1,721,312 research outputs found
Branch and Bound and Dynamic Programming Approaches for the Path Avoiding Forbidden Pairs Problem
No full textWe propose a branch and bound (B&B) and a dynamic programming algorithm for the Path Avoiding Forbidden Pairs Problem (PAFPP). Given a network and a set of forbidden node pairs, the problem consists in finding the shortest path from a source node s to a target node t, avoiding to traverse both nodes of any of the forbidden pairs. The problem has been shown to be NP-complete. In this work, we describe the problem, its mathematical model and we propose two exact algorithms. We compare their performances against those of a commercial solver solving instances for two different graph topologies: fully random graphs and grid graphs
Somatostatin receptor expression and patients' response to targeted medical treatment in pituitary tumors: evidences and controversies.
No full textThe Rainbow Steiner Tree Problem
No full textGiven an undirected and edge-colored graph with non-negative edge lengths, the aim of the Rainbow Steiner Tree Problem (RSTP) is to find a minimum Steiner Tree that uses at most one edge for each color. In this paper, the RSTP is introduced, a mathematical model is proposed to formally represent the problem and its theoretical properties are investigated. Since the RSTP belongs to the NP-class, two heuristic methods are designed: a Lagrangian relaxation approach and a multistart algorithm. Extensive computational experiments are carried out on a significant set of test problems to empirically evaluate the performance of the proposed approaches. The computational results show that the two approaches are both effective and efficient compared to the ILOG CPLEX solver
Use of octreotide long acting repeatable (LAR) as second-line therapy in advanced neuroendocrine tumors in different clinical settings: an Italian Delphi survey
No full textBackground: Somatostatin receptor ligands including octreotide LAR are first-line therapy in locally advanced or metastatic NETs that are nonresectable and well differentiated and are recommended as first-line therapy in functioning and in G1/low G2 nonfunctioning NETs. However, several questions remain that are not adequately addressed in current guidelines regarding its use in clinical scenarios in which the tumor progresses. These include use of nonconventional doses or schedules of octreotide LAR in tumors with hormonal symptoms or showing clinical-radiological progression, administration in combination with everolimus, peptide receptor radionuclide therapy, and chemotherapy, following first-line treatment with octreotide LAR. Methods: An expert panel was gathered to obtain consensus using Delphi methodology on a series of statements regarding further administration of octreotide LAR after its use in first-line therapy in these settings in patients who experience disease progression. Results: Consensus was reached for 8 of the 10 statements proposed in the above clinical scenarios; consensus was not achieved for two statements. Conclusions: The present statements aim to fill current gaps in treatment guidelines by providing recommendations based on expert consensus in clinical settings in which patients progress following first-line therapy with octreotide LAR
A dynamic programming algorithm for solving the k-Color Shortest Path Problem
No full textSeveral variants of the classical Constrained Shortest Path Problem have been presented in the literature so far. One of the most recent is the k-Color Shortest Path Problem (k-CSPP), that arises in the field of transmission networks design. The problem is formulated on a weighted edge-colored graph and the use of the colors as edge labels allows to take into account the matter of path reliability while optimizing its cost. In this work, we propose a dynamic programming algorithm and compare its performances with two solution approaches: a Branch and Bound technique proposed by the authors in their previous paper and the solution of the mathematical model obtained with CPLEX solver. The results gathered in the numerical validation evidenced how the dynamic programming algorithm vastly outperformed previous approaches
Shortest path tour problem with time windows
No full textThis paper aims at studying a new variant of the shortest path tour problem, where time window constraints are taken into account. This is the first work dealing with the shortest path tour problem with time windows. The problem is formally described and its theoretical properties are analyzed. We prove that it belongs to the NP-hard class of complexity by polynomial reduction from the knapsack problem. An optimal solution approach based on the dynamic programming paradigm is devised. Labelling algorithms are defined along with well-tailored pruning strategies based on cost and time. The correctness of the bounding strategies is proven and the empirical behavior is analyzed in depth. In order to evaluate the performance of the proposed approach, extensive computational experiments have been carried out on a significant set of test problems derived from benchmarks for the shortest path tour problem. Sensitivity analysis is carried out by considering both algorithmic and instance parameters
A generalized shortest path tour problem with time windows
No full textThis paper studies a generalization of the shortest path tour problem with time windows (GSPTPTW). The aim is to find a single-origin single-destination shortest path, which has to pass through an ordered sequence of not necessarily disjoint node-subsets. Each node has a time window for each node-subset to which it belongs. We investigate the theoretical properties of GSPTPTW and propose a dynamic programming approach to solve it. Numerical results collected on a large set of new benchmark instances highlight the effectiveness of the proposed solution approach
A simheuristic algorithm for video streaming flows optimisation with QoS threshold modelled as a stochastic single-allocation p-hub median problem
No full textModern telecommunication networks are comprised of a countless number of nodes exchanging data among them. In particular, multimedia traffic–composed of audio, video, and images–represents a challenging scenario requiring link optimisation techniques. The hub-and-spoke topology is frequently used to design more effective telecommunication networks. This work considers a hub-and-spoke network in which a large number of nodes are exchanging real-time multimedia data, and where the quantity of data sent from one node to another is a random variable. Given a fixed number of hubs, (Formula presented.), the goal is to select the best location for these (Formula presented.) hubs in order to minimise the total expected cost of transmission. This scenario is modelled as an uncapacitated single-allocation (Formula presented.) -hub median problem under uncertainty conditions. Additionally, with the purpose of considering the effect of transmission delays on the video signal, service quality thresholds are assigned to every potential hub in the network. Since real-life networks tend to be large in size, we propose a simheuristic algorithm to cope with this stochastic and large-scale optimisation problem. A series of computational experiments illustrate these concepts and allow for testing the performance of our simheuristic approach. Finally, a statistical analysis of the obtained results is provided
Acromegaly Management in a Tertiary Referral Center After 1 Year of the Coronavirus 2019 Pandemic: A Double Challenge
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