1,721,055 research outputs found
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
Tactical planning in maritime transportation of crude oil
No full textThe global crude oil distribution network mainly comprises of ocean shipping links that make use of massive and exceedingly expensive oil tankers. Oil companies rely on these tankers to exploit the economies of scale. However, it also means stern planning and managerial challenges in the presence of uncertain oil demand, freight rates volatilities, high operating costs, long delivery lead times and the associated environmental risks. These challenges vary from long term or strategic issues such as distribution network design, to medium-short term tactical planning issues such as order delivery scheduling and vessel chartering, besides some other day-to-day operational issues On a thematic level, this work presents an integrated approach, through a compatible set of frameworks, to the key tactical planning problems faced by an oil supplier. More specifically, there are at least four major contributions. In the first contribution, we present a cost-of-spill approach for selecting tanker routes for maritime transportation of crude oil. The proposed method is in line with the Formal Safety Assessment (FSA) guidelines proposed by the International Maritime Organization. In the second contribution, we present a time dependent periodic scheduling approach that exploits the crude oil demand structure and resource characteristics. In the third contribution, we present a simulation-optimization based fleet management framework that overarches the proposed scheduling model. Finally, our last contribution integrates and extends the earlier approaches into scheduling model, which would cater to a manager's risk-cost preference by generating a Pareto frontier of non-dominated solutions. a single bi-objective risk-cost based tanker routing and delivery.Includes bibliographical references
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
Analytical approaches to planning intermodal transportation systems for regular and hazmat freight
No full textThe world container transportation industry has grown significantly over the past few decades. Large numbers of containers are transported everyday over long distances via a single or combinations of different modes of transportation (road, rail, water and air). Many of these containers contain hazardous materials (hazmat) whose transportation is regulated by governments due to the related risks. In contrast to other areas of transportation, operations-research-based models for intermodal transportation of containers, specifically hazmat ones, is still a young domain.
The purpose of the thesis is to provide analytical approaches to planning intermodal transportation for regular and hazmat freights. Planning of intermodal transportation can be addressed at the strategic, tactical or operational level. In this regard, this thesis contributes to the current literature in the following three ways. First, at the operational level, we study crane scheduling at an intermodal terminal, such that the unloading of inbound vessels and the loading of outbound vehicles could be completed in minimum weighted time. The approach calls for a multi-processor multi-stage scheduling methodology, where each crane has availability time windows. Second, at the tactical level, we propose a routing framework for transportation of hazmat and regular containers in a congested network to minimize two objectives: total cost and total risk. The model considers congestion as a source of exposure and makes a trade-off between congestion exposures and capacity costs. Third, at the strategic level, we study the regulation of intermodal transportation for hazardous materials. A bi-level network design model and a bi-level bi-objective toll-setting policy model, which consider government and carrier at two levels of administration, are proposed to mitigate the transportation risk.
The thesis concludes with comprehensive remarks. We summarize the contributions of this thesis, show the overall results obtained, and present the possible directions that this research may take in the future.Includes bibliographical references (pages 145-157)
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
Analytical Approaches to Risk Assessment and Management for Railroad Transportation of Hazardous Materials
Get PDFHazardous materials (hazmat), such as crude oil and gasoline, are harmful to humans and the environment because of their toxic ingredients, but their transportation is integral to sustain our industrial lifestyle. In North America, a significant portion of hazmat shipments is moved via the railroad network. Rail hazmat incidents are rare though the consequences could be catastrophic. The low probability–high consequence nature of such events mandate that a risk-averse plan be implemented for routing hazmat shipments.
We propose a value-at-risk (VaR) and conditional value-at-risk (CVaR) methodology to route rail hazmat shipments, using the best train configuration, over a given railroad network with limited number of train services, such that the transport risk is minimized. Freight train derailment records of the Federal Railroad Administration (FRA) were analyzed to model the behavior of railroad accidents, and to estimate their conditional probabilities. The proposed methodologies were used to study several problem instances generated using the realistic network of a railroad operator in Midwest United States, and to demonstrate that they are superior to the existing risk measures in the literature in regard to providing risk-averse routing of hazmat shipments and being versatile enough to yield various routes based on the risk preferences of decision makers.
Next, we propose a CVaR model, as a risk-averse routing plan for multiple rail hazmat shipments and multiple origin-destinations pairs, such that the total transport risk in the railroad network as measured by CVaR is minimized. However, it may happen that certain links and yards of the railroad network tend to be overloaded with hazmat traffic and risk. To overcome this issue, we also promote equity in the spatial distribution of risk. Therefore, the main problem is to find minimum risk routes, while limiting and equitably spreading the risk in any zone where the railroad network is embedded. The problem is mathematically formulated, and a heuristic algorithm is proposed for its solution, which takes into consideration the risk load limits on arcs and transferring yards and spreads the risk equitably throughout the network. Moreover, a lower bound based on a Lagrangian relaxation of the mathematical formulation is also provided. Finally, several computational experiments are developed using the above realistic railroad network.ThesisDoctor of Philosophy (PhD
Mitigating Disruption Risks in Supply Chain Financing and Railway Transportation
No full textThis dissertation examines the challenges associated with disruptions in supply chain financing and the railway transportation network. The study is divided into six chapters:
In Chapter 1, we introduce the core problems under investigation. Chapter 2 investigates supply chain financing, emphasizing trade credit and bank credit—two predominant external financing mechanisms. Given the inherent uncertainties in demand, interest rates, and supplier credit ratings, this chapter introduces a stochastic programming model accounting for demand uncertainty. Subsequently, a robust optimization program is applied, whose complexity demands a specialized solution methodology. By analyzing a case study centered around a prominent U.S. retailer, the research reveals key insights into decision-making processes related to financing, the effects of bargaining power on portfolio mix and profits, and the relative importance of interest rate uncertainties over supplier credit ratings.
