Doctor of Philosophy

dissertationThis work tested the viability of microfabricated humidity sensors based on Y-doped BaZrO3 by developing thin film deposition processes, fabricating devices, and characterizing the device response. At high emperatures, this material becomes conductive depending on temperature, water vapor, and other gas concentrations. Such devices should help increase efficiency and decrease emissions through improved combustion process control. Using microfabrication may lead to reduced size and faster sensor response. Two hundred and twelve variations of thin film layers were deposited and characterized out of which 112 were used in sensors. BaZrO3:Y thin films (200 - 750 nm) were sputtered onto oxidized n-type silicon substrates at room temperature from a ceramic target in an Ar sputtering ambient. Various deposition pressures and powers were used to correlate process parameters with film properties. Films were annealed at 800 and 1000°C (3 hours, air) and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) to determine microstructure, surface morphology, and film composition. For comparison, 30 - 500 nm thick films were deposited onto identical substrates using PLD (various substrate temperatures) and characterized as deposited. Selected samples were annealed at 1000°C (3 hours in air) and characterized again. Transmission electron microscopy (TEM) of 30 and 50 nm PLD films confirmed the iv particle sizes found by AFM of 19 - 25 nm. Although all layers show Barium deficiencies, stable process windows were established for sputtering and PLD close to stoichiometric compositions. Sensors with the sensitive material deposited on top of the interdigitated test structure (IDE) showed no response to changes in humidity. Sensors with the IDE placed on top of the sensing film showed sensitive response, suggesting a strong surface dominated sensing effect. Ti/Pt as contact metal yielded an unrepeatable humidity response. Cr/Au gave sensitive, selective, and long term stable humidity response. All films were exposed to varying partial pressures of water vapor, (400 to 650°C) with and without exhaust gas mixtures. Sensitivities of 0.2 to 62 atm-1 were demonstrated with tenfold selectivity towards other gases and sensor life time in excess of a year. Response times are 4 - 20 times faster than reports in literature

A Study on the Construction of a Multi-Level Autonomous Learning Mode in College English Teaching

This article probes into the construction of a multi-level autonomous learning mode in the light of the problems existing in the college English teaching in China. A tentative study has been conducted to facilitate students’ personalized learning and autonomous learning by the establishment and operation of this learning mode, and the principles of guiding autonomous learning, emphasizing responsive interaction, advocating collaborative constructivism and manifesting humanistic atmosphere are also elaborated on for reference

Retrieval of electron-atom scattering cross sections from laser-induced electron rescattering of atomic negative ions in intense laser fields

We investigated the two-dimensional electron momentum distributions of atomic negative ions in an intense laser field by solving the time-dependent Schrodinger equation (TDSE) and using the first- and 2nd-order strong-field approximations (SFA). We showed that photoelectron energy distributions and low-energy photoelectron momentum spectra predicted from SFA are in reasonable agreement with the solutions from the TDSE. More importantly, we showed that accurate electron-atom elastic scattering cross sections can be retrieved directly from high-energy electron momentum spectra of atomic negative ions in the laser field. This opens up the possibility of measuring electron-atom and electron-molecule scattering cross sections from the photodetachment of atomic and molecular negative ions by intense short lasers, respectively, with temporal resolutions in the order of femtoseconds.Comment: 6 papges, 5 figure

Examining Antecedents of Brand Loyalty on Sportswear: An Empirical Investigation of University Students in Hong Kong

To extend the current understanding of brand loyalty in the sportswear industry, this article discusses six factors that influence brand loyalty of university students towards the Hong Kong sportswear market. Conclusions were drawn based on responses collected through online questionnaires. A total of 205 college students participated in the study. The final results showed that only product quality and brand name affect Hong Kong university students’ brand loyalty towards sportswear. However, based on the whole study, other factors (i.e., service quality, store environment, style and promotions) also play a vital role in sportswear marketing. This research provided insight for sportswear marketers in creating proper marketing strategies for the sportswear industry

Time at treatment of severe retinopathy of prematurity in China: recommendations for guidelines in more mature infants.

