Página 5 dos resultados de 2122 itens digitais encontrados em 0.080 segundos

‣ Variational sensitivity analysis and data assimilation studies of the coupled land surface-atmospheric boundary layer system

Margulis, Steven A. (Steven Adam), 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 205 p.; 9957419 bytes; 9957227 bytes; application/pdf; application/pdf
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One of the fundamental components of Earth system science is understanding coupled land-atmosphere processes. The land plays an especially important role in the climate system principally via the regulation of surface fluxes of moisture and energy into the atmosphere. Due to the mutual dependence of these fluxes on surface and atmospheric states, the land and boundary layer comprise a coupled system with complicated interactions and feedbacks which are significant factors in modulating the variability of the weather and climate. In this thesis we develop a framework for exploratory sensitivity analysis and data assimilation in the coupled land-atmosphere system using a variational (or adjoint) approach. The framework is applied to three distinct case studies of interest. First, the variational framework is used to quantify land-atmosphere coupling and feedbacks. The model and its adjoint are used to investigate the differences in the daytime sensitivities of land surface fluxes to model states and parameters when used in coupled and uncoupled modes. Results show that the sensitivities between the two cases are significantly different because of boundary layer feedbacks. Depending on the particular case, sensitivities can be either amplified or dampened due to the presence of an interactive boundary layer. Next...

‣ Planning for robust airline operations : Optimizing aircraft routings and flight departure times to achieve minimum passenger disruptions

Lan, Shan, 1970-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 123 leaves; 4530108 bytes; 4529917 bytes; application/pdf; application/pdf
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Airlines typically construct schedule plans based on the assumption that every flight leg departs and arrives as planned. Because this optimistic scenario rarely occurs, these plans are frequently disrupted and airlines often incur significant costs in addition to the originally planned costs. Flight delays and schedule disruptions also cause passenger delays and disruptions, and disrupted passengers experience very long delays and contribute to a significant amount of the total passenger delay. A more robust plan can alleviate flight and passenger delays and disruptions and their effects in the operation, and eventually reduce the operation costs. In this dissertation, we first define various robustness criteria in the context of airline schedule planning. Then we present two new approaches for robust airline schedule planning to achieve minimum passenger disruptions: Robust Aircraft Maintenance Routing, and Flight Schedule Retiming. Because each airplane usually flies a sequence of flights, delay of one flight might propagate along the aircraft route to downstream flights and cause further delays and disruptions. We propose a new approach to reduce delay propagations by intelligently routing aircraft. We formulate this problem as a mixed integer programming problem with stochastically generated inputs. An algorithmic solution approach is presented. Computational results obtained by using data from a major U.S. airline show that this approach could reduce delay propagations significantly...

‣ Distributed quantitative precipitation forecasts combining information from radar and numerical weather prediction model outputs

Ganguly, Auroop Ratan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 218 p.; 29195597 bytes; 29195353 bytes; application/pdf; application/pdf
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Applications of distributed Quantitative Precipitation Forecasts (QPF) range from flood forecasting to transportation. Obtaining QPF is acknowledged to be one of the most challenging areas in hydrology and meteorology. Recent advances in precipitation physics, Numerical Weather Prediction (NWP) models, availability of high quality remotely sensed measurements, and data dictated forecasting tools, offer the opportunity of improvements in this area. Investigative studies were performed to quantify the value of available tools and data, which indicated the promise and the pitfalls of emerging ideas. Our studies suggested that an intelligent combination of NWP model outputs and remotely sensed radar measurements, that uses process physics and data dictated tools, could improve distributed QPF. Radar measurements have distributed structure, while NWP-QPF incorporate large scale physics. Localized precipitation processes are not well handled by NWP models, and grid average NWP-QPF are not too useful for distributed QPF owing to the spatial variability of rainfall. However, forecasts for atmospheric variables from NWP have information relevant for modeling localized processes and improving distributed QPF, especially in the Summer. Certain precipitation processes like advection and large scale processes could be modeled using physically based algorithms. The physics for other processes like localized convection or residual structures are not too well understood...

