Página 19 dos resultados de 2122 itens digitais encontrados em 0.036 segundos

‣ Winter climate response to continental snow anomalies

Gong, Gavin, 1969-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 142 p.; 10730242 bytes; 10729996 bytes; application/pdf; application/pdf
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Climate variability has emerged in recent decades as an important field of geoscience research. A thorough understanding of the patterns and causes of climate variability is required to predict and prepare for upcoming climatic shifts, and also to accurately distill anthropogenic climate change signals from naturally occurring variations. In the extratropical Northern Hemisphere, regional climate patterns are strongly related to a hemispheric-scale mode of variability known as the Arctic Oscillation (AO). A major challenge for current climate variability studies is to predict the phase and magnitude of the AO, as it is a fundamental, internal mode of the atmosphere, but can nevertheless be triggered through a myriad of external perturbations. In this thesis the influence of one hypothesized external perturbation, continental-scale land surface snow anomalies, is investigated. Satellite observations of historical autumn-winter snow cover are used to develop model boundary conditions for a series of snow-forced numerical General Circulation Model (GCM) experiments. Realistic snow forcing over Siberia is found to exert a modulating influence on the winter season AO mode, which is consistent with observations. This winter climate response occurs via anatmospheric teleconnection pathway involving established stationary wave - mean flow interaction processes throughout the troposphere and stratosphere. The pathway is enabled by the specific and unique geographic and orographic conditions that exist in Siberia...

‣ Household scale slow sand filtration in the Dominican Republic

Donison, Kori S. (Kori Shay), 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 96 leaves; 5983053 bytes; 5993919 bytes; application/pdf; application/pdf
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Slow sand filtration is a method of water treatment that has been used for hundreds of years. In the past two decades, there has been resurgence in interest in slow sand filtration, particularly as a low-cost, household-scale method of water treatment. During January 2004, the author traveled to the northwestern Dominican Republic to evaluate the performance of BioSand filters installed over the past two years. BioSand filter performance was evaluated based on flow rate, turbidity removal and total coliform removal in communities surrounding the cities of Mao, Puerto Plata and Dajabon. Filter owners were interviewed about general filter use, water storage methods, filter maintenance practices, and water use. Data analysis revealed that even though the majority of filters were removing large portions of both total coliform and E. coli contamination, no filters met the WHO water quality guideline of less than one CFU/100 ml. Analysis also revealed that at low turbidities, turbidity removal and total coliform removal are not correlated. Examination of flow rate and bacterial removal near Puerto Plata revealed that filters with fast flow rates and intermittent chlorination were observed to have the lowest total coliform removal rates. Analysis of storage data revealed that failure to use safe water storage containers leads to recontamination of filtered water. During Spring of 2004...

‣ Modeling influencing factors in a microscopic traffic simulator

Sterzin, Emily D., 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 95 p.; 3679356 bytes; 3679165 bytes; application/pdf; application/pdf
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Microscopic traffic simulation is an important tool for traffic analysis and dynamic traffic management as it enables planners to evaluate traffic flow patterns, predict and evaluate the outcome of various response plans and assists in decision making. It is a vital tool for traffic management centers and can be helpful in developing contingency plans to enhance the safety and security of the transportation system. This thesis investigates the current state-of-the-practice in traffic microsimulation tools. A survey was developed and administered to developers. Results of the survey indicate critical gaps in including influencing external factors beyond the interaction of vehicles, such as incidents, work zones, or inclement weather, in traffic simulators. This thesis introduces a framework for incorporating such factors in existing models. The nature of the influencing factors limits disaggregate trajectory data collection generally needed to estimate driving behavior models. Therefore, an approach using aggregate calibration to refine and enhance existing driving behavior models is formulated. The aggregate calibration methodology is illustrated with a case study incorporating the effects of weather in driving behavior models using a freeway corridor in the Hampton Roads region of Virginia.; (cont.) MITSIMLab...

