Search

A combined Truck–drone system that delivers packages from a warehouse to multiple customers is investigated. The truck movements are restricted to the potential stops from which the drone with limited capacity takes off or lands. The aim is to determine both the best or 'optimal' sequence of the drone delivery trips and the best or 'optimal' trucks stops that will minimize the total combined truck drone delivery cost. This is an innovative delivery process which also falls under the umbrella of last mile delivery which is known to be one of the most challenging activities within logistics. The problem is first formulated as a 0–1 Linear programming model. A Variable Neighborhood Search (VNS) algorithm is then designed. The proposed metaheuristic is assessed on test problems from the online TSP library. A sensitivity analysis which examines the effect of a neighborhood removal, and the neighborhood sequencing is carried out. The metaheuristic has also shown to be reliable when tested against our mathematical model using the commercial optimizer CPLEX. Interesting overall results are discovered which demonstrate the robustness of the proposed VNS. [ABSTRACT FROM AUTHOR]

The hydraulic model is a set of closed-form, deterministic equations used to predict average crowd speeds and movement times of evacuees exiting a building. The standard SFPE hydraulic model assumes that crowd speed is only influenced by crowd congestion and type of terrain, when in fact, it is also affected heavily influenced by smoke, which not only causes evacuees to slow down due to poorer visibility but may also force them to switch a different movement mode: crawling. This paper gathers and refines empirical data from various published experiments involving individuals and groups moving through smoke by walking upright and crawling, to establish two new variants of the hydraulic model describing the movement of crowds through smoke by the two movement modes. [ABSTRACT FROM AUTHOR]

Main conclusion: Plant traits of interest for sorghum breeders to develop dual-purpose varieties are stem diameter, flag leaf size, crop cycle, and number of grains per panicle. To develop dual-purpose varieties, breeders need to improve traits linked both to grain and biomass production. To identify these traits, we studied the phenotypic plasticity of eighteen traits and the performance of ten contrasting sorghum genotypes, used in West Africa. Trials were carried out in a randomized complete blocks design with four replicates from 2013 to 2016 in Bambey, Sinthiou Malem and Nioro du Rip in Senegal. The results revealed three plant types. The first type, “biomass production”, contained genotypes IS15401 and SK5912, and was linked to cycle duration, leaf area, and plant height. The second type, “grain production”, grouped the caudatum race sorghum 621B, F2-20 and Soumba, and was associated with the number of grains per panicle and the width of the flag leaf. The third group, “dual-purpose”, corresponding to the genotypes Fadda, Nieleni and Pablo, combined some favourable traits for grain and biomass: stem diameter, internode length, number of green leaves and number of grains per panicle. The study showed that high and stable grain yields were associated with stability in flag leaf size, phenology and number of grains per panicle, and a high and stable biomass yield was associated with stability in stem diameter. Those stable plant traits might be of interest for sorghum breeders selecting to develop dual-purpose varieties. [ABSTRACT FROM AUTHOR]

A petrochemical industry produces multiple grades of products along with a significant amount of ‘off-spec’ grades which are bi-products resulting from a transition phase between production of any two grades. While the optimization of grades production in different reactors is important, it is equally important to minimize the production of off-spec grades to minimize loss and reduce safety risks imposed on the reactor in every transition. The production of off-spec grades depends on many factors, particularly the number of grades produced in the reactor and the nature and duration of the transitions. In this study, an adoption of a ‘focused plant’ approach is used that meets the demand of different grades by assigning limited or focused grades to selected reactors based on their capabilities and constraints. A mixed-integer linear programming model is presented to determine the optimum grades selection for focused reactors of a plant and the quantity to be produced in each reactor to maximize overall profit. The model is applied on a case study with six reactors and twelve grades over a period of 1 year. [ABSTRACT FROM AUTHOR]

The prediction of intercity distances by means of distance functions has been widely discussed in the field of location analysis. In this study, we develop distance parameter estimations for the region of Saudi Arabia, using two different methodologies for two commonly used functions, the weighted l norm and the $${l_{b_1,b_2, \theta}}$$ norm. We first use a more traditional approach of determining global parameters for the country taking into consideration the cities spread across the region. In a second approach, we introduce separate city-wise parameters for all considered cities and use the result to present a new parametric distance map for the country. Finally, we determine the confidence interval of the distance estimators for the two approaches to show that the new mapping method provides consistently a better interval estimates. [ABSTRACT FROM AUTHOR]

The maximum capture (MAXCAP) model and its variants have been widely used to find the maximum capture that a firm can get as it enters a spatial market where there are already existing (competitor's) facilities. While the model obtains the optimal demand capture, it however allows the customers to be assigned to the non-closest facility which may incur additional operating costs. A two stage method can be used that overcomes the drawback of the original model while requiring a negligible extra computational effort. To make the original model mathematically self contained and more concise two revised formulations of the problem RMAXCAP-1 and RMAXCAP-2 are proposed which assure that the customers patronize only their closest entering facilities. These models are tested on different sizes of datasets and their performances are compared. [ABSTRACT FROM AUTHOR]

The article provides an overview of the partnerships in the education system of Senegal. It offers information on the country's educational policies. The problems besetting the country's education system are identified. The role of the various partners in the country's education system, including the trade unions, the press, school parents, teachers, local authorities, grassroots community organizations, technical and financial partners and non-governmental organizations are discussed.