‣ Controls on arsenic mobility in contaminated wetland and riverbed streams

Keon, Nicole E. (Nicole Elise), 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 157 leaves; 12061938 bytes; 12061688 bytes; application/pdf; application/pdf
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Arsenic mobility and transport in the environment are strongly influenced by associations with solid phases. This dissertation investigates the mechanisms affecting arsenic retention in contaminated wetland and riverbed sediments. A sequential extraction procedure was designed and tested to differentiate solid phase arsenic speciation, including adsorbed As and As coprecipitated with amorphous and crystalline oxides and sulfides. The sequential extraction was performed on Wells G & H wetland (Woburn, MA) sediments, and the inferred As associations were compared to XANES analyses. Geochemical modeling was used to predict redox conditions and As associations. We found that most As in the wetland was adsorbed onto amorphous Fe (hydr)oxide phases. Riverbed sediments differed from wetland sediments in that redox conditions were more reducing, and As was associated with more reducing and crystalline phases, including sulfides. As(lll) and As(V) oxidation states coexist in the wetland and riverbed sediments, with more oxidized As in the wetland. We tested the hypothesis that As associations with more oxidized phases in the wetland may result from wetland plant activities, including root oxygenation in anoxic sediments. We investigated the extent of Fe plaque formation on Typha latifolia roots (cattail)...

‣ Chemomechanics of calcium leaching of cement-based materials at different scales : the role of CH-dissolution and C-S-H degradation on strength and durability performance of materials and structures

Heukamp, Franz H. (Franz Hoyte), 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 380 p.; 16345201 bytes; 16345001 bytes; application/pdf; application/pdf
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Calcium leaching is a durability threat for cement-based materials employed in critical infrastructures, such as Nuclear Waste Storage Systems. This thesis presents a comprehensive study of the material and structural consequences of calcium leaching on the strength and deformation behavior of cementitious materials. Starting from a three-level microstructural division of the heterogeneous microstructure of cement-based materials, a series of experimental and theoretical investigations is conducted leading to the development of a novel constitutive model and model-based simulations of the long-term mechanical performance of concrete structures subjected to calcium leaching. A chemically accelerated leaching device is developed using an ammonium nitrate solution to obtain asymptotically leached specimens in short times. An acceleration rate of 300 compared to natural leaching is obtained. The strength domain of leached cement pastes and mortars is evaluated through triaxial compression tests and uniaxial tension tests, revealing an important strength loss and an increased pressure sensitivity of the materials at failure, associated with leaching. A micromechanical approach for the homogenization of the elastic properties and the strength properties based on the three microstructural levels is developed. These developments allow estimating the relations between the microstructural changes and poroelastic properties including Biot-coefficient and Biot-modulus. In addition...

‣ Simple models for turbulent wave-current bottom boundary layer flow : theoretical formulations and applications

Sleath, Alison I., 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 190 leaves; 4930801 bytes; 4930609 bytes; application/pdf; application/pdf
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This study presents the theoretical formulations and applications of simple models for turbulent wave-current bottom boundary layer flow. Eddy viscosity formulations are presented for each model in order to analytically solve the governing equations for the bottom boundary layer. Approximations and procedures for obtaining practical solutions of the current velocity profile are presented for the two-layer Madsen-Salles (1998) and three-layer Barreto-Acobe (2001) flow models. Bottom roughness and ripple geometry models are developed for each model using fixed bed laboratory data and movable bed laboratory and field data. Wave attenuation measurements and current profile data are used in order to investigate the bottom roughness length scale for the cases of pure waves, waves in the presence of a current, and currents in the presence of waves. Wave and sediment characteristics are used to formulate a model for wave-generated ripples based on available laboratory and field data. The two-layer Madsen-Salles (1998) and three-layer Barreto-Acobe (2001) flow models are applied in conjunction with the ripple geometry and roughness models for the cases of known and unknown ripple geometry, and an assessment of expected accuracy of application of the models is presented.; by Alison I. Sleath.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Mass transfer and dispersion processes in connected conductivity structures : simulation, visualization, delineation and application

Zinn, Brendan Anderson, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 167 p.; 7595380 bytes; 7595188 bytes; application/pdf; application/pdf
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This thesis focuses on mass transfer behavior, i.e., tailing, in solute transport, and on hydraulic conductivity heterogeneity. Macrodispersive theory, generally used to incorporate heterogeneity into solute transport, does not account for this tailing and makes assumptions about the structural characteristics of the heterogeneity, specifically that the field is multivariate gaussian. We move away from the multigaussian assumption to focus on the concept of connected pathways of high or low conductivity. We first motivate the importance of connected extreme conductivity values through the numerical creation of two-dimensional conductivity fields with nearly identical univariate conductivity distributions and covariances, but with varying connectedness of extreme values. We simulated flow and transport through these fields, using a particle tracking approach that incorporates advection and diffusion. We demonstrate that connectedness impacts flow by influencing the effective conductivity of the field, and connected high conductivity fields with relatively high variance displayed mass transfer behavior, driven by both advective and diffusive processes. We then conducted laboratory experiments to study three flow situations demonstrated by the first part of the work - classic dispersion...