‣ A landslide risk rating system for the Baguio City, Philippines area

Saldivar-Sali, Artessa Niccola D., 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 156 leaves; 6602887 bytes; 6602694 bytes; application/pdf; application/pdf
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This research formulates a LANDSLIDE RISK RATING SYSTEM for the Greater Baguio area in the Philippines. It is hoped that the tool will be made a part of the physical/urban planning process when used by engineers and planners and used to address risks posed by landslides given the rapidly increasing concentration of population and the development of infrastructure and industry in the Baguio area. Reports and studies of individual landslides in the area are reviewed in order to discover the causal factors of mass movements and their interactions. The findings of these research works are discussed in the first portion of this paper. A description of the LANDSLIDE RISK RATING SYSTEM, remedial measures, and recommendations form the rest of the paper. This SYSTEM integrates different hazard (bedrock geology, slope gradients, vegetation) and risk (population, land use) factors. The selection of hazard factors takes into account the results of the analysis of causal factors of mass movements in the area. This analysis is based on the specific attributes of the subject study area, namely: a relatively extreme topographic relief, variable bedrock geology, and no significant differences in rainfall from one zone to another. The study assumes that the entire Greater Baguio area is subject to a uniform amount of rainfall during any given precipitation event. Although this study is area-specific it can have wider application.; (cont.) Finally...

‣ An overview of progressive collapse in structural systems

Georgakopoulos, Phillip J. (Phillip John), 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 55 leaves; 4786326 bytes; 4791089 bytes; application/pdf; application/pdf
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It has become evident recently that abnormal loads need to be considered in the design of structures so that progressive collapse can be prevented. Building collapses such as the Ronan Point, Alfred P. Murrah, and World Trade Center have shown the catastrophic nature of progressive collapse and with an increasing trend towards more terrorist action in the future, it is clear structural design must include progressive collapse mitigation. The most critical abnormal loadings that have potential to cause progressive failure are blast and impact. These loads are impulsive and dynamic in nature with the potential to induce destructive forces, and to further complicate matters is the random nature of occurrence which makes it difficult to predict adequate levels of design. Much research has been conducted over the past several decades, but to this day very little standardized language has been published to help designers create progressive collapse resistant structures. What is known is that robust structures can be built economically by following a general design philosophy of redundancy, ductility, and overall structural integrity. Reinforced concrete structures are especially well suited for resisting progressive collapse by specifying steel reinforcement detailing such as continuous top and bottom reinforcement...

‣ Towards understanding the impacts of congestion pricing on urban trucking

Waliszewski, Janine M
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 111 p.; 6174096 bytes; 6187678 bytes; application/pdf; application/pdf
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Understanding policy impacts on freight is essential for planners who have overlooked this transport group in the past and must evaluate new congestion alleviation policies with respect to regional economic and social goals. Since urban areas are limited in infrastructure expansion and travel demand continues to rise, congestion pricing is a potentially compelling policy alternative. This thesis focuses on measuring the impacts of congestion pricing policies on urban freight. We differentiate from prior studies which measure the impacts of urban freight and present tools to measure the impacts on urban freight according to three stakeholder groups: shippers, carriers, and the public sector. We recognize that the impacts of urban freight may be the motivators for policy change or project implementation and the continued study of these impacts is critical to the public sector who aims to minimize externalities of increasing truck traffic (and is also an urban freight stakeholder); however, we suggest that the impacts that these projects or polices have on freight is particularly important given the economic value associated with goods movement. For each of these stakeholder groups, we evaluate their goals, enumerate the possible responses to the scheme...

‣ A method for using polyethylene passive samplers to measure polycyclic aromatic hydrocarbon chemical activity in sediments

Fernandez, Loretta A. (Loretta Ana)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 83 p.; 3607213 bytes; 3615087 bytes; application/pdf; application/pdf
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In order to aid in the determination of the hazards posed by hydrophobic organic compounds (HOCs) in sediment beds, a method for the use of polyethylene (PE) sheets as passive sampling devices for measuring chemical activities was explored. A model which depends on a concentration gradient and two mass transfer limiting zones in series was used. Internal tracer chemicals within the polyethylene devices (PEDs) were used to calibrate the mass transfer model which can have different mass transfer coefficients depending on the site and target chemicals being investigated. The model allowed for the measurement of HOC chemical activities by measuring the change of mass of tracer and target chemical within the PED, and knowing the PE-water partitioning coefficient, ..., and the liquid solubility, ..., of the target chemical. The method was tested using PEDs impregnated with dlO-phenanthrene and dlO-pyrene. First, PEDs were used to measure known concentrations of phenanthrene and fluoranthene in stirred seawaters. Seeing that the PEDs performed well, returning results which were within 25% of the known chemical activities, PEDs were then tested for measuring phenanthrene, fluoranthene, and pyrene in Boston Harbor sediments.; (cont.) Porewaters of Boston Harbor sediments were extracted as a benchmark against which to assess the performance of three methods for measuring sediment chemical activities: (1) PEDs using impregnated tracers exposed for 52 and 92 days to simulated sediment beds...

