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  • 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.
1

Geopolymer, Next Generation Sustainable Cementitious Material − Synthesis, Characterization and Modeling

Zhang, Mo 28 April 2015 (has links)
Geopolymers have received increasing attention as a promising sustainable alternative to ordinary Portland cement (OPC). However, the relationship among the synthesis, geopolymerization process, microstructures, molecular strucutres and mechanical properties of geopolymers remains poorly understood. To fill this knowledge gap, this dissertation focuses on the correlation of chemical composition-reaction kinetics-microstructure-mechanical properties of geopolymers. This study also sheds light on the durability, environmental impact and engineering applications of geopolymers from practical perspectives. The first part of this dissertation presents a comprehensive study on red mud-class F fly ash based geopolymers (RFFG). Firstly, RFFG with a high 28-day mechanical strength were successfully synthesized under the ambient condition of 23°C and 40 to 50% relative humidity. A nominal Na/Al molar ratio of 0.6 ~ 0.8 with a Si/Al ratio of 2 was found to be a good starting chemical composition for RFFG synthesis. Secondly, the reaction kinetics and its relation to the mechanical properties of RFFG were investigated by monitoring the development of geopolymer gels, reaction rate, porosity and mechanical properties of RFFG samples cured at room temperature, 50°C and 80°C for up to 120 days. The asymmetric stretching FTIR band of Si-O-T (T is Si or Al) centered around 960-1000 cm-1, which is the characteristic band of geopolymer gels, was observed to shift to a lower wavenumber at the early stage of the synthesis and shift to a higher wavenumber later on during the synthesis. The shift of Si-O-T band indicates that the geopolymerization took place in three stages: dissolution to Al-rich gels at Stage I, Al-rich gels to Si-rich gels at Stage II and Si-rich gels to tectosilicate networks at Stage III. The mechanical strength of RFFG barely increased, increased slowly by a limited amount and developed significantly at these three stages, respectively. An elevated curing temperature enhanced the early strength of RFFG, whereas an excessively high curing temperature resulted in a higher pore volume that offset the early-developed strength. Lastly, the remaining mechanical properties of the RFFG samples after soaking in a pH = 3.0 sulfuric acid solution for up to 120 days and the concentration of heavy metals leached from RFFG samples after the soaking were measured. The RFFG samples’ resistance against sulfuric acid was found to be comparable to that of OPC, and leaching concentrations of heavy metals were much lower than the respective EPA limits for soil contaminations. The degradation in mechanical properties of the RFFG samples during soaking in the acid was attributed primarily to the depolymerization and dealumination of geopolymer gels. The second part of this dissertation is devoted to the investigation of nano-scale mechanical properties and molecular structures of geopolymer gels with grid-nanoindentation and molecular modeling. Four phases (e.g., porous phase, partially developed geopolymer gels, geopolymer gels and unreacted metakaolin or crystals) and their nano-mechanical properties were identified in metakaolin based geopolymers (MKG) with grid-nanoindentation technique. It was found that the proportion of geopolymer gels largely determines the mechanical strength of the resulting geopolymers while other factors (e.g., pores and cracks) also play some roles in macro-scale mechanical strength of geopolymers. The final setting time of the geopolymers increased with the increase in Si/Al ratio and the decrease in Na/Al ratio, while the proportion of geopolymer gels and macro-mechanical strength of geopolymers increased with the increase in both Si/Al and Na/Al molar ratios, within the range of 1.2~1.7 and 0.6~1.0, respectively. In the molecular modeling, a combined density function theory (DFT)-molecular dynamic (MD) modeling simulation was developed to “synthesize� geopolymers. DFT simulation was used to optimize reactive aluminate and silicate monomers, which were subsequently used in reactive MD simulations to model the polymerization process and computationally synthesize geopolymer gels. The influence of Si/Al ratio and simulation temperatures on geopolymerization and resulting molecules of geopolymer gels was also examined. The computationally polymerized molecular structures of geopolymer gels were obtained. The distribution of Si4(mAl) and radial distribution fuctions of Si-O, Al-O, O-O and Na-Al for the models were compared and qualitatively agreed well with the experimental results from nuclear magnetic resonance (NMR) and neutron/X-ray pair distribution function in previous literature. Three polymerization stages: oligomerization, ring formation and condensation, were identified based on the nature of polymerization process, which were found to be affected by the temperature and Si/Al ratio. A higher temperature enhanced the reaction rate while a lower Si/Al ratio resulted in more compact geopolymer networks. The final part of this dissertation presents an experimental feasibility study of using geopolymer in shallow soil stabilization, in which a lean clay was stabilized with MKG at different concentrations. The study confirmed that MKG can be used as a soil stabilizer for clayey soils and the unconfined compressive strength, Young’s modulus and failure strain are comparable to or even better than OPC when the MKG’s concentration is higher than 11%. The binding effect of geopolymer gels on the soil particles was confirmed as the main mechanism for the improvement in mechanical properties of the stabilized soils with the scanning electron microscopy imaging, energy dispersive X-ray spectroscopy analyses and X-ray diffractometry characterization.
2