‣ Equilibrium and transient morphologies of river networks : discriminating among fluvial erosion

Gasparini, Nicole Marie, 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 232 p.; 8348940 bytes; 8348749 bytes; application/pdf; application/pdf
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We examine the equilibrium and transient morphology of alluvial and bedrock river networks. We apply analytical methods and an iterative model to solve for equilibrium slope-area and texture- area (in alluvial networks) relationships under different tectonic and climatic forcings. Transient morphology resulting from a change in uplift or precipitation rate is simulated using the CHILD landscape evolution model. In alluvial networks, it is well recognized that both channel slope and mean grain size usually decrease downstream. These variables play an important role in determining sediment transport rates, and their mutual adjustment to a change in the forces that drive erosion can yield surprising results. Adjustments in grain size can lead to spatially variable channel concavity and larger trans port rates on shallower slopes. As a consequence, equilibrium channel slopes may decrease under higher uplift conditions (or, similarly, faster base-level lowering). Selective erosion and deposition can cause transient channel slopes to both increase and decrease and surface texture to both coarsen and fine, all in response to a single change in forcing. In bedrock rivers, increasing attention has been given to the role of sediment flux on incision processes. We find that all applied erosion rules (stream-power and three sediment-flux models) produce similar equilibrium morphologies...

‣ Wavelets and multirate filter banks : theory, structure, design, and applications

Chen, Ying-Jui, 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 232 p.; 9527413 bytes; 9527221 bytes; application/pdf; application/pdf
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Wavelets and filter banks have revolutionized signal processing with their ability to process data at multiple temporal and spatial resolutions. Fundamentally, continuous-time wavelets are governed by discrete-time filter banks with properties such as perfect reconstruction, linear phase and regularity. In this thesis, we study multi-channel filter bank factorization and parameterization strategies, which facilitate designs with specified properties that are enforced by the actual factorization structure. For M-channel filter banks (M =/> 2), we develop a complete factorization, M-channel lifting factorization, using simple ladder-like structures as predictions between channels to provide robust and efficient implementation; perfect reconstruction is structurally enforced, even under finite precision arithmetic and quantization of lifting coefficients. With lifting, optimal low-complexity integer wavelet transforms can thus be designed using a simple and fast algorithm that incorporates prescribed limits on hardware operations for power-constrained environments. As filter bank regularity is important for a variety of reasons, an aspect of particular interest is the structural imposition of regularity onto factorizations based on the dyadic form uvt. We derive the corresponding structural conditions for regularity...

‣ Landslide hazards assessment and uncertainties

Karam, Karim S. (Karim Semaan), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (750 p.); 34981643 bytes; 35014786 bytes; application/pdf; application/pdf
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Landslides are natural phenomena which are difficult to predict because their initiation depends on many factors and on the interaction between these factors. The annual number of causalities caused by landslides is in the thousands, and infrastructural damage is in the billions of dollars. To satisfy the increasingly urgent societal demand for protection against landslides, it is necessary to systematically assess and manage landslide hazard and risk. This can be done using principles of decision making under uncertainty. We develop an advanced combined hydrologic - stability model that is better capable of assessing landslide hazards than current models used in landslide analyses. This model allows one to evaluate landslide hazards deterministically. We use the model to study landslide failure mechanisms, and classify these according to the manner in which a slope gets saturated during rain. We showed that slopes with great depths to bedrock and shallow depths to the water table, tend to fail by saturation from below, resulting in deep seated landslides, and slopes with deep lying water tables tend to fail by saturation from above, resulting in shallow landslides.; (cont) Landslide hazards include, by definition, uncertainties which can be expressed probabilistically. Uncertainties arise from parameters and from models. We develop efficient techniques to formally incorporate parameter uncertainties into the combined hydrologic - stability model...