‣ The application of "Decision Aids for Tunneling (DAT)" to the Sucheon tunnel in Korea; Application of DAT to the Sucheon tunnel in Korea

Min, Sangyoon, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 158 p.; 2100828 bytes; 2100544 bytes; application/pdf; application/pdf
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The Decision Aids for Tunneling (DAT) allow engineers to simulate tunnel construction considering uncertainties in geology and construction processes for a given tunnel project and to obtain, as a result, distributions of the total cost and duration of tunnel construction. The DAT can be applied to every tunnel situation and can deal with any condition regarding a particular tunnel. The research presented in this thesis demonstrates the applicability and suitability of the DAT for the Sucheon tunnel in Korea. For this study, several developments or modifications of the program, SIMSUPER (the computer code of the DAT) were made and many simulations were run with several case studies and some parametric studies. The different time-cost distributions and other results reflecting differences in tunnel construction were analyzed. A new development of the DAT in form of calendars in SIMSUPER was made to be able to keep track of specific and real calendar dates. This study on the DAT application to the real tunnel project in Korea can be a model for the future DAT applications in tunnel projects and this will also lead and accelerate further applications of the DAT to other tunnel projects.; by Sangyoon Min.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Coupling of Integrated Biosphere Simulator to Regional Climate Model version 3; Coupling of IBIS to RegCM3

Winter, Jonathan (Jonathan Mark)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 102 p.; 1905792 bytes; 1939926 bytes; application/pdf; application/pdf
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Presented in this thesis is a description of the coupling of Integrated Biosphere Simulator (IBIS) to Regional Climate Model version 3 (RegCM3), and an assessment of the coupled model (RegCM3-IBIS). RegCM3 is a 3-dimensional, primitive equation limited area model used throughout the world for seasonal predictability and regional climate studies. IBIS is a dynamic global vegetation model that includes representations of land surface processes, canopy physiology, vegetation phenology, terrestrial biogeochemistry, and vegetation dynamics. A single subroutine was created that allows RegCM3 to use IBIS instead of Biosphere-Atmosphere Transfer Scheme 1 e (BATS 1 e) for surface physics calculations. In addition to coupling the two models, a revised initialization scheme was implemented for RegCM3-IBIS, including an IBIS specific prescription of vegetation and soil types, as well as a new scheme for initializing soil moisture, soil ice, and soil temperature based on simulations using the offline version of IBIS. A series of six 1-year numerical experiments were completed to assess the ability of RegCM3-IBIS to simulate the energy and water budgets, as well as surface temperature.; (cont.) The evaluation of RegCM3-IBIS was primarily based on NCEP reanalysis data...

‣ Analysis of future ticketing scenarios for transport for London

Mehta, Saumil (Saumil Jayant)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 106 p.; 5242519 bytes; 5246904 bytes; application/pdf; application/pdf
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Rapid advances in information and communications technology in the recent past have opened up new possibilities for ticketing in public transit systems. These systems offer several benefits like replacing cash, deployment of a richer fare structure and minimizing queuing times. Although smart card ticketing systems have existed for several years now, the full potential of the developments in information technology have yet to be leveraged in terms of cost effectiveness and diverse fare collection strategies. In 2002, TfL (Transport for London) has introduced the Oyster card as a means of smart card ticketing. However TfL has the option to extend or possibly depart from the Oyster Card system in the years 2010 or 2015, when the existing contractual agreements for are open to change. With the aim of understanding the future requirements of ticketing systems, TfL wants to explore ticketing policy and technology options that would be effective and feasible over the next 5 to 10 years. The study results will then guide the development of hardware and software concepts to support such systems. We have proposed seven options for future ticketing systems, which can be broadly categorized into seven categories based on their principal technologies used.; (cont.) The present work is aimed at guiding TfL to specify the system requirements of the future technology that will best suit the needs of TfL and its customers. A software model has been developed to analyze the effectiveness of the several possible alternatives by estimating their costs and the potential revenues that each of them can generate. The system costs and revenues that can be generated highly depend upon the fare structure used for pricing tickets which in turn depend on the ticketing media...

