755 research outputs found
Degree Variance And Emotional Strategies Catalyze Cooperation In Dynamic Signed Networks
No full textWe study the problem of the emergence of cooperation in dynamic signed networks where agent strategies coevolve with relational signs and network topology. Running simulations based on an agent-based model, we compare results obtained in a regular lattice initialization with those obtained on a comparable random network initialization. We show that the increased degree heterogeneity at the outset enlarges the parametric conditions in which cooperation survives in the long run. Furthermore, we show how the presence of sign-dependent emotional strategies catalyze the evolution of cooperation with both network topology initializations. Proceedings 28th European Conference on Modelling and Simulation © ECMS Flaminio Squazzoni, Fabio Baronio, Claudia Archetti, Marco Castellani (Editors)
The Vehicle Routing Problem with Divisible Deliveries and Pickups
No full textThe vehicle routing problem with divisible deliveries and pickups is a new and interesting model within
reverse logistics. Each customer may have a pickup and delivery demand that have to be served with
capacitated vehicles. The pickup and the delivery quantities may be served, if beneficial, in two separate visits.
The model is placed in the context of other delivery and pickup problems and formulated as a mixed-integer
linear programming problem. In this paper, we study the savings that can be achieved by allowing the pickup
and delivery quantities to be served separately with respect to the case where the quantities have to be served
simultaneously. Both exact and heuristic results are analysed in depth for a better understanding of the problem
structure and an average estimation of the savings due to the possibility of serving pickup and delivery
quantities separately
NA is enriched in Archetti bodies as well as at the tip of non-Archetti budding influenza filaments.
No full textA) Diffraction limited image of A/Udorn/72 filaments stained with for HA (green) and NA (red) budding out of an infected cell. White line denotes a filament with an Archetti body (arrow) at the tip. Scale bar 1 μm. B) Intensity trace of the NA signal from the filament highlighted in A), showing higher NA signal at the Archetti body at the tip. C) Normalised averaged intensity traces of the NA signal from filaments without obvious Archetti body structures at the tip, showing an enrichment at the filament ends furthest from the cell membrane. (JPG)</p
A new formulation and a branch-and-cut algorithm for the set orienteering problem
No full textIn this study we address the Set Orienteering Problem, which is a generalization of the Orienteering Problem where customers are clustered in groups. Each group is associated with a profit which is gained in case at least one customer in the group is served. A single vehicle is available to serve the customers. The aim is to find the vehicle route that maximizes the profit collected without exceeding a maximum route cost, which can be interpreted also as route duration. The problem was introduced in Archetti (2018) together with a mathematical programming formulation. In this paper, we propose a new formulation which uses less variables. We also derive different classes of valid inequalities to strengthen the formulation. In addition, separation algorithms are developed, some of which are new with respect to those presented in the literature. A branch-and-cut algorithm is implemented to solve the problem and tests are made on benchmark instances. The results show that the branch-and-cut algorithm is effective in solving instances with up to 100 customers. Moreover, the difficulty of solving the problem largely depends on the maximum route duration. We also show that valid inequalities are effective in speeding up the solution process. Finally, a comparison with two exact benchmark approaches proposed in the literature shows that the branch-and-cut algorithm proposed in this paper is the new state-of-the-art exact approach for solving the Set Orienteering Problem
Recent challenges in Routing and Inventory Routing: E‐commerce and last‐mile delivery
No full textIn the e-commerce era, vendors have to satisfy a large number of on-line orders, mainly from private customers, with low weight and volume, reduced delivery time, and overlap of customers' time windows. Production is made available all day long. New strategies and new technologies are emerging for deliveries. The processing time of the orders is reduced. These new features generate interesting challenges in formulating and solving Routing and Inventory Routing problems. After discussing these features and the corresponding challenges, we recall the relevant literature in Routing and Inventory Routing and provide future research directions, mainly related to routing problems with release dates, routing problems with crowdshipping, and inventory routing problems in the e-commerce era
Robot Motion Planning in ROS Environment
No full textThis paper proposes a method for motion planning and simulation for manipulator robots in the presence of obstacles in the workspace realizing large movements without dividing the stroke into successive parts. The approach has been tested with different solvers. In particular, it is observed that the RRT Connect planner has very good abilities to solve the problem although some difficulties remain when a large part of the workspace between the initial and final position is occupied by an obstacle
The hazardous orienteering problem
No full textThis article studies the Hazardous Orienteering Problem (HOP), a variant of the more famous Orienteering Problem (OP). In the OP, a vehicle earns a profit for each customer it visits (e.g., to pick up a parcel) subject to an upper bound on the tour time. In the HOP, the parcels picked up at some customers have a probability of triggering a catastrophic event. The probability depends on how long the parcels travel on the vehicle. If any catastrophic event triggers, the entire collected profit is lost. The goal is to determine the tour that maximizes the expected profit. The problem has interesting applications in routing of hazardous material, cash-in-transit, and law enforcement. We propose a mixed-integer nonlinear formulation and techniques both to obtain dual bounds and to produce primal solutions. Computational tests investigate the efficacy of the methods proposed and allow to gain insights into solution features.The work of Alberto Santini has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement number 945380
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