‣ R&D and deployment valuation of intelligent transportation systems : a case example of the intersection collision avoidance systems; Research and development and deployment valuation of intelligent transportation systems

Hodota, Kenichi
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 154 p.; 30096256 bytes; 30095708 bytes; application/pdf; application/pdf
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Compared with investments in the conventional infrastructure, those in Intelligent Transportation Technology (ITS) include various uncertainties. Because deployment of ITS requires close public-private partnership, projects concerning the R&D and deployment of ITS technology involve project risks and market risks induced by both the public and private sector. This characteristic makes it difficult to evaluate the value of the project through traditional valuation method such as the benefit cost analysis (BCA) or the discounted cash flow (DCF) method. To address the difficulty, this thesis proposes two appropriate valuation methodologies for R&D and deployment of ITS: decision analysis and "hybrid real options" analysis that combines decision analysis and real option analysis. This thesis applies the proposed methodologies to a case example of the ongoing R&D and deployment project to reduce the automobile crashes at intersection under public-private partnerships. The proposed systems in the project consist of two conflicting concepts; one depends on user acceptance of in-vehicle ITS technology employed, and the other one does not require user acceptance of this ITS technology.; (cont.) To evaluate the value of two concepts, this thesis identifies various uncertainties associated with the project and quantifies them by utilizing various quantitative techniques including the product diffusion model to formulate project risks and market risks. This thesis finally compares the financial value in two concepts and demonstrates that the concept without in-vehicle ITS technology is a more promising system for crash prevention at an intersection than that with this technology and recognizes the value of real option in case of the unfavorable outcome of the R&D stage. The results imply that developing attractive new product and obtaining user acceptance of ITS technology are the most crucial factors to influence the project value and future success of the countermeasures.; by Kenichi Hodota.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Upscaling reactive transport in porous media : laboratory visualization and stochastic models

Oates, Peter M. (Peter Michael), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 241 leaves
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Solute transport models are essential tools for understanding and forecasting chemical concentrations in groundwater. Advection-dispersion based models can adequately predict spatial averages of conservative solute concentrations without using explicit maps of pore structures or variations in hydraulic conductivity. However, coupling advection-dispersion based transport models to chemical reaction models is inaccurate because it implicitly assumes complete mixing. Mixing in natural porous media is a slow process that can control the overall rate of chemical reactions, and the lack of mixing causes concentrations to be spatially variable. This thesis develops and experimentally validates a new solute transport modeling framework that approximates the correct amount of chemical reaction and provides concentration probability density functions, which are needed to address laws and regulations based on maximum contaminant levels. To study solute mixing and reaction in porous media, we conducted highly detailed lab-scale experiments by digitally imaging the movement of colored dye tracers and colorimetric chemical reactions through illuminated clear homogeneous and heterogeneous porous media.; (cont.) The resulting sequence of solute concentration maps demonstrates the problem of conventional solute transport models and shows that concentrations can be well approximated with Beta distributions. Conservative Beta distributions can be modeled with partial-differential equations for concentration mean and variance. These conservative distributions can then be transformed into joint reactant distributions...

‣ A comparative analysis of supply chain management practices by Boeing and Airbus : long-term strategic implications

Horng, Tzu-Ching
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 140 p.
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The goal of this research is to develop an improved understanding of supply chain management strategies and practices being pursued by Boeing and Airbus in the 787 Dreamliner and the A380 Navigator programs, respectively, and to identify their long-term strategic implications for supply chain management in the future. The research takes as its point of departure a review and synthesis of supply chain management principles and practices, with particular emphasis on lean supply chain management concepts. Guided by this review, the research focuses on the common set of suppliers supporting both programs and employs a questionnaire survey, followed by telephone interviews with representatives of selected suppliers. The research also makes extensive use of the open source information on both companies, on both programs and on the common suppliers.; (cont.) A major finding is that Boeing's new supply chain model in the 787 program represents a significant break with past practices in the aerospace industry, allowing major partnering suppliers an unprecedented role in terms of design, development, production and after-market support, where they are integrated early in the concept development stage and are incentivized to collaborate with Boeing...

