Página 9 dos resultados de 2122 itens digitais encontrados em 0.022 segundos
Resultados filtrados por Publicador: Massachusetts Institute of Technology

‣ Field and laboratory observations of small-scale dispersion in wetlands

Lightbody, Anne F. (Anne Fraser), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 173 p.; 6215149 bytes; 6214954 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.2486%
Estimating longitudinal dispersion in wetlands is a necessary first step in predicting the behavior of dissolved species and suspended particles. However, many processes are involved, and they can interact in nonlinear ways. Relevant processes include turbulent diffusion, which describes net solute flux created by turbulent eddies. Other dispersive processes result from the retardation of a portion of the solute relative to the rest of a cloud. This retardation can be provided by trapping in the vortex structure behind stems (hold-up dispersion), velocity deficits well downstream of stems (stem-wake dispersion), or transverse gradients in longitudinal velocity (shear dispersion). To better understand the relative magnitude of these various dispersive processes, measurements were taken of velocity, vertical diffusion, and longitudinal dispersion in both the laboratory and the field. Laboratory flume experiments were conducted using an emergent canopy of rigid cylinders with different cylinder densities over depth. Field experiments were conducted in a natural salt marsh. Drag due to local stem density was found to control horizontal velocity in both the lab and field studies over most of the depth. The resulting non-uniform velocity profile generated shear dispersion...

‣ Support vector machine and its applications in information processing

Saxena, Vishal, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 72 leaves; 2368620 bytes; 2368427 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.2486%
With increasing amounts of data being generated by businesses and researchers there is a need for fast, accurate and robust algorithms for data analysis. Improvements in databases technology, computing performance and artificial intelligence have contributed to the development of intelligent data analysis. The primary aim of data mining is to discover patterns in the data that lead to better understanding of the data generating process and to useful predictions. One recent technique that has been developed to handle the ever-increasing complexity of hidden patterns is the support vector machine. The support vector machine has been developed as robust tool for classification and regression in noisy, complex domains. Current thesis work is aimed to explore the area of support vector machine to see the interesting applications in data analysis, especially from the point of view of information processing.; by Vishal Saxena.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.; Includes bibliographical references (leaves 59-61).

‣ Simulation and visualization of fields and energy flows in electric circuits with idealized geometries

Ohannessian, Mesrob I., 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 64 p.; 2752272 bytes; 2758338 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25305%
This thesis develops a method to simulate and visualize the fields and energy flows in electric circuits, using a simplified physical model based on an idealized geometry. The physical models combine and extend previously proposed models, to produce a rich array of interactive configurations of circuits. For example, both driven and undriven series RLC circuits can be simulated. The computation underlying the simulations is primarily the numerical solution of several first order differential equations and of a boundary value problem. The proposed visualization of these numerical results provide an appealing and physically meaningful representation of the fields and electromagnetic energy flows in these circuits.; by Mesrob I. Ohannessian.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.; Includes bibliographical references (p. 63-64).

‣ Sources of high temperature degradation of cement-based materials : nanoindentation and microporoelastic analysis

DeJong, Matthew J. (Matthew Justin)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 213 p.; 11164139 bytes; 11191853 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25305%
The effects of high temperature exposure on cement-based materials have been under investigation for quite some time, but a fundamental understanding of the sources of high temperature degradation has been limited by measurement capabilities. Using recent developments in nanotechnology and microporoelastic modeling, this study identifies sources of high temperature degradation at the nanoscale for the first time. For reference and comparison with existing literature, the traditional methods of thermo-gravimetry, uniaxial compression, and resonant frequency are used to measure mass loss, compressive strength and elastic modulus, respectively. However, microscopic measurement of the elastic modulus and hardness is the primary experimental focus of this study. Microindentation is used to measure the properties of homogenized cement paste, whereas nanoindentation is used to measure the properties of the various phases which make up cement paste. All experimental methods are performed on cement paste subjected to specified investigation temperatures ranging from 250C to 700C. Using experimental results in combination with data in the literature, microporoelastic modeling is used to identify the sources of high temperature elasticity degradation which are inherent to each cement paste phase. Only through this unique combination of experimental and theoretical investigations are two primary sources of high temperature elasticity degradation separately identified at the nanoscale: 1) dehydration (loss of bound water) within the elementary building block of C-S-H...

