Doctor of Philosophy

dissertationTiO2 is an extensively studied material due to its nontoxic, environmental friendly, corrosion-resistant nature and wide band gap (~3 eV). TiO2 nanotubes (T-NTs) synthesized via electrochemical anodization have been studied extensively, with particular focus on their electrical and optical properties. The advantage of T-NT is the large surface area to volume ratio. T-NT has been used to demonstrate many applications such as sensors and energy harvesting. These applications have traditionally been demonstrated via T-NT synthesized on Ti foil. However, there is currently no commercially available T-NT- based device, which may be due to a lack of fabrication techniques, to make such devices on a large scale. One of the requirements for fabricating compact T-NT- based devices is the need for a stable and planar substrate. The titanium foils commonly used for T-NT synthesis are mechanically flexible, making them more prone to bending, limiting the integration of T-NT with microfabrication techniques. Here, we present the synthesis of T-NT on Si wafer at room temperature from direct current (D.C.) sputtered as well as e-beam evaporated thin Ti film. Hundred nm SiO2 was used to electrically isolate the T-NT from the substrate. We demonstrate integration of the synthesis of T-NT with photolithography, which is one of the most important requirements for scaling up a T-NT-based device. The T-NT was stable up to 500oC, which is required for improved charge transport. The T-NT was 1.4 times longer than the thickness of the Ti film, showing selective electric field-assisted etching of Ti by the electrolyte. We also report site-specific and patterned growth of the T-NT. The effect of properties of thin films such as grain size, residual stress and density on the morphology of T-NT was studied to improve the stability and quality of the T-NT. We demonstrate the synthesis of TiO2-WO3 composite nanotubes for photoelectrochemical cells with up to a 40% increase in photocurrent in comparison to plain T-NT. The T-NT was extensively studied and characterized using SEM, AFM, UV-Vis spectroscopy, XRD, and XPS

Installed performance assessment of a boundary layer ingesting distributed propulsion system at design point

Boundary layer ingesting systems have been proposed as a concept with great potential for reducing the fuel consumption of conventional propulsion systems and the overall drag of an aircraft. These studies have indicated that if the aerodynamic and efficiency losses were minimised, the propulsion system demonstrated substantial power consumption benefits in comparison to equivalent propulsion systems operating in free stream flow. Previously assessed analytical methods for BLI simulation have been from an uninstalled perspective. This research will present the formulation of an rapid analytical method for preliminary design studies which evaluates the installed performance of a boundary layer ingesting system. The method uses boundary layer theory and one dimensional gas dynamics to assess the performance of an integrated system. The method was applied to a case study of the distributed propulsor array of a blended wing body aircraft. There was particular focus on assessment how local flow characteristics influence the performance of individual propulsors and the propulsion system as a whole. The application of the model show that the spanwise flow variation has a significant impact on the performance of the array as a whole. A clear optimum design point is identified which minimises the power consumption for an array with a fixed configuration and net propulsive force requirement. In addition, the sensitivity of the system to distortion related losses is determined and a point is identi ed where a conventional free-stream propulsor is the lower power option. Power saving coefficient for the configurations considered is estimated to lie in the region of 15%

TiO2-WO3 composite nanotubes from co-sputtered thin films on si substrate for enhanced photoelectrochemical water splitting

pre-printElectrochemical anodization of a Ti-W nano-composite thin films deposited on a Si substrate by simultaneous magnetron sputtering of Ti and W resulted in the formation of TiO2-WO3 nanotubular arrays. A change in the morphology of TiO2-WO3 composite nanotubes with varying percentage of W in Ti-W composite thin films was observed. With a W density of less than or equal to 1.75 × 1019 W atoms per cm3 (after anodization), the morphology of the composite nanotubes were similar to that of plain TiO2 nanotubes. Whereas with further increase in W density resulted in a nanoporous morphology. Ti-W composite films were also deposited on Si substrates with a 100 nm thick layer of tin doped indium oxide (ITO) to examine the PEC activity of the formed oxide composites. The TiO2-WO3 composite nanotubes with 1.05 × 1019 W atoms per cm3 (3.15 × 1018 W atoms per cm3 before anodization) demonstrated to be an optimal W density for this system, giving rise to 40% increase in photocurrent at 0.5 V (vs. Ag/AgCl) compared to plain TiO2 nanotubes