‣ Lessons learned in the design and erection of box girder bridges from the West Gate collapse

Burton, Alia Christine
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 96 p.
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The West Gate Bridge, intended to span the Yarra River in Australia, collapsed during its third year of construction in 1970. Investigation into the project revealed numerous issues in the bridge's design and construction. The West Gate Bridge is one of a number of box girder bridges built during the mid 20th century, and was one of four to fail in a three year period. An overview of the design and erection issues is presented, particularly those dealing with thin elements in compression. A comparison of moments and stresses resulting from the use of concrete blocks and jacks to reduce the camber difference encountered on span 10-11 shows that the latter method would have been preferable. The failure of three other box girder bridges between 1969 and 1971, and the required strengthening of dozens of others, reveal the lack of understanding of the slender compressive elements present in such structures. A brief literature review presents the buckling and deformation modes found in stiffened plates under compressive loading, showing the development of understanding of these systems from papers written or published in 1997, 2001, 2004 and 2006 - over three decades after the West Gate collapse.; (cont.) Criteria by AASHTO and by B. H. Choi and C. H. Yoo for the minimum moment of inertia of longitudinal and transverse stiffeners of box girders are presented. The resulting values are compared to the moment of inertia of sections used to strengthen the West Gate Bridge after the collapse of a similar bridge. This comparison shows that the requirements are quite sensitive to scale and can provide inconsistent requirements for stiffness. Thus...

‣ Health and water quality monitoring of Pure Home Water's ceramic filter dissemination in the northern region of Ghana

Johnson, Sophie M. (Sophie Marie)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 146 p.
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Pure Home Water (PHW) is a social enterprise that promotes and disseminates household drinking water technologies in the Northern Region of Ghana. Currently their main product is a pot-shaped Potters for Peace-type ceramic water filter, locally known as the Kosim filter. This study used household surveys and water quality testing to monitor the success of their filter program. This work builds upon the household surveys and water quality testing done by Rachel Peletz of predominately modem middle class PHW customers in January 2006 by gathering data that is newly available now that PHW has filter users in traditional communities. Thirty-five households from traditional communities and six households from modem communities were surveyed. For the water quality tests, a drinking water sample was collected from households without a filter, and unfiltered and filtered water samples were collected from households with a filter. These samples were tested for turbidity and for bacterial contamination using membrane filtration, 3MTM PetrifilmTM, and hydrogen sulfide techniques. The surveys determined that PHW is reaching poor communities: 0% of traditional filter users have access to improved water or sanitation, and monthly expenses averaged US $6.30 (GHC 57...

‣ Rail transit OD matrix estimation and journey time reliability metrics using automated fare data

Chan, Joanne, S.M. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 191 p.
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The availability of automatic fare collection (AFC) data greatly enhances a transit planner's ability to understand and characterize passenger travel demands which have traditionally been estimated by manual surveys handed out to passengers at stations or on board vehicles. The AFC data also presents an unprecedentedly consistent source of information on passenger travel times in those transit networks which have both entry and exit fare gates. By taking the difference between entry and exit times, AFC transactions can be used to capture the bulk of a passenger's time spent in the system including walking between gates and platforms, platform wait, in-train time, as well as interchange time for multi-vehicle trips. This research aims at demonstrating the potential value of AFC data in rail transit operations and planning. The applications developed in this thesis provide rail transit operators an easy-to-update management tool that evaluates several dimensions of rail service and demand at near real-time. While the concepts of the applications can be adapted to other transit systems, the detailed configurations and unique characteristics of each transit system require the methodologies to be tailored to solve its needs.; (cont.) The focus of this research is the London Underground network which adopted the automatic fare collection system...

‣ Operational, aesthetic, and construction process performance for innovative passive and active solar building components for residential buildings

Settlemyre, Kevin (Kevin Franklin), 1971-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 300 p.; 23631083 bytes; 23630836 bytes; application/pdf; application/pdf
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A system-based framework creates the ability to integrate operational, aesthetic, and construction process performance. The framework can be used to evaluate innovations within residential construction. By reducing the constraints for use, the framework is adaptable and flexible to specific projects and to the alternatives developed by the user. Passive and active solar design strategies are brought together in the creation of the Energy Producing Wall (EPW) components. Two component types, EPW1 & EPW2, can be adapted to create five different panel types. These units can be installed on the roof or vertical walls, and provide the innovative subject for evaluation within the framework. Four alternatives within two prototype homes, located in two climates, were analyzed to represent the existing and potential stock of housing and to provide the source of input data into the framework. An adaptable spreadsheet analysis, based on past and current analytical methods, establishes the EPW's potential benefit on the heating, cooling, electricity and total energy consumption loads within the prototype designs . Visualization models combined with physical models assess the aesthetics. The development of a Dynamic Process Model for Light Wood Framing (DPM-LWF) represents the framing construction process for the prototype designs...