Experimental Study on the Orbital Motion Induced by Internal Solitary Wave

Wang, Wei-Hung 04 July 2008 (has links)
Many oceanographers have conducted field experiments on internal waves in the South China Sea using SAR imagery, ADCP and CTD. The results arising from these field studies are mostly in terms of wave amplitudes and flow velocities. Despite schematic diagram depicting the orbits of water particle motion has been accepted for more than decades, evidence has not been available from field observations or laboratory experiments. Laboratory experiments on water-particle motion were conducted on the propagation of elevation and depression ISW in a stratified two-layer fresh/brine fluid system in a steel-framed wave tank of 12 m long with cross section of 0.7 m high by 0.5 m wide. Numerical modeling was also performed using in put data identical to laboratory experiments. Based on our results of the numerical and laboratory experiments, the velocity field displays significant vortex while an internal solitary wave (ISW) propagates on a flat bottom. The strong vortex appears in the region of wave crest or trough. The track of fluid particle velocity in the upper layer is asymmetric and is moving in the opposite direction to that in the lower layer. The maximum horizontal velocity occurs at the crest of an elevation ISW and at the trough of a depression ISW. However, no horizontal flow is found on the interface of the still water level, and no vertical velocity at the wave peak. The vertical and horizontal velocities are antecedent with the water depth. For an elevation ISW, the maximum horizontal velocity appears in the lower layer, and vice versa for a depression ISW. The direction of the horizontal velocity in the upper layer is opposite to that in the lower layer. This study presents the results of numerical calculations and laboratory observations of the particles originally resting on a specific level and their movements within an ISW. The finding generated from this research would benefit others on the verification of field results or analytical theory for fluid particle motions associated with ISW.
3

Effects of Solcoseryl on Flap Survival

OKA, TOHRU, KANEDA, TOSHIO, TORII, SHUHEI, AKITA, SUSUMU, UEDA, MINORU 11 1900 (has links)
No description available.
4

An experimental investigation of turbulent flow characteristics beneath a simulated ice jam

Pahlavan, Hoda 14 September 2016 (has links)
Ice jams have caused serious hazards such as floods in northern countries. Despite several studies focused on river ice jams, a lack of research has been identified in the existing literature to analyze impacts of an ice jam on turbulent flow characteristics. Thus, this research attempts to address this knowledge gap. A better comprehension of flow features beneath an ice jam will help river ice engineers to reduce economic, environmental, and ecological damages. Technical difficulties and safety concerns limit data collection in ice jam field studies. Therefore, a physical model of a river ice jam was constructed in the Hydraulics Research & Testing Facility at the University of Manitoba. Two scenarios were proposed to simulate an ice jam. The first scenario was to use a basic model with constant upstream and downstream water depth. The second scenario was developed as an extension of the first scenario, with a modified setup to allow the upstream water depth to be greater than the downstream water depth. This was done to increase similarity with the real ice jam in nature and improve the results. For the second scenario, different roughness ratios of channel bed to ice jam were defined. Experiments were conducted to quantify the turbulent flow characteristics including streamwise velocity and streamwise turbulence intensity distribution beneath the ice jam. The flow velocities were measured at different locations beneath the ice jam using an acoustic Doppler velocimeter. The turbulence intensities and bed shear stresses were calculated using the measured velocities. The results indicated that the flow velocity and turbulence intensity were a function of the streamwise location beneath the ice jam as well as the roughness of the bed and ice jam. Significant changes were observed in the velocity and turbulence intensity profiles where the boundaries were fully rough, which could influence an ice jam formation, sediment concentration and water quality, as well as river bed deformation. It is believed that the results from this research will improve our fundamental understanding of flow beneath an ice jam, and can be used for validation of subsequent ice jam numerical models. / October 2016
5

