which models phase transitions in two-phase systems. The technique relies on the penalty approximation of the differential inclusion describing the phase dynamics, solving a constrained minimization problem, and passing to the limit