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Open Access Publications from the University of California

Mechanical and Aerospace Engineering - Open Access Policy Deposits

This series is automatically populated with publications deposited by UC Irvine Samueli School of Engineering Mechanical and Aerospace Engineering researchers in accordance with the University of California’s open access policies. For more information see Open Access Policy Deposits and the UC Publication Management System.

Cover page of Methane Hydrate Structure I Dissociation Process and Free Surface Analysis

Methane Hydrate Structure I Dissociation Process and Free Surface Analysis

(2024)

Methane hydrates are crystalline solids of water that contain methane molecules trapped inside their molecular cavities. Gas hydrates with methane as a guest molecule form structure I hydrates with two small dodecahedral cages and six tetra decahedral large cages. This study assesses the influence of occupation and the behavior of methane release from the molecular perspective during the dissociation process, particularly for the purpose of testing a series of molecular dynamics simulations. The dissociation cases conducted include an ideal 4 × 4 × 4 and 2 × 2 × 2 supercell methane hydrate system while inducing dissociation with two different types of temperature-rising functions for understanding the limitation and capability. These temperature-rising functions are temperature ramping and a single temperature step simulating in 5-7 various conditions. Temperature step results showed the earliest dissociation starting 50 ps into the simulation at an ΔT of 100 K, while at an ΔT of 80 K, dissociation was not observed. There was not a distinct dissociation preference observed between large and small cages, so it appears that the dissociation affects the entire structure uniformly when temperature increases are applied throughout the system rather than transport from a boundary. Temperature ramping simulations showed that the dissociation temperature increased with a higher heating rate. The mean-squared displacement results for the oxygen atoms in the water molecules at a high heating rate of 400 TK/s showed behavior similar to that for methane gas. As in the temperature step simulation, there were no clear differences in dissociation between large and small cages, which suggested homogeneous dissociation in all cases. Finally, a coordination analysis was performed on a 3 × 4 × 4 structure I methane hydrate with two free surfaces to demonstrate clear free surface boundaries and its location.

Cover page of Methodology for Assessing Retrofitted Hydrogen Combustion and Fuel Cell Aircraft Environmental Impacts

Methodology for Assessing Retrofitted Hydrogen Combustion and Fuel Cell Aircraft Environmental Impacts

(2024)

Hydrogen (H2) combustion and solid oxide fuel cells (SOFCs) can potentially reduce aviation-produced greenhouse gas emissions compared to kerosene propulsion. This paper outlines a methodology for evaluating performance and emission tradeoffs when retrofitting conventional kerosene-powered aircraft with lower-emissionH2 combustion and SOFC hybrid alternatives. The proposed framework presents a constant-range approach for designing liquid hydrogen fuel tanks, considering insulation, sizing, center of gravity, and power constraints. A lifecycle assessment evaluates greenhouse gas emissions and contrail formation effects for carbon footprint mitigation, while a cost analysis examines retrofit implementation consequences. A Cessna Citation 560XLS+ case study shows a 5% mass decrease for H2 combustion and a 0.4% mass decrease for the SOFC hybrid, at the tradeoff of removing three passengers. The lifecycle analysis of green hydrogen in aviation reveals a significant reduction in CO2 emissions for H2 combustion and SOFC systems, except for natural-gas-produced H2 combustion, when compared to Jet-A fuel. However, this environmental benefit is contrasted by an increase in fuel cost per passenger-km for green H2 combustion and a rise for natural-gas-produced H2 SOFC compared to kerosene. The results suggest that retrofitting aircraft with alternative fuels could lower carbon emissions, noting the economic and passenger capacity tradeoffs.

Cover page of HyperXite 9

HyperXite 9

(2024)

The overall objective for HyperXite 9 was to design and build a more robust, and reliable pod, capable of proving the feasibility of a high-speed transportation system. We are working to improve a linear induction motor as the pod's propulsion system. We are also designing and implementing a thermal cooling system to actively dissipate the heat generated by this propulsion system. Our team is comprised of the following 7 subteams: Static Structures, Braking & Pneumatics, Dynamic Structures, Propulsion, Power Systems, Control Systems, and Outreach.

Cover page of Electrokinetic Manipulation of Biological Cells towards Biotechnology Applications.

Electrokinetic Manipulation of Biological Cells towards Biotechnology Applications.

