Digital Commons Network^™

Characterization Of Porous Media And Refractory Materials, Xin Chen

Doctoral Dissertations

Because of its unique advantages on energy savings and casting complex shaper, Lost Foam Casting (LFC) has been widely used as a replacement to the conventional techniques (sand and investment castings). In order to continuously improve the quality of the Lost Foam Casting process for reducing scrap rate and increasing energy savings, the US Department of Energy through its National Industrial Competitiveness through Energy, Environment, and Economics (NICEEE) program sponsored the present study to develop new characterization techniques for enhancing the understanding of the fundamental properties of the refractory materials used in The Lost Foam Casting process. In this study, …

Modeling And Source Apportionment Of Primary And Secondary Pm2.5 In The Atmosphere, Prakash Doraiswamy

Doctoral Dissertations

Source apportionment of PM_2.5 is important to identify the source categories that are responsible for the concentrations observed at a particular receptor. Although receptor models have been used to do source apportionment, they do not fully take into account the chemical reactions (including photochemical reactions) involved in the formation of secondary fine particles. Secondary fine particles are formed from photochemical and other reactions involving precursor gases such as sulfur dioxide (SO₂), oxides of nitrogen (NO_x), ammonia (NH₃) and volatile organic compounds (VOC). The purpose of this research work was to model primary and …

Volatile Fatty Acids Effects On Nitrite Removal And Nitrate Formation During Activated Sludge Treatment, Merve Oguz

Doctoral Dissertations

Reaction sequences of nitrifying and denitrifying bacteria are widely used to eliminate nitrogenous compounds from wastewater. During nitrification, ammonia is oxidized to nitrite by autotrophic ammonia oxidizing bacteria and nitrite is further oxidized to nitrate by nitrite oxidizers. Subsequently, nitrate or nitrite is reduced by denitrifying bacteria to gaseous nitrogen compounds. It is common knowledge that nitrification is an aerobic process and denitrification an anaerobic process. However, recent research has shown that denitrification can occur under aerobic conditions in pure cultures. Volatile fatty acids (VFAs), produced during anaerobic treatment processes, can affect both nitrite oxidation and aerobic denitrification. VFAs were …

Travel Characteristics Of Urban Freight Vehicles And Their Effects On Air Quality, Annie Protopapas

Doctoral Dissertations

This research study collected local commercial vehicle data in Knox County, Tennessee from the United States Postal Service and two companies engaged in package pickup and delivery. A second urban commercial vehicle dataset from a wider spectrum of companies in North Carolina was also obtained for comparative analysis. The two datasets are analyzed in a similar manner to develop and compare travel characteristics/parameters commonly used in transportation engineering, such as Daily VMT, Daily Number of Trips, Vehicle Speed, Trip Length, Trip Travel Time and Stop Duration. Statistical tests demonstrate the similarities between certain vehicle classes from the two datasets and …

Three-Dimensional Mechanical Behavior Of Kaolin Clay With Controlled Microfabric Using True Triaxial Testing, Amit Prashant

Doctoral Dissertations

Clays in their natural state are mostly anisotropic because of their modes of deposition. Many boundary value problems in geotechnical engineering involve soil elements that are subjected to stress paths with varying relative magnitudes and orientation of principal stresses. In clay, these soil elements may also have different orientations of its microfabric. It is a well-known fact that the variation in relative magnitudes and orientation of principal stresses and the microfabric of clay have significant effect on the stress-strain, pore pressure and shear strength behavior of clay. In order to study this behavior of clay from a normally consolidated to …

Dynamic Left-Turn Phase Optimization Using Fuzzy Logic Control, Zhenyang Li

Doctoral Dissertations

The left-turn movement at an intersection has long been a concern of traffic engineers as it is a major capacity reduction factor. Different left-turn signal phasings have been shown to result in significant differences in delay, intersection capacity, and even safety level.

First, past studies about leading and lagging signal phases and signal control application are overviewed. Then this research gives a theoretical analysis of signal left-turn phase operations at both isolated and coordinated signalized intersections, compares the difference in delay based on leading and lagging left-turn signal phase designs, analyzes the influences of traffic control delay components for leading …