‣ Representation of water table dynamics in a land surface scheme : observations, models, and analyses

Yeh, Pat Jen-Feng, 1969-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 212 leaves; 15911365 bytes; 15911172 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25305%
A recent regional-scale water balance analysis has indicated that the groundwater storage and groundwater runoff are significant terms in the monthly and annual water balance for areas with a shallow water table. However, most of the current land surface parameterization schemes lack any representation of regional groundwater aquifers. Such a simplified representation of subsurface hydrological processes would result in significant errors in the predicted land-surface states and fluxes especially for the shallow water table areas in humid regions. This study attempts to address this deficiency. To incorporate the water table dynamics into a land surface scheme LSX, a lumped aquifer model is developed to represent the regional unconfined aquifer as a nonlinear reservoir, in which the aquifer simultaneously receives the recharge from the overlying soils, and discharges runoff into streams. The dependence of groundwater runoff on the water table depth (WTD), i.e., groundwater rating-curve, is parameterized empirically based on the observations in Illinois. The unconfined aquifer model is linked to the soil model in a land surface scheme LSX through the groundwater recharge flux (i.e., soil drainage flux). The total thickness of the unsaturated zone varies in response to the water table fluctuations...

‣ A comparison of the airline benefits of European-style and American-style aircraft purchase options in periods of high demand

Miller, Owen (Owen Charles)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 73 p.
Português
Relevância na Pesquisa
138.25181%
Commercial Aircraft are commonly acquired by an airline in a contract that specifies a fixed quantity of firm orders as well as options that allow the airline to obtain additional aircraft at a future time for an agreed price. This option purchasing process allows the customer to avoid taking delivery of aircraft if economic circumstances are not favorable. However, this model can have drawbacks in circumstances when the product in question is in very high demand. Exercising a rolling-style aircraft purchase option in such circumstances may result in a delivery lag of several years, during which profitable opportunities may be lost. Shortening the time between exercising an option and taking delivery of the aircraft would allow for better timing of the delivery and reduce the effect of a significant negative event such as an economic recession or a terrorist attack occurring between the exercise date and the delivery date.; (cont.) In this thesis, an alternative purchasing system using fixed-term aircraft purchase options is presented. In this system, customers are able to make the decision to exercise an option at a later point in time, with more information, yet receive the aircraft at the same time as the current system. Additionally...

‣ The application of Intelligent Transportation Systems (ITS) and Information Technology systems to disaster response; The application of ITS and IT systems to disaster response

Pinelis, Lev
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 199 p.
Português
Relevância na Pesquisa
138.25035%
Disaster response operations during recent terrorist attacks and natural disasters have been a cause for concern. Lack of planning is one source of difficulties with these operations, but even if a perfect plan is agreed upon before a disaster occurs, it is unlikely that disaster response operations will be successful without better technological support. For this thesis, three prominent and recent disaster cases are analyzed in order to better understand current disaster response problems that result from insufficient Information Technology (IT) and Intelligent Transportation Systems (ITS) support. After presenting this analysis, we provide results of a technology review, whose goal was to search for emerging technologies that could perform better during a disaster response than the standard, currently available systems. .; (cont.) Using these emerging technologies, a Disaster Response Support System (DRSS) is proposed that would provide improved capability, interoperability, and robustness compared to the currently available support systems. Finally, potential barriers to deployment of a system such as the DRSS are discussed and ways in which these barriers can be overcome are suggested; by Lev Pinelis.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Dynamic airline scheduling and robust airline schedule de-peaking