‣ Case studies of postponement in the supply chain

Rietze, Susan M. (Susan Marie)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 88 p.; 4581073 bytes; 4585433 bytes; application/pdf; application/pdf
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The thesis addresses the growing trend in business to offer a wide variety of products while maintaining customer order fulfillment expectations. This trend is happening at the same time the US is losing manufacturing jobs to overseas labor markets, namely China, India, and Central America. While it may not be possible for the US to compete with these countries on the basis of labor costs or even quality in manufacturing, it can compete in the area of faster delivery times and product-service interaction which must inherently take place onshore. Postponement is a strategy that allows businesses to take advantage of the offshore capacity and labor for manufacturing in addition to local finishing centers for final assembly, packaging, and distribution. Postponement is widely used in the automotive, apparel, and consumer electronics industries. Many companies produce products that are candidates for postponement but are unlikely to undergo the implementation changes necessary to support it. This thesis highlights some of the leading companies who are pioneers of postponement and includes case studies of additional companies who have followed their lead.; (cont.) They have seen the tangible benefits of lower inventory costs, quicker response time...

‣ Longitudinal dispersion in vegetated flow

Murphy, Enda
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 183 p.; 7722744 bytes; 7730436 bytes; application/pdf; application/pdf
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Vegetation is ubiquitous in rivers, estuaries and wetlands, strongly influencing both water conveyance and mass transport. The plant canopy affects both mean and turbulent flow structure, and thus both advection and dispersion. Accurate prediction of the fate and transport of nutrients, microbes, dissolved oxygen and other scalars depends on our ability to quantify vegetative impacts. In this thesis, the focus is on longitudinal dispersion, which traditionally has been modeled by drawing analogy to rough boundary layers. This approach is inappropriate in many cases, as the vegetation provides a significant dead zone, which may trap scalars and augment dispersion. The dead zone process is not captured in the rough boundary model. This thesis describes a new theoretical model for longitudinal dispersion in a vegetated channel, which isolates three separate contributory processes. To evaluate the performance of the model, tracer experiments and velocity measurements were conducted in a laboratory flume. Results show that the mechanism of exchange between the free stream and the vegetated region is critical to the overall dispersion, and is primarily controlled by the canopy density.; (cont.) A numerical random walk particle-tracking model was developed to assess the uncertainty associated with the experimental data. Results suggest that the time scale required to obtain sound experimental data in tracer studies is longer than the commonly used Fickian time scale.; by Enda Murphy.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Probability of derailment under earthquake conditions

Guillaud, Lucile M. (Lucile Marie)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 144 leaves
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A quantitative assessment of the probability of derailment under earthquake conditions is presented. Two derailment modes are considered: by vibratory motion - during the ground motion - and by permanent track deformation - after the motion ended. Criteria for derailment that apply to both modes are derived in terms of peak transversal acceleration and peak transversal displacement. This allows a direct comparison between the two causes of derailment. We find that the first mode of derailment (by vibratory motion) dominates over the second mode (by track damage). The model considers the effect of spatial non-homogeneities in soil and structural characteristic and the incoherence of the ground motion into the assessment of derailment risk. The lateral motion experienced by the train under non-synchronous vibration of the track is obtained as the superposition of two contributions: one is the track motion at a fixed location and the other is the motion as the train travels on deformed tracks. Under linear elastic conditions, a method to obtain the power spectral density function for ground acceleration is presented and used to obtain acceleration and displacement response spectra.; (cont.) The second component of motion depends on speed. It is found that the train motion due to track deformation has small effects at ordinary speeds but that it becomes noticeable as the speed increases and the support spacing decreases. In general...