The Upstream Sources Of Bias: Investigating Theory, Design, And Methods Shaping Adaptive Learning Systems

Adaptive systems in education need to ensure population validity to meet the needs of all students for an equitable outcome. Recent research highlights how these systems encode societal biases leading to discriminatory behaviors towards specific student subpopulations. However, the focus has mostly been on investigating bias in predictive modeling, particularly its downstream stages like model development and evaluation. My dissertation work hypothesizes that the upstream sources (i.e., theory, design, training data collection method) in the development of adaptive systems also contribute to the bias in these systems, highlighting the need for a nuanced approach to conducting fairness research. By empirically analyzing student data previously collected from various virtual learning environments, I investigate demographic disparities in three cases representative of the aspects that shape technological advancements in education: 1) non-conformance of data to a widely-accepted theoretical model of emotion, 2) differing implications of technology design on student outcomes, and 3) varying effectiveness of methodological improvements in annotated data collection. In doing so, I challenge implicit assumptions of generalizability in theory, design, and methods and provide an evidence-based commentary on future research and design practices in adaptive and artificially intelligent educational systems surrounding how we consider diversity in our investigations

Predicting Math Success in an Online Tutoring System Using Language Data and Click-Stream Variables: A Longitudinal Analysis

Previous studies have demonstrated strong links between students\u27 linguistic knowledge, their affective language patterns and their success in math. Other studies have shown that demographic and click-stream variables in online learning environments are important predictors of math success. This study builds on this research in two ways. First, it combines linguistics and click-stream variables along with demographic information to increase prediction rates for math success. Second, it examines how random variance, as found in repeated participant data, can explain math success beyond linguistic, demographic, and click-stream variables. The findings indicate that linguistic, demographic, and click-stream factors explained about 14% of the variance in math scores. These variables mixed with random factors explained about 44% of the variance

To assess the thermoregulation of neonates in the postnatal wards of the hospital: A prospective study

Introduction: Hypothermia is a major cause of neonatal morbidity and mortality. Objective: To know the frequency of hypothermia in the postnatal wards and to know the relation of gestation and birth weight with the temperature of the neonates. Materials and Methods: Rectal temperature of 420 consecutive neonates shifted to postnatal wards of the hospital was measured. The gestation and birth weight of the neonates were recorded. The details were entered, and association of temperature to the birth weight and gestation was calculated. Results: About 70% of the neonates showed mild hypothermia. Gestation and weight of the neonates showed no significant association. Conclusion: The study shows the need to have more vigorous efforts to maintain the temperature in all the neonates in the postnatal wards

Phishing Training: A Preliminary Look at the Effects of Different Types of Training

In this paper, we present the preliminary results of an experiment conducted to observe the impact of the different training techniques to increase the likelihood of participants identifying and reporting phishing messages. Three different training approaches were used – general video/quiz training, just-in-time training with simulated phishing emails, and a leaderboard, which awarded users points for forwarding correct phishing messages and penalized them for incorrect ones. The experiment emulated a normal working day of an executive assistant of a manager in an organization. Each participant was expected to accomplish work tasks and respond to work-related emails while watching for and reporting phishing messages. We observed that both general training and the presence of a leaderboard decreased the propensity to click on a phishing message, while we found no effect for different types of just-in-time training

Growth and characterization of TiO2 nanotubes from sputtered Ti film on Si substrate

