1,720,955 research outputs found
Impact of Arrivals on Departure Taxi Operations at Airports
Get PDFAircraft taxi operations are a major source of fuel burn and emissions on the ground. Given rising fuel prices and growing concerns about the contributions of aviation to air pollution and greenhouse gas emissions, recent research aims to develop strategies to reduce fuel burn at airports. In order to develop such strategies, an understanding of taxi operations and the factors that affect taxi-out times is required. This paper describes an analysis of taxi-out times at two major U.S. airports in order to identify the primary causal factors affecting the duration of taxi-out operations. Through an analysis of departures out of John F. Kennedy International Airport and Boston Logan International Airport, several variables affecting taxi-out times were identified, including primarily the number of arrivals and number of departures during the taxi-out operation of an aircraft. Previous literature suggests that the number of arrivals on the surface has limited influence on taxi-out times; however, this analysis demonstrates that the number of arrivals is in fact significantly correlated with taxi-out times. Furthermore, we find that arrivals have a greater impact on taxi-out times under runway configurations where there is increased interaction between arrivals and departures
The climate impacts of HSR and air transportation : a global comparative analysis
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2012."September 2012." Cataloged from PDF version of thesis.Includes bibliographical references.Growing concerns about the energy use and climate impacts of the transportation sector have prompted policymakers to consider a variety of options to meet the future mobility needs of the world's population, while simultaneously addressing the impact of these systems on our environment. This dissertation focuses on air transportation and high-speed rail (or "high-speed transportation"), a sector for which demand is projected to grow substantially, and for which infrastructure and vehicle investment decisions are costly and long-lived. This research examines high-speed rail (HSR) and aviation systems in three regions to explore: 1) the historical context of high-speed rail and aviation demand; 2) potential policies that may shape HSR and aviation system demand and their environmental impacts in the future; and 3) individual mode choice between HSR and aviation. The goal of this work is to improve our understanding of demand for these systems and methods to examine their climate impacts. Chapters 3 and 4 provide an empirical analysis of the European experience with highspeed rail and aviation systems. First, we contribute to econometric analyses of air travel demand by examining the impact of high-speed rail on air traffic. Using origin-destination demand data as well as airport demand data for two decades, our econometric analysis shows that the introduction of high-speed rail has resulted in substantial decline in air traffic on short-haul routes, as well as domestic air traffic in nations with high-speed rail infrastructure. Those cities that have higher density experience an even larger reduction in air traffic. However, we find that over this same time period, the expansion of low-cost carriers in Europe has had an even more substantial impact on increasing total air traffic within the European aviation system. Second, we explore cooperation versus competition between high-speed rail and air transportation systems. Through case studies and travel demand analysis, we examine how air-rail connections have formed in Europe, factors that contribute to high utilization of these connections, and their impact on travel demand. We find that although capacity shifts within the air transportation system have occurred as a result of these connections, there are a number of unique factors that contribute to their success. In Chapter 5, we shift our attention to the United States to conduct an integrated analysis of transportation and climate policies. By developing a new model to examine high-speed rail and aviation demand and their environmental impacts under alternative climate and energy policies, we find that the energy and CO2 emission savings of high-speed rail increase substantially when combined with such policies. These savings are primarily due to the relative efficiency of high-speed rail systems combined with a shift towards less carbon-intensive efficiency of high-speed rail systems combined with a shift towards less carbon-intensive electricity generation. The first three analyses assume that price and travel time are the dominant factors influencing intercity travel choice between high-speed rail and air transportation. In Chapter 6, we explore the potential influence of environmental attitudes on individual choices between high-speed rail and air transportation. By conducting an intercept survey in China, we find that rail passengers tend to be more concerned about the environment than those individuals likely to choose air travel. Second, we find that high-speed rail accidents do have a significant impact on future mode choice, and that safety concerns play a significant role in intercity travel choice. This dissertation concludes with an analysis of current policies that influence high-speed rail and aviation in the United States, and their long-range environmental impacts. Integrating our findings from the three regional analyses of high-speed rail and aviation, we make recommendations for future policies that shape these long-lived infrastructure systems. Given likely growth in demand for high-speed transportation in the United States and other regions, our goal is to inform future investment decisions and policies that meet these mobility needs while mitigating their energy and climate impacts.by Regina Ruby Lee Clewlow.Ph.D
The impact of high-speed rail and low-cost carriers on European air passenger traffic
Get PDFThe expansion of high-speed passenger rail service is often argued as a potentially effective, lower-carbon substitute for intercity air travel. Previous studies on high-speed rail on air travel in Europe and Asia have primarily examined the impact of travel time and price on market share for a specific city pair (or a handful of city pairs). There has been little focus on the extent to which high-speed rail (HSR) has reduced total short-haul air travel demand (versus market share), or on the potential impacts of high-speed rail on system-wide air travel demand. This paper presents an empirical, econometric analysis of air travel demand in Europe, utilizing an expanded data set to explore: 1) the impact of rail travel times, population density, and market characteristics on air tra c; and 2) the impact of high-speed rail and low-cost-carriers on system-wide air traffic. Although improvements in rail travel times have resulted in reductions in short-haul air travel, variations in city and airport characteristics significantly influence the substitution between air and rail. This paper also finds that HSR substitution has resulted in a modest reduction in system-wide air travel demand, whereas the expansion of low-cost carriers has led to a significant increase in total European air traffic. As concerns about the climate impacts of transportation grow, these results have significant implications for future transport and energy policy
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
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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