‣ Low cost monitoring system to diagnose problematic rail bed : case study of Mud Pumping Site

Aw, Eng Sew, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 203 p.
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This thesis describes the development of low cost sensors and wireless sensor network (WSN) platform aimed at characterizing problematic rail beds (subgrade). The instrumentations are installed at a busy high-speed Northeast Corridor (NEC) railway site that is experiencing recurring mud pumping problems and requires frequent (bi-monthly) track maintenance. The field instrumentation program addresses some of the challenges faced with designing and installing the subgrade sensors: adoption of new low-cost sensor technologies, fabrication for harsh railway environment, ease of installation with minimal traffic disruption; adoption of advances in WSN for remote data gathering, two-way communications, back-end processing, and near real-time viewing of data. The subgrade sensors consist of piezometers, accelerometers, liquid-based settlement probes, and temperature sensors (thermistors). The piezometers measure the long-term variation in the ground water table and short-term load induced pore pressures. The accelerometers measure the dynamic wheel-induced accelerations at the tie and the top subgrade. The liquid-based settlement probes are designed for long-term settlement measurements although they are not important at this particular site that exhibits greater track vibrations than long-term settlement. The temperature sensors installed at three different levels are able to track the atmospheric...

‣ Improving parameterization of scalar transport through vegetation in a coupled ecosystem-atmosphere model

Link, Percy Anne
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 123 p.
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Several regional-scale ecosystem models currently parameterize subcanopy scalar transport using a rough-wall boundary eddy diffusivity formulation. This formulation predicts unreasonably high soil evaporation beneath tall, dense forests and low soil evaporation beneath short, sparse grass. This study investigates alternative formulations by reviewing literature on flow and scalar transport in canopies, taking field measurements of subcanopy latent heat flux, and testing alternative model formulations in constrained numerical experiments. A field campaign was conducted in a dense rainforest in Luquillo National Forest, Puerto Rico, to measure wind and fluxes with eddy covariance devices. Wind velocities and fluxes of latent heat, sensible heat, and momentum were found to be much smaller below the canopy than above it. Modeling experiments tested a mixing-layer-based formulation of eddy diffusivity and a soil evaporation cutoff based on vortex penetration depth. The vortex penetration cutoff was found to be the most physically accurate and computationally simple option, and this study recommends that ecosystem and land-surface models adopt this formulation for subcanopy scalar transport.; by Percy Anne Link.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ Application of knee-bracing system on high-rise buildings

Gerasimidis, Symeon
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 64 leaves; 31600943 bytes; 31600569 bytes; application/pdf; application/pdf
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The need and ambition of humanity to go higher and higher is something that is amplified as time evolves. It is the same need that leads engineers to push their structures to higher limits. However, when engineers design higher structures their knowledge and their abilities are challenged. In that sense, during the design process of a high-rise building all the strange phenomenon of the behavior of the structure must be considered. A very significant factor that affects the limits of today's high-rise construction is the wind loading. Bracing the building in a clever and more efficient way was always a difficult task for designers and engineers. This thesis deals with a bracing system called the knee-bracing system. The application of knee-bracing system for high-rise buildings is not yet fully determined and this study will try to describe the problem and provide some solutions. Knee-bracing will be checked and the possibility of providing the required results using the minimum amount of material and giving the maximum space for use from the residents or workers of the building will be examined.; (cont.) Several different cases of loading and knee-bracing systems are considered and an optimization for the design of such systems is described. The last part of the document describes the idea of adaptive stiffness...

‣ An adaptive domain-independent agents-based tutor for Web-based supplemental learning environments

Niemczyk, Steven, 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 185 p.; 8835591 bytes; 8835400 bytes; application/pdf; application/pdf
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The Physics Interactive Video Tutor (PIVoT) is a Web-based multimedia resource for college-level Newtonian mechanics. The Personal Tutor (PT) is an intelligent tutoring system (ITS) integrated into PIVoT, assisting students and teachers in navigating through, understanding, and assessing PIVoT's educational media. PT is adaptive in that it personalizes its functionality to the preferences of its user. The combined PIVoT / PT system was designed to be domain-independent with respect to the style of pedagogy, models of user learning, and instructional algorithms. Thus, this design is easily adapted for use beyond the tested domain of introductory college physics. PT is designed in the object-oriented paradigm, building upon the recent work in multi-agent systems (MAS). This agents-based approach, along with innovations in negotiating student-agent control and communication, allow current and future competing pedagogical strategies and cognitive theories to coexist harmoniously. New efficient, domain-independent techniques for discovering, updating, and presenting students' contextual interests improve information retrieval and site navigation. Unlike other computer-based instruction systems used as a tool for primary learning and assessment...

