Browsing by Author "Yan, Jun"

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    A Numerical and Experimental Investigation of the Machinability of Elastomers
    (2006-08-15) Yan, Jun; Zhilin Li, Committee Member; Kara J. Peters, Committee Member; John S. Strenkowski, Committee Chair; Eric C. Klang, Committee Member
    The machinability of elastomers is investigated in this dissertation. The main objective of this research is to determine the favorable machining conditions for which elastomers can be machined with a good surface finish. Both orthogonal cutting experiments and finite element model simulations were conducted to achieve this goal. In the orthogonal cutting tests, a wide variety of cutting parameters were examined. Cutting forces, machined surface roughness and temperature were measured to evaluate the effects of various parameters. Rake angle and workpiece temperature were found to have a significant effect on the machined surface roughness during cutting. Large rake angle tools and cryogenic machining produced a smooth machined surface with corresponding continuous ribbon-like chips. In contrast, small rake angle tools generated a rough machined surface. A plane strain finite element cutting model was developed using ABAQUS/Explicit for simulating the orthogonal rubber cutting process. The model was used to predict the cutting forces, chip shape, stress and strain contours, the strain energy density field, and strain energy history in the chip and workpiece. Good agreement was found between the predicted and measured cutting forces. The finite element simulations demonstrated the ability of the model to predict the characteristics of rubber cutting process. A tensile stress and strain in the cutting direction in the workpiece machined surface near the tool tip was observed when a smooth machined surface was produced. New insight into the chip formation mechanism of rubber was achieved by using strain energy concepts. The strain energy density near the tool edge was found to be not only larger but it also extended over a larger area when a rough surface was generated. It was found that the strain energy release rate was closely related to the machined surface quality. A large strain energy release rate corresponded to the generation of a rough machined surface. The understanding gained from the finite element models in this research can be used to develop future guidelines for operating conditions that result in a smooth machined surface finish for machining of elastomers.
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    Using Boronic Acid as the Recognition and Signaling Moiety for Sugar Sensing
    (2004-12-26) Yan, Jun; Bruce Eaton, Committee Member; George H. Wahl, Committee Member; Daniel L. Comins, Committee Member; Binghe Wang, Committee Chair
    The interaction between a boronic acid and a diol is known to be one of the strongest single-pair reversible functional group interactions in an aqueous environment. During the last decade, much effort has been devoted to the development of boronic acid-based sensors for carbohydrates and other diol-containing compounds, and a great deal of progress has been made in this area. However, there are still several fundamental issues that have not been addressed, which hinder the development of such kind of sensors. For example, several factors have long been recognized as important in influencing the binding affinity of boronic acids to diol-containing compound, but there has never been a systematic examination of the relationship among those factors. To address these issues, in Chapter 2 we carefully examined a series of 25 arylboronic acids with various substituents and selected binding affinities with a series of diols at varying pH value. We have found that (1) the pKa of monosubstituted boronic acids can be predicted based on the substituent effect using a Hammet plot; (2) the common belief that boronic acids with lower pKa's have greater binding affinities at neutral pH is not always true; and (3) the optimal pH for binding is not always above the pKa of the boronic acid, instead it is related to the pKa values of both the boronic acid and the diol, although in a manner that cannot be readily predicted. Second, critical to the construction of fluorescent sensors for carbohydrates is the availability of practical fluorescent reporters that respond to the binding event with significant fluorescence intensity changes under physiological conditions. So far a few boronic acid reporters have been described in the literature, but those reporters have undesirable properties such as low water solubility and poor photochemical stability. As described in chapter 2, we have discovered a novel type of fluorescent carbohydrate reporter, 8-quinolineboronic acid (8-QBA). It showed about 40 fold fluorescence increase upon binding of a carbohydrate compound and has very good water solubilty. All these properties make such a system ideal for the construction of fluorescent carbohydrate biosensors for biological applications. With this reporter compound in hand, we designed and syntesized a series of dibornic acids, developed an effective synthetic route for a different kind of 8-QBA-based diboronic acid compound. These results are described in Chapter 4.
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    Well-Balanced Schemes for the Non-Hydrostatic Saint-Venant System and Atmospheric Flow Equations with Gravity.
    (2021-03-26) Yan, Jun; Alina Chertock, Chair; Zhilin Li, Member; Hien Tran, Member; Yunan Liu, Member