118,415 research outputs found
The impact of kombi-taxis on public transport
No full textIncludes bibliography.This thesis attempts to quantify the impact of kombi-taxis on the conventional modes of public transport, in particular the bus, in the Cape Town Metropolitan Area. The impact is quantified in terms of the resultant modal shift of commuters from the buses, trains, cars and walking, in favour of the kombi-taxi. The approach adopted involved a study of the kombi-taxi and bus operations and characteristics on the different kombi-taxi routes in the study area. Five representative routes were selected for a detailed study, involving an Observation survey and an Interview survey directed at the bus and kombi-taxi users on these routes. On a further 66 routes, a bus-taxi modal split survey was conducted. The findings of the study show• that the majority of present kombi-taxi users are former bus users. Conservatively, an estimated 30.6% of all the daily bus passenger trips have been lost to the kombi-taxi. The effect on trains has not been insignificant with an estimated 4.4% of all commuter train trips having been converted to kombi-taxi trips
'Boda boda' bicycle taxis and their role in urban transport systems : case studies of Nakuru and Kisumu, Kenya
No full textIncludes abstract.Includes bibliographical references (leaves 117-120).The bicycle taxi has a padded cushion fitted onto a reinforced rear seat; typically removed when transporting goods. The research aimed, firstly, to understand the operating characteristics of, and challenges facing, ‘boda boda’ services, and secondly, to explore the measures that might be formulated by the concerned authorities to manage and support them. With regard to the latter aim, given the growth in motorcycle taxis at the expense of bicycle taxis elsewhere in the region, the research sought to make a recommendation on whether authorities should embrace or resist this trend
Taxis-Based Motion Control of Biohybrid Microrobots
No full textMiniaturization of on-board actuation and powering engenders the proliferation of biohybrid microrobots, which integrate motile bacteria or cells with synthetic functional components to achieve micron-scale actuations. Flagellated bacteria like S. marcescens are among the leading candidates for the actuators of swimming microrobots. However, the high intrinsic stochasticity in bacteria-driven microrobots severely limits their potential applications, such as targeted drug delivery. Taxis behaviors (e.g., chemotaxis), which help free-swimming bacteria to navigate towards favorable environments and away from hazardous ones, may offer an elegant means to control the motion of bacteria-driven microrobots. Therefore, this thesis focuses on: (a) addressing the motion guiding of bacteria-driven microrobots using common bacterial taxis behaviors, specifically chemotaxis and pH-taxis, (b) explaining the physical mechanisms associated with the tactic motions in bacteria-driven microrobots, and (c) developing a biophysical model to describe the bacterial propulsion and the chemotaxis in bacteria-driven microrobots. In order to produce considerable chemotactic motion in bacteria-driven microrobots, an appropriate chemical concentration profile needs to be determined, which requires the knowledge of the chemotaxis response of the integrated bacterial species. Thus, we first propose an experimental and modeling framework to characterize bacterial chemotaxis. The chemotaxis response of a species against a chemoattractant is experimentally quantified under a linear concentration gradient of the attractant. A signaling pathway model is fitted to the experimental measurements over a series of gradients to determine the species-specific parameters in the model, thereby fulfilling an analytical characterization of the chemotaxis. Subsequently, in a multi-bacteria-driven microrobotic system, we quantify the chemotactic drift of the microrobotic swarms towards a potent chemoattractant L-serine and elucidate the physical mechanisms associated with the drift motion by statistical trajectory analysis. It shows that the microrobots have an apparent heading preference for moving up the gradient, which constitutes the major factor that produces the chemotactic drift. The apparent heading bias is caused by a higher persistence in the heading direction when a microrobot moves up the the L-serine gradient compared to traveling down the gradient. Besides chemotaxis, we explore the potential of utilizing ambient pH to guide the motion of the bacteria-driven microrobots. Under three different pH gradients, we demonstrate that the microrobots exhibit both unidirectional and bidirectional pH-tactic behaviors. Two factors, a swimming heading bias and a speed bias, are found to be responsible for the pH-tactic motion while the heading bias contributes more. Like in chemotaxis, the heading directions of the microrobots are also significantly more persistent when they move towards favored pH regions. Finally, a biophysical model is developed to describe the bacterial propulsion and the chemotaxis in an extensively adopted design of bacteria-driven microrobots. The model traces helical trajectories and chemotactic motion that resemble those observed from experiments, which validates the basic correctness of the model. The model simulation also suggests that the seemingly collective chemotaxis among the multiple bacteria attached to a microrobot could be explained by a synchronized signaling pathway response among these bacteria. Furthermore, we investigate the dependencies of the microrobots’ per</p
Taxicab regulation and urban residents' use and perception of taxi services: a survey in eight cities
No full text1. Several market failures would justify some forms of price control and entry regulation in the taxicab industry. Unfortunately, history shows that very often the taxi regulators get captured by taxi operators' lobbies and fail to adapt their regulation to changing market conditions. Hence, faced with a sclerotic service supply, several cities and countries have thoroughly deregulated their taxi industry... only to gradually bring back some elements of regulation later on. Since the late 1960s academics have at length debated the pros and cons of price and entry regulations for the taxi market, either using very simplified models of selected segments of the market or referring to empirical data comparing service supply before and after deregulation in one or in several case studies. Because of the paucity of available data on the demand side, most of these empirical studies generally only consider the supply side, overlooking the impact of regulation or deregulation on taxi use and on the perception of taxi services by their clients. We have selected eight capital cities with contrasting regulatory systems and carried out a survey among their residents to understand why and how they use taxis and to collect their opinion about the quality of the service provided. Some 3200 respondents answered about 40 questions. Taxi use varies greatly from one city to the other, both in terms of trip frequency and of trip purposes. A statistical analysis of the results enabled us to draw some conclusions about the impacts of various elements of taxicab regulation on the mobility of urban residents.taxi; regulation; deregulation; mobility; London; Paris; New York; Amsterdam; Dublin; Berlin; Stockholm; Lisbon
Water Taxis in the San Francisco Bay Area: From travel time to quality time: Is there a viable service concept?
No full textThis thesis presents a discrete-choice model as the basis to forecast market shares for high-end water taxis in the San Francisco Bay Area. Waterborne mobility studies are growing in numbers, but studies towards the potential of personalized versions thereof is scarce. Three service concepts are designed as business models and compared on business potential. It is surprising to see that, compared to the very low public transit prices, this service still seems to reach market shares of 10% at ticket prices of up to $50 per single trip.Transport and Logistics' OrganisationTechnology, Policy and Managemen
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Letter from unknown writer to Jesse L. Boyce
No full textLetter to Jesse L. Boyce from unknown author (possibly Jack) about the investigation into the powder magazine located in the Grand Canyon. Some personal news is included in the letter such as the writer's marriage to the daughter of C.A. Taylor, former Supervisor of Cochise County
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
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