• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2839
  • 1316
  • 345
  • 340
  • 168
  • 92
  • 69
  • 59
  • 44
  • 36
  • 26
  • 25
  • 21
  • 21
  • 21
  • Tagged with
  • 6619
  • 1241
  • 1176
  • 1075
  • 538
  • 512
  • 462
  • 440
  • 422
  • 413
  • 396
  • 353
  • 324
  • 315
  • 302
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
161

Re-Visioning Sustainable Urban Housing in2020, the year of perfect vision

Arvai, James January 2009 (has links)
Civilization’s vantage point has shifted with advances in technology from an eye-level view of the horizon to a bird’s eye view from a plane, to a planet-wide view from space. This relatively new global view is now the cultural perspective and embraces the holistic view of the biosphere as a large, interconnected, complex habitat that is subject to ever increasing anthropogenic pressures. The newly realized global perspective and realizations of global scale man-made impacts has added the concept of sustainability to the architectural realm. Architectural design issues of sustainability are inherently multi-scale, interconnected, and complex; and can not be resolved with western reductionist science alone. The holistic perspective is a core component of the evolving analysis methodology for pursuing insights on the interactions and connectivity of sustainable design. This thesis will speculate on the future of sustainable urban housing as a nonlinear outcome resulting from the rebalance of culture, technology and economy interacting with choice in our society. Through time, the interactions of these changing major forces is converging on a new equilibrium point that, to some extent, can be moved by choice. The architecture of urban housing has a potential role to play in moving that rebalance point in the future towards sustainability. This thesis will attempt to put on stage a context for urban housing in Canadian society that is transitioning towards sustainability in 2020, the year of perfect vision.
162

Determining cosmological parameters from the brightest SDSS quasars

Janzen, Daryl 25 January 2008 (has links)
According to current cosmological theory, the rate of expansion of the universe depends on the average energy densities of matter, radiation, and a possible vacuum energy described by a cosmological constant, &Lambda;, in the Einstein equation.<p>Observations of galaxies and radiation, along with an assumption that we hold no special place in the universe, imply an isotropic and homogeneous energy distribution, for which the universal rate of expansion for most of the history of the universe may be constructed to depend only on present values of the dimensionless matter and vacuum energy density parameters, &Omega;<sub>M</sub> and &Omega;<sub>&Lambda;</sub>, respectively, and the present rate of expansion of the universe, H<sub>0</sub>. Over the past decade, much progress has been made in determining the values of the three density parameters using a variety of independent methods. In particular, observations of type Ia supernovae in the late 1990s provided the first evidence that &Lambda; &ne; 0 and that universal expansion is accelerating.<p>This study has determined values for &Omega;<sub>M</sub> and &Omega;<sub>&Lambda;</sub> using the brightest quasars in the Sloan Digital Sky Survey Data Release 5, which are located at a range of distances - equivalently, a range of lookback times - that have not been accessible through any other observations. After fitting the apparent magnitudes of the brightest quasars at various redshifts to the distance modulus equation with a luminosity evolution term, values for the density parameters were determined to be &Omega;<sub>M</sub> = 0.07 and &Omega;<sub>&Lambda;</sub> = 1.13.
163

Temperature and Scaling Studies from Projectile Fragmentation of 86,78Kr+64,58Ni at 35 MeV/A.

Wuenschel, Sara K. 14 January 2010 (has links)
Many observables have been developed to study the effects of the two component nature of nuclei. This dissertation has experimentally probed caloric curves as well as scaling observables for their dependence on the asymmetric portion of the nuclear equation of state. Projectile fragmentation sources were identified from the reactions of 86,78Kr+64,58Ni at 35 MeV/A taken on the NIMROD-ISiS array. The angular coverage, excellent isotopic resolution, and Neutron Ball allow for quasi-complete event reconstruction in both charge and mass. A new thermometer for nuclear fragmentation studies has been derived and is presented here. In this thermometer, the temperature is obtained from fluctuations of the transverse momentum. The proton transverse momentum fluctuations are used in this thesis to study the N/Z dependence of the nuclear caloric curve. The caloric curve constructed from proton momentum fluctuations does not show a significant dependence on the source N/Z ratio. Two other thermometers have also been studied in this thesis: the double isotope ratio, and moving source slope thermometers. These thermometers show no statistically significant dependence on the source N/Z. The source density has been derived from the evolution of fragment Coulomb barriers with increasing E*/A. This density showed no source N/Z dependence. However, a strong evolution in source density over the E*/A=1.5-7.5 MeV region was observed. Fragment scaling was investigated through isoscaling and power law scaling. The power law scaling showed a strong dependence on the source N/Z. This source N/Z dependence was further investigated through isoscaling. The fragment yields of this data have been shown to exhibit consistent isoscaling for Z=1-17. In addition, isoscaling was observed in data cut on the E*/A of the source yielding decreasing slopes (a) as a function of E*/A. This decrease, normalized to the asymmetries of the sources (a/delta), has been linked to a decrease in the asymmetry coefficient Csym. This dissertation has shown that the experimentally observed decrease in Csym with E*/A is well correlated to the temperature and density changes experimentally observed in this data.
164