(2024)

The presented study demonstrates the capability of the template-based electrokinetic assembly (TEA) and guidance to manipulate and capture individual biological cells within a microfluidic platform. Specifically, dielectrophoretic (DEP) focusing of K-562 cells towards lithographically-defined wells on the microelectrodes and positioning singles cells withing these wells was demonstrated. K-562 lymphoblast cells, are widely used in immunology research. The DEP guidance, particularly involving positive DEP (pDEP), enables the controlled guidance and positioning of conductive and dielectric particles, including biological cells, opening new directions for the accurate and efficient microassembly of biological entities, which is crucial for single cell analysis and other applications in biotechnology. The investigation explores the use of glassy carbon and gold as electrode materials. It was established previously that undiluted physiological buffer is unsuitable for inducing positive DEP (pDEP); therefore, the change of media into a lower ionic concentration is necessary. After pDEP was observed, the cells are resubmerged in the Iscoves modified Dulbeccos medium (IMEM), a cell culturing media, and incubated. A dead/alive staining assay was performed on the cells to determine their survival in the diluted buffer for the period required to capture them. The staining assay confirmed the cells survival after being immersed in the diluted biological buffer necessary for electrokinetic handling. The results indicate the promise of the proposed electrokinetic bio-sorting technology for applications in tissue engineering, lab-on-a-chip devices, and organ-on-a-chip models, as well as contributing to the advancement of single cell analysis.

Cover page of Doxorubicin Conjugated γ-Globulin Functionalised Gold Nanoparticles: A pH-Responsive Bioinspired Nanoconjugate Approach for Advanced Chemotherapeutics.

Doxorubicin Conjugated γ-Globulin Functionalised Gold Nanoparticles: A pH-Responsive Bioinspired Nanoconjugate Approach for Advanced Chemotherapeutics.

(2024)

Developing successful nanomedicine hinges on regulating nanoparticle surface interactions within biological systems, particularly in intravenous nanotherapeutics. We harnessed the surface interactions of gold nanoparticles (AuNPs) with serum proteins, incorporating a γ-globulin (γG) hard surface corona and chemically conjugating Doxorubicin to create an innovative hybrid anticancer nanobioconjugate, Dox-γG-AuNPs. γG (with an isoelectric point of ~7.2) enhances cellular uptake and exhibits pH-sensitive behaviour, favouring targeted cancer cell drug delivery. In cell line studies, Dox-γG-AuNPs demonstrated a 10-fold higher cytotoxic potency compared to equivalent doxorubicin concentrations, with drug release favoured at pH 5.5 due to the γ-globulin coronas inherent pH sensitivity. This bioinspired approach presents a novel strategy for designing hybrid anticancer therapeutics. Our study also explored the intricacies of the p53-mediated ROS pathways role in regulating cell fate, including apoptosis and necrosis, in response to these treatments. The pathways delicate balance of ROS emerged as a critical determinant, warranting further investigation to elucidate its mechanisms and implications. Overall, leveraging the robust γ-globulin protein corona on AuNPs enhances biostability in harsh serum conditions, augments anticancer potential within pH-sensitive environments, and opens promising avenues for bioinspired drug delivery and the design of novel anticancer hybrids with precise targeting capabilities.

Cover page of Early Feasibility Study of a Hybrid Tissue-Engineered Mitral Valve in an Ovine Model

Early Feasibility Study of a Hybrid Tissue-Engineered Mitral Valve in an Ovine Model

(2024)

Tissue engineering aims to overcome the current limitations of heart valves by providing a viable alternative using living tissue. Nevertheless, the valves constructed from either decellularized xenogeneic or purely biologic scaffolds are unable to withstand the hemodynamic loads, particularly in the left ventricle. To address this, we have been developing a hybrid tissue-engineered heart valve (H-TEHV) concept consisting of a nondegradable elastomeric scaffold enclosed in a valve-like living tissue constructed from autologous cells. We developed a 21 mm mitral valve scaffold for implantation in an ovine model. Smooth muscle cells/fibroblasts and endothelial cells were extracted, isolated, and expanded from the animal's jugular vein. Next, the scaffold underwent a sequential coating with the sorted cells mixed with collagen type I. The resulting H-TEHV was then implanted into the mitral position of the same sheep through open-heart surgery. Echocardiography scans following the procedure revealed an acceptable valve performance, with no signs of regurgitation. The valve orifice area, measured by planimetry, was 2.9 cm2, the ejection fraction reached 67%, and the mean transmitral pressure gradient was measured at 8.39 mmHg. The animal successfully recovered from anesthesia and was transferred to the vivarium. Upon autopsy, the examination confirmed the integrity of the H-TEHV, with no evidence of tissue dehiscence. The preliminary results from the animal implantation suggest the feasibility of the H-TEHV.

