Browsing by Author "Zhao, Xin"

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    Effect of Kaolin clay, Planting Dates, and Color Mulches on Summer Tomato Production in the Eastern Shore of Virginia
    Gandini Taveras, Ricardo Jose (Virginia Tech, 2024-04-15)
    As climate change exacerbates heat stress during the summer season, it becomes increasingly critical to develop effective strategies to safeguard the productivity of tomato plants (Solanum Lycopersicon L.). This research delves into the tools and techniques aimed at enhancing the cultivation of summer tomatoes in the coastal region of Virginia. The study explores the optimization of transplant dates, the implementation of reflective mulches, and the application of kaolin clay particle films. Field trials spanning two seasons were carried out, comparing different planting dates in May, June, and July, as well as the use of reflective, black, and white plastic mulches, both with and without foliar kaolin sprays. The findings of this study underscore the impact of transplanting tomatoes in May, demonstrating a substantial increase in yields when compared to transplanting in June and July. Reflective mulches enhanced plant height and fruit production relative to the conventional black plastic mulch. The combination of kaolin clay sprays with standard black mulch, resulting in yield increases of over 35%, rivaling the outcomes achieved with reflective and white mulch treatments. The application of kaolin did not significantly affect leaf-level physiological processes. These results highlight the significant potential of strategic early planting and the adoption of emerging heat mitigation technologies, such as kaolin clay films, in sustaining and enhancing the productivity of summer tomatoes. This becomes particularly relevant as growing conditions continue to evolve due to rising temperatures and the increasing extremity of weather events resulting from climate change.
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    Electropolishing of Niobium in Sulfuric Acid-Methanol Electrolytes: Development of Hydrofluoric Acid-Free Electrolytes
    Zhao, Xin (Virginia Tech, 2009-07-16)
    Niobium (Nb) has the highest superconducting transition temperature (9.2 K) of the pure metals, which makes it the most used material for the construction of superconducting radio frequency (SRF) accelerators. The performance of the accelerator is critically dependent upon the quality of Nb surface. Electropolishing (EP) in hydrofluoric acid (HF)-containing electrolytes is the currently accepted treatment process. The presence of HF is necessary for the removal of the passive oxide surface film formed in aqueous electrolytes. But HF is hazardous and must be contained without human exposure and eliminated in an environmentally appropriate manner. In the present dissertation project, HF-Free EP of Nb was performed in sulfuric acid-methanol electrolytes. Sulfuric concentrations of 0.1 M, 0.5 M, 1 M, 2 M, and 3 M were used. Cyclic voltammetry and potential hold experiments were performed in cells of both two-electrode and three-electrode setups to evaluate the electrochemical process. The influence of electrolyte concentration, temperature, and EP duration was investigated. At room temperature, both the corrosion rate and the surface quality obtained were comparable to those currently obtained with HF-based processing. With decreasing temperature, the mean current level decreased and the surface quality improved substantially. For a desired average material removal of 100 μM, nanometer scale surface roughness was obtained under multiple conditions. Mechanism of EP was also investigated by electrochemical impedance spectroscopy (EIS). The EIS diagram indicates the presence of a compact film during EP at mass transport controlled limiting current and a film-free surface during EP at ohmic controlled current. Transfer from a film-free surface to an anodic film precipitation with decreasing temperature was also observed. Microsmoothing is only achieved under mass transport control. Nb⁵⁺ ions are determined to be the mass transport limiting species.
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    Internationalizing sustainable agriculture education
    Schroeder-Moreno, Michelle S.; Clark, Susan F.; Byker Shanks, Carmen; Zhao, Xin (2012)
    Integration of international learning experiences into sustainable agriculture (SA) educational programs represents a unique and effective approach to help students improve their global awareness and citizenship, intercultural communication, problem-solving skills, and career development. While there are challenges to establishing international educational activities in emerging SA programs, the benefits of providing students with a global perspective to the worlds' food systems far exceed those challenges. This paper formalizes key considerations and diverse approaches for developing student-centered international educational opportunities for sustainable agriculture that have been assembled from literature research and from the collective experiences of the authors. A holistic approach is described, beginning with developing strong international partnerships built on reciprocity and understanding the diversity of international learning opportunities and development considerations; establishing learning outcomes and assessment; and appreciating current opportunities and challenges. While many of the experiences and examples come from land-grant universities (LGUs), enhancing a global perspective to all types of SA programs at various institutions is vital for preparing future food system leaders to advance sustainable agriculture in the global community. The information in this paper is valuable for SA educators interested in developing new international educational opportunities and also may stimulate further communication about shared pedagogical strategies related to international SA education.
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    Study of Multimode Extrinsic Fabry-Perot Interferometric Fiber Optic Sensor on Biosensing
    Zhao, Xin (Virginia Tech, 2006-08-01)
    The electrostatic self-assembly (ESA) method presents an effective application in the field of biosensing due to the uniform nanoscale structure. In previous research, a single mode fiber (SMF) sensor system had been investigated for the thin-film measurement due to the high fringe visibility. However, compared with a SMF sensor system, a multimode fiber (MMF) sensor system is lower-cost and has larger sensing area (the fiber core), providing the potential for higher sensing efficiency. In this thesis, a multimode fiber-optic sensor has been developed based on extrinsic Fabry-Perot interferometry (EFPI) for the measurement of optical thickness in self-assembled thin film layers as well as for the immunosensing test. The sensor was fabricated by connecting a multimode fiber (MMF) and a silica wafer. A Fabry-Perot cavity was formed by the reflections from the two interfaces of the wafer. The negatively charged silica wafer could be used as the substrate for the thin film immobilization scheme. The sensor is incorporated into the white-light interferometric system. By monitoring the optical cavity length increment, the self-assembled thin film thickness was measured; the immunoreaction between immunoglobulin G (IgG) and anti-IgG was investigated.