A step towards quantitative lipoprotein density profiling analysis: applied Rayleigh scattering

Nowlin, Michael 15 May 2009 (has links)
Ultracentrifugation and imaging techniques of human blood serum are precise and information-rich methods for obtaining information about an individual’s lipoprotein particle content. The information derived from lipoprotein separations via an ultracentrifuge plays a key role in the area of preventative medicine in regards to atherosclerosis. Two of the most critical lipoprotein characteristics, diameter and density, are well preserved with the proper isopycnic gradient. Currently, lipoprotein particles are stained, ultracentrifuged, and profiled through image analysis. This particular technique is helpful in determining particle density and can be correlated loosely with particle concentration. The need to completely quantify lipoprotein concentrations is imperative in assessing risk factors accurately. Light scattering techniques, primarily Rayleigh scattering, are applied to density separated serum samples in resulting in improved qualitative data with progress in quantitative measurements through imaging alone. The Rayleigh theory dictates that a particle’s scattered intensity is based upon the incident intensity, the particle’s diameter, and the particle’s concentration when strict criteria are met within the sample and imaging apparatus. Applying this innovative imaging technique of Rayleigh scattering to ultracentrifuge tubes containing separated lipoproteins, particle concentrations at differing diameters can be calculated. This thesis primarily goes through the time consuming task of optimizing the innovative Rayleigh scattering system so that correct quantitative estimations can be performed. Constrained by Rayleigh theory and system limitations, lipoproteins of 15 nm to 35 nm are focused upon. By doing so, previously disguised data in regards to lipoprotein subclasses is exposed. Lipoprotein diameters are estimated from Rayleigh imaged serum profiles and the estimations are confirmed through secondary size analysis achieved by dynamic light scattering instrumentation. In addition to Rayleigh optimization, a strategy for quantifying the ultracentrifuged lipoprotein particles using the recently applied scattering technique is explained in detail providing a foundation for further research. In regards to all feasibility studies presented within this thesis, much success was achieved in furthering quantitation efforts in lipoprotein density profiling.
165

Impact of Cotton Harvesting and Storage Methods on Seed and Fiber Quality

Hamann, Mark Thomas 2011 December 1900 (has links)
There are currently two main types of machinery used for harvesting cotton in the United States, cotton pickers and cotton strippers with or without field cleaners. These different machine types package seed cotton with varying amounts of burrs, sticks, and leaves. Harvested cotton is placed in modules for storage prior to ginning. Recent developments in the industry include on-board module builders that package seed cotton as they harvest. This leads to three methods of storage: 1) traditional seed cotton modules, 2) half-modules, and 3) round modules utilized by harvesters with on-board module builders; all of these have different levels of packaging density. Cotton is harvested under widely varying conditions throughout the country and the moisture content of seed cotton at the point of containerization can be an important factor in the final quality of the crop. Seed cotton is being stored for increasing periods of time before being processed by cotton gins. The number of cotton gins in the U.S. has decreased while the production of cotton has increased. All cotton is harvested as it matures and the harvesting rate greatly exceeds the ginning rate. As a consequence of fewer gins, increased harvesting rates and increased quantities of cotton, the storage time of seed cotton prior to ginning has increased. It is hypothesized that the impact of varying densities, varying trash contents, and increased storage times prior to ginning is impacting the quality of the cotton lint and seed. The goal of this research is to quantify the impacts of these factors. The purpose of this research is to evaluate the effects of packaging seed cotton from any of the three different harvesting methods into varying types of storage as a function of differing moisture content and increased storage time. Results are indicated in terms of quality of both the fiber and the seed of ginned samples, as well as how the quality changes affect the value of the processed cotton. Samples of seed cotton are sealed in plastic containers for up to three months at varying levels of moisture, density, and trash content. Temperature and oxygen levels are monitored during storage. Samples are ginned and cottonseed and fiber are analyzed. The results of this research indicate that density does not affect the final quality of the lint and seed harvested. Increased moisture contents have a negative effect on both the quality and the value of the seed cotton, and this effect becomes more pronounced as the length of storage increases.
166