‣ Evaluating airline-transit cooperation in airport rail and remote check-in services : a strategic approach for increased ridership

Molina Cecchetti, Miguel Angel, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 135 p.; 8052364 bytes; 8052171 bytes; application/pdf; application/pdf
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This thesis applies Lean Principles and Practices to the public transportation services sector. It is an innovative approach since the area of knowledge is most actively used in the production and manufacturing field. Other theories, Stakeholder Theory, Systems Theory, and Transaction Cost Economics, have been incorporated to complement lean thinking and create a strategic management framework for studying airport rail and remote check-in (ARRCI) systems as enterprises. The purpose of using lean and elements of these research areas is to better understand the relationship between two critical and most salient stakeholders, airlines and ARRCI operators. The underlying hypothesis is if the values and vision of these two stakeholders are aligned, then performance improves as the friction impacting the cooperation is structural waste eliminated. The framework for analyzing ARRCI systems is mostly lean thinking. An original development in this thesis is the integration of transaction cost economics to the lean methodology allowing a better comprehension of the interactions between airlines and rail service operators. The new association was applied to three ARRCI cases. Together they provide a source of experiences which should be considered as examples for new systems in the future. Several important observations and conclusions...

‣ Regional planning and operations architectures as means to foster transportation integration in the Mexico City Metropolitan Area; RPA and ROA as means to foster transportation integration in the MCMA

Ortiz Mantilla, Bernardo Jose, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 262 p.; 16335790 bytes; 16370916 bytes; application/pdf; application/pdf
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The MCMA complexity in political, institutional, economical, and jurisdictional terms has resulted in limited coordination between MCMA authorities that in conjunction with the limited role of metropolitan transportation authorities have created the need for innovative institutional cooperation in order to meet the MCMA's transportation needs. The ready applicability of the extensive research conducted at MIT in regional strategic transportation planning in general and in regional architectures in particular has motivated this exploration of how the current MCMA institutional arrangements can be improved. The concept of regional architectures provides a framework that explicitly addresses the interaction between transportation institutions and therefore can serve as a framework to help solve the institutions shortcomings of MCMA transportation planning and operations. In addition, regional architectures can assist MCMA institutions to better align their roles and responsibilities with the transportation goals of the region. The purpose of this thesis is to propose a new Regional Planning Architecture (RPA) that would describe the fundamental relationships between transportation authorities in providing metropolitan transportation planning and a new Regional Operations Architecture (ROA) that would describe the fundamental relationships between transportation authorities in providing metropolitan transportation operations. In addition...

‣ Pricing and competition in US Airline markets : changes in air travel demand since 2000; Pricing and competition in United States Airline markets : changes in air travel demand since 2000

Geslin, Célia
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 104 p.
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Since 2000, the US airline industry has been in turmoil. The economic downturn, September 11 and other factors all have had a negative impact on the spending behavior of consumers, and consequently airlines have posted tremendous revenue losses. The objective of this thesis is to analyze fare and passenger changes in the United States between 2000 and 2004 and to observe how air travel demand has changed recently. The Origin and Destination Survey of the US Department of Transportation is the main data source from which the Top 1000 Markets of 2004 were extracted and consistently matched back to 2000 in order to observe market changes. First, an aggregate statistical analysis was performed to conclude that average fares had decreased 16.4% by 2004, whereas traffic rebounded to 2000 levels after dropping by 11%. As a result, revenues had dropped 17.3% by 2004 compared with 2000. The total market sample was then segmented by distance, hub versus non-hub, low-fare airlines' market share, and overall market competition to determine the impact of each factor. These analyses resulted in the following findings. New entry of low-fare airlines resulted in the greatest decline of 31.3% in average fare by 2004.; (cont.) Short-haul travel demand declined by 16% while fares remained stable; on the other hand...