Jiang, Hai, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 156 p.
Português
Relevância na Pesquisa
138.25305%
Demand stochasticity is a major challenge for the airlines in their quest to produce profit maximizing schedules. Even with an optimized schedule, many flights have empty seats at departure, while others suffer a lack of seats to accommodate passengers who desire to travel. Recognizing that demand forecast quality for a particular departure date improves as the date comes close, we tackle this challenge by developing a dynamic scheduling approach that re-optimizes elements of the flight schedule during the passenger booking period. The goal is to match capacity to demand, given the many operational constraints that restrict possible assignments. We introduce flight re-timing as a dynamic scheduling mechanism and develop a re-optimization model that combines both flight re-timing and flight re-fleeting. Our re-optimization approach, re-designing the flight schedule at regular intervals, utilizes information from both revealed booking data and improved forecasts available at later re-optimizations. Experiments are conducted using data from a major U.S. airline. We demonstrate that significant potential profitability improvements are achievable using this approach.; (cont.) We complement this dynamic re-optimization approach with models and algorithms to de-peak existing hub-and-spoke flight schedules so as to maximize future dynamic scheduling capabilities. In our robust de-peaking approach...

‣ Impacts of lateral code changes associated with the 2006 International Building Code and the 2008 California Building Code

Ratley, Desirée Page
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 96 leaves
Português
Relevância na Pesquisa
138.25305%
The 2008 California Building Code (CBC) will adopt the structural section of the 2006 International Building Code (IBC), which includes alterations to the procedure to determine earthquake design loading, and a drastic move to a complicated method to determine design wind pressures. The implementation of the revised 2006 International Building Code, and the subsequent California adoption of the structural section will have significant effects on the design and construction of structures not only in California, but also the rest of the country. Through a comparison of the design of a steel moment-resisting frame low-rise structure, it was determined that the new code will result in design values that differ from those resulting from the previous codes. In order to compare the relevant codes in different areas of the country, this thesis considers three design scenarios for the low-rise structure: seismic loading in Southern California to compare the 2001 CBC, the 2003 and the 2006 IBC, seismic loading in the Midwest to compare the 2003 IBC and the 2006 IBC, and wind loading in Northern California to compare the 2001 CBC and the 2006 IBC.; (cont.) In the first case, the change from the 2001 CBC to the 2003 IBC was an 8 percent increase in base shear...

‣ Hydrologic data assimilation of multi-resolution microwave radiometer and radar measurements using ensemble smoothing

Dunne, Susan Catherine
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 208 leaves
Português
Relevância na Pesquisa
138.25181%
Previously, the ensemble Kalman filter (EnKF) has been used to estimate soil moisture and related fluxes by merging noisy low frequency microwave observations with forecasts from a conventional though uncertain land surface model (LSM). Here it is argued that soil moisture estimation is a reanalysis-type problem and thus smoothingis more appropriate than filtering. An ensemble moving batch smoother, an extension of the EnKF in which the state vector is distributed in time, is used to merge synthetic ESTAR observations with modeled soil moisture. Results demonstrate that smoothing can improve over filtering. However, augmentation of the state vector increases the computational cost significantly, rendering this approach unsuitable for spatially distributed problems. The ensemble Kalman smoother (EnKS) is an inexpensive alternative as the costly computations are already performed in the EnKF which provides the initial guess. It is used to assimilate observed L-band radiobrightness temperatures during the Southern Great Plains Experiment 1997. Estimated surface and root zone soil moisture is evaluated using gravimetric measurements and flux tower observations. It is shown that the EnKS can be implemented as a fixed-lag smoother with the required lag determined by the memory in subsurface soil moisture. In a synthetic experiment over the Arkansas-Red river basin...