experimental study of natural and forced modes in an axisymmetric jet

Raman, Ganesh Ganapathi January 1991 (has links)
No description available.
6

EFFECTS OF ADVANCE ORGANIZERS ON LEARNING AND RETENTION FROM A FULLY WEB-BASED CLASS

Chen, Baiyun 21 May 2007 (has links)
The purpose of this study is to investigate the short-term and long-term effects of two kinds of advance organizers (AOs), a visual concept map and a text outline. The AOs were administered in a fully Web-based course in health care ethics. The outcome measures are students' knowledge acquisition and application in two posttests. This study was conducted through a post-test only control group design with a random assignment. The population of the study involved 166 college students who participated in this online class in their junior or senior year. The voluntary research participants were randomly assigned into the two treatment groups and one control group. The treatment of AO was administered as an integral part of a one-week-long online module on the topic of patient-physician relationships. Students of the two treatment groups were presented with one of the two AOs, while the control group was instructed to proceed to textbook reading without an AO. Then, students were tested on the subject matter with two parallel posttests. Both posttests were composed of a multiple-choice question quiz and a set of scenario-based essay questions. The students took posttest I at the end of the instructional week, and posttest II four weeks after. A survey and interviews were also conducted to supplement the quantitative results with contextual information. The findings do not demonstrate a statistically significant AO effect among the treatment groups and the control group. However, in agreement with the previous research, this study shows a positive but inconclusive benefit of using AOs for students' short-term knowledge acquisition. The students using a concept map consistently obtained higher learning achievements than individuals using a text outline. More importantly, this study reiterated the proposition that students of lower-learning abilities benefit more from using an AO for online learning than those of higher-learning abilities. The current study extends our knowledge on the use of AOs in fully Web-based educational environments. The results indicated that although AOs more often than not have small facilitative effects for learners, they are not equally effective for all learners in all learning situations. The incorporation of the instructional strategies, such as AOs, in Web-based courses and programs might benefit online learners, especially those students of lower verbal and analytical abilities, or of lower prior knowledge of the material-to-be-learned. / Ph.D. / Department of Educational Research, Technology and Leadership / Education / Education: Ph.D.
7

Does Growth Data Make a Difference?: Teacher Decision Making Processes Using Growth Data versus Status Data

Fox, Patricia 10 December 2010 (has links)
This experiment examined decisions made by teachers using only status data with those made by teachers using growth and status data. Middle school math teachers from five schools within a single school division located in Virginia participated in the study. Participants were randomly assigned to either the status only or growth and status group. They were then asked to analyze a sample set of class data and complete a survey in which they rated the success of four types of students, identified teacher strengths and weaknesses, and rated their confidence in and the usefulness of the data received. Teachers with access to growth and status data differed significantly in their ratings of three of the four types of students. Students with high growth/low achievement were rated more favorably by teachers with growth and status data (p < .05). Students with low growth/high achievement and those with low growth/low achievement were rated less favorably by teachers with access to growth and status data (p < .05). Teachers with access to growth and status data also chose different strengths and weaknesses than those with access to only status data. Teachers did not differ significantly in their confidence in the data or the perceived usefulness of the data, although limitations may have influenced this finding.
8

