1,720,963 research outputs found
Improving Decision Making in Real-world Applications by Solving Combinatorial Optimization Problems
Get PDFThe motivation for this work is to study complex real-world scenarios and provide tools that can actually improve decision-making in those problems. To do so, we mainly adopt techniques from the fields of Operations Research and Combinatorial Optimization.
In this dissertation, we focus on three real-world applications from different industries that can be modeled as combinatorial optimization problems and address them with operations research techniques. The dissertation is divided in chapters, each of which is related to a different topic.
In Chapter 1, a problem concerning the transportation of biological samples from draw centers to a main laboratory for analysis is presented. The problem arises from a healthcare application in Bologna, Italy, where the healthcare authority decided to centralize the analysis of all biological samples of the area to a main laboratory, in order to exploit economies of scales and reduce the costs for samples’ analysis. Of course, such an improvement goal also created a new complex problem: all the samples must be transported from draw centers to the main lab. A fleet of vehicle is available for the transportation and must collect the samples from draw centers during given times of the day and deliver them within a certain time, since samples are perishable. Vehicles can also exploit the existence of dedicated centers that can extend the lifespan of the samples and where samples can be transferred from one vehicle to another. It is clear from this brief description how hard it could be to decide which is the routing of all the vehicles which minimizes the traveling costs while delivering all samples on time. For this problem we developed different mixed integer linear programming models, metaheuristic algorithms, and grouping policies for the samples that are able to tackle the complexity of the problem and improve routing decisions. All methods have been tested through an extensive computational campaign using real-world data, showing the effectiveness of the proposed approaches.
In Chapter 2, a problem related to the agricultural industry is presented. The problem arises from a real-world application in Italy and it is that of planning the use of the available land of a farm for a given number of years, given a set of crops that can be grown. The objective is to maximize the farmer’s profit, but the farmer is subject to several rules both from an agronomic and from a regulation point of view. In fact, many constraints exist regarding agronomic principles, such as maximum replanting, botanical family constraints and crop rotation issues. One of the goals of this work is indeed that of evaluating the risks and benefits of following or not the best practices regarding crop rotation issues in the Mediterranean pedo-climatic context. Furthermore, we want to evaluate the effectiveness of public and private initiatives regarding sustainable agriculture. In fact, it is more and more important nowadays to face these challenges in the food supply chain, which is one of the most discussed industries when it comes to sustainability. In particular, we analyze two different initiatives, namely the Common Agricultural Policy by the European Union and “La Carta del Mulino” by Barilla Group S.p.A.. Both initiatives introduce economic incentives for the farmers following virtuous behaviors from a sustainability point of view. Practically, these behaviors are constraints increasing the complexity of the problem and the difficulty in the decision-making process. For this problem, we will give a formal characterization and study its complexity, also analyzing special cases. We will also present a network-flow based model to solve a special case of the problem and integer linear programming models developed to solve three variants accounting for different sustainability scenarios. Real-world data from 23 Italian farms were used in an extensive computational campaign. The analysis of the results shows that the models can be helpful tools for farmers to plan their production and for authorities to evaluate the effectiveness (and efficiency) of their sustainability initiatives.
In Chapter 3, we discuss a problem concerning the sequencing of unreliable jobs on parallel machines. Even if the problem is not taken from a specific application, it may have several applications in real-world scenarios, such as in manufacturing and planning of complex computations on multi-processors computers. In this problem, we have n unreliable jobs providing a reward when successfully completed, but each job has a probability of not being carried out. We have m parallel identical machines at our disposal, and we want to schedule the jobs on the machines in order to maximize the total expected reward. To increase the probability of completing the jobs, we create m copies of each job and schedule each copy on a different machine. For this problem, we will present a complexity analysis showing that the problem is NP-complete for two machines. For the problem with two machines, we derived some theoretical properties and developed a quadratic integer programming model, a tabu search algorithm, and an upper bound based on the Three-Dimensional Assignment problem. A computational campaign on different sets of instances shows that the tabu search outperforms the model. Then we focused on the general case with m machines. In particular, we developed several heuristics and proved some theoretical results, including the worst case performance guarantee of two heuristics. We also devised a generalized tabu search algorithm and a new, improved, upper bounding scheme based on a relaxation of the problem. Computational experiments are performed for the new methods on the problems with two and three machines. The results show that good optimality gaps are reached on all the instances
Optimization models and algorithms for sustainable crop planning and rotation: An arc flow formulation and a column generation approach
Get PDFSustainable agriculture is essential for ensuring long-term food security and environmental health, as it addresses key challenges such as resource depletion, biodiversity loss, and climate change. To promote the adoption of sustainable agricultural practices, several initiatives have been introduced, offering economic incentives in exchange for compliance with sustainability policies. However, these new environmental regulations add complexity to long-term crop planning, further increasing the challenges associated with resource management and crop rotation constraints. As a result, farmers require decision-support tools to help them optimize their crop planning strategies while meeting sustainability requirements. In this paper, we present decision models and algorithms designed to assist farmers in solving multi-period crop rotation planning problems with sustainability constraints. In this setting, both the yield and profitability of a crop depend on the sequence of previous crops grown on the same plot of land, and the objective is to maximize farmers’ total profit. To address this challenge, we propose an arc-flow Integer Linear Programming model and a matheuristic algorithm, based on column generation, to efficiently solve the problem. Additionally, we analyze the complexity of the pricing problems and introduce an optimal dynamic programming algorithm for a special case. We evaluate our approach through an extensive experimental study using real-world data from Italian farms and incorporating the sustainability regulations of the European Union's Common Agricultural Policy. The numerical results demonstrate the effectiveness of our proposed methods in optimizing crop rotation planning while ensuring compliance with sustainability constraints. © 2025 The Author
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Solving crop planning and rotation problems in a sustainable agriculture perspective
Get PDFIn this paper, the problem of planning the allocation of crops to arable lands, taking into account crop rotations principles and diversification strategies promoted by sustainable agriculture is addressed. Optimization models for solving multi-period planning problems are proposed, able to decide how to allocate crops in each growing season in order to maximize the total expected profit. The allocation decisions are made considering the crop rotation benefits across seasons and the sustainable requirements stated by current regulations. A complexity analysis is performed, and polynomial special cases are presented. Integer Linear Programming models are proposed, for a case study related to structured professional Italian farms specialized in arable crops, following sustainability rules coming from public regulations and private initiatives, i.e., the Common Agricultural Policy by the European Union and “La Carta del Mulino” by the Barilla Group. Numerical experiments conducted on real data show the effectiveness of the proposed solution approaches
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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