‣ Incentive compensation : bonusing and motivation

Wang, Shun Linda, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 89 leaves; 2392429 bytes; 2402540 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25035%
Management is often frustrated by the lack of motivation generated by end of the year bonuses. Currently, there are two compensation ideals, merit-based versus incentive-based. Merit based compensation correlates compensation to one's job performance, whereas incentive based on set goals and correlates bonus rewards before the time frame used to evaluate the performance. An effective incentive program contributes to a company's overall competitiveness by encouraging superior performance as well as improving the company's earning and cash flow. An incentive compensation program is not a substitute for lack of staff accountability, rather it should be used to motivate individuals and align the goals of individuals with those of the company. The purpose of this study is three-fold. First to determine current incentive package in A/E/C firms and comparing them with other industries' compensation. Second, research how more fitting incentive packages will help to make the industry more efficient, and transform the industry to a non-zero sum situation for all parties. Lastly, determine factors needed to have a complete incentive package, as well as explore possible ways of implementation of the incentive programs. In conclusion, not all A/E/C firms will benefit from incentive programs...

‣ A study of the dynamics of shells with boundary layers and a study of the MITC3 shell element; Study of the MITC3 shell element

Malek, Samar R. (Samar Rula)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 63 leaves
Português
Relevância na Pesquisa
138.25181%
Shell structures are frequently used for their aesthetic appeal, and material efficiency. They can be found everywhere, in all sorts of contexts. For example, they can serve as roofs to encapsulate large areas (think Millennium Park in Chicago); as fuselage for an airplane; as the frame of a car; as chemical containers (such as pressure vessels); even submarines. One of the most challenging phenomena in shells is boundary layers. Boundary layers are high concentrations of energy due to either irregular loadings, or incompatible boundary conditions, or geometric discontinuities. Previous studies have determined the location of this concentrated energy and how that location varies depending on the thickness of the shell; up to now however, any correlation between the boundary layers and the vibrations of the shell has not yet been examined. In our first study, we review the boundary layer behavior, and we investigate the dependence of the shell's natural frequencies on the boundary layer phenomenon for two shell benchmark problems: the Scordelis-Lo Roof and the Clamped Hyperboloid.; (cont.) In our second study, we shortly review the MITC3 shell element. This element is known to lock in plate bending cases for a specific mesh pattern. Finally...

‣ Fair adjustment strategies for airline revenue management and reservation systems

Soo, Yin Shiang Valenrina
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 95 p.
Português
Relevância na Pesquisa
138.25181%
With the growth of Low Cost Carriers (LCC) and their use of simplified fare structures, the airline industry has seen an increased removal of many fare restrictions, especially in markets with intense LCC presence. This resulted in "semi-restricted" fare structure where there are homogenous fare classes that are undifferentiated except by price and also distinct fare classes which are still differentiated by booking restrictions and advance purchase requirements. In this new fare environment, the use of traditional Revenue Management (RM) systems, which were developed based on the assumption of independence of demand of fare classes, tend to lead to a spiral down effect. Airlines now have to deal with customers who systematically buy the lowest fare available in the absence of distinctions between the fare classes. This result in fewer bookings observed in the higher fare classes, leading to lower forecast and less protection of seats for the higher yield passengers. This thesis describes Fare Adjustment, a technique developed for network RM systems, which acts at the booking limit optimizer level as it takes into account the sell-up potential of passengers (the probability that a passenger is willing to buy a higher-fare ticket if his request is denied).; (cont.) The goal of this thesis is to provide a more comprehensive investigation into the effectiveness of fare adjustment as a tool to improve airline revenues in this new environment by 1) extending the investigation of the effectiveness of fare adjustment with standard forecasting to leg-based RM systems (namely EMSRb and HBP) and also a mixed fare structure where different fare structures are used for different markets...