Search and retrieval of source code using the faceted approach

Mendes, Rodrigo Cavalcante 31 January 2008 (has links)
Made available in DSpace on 2014-06-12T15:54:33Z (GMT). No. of bitstreams: 2 arquivo1977_1.pdf: 1819935 bytes, checksum: 4162d549c75996e549bcc53383212659 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Software Reuse has been considered a key concept to increase the quality and productivity of the software development by the reuse of existing artifacts, avoiding build new ones from scratch. However, In order to obtain effective benefits from the software reuse is necessary a set of complementary resources such as: education, active management support and the introduction of appropriate process and tools. In fact, resources that provide mechanism to ease the access of reusable components, such as search and retrieval tools, appear as potential instruments in favor of reuse programs adoption in the organizations. One of the challenges of the search and retrieval tools is how to make that existing components returned have a significant relevance. In this sense, the use of the faceted approach rises as a suitable alternative. This approach proposes the creation of a vocabulary supported by attributes, dividing the components into group of classes based on pre-defined keywords, increasing the level of precision and providing a more flexible classification. Thus, this work presents an extension of search and retrieval tool of reusable components, source code in particular, using the faceted classification approach. In addition, also was developed an auxiliary tool to aid the Domain expert to perform his activities using this approach. Finally, an experimental study evaluates the proposed solution
9

Seeing or hearing? Perceptual independence, modality confusions, and crossmodal congruity effects with focused and divided attention

McIlhagga, William H., Baert, J., Bundesen, C., Larsen, A. January 2003 (has links)
No / Observers were given brief presentations of pairs of simultaneous stimuli consisting of a visual and a spoken letter. In the visual focused-attention condition, only the visual letter should be reported; in the auditory focused-attention condition, only the spoken letter should be reported; in the divided-attention condition, both letters, as well as their respective modalities, should be reported (forced choice). The proportions of correct reports were nearly the same in the three conditions (no significant divided-attention decrement), and in the divided-attention condition, the probability that the visual letter was correctly reported was independent of whether the auditory letter Was correctly reported. However, with a probability much higher than chance, the observers reportedihearing the visual stimulus letter or seeing the spoken stimulus letter (modality confusions). The strength of the effect was nearly the same with focused as with divided attention. We also discovered a crossmodal congruity effect: Performance was better when the two letters in a stimulus pair were the same than when they differed in type.
10

Selective Biodegradation in Hair Shafts Derived from Archaeological, Forensic and Experimental Contexts

Wilson, Andrew S., Dodson, Hilary I., Pollard, A. Mark, Tobin, Desmond J., Janaway, Robert C. January 2007 (has links)
No / Background Hair is degraded by the action of both dermatophytic and nondermatophytic microorganisms. The importance of understanding hair sample condition in archaeological and forensic investigation highlights the need for a detailed knowledge of the sequence of degradation in samples that have been either buried or left exposed at the ground surface. Objectives To investigate the sequence of biodegradative change to human terminal scalp hair from archaeological and forensic contexts. Methods Cut modern scalp hair from three individuals with caucasoid-type hair was inoculated with soil microorganisms through soil burial in the field and under laboratory conditions to produce experimentally degraded samples. The degraded hair fibres were subjected to detailed histological examination using a combination of high-resolution light microscopy, transmission electron microscopy and scanning electron microscopy to investigate the nature and sequence of degradative change to hair structural components. Results/discussion Degradation was found to occur first within the least structurally robust components that afford the least resistance to microbial/chemical attack. The sequence of degradation (most to least-reflecting degree of vulnerability) in the hair cuticle was as follows: (1) intercellular 6-layer (cell membrane complex); (2) endocuticle; (3) cell membrane ß-layers; (4) exocuticle; (5) epicuticle; and (6) A-layer. In the hair cortex this was as follows: (I) intercellular 6-layer (cell membrane complex); (II) cell membrane ß-layers; (III) intermacrofibrillar matrix/nuclear remnants; (IV) microfibrils; (V) intermicrofibrillar matrix; and (VI) pigment granules (the hair fibre component that was the least vulnerable to degradation). Conclusions The selective progress of degradation in the hair shaft has been charted and this provides a basis for further histological work in better understanding the condition of hair fibres derived from archaeological or forensic contexts as well as being relevant to investigation of diseased hair, in particular hair infected by dermatophytes and hair weakened by genetic hair shaft abnormalities.

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