In this paper, we present the synthesis of self-organized TiO(2) nanotube arrays formed by anodization of thin Ti film deposited on Si wafers by direct current (D.C.) sputtering. Organic electrolyte was used to demonstrate the growth of stable nanotubes at room temperature with voltages varying from 10 to 60 V (D.C.). The tubes were about 1.4 times longer than the thickness of the sputtered Ti film, showing little undesired dissolution of the metal in the electrolyte during anodization. By varying the thickness of the deposited Ti film, the length of the nanotubes could be controlled precisely irrespective of longer anodization time and/or anodization voltage. Scanning electron microscopy, atomic force microscopy, diffuse-reflectance UV–vis spectroscopy, and X-ray diffraction were used to characterize the thin film nanotubes. The tubes exhibited good adhesion to the wafer and did not peel off after annealing in air at 350 °C to form anatase TiO(2). With TiO(2) nanotubes on planar/stable Si substrates, one can envision their integration with the current micro-fabrication technique large-scale fabrication of TiO(2) nanotube-based devices

Tumor Vascular Permeability to a Nanoprobe Correlates to Tumor-Specific Expression Levels of Angiogenic Markers

© 2009 Karathanasis et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.DOI: 10.1371/journal.pone.0005843Background. Vascular endothelial growth factor (VEGF) receptor-2 is the major mediator of the mitogenic, angiogenic, and vascular hyperpermeability effects of VEGF on breast tumors. Overexpression of VEGF and VEGF receptor-2 is associated with the degree of pathomorphosis of the tumor tissue and unfavorable prognosis. In this study, we demonstrate that non-invasive quantification of the degree of tumor vascular permeability to a nanoprobe correlates with the VEGF and its receptor levels and tumor growth. Methodology/Principal Findings. We designed an imaging nanoprobe and a methodology to detect the intratumoral deposition of a 100 nm-scale nanoprobe using mammography allowing measurement of the tumor vascular permeability in a rat MAT B III breast tumor model. The tumor vascular permeability varied widely among the animals. Notably, the VEGF and VEGF receptor-2 gene expression of the tumors as measured by qRT-PCR displayed a strong correlation to the imaging-based measurements of vascular permeability to the 100 nm-scale nanoprobe. This is in good agreement with the fact that tumors with high angiogenic activity are expected to have more permeable blood vessels resulting in high intratumoral deposition of a nanoscale agent. In addition, we show that higher intratumoral deposition of the nanoprobe as imaged with mammography correlated to a faster tumor growth rate. This data suggest that vascular permeability scales to the tumor growth and that tumor vascular permeability can be a measure of underlying VEGF and VEGF receptor-2 expression in individual tumors. Conclusions/Significance. This is the first demonstration, to our knowledge, that quantitative imaging of tumor vascular permeability to a nanoprobe represents a form of a surrogate, functional biomarker of underlying molecular markers of angiogenesi

Reduced Levels of Membrane-Bound Alkaline Phosphatase Are Common to Lepidopteran Strains Resistant to Cry Toxins from Bacillus thuringiensis

Development of insect resistance is one of the main concerns with the use of transgenic crops expressing Cry toxins from the bacterium Bacillus thuringiensis. Identification of biomarkers would assist in the development of sensitive DNA-based methods to monitor evolution of resistance to Bt toxins in natural populations. We report on the proteomic and genomic detection of reduced levels of midgut membrane-bound alkaline phosphatase (mALP) as a common feature in strains of Cry-resistant Heliothis virescens, Helicoverpa armigera and Spodoptera frugiperda when compared to susceptible larvae. Reduced levels of H. virescens mALP protein (HvmALP) were detected by two dimensional differential in-gel electrophoresis (2D-DIGE) analysis in Cry-resistant compared to susceptible larvae, further supported by alkaline phosphatase activity assays and Western blotting. Through quantitative real-time polymerase chain reaction (qRT-PCR) we demonstrate that the reduction in HvmALP protein levels in resistant larvae are the result of reduced transcript amounts. Similar reductions in ALP activity and mALP transcript levels were also detected for a Cry1Ac-resistant strain of H. armigera and field-derived strains of S. frugiperda resistant to Cry1Fa. Considering the unique resistance and cross-resistance phenotypes of the insect strains used in this work, our data suggest that reduced mALP expression should be targeted for development of effective biomarkers for resistance to Cry toxins in lepidopteran pests