‣ Optimal adaptive routing and traffic assignment in stochastic time-dependent networks

Gao, Song, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 237 p.; 11455739 bytes; 11527241 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25411%
A stochastic time-dependent (STD) network is defined by treating all link travel times at all time periods as random variables, with possible time-wise and link-wise stochastic dependency. A routing policy is a decision rule which specifies what node to take next out of the current node based on the current time and online information. A formal framework is established for optimal routing policy problems in STD networks, including generic optimality conditions, and a comprehensive taxonomy with insights into variants of the problem. A variant pertinent to road traffic networks is studied in detail, where a discrete joint distribution of link travel times is used to accommodate the most general stochastic dependency among link travel times, and the access to perfect online information about link travel times is assumed. Both exact and approximation solution algorithms are designed and tested. The criteria of optimality are then extended to reliability measures, such as travel time variance and expected early/late schedule delays. The first routing-policy-based stochastic dynamic traffic assignment (DTA) model is established. A general framework is provided and the equilibrium problem is formulated as a fixed point problem with three components: the optimal routing policy generation module...

‣ Airline fleet assignment and schedule design : integrated models and algorithms

Lohatepanont, Manoj, 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 195 p.; 14493211 bytes; 14492967 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25411%
In scheduled passenger air transportation, airline profitability is critically influenced by the airline's ability to construct flight schedules containing flights at desirable times in profitable markets. In this dissertation, we study two elements of the schedule generation process, namely, schedule design and fleet assignment. The schedule design problem involves selecting an optimal set of flight legs to be included in the schedule, while the fleet assignment problem involves assigning aircraft types (or fleets) to flight legs to maximize revenues and minimize operating costs simultaneously. With the fleet assignment problem, we investigate the issues of network effects, spill, and recapture. On a constrained flight leg in which demand exceeds capacity, some passengers are not accommodated, or spilled. When passengers travel on two or more constrained legs, flight leg interdependencies or network effects arise because spill can occur on any of these legs. In most basic fleet assignment models, simplistic modeling of network effects and recapture leads to sometimes severe, miscalculations of revenues. Recapture occurs when some of the spilled passengers are re-accommodated on alternate itineraries in the system. In this dissertation...

‣ Development and implementation of a coral health assessment tool for St. John, USVI

Detlefsen, William Robert
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 231 p.
Português
Relevância na Pesquisa
138.25305%
Coral health in St. John, US Virgin Islands, has shown tremendous declines in recent years, with more than 50% declines in live coral cover. As one component of a group project to assess the possible impacts of anthropogenic development on coral health, a Coral Health Assessment Tool (CHAT) was developed using Microsoft Access ® and used to assess coral health in four bays in St. John. The tool builds on data management techniques that are currently employed by the National Park Service in St. John. The CHAT includes an Access form-based user interface that allows for random image selection and iterative analysis of still images that have been extracted from video of coral conditions. The database is dynamically linked to Microsoft Excel ® Pivot Table outputs that provide users with extensive data manipulation and exploration capabilities. The CHAT is constructed to allow extensibility and customization by developers and users. While this implementation of CHAT was specific to St. John, the tool's structure lends itself to further development and implementation in coral reef assessment programs worldwide. The health assessment employed a multi-parameter index, allowing bays to be ranked by relative coral health.; (cont.) This index combined multiple coral health factors...

‣ Driving confidence and in-vehicle telematics : a study of technology adoption patterns of the 50+ driving population

Hutchinson, Thomas E. (Thomas Ely), 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 98, [6] leaves; 4827064 bytes; 4826873 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25305%
In-vehicle telematics is a term that encompasses a wide range of technologies, which aid the driving function through features assisting in safety and service tasks. These technologies are designed to give the operator and passengers added safety control and convenient service amenities- both of which contribute to an overall increase in piece of mind and satisfaction in the driving experience. Much effort has been exercised in the rapid development of technologies that comprise in-vehicle telematics systems. But, as is the case with many emerging technologies, these systems appeared on the market before thorough study of their impact on end users had even begun. In recent years, several studies have shown the effects of various technologies on driver distraction, and many insightful results have emerged from that work. However, little has been done to understand consumer perception of these in-vehicle technologies. This thesis provides understanding of the role of in-vehicle telematics in today's automobiles and an analysis of survey data on driving confidence. Particular attention is given to the 50+ driving population, the nature of self-regulation among drivers in this age cohort, and the role that in-vehicle telematics can play in increasing confidence of older drivers. The objective of this thesis is to present the findings of a consumer perception survey in the context of the evolving dialogue on in-vehicle technologies and lay the groundwork for future studies on related topics. Findings in this work show that telematics can positively affect driving confidence...