Chapter 3 introduces a game-theoretical model designed to hedge financing risks in supply chains, with a focus on the application of insurance for both trade and bank credits. To support the design of effective supply chain finance contracts, three distinct contracts are developed, aiming to synchronize both financial and material flows within the supply chain. A significant feature of this chapter is the data-driven approach employed to address the potential bankruptcy risks that can arise from borrowing loans. Alongside this, a novel solution algorithm is introduced to solve the proposed non-convex models. A case study involving Ford Motor Company and a Chicago-based retailer enriches the research with real-world context. The findings offer several managerial insights: the strategic advantages of different insurance services vary based on the risk attitudes and profit margins of participants. For example, when a retailer operates with a lower profit margin, the use of Trade Credit Insurance (TCI) is recommended in conjunction with a risk-seeking retailer, while a risk-averse retailer might diminish the benefits of TCI. Conversely, with high profit margin retailers, the adoption of Payment Protection Insurance (PPI) is advised under all conditions.
In Chapter 4, a game-theoretical model for risk mitigation within railway transportation is introduced. This model addresses random disruptions by employing strategies like repair, re-routing, third-party services, and leasing capacity from competing rail companies. Through a U.S. case study, the efficacy of these strategies is examined, with renting railcars emerging as a particularly potent approach to enhance resilience and reduce third-party expenses. The research further suggests that negotiations extending delivery dates can significantly diminish post-disruption costs.
Finally, Chapter 5 summarizes the primary contributions of this research, laying the groundwork for prospective studies in this domain.ThesisDoctor of Philosophy (PhD
Analytical approaches to protection planning in rail-truck intermodal transportation
No full textA significant volume of traffic uses a rail-truck intermodal transportation network, making it the preferred transportation medium for customers. Thus, the associated infrastructure of rail-truck intermodal transportation should be considered critical, i.e., systems and assets whose destruction (or disruption) would have a crippling effect on security, economy, public health, and safety. Disruptions could be induced by nature such as hurricane Katrina in 2005, or man-made disturbances such as the 9/11 terrorist attacks in the United States. This thesis proposes an analytical approach to preserve, as much as possible, the functionality of a rail-truck intermodal transportation system in the wake of worst-case attacks. As such, it will serves as an aid to the top managers to compare the cost of implementing protective measures with the benefits that such measures could bring. A tri-level Defender-Attacker-Defender (DAD) approach is proposed to model this situation, where the outermost problem belongs to the network operator with a limited budget to protect some of the terminals, the middle level problem belongs to the attacker with enough resources to interdict some of the un-protected terminals, and the innermost problem belongs to the intermodal operator who attempts to meet the demand on a reduced network with the minimum cost. Since the resulting model is very difficult to solve by any optimization package, efficient solution techniques have been developed for solving this model. Finally, the proposed framework is applied to the rail-truck intermodal transportation network of a Class I railroad operator in North America to discover the optimal way to protect the system.Includes bibliographical references (pages 110-116)
Risk Mitigation and Management Strategies for Routing Hazardous Materials over Railroad Network in Canada
Get PDFRailroad transportation of hazardous materials (hazmat) has grown significantly in recent years in Canada. Although rail is one of the safest modes for hazmat transport, the risk of catastrophic events such as the Lac Mégantic train disaster, does exist. In this thesis, we study a number of measures to manage and mitigate the risk associated with rail hazmat shipments. First, we propose a methodology that makes use of analytics to dis-aggregate national freight data to estimate hazmat traffic on rail-links and at rail-yards in Canada. Further, a focused analysis is conducted on crude oil rail shipments to develop long-term forecasts and evaluate the impact of proposed pipeline projects. Second, we present an emergency response planning problem, aimed at the effective and efficient response to rail hazmat incidents. A two-stage stochastic programming problem is solved over part of the Canadian railroad network, which provides recommendations on where to locate response facilities, and which equipment packages to stockpile at each facility. Finally, we study infrastructure investment as a strategy to mitigate the risk associated with rail hazmat shipments. This strategy is based on building new railway tracks to provide alternative routes to the riskiest parts of the network. Given the hierarchical relationship between the decisions made by regulatory agencies and railroad companies, a bilevel programming approach is used to identify the optimal set of infrastructure investment options given an allocated budget. Our computational experiments show that significant network-wide risk reduction is possible if hazardous shipments are routed using some of the proposed alternative rail tracks.ThesisDoctor of Philosophy (PhD
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