‣ The UV/H2O2 advanced oxidation process in UV disinfection units : removal of selected phosphate esters by hydroxyl radical

Machairas, Alexandros, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 103 leaves; 3115454 bytes; 3115262 bytes; application/pdf; application/pdf
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In this work, the issue of how to remove phosphate esters from drinking water is examined. From the various treatment processes available, the oxidation of phosphate esters through hydroxyl radical generated by the UV/H202 process applied at a UV disinfection unit was selected for evaluation. The second-order rate constants of the reactions of two phosphate esters, Tri(2-butoxyethyl) phosphate (TBEP) and Tri-2-chloroethyl phosphate (TCEP) , with hydroxyl radical were estimated from our experimental data to be 2.1000 M-1s-1 and 2 109 M-is-1 respectively A comprehensive kinetic model of the oxidation process was derived. Finally computer simulations were used to exhibit the potential of this treatment process and to examine the effects of pH, total carbonate species concentration, initial hydrogen peroxide dose, and light intensity on its efficiency. The results are not very encouraging when a UV unit designed for disinfection is used. For typical values of pH and total carbonate species (pH=8 and CT=5' 10-4 M) the 1 s order rate coefficients for removal of the phosphate esters are 6.3 10-4 (s-1) for TBEP and 6.3 10-5 (s-1) for TCEP. If higher light intensity is applied in the reactor (50 times higher), and initial hydrogen peroxide dose of 10-3 M and CT remains 5 10-4 M...

‣ Use of discrete choice models with recommender systems

Chaptini, Bassam H., 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 133 leaves; 7159995 bytes; 7177223 bytes; application/pdf; application/pdf
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Recommender systems, also known as personalization systems, are a popular technique for reducing information overload and finding items that are of interest to the user. Increasingly, people are turning to these systems to help them find the information that is most valuable to them. A variety of techniques have been proposed for performing recommendation, including content-based, collaborative, knowledge-based and other techniques. All of the known recommendation techniques have strengths and weaknesses, and many researchers have chosen to combine techniques in different ways. In this dissertation, we investigate the use of discrete choice models as a radically new technique for giving personalized recommendations. Discrete choice modeling allows the integration of item and user specific data as well as contextual information that may be crucial in some applications. By giving a general multidimensional model that depends on a range of inputs, discrete choice subsumes other techniques used in the literature. We present a software package that allows the adaptation of generalized discrete choice models to the recommendation task. Using a generalized framework that integrates recent advances and extensions of discrete choice allows the estimation of complex models that give a realistic representation of the behavior inherent in the choice process...

‣ Accessibility-based transit planning

Busby, Jeffrey R
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 115 p.; 9006253 bytes; 9013013 bytes; application/pdf; application/pdf
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A method for evaluating transit planning proposals using accessibility metrics is advanced in this research. A transit-accessibility model is developed intended for use by in-house transit agency planning staff as a preliminary project design and evaluation tool. It relies on readily available socioeconomic and travel data and a GIS-supported representation of the transit network. It is intended to inform planning decisions using transparent and intuitive models in a less time consuming and expensive manner than more elaborate and comprehensive planning methods. Emphasis is placed on the visualization of changes in transit level of service resulting from major facility investments. In this capacity, the accessibility metric can assist in identifying the potential ridership change and development impacts of a project. The accessibility model relies on the travel-time outputs of a transit network model, socio-economic data and information on current travel patterns. Development of a network model of transit service in the Chicago region with a focus on CTA bus and rapid transit and METRA commuter rail service is documented. The network model is intended to support on-going research, beyond the scope of this thesis, as part of the collaborative Chicago Transit Authority-MIT research effort. The impact of the proposed Circle Line rail project on employment access and commercial development potential is analyzed to illustrate the potential of the accessibility metric. The model is also applied as a sketch planning tool for intermediate stations on proposed Airport Express trains between downtown Chicago and its two major airports.; (cont.) Findings suggest that much of the improvements in employment access from the Circle Line occur in early project phases...