1,721,147 research outputs found
Multi-agent single machine scheduling
Full text linkWe consider the scheduling problems arising when several agents, each owning a set of nonpreemptive jobs, compete to perform their respective jobs on one shared processing resource. Each agent wants to minimize a certain cost function, which depends on the completion times of its jobs only. The cost functions we consider in this paper are maximum of regular functions (associated with each job), number of late jobs and total weighted completion time. The different combinations of the cost functions of each agent lead to various problems, whose computational complexity is analysed in this paper. In particular, we investigate the problem of finding schedules whose cost for each agent does not exceed a given bound for each agent
Demand allocation with latency cost functions
No full textWe address the exact resolution of a Mixed Integer Non Linear Programming model where resources can be activated in order to satisfy a demand (a covering constraint) while minimizing total cost. For each resource, there is a fixed activation cost and a variable cost, expressed by means of latency functions. We prove that this problem is NP-hard even for linear latency functions. A branch and bound algorithm is devised, having two important features. First, a dual bound (equal to that obtained by continuous relaxation) can be computed very efficiently at each node of the enumeration tree. Second, to break symmetries resulting in improved efficiency, the branching scheme is n-ary (instead of binary). These features lead to a successful comparison against two popular commercial and open-source solvers, CPLEX and Bonmin
Partitioning of Biweighted Trees
Full text linkA districting problem is formulated as a network partitioning model where each link has one weight to denote travel time and another weight to denote workload. The objective of the problem is to minimize the maximum diameter of the districts while equalizing the workload among the districts. The case of tree networks is addressed and efficient algorithms are developed when the network is to be partitioned into two or three districts
Optimal allocation plan for distribution centres of a frozen food company
No full textIn this paper, we analyse the distribution system of an Italian company operating in the ice cream and frozen food industry. In particular, we address the problem of optimally allocating products demand to distribution centres spread over the Italian territory and develop a mixed integer programming model. We present our computational experience in which the optimal solution is compared with the actual distribution policies and show how to use our model as a decision support tool for the company management
Optimal power control in OFDMA cellular networks
No full textThis article addresses the problem of allocating users to radio resources in the downlink of an OFDMA cellular system. We consider a classical multicellular environment with a realistic interference model and a margin adaptive approach, i.e., we aim at minimizing total transmission power while maintaining a certain given rate for each user. We discuss computational complexity issues of the resulting model and present a heuristic approach that finds optima under suitable conditions or reasonably good solutions in the general case. Computational experiments show the effectiveness of the proposed heuristic in a comparison with both a commercial state-of-the-art optimization solver and other approaches from the literature. Copyright © 2011 Wiley Periodicals, Inc
A Stackelberg knapsack game with weight control
No full textWe address a bilevel knapsack problem where a set of items with weights and profits is given. One player, the leader, may control the weights of a given subset of items. The second player, the follower, outputs the actual solution of the resulting knapsack instance, maximizing the overall profit. The leader receives as payoff the weights from those items of its associated subset that were included in the solution chosen by the follower.We analyze the leader's payoff maximization problem for three different solution strategies of the follower and discuss the complexity of the corresponding problems. In particular, we show that, when the follower adopts a greedy strategy, setting the optimal weight values is NP-hard. Also, it is NP-hard to provide a solution within a constant factor of the best possible solution. However, a MIP-formulation can be given. Moreover, the truncated greedy strategy allows an easy answer for the revision of weights. For the additional case, in which the follower faces a continuous (linear relaxation) version of the above problems, the optimal strategies can be fully characterized and computed in polynomial time. (C) 2019 Elsevier B.V. All rights reserved
Updates in regenerative medicine applied to dental sciences
No full textMesenchymal stem cells (MSCs) are found in high concentrations in several tissues, such as umbilical cord, adipose tissue and dental tissue. Dental stem cells reside in many areas of the oral cavity. Thanks to their abilities, dental stem cells could be used to treat diseases and to understand the basic mechanisms of developmental pathologies. There are currently numerous ongoing clinical trials evaluating a broad spectrum of conditions and situations using different stem cell populations. However, stem cell studies are raising profound ethical questions that weigh on the world of scientific research. Stem cells are always a hot topic in the scientific community. Their use is related also to their banking, as cell manipulation is also often related to medical and ethical issues. Many biomedical studies aim to treat diseases that were previously considered incurable with MSCs. All this has created the need to quickly and safely storage stem cells, usually in a stem cell biobank (SCB). Regenerative medicine is the most important approach for achieving complete tissue regeneration using stem cells isolated from adult tissues, embryonic stem cells, but also through the application of induced pluripotent stem cells (iPSC). iPSCs are non-pluripotent cells that are engineered to acquire the ability to differentiate into all different types of cells. In conclusion, the daily use of stem cells in regenerative procedures is still far from being safe and predictable, especially because of the biomedical component, often requiring experienced biologists and complex technologies for cell manipulation and cell banking.
The Uncertain Times of COVID Mass Vaccine Deliveries: from Start-up to Steady-State
No full textMass vaccination campaigns have been adopted throughout the world as a major tool to stop the spread of COVID or at least abate its lethal consequences. Smart vaccination strategies have been proposed to make the most efficient use of the scarce resources (e.g., medical and nursing staff) and achieve vaccination aims (i.e., vaccinating as many people as possible in the shortest possible time). However, smart strategies may fail if vaccine deliveries are erratic or do not exhibit even statistical regularity. In this paper, we perform a statistical analysis of up-to-date vaccine delivery data to uncover regularities and use them to draw a probabilistic model of vaccine deliveries that may help optimize and evaluate smart vaccination strategies. We find that for two out of three vaccine manufacturing companies, deliveries concentrate on one or at most two days over a week, though the actual day may be modelled by an arithmetic distribution
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