PURPOSE: To investigate the postmenstrual (PMA) age at treatment of severe retinopathy of prematurity (i.e. Type 1 prethreshold or threshold) in infants in a tertiary referral center in China. PRINCIPAL FINDINGS: 76.6% (359/469) of infants were treated for threshold disease. 67.5% (317/469) of infants had a birth weight (BW) of 1250 g or above and almost 30% (126) had a gestational age (GA) of 32 weeks or above. There was little difference in the characteristics of infants treated for Type 1 prethreshold or threshold ROP. After controlling for GA, PMA age at treatment was highest in infants with BW ≥2000 g (mean PMA 40.3±4.4 weeks, p34 weeks, p<0.001). For every three weeks increase in GA there was a two-week increase in PMA at treatment (R2 = 0.20, p<0.001). The time at treatment of Type 1 prethreshold disease was similar to that for threshold disease i.e. chronological age 5.6∓7.4 weeks, or PMA 34.1∓40.2 weeks but the lower end of the 95% confidence interval for chronological age for Type 1 prethreshold disease among infants with BW ≥2000 g was 3.7 weeks (i.e. before the recommended interval of 4∓6 weeks after birth). SIGNIFICANCE: The Chinese guidelines regarding timing of the first examination are appropriate for infants with BW <2000 g, but more mature infants should be examined a little earlier, at 3 weeks after birth, in order to detect Type 1 prethreshold disease which has a better prognosis than threshold

DPL: Decoupled Prompt Learning for Vision-Language Models

Prompt learning has emerged as an efficient and effective approach for transferring foundational Vision-Language Models (e.g., CLIP) to downstream tasks. However, current methods tend to overfit to seen categories, thereby limiting their generalization ability for unseen classes. In this paper, we propose a new method, Decoupled Prompt Learning (DPL), which reformulates the attention in prompt learning to alleviate this problem. Specifically, we theoretically investigate the collaborative process between prompts and instances (i.e., image patches/text tokens) by reformulating the original self-attention into four separate sub-processes. Through detailed analysis, we observe that certain sub-processes can be strengthened to bolster robustness and generalizability by some approximation techniques. Furthermore, we introduce language-conditioned textual prompting based on decoupled attention to naturally preserve the generalization of text input. Our approach is flexible for both visual and textual modalities, making it easily extendable to multi-modal prompt learning. By combining the proposed techniques, our approach achieves state-of-the-art performance on three representative benchmarks encompassing 15 image recognition datasets, while maintaining parameter-efficient. Moreover, our DPL does not rely on any auxiliary regularization task or extra training data, further demonstrating its remarkable generalization ability.Comment: 11 pages, 5 figures, 8 table

A Zebrafish Model for Studies on Esophageal Epithelial Biology

Mammalian esophagus exhibits a remarkable change in epithelial structure during the transition from embryo to adult. However, the molecular mechanisms of esophageal epithelial development are not well understood. Zebrafish (Danio rerio), a common model organism for vertebrate development and gene function, has not previously been characterized as a model system for esophageal epithelial development. In this study, we characterized a piece of non-keratinized stratified squamous epithelium similar to human esophageal epithelium in the upper digestive tract of developing zebrafish. Under the microscope, this piece was detectable at 5dpf and became stratified at 7dpf. Expression of esophageal epithelial marker genes (Krt5, P63, Sox2 and Pax9) was detected by immunohistochemistry and in situ hybridization. Knockdown of P63, a gene known to be critical for esophageal epithelium, disrupted the development of this epithelium. With this model system, we found that Pax9 knockdown resulted in loss or disorganization of the squamous epithelium, as well as down-regulation of the differentiation markers Krt4 and Krt5. In summary, we characterized a region of stratified squamous epithelium in the zebrafish upper digestive tract which can be used for functional studies of candidate genes involved in esophageal epithelial biology

Surgical Models of Gastroesophageal Reflux with Mice

Multiple surgical procedures have been reported to induce gastroesophageal reflux in animals. Herein, we report three surgical models with mice aiming to induce reflux of gastric contents, duodenal contents or mixed contents. Surgical procedures and general principles have been described in detail. A researcher with surgical experience should be able to grasp the technique after a short period of practice. After surgery, most mice can survive and develop reflux esophagitis similar to that in humans. However, it should be noted that histological differences between mouse and human esophagus are the inherent limitations of these surgical models. If used for research on Barrett’s esophagus and adenocarcinoma, these procedures may need to be combined with genetic modifications