Cover page of Modeling Ember Behavior and Accumulation Patterns on and Around Sample Homes During a Wildfire

Modeling Ember Behavior and Accumulation Patterns on and Around Sample Homes During a Wildfire

(2023)

Embers are a potent mechanism for wildfire propagation because the particles can carry farther than the flame front and nullify defensible zones. PyroSim, a Fire Dynamics Simulator (FDS) tool that visually processes text editor inputs for simulating fire-driven fluid flow, is leveraged to model ember transport and accumulation patterns on buildings during a wildfire. This research begins with benchmark analysis against existing findings in literature for validating its usage. It focuses particularly on the transport and accumulation patterns of non-combusting particles with realistic ember parameters which are carried via wind over sample buildings. This study tested various ember sizes, ember densities, wind speed in the horizontal and vertical direction, rooftop styles, and fire effects to examine how each factor impacted ember behavior. Results indicate that roofs with a ridge line perpendicular to wind direction are more likely to accumulate embers. Additionally, horizontal and vertical wind speeds must be strong to facilitate ember transport but not so great that embers are unable to deposit and settle onto buildings. Regardless of building design, a plurality of embers come to rest against the front-facing walls of the structure, posing the biggest risk to fire spread. Surface fires impact flow behavior, so a ground fire was introduced to the model to examine how results change. Ultimately, it is theorized that fire-driven turbulence may facilitate ember transport but negate accumulation in unstable regions, such as rooftops.

Cover page of Dynamic simulation of carbonate fuel cell-gas turbine hybrid systems

Dynamic simulation of carbonate fuel cell-gas turbine hybrid systems

(2016)

Hybrid fuel cell/gas turbine systems provide an efficient means of producing electricity from fossil fuels with ultra low emissions. However, there are many significant challenges involved in integrating the fuel cell with the gas turbine and other components of this type of system. The fuel cell and the gas turbine must maintain efficient operation and electricity production while protecting equipment during perturbations that may occur when the system is connected to the utility grid or in stand-alone mode. This paper presents recent dynamic simulation results from two laboratories focused on developing tools to aid in the design and dynamic analyses of hybrid fuel cell systems. The simulation results present the response of a carbonate fuel cell/gas turbine, or molten carbonate fuel cell/gas turbine, (MCFC/GT) hybrid system to a load demand perturbation. Initial results suggest that creative control strategies will be needed to ensure a flexible system with wide turndown and robust dynamic operation. Paper No. GT2004-53653,

Cover page of Controlling the Movement of a TRR Spatial Chain with Coupled Six-bar Function Generators for Biomimetic Motion

Controlling the Movement of a TRR Spatial Chain with Coupled Six-bar Function Generators for Biomimetic Motion

(2015)

This paper describes a synthesis technique that constrains a spatial serial chain into a single degree-of-freedom mechanism using planar six-bar function generators. The synthesis process begins by specifying the target motion of a serial chain that is parameterized by time. The goal is to create a mechanism with a constant velocity rotary input that will achieve that motion. To do this we solve the inverse kinematics equations to find functions of each serial joint angle with respect to time. Since a constant velocity input is desired, time is proportional to the angle of the input link, and each serial joint angle can be expressed as functions of the input angle. This poses a separate function generator problem to control each joint of the serial chain. Function generators are linkages that coordinate their input and output angles. Each function is synthesized using a technique that finds 11 position Stephenson II linkages, which are then packaged onto the serial chain. Using pulleys and the scaling capabilities of function generating linkages, the final device can be packaged compactly. We describe this synthesis procedure through the design of a biomimetic device for reproducing a flapping wing motion.

Cover page of Controlling the Movement of a TRR Spatial Chain with Coupled Six-bar Function Generators for Biomimetic Motion

Controlling the Movement of a TRR Spatial Chain with Coupled Six-bar Function Generators for Biomimetic Motion

(2015)

This paper describes a synthesis technique that constrains a spatial serial chain into a single degree-of-freedom mechanism using planar six-bar function generators. The synthesis process begins by specifying the target motion of a serial chain that is parameterized by time. The goal is to create a mechanism with a constant velocity rotary input that will achieve that motion. To do this we solve the inverse kinematics equations to find functions of each serial joint angle with respect to time. Since a constant velocity input is desired, time is proportional to the angle of the input link, and each serial joint angle can be expressed as functions of the input angle. This poses a separate function generator problem to control each joint of the serial chain. Function generators are linkages that coordinate their input and output angles. Each function is synthesized using a technique that finds 11 position Stephenson II linkages, which are then packaged onto the serial chain. Using pulleys and the scaling capabilities of function generating linkages, the final device can be packaged compactly. We describe this synthesis procedure through the design of a biomimetic device for reproducing a flapping wing motion.