Development and Improvement of Shortwave Communication Prediction Models

Chiu, Chin-Hung 15 July 2001 (has links)
A range of shortwave frequencies will be returned to earth by the ionosphere such that long-distance shortwave communication is accomplished. Because of ionospheric variations, operation parameters are not the same in different time duration. We must select optimized parameters with the aim of utilizing the ionosphere effectively for shortwave radio communications. Shortwave propagation prediction programs can provide such information. Empirical models are often used to represent the variations of the electron density with height in the ionosphere, since radio propagations are concerned with electron density. We develop a graphical user interface based on VOACAP that is one of the most widely used prediction programs. We also improve the electron density model in VOACAP. A gradient discontinuity occurs in the original parabolic ionospheric model. We incorporate an electron density model that does not contain any gradient discontinuities. In this model the electron density profile is composed of three segments: (1) a cosine F2 layer; (2) an E-F layer comprising a secant function, and optional cosine function to provide an F1 ledge (3) a parabolic E layer. Compared with experimental data, our modified model results in more accurate predictions.
167

Rethinking the nonmetropolitan turnaround: renewed rural growth or extended urbanization?

Wang, Xiaodong 25 April 2007 (has links)
This dissertation proposes a new, synthesized perspective for explaining the “Nonmetropolitan Turnaround” in the 1970s and 1990s. By studying the definition of urbanization carefully, using the human ecological perspective, many processes happening during the “Nonmetropolitan Turnaround” in the 1970s and 1990s, such as suburbanization, deconcentration, and counterurbanization, can be understood as different forms of the urbanization processes. When the majority of the population was rural, the dominant pattern of urbanization was rural-urban migration. When the majority of the population became urban, the dominant urbanization pattern reversed to urbanrural migration because urban centers had reached beyond their optimal density and processes operated to reduce their density. This paper hypothesizes that the two “turnarounds” were simply the result of different aspects of urbanization complicated by metropolitan status reclassifications. The perspectives of suburbanization, counterurbanization and deconcentration are integrated into the urbanization perspective. Using migration flow data compiled by the Census Bureau from 1975 to 1980 and from 1995 to 2000, the summary analyses confirmed that the net migration due to the three forms of urbanization largely accounted for all of the net migrant flows. This dissertation further tested the validity of optimal density theory with net migration data and confirmed the utility of this perspective in predicting the direction of net migration.
168

Growth of c-plane InN with Various Si Doping by Plasma-assisted Molecular Beam Epitaxy and Raman Spectroscopy Study

Chang, Yu-lin 28 August 2008 (has links)
Among nitide sremiconductor, InN has the highest electron drift velocity and the smallest effective mass. InN has also been proven to be a narrow band gap semiconductor with a band gap energy of about 0.6-0.7 eV at room temperature. During the past few years, InN has attracted extensive attention due to is potential applications in semiconductor devices such as light-emitting diodes, lasers, and high efficiency solar cells. With the improvement of growth techniques in recently years, high quality InN films grown by plasma-assisted molecular-beam epitaxy (PAMBE) are now readily available. But there is no explicit knowledge for the physical properties of InN. In our experiment, we grow a serious of Si-doped InN with carrier concentration from 1.15 ¡Ñ 1018 cm-3 to 1.90¡Ñ1019 cm-3 by PAMBE . In this thesis we will introduce the instrument and describe the characteristics of Si-doped InN by photoluminescence, high-resolution x-ray diffraction, Raman spectroscopy, Scanning Electron Microscopy and cathodoluminescence
169

Some aspects of the dynamics of many-body systems

D'Amico, Irene, January 2000 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 121-122). Also available on the Internet.
170

Prediction of the molecular structure of ill-defined hydrocarbons using vibrational, ¹H and ¹³C NMR spectroscopy

Obiosa-Maife, Collins. January 2009 (has links)
Thesis (M. Sc.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on Dec. 30, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Materials Engineering, Department of Chemical and Materials Engineering, University of Alberta." Includes bibliographical references.

Page generated in 0.0891 seconds