Browsing by Author "Liu, James, committee member"

Now showing 1 - 4 of 4

Open Access
Cellulose nanocrystals extracted from hemp agro-waste as a potential coating for titanium medical devices
(Colorado State University. Libraries, 2024) Heacock, Jesse Andrew, author; Li, Yan Vivian, advisor; Kipper, Matt, committee member; Liu, James, committee member
Increases in biowaste worldwide have created a unique opportunity to extract natural polymers for a variety of uses. Over the last few decades, hemp has increased in popularity as a desirable industrial agricultural plant. Increases in hemp production for commercial product use have increased the amount of hemp agro waste (HAW). This agro-waste is a potentially great source for extraction of the natural polymer cellulose and the creation of a circular economy. Cellulose can be found ubiquitously in plants and has gained great interest as an alternative to synthetic polymers. In this work, cellulose nanocrystals (CNCs) were extracted from HAW using a one-step ammonium persulfate (APS) oxidation method. APS oxidation was used due to its reduction in hazardous wastes, making it a more environmentally friendly method for CNC extraction compared to other chemical methods. HAW, specifically the woody core of hemp known as hurd, underwent CNC extraction and the properties of the final product were analyzed. Depending on the initial source and method of extraction, CNCs properties have been shown to vary, creating a potential for selectivity when applying CNCs for different uses. It was found that changes in reaction time directly impact CNCs size, surface properties, final product mass, and hydrophilicity. Of note, as reaction time increased from 8 hours to 48 hours, the size of the nanocrystals significantly decreased in length and width. While other properties, such as mechanical strength, morphology, surface charge, and cytotoxicity, underwent no statistically significant changes due to increases in reaction time. The results suggest that HAW is a good source for CNC extraction and that changes in APS oxidation can allow for selective tuning of some CNC properties.
Open Access
Computational feasibility of simultaneous analysis and design in interior point topology optimization
(Colorado State University. Libraries, 2023) O'Connor, Justin, author; Bangerth, Wolfgang, advisor; Weinberger, Chris, committee member; Shipman, Patrick, committee member; Liu, James, committee member; Weinberger, Chris, committee member
Topology optimization is a class of algorithms designed to optimize a design or structure to accomplish some goal. It is part of a process of computer generated design that allows engineers to design better products faster. One such algorithm that has piqued the imagination of developers is called Simultaneous Analysis and Design (SAND), especially in the context of Interior Point Optimization (IPO). This method is known to generate extremely optimal designs, and is good at avoiding local minima. However, this method is not used in practice, due to its computational cost. This thesis examines the SAND IPO method, and develops an effective algorithm to generate a design using it. I begin by discussing nonlinear optimization algorithms, selecting pieces that work together for this problem, to generate a cohesive algorithm for the whole process. Inside this developed algorithm, as with most nonlinear optimization algorithms, the most ex- pensive part is a linear solve. In my case, it is a linear solve of a block system. I develop and implement a multi-tier preconditioning approach to solve this system in a reasonable amount of time. Finally, I present a large topology optimization problem presented in three dimensions that has been solved using IPO and SAND, demonstrating the usability of the implemented algorithm.
Open Access
Modeling local pattern formation on membrane surfaces using nonlocal interactions
(Colorado State University. Libraries, 2015) Adkins, Melissa, author; Zhou, Yongcheng, advisor; Krapf, Diego, committee member; Liu, James, committee member; Mueller, Jennifer, committee member
The cell membrane is of utmost importance in the transportation of nutrients and signals to the cell which are needed for survival. The magnitude of this is the inspiration for our study of the lipid bilayer which forms the cell membrane. It has been recently accepted that the lipid bilayer consists of lipid microdomains (lipid rafts), as opposed to freely moving lipids. We present two lipid raft models using the Ginzburg-Landau energy with addition of the electrostatic energy and the geodesic curvature energy to describe the local pattern formation of these lipid rafts. The development and implementation of a C⁰ interior penalty surface finite element method along with an implicit time iteration scheme will also be discussed as the optimal solution technique.
Open Access
Nucleation and growth: modeling the NH3 - HCL reaction
(Colorado State University. Libraries, 2012) Shinn, Jaime M., author; Shipman, Patrick, advisor; Liu, James, committee member; Mueller, Jennifer, committee member; Thompson, Stephen, committee member
One of the trademarks of a Liesegang ring system is the exhibition of a moving reaction front to form a periodic precipitation pattern. This phenomenon has been studied by both chemists and mathematicians. The periodic patterns produced have developed an interest from a mathematical perspective, while the theory and mechanism behind these patterns has created interest from a chemist's point of view. Many mathematical models have been proposed, and much interest has been invested in studying the mechanism behind these Liesegang ring systems. In particular, we will consider the NH3-HCl system, a gas-phase system in which the two gases (NH3 and HCl) diffuse into a tube and meet to form a solid precipitate. The reaction front then moves down the tube, forming a Liesegang banding pattern along the way. In this thesis, we derive a model for this system and examine some results of the model, which contribute to the theory and mechanism behind the NH3-HCl system. We predict the position of the first and last Liesegang band formed, and we examine the effect of the tube length of our system. Front velocity data from the model has also been obtained and is shown to correlate well with experimental data. We also note that the width of the heterogeneous nucleation zone increases as the concentration ratio of NH3 to HCl decreases, and we discuss the effect that water vapor has on the system.