‣ The evolution of airline distribution channels and their effects on revenue management performance

Dorinson, Diana M. (Diana Marie), 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 134 p.; 5938167 bytes; 5937976 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25411%
Over the past ten years, the development of more advanced computer systems and the growth in the use of the Internet have led to numerous changes in airline ticket distribution strategies. For example, the use of websites for booking and ticketing air travel continues to increase, and the Internet is often cited as the preferred model for a low-cost distribution channel. At the same time, Network Revenue Management methods are now viewed as a key tool for airlines to maximize revenue in an increasingly competitive marketplace. These new systems and tools have helped the airlines achieve record profits in the strong economy of the late 1990s, but these profits may have masked hidden costs of using the new technology. Examples of hidden costs include the added computational burden of increased search engine requests to the computer reservations system as well as the increased opportunity for automated systems to bypass the booking limits set by the revenue management system. Such costs have yet to be examined and quantified in an academic research effort. The purpose of this thesis research is to understand a variety of issues related to how the technologies of more advanced distribution channels and more sophisticated revenue management systems interact with each other and impact air travel providers.; (cont.) First...

‣ How many people can China feed? : assessing the impact of land and water constraints

Watson, Amy Beth, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 126 p.; 4894874 bytes; 4894679 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25305%
Land and water resources are becoming increasingly scarce in China, threatening the nation's ability to feed its growing population. The limitations of these resources must be considered simultaneously to determine China's ability to produce food. In this thesis we present an optimization model to identify the maximum population that can be sustainably supported subject to land and water constraints. This model can be used to inform water resource management decisions. The optimization model specifies the spatial allocation of cropland and water, subject to various physical constraints. As more land is used for crops, more water is consumed by agriculture. The model's water constraints are based on steady- state, annual water balances for major river basins and precipitation and evapotranspiration climatology. The movement of water is constrained by a coarse resolution stream network within each river basin. Food produced within each river basin may be consumed anywhere within China. The model's land constraints are based on reported values for total and irrigated cropland. The irrigated cropland constraint can be relaxed to examine production increases due to possible expansion of irrigated infrastructure beyond current levels. The use of this model is demonstrated with preliminary data. The results suggest that China can support 693 million people sustainably with its resources...

‣ Structure glass technology : systems and applications

Leitch, Katherine K. (Katherine Kristen)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 73 leaves; 4127222 bytes; 4134781 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
138.25181%
Glass cannot compete with steel in terms of strength or durability, but it is the only structural material that offers the highly sought after qualities of translucency and transparency. The use of glass has evolved from purely decorative or architectural to structural, encouraging glass technologies to advance concurrently with increased demand. As a result, contemporary methods used to produce structural glass provide excellent strength characteristics, particularly after treatments including annealing, tempering, and heat-strengthening, which reduce its vulnerability to cracking and sudden brittle failure. Its modulus of elasticity is roughly equal to that of aluminum-greater than both wood and concrete-but doesn't allow any plastic deformation. Lamination dramatically improves both the strength and durability of glass by joining strengthened layers of glass using resin or a polyvinyl butyral foil. No comprehensive design code is currently available to aid in the design of structural glass members. The behavior of glass is examined through a variety of structural applications including beams, columns, walls, roofs and floors, and domes. Case studies are explored to underscore the technical principles discussed for each structural glass element utilized in place of more traditional building materials.; by Katherine K. Leitch.; Thesis (M. Eng.)--